Gas sensors based on semiconductor materials enable a large range of practical applications because of their easy implementation and low cost. Advances in nano-engineering allow dramatically increase the response of these materials and their overall performance, mostly because of increasing the exposed surface volume. One of the successful metal oxide semiconductor materials is a mixture of Cr2O3 and TiO2, used in sensors in the form of pellets or thick films. In the present work, pulsed laser deposition (PLD) technique has been used for the growth of (1-x)Cr2O3-xTiO2 (x=5-20wt%) materials with the aim to find the feasibility and optimal conditions for the growth of nanostructured (ultra)thin films. Target materials were prepared by sintering the fine mixture of TiO2 and Cr2O3 at 1300C for 5h. The films were deposited by KrF excimer laser on Si [100] substrates in partial oxygen atmosphere, and were characterized by XRD, RHEED, and AFM. The substrate temperature (400 - 700 C), oxygen pressure (1.10-3 - 5.10-2 mbar) and laser energy density (1.5 - 4.5 J/cm2) were varied for optimising the growth conditions. Structural analysis showed that the crystallisation of the films started at oxygen pressures at or above 10-2 mbar. At highest gas pressure (5.10-2 mbar) the crystalline structure began to reveal above the temperatures 450 C for x=20% and 500 C for x=5%. Relatively fast change towards crystalline phase occurred at around 550 C as indicated both by surface roughness analysis and by structural data. Smallest crystallite sizes (<10 nm) were obtained at 550 C, whereas the amount of amorphous phase was estimated to be around 20%. Bigger proportion of crystalline phase was obtained, if lower laser energy density and larger number of laser pulses were used during the growth.
[ABSTRACT TRUNCATED TO 2000 LETTERS] |