Biomedical subjects

Haoquan Yan

Publications and source records attributed to Haoquan Yan.

5 recordsLinked to original sources

PubMed2005

Semiconductor nanowires for subwavelength photonics integration.

This article focuses on one-dimensional (1D) semiconductor subwavelength optical elements and assesses their potential use as active and passive components in photonic devices. An updated overview of their optical properties, including spontaneous emission, ultrafast carrier dynamics, cavity resonance feedback (lasing), photodetection, and waveguiding, is provided. The ability to physically manipulate these structures on surfaces to form simple networks and assemblies is the first step toward integrating chemically synthesized nanomaterials into photonic circuitry. These high index semiconductor nanowires are capable of efficiently guiding light through liquid media, suggesting a role for such materials in microfluidics-based biosensing applications.

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PubMed2005

Optical routing and sensing with nanowire assemblies.

The manipulation of photons in structures smaller than the wavelength of light is central to the development of nanoscale integrated photonic systems for computing, communications, and sensing. We assemble small groups of freestanding, chemically synthesized nanoribbons and nanowires into model structures that illustrate how light is exchanged between subwavelength cavities made of three different semiconductors. The coupling strength of the optical linkages formed when nanowires are brought into contact depends both on their volume of interaction and angle of intersection. With simple coupling schemes, lasing nanowires can launch coherent pulses of light through ribbon waveguides that are up to a millimeter in length. Also, interwire coupling losses are low enough to allow light to propagate across several right-angle bends in a grid of crossed ribbons. The fraction of the guided wave traveling outside the wire/ribbon cavities is used to link nanowires through space and to separate colors within multiribbon networks. In addition, we find that nanoribbons function efficiently as waveguides in liquid media and provide a unique means for probing molecules in solution or in proximity to the waveguide surface. Our results lay the spadework for photonic devices based on assemblies of active and passive nanowire elements and presage the use of nanowire waveguides in microfluidics and biology.

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PubMed2003

Dendritic nanowire ultraviolet laser array.

Self-organized dendritic crystal growth is explored to assemble uniform semiconductor nanowires into highly ordered one-dimensional microscale arrays that resemble comb structures. The individual ZnO nanowires have uniform diameters ranging from 10 to 300 nm. They are evenly spaced on a stem with a regular periodicity of 0.1-2 micrometer. Under optical excitation, each individual ZnO nanowire serves as a Fabry-Perot optical cavity, and together they form a highly ordered nanowire ultraviolet laser array.

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PubMed2003

Single-crystal gallium nitride nanotubes.

Since the discovery of carbon nanotubes in 1991 (ref. 1), there have been significant research efforts to synthesize nanometre-scale tubular forms of various solids. The formation of tubular nanostructure generally requires a layered or anisotropic crystal structure. There are reports of nanotubes made from silica, alumina, silicon and metals that do not have a layered crystal structure; they are synthesized by using carbon nanotubes and porous membranes as templates, or by thin-film rolling. These nanotubes, however, are either amorphous, polycrystalline or exist only in ultrahigh vacuum. The growth of single-crystal semiconductor hollow nanotubes would be advantageous in potential nanoscale electronics, optoelectronics and biochemical-sensing applications. Here we report an 'epitaxial casting' approach for the synthesis of single-crystal GaN nanotubes with inner diameters of 30-200 nm and wall thicknesses of 5-50 nm. Hexagonal ZnO nanowires were used as templates for the epitaxial overgrowth of thin GaN layers in a chemical vapour deposition system. The ZnO nanowire templates were subsequently removed by thermal reduction and evaporation, resulting in ordered arrays of GaN nanotubes on the substrates. This templating process should be applicable to many other semiconductor systems.

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PubMed2002

Inorganic semiconductor nanowires: rational growth, assembly, and novel properties.

Rationally controlled growth of inorganic semiconductor nanowires is important for their applications in nanoscale electronics and photonics. In this article, we discuss the rational growth, physical properties, and integration of nanowires based on the results from the authors' laboratory. The composition, diameter, growth position, and orientation of the nanowires are controlled based on the vapor-solid-liquid (VLS) crystal growth mechanism. The thermal stability and optical properties of these semiconductor nanowires are investigated. Particularly, ZnO nanowires with well-defined end surfaces can function as room-temperature ultraviolet nanolasers. In addition, a novel microfluidic-assisted nanowire integration (MANI) process was developed for the hierarchical assembly of nanowire building blocks into functional devices and systems.

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