Nanoscience and nanotechnology

Module 4

1. NANOSCIENCE AND NANOTECHNOLOGY Presented by Suja Devi V AssistantProfessor Dept.of Applied Science, SCT college

2. Nanoscience and Nanotechnology The origin of nanotechnology is from the lectures delivered by Richard Feynmann which is entitled as “There is plenty of room at the bottom”. The word “ nano ” is derived from a Greek word meaning dwarf and 1nm=10 -9 m. Nanoscience is the study of fundamental principles of molecules and structures with atleast one dimension roughly between 1nm and 100nm. Application of nanoscience to productive scale/manufacturing scale is nanotechnology.

3. * Two main factors that causes significant change in the properties of nanomaterials from their bulk counterpart Increased surface area to volume ratio and Quantum effects These factors can enhance properties such as strength, reactivity, electrical optical,mechanical etc..

4. Increase in surface to volume ratio for nanomaterials To understand this we consider a spherical material of radius r, Surface area of sphere/Volume of sphere =4 ᴫ r 2 /(4/3 ᴫ r 3 ) =3/r. As the size of sphere decreases, the above ratio increases. The reactivity of materials depends on molecules on the surface and nanomaterials have large surface area with large no: of particles and hence their surface energy will be more which results in enhanced reactivity and thermodynamical properties.

5. Quantum confinement The quantum effects dominate the behaviour of matter at nanoscale affecting optical, electrical and magnetic properties. According to band theory,solid materials have energy bands and isolated atoms possess discrete energy levels.For nanomaterials,if the dimensions of potential wells or boxes are of the order of the deBroglie wavelength of electrons,then the energy levels of electron change and the electron will remain confined to a small region of the material.This is called quantum confinement.

6. Properties of nanomaterials Nano materials shows specific properties different from their bulk counterpart due to large surface area to volume ratio, large surface energy ,spatial confinement and reduced imperfections. Mechanical properties. The mechanicalstrength of nanostructures is enhanced due to less surface defects. Due to large surface to volume ratio nanomaterials have lower melting point and reduced lattice constant In nanoscale level -hardness and toughness of metals and alloys are increased. The transition from bulk to nanophase reduces elastic strength and increases plastic behaviour Some brittle materials becomes ductile by reducing their grain size.

7. Optical properties Optical properties are due to increase in energy level spacing and surface plasmon resonance Different sized nanoparticles scatter different wavelengths of light incident on it ( they have different absorption spectra)and hence they appear with different colours.For eg:nano gold appears in purple,red,green etc. depending on their grain size. The bulk copper is opaque whereas in nanoscale it is transparent. In nanoparticles of semiconductor elements such as Ge,Si etc.. – a shift in optical absorption spectra is seen.

8. Electrical properties The electrical conductivity and energy bandwidth of some materials change when they pass from bulk to nanophase.Eg: bulk silicon is a semiconductor whereas in nanophase it is conductor. Electrical conductivity of nanomaterials depends on increased perfection, reduced impurity and dislocations. In metals Conductivity decreases with reduced size as their energy bands become narrower and hence the ionisation potential energy increases. Also conductivity may be enhanced due to better ordering in microstructure and decreased due to increased surface scattering.

9. Applications In microelectronics- the reduction in size of electronic components leads to faster switching times. The magnetic strength of material is directly proportional to the surface to volume ratio.The nanocrystalline high power rare earth magnet finds applications in submarines,electric motors,MRI instruments and in ultrasensitive analytical instruments. In computers- Quantum computers use fast quantum algorithms and have quantum bit memory space( qubit ),so it involves in several computations at the same time. Energy efficiency -Nanostructures with a continuum of energy band gaps have an increased solar energy conversion efficiency as compared to ordinary semiconductor solar cells.

10. Other applications Medical field- -Nano materials are used for the development of diagnostic devices,drug delivery systems etc. Magnetic nanoparticles are used to label molecules,structures or micro organism of an antibody. Iron nanoparticles are used in cancer treatment. Nanotechnology is used to reproduce or repair damaged tissues. The genetic sequence of a sample can bedetected by tagging gold nanoparticles with small segment of DNA. In textile industry- clothes made of nanofibres are water and stain resistant and wrinkle free.

11. Answer the following questions . 1.Explain the significance of nanoscale ? Key:Explain the factors responsible for change in properties at nanorange . 2.Give some medical applications applications of nanomaterials 3.List the classifications of nanomaterials . 4.Describe the mechanical,electrical and optical properties of nanomaterials .(essay qn.part ) Refer Text also.

12. ThankYou