Single Benzene Molecule Research Articles

Multi-terminal quantum transport through a single benzene molecule: Evidence of a molecular transistor

We explore multi-terminal quantum transport through a single benzene molecule attached to metallic electrodes. A simple tight-binding model is used to describe the system and all the calculations are done based on the Green function formalism. With a brief description of two-terminal quantum transport, we present a detailed study of three-terminal transport properties through the benzene molecule to reveal the actual mechanism of electron transport. Here we address numerical results which describe multi-terminal conductances, reflection probabilities and current–voltage characteristics. Most significantly we observe that, the molecular system where the benzene molecule is attached to three terminals can be operated as a transistor, and we call it a molecular transistor. This aspect can be utilized in designing nano-electronic circuits and our investigation may provide a basic framework to study electron transport in any complicated multi-terminal quantum system.

Electrical conductance of single C60 and benzene molecules bridging between Pt electrode

The electrical conductance of single C60 and benzene molecules bridging between Pt electrodes was investigated at room temperature in ultrahigh vacuum. The conductance of the Pt/C60/Pt junction was 0.7 G0(2e2/h), which was close to that of the metal atomic contact. The single C60 molecular junction showed a high and fixed conductance value, by the direct binding of the C60 to the Pt electrodes without using anchoring group. The conductance of the Pt/C60/Pt junction decreased and its stability increased with the amount of deposited C60 molecule, which could be explained by the C60 adsorption on the stem part of the electrode. In contrast with the Pt/C60/Pt junction, the Pt/benzene/Pt junction did not show a fixed conductance value, reflecting the planar molecular shape.

Measurement of single-molecule frictional dissipation in a prototypical nanoscale system

A picosecond technique for measuring the kinetic friction of a single benzene molecule on graphite reveals continuous Brownian motion, rather than the jerky hopping observed on most other surfaces. Fast-moving nanoscale systems offer the tantalizing possibility for rapid processing of materials, energy or information1. Frictional forces can easily dominate the motion of these systems, yet whereas nanomechanical techniques, such as atomic force microscopy, are widely used to measure static nanoscale friction2, they are too slow to measure the kinetic friction crucial for short-timescale motion. Here, we report measurements of frictional damping for a prototypical nanoscale system: benzene on a graphite surface, driven by thermal motion. Spin-echo spectroscopy is used to measure the picosecond time dependence of the motion of single benzene molecules, indicating a type of atomic-scale continuous Brownian motion not previously observed. Quantifying the frictional coupling between moving molecules and the surface, as achieved in these measurements, is important for the characterization of phononically driven nanomechanical tools. The data also provide a benchmark for simulations of nanoscale kinetic friction and demonstrate the applicability of the spin-echo technique.

Revisiting magnetic coupling in transition-metal-benzene complexes with maximally localized Wannier functions

Construction of maximally localized Wannier functions (MLWFs) has been implemented within the linear combination of pseudoatomic orbital method. Detailed analysis using MLWFs is applied to three closely related materials, single benzene (Bz) molecule, organometallic vanadium-Bz infinite chain, and ${\text{V}}_{2}{\text{Bz}}_{3}$ sandwich cluster. Two important results come out from the present analysis: (1) for the infinite chain, the validity of the basic assumption in the mechanism of Kanamori and Terakura for the ferromagnetic (FM) state stability is confirmed; (2) for ${\text{V}}_{2}{\text{Bz}}_{3}$, an important role played by the difference in the orbital energy between the edge Bzs and the middle Bz is revealed: the on-site energy of $p\ensuremath{\delta}$ states of edge Bzs is higher than that of middle Bz, which further reduces the FM stability of ${\text{V}}_{2}{\text{Bz}}_{3}$.

Manipulation of benzene on Cu(110) by dynamic force microscopy: Anab initiostudy

Based on ab initio calculations, we simulated how a single benzene molecule adsorbed on a Cu(110) surface can be mechanically manipulated by dynamic force microscopy using a clean silicon tip. Such a tip pushes the benzene molecule from one adsorption site to another and can therefore be used for lateral manipulation processes. On the other hand, a copper-terminated tip binds to the benzene molecule lifting it from the Cu surface.

Local Spectroscopy of Image-Potential-Derived States: From Single Molecules to Monolayers of Benzene on Cu(111)

Stark-shifted image-potential states were measured with an STM tip for benzene adsorbed on a Cu(111) surface. A single benzene molecule locally shifts the position of the first image state toward the Fermi level by 0.2 eV relative to its position on the clean surface. The energetic position of this molecule-modified state shifts to lower energy with increasing coverage of benzene on the surface. This is attributed to local surface potential changes that are correlated with the lowering of the crystal work function due to adsorption of benzene.

Evidence of a shift between one- and two-photon processes associated with benzene trapped in helium nanodroplets

Two-photon ionisation has been observed at ∼259 nm for single benzene molecules trapped in small helium droplets. Four spectral features have been identified corresponding to vibrational excitations coupled with the forbidden 1B 2u ← 1A 1g electronic transition. When compared with single-photon depletion signals, three of the REMPI signals exhibit a small (∼1 cm −1) blue shift. The ion signals also exhibit a size-dependence, which maximises at droplets containing ∼1500 atoms, and is interpreted in terms of a critical size needed to either pick up molecule, or to evaporate completely all of the remaining helium atoms prior to detection of the benzene ion.

Quantum interference in polycyclic hydrocarbon molecular wires

Abstract The construction of devices based on molecular components depends upon the development of molecular wires with adaptable current–voltage characteristics. Here, we report that quantum interference effects could lead to substantial differences in conductance in molecular wires which include some simple polycyclic aromatic hydrocarbons (PAHs). For molecular wires containing a single benzene, anthracene or tetracene molecule a large peak appears in the electron transmission probability spectrum at an energy just above the lowest unoccupied orbital (LUMO). For a molecular wire containing a single naphthalene molecule, however, this same peak essentially vanishes. Furthermore, the peak can be re-established by altering the attachment points of the molecular leads to the naphthalene molecule. A breakdown of the individual terms contributing the relevant peak confirms that these results are in fact due to quantum interference effects.

Interaction of water, methanol and benzene molecules with hydrophilic centres at a partially oxidised model graphite surface

Abstract Adsorption of water, methanol and benzene at carboxyl groups at the edge of the graphene sheets at the side face of graphite microcrystallites is studied. The adsorption enthalpies of the studied substances are determined using quantum chemical calculations. The adsorption of water molecules is shown to result in the formation of dimers at the adsorption centre, while only single methanol or benzene molecules are adsorbed. The formation of water molecule clusters on a hydrophilic centre at the surface of graphite and other adsorbents is shown to be a characteristic feature of water adsorption.

Cobalt–benzene cluster anions: Mass spectrometry and negative ion photoelectron spectroscopy

( Cobalt ) n ( benzene ) m − cluster anions, (n,m) were generated by laser vaporization and studied by both mass spectrometry and anion photoelectron spectroscopy. Our assignment of the photoelectron spectrum of the (1,2) cluster anion suggests that it possesses a sandwich structure with the cobalt atom located between two parallel benzene rings, that the ground state of this anion is a singlet, and that the ground state of its corresponding neutral is a doublet. The photoelectron spectra of cobalt-rich cluster anions of the form (n,1) are interpreted as cobalt metal cluster anions which have been solvent-stabilized by their interaction with, in each case, a single benzene molecule. The photoelectron spectra of the benzene-rich cluster anions, (2,3), (2,2), and (3,3), are tentatively interpreted as suggesting extended sandwich structures for these anion complexes.

Total pressure measurements for benzene with 1-propanol, 2-propanol, 1-pentanol, 3-pentanol, and 2-methyl-2-butanol at 313.15 K

Total pressure measurements at 313.15 K are reported for binary systems of benzene and 1-propanol, 2-propanol, 1-pentanol, 3-pentanol, and 2-methyl-2-butanol. The results are interpreted by an extended form of the Kretschmer–Wiebe association model, in which it is assumed that linear alcohol chains may solvate with a single benzene molecule.

Electronic and vibrational excitation of single molecules with a scanning tunneling microscope

The electronic and vibrational excitations of single acetylene, pyridine, and benzene molecules on Cu(001) were studied by scanning tunneling microscopy at 9 K. Electrons of 0–5 eV were used to induce dissociation, desorption, diffusion, rotation, and vibrational excitation of these molecules. The dissociation products were characterized by imaging, single molecule vibrational spectroscopy, and rotational excitation. The STM is shown to be a very versatile tool for inducing a molecule to explore its excited state potential energy surface and describing the possible results.

Imaging benzene on nickel and copper {110} surfaces with low temperature STM:: the adsorption site

Single benzene molecules have been imaged on the {110} surfaces of both copper and nickel with an Eigler-type low temperature scanning tunnelling microscope. Conditions were chosen such that the molecule and the lattice atoms could be resolved at the same time within one image frame. On Ni{110} benzene was found to adsorb in the hollow site between the close-packed rows. For the more weakly bound molecule on Cu{110} the imaging conditions had to be changed since, for the tunnelling conditions under which the lattice atoms are resolved, a strong interaction between the tip and the benzene takes place. This results in the molecule being “dragged” along the surface. By changing the tunnelling conditions within one image frame, however, it is possible via extrapolation of the substrate lattice to show that the molecule adsorbs in the long-bridge site. The shapes of the images of individual molecules are discussed.

An engineered allosteric switch in leucine-zipper oligomerization.

Controversy remains about the role of core side-chain packing in specifying protein structure. To investigate the influence of core packing on the oligomeric structure of a coiled coil, we engineered a GCN4 leucine zipper mutant that switches from two to three strands upon binding the hydrophobic ligands cyclohexane and benzene. In solution these ligands increased the apparent thermal stability and the oligomerization order of the mutant leucine zipper. The crystal structure of the peptide-benzene complex shows a single benzene molecule bound at the engineered site in the core of the trimer. These results indicate that coiled coils are well-suited to function as molecular switches and emphasize that core packing is an important determinant of oligomerization specificity.

Multiphoton ionization studies of clusters of immiscible liquids. II. C6H6–(H2O)n, n=3–8 and (C6H6)2–(H2O)1,2

Resonant two-photon ionization (R2PI) time-of-flight mass spectroscopy is used to record S0–S1 spectra of the neutral complexes C6H6–(H2O)n with n=3–8 and (C6H6)2–(H2O)1,2. Due to limitations imposed by the size of these clusters, a number of vibronic level arguments are used to constrain the gross features of the geometries of these clusters. Among the spectral clues provided by the data are the frequency shifts of the transitions, their van der Waals structure, the fragmentation of the photoionized clusters, and the complexation-induced origin intensity and 610 splitting. In the 1:3 cluster, simple arguments are made based on the known structures of the 1:1 and 1:2 clusters which lead to the conclusion that all three water molecules reside on the same side of the benzene ring. Three structures for the 1:3 cluster are proposed which are consistent with the available data. Of these, only one is also consistent with the remarkable similarity of the 1:4 and 1:5 spectra to those of the 1:3 cluster. This structure involves a cyclic water trimer in which one of the water molecules is near the sixfold axis in a π hydrogen-bonded configuration. This structure is then expanded in the 1:4 and 1:5 clusters to incorporate the fourth and fifth water molecules in cyclic structures which place the additional water molecules far from the benzene ring without disturbing the interaction of the other water molecules with the benzene ring. For 1:n clusters with n≥6, subtle and then significant changes are observed in the spectra which indicate changes in the way the water cluster interacts with the benzene ring. This development occurs at precisely the water cluster size which calculations predict that cagelike water cluster structures will begin to compete and eventually be favored over large cyclic structures. Finally, cursory scans of the 2:1 cluster show that this cluster also fragments efficiently upon photoionization by loss of a single water molecule and that it possesses a distinctly asymmetric structure with a sizable 610 splitting. Two potential structures are proposed for the 2:1 cluster which can both reasonably explain the observations—a BBW structure in which the water molecule (W) is π hydrogen bonded to a single benzene molecule (B) and a BWB structure in which the water molecule bridges the two benzenes via π hydrogen bonds to both.

Multiphoton mass spectrometry of clusters: Dissociation pathways and energetics of heterogeneous van der Waals cluster ions

In this work the metastable decay of heterogeneous benzene/toluene, benzene/cyclohexane, and benzene/para-difluorobenzene van der Waals cluster ions [(MiNk)+ with n=i+k<12] is investigated. Two-photon ionization leads to an internal energy of less than 1.5 eV. On the 100 μs time scale of the linear reflectron time-of-flight mass spectrometer used in this work, the main dissociation process of the cluster ions is the evaporation of a single molecule. A uniform decay behavior is observed for benzene/toluene and benzene/cyclohexane cluster ions; the only dissociation pathway being the evaporation of a single benzene or cyclohexane molecule, respectively. By contrast, the evaporation of either a benzene or a para-difluorobenzene molecule is observed for benzene/para-difluorobenzene cluster ions, depending on the size and the composition of the heterocluster. We apply an energetic model to explain the observed dissociation pathways. This model assumes the total miscibility of the different molecular species and a total dilution of charge. Despite these assumptions, the model predictions are in good agreement with our experimental data.

Solubilization of benzene by aqueous sodium octylsulfate: Effect of added sodium chloride

Highly precise vapor pressure-solubility data have been obtained for benzene in aqueous solutions of sodium octylsulfate (SOS) containing approximately 0.4 M sodium chloride, at 15, 25, 35, and 45°C. A mass action model, using a form of the Poisson distribution equation modified to include cooperative benzene-benzene interactions within the micelle, provides an excellent fit of the solubilization data at each temperature. Values are reported of equilibrium constants for the interaction of a single benzene molecule with micellar SOS, the cooperativity parameters in the Poisson model, and activity coefficients for benzene solubilized in the micelle. A comparison of the solubilization results with those obtained for SOS solutions with no added salt indicates the influence of NaCl on properties of the micelles and micelle solubilizates. As has been reported previously, careful measurements of the dependence of extent of solubilization on the solubilizate activity indicate that solute-solnte interactions within the micelles lead to significant departures from Henry's law.