Formation Of Si-H Bonds Research Articles

Flexible multi-wavelength photodetector based on porous silicon nanowires.

Porous silicon nanowires (PSi NWs) responding to red, green and blue lights simultaneously are reported in this study. NWs with a diameter of 120 nm were prepared from p-type Si wafer by metal-catalyst-assisted etching. The NWs produced in this manner had an outer porous region consisting of Si nanocrystals small enough to ensure the quantum confinement effect. Hydrazine treatment passivated the porous region by reduction of the surface oxides and the formation of Si-H bonds. The energy band structure of the porous region was a direct transition type, while the emission/absorption energies corresponded to red (1.94 eV), green (2.24 and 2.44 eV) and blue (2.98 eV) light photons. A device structure prepared by suspending 10 PSi NWs between two Al electrodes by dielectrophoresis generated photocurrents upon exposure to red, green and blue lights. The rising and decay times were both 30 μs and the ratio of photocurrent to dark current was 92.0, 59.8 and 24.4 for the blue, green and red lights, respectively. The device could be bent down to the bending radius of 5 mm without any significant deterioration of the photoresponse performances. Further, the device survived repeated bending and unbending over 10 000 cycles with this bending radius, demonstrating its application potential as a flexible device with multiple-wavelength photosensing capabilities.

Effect of Assisted-Ion-Beam Gases on the Structure of Amorphous Silicon Thin Films Prepared by Ion-Beam-Assisted Sputtering

In this work, amorphous silicon (a-Si) thin films were prepared by ion-beam-assisted sputtering, the effect of assisted-ion-beam gases on the thin-film structure were investigated using Raman spectroscopy, Fourier transform infrared spectroscopy, and spectroscopic ellipsometry. It was observed that the introduction of assisted-ion beam improved the thin-film structure, and the ion-beam-assisted sputtering a-Si thin films possessed higher short-range order, intermediate-range order, lower microstructure parameter (R*) and defect density of states with the increased of hydrogen concentration in the assisted-ion beam gases, which due to the transfer of energy from ion to the surface Si atoms and the formation of Si-H bonds in the a-Si thin films. The a-Si thin films deposited with hydrogen-ion beam possessed the absorption coefficient at 0.8 eV and microstructure factor of 0.7 cm-1 and 0.48. It was illumined that the device-quality a-Si thin films can be achieved under the ion-beam-assisted sputtering.

Ammonia modification of oxide-free Si(111) surfaces

Amination of surfaces is useful in a variety of fields, ranging from device manufacturing to biological applications. Previous studies of ammonia reaction on silicon surfaces have concentrated on vapor phase rather than wet chemical processes, and mostly on clean Si surfaces. In this work, the interaction of liquid and vapor-phase ammonia is examined on three types of oxide-free surfaces – passivated by hydrogen, fluorine (1/3 monolayer) or chlorine – combining infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and first-principles calculations. The resulting chemical composition highly depends on the starting surface; there is a stronger reaction on both F- and Cl-terminated than on the H-terminated Si surfaces, as evidenced by the formation of Si-NH2. Side reactions can also occur, such as solvent reaction with surfaces, formation of ammonium salt by-products (in the case of 0.2M ammonia in dioxane solution), and nitridation of silicon (in the case of neat and gas-phase ammonia reactions for instance). Unexpectedly, there is formation of Si-H bonds on hydrogen-free Cl-terminated Si(111) surfaces in all cases, whether vapor phase of neat liquid ammonia is used. The first-principles modeling of this complex system suggests that step-edge surface defects may play a key role in enabling the reaction under certain circumstances, despite the endothermic nature for Si-H bond formation.

Blue Light Emission from Porous Silicon

ABSTRACTThrough a post treatment of light emitting porous silicon in boilingwater, a large blue shift of its photoluminescence (PL) spectrum hasbeen observed and a stable blue-green light emission at the peak wavelength down to 500 nm is achieved. The effect of boiling water treatment is suggested to be a kind of oxidation, which could reduce thesize of the Si column, fill up some micropores and strengthen the Siskeleton. The photoluminescence microscopic observation shows that the surface of blue light emitting porous silicon is composed of manysmall uniformly light-emitting domains at the size of several tens of μm. Fourier transform infrared reflection (FTIR) measurements show that the formation of Si-H bonds is not responsible for the visible luminescence in the very thin Si wires.