Room temperature and high-pressure-pulsed laser deposition of nanocrystalline VO_2 thin films on glass substrate: plasma and film analyses

摘要

In this contribution, we demonstrate room temperature growth of highly oriented single-phase nanocrystalline films of VO_2(A) on glass substrates using pulsed laser deposition (PLD) technique under high oxygen pressure and small target-substrate separation. The structural, morphological, optical, electrical and compositional properties of the deposited thin films have been studied by means of X-ray diffraction, atomic force microscopy, spectrophotometry, 04-point probe method and X-ray photoelectron spectroscopy, respectively. The plasma under which VO_2(A) was grown has been analyzed by means of time- and space-resolved optical emission spectroscopy (OES) and Langmuir probe (LP) techniques. We evidenced a correlation between growth conditions and plasma characteristics. While OES showed that at the deposition distance corresponding to the length of the visible plasma, the plasma species are completely thermalized and characterized by a very low degree of excitation, the LP technique indicated a formation of charged clusters within the gas phase. By combining OES and LP data, a quadruple plasma structure has been shown. The growth of under-stoichiometric (comparing to the parent V_2O_5 target) nanocrystalline VO_2(A) phase has been attributed to nanoparticle formation in the gas phase under a plasma environment rarefied in oxygen atoms due to the scattering and backscattering effects. This finding opens up the opportunity to grow VO_2 polymorphs at very low temperature by PLD for novel promising new device functionalities.