ALCHEMI for coexistent Heusler and half-Heusler phases in TiNi1.5Sn

Atomic location by channeling-enhanced microanalysis (ALCHEMI) is an effective technique to clarify the atomic configurations in multicomponent compounds. Recent development of the theory on the characteristic X-ray emission has made ALCHEMI a more reliable and expansive technique. In this revised ALCHEMI, the characteristic X-ray intensities are measured at various electron-incidence directions, and are compared with the X-ray intensities calculated from first principles. In the present work, this technique was applied to coexistent Heusler and half-Heusler phases in a thermoelectric material, TiNi_1.5Sn. The X-ray intensities calculated for both phases were significantly dependent on the fitting parameters of the atomic occupancy on each site and the sample thickness. Using the Levenberg–Marquardt least-squares method, the residual errors between the experimental and the calculated X-ray intensities were minimized to determine the fitting parameters quantitatively. In the Heusler phase, the ordered structure was observed because the atoms of each element almost occupy each site. On the other hand, in the half-Heusler phase, the “Heusler-like” structure was observed because the occupation probabilities of Ni atoms on the Ni-site and on the vacancy-site were measured as 0.49±0.01 and 0.49±0.01, respectively, whereas 1 and 0 is expected for the normal half-Huesler structure.     

Ordering and site occupancy of D03 ordered Fe3Al-5 at%Cr evaluated by means of atom probe tomography

Addition of ternary elements to the D0₃ ordered Fe₃Al intermetallic phase is a general approach to optimise its mechanical properties. To understand the physical influences of such additions the determination of the probability of site occupancies of these additions on the lattice site and ordering parameters is of high interest. Some common experimental techniques such as X-ray diffraction or Atom Location by Channelling Enhanced Microanalysis (ALCHEMI) are usually applied to explore this interplay.Unfortunately, certain published results are partly inconsistent, imprecise or even contradictory. In this study, these aspects are evaluated systematically by atom probe tomography (APT) and a special data analysis method. Additionally, to account for possible field evaporation effects that can falsify the estimation of site occupancy and induce misinterpretations, APT evaporation sequences were also simulated. As a result, chromium occupies most frequently the next nearest neighbour sites of Al atoms and local ordering parameters could be achieved.     

A generalization of atom location by channelling enhanced microanalysis

The technique of atom location by channelling enhanced microanalysis (ALCHEMI), has limitations in practical application. A generalization of this technique, with the underlying idea that additional relationships can be generated by performing these experiments at an appropriate number of orientations depending upon the stoichiometry of the original compound has been developed. The precise number of orientations required to solve the distributions in a whole class of related compounds is expressed in terms of the stoichiometry of the original compound along with the alloying additions.     

纳米半导体复合薄膜的非线性光学性质及其在激光器中的应用

采用射频磁控溅射技术制备了Ge掺二氧化硅（Ge-SiO₂）和Ge,Al共掺二氧化硅（Ge/Al-SiO₂）两种复合薄膜,并进行了热退火处理形成了纳米Ge镶嵌结构。通过紫外-可见吸收谱测量,确定了两种薄膜中纳米Ge的光学带隙,并采用皮秒激光Z-扫描技术研究了薄膜的非线性光学性质。测试结果显示,在1 064 nm激发下得到的Ge-SiO₂和Ge/Al-SiO₂薄膜的非线性吸收系数分别为-1.23×10^-7 m/V和4.35×10^-8 m/W,前者为饱和吸收,而后者为双光子吸收。把两种薄膜作为可饱和吸收体均可实现1.06 μm激光的被动调Q和被动锁模运转。与Ge-SiO₂薄膜比较,采用Ge/Al-SiO2薄膜可以获得较窄的调Q脉冲和锁模脉冲。最后,理论分析和实验比较了两种薄膜实现被动调Q和锁模的机理。     

Formation of Ge/Si and Ge/Ge x Si1−x /Si nanoheterostructures by molecular beam epitaxy

A kinetic diagram of Ge growth on Si is constructed by methods of fast electron diffraction and scanning electron microscopy. Activation energies of morphological transitions from two-dimensional to three-dimensional growth and from hut-clusters to dome-type islands are determined. The curve of the 2D–3D transition has two segments that follow the Arrhenius law and refer to different mechanisms of two-dimensional growth: two-dimensional island mechanism in the temperature range of 300–525 °C with the activation energy of ?0.11 eV and step motion in the temperature range of 525–700 °C with the activation energy of 0.15 eV. Transitions from hut-islands to dome-islands are also observed. The curve constructed for the hut-dome transition is approximated by two exponential segments that obey the Arrhenius law. The hut-dome transition activation energy is 0.11 eV in the temperature range of 350–550 °C and 0.24 eV in the temperature range of 550–700 °C. The maximum density of islands in the case of Ge growth on a Ge _x Si_1?x layer reaches 4 · 10¹¹ cm^?2. An increase in the composition leads to an increase in the density of Ge islands owing to a decrease in the length of migration of Ge adatoms on the Ge _x Si_1?x surface, as compared to the case of Ge growth on Si. The periodicity N, which is manifested as a (2 × N) superstructure, decreases during the reconstruction from 14 to 8 with increasing Ge content in the Ge _x Si_1?x layer. An increase in thickness or temperature leads to a decrease in periodicity and testifies to Ge segregation; in this case, stress relaxation occurs, which reduces the Ge diffisivity.     

A new method of scanning tunneling spectroscopy for study of the energy structure of semiconductors and free electron gas in metals

In this study, anew method for the scanning tunneling spectroscopy (STS) of direct and indirect gap semiconductors and free electron gas in metals is proposed. Band structures of Si, porous Si, and Ge were studied. The tunneling current-voltage characteristics of Si and porous Si surfaces were measured over different voltage intervals from tens of mV to 20 V under incident light from an Xe lamp and those of a Ge surface in the dark. The correlation between the shapes of the I-V curves and band structure of the materials was calculated. It was found that the curves are linear if measured in the voltage range V₀ E_g/(2e) and nonlinear when V₀ α E_g/(2e) (in the measurements the applied voltage was changed from -V₀ to V₀). The method was used for the observation of a new effect of tunneling of free electron gas having thermal energies from a metal tip to a band gap state of the semiconductor. The energy spectrum of free electron gas was measured.     

Materials science aspects of dielectric film compositions in the planar technology of Ge-based MIS structures

A new fabrication route for Ge based metal-insulator-semiconductor (MIS) transistors has been developed based on materials research of dielectric layer compositions. Unwanted impurities were encapsulated in the Ge substrate by using the gate-first process and a modified thermal GeO₂ layer with increased viscosity at the interface with the Ge substrate. Increasing the density of the oxide layer near germanium interaction with the deposited Si₃N₄ film hindered diffusion of the impurities adsorbed by the substrate surface into the transistor channel. This increased the electron mobility in the MIS transistor and prevented its decrease at cryogenic temperatures.     

Development of a high-voltage waveguide photodetector comprised of Schottky diodes and based on the Ge–Si structure with Ge quantum dots for portable thermophotovoltaic converters

This paper demontstrates the possibility of developing a high-voltage waveguide photodetector comprised of Schottky diodes and based on a Au/Ge — Si structure with Ge quantum dots pseudomorphic to a silicon matrix, which ensures an increase in the external quantum yield and open-circuit voltage. It is shown on this photodetector that there is a great increase and broadening in sensitivity up to λ = 2.1 μm, which coincides with the main radiation range of a black (gray) body at the emitter temperatures from 1200 to 1700 °C, practically used in thermophotovoltaic converters. This state of the ensemble of Ge quantum dots by means of molecular beam epitaxy can be obtained only under the condition of low growth temperature (250–300 °C). It is established that, below the Si absorption edge, photoresponse on the photodetectors under consideration is determined by two main mechanisms: absorption on the ensemble of Ge quantum dots and Fowler emission. It is shown by the analysis of the Raman scattering spectra on the optical photons of Ge–Si structures that the quantum efficiency of photodetectors based on them in the first case is due to the degree of nonuniform stress relaxation in the array of Ge quantum dots. The photoresponse directly associated with the Ge quantum dots is manifested on Schottky diodes with a superthin intermediate oxide layer SiO₂, which eliminates the second mechanism. In further development, the proposed photodetector architecture with pseudomorphic Ge quantum dots can be used both for portable thermophotovoltaic converters and fiber-optic data transmission systems at wavelengths corresponding to basic telecommunication standards (λ = 0.85, 1.3 and 1.55, 1.3, and 1.55 μm) on the basis of silicon technologies.     

A Technological Test of the Mir-Station Orbital Flight Modes for Semiconductor Single Crystal Growth

By using a method for testing the microgravity conditions aboard the orbital station (OS) proposed by the authors, different effects of the main OS orbital modes on crucibleless melting and heat-transfer processes in Ge melts were revealed. Even a minimal actually attainable level of onboard variable low-frequency accelerations (4 × 10^–6–2.5 × 10^–5)g ₀is insufficient for eliminating nonstationary forced convection in the melt. The necessity of utilizing vibration-isolation mounts for crystal-growth equipment disposition on board the OS was confirmed.     

EFFECT OF SURFACE ENERGY ON THE GROWTH OF DIAMOND-LIKE CARBON/AMORPHOUS SILICON FILMS ON VARIOUS SUBSTRATES

Diamond-like carbon/amorphous silicon bilayer films were deposited on SiO₂, Ge, and Ta₂O₅ substrates using a pulsed filtered cathodic arc (PFCA) system. Amorphous silicon (a-Si) layer was firstly deposited on three substrates using DC magnetron sputtering, then diamond-like carbon (DLC) film was deposited on a-Si layer via pulsed filtered cathodic arc. The thicknesses of a-Si layer and DLC film as monitored by in-situ ellipsometry during the film deposition were 7 and 10 nm, respectively. The surface energy of SiO₂, Ge, and Ta₂O₅ substrates was determined by measuring the contact angle of water on these substrates. It was found that the contact angles of water on SiO₂, Ge, and Ta₂O₅ substrates were 53°, 63°, and 75°, respectively. This result indicates that SiO₂ has the highest surface energy while Ta₂O₅ has the lowest surface energy. The thickness of the a-Si layer and DLC film was determined from the cross-section transmission electron microscopy (TEM) images. The thinnest a-Si layer of 5.64 nm was obtained from SiO₂ substrate which has the highest surface energy. The thickest a-Si layer of 6.97 nm was obtained from Ta₂O₅ corresponding to the lowest surface energy. This study shows that the thickness of the growth film strongly depends on the surface energy of the substrate. However, the DLC films deposited on each a-Si layer of three substrates have the same thickness approximately of 9.9 nm, because all of them were deposited on a-Si layers having the same surface energy.     

Manufacturing garnet ferrite film resonators using the chemical etching technique

A procedure of manufacturing microwave resonators on the basis of epitaxial Y₃Fe₅O₁₂ and (Y, Sm, Lu, Ca)₃(Fe, Ge)₅O₁₂ garnet ferrites with thicknesses of ≤5 μm, which are grown on gallium-gadolinium garnet substrates, is described. To obtain circular garnet ferrites—resonators with diameters of 0.5–3.0 mm-via chemical etching in orthophosphoric acid at T = 60–175°C, protecting SiO₂, silicon adhesive, and photoresist coatings are used. It is established that the resonators that were manufactured using a protective FP-383 photoresist coating have the narrowest ferromagnetic-resonance line.     

Superthin Solar Cells Based on A<Superscript>III</Superscript>B<Superscript>V</Superscript>/Ge Heterostructures

A comparative analysis of the prospects of creating superthin, light-weight, and highly efficient solar cells based on A^IIIB^V/InGaAs and A^IIIB^V/Ge heterostructures is performed. Technological problems and prospects of each variant are discussed. A method of thinning of A^IIIB^V/Ge heterostructures with the use of an effective temporary carrier is proposed. The method allows the process to be performed almost with no risk of heterostructure fracture, thinning of the Ge junction down to several tens of micrometers (or even several micrometers), significant enhancement of the yield of good structures, and also convenient and reliable transfer of thinned solar cells to an arbitrary light and flexible substrate. Such a technology offers a possibility of creating high-efficiency thin and light solar cells for space vehicles on the basis of mass-produced A^IIIB^V/Ge heterostructures.     

KSpaceNavigator as a tool for computer-assisted sample tilting in high-resolution imaging, tomography and defect analysis

This article describes a novel software tool, the KSpaceNavigator, which combines sample stage and crystallographic coordinates in a control sphere. It also provides simulated kinematic diffraction spot patterns, Kikuchi line patterns and a unit cell view in real time, thus allowing intuitive and transparent navigation in reciprocal space. By the overlay of experimental data with the simulations and some interactive alignment algorithms, zone axis orientations of the sample can be accessed quickly and with great ease. The software can be configured to work with any double-tilt or tilt–rotation stage and overcomes nonlinearities in existing goniometers by lookup tables. A subroutine for matching the polyhedral shape of a nanoparticle assists with 3D analysis and modeling. The new possibilities are demonstrated with the case of a faceted BaTiO₃ nanoparticle, which is tilted into three low-index zone axes using the piezo-controlled TEAM stage, and with a multiply twinned tetrahedral Ge precipitate in Al, which is tilted into four equivalent zone axes using a conventional double-tilt stage. Applications to other experimental scenarios are also outlined.     

Transmission Electron Microscope Investigations Of Defects Produced By Individual Displacement Cascades In Si And Ge

Monocrystalline {111} Si and Ge specimens have been irradiated with atomic and molecular heavy ions in order to study the influence of the cascade energy density and the interaction between displacement cascades on the defect production. Transmission electron microscope (TEM) studies were performed to investigate the defect parameters. After atomic irradiation of Si and Ge the defects analysed (typical size 3–5 nm) are of interstitial type. Both defects with three-dimensional strain centres and defects with a strongly asymmetric strain field were observed. An analysis of the yield and the defect size in Si as a function of ion dose suggests that the defects are formed within individual cascades rather than by a process involving overlapping cascades. Changes of the energy density locally deposited in the lattice do not affect yield and size significantly. Under otherwise similar experimental conditions, the average defect depth is significantly larger for Bi₂+ irradiations than for Bi+ irradiations.     

Laminar and turbulent channel flow simulation using residual based variational multi-scale method

We present a residual-based isogeometric variational multiscale method to solve laminar and turbulent channel flow. Residual-based variational multiscale method is a new finite element formulation for solving turbulent flows using a large-eddy simulation type modeling. Isogeometric analysis, a new finite element method using CAD blending functions as its basis functions, is employed for higher order approximation of the solution. First, laminar flow with Re _τ 0.55 = through flat channel is considered and linear, quadratic and cubic basis functions, which are C ⁰, C ¹, and C ²-continuous across element boundaries, respectively are employed and their accuracy is presented by the comparison with analytical result. Next, same methodology is applied to the turbulent channel flow with Re_r = 180. Current results are validated by the comparison of turbulence statistics using available DNS data.     

APFIM investigations on site occupancies of the ternary alloying elements Cr, Fe, and Re in NiAl

The site occupancies of the transition metals Cr, Fe, and Re dissolved in NiAl of stoichiometric composition have been determined by atomic layer resolved atom probe field-ion microscopy (APFIM). The investigations were supported by X-ray diffraction studies to evaluate the lattice parameters. These are influenced by atomic size effects and constitutional lattice defects like Ni antistructure atoms in the Al sublattice and vacancies in the Ni sublattice. The APFIM results were compared with ALCHEMI data and calculated site preference energies published in the literature. Chromium additions to stoichiometric NiAl with 0.8 at% in solid solution exhibit a strong preference for Al sites. The lattice parameter of NiAl(Cr) solid solution is decreased. Iron atoms dissolved in higher concentrations of 5 at % in NiAl are almost equally distributed within both sublattices. They are possessing a weak preference for Al sites, which causes a lattice expansion of NiAl(Fe) solid solution. ALCHEMI results and site preference energy data show a strong site preference of Cr atoms for the Al sublattice. In contrast, iron atoms exhibit a weak site preference for Ni sites depending upon the stoichiometry of the NiAl host lattice. Re solutes in low concentrations of about 0.2 at % in NiAl possess a strong site preference for the Ni sublattice. The increase of the lattice parameter of NiAl(Re) is due to the pronounced size effect of Re atoms. For these species no ALCHEMI and site preference energy data are available in the literature.     

Carbon-stimulated self-organization of Ge nanoislands during molecular beam epitaxy of Ge/CaF<Subscript>2</Subscript>/Si(111) heterostructures

The self-organization of germanium nanoislands on the surface of calcium fluoride was studied using atomic-force microscopy and reflection electron diffraction. A Ge/CaF₂/Si(111) structure was grown by molecular beam epitaxy. The surface of the calcium fluoride film was modified by submonolayer carbon coverage to stimulate the formation of germanium nanoislands. The parameters of an array of nanoislands were found to depend on the coverage.     

Variable cosine windowing of intrinsic mode functions: Application to gear fault diagnosis

Gear pair is used for speed reduction or increasing torque and/or to change the direction of rotation. Gears are considered critical element in various mechanical systems. When gears are in use, the multi component vibration signals are generated. These vibration signals can be captured by mounting accelerometers at suitable locations. Vibration signal analysis is very effective tool in finding gear fault at early stage. The methods based on empirical mode decomposition (EMD) have been used for gear fault diagnosis in mechanical systems. The EMD method decomposes an original signal into different frequency-bands in time domain, known as intrinsic mode functions (IMFs). A serious problem in application of EMD is boundary distortion of IMFs. While doing statistical analysis of IMFs, boundary distortion may provide high values of statistical indicator (e.g. kurtosis, S_r, S_α), even if fault is not present. Several extension-based methods are employed to eliminate the boundary distortion problem. Extension-based methods cannot completely eliminate the boundary distortion, especially when the low-frequency component of the analyzed signal is weak. Recently, cosine window-based method has been proposed by which the boundary distortion can be controlled in boundaries of the signal and the middle component of it can be exactly decomposed into IMFs. The cosine window-based method works only for a particular IMF depending on the size of window. Since, in EMD process, the boundary distortion of successive IMFs increases, a variable cosine window is proposed in this paper to address the increasing boundary distortion problem. In the proposed method boundary distortion problem is minimized by using variable cosine window for all IMFs. The simulation and experimental results for three statistical indicators viz. kurtosis, S_r, S_α show that the proposed method based on variable cosine window is a powerful and reliable technique for fault diagnosis.     

Machining Characteristics of Al2O3/6061Al Composite using Rotary EDM with a Disklike Electrode

This work optimises the cutting of Al₂O₃/6061Al composite using rotary electro-discharging machining (EDM) with a disklike electrode by using Taguchi methodology. The Taguchi method is used to formulate the experimental layout, to analyse the effect of each EDM parameter on the machining characteristics, and to predict the optimal choice for each EDM parameter. Four observed values, MRR, EWR, REWR, and SR, are used to verify this optimisation of the machining technique. In addition, six independent parameters are chosen as variables in evaluating the Taguchi method and are categorised into two groups: 1. Electrical parameters, e.g. polarity, peak current, pulse duration, and powder supply voltage. 2. Non-electrical parameters, e.g. circumferential speed of electrode, reciprocating speed. The analysis of the Taguchi method reveals that, in general, the electrical group more significantly affects the machining characteristics than the non-electrical group. Also derived herein are semi-empirical equation that contain all of the machining characteristics. Experimental results are presented to illustrate the proposed approach.     

Comparison between two process capability indices using generalized confidence intervals

Processcapability indices (PCIs) are extensively used statistical measures to assess process performance in manufacturing industry. In this paper, confidence intervals for the difference between PCIs for two processes are derived by the generalized pivotal quantity method. The indices C _pk , C _pmk , and C _pm are considered in this study. The performance of the proposed method is assessed using simulation study. The results are also illustrated using an example from industrial contexts.