Hello and welcome to the Methods of Surface Analysis video course. First of all I wanted to talk about why… why we talk about surface, why we… why don't we talk about methods of may be solid body analysis. Of course, there is such a course may be… But we talk about methods of surface analysis. And why? Well, because surface is the interface between any kind of impact on a solid body. Everything you do to a solid body goes through the surface. So, by analyzing the surface and its state we can tell its story, what happens to our sample. Whether this may be the mechanical impact or some kind of particle irradiation, electron, ion irradiation or any kind of photon irradiation, visible, X-ray irradiation. Everything goes through the surface. So if we analyze the surface, we can tell what happened to the sample and what it can tell to us. And, of course, not always when we talk about surface, we mean an infinite thickness, zero thickness layer — atop of the sample. Sometimes we mean the finite thickness, whether it could be 10 nanometers or several microns or even millimeter, this could be. But scientists tend to talk about surface when we talk about these layers. So what can we know about the sample when we analyze the surface? Well, first of all, that’s obvious, we can talk about surface relief — surface morphology, how does it look like. And of course, we talk about composition of the sample. When we talk about composition, that's when we talk about some finite thickness of the surface. And many other characteristics can be known about the surface. There are hundreds of them: mechanical characteristics, hardness, friction, roughness, corrosion characteristics, chemical characteristics, all of them, electrical characteristics, conductivity, and so on. But these are so-called special characteristics. We, of course, will talk about them, but mostly when we talk about surface analysis techniques we will talk about techniques that tell us information about surface relief and surface composition. So how do we get the information about the surface? Of course, we must provide some kind of impact on the surface and get the so-called answer from the surface. So we can talk about question-and-answer. And they can be in the very different forms. This could be any kind of a irradiation, any kind of particle irradiation and other impacts like electromagnetic fields and so on. And we could register an answer from the surface in different ways also. And this could be combined in very different ways. I've drawn some arrows here just for example, but in reality there are far many of them. So for example you could provide an impact with some kind of radiation. And you get an answer in... for example particles being emitted from the surface. But… Again I want to stress that there are hundreds or even thousands of possibilities here. If you look through the just the Internet, through the lists of methods of surface analysis, you get may be this kind of a list. But you must not be afraid, because there are not so many basic branches of methods. These are all variations. And they all come from maybe tens of basic methods. And that's what we are going to talk about. But anyway why so many methods? Why there are so many? Well, because researchers, they tune and modify methods according to their needs. And if they modify them sufficiently this could give way to development of a new method. And it will be included in that list and that’s how they come to life. And it's common that in one device several methods are realized, because some of them are quite close to each other. And they require similar devices to be realized. So it's very common to have several methods to be realized in one device. And, of course, none of them are perfect. There is none… no such a perfect method for any kind of research, of course. Every method has its pros and cons. Some is better for this kind of study and some for another kind of study. They have their own drawbacks and advantages. And that's what we are going to talk about also. Every method is a compromise. Maybe the biggest compromise is the compromise between sensitivity, composition sensitivity, and analytical spot size. I'm talking about the actual spot size you're analyzing in the area of this sample. So, on this graph we have areas and each method has its own area in the terms of spot size and composition sensitivity. So, on the x-axis we have the spot size and on the y-axis we have the composition sensitivity. And it goes… The scale is logarithmic as you can see. So on the top there we have a hundred percent and on the bottom you have 10 ppt. What's that? If you know, you may know ppm (it's on the upper part of the axis). That 100 ppm, 10 ppm — that’s parts-per-million. And if we go lower, we get ppb, which is parts-per-billion. And if we go even lower, we get ppt, which is parts-per-trillion. So that's quite high sensitivity. So for example, if we take one of the methods, for example RBS, we see that the area of RBS is on the top right of the graph. So we can judge that the spot sizes in RBS are about on the order of several millimeters and the composition sensitivity is on the order of at the best 10 ppm. Comparing to other methods presented on this graph, this might seem as not the best method in terms of spot size and composition sensitivity. But it has its own advantages and we will talk about that also. Sure. So in terms of composition sensitivity one might see that the best method is dynamic SIMS. It goes all the way to that ppt figures. And in terms of spot sizes the best is STEM, which goes to several nanometers of spots sizes. But you cannot combine this together and get the best composition sensitivity and the best, the smallest spot size. And the reason is also a physical limit. You can see it on the graph, that diagonal line is a physical limit. Where does it come from? It's quite simple. You are analyzing a some kind of volume on the sample, right? Let's look at this volume as a cylinder. So it has a diameter of the spot size we are analyzing and the depth. It’s unique for each method, the depth we're analyzing. Let's say the diameter is ten nanometers and the height of the cylinder, the thickness we're analyzing is also ten nanometers. We can actually calculate how many atoms there are inside such the cylinder. And actually there are about 10,000 of them inside. So let's say it's a uniform material. And it has an impurity. What is the smallest impurity we could get in such a volume? The smallest impurity is one atom in 10,000 or else we wouldn't see it, right? But one atom in 10,000 gives only the concentration of 0.01 %. We're not talking about ppb, ppm and so on. If the impurity composition is lower than 0.01 %, by analyzing such volume, we either won't get any inside. Or if we are lucky we may get one atom in 10,000, and that will give us 0.01 % impunity. So that's it, that's where the physical limit comes from. And we can see that some of the methods are quite close to this border. So, we can say that they're almost perfect, they go up to the physical limit. So yes, all the methods have a different thickness they analyze. In this chart we have some representation of that. We will talk about each method for sure. But just for now you can see that they vary in great orders from several nanometers to thousands of microns. So what we will learn in this course? In this course we will look through the most basic and fundamental methods of surface analysis. We will learn how are they realized, what are their actual structural components in these methods, how do they work, what they can give us, what they cannot give us – which information, the basic features, abilities, advantages and drawbacks, strong and weak sides. And of course in each method we will look at the results interpretation. So when you look at the graph you obtain from any kind of methods. What information do you get, which is, what is true, what is arguable and how to interpret that? Well that's it. So let's go on to our first method.