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: This mini-review highlights the recent innovative diagnostic imaging aspects of porous silicon (PSi) materials and emphasizes their potential as theranostic platforms and tools for the clinic.
Abstract: Advances in nanotechnology have prompted rapid progress and versatile imaging modalities for diagnostics and treatment of diseases. Molecular imaging is a powerful technique for quantifying physiological changes in vivo using noninvasive imaging probes. These probes are used to image specific cells and tissues within a whole organism. Currently, imaging is an essential part of clinical protocols providing morphological, structural, metabolic and functional information. Using theranostic micro- or nanoparticles, which combine both therapeutic and diagnostic capabilities in one single entity, holds a true promise to propel the biomedical field toward personalized medicine. With this approach, biological processes can be directly and simultaneously monitored with the treatment of the diseases. This mini-review highlights the recent innovative diagnostic imaging aspects of porous silicon (PSi) materials and emphasizes their potential as theranostic platforms and tools for the clinic. Multiple biomedical imaging applications of the PSi materials are also outlined.
58 citations
Patent•
28 Sep 1995TL;DR: In this paper, a getter material (29) of porous silicon is deposited on the substrate (26) between the conductive regions (28) of the anode plate (10).
Abstract: An anode plate (10) for use in a field emission flat panel display device (8) includes a transparent substrate (26) having a plurality of spaced-apart, electrically conductive regions (28) are covered by a luminescent material (24) and from the anode electrode. A getter material (29) of porous silicon is deposited on the substrate (26) between the conductive regions (28) of the anode plate (10). The getter material (29) of porous silicon is preferably electrically nonconductive, opaque, and highly porous. Included are methods of fabricating the getter material (29) on the anode plate (10).
58 citations
TL;DR: In this paper, a procedure for patterned synthesis of porous Si exhibiting visible luminescence is described, and positive and negative patterns of luminescent porous Si are etched into n and p-type Si samples, respectively, by projecting a high-contrast image on the electrode surface during the etching process.
Abstract: A procedure for the patterned synthesis of porous Si exhibiting visible luminescence is described. Anodic electrochemical etch of n‐ or p‐type Si in ethanol/HF solution leads directly to porous Si that luminesces with λmax between 750 and 650 nm. Positive and negative patterns of luminescent porous Si are etched into n‐ and p‐type Si samples, respectively, by projecting a high‐contrast image on the electrode surface during the etching process. Lithographic resolution obtained is on the order of 20 μm.
58 citations
TL;DR: In this article, an inexpensive silicon precursor, namely rice husk, was employed for the synthesis of Si NPs by rapid microwave heating, which exhibited observable green luminescence with a quantum yield of ∼60%.
Abstract: Silicon nanoparticles (Si NPs) exhibiting observable luminescence have many electronic, optical, and biological applications. Owing to reduced toxicity, they can be used as cheap and environmentally friendly alternatives for cadmium containing quantum dots, organic dyes, and rare earth-based expensive phosphors. Here, we report an inexpensive silicon precursor, namely rice husk, which has been employed for the synthesis of Si NPs by rapid microwave heating. The Si NPs of ∼4.9 nm diameter exhibit observable green luminescence with a quantum yield of ∼60%. They show robust storage stability and photostability and have constant luminescence during long-term UV irradiation extending over 48 h, in contrast to other luminescent materials such as quantum dots and organic dyes which quenched their emission over this time window. Green luminescent Si NPs upon mixing with synthesized red and blue luminescent Si NP species are shown to be useful for energy-efficient white light production. The resulting white light ...
58 citations
TL;DR: A variety of silicon-based nanostructures with dimensions in the 1-5 nm range now emit tunable photoluminescence (PL) spanning the visible range, and a number of other proposed uses of ultra-efficient PL from "nano-Si" could become viable in cosmetics, catalysis, security and forensics.
Abstract: A variety of silicon-based nanostructures with dimensions in the 1–5 nm range now emit tunable photoluminescence (PL) spanning the visible range. Achievement of high photoluminescence quantum efficiency (PLQY) relies critically on their surface chemistry passivation and an impressive “tool box” of options have been developed. Two distinct PL bands are dominant. The “S-Band” (red–green emission with Slow microsecond decay) has PLQY that has steadily improved from ∼3% in 1990 to 65 ± 5% by 2017. The “F-Band” (blue–yellow with Fast nanosecond decay) has reported PLQY values that have improved from ∼0.1% in 1994 to as high as ∼90% by 2016. The vast literature on both bands is surveyed and for the S-band, size-structure-PL correlations and selective photo-excitation studies are highlighted. Resonant photoexcitation and single quantum dot studies have revealed the key role of quantum confinement and the excitonic phonon-assisted nature of the radiative transitions. For the F-band, in contrast, specific phenomenological studies are highlighted that demonstrate similar emission without the presence of silicon nanostructures. Low PLQY F-band emission from pure silicon–silica core shell systems is probably associated with oxide-related defects, but ultrahigh PLQY from many lower temperature synthesis routes is likely to be from carbon-based nanostructures or chromophores, not silicon nanostructures. Potential applications for both PL bands include sensing, medical imaging, theranostics, photovoltaics, LED colour converters and nano-thermometry. Emerging “green” synthesis routes are mentioned. If scalability and cost are significantly improved then a number of other proposed uses of ultra-efficient PL from “nano-Si” could become viable in cosmetics, catalysis, security and forensics.
58 citations
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