The electrical conductivity of graphite intercalated with superacid fluorides: experiments with antimony pentafluoride

The electrical conductivity in graphite measured normal to the crystallographic c-axis is observed to increase after intercalation with acid molecules which act as acceptors. This behaviour is regarded as the result of ionization of the acid molecule which, in turn, increases the positive current carriers in the host graphite. Since the carrier density depends on the degree of ionization of the acid, it follows that the stronger the acid the greater the increase in carrier concentration, and assuming no adverse mobility effects, the greater the electrical conductivity. The hydrogen fluoride-antimony pentafluoride system produces some of the strongest acid substances known. The experiments described here represent the initial examination of the electrical conductivity resulting from intercalation of this material into graphite. The experiments consisted of intercalating graphite powder with antimony pentafluoride in a copper tube and swaging the sheathed compound into wire. The measured conductivity of the graphite intercalation compound, when the copper conductivity is subtracted out and allowance is made for departure from ideal density, is about 1×10^{6 –1} cm^–1. This is approximately 40 times the conductivity of pristine graphite and more than one and a half times the conductivity of pure copper.     

Method to probe the electrical activity of dislocations in non-intentionally doped n-GaN

Here is presented a method to probe the electrical activity of dislocations in non-intentionally doped n-GaN epitaxial layers based on the study of their sub-band gap photoconductivity, monitoring their electron concentration and mobility. Non-intentionally doped n-GaN layers bearing charged and thus highly dispersive and recombining dislocations when illuminated with sub-band gap photons show a strong increase on their conductivity, due to an equivalent increase on the electron mobility while the electron concentration remains unchanged. On the other side, non-intentionally doped n-GaN layers bearing electrically inactive dislocations display almost no photoconduction, as both; carrier concentration and their mobility remain unchanged under the same illumination conditions. The method, simultaneously assess the electrical activity of dislocations and the material quality, and can be applied to any other semiconducting material bearing high dislocations densities.     

晶体面缺陷对FeS2薄膜电学性能的影响

采用Fe膜热硫化技术制备了具有不同比表面积和比晶界面积的FeS2薄膜,并测定其载流子浓度和电阻率,研究了FeS2薄膜表面和晶界等面缺陷对FeS2薄膜电学性能的影响.结果表明,表面和晶界两种面缺陷对FeS2薄膜的电学性能有类似的影响规律.在一定范围内,随着薄膜比表面积和比晶界面积的增大,载流子浓度提高而电阻率下降.面缺陷数量的变化可导致FeS2晶体中点缺陷数量、禁带中缺陷能级密度、不充分相变产物比例和相变应力水平的变化,从而导致载流子浓度和电阻率的变化.     

Electrical properties of La-doped SrTiO3 (La: 0.1 to 2.0 at %) single crystals grown by xenon-arc image floating zone method

Lanthanum-doped semiconducting strontium titanate single crystals having various lanthanum contents were grown in an air atmosphere by the xenon-arc image floating zone method. The crystals were characterized by X-ray powder diffraction, EPMA analysis and chemical analysis. Each lanthanum was accompanied by a trivalent titanium ion in the grown crystal. The electrical conductivity of these crystals was measured at 20 to 1150° C, and it was found to increase linearly with increasing lanthanum content. The mobility of the charge carrier was estimated from the concentration of trivalent titanium and the conductivities of the crystals. The mobility in the low temperature region agreed with previous studies. However, a significant difference was found at high temperatures. An error in the temperature dependence in the previous study is responsible for this difference. It is stressed that care is necessary in applying the results of single crystalline studies when discussing high-temperature bulk defect chemistry.     

由椴木木粉和酚醛树脂制备木材陶瓷的研究

以椴木木粉和酚醛树脂为原料制成一种新的木材陶瓷.用TGA、XRlD和SEM技术分别对木材陶瓷的形成机理、物相构成和微观结构进行了表征与研究.详细讨论了碳化温度和酚醛树脂用量对木材陶瓷显气孔率、体积电阻率和弯曲强度的影响.结果表明,木材陶瓷是由酚醛树脂生成的玻璃态的硬碳和由木粉生成的无定形的软碳组成的多孔性碳复合材料;随碳化温度升高或酚醛树脂用量的增加,木材陶瓷的显气孔率和弯曲强度增大,体积电阻率下降;碳化温度升高可以使(002)衍射峰逐渐变窄,强度增大,并且向高角度移动,晶面间距d₍₀₀₂₎减小,而酚醛树脂用量的增加对(002)衍射峰和晶面间距d₍₀₀₂₎基本没有影响;当碳化温度为1350℃,酚醛树脂用量为160wt％时,木材陶瓷的显气孔率、体积电阻率和弯曲强度分别达到了50％、2.0×10^-2Ω·cm和25MPa.     

Effects of Hf incorporation in solution-processed Hf-InZnO TFTs

In this study, the structural, optical, and electrical effects of Hf incorporation as a function of Hf atomic concentration were investigated using the solution process. Increases of Hf incorporation in Hf-InZnO (HIZO) thin films were associated with segregation of each element, and enhancement of optical bandgap energy and absorbance. We suggested that Hf could replace Ga as a carrier suppressor in the InZnO (IZO) system due to its low standard electrode potential, a property that reflects the oxidizing tendency of a metal cation. We observed that even small doses of Hf also resulted in the effective reduction of the carrier concentration in the IZO system. An increase of Hf incorporation in HIZO TFTs caused electrical properties including on-current, threshold voltage, and subthreshold swing to decrease, shift positively, and increase, respectively.     

硝酸掺杂提高石墨烯透明导电膜导电性研究

石墨烯同时具备高透过率和良好的导电性可作为透明导电材料,然而由于CVD法制备的石墨烯的多畴特性,以及石墨烯本征载流子浓度较低,目前石墨烯透明导电膜方阻偏高,还无法满足实际应用需要,因此探索提高石墨烯的导电性对推进石墨烯透明导电膜应用发展是非常重要的。通过掺杂提高石墨烯的载流子浓度从而提高石墨烯的导电性是其中一条重要途径。采用CVD法在铜箔上制备了石墨烯透明导电膜,并用硝酸处理石墨烯,研究了掺杂作用对石墨烯载流子浓度以及电导率的影响。实验结果证实硝酸处理会在石墨烯中引入P型掺杂,掺杂使得载流子的浓度增加了约2．5倍。方阻从530～205Ω/□,显著改善了石墨烯的导电性能,而石墨烯高透过率特性并未因掺杂而降低。     

Grain boundary effect on the electrical properties of boron-doped polysilicon films

The effect of grain boundary width has been accounted for and a modified simple model of average carrier concentration is presented considering the transport mechanism of charge carriers by thermionic emission only. It is found that the electrical properties of polysilicon are very sensitive to doping concentration when the grain size is small and the effect of grain boundary width on electrical properties increases as the grain size decreases. The inclusion of grain boundary width in resistivity and mobility formulae also gives better results near the critical doping concentration. The proposed model gives better agreement between experimental data and theoretical results.     

Influence of assistant ion beam on the opto-electrical properties of molybdenum doped zinc oxide films deposited on polyethersulfone via dual ion beam sputtering

An alternative transparent conductive oxide, molybdenum doped zinc oxide (MZO) was deposited onto a flexible polyethersulfone (PES) substrate by using a dual ion beam sputtering system. One argon ion beam was used to sputter a MZO target and another assistant argon ion beam was for bombarding deposits simultaneously. The assistant ion source discharge voltage and current were changed respectively for investigating their influences on the conductivity of deposited MZO films. Changing the discharge voltage shows that, the film crystallinity, carrier concentration and mobility in films all increase with the discharge voltage and subsequently decrease when the applied voltage is over 100 V. Changing the discharge current also shows a similar trend. The film crystallinity and carrier concentration initially increase with the discharge current, and thereafter a minimum for 1.4 A, and a subsequent increase in resistivity is observed. According to the results, properly raising the discharge voltage and current of assistant ion source can improve both electrical conductivity and optical transparency of deposited MZO films, but the excess discharge voltage and current will cause the grain refinement which may retard the carrier mobility and result in the lower conductivity of MZO films.     

Electrical properties of polycrystalline germanium-metal films

The electron transport properties of crystalline and crystallized Ge-metal (Al, Ga, Ag, Au, Cu and Fe) films were studied as functions of the metal concentration (up to 10 at.%) and temperature (150–500 K). The addition of aluminium and gallium decreases the electrical resistivity and thermoelectric power (TEP). The carrier concentration increases rapidly and there is a gradual decrease in the Hall mobility. Silver affects these transport properties only slightly in crystalline films but large effects are observed in crystallized GeAg films. There is a gradual decrease in the electrical resistivity and TEP of crystalline and crystallized GeAu films. The carrier concentration increases slowly and the Hall mobility shows a maximum. The carrier concentration in crystalline GeCu and GeFe films decreases slowly but shows an increase in the corresponding crystallized films. The Hall mobility in crystalline films decreases but shows a maximum in the crystallized films. In crystalline GeCu films the TEP decreases initially (up to approximately 2 at.% Cu) and then increases. The electron transport properties in these films are explained in terms of the formation of solid solution/segregated ordered phases.     

Influence of film thickness on the texture, morphology and electro-optical properties of indium tin oxide films

In the present study, the structural, electrical, and optical properties of indium tin oxide (ITO) films are reported as a function of film thickness (162-840 nm). The properties are discussed in terms of the (100) preferred orientation evolution with the increase of film thickness. This preferred orientation allowed accommodation of more oxygen vacancies, resulting in the increase of carrier concentration from 2.43 × 10²⁰ cm⁻³ to 7.11 × 10²⁰ cm⁻³ and therefore enhancing the electrical conductivity. The absorption in the infrared region was also found to increase with the increasing free carrier concentration, which was attributed to the plasma excitation. The X-ray photoelectron spectroscopy depth profile showed that the Sn⁴⁺ concentration did not change with film thickness. However, the oxygen concentration was decreased slightly after the thickness of the ITO films was increased to 100 nm, as the consequence of the formation of the (100) texture allowing the accommodation of more oxygen vacancies. The results show that the fabrication process can be manipulated to control the electrical properties and the infrared absorption of the sputtered ITO films.     

Electrocatalytic behavior of calcium doped LaFeO3 as cathode material for solid oxide fuel cell

La(1-x)Ca(x)FeO3 (X = 0.0, 0.2, 0.4, abbreviated as LCF) as cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC) was synthesized by new route of glycine nitrate method. LCF materials were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), electrical and electrochemical impedance spectroscopy (EIS). The powder LCFs exhibited single phase with orthorhombic structure, highly porous and small nanoparticles with average size of 200-300 nm. The electrical conductivities of LCFs increased as increasing the Ca content and achieved the maximum electrical conductivity of 148 Scm(-1) for La0.6Ca0.4FeO3 (X = 0.4) at 550 degrees C. The improved conductivity of LCFs could be a promising cathode material for IT-SOFCs. In the impedance analysis of fabricated symmetry cell with the optimized La0.6Ca0.4FeO3 cathode and Ce0.8Sm0.2O3 (SDC) electrolyte, the minimum area specific resistance (ASR) of 0.15 omegacm2 was observed at 850 degrees C, which may due to the lowest activation energy (1.55 eV), resulting from the reduction of oxygen molecules into oxygen ions. It was found that calcium doping was essential to increase the charge carrier concentration of lanthanum iron oxide materials, resulting in the high conductivity at intermediate temperature.     

The influence of substrate temperature and sputtering gas atmosphere on the electrical properties of reactively sputtered indium tin oxide films

Tin-doped indium oxide (ITO) films were prepared by d.c. magnetron sputtering of an In-Sn alloy target, and the influence of the sputtering gas atmosphere and substrate temperature on their electrical properties was studied.The conditions for the deposition of the transparent ITO films were divided into three regions by varying the sputtering gas pressure. The first region was characterized by a high efficiency of oxygen gas consumption for film formation and a high deposition rate. In the second region the as-deposited films contained slightly less than the stoichiometric amount of oxygen. The third region was characterized by a low efficiency of oxygen consumption and a low deposition rate. The ratio of the amount of oxygen consumed to the amount of oxygen admitted to the sputtering chamber was about 15% when films with resistivities as low as 6 × 10^-4Ω cm were prepared at the optimum oxygen partial pressure.In the case of metallic deposited in an oxygen-poor atmosphere the carrier mobility, which mainly depends on the crystal structure, increased and the carrier concentration, which depends on the number of oxygen vacancies and donor centres, decreased with increasing substrate temperature. The opposite results were obtained for films deposited in an oxygen-rich atmosphere. Well-defined grain growth was observed, particularly for metallic films deposited at high substrate temperatures, and this caused the low carrier mobility.Subsequent heat treatment improved the resistivity of films deposited at substrate temperatures below 100°C, mainly because of the increase in carrier mobility, but it had little effect on the resistivity of films deposited at substrate temperatures above 150 °C because the increase in carrier mobility was cancelled by the decrease in carrier concentration.     

Analysis of critical doping level of sprayed antimony doped tin oxide films

Antimony doped tin oxide films are fabricated using a simplified and inexpensive spray pyrolysis technique. The variation in the sheet resistance, as a function of Sb/Sn ratio in the spraying solution, is studied. The sheet resistance decreases with the increase in doping level, attains a minimum at a particular doping level and increases with further doping. This critical value of the doping ratio (Sb/Sn_critical), at which the transition takes place, is found to be 2.5 at.%, when the concentration of the precursor solution is 0.8 M and 4.5 at.% when the concentration is 0.4 M. The reason for this variation is analyzed with the support of the Sb/Sn_critical values, obtained by various researchers. This Sb/Sn_critical is found to depend mainly on the carrier concentration of the films.     

Numerical investigation on the electrical transmission ability of a shearing powder layer

Recent developments in powder technology gave birth to a new lubricant—powder lubricant. Compared to liquid lubricant, powder lubricant like graphite powder has several advantages, such as good electrical conductivity and good thermal resistance. Such advantages are especially appreciated in sliding electrical contacts. Thus, the study of the electrical transmission ability of a shearing powder layer under different dynamical constraints appears to have a great interest. Recent works allowed to model the coupling of mechanical and electrical effects in a discrete medium. This algorithm was extended to study the electrical properties of a shearing powder layer with discrete element method. The mechanical and electrical behaviors of the sample were studied in different dynamical regimes, characterized by the inertial number I. The results exhibit an interesting relationship between the average contact resistance and the inertial number I. An exponential increase of the sample’s electrical resistance as well as the induced electrical noise are observed closed to the dense flow limit. Such observations underline the fact that to ensure the electrical transmission ability of the powder layer, one must keep the particle size and shear rate small, and a sufficiently large pressure.     

炭基体的结构对C/C复合材料导电性能的影响

采用CVI+PIC工艺制备以2D碳纤维预制体为增强体、由不同炭基体结构组成的C/C复合材料,随后在不同温度对其进行热处理得到不同石墨化度的炭基体结构,研究了PyC/ReC比值和石墨化度对材料电阻率的影响。结果表明,随着PyC/ReC比的提高低密度C/C复合材料的电阻率在27.3×10^-6~28.0×10^-6 Ω·m间基本不变,因为石墨微晶的尺寸和结构完整性的增大与材料孔隙率的提高对电阻的影响相反。随着PyC/ReC比的提高,高密度C/C复合材料的电阻率从24.9×10^-6 Ω·m降低到20.5 ×10^-6 Ω·m。其可能的原因是,材料内部的孔隙较少,孔隙率的轻微提高使阻碍载流子在导电网络中的有效传递的作用显著下降。随着热处理温度从1800℃提高到2500℃,C/C复合材料的石墨化度明显提高,电阻率明显降低,其主要原因是载流子浓度的提高和晶界散射的减弱。     

Crystal structure, thermal expansion and electrical conductivity of Nd0.7Sr0.3Fe1−xCoxO3 (0≤x≤0.8)

The crystal structure, thermal expansion and electrical conductivity of the solid solution Nd_0.7Sr_0.3Fe_1−xCo_xO₃ for 0≤x≤0.8 were investigated. All compositions had the GdFeO₃-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction (XRPD). The pseudo-cubic lattice constant decreased continuously with x. The average linear thermal expansion coefficient (TEC) in the temperature range from 573 to 973 K was found to increase with x. The thermal expansion curves for all values of x displayed rapid increase in slope at high temperatures. The electrical conductivity increased with x for the entire temperature range of measurement. The calculated activation energy values indicate that electrical conduction takes place primarily by the small polaron hopping mechanism. The charge compensation for the divalent ion on the A-site is provided by the formation of Fe⁴⁺ ions on the B-site (in preference to Co⁴⁺ ions) and vacancies on the oxygen sublattice for low values of x. The large increase in the conductivity with x in the range from 0.6 to 0.8 is attributed to the substitution of Fe⁴⁺ ions by Co⁴⁺ ions. The Fe site has a lower small polaron site energy than Co and hence behaves like a carrier trap, thereby drastically reducing the conductivity. The non-linear behaviour in the dependence of log σT with reciprocal temperature can be attributed to the generation of additional charge carriers with increasing temperature by the charge disproportionation of Co³⁺ ions.     

The influence of the hydrogen reduction process on the electrical properties of In2O3:Sn thin films

Highly degenerate thin In₂O₃:Sn films were prepared by d.c. reactive sputtering of InSn alloy targets in ArO₂ mixtures with a wide range of oxygen concentrations. The influence of both the oxygen concentration in the reactive mixture and the tin content of the target on the structure and electrical properties was studied. Hall measurements indicate that ionized impurities and interphase boundaries play a dominant role as causes of carrier scattering. The effectof post-deposition heat treatment in vacuum and in hydrogen was also studied. The considerable increase in the carrier concentration during reduction in hydrogen is explained in terms of the reduction mechanism.     

Dissolution of Nalidixic Acid Solid Dispersions: Systems of NAL-Inclusion and Linear Polymeric Compounds

The solubility and dissolution rate enhancement of nalidixic acid powder, applying solid dispersion technique, with inclusion and linear polymeric compounds were studied. At 100 g/L carrier concentration, the increase in drug solubility was 3.3, 2.0, 1.4 and 1.1 times that of the powdered drug for urea, PEG 4000, PEG 6000 and PVP, respectively. The increase in carrier ratio enhanced the drug dissolution. At four fold carrier concentrations, the amount dissoluted after one hour was 50, 55 mg/L for samples prepared by fusion with urea and PEG 6000, respectively. The coprecipitation with FTP dissoluted 65 mg/L of nalidixic acid after one hour compared to only 27.5 mg/L of powdered drug alone.     

二次酸化表面改性制备高体积电阻率FeSiCr合金磁粉芯

FeSiCr合金粉末具有强耐腐蚀性,通过弱酸磷化的方式无法有效改善FeSiCr合金磁粉芯的绝缘性.本研究以盐酸乙醇溶液作为二次酸化剂,对磷化(一次酸化)的FeSiCr合金粉末表面改性,制备高体积电阻率FeSiCr合金磁粉芯.通过扫描电镜、LCR电桥和超高阻微电流测试仪分析盐酸乙醇溶液浓度对FeSiCr合金粉体微观形貌,...