化学气相沉积法ZnS块材料的生长

本文用化学气相沉积法制备了ZnS薄膜和块材料;观察了ZnS在具有不同表面粗糙度的石墨和石英基体上的成核和长大行为;研究了沉积温度、H₂S和Zn蒸汽流量对ZnS生长速率的影响规律．     

Unique Bond Breaking in Crystalline Phase Change Materials and the Quest for Metavalent Bonding

Laser‐assisted field evaporation is studied in a large number of compounds, including amorphous and crystalline phase change materials employing atom probe tomography. This study reveals significant differences in field evaporation between amorphous and crystalline phase change materials. High probabilities for multiple events with more than a single ion detected per laser pulse are only found for crystalline phase change materials. The specifics of this unusual field evaporation are unlike any other mechanism shown previously to lead to high probabilities of multiple events. On the contrary, amorphous phase change materials as well as other covalently bonded compounds and metals possess much lower probabilities for multiple events. Hence, laser‐assisted field evaporation in amorphous and crystalline phase change materials reveals striking differences in bond rupture. This is indicative for pronounced differences in bonding. These findings imply that the bonding mechanism in crystalline phase change materials differs substantially from conventional bonding mechanisms such as metallic, ionic, and covalent bonding. Instead, the data reported here confirm a recently developed conjecture, namely that metavalent bonding is a novel bonding mechanism besides those mentioned previously.     

Chemical Bonding in Chalcogenides: The Concept of Multicenter Hyperbonding

The precise nature of chemical-bonding interactions in amorphous, and crystalline, chalcogenides is still unclear due to the complexity arising from the delocalization of bonding, and nonbonding, electrons. Although an increasing degree of electron delocalization for elements down a column of the periodic table is widely recognized, its influence on chemical-bonding interactions, and on consequent material properties, of chalcogenides has not previously been comprehensively understood from an atomistic point of view. Here, a chemical-bonding framework is provided for understanding the behavior of chalcogenides (and, in principle, other lone-pair materials) by studying prototypical telluride nonvolatile-memory, “phase-change” materials (PCMs), and related chalcogenide compounds, via density-functional-theory molecular-dynamics (DFT-MD) simulations. Identification of the presence of previously unconsidered multicenter “hyperbonding” (lone-pair–antibonding-orbital) interactions elucidates not only the origin of various material properties, and their contrast in magnitude between amorphous and crystalline phases, but also the very similar chemical-bonding nature between crystalline PCMs and one of the bonding subgroups (with the same bond length) found in amorphous PCMs, in marked contrast to existing viewpoints. The structure–property relationship established from this new bonding-interaction perspective will help in designing improved chalcogenide materials for diverse applications, based on a fundamental chemical-bonding point of view.     

固态晶体生长及其在平面波导结构制备上的应用

研究了烧结温度、晶粒大小以及掺杂离子对固态晶体生长的影响。在热致固态晶体生长的过程中, 接近键合面的陶瓷会被单晶诱导而转变成取向一样的单晶, 同时形成稳固的键合。实验利用这种方法制备核层为12at%Yb:YAG陶瓷(100 mm), 包层为YAG晶体的平面波导结构。这种方法制备的波导结构没有Yb离子的浓度扩散现象。同时, 还测试了平面波导结构的激光性能: 通过设计平平腔实现了1.14 W, 斜率效率16.09%的激光输出; 在三镜腔中实现1.83 W, 斜率效率9.59%的激光输出。并且激光输出在1027.5 nm到1033.5 nm间连续可调。     

Influence of the Substrate Orientation on the Isothermal Solidification during TLP Bonding Single Crystal Superalloys

Angle deviations between the two substrates during transient liquid phase （TLP） bonding single crystal superalloys cannot be avoided. In the present work, specimens have been prepared to investigate the influences of the various substrate orientations. It is found that the width of the non-isothermal solidification zone （NSZ） is linear with the square root of the isothermal solidification time. This suggests that the isothermal solidification process is B-diffusion controlled in different substrate orientation deviations. And also the width of the NSZ increases with increasing angle deviation, indicating that the isothermal solidification time needed in the TLP bonding increases with increasing orientation deviation between the two substrates.     

Chalcogenides by Design: Functionality through Metavalent Bonding and Confinement

A unified picture of different application areas for incipient metals is presented. This unconventional material class includes several main-group chalcogenides, such as GeTe, PbTe, Sb₂Te₃, Bi₂Se₃, AgSbTe₂ and Ge₂Sb₂Te₅. These compounds and related materials show a unique portfolio of physical properties. A novel map is discussed, which helps to explain these properties and separates the different fundamental bonding mechanisms (e.g., ionic, metallic, and covalent). The map also provides evidence for an unconventional, new bonding mechanism, coined metavalent bonding (MVB). Incipient metals, employing this bonding mechanism, also show a special bond breaking mechanism. MVB differs considerably from resonant bonding encountered in benzene or graphite. The concept of MVB is employed to explain the unique properties of materials utilizing it. Then, the link is made from fundamental insights to application-relevant properties, crucial for the use of these materials as thermoelectrics, phase change materials, topological insulators or as active photonic components. The close relationship of the materials' properties and their application potential provides optimization schemes for different applications. Finally, evidence will be presented that for metavalently bonded materials interesting effects arise in reduced dimensions. In particular, the consequences for the crystallization kinetics of thin films and nanoparticles will be discussed in detail.     

化学气相沉积SiC涂层生长过程分析

以高纯石墨为沉积基体,MTS为先驱体原料,在负压条件下沉积了CVD SiC涂 层.利用SEM和XRD分别对涂层的形貌及晶体结构进行了表征,SiC涂层表面呈菱柱状, (111)面为择优取向面.利用高分辨透射电镜对涂层与基体的界面结构、涂层的显微结构进行 了研究,得出CVD SiC涂层生长过程如下:SiC最初是沿着石墨基体的晶面取向开始生长 的}随后经历一段取向淘汰及调整的过程后,开始(111)晶面的生长.     

硅灰石晶体在三元氧化物熔体中的生长行为研究

利用耦合FACTSage Toxide 热力学数据库的定量相场模型, 本研究模拟了硅灰石(CaSiO₃)在CaO-Al₂O₃-SiO₂体系中的恒温晶体生长过程, 并研究了熔体组分和温度对CaSiO₃结晶过程的影响。结果表明, 硅灰石的形貌主要由其表面能的各向异性所决定, 而几乎不受界面动力学的各向异性所影响。此外, 随着温度的降低, 析出的硅灰石的生长方式由平面生长向枝晶生长方式转变, 于此同时, 更加精细的枝晶结构也逐渐呈现出来。模拟所得的枝晶生长速度和尖端半径与Ivanstov理论所得结果一致, 和实验测得的数据也处于同一数量级。     

An investigation into the interactions between self-assembled adenine molecules and a Au(111) surface

Two molecular phases of the DNA base adenine (A) on a Au(111) surface are observed by using STM under ultrahigh-vacuum conditions. One of these phases is reported for the first time. A systematic approach that considers all possible gas-phase two-dimensional arrangements of A molecules connected by double hydrogen bonds with each other and subsequent ab initio DFT calculations are used to characterize and identify the two phases. The influence of the gold surface on the structure of A assemblies is also discussed. DFT is found to predict a smooth corrugation potential of the gold surface that will enable A molecules to move freely across the surface at room temperature. This conclusion remains unchanged if van der Waals interaction between A and gold is also approximately taken into account. DFT calculations of the A pairs on the Au(111) surface show its negligible effect on the hydrogen bonding between the molecules. These results justify the gas-phase analysis of possible assemblies on flat metal surfaces. Nevertheless, the fact that it is not the most stable gas-phase monolayer that is actually observed on the gold surface indicates that the surface still plays a subtle role, which needs to be properly addressed.     

不同过饱和度下DKDP晶体生长和缺陷的研究

过饱和度是影响DKDP晶体生长和质量的关键因素. 本文采用“点籽晶”快速生长技术在不同的过饱和度下从氘化程度为75%的溶液中生长DKDP晶体并选取部分样品进行同步辐射X射线形貌术和粉末X射线衍射测试. 研究了不同过饱和度下DKDP晶体的生长和缺陷. 实验证明, DKDP晶体可以在的过饱和度下实现快速生长, 但晶体的缺陷随着过饱和度的增大而增加.     

Direct Growth of Ultrafast Transparent Single‐Layer Graphene Defoggers

The idea flat surface, superb thermal conductivity and excellent optical transmittance of single‐layer graphene promise tremendous potential for graphene as a material for transparent defoggers. However, the resistance of defoggers made from conventional transferred graphene increases sharply once both sides of the film are covered by water molecules which, in turn, leads to a temperature drop that is inefficient for fog removal. Here, the direct growth of large‐area and continuous graphene films on quartz is reported, and the first practical single‐layer graphene defogger is fabricated. The advantages of this single‐layer graphene defogger lie in its ultrafast defogging time for relatively low input voltages and excellent defogging robustness. It can completely remove fog within 6 s when supplied a safe voltage of 32 V. No visible changes in the full defogging time after 50 defogging cycles are observed. This outstanding performance is attributed to the strong interaction forces between the graphene films and the substrates, which prevents the permeation of water molecules. These directly grown transparent graphene defoggers are expected to have excellent prospects in various applications such as anti‐fog glasses, auto window and mirror defogging.     

Design rules for phase-change materials in data storage applications

Phase-change materials can rapidly and reversibly be switched between an amorphous and a crystalline phase. Since both phases are characterized by very different optical and electrical properties, these materials can be employed for rewritable optical and electrical data storage. Hence, there are considerable efforts to identify suitable materials, and to optimize them with respect to specific applications. Design rules that can explain why the materials identified so far enable phase-change based devices would hence be very beneficial. This article describes materials that have been successfully employed and dicusses common features regarding both typical structures and bonding mechanisms. It is shown that typical structural motifs and electronic properties can be found in the crystalline state that are indicative for resonant bonding, from which the employed contrast originates. The occurence of resonance is linked to the composition, thus providing a design rule for phase-change materials. This understanding helps to unravel characteristic properties such as electrical and thermal conductivity which are discussed in the subsequent section. Then, turning to the transition kinetics between the phases, the current understanding and modeling of the processes of amorphization and crystallization are discussed. Finally, present approaches for improved high-capacity optical discs and fast non-volatile electrical memories, that hold the potential to succeed present-day's Flash memory, are presented.     

石墨高温粘接界面的组成及其与粘接强度间的关系

以酚醛树脂和碳化硼为原料制备了性能良好的调温粘结剂并对石墨材料进行粘接。通过XPS的测试，研究了石墨调温粘接样品在不同的温度热处理后的界面组成，相对含量变化及其与粘接性能间的相关性。结果表明，粘接界面上主要存在着C，B，O等元素，其中，酚醛树脂（PF）炭化产生的无定形炭构成了胶层骨架，其相对含量的变化影响着胶层结构的致密稳定性；B在粘接样品中以B4C或B2O3形式存在，其存在形式对粘接强度有着重要的影响。     

外尔半金属TaAs单晶的研究进展

外尔半金属是当两个自旋非简并能带在三维动量空间通过费米能级附近时,其低能准粒子激发具有外尔费米子的所有特征的一类材料体系。外尔费米子是狄拉克方程的无质量解,可以看作是在三维空间一对重叠在一起且具有相反手性的粒子。TaAs单晶作为一种非磁性的外尔半金属,在其中能够观测到外尔费米子,并产生许多奇异的物理现象,如费米弧、负磁阻效应、量子反常霍尔效应等,使其在发展新型电子器件和拓扑量子计算等领域有着重要应用潜力。介绍了外尔半金属的相关基础理论和重要实验,重点探讨了TaAs单晶生长相关的技术问题,分析了化学气相传输法的优缺点。     

化学气相沉积法制备ZnS块材料的相结构

用化学气相沉积法制备了红外晶体ＺｎＳ块材料；分别用ＸＲＤ和ＴＥＭ分析了所沉积ＺｎＳ的相结构，并用ＩＲ测试了其红外透过率。结果表明：在沉积温度为５５０～７００℃，Ｈ２Ｓ／Ｚｎ摩尔流量比为０．５～２０的条件下所沉积ＺｎＳ的相结构主要为闪锌矿结构；随着沉积温度的升高和Ｈ２Ｓ／Ｚｎ摩尔流量比的增大，ＺｎＳ中有纤锌矿结构出现且其含量增多，导致了ＺｎＳ红外透过率的降低。     

Understanding the Structure and Properties of Sesqui‐Chalcogenides (i.e., V2VI3 or Pn2Ch3 (Pn = Pnictogen,Ch = Chalcogen) Compounds) from a Bonding Perspective

A number of sesqui‐chalcogenides show remarkable properties, which make them attractive for applications as thermoelectrics, topological insulators, and phase‐change materials. To see if these properties can be related to a special bonding mechanism, seven sesqui‐chalcogenides (Bi₂Te₃, Bi₂Se₃, Bi₂S₃, Sb₂Te₃, Sb₂Se₃, Sb₂S₃, and β‐As₂Te₃) and GaSe are investigated. Atom probe tomography studies reveal that four of the seven sesqui‐chalcogenides (Bi₂Te₃, Bi₂Se₃, Sb₂Te₃, and β‐As₂Te₃) show an unconventional bond‐breaking mechanism. The same four compounds evidence a remarkable property portfolio in density functional theory calculations including large Born effective charges, high optical dielectric constants, low Debye temperatures and an almost metal‐like electrical conductivity. These results are indicative for unconventional bonding leading to physical properties distinctively different from those caused by covalent, metallic, or ionic bonding. The experiments reveal that this bonding mechanism prevails in four sesqui‐chalcogenides, characterized by rather short interlayer distances at the van der Waals like gaps, suggestive of significant interlayer coupling. These conclusions are further supported by a subsequent quantum‐chemistry‐based bonding analysis employing charge partitioning, which reveals that the four sesqui‐chalcogenides with unconventional properties are characterized by modest levels of charge transfer and sharing of about one electron between adjacent atoms. Finally, the 3D maps for different properties reveal discernible property trends and enable material design.