Nanoparticle-modified metal-oxide-silicon structure enhancing silicon band-edge electroluminescence to near-lasing action

With the insertion of SiO(2) nanoparticles in the oxide layer, near-lasing actions such as threshold behavior and resonance modes are observed at the Si bandgap energy of metal-oxide-silicon (MOS) structure. The threshold current is ~12 mA . The SiO(2) nanoparticles cause simultaneous localization of electrons and holes to enhance phonon-assisted radiative recombination. Electroluminescence at Si bandgap energy is increased to orders of magnitude larger than in similar MOS structures without SiO(2) nanoparticles. The efficient light emission at the Si bandgap energy indicates that a direct bandgap nature is not necessarily the basic requirement for radiative recombination.     

Resonant diffusive radiation in random multilayered systems

We have theoretically shown that the yield of diffuse radiation generated by relativistic electrons passing random multilayered systems can be increased when a resonant condition is met. The resonant condition can be satisfied for the wavelength region representing visible light as well as soft X rays. The intensity of diffusive soft X rays for specific multilayered systems consisting of two components is compared with the intensity of Cherenkov radiation. For radiation at a photon energy of 99.4 eV, the intensity of resonant diffusive radiation (RDR) generated by 5-MeV electrons passing a Be/Si multilayer exceeds the intensity of Cherenkov radiation by a factor of ≈60 for electrons with the same energy passing a Si foil. For a photon energy of 453 eV and 13 MeV, electrons passing a Be/Ti multilayer generate RDR exceeding the Cherenkov radiation generated by electrons passing Ti foils by a factor ≈130.     

Broad band light emission from Ag-ion implanted silicon nanocrystals

Silicon nanoparticles formed using low energy (<50 keV) silver ion implantation in crystalline Si exhibit broad band light emission from ultraviolet (UV) to green. The formation of nanoparticles is confirmed using high resolution electron microscopy (HRTEM) and the resulting microscopy is used to obtain the size distribution of Si nanoparticles. Photoluminescence (PL) spectra were observed in the range of the UV to the green. The origin of emission is most likely from highly localized defects at the Si/SiO2 which is further confirmed from Photoluminescence Excitation (PLE) and effective mass theory estimation.     

Silicon nanoparticles formation in annealed SiO/SiO2 multilayers

We present a study on amorphous SiO/SiO₂ superlattice performed by grazing-incidence small-angle X-ray scattering (GISAXS). Amorphous SiO/SiO₂ superlattices were prepared by high-vacuum evaporation of 3 nm thin films of SiO and SiO₂ (10 layers each) onto Si(1 0 0) substrate. After the deposition, samples were annealed at 1100 °C for 1 h in vacuum, yielding to Si nanocrystals formation. Using a Guinier approximation, the shape and the size of the crystals were obtained. The size of the growing nanoparticles in the direction perpendicular to the film surface is well controlled by the bilayer thickness. However, their size varies more significantly in the direction parallel to the film surface.     

Nanoparticle-induced multi-functionalization of silicon: A plug and play approach

Here, we demonstrate a “plug and play” approach to achieve multi-functionalization of Si. In this approach, externally synthesized functional nanoparticles are introduced onto device quality Si wafers and the surface chemical bonds are manipulated. Sonochemically synthesized Fe₂O₃ nanoparticles are introduced onto Si from an alcohol suspension. On annealing this sample in ultra-high vacuum, the oxygen atoms change the bonding partner from Fe to Si and desorb as SiO at 750 °C. This results in the formation of nanoparticles of Fe on the surface and exhibits ferromagnetic behavior. Deposition of a thin layer (2 nm) of Si onto the sample containing the metallic Fe nanoparticles followed by annealing at 560 °C leads to optically active Si. Photoluminescence measurements show that this sample emits light at three different wavelengths, namely 1.57, 1.61 and 1.63 μm, when excited by He–Ne or Ar lasers. Oxidation of this material results in the formation of a selective capping layer of SiO₂. Thus we obtain multi-functional Si in an “all in one” form and we believe that this approach is universal.     

Nanofilms of Si clusters confined in SiO nanoparticles prepared by low energy cluster beam deposition

Cluster-based nanostructured films of Si clusters embedded in SiO nanoparticles have been prepared by low energy deposition of SiO cluster beam formed by inert gas aggregating method. The microstructures of the nanofilms have been characterized by TEM and the chemical components of the nanofilms have been analyzed by XPS spectra. It is shown that the film is assembled by the ultrafine spherical nanoparticles, which are distributed randomly and uniformly in the film, while the Si clusters produced by SiO disproportionation reaction are embedded dispersedly in the nanoparticles. Furthermore, the photoluminescence properties of the films have been measured and a blue PL band at wavelength of 400 nm with a shoulder peak at 393 nm has been observed. The PL band at 400 nm may be attributed to quantum confinement effect of the Si cores confined in SiO nanoparticles and energy potential barrier effect of outer SiO layer, while the 393 nm PL shoulder peak may be caused by the oxygen-deficient-associated defect centers.     

Surface-mediated four-wave mixing of nanostructures with counterpropagating surface plasmon polaritons

We demonstrate that four-wave mixing (FWM) signals from individual Si nanoparticles can be generated by the surface fields of traveling surface plasmon polariton modes. We have chosen a counterpropagating excitation scheme in which the nanoparticle is exposed only to surface excitation fields and not to direct laser illumination. We show that background-free, surface-mediated FWM of nanoparticles can be acquired, and that the resulting nonlinear radiation is coherent.     

Solar cell performance improvement via photoluminescence conversion of Si nanoparticles

Photoluminescence (PL) conversion of Si nanoparticles by absorbing ultraviolet (UV) lights and emitting visible ones has been used to improve the efficiency of crystalline Si solar cells. Si nanoparticle thin films are prepared by pulverizing porous Si in ethanol and then mixing the suspension with a SiO2 sol-gel (SOG).This SOG is spin-deposited onto the surface of the Si solar cells and dries in air. The short-circuit current as a function of Si nanoparticle concentration is investigated under UV illumination. The maximal increase is found at a Si concentration of 0.1 mg/mL. At such concentration and under the irradiation of an AM0 solar simulator, the photoelectric conversion efficiency of the crystalline Si solar cell is relatively increased by 2.16% because of the PL conversion.     

Tachyonic Cherenkov emission from Jupiterʼs radio electrons

Tachyonic Cherenkov radiation from inertial relativistic electrons in the Jovian radiation belts is studied. The tachyonic modes are coupled to a frequency-dependent permeability tensor and admit a negative mass-square, rendering them superluminal and dispersive. The superluminal radiation field can be cast into Maxwellian form, using 3D field strengths and inductions, and the spectral densities of tachyonic Cherenkov radiation are derived. The negative mass-square gives rise to a longitudinal flux component. A spectral fit to Jupiter?s radio spectrum, inferred from ground-based observations and the Cassini 2001 fly-by, is performed with tachyonic Cherenkov flux densities averaged over a thermal electron population.     

Evidence of SiO at the Si-oxide interface by surface soft X-ray absorption near edge spectroscopy

Using synchrotron radiation a new surface sensitive spectroscopy has been applied to determine the local structure of the first surface oxide layer formed on the Si(111) surface. The Surface Soft X-ray Absorption (SSXA) spectra have been measured. From the analysis of the X-ray Absorption Near Edge Structures (XANES) we have extracted structural information. We have first determined that bulk amorphous SiO has a characteristic microsopic structure, which cannot be described by the random alloy or microcrystalline (Si + SiO₂) mixture models. The oxide layer formed on the Si(111) surface by ground-state molecular excitation in ultra high vacuum at temperatures (～700°C) approaching the oxide dissociation point has this unique SiO local structure. Such SiO layer not formed at room temperature is expected to be present in the SiSiO₂ interface grown at high temperature. An electronic transition to empty states at the SiSiO₂ interface has been observed.     

掺杂Si/SiO_2界面电子结构与光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理方法,在局域密度近似(LDA)下研究了B掺杂Si/SiO_2界面及其在压强作用下的电子结构和光学性质.能带的计算结果表明:掺杂前后Si/SiO_2界面均属于直隙半导体材料,但掺B后界面带隙由0. 74 eV减小为0. 57 eV,说明掺B使材料的金属性增强;对B掺杂Si/SiO_2界面施加正压强,发现随着压强不断增大,Si/SiO_2界面的带隙呈现了逐渐减小的趋势,并且由直隙逐渐转变为间隙.光学性质的计算结果表明:掺B对Si/SiO_2界面在低能区(即红外区)的介电函数虚部、吸收系数、折射率以及反射率等光学参数有显著影响,且在红外区出现新的吸收峰;对B掺杂Si/SiO_2界面施加正压强,随着压强增大,红外区的吸收峰逐渐消失,而在紫外区出现了吸收峰.上述结果表明,对Si/SiO_2界面掺B及施加正压强均可调控Si/SiO_2界面的电子结构与光学性质.本文的研究为基于Si/SiO_2界面的光电器件研究与设计提供一定的理论参考.     

Frequency-domain interferometric second-harmonic spectroscopy

We report a new spectroscopic technique to measure simultaneously the intensity and the phase of second-harmonic (SH) radiation over a broad spectral range without laser tuning. Temporally separated SH pulses from two sources, excited by the same broad-bandwidth 15-fs Ti:sapphire fundamental pulse, interfere in a spectrometer to yield frequency-domain interference fringes. We demonstrate the technique by measuring the strongly bias-dependent phase of SH radiation from a Si/SiO(2)/Cr metal-oxide-semiconductor capacitor in the spectral range of the SiE(1) critical point.     

Time-gated Cherenkov emission spectroscopy from linear accelerator irradiation of tissue phantoms

Radiation from a linear accelerator induces Cherenkov emission in tissue, which has recently been shown to produce biochemical spectral signatures that can be interpreted to estimate tissue hemoglobin and oxygen saturation or molecular fluorescence from reporters. The Cherenkov optical light levels are in the range of 10(-6) to 10(-9) W/cm2, which limits the practical utility of the signal in routine radiation therapy monitoring. However, due to the fact that the radiation is pulsed, gated-acquisition of the signal allows detection in the presence of ambient lighting, as is demonstrated here. This observation has the potential to significantly increase the value of Cherenkov emission spectroscopy during radiation therapy to monitor tissue molecular events.     

SiO/SiO_2超晶格结构界面发光的研究

利用热蒸发技术在硅衬底上制备了层厚不同的SiO/SiO2超晶格样品.对其光致发光谱进行研究发现,随着SiO/SiO2超晶格中SiO层厚度的增加,发光峰在400～600 nm之间移动.研究表明,样品的发光中心来自于SiO/SiO2界面处的缺陷发光(界面态发光).即在样品沉积的过程中,在SiO/SiO2的界面处由于晶格的不连续性,会形成大量的Si-O悬挂键,这些悬挂键本身相互结合可以形成一定数量的缺陷,同时由于O原子容易脱离Si原子的束缚而产生扩散,因此,这些悬挂键可以与扩散的O原子结合,随着SiO层厚度的增加,在SiO/SiO2的界面处先后出现WOB(O3<≡Si-O-O·),NOV(O3≡Si-Si≡O3),E'中心(O≡Si·),NBOHC(O3≡Si-O·)等缺陷,这些缺陷在SiO层厚度增大的过程中对发光先后起到主导作用,从而使得发光峰产生红移.     

Fabrication of SiO2 microdisk optical resonator

The silica microdisk optical resonator which exhibits whispering-gallery-type modes with quality factors of 9.67 × 104 is fabricated with photolithographic techniques. Reactive ion beam etching (RIBE) is used to get the silica disks with photoresist masks on SiO2/Si made by standard ultraviolet (UV) photolithography,and spontaneous silicon etching by XeF2 is used to fabricate the silicon micropillars. This fabrication process can control the microcavity geometry, leading to high experiment repeatability and controllable cavity modes. These characteristics are important for many applications in which the microcavity is necessary, such as the quantum gate.     

Photo-modification and synthesis of semiconductor nanocrystals

Both photo-oxidation and photosynthesis manifest a strong interaction between nanoparticles and photons due to the large surface area-to-volume ratio. The final sizes of the semiconductor nanocrystals are determined by the photon energy during these phenomena. The photosynthesis is demonstrated in a Si-rich oxide and is similar to thermal synthesis, which involves the decomposition of SiO_x into Si and SiO₂, that is well known and often employed to form Si or Ge nanocrystals embedded in SiO₂ by annealing SiO_x at high temperature. However, photosynthesis is much faster, and allows the low-temperature growth of Si nanocrystals and is found to be pronounced in the SiO nanopowder, which is made by thermal CVD using SiH₄ and O₂. The minimum laser power required for the photosynthesis in the SiO nanopowder is much lower than in the Si-rich oxide formed by the co-sputtering of Si and SiO₂. This is attributed to the weak bond strength of Si-Si and Si-O in the SiO nanopowder. Photosynthesis, which can control the size and position of Si nanocrystals, is a novel nanofabrication technique making the best use of the strong interaction between photons and nanoparticles.     

利用高压拉曼散射研究Ge/SiO_2/Si纳米系统的压力/张力(英文)

pacc:7830,8100 WereportthepressuredependenceofGe nanocrystalsembeddedinSiO2filmmatrixonSi substrateusingRamanscatteringandfiniteele mentanalysis.DelaminationofSiO2filmfromthe Sisubstrateoccursat～23kbarduetothelarge differencebetweenthecompressibilityoft…     

Instabilities Driven by an Intense Beam in a Plasma-Filled Dielectric-Lined Waveguide Immersed in a Finite Axial Magnetic Field

A linear analysis is described on stabilities driven by an intense relativistic electron beam in an infinitely long, plasma-filled, and dielectric-lined circular waveguide immersed in a finite strength axial magnetic field. A dispersion equation is derived from the cold fluid theory and solved numerically. Beam-plasma instabilities due to interaction between beam modes and the Trivelpiece-Gould modes appear as well as the Cherenkov and the cyclotron Cherenkov instabilities. Parametric researches are carried out varying magnetic field strength, plasma density, and dielectric constant. Effects of a finite magnetic field and plasma filling are discussed in connection with the possibilities of using this system as a microwave radiation source.     

Spontaneous and induced Cherenkov radiation generated by electrons in cylindrical dielectrics

A theory of induced Cherenkov radiation in cylindrically symmetrical dielectrics in the case when an electron beam is moving close to the dielectric surface is presented. The spectrum of excited radiation modes has been investigated, and analytical expressions for the gain at the frequencies of various modes have been derived. Zh. éksp. Teor. Fiz. 111, 847–861 (March 1997)     

Cherenkov and transition radiation generated in 200 kV electron microscope

Abstract

Cherenkov radiation emitted from electron irradiated dielectrics such as mica, quartz and BaTiO₃ was detected in a transmission electron microscope with the accelerating voltages of 80 kV to 200 kV. Transition radiation was also observed from metals (Al, Ag, Au) and semiconductors (GaAs, Si). Dependence of their intensities and spectra on accelerating voltage and crystal thickness was investigated.