Welcome to Conducting Observational Research, part of the Research and Assessment Cycles Toolkit offered by the Association of Research Libraries and made possible by a grant from the U.S. Institute of Museum and Library Services. This presentation is part of a module that focuses on collecting data, evidence, input, or other information for library assessment projects. It describes observational research methods, including techniques for conducting online and in-person observations and analyzing findings from this type of study. We hope the content is useful to library practitioners seeking to conduct assessment projects. At the close of the presentation, you will find a link to a feedback form. Please let us know what elements were useful to you. We'll start by talking about what observational studies are good for and not so good for. Next, I'll go over a couple of types of observational studies and then walk through the logistics of conducting an observational test. I'll wrap up with a few pointers for analyzing findings gathered through observational studies. In general, observational studies work well for discovery and exploration. Observational studies can be used for developing a broad, holistic understanding of the problem space, broader than you can get with interviews or usability tests. They can reveal the larger context of where a system fits into a user's life, not just in the context of a user-specific workplace, but also to set social elements to a user's interactions with a system. Observational studies can be used to discover different kinds of constraints a user encounters, including physical and social barriers. For instance, is there a physical barrier that makes a service or space hard to access? These studies can also be used to uncover behavior patterns you may not have seen before, as well as unmet needs. Observations will also give you a glimpse of natural behavior or as natural as you can get and likely more natural than what you see in usability studies or that you can learn through interviews when participants might be inclined to perform or tell you what they think you want to hear. That said, it is important to remember that participants who know they are being observed may behave differently just because they are being observed, something called the Hawthorne Effect. You will likely find that some of your participants may behave slightly differently. For instance, they might check Facebook less, read web pages more carefully, simply because they know they are being observed. Unfortunately, there's really no way around this. A synchronous observation is often as close as you can get to witnessing natural behavior. It's also important to remember that your interpretation of their behavior is always mediated by you, the observer. Like other qualitative methods, observational studies are not good at getting quantitative results. They're not good at gathering evidence to validate particular decisions and they're not good at gathering evidence for anything quickly. Observational methods can be very time intensive and even a bit boring at times. These studies are also not good at answering specific interface questions. If you want to test an interface, it's likely better to conduct a usability study or an AB test. There are several different kinds of observational methods. For the purposes of this module, we'll discuss two. Fly on the wall observations, which typically happen synchronously in physical spaces and online observations, which happen online either synchronously or asynchronously through a web recording that you review at a later point. The traditional way of doing fly on the wall is a physical space when users are engaging with a service or space, for instance, a new piece of furniture or equipment in a study area or a library service point. While it's technically possible to do a fly on the wall study of an online application or interface, it can be hard to do successfully because it's difficult to observe what's happening on participant screens unless you're very close and sitting so close will likely disrupt participants natural behavior. You can certainly try to walk by your participants periodically and catch responses of what they're doing, but that will only give you occasional momentary slices rather than a continuous stretch of activity. When studying online interfaces, you may want to design a digital observation. With this method, you'll recruit participants who are willing to record their online behavior for a period of time. You'll likely specify the length of time you're screencasting. You won't find a lot of people willing to observe, willing to let you observe their online activities for a whole day, for instance. It's not possible to do this kind of observation secretly, as you'll need participant consent. This, of course, means that your participants might alter their behavior slightly because they know you're observing them. Still, this kind of study can give you rich information about how users engage with library and other interfaces and systems. Note that observations are often paired with interviews. You might consider conducting an observational study and then talking to participants to get more detail and explanations of their behavior. Now, let's talk about conducting an observational study. When designing your study, you'll want to articulate your goals. For observational studies, your research question might be a little more open, but you'll still want to have questions and goals firmly in mind. For example, you might do an observational study to learn more about how undergraduates locate information when they're beginning a research paper or how graduate students conduct literature reviews as part of their dissertation research. Your research questions will likely evolve over time, and doing this type of study may generate additional research questions. It's important to select the style of observation, physical or fly on the wall, digital, that's best suited to the particular questions your study aims to answer. If you are interested in online information-seeking behavior, digital observation is probably most appropriate. If you go this route, you'll want to think about the phase of research or information seeking you're most interested in. For instance, their initial information gathering phase, their paper writing phase, et cetera. It often works well to request an hour-long slice of users' virtual interactions. You might also consider setting up multiple appointments with the same participant in order to observe several phases of their research process. You might decide that your research questions warrant a physical observation of users engaging with physical spaces or service points in a library. In this case, you would observe how students interact with each other and librarians, how they interact with their environment while working, how frequently they use personal or library technology, and what kinds of unrelated activities they perform while in the library, like eating or listening to something using headphones. Note that it is possible to do this kind of study secretly and that this study requires fewer resources than one that includes multiple phases or is more participatory in nature. Observational studies are resource-intensive and somewhat intrusive for the participants, so it's often difficult to conduct this type of study with large sample sizes. Practically speaking, you might want to start with five to seven participants and then expand if needed. You won't be able to draw a generalizable conclusion from a sample of five, but you'll still have really rich recordings that can generate new ideas or research questions. You'll also want to think about how long each session will last. An hour-long session is a reasonable baseline, and then again, you can expand if needed and appropriate for your study. You'll want to base your incentive on the length or total number of sessions, providing higher incentives for a longer or multi-part observation. When recruiting participants, you'll face some of the same concerns about sampling bias as with any other studies. Get the word out among as many segments of your target population as you can. You might try using word of mouth, flyers, table tents, and other methods to recruit participants. You might also consider developing a short screening survey to select your participants. In the screening survey, ask questions that are pertinent to your study. For instance, if you want to observe behavior related to online research, ask participants a little about their research project and where they are in the research. Learning this information advance will help you select your participants and determine when to observe them. For instance, if they're only starting a project and you really want to observe the end of their research project or process, you'll want to hold off on screen casting until that point in their research. Of course, with physical fly-on-the-wall studies, recruitment and incentives are not necessary.  These studies can require a little less advanced planning and overhead than an online observation. Let's talk about some of the logistics of a synchronous online observation. Because you're recording this session, you really only need one person to moderate, so it can be beneficial to have someone else watching to help take notes or to be a second set of eyes and ears. Ideally, the moderator will be the same person who is in contact with the participant during recruitment and screening. This isn't absolutely critical, but it can help participants feel more at ease if they already have some familiarity with the person who's helping to conduct the study. While it's possible for others to sit in on the synchronous observation, I'd recommend restricting the number of people watching live. The participant might find it unsettling to know that several people are watching their every mouth move. If you go this route, you will certainly want to let the participant know that others are quietly observing. You might find that it's easiest for all involved to limit the number of people watching live and simply record the session for later viewing. Either way, be sure to let your participant know that you'll be recording their screencast and that others might possibly view later, but assure them that the recording will not be shared publicly. Regardless of whether the session is synchronous or asynchronous, you should be sure to get your participant's consent before recording them. Tell them who will see the recording and what the data will be used for. In general, it's good to restrict who can view the recording to the research team, so you may want to reserve the right to use clips and presentations or images and publications if needed. Check to see what guidelines are for your institution in terms of human research and then be sure to follow your institution's protocols. You'll also want to choose your recording platform. I'd recommend using something that is familiar to you and your users, like Zoom or Teams, Adobe Connect, WebEx, whatever is mostly, most widely used and supported in your community. If you don't have access to a recording service, you may simply point a camera at your computer screen to record your participant's shared screen. When conducting your observation project, I'd highly recommend that you do a pilot before you start your observation session. You'll want to be sure your screencasting and recording setup works properly and that your participant isn't confused by your instructions. If you're doing a physical fly-on-the-wall observation, I highly recommend testing your observation log or note-taking template in the actual space you plan to observe. Record findings in the log and then make adjustments to your note-taking guide to be sure it works well for your needs. If you end up with good data during your pilot observation, you can always incorporate those into your final findings. If the observation is synchronous, be sure to provide a very short introduction to reintroduce your project and reiterate any confidentiality clauses. And she might be catching personal interactions like social media and email, reassure participants that you won't share identifying information even if you share portions of the recording. While the physical or online observation is underway, keep in mind that you are meant to be a fly-on-the-wall. Just watch, listen, and observe. As I mentioned earlier, you'll want a fairly structured and detailed note-taking log for physical observation. This isn't as critical for a digital observation since you'll be able to refer back to the recording after the session, but it still might be helpful to take notes. You never know when you're going to have a technical failure and it's also easier to ask follow-up questions in a post-session questionnaire or another study if you jot things down that you know you want to ask about. Taking notes during the observation will also make it easier to familiarize yourself with your data and then analyze it once you're at that stage. Finally, you might consider developing a short post-session questionnaire when you ask where you will ask follow-up questions about what happened during the synchronous recording. Some of your questions may be based on the session itself, or you may want to ask questions about whether the participant felt the session was representative of their top typical online behavior. When asking follow-up questions, be sure to keep them open-ended. For instance, if you're interested in how representative the session was, you could ask them how the session compared to the past experiences engaging in the same activity or ask if there were problems they encountered during this session they don't typically encounter or vice versa. And of course, be sure to thank the participant when you're done. So once the observation is complete, it's time to analyze your findings. Observational data is very rich and because it's so unstructured, it's important to keep in mind that what you find depends on what you're looking for. Because of that, be aware of just looking for evidence of the answer you expect to find. This may lead to an unreliable reading of the data and you'll also miss out on other discoveries latent in your recording. When analyzing your data, start by reviewing your notes and the recording. The more acquainted you are with the data, the better. You might consider this process. During or immediately after the observation, take detailed notes about what you saw and what questions come to mind. Then take some time away from the data, at least several hours or even a few days so you can come back to it with fresh eyes and a more objective perspective. At that point, begin to look for overarching themes and concepts in your notes or structured observational logs. Begin to define or code those themes. Look for inconsistencies or consistencies in the data and continue to make note of what you still don't know, what requires additional research or consideration. Focus on information most relevant to your questions first. The online recordings have a simultaneously unstructured and narrative feel because of recordings of real life and it can be easy to get lost in the recordings and not know where to focus your research or efforts. Start with information pertinent to your research question but make note of anything else that's interesting to come back to later. When going through your data, consider implications and new opportunities for services, online, enhancements or research studies. Don't worry if you view your data and feel like you don't have a clear idea of what to do with it. This frequently happens with observational studies because they are by definition unstructured. There isn't a Q&A or task format you may be familiar with in interviews or usability tests. This means that you'll need to be very proactive in thinking about design implications. Be creative. Your findings might apply to things outside of the realm that you set out to observe. One of the strengths of this kind of study is that it allows for findings that may help you understand more fully of something entirely different from what you had in mind when you started. For instance, in a study about undergraduates online information seeking habits, you may find that undergraduates frequently begin with accessible sources like online videos or Wikipedia before delving into scholarly sources. Based on the finding, you might recommend that in-person and web-based instruction sessions and help docs address how best to leverage these sites of sources and where to find such sources. You should also spend time thinking about how your findings shape your understanding of the problem space as a whole. For instance, your undergraduate online information seeking behavior studies might yield findings on undergraduate perceptions of research as a whole and the types of search strategies that are most successful in particular contexts. Although such an understanding might not result in an immediate design implication, this can certainly help shape future inquiries and your approach to designing online interfaces for undergraduates. You'll likely also come up with all kinds of new research questions about the problem space you observed during your study. Once you've analyzed your data, it's a good idea to capture your findings in writing either formally or informally. Take screenshots of the interfaces in question to illustrate your recommendations. These screenshots will serve as a nice reminder of what your interfaces look like before you introduce changes. It's also worthwhile to include both your design recommendations and any new understanding of the problem you're exploring in your write-up or short report. It's important to reflect on and internalize these new types of understanding and taking the time to write out the more abstract findings, both advances your own understanding of the problem space and make sure observations available for future reflections. What you should not do with your findings is sit on them. When your findings reveal major problems with your website or library services, it's easy to say that you'll get to it later and then never actually do anything about it. Even if it takes a long time to fix, in the long run, it's much better for your users and your institution to solve problems where you can. There are certainly more than enough problems that we can't solve, so it's important to address the issues that we do have some control over. You should also be wary of following every user suggestion literally. There's a possibly apocryphal quote by Henry Ford.  Whether or not he actually said that, it's good to keep in mind that your users are not designers. If they say they want a link to Web of Science in the middle of the webpage because that's their favorite database, that doesn't mean you should put a link to Web of Science right in the middle of the homepage. What if your next user says they want to link to JSTOR? Instead, when your user proposes a solution, think about what the problem actually is. In this case, the user is saying that their favorite database is inconvenient to get to and they want it to be more convenient. Then it's up to you and your colleagues to determine the best solution for giving users easier access for the research tools they need. And finally, don't be too invested in finding the answer you expect. It's easy to get emotionally invested in something you think is true about your users. And it could be that it's true for some users, but you might also find that the situation is much more complicated than you initially anticipated. We all have our biases and it's hard to get around those. Studies like this one are opportunities to learn directly from our users and working collaboratively to design and implement a study can help even outbuy us and guide the best design decisions. Thank you for viewing this presentation on conducting observational studies. Please use the link provided to complete a feedback form on the usefulness of this information for your purposes. Thanks again.


We stopped here in the next module where we showed you the electron-electron coupling time constants for silver particles. Now let us go on and talk about gold nanodots. Gold nanodots have a more interesting spectrum as may be expected than gold nanoparticles. Why because here there are 2 axes right. If you have a rod then you have a length and you have a diameter okay. So you have actually 2 modes a longitudinal mode and a transverse mode which one will be associated with a higher energy yeah transverse mode. So here you see a spectrum from Norbert Scherer and co-workers where you can see this is the longitudinal mode it is at about 800 nanometer 1.6 electron volt and here you have the transverse mode around 2.3 electron volt something like 500 nanometer. So 500 nanometer roughly is what you get for the nanoparticles right spherical nanoparticles. So that more or less matches because the width is comparable to the diameter of the nanoparticles that we discussed earlier and here you see TM image of this other good looking gold nanodots. Now what Scherer's group did was not just regular pump probe spectroscopy but they used heterodyne detection. We will come back and talk a little bit about heterodyne detection when we talk about surface sum frequency generation later. But let me just tell you now that when you do heterodyne detection you can get to know not only about the intensity but also about field. So intensity is basically mod square of field right. So once you take intensity you do not have any idea about the sign but when you do heterodyning what heterodyning is will speak briefly little later in one of the later modules then you can actually get an idea of the field along with its sign okay. So it is a more complicated experiment than simple pump probe but the time constants that they got were this. First TH means thermalization electron-electron interaction for that you see from 200 picosecond the time constant went up to 750 picosecond as pulse energy went up and the amplitude went up as well. Well amplitude has gone up here as well electron phonon coupling time constant goes up from 1.6 picosecond to 2.9 picosecond and phonon-phonon coupling that is not affected that remains 120 picosecond throughout. So that is what they had observed. So this is one thing that when you go to gold nano rod you actually get to see different things. And in fact if it is possible to look at the dynamics so the question is are the dynamics different for longitudinal transverse mode that is not answered in this paper it said that it is same is it really same is it different that perhaps is still an open question. Another rather interesting work that has been done more recently is how are the dynamics affected by how good a crystal you prepare. So this is PNS 2007 here you see the TEM image of the so they basically made 2 different kinds of crystals and the focus of the paper really is on preparation which we are not discussing. So they prepare the nanoparticles in 2 different ways in one they got highly single crystals in one and in the other one they get what they call empty crystals where well empty basically let us just say that they are not there are different kinds of crystalline forms in them. So what they see is this first thing is they look at electron phonon coupling time and hence they work out the well they have actually plotted the electron phonon coupling time constants this one this plot is for single crystalline nanoparticles this one is for non crystalline less crystalline nanoparticles okay. What do you see for every an X axis is a little different from what we are using to used to seeing it is actually pump power but they have a way of calculating how much of the pump power is actually absorbed by the nanoparticles that is a to be honest more relevant parameter does not all the pump power is absorbed right. So who has said that as you increase pump power the amount of light that is absorbed increases linearly especially for nanoparticles it may not be the case in fact it is not the case so they have worked out what is the actual pump power that is absorbed that is there in the X axis I do not know if you can read it the figure quality is not all that great. So for every pump power what do you observe the time constant is larger for the crystalline form than for the non crystalline form what does that mean coupling is less electron phonon. So what they are saying is that if you can make a better crystal then electron phonon coupling is less efficient and hence they go on to say that it is defects crystal defects that actually promote electron phonon coupling. And they have not just done simple transient absorption what you see here is sort of residual remember residual we talked about it in TCSPC actual data minus the fitting curve and if you want weighted residual then you have to divide it by square root of Y provided you are doing photon counting I do not think they have done that here so you see this is damped oscillation I hope you understand what this is let us say this is your data I have overemphasized the oscillations and let us say this is your fit if you subtract your fit from data then you essentially get the residuals and they would look like this damped oscillation. Now what we have said so far is that this distribution around two sides is due to noise but here noise is eliminated completely I think by using a lock in amplifier this is a very very high quality transient absorption data when you can do that you can see in fact this is not the first time we are seeing data like this remember Amidstuel's experiment right one picosecond periodicity it was more or less obtained by the same way so you have this from here remember x axis is time. So what you have is you have an damped oscillation and it is very easy from here to find out the period of oscillation right simple Fourier transform will give you frequency domain data from there you can work out the period of oscillation there are other ways of doing it but this is the simplest way give a fit to whatever number of exponential is required look at the residuals and Fourier transform the residuals to get the frequency domain data from there work out the periodicity so that is essentially what they have done here you can see this is for the black one is for single crystals this one is for non crystalline nanoparticles and they have been able to work out the frequencies what do you see here first of all the frequencies remain the same irrespective of the pump power absorbed secondly which one is higher which one is lower are the SC's higher or lower lower so this oscillation period is lower for the SC's than for the non crystalline forms this also tells you that coupling is weaker so this oscillation is also because of electron phonon coupling right so the coupling between electrons and phonons is weaker when you have crystals of better quality. Now let us talk a little bit about absorption in gold aggregates what happens when you do not have gold nanodots at least in this study you can see it is long ago 1999 they did not really bother about crystallinity but what they did is once again this is link and L-cell paper they prepared aggregates of gold and what they saw is that immediately in the absorption spectrum is a little disheartening to see absorbance AU in this paper of all papers what in absorption spectrum you see that you do not have a single surface plus one band it is quite broad and the idea is that the surface plus one band comes from different kinds of gold aggregates that is why you do not get a nice Gaussian band or anything and what they had done is that they had found out the time constant for electron phonon coupling across the spectrum you can see that these decays are all very different the other thing that you can see is that the decays are not good looking so data quality here is nothing compared to the data quality that we discussed in the last couple of cases but anyway what you see is that this electron phonon coupling as wavelength increases electron photon coupling becomes smaller now this is a little sloppy way of doing things because we know very well that whatever signal we get at whatever wavelength is not from one species it is impossible to select one species by just changing the wavelength okay so it is always a mixture but it has been fit to this simple model keeping in mind what I had shown you in the last module there are three kinds of decays but the idea here is that the electron phonon coupling time constant itself is different for different aggregates it is a mixture so one really needs a little better data analysis for this kind of a thing so at the moment we are trying to do something similar in a related system right that being said let us move over to multi component nanoparticles remember in the last module we had said that one of the things that this time constant depend upon is composition so until now composition was a moot question because everything was pure so multi component nanoparticles here we start talking about platinum gold alloy nanoparticles you see when you have multi component nanoparticles you can think of two extreme situations one is alloy that means the composition is homogeneous throughout the nanoparticle 5% platinum 95% gold everywhere if you could take samples from different parts of the nanoparticle you get the same thing the other is a core shell where maybe you have a gold core and a platinum shell both are useful in their own ways we are not really talking about the applications here we are just going to see what the time constants are and why but both have different kinds of application okay so what we see here is that the moment you have some platinum the time constant becomes smaller right this first one is the decay this is basically once again looking at the bleach recovery Y axis transient bleach and here it is arbitrary unit because they have been normalized so this is what you have for pure gold nanoparticle and this is what you have when you have a little bit of platinum energy well if you separately look at and we are going to show you the values of electron phonon coupling times of gold and platinum they are not same so you might think that you keep on increasing when you have 5% platinum I will say a little bit of difference from gold then when I have 50% platinum I will see more difference right but actually that is not the case upon plotting the time constants for electron phonon coupling against composition composition means mole fraction of gold what you see is from pure gold to say 10% or 12% platinum there is a huge decrease and then it tapers off okay the points are experimental data the line is not an arbitrary line I will tell you what it is but the crux of the matter is that it is not linear not linear with composition just composition why not because so these people Hartner and coworkers worked out this kind of an expression 1 by tau EPH and why 1 by tau because essentially the rate constant is the more fundamental quantity that is what they are comparing when 1 by tau of electron phonon coupling for the multi component nanoparticle is equal to alpha gold divided by tau electron phonon gold plus 1 minus alpha gold divided by tau electron phonon gold what does that mean in the ideal scenario that these alpha should have been x mole fraction right but actually it is not this is what it is alpha gold is equal to mole fraction of gold multiplied by rho of epsilon f of gold divided by mole fraction of gold multiplied by rho of epsilon f of gold plus 1 minus a mole fraction of gold into rho of epsilon f of platinum what is this rho rho of epsilon f is essentially density of states at Fermi level what is Fermi level yes that is right at zero Kelvin at zero Kelvin the highest occupied level that is your Fermi level right now so when you have discretization coming in then all these levels are there are actually many closely spaced energy levels that are present there right so what is the density of those states near Fermi level that is what determines it now the values of electron phonon coupling constant of gold of course is known from previous experiments it is 0.65 picosecond I talked about it earlier and that for platinum is 0.21 picosecond and the issue is this electron phonon coupling is really due to phonon emission for populated electronic states near the Fermi level that is why it is not enough just to look at mole fraction this density of states of platinum density of states of gold they also have to be considered all right it is not just how much of gold is there the density of states are not the same the different material okay so density of states is what determines the efficiency of electron phonon coupling so you have to consider this as well so this curve that you see here really is the calculated curve from here okay see you know everything is it not you know what the mole fraction is this density of states is obtained by TDDFT calculation and electron phonon coupling times are known so this is a simulation of how tau would change as a function of X keeping into account this equation and you find that the experimental points fall more or less on the simulated curve so this is most important take home lesson from this study that for multi component systems you have to consider density of states as well it is not very straightforward so I hope the message that has come out in all this discussion in the in this module and the previous one is that data analysis in this apparently simple system is actually not simple one is to take into account many things then only we can get meaningful data okay now let us talk about something else gold silver alloy very widely studied system so they have here there will be many studies right at the beginning when the this field opened so here there are two examples there are many more one by else says group one by Hartner's group where they studied gold silver alloy nanoparticles as well as coarser nanoparticle and what they reported is there is no change in electron for on coupling time but the problem is that they worked at very high power so for the next seven eight years this was the state of the art that you take these gold silver alloy and coarser nanoparticles there is no change in electron for on coupling time with anything with composition nothing but then more recently in 2008 there is this is faraday discussion paper by Langert and Langert et al where they have shown that the this time constants are really linear they have a linear dependence on the pump power absorbed problem is after certain range it becomes flat so it does not matter but here you have different sized nanoparticles and for them there is a linear dependence x axis is mole fraction of gold mole fraction of gold remember what happened for gold platinum these plots were not linear is it remember it fell here it is linear why is it linear what is the difference between gold silver and gold platinum the difference is that these rows are the same for gold and silver they are more alike each other so alpha of gold is really equal to x of gold go back to that equation that we showed a little while ago and plug this values in you will see this interestingly it was reported that for nickel silver coarser nanoparticles you do not get what you get earlier for gold platinum you do not get a linear variation either what you do get is what looks like it goes to a maximum why that happens at least in 2008 it was not there have been more studies after that I do not think this question is enucidated completely okay well that brings us almost to the end of our discussion of this noble metal nanoparticles the closing note as I said at the very beginning is this that there have been many many studies on pump probe of noble metal nanoparticles roughly it was the last 5 years or so there have been consistent reports of light emission for gold nanoparticles especially when you use ultrafast lasers to pump them and this first came up because see gold nanoparticles are used commonly in ACRS because they have a signal so there it was reported that there is some extra light that comes in and misses of the signal where did that come from that is when people understood that it is not only non-radiative relaxation radiative relaxation is also there and this is now being reported by many workers it is not difficult to miss if you are not careful but for example in this nanorator paper only 2 years ago they observed this light emission for gold nanoparticles they used an ultrafast NIR excitation and then the question that they discussed was what is this is it thermal radiation is it inelastic light scattering or is it multi photon luminescence very similar questions were asked by Raman and Krishnan when they observed Raman effect for the first time in fact to start with they thought that it is feeble luminescence only after the did polarization studies did the understand that it was something very new and that is how Raman effect came into being that was several decades ago what we are discussing now is the slide that is coming out what is it and so far even in this paper the consensus is that it is actual emission it is not inelastic light scattering it is not thermal radiation it is actually multi photon luminescence will not discuss this further but I would encourage everybody to read papers that have been published in the last 5 years on this luminescence of gold nanoparticles not only gold well noble metal nanoparticles okay that brings us to the end of this discussion in the next module we will talk about what happens we keep on making the size smaller and smaller.