Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers
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.
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19 Dec 2000TL;DR: In this paper, the use of deposited thin films for chemical or biological analysis is discussed, which relates to the application of these thin films in separation adherence and detection of chemical of biological samples.
Abstract: The present invention is directed to the use of deposited thin films for chemical or biological analysis. The invention further relates to the use of these thin films in separation adherence and detection of chemical of biological samples. Applications of these thin films include desorption-ionization mass spectroscopy, electrical contacts for organic thin films and molecules, optical coupling of light energy for analysis, biological materials manipulation, chromatographic separation, head space adsorbance media, media for atomic molecular adsorbance or attachment, and substrates for cell attachment.
53 citations
TL;DR: The light emission properties of boron-doped wurtzite silicon nanowires measured by cathodoluminescence spectroscopy at room temperature are shown and the evolution of the light emission property as function of the borons doping concentration and the growth temperature is presented.
Abstract: Silicon, the mainstay semiconductor in microelectronic circuitry, is considered unsuitable for optoelectronic applications owing to its indirect electronic band gap, which limits its efficiency as a light emitter Here we show the light emission properties of boron-doped wurtzite silicon nanowires measured by cathodoluminescence spectroscopy at room temperature A visible emission, peaked above 15 eV and a near infra-red emission at 08 eV correlate respectively to the direct transition at the Γ point and to the indirect band-gap of wurtzite silicon We find additional intense emissions due to boron intra-gap states in the short wavelength infra-red range We present the evolution of the light emission properties as function of the boron doping concentration and the growth temperature
53 citations
TL;DR: In this paper, the electronic and optical properties of nanoporous silicon were investigated and the photovoltaic efficiency was analyzed as a function of pore size and spacing, and it was shown that nanoporous Si is a promising material for thin-film PV applications.
Abstract: Bulk silicon is a poor light emitter and absorber, but its optical properties are significantly enhanced by nanostructuring. We use first-principles calculations to investigate the electronic and optical properties of nanoporous silicon. We determine and analyze the electronic structure, optical coefficients, and photovoltaic conversion efficiency as a function of pore size and spacing. Our results show that the visible-range absorption coefficient of nanoporous Si is greatly improved compared to the bulk for pore spacings and sizes on the scale of a few nanometers. The photovoltaic efficiency is improved to up to 2.7 times compared to bulk Si, and the theoretical maximum conversion efficiency reaches up to 6.3% for a thin-film nanoporous material thickness of 135 nm. Our results show that nanoporous Si is a promising material for thin-film photovoltaic applications.
53 citations
TL;DR: Integration of the above functional components may result in ncSi-MPM becoming a promising multifunctional carrier for drug delivery and biomedical applications.
Abstract: A core–shell structured multifunctional carrier with nanocrystalline silicon (ncSi) as the core and a water-soluble block copolymer as the shell based on a poly(methacrylic acid) (PMAA) inner shell and polyethylene glycol (MPEG) outer shell (ncSi-MPM) was synthesized for drug delivery. The morphology, composition, and properties of the resulting ncSi-MPM were determined by comprehensive multianalytical characterization, including 1H NMR spectroscopy, FTIR spectroscopy, XPS spectroscopy, TEM, DLS, and fluorescence spectroscopy analyses. The size of the resulting ncSi-MPM nanocarriers ranged from 40 to 110 nm under a simulated physiological environment. The loading efficiency of model drug doxorubicin (DOX) was approximately 6.1–7.4 wt % for ncSi-MPM and the drug release was pH controlled. Cytotoxicity studies demonstrated that DOX-loaded ncSi-MPM showed high anticancer activity against Hela cells. Hemolysis percentages (<2%) of ncSi-MPM were within the scope of safe values. Fluorescent imaging studies show...
53 citations
TL;DR: The aim here is to describe recent advances in the development of in vivo imaging tools based on nanostructured silica and silicon, and their applications in single and multimodality imaging.
Abstract: Recent progress in the development of silica- and silicon-based multimodality imaging nanoprobes has advanced their use in image-guided drug delivery, and the development of novel systems for nanotheranostic and diagnostic applications. As biocompatible and flexibly tunable materials, silica and silicon provide excellent platforms with high clinical potential in nanotheranostic and diagnostic probes with well-defined morphology and surface chemistry, yielding multifunctional properties. In vivo imaging is of great value in the exploration of methods for improving site-specific nanotherapeutic delivery by silica- and silicon-based drug-delivery systems. Multimodality approaches are essential for understanding the biological interactions of nanotherapeutics in the physiological environment in vivo. The aim here is to describe recent advances in the development of in vivo imaging tools based on nanostructured silica and silicon, and their applications in single and multimodality imaging.
53 citations
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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
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
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
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