The thermoelectric and transport properties of a Fe 3 O 4 /SiO 2 /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/K 2 m at 260K which is an underestimated, lower limit value and is related to the density of states and difference in the work functions of Fe 3 O 4 and Si(100) that create an accumulation of majority holes at the p-Si/SiO 2 interface.

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This paper reports on the structural and optical properties of Co-doped TiO2 thin films grown onto (0001)Al2O3 substrates by non-reactive pulsed laser deposition (PLD) using argon as buffer gas. It is shown that by keeping constant the substrate temperature at as low as 310 degrees C and varying only the background gas pressure between 7 Pa and 70 Pa, it is possible to grow either epitaxial rutile or pure anatase thin films, as well as films with a mixture of both polymorphs. The optical band gaps of the films are red shifted in comparison with the values usually reported for undoped TiO2, which is consistent with n-type doping of the TiO2 matrix. Such band gap red shift brings the absorption edge of the Co-doped TiO2 films into the visible region, which might favour their photocatalytic activity. Furthermore, the band gap red shift depends on the films' phase composition, increasing with the increase of the Urbach energy for increasing rutile content.

Chromium oxides, Cr x O y , are of great interest due to the wide variety of their technological applications. Among them, CrO 2 has been extensively investigated in recent years because it is an attractive compound to be used in spintronic heterostructures. However, its synthesis at low temperatures has been a difficult task due to the metastable nature of this oxide. This is indeed essential to ensure interface quality and the ability to coat thermal-sensitive materials such as those envisaged in spintronic devices. Pulsed Laser Deposition (PLD) is a technique that has the potential to meet the requirements stated above.In this work, we describe our efforts to grow chromium oxide thin films by PLD from Cr 8 O 21 targets, using a KrF excimer laser. The as-deposited films were investigated by X-ray diffraction and Rutherford backscattering spectrometry. Structural and chemical composition studies showed that the films consist of a mixture of amorphous chromium oxides exhibiting different stoichiometries depending on the processing parameters, where nanocrystals of mainly Cr 2 O 3 are dispersed. The analyses do not exclude the possibility of co-deposition of Cr 2 O 3 and a low fraction of CrO 2 . In this paper, we present results on chromium oxide films produced onto Si (100) by room temperature PLD in oxygen atmosphere and using Cr 8 O 21 as target material. PACS Experimental details Film growthChromium oxide films were grown by reactive pulsed laser deposition (RPLD) using a stainless steel HV deposition chamber and a pulsed UV laser (KrF, 248 nm wavelength, 30 ns pulse duration) with associated beam delivery optics. The laser was operated at 5 Hz and the laser beam was incident at an angle of 45º with respect to the target surface. The target was produced from Cr 8 O 21 powder, as described below, and was continuously rotated and periodically translated during laser ablation to renew the irradiated surface and to prevent crater formation. The ablated material was collected onto a Si(100) substrate, at room temperature, placed in front of and at 6.2 cm from the target. Prior to an experiment, the chamber was evacuated to 2-7×10 -4 Pa, a screen was placed between the substrate and the target for protection, and the target surface was cleaned for several minutes by irradiating with the non-focused KrF laser beam. During deposition, oxygen (99.999 %) was flown through the chamber and the background pressure was varied between 0.3 and 1.9 Pa. The laser fluence was kept at 4.0 ± 0.3 J cm -2 . 2 Target preparationPowder of Cr 8 O 21 was obtained by slow thermal decomposition of CrO 3 powder in air at 260 ºC. Afterwards, the powder was crushed to nanometre size and sintered at 220 ºC and 0.2 GPa into pellets 20 mm in diameter and 2 mm thick. Sample characterisationStructural analysis of the films was carried out in a Siemens D5000 diffractometer by glancing incidence X-ray diffraction (GIXRD), using CuKα radiation at 1º angle of incidence to the specimen surface. The identification of crystalline phases was d...

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