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: In this paper, the porosity and pore size of porous silicon membranes can be tuned, the pore geometry has near-unity tortuosity, and membranes can also be made thin and with integrated support structures.
Abstract: N-type porous silicon can be used to realize electroosmotic pumps with high flow rates per applied potential difference. The porosity and pore size of porous silicon membranes can be tuned, the pore geometry has near-unity tortuosity, and membranes can be made thin and with integrated support structures. The size of hexagonally packed pores is modified by low-pressure chemical vapor deposition (LPCVD) polysilicon deposition, followed by wet oxidation of the polysilicon layer, resulting in a pore radius varying from 1 to 3 /spl mu/m. Pumping performance of these devices is experimentally studied as a function of pore size and compared with theory. These 350-/spl mu/m-thick silicon membranes exhibit a maximum flow rate per applied field of 0.13 ml/min/cm/sup 2//V. This figure of merit is five times larger than previously demonstrated porous glass EO pumps.
80 citations
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TL;DR: In this paper, the authors outline the data and arguments that have been presented to support the quantum confinement model, along with the shortcomings of such a model, and examine more recent models in which the chemical and structural properties of the surface regions of the nanostructures have been incorporated.
Abstract: Although silicon is the material of choice in the semiconductor industry, it has one serious disadvantage: it is an extremely poor optoelectronic material. This is because it is an indirect gap semiconductor, in which radiative transition results in extremely weak light emission in the infrared part of the spectrum. Thus, the discovery of strong visible luminescence from a silicon-based material (porous silicon) has been quite surprising and has generated significant interest, both scientific and technological. This material differs from bulk silicon in one important way, in that it consists of interconnected silicon nanostructures with very large surface to volume ratios. Although the first mechanism proposed to explain this emission process involved carrier recombination within quantum size silicon particles, more recent work has shown that the surface chemistry appears to be the controlling factor in this light emission process. Thus, the aim of this work is to outline the data and arguments that have been presented to support the quantum confinement model, along with the shortcomings of such a model, and to examine more recent models in which the chemical and structural properties of the surface regions of the nanostructures have been incorporated.
80 citations
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TL;DR: In this paper, an overview of the advantages and disadvantages of silicon for electroosmotically driven separation techniques is presented, and some silicon-derived insulating microstructures and their potential application in chemical analysis are also shown.
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TL;DR: In this article, the exciton ground states in Si and 3C-SiC quantum dots were investigated by using the effective mass theory, taking account of the conduction and valence-band mass anisotropy as well as the small spin-orbit splitting energy.
Abstract: We investigate exciton ground states in Si and 3C-SiC quantum dots by using the effective mass theory, taking account of the conduction- and valence-band mass anisotropy as well as the small spin-orbit splitting energy. The degenerate hole and exciton states are partly split by the mass anisotropy. The anisotropy splitting energies in quantum dots are different dramatically from their bulk value due to quantum size effects. The assumed changeable spin-orbit splitting energy may change the ordering of the anisotropy-split energy levels. Taking account of the exchange interaction, the degeneracy of the exciton states is further lifted. Due to the anisotropy and exchange splitting, the 48-fold exciton ground state will be split into two 18-fold triplets and two 6-fold singlets. The lowest three states are optically forbidden for Si quantum dots, which leads to a Stokes shift of luminescence. The theroretical shift agrees well with the experimental data. Furthermore, the exciton band gap and binding energy as a function of dot radius are presented both for Si and for 3C-SiC quantum dots. The band gap of Si quantum dots agrees well with the recent photoluminescence results of size-separated quantum dots by Ledoux et al. and absorption data of Furukawa et al.
80 citations
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TL;DR: The EFs derived from analysis of the acquired fluorescence microscopy images indicate that silicon nanopillar structures can provide enhancements comparable or even stronger than those typically achieved using plasmonic SEF structures without the limitations of the metal-based substrates, such as fluorescence quenching and an insufficiently large probe volume.
Abstract: Silicon nanowire and nanopillar structures have drawn increased attention in recent years due in part to their unique optical properties. Herein, electron beam lithography combined with reactive-ion etching is used to reproducibly create individual silicon nanopillars of various sizes, shapes, and heights. Finite difference time domain analysis predicts local field intensity enhancements in the vicinity of appropriately sized and coaxially illuminated silicon nanopillars of approximately 2 orders of magnitude. While this level of enhancement is modest when compared to plasmonic systems, the unique advantage of the silicon nanopillar resonators is that they enhance optical fields in substantially larger volumes. By analyzing experimentally measured strength of the silicon Raman phonon line (500 cm–1), it was determined that nanopillars produced local field enhancements that are consistent with these predictions. Additionally, we demonstrate that a thin layer of Zn phthalocyanine on the nanopillar surface w...
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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
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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
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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
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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