Biomedical subjects

Linyou Cao

Publications and source records attributed to Linyou Cao.

5 recordsLinked to original sources

PubMed2006

Enhanced Raman scattering from individual semiconductor nanocones and nanowires.

We report strong enhancement (approximately 10(3)) of the spontaneous Raman scattering from individual silicon nanowires and nanocones as compared with bulk Si. The observed enhancement is diameter (d), excitation wavelength (lambda(laser)), and incident polarization state dependent, and is explained in terms of a resonant behavior involving incident electromagnetic radiation and the structural dielectric cross section. The variation of the Raman enhancement with d, lambda(laser), and polarization is shown to be in good agreement with model calculations of scattering from an infinite dielectric cylinder.

Journal Article↗

PubMed2006

Instability and transport of metal catalyst in the growth of tapered silicon nanowires.

During metal-catalyzed growth of tapered silicon nanowires, or silicon nanocones (SiNCs), Au-Si eutectic particles are seen to undergo significant and reproducible reductions in their diameters. The reductions are accompanied by the transfer of eutectic droplet mass to adjacent, initially metal catalyst-free substrates, producing secondary nucleation and growth of SiNCs. Remarkably, the catalyst particle diameters on the SiNCs grown on the adjacent substrates are strongly correlated with those on the SiNCs grown on the initially Au-nanoparticle-coated substrate. These post-growth nanoparticle sizes depend on temperature and are found to be independent of the initial nanoparticle sizes. Our modeling and analysis indicates that the size reduction and mass transfer could be explained by electrostatic charge-induced dissociation of the droplet. The reduction in size enables the controlled growth of SiNCs with tip sharpnesses approaching the atomic scale, indicating that metal-catalyst nanoparticles can play an even more dynamic role than previously thought, and suggesting additional modes of control of shape, and of nucleation and growth location.

Catalysis↗

PubMed2005

Diamond-hexagonal semiconductor nanocones with controllable apex angle.

We report on the synthesis of nanostructured and crystalline tapered Si and Ge polyhedra via metal-catalyzed chemical vapor deposition. These Si and Ge nanocones (SiNCs, GeNCs) possess tips with near-atomic sharpness, micron-scaled bases, hexagonal cross-sections, and controllable apex angles. High-resolution transmission electron microscopy, selected-area electron diffraction and Raman scattering spectroscopy and analysis indicate that the SiNCs are of the diamond-hexagonal Si(IV) phase.

Gold↗

PubMed2005

Formation mechanism of nonspherical gold nanoparticles during seeding growth: roles of anion adsorption and reduction rate.

A small section of nonspherical particles can be observed in the further growth of spherical gold colloids exposed to a mixture of NH2OH and HAuCl4. The concentration ratio of [NH2OH]:[HAuCl4] is critical for the formation of nonspherical particles as higher ratios produce lower yields and smaller of such particles. These concentrations also affect the reaction kinetics; the reaction rate increases with [NH2OH], while independent of [HAuCl4], which we believe is due to the specific adsorption of AuCl4- onto gold surface. These nonspherical particles come from the preferential growth of {111} facets as indicated by their TEM images and electron diffraction patterns. We propose this preferential growth is ascribed to the preferential adsorption of AuCl4- on {111} facets, and some competition which determines the yield of nonspherical particles exists between the AuCl4- adsorption and the AuCl4- reduction, faster reduction counteracting the effect of this preferential adsorption and thus suppressing nonspherical particle. This result probably provides some guidance to develop a shape-controlled synthesis of gold particles without any additives.

Journal Article↗

PubMed2005

Surface-enhanced Raman scattering of p-aminothiophenol on a Au(core)/Cu(shell) nanoparticle assembly.

Surface-enhanced Raman scattering (SERS) of p-aminothiophenol (PATP) molecules adsorbed onto assemblies of Au(core)/Cu(shell) nanoparticles is reported. We compare it with the SERS spectrum of PATP adsorbed onto gold nanoparticles: both the absolute and relative scattered intensities of various bands in the two spectra are very different. The difference in relative intensity can be ascribed to chemical effects; the chemical enhancement ratio of the two substrates is approximately 3-5. A theoretical analysis based on a charge-transfer model is carried out, which yields a consistent result and shows that the difference in chemical enhancement is mainly due to the state densities and Fermi levels of the substrates. The difference in absolute intensity originates from electromagnetic (EM) enhancement. EM enhancement of Au(core)/Cu(shell) nanoparticles is unlike that of single-component gold or copper SERS-active substrates. The core/shell particle size for optimal enhancement is about 20 nm in the case of a 632.8 nm incident laser (the size ratio of the core and shell layers is about 0.6).

Journal Article↗