Very high thermoelectric power factor in a Fe3O4/SiO2/p-type Si(100)heterostructure

The thermoelectric and transport properties of a Fe3O4/SiO2/p-Si(100) heterostructure have been investigated between 100 and 300 K. Both Hall and Seebeck coefficients change sign from negative to positive with increasing temperature while the resistivity drops sharply due to tunneling of carriers into the p-Si(100). The low resistivity and large Seebeck coefficient of Si give a very high thermoelectric power factor of 25.5mW/K2m at 260K which is an underestimated, lower limit value and is related to the density of states and difference in the work functions of Fe3O4 and Si(100) that create an accumulation of majority holes at the p-Si/SiO2 interface

Cr2O3 thin films grown at room temperature by low pressure laser chemical vapour deposition

Chromia (Cr2O3) has been extensively explored for the purpose of developing widespread industrial applications, owing to the convergence of a variety of mechanical, physical and chemical properties in one single oxide material. Various methods have been used for large area synthesis of Cr2O3 films. However, for selective area growth and growth on thermally sensitive materials, laser-assisted chemical vapour deposition (LCVD) can be applied advantageously. Here we report on the growth of single layers of pure Cr2O3 onto sapphire substrates at room temperature by low pressure photolytic LCVD, using UV laser radiation and Cr(CO)6 as chromium precursor. The feasibility of the LCVD technique to access selective area deposition of chromia thin films is demonstrated. Best results were obtained for a laser fluence of 120 mJ cm-2 and a partial pressure ratio of O2 to Cr(CO)6 of 1.0. Samples grown with these experimental parameters are polycrystalline and their microstructure is characterised by a high density of particles whose size follows a lognormal distribution. Deposition rates of 0.1 nm s-1 and mean particle sizes of 1.85 {mu}m were measured for these films.