Ga在SiO2／Si系下的扩散模型与分布规律

为给出受主杂质Ga通过SiO2／Si系统实现开管掺杂过程的模型描述和Si体内遵循的主要分布规律，利用二次离子质谱分析(SIMS)、薄层电阻(R□)测量方法，对Ga在SiO2／Si系下的扩散特性、硅表面及体内分布进行了系统研究，得出新的结论：(1)Ga在SiO2中的固溶度较低而扩散系数很大，故形成线性分布形式，Ga在Si中的溶解度相比SiO2很大，SiO2-Si界面的分凝使其以较高平衡浓度分配入硅中，两者的连续确立了开管扩Ga模型。(2)在严格控制硅片温度TSi、杂质源分解温度TGa2O3、反应气体流量CH3，调整预沉积、再分布及其两者的重复组合，便可在硅内得到任意理想的杂质分布；(3)Ga原子是通过理想表面(SiO2-Si界面)扩散入体内，避免与外界的接触沾污，获得了高均匀性、高重复性的扩散表面及非常平行的平面结。     

Ga在SiO2-Si复合结构中的热分布研究

用H2和Ga2O3的高温反应形成元素Ga的恒定表面源，通过SiO2-Si复合结构实现了Ga在Si中的高均匀性掺杂；利用二次离子质谱分析(SIMS)、扩展电阻(SRP)、四探针测试等方法，对P型杂质Ga在SiO2薄膜、SiO2-Si两固相接触的内界面、近Si表面的热分布进行分析；揭示出开管方式扩散Ga的实质是由SiO2薄膜对Ga原子的快速输运及其在SiO2-Si内界面分凝效应两者统一的必然结果；并对该过程Ga杂质浓度分布机理进行了分析和讨论。     

Ga杂质分布对晶体管V-I特性的影响

利用低浓度掺杂-结深推移-高浓度掺杂设计方法形成Ga基区，制备出NPN晶体管样品。实验结果与理论分析表明：Ga的线性缓变分布和SiO2薄膜覆盖下的扩散，大幅度提高了器件耐压水平与综合电学性能：IC-VCE中的负阻效应是由Ga原子表面浓度经二次氧化变为耗尽状态所致，对此，可采用Si3N4/SiO2／Si复合结构加以改善；总之，开管扩镓是一种制备高压器件不可比拟的新途径。     

SiO2-Si界面实现Ga掺杂的研究

通过原子力显微镜（AFM）、二次离子质谱（SIMS）、扩展电阻（SRP）等方法对Ga在SiO2薄层、SiO2-Si界面的扩散特性进行测试表征与机理分析。其结果表明：源于H2和Ga2O3高温反应新生成的元素Ga，经SiO2薄层的快速吸收和输运，到达SiO2-Si的界面，其吸收-输流量在确定的扩散条件下正比于掺杂时间；Ga在SiO2-Si界面按照固-固扩散原理和凭借在Si内有较高溶解度特性实现了Si体内有效扩散；上述两者的有机结合，使Ga原子通过理想表面扩入硅体，从而得到高均匀性、高重复性的扩散结果。     

气体渗氮扩散渗透动力学的电子计算机模型设计

气体渗氮是一种在零件表面形成多相扩散层的处理金属与合金的化学热处理方法。扩散层厚度与相成分决定于工艺过程的技术规范。一般情况下,这种工艺的温度并非恒定,气氛成分也有变化。在非稳定规范条件下,预测多相系统扩散渗透动力学是复杂的。因为这种系统为非线性,难以描述和进行数字运算。本文提供的渗氮过程模型,可使基本工艺参数(气氛成分、压力与温度)同决定渗氮层组织,相成分及厚度的扩散层内氮浓度分布相联系。模型以对渗氮过程各阶段的物理化学描述为基础。     

氧、氢和碳原子在α-铀(001)表面吸附与扩散特性的第一性原理研究

应用第一性原理密度泛函理论系统研究氧、氢和碳原子在α-铀(001)表面的吸附与扩散特性。研究发现:在铀表面氧原子与氢原子择优吸附在H2位置,碳原子倾向于占据在H1位置;氧原子在铀表面的扩散势垒较低,容易在铀表面上扩散,形成表面氧化层;氢原子的扩散势垒较高,碳原子的扩散势垒最大,难以在表面扩散。吸附原子从铀表面向次表面层扩散时,氧原子的扩散势垒很高,难以向次表面扩散;碳和氢原子的扩散势垒较低,特别是在氧的辅助作用下,碳原子向次表面的扩散势垒降低约0.5 eV,使碳原子易于向次表面层扩散;铀表面上会形成氧化层,次表面会形成富碳层,可对铀的进一步氧化起到抑制作用,这与相关实验结果符合较好。     

以二氧化硅为渗硅源获得致密无孔隙的渗硅层

众所周知,渗硅可以明显提高钢铁材料的耐蚀性、抗高温氧化性及表面硬度。但是过去的传统渗硅剂(成份:硅粉或硅铁粉为渗硅源、NH_4Cl为活化剂、Al_2O_3为缓冲剂)由于Fe、Si扩散不均匀,Si的扩散系数比Fe大,所以在Si扩散的同时会伴随空洞出现,导致渗硅层内有许多孔隙,渗层不致密,这样也就限制了渗硅在工业中的应用。     

HVOF喷涂NiCrAlY涂层在1200℃时的循环和等温氧化

用热重分析法(TGA)、扫描电子显微镜(SEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)研究了Ni-20Cr-10A1-1Y厚涂层在1200℃的等温氧化和循环氧化。用HVOF技术制备的涂层在热处理后非常致密，且无裂纹。SEM分析发现。形成的抗氧化层在循环氧化过程中没有剥落。此外，根据分析TGA数据验证了三种氧化方式。两种低于1000℃，第三种约1200℃。1000℃以下的与在涂层表面和次表面上元素选择性氧化相对应。而第三种方式涉及到元素从涂层内向表面的扩散，氧化方式变成在1200℃时形成稳定氧化物的渐近过程。用X射线衍射分析证实，存在水蒸汽既不影响在表面形成的氧化物晶体的方位，也不影响其厚度。XPS和X射线衍射分析结果表明，涂层和基体之间的相互扩散使其界面上的Cr浓度略有增加，氧化层内元素分布有下面的次序：从氧化层的外层到涂层的体内分别为：Al-氧化物／Y-氧化物／Ni-氧化物／NiCrAlY。这些结果表明。致密的Ni-20Cr-10Al-1Y的HVOF喷涂涂层可以用于在1200℃等温氧化和循环氧化的抗氧化阻挡层。     

MCrAlY高温防护涂层界面扩散行为研究进展（英文）

MCr Al Y涂层在高温环境下可在涂层表面生成致密连续的氧化层,以阻止阳离子和氧离子的扩散,在保护镍基高温合金基体免受高温氧化和腐蚀方面发挥着重要作用。氧化层主要由α-Al_2O_3组成,其具有较高的热稳定性和化学稳定性,同时在其六方密堆积(HCP)结构中氧离子和金属离子具有较低的扩散系数。随着氧化铝层的生长,使得涂层/氧化层界面铝浓度降低,进一步抑制了连续的Al_2O_3层的生长,导致氧化层中形成混合氧化物和裂缝以及空隙。同时,伴随着界面扩散过程,使得氧化层的微观结构因化学成分的变化而转变,这将对涂层的抗氧化性能产生显著影响。在高温条件下,由于扩散的热活化特性及涂层与基体化学成分的差异,涂层/镍基合金基体界面扩散过程将对基体合金产生有害影响。此时,Al会从涂层内扩散至基体合金中,同时Ni会从基体合金扩散至涂层中,使得基体合金的微观结构发生相转变(γ-Ni相→γ'-Ni_3Al相),形成互扩散区(IDZ)。镍基合金微观结构的相转变使得难熔元素析出,形成二次反应区(SRZ),其主要由富含难熔元素的拓扑密堆积(TCP)相组成,例如σ、μ和Laves相等,且具有枝状晶结构。因此,TCP相的析出将会对镍基合金的高温疲劳寿命产生严重影响。本文综述了MCr Al Y涂层界面扩散的详细过程,同时对界面扩散过程的影响进行了总结。这将有利于深入了解涂层在氧化过程中的组织结构变化和元素扩散行为,对提高涂层的高温抗氧化性能及研究涂层的失效机理具有借鉴意义。     

渗铝钢扩散层空洞对循环氧化和剥落性能的影响

研究了热浸渗铝钢扩散层空洞对循环氧化和剥落性能的影响规律及其机理。结果表明，随扩散温度升高和时间延长，扩散层空洞不断增加，次外层和过渡层之间空洞逐步聚集连接成平行于表面的波浪线状空洞带，使高温氧化过程中扩散层产生了内氧化，氧化动力学曲线偏离平方抛物线规律而呈现抛物线一直线规律。因此，渗铝钢的长期氧化速度同时受扩散层内氧化和外氧化的控制。空洞(空洞带)的形成对循环剥落性能也产生严重影响。探讨了空洞(空洞带)和内氧化的形成机理。     

Ga在裸Si系的扩散模型及掺杂效应分析

依据Ga在Si中的扩散行为、开管扩Ga系统的特征及扩Ga样品的XPS、EPMA和R<,s>的测试结果分析,提出了Ga在裸Si系的扩散模型,并从机理上分析了Ga的掺杂效应.结果表明:Ga在裸Si系下扩散,易产生合金点、腐蚀坑和"白雾"等缺陷,并造成R<,s>值不均匀.扩Ga产生的缺陷与硅片的导电类型、电阻率大小、晶向和表面光洁度无关.     

Purification of metallurgical silicon using iron as impurity getter,part II: Extent of silicon purification

Purification of metallurgical grade silicon (MG-Si), using iron as the impurity getter has been investigated. The technique involves growing Si dendrites from an alloy of MG-Si with iron, followed by their separation using a gravity based technique and acid leaching. The effects of cooling rate of the alloy and the subsequent quenching temperature on the segregation of the impurities were studied. It was found that slow cooling of the alloy below the eutectic temperature causes an increase in the Si impurity concentration due to diffusion of the impurities from the alloy to the Si. Quenching the alloy from temperatures above the eutectic eliminated this effect, increasing the purity of the Si product. A significant reduction in the concentration of the major impurities was achieved, making the Si product a suitable feedstock for solar grade silicon generation. The concentrations, in ppmw, of some elements in the Si product are Al: 10, B: 2, Mn: 3, Ni: 3, Cr: 1, Fe: 1, P: 29. Other impurities including V, Ba, Li, Be, and Mg were all below 0.5 ppmw.     

合金元素对Ag-Cu-Zn系钎料影响的研究现状及发展趋势

介绍了银基钎料的基本性能、应用现状及其分类,重点介绍了Ag-Cu-Zn系钎料的国内应用状况,并对该系列钎料的基础成分进行了简单分析.概述了Ag-Cu-Zn系钎料中杂质元素的研究状况及应对措施.分析了国内市场上无镉银钎料、含镉银钎料的性能、特点及主要用途.阐述了添加不同合金元素Mn和Ni、Si和P、Ga和In及稀土元素对Ag-Cu-Zn系钎料性能的影响,展望了Ag-Cu-Zn系钎料的发展方向,并指出通过添加多种微量元素优化钎料成分来保持原有优良性能将是未来研究的重点和热点.     

Phase equilibria in the Ti-rich corner of the Ti-Si-Ga system

Phase relations in the ternary Ti-Si-Ga system have been established experimentally by means of a study of alloy samples in the as-cast condition and annealed at 1350 °C. The alloys were prepared by arc melting. The investigation was carried out using physico chemical methods of analyses (metallography, X-ray powder diffraction, differential thermal analysis, and electron probe microanalysis over a limited composition range with samples containing less than 38 at.% Ga and more than 62 at.% Ti. Liquidus and solidus surface projections, the isothermal section at 1350 °C, and the isopleth at 68 at.% Ti are presented. Three surfaces of primary crystallization of phases have been established: extended ones for Ti₅(Si,Ga)₃ and β (Ti-base solid solution) and a narrow one of Ti₂Ga. The monovariant curves separating these are due to the eutectic reactions L↔β+Ti₅(Si,Ga)₃ and L↔β+Ti₂Ga and to the L+Ti₅(Si,Ga)₃↔Ti₂Ga peritectic reaction. The three-phase region (β+Ti₅(Si,Ga)₃+Ti₂Ga) results from the four-phase eutectic reaction L↔β+Ti₅(Si,Ga)₃+Ti₂Ga. The composition of the ternary eutectic point E and the compositions of the coexisting solid phases have been determined. The solubilities of Si in the gallides, and of Ga in Ti₅Si₃ and of both the elements in Ti are given.     

Phase equilibria in the Ti-rich corner of the Ti-Si-Ga system

Phase relations in the ternary Ti-Si-Ga system have been established experimentally by means of a study of alloy samples in the as-cast condition and annealed at 1350 °C. The alloys were prepared by arc melting. The investigation was carried out using physico chemical methods of analyses (metallography, X-ray powder diffraction, differential thermal analysis, and electron probe microanalysis over a limited composition range with samples containing less than 38 at.% Ga and more than 62 at.% Ti. Liquidus and solidus surface projections, the isothermal section at 1350 °C, and the isopleth at 68 at.% Ti are presented. Three surfaces of primary crystallization of phases have been established: extended ones for Ti₅(Si,Ga)₃ and β (Ti-base solid solution) and a narrow one of Ti₂Ga. The monovariant curves separating these are due to the eutectic reactions L↔β+Ti₅(Si,Ga)₃ and L↔β+Ti₂Ga and to the L+Ti₅(Si,Ga)₃↔Ti₂Ga peritectic reaction. The three-phase region (β+Ti₅(Si,Ga)₃+Ti₂Ga) results from the four-phase eutectic reaction L↔β+Ti₅(Si,Ga)₃+Ti₂Ga. The composition of the ternary eutectic point E and the compositions of the coexisting solid phases have been determined. The solubilities of Si in the gallides, and of Ga in Ti₅Si₃ and of both the elements in Ti are given.     

Fabricating Ni–Mn–Ga microtubes by diffusion of Mn and Ga into Ni tubes

Tubes of the ferromagnetic shape-memory alloy Ni–Mn–Ga of composition near the Ni₂MnGa Heusler phase can be used, alone or combined in structures, in magnetic actuators or magnetic refrigerators. However, fabrication of Ni–Mn–Ga tubes with sub-millimeter diameter by classical cold or hot drawing methods is hampered by the brittleness of the alloy. Here, we demonstrate a new process, where Ni–Mn–Ga tubes are fabricated by interdiffusion of Mn and Ga into drawn, ductile Ni tubes with 500 and 760 μm inner and outer diameters. After interdiffusion and homogenization of Mn and Ga at 1000 °C for 24–36 h, Ni–Mn–Ga tubes with ∼300 and ∼900 μm inner and outer diameters were obtained with homogeneous radial composition distribution, independently of the diffusion sequences (i.e., Mn and Ga diffused sequentially or simultaneously). Longitudinal composition was uniform over lengths of ∼1 mm, but variable over longer length due to incomplete process control. For two of the three diffusion sequences, a sizeable (20–80 μm) region exhibiting Kirkendall pores formed at the outer surface of the tubes. Magnetization values as high as ∼60 emu/g were measured, which is comparable to the magnetization of the Ni₂MnGa Heusler phase. X-ray diffraction on the tube with the highest magnetization confirmed the room-temperature structure as cubic austenite.