Three- and low-dimensional inorganic semiconductors

An apparatus and method for enhancing the infrastructure of a network such as the Internet is disclosed. Multiple edge servers and edge caches are provided at the edge of the network so as to cover and monitor all points of presence. The edge servers selectively intercept domain name translation requests generated by downstream clients, coupled to the monitored points of presence, to subscribing Web servers and provide translations which either enhance content delivery services or redirect the requesting client to the edge cache to make its content requests. Further, network traffic monitoring is provided in order to detect malicious or otherwise unauthorized data transmissions.

Apparatus and method for domain name resolution

Low temperature electronic vaporization devices and method are described herein for emulating smoking wherein the devices generate an aerosol for inhalation by a subject by heating a viscous material that can have a tactile response in the mouth or respiratory tract

Low temperature electronic vaporization device and methods

Silicon nanoparticles are synthesized from a mixture of argon/silane in a continuous flow atmospheric-pressure microdischarge reactor. Particles nucleate and grow to a few nanometers (1−3 nm) in diameter before their growth is abruptly terminated in the short residence time microreactor. Narrow size distributions are obtained as inferred from size classification and imaging. As-grown Si nanoparticles collected in solution exhibit room-temperature photoluminescence that peaks at 420 nm with a quantum efficiency of 30%; the emission is stable for months in ambient air.

Synthesis of blue luminescent si nanoparticles using atmospheric-pressure microdischarges.

A broad absorption band around 500 nm is observed in ZnS nanoparticles. The absorption becomes more intensive and shifts to the blue as the particle size is decreased. The absorption energy is lower than the band gap of the particles and is considered to be caused by the surface states. This assignment is supported by the results of the fluorescence and of the thermoluminescence of the surface states. Both the absorption and the fluorescence reveal that the surface states are size dependent. The glow peak of the semiconductor particles is not varied as much upon decreasing size, indicating the trap depth of the surface states is not sensitive to the particle size. Considering these results, a new model on the size dependence of the surface states is proposed, which may explain our observations reasonably.

Absorption and luminescence of the surface states in ZnS nanoparticles

Silicon (Si) nanocrystallites have been synthesized using pulsed-laser ablation in inert background gases, for studying the structures and optical properties as one of the quantum confinement effects. We extracted a process condition where well-dispersed Si nanocrystallites devoid of droplets and debris are prepared, by varying excitation laser conditions. Furthermore, we investigate the influence of the inert background gas pressures on transition from amorphous-like thin films to nanocrystallites. It was clarified that there is a processing window of the inert background gas pressure in which the quantum confinement effects for carriers and phonons become apparent.

Structures and optical properties of silicon nanocrystallites prepared by pulsed-laser ablation in inert background gas

We have developed an integrated process system for the formation of nanoparticles by pulsed laser ablation (PLA) in helium background gas, size classification using a differential mobility analyzer (DMA), and deposition on a substrate. The DMA has been improved to operate at pressures of less than 10 Torr. The classification resolution of the low-pressure operating DMA (LP-DMA), transporting properties of nanoparticles under low pressure, have been investigated theoretically in order to evaluate the performance of the size classification for the integrated system. By operating the integrated system at less than 10 Torr, we have measured the size distribution of Si nanoparticles in the gas phase formation field by sweeping the applied voltage to the LP-DMA and counting the charged nanoparticle concentration with an electrometer. Moreover, we successfully deposited the classified Si nanoparticles on a substrate by fixing the voltage. We have verified that the integrated system can be applied to the clean physical vapor deposition process for accurately size-controlled nanoparticles.

Size classification of Si nanoparticles formed by pulsed laser ablation in helium background gas

Some size effects of the relaxation mechanism of optically excited electrons in CdS fine particles were investigated by means of photoacoustic and luminescence spectroscopies. The intensity of green luminescence (~2.47 eV) decreased and its peak position shifted to the lower-energy side upon decreasing the particle size. The impurity luminescence which appears in the longer-wavelength region, red emission (~1.7 eV), did not vary as much upon decreasing the particle size to ~40 nm in diameter. The absorption spectrum in the intrinsic energy region for a small-size particle, which was determined from the photoacoustic effect, formed a long tailing towards the lower-energy side. The non-radiative recombinalion rate, thermal relaxation rate, increases with decreasing particle size. These phenomena were interpreted to originate from the increment of the ratio of the surface to volume in small-size particles.

Photoacoustic and luminescence spectra of CdS fine particles

We have observed a drastic change in the properties of indium oxide (In2O3) thin films prepared by pulsed laser deposition in a pure helium (He) background gas on unheated glass substrates. At high He pressures above 1.0 Torr, transparent crystalline In2O3 films could be prepared, even though the deposition was carried out without the introduction of oxygen gas and substrate heating. At lower He pressures, blackish opaque films were deposited. These results can be accounted for by the inert background gas effects, which cause spatial confinement of the ablated species in the high-pressure and high-temperature region. Facilitated oxidation in this region would suppress oxygen deficiency in the deposited films.

Stoichiometric indium oxide thin films prepared by pulsed laser deposition in pure inert background gas

We demonstrate the synthesis of monodispersed, nonagglomerated silicon (Si) nanocrystallites, using an integrated process system composed of a unit for the formation of nanocrystallites by pulsed-laser ablation in an inert background gas, a unit for classification using a differential mobility analyzer (DMA), and a unit for deposition onto a substrate using a nozzle jet. The DMA has been designed to operate under pressures less than 5.0 Torr. We have synthesized nonagglomerated Si nanocrystallites of 3.8 nm mean diameter and 1.2 geometrical standard deviation on carbon thin films using this integrated process system.

Takehito Yoshida

Papers

Structures and optical properties of silicon nanocrystallites prepared by pulsed-laser ablation in inert background gas

Size classification of Si nanoparticles formed by pulsed laser ablation in helium background gas

Photoacoustic and luminescence spectra of CdS fine particles

Stoichiometric indium oxide thin films prepared by pulsed laser deposition in pure inert background gas

Monodispersed, nonagglomerated silicon nanocrystallites