Three-terminal devices to examine single molecule conductance switching

We report electronic transport measurements of single-molecule transistor devices incorporating bipyridyl-dinitro oligophenylene-ethynylene dithiol (BPDN-DT), a molecule known to exhibit conductance switching in other measurement configurations. We observe hysteretic conductance switching in 8% of devices with measurable currents, and find that dependence of the switching properties on gate voltage is rare when compared to other single-molecule transistor devices. This suggests that polaron formation is unlikely to be responsible for switching in these devices. We discuss this and alternative switching mechanisms.Comment: 5 pages, 4 figures. Supporting material available upon reques

Controlling charge injection in organic field-effect transistors using self-assembled monolayers

We have studied charge injection across the metal/organic semiconductor interface in bottom-contact poly(3-hexylthiophene) (P3HT) field-effect transistors, with Au source and drain electrodes modified by self-assembled monolayers (SAMs) prior to active polymer deposition. By using the SAM to engineer the effective Au work function, we markedly affect the charge injection process. We systematically examine the contact resistivity and intrinsic channel mobility, and show that chemically increasing the injecting electrode work function significantly improves hole injection relative to untreated Au electrodes.Comment: 5 pages, 2 figures. Supplementary information available upon reques

Kondo resonances and anomalous gate dependence of electronic conduction in single-molecule transistors

We report Kondo resonances in the conduction of single-molecule transistors based on transition metal coordination complexes. We find Kondo temperatures in excess of 50 K, comparable to those in purely metallic systems. The observed gate dependence of the Kondo temperature is inconsistent with observations in semiconductor quantum dots and a simple single-dot-level model. We discuss possible explanations of this effect, in light of electronic structure calculations.Comment: 5 pages, four figures. Supplementary material at http://www.ruf.rice.edu/~natelson/publications.htm

Functionalization of Organic Semiconductor Crystals via the Diels-Alder Reaction

A surface adlayer is generated on organic single crystals (tetracene and rubrene) using the site specific Diels–Alder reaction and a series of vapor phase dienophiles. X-ray photoelectron spectroscopy (XPS) confirms adsorption on the surfaces of tetracene and rubrene and mass spectrometry demonstrates the reaction’s applicability to a range of dienophiles

Inelastic electron tunneling via molecular vibrations in single-molecule transistors

In single-molecule transistors, we observe inelastic cotunneling features that correspond energetically to vibrational excitations of the molecule, as determined by Raman and infrared spectroscopy. This is a form of inelastic electron tunneling spectroscopy of single molecules, with the transistor geometry allowing in-situ tuning of the electronic states via a gate electrode. The vibrational features shift and change shape as the electronic levels are tuned near resonance, indicating significant modification of the vibrational states. When the molecule contains an unpaired electron, we also observe vibrational satellite features around the Kondo resonance.Comment: 5 pages, 4 figures. Supplementary information available upon reques

Single-Molecule Transistors: Electron Transfer in the Solid State

Single-molecule transistors (SMTs) incorporating individual small molecules are unique tools for examining the fundamental physics and chemistry of electronic transport in molecular systems at the single nanometer scale. We describe the fabrication and characterization of such devices, and the synthesis and surface attachment chemistry of novel transition metal complexes that have been incorporated into such SMTs. We present gate-modulated inelastic electron tunneling vibrational spectroscopy of single molecules, strong Kondo physics (TK ∼ 75 K) as evidence of excellent molecule/electrode electronic coupling, and a demonstration that covalent attachment chemistry can produce SMTs that survive repeated thermal cycling to room temperature. We conclude with a look ahead at the prospects for these nanoscale systems

AC losses and critical current density of superconducting GdBa2Cu3O7−x

Energy losses occurring in a cylindrical sample of Gd-Ba-Cu-O, subjected to an external AC magnetic field were examined. The loss dependence on the amplitude of the magnetic induction exhibits two stages of flux penetration into the superconductor. Critical current densitities for both stages of penetration were examined and an explanation for such behaviour is proposed. Support for this point of view is obtained by measurements on pulverized sample material. All measurements were performed at a temperature of 4.2 K and in absence of a background field.\ud \ud Analysis of the data provides two critical current densities: an inter-granular critical current density at weak alternating magnetic fields and an intra-granular critical current density at higher magnetic fields. The intra-granular critical current density is at least two orders of magnitude larger than the inter-granular one

Course variability of the atlantic (V3) segment of vertebral artery: anatomical study with clinical implications

Background: The atlantic segment of vertebral artery (V3) located at the centre of the cranio-vertebral junction is known for its variability and asymmetry, and is either the target or on the way of numerous procedures in this region. The aim of the study was to visualise variability of V3 segment. Materials and methods: The V3 segment was studied in 49 specimens of the suboccipital region injected with coloured gelatine. Direct measurements were performed and probabilistic maps were created using digital photography. Results: The V3 segment has wavy course with possible lateral and significant postero-inferior expansions. In relation to the foramen transversarium the V3 reached up to 5 mm laterally, 23 mm posteriorly, 27 mm medially and up to 11 mm downward. Looking from the medial aspect the course of the V3 is less predictable compared to the lateral approach. Linear measurements and probabilistic maps revealed significant variability and large range of variation. There were 11 cases of V3 tortuosity found in studied material. Conclusions: The complex and variable spatial conformation of V3 makes individual diagnostic and preoperative approach necessary

Median aperture of the fourth ventricle revisited

Background: The median aperture of Magendie is the largest of three openings of the fourth ventricle and thus it forms the main path for the outflow of the cerebrospinal fluid from the ventricle. The Magendie aperture connects the fourth ventricle with the cisterna magna and makes a natural corridor for neurosurgical approach and inspection of the ventricle and its floor. The purpose of this study was to give a contemporary anatomical view of this structure in the context of historical data. Material and methods: The Magendie foramen was studied in 30 fixed specimens of human brainstems with cerebella. The microdissection technique was used. Measurements were taken with a microscope ocular ruler. Results: The aperture is limited by the following structures: obex and gracile tubercles inferiorly, and tela choroidea with choroid plexus superolaterally. Obex tubercles usually have the form of a piece of neural tissue bridging two halves of the brainstem above the entrance to the central canal. Gracile tubercles together are 8.15 mm wide and the maximal width of the foramen is 6.53 mm. Tela choroidea attaches laterally at both sides to the inferior medullary velum. In most cases the right and left choroid plexus are connected to each other with a triangular membrane of tela choroidea, which protrudes through the median foramen and attaches to the vermis at a highly variable level. Conclusions: We hope that the presented description of anatomical relations around the Magendie aperture, with its new measurements, will be helpful for those operating in the area and will explain some of the inaccuracies found in literature. (Folia Morphol 2011; 70, 2: 84–90

The anatomy of the fundic branches of the stomach: preliminary results

The fundic branches of the stomach can be defined as a group of vessels that can arise either directly or indirectly from the following source arteries: the left inferior phrenic artery, the accessory left hepatic artery, the left gastric artery, the left middle suprarenal artery, the main trunk of the splenic artery, the posterior gastric artery, the superior polar artery, the gastrosplenic artery, the left gastroepiploic artery and the splenic artery with its inferior and superior terminal branches. It is worth mentioning that the fundic branches of the left gastroepiploic artery and the superior and inferior terminal branches of the splenic artery, like other vessels arising from these three source arteries and supplying the stomach, are defined as short gastric arteries. The anatomy of these fundic branches, particularly relevant to some surgical procedures, is not sufficiently described, and the current literature suffers from lack of publications on this particular topic. We therefore decided to explore in detail the arterial vascularisation of the gastric fundus. The research was carried out on material consisting of 15 human stomach specimens. The anatomical analysis comprised the following: the number of occurrences of fundic branches in each of the source arteries defined above, the distance between the origins of the source artery and its arising fundic branch, the way in which the fundic branches arose, the length, diameter at point of origin and morphology of the fundic braches, as well as the exact point of perforation of each fundic branch on the fundus. The highest incidence of the direct-branching pattern of fundic branches was in the left middle suprarenal artery, the gastrosplenic artery and the left gastrosplenic artery. The accessory left hepatic artery, the left gastric artery and the main trunk of the splenic artery were the most frequent site of the indirectly arising pattern of fundic branch. The highest median value of fundic branch length was 63.05 mm, found in the accessory left hepatic artery group. The largest median diameter value of the vessel was encountered among those originating in the left middle suprarenal artery and reached 2.17 mm. The posterolateral quadrant of the fundus received the largest number of fundic branches, amounting to 46.5% of all the fundic branches studied. (Folia Morphol 2008; 67: 120–125