新的碳同素体卡宾

众所周知,在由碳原子组成的典型结晶体中,存在着金刚石和石墨两种晶体。而新的第三种同素体卡宾的存在,却鲜为人知。卡宾(Carbyne,Carbine)是约20年前发现的物质。最近,对它的研究有了进展,有关卡宾的实质逐渐开始清楚起来,但还存在一些未知部分。     

紫外光辐照下钛硅共掺杂类金刚石薄膜微结构的演化

采用中频磁控溅射Ti80Si20合金靶在单晶硅表面制备了钛硅共掺杂的类金刚石薄膜。利用紫外-可见光多波长Raman光谱表征薄膜微结构, 并结合FTIR光谱研究了紫外光辐照对类金刚石薄膜微结构的影响, 进一步讨论了紫外光辐照下薄膜微结构的演化机理。结果表明: 非晶结构的类金刚石薄膜出现反式聚乙炔和聚对苯乙炔类聚合物结构以及sp杂化的线型卡宾碳结构。紫外光辐照诱导薄膜微结构驰豫和重构, 薄膜Si-O和C-O键含量增加, C=C和C-H键含量减少; 同时薄膜sp²团簇尺寸减小而无序度增大。     

无氢类金刚石碳膜的研究进展

介绍了无氢类金刚石碳膜的制备方法，它们的机械、光学、电学性能，将无氢与含氢的类金刚右碳膜进行了简单比较，总结及探讨了它们的应用。     

等静压石墨的中子辐照行为

一、简介大约十至十五年前,在德国反应堆石墨研制中,等静压石墨承担了重要角色。除了挤压和模压外,利用了等静压工艺生产各向同性石墨,此项工艺甚至使用了非各向同性焦为原料,特别是在天然沥青焦(Gilsonite)愈来愈难获得的时候。在七十年代,德国高温反应堆的原理得到了发展,这种反应堆的概念是假定当大约400℃时,在侧面反射层的一些地区,快中子负载可以达到4×10~(26)个中子/m~3(等价     

碳的线型同素异形体-卡宾(Carbyne)研究进展

介绍了卡宾（Ｃａｒｂｙｎｅ）的发现及研究史，评述了其合成、结构的研究进展。     

类金刚石薄膜的紫外辐照研究

对射频等离子体方法制备的类金刚石（以下简称DLC）薄膜样品进行了紫外辐照，采用电阻率，Raman光谱及红外光谱研究了紫外光（以下简称UV）辐照对DLC薄膜结构与特征的影响，Raman光谱表明：紫外光对DLC薄膜中SP^3C-H键的破坏作用非常明显，红外（IR）光谱结果进一步验证了这一结果，经UV辐照后，DLC薄膜的电阻率呈变小趋势，这说明薄膜被强烈氧化，最后呈现石墨化趋势。     

无氢类金刚石碳膜的研究进展

介绍了无氢类金刚石碳膜的制备方法 ,它们的机械、光学、电学性能 ,将无氢与含氢的类金刚石碳膜进行了简单比较 ,总结及探讨了它们的应用     

不锈钢中子辐照加速应力腐蚀开裂的带电粒子辐照模拟

通过对比电子、质子和重离子在作用机理、损伤形态、损伤分布、穿透深度的差异性,确定进行中子辐照模拟的最优选粒子,然后量化分析最优选粒子辐照与中子辐照在材料微区化学成分、微观结构、硬度与IASCC敏感性等方面的差异.     

反应气压对MWPCVD金刚石膜中 非金刚石相碳含量的影响

在水冷反应室式MWPCVD装置中以CH4和H2为反应气体进行了金刚石膜的沉积实验,研究了反应气体的压强对金刚石膜中非金刚石碳相含量的影响。实验发现,当微波输入功率较小时,随着反应气压的上升,沉积膜中非金刚石相碳的含量单调下降;当微波输入功率较大时,沉积膜中非金刚石相碳的含量先随着反应气压的上升而降低,后又随着反应气压的上升而稍稍增加。     

线状卡宾碳的研究进展和稳定性讨论

综合评述了所有存在的太空星际空间、地球和多种生物体中的线状卡宾碳以及在实验室合成的各种线状卡宾碳，重点评述了线状卡宾碳的稳定性和存在性。分析认为线状卡宾碳的稳定性与其类型、所处气氛、环境有关，提出可以通过插层化合物和端部基团连接等方法获得稳定的线状卡宾碳。     

Crystalline-to-amorphous transition in silicon carbide under neutron irradiation

We have investigated the neutron-induced amorphization in silicon carbide (SiC) film using molecular dynamics (MD) simulations with a modified Tersoff potential. The crystalline-to-amorphous (c-a) transition occurs at about 0.27 dpa along with a structural relaxation, indicating that the amorphization mechanism of neutron-irradiated 3C-SiC is homogeneous. The amorphization level will further be improved during more irradiation, which could be deduced from the increase of C-C bonds and decrease of C-Si bonds after c-a transition. The point defects tend to accumulate in defect-rich areas with C-depleted regions in the core and C-rich regions in the boundary. Such defect-rich areas caused by the displacement spikes results in the local inhomogeneity of C and Si atom distribution in the system, which will enhance the driving force for c-a transition based on thermodynamics. Evidences suggest that the displacement spike plays an important role in amorphization of 3C-SiC.     

Investigation of phase transformations by in-situ neutron diffraction in a Co-Re-based high temperature alloy

In-situ neutron diffraction at high temperatures was used to investigate phase transformation in a Co-Re-based alloy. Stability of carbides and transformation of Co matrix from ε (hcp) to γ (fcc) phase were studied. The ε ? γ phase transformation exhibited a large hysteresis with temperature. The alloy has a complex microstructure with Cr₂₃C₆, TaC and σ phase stable over a wide temperature range. The hysteresis is the result of composition interplay between Co-matrix and other phases, e.g. Cr-carbide and σ. TaC is stable at high temperatures up to 1300 °C.     

Thermoluminescent behaviour of diamond films subjected to UV irradiation

The thermoluminescent behaviour of diamond films subjected to UV irradiation was studied by using an UV lamp of 254 nm wavelength. The UV irradiation was achieved by placing the samples 15 cm away from an UV source for different periods. The thermoluminescent signal was integrated from 0 to 350°C at a linear heating rate of 10°C/s in a N₂ atmosphere. The corresponding luminescence spectra show an excitation band centered at 450 nm while the emission band is centered around 500 nm at room temperature. The diamond films were synthesized on molybdenum substrates by the combustion flame technique and characterized by Raman spectroscopy and scanning electron microscopy. Received: 31 May 1999 / Reviewed and accepted: 22 July 1999     

Mid-infrared ridge waveguide in MgO:LiNbO3 crystal produced by combination of swift O5+ ion irradiation and precise diamond blade dicing

We report on the fabrication of ridge waveguide operating at mid-infrared wavelength in MgO:LiNbO₃ crystal by using O⁵⁺ ion irradiation and precise diamond blade dicing. The waveguide shows good guiding properties at the wavelength of 4 μm along the TM polarization. Thermal annealing has been implemented to improve the waveguiding performances. The propagation loss of the ridge waveguide has been reduced to be 1.0 dB/cm at 4 μm after annealing at 310 °C. The micro-Raman spectra indicate that the microstructure of the MgO:LiNbO₃ crystal has no significant change along the ion track after swift O⁵⁺ ion irradiation.     

High-temperature Raman study in CVD diamond

Measurements of the Raman spectra in chemical vapour deposition (CVD) diamond films at temperatures up to 1200 K are presented. Specifically, the evolution of Raman line position, line width, and intensity were monitored as a function of heating time. The red shifting and the line width broadening of CVD diamond's Raman line with temperature are very similar to that of natural diamond's. However, the detailed temperature dependence of Raman line width depends on the orientation of the CVD diamond crystal and the ambient gas used during thermal treatment. Since the CVD diamond usually exhibited a broader Raman spectra than natural diamond, the evolution of the line width upon heating is thus expected to depend on the origins and the annealing effects of the residual stress. For (111) CVD diamond subjected to annealing in air at 973 K, the line width decreased by more than one wavenumber while the line intensity increased by more than an order of magnitude before it decreased subsequently. In contrast, there is hardly any observable changes of the line width for (100) CVD diamond heated in air at 1173 K. Measurements conducted in He versus in air suggested that the reduction of the non-diamond carbon phase (therefore, the reduction of stress) is likely due to oxidation, which occurs more readily in (111) than in (100).     

On coherence in neutron imaging

The variety of imaging signals in neutron radiography and tomography became quite large compared to the pure absorption and scattering contrast in neutron radiographies and topographies in the early sixties or seventies of the last century. The diversity of absorption based techniques for neutron radiography and tomography is comparable to coherence based imaging techniques such as phase contrast, differential phase contrast, dark field imaging, diffraction enhanced contrast, refraction contrast, ultra small angle scattering contrast, grating interferometry and crystal interferometry, also the spin of the neutron was successfully used for imaging [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11] and [12]. We show which effects (total reflection, diffraction, refraction) contribute to e.g. a step boundary or a phase boundary. Taking this simple object, one can learn to understand the imaging procedure and what is displayed in a radiograph.     

Growth of diamond thin films by chemical vapour deposition

Deposition of diamond thin films on non-diamond substrates at low pressures (<760 torr) and low temperatures (<2000°C) by chemical vapour deposition (CVD) has been the subject of intense research in the last few years. The structural and the electrical properties of CVD diamond films grown on p-type 〈111〉 and high-resistivity (>100 kΩ-cm) 〈100〉 oriented silicon substrates by hot filament chemical vapour deposition technique are described in this review paper.     

Measurement of neutron flux and beam divergence at the cold neutron guide system of the new Munich research reactor FRM-II

A sophisticated neutron guide system has been installed at the new Munich neutron source FRM-II to transport neutrons from the D₂ cold neutron source to several instruments, which are situated in a separate neutron guide hall. The guide system takes advantage of supermirror coatings and includes a worldwide unique “twisted” guide for a desired phase space transformation of the neutron beam. During the initial reactor commissioning in summer 2004, the integral and differential neutron flux as well as the distribution of beam divergence at the exit of two representative and the twisted neutron guide were measured using time-of-flight spectroscopy and gold-foil activation. The experimental results can be compared to extensive simulation calculations based on MCNP and McStas. The investigated guides fulfill the expectations of providing high neutron fluxes and reveal good quality with respect to the reflective coatings and the installation precision.     

Structure of diamond polycrystalline films deposited on silicon substrates

The article presents results of structural studies of polycrystalline diamond thin films deposited by hot filament CVD on silicon substrates. The films were characterized using Scanning Electron Microscopy (SEM), Raman Spectroscopy (RS), Electron Backscattered Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS) and Secondary Ion Mass Spectroscopy (SIMS). Both the EBSD patterns and Raman spectra confirm that the grains visible in the electron micrographs are diamond micro-crystallites. The residual stress in the films is found to be in the range between −4.29 GPa and −0.56 GPa depending on the sample thickness. No evidence of lonsdalite and graphite has been registered in the polycrystalline material of the investigated samples. Evidence of the existence of silicon carbide at the diamond/silicon interface is presented. It is also suggested that an amorphous carbonaceous film covers the silicon surface in the regions of holes in the thin diamond layers.