Modification Of Electronic Properties Research Articles

Identifying site-dependent effects of an extra Co atom on electronic states of single Co-phthalocyanine molecule

We investigate the modification of electronic properties of single cobalt phthalocyanine (CoPc) molecule by an extra Co atom co-adsorbed on Au (111) surface using scanning tunneling microscopy (STM), joint with density functional theory (DFT) calculations. By manipulating CoPc molecules using the STM tip to contact individually adsorbed Co atom, two types of relatively stable complexes can be formed, denoted as CoPc-Co(I) and CoPc-Co(II). In CoPc-Co(I), the Co atom is at an intramolecular site close to aza-N atom of CoPc, which induces significant modifications of the electronic states of CoPc, such as energy shifts and splitting of nonlocal molecular orbitals. However, in CoPc-Co(II) where the Co atom is underneath a benzene lobe of CoPc, it only slightly modifies the electronic states of CoPc, and mainly local characteristics of specific molecular orbitals are affected, even though CoPc-Co(II) is more stable than CoPc-Co(I). Our DFT calculations give consistent results with the experiments, and related analyses based on the molecular orbital theory reveal mechanism behind the experimental observations.

Enhanced Hydrogenation Properties of Size Selected Pd–C Core–Shell Nanoparticles; Effect of Carbon Shell Thickness

Effect of nanoparticle size and alloying has been well studied in Pd and Pd alloy nanoparticles and explained on the basis of modifications in the crystal structure and Pd 4d binding energy position. In the present study, the effect of carbon shell thickness on the hydrogenation properties of gas phase synthesized Pd–C core–shell nanoparticles having controllable nanoparticle core and shell thickness has been investigated. A large improvement in H/Pd ratio and increased hydrogen induced lattice expansion is observed in Pd–C nanoparticles. These results are explained on the basis of lowering of coordination number of Pd surface sites at Pd–C core–shell interface revealed by the increase in the Pd 4d binding energy on increase in shell thickness. By combining the modification in electronic properties due to the size and the alloying effects with that due to carbon shell thickness, as reported in the present study, Pd–H interaction can be significantly enhanced.

Modulation of Electronic Properties in Laterally and Commensurately Repeating Graphene and Boron Nitride Composite Nanostructures

Graphene and hexagonal boron nitride (h-BN) nanoribbons of diverse widths and edge geometries are laterally repeated to form commensurate, single-layer, hybrid honeycomb structures. The resulting composite materials appear as continuous, one atom thick stripes of graphene and BN having the average mechanical properties of constituent structures. However, depending on the widths of constituent stripes they can be metal or semiconductor with band gaps in the energy range of the visible light. These two-dimensional (2D) composite materials allow strong dimensionality in electrical conductivity and undergo transition from 2D to one-dimensional (1D) metal in a 2D medium, resulting in multichannel narrow conductors. As for the composite ribbons, such as one dielectric BN stripe placed between two graphene stripes with bare zigzag edges, charge separation of opposite polarity is possible under applied electric field and they exhibit resonant tunneling effects at nanoscale. Graphene/BN composite materials also fo...

Facile synthesis of cadmium sulphide-polyaniline (CdS-PANI) nanocomposite and its field emission investigations

A simple two step chemical route has been employed to synthesize cadmium sulphide - polyaniline (CdS-PANI) nanocomposite. In the first step PANI nanotubes are synthesized by oxidative polymerization followed by deposition of CdS nanoparticles on them. In order to investigate the structural, chemical and optical properties of the CdS-PANI nanocomposite, various characterization techniques have been used. The microscopic analysis reveals that the PANI nanotubes having length in several microns with cavity diameter of ~ 10 to 20 nm are decorated with CdS nanoparticles of 5 to 10 nm. The XRD spectrum indicates formation of crystalline hexagonal phase of CdS, supported by the SAED pattern obtained during TEM analysis. The FTIR and UV-visible spectra confirm formation of the conducting phase of PANI. The field emission studies of the CdS-PANI nanocomposite indicate low turn on field of 1.4 V/μm, corresponding to emission current density ~ 1 μA/cm2, and emission current density of ~ 5.5 mA/cm2 has been drawn at an applied field of 3.8 V/μm. Furthermore the emission current is observed to be fairly stable at the preset values over long term duration. The enhanced field emission properties, exhibited in terms of low turn on field, and delivery of very high emission current density at relatively lower applied field, are attributed to the nanometric dimensions of the PANI nanotubes and CdS nanoparticles, and modulation of electronic properties due to formation of heterojunction. The overall field emission results propose the CdS-PANI nanocomposite as a promising material for field emission based devices.

Selective cleavage of C[sbnd]O bond in benzyl phenyl ether to aromatics over Pd–Fe bimetallic catalyst supported on ordered mesoporous carbon

Bimetallic Pd–Fe catalyst supported on ordered mesoporous carbon (Pd–Fe/OMC) was prepared by a surfactant-templating method and a subsequent incipient wetness impregnation method. The catalyst was applied to the catalytic cleavage of CO bond in benzyl phenyl ether to aromatics. For comparison, monometallic Pd/OMC and Fe/OMC catalysts were also investigated. Benzyl phenyl ether was used as a lignin model compound for representing α-O-4 linkage in lignin. The combined effect of palladium and iron on the physicochemical properties and catalytic activities of Pd–Fe/OMC was investigated. Although Pd/OMC catalyst showed the highest conversion of benzyl phenyl ether, selectivity for aromatics was low due to saturation of aromatic ring. On the other hand, Fe/OMC catalyst showed lower conversion of benzyl phenyl ether than Pd/OMC, but Fe/OMC catalyst showed higher CO bond cleavage selectivity than Pd/OMC catalyst without saturation of aromatics. Bimetallic Pd–Fe/OMC catalyst showed the highest yield for aromatics. The introduction of Fe into Pd/OMC catalyst resulted in the modification of electronic properties of Pd by electron transfer from Fe to Pd, which led to the enhanced yield for aromatics.

Dynamic modulation of electronic properties of graphene by localized carbon doping using focused electron beam induced deposition.

We report on the first demonstration of controllable carbon doping of graphene to engineer local electronic properties of a graphene conduction channel using focused electron beam induced deposition (FEBID). Electrical measurements indicate that an "n-p-n" junction on graphene conduction channel is formed by partial carbon deposition near the source and drain metal contacts by low energy (<50 eV) secondary electrons due to inelastic collisions of long range backscattered primary electrons generated from a low dose of high energy (25 keV) electron beam (1 × 10(18) e(-) per cm(2)). Detailed AFM imaging provides direct evidence of the new mechanism responsible for dynamic evolution of the locally varying graphene doping. The FEBID carbon atoms, which are physisorbed and weakly bound to graphene, diffuse towards the middle of graphene conduction channel due to their surface chemical potential gradient, resulting in negative shift of Dirac voltage. Increasing a primary electron dose to 1 × 10(19) e(-) per cm(2) results in a significant increase of carbon deposition, such that it covers the entire graphene conduction channel at high surface density, leading to n-doping of graphene channel. Collectively, these findings establish a unique capability of FEBID technique to dynamically modulate the doping state of graphene, thus enabling a new route to resist-free, "direct-write" functional patterning of graphene-based electronic devices with potential for on-demand re-configurability.

Targeting metallo-carbapenemases via modulation of electronic properties of cephalosporins.

The global proliferation of metallo-carbapenemase-producing Enterobacteriaceae has created an unmet need for inhibitors of these enzymes. The rational design of metallo-carbapenemase inhibitors requires detailed knowledge of their catalytic mechanisms. Nine cephalosporins, structurally identical except for the systematic substitution of electron-donating and withdrawing groups in the para position of the styrylbenzene ring, were synthesized and utilized to probe the catalytic mechanism of New Delhi metallo-β-lactamase (NDM-1). Under steady-state conditions, K(m) values were all in the micromolar range (1.5-8.1 μM), whereas k(cat) values varied widely (17-220 s(-1)). There were large solvent deuterium isotope effects for all substrates under saturating conditions, suggesting a proton transfer is involved in the rate-limiting step. Pre-steady-state UV-visible scans demonstrated the formation of short-lived intermediates for all compounds. Hammett plots yielded reaction constants (ρ) of -0.34 ± 0.02 and -1.15 ± 0.08 for intermediate formation and breakdown, respectively. Temperature-dependence experiments yielded ΔG(‡) values that were consistent with the Hammett results. These results establish the commonality of the formation of an azanide intermediate in the NDM-1-catalysed hydrolysis of a range cephalosporins with differing electronic properties. This intermediate is a promising target for judiciously designed β-lactam antibiotics that are poor NDM-1 substrates and inhibitors with enhanced active-site residence times.

Uniaxial strain-induced mechanical and electronic property modulation of silicene.

We perform first-principles calculations of mechanical and electronic properties of silicene under uniaxial strains. Poisson's ratio and the rigidity of silicene show strong chirality dependence under large uniaxial strains. The ultimate strains of silicene with uniaxial strain are smaller than those with biaxial strain. We find that uniaxial strains induce Dirac point deviation from the high-symmetry points in the Brillouin zone and semimetal-metal transitions. Therefore, no bandgap opens under the uniaxial strain. Due to its peculiar structure and variable sp3/sp2 ratio of the chemical bond, the deviation directions of Dirac points from the high-symmetry points in the Brillouin zone and variation of Fermi velocities of silicene exhibit significant difference from those of graphene. Fermi velocities show strong anisotropy with respect to the wave vector directions and change slightly before the semimetal-metal transition. We also find that the work function of silicene increases monotonously with the increasing uniaxial strains.PACS numbers61.46.-w; 62.20.D-; 73.22.Dj

An optoelectronic framework enabled by low-dimensional phase-change films.

The development of materials whose refractive index can be optically transformed as desired, such as chalcogenide-based phase-change materials, has revolutionized the media and data storage industries by providing inexpensive, high-speed, portable and reliable platforms able to store vast quantities of data. Phase-change materials switch between two solid states--amorphous and crystalline--in response to a stimulus, such as heat, with an associated change in the physical properties of the material, including optical absorption, electrical conductance and Young's modulus. The initial applications of these materials (particularly the germanium antimony tellurium alloy Ge2Sb2Te5) exploited the reversible change in their optical properties in rewritable optical data storage technologies. More recently, the change in their electrical conductivity has also been extensively studied in the development of non-volatile phase-change memories. Here we show that by combining the optical and electronic property modulation of such materials, display and data visualization applications that go beyond data storage can be created. Using extremely thin phase-change materials and transparent conductors, we demonstrate electrically induced stable colour changes in both reflective and semi-transparent modes. Further, we show how a pixelated approach can be used in displays on both rigid and flexible films. This optoelectronic framework using low-dimensional phase-change materials has many likely applications, such as ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent 'smart' glasses, 'smart' contact lenses and artificial retina devices.

Modification of electronic properties of the surface of (100) silicon crystals under microwave plasma micromachining

The behavior of the effect of microwave plasma micromachining on electronic properties of (100) silicon crystal surfaces at weak adsorption was investigated. Model process mechanisms and factors providing stable modification of the electronic properties of the silicon surface by the formation of built-in surface potentials determined by chemical reactivity of the used working gases and modes of microwave plasma treatment were considered. The possibility in principle of the active formation of electronic properties of the surface of semiconductor crystals to extend their electrophysical and functional properties was shown.

Modulation of structural, energetic and electronic properties of DNA and size-expanded DNA bases upon binding to gold clusters

A strong modulation in electronic properties, indicating that such complexes have the potential to serve as scaffolds for building nano electronic devices.

Structural and electronic properties of GeTe under pressure: ab initio study

The versatile phase transition character and associated intriguing electronic properties of germanium telluride (GeTe) have attracted intense interests from both academic and industrial perspectives. At ambient pressure, GeTe falls into a rhombohedral structure. With hydrostatic pressure applied, the rhombohedral R3mH GeTe transforms into NaCl (B1) structure at 3·2 GPa, and at 34·3 GPa, it transforms into CsCl (B2) structure. Diverse phase transitions under pressure lead to significant modulations in energy band gaps, which is still not clear. The aim of this research is to investigate the energy band gap of GeTe under pressure. Using first principles calculations, the proposed research investigates the structural phase transition and corresponding electronic energy band behaviour of GeTe under pressure. From the energy band structure analysis, it was found that the B2 phase is metallic, while the B1 and R3mH phases possess a narrow band gap at the equilibrium state. With pressure applied, the insulating gaps of both structures close gradually under positive pressure and enlarge upon negative pressure. The novel aspect of this work is the modulation of energy band gaps by mechanical pressure. The predicted band gaps can change over a wide range, which suggests possible and efficient electronic property modulation using external pressure. Furthermore, these findings are helpful in predicting the structural stability and optical band gap associated performance in GeTe based advanced materials under pressure.

INTRODUCTION TO THE TOPICAL ISSUE ON THERMOELECTRIC MATERIALS AND DEVICES

More than 50% of the primary energy input in the global economy is lost to waste heat, a substantial fraction of which is recoverable in principle. For example, approximately half of the waste heat in a car or truck is in the form of high temperature exhaust gas. It is therefore no surprise that there has been a resurgence of interest in thermoelectric materials. Thermoelectrics provide a modular, solid-state technology for extracting electrical energy from heat. The key limitation has been low efficiency limited by the performance of known materials. This is characterized by a figure of merit, ZT. A decade ago the best practical materials had ZT of roughly unity, a figure that had not changed for many years. Efforts over the past decade have led to a doubling of this figure. This accelerating progress underlies the scientific excitement around this field. This topical issue contains a selection of papers covering various aspects of thermoelectric research, including both characterization techniques and thermoelectric materials. The issue emphasizes green materials, which are particularly important for many energy applications. This includes a paper on characterization of oxide-based modules, as well as papers on silicides, chalcogenides, and skutterudites including both theory and experiment. Nano-structure is a key theme in thermoelectrics research, both for control of thermal conductivity and for modification of electronic properties. Several papers in this issue concern aspects of nanostructure and its effect on thermoelectricity. Finally, we remark that thermoelectric performance depends on simultaneous optimization of normally contradictory properties such as conductivity and thermopower. This leads to a particularly fruitful interplay of theory and experiment as well as the exploration of unusual materials that show a fascinating variety of physical properties. We hope that this issue captures the excitement that results.

Comparison of modification of electronic properties of single-walled carbon nanotubes filled with metal halogenide, chalcogenide, and pure metal

In present work, thulium chloride, gallium selenide, bismuth telluride, and silver were encapsulated into the channels of single-walled carbon nanotubes (SWCNTs). The structural properties of obtained nanostructures were studied by high-resolution transmission electron microscopy, and the modification of electronic properties of nanotubes as result of filling their channels with chosen substances was investigated by Raman spectroscopy and X-ray photoelectron spectroscopy. It was shown that the electronic properties of filled SWCNTs depend on the chemical nature of incorporated materials. The encapsulation of TmCl3 and GaSe into the carbon nanotube channels leads to acceptor doping of the SWCNTs, and this effect is more prominent for thulium chloride. The incorporation of bismuth telluride into the nanotube cavities does not result in any modification of their electronic properties. The filling of the nanotube channels with silver leads to donor doping of the single-walled carbon nanotubes.

The Structure and Function of Quinones in Biological Solar Energy Transduction: A Cyclic Voltammetry, EPR, and Hyperfine Sub-Level Correlation (HYSCORE) Spectroscopy Study of Model Naphthoquinones

Quinones function as electron transport cofactors in photosynthesis and cellular respiration. The versatility and functional diversity of quinones is primarily due to the diverse midpoint potentials that are tuned by the substituent effects and interactions with surrounding amino acid residues in the binding site in the protein. In the present study, a library of substituted 1,4-naphthoquinones are analyzed by cyclic voltammetry in both protic and aprotic solvents to determine effects of substituent groups and hydrogen bonds on the midpoint potential. We use continuous-wave electron paramagnetic resonance (EPR) spectroscopy to determine the influence of substituent groups on the electronic properties of the 1,4-naphthoquinone models in an aprotic solvent. The results establish a correlation between the presence of substituent group(s) and the modification of electronic properties and a corresponding shift in the midpoint potential of the naphthoquinone models. Further, we use pulsed EPR spectroscopy to determine the effect of substituent groups on the strength and planarity of the hydrogen bonds of naphthoquinone models in a protic solvent. This study provides support for the tuning of the electronic properties of quinone cofactors by the influence of substituent groups and hydrogen bonding interactions.

Modulation of electronic properties of π-conjugated copolymers derived from naphtho[1,2-b:5,6-b′]dithiophene donor unit: A structure-property relationship study

A set of three donor-acceptor conjugated (D-A) copolymers were designed and synthesized via Stille cross-coupling reactions with the aim of modulating the optical and electronic properties of a newly emerged naphtho[1,2-b:5,6-b′]dithiophene donor unit for polymer solar cell (PSCs) applications. The PTNDTT-BT, PTNDTT-BTz, and PTNDTT-DPP polymers incorporated naphtho[1,2-b:5,6-b′]dithiophene (NDT) as the donor and 2,2′-bithiazole (BTz), benzo[1,2,5]thiadiazole (BT), and pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP), as the acceptor units. A number of experimental techniques such as differential scanning calorimetry, thermogravimetry, UV–vis absorption spectroscopy, cyclic voltammetry, X-ray diffraction, and atomic force microscopy were used to determine the thermal, optical, electrochemical, and morphological properties of the copolymers. By introducing acceptors of varying electron withdrawing strengths, the optical band gaps of these copolymers were effectively tuned between 1.58 and 1.9 eV and their HOMO and LUMO energy levels were varied between −5.14 to −5.26 eV and −3.13 to −3.5 eV, respectively. The spin-coated polymer thin film exhibited p-channel field-effect transistor properties with hole mobilities of 2.73 × 10−3 to 7.9 × 10−5 cm2 V−1 s−1. Initial bulk-heterojunction PSCs fabricated using the copolymers as electron donor materials and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as the acceptor resulted in power conversion efficiencies in the range of 0.67–1.67%. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2948–2958

Modification of electronic properties of top-gated graphene devices by ultrathin yttrium-oxide dielectric layers

We report the structure characterization and electronic property modification of single layer graphene (SLG) field-effect transistor (FET) devices top-gated using ultrathin Y(2)O(3) as dielectric layers. Based on the Boltzmann transport theory within variant screening, Coulomb scattering is confirmed quantitatively to be dominant in Y(2)O(3)-covered SLG and a very few short-range impurities have been introduced by Y(2)O(3). Both DC transport and AC capacitance measurements carried out at cryogenic temperatures demonstrate that the broadening of Landau levels is mainly due to the additional charged impurities and inhomogeneity of carriers induced by Y(2)O(3) layers.

Tuning metal-insulator transition by one dimensional alignment of giant electronic domains in artificially size-controlled epitaxial VO2 wires

We demonstrate control of spatial dimensionality of disordered configurations of giant electronic domains in systematically size-changed VO2 wires on TiO2 (001) substrates. One-dimensional alignment of the domains appears in wires narrower than 15 μm width, while two-dimensional configurations were observed for larger ones. The rearrangement of domains from two to one dimension causes modification of electronic properties.

Modification of Electronic Properties of Graphene with Porphyrin Self-Assembled Monolayers and Photoinduced Interactions

Modification of Electronic Properties of Graphene with Porphyrin Self-Assembled Monolayers and Photoinduced Interactions

Octahedral tilting in strained LaVO3thin films

The effect of biaxial strain on the oxygen octahedra rotations in a LaVO${}_{3}$ thin film is investigated using synchrotron radiation. First, we find that the film adopts a distorted orthorhombic structure under the compressive stress induced by the SrTiO${}_{3}$ substrate. Second, we separate the contribution to the superstructure peaks arising from cation displacement and VO${}_{6}$ rotations in order to quantify the rotation angles. Finally, we find an original ${a}^{\ensuremath{-}}{a}^{+}{c}^{\ensuremath{-}}$ tilt system, which is induced by the biaxial strain imposed by the substrate. These quantitative results may open up new directions for understanding the modification of electronic properties of engineered oxide films.