Modification Of Electronic Properties Research Articles

One step hydrothermal synthesis of SnO2-RGO nanocomposite and its field emission studies

Field emission (FE) properties of hydrothermally synthesized, SnO2-RGO nanocomposite have been investigated at a base pressure of 1×10−8mbar. The results reveal that the SnO2-RGO nanocomposite emitter prevails over the pristine RGO emitter. The values of turn-on field, defined at emission current density of 1 μA/cm2, are found to be 1.8 and 2.2V/μm for the SnO2-RGO and pristine RGO emitters, respectively. Furthermore, the SnO2-RGO emitter delivers maximum emission current density of ~800µA/cm2 at an applied field of 5V/μm. The observed values of applied field corresponding to emission current densities of 1 μA/cm2 and 10µA/cm2 are superior to those reported for various emitters due to SnO2 nanostructures and their composites. The emission current at the pre-set value of 1µA is found to be very stable over a period of 3hrs. The enhanced FE behaviour of SnO2-RGO nanocomposite emitter has been attributed to synergic effect due to its nanometric dimensions offering high aspect ratio and modulation of electronic properties via formation of heterostructure. The results obtained herein propose the SnO2-RGO nanocomposite as a prospective candidate for FE based vacuum microelectronic devices.

Strain and water effects on the electronic structure and chemical activity of in-plane graphene/silicene heterostructure

By using first-principles calculations, the electronic structure of planar and strained in-plane graphene/silicene heterostructure is studied. The heterostructure is found to be metallic in a strain range from −7% (compression) to +7% (tension). The effect of compressive/tensile strain on the chemical activity of the in-plane graphene/silicene heterostructure is examined by studying its interaction with the H2O molecule. It shows that compressive/tensile strain is able to increase the binding energy of H2O compared with the adsorption on a planar surface, and the charge transfer between the water molecule and the graphene/silicene sheet can be modulated by strain. Moreover, the presence of the boron-nitride (BN)-substrate significantly influences the chemical activity of the graphene/silicene heterostructure upon its interaction with the H2O molecule and may cause an increase/decrease of the charge transfer between the H2O molecule and the heterostructure. These findings provide insights into the modulation of electronic properties of the in-plane free-standing/substrate-supported graphene/silicene heterostructure, and render possible ways to control its electronic structure, carrier density and redox characteristics, which may be useful for its potential applications in nanoelectronics and gas sensors.

Modulation of electronic properties of tin oxide nanobelts via thermal control of surface oxygen defects

Nanomaterials made from binary metal oxides are of increasing interest because of their versatility in applications from flexible electronics to portable chemical and biological sensors. Controlling the electrical properties of these materials is the first step in device implementation. Tin dioxide (SnO2) nanobelts (NB) synthesized by the vapor–liquid–solid mechanism have shown much promise in this regard. We explore the modification of devices prepared with single crystalline NBs by thermal annealing in vacuum and oxygen, resulting in a viable field-effect transistor (FET) for numerous applications at ambient temperature. An oxygen annealing step initially increases the device conductance by up to a factor of 105, likely through the modification of the surface defects of the NB, leading to Schottky barrier limited devices. A multi-step annealing procedure leads to further increase of the conductance by approximately 350% and optimization of the electronic properties. The effects of each step is investigated systematically on a single NB. The optimization of the electrical properties of the NBs makes possible the consistent production of channel-limited FETs and control of the device performance. Understanding these improvements on the electrical properties over the as-grown materials provides a pathway to enhance and tailor the functionalities of tin oxide nanostructures for a wide variety of optical, electronic, optoelectronic, and sensing applications that operate at room temperature.

Influence of laser irradiation on local electronic properties of graphene in the presence of water adsorbate

The effect of volatility of local electronic properties in multilayered (3–6 layers) graphene irradiated by nanosecond laser pulses with a wavelength 532nm in humid atmosphere was found. The experiments were carried out in situ in a scanning probe microscope (SPM) with Pt/Si tip. It was established that along with local profile transformation of graphene sheet (the formation of "nanocrater" with depth up to 2nm and ~1µm diameter) in the zone of the laser action (~0,5µm) a decrease (~20meV) of the electrons work function was observed. It takes place in the region larger but comparable with the irradiation spot size. Analysis of the experimental data on local electrical conductivity have shown that the bottom of conduction band for graphene in laser irradiation area was reduced by ~ 50meV. The observed changes of graphene physical properties were associated with the laser-induced radial displacement of the water layer intercalated between graphene and substrate. In addition, it was experimentally established that the graphene work function was decreased significantly less than can be expected for an "ideal" 3 - 6 layer graphene. The investigated process of laser-induced changes of graphene properties demonstrated the reproducible character and long-term stability. Possibility of laser fabrication of arrays in graphene with periodic modulation of electronic properties was demonstrated.

Modulation of electrical potential and conductivity in an atomic-layer semiconductor heterojunction.

Semiconductor heterojunction interfaces have been an important topic, both in modern solid state physics and in electronics and optoelectronics applications. Recently, the heterojunctions of atomically-thin transition metal dichalcogenides (TMDCs) are expected to realize one-dimensional (1D) electronic systems at their heterointerfaces due to their tunable electronic properties. Herein, we report unique conductivity enhancement and electrical potential modulation of heterojunction interfaces based on TMDC bilayers consisted of MoS2 and WS2. Scanning tunneling microscopy/spectroscopy analyses showed the formation of 1D confining potential (potential barrier) in the valence (conduction) band, as well as bandgap narrowing around the heterointerface. The modulation of electronic properties were also probed as the increase of current in conducting atomic force microscopy. Notably, the observed band bending can be explained by the presence of 1D fixed charges around the heterointerface. The present findings indicate that the atomic layer heterojunctions provide a novel approach to realizing tunable 1D electrical potential for embedded quantum wires and ultrashort barriers of electrical transport.

First-principles study of size-, surface- and mechanical strain-dependent electronic properties of wurtzite and zinc-blende InSb nanowires

Using first-principle calculations with density functional theory, we investigated the modification of electronic properties in zinc-blende (ZB) and wurtzite (WZ) InSb nanowires (NWs) grown along the [111] and [0001] directions for different size, different surface coverage and different mechanical strain. The results show that before the surface passivation, ZBNWs and WZNWs exhibit the metallic character and the semiconductor character, respectively. WZNWs show a crossover from a direct to an indirect as diameter decreases. After the surface passivation, both ZBNWs and WZNWs are found to be direct-gap character. The electronic band structure shows a significant response to changes in surface passivation with pseudo hydrogen and halogen. The band structure with mechanical strain is strongly dependent on the crystal orientation and the NW diameter. In ZBNWs, compressive strain induces the indirect band gap character, whereas tensile strain can not form it. WZNWs have various strain dependence in that both compressive and tensile strain make InSb show a direct band gap character. A brief analysis of these results is given.

Modification of electronic properties of graphene by using low-energy K+ ions

Despite its superb electronic properties, the semi-metallic nature of graphene with no band gap (Eg) at the Dirac point has been a stumbling block for its industrial application. We report an improved means of producing a tunable band gap over other schemes by doping low energy (10 eV) potassium ions (K+) on single layer graphene formed on 6H-SiC(0001) surface, where the noble Dirac nature of the π-band remains almost unaltered. The changes in the π-band induced by K+ ions reveal that the band gap increases gradually with increasing dose (θ) of the ions up to Eg = 0.65 eV at θ = 1.10 monolayers, demonstrating the tunable character of the band gap. Our core level data for C 1s, Si 2p, and K 2p suggest that the K+-induced asymmetry in charge distribution among carbon atoms drives the opening of band gap, which is in sharp contrast with no band gap when neutral K atoms are adsorbed on graphene. This tunable K+-induced band gap in graphene illustrates its potential application in graphene-based nano-electronics.

Modulation of electronic properties from stacking orders and spin-orbit coupling for 3R-type MoS2

Two-dimensional crystals stacked by van der Waals coupling, such as twisted graphene and coupled graphene-BN layers with unusual phenomena have been a focus of research recently. As a typical representative, with the modulation of structural symmetry, stacking orders and spin-orbit coupling, transitional metal dichalcogenides have shown a lot of fascinating properties. Here we reveal the effect of stacking orders with spin-orbit coupling on the electronic properties of few-layer 3R-type MoS2 by first principles methods. We analyze the splitting of states at the top of valence band and the bottom of conduction band, following the change of stacking order. We find that regardless of stacking orders and layers’ number, the spin-up and spin-down channels are evidently separated and can be as a basis for the valley dependent spin polarization. With a model Hamiltonian about the layer’s coupling, the band splitting can be effectively analyzed by the coupling parameters. It is found that the stacking sequences, such as abc and abca, have the stronger nearest-neighbor coupling which imply the popular of periodic abc stacking sequence in natural growth of MoS2.

Fluorodiphenylethene-Containing Donor–Acceptor Conjugated Copolymers with Noncovalent Conformational Locks for Efficient Polymer Field-Effect Transistors

The diphenylethene moiety is a versatile building block that offers several chemically functionalizable sites, allowing easy modulation of electronic properties of the resulting polymers and providing numerous opportunities for discovering related structure–property relationships. In this study, we report a series of difluorodiphenylethene-based copolymers with noncovalent conformational locks for applications in polymer field-effect transistors. Different fluorination positions lead to different type of intra- and intermolecular interactions, backbone conformations, and eventually different device performances. 2,2′-Difluorodiphenylethene-based copolymers P2DFPE-n containing F···H–C conformation locks exhibit obviously enhanced hole mobilities of 1.3–1.5 cm2 V–1 s–1, whereas 3,3′-difluorodiphenylethene-based copolymers P3DFPE-n containing F···H–C and F···S conformation locks show lower mobilities of 0.2–0.4 cm2 V–1 s–1. AFM and 2D-GRXD investigations indicate that P2DFPE-n takes predominantly edge-on ori...

Effects of strain on electronic properties of monolayer α-Fe2O3

Density functional theory was employed to study the strain-induced modification of electronic properties of advanced monolayer α-Fe2O3 for the first time. Theoretical results indicated that there was obvious dependency of band structure on strain. The band gap modulation could reach up to −29.0% for 7% compressive strain and to 10.6% for 7% tensile strain. The analytical results of fat-band structures demonstrated that the considerable modulation range of band gaps was mainly caused by the Fe-dz2 orbital.

Facile, single step synthesis of CdS—RGO heterostructure and its photo enhanced field emission investigations

CdS–RGO heterostructure was synthesized by a thermal evaporation method and characterized using x-ray diffraction, SEM, TEM, photoluminescence spectroscopy (PL) and Raman spectroscopy so as to reveal its structural, compositional and electronic properties, prior to field emission (FE) investigations. The FE characteristics with and without visible illumination of the CdS–RGO heterostructure planar emitter were measured at base pressure 1 × 10−8 mbar. The values of turn-on field, corresponding to emission current density of 1 μA/cm2 without and with illumination, are found to be 2.3 and 2.0 V μm−1, respectively. Furthermore, under pulsating illumination, the emitter exhibits emission current pulses depicting nearly four times enhancement in the emission current, with rise and fall time constants as 4.4 and 6.4 s, respectively. The photoenhanced FE behaviour is attributed to the modulation of electronic properties due to the CdS nanostructures. The results obtained herein propose the CdS–RGO heterostructure emitter as a photo-sensitive field emission switch in next generation optoelectronic nanodevices.

Efficient nitrogen doping of graphene by plasma treatment

Doping of pristine materials can change their chemical and electrical properties. Namely nitrogen doping of graphene results in modulation of electronic properties of graphene. In this work we present experimental results on nitrogen doped graphene fabricated in two steps. At first, the graphene samples were synthesized by a chemical vapor deposition method on copper foils. Then they were treated with ammonia radio frequency discharge plasma. The prepared samples were investigated by atomic-force microscopy (AFM), scanning electron microscopy (SEM), Raman spectroscopy, optical absorption spectroscopy including Fourier transform infrared spectroscopy (FTIR), X-ray and ultraviolet photoelectron spectroscopy. In doped graphene a dependence of N-atom concentration on the treatment parameters has been revealed. A maximum doping level of 3 atomic % has been obtained and the shift of valence band maximum of 0.2 eV was observed at this concentration of nitrogen.

Electronic Property Modulation of One-Dimensional Extended Graphdiyne Nanowires from a First-Principle Crystal Orbital View.

Graphdiyne and derivatives with delocalized π‐electron systems are of particular interest owing to their structural, electronic, and transport properties, which are important for potential applications in next‐generation electronics. Inspired by recently obtained extended graphdiyne nanowires, explorations of the modulation of the band gap and carrier mobility of this new species are still needed before application in device fabrication. To provide a deeper understanding of these issues, herein we present theoretical studies of one‐dimensional extended graphdiyne nanowires using first‐principle calculations. Modulation of the electronic properties of the extended graphdiyne nanowire was investigated systemically by considering several chemical and physical factors, including electric field, chemical functionalization, and carbo‐merization. The band gap was observed to increase upon application of an electric field parallel to the plane of the synthesized graphdiyne nanowire in a non‐periodic direction. Although chemical functionalization and carbo‐merization caused the band gaps to decrease, the semiconducting property of the nanowires was preserved. Band gap engineering of the extended graphdiyne nanowires was explored regarding the field strength and the number of −C≡C− units in the carbon chain fragments. The charge carrier mobility of chemically functionalized and carbo‐merized extended graphdiyne nanowires was also calculated to provide a comparison with pristine nanowire. Moreover, crystal orbital analysis was performed in order to discern the electronic and charge transport properties of the extended graphdiyne nanowires modified by the aforementioned chemical and physical factors.

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.