Pulsed Laser Deposition of Epitaxial SrVO 3 Films on (100)LaAlO 3 and (100)Si
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Mat. Res. Soc. Symp. Proc. Vol. 623 © 2000 Materials Research Society
EXPERIMENT In this work the SVO films were grown on (100)LAO and (100)Si substrates by the usual pulsed laser deposition (PLD) method. A KrF excimer laser (X = 248 nm) with a repetition rate of 10 Hz was used. The laser fluence was kept at 2 and 3 J/cm 2 for the TiN and SVO film depositions respectively. The target and substrate distance was maintained at 4.5 cm. A rotating multi-target holder incorporated into our chamber was used for in-situ deposition of TiN and SVO heterostructures. The SVO targets were prepared by the standard solid state reaction using high purity SrCO 3 and V20 5 powders. They were initially weighted and mixed according to the stoichiometric composition ratio. They were then ground into fine powders and sintered at 850'C for 5 hours in air. Afterwards they were pressed into circular pellets of 22 mm diameter and 5 mm thick. Finally the pellets were sintered at 950'C for 5 hours in air again. The TiN targets were bought from a commercial supplier with a stated purity of 99.5 %. The substrates were ultrasonically degreased with acetone and thoroughly rinsed with deionized water. Si substrates were additionally etched by 10 % HF solution for 10 minutes to rid of the oxide layer. All substrates measuring 5× 10 mm2 were adhered to the faceplate of the ohmic heater with high temperature silver paste. A thermal couple was embedded in the faceplate and placed directly underneath the substrate for accurate monitoring of the film deposition temperatures. Before the ablation, the chamber was evacuated to a base pressure of 2x 10-7 Torr by a cryo-pump. SVO films were deposited under ambient oxygen pressure between 10-6 and 10-2 Torr and in temperature range of 450'C - 750'C. TiN films were grown at the base pressure with a fixed substrate temperature of 550'C. No additional post-annealing was made. The structural properties of the as-deposited SVO/LAO and SVO/TiN/Si were characterized by a four-circle X-ray diffractometer using CuKa radiation. The resistivitytemperature (R-T) curves of the SVO films were measured by a standard four-point probe technique over a temperature range from. 77 K to room temperature. X-ray photoelectron spectroscopic (XPS) study of the SVO films was carried out to identify the valency state of Vanadium. RESULTS SrVO9/LAO SVO was grown on LAO substrate at deposition temperature range of 450'C - 750'C. The ambient oxygen pressure was kept between 10-6 and 10-2 Torn. Except those deposited at high vacuum of 10-6 Torr, all SVO films show poor crystallinity and high resistivity. So, in subsequent studies, SVO films were grown at 10-6 Torr ambient pressure. Fig. I shows the Xray 0 - 20 diffraction pattern for SVO/LAO at substrate temperature of 650'C. It is seen that only strong (hOO) reflections were recorded. The X-ray wo-scan rocking curves of the (200)SVO reflection shows a full width at half maximum (FWHM) of about 0.90. It indicates that the film is highly oriented. The X-ray 3600 4-scan on (220)SVO and
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