 Now, that we have classified nano crystals and nano structures and nano materials based on dimension. One fundamental question which we have to ask ourselves is that what is the dimensionality of a system. In other words, how many dimensions as an object have? Now, this question obviously is a practical question. It is a question related to the physics of the dimension and this is in other words very closely related to the question which we had asked before that what is a bulk material and clearly we had noted that a bulk material could be defined based on a particular property that we are taking into consideration. Similarly, we can ask ourselves the question that even though we live in a 3D world that means that the dimensionality of the world we live in is 3D and hence any tangible object is going to be 3 dimensional. But in terms of the physics or in terms of the effects we see can there be some other dimensions to a given kind of a structure or given some kind of a physical property. For instance, suppose I take graphene which is almost a single layer of graphite is almost as close to an ideal 2 dimensional crystal that we can think of. So, this is just an atomic layer peak and therefore, I would like to treat this system as a 2 dimensional system rather than a 3 dimensional system even though we know that this object has an embedding in 3 dimensions. Similarly, suppose I look at some of the other derivatives like a carbon nanotube which can be thought of as a folded version of graphene. This also can be thought of as a curved 2 dimensional space which would be a cylindrical 2 dimensional space and a fuller in molecule can be thought of as what is called an S 2 space or spherical 2 dimensional space. Therefore, it is even though we live in the 3 dimensional world with respect to a given property or a structure we have to talk about other dimensions which could be lower than a 3 dimensional world which could be 2 dimensions or as we shall see sometime even 1 dimensional. Now, let us take a very classic example a cantilever beam. A cantilever beam typically which has a very long aspect ratio which has an L by D greater than 20 which is sometime called the Euler beam is a thin beam and the variation shear stresses in the radial direction during bending can be neglected for this case and sometime in for many considerations this beam can be treated as a 1 dimensional beam. So, let me the thin beam I am talking about is drawn here. So, it is an extremely long beam with very little thickness very very little thickness as compared to the length of the beam. So, L by D is greater than 20. Now, it simplifies my overall calculations when I talk about this beam as a 1 dimensional beam rather than considering it as a completely 3 dimensional system. Similarly, let us take another example for instance a plate shown here which has an height B a length L and a thickness T. Suppose, my thickness is very large as compared to the length of the bread or in I can even pick 1 of the 2 dimensions like length and see the thickness is very large. Then such a plate can actually be solved the equations for such a plate can be solved in 2 dimensions and the condition under which it is solved is called a 2 dimensional plane strain condition. That means, the strain in the third dimension can be treated as 0 because whatever I am loading I am applying on this body assuming that it has no 3 dimensional content it is not along the it is constant along the third dimension. Then I can take treat this body like a 2 dimensional body and solve my equations assuming the third dimensional strain which is now for instance suppose I have to call this the z direction the direction of the depth as my z direction of course, I can call this my y direction and this my x direction. So, if it is very large in the z dimension then I can treat this problem effectively as a 2 dimensional problem very thin bodies like a almost like a thin lamina can be actually treated like even as what is known as a plane stress condition in which the stress in the third direction can be neglected. And so the message from these 2 examples the example of graphene and the example of these 2 kind of what you might call a thin beam in a plate is that in terms of structures and in terms of properties and effective equations I need to solve. I may want to consider a low dimensional body which actually is very meaningful in terms of the physics I am trying to study. In nano materials again these I can extend this concepts which I have just learnt and such concepts similar concepts are also applicable. A nice example for this would be the case of nickel films which are grown on copper 1 0 0 substrates. I am taking a very specific example to illustrate the point, but the concept obviously has a much more general application and very often this treating this higher dimensional system as a lower dimensional system can save a lot of my time in terms of the computation can save a lot of time in terms of the understanding of the physics and it is worthwhile to treat them in the appropriate dimension. Now, in the case of the nickel film on copper substrates and we know that nickel is a ferromagnetic material while copper is not and now this copper 1 0 0 is a single crystal on which I am growing my nickel film. When I am growing the film layer by layer and I notice that if my film thickness is greater than about 7 mono layers the system behaves like a 3 D Heisenberg ferromagnetic. The details of all the magnetic properties we will deal with later, but for now what we are just worried about one important concept which will become clear as I go along and if I am below 7 mono layers the system behaves like a 2 D system. Now, how am I differentiating a 2 D system was vis-a-vis a 3 D system in the 2 D system all the spins are in plane while in the 3 D system there are spins out of plane and typically in this system there are spins which can't out of the plane therefore. So, let me take the system and draw a schematic here. So, I have my copper substrate and this is now a single crystal and on top of it I am growing my ferromagnetic nickel layer. I have 2 cases thickness less than 7 mono layers and thickness greater than 7 mono layers. So, I am talking about the number of mono layers of nickel on this copper substrate nickel being ferromagnetic. So, for the case of the 7 mono layers or less than 7 mono layers it behaves like a 2 D ferromagnetic and here suppose I were to draw a schematic of the layer I would notice that all the spins schematically I am showing here all the spins are in plane. But, suppose I am talking about a thicker film then I would notice that some of the spins would actually can't out of the plane that means there is a 3 D component to the system. So, effectively this system can be treated like a 2 D system and this system can will have to be talked about as a 3 D system. Therefore, we clearly see that with respect to the physical property of spin alignment and also the spin orientation we can have a lower dimensional system or a higher dimensional system based on a specific geometry and based on the specific property I am considering. And you would notice that in nano material since we are going down to low dimensions very often that we can actually treat systems in a lower dimensional manner keeping fully in view that actually the system is 3 dimensional because we live in a 3 dimensional world. And when we are talking about a reduced dimensionality is either it is with respect to a structure like the graphene or it is with respect to a ferromagnet property like ferromagnetic spin alignment. So, we have to keep this in mind while we are treating systems and solving equations which are important. Now, one important question which comes to the mind and which will often we ask for people and researchers and teachers working in the area of nano materials and nano structures is that what is new about nano because if you go back in history you would notice that in stained glass the f centers and nano crystals is what provide the color or stain in the transparent color less glass. And you know stained glass has been found in very ancient churches. If you look at material science for more than 100 years GP zones have been which are typically coherent and when they grow they become semi coherent into the form of theta double prime precipitates. In the aluminum copper system they have been providing strength and hardness. That means that for more than 100 years we have been dealing with GP zones and systems which are now giving us hardness. Though the exact structure of GP zones and the details came on were actually discovered only after the transmission electron microscope came to be. We all know that we are made of genetic material which is DNA and we have already said that DNA itself is a nano structure. Therefore, if somebody were to like question that where nano materials always in existence the answer has to be yes, yes they were all there for a long time nature is abound with them. In fact when you take your candle and collect a suit on top suppose I blame a frame candle and collect suit on the top then I would find many of the nano structures which have been discovered in the last 30 years actually formed in a common suit. Therefore, in some sense nano materials and nano structures always existed, but then what is new about nano that is a question which will come to our mind and we will try to answer this question in the coming slides. The crux of the problem lies in the fact that there are very many new effects which have been discovered after the advent of intense study in the area of nano science and these effects were not known to science before the advent of what you might call research into nano materials and nano structures before the advent of nano technology. And we will take up a few of these effects which we can call absolutely new about nano and here we are talking about effects and phenomena which have perhaps no bulk counterparts. In other words they are never not observed in the bulk materials they are very very specific to nano structures and nano materials. So, we will take a few of these the details of these we will obviously, consider with respect to the whenever we go to the relevant topic and we will discuss some of these in detail. For instance when we are talking about hall patch effect when we are dealing with mechanical behavior we will talk about hall patch effect when we are talking about for instance magnetism in detail we will take up giant magnetor resistance. At this stage it is important just to note that in spite of the field of nano in some sense existing for ages. In fact, you can even say it is ancient there are new things which have come up of late. And therefore, it warrants a separate place in our study in the scheme of things for us to study nano materials and nano structures as a separate branch where in we pay specific attention to some of these aspects. Of course, we are only listing a few of these kind of new effects here and further many more effects we will consider in relevant topics. So, let us start with the inverse hall patch relation it is well established that on decreasing the grain size the hardness and strength of the material increases. This is primarily comes from the fact that the grain boundaries pose an impediment to the motion of dislocations. And one of the classic models in this case is the dislocation pile up mechanism which is supposed to lead to the inverse hall patch relationship. There are still issues to be resolved regarding the origin the mechanism of how the inverse or the hall patch relationship comes about, but we will not go into the details for now. We will just assume that the hall patch relationship is coming because of the impediment posed by grain boundaries to the motion of dislocations. So, it is dislocations which are weakening the crystal and if there are impediments to its motion then we are going to get an increased strength. But this hall patch relationship on one hand in very large grain size materials is has been questioned, but that is not our region of interest in very small grain sizes when you are talking about tens of nanometers typically less than about 15 nanometers. It has been observed that the grain itself cannot support a dislocation pile up. And it is seen that the hall patch relationship actually breaks down. In very specific experiments of course, many of these experiments still need a confirmation in a larger spectrum of materials, but they are having reports that not only that the these traditional hall patch behavior break down, but there can actually be something known as the inverse hall patch relationship. So, in the hall patch relationship typically we observe that if I am plotting 1 by root d this is same as with respect to that means the decreasing grain size I would notice that the decreasing grain size to write I would notice that there is a straight line. And this is my some kind of a strength parameter which could be for instance an yield strength. Now, when you go to very small grain sizes and here say for instance I am talking about this is my order of about 15 nanometers or less. There are three possibilities which come about either I can continue to harden the way it is, but typically what is observed is that the hardening rate actually comes down, but in very some very specific experiments people have actually observed that the hardening may even come down. The third possibility is the hardening becomes constant with respect to grain size. So, it is very clear that when you go to small sizes the hall patch relationship breaks down the grain is too small to support a pile up. And even if you are not talking about a pile up mechanism this is now an experimental result and you have to take it the way it is. I will notice that the hardening rate changes with respect to the grain size d is my average grain size of course, it may the rate of hardening may become constant that means it may become invariant of the grain size, but in very specific cases you may actually observe the inverse hall patch relationship. So, the inverse hall patch relationship obviously it is not observed in large grain sizes. And therefore, it has no bulk counterpart it is only observed in very small grain size materials. And the inverse hall patch typically kicks in at a grain size about in the range of what 5 nanometers. So, it is very clear that when I am going to very small grain sizes now I am talking about nano structured material that means the material is bulk, but the grain size is in nano scale the mechanism of deformation can change. The mechanism of deformation or the mechanism of strengthening can change and since this mechanism is changing you would observe that the traditional relationship like a hall patch relationship which is valid in the large grain size regime is no longer valid in the small grain size regime. And if course, depending on this what you might call the experimental details the kind of material the kind of for instance the starting material conditions etcetera. You may even observe what is known as an inverse hall patch relationship which has a no bulk counterpart. The second example we consider is from the world of magnetism and we take up an effect known as giant magneto resistance typically the acronym used for this is GMR. Again like the previous example there is no bulk counterpart to this and it is actually found in hybrids at the nano scale. In normal magneto resistance we observe that in a presence of a magnetic field the resistance increases while in the absence of a magnetic field the resistance is a low resistance state. In giant magneto resistance this magneto resistive effect takes a new higher order all together which could reach 80 percent or more. Because in normal magneto resistance the values of magneto resistance about 5 percent here we are having a much higher enhancement in the electrical resistance and this happens in the presence of a magnetic field. So, here we make what is known as an anti ferromagnetic coupled hybrid in other words I take two materials and in the I will just take one example now the details of which we will talk about later. So, I make an hybrid of three layers and this is a non magnetic layer and these are anti ferromagnetically coupled ferromagnetic layers. So, the coupling between the two is anti ferromagnetic, but these layers by themselves are ferromagnetic. So, in the presence in the absence of a magnetic field the spins in one layer is pointing opposite to the spins in other layer and this is now my high resistance state and the resistance is coming from spin dependent electron scattering. Now, what happens suppose I switch on my magnetic field. So, in the presence of a magnetic field like B what I get here is a state in which my spins are ferromagnetically coupled. So, this is my magnetic layer this is my magnetic layer and in between layer is the non magnetic layer and you would know and the thickness of the middle layer is less than the what is known as spin diffusion length and if they get ferromagnetically coupled then I get a low resistance state. The difference between the resistance of this low resistance state which happens in the case of with the magnetic field vis-a-vis the high resistance state which is in the absence of a magnetic field wherein the two ferromagnetic layers are anti ferromagnetically coupled is very large and this is the effect of giant magnetor resistance. Now, obviously you it is very clear that the thickness of this layer the thickness of these layers are very very small this layer thickness internal spacing layer thickness is very very important because this has to be in the spin diffusion length of the material. And the mode of scattering here which is giving rise to the electron scattering giving rise to resistance as I pointed out is actually spin dependent and this is spin dependent scattering which is giving rise to the resistance in the material. Of course, I am ignoring here scattering from the interfaces they could also be scattering from this interface and scattering from this interface which would add on to the resistance which is present. But, if you are looking at the difference in resistance between the between the ferromagnetically coupled layers and anti ferromagnetically coupled layers then it is basically the spin dependent scattering. Now, this particular configuration actually has important applications in reading heads etcetera and this can also be used for detection of magnetic fields which are very small. Therefore, clearly there is no classical analog to this because here we have made a sandwich structure or more precisely a hybrid which is with the whole mechanism of which operates because of the nanoscale in which the spacing layer is present the anti ferromagnetic coupling between the ferromagnetic layers. And therefore, there is no classical analog or the bulk analog to this. Therefore, when we are talking about giant magnet resistance this is absolutely a new phenomena which is present in what is called present at the nanoscale. They are very close cousins of this which are also present like tunnel magnet resistance and some of the other things which we will consider very soon. So, it is clear that when you are going to nanoscale there are new things which are observed extremely fascinating new things which have no bulk counterparts. Therefore, it definitely makes it worthwhile to study what you might call nanomaterials and nanostructures from a completely new perspective and try to understand some of the effects which come in there. Once other effect which we can talk about now is super paramagnetism it is very well known that when you heat a ferromagnetic material above the curie temperature it becomes paramagnetic. If I happen external field to a paramagnetic material then there is a tendency for alignment of the spins in the paramagnetic material, but it is constantly fighting against the thermal disordering. Suppose, I take a molecule like oxygen which is paramagnetic the typical susceptibility is very very small. That means, it has susceptibility of the order of 10 power minus 6 that means the alignment in the presence of a magnetic field is very small. The reason the alignment is very small is because this oxygen is not ferromagnetic. Now, there is an alternate way of producing a what you might call a paramagnetic material as I pointed out like that is from starting with a ferromagnetic material. There are two ways of producing a paramagnetic material from a ferromagnetic material one of them as I pointed out is by actually heating the material above the curie temperature. An alternate method is to actually reduce the particle size to very small sizes. So, let me write down summarize the ways I produce I can produce actually my paramagnetic material. So, there are materials like for instance I can write an example of oxygen which are always paramagnetic and we are not talking about these substances. Here, we are actually talking about materials like iron which are actually ferromagnetic, but which can be made into paramagnetic state by heating or by reducing the particle size. In some sense both heating and reducing the particle size as we shall see is equivalent when you when it comes to the essential physics what is happening here and we will see that how this leads to the phenomenon known as super paramagnetism. So, when you reduce the particle size to very small sizes typically say less than about 20 nanometers the entire particle becomes a single domain. We know that we had already seen that when you have a bulk magnetic material it is actually split into multiple domains. Now, when it goes when the particle size goes to less than 20 nanometer and now this is a single crystal then I would note that the entire particle becomes because the domain wall thickness is too large the particle size is already is too small. Therefore, it cannot support any domain walls within the particle and the entire particle becomes a single domain. Now, at this state this material is still ferromagnetic even though it is a single domain, but suppose I reduce the size even further and take it to a size say of the order of 5 nanometers and now I am assuming a pure iron particle there are no oxide layers covering it. Then the particle size is so small that the inherent tendency for all the spins to align within the particle is become small because I simply do not have enough number of atoms in the material to give me my effective spin alignment. Therefore, the tendency for alignment is become smaller and smaller as I reduce my particle size and it about a critical size about 5 nanometer what happens is the temperature becomes the temperature which is trying to disorder this alignment of spins spins over and therefore, I get into a paramagnetic state. So, now this is a paramagnet and obviously, as I pointed out this is the reduction of particle size is very very similar to in heating the material because overall it is actually the disordering effect of temperature which is actually fighting against the ordering effect of the inherent ferromagnetic spins. And of course, when you talking about ferromagnetic alignment I mean the spins are aligned parallely in the same direction. Now, since the particle size is too small and thermal disordering effects have taken over this material becomes paramagnetic. But, such a material is very much different from the paramagnetic material like for instance oxygen which has no inherent tendency for alignment of spins. Since this material is paramagnetic is inherently ferromagnetic which has become paramagnetic if I apply even a small field just below the critical size at which it becomes paramagnetic then. So, below the critical size at which it becomes paramagnetic even a small magnetic field will tend to align the magnet and when I remove the field again it gets into a paramagnetic state. In other such a material is having a tendency to align all its spins even in the presence of a weak field. In other words this is unlike the oxygen case in which very high fields are required even to get a partial alignment of the spins. Here the spins automatically orient themselves and therefore, you get a very high enhancement in the what you might call the paramagnetic susceptibility and such a material therefore, is called a super paramagnet. And this is purely coming from the effect which is the size reduction effect. So, by reducing size I have made the material which is normally ferromagnetic into a paramagnetic material. This paramagnetic material in the presence of a field tends to align all the magnetic movements and therefore, there is a very high susceptibility and such a material would not have any hysteresis. Therefore, I have very interesting effect again related to magnetism coming from this particle size reduction. Let me move on to the next example which is from a totally different physical property coming from a totally different physical property. This is the area of super hydrophobicity. All of you must have observed then you take a lotus leaf for instance and you put water on the lotus leaf it tends to bead up very similar to what beading may happen if you put a water droplet on a glass. So, you would notice that if you put a water droplet on glass will tend to bead up rather than become a smooth layer on tops. This is not what happens with water it tends to bead up and you would notice that if you put water on wax for instance this is a similar effect you would observe. Therefore, such materials do not tend to be wetted by water. There is a reason why the lotus leaf should not be wetted by water because if water will where to wet the lotus leaf the lotus leaf would sink. And therefore, this is not a desirable property for the life of a lotus leaf. So, the important point which comes about when you study the lotus leaf is the fact that it is not just hydrophobic the word hydrophobic meaning that it ripples water, but it is actually super hydrophobic. The difference between hydrophobicity and super hydrophobicity can be understood by measuring the contact angle. So, my contact angle if I understand. So, I put a droplet and I measure the contact angle. So, this is my contact angle that the droplet makes. So, I measure the contact angle and see what is the contact angle and I will observe that for normal hydrophobicity I can get a maximum of 120 degree contact angle. Even 120 degree is possible only when I have the best available substrate with least surface energy. That means such a substrate does not want to be wetted by water. And at best I can go by making a very low energy substrate is about 120 degrees. I cannot get hydrophobicity larger than 120 degrees, but in the case of the lotus leaf you can observe that you can actually go up to 165 degrees. So, this is what defines my property of super hydrophobicity. In other words super ability to repel water. So, that such a substrate does not want to be wetted by water. So, the question arises how may able to go from a value of 120 degree which is possible purely by low surface energy which is coming from the chemical character of the surface to something like 165 degree. Where in something more is involved obviously it cannot be just the chemical nature of the surface because that can only give you 120 degree. So, what is this which can give you 165 degree we will take up very soon, but this phenomena is absolutely coming because of certain structures at the nano scale. And therefore, not only structures at the nano scale, but we will consider this as a very beautiful example of what is known as a hierarchical structure. So, when we soon talk about hierarchical structure this will be cited as one of the important examples when hierarchical architecture actually gives us the super hydrophobicity. But for now we will just assume that we have super hydrophobicity and this is coming from an hierarchical structure. Where in you have not just low surface energy, but in certain structural contribution which is giving rise to that and soon we will see what is that structural contribution. But from learning from super hydrophobicity we can actually make non-wetting clothes. So, this is very important practical applications we can make self-cleaning windows, non-bio-falling surfaces typically you might have noticed that ships actually have barnacles sticking to them. And therefore, you have to coat these ships with some kind of a paint, but the problem with these paints is that they are sometime very environment non-friendly. That means, they are very bad for the environment and therefore, you do not want to be coating your ships with some of these kind of chemicals. But suppose I have a super hydrophobic surface then there is very little chance that anything sticks to it. Now, suppose I am talking about an application where in certain chemical is being transported in a utensil. Then I would want to empty the entire utensil later on or the vessel without any of the chemical being left. This serves me two purposes of course, when I am going to refill this utensil I do not have to clean it prior to my refilling second thing my gain is 100 percent. In other words, all the chemical I transported can be easily emptied into whatever application for which and actually now in it is now a commercial product that people are actually manufacturing inner surfaces of these vessels which have an architecture very similar to what we have learnt from the lotus leaf. And these are hydrophobic or super hydrophobic surfaces and therefore, they are very very interesting applications when it comes to using the phenomenon of super hydrophobicity. In some sense this can also be called biomimetic materials or biognostic materials wherein we are learning from nature to actually engineer our surfaces to have what you might call low wetting capability. Typically surfaces in the macro scale are either hydrophobic or liophobic. In other words either they repel water or they repel oil, but in nano scale it is there are certain surfaces which have been engineered which are both liophobic and hydrophobic. So, there are these very interesting possibilities when we go to the nano scale materials. One other example which of course, it to some may not be very surprising on new is a concept of super surface activity. Now, we know that when you go to small sizes for a given volume of material the surface energy or the surface area is going to increase. Later on during the lectures we will actually make a calculation to see that for a given volume suppose I reduce my particle size how much of new surface area I am going to create. So, the phenomenon I am talking about here is keeping the volume of a particle constant. So, I consider volume then I split this particle into two particles and further I may want to split this particle into two particles and carry on this chain further and when I go on doing this at some point of time my particle size will become nanometers. Therefore, I am keeping a volume of the particle constant, but I am keeping on dividing the particles just this is of course, the visualization this may not be the way actually the nanoparticles may be actually manufactured, but the essential concept we are dealing with here is for a given volume of material my surface area is increasing and increasing drastically. This increased surface area of course, means that I have a large amount of high interface energy present in the material. Of course, the interface energy is the surface energy because the surface is actually a region of unsatisfied bonds. The bulk of the material suppose I talk about a bonding inside the material taking a particle like this I have a I am just going a pure schematic this is bonded for instance on all sides. So, for instance this could be bonded in some sense with nearest and next nearest neighbors to for instance. So, many of these neighbors. So, it is 1 2 3 4 5 6 7 8 of these, but suppose I add them sitting on the surface may be actually bonded only to a few of them. Therefore, there are these unsatisfied bonds which cause the material energy and this is of course, we know the origin of surface energy this is also the origin of the concept of surface tension. Now, since the surface area is increasing drastically there is a significant amount of energy stored on the surface or available at the surface and therefore, the surface can become extremely active. This highly active surface can actually be used and has actually be used for quite some time for instance in absorption of toxic gases in catalysis etcetera. So, this is for instance we all know that activated charcoal can be used as an adsorption medium for gases and furthermore in when you are talking about for instance an application wherein you are trying to store hydrogen in the solid state for for instance for an transport application this kind of an approach wherein you are increasing the surface area to a large amount helps in actually first of all of course, breaking up the hydrogen into H which can further diffuse into the material and then be stored in the interior of the material. Therefore, this super surface activity is a natural consequence of the presence of a large amount of surface area for a given volume of material. We will return to this topic very frequently of how this increase in surface area is in some sense important and also in some sense the what you may call the least of the expectations we have from a nano material. Additionally, we should note that as we said there are new phenomena which are new when you are talking about nano materials, but we also should note that new functions can be performed using nano materials which otherwise would not be possible. So, essentially we are asking ourselves this question what is new about nano? Why would if somebody comes and tells you that nano always existed we have to conquer with him, but also we have to point out to him that there are new functions, there are new phenomena, there are new applications and new devices which otherwise have no classical counterpart. So, some of these functions rely on the effects which we have described before. We will take a few examples to illustrate the what you may call the power of nano materials and the nano technology which has come from the use of nano materials. Most of this is targeted drug delivery, nano particles can be loaded with a specific sensor and for instance a drug molecule. So, this is now as what you may call a smart nano particle. The drug can be transported to the required side through the blood stream and if you are talking about a magnetic nano particle, an external magnetic field can be assisted to bring this particle which is now be noted with loaded with not only a sensor, but also the drug molecule too very close to the tissue which has been affected. On detection of the affected tissue or cells or area by the functionalized surface group, the drug is released locally to the desired target. So, now there are three components to this whole process, but let us first look at the benefits of doing. So, when you are doing a targeted drug delivery obviously you do not have to over saturate the system the entire body with a lot of drug. So, you save on the amount of drug present you may end up actually having lot of side effects. If this drug is put into the general system and you can avoid side effects by making the drug only go to the specific location where you want the drug to be delivered. The amount of as I said there can be saving in the amount of drug which can be used and further you may want to give only a very specific amount of drug and as the sensor may tell you that if the drug may not be required throughout it may be required during specific times and only when the drug is required we can actually deliver the drug. Therefore, we make it side specific quantity specific and also time specific. So, this is possible by using what you may call as smart nano material where in the nano particle has been functionalized and we will talk a little more about functionalization soon. And the nano particle is what you may call empowered with a sensor and also the treatment drug molecule. So, now this is a beautiful example and already lot of field trials are going on to use this concept of targeted drug delivery and the future we are going to find that more and more drugs are going to be delivered in a very specific side specific manner or we going to have more and more of targeted drug delivery which is going to be what you might call helpful for both the curing of the drug what curing of the disease and also in avoiding the side effects which come from saturating the system with lot of this drug. So, this is actually a very beautiful application of nano materials in the field of medicine and as I pointed out there could two levels at which this side specificity could be obtained. One is the particle itself sensing a specific area, but the second before that we can actually take this particle to the specific area by for instance use of an external magnetic field if the particle is made magnetic. So, my nano particle is now becoming a smart device all by itself which is now not only empowered with the sensor, but also empowered with the treatment method. We have already seen this example of achieving super hydrophobic surfaces that means we can actually get anti bio falling surfaces and we will soon see when we talk a little more deep rail that this super hydrophobicity actually comes from certain kind of roughness which is now in the nano scale and this can be used for making coatings which are which repel or do not allow the growth of fungus and algae. So, this is a nice another applications and these functions will not be able we will not achieve these functions by use of conventional coatings on surfaces therefore, we have to rely on nano structured or nano structures on the surface. One other interesting application is the emergence of transparent ceramics typically if you take a ceramic like zirconia or alumina you would notice that it is opaque. Alumina for instance can become opaque because of the fact that there are porosities and defects in the poly crystalline alumina which include the grain boundaries and these grain boundaries and porosities have a length scale which is comparable to the wave length of the incident light. Therefore, this scattering of light arising from these defects which is now my grain boundaries and porosity within the material is now impeding or making this material opaque. If by suitable processing which will shall see soon what kind of suitable processing can take up we can actually reduce the defects in the material and this happens when you actually produce a few nanometers grain sized ceramic we can actually get what is known as a transparent ceramic. So, again we have to rely on nanomaterials or nanotechnology for the making these transparent ceramics and a typical as you can see the typical alumina sample is actually opaque. Now, what are the uses of this transparent ceramic we will see very very soon that how this transparent ceramic can perform roles which are otherwise not possible with conventional lenses made out of normal glasses. We had already pointed out that the increased surface area also means that we are going to get a high amount of what you might call ability to for a material to perform like a catalyst. The startling example is the case of gold gold in its macro scale does not have any catalytic role typically, but suppose I am talking about gold in the nano scale and if I am specifically considering say gold in the nano scale embedded for instance in an Fe 2 O 3 kind of a substrate then you would notice that gold which is otherwise does not show any catalytic property turns into a good catalyst and actually gets lot of specificity in the kind of process that can be controlled with this kind of a catalyst if reduced to the nano scale. So, surface activity of nano particles is enhanced many fold sometimes a few orders of magnitude and this is because of the increased surface area available to react as we go down in size which is what we noted when you are trying to divide a particle into smaller and smaller sizes and the unsatisfied bonds lead to instability of nano particle itself since the synergistic effects of a combination of enhance surface and high energy associated with nano particles enhances their catalytic activity drastically. Therefore, if I have a catalyst which is performing a certain role in the bulk state if I now make it in the nano scale then I definitely have a chance of increasing its catalytic activity by a few orders of magnitude and the startling example as I pointed out there are cases where the normal material or the bulk material is not does not show any catalytic activity, but when reduced nano scale in the case of gold for instance it assumes a catalytic role that to a very important catalytic role. We already have seen an example of how functionalization is very important and this we saw in the case of what you meant called taking a nano particle and functionalizing its surface with the an attaching for instance a drug molecule. Functionalization is the addition of one or more functional groups on the surface of a material or particle in this current context and usually the surface modification is achieved by chemical synthesis methods to impart certain properties to the surface. For example, we can enhance the affinity of the surface for a particular species to make the surface water repellent. It is easier to functionalize nano particles as a process higher surface activity functionalize nano particles find applications in rapid catalysis targeted drug delivery sensors etcetera. So, therefore, functionalization is much more what you call in feasible because of the presence of this highly active surfaces and now I can not only load my part nano particle with one kind of functional molecule, but I can use multiple functional molecules which can perform multiple roles. And therefore, I may have actually achieved multiple task in a single with a single nano particle. So, what kind of devices can I envisage using the some of the effects and some of the what you might call the process that we have seen just now that is what we are going to consider next. A huge variety of devices and products are already in the market many more on the way and as you can see that they are what you might say they are filling into lot of niche areas where conventional materials cannot solve our problems. One example is nano porous membrane filters we already seen that an example of how we can make a nano porous material which is in hybrid of matter and air or matter and vacuum. And such membrane filters can see about harmful bacteria and are permeable only to molecules which can pass through the nano porous membrane. In other words I may want to see what particularly harmful species like bacteria, but want other molecules to pass through these membrane and I can actually make a membrane which is just this dual role of keeping out bacteria and allowing the important molecules to pass through. And these have been utilized in actually filtering water to get bacteria free water. Another nice example is the production of sanitizing washing machine. So, here the washing or the washing process is has a dual role and this in fact has this kind of sanitizing washing machine is now commercial available in the market. And I think more than one company is producing such kind of sanitizing washing machine. And in this basically during the wash two things are happening of course, we are getting rid of dirt, but additionally we are also having an antibacterial effect which is coming from the washing. This is achieved by actually having silver nanoparticles in the interior surface of the washing machine. And this silver nanoparticles release billions of silver ions during the wash. And these silver ions have an antibacterial property which not which kills the bacteria present in the fabrics. Therefore, now I have a fabric which is not only clean of dirt, but also clean of bacteria. So, this is a nice commercial product which is now available in the market. Where in the well known principles for instance the toxicity of silver ions to bacteria. And the fact that large surface area provided by the nanoparticles can actually help this release of silver ions have been put together to produce something very useful and common which can be found in every house. We have already seen the example of non wetting clothing. And we always want non wetting clothing because we do not for instance in when you are wearing a coat you do not want certain spills to get into the coat which could be harmful for the coat or you know come into contact with the skin. And the beautiful thing about is that these nanoparticles which are embedded in these kind of fabric are transparent and invisible to the eye. Therefore, they do not in any way alter the look or the texture of the fabric and it is basically done by coating nanoparticles to the fabric. And even in a common application for instance suppose I pour some coffee into a trousseau made of such a material then the coffee will not penetrate the cloth and actually flow away. And therefore, this has applications from very specific applications wherein you want the coat to be resistant to acids and other kind of very harmful chemicals to very common application wherein you do not want to get hot scalding coffee into your skin. We already seen one example of a nanoscale sensor, but the general area of sensors and especially biological sensors nanoscale materials are making serious in roads because now the amount of material I need to actually make a sensor. And number two the amount of material which can be detected by the sensor is very very small. Therefore, I can now detect those concentrations of for instance very harmful molecule like carbon monoxide. Though carbon monoxide by itself is not toxic, but it actually deprives the human system of oxygen. In fact it potentially bonds with hemoglobin and therefore, you get carboxy hemoglobin instead of oxy hemoglobin. And therefore, your blood could be deprived of oxygen which is very bad for us. And I am suppose I want to detect carbon monoxide in the atmosphere. I can use surface functionalized nanoparticles which can now have a sensitivity which is much higher than that if I were to use some conventional kind of a detector. And if this were connected to a complete device wherein the change in the potential of the surface potential of the nanoparticle can be detected, this can set off an alarm and this alarm can tell us that the carbon monoxide levels in the atmosphere is succeeded what you might call a leak which is now can be fatal. And therefore, I can avoid you know there is an evacuation procedure or a certain kind of remedial procedure can be detected. Another such example of an important detection would be to detect for instance acetone in the breath of a patient. So, suppose I see that there is acetone then this could be a sign of an impending diabetes or the presence of diabetes. And this can lead to an early detection in a patient and also therefore, I can take lot of preventive or curative measures which can actually help us to you know before the disease spreads to a large extent wherein it can no longer be treated effectively. So, the area of sensors holds lot of promise wherein when it comes to detection of gaseous molecules, molecules in solution which typically can be harmful or can be assigned for certain kind of diseases in living beings. We had already talked about this a little bit that how we can make transparent ceramics. These transparent ceramics can actually be put to fantastic use by making scratch resistant lenses. Suppose, I am talking about an aerospace application wherein I need a lens which of course, we know that in aerospace applications if I am talking about outer space cannot be service if there is a scratch in the lens it cannot be easily replace. Then I need a kind of lens which is wear assisted optically transparent and additionally has good hardness and fracture toughness. So, that any kind of an impact which is occurring in outer space or during the application cannot destroy my lens and normal glasses as you know are very brittle they easily fracture. And therefore, making a lens out of a normal glass is not a very good idea when it comes to outer space applications. Now, we can actually produce this transparent alumina ceramic lenses which is produced by spark plasma sintering fully dense pellets. And this transparent ceramics can be used to make a lenses which have superior strength high hardness and good thermal shock resistance. This thermal shock resistance as you may appreciate is also very important outer space because if my for instance the lens is facing the sun side or facing the other side the temperature difference could be large. And therefore, if I have additional thermal shock resistance this helps in making a good kind of a lens for outer space applications. So, in some sense these scratch resistant lenses are in a perfect lens which would I would like to incorporate in an what you may call an optical system especially for good high end applications. Another example which is just an extension of the phenomena we just encountered. We had encountered the phenomena of giant magnitude resistance and spin valves can be made using this concept of giant magnitude resistance. An applied magnetic field can be used to switch the material showing GMR effect from a high resistance state to a low resistance state and this is what we had just seen. This very effect of showing giant magnitude resistance also means that the device behaves like a spin valve. In other words if I have a material a multi layer which is now showing my giant magnitude resistance and I am talking about a state wherein the two layers bottom and bottom layer with the ferromagnetic layers are ferromagnetically coupled. Then if I have electron spins with this kind of a spin electron this will pass through. On the other hand suppose I switch off my magnetic field then I get into a state which we had drawn before wherein my spins are anti ferromagnetically coupled. So, this is in the presence of a magnetic field B and this is in the absence of magnetic field B and in the state this electron will tend to get scattered from the second layer which is now opposite in spin compared to the spin of the electron. Therefore, I can selectively now control the kind of spin which passes through. I can switch on here or switch off the passage of electrons by using the fact that now I have a spin dependent electron scattering and this is done by switching on and switching off the magnetic field. Therefore, I have a valve for spins and therefore, this is effectively a spin valve which now allows only spin of certain kind to go through. Therefore, now I can use spin valve itself for instance in making what is known as a spin valve transistors wherein silicon is used as a emitter and collector. This can also be used in the direction of magnetic fields especially of low magnitude. Therefore, I can see that when I have a giant magnet resistance effect this can be actually treated like an effectively like a spin valve and this spin valve can be used to make nice devices like a magnetic field detector. This whole concept of a spin valve and giant magnet resistance has occurred in fact entire area which is can be called spin tronics wherein you do spin transport electronics or magneto electronics. In spin tronics instead of now playing with charge of the electron we are actually playing with the spin of the electron. And of course when I am talking about spin I am talking about the associated magnetic moment which comes from the angular moment vector. In this we use a spin of the electron is utilized along with of course, the usual charge because electron is always associated with charge in the fabrication of solid state devices. Spin dependent electron transport is the heart of such devices that means now I am controlling my passage of electron relying on the property of spin apart from the fact that of course, it will be transporting charge. And spin polarized electrical injection has been used in the conduction in the construction of semiconducting lasers. So, this is already found application wherein you are using spin polarized electrical injection to make a laser which is a semiconducting lasers. Spin based transistors also been envisaged as we saw in the previous application. So, therefore when you are dwelling in the realm of nano materials and nano structures we see that we not only can deal with the charge of an electron we can actually control the spin of an electron. We can make devices which specifically deal with the spin of an electron and therefore, we can have an entire new field which has come up which is the field of spin tronics. So, there is an overall benefit to all these effects and all these things and we will this half of which I am going to list here is going to come actually come from what you might call as societal application or an application from policy. So, let us