Bi-stable tunneling current through a molecular quantum dot

An exact solution is presented for tunneling through a negative-U d-fold degenerate molecular quantum dot weakly coupled to electrical leads. The tunnel current exhibits hysteresis if the level degeneracy of the negative-U dot is larger than two (d>2). Switching occurs in the voltage range V1 < V < V2 as a result of attractive electron correlations in the molecule, which open up a new conducting channel when the voltage is above the threshold bias voltage V2. Once this current has been established, the extra channel remains open as the voltage is reduced down to the lower threshold voltage V1. Possible realizations of the bi-stable molecular quantum dots are fullerenes, especially C60, and mixed-valence compounds.Comment: 5 pages, 1 figure. (v2) Figure updated to compare the current hysteresis for degeneracies d=4 and d>>1 of the level in the dot, minor corrections in the text. To appear in Phys. Rev.

Driving current through single organic molecules

We investigate electronic transport through two types of conjugated molecules. Mechanically controlled break-junctions are used to couple thiol endgroups of single molecules to two gold electrodes. Current-voltage characteristics (IVs) of the metal-molecule-metal system are observed. These IVs reproduce the spatial symmetry of the molecules with respect to the direction of current flow. We hereby unambigously detect an intrinsic property of the molecule, and are able to distinguish the influence of both the molecule and the contact to the metal electrodes on the transport properties of the compound system.Comment: 4 pages, 5 figure

Determinants of environmental management in the red sea hotels: Personal and organizational values and contextual variables

What motivates firms to adopt environmental management practices is one of the most significant aspects in the contemporary academic debate in which the review of the existing literature yields, with an obvious contextual bias toward developed world, contested theories and inconclusive findings. Providing a unique model that brings together the individual and organizational levels of analysis on firms' adoption of environmental management practices, this study aims to provide a new insight from the context of developing world. Data from 158 Red Sea hotels reveal two identifiable dimensions of environmental management-planning and organization, and operations-that can be explained as originating from different values. Whereas organizational altruism is a powerful predictor of both dimensions, managers' personal values and organizational competitive orientation are only relevant to environmental operations. The evidence also indicates that contextual variables such as chain affiliation, hotel star rating, and size are important to explain hotels' environmental management behaviors. © 2012 ICHRIE

Current hysteresis and memory effect in a molecular quantum dot with strong electron-vibron interaction

Theory of current hysteresis for tunneling through a molecular quantum dot (MQD) with strong electron-vibron interactions and attractive electron-electron correlations is developed. The dot is modeled as a d-fold degenerate energy level weakly coupled to the leads. The effective attractive interaction between polarons in the dot results in a "switching" phenomenon in the current-voltage characteristics when d>2, in agreement with the results for the phenomenological negative-U model. The degenerate MQD with strong electron-vibron coupling has two stable current states in certain interval of the bias voltage below some critical temperature.Comment: 8 pages, 4 figure

Field-induced p-n transition in yttria-stabilized zirconia

Oxide ion conducting yttria-stabilised zirconia ceramics show the onset of electronic conduction under a small bias voltage. Compositions with a high yttria content undergo a transition from p-type to n-type behavior at voltages in the range 2.4 to 10 V, which also depends on oxygen partial pressure. Surface reactions have a direct influence on bulk electronic conductivities, with possible implications for voltage-induced flash phenomena and resistive switching

High-yield single-step catalytic growth of graphene nanostripes by plasma enhanced chemical vapor deposition

We report a single-step growth process of graphene nanostripes (GNSPs) by adding certain substituted aromatics (e.g., 1,2-dichlorobenzene) as precursors during the plasma enhanced chemical vapor deposition (PECVD). Without any active heating and by using low plasma power (≤60 W), we are able to grow GNSPs vertically with high yields up to (13 ± 4) g/m^2 in 20 min. These GNSPs exhibit high aspect ratios (from 10:1 to >∼130:1) and typical widths from tens to hundreds of nanometers on various transition-metal substrates. The morphology, electronic properties and yields of the GNSPs can be controlled by the growth parameters (e.g., the species of seeding molecules, compositions and flow rates of the gases introduced into the plasma, plasma power, and the growth time). Studies of the Raman spectra, scanning electron microscopy images, ultraviolet photoelectron spectroscopy, transmission electron microscopy images, energy-dispersive x-ray spectroscopy and electrical conductivity of these GNSPs as functions of the growth parameters confirm high-quality GNSPs with electrical mobility ∼10^4 cm^2/V-s. These results together with residual gas analyzer spectra and optical emission spectroscopy taken during PECVD growth suggest the important roles of both substituted aromatics and hydrogen plasma in the rapid vertical growth of GNSPs with large aspect ratios

High-yield single-step catalytic growth of graphene nanostripes by plasma enhanced chemical vapor deposition

We report a single-step growth process of graphene nanostripes (GNSPs) by adding certain substituted aromatics (e.g., 1,2-dichlorobenzene) as precursors during the plasma enhanced chemical vapor deposition (PECVD). Without any active heating and by using low plasma power (≤60 W), we are able to grow GNSPs vertically with high yields up to (13 ± 4) g/m^2 in 20 min. These GNSPs exhibit high aspect ratios (from 10:1 to >∼130:1) and typical widths from tens to hundreds of nanometers on various transition-metal substrates. The morphology, electronic properties and yields of the GNSPs can be controlled by the growth parameters (e.g., the species of seeding molecules, compositions and flow rates of the gases introduced into the plasma, plasma power, and the growth time). Studies of the Raman spectra, scanning electron microscopy images, ultraviolet photoelectron spectroscopy, transmission electron microscopy images, energy-dispersive x-ray spectroscopy and electrical conductivity of these GNSPs as functions of the growth parameters confirm high-quality GNSPs with electrical mobility ∼10^4 cm^2/V-s. These results together with residual gas analyzer spectra and optical emission spectroscopy taken during PECVD growth suggest the important roles of both substituted aromatics and hydrogen plasma in the rapid vertical growth of GNSPs with large aspect ratios

Bridging fluorescence microscopy and electron microscopy

Development of new fluorescent probes and fluorescence microscopes has led to new ways to study cell biology. With the emergence of specialized microscopy units at most universities and research centers, the use of these techniques is well within reach for a broad research community. A major breakthrough in fluorescence microscopy in biology is the ability to follow specific targets on or in living cells, revealing dynamic localization and/or function of target molecules. One of the inherent limitations of fluorescence microscopy is the resolution. Several efforts are undertaken to overcome this limit. The traditional and most well-known way to achieve higher resolution imaging is by electron microscopy. Moreover, electron microscopy reveals organelles, membranes, macromolecules, and thus aids in the understanding of cellular complexity and localization of molecules of interest in relation to other structures. With the new probe development, a solid bridge between fluorescence microscopy and electron microscopy is being built, even leading to correlative imaging. This connection provides several benefits, both scientifically as well as practically. Here, I summarize recent developments in bridging microscopy