236 research outputs found
From Nanofabrication to Self-fabrication – Tailored Chemistry for Control of Single Molecule Electronic Devices
Single molecule electronics is a field of research focused on the use of single molecules as electronics components. During the past 15 years the field has concentrated on development of test beds for measurements on single molecules. Bottom–up approaches to single molecule devices
are emerging as alternatives to the dominant top–down nanofabrication techniques. One example is solution-based self-assembly of a molecule enclosed by two gold nanorod electrodes. This article will discuss recent attempts to control the self-assembly process by the use of supramolecular
chemistry and how to tailor the electronic properties of a single molecule by chemical design
Design and construction of a heat stage for investigations of samples by atomic force microscopy above ambient temperatures
Charge transport through image charged stabilized states in a single molecule single electron transistor device
The present paper gives an elaborate theoretical description of a new
molecular charge transport mechanism applying to a single molecule trapped
between two macroscopic electrodes in a solid state device. It is shown by a
Hubbard type model of the electronic and electrostatic interactions, that the
close proximity of metal electrodes may allow electrons to tunnel from the
electrode directly into a very localized image charge stabilized states on the
molecule. Due to this mechanism, an exceptionally large number of redox states
may be visited within an energy scale which would normally not allow the
molecular HOMO-LUMO gap to be transversed. With a reasonable set of parameters,
a good fit to recent experimental values may be obtained. The theoretical model
is furthermore used to search for the physical boundaries of this effect, and
it is found that a rather narrow geometrical space is available for the new
mechanism to be effective: In the specific case of oligophenylenevinylene
molecules recently explored in such devices several atoms in the terminal
benzene rings need to be at van der Waal's distance to the electrode in order
for the mechanism to be effective. The model predicts, that chemisorption of
the terminal benzene rings too gold electrodes will impede the image charge
effect very significantly because the molecule is pushed away from the
electrode by the covalent thiol-gold bond.Comment: 9 pages, 5 figue
X-ray diffraction and molecular dynamics studies: Structural analysis of phases in diglyseride monolayers
Deterministic assembly of linear gold nanorod chains as a platform for nanoscale applications
We demonstrate a method to assemble gold nanorods highly deterministically into a chain formation by means of directed capillary assembly. This way we achieved straight chains consisting of end-to-end aligned gold nanorods assembled in one specific direction with well-controlled gaps of [similar]6 nm between the individual constituents. We determined the conditions for optimum quality and yield of nanorod chain assembly by investigating the influence of template dimensions and assembly temperature. In addition, we transferred the gold nanorod chains from the assembly template onto a Si/SiO2 target substrate, thus establishing a platform for a variety of nanoscale electronic and optical applications ranging from molecular electronics to optical and plasmonic devices. As a first example, electrical measurements are performed on contacted gold nanorod chains before and after their immersion in a solution of thiol end-capped oligophenylenevinylene molecules showing an increase in the conductance by three orders of magnitude, indicating molecular-mediated transport
Influence of Lipid Heterogeneity and Phase Behavior on Phospholipase A2 Action at the Single Molecule Level
We monitored the action of phospholipase A2 (PLA2) on L- and
D-dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers by mounting a
Langmuir-trough on a wide-field fluorescence microscope with single molecule
sensitivity. This made it possible to directly visualize the activity and
diffusion behavior of single PLA2 molecules in a heterogeneous lipid
environment during active hydrolysis. The experiments showed that enzyme
molecules adsorbed and interacted almost exclusively with the fluid region of
the DPPC monolayers. Domains of gel state L-DPPC were degraded exclusively from
the gel-fluid interface where the build-up of negatively charged hydrolysis
products, fatty acid salts, led to changes in the mobility of PLA2. The
mobility of individual enzymes on the monolayers was characterized by single
particle tracking (SPT). Diffusion coefficients of enzymes adsorbed to the
fluid interface were between 3 mu m^2/s on the L-DPPC and 4.6 mu m^/s on the
D-DPPC monolayers. In regions enriched with hydrolysis products the diffusion
dropped to approx. 0.2 mu m^2/s. In addition, slower normal and anomalous
diffusion modes were seen at the L-DPPC gel domain boundaries where hydrolysis
took place. The average residence times of the enzyme in the fluid regions of
the monolayer and on the product domain were between approx. 30 and 220 ms. At
the gel domains it was below the experimental time resolution, i.e. enzymes
were simply reflected from the gel domains back into solution.Comment: 10 pages, 10 figure
Evidence of Strong Hydration and Significant Tilt of Amphiphilic [2]Rotaxane Molecules in Langmuir Films Studied by Synchrotron X-ray Reflectivity
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