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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TL;DR: Alkyl-capped and alkyl/alkoxycapped silicon nanocrystals have been prepared by the oxidation of magnesium silicide with bromine using high-resolution transmission electron microscopy as discussed by the authors.
Abstract: Alkyl-capped and alkyl/alkoxy-capped silicon nanocrystals have been prepared by the oxidation of magnesium silicide with bromine High-resolution transmission electron microscopy confirmed the crystalline nature of the nanoparticles and provided an average diameter of 45 (20) nm for the alkyl-capped and for the alkyl/alkoxy-capped nanoparticles Energy-dispersive X-ray spectroscopy showed that the nanoparticles are composed of silicon, with no evidence of unreacted bromine FTIR spectra were consistent with alkyl- and alkyl/alkoxy-capped surfaces Fluorescence spectroscopy indicated strong ultraviolet-blue photoluminescence, which was attributed to both quantum confinement and surface termination These nanoparticles displayed long-term stability and no degradation of the photoluminescence was observed for a period of 1 year
153 citations
TL;DR: In this article, the state-of-the-art in local probe techniques for studying the properties of nanostructures, concentrating on methods involving monitoring the properties related to photon emission.
Abstract: With the rapid development of technologies for the fabrication of, as well as applications of low-dimensional structures, the demands on characterization techniques increase. Spatial resolution is especially crucial, where techniques for probing the properties of very small volumes, in the extreme case quantum structures, are essential. In this article we review the state-of-the-art in local probe techniques for studying the properties of nanostructures, concentrating on methods involving monitoring the properties related to photon emission. These techniques are sensitive enough to reveal the electronic structure of low-dimensional semiconductor structures and are, therefore, able to give detailed information about the geometrical structure, including fabrication-related inhomogeneities within an ensemble of structures. The local luminescence probe techniques discussed in this review article can be divided into four categories according to the excitation source: (i) spatially localized microphotoluminescence spectroscopy using either strong focusing or masking; (ii) near-field optical microscopy to reach below the diffraction limitation of far-field optics, by either exciting, detecting, or both exciting and detecting in the near field; (iii) cathodoluminescence using focused energetic electrons in an electron microscope; and (iv) scanning tunneling luminescence, using low-energy electrons injected or extracted from the tip of a scanning tunneling microscope.
152 citations
TL;DR: It is demonstrated visible electroluminescence from colloidal silicon in the form of a hybrid silicon quantum dot-organic light emitting diode that depends strongly on the organic transport layers employed as well as on the choice of solvent from which the Si quantum dots are cast.
Abstract: We herein demonstrate visible electroluminescence from colloidal silicon in the form of a hybrid silicon quantum dot-organic light emitting diode. The silicon quantum dot emission arises from quantum confinement, and thus nanocrystal size tunable visible electroluminescence from our devices is highlighted. An external quantum efficiency of 0.7% was obtained at a drive voltage where device electroluminescence is dominated by silicon quantum dot emission. The characteristics of our devices depend strongly on the organic transport layers employed as well as on the choice of solvent from which the Si quantum dots are cast.
152 citations
TL;DR: In this paper, density functional theory calculations have been carried out in order to study the structural, electronic, and optical properties of oxidized silicon clusters and silicon nanocrystals embedded in a matrix.
Abstract: Density-functional theory calculations have been carried out in order to study the structural, electronic, and optical properties of oxidized silicon clusters and silicon nanocrystals embedded in $\mathrm{Si}{\mathrm{O}}_{2}$. For the isolated clusters, different $\mathrm{Si}∕\mathrm{O}$ bonding geometries and various levels of oxidation have been investigated, checking also the dependence of the results on the structure size. We provide strong evidences that not only the quantum confinement effect but also the chemistry at the interface has to be taken into account in order to understand the physical properties of these systems. In particular we show how the multiple presence of silanonelike $\mathrm{Si}\mathrm{O}$ bonds can be a reliable model for explaining the photoluminescence redshift observed in oxidized porous silicon samples and it can be used as possible explanation also for the unexpected large photoluminescence bandwidth in single oxidized Si quantum dots. For the silicon nanocrystals embedded in a $\mathrm{Si}{\mathrm{O}}_{2}$ matrix, the electronic and optical properties are discussed in detail. The strong interplay between the nanocrystal and the surrounding host environment and the active role of the interface region between them is pointed out, in very good agreement with the experimental results.
152 citations
TL;DR: In this article, the use of porous silicon (PS) as a nanomaterial which is extensively investigated and utilized for various applications, eg, in the fields of optics, sensor technology and biomedicine is discussed.
Abstract: This work reviews the use of porous silicon (PS) as a nanomaterial which is extensively investigated and utilized for various applications, eg, in the fields of optics, sensor technology and biomedicine Furthermore the combination of PS with one or more materials which are also nanostructured due to their deposition within the porous matrix is discussed Such nanocompounds offer a broad avenue of new and interesting properties depending on the kind of involved materials as well as on their morphology The filling of the pores performed by electroless or electrochemical deposition is described, whereas different morphologies, reaching from micro- to macro pores are utilized as host material which can be self-organized or fabricated by prestructuring For metal-deposition within the porous structures, both ferromagnetic and non-magnetic metals are used Emphasis will be put on self-arranged mesoporous silicon, offering a quasi-regular pore arrangement, employed as template for filling with ferromagnetic metals By varying the deposition parameters the precipitation of the metal structures within the pores can be tuned in geometry and spatial distribution leading to samples with desired magnetic properties The correlation between morphology and magnetic behaviour of such semiconducting/magnetic systems will be determined Porous silicon and its combination with a variety of filling materials leads to nanocomposites with specific physical properties caused by the nanometric size and give rise to a multiplicity of potential applications in spintronics, magnetic and magneto-optic devices, nutritional food additives as well as drug delivery
152 citations
Cites background from "Silicon quantum wire array fabricat..."
...luminescence in the red, the so called “S-band”, has been attributed to 2D quantum confinement within silicon quantum wires leading to a widening of the band gap [18]....
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...Canham, who showed room-temperature photoluminescence of an anodized p-type silicon wafer [18]....
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References
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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