Effect of the interfacial electric field on the HER on Pt(111)modified with iron adatoms in alkaline media

The study of the hydrogen evolution reaction(HER)aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen production as an energy vector in the so-called hydrogen economy.In previous works,laser-induced temperature jump(LITJ)experiments on Pt(111)modified with Ni(OH)_(2)in alkaline media have revealed the importance of the interfacial electric field in the rate of the HER.It was hypothesised that small amounts of Ni(OH)_(2)cause a decrease of the electric field because of a negative shift of the pzfc toward the onset of the hydrogen evolution.In this work,to test the validity of this hypothesis,the study has been extended to Pt(111)surfaces modified with Fe(OH)_(2).The modified surfaces have been studied voltammetrically,and the voltammetric charges have been analysed.The voltammograms show a peak in the hydrogen evolution region that suggest the transformation in the adlayer from Fe(II)to Fe(0).In agreement with the coulometric analysis,the voltammetric features in the OH adsorption region would be related with the oxidation to the+3 valence state.The results obtained with LITJ method reflect the existence of a strong interaction of the Fe oxophilic species with the water molecules,shifting the potential of maximum entropy away from the onset of the HER.Hence,the most catalytic surface is the one with the lowest Fe coverage.

Influence of Pb adatom on adsorption of oxygen molecules on Pb(111) surface:a first-principles study

Using first-principles calculations, we systematically study the influence of Pb adatom on the adsorption and the dissociation of oxygen molecules on Pb（111） surface, to explore the effect of a point defect on the oxidation of the Pb（111） surface. We find that when an oxygen molecule is adsorbed near an adatom on the Pb surface, the molecule will be dissociated without any obvious barriers, and the dissociated 0 atoms bond with both the adatom and the surface Pb atoms. The adsorption energy in this situation is much larger than that on a clean Pb surface. Besides, for an adsorbed oxygen molecule on a clean Pb surface, a diffusing Pb adatom can also change its adsorption state and enlarge the adsorption energy for O, but it does not make the oxygen molecule dissociated. And in this situation, there is a molecule-like PbO2 cluster formed on the Pb surface.

Adsorptions of metal adatoms on graphene-like BC3 and their rich electronic properties： A first-principles study

Density functional calculations have been performed to investigate the adsorption of twenty two different kinds of metal adatoms on graphene-like BC3. In contrast to the graphene adsorbed with adatoms, the BC3 with adatoms shows many interesting properties.（1） The interaction between the metal adatoms and the BC3 sheet is remarkably strong. The Li, Na, K, and Ca possess the binding energies larger than the cohesive energies of their corresponding bulk metals.（2）The Li, Na, and K adatoms form approximately ideal ionic bonds with BC3, while the Be, Mg, and Ca adatoms form ionic bonds with BC3 with slight hybridization of covalent bonds. The Al, Ga, In, Sn, and all transition metal adatoms form covalent bonds with BC3.（3） For all the structures studied, there exhibit metal, half-metal, semiconducting, and spin-semiconducting behaviors. Especially, the BC3 with Co adatom shows a quantum anomalous Hall（QAH） phase with a Chern number of -1 based on local density approximation calculations.（4） For Li, Na, K, Ca, Ga, In, Sn, Ti, V, Cr,Ni, Pd, and Pt, there exists a trend that the adatom species with lower ionization potential have lower work function. Our results indicate the potential applications of functionalization of BC3 with metal adatoms.

Topological Transition in Monolayer Blue Phosphorene with Transition-Metal Adatom under Strain

We carried out first-principles calculations to investigate the electronic properties of the monolayer blue phosphorene(BlueP)decorated by the group-IVB transition-metal adatoms(Cr,Mo and W),and found that the Cr-decorated BlueP is a magnetic half metal,while the Mo-and W-decorated BlueP are semiconductors with band gaps smaller than 0.2 eV.Compressive biaxial strains make the band gaps close and reopen,and band inversions occur during this process,which induces topological transitions in the Mo-decorated BlueP(with strain of-5.75%)and W-decorated BlueP(with strain of-4.25%)from normal insulators to topological insulators(TIs).The TI gap is 94 meV for the Mo-decorated BlueP and218 me V for the W-decorated BlueP.Such large TI gaps demonstrate the possibility to engineer topological phases in the monolayer BlueP with transition-metal adatoms at high temperature.

Molecular dynamics simulation of nanoscale surface diffusion of heterogeneous adatoms clusters

Molecular dynamics simulation employing the embedded atom method potential is utilized to investigate nanoscale surface diffusion mechanisms of binary heterogeneous adatoms clusters at 300 K, 500 K, and 700 K. Surface diffusion of heterogeneous adatoms clusters can be vital for the binary island growth on the surface and can be useful for the formation of alloy-based thin film surface through atomic exchange process. The results of the diffusion process show that at 300 K, the diffusion of small adatoms clusters shows hopping, sliding, and shear motion; whereas for large adatoms clusters（hexamer and above）, the diffusion is negligible. At 500 K, small adatoms clusters, i.e., dimer, show almost all possible diffusion mechanisms including the atomic exchange process; however no such exchange is observed for adatoms clusters greater than dimer. At 700 K, the exchange mechanism dominates for all types of clusters, where Zr adatoms show maximum tendency and Ag adatoms show minimum or no tendency toward the exchange process. Separation and recombination of one or more adatoms are also observed at 500 K and 700 K. The Ag adatoms also occupy pop-up positions over the adatoms clusters for short intervals. At 700 K, the vacancies are also generated in the vicinity of the adatoms cluster,vacancy formation, filling, and shifting can be observed from the results.

Pits and adatoms at the interface of 1-ML C_(84)/Ag(111)

We prepare a well-defined C84 monolayer on the surface of Ag （111） and study the geometric structure by scanning tunneling microscopy （STM）. The C84 molecules form a nearly close-packed incommensurate R30° lattice. The lattice is long-distance ordered with numerous local disorders. The monolayer exhibits complex bright/dim contrast; the largest height difference between the molecules can be greater than 0.4 nm. Annealing the monolayer at 380 ℃ can desorb part of the molecules, but more than sixty percent molecules stay on the Ag （111） surface even after the sample has been annealed at 650 ℃. Our analyses reveal that the 7-atom pits form beneath many molecules. Some other molecules sit at the 1-atom pits. Ag adatoms （those removed substrate atoms, accompanying the pit formation） play a very important role in this system. The adatoms can either stabilize or destabilize the monolayer, depending on the distribution manner of the adatoms at the interface. The distribution manner is determined by the co-play of the following factors： the dimension of the interstitial regions of the C84 overlayer, the number of the adatoms, and the long-distance migration of part adatoms.

Oxygen adatoms and vacancies on the (110) surface of CeO2

The behavior of oxygen on ceria surfaces is closely related with the applications of ceria as a catalyst and oxygen conductor in solid-oxide fuel cells. Here, the atomic configurations of oxygen adatoms and vacancies on the(110) surface of CeO_2 have been studied combining aberration-corrected transmission electron microscopy and first-principles calculations. The oxygen adatoms were estimated to be located on top of Ce atoms with 50% coverage, forming a c(2×2) reconstruction. The oxygen vacancies can form stable configuration, with the Ce atoms partly reduced.

Anomalously enhanced thermal stability of phosphorene via metal adatom doping: An experimental and first-principles study

Atomically thin black phosphorus, also known as phosphorene, is an emerging two-dimensional (2D) material, which has attracted increasing attention due to its unique electronic and optoelectronic properties. However, the reduced thermal stability of phosphorene limits its suitability for high-temperature fabrication processes, which could be detrimental for the performance of phosphorenebased devices. Here, we investigate the impact of doping by Al and Hf transition metal adatoms on the thermal stability of phosphorene. The formation of Al–P covalent bonds was found to significantly improve the thermal coefficients of the Ag1, B2g, and Ag2phonon modes to 0.00044, 0.00081, and 0.00012 cm–1·°C–1, respectively, which are two orders of magnitude lower than those observed for pristine P–P bonds (~0.01 cm–1·°C–1). First-principles calculations within the density functional theory framework reveal that the observed thermal stability enhancement in the Al-doped material reflects a significantly higher Al binding energy, due to the stronger Al–P bonds compared to the weak van der Waals interactions between adjacent P atoms in the undoped material. The present work thus paves the way towards phosphorene materials with improved structural stability, which could be promising candidates for potential nanoelectronic and optoelectronic applications. [Figure not available: see fulltext.] © 2016, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.

吸附缺陷对armchair型石墨烯纳米条带输运性质的影响

本文基于第一性原理研究了单个氢原子吸附缺陷对armchair型石墨烯纳米条带电子输运性质的影响。研究发现,吸附缺陷使armchair型石墨烯纳米条带在费米面附近的导电性有所降低,但透射能隙依然存在。缺陷对透射抑制的强弱与其吸附位置有关。在完整石墨烯纳米条带的布洛赫波函数分布几率较大处引入缺陷对电子输运的阻碍作用较大。对于布洛赫波函数分布相同的情况,吸附位置越靠近石墨烯纳米条带中心,则对电子输运的阻碍作用越大。

Tailoring the Self-assembly of Melamine on Au（111） via Doping with Cu Atoms

The doping effect of Cu on the self-assembly film of melamine on an Au（111） surface has been investigated with scanning tunneling microscopy （STM）. The evaporated Cu adatoms occupy the positions underneath the amino groups and change the hydrogen bonding pat- tern between the melamine molecules. Accordingly, the self-assembly structure has changed stepwise from a well-defined honeycomb into a track-like and then a triangular structure depending on the amount of Cu adatoms. The interaction between Cu adatom and melamine is moderate thus the Cu adatoms can be released upon mild heating to around 100 ℃. These findings are different from previous observations of either the coordination assembly or the physically trapped metal adatoms.

Transport properties of zigzag graphene nanoribbons adsorbed with single iron atom

We have performed density-functional calculations of the transport properties of the zigzag graphene nanoribbon （ZGNR） adsorbed with a single iron atom. Two adsorption configurations are considered, i.e., iron adsorbed on the edge and on the interior of the nanoribbon. The results show that the transport features of the two configurations are similar. However, the transport properties are modified due to the scattering effects induced by coupling of the ZGNR band states to the localized 3d-orbital state of the iron atom. More importantly, one can find that several dips appear in the transmission curve, which is closely related to the above mentioned coupling. We expect that our results will have potential applications in graphene-based spintronic devices,

载能Ni原子斜入射Pt(111)表面的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,利用分子动力学模拟,详细研究不同角度入射的载能Ni原子在Pt(111)基体表面的沉积过程.结果表明,随着入射角度θ从0°增加到80°,溅射产额、表面吸附原子产额、空位产额的变化情况均可按入射角度近似地分为θ≤20°,20°<θ<60°和θ≥60°三个区域.当θ≤20°时,载能沉积对基体表面的影响与垂直入射时的情况类似,表面吸附原子的分布较为集中,入射原子容易达到基体表面第二层及以下,对基体内部晶格产生一定的影响;在20°<θ<60°的范围内,入射原子的注入深度有所下降,对基体内部晶格的影响减小,表面吸附原子的分布较为均匀,有利于薄膜的均匀成核与层状生长;当θ≥60°时,所有入射原子均直接被基体表面反射,表面吸附原子产额、溅射产额、表面空位产额均接近0,载能沉积作用没有体现.

铜合金表层原子胞体运动的类液振荡模拟

用流体模型对铜合金表层在常温常压下出现的原子胞体的运动进行模拟分析,结果表明,这类由原子堆积而成的胞体的运动具有明显的类液振荡行为.当内摩擦增强时,波胞振幅按指数规律随时间衰减.理论分析与实验符合较好.在合金及非金属表层上都观测到了这种类液振荡花样,可以认为,固体表层上出现的这类原子位形有一定的普遍性.

固体表面动态现象的研究进展

总结了近年来国内外固体表面动态现象研究的最新进展,其中包括金属和半导体表面原子岛的塌落现象、金属和半导体表面台阶波动、半导体表面特异集团的跳跃、金属袁面非线性振荡现象及其它一些动态现象;描述了这些动态现象特征及形成机制,并展望了动态现象的研究方向和应用前景。

生长温度和表面增原子对外延薄膜中失配位错形成的影响

用分子动力学方法模拟了三维外延铝薄膜晶体中温度和表面增原子对失配位错形成的影响,采用的原子间相互作用势是嵌入原子法(EAM)多体势。模拟再现了薄膜中位错形成过程,结果分析表明:较高的温度和表面增原子团存在对薄膜中失配位错形成都有促进或诱发作用;模拟中观察到两种不同的位错形核过程:一种是经历多余半原子面挤出过程而直接得到一个全位错,另一种是先形成由两个部分位错夹着一片层错的扩展位错,之后才得到全位错,这两个位错的伯格斯矢量都是与失配方向平行的刃型位错。

Growth and characterization of straight InAs/GaAs nanowire heterostructures on Si substrate

Vertical InAs/GaAs nanowire （NW） heterostructures with a straight InAs segment have been successfully fabricated on Si （111） substrate by using AlGaAs/GaAs buffer layers coupled with a composition grading InGaAs segment. Both the GaAs and InAs segments are not limited by the misfit strain induced critical diameter. The low growth rate of InAs NWs is attributed to the AlGaAs/GaAs buffer layers which dramatically decrease the adatom diffusion contribution to the InAs NW growth. The crystal structure of InAs NW can be tuned from zincblende to wurtzite by controlling its diameter as well as the length of GaAs NWs. This work helps to open up a road for the integration of high-quality III-V NW heterostructures with Si.

Simple statistical model for predicting thermal atom diffusion on crystal surfaces

A simple model based on the statistics of single atoms is developed to predict the diffusion rate of thermal atoms in （or on） bulk materials without empirical parameters. Compared with vast classical molecular-dynamics simulations for predicting the self-diffusion rate of Pt, Cu, and Ar adatoms on crystal surfaces, the model is proved to be much more accurate than the Arrhenius law and the transition state theory. Applying this model, the theoretical predictions agree well with the experimental values in the presented paper about the self-diffusion of Pt （Cu） adatoms on the surfaces.

Density behaviors of Ge nanodots self-assembled by ion beam sputtering deposition

Self-assembled Ge nanodots with areal number density up to 2.33× 1010 cm-2 and aspect ratio larger than 0.12 are prepared by ion beam sputtering deposition. The dot density, a function of deposition rate and Ge coverage, is observed to be limited mainly by the transformation from two-dimensional precursors to three-dimensional islands, and to be associated with the adatom behaviors of attachment and detachment from the islands. An unusual increasing temperature dependence of nanodot density is also revealed when a high ion energy is employed in sputtering deposition, and is shown to be related to the breaking down of the superstrained wetting layer. This result is attributed to the interaction between energetic atoms and the growth surface, which mediates the island nucleation.

Structural,electronic,and magnetic properties of vanadium atom-adsorbed MoSe2 monolayer

Using the first-principles calculations, we study the structural, electronic, and magnetic properties of vanadium adsorbed MoSe_2 monolayer, and the magnetic couplings between the V adatoms at different adsorption concentrations. The calculations show that the V atom is chemically adsorbed on the MoSe_2 monolayer and prefers the location on the top of an Mo atom surrounded by three nearest-neighbor Se atoms. The interatomic electron transfer from the V to the nearestneighbor Se results in the polarized covalent bond with weak covalency, associated with the hybridizations of V with Se and Mo. The V adatom induces local impurity states in the middle of the band gap of pristine MoSe_2, and the peak of density of states right below the Fermi energy is associated with the V- dz^2 orbital. A single V adatom induces a magnetic moment of 5 μBthat mainly distributes on the V-3d and Mo-4d orbitals. The V adatom is in high-spin state, and its local magnetic moment is associated with the mid-gap impurity states that are mainly from the V-3d orbitals. In addition,the crystal field squashes a part of the V-4s electrons into the V-3d orbitals, which enhances the local magnetic moment.The magnetic ground states at different adsorption concentrations are calculated by generalized gradient approximations（GGA） and GGA＋U with enhanced electron localization. In addition, the exchange integrals between the nearest-neighbor V adatoms at different adsorption concentrations are calculated by fitting the first-principle total energies of ferromagnetic（FM） and antiferromagnetic（AFM） states to the Heisenberg model. The calculations with GGA show that there is a transition from ferromagnetic to antiferromagnetic ground state with increasing the distance between the V adatoms. We propose an exchange mechanism based on the on-site exchange on Mo and the hybridization between Mo and V, to explain the strong ferromagnetic coupling at a short distance between the V adatoms. However, the ferromagnetic exchange mechanism is sensitive to both the increased inter-adatom distance at low concentration and the enhanced electron localization by GGA＋U, which leads to antiferromagnetic ground state, where the antiferromagnetic superexchange is dominant.

钯原子修饰的金纳米颗粒乙醇氧化电催化剂(英文)

钯催化剂对碱性溶液的乙醇电催化氧化反应表现较好的催化活性.本文通过简单的化学沉积法,将钯原子成功修饰到金纳米颗粒表面,制备的催化剂对乙醇电催化氧化反应表现出比钯更好的催化性能.研究发现,钯原子不均匀地覆盖在金核表面,部分金原子暴露在外层.制备的催化剂的峰电流密度是钯催化剂的4.6倍,起始电势低100 m V.该催化剂较好的催化性能可能归因于金核的电子效应和表面双功能电催化反应机制.