Acousto-optic cell based on paratellurite crystal with surface excitation of acoustic waves

An acousto-optic cell based on a paratellurite (TeO₂) crystal, in which bulk acoustic waves are excited directly from the surface due to an intrinsic piezoelectric effect in the material, has been studied. The bulk shear acoustic waves with a frequency of 50 MHz propagate along the [001] and [110] axes with a polarization along the [ [`1]10 ]left[ {bar 110} right] axis. The ultrasound has been excited by a simple system of two electrodes formed on one face of the crystal. Characteristics of the acousto-optic cell have been determined and the parameters of acoustic waves have been measured at 633 nm by optical beam diffraction on the acoustic diffraction grating.     

Acoustooptic interaction in uniaxial gyrotropic paratellurite crystals

An analysis is made of an intermediate mode of light diffraction by ultrasound in a uniaxial gyrotropic paratellurite crystal. A system of coupled wave equations is presented to calculate the polarization and energy characteristics of the diffracted light for the Raman-Nath, intermediate, and Bragg modes of acoustooptic interaction. The diffraction of light propagating at small angles to the crystal optic axis by a slow ultrasonic shear wave propagating along the [110] crystallographic axis is studied. The amplitude-frequency characteristics of a modulator-deflector for optical radiation are investigated. Curves of the diffraction efficiency as a function of the ultrasonic wave intensity are plotted for various acoustooptic interaction lengths. Pis’ma Zh. Tekh. Fiz. 23, 84–89 (January 12, 1997)     

基于飞秒激光制备润滑表面及光响应液滴操控

运用光诱导在润滑剂注入型光滑多孔表面(SLIPS)实现液滴动态操控,具有非接触性和不受时空间限制等显著优势,但传统光响应SLIPS制备过程需要模板转印及氟化处理,操作繁琐且不环保.本文利用飞秒激光正交线扫描和光热响应Fe3O4纳米颗粒制备出仿猪笼草光热响应SLIPS,通过调整单侧近红外光触发位置,利用液滴润湿梯度和内部...     

Thermal dehydroxylation in surface modified kaolinite

Metakaolinite with increased surface area has been prepared by a thermal decompositionhydration-redecomposition technique. An attempt has been made to characterize the new phase using solid state nuclear magnetic resonance (NMR) and Raman spectroscopy, and transmission electron microscopic (TEM) studies, and to compare with the metakaolinite obtained by normal heating. Raman and solid state NMR spectral data indicate that additional vacuum treatment procedure removes further hydroxyls from the metakaolinite. TEM studies show the changes in shape and size Of particles during the dehydroxylation treatments. Dielectric properties measured on samples of kaolinite, metakaolinite and the vacuum-treated kaolinite showed distinct evidence of the dehydroxylation reactions taking place as a result of the thermal treatments.     

Thermal striping fatigue damage in multiple edge-cracked geometries

Thermal fatigue striping damage may be caused when incompletely mixed hot and cold fluid streams pass over the surface of a component or structure containing a defect. Stress intensity factor (SIF) fluctuations are developed in response to the surface temperature fluctuations. An existing methodology for the analysis of striping damage in geometries containing a single edge‐crack geometry is extended to such an analysis of multiple edge cracks. SIFs are calculated as functions of crack depth, when an edge‐cracked plate and semi‐infinite solid, each containing multiple cracks, are subjected to thermal striping. The effect of various restraint conditions and striping frequencies on the SIF values for a stainless steel plate is examined. The degree of conservatism is shown when an assessment of thermal fatigue striping damage is based on a single, rather than multiple, crack analysis. Accurate curve fits are developed resulting in practical weight functions for an edge‐cracked plate and semi‐infinite solid.     

Weak anchoring of nematic liquid crystals on photo-induced surface relief gratings of organic polysilane

Surface relief gratings on organic polysilane thin films are fabricated by holographic exposure of ultra-violet light, and Au gratings are subsequently prepared on polysilane gratings by vapor deposition of Au. The anchoring energies of 4-pentyl-4′-cyanobiphenyl (5CB) nematic liquid crystal on the fabricated gratings are determined with a saturation voltage method. The anchoring energies of Au gratings are weaker than those of organic polysilane gratings because of suppression of π–π interaction between the liquid crystal and the alignment layer. The polar anchoring energies of Au gratings are also weaker than those reported in literature.     

Dynamics of surface damage in dry friction

A new approach is proposed to describe friction, based on the dynamic interaction of surface roughnesses. An analysis is made of two types of interaction, one causing only deformation of the roughnesses and the other ultimately leading to the appearance of damage particles. Pis’ma Zh. Tekh. Fiz. 23, 75–78 (August 12, 1997)     

Thermal healing of the sub-surface damage layer in sapphire

The sub-surface damage layer formed by mechanical polishing of sapphire is known to reduce the mechanical strength of the processed sapphire and to degrade the performance of sapphire based components. Thermal annealing is one of the methods to eliminate the sub-surface damage layer. This study focuses on the mechanism of thermal healing by studying its effect on surface topography of a- and c-plane surfaces, on the residual stresses in surface layers and on the thickness of the sub-surface damage layer. An atomically flat surface was developed on thermally annealed c-plane surfaces while a faceted roof-top topography was formed on a-plane surfaces. The annealing resulted in an improved crystallographic perfection close to the sample surface as was indicated by a noticeable decrease in X-ray rocking curve peak width. Etching experiments and surface roughness measurements using white light interferometry with sub-nanometer resolution on specimens annealed to different extents indicate that the sub-surface damage layer of the optically polished sapphire is less than 3 μm thick and it is totally healed after thermal treatment at 1450 °C for 72 h.     

石英纤维热损伤机制

通过TG/DSC和高温XRD对石英纤维的高温相转变行为进行了研究,通过高分辨SEM对经不同温度处理过的石英纤维的表面形貌进行了研究,并用抗拉强度实验机测量了这些石英纤维的抗拉强度。研究结果表明,低于1000℃ 处理的石英纤维热损伤可分为两个阶段: (1) 在低于600℃的热处理温度范围内,由于石英纤维表面处理剂的挥发 , 石英纤维直径逐渐减小,原来表面的裂纹、条状和圆形凸起等缺陷逐渐显露出来,导致石英纤维抗拉强度缓慢降低;(2) 在600～1000℃ 的热处理温度范围内 , 石英纤维表面处理剂挥发完毕,在热处理的升降温过程中,由于热应力的作用,表面的条状和圆形凸起开始剥落,造成一定数量的新的表面裂口和裂纹缺陷。温度越高,石英纤维表面的条状和圆形凸起剥落现象越明显,这是造成这一温度条件下石英纤维强度显著降低的主要因素之一。此外,结合TG/DSC和XRD的研究结果,石英纤维低于1000℃热处理后,虽然没有明显的相变化,但是晶体结构有序化程度提高,表面开始析出α-方石英并导致纤维表面形成一定数量的凸起缺陷,这也是导致高温处理后石英纤维热损伤的原因之一。      

Nearly backward reflection of elastic waves in an acousto-optic crystal of paratellurite

Some features of the propagation and reflection of acoustic waves in the XY plane of a paratellurite crystal have been studied. It is established that the acoustic waves exhibit an unusual backward reflection from the side crystal facet in the case of glancing incidence onto the crystal-vacuum interface. The experimental results are in good agreement with theoretical predictions.     

Thermal desorption spectroscopy evaluation of hydrogen-induced damage and deformation-induced defects

ABSTRACT

Thermal desorption spectroscopy (TDS) was performed on ultra-low carbon (ULC) steel with various degrees of hydrogen-induced damage and deformation-induced defects. First, the extent to which hydrogen-induced damage manifests itself in TDS measurements was evaluated. Application of multiple test conditions on cold deformed ULC steel with and without the presence of hydrogen-induced damage showed that such damage did not appear as a hydrogen signal on the TDS spectra. Second, interesting features observed on the TDS spectra of cold deformed ULC steel were further investigated by assessing the TDS spectra of recrystallised and annealed ULC steel. As such, the four peaks in the TDS spectra were linked to microstructural features: interstitial lattice positions, grain boundaries, dislocations and microvoids.     

Self-organization processes in semiconductor under photo-induced Gunn effect

Theoretical investigation of self-organization of non-equilibrium carriers system in n-GaAs under photo-stimulated Gunn effect was performed. It was shown that the behavior of carrier system could be controlled using incident light intensity resulting in different oscillation regimes. Results obtained allow us to predict application ranges for devices working on the phenomena investigated.     

How surface damage removal affects fatigue life

The effect of the removal of work hardened surface layers from specimens of 2024-T4 aluminum alloy and AISI-4130 steel on their fatigue lives has been investigated. Specimens were fatigued at selected stress levels for a given number of cycles and the surface layer was removed followed by subsequent fatigue cycling. Results confirm that when a material is subjected to fatigue loading, damage accumulates in the surface layers in the form of work hardening. Removal of the surface layer brings the specimen back to its pre-fatigued condition.     

Electric field control photo-induced Hall currents in semiconductors

We generate spin-polarized carrier populations in GaAs and low temperature-grown GaAs (LT-GaAs) by circularly polarized optical beams and pull them by external electric fields to create spin-polarized currents. In the presence of the optically generated spin currents, anomalous Hall currents with an enhancement with increasing doping are observed and found to be almost steady in moderate electric fields up to 120 mV μm⁻¹, indicating that photo-induced spin orientation of electrons is preserved in these systems. However, a field 300 mV μm⁻¹ completely destroys the electron spin polarization due to an increase of the D’yakonov–Perel’ spin precession frequency of the hot electrons. This suggests that high field carrier transport conditions might not be suitable for spin-based technology with GaAs and LT-GaAs. It is also demonstrated that the presence of the excess arsenic sites in LT-GaAs might not affect the spin relaxation by Bir–Aronov–Pikus mechanism owing to a large number of electrons in n-doped materials.     

Thermal optimization in transient thermoelasticity using response surface approximations

Response surface methodology is used to construct approximations to temperature and stress in transient thermoelastic analysis of non-linear systems. The analysis forms the core component of a heating/cooling rate maximization problem in which the ordinates of the ambient temperature at equally spaced time intervals are chosen as the design variables. Polynomials or cubic splines are fitted through the ordinates to describe the ambient temperature profile required for the convective heat transfer analysis. An experimental design method based on D-optimality and a genetic algorithm was used to select the design points used to create the approximations. Linear response surfaces were found to be sufficiently accurate, thereby minimizing the number of finite element analyses. Two examples of which one is a thick-walled pressure vessel are used to illustrate the methodology. © 1998 John Wiley & Sons, Ltd.     

Thermal effects and plasma damage upon encapsulation of polymer solar cells

A barrier structure consisting of silicon oxide and silicon nitride films was deposited via plasma-enhanced chemical vapor deposition (PECVD) for the encapsulation of polymer solar cells (PSCs). The total concentration of the solution and the ratio of P3HT and PCBM on the performance of polymer solar cells were studied by UV-Vis absorption spectroscopy, atomic force microscopy and photocurrent measurement. Base on these measurements, there is a compromise between light absorption and phase separation with increasing blend concentration. The PSCs were annealed at 80, 100, 120 and 140 °C for 10-60 min to investigate the thermal effects and to estimate the best deposition temperature of the barrier layers. Nevertheless, the devices with the encapsulation of barrier layers had relatively low power conversion efficiencies (PCE) of 0.98% comparing to the devices heated in the PECVD system (1.57%) at the same condition of 80 °C for 45 min due to the plasma damage during the film deposition process. After inserting a 5-nm TiO_x layer between Al/barrier structure and active layer against the plasma damage, the annealed devices presented an average PCE of 2.26% and demonstrated over 50% of their initial value after constant exposure to ambient atmosphere and sunlight for 1500 h.     

Role of surface oxides in modifying solid particle impact damage

Abstract

In this paper the interaction between impacting particles and a growing surface oxide scale is examined for conditions pertinent to high temperature erosion. The impact condition is analysed to predict the impact damage morphology and oxide fracture and hence high temperature erosion behaviour. The importance of oxide scale thickness relative to the impacting particle size is highlighted as the critical parameter in determining scale fracture and the onset of plastic damage to the target surface.

MST/1177