 Well, this is the last lecture on the advanced spectroscopic technique which we have been discussing. So, the last technique which I started discussing on is on yields that is on electron energy loss spectroscopy and I have discussed with you the basics of yields is technique is relies on the aspect that electrons when falling on the samples of any type undergoes something known as inelastic scattering obviously electrons are used for electron diffraction in the electron microscopes and electron diffraction is more mostly because of the elastic scattering in which both energy and the momentum are conserved. But in case of inelastic scattering there is always some energy loss of the incident electron and the electron which has passed through which has basically passed to the sample this energy loss can be always due to certain kinds of electronic transitions happening in the material or it can be actually termed as atom electron excitations which are taking place. So, therefore if you analyze this electrons which are basically undergone inelastic scattering we can get informations regarding electronic structure band structure we let morning type and quantitatively also we can measure certain amount of element present in the material. So, first and foremost thing which I have done is that I looked at different kinds of energy losses and electron can undergo and showed you that there are different types of energy losses possible I will go back to the slide where I have shown you the first thing which happens is in a energy loss spectroscopy is division of the regions based on the energy. So, in case of low loss regions which is less than about 50 electron volts we always have phonon excitations which is very small actually close to 1 ev or less than 1 ev and they are not of any significance for the measurements because the beams which are used for measurements for electron spectroscopy are not so much monochromatized that we can talk about the energy split of our 0.5 electron volts. So, they are not resolved at all second important things which always happens in the low loss region is called inter band or inter band transitions between the electrons as you know the electrons moves in the orbital in the atoms. So, therefore when an electron coming from high energy source like an electron microscope is you know applies its all energy to eject certain electrons from one cell. So, that thing becomes that place become vacant and this can lead to inter or inter band transitions and this kind of things can give us a signature of the structure of the material because electronic energies are basically proportional to the type of atoms or type of element it is and they actually happens in the energy range of 5 to 25 electron volts well these are very important and we are going to we have already discussed about it we will discuss more and then you have something known as high energy loss where energy losses are more than 50 electron volts and things which happens they are here two things one is called plasmon excitation you know the plasmon's are basically you know collective oscillations of the of the electrons for the for the models and where the free electrons are large they are very strong and there can be both type of plasmon's at both surface plasmon or bulk plasmon one is a task piece task bus wave other one is a long cheer only because these are all collective oscillations. So, therefore there are nature's wave in nature and last thing which can happen is basically inner shell ionization that means you have different cells in the atoms KLM and OP we know that. So, in our cells which are KLM or KLM basically they contains very tightly bonded electrons and if the energy of the incoming electrons are very high this can eject an inner cell electron and this can lead to an ionization of the element and that can be used to detect an element in fact because energy levels of this electrons in the KLM cells are very well defined for different elements. So, this is I this actually nutshell the yield signals and this is what I have discussed with you and that is what actually obtained in yields particular signal I will show you the yields spectra yes. So, the zero loss in yield spectra corresponds to elastic scattering that means the electrons which are passed through and you know that any kind of electron microscopist will tell you that large number of electrons passes through the samples. So, therefore this particular peak in yield spectra we have very high intensity in fact this is the highest intensity. This is followed by plasmons plasmons comes in a energy range very close to the zero loss peak and then there are characteristics peaks like elemental peaks followed by other things like we know as ELNES and EXELFS they are all energy loss near a structures or extended energy loss near a finite structures which we will discuss now. So, these gives you lot of things about the electronic structure in the material before that let me just go into the band structure whatever we started with and where I will tell you how the bands can be yeah you know that yields maps can be used to get the band structure in a material it is possible actually and this is what has been shown in the slides is basically electrons which are ejected from the co-levels where the KLMN just now I discussed by the incident electron can scatter all into available states which are available to them and thus energy imparted by the incident electrons to get them basically to these transitions will reflect the density of states as simple as that. So, analysis results in electrons which are ejected from the co-states into the empty states above the Fermi levels and when that happens we can get informations of the band structure this is why these are actually called edges not peaks because they are just onset of transitions they are not actually taking a talking about the whole transition they are talking about on special let me explain let us suppose this is what the first picture has shows this is the empty state then this is the another the family level because below family level all the states are occupied our family level states are not occupied unoccupied and below family level you have conduction and the balance bands as you can see here well now let us assume that KLM there are three cells which are inner cells and energy levels coming out are basically suppose electrons which are ejected from K cell or M cell or L cell can basically have energies sufficient enough to travel into this conduction or balance state. In fact it may have energy sufficient enough to cross this many cases cause this you know family barrier family level and enter into empty states this is highly possible here I am just showing you a case of nickel oxide yield spectrum where you can see even the M cell energies of which have electrons which have actually moved inside the conduction like balance band very close to the yields very close to the family energy level as you know lead into a peak formation here and so this is the aim transition and this peak is correspond to those kind of states which were unfilled actually at the beginning in case of an ion yield spectrum. So that is how actually the band structure of the whole material can be obtained this is what again showed here this is a plot between any versus E as you can see here and this is the family level so these are the field state and these are the empty states and then you have basically density of states can be shown like this. So if I do certain kind of experiment like that means if I have electron energy is more than the transition energies then it can eject the electrons from the cells with sufficient ion energy so that this electrons can move into this empty states you can get something like this kind of extended structure fine structure information in the yield spectrum. Well that is you know very dependent upon what kind of transitions you are allowing like in EDX observable images are directly to the elemental cells that means we can always see K L M H S in EDS we know that but depending on the atomic of the material also we see that but here you can have even interband transitions like in within the M cells you have M 1 M 2 through 3 M 4 or within N cell N 1 N 2 3 N 4 N 6 7 like that so these transitions are also possible these are actually spin orbital transitions. Now obviously it can also give us information about the energy loss nearest structures which are there which I just I have shown you in the last slides. So let us now talk about in terms of schematic pictures this is energy band you see this is EV versus distance plot on the left side and then you see this is the family level this is the valence band EV and these are actually different atoms 1 2 3 4 5 and this within 1 atoms this electrons are sitting in K L M N OP but these are the 3 unit cells which are shown inside arena cells and this is the conduction band so the up to these field cells are there up to actually a family level and they have empty states and above empty states you have valence band. So actually in else what happens you can have an incident electron with a sufficiently high energy it can eject one of the electrons M L K in the cells and they can then move into this empty states and if they have even higher energy they can even move into the valence bands also now if I go back to the right hand side structure it will be more clear so the C K L M are the core states and they have valence bands and above that you have conduction bands and then EV is there so these kind of transitions from L 2 3 2 even empty states can give us information regarding this part this part of the energy levels and these are all actually called electron loss energy electron loss near a structures or extended electron loss finite structures. So first one is gives you the DOS or density of states in the conduction bands these are actually very well known and well understood now and they are used extensively second one it is not so widely used it actually can give us information regarding chemical bonding but it is still a lot of research needs to be done to understand this electronic transitions for electron extended energy loss fine scale structure this is just like x-saps in case of x-rays let me give you some more things about ELS how it can be used as finger printing in fact this is what is actually people do nowadays to know the exactly the electronic states a particular atom first let us talk about titanium titanium in three different compounds calcium titanate titanium dioxide and Ti 2 O 3. So in both calcium titanate Ti 2 O Ti O 2 the titanium actually has a plus 4 states and in case of Ti 2 O 3 it has plus 3 states if I look at the ELS spectra of titanium in all these three compounds I could see that depending on this electronic state there is this thing difference in terms of this illness spectra in case of calcium titanate titanium dioxide you have you can see four splits but in case of Ti 2 O 3 there is only two not only that there is a shift of energy losses to the lower values for Ti 2 O 3. So that means L 2 3's edge obtained from Ti 2 O 3 differs markedly from the tetravalent compounds like Ti O 2 or calcium titanate not only that in fact one can look at differences of Ti O 2 titanium state of titanium in Ti O 2 form a grain and from a twist boundary it can be done in electro micro so we can see a boundary of the twist type or tilt type. You can see the nature of the spectra a spectra actually remains same for both whether titanium oxide dioxide is present in the grain inside the grain or at the twist boundary but there is a distinct difference as per the energy levels are concerned they are not same. So there is this little difference so therefore Ti L 2 3 edge from a twist boundary all the closely matches with the structure of Ti O 2 standards but the fine structures are different that cannot be discussed within the framework of this lecture because one is to know what is the tilt boundary structure and what all things can be there a twist boundary structure so therefore it can be done this is this particular things are taken from Seth Taylor of G. Goval research and they are very important information well so after giving you band structure illness or the energy loss near a structures let us just you know compare EDS with yields there are many comparisons for EDS and yields I will give you a chart also at the end of this lecture you know yields are actually much more you know quantitatively qualitatively much more superior than EDS that is what will be taught by different books as you have seen number of counts in yields are very very large as compared to EDS first of all and both of them function actually like a collection angle EDS collects small angular distribution of the all emitted x-rays but yields actually in last scattering of electrons lastly forward scatter so therefore they are collected and that is why if the signals are more so therefore there will be higher quality of data now it can be shown here also you have a thin specimen here electrons are falling from the incident beam and then x-rays generated by detector by the EDS detector or x-ray detectors normally contains at this basically within a small window you can see this is the window only contains as a minus 4 to minus 2 of the emitted x-rays that means we collect very small amount of information which is generated that is the problem in EDS in TM that is why actually nowadays because of this problem many microscope especially the high end microscope uses several EDS detectors at least four within the TM column so that the quantity of information the quantity of the x-rays which can be gathered from the samples could be very large or at least it can be increased in case of pills the electrons pass through the sample and you collect the solid electrons which are undergone in last scattering in a solid angle of pi beta square of beta is incident angle or this actually this angle it contains most of the energy loss electrons so that is why eels is always preferred but you know eels requires lot of alignment of the microscope and many other things and is costly compared to EDS that is why very few labs has EDS. Now more on illness if we want to give it but I do not want to talk much details this is basically as I said they are all fine scale structures and they can be used for determination of the fine scale structure illness comes very near lower energy levels than the EXELFS and ELXC wave they all talk about density of state in fact you can obtain a radial distribution functions also because it talks about the near element configurations of the of a particular atom and therefore it is possible to obtain the radial distribution functions. So to give you some more ideas about that you know the two things one is important which one is to consider one is called single scattering and it is called puller scattering. When you have atoms in a you know surrounded by several atoms so what this black atom is surrounded by six atoms other atoms types and this is what actually we would like to know how these atoms are distributed around the black atom. So in a puller scattering the electron which comes like that it can come from the actually get scattered from the black atom then goes and gets scattered from all the six atoms and then come out that will carry the information regarding all the surrounding atoms and that is what actually they are in electron loss near a structures but on the other hand in case of X extended in electron energy law a fine scale structures fine structures you have only single scattering so one electron once electron actually scattered from the black atom goes to the one of these surrounding atoms and then comes back. So this is just for sake of understanding a convenience I am talking about this is all available in this books which I already refer to you so this kind of scattering actually are reflected in the X that is why in X C E L F S you have only very small minima present but in case of E L N E S you have large variation of the minima or maxima. So these signals are not so strong but these signals are quite stronger and fine can be can be used to determine density of states of band structures but warning type information which are there in the X C E L F S is not so clear is still under investigations of this has to be done well after giving lot of things about the different kinds of information which yields can generate we need to talk about what is the kind of resolution we can get or what is the kind of spatial resolution other we can get you know nowadays costly microscopes come up which with a very nice beam finds probe stable beam but still for the best performance you need to have very thin specimen because the more thicker is the specimen there will be more chance of analysis scattering and that can mask the information which are coming out from the electrons which are in less scattering catered you know through the sample. We also need to have electron gun of fake type that is the field emission gun because field emission guns gives you very high brightness of the beam and coherent because energy spread of the electrons in the field emission gun is very small. So therefore and also because the high brightness so you have a you can always have a small probe and normally the fake has a probe side will less than nowadays possible about 2 Armstrong. So we can actually obtain resolutions of that level this is what has been shown suppose you have a beam which is focused on the sample of diameter T and then once this is if possible sample you can see the spread increases. So therefore resolution actually not only depend on this size but also this size. So that is why we need to have finer probe so this size is finer this will be also finer that is what I am saying and in case of thermodynamic emission like tungsten or the lab 6 filaments the probe size is what are some magnitude larger. So therefore you cannot get kind of information which you like to get for the microscope when you are analyzing the samples. Very important which you also like to know when you are doing such a kind of investigation is the sensitivity of the ills as opposed to EDS you know sensitivity means if I have an element present in suppose 0.01 percentage can I detect you all well said and done EDS cannot detect an elements or rather resolution of BDX actually as they say sensitivity BDX is very poor when the element percentage is as low as 0.01 percentage. So the minimum detectable mass in case of you know EDS is tends to hundreds of atoms but with ills it is very large it should be hundreds of atoms. So that is why the ills actually is better and so it depends obviously on the microscopic sample this is what has been shown here minimum mass function detectable weight percentage versus spatial resolution. You can see here the this is the nickel and Fe in 100 kilo volt analytical microscope this is nickel and Fe in 30 kilo volt analytical microscope a very large probe size but you have a detectable levity is very small let me let me you can detect 0.01 percentage of the mass but here you can detect only one percentage. So in case of copper manganese in copper actually for 120 kilo volt AEM analytic electron microscope this is what is the case but in case of FEG the basically you can have very small probe size and you can also have minimum mass fraction as low as less than 0.1. So that is why we use always FEGs FEG means for the filimission gun electron microscopes the last thing which I am going to talk about is energy filter imaging or what is known as EFTM. As you know the electrons which are coming out from the from the sample which are in less C scatter they contains all the chemical information I showed you the type of element presents the what is called amount of element present we can also did do that the electronic states. So why cannot you use this electrons to map actual image. So that is known as energy filter image obviously one needs to if one needs to map properly you need to filter the electrons which are in less C scatter depending on the energy levels. So I will tell you how it is possible as a time as the slides up so on. So what is done here this is a simple a map of an in spectra so they basically the you know this is what the sample is sitting there this is a beam screen and the energy in a static electron passes through aperture then some alignment coils then the magnetic prism then it passes to six quadruples and six sexta poles fall finally we detect them in a CCT detector. So we can actually map this electrons on the image that is what I am trying to say and that can be done as I said by energy filter so what can be done actually here the change of my configuration in a microscope as you see this is the specimen this is the objective lens and there are all intermediate lens and then once this things are coming out from the intermediate lens it passes through this kind of setup which is known as sector full lens gamma filter is patented by Garten corporation USA and they can split the actually the in a CCT electrons in different energy levels they can filter actually and then it can passes to set of other lenses and then we can get the image. So that means you have to attach this part inside the column of the electron microscope to obtain this kind of energy filter imaging that is what I am to say so that means extra cost basically you have to add this filters within the columns to get energy filter imaging. Let us see how this is basically done it is nothing but a contrast enhancement technique as I said it improves the contrast in images also diffraction patterns by removing the elastic scatter electrons that produce the heavy background that is the first thing it is also mapping technique so first thing is we can do is that we can remove the elastic scattering unit you can block them all of them we can only have you know image produced by elastic scatter electrons so that way the quality of the image or contrast of the image will be improved that is the first thing one can do second thing one can do is the is used a mapping you know EDS case used as a mapping technique so this also can be used to create elemental maps by forming images with elastic scatter electron of particle energy levels also this is and you know analytical technique it can records your electron energy loss spectra or even maps to provide precise chemical analysis of the samples so that is actually a national and EFTM can do so first thing I will show you probably the first example and this is I think do not need to show you this is actually exactly what is done I have shown already to you so let me skip and in a in a energy electron mind expect prism is needed to separate the relative evidence that is what is done here you see this is the energy loss this is what is called scatter in a less scatter so therefore you can separate them and so therefore if I put a filter if I just put a if I allow only this beam which is elastic is scattered and then I can basically get nice images contrast enhancing if I only this one skill in less scatter electrons then I can get you know much other information that is what I am trying to say so you can use a prism electromagnetic prism here extra which is nothing but a omega filter and to separate them out in fact one can actually take this in a C scatter electrons and then separate them out depending on energy levels that is also possible so let us give me why I let me give you some examples this is taken from Rudeau Gidman from Max Plan Institute biochemy and as you see here this is basically a zero loss contest enhancement by zero loss filtering and you see here once this is original image and this is after the you know filtering so you can see there is a huge change from the contrast I do not know whether it can be seen on the skin but at least for the image I can see this this lot of other features are vanished and you can see when the corresponding diffraction pattern has quality has improved so you can always claim that using FTM we can always create better images and diffraction patterns to give some more informations how energy filter TM can be used to produce better diffraction patterns this is the conventional TM we can see sticks passing through this and once you map the intensity you can see this kind of broad things and also followed by this small you know picks but once you use energy filter TM we can enhance this small speaks so what you see here very clearly change the diffraction pattern these brightest parts are the brightest parts surrounded by six weakest parts which is not visible there so that is how actually you can improve the contrast of the electronic diffraction pattern which is not possible use other so here we have removed all the secretive electron by using the prism well one can actually create an image using this electrons that are slowed down by the interaction of the specific elements and they are all called electron spectroscopic that is what I showed here so basically it is a in a strictly scattered electrons which are produced image and this is accomplished by using increasing the extended voltage of TM precisely by the addition energy needed one can go actually up to 1,100,000 EV what is done here is simple like this this is the global avenging setup this is what is the quadrupole gamma filter omega filter so you have a specimen electron energy comes energy loss and then it passes through that and then you can basically have a elastic scatter electron elastic scatter electron is basically without slit so if you use a slit you can separate them out nicely this is what is actually done in omega filters and one can use different kinds of filters there is no need of showing that it is Gatron as the filters the O house also filters different components are making different filters last things which I am going to show you is called stem yields stem yields in a sense that it can be used to you know determine the particular atom present in a highly high resolution or microscopy actually what is done is let me tell you that so suppose this is the atomic gasment of certain held you know certain compound elements or let us say compound here because there are different covers atoms so you have a electron falling on to that and then each atom has different scattering power right that depends on the atomic electronic configurations so depending on this scattering power electrons they will get scattered different angles now if we apply an annular detector like this is annular this is a central hole is like this central hole and this is a detector so if I have annular detector I can collect the electrons coming scattered electrons coming at different angles from the incident beam this this or this or this like that which is scattered after it passes the sample the sample is here and once I correct that and I know the different atoms different atoms of different scattering power so therefore I can actually image the the atoms in high resolution microscope at the same time if I take yield yields from each of these atoms atomically you know I can detect what atom is presents so therefore by using together is Steven yields one can actually determine the atoms in the high resolution electron microscope which is not possible so far but with the advent of you know new kind of contest magazine like in Titan this has become obsolete because in Titan I can equal get contrast form even each atom differently you do not need to actually do the stem so I will give you some example of EFTM this is just the different layers in a thin multi-layer thin film so you can see the contrast here is different than the contrast here so you can actually see this is graded silicon germanium multi-layers not SI layer between them the only two multiple monolayers single molar detection is very easy so you can see single molar this are high resolution images you can see when the atomic planes and rapid acquisition also possible so you can quantify that this is again taken from my own our own work this is basically I have shown you at the beginning of the this this course when you deposit copper using pulse electro deposition techniques we always use the theory and theory has many roles to play it can control the nucleus and mechanism for the thin film deposition you can control the growth also it is postulated that theory contains lot of sulfur and sulfur gets collected at the gain boundaries of the grains this is a grain copper grain nano crystalline you can say approximately about 50 nanometers and once they collected around the grain that it will present the gain boundaries and this sulfur atoms then can pin the gain boundaries for further growth so therefore theory I can act as a gain you know inhibitor and that can be proved using energy filter imaging so if I use sulfur energy edge that means if I only allow the energy loss due to sulfur atoms in the yield spectra and then I will image that on to the on to the image so I can see that all this gain boundaries are getting bright enough you can see here you can see there so you can see there so that means indeed sulfur atoms are present the gain boundaries so that means our postulation that theory I act as a gain got inhibitor can be proved by this way this is now published and journal this is now published in the reputed journal so one can actually look at details but it is possible to take up certain kind of issue and then to the energy filter imaging and to show that these are actually true well one can also actually do much better things if you this is again taken from our my own work or our own examples these are actually nanoparticles created when you leach aluminium nickel cobalt cost crystals so they create this kind of you know blocky crystals and you can see they are actually nickel cobalt FCC and you know nickel cobalt has almost you know atomic numbers very nearby so it is very difficult to say that nickel or cobalt present in the coin these particles by edx analysis so only here we can show is by using eftm mapping so you can see here this is a big size particles even more than 100 nanometers quite close to about 250 nanometers you can map nickel and cobalt in this and if you look at carefully the nickel is much less in these particles than cobalt because cobalt map shows much better regions than the nickel map and if I do it is in a function of size suppose if you go to intermediate size you can see still nickel quantity is less than the cobalt in those particles if you do the nickel and cobalt map these are impossible in edx actually you cannot do that because they are atom and nickel and cobalt atomic numbers are nearby if you go to very small particles you can see suppose look at this one nickel and cobalt distribution is almost uniform you may ask me what the need of doing this well as you know these small particles which are actually alloys of nickel and cobalt nanoparticle they are used as a catalyst so catalytic behavior of those particles will depend upon the animal to distribution and also the atomic electronic structure so by using yields one can actually obtain all kinds of informations and then use it understand the catalytic behavior of this this is what is our aim also to do that but I am showing a part of the work so by this way we can actually go down to a very small particles which is actually approximately about 40 nanometers and do mapping nickel and cobalt this is not so good but still you can see cobalt is almost as quantity is almost same as the nickel so by this way we can actually do all kinds of analysis so as I said at some time in the lecture that I will tell you detailed comparison of the yields and eds well yields as a higher spatial resolution as edx may be affected by background scattering yields as a higher energy resolution than edx around one electron volts yields is better in detecting lighter elements than eds eds can be used to detect elements which are atomic number less than carbon or C6 yields contains information of electronic structure we do eds does not contain eds is easy to operate that is why everybody uses and quick for qualitative analysis however yield spectra from thick specimens may be difficult to intermediate because of the pool scattering which has shown you interpretation of fine structure sometime requires software lot of sophisticated calculations which I could not show you because with time constant so with this I conclude this lecture the next lecture I am going to start with the surface characterization techniques mostly XPS and XPS and the Augia spectroscopy and move on.