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The recent development of perovskite-based lasers showcased the outstanding optical properties of the material such as high absorption coefficient and high quantum yield. The lasers were demonstrated in the form of nanowires and nanoplates, which are difficult to be integrated on a chip in the form of high-density arrays due to the difficulties in positioning them on the chip. The solution to this problem should be to use the well-known lithography process in the fabrication process of the lasers. In this work, we demonstrate several perovskite-based plasmonic lasers that were fabricated by using the lithographic in-mold patterning method that relies on the electron beam lithography process. The lasers utilized CsPbBr3 perovskite nanocrystals as the gain material and plasmonic distributed Bragg reflector grating structure as the optical feedback provider to achieve a low lasing threshold of 42.5 μJ/cm2 with a linewidth of 0.6 nm (FWHM) at room temperature. The use of the lithographic process in the fabrication of the lasers makes it possible to fabricate and integrate them on a chip in a relatively high-density manner, so that they can be used extensively in quantum optics and on-chip integrated photonics applications.

Liquid crystal random fiber lasers (LC-RFLs) exhibit low spatial coherence, extraordinary tunability, and high flexibility and are therefore promising for use in imaging and related applications. They nevertheless suffer from ineffective emission along the fiber axis. This work develops an end-emitting LC-RFL that is based on a pump-induced gain–loss structure, which effectively modulates the optical feedback, thereby providing directional random lasing along the fiber. The laser emission comprises ∼10 000 transverse spatial modes that are mutually incoherent, resulting in a negligible speckle contrast of ∼0.7% (far below the speckle-perception threshold of human eyes). The developed LC-RFL is used to perform speckle-free full-field imaging in a setting with strong optical crosstalk in a multimode fiber. Our findings support the potential widespread use of LC-RFL as a spatially incoherent, flexible laser source.

Selection of the bandedge lasing mode of a photonic crystal laser has been realized in a fluorescent dye doped chiral nematic liquid crystal by exerting electrical control over the mode competition. The bandedge lasing can be reversibly switched from the short-wavelength edge mode to the long-wavelength edge mode by applying a voltage of only 20 V, without tuning the bandgap. The underlying mechanism is the field-induced change in the order parameter of the fluorescent dye in the liquid crystal. The orientation of the transition dipole moment determines the polarization state of the dye emission, thereby promoting lasing in the bandedge mode that favors the emission polarization. Moreover, the dynamic mode-selection capability is retained upon polymer-stabilizing the chiral nematic liquid crystal laser. In the polymer-stabilized system, greatly improved stability and lasing performance are observed.

The Schottky barrier heights of various metals on the high permitivity oxides tantalum pentoxide, barium strontium titanate, lead zirconate titanate, and strontium bismuth tantalate have been calculated as a function of the metal work function. It is found that these oxides have a dimensionless Schottky barrier pinning factor S of 0.28–0.4 and not close to 1 because S is controlled by Ti–O-type bonds not Sr–O-type bonds, as assumed in earlier work. The band offsets on silicon are asymmetric with a much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate are relatively poor barriers to electrons on Si.

The band structure of the layered perovskite SrBi2Ta2O9 (SBT) was calculated by tight binding and the valence band density of states was measured by x‐ray photoemission spectroscopy. We find both the valence and conduction band edges to consist of states primarily derived from the Bi–O layer rather than the perovskite Sr–Ta–O blocks. The valence band maximum arises from O p and some Bi s states, while the conduction band minimum consists of Bi p states, with a wide band gap of 5.1 eV. It is argued that the Bi–O layers largely control the electronic response whereas the ferroelectric response originates mainly from the perovskite Sr–Ta–O block. Bi and Ta centered traps are calculated to be shallow, which may account in part for its excellent fatigue properties.

We report the discovery of superconductivity with an onset temperature of ∼0.6 K in a platinum-silicon interface. The interface was formed by using a unique focused ion beam sputtering micro-deposition method in which the energies of most sputtered Pt atoms are ∼2.5 eV. Structural and elemental analysis by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy reveal a ∼ 7 nm interface layer with abundant Pt, which is the layer likely responsible for the superconducting transport behavior. Similar transport behavior was also observed in a gold-silicon interface prepared by the same technique, indicating the possible generality of this phenomenon.

This work proposes two mechanisms for switching the direction of stripes in cholesteric liquid crystal (CLC) gratings. The stripe direction depends on the ratio of cell gap to the natural pitch length (d/P0) of a CLC sample. Electrical switching is based on the different pitches at the planar and the transient planar states. Optical switching, however, changes pitch by using the photo-isomerization effect of the azobenzene doped in a CLC sample. Using the two mechanisms, we can switch the stripe directions in two orthogonal directions. Furthermore, the beam-steering capability of CLC gratings also remains effective after switching directions.

We demonstrate an enhancement of infrared light harvesting of inorganic PbS nanocrystal photovoltaic and photodetector devices based on the transparent graphene electrode. Due to high infrared transparency of the graphene electrode with respect to indium tin oxide (ITO), the infrared photoresponse of the graphene-based device is superior to the ITO-based counterpart, in spite of a higher sheet resistance of the graphene electrode. The outstanding infrared characteristics of the devices based on the graphene electrode make it a promising candidate for infrared optoelectronic applications such as solar cells, imaging and sensing, or optical communication.

The surface plasmon (SP) excitations of gold/silica nanowire, investigated by electron energy-loss spectroscopy in conjunction with scanning transmission electron microscopy, are found to be anisotropic with stronger SP intensities observed along the transverse direction of the nanowire. This indicates that the charge carriers generated near the surface of the nanowires by the decay of SP resonance play a significant role to the enhanced photoconductivity. This conclusion is reaffirmed by the polarization dependent photoconductivity measurement.

We have demonstrated an improvement of photovoltaic performance based on the nanostructured ZnO/poly(3-hexylthiophene) (P3HT) hybrid through interface molecular modification on ZnO nanorod surface. By probing the carrier dynamics at ZnO/P3HT interfaces, we have found that the interfacial molecules can play the role of assisting charge separation and suppression of back recombination at interfaces, which accounts for the observed enhanced short circuit current (Jsc) and open circuit voltage (Voc) in photovoltaic performance.

In this article, we have proposed a nanostructured near-ultraviolet photodetector (

The deposition and optoelectronic properties of reduced graphene oxide thin films are described. Thin films with thicknesses ranging from 1–10nm have been deposited by the vacuum filtration method. The conductivity of the thin films can be varied over six orders of magnitude by varying the filtration volume of the graphene oxide aqueous suspension while maintaining the transmittance between 60%–95%. In addition, enhancement in the conductance through Cl doping is demonstrated. The combination of the reduction and Cl treatments make the reduced graphene oxide thin films sufficiently conducting to incorporate them as the hole collecting electrode in proof of concept organic photovoltaic devices.

In this study, polarized-Raman scattering measurements of an individual ZnO nanorod were carried out by using a confocal microscope together with a high-resolution piezoelectric stage. A predominant A1 (TO) mode at 378cm−1 in the parallel polarization (E∥) configuration and a predominant E2 (high) mode at 438cm−1 in the perpendicular polarization (E⊥) configuration demonstrate the strong polarization dependent Raman scattering signals of an individual ZnO nanorod. The Raman intensity images of the individual ZnO nanorods with different orientation configurations can also be obtained, which reflect the interplay between the local phonon behavior and geometric anisotropy.

In this article, the polymer photovoltaic devices based on the poly(3-hexylthiophene)/TiO2 nanorods hybrid material is present. An enhancement in the device performance can be achieved by removing or replacing the insulating surfactant on the TiO2 nanorod surface with a more conductive ligand, which can play the role to assist charge separation efficiency or also to prevent from back recombination, giving a large improvement in the short circuit current and fill factor. The relatively high power conversion efficiency of 1.7% under simulated AM 1.5 illumination (100mW∕cm2) can be achieved, providing a route for fabricating low-cost, environmentally friendly polymer photovoltaic devices by all-solution processes.

Nearly defect-free InN microcrystals grown on Si(111) substrates have been realized by plasma-assisted molecular beam epitaxy. High-resolution transmission electron microscope images reveal that these microcrystals exhibit single-crystalline wurtzite structure. Low temperature photoluminescence (PL) shows a strong emission peak at 0.679eV with a very narrow linewidth of 17meV at excitation power density of 3.4W∕cm2. Temperature-dependent PL spectra follow the Varshni equation well, and peak energy blueshifts by ∼45meV from 300to15K. Power-density-dependent PL spectroscopy manifests direct near-band-edge transition. A low carrier density of 3×1017cm−3 has been estimated from PL empirical relation, which is close to the critical carrier density of the Mott transition of 2×1017cm−3.

Comprehensive studies of temperature-dependent gate-metal-related impact ionization in metamorphic high electron mobility transistors (MHEMTs) are demonstrated. It is known that, from experimental results, the electric field and temperature dependences of impact ionization mechanisms in MHEMT’s operation are dominated by the ionization threshold energy and hot electron population. The peak impact ionization-induced gate current could be substantially decreased by the presence of specific gate contact with a higher Schottky barrier height. Therefore, the suppressions of bell-shaped behavior and related impact ionization effect are observed by using the appropriate Schottky gate contacts.

The electro-optical modulation effect of a (10,0) boron nitride nanotube is investigated by first-principles, density functional theory calculations. The optical properties of boron nitride nanotubes can be tuned through perturbation by a transverse electric field. Large optical anisotropy in variations of the absorption spectra and refractive indices in response to external electric field is found. In addition, a method called the band-resolved absorption density analysis technique is developed to investigate the detailed optical absorption transition processes. The result is consistent with the recent experimental observation [M. Ishigami et al., Phys. Rev. Lett. 94, 56804 (2005)] and suggests that the boron nitride nanotubes can be a promising material for electro-optical modulation device applications.

Cathodoluminescence (CL) spectroscopy has been employed to study the electronic and optical properties of well-aligned ZnO nanorods with diameters ranging from 50to180nm. Single-nanorod CL studies reveal that the emission peak moves toward higher energy as the diameter of the ZnO nanorod decreases, despite that their sizes are far beyond the quantum confinement regime. Blueshift of several tens of meV in the CL peak of these nanorods has been observed. Moreover, this anomalous energy shift shows a linear relation with the inverse of the rod diameter. Possible existence of a surface resonance band is suggested and an empirical formula for this surface effect is proposed to explain the size dependence of the CL data.

Photoconductivity of amorphous silicon carbon nitride (a-SiCN) as a function of incident photon energies has been studied. A metal-semiconductor-metal photodetector device based on the a-SiCN thin film demonstrates excellent selective ultraviolet sensing features. A large photo-to-dark current ratio about 5000 and a relative quantum efficiency about ∼105 under illumination of the 250nm light source and a bias voltage of 5V were observed. A model based on the heterogeneous structure in the a-SiCN thin film which consists of π−π* bands and σ−σ* bands was introduced to account for the observed photoconductive transport properties.