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Metal catalyzed, CVD-grown silicon nanowires decorated by chemical assembly of closely spaced Ag nanocrystals were modified with the well-known "silver mirror" reaction and investigated as substrates for surface-enhanced Raman (SERS) and hyper-Raman (SEHRS) spectroscopy. Four chromophores were examined: Rhodamine 6G, crystal violet, a cyanine dye, and a cationic donor-acceptor substituted stilbene. After soaking the substrates overnight in 10(-4) M aqueous chromophore solutions, all four chromophores gave good-quality SERS spectra in < or =60 s using <1 microW of 458-nm cw laser power, and SEHRS spectra are obtained in < or =120 s using <1 mW of mode-locked 916-nm laser power. Results from this substrate are compared with those on colloidal silver nanoparticles deposited as a film, as well as surfaces grown by the silver mirror reaction.

Visible and near-infrared photoluminescence (PL) at room temperature is reported from Si nanowires (NWs) grown by chemical vapor deposition from TiSi2 catalyst sites. NWs grown with average diameter of 20 nm were etched and oxidized to thin and passivate the wires. The PL emission blue shifted continuously with decreasing nanowire diameter. Slowed oxidation was observed for small nanowire diameters and provides a high degree of control over the emission wavelength. Transmission electron microscopy, PL, and time-resolved PL data are fully consistent with quantum confinement of charge carriers in the Si nanowire core being the source of luminescence. These light emitting nanowires could find application in future CMOS-compatible photonic devices.

Alkylsiloxane self-assembled monolayers (SAMs) were formed on surface relief created by nanoimprinting and etching recesses into Si and SiO2. Rather than exhibiting the isolated domains seen on unpatterned surfaces after limited formation time, the SAM on nanoimprinted surfaces became continuous and uniform after only a short (∼5–10 min) reaction time. The hydrocarbon chains are densely packed and nearly vertically oriented. X-ray photoemission spectroscopy indicates complete hydrolysis and elimination of Cl from the octadecyltrichlorosilane precursor. The results suggest that the pattern edges enhance the nucleation rate, leading to the rapid coverage, and provide in-plane order within the SAM. [ABSTRACT FROM AUTHOR]

Dense ensembles of silicon nanowires were prepared by metal-catalyzed chemical vapor deposition on silicon substrates. Some of these ensembles were doped with phosphorus during growth. The nanowires were characterized using scanning electron microscopy, x-ray diffraction, and mass spectroscopy. Field emission of electrons from these structures was studied at room temperature in ultrahigh vacuum. The measurements were carried out using a parallel-plate diode cell. At high applied fields, the current-voltage characteristics deviate from the Fowler-Nordheim law and exhibit a stepwise increase of the current with increasing voltage at 300 K. [ABSTRACT FROM AUTHOR]

Metal catalyzed, CVD-grown silicon nanowires decorated by chemical assembly of closely spaced Ag nanocrystals were modified with the well-known ‘silver mirror’ reaction and investigated as substrates for surface-enhanced Raman (SERS) and hyper-Raman (SEHRS) spectroscopy. Four chromophores were examined: Rhodamine 6G, crystal violet, a cyanine dye, and a cationic donor-acceptor substituted stilbene. After soaking the substrates overnight in 10-4 M aqueous chromophore solutions, all four chromophores gave good-quality SERS spectra in ≤60 s using < 1 μW of 458-nm cw laser power, and SEHRS spectra are obtained in ≤ 120 s using < 1 mW of mode-locked 916-nm laser power. Results from this substrate are compared with those on colloidal silver nanoparticles deposited as a film, as well as surfaces grown by the silver mirror reaction. [ABSTRACT FROM AUTHOR]