KrF pulsed laser deposition of chromium oxide thin films from Cr8O21 targets

Abstract

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...

Excimer laser processing of novel materials for optoelectronic and spintronic applications

“…several orders of magnitude greater than MBE, while still retaining the advantages of high and ultra-high vacuum deposition techniques. However, most PLD work has been performed in an O 2 ambient [15][16][17] and no clear evidence on the formation of CrO 2 has been shown. RP-PLD could prove to be a more suitable technique to synthesize the CrO 2 phase, as it offers the capability of controlling the chemical composition and the oxidation state of the grown layers through the interaction of the laser ablated species with activated O atoms generated by a remote plasma source as opposed to ground state O 2 molecules, as is the case in reactive PLD.…”

Structural and optical characterization of Cr2O3 nanostructures: Evaluation of its dielectric properties

“…Among these modifications, Cr 2 O 3 is the most stable magnetic-dielectric oxide-material. 6 It belongs to rhombohedral crystal system with lattice parameter a = b = 4.953 Å, c = 13.578 Å and space group R-3c (167). 7 It has wide variety of applications such as: catalysts, hydrogen storage, wear resistance materials, dye and pigment, advanced colorants, digital recording system, black matrix films, solar energy application, coating materials for thermal protection, and electrochromic material.…”

Pulsed laser deposition of half-metallic CrO<inf>2</inf> thin films for spintronic applications

“…PLD can be a very promising tool for the fabrication of high quality thin films of CrOz. It is a versatile method for the stabilization of otherwise metastable phases under non-equilibrium thermodynamic conditions [20][21].…”