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Al_2O_3/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;Al_2O_3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格位置距离为0.18埃。室温下,Al(100)氧吸附层的元素成份在氧原子覆盖度较低时主要为AlO。     

氧化铝与Al（100）基体间界面原子结构研究

本文介绍了用M e v 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AI_2_O_3_/ Al ( 1 0 0) 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;AI_2_O_3_ 膜和Al (100)基体之间的界面极其陡峭, 氧化铝膜下Al (1 0 0 ) 基体表面的再构层不大于一个原子层. 由实验测量与用Monte corlo 方法计算结果比较, 得到再构层原子离开原来晶格位置距离为0.18埃. 室温下,Al ( 1 0 0 ) 氧吸附层的元素成份在氧原子覆盖度较低时主要为AlO. 关键词：     

表面氧化层对共振反应寿命测量影响的Monte-Carlo模拟

本文用两次碰撞近似的Monte-Carlo模拟计算了Al单晶中在2000?深度发射的、能量为2.12MeV的α粒子沿<110>轴的阻塞角分布。计算中除了考虑晶格原子热振动、电子多次散射等因素,在Al单晶表面引入了Al₂O₃有效氧化层。计算结果表明:考虑了无定形表面氧化铝层以后,模拟的阻塞角分布比未考虑氧化层时更接近于实验曲线。 关键词：     

原子级控制的约瑟夫森结中Al2O3势垒层制备工艺

传统热氧化方式制备约瑟夫森结中AlO_X势垒层是将高纯度氧气扩散到Al表面进行,但该方式制备的势垒层氧化不完全,厚度难以精准控制.本文采用原子层沉积方式在金属Ti表面逐层生长Al₂O₃势垒层,并制备出三明治结构的Ti/Al₂O₃/Ti约瑟夫森结.通过调节Al₂O₃势垒层的沉积厚度和约瑟夫森结的面积研究了其相应的微观结构及电学性质.实验结果表明,原子层沉积方式生长的单层Al₂O₃薄膜厚度约为1.17?(1?=10^-10 m),达到原子级控制势垒层厚度,通过调节势垒层厚度实现了对结室温电阻值的控制,并通过优化结面积获得了室温电阻均匀性良好的约瑟夫森结.     

α-Al2O3(0001)基片表面结构与能量研究

对α-Al₂O₃(0001)晶体表层三种不同终止原子结构的计算模型， 在三维周期边界条件下 的κ空间中，采用超软赝势平面波函数描述多电子体系.应用基于密度泛函理论的局域密度 近似，计算了不同表层结构的体系能量，表明最表层终止原子为单层Al的表面结构最稳定. 对由10个原子组成的菱形原胞进行了结构优化，得到晶胞参数值(a₀＝0.48178n m)与实验 报道值误差小于1.3%.进一步计算了超晶胞(2×2)表面弛豫，弛豫后原第2层O原子层成为最 表层； 对不同表层O，Al原子最外层电子进行了布居分析，表面电子有更大的概率被定域在 O原子的周围，表面明显地表现出O原子的电子表面态. 关键词： 2O₃(0001)')" href="#">α-Al₂O₃(0001) 超软赝势 表面结构 表面态     

Al(100)表面原子结构的高能离子散射研究

本文介绍了用高能(MeV)离子散射研究表面、界面原子结构的方法、实验装置;报道了获得Al单晶清洁表面的方法,用高能离子散射、沟道效应研究Al(100)表面原子结构的实验结果:Al(100)表面层原子的热振动振幅较体内原子大20—30％,Al(100)表面层原子的弛豫量小于-0.05?。 关键词：     

原子层沉积与聚焦离子束切片法制备X射线波带片

针对X射线波带片对大高宽比的应用需求,采用原子层沉积法在光滑的金属丝表面生长膜厚可高精度控制的多层膜环带结构,再利用聚焦离子束切片技术获得大高宽比的多层膜X射线波带片。采用复振幅叠加法设计了以Al₂O₃/HfO₂分别为明环和暗环材料的X射线波带片,实验上利用原子层沉积在直径为72μm的金丝表面交替沉积了10.11μm的Al₂O₃/HfO₂多层膜,环带数为356,总直径为92.22μm,最外环宽度为25 nm。通过聚焦离子束切割得到高为1.08μm、高宽比达43∶1的X射线多层膜菲涅耳波带片。该波带片应用于上海光源(BL08U1A)软X射线成像线站时,在1.2 keV X射线下实现聚焦成像功能,展现出利用该技术制备多层膜X射线波带片的潜力。     

TiN/Al2O3纳米多层膜的共格外延生长及超硬效应

采用多靶磁控溅射法制备了一系列具有不同Al₂O₃调制层厚度的TiN/Al₂O₃纳米多层膜. 利用X射线能量色散谱、X射线衍射、扫描电子显微镜、高分辨透射电子显微镜和微力学探针表征了多层膜的成分、微结构和力学性能. 研究结果表明，在TiN/Al₂O₃纳米多层膜中，单层膜时以非晶态存在的Al₂O₃层在厚度小于1.5 nm时因TiN晶体层的模板效应而晶化，并与TiN层形成共格外延生长，相应地，多层膜产生硬度明显升高的超硬效应，最高硬度可达37.9 GPa. 进一步增加多层膜中Al₂O₃调制层的层厚度，Al₂O₃层逐渐形成非晶结构并破坏了多层膜的共格外延生长，使得多层膜的硬度逐步降低. 关键词： 2O₃纳米多层膜')" href="#">TiN/Al₂O₃纳米多层膜 外延生长 非晶晶化 超硬效应     

Fe-Cr-Al合金氧化膜形成机理电子理论研究

通过自编软件建立了Fe-Cr-Al合金表面、氧化膜/基体界面模型,采用递归法计算了合金元素在Fe-Cr-Al合金表面、氧化膜/基体界面的环境敏感镶嵌能、亲和能、结合能、态密度等电子结构参数.从电子层次系统研究了Fe-Cr-Al合金氧化膜的形成机理、稀土元素和杂质硫对氧化膜形成过程及黏附性的影响机理.研究表明Fe-Cr-Al合金中Al的偏聚驱动力远大于Y,Cr.氧化初期氧从合金表面向合金内部扩散,合金内部Al向合金表面扩散,使合金形成富铝、氧表面层;氧与Al间的亲和力较大（亲和能低）,氧原子容易与Al结合生成Al₂O₃保护膜;合金中加入Y后,Y在合金表面偏聚,抑制Al向合金表面扩散,氧化膜的横向生长得到有效控制,从而避免氧化膜皱褶形貌的发生,提高氧化膜的黏附性;合金内部的S通过扩散汇集在基体/氧化膜界面,S使界面区原子的总能增高,总态密度降低,减小了界面的稳定性,进而削弱氧化膜与合金基体的结合力. 关键词： 电子结构 高温氧化 Fe-Cr-Al合金     

Bi2Te3(111)和Al2O3(0001)衬底对Bi(111)双原子层的电子结构及拓扑性质的影响

晶体铋沿(111)面方向的双原子层及薄膜具有新奇的拓扑性质.在实验生长或者实际应用中,其必然与衬底接触.本文采用紧束缚近似方法与第一性原理计算研究了Bi双原子层及其与Bi₂Te₃和Al₂O₃衬底形成的异质结的电子结构.计算结果表明, Bi双层是具有0.2 eV的半导体.当其与具有拓扑表面态的Bi₂Te₃形成异质结时,两者电子态之间有很强的杂化,不利于Bi(111)双层拓扑电子态的观测.将其放在绝缘体Al₂O₃(0001)时,导带与价带与衬底电子态杂化较小,并且展现出巨大的Rashba自旋劈裂.这是由于衬底诱导Bi(111)双原子层中心反演对称性破缺和自旋-轨道耦合共同作用的结果.进一步采用紧束缚近似计算得到的结果发现,衬底Al₂O₃(0001)对Bi(111)双层的作用等效于一个约为0.5—0.6 V/?(1?=0.1 nm)的外电场.此外, Bi(111)双原子层与衬...     

Nb-Al合金高温氧化机理

通过自编软件建立了铝氧化膜与基体铌界面的原子集团模型,用递归法计算了合金的原子埋置能、原子结合能等电子参数,从电子层面分析铌合金高温氧化机理.研究表明:铝通过晶界扩散偏聚在合金表面,并与氧结合生成致密的Al2O3氧化膜,阻挡氧向铌基体扩散.晶界和稀土元素能提高氧化膜与基体间的原子结合能,增加其界面的结合强度,加强氧化膜与基体铌间的黏附性.因此,通过在合金中添加稀土元素或细化合金晶粒均能提高铌合金的抗高温氧化性能.     

Interfacial reactions and oxidation behavior of Al2O3 and Al2O3/Al coatings on an orthorhombic Ti2AlNb alloy

The uniform and dense Al₂O₃ and Al₂O₃/Al coatings were deposited on an orthorhombic Ti₂AlNb alloy by filtered arc ion plating. The interfacial reactions of the Al₂O₃/Ti₂AlNb and Al₂O₃/Al/Ti₂AlNb specimens after vacuum annealing at 750 °C were studied. In the Al₂O₃/Ti₂AlNb specimens, the Al₂O₃ coating decomposed significantly due to reaction between the Al₂O₃ coating and the O-Ti₂AlNb substrate. In the Al₂O₃/Al/Ti₂AlNb specimens, a γ-TiAl layer and an Nb-rich zone came into being by interdiffusion between the Al layer and the O-Ti₂AlNb substrate. The γ-TiAl layer is chemically compatible with Al₂O₃, with no decomposition of Al₂O₃ being detected. No internal oxidation or oxygen and nitrogen dissolution zone was observed in the O-Ti₂AlNb alloy. The Al₂O₃/Al/Ti₂AlNb specimens exhibited excellent oxidation resistance at 750 °C.     

Co on thin Al2O3 films grown on Ni3Al(1 0 0)

The growth of Co on thin Al₂O₃ layers on Ni₃Al(1 0 0) was investigated by Auger electron spectroscopy, high resolution electron energy loss spectroscopy (EELS), and scanning tunneling microscopy. At 300 K, Co grows in three-dimensional clusters on top of the Al₂O₃ layer. A defect structure of the alumina layer plays a crucial role during the early stage of Co growth. After deposition of 10 Å of Co, a complete screening of the dipoles of the Al₂O₃ layer due to the Co film is found in the EELS measurements. Annealing the Co film reveals a process of coalescence of Co clusters and, above 700 K, diffusion of the Co atoms through the oxide film into the substrate takes place.     

The leakage current mechanisms in the Schottky diode with a thin Al layer insertion between Al0.245Ga0.755N/GaN heterostructure and Ni/Au Schottky contact

This paper investigates the behaviour of the reverse-bias leakage current of the Schottky diode with a thin Al inserting layer inserted between Al0.245Ga0.755 N/GaN heterostructure and Ni/Au Schottky contact in the temperature range of 25-350°C. It compares with the Schottky diode without Aluminium inserting layer. The experimental results show that in the Schottky diode with Al layer the minimum point of I-V curve drifts to the minus voltage, and with the increase of temperature increasing, the minimum point of I-V curve returns the 0 point. The temperature dependence of gate-leakage currents in the novelty diode and the traditional diode are studied. The results show that the Al inserting layer introduces interface states between metal and Al0.245Ga0.755N. Aluminium reacted with oxygen formed Al2O3 insulator layer which suppresses the trap tunnelling current and the trend of thermionic field emission current. The reliability of the diode at the high temperature is improved by inserting a thin Al layer.     

Effect of surface roughness on the development of protective Al2O3 on Fe-10Al (at.%) alloys containing 0-10 at.% Cr

The effect of alloy surface roughness, achieved by different degrees of surface polishing, on the development of protective alumina layer on Fe-10 at.% Al alloys containing 0, 5, and 10 at.% Cr was investigated during oxidation at 1000 °C in 0.1 MPa oxygen. For alloys that are not strong Al₂O₃ formers (Fe-10Al and Fe-5Cr-10Al), the rougher surfaces increased Fe incorporation into the overall surface layer. On the Fe-10Al, more iron oxides were formed in a uniform layer of mixed aluminum- and iron-oxides since the layer was thicker. On the Fe-5Cr-10Al, more iron-rich nodules developed on an otherwise thin Al₂O₃ surface layer. These nodules nucleated preferentially along surface scratch marks but not on alloy grain boundaries. For the strong Al₂O₃-forming Fe-10Cr-10Al alloy, protective alumina surface layers were observed regardless of the surface roughness. These results indicate that the formation of a protective Al₂O₃ layer on Fe-Cr-Al surfaces is not dictated by Al diffusion to the surface. More cold-worked surfaces caused an enhanced Fe diffusion, hence produced more Fe-rich oxides during the early stage of oxidation.     

The improvement of Al2O3/AlGaN/GaN MISHEMT performance by N2 plasma pretreatment

This paper discusses the effect of N 2 plasma treatment before dielectric deposition on the electrical performance of a Al2O3 /AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor(MISHEMT),with Al2O3 deposited by atomic layer deposition.The results indicated that the gate leakage was decreased two orders of magnitude after the Al2O3 /AlGaN interface was pretreated by N 2 plasma.Furthermore,effects of N 2 plasma pretreatment on the electrical properties of the AlGaN/Al2O3 interface were investigated by x-ray photoelectron spectroscopy measurements and the interface quality between Al2O3 and AlGaN film was improved.