氧化铝与Al(100)基体间界面原子结构研究

本文介绍了用MeV离子散射和沟道效应研究单晶铝表面无定型氧化层与基体之间界面原子结构的方法。报道了Al₂O₃/Al(100)界面原子结构的实验结果。实验表明,在纯氧气氛围中400℃下生成的氧化铝膜,铝和氧原子浓度比例严格为2与3之比;Al₂O₃膜和Al(100)基体之间的界面极其陡峭,氧化铝膜下Al(100)基体表面的再构层不大于一个原子层。由实验测量与用Monte Carlo方法计算结果比较,得到再构层原子离开原来晶 关键词：     

用正电子湮没技术研究a-Si:H/a-SiNx:H多层膜中的界面缺陷

本文报道应用正电子湮没技术(PAT)对a-Si:H/a-SiN_x:H(x≈0.5)多层膜系列样品所进行的研究。发现,由于a-Si:H和a-SiN_x:H在结构方面的失配,导致在a-Si:H/a-SiN_x:H多层膜中的界面区,产生大量缺陷。在a-Si:H子层中,紧靠界面的是应变层,厚度约为8?;在应变层之后是过渡层,厚度约为50?。在过渡层中存在大量缺陷,这就是所谓界面缺陷。 关键词：     

溅射压强对TiN/SiNx纳米多层膜微观结构及力学性能的影响

利用磁控溅射方法在不同溅射压强条件下制备了TiN/SiN_x纳米多层膜.多层膜的微观结构及力学性能分别用X射线衍射仪、原子力显微镜及纳米压痕仪来表征.结果表明随着溅射压强的增大,多层膜的界面变模糊,TiN层的择优取向由(200)晶面过渡到(111)晶面.与此同时,多层膜的表面粗糙度增大,硬度和弹性模量随溅射压强的增大而减小.多层膜力学性能的差异主要是由于薄膜的周期性结构及致密度存在差异所致. 关键词： x多层膜')" href="#">TiN/SiN_x多层膜 界面宽度 表面形貌     

TiN/TiB2异结构纳米多层膜的共格生长与力学性能

采用多靶磁控溅射法制备了一系列具有不同TiB₂调制层厚度的TiN/TiB_{2纳米多层膜.利用x射线衍射仪、高分辨电子显微镜和微力学探针研究了TiB2层厚变化对多层膜生长结构和力学性能的影响.结果表明，在fcc-TiN层(111)生长面的模板 作用下，原为非晶态的TiB2层在厚度小于2.9nm时形成hcp晶体态，并与fcc-TiN 形成共格外延生长；其界面共格关系为{111}TiN//{0001}TiB2，〈110〉TiN//〈1120〉TiB2.由于共格界面存在晶格失配 度，多层膜中形成拉、压交变的应力场，导致多层膜产生硬度和弹性模量升高的超硬效应， 最高硬度和弹性模量分别达到46.9GPa和465GPa.继续增加TiB2层的厚度，TiB2形成非晶态并破坏了与TiN层的共格外延生长，多层膜形成非晶TiN层和非晶TiB< sub>2层交替的调制结构，其硬度和弹性模量相应降低. 关键词： 2}纳米多层膜')" href="#">TiN/TiB₂纳米多层膜 共格生长 晶体化 力学性能     

硅—二氧化硅界面过渡区的XPS研究

本文报道了用X射线光电子能谱的角度效应研究硅-二氧化硅界面过渡区的结果。样品为(111)取向的硅单晶片上低温(700℃)氧化生成的超薄氧化膜,膜的厚度不大于50?。氧化膜与单晶衬底中Si_2p光电子谱峰之间的化学位移(δ)和强度比(I_0x/I_si)随光电子发射角(θ)的变化明显地偏离理想界面所预期的结果,表明在硅-二氧化硅的界面处存在化学比为SiO_x(0yO_4-y(0≤y≤4)型四面体。比较实验曲线与随机成键模型的计算结果,估计出过渡区的宽度不大于20?,小于Si_2p光电子在二氧化硅中的平均逃逸深度。对改变氧化时间结合Ar⁺刻蚀制得的氧化膜厚度不同的样品所作的测量,得到与角度实验相一致的结果。 关键词：     

基于Si-rich SiNx/N-rich SiNy多层膜结构的量子点构筑及发光特性

利用等离子体增强化学气相沉积法制备Si-rich SiN_x/N-rich SiN_y多层膜,分别使用热退火和激光辐照技术对多层膜进行退火,以构筑三维限制、尺寸可控、有序的硅纳米晶.实验结果表明,经退火后,纳米硅晶粒在Si-rich SiN_x子层内形成,其尺寸可由Si-rich SiN_x子层厚度调控.实验还发现,激光辐照技术相比于热退火能更有效地改善多层膜的微结构,提高多层膜的晶化率,以激光技术诱导晶化的Si-rich SiN_x/N-rich SiN_y多层膜作为有源层构建电致发光器件,在室温下观察到了增强的电致可见发光,并且发光效率较退火前提高了40%以上. 关键词： 氮化硅 多层膜 限制结晶 纳米晶硅     

真空退火对Ni80Fe20/Cu多层膜微结构的影响

用直流磁控溅射法在Si(001)衬底上制备了以Ta为缓冲层、含有15周期的Ni₈₀Fe₂₀（4nm)/Cu(6nm)多层膜.样品分别在150,250,350℃进行了真空退火处理.用低角和高角X射线衍射法研究了多层膜的微结构.结果表明,所有样品均有较好的[111] 取向,而且随退火温度或时间的增加,[111]取向程度变得更高.超晶格周期、平均面间距在退火后略有减小,表明多层膜结构在退火后变得更为致密.多层膜界面粗糙度随退火温度或时间的增加而增大,平均相关长度随退火温度或时间的增加而减小,分析认为这是由于Ni₈₀Fe₂₀/Cu界面存在严重的互扩散所导致的.模拟Ni₈₀Fe₂₀/Cu多层膜高角X射线衍射谱,发现在Ni₈₀Fe₂₀/Cu蜀面有非常厚的混合层存在,而且混合层厚度随退火温度或时间的增加而增大.模拟结果还表明,随退火温度或时间的增加,Ni₈₀Fe₂₀层面间距几乎保持不变,Cu层面间距则随退火温度的增加而略有减小. 关键词：     

TaN/TiN和NbN/TiN纳米结构多层膜超硬效应及超硬机理研究

采用射频磁控溅射方法制备单层TaN,NbN和TiN薄膜和不同调制周期的TaN/TiN和NbN/TiN纳米多层膜.薄膜采用X射线衍射仪、高分辨率透射电子显微镜和显微硬度仪进行表征.结果表明TaN/TiN和NbN/TiN纳米多层膜在一定的调制周期范围内均呈共格界面,相应地均出现了超硬效应,且最大硬度值接近.分析了TaN/TiN与NbN/TiN纳米多层膜的超硬机理,TaN/TiN的晶格错配度与NbN/TiN的接近,但TaN/TiN的弹性模量差与NbN/TiN的有一定的差别,表明由于晶格错配使共格外延生长在界面处 关键词： TaN/TiN纳米多层膜 NbN/TiN纳米多层膜 外延生长 超硬效应     

二己二硫醚多层膜局域结构的近边x射线吸收精细结构研究

利用多重散射团簇(MSC)方法计算了二己二硫醚［CH₃(CH₂)₅S］₂单分子和多分子硫原子近边x射线吸收精细结构(NEXAFS)谱，给出了二己二硫醚多层膜的局域结构模型. MSC研究显示多层膜中二己二硫醚分子作平行有序排列，彼此相距0.47nm，其横截面呈规则的正方形. 利用离散变分Xα方法计算了二己二硫醚单分子和多分子的电子结构，验证了MSC的计算结果；并阐明了NEXAFS谱中各峰的物理起源. 对多层膜中分子之间的相互作用进行了讨论，发现多层膜的局域结构有分子自组装的特性. 关键词： 3(CH₂)₅S］₂多层膜')" href="#">二己二硫醚［CH₃(CH₂)₅S］₂多层膜 近边x射线吸收精细结构 多重散射团簇方法 离散变分Xα方法     

Role of interfaces in shock-induced plasticity in Cu/Nb nanolaminates

We investigate deformation of pure Cu, pure Nb and 30?nm Cu/30?nm Nb nanolaminates induced by high strain rate shock loading. Abundant dislocation activities are observed in shocked pure Cu and Nb. In addition, a few deformation twins are found in the shocked pure Cu. In contrast, in shocked Cu/Nb nanolaminates, abundant deformation twins are found in the Cu layers, but only dislocations in the Nb layers. High resolution transmission electron microscopy reveals that the deformation twins in the Cu layers preferentially nucleate from the Cu(112)//Nb(112) interface habit planes rather than the predominant Cu(111)//Nb(110) interface planes. Our comparative study on the shock-induced plastic deformation of the pure metals (Cu and Nb) and the Cu/Nb nanolaminates underscores the critical role of heterogeneous phase interfaces in the dynamic deformation of multilayer materials.     

Modelling the energy gap in transition metal/aluminium bilayers

We present an application of the generalised proximity effect theory. The theory has been used to determine the energy gap (Δ_g) in proximised transition metal/aluminium bilayer structures such as Nb/Al, Ta/Al, V/Al and Mo/Al. These bilayers have different film thicknesses ranging from 5 to 260 nm. For the cases of Nb/Al, Ta/Al and V/Al bilayers, the interface parameters γ and γ_BN (here we define γ as the ratio of the products of normal state resistivity and coherence length in each film of the bilayer while γ_BN is the ratio of the boundary resistance between films 1 and 2 to the product of the resistivity and coherence length in the second film), which were used as input parameters to the model, were inferred experimentally from an existing bilayer of each kind and then suitably modified for different film thicknesses. This experimental assessment is therefore based on a comparison of measurements of the critical temperature and the energy gap at 300 mK with the predictions from the model for various values of γ, γ_BN. The energy gap of the bilayer was experimentally determined by using symmetrical superconducting tunnel junctions (STJs) of the form S–Al–AlO_x–Al–S, where each electrode corresponds to a proximised bilayer. However for the case of Mo/Al bilayers the interface parameters were determined theoretically since currently no STJ data for this configuration are available. The results for the Nb/Al, Ta/Al and V/Al bilayers have also then been compared to experimentally determined energy gaps found for a series of STJs with different film thicknesses. The correspondence between experiment and theory is very good.     

Improvements of performance on sputter-coated niobium films for superconducting cavities by adding a NbN interlayer

A new type of superconducting film is studied at Peking University in order to improve the properties of sputter-coated films for superconducting cavities. NbN film and NbN–Nb film have been prepared by DC diode sputtering technology at certain nitrogen content and temperature. NbN film is prepared between copper and Nb film as a barrier against copper diffusion into Nb. Micro-structure analyses show that the NbN–Nb films grow well on the copper substrate. The T_c of the Cu–NbN–Nb increases to 9.5 K compared to the 9.2 K transition temperature of bulk Nb.     

Parallel upper critical field of niobium/graphite bilayers

The influence of the superconducting proximity effect to the upper critical field (H_C) in niobium/graphite bilayers was studied and related to the ratio : and are the transition temperature of Nb/KG film and that of Nb film respectively. The thickness of niobium (Nb) film was controlled about 40 nm, and that of graphite (kish graphite: KG) film ranged from 120 nm to 140 nm. For making a specimen, Nb was deposited on a KG film and a quartz glass substrate simultaneously, and magnetic field was applied parallel to the Nb/KG interface. H_C of Nb/KG film () lowered from that of Nb film () at all temperatures within this work, and the value of ΔH_C defined as showed different temperature dependence among samples, depending on whether < or 1.00. This behavior of H_C suggests the additional existence of the interference of electrons in the clean KG film.     

Structural and magnetic properties of Co-C composite films and Co/C multilayer films

CoC composite films and Co/C multilayer films have been prepared by a method incorporating ion beam sputtering and plasma chemical vapor deposition. It has been found that the structure and magnetic properties of both the Co-C composite and the Co/C multilayer films depend strongly on the substrate temperature during deposition. The Co-C composite film deposited at room temperature is amorphous, with relatively low saturation magnetization and coercivity. On the other hand, the film deposited at 250 °C is composed of fine Co crystallites separated by amorphous C or Co-C phase. As a result, both the saturation magnetization and coercivity are increased compared with the film deposited at room temperature. When deposited at room temperature, the Co/C multilayer film exhibits good periodicity, with a period of 70 nm (Co: 40 nm, C: 30 nm) and sharp and flat Co-C interfaces. High magnetization (602 emu/cm³) and low coercivity (1.6 Oe) are obtained for such a film. However, increasing the substrate temperature to 250 °C was found to be detrimental to the magnetic properties due to the formation of cobalt carbide at the Co-C interface. Received: 11 July 2000 / Accepted: 13 July 2000 / Published online: 30 November 2000     

插入二氧化铈薄膜提高MOD-YBa2Cu3O7-x厚膜超导性能的研究

YBa₂Cu₃O_7-x(YBCO)膜存在“厚度效应”: 随着厚度增加, YBCO薄膜的临界电流密度下降, 尤其是YBCO薄膜的厚度超过1 μm时, 它的临界电流密度急剧下降. 本文在YBCO薄膜之间引入极薄的二氧化铈(CeO₂)薄膜, 成功制备出结构为YBCO/YBCO/CeO₂/YBCO的超导厚膜. 所制备的厚度为2 μm的YBCO膜临界电流密度为1.36 MA/cm² (77 K, 自场), 其性能比相同厚度的纯YBCO膜有了较大幅度的提升. 研究表明CeO₂薄膜起到了传递织构、松弛应力的作用.     

纳米厚度贫铀/Au多层膜的制备及特性研究

理论和实验研究表明,纳米厚度周期调制的贫铀(DU)/Au多层膜材料具有高效的激光X射线转换效率. 采用交替磁控溅射制备纳米厚度的DU/Au平面多层周期结构,通过白光干涉仪、扫描电子显微镜、 X射线光电子能谱对DU/Au多层膜的几何参数、表面形貌、成分以及界面形貌进行表征.实验结果表明: 8 nm为Au连续成膜的厚度阈值,结合理论计算最优化原子配比,选取DU层厚度为30 nm、 Au层厚度为8 nm的调制周期结构;实测周期厚度为37 nm;扫描电子显微镜照片显示DU/Au分层明显; X射线光电子能谱深度刻蚀分析表明DU/Au界面处存在扩散, DU, Au, O三者原子比为73:26:1; 由于团簇效应, Au原子4f电子结合能向高能端移动,没有观察到DU相应的电子结合能移动现象.     

Vortex Pinning due to Dynamic Spin-Vortex Interaction in aSuperconductor/Ferromagnet Multilayer

We investigate the mutual interaction between superconductivity and ferromagnetism in a Nb/Ni81 Ee19 multilayer by ac susceptibility measurements. Compared with a pure superconducting Nb film, the critical current density of the multilayer is apparently enhanced in a low magnetic field region but remains nearly the same in high magnetic fields, which indicates that a continuous ferromagnetic layer with in-plane magnetization can produce strong vortex pinning in a low field region. We interpret this unusual vortex-pinning phenomenon as a consequence of dynamic spin vortex interaction which induces a spin rotation following vortex movement. In addition, we propose that this dynamic interaction could be used for spin manipulation via a superconductor.     

Electron-Spectroscopic Studies of Thermal Stability of Pd/Nb Surfaces

The room-temperature growth of Pd on a clean quasiamorphous, nanostructured Nb surfaces and thermal stability of Pd/Nb interface in the temperature range (295-660) K have been studied by X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy. The measured spectra of Pd (3d) and Nb (3d) electrons indicate presence of a surface Pd-Nb alloy-like phase in the region of submonolayer Pd coverage at room temperature. The Pd (3d) core level shifts can be explained in terms of initial state effects. For multilayer deposits an intermetallic phase is observed in the Pd/Nb interface at room temperature. Inward diffusion of Pd occurs folowed by the formation of three-dimensional alloy at temperatures above 500 K.     

Curie temperatures of CoPt ultrathin continuous films

The effects of layer thickness and thermal annealing on Curie temperature have been studied for CoPt ultrathin continuous layers in AlN/CoPt multilayer structures. It is found that there exists a critical thickness below which Curie temperature rapidly decreases due to the loss of spin-spin interactions in the vicinity of interface. After high temperature annealing, the in-plane lattice constant of CoPt film is increased and the exchange coupling parameter is decreased. Consequently, Curie temperatures decrease for some films with large thickness, compared with as-deposited state. Upon annealing at 600?^°C, CoPt undergoes ordering transformation, which also contributes to the degradation of the Curie temperature. However, when the CoPt film thickness is below 2?nm, the Curie temperature is increased after annealing. Especially for 1?nm thick film, the Curie temperature is strikingly increased from 173?^°C to 343?^°C after annealing at 600?^°C. This effect is attributed to the out-of-plane lattice deformation of CoPt thin layers in AlN/CoPt multilayer structures.