Electromagnetic coupling on an atomic scale

Light emission from a scanning tunneling microscope is used to investigate the electromagnetic coupling (EMC) of a metal tip and a metal sample. Subatomic scale modifications of the tip-sample region cause spectral shifts of the fluorescence as demonstrated for a monatomic step and by variation of the tip-sample distance. For sharp tips the EMC is confined to a lateral range of a few nm. The results are consistent with model calculations of the electromagnetic response of an appropriate tip-sample geometry.     

原子尺度上的异质催化

现实中的催化剂是个相当复杂的系统体系，且为粉末状，限制了多种表面科学表征手段的应用,科学家通过建立简化的催化剂模型，充分利用目前多种有力的科技分析手段，如扫描隧道显微镜（STM）、透射电镜（TEM）、光电子能谱（XPS）、傅里叶变换红外吸收谱（FTIR）、电子能量损失谱（EELS）等，直观地在原子尺度上研究催化反应的机理，从而使得人们能够设计出选择性能更高、催化性能更好的催化剂．     

原子尺度上的异质催化

现实中的催化剂是个相当复杂的系统体系,且为粉末状,限制了多种表面科学表征手段的应用.科学家通过建立简化的催化剂模型,充分利用目前多种有力的科技分析手段,如扫描隧道显微镜(STM)、透射电镜(TEM)、光电子能谱(XPS)、傅里叶变换红外吸收谱(FTIR)、电子能量损失谱(EELS)等,直观地在原子尺度上研究催化反应的机理,从而使得人们能够设计出选择性能更高、催化性能更好的催化剂.     

原子尺度上水与物质的相互作用

水是生命活动和工业生产的重要组成部分,而水与物质表面的相互作用是其发挥功能的重要途径。人们通过大量研究发现,在原子尺度上,水与物质的相互作用会导致很多反常的物理现象,从而影响到水体系的宏观性质。文章简述了近年来作者所在的研究组对水与物质在原子尺度上的相互作用的部分研究进展,主要包括分子扩散导致的表面超亲水—超疏水转变、晶格常数改变诱导的反常浸润机制,石墨炔纳米孔中水的量子化传输,以及等离激元诱导的水分解等。     

The atomic scale modelling of nanomaterials

Atomic scale modelling of various nano-clusters has been performed. Amorphous/crystalline transition has been modelled in phase change memory materials. The modelling gives the possibility to select the physically realistic configurations, to be prepared and applied in nano-devices.     

Electromagnetic coupling at an atomic scale

We report the first spectrally resolved measurements of scanning tunnelling microscope induced fluorescence from monatomic steps. As a function of lateral distance from the step edge, on a sub nanometre scale, increasingly large red (blue) shifts of the emission are observed as the tip approaches the lower (upper) step edge.     

Interface of transition metal oxides at the atomic scale

Remarkable phenomena arise at well-defined heterostructures, composed of transition metal oxides, which is absent in the bulk counterpart, providing us a paradigm for exploring the various electron correlation effects. The functional properties of such heterostructures have attracted much attention in the microelectronic and renewable energy fields. Exotic and unexpected states of matter could arise from the reconstruction and coupling among lattice, charge, orbital and spin at the interfaces. Aberration-corrected scanning transmission electron microscopy (STEM) is a powerful tool to visualize the lattice structure and electronic structure at the atomic scale. In the present study some novel phenomena of oxide heterostructures at the atomic scale are summarized and pointed out from the perspective of electron microscopy.     

HREM study of the YBCO/MgO interface on an atomic scale

The film-substrate interface of c oriented YBCO thin films grown by sputtering or laser ablation on (001) MgO substrate has been investigated with high-resolution electron microscopy. The first atomic plane of the YBCO lattice is a CuO chain layer. Two interface configurations occur: (1) the YBCO lattice and the MgO lattice continue up to the interface (this configuration is occasionally associated with some periodic strain in the MgO lattice; (2) the YBCO lattice and the MgO lattice are separated by an (almost) amorphous layer with a thickness of the order of two atomic layers. This amorphous layer is found to lead to the absence of strain. In some cases the surface roughness coincided with misoriented grains but most of the steps in the MgO substrate were accommodated by steps in the YBCO of one or more complete unit cells in height and some lattice bending in the YBCO film.     

Evaluation of the magnetic dipolar fields from layered systems on atomic scale

Exact analytical expressions for the magnetic dipolar fields produced by a plane square lattice with localized magnetic moments are derived. Basing on these expressions surface roughness of a magnetic thin film is considered. Influence of the bipolar fields on the surface anisotropy and hyperfine fields is discussed.     

The atomic scale structure of saccharose-based carbons

Abstract

Activated carbons (ACs) have a wide range of applications, in which the largely expanded specific surface plays a major role. The question of their structure came back to the limelight with the discovery of nanotubes fullerenes, which suggested that curved surfaces may be present in their structure and which incorporates well into the ideas of ACs porous structure. The source of those curved surfaces is atomic defects present inside the in-plane graphitic honeycomb lattice. Such defects have a crucial influence on the macroscopic morphology as well as physical properties of the material. The activated carbon (AC) in this work was derived from carbonised saccharose by activation with NaOH. Both materials – before and after activation were investigated. The main methods used in this study are wide angle neutron scattering and wide angle X-ray scattering combined with computer simulations. Confirmation of the proposed structures was sought with high-resolution transmission electron microscopy and Raman scattering. In this case, the use of classical crystallography to interpret experimental data was impossible due to the lack of periodic three-dimensional symmetry. Due to this fact, the data was analysed both in real and reciprocal space in the form of a pair correlation function and a structure factor. The experimental data were compared with calculated atomistic models. As a validation, the discrepancy factor between the theoretically and experimentally obtained functions was used. The presented innovative approach can be applied to different carbon materials with varying degrees of disorder.     

Three-dimensional atomic scale analysis of nanostructured materials

The 3-dimensional atom probe (3DAP) has been used to provide atomic-scale microcharacterisation of a number of nanostructured materials. Grain boundary segregation has been investigated in electrodeposited nanocrystalline nickel and Ni-P. In the nanocrystalline nickel, there was no observable grain boundary segregation in the as-deposited condition. After annealing, carbon and sulphur contamination was found at the boundary of an abnormally-grown grain. In the as-deposited Ni-P alloy, only limited grain boundary segregation of P is seen, but annealing produces significant segregation and the formation of Ni₃P precipitates at grain boundaries. The phase chemistry in a melt-spun amorphous Fe-Si-Cu-Nb-B-Al (FINEMET-type) alloy has also been studied, and the hetereogeneous nucleation of Fe-Si nanocrystals at Cu precipitates shown conclusively. It is found that at early stages of crystallisation, there is only limited partitioning of the Si between the nanocrystals and the amorphous matrix. Atom probe studies of thin layered films have historically been limited by specimen preparation problems, but recent advances have now yielded data on metallic multilayer films. This has allowed atomic-scale measurements of interface chemistry in these films for the first time.     

Direct measurement of intrinsic atomic scale magnetostriction

Using differential x-ray absorption spectroscopy (DiffXAS) we have measured and quantified the intrinsic, atomic-scale magnetostriction of Fe81Ga19. By exploiting the chemical selectivity of DiffXAS, the Fe and Ga local environments have been assessed individually. The enhanced magnetostriction induced by the addition of Ga to Fe was found to originate from the Ga environment, where lambda;{gamma,2}( approximately (3/2)lambda_{100}) is 390+/-40 ppm. In this environment, 001 Ga-Ga pair defects were found to exist, which mediate the magnetostriction by inducing large strains in the surrounding Ga-Fe bonds. For the first time, intrinsic, chemically selective magnetostrictive strain has been measured and quantified at the atomic level, allowing true comparison with theory.     

Tunable magnetic interaction at the atomic scale in oxide heterostructures

We report on a systematic study of a number of structurally identical but chemically distinct transition metal oxides in order to determine how the material-specific properties such as the composition and the strain affect the properties at the interface of heterostructures. Our study considers a series of structures containing two layers of ferromagnetic SrRuO?, with antiferromagnetic insulating manganites sandwiched in between. The results demonstrate how to control the strength and relative orientation of interfacial ferromagnetism in correlated electron materials by means of valence state variation and substrate-induced strain, respectively.     

新型轻质储氢材料的第一性原理原子尺度设计

综述了近几年涌现出的一批新型轻质储氢材料,包括：碳纳米管、金属有机框架多孔材料、Al/B系复杂氢化物、金属-氮-氢系、金属有机复合物等,对其中采用第一性原理研究所取得的成果和最新的进展做了介绍,并结合实验结果做了应用分析.总结了各轻质储氢材料关联,为各种储氢材料设计之间提供了可以相互借鉴的方法,以便发展新的研究思路. 关键词： 储氢材料 第一性原理 从头算 密度泛函理论     

Evidence for contact delocalization in atomic scale friction

We analyze an advanced two-spring model with an ultralow effective tip mass to predict nontrivial and physically rich "fine structure" in the atomic stick-slip motion in friction force microscopy (FFM) experiments. We demonstrate that this fine structure is present in recent, puzzling experiments. This shows that the tip apex can be completely or partially delocalized, thus shedding new light on what is measured in FFM and, possibly, what can happen with the asperities that establish the contact between macroscopic sliding bodies.     

Investigation on quenching at a high-angle Cu grain boundary on an atomic scale

We have performed molecular dynamics simulations of structural changes due to quenching the melting interface at a Cu $\Sigma $5(310)/[001] symmetrical tilt grain boundary. The simulation results suggest that the grain boundary structures due to quenching are different from those due to heating up to the same temperature. The calculated atom density profiles show that the grain boundary structures can be significantly changed as they are quenched to quite low temperatures.     

Graphene on Ru(0001): contact formation and chemical reactivity on the atomic scale

Graphene on Ru(0001) is contacted with Au tips of a cryogenic scanning tunneling microscope. The formation and conductance of single-atom contacts vary within the moiré unit cell. Density functional calculations reveal that elastic distortions of the graphene lattice occur at contact due to a selectively enhanced chemical reactivity of C atoms at hollow sites of Ru(0001). Concomitant quantum transport calculations indicate that the graphene-Ru distance determines the conductance variations.