A negative deviation from Porod’s law in SAXS of organo—MSU—X

Small-angle X-ray scattering(SAXS)using synchrotron radiation as X-ray source has been employed to charactcizc the microscopic structrure of organo-modified mesoporous molecular sieves(organo-MSU-X)prepared by a one-pot template-directed synthesis.It is shown that the SAXS profile is hardly constant with Porod’s law showing a negative slope,i.e.,negative deviation.This suggests that there is diffuse interfacial layer located between the pores and the matrix.This suggests that the organic groups remain covalently linked to the matrix,as indicated by ^29SiCP MAS NMR and FT-IR.The average thickness of the interfacial layer was found to be about 1nm for each of the three samples with different kinds and the same amounts(20? of organic groups.This kind of material has also been proved to possess both surface and mass fractal structure of the amophous porous silica materials.2001 Elsevier Science B.V.All rights reserved.     

STUDY OF MESOPOROUS SILICA MATERIALS BY SMALL ANGLE X—RAY SCATTERING

Small angle X-ray scattering experiments have been performed to study the microstructure of messoporous silica meterials prepared by condensation of tetraethylorthosilicate using nonionic alkylpolyethyleneoxide(AEO9) and ionic cetyltrimethylammonium bromide (CTAB) surfactant as templates.It is the pores within the nanometre range that produce the main cattering.The scattering of the pure silica systems obey Porod’s law.This may be because the templates produce some additional scattering background and then make the scattering of pores distorted.The results show that the full removal of templates from the pores of the materials by Soxhlet extraction is very easy for AEO9,but it is difficult for CTAB.The positive deviation correction is also perfromed.     

Determination of interface layer thickness of a pseudo two—phase system by extension of the Debye equation

The Debye equation with slit-smeared small angle x-ray scattering(SAXS) data is extended form an ideal two-phase system to a pseudo two-phase system with the presence of the interface layer,and a simple accurate solution is proposed to determine the average thickness of the interface layer in porous materials.This method is tested by experimental SAXS data,which were measured at 25℃,of organo-modified mesoporous silica prepared by condensation of tetraethoxysiland(TEOS) and methyltriethoxysilane(MTES) using non-ionic neutral surfactant as template under neutral condition.     

Positive deviation from debye‘s theory in small—angle x—ray scattering

The small-angle x-ray scattering (SAXS) resulting from a non-ideal two-phase system having sharply defined phase boundaries but with micro-fluctuations of electron density within any phase shows a positive deviation from Debye's theory. We have found a simple method suitable for fitting the slit-smeared SAXS data and correcting the positive deviation. The validity of this procedure is tested on porous ZrO_2 xerogel prepared using the sol-gel process.     

Determination of Al Composition in Strained AlGaN Layers

AlxGa1-xN/GaN heterostructures are grown on c-sapphire with the Al composition x from 0.2 to 0.4 and thicknesses from 20nm to 30nm. The lattice parameters a and c are determined from 2θ/ω scan. The AIGaN layers are found to be under tensile strain by using x-ray diffraction. Vegard＇s law induces a large deviation in Al composition determination by only considering the linear relationship between one lattice parameter （α or c） and Al composition. The accurate determination of Al composition is only possible with consideration of both the lattice parameters α and c, by assuming the tetragonal distortion in the AlGaN layer. Additionally, the results obtained from x-ray diffraction are verified by Rutherford backscattering.     

Growth of a-Plane InN Film and Its THz Emission

We report the growth of a-plane InN on an r-plane sapphire substrate by plasma-assisted molecular-beam epitaxy. It is found that the a-plane InN is successfully grown by using a CaN buffer layer, which has been confirmed by reflection high-energy electron diffraction, x-ray diffraction and Raman scattering measurements. The Hall effect measurement shows that the electron mobility of the as-grown a-plane InN is about 406 cm^2/V·s with a residual electron concentration of 5.7 × 10^18 cm^-3. THz emission from the a-plane InN film is also studied, where it is found that the emission amplitude is inversely proportional to the conductivity.     

Determination of Average wall Thickness of Mesoporous silica

Small X-ray Scattering (SAXS) experiment using Synchrotron Radiation as X-ray source was used to determine the average wall thickness of mesoporous silica prepard by condensation of tetraethylorthosilicate(TEOS) using non-ionic alkylpolyethyleneoxide(AEO9) surfactant as templates.The results agreed with that of high-resolution TEM(HRTEM) measurement.     

Synchrotron Small-Angle X-Ray Scattering Investigation on Integral Membrane Protein Light-Harvesting Complex LH2 from Photosynthetic Bacterium Rhodopseudomonas Acidophila

Structures of membrane protein in solution are different from that in crystal phase. We present the primary results of small angle x-ray scattering （SAXS） resolved topological structures of a light harvesting antenna membrane protein complex LH2 from photosynthetic bacteria Rhodopseudomonas acidophila in detergent solution for the first time. Our results show that the elliptical shape of the LH2 complex in solution clearly deviates from its circular structure in crystal phase determined by x-ray diffraction. This result provides an insight into the structure and function interplay in LH2.     

Impact of nitrogen plasma passivation on the interface of germanium MOS capacitor

Nitrogen plasma passivation(NPP) on(111) germanium(Ge) was studied in terms of the interface trap density,roughness, and interfacial layer thickness using plasma-enhanced chemical vapor deposition(PECVD). The results show that NPP not only reduces the interface states, but also improves the surface roughness of Ge, which is beneficial for suppressing the channel scattering at both low and high field regions of Ge MOSFETs. However, the interfacial layer thickness is also increased by the NPP treatment, which will impact the equivalent oxide thickness(EOT) scaling and thus degrade the device performance gain from the improvement of the surface morphology and the interface passivation. To obtain better device performance of Ge MOSFETs, suppressing the interfacial layer regrowth as well as a trade-off with reducing the interface states and roughness should be considered carefully when using the NPP process.     

Effect of Trimethyl Aluminium Surface Pretreatment on Atomic Layer Deposition Al2O3 Ultra-Thin Film on Si Substrate

Ultra-thin Al2O3 dielectric films have been deposited on Si substrates by using trimethyl aluminium （TMA） and water as precursors in an atomic layer deposition （ALD） system. Growth of the interracial layer between ultra-thin Al2O3 and the Si substrate is effectively suppressed by a long-time TMA surface pretreatment of the Si substrate prior to A1203 atomic layer deposition. High resolution transmission electron microscopy （TEM） images show that the thickness of the interracial layer is reduced to be 0.5nm for the sample with TMA pretreatment lasting 3600s. The x-ray photoelectron spectroscopy results indicate that the A1203 film deposited on the TMApretreated Si surface exhibits very good thermal stability. However, a hysteresis of about 50mV is observed in the C- V curve of the samples with the TMA pretreatment.     

Synergistic effects of total ionizing dose on single event upset sensitivity in static random access memory under proton irradiation

Nitrogen plasma passivation （NPP） on （111） germanium （Ge） was studied in terms of the interface trap density, roughness, and interfacial layer thickness using plasma-enhanced chemical vapor deposition （PECVD）. The results show that NPP not only reduces the interface states, but also improves the surface roughness of Ge, which is beneficial for suppressing the channel scattering at both low and high field regions of Ge MOSFETs. However, the interracial layer thickness is also increased by the NPP treatment, which will impact the equivalent oxide thickness （EOT） scaling and thus degrade the device performance gain from the improvement of the surface morphology and the interface passivation. To obtain better device performance of Ge MOSFETs, suppressing the interfacial layer regrowth as well as a trade-off with reducing the interface states and roughness should be considered carefully when using the NPP process.     

Determination of Tungsten Layer Profiles in Bilayer Structures Using X-Ray Reflectivity Method

An effectual method is presented to determine the profiles of a tungsten （W） layer, such as the density, the thickness and the roughness in the multilayer structures, using the x-ray reflectivity technique. To avoid oxidation effects of tungsten, a B4 C capping layer is deposited onto to the W layer. To observe the profiles of the tungsten layer with different thicknesses, three groups of W/B4 C bilayers with different thicknesses are prepared by using ultra high vacuum dc magnetron sputtering and measured by an x-ray diffractometer. A type of genetic algorithm called the differential evolution is used to simulate the measurement data so as to obtain the parameters of bilayers. According to the simulation, it is shown that the W layer density varies from 95.26% to 97.51% compared to the bulk. In our experiment, the deposition rate is 0.044 nm/s, and the thickness is varied in the range of 9.8-19.4 nm.     

Asymmetric diffusion model for oblique-incidence reflectometry

A diffusion theory model induced by a line source distribution is presented for oblique-incidence reflectometry.By fitting to this asymmetric diffusion model,the absorption and reduced scattering coefficients μa and μ’s of the turbid medium can both be determined with accuracy of 10% from the absolute profile of the diffuse reflectance in the incident plane at the negative position-1.5 transport mean free path(mfp’) away from the incident point;particularly,μs’ can be estimated from the data at positive positions within 0-1.0 mfp’ with 10% accuracy.The method is verified by Monte Carlo simulations and experimentally tested on a phantom.     

Solution conformation of the response regulator proteins from Deinococcus radiodurans studied by SAXS

In this paper the solution conformation of the response regulator proteins from Deinococcus radiodurans was studied by small-angle X-ray scattering (SAXS). The SAXS curves of Dr-rrA in solutions were obtained at Beamline 1W2A of Beijing Synchrotron Radiation Facility (BSRF). Two possible conformations of the response regulator proteins, compact and incompact conformations, have been represented by the known crystallographic structures. And theoretical solution scattering curves of the two possible conformations were calculated and fitted to the experimental scattering curve of Dr-rrA, respectively. The result indicates that the solution conformation of the response regulator proteins is inclined to the compact one, which is in agreement with the result of biochemical experiments.     

Low—Lying Resonance States of Slow Electron Collisions With Atomic Oxygen

A 39-target state close-coupling calculation of low-energy electron scattering from atomic oxygen is carried out with core-valence electron correlation by using R-matrix method. It is shown that the elastic cross section has a huge and sharp increase with the electron energy going down below 1eV. This remarkable structure is attributed to a few very low-lying potential resonances and the features of these resonances are given with partial cross sections. It is also shown that after considering excitations of two electrons from 2s shell, the three lowest atomic energy levels are in agreement with experimental results better than that just considering excitations of two electrons from the 2p shell as well as only one electron from the 2s shell. Elastic and two excitation (^3P→^1D and ^3P→^1S) cross sections are given and compared with the other theoretical and experimental results.     

Interfacial and electrical properties of HfAIO/GaSb metal-oxide-semiconductor capacitors with sulfur passivation Interfacial and electrical properties of HfAIO/GaSb metal-oxide-semiconductor capacitors with sulfur passivation Interfacial and electrical properties of HfAIO/GaSb metal-oxide-semiconductor capacitors with sulfur passivationInterfacial and electrical properties of HfAIO/GaSb metal-oxide-semiconductor capacitors with sulfur passivation

Interfacial and electrical properties of HfA10/GaSb metal-oxide-semiconductor capacitors （MOSCAPs） with sulfur passivation were investigated and the chemical mechanisms of the sulfur passivation process were carefully studied. It was shown that the sulfur passivation treatment could reduce the interface trap density Dit of the HfAIO/GaSb interface by 35% and reduce the equivalent oxide thickness （EOT） from 8 nm to 4 nm. The improved properties are due to the removal of the native oxide layer, as was proven by x-ray photoelectron spectroscopy measurements and high-resolution cross-sectional transmission electron microscopy （HRXTEM） results. It was also found that GaSb-based MOSCAPs with HfA10 gate dielectrics have interfacial properties superior to those using HfO2 or A1203 dielectric layers.     

The influence of defects on the effective Young’s modulus of a defective solid

It is difficult to establish structure-property relationships in a defective solid because of its inhomogeneous-geometry microstructure caused by defects. In the present research, the effects of pores and cracks on the Young’s modulus of a defective solid are studied. Based on the law of the conservation of energy, mathematical formulations are proposed to indicate how the shape, size, and distribution of defects affect the effective Young’s modulus. In this approach, detailed equations are illustrated to represent the shape and size of defects on the effective Young’s modulus. Different from the results obtained from the traditional empirical analyses, mixture law or statistical method, for the first time, our results from the finite element method (FEM) and strict analytical calculation show that the influence of pore radius and crack length on the effective Young’s modulus can be quantified. It is found that the longest crack in a typical microstructure of ceramic coating dominates the contribution of the effective Young’s modulus in the vertical direction of the crack.     

Growth and Optical Properties of Double Heterostructure GaN／InGaN／GaN Films with Large Composition

The double heterostructure GaN/InGaN/GaN films with different thicknesses of the InGaN layer were grown at 780℃ or 800℃ by metal-organic chemical vapour deposition.The samples were investigated using x-ray diffraction (XRD),room-temperature photoluminescence (PL) and Raman scattering.The dependences of the samples on both the growth temperature and the thickness of the InGaN layer were studied.The composition of InGaN was determined by the results of XRD,and the bowing parameter of InGaN was calculated in terms of the PL spectra.When the thickness of the InGaN layer was reduced,the phase separation of InGaN was found in some samples.The raman frequency of the A1(LO) and E2(low) modes in all the samples shifted and did not agree with Vegard‘s law.     

Interfacial and electrical properties of HfAlO/GaSb metal-oxide-semiconductor capacitors with sulfur passivation

Interfacial and electrical properties of HfAlO/GaSb metal-oxide-semiconductor capacitors(MOSCAPs) with sulfur passivation were investigated and the chemical mechanisms of the sulfur passivation process were carefully studied. It was shown that the sulfur passivation treatment could reduce the interface trap density Ditof the HfAlO/GaSb interface by 35% and reduce the equivalent oxide thickness(EOT) from 8 nm to 4 nm. The improved properties are due to the removal of the native oxide layer, as was proven by x-ray photoelectron spectroscopy measurements and high-resolution cross-sectional transmission electron microscopy(HRXTEM) results. It was also found that GaSb-based MOSCAPs with HfAlO gate dielectrics have interfacial properties superior to those using HfO2 or Al2O3 dielectric layers.