吸附原子及二聚物在Ag（111）和Cu（111）表面上的扩散和解离研究

采用分子动力学静态计算的方法分别对Ag、Cu和Ag2、Cu2在Ag（111）和Cu（111）表面上的扩散势垒分别进行了计算,探讨同质和异质以及异质中互换衬底和吸附原子的情况下吸附原子或二聚物在表面上的扩散和解离势垒的特点,并与吸附原子或二聚物与衬底的结合能、匹配关系等进行比较,探讨吸附原子和二聚物的扩散势垒与结合能、失配度等的关系．原子间相互作用采用半经验的EAM势．结果表明：对于同一衬底表面来说,不同的吸附原子或二聚物在表面上的扩散势垒似乎和它们与表面的结合能有关;在不同的衬底表面上,单个吸附原子或二聚物的扩散势垒和它们与衬底的匹配关系关联密切．     

Ag表面对聚乙烯吡咯烷酮的吸附及纳米结构表面选择机制

为了查明Ag纳米线的选择形成机制以及与表面活性剂之间的相互作用，本文采用了基于密度泛函理论的第一性原理方法研究了不同Ag晶面结构在聚乙烯吡咯烷酮(PVP)体系中稳定性及吸附影响.结果表明：PVP分子体系严重影响不同Ag晶面结构的稳定性，对Ag(200)和Ag(111)晶面结构具有选择性.此外，随着PVP分子聚合度的增加，PVP与Ag(200)晶面的结合比Ag(111)更强，这有助于Ag(200)纳米结构的形成.本文从分子和原子的角度查明了长链PVP分子对Ag纳米结构的调控机制主要受PVP分子中的酮基氧与表面Ag原子之间的成键作用，以及PVP与Ag(200)表面之间的范德华力的影响.     

金属配合物表面诱导解离和有序银单原子层形成

报道了乙腈介质中金属有机配合物[(dptap Ag)2](NO3)2(其中dptap为2 (2 吡啶亚氨基) 2H 1,2,4 噻二唑并[2,3 a]吡啶,2 (2 pyridylimino) 2H 1,2,4 thia diazolo[2,3 a]pyridine)在Au(111)表面诱导离解并形成有序银原子层的研究.STM结果显示,经在上述配合物的乙腈溶液中浸泡后,Au(111)表面形成(4×4)的吸附结构,此结构与Ag在Au(111)上较高欠电位下沉积所得到的结果类似.XPS结果证实所形成的吸附层中仅含有银原子.进一步用电动势法测定了[(dptap Ag)2](NO3)2的解离常数,并推测有序银原子层系与金表面相互作用从而诱导配合物的离解及Ag+的还原而形成.量子化学的计算结果与上述实验事实相符.这一表面诱导解离有望拓展至其他合适的有机金属配合物体系,从而发展为一种溶液法制备有序金属吸附层的通用方法.     

Ag在单晶硅(111)基面上的反应润湿与固液界面能计算

采用滴座法研究Ag在高定向生长单晶硅(111)基面上的高温反应润湿行为及固液界面结构.结果表明,Ag/Si(111)润湿体系在1 200℃高温下的最终润湿角为96.7°,呈现不润湿现象,反应润湿界面有Si原子溶解到液态Ag中,但没有新相生成,Si和Ag仍以单质形式存在,因此Ag(l)/Si(s)界面能保持不变.通过计算得到1 200℃下Ag/Si(111)润湿体系的固体表面能和固液界面能分别为565.6和667.1 mJ.m-2.     

覆盖度对S原子在不同过渡金属表面吸附性质影响

采用第一性原理方法对不同覆盖度下S原子在Co(0001)表面吸附能、吸附引起体系表面功函和电子态密度分布变化进行计算并与S/Pd(111)等体系结果进行对比.结果表明:在Co(0001)表面S原子吸附能值随覆盖度增加而降低,在覆盖度1.0 ML时形成S2吸附结构；S原子吸附后体系功函变化和电子态密度分布变化与S/Pd(...     

H和B原子在有序态Ni3Fe表面的吸附

采用基于密度泛函理论(density functional theory,DFT)的第一性原理方法,对H和B原子在有序态Ni3Fe合金(111)表面的吸附进行研究.结果表明,B原子在有序态Ni3Fe合金(111)表面的吸附能远低于H原子,从而更容易被有序态Ni3Fe合金(111)表面吸附,形成稳定结构.这导致H原子在有序态Ni3Fe合金表面的吸附机会大大减少,降低了有序态Ni3Fe合金在氢气中的环境氢脆.进一步的电子结构分析表明,H原子的表面吸附能高于B原子是由于H原子在有序态Ni3Fe合金(111)表面吸附时,H原子的反键态被推到了费米面以上所引起的.     

Si在Si（111）表面吸附过程的分子动力学模拟

利用Tersoff半经验多体相互作用势和分子动力学模拟方法研究了荷能的硅原子在Si(111)表面的吸附过程.对100K时,初始入射动能分别为5,15,25,30eV的硅原子从6个不同位置轰击Si(111)表面进行了模拟,观察到了硅原子在Si(111)表面形成的吸附结构,并讨论了不同入射位置和入射能量对吸附结构的影响.结果表明,硅原子相对于表面不同的局部构型发生不同的碰撞过程,而硅原子入射能量的提高有利于成键过程的发生,从原子尺度模拟了沉积机制.     

体心立方过渡金属低指数表面单空位的改进分析型嵌入原子法模拟

应用改进分析型嵌入原子法(modified analytical embedded-atom method,MAEAM),计算了7种体心立方(body-centered cubic,BCC)过渡金属Fe、W、Mo、Cr、Ta、Nb和V等低指数(100)、(110)和(111)表面前9层上的单空位形成能.结果表明,对每一种金属,单空位形成能在同一低指数表面层中的第1层最低,且在表面第1层和第2层(Nb除外)随表面原子密度的减小而降低,即E(11f11),1相似文献   

单原子合金催化剂热稳定性的反应力场分子动力学研究

通过反应力场(ReaxFF)模型分子动力学模拟,研究了负载模型和掺杂模型单原子催化剂(分别记为M_1/Cu(111)和M_1@Cu(111),M=Pt,Ni,Ag,Fe)的热稳定性.模拟结果显示:对于M_1@Cu(111)掺杂模型,Pt(Ni,Fe)_1@Cu(111)的稳定性远高于Ag_1@Cu(111),温度大于500K时依旧可以保持稳定.而负载模型M_1/Cu(111)除了Fe_1/Cu(111)以外,其余模型在100～500K的温度范围中均无法保持稳定,单个金属原子会在Cu(111)表面迁移并相互聚集最终形成纳米颗粒.同时发现,随着温度的升高,Fe不同于其他金属单原子的烧结过程,会向亚表层扩散,进入合金体相.此外,还优化了Cu/Pt/H/O的力场参数,并研究了H_2气氛对单原子催化剂(SAA)催化剂模型表面稳定性的影响,发现H_2气氛的存在导致M_1@Cu(111)模型稳定性降低.理论模拟结果发现M_1/Cu(111)型SAA催化剂即使在低温下也不是一个很好的候选催化剂,而多数M_1@Cu(111)型催化剂在较高温度下依旧可以保持稳定.     

Ag在Si表面吸附的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法计算优化了Ag原子在硅惯习面Si(111)和Si（220）晶面的最佳吸附位置,并计算了Ag/Si(111)和Ag/Si(220)体系的表面吸附能和表面态电子结构．研究表明:Si基表面Ag原子的最稳定吸附居于Si(220)晶面的穴位,此时的吸附能最低,其值为5.2569eV,属于强化学吸附;同时由于在Ag/Si(220)体系中,Ag-4d轨道和表面态Si-3s、3p轨道电子的强相互作用,以及Ag-4p轨道的电子云强偏向于Si-3s、3p轨道使得体系的能隙宽度变窄,导电性急剧增大．     

银在M-掺杂石墨烯上吸附的第一性原理计算

Graphene is an ideal reinforcing phase for a high-performance composite filler, which is of great theoretical and practical significance for improving the wettability and reliability of the filler. However, the poor adsorption characteristics between graphene and the silver base filler significantly affect the application of graphene filler in the brazing field. It is a great challenge to improve the adsorption characteristics between a graphene and silver base filler. To solve this issue, the adsorption characteristic between graphene and silver was studied with first principle calculation. The effects of Ga, Mo, and W on the adsorption properties of graphene were explored. There are three possible adsorbed sites, the hollow site (H), the bridge site (B), and the top site (T). Based on this research, the top site is the most preferentially adsorbed site for Ag atoms, and there is a strong interaction between graphene and Ag atoms. Metal element doping enhances local hybridization between C or metal atoms and Ag. Furthermore, compared with other doped structures (Ga and Mo), W atom doping is the most stable adsorption structure and can also improve effective adsorption characteristic performance between graphene and Ag.     

保护层Ag对Ag/TbFeCo光学性质的影响

磁光记录介质非晶稀土-过渡金属合金TbFeCo薄膜覆盖Ag保护层可减小稀土元素的氧化且能增强其磁光克尔效应。利用直流磁控溅射法制备出Ag/TbFeCo／Si(100)磁光薄膜,利用可变入射角椭圆偏振光谱仪测量了其可见光区的光学常数,给出薄膜介电函数实部和虚部随入射光子能量的变化规律,同时把Ag／Si、Ag／TbFeCo／Si和TbFeCo／Si的光谱进行了比较。实验结果与经典的Drude模型相一致,而且Ag／TbFeCo／Si的光谱更接近Ag。不同厚度Ag/TbFeCo／Si薄膜其光学参数变化趋势相同,且随Ag厚度的增加变化幅度减小。     

银纳米杆中原子能量分布特征的分子动力学研究

采用分子动力学方法和嵌入原子法（EAM）多体势函数,模拟研究了银纳米杆能量分布特征在不同温度直到熔化过程中的变化。结果显示：纳米杆中原子的势能分布曲线呈现多个分立的峰;随着温度的变化,分布曲线各个峰的位置保持不变,但峰高和峰宽明显变化;纳米杆熔化后这种能量分布特征完全消失,只有一个宽化的峰。模拟结果分析表明：纳米杆中原子势能分布曲线中每个峰对应于一定的最近邻原子数,纳米杆中每个原子的势能所处峰位由其最近邻原子数决定,偏离峰值程度则由其次近邻原子数决定。     

Mechanism of Ag and Al on improving the glass forming ability of CuZr-based alloys

By a mean field theoretical computation,the equilibrium distributions of additional Ag and Al in the crystalline phase of CuZr-based alloys were determined to occupy the two sublattices of the B2 structure randomly.With the molecular dynamics technique,the effects of Ag and Al on the enthalpy difference(ΔH) between the supercooled melt and the crystalline phase were evaluated.The improved glass forming ability of Cu45Zr45Al10 and Cu45Zr45Ag10 can be attributed to their remarkably smaller ΔH than that of CuZr.The calculated diffusion coefficients are more sensitive to the atomic weight of the component atoms than to their interaction strength.As the component atom with the largest mass,the additional Ag increases the viscosity of the supercooled melt significantly and the experimentally stronger glass formation ability of Cu45Zr45Ag10 than Cu45Zr45Al10 can be well understood.     

高密度有序银纳米球阵列的模板辅助退火制备

纳米结构的有序性对表面拉曼增强光谱（SERS）的均匀性起决定性作用,然而如何大面积制备有序的超高密度贵金属纳米结构依旧是个挑战. 文中提出了一种通过模板辅助退火方法,用于大面积制备结构可控、高密度有序的银纳米球阵列,研究了退火温度、压强和银膜厚度对银纳米球阵列形貌结构的影响. 制备的高密度有序银纳米球阵列可以进一步应用于SRES基底.     

Epitaxial growth of Fe/Ag single crystal superlattices and their magnetic properties

Single crystal Fe/Ag(001) superlattices with various periodicities were fabricated using ultrahigh vacuum evaporation deposition. It was found that single crystal bcc Fe layers and single crystal fcc Ag layers can epitaxially grow on a single crystal Ag buffer layer alternately, which was deposited on NaCl single crystal chips by ion beam assisted deposition. The magnetic measurements of the superlattices reveal an oscillation coupling between ferromagnetism and antiferromagnetism as a function of the Ag layer thickness. The oscillation period, which is 1 nm (5 Ag layers), is in good agreement with the calculated values when the Ag thickness is greater than 1.5 nm. While the thickness of the Ag spacer layer decreases to 1 nm, the oscillation coupling varies from calculations, which can be attributed to the intermixing of the interlayers according to the annealing results.     

Au, Ag and Au:Ag colloidal nanoparticles synthesized by pulsed laser ablation as SERS substrates

Chemically pure colloidal suspensions of gold and silver nanoparticles were synthesized using pulsed laser ablation.The dependence of laser fl uence on the surface plasmon characteristics of the nanoparticles was investigated.Au:Ag colloidal suspensions were prepared by mixing highly monodisperse Au and Ag nanocolloids.The plasmon band of these mixtures was found to be highly sensitive to Au:Ag concentration ratio and wavelength of the laser beam used in the ablation process.The Au:Ag mixture consists of almost spherical shaped nanostructures with a tendency to join with adjacent ones.The surface enhanced Raman scattering activity of the Au,Ag and Au:Ag colloidal suspensions was tested using crystal violet as probe molecules.Enhancement in Raman signal obtained with Au:Ag substrates was found to be promising and strongly depends on its plasmon characteristics.     

Structure of Ag/Bi multilayers

Conclusion The structure of Ag/Bi prepared by the ion beam sputtering technique is studied by using X-ray diffraction. The longer the modulation period, the more the modulation peaks. This is because a deposition layer can “heal” the roughness of the previous layer, and by lengthening the modulation period, the ability of ”healing” may be reinforced. The internal structures in Ag/Bi multilayers whose substrate is cooled by liquid nitrogen are found to consist of nanocrystalline Ag and Bi; however, the internal structure in multilayers cooled by cooling water is composed of polycrystalline sublayers. The deposition temperature has no effect on interfacial roughness.     

化学法在Ni-W基带上制备Ag缓冲层研究

在双轴织构的Ni-W基带上,采用化学镀银法为YBa2Cu3O7-δ(YBCO)涂层导体制备Ag缓冲层薄膜,并通过XRD和φ扫描研究烧结温度和镀银次数对Ag薄膜取向的影响。结果表明,在Ar-H2混合气氛下,于870℃镀银5次所制备的薄膜具有(200)晶面单一取向;采用化学法制备的Ag薄膜有较好的外延性,且适用于涂层导体中的单一导电型缓冲层。     

Height measurement of DNA molecules with lift mode AFM

Atomic force microscopy (AFM) can be used to im-age and study the local properties of the sample surfacethrough tip/sample interactions. There are three operationmodes: contact mode, non-contact mode and tappingmode. Mostly, the measured heights of dsDNA were only0.7—0.8 nm[1—8] in air by tapping mode atomic force mi-croscopy (TMAFM), which were much less than the gen-erally accepted diameter of 2.0—2.2 nm[9]. In TMAFM, stable imaging is available when the tip is closer to sample surf…