 So today we are going to first talk about in situ experiments in TM then I will move on to the scanning electron microscopy experiments like in situ scanning electron microscopy and the electron backscatter diffraction that is called EBST those kind of advanced characterization tools used in the ACM. So let us first discuss about the in situ TM we know that in situ experiments are very popular even from the very beginning of the Tasmish electron microscopy when first time the high voltage electron microscope came up in 1960s people started looking at the motions of dislocations inside the material impact people started looking at the experiments on different kinds of solid state phase transformations in the materials while looking at in a high voltage microscope. But things have changed over the time scale nowadays we can even do in situ experiments inside a normal TM we do not need a high voltage electron microscope the reason the high voltage electron microscopes are used in those days is because of the use of the thicker samples because we know that the behavior of a material in a electron transparent thin sample will be completely different than a thick sample which we normally do experiments in the lab so that is why to simulate the exact conditions people used to use thick thin foils or thicker foils actually not thin foils thicker foils inside the TM columns and then study different kinds of dynamic behavior of the material by in response to heat or strain or deformation or even cooling so the because of that different kinds of TM sample holders were prepared sample shoulder which can do experiments during heating is basically consisting of a heater or consisting of furnace inside the holder and then we can load the sample inside this holder and heat it up to see the what is happening in the sample and record it in a video device similarly sample can be cooled down using a cooling stage holder within the tasmish electron microscopic column and this cooling can be done using liquid nitrogen so therefore depending on the type of stimuli you want to use inside the holder you can have different kind of holders that is at some the cost of the microscopy because you need different kind of holders one can actually use the strain or the deformation also as on the stimuli so that you can indent a particular percent of sample you can strain even by applying a load tensile kind of loading but most popular one for the in situ behavior of material during application of the load or stimuli like strain is the nano indentation inside TM column so we are going to discuss some of these experiments today so dynamic behavior of material during a particular stimuli has become a very important because of advent of the nano crystalline material this is one kind of experience to the experiment people do in the literature other kinds of experience which people do is the in situ growth that is suppose you want to growth indium phosphide nano crystal or you want to growth some semiconductor crystals inside a microscope column so there are groups working in this world where microscope can be modified in such a way then one can deposits these crystals are the seeds of the crystal and in the presence of the different kinds of vapor of the elements how this crystal grow at the resolution of the electron microscope can be studied very easily in the using in situ microscopic techniques and this has become very popular in different groups around the world where one can actually look at different in situ experiments different growth behavior of the materials at the resolution of these at relation of the electron microscope and then infer information regarding the growth behavior of this material and correlate with the existing theories so I cannot talk about all these things in this lecture because of the time constraint but what I am going to do is I would be some going to show you some examples of those kind of experiments which can be done inside test TM column and obtain information during the experiments now it is with the advent of very good imaging devices like CCD cameras in the electron microscope one can actually take video of the whole dynamic experiments in terms of digital imaging and then analyze the video later on to arrive at different kinds of conclusions from the experiment so compared to previous days where the videos were very what is called low resolutions now even images can be obtained the same resolution as the microscope provides us and then analyze them to the best possible way. So first of all let me just tell you in a heating experiment normally heating experiment is done you see heating holder first thing you understand from this experiment is that TM remains same all the thing we are changing is the holder so if you have different sets of holder one can run the same experiments different kind of experiments actually inside a any TM available in this world you do not need to have a special setup for this TM so most importantly the highly suitable microscope by the pole piece gap is very small they are normally people do not allow the this kind of holders to be inserted in because the holders are normally thicker so if the gap pole piece gap is small then this holders may not be inserted properly and can create damage to the pole piece or any other detectors they are present during heating of cooling or straining. So therefore normally the microscope conventional TEMs can be used except the highly used in configured microscope impact there are reports that Titan can also be used to doing high-situ experiments. So here I am showing a such a holder which is which is basically provided by the company called Gatton incorporation this is this slide is basically because of the courtesy to Gatton incorporations and you can see that is holder has basically a for simple specimen loading setup here which can be seen in zoomed up viewer where there is a furnace around the specimen holding positions and then this sample is basically inserted inside it screwed down and obviously one is to use different kinds of spacer. So that sample during heating will not get welded and with the holder and this holder can be cooled down using water inside this furnace channeling the water to this furnace and it can be tilted the single tilt or double tilt mode both are both kinds of situations available and depending the type of furnace is used you can go up to maximum temperature up to some cases 1500 D Celsius. So it allows us to heat a sample to different temperatures depending on our need. So that as I said different kinds of holder available in this world then Gatton there are many other manufacturers which are preparing these holders so these are very generic so I am not going to go in detail of this holder style but I will show you some experiments this experiment this particular one is taken from my own PD thesis. So I worked on iron germanium thin plumes and as you can see at if I deposit a thin plumes using a physical vapor deposition like laser ablation here the structure is basically amorphous what can be obtained from this diffraction pattern is a very broad amorphous ring and this corresponds to that this thin plumes are amorphous in nature so basically one would like to know what will happen to the amorphous thin flame when it is heated or rather one would like to know the stability of the thin plumes this can be done is easily in a heating holder the one I have shown you we just insert the sample inside heating holder and the heated up as a heated up from room temperature to about 473 K that means 200 is Celsius as you see there is a distinct change in the bright field microgap correspondingly electron microscope the diffraction pattern gets little bit modified but not clearly seen but there are black regions increasing in this microgap as compared to the room temperature one as you keep on heating from 470 to 573 K there are visible changes happening but most visible change takes place at 673 K where you started seeing this black crystals where they are quite big as you have to remember this is 100 nanometer bar this crystals will be approximately about 20 to 30 nanometers and similarly the diffraction pattern got changing you started seeing the spotty rings here there so you started seeing the crystals coming into picture and as you heat alone at a temperature 773 K that is approximately 500 is Celsius temperature so you see this whole thin plume has been crystallized and the ring diffraction pattern shows the real nature. So therefore if you want to do such a kind of experiments in the inside a TM column you need to have to take the diffraction patterns and then along with the bright field of dark field images so once this thin plume is fully crystallized 773 K it can be cooled down by switching of the furnace and then can be looked into the microscope again and as you look into the microscope again for the individual crystals which is formed like this one such a bigger one we can actually obtain very nicely the micro diffraction patterns from these crystals and so they are indeed DO3 order in this case DO3 is a particular nomenclature used to depict kind of ordering presence and in fact one can actually show that there are anti-page domains in send the particles by doing these experiments. So what you understand from this experiment is that just by simply heating a thin flume inside a microscope column with a heating holder can provide us so much of information. Similarly one can actually do routinely this is again taken from routinely the heating and cooling experiments for the melting solidification study of the biphagic two-phase nanoparticles which you routinely do during as a part of our own research activities whereas this is one I have shown you in the very first lecture of this course what you see here is basically this two-phase nanoparticle present in the hard if you may this is basically a hard if image high angle and dark field image and in the in the bad field image you can see that this is basically laid and this is a tin crystals in a one single particle and obviously as a material scientist one would like to know how stable are these particles whether there any interaction between the latent in parts during heating or even during cooling also from the high temperature to low temperature and as you know latent melts about 183 degrees Celsius temperature so therefore therefore heating in need not to be done at a very high temperatures so this can be done very easily in any heating holder provided that heating holder can precisely determine the temperature. So this is this snapshot of pictures what happens is again taken from my own our own work from our research group if we align the micro the particle in such way the lead gets basically illuminated during dark field and tin is basically not oriented properly so that the dark field can be obtained as we heat from room temperature to 90, 140, 157 to even 182 degrees Celsius temperature as we see there is a proof change in the in the particle during heating so from room temperature to 157 D Celsius temperature there is not much change except the volume fraction of the lead and tin is getting changed but as you heated to 171 D Celsius temperature whole particle become fully laid solutions and then at 178 D Celsius temperature starts melts down and finally at 182 degrees Celsius temperature is getting molten fully therefore this kind of particles which are embedded inside a matrix can be easily you know studied by in situ heating microscopy and lot of experimental information results can be obtained from there we can get information regarding stability of the particles and behavior of the particles at the heating at even microscopic resolution level this provides of the information regarding the the alloying at the nanoscale so this is one such experiments which people do routinely nowadays inside a microscopic column another kind of stage another kind of what other holder used in the real microscope experiment is called staining stage this one is taken from high Ctron thanks to them so there is a holder where actually one can actually do nano-unitism test inside the transmission electron column what you see is in basically the sample mounting stage and this is the in enter at this position so once you mount the sample inside this on this on this rod and then this has to be electron transparent obviously and then apply a load to this in enter in enter will go and hit the sample and then we can actually get information regarding the formation behavior of the sample to show you one such again from our one work if we take a silver nanoparticle and bring the in enter at the close to the particle what are the changes happens as you see in enter is basically looking not like a shot in enter at the microscopy level this is remember this is 10 nanometer bar so the the my at this resolution level this is looks like a flat or round rather and that is come close to the particles particle gets squeezed as you see there particle gets squeezed and once in enter is taken out since leaves behind so permanent deformation in the silver part nanoparticles this is again can be done on anything you can do on any kind of material just putting inside the microscope column and then just deform it using the standing stage. So in short I just wanted to show you in that in the last 10 minutes a show that what kinds of different experiments can be done using this what is called it in situ studies well obviously there are problems while doing the in situ experiments in a transmit electron microscope column we cannot neglect the effect of electron during hitting out of the sample or during in fact phase transformation of the different phases during the experiments that cannot be neglected. So therefore there is always an effect of this electron beam highly electron beam affecting the behavior of the material during these in situ experiments then there are problems of the what is called the resolution problems of viewing them view the material during the experiments many cases some cases what happens while you are viewing this sample during the hitting day or cooling stage experiments sample gets contaminated so much because of the material present around in the sample we do not get any information at all. So these are the caveats you must remember once you are doing experiments and once you are analyzing the experimental results from the in situ experiments the next thing which you are going to discuss are basically we are going to switch over from now on was from TM to the SCM characterization techniques as I told you in the last class. So the scanning electron microscope which is a routinely used by all kinds of users because of the easiness to use for characterizing the microstructure of the different kinds of samples can be used for advanced characterization also nowadays can electron microscopes are available at a very high resolutions and also with a very high beam current also because of that lot of experimental studies can be done which can provide us information regarding the sample behavior in the microscope in the real processing conditions. So EBSD is one such but before I discuss EBSD I would like to give you some idea of the scanning electron microscope because you might have forgotten from your basic characterization course. So to just next five minutes or so to just give you some basic idea about the electron microscope scanning electron microscope then I move on to the EBSD. So scanning electron microscope is basically very simple as complete as basic electron microscope it is a very simple microscope the sensor number of lenses are small and the accelerating voltage is pretty low compared 200 or 300 kilo volts we are going to use probably 20 to 40 kilo volts and not only that the imaging basically imaging is totally different as compared to this kind of electron microscope here. So what you see here basically is electron gun source which can be either a tungsten or lab 6 or Feg the field emission gun which is normally used nowadays and then this is basically a line of focus that are using a lens assembly this is a condenser lenses and then there is objective lens which actually focuses the lens the electron beam or the sample and then you can have a scanning coil here sitting which will allow you to raster the beam on the sample surface and then obtain the images at the same scan rate as the raster speed and obviously this is a sample chamber in a electron microscope scanning electron microscope and there you can fit a lot of things as I discussed with you that when the electron may falls on sample it interacts with sample and generates all kinds of information from the sample starting from the second electron beam to basket electron beam to the exit x-rays or maybe you know other information like odd year electrons everything is possible to obtain depending on the type of detector used in scanning electron microscope you can actually use these signals to obtain images and this images can be further studied. So normally in a scanning electron microscopes what you basically is nothing but a TV as you will look at it that is what I can say you. So there is a filament which gives electrons and there is a sample policies false electron falls interacts with sample and obviously electron beam can be focused by using electromagnets which is like nothing but a objective lens and then after this interaction of the electrons with sample the generate signal the signals can be in process using different kind of detectors normally one can use second electron detectors or basket electron detectors for the normal imaging processes which are mounted here very near to the sample or one can actually use x-rays to detect the different kind of elements present and quantify them this is as very simple one as compared to the TM as I showed you this slide I have showed you in the beginning of this of the discussion of the microscopic techniques as the electron falls on the sample it generates all kind of signals you can have a secondary electrons or you can have a basket of electrons which is very standard you can have a x-rays or you can have all your electrons or you can have a cathodoluminescence on the coming from the top surface of sample only the electron is falling on the other hand if the electron passes through it generates other kinds of signals which are not used for the SCM normally which are this kind of signals are used in TM which you have discussed you can have elastic scatter electrons elastic scatter electron or unscatter electrons or many other things possible which we have discussed in the time is electron microscopy. So obviously as you see there there are electron signal and photon signals coming from the samples and in a scanning electron microscope electron signal I select a secondary electron and backscatter electron beams or object electron beams sorry both this secondary and the scattered backscatter electron beams they are used to image for the x-rays which are basically photons they can be used for determining the element and elemental compositions also okay see once therefore basically is using the signal and plotting this signal on a TV screen just that is the SCM scanning electron microscope this is the conventional wisdom of any material scientist whoever use scanning electron microscopes or they have seen a scanning electron microscope but very rarely you will find people or very rarely you will find the idea that scanning electron microscope can also be used to obtain crystallographic information normally our basic understanding is that we can obtain all kind of crystallographic information or diffraction contrast in a time is electron microscope but in a scanning electron microscope also we can get lots of this information provided we know that the how to obtain this information and how to use that that is what is related to the discovery of electron backscatter diffraction if you look back in the history electron backscatter diffraction has come from channeling patterns or channeling patterns which normally people have seen even long back but only in 1990s with the advent of computers and advent of the processing of this electron backscatter diffraction signals we could see a rapid change in a study of the material using this technique. So many of these microscopes which you see nowadays fitted with the VSE detectors are actually come up in 1990s a letter previously people used to do all kinds of some kinds of diffraction study in scanning electron microscope but they are very limited. So therefore this is again I have shown it here therefore in how the basket electron comes in the picture because basket electron is very important for the VHG study. So as the electron falls it just goes in the sample and generates secondary electrons but it can actually get scattered and come out many times basically people says back scatter electron is same as which has been fallen off fallen on the sample and getting scattered back that is why it is called backscatter electron in the scanning electron microscope and this basket electron actually having very high energy more than actually 50 to even higher electron volts. So this backscatter electron can be then obtained and as they say they carry the channel the crystallography information which you will see right now. So first let me just go to the board and tell you what actually happens or what is unique unique to the backscatter image is the information led to the crystallographic nature of a sample. So origin of this contrast can be easily obtained from these two pictures let us suppose these dots white dots actually atoms in a crystal and then electron beams are falling on the sample in the first to the left hand side of this picture is to see which I am just putting my finger my hands on why the electron is falling randomly if the electron may falls on the randomly and then gets scattered by the atom or nucleus and then they can produce backscatter electrons. So if that is the case then backscatter yield will be very high because we are generating large number of backscatter electrons by this way on the other hand if suppose you have these sample or the crystal is oriented very nicely and electron beam is falling at an along the symmetry any of the symmetry direction of a crystal then what will happen in that case is that electron incident electron is tend to channel between the lattice plane that is what I have shown you can see that between the lattice planes electron beams are channeling through this lattice planes and this because of this the backscatter yield electron yield will be very low because all the electron beams are channel through very very less number of electron beams will be scattered and produce backscatter electrons. So therefore although this is the physically white people think the reason the origin of the channel channeling in a basically crystal now so that there is no way of conforming it or doing an experiment and see that this is what the normal concept or idea we have now suppose if the angle of incident actually of the electrons beam and the crystal can be varied at a you know from the random incidents to the along a particular direction of the crystal it can be varied then what will happen is that we can modulate the backscatter electron yield at different angles corresponding to the symmetry axis of the crystals. And if we do that once you if we do that actually if we just vary this electron incident angle from these random to the this relative symmetry directions then we can actually modulate the electron intensity the intensity of the backscatter electrons or actually yield the backscatter electrons and get what is known as channeling patterns. And this is what I have shown you here let me show you one such pattern you can clearly see that the channeling pattern looks like bands okay they are actually bands like this and then this bands actually meeting at certain points this one is taken from pure iron crystals which is taken from again for our own work and this bands actually some cases meets like this those of you who have done commission transmission electron microscopy they are actually similar to the Kikuchi bands in the in the in the electron microscope in fact origin of these bands can be traced back to the Kikuchi nature that is because of the English scattering of the electron beams. Now obviously then if that is the case then this can be related with lattice spacing or basically they can be we can get information regarding the crystal the atomic spacing a lattice spacing. So angular width of this band is basically this one is the approximately twice the appropriate bi-angle for the given lattice spacing and the electron wavelength so that accelerating voltage is perceiving can be reduced from the measure width after angular scale or the pattern is obtained most importantly what you understand from the basic thing which I am showing you I am going to discuss in detail about how this patterns are obtained and how this analysis done. So from this is that this contain both the spatial and the angular information spatial information is basically nothing but the position of the crystal from where we are getting or the microstructure from where we are getting this patterns and angular information means from the crystal itself this how this bands are related to the orientation of the crystal both this information are in build within this patterns. So what I am going to do it in next 5-10 minutes time is that to show you how these are actually obtained and then I will go back to the microscope I will actually take you to the real microscope which you will have in our IIT Kanpur campus and I will show you how these are obtained while doing an experiments and then I will show you how this can be processed also. So first let me just show you some final models in inside the scanning electron microscope. So what is done in a normal scanning electron microscope is that the sample is basically tilted the reason it is tilted to very high angle like 60-70 degrees is because the basket electron yield can be increased the detector basket it can be made to close very close and electrons which are generated coming out from a sample surface will be allowed or will be we will be going to the detector of a much larger fraction. So basket electron can be increased normally the we use fake are the columns like the fake guns like free emission guns in the electron microscope so that beam intensity is quite high and the detector here is basically obviously phosphor skin or we can use phosphor skin plus CCD camera and this patterns which are called electron basket or diffraction patterns or electron basket or patterns either EBSD patterns or EBSB patterns. So they actually contains Kikuchi bands as I told just now or obviously they will be aligned in a certain zone axis pattern which I have shown you here and they contain information regarding the orientation of the crystals with the angle resolution of 0.5 degrees and obviously there will be other effects like sampling can be cannot be done if the crystal size is less than about 50 nanometers because then there will be overlapping of the of the informations and there is obviously surface information surface sample position is very important because if there is a there is a oxide layer the surface we really do not get any informations from the actual crystals because beam will fall on this oxide layer and produce amorphous like that is nothing but nothing but use we use less thing in a EBSD. So this is what is shown you have a pole piece here this is nothing but a pole piece of the objective lens the sample which is tilted very high angle approximately 70 degrees or more in this case and then there is a camera with a CCD and phosphor skin sitting here phosphor skin and the back square electrons comes and fall on this and it produce a sterling pattern like the one which is shown here. So that is how we get information now we have a if you have very large number of crystal sample one can actually obtain this information from each point of the crystal and then process it this is how actually experiments are done but remember that the sample needs to be very clean it is to be electro power is many cases to obtain oxide free surface layer so that very good quality deflection pattern can be obtained okay how actually it works is very again not very complex like many of the terms electron techniques so you have a crystal oriented like this what I am showing you silicon crystal here okay diamond cubic structure and then if the electron beams falls like on the crystals it falls on a particular plane or a set of planes rather and scattering of the electron beam happens from this from the like this and the scattering of electron travels in all direction in a small volume and electron that travel in directions that satisfies the Bragg's law that is n lambda equal to 2 d sin theta for a particular plane are channeled and these actually leads to the permission of Kikuchi bands electrons hit the imaging for phosphor skin and produce a light as you know in a time electron microscope also uses with the phosphor skin on which electron falls and creates the light so light can be detected by a CCD camera and then CCD camera can be used to convert this to image and these patterns which are obtained routinely can then be indexed by knowing the crystal structure of the material and then by knowing that we can obtain how each crystal is oriented in the sample the real advantage of this kind of technique is compared to the TM is that here actually we can get information from very large crystals or large number of crystals in the microstructure because ACM can allow us to see large number of crystals this is just one such picture what I am showing you this is as we see the different grains are mapped to different colors okay this is how the data is visualized this is taken from one of the HK Libis G software manufacturing company in UK the Oxford instruments we have the facility installed in our microscopy is again Oxford instruments this is just for the routine data so what you see is that the grains are different color depending on the orientations so if the once you obtain the orientation of the grains and depending on the orientations of the grains we can actually create a color map or game orientation map which is routinely done and this gives provides us lots of information regarding the orientation of the grain boundary type of defects presence and many other things which we will discuss after we see the actually BSD in the microscope next in the subsequent lectures.