Explanation for the appearance of alumina nanoparticles in a cold wall Atomic Layer Deposition system and their characterization

An explanation for the possible mechanism of formation of alumina nanoparticles in Atomic Layer Deposition process of Alumina using Trimethyl aluminum (TMA) and water in a cold wall ALD chamber is given based on the physisorption of TMA and surface energy of alumina thin films. The sorption mechanism proposed is physisorption at the cold walls rather than the conventional chemisorption at the hot substrates as in the case of typical ALD. It is argued that when the surface energy of alumina is larger than the physorption energy, the newly forming film will try to reduce the surface area and assume spherical shape forming nano particles. Synthesized particles were characterized using XRD, SEM, HRTEM, SAED, FTIR and EDS. It was found that the particle size varied from ∼20 nm to 45 nm. The samples were identified as slightly aluminum rich alumina. The as prepared samples were amorphous whereas annealing at 1200 deg C made them crystalline. Dielectric studies of pelletized samples yielded a dielectric constant of 9.08 which agreed well with reported values.