共查询到20条相似文献，搜索用时 78 毫秒
1.
We analyzed the transport of ballistic electrons through organic molecules on uniformly flat surfaces of bismuth grown on silicon. For the fullerene C60 and for a planar organic molecule (3,4,9,10-perylene-tetracarboxylic acid dianhydride), the signals revealed characteristic submolecular patterns that indicated where ballistic transport was enhanced or attenuated. The transport was associated to specific electronic molecular states. At electron energies of a few electron volts, this "scanning near-field electron transmission microscopy" method could be applied to various adsorbates or thin layers. 相似文献
2.
A link between scanning tunneling microscopy (STM) and conventional transmission electron microscopy has been established for biological material by applying STM on freeze-dried recA-DNA complexes coated with a conducting film. The topography of the complexes observed by means of STM revealed a right-handed single helix composed of about six recA monomers per helical turn. 相似文献
3.
A combination of chemical vapor deposition and scanning tunneling microscopy techniques have been used to produce nanometer-scale, iron-containing deposits with high aspect ratios from an iron pentacarbonyl precursor both on a substrate and on the tunneling tip itself. The structure and composition of the resulting nanodeposits were determined by transmission electron microscopy and high spatial resolution Auger electron spectroscopy. Either polycrystalline, relatively pure, body-centered-cubic iron or disordered carbon-rich material can be deposited, depending on the bias conditions of the tip sample junction and the precursor pressure. Two mechanisms of decomposition are inferred from the growth phenomenology. 相似文献
4.
Narayanamurti V 《Science (New York, N.Y.)》1987,235(4792):1023-1028
The ability to artificially structure new materials on an atomic scale by using advanced crystal growth methods such as molecular beam epitaxy and metal-organic chemical vapor deposition has recently led to the observation of unexpected new physical phenomena and to the creation of entirely new classes of devices. In particular, the growth of materials of variable band gap in technologically important semiconductors such as GaAs, InP, and silicon will be reviewed. Recent results of studies of multilayered structures and interfaces based on the use of advanced characterization techniques such as high-resolution transmission electron microscopy and scanning tunneling microscopy will be presented. 相似文献
5.
Vibrational spectra for a single molecule adsorbed on a solid surface have been obtained with a scanning tunneling microscope (STM). Inelastic electron tunneling spectra for an isolated acetylene (C2H2) molecule adsorbed on the copper (100) surface showed an increase in the tunneling conductance at 358 millivolts, resulting from excitation of the C-H stretch mode. An isotopic shift to 266 millivolts was observed for deuterated acetylene (C2D2). Vibrational microscopy from spatial imaging of the inelastic tunneling channels yielded additional data to further distinguish and characterize the two isotopes. Single-molecule vibrational analysis should lead to better understanding and control of surface chemistry at the atomic level. 相似文献
6.
The scanning tunneling microscope is revolutionizing the study of surfaces. In ultra-high vacuum it is capable not only of imaging individual atoms but also of determining energy states on an atom-by-atom basis. It is now possible to operate this instrument in water. Aqueous optical microscopy is confined to a lateral resolution limit of about 2000 angstroms, and aqueous x-ray microscopy has yielded a lateral resolution of 75 angstroms. With a scanning tunneling microscope, an image of a graphite surface immersed in deionized water was obtained with features less than 3 angstroms apart clearly resolved. Further, an image measured in saline solution demonstrated that the instrument can be operated under conditions useful for many biological samples. 相似文献
7.
The ability of scanning tunneling microscopy to probe the pathways of thermally activated high-barrier surface processes is frequently limited by competing low-barrier processes that can confuse measurement of the true initial and final configuration. We introduce an approach to circumvent this difficulty by driving the surface process with nanosecond laser heating. The method is applied to determine the pathway of recombinative desorption in the H/Si(001) system. The observed configuration of dangling bonds after laser heating reveals that the desorbed hydrogen molecules are not formed on single dimers, but rather from neighboring silicon dimers via an interdimer reaction pathway. 相似文献
8.
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
9.
A method has been developed for performing fast time-resolved experiments with a scanning tunneling microscope. The method uses the intrinsic nonlinearity in the microscope's current versus voltage characteristics to resolve optically generated transient signals on picosecond time scales. The ability to combine the spatial resolution of tunneling microscopy with the time resolution of ultrafast optics yields a powerful tool for the investigation of dynamic phenomena on the atomic scale. 相似文献
10.
By means of scanning tunneling microscopy, it is observed that molecules of the form n-alkylcyanobiphenyl, where n = 8 to 12, form two-dimensional crystalline domains when adsorbed onto graphite. The layer spacings measured by tunneling microscopy are 20% larger than those measured previously on bulk material by x-ray diffraction. The structure of the adsorbed molecules is quite different from that of the bulk. 相似文献
11.
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
12.
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
13.
Erythrocytes: pits and vacuoles as seen with transmission and scanning electron microscopy 总被引：3，自引：0，他引：3
Vacuoles containing inclusions were observed by transmission electron microscopy in erythrocytes of a splenectomized patient with hemoglobin Ann Arbor. The membranes of these vacuoles became fused with the surface membrane of the red cell, thus opening the vacuoles and exposing their contents to the outside. These vacuoles when they have become thus attached to the cell membrane of the erythrocyte are responsible for the pits observed with scanning electron microscopy. 相似文献
14.
We have studied the formation kinetics of the copper-tin alloy bronze when tin is deposited on the (111) surface of copper at room temperature. Low-energy electron microscopy and atomic-resolution scanning tunneling microscopy reveal that bronze forms on the surface by a complicated, unanticipated cooperative mechanism: Ordered two-dimensional tin islands containing several hundred thousand atoms spontaneously sweep across the surface, leaving bronze alloys in their tracks. We propose that this process, driven by surface free energy, is a version of the "camphor dance" observed on liquid surfaces, and should be a general mechanism of surface alloying when surface diffusion is faster than exchange into the substrate. 相似文献
15.
Lastapis M Martin M Riedel D Hellner L Comtet G Dujardin G 《Science (New York, N.Y.)》2005,308(5724):1000-1003
Tunneling electrons from a low-temperature (5 kelvin) scanning tunneling microscope were used to control, through resonant electronic excitation, the molecular dynamics of an individual biphenyl molecule adsorbed on a silicon(100) surface. Different reversible molecular movements were selectively activated by tuning the electron energy and by selecting precise locations for the excitation inside the molecule. Both the spatial selectivity and energy dependence of the electronic control are supported by spectroscopic measurements with the scanning tunneling microscope. These experiments demonstrate the feasibility of controlling the molecular dynamics of a single molecule through the localization of the electronic excitation inside the molecule. 相似文献
16.
Moon CR Mattos LS Foster BK Zeltzer G Ko W Manoharan HC 《Science (New York, N.Y.)》2008,319(5864):782-787
Quantum phase is not directly observable and is usually determined by interferometric methods. We present a method to map complete electron wave functions, including internal quantum phase information, from measured single-state probability densities. We harness the mathematical discovery of drum-like manifolds bearing different shapes but identical resonances, and construct quantum isospectral nanostructures with matching electronic structure but divergent physical structure. Quantum measurement (scanning tunneling microscopy) of these "quantum drums"-degenerate two-dimensional electron states on the copper(111) surface confined by individually positioned carbon monoxide molecules-reveals that isospectrality provides an extra topological degree of freedom enabling robust quantum state transplantation and phase extraction. 相似文献
17.
Real-space observations of long-range electronic perturbations caused by defects have been made with scanning tunneling microscopy. The defects are isolated adsorbed molecules on the surface of graphite. These defects perturb the charge density, giving periodic oscillations similar to Friedel oscillations. The oscillations have a wavelength radical3 times that of the graphite lattice, and the symmetry of the oscillations reflects the nature of the defect. 相似文献
18.
Molecular structure of DNA by scanning tunneling microscopy 总被引：5，自引：0，他引：5
A Cricenti S Selci A C Felici R Generosi E Gori W Djaczenko G Chiarotti 《Science (New York, N.Y.)》1989,245(4923):1226-1227
Uncoated DNA molecules marked with an activated tris(l-aziridinyl) phosphine oxide (TAPO) solution were deposited on gold substrates and imaged in air with the use of a high-resolution scanning tunneling microscope (STM). Constant-current and gap-modulated STM images show clear evidence of the helicity of the DNA structure: pitch periodicity ranges from 25 to 35 angstroms, whereas the average diameter is 20 angstroms. Molecular structure within a single helix turn was also observed. 相似文献
19.
Vdovin EE Levin A Patanè A Eaves L Main PC Khanin YN Dubrovskii YV Henini M Hill G 《Science (New York, N.Y.)》2000,290(5489):122-124
Magnetotunneling spectroscopy is used as a noninvasive and nondestructive probe to produce two-dimensional spatial images of the probability density of an electron confined in a self-assembled semiconductor quantum dot. The technique exploits the effect of the classical Lorentz force on the motion of a tunneling electron and can be regarded as the momentum (k) space analog of scanning tunneling microscopy imaging. The images reveal the elliptical symmetry of the ground state and the characteristic lobes of the higher energy states. 相似文献
20.
With photon tunneling microscopy it is possible to image polymeric and other dielectric surfaces by means of the unusual properties of photon tunneling or evanescent waves. Vertical resolution is 1 nanometer, limited by the detector, over a vertical range of half a wavelength. Lateral resolution is better than a quarter of a wavelength over a field of view up to 125 micrometers. Samples can be surveyed in real time in air, with no need for metallization, and without shadowing or the intrusive effects of electrons or scanning probes. The use of this technique to study single crystals of polyethylene and processes such as latex film formation and the evolution of polystyrene topography while dewetting above the glass transition temperature are described. 相似文献