We demonstrate semi-metallic transport in graphene oxide layers treated with an organic acid through a nearly linear current-vs.-voltage relationship and the weak temperature dependence of resistance from high temperatures down to 20 K. Additionally an energy gap was observed below 17 K due to the formation of local barriers by residual oxygen groups and disorder in reduced graphene oxide (RGO) sheets. At higher temperatures resistance shows a negative T 2 temperature dependence. Temperature dependent magnetization measurements showed a phase transition from diamagnetic to ferromagnetic at around 10 K, in agreement with the electronic transport properties of the RGO films.
This study illuminates the specific role of the nitrogen potential in relation to the Fermi level (EF) in nitrogen incorporated amorphous carbon (a–CN) superlattice structures. In a–CN systems, the variation of conductivity with nitrogen percentage has been found to be strongly non-linear due to the change of disorder level. Here, we investigate the effect of correlated carbon (C) and nitrogen (N) disorder in conjunction with the nitrogen potential through the analysis of transmission spectra, calculated using a tight binding Hamiltonian, which show two broad peaks related to these species. The characteristic time of transmission through N centers can be controlled through a combination of the N potential and correlated disorder. In particular, by controlling the arrangement of the nitrogen sites within the sp2−C clusters as well as their energetic position compared to EF, a crossover of the pronounced transmission peaks of N and C sites can be achieved. Furthermore, N incorporated as a potential barrier can also enhance the transmission in the a–CN superlattice structures. The strong non-linear variation of resistance and the characteristic time of the structures can explain the transport features observed experimentally in a–CN films. These results will find application in the design of new a–CN fast-switching devices, whose characteristics can be tuned by the nitrogen potential and associated structural disorder.
Resonant tunneling features through impurity clusters embedded in an insulating matrix have been examined through the inter-play between the size of the clusters and the inter-cluster distance. Constructive interference phenomena were tuned through a systematic study of different geometrical configurations, thereby controlling confinement in quasi-bound states. Gaussian trap potentials have been used to simulate the imperfect barrier-well interface associated with disordered materials. Strongly localized states can be formed successfully despite weak disorder as illustrated by breaking the symmetry in the horizontal configuration. To this end, triangular cluster configurations were investigated under a variety of conditions including various shapes and orientations. The effects of disorder created effectively by the arbitary configurations destroy the Fano resonance, which is previlent in conductance spectra and consequently reduce the peak to valley ratio of the resonant peak in current vs. voltage curves. However the formation of two quasi-bound states is demonstrated, suggesting possible applications for disordered naturally grown systems of impurity clusters. This work addresses the controlled lifetime of quasi-bound states and can inform the design of fast switching devices based on high band gap materials by the astute incorporation of impurity clusters with specific geometrical configurations.
We report nitrogen-induced enhanced electron tunnel transport and improved nanomechanical properties in band gap-modulated nitrogen doped DLC (N-DLC) quantum superlattice (QSL) structures. The electrical characteristics of such superlattice devices revealed negative differential resistance (NDR) behavior. The interpretation of these measurements is supported by 1D tight binding calculations of disordered superlattice structures (chains), which include bond alternation in sp(3)-hybridized regions. Tandem theoretical and experimental analysis shows improved tunnel transport, which can be ascribed to nitrogen-driven structural modification of the N-DLC QSL structures, especially the increased sp(2) clustering that provides additional conduction paths throughout the network. The introduction of nitrogen also improved the nanomechanical properties, resulting in enhanced elastic recovery, hardness, and elastic modulus, which is unusual but is most likely due to the onset of cross-linking of the network. Moreover, the materials' stress of N-DLC QSL structures was reduced with the nitrogen doping. In general, the combination of enhanced electron tunnel transport and nanomechanical properties in N-DLC QSL structures/devices can open a platform for the development of a new class of cost-effective and mechanically robust advanced electronic devices for a wide range of applications.
Catheter-related blood stream infections increase morbidity, mortality, and costs. This study investigated whether Certofix® protect antimicrobial catheters carry a surface charge and whether this inhibits biofilm formation. The capacitance of the catheter surfaces was measured and, to determine if the catheters released ions, distilled water was passed through and current measured as a function of voltage. With probes touching the inner and outer surfaces, capacitance was not voltage-dependent, indicating surfaces were uncharged or carried a similar charge. When one probe penetrated the catheter wall, capacitance was weakly voltage-dependent, indicating the presence of a surface charge. Standard and charged catheters were also exposed to phosphate buffered saline as controls or 2×106 colony forming units/mL (in phosphate buffered saline) of six different microorganisms for 60 or 120 minutes. When the growth of detached bacteria was measured, biofilm formation was significantly reduced, (P<0.05), for charged catheters for all organisms.
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