Room-temperature photoluminescence (PL) from Si chemically etched (CE) in HF-HNO3-based solution has been observed. Scanning electron microscopy reveals that the etched Si has a surface morphology similar to that of luminescent porous Si fabricated by conventional anodization. PL spectra show an order of magnitude smaller luminescent intensity and a shorter wavelength intensity peak for CE Si. A CE Si thickness limitation was observed. The formation of CE Si can be readily explained by a local anodization model.

Thermal annealing studies of the photoluminescence (PL) intensity and Fourier-transform infrared spectroscopy have been performed concurrently on porous Si. A sharp reduction in the PL intensity is observed for annealing temperatures ≳300 °C and this coincides with desorption of hydrogen from the SiH2 surface species. A brief etch in HF can restore the luminescence of the samples annealed below 400 °C. We conclude that SiH2 is essential to the visible luminescence in porous Si.

The recent observation of room temperature photoluminescence (PL) from porous Si layers (PSLs) has received considerable attention. Bulk crystalline Si does not luminesce efficiently at room temperature due to the indirect nature of the energy bandgap minimum. The PL from PSLs has been attributed to quantum confinement effects in nanometer‐sized crystalline features found in PSLs, typically of high porosity. In this paper, we review some of the major results and discuss the controversies of subsequent research. The basic methods of fabricating luminescent PSLs are described, including conventional anodic etching and chemical etching. The latter technique requires no applied bias, but is modeled as an electrochemical process. Other processing issues are also addressed, particularly with respect to postanodization control of the PL spectrum. Microscopic and spectroscopic studies of the material and optical characteristics of PSLs fabricated by the various techniques are presented and discussed. The basic models for the luminescence mechanism are described, including quantum‐sized crystalline Si, surface passivation, normalSi‐Hx , alloys, and molecular electronics. These models are discussed in terms of the supporting and contradicting evidence. Electroluminescence (EL) studies are discussed, including EL from anodic oxidation of PSLs as well as from light‐emitting diodes. The results are promising for optoelectronic applications. However, fundamental questions about the underlying chemistry, physics, and microstructure remain unanswered. More research will be required before any definitive statements can be conclusively made regarding the luminescence mechanism.

The formation of photoluminescent porous Si in an &chant solution made from the HF-HNOs-CH,COOH system is reported. The porous Si is characterized on the basis of its photoluminescence (PL) spectra and the degradation of the PL during exposure to laser irradiation. The surface topography as characterized by atomic force microscopy (AFM) reveals features on the order of 400-600 A. The effect of annealing the porous Si in vacuum on the PL intensity is described and correlated to the breakdown of Si-H bonds on the porous Si surface.

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Two-dimensional (2D) arrays of gold nanoparticles with sulfur-containing fullerene nanoparticles were self-assembled through the formation of Au-S covalent bonds. Disulfide functional groups were introduced into the C60 molecule by reacting propyl 2-aminoethyl disulfide with C60. The 2D arrays were formed at the interface of the aqueous phase of gold particles and organic phase of fullerene particles as a blue transparent film. Transmission electronic microscope images showed that the fullerene spacing between adjacent Au (∼10 nm) particles was about 2.1 ( 0.4 nm, which was consistent with the result of 2.18 nm by molecular molding calculations (MM + ). The UV-visible spectrum of this film showed a red shift and increased bandwidth due to the small spacing between gold nanoparticles. The arrays were deposited on the top of pairs of gold electrodes to form 2D colloidal single electron devices. The electrode pairs were made by electron beam lithographic techniques, and the separation between tips of the two electrodes in a pair was about 100 nm. Electron transport measurements at low temperatures exhibited Coulomb blockade type current-voltage characteristics due to the charge effects. The assembled arrays have potential applications as nanoelectronics.

We demonstrate the applicability of thermal oxidation to control the photoluminescence (PL) from quantum-sized structures in porous silicon. Uniform photoluminescence samples with intense visible light observed under ultraviolet light at room temperature were quickly obtained without a long time hydrofluoric acid (HF) immersion. Applying different oxidation times or temperatures provides a very practical technique to control the luminescence color. By this way, we have observed a shift in the luminescence peak from 7600 to 6200 Å and a reduction in the spectral width from ∼1600 to ∼950 Å.

We have studied photoluminescence (PL) from porous Si anodized laterally along the length of the Si wafer. Broad PL peaks were observed with peak intensities at ∼640 to 720 nm. Strong PL intensity could be observed from 550 to 860 nm. Room-temperature peak intensities were within an order of magnitude of peak intensities of AlGaAs/GaAs multi-quantum wells taken at 4.2 K, and total intensities were comparable. A blue shift of peak intensities from ∼680 to 620 nm could be observed after thermal anneal at 500 °C in O2 and subsequent HF dip.