We investigated the O-doping profile along ZnTe nanowires using laser powerdependent microphotoluminescence measurements. ZnTe nanowires were grown by physical vapor transport catalyzed by bismuth. The photoluminescence spectra consisted of band-edge green photoluminescence and red photoluminescence due to a highly luminescent intermediate band formed by unintentional O doping. An obvious color-tuning effect of photoluminescence was observed along the nanowire and was suggestive of the competition between two luminescence bands. A significant variation in the intensity of red luminescence from the catalyst tip to the bottom was observed, and the photoluminescence intensity as a function of excitation power at each sampling spot along the nanowire was analyzed using a power law. The exponent value in the power law, from the sampling spots, was determined to be 0.58 ± 0.11, indicating an identical recombination channel for red luminescence. However, the O-doping density shows a superlinear increase from the catalyst tip to the bottom. Besides the direct impingement of doping species on the side wall, the additional incorporation of the doping species surfacemigrating from the substrate may explain the nonlinear O-doping profile along the nanowire.

ZnTe nanotrees and nanowires were grown on fluorine-doped tin oxide glass by physical vapor transport. Sn from a fluorine-doped tin oxide layer catalyzed the growth at a growth temperature of 320 °C. Both the stem and branch nanowires grew along ⟨0001⟩ in the rarely observed wurtzite structure. SnTe nanostructures were formed in the liquid catalyst and simultaneously ZnTe nanowire grew under Te-limited conditions, which made the formation of the wurtzite structure energetically favorable. Through polarization-dependent and power-dependent microphotoluminescence measurements from individual wurtzite nanowires at room temperature, we could determine the so far unknown fundamental bandgap of wurtzite ZnTe, which was 2.297 eV and thus 37 meV higher than that of zinc-blend ZnTe. From the analysis of doublet photoluminescence spectra, the valence band splitting energy between heavy hole and light hole bands is estimated to be 69 meV.

Zn 3 P 2 twinning superlattice nanowires with diameters of 100−300 nm were grown under Sn catalysis on fluorine-doped tin oxide glass by physical vapor transport. The nanowires grew along the [101] direction with nonparallel {101} side facets. The Zn 3 P 2 twinning superlattices had no noticeable crystallographic defects except periodic twin defects. A nonlinear relationship between the twin plane spacing and nanowire diameter was observed. The twin plane formation energy (4.0 × 10 −2 to 4.3 × 10 −2 J/m 2 ) was estimated by fitting the relationship from the nucleation model with a hexagonal nucleus with monolayer height at the triple-phase boundary. The unexpected nonlinear behavior despite the relatively high twin plane formation energy was ascribed to the strong interaction of P atoms dissolved in Sn droplets with the growth interface. P atoms in the droplets may have acted as a surfactant to reduce the liquid−solid surface energy.

The growth of CdTe nanowires, catalyzed by Sn, was achieved on fluorine-doped tin oxide glass by physical vapor transport. CdTe nanowires grew along the 〈0001〉 direction, with a very rare and phase-pure wurtzite structure, at 290 °C. CdTe nanowires grew under Te-limited conditions by forming SnTe nanostructures in the catalysts and the wurtzite structure was energetically favored. By polarization-dependent and power-dependent micro-photoluminescence measurements of individual nanowires, heavy and light hole-related transitions could be differentiated, and the fundamental bandgap of wurtzite CdTe at room temperature was determined to be 1.562 eV, which was 52 meV higher than that of zinc-blende CdTe. From the analysis of doublet photoluminescence spectra, the valence band splitting energy between heavy hole and light hole bands was estimated to be 43 meV.

We perform photocurrent measurements in few-layered ReS 2 with multiple electrodes using scanning photocurrent microscopy and investigate the photocurrent mechanism of the ReS 2 device. In particular, we have investigated how the photocurrent responds to the different configurations of a current-collecting electrode, ground electrodes and floating electrodes. When all electrodes are electrically connected, the circuit is short. If any electrodes are floating, we refer the circuit is open. Remarkably, open-circuit devices show a similar photocurrent response with short-circuit devices. The observed photocurrent is attributed to the electron response to the modulating electric field that is generated by time-varying laser heating. We further show that the observed photocurrent is tunable by gate voltages.