Selective internal manipulation of a single molecule by scanning tunneling microscopy (original) (raw)
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Single Molecules, 2000
With the scanning tunneling microscope (STM) it became possible to perform controlled manipulations down to the scale of small molecules and single atoms, leading to the fascinating aspect of creating manmade structures on atomic scale. Here we present a short review of our work in the last five years on atomic scale manipulation investigations. Upon soft lateral manipulation of adsorbed species, in which only tip/particle forces are used, three different manipulation modes (pushing, pulling, sliding) can be discerned. We show that also manipulation of highly coordinated native substrate atoms is possible and demonstrate the application of these techniques as local analytic and synthetic chemistry tools with important consequences on surface structure research. Vertical manipulation of Xe and CO is presented, leading to improved imaging and even chemical contrast with deliberately functionalized tips. For the transfer of CO it is shown that beside tip voltage current effects play also an important role. This is also the case for the dissociation of molecules. With CO transferred deliberately to the tip we have also succeeded to perform vibrational spectroscopy on single molecules. Furthermore, first experiments aiming for the transfer of all manipulation modes to thin insulating films are described.
Physical Review Letters, 2000
A scanning-tunneling microscope has been used to induce efficient local desorption of benzene from Si(100) at low currents (,100 pA), sample biases (ϳ22.4 V) and temperatures (22 K). A theoretical model based upon first principles electronic structure calculations and quantum mechanical wave packet dynamics describes this process as occurring via transient ionization of a p state of the adsorbed molecule. This model accounts for the unexpected efficiency and sharp threshold of the yield. PACS numbers: 68.45.Da, 07.79.Cz, The development of the scanning tunneling microscope (STM) has made possible not only visualization but also manipulation of individual adsorbates . Intensive research in this area has been motivated by the desire to better understand adsorbate-substrate interactions, surface dynamics, and the potential of local tip-induced modifications to fabricate nanoscale devices and induce novel molecular-scale chemical reactions. Earlier research focused on manipulation of atoms and diatomic molecules [1-4] but the exciting avenue of inducing single-molecule reactions in complex, multidimensional systems is now beginning to be explored . Organic molecules, whose properties can be systematically tailored via the use of appropriate functional group substitutions, offer a rich variety of opportunities for both fundamental and technological studies.
Study and Manipulation of Single Functionalized Molecules by Low Temperature STM
Journal of Scanning Probe Microscopy, 2007
Two types of functionalized molecules, wheels and switches, are studied with a low temperature scanning tunneling microscope. Lateral manipulation of wheel-dimer molecules is performed on a Cu(110) surface. If suitable parameters are chosen, not only a hopping, but also a rolling motion of the molecular wheels can be induced if the surface corrugation in the direction of motion is sufficient. The experimental observations clearly reflect the different mechanisms of hopping and rolling. While mostly only one wheel rolls, in some cases the rolling of both wheels is observed. The isomerization of single azobenzene derivatives on Au(111) is induced by applying a bias voltage between tip and sample. The process turns out to be perfectly reversible as the molecules, adsorbed in highly ordered islands, precisely restore their initial appearance after two subsequent switching events from trans to cis and back to trans. A detailed investigation of the driving process, studying the dependence of the threshold voltage on the tip-sample distance, reveals different mechanisms.
Physical Review Letters, 2003
We report a systematic experimental investigation of the mechanism of desorption of chlorobenzene molecules from the Si111 ÿ 7 7 surface induced by the STM at room temperature. We measure the desorption probability as a function of both tunneling current and a wide range of sample bias voltages between ÿ3 V and 4 V. The results exclude field desorption, thermally induced desorption, and mechanical tip-surface effects. They indicate that desorption is driven by the population of negative (or positive) ion resonances of the chemisorbed molecule by the tunneling electrons (or holes). Density functional calculations suggest that these resonant states are associated with the orbitals of the benzene ring.
Scanning tunneling microscope-induced molecular motion and its effect on the image formation
Surface Science, 1998
The effect of tip-induced molecular motion on the appearance of scanning tunneling microscope (STM ) images of anthracene on Ag(110) was investigated for various tunneling parameters and at various temperatures. At 50 K, isolated molecules can be imaged at a high tunneling resistance. For an increased tip-molecule interaction at a decreased resistance, apparent one-dimensional and two-dimensional molecular superstructures arise in the STM images that are due to an interplay between tip-induced motion, transient binding at specific substrate sites and repeated imaging of a molecule. At an even higher tip-molecule interaction strength, molecules can be dragged over the surface such that an atomically resolved substrate lattice is discernible. The slid molecule acts as an amplifier of the charge corrugation of the metallic surface.
Journal of Physics: Conference Series, 2005
Initially invented to image surfaces down to atomic scale, the scanning tunneling microscope (STM) has been further developed in the last few years to an operative tool, with which atoms and molecules can be manipulated at low substrate temperatures at will with atomic precision in different manners by using solely the tip-adparticle forces. In this way various artificial structures on naoscale have been created and in situ characterized with the STM. Such structures as well as single molecules can be investigated by scanning tunnelling spectroscopy (STS) both with respect to their local electronic and even vibrational properties. Modifications of single molecules can be induced by using the tunnelling electron current: Rotations, diffusional jumps, vibrational excitations, desorption, dissociation and even association can be induced in individual molecules, often in a rather precise way by tuning the voltage into the energy levels of specific vibrations or electronic levels. These possibilities give rise to startling new opportunities for physical and chemical experiments on the single atom and single molecule level. Here a brief overview on results obtained with these new techniques is given.
Physical Review Letters, 2004
A novel scanning tunneling microscope manipulation scheme for a controlled molecular transport of weakly adsorbed molecules is demonstrated. Single sexiphenyl molecules adsorbed on a Ag(111) surface at 6 K are shot towards single silver-atoms by excitation with the tip. To achieve atomically straight shooting paths, an electron resonator consisting of linear standing wave fronts is constructed. The sexiphenyl manipulation signals reveal a π-ring flipping as the molecule moves from hcp to fcc site. Abinitio calculations show an incorporation of the Ag atom below the center of a π-ring. * Coressponding author, Email: hla@ohio.edu, web: www.phy.ohiou.edu/\~hla PACS: 82.37.Gk, 68.37.Ef, 33.15.Bh ___________________________________________________ The advances in scanning tunneling microscope (STM) manipulation allow probing physical/chemical properties of single molecules or construction of atomic scale structures on surfaces [1-9]. STM manipulation requires a precise control over the tip-molecule-surface junction. A weakly adsorbed molecule on a surface can be easily displaced with the STM-tip but its movement is extremely difficult to control. Most surface chemical reactions involve weakly adsorbed molecular species; however, investigations on their detailed dynamics and reactivity are hindered by instrumentation limits. Here, we have chosen weakly adsorbed sexiphenyl on Ag(111) as a model system to develop an STM manipulation scheme. Sexiphenyl (C 36 H 26 ) is composed of six π-rings connected to form a linear chain [10] and due to its potential applications in display electronic devices, sexiphenyl has been studied intensely in the past years .
Manipulation of Atoms and Molecules with the Low-Temperature Scanning Tunneling Microscope
Japanese Journal of Applied Physics, 2001
The controlled manipulation with a scanning tunneling microscope (STM) down to the scale of small molecules and single atoms allows the buildup of molecular and atomic nanostructures. In the case of the lateral manipulation of adsorbed species, in which only tip/particle forces are used, three different manipulation modes (pushing, pulling, sliding) can be discerned. Vertical manipulation of Xe and CO is demonstrated, leading to the formation of functionalized tips, which can be used for improved imaging and even to perform vibrational spectroscopy on single molecules. Furthermore, we describe how we have reproduced a full chemical reaction with single molecules, whereby all basic steps, namely, preparation of the reactants, diffusion and association, are induced with the STM tip.
Surface Science, 1998
Semi-empirical molecular orbital calculations reveal the local surface density of states for the adsorbed molecules on the Si surface. The organic molecules adenine, thymine, cytosine, and pentacene, which are adsorbed on Si(100)2×1 surfaces have been imaged by scanning tunneling microscopy (STM). The molecular images obtained by STM exhibit distinct shapes corresponding to the expected shapes for adsorption configurations. The energy level diagrams of the molecular orbitals (MOs) of the Si cluster on which the molecules are adsorbed are shown. The calculated MOs for adenine and thymine are in good agreement with the molecular images observed in STM. The bias dependence image of adsorbed cytosine is also explained by the calculated MOs of the molecule.
Surface Science, 2014
Low coverages of 4,4"-diamino-p-terphenyl (DAT) molecules deposited on a Si(001)-(2×1) surface in ultrahigh vacuum at room temperature were observed by scanning tunneling microscopy (STM). The linear framework of DAT, consisting of a central benzene ring, two phenyl rings (terphenyl) and two amino groups at both ends, mostly lay down laterally on the surface. The majority of DATs were tilted at about 17° with respect to the direction of a Si dimer row on the surface, though a variety of DAT configuration with different angles was found by STM. The histograms of the tilted angles showed that the most frequent angle was 17°. The apparent height of DAT tilted at 17° looked hollow at the center and lower than that of other configurations of DAT in STM images. This indicates that the DAT tends to take a double arched shape at the tilted angle of 17° in a stable conformation with butterfly-like bonding through the central benzene ring to a Si dimer as well as the two amino groups bonded to respective Si atoms on the dimer row.