Question

Materials in the nano-scale may exhibit remarkable properties. Give three examples. (15 points)

Answer 1

When particle sizes in normal scale are examined, there is not much difference in Physical Properties of material depending upon size. However, when materials are arranged in Nano Scle, properties change drastically with change in sizes. Examples of such occurrences are:

1. Nano scale gold particles are not Yellow (which is common colour for Gold at normal sizes). Instead, nano scale gold particles exhibit Red or Purple colour. At nano scales, electrons do not move freely as compared to normal size gold particles. This leads to difference in how gold particles react to light & thus their colour is different from normal sized Gold particles.

2. In normal sized particles, melting points of metal does not depend upon size. But generally melting point of nano scale metal is lower than normal scale material because in nano scale surface atoms require less energy to move as they are in contact with fewer atoms.

3. In semiconductors, band gaps change when we arrange particles in nano scale. On reducing the size in nano scale, band gap (which is the energy required to move electron from valence band to conductance band) in creases. It leads to higher energy requirement to move electron from valence band to conductance band. Therefore, nano particles exhibit lower electrical conductivity compare to bulk material (arranged in normal sizes).