The study of quantitativeness in atom probe analysis of alloying elements in steel

The quantitativeness in atom probe analysis of dilute solute alloying elements in steel was systematically investigated. The samples of binary Fe–Si, Fe–Ti, Fe–Cr, Fe–Cu, Fe–Mn and Fe–Mo alloys were prepared for present study. The apparent compositions of alloying elements were examined by three-dimensional atom probe (3DAP) under various experimental conditions. The temperature dependence of the apparent compositions varied largely with the alloys, which indicated that the degree of preferential evaporation or retention varied with the alloying elements. Furthermore, the analysis direction dependence of the apparent Mn composition was examined in the Fe–Mn alloy. The experimental results indicated that the order of the field evaporation rate of elements in steel was Cu>Cr>Mn∼Mo>Fe>Ti∼Si. The field evaporability of alloying elements in steel was discussed in terms of the solution enthalpy of the alloying elements and the phase types of the binary Fe alloys.     

Accuracy and precision in model based EELS quantification

We present results on model based quantification of electron energy loss spectra (EELS), focusing on the factors that influence accuracy and precision in determining chemical concentrations. Several sources of systematical errors are investigated. The spectrometer entrance aperture determines the collection angle, and the effects of its position with respect to the transmitted beam are investigated, taking into account the diffraction by the crystal structure. The effect of the orientation of the sample is tested experimentally and theoretically on SrTiO3, and finally, a simulated experiment on c-BN at different thicknesses confirms the superior results of the model based method with respect to the conventional method. A test on a set of experimental reference compounds is presented, showing that remarkably good accuracy can be obtained. Recommendations are given to achieve high accuracy and precision in practice.     

Landé g-factor and cyclotron effective mass in a cylindrical GaAs-(Ga,Al)As quantum pillbox under the influence of an axis-parallel applied magnetic field

We have performed a theoretical study of electronic states and the parallel Landé g-factor in a quantum dot (QD), assumed to be in the form of a pillbox, in the presence of an uniform magnetic field applied parallel to the pillbox axis. The quantum pillbox is assumed to consist of a finite length cylinder of GaAs material surrounded by Ga_1-xAl_xAs which describe the realistic finite potential confinement. The calculations have been performed by using the Kummer confluent hypergeometric functions. This study is performed for different radii and lengths of the cylindrical GaAs pillbox and the limit cases have been studied to prove the validity of the model. Our results are in good agreement with the previous theoretical results [F.E. López, B.A. Rodríguez, E. Reyes-Gómez, L.E. Oliveira, in press] in the limit geometry of a quantum well wire (QWW).     

Realisation of ‘Solar Blind’ AlGaN Photodetectors: Measured and calculated spectral response

Al_xGa_1−xN solar blind photoconductors are fabricated and characterized. The cutoff wavelength of these detectors is as low as 275 and 271 nm with aluminium fraction of 49.6 and 54.1%, respectively. The used AlGaN active layers were grown on (0001) sapphire substrates by low pressure metalorganic chemical vapour deposition (LP-MOCVD). The full width at half maximum (FWHM) of X-ray rocking curve from (0002) diffraction indicates the good quality of these samples. Optical properties are investigated with photoluminescence and absorption measurements. The variation of the spectral response with applied voltage and modulation frequency is investigated. Better results are obtained with 12 Hz and 20 V. Compared to other researches, a high rejection ratio is obtained. The simulation of the photoresponse using the voltage dependent responsivity allows the determination of the carrier lifetime. We obtained a value of 0.15 and 0.13 ms for x=0.49 and 0.54, respectively.     

低介电常数和低介质损耗覆铜板材料的介绍

随着先进通讯设备和技术的发展,广泛应用于通讯领域的各种高频电子设备的需求也在飞速增长.为满足高频信号的传输,高传输速度和高频低损耗的需求,各种低介电常数(Dk)和低介质损耗(Df)的覆铜板基材也在不断的发展中.目前低介电常数和低介质损耗的板材通常使用氰酸脂、苯乙烯马来酸酐、PP0/APPE、PTFE、PI或他们的混合物来制造,还可以结合使用低介电常数、低介质损耗的玻璃纤维布来生产.文章主要针对高频电路的特点、板材实现低Dk/Df的方法及相应的一些表征方式与计算方法做了一些介绍.     

Three-dimensional atom probe analysis of heavily drawn steel wires by probing perpendicular to the pearlitic lamellae

Three-dimensional atom probe analysis of heavily drawn pearlitic steel wires was conducted by probing in the direction perpendicular to the pearlitic lamellae. A needle tip perpendicularly intersecting the lamellar structure was prepared using focused ion beam (FIB) milling combined with the lift-out method. The specimen preparation technique enabled the analysis of many lamellae and their interfaces with higher depth spatial resolution, which was suitable for drawn pearlitic steel wires having inhomogeneous and fine lamellar structure. Carbon concentration peaks at the cementite lamellae appeared higher and narrower than those obtained by probing parallel to the lamellae, which implies that the conventional analysis overestimated the extent of cementite decomposition in drawn pearlitic steel wires.     

A program for confidence interval calculations for a Poisson process with background including systematic uncertainties: POLE 1.0

A Fortran 77 routine has been developed to calculate confidence intervals with and without systematic uncertainties using a frequentist confidence interval construction with a Bayesian treatment of the systematic uncertainties. The routine can account for systematic uncertainties in the background prediction and signal/background efficiencies. The uncertainties may be separately parametrized by a Gauss, log-normal or flat probability density function (PDF), though since a Monte Carlo approach is chosen to perform the necessary integrals a generalization to other parameterizations is particularly simple. Full correlation between signal and background efficiency is optional. The ordering schemes for frequentist construction currently supported are the likelihood ratio ordering (also known as Feldman-Cousins) and Neyman ordering. Optionally, both schemes can be used with conditioning, meaning the probability density function is conditioned on the fact that the actual outcome of the background process can not have been larger than the number of observed events.

Program summary

Title of program: POLE version 1.0Catalogue identifier: ADTAProgram summary URL:http://cpc.cs.qub.ac.uk/summaries/ADTAProgram available from: CPC Program Library, Queen's University of Belfast, N. IrelandLicensing provisions: NoneComputer for which the program is designed: DELL PC 1 GB 2.0 Ghz Pentium IVOperating system under which the program has been tested: RH Linux 7.2 Kernel 2.4.7-10Programming language used: Fortran 77Memory required to execute with typical data: ∼1.6 MbytesNo. of bytes in distributed program, including test data, etc.: 373745No. of lines in distributed program, including test data, etc.: 2700Distribution format: tar gzip fileKeywords: Confidence interval calculation, Systematic uncertaintiesNature of the physical problem: The problem is to calculate a frequentist confidence interval on the parameter of a Poisson process with known background in presence of systematic uncertainties in experimental parameters such as signal efficiency or background prediction.Method of solution: A PDF for the confidence interval construction is constructed by folding a Poisson density function with a parametrization describing the posterior PDF of the systematic uncertainties. The construction is then performed with this new PDF according to different ordering schemes. The convolution is performed using a Monte Carlo integration method, providing greatest possible flexibility with respect to the parametrization.Restriction on the complexity of the problem: No restrictions.Typical running time: for calculation of a single confidence interval with 1000 steps in signal hypothesis space the wall clock time on a DELL PC 1 GB 2.0 Ghz Pentium IV with 4 GB swap is ca. 500 seconds. The wall clock time scales roughly linear with the number of steps in signal space.Unusual features of the program: POLE uses routines from the CERNLIB library [http://wwwasd.web.cern.ch/wwwasd/cernlib], which have to be linked in during compilation. It should be noted that the number of steps in signal space (maximal s required divided by the step-width) should not exceed 1000, since the corresponding arrays are predimensioned.References: [1] J. Conrad, O. Botner, A. Hallgren, C. Perez de los Heros, Including systematic uncertainties in confidence interval construction for Poisson statistics, Phys. Rev. D 67 (2003) 012002, hep-ex/0202013.     

Milling time effects on the magnetic and structural properties of the Fe70Si30 system

The magnetic and structural properties of the Fe_0,70Si_0,30 alloy are analyzed by using X-ray diffraction and Mössbauer spectrometry. The samples were prepared by mechanical alloying in a planetary ball mill pulverisette 5 during 1, 5, 9, 15, 75 and 100 h milling, with a ball mass to powder mass relation of 10:1. The X-ray diffraction patterns showed a coexistence of BCC, DO₃ and FeSi structural phases; however, for 1-5 h process, we observed additional peaks which correspond to iron and silicon elements. These results indicate us that the alloy is still a non-fully consolidated sample. The grain size decreases drastically from 1 to 5 h, then slowly up to 15 h, and finally it remains nearly constant. The lattice parameter for each phase remains nearly constant (2838 A for the BCC structure). The shape of hyperfine field distributions used to describe the Mössbauer spectra is discussed.     

Exciton-related nonlinear optical properties in cylindrical quantum dots with asymmetric axial potential: combined effects of hydrostatic pressure, intense laser field, and applied electric field

ABSTRACT: The exciton binding energy of an asymmetrical GaAs-Ga1-xAlxAs cylindrical quantum dot is studiedwith the use of the effective mass approximation and a variational calculation procedure. Theinfluence on this quantity of the application of a direct-current electric field along the growthdirection of the cylinder, together with that of an intense laser field, is particularly considered. Theresulting states are used to calculate the exciton-related nonlinear optical absorption and opticalrectification, whose corresponding resonant peaks are reported as functions of the external probes,the quantum dot dimensions, and the aluminum molar fraction in the potential barrier regions.