JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Pharmacy IV NANO TECHNOLOGY Previous Question Paper (September - 2022 - R17)

When materials are reduced to the nano-dimension, their physical properties change significantly due to two primary factors: the quantum confinement effect and the high surface-to-volume ratio.

1. Optical Properties: As particle size decreases, the band gap increases, leading to blue shifts in absorption and emission spectra. This is observed in quantum dots, where the color of light emitted is tunable by changing the particle size.

2. Magnetic Properties: Materials that are ferromagnetic in bulk can become superparamagnetic at the nanoscale. The magnetic coercivity increases as particle size decreases until a critical size is reached, after which it drops to zero.

3. Mechanical Properties: Nanomaterials exhibit enhanced hardness and strength compared to their bulk counterparts. This is often explained by the Hall-Petch relationship, where the reduction in grain size restricts dislocation movement, thereby increasing yield strength.

4. Electrical Properties: Conductivity changes due to electron scattering at surfaces and grain boundaries. In some cases, materials transition from metallic to semiconducting behavior as the density of states becomes discrete rather than continuous.

Nanostructured materials are classified based on the number of dimensions that fall outside the nanometer range (typically less than 100 nm). This dimensionality determines the confinement of electrons and the behavior of the material.

1. Zero-Dimensional (0D) Nanostructures: These materials have all three dimensions in the nanoscale range (x, y, z < 100 nm). They exhibit quantum confinement in all three directions, resulting in discrete energy levels similar to atoms. Examples include quantum dots, nanoparticles, and nanoclusters.

2. One-Dimensional (1D) Nanostructures: These materials have two dimensions in the nanoscale range, while the third dimension is relatively large. Electrons are confined in two directions but are free to move along the long axis. This leads to unique electrical and thermal transport properties. Examples include nanowires, nanotubes (e.g., Carbon Nanotubes), and nanorods.

3. Two-Dimensional (2D) Nanostructures: These materials have only one dimension in the nanoscale range, while the other two dimensions are extended. This results in quantum confinement in one direction, creating a thin film or sheet structure. Examples include graphene, thin films, and nanocoatings.

4. Three-Dimensional (3D) Nanostructures: These are bulk materials composed of nanometer-sized building blocks (nanocrystals or grains). While the individual grains are in the nanoscale, the overall structure is macroscopic. Examples include polycrystalline materials, bulk nanostructured metals, and nanocomposites.