Week 1: Introduction to Nanotechnology, Part 1

1.1

Hello my name is Hossam Haick and I will serve as the lecturer of the MOOC course on nanotechnology and nanosensors. I wish you a successful course on the great journey into the amazing world of nanotechnology and nanosensors. Today I will make an introduction to the field of nantechnology. I will start with defining the main phrases that include the word nano. Then I will present the main and unique features of the materials and technologies that exist at the nanoscale level. I will end this topic by making a generic presentation of the main categories of the materials that exist at the nanoscale level. The prefix nano is derived from the ancient Greek nanos, which means dwarf. Today, nano is used as a prefix that means, billionth or a factor of 10 to the minus 9. Coupling the word nano with the unit meter brings the term nanometer, which actually indicates a unit of spatial measurement that is one billionth of a meter. With this in mind, we shall define nanotechnology as the science, engineering, and technology conducted at the scale that ranges between one to 100 nanometers. The idea and the concept behind the nanotechnology started with a talk entitled, There is Plenty of Room at the Bottom, by the physicist Richard Feynman, at the American Physical Society meeting, at the California Institute of Technology, CalTech, in a meeting that was held in 1959. In his talk, Feynman described a process in which scientists would be able to manipulate and control individual atoms as well as individual molecules. Over a decade later, Professor Norio Taniguchi coined the term nanotechnology during his explorations and research in the field of ultra precise machining process. However, practicing the modern nanotechnology began only in 1981, when the scanning tunneling microscope, which basically could see individual atoms or could see individual molecules, was developed and used. To demonstrate the length of scale of the nanometer, I will present first the units or measures used in our daily life. If we cut a meter into 100 equal pieces, then each piece would be one centimeter in size. This is equivalent to the size of your pinky finger or a sugar cube. If we cut a centimeter into 100 equal pieces, each piece will be one millimeter. A cent coin is approximately one millimeter thick, and a grain of sand ranges from 0.1 millimeter to 2 millimeter in size. Objects as small as millimeter can be seen with our own eyes. However, when things get smaller than a millimeter, it gets harder and harder to see them with just our eyes. If we cut up a millimeter into 100 equal pieces, each piece will be a micrometer. In other words, a micrometer is equal to one millionth of the meter. For example, the diameter of hair is about 40 to 50 micrometers wide, red blood cells are six to ten micrometers in diameter and many types of bacteria typically measure five to 20 micrometers in diameter or in size. Things on this scale usually cannot be seen with our own eyes, but rather, can be seen with a magnifying glass or with a microscope. If we cut a micrometer, now, into 1,000 equal pieces, then each piece will be one nanometer. In other words, a nanometer is equal to one billionth of a meter. When things are as small as the nanometer you cannot see them with your own eyes, or even you cannot see them with a light microscope. Objects this small require special tools of imaging. Things that have a nanometer scale include viruses which have a characteristic size of 30 to 50 nanometer. DNA, which have a diameter of one to two nanometer. Buckyballs with have a characteristic size or diameter of one nanometer. And also carbon nanotubes which have a characteristic diameter of one nanometer. In this context I would like to clarify that atoms are smaller than a nanometer. Actually, one atom measures 0.1 to 0.3 nanometer, and this, of course, depends on the element that is examined. Now I will give you some examples for objects from our daily life that are measured in nanometer. One inch is equal to 25.4 million nanometers, and a sheet of paper is about 100,000 nanometers think. A human hair measures roughly 50,000 to 100,000 nanometers in diameter, and please note that your fingernails grows one nanometer every second. It is acceptable that a picture is worth 1,000 of words, and that a video is worth thousand of pictures. Therefore, our, I will add with the presented short video to further demonstrate the meaning of nano. Of course, I will give the girl in the video the privilege to talk on her behalf. [MUSIC] >> Hey. Do you know what nano means? It means small, very small. It is a million times smaller than the smallest measure on a ruler. If you want to get an idea for how small a nanometer really is, you'll need to take a piece of hair from your head. Go on, it won't hurt. Got it. Now, take a good, close look at that strand of hair. Not much to look at, is it? If we were to shrink you down, smaller than the smallest thing you can see with the naked eye, you will find that your piece of hair starts to look a lot more interesting. You are now about the size of a red blood cell. Your strand of hair is a massive tree compared to you. Even at this size, you're still about 1000 times too big to be considered nano. To get you down to the nano scale, we will have to shrink you to about 100 nanometers tall. Hey, where are all the lights? You are now smaller than the wavelength of visible light. You are practically invisible. But for the sake of demonstration, I think we should turn on some lights. At this size, the red blood cell is 1,000 times bigger than you are. It is like an enormous stadium. Welcome to the nanoscale. You could probably hold the common cold virus in your hands quite comfortably now. The rhinovirus is only about 30 nanometers across, and is nearly impossible to see next to the red blood cell. A red blood cell is too big to be considered nano. However, it's made up of all kinds of nanomaterials. If you were to look close enough, you would see that the outer walls of the cell are stabilized by a flexible mesh-like protein skeleton. The bars and connectors that make up this mesh are considered part of a nanomaterial. Without these reinforcing nanostructures, the cell would be much more fragile, and not nearly as flexible. It wouldn't stand a chance in your body. Everything is made up of nanomaterials. Nanomaterials are an arrangement of molecules and atoms that, when combined create stable building blocks that can be made into larger, more complex materials and structures. >> After this demonstration I will give right now an example for the importance of miniaturization ability of the nanotechnology. A such example, let's have a look on how cell phones developed from the bulky walkie talkie to today's miniaturized architecture. In 1985 mobile phones used to look huge in size and with a pretty long antenna. On the other hand in present we have the smartphones which are becoming a computer, GPS, radio, and actually our lifeline to the Internet. And to still be able to fit our pockets. With the help of nanotechnology, mobile phones will be further evolved in terms of their performance, and features. And would include for example, augmented reality, flexible screens, in built projector, seamless voice control, three-dimensional screens and holograms, and of course it might include also remote medical diagnosis features and many, many more features. Nanotechnology in one sense is the natural continuation of the evolution that we have witnessed over the last decade. Where millionth of a meter electronics, which we call usually micro electronics, became commonplace. Thus enabling the construction of higher quality of materials and devices and many more applications on equivalent or even smaller areas than we have knew previously. So far, the miniaturization ability of the microelectronics allow the integration or placement of thousands of chips into an equivalent area. Further miniaturization with the help of nanotechnology would allow putting millions of currently available electronic devices over an area that is less that few millimeters over few millimeters. In a constituent example, a team from the Technion Israel Institute of Technology leveraged the power of nanotechnology to engrave all the content of the Old Testament on a piece of silicon that is less than one millimeter by one millimeter, as could be seen by the image in the bottom right of the screen. One of the parameters that is directly connected with the miniaturization and nano technology is termed surface to volume ratio. This parameter is of fundamental importance in the applications involving chemical catalysis and nucleation of physical processes. Usually, surface area to volume ratio increases with a decrease in characteristic dimensions of the material, and vice versa. Therefore as the material size decreases, a greater portion of the atoms are found on the surface compared to those found in the bulk or inside the same material. As growth and catalytic chemical reaction occurs at the surfaces, therefore a given mass of nanomaterial will be much more reactive than the same mass of material made up of larger particles. It is also found that materials which are inert in their bulk from form a reactive when produced in their nanoscale form. And therefore they can improve their properties. To demonstrate the relationship between the miniaturization of the materials and the surface to volume ratio, let's consider a cube made of a silicon with a characteristic size of ten nanometers. In this case, the number of the unit cells in this nanocube is estimated by 6,250, which is actually equivalent to to fif, to 50,000 atoms. On the other hand, the number of the unit cells that are located on each face is 340, thus resulting in 680 atoms on each face of the nanocube, and 4,080 atoms on all faces of the nanocube. Dividing the number of the atoms available on the surface of the nanocube, namely 4080 atoms, by the number of the atoms available in all parts of the nanocube, which is basically 50,000 atoms, brings to the conclusion that around 10% of the atoms in the nanocube are located on the surface. On the other hand if we applied a similar consideration with a piece of silicon of ten square centimeters and the thickness of one micrometer. This leads to the conclusion that only 0.03% of the silicon atoms in this structure are available on the surface. Therefore, nanomaterials have a much greater surface area per unit volume compared with the larger particles. Actually this leads to nanoparticles that are more chemically reactive. This is so because the molecules at the surface of the material don't have full allocation of covalent bonds and are in energetically unstable states. Since many more molecules are located on the surface are in energetically unstable states, nanomaterials are more reactive compared to the microscale or to the macroscale materials. With the higher reactivity almost all types of nanomaterials are capable of catalyzing reactions and free nanomaterials tend to agglomerate into bigger particles. On to the specific physical and chemical properties of the nanoparticles there are expect, expected to interact with substances such as proteins, lipids, carbohydrates, and nucleic acids that present in food, biological, or during desalination processes. Other applications of such feature include drug delivery, clothing insulation, and many, many more. With this, we come now to the end of class number one, session number one. Thank you.

1.2

Welcome to class number 1, session number 2. A nanostructure is an object that have at least one dimension in the range of 1 to 100 nanometers. In describing nanostructures, it is needed to differentiate between the number of dimensions on the, on the nanoscale. Nanoclusters are structures that are 1 to 100 nanometer in each spacial dimension. These structures are categorized as zero dimensional nanostructures. Nanocubes and nanowires have a characteristic diameter between 1 and 100 nanometers. And the length that could be much greater than that. These structures are categorized as one-dimensional nanostructures. Nanocomposite surfaces or thin films have a thickness between 1 and 100 nanometers, while the other two dimensions are much greater. These structures are categorized as two-dimensional complex materials. Finally, bulk materials with all dimensions above 100 nanometer, but that contain zero dimension or one dimension, and or two-dimensional nanostructures are termed three-dimensional nanostructures. We will describe each of these nanostructure in more details in the next sessions. We will start now with defining a zero dimensional nanostructure, which include basically, the nanoparticles and the quantum dots. Nanoparticles are defined as small objects that are sized between 1 and 100 nanometers, and that behave as a whole unit with respect to its transport properties. Nanoparticles are size dependent. Namely, the properties of the materials change as their size approaches the nano scale, and as the percentage of the atoms at the surface of the material becomes significant. The interesting and the unexpected properties of the nanoparticles are therefore significantly due to the large surface area of the material, which dominates the contributions by, made by the small bulk of the material. For the sake of comparison, bulk materials, mainly particles larger than one micrometer, contain insignificant percentage of atoms at the surface in relation to the number of atoms in the bulk of the same material. And therefore they don't behave or exhibit size dependent changes in their physical properties. Nano-particles often posses unexpected optical properties as they are small enough to confine their electrons and produce quantum effects. Besides the pendant color of the nano-particles was utilized though without any intention by artists as far as the 9th Century for generating a glittering effects on the surface of spots or colors in stained glass. The unique physical properties of the nanoparticles allow much higher absorption of solar radiation in photodyetic cells that are composed of nanoparticles than in thin films of continuous sheets, even that is composed from the same material. Other size dependent properties change include, quantum confinement in semiconductor particles, surface plasma resonance in some metal nanoparticles, and chemical reactivity that are utilized for image formation in photography field. Now, from the zero dimensional nanostructures, we will move to one dimensional structures which include among the rest nanowires, quantum wires, nanorods and nanotubes. A nanowire is a nanostructure with a diameter of the order of nanometer. Alternatively, nanowires can be defined as structures that are having a thickness or a diameter constraint to tens of nanometers or less, and unconstrained length. These scales quantum mechanical effects are important, and therefore they are coined the term quantum wires. Many different types of nanowires exist. These include of course metallic nanowires, semi-conducting nanowires, and insulating nanowires. More details about each of these nanowires could be seen on the slide, and we will explain about these in the next lectures. On the other hand, molecular nanowires are composed of repeating molecular units. Either organic, for example DNA, or inorganic material. New forms of nanowires include coaxial super lattices nanowires, as seen in the bottom figure in this slide. Nanowires have two quantum confined directions while still leaving one unconfined direction for electrical conduction. Basically, this feature allows the nanowire to be used in applications where electrical induction is required. And because of their unique density of electron states, nanowires in the limit of small diameters are expected to exhibit significantly different optical, electrical and magnetic properties from their both three-dimensional crystalline counterparts. We will move now, right now to the carbon nanotubes. Carbon nanotubes are a long whole structure with the walls formed by one atom thick sheet of carbon, which we call usually in the scientific literature, graphene. These sheets are rolled at specific and discreet chiral angles. And the combination of the rolling angle and the radius decides the nanotube properties. Individual nanotubes naturally align themselves into ropes held together by the so-called Van der Waals forces, or more specifically pi-stacking. Usually, the end of the carbon nanotube end with half buckyball like carbon structure. Carbon nanotubes have unusual properties which are valuable for the nanotechnology, electronics, opitcs and other fields of materials science and technology. In particular, onto their extra ordinary thermal conductivity and mechanical, and electrical properties, carbon nanotubes find applications as additives to various structural materials. For instance, nanotubes form a tiny portion of the material in some of their carbon fiber, baseball bats, gold clubs, or car parts. An inorganic nanotube is often composed of metal oxides. Inorganic nanotubes show various advantages such as easy synthetic ax, access, and high crystallinity, good uniformity and dispersion, predefined electrical conductivity, good adhesion to a number of polymers, and high impact resistance. These materials are therefore promising candidates as filters for polymer composites with ev-, eh, with enhanced thermal, mechanical and electrical properties. Inorganic nanotubes are heavier than the carbonyltube, which was, have explained in the last slide. And therefore they don't, have a strong sickness under tensile stress, but they are particularly strong under compression, thus leading to potential applications in impact resistant applications such as [INAUDIBLE] visits. Two representative examples of inorganic nanotubes include, as could be seen on the slide, boron nitride nanotubes. This case, for example, or this material, have a high resistance to oxidation suited for high temperature. It has also Young modulus of 1.22 Terapascal. It's also behave as a secu, semiconducting material. And of course the electronic properties of this material are predictable. And on the other hand, I would represent on the same slide an example on the Silicon Carbon nanotubes, which have also high resistance to oxidation and it's quite suitable for harsh environments, and can be functionalized with organic modulars on their surfaces. With this we come now to the end of class number one, session number two. Thank you.

1.3

Welcome to class number 1, session number 3. In this session, we will continue what we have already started in session number two of class number one. Two-dimensional structures include thin films, planar quantum well, and super lattices as could be seen on the screen. As a representative example of thin film, please have a look on scanning tunneling microscope image of a self assembled monomer of [UNKNOWN] on gold surface. As seen in the image, the individual molecules closely packed into hexagonal array. Also, besides that, one can see clearly the features of the assembly and the surface. Namely, one can see the main boundaries which are highlighted with light blue strips on the figure. And one can see also goldbeckansie islands, which can be seen as circular blue spots. In the lower image of the screen, you can see a transmission electromicroscope image of a superlattice, where alternate layers of two different materials exist. In this context, please note that the thickness of each layer is only two nanometer in thickness. One of the major groups in two dimensional structures is thin film. Namely, two dimensional film with a thickness that range between 1 to 100 nanometer. When films are very thin, their electronic and optical properties deviate substantially from those of the bulk material. As the material is miniaturized towards the nano scale, the confining dimension that surely decreases, but the characteristics are no longer average by the bulk. The energy spectrum becomes in this case discreet, and measured by quanta rather than continuous as in the bulk materials. The confinement of the electrons that exist in these systems change their interaction with the electromagnetic radiation significantly. Electrons are confined in the direction that is perpendicular to the substrate, and thus affect the wave function as well as the density of the states. Similarly, phonons that are confined in the direction that is perpendicular to the substrate affect therefore the thermal property. All transport phenomena in the two dimensional structures are highly affected by the fixed boundaries and interfaces that might exist in or at the vicinity of the thin film. More details about all of these effects will be given in the next classes. Now, we will move to the three-dimensional structure, which include bulk nanocrystalline, as well as nanocomposites. Nanostructured bulk materials include several sub-categories, which are Mentioned in the following. The first subcategory is a crystalline materials. In this category, the atoms molecules, or ions, which make up a material are arranged in an orderly repeating pattern. In some cases, the regular ordering can continue unbroken over a large scale. Such as in the example of diamonds where each diamond is only single crystal. The second subcategory is called polycrystaline materials. Salt objects that are large enough to see and to handle, are rarely composed of single material. But instead are made of large number of singular crystals known as crystalites whose size can very from a few nanometers to several meters. Such materials are called polycrystalline as mentioned previously. Almost all common metals and many ceramics are fully crystalline in their properties. The third subcategory of this material is called amorphous materials. This category, which we call also nano-crystalline solid, is a solid that lacks the long range order characteristic of a crystalline. Indeed, amorphous materials have some short range order at the atomic length scale due to the nature of chemical bonding. Such solids include, amongst the rest, glass, plastic, and gel. Now, we will move to the nano-composites. A nanocomposite is a multiphase solid material where one of the phase has one, two, or three dimensions of less than 100 nanometer. In the broadest sense, this definition is more usually taken to mean the solid combination of a belt matrix and nanodimenstional phase differing in properties due to these similarities in structure and chemistry. The mechanical electrical, thermal, optical, electrochemical catalytic properties of the nanocomposite differ quite significantly from those of the component material. Size limits for these effects have been proposed in the scientific literature and include amongst the rest the following. Composites with less than five nano-meter, nano-materials are designated for catalytic activity. Composites with less than 20 nanometer nanomaterials are designated for making hard magnetic material. And composites with less than 50 nanometer nanomaterials are designated for refractive index changes. And finally, a composite with less than 100 nanometer nanomaterials are designated for achieving mechanical strengthened or restricting matrix dislocation movement. Nanocomposites might include combinations of organic material and organic material. It also can include a combination of organic and inorganic material. And finally, it can include a combination of inorganic and inorganic materials. This large amount of reinforcement surface area means that a relatively small amount of nanoscale reinforcement can have an observable effect on the microscale properties of the composite. For example, adding carbon nanotubes improves the electrical and thermal conductivity. Other kinds of nanoparticulates may result in enhanced optical properties, dielectrical properties, heat resistance, or mechanical properties such as stiffness, strength, and resistance to ware and damage. We will come now to the end of class number one session number three. Thank you.

Question 3 ( 1.8 billon)

Question 7 ( 1-D)

Question 11 (increases)