PubMed Health⌕ Search

Biomedical subjects

Zhong Lin Wang

Publications and source records attributed to Zhong Lin Wang.

At least 37 records · Page 2Linked to original sources
PubMed2005

Morphology-tuned wurtzite-type ZnS nanobelts.

Nanometre-sized inorganic dots, wires and belts have a wide range of electrical and optical properties, and variable mechanical stability and phase-transition mechanisms that show a sensitive dependency on size, shape and structure. The optical properties of the semiconductor ZnS in wurtzite structures are considerably enhanced, but the lack of structural stability limits technological applications. Here, we demonstrate that morphology-tuned wurtzite ZnS nanobelts show a particular low-energy surface structure dominated by the +/-[210] surface facets. Experiments and calculations show that the morphology of ZnS nanobelts leads to a very high mechanical stability to approximately 6.8 GPa, and also results in an explosive mechanism for the wurtzite-to-sphalerite phase transformation together with in situ fracture of the nanobelts. ZnS wurtzite nanobelts provide a model that is useful not only for understanding the morphology-tuned stability and transformation mechanism, but also for improving synthesis of metastable nanobelts with quantum effects for electronic and optical devices.

Atmospheric Pressure↗
PubMed2005

DNA functionalized single-walled carbon nanotubes for electrochemical detection.

Single-walled carbon nanotubes (SWNTs) were effectively dispersed and functionalized by wrapping with single-stranded DNA (ssDNA). The ssDNA-SWNTs attach strongly on glass substrate and easily form a uniform film, making it possible for electrochemical analysis and sensing. The film was fabricated into a working electrode, which exhibited good electrochemical voltammetric properties, such as flat and wide potential window, well-defined quasi-reversible voltammetric responses, and quick electron transfer for a Fe(CN)6(3-)/Fe(CN)6(4) system, indicating that the ssDNA-SWNTs film should be a good analytical electrode for electrochemical detection or sensing. This was demonstrated by highly selective and sensitive detection of a low concentration of dopamine in the presence of excess ascorbic acid.

Carbon↗
PubMed2005

Bismuth spheres grown in self-nested cavities in a silicon wafer.

We have developed a one-step, hydrofluoric acid-free hydrothermal etching method that not only produces bismuth nano/micrometer-sized spheres but also prepares porous silicon with vertical holes. By controlling the heating temperature and time, nanoscale vertical-channeled porous silicon can be received. Our result indicated that the Bi clusters were formed first on the wafer surface. Then the etching of the Bi to the wafer creates the holes. Later, the Bi spheres went into the holes and expedited the etching process. A formation mechanism and chemical process have been proposed on the basis of experimental data. This simple chemistry approach may be of great scientific and technological importance for preparing porous silicon wafer.

Journal Article↗
PubMed2005

Formation of PbSe nanocrystals: A growth toward nanocubes.

In this paper we report an electron microscopic observation of crystal shape development when PbSe nanocrystals were synthesized using a dynamic injection technique at different temperatures in the presence of oleic acid. A two-step evolution mechanism was proposed, indicating that the shape evolution of PbSe nanocrystals is dependent on the growth time, whereas the crystalline size can be tuned by varying the growth temperature under the studied conditions. It also implies that a higher growth rate in the 111 direction compared to that in the 100 direction results in the formation of nanocubes.

Journal Article↗
PubMed2005

Conversion of zinc oxide nanobelts into superlattice-structured nanohelices.

A previously unknown rigid helical structure of zinc oxide consisting of a superlattice-structured nanobelt was formed spontaneously in a vapor-solid growth process. Starting from a single-crystal stiff nanoribbon dominated by the c-plane polar surfaces, an abrupt structural transformation into the superlattice-structured nanobelt led to the formation of a uniform nanohelix due to a rigid lattice rotation or twisting. The nanohelix was made of two types of alternating and periodically distributed long crystal stripes, which were oriented with their c axes perpendicular to each other. The nanohelix terminated by transforming into a single-crystal nanobelt dominated by nonpolar (0110) surfaces. The nanohelix could be manipulated, and its elastic properties were measured, which suggests possible uses in electromechanically coupled sensors, transducers, and resonators.

Journal Article↗
PubMed2005

Electron energy-loss spectroscopy study of ZnO nanobelts.

Nanobelts of ZnO have well-defined shapes that are enclosed by {0001}, {0110} and {2110} facets. The nanobelts grow along [0110] and [2110] with large flat surfaces of +/-(0001) and +/-(0110), respectively. Electron energy-loss spectroscopy has been applied to study the electronic structure of ZnO nanobelts of different growth orientations. A plasmon peak observed at 13 eV is suggested to be the result of polar surface excitation. The energy-loss near-edge structure of the oxygen K and zinc L3 edges acquired from the two types of nanobelts show clear orientation dependence, and they agree well to the calculated results.

Journal Article↗
PubMed2005

Bismuth telluride hexagonal nanoplatelets and their two-step epitaxial growth.

We report a synthesis of discrete, single-crystal, defect-free, and hexagonal Bi2Te3 nanoplatelets using a high-temperature organic solution approach, and we demonstrate a two-step epitaxial growth of the cylindrical strings of Bi2Te3 nanoplatelets on the surface of the Te rod by packing them along c-axis in a top-bottom-top-bottom sequence. This type of building-up provides additional opportunity for the exploration of novel thermoelectric properties from such quantum-confined materials, in which the boundary scattering of phonons is anticipated to enhance.

Journal Article↗
PubMed2005

Controlled growth of large-area, uniform, vertically aligned arrays of alpha-Fe2O3 nanobelts and nanowires.

Vertically aligned iron oxide nanobelt and nanowire arrays have been synthesized on a large-area surface by direct thermal oxidation of iron substrates under the flow of O(2). The effects of reactive gas pressure, composition, and temperature have been systematically studied. It was found that nanobelts (width, tens of nanometers; thickness, a few nanometers) are produced in the low-temperature region (approximately 700 degrees C) whereas cylindrical nanowires tens of nanometers thick are formed at relatively higher temperatures (approximately 800 degrees C). Both nanobelts and nanowires are mostly bicrystallites with a length of tens of micrometers which grow uniquely along the [110] direction. The growth habits of the nanobelts and nanowires in the two temperature regions indicate the role of growth rate anisotropy and surface energy in dictating the ultimate nanomorphologies.

Ferric Compounds↗
PubMed2004

Perfect orientation ordered in-situ one-dimensional self-assembly of Mn-doped PbSe nanocrystals.

We demonstrate a novel approach for the large-scale, shape-controlled synthesis of one-dimensional (1D) corrugated nanoarrays of Pb(1-x)Mn(x)Se nanocrystals (0.002 < or = x < or = 0.008) through an in-situ self-assembly without using either capping polymer or ionic surfactant. The one-step-prepared 1D nanoarrays exhibit a well-defined morphology, single-crystal orientation, and clean surface without amorphous contamination. The average diameter of the 1D nanoarrays can be controlled and varied from <10 to 80 nm by finely tuning the assembly temperature and the growth time. Four growth models were suggested to explain the in-situ self-assembly processes based on the fundamental building blocks of octahedral nanocrystals by sharing [111] facets.

Journal Article↗
PubMed2004

Crystal orientation-ordered ZnS nanowire bundles.

We report a novel approach for growing aligned and orientation-ordered ZnS nanowires. Our method relies on a buffer layer of CdSe grown on a Si(111) substrate, on which ZnS nanowires are grown. The growth process of the nanowire bundles is presented. The technique demonstrated could be an effective pathway for growing patterned, aligned, size-controlled, and orientation-ordered ZnS nanowires.

Journal Article↗
PubMed2004

Single-crystal nanorings formed by epitaxial self-coiling of polar nanobelts.

Freestanding single-crystal complete nanorings of zinc oxide were formed via a spontaneous self-coiling process during the growth of polar nanobelts. The nanoring appeared to be initiated by circular folding of a nanobelt, caused by long-range electrostatic interaction. Coaxial and uniradial loop-by-loop winding of the nanobelt formed a complete ring. Short-range chemical bonding among the loops resulted in a single-crystal structure. The self-coiling is likely to be driven by minimizing the energy contributed by polar charges, surface area, and elastic deformation. Zinc oxide nanorings formed by self-coiling of nanobelts may be useful for investigating polar surface-induced growth processes, fundamental physics phenomena, and nanoscale devices.

Journal Article↗
PubMed2004

Catalyst-nanostructure interfacial lattice mismatch in determining the shape of VLS grown nanowires and nanobelts: a case of Sn/ZnO.

Vapor-liquid-solid (VLS) is a well-established process in catalyst-guided growth of nanowires. The catalyst particle is generally believed to be in liquid state during growth, and it is the site for adsorbing incoming molecules; the crystalline structure of the catalyst may not have any influence on the structure of the grown one-dimensional nanostructures. In this paper, using tin particle guided growth of ZnO nanostructures as a model system, we show that the interfacial region of the tin particle with the ZnO nanowire/nanobelt could be ordered (or partially crystalline) during the VLS growth, although the local growth temperature is much higher than the melting point of tin, and the crystallographic lattice structure at the interface is important in defining the structural characteristics of the grown nanowires and nanobelts. The interface prefers to take the least lattice mismatch; thus, the crystalline orientation of the tin particle may determine the growth direction and the side surfaces of the nanowires and nanobelts. This result may have important impact on the understanding of the physical chemical process in the VLS growth.

Journal Article↗
PubMed2004

Single-crystal CdSe nanosaws.

We report the first successful synthesis and characterization of single-crystal wurtzite CdSe nanoribbons through a simple thermal evaporation process. Asymmetric growth of the nanoribbons occurs, yielding a sawlike shape with sharp teeth on one side. This asymmetric growth is suggested to be induced by the polarization of the c-plane in the wurtzite crystal structure.

Journal Article↗
PubMed2004

Properties of nanobelts and nanotubes measured by in situ TEM.

Characterizing the physical properties of individual nanostructures is challenging because of the difficulty in manipulating the objects of sizes from nanometers to micrometers. Most nanomeasurements have been carried using scanning probe microscopy. In this article, we demonstrate that transmission electron microscopy can be a powerful tool for quantitative measurements of the mechanical and electrical properties of a single nanostructure. Dual-mode resonance of an oxide nanobelt has been observed, and its bending modulus has been measured. An in situ technique was demonstrated for measuring the work function at the tip of a carbon nanotube. The ballistic quantum conductance of a multiwalled carbon nanotube was observed at room temperature using the setup in TEM. It is concluded that in situ measurement by directly linking structure with property is a future direction of electron microscopy.

Electric Conductivity↗
PubMed2004

Functional oxide nanobelts: materials, properties and potential applications in nanosystems and biotechnology.

Nanobelt is a quasi-one-dimensional structurally controlled nanomaterial that has well-defined chemical composition, crystallographic structure, and surfaces (e.g., growth direction, top/bottom surface, and side surfaces). This article reviews the nanobelt family of functional oxides, including ZnO, SnO2, In2O3, Ga2O3, CdO, and PbO2 and the relevant hierarchical and complex nanorods and nanowires that have been synthesized by a solid-vapor process. The nanobelts are single crystalline and dislocation free, and their surfaces are atomically flat. The oxides are semiconductors that have been used for fabrication of nanosize functional devices of key importance for nanosystems and biotechnology, such as field-effect transistors, gas sensors, nanoresonators, and nanocantilevers. The structurally controlled ZnO nanobelts that exhibit piezoelectric properties are also reviewed. By controlling growth kinetics, we show the success of growing nanobelt-based novel structures whose surfaces are dominated by the polarized +-(0001) facets. Owing to the positive and negative ionic charges on the zinc- and oxygen-terminated +-(0001) surfaces, respectively, a spontaneous polarization is induced across the nanobelt thickness. As a result, helical nanostructures and nanorings are formed by rolling up single-crystal nanobelts; this phenomenon is a consequence of minimizing the total energy contributed by spontaneous polarization and elasticity. The polar surface-dominated ZnO nanobelts are likely to be an ideal system for understanding piezoelectricity and polarization-induced ferroelectricity at nano-scale and they could have applications as one-dimensional nano-scale sensors, transducers, and resonators.

Biotechnology↗
PubMed2003

Monopod, bipod, tripod, and tetrapod gold nanocrystals.

Multipod gold nanocrystals have been synthesized via a simple solution-phase chemical reduction method at room temperature. Two types of structurally different particles are observed, including the regular tripod, which lies on the substrate with its {111} plane, and the cross-like tetrapod that sits on its {100} plane. Both structures have pods of 10 nm sizes and grow along 110 directions. Variously shaped particles, including tadpole-like or teardrop-like monopods, 90 degrees L-shaped, 180 degrees I-shaped, and 120 degrees V-shaped bipods, T-shaped, Y-shaped, and regular triangular tripods, and cross-like tetrapods, have been produced. Due to the high conductivity of metal, these branched structures are quite promising considering their applications as interconnections in the "bottom-up" self-assembly approach toward future nanocircuits and nanodevices, as well as in other related fields.

Journal Article↗