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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
Z.M. Rittersma1
TL;DR: A review of miniaturized humidity sensors is presented in this article, focusing on the integration issues and technological challenges of the miniaturised humidity sensors, and focusing on capacitive-, hygrometric-, gravimetric-, optical and integrated sensors.
Abstract: A review of miniaturised humidity sensors is presented. Recent achievements in capacitive-, hygrometric-, gravimetric-, optical- and integrated sensors are discussed. Attention is paid to a general perspective of miniaturised humidity sensors, emphasising on integration issues and technological challenges. A table summarising most of the reviewed devices is included.

554 citations

Journal ArticleDOI
TL;DR: In this article, a facile fabricating method has been established for large-area uniform silicon nanowires arrays, which were obtained by single crystals and epitaxial on the substrate.
Abstract: A facile fabricating method has been established for large-area uniform silicon nanowires arrays All silicon nanowires obtained were single crystals and epitaxial on the substrate Six kinds of silicon wafers with different types, surface orientations, and doping levels were utilized as starting materials With the catalysis of silver nanoparticles, room-temperature mild chemical etching was conducted in aqueous solution of hydrofluoric acid (HF) and hydrogen peroxide (H2O2) The corresponding silicon nanowires arrays with different morphologies were obtained The silicon nanowires possess the same type and same doping level of the starting wafer All nanowires on the substrate have the same orientation For instance, both (100)- and (111)-oriented p-type wafers produced silicon nanowires in the (100) direction For every kind of silicon wafer, the effect of etching conditions, such as components of etchant, temperature, and time, were systemically investigated This is an appropriate method to produce a

527 citations

Journal ArticleDOI
TL;DR: A review of experimental work on freezing and melting in confinement is presented in this paper, where a range of systems, from metal oxide gels to porous glasses to novel nanoporous materials, are discussed.
Abstract: A review of experimental work on freezing and melting in confinement is presented. A range of systems, from metal oxide gels to porous glasses to novel nanoporous materials, is discussed. Features such as melting-point depression, hysteresis between freezing and melting, modifications to bulk solid structure and solid-solid transitions are reviewed for substances such as helium, organic fluids, water and metals. Recent work with well characterized assemblies of cylindrical pores like MCM-41 and graphitic microfibres with slit pores has suggested that the macroscopic picture of melting and freezing breaks down in pores of molecular dimensions. Applications of the surface force apparatus to the study of freezing and melting phenomena in confinement are discussed in some detail. This instrument is unique in allowing the study of conditions in a single pore, without the complications of pore blockage and connectivity effects. The results have confirmed the classical picture of melting-point depression in larger pores, and allowed the direct observation of capillary condensation of solid from vapour. Other results include the measurement of solvation forces across apparently fluid films below the bulk melting point and a solid-like response to shear of films above the bulk melting point. These somewhat contradictory findings highlight the difficulty of using bulk concepts to define the phase state of a substance confined to nanoscale pores.

515 citations

Journal ArticleDOI
TL;DR: In this article, the authors observed visible light emission from nanosize gold clusters and found that relatively intense photoluminescence occurs only when the size of the metal nanocluster is sufficiently small (<5 nm.
Abstract: We have observed visible light emission from nanosize gold clusters. Liquid chromatographic analysis of the metal clusters shows that relatively intense photoluminescence occurs only when the size of the metal nanocluster is sufficiently small (<5 nm). The emission is strongly Stokes shifted and is assigned to radiative recombination of Fermi level electrons and sp- or d-band holes. The electron and/or hole states are perturbed by surface states, as indicated by the dependence of the emission spectrum on the nature of the cluster surface. Finally, we found that large, nonemitting gold clusters can also be made luminescent by partial dissolution using KCN.

512 citations

Journal ArticleDOI
TL;DR: In this paper, strong room-temperature photoluminescence (PL) in the wavelength range 650-950 nm has been observed in high temperature annealed (1000-1300 °C) substoichiometric silicon oxide (SiOx) thin films prepared by plasma enhanced chemical vapor deposition.
Abstract: Strong room-temperature photoluminescence (PL) in the wavelength range 650–950 nm has been observed in high temperature annealed (1000–1300 °C) substoichiometric silicon oxide (SiOx) thin films prepared by plasma enhanced chemical vapor deposition. A marked redshift of the luminescence peak has been detected by increasing the Si concentration of the SiOx films, as well as the annealing temperature. The integrated intensity of the PL peaks spans along two orders of magnitude, and, as a general trend, increases with the annealing temperature up to 1250 °C. Transmission electron microscopy analyses have demonstrated that Si nanocrystals (nc), having a mean radius ranging between 0.7 and 2.1 nm, are present in the annealed samples. Each sample is characterized by a peculiar Si nc size distribution that can be fitted with a Gaussian curve; by increasing the Si content and/or the annealing temperature of the SiOx samples, the distributions become wider and their mean value increases. The strong correlation betw...

508 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