178 Nanosensors: Physical, Chemical, and Biological
purged with an inert gas, or evacuated, which removes any excess precur-
sor molecules and volatile (evaporating readily at normal temperatures and
pressures) by-products from the reaction chamber, thus eliminating the pos-
sibility of occurrence of unwanted gas phase reactions.
How does ALD differ from conventional CVD? In marked contrast to tradi-
tional thermal CVD, which involves pyrolysis (thermolysis: thermochemi-
cal decomposition of materials at elevated temperatures in the absence of
oxygen) of precursor molecules, (i) ALD proceeds through surface exchange
reactions, such as hydrolysis (subjecting to chemical action of water), between
chemisorbed metal-containing precursor ...