High Fluence Ion Irradiation of Thin Fullertte Films

Abstract

Thin fullerite films - partly covered with a thin Au layer -have been irradiated with 100 keV Arⁿ⁺ (n = 1, 6, and 12), 250 keV N⁺, and 30 keV Au⁺ ions up to high fluences, and subsequently analyzed by profilometry, Rutherford Backscattering Spectrometry (RBS), and Atomic Force Microscopy (AFM). Depending on the system, either an increase or a decrease of the film thickness after the irradiations was found, and the probing RBS α particles suffered sometimes an enhanced, and sometimes a reduced energy loss upon passage through the films. The comparison of profilometry and RBS results on uncovered and covered samples allows us to separate the different effects which influence the behavior of high-fluence irradiated fullerite samples clearly from each other. Such effects might be the incorporation of the projectile ions, density changes, phase changes, sputtering, and transport of neighbored unirradiated matter into the irradiated zone.

It is remarkable that ion irradiation of fullerite can lead as well to a densified material, with densities of about 2.1 g-cm^?3, as to a foam-like carbonaceous material with a density around 0.35 g-cm^?3 - depending on the type of projectile and its range. The latter case appears to be characteristic for high-fluence heavy noble gas implantation into fullerite. Fullerite sputtering was reconfirmed to decrease inversely with the fluence.     

(111)-Oriented BaTiO3 thin films hydrothermally formed on TiO2/Si substrate

Abstract

Barium titanate (BaTiO₃) thin films with high (111)-orientation were successfully grown on TiO₂-covered Si(111) substrate using hydrothermal method, where the TiO₂ layer was previously fabricated at room temperature by means of ion-beam-assisted deposition. This processing method provides a simple mild-chemical route for directly producing the analogous crystalline films on different substrates. The BaTiO₃ films did not reach the TiO₂/Si interface even if the hydrothermal treatment was prolonged to 24 hours. Both Rutherford backscattering and spread-resistance profiling characterizations confirmed the diffusion nature of the formed Ba-TiO₃/TiO₂/Si system.     

AA6111合金在热轧过程中保持时间对晶体织构的影响

使用EBSD研究了AA6111合金在两次热轧过程中不同保持时间对晶体织构演变的影响.结果显示:变形织构主要由α和β纤维组成.从主要织构组分的取向强度看出,随着保持时间的增加,Brass和Copper理想织构组分显著增加,S织构没有明显变化.     

Microstructure and Residual Stress Formation in Induction‐Assisted Laser Welding of the Steel S690QL

Steels of high mechanical strength combined with high toughness, such as those in quenched and tempered condition are required to reduce weight in industrial machinery. Their mechanical performance is impaired by welding operations which often cause a reduction of toughness and increase the probability for cold cracking due to martensite formation in the weld seam. The limited weldability of high‐strength steels therefore demands appropriate joining procedures to increase their use in industrial construction and reduce reworking costs. Induction heating is capable of directly producing heat inside a work piece. This enables the integration of induction heat‐treatments into serial welding processes. In this work, the effect of induction‐assisted laser welding on the microstructure and residual stresses in S690QL butt joints was investigated. The results reveal that conventional laser welding causes strong martensite formation in the weld seam and the heat‐affected zone. This leads to prohibitive hardness values. Induction heat‐treatments result in an efficient reduction of hardness in the fusion zone. However, the efficiency decreases with increasing sheet thicknesses. The residual stress distributions after laser welding with and without induction heating are typical of fusion welding. Although an effective reduction of hardness is achieved by induction‐assisted laser welding, the residual stresses remain significantly high.     

金属目标表面温度场对后向散射偏振结构的影响

文章采用基尔霍夫法和微扰法,探讨了表面为大粗糙度表面和微粗糙表面两种情况 下,入射角、金属目标表面温度场对后向散射偏振结构的影响。根据现有条件设计了实验装置,并用该装置测量了部分实验数据,相关结论对激光探测等领域的研究具有一定的参考价值。     

空间差分干涉的光纤分布式水下声波测量

为了实现大范围的水下微弱声波探测,提出了一种基于后向瑞利散射空间差分干涉的光纤分布式声波检测(DAS)技术。声波振动引起单模传感光纤中后向瑞利散射光的变化,将含有声波信息的后向瑞利散射光注入到非平衡迈克尔逊干涉仪,调节干涉仪的臂长差实现不同长度的相邻空间段的后向瑞利散射光干涉,然后采用3×3耦合器解调技术解调出相位信息,实现声波信号的测量。实验搭建了一套基于DAS技术的水下声波测量系统,该系统不仅能够实时准确定位两个声波位置,还能还原声波的幅值、频率、相位等信息,并且实现了1kHz情况下的-148.8dB(re rad/μPa)水下声压相位灵敏度,100~1 500Hz频率的频响平坦度在1.2dB之内。实验结果证实DAS技术能够实时快速地实现多个声波信息的定量测量。     

用于微米球形颗粒超分辨尺度测量的背向弹性散射光谱的获取

背向弹性散射光谱法可用于研究生物细胞内部颗粒的结构组成,本文探讨了背向弹性散射光谱测量获取光谱的不同实验方法及其优缺点。针对微米量级的球形颗粒测量,基于实验分析比较了目前普遍使用的光纤探头测量和透镜系统测量这两种背向散射光谱获取方法的优缺点。研究表明,由于透镜系统获取光谱所对应的散射角有更明确的定义,故透镜系统获取光谱与Mie散射计算的互相关拟合系数(0.96)高于光纤探头优化条件下获取光谱的结果(0.93)。因此,在提取颗粒尺度精度要求较高时,应该选用透镜测量方法,并且采用滤波去噪声信号处理的手段来提高颗粒尺寸提取精度;而提取颗粒尺度精度要求不高时,光纤探头光谱获取方法具有简单易行的优点。     

Theory experiment comparison of the electron backscattering factor from solids at low electron energy (250-5,000 eV)

The electron backscattering factor was measured from 24 different elements at low primary beam energy (250-5,000 eV). The results were compared with Monte Carlo simulations from a variety of freely available programs and an in-house developed program. The results suggest that a thin film of oxide can modify the backscattering factor at low primary energy. In addition, a number of problems have been identified with the freely available programs.     

Measurement of crystal parameters on backscatter kikuchi diffraction patterns

Electron backscatter Kikuchi diffraction patterns (BKDPs) recorded in the scanning electron microscope (SEM) require measurements on the plane of the photographic film or on the recording screen. The parameters that require measurements are the equivalent electron source point on the pattern, or pattern centre, specimen-to-film distance, true interzonal angles, true interplanar angles, Bragg angles, and interplanar spacing. In this paper, the geometry and the methods of calculation of these parameters on BKDPs recorded directly on film are described in detail. The methods described are suitable for practical purposes, providing speed of calculation but limited accuracy. The inherent factors that limit the accuracy of any measurements on BKDPs are the limitations of the gnomonic projection, resulting in projected distortions in Kikuchi bands and diffuseness of Kikuchi band edges originating from inelastic scattering of electrons. The methods described are applied to crystallographic analysis of BKDPs recorded from silicon and polycrystalline copper.     

RBS/channeling studies on the heteroepitaxially grown Y2O3 film on Si(100)

The heteroepitaxially grown yttrium oxide layer by an ionized cluster beam (ICB) on a Si(100) substrate was investigated by Rutherford backscattering spectrometry (RBS)/channeling. The channeling minimum value (χ_min) of the Y₂O₃ layer on Si(100) is 0.28, and this is the smallest value among those reported. From the channeling polar plots, it is found that Y₂O₃ film grown on Si(100) oriented with (110) direction and has a double domain structure. The 110 axis of Y₂O₃ layer is exactly parallel to the 100 axis of the Si substrate. It is also observed that the interface region of Y₂O₃ film has more crystalline defects than the surface region.