Seeding Molecular Rotators on a Passivated Silicon Surface (original) (raw)
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Anchoring Molecular Rotors by On-Surface Synthesis
Building and Probing Small for Mechanics, 2020
Single molecular rotor is an important component for constructing bottom up molecular mechanical machines and a window for shedding light on complex physical and chemical questions about motions of organic molecules on surfaces. Stability of each component in such a molecular construction site is a crucial prerequisite. To realize a stable stepwise rotation of a molecule by a low temperature scanning tunneling microscope (LT-STM), atomic scale axles is particularly important. An ideal atomic scale axle is expected to balance between anchoring and mobility of rotating a single molecule on a metal surface under external excitations. In this Chapter, several chemical anchoring strategies on how to pin a molecular rotor are tested and discussed. Tip-induced manipulation and motion analysis are used as tools to investigate the properties and functionality of the proposed strategies.
Sensors, 2012
The use of a functional molecular unit acting as a state variable provides an attractive alternative for the next generations of nanoscale electronics. It may help overcome the limits of conventional MOSFETd due to their potential scalability, low-cost, low variability, and highly integratable characteristics as well as the capability to exploit bottom-up self-assembly processes. This bottom-up construction and the operation of nanoscale machines/devices, in which the molecular motion can be controlled to perform functions, have been studied for their functionalities. Being triggered by external stimuli such as light, electricity or chemical reagents, these devices have shown various functions including those of diodes, rectifiers, memories, resonant tunnel junctions and single settable molecular switches that can be electronically configured for logic gates. Molecule-specific electronic switching has also been reported for several of these device structures, including nanopores containing oligo(phenylene ethynylene) monolayers, and planar junctions incorporating rotaxane and catenane monolayers for the construction and operation of complex molecular machines. A specific electrically driven surface mounted molecular rotor is described in detail in this review. The rotor is comprised of a monolayer of redox-active ligated copper compounds sandwiched between a gold electrode and a highly-doped P + Si. This electrically driven sandwich-type monolayer molecular rotor device showed an on/off ratio of approximately 10 4 , a read window of about 2.5 V, and a retention time of greater than 10 4 s. The rotation speed of this type of molecular rotor has been reported to be in the picosecond timescale, which provides a potential of high switching speed applications. Current-voltage spectroscopy (I-V) revealed a temperaturedependent negative differential resistance (NDR) associated with the device. The analysis of the device I-V characteristics suggests the source of the observed switching effects to be the result of the redox-induced ligand rotation around the copper metal center and this attribution of switching is consistent with the observed temperature dependence of the switching behavior as well as the proposed energy diagram of the device. The observed
A Chemically Switchable Molecular Pinwheel
Angewandte Chemie International Edition, 2006
The bottom-up fabrication of nanoscopic devices such as gears, [1] ratchets, [2] turnstiles, [3] switches, [4] and elevators [5] continues to attract much attention. The interest in molecular rotors in solution, [6] inside crystals, [7-9] and in the gas phase [10] has recently been extended to surface-mounted rotors; [11-13] most recently, a light-driven molecular rotor anchored to a gold surface has been demonstrated, [13] and a recent comprehensive review of artificial molecular rotors is available. [14] Derivatized porphyrins are versatile building blocks for the creation of many different types of assemblies, including supramolecular structures. [15] When adsorbed on surfaces, they can be imaged with scanning tunneling microscopy (STM). Copper tetra-(3,5-di-tert-butylphenyl)porphyrin (Cu-TBPP) adsorbed on Cu(100) was the first case in which singlemolecule manipulation at room temperature [16] and conformational recognition were achieved by means of STM. [17] In subsequent work with Cu-TBPP, Moresco et al. [18] were able to observe tip-induced conformational changes in individual di-tert-butyl phenyl (tBP) groups through height changes in the STM images. More recently, a metal-free TBPP functionalized with cyanophenyl terminal groups and adsorbed on Au(111) was used to form molecular assemblies including tetramers and one-dimensional wires; the structures of these assemblies were controlled by purposeful synthetic design of the monomer molecule. [19] Photoexcited molecular rotors have been observed in solution, [20] and the rotation of individual adsorbed molecules has been induced by manipulation with an STM tip; [11] however, reports of surfacemounted rotors are extremely sparse. [14] We describe herein a self-assembly method for switching on the rotation of adsorbed porphyrin molecules by mounting them on an appropriately functionalized ligand, one end of which binds to the surface, the other to the "hub" of the porphyrin. This was achieved by using zinc tetra-(3,5-di-tert-butylphenyl)porphyrin [21] (Zn-TBPP; Scheme 1 a), whose structure is such that interaction between the macrocycle component and the Ag(100) surface is minimized. As a result of steric repulsion, [*] O.
Atomic-scale STM experiments on semiconductor surfaces: towards molecular nanomachines
Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 2004
The electronic or quantum control of individual molecules with the scanning tunnelling microscope offers exciting perspectives on operating molecular nanomachines. This implies the use of semiconductor surfaces rather than metallic surfaces which would rapidly quench the electronic excitations. We review recent results illustrating the state of the art and the main problems which need to be solved: the choice, design and properties of functionalized organic molecules on semiconductor surfaces; the control of the inelastic electronic channels through a single molecule; and the search for well-controlled atomic-scale wide-band-gap semiconductor surfaces.
Molecular Engineering of Semiconductor Surfaces and Devices
Accounts of Chemical Research, 2002
Grafting organic molecules onto solid surfaces can transfer molecular properties to the solid. We describe how modifications of semiconductor or metal surfaces by molecules with systematically varying properties can lead to corresponding trends in the (electronic) properties of the resulting hybrid (molecule + solid) materials and devices made with them. Examples include moleculecontrolled diodes and sensors, where the electrons need not to go through the molecules (action at a distance), suggesting a new approach to molecule-based electronics.
Constructing an Array of Anchored Single-Molecule Rotors on Gold Surfaces
Physical Review Letters, 2008
Molecular rotors with a fixed off-center rotation axis have been observed for single tetra-tert-butyl zinc phthalocyanine molecules on an Au(111) surface by a scanning tunneling microscope at LN 2 temperature. Experiments and first-principles calculations reveal that we introduce gold adatoms at the surface as the stable contact of the molecule to the surface. An off-center rotation axis is formed by a chemical bonding between a nitrogen atom of the molecule and a gold adatom at the surface, which gives them a welldefined contact while the molecules can have rotation-favorable configurations. Furthermore, these singlemolecule rotors self-assemble into large scale ordered arrays on Au(111) surfaces. A fixed rotation axis off center is an important step towards the eventual fabrication of molecular motors or generators.
Nanostructure Science and Technology, 2004
As discussed in the previous chapter, the limits of silicon-based computer technology (microelectronics) are fast approaching. Alternative technologies are thus being investigated.
Molecular engineering of the polarity and interactions of molecular electronic switches
Journal of the American Chemical Society
We have investigated and learned to control switching of oligo(phenylene ethynylene)s embedded in amide-containing alkanethiol self-assembled monolayers on Au{111}. We demonstrate bias-dependent switching of the oligo(phenylene ethynylene)s as a function of the interaction between the dipole moment of the oligo(phenylene ethynylene)s and the electric field applied between the scanning tunneling microscope tip and the substrate. We are able to invert the polarity of the switches by altering their designsinverting their dipole moments. For appropriately designed switches and matrix molecules, the conductance states are stabilized by intermolecular hydrogen bonding. These results further support the hypothesis that conductance switching in these molecules is due to hybridization changes at the molecule-substrate bonds due to tilting of the switch molecules.