Xiaopeng Hao

Exfoliation of Hexagonal Boron Nitride by Molten Hydroxides

Hexagonal boron nitride (h-BN) nanosheets are prepared by a novel and effective method, in which sodium hydroxide and potassium hydroxide molten salts are used to exfoliate h-BN to obtain nanosheets. BN nanoscrolls are also obtained. The as-prepared products can be readily dispersed in a wide range of solvents, including water and ethanol, and form stable dispersions.

One-step exfoliation and fluorination of boron nitride nanosheets and a study of their magnetic properties.

A novel, simple, and efficient method for the preparation of the fluorinated hexagonal boron nitride nanosheets (F-BNNSs) and the corresponding magnetic properties is presented. A one-step route is used to exfoliate and fluorinate the BNNSs by ammonium fluoride (NH4F) from hexagonal boron nitride (h-BN) powder. Through related instrument characterizations and theoretical calculations, we confirm that large-area and few-layer F-BNNSs were successfully produced by this method, which can be attributed to a fluorination-assisted exfoliation mechanism from the bulk h-BN in NH4F. More intriguingly, we initially verified that the as-prepared F-BNNSs exhibit ferromagnetic characteristics, which would have good potential applications in spintronic devices.

A facile chemical exfoliation method to obtain large size boron nitride nanosheets

Owning many peculiar properties, hexagonal boron nitride nanosheets (BNNSs) have lots of potential applications, such as electronic devices and deep ultraviolet emitters. In this article, a chemical exfoliation method to prepare few-layer and large size BNNSs is reported. Through related instrument characterizations, we demonstrated that this preparation method can allow the exfoliation of BNNSs from bulk BN powder successfully. From CL spectra, the as-prepared BNNSs were proved to show stronger CL emission ability than BN powder. Based on the experiment results analysis, we proposed an exfoliation mechanism and verified it through in situ SEM detection.

Efficient graphene Q switching and mode locking of 1.34 μm neodymium lasers

We demonstrate that few-layered graphene sheets used as a saturable absorber can provide efficient Q-switching and mode-locking modulation in 1.34 μm Nd:GdVO(4) bulk lasers. The minimum Q-switched pulses were 450 ns for 260 mW average power, 43 kHz repetition rate, and 2.5 μJ pulse energy. For the mode-locked laser, an average power of 1.29 W was achieved with 11 ps pulse duration and 13 nJ pulse energy. To our knowledge, this average power is the highest yet obtained from a graphene mode-locked laser, and the corresponding optical-optical efficiency of 23% is the best result among 1.3 μm neodymium mode-locked lasers. The quality factor M(2) of the Q-switched beam was 1.4 and 1.6 in the horizontal and longitudinal planes, respectively, and the M(2) of the mode-locked beam reached 1.1 and 1.0. These results clearly indicate the advantages of few-layered graphene as a saturable absorber.

Reduced graphene oxide–CdS nanocomposites with enhanced visible-light photoactivity synthesized using ionic-liquid precursors

A series of reduced graphene oxide and CdS nanocomposites (RGO–CdS) with different weight ratios of RGO have been synthesized by a facile microwave-assisted solvothermal method, in which the room temperature ionic-liquid 1-butyl-3-methylimidazolium thiocyanate ([BMIM]·SCN) served as sulfur source as well as stabilizing agent. RGO sheets were uniformly decorated by CdS nanospheres in the as-prepared samples. Only aggregates of CdS particles over 100 nm were obtained, when graphene oxides were not employed. The existence of RGO could effectively enhance the photocatalytic activity for the degradation of rhodamine B (RhB) under visible light irradiation and the RGO–CdS-10% sample possessed the highest activity and excellent stability. The improved photocatalytic efficiency of RGO–CdS nanocomposites could be attributed to the enhanced adsorbability of RhB molecules, a broadened light response range in the visible spectrum and improved separation efficiency of electron–hole pairs, all of which result from the introduction of RGO. It is hoped that this facile and efficient synthesis route can promote the exploration and utilization of graphene-based semiconductor nanocomposites as visible-light photocatalysts.

Preparation of InN nanocrystals by solvo-thermal method

Abstract Indium nitride (InN) nanocrystals were successfully prepared by the reaction of InCl 3 and Li 3 N at 250°C with xylene as the solvent. X-ray powder diffraction and TEM observation showed that the two phases of cubic InN and hexagonal InN coexist in the nanocrystals prepared by the solvo-thermal method.

Gallium Nitride Crystals: Novel Supercapacitor Electrode Materials.

A type of single-crystal gallium nitride mesoporous membrane is fabricated and its supercapacitor properties are demonstrated for the first time. The supercapacitors exhibit high-rate capability, stable cycling life at high rates, and ultrahigh power density. This study may expand the range of crystals as high-performance electrode materials in the field of energy storage.

Enhancement of light extraction in GaN-based light-emitting diodes using rough beveled ZnO nanocone arrays

A remarkable enhancement of light extraction efficiency in GaN-based blue light-emitting diodes (LEDs) with rough beveled ZnO nanocone arrays grown on the planar indium tin oxide (ITO) layer is reported. The light output power of LEDs with rough beveled ZnO nanocone arrays was increased by about 110% at 20 mA compared with conventional LEDs with planar ITO. The light extraction efficiency of GaN-based LEDs with rough-beveled ZnO nanocones is measured much greater than with smooth-surface hexagonal ZnO nanorods. The light-ray tracing analysis showed that ZnO nanocones with rough surfaces enlarge the light escape cone of GaN-based LEDs and have a greater advantage for extracting light compared with ZnO nanorods.

The effect of temperature on the synthesis of BN nanocrystals

Abstract Boron nitride (BN) nanocrystals have been synthesized by the reaction of Li3N and BBr3 in organic solvent. The experimental results indicated that, at low temperature, hexagonal BN (hBN) is the dominant phase in the sample. The content of cubic BN (cBN) increased with temperature, and it reached a maximum at 480°C. As the temperature increased further, the content of cBN decreased, and hBN became the dominant phase again. This phenomenon was discussed briefly in this paper.

Three-Dimensional MoS2@CNT/RGO Network Composites for High-Performance Flexible Supercapacitors

Two-dimensional atomically thick materials, reduced graphene oxide (RGO), and layered molybdenum disulfide (MoS2 ) have been investigated as potential novel energy storage materials because of their distinct physicochemical properties. These materials suffer, however, from rapid capacity decay and low rate capability. This study describes a facile, binder-free approach to fabricate large-scale, 3D network structured MoS2 @carbon nanotube (CNT)/RGO composites for application in flexible supercapacitor devices. The as-obtained composites possess a hierarchical porosity, and an interconnected framework. The electrochemical supercapacitive measurements of the MoS2 @CNT/RGO electrode show a high specific capacitance of 129 mF cm-2 at 0.1 mA cm-2 . The symmetric supercapacitor devices based on the as-obtained composites exhibit a long lifetime (94.7 % capacitance retention after 10 000 cycles), and a high electrochemical performance (29.7 mF cm-2 ). The present experimental findings will lead to scalable, binder-free synthesis of MoS2 @CNT/RGO hybrid electrodes, with enhanced, flexible, supercapacitive performance, in portable and wearable energy storage devices.