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: Recent developments in the experimental study of morphological, structural and compositional aspects of ripple patterns generated on a silicon surface after medium keV (30-120 keV) argon bombardment mainly at an angle of ion incidence of 60° are reviewed.
Abstract: The formation of a self-organized nanoscale ripple pattern after off-normally incident ion bombardment on the surface of amorphous materials, or on semiconductors like silicon that are easily amorphized by ion bombardment, has attracted much attention in recent years from the point of view of both theory and applications. As the energy of the impinging ions increases from low to medium, i.e.?several hundred eV to a few tens of keV, the ratio of amplitude to wavelength of the generated ripple pattern becomes so large that inter-peak shadowing of the incident ion flux takes place. Morphologically, the sinusoidal surface profile starts to become distorted after prolonged ion bombardment under such conditions. Structural and compositional modifications of the ripple morphology generated under shadowing conditions include the formation of a thicker amorphous layer with high incorporation of argon atoms in the form of nanometer sized bubbles around the middle part of the front slope of the ripple facing the ion beam, as compared to the rear slope. The present paper reviews recent developments in the experimental study of morphological, structural and compositional aspects of ripple patterns generated on a silicon surface after medium keV (30?120?keV) argon bombardment mainly at an angle of ion incidence of 60?.
55 citations
TL;DR: The photoluminescence (PL) peak energies of crystalline silicon and amorphous silicon nanostructures are blueshifted from those of bulk c-Si and a-Si.
55 citations
TL;DR: An unprecedented alloying mode by way of AGR is reported, in which foreign atoms induce structural transformation of the mother nanoparticles and enter the nanoparticles in a non-replacement fashion, and a novel, active-metal-doped, gold nanoparticle was synthesized, and its structure resolved.
Abstract: Anti-galvanic reaction (AGR) not only defies classic galvanic theory but is a promising method for tuning the compositions, structures, and properties of noble-metal nanoparticles. Employing AGR for the preparation of alloy nanoparticles has recently received great interest. Herein, we report an unprecedented alloying mode by way of AGR, in which foreign atoms induce structural transformation of the mother nanoparticles and enter the nanoparticles in a non-replacement fashion. A novel, active-metal-doped, gold nanoparticle was synthesized by this alloying mode, and its structure resolved. A CdSH motif was found in the protecting staples of the bimetal nanoparticle. DFT calculations revealed that the Au20 Cd4 (SH)(SR)19 nanoparticle is a 8e superatom cluster. Furthermore, although the Cd-doping does not essentially alter the absorption spectrum of the mother nanocluster, it distinctly enhances the stability and catalytic selectivity of the mother nanoclusters.
55 citations
TL;DR: The effects of organoamine molecules on the luminescence of porous silicon has been examined by steadystate photoluminescence (PL) and Fourier transform infrared spectroscopies as mentioned in this paper.
Abstract: The effects of addition of a series of organoamine molecules on the luminescence of porous silicon has been examined by steady‐state photoluminescence (PL) and Fourier transform infrared spectroscopies. These samples, prepared nonanodically via stain etching techniques and characterized by atomic force microscopy, show dramatic quenching of visible PL upon addition of dilute solutions of the above Lewis base adsorbates. The fractional changes in integrated PL intensity as a function of quencher concentration obey a simple equilibrium model, demonstrating Langmuir‐type behavior from which equilibrium constants can be calculated. An observation concomitant with this loss of PL is a diminution of the silicon hydride stretching frequencies near 2100 cm−1.
55 citations
TL;DR: In this article, the origin of surface-functionalized SiNC photoluminescence was investigated, and the authors showed that SiNC PL arises from surface states independent of nanocrystal size.
Abstract: The origin of photoluminescence (PL) in silicon nanocrystals (SiNCs) remains a subject of considerable debate. Size-dependent PL that supports the quantum confinement model has been proposed by several researchers. On the other hand, SiNC PL arising from surface states that are independent of nanocrystal size has also been shown. This work addresses the origin of surface-functionalized SiNC PL as relating to surface states and the NC size. SiNCs of different sizes (3 and 5 nm diameters) were prepared with three distinct surface chemistries. Steady-state and time-resolved PL measurements were performed at temperatures ranging from 37 to 377 K. Temperature-dependent luminescence consistent with core emission was observed for alkyl-terminated SiNCs, while alkylamine-functionalized SiNCs displayed minimal temperature-dependent luminescence, consistent with a charge-transfer mechanism. Lightly oxidized alkyl SiNCs had similar emission profiles to alkyl SiNCs; however, they showed longer luminescence lifetimes ...
55 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