Electrical Properties of DC Reactive Magnetron Sputtered ZnO:Al Films from Optical Spectra

Reactive direct current (DC) sputtered ZnO:Al films were prepared using the plasma emission monitoring (PEM) system. Films were deposited using PEM setpoints ranging from 50 to 80%. Transmittance and reflectance of the films were measured by using the UV-VIS-NIR Lambda 900 double beam spectrophotometer. The sheet resistance was measured using the four-point probe. Films optical spectra were fitted with the Drude model to determine their charge carrier concentration, mobility and the alternating current (AC) resistivity. The highest values of mobility and charge carrier concentration were 8.31cm2/Vs and 2.14 x 1021cm-3 respectively. The lowest value of the AC resistivity was given by the ZnO:Al film with the highest value of the product (Nμ) of charge carrier concentration (N) and mobility (μ). The DC and AC resistivity were of the same orders of magnitude. The optical bandgap was found to increase with the increase in charge carrier concentration. A linear variation of N2/3 with the optical bandgap, which concurs with theBurstein-Moss shift theory, was obtained.Keywords: ZnO:Al, PEM, Drude model, transmittance, reflectance, sputtering

Engineering grain boundaries at the 2D limit for the hydrogen evolution reaction

Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~1012 cm−2. We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec−1), thus indicating an intrinsically high activation of the TMD GBs