Argon assisted chemical vapor deposition of CrO2: An efficient process leading to high quality epitaxial films

Abstract

A comparative study of the structural, microstructural and magnetic properties of CrO 2 thin films grown onto (110) and (100) TiO 2 rutile single crystal substrates by chemical vapor deposition (CVD), using CrO 3 as chromium precursor and either oxygen or argon as carrier gas is presented. Our results show that growth under argon carrier gas leads to high quality CrO 2 epilayers with structural and magnetic properties similar to those obtained using the more standard oxygen carrier gas. Furthermore, we interpret the larger magnetic coercivity observed for the (110) oriented films in terms of their microstructure, in particular of the highest strain and edge roughness of the building structures of the CrO 2 epilayers, which are settled by the substrate crystallographic orientation. * [19][20][21][22]. But the studies on chromium dioxide have not been limited to fundamental or applied science. Indeed, CrO 2 has been used in industry covering a wide range of applications e.g. audio, video, instrumentation and computer technology due to its exceptional properties as a magnetic storage material [13].Although some attempts have been pursued to grow thin films of the single CrO 2 compound by physical vapor deposition methods [23][24][25], only chemical vapor deposition (CVD) has shown to lead to high quality CrO 2 layers [26][27][28][29][30]. CrO 2 epitaxial layers are currently grown on TiO 2 rutile phase and sapphire substrates by CVD using CrO 3 as the chromium precursor, which is carried out into the reaction zone by an oxygen flux. While chromium precursors other than CrO 3 , e.g. Cr 8 O 21 [31] and CrO 2 Cl 2 [8,10], have also been used in the CVD of CrO 2 yielding films with similar properties, the use of an oxygen flux has been pointed out as critical for the overall CrO 2 synthesis process. To our knowledge, only the work of Ivanov et al. [31] briefly refers that the use of argon as carrier gas makes the process very inefficient and leads to films with poorer crystallinity.Currently, the demand for fast and cost-efficient fabrication processes of high-quality materials and devices is on the agenda. Hence, an in-depth study of the feasibility of growing high quality epitaxial films of CrO 2 using argon as carrier gas becomes crucial, especially because of the well-known price difference between the two gases, with cost advantage to Page 3 of 27 argon. Besides, argon is a more user-friendly gas. Therefore, the fact that the use of argon could eventually limit the CrO 2 synthesis reaction may be seen as a drawback to the envisaged scaling-up of the CrO 2 CVD process at an industrial level.This work reports on the synthesis and properties of CrO 2 thin films grown onto single crystal TiO 2 rutile substrates by CVD, using CrO 3 as chromium precursor and either oxygen or argon as carrier gas. A comparative study of the structural, microstructural and magnetic properties of the different films are presented. Experimental detailsThe CrO 2 films were prepared in a tubular single-zone CVD furnace with independent control...

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