Hopping conductivity in amorphous carbon films

The electrical resistivity of amorphous carbon films getter-sputtered at 95°K is well fitted between 300 and 20°K by the relation $\text{? = ?}{}_0\text{exp}\text{[(T}{}_0\text{/T)}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{]}$ with T₀ ? 7 × 10⁷K. This behavior suggests a hopping conductivity very similar to that found in other amorphous semiconductors.     

Frequency dispersion of the magnetic anisotropy field in metallic magnetic films with the plane anisotropy of electrical conductivity

Presence of the frequency dispersion of the field of induced single axis magnetic anisotropy and the angular position of the axis of easy magnetization in the film plane has been determined in metallic magnetic films with plane anisotropy of electrical conductivity. Theoretical dependences have been obtained which given satisfactory agreement with experimental data for cobalt and permalloy films prepared by sputtering on glass substrates and using the incident molecular beam under an angle with the substrate.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 76–78, January, 1986.In conclusion, we thank D. I. Sementosva for a useful critique during the discussion of the subject-matter of the present work.     

Electrical conductivity of nitride carbon films with different nitrogen content

The electrical conductivity of nitride carbon (DLC: N) films has been studied. It is found that the electrical conductivity of the deposited films increases slowly with increasing nitrogen content, however, it decreases after the nitrogen content in the film reaches a certain value of 12.8 at%. Thermal treatment results show that the electrical conductivity of the lowly nitrogen doped DLC film increases rapidly, while that of the heavily doped film decreases after annealing at 300 °C for 30 min. Raman and XPS spectra results show that when the nitrogen content in the films reaches a certain value, there appears nonconductive phases. Therefore the electrical conductivity of the heavily doped films decreases. FTIR spectra analysis results show that the nitrogen atom as an impurity center undergoes an ‘activation’ process during the thermal treatment, which leads to the increase of the electrical conductivity. Therefore, the nitrogen in these two kinds of films has different effects on the electrical conductivity.     

Unusually high thermal conductivity of carbon nanotubes

Combining equilibrium and nonequilibrium molecular dynamics simulations with accurate carbon potentials, we determine the thermal conductivity lambda of carbon nanotubes and its dependence on temperature. Our results suggest an unusually high value, lambda approximately 6600 W/m K, for an isolated (10,10) nanotube at room temperature, comparable to the thermal conductivity of a hypothetical isolated graphene monolayer or diamond. Our results suggest that these high values of lambda are associated with the large phonon mean free paths in these systems; substantially lower values are predicted and observed for the basal plane of bulk graphite.     

Ac conductivity in boron doped amorphous carbon films

Experimental results on frequency and temperature dependence of ac conduction in boron doped amorphous carbon films are analyzed in the framework of available microscopic models. Depending on the response, the conductivity plot is divided into three regimes (low frequency high temperature; moderate frequency intermediate temperature; high frequency low temperature) and the data in the respective regimes are corroborated with the various theoretical models accordingly. The conductivity data at high frequency and low temperature suggests that relaxation via quantum mechanical tunneling might be the dominant conduction mechanism. At intermediate temperatures and moderate frequencies, the conductivity data is in good agreement with extended pair approximation model with interaction correction. Signature of enhanced interaction effect is observed at low temperature.     

Electrical conductivity anisotropy in alkali feldspar at high temperature and pressure

The electrical conductivity of alkali feldspar along different orientations was determined at 1.0 GPa and at temperatures of 823–1286 K in a cubic anvil apparatus using alternating current impedance spectroscopy. Impedance arcs representing crystal conductivity occur in the frequency range of ～10³–10⁶ Hz. The electrical conductivity of alkali feldspar increases with increasing temperature. The highest electrical conductivities in alkali feldspars were measured along the a-axis, with somewhat lower conductivities along the b-axis, and the lowest conductivities along the c-axis, suggesting minor anisotropy. The activation enthalpies ranged from 100 to 110 kJ/mol. The anisotropic results were combined to yield an isotropic model with an activation enthalpy of 102 kJ/mol. By comparing these results with previous results, we suggest that the dominating charge carriers for alkali feldspars are alkali ions. The minor anisotropy in conductivity for alkali feldspar may not account for the anisotropy of the crust.     

Thermo-e.m.f. anisotropy in magnetic films of Co and Ni and its comparison with anisotropy in electrical conductivity

Summary Films of cobalt and nickel were electroplated in the presence of an external magnetic-induction field. This resulted in the deposition of magnetic films which show, in addition to a magnetic anisotropy, also thermo-e.m.f. anisotropy. The latter is a new effect, not deriving from the anisotropy in electrical conduction deduced earlier by Kornevet al. on the basis of measurements of transmission coefficients of polarized RF field.     

Pre-exponential factor of the hopping conductivity in disordered carbon films

The conductivity of carbon films grown by polymethylphenylsiloxane vapor decomposition in stimulated dc discharge plasma was studied. It is found that the Mott hopping conductivity $ \sigma \left( T \right) = \sigma _0 \left( T \right)\exp \left\{ { - \frac{{T_0 }} {T}^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} } \right\} $ \sigma \left( T \right) = \sigma _0 \left( T \right)\exp \left\{ { - \frac{{T_0 }} {T}^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} } \right\} is characteristic of the samples under study in the temperature range of 80–400 K in the electric field E to 5 · 10⁴ V/cm. An analysis of the pre-exponential factor σ ₀(T) = σ ₀₀(T ₀)T ^α allowed the conclusion that the hopping transport is most adequately described in the model with the exponential energy dependence of the density of localized states for which α = −1/2 and the universal relation ln σ ₀₀ −T ₀^1/4 0 is valid, which is satisfied in the range where the parameter σ ₀₀ varies by eight orders of magnitude.     

Underlayer diffusion-induced enhancement of coercivity in high anisotropy FePt thin films

The L1₀ ordered FePt films have been prepared at 300 °C with a basic structure of CrRu/MgO/FePt, followed by a post-annealing process at temperatures from 200 to 350 °C. The magnetic properties and the microstructure of the films were investigated. It is found that coercivity of FePt films increases greatly from 3.57 to 9.1 kOe with the increasing annealing temperature from 200 to 350 °C. The loop slope of the M–H curves decreases with the increasing annealing temperature, which is due to the grain isolation induced by MgO underlayer diffusion during the annealing process. The underlayer diffusion could be a useful approach to prepare the FePt-based composite films for high-density recording media.     

Improving the conductivity of diamond-like carbon films with zinc doping and its material properties

Zinc doped diamond-like carbon (DLC) nanocomposite thin films are fabricated by KrF pulsed laser deposition. Carbon targets containing 3.0, 5.0 and 10.0 atomic percentages of zinc are used as the source for the laser system. Investigation of electrical properties by the four-point probe shows that doping zinc into DLC can lower the electrical sheet resistivity. Microstructural analysis by Raman spectroscopy and XPS show a lower sp³ content but a higher SiC content with an increasing amount of zinc incorporation. The increase of SiC leads to an increase in adhesion strength. Surface roughness of the films also increases while the coefficients of friction for the films do not change.     

Features of the tunneling conductivity of two-dimensional ordered linear-chain carbon films

Two-dimensional ordered linear-chain carbon films with different thicknesses (50 and 500 nm) have been studied by the tunneling spectroscopy method. The oscillatory dependence of the differential conductivity of the studied structures has been found. The obtained results have been interpreted with the use of the model of the formation of the charge density waves on the regular bends of the structure of linear-chain carbon.     

电化学法制备高密度导电聚吡咯的性能研究

系统地研究了溶剂、温度和聚合电流密度对电化学制备本征导电聚吡咯 (PPy)膜密度的影响,分别用四探针法和热失重(TG)法研究了不同密度的PPy膜的电导率和热稳定性.用循环伏安法(CV)和电化学阻抗谱(EIS)法比较了不同密度的PPy膜的电化学性能.研究表明,在室温下,在乙氰/水(AN/H₂O, 99/1)溶液比在水溶液中容易得到高密度的PPy膜.高聚合电流密度(如10mA/cm²)可以进一步提高PPy膜的密度,用X射线光电子能谱(XPS)对其结构进行了分析.在AN/H₂O(99/1)溶液中用小电流密度(0.1mA/cm²)聚合时,低温(-20℃)有利于提高PPy膜的密度;然而在高电流密度(10mA/cm²)时, 低温(-20℃)不利于提高PPy膜的密度.高密度的PPy膜(1.42g/cm³)用电流密度10mA/cm²在0℃的AN/H₂O(99/1)溶液中制得.该合成方法和常用的低温低电流密度方法制备高密度的PPy膜相比, 合成时间短,条件易实现,更利于实用化.更重要的是,高密度的PPy膜不仅具有高电导率(～220S/cm)和高热稳定性,还具有低的电化学活性.因此,高密度的PPy膜不仅是一种优异的电子导电的电极材料,而且是一种潜在的优异的防腐材料. 关键词： 聚吡咯膜 密度 电导率 热稳定性     

Galvanomagnetic properties of thin films with unidirectional anisotropy

Galvanomagnetic effect was used for studying the magnetization reversal processes in thin NiFe-NiFeMn films with the unidirectional anisotropy. The experimental results were compared with the simple coherent magnetization rotation model. A large contribution of rotation of the magnetization vectorM _s to the reversal process in easy direction was found (around 22°). The dependence of angular dispersion ₄₅ on external fieldH was also measured.     

The conductivity at high fields in films of amorphous niobium dioxide

Amorphous films of NbO_2.00 have been prepared by sputtering solid targets of NbO₂ in an atmosphere of 10% vol. of H and 90% vol. of Ar. Measurements of the conductivity at high electric fields show that the high field conductivity σ(F) can be described by: $\text{σ(}\text{F}\text{) =}\text{σ(0)}\text{Sinh}\text{(}\text{edF}\text{2}\text{kT}\text{)}\text{edF}\text{2}\text{kT}$ where d represents the hopping distance between defect centres having a density of ～ 3 × 10¹⁹cm^?3. Similar behaviour has been observed previously in other transition metal oxides with the defect centres attributed to oxygen vacancies.     

High-frequency conductivity of films with different surfaces

The high-frequency conductivity of films with different surfaces and spherically symmetric energy band is calculated. General expressions are obtained for the conductivity for arbitrary values of the following quantities: the film thickness, the frequencies of the incident wave, and the specularity parameters with allowance for the bulk scattering mechanisms. A detailed analysis is made of the influence of the boundedness of the sample and the different surfaces on the conductivity in limiting cases with respect to the film thickness and the frequency of the incident wave. In particular, it is shown that in the case of thin films and low frequencies the conductivity decreases with decreasing thickness. The influence of different surfaces on the conductivity is also considered. The dependence of the coefficient of absorption of the wave on the film thickness and the carrier density is analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 88–92, July, 1980.We are sincerely grateful to Professor B. M. Askerov for his interest in the work and a helpful discussion of the obtained results.     

Core-level and valence-band characteristics of carbon nitride films with high nitrogen content

Carbon nitride films with high nitrogen content were prepared by reactive pulsed-laser deposition at nitrogen partial pressures varying from 0.1 to 20.0 Torr. It was found that the nitrogen content in the films first increases with increase of the nitrogen pressure, reaches a maximum of 46 at. % at 5.0 Torr, and then decreases to 37 at. % at 20.0 Torr. The almost pure carbon nitride films were systematically characterized by using X-ray photoelectron spectroscopy (XPS) concerning the core-level and valence-band structures. Some fingerprint information, which shows the role of nitrogen in controlling the electronic structure of carbon nitride films, was found based on the XPS studies. With enhancing the nitrogen incorporation, both the binding energy and the peak intensity of the core-level and the valence-band spectra vary systematically as a function of nitrogen content in the films. Received: 26 June 2000 / Accepted: 26 June 2000 / Published online: 20 September 2000     

High coercivity sputtered Nd-Fe films with perpendicular anisotropy

Thin films of Nd-Fe prepared by rf sputtering are shown to exhibit marked perpendicular anisotropy. Hysteresis loops with a sqaureness ratio of essentially 1.0 with large coercivities and significant polar Kerr rotations are reported for films with 60 at% Nd.