nice to meet you sir again sorry hello am I audible yes you are okay so previously I asked the same question with Martin sir I just wanted to I just wanted to show you my UI vision because I wanted to discuss about the UI how it's going to implement excuse me let's start from the process specific questions and then yeah then we will switch to project specific ones if you don't mind okay thank you sure you're asking me right I it was it is related to the project itself yeah sorry so let's just spend some time on whatever organizational questions and we go to the project specific discussion okay okay okay doesn't really have any organizational questions okay if not then we can do project ideas etc okay may I start if you let's continue okay so I wanted to know the exact UI pattern of the project artifact promotion plugin so I'll share my screen okay so I just wanted to ask that this new item section that we see here when the promoted the new plugin is implemented then where would it be placed like like will it be placed alongside these projects freestyle projects there will be something like promotion promotion of artifacts would it be placed at this particular place or like the job we were actually creating the job yeah a new job right so would it be placed alongside these projects or I don't yes so it's a part of the design you can do it in different ways okay my personal understanding was that it would be just a subtype of pipeline so yeah it would appear in this list unless you deliberately filter it out okay wouldn't it just be a property of a job pipeline not a special type well it would be a property in terms of configuration how you somebody is tapping their microphone okay I'll mute everybody so there are two parts of the question one is how it's being defined and another one how it's being presented in general so yeah it would be great if you could define promotions and promotion logic directly in pipeline definitions or in declarative pipeline and special sections but in my understanding it would still appear as a separate job type on the management page since it is being mentioned that there should be a common standalone plugin right so it should stay in this case and next question would be sir like whenever I go inside a certain project and go inside a particular build right so inside the configure section we have this section like promote builds when this section this would be migrated to that job right the new job as execution or as definition because so you can still define this promotion process inside your pipeline if you want like if I want to make okay okay all right okay I can also define this in the pipeline or I can make a common job that was what you meant yeah I'm sure I get your question so this thing the promote builds when this section would be migrated to the new job if I'm not wrong so you can define it in both ways depending on your preference you can define it inside an existing pipeline as a property like claus suggested or is a special clause for example in the clarity pipeline or you can define it in external job so it's a matter of definition and you rather expect you as a student to come up this proposal the both options are technically possible and both options many find some users so it's up to you to see how you would implement if you both are fine either or both are fine so right either like both of the options are fine like I can implement any of them yes um Oleg can can you elaborate on the the reason to create a new type there so there is no reason to create a new type of job there is a reason to have promotions as separate job entities so like we were discussing yesterday I believe promotions currently are not well mapped in the Jenkins job architecture so what we would like is we would like to have promotions as separate job entities which map the current structure so for example there may be a folder or multi-branch pipeline inside this entity there is a common job definition so you don't use hax as item groups which are represented as job properties but this is an architectural thing if we talk about job types etc now I do not think that it has to be a new job type because yeah if you talk about promotion support for pipeline it would be rather expected that the promotion is also pipeline it's a probability that you kind of define in there either either as an automatic promotion or a manual promotion yeah right but inside it will be still a pipeline code it would be still executed as a separate job entity or maybe as a separate run entity depending upon how you implement it but yeah it would be just a part of the architecture architecture thing definition as I tried to say it may be different so definition of promotional logic it may be inside your original job it may be defined in external job it depends on how you implement it I could I could see the view the view part as a separate entity it's kind of because it goes across the whole the whole Jenkins whereas the execution would be an extension of the current architecture does that make sense maybe so I think that we should really plan a separate meeting for this specific project so that we could deep dive in the architecture so maybe if you guys have some time we should take it offline and schedule a meeting like we do for other projects that's right that would be great so that would be a great help so my next question is sir like as your guidance I went I read the release plugin since it's compatible with the pipeline so I just read through all the code base and what I found is one in one of those classes inside the release plugin like the release promotion condition.java in this class what it does is it extends a promotion condition which is which happens to be the class of promoted build plugin so this means that most of the classes which are inside the promotion build are compatible with the pipeline but there are some which are not so how do I distinguish between those which are compatible to those which are not so the rule of thumb is that if you see classes like abstract project or abstract build in the class you can expect that this class or this method is not compatible with the pipeline okay like promotion.java promotion process.java job property these are not compatible because they've got abstract classes like abstract builds that's why am I correct okay that's right okay sir okay next question is like if abstract builds are not supported by pipelines if abstract projects are not supported by pipelines then what are the what is the actual project type which is compatible with pipeline which is supported by pipeline that's a tricky thing because pipeline is a separate project type so yeah it may be useful for the students as well probably I'll just share my screen if you don't mind okay yeah so probably yeah let's just try to timebox a bit okay so job is kind of top-level entity for executable types so job has methods like so it generally contains runs and this runs somewhere how they're there are many implementations of jobs if you see here you may see that there is abstract project which is a part of job so it's one of implementations of jobs another implementation is pipeline it's on the same three level there are the project types for example inheritance project or other projects which inherit job type so what it means that these project types are really independent and these are a part of the tree all they shade is this job interface and also all classes up to the hierarchy so you may see that job implement abstract items so that it may be a part of the item tree inside Jenkins that is actionable so it may contain actions and then may persist actions and yeah that's it but job is the basic definition which just yeah it just applies for every job type in Jenkins same for runs for run so that is the basic lies full run which is exactly the same okay so for which exact build type would be supported from in the pipeline of the job type pipeline because pipeline is a separate job type okay yeah if you see a use case for supporting jobs in general so for example supporting freestyle job as a promotion logic for pipeline then you can definitely do that in your proposal if you feel it's reasonable but yeah our expectation would be that at least pipeline promotion logic supported okay okay so next question is there's in the in the project proposal it's mentioned it has mentioned that detach detach the existing promotion condition extension point and implementations from promoted builds plugin what does that mean so like getting rid of all the existing extension point of the plugin well so what it means is it being a common Jenkins architecture thing is that there are many epi plugins so plugins which provide shared functionality and being reused by other plugins for example promoted builds already includes extension points for defining promotion conditions for example manual promotion condition when somebody clicks a button or depends on whatever other event in Jenkins there are maybe a dozen of implementations for this promotion condition so the idea of this line is that if you create a epi plugin and if you move reusable functionality out of promoted builds then other plugins can consume this functionality without including the rest of the promoted builds code so the idea of this value that you just detach the plugins and effectively reuse the usable components of existing plugin okay so for the for the for the code part which is to be implemented by the pipeline I should mention the extension point in it right like in a file the class which is along with the at the extension point it is read by the pipeline that's the exact mechanism of how pipeline works right sir i'm sorry okay okay okay so last question sir like you mentioned in your vision in your vision that in the properties section we must include we can include the environment like where where the build is going to be deployed and can we do that by using the existing fingerprint that is being used in the promotion build already yes okay what do you mean by deployed in this in this case here meaning like certain builds after being promoted they would be deployed into some sort of the next stage they would be passed to the next stage so just to track where it is being deployed can we use fingerprinting that was my question yeah so fingerprinting can be used for tracing of any dependencies between builds and between any kinds of artifacts within Jenkins and you can use it here to track dependencies okay so last question last question is like what would like if i need to refactor the codes the classes which are not compatible to pipelines what would what should be my what should be my general approach what should be my general approach to refactor them so that i could make them compatible with the pipeline like abstract like i need to replace that with some other build type or like promotion job i need to change that what should be my general approach to refactoring those codes yeah so again general practice in Jenkins project promoted builds that we're interested to retain compatibility where possible so if you see that you need to perform significant refactoring there are ways to retain binary compatibility there are a special weak page which explains how to do that and if you work on any project and if you need to do a massive change it might be a page you want to start from so Jenkins binary compatibility i believe let's see i'm not sure hints or retaining backward compatibility so this would be one of the starting pages for for you because it references several Jenkins specific ways to retain compatibility for example when you change the data or when you remove a field or remove a method but yeah if you see any significant change apis it's definitely something which will require significant design and before doing that you see whether there are alternate options it doesn't apply to on this project it applies to all projects like in one of the tutorials in the plugin development i came across the fact that variable substitution that is not enabled by plugins so there was an idiom that was given so by including that it can be made compatible with both form of projects from from pipeline and a freestyle it mentioned something like that about the idiom of extension points i so would that be the exact tutorial not sure so yeah again when you have a specific question you may see that it's not really effective to ask them on the call because sometimes it's hard to express what you need and that's why we recommend using mainly please or get a chance for that because it may be more effective in many cases okay okay sir thank you sir thank you yeah so i propose to just take it offline because yeah we have limited time we have other students all right yeah so if we have some time after the call we can return back to that but yeah my proposal is really rotate to other questions and probably next time we will be just trying to turn box questions to five minutes and we will be rotating between students so that sure sir sure okay thank you thank you again let's see if we can discuss it a bit later so here's a can I can you show my screen right now okay so i'm not sure my screens wait a minute okay so there are some questions concerning was um AWS CFS port so basically in the cloud storage for example workspaces I found some really like confusing points of this idea that is there are some problems with AWS EFS support the first one is it only runs with EC2 instance so actually it is highly integrated with the existing AWS EC2 and the second one is I think AWS wants their user mount their EFS to EC2 actually when I when I create an EC2 instance and I only need to run one command line to mount those EFS to EC2 so if you want to Jenkins do the job for the user it might be much harder than the user's do itself so there might not be much uh benefits to the user if they have to use Jenkins yeah it depends on how you implement a EFS market because we talk about use case when you provision an agent an agent has EFS out of the box then yes you probably don't need to implement something specific but imagine you need to provision the EFS on demand within pipeline for example your pipeline reaches whatever massive testing state stage or coverage and it needs more data in such case you can use EFS APIs to get more data on your machine but an agent-addition model one of the use cases another use case is still the same EFS instances between machines which can be also done inside the work server workspace manager plugin so for example you need to pass workspace between multiple agents and you use EFS to implement it and yes okay you can continue yeah so I just provide my examples and again EFS is just an example so if you don't see much benefit of using EFS as a reference implementation you may think about other implementations because EFS was just provided as one of the examples which could be yes actually I have discovered something interesting during the exploration of the EFS so I think that it is doable for AWFFS and there are an existing EFS support that is an EC2 plugin so basically I think the most hard the hardest part of implementing the EFS support is I need to get access to the users access rights right I need to make my Jenkins as a user so I need the credit user user names or something like that to log into their console I think this is most the difficult part but it's already done in the EC2 plugins it's just in the EC2 plugin this is a widely used plugin so in this EC2 plugin it has already implemented the ways to get access to the console and then through that console we can send a request AWS and so that includes create the EC2 instance long-chain EC2 instance and maybe do other things that a normal user can do so basically if we really want to implement the EFS we can make use some of the code of the EC2 plugin I don't know if that is doable if you have any doable there are multiple ways to do that firstly you may want to declare dependency on EC2 plugin directly so as we discussed before there are extension points in Jenkins these extension points may be mandatory they may be optional so for example you can declare optional dependency on EC2 plugin with optional extension point implementations so that you can still use external workspace manager plugin without EC2 if needed or there may be other ways for example moving shared functionality from EC2 to another plugin like API plugin for example there is a plugin called AWS credentials which allows managing surprise AWS credentials so maybe something could be done like that for EFS just one of the examples so yeah if you really want to focus on EFS in your project then it's nice that you discover this EC2 plugin the recommendation is to think how you integrate the things with each other and it would be a great part of your project proposal if you explore this area and see how you do it together okay so actually this is another idea here is that I think that every if we want to support to different cloud service providers we need to offer an API plugin for those of all the for each of the the cloud providers I think that is a better practice better line because if any other plugins wants to use the API it might then just need to access the cloud providers so as you mentioned and there is a admc credential plugin so I think that might be really helpful for this job because if I can just use it and then I can use something like maybe a dummy console to send requests to the adb so that would be more doable for me if so basically I think that is a way so here's at least another project idea so and as you mentioned in the the original project project ideas I think there would be some cloud service providers that didn't consider like for example adb cloud is a very good cloud service provider in China so I think for as a Chinese I would like to implement something for the adb and for me I think the best way to support external workspace manager with a specific cloud service provider and better to first of all like I have to implement it on cloud service provider API plugin and then use like here log into the cloud service provider and then issues requests I think this would be a more doable design for for all the kind of things like the couple what we do in external workspace manager and log into the service provider what do you think it might be feasible design and if you want to do such thing you could also take a look at jclouds so what there is a project called Apache jclouds it's effectively a set of libraries for working with different cloud platforms using unified APIs I've listed the link in the chat so it might be one of items you would like to take a look and if you want to go with this unified APIs idea and so here since the discussion is over I would like to I want to solidate on which one we really want to do because in the proposals I'm not sure which one is better so if anyone can give me some suggestions like how do I gonna implement for example AWS EFS support in the external workspace manager and from the choices I mentioned above and if I set my piece maybe Alex or Martin would like to add something maybe anybody else I'm not very sure I did understand the question so can you like quickly repeat please so basically there is two ways to support AWS EFS support the first one is I do I write the code that I'm logging to the cloud service provider that is I become a user of the AWS and write this part of code in the external workspace manager code base and that's design but if we want to support multiple cloud providers the cloud base of the external workspace manager will become really large and the other solution is I first write a like AWS or some other cloud providers API plugin so that offers me a function to looking for other servers to act as a cloud user and then I can use those API plugins to send actual requests of some specific requests to the cloud providers and I think that is a more a clean design of it which one do you think is better yeah I also agree with you I think the second one is clear because you actually decoupled the logic from from the AWS plugin with the actual logging and credentials and stuff like that in another plugin but I'm wondering if you can integrate this somehow with what Oleg mentioned earlier with the AWS credentials plugin or something like this I'm not very sure if they can be integrated together somehow so so so that you don't need to actually write another plugin you can just rely on that plugin to to use the credentials for the AWS but but the main idea is that separating these I think it would be a better idea than just having the code inside the external workspace manager plugin yes for AWS EFS I might have already an existing plugins to use but for other cloud providers with Alibaba Mediathe or something like that I might need to write for a write different maybe I need to write different plugins or use the one the oracle to see what I'm not sure what is that but just as Oleg mentioned it looks like it can offer a uniform and API tools all the cloud service providers so I think that would be after investigation I can maybe clear it and clarify it in my proposals so here's another question so can I just write it those proposals in the cloud space a cloud storage support for external space so in this project ideas or do I need to write an individual project ideas I would say that you should write in the same document but maybe Oleg knows how this should be done best but you could write like your ideas and say that okay if we want additional cloud storage with different providers then we can perform we should write this plugin and then you write details about the plugin you would like to additionally implement that's what I would say so I would say it should be in the same document but I'm not very strict with this okay what do you think Oleg yeah I think that if you have such multiple ideas in your project proposal so what we need is to actually understand what would be your approach for example how you start the exploration how you make decisions for example you can say that during the community bonding and first coding phase you implement something generic and then you have a decision making point where you decide which option you proceed so as long as it's traceable as a project it's perfectly fine to have optional conditions in the proposal okay so maybe like if time permits I'm gonna do this sort of stuff yes right and I think that is a good part so it really helped me a lot because I really don't know which one to I don't know how and can I concretely ideas in my mind so today's so if anyone has gotten another questions please go off I'm done with my questions okay thank you so any other questions okay so Natasha let the call so yeah we're just in the chat if there is no questions we could probably close down okay so like can I ask a question if no one have any other okay yeah so probably I need to share my screen I hope it's visible oh yeah so like in the previous question one doubt was created regarding this point that whether by implementing this point can we you know discard both work spaces and builds or we can only just discard the builds only by using the information through fingerprinting so I think I and Martin are discussing and like we both like I was you know a little bit confused regarding this maybe I can give a bit of context and continue yeah so Oleg last session we have discussed also with Martin and we have suggested that so external workspace manager plugin is integrated with fingerprints so if you get the fingerprint for a specific workspace you have all the information you need to actually delete that workspace so Martin and I suggested to to make use of this fingerprints to be able to integrate with the discard plugin and be able to delete the workspace does it make sense what I'm saying yeah it definitely makes sense but I think like from you know getting the workspace path and all that we can also get some information about the builds like the build the build information right so like what my question is that uh can we just discard the builds using that information or uh we need to go through another path for discarding the builds uh which are going on in these multiple workspaces the the thing is I don't know how the discard plugin works but I would assume that you just give that plugin a path and uh yeah so yeah yeah so like I'll just give an overview that uh the delete method which is currently used by the log router what it what does it do is like it first of all phases the path of the root directory and by getting that root directory it uses some logic and it just discards the builds so what I thought is that by the by fingerprinting we can definitely discard workplaces but we can also get the path of its root directory and by using that we can uh you know just reach to that build and we can discard that build too yes so yeah so I think that here the main idea would be to discuss workspaces of course uh workspace um discarding builds not the main purpose of this plugin yes you can do that but if you talk about all workspace uh logic it would be only discarding workspaces and for builds it should be an hook so when something just decides to discard the build this process happens and then there will be location for discarding uh workspaces as we discussed before as a reasoner and then you will be discussing discarding workspaces as a part of a build to discard procedure but yeah if you talk about specific path for external workspace manager integration I would expect it to be managing only workspaces because the build definition will be handled on a higher level okay so like for a specific implementation with the external workspace manager uh you suggest of discarding only the workspaces uh not builds right now yeah it can be done but at a higher level right yes okay so I just include the uh so okay so like according to this point the workspaces will be discarded according to the user so I think this point is much more clear uh okay uh so Martin sir uh I think this comment can be resolved right right I wanted to make sure that the understanding was was correct um workspaces do not contain builds it's yeah yeah yeah it's build objects that have references to workspaces ultimately yeah okay so I just resolved okay and the one more point which I need to discuss with you Olexa is uh that uh uh okay yeah so your comment regarding to this feature which I mentioned uh according to me so uh so so actually uh what I meant by this is that uh I wanted to you know I had a feature like uh some type of recycle being uh you know where if uh if uh due to some user mistakes uh few of the builds get discarded which were important but and now if once they're discarded and if a particular user wants some information regarding that so you know by adding this feature it can be accessed so yeah uh so definitely I have written that if time permits and if all my other features gets completed then I will try to implement this so uh you know uh so like here you are uh just commented that uh it might be preferable to have it on a higher level outside this plugin so yeah definitely it's right but uh I have uh you know just added a few points regarding to this in the uh like in this extra feature uh part that uh uh maybe this uh can be uh you know worked for that uh one comment to discarding workspaces uh the current git plugin is using workspaces for triggering if uh you have wild cars there uh wouldn't that be a problem if you just got the workspace then it will trigger itself again oh yeah so like uh at that type uh workspaces would be needed but uh like what I am suggesting is like a feature like press bin you know where uh for some of us uh some details of the discarded builds or workspaces can be available for the user so like uh in any you know case of emergency or like due to some like due to any mistake if anyone wants any information regarding that then uh you know we can just provide the user that facility well actually um I don't know historically why it it needs the workspace for triggering if it's wildcarded but uh we probably need to be be looked at so we don't get into a a uh a continuing uh triggering and deleting workspaces etc uh okay yeah so like I'll just have a look on it the current git plugin will use the workspace for uh polling the or fetching from the remote server in order to figure out if there is a new commit for example uh and if you're and then it will also trigger if it doesn't have workspace so the first time you configure it it will actually uh restore a workspace so if you're then deleting it then basically you're keep an infinite loop of builds okay yeah yeah okay I just got that yeah okay so like I'll just have a look on it once more and uh oh yeah one more thing clarify with Oleg sir that he has commented here that why I mentioned the data structures point in the proposal so uh Oleg sir what I meant was that uh you know uh first of all you know uh yeah so uh like uh efficient if you give me some time to process your feedback oh yeah okay sure sure no problem because yeah I haven't taken a look at your proposal yet I'll try to do it tomorrow on Friday yeah I can guarantee that I'll try to give you the uh yeah so like uh sir like uh I'll you know uh just mention uh like there are a few changes needed in the proposal so like I'll just do it uh you know by by one or two days and then I'll you know just uh add a message in the guitar chat room of that GSOC build discover uh to uh you know for review so at that time uh you can review uh you know the latest proposal of mine okay and one more doubt that uh regardless of uh you know giving uh these proposals for review to the mentors in a specific guitar chat room where should I post my document link so that you know any mentors or you know is anyone from the community can uh give comments or or suggestions so yeah if you want to have to ask something specific to development the best way to do that is to ask in the jenki's developer my name is or if you have specific questions not related to your project directly the results jenki's guitar channel there is IRC channel so you can use these generic resources not to ask common questions it would be my recommendation if you want to have more people participating in the review yeah okay sure sir like I'll just post my link uh you know like after my final proposal uh you know after your one or two reviews and after all the changes I'll just post the link in the uh or two mailing list one will be the GSOC open for all mailing lists and second will be the developer of mailing list so that uh the mentors or the community you know can just go through the proposal and I can get more and more reviews exactly yeah sure thank you okay so are there any any other questions left yeah just not so we have a few minutes left so if there are any topics to discuss we have several mentors on the call maybe we can briefly do that so let's just pass it in my Gitterchats because yeah as I said in the chat I will think how to improve the communication at this point in meetings because yeah probably we need to somehow time box the questions and yeah we should really do the most of technical discussions in the mailing list on Gitterchannels because yeah now it may be complicated some people like the context so yeah it would be more efficient yeah sure and uh uh let's say one more request that so like if you you know just see that any other section needs to be presented in my proposal then please just inform me so that you know I can add that section like in my proposal I have taken care for most of the sections you know like my personal information and synopsis project description timelines and all that but and you know my working time commitments and all that but like if you know it's already 15 pages we don't really want to submit proposals in several editions okay I think that critical sessions are addressed there if you want to add something it's looking to do that but yeah as I said before usually proposals are from two to five pages so when you go beyond yeah most likely it's about additional information you put to appendix yeah okay yeah so like I'll just go through it once and you know I'll just remove the information which is not much more relevant to the so to that so that the size can be reduced okay so if there is no other questions thanks everybody for participating and again we have chats we have other public resources and see you there you okay see you bye


thermodynamics and that's true whether we're doing the electrochemical current or time result spectroscopy so when we're looking at experiments we're looking at activation barrier heights for example the rhenius law instead of these thermodynamic delta g1s of the minima if you do know something about that transition state you can frame it in terms of transition state theory and an activation free energy if we can separate out these electron and proton transfer steps so that you're just looking at an electron transfer step you could use marcus theory and that would essentially relate these kinetics to delta g1 using a reorganizational energy for example the reorganization of the metal oxygen bonds around the intermediate now one of the most general ways to relate kinetics to thermodynamics is using equilibrium constants their ratio should be the equilibrium constant and what i'm going to propose is that essentially time results spectroscopy is suited to do that because we can isolate these steps all right so with that i'm going to tell you about our experimental setup what we have is a semiconductor it's a strontium titanate single crystal and that's sitting in water and when you do that you get a nice electric field a shocky barrier in the semiconductor and you can use that with light to initiate the water oxidation reaction so that's been done a lot in the past we simply do it with an ultrafast light pulse such that we can get the time resolution and we get this is a band gap light pulse we get electron holes and we get quite good charge separation even though we're doing this with pulse light you measure steady state current and this is an example of it this is the current versus voltage this is with the light on this bending here is indicative of this band bending here of the shocky barrier we do our experiments essentially at zero volts versus scd so everything to show you with current is there so this tells you about the charge separation we can also measure the oxygen and the electrolyte using a Clark electrode and we get approximately faraday oxygen evolution of a four volts two one two one oxygen so with that we combine it with a pump probe setup this is the steady state version we initiate that steady state with this pump and then with a delayed probe beam we interrogate the reaction that pulse sequence looks like this so we have kilohertz light pulses and so there's two milliseconds apart because one is used for the the unexcited state in between we have the probe to interrogate the reaction we use a full electrochemical cell so this is the working electrode this is the other half reaction with a reference electrode we are constantly we don't we do do measurements with fluence to some extent but we try to keep it as much as possible to a single fluence that's one light pulse can only excite as much as two percent of the surface sites and that's essentially to keep these interfacial energetics the same all right so now i want to locate this semiconductor photo driven surface within the oxygen evolution reaction because that's usually thought of as a potential and a metal electrode and the essential thing that i'm going to point out here this is now the Gibbs free energy versus the reaction coordinate is that we first put the sample in the electrolyte and it equilibrates that a cologne can change the surface hydroxylation and then we have an instantaneous light pulse that creates those valence band holes and that's what drives the reaction downhill these essentially this is one of the things that's different and it essentially separates out the electron and proton transfer step into two separate reactions the first is a proton transfer step that occurs in the dark and i'll be showing this to you during the talk so the proton transfer occurs in the dark i'm going to write it that proton as a that's usually as a product here as a reactant hydroxyl anion that's because we're going to be changing the ph of the solution in basic conditions but into the standard state this would be a simple proton transfer reaction where you have a water absorbed surface hydroxylated here plus a proton it's the surface metal pka it is also what defines for a semiconductor the shift in the valence band edge with ph so after we do that we that's the explicit equilibrium in the dark we then shine light and instantaneously create holes in the valence band and they can trap preferentially on these hydroxylated sites to create the first oxidative intermediate i'm going to be calling this tioh star this can also have several different geometries we're going to be looking at one of them those geometries are based on where the oxygen is that's been oxidized and where the proton ends up so that can be somewhere on the surface as well so we use we actually learn a lot from the papers by michael sprig and jen chang they have calculated this free energy difference for titanium dioxide surface and that free energy difference is between a delocalized valence band hole and a trapped hole on the surface they did that with dft and amd calculations and they also very nicely put it within the context of marcus theory since this is a simple electron transfer reaction now i should say i now wrote that electron what's the product here is the reactant hole because that makes sense in terms of a photo driven reaction okay so already i've probably complicated the idea of a computational hydrogen electrode but this is very nice experimentally because we can use this dark equilibrated surface to understand what the photo driven surface looks like so if we're going to do that we better be able to measure it and you get got a good introduction to xps in the last talk we use ambient pressure xps this is also at berkeley at the beam line 11 we did that for our strontium titanate samples and this is for undoped and essentially for lightly doped as well samples these are aimd simulations by das demirage and this is a dft configuration here where you have one water absorbed group on the titania and a neighboring one that's hydroxylated we essentially did experiments on this and looked at the theory as well and this is the number density of the hydroxylated groups this is the number density of the water groups as a function of relative humidity or the water that you put in the chamber and the the calculations and experiments agree pretty well in terms of saying that strontium titanate is partial dissociation in other words every other titania is water absorbed and the other one is hydroxylated so if we want to preserve this surface in our experiments we actually have to do a scanning mode so we have to take our sample and literally scan it while we're doing the time resolved experiment so this is what our sample looks like at the very end in an scm and what we did is we scanned it for faster and faster scan so that's the green to the blue and you can see that the kinetics converge this is an optical probe versus the delay we can also take and go to a new fresh sample spot for a new delay position you can see that traces the converged curve so this is analogous to in a cat in a homogeneous catalyst just flowing the solution and taking the data as the catalyst goes by and what it does for us is essentially says that the kinetics we measure is coming from a point on the surface that we can define in the dark so the reason we have to do this is because as we have heard water oxidation restructures the catalyst and we can look at this x-situ with both t-em and s-em and the way we do this i'm not going to go into the details of this but we take the t-em thickness that's been changed after the water oxidation in the s-em area and the current evolved during the water oxidation which we tried to keep with the scanning method about a standard deviation of 0.5 percent is the current so we're always having the same current of all and then what we can do with that is look at the volume change to assume that that entire volume change just dissolved into the liquid and understanding two holes per oxygen we can put a limit of how much of the current went to restructuring the surface rather than water going to O2 and that is a limit of about five percent and so five percent of it is going there but that means a lot for the surface and it means a lot for your optical reflectivity so that's why we do the scanning mode but that that's what's going on in the bulk we can also look at this in elemental analysis and we see the main thing that's being dissolved is strontium into the solution and we can correlate that with ICPE beta okay so with that I'm going to be telling you a couple of stories the first two are a deep dive into the hole transfer reaction at the strontium titanate aqueous surface and the following two are the fate of these TiOH star intermediates and I will be talking about screening but that'll be at the end okay and it'll be involved with the fate of these intermediates so first about forming this TiOH star from which we're going to use ultrafast spectroscopy and the first thing I want to talk about is the structure of these intermediates and the way to get this structure one of the good ways to get this structure is through vibrational spectroscopy so this is a mid IR probe beam and this is an electrochemical cell and inside this electrochemical cell there's a little diamond that diamond is an attenuated total reflection crystal which takes this propagating mid IR beam and creates an evanescent one so one that's decaying in space and what that allows us to do is be sensitive to molecular modes and not to bulk modes of the crystal especially when we have that crystal sitting at a distance from the ATR crystal such that we allow the wave to decay fully that means in the background when we're doing the ground state we're not sensitive to the optical phonons and the bulk all right so with this what we were able to do is identify one geometry of these intermediates and that's the oxyl with the terminal oxygen and a proton transferred to a nearby site that vibration associated with this intermediate looks like this this is the change in absorption we see we only get it when we have whole excitation to the surface we can quench it with methanol which means it's related to oxygen and we do this detailed analysis experimentally using a phano resonance that describes these changes in line shape here so briefly a phano resonance is a discrete mode that's coupled to the continuum and so we're in the middle of a solid liquid interface so we have a lot of continuum and we can couple actually to the solid side as well as the electrolyte side so on this side you're looking at changing the doping density of the strontium titanate and that changes the electronic excitations within this window I should say this is in the window of titanium oxygen stretches but you can also have these mid IR electronic excitations and those are these plasma excitations they couple to that mode and they give you this asymmetric line shape on the other hand you can also couple to the electrolyte so we can get differences by going from air to electrolyte and also by changing the duration of the electrolyte going to hydrogen deuterium and so what's coupling here in this wave number region is vibrational modes of the water so this tells us that it's an interfacial mode so experimentally so we are sensitive to the interface there I will say that they are very nice phano line shapes in terms of what you can see out there I will give you the the details are here I will also point out that if you look at you phanos paper in section four it's a perturbative theory so it means that all the couplings add so that's why you can get the same phano resonance when you have to continue that's coupling to and I think this is a good example of that all right now I want to that's the structure of one of the intermediates that we can get and I'm now go to the formation time of these ti rate star and I'm going to look at that first through up oh I am sorry I am sorry so I jumped so actually to get this vibration to be associated with this axial there was quite a large amount of theory that was done and that was done in collaboration with Dasque Maraju and David Prendergrass and what they did was a strontium titanate slab where they calculated infrared absorption in the bulk in the in the ground state and with the axial configuration this is the optical phonon that we're not sensitive to in the spectroscopy and what they found in particular in the axial configuration is that there's a separated M1 mode here that's due to vibrations of the oxygen underneath that axial and you can think of this a bit in an inorganic chemistry way because what's happening here is when you trap the hole you lengthen the titanium oxygen bond this contracts the unit cell underneath and essentially separates this motion from the rest so already just with the structure we can start thinking about how do we map to this delta G1 axis of the first oxidative intermediate and since this bond is lengthening it essentially puts it on the weak binding side whereas Heinz Frey and Thomas Hammond who have respectively studied cobalt oxide and iron oxide found upon hole trapping an oxo which would be a shortening of the bond which would horristically place it on the strong binding side. Okay so now I want to go to the formation of the TOA start in a radius and the way we're going to do that is first optically. So you have a valence band you have the holes that you're creating here and when they trap on the surface you're essentially taking a valence band state and you're creating a mid gap state such that that reaction is spontaneous for the hole. Now when you do this you're going to get new optical transitions one will be an excited state absorption when you're promoting an electron another will be an excited state emission when you're from the valence band another would be an excited state emission when you're using an electron from the conduction band. Now these are at different energies than this free energy because they're electronic but more importantly they're vertical optical transitions that have to do with where the mid gap state is in the reaction coordinate as well as the valence band and the conduction band. I will just say that this transition at the very end of the potential energy surface this means you're on the excited state potential energy surface so you have an electron hole pair remaining here you're on the ground state surface. So this has been looked at by a number of theorists and and experimentalists and because these are optical transitions they're fairly broad so you can be looking at the axial but you can also be looking at the bridge intermediate which is hole trapping on the lattice oxygen. Generically they're called O- also hole polar on and the only thing I want to say about this is that essentially both experiment theory see UV-viz transitions associated with these mid gap states and hole trapping. So we looked at that in strontium tightening under water oxidation and so this is an example of our optical maps we're going from picosecond to nanosecond time scales here from 2EV to 3.2EV this is around the band gap of strontium tightening and you can see in the middle of the gap that you have these absorptive transitions as well as emissive transitions. This is in closed circuit when we have current and this is open circuit when we go. So I want to concentrate now on this emissive transition because you can see that there is a clear growth so that clear growth means that it could be related to the time scale of hole trapping. So we do get a very well-defined time scale so 1.3 picoseconds of that growth. We can then identify the nature of it since these are broad optical transitions using our vibrational probe and we find that the vibration of the axial also occurs with that same 1.3 picosecond time scale. So this emission we find nicely counts the TiOH star intermediates whereas the absorption occurs within the ultrafast light poles so within the generation of electron hole pair carriers and then decays which suggests it has a large portion of the population associated with the valence band holes. Now you might glean that from a simple diagram like this this is just a suggestion as to why this is happening but when you're taking a state from the valence band and you're using it to create the mid gap state this transition is going to have be complicated by essentially the valence the the complicated by the population of the valence band states you have left to create it whereas the electron and the conduction band here is not at all related to whole arm group formation so it can be a sort of independent count of these mid gap states. So I have one more way of defining this as the time constant of the whole trapping reaction and that's some recent work we did in the lab so these are optical transitions these are mid IR transitions we also looked at coherent phonons so when you create this TROH star you're distorting the structure at the surface for each one and you create many of them you could create a continuum interfacial strain and if you do that at an interface what's going to happen is you're going to get an acoustic propagating pulse into the bulk of the crystal and then our optical probe will scatter off of that acoustic strain pulse and across the interface and have coherent oscillations in the data and those oscillations will have a frequency that depends on the optical wavelength because this propagating wave is propagating you're going to get a dispersion relation so this is the frequency of each of these oscillations versus the optical wavelength and the model essentially includes the acoustic velocity in strontium tightening these are the oscillations we see in the data we can remove them by that model by knowing the dispersion relation and what you have as data is essentially the phase of these oscillations as well as the amplitude and what Ilya Vinogradov did in the lab is he took a model that was done before but expanded it to kind of the broadband spectroscopic range and that model includes the electromagnetic interaction so how these interfere with each other as well as how that's propagating acoustic strain is related to the interfacial strain so this is the propagating wave and this is the interfacial strain and so what's input into the model is the spatial decay of that interfacial strain which is exponential and a formation time which is an exponential rise and so this is that strain wave this is what's related to the spatial decay this is relates the formation time and this is just a convolution with the time resolution of the experiment and with that you can start understanding the phase and amplitude of those weights and particularly from the phase we can get a good amount of information so this is the phase in the closed circuit experiment and what's fit here is that we get a formation time for the interfacial strain also of 1.3 picoseconds which helps assign it to the TiOH star that are being created now it's also an independent measure because it's a phase we can also do that with different experimental conditions that phase also tells you that the essential the nature of the strain at the surface which is a C elongation versus the A and that C is in the direction of the electrode electrolyte interfaces so you can think of overall an expansion we can also do this experiment in open circuit where we're not creating a lot of these polar arms and what we see there is we can only see these oscillations at very high fluids and that phase also the phase is very different that all gives us that this is really carriers that are coupling to the lattice where this is polar arm formation all right we can now so we can do do something with that or I think I could do did that really well with this model and I refer to you to this paper we can get that formation time to the air that's shown there but the spatial decay is something that is harder to get at and what we could do is only put a lower limit and that lower limit means that there's an upper magnitude to the strain of about a percent so what I think that this does is I'm just going to summarize the formation of these tioh star intermediates is we can see them through the emission using electron volt energies we can see the formation also using hundreds of milliolectron volt energies and we can also go to the gigahertz which is fractions of a milliov and see them there so that means that we can look at them from the electronic transitions we can look at them from the normal modes they create as well as from the environment this is kind of the continuum strain you would expect from a collective all of these are states that you would expect to go into defining a free energy of the product tioh star so we assume we know what we're starting with which is valence band holes and we're defining the states of the product the fact that we see a close 1.3 picoseconds between all of these states tells me that we can define a common temperature for that free energy it might be some elevated temperature and most likely is because we're using an ultraviolet light pulse but common enough to the states so i think that's important i think from an experimental point of view this is also seeing this across electromagnetic spectrum is important because we can use this as cards in the experiment here this is better at calculating or seeing the total tioh star population whereas this will track a particular geometry and this will tell me something about the environment so with that we have a time scale for the whole trapping event now i want to that begs the question can we get a reaction free energy difference from our spectroscopy and the way okay so that's going to the next part of the talk which is essentially this tioh star intermediates are creating this picosecond time scale and they're fairly stable and that suggests that we could get an equilibrium constant from it and the way we're going to get the equilibrium constant though is not going to be following exactly the time scale of the back transport but rather shifting reaction conditions so i'm going to shift the reaction condition of ph in the dark that's easy for me to do and easy for the lab to do in ph just change the concentration OH minus through the ph and see how that affects the products that we create so this is the spectra that we get so again these optical naps delay and energy but now as a function of ph and you can see that the emission becomes a lot more as we go to ph 13 so already suggesting that we're creating more to a OH star when we have higher ph or a higher hydroxylated surface but if we're going to get free energies and we're going to get equilibrium constants this reaction better be common to this data which means i want to be tracking a common enough species on the product side and reaction kinetics that are essentially the same so how do you go about answering that question and one of the ways is to see if you can get a common basis set across the data and that's what ilia and a retro did they used a principal component analysis and both of them started with a singular value decomposition and singular value decomposition for each of these optical maps immediately spits out for you that you have two dominant components and then what ilia did is he took those two dominant components for ph 13 and just reconstructed the ph 13 data from them and then he took the two dominant components from ph 7 and used them to reconstruct the ph 13 data this is a simple rotation of the basis okay so that's a nice mathematical way we can do that as a function of a large range of ph and so we're basically taking the time scale the energy scale the ph as a data set and saying that we have a common basis that's a mathematical description of it but we really want this basis set to also reflect the optical spectroscopy and that's what a retro did and he constrained the basis it's not a simple rotation basis anymore but constrained it to have a pure absorptive component within our broadband window and a pure missive component and so this is the common spectra across that entire data set so it tells us that essentially we have t i r h star species that we can count by this emission that is fairly common across the data okay we can then look the kinetics associated with these species and we see that we have that picosecond component and then we also have another 60 picosecond component but the point here is the kinetics is common and we're just changing amplitudes so changing populations so now i'm going to look at this two picosecond component that we've already assigned and that is the one that has the nice ph dependence so this is the amplitude as a function of ph and this is its growth the 60 picosecond component which we haven't assigned yet doesn't contain that ph dependence now all of this analysis suggests that this is still related to 2 a h star that might be essentially from a different origin i want to take a look at this nice ph dependence here which if you look at it is in fact a sigmoid okay a sigmoid harkens of a reaction isotherm so if i were to think about just a simple absorption isotherm like this and this would be the coverage of the hydroxylated species if i tune the ph i'm going more i'm creating more of the product and this rise in the sigmoid would tell me something about its equilibrium constant the fact that you have a flattening here in the sigmoid means that it's a langmuir isotherm so that you have a limited amount of surface sites that can be hydroxylated now this isn't of a simple absorption isotherm it is of a metastable intermediate so this coverage is of tioh star so that what he immediately told us is that well we can construct an effective equilibrium constant here of the two sequential reactions and in this reaction okay the limiting reaction would be what's conserved is the number of holes i've created by my laser pulse which is either in the valence band hole or in the trapped hole so in this reaction i'm exchanging this for this and this is my tuning variable so as to say in this context that the number of holes we can create is only two percent of the surface site so you have many more of these than of these that you can create so with that we combine these two reactions through the common reactant which is the hydroxylated site and we get again a langmuir isotherm but now an effective k hey there's one approximation here but it's quite negligible so that k is now a combined k of the surface p k a and then of the hole trapping reaction and this is how we define our equilibrium constants so what i think this shows is that if you can time resolve intermediate populations you can in their meta stable you can start getting to thermodynamic parameters of the driven catalytic surface so you might ask me well i said a lot about this reaction here what about this reaction well okay maybe you can tune it with ph but is that really happening so what we can do is we can change our sample to change the nature of this reaction and so we did that by going from lightly dope strontium tightening everything i've been showing you here is lightly dope strontium tightening niobium replaces the titanium here and that's what gives us the shocky barrier and you can also get the shocky barrier get water oxidation with a highly dope sample get all the restructuring as well everything happens here too but here you have a ph dependence and here you don't and you can that bears fruit in the principal component analysis there's ph dependence here and there's no ph dependence here if you look then at the ambient pressure xps which is telling us what the surface looks like under neutral conditions you see that in the partial in the lightly doped strontium tightening you get a partially hydroxylated surface so this mimics a lot the undoped sample that i showed you earlier yeah so these are the hydroxyl groups we're fitting these are the water absorbed groups this is the carbon species this is the lattice oxygen and this is gas phase water when we go to a highly dope sample we have essentially a factor of two to three increase in the hydroxylation and that suggests a closely fully hydroxylated surface near the neutral conditions so we're we're dealing we are getting to the detailed coverages here but i will say that if you look at the low relative humidity range when you have water the amount of dissociation that you have there is about less than 10 maximum 10 which is this is at least 50 percent and then it grows what with relative humidity at ultra high vacuum these samples look quite alike okay so it's only when you add water that does it does it change so um this gives a picture oops this gives a picture of essentially a lightly doped sample where we have hydroxylated surface sites among a water network so there are two reasons i believe we can get this sigmoid is that we can push the hydroxylation in the basic pH range and the other reasons is we're look using the optical emission to average over all the different intermediates the surface so we can get basically something that's common on the product side that we're looking at so doing this i think we were able to isolate the first reaction step of water oxidation using the surface acidity in the dark should say this is a collaboration with Jan Rosmicell he did teach me a number of things about the oxygen pollution reaction made me more confident about the model with that i want to now place these two reaction steps so now we have a surface pka and a whole trapping reaction on the one delta g one that's the usual one that people use for volcano bots okay so these are these two steps here okay and we want to create a delta g one that we can put on an electrochemical scale for example strut weak binding here to strong binding there so this is non-trivial and it requires a couple of steps one is that we start off with the equilibrium constant that we measure and however that equilibrium constant that we measure is one of surface coverages where we have a laser creating many holes in the valence band when you want to compare to calculation this is a single site so you take a single hole single tioh minus site is calculated and then you get the delta g and you can get bright and equilibrium constant for that but we have a degeneracy of holes on the valence band side so you have to divide basically divide the partition function by that hole density so that's what we do to connect to the calculation to a single particle like delta g right and then what we do is we have two parts here we have the pka and then we have the whole trapping delta g we take from calculation the pka which is a pka of eight and then we take a calculation that was done for specifically for strontium titanate by das we take the highest one that was calculated so minus point four eb we put that in and then we derive back our experimental k and that is five in our experiment we get an equilibrium constant of 150 so what that would do would push the sigmoin from ph 11.7 for k of 150 to ph of 13 for k of five okay so it gives you an idea of the difference with that we can then essentially extract out that minus point four eb and add it to the valence band edge to put it on the electrochemical scale so in this context in this delta g one all the ph dependence is in the valence band edge so that's the surface pka reaction we're saying and that on an rhe scale would give you one number on an nhe scale would change with ph so with that we can put that on these volcano plots and this is then gives us essentially 2.4 electron volts puts it on the weak binding side now this is still approximate and i think that it's partly maybe theory but not from an experimental side i think the major issue is this part here dividing by the whole density because not all of the holes we initiate with the laser pulse are necessarily going to be evolved in this one reaction however even given that i am comfortable with putting it on the weak binding side because essentially this equilibrium constants can change by a lot and this is a reasonable place for it to be um for the pka and and for for what the delta g's are um okay and it also just the idea of seeing an equilibrium constant is important for defining a metastable intermediate of a reaction so um with that i am now going to go to the fate of these taoh star intermediates and that's going to be on the microsecond time scale so i'm going to start with just a proposed mechanism and this is just a proposed mechanism right now um to guide our discussion so the idea is is we create these first oer i mean the intermediates all at early time scales and then there's essentially dark and chemical steps that leads you to the rest and so that would then mean we're going to be looking at the decay of these intermediates towards those dark and chemical steps and so it suggests um because we're looking at a decay and because the dark chemical steps the transition state theory would be important a hallmark of this would be if essentially you create all of these initially and then the time dynamics is fairly uneventful until you get to the transition state and then you see a marked decay okay so we looked at the emission again at um microsecond time scales and we're looking at this here with just a single wavelength probe at 400 nanometers and it's okay it's fairly unembedent full in the nanosecond time scale but we are now going to be looking at that more closely um this was done with a 30 nanosecond laser but now we have a better one that we can really track with a picosecond through the microsecond with the full broadband spectroscopy but this is what we've done in the past we do get a marked decay on the microsecond time scale so why you might see a decay in the emission um going towards the next step in the cycle is because these tioh star intermediates contain charge and so they would be in the middle of the gap but if you form some neutral oxygen oxygen bond they would no longer be in the middle of the gap so we now um take this and we fit it with bi exponential decays and we get distinct time constants so marked microsecond times constant we get one of six microseconds something okay one of um eight microseconds one of 60 microseconds and we have the fact that we're fitting this with these um this kind of exponential these bi exponential decays means we have two parallel decay routes so the tioh star population starts out here and then it bifurcates into two populations that bifurcation is ph dependent so at higher ph the faster pathway is favored and at lower ph the slower pathway is favored we also deuterate the solution so we go from hydrogen to deuterium and we get a very nice and marked kinetic isotope effect of 1.75 on the slower route that you can see directly in the kinetics when you compare the ph the ph solution to the pd solution here so blue to red so that suggests that we have some on the slower route some marked oh breaking event that is screened so it's a low k k k i e all right this bifurcation is also there so we change the salt concentration in the solution and keep the ph constant and you can see the changes in the bi exponential decays that we analyze here so these are the amplitudes of those populations as a function of the salt concentration this is the slower pathway that's what's favored at low salt concentrations and you can see that the faster pathway grows in with direct exchange to the slower pathway so we haven't normalized at all these amplitudes okay and it does so up to a certain saturation point okay so this direct exchange is what suggests to me that the screening layer is involved so here if you basically increase the salt concentration you can screen a constant charge at the surface with a single layer of that salt whereas when you have less of that salt concentration in solution you would have a thicker screening layer okay so the reason i haven't mentioned the screening until now is because in the whole trapping reaction we don't see a dependence on the salt concentration and why we might not see that is because we have a constant voltage and we have a constant fluency excitation so a constant amount of charge here that we're putting on the electrode and so the potential difference between that and the counter ions would be the same with increased and maybe the potential difference is what's relevant for the whole trapping reaction whereas in this microsecond timescale what we are changing is the electric field so when we go to higher concentrations we're creating a screening layer in a thinner distance this is just the debiling which would imply that the electric field increases so the suggestion here is that this bifurcation is related to strengthened electric field allowing essentially the faster pathway to come into play okay so that's just a suggestion based on this bifurcation and where this effect saturates so i've been talking about these pathways and of course these pathways should relate to activation barrier heights so then we should be able to modulate those activation barrier heights so we did that first in the conventional way using temperature and this is the rhenius law you have the log of those kinetics versus inverse temperature and you get slopes for each of them in the range of 0.4 to 0.5 EV for the activation barrier height you get prefactors in the terahertz range which by transition state theory would suggest that there's vibrational motion that helps you get to the transition state so that's a conventional way to identify activation barriers but there's another way we can do that which is using the screening dependence and so what we find is that you have a log of the kinetics and those rate constants are also dependent on the screening and here we now cast that screening as an ionic strength and those rates increase with ionic strength okay so how screening might be involved is that these counter ions can screen a charged transition state helping if these are like intermediates they can help and get through that transition state to the next step now what I have shown here which I learned earlier on is that the Bronsted-Beriem equation I learned it predated actually transition state theory and what it said it was is usually used for homogeneous solutions is that is essentially describing this screening of a charged transition state where z is the charge in the transition state and the square root describes that it's a screening effect and i describe is what we modulate in the experiment and what we get is approximately a square root behavior but what we also get is a charge that's reasonable and that it's less than the full proton transfer and the charge is higher for the pathway that's favored at higher ionic strengths okay so what we then did is this is basically kinetics of the decay of this TIH star population we simply mapped it onto two different possible mechanisms for these activation barriers so there's a lot more work to do here and to elucidate these mechanisms we just mapped it onto them based on the reaction condition dependence and so we mapped the faster pathway to biradical recombination to form the O-obon and that's because it happens at higher ionic strengths the nucleophilic attack pathway we mapped onto the slower pathway essentially because it occurs with some HDKIE and it is slower so it would involve some lattice intermediate all right um there's a lot more to do as i said we are uh planning to do right now with those maps that i showed you those optical maps to do vibrational spectroscopy on them using kind of second stimulated resonance Raman spectroscopy and that's where we hope to try to resolve the oxygen-oxygen bond on the microsecond time scale and maybe something about these transition states so that's experiment long time and coming and part of it was to get really nice optical spectra was point one so i want to just introduce two other experiments we've done not on strontium titanate but onto other ones and it's just one slide actually but it has to do with the screening layer as well so the fact that these TiRH star population bifurcates like this and that there might be dark chemical steps that guide the bond formation uh suggests that surface mobility is really important and that's something where it's really hard to get to experimentally and it's hard to get to experimentally on transition metal oxide surfaces especially but early on we looked at this with just a simple simple conventional semiconductor gallium nitride and what we did is we um created a grading of charge carriers in the semiconductor and we could change that grading spacing and then we can diffract off of that grading using our spectroscopy and this is the diffracted pulse to get the rate at which the decay the grading is decaying so the great leaving and that would tell us about the diffusion or the lateral diffusion along the surface so this is done in an undoped gallium nitride semiconductor and this is the rate at which that grading decays versus the cue spacing of that grading which we can control and from the slopes what you get is the diffusivity and it's the charge diffusivity it can be of electrons it could be of holes or it can be of electrons and holes and so in undoped we basically mimicked what the what was seen before um 400 gallium nitride also using this transient grading spectroscopy and then what we did is we simply put it in a semiconductor surface and uh so then we took instead of an undoped gallium nitride we took an undoped gallium nitride surface and we looked at it in air and we got the same slope as we would get for the um for the undoped one but when we put it in um solution we got a much higher slope which means a higher diffusivity okay and so uh that suggested that essentially when we have charge carriers localized at the interface with an electrolyte uh that electrolyte helps that charge it increases its diffusivity or its mobility and you can see that by all the checks we made here on the different types of samples just undoped air undoped electrolyte undoped then gallium night or doped gallium nitride air and with two electrolytes and here is only when we get that factor to increase so we need the charge and the electrolyte to increase um the charge diffusivity and this is a holes at the interface so Tony I think we lost you we cannot hear you anymore hear us please disconnect and reconnect let's see something like this had to happen at a certain point that is uh what I was afraid of yes but in your case it worked perhaps someone can text her a message or some other way I just yeah I wrote an email but if the internet collection went down yeah but somehow I doubt that the internet connection is completely down to bolder does someone of you have her presentation no also even if you had the presentation you wouldn't be able to explain what is true it can be done by phone it already happened okay if one of you oh no okay you can give her a few minutes tomorrow no yeah yeah sure that is also true yes yeah tomorrow we have a shorter day so we'll be totally well we can give her a couple of minutes to see if she comes back if not yes it was almost yeah this is Francesca I texted her I can try to call her and see if she okay did you hear the last part of my talk or was it gone depends on how long did you keep talking exactly yes the class was something like five minutes ago we had the cut let's say but I didn't pay attention to the slide number was it oh god but but we can confirm which one you you said five minutes so I would say yes this one did you see yeah yeah and this one did you see yes okay so it's just the last one okay good okay add my my conclusion slide okay all right but it might have been worse for the questions I don't know do you want no questions you close the sharing again oh do you want the sharing okay okay let's do the sharing no please go ahead and finish your your presentation even if we're on 10 minutes yeah yeah yeah go ahead and finish okay I'm just I don't know what I just did presentations summer I will get this okay excuse me stopped at least the last yeah okay share do you see it no you see my oh no I have to share it and mention do you see this we see now you see the other one the presentation mode okay now you see it right yep okay I'm gonna go to my last one so this is the what you didn't see so basically charge diffusivity mobility is really important at these interfaces it could be very important for dark chemical steps but it's really hard for us to see it in transition metal oxides early on we did something on a simple semiconductor where we created a grading of carriers inside the semiconductor and we diffracted off of it and that grading essentially as it disappears is going to tell you about the diffusivity of charge along the interface so this is the decay of that grading that rate versus the q spacings and from the slope basically you're changing how close these peaks are to each other but from the slope you can get that diffusivity constant and so this is an undone gallium nitride this is an air and an electrolyte so we get the same thing and both and that was done before and we could say okay we had the same thing that others had and then we went to end up gallium nitride surface and there you would get mid gap states so you would get charged into you know things that are trapped at the interface and when we did it in air we essentially get the same thing for the whole diffusivity that we would get in the undone but when we put it in the electrolyte we got a higher diffusivity and so that suggested that essentially a picture like this when you trap the charge the electrolyte helps it move along the surface and so here's this undone gallium nitride and air and electrolyte we get the same whole diffusivity and end dope gallium nitride and air or we get the same whole diffusivity but in electrolyte we get a factor of two higher then the other part was that we were so this is all about the screening layer essentially and um we also looked at that in a battery electrolyte not the diffusivity but here we're just counting charge um the positive charge in the lithium ions and negative charge in the perforate and we're using this atr spectroscopy which found pretty powerful to get at that and we looked at the number density through our absorption cross section versus potential this is the nominal pzc which we define as the open circuit voltage go into the negative side or positive side and including lithium ions here cumulant perchlorate ions here and um and then we did an agreement with oligodon on this oligodon into the nd simulations what you do require for this is putting a factor for the surface enhancement that we observe on these gold electrodes but that factor is on every potential the same and then just this is the summary slide if people want to see this is essentially what I talked to you about is forming this to OH star intermediates through their electronic states and emission through their normal modes with vibrations and something about the continuum strain within coherent phonons that all gave us a whole trapping energy of 1.3 picoseconds that allowed you asked to ask the question well what is the reaction free energy difference and we isolated the equilibrium constant of this by changing but by the century the surface acidity in the dark and we got an equilibrium constant of 150 which placed this on the weak binding side of the volcano and then we looked at the fate of these in marine intermediates at six at microsecond time scales we see two transition state pathways which we loosely assigned to these two mechanisms and then hopefully I giving you an understanding that this is we it's it is important to isolate individual reaction steps within a continuous cycle and I think fundamental logical theory is a good bridge to try to help you know theoretical descriptors be related to time result kinetics I think if we see this more and more we're going to see that there's going to be a lot of opportunities to select for different pathways by for example surface modification I showed you one with the salt concentration and the EDL so that's my talk thank you so I will ask the audience if they if they have any questions and if not I have a ton but please go ahead if there is yeah James Darant just a second yeah you can unmute yourself yes I have it's fine thank you Tanya that was very nice I enjoyed um I was obviously one of the things we think a lot about is what the energy the surface um holes or the TIOH you talk the states are on the surface and you can consider the energy of those states versus depending on the edge but probably it's more relevant to consider it versus the energy of localised bulk polo arms I I wonder how and I'm there's quite a lot of work now on electron polo information but I'm not so familiar with whole polo information I I wonder what you think about how much this the relaxation energy of the surface TIOH groups might be compared to the relaxation associated with whole polo information so that that's actually been um calculated in strontium titanate and then I'll say experimentally but the calculation is that um this was done by Genotti for strontium titanate and um he did and he found for the that there is a whole because there's electron polo arms in in strontium titanate and I draw those kind of close to the conduction band when you dope but the whole polo run is minus 0.05 EV versus the valence band edge and this is what Das calculated for for these bridge and oxyles is minus 0.4 so that's the difference in the calculation um experimentally though um one should keep in mind that even if you have like a small difference to or small free energy to create the whole polar on it can create UV vis absorption because these are optical transitions that are reaction coordinate and for example Genotti finds and he actually calculated that for the bulk whole polar on is 2.5 electron volts would be the emission and um so how we relate this to surface poles is um because it's essentially a sensitive to the surface and not the bulk um but and and that they are much more favorable to be created. I also think and I know uh Mikhail Sprague has probably calculated this in TIO2 the bulk versus this is surface. Yes um I am I never trusted these results can I can I show this to you? Sure. I have to uh share my screen is that possible? Oh I will stop sharing. Maybe this is asking too much for me. I'm not sure whether can I? No then I will just tell the results um so this is uh um calculation we did with Jung and what we found very disturbingly that the A the reorganization energy for the OH-2 OH dot is the same as in bulk water and not only that even the levels themselves are in the same place so the surface OH- is very hard to distinguish from a bulk OH- both with respect to the levels and of course the reorganization energy. We know where the hole is because that's where the proton is missing but I never dare to publish it and Jung probably was rather happy that I didn't because it can be a DFT error, right? You understand what I'm saying? The pictures are the same. So you're saying that the OH- to OH radical in the electrolyte is the same as on the surface? That's right, yeah. Yeah I mean what we're looking at is on the surface, right? There's uh that we don't see OH- and OH- radical in the solution based on our structure. No no I understand that but I was just mentioning that uh so my my my explanation was that the tight hydrogen bonding of the guy on the surface is essentially the same as in the water but that was of course mere speculation. Yeah that is surprising to me because I remember your paper with the transient OH. I don't know if you guys remember the the JVCC you had a transient OH and it was very short amount of time and then it became the TOH star that I'm talking about and the free energy difference. Yeah yeah no I work this out a little better now. I can send you the picture by email and you can stare at it. That's not that transient OH but it's it's okay yeah I would love to see it. Yeah so as you understand the whole the un-relaxed hole is below the valence band so obviously it doesn't exist for too long. Okay I'll send it to you. Oh the un-relaxed hole of the TOH minus or the transient TOH is below the valence band so it doesn't live that long yeah yeah that's that's published right that's not something about one volt. Yeah yeah yeah a question a question I have is regarding hole accumulation at the surface so you might have seen Professor Darren's talk the fact that holes can accumulate the surface and then drive a series of chemical reactions chemical steps and it seems to me that your cartoon in which you had that cascade of steps and you mentioned the fact that the first one is light driven and then you have a series of steps that are dark steps yeah so is this consistent with the picture that Professor Darren has proposed so you accumulate the holes at the surface right yeah some chemistry happens right but chemistry is not a sequence of one electron oxygen but it is can be single steps can be multiple steps so this is like a thermo chemistry it's not an electrochemical step is that emerging from your work too? I would say that on TiO2 so we're very much on strontium titanate but on TiO2 the picture that you just said I would say is consistent with this we still have to look at this picosecond to nanosecond range like I said and also assign the 60 picosecond times constant but if I look globally that idea that there's like something on basically we have a similar optical cross section at nanoseconds that hundreds of nanoseconds that we did at two nanoseconds and that's a little bit so but we want to do that in detail I want to say we're going to say but then a March decay afterwards suggests that these electron transfers are happening early and then there's dark chemical steps and yeah that's that's yeah but now you also have a way to to measure the coverage of these intermediates so you could do the very same thing that Darant has done with optical spectroscopy to correlate coverage of whole trapping intermediates and photorelectrochemical performance to see if indeed there is this multi-hole radar terminus step or not so it would be two different ways to different spectroscopies to address yeah the same issue right so one thing that we don't do a lot of but we do some of is a fluence dependence which is essentially what James Duran is using part of the reason we don't do that is because we want to keep the interfacial energetics the same for what we're looking at and then we're spanning the reaction conditions so in in the what I want to do to make a connection here is that in order for us to really make this connection we need both the TAOH star as the well as the bulk holes we need a count of both and I think that's why I put that the TAOH star is a good count of emission through the emission through for all these reasons whereas the absorption has a lot and I showed on one of the slides it's really with the ultrafast light pole so which with carriers coming and then has a lot of the valence band holes but I can't say that it's all the valence band hole population because it is a 1d spectroscopy so it's the populations of both and we're using the valence band states for that transition that are the ones that are also creating the whole polarons or the star so the time dynamics is going to be a complicated by the valence band states how they're changing in time as well as the whole polaron states how they're changing in time whereas the electrons are coming from the conduction band are independent the other thing is you're going to have overlapping transitions that's another thing and the reason I just point out this is because it's 2EV we have a peak there people assign this to O- in oxides and so on but I think if we get more data for both of these transitions perhaps we can take out the populations and then for example do a fluence dependence to see because one of the things that also when we're doing the equilibrium constant what I would like to know is how many holes are involved exactly to create this amount of TiOH star and we're gonna we have more holes than we have TiOH star from what it looks like right so and and it could be 50% or something so calibrating that would be good and so I think what we need is a broadband spectroscopy where we have more information on the two populations and then a fluence depends I will say in terms of fluence because I didn't get to in the talk is that you're going to saturate the emission if we do this scanning mode where we're really looking at a fresh sample spot you saturate the emission at a certain fluence which makes sense because you only have too much so much TiOH minus there at the surface that you're using whereas the absorption increases linearly that linear increase though can be of valence band holes you're creating or of total charge at the surface right it linear increases one has to you know and deconvolve a bit so I think that I think yes I think that in short we should be able to eventually make that I also think theoretical input would be good here for the optical admission and absorption and what it's going on perhaps some ideally DFT calculation but I know that's very hard for electronic transitions but even in terms of what I'm talking about like if we have kind of like you know Fermi's golden rule you know what are the you know I can give you the number of poles that we create and things like this and that's something that would be good perhaps as you as you were referring to my work as Emanuele I maybe I should have a little comment on that as far as I understand a lot of the first part of your talk kind of was the formation of the surface holes which then in my talk I focused on how those holes or surface TIOH groups come together to drive or draw stations so in that sense I think what we do is quite complementary the bit where maybe we have some differences on the time scale of decay of those holes at the surface where you see quite a lot faster kinetics than we observe and I am aware within ultra-fast measurements it's quite hard sometimes to avoid recombination losses and I know you've done quite a lot of work to try and show it's not recombination and all this sort of thing and maybe strontium titanate is really unusual at having much faster kinetics than other materials we've started to look at that and we haven't I'm aware the measurement the reason why we do our measurements with these long LED pulses is to try to avoid the issues of the ultra-fast laser pulses and all the high intensities they create and all this sort of thing but we're certainly planning to do some lower light flux measurements on the STO to see if we get similar time scales to you or while our slower time scales so yeah we are you asking and you know we do do use as ultra-fast laser pulses we do get 75% in greater quantum efficiency with it and I know that sounds unusual but it's not that unusual in the context of a single crystal because if you actually use the diode well I mean the diode is but and but it does limit that we it's hard to get to other materials so we use this as a model system and then um in the future try to get it to other materials too with it but I think you were pointing out microsecond time scales versus your millisecond yeah because most of our warthog stage is pretty second to seconds um yes and no it depends on what special region you're talking about like these microsecond kinetics are not inconsistent with oh oh bond formation because I mean oxygen evolution might have you know so oh oh bond formation it's half an EV electron volt scale and terahertz so the the time scale you're looking at also depends on the spatial scale you're looking at you know and where you're going from and so um yeah I I think it's and and we do we do are seeing oxygen in the in the electrolyte we are seeing ultrafast we're seeing start separation so most of that shot yeah most of that is leaving at microsecond time scales but it might be that other things are rate limiting of the reaction like the oxygen evolving um and it's very hard for me to connect to the turnover rate yet and um because it's very site dependent how many sites are involved in that millisecond time scale let people talk about or second notes I know that our for our spatial site we're we're doing one oxygen per the per site per second for for the spatial region that we have which is not inconsistent with with some of the things on oxides and that that's how what we produce and what um what we produce is that and then I forgot what else I was going to say it was fine okay I went out there was a you know I hope you know there's a lot of things of operando and in situ and that kilohertz laser pulses aren't catalysis necessarily and I just I don't know how to answer that because catalysis is inherently transient and that transient steps give you a steady state we pulse that catalysis and we get a steady state we get a steady state on those scans of 0.5 standard degree we can we can do that on a clean enough sample you know do that for for a while so the idea that catalysis isn't inherently something that you can control by pulsed excitation to get a given steady state I don't think is true because you can also continuously light excite and just continuously have holes but that's just one rendition of that steady state because the process itself is inherently transient I mean I suspect if we get into too much detail on the transits of adoscopy that might not be quite everyone we can have more discussion about the best way to do the details that was not just to you James it was just a general what I've been thinking yeah okay so yeah I think we're done for today thanks a lot to all the speakers and all the people that participated in the discussion and we can reconvene tomorrow in the afternoon for the last part of the of the workshop so thanks again professor bandical nice to meet you actually I I uh Elena Magnano was in my lab for a little while and we did some resident xps I know nothing about it but she did it for us and then yeah I just want to tell you nice to meet you too great talk yeah okay see you bye bye bye everyone right


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