 In this lecture, we will learn about OJ electron spectroscopy. Here, we say that O U G G E R it is not pronounced as O Auger, but it is pronounced as OJ A U Z E Y. So, pronunciation is more like OJ electron spectroscopy and as we see that we utilize OJ electrons for the for achieving a particular spectrum. So, that is the reason we call it OJ electron spectroscopy and OJ electron spectroscopy the OJ effect was initially observed by Pierre Auger, a French physicist, since in mid 1920s and this process has developed only in the late 1960s and this particular process utilizes emission of low energy electrons which are generated by the OJ process. What is this OJ process? We will see, we will understand that later on, but it is a surface analytical technique for determining the composition of the surface layer. So, it is highly surface sensitive technique and that is what we will see in this particular lecture. So, this OJ electron it was first discovered by Pierre Auger on which this particular spectroscopic technique is named on and it was later on developed only in 1960s which utilizes a low energy electron which is a OJ electron to achieve a chemical composition mainly of the surface. It is highly surface a sensitive technique and once we initiate a electron beam, how does this particular process emerges? We will see initially the how the electron beam interacts with the material. So, we have this electron beam which comes and interacts with the material. So, there is there are certain interactions which are which keep occurring and it forms overall interaction is contribute certain region of the or the depth of a material. So, we certain regimes which are which are more like this that we see only as very surface depth of 0.5 to 5 nanometer which generates something called OJ electron O U G E or OJ electrons and this is nothing but the incident beam which is tracking on to the surface of a material and beneath the surface we will have some interactions from the which comes out as a secondary electron. Then we have some elastically scattered electron some regime of back scattered electrons. Then we have something which is corresponding to the regime of interaction with the electron beam to produce x-rays and then this is regime of primary electrons and this regime is coming out from the core level ionization. So, we see that the OJ the how the electron beam is interacting with the material. We see that the incident beam the incident beam actually which is out here like this is the incident beam it is interacting with the material and the surface layer generates OJ electrons and OJ electrons are characteristic within a certain regime of around 0.5 to 5 nanometers and beneath that we have some electrons which are emerging which are called secondary electron. These are again in elastically scattered electrons and then we have some elastic scattering with the material which result backside electrons and in this particular lecture we are more interested in what is happening at the surface layer. So, we are mostly interested in the OJ process for this particular case and the OJ analytical volume it means how much volume is being interacted once the electron is interacting with the material to generate some OJ electrons. So, we see that once the electron beam is being incident on to the material it is interacting only very small amount which is corresponding to around 0.5 to 5 nanometer and this particular analytical volume this is the overall interaction volume and then if we consider this is an electron beam which is incidenting on to the material only a very low level of volume which is limited to may be couple of nanometers 5 to 10 nanometers is really interacting with the material to result OJ electrons and as we say that this is highly surface sensitive because all the all the interactions they are they are being coming to detector only within a surface regime of 5 to 10 nanometer. It does not mean that the OJ electrons are not being generated in any other location it just means that only the surface electrons surface OJ electrons which are generated they are able to escape the surface of the material or the sample to reach the detector. So, OJ electrons are being generated even inside the material once the beam is interacting with the material. So, we see in this particular process though electrons are OJ electrons are being generated that they do not acquire sufficient energy to come back to the to leave the sample surface and that is what we see that the interaction volume is limited to around 5 to 10 of nanometers. So, basically that is what the characteristic of OJ electron is that OJ electrons fail to emerge with their characteristic energies if they are deeper than about 0.5 to 5 nanometer from the surface. So, that is what is all about the OJ analytical volume. So, we see how the beam is interacting with the material and the OJ electrons are being generated only from the surface though they generated throughout the material like till where the electron beam is interacting with the material all the OJ electrons cannot escape out. So, that is what leads to the OJ analytical volume which is limited which makes it highly surface sensitive and since it is highly surface sensitive and it is coming out from a very narrow regime it basically has very high resolution and it can specially resolve chemical images which are approximately to the order of 100 angstroms or 10 nanometers. And additionally OJ electrons spectroscopy can also be utilized for performing depth profiling and it basically we remove the surface layer we see what is on the surface and we start utilizing some iron etching we can start removing the surface layer and see what is beneath the material. So, we can have the composition of the top surface and it might be an oxide of for a particular material then we start etching out using certain iron guns and then once we etch out the material we see what is the composition beneath that particular layer and that is called depth profiling and OJ electrons spectroscopy can be utilized to determine the underlying compositions. So, that is what so nice about it and it is one of the very essential evaluation tool in the microelectronic industry because we want to see what are the basic interconnects or what is is there any oxide forming on the surface or there are very certain connectors or the gold coatings which are basically plated on to microelectronic devices. So, it my AES becomes a very essential tool in terms of analyzing or in terms of confirming whether the proper connection is achieved or what is the overall this is the surface very clean enough to have the conduction at particular level. So, that is what it has become an essential tool and it is highly versatile and sensitive as it can detect up to 0.1 atom percent for a particular composition and therefore, it has become a standard analytical tool also in the research lab. So, that tells its applicability of how OJ electrons spectroscopy can be utilized because it has very high resolution in terms of 10 nanometers and then it can it is highly sensitive in terms of being able to detect up to 0.1 atom percent concentration for a particular sample and that is that makes it very useful in research as well as proper analysis of certain materials and though it is highly sensitive it can detect up to one monolayer which is lying on the surface. So, that tells its capability in terms of detecting a particular composition which is even a single or monolayer and it can detect all the elements except hydrogen and helium why these things cannot be detected will come back as we learn about the OJ process it needs a minimum of 3 electrons in the process the OJ process and since hydrogen and helium they only have 1 and 2 electrons in the outer shell it cannot really yield a OJ electron and since it is highly sensitive it can also be used for monitoring the surface cleanliness of samples. Since the process is highly surface dependent like what is the surface composition it is highly surface sensitive that is the reason we can also detect or monitor what is the cleanliness of a particular sample and again it can also do some quantitative compositional analysis of surface regimes by comparing it with some standard sample. So, basically we come to that it can detect even single monolayer it can also monitor the overall surface cleanliness and also it becomes a essential tool in terms of quantitative compositional analysis only once when we have some standard sample also available for its comparison and as we said earlier the limitations extend to that it cannot detect hydrogen and helium just because the OJ process itself requires minimum of 3 electrons in its outermost shell that is the reason hydrogen and helium are eliminated from the from its detection and at the same time it will not provide a non destructive depth profile. So, if you want to see what is beneath the surface we obviously need to cut it we need to remove it. So, that is the reason OJ electron OJ electron spectroscopy it can provide depth analysis only once the surface layers are removed it is unlike that X-ray diffraction where X-ray can penetrate much more depth in couple in many many microns to be able to detect the information from the bulk, but AES OJ electron spectroscopy cannot do that because it is highly surface sensitive it can penetrate only a depth of around 5 to 10 nanometers not more. And it also requires that samples be small and compatible with high vacuum this is because that OJ electron they they they are very low energy electron and since if the electron has to come out of the surface it has to come out without any interaction it should be able to come out without any collisions with the atmospheric atoms. If it is colliding with the atmospheric atoms it means it is losing the information and that is the reason that the samples they have to be compatible with the high vacuum and most of the time sometimes that non conducting samples also become a problem because we are always bombarding the sample with certain electrons and once you bombarding the sample with the electrons that charge also has to be removed it has to be grounded. If sample itself is non conducting in nature basically the charge is not going away it is not getting earthed. So, for this particular OJ electron spectroscopy means the sample to be conductive and because to avoid any charge development on the surface. So, in this particular case the non conducting samples they develop charge and it becomes impossible to really analyze them because of the electron beam bombardment. So, that is a particular one more limitation of it that hydrogen helium cannot be detected it cannot provide non non destructive depth analysis depth profile and it requires the sample be compatible to that of for high vacuum it becomes little bit problem in certain biological samples or polymer samples where the samples themselves cannot take much of vacuum as the start as the might start decomposing. So, this is one of the very major limitations that it cannot be used for detecting certain biological samples. So, and again it also cannot have it cannot take the non conducting samples as well. So, that makes it is certain limitations of the OJ electrons spectroscopy and once the interact the electrons are interacting with the matter. So, the basically the excited electrons it can return to its lower energy state because if sample is interacting with an electron beam it can excite the electron and the excited electron can come back or it can relax in certain different processes. So, there are two competing processes one is that the electron will simply return to the coral level state. So, once we have excited electron it has gone out one electron is knocked out from the core shell and then one electron will come back to to its core and coral level state which was earlier knocked off and the difference in energy will yield to some extra fluorescence. So, we had certain knocked off electron that knocked off electron core shell is being occupied by electron from a higher energy shell and that basically the difference in energy is left as a extra fluorescence or secondly it can also happen that the one the knocked off shell is it is gone off when knocked electron is knocked off one electron can jump from higher energy to a lower energy state from a higher shell to a lower shell and once it has happened that particular energy can be acquired by a second electron which basically leaves the particular sample surface as OJ electron. So, instead of going out as a photon with certain with certain X-ray X-ray photon that energy can be absorbed by a secondary electron which is in a little higher shell and then it can have acquired certain energy as well and that is called a OJ electron to provide a picturesque explanation of this one how the particular things really work out. But before that it just makes that OJ and the X-ray they are more complementary in nature. So, whatever we have like we have some atomic number out here. So, we write atomic number atomic number in this particular axis X axis and say we have yield of either X-ray or OJ. So, we will realize that the lower atomic number the lower atomic number elements will have very high OJ yield and it will droop down with atomic number. So, OJ yield is typically very high for say up to 15 to 20 atomic number whereas, X-ray yield is complementary to it. So, it will start building up from here and then the total will always be 1. So, X-ray plus OJ will yield a total yield of 1. So, if say this was 1.0 this one will be 0.0 and generally the OJ yield is very high for lower atomic number elements. So, it is very high for lower atomic number low Z elements whereas, X-ray yield is typically very high for higher atomic number and the OJ yield is typically very low for higher atomic number. So, this OJ electron spectroscopy is generally utilized for low atomic number elements since the yield is very high. So, the detection becomes very very easier. So, that is the overall explanation of overall yield which is which combines OJ and X-ray. So, this is what the overall chart tells you about that the OJ yield will drop down with increasing atomic number whereas, X-ray yield will keep increasing for higher atomic number and we keep OJ limited to like up to 50 in the KLL I will come to the transitions, but it can be detected up to like 40 or 45 atomic number. We can have a considerable OJ yield and till there we can utilize the OJ electron spectroscopy because after that X-ray yield is so high that it becomes much more easier to go with X-ray and then it gives it might give a very high background for higher atomic number elements and. So, OJ process how it is to be defined it is defined by three basic steps. So, as we say that we bombard the surface with very high energy high energy beam and that basically leaves leads to atomic ionization and atomic ionization means that we are removing an electron of from a core shell or K shell. So, the first step is that a electron is removed from the K shell of the material and now the material or the sample is in higher energy state. So, now that higher energy state has to go out either via X-ray fluorescence or via electron emission which leads to the OJ process and third step is once the OJ electron has released from the surface it is the characteristics of a particular material and then we analyze that emitted OJ electron and that basically completes the process of OJ spectroscopy. So, initially we have atomic ionization relaxation by the emission of OJ electrons and then detecting that particular OJ electron to get the overall composition of a material. So, that basically completes the OJ process and how exactly what is happening at the atomic level let us go to that particular part. First of all the electronic structure which is being defined it will have certain non-zero value of orbital angular momentum like we have a principal quantum number we have angular quantum number and then we have certain shells like PEDF level shells and all these show spin orbit splitting because we have more than one electron in the P shell. So, like in S we have plus spin and minus spin whereas in P we have certain shells which will lead to the splitting of the shell as we have S and P orbitals. So, like in 1S we have one level, but once it goes to 2S and 2P. So, 2S and 2P will show different energy levels because the overall structure of this S shell and P shell itself is different and so on it can keep going on for once we have 3S, 3P, 3D and similarly for other levels we can see certain splitting between these particular bands. So, these all will lead to certain splitting in the electronic structure. Let us not come to that right now, but again once crossing that we have a vacuum level and then we also can have valence band if required out here for some conducting materials. So, the electron has to cross certain binding energy that is that is what being defined where the electron is really placed either in 1S, 2S, 2P. So, that is overall the electronic structure which is defined by the overall shells which the material has and the kind of valence vacuum level where it has to overcome the barrier in terms of getting released from the surface and so the OJ state can be defined like this. So, we have initial state we have the intermediate state and then the final state. So, intermediate state is more like that initially we take the particular electron. So, we have particular electron and then we are supplying certain energy with H mu. So, we have electrons in the S shell K shell or L shell and then higher shells. So, we have certain particular materials. So, because of this high energy photon it basically will knock off an electron. So, that electron in the K shell is basically knocked off. Now, what will happen that the intermediate state we have we have one electron jumping from higher energy shell to a low energy shell. So, basically what is happening is we had this K shell L shell M shell. So, say an electron is jumping from M shell to K shell to basically take the position of a electron which was knocked off or the vacancy which was created out here. So, we can so it can lower its energy. So, we have some sort of a relaxation which is which is occurred by the jumping of electron from higher shell to a lower shell this is something called intermediate stage. But the final state will be more like this that the additional energy which is being released by the material it is acquired by electron in a higher shell it acquires the overall energy and then it basically leaves off as a OJ electron. So, in the first state we had knock off electron from K shell and the second level in the intermediate state we had jumping of electron from higher shell jumping of electron from higher shell to K shell or L shell it can also be L shell, but coming to a core level core level shell and then the energy is being absorbed by electron which is which is in the higher shell and that basically is the OJ electron which comes out with certain kinetic energy and this kinetic energy is the typical characteristic of a particular material. So, that is that is what we see that the in the initial stage we have a knocking of a electron from a core shell and then the intermediate state we see a electron is jumping to the core shell and in the final state we see the emission of a OJ electron. So, that is what is telling the OJ process and these things are classified as ionization, relaxation and OJ emission. So, we see that OJ process is again divided into three parts. So, coming back to the electronic structure of it we can see that we have a vacuum level and then we have shells we can call it L 2 3 for for the P orbital L 1 for the S orbital and then we have K shell which is nothing but the our 1 S 1 S orbital. So, we will have two electrons out here two electrons out here and basically six electrons out here and then we will have a vacuum level. So, first process ionization it is nothing but the removal of electron from K shell. So, we have our vacuum level it remains as such and then L 2 3 it it will still have six electrons L 1 it will have two electrons, but in K shell we have one core or the one of the electrons has been knocked off. So, we say that this electron was knocked off because of the high incident energy which is being incident on the particular material and the prime energies are in the range of 2 to 10 k v which is which are nothing but the ionization energy of any material. So, we see that once we are incidenting certain energy or electron beam on a certain material it is knocking off an electron from core level shell which is the K shell and it creates a vacancy or a core in the K shell. So, the first the first step in this particular OJ process is that we see that a core is created and then the other shells remains as such. So, L 1 and L 2 3 they remain as such and the only thing is we are creating a particular core hole in this first first step. And going to the second step of relaxation and OJ emission we see that that one electron from a higher level jumps to fill an initial core. So, the same thing we see here that we had created a hole earlier. So, this was our vacuum level and then we had this L 2 shell then we had L 1 shell L 2 3 and L 1 and then we had a K shell. So, since we had a core an electron can jump from higher shell to a lower shell or it means from L 1 or L 2 3 any one of the electrons will jump to the lower energy shell. So, we see that one of the electrons is jumping out here from L 1 to K and then this released energy because once the electron is jumping from a higher energy shell to a lower energy shell basically there will be some additional energy which will be available with the material and that particular extra energy is now being released. So, first step was ionization in the second step we have jumping of electron from higher energy shell to a lower energy shell. Therefore, there is some gap or some difference in energy which is being released. So, that is what we are seeing. So, we will have certain energy release and that will again lead to. So, that that can again we go back that we now our K shell is already filled and L 1 and L 2 3 if the electron had jumped from L 1. So, we had only two electrons out here. So, now we will have only one electron out here and then we will have certain say couple of six electrons, but now that additional energy can be occupied by this particular electron it can go out as a OJ electron while overcoming any binding energy. So, this OJ electron has to cross certain energy barrier to be able to release to get released from the surface. So, we see the overall thing firstly a material is getting ionized K shell electron is getting released then there is a jumping of electrons from a higher energy shell like L shell say in this case we had a jumping of L 1 electron to the K shell. So, that now that will release certain energy and that particular energy is being absorbed by the electron in the L 2 3 shell and that goes off as OJ electron while overcoming the binding energy barrier. So, this energy is basically being utilized for overcoming the binding energy of this second electron. So, this particular second electron is this particular case and this thing basically it is coming out as OJ electron and it will have certain kinetic energy as well because the overall energy is overcoming binding energy plus acquiring certain energy which is nothing but the kinetic energy of the release electron. So, we have this energy which was which was attained by a jumping of electron from L shell to K shell that energy is being absorbed by an electron which over comes which that energy it is utilized in overcoming certain binding energy and rest of it becomes its kinetic energy. So, that is what is nothing but the OJ electron with certain kinetic energy. So, we have this particular energy as a sum of the binding energy plus some kinetic energy. So, this tells the overall process what is the OJ electron spectroscopy, but that we can come back to it that we can make a rough estimate of the kinetic energy of the OJ electron from the binding energy of the various levels in which the electrons are involved. And in this particular case we can see that we had the energy which is being released is the difference between the energy levels of E k minus E L 1 because we had E L 1 electron L 1 electron had jumped to the K level electron. So, this is the overall energy which was being released and this energy is again absorbed by the L 2 3 in overcoming its binding energy. So, we see that kinetic energy is the is equal to E k minus E L 1 minus E L 2 3 again if we rearrange this particular equation as below and we make it kinetic energy of the electron or the OJ electron is E k minus E L 1 and minus E L 2 3 or in the bracket L 1 plus L 2 3 if this becomes similar to E k minus E L 2 3 minus E L 1. It means had the electron jumped from E L 2 3 and the E L 1 would have gone as the OJ electron still the kinetic energy of the OJ electron would not have changed. It means that all the three electrons which are participating the kinetic energy depends only on those three electrons. It does not matter whether electron had jumped from L 1 or L 2 3. So, these two electrons become indifferentiable and since the latter two terms of the energy could be interchanged without any effect because the kinetic energy is remaining the same as we saw earlier that kinetic energy is remains same whether it is E L 2 3 which is being subtracted first or E L 1 which is being subtracted first. So, the overall kinetic energy is just written as E k minus E L 1 plus E L 2. So, which tells that these two energy terms could be interchanged. So, which makes that it is actually impossible impossible to say which electron fills the initial core level and which electron is ejected as a OJ electron. So, that is the beauty of this particular process that one electron is jumping from higher initial to fill the core level shell and second electron is getting emitted as a OJ electron, but these two electrons are indistinguishable because the energy will matter only where the initial core level electron was there and where the two electrons which have participated from higher shell. So, overall these two electrons are indistinguishable. The two electrons which are participating which are one is jumping and which one is coming out they are basically indistinguishable. And therefore, an OJ transition is characterised characterised primarily by the location of the initial hole. In this case it was a k level k shell and the location of final two holes. One is via jumping one core is created by the jumping of electron from L shell L 1 to k shell and second one was emission of OJ electron from the L 2 3 shell. So, now we had core in L 1 and L 2 3. So, this is the location of final two holes and this is the location of our initial hole. So, overall OJ process will depend what was the location of the initial hole the k shell and what is the location of the final two holes which was either jumping L 1 and L 2 3. So, this one will come out here the location of an initial hole was k and the location of final two holes is L 1 and L 2 3. So, that is what as that was that is all what governs the overall OJ process. So, basically we can interchange whether the transition was occurring from L 2 3 to k and then L 1 had released as a OJ electron or the or vice versa. So, these two electrons are nothing but indistinguishable and the energy remains same the kind of energy remains same whether the electron is jumped from L 1 or L 2 3. So, that that is all what the overall significance of this particular OJ process and as we said earlier that OJ electron depends on the atomic number and we also saw that the yield is much higher in case of lower atomic number just because the probability is very high in that the k electron can go away or the electron can go away and they can be jumping from higher higher energy shells to yield this particular process. But for higher atomic number the X ray takes the predominance and the overall OJ level basically keeps going down and basically we see that the there are certain OJ peaks which are which can come out by when an incident beam is applied on a material and there are stronger K L L signals. It means that the location of three electrons is from K shell L shell and L shell and MNM signals are much stronger for higher atomic number. It means the transitions are occurring by creating a hole in the M shell and then N shell and N shell are participating in the jumping of electron to M shell and then release of OJ electron from the N shell and generally typically we see that the if atomic number is on on this particular side on particular Epsis curve your Y axis then we see that this is atomic number and in this case we have said the electron energy which is being acquired electron energy which is being supplied to the material for creating the ionization. We will see something like that let let this is the nothing but the atomic number in this case and we see that the K L L transitions are occurring something like this L L M M transitions will occur more like this and M M N N transitions will occur more like this something like this. So, we will see that K L L transitions are very predominant for certain atomic number and then we will have L M M transitions for little higher atomic numbers which are much more predominant and then M N N. And this is so true why because if this is up to may be say 15 to 20 atomic number we have more K L L transitions why because till then we do not have M shell and as soon as the M shell starts coming in it governs that basically the L M M transitions become much more probable because it is very difficult for a particular atom that if it has a M shell N shell higher in higher order shells it is very difficult for an electron beam to penetrate through the material and knock off a K electron because it is again surrounded by a L shell M shell N shell. So, this becomes very very improbable so that is the reason this OJ process is very dominant for K L L transitions in low atomic numbers and L M transitions for little higher atomic number higher atomic number elements and then again M M N transitions will become very very predominant for even higher atomic numbers. So, approximately up to around 50 L M M transitions are much more probable and again 80 90 atomic number M N N transitions they are much more probable and so we can see that the this detection limit of the K L L transitions they are very stronger for the low atomic numbers where is up to 50 it is a medium atomic numbers we have this L M M transition which are more probable and for higher atomic numbers we have basically M M N N transitions which are much more probable and we require certain level of energy to basically ionize a particular material and those basically run up to in maybe from maybe say a couple of K E V. So, we have the initial incident beam from running from 2 to 10 K E V to ionize the core shells. So, that is what is required in terms of ionizing the material and leading to a generation of a core hole and so that the OJ process can really occur and as we see in this particular process we require at least three electrons one transition to cause ionization and two more electrons to cause a jump and release of OJ electrons that is the reason we need minimum three electrons and hydrogen and helium cannot be detected. So, the minimum element which can be detected is lithium. So, that is what the overall dependence of this K L L transitions and above. So, the OJ spectrum looks more like this that we have we have to supply certain electron beam which ranges from around 2 to 10 K E V to ionize a particular material and then, but these peaks are basically they generate they are on a very high background why because it is it also undergoes a multitude of inelastic scattering processes during the OJ while achieving the OJ spectrum. So, we have certain signal and the K E which is being detected from the particular from a particular detector. So, we have signal and again it has very high background and certain peaks for certain material and then it goes off. So, the overall background is very high for particular signal in the OJ process. So, basically that is not really good for detecting and it is not good for achieving a particular repeatability. So, that is the reason this particular signal is differentiated with respect to the kinetic energy of a material and then basically we can achieve one more spectrum which is much more repeatable. So, we have something d n with respect to d e and then we have this particular in terms of K E and electron volts and then we see that we achieve a very nice background with peaks very sharp peaks and very repeatable peaks. So, let me draw it again. So, we have this particular peak and then we have achieved certain peaks and then it goes on. So, that this is nothing but a kind of a zero background and we achieve certain peaks which are highly repeatable. So, it is actually possible to measure spectra directly in this particular form and it gives very good sensitivity because now this peaks are more repeatable and they are also very sensitive to particular materials. So, it is again reproducible for a particular referencing if you want to reference it. So, this was peak for say silver and then the differentiated form will also give out this particular peak again at the same location and it would not be much with the background. It would not be more hazy like we saw in the earlier case the peaks were more hazy and they were not really very sharp. So, that is the advantage of utilizing a differentiated form which is d n by d e the number of counts with respect to the kinetic energy because it also considers a way of taking the probability which was not. So, being defined in the earlier case in this case we know a particular transmission will occur at a certain energy level. So, that differentiation with respect to energy makes it very sensitive and reproducible. So, that is the advantage of using a differentiated peak also the sensitivity is gone high because this particular ratio with respect to background it also increases. So, that is the advantage of utilizing a differentiated form of AES that we have much more higher peak or better peak and again it can be utilized for detecting very small concentrations like we had certain spectra something like this it can be certain spectra like this in the differentiated form. We can see that there is certain peaks which will correspond to similar same elements because we have transitions from KLL, LMM and MNN. So, we can see that the higher energy the higher atomic number materials they can have multitude of peaks. So, we can see certain peaks which can say belong to say chromium then again chromium or they can also have more peaks something from nickel or nickel or it can also be that like in case of certain materials like in steel we have very small very fine contributions from sulphur phosphorous elements like that which are very which have very low concentration less than say 0.03 weight percent. Still we can see that this OJ spectra can detect even that. So, even such a lower concentration can be defined by say sulphur or say some peaks in phosphorus. So, those peaks can also be detected very easily in the OJ spectra. So, we had this end in terms of energy and it can be again differentiated with respect to energy and this is again the energy. So, we can detect always some peaks which are which were really not probable with concentrations of less than 0.03 weight percent. We are seeing that OJ spectra can detect the major peaks which can come out either say from major peaks can be either from chromium or say nickel or even iron because for a stainless steel the major composition will be say iron and then chromium will be say around 25 may be say 15 to 25 percent the nickel can also be from 12 to say 15 to 20 percent. So, that those are the major peaks what you what you might expect to see in the OJ spectra and then again sulphur and phosphorus very low in quantity, but those will also be detected if you utilize the OJ spectra. So, that is the beauty of this particular process that even elements with very small concentrations less than 0.03 weight percent can also be detected in the OJ process and in this particular processing we require very ultra high vacuum to the order of 10 to the power minus 9 tor. Why because the OJ electrons they are very low energy electrons and once they have to leave the surface and get detected at the detector. So, they need to undergo the detection process without collision with the atmosphere if it is colliding with the atmosphere atoms then it is basically losing the energy and that will increase the background. So, this particular vacuum level will create a mean free path which is approximately 40 kilometer and as we said earlier that the OJ effects are much dominant for atomic number less than 15 and for a l n m shell transitions it can be measured up to atomic number of up to 50. So, that is the overall thing which we saw earlier because of the presence of the different shells and this is the very much requirement that it requires a ultra high vacuum of order of 10 to the power minus 9 tor and coming to the components of OJ electron spectroscopy basically we require an electron source which will have a variable energy because we want to see what is the overall kinetic energy and how it is dependent on the ionization because we are applying certain energy and it is basically knocking off an K shell electron. So, we want to see how the transitions are occurring and again this particular variable source of energy is also useful in terms of describing a very fine spot of electrons. So, we should have an electron source which should have a variable energy source and then this electron has to go through a electron energy analyzer and there are different types of analyzer which can be a spherical sector or hemispherical sector and then it has to basically pass through a electron detector. So, electron analyzer will separate out of the energies and then those energies once it is filtered it will basically get at electron detector where it can basically be detected that this is an electron and then that the intensity of that particular detection will be counted. At the same time the measurements have to be done in the ultra high vacuum just because that the OJ electrons which can travel from surface to the detector without any collision and secondly the surface cleaning is also one of the very critical features out here that once as soon as we take the sample from particular location to the OJ chamber then it can get contaminated depending on its reactivity. So, we want to keep the sample clean and so to to avoid the particular contamination we want to use a ultra high vacuum which is to the order of 10 to 10 to the power minus 9 tor and there are certain other options which can be available with OJ electrons spectroscopy is something called iron source. Iron source can be utilized for cleaning the surface prior to the analysis. So, if you want to measure very clean surface if you take a sample it gets oxidized you want to clean the surface to see what is the actual surface and so that we can measure its concentration depth profile and then we can measure it. So, that is that is an accessory to the OJ electron spectroscopy and coming to the analyzer part there are certain analyzers one is one of them is cylindrical mirror analyzer it has basically some concentric electrodes and then those electrodes are basically only it is it is it is it is we apply certain bias to it and then it can allow only certain energy levels to pass through it. If it is higher energy it will be absorbed by one of the electrodes lower energy than it will be absorbed by another electrode and that those two electrodes are again earth. So, basically certain energy gap can only traverse through a particular concentric electrode setup. So, cylindrical mirror setup so that basically determines the pass energy and then it allows only a certain or a narrow range of kinetic energy to pass through it and basically the similar system also can be utilized by using a hemispherical analyzer. So, how the particular analyzer looks like let us go back to it and let us see how the cylindrical mirror analyzer looks like. So, we have this particular electron energy source which goes and bombards a particular sample surface and then we have the electrodes electrodes like this and then only a certain level of energy of the OJ electrons will pass through this particular electrodes setup for electrodes and it will reach the detector. If it basically coincides with one of the electrodes this electrode or this electrode the energy level all the electron will get absorbed on to the electrodes. So, the only the bias on these two electrodes will basically decide how much how much the particular energy is allowed through the particular analyzer. So, we have electron electron use source which interacts with the sample and then we have the OJ electrons which are emitted and they pass through the analyzer and only a certain energy is basically allowed to pass through and to reach the detector and that is how this particular cylindrical mirror analyzer really works and this was a one pass filter. We can also have two pass filter where we can see more like this that electron gun it is interacting with the material and then basically it is coming out at a certain certain energy is coming out and to verify that that this is again the same energy level we can have one more set of electrodes out here again these electrodes will make a second pass. So, this is first pass and then again you have certain kind of opening and then you again have these two electrodes which will again decide the overall energy and then it will have a detector. So, this is nothing, but the second pass. So, we had this particular electron gun it is interacting with the sample out here and then we have OJ electrons which pass through the first detect the first first pass and then this becomes the second pass and then we have again electrons going out from through the analyzer like this. So, we have again the detector out here and which detects the overall intensity of electrons through this particular process and now comes the important part once it has passed through the detection pass through the analyzer now we have to detect what is the overall count of the OJ electrons. So, basically we have we have to focus the electrons which are which were basically coming out. So, basically we have focused the electrons are incident on a sample and then they are passed through the cylindrical mirror analyzer for the analysis part and then we have its detection where they are multiplied and signal is sent to the data processing. So, we have photomultiplier tubes or the dienotes which basically take the the electron and multiply it. So, again we can have single channel detector or multi channel detector depending on it can be a continuous dienote surface or photomultiplier tube and then the collected OJ electrons are basically captured and then they are plotted as a function of energy against the broad secondary electron background spectrum. So, since it has a very huge background then again it can be again later on differentiated to achieve a very nice repeatable sensitive OJ spectrum which is d n by d e with respect to the energy and that is what we have we have first it is analysis and then the detection part comes through the multi channel or the single channel detector or the photomultiplier tube or through continuous dienote surfaces and one more thing to mention is that the energy of OJ electrons is in between that of a secondary electron and a backside electron and again once we have detected it we can have the quantitative measurement of OJ composition that the atomic concentration of an element can be given by this particular equation where x is the intensity of the unknown specimen. So, x is the intensity coming out from an unknown specimen and i is the pure element. So, i is the pure element and x is the unknown specimen and then we have i the i is the intensity of the OJ signal and s is coming out from the relative and is the relative intensity. So, by comparing in this particular manner we can see what is the overall signal which is coming out from the sample and what is the overall signal which is coming out from the standard sample. So, by comparing those two we can say what is the overall concentration of x in particular sample. So, we need to have pure samples available to be able to say what is the overall concentration of that particular material in the unknown sample and again it can be utilized for OJ death profiling and it can detect what is beneath the surface or the buried layer what are the overall compositions which are basically can be attained out here. So, basically we have a surface and it is being bombarded by an iron source. So, it basically starts eating the surface and now we have some surface which is beneath the original layer. So, the OJ process it can detect its composition from step one and it can also detect composition after it as the sample has been etched. So, this can particularly provide what is the composition at level one and what is the composition level at level two and while this particular iron beam is etching the surface it is necessary to know what is the etching time because depending on the material depending on the energy of the iron beam the way it will eat out the material will be very different. One material will be eaten away quicker second material can be eaten away little slower also depending on the current or the iron beam intensity again the etching level will be little different. So, but then the OJ signals which are coming out coming out from the surface they can be correlated with the overall depth of a particular material and it can provide us information of what is the particular material concentration with respect to depth. So, this depth or the etching time can be correlated here with respect to percent composition out here. So, coming to just one example. So, say if we had a particular material and say we saw some peaks out here and then it is dying out like this it means this particular material was sensitive only on the surface for say certain of certain nanometer regime. So, it was 2 or 3 nanometer in terms of depth in terms of percent composition. So, this particular material and then we can also see something more is something more is forming on the surface. So, this was oxygen and say this one was silicon. So, we can say there is some formation of silicon oxide on the surface. So, we can say that probably oxygen level will go down and then we can say that there was some higher concentration of a material say it was silicon and then again oxygen. We can say silicon oxide was basically predominant at this particular on the surface whereas, say the bulk was say something like this silicon and then oxygen and then say we have something like indium. So, we can say the bulk of it is formed of indium whereas, it was probably coated with some silicon and which is formed of oxide. So, we can say that SiO2 is forming on an indium bulk. So, that is how it will tell that what is the overall material which is basically being what is really happening on the surface and how this depth of oiling can help us identify what is happening beneath the surface. So, via ion etching we can this particular process we can see with the increasing depth we are seeing increasing concentration of indium and decreasing concentration of silicon and oxygen. So, it means that there was some silicon oxide which might have formed on the surface. One more dimension can be given to it is that it can also happen that we had silicon and then it was going like this and then we had some oxygen and then it drops much earlier to that. So, it means that silicon oxide is forming only to a certain thickness and there is again some more regime where silicon is still intact. So, we have formation of some silicon oxide on the surface beneath that we have some silicon and then we have some indium on which the particular silicon might have been coated. So, that tells the overall depth profile of a particular O.G. process. So, now coming back to the overall features of the O.G. electron spectroscopy to summarize the overall lecture that we have characteristic energy losses. They can occur because of plasma losses or which can be again channeled through in the electron photo electron spectroscopy. So, they basically create the background and then they can be a charging of insulating samples. So, by choosing a proper incidence angle and by choosing proper beam energy we can take care of that by lowering the beam energy and by inclining the surface and then O.G. electron spectroscopy can also be utilized for qualitative and quantitative spectroscopy. It can also be used for the death profiling part and basically in this O.G. electron spectroscopy we realize that we have basically O.G. process arising from three electrons one is the core level electron which is basically knocked off. Then we have one electron jumping from higher energy shell to a lower energy shell and then third thing that energy is absorbed by a electron which basically is emitted via overcoming the binding energy that is called the O.G. electron. And we saw that how the overall instrumentation is also done that we have incident electron beam energy source and then we have certain something called analyzer that basically allows only a certain energy levels to pass through it and that allows only certain electrons to come out with certain energy levels and that is being detected by a detector where some dinodes or photo multiplier tubes and that thing is again plotted as curve with respect to energy. So, we have signal count with respect to energy and to make it much more precise we take a differentiated form in with respect to d n by d e with respect to energy and that is much more sensitive and much more repeatable. And then we also saw that the O.G. electron spectroscopy can also be utilized for death profiling via doing the surface by applying certain ion beam and then etching out the surface and then seeing what is happening beneath the surface to comment on what is the overall composition of the overall sample which was under consideration and it can also tell you what is happening beneath the surface and so on. So, basically we end our lecture here. Thanks a lot.