共查询到20条相似文献，搜索用时 203 毫秒
1.
A method for confining electrons to artificial structures at the nanometer lengthscale is presented. Surface state electrons on a copper(111) surface were confined to closed structures (corrals) defined by barriers built from iron adatoms. The barriers were assembled by individually positioning iron adatoms with the tip of a 4-kelvin scanning tunneling microscope (STM). A circular corral of radius 71.3 A was constructed in this way out of 48 iron adatoms. Tunneling spectroscopy performed inside of the corral revealed a series of discrete resonances, providing evidence for size quantization. STM images show that the corral's interior local density of states is dominated by the eigenstate density expected for an electron trapped in a round two-dimensional box. 相似文献
2.
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
3.
High-resolution transmission electron microscopy and scanning tunneling microscopy have been combined to examine the structure of the thin "native" oxide that forms on silicon surfaces at room temperature. Differences in the cleaning procedures for silicon wafers may affect the morphology of this oxide and critically influence further processing on the silicon substrates. An etch that ended with a dip in hydrofluoric acid provided a thinner oxide and a lower interface step density than did a sulfuric peroxide treatment. The availability of complementary information from high-resolution transmission electron microscopy and scanning tunneling microscopy is discussed. 相似文献
4.
The use of scanning tunneling microscopy in an electrochemical environment as a tool for the nanoscale modification of gold electrodes was demonstrated. Small copper clusters, typically two to four atomic layers in height, were precisely positioned on a gold(111) electrode by a process in which copper was first deposited onto the tip of the scanning tunneling microscope, which then acted as a reservoir from which copper could be transferred to the surface during an appropriate approach of the tip to the surface. Tip approach and position were controlled externally by a microprocessor unit, allowing the fabrication of various patterns, cluster arrays, and "conducting wires" in a very flexible and convenient manner. 相似文献
5.
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
6.
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
7.
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
8.
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
9.
We demonstrate electron-stimulated migration for carbon monoxide (CO) molecules adsorbed on the Pd(110) surface, which is initiated by the excitation of a high-frequency (HF) vibrational mode (C-O stretching mode) with inelastic tunneling electrons from the tip of scanning tunneling microscopy. The hopping phenomenon, however, cannot be detected for CO/Cu(110), even though the hopping barrier is lower than in the CO/Pd(110) case. A theoretical model, which is based on the anharmonic coupling between low-frequency modes (the hindered-translational mode related to the lateral hopping) and the HF mode combined with electron-hole pair excitation, can explain why the hopping of CO is observed on Pd(110) but not on Cu(110). 相似文献
10.
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
11.
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
12.
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
13.
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
14.
Krause S Berbil-Bautista L Herzog G Bode M Wiesendanger R 《Science (New York, N.Y.)》2007,317(5844):1537-1540
Switching the magnetization of a magnetic bit by injection of a spin-polarized current offers the possibility for the development of innovative high-density data storage technologies. We show how individual superparamagnetic iron nanoislands with typical sizes of 100 atoms can be addressed and locally switched using a magnetic scanning probe tip, thus demonstrating current-induced magnetization reversal across a vacuum barrier combined with the ultimate resolution of spin-polarized scanning tunneling microscopy. Our technique allows us to separate and quantify three fundamental contributions involved in magnetization switching (i.e., current-induced spin torque, heating the island by the tunneling current, and Oersted field effects), thereby providing an improved understanding of the switching mechanism. 相似文献
15.
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
16.
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
17.
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
18.
We have measured the angular dependence of chemical bonding forces between a carbon monoxide molecule that is adsorbed to a copper surface and the terminal atom of the metallic tip of a combined scanning tunneling microscope and atomic force microscope. We provide tomographic maps of force and current as a function of distance that revealed the emergence of strongly directional chemical bonds as tip and sample approach. The force maps show pronounced single, dual, or triple minima depending on the orientation of the tip atom, whereas tunneling current maps showed a single minimum for all three tip conditions. We introduce an angular dependent model for the bonding energy that maps the observed experimental data for all observed orientations and distances. 相似文献
19.
Scepaniak JJ Vogel CS Khusniyarov MM Heinemann FW Meyer K Smith JM 《Science (New York, N.Y.)》2011,331(6020):1049-1052
Despite being implicated as important intermediates, iron(V) compounds have proven very challenging to isolate and characterize. Here, we report the preparation of the iron(V) nitrido complex, [PhB((t)BuIm)(3)Fe(V)≡N]BAr(F24) (PhB((t)BuIm)(3)(-) = phenyltris(3-tert-butylimidazol-2-ylidene)borato, BAr(F24) = B(3,5-(CF(3))(2)C(6)H(3))(4)(-)), by one electron oxidation of the iron(IV) nitrido precursor. Single-crystal x-ray diffraction of the iron(V) complex reveals a four-coordinate metal ion with a terminal nitrido ligand. M??bauer and electron paramagnetic resonance spectroscopic characterization, supported by electronic structure calculations, provide evidence for a d(3) iron(V) metal center in a low spin (S = 1/2) electron configuration. Low-temperature reaction of the iron(V) nitrido complex with water under reducing conditions leads to high yields of ammonia with concomitant formation of an iron(II) species. 相似文献
20.
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