 So, welcome to this course again. So, we are going to start a new topics today, actually on surface characterization techniques. As you know there are many surface characterization techniques and in this course, we are going to talk about some of the advanced surface characterization techniques. Simple surface characterization techniques involves measurement of composition of the surface of any material or even measurement of the oxidation, oxygen concentration or nitrogen concentration which are present on any surface of the material. In case of material science, they are very important because we know most of the things starts start happening at the surface. So, therefore, surface needs to be fully characterized not even that the best example of surface effect on the material behavior is in catalysis. As we know the catalytic reactions take place at the surface. So, therefore, surface structure, this composition invent the atomic electronic state of the atoms at the surface do play a tremendous role in catalysis. So, therefore, surface is studies extensively and because of advent of new techniques, surface characterization has become very important. In this about 9 lectures which I am going to take. Obviously, we cannot discuss everything of surface characterization, we have to limit ourselves because with time constraint. I am going to discuss several important aspects, but before that let me just give you the reference books. The first reference books is very important, it is called ESCA, Modern ESCA Principles and Practice of ESCA Photonics and Spectroscopy. This is by Tony Teribir, published by CSC Space and this one the next one is Encyclopedia of Material Capturation Editing by Editors by the Bundle and Evans, they are Wilson published by Butterworth, Henman, Boston. It is also very important book where you can get all the information. There are many other books available in the literature which you can refer or even there is a lot of information available on internet. So, you can also look at it. So, the way outline of this particular chapter or particular portion of the course is made is like this, first I am going to talk that is a today I am going to talk about importance of the surface characterization techniques. Why do you need surface characterization techniques? This is what we are going to talk today. And then I will talk about other techniques which are involved, first one is the XA photoelectron spectroscopy, second one is the Auger Electron spectroscopy and the last one is called secondary ion mass spectroscopy. So, XPS is what is called XA photoelectron spectroscopy, AES what is called Auger Electron spectroscopy and SIMS what is called secondary ion mass spectroscopy. These three techniques will be detailed in this course. Finally I am going to compare this surface analysis technique so that you can get an idea which technique has advantage in certain aspects over the others. Well before I go into the detail of this techniques obviously it is very important to know why do you need to use surface characterization techniques that to advanced. You know when in our labs technique facilities available we start using it extensively, but that is not the way to do. We need to understand that we need to have information regarding the scientific investigation of any kind of activity or material science. That means whether a technique can be used to divulge scientific information to understand certain phenomena. That is why actually the importance and applicability of particular scientific experiment technique comes into picture. And one need to really understand it as the course goes on probably you are getting and feeling that there are lot of techniques we are talking about it what which technique we need to use for what kind of applications is not dealt with. Well that is what actually I am going to plan to do it at the end of the course I will go to give you some examples where a set of techniques are used and a scientific understanding of the phenomena going on in a doing a materials processing and application will be talked about it. This one I am going to talk about for copper lead alloys most importantly the copper lead powder metallurgy alloys which actually I have talked about this in the first lecture of this course you know that this alloys are used for bearing applications. So therefore there are certain aspects of microstructure which we need to have in the applications. So most importantly we need to have a duplex microstructure with a homogeneous distribution of softer phase in a hard phase or hard matrix and therefore hard matrix will resist the wire and softer matrix will act as a lubricant and that is what actually used in the bearing applications and most common technique which is used to produce copper lead alloys is by casting route but as you know lead is heavier than copper much heavier than copper. So if you want to do casting lead will segregate and create a homogeneous distribution of lead in a microstructure and obviously course distribution will happen because of the microsegregation and this is bad so therefore casting techniques cannot be used for preparation of this bearing alloys we need to use some other technique. So then people tried with powder metallurgy route where you mix copper and lead very nicely and then make a in pallet sinter it but if you do sinter normal atmosphere a problem is oxidation first of all because in pestle sintering those of you know our pestle sintering you just put in the furnace for long time at high temperatures about 600-700 degree Celsius temperature to sinter it to the optimum density about 90-95% of theoretical density you start increasing the copper grain size and also start creating the problem of oxidation. So commissar sintering has this problem of extensive gain growth and oxidation and this leads to inferior properties. So what is the solution not only that nowadays people talk about lot of things about nano crystalline alloys they have excellent properties if a copper is one such material while nano crystalline grains of copper can give very high hardness very high strength at the same time it can also you know impart lot of other advantages in bearing alloys. So that is why actually we started looking at nano crystalline copper alloys in fact it is a part of our own research activities one of my own students have done this work and we have used a phasal sintering technique called splasploma sintering to produce this kind of microstructures as you see here this is a copper 10% 10% late copper 12% late and copper 15% late one can go on increase but then what will happen is after certain time the lead will be agglomerated and distribution not be proper what you see here is that lead is uniform distributed in the microstructure there are few pros present obviously that is a problem of any powder metallurgy prop product but to understand whether we are able to produce nano crystalline grains or not retain this is what the TM picture you can see here this grains actually copper and they are of the order of 80 to 100 nanometers or maybe little bit higher than 100 nanometers a diffraction pattern is taken from one such copper grain this is a micro diffraction pattern taken from one such copper grain showing it's a copper not oxide and you have laid sitting like this like this and one as a lenticular lead between the two grains or at the grain junction points these are what the late seats so therefore it is possible to get retain the nano crystalline copper grains at the same time distribute the lead in a very nice manner and this kind of microstructures which is shown here it's a good candidate for study where so we need to do that and that's what is done because bearing application means where and here so why needs to be studied so once we do this where for different late concentration 12.5 15 this is also 12.5 as you see no the idea this is 10 sorry this is 10 12.5 and 15 so this is 10% late this is 15% late this is 12.5% late so if you look at the coefficient of friction values this is done in fitting where because fitting is more severe than sliding where and most of bearing actually undergo kind of fitting where so that is why you want to do it in a normal atmosphere because that is what actually they are applied and fit this you could see the coefficient of friction for fitting cycles up to 100,000 it remains constant for most of the cases close to 0.4 this is again steel ball that this wire test has been done so the fretting ball is steel as we know the coefficient of friction between copper and steel is actually against steel is actually 0.7 8.8 almost close to so therefore we are able to reduce the coefficient of friction extensively that is the biggest advantage of applying lead lead acts as a lubricant and reduces this so but what does actually happen in the oxidation in the wire phenomena is not clear now we only see the friction of coefficient now if you look at the wire surface then terms of picture become things become clear and here I am showing you the uses of scanning electron microscope as you see here this is the own area you can see lot of cracks fissures and you can even see delamination formation of tribal air and if I take the wire debris you could see the oxygen present layer is present there you can see white color and copper is present in it delaminated form so that is what I have seen this is when the seat is entered 350 and load was 55 new to 1 now it does not even tell you what is happening the wire process if you do a Raman spectroscopy that is what actually spectroscopic techniques comes into picture I have shown you Raman's discuss with Raman spectroscopy if you use Raman spectroscopy start is saying lot of oxides presence and this tells us actually the what is called state of electrons atoms you have seen iron oxide copper oxide iron is coming from steel ball lead oxides now later has different kind of oxides PBO Pb3O4 well although it gives you very nice signals very broad signals Raman spectroscopy of the oxides but that may not be sufficient enough to really pinpoint what kind of late oxides present that is what is this electronic state of the lead and oxygen is not clear that can only be done if you use XPS the X-ray photoelectron spectroscopy and that is done here as you can see here very clearly this is the state of the lead of the of the one such particles on the own surface and this is the energy level binding energy is basically explicit plot of between intensity and binding energy this can be easily fitted with lead 4F state and in fact I am not going to talk about it can be even done better so which I will discuss you detail when I do XPS analysis XPS discussion and oxygen is one state so therefore it is PBO not PbO 3O4 that can be confirmed so one can actually keep on understand I know what can use actually this techniques to make the understanding of the whole process very clear that is what has been done to understand the where mechanism of this nano crystalline copper lead allies we need to use this spectroscopic techniques both surface characterization surface advanced characters and techniques and also bulk to know what is happening there so it is an oxidative wire which do takes place in the copper lead allies when you use in normal atmospheric pressure now detail of this works are published now one can look at literature from our group but obviously oxidation means a host of oxides lead oxide iron oxide copper oxides they are very hard so what is the actual you know effect of that of this oxidized oxides on the wear behavior is very interesting thing so you understand that if I use this coxides and on a on a in case of oxygen bearing alloy they are loose but they were hard so they will basically abrade the counter interface more easily that is one example second example is again from my our own work one of my speed students work is half titanium composites which are used for biological bio medical applications basically for orthopedic applications half is hydroxyapatite for your informations hydroxyapatite is the bone you know it is a constant of the bone the inorganic constants of the bones are therefore most of the biomedical applications requires development of new materials one such a material which is important for both dental and the bone application is hydroxyapatite based and hydroxyapatite is a noble material the sense that it allows is basically biocompatible and bioactive that means once it goes in the body it allows the cells to grow on this on it and helps the resale preservation process and many other things so but there is a problem hydroxyapatite is very little this fracture terminus is point K1C is basically 0.5 MPa root meter is very low normal bone as a fracture terminus between 2 to 12 cortical bones actually MPa root meter so it is very you know much much lower than what is to be expected so there is always research activity to improve this fracture terminus or mechanical behave properties so that it can be used for load bearing application like bones or even teeth because in your teeth you are applying lot of forces to chew your food so what to do you add a metal and you can add all metals so people add titanium titanium is a biocompatible but by not and it is having high corrosion resistance as you know super titanium titanium gets distributed like this here shown these are the titanium and hydroxyapatite grains so once you put this hydroxyapatite titanium composites inside your body it comes in contact the body fluid and as you go on doing our a daily and have daily activities it undergoes volunteer so one is to understand what happens is what happens to the wire behavior under such conditions so what people do normally is to study the where we are in simulated body fluids simulated body fluids have almost similar composition that of the body fluid and then we do this fitting where they are as you can see here that under different conditions wet and dry pure hydroxyapatite and hydroxyapatite 10 ti the coefficient friction behaviors are given this is again published literature it is under publication so there is no problem so as you can see here if you use wet conditions you have lower value of coefficient frictions basically we add certain proteins also here albumin to you know create more likely situation when in first physiological situations and coefficient friction values varies from 0.3 to 0.6 depending on the material depending on the kind of you know weight or dye conditions and if you look at the wear rate it is also pretty low you can see here the wear rate under dry kind of wet condition is reduced substantially so that means this materials will be able to do better job inside the body but what actually what is the mechanism where that is what one is to understand so if you look at this again the morphology bone surfaces for pure ha dry and pure ha wet I am showing you can see the laminated layers and breakage of that not only that if you if you look at morphology more closely you can see this so that is as you can see the appetite crystal forming on the surface and they help in reducing the wear if you look at 10 ti you can see even the laminated layers but you also see the small particles presence other than titanium is a titanium big ones small particles presence they are here okay they are actually appetite crystals which forms when this materials comes in contact with the simulated body fully splits and they are good because they are appetite they are good for the body they are good for many things so they actually start interacting with it with the with the wounds and the counter body and that's all actually where behavior changes to understand it more we have done actually the this morphology of wire this is actually edax mapping I have already showed you the in as we discussed spectroscopy mapping is possible if you map it these are the titanium's and that these are the actually hidex appetite but you start is seeing this kind of crystals inside this kind of crystals which are basically you know appetite crystals which form because of the interaction with the simulated body fluids so we can see the formation of you know appetite crystals also in our land cracking now once you take this kind of material and do what do I say the XPS after where some own surface you start is seeing this calcium two states which are a signature of two different compounds so one is had it separated other one is the appetite which is present you also see the carbon peaks obviously the carbon will present because you have added a lot of solutions then phosphorus 2s and purpose 2p peaks oxygen is abundantly presents okay you actually see a titanium peak but not very clear so therefore the presence of appetite crystals are very clear by doing this as I have been telling you this crystal actually form during this process of where changes the wire mechanism much because it's forming a layer on the surface of the of the of the material and then it the contact between the counter body and the surface is no longer there new contact develops and that's the way we with changes so using these kind of techniques one can really understand the actual inside actual scientific phenomena actually one can go into the details of a scientific phenomena which is there these are normally not done routinely but if you really want to do scientific understanding of any process that's why actually you need to understand this characters in techniques you need to use it many labs actually have impact IIT Kanpur is also going to get XPS very soon and it's available routinely so one can do that well the third example which I am going to give is from my own PhD work that is on iron germanium 25 percent germanium laser ableted thin films you know thin films are actually routinely used many applications we wanted to understand if I take iron 25 percent germanium alloy and from a thin film by laser ablation which is very well known technique what kind of structure develop as you see here these are all very high resolution pictures thermos electron pictures the reason actually I am bringing you all these things is that I have already taught you high resolution it is electron microscopy various spectroscopic techniques and I want to bring them together and make you that this you know why I we need to use surface characterization techniques to decipher the scientific insights of these processes of these structures as you can clearly see we see clusters you see this kind of clusters well order clusters inside these thin films when they are as deposits conditions well little conditions all will be available in the literature you can search but that is not the issue what you see here is this well order structure you can see this one also they are not atoms remember they are clusters of atoms that's what is very important to note and if you if you do the deflection analysis you see board rings signature of amorphous structure that's what happens if you take any kind of alloy started doing as other ablations most of the cases you started forming an amorphous thin films now this thin films which you deposit on the surface there needs to be trouble phenomena there and as a function of temperature also as a function of in the compositions then only they can be used for applications because real application temperature may increase so what do people need to study big and the actually the thermal response on these thin films and that is very important in the sense that you know this amorphous structures are normally considered to be not stable so they are actually prone to get transform into crystalline forms so to do that actually and this is in a better solution picture and in fact one can actually do it is using a modern microscope TEMs and you can see here some kind of this kind of clusters present there I don't know whether you can see you will be able to see them and this cluster sexually are you know you can take actually nano diffraction pattern that means we can take a nano beam and put it there and grab a diffraction pattern that is what is done here if you do that we started seeing diffraction spots here you can see and this defraction for D values are written if you look at that they are very close to Rn BCC Rn okay 1145 and nabstone is basically close to 2 0 0 plane spacing of BCC Rn and 2.003 is basically 1 on 0 so that means we can actually see this clusters actually pure Rn time they are not actually pure Rn for some kind of solution between BCC Rn with germanium germanium is there so things will be very clear once I started showing this pictures this is actually in situ heating microscopic this thin films if I put inside a heating holder in a touch miss electron microscope and then heat it inside the microscope and observe it during this heating that is what is actually done here so you take this 10 films and then heat it up once you heat it up inside the microscope insert seeing changes so that is what you see here you see this is getting changed to this this and finally from 300 to 770 to K you started forming crystalline things and you can see from the diffraction pattern itself actually started forming this thin crystal this black region the crystals signifying this ring weak ring in the in the diffraction pattern and it is fully getting transferred at 770 K if you do it careful diffraction analysis okay if you are a good electron microscope you can do that and you also have to have a good electron microscopes then you can see these grains which are there they are actually order there actually do the order structure does not get into that and they are bc B2 domains and also DO3 moments this is B2 this is DO3 domains presence so that means they have got order at solid state and therefore you can see this order domains now first of all that means we are starting forming when you heat treat it we crystallize this BCC iron BCC actually solution of germinium in iron and that gets ordered later on to form B2 and further order in this DO3 structure so the nucleating phase is basically BCC solution of power why does it happen does the thin film has this clusters presence which I have been indicating you well diffraction analysis do suggest this kind of clusters presence but no conclusive evidence this all you know kind of one spot coming and then we are saying that so what we can do we can actually do a mass spectroscopy of this you know clusters during the deposition of thin film that is called in flight mass spectroscopy and this in flight mass spectroscopy will tell us what kind of mass is present this is that thing but intensity versus mass in attaining mass unit okay you would see large error bus that is okay for FEDC integral the most intense peak is for 240 that corresponds to that FEDG you know clusters which are present there so this confirms actually our thought process our experimental you know thought whatever happening in experiments whatever they are thinking or whatever contemplating it proves and that self has been publishing this paper also so I am just saying you that by using this surface characterization techniques or the techniques which will allow us to study the surfaces is basically giving us scientific insight into the problems there are a host of example one can talk actually I can keep on talking about it that is not the way because there are time limitations of that also so I am just going to show you few examples and these are the things which you do in your research activities where you need to understand the scientific process happening so that you can actually bring about the you know process control later on and that is why these are used now let me just get into some of these things in the today's class you know this basically the most important technique surface characteristics is called XPS X-ray photo electron spectroscopy it comes from Einstein's discovery in 1921 he got an old price for that a photoelectric effect what is it well this is what is shown in this picture here if I may X-ray photons okay X-ray photon has energy h nu nu is the frequency edges these flag constant it falls allowed to fall on oxygen atom what is going to do it has a very high energy it is going to knock out an electron from the inner cell 1 a cell 1 a cell at 2 electrons it is going to knock out 1 electron and this electron comes out now this electron has a specific energy obviously it has been knocked out from this cell because the X-rays which has fallen on this has high energy higher than the binding energy electron otherwise it cannot knock out so it has been knocked out and also it has been given certain kinetic energy so h nu must be equal to the binding energy of the electron plus the kinetic energy right that is what is actually the energy balance so now if I know the kinetic energy obviously I know h nu because I know what is the wavelength of the X radiation so I can calculate the binding energy and as you know the binding energy of an electron in any atom is very fixed it will vary from one element to other element if I take nitrogen binding energy of 1 s electron will be different from the oxygen so by using the cat by measuring the binding energy I can exactly say what kind of element is present what is state electronic state of the electron whether this is kind of 1 s l 2 s l or 2 p s l I can tell that also not only that one can actually tell even the speed of the electrons is present that's why there is a 2 p 1 third 2 p 2 p 1 by 2 or 2 p 3 by 2 one can tell what kind of speed it has so this is what actually is a major discovery done by Kai seg 1 in 1981 he got noble price for this you must not forget so the concept of Einstein for photo electrons has been used by SIG 1 for a basic principle and which I will discuss in detail about that so XPS what is known as a sky is now the most widely used surface analysis technique because of its relief relative simplicity in use in a data interpretation I have already discussed what it there are various versions of SPS first one is XPS second one is a SCA electron spectroscopy for chemical analysis the principles are same third one is ultraviolet photo electron spectroscopy instead of x-ray you can use ultraviolet ray and last one is called PES photo emission spectroscopy you can use a light to emit electron that's what photo emission so never in light is nothing but laser beam in the helium neon laser can be used to or any other laser actually which wavelength comes in the light in a spec in a visible range can be used so there are host of techniques the most important ones are these two which are we are going to discuss in detail well again to tell you details of that okay because we are starting off as I have discussed this is what is going to have kinetic energy electron is going to be h2-Eb plus 5 5 is the work function well to modify it so therefore this is the suppose binding energy this is 1s 2s 2p 3s electrons and suppose a photon comes in terms of x-ray or in terms of ultraviolet or terms of photo photo you have my light photon and then it emits it ejects an electron from this 2p cell and this will become photo electron so it has to go above the fermi level and then if has more energy had energy then the work function it will go even above the vacuum so that's so actually is written ke kinetic energy of that electron is h new minus this you know the binding energy of the electron plus 5 so if you know this K we can calculate what is the binding energy x-ray spectrum actually basically nothing but intensity of photo electron versus eb or ke we can either plot eb or kb ke versus the sorry this should be wrong the this is eb or ke versus intensity this is what is plotted this is what I have shown you so it allows of the element interface identification chemical set by element relative composition of the constituents also balance band structure all these things are possible well I am not going to detail about that but you can see that this is what I have been shown this core level electron binding energy going to face Fermi level from family level if you apply more energy that is basically called you know the phi and then it goes to vacuum level and this is the theory or if it's same level spectrometer actually that's how the fixed meter works then electron comes it comes a family level they are to family level and spectrometer detectors so therefore binding energy is given by this second technique which you will discuss in detail is OGR OGR is little bit different which I will discuss now than the but OGR is electrons comes from much lower surface depth than the X this XPS photo electron spectroscopy based on a single photon any electron out process and from many viewpoint it is a very important in XPS that's what I have showed you okay you have core electrons emitted and comes in OGR actually in OGR actually what happens you emit you have a photo electrons emit so you have a photon coming emit and core electrons and the electrons actually heat and the electron in the in the outer cell and the electron from the outer cell get ejected so therefore the electron which is coming out because of this process has much lower kinetic energy and therefore it can only comes from the surface of the material it cannot come much lower larger depth so therefore exact surface probing is possible by using OGR okay and this is a no one can actually calculate the kinetic energy binding as of a electron and then use it for many purposes and that's what is done in OGR and in same secondary iron mass electron secondary iron mass spectroscopy is basically as it was in mass spectroscopy in seems actually what is used is basically a helium ion source and this helium ion source then eject some ions inside the sample and we detect the mass of those ions and that's why it's called secondary iron mass spectroscopy and then it is used to basically measure what kind of mass of this ions which are coming out and from that we can tell exactly the type of you know PCs present in the material and that's how it is used anyway so we are going to discuss in detail of these of this technique in the subsequent lectures