Electrical conductance of molecular junctions by a robust statistical analysis

We propose an objective and robust method to extract the electrical conductance of single molecules connected to metal electrodes from a set of measured conductance data. Our method roots in the physics of tunneling and is tested on octanedithiol using mechanically controllable break junctions. The single molecule conductance values can be deduced without the need for data selection.Comment: 4 figure

Optical Near-Field Electron Microscopy

Imaging dynamical processes at interfaces and on the nanoscale is of great importance throughout science and technology. While light-optical imaging techniques often cannot provide the necessary spatial resolution, electron-optical techniques damage the specimen and cause dose-induced artefacts. Here, Optical Near-field Electron Microscopy (ONEM) is proposed, an imaging technique that combines non-invasive probing with light, with a high spatial resolution read-out via electron optics. Close to the specimen, the optical near-fields are converted into a spatially varying electron flux using a planar photocathode. The electron flux is imaged using low energy electron microscopy, enabling label-free nanometric resolution without the need to scan a probe across the sample. The specimen is never exposed to damaging electrons

Quantitative analysis of spectroscopic Low Energy Electron Microscopy data: High-dynamic range imaging, drift correction and cluster analysis

For many complex materials systems, low-energy electron microscopy (LEEM) offers detailed insights into morphology and crystallography by naturally combining real-space and reciprocal-space information. Its unique strength, however, is that all measurements can easily be performed energy-dependently. Consequently, one should treat LEEM measurements as multi-dimensional, spectroscopic datasets rather than as images to fully harvest this potential. Here we describe a measurement and data analysis approach to obtain such quantitative spectroscopic LEEM datasets with high lateral resolution. The employed detector correction and adjustment techniques enable measurement of true reflectivity values over four orders of magnitudes of intensity. Moreover, we show a drift correction algorithm, tailored for LEEM datasets with inverting contrast, that yields sub-pixel accuracy without special computational demands. Finally, we apply dimension reduction techniques to summarize the key spectroscopic features of datasets with hundreds of images into two single images that can easily be presented and interpreted intuitively. We use cluster analysis to automatically identify different materials within the field of view and to calculate average spectra per material. We demonstrate these methods by analyzing bright-field and dark-field datasets of few-layer graphene grown on silicon carbide and provide a high-performance Python implementation

Charge transport in a single superconducting tin nanowire encapsulated in a multiwalled carbon nanotube

The charge transport properties of single superconducting tin nanowires, encapsulated by multiwalled carbon nanotubes have been investigated by multi-probe measurements. The multiwalled carbon nanotube protects the tin nanowire from oxidation and shape fragmentation and therefore allows us to investigate the electronic properties of stable wires with diameters as small as 25 nm. The transparency of the contact between the Ti/Au electrode and nanowire can be tuned by argonion etching the multiwalled nanotube. Application of a large electrical current results in local heating at the contact which in turn suppresses superconductivity

Growing a LaAlO3/SrTiO3 heterostructure on Ca2Nb3O10 nanosheets

The two-dimensional electron liquid which forms between the band insulators LaAlO3 (LAO) and SrTiO3 (STO) is a promising component for oxide electronics, but the requirement of using single crystal SrTiO3 substrates for the growth limits its applications in terms of device fabrication. It is therefore important to find ways to deposit these materials on other substrates, preferably Si, or Si-based, in order to facilitate integration with existing technology. Interesting candidates are micron-sized nanosheets of Ca2Nb3O10 which can be used as seed layers for perovskite materials on any substrate. We have used low-energy electron microscopy (LEEM) with in-situ pulsed laser deposition to study the subsequent growth of STO and LAO on such flakes which were deposited on Si. We can follow the morphology and crystallinity of the layers during growth, as well as fingerprint their electronic properties with angle resolved reflected electron spectroscopy. We find that STO layers, deposited on the nanosheets, can be made crystalline and flat; that LAO can be grown in a layer-by-layer fashion; and that the full heterostructure shows the signature of the formation of a conducting interface.Comment: 11 pages, 7 figure

Observation of Quantum Interference in Molecular Charge Transport

As the dimensions of a conductor approach the nano-scale, quantum effects will begin to dominate its behavior. This entails the exciting possibility of controlling the conductance of a device by direct manipulation of the electron wave function. Such control has been most clearly demonstrated in mesoscopic semiconductor structures at low temperatures. Indeed, the Aharanov-Bohm effect, conductance quantization and universal conductance fluctuations are direct manifestations of the electron wave nature. However, an extension of this concept to more practical emperatures has not been achieved so far. As molecules are nano-scale objects with typical energy level spacings (~eV) much larger than the thermal energy at 300 K (~25 meV), they are natural candidates to enable such a break-through. Fascinating phenomena including giant magnetoresistance, Kondo effects and conductance switching, have previously been demonstrated at the molecular level. Here, we report direct evidence for destructive quantum interference in charge transport through two-terminal molecular junctions at room temperature. Furthermore, we show that the degree of interference can be controlled by simple chemical modifications of the molecule. Not only does this provide the experimental demonstration of a new phenomenon in quantum charge transport, it also opens the road for a new type of molecular devices based on chemical or electrostatic control of quantum interference

Uni- and bi-directional light-induced switching of diarylethenes on gold nanoparticles

Photochromic studies of diarylethenes with their switching unit linked to the surface of gold nanoparticles via a conjugated aromatic spacer show linker-dependent switching behavior

Interpretation of Transition Voltage Spectroscopy

The promise of transition voltage spectroscopy (TVS) is that molecular level positions can be determined in molecular devices without applying extreme voltages. Here, we consider the physics behind TVS in more detail. Remarkably, we find that the Simmons model employed thus far is inconsistent with experimental data. However, a coherent molecular transport model does justify TVS as a spectroscopic tool. Moreover, TVS may become a critical test to distinguish molecular junctions from vacuum tunnel junctions.

Data underlying: Stacking domain morphology in epitaxial graphene on silicon carbide

 This dataset contains stitched AC-LEEM overviews visualizing stacking domain boundaries in three different, high-quality graphene on SiC samples, grown in three different manners. The samples exhibit domain boundaries with different morphology, as explored in the corresponding paper. More details on the files can be found in the README.</p