Temperature dependence in sputtering

We have obtained the result on the temperature dependence in sputtering of silver which is contrary to the current believes by taking steps to eliminate spurious effects due to changes of residual gas pressure and target temperature, and by determining the relevant energy range for thermal sputtering. The result i3 thought to be due basically to the thermal spike effect, and agreement is shown with a postulated thermal spike model, in which the instantaneous variation of spike temperature against thermal diffusivity is treated on the basis of Carslaw's solution of the normal heat conduction equation. The thermal diffusivity is shown to be proportionate to the thermal conductivity subject to a constant metal density in the temperature range 300–500K and a heat capacity that obeys the Dulong-Petit law which holds good for most metals at high temperatures (> θ_D). The thermal conductivity versus preheat target temperature curve matches the Makinson electronic thermal conductivity curve for metals.     

Étude de la chimisorption de O2 À 77 K à l'aide d'isothermes d'adsorption physique à marches: Systèmes CdOKr et CdOCF4

The evolution of stepwise isotherms of CF₄ and Kr on cadmium at 77.4 K, when increasing oxygen quantities are prechemisorbed at the same temperature, brings out some information about that chemisorption. It can be deduced from the splitting of steps that, at 77.4K, oxygen chemisorbs as rather homogeneous patches. It seems to be islands spreading in proportion to the chemisorbed quantities. As a mean, 4 oxygen atoms seem to be adsorbed for every surface cadmium atom. Such a number involves a reaction with slightly deeper Cd atoms. Over these oxidized patches, oxygen seems to physisorb (precursor state of oxidation) more readily than upon the bare part of the metal. This suggests one modification in the set of hypotheses usually acknowledged for the analysis of oxidation kinetics in that temperature range. A brief comparison is made with the somewhat different islands that are known to grow on metals when oxidization, or sulfurization, occurs at higher temperatures. Some remarks are aimed at the effects of “thermal regeneration” under vacuum.     

Pressure and Electrical Resistivity Measurements on Hot Expanded Metals: Comparisons with Quantum Molecular Dynamics Simulations and Average‐Atom Approaches

We present experimental results on pressures and resistivities of expanded nickel and titanium at respective densities of 0.1 g/cm³ and 0.2 g/cm³, and in a range of temperature of 1‐3 eV that corresponds to the warm dense matter (WDM) regime. These data are used to benchmark different theoretical approaches. A comparison is presented between fully 3‐dimensional quantum molecular dynamics (QMD) methods, based on density functional theory, with average‐atom (AA) methods, that are essentially one dimensional. AA methods are used to identify interband transitions and photoionization thresholds. In this regime the evaluation of the thermodynamic properties as well as electrical properties is difficult due to the concurrence of density and thermal effects which directly drive the metal‐non‐metal transition. QMD simulations are also helpful to give a precise estimation of the temperature of experiments which is not directly accessible [1] (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

光谱法研究闪电回击放电通道的电阻及电流的热效应

闪电放电通道的电阻及电流产生的热效应对雷电灾害研究以及防护设计都具有重要意义,放电通道的热力学特性与其等离子体辐射光谱密切相关。利用无狭缝摄谱仪获得的两次云对地多回击闪电放电的等离子体辐射光谱,依据谱线波长、强度等信息,结合同步地面电场变化资料,应用空气等离子体传输理论,计算了闪电回击放电通道的电导率、峰值电流、核心通道半径,进而得到了闪电回击等离子体通道单位长度的电阻、峰值电流时的热功率及在回击初始前5 μs内通道储存的热能。并与常规金属导体进行比较,分析了闪电回击放电在峰值电流时等离子体通道的热功率与电阻、电流平方之间的相关性关系。结果表明：利用光谱研究得到的闪电放电通道的电阻为0.04～8.41 Ω·m-1、峰值电流时的热功率为0.88×108～2.20×108 W·m-1、回击初始前5 μs内通道储存的热能为1.47×102～3.66×102 J·m-1,以上结果与文献报道的利用其他方法得到的结果相比,在合理的范围内;与常规金属导体相比,闪电回击放电等离子体通道在峰值电流时的热功率与电阻成正比,但与电流的平方呈指数减小的关系;由于闪电等离子体通道的电阻与温度的3/2次方成反比,通常回击放电通道中峰值电流越大,通道温度越高,而电阻会迅速降低,因此热功率也会急剧减小。此结论进一步验证了采用欧姆加热方法加热等离子体的致命缺点。     

Predicting the thermal conductivity enhancement of nanofluids using computational intelligence

Nanofluids, composed of nanoparticles in base liquids, have drawn increasing attention in heat transfer applications due to their anomalously increased thermal conductivity. Pertinent parameters, including the base liquid thermal conductivity, particle thermal conductivity, particle size, particle volume fraction, and temperature, have been shown to have significant but complex effects on thermal performance of nanofluids, which is commonly characterized by the thermal conductivity enhancement, E%. In this work, machine learning is used to develop the Gaussian process regression model to find statistical correlations between E% and aforementioned physical parameters among various types of nanofluids. Nearly 300 nanofluid samples, dispersions of metal and ceramic nanoparticles in water, ethylene glycol, and transformer oil, are explored for this purpose. The modeling approach demonstrates a high degree of accuracy and stability, contributing to efficient and low-cost estimations of E%.     

Magnetic and thermal properties of CuFeS<Subscript>2</Subscript> at low temperatures

The magnetic moment M, the magnetic susceptibility χ, and the thermal conductivity of chalcopyrite CuFeS₂, which is a zero-gap semiconductor with antiferromagnetic ordering, have been measured in the temperature range 10–310 K. It has been revealed that the quantities χ(T) and M(T) increase anomalously strongly at temperatures below ∼100 K. The temperature dependence M(T) is affected by the magnetic prehistory of the sample. An analysis has demonstrated that the magnetic anomalies are associated with the presence of a system of noninteracting magnetic clusters in the CuFeS₂ sample under investigation. The formation of the clusters is most likely caused by the disturbance of the ordered arrangement of Fe and Cu atoms in the metal sublattice of the chalcopyrite, which is also responsible for the phase inhomogeneity of the crystal lattice. The inhomogeneity brings about strong phonon scattering, and, as a result, the temperature dependence of the thermal conductivity coefficient exhibits a behavior characteristic of partially disordered crystals.     

Thermal conductivity of the YbMgCu<Subscript>4</Subscript> “light” heavy-fermion system

The thermal conductivity and electrical resistivity of a sample of YbMgCu₄ belonging to “light” heavy-fermion compounds have been measured in the temperature range 5–300 K. The sample studied was in the region of homogeneity of this compound. It is shown that, throughout the temperature range studied, the phonon thermal conductivity of the sample has an amorphous-like character, which should be assigned to the homogeneous mixed valence of the Yb ion in YbMgCu₄.     

Thermal conductivity and thermal diffusivity of SiO<Subscript>2</Subscript> nanopowder

A 3ω approach for the simultaneous determination of the effective thermal conductivity and thermal diffusivity of nanopowder materials was developed. A 3ω experimental system was established, and the thermal properties of water and alcohol were measured to validate and estimate the accuracy of the current experimental system. The effective thermal conductivity and thermal diffusivity of the SiO₂ nanopowder with 375, 475, and 575 nm diameters were measured at 290–490 K and at different densities. At room temperature, the effective thermal conductivity and thermal diffusivity of the SiO₂ nanopowder increased with temperature; however, both values decreased as the particle diameter was reduced. An optimum SiO₂ powder density that decreased with decreasing diameter was also observed within the measurement range. The minimum effective thermal conductivity and maximum effective thermal diffusivity were obtained at 85 × 10⁻³ kg/L, when the particle diameter was 575 nm. The optimum densities of the particles with 375 and 475 nm diameters were less than 50.23 × 10⁻³ and 64.82 × 10⁻³ kg/L, respectively.     

The vibrational contribution to the thermal conductivity of a polyatomic fluid

A simple analytical expression is proposed in this article to calculate the vibrational contribution to the thermal conductivity of a polyatomic fluid. The analytic expression was obtained based on the assumption that the self-diffusion process is the major mechanism in the transport of vibrational energy. The proposed expression is validated by comparing the thermal conductivity of CO₂ calculated by molecular dynamics (MD) simulations to experimental data over a wide range of temperature and pressure. It is also demonstrated that the proposed analytic expression greatly increases the accuracy of calculated thermal conductivity for CO₂ at the supercritical state.     

Transport properties of a binary mixture of CO₂-N₂ from the pair potential energy functions based on a semi-empirical inversion method

The potential energy surface of a CO 2 –N 2 mixture is determined by using an inversion method, together with a new collision integral correlation [J. Phys. Chem. Ref. Data 19 1179 (1990)]. With the new invert potential, the transport properties of CO2–N2 mixture are presented in a temperature range from 273.15 K to 3273.15 K at low density by employing the Chapman–Enskog scheme and the Wang Chang–Uhlenbeck–de Boer theory, consisting of a viscosity coefficient, a thermal conductivity coefficient, a binary diffusion coefficient, and a thermal diffusion factor. The accuracy of the predicted results is estimated to be 2% for viscosity, 5% for thermal conductivity, and 10% for binary diffusion coefficient.     

An anomalous thermal expansion in the perovskite system,Gd1−xSrxMnO3 (0 ≤ x ≤ 0.3)

The thermal expansion behavior of sintered samples of Gd_1−xSr_xMnO₃ (X = 0.0–0.4) was studied. The sintered bodies in this system showed negative thermal expansion over a wide temperature range. The detailed crystal structure refinements with respect to temperature showed that the volume of the orthorhombic perovskite lattice monotonically increased with temperature, however, in addition to this, the release of distortion from the Jahn-Teller effect of Mn³⁺ ion occurred over a wide temperature range, which brought the negative expansion of the a-axis, although the b- and c-axes increased with temperature. The anomalous thermal expansion is explained by the sum of the effects of the shrinkage of the a-axis and absorption of the b- and c-axes' expansion by the pores in the sintered body.     

First-principles study of the anisotropic thermal expansion of hcp metals Be and Y

A first-principles study of the anisotropic thermal expansion of hcp metals Be and Y is reported. According to quasiharmonic approximation, the phonon spectra were computed at a set of lattice parameters using the pseudopotential plane wave method with the local density approximation in the framework of the density functional perturbation theory. The free energies were obtained according to the calculated phonon spectra and thermal properties such as specific heat at constant volume (pressure) were calculated. The electronic contribution to specific heat was found important to metal Y not only at very low temperature but also over room temperature. The calculated results are in good agreement with available experimental data in a wide range of temperature.     

氢化非晶硅薄膜的热导率研究

采用铂电极为加热电阻,研究了厚度为300—370nm等离子体化学气相沉积(PECVD)工艺制备的氢化非晶硅(a-Si：H)薄膜的热导率随衬底温度的变化规律.用光谱式椭偏仪拟合测量薄膜的厚度,得到了沉积速率随衬底温度变化规律,傅里叶红外(FTIR)表征了在KBr晶片衬底上制备的a-Si：H薄膜的红外光谱特性,SiH原子团键合模的震动对热量的吸收降低了薄膜热导率.从动力学角度分析了薄膜热导率随平均温度升高而增大的原因,并比较了声子传播和自由电子移动在a-Si：H薄膜热导率变化上的作用差异. 关键词： 非晶硅 热导率 薄膜 热能     

Provide a suitable range to include the thermal creeping effect on slip velocity and temperature jump of an air flow in a nanochannel by lattice Boltzmann method

The thermal creeping effect on slip velocity of air forced convection through a nanochannel is studied for the first time by using a lattice Boltzmann method. The nanochannel side walls are kept hot while the cold inlet air streams along them. The computations are presented for the wide range of Reynolds number, Knudsen number and Eckert number while slip velocity and temperature jump effects are involved. Moreover appropriate validations are performed versus previous works concerned the micro–nanoflows.The achieved results are shown as the velocity and temperature profiles at different cross sections, streamlines and isotherms and also the values of slip velocity and temperature jump along the nanochannel walls. The ability of the lattice Boltzmann method to simulate the thermal creeping effects on hydrodynamic and thermal domains of flow is shown at this study; so that its effects should be involved at lower values of Eckert number and higher values of Reynolds number especially at entrance region where the most temperature gradient exists.     

Molecular alloys as phase change materials (MAPCM) for energy storage and thermal protection at temperatures from 70 to 85 °C

Molecular alloys, that combine a relatively high heat of melting with a suitable melting temperature adapted to the application temperature, are excellent materials for thermal protection and for thermal energy storage. Of special interest is the fact that, by making alloys of molecular materials; the range of melting can be adjusted over a range of temperatures. The present paper reports on the design of MAPCMs to be used for energy storage and thermal protection at temperatures from 70 to 85 °C. The aim is to use these materials for thermal protection in the catering sector in order to avoid proliferation of micro organisms; the minimal temperature required is higher than 65 °C. The work illustrates how some fundamental studies are helpful in choosing the right composition that is able to work at the temperature required for an application. Several molecular alloys using the n-alkanes are elaborated and characterized. The preparation of mixed crystals, their crystallographic and thermodynamic properties and stability, phase change behaviour, and their use in practical applications are reported.     

Effect of external fields on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe<Subscript>2</Subscript>

The effect of external fields (dc electric field, light illumination) on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe₂ is studied using the measured dielectric constant. The results obtained are discussed. It is shown for the first time that the effect of external fields on the anomaly related to the memory effect in TlGaSe₂ can be reduced to the following universal empirical rule: when a sample is held for many hours at a constant temperature T ₀ in the temperature range of the incommensurate phase in a dc electric field, the deflection amplitude in the low-temperature part of the anomaly in the temperature dependence of the relative change in the dielectric constant Δ?/? increases (the deflection in the high-temperature part of the Δ?/? anomaly disappears) as compared to this segment in the dependence obtained during isothermal annealing of this sample at the same temperature without an electric field. The crystal remembers its thermal history at a temperature that is several kelvins higher than T ₀. Light illumination increases the deflection amplitude in the high-temperature part of the Δ?/?(T) anomaly and shifts the temperature at which the crystal remembers its thermal history toward lower temperatures with respect to T ₀.     

The Global Optimization of Pt<Subscript>13</Subscript> Cluster Using the First-Principle Molecular Dynamics with the Quenching Technique

The high-temperature first-principle molecular dynamics method used to obtain the low energy configurations of clusters [L. L. Wang and D. D. Johnson, PRB 75, 235405 (2007)] is extended to a considerably large temperature range by combination with the quenching technique. Our results show that there are strong correlations between the possibilities for obtaining the ground-state structure and the temperatures. Larger possibilities can be obtained at relatively low temperatures (as corresponds to the pre-melting temperature range). Details of the structural correlation with the temperature are investigated by taking the Pt₁₃ cluster as an example, which suggests a quite efficient method to obtain the lowest-energy geometries of metal clusters.     

Calculation of the Thermal Parameters of Boron Silicide by Differential Scanning Calorimetry

The DSC, TG, DTA, and DTG analyses of boron silicides, which are widely applied in radiation material science and nuclear technology, have been performed depending on the thermal treatment rate. The kinetic parameters (energy, enthalpy, oxidation reaction rate, heat capacity, and activation energy) of effects occurring in the thermal treatment of boron silicides of 99.5% purity within a temperature range of 25–900°C at a rate of 5–20°C/min have been established. It has been established that the phase transition typical for silicides with its central peak at a temperature 572 ± 5°C can exist in boron silicides depending on the thermal treatment rate. In TG and DTG spectra, this appears as an oxidation thermal effect at T ≥ 660°C with a change increase in mass of nearly 9%.     

Measurement of thermal conductivity of fluids using 3-<Emphasis Type="Italic">ω</Emphasis> method in a suspended micro wire

A thermally controlled, compact device employing the 3-ω technique, used to measure the thermal conductivity of fluids, is designed, developed, and presented in this paper. The 3-ω method, which analyzes temperature oscillations data in the frequency domain, requires a microscopic sample and extremely low heating power. The functionality is derived from the approximate solutions of temperature oscillations of a line heater based on the infinite line-heater model over an empirically and analytically chosen range of frequencies. The method is devoid of errors related to transient measurements, fluid thermal stratification and mobility errors, which pose difficulties in other methods. A platinum (99.99% pure) wire of 50 μm diameter and a length of 30 mm, suspended in a sample volume of 25 μl of the test fluid, serves simultaneously as the heater and thermometer. Structure-wise, the device is designed to support measurements over a range of temperatures and fluid pressures providing modularity and flexibility to the instrument. The device is successfully employed to measure the thermal conductivity of de-ionized water for temperatures between 15 and 35°C with an accuracy of ±1.2% inmeasurement.     

Synthesis of In<Subscript>2</Subscript>O<Subscript>3</Subscript>nanoparticles by thermal decomposition of a citrate gel precursor

This paper describes the synthesis of indium oxide by a modified sol–gel method, and the study of thermal decomposition of the metal complex in air. The characterization of the intermediate as well as the final compounds was carried out by thermogravimetry, differential thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and small angle X-ray scattering. The results show that the indium complex decomposes to In₂O₃ with the formation of an intermediate compound. Nanoparticles of cubic In₂O₃ with crystallite sizes in the nanosize range were formed after calcination at temperatures up to 900°C. Calcined materials are characterized by a polydisperse distribution of spherical particles with sharp and smooth surfaces.This revised version was published online in August 2005 with a corrected issue number.