共查询到20条相似文献，搜索用时 314 毫秒
1.
We studied the dynamics of a single cobalt (Co) atom during lateral manipulation on a copper (111) surface in a low-temperature scanning tunneling microscope. The Co binding site locations were revealed in a detailed image that resulted from lateral Co atom motion within the trapping potential of the scanning tip. Random telegraph noise, corresponding to the Co atom switching between hexagonal close-packed (hcp) and face-centered cubic (fcc) sites, was seen when the tip was used to try to position the Co atom over the higher energy hcp site. Varying the probe tip height modified the normal copper (111) potential landscape and allowed the residence time of the Co atom in these sites to be varied. At low tunneling voltages (less than approximately 5 millielectron volts), the transfer rate between sites was independent of tunneling voltage, current, and temperature. At higher voltages, the transfer rate exhibited a strong dependence on tunneling voltage, indicative of vibrational heating by inelastic electron scattering. 相似文献
2.
We have measured the quantum yield for exciting the motion of a single Co atom in CoCu(n) linear molecules constructed on a Cu(111) surface. The Co atom switched between two lattice positions during electron excitation from the tip of a scanning tunneling microscope. The tip location with highest probability for inducing motion was consistent with the position of an active state identified through electronic structure calculations. Atom motion within the molecule decreased with increased molecular length and reflected the corresponding variation in electronic structure. 相似文献
3.
We report a method for controllably attaching an arbitrary number of charge dopant atoms directly to a single, isolated molecule. Charge-donating K atoms adsorbed on a silver surface were reversibly attached to a C60 molecule by moving it over K atoms with a scanning tunneling microscope tip. Spectroscopic measurements reveal that each attached K atom donates a constant amount of charge (approximately 0.6 electron charge) to the C60 host, thereby enabling its molecular electronic structure to be precisely and reversibly tuned. 相似文献
4.
The atomic force microscope images surfaces by sensing the forces between a sharp tip and a sample. If the tip-sample interaction is dominated by short-range forces due to the formation of covalent bonds, the image of an individual atom should reflect the angular symmetry of the interaction. Here, we report on a distinct substructure in the images of individual adatoms on silicon (111)-(7x7), two crescents with a spherical envelope. The crescents are interpreted as images of two atomic orbitals of the front atom of the tip. Key for the observation of these subatomic features is a force-detection scheme with superior noise performance and enhanced sensitivity to short-range forces. 相似文献
5.
Ternes M Lutz CP Hirjibehedin CF Giessibl FJ Heinrich AJ 《Science (New York, N.Y.)》2008,319(5866):1066-1069
Manipulation of individual atoms and molecules by scanning probe microscopy offers the ability of controlled assembly at the single-atom scale. However, the driving forces behind atomic manipulation have not yet been measured. We used an atomic force microscope to measure the vertical and lateral forces exerted on individual adsorbed atoms or molecules by the probe tip. We found that the force that it takes to move an atom depends strongly on the adsorbate and the surface. Our results indicate that for moving metal atoms on metal surfaces, the lateral force component plays the dominant role. Furthermore, measuring spatial maps of the forces during manipulation yielded the full potential energy landscape of the tip-sample interaction. 相似文献
6.
The controlled manipulation of silicon at the nanometer scale will facilitate the fabrication of new types of electronic devices. The scanning tunneling microscope (STM) can be used to manipulate strongly bound silicon atoms or clusters at room temperature. Specifically, by using a combination of electrostatic and chemical forces, surface atoms can be removed and deposited on the STM tip. The tip can then move to a predetermined surface site, and the atom or cluster can be redeposited. The magnitude of such forces and the amount of material removed can be controlled by applying voltage pulses at different tip-surface separations. 相似文献
7.
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
8.
Grooves a few nanometers wide can be formed on a Si(111) surface with a scanning tunneling microscope when the tip is above a critical voltage. This may provide a promising approach to nanodevice fabrication. The dependence of the critical voltage on tunneling current, tip polarity, and tip material was studied with silver, gold, platinum, and tungsten tips. The results are consistent with field emission of positive and negative silicon ions. The variation of critical voltage with current is explained quantitatively by a simple tunneling equation that includes the effect of the contact potential between tip and sample. 相似文献
9.
A scanning tunneling microscope (STM) was used to manipulate the bonding of a carbon monoxide (CO) molecule and to analyze the structure and vibrational properties of individual products. Individual iron (Fe) atoms were evaporated and coadsorbed with CO molecules on a silver (110) surface at 13 kelvin. A CO molecule was transferred from the surface to the STM tip and bonded with an Fe atom to form Fe(CO). A second CO molecule was similarly transferred and bonded with Fe(CO) to form Fe(CO)(2). Controlled bond formation and characterization at the single-bond level probe chemistry at the spatial limit. 相似文献
10.
Tunneling electrons from the tip of a scanning tunneling microscope were used to induce and monitor the reversible rotation of single molecules of molecular oxygen among three equivalent orientations on the platinum(111) surface. Detailed studies of the rotation rates indicate a crossover from a single-electron process to a multielectron process below a threshold tunneling voltage. Values for the energy barrier to rotation and the vibrational relaxation rate of the molecule were obtained by comparing the experimental data with a theoretical model. The ability to induce the controlled motion of single molecules enhances our understanding of basic chemical processes on surfaces and may lead to useful single-molecule devices. 相似文献
11.
Zhao A Li Q Chen L Xiang H Wang W Pan S Wang B Xiao X Yang J Hou JG Zhu Q 《Science (New York, N.Y.)》2005,309(5740):1542-1544
We report that the Kondo effect exerted by a magnetic ion depends on its chemical environment. A cobalt phthalocyanine molecule adsorbed on an Au111 surface exhibited no Kondo effect. Cutting away eight hydrogen atoms from the molecule with voltage pulses from a scanning tunneling microscope tip allowed the four orbitals of this molecule to chemically bond to the gold substrate. The localized spin was recovered in this artificial molecular structure, and a clear Kondo resonance was observed near the Fermi surface. We attribute the high Kondo temperature (more than 200 kelvin) to the small on-site Coulomb repulsion and the large half-width of the hybridized d-level. 相似文献
12.
An atomic force microscope was used to study single-electron motion in nanotube quantum dots. By applying a voltage to the microscope tip, the number of electrons occupying the quantum dot could be changed, causing Coulomb oscillations in the nanotube conductance. Spatial maps of these oscillations were used to locate individual dots and to study the electrostatic coupling between the dot and the tip. The electrostatic forces associated with single electrons hopping on and off the quantum dot were also measured. These forces changed the amplitude, frequency, and quality factor of the cantilever oscillation, demonstrating how single-electron motion can interact with a mechanical oscillator. 相似文献
13.
The miniaturization of magnetic devices toward the limit of single atoms calls for appropriate tools to study their magnetic properties. We demonstrate the ability to measure magnetization curves of individual magnetic atoms adsorbed on a nonmagnetic metallic substrate with use of a scanning tunneling microscope with a spin-polarized tip. We can map out low-energy magnetic interactions on the atomic scale as evidenced by the oscillating indirect exchange between a Co adatom and a nanowire on Pt(111). These results are important for the understanding of variations that are found in the magnetic properties of apparently identical adatoms because of different local environments. 相似文献
14.
We used a scanning tunneling microscope to probe the interactions between spins in individual atomic-scale magnetic structures. Linear chains of 1 to 10 manganese atoms were assembled one atom at a time on a thin insulating layer, and the spin excitation spectra of these structures were measured with inelastic electron tunneling spectroscopy. We observed excitations of the coupled atomic spins that can change both the total spin and its orientation. Comparison with a model spin-interaction Hamiltonian yielded the collective spin configuration and the strength of the coupling between the atomic spins. 相似文献
15.
Spatial resolution at the atomic scale has been achieved in the coupling of light to single molecules adsorbed on a surface. Electron transfer to a single molecule induced by green to near-infrared light in the junction of a scanning tunneling microscope (STM) exhibited spatially varying probability that is confined within the molecule. The mechanism involves photo-induced resonant tunneling in which a photoexcited electron in the STM tip is transferred to the molecule. The coupling of photons to the tunneling process provides a pathway to explore molecular dynamics with the combined capabilities of lasers and the STM. 相似文献
16.
The platinum-rhodium tip of a scanning tunneling microscope that operates inside of an atmospheric-pressure chemical reactor cell has been used to locally rehydrogenate carbonaceous fragments deposited on the (111) surface of platinum. The carbon fragments were produced by partial dehydrogenation of propylene. The reactant gas environment inside the cell consisted of pure H(2) or a 1:9 mixture of CH(3)CHCH(2) and H(2) at 300 kelvin. The platinum-rhodium tip acted as a catalyst after activation by short voltage pulses. In this active state, the clusters in the area scanned by the tip were reacted away with very high spatial resolution. 相似文献
17.
RP Andres T Bein M Dorogi S Feng JI Henderson CP Kubiak W Mahoney RG Osifchin R Reifenberger 《Science (New York, N.Y.)》1996,272(5266):1323-1325
Double-ended aryl dithiols [alpha,alpha'-xylyldithiol (XYL) and 4,4'-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed "Coulomb staircase" behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (approximately18 ± 12 megohms). 相似文献
18.
The charge distribution in atoms with closed electron shells is spherically symmetric, whereas atoms with partially filled shells can form covalent bonds with pointed lobes of increased charge density. Covalent bonding in the bulk can also affect surface atoms, leading to four tiny humps spaced by less than 100 picometers in the charge density of adatoms on a (001) tungsten surface. We imaged these charge distributions by means of atomic force microscopy with the use of a light-atom probe (a graphite atom), which directly measured high-order force derivatives of its interaction with a tungsten tip. This process revealed features with a lateral distance of only 77 picometers. 相似文献
19.
Lantz MA Hug HJ Hoffmann R van Schendel PJ Kappenberger P Martin S Baratoff A Güntherodt HJ 《Science (New York, N.Y.)》2001,291(5513):2580-2583
We report direct force measurements of the formation of a chemical bond. The experiments were performed using a low-temperature atomic force microscope, a silicon tip, and a silicon (111) 7x7 surface. The measured site-dependent attractive short-range force, which attains a maximum value of 2.1 nanonewtons, is in good agreement with first-principles calculations of an incipient covalent bond in an analogous model system. The resolution was sufficient to distinguish differences in the interaction potential between inequivalent adatoms, demonstrating the ability of atomic force microscopy to provide quantitative, atomic-scale information on surface chemical reactivity. 相似文献
20.
Liu X Zhang Y Goswami DK Okasinski JS Salaita K Sun P Bedzyk MJ Mirkin CA 《Science (New York, N.Y.)》2005,307(5716):1763-1766
We present a method for controlling the initiation and kinetics of polymer crystal growth using dip-pen nanolithography and an atomic force microscope tip coated with poly-dl-lysine hydrobromide. Triangular prisms of the polymer epitaxially grow on freshly cleaved mica substrates, and their in-plane and out-of-plane growth rates can be controlled by raster scanning the coated tip across the substrate. Atomic force microscope images were concomitantly recorded, providing a set of photographic images of the process as it spans the nanometer- to micrometer-length scales as a function of environmental conditions. 相似文献