真空环境中多场耦合对Au/Cu/Si薄膜界面结构的影响

采用磁控溅射方法在Si基底上制备了Au/Cu薄膜.利用扫描俄歇微探针(SAM)纳米化分析技术进行表面成分分析与深度剖析,研究在真空环境中,紫外辐照、微氧氧含量及处理温度等因素作用对Au/Cu薄膜界面结构的影响.实验结果表明:环境温度的升高,使薄膜内缺陷增加,为Cu原子的扩散提供了更多的扩散通道;紫外辐照产生了等同的热效应,加剧了Cu原子在Au层中的扩散;微氧的存在诱导了Cu原子的扩散.三种因素协同作用下,诱导迁移扩散机制在室温下形成,并于处理温度达到100℃后趋于稳定.     

离子溅射合金表面组份再分布的模拟计算

离子溅射合金和化合物后会引起表面成分的再分布。根据 Kelly 的理论分析观点,综合考虑了择优溅射(PS),离子辐照诱导偏析(RIS)和辐照增强扩散(RED)效应,得到了合金表面成分变化的基本关系。用此分析关系对 Au—Cu、Cu—Ni 合金离子轰击后表面成分的变化、Au—Pd 和 Cu—Ni 合金离子轰击后的 X 射线光电子谱、俄歇电子谱的分析结果进行了模拟计算,计算结果与实验完全吻合。通过分析计算认为,离子辐照增强扩散系数的大小对表面成分的变化有很大的影响。初步计算得到的增强扩散激活能约为0.09eV,与实验结果(0.06eV)相一致,约为通常热扩散激活能的二十分之一。     

Pt和Au修饰锐钛矿型TiO2(101)面的第一性原理研究

采用平面波超软赝势方法研究了Pt和Au修饰锐钛矿型TiO₂(101)面的结构稳定性及电子结构。结果显示贵金属原子在TiO₂(101)符合化学计量比的条件下, 在其表面的吸附作用不强, 对电子结构的影响也较小。但是发现在富O条件下, Pt和Au原子容易吸附在表面Ti空位的位置, 与Au原子不同, Pt原子有从TiO₂表面扩散进入体相晶格中的趋势。而在富Ti条件下, Pt和Au原子容易吸附在O1空位的位置。对可能存在的几种空位缺陷吸附模型进行了电子结构的计算。结果表明: 空位缺陷的产生不仅有利于Pt和Au原子“湿化”TiO₂(101)表面, 也有利于带隙中产生贵金属原子的5d杂质能级。     

UHV/CVD生长锗硅材料的偏析现象

本文对利用超高真空CVD方法生长的Si1-xGex合金外延层中的锗表面分布情况和Ge在界面偏析现象进行了深入的研究.通过XPS和SIMS图谱的研究,指出表面由于锗的偏析,造成锗在体内和表面的含量不同,在低温时生长锗硅合金,表面氢原子的吸附可有效地抑制锗的偏析,但随着温度的升高,氢的脱附造成锗的偏析现象更加明显.     

荷能束辐照致使Cu/Ag表面偏析的研究

本文研究了金属(Cu)/金属(Ag衬底)系统的荷能束辐照引起的表面偏析现象。观察到Cu在多晶Ag衬底上溅射淀积过程中,Ag原子在Cu膜表面的偏析,且淀积Cu原子能量越大,Ag原子偏析程度越大,即观察到了淀积Cu原子10~(-1)～1eV量级的平均能量差异对膜层表面偏析行为的影响。对溅射淀积所得膜层进行keV量级的离子束辐照,Ag原子的表面偏析程度更甚。     

表面偏析浓度非连续变化现象的定量解释

本文利用修正的Darken模型,对合金体系表面偏析浓度随温度和体浓度非连续变化现象给予了定量的解释,并对Cu(111)Ag合金中,表面偏析浓度随银体浓度变化的实验数据进行了拟合,获得了相应的表面偏析参数。     

Pt/Au/p-Si溅射薄膜组织结构特征

在p-Si衬底上,分别淀积5 nm Au膜和5nmPt膜,形成Pt/Au/p-Si结构,500℃退火后形成硅化物薄膜.采用X射线光电子谱和X射线衍射谱研究薄膜成分和相分布,利用原子力显微镜和高分辨电子显微镜观察薄膜表面形貌和界面结构.测试结果表明,薄膜中含有PtSi相和Au相,表面较平坦,PtSi相形成层状结构,Au原子聚集成岛状结构.     

二元合金薄膜的表面偏析

本文评述了广泛应用于描述平衡态和动态偏析的修正Darken模型。该模型首次提出了偏析的驱动力是化学势梯度,并成功地应用于定量描述体块材料的平衡态和动态的表面偏析。在考虑到薄膜体系中的尺寸效应后,引入了一个约束条件,再将其应用于修正的Darken模型,实现了在所有的浓度和薄膜厚度范围内,对合金薄膜体系的平衡态和动态的表面偏析的模拟计算。并利用该模型模拟了N(i111)Cu二元合金薄膜系统的平衡态和动态的表面偏析。     

Cu—Cr—Zr合金强化机理电子理论研究

通过自编软件建立了Cu合金液体、位错、晶界等原子集团模型,采用递归法计算了Cu合金电子结构。研究表明：Y在晶粒、表面、液体的环境敏感镶嵌能依次降低,Y从晶粒内向晶粒表面、液体Cu中扩散。扩散过程中Y原子填补在Cu晶粒表面缺陷处,阻碍Cu原子结晶,同时进入液体中的Y在晶粒周围形成含有高浓度Y的薄层,使晶粒生长受阻,晶粒细化。Sn向位错扩散,抑制Cr的沉淀析出,并能钉扎位错的攀移运动,推迟回复和再结晶。S在晶界偏析,使晶界结合强度降低。偏聚在晶界的S可将合金中的Zr吸附到晶界,使晶界得到强化。Cu晶粒、晶界与位错处的费米能级不同,电子在这些区域之间发生偏移,使合金内产生微电场。微电场对电子产生散射作用,使合金电阻增大。     

双层石墨烯掺杂Pd对CO和NO的气敏特性研究

采用基于密度泛函理论的第一性原理计算方法,研究了AA堆叠型双层石墨烯掺杂Pd原子(Pd/BG)后对气体分子CO和NO的气敏特性和吸附机理.结果表明,Pd原子的掺杂改变了双层石墨烯的电子性质和局部几何结构.Pd原子替代双层石墨烯的一个碳原子后,杂质原子突出层外区域(Po)和突入层间区域(Pi)都可以形成稳定结构,但是突出(Po)构型更有利于气体分子的吸附.对于Po构型,CO和NO吸附在Pd/BG上的最稳定结构是不同的,CO分子与石墨烯表面呈一定夹角,而NO分子近似垂直于石墨烯表面.Pd/BG对NO分子的吸附强于CO分子.气体分子在Po构型上属于化学吸附,而在Pi构型上属于物理吸附.Pd/BG吸附CO和NO气体分子后具有不同的电子性质.Pd/BG体系为半导体性质,在吸附CO气体分子后,转变为金属性,系统无磁性;而在吸附NO气体分子后变为金属性且具有较大磁矩.这种电子性质的变化能够阐明气体分子吸附的敏感程度.研究结果能够为石墨烯基的气体传感器或者探测器提供理论基础和实验指导.     

Dealloying by metallic melt

Dealloying, which commonly involves corrosion processes in aqueous solutions, is a promising technique for preparing functional nanoporous metals. While this technique is ideal for preparing nanoporous noble metals such as of Au, it is not readily applicable to less-noble metals. Here, we propose a novel dealloying method employing a metallic melt, instead of an aqueous solution, as the dealloying liquid for a preparing of nanoporous metals. An atomic interaction among alloy components and metallic melt causes specific component to dissolve out from the alloy solid into the melt with self-organizing nanoporous structure by the remaining component. The dealloying method can be applied for preparation of nanoporous less-noble metal such as of Ti for the development of functional materials such as fluid filters, gas absorption media, and biomaterials.     

Dealloying of Au-Ag thin films with a composition gradient: Influence on morphology of nanoporous Au

Nanoporous Au can be formed by dealloying Au-Ag alloys and, depending on the initial alloy composition, produce a variety of microstructural features. We investigated a wide compositional range and found three regimes, based on initial Au content, that yield varying degrees of dealloying in thin films. Between 22 and 26 at.% Au, dealloying produces nearly pure Au with an open nanoporous structure. However, above 36 at.% Au, only the grain boundaries dealloy, leaving islands of retained Au-Ag alloy. For intermediate compositions, a transitional microstructure results, with final Ag concentration ranging from 50 at.% down to 4 at.%. Film cracking was observed after dealloying, and lower initial Au content correlated with a higher degree of cracking and a higher pore fraction.     

Facile synthesis of metal and alloy nanoparticles by ultrasound-assisted dealloying of metallic glasses

Metal and alloy nanoparticles synthesized by chemical reduction have attracted increasing attention due to their superior physical,chemical,and biological properties.However,most chemical synthesis processes rely on the use of harsh reducing agents and complicated chemical ingredients.Herein,we report a novel reduction-agent-free and surfactant(stabilizer)-free strategy to synthesize Cu,Ag,Au,Cu-Pt,Cu-Au,Cu-Au-Pt-Pd,and Au-Pt-Pd-Cu nanoparticles by ultrasound-assisted dealloying of Mg-based metallic glasses.The formation mechanism of the metal and alloy nanoparticles is revealed by a detailed investigation of sequential intermediate products.We demonstrate that the glass-liquid phase transition of the initially dealloying metallic glasses,together with the synergistic effect of dealloying and ultrasound-driven ligament-breakage of small enough nanoporous intermediates,play key roles in preparing the uniformly dispersed metal and alloy nanoparticles.This approach greatly simplifies the up-scaling synthesis of monometallic and bimetallic nanoparticles,and also provides a general strategy for synthesizing unprecedented multimetallic nanoparticles.     

Performance of Preformed Au/Cu Nanoclusters Deposited on MgO Powders in the Catalytic Reduction of 4‐Nitrophenol in Solution

The deposition of preformed nanocluster beams onto suitable supports represents a new paradigm for the precise preparation of heterogeneous catalysts. The performance of the new materials must be validated in model catalytic reactions. It is shown that gold/copper (Au/Cu) nanoalloy clusters (nanoparticles) of variable composition, created by sputtering and gas phase condensation before deposition onto magnesium oxide powders, are highly active for the catalytic reduction of 4‐nitrophenol in solution at room temperature. Au/Cu bimetallic clusters offer decreased catalyst cost compared with pure Au and the prospect of beneficial synergistic effects. Energy‐dispersive X‐ray spectroscopy coupled with aberration‐corrected scanning transmission electron microscopy imaging confirms that the Au/Cu bimetallic clusters have an alloy structure with Au and Cu atoms randomly located. Reaction rate analysis shows that catalysts with approximately equal amounts of Au and Cu are much more active than Au‐rich or Cu‐rich clusters. Thus, the interplay between the Au and Cu atoms at the cluster surface appears to enhance the catalytic activity substantially, consistent with model density functional theory calculations of molecular binding energies. Moreover, the physically deposited clusters with Au/Cu ratio close to 1 show a 25‐fold higher activity than an Au/Cu reference sample made by chemical impregnation.     

Fabrication of cubic nanocages and nanoframes by dealloying Au/Ag alloy nanoboxes with an aqueous etchant based on Fe(NO3)3 or NH4OH

This paper describes a two-step procedure for generating cubic nanocages and nanoframes. In the first step, Au/Ag alloy nanoboxes were synthesized through the galvanic replacement reaction between Ag nanocubes and an aqueous HAuCl4 solution. The second step involved the selective removal (or dealloying) of Ag from the alloy nanoboxes with an aqueous etchant based on Fe(NO3)3 or NH4OH. The use of a wet etchant other than HAuCl4 for the dealloying process allows one to better control the wall thickness and porosity of resultant nanocages because there is no concurrent deposition of Au. By increasing the amount of Fe(NO3)3 or NH4OH added to the dealloying process, nanoboxes derived from 50-nm Ag nanocubes could be converted into nanocages and then cubic nanoframes with surface plasmon resonance (SPR) peaks continuously shifted from the visible region to 1200 nm. It is also possible to obtain nanocages with relatively narrow SPR peaks (with a full width at half-maximum as small as 180 nm) by controlling the amount of HAuCl4 used for the galvanic replacement reaction and thus the optimization of the percentage of Au in the alloy nanoboxes.     

Enhanced thermal stability of laccase immobilized on monolayer-modified nanoporous Au

Nanoporous Au was fabricated by the dealloying of Au-Ag alloy in nitric acid, and was modified with a self-assembled monolayer (SAM) of 4-aminothiophenol, for the enhancement of high-temperature activity of immobilized laccase. Immobilized laccase exhibited much higher activity than that of free laccase at > 45 °C. SAM surface modification greatly improved the thermal stability and reusability of immobilized laccase. For example, little degradation in laccase activity when immobilized on SAM-modified nanoporous Au was observed after 2 h incubation at 50 °C. This suggested the nanoporous structure and SAM synergistically prevented the conformational change of laccase, and resulted in the enhancement of high-temperature activity.     

First-principles study on the effect and magnetism of iron segregation in Cu grain boundary

The atomic configurations and electronic structures of iron on CuΣ5 symmetrical tilt grain boundary (GB) have been studied based on the density functional theory. Different segregation positions of iron are considered. A weak tendency of iron segregating to GB is arrived due to the segregation energy. In addition, iron segregation shows a cohesion strengthening effect of Cu GB according to Rice–Wang model, which is mainly contributed by the charge redistribution. Finally, an enhancement of the local magnetic moment of iron in Cu GB or bulk or surface is explored due to larger atomic volume than the FCC iron crystal and the Cu atoms surrounding iron are slightly polarized by the doped iron. This study can enrich the understanding of the effects of iron on the cohesion of Cu–Fe alloy and also might supply an indirect guidance to expand the application of Cu–Fe alloy in electronic device manufacture field.     

Preparation and characterization of nanoporous Cu6Sn5/Cu composite by chemical dealloying of Al–Cu–Sn ternary alloy

In this article, a new ternary Al–Cu–Sn alloy system has been exploited to fabricate nanoporous Cu₆Sn₅/Cu composite slices through chemical dealloying in a 20 wt% NaOH solution at an elevated temperature. The microstructure of the sliced nanoporous Cu₆Sn₅/Cu composite was characterized using x-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, and transmission electron microscopy. The experimental results show that multi-phase precursor alloy comprises α-Al, Sn, and θ-Al₂Cu phases. The new phase Cu₆Sn₅ emerges through dealloying, and the as-dealloyed samples have three-dimensional (3D) structure composed of large-sized channels (hundreds of nanometers) and small-sized channels (tens of nanometers). Both the large- and small-sized pores are 3D, open and bicontinuous. The synergetic dealloying of α-Al and θ-Al₂Cu in the three-phase Al–Cu–Sn alloy and fast surface diffusion of Cu atoms and Sn atoms result in the formation of Cu₆Sn₅/Cu composite with bimodal channel size distributions. In addition, the dealloying duration plays a significant role in the formation of Cu₆Sn₅ and the length scales of the small-sized ligament/channels at a settled temperature.     

Defect Effects on TiO2 Nanosheets: Stabilizing Single Atomic Site Au and Promoting Catalytic Properties

Isolated single atomic site catalysts have attracted great interest due to their remarkable catalytic properties. Because of their high surface energy, single atoms are highly mobile and tend to form aggregate during synthetic and catalytic processes. Therefore, it is a significant challenge to fabricate isolated single atomic site catalysts with good stability. Herein, a gentle method to stabilize single atomic site metal by constructing defects on the surface of supports is presented. As a proof of concept, single atomic site Au supported on defective TiO₂ nanosheets is prepared and it is discovered that (1) the surface defects on TiO₂ nanosheets can effectively stabilize Au single atomic sites through forming the Ti–Au–Ti structure; and (2) the Ti–Au–Ti structure can also promote the catalytic properties through reducing the energy barrier and relieving the competitive adsorption on isolated Au atomic sites. It is believed that this work paves a way to design stable and active single atomic site catalysts on oxide supports.     

Intermetallic reactions in a Sn-3.5Ag-1.5In solder ball-grid-array package with Au/Ni/Cu pads

In this paper, the interfacial reactions between Sn-3.5Ag solder and Sn-3.5Ag-1.5In solder and Au/Ni/Cu pads in ball-grid-array (BGA) packages during solid aging were investigated by microstructural observations and phase analysis. During the solid aging, the intermetallic compound (IMC) layer in Sn-3.5Ag/Au/Ni/Cu solder joints evolved from the (Ni, Au)Sn₄ phase to the Ni₃Sn₄ phase, but the rate of growth of the IMC layer did not change significantly. While, in Sn-3.5Ag-1.5In/Au/Ni/Cu solder joints, the phases evolved from the (Ni, Au)Sn₄ and Ni₃Sn₄ phases into Ni₃(Sn, In)₄ phase. The distribution of In atoms in the solder alloy weakened interatomic force in the Sn-3.5Ag-1.5In solder alloy and the involvement of In atoms in the interfacial reaction generated more energy of distortion of the Ni₃(Sn, In)₄ and (Ni, Au)(Sn, In)₄ lattices. These both accelerated the diffusion of Sn atoms and the rate of growth of the whole IMC layer, but this effect reduced gradually after prolonged aging.