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Journal ArticleDOI

Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers

03 Sep 1990-Applied Physics Letters (American Institute of Physics)-Vol. 57, Iss: 10, pp 1046-1048
TL;DR: In this paper, free standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography using electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers.
Abstract: Indirect evidence is presented that free‐standing Si quantum wires can be fabricated without the use of epitaxial deposition or lithography. The novel approach uses electrochemical and chemical dissolution steps to define networks of isolated wires out of bulk wafers. Mesoporous Si layers of high porosity exhibit visible (red) photoluminescence at room temperature, observable with the naked eye under <1 mW unfocused (<0.1 W cm−2) green or blue laser line excitation. This is attributed to dramatic two‐dimensional quantum size effects which can produce emission far above the band gap of bulk crystalline Si.
Citations
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Journal ArticleDOI
TL;DR: In this article, a planar-type visible light emission using ballistic electrons as excitation source was presented, which is composed of a semitransparent top electrode, a thin film of fluorescent material, a nanocrystalline porous silicon (nc-PS) layer, an n-type silicon wafer, and an ohmic back contact.
Abstract: A principle of planar-type visible light emission is presented using ballistic electrons as excitation source. The device is composed of a semitransparent top electrode, a thin film of fluorescent material, a nanocrystalline porous silicon (nc-PS) layer, an n-type silicon wafer, and an ohmic back contact. When a positive dc voltage is applied to the top electrode with respect to the substrate, electrons injected into the nc-PS layer are accelerated via multiple-tunneling through interconnected silicon nanocrystallites, and reach the outer surface as energetic hot or quasiballistic electrons. They directly excite the fluorescent film, and then induce uniform visible luminescence. This solid-state light-emitting device, regarded as a “vacuum-less cathode-ray tube,” has many technological advantages over the conventional luminescent devices. It may lead to big innovations in the development of large-area thin flat-panel display and other electronic devices.

59 citations

Journal ArticleDOI
TL;DR: In this paper, Nanosecond pulsed laser ablation of bulk silicon crystal upon the excitation of 532 nm was conducted in supercritical CO2 to generate silicon nanocrystals, whose properties were studied by seven experimental methods.
Abstract: Nanosecond pulsed laser ablation of bulk silicon crystal upon the excitation of 532 nm was conducted in supercritical CO2 to generate silicon nanocrystals, whose properties were studied by seven experimental methods. According to the photoluminescence spectra and fluorescence microscope images, emissions of near-ultraviolet, violet, blue, green, and red were observed in air, at room temperature, and without cooling in liquid nitrogen or a helium cryogenic system. A preferable emission channel of carriers, generated by photoexcitation of Si/SiO2 of core/shell structure, was responsible for interface states with defect sites. This luminescence process caused color changes and intensity increase, enhanced by a factor of 100, where thermal properties of supercritical CO2 were maximized, due to critical anomaly. It was found that colors and intensities of photoluminescence of silicon nanocrystals are controlled by a cooling rate during ablation, whose quantity is manipulated by the supercritical fluid pressure.

59 citations

Journal ArticleDOI
TL;DR: In this article, a correlation between visible room-temperature photoluminescence and the formation of diamond cubic nanocrystals approximately 2-5 nm in diameter in annealed samples was found.
Abstract: Ion beam synthesis of Si and Ge nanocrystals in an SiO 2 matrix is performed by precipitation from supersaturated solid solutions created by ion implantation. Films of SiO 2 on (100) Si substrates are implanted with Si and Ge at doses 1 × 10 16 /cm 2 - 5 × 10 16 /cm 2 . Implanted samples are subsequently annealed to induce precipitation of Si and Ge nanocrystals. Raman spectroscopy and high-resolution transmission electron microscopy indicate a correlation between visible room-temperature photoluminescence and the formation of diamond cubic nanocrystals approximately 2–5 nm in diameter in annealed samples. As-implanted but unannealed samples do not exhibit luminescence. Rutherford backscattering spectra indicate a steepening of implanted Ge profiles upon annealing. Photoluminescence spectra are correlated with annealing temperatures, and compared with theoretical predictions for various possible luminescence mechanisms, such as radiative recombination of quantum-confined excitons, as well as possible localized state luminescence related to structural defects in SiO 2 . Potential optoelectronic device applications are also discussed.

58 citations

Journal ArticleDOI
TL;DR: In this paper, photoluminescence (PL) and optical absorption results on silicon nanocrystals in SiO2 matrices prepared by RF sputtering method are presented, where the samples have varying Si/SiO2 compositional fraction and are annealed at different temperature and duration.
Abstract: Raman, photoluminescence (PL) and optical absorption results on silicon nanocrystals in SiO2 matrices prepared by RF sputtering method are presented. The samples have varying Si/SiO2 compositional fraction and are annealed at different temperature and duration. The average size of the nanocrystals is determined by the lineshape analysis of the first-order Raman spectra. Raman results further indicate the existence of a threshold annealing temperature for the formation of nanocrystals and increase in the nanocrystal size with increasing temperature and duration. Size-dependent blue shift of the absorption edge is observed from absorption experiments and is supported by Raman results. Room temperature and temperature dependent PL results are analyzed with the help of a phenomenological model. The PL results in conjunction with the Raman and absorption results indicate the involvement of both the core states and the interfacial states in the luminescence process.

58 citations

Journal ArticleDOI
TL;DR: In this paper, a multistage vector delivery system comprising biodegradable and biocompatible nanoporous silicon particles (S1MPs) was developed to host, protect, and deliver second-stage therapeutic and diagnostic nanoparticles (S2NPs) on intravenous injection.
Abstract: In the development of new nanoparticle-based technologies for therapeutic and diagnostic purposes, understanding the fate of nanoparticles in the body is crucial. We recently developed a multistage vector delivery system comprising biodegradable and biocompatible nanoporous silicon particles (first-stage microparticles [S1MPs]) able to host, protect, and deliver second-stage therapeutic and diagnostic nanoparticles (S2NPs) on intravenous injection. This delivery system aims at sequentially overcoming the biologic barriers en route to the target delivery site by separating and assigning tasks to the coordinated logic-embedded vectors constituting it. In this work, by conjugating a near-infrared dye on the surface of the S1MP without compromising the porous structure and potential loading of S2NPs, we were able to monitor the in vivo distribution of S1MPs in healthy mice using an optical imaging system. It was observed that particles predominantly accumulated in the liver and spleen at the end of 24 hours. ...

58 citations

References
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Journal ArticleDOI
TL;DR: In this article, the properties of electrolyte-semiconductor barriers are described, with emphasis on germanium, and the use of these barriers in localizing electrolytic etching is discussed.
Abstract: Properties of electrolyte-semiconductor barriers are described, with emphasis on germanium. The use of these barriers in localizing electrolytic etching is discussed. Other localization techniques are mentioned. Electrolytes for etching germanium and silicon are given.

1,039 citations

Journal ArticleDOI
TL;DR: It is found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive, which has implications for the ultimate efficiency of silicon solar cells.
Abstract: We have found that a standard, widespread, chemical-preparation method for silicon, oxidation followed by an HF etch, results in a surface which from an electronic point of view is remarkably inactive. With preparation in this manner, the surface-recombination velocity on Si111g is only 0.25 cm/sec, which is the lowest value ever reported for any semiconductor. Multiple-internal-reflection infrared spectroscopy shows that the surface appears to be covered by covalent Si-H bonds, leaving virtually no surface dangling bonds to act as recombinatiuon centers. These results have implications for the ultimate efficiency of silicon solar cells.

910 citations

Journal ArticleDOI
TL;DR: In this paper, multiple internal infrared reflection spectroscopy has been used to identify the chemical nature of chemically oxidized and subsequently HF stripped silicon surfaces, and these very inert surfaces are found to be almost completely covered by atomic hydrogen.
Abstract: Multiple internal infrared reflection spectroscopy has been used to identify the chemical nature of chemically oxidized and subsequently HF stripped silicon surfaces. These very inert surfaces are found to be almost completely covered by atomic hydrogen. Results using polarized radiation on both flat and stepped Si(111) and Si(100) surfaces reveal the presence of many chemisorption sites (hydrides) that indicate that the surfaces are microscopically rough, although locally ordered. In particular, the HF‐prepared Si(100) surface appears to have little in common with the smooth H‐saturated Si(100) surface prepared in ultrahigh vacuum.

588 citations

Journal ArticleDOI
TL;DR: In this article, the authors measured hydrogen desorption from monohydride and dihydride species on crystalline-silicon surfaces using transmission Fourier-transform infrared (FTIR) spectroscopy.
Abstract: Hydrogen desorption kinetics from monohydride and dihydride species on crystalline-silicon surfaces were measured using transmission Fourier-transform infrared (FTIR) spectroscopy. The FTIR desorption measurements were performed in situ in an ultrahigh-vacuum chamber using high-surface-area porous-silicon samples. The kinetics for hydrogen desorption from the monohydride and dihydride species was monitored using the SiH stretch mode at 2102 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and the ${\mathrm{SiH}}_{2}$ scissors mode at 910 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, respectively. Annealing studies revealed that hydrogen from the ${\mathrm{SiH}}_{2}$ species desorbed between 640 and 700 K, whereas hydrogen from the SiH species desorbed between 720 and 800 K. Isothermal studies revealed second-order hydrogen desorption kinetics for both the monohydride and dihydride surface species. Desorption activation barriers of 65 kcal/mol (2.82 eV) and 43 kcal/mol (1.86 eV) were measured for the monohydride and dihydride species, respectively. These desorption activation barriers yield upper limits of 84.6 kcal/mol (3.67 eV) and 73.6 kcal/mol (3.19 eV) for the Si-H chemical bond energies of the SiH and ${\mathrm{SiH}}_{2}$ surface species.

479 citations