 So we have discussed about Auger electron spectroscopy in the last class and this is the continuation of the that lecture and I have basically talked about the basic principles of Auger spectroscopy the applications where it can be used and I have given you some basic equations and diagrams to explain how the Auger electrons are generated. Now in the subsequent lecture of so today we are going to see different applications of Auger electron spectroscopy and finally I am going to show you the actual machine or actually configuration of a machine in the Auger spectroscopy. So before that let me just reiterate the following thing which I was I should do it very carefully the reason Auger is very famous and very useful technique is because the signals which we get from the samples are basically from a very small thickness very small thickness of the surface this is what is shown here if you look at the sample surface and then there are different kinds of signals which is generated because of the inherent excitement are excited by the primary electrons as the primary electron falls on the samples it causes a lot of excitation and that leads to different kinds of signals. Signals can be backscattered electrons can be secondary electrons or it even a characteristic x-rays which are used in the scanning electron microscopes and also we will have Auger electrons as if you look at the interaction volumes from which the signals generate or get generated is varies from very large thickness to a very small thickness depending on the type of signal. So for the characteristic x-rays the interaction volume actually is very large the depth form is the information can be can come is of the order of 3 less than 3 micron 1 to 3 micron actually on the other hand the backscattered electron comes about you see a backscattered electron comes about approximately about 2 micron secondary electrons come from about approximately about couple of hundreds of my am strong that is hundreds of actually nanometers not I am strong but Auger which is very significant in radiation comes from only 4 to 50 am strong depth and it is only possible to cause Auger excitation for atomic numbers higher than 3 so you can always get excitation from electrons form elements which are having atomic number more than 3 that is higher than the lithium. So that means the information which is coming for Auger is basically coming from a very small depth on the sample surface and that is why is very very very significant tool to analyze those kind of small you know features on the sample surface in the Auger. So this is what is shown here this is the electron beam you can see here and then this is a depth from which the information comes in the Auger depending on the spot size also I know not only spot size spot size electron gone the spatial resolution resolution in this way resolution spatial means this not the depth but the XY would depend on in the direction purpose surface analysis volume depends on the electron mean free path that is what I am shown mean free path is high then electrons can generate more Auger it is low then it is mean free path is shown here as a function of electron voltage electron energy actually have you see at gold and this is silver they have a very small mean free path mean free path increases to you know like molybdenum cerium beryllium okay. So that means all even some other elements like phosphorus so that means the mean free path actually depends on a little extra energy is very high for the gold silver others but very low for the beryllium and other and the phosphorus and iron also so that that actually tells us that you know perpendicular depth will also vary depending on the mean free path of the electron and different elements this also sets that what kind of elements you can analyze for a particular depth well now let us move into the applications as I said we are going to discuss today that the analysis depth was just information I wanted to convey clearly we have already discussed about the chemical analysis by using XPS or excess photolysis spectroscopy is around the best complemented techniques for XPS in the chemical analysis depending on the kinetic energy of the Auger electrons is more sensitive to surface than the XPS heat also gives us chemical shifts depending on the characteristics are the basically ionic state of the element present Auger landscapes can be used to determine the chemical state of a given element in a sample and then studies the charge transfer in alloys this is very important one can actually study the charge transfer in alloys let us now look at the differences in the line shape and the peak positions for the carbon nausea spectra KVV VB stands for vacuum in different CX and HY compounds first let us talk about it you know acetylene C2 H2 there are you know triple bonds between two carbon atoms you can clearly see the three distinct peaks one broad and two very sharp peaks coming at around from about to 40 to 260 255 actually KV but if you go to C2 H4 that is it the ethylene but there is a double bond you can clearly see this peak splits 1 2 3 4 5 6 not only that the positions of the peaks also little bit has shifted to the left side that is lower kinetic energies now if I go to the element they see H4 that is a methane I can clearly see one big strong peak clearly visible and others very small peaks visible so that means the electron yield versus kinetic energy diagram can distinctly differentiate between carbon compounds from ethylene from acetylene to ethylene to methane this is just basically to detect and a particular compound we can use these signatures to detect whether they are present in the sample or not this is the first thing you must know that means chemical analysis means quality and quantitative analysis quality analysis means whether we are able to detect a particular compound or element or particular pieces on the sample surface or not a second thing if I able to detect many chemical pieces says whether we can quantify the amount of the each of these elemental pieces or compounds present in the sample surface this is very typical of any spectroscopy but as you are all gives us much you know extra information are then these only well now let us talk about little bit about the you know elemental ships for the different you know first transition metal series Scandium Titanium can name 10 for 21 and then gene stands for actually 30 so if you go from 21 to 30 2p 3 by 2px actually shifts 399 electron volts to 1022 electron volts 3p6 from 29 to 89 now if you make alloys between them actually suppose if you make alloys between Scandium and Titanium there will be shift of 327 similarly between Titanium and a shift of seat 421 so you can clearly see the ships because of the formation of alloys among the different elements this alloys means solution types well not only that one can actually look at the chemical ships in terms of atomic number versus electron and the diagram this one I have already shown to you now if you if you carefully look at this diagram it says different transitions like KLL transition LMM transition MNN transitions and higher depend on the atomic number so obviously if the atomic number is less than about say 16 that is for sulfur you will not have any you will have only KAL transitions only when atomic numbers of the elements higher than 16 and lower than about 45 you have basically LMM transitions L and and and there is a small overlap obviously between LMM and the KAL transitions similarly small overlap between MMM MNN and LMM transitions also but MNN transitions actually occurs mostly for the elements with a very high atomic number like more than 45 and less than about 84 let 3 so that means depending on this from this from this diagram actually one can actually understand that if I have alloys suppose if I have alloys between the aluminium and the niobium obviously there will be chemical shift of the peaks from both aluminium and niobium because of these different transitions not only that there will be also chemical shift if you consider only suppose elements which are very close by suppose we consider boron and you know aluminium so there will be some chemicals if possible even in KLL transitions because of the atomic configuration electronic configuration change or task task task transfer issues in the alloys to give you much better perspectives how the chemical shift actually is observed in the OGR I am not actually discussing the exact physics behind the chemical because this is what I have done in a XPS the theory is same whether it is for SPS or OGR only thing which I am describing here is that how this chemical shifts can be used to detect a particular type of chemical bonding a particular type of you know electronic configuration that is considered silicon and oxidized silicon in silicon you have silicon-silicon bonds and if I take OGR spectra the silicon-silicon bond gives us a very characteristic peaks at about 1600 and 17 to 18 electron and volt that when the silicon is oxidized this is most of the cases happens on the surface of the silicon you have a silicon-oxygen bond so therefore because of the presence of silicon-oxygen bond the peak form this one gets shifted to the lower value and it has been observed the peak comes at about 1600 and 5 electron volts. So OGR spectrum a spectra from the elemental silicon which is very pure and the oxidized silicon which is having oxygen as a one of the element present in the along the silicon can distinguish the type of bonding between these two very clearly and it is even much clear in OGR than in XPS that this kind of chemical shifts are actually observed and can be used to differentiate between the different kinds of bondings bonding in the sense of whether it is a bond between similar atoms or dissimilar atoms oxidized nitrides all can be detected there to give you much even higher no much better perspective in the sense let us now talk about elemental germanium and germanium with a thin oxide layer same as silicon but here the elemental germanium is a germanium syn crystals so you have germanium zero peak germanium four peak you can see this is germanium LNM transitions on the other hand if you look at if that is oxide that is how they basically these two this is actually from the pure germanium this is from the oxidized peaks so this is oxide this is pure germanium so you have oxide layer this is shipped from the pure germanium zero and germanium four peaks to the lower level say from 1175 1175 to 11 you know 45 germanium zero peak ships not only that even the object is very sensitive to presence of very small quantum element like semiconductor doping let us talk about semiconductor doping of a silicon the difference between P and N type silicon can also be distinguishedly seen in the object spectrum that is what is shown in the slide so I know you know that P and N type silicons can be created by doping different elements if you dope with you know P the five you know boron the like phosphorus with silicon you get P type and if you do P boron you get P type or other elements like so this is the yield in XPS and kinetic energy plot you can see N type and P type that is a distinct you know position of the peaks and the another difference between these two peaks are about 0.6 electron volts so that means XPS is so sensitive it can also detect this much of energy spread when you dope the silicon to make it N or P type the small shift is sufficient enough to tell us let us know that it is indeed a N type or P type well one can actually detect even this big ship this picture is not very clear I have taken from a book but it is not clear but still I want to show you because so that you can get idea so this is basically different between N and P type this is N type this is P type silicon in the image so we can actually take a silicon single crystal and dope elements of different types and make as NPN junction or PN junction basically here N and P this is the junction so you can see that pick shift changes pick shift as a distance is basically changes continuously from N type to P type this is basically the quantified value of the pick shift from N type region to P type region. So one can actually get an idea of continuous you know change in the in the doping characteristics as a function of distance by doing taking XPS spectra at different points on the sample surface like this this is possible there is a major applications next thing which I would like to discuss is the quantification in XAES I think I have discussed a lot about quantification XPS similarly Augie spectra's can also be used to quantify different elements. So quantified analysis using first principle is possible but normally not done to do large difference between these coupling schemes that govern the object transitions in a multi ionized atom what is it means is that if there is a multi ionized atom then there will be large differences between the couplings of different transitions and this makes the quantification difficult the most common analysis use sensitive factors derived from the pure materials or standards these materials also have lot of problem of position and should be used judiciously because I like to know like you to know that is allows us to quantify different elements present on the sample surface but positions are much poor the next piece so what is the actual mathematical equation which uses sensitive factor actually Augie electron density in a penny position XYZ is given by this big equation this is the instrument in city this is cost section this is the energy level this is the diameter from which it is coming is also function of energy level and the instant beam angle and these are all this is the atom in the number of atoms which has undergone transitions exponential transition wavelengths and cost it as a scattering this is very complex formula and I do not want to discuss in detail that requires you know a lot of theories to be first discussed simplified formula for homogeneous material is that XI the amount of particular element I present is given by IS by SI divided by summation of IJ by SJ but J is get me summed over so therefore IS is basically the scattering factor and I is the intensity so if I know the scattering factors of the elements present and if I know the intensities of the each piece I can actually indirectly calculate what is the amount of present in the particular specimen so let us go back to the Augie spectra this is Augie spectra coming from oxygen iron nickel and obviously carbon is inevitably present or omnipresent in any sample so a small carbon pick which is sometime used to remain calibrate so oxygen KLL transition here then iron LMM transition here and nickel there is a small peak here and these two peaks basically LMM transition nickel now as you see here the big picks are this one for oxygen this one for iron and this one for nickel correct now I can actually calculate the area under these three peaks and get the intensity right so and then if I know the scattering factor I can calculate or quantify each of this element presence one one can actually take basically differentiate these it intensity aspect energy then gamma big gate can get much better spot which I have discussed already about the Augie spectra oxygen spectra becomes like this nickel comes like that so this way one can actually improve the quantification position much better way well let us now look in your much detail this is the sensitive factor with buses atomic number sensitive factor is what I discussed this is a sensitivity factor as you see from this part to this part it contains the transitions energy level the scattering cross sections incident beam energy level so sensitive factors may vary from 10 to the minus 2 to 10 depending on the atomic number and depending on the transitions for a 3 kilo kilo volt primary electron this is calculated for KLL transition sensitive factor will be very much lower and it basically close to one for most of the elements you studied this is very important because you know KLL transitions is normally seen for all the elements less than atomic number less than 16 or which are lower actually than sulfur and so therefore this is what we get and the sensitive factor is low that means the quantification done from this elements by is even much less precise the highest sensitive factor is obtained for LMM transitions and LMM transition actually takes place for a large number of you know at elements starting from atomic number 16 to atomic number about 45 65 let me just go back there and to show you what is that so this is yeah this is 45 so it basically starts from 12 to 45 so there is a large range that's and that is the range we are having a very large value so you can see here this is something like 12 this is what love something like 35 or 40 40 here so in this range from these to these actually the sensitive factor is quite high so therefore measurements will be better a moment and the end and transitions actually occurs at large atomic numbers more than 40 and about to 85 and this is also very high for a you know atomic number ranges from 38 to 62 so that means from the all the atomic elements with atomic number from about 16 to about 62 the sensitive factor is quite good and actually it is higher than 0.5 so that means we can actually use as he is for this elements to get much better quantification analysis well if I this also depends on the primary beam as you know if I use a 10 click electron primary beam this is how the curves get shifted well not much shifting has happened except for the you know we are getting an extra transition at LMM transitions but LMM transitions actually we are getting still extended LMM transitions you can see there so little bit of change happens but not much now we can actually do it this is the sensitivity factor sorry so we can actually do it much better way that by assuming the concentration to be relative ratio of atoms we can neglect the terms that depends on the instruments so we get this is AI Sigma I I think with there is no need of discussing I have already discussed about that but this is a step and scheme the important thing is here to understand is a semi-quantitative techniques not a quantitative technique per say like XPS well to determine the peak intensity I know that is what is very important because you want to calculate the area under the peak to know the actual intensity so one has to be very careful about to measure the peak intensity I am showing you some plots to make you understand how that you know judgment is very important so this is the kind of can this is the CPS as you see this is the plot of silicon the P and B is basically the peak and the background so you have to consider the peak area this way on the other hand if you take D any by D but it is kind of energy you get a much better peak this is your peak area correct so that means it is better to use D any by D than any by E buses can take energy plot determine the area under the peaks so that quantification is much precise well to give you a analysis as compared to the you know others for compounds nitrogen compounds like this chromium nitride pharnium nitride titanium nitride scandium nitrides the fast to transition metal nitrides you have basically L3M2 or 3M2 peaks for this you can see these are the peak positions the changes and for L3M2 empty the peak positions actually are then this is what is important in as deposited condition this how the intensity ratios varies you know one B stands for you know for these ones this is the severe wall up so you cannot detect B means we cannot detect that's a wall up these are the ratios after iron bombardment ratio gets modified right on the other hand if you do using RBS that is what we will discuss in the next the RBS means other for backscattering which is the same stool the secondary and mark spectroscopy this is the data we get so you can see this is very close for the vanadium scandium nitride okay but this is not this is close to vanadium nitride this is little bit lower the actual value so that means ES is not that gate analysis as far as it seems or XPS is concerned second important observation from this is that if you do the bombardment after bombardment and before bombardment there is a change in the natural to metal pig ratio this is the natural to metal pig ratio I ? by I alpha this pig ratio actually decreases after sputtering that is what you see here from one from two it becomes 1.82 2.5 to become 2.1 1.4 to become 1.01 1.3 become 0.94 that is clear that is because nitrogen actually gets removed in sputtering because there is a light element so many times partnering is bad that is why it is better to do this analysis in the vacuum without any sputtering next thing so after giving you an idea of chemical shift chemical detection of different elements or different species as well as quantification let us go to depth profiling audio depth profiling well what is audio depth profiling actually as you know you have this is a sample suppose and you have it is an electron in coming into picture and then you generate all the electrons it goes to the electron energy analyzer and then you get the peaks many times actually you can routinely get this fix now we can actually use argon ions to sputter the sample surface sequentially that means if I have a sample initially like this this is taken from this website anyway then I take information at the beginning from this much area get the object spectra then using argon ion I remove small thickness very small thickness sputter out of the order of tens of 10 to 20 micro sorry I am strong and then again collect the object spectra that is how I keep on doing it so that means slowly slowly I increase the depth or so slowly increase the depth of sputtering and collect the object spectra and if you do that then one can actually do the profiling that means one can actually determine the elements present at each depth and also quantify different elements presents so this is one plot which is showing here and this is parting time buses you know intensity as you see here you have a aluminum concentration gold constant decrease aluminum increases oxygen increases titanium so you have chromium titanium gold aluminum oxygen okay this is basically a gold layer the top of aluminum oxide at the bottom and then you have a interlayer between this cold and these aluminum oxide the interlayer consist of chromium and titanium and that is what you see in the Intel this concentration of the chrome titanium is very high in the intermediate zone gold concentration was high at the beginning that is from 0 to about 20 minutes you have a large cold concentration then it decreases and finally once you reach the aluminum layer aluminum oxide layer you have aluminum oxygen so what does it mean this is a very important aspect which you must know this is actually required in material science that means that this is all this very sensitive technique this can be used even do such a fine scale depth profiling by using argon ion sputtering well it looks very simple and very you know genuine and very interesting method but it has lot of problems it can lead to different artifacts what it can lead to sample charging because of the you know sputtering it can be topographical feature resulting from non-unimum suffering of sample it can lead to means preferences partnering depends on the element present some elements will partner easily some elements part are less easily then there are be effects like argon ion beams and it can also lead to most notably ion be mixing because you are putting R and argon ions that can lead to mixing of two different elements of two different species and that can modify the results so one must remember these are the problems in audio depth profiling otherwise this is a very nice technique well this is not clear to you visible but just to show you that AFM actually leads to very small thickness on the top surface or gear is approximately of 100 micron so odd year this is odd year AES is about 100 micron depth analysis can be done others like XPS can go up to very high RBS can go up to even my a couple of thousands of mic amstrong and FTR things can go up to even micron level which I will discuss in detail when I compare these different techniques so to give you much better idea this is another example sputtering and non-sputtering copper and nickel aluminum alloys presence and as you see here copper and nickel alloy actually not aluminum copper alloys as you see here this is the tail for filing of the pacificated layer this is the clean sample the clean sample is giving much better results signals than the passivated passivated means it might have got oxy surface layer so odd year sputtering profiles for the copper and nickel alloys is basically taken from Macquery at all it tells us that it is always better to clean the sample surface by sputtering and before taking even the profiles another example this is a gallium 90 substrate with a PD inter layer and there is a aluminum layer this is 200 micron 200 amstrong PD layer and 1100 mic amstrong aluminum layer this is basically a multi-layer as grown now one can actually do these schematic profile and that's good for this is the aluminum depth PD depth and gallium nickel you can see the quality of data one can get very good quality data one can get using this this is another example I think this is PD germanium oxygen aluminum many things that presents this is part of time versus atomic concentration this is aluminum this is oxygen this is PD this is gallium this is nitrogen what you can carefully do that same sample actually and then if I anneal it it gets changed I can see that the oxygen actually profile has remained same palladium profile has got changed this pallimony has moved into our inside the aluminum and on the nickel gallium remains same so one can actually do this kind of analysis also in the actual sense the last technique which is useful which I am going to discuss is the scanning or gear electron microscope actually or Inland spectroscopy you can actually scan the surface and do that what you do is basically you can use the same technology as using a cm and your beam which is coming and electronic which is coming and following the sample surface can be you know allowed to raster on the sample surface or can be allowed to basically scan the sample surface so as you scan the sample surface you can actually gather information from each point on the sample surface due to interaction of the electron beams with a sample surface and then generate an image instead of depth of piling you can generate actually an image so details is shown here what do you see here this is scanning coil this is the electron infillaments this is the objective lens so this is the coordination lens so the scanning coil it will scan the beam scanning squall is nothing but basically same as an electron scan electron microscope then you have a secondary electron detector here this iron detector net here which is part of the sample scrucil so and the actual pipe picture is shown here this is taken from University Illinois they have a facility like this so what is done here let me describe a schematic diagram this is an electron beam falling on the sample surface so you are basically generating K1 K3 K2 different kinds of you know transitions of energy is electronic different energies this can be detected because of the presence of different elements actually when you scan and then you can image this image actually is I do not know this is the blue is basically titanium this is taken from this website not from my work so they are pictures the sulphur is basically the green green is basically for sulphur and red is basically for silicon as you can see this is the cross-sectional conventional a same image which does not give much data it is only shows there are different areas sample surface red and the black this has been basically made color I think this is sulphur backscatter image here sulphur backscatter image so this is basically sulphur regions so as you can see a sulphur is green and in the a a Sam or the scanning or yes microscopy you can see this red regions are basically coming from silicon these are all silicon okay these three regions silicon silicon and then you have sulphur and the titanium sitting so the blue here this much smaller is blue and this is this is a green sorry blue hair is basically titanium green is basically for sulphur so can you let on microscope shows a large area of sulphur or give a microscope so there is a thin region of sulphur between silicon and the titanium that is the difference actually one can clearly see when you use scanning or your microscope which is much more sensitive than the EDS analysis electron you know energy dispersepective scanalysis in the scanning electron microscope well last thing which I am going to discuss is the OGS setup or how the OGM electron OGR electron spectroscopy is done yes so as you see here the schematic diagram here which is quite complex this is basically four grid LED optics setup which is used to detect data this is a sample and this is the electron gun so electron comes from the gun and follow sample and then you have basically secondary electrons are not a OGR electrons are not it so one needs to detect them and that is why four grid LED optics is used this signal this one is fed to a pre-amplifier then there is a phase shifter then there is a lock amplifier and then it goes through different kinds of things finally you just detect the signal in a computer these are basically electronics used to modify not to modify to actually improve the signal to noise ratio and this is a geometry that means basically is a kind of a hemispherical geometry is used to detect all the OGR electrons patient remember we cannot actually throughout fully the secondary electrons and that remains in the OGS spectroscopy always so this is a cylindrical mineral analyzer is basically use the same thing this electron gun so it falls on a sample the sample actually electron for samples and there is a you apply pass energy and then you can actually remove the secondary electrons to that so energy solution scale up to EP and then you have you have a coaxial design coaxial means like this you can actually limit siding effect you can have better transmission relative sort of distance normally lock in interplus get different cell distribution very deeply that is the DNA by D that is what I plot DNA by D versus E is plotted in OGR so this is why we need to use lock in amplifiers you can always use hemispherical analysis what I have discussed the beginning this is the inner his particular energy and is the aperture the sample electronic falls and then it falls to the goes to the hemispherical detector and detector well I think that is all there are so things cannot this will be if I get time we will discuss otherwise next lecture I am going to start the secondary iron mass spectroscopy which is the last surface spectroscopic advanced surface spectroscopy technique in this course and then I am going to compare the these three techniques and wind up this particular portion of the syllabus.