Baodan Liu

Fabrication of High-Quality In2Se3 Nanowire Arrays toward High-Performance Visible-Light Photodetectors

The synthesis of high-quality In2Se3 nanowire arrays via thermal evaporation method and the photoconductive characteristics of In2Se3 individual nanowires are first investigated. The electrical characterization of a single In2Se3 nanowire verifies an intrinsic n-type semiconductor behavior. These single-crystalline In2Se3 nanowires are then assembled in visible-light sensors which demonstrate a fast, reversible, and stable response. The high photosensitivity and quick photoresponse are attributed to the superior single-crystal quality and large surface-to-volume ratio resulting in fewer recombination barriers in nanostructures. These excellent performances clearly demonstrate the possibility of using In2Se3 nanowires in next-generation sensors and detectors for commercial, military, and space applications.

Synthesis, characterization and field-emission properties of bamboo-like β-SiC nanowires

Single-crystalline bamboo-like beta-SiC nanowires with hexagonal cross-sections were synthesized by thermal evaporation of mixed SiO+C+GaN powders in an Ar atmosphere. The as-synthesized nanowires were studied by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. Studies found that the as-synthesized SiC nanowires are composed of hexagonal stems decorated with larger diameter knots along their whole length with the [Formula: see text] growth direction. The growth of bamboo-like SiC nanowires is governed by the vapour-liquid-solid mechanism. Field-emission properties of the peculiar nanostructures were also explored, showing a turn-on field of about 10.1 V microm(-1).

Tube-in-Tube TiO2 Nanotubes with Porous Walls Fabrication, Formation Mechanism, and Photocatalytic Properties

Self-organized, freestanding TiO2 nanotube arrays that exhibit tube-in-tube morphology are fabricated using a one-step anodic method. These arrays are uniform and compact. The tubes within the arrays are several micrometers long with a 200 nm outer diameter. They have a coarse lateral profile that leads to a large aspect ratio and guarantees good photocatalytic properties.

Enhancement and patterning of ultraviolet emission in ZnO with an electron beam

An intense enhancement of ultraviolet (UV) emission was observed in various kinds of ZnO samples that were prepared using a wet chemical method when they were under electron-beam irradiation. The UV emission can increase to more than two times its initial value, whereas the visible emission reduces to a negligible value. We suggest that this enhancement effect mainly results from electron-stimulated desorption of adsorbed water. Applying this effect, we have developed a simple technique of directly writing submicrometer UV emission patterns in ZnO with an electron beam without changing the material’s surface morphology.

Quasi-aligned single-crystalline GaN nanowire arrays

Quasi-aligned GaN nanowire arrays have been fabricated via a thermal evaporation of the starting reactants Ga2O3∕GaN. The GaN nanowires have uniform diameters of ∼300nm, lengths up to tens of micrometers and possess a sharp six-fold symmetrical pyramidlike tip. High-resolution transmission electron microscopy (TEM) analysis indicated that majority of GaN nanowires have a preferential growth direction along the [0001] direction. Room-temperature field-emission measurement showed that the as-synthesized GaN nanowire arrays have a lower turn-on field of 7.0V/μm. It is believed that both the sharp tips and rough surface of GaN nanowires contribute to the excellent electron emission behavior.

Nanomaterial Engineering and Property Studies in a Transmission Electron Microscope

Modern methods of in situ transmission electron microscopy (TEM) allow one to not only manipulate with a nanoscale object at the nanometer-range precision but also to get deep insights into its physical and chemical statuses. Dedicated TEM holders combining the capabilities of a conventional high-resolution TEM instrument and atomic force -, and/or scanning tunneling microscopy probes become the powerful tools in nanomaterials analysis. This progress report highlights the past, present and future of these exciting methods based on the extensive authors endeavors over the last five years. The objects of interest are diverse. They include carbon, boron nitride and other inorganic one- and two-dimensional nanoscale materials, e.g., nanotubes, nanowires and nanosheets. The key point of all experiments discussed is that the mechanical and electrical transport data are acquired on an individual nanostructure level under ultimately high spatial, temporal and energy resolution achievable in TEM, and thus can directly be linked to morphological, structural and chemical peculiarities of a given nanomaterial.

Macroporous Silicon Oxycarbide Fibers with Luffa-like Superhydrophobic Shells

High-surface-area silicon oxycarbide macroporous fibers were fabricated through in situ cross-linking of a preceramic precursor without a prepatterned template. The unique luffa-like shell combined with intrinsic silicon-containing groups accounts for the resultant superhydrophobic property. Meanwhile, the oil-uptake capacity of the corresponding fiber mat is significantly improved by the capsulated nanoparticles.

Wurtzite-type faceted single-crystalline GaN nanotubes

We report on the direct fabrication of single-crystalline wurtzite-type hexagonal GaN nanotubes via a newly designed, controllable, and reproducible chemical thermal-evaporation process. The nanotubes are single crystalline, have one end closed, an average outer diameter of ∼300 nm, an inner diameter of ∼100 nm, and a wall thickness of ∼100 nm. The structure and morphology of the tubes are characterized using a scanning electron microscope and a transmission electron microscope. The cathodoluminescence of individual nanotubes is also investigated. The growth mechanism, formation kinetics, and crystallography of GaN nanotubes are finally discussed.

Origin of Yellow-Band Emission in Epitaxially Grown GaN Nanowire Arrays

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.

High Piezo-photocatalytic Efficiency of CuS/ZnO Nanowires Using Both Solar and Mechanical Energy for Degrading Organic Dye

High piezo-photocatalytic efficiency of degrading organic pollutants has been realized from CuS/ZnO nanowires using both solar and mechanical energy. CuS/ZnO heterostructured nanowire arrays are compactly/vertically aligned on stainless steel mesh by a simple two-step wet-chemical method. The mesh-supported nanocomposites can facilitate an efficient light harvesting due to the large surface area and can also be easily removed from the treated solution. Under both solar and ultrasonic irradiation, CuS/ZnO nanowires can rapidly degrade methylene blue (MB) in aqueous solution, and the recyclability is investigated. In this process, the ultrasonic assistance can greatly enhance the photocatalytic activity. Such a performance can be attributed to the coupling of the built-in electric field of heterostructures and the piezoelectric field of ZnO nanowires. The built-in electric field of the heterostructure can effectively separate the photogenerated electrons/holes and facilitate the carrier transportation. The CuS component can improve the visible light utilization. The piezoelectric field created by ZnO nanowires can further separate the photogenerated electrons/holes through driving them to migrate along opposite directions. The present results demonstrate a new water-pollution solution in green technologies for the environmental remediation at the industrial level.