First Principles Study on the Electronic Structure and Interface Stability of Hybrid Silicene/Fluorosilicene Nanoribbons

© 2015 Macmillan Publishers Limited. The interface stability of hybrid silicene/fluorosilicene nanoribbons (SFNRs) has been investigated by using density functional theory calculations, where fluorosilicene is the fully fluorinated silicene. It is found that the diffusion of F atoms at the zigzag and armchair interfaces of SFNRs is endothermic, and the corresponding minimum energy barriers are respectively 1.66 and 1.56 eV, which are remarkably higher than the minimum diffusion energy barrier of one F atom and two F atoms on pristine silicene 1.00 and 1.29 eV, respectively. Therefore, the thermal stability of SFNRs can be significantly enhanced by increasing the F diffusion barriers through silicene/fluorosilicene interface engineering. In addition, the electronic and magnetic properties of SFNRs are also investigated. It is found that the armchair SFNRs are nonmagnetic semiconductors, and the band gap of armchair SFNRs presents oscillatory behavior when the width of silicene part changing. For the zigzag SFNRs, the antiferromagnetic semiconducting state is the most stable one. This work provides fundamental insights for the applications of SFNRs in electronic devices

Enhancement of CO detection in Al doped graphene

A principle of the enhancement of CO adsorption was developed theoretically by using density functional theory through doping Al into graphene. The results show that the Al doped graphene has strong chemisorption of CO molecule by forming Al-CO bond, where CO onto intrinsic graphene remains weak physisorption. Furthermore, the enhancement of CO sensitivity in the Al doped graphene is determined by a large electrical conductivity change after adsorption, where CO absorption leads to increase of electrical conductivity via introducing large amount of shallow acceptor states. Therefore, this newly developed Al doped graphene would be an excellent candidate for sensing CO gas. © 2008 Elsevier B.V. All rights reserved

The tuned absorptance in multilayer graphene-dielectric structures by intraband transition

© 2017 Author(s). In this work, using the transfer-matrix method, the optical transport process is investigated, with graphene inserted into multilayer dielectric structures, theoretically and numerically in the THz regime. When the incident frequency is lower than the graphene Fermi energy, the optical intra-band transitions provide the main contribution to the graphene surface current. The absorptance can be enhanced to about 50% with only one graphene/dielectric layer in air. When increasing the number of dielectric layers coated with graphene, the absorption increases. Periodic absorption peaks are observed in multilayer structures. The positions of the absorption peaks as a function of the frequency and the incident angle are in accordance with the positions of the abrupt change in the reflection coefficient phase and of the imaginary solution of the Bloch wavevector in expanding periodic structures using Bloch theorem

Density functional theory study on the electronic properties and stability of silicene/silicane nanoribbons

© The Royal Society of Chemistry 2015. The thermal stability of silicene/silicane nanoribbons (SSNRs) has been investigated by using density functional theory calculations, where silicane is the fully hydrogenated silicene. It was found that the minimum energy barriers for the diffusion of hydrogen atoms at the zigzag and armchair interfaces of SSNRs are 1.54 and 1.47 eV, respectively, while the diffusion of H atoms at both interfaces is always endothermic. Meanwhile, the minimum diffusion energy barriers of one H atom and two H atoms on pristine silicene are 0.73 and 0.87 eV, respectively. Therefore, the thermal stability of SSNRs can be significantly enhanced by increasing the hydrogen diffusion barriers through silicene/silicane interface engineering. In addition, the zigzag SSNR remains metallic, whereas the armchair SSNR is semiconducting. However, the silicene nanoribbons part-determine the metallic or semiconducting behaviour in the SSNRs. This work provides fundamental insights for the applications of SSNRs in electronic devices. This journal i

Enhanced hydrogen sensing properties of graphene by introducing a mono-atom-vacancy

To facilitate the dissociative adsorption of H2 molecules on pristine graphene, the addition of a mono-atom-vacancy to graphene is proposed. This leads to reduction of the dissociative energy barrier for a H2 molecule on graphene from 3.097 to 0.805 eV for the first H2 and 0.869 eV for the second, according to first principles calculations. As a result, two H2 molecules can be easily dissociatively adsorbed on this defected graphene at room temperature. The electronic structure and conductivity of the graphene change significantly after H2 adsorption. In addition, the related dissociative adsorption phase diagrams under different temperatures and partial pressures show that this dissociative adsorption at room temperature is very sensitive (10-35 mol L -1). Therefore, this defected graphene is promising for ultra-sensitive room temperature hydrogen sensing. © 2013 the Owner Societies

Temperature- and thickness-dependent elastic moduli of polymer thin films

The mechanical properties of polymer ultrathin films are usually different from those of their counterparts in bulk. Understanding the effect of thickness on the mechanical properties of these films is crucial for their applications. However, it is a great challenge to measure their elastic modulus experimentally with in situ heating. In this study, a thermodynamic model for temperature- (T) and thickness (h)-dependent elastic moduli of polymer thin films Ef(T,h) is developed with verification by the reported experimental data on polystyrene (PS) thin films. For the PS thin films on a passivated substrate, Ef(T,h) decreases with the decreasing film thickness, when h is less than 60 nm at ambient temperature. However, the onset thickness (h*), at which thickness Ef(T,h) deviates from the bulk value, can be modulated by T. h* becomes larger at higher T because of the depression of the quenching depth, which determines the thickness of the surface layer δ

Endogenous cholinergic inputs and local circuit mechanisms govern the phasic mesolimbic dopamine response to nicotine

Nicotine exerts its reinforcing action by stimulating nicotinic acetylcholine receptors (nAChRs) and boosting dopamine (DA) output from the ventral tegmental area (VTA). Recent data have led to a debate about the principal pathway of nicotine action: direct stimulation of the DAergic cells through nAChR activation, or disinhibition mediated through desensitization of nAChRs on GABAergic interneurons. We use a computational model of the VTA circuitry and nAChR function to shed light on this issue. Our model illustrates that the α4β2-containing nAChRs either on DA or GABA cells can mediate the acute effects of nicotine. We account for in vitro as well as in vivo data, and predict the conditions necessary for either direct stimulation or disinhibition to be at the origin of DA activity increases. We propose key experiments to disentangle the contribution of both mechanisms. We show that the rate of endogenous acetylcholine input crucially determines the evoked DA response for both mechanisms. Together our results delineate the mechanisms by which the VTA mediates the acute rewarding properties of nicotine and suggest an acetylcholine dependence hypothesis for nicotine reinforcement.Peer reviewe

Pharmaceutical electrochemistry: the electrochemical detection of aspirin utilising screen printed graphene electrodes as sensors platforms.

A sensitive electrochemical sensor was designed for acetyl salicylic acid detection using graphene modified Screen Printed Electrodes. The electrochemical response of the sensor with graphene was improved compared to Screen Printed Electrodes without graphene and displayed an excellent analytical performance for the detection of acetyl salicylic acid. The high acetyl salicylic acid loading capacity on the electrode surface and the outstanding electric conductivity of graphene were also discussed in this manuscript. When a range of different concentrations of acetyl salicylic acid from 0.1 to 100 μM into a pH 4 buffer solution (N defined as the sample size N = 9) were plotted against the oxidation peak a linear response was observed. The detection limit was found to be 0.09 μM based on (3-σ/slope). Screen Printed Graphene electrodes sensors methodology is shown to be useful for quantifying low levels of acetyl salicylic acid in a buffer solution as well as in biological matrixes such as human oral fluid. A linear response was obtained over a range of concentrations from 10 to 150 μM into a human oral fluid solution (N = 10) giving a detection limit of 8.7 μM

Cooperative Effects in the Photoluminescence of (In,Ga)As/GaAs Quantum Dot Chain Structures

Multilayer In0.4Ga0.6As/GaAs quantum dot (QD) chain samples are investigated by means of cw and time-resolved photoluminescence (PL) spectroscopy in order to study the peculiarities of interdot coupling in such nanostructures. The temperature dependence of the PL has revealed details of the confinement. Non-thermal carrier distribution through in-chain, interdot wave function coupling is found. The peculiar dependences of the PL decay time on the excitation and detection energies are ascribed to the electronic interdot coupling and the long-range coupling through the radiation field. It is shown that the dependence of the PL decay time on the excitation wavelength is a result of the superradiance effect

MAGE I Transcription Factors Regulate KAP1 and KRAB Domain Zinc Finger Transcription Factor Mediated Gene Repression

Class I MAGE proteins (MAGE I) are normally expressed only in developing germ cells but are aberrantly expressed in many cancers. They have been shown to promote tumor survival, aggressive growth, and chemoresistance but the underlying mechanisms and MAGE I functions have not been fully elucidated. KRAB domain zinc finger transcription factors (KZNFs) are the largest group of vertebrate transcription factors and regulate neoplastic transformation, tumor suppression, cellular proliferation, and apoptosis. KZNFs bind the KAP1 protein and direct KAP1 to specific DNA sequences where it suppresses gene expression by inducing localized heterochromatin characterized by histone 3 lysine 9 trimethylation (H3me3K9). Discovery that MAGE I proteins also bind to KAP1 prompted us to investigate whether MAGE I can affect KZNF and KAP1 mediated gene regulation. We found that expression of MAGE I proteins, MAGE-A3 or MAGE-C2, relieved repression of a reporter gene by ZNF382, a KZNF with tumor suppressor activity. ChIP of MAGE I (-) HEK293T cells showed KAP1 and H3me3K9 are normally bound to the ID1 gene, a target of ZNF382, but that binding is greatly reduced in the presence of MAGE I proteins. MAGE I expression relieved KAP1 mediated ID1 repression, causing increased expression of ID1 mRNA and ID1 chromatin relaxation characterized by loss of H3me3K9. MAGE I binding to KAP1 also induced ZNF382 poly-ubiquitination and degradation, consistent with loss of ZNF382 leading to decreased KAP1 binding to ID1. In contrast, MAGE I expression caused increased KAP1 binding to Ki67, another KAP1 target gene, with increased H3me3K9 and decreased Ki67 mRNA expression. Since KZNFs are required to direct KAP1 to specific genes, these results show that MAGE I proteins can differentially regulate members of the KZNF family and KAP1 mediated gene repression