Galvanomagnetic properties of AsF5-intercalated graphite

The galvanomagnetic properties of AsF₅-intercalated, highly-oriented, pyrolytic graphite (HOPG) were determined for stages 1 to 4 in the temperature range from 4.2 to 300 K using contactless eddy current methods forthe measurement of electrical conductivity and magneto-resistance and a new inductive technique forthe Hall effect. From the results p-type conduction, mean carrier mobility, total carrier concentration and charge transfer are deduced. The mobility is diminished upon intercalation due to an effective mass increase when the Fermi level is shifted by charge transferfrom AsF₅ to graphite layers. Charge transfer reaches a maximum of 1/3 for stage-2 compounds. The temperature dependence of galvanomagnetic effects yields carrier scattering at crystallite boundaries for low temperatures and scattering at phonons of both intercalated layers and graphite sheets for higher temperatures. Magnetoresistance of low-sage compounds exhibits anomalies at low temperatures resulting in an overestimation of mobility and saturation at magnetic Wd strengths where the low field approximation still should be vali? For magnetic fields of several kiloGGuss a reduction of the magnetoresistance was observed. It is suggested that these effects are due to trigonal warping of the graphite energy bands and to diffuse scattering at crystallite boundaries.     

Electrical transport properties of natural and synthetic graphite

Resistivity and magnetoresistance measurements were performed on a series of natural graphite crystals and highly oriented pyrolytic graphite (HOPG) samples as a function of temperature from 4.2 K to 293 K using a contactless r.f. technique. Resistance ratios of the natural graphite between 4.2 K and 293 K ranged from about 30 to 49. Carrier mobility of natural graphite was observed to obey at T^–3/2 behaviour up to about 35 K. An anomalously high power dependence of versus T was observed below 35 K. A new model describing the dispersion of mobility of electrons and holes is presented which gives exact agreement with magnetoresistance results in the low field regime.     

Electrical transport properties of graphene nanoribbons produced from sonicating graphite in solution

A simple one-stage solution-based method was developed to produce graphene nanoribbons by sonicating graphite powder in organic solutions with polymer surfactant. The graphene nanoribbons were deposited on a silicon substrate, and characterized by Raman spectroscopy and atomic force microscopy. Single-layer and few-layer graphene nanoribbons with a width ranging from sub-10 nm to tens of nanometers and lengths ranging from hundreds of nanometers to 1 μm were routinely observed. The electrical transport properties of individual graphene nanoribbons were measured in both the back-gate and polymer-electrolyte top-gate configurations. The mobility of the graphene nanoribbons was found to be over an order of magnitude higher when measured in the latter than in the former configuration (without the polymer-electrolyte), which can be attributed to the screening of the charged impurities by the counter ions in the polymer-electrolyte. This finding suggests that the charge transport in these solution produced graphene nanoribbons is largely limited by charge impurity scattering.     

Electrical and optical properties of Al3+-intercalated InSe and GaSe

We have studied the electrochemical, electrical, and optical properties of aluminum-intercalated indium and gallium monoselenides. Electron probe X-ray microanalysis data demonstrate that aluminum ions are incorporated into the host together with their solvation shell. Such Al³⁺ incorporation leads to changes in the electrical properties of InSe layered crystals when the intercalate concentration reaches the level N _Al ?? 10²⁰ to 10²¹ cm^?3, which corresponds to the formation of the final reaction product [Al _x ⁺ (R-PC)_y]InSe^? (where PC stands for propylene carbonate). At 77 K, the energy position of the exciton peak in the Al _x InSe and Al _x GaSe intercalation compounds is a nonmonotonic function of aluminum concentration.     

Electrical transport properties of III-nitrides

Excellent n-type GaN layers have been grown by all of the major epitaxial techniques: MBE, MOCVD, and HVPE. In this work, we analyze the band conduction in such samples by temperature-dependent Hall-effect measurement and theory, and determine quantitative information on donor and acceptor concentrations, as well as donor activation energies. In HVPE layers it is necessary to take account of a degenerate n-type layer at the GaN/sapphire interface in order to correctly analyze the bulk material. We also investigate hopping conduction, which occurs at low temperatures in conductive material, and at both low and high temperatures in semi-insulating material. Finally, we show by analysis of electron-irradiation data that both the N vacancy and the N interstitial are electrically active, demonstrating donor and acceptor character, respectively.     

Interaction of FeCl3-intercalated graphite with intercalants of different strengths

This paper examines reactions of stage I and II FeCl₃-graphite intercalation compounds (GICs) with intercalants of different strengths: nitric acid and tetrahydrofuran (THF). The reaction of GIC-FeCl₃ with nitric acid, a strong intercalant, leads to HNO₃ substitution for the FeCl₃ in the interlayer spaces of the graphite and formation of a stage II GICs with HNO₃. THF, a weak intercalant, does not form any compounds with a stage I or II GIC with FeCl₃; instead, it diffuses to intercrystalline regions of the graphite host. Flash heating of the synthesized GICs in air leads to the formation of exfoliated graphite (EG) containing α-Fe₂O₃ particles, which has low bulk density, down to 6.5 g/L, and high ferric oxide content, up to 33 wt %. Reduction in flowing hydrogen at 600°C leads to the formation of EG with up to 23 wt % α-Fe particles supported on it and with a saturation magnetization of 50 emu/g.     

Electrical transport properties of some liquid metals

In the present article, we report the electrical transport properties, namely, the electrical resistivity ( ρ), the thermoelectric power (TEP) ( α), and the thermal conductivity (σ) of several monovalent, divalent and polyvalent liquid metals of the different groups of the periodic table on the basis of model potential formalism. The well known empty core model (EMC) potential of Ashcroft is used for the first time with seven local field correction functions proposed by Hartree (H), Hubbard-Sham (HS), Vashishta-Singwi (VS), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) in the present computation and found suitable for such study. In the calculation of these properties, we have used the values of the theoretical structure factors due to hard core fluid theory. It is concluded that the comparisons of present and theoretical or experimental findings, wherever they exist, are highly encouraging. Published in Russian in Teplofizika Vysokikh Temperatur, vol. 46, No. 6, 2008, pp. 870–880.     

Electrical transport properties of copper-doped tellurium films

Polycrystalline films of copper-doped tellurium were grown by co-evaporating copper and tellurium from separate boats. Measurements were made of the electrical transport properties of these films. It was observed that the addition of copper decreases the activation energies of both the conductivity and the mobility. The low temperature conduction data were interpreted on the basis of a variable range hopping mechanism while the high temperature data indicate the dominance of the grain boundary scattering mechanism.     

Electrical transport properties of thallium-doped p-type PbTe films

Hall measurements were made in the temperature range 77–700 K on thallium- doped p-type epitaxial films of PbTe having free carrier concentrations in the range 5×10¹⁷?6×10¹⁹cm^?3 at 300 K. The various band parameters, i.e. mobility, effective mass and population ratios for light and heavy holes, were estimated as functions of temperature and carrier concentration. These results were compared with reported data on bulk samples.     

Electrical conductivity and optical properties of polyaniline intercalated graphite oxide nanocomposites

Layered graphite oxide is used as host material for the synthesis of conducting polymer intercalated nanocomposites. Powder X-ray diffraction, Fourier transform infrared, and UV-VIS absorption spectra indicate the formation of polyaniline within the interlamellar spaces of graphite oxide. The red shift of UV-VIS absorption associated with graphite oxide is found. The direct current (dc) conductivity increases by about three orders of magnitude compare with pristine graphite oxide. The temperature dependence dc conductivity of the nanocomposite follows Mott's three-dimensional variable range hopping. The alternating current (ac) conductivity suggests correlated barrier hopping of conduction process. The conductivity relaxation time varies in the range of 10(-5)-10(-7) Sec.     

Electrical resistance anisotropy of a POCO AXM-5Q1 graphite

The electrical resistance of segments from a POCO AXM-5Q1 cylindrical graphite specimen, which was previously used for measurement of thermal diffusivity, was measured at 20°C. The objective of the measurements was to establish the existence and type of structural anisotropy that might affect the directional thermal transport properties of this material.     

Electrical transport properties of hydrogen-exposed n-type InSb films

Hall coefficients and d.c. conductivities were measured for polycrystalline n-type InSb films exposed to H₂ gas at different pressures. It was found that H₂ gas molecules act as donor impurities for the films and the donor action increases with increasing pressure of the gas. The mobility, however, was found to decrease, showing the increasing contribution of ionized impurity scattering with increasing pressure of the gas.     

纳米片层石墨填充聚氨酯泡沫塑料的制备和电学性能

Using polyester polyol and diphenylmethane diisocyanate(MDI)as basic component,and using graphite as conduct.ive filler,polyurethane/graphite nanosheet foam plastics is produced by filling mould curing reaction.Also the electrical properties of the foam plastics are studied.     

Electrical transport properties of iron (II) molybdate

Electrical conductivity, thermoelectric power and static dielectric constant of iron (II) molybdate have been measured in the temperature range 300 to 1000 K on pressed pellets of polycrystalline sample. It has been found that FeMoO₄ is a p-type semiconductor with energy gap 4.1 eV. Different conduction mechanisms have been found below and above 700 K. Below 700 K conduction is due to a small polaron hopping mechanism and above 700 K conduction is due to large polarons as well as normal band conduction mechanism. Activation energy W, ₀ (T) and charge carrier mobility have been estimated in the two temperature ranges 300 to 700 K and 700 to 1000 K. Dielectric constant increases slowly with temperature up to 700 K and above 700 K, it increases exponentially with temperature.     

Electrical and mechanical properties of expanded graphite/high density polyethylene nanocomposites

High density polyethylene (HDPE) were filled with expanded graphite particles that have different particle sizes, 5–7 μm (EG5) and 40–55 μm (EG50) in diameter. Nanocomposites were prepared by the melt-mixing technique using EG5 and EG50 at different weight ratios. Transmission Electron Microscopy (TEM) was used to observe the morphology of the nanocomposites. X-ray diffraction patterns of EG5-HDPE and EG50-HDPE nanocomposites were investigated. Tensile tests were carried out to determine tensile strength, Young’s modulus and elongation at break values. The storage modulus and loss modulus were evaluated by Dynamic Mechanical Analysis (DMA). The effect of EG5 and EG50 on electrical conductivity of HDPE was also determined. The tensile strength of HDPE increased 18.7% and 8.5% when 40 wt% EG5 and EG50 was added into HDPE, respectively. The storage modulus of EG5-HDPE and EG50-HDPE is higher compared to that of HDPE. Incorporation of EG5 and EG10 into HDPE also increased the relaxation transition peak of HDPE. The values of electrical conductivity for EG50-HDPE nanocomposites under the same filler content obtained higher in comparison with those for EG5-HDPE nanocomposites.     

Electrical transport properties of La1−xSrxFeO3

La_1? x _Sr?x _FeO3 (0·1?x?0·4) samples exhibit nearly the same low resistivity value around the Neél temperatures. AboveT _N, electrons seem to become itinerant as suggested by Mōssbauer data.     

Electrical transport properties of fullerene peapods interacting with light

In this paper, we investigate the transport properties of field-effect transistors (FETs) based on various kinds of fullerene (C(60), C(70), and C(84)) peapods. The encapsulation of various fullerenes inside single-walled carbon nanotubes (SWNTs) is characterized by TEM and Raman spectroscopy. Our results indicate that the transport characteristics of p-type SWNTs are extremely sensitive to the encapsulation of various kinds of fullerene. In the absence of light illumination, the threshold voltage of p-type SWNTs shifts towards positive values after C(60) and C(70) encapsulation, and ambipolar transport characteristics are observed for C(84) peapods. The photoinduced electron transfer phenomenon is observed for fullerene peapods under light illumination. The optical response for C(60) and C(70) peapod FET devices is reflected in a shift of threshold voltage towards negative values, and a recoverable characteristic is observed when light is off. After a long period of light illumination, in contrast to p-type C(60) and C(70) peapods, an n-type transport characteristic is observed on C(84) peapods.