真空室内金属杂质污染对光学薄膜性能的影响

真空室内金属粒子污染是降低激光薄膜性能的一个重要因素。采用高真空残余气体分析仪,对薄膜沉积过程中的气氛进行分析。发现由黄铜制作的加热灯架在工作时会分解出Zn,在这种条件下沉积薄膜,会使薄膜中掺入金属杂质,导致薄膜激光破坏阈值降低。采用表面分析技术对薄膜的组分进行分析,证实薄膜中锌杂质的存在。激光破坏实验证明,含有锌杂质的薄膜的破坏阈值明显降低。

Vaporization of heated materials into discharge plasmas

The vaporization of condensed materials in contact with high-current discharge plasmas is considered. A kinetic numerical method named direct simulation Monte Carlo (DSMC) and analytical kinetic approaches based on the bimodal distribution function approximation are employed. The solution of the kinetic layer problem depends upon the velocity at the outer boundary of the kinetic layer which varies from very small, corresponding to the high-density plasma near the evaporated surface, up to the sound speed, corresponding to evaporation into vacuum. The heavy particles density and temperature at the kinetic and hydrodynamic layer interface were obtained by the analytical method while DSMC calculation makes it possible to obtain the evolution of the particle distribution function within the kinetic layer and the layer thickness.

Influence of vacuum organic contaminations on laser-induced damage of 1064 nm anti-reflective coatings

We investigate the influence of vacuum organic contaminations on laser-induced damage threshold (LIDT) of optical coatings. Anti-reflective (AR) coatings at 1064 nm made by Ta2O5/SiO2 are deposited by the ion beam sputtering method. The LIDTs of AR coatings are measured in vacuum and in atmosphere, respectively. It is exhibited that contaminations in vacuum are easily to be absorbed onto optical surface because of lower pressure, and they become origins of damage, resulting in the decrease of LIDT from 24.5 J/cm(2) in air to 15.7 J/cm(2) in vacuum. The LIDT of coatings in vacuum has is slightly changed compared with the value in atmosphere after the organic contaminations are wiped off. These results indicate that organic contaminations are the main reason of the LIDT decrease in vacuum. Additionally, damage morphologies have distinct changes from vacuum to atmosphere because of the differences between the residual stress and thermal decomposability of filmy materials.

Relaxed GexSi1-x layer formation with reduced dislocation density grown by ultrahigh vacuum chemical vapor deposition

A new alternative method to grow the relaxed Ge0.24Si0.76 layer with a reduced dislocation density by ultrahigh vacuum chemical vapor deposition is reported in this paper. A 1000-Angstrom Ge0.24Si0.76 layer was first grown on a Si(100) substrate. Then a 500-Angstrom Si layer and a subsequent 5000-Angstrom Ge0.24Si0.76 overlayer followed. All these three layers were grown at 600 degrees C. After being removed from the growth system to air, the sample was first annealed at 850 degrees C for 30 min, and then was investigated by cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy. It is shown that the 5000-Angstrom Ge0.24Si0.76 thick over layer is perfect, and most of the threading dislocations are located in the embedded thin Si layer and the lower 1000-Angstrom Ge0.24Si0.76 layer. The relaxation ratio of the over layer is deduced to be 0.8 from Raman spectroscopy.

Direct Wafer Bonding Technology employing vacuum-cavity pre-bonding

A novel low temperature direct wafer bonding technology employing vacuum-cavity pre-bonding is proposed and applied in bonding of InGaAs/Si couple wafers under 300 degrees C and InP/GaAs couple wafers under 350 degrees C. Aligning accuracy of 0.5 mu m is achieved. During wafer bonding process the pressure on the couple wafers is 10MPa. The interface energy is sufficiently high to allow thinning of the wafers down from 350um to about 100um. And the tensile strength test indicates the bonding energy of bonded samples is about equal to the bonded samples at 550 degrees C.

Research on nitrogen implantation energy dependence of the properties of SIMON materials

With different implantation energies, nitrogen ions were implanted into SIMOX wafers in our work. And then the wafers were subsequently annealed to form separated by implantation of oxygen and nitrogen (SIMON) wafers. Secondary ion mass spectroscopy (SIMS) was used to observe the distribution of nitrogen and oxygen in the wafers. The result of electron paramagnetic resonance (EPR) was suggested by the dandling bonds densities in the wafers changed with N ions implantation energies. SIMON-based SIS capacitors were made. The results of the C-V test confirmed that the energy of nitrogen implantation affects the properties of the wafers, and the optimum implantation energy was determined. (c) 2005 Elsevier B.V. All rights reserved.

Epitaxial growth of GaNAs/GaAs heterostructure materials

A series of systematic experiments on the growth of high quality GaNAs strained layers on GaAs (001) substrate have been carried out by using DC active Nz plasma, assisted molecular beam epitaxy. The samples of GaNAs between 3 and 200 nm thick were evaluated by double crystal X-ray diffraction (XRD) and photoluminescence (PL) measurements. PL and XRD measurements for these samples are in good agreement. Some material growth and structure parameters affecting the properties of GaNAs/GaAs heterostructure were studied; they were: (1) growth temperature of GaNAs epilayer; (2) electrical current of active N-2 plasma; (3) Nz flow rate; (4) GaNAs growth rate; (5) the thickness of GaNAs strained layer. XRD and PL measurements showed that superlattice with distinct satellite peaks up to two orders and quantum well structure with intensity at 22 meV Fourier transform infrared spectroscopy (FWHM) can be achieved in molecular beam epitaxy (MBE) system. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Vacuum window of intermediate energy heavy-ion microbeam irradiation facility

The beam must be extracted into the air through the vacuum window to irradiate the living cell. In the window design, the material and thickness must be chosen to compromise the beam spot size broadening and the window safety. The structure-static analysis on the window of different structures and materials is done with the finite element analysis method, and the deformation and the equivalent stress axe simulated. The safety of these candidates is investigated using the intensity theory. In addition, the small angle scattering and the transverse range of ions are simulated using SRIM code, including all the effects on the beam spot size broadening, such as the incident ion energy, the material and the thickness of the window and the air composing. At last, the appropriate vacuum windows are presented, including the structure, material and thickness.

Luminescent properties of Mn2+ in hexagonal aluminates under ultraviolet and vacuum ultraviolet excitation

Mn2+-doped xBaO center dot 6Al(2)O(3) and BaMgAl10O17 phosphors were prepared by solid-state reaction. The investigation of vacuum ultraviolet (VUV) excitation spectra of these phosphors exhibits that 0.82BaO center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ have a stronger absorption than BaO center dot 6Al(2)O(3):Mn2+ at about 147 nm. The emission spectra under VUV excitation demonstrated that 0.82BaOBa center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ have a higher luminescent intensity than BaO center dot 6Al(2)O(3):Mn2+. The lifetime analysis indicates that they have similar decay times, indicating that 0.82BaOBa center dot 6Al(2)O(3):Mn2+ and BaMgAl10O17:Mn2+ can be used as luminescent materials for plasma display panels. We observed that the critical concentration of the Mn2+ ions by host excitation is different from that of Mn2+ direct excitation, revealing a different mechanism of energy transfer. The critical distance was calculated. A model was suggested to explain the process of the energy transfer from the host to the Mn2+ ions.

Heterojunction ambipolar organic transistors fabricated by a two-step vacuum-deposition process

Ambipolar organic field-effect transistors (OFETs) are produced, based on organic heterojunctions fabricated by a two-step vacuum-deposition process. Copper phthalocyanine (CuPc) deposited at a high temperature (250 degrees C) acts as the first (p-type component) layer, and hexadecafluorophthalocyaninatocopper (F16CuPc) deposited at room temperature (25 degrees C) acts as the second (n-type component) layer. A heterojunction with an interpenetrating network is obtained as the active layer for the OFETs. These heterojunction devices display significant ambipolar charge transport with symmetric electron and hole mobilities of the order of 10(-4) cm(2) V-1 s(-1) in air. Conductive channels are at the interface between the F16CuPc and CuPc domains in the interpenetrating networks. Electrons are transported in the F16CuPc regions, and holes in the CuPc regions. The molecular arrangement in the heterojunction is well ordered, resulting in a balance of the two carrier densities responsible for the ambipolar electrical characteristics. The thin-film morphology of the organic heterojunction with its interpenetrating network structure can be controlled well by the vacuum-deposition process.

Vacuum ultraviolet optical properties of (La,Gd)PO4 : RE3+ (RE = Eu, Tb)

Vacuum ultraviolet excitation spectra of phosphors (La,Gd)PO4:RE3+ (RE = Eu or Tb) and X-ray photoelectron spectra of LaPO4 and GdPO4 are investigated. The vacuum ultraviolet excitation intensity of (La,Gd)PO4:RE3+ is enhanced with the increasing of Gd3+ content, which implies that Gd3+ plays an intermediate role in energy transfer from host absorption band to RE3+. When Gd3+ is doped into LaPO4:Eu, charge transfer band (CT band) begins to shift to higher energy region and the overlap degree of CT band and the host absorption band gets greater with more Gd3+ doped into LaPO4. These results suggest that the dopant (Gd3+) gives an important influence on energy transfer efficiency. The top of LaPO4 valance band is formed by the 2p level of O2-, whereas that of GdPO4 valance band is formed by the 2p level of O2- and the 4f level of Gd3+, showing the differences in band structures between LaPO4 and GdPO4.

A novel method to synthesize amorphous silica-alumina materials with mesoporous distribution without using templates and pore-regulating agents

In this study, a novel sol-gel method is used to synthesize amorphous silica-alumina materials with a narrow mesoporous distribution and various Si/Al molar ratios without using any templates and pore-regulating agents. During the preparation procedure, only inexpensive inorganic salts were used as raw materials, instead of expensive and harmful alkoxides. The precursor sol was dried at room temperature in a vacuum box kept at 60 mmHg until it began to form the gel. The results of a nitrogen sorption experiment indicate that the synthesized materials with different Si/Al molar ratios have similar mesoporous distributions (within 2-12 nm). Moreover, it was found that the material's pore size distribution remains at a similar value during the heat treatment from room temperature to 550 degreesC. On the basis of the nitrogen sorption, TEM, and AFM characterization results, a formation mechanism of mesopores which accounts for the experimental data is also suggested. This suggested mechanism involves rearrangement of the primary particles during the drying process to form the precursors of the similarly sized mesopores. The synthesized materials were characterized by XRD, thermal analysis (TG/DTA), Al-27 and Si-29 MAS NMR spectroscopy, SEM, TEM, and AFM. The results of Al-27 and 29Si MAS NMR indicate that the distribution of silicon and aluminum in the synthesized materials is more uniform and homogeneous than that in the mixed oxides prepared via the traditional sol-gel method even at high alumina contents. The type and density of the acid sites were studied using pyridine adsorption-desorption FTIR spectroscopy. It was shown that the acidity of the synthesized materials is higher than that of the silica-alumina materials prepared by conventional methods.

Effects of Microstructural Heterogeneity on the Spallation Behavior of Materials

It is of utmost importance to understand the spallation behaviour of heterogeneous materials. In this paper, a driven nonlinear threshold model with stress fluctuation is presented to study the effects of microstructural heterogeneity on continuum damage evolution. The spallation behavior of heterogeneity material is analyzed with this model. The heterogeniety of mesoscopic units is characterized in terms of Weibull modulus m of strength distibution and stress fluctuation parameter k. At high stress, the maximum damage increases with m; while at low stress, the maximum damage decreases. In addition, for low stress, severe stress fluctuation causes higher damage; while for high stress, causes lower damage.

Fracture mechanics of piezoelectric materials

This paper presents an analysis of crack problems in homogeneous piezoelectrics or on the interfaces between two dissimilar piezoelectric materials based on the continuity of normal electric displacement and electric potential across the crack faces. The explicit analytic solutions are obtained for a single crack in an infinite piezoelectric or on the interface of piezoelectric bimaterials. For homogeneous materials it is found that the normal electric displacement D-2, induced by the crack, is constant along the crack faces which depends only on the remote applied stress fields. Within the crack slit, the perturbed electric fields induced by the crack are also constant and not affected by the applied electric displacement fields. For bimaterials, generally speaking, an interface crack exhibits oscillatory behavior and the normal electric displacement D-2 is a complex function along the crack faces. However, for bimaterials, having certain symmetry, in which an interface crack displays no oscillatory behavior, it is observed that the normal electric displacement D-2 is also constant along the crack faces and the electric field E-2 has the singularity ahead of the crack tip and has a jump across the interface. Energy release rates are established for homogeneous materials and bimaterials having certain symmetry. Both the crack front parallel to the poling axis and perpendicular to the poling axis are discussed. It is revealed that the energy release rates are always positive for stable materials and the applied electric displacements have no contribution to the energy release rates.

FEM Simulations and Optimization about Residual Stresses in Coating Structures with Functionally Graded Materials Layer

An elasto-plastic finite element method is developed to predict the residual stresses of thermal spraying coatings with functionally graded material layer. In numerical simulations, temperature sensitivity of various material constants is included and mix