共查询到20条相似文献，搜索用时 25 毫秒
1.
J A Zasadzinski J Schneir J Gurley V Elings P K Hansma 《Science (New York, N.Y.)》1988,239(4843):1013-1015
The high resolution of the scanning tunneling microscope (STM) makes it a potentially important tool for the study of biomaterials. Biological materials can be imaged with the STM by a procedure in which fluid, nonconductive biomaterials are replaced by rigid and highly conductive freeze-fracture replicas. The three-dimensional contours of the ripple phase of dimyristoylphosphatidylcholine bilayers were imaged with unprecedented resolution with commercial STMs and standard freeze-fracture techniques. Details of the ripple amplitude, asymmetry, and configuration unobtainable by electron microscopy or x-ray diffraction can be observed relatively easily with the STM. 相似文献
2.
Reetz MT Helbig W Quaiser SA Stimming U Breuer N Vogel R 《Science (New York, N.Y.)》1995,267(5196):367-369
Scanning tunneling microscopy (STM) and high-resolution transmission electron microscopy (TEM) have been used to determine the dimensions of a series of palladium clusters stabilized by tetraalkylammonium salts. Electrochemically prepared colloids were used in which the average diameter of the inner metal core was varied between 2 and 4 nanometers, and the size of the ammonium ions was adjusted in the series (+)N(n-C(4)H(9))(4) < (+)N(n-C(8)H(17))(4) < (+)N(n-C(18)H(37))(4). The difference between the mean diameter determined by STM and that measured by TEM allows the determination of the thickness of the protective surfactant layer. On the basis of these studies, a model of the geometric properties of ammonium-stabilized palladium clusters has been proposed. Suggestions for the mechanism of the STM imaging process are also made. 相似文献
3.
在深入分析电化学腐蚀原理的基础上,发现了一种提高针尖的尖锐程度的新方法,即:利用下端腐蚀方法得到了比传统的上端腐蚀方法更尖锐的针尖.通过对腐蚀电压、腐蚀溶液浓度、切断时间的研究和分析,总结出下端腐蚀法制备纳米级STM探针的最佳综合条件;并通过对前人方案的修改和完善,研制了一套自动控制切断电路装置,该电路装置可以任意设置切断条件,以此得到不同粗细的针尖;最后将据此制作的纳米级针尖成功地应用于Unisoku-STM仪器的扫描,得到了清晰、稳定的原子级分辨Bi(0001)图像. 相似文献
4.
Merte LR Peng G Bechstein R Rieboldt F Farberow CA Grabow LC Kudernatsch W Wendt S Lægsgaard E Mavrikakis M Besenbacher F 《Science (New York, N.Y.)》2012,336(6083):889-893
The diffusion of hydrogen atoms across solid oxide surfaces is often assumed to be accelerated by the presence of water molecules. Here we present a high-resolution, high-speed scanning tunneling microscopy (STM) study of the diffusion of H atoms on an FeO thin film. STM movies directly reveal a water-mediated hydrogen diffusion mechanism on the oxide surface at temperatures between 100 and 300 kelvin. Density functional theory calculations and isotope-exchange experiments confirm the STM observations, and a proton-transfer mechanism that proceeds via an H(3)O(+)-like transition state is revealed. This mechanism differs from that observed previously for rutile TiO(2)(110), where water dissociation is a key step in proton diffusion. 相似文献
5.
Kummel AC 《Science (New York, N.Y.)》2003,302(5642):69-70
Junctions between metals and molecules play an important role in molecular electronics. Advances in this field are hampered by the lack of understanding of the electronic structure of organic-metal interfaces. In his Perspective, Kummel highlights the report by Nazin et al. (3), who have used scanning tunneling microscopy (STM) to assemble a metal-molecule-metal junction. Subsequently, they employed the STM tip to probe the atomic structure and local electronic properties of the metal-molecule interface in unprecedented detail. They find evidence for strong coupling between the molecular and metal states. Such coupling affects the conductivity of metal-molecule-metal junctions. 相似文献
6.
Klimov NN Jung S Zhu S Li T Wright CA Solares SD Newell DB Zhitenev NB Stroscio JA 《Science (New York, N.Y.)》2012,336(6088):1557-1561
We determined the electromechanical properties of a suspended graphene layer by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements, as well as computational simulations of the graphene-membrane mechanics and morphology. A graphene membrane was continuously deformed by controlling the competing interactions with a STM probe tip and the electric field from a back-gate electrode. The probe tip-induced deformation created a localized strain field in the graphene lattice. STS measurements on the deformed suspended graphene display an electronic spectrum completely different from that of graphene supported by a substrate. The spectrum indicates the formation of a spatially confined quantum dot, in agreement with recent predictions of confinement by strain-induced pseudomagnetic fields. 相似文献
7.
A stable high-index surface of silicon, Si(5 5 12), is described. This surface forms a 2 x 1 reconstruction with one of the largest unit cells ever observed, 7.7 angstroms by 53.5 angstroms. Scanning tunneling microscopy (STM) reveals that the 68 surface atoms per 2 x 1 unit cell are reconstructed only on a local scale. A complete structural model for the surface is proposed, incorporating a variety of features known to exist on other stable silicon surfaces. Simulated STM images based on this model have been computed by first-principles electronic-structure methods and show excellent agreement with experiment. 相似文献
8.
Otero R Lukas M Kelly RE Xu W Laegsgaard E Stensgaard I Kantorovich LN Besenbacher F 《Science (New York, N.Y.)》2008,319(5861):312-315
Nonsymmetrical organic molecules adsorbed on solid surfaces may assemble into random networks, thereby providing model systems for organic glasses that can be directly observed by scanning tunneling microscopy (STM). We investigated the structure of a disordered cytosine network on a gold(111) surface created by thermal quenching, to temperatures below 150 K, of the two-dimensional fluid present on the surface at room temperature. Comparison of STM images to density functional theory calculations allowed us to identify three elementary structural motifs (zigzag filaments and five- and six-membered rings) that underlie the whole supramolecular random network. The identification of elementary structural motifs may provide a new framework for understanding medium-range order in amorphous and glassy systems. 相似文献
9.
The various products from the reaction of chlorine (Cl) with the adatom layer of the Si(111)-(7x7) surface have been identified with scanning tunneling microscopy (STM). Initially, a single Cl atom reacts with the adatom dangling bond. At higher surface coverage, additional Cl atoms insert themselves into the Si-Si backbonds between the adatom and rest-atom layers, producing adatoms that have reacted with two or three Cl atoms. These products are characterized by different registries with respect to the underlying rest layer and appear in STM images as adatoms of different sizes, consistent with the breaking of Si-Si backbonds and the formation ofnew Si-Cl bonds. 相似文献
10.
Wachowiak A Yamachika R Khoo KH Wang Y Grobis M Lee DH Louie SG Crommie MF 《Science (New York, N.Y.)》2005,310(5747):468-470
We present a low-temperature scanning tunneling microscopy (STM) study of K(x)C60 monolayers on Au(111) for 3 < or = x < or = 4. The STM spectrum evolves from one that is characteristic of a metal at x = 3 to one that is characteristic of an insulator at x = 4. This electronic transition is accompanied by a dramatic structural rearrangement of the C60 molecules. The Jahn-Teller effect, a charge-induced mechanical deformation of molecular structure, is directly visualized in the K4C60 monolayer at the single-molecule level. These results, along with theoretical analyses, provide strong evidence that the transition from metal to insulator in K(x)C60 monolayers is caused by the Jahn-Teller effect. 相似文献
11.
The structure of model silica-supported copper catalysts has been investigated with scanning tunneling microscopy (STM) and infrared reflection-absorption spectroscopy (IRAS). The IRAS studies of CO on the model silica-supported copper catalysts indicate that there are several types of copper clusters with surface structures similar to (111), (110), and other high-index planes of single-crystal copper. The STM studies show several types of copper clusters on silica and reveal images of metal clusters on an amorphous oxide support with atomic resolution. 相似文献
12.
Negative differential resistance (NDR) is the essential property that allows fast switching in certain types of electronic devices. With scanning tunneling microscopy (STM) and scanning tunneling spectroscopy, it is shown that the current-voltage characteristics of a diode configuration consisting of an STM tip over specific sites of a boron-exposed silicon(111) surface exhibit NDR. These NDR-active sites are of atomic dimensions ( approximately 1 nanometer). NDR in this case is the result of tunneling through localized, atomic-like states. Thus, desirable device characteristics can be obtained even on the atomic scale. 相似文献
13.
Near-atomic resolution images of a two-dimensional heteroepitaxial crystal composed of the relatively "functionally rich" chiral liquid crystal mesogen MDW 74 on graphite have been obtained by scanning tunneling microscopy (STM). This work is aimed at developing an improved understanding of the commercially crucial phenomenon of liquid crystal alignment by studying well-characterized surfaces. Herein is reported molecular-level characterization of the surface underlying a ferroelectric liquid crystal in situ, a requisite starting point for understanding the liquid crystal-solid interface at the molecular level. The results are also important in the context of developing a model for the molecular. origins of the contrast observed in STM images of organic monolayers on conductor surfaces. The data and analysis provide strong evidence that neither frontier orbital alone (highest occupied or lowest unoccupied molecular orbital) is sufficient to describe the observed tunneling efficiency. 相似文献
14.
Scanning tunneling microscopy (STM) studies have demonstrated that monolayer-deep, flat-bottomed, circular etch pits can be grown on highly ordered pyrolytic graphite by high-temperature etching in the presence of oxygen. In this work, these graphite etch pits are used as "molecule corrals" to isolate ensembles of molecules for study by STM. The nucleation of self-assembled molecular films in the corrals took place by nucleation events separate from those leading to self-assembly on the surrounding terrace and allowed the measurement of the nucleation rate constant in the corrals. The dependence of the nucleation rate for self-assembly on pit size shows that nucleation occurs at open terrace sites and that step edges (that is, the corral's perimeter) and confinement inhibit film growth. 相似文献
15.
Boland JJ 《Science (New York, N.Y.)》1993,262(5140):1703-1706
Chlorine atoms strongly chemisorbed at dangling bond sites on the Si(100)-(2 x 1) surface are observed by scanning tunneling microscopy (STM) to hop between adjacent sites. The origin of this behavior is suggested to be an interaction between the field of the probe tip and the dipole moment of the silicon-chlorine bond. Chlorine atom migration is shown to be facilitated by the presence of a metastable chlorine bridge-bonded minimum. The STM probe was used to excite single chlorine atoms into this bridging configuration, resulting in a local population inversion. Selective application of voltage pulses between the probe tip and the surface rearranged the local bonding and induced transformations between different types of chlorine sites. In this manner, adsorbed species can be dissected and their composition and structure directly probed. 相似文献
16.
The structural and electronic effects of lead substitution in the high-temperature superconducting materials Pb(x)Bi(2-x)Sr(2)CaCu(2)O(8) have been characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Large-area STM images of the Bi(Pb)-O layers show that lead substitution distorts and disorders the one-dimensional superlattice found in these materials. Atomic-resolution images indicate that extra oxygen atoms are present in the Bi(Pb)-O layers. STS data show that the electronic structure of the Bi(Pb)-O layers is insensitive to lead substitution within +/-0.5 electron volt of the Fermi level; however, a systematic decrease in the density of states is observed at approximately 1 electron volt above the Fermi level. Because the superconducting transition temperatures are independent of x(Pb) (x 相似文献
17.
Scanning tunneling microscopy (STM) and point-probe electrical conductivity measurements of electrochemically protonated films of the emeraldine-base form of the conducting polymer, polyaniline are reported. The conductivity varies spatially, dependent on the size (L(M) \m=~\ 200 to 300 angstroms) of granular metallic regions which relate directly to the inhomogeneous micromorphology of the electrodeposited films. The normalized conductivity at zero bias is observed to increase with doping, indicating an increase in states at the Fermi level. The STM electronic measurements also show regions of negative differential resistance. Negative differential resistance is observed for all samples, although more frequently on less oxidized samples. 相似文献
18.
Two-dimensional molecular patterns were obtained by the adsorption of long-chain alkanes, alcohols, fatty acids, and a dialkylbenzene from organic solutions onto the basal plane of graphite. In situ scanning tunneling microscopy (STM) studies revealed that these molecules organize in lamellae with the extended alkyl chains oriented parallel to a lattice axis within the basal plane of graphite. The planes of the carbon skeletons, however, can be oriented either predominantly perpendicular to or predominantly parallel with the substrate surface, causing the lamellar lattice to be either in or near registry with the substrate (alkanes and alcohols) or not in registry (fatty acids and dialkylbenzenes). In the case of the alcohols and the dialkylbenzene the molecular axes are tilted by +30 degrees or -30 degrees with respect to an axis normal to the lamella boundaries, giving rise to molecularly well-defined domain boundaries. Fast STM image recording allowed the spontaneous switch between the two tilt angles to be observed in the alcohol monolayers on a time scale of a few milliseconds. 相似文献
19.
Small-diameter (1 to 7 nanometers) silicon nanowires (SiNWs) were prepared, and their surfaces were removed of oxide and terminated with hydrogen by a hydrofluoric acid dip. Scanning tunneling microscopy (STM) of these SiNWs, performed both in air and in ultrahigh vacuum, revealed atomically resolved images that can be interpreted as hydrogen-terminated Si (111)-(1 x 1) and Si (001)-(1 x 1) surfaces corresponding to SiH3 on Si (111) and SiH2 on Si (001), respectively. These hydrogen-terminated SiNW surfaces seem to be more oxidation-resistant than regular silicon wafer surfaces, because atomically resolved STM images of SiNWs were obtained in air after several days' exposure to the ambient environment. Scanning tunneling spectroscopy measurements were performed on the oxide-removed SiNWs and were used to evaluate the electronic energy gaps. The energy gaps were found to increase with decreasing SiNW diameter from 1.1 electron volts for 7 nanometers to 3.5 electron volts for 1.3 nanometers, in agreement with previous theoretical predictions. 相似文献
20.
Mo YW 《Science (New York, N.Y.)》1993,261(5123):886-888
The scanning tunneling microscope (STM) was used to control the configuration of antimony clusters on the (001) surface of silicon. In particular, the STM tip induced a reversible rotation between two orthogonal orientations of individual antimony dimers on the surface. This simple rotation can be explained by an atomic-scale torque exerted on the antimony dimers by the STM tip. The reversibility of this process could provide a basis for making atomic-scale memory cells. 相似文献