 So, in surface coating technology we already know that this vacuum system is one of the very important peripheral support and it maintains a certain level of pressure within the system. It depends upon a particular coating process and among one family say for example, C V D we have different degree of vacuum which will be essential to maintain a steady state in the process and to finally, achieve a quality coating. Similarly, P V D is also a process where also we need to maintain a certain degree of vacuum that means, the process pressure within the chamber, but more importantly evacuation of the system before initiation of this process that is also very important. So, from that point of view we have two classes of equipment vacuum equipment namely the pumps and as we have already mentioned the basic purpose of this pump is to reduce the number of gas molecules within the reaction chamber within the this coating chamber so that the process can be initiated and in this we have two types of pumping system and today we shall discuss this production of high vacuum, how we can produce high vacuum inside the system and that for that we have to really look into what are the types of pumps. Now here what we can see that a pump for the high vacuum it can be just a moving it can be even stationary that means, there is no moving part and then it can have further classification that means, it is mostly mechanically working and here it is stationary so there is no rotor as such no rotor or impeller. However, in this moving one we have to finally, find out whether the waste is thrown outside that means, whether it needs one exhaust. So, in the stationary pump also we have one such variety where we need also this exhaust that means, that is delivered outside. However, in this stationary group we have another one where this residual gas molecules which were very much in the present in the pump those are not thrown outside and, but what has what is done then it actually in this case what we call it is actually immobilized. So, these gas molecules are really immobilized within the chamber itself and there are certain parts or certain surfaces on which this whole thing will be adsorbed or trapped. So, this is also another way of doing the thing. So, here we should look into and we shall see how all these pumps are working and all these are definitely working based on certain principle. So, let us look one by one what are those pumps. Now, pumps for high vacuum that we what we are going to discuss today. So, this is actually a vapour ejector pump. In fact, what we can write here this is actually a vapour pump. Vapour pump means we take the help of some vapour of some element it can be vapour of mercury or it can be vapour of some oil and that is used and that entrance the gas molecules and it is along with that this oil vapour which attains certain velocity and since it it entrance that gas molecule. So, that gas molecule is thrown outside and this way we have two types of vapour pump one we call vapour ejector pump ejector pump and another is diffusion pump. So, this vapour ejector pump that actually works in the principle of molecular drag and turbulence. So, it is actually the drag force which is arising out of this viscous force and that is called a viscous drag. So, let us look have a look quickly this pump just looking at this line diagram. So, here we have this one chamber which is a reservoir of the oil. So, this is a reservoir of the oil and that is the extension of this oil reservoir. So, this is actually the reservoir of the oil and then this tube is bent it is bent and then what we have in addition to this is one vessel it goes inside and here what we have a cone like thing. So, this is actually going to outside and here we have this tube. So, here we have a connection like this. So, this is actually a connection. So, this is more or less the basic thing what we have shown with this light diagram let us also recognize the various parts. So, here what we see that is the opening that means that is the inlet this is actually the inlet. So, this is inlet and this is actually the outlet and what we have here this we can join. So, this is actually the tube. So, this oil vapor so, in just beneath it we have one heater. So, this oil vapor this is heated and then this is moving upward because of this vapor pressure and at this point what happens if there is some gas molecules from the chamber vacuum chamber is on this side. So, that will be in contact with this oil vapor and since it is moving in this direction then that will this oil vapor will entrain this gas molecules and that will move in this direction and since we have one convergent this cone shape that means in this case the velocity will increase and as a result the whole thing will move in this direction and then by proper cooling. So, here we have water cooling in this here. So, in this water cooling in this zone we can recycle this oil vapor which will come that means which will be flown back through this line and it will be recycled. So, it is actually creation of the oil vapor and this oil vapor entrance this gas molecule from the chamber and then that will be dragged and why it is called it is actually viscous drag and turbulence that means this mixing that means this gas molecules that is actually entrained by this gas this oil vapor. So, this is actually the oil vapor this is oil. So, it is actually the viscous drag and the turbulence because of this simple reason here we have one dimension and that we called the throat width throat width and in this case this throat width that is greater than lambda what we called the mean free path. So, in this case since it is greater than lambda. So, in this case there will be collision and between this molecules and as a result of that we have viscous drag and turbulence and as a result of that this will be delivered in this direction and that is going to be one outlet. One thing we have to be careful here that this outlet pressure is still not atmospheric and it is in the order of 10 to the power minus 2 order or 10 to the power minus 1 and in this case just it cannot work. So, on this side we need one rotary van pump which is used for evacuating the system down to 10 to the power minus 2. So, from 10 to the power minus 2 the pressure will be raised to atmospheric pressure atmosphere and with that it can be thrown outside and the job will be done effectively and successfully. So, this is actually vapor ejector pump. So, here this ejection is done by this viscous drag and turbulence. Now comes diffusion pump. In fact, here what happens what we have said throat area that means just at the entry point that means near the inlet. Near the inlet we have a throat area and that term that parameter that is called width of the throat and this width of the throat in this case, width of the throat, width of the throat in this case that is actually less than lambda that means in this case we do not expect any collision within the gas molecules because the mean free path is larger than this one greater than this one. So, in this case it will be just like diffusion and it is almost resembling the diffusion process that means what we can see just by looking at this construction of the diffusion pump. So, it is actually the oil vapor creation of the oil vapor then this oil vapor will be deflected through a nozzle through a slit thereby attending a supersonic speed and with this supersonic speed it is going to entrain that gas molecule which comes by chance in front of the throat which we like to which we can see just now and by that process it will move with a very high velocity in the downstream direction and then just pushing this thing in the delivery side that means on the exhaust side. So, let us look how does it work it is basically a concentric tubes that is in the construction of this pump. So, this is one tube over which we have what we call one umbrella and then further to this what we have we have here another umbrella and then we have another concentric tube. So, this is the second stage we can also have the third one and in this case we have another concentric tube. So, this is more or less the construction and you have 1, 2 and 3 concentric tubes and these are called this is one chimney then you have one second one and that is the third one and here we see the three umbrellas and what we can show further to this here this is the outermost surface that means the shell. So, that is the casing and just beneath this we have one heater. So, this area actually filled with oil this is the oil reserve. Now, what we can see here? So, what we call throat? So, let us put this way. So, that is the flange and on this side we have the chamber. So, this side we have the chamber that evacuate to be evacuated. So, this is actually the inlet side inlet and what we call throat area actually this is the throat area. So, this is called the throat area. So, width of the throat means this gap. So, what we can see here that stream of vapour that will move in this move upward, but it will be deflected and here we have cooling coils cooling coil and what we have further to this here? We have one opening here this is the opening and that is going to the exhaust. It is not exactly exhaust it will be connected to the backing pump this is the backing pump it will be connected. So, let us look how does it work? So, this will be deflected and here we have the stream. Similarly, we have another stream emerging out through this second stage we have also another stream flux that is also moving this way and here we have the gas molecules which are on this side on the chamber side. So, what we can see here that this part this particular portion this portion from this to this it is actually the vapour, but if we magnify this thing it will look like a cone it is a truncated cone that means, virtually it is going to be a truncated cone having this shape and in this truncated cone that means, this vapour stream is diverted it is deflected and now it is falling just almost like making one truncated cone. So, for this pump this surface this conical surface which is part of the cone that is actually the active pumping surface. This is actually the active pumping surface on which this gas wheel this particle is going to impinge. Now, when it does impinge with a strikes it is already entrained and at the same time this stream is going to strike or hit this cold wall of this chamber. So, first is impingement of this gas gas molecule gas particle from this chamber this is impingement number 1, then it is entrained now it is moving and at the same time it is going to hit this straight forward this cold wall and it is cooled by chilled water and there this oil gets condensed and this condensation is continued throughout this down this height down this length of this outermost shell and what is what happens then the oil which gets condensed that is flown back to this surface to this surface that means, this is the oil reserve it flows back and then the process repeats itself. So, that means, there will be continuous evaporation vapour production of vapour of the oil through these three tubes this is the core these are the two annular tube and at the same time there will be deflection of this vapour where it attains supersonic speed. So, here it is moving with a supersonic speed and then it is the impingement of the air molecule or gas molecule then the whole thing moves with this high velocity and in the process it strikes the wall this gets condensed and what happens this gas molecules which is separated that is accumulated here and then this is actually the opening and through this opening it is going in this side and here we can expect a pressure of 10 to the power minus 5 with a ordinary diffusion pump at this throat area very close to that inlet and the pressure very close to 1 into 10 to the power minus 1 at this stage. So, what we can say here that this is actually the first stage compression here. So, this is the first stage compression this is the second stage compression and this is going to be the third stage compression here this is going to be the third stage compression and as a result of this what we see here that this will be a choked. So, here we also have the fourth stage of compression. So, pressure will be raised from 1 into 10 to the power minus 5 to 10 to the power minus 1, but since it is already got into this oil vapour and it is almost resembling a diffusion process and from this we need to have a backing pump say for example, a van pump and this van pump will be connected here. So, that will be a backing line which has been already discussed in some of those previous lecture. So, that will be the total system consisting of the diffusion pump and the mechanical pump and that actually constitutes the backing line. So, this way the diffusion pump work actually this diffusion pump this can be explained by one principle suppose if we have a tube and here we have at right angle a connection and then what we have here a vessel which is filled with some gas. So, this is actually gas filled and here say this is point a b this is c and this is d this part we have a water jacket. So, it is actually mercury vapour which is flowing in this direction this is mercury vapour. If we cool this area cool this area then what is going to happen all on a sudden there will be condensation of the gas and there will be a fall of pressure. So, this will move in this direction and in this process it will be entrained by this mercury vapour. So, mercury vapour will entrained that one and as a result of that it will flow with the mercury vapour and there will be a continuous flow of gas and this process is very similar to a diffusion process. So, this principle what we what we understand here just by condensing the vapour and then just dragging it that is exactly what we have applied or what based on which principle this diffusion pump works. Now comes turbo molecular pump. So, what we have seen diffusion pump actually this diffusion pump it is a non rotating part no part no component of this system is a moving one. So, it is a stationary one, but it is it actually throws this thing this residual gas to the outside and then that is why we need a backing pump. So, it is not absorbed in the system or the residual gas is not immobilized, but this turbo molecular pump that is a rotating one and in this case what happens in fact, the principle is something like this that means, suppose there is a surface which is moving at a very high velocity and if one gas molecule strikes that one then a directional velocity will be imparted on that. So, this is actually the principle of the turbo molecular pump that means, the gas molecule is imparted with a high directional momentum when it strikes or encounters actually a moving surface. In fact, this turbo molecular pump it is just like the turbine of turbine of aircraft. So, it has sets of stator rotors and stator and this rotor that is actually consists of blades just like the turbine. So, this rotor that is a disc it consists a number of blades similarly in the stator we have also the corresponding number of slits. So, this way it works now let us look into the basic construction of this pump. So, here what we have? So, there is a shaft and it is moving this way at a very high speed it can be 50000, 60000 it can be even 100000. Now, what we can see here that on this we can have just like these blades. So, similarly what we can show in this side this one. So, this is one set similarly this is actually the rotor. Now, just adjacent to this we have the stator. So, this is one set. So, this is stator and this is rotor and what we have just on this side. So, this is one stage we can draw another stage also like this and another set of stator. So, the whole thing. So, that means, this is actually rotating. So, if we consider the velocity linear velocity it will be directed in this direction. So, this is also another rotor. So, let us put this thing. So, it is moving in this direction this is also moving in this direction. So, this is also rotor and this is the stator and what we have further to this. So, we can have I have shown just two stages we can have 5, 6 stages and this way the thing will go and here what we have we have one outlet from this turbine pump in this direction and that is going to be that is actually just like the backing line of the diffusion pump. So, that can go to the vane pump. So, it is just like a backing support. So, what we see here in this case the gas molecules. So, this is just like the opening. So, this is the inlet and that is the outlet. So, the gas molecules these are actually when it hits this surface it attains a directional velocity and momentum and here what we can see that these are not parallel to the axis, but they are inclined. So, that means, there are slots. So, these are the radial slots which are cut on this disk and this radial slots which are having certain angle. So, this is the angle. So, it is in an oblique manner it is cut and in the process what happens if the gas particle encounters here. So, it will be heated by this surface as a result of that it is going to be adsorbed on this surface. So, it is actually adsorption that means, it is approaching and it is absorbing at the type of absorption on this blade. So, these are the blades. So, it is adsorption and it is actually arriving with certain incident velocity and then it will also dissolve with after some residence time desorption. So, adsorption and desorption that will also take place. So, from that point what is going to happen it will have a normal velocity and with this normal velocity it will move in this direction that means, the direction is such that this particular material will move in this it is inclined in such a manner that this gas molecules when they are re-emitted. So, desorption and it is called re-emission re-emission and during re-emission what is going to happen that during re-emission this particle will be directed towards this surface mostly because of this particular orientation. So, that means here in the design what is very important that as this material heats the surface of the blade then it receives a directional velocity and momentum and this directional velocity favours its further movement to the stator in this direction. So, this orientation of this blade that favours that directional momentum and velocity towards this stator and this rotor is also moving. So, compared to this stator it has also certain relative velocities though it is stationary, but if we consider this speed of this compared to this it also has one relative velocity. So, in this way there will be a effect in series. So, the thing will move after striking this surface it will move to that and then it will be re-directed and finally, it will come out from this surface and where we have no further rotor. So, from this surface it will be pushed through this line and because of this very high velocity it will have a movement and in this case there will be a van pump which will do the remaining part of the operation. That means, if it leaps at a pressure of 10 to the power minus 1 which is tor which is below atmosphere then it will also from this pressure residual pressure it will raise the pressure up to the atmosphere. So, that the remaining gas molecules which are actually evacuated from this vacuum chamber that will be actually pushed through this tube and through the van pump it will be thrown to the atmosphere. So, the basic principle is like this here the high velocity of this rotor that is utilized to give a directional velocity and momentum to the gas molecule which is going to strike this surface and this surfaces are designed in such a manner that means, there should not be any backward flow and flow will be always from inlet to this discharge spout and in this case this angle that is one of the parameter of the design that should be taken into consideration and this way a high vacuum can be created. And here one thing can be noted that earlier there was a requirement of giving just a gap between the stator and rotor of just 20 micron and that was not an easy task in the very construction of this pump in the mechanical construction of this pump. So, it was not that very attractive equipment for all ultra high vacuum activity, but with some improvement and modification of this design thus requirement has been now much more liberalized and just a gap of as high as 1 millimeter now is allowed between the stator and the rotor and that makes the task of fabrication of pump is rather easy and with that what we can have we can have further use much more use extensive use of this pump in all ultra high vacuum activity. One of the greatest advantage of this pump with respect to the diffusion pump that we can have a quick look here when we discuss this diffusion pump we have already always assumed that there is this deflection and that is actually in the downward direction, but for unfortunate eventuality if we do not have proper cooling and condensation if there be some backstripping of this vapour that can contaminate the chamber and the specimen, but such thing we do not foresee in this case here only the thing is that rotational speed and this pumps are actually put in the with a vertical shaft vertical axis because of the orientation of the chamber and in that case naturally alignment of any shaft with two end bearing support in the vertical position and that is considering any mechanical assembly that is one of the greatest challenging task in the construction and fabrication of this diffusion pump. So, this turbo molecular pump it works at a very high velocity and with this high velocity we attain a high momentum which is transferred to this. Actually it is no more a molecular drag rather it is one should say that it is actually transfer of momentum in a particular direction when the material gas molecule actually impinge on this blade surface. So, it is just like this momentum transfer that means, this gas particle molecule this acquires a high magnitude directional momentum. Now, we can see this cryo pump that means, it is actually use of cryogenic medium. Now, when we have seen sorption pump that means, that we have already discussed sorption pump and here we also have seen that it is actually adsorption on the surface of molecular ship and which is super cooled by liquid nitrogen. So, that was the principle of this sorption pump and it was mostly physical adsorption on this surface. So, this was the molecular ship which surface was used for adsorbing the molecule and it is actually a not a high vacuum pump, but it is a roughing pump it can be considered as one of the substitute for a rotating vane pump. But this cryo pump that is actually a vacuum pump and here what we see that it is actually the liquid helium that is instrumental in getting this high vacuum. So, this is actually one stage and here we have the provision. So, this is the chamber we can have some gap ok. So, let us have a quick. So, this is actually the chamber. So, this is one stage. So, this is actually this is the pump this is cryo pump. Now, this one is a super cooled stage and it is cooled by passing not liquid nitrogen, but liquid helium it is H e and here the temperature that is kept on this surface it is 20 K Kelvin and here what we have some condensing arrays of metal plates condensing array and that is kept at about 80 K. So, these surfaces are used for condensing water that means, trapping the moisture and this surface that is for trapping all sort of gases. So, here these will be adsorbed on these surfaces except hydrogen and helium and for this what is used what is used activated charcoal that is used that can be also used and that can be kept at 20 K also 20 degree Kelvin and that will be most effective material for also trapping this hydrogen and helium. So, this is one thing we can also use and this is not only it is non rotating and also here what we have seen it is unlike that of vapor ejector pump or diffusion pump here the material is adsorbed and it is made totally immobilized and that has to stay here and later on this thing can be heated to move it out, but at that point this surface will be adsorbed by this condensation of these gases at this point. So, this is called what we call a cryo pump. Now, this is called Gatering pump Gatering pump it fact it is it means that a particular substance that capture or gets the gas molecules on its surface. So, it is just the intention here how to get those gas molecules on this surface of a particular metal it is a strategic metal which can capture those thing on its surface and it gets all those material on its surface and that is why it is called a Gatering pump. In fact, in a Gatering pump the material which gets this some gas molecules that is nothing but titanium. So, it is actually a titanium Gatering pump and we can also call it titanium sublimation pump sublimation pump titanium sublimation pump. So, what is done in this case it is also a non-rotating pump where this gas molecules are immobilized. So, they are not pushed anywhere outside the pump. So, what we can see in this case say this is the chamber and what we have we can have here say for example, one titanium foil or a titanium coil. So, this can we can put this way. So, this is titanium. So, it has a lead wire which can go on this surface and we can close this sorry we can close this like the like this one and on this side we have the lead wire connection and the whole idea here that with this vacuum it has to sub limit. That means, it will be heated and the material from this titanium coil or titanium foil that will keep on evaporating. That means, we can also show this way say this is one titanium coil and it has just it is placed and it has just one annular surface it is just having one annular surface here. So, by heating this the entire surface will be covered by titanium and by this cover we get a surface with an enlarged surface coated with titanium and that surface will be used for getting those gas molecules which are to be removed from the evacuation vacuum chamber and in this case it is mostly chemisoption of those gas molecules because titanium is well known as a reactive material. So, it is through this chemisoption we can get a reduction of pressure and this is normally done in any sputtering process just to evaporate if we have a titanium target just to evaporate sputter titanium and it can coat some of the surfaces and thereby we can get a relatively high vacuum which is just not possible without this sputtering of titanium. So, this is actually this gatoring pump or titanium sublimation pump. Now, we get this ion pump. Now, ion pump is something here what we are going to do that the gas which is present inside the chamber that will be ionized and when it is ionized and if we can keep one cathode inside the chamber which is polarized with negative this negative potential. So, this is a cathode. So, that means, first of all within the chamber we must have electron available which will be used to ionize the gas. So, it is actually ionization of the gas followed by attracting this ion ions in a in a directional manner by putting one electric field that means, here this ions will be attracted electrically by this plate and by that there is movement of gas molecule gas particle not just as a neutral, but just like an ion and this is actually in principle known as the ion pump or ion pumping. So, these are attracted by this cathode. Now, in this ion pump we can also have sputter ion pump or evaporation ion pump two types of pump either evapor it is called evapor ion pump or sputter ion pump. Now, in both the cases what happens in this case the material say for example, titanium, titanium can be evaporated and this material the place where it is going to be evaporated that is actually polarized and that surface which is coated with titanium that which is coated with titanium as a result of evaporation that will be polarized with negative bias that means, that will be now used as cathode and then this ionized gas that will be attracted towards this surface. So, this is actually called evaporation ion pump that means, titanium will be evaporated gas will be ionized and this evaporated surface of titanium will be polarized with negative potential and this ionized gas will be attracted on this titanium coated surface which is now serving as a cathode. Now, sputter ion pump here instead of evaporation we sputter the surface of interest by titanium and here the coating is done by sputtering and this particular gas which is a reactive gas that can be absorbed on the surface which is actually sputter coated with titanium. So, these are the pumps that means, ion pump then sublimation pump and this cryo pump these are the pumps which are used for evaporation and also for immobilizing the gas particle which are present within the chamber. Now, with this we can summarize today's discussion that for high vacuum operation we have two types of pumps one is rotating another is non rotating and in rotating we have turbo molecular pump where this gas particles acquire a directional momentum of a very high magnitude and through that it can attain sufficient velocity to be moved from the inlet towards the exhaust following various stages of a rotor stator state of the turbo molecular pump which is just like a turbine of one aircraft. Now, here we have also diffusion pump which is also very commonly used here actually the oil vapor entrance the gas molecules once it comes in close proximity and by this supersonic speed it drags it down the pump shell and thereby it releases and it gets the oil vapor gets condensed and then a four pump there which does the remaining part of the job that means, raises the pressure to atmospheric. We have further to this those pumps where those gas molecules are immobilized and these are non rotating in cryo pump it is adsorption of the gas molecules on a super cooled surface and when it is sublimation pump or ion pump either evaporation ion or sputter ion in both the cases it is actually chemisorption of this gas molecules on the surface of titanium coated surface.