The photoconductive characteristics of CdS single nanoribbons were investigated. The device characteristics, including spectral response, light intensity response, and time response, were studied systematically. It is found that CdS nanoribbon has the response speed substantively faster than those ever reported for conventional film and bulk CdS materials and the size of nanoribbons has a significant influence on the response speed with smaller CdS nanoribbons showing higher response speed. The high photosensitivity and high photoresponse speed are attributable to the large surface-to-volume ratio and high single-crystal quality of CdS nanoribbons and the reduction of recombination barrier in nanostructures. Measurements in a different atmosphere demonstrate that the absorption of ambient gas (mainly oxygen) can significantly change the photosensitivity of CdS nanoribbons through trapping electrons from the nanoribbons.

Tetragonal CsPbBr nanosheets were obtained by an oriented attachment of orthorhombic CsPbBr nanocubes, involving a lateral shape evolution from octagonal to square. Meanwhile, the experimental results, together with DFT simulation results, indicated that the tetragonal CsPbBr is an indirect bandgap semiconductor that is PL-inactive with a bandgap of 2.979 eV.

Arrays of well‐aligned single‐crystal zinc oxide (ZnO) nanowires of uniform diameter and length have been synthesized on a (100) silicon substrate via a simple horizontal double‐tube system using chemical vapor transport and condensation method. X‐ray diffraction and transmission electron microscopy (TEM) characterizations showed that the as‐grown nanowires had the single‐crystal hexagonal wurtzite structure with detectable defects and a <0002> growth direction. Raman spectra revealed phonon confinement effect when compared with those of ZnO bulk powder, nanoribbons, and nanoparticles. Photoluminescence exhibited strong ultraviolet emission at 3.29 eV under 355 nm excitation and green emission at 2.21 eV under 514.5 nm excitation. No catalyst particles were found at the tip of the nanowires, suggesting that the growth mechanism followed a self‐catalyzed and saturated vapor–liquid–solid (VLS) model. Self‐alignment of nanowires was attributed to the local balance and steady state of vapor flow at the substrate. The growth technique would be of particular interest for direct integration in the current silicon‐technology‐based optoelectronic devices.

Photodetectors are fabricated from individual single‐crystal CdSe nanoribbons, and the photoresponse properties of the devices are studied systematically. The photodetector shows a high sensitivity towards excitation wavelength with a sharp cut‐off at 710 nm, corresponding to the bandgap of CdSe. The device exhibits a high photo‐to‐dark current ratio of five orders of magnitude at 650 nm, and can function with excellent stability, reproducibility, and high response speed (< 1 ms) in a wide range of switching frequency (up to 300 Hz). The photocurrent of the device shows a power‐law dependence on light intensity. This finding together with the analysis of the light intensity‐dependent response speed reveals the existence of various traps at different energy levels (shallow and deep) in the bandgap. Coating with a thin SiO2 isolating layer increases the photocurrent but decreases the response speed of the CdSe nanoribbon, which is attributed to reduction of recombination centers on ribbon surface.

ExperimentalOpals shown in this work have been prepared following a method described previously [1,24]. This sol±gel method provides size-controlled spheres for further sedimentation by gravity. The sediments are sintered (thermal annealing at 950 C for 3 h) to control the lattice parameter (a), and to strengthen the structures for consequent infillings. The usual size of the opal bits used for infiltration is 5±9 mm 2 in surface area by 0.5 mm thickness. The sphere diameter is 410 nm and, accordingly, the lattice parameter a = 580 nm.Fixed-Flow Reactor: Sb 2 O 3 -silica composites were placed in the bottom bed of an upflow fixed-bed quartz reactor at atmospheric pressure. The gas flow rate was kept constant at 34 mL min ±1 . The composition of the reactant gas from cylinders controlled by mass flow controllers was 20 vol.-% H 2 S in N 2 .Operating temperature and reaction time were the variables affecting the sulfide growth. Temperatures around 280±300 C are considered optimal for the sulfidation. Samples cracks are apparent as the operating temperature rises up to 550 C (melting point of Sb 2 S 3 ). Sulfidation times of 10 h resulted in almost complete oxide conversion (96 %).Band structure calculations were carried out by using the MIT package software. In this program, the fully vectorial Maxwell equations are solved for plane-wave propagation in a periodic dielectric medium. The system is characterized by the dielectric functions of the voids and backbone, the crystalline structure, and the value of the lattice parameter.Optical Characterization: The measurements were performed with a Fourier transform infrared spectrometer (FTIR), IFS 66S from Bruker with a IRScope II microscope attached. A 36 X Cassegrain objective was used to focus and collect the light. The incident and collected light cover external angles from 15 to 30 from normal incidence with respect to (111) family of planes.The X-ray powder diffraction (XRD) study was carried out in a Siemens 5000 diffractometer using Cu Ka radiation.The reference sample is the commercial product from Aldrich, Antimony trisulfide 99 %+.

Despite the great potential of all-inorganic CsPbX 3 (X = Br or I) quantum dots (QDs) for light-emitting diodes (QLEDs), their emission properties have been impeded by the long insulating ligands on the QD surface. To address the problem, an efficient surface ligand engineering method has been executed by using a short conjugation molecular ligand phenethylamine (PEA) as ligands to synthesize CsPbX 3 QDs and then treating the CsPbX 3 QD films with phenethylammonium bromide (PEABr) or phenethylammonium iodide (PEAI). The results indicate that the short conjugation molecular ligand is successfully adsorbed on the surface of CsPbX 3 QDs to instead long insulating ligands, resulting in the remarkable enhancement of the carrier injection and transport. The incorporation of phenethylamine (PEA) as synthetic ligand causes the fewer trap states in both CsPbBr 3 and CsPbI 3 QDs, exhibiting the near-unity photoluminescence quantum yields (PLQYs) of 93% and 95%, respectively. The luminance of CsPbBr 3 and CsPbI 3 QLEDs could be improved to 21470 and 1444 cd m −2 , respectively, when the long insulating ligands were further replaced with conjugation molecular ligands. Particularly, the external quantum efficiency (EQE) of CsPbI 3 QLEDs reaches 14.08%, which is among the highest efficiency of red perovskite LEDs.

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Zinc selenide nanoribbons and nanowires were obtained using laser ablation of ZnSe pressed powders. Their formation appeared to follow the vapor−solid and vapor−liquid−solid growth mechanisms, respectively. The product was characterized by means of scanning electron microscopy, transmission electron microscopy, micro-Raman scattering, and energy-dispersive X-ray spectroscopy. The ZnSe nanoribbons had a perfect wurtzite-2H single-crystal structure with a [120] growth direction and the {001} close-packed lattice planes of hexagonal ZnSe stacking along the nanoribbon width axis. The ZnSe nanowires grew with the {001} close-packed lattice planes of the wurtzite-2H structure stacking along the nanowire length axis. Both the longitudinal optic (LO) and transverse optic (TO) phonon peaks of the ZnSe nanowires and nanoribbons showed a clear shift toward low frequency relative to bulk values, probably because of small size and large surface effects. The ZnSe nanostructures exhibited strong self-activated luminescence centered at 596 nm.