Epitaxial growth and properties of MoOx(2<x<2.75) films

Abstract

We report the growth of epitaxial molybdenum oxide (MoOx,2<x<2.75) films on c plane of sapphire substrate using pulsed laser deposition in oxygen environment. The structure was characterized using x-ray diffraction, high resolution transmission electron microscopy and x-ray photoelectron spectroscopy (XPS). Electrical resistivity and optical properties were investigated using four-point-probe resistivity measurements and spectroscopy techniques, respectively. It was found that the film had a monoclinic structure based on MoO2 phase and showed an unusual combination of high conductivity and high transmittance in the visible region after annealing. The unusual combination of these properties was realized by systematically controlling the relative fraction of different oxidation states of molybdenum, namely Mo4+, Mo5+, and Mo6+ in the monoclinic phase. For a film 60nm thick and annealed at 250°C for 1h, the ratio of Mo6+∕(Mo4++Mo5+) was determined to be ∼2.9∕1 using XPS, and a typical value of transmittance was ∼65% and resistivity close to 1×10−3Ωcm. These results demonstrate growth of epitaxial MoOx films with tunable electrical and optical properties. Further optimization of these properties is expected to result in applications related to display panels, solar cells, chromogenic (photochromic, electrochromic, gasochromic) devices, and transparent conducting oxides. Our ability to grow epitaxial MoOx films can further aid their integration with optoelectronic and photonic devices.

Crystalline Molybdenum Oxide Thin-Films for Application as Interfacial Layers in Optoelectronic Devices

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 based on the intensities of measured peaks of Kα-lines relative to calculated or measured intensities of standards. It has been shown by Bhosle et al 23 that MoO x epitaxially grown on c-plane sapphire by pulsed laser deposition (PLD) leads to a monoclinic structure which is characteristic for the MoO 2 phase where the structure follows the growth along the (0001) direction, consisting of 60% 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Bright-field LEEM images are formed from elastically reflected intensity of a coherent bea...…”

“…by increasing both carrier mobility and carrier concentration in the films. 18,23 Therefore, a full understanding of the MoOx films microstructure and its correlation to the electronic properties is needed for improving its use in device applications.…”

Electronic structure of face-centred cubic MoO2: A comparative study by the full potential linearized augmented plane wave method, X-ray emission spectroscopy and X-ray photoelectron spectroscopy

“…10 eV for MoO 2 oxides [17,29]. Nonstoichiometric molybdenum oxide films prepared by various deposition techniques [44][45][46] show interesting physical properties that are respected to result in different technological applications, e.g. chromogenic devices, display panels and solar cells.…”

Van der Waals epitaxy of functional MoO2 film on mica for flexible electronics

“…The q-T results are in agreement with previous studies of MoO 2 films on the conventional substrates. 39 We also performed temperature dependent Hall measurements to characterize the charge carrier type and carrier concentration of the MoO 2 films. Figure 4(b) shows a typical result of the vertical resistance R xy versus magnetic field, in the range from À2 T to 2 T at 10 K. The positive slope indicates that the charge carriers in MoO 2 are p-type.…”