Reaction mechanism discrimination using experimental film profiles in features

Film profiles in features on patterned substrates are employed as a tool to test proposed reaction mechanisms for low pressure chemical vapor deposition processes. Simulated film profiles in long trenches generated using EVOLVE, a physically based deposition process simulator, are compared to experimental film profiles to determine whether a particular mechanism or rate form should be rejected. We consider two examples: (1) silicon dioxide deposition from tetraethoxysilane (TEOS), and (2) tungsten deposition from hydrogen reduction of tungsten hexafluoride. Of three proposed mechanisms for the deposition of silicon dioxide from TEOS, we find that the mechanism in which TEOS undergoes heterogeneous decomposition with inhibition by a strongly adsorbing byproduct provides the best fit to the experimental profiles. In the second example, we demonstrate that a mechanism that assumes a single rate limiting step is apparently not valid for tungsten depositions involving features that close. A semi-empirical rate expression is presented which can be used to simulate depositions up to and beyond feature closure.     

Dependence of segregated microstructure in sputter-deposited CoCr film on deposition conditions

The compositional segregation of sputter-deposited CoCr films prepared under substrate temperatures Ts of 90-160°C and Ar gas pressures PAr of 4-30 mTorr are studied by transmission electron microscopy. The segregated microstructure depends on Ts and PAr. The degree of the segregation increases as Ts increases, and is maximized at a medium PAr. Saturation magnetization increases as the degree of the segregation increases. Vertical coercivity in film with the same degree of the c-axis orientation increases as the degree of segregation increases.     

A simple method to estimate phosphorus mobilization in hemodialysis using only predialytic and postdialytic blood samples

We have recently developed a pseudo one-compartment model to describe intradialytic and postdialytic rebound kinetics of plasma phosphorus. In this model, individual patient differences in phosphorus kinetics were characterized by a single parameter; the phosphorus mobilization clearance (K(M) ). In this work, we propose a simple method to estimate K(M) from predialytic and postdialytic plasma phosphorus concentrations. Clinical data were collected from 22 chronic hemodialysis patients that underwent a 4-hour treatment session. A simple algebraic equation was derived from the pseudo one-compartment model to determine K(M) from predialytic and postdialytic plasma phosphorus concentrations. K(M) values computed using this equation were compared with values obtained from nonlinear regression of the full kinetic model to frequent intradialytic and postdialytic measurements of plasma phosphorus concentrations. There was good agreement between K(M) values (concordance correlation coefficient of 0.94) obtained from the simple method (105?±?52?mL/min, mean?±?SD) and from the full model (99?±?47?mL/min). The 95% confidence interval for the difference between estimated K(M) values was -26 to 36?mL/min. The proposed simple method requires the use of only predialytic and postdialytic blood samples to estimate patient specific K(M) ; this approach may allow easy clinical evaluation of phosphorus kinetics in hemodialysis patients.     

二维自由振动的有限元线法自适应分析新进展

该文建立圆弧形曲梁裂纹的截面损伤缺陷比拟方案,实现裂纹大小(深度)、位置、数目的模拟。引入变截面Euler-Bernoulli梁的h型有限元网格自适应分析方法,求解含裂纹损伤圆弧曲梁弹性屈曲问题,得到优化的网格和满足预设误差限的高精度屈曲荷载和屈曲模态解答。数值算例表明该算法中网格非均匀加密可适应裂纹损伤引起的屈曲模态变化,应用于各类曲梁夹角和裂纹损伤分布工况下的弹性屈曲研究,定量分析了裂纹损伤程度对圆弧曲梁的屈曲荷载和屈曲模态的影响,检验了该文算法的精确性和可靠性。     

A method to estimate mass dispersion in inhomogeneous convective flows

A diffusion-model-based generalizing method for estimating the dispersion of mass in inhomogeneous convective flows is considered. An admissible class of exact solutions, a comparison with which allows one to establish the dispersion coefficient and the error of application of the model in each specific case, has been determined. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 1, pp. 120–123, January–February, 2007.     

A method to estimate the circulated composition in refrigeration and heat pump systems using zeotropic refrigerant mixtures

In recent years a number of refrigerant mixtures have appeared on the market. Some of these refrigerant mixtures are zeotropic, e.g. R407C and R417A. When zeotropic refrigerant mixtures are used in a system, the circulated composition may change from the nominal to a different composition. The changes in composition may be due to leakage or hold-ups of liquid or vapour phase, different solubility in the oil by the different components, or the fact that the system has been charged in an incorrect way. For the understanding of performance measurements made on systems, it is important to know the composition of the circulated refrigerant mixture. A promising method to estimate the circulated composition has been developed. The method has been applied and evaluated on a well equipped lab rig at the Department of Energy Technology at the Royal Institute of Technology. The tests show that it is possible to estimate the composition of the circulated refrigerant mixture to within 2%, by measuring only two temperatures and pressures.     

Imposing boundary conditions in the meshless local Petrov-Galerkin method

A particular meshless method, named meshless local Petrov-Galerkin is investigated. To treat the essential boundary condition problem, an alternative approach is proposed. The basic idea is to merge the best features of two different methods of shape function generation: the moving least squares (MLS) and the radial basis functions with polynomial terms (RBFp). Whereas the MLS has lower computational cost, the RBFp imposes in a direct manner the essential boundary conditions. Thus, dividing the domain into different regions a hybrid method has been developed. Results show that it leads to a good trade-off between computational time and precision.     

An automatic system using mobile-agent software to model the calculation process of a chemical vapor deposition film deposition simulator

We have developed an automatic modeling system for calculation processes of the simulator to reproduce experimental results of chemical vapor deposition (CVD), in order to decrease the calculation cost of the simulator. Replacing the simulator by the mathematical models proposed by the system will contribute towards decreasing the calculation costs for predicting the experimental results. The system consists of a mobile agent and two software resources in computer networks, that is, generalized modeling software and a simulator reproducing cross-sections of the deposited films on the substrates with the micrometer- or nanometer-sized trenches. The mobile agent autonomously creates appropriate models by moving to and then operating the software resources. The models are calculated by partial least squares regression (PLS), quadratic PLS (QPLS) and error back propagation (BP) methods using artificial neural networks (ANN) and expresses by mathematical formulas to reproduce the calculated results of the simulator. The models show good reproducibility and predictability both for uniformity and filling properties of the films calculated by the simulator. The models using the BP method yield the best performance. The filling property data are more suitable to modeling than film uniformity.     

Pulsed ion beam characterization of CVD diamond surfaces under thin film deposition conditions

Diamond and diamond-like carbon have properties which in principle make them ideally suited to a wide variety of thin-film applications. The widespread use of diamond thin films, however, has been limited for a number of reasons related largely to the lack of understanding and control of the nucleation and growth processes. Real-time, in-situ studies of the surface of the growing diamond film are experimentally difficult because these films are normally grown under a relatively high pressure of hydrogen, and conventional surface analytical methods require an ultrahigh vacuum environment. Pulsed ion beam based analytical methods with differentially pumped ion sources and particle detectors are able to characterize the uppermost atomic layer of a film during growth at ambient pressures in the range 0.7–27 Pa (4–6 orders of magnitude higher than other surface-specific analytical methods). We describe here a system which has been developed for the purpose of determining the hydrogen concentration and bonding sites on diamond surfaces as a function of sample temperature and ambient hydrogen pressure under hot-filament chemical vapor deposition (CVD) growth conditions. It is demonstrated that as the hydrogen partial pressure increases the saturation hydrogen coverage of the surface of a CVD diamond film increases, but that the saturation level depends on the atomic hydrogen concentration and substrate temperature. At the highest temperatures studied (700 °C), it was found that the surface hydrogen concentration did not exceed 1/4 monolayer.     

A critical comparison of silicide film deposition techniques

Three different film deposition techniques are compared. WSi₂ was chosen as a test sample. Fabrication of films with the desired composition and lowest electrical resistivities are emphasized. Rutherford backscattering analysis was found to be a very useful tool to perform rapid non-destructive examination of in-depth composition variation and determination of relative thickness. Co-evaporation of tungsten and silicon was found to provide films with the lowest resistivity but was the most difficult method of film deposition. Co-sputtering is slightly simpler than co-evaporation but it is preferable to sputter from a compound or composite target of high purity if available. Low pressure chemical vapor deposition is the simplest method for tungsten silicide film deposition with uniformity and high throughput. However, these films contain more impurities, and thus the resulting resistivities are higher than those of purer films deposited by other techniques.     

Optimal conditions for protein array deposition using continuous flow

Optimal conditions for depositing protein microarrays using a continuous-flow microfluidic device, the continuous-flow microspotter (CFM), have been determined using a design of experiments approach. The amount of protein deposited on the surface depends on the rates of convective and diffusive transport to the surface and binding at the surface. These rates depend on parameters such as the flow rate, time, and capture mechanism at the surface. The process parameters were optimized, and uniform protein spots were obtained at a protein concentration of 10 microg/mL and even at 0.4 microg/mL. A 150-fold dilution in protein concentration in the sample solution decreased surface concentration by a factor of only 16. If the capture mechanism of the protein on the substrate is nonspecific, optimal deposition is obtained at higher flow rates for short periods of time. If the capture mechanism is specific, such as biotin-avidin, deposition is optimal at medium flow rates with little advantage beyond 30 min. The CFM can be used to deposit protein arrays with good spot morphology, spot-to-spot uniformity and enhanced surface concentration. The CFM was used to deposit an array of various antibodies, and their interactions with an antigen were studied using surface plasmon resonance (SPR). Affinity values were obtained at low antibody concentrations (5 microg/mL) with low coefficients of variation. Thus, the CFM can be used to effectively capture proteins and antibodies from dilute samples while depositing multiple spots, thereby increasing the quality of spots in protein microarrays and especially improving screening throughput of SPR.     

A new method of depositing high figure-of-merit porous PZT pyroelectric thick film using [001]-oriented PZT nanorod by electrophoresis deposition

The effects of hydrothermal synthesized [001]-oriented PZT nanorods on the pyroelectric properties of PZT thick film fabricated by electrophoresis deposition were studied in a range from 750 to 900 °C. It was revealed by scanning electron microscopy that the pores are mainly distributed in the film body but not at the electrode interface, which would improve the adhesion and electric contact between the thick film and electrode. The formation and distribution of the pores resulted from the PZT nanorods were schematically explained. It was found that the relative dielectric constant (ε _r ) of the PZT nanorod-doping film sintered at 800 °C was lowered by approximate 46.5 %. Accordingly, the calculated figures of merit for voltage responsivity (F_V) and detectivity (F_D) were improved by 125 and 114 %, respectively. These results demonstrated that a new way to deposit PZT porous thick film with low dielectric constant and high figures of merit was established.     

A method to estimate entropies and heat capacities applied to alkali oxides

We present a method that is useful in the estimate and assessment of heat capacity data. The approach is based on an analysis of the logarithmic average of the phonon frequencies. In this quantity, that may be easily derived from experimental data on the vibrational entropy, the influence of atomic masses can be exactly accounted for even in polyatomic solids. Our method is applied to Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O. In particular, literature data for K₂O are critically examined.     

Epitaxial growth of lithium niobate film using metalorganic chemical vapor deposition

Lithium niobate films grown epitaxially on sapphire substrate were prepared using a thermal chemical vapor deposition method from the metalorganic compounds Li(C₁₁H₁₉O₂) and Nb(OC₂H₅)₅. The range of operating conditions for obtaining pure epitaxially grown LiNbO₃ without other oxides is within that for obtaining pure polycrystalline LiNbO₃ grown on silicon substrate. On analyzing the composition of the epitaxially grown LiNbO₃ film, the composition of the film was similar to that of the LiNbO₃ solid solution in the phase diagram of the Li-Nb composite oxide obtained for crystal growth from a molten solution.     

Fabrication of high-performance fluorine doped-tin oxide film using flame-assisted spray deposition

A high-performance fluorine-doped tin oxide (FTO) film was fabricated by flame-assisted spray deposition method. By varying the NH₄F doping concentration, the optimal concentration was established as 8 at.%. X-ray diffractograms confirmed that the as-grown FTO film was tetragonal SnO₂. In addition, the FTO film was comprised of nano-sized grains ranging from 40 to 50 nm. The heat-treated FTO film exhibited a sheet resistance of 21.8 Ω/? with an average transmittance of 81.9% in the visible region (λ = 400-800 nm). The figures of merit shows that the prepared FTO film can be used for highly efficient dye-sensitized solar cells electrodes.