Crystalline GaN nanosheets hold great challenge in growth and promising application in optoelectronic nanodevices. In this work, we reported an accessible template approach toward the rational synthesis of GaN nanosheets through the nitridation of metastable γ-Ga2O3 nanosheets synthesized from a hydrothermal reaction. The cubic γ-Ga2O3 nanosheets with smooth surface and decent crystallinity can be directly converted into hexagonal GaN nanosheets with similar morphology framework and comparable crystal quality in NH3 at 850 °C. UV–vis spectrum measurement reveals that the GaN nanosheets show a band gap of 3.30 eV with strong visible absorption in the range of 370–500 nm. The template synthetic strategy proposed in this work will open up more opportunities for the achievement of a variety of sheetlike nanostructures that can not be obtained through conventional routines and will undoubtedly further promote the fundamental research of newly emerging sheetlike nanostructures and nanotechnology.Keywords: GaN; HRTEM; nanosheets; optical property; template synthesis; γ-Ga2O3;

The detection of UV-A rays (wavelength of 320–400 nm) using functional semiconductor nanostructures is of great importance in either fundamental research or technological applications. In this work, we report the catalytic synthesis of peculiar bicrystalline GaN nanowires and their utilization for building high-performance optoelectronic nanodevices. The as-prepared UV-A photodetector based on individual bicrystalline GaN nanowire demonstrates a fast photoresponse time (144 ms), a high wavelength selectivity (UV-A light response only), an ultrahigh photoresponsivity of 1.74 × 107 A/W and EQE of 6.08 × 109%, a sensitivity of 2 × 104%, and a very large on/off ratio of more than two orders, as well as robust photocurrent stability (photocurrent fluctuation of less than 7% among 4000 s), showing predominant advantages in comparison with other peer semiconductor photodetectors. The outstanding optoelectronic performance of the bicrystalline GaN nanowire UV-A photodetector is further analyzed based on a detailed high-resolution transmission electron microscope (HRTEM) study, and the two separated crystal domains within the GaN nanowires are believed to provide separated and rapid carrier transfer channels. This work paves a solid way toward the integration of high-performance optoelectronic nanodevices based on bicrystalline or horizontally aligned one-dimensional semiconductor nanostructures.Keywords: bicrystalline nanowires; GaN; HRTEM; photodetectors; UV-A ray;

High performance ultraviolet (UV) photodetectors based on semiconducting nanowires are expected to have extensive applications in UV-ray detection, optical communication and environmental monitoring. In this work, GaN nanowire photodetectors have been fabricated and giant UV photoresponse has been achieved with Pt nanoparticle (NP) modification. The peak responsivity and external quantum efficiency (EQE) of the GaN nanowire UV photodetector were increased from 773 to 6.39 × 104 A W−1 and from 2.71 × 105% to 2.24 × 107%, respectively, and the response time and sensitivity were improved greatly after Pt NP decoration on the GaN nanowire surface. Moreover, the Pt–GaN nanowire photodetector still presents its spectrum selectivity in the UV region. Our results reveal that Pt nanoparticles play a key role in enhancing the photodetection performance of the nanodevice due to the strong absorption and scattering of incident light induced by localized surface plasmon resonance (LSPR) and the improvement of interfacial charge separation owing to the special device configuration. These findings offer an efficient avenue toward the performance enhancement of GaN nanowire and related optoelectronic devices or systems.

In present work, diamond/β-SiC composite interlayers were deposited on cemented tungsten carbide (WC-6%Co) substrates by microwave plasma enhanced chemical vapor deposition (MPCVD) using H2, CH4 and tetramethylsilane (TMS) gas mixtures. The microstructure, chemical bonding, element distribution and crystalline quality of the composite interlayers were systematically characterized by means of field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), electron probe microanalysis (EPMA), Raman spectroscopy and transmission electron microscropy (TEM). The influences of varying TMS flow rates on the diamond/β-SiC composite interlayers were investigated. Through changing the TMS flow rates in the reaction gas, the volume fraction of β-SiC in the composite interlayers were tunable in the range of 12.0%–68.1%. XPS and EPMA analysis reveal that the composite interlayers are composed of C, Si element with little cobalt distribution. The better crystallinity of the diamond in the composite is characterized based on the Raman spectroscopy, which are helpful to deposit top diamond coatings with high quality. Then, the adhesion of top diamond coatings were estimated using Rockwell C indentation analysis, revealing that the adhesion of top diamond coatings on the WC-6%Co substrates can be improved by the interlayers with the diamond/β-SiC composite structures. Comprehensive TEM interfacial analysis exhibits that the cobalt diffusion is weak from WC-6%Co substrate to the composite interlayer. The homogeneous microcrystalline diamond coatings with the most excellent adhesion can be fabricated on the substrates with the composite interlayer with the β-SiC/diamond ratio of about 45%. The composite structures are appropriate for the application in high-efficiency mechanical tool as a buffer layer for the deposition of the diamond coating.

Neurological disorders have always triggered the interest of scientists due to the effects they have on the quality of life and the complexity they provide in their perception. Herein, we report a cellular-membrane inspired surface modification to fabricate a chemosensor for selective epinephrine detection. For this, well aligned ZnO nanorod arrays were grown on a silicon substrate using a feasible hydrothermal method and further utilized for the immobilization of a lipid membrane incorporated with calix[6]arene (in a 100 : 1 ratio) after modification with 1-octadecanthiol. Such surfaces were employed for selective epinephrine detection using electrochemical impedance spectroscopy as a transduction method. The detection process was based on the Lock & Key mechanism. A distinctive increase in charge transfer resistance was observed for epinephrine as compared to dopamine, leading to the conclusion that the sensor is sensitive and selective to epinephrine. This selectivity for epinephrine can be attributed to the slight differences in the molecular sizes of dopamine and epinephrine. Such electrochemical sensors can provide a very useful platform for the manufacturing of devices for monitoring the physiological concentrations of epinephrine.

Well-aligned GaN nanowires are promising candidates for building high-performance optoelectronic nanodevices. In this work, we demonstrate the epitaxial growth of well-aligned GaN nanowires on a [0001]-oriented sapphire substrate in a simple catalyst-assisted chemical vapor deposition process and their alignment control. It is found that the ammonia flux plays a key role in dominating the initial nucleation of GaN nanocrystals and their orientation. Typically, significant improvement of the GaN nanowire alignment can be realized at a low NH3 flow rate. X-ray diffraction and cross-sectional scanning electron microscopy studies further verified the preferential orientation of GaN nanowires along the [0001] direction. The growth mechanism of GaN nanowire arrays is also well studied based on cross-sectional high-resolution transmission electron microscopy (HRTEM) characterization and it is observed that GaN nanowires have good epitaxial growth on the sapphire substrate following the crystallographic relationship between (0001)GaN∥(0001)sapphire and (100)GaN∥(110)sapphire. Most importantly, periodic misfit dislocations are also experimentally observed in the interface region due to the large lattice mismatch between the GaN nanowire and the sapphire substrate, and the formation of such dislocations will favor the release of structural strain in GaN nanowires. HRTEM analysis also finds the existence of “type I” stacking faults and voids inside the GaN nanowires. Optical investigation suggests that the GaN nanowire arrays have strong emission in the UV range, suggesting their crystalline nature and chemical purity. The achievement of aligned GaN nanowires will further promote the wide applications of GaN nanostructures toward diverse high-performance optoelectronic nanodevices including nano-LEDs, photovoltaic cells, photodetectors etc.

(GaN)1−x(ZnO)x solid solution has attracted extensive attention due to its feasible band-gap tunability and excellent photocatalytic performance in overall water splitting. However, its potential application in the photodegradation of organic pollutants and environmental processing has rarely been reported. In this study, we developed a rapid synthesis process to fabricate porous (GaN)1−x(ZnO)x solid solution with a tunable band gap in the range of 2.38–2.76 eV for phenol photodegradation. Under visible-light irradiation, (GaN)0.75(ZnO)0.25 solid solution achieved the highest photocatalytic performance compared to other (GaN)1−x(ZnO)x solid solutions with x = 0.45, 0.65 and 0.85 due to its higher redox capability and lower lattice deformation. Slight Ag decoration with a content of 1 wt% on the surface of the (GaN)0.75(ZnO)0.25 solid solution leads to a significant enhancement in phenol degradation, with a reaction rate eight times faster than that of pristine (GaN)0.75(ZnO)0.25. Interestingly, phenol in aqueous solution (10 mg L−1) can also be completely degraded within 60 min, even under the direct exposure of sunlight irradiation. The photocurrent response indicates that the enhanced photocatalytic activity of (GaN)0.75(ZnO)0.25/Ag is directly induced by the improved transfer efficiency of the photogenerated electrons at the interface. The excellent phenol degradation performance of (GaN)1−x(ZnO)x/Ag further broadens their promising photocatalytic utilization in environmental processing, besides in overall water splitting for hydrogen production.

(GaN)1−x(ZnO)x solid-solution nanostructures with superior crystallinity, large surface areas and visible light absorption have been regarded as promising photocatalysts for overall water splitting to produce H2. In this work, we report the preparation of (GaN)1−x(ZnO)x solid-solution nanorods with a high ZnO solubility up to 95% via a two-step synthetic route, which starts from a sol–gel reaction and follows with a nitridation process. Moreover, we clearly demonstrated that the crystallographic facets of (GaN)1−x(ZnO)x solid-solution nanorods can be finely tailored from non-polar {100} to semipolar {101} and then finally to mixed {101} and polar {000} by carefully controlling the growth temperature and nitridation time. Correspondingly, the ZnO content in the GaN lattice can be achieved in the range of ∼25%–95%. Room-temperature cathodoluminescence (CL) measurements on the three types of (GaN)1−x(ZnO)x solid-solution nanorods indicate that the minimum band-gap of 2.46 eV of the solid-solution nanorods is achieved under a ZnO solubility of 25%. The efficiency and versatility of our strategy in the band-gap and facet engineering of (GaN)1−x(ZnO)x solid-solution nanorods will enhance their promising photocatalytic utilizations like an overall water splitting for H2 production under visible-light irradiation.

To date, numerous approaches have been developed for fabricating high quality organometal halide perovskite thin films, however, perovskite films obtained by such methods reveal a brown or dark-brown color, which might restrain their light absorption ability. Here we report a route to synthesize dark-blue mirror-like perovskite dense films via a two-step spin-coating process assisted by treatment of nonpolar solvent scouring. Photovoltaic cells based on such dark-blue films demonstrate a high short-circuit current density (Jsc) of ∼23 mA cm−2 and a power conversion efficiency (PCE) of 16.1%. Our method would provide a new candidate method for the fabrication of perovskite solar cells with high performance.

MnWO4 nano photocatalysts with plate shapes and in high yields are in situ synthesized on the surface of a porous TiO2 film by the conventional plasma electrolytic oxidation (PEO) method combined with a subsequent ambient annealing process. Transmission electron microscopy (TEM) analysis shows that the MnWO4 nano photocatalysts are single crystals free of structural defects and scanning electron microscopy (SEM) observation on the cross-section reveals that these MnWO4 nano photocatalysts are in situ grown on the porous TiO2 film surface with strong adhesion. The morphology and dimension size can be selectively tailored through controlling the reaction time, showing the simplicity and versatility of the proposed method. In addition, the photodegradation of methylene blue (MB) solution using the MnWO4/TiO2 photocatalysts demonstrated the superior photocatalytic performance with high efficiency and excellent photostability. A high photodegradation rate of MB solution of over 90% in 60 min has been achieved and a superior cyclic capability is also obtained. The superior photocatalytic performance of MnWO4/TiO2 photocatalysts can be mainly attributed to the good crystallinity, all-surface covering and strong mechanical properties of the MnWO4 nanostructures with TiO2 film. The prevailing advantage of the PEO method in combination with the ambient annealing process will open up more opportunity for the rational synthesis of a wide range of oxide photocatalysts ranging from tungstate to titanate, molybdate and vanadate for promising catalytic applications in diverse fields.

Nanoscale semiconductor heterostructures with superior crystal quality, large surface area and designed interfaces provide more opportunities for building high-performance optoelectronic nanodevices and harvesting clean energy. In this work, we report the rational synthesis of In2S3/In2O3 heterostructures through a two-channel chemical vapor deposition (CVD) process. The In2S3/In2O3 heterostructures feature a bundle-like morphology with In2S3 nanowires covering randomly distributed In2O3 nanoparticles. High-resolution transmission electron microscopy (HRTEM) analysis on the In2S3/In2O3 heterostructures finds that both In2S3 nanowires and In2O3 nanoparticles show a crystalline nature, but the lattice matching between the two crystal domains is not observed at the interface, implying that the heterostructure is formed via a simple physical adsorption. Cathodoluminescence (CL) studies on In2S3/In2O3 heterostructures indicate that the as-synthesized heterostructures have a broad emission in the range of 400–950 nm, covering the whole visible light spectrum from violet to infrared. Finally, the formation process of In2S3/In2O3 heterostructures and their optical emission behaviors are discussed based on detailed structural analyses.

•Large-scale heteroepitaxial 3C-SiC film on 4-in. Si wafer was obtained by MPCVD through altering power and TMS flow rate.•XPS indicates the information of SiC film surface and its depth profiles, proving the uniformity of elements distribution.•The film morphology transforms from the heteroepitaxial SiC film into 2D nanosheets with increasing chamber pressure.The controllable growth of heteroepitaxial cubic SiC (3C-SiC) films and two dimensional (2D) nanosheets arrays has been successfully achieved using a 915 MHz microwave plasma enhanced chemical vapor (MPCVD) deposited technique using tetramethylsilane (TMS) and hydrogen as the resource gases. A comprehensive analysis of the surface morphology of the 3C-SiC films was performed by tuning microwave power, TMS flow rate and gas pressure. With increasing microwave power, the morphology of the SiC crystals evolves from randomly oriented nanocrystals to well-oriented pyramid shaped crystals. The rocking curve results shows that the 3C-SiC film deposited at microwave power of 9 kW and gas pressure of 50 mbar remains epitaxial feature with increasing of TMS gas flow rate. As a result, uniform heteroepitaxial 3C-SiC film was deposited on 4-in. silicon wafer at low deposition temperature (~ 860 °C). The structure of SiC film along the radial direction was measured by X-ray diffraction (XRD) results. X-ray photoelectron spectroscopy (XPS) spectra indicate the chemical information of SiC film surface and the depth profiles, which prove the uniform of elements distribution. Moreover, with increasing gas pressure, the film morphology transforms from the heteroepitaxial SiC film into 2D nanosheets, which is due to the increased ion current.

Color tuning and luminescence enhancement are predominant challenges for improving the performance of white light emitting diodes (LEDs) toward commercial application. In this paper, a novel promising Ba2−xCaxSiO4−yN2/3y:Eu2+ phosphors with tunable and enhanced luminescence for phosphors converted LEDs (pc-LEDs) have been successfully synthesized by a direct gas-reduction nitridation method. The effects of Ca and N doping on the phase purity, morphology and optical properties of Ba2−xCaxSiO4−yN2/3y:Eu2+ phosphors were also systematically investigated. The optical results show that Ba2−xCaxSiO4−yN2/3y:Eu2+ phosphors can be actively excited over a broad range from 250 to 430 nm. With the adding of different concentrations of Ca2+ ions in phosphors, the emission color wavelength can be tailored from 501 to 441 nm by a 375 nm NUV LED excitation source. Furthermore, it has been found that the emission and absorption of Ba2−xCaxSiO4:Eu2+ phosphor can be significantly improved when N3− ions were introduced into the host lattices. The intensity of Ba1.5Ca0.5SiO4−yN2/3y:Eu2+ phosphor was 3.4 times higher than the phosphor without N doping. The fabrication and characterization of pc-LEDs using Ba2−xCaxSiO4−yN2/3y:Eu2+ phosphors-silica gel as the coating layer onto 375 nm-emitting InGaN LED caps demonstrated the superior optical and current tolerant properties, making it a promising and competitive candidate for commercial utilization in white LED applications.

As a potential material for biosensing applications, gallium nitride (GaN) films have attracted remarkable attention. In order to construct GaN biosensors, a corresponding immobilization of biolinkers is of great importance in order to render a surface bioactive. In this work, two kinds of n-alkenes with different carbon chain lengths, namely allylamine protected with trifluoroacetamide (TFAAA) and 10-aminodec-1-ene protected with trifluoroacetamide (TFAAD), were used to photochemically functionalize single crystalline GaN films. The successful linkage of both TFAAA and TFAAD to the GaN films is confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurement. With increased UV illumination time, the intensity of the secondary ions corresponding to the linker molecules initially increases and subsequently decreases in both cases. Based on the SIMS measurements, the maximum coverage of TFAAA is achieved after 14 h of UV illumination, while only 2 h is required in the case of TFAAD to reach the situation of a fully covered GaN surface. This finding leads to the conclusion that the reaction rate of TFAAD is significantly higher compared to TFAAA. Measurements by atomic force microscopy (AFM) indicate that the coverage of GaN films by a TFAAA layer leads to an increased surface roughness. The atomic terraces, which are clearly observable for the pristine GaN films, disappear once the surface is fully covered by a TFAAA layer. Such TFAAA layers will feature a homogeneous surface topography even for reaction times of 24 h. In contrast to this, TFAAD shows strong cross-polymerization on the surface, this is confirmed by optical microscopy. These results demonstrate that TFAAA is a more suitable candidate as biolinker in context of the GaN surfaces due to its improved controllability.

Hybrid diamond/graphite nanostructures were synthesized in CH4/H2 mixture gas using microwave plasma enhanced chemical vapor deposition (MPCVD) at a power of 10 kW. The microstructure and the composition of the films were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), Raman spectroscopy and X-ray diffraction (XRD). The as-deposited diamond films at high methane level in hydrogen plasma show good conductivity and excellent electrochemical activity, owing to the co-existence of diamond and graphite phases in the films. The largest electrochemical potential window of the hybrid diamond/graphite films is 3.1 V, which is comparable with the B-doped diamond. The films exhibit quasi-reversible, mass controlled electrode reactions in both aqueous and organic solutions. In the application of trace heavy metal ion detection, the hybrid diamond/graphite electrodes present low background currents and detection limits (S/N ≥ 3): ∼1.5 μA/cm2 and 5.8 ppb for Ag+, ∼4.7 μA/cm2 and 5.6 ppb for Cu2+. The diamond/graphite electrodes also possess good linearity over a wide concentration range from 10 ppb to 1 ppm. In addition, the simultaneous determination of silver and copper ions was also successful. The good recovery values for the analysis of the tap water samples with standard addition method demonstrate the accuracy of the hybrid diamond/graphite electrodes. Hence, the hybrid diamond/graphite films are promising for electrochemical applications such as trace heavy metal ions detection because of its wide potential window, lower background current and high sensitivity.

In this work, we demonstrate a new strategy to create WZ-GaN/3C-SiC heterostructure nanowires, which feature controllable morphologies. The latter is realized by exploiting the stacking faults in 3C-SiC as preferential nucleation sites for the growth of WZ-GaN. Initially, cubic SiC nanowires with an average diameter of ∼100 nm, which display periodic stacking fault sections, are synthesized in a chemical vapor deposition (CVD) process to serve as the core of the heterostructure. Subsequently, hexagonal wurtzite-type GaN shells with different shapes are grown on the surface of 3C-SiC wire core. In this context, it is possible to obtain two types of WZ-GaN/3C-SiC heterostructure nanowires by means of carefully controlling the corresponding CVD reactions. Here, the stacking faults, initially formed in 3C-SiC nanowires, play a key role in guiding the epitaxial growth of WZ-GaN as they represent surface areas of the 3C-SiC nanowires that feature a higher surface energy. A dedicated structural analysis of the interfacial region by means of high-resolution transmission electron microscopy (HRTEM) revealed that the disordering of the atom arrangements in the SiC defect area promotes a lattice-matching with respect to the WZ-GaN phase, which results in a preferential nucleation. All WZ-GaN crystal domains exhibit an epitaxial growth on 3C-SiC featuring a crystallographic relationship of [12̅10]WZ-GaN //[011̅]3C-SiC, (0001)WZ-GaN//(111)3C-SiC, and dWZ-GaN(0001) ≈ 2d3C-SiC(111). The approach to utilize structural defects of a nanowire core to induce a preferential nucleation of foreign shells generally opens up a number of opportunities for the epitaxial growth of a wide range of semiconductor nanostructures which are otherwise impossible to acquire. Consequently, this concept possesses tremendous potential for the applications of semiconductor heterostructures in various fields such as optics, electrics, electronics, and photocatalysis for energy harvesting and environment processing.

Zn doped GaN nanowires with different doping levels (0, <1 at%, and 3–5 at%) have been synthesized through a chemical vapor deposition (CVD) process. The effect of Zn doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a hexagonal wurtzite (WZ) structure with good crystallinity. Several kinds of twin boundaries, including (103), (101) and (201), as well as Type I stacking faults (…ABABBCB…), are observed in the nanowires. The increasing Zn doping level (<1 at%) induces the formation of screw dislocations featuring a predominant screw component along the radial direction of the GaN nanowires. At high Zn doping level (3–5 at%), meta-stable cubic zinc blende (ZB) domains are generated in the WZ GaN nanowires. The WZ/ZB phase boundary (…ABABABA…) can be identified as Type II stacking faults. The density of stacking faults (both Type I and Type II) increases with increasing the Zn doping levels, which in turn leads to a rough-surface morphology in the GaN nanowires. First-principles calculations reveal that Zn doping will reduce the formation energy of both Type I and Type II stacking faults, favoring their nucleation in GaN nanowires. An understanding of the effect of Zn doping on the defect evolution provides an important method to control the microstructure and the electrical properties of p-type GaN nanowires.

GaN nanowires with homoepitaxial decorated GaN nanoparticles on their surface along the radial direction have been synthesized by means of a chemical vapor deposition method. The growth of GaN nanowires is catalyzed by Au particles via the vapor–liquid–solid (VLS) mechanism. Screw dislocations are generated along the radial direction of the nanowires under slight Zn doping. In contrast to the metal-catalyst-assisted VLS growth, GaN nanoparticles are found to prefer to nucleate and grow at these dislocation sites. High-resolution transmission electron microscopy (HRTEM) analysis demonstrates that the GaN nanoparticles possess two types of epitaxial orientation with respect to the corresponding GaN nanowire: (I) [1̅21̅0]np//[1̅21̅0]nw, (0001)np//(0001)nw; (II) [1̅21̅3]np//[12̅10]nw, (101̅0)np//(101̅0)nw. An increased Ga signal in the energy-dispersive spectroscopy (EDS) profile lines of the nanowires suggests GaN nanoparticle growth at the edge surface of the wires. All the crystallographic results confirm the importance of the dislocations with respect to the homoepitaxial growth of the GaN nanoparticles. Here, screw dislocations situated on the (0001) plane provide the self-step source to enable nucleation of the GaN nanoparticles.Keywords: dislocation; GaN; growth; nanostructures; nucleation

Zinc oxide (ZnO) is considered to be one of the most promising candidates for the third-generation DNA biosensor because of its good chemical stability, wonderful biocompatibility, easy surface modification, and numerous kinds of nanostructures. In this work, we report a new and simple method to modify ZnO surface for the immobilization of oligonucleotides by electrochemical covalent grafting of diazonium salts. The atomic force microscope, X-ray photoelectron spectroscopy, surface contact angle system, and electrochemical workstation were employed to characterize the functionalization process. Fluorescence results show that this kind of DNA biosensor from covalently linking strategy has an enhanced performance compared to that based on an electrostatic adsorption route. The functionalized ZnO biosensor has the capability to distinguish four-base mismatched, one-base mismatched, and complementary DNA sequences. Moreover, a linear relationship has been observed between the fluorescence intensity and the concentration of the complementary DNA in the solution within the range from 10–6 to 10–9 M, offering us a possibility in the qualitative determination of the level of target DNA.Keywords: covalent bond; DNA biosensor; electrochemistry; fluorescence; functionalization; ZnO;

The luminescence of semiconductor nanostructures is strongly dependent on their size, dimensions, morphology, composition, or defects, and their band emissions can be properly and selectively tailored through the rational manipulation of these parameters during material growth. Using spatially-resolved cathodoluminescence spectroscopy, monochromatic contrast maps and high-resolution transmission electron microscopy, an obvious red-shift of the near-band-edge emission of wurtzite ZnS nanobelts, resulting from a strip of stacking faults or a zinc-blende phase with tens of atomic layers in width, has been observed and its related mechanism has been discussed. This finding is not specific to the defect-dependent optical properties tailoring of ZnS nanostructures and represents a general validity for clarifying the mechanism of peak-shift (band-gap expansion or shrinking) of a wide range of semiconductor nanostructures with various defects. In addition, the general formation mechanism of the belt-like nanostructure was proposed based on precise microstructure analyses on a ZnS nanobelt with atomic terrace growth fronts.

Here, we report the origin of the yellow-band emission in epitaxial GaN nanowire arrays grown under carbon-free conditions. GaN nanowires directly grown on [0001]-oriented sapphire substrate exhibit an obvious and broad yellow-band in the visible range 400–800 nm, whereas the insertion of Al/Au layers in GaN–sapphire interface significantly depresses the visible emission, and only a sharp peak in the UV range (369 nm) can be observed. The persuasive differences in cathodoluminescence provide direct evidence for demonstrating that the origin of the yellow-band emission in GaN nanowire arrays arises from dislocation threading. The idea using buffering/barrier layers to isolate the dislocation threading in epitaxially grown GaN nanowires can be extended to the rational synthesis and structural defect controlling of a wide range of semiconductor films and nanostructures with superior crystal quality and excellent luminescence property.Keywords: epitaxial growth; GaN; interface; nanowire arrays; yellow-band emission

•Sb/P co-doped GaN nanowires were synthesized through a well-designed multi-channel chemical vapor deposition (CVD) process.•Sb/P co-doping leads to the crystallinity deterioration of GaN nanowires.•Sb/P co-doping caused the red-shift of GaN nanowires band-gap in UV range.•Compared with Sb doping, P atoms are more easy to incorporate into the GaN lattice.Sb/P co-doped Gallium Nitride (GaN) nanowires were synthesized via a simple chemical vapor deposition (CVD) process by heating Ga2O3 and Sb powders in NH3 atmosphere. Scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS) measurements confirmed the as-synthesized products were Sb/P co-doped GaN nanowires with rough morphology and hexagonal wurtzite structure. Room temperature cathodoluminescence (CL) demonstrated that an obvious band shift of GaN nanowires can be observed due to Sb/P co-doping. Possible explanation for the growth and luminescence mechanism of Sb/P co-doped GaN nanowires was discussed.

One-dimensional GaN nanorods with corrugated morphology have been synthesized on graphite substrate without the assistance of any metal catalyst through a feasible thermal evaporation process. The morphologies and microstructures of GaN nanorods were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results from HRTEM analysis indicate that the GaN nanorods are well-crystallized and exhibit a preferential orientation along the [0001] direction with Ga3+-terminated (101̅1) and N3–-terminated (101̅1̅) as side facets, finally leading to the corrugated morphology surface. The stabilization of the electrostatic surface energy of {101̅1} polar surface in a wurtzite-type hexagonal structure plays a key role in the formation of GaN nanorods with corrugated morphology. Room-temperature cathodoluminescence (CL) measurements show a near-band-edge emission (NBE) in the ultraviolet range and a broad deep level emission (DLE) in the visible range. The crystallography and the optical emissions of GaN nanorods are discussed.Keywords: cathodoluminescence; crystallography; GaN; graphite; nanorods;

Quaternary solid-solution nanowires made of GaP and ZnS have been synthesized through well-designed synthetic routines. The as-synthesized GaP–ZnS solid-solution nanowires exhibit decent crystallinity with the GaP phase as the host, while a large amount of twin structural defects are observed in ZnS-rich nanowires. Cathodoluminescence studies showed that GaP-rich solid-solution nanowires have a strong visible emission centered at 600 nm and the ZnS-rich solid-solution nanowires exhibited a weak emission peak in the UV range and a broad band in the range 400–600 nm. The formation mechanism, processes, and optical emissions of GaP–ZnS solid-solution nanowires were discussed in detail.Keywords: crystallography; nanowires; optical property; solid solution; synthesis;

Pyramid-like GaN nanorods have been epitaxially grown on a [001]-oriented sapphire substrate. The as-synthesized GaN nanorods exhibited decent crystal quality and a strong luminescence in UV range.

To date, numerous approaches have been developed for fabricating high quality organometal halide perovskite thin films, however, perovskite films obtained by such methods reveal a brown or dark-brown color, which might restrain their light absorption ability. Here we report a route to synthesize dark-blue mirror-like perovskite dense films via a two-step spin-coating process assisted by treatment of nonpolar solvent scouring. Photovoltaic cells based on such dark-blue films demonstrate a high short-circuit current density (Jsc) of ∼23 mA cm−2 and a power conversion efficiency (PCE) of 16.1%. Our method would provide a new candidate method for the fabrication of perovskite solar cells with high performance.

(GaN)1−x(ZnO)x solid solution has attracted extensive attention due to its feasible band-gap tunability and excellent photocatalytic performance in overall water splitting. However, its potential application in the photodegradation of organic pollutants and environmental processing has rarely been reported. In this study, we developed a rapid synthesis process to fabricate porous (GaN)1−x(ZnO)x solid solution with a tunable band gap in the range of 2.38–2.76 eV for phenol photodegradation. Under visible-light irradiation, (GaN)0.75(ZnO)0.25 solid solution achieved the highest photocatalytic performance compared to other (GaN)1−x(ZnO)x solid solutions with x = 0.45, 0.65 and 0.85 due to its higher redox capability and lower lattice deformation. Slight Ag decoration with a content of 1 wt% on the surface of the (GaN)0.75(ZnO)0.25 solid solution leads to a significant enhancement in phenol degradation, with a reaction rate eight times faster than that of pristine (GaN)0.75(ZnO)0.25. Interestingly, phenol in aqueous solution (10 mg L−1) can also be completely degraded within 60 min, even under the direct exposure of sunlight irradiation. The photocurrent response indicates that the enhanced photocatalytic activity of (GaN)0.75(ZnO)0.25/Ag is directly induced by the improved transfer efficiency of the photogenerated electrons at the interface. The excellent phenol degradation performance of (GaN)1−x(ZnO)x/Ag further broadens their promising photocatalytic utilization in environmental processing, besides in overall water splitting for hydrogen production.

High performance ultraviolet (UV) photodetectors based on semiconducting nanowires are expected to have extensive applications in UV-ray detection, optical communication and environmental monitoring. In this work, GaN nanowire photodetectors have been fabricated and giant UV photoresponse has been achieved with Pt nanoparticle (NP) modification. The peak responsivity and external quantum efficiency (EQE) of the GaN nanowire UV photodetector were increased from 773 to 6.39 × 104 A W−1 and from 2.71 × 105% to 2.24 × 107%, respectively, and the response time and sensitivity were improved greatly after Pt NP decoration on the GaN nanowire surface. Moreover, the Pt–GaN nanowire photodetector still presents its spectrum selectivity in the UV region. Our results reveal that Pt nanoparticles play a key role in enhancing the photodetection performance of the nanodevice due to the strong absorption and scattering of incident light induced by localized surface plasmon resonance (LSPR) and the improvement of interfacial charge separation owing to the special device configuration. These findings offer an efficient avenue toward the performance enhancement of GaN nanowire and related optoelectronic devices or systems.