We report here the selective formation of nanosized cavities on barium titanate (BaTiO3) nanocubes through a simple acid etching route in hydrothermal environment. Microstructural analysis reveals that the etching process is size dependent with small cavity preferentially formed on the nanocubes greater than a characteristic length of ∼60 nm. A dislocation assisted etching mechanism is proposed to account for the experimental observations and discussed on the basis of the classical dislocation theory. This simple method could be extended to other perovskites for fabricating novel and complex ferroelectric nanostructures.

•The wetting behaviors of N-polar GaN were studied for the first time.•A hydrophobic and highly adhesive N-polar GaN was obtaind.•The static friction of the modified N-polar GaN was estimated to be ∼15 mJ/m2.We report here the wetting behaviors of nanostructured N-polar GaN wafers. The nanostructured GaN samples were obtained by wet photochemical etching under UV illumination. It is confirmed that the wetting behavior of the nanostructured N-polar GaN surfaces follows the Wenzel model. Both surface roughening and decoration with Au nanoparticles will reduce the contact angle (CA), while modification with lauric acid will increase hydrophobility with CAs that change from 42.1° to 129.5°. Besides, the nanostructured surface shows high contact angle hysteresis due to strong static friction that can reach ∼15 mJ/m2.Download high-res image (70KB)Download full-size image

Patterns on semiconductors are crucial for optoelectronic microdevices in a wide variety of applications. We report here a facile photochemical method based on laser interference etching for fabrication of two-dimensional (2D) gratings and quasi-hexagonal photonic patterns on GaAs wafers. The periods of the patterns can be adjusted by tuning the incident angles without any significant change of the optical alignment. We find that the optical reflectivity of the etched samples is greatly reduced, especially for samples after three-beam interference etching with the minimum average reflectance of less than 2%, which can be easily adopted for fabricating anti-reflection layer of solar cells. Photoluminescence (PL) study shows that slightly blue shifted PL peaks can be observed due to quantum confinement effect.

We report here enhanced photoluminescence (PL) from GaP, an indirect band gap semiconductor, by metallic Au and Ag nanoparticles. The metallic Au and Ag nanoparticles were sputtering-coated onto GaP followed by heat treatment. After optimization of the surface coverage ratios, we find 5.6-fold and 14.5-fold PL enhancement for the Au and Ag coated samples, respectively. Time resolved photoluminescence spectroscopy indicates that Ag nanoparticles can effectively accelerate the PL decay time. Our results indicate that the PL enhancement comes from enhanced photon scattering and localized field enhancement of metallic Au and Ag nanoparticles.

We report here a new method to improve the performance of GaInP solar cells by fabricating Ag nanoparticles (Ag NPs) atop the devices through a simple wet-chemical method. The size and density of Ag NPs can be easily optimized by changing the concentration of AgNO3 solution and/or the reaction time. The Ag NPs support surface plasmonic resonances (SPRs) and thus greatly increase light absorbance and photocurrent responses of the solar cells by the scattering and re-reflection of incident light. We find that, for a Ag NPs density of ∼3.37 × 1010 cm−2, the short-circuit current density (Jsc) increases by 19.5% from 14.9 to 17.8 mA cm−2, and the power conversion efficiency (PCE) increases by 20.4% from 15.2% to 18.3%.

We report here on significant enhancement of the photochemical etching of p-type gallium phosphide (GaP) by Au plasmonic nanostructures. The photochemical etching rate of defect (dislocation) states of Au-coated p-GaP samples is ten times higher than blank samples when irradiated with 532 nm laser. It is confirmed that the enhancement of photochemical etching is wavelength selective. Only 532 nm laser can efficiently increase the photochemical etching rate, while lasers of other wavelengths (375, 405, 445, and 473 nm) show limited or negative effects. This observation can be attributed to defect (dislocation) enhanced photochemical etching through localized surface plasmon resonance of Au nanostructures. This method may open a new pathway for controlled fabrication of novel optoelectronic devices.

We report a novel method for fabricating periodic indentation patterns on AlGaInP light emitting diodes (LEDs) that can effectively improve the light extraction efficiency. The patterns consist of hemispherical pits created by directly imprinting the top GaP window layer of AlGaInP LEDs with patterned sapphire (PS). The angle resolved electroluminescence tests reveal that the patterned chips show an average light emission enhancement of 155% over the original planar chips.

Laser nanofabrication has attracted great interest for mass production of microstructures with desired or improved properties. We report here a facile, maskless method for fabricating two-dimensional (2D) quasiperiodic patterns on AlGaInP light-emitting diodes (LEDs) by photochemical laser interference etching. The interference pattern produced by two 532 nm laser beams is transferred to the top GaP window layer of the AlGaInP LEDs by photochemical etching of GaP in an etchant composed hydrofluoric acid (HF) and hydrogen peroxide (H2O2). The etched GaP surface contains 2D quasiperiodic pyramidal structures with a period of 150 ± 10 nm, which can dramatically increase the light extraction efficiency of the AlGaInP LEDs by 70%. This maskless patterning method is general and can be applied to fabricating patterns on optoelectronic devices based on other semiconductor materials.

Ag nanostructures with controlled morphologies have been synthesized on GaN epitaxial films through a convenient, fast, and surfactantless photochemical method. On n-type GaN, uniform spheroidic Ag nanoparticles (NPs) of high density were obtained after photochemical reaction for a short time (30 s to 5 min) in AgNO3 aqueous solution. Reducing AgNO3 concentration yielded branched Ag nanostructures. The Ag NPs on the GaN substrates exhibit a Fabry–Perot-type surface plasmon resonance (SPR). On p-type GaN, Ag nanocrystals (NCs) with well-defined shapes ranging from cubes, truncated cubes, cuboctahedra, truncated octahedra, and octahedra were obtained through varying the concentration of AgNO3 solution. We propose that the formation of polyhedral Ag NCs is induced by the separation of the nucleation and growth processes by the GaN surface. Both surface states and carrier concentration are considered to play substantial roles during the growth process. This surfactantless photochemical method is general and enables the facile synthesis of Ag nanostructures at room temperature, which may be extended for the synthesis of other noble metal nanostructures, e.g.Au, Pt, and Pd, on GaN or other wide bandgap semiconductors, e.g.SiC. The obtained Ag/GaN hybrid systems show potential application as solid substrates for surface enhanced Raman scattering (SERS) analysis.

We report here the synthesis of barium titanate (BaTiO3) microcrystallites by using Ti2O3 powders as the raw material through a modified hydrothermal method. The BaTiO3 contains abundant (1 1 1) twinned microcrystallites, along with a large amount of oxygen vacancies and Ti3+ cations. It is considered that (1 1 1) twins nucleate and grow from the face-shared TiO octahedra of rhombohedral Ti2O3. This unique BaTiO3 structure presents lower phase transition temperature than normal BaTiO3 and exhibits reversible photochromic effects under UV and NIR irradiation.

We report the laser output of transparent Nd:YAG (Nd:Y3Al5O12) ceramics fabricated from Nd:YAG precursors through the microwave-assisted homogenous precipitation (MAHP) method. Pure phase and uniform Nd:YAG nano-powders with average sizes less than 100 nm were obtained by heating treatment of the Nd:YAG precursor particles aged for 6 d in vessel with humidity of 30%–50% at 25°C. Transparent Nd:YAG ceramic pellets were obtained by vacuum sintering at 1730°C for 10 h. Laser output (305 mW) with a slope efficiency of 5.1% was realized through an end-pumped configuration. Our results indicate that the MAHP method could potentially be used for the fabrication of laser ceramic products.

We report here the controlled synthesis of (111) twinned BaTiO3 microcrystallites, which are widely known for their (110) ferroelectric twins. This (111) twinned structure was obtained through a composite hydroxide mediated process by using amorphous TiO2 powders. A twin assisted re-entrant growth model is proposed to account for the microstructural aspects determined. It is considered that the (111) twins originate from the Ti–O octahedra of the amorphous TiO2 powders. The role of oriented aggregation is also discussed.

We report here the electrical and photoluminescent behaviors of lanthanum hydroxide [La(OH)3] nanobelts doped with Ce3+ and Er3+. It is found that both the electrical conductivity and the fluorescence properties of the doped La(OH)3 can be significantly improved in comparison with their undoped counterparts. Microstructural and morphological aspects of La(OH)3 nanobelts before and after the doping process were examined by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Experimental results are discussed on the basis of classical semiconductor theory.

Defect-induced ferromagnetism in nanoparticles has recently attracted extensive attention. We report here that (111) twinned BaTiO3 crystallites synthesized through a modified hydrothermal method can exhibit ferromagnetic properties. The unexpected ferromagnetism is verified to originate from the point defects. We also find that UV irradiation can significantly enhance the ferromagnetism through creating more lattice defects. The photochromic effect is also observed and discussed.Keywords (keywords): (111) twin; BaTiO3; defects; ferromagnetism; photochromism;

We report here on significant enhancement of the photochemical etching of p-type gallium phosphide (GaP) by Au plasmonic nanostructures. The photochemical etching rate of defect (dislocation) states of Au-coated p-GaP samples is ten times higher than blank samples when irradiated with 532 nm laser. It is confirmed that the enhancement of photochemical etching is wavelength selective. Only 532 nm laser can efficiently increase the photochemical etching rate, while lasers of other wavelengths (375, 405, 445, and 473 nm) show limited or negative effects. This observation can be attributed to defect (dislocation) enhanced photochemical etching through localized surface plasmon resonance of Au nanostructures. This method may open a new pathway for controlled fabrication of novel optoelectronic devices.

Ag nanostructures with controlled morphologies have been synthesized on GaN epitaxial films through a convenient, fast, and surfactantless photochemical method. On n-type GaN, uniform spheroidic Ag nanoparticles (NPs) of high density were obtained after photochemical reaction for a short time (30 s to 5 min) in AgNO3 aqueous solution. Reducing AgNO3 concentration yielded branched Ag nanostructures. The Ag NPs on the GaN substrates exhibit a Fabry–Perot-type surface plasmon resonance (SPR). On p-type GaN, Ag nanocrystals (NCs) with well-defined shapes ranging from cubes, truncated cubes, cuboctahedra, truncated octahedra, and octahedra were obtained through varying the concentration of AgNO3 solution. We propose that the formation of polyhedral Ag NCs is induced by the separation of the nucleation and growth processes by the GaN surface. Both surface states and carrier concentration are considered to play substantial roles during the growth process. This surfactantless photochemical method is general and enables the facile synthesis of Ag nanostructures at room temperature, which may be extended for the synthesis of other noble metal nanostructures, e.g.Au, Pt, and Pd, on GaN or other wide bandgap semiconductors, e.g.SiC. The obtained Ag/GaN hybrid systems show potential application as solid substrates for surface enhanced Raman scattering (SERS) analysis.