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Nonaqueous organic electrolyte was utilized to etch GaN via photo-electrochemical etching technique. From the point of electrochemical window, the organic electrolyte has wider electrochemical window than conventional aqueous etchants. SEM images show that the pore density is up to 1.2 × 107 per square centimeter. The difference of XPS spectra about survey, Ga 3d and N 1s between the non-etched and freshly etched GaN surface can be explained the formation of Ga(BF4)3. The proposed dissolution mechanism can be broadly applied for explaining the etching process of nonaqueous etchants under the assist of electric field and strong light.

Porous gallium nitride (GaN) luminescent materials were fabricated by photoelectrochemical etching using three different 1-ethyl-3-methylimidazolium ([EMIM])-based ionic liquids as the etchants. The as-etched porous GaN presents honeycomb shape, deep gully with some holes in the surroundings, and overlapping hole structure, which are significantly different from the planar GaN. Moreover, photoluminescence (PL) spectra indicates that the porous GaN has more excellent PL performance than the planar GaN. In general, reducing the etching time to 1 min, the PL intensity of porous GaN etched by [EMIM][OTF] is 9.27 times than that of the planar one. These results suggest that porous GaN etched by ionic liquid can be an outstanding substrate in the field of the luminescent material.

Three-dimensional (3D) metal-semiconductor nanostructures as surface-enhanced Raman scattering (SERS) substrates were designed by in situ electrodeposition of gold nanoparticles (AuNPs) or in situ photodeposition of silver nanoparticles (AgNPs) on gallium nitride (GaN) nanoflowers (NFs) supports fabricated by metal-assisted photochemical etching of single crystalline GaN. 3D AuNPs/GaN NFs and AgNPs/GaN NFs substrates exhibit excellent enhancement effect for Rhodamine 6G (R6G) due to more “hot spots” in the same probing volume compared to 2D GaN based substrates. The enhancement factors of the AuNPs/GaN NFs and AgNPs/GaN NFs substrates are up to 2.1 × 10 7 and 5.9 × 10 7 , respectively, and the corresponding detection limits of R6G are 10 −8 and 10 −10 M, respectively. Moreover, further study reveals both substrates have good reproducibility and long-term stability. The performance of the prepared substrates for biological application was demonstrated by the detection of bovine serum albumin (BSA). A series of characteristic bands of amides suggest BSA can be well adsorbed on the surface of the AuNPs/GaN NFs and AgNPs/GaN NFs substrates, which demonstrates our substrates have good biocompatibility and are promising candidates for SERS biosensors.

In this study, we report for the preparation of nickel phthalocyanine (NiPc) free-standing films on ionic liquid (IL) surface by a physical vapor deposition method. Different from on the solid substrate, the as-obtained film is α phase and with a 2D network structure. In addition, the good transferability of the film make it can be easily transferred onto any substrate for further device applications. The device based on these films shows good photoelectrical property, high stability and high photosensitivity.

Gallium nitride (GaN) nanowires (NWs) were fabricated by metal-assisted photochemical etching (MaPEtch). Gold nanoparticles (AuNPs) as metal catalyst were electrodeposited on the GaN substrate. SEM and HRTEM images show the surface of GaN NWs is smooth and clean without any impurity. SAED and FFT patterns demonstrate GaN NWs have single crystal structure, and the crystallographic orientation of GaN NWs is (0002) face. On the basis of the assumption of localized galvanic cells, combined with the energy levels and electrochemical potentials of reactants in this etching system, the generation, transfer and consumption of electron-hole pairs reveal the whole MaPEtch reaction process. Such easily fabricated GaN NWs have great potential for the assembly of GaN-based single-nanowire nanodevices.

The structural relaxation times of metallic glasses (MGs) are generally believed to decrease with increasing flow rate, also known as shear thinning. In this work, an extraordinary loading rate-independent creep relaxation time, in contrast to the decreasing Maxwell relaxation time with increasing loading rate, is observed for a La-based MG with pronounced Johari–Goldstein relaxation under nanoindentation. The Johari–Goldstein relaxation in the flow of MGs is suggested to be a form of local Newtonian flow and may be not crucial in shear thinning, whereas the main α relaxation is proposed to predominate in the shear thinning of MGs, based on the disparity between the creep relaxation time and the Maxwell relaxation time. These results improve the current understandings on the structural relaxation and its role in the shear thinning and plastic deformation of MGs.

Gallium nitride (GaN) surface was etched by 0.3 M ethylenediamine tetraacetic acid disodium (EDTA-2Na) via photoelectrochemical etching technique. SEM images reveal the etched GaN surface becomes rough and irregular. The pore density is up to 1.9 × 10 9 per square centimeter after simple acid post-treatment. The difference of XPS spectra of Ga 3d, N 1s and O 1s between the non-etched and freshly etched GaN surfaces can be attributed to the formation of Ga–EDTA complex at the etching interface between GaN and EDTA-2Na. The proposed complexation dissolution mechanism can be broadly applicable to almost all neutral etchants under the prerequisite of strong light and electric field. From the point of view of environment, safety and energy, EDTA-2Na has obvious advantages over conventionally corrosive etchants. Moreover, as the further and deeper study of such nearly neutral etchants, GaN etching technology has better application prospect in photoelectric micro-device fabrication.

Porous gallium nitride (PGaN) layers were fabricated by metal-assisted photochemical etching (MaPCE) using electrodeposited platinum nanoparticles (PtNPs) or gold nanoparticles (AuNPs) as catalysts. After identification of a suitable negative potential and appropriate cyclic voltammetry (CV) conditions, high-density PtNPs or AuNPs were deposited onto a planar GaN substrate. Based on the concrete numerical values of energy levels, the generation, transfer and consumption of electrons and holes, and the assumption that localized galvanic cells are formed, an etching mechanism was proposed which may provide theoretical guidance for future work on etching of GaN and other semiconductor materials. Keywords: Gallium nitride, Metal-assisted photochemical etching, Electrodeposition, Noble metal nanoparticles

Here we report the electrodeposition of gold nanoparticles (AuNPs) onto porous GaN electrode obtained by photoelectrochemical etching planar GaN to fabricate a non-enzymatic hydrogen peroxide (H2O2) sensor. SEM images revealed porous GaN has uniformly high-porosity structure and the diameter of AuNPs is 5–16 nm. The AuNPs/porous GaN electrode exhibited good electrocatalytic activity toward the reduction of H2O2 and performed as amperometric sensor for the detection of H2O2. The AuNPs/porous GaN electrode showed linear amperometric responses for H2O2 in the concentration range from 10 to 100 μM with the sensitivity of 281.5 μA mM−1. The limit of detection (LOD) is 2 μM with a signal-to-noise ratio of 3. In addition, the AuNPs/porous GaN electrode exhibited good repeatability, reproducibility, selectivity and long-term stability for H2O2 detection, in the meanwhile, AuNPs showed excellent adhesive capacity to the porous GaN electrode, which was tested by continually sonicating the AuNPs/porous GaN electrode for 3 h. Above results demonstrated this simply prepared H2O2 sensor has good practicability and is promising to measure the analyte in practical applications.

Here we report an environment-friendly approach to fabricate porous GaN photoelectrode using ionic liquid as the etchant. SEM images revealed photo-assisted electrochemical etching (PECE) has better etching effect than electrochemical etching (ECE). Furthermore, Raman spectra demonstrated porous GaN obtained by PECE has better lattice integrity than that obtained by ECE. The photocurrent of porous GaN prepared by PECE is six times and two times of planar and porous GaN fabricated by ECE, respectively. Above results indicated porous GaN obtained by PECE can be a promising photoelectrode for optoelectronic applications.

We demonstrated a simple method for the fabrication of gold nanoparticles/porous GaN composite by using photo-assisted electrochemical etching and electrochemical deposition methods based on planar GaN film for photocatalytic degradation of methyl orange. Scanning electron microscopy (SEM) images revealed porous GaN has uniformly high-porosity structure and the diameter of gold nanoparticles (AuNPs) is 4–20 nm. Moreover, the pore diameter of porous GaN can be easily adjusted by changing etching time. Uniformly small AuNPs can be obtained by optimized deposition cycles of cyclic voltammetry (CV). The photocatalysis activity under simulated sunlight irradiation was enhanced via electrodepositing AuNPs onto porous GaN substrate. Above results indicated such porous GaN could be an excellent candidate to study the photocatalytic performance of porous wide band-gap semiconductor-based composite materials.

By virtue of instability analysis, an index of shear banding susceptibility of metallic glasses (MGs): the critical strain localization factor to initiate an embryonic shear band: χ = γ b / γ m ( γ b shear strain in the embryonic shear band and γ m in the matrix) is derived in analogue to the emergence of geometrically necessary dislocations (GND) in crystals. Physical properties, like Poisson ratio υ , Young's modulus E and the surface energy density ζ , are explicitly incorporated into the formulae of χ with which the origin of the plasticity of MGs are unraveled.

Heterogeneous dynamics in the flow of supercooled metallic liquids are revealed as the oscillated mechanical response in compression and evidenced to be consistent with the range of medium length scales over which structural rearrangements occur detected by small angle X-ray scattering (SAXS) in heating from room temperature to the supercooled liquid region. This range of medium length scales is suggested to be the structural origin of the heterogeneous dynamics of metallic glasses. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A heterojunction of ZnO/porous GaN (ZnO/PGAN) was fabricated and directly applied to a diode-type humidity sensor. ZnO disks were loaded onto PGAN using a spraying process. The structure and surface morphology of the ZnO/PGAN were characterized using X-ray diffraction and scanning electron microscopy. The heterojunction displayed an excellent diode nature, which was investigated using photoluminescence spectra and I–V characteristics. The excellent transport capability of ZnO/PGAN contributes to enhanced electron transfer, and hence results in high sensitivity and quick response/recovery properties under different relative humidity (RH) levels. In the range of 12–96% RH, a fast sensing response time as low as 7 s and a recovery time of 13 s can be achieved. The simple design of a ZnO/PGAN based humidity sensor highlights its potential in various applications.

Free-standing films of metal octaethylporphyrins (MOEPs) were prepared for the first time by a physical vapor deposition on surface of an ionic liquid (IL). Different from those on solid surfaces, the as-obtained films were very compact and with plannar structure. The monitoring of time-dependent process indicated that the high surface energy of IL and the strong π…π interaction between MOEP molecules played key roles in forming such films. Furthermore, the as-obtained film showed good transferability, which made it possible to be easily transferred to any substrates for further device application. More importantly, the prototype photodetectors based on free-standing films of MOEP showed ultra flexibility, mechanical stability, and durability.

Upon mechanically milling with as-prepared single-walled carbon nanotubes, the dehydriding/rehydriding kinetics of LiBH 4 can be markedly improved, thus rendering the system partial reversibility at reduced temperature/pressure conditions. Based on the property/phase analysis results, as well as the results of the designed experiments, the observed catalytic enhancement was understood as combined effects of metallic Ni, Co, Fe or their borides nanoparticles, and carbon nanotubes.

Quaternary Heusler alloy Ni50Mn8Fe17Ga25 has been synthesized by melt-spinning method. Pole figure examination suggested that the ribbon samples have a strong preferentially orientation in [400] about 5-10degrees tilted from the ribbon normal. The effect of heat treatment on the magnetic and phase transformation properties of Ni50Mn8Fe17Ga25 ribbon has been investigated. Annealing increased the martensitic transformation temperature, Curie temperature and decreased the transformation hysteresis and magnetic hysteresis due to the change of atomic chemical ordering. Thermoelastic transformation strain was decreased from -0.19% to -0.17% after annealing. At the same time, a slighter decrease of transformation strain by adding external bias field was observed in the as-annealed ribbons, which has not been found in the as-spun ribbons. These can be attributed to the relaxation of the internal stress through annealing. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

alpha-MoO3 whiskers were prepared via an oxidation process of a Mo slice in oxygen. MoO3 vapors condensed to form the alpha-MoO3 whiskers with white color. On surfaces of the MoO3 whiskers, the atom ratio of oxygen to molybdenum was 4.4, which was higher than that of bulk MoO3. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The growth behavior and surface morphology of a rough film system, deposited on silicone oil drop surfaces by a r.f. magnetron sputtering method, have been studied. An anomalous film growth relaxation is observed during the deposition process. The relaxation rate is extremely sensitive to the substrate temperature. The surface morphology at the micrometer length scale is very susceptible to the substrate temperature, the incident r.f. capacity, and the nature of the solid substrate on which the oil drop is dripped. A discussion on the physical origins of these phenomena is also presented.

The temperature dependence of the magnetic field-induced strain (MFIS) and the field-controlled shape memory effect in Ni/sub 52/Mn/sub 16.4/Fe/sub 8/Ga/sub 23.6/ single crystals were investigated by measuring the MFIS and measuring the magnetic field-enhanced transformation strain with a field bias applied in the [001] and [010] directions of the parent phase, respectively. The results show that such material combined with the martensitic transformation can product large field-enhanced transformation strain and large MFIS. The strain accompanying the martensitic transformation is -1.61% in zero field and can be enhanced to -3.30% by a field of 960 kA/m. A MFIS of 1.04% has been induced along [001] in unstressed crystals with saturated magnetic field of 600 kA/m applied along the same direction at near martensitic transformation temperature. It was found that the MFIS is almost temperature independent; the maximum decrease of the saturated MFIS is less than 10%, from 265 K to 100 K. This well-behaved temperature response makes this alloy particularly valuable for industrial and military smart actuators and transducers. Furthermore, it was found that the direction in which the MFIS has the largest value is always the [001], namely, the growth direction of the crystals.

In this paper described about the synthesis of the magnetic shape memory alloys Ni/sub 2/FeGa, Mn/sub 2/FeSn and Co/sub 50/Ni/sub 30/Ga/sub 20/ and their characterization magnetic susceptibility, martensitic transformation, XRD, TEM were studied.

ReTiO3+delta/2 (Re = La and Nd) thin films have been grown on (100)SrTiO3 and (100)LaAlO3 by using the pulsed laser deposition technique. Oxygen content in the films was tuned by adjusting the oxygen pressure during film growth. At higher pressures, the films tend to be in their fully oxidized insulating form ReTiO3.5 with a twinned structure and (01 (2) over bar) orientation. Grown in vacuum, the films are lightly doped with a small 6, and retain the near-cubic perovskite structure. The films grown on different substrates show distinct magnetic and transport properties, which cannot be fully attributed to the conducting SrTiO3 substrates or the interdiffusion. In metallic films, a decrease of the carrier density and an increase of the Hall mobility at low temperatures was observed, and the transport behaviors can be fitted by a small-polaron coherent conduction model (R-s(T) = R-s(0) + C omega(alpha)/sinh(2) (T-omega/T)). (c) 2007 Elsevier B.V. All rights reserved.

Carrier transport through an n-type semiconductor grain boundary with a double Mott barrier consisting carrier depletion layers,acceptor defect layers (ACLs) on grain surface and negative-charged interface by trapping of majority carriers is studied.The effect of ACL on the barrier,current,nonlinearity and capacitance is especially treated.The change of barrier under bias governs transport properties,and ascertains the existance of pre-breakdown,breakdown and upturn regions.ACLs result in a change of barrier and its intensifying decline under bias,and thus enhance the current change and nonlinearity,and largely determine the leakage current.And ACLs reduce capacitance at high frequency by broaden barrier but increase capacitance peak originated from the resonant response of interface charge under bias.

The quantitative analyses for our proposed potential-barrier model are given in this paper. The results quantitatively explain how the semiconductiong BaTiO3 ceramics transforms from PTC effect to GBBL capacitor. The designs of PTC resistors and GBBL capacitors from this model are made, and the design properties are much better than that of present experimental data. The mathods improving the properties of relevant devices are discussed. The model provides a theoretical basis for the design, manufacture and property improvement of semiconducting BaTiO3 ceramic devices.