Automated instrumentation for high-temperature Seebeck coefficient measurements

The fabrication of automated instrumentation for high-temperature Seebeck coefficient measurements is presented. K-type thermocouples were used to measure the average temperature of the sample and the Seebeck voltage. The temperature dependence of the Seebeck coefficients of the thermocouple and its negative leg were obtained by the integration method. A steady-state-based differential technique was used for Seebeck coefficient measurement. The use of limited components and a thin heater simplified the sample holder design and minimized heat loss. The power supplied to the heater determined the temperature difference across the sample and the measurement was carried out by achieving a steady state. A LabVIEW-based program was constructed to automate the measurements. The complete setup was fabricated using commonly available materials. This instrument is standardized for materials with a wide range of Seebeck coefficients and temperature differences. High temperature measurements for iron, constantan, bismuth, and Bi_0.36Sb_1.45Te₃ were carried out and the results were in good agreement with standard values.     

Automated instrumentation for the determination of the high-temperature thermoelectric figure-of-merit

Here we report the fabrication of high temperature measurement instrumentation to measure the thermoelectric figure of merit. This setup facilitates the simultaneous measurement of Seebeck coefficient, thermal conductivity, and electrical resistivity required to evaluate the figure of merit. Measurement of temperature, as well as voltages using same thermocouples, simplified the design by minimizing sensors and wires. The limited number of components in the sample holder further simplify the design and make it small in size and lightweight. A dedicated thin heater has been constructed to minimize heat losses. Further, low heat loss is achieved by optimizing the insulator dimensions. To measure power delivered to the heater, the four-wire technique was used. Low cost and commonly available materials used in the fabrication of various components make it more accessible to the user as any parts can be easily replaced in case of damage. A dedicated program was built in the Python language to automate the measurement process. A p-type Bi_0.36Sb_1.45Te₃ sample was used to calibrate the instrumentation. The measured values were in good agreement with the literature results.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

CASINO: A new monte carlo code in C language for electron beam interaction —part I: Description of the program

This paper is a guide to the ANSI standard C code of CASINO program which is a single scattering Monte CArlo SImulation of electroN trajectory in sOlid specially designed for low-beam interaction in a bulk and thin foil. CASINO can be used either on a DOS-based PC or on a UNIX-based workstation. This program uses tabulated Mott elastic cross sections and experimentally determined stopping powers. Function pointers are used for the most essential routine so that different physical models can easily be implemented. CASINO can be used to generate all of the recorded signals (x-rays, secondary, and backscattered) in a scanning electron microscope either as a point analysis, as a linescan, or as an image format, for all the accelerated voltages (0.1–30 kV). As an example of application, it was found that a 20 nm Guinier-Preston Mg₂Si in a light aluminum matrix can, theoretically, be imaged with a microchannel backscattered detector at 5 keV with a beam spot size of 5 nm.     

Electron energy-loss near edge structure (ELNES) of InGaN quantum wells

Lasers and light‐emitting diodes (LEDs) that emit in the blue to green region are often based on In_xGa_1–xN quantum well structures. Ionization edges in the electron energy‐loss spectrum contain fine structures (called the energy‐loss near edge structure (ELNES)) and provide information about the electronic structure. In this paper we compare the experimental and calculated ELNES for the N‐K ionization edge of In_xGa_1–xN quantum wells. When the effects of the core‐hole are included in the calculations, agreement between experimental and calculated spectra is very good. Strain has been shown to accentuate the effects of In on the ELNES and moves the ionization edge onset down in energy, relative to the other features. These results suggest that ELNES may provide an alternative method to lattice imaging to determine the presence of strain in this system.     

Stoichiometry and valence measurements of niobium oxides using electron energy-loss spectroscopy

Qualitative and quantitative electron energy‐loss spectroscopy analyses have been performed on niobium and stable niobium oxides (NbO, NbO₂ and Nb₂O₅). At integration windows (Δ) greater than 75 eV, k‐factor analysis can be used to distinguish between the stoichiometry of the three oxides within 5.7% error. As seen in other metal oxides, with increasing oxidation state the metal ionization edges shift to higher energies relative to the O‐K edge. Normalized M_2,3 white‐line intensities show a strong correlation with 4d occupancy for each compound. The data are in correspondence with that observed in the literature for 4d transition metals using normalized L_2,3 white lines. Lastly, a distinctive energy‐loss near‐edge, structure of the O‐K edge was observed for each oxide, which could be used as a fingerprint for analysis of unknowns.     

Numerical simulation of the energy spectrum of recoil nuclei and α particles from interactions of fast neutrons with diamond

The energy spectra of recoil nuclei and α particles produced in interactions of fast (8.0–14.1 MeV) neutrons with diamond were simulated. Differential cross sections for five channels (nuclear reactions) of elastic and inelastic collisions were used. It was shown that a substantial distortion of the simulated energy spectrum could be attributed to the reaction ¹²C(n, n′3α). The spectrum of α₀ particles was obtained for different opening angles in the reaction ¹²C(n, α ₀)⁹Be.     

Two-dimensional fast Fourier transform and power spectrum for wear particle analysis

Statistical parameters, such as R_a and R_q, have been widely used to investigate the roughness of wear particle surfaces in the literature. It has been reported that wear particle analysis based only on numerical characterization is often insufficient to distinguish certain types of wear debris. In this study, two-dimensional fast Fourier transform, power spectrum and angular spectrum analyses are applied to describe wear particle surface textures in three dimensions. Laminar, fatigue chunk and severe sliding wear particles, which have previously proven difficult to identify by statistical characterization, have been studied. The results show that spectral analysis effectively identifies the surface texture pattern (e.g. isotropy or anisotropy) and can be applied to classify these three types of wear particles.     

Dose-rate dependence of electron-induced mass loss from organic specimens

Electron energy-loss measurements on thin films of collodion at low temperatures (90 K) show that the characteristic electron dose D_e for mass loss first increases and then decreases with increasing dose rate (current density). This behaviour is explained in terms of the limited diffusion rates at low specimen temperature and the heating effect of the electron beam, and can be approximately modelled using a simple computer program. For a small-diameter electron probe, the increase in D_e can be several orders of magnitude, suggesting a substantial advantage of STEM (in comparison to fixed-beam TEM) for examining beam-sensitive specimens.     

An Automated High-Sensitivity Vibrating-Coil Magnetometer

A magnetometer allows the measurement of the magnetic moment of samples in a range from 1.3 × 10^–8 to 5.45 × 10^–4 A m². The range of variation of the magnetic field strength is from 0 to 56 kA/m; the temperature range is 20–700°C. Measurements are performed in an air atmosphere. The obtained data are automatically inputted into a PC. In addition, the magnetometer can measure the coercive force H _c and the destructive field H _cr. It can also be used to study the formation of thermoremanent and viscous magnetizations and measure the Curie-temperature spectrum and the blocking-temperature spectrum. Measurements of the field, temperature, and time dependences of the magnetic moment can also be performed by the researcher or by special software using a more complicated algorithm.     

EELS log-ratio technique for specimen-thickness measurement in the TEM

We discuss measurement of the local thickness t of a transmission microscope specimen from the log-ratio formula t = λ In (I_t/I₀) where I_t and I₀ are the total and zero-loss areas under the electron-energy loss spectrum. We have measured the total inelastic mean free path λ in 11 materials of varying atomic number Z and have parameterized the results in the form λ = 106F (E₀/E_m)/ln (2βE₀/E_m) where F = (1 + E₀/1,022)/(1 + E₀/511)², the incident energy E₀ is in keV, the spectrum collection semiangle β is in mrad, and E_m = 7.6Z^0.36. This formulation should allow absolute thickness to be determined to an accuracy of ±20% in most inorganic specimens.     

An analytical study on the performance analysis of a unit-injector system of a diesel engine

A numerical algorithm is developed to analyze the performance of a Unit-injector (UI) System for a diesel engine. The fundamental theory of the algorithm is based on the continuity equation of fluid dynamics. The loss factors that should be seriously regarded on the continuity equation are the compressibility effect of liquid fuel, the wall friction loss in high-pressure fuel lines of the system, the kinetic energy loss of fuel in the system, and the leakage of fuel out of the control volume. For an evaluation of the developed simulation algorithm, the calculation results are compared with the experimental outputs provided by the Technical Research Center of Doowon Precision Industry Co. (DPICO); the maximum pressure in the plunger chamber (P _p ) and total amount of fuel injected into a cylinder per cycle (Q_f) at each operational condition. The result shows that the average error rate (%)of P _p andQ _f are 2.90% and 4.87%, respectively, in the specified operational conditions. Hence, it can be concluded that the analytical simulation algorithm developed in this study can be reasonably applied to the performance prediction of newly designed UI system.     

Quantitative FRET measurement using emission‐spectral unmixing with independent excitation crosstalk correction

Quantification of fluorescence resonance energy transfer (FRET) needs at least two external samples, an acceptor‐only reference and a linked FRET reference, to calibrate fluorescence signal. Furthermore, all measurements for references and FRET samples must be performed under the same instrumental conditions. Based on a novel notion to predetermine the molar extinction coefficient ratio (R_C) of acceptor‐to‐donor for the correction of acceptor excitation crosstalk, we present here a robust and independent emission‐spectral unmixing FRET methodology, Iem‐spFRET, which can simultaneously measure the E and R_C of FRET sample without any external references, such that Iem‐spFRET circumvents the rigorous restriction of keeping the same imaging conditions for all FRET experiments and thus can be used for the direct measurement of FRET sample. We validate Iem‐spFRET by measuring the absolute E and R_C values of standard constructs with different acceptor‐to‐donor stoichiometry expressed in living cells. Our results demonstrate that Iem‐spFRET is a simple and powerful tool for real‐time monitoring the dynamic intermolecular interaction within single living cells.     

Contrast in the electron spectroscopic imaging mode of a TEM

The ratio of inelastic-to-elastic total cross-sections has been measured in an energy-filtering electron microscope for different elements. Formulae for the transmission of elastically and inelastically scattered electrons in part I were used to calculate the optimum conditions for a Z-ratio contrast in the electron spectroscopic imaging mode. Structure-sensitive contrast can be observed for all non-carbon atoms in biological sections when filtering with an energy loss at ΔE ～ 250 eV below the carbon K edge. Model experiments with evaporated layers of different elements on a carbon film allow measurement of the contrast increase. Filtering with the carbon plasmon loss shows a lower phase contrast than with zero-loss filtering. This can be explained by calculating contrast transfer functions for inelastically scattered electrons.     

Neutral particle analyzer measurements on the SSPX spheromak

A neutral particle analyzer is used to measure the time-resolved energy spectrum of neutral hydrogen leaving a spheromak plasma. A gas cell filled with 10-50 mTorr of helium is used to strip electrons from incoming neutral hydrogen, lowering the minimum detectable energy well below that obtained with thin foils. Effective neutral particle temperature is calculated by fitting a Maxwellian energy distribution to the measured energy spectrum above and below approximately 300 eV. A computational model with approximated profiles of plasma density and neutral density is used with the measured neutral hydrogen flux to estimate the ion temperature. Measurement of the power flux due to neutral hydrogen emitted at the measurement location is extended to the whole plasma surface to estimate the total charge exchange power loss from the plasma. The initial results indicate that the charge exchange power loss represents only 2% of the total input gun power during the sustainment phase of the discharge.     

Strengthening caused by power law creep deformation of dispersed particles in an elastic matrix

The interaction energy is approximated between an edge dislocation and a particle deformable by power law creep in an elastic matrix. The stress required to overcome the interaction energy barrier is found to be greater than the Orowan stress, and the dislocation bulges to escape the particle. If the ratio of the shear modulus of the matrix to the viscosity of the particle (μt^m/σ₀) is large, the stress required to climb over the particle is larger than the Orowan stress and the dilocation bulges before it climbs. It is concluded that even if the particle is soft enough to exhibit creep, the strengthening of alloys can be achieved by an Orowan mechanism. The critical resolved shear stress (CRSS) of Cu-B₂O₃, obtained experimentally by Onaka et al. [11], agrees closely with that obtained in our analysis. This supports our analysis that the strength of Cu-B₂O₃ alloy at high temperature may be accounted for by the Orowan mechanism and the attraction between a dislocation and viscous particles. The energy and the force to overcome the energy barrier increases significantly with decrease of m, the strain rate exponent associated with the power law creep particle. It is found through analysis that for m < 1.0 and for certain values of μt^m/σ₀ > 1, the particle repulses the dislocation, while for m = 1.0 and for all values of μt^m/σ₀ > 1, the particle attracts the dislocation, which is the expected interaction between an elastic particle and a dislocation in an elastic matrix.     

Effect of molybdenum tri-oxide molar ratio on the optical and some physical properties of tellurite-vanadate-molybdate glasses

Glasses with composition (60 − x)V₂O₅-40TeO₂ − x MoO₃ with 20 ? x ? 60 (in mol%) have been prepared using the usual melt quenching method. The optical absorption spectra of the glasses have been recorded in the wavelength range 300-800 nm. The position of the absorption edge and therefore the optical band gap values were found to be depend on the glass composition. For these glasses, the optical band gap was found to be in the range 2.03-2.86 eV with increasing of MoO₃ concentration. The absorption spectrum fitting method was employed to obtain the energy gap. In this method, only the measurement of the absorbance spectrum of the glass is needed. For each sample, the width of the band tail was determined. Also, the density and glass transition temperature values indicate that the rigidity and packing of the samples increase with increase in MoO₃ concentration as a network former.     

Radiation damage to lyophilized mineral solutions during electron probe analysis: quantitative study of chlorine loss as a function of beam current-density and sample mass-thickness

The quantitative effects of beam current-density and sample mass-thickness on the loss of chlorine which occurs from lyophilized solutes of micro-droplets of mineral salt solutions irradiated in an electron probe analyser were studied. Results are reported for chlorine loss from lyophilized deposits with mass-thickness varying between 5 and 50 mg mm^?2 for NaCl salts and 5 and 80 mg mm^?2 for KCl salts. Electron accelerating voltage was kept constant at 15 kV. The range of beam current-density (I/S, current/sample surface area) was from 0.1 to 1.5 A mm^?2. Samples were irradiated for 1200 s. The results show that under some conditions there is a period of stable chlorine signal before chlorine loss occurs. This is observed between 0.1 and 1 A mm^?2, for a period which can last several hundred seconds depending on beam current-density and sample mass-thickness. For each value of I/S, however, no stable chlorine signal can be observed for samples whose mass-thickness exceeds a value negatively correlated with I/S. The curves of decrease of characteristic chlorine X-ray signal (expressed as per cent of count rate in the initial counting interval) versus irradiation time can be fitted by the sum of two exponentials with half lives T₁ and T₂. In NaCl, T₁ and T₂ values are highly correlated with I/S but not with mass-thickness. In KCl, T₁ is correlated only with mass-thickness and T₂ only with I/S. Mixing plasma with mineral solutions prevents chlorine loss.     

Study of changes in L32 EELS ionization edges upon formation of Ni-based intermetallic compounds

EELS L₃₂ ionization edges in several Ni‐based intermetallic compounds have been studied and interpreted in terms of the distribution of electrons in the valence d‐bands. It is demonstrated that the integral EELS cross‐sections change only slightly upon the formation of intermetallic compounds and therefore the charge transfer between atoms is negligible. On the other hand, the changes in the fine energy‐loss near‐edge structure (ELNES) of the Ni L₃ edge can be readily detected indicating an important redistribution of d‐electrons at the Ni site with alloying. These features are well reproduced by ab‐initio calculations with a FLAPW method in its WIEN97 implementation. In contrast to the drastic effect of chemical environment, structural transformations in the investigated intermetallics result in smaller ELNES changes, which can be detected by only exceptional instruments with a higher energy resolution.     

Analysis of EEL spectrum of low-loss region using the C(s)-corrected STEM-EELS method and multivariate analysis

We analyzed a Si/SiO₂ interface using multivariate analysis and spherical aberration-corrected scanning transmission electron microscopy-electron energy loss spectroscopy which is characterized by using the electron energy loss spectrum of the low-loss region. We extracted the low-loss spectra of Si, SiO₂ and an interface state. Even if the interface is formed from materials with different dielectric functions, the present method will prove suitable for obtaining a more quantitative understanding of the dielectric characteristic.