 So, with the last class, I have shown you the efficacies of transmission electron microscope, in which I discussed about the resolution and the depth of field. I have discussed how to use microscope to obtain different kind of images. Today, I am going to show you the real microscope. This microscope is in housed in the department of materials science engineering of IIT, Kanpur. We have been using this microscope for the last 5 years. So, I am going to show you first actual microscope, different parts of the microscope and then describe how we can use it. So, in a transmission electron microscope is basically and versatile in equipment, in the sense that we can use this machine for many such analysis of materials and get information from starting from the diffraction to composition or spectroscopic analysis to highlights and microscopy. So, obviously microscope will have a basic features and lot of attachments to get information on the spectroscopic related things and also the other aspects which I will discuss slowly. So, in a real microscope, we start from the top. Basically, in an electron microscope, the source is electron. So, electrons are to be generated by certain means. Electrons can be generated by many means. One way of generating electron is to use thermo ionic emission of tungsten filament or the lanthanum hexaprolet filaments. Otherwise, we can use field emission guns. So, all the modern day highly lucid electron microscope has field emission guns. In this microscope, the top part is basically the gun. You can see there is a power cable coming and sitting on the gun and that assembly actually contains a hair fin tungsten filament. This is nothing but in just like a tungsten filament in a incandescent bulb, we see in the real homes. So, tungsten in the form of wire less than about 0.1 millimeter is bent to create a hair fin like structure. Then, if you apply a voltage or if you heat up the tungsten filament, it emits electrons. Therefore, that is the main source of electron, but problem is in thermo ion incandescent is that because it is a tungsten filament. Therefore, the electrons which are coming on the surface may have different energies. So, that is why many times we use another kind of hair fin filament known as lanthanum hexaprolet. Lanthanum hexaprolet crystals are actually grown along 110 directions and these crystals then can be used to get emission from the by heating. So, they are much better than tungsten in the sense that the emission is much more stable. So, the emission is less and the brightness of the beam is higher and in modern day technologies we use the field emission guns or called FEG. So, field emission guns are again tungsten filament grown or single crystal tungsten grown along 1110 directions and then we have a very fine tip less than about 0.01 millimeter and if you apply a very high electrical field of the order of 10 to the power 6 volts per centimeter between this filament and another electrode. So, they are not then we can actually force electrons to tunnel through this electrode and come out as a electron. So, these are the sources which is normally used in this microscope we use tungsten filament or lab 6 depending on our uses. So, in FEG we need to have a very high vacuum system because FEG filaments needs to be very clean, contaminant and free. So, therefore, if you want to use FEG filament these top portion of the gun needs to be evacuated to a level of 10 to the power minus 10 torr. So, that is basically additional cost that is why many of the microscopes normal center microscope do not have FEG column otherwise one can actually heat up the tungsten filament in a FEG microscope. So, that any oxide which form the surface can be removed what are may be the way the cost is very high for tungsten filaments. Now, once the electrons are generated they need to be focused they are focused by set of condenser lenses which are situating here. So, normally a normal microscope there will be two condenser lenses and in a microscope square you need to have a convergent electron diffraction you can you need to have three lenses what is known as a extra lens is nothing but a condenser mini lens which can force the electrons to get converge into a small spot and that is required for scanning tungsten electron microscopic purposes. We have built in here and in a microscope normally the most important part followed by these the illumination section that is the condenser lenses source and the condenser lenses is the objective lens and you can see here this is a sample holder and this is the objective lens and the objective lens is basically just like a twin lens here it is a alter twin lens or in twin lens if sample is inside it between these two twin pole pieces and then the the beams which falls on a sample are passing to the sample they are actually focused by the objective lens to either generate an image or generate the diffraction pattern by a set of lenses which is sitting here they are called intermediate lenses and the projector lenses. Obviously, electrons cannot be seen in a microscopes so one needs to have a viewing skin and you if you look at any microscope this is the viewing skin with the binoculars and viewing skin is nothing but a frozen screen made of zinc sulphide on which if electron falls can create light and our eyes human eyes can only see light cannot see electrons if the electron falls in eyes if you in fact will be blinded. So, that is why this is fully protected there is there is a glass lead based glass which is not allow anything come out of the sample so remember this is very hyzerosic equipment unless and until it is protected so that is why all these things are actually nicely covered and you only you cannot temper about you only view the skin and do all kinds of analysis and in a normal modern day microscopes the panels are like this they are very small in which you can have very less number of buttons which can allow us to control the microscopes and it is attached to a computer computer controls all the mechanisms in the in the microscopes. In fact, microscope control like the valves vacuum systems and the height lens and everything is controlled by that. So, let me also tell you that as a electrons comes from the from the source they need to be accelerated for any electron microscope because that only energy of the electron can be increased this is done by a high tension tank. So, high tension tank actually steps up the voltage from normal supplied voltage 220 volts in a in in our country to about 200 kilovolts in the microscopes this microscope which can like actually use higher voltages like 300 400 or may be 1000 volt kilovolts. So, depending on the the kind of microscope which you have you need to have a very large tank in this microscope which is basically dedicated high resolution microscope you have a the object lens which is separately cooled. So, that temperature of the lens cannot be increased so much that focal length can be changed. Other than this lenses we have apertures apertures basically used to select a particular you know beam or basically to the the size of the beam. We have aperture here just in below the condenser lens first condenser lens which can actually make the sparse size very precisely. So, one can change aperture and set at different level depending on the intensity level of what you want then you have aperture in the objective lens column which can allows us to select the the basically the whether we can we want to image using transmissible transmitted beam of or we want to image using the diffracted beam or we want to do high resolution electron microscopy which I will show just within few minutes time. Then you also have a aperture in the SID or called selected a diffraction basically if you want to select a particular region of sample and do the diffraction analysis you need to use and this aperture there are actually three or four apertures depending on the kind of investigation you would like to do one can select this apertures and then get a diffraction information remember in electron microscope diffraction pattern forms of the back focal plane of the objective lens. So, depending on the your wish whether to use the diffraction pattern or the image you can actually adjust the intermediate lens more or less and to get either diffraction pattern on the skin or the image and that is normally routinely done by the microscope system we do not need to bother we just sit upon the microscope and do it other than that this microscope has basically you know to make the vacuum system clean we need to have a liquid nitrogen cooled setup where there is the liquid nitrogen chamber which can take care all the contamination on the sample because most of samples will have contamination not only when the electron falls on a sample it can generate contamination those contamination cannot be allowed to go to the vacuum system or it can actually create the system vacuum system there to be you know contaminated. So, to get it anti-contamination free we have anti-contamination device like a liquid nitrogen cooled trap which can take care all the all these contaminations. So, this liquid nitrogen tank needs to be refilled intermittently to get a very good vacuum inside the column of the microscope. Well, there are several attachment to this microscope the first one is this attachment which is known as an algebra disperses spectroscopy or EDACS which is again basically free the ultrathin window EDACS. So, we can use the as the electron falls and I have discussed in the last class it generate X-rays and this X-rays can be used to basically quadratively and quantitatively determine a particular electron an element also figure out amount of the material that particular element present in the sample. So, this is done by the EDACS which will be which have already been discussed in your material characterization course. So, I will also discuss after what is called sometime in the course also. Another important thing which you have is basically here is known as hard if or high angle annular detector which is sitting over there this detector is basically mean to get jet contrast images as I discussed in the class the electrons which as it falls on the sample very thin transparent sample it get diffracted and diffraction pair power of the you know material depends on kind of element present in the material. If the sample contains very heavy element they will diffract strongly on the other hand light elements like lithium, aluminium, silicon as compared to palladium, bismuth they will diffract very slowly. So, therefore we can actually get this different diffracting different we can actually get the diffraction beams which are kind of sample collected by this detector at an annular space or at an annular space from the transmitted beam and by using this detector one can actually see the actual you know jet contrast image on the sample this is just like in a scanning electron microscope as we use basket and imaging mode, but here we do not use the same technology or same concept like in scanning electron microscope whether we using a diffraction contrast imaging which is basically governed by the atomic number of the element. So, that is attached to this microscope other than that one can have other many other things which includes energy loss spectroscopies analysis which can be attached at the bottom of these microscopes or one can have different video ports to do in-situ microscope. Remember we do not have in-situ microscopic stage here, but one can attach this to this microscope in-situ microscopy means we can put the sample inside the microscope then we can heat or cool it down and observe the sample what are the kind of changes happening in the sample and this can be recorded in a video by attaching a video port or this can be recorded in normal mode also which I am going to discuss in a next time. So, therefore depending on our use we can attach different kinds of things in the microscopes one can actually even attach other things like people sometime use what is called the cold stage microscopy where the holder itself is a cold stage and this kind of stage is actually used for biological sample viewing. So, depending on the use or depending on the need a transmit electron microscope can be used for any purposes. Now as far as the recording is concerned because images needs to be recorded or the whatever you are viewing on the skin needs to be recorded earlier days people used to record using a photographic plates just like a normal photographic plates we do, but these plates are very big and long. So, they can be pushed at the placed at the just below this viewing screen and because transmit electron microscope has a very large depth of field. So, therefore whatever will be focused on the screen can be assumed to be focused on the photographic plate and on this photographic plates are exposed by the electron beam they can be just developed and images can be obtained. But those days are over now normally nowadays we use a digital camera which is there at the bottom of these things this is basically digital camera from Garten incorporation and this digital camera actually very sensitive to electron beam. So, depending on the imaging conditions we can actually collect this images directly on the digital camera and then view it on the screen. So, depending on that so, I cannot show you one such image which is we have collected in the microscope. So, you can see here there is an image which is collected by this from this microscope. So, there are many features. So, one can actually do this image collection directly from the camera and camera technology has improved extensively for the over the time scale as per the resolution of the camera sensitivity of the camera also the exposure to the camera all has been developed to the optimum level. Nowadays we can have a very high-resolution camera which can even grab the high-resolution images to the exact resolution what you see on the screen. So, but still many people use both the imaging systems and for day to day life. The another kind of imaging system which has been developed nowadays which are used is called photographic plates which are sensitive to light. So, those photographic plates can be used for recording and then image can be transferred on a computer from the photographic plate and then this images can be erased or the photographic plates the memory of the photographic plate can be erased and they can be reused. They are very sensitive to the lights, but they are not used for the normal microscopes only for very exceptional cases where you want to record diffraction patterns which are energy filtered that can be done well that is basically the basic future of electron microscope here, but normally in electron microscope there are many other instrument behind as you can you may not be able to see from the from the video, but there will be UPS the emulator power supply that is needed or there will be chillers because these lenses which are basically used to image the sample in the microscopes need to be water cooled because they are electromagnetic lenses and this water cooling is done by a chiller which are normally kept outside this microscope rooms and then you can also have sample cleaning system before you put the sample one can clean the sample using a plasma cleaner nowadays we have we also have a plasma cleaner which will show you just within after just a finish the discussion here. So, using the plasma cleaner one can clean the sample very nicely so that one can get a very nice region of sample and view it well the these are all background things what one is to have for a microscope. So, that is why other than that the microscope needs to be kept in a very neat environment free from any kind of vibration free from any kind of magnetic field also free from noise as probably we will see sometime down the line if I have the opportunity I will show a microscope which is the best with best possible resolution called Titan which will be installed in our in the IIT Kanpur in a normal Titan microscope even the person who is sitting in the front of microscope cannot speak a word or even cannot in the cannot even you know beyond by doing so you can actually create the problem in the image because the vibration which is generated by that can actually reduce the resolution of the microscope that is why those microscopes are remotely controlled you can insert the sample then go out a separate room and remotely controlled. So, but here that is not the case because the resolution of this microscope is not that so in those cases not only the microscopes are to be kept in a very clean and neat environment, but also the environment has to be free from all kinds of noises even the noise from the air conditioner can create problem. So, these are the these are the way high resolution microscopy has developed over the time scale from 2006 onwards the Titan microscopes has come up in this world and it has changed the whole concept of electron microscopy all throughout in the class I will show the images of the microscopy. Now, let us switch on the beam on the microscope and just see that light of the. So, I just take on this chair and just switch on the beam here by using the computer which you may not be able to see and once I switch on the beam once I switch on the beam in the microscope I can clearly see that the fluorescent scheme lights up that means I have the beam aligned in the microscopes remember the for normal microscope and high resolution microscopy electron beam needs to be aligned properly. So, I just then bring the sample in the microscope into the field of view and then I will just set up the microscope. I will not show you the basic features of the microscopic investigations we have already a sample inserted into the microscope and I am I want to show you most of the things on the screen. So, so that you can observe because seeing here is always difficult task on the screen this is small arena. So, I just what I did is basically I put the sample in and focus the beam and just put the apertures both the object aperture and the on this electric apertures using that I can form a bit fill image which I will show you in a moment's time. So, please view it on the screen here. So, you can see basically the image on the on a screen. So, this is a typical bite fill image in the electron microscope at the field of the beam is bright and one can see that there are different features on the on the microscope on the on the image. So, the features actually tells each feature will tell us some contrasts are basically this kind of image is based based on the diffraction contrasts in the electron microscopes as the electron falls of the sample the it undergoes diffraction. So, by using this the diffraction information we can form different kind of images. So, the first kind of images form as it known as a bite fill image in which the transmitted beam or the furrow scatter beam is used to image that. So, whatever intensity information is there in the furrow scattered image will be seen on this on this image. On the other hand if you use a diffracted beam then we can see the information regarding a dark field. The most important thing in a microscope when somebody sits is the diffraction pattern because diffraction pattern is basically formed by the diffraction of the of the crystals in the sample during as the electron falls in a sample. So, electron getting diffracted can lead to this kind of diffraction patterns and they contain all information regarding the sample type regarding the features present in the sample whether the defects are not or not even that depending on the orientation of the crystals this diffraction can be changed. So, that is why the diffraction pattern is is something which is known as the most important thing in a micro in a in a transmission electron microscope. By using the diffraction pattern subsequently one can generate either a bite fill image or a dark fill image or even one can use this as a highly selected electron microscopy. So, this is the very powerful process. So, that one can actually analyze almost all features which are present in the sample at the at the fine scale to the level of I am strong or some I am strong nowadays possible one can actually gather informations. That is the reason I have told you in the last lecture or this lecture that transmission electron microscope is basically a versatile equipment can be used for many many kinds of analysis of the sample. So, let me just now go back to the microscope and try to figure out a diffraction pattern and this. So, this is very in a microscope very typical they can now one day nowadays everybody grab the images on the computer scheme. You do not come into picture you see that. So, we can actually gather diffraction pattern by using the selected aperture select the particular region of sample and this is one such diffraction pattern we can see on the screen. So, diffraction pattern has a transmitted beam or the forward shutter beam and diffracted beams sitting on the sample say different places. So, if I put the aperture here on the transmitted beam then I can basically a great they buy filmage the one which is so new there here. Now, if I select any of these diffracted beams and put the aperture in the diffracted beam object aperture in effect when I can get the dark filmage. On the other hand if I select the large number of diffracted spot along in the transmitted spot by using a bigger aperture I can get basically I can make them interfere and get the interference pattern which is nothing but higher resolution image. Nowadays one even do not need to do that because the lenses in the lens are so good actually it generates the high resolution image in the very high magnification. So, this is a dark film image which can be actually obtained by using one of those diffracted spots in the microscopes and it will light up the regions which are diffracting strongly in the microscopes. So, this dark film image can be obtained even in that is called scanning transmission electron microscopy a stem mode also and the dark film image stem mode will give you again some kind of jet contrast if we use hard disk in a dark field. Let us call high angle angular dark film image which can be done. So, routinely in the microscope nowadays but one is to insert this particular detector inside the column to gather the information. So, other than that one can actually select these any of these regions of the sample and then do the any of the regions of the sample here and do the spectroscopic analysis using the EDACs or one can use another law of spectroscopic features to basically do the composition analysis of the sample. But those are very involved techniques to show them in the microscope requires lot of time. So, I will not be able to show you in front of in the microscopes, but I will discuss in the class in subsequent lectures when I discuss about the yields and the stem. I will show you the basic features and when I will show you some examples of our own study which we have done in the process of our own research even using this microscopes or maybe some other microscopes which I am going to show in the class. Modern day electron microscope requires sample preparation. Sample preparation is the one of the biggest bottleneck of the getting highlights in microscopic images. So, that is why sample preparation technique has seen a sea change over the time. So, I will not be able to discuss exactly different sample preparation procedures, but off late even after TM sample is perforated and thinned down to the electron transparency level. The sample surface can have oxides or other contaminations to make it contamination free this for the normally for the analytical microscopic purpose also for highlights and purpose. The machine which is used is known as a plasma kinam is generated the plasma using a gas or gas mixture like hydrogen oxygen inside this machine and we can actually load the sample in a TM sample holder and inside this one and clean it using the plasma. This is very fast and very what is called authentic technique to get sample contamination free. This is very important for many analysis as I said not only high lection, but also compression analysis and also in stem because in the stem we use a focused beam or a converge beam rather not a converge beam and as if the sample has contaminations the converge beam will interact the contamination and sample will be basically more contaminated as the investigation goes on. That is why in all normal days all the microscopic samples needs to be first cleaned in a plasma kinam before you can inside the TM column that also saves the vacuum system of the TM column. So, this has been a new feature. In fact many people nowadays use something known as a nanomail where even after the normal thinning of the sample the sample is cleaned by using very low energy argon beams in a nanomail very precisely. So, the surface oxide layers are removed and very controlled manner and so that we can get a actual high lection image in the microscope. So, following that this machine can actually remove all the further contamination at all there, but nanomail is very expensive very few people in this world can buy it. So, we do not have. So, many people in this world actually use the plasma kinam to clean the sample.