Growth of Monolayer MoS2 Flakes via Close Proximity Re-Evaporation.

We report a two-step growth process of MoS2 nanoflakes using a low-pressure chemical vapor deposition technique. In the first step, a MoS2 layer was synthesized on a c-plane sapphire substrate. This layer was subsequently re-evaporated at a higher temperature to form mono- or few-layer MoS2 flakes. As a result, the close proximity re-evaporation enabled the growth of pristine MoS2 nanoflakes. Atomic force microscopy analysis confirmed the synthesis of nanoclusters/nanoflakes with lateral dimensions of over 10 µm and a flake height of approximately 1.3 nm, demonstrating bi-layer MoS2, whereas transmission electron microscopy analysis revealed triangular MoS2 nanoflakes, with a diffraction pattern proving the presence of single crystalline hexagonal MoS2. Raman data revealed the typical modes of high-quality MoS2 nanoflakes. Finally, we presented the photocurrent dependence of a MoS2-based photoresist under illumination with light-emitting diode of 405 nm wavelength. The measured current-voltage dependence across various luminous flux outlined the sensitivity of MoS2 to polarized light and thus opens further opportunities for applications in high-performance photodetectors with polarization sensitivity.

The Effect of Post Deposition Treatment on Properties of ALD Al-Doped ZnO Films.

In this paper, aluminum-doped zinc oxide (ZnO:Al or AZO) thin films are grown using atomic layer deposition (ALD) and the influence of postdeposition UV-ozone and thermal annealing treatments on the films' properties are investigated. X-ray diffraction (XRD) revealed a polycrystalline wurtzite structure with a preferable (100) orientation. The crystal size increase after the thermal annealing is observed while UV-ozone exposure led to no significant change in crystallinity. The results of the X-ray photoelectron spectroscopy (XPS) analyses show that a higher amount of oxygen vacancies exists in the ZnO:Al after UV-ozone treatment, and that the ZnO:Al, after annealing, has a lower amount of oxygen vacancies. Important and practical applications of ZnO:Al (such as transparent conductive oxide layer) were found, and its electrical and optical properties demonstrate high tunability after postdeposition treatment, particularly after UV-Ozone exposure, offers a noninvasive and easy way to lower the sheet resistance values. At the same time, UV-Ozone treatment did not cause any significant changes to the polycrystalline structure, surface morphology, or optical properties of the AZO films.

ALD Deposited ZnO:Al Films on Mica for Flexible PDLC Devices.

In this work, highly conductive Al-doped ZnO (AZO) films are deposited on transparent and flexible muscovite mica substrates by using the atomic layer deposition (ALD) technique. AZO-mica structures possess high optical transmittance at visible and near-infrared spectral range and retain low electric resistivity, even after continuous bending of up to 800 cycles. Structure performances after bending tests have been supported by atomic force microscopy (AFM) analysis. Based on performed optical and electrical characterizations AZO films on mica are implemented as transparent conductive electrodes in flexible polymer dispersed liquid crystal (PDLC) devices. The measured electro-optical characteristics and response time of the proposed devices reveal the higher potential of AZO-mica for future ITO-free flexible optoelectronic applications.

Octahedral tilting in Pb-based relaxor ferroelectrics at high pressure.

We have employed a combination of powder neutron diffraction and single-crystal synchrotron X-ray diffraction to characterize the pressure-induced phase transitions that occur in the perovskite-type relaxor ferroelectric PbSc(0.5)Ta(0.5)O(3) (PST) and Pb(0.78)Ba(0.22)Sc(0.5)Ta(0.5)O(3) (PST-Ba). At ambient pressure the symmetry of the average structure for both compounds is Fm3m as a result of partial ordering of the Sc and Ta cations on the octahedral sites. At pressures above the phase transition both the neutron and X-ray diffraction patterns exhibit an increase in the intensities of h,k,l = all odd reflections and no appearance of additional Bragg reflections. Synchrotron single-crystal X-ray diffraction data show that the intensity of hhh peaks, h = 2n + 1, does not change with pressure. This indicates that the structural distortion arising from the phase transition has a glide-plane pseudo-symmetry along the 111 cubic directions. Rietveld refinement to the neutron powder data shows that the high-pressure phase has either R3c or R3 symmetry, depending on whether the presence of 1:1 octahedral cation ordering is neglected or taken into account, and comprises octahedral tilts of the type a(-)a(-)a(-) that continuously evolve with pressure. The cubic-to-rhombohedral transition is also marked by a large increase in the anisotropy of the displacement ellipsoids of the Pb cations, indicating larger displacements of Pb cations along the rhombohedral threefold axis rather than within the perpendicular plane. For PST the anisotropy of the Pb displacement parameters decreases at approximately 3 GPa above the phase-transition pressure. For both PST and PST-Ba the average magnitudes of Pb-cation displacements expressed in terms of isotropic displacement ellipsoids gradually decrease over the entire pressure range from ambient to 7.35 GPa.