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1.
Si/SiO2 Fabry–Pérot microcavities with a silicon nanocrystal (Si-nc) active spacer have been realized using a novel process based on a reactive magnetron sputtering of a pure silica target. Spectral, spatial and temporal behaviours of the quantum dots confined inside the resonator are detailed. Compared with a reference sample, the spectral and spatial emission distributions are significantly narrowed and the forward emission intensity is enhanced. Time resolved photoluminescence measurements also revealed an increase of the spontaneous emission rate. PACS 42.70.Qs; 78.55.-m; 78.66.-w  相似文献   

2.
Optical second-harmonic generation (SHG) studies of Si/SiO2 interfaces by resonant two-photon excitation of Si interband transitions are reviewed. Three different types of interband resonances at Si interfaces are identified in SHG spectra: (i) E1 and E2 critical-point bulk interband transitions in the space-charge region of charged Si interfaces, (ii) E1- and E2-type transitions associated with Si atoms at the interface in bulk-like tetrahedral coordination, and (iii) transitions related to Si interface atoms with bonding properties specific of the atomic structure of the interface. The effects of the polarity of space-charge fields on SHG spectra of Si(100)/SiO2 interfaces are also discussed. PACS 73.40.Qv; 73.20.-r; 42.65.Ky  相似文献   

3.
The influence of the ‘storage time’ τs on the threshold fluence φcl and the efficiency in dry laser cleaning is investigated. τs denotes the time between the deposition of particles and the cleaning. As a model system we employed silica spheres with diameters of 500 nm and 1500 nm on commercial silicon wafers and single-pulse KrF excimer laser radiation (τFWHM=28 ns). For the 1500-nm silica spheres, φcl was found to increase from about 65 mJ/cm2 to 125 mJ/cm2 for storage times of 4 h and 362 h, respectively. For 500-nm silica spheres the increase in the threshold fluence was less than 20% for storage times up to 386 h. Received: 12 July 2002 / Accepted: 12 July 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. E-mail:dieter.baeurle@jku.at  相似文献   

4.
The discrete breathers in graphane in thermodynamic equilibrium in the temperature range 50–600 K are studied by molecular dynamics simulation. A discrete breather is a hydrogen atom vibrating along the normal to a sheet of graphane at a high amplitude. As was found earlier, the lifetime of a discrete breather at zero temperature corresponds to several tens of thousands of vibrations. The effect of temperature on the decay time of discrete breathers and the probability of their detachment from a sheet of graphane are studied in this work. It is shown that closely spaced breathers can exchange energy with each other at zero temperature. The data obtained suggest that thermally activated discrete breathers can be involved in the dehydrogenation of graphane, which is important for hydrogen energetics.  相似文献   

5.
The thermal effects produced by continuous-wave laser radiation on free-standing Si/SiO2 superlattices are studied. We compare two samples with different SiO2 layer thicknesses (2 and 6 nm) and the same Si layer thickness (2 nm). The as-prepared free-standing superlattices contain some amount of Si nanocrystals (Si-nc). Intense laser irradiation at 488 nm of the as-prepared samples enhances the Raman scattering of Si-nc by two orders of magnitude. This laser-induced crystallization originates from melting of Si nanostructures in silica, which makes Si-nc better ordered and better isolated from the oxide surrounding. Continuous-wave laser control of Si-nc stress was achieved in these samples. In the proposed model, intense laser radiation melts Si-nc, and Si crystallization upon cooling down from the liquid phase in a silica matrix leads to compressive stress. The Si-nc stress can be tuned in the ∼3 GPa range using laser annealing below the Si melting temperature. The high laser-induced temperatures were verified with Raman spectroscopy. The laser-induced heat leads to a strongly nonlinear rise of light emission. The light emission is also observed in the anti-Stokes region, and its temperature dependence is practically the same for the two studied samples. The laser-induced temperature is essentially controlled by the absorbed laser power. PACS 78.55.-m; 78.20.-e; 68.55.-a; 78.30.-j  相似文献   

6.
Using a pulsed microplasma source, clusters were produced through the ablation of a Si cathode and successive supersonic expansion. The Si cluster beam was deposited onto different substrates and the partial oxidation of the cluster surface avoided the growth of large agglomerates, preserving their nanocrystalline morphology. Micro-Raman spectroscopy was used for an accurate size diagnosis of the deposited nanoparticles. The size of the Si dots ranges between 2 and about 15 nm. The Si dots appear to have a Si oxide shell, as confirmed also by structural and compositional analysis through transmission electron microscopy and atomic force microscopy. Double Raman peaks were attributed to small Si agglomerates having a thin substoichiometric Si-O interface.  相似文献   

7.
The electrical properties of Si nanowires covered by a SiO2 shell are influenced by the properties of the Si/SiO2 interface. This interface can be characterized by the fixed oxide charge density Qf and the interface trap level density Dit. We derive expressions for the effective charge carrier density in silicon nanowires as a function of Qf, Dit, the nanowire radius, and the dopant density. It is found that a nanowire is fully depleted when its radius is smaller than a critical radius acrit. An analytic expression for acrit is derived. PACS 68.65.-k; 61.46.+w; 81.10.Bk  相似文献   

8.
Using the coupled cluster method we investigatespin-s J 1-J′ 2 Heisenberg antiferromagnets (HAFs) on an infinite, anisotropic, two-dimensional triangular lattice for the two cases where the spin quantum number s = 1 and s = $\frac{3} {2}$\frac{3} {2}. With respect to an underlying square-lattice geometry the model has antiferromagnetic (J 1 > 0) bonds between nearest neighbours and competing (J′ 2 > 0) bonds between next-nearest neighbours across only one of the diagonals of each square plaquette, the same diagonal in each square. In a topologically equivalent triangular-lattice geometry, the model has two types of nearest-neighbour bonds: namely the J′ 2κJ 1 bonds along parallel chains and the J 1 bonds producing an interchain coupling. The model thus interpolates between an isotropic HAF on the square lattice at one limit (κ = 0) and a set of decoupled chains at the other limit (κ → ∞), with the isotropic HAF on the triangular lattice in between at κ = 1. For both the spin-1 model and the spin-$\frac{3} {2}$\frac{3} {2} model we find a second-order type of quantum phase transition at κ c = 0.615 ± 0.010 and κ c = 0.575 ± 0.005 respectively, between a Néel antiferromagnetic state and a helically ordered state. In both cases the ground-state energy E and its first derivative dE/ are continuous at κ = κ c , while the order parameter for the transition (viz., the average ground-state on-site magnetization) does not go to zero there on either side of the transition. The phase transition at κ = κ c between the Néel antiferromagnetic phase and the helical phase for both the s = 1 and s = $\frac{3} {2}$\frac{3} {2} cases is analogous to that also observed in our previous work for the s = $\frac{1} {2}$\frac{1} {2} case at a value κ c = 0.80 ± 0.01. However, for the higher spin values the transition appears to be of continuous (second-order) type, exactly as in the classical case, whereas for the s = $\frac{1} {2}$\frac{1} {2} case it appears to be weakly first-order in nature (although a second-order transition could not be ruled out entirely).  相似文献   

9.
Structures based on the SiO2/n-Si and SiO2/p-Si systems, with nanopores in silicon dioxide layers filled with Cu and Ni nanoparticles, have been prepared and investigated using the fast heavy ion technology, which includes irradiation with 197Au26+ ions, chemical etching of ion tracks, and subpotential electrochemical deposition. The selectivity of filling nanopores with metals and cluster character of their formation in tracks is shown.  相似文献   

10.
The Si/SiO2 composites, in which the concentration of the conducting silicon phase is close to the percolation threshold, have been prepared using the ceramic technology and studied at an alternating current. It has been found that an increase in the potential difference in a direct-current electric field leads to a decrease in the dispersion of time constants of dielectric spacers in the “Si grain-SiO2 spacer-Si grain” structures forming a conducting cluster in the composite.  相似文献   

11.
Six absorption bands of Tm3+:Sc2SiO5 crystal have been investigated by decomposing each absorption band into a series of Lorentzian peaks. Polarized light of two polarizations was transmitted in three perpendicular directions through a crystal shaped as a parallelepiped with polished faces. The results are presented in the form of tables containing the parameters of the found Lorentzian peaks: central wavelength, width, and height.  相似文献   

12.
The effect of annealing on the ion-beam synthesis of silicon nanocrystals in Si layers was investigated by low-frequency Raman scattering (RS). The occurrence of crystal nuclei in a matrix of glass results in an additional contribution to density of the acoustic vibrational states associated with the surface vibrational modes of nanocrytals. The low-frequency RS caused by interaction of light with acoustic vibration modes of nanoparticles is an effective method of research. The low-frequency Raman spectra show that the samples do not have a smooth distribution of nanoparticle size, but have two specific sizes of nanoparticles, 3 and 6 nm.  相似文献   

13.
A nonmonotonic dependence of the lateral photoconductivity (PC) on the interband light intensity is observed in Si/Ge/Si and Si/Ge/SiOx structures with self-organized germanium quantum dots (QDs): in addition to a stepped increase in PC, a stepped decrease in PC is also observed. The effect of temperature and drive field on these features of the PC for both types of structures with a maximum nominal thickness of the Ge layer (NGe) is studied. The results obtained are discussed in the context of percolation theory for nonequilibrium carriers localized in different regions of the structure: electrons in the silicon matrix and holes in QDs.  相似文献   

14.
Nanoporous Si and SiO2 melting observed under high-power ion beam irradiation of nanosecond duration was investigated. The sizes of ellipsoidal particles formed in Si and those of holes formed in SiO2 under irradiation were determined. The possible origin of these morphology features was discussed.  相似文献   

15.
The structure of polycrystalline Fe films grown on an oxidized Si(001) surface at room temperature has been studied by the technique of high-energy electron diffraction. It has been found that the grain orientation in the films depends of the amount of deposited iron. In Fe films less than 5 nm thick, grains have been found to be randomly oriented. Fe films more than 5 nm in thickness exhibit the (111) texture with an axis coinciding with the surface normal. The angular dispersion of the [111] direction in the Fe lattice from the surface normal is ±25°. It has been found that as the Fe films become thicker, the (111) texture changes to the (110) texture.  相似文献   

16.
Films of 260 nm thickness, with atomic composition Ta42Si13N45, on 4″ silicon wafers, have been irradiated in air with single laser pulses of 200 femtoseconds duration and 800 nm wave length. As sputter-deposited, the films are structurally amorphous. A laterally truncated Gaussian beam with a near-uniform fluence of ∼0.6 J/cm2 incident normally on such a film ablates 23 nm of the film. Cross-sectional transmission electron micrographs show that the surface of the remaining film is smooth and flat on a long-range scale, but contains densely distributed sharp nanoprotrusions that sometimes surpass the height of the original surface. Dark field micrographs of the remaining material show no nanograins. Neither does glancing angle X-ray diffraction with a beam illuminating many diffraction spots. By all evidence, the remaining film remains amorphous after the pulsed femtosecond irradiation.  相似文献   

17.
An analysis of the influence of standing waves on the angular dependencies of the fluorescent yield from an ultrathin iron layer buried inside a multilayer structure of Nb(50 nm)/Fe(3.9 nm)/[Si/Mo(6.77 nm)]40/SiO2 is presented. These angular dependencies of reflectivity and FeK α-fluorescence yield were measured at the Station for high-precision X-ray optics (HPXO) of the Kurchatov Center for Synchrotron Radiation and Nanotechnology. The measured data was analyzed with the help of our FLUO software package. As a result of the complex treatment of reflectivity and Fe fluorescent yield data, the depth profile for iron atomic density was restored.  相似文献   

18.
Fabrication of patterned materials in ferroelectric LiNbO3 and LiTaO3 crystals using femtosecond laser micromachining is presented and discussed. Damage feature sizes in the 10–100 μm range were achieved using 800-nm, 50-fs (FWHM) ultra-fast laser pulses with energies ranging from 10 μJ up to 350 μJ. Fabrication of polaritonic devices such as waveguides, resonators, focusing reflectors, diffractive and dispersive elements, photonic band gap materials, and other microstructures is demonstrated. PACS 77.84.Dy; 42.62.Cf; 71.36.+c  相似文献   

19.
The processing of synthetic quartz glass by use of the second harmonic of a picosecond Nd:YVO4 laser was examined. The threshold irradiation pulse energy density to process the glass using a picosecond pulse is about 3.8 J/(cm2 pulse). The groove depth does not increase effectively by scanning with a single line even if the number of scans is increased. It becomes easy to process a thick material when the aperture is widened. A through hole (entrance side diameter 106 μm) was formed through a 0.3-mm-thick synthetic quartz glass plate without cracking by the use of circular scanning. The trepanning of a ring (outer diameter 3 mm, inner diameter 1 mm) from 0.3-mm synthetic quartz glass was achieved. PACS 52.38.Mf; 42.62.Cf; 81.05.Kf  相似文献   

20.
The spatial mode and impedance matching of an IR diode laser beam with a ring cavity has been investigated by the example of second-harmonic generation in a KNbO3 crystal placed in the cavity. The frequency conversion efficiency into blue light is found to be as high as 20%.  相似文献   

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