Modification Of Electrical Properties Research Articles

Localized Plasmon-Stimulated Nanochemistry of Graphene Oxide on a SERS Substrate.

In recent years, there has been remarkable progress in the reduction and functionalization of graphene oxide (GO) using nanoparticles and high-energy optical photons. Most of these reactions are carried out in solutions, whereas the local modification of GO on solid substrates still remains a challenge. In this work, we demonstrate the local reduction of GO and its further destruction, leading to the synthesis of polyaromatic hydrocarbons (PAHs) stimulated by localized surface plasmons (LSPs). The reduction of GO and the synthesis of PAHs have been carried out on a substrate designed for surface-enhanced Raman spectroscopy (SERS). We found that LSPs initiate the destruction of water molecules entrapped in the nanogaps between silver nanoparticles after the deposition of GO from the aqueous suspension. It was demonstrated that OH radicals, as a result of water decomposition, initiate the reduction of GO, leading to the synthesis of PAHs. The reactions have been observed in real time by using SERS. The measurement of current-voltage (I-V) characteristics through conductive atomic force microscopy (AFM), recorded in an LSP-stimulated area, have shown the increased electrical conductivity (more than ten times) compared with the conductivity of GO. The synthesis of new compounds in the LSP-stimulated area has been confirmed by the appearance of new peaks in the Raman spectra and nonlinear I-V characteristics typical for PAHs. We show that the used method allows the local modification of electrical properties of GO and controlled nanopattering of organic compounds on the surface.

Modification of electrical properties and carrier transportation mechanism of ALD-derived HfO2/Si gate stacks by Al2O3 incorporation

Effect of Al2O3 incorporation on the electrical properties and carrier transportation of atomic-layer-deposited (ALD) HfAlO high-k gate dielectrics on Si substrates have been investigated. Electrical analyses indicate that interfacial properties of HfAlO/Si gate stack have been improved and leakage current is reduced after Al2O3 incorporation into HfO2. Additionally, the HfAlO sample with precursor ratio (TEMAH: TMA) of 4:2 exhibits the lowest interface state density (Dit) of 3.6 × 1011 cm−2 eV−1, the lowest border trapped oxide charge density (Nbt) of 2.4 × 1011 cm−2, the lower density of oxide charge (Qox) of 0.9 × 1012 cm−2, and the lowest frequency dispersion of 0.15%. In addition, the carrier transportation mechanism for both HfO2 and HfAlO has been investigated systematically. Based on the analysis, it can be concluded that Poole-Frenkle (P–F) emission is main conduction mechanism at the low electric field, and direct tunneling (D-T) dominates the conduction mechanism at the high field, respectively.

Effect of TiO2Rutile Additive on Electrical Properties of PPy/TiO2Nanocomposite

Polypyrrole/titanium dioxide nanocomposite (PPy/TiO2) was synthesized byin situchemical polymerization of pyrrole (Py) monomer in colloidal suspension of TiO2rutile. TEM and SEM images show that the TiO2is covered by PPy forming a core-shell structure. The PPy/TiO2core-shell will createn-pjunction and bring in an inversion layer on the PPy-shell surface. The feature is accounted for the modification in electrical properties of the PPy/TiO2nanocomposite. On the exposure to oxygen the conductivity of the nanocomposite exhibits an increase in 16–18-folds that are accounted for the interaction between oxygen (an electron acceptor) and the inversion layer. The cyclic voltammetry diagrams have shown that at around 15% TiO2and scan rate 100 mV/s the nanocomposites can reach a specific capacitance about 176 F/g.

Modification of electrical and piezoelectric properties of ZnO nanorods based on arsenic incorporation via low temperature spin-on-dopant method

We report on the control of the electrical and the piezoelectric properties of ZnO nanorods (NRs) by incorporation of arsenic (As) elements via a low-temperature processed spin-on-dopant (SOD) method. The structural investigations for the SOD-treated ZnO NRs at different temperatures show a negligible change in morphology at temperatures up to 550 °C and melting of the ZnO NRs at 600 °C. Low-temperature photoluminescence (PL) spectra show gradual development of acceptor-related emission peaks with increasing SOD treatment temperature from 450 to 550 °C, which indicates the successful incorporation of As atoms into the ZnO NRs. An AsZn-2VZn shallow acceptor model is suggested by considering the formation energy of the interstitial point-defect complex for the modification of the electrical properties of ZnO NRs. A ZnO NR/n-Si heterojunction showed better rectifying behavior with increasing SOD treatment temperature, indicating better incorporation of As-dopants at higher SOD treatment temperatures. A piezoelectric nanogenerator was fabricated as a device application of the electrical-property-modified ZnO NRs. The nanogenerator showed enhanced piezoelectric output potential after doping due to the elimination of the screening effect by free charge carriers in the ZnO NRs.

Modifications in electrical properties of ZnO:In/PS/Si (100) heterojunction by ZnO intermediate layer

The sol-gel method has been used for the synthesis of indium doped zinc oxide (IZO) aerogel nanopowder; the obtained product was used in the target as a source for the deposition of thin IZO layers onto p-type porous silicon (PS) substrate by radio frequency magnetron sputtering. We deposited two heterostructures with (IZO/ZnO/PS/Si) and without (IZO/PS/Si) ZnO intermediate layer to study its role on the electrical properties. The obtained IZO thin films with a thickness of about 400 nm using indium concentration of 4 at%, were polycrystalline with a hexagonal wurtzite structure and preferential orientation in the (002) crystallographic direction. The effect of the intermediate ZnO layer on the electrical properties of the two heterojunctions, n-IZO/PS/p-Si and n-IZO/ZnO/PS/p-Si, was systematically investigated by current–voltage (I–V), capacitance–voltage (C–V), and capacitance–frequency (C–F) characteristics. Our measurements show that the junction properties strongly depend on temperature and the intermediate ZnO layer has significant impact on the transport properties in the n-IZO/ZnO/PS/p-Si heterostructure. The junction fabricated without intermediate ZnO layer possessed ideal rectifying behaviors (IF/IR = 32 at 300 K and 6 × 103 at 80 K for ±3 V). However, the rectifying behavior degrades for the n-IZO/ZnO/PS/p-Si heterojunction (IF/IR ∼ 8 at 300 K and 7 at 80 K for ±3 V). The ambiguous behavior of IF/IR in the low temperature range (80–140 K) for the n-IZO/ZnO/PS/p-Si heterojunction was explained by the existence of tunnel paths active in this temperature range. The transport properties of the two diodes were explained in terms of the Anderson model and the space charge limited current model. The C–V measurements show a complex electrical behavior for the IZO/ZnO/PS/Si heterojunction, which is attributed to indium diffusion in the undoped ZnO intermediate layer during the growth process.

Improving the electrical properties of graphene layers by chemical doping

Although the electronic properties of graphene layers can be modulated by various doping techniques, most of doping methods cost degradation of structural uniqueness or electrical mobility. It is matter of huge concern to develop a technique to improve the electrical properties of graphene while sustaining its superior properties. Here, we report the modification of electrical properties of single- bi- and trilayer graphene by chemical reaction with potassium nitrate (KNO3) solution. Raman spectroscopy and electrical transport measurements showed the n-doping effect of graphene by KNO3. The effect was most dominant in single layer graphene, and the mobility of single layer graphene was improved by the factor of more than 3. The chemical doping by using KNO3 provides a facile approach to improve the electrical properties of graphene layers sustaining their unique characteristics.

Effect of carbonylcyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP) on the interaction of 1-anilino-8-naphthalene sulfonate (ANS) with phosphatidylcholine liposomes

The weak hydrophobic acid carbonylcyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP) is a protonophoric uncoupler of oxidative phosphorylation in mitochondria. It dissipates the electrochemical proton gradient (ΔμH (+)) increasing the mitochondrial oxygen consumption. However, at concentrations higher than 1μM it exhibits additional effects on mitochondrial energy metabolism, which were tentatively related to modifications of electrical properties of the membrane. Here we describe the effect of FCCP on the binding of 1-anilino-8-naphthalene sulfonate (ANS) to 1, 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) unilamellar vesicles. FCCP inhibited the binding of ANS to liposomes either in the gel or in the liquid crystalline phase, by increasing the apparent dissociation constant of ANS. Smaller effect on the dissociation constant was observed at high ionic strength, suggesting that the effect of FCCP is through modification of the electrostatic properties of the membrane interface. In addition, FCCP also decreased (approximately 50%) the quantum yield and increased the intrinsic dissociation constant of membrane-bound ANS, results that suggest that FCCP makes the environment of the ANS binding sites more polar. On those grounds we postulate that the binding of FCCP: i) increases the density of negative charges in the membrane surface; and ii) distorts the phospholipid bilayer, increasing the mobility of the polar headgroups making the ANS binding site more accessible to water.

Modification of electrical properties of TiO<sub>2</sub> by continuous-wave ytterbium fiber laser irradiation

Modification of electrical properties of TiO<sub>2</sub> by continuous-wave ytterbium fiber laser irradiation

Modification of Electrical Properties of Graphene by Substrate-Induced Nanomodulation

A periodically modulated graphene (PMG) generated by nanopatterned surfaces is reported to profoundly modify the intrinsic electronic properties of graphene. The temperature dependence of the sheet resistivity and gate response measurements clearly show a semiconductor-like behavior. Raman spectroscopy reveals significant shifts of the G and the 2D modes induced by the interaction with the underlying grid-like nanostructure. The influence of the periodic, alternating contact with the substrate surface was studied in terms of strain caused by bending of graphene and doping through chemical interactions with underlying substrate atoms. Electronic structure calculations performed on a model of PMG reveals that it is possible to tune a band gap within 0.14-0.19 eV by considering both the periodic mechanical bending and the surface coordination chemistry. Therefore, the PMG can be regarded as a further step toward band gap engineering of graphene devices.

Modification of electrical properties induced by annealing of ZnO:B thin films deposited by chemical vapour deposition: Kinetic investigation of evolution

Abstract In this study temperature dependent Hall effect measurements combined with Fourier Transformed Infra-Red (FTIR) spectroscopy measurements is used to determine the evolution of the scattering mechanisms ascribable to in-grain and grain boundaries on Boron doped ZnO thin films deposited by Low Pressure Chemical Vapour Deposition (LPCVD). Through Hall effect measurements during in situ isothermal annealing, changes in electrical characteristics of zinc oxide could be followed in real time. Whereas only degradation is observed in air, an improvement of layer conductivity could be achieved at low temperatures by annealing under argon atmosphere. A study of the conductivity during isothermal annealing offers the possibility to extract activation energies, which have been compared to migration energies of the different intrinsic defects in ZnO.

Modification of Electrical Properties of Thin La0.67Ca0.33MnO3 Films by Pulsed Thermocycling

Highly resistive states were formed in nonhomogeneous thin La 0.67 Ca 0.33 MnO 3 films at 80 K temperature after resistance switching induced by the pulsed thermocycling. Heating up to room temperature does not destroy the resistive states. They demonstrate high values of electroresistance at applied pulsed electric field. It was registered formation of novel highly resistive state by resistance switching at 130 K in T m region. We suppose that local temperature increase in the film is responsible for the formation of the resistive states in both cases and present a plausible explanation of the obtained results. The method of cyclic nanosecond temperature increase and decrease can be useful for modification of material properties having strongly correlated electron system and of ferroelectrics. Questions of practical realization of proposed method are discussed. DOI: http://dx.doi.org/10.5755/j01.ms.18.3.2427

Controlling Semiconducting and Insulating States of SnO2 Reversibly by Stress and Voltage

By applying mechanical stress (by bending a flexible substrate) and an appropriate voltage, the conductance of a single-crystal SnO(2) microrod on a flexible substrate can be tuned in a reversible and nonvolatile manner. The creation and elimination of lattice defects controlled by strain and electrical healing is the origin of this novel transition. A SnO(2) microrod changes continually from its normal semiconducting state to an insulating state by bending the flexible substrate. The insulating state is maintained even after straightening the substrate. Interestingly, by applying an appropriate voltage, the defects are electrically healed and the insulating state reverts to the original semiconducting state. The structural changes in the SnO(2) microrod observed in the Raman spectra are consistent with the nonvolatile property of the transport. This flexible SnO(2) device with the reversible and nonvolatile modification of electrical properties is expected to lead to a better understanding of the mechanism of defect creation and elimination and has potential application in novel flexible strain sensors and switches.

Post-growth modification of electrical properties of ZnTe nanowires

ZnTe nanowires, grown by a vapor–liquid–solid technique are p-type and show a very high intrinsic resistivity. Enhancement of the nanowire conductivity was investigated by vacuum annealing, doping and Joule heating. The current–voltage (I–V) characteristics were measured in all cases and electrical parameters such as resistivity, carrier concentration and mobility were computed from the I–V curves. An improvement of five orders of magnitude in the electrical conductivity was seen after thermal annealing and Joule heating, comparable to the enhancement in conductivity obtained by doping.

Modification of electrical properties of Al/p-Si Schottky barrier device based on 2′-7′-dichlorofluorescein

The charge conduction mechanism and electrical properties of Al/p-Si Schottky barrier device based on 2′-7′-dichlorofluorescein (DCF) were investigated by current density–voltage (J–V) and capacitance–voltage (C–V) methods. Thin film of DCF organic compound was deposited on p-Si substrate as an interfacial layer by spin-coating technique. The dark J–V characteristics indicate that the rectifying junction is formed at DCF/Al interface. The ideality factor and barrier height of the Al/DCF/p-Si Schottky diode are higher than that of Al/p-Si Schottky diode. The effect of the thickness of the DCF organic layer was investigated by evaluating electrical parameters, such as the barrier height, ideality factor, series resistance, and interface state density. It is seen that the thickness of the DCF layer significantly affects the electrical properties by influencing the space charge region of the Al/DCF/p-Si Schottky junction. The interface state density of the diode was determined using low-high frequency C–V plots and was of order of ≈1011 eV−1cm−2. The order of the interface state density of Al/DCF/p-Si is lower than most of metal/organic compound/inorganic semiconductor devices. The values of the barrier height of the studied diodes are significantly larger than those of conventional Al/p-Si Schottky diodes. The J–V curves in the reverse direction are taken and interpreted via both Schottky and Poole–Frenkel effects. Poole–Frenkel effect was found to be dominant in the reverse direction.

Force modulation for enhanced nanoscale electrical sensing

Scanning probe microscopy employing conductive probes is a powerful tool for theinvestigation and modification of electrical properties at the nanoscale. Application areasinclude semiconductor metrology, probe-based data storage and materials research.Conductive probes can also be used to emulate nanoscale electrical contacts. However,unreliable electrical contact and tip wear have severely hampered the widespread usage ofconductive probes for these applications. In this paper we introduce a force modulationtechnique for enhanced nanoscale electrical sensing using conductive probes. This techniqueresults in lower friction, reduced tip wear and enhanced electrical contact quality.Experimental results using phase-change material stacks and platinum silicide conductiveprobes clearly demonstrate the efficacy of the proposed technique. Furthermore,conductive-mode imaging experiments on specially prepared platinum/carbonsamples are presented to demonstrate the widespread applicability of this technique.

Modification of electrical properties of zinc oxide by continuous wave ytterbium fiber laser irradiation

The polycrystalline plate-like ZnO samples were irradiated by a continuous wave Yb fiber laser and electrical properties of modified layer were investigated. The laser beam of spot size of 16 μm in diameter was scanned on the surface at a velocity of 5mm/s. There was a threshold for the laser modification. The laser etched grooves were formed above laser power of 20 W. The laser etched depth increased in relation to the laser power, 0.46 mm at 20 W and 5.0 mm at 126 W. The surface layers of laser etched grooves were modified in color and electrical property. The color changed from light yellow to black, and the electrical resistivity drastically decreased from initial value of 1.1×105 Ωcm to 3.2×10−1 Ωcm at 56 W, 2.8×10−1 Ωcm at 91 W, and 2.0×10−1 Ωcm at 126 W. The Hall measurement showed that the modified surface layer was an n-type semiconductor and carrier concentration of the layer was 1.5×1017 cm−3 at 56 W, 7.2×1017 cm−3 at 91 W, and 1.9×1018 cm−3 at 126 W.

Degradation of Poly(3-hexylthiophene):Methano-Fullerene [6,6]-Phenyl-C71 Butyric Acid Methyl Ester Bulk Heterojunction Solar Cells and Annealing Effect on the Degraded Devices

We have studied the degradation of poly(3-hexylthiophene):methano-fullerene [6,6]-phenyl-C71 butyric acid methyl ester (P3HT:PC71BM) bulk heterojunction BHJ solar cells and the annealing effect on the degraded devices. Firstly, the modification of electrical properties of the BHJ solar cells was monitored as a function of illumination time. The degradation of BHJ solar cell is dominated by the filling factor reduction and an irradiation to the solar cell accelerates the gradual degradation. Secondly, we found that inserting LiF between Al cathode and active layer, alleviating degradation, improves the device properties of the solar cell as well as its stability. Moreover, annealing on the degraded device helps partially recover the properties of the solar cell and the diode function. We speculated that this partial recovery caused by annealing is attributed to the rearrangement of P3HT as well as the aggregation of PC71BM.

Effect of illumination and annealing on electrical properties of indium tin oxide/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/poly(3-hexylthiophene)/Al device

We have studied the modification of electrical properties in poly(3-hexylthiophene) (P3HT) thin film by means of illumination and annealing. The hole mobility of P3HT was monitored by impedance spectroscopy and the density of localized states in the band gap near the Fermi level was calculated using the step-by-step method based on the space-charge-limited-current model. With the illumination, we found that the bulk trap density increased from 2.51 to 2.85×1016 cm−3 eV−1 and the hole mobility of P3HT decreased from 1.88×10−4 cm2 V−1 s−1 to 4.22×10−5 cm2 V−1 s−1. With the annealing at 70 °C for 30 min, it is found that the mobility then partially recovers to 1.18×10−4 cm2 V−1 s−1.

Electrical property modifications of In-doped ZnO films by ion irradiation

Zinc oxides doped with trivalent elements are known as an n-type transparent semiconductor. We have studied ion irradiation effects on electrical properties, atomic structure and optical properties of In-doped ZnO films. We have observed increase in the electrical conductivity and this is ascribed to ion-induced replacement of Zn on lattice site by In.

Effect of aspect ratio and water contamination on the electric properties of nanostructured insulating materials

Organically-modified nanofiller clays can have significantly different aspect ratios as well as accumulate a relatively large amount of water in the composite bulk due to the contribution of the filler itself and the interaction between filler and polymer matrix. This paper investigates the effect of water absorption in a nanostructured thermoplastic polymer, namely ethylene-vinyl-acetate (EVA), on electrical property modifications considering the contribution of aspect ratio. The change of electrical properties (particularly space charge accumulation, electric strength, bulk conductivity and permittivity/losses) is studied as a function of water content absorbed by nanofillers having different aspect ratio, i.e. fluorohectorite and bohemite. An increase of the space charge build up and of the conductivity (and decrease of the electric strength) is observed as a function of the water content for specimens containing layered silicates as nanofillers (fluorohectorite), while the electric properties of bohemite specimens do not show significant variations with the absorbed water content. This behavior can be associated with the different aspect ratio of the nanofillers. A filler having higher aspect ratio, in fact, seems to be more effective in worsening the electrical properties of the final nanocomposite. This could be explained considering that the higher the aspect ratio of the nanoparticles, the larger the percolation probability. To quantify how water content may affect electric properties of the final nanocomposite a simplified model providing the percolation probability as a function of water content and geometry of the particles is developed in this paper.