Average Size Of Nanocrystals Research Articles

Size classification of silicon nanocrystals

We report on the synthesis of size-classified silicon nanocrystals by differential mobility classification of a polydisperse ultrafine silicon aerosol. Using the described technique, the average nanocrystal size can be tuned by simply adjusting an electric field. Samples of nonagglomerated silicon nanocrystals have been obtained and size control has been achieved within 15%–20% in the 2–10 nm size regime.

Novel approach for synthesizing of nanometer-sized Si crystals in SiO 2 by ion implantation and their optical characterization

Nanocrystals of Si have been fabricated inside SiO 2 by ion implantation and subsequent vacuum thermal annealing. The microstructure and optical properties of Si implanted layers have been studied by transmission electron microscopy and photoluminescence spectroscopy. The formation of Si nanocrystals after annealing at 1100°C and the growth in average size of nanocrystals with increasing annealing time have been confirmed. Strong visible photoluminescence around 1.7 eV has been achieved in specimens with Si nanocrystals in SiO 2. The shape of the emission spectrum of the photoluminescence is found to be independent of both excitation energy and annealing time. However, the luminescence intensity grows and then decreases as the annealing time increases. Based on these results, we conclude that the photons are absorbed by Si nanocrystals, for which the bandgap energy is modified by the quantum confinement effects, and the emission of photons is not due to direct electron-hole recombination inside Si nanocrystals but is related to defects probably at the interface between Si nanocrystals and SiO 2. The method for the formation of Si nanocrystals inside SiO 2 is fully compatible with silicon microelectronic technology.

Visible photoluminescence from silicon nanocrystals formed in silicon dioxide by ion implantation and thermal processing

A novel method for the fabrication of nanometer-sized Si crystals in an amorphous SiO2 matrix by ion implantation and thermal processing is reported. Transmission electron microscopy indicates the formation of Si nanocrystals by annealing at 1 100°C, and the growth in average size of Si nanocrystals with increasing annealing time. The shape of the emission spectrum of the photoluminescence is found to be independent of both excitation energy and annealing time, while the excitation spectrum of photoluminescence increases as the photon energy increases and its shape depends on annealing time. The results indicate that the photons are absorbed by Si nanocrystals, for which the bandgap energy is modified by the quantum confinement effects, and the emission of photons is not due to direct electron-hole recombination inside Si nanocrystals but is related to defects probably at the interface between Si nanocrystals and SiO2. This method is fully compatible with silicon microelectronic technology.

Blue Luminescence from SiOx Films Containing Ge Nanocrystals

AbstractWe present a systematic analysis of SiOx alloys films containing Ge nanocrystals prepared by dc magnetron sputtering. Increasing the sputtering power (50–175W) reduces the average Ge nanocrystal size exponentially down to ∼2nm. Broad band photoluminescence spectra are observed in the visible at room temperature centered at ∼3eV or/and ∼2eV. Neither the 3eV nor the 2eV luminescence can be correlated to the change in the size. Excluding the quantum-confined origin, the presence of a luminescence center located in the inhomogeneous strain field of the Ge nanocrystal surface is discussed.

Synthesis of Size-Classified Silicon Nanocrystals

AbstractWe report the synthesis of size-classified silicon nanocrystals by applying differential mobility analysis to an originally polydisperse aerosol of ultrafine silicon crystallites. Using the described technique, the average nanocrystal size can be tuned by simply adjusting an electric field. Samples of uncoagulated silicon nanocrystals have been obtained and size control has been achieved within 15–20% in the 2–10 nm size regime.

Luminescent Nanometer-Sized Si Crystals Formed in an amorphous Silicon Dioxide Matrk by Ion Implantation and Annealing

AbstractSi ion implantation followed by thermal annealing has been used to synthesize luminescent nanometer-sized Si crystals in an amorphous Si02 matrix. Transmission electron microscopy indicates the formation of Si nanocrystals by annealing at 1100 °C, and the growth in average size of Si nanocrystals with increasing annealing time. the shape of the emission spectrum of the photoluminescence is found to be independent of both excitation energy and annealing time, while the excitation spectrum of photoluminescence increases as the photon energy increases and its shape depends on annealing time. the results indicate that the photons are absorbed by Si nanocrystals, for which the band-gap energy is modified by the quantum confinement effects, and the emission of photons is not due to direct electron-hole recombination inside Si nanocrystals but is related to defects probably at the interface between Si nanocrystals and Si02.

Origin of the Infrared Band From Porous Silicon

ABSTRACTThe photoluminescence (PL) infrared (IR)-band of p-doped porous Si (PS) films is studied by steady-state and time-resolved PL and by photoluminescence excitation (PLE) in detail. In analogy to the S-band in the visible the IR-band shifts to higher energies with reduced average nanocrystal size. The IR- and S-bands are very different in their decay behavior and in their recombination lifetimes. The temperature-dependent PL intensity shows non-exponential decay with lifetime distributions in the nsec-µsec range in contrast to the stretched exponential decay shape of the S-band corresponding to lifetime distributions in the μsec -msec range. The origin of the IR-band is likely related to radiative recombination at deep defects in Si nanocrystals with quantum-upshifted band gaps.

Raman studies of sol-gel alumina: Finite-size effects in nanocrystalline AlO(OH).

A systematic Raman-scattering investigation has been carried out on sol-gel alumina prepared by the hot-water hydrolysis and condensation of Al(${\mathrm{OC}}_{4}$${\mathrm{H}}_{9}$${)}_{3}$, the Yoldas process, as a function of process variables such as the time spent in the sol phase. Nanocrystalline boehmite, \ensuremath{\gamma}-AlO(OH), is the principal component of these materials. We have found small but systematic changes, as a function of sol aging time, in the line shape and position of the dominant boehmite Raman band observed in the alumina hydrogels. These spectral changes are interpreted in terms of nanocrystallinity-induced finite-size effects associated with the slow growth of AlO(OH) nanocrystals in the sol. X-ray-diffraction experiments were used to determine nanocrystal sizes (as small as 3 nm for gels prepared from fresh sols) and to estimate growth kinetics from the Raman-line-shape results. The Raman peak-position shift is proportional to ${\mathit{L}}^{\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\alpha}}}$, where L is the average nanocrystal size and \ensuremath{\alpha} is a Raman-versus-size scaling exponent. For AlO(OH) we find \ensuremath{\alpha} to be 1.0, close to the scaling-exponent values reported for graphite and boron nitride (BN) and different from the values (about 1.5) that describe the reported behavior of Si and GaAs.