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Amorphous twisted SiO2 nanobelts have been synthesized on Si wafers using facile thermal evaporation. These nanobelts are produced together with SiO2 nanowires and a small quantity of SiO2 nanosprings. Spectral and microstructural analyses suggest that the twisted SiO2 nanobelts and nanosprings form via a polar surface driven process. Spontaneous polarization on the very thin polar crystalline SiO2 layers on the amorphous SiO2 nanobelt and nanospring surfaces makes the nuclei rearrange orderly and causes the nanobelt and nanowire to roll up at a certain twisty angle. The cathodoluminescence spectrum acquired from these SiO2 nanostructures reveals three emission bands at 4.4, 3.7, and 2.7 eV originating from oxygen-related defect centers. The polar surface driven mechanism can adequately explain the growth of these novel twisty nanobelts and nanosprings which have potential applications in sensors, transducers, resonators, and photonics. [ABSTRACT FROM AUTHOR]

Efficient resonant electron transfer from the surface bonding structure to the conduction band of quantum confined Si nanocrystals is observed by Si nanocrystals in a toluene suspension. Based on the electron transfer mechanism, the enhancement of photoluminescence originates from the band-to-band recombination in the p-type Si nanocrystals suspended in a toluene solution. The energy levels of the electrons in the Si nanocrystals chemisorbed with toluene molecules are calculated using the method of linear combination of atomic orbitals, and the characteristics of the obtained density of states is in good agreement with the observed photoluminescence properties. [ABSTRACT FROM AUTHOR]

Ge and Si nanocrystals (nc-Ge and nc-Si) with average sizes in the range of 2–7 nm, embedded in silica matrix, were fabricated for investigating their acoustic-phonon vibrational properties. The freely elastic sphere theory was found to be unsuitable for explaining the low-frequency phonon vibration character of both nc-Ge and nc-Si in our current experiments. We have assigned the observed low-frequency Raman peaks to “LA-like mode” and “TA-like mode” in terms of their polarization and depolarization behaviors. In addition, it is revealed that the lattice contraction phenomenon exists in nc-Ge and nc-Si with sizes smaller than 4 nm, which leads to a contrary effect against matrix traction on the phonon vibrational frequencies. [ABSTRACT FROM AUTHOR]

Using C60 molecule as a kind of surface-passivated agent to modify the electronic structure of Si nanocrystallites in porous silicon, we disclose that this kind of C60/nanocrystalline Si coupling system can show a strong blue emission at ∼460 nm when stored in air for more than one year. After a full characterization of the photoluminescence properties, we propose a luminescent center in the SiOx layer at the surface of a Si nanocrystallite. It is a pair consisting of an oxygen vacancy and an interstitial oxygen. The interstitial oxygen also forms a peroxy linkage with a neighboring lattice oxygen. Radiative recombination of carriers photogenerated from Si nanocrystallite cores in the luminescent centers results in the observed blue photoluminescence. Neutron irradiation experiments support our assignment of the blue emission mechanism. This work improves the understanding of the origin of blue emission from silicon/oxygen-related nanostructured materials. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the photoluminescence spectra of partially oxidized porous silicon (Si) coated with Si thin films. Stability of the photoluminescence; Role of the optical transitions in the enhancement and stability of the photoluminescence.

Via electroless metal deposition and industrial plasma technology, we have successfully synthesized unique composite silicon nanowire structures with diamondlike carbon (DLC) sheaths acting as inorganic passivation layers. We have also discussed their growth mechanism in terms of a self-organization process. The thickness of the DLC sheaths were quantified with Raman spectroscopy. The Raman analytical result is in good agreement with direct microstructure observations. [ABSTRACT FROM AUTHOR]

The nature of the ∼370-nm (3.35-eV) photoluminescence (PL) in Si oxide and nanostructures, which has a PL excitation band at ∼260 nm, is studied experimentally and theoretically. It is revealed that the PL occurs at the interface between Si structure and its oxide and is closely associated with a characteristic infrared absorption band at ∼1250 cm-1. Spectral analyses suggest that the ∼370-nm PL originates in the –SiO3 group, which bonds to Si structural surface. The density functional theory calculations are consistent with our experiments. This work clarifies some controversies regarding the ∼370-nm PL mechanisms in a number of Si oxide and nanostructures. [ABSTRACT FROM AUTHOR]

A large quantity of monocrystalline germanium nanorods and their arrays were produced on a porous anodic alumina (PAA) template utilizing saturated vapor adsorption, during which the Ge gas pressure was saturated at a high temperature in an airtight quartz tube. Raman scattering and photoluminescence (PL) results were acquired from the Ge nanorod array and discussed in details. Using Si-based PAA template with 25 nm nanopores, Si-based Ge nanorod array with a large area (larger than 1×1 cm2) was obtained and the quantum confinement effect is demonstrated in Raman spectrum. [ABSTRACT FROM AUTHOR]

C[sub 60] molecules were chemically coupled in the pores of porous Si through a coupling agent and then coated with a layer of Si, and followed by N[sub 2] annealing. X-ray diffraction results indicate that the fabricated samples contain β-SiC particles which may exist in the pores, in addition to Si, SiO[sub 2], and graphite. The photoluminescence (PL) spectra show an asymmetrical broadband, which can be Gaussian divided into two bands at 380 (3.26 eV) and 454 (2.73 eV) nm. Spectral analyses and the experimental results from infrared spectroscopy and PL excitation measurements suggest that the 380 nm PL band is related to oxygen-vacancy defects in the SiO[sub 2] matrix, whereas the blue PL band is closely connected with the β-SiC particles. Our experiments provide a way for fabricating stable blue-emitting β-SiC materials. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]