The Nano materials - Basic Introductions

Nano material

1. 1 Nano-materials ( Unit-4 Engineering Physics) Dr. Shyam Sunder Sharma Department of Physics (H & S) Women Engineering College, Ajmer- 305002, India (An Autonomous Institute of Govt. of Rajasthan) [email protected]

2. Nano-materials: Significance of nanoscale Properties of nanomaterials Basics of Synthesis of nanomaterials: top-down and bottom-up approach Applications of nanomaterials Topics to be covered:

3. Nano-science is the study of structures and materials at atomic and molecular scales , where properties differ significantly from those at a larger scale. Nanotechnology is the design, characterization , production and application of structures, devices and systems by controlling shape and size at nanometre scale. When the material size of the object is reduced to nanoscale, then it exhibits different properties than the same material in bulk form.

4. The word nano technology is relatively new, the existence of nanostructures and nano-devices is not new. Such structures existed on the earth as life itself. Although it is not known when humans began to use nanosized materials, the first known, Roman glassmakers were fabricated glasses containing nanosized metals. Richard Feynman is considered as the Father of modern day Nanotechnology. In 1959, he delivered a lecture in annual meeting of American Physical Society, with title: “ There is a Plenty of Room at the Bottom ”. The focus of his speech was about the field of miniaturization and how he believed man would create increasingly smaller and powerful devices. After fifteen years, Norio Taniguchi, a Japanese scientist was the first to use and define the term “nanotechnology” in 1974. Origin of Nano technology

5. The prefix ‘nano’ is referred to a Greek prefix meaning ‘dwarf’ or something very small and depicts one thousand millionth of a meter. Nanometer (nm) = one billionth of a meter or one thousand millionth of a meter (10 −9  m ). Nanomaterials are commonly defined as materials with an average grain size in the range 1- 100 nm. These have extremely small size which having at least one dimension 100 nm. A human hair is 80,000 nm wide Atoms are extremely small and the diameter of a single atom varies from 0.1 to 0.5 nm depending on the type of the element. For example, one carbon atom is approximately 0.15 nm in diameter and a water molecule is almost 0.3 nm across. A red blood cell is approximately 7,000 nm wide and human hair is 80,000 nm wide.

6. Nanometre scale- DNA 2 nm http:// www.gala-instrumente.de/ images/ deben _ CCD_DNA.jpg

7. Nanostructures Nanoparticles

8. Nanostructures Fullerenes ( buckyballs) and carbon nanotubes (CNTs)

9. Nano materials are materials that have at least one of the dimensions in the range 1- 100 nm . Therefore, Nanomaterials/ Nanostructures are divided into three categories: 0-dimensional (0D)- If all three dimensions of the material are less than 100 nm , such materials are called 0-dimensional nanomaterials such as nanoparticles and quantum dots. 1-dimensional (1D)- I f only two dimensions are less than 100 nm, they are called 1-dimensional nanomaterials such as nanotubes, nanowires and nanorods. 2-dimensional (2D)- If only one dimension is less than 100 nm, it is called 2-dimensional (thin film) nanomaterials such as nanosheets, nanoplates, nanowalls and nanodisks . Nano materials

10. Examples of 0-D Nanomaterials Examples of 1-D Nanomaterials Examples of 2-D Nanomaterials

11. Basic principles of nano materials When the material size of the object is reduced to nanoscale, then it exhibits different properties than the same material in bulk form. The factors that differentiates the nanomaterials form bulk material is Increase in surface area to volume ratio and Quantum confinement effect Increase in surface area to volume ratio The ratio of surface area to volume ratio is large for nano materials. Surface size is larger so a greater amount of the material comes into contact with surrounding materials and increases reactivity. To understand this let us consider a spherical material of radius ‘r’. Then its surface area to volume ratio is 3/r. Due to decrease of r, the ratio increases predominantly.

12. a) Surface to volume area ratio As objects get smaller they have a much greater surface area to volume ratio. Due to increase of surface of surface area, more number of atoms will appear at the surface of compared to those inside. For example, a nano material of size 10 nm has 20% of its atoms on its surface and 4 nm has 50% of its atoms. This makes the nanomaterials more chemically reactive and affects the properties of nano materials. 2 cm 2 cm cube has a surface area of 24 cm 2 and a volume of 8 cm 3 (ratio = 3:1) 10 cm cube has a surface area of 600 cm 2 and a volume of 1000 cm 3 ( ratio = 0.6:1) 10 cm

13. b) Quantum confinement effect In Nano Crystals, the Electronic energy levels are not continuous as in the bulk but are discrete, because of the confinement of the electronic Wave function to the physical dimensions of the particles. This phenomenon is called Quantum confinement and therefore Nanocrystals are also referred to as quantum dots (QDs). 2-D or Quantum Wells: The carriers act as free carriers in a plane. 1-D or Quantum Wires: The carriers are free to move down the direction of the wire, and 0-D or Quantum Dots: Systems in which carriers are confined in all directions (no free carriers ). One of the most direct effects of reducing the size of materials to the nanometer range is the appearance of quantization effects due to the confinement of the movement of electrons. This leads to discrete energy levels depending on the size of the structure. Control over dimensions as well as composition of structures thus makes it possible to tailor material properties to specific applications . Hence, quantum confinement effect affects the optical, electrical and magnetic properties of nanomaterials.

14. Significance of nanoscale When particles are created with dimensions of about 1–100 nanometers, the material’s properties change significantly from those at larger scales. This is the size scale where so-called quantum effects rule the behaviour and properties of particles. Properties of materials are size-dependent in this scale range. Thus, when particle size is made to be nanoscale, properties such as melting point, fluorescence, electrical conductivity, magnetic permeability, and chemical reactivity change as a function of the size of the particle . Thus, the nanoscale has become very significant and important as The quantum mechanical properties of the particles at the nanoscale influence a lot on the physical properties of the particles . By  nanoscale design of the materials it is possible to vary micro and macroscopic properties such as charge capacity, magnetization, melting temperature without changing their chemical composition. Nanoscale components have high surface area to volume ratio making them idle for the use in composite materials, drug delivery and chemical storage.

15. Synthesis of Nanomaterials The nanomaterials can be synthesized in two ways, namely Top-down approach and Bottom –up approach Top-down approach: In this method, the nanomaterials are synthesized by dis-assembling the solids into finer pieces until the particles are in the order of nanometers. Examples: Ball milling, plasma arching , Laser Ablation, Sputtering, Thermal evaporation etc. Bottom-up approach: In this method, the nanomaterials are synthesized by assembling the atoms and molecules together. Examples: Sol-gel method, chemical vapour deposition method, hydrothermal, co-precipitation, solvothermal , Miniemulsion etc.

16. Top-down approach

17. Ball milling Ball milling is a grinding method that grinds nanotubes into extremely fine powders. During the ball milling process, small hard balls are made to continue moving inside a container to being allowed to fall on a solid to crush it into nano crystals with large strength. When the balls are allowed to rotate with particular rpm inside of a container, the necessary energy is transferred to the powder which in turn reduces the powder grain-sized structure to ultrafine or nano range particles . Hard core steel or tungsten carbide balls are placed in a tightly closed container with a powder . At a huge scale, nanoparticles ranging from a few milligrams to several kilograms may be manufactured in a short period of time. Ball method is to prepare a wide range of elemental and oxide powders.

18. Plasma arching method To produce plasma ( an ionized gas), high potential difference is applied across the electrodes. An arc passes from one electrode to another. The gas yields up its electrons and positive ions at anode. Positively charged ions pass to other electrode (cathode) pick up electrons and are deposited to form nano particles . Using this plasma arching method, very thin films of the order of atomic dimensions can be deposited on the surface of an electrode. This deposition is carried in vacuum or in an inert gas. By using carbon electrodes, carbon nanotubes can be formed on the surface of the cathode.

19. Laser ablation The process of removing atom, molecules from solid material by the influence of irradiated Laser beam . It utilizes a thermal or non-thermal process to remove its components, generally a complex process. Thermal decomposition Compound decomposition due to application of heat, forming two or more products from one reactant . It is a first developing procedure for nanomaterial synthesis. Iron oxide formation from iron oxalate complex under heat treatment is an example of thermal decomposition . Sputtering In this process ionized gas molecules accelerated towards the target. Atoms eject from the surface of the target. Generally a physical process.

20. Bottom-up approach

21. Sol-gel Method The sol-gel process is a wet technique i.e., chemical solution deposition technique used for the production of high purity and homogeneous nanomaterials. In solutions ,the molecules of nanometer size are dispersed and move around randomly and hence the solution are clear. In colloids the molecules are suspended in a solvent. When mixed with a liquid is called as sol. A suspension that keeps its shape is called a gel. Thus the colloids are suspensions of colloids in liquids that keep their shape. The formation of sol-gels involves hydrolysis, condensation growth of particles and formation of networks. The sol is then evaporated during the production of an inorganic network containing gel. A drying procedure is followed by calcinations to eliminate the liquid phase from the gel. This is commonly employed in spherical shaped powders, thin film coatings, ceramic fibers, and very porous aerogels, among other purposes. Precursors with high purity, such as metal alkoxides , make it simple to create high-quality, cost-effective materials. The temperature required in the process is low, and no delicate vacuum equipment is necessary. Despite its benefits, the sol-gel technique has certain drawbacks. Due to poor bonding, low wear resistance, high permeability, and difficulty controlling porosity, the sol-gel process is not commonly used in industry.

22. Chemical vapour deposition In chemical vapour deposition is a well known process in which a solid is deposited on a cooled surface via chemical reaction from gas phase. The basic steps involved in this process are (i) Generation of vapour by boiling or subliming a source material (ii) Transformation of the vapour from the source to the substrate and (iii) Condensation of vapour on the cool substrate. In this method, the atoms/molecules are in gases state allowed to react homogenously or heterogeneously depending on the applications. This method is an excellent method which is used to control the particle size, shape and chemical compositions. This method is used to produce the nano powders of oxides and carbides of metals. Production of pure metal powders is also possible using this method.

23. Co-precipitation It is comprised of the following steps: nucleation, growth, coarsening, and agglomeration. Metals , such as nitrates, chlorides, and sulphates , are commonly utilized as reactants in this process. The pH of the resulting homogenous solution is adjusted. The procedure of refluxing is used to convert the solution to precipitate. The precipitate is then cleaned and dried. In comparison to other techniques, co-precipitation is a highly needed after one due to its simplicity. It is characterized by a large applicability for the introduction of dopants, cost effectiveness, and suitability for mass production, in addition to its simplicity. The method of co-precipitation has a number of advantages. The reaction temperature may be reduced due to a homogeneous combination of reactant precipitates. Directly synthesizing thin metal oxide nanoparticles is a simple process. When sintering at low temperatures, the produced nanomaterials are extremely reactive.

24. Hydrothermal Method Water at higher temperature is used in hydrothermal synthesis, which is a component of solvothermal synthesis. When tiny crystals are exposed to high temperatures and pressures, they will homogeneously nucleate and develop from solution. Water serves as a catalyst as well as a solid-state phase component during the nucleation and growth process. Water becomes supercritical under the harsh conditions of the synthesis vessel (autoclave or bomb), enhancing the dissolving power, diffusivity, and mass transport of the liquid by lowering its viscosity. Hydrothermal synthesis is environmentally friendly, affordable, and allows for the lowering of free energy for various equilibriums when compared to other methods.

25. Properties of Nanomaterials Nanomaterials differ from bulk materials in terms of their characteristics. On the other hand, nanoscale materials do not have the same physical properties as bulk materials because of their small dimensions. Some materials have different and distinct properties when decreased to nano dimensions compared to their bulk equivalent. By changing into a nanoparticle, chemical reactivity can be increased or decreased. The majority of nanostructure materials are crystalline, and they have unique properties like surface area to volume ratio and quantum confinement. Surface properties including energy levels, electronic structures, and reactivity can indeed be somewhat unique from within the states, and lend credence to quite different nanomaterial properties .

26. Optical properties of Nanomaterials are influenced by factors for example size, shape, surface area to volume ratio, and other factors such as doping and interaction with the environment. Gold and silver nanoparticles of different size have different color. The colour changes because each colour has a specific wavelength . Different sized nano particles scatters different of light incident on it and hence they appear with different colours. For example nano gold does not act as bulk gold. The nano particles of gold appear as orange, purple, red or greenish in colour depending on their grain size. The bulk copper is opaque where as nanoparticle copper is transparent. 1. Optical properties

27. 2. Physical properties When the material size is reduced to nanoscale, surface area to volume ratio increases. Due to increase of surface of surface area, more number of atoms will appear at the surface of compared to those inside. So Interatomic spacing decreases with size. 3. Thermal properties Thermal properties of nano materials are different from that of bulk materials. The Debye Temperature and ferroelectric phase transition temperature are lower for nano materials. The melting point of nano gold decreases from 1200 K to 800K as the size of particle decreases form 30 nm to 20 nm. 4. Magnetic properties The magnetic properties of nano materials are different from that of bulk materials. In explaining the magnetic behavior of nanomaterials, we use single domains unlike large number of domains in bulk materials. The coercivity values of single domain is vary large. For example, Fe,Co , and Ni are ferromagnetic in bulk but they exhibit super par magnetism. Na, K, and Rh are paramagnetic in bulk but they exhibit ferro -magnetic. Cr is anti ferromagnetic in bulk but they exhibit super paramagnetic.

28. 5. Mechanical properties The mechanical properties such as hardness, toughness, elastic modulus, young’s modulus etc., of nano materials are different from that of bulk materials. In metals and alloys, the hardness and toughness are increased by reducing the size of the nano particles. In ceramics, ductility and super plasticity are increased on reducing grain size. Hardness increases 4 to 6 times as one goes from bulk Cu to nanocrystalline and it is 7 to 8 times for Ni. 6. Chemical properties Nanocrystalline materials are strong, hard, erosion and corrosion resistant. They are chemically active and have the following chemical properties. In electrochemical reactions, the rate of increase in mass transport increases as the particle size decreases. The equilibrium vapour pressure, chemical potentials and solubilites of nanoparticles are greater than that for the same bulk material. Most of the metals do not absorb hydrogen. But the hydrogen absorption increases with the decrease of cluster size in Ni, Pt and Pd metals.

29. Applications of nanomaterials Nano materials have unique physical , chemical and mechanical properties, they can be used for a wide verity of applications. 1. Material technology Nanocrystalline aerogel are light weight and porous, so they are used for insulation in offices homes . Cutting tools made of nanocrystalline materials are much harder, much more wear- resistance and last stranger. Nanocrystalline material sensors are used for smoke detectors, ice detectors on air craft wings, etc ,. Nanocrystalline materials are used for high energy density storage batteries. Nanosized titanium dioxide and zinc dioxide are used in sunscreens to absorb and reflect ultraviolet rays. Nan coating of highly activated titanium dioxide acts as water repellent and antibacterial. The hardness of metals can be predominately enhanced by using nanoparticles. Nanoparticles in paints change colour in response to change in temperature or chemical environment, and reduce the infrared absorption and heat loss. Nanocrystalline ceramics are used in automotive industry as high strength springs, ball bearings and valve lifters.

30. 2. Electronics and Information technology Nanotechnology has reduced the size of transistors. Nanoparticle copper suspensions is more trustable alternative to lead-based weld and other toxic substances commonly used in the assembly process to fuse electronics. Nanoscale fabricated magnetic materials are used in data storage. Nano computer chips reduce the size of the computer. Nanocrystalline starting light emitting phosphors are used for flat panel displays. Nanoparticles are used for information storage . Nanophotonic crystals are used in chemical optical computers. 3. Biomedicals Biosensitive nanomaterials are used for ragging of DNA and DNA chips. In the medical field, nanomaterials are used for disease diagnosis, drug delivery and molecular imaging. Nanocrystalline silicon carbide is used for artificial heart valves due to its low weight and high strength. 4. Energy storage Nanoparticles are used hydrogen storage. Nano particles are used in magnetic refrigeration. Metal nanoparticles are useful in fabrication of ionic batteries. Nanotechnology is also included into solar panels to increase the efficiency, resulting in future solar power.