Today, I will be dealing with another interesting topic on spectroscopy and this is one of the spectroscopic tool widely used in many research labs. However, considering our own limitations for getting such a sophisticated spectroscopic tool, in our country we have not really measured on this spectroscopy and therefore, I would like to singly emphasize more about the usefulness of this spectroscopic tool, which has come into the study of materials in a bigger way. This is popularly called as X-ray absorption spectroscopy and this is also complementary to whatever information that we are getting from X-ray photoelectron spectroscopy, which we have seen in the previous lecture, where we have highlighted that XPS spectroscopy is or XPS spectra is a very good surface analysis tool, where up to 10 nanometer thick surfaces can be studied in greater detail, talks about the impurities that can happen in the surface and then how we can probe the different metal ions that are present and also on the characteristic X-ray that is coming out. Therefore, XPS is a very good analytical tool, but today what we are going to see is a absorption phenomena, which has been used very nicely to explore unusual oxidation states. So in this lecture, I will give you some principles about how X-ray absorption spectroscopy can be understood and then little bit on the instrumentation and I will take one particular group of oxide and do a thorough study on how we can use excess information for analyzing a particular perovskite compound. As you would see the incident rays that are falling on a sample actually is undergoing lot of change. One is you can get scattered X-rays from the sample or we can get a fluorescent X-rays which are used for X-ray fluorescent spectroscopy or we can get photoelectrons. The light can also be transmitted, but not in the same magnitude of that of the incident ray and therefore, we can try to map the intensity ratio as a function of mu X and X is your thickness and mu is your absorption coefficient. So if your sample is sufficiently thin, it is possible even to map the transmitted X-rays and the phenomena that is happening when X-rays are absorbed by the sample, it can either come out as a photoelectron or as a ogre electron and then a fluorescent photon. So from the way we harvest the secondary processes that happen due to the interaction between the material and the incident X-rays, we can categorize different sort of spectroscopies. In the last lecture, I showed the same view graph where I characterized two important techniques. One is based on electron spectroscopies and one based on ion spectroscopies, especially I talked to you about ogre electron and discussed to you in detail about X-ray photoelectron spectroscopy. It gave you some idea about RBS which is specially used to look at epitaxial layers and how the thin fins are growing as single crystals. So I told what this X-ray photoelectron spectroscopy is, basically this is reflecting a photoelectric effect and this simple photoelectric effect can be transformed or exploited to analyze and quantify several chemical reactions. And there we looked at what this photoelectric process is. The ejected photoelectron is what we are trying to map and in the process you also have the ogre electron that is coming out from here. Now to draw a parallel between X-ass and XPS, I just want to make some comments. One is core holes are created anyway when a core electron is actually knocked out and therefore by ionization it can happen and that forms the basis for X-ray photoelectron spectroscopy. Core holes are created by ionization by the incident X-rays and therefore those are called as X-ray photoelectron spectroscopy and core holes are formed by excitation of electron which forms the basis for the X-ray absorption spectroscopy. So in both cases XPS and X-ass we can say that the final states are highly unstable when the core hole decays by non-radiant process. One is either a ogre relaxation which ends up in a ogre electron spectroscopy or by radiant X-ray emission process which is called as X-ray emission spectroscopy. So this X-ray emission spectroscopy is actually a secondary phenomena that goes along with X-ass whereas AES is a secondary phenomena that happens because of XPS. So in some sense both have a parallel so when we talk about X-ass we also take into concentration X-ray emission that is coming out. To make things look simpler how do we get this absorption spectra we can say that there is a beam of different wavelength you can use any sort of wavelength and this beam source is actually incident on the radiation and now the electron is actually absorbs energy and it can go to any of the bound states or to any of the states near to the continuum that is the vacuum level or it can go into the vacuum level and depending on that then we can try to populate those regions selectively and then the transmitted radiation can be mapped and this is what comes out as a absorption spectra which we can try to analyze. Now there are two things that we need to have in mind one thing is when in X-ray absorption spectroscopy if we have a core electron which is excited into unoccupied atomic or molecular orbitals above the Fermi level then X-ass can be divided into two regimes one we can call this as X-ray absorption fine structure or we can call this as extended X-ray absorption fine structure when the outgoing electron is well above the ionization continuum. And if it is somewhere in the bound states for example we talk about a 2P going to 3D level or 2P to 4D level then we talk about bound states and low energy resonances in the continuum. So either of this can happen as you see from this view graph electron is knocked out and it is actually going above the Fermi level but it is not actually going into the continuum. So this is one of the bound states and depending on that you will get a typical characteristic feature of X-ray which will tell what sort of excitations are possible in this case you can see nitrogen is absorbed on nickel 100 and when it is glued or to the surface when it is absorbed to the surface then you get a clear reflection for a 2P interaction and this is a typical X-ass peak that you would get for nitrogen 1S to 2P transition 2P star transition will come to this issue in example. So just to map what are all the different studies that we can do in X-ass we can actually talk about a pre-edge which can be characterized here as X-ray absorption near edge structures X-A-NES and this is what is the region where you can actually map the information that you are getting. In fact you would get several features around this edge so this is what you call it as X-ray absorption near edge structure and this is the region where you actually play around for X-ray absorption spectroscopy. I will tell you what sort of peaks that you can get out of this and this is the region where you have the transitions happening between 1S to N plus 1P level or it could be P to N plus 1D level. So this region actually takes care of such bound states and this is the region where you can talk about the pre-edge and if you are talking about 1S electron knocked out of the continuum or if the knocked out electron is well within the continuum then you talk about the extended X-ray absorption fine structure. So several of these processes happen all these are mapped under the same phenomenon of X-ray absorption spectroscopy. So we will especially look it is not possible in one single lecture to cover the whole spectrum of manifestation of this spectroscopy. So I would like to take some interest to talk about different things that can happen in this edge that is why it is called as edge spectroscopy and this edge is actually attached to the sort of excitations that can happen. It can be called as KH or L or M we will see that in the next slide. As I told in the previous one we are talking about different forms of spectroscopy here and this is the XS edge spectroscopy that we are precisely talking about and the relative scale of energy that involves each of the spectroscopy is also given. Therefore we can single out and say that I am exactly talking about XFs or I am talking about XANES or I am talking about XS based on the energy range that we are using for these spectroscopies. Now when we talk about edge we are talking about different transitions that can happen, absorptions that can happen. If KH is happening then the electron from 1S is actually excited and therefore we call this as a KH. If it is L then it can involve both 2S and 2P but we differentiate that between L1, L2 and L3. L1 is typical for 2S electrons getting to the continuum or it could be 2P or 2P 3 by 2. So both these are characterized by L2 and L3. When we actually talk about bigger metal ions this L2 and L3 give a very rich information about the oxidation states. Similarly we can go for M1, M2 and M3 so on. Each one is designated by the orbitals that are associated with it. So XS data are obtained by tuning the photon energy using a crystalline monochromator to a range where core electrons can be excited and the range is typical of the order of 0.1 to 100 keV photon energy. Depending on the range then we can selectively try to knock out the particular core electron. So if we talk about K then we are talking about a very high energy radiation. If we talking about 2P levels that is LH medium range and then still smaller ranges for 3S and 3P. So this is how we designate this KH, L1, L2 and L3. L2 and L3 we try to categorize based on the LS coupling. So if your transition is from P to D or S to P then your L is equal to 1 and this 1 can coupled with either S is equal to half or S is equal to 0 and depending on that you will actually get this half or 3 by 2 which is nothing but your LS coupling. So based on this you can get L2 and L3 always we can remember as a notation L3 we always talk about 3 by 2. It is easy to remember that way L2 is half. So L2, L3 edges are nothing but 2 states from the same transition resulting out of the spin orbit coupling. Typically if you look at XS mapping you can see a sharp edge for K and this is for L1, this is for L2 and this is for L3 and as you would see here L3 always comes at higher energy compared to L2. So in a typical spectra of XS your higher energy spectra will always be associated with L3 and the low energy peak will be associated with L2 and there are other things that happen apart from the edge where you have for example this platinum tetracyano complex where you see additional features that are coming and these are called the near edge fine structure due to XS and this peak comes from a constructive interference and this peak comes from a destructive interference. So this fine structure can give us idea about the local coordination and other information about bonding and the nearest neighbor occupancy and so on. So this is also a very useful tool that is being proved. Now where is XS becoming more crucial and more sophisticated as I mentioned to you the way we produce X rays are very typical. We use filament to get electrons which will knock at a particular target which is copper molybdenum or anything any particular metal and when it strikes characteristic X ray comes out of it which we categorize as K alpha or K beta radiation. But in synchrotron radiation or in XS we actually get a high energy X ray and not the conventional one that we generate in our usual lab practices. What we do here is get the same X ray and this X ray is actually confined to a ring and in this ring we try to boost the speed of this electron such a way it is an accelerated electron which will X ray beam which will actually come out and that will collide with your material to have a very selective excitations made. So what we are trying to do is generate the same X ray as that of the lab experiments but we are trying to accelerate in a confined space. So this is your conventional X ray machine X ray comes interacts with your material and then it goes to the detector. In synchrotron source we actually try to boost the speed of the electron and then the X rays are X ray beam is actually brought out with a greater force. So one of this can selectively go and hit. So when it is actually spinning at different points you can collect the X ray beam. Therefore this is called a synchrotron because in one space you can have many stations where you can try to get it with the different centrifugal inclination at different tangents you can try to get the source output and as a result we can study from one synchrotron source many experiments parallel. So this is that way a very sophisticated instrumentation and just to show you one of the major facilities is in Germany it is called DESI and there is another one is called DESI in Berlin and DESI is in Hamburg. As you would see here it is more of a consortium it is not a single man's property most of the research institutes foundations including government they pitch in to sustain such a major facility. Therefore this is not a simple stuff definition of a synchrotron we can take it from here. When high energy particles are in rapid motion including electrons they are forced to travel in a curved path by a magnetic field which we call it as booster and then synchrotron radiation is thus produced. We will look at Bert's eye view of one synchrotron facility which is there this is your linear accelerator I will also show a animation the next slide this linear accelerator actually pumps in X ray which is actually getting boosted here with a magnetic coil and then on gaining momentum this will actually go into the outer sphere and then from here at different points you can actually collect this fast moving X rays and these are the substations these are your substations where you can bring any of your instrument. If you are only interested in analyzing a particular sample you can try to do that or if you want a deposition chamber also to be transported you are free to come and house your equipment here study for a particular time and then you can take it back. Therefore this is more of a central facility confined in a very large space and many laboratories can be housed together and the output is actually shared by everyone at the same time. Therefore it is a very sophisticated structure and the dimension of this synchrotron facility is quite huge we will look at one of the slide to understand this. We will see a short animation on what this facility will look like and this is the inner side of the advanced light source where you can see the inner core actually is generating X ray from a linear accelerator which is boosted up by the booster rings and the booster rings are those which are having magnetic field and once it comes out to the periphery then it can actually go through several substations where this accelerated X rays can be used and this is how the booster actually works and once it comes out then it can be monochromatized and it can interact with the material giving many informations that is needed not just on the spectroscopy in fact even imaging of structures can be used using this map. Having seen the sophistication that is involved in this I should also mention to you that this is a very selective facility that is available across the world and here is a list of all the synchrotron radiation facilities that is available it is also called as advanced light source and as you would see here many countries are really competing in this field. What is important to notice is the circumference of the synchrotron radiation source that we can look for in terms of meters and then the energy that is generated in this list you would see that the major players are actually in Europe and in US and most of the facilities are housed in US therefore this is a very costly equipment that has to be sustained and one of the oldest as you would see here is from Lawrence Berkeley laboratory commissioned and it was also decommissioned in 1993 subsequently a new advanced light source has come into picture and then another one has been commissioned when the previous one was decommissioned that is in 1993. You can actually look at the sophistications involved the amount of giga electron that it can generate these are some of the largest facilities in the world as of now with a very very massive infrastructure one is in Argan National Lab and equally important are those in Germany but we are also in the game in a smaller way for example if you look at Indian situation we have two synchrotron light source both are housed in indoor and this is called Indus 1 and Indus 2 but you would see the circumference or the dia of your source is very very small compared to what we saw in the earlier case they have circumference of 1000 meters but we have fairly very small unit and the capability also is very less therefore we can only study organic molecules using this facility it is not possible to study heavier atoms so this is limited nevertheless we are also in the map as far as synchrotron radiations are concerned I am sure in the days to come there will be lot more progress and we will improvise on this facility as a nation. So this just to give you some idea about how these are localized and there is there are also programs in our own country where we tie up with this advanced light source specially our country encourages lot of projects which can be written to Triester in Italy where there is a synchrotron facility so it is possible for those who are looking for this spectroscopy to make a proposal and go and do a time bound research but what we should also understand is that if you are really looking for inside to equip experiments then we need to take the whole equipment and attach it to the beam line to study this. Most of the reactions that are done is all inside to it is not excited so therefore it is a very sophisticated way of looking at it. Now let us look at the spectral features of this study and then understand little bit about what we can learn in the simplest case that of a cupric that is copper 2 complex the 2p to 3d transition actually produces a 2p 5 3d 10 final state. So when an electron is actually removed from 2p 5 then what really happens to that the 2p 5 core actually which is created in the transition this has a orbital angular momentum and which couples with the spin angular momentum therefore it produces two states J is equal to 3 by 2 and J is equal to half state and this actually comes out as a exact speak which we call it as L 2 and L 3 H. So the intensities also are almost of the same order these states are directly observable in the L H spectrum as the 2 main peaks. So whenever we talk about L H spectra using xx we are talking about L 3 and L 2 that is actually coming from a transition of p to d or s to p orbital. So as we move across the periodic table specially from copper you go down go on the left side across the period then you will see we create additional holes in the metal 3d orbitals. Let us take the case of iron which is a low spin and in low spin it is actually iron 3 is T 2 g 5 E g 0 and therefore this is your ground state and in T 2 g 5 E g 0 resulting in transitions to the T 2 g and E g d sigma sets. Therefore there are two possible final states that can happen when you are actually promoting a 2p electron through to either of this 3d orbitals you can end up with a T 2 g 6 that is what is denoted here or we can end up with a T 2 g 5 E g 1 and depending on these two then you can actually get a peak like this and this peak actually corresponds to the electron promoted to this final state and this peak corresponds to electron that is promoted to this state. So since the ground state metal configuration has one hole in the T 2 g orbital set and 4 holes in the E g orbital set and intensity ratio of 1 is to 4 is actually expected as you would see here between T 2 g and E g depending on the number of holes the intensity of the peak also would vary in the ratio 1 is to 4 but it is not always true what will happen is this does not d 6 excited state will further split in energy due to d d electron repulsion as a result you would see a much more complicated or a split pattern of these two peaks. So these two peaks need to be analyzed rather more carefully because there are other things that would compound with these structures. So if you single out just the L H spectral component and try to look at it specially for complexes with the metal center then your Tanape-Sugano diagram will help you simulate theoretically how many L H spectrum can originate as you would see here you go from lower energy to higher energies region that spectral features actually becomes more complicated therefore more and more transitions are expected when you go to higher regions and that is what you see here other factors like P D electron repulsion spin orbit coupling all this has to be considered when you try to simulate all the possible L H spectral components that are there. So for ferric system if you consider there are theoretically there are 252 initial states and 1260 possible final states are possible together with the final L H spectrum but what you would find here despite all this possible state it has been established that the low spin ferric system the lowest energy peak is due to the transition to the T 2 G hold and a more intense higher energy peak is that to the unoccupied E G orbitals. So although there are several states possible selectively these two states predominate over the other contributions which can actually be mapped and you can see the see that from the L 3 H although there are split patterns then you will be able to resolve which one is due to T 2 G and which one is due to E G. So there are two things that we need to understand within L 3 there will be two peak which will correspond to excitation to T 2 G or E G and then you also have the L 2. So both this come into picture when we look at the excess for a complex like this which is a hexasino ion 3 complex you would see for a low spin this first peak corresponds to transition to T 2 G and the second peak actually corresponds to E G and then the third peak corresponds to the M level that is your pi star. So this is for this is for a L 3 and this is for L 2 and similarly for other transition metals you can see this is a inner sphere complex and this is outer sphere complex and in both cases you would see the spectral features are actually different. I will take one example from our own work on perovskite manganese and try to see how we have resolved some of the fundamental interactions that are happening within the unit cell using excess as a tool. As you know perovskite manganese show interesting properties both in terms of magnetism and electrical conductivity and this actually comes from a phenomena called double exchange where you have from M n 3 the E G electron actually goes to M n 4 plus E G shell which is unoccupied as a result when this is actually transferring to the M n 4 plus core and if it is ferromagnetically aligned to the localized T 2 G electrons then this will actually become a M n 3 plus because the electron has come here and in the process this M n 3 will actually become M n 4. As a result there will be a shift of this electron back and forth which is called as double exchange and because of this double exchange phenomena that is happening mainly because of the presence of M n 3 and M n 4 then there is an interesting change from a paramagnetic to ferromagnetic state and from an insulator to a metallic state. So, two things happen when we try to initiate this electron transfer process and this transfer of electron is given as transfer integral that is T i j which is proportional to cos theta i j. So, this cos theta i j is nothing but the angle that is made between these two ion cores. So, if this is going to be 180 then the transfer integral is going to be at its maximum. If this is actually going to be like this for example, then this will get locked up at 90 degree. So, this transfer integral has to be approximately theta has to be approximately theta i j 180 degree for a collinear ferromagnetism to operate. Now in this situation you need both the case of M n 3 and M n 4 which is called as Zener pair M n 3 plus and M n 4 plus which is very crucial. So, I just want to emphasize that this Zener pair M n 3 M n 4 plus ratio is critical for this spectacular manifestation of magnetic and electrical conducting properties to occur at the same transition temperature. Now as I told you M n 3 M n 4 is more sensitive. Therefore, if I try to alter this M n 3 M n 4 ratio M n 4 plus ratio then this double exchange or this strange occurrence of paramagnetic to ferromagnetic transition will be disturbed or it will be killed. As a result this ratio has to be maintained at all cost. What we have tried to do is to put ruthenium into this site either manganese 3 plus or 4 plus set and try to see whether this interaction can still be maintained and how x axis can be used to ascertain the interaction between manganese and ruthenium core centers. In the next slide we will see how ruthenium when it is substituted into manganese sites what will happen to the ferromagnetic interaction. From this cartoon in the top you would see the plot of magnetization as a function of temperature and this is a typical ferromagnetic transition that is happening and during this transition if you keep on adding ruthenium as I told you M n 3 plus M n 4 plus ordering is very important and if little amount of M n 4 plus is also reduced then immediately it will spoil the double exchange phenomena and you can clearly see that the more ruthenium that is doped the lesser the ferromagnetic transition and the ferromagnetic transition is decreasing to lower temperature from room temperature. But what is interesting is even up to 40 percent of ruthenium that you dope into the manganese site you can still observe a very strong collinear ferromagnetism and this suggests that something else should be happening for this double exchange phenomena to occur or to sustain otherwise even 10 percent of any 3D metal if we try to dope in manganese site will actually kill this whole magnetic interaction from a paramagnetic to a antiferromagnetic or to a insulating phase. So this is the maximum that has been considered as the limiting composition for doping into manganese site either by iron, chromium or any other metal ions. So what is special about this ruthenium why when ruthenium 4 is substituted this long range ferromagnetism is still sustained. Why I am particularly emphasizing this here is when you consider a unit lattice of manganese, manganese, manganese and ruthenium for example. So ruthenium 3 manganese 3 plus is there manganese 4 plus is there. If you are increasing the proportion to 40 we are saying at every alternate position next to manganese we are almost bringing another ruthenium. So in a basal plane AB basal plane where we have manganese ruthenium manganese ruthenium then we are almost evolving at a new perovskite phase and this is not known or reported so far. So in this case what is that which is happening special to ruthenium doping compared to all other transition metals is the question and how we can use excess to prove this point. As I told you from the previous graph this long range ferromagnetism is also exemplified in the plot of resistance versus temperature as you can see here even with 30 and 40 percent ruthenium doping 40 percent ruthenium doping you can still this see this metal insulated transition on and in these three cases metallic behavior is still seen. So this is quite unusual for a ruthenium doping to show such a long range ferromagnetism and not only to this 3D perovskites or 3D manganese if we take any two-dimensional layered manganese like this in two-dimensional layered manganese like LA 1.2, CA 1.8, MN 2 minus X, RUX you actually have this collinear ferromagnetism which is confined only in the AB axis and along the C axis it is not possible along the C axis it is not magnetically ordered. So this is called as two-dimensional manganese where magnetism is confined only in two dimensions. But even in this case as you see if you put ruthenium instead of killing the ferromagnetism it is only improving on the ferromagnetic transition. In other words with more and more of ruthenium concentration you are able to push the TC even to 20 Kelvin which is a very unusual state. So something very unusual is happening when ruthenium is doped into manganese and you can see that the same case happens when you change from strontium to calcium again increase in magnetization and therefore there is some thing that we can draw. There is a clear double exchange which is dominating over super exchange in the up to 20 percent of ruthenium doping beyond which there seems to be some competing magnetic interactions which I will discuss in some other module about the different magnetic phase. I will quickly go through another example of a simple manganate LA 0.7 calcium 0.3 manganese 1.x ruthenium x. In this case even if you keep on changing ruthenium you can look at the L2 L3 H and see how the nature of this X-ray absorption peak changes. For example you we can actually try to compare the L2 L3 H with respect to ruthenium strontium ruthenium SR RUO3 because SR RUO3 in this case the valency of ruthenium is proven. So if you make a comparison with that and you can clearly see that in the case of the ruthenium L2 L3 H we can clearly see that there is a shift for above ruthenium 0.2 in this compositions. So therefore the ruthenium valency seems to be varying somewhere from 4 plus to some other valency which is actually contributing to stabilizing the ferromagnetic interaction. And as you see here the solid lines represent L3 and the open circles represent L2 and L2 is actually shifted L2 is supposed to come here in the lower energies L2 is supposed to come somewhere here but it is purposely pushed here so that there is a comparison between L2 and L3 edges are made. So what we see from this curve is that there is some issue that is significantly happening with the ruthenium oxidation state. Now let us take another example of SR RUO3 as I told you in SR RUO3 which is the parent compound ruthenium is in 4 plus therefore instead of doping ruthenium into manganite we can now do a reverse doping where we put manganese into a known ruthenium oxide. So in that case also you would see this is a ferromagnetic metal whereas SR MNO3 is a anti ferromagnetic insulator. Now if you keep on doping manganese into ruthenium you would see that there is a very strong ferromagnetic signal there even up to 70 percent we can see a ferromagnetic transition that is happening there is a sustained DC this is very very unusual. So there is something happening not only in ruthenium there is something happening in manganese also. So what is that which is stabilizing ferromagnetism between ruthenium and manganese centers this is what we can probe and I am just listing out some of the parameters from the magnetic study TC as you can see because it is a broad transition we can try to derivatize the curve and take the TC even up to 50 percent of manganese doping we still see a very clear Q D temperature that is ferromagnetic ordering and although the TC is dropping nevertheless it is not becoming non magnetic. Now to probe this let us take the case of manganese L 2 3 spectra and if we look at the L 2 H and the L 3 H L 3 H seems to be going through a very different feature compared to L 2 and therefore if we carefully probe this as you increase the concentration of manganese in strontium ruthenium this particular C peak is actually growing in strength than B. So we can say that as we increase the concentration of manganese then something is happening to the oxidation state of manganese it may be either 3 or it should be 4 and that is why this particular intensity has grown very significantly compared to position B. And now let us take the same L 2 3 H for manganese core and try to compare this equiautomic composition that is 50 50 of ruthenium and manganese and make comparison between Mn O 2 and L i Mn 2 O 4 you can clearly see that this 50 50 composition is resembling more of L i Mn 2 O 4 compared to Mn O 2 because in Mn O 2 you actually have Mn only in 3 plus state whereas L i Mn 2 O 4 is a solid state battery material it is a electrolyte sorry it is an electrode and in this case manganese is present both in 3 and 4 state. So what we can say at this stage is when manganese is doped into ruthenium or ruthenates manganese is undergoing a mixed valence state similar to what we saw in ruthenium substituted manganese. Now let us go one more step and try to map the ruthenium L 2 3 spectra carefully for all these substitutions as a function of x as you see here this x is equal to 0 is SR R U O 3 and once you go up to 0.5 you can clearly see that there is a shift in the H for both L 2 and L 3 and also this L 3 peak intensity is growing in intensity. So that clearly says that there is a shift in the ruthenium valence. So instead of 4 plus ruthenium there seems to be a shift to higher valence state because the shift is more towards higher energy therefore it should be ruthenium 4 to either ruthenium 5 or ruthenium 6 this much we can analyze from there.   So we can say clearly that the position of the 50 50 composition clearly suggest that ruthenium is in both 4 plus and 5 plus state. So because of that we seem to be seeing a unusual ferromagnetic interaction now this can actually be compared to another well known well characterized system which is L A S R copper ruthenium structure which is a recently found ferromagnetic compound and this particular one has ruthenium in both 4 plus 5 plus ratio and as a result we can say that it is ruthenium which is undergoing a transformation to 5 plus state. Now to exclude the possibility of the crystal field contributions that can come other than or due to manganese doping we can actually try to do a theoretical calculation also where we can try to map the L 2 L 3 H of both 4 D 4 and 4 D 3 states 4 D 4 and 4 D 3 states. In this case we can try to change the slatter angle which is nothing but your 10 D Q value and see how the L 2 and L 3 edges behave and this is the case for 4 D 4 this is the case for 4 D 3 plus 4 D 3 plus incidentally is your ruthenium 4 and 4 D 3 plus and in this case this is 4 D 4 plus which is your ruthenium 5 plus as you would see very clearly not much change is happening because only in this case you see the intensity of this A peak growing but nevertheless you do not see any new features coming because this is corresponding only to 0.2 electron volt. So, 0.2 electron volt cannot substantiate for a promotion of 4 plus 2 or 5 plus state. So, all we can say is the contribution is actually coming not from crystal field but it is coming purely from the oxidation state and for this calculation we have actually used a Hamiltonian. This Hamiltonian actually talks about the H average which is coming from the crystal field and then this is the one which is the Hamiltonian due to multiple splitting and this Hamiltonian M s is coming both from the L s coupling of your 2 p electron, L s coupling of your 4 D electron and then your cubic crystal field contribution and also this is from the exchange integral and the coulomb integral of your electrons that is from 2 p to 4 D. So, this contribution is actually coming from your coulomb and exchange integral and this exchange integral g i j is what we call it as slatter integral. So, all we can say from this calculation is that the crystal field is not contributing to this splitting but this is truly coming from the oxidation state. Having said that what we can say what are the consequence of the presence of ruthenium 5 plus in this state and how does it influence on the ferromagnetic state. So, this is sum up contour just to understand having understood that there is a mixed valence state in manganese and having understood that there is a mixed valence in ruthenium how can we make a case for this as you would see from a typical perovskite of manganite the a axis and the b axis can be represented like this and in this we told that this e g electron can go to this site if it is ferromagnetically ordered when this angle is 180 degree. Now, when we try to substitute ruthenium into this place what is happening ruthenium 4 plus gets oxidized to ruthenium 5 plus and in the bargain part of your manganese 4 plus is actually getting reduced to manganese 3 plus. As a result now if you carefully look at the t 2 g e g level of ruthenium 5 plus and t 2 g e g level of your manganese 4 plus the parent head parentage of the t 2 g e g orbital is the same. In other words we are almost providing two pathways for this itinerant e g electron to hop one it can go from here to manganese 4 plus or it can go from here to ruthenium 5 plus because as far as the t 2 g e g occupation it remains the same for both. As a result even if you are going to substitute ruthenium to the order of 50 percent you still can see a ferromagnetic ordering because of the isoelectronic configuration not only that the coupled manganese 3 4 has a size which is comparable to that of manganese 4 5 and also both have a comparable redox potential in this case redox potential for this is 1.0 1 and in this case it is 1.13 e v therefore because of the matching redox potential whenever you try to put ruthenium 4 plus into manganese immediately it promotes to ruthenium 5 plus. So even though ruthenium 4 plus is getting reduced to manganese 3 plus you are almost creating another site for this electron hopping to occur as a result a ferromagnetism can be substantiated. So this is a this is one case that I have tried to explain to you where excess can without any doubt can resolve this issue because it gives you precise information about the local structure the oxidation state as a result we can propose a mechanism which is very unique of this particular compound. So with this I would like to finish and there is a small animation that we can try to look at and how the instrumentation is housed and what are all the facilities that we can see here is where the yellow line signifies that the high energy x-rays are diverted to many places and we can also typically see how this can be used in different substations and these are the many beam lines that we see in this advent light source a typical substation actually will have a lab as the lab that we see here and not only we can look at the spectroscopy as you would see in this particular lab which is using ALS source we actually have a scanning tunneling microscopy which is being conducted and this is specially on an isolated carbon nanotube and here is a person working on carbon nanotubes and the images are being seen here.


Hello, Joseph Coylo here. I'm a children's author and poet and I've been asked by the British Library to talk to you about notebooks and poetry. Many writers of poems, short stories, longer fiction, non-fiction, write in notebooks. As a poet and as a children's author, I often use notebooks. I've got loads of notebooks here behind me of notebooks I've filled up over the years and I always have loads of blank notebooks to hand so that I can grab one and then start a new project and get my ideas written down. This is an old notebook that I've got here. I've had the notebook for years but I've only actually started writing in it relatively recently. And I have an example in here of a poem that I was working out in this book, a poem from one of my latest poetry collections called The Girl Who Became a Tree. And here you can see I've just kind of scribbled in pencil the title that I think the poem may have had. Down the side I've put a guide for the poem because I was writing a villanelle which has a set structure so I've labelled each line so I know what kinds of rhymes I need. As you can see I've crossed a great deal of words out, words that I wasn't happy with, words that I felt needed changing. And I've also put rhyme lists so a rhyme list is just a list of words that sound the same. So in my rhyme list I've got free, tree, enemy and pain, gain, main, stain, frame. All these wonderful words that I can just grab whilst I'm writing just by looking up and then include in the poem. And you can see I've crossed some off as I've used them in the poem to make sure I don't use them again. So a notebook is a fantastic tool to carry around with you to have by your bedside at night so that when those ideas strike you can write them down in your notebook. And a notebook can take any form. It can be a notebook like this which I got from a shop or it can be one that you make yourself. It might just be a few scraps of paper that you fold together and staple at the top or keep held together with a paper clip. I actually made my own snazzy little notebook for the British Library's mini book project. Now I was very lucky I had an old leather bag that was very very old and ready to be thrown out. So I recycled some of the leather and I made a leather bound book. I even found an old fossil on the beach which I stuck to the front. And the inside is just cardboard and paper glued in. I wrote a short story. I wrote it out on scrap paper first. And then I copied it very carefully into my little notebook making sure that I wasn't making any mistakes because this book is a one in a kind. It's even got a wax seal on the back with my initials on. So that is great fun. It's great fun to make your own little notebook. So maybe you'll have that and you'll give that a go. I know that the British Library have some videos showing you how to make a fantastic notebook with a pop-up element. I absolutely love pop-up books but once you've made your little book with a pop-up element you'll need a poem to put into it. So I'm going to show you over my desk now how to write a poem suitable for a pop-up book. Shall we go over and give it a go? See you in a bit. Hello. So here I am over at my desk with my old notebook. I just realised this is a very old notebook.  So I filled up most of this notebook but I still have some pages at the back. So I'm going to get my special pencil from Grim and Co which has magic at this end and mistakes at this end. And I'm going to show you a very easy way that you could write a rhyming poem for your very own pop-up books. Now pop-up books have that wonderful word pop in them. So in this book, in this poem I mean, we're going to have lots of words that rhyme with pop. So we're going to make a little rhyme list. Pop, we could have hop, we could have slop, top, stop. What else could we have? Shop, pop, hop, slop, top, stop, shop. There must be something I'm missing. Can you think at home? Pop, hop, slop, top, stop, shop, drop. Okay, so we've got lots of wonderful rhyming words. And then when I'm writing the poem I don't need to think about, oh what can I use to rhyme with hop or pop or slop. I can just look up to this list and cross words off as I use them. I don't need to use all of these words, they're just there to help me write the poem. And I'm going to imagine it's a poem about opening a pop-up book. So I'll start with, I opened my book with a pop. I think that's a good start. I opened my book with a pop. Cool, got my first line. I'm quite happy with that. I'm going to cross off pop though I might use pop again. If I want to I can. It's my poem, it's up to me. I open my book with a pop. I'm going to leave a line just to give myself a bit more working space in case I need to cross anything out or change any of the words. I open my book with a pop, a rabbit arose, a rabbit appeared and started to hop, a rabbit appeared and started to hop. So I'm imagining this pop-up book has a rabbit in it. I open my book with a pop, a rabbit appeared and started to hop. It hopped so high I wanted it to stop. No, I turned the page to a lovely cake shop. Nice. I turned the page to a lovely cake shop. See, I've got my other rhyming word shop. Full of, what do you have in a cake shop? You have cupcakes and donuts. Donuts could be good. Full of donuts that started to drop. Full of scones that started to drop. Full of scones. I like scones. Do you like scones? Full of scones that started to drop. Cool. So in our pop-up book there's a rabbit that started to hop. We've turned the page to a lovely cake shop. Full of scones that started to drop. The cake's made a mess. So I turned... Oh, I've used droppers. The cake's made a mess. I wanted it to stop. So I turned the page. Yes. The cake's made a mess. I wanted it to stop. I wanted it to stop. So I've used stop. So I turned the page. Oh, made a mistake. Doesn't matter. Cross it out. I turned the page. So I turned the page to a... What have I got? Top. Slop. So I turned the page to a mountain top. Nice. To a mountain top. So in this spread in the imaginary pop-up book there's a whole mountain. So I turned the page to a mountain top. Where rain, where rain, where rain poured down in a great big slop. Where rain poured down in a big, in a big slop. Nice wet sound, isn't it? I opened my book with a pop. A rabbit appeared and started to hop. I turned the page to a lovely cake shop full of scones that started to drop. The cake's made a mess. I wanted it to stop. So I turned the page to a mountain top where rain poured down. Where rain poured down in a great big slop. So I closed the book with a great big pop. With an almighty, with an almighty pop. So I closed the book with an almighty, it's a lovely word, pop. I'm going to squeeze it in there because I ran out of space. So I used all the rhyming words. How wonderful. And I used pop twice. One, two, three, four, five, six, seven, eight. An eight line poem using one, two, three, four, five, six, seven rhyming words because we repeated pop all about imagining a pop-up book. So I hope you have lots of fun creating your very own pop-up books and writing your own rhyming poem using lots of rhyming words with a rhyme list. Just like this. I'm going to put rhyme list. Good luck and have fun.


Greetings and welcome to the Introduction to Astronomy. In this week's Misconception in Astronomy we are going to talk about the Sun and figure out what color the Sun is. So is the Sun really yellow? Let's go ahead and look at this and what we find is what is the color of the Sun? Well it really depends. We often see images such as this one of a yellow Sun. However, that's not really the case. The Sun actually emits all visible colors in roughly the same amounts. So that means everything, all the colors of the rainbow. If we actually calculate where the peak wavelength of the Sun is, we can do that based on its temperature and it will peak at 502 nanometers. That's actually in the green portion of the spectrum. So if we really want to be particular, the Sun is emitting more green light than any other type of light that we see. So green would be the peak and then things around that it would start to fade off. We'd have less in the red and less in the violet on the edges of the spectrum. However the whole combination of light that we see from the Sun is what our eyes have developed to see as white light. So if we look from space, we would see the Sun as being white. That is just our definition of white light. So our atmosphere is what affects this a bit. And we know of this if we look at the Sun at rising or setting. So let's look at an example of that here. What does our atmosphere do? The atmosphere absorbs shorter wavelengths. That's things like the blues and the greens. They get absorbed. So when the Sun is lower in the atmosphere, it is going to look very red in the sky. And we see that. We watch a sunset. What happens to the Sun? Well, we'll see a yellowish color and then it will slowly turn to an orange and then to a red. We can't actually look at the Sun and that's a good thing. We don't want to sit there and stare at the Sun when it's at its highest in the sky, going through the least atmosphere and would look the most white looking straight overhead. So we can't look at it. It's simply way too bright to be able to be looked at directly in that case. So it's effects of the atmosphere that give us the yellow Sun as that's what we can see when it gets closer to the horizon. In reality, the Sun is giving off most. It peaks in the green light, but that does not mean that it looks green. That means that it's giving off a range of wavelengths in the visible spectrum and that's just where the peak happens to fall. So let's go ahead and summarize what we've looked at here a little bit. And what we've seen is that we sometimes do consider the Sun to be a yellow star. However, the calculation will show that the Sun actually peaks in the green portion of the spectrum. What the thing is is the color is affected by that light traveling through Earth's atmosphere and above the atmosphere the Sun would appear white, a mixture of all of the colors of the rainbow. So that concludes this week's misconception in astronomy. We'll be back again next time for another misconception. So until then, have a great day everyone and I will see you in class!