Full Temperature Range Research Articles

High-Temperature Electromechanical Characterization of AlN Single Crystals.

Hexagonal AlN is a non-ferroelectric material and does not have any phase transition up to its melting point (>2000°C), which indicates the potential use of AlN for high-temperature sensing. In this work, the elastic, dielectric, and piezoelectric constants of AlN single crystals were investigated at elevated temperatures up to 1000°C by the resonance method. We used resonators of five different modes to obtain a complete set of material constants of AlN single crystals. The electrical resistivity of AlN at elevated temperature (1000°C) was found to be greater than 5 × 10(10) Ω · cm. The resonance frequency of the resonators, which was mainly determined by the elastic compliances, decreased linearly with increasing temperature, and was characterized by a relatively low temperature coefficient of frequency, in the range of -20 to -36 ppm/°C. For all the investigated resonator modes, the elastic constants and the electromechanical coupling factors exhibited excellent temperature stability, with small variations over the full temperature range, <11.2% and <17%, respectively. Of particular significance is that due to the pyroelectricity of AlN, both the dielectric and the piezoelectric constants had high thermal resistivity even at extreme high temperature (1000°C). Therefore, high electrical resistivity, temperature independence of electromechanical properties, as well as high thermal resistivity of the elastic, dielectric, and piezoelectric properties, suggest that AlN single crystals are a promising candidate for high-temperature piezoelectric sensing applications.

Self‐aggregation of convection in long channel geometry

Cloud cover and relative humidity in the Tropics are strongly influenced by organized atmospheric convection, which occurs across a range of spatial and temporal scales. One mode of organization that is found in idealized numerical modelling simulations is self‐aggregation, a spontaneous transition from randomly distributed convection to organized convection despite homogeneous boundary conditions. We explore the influence of domain geometry on the mechanisms, growth rates and length‐scales of self‐aggregation of tropical convection. We simulate radiative–convective equilibrium with the System for Atmospheric Modeling (SAM), in a non‐rotating, highly elongated three‐dimensional (3D) channel domain of length &gt;104 km, with interactive radiation and surface fluxes and fixed sea‐surface temperature varying from 280–310 K. Convection self‐aggregates into multiple moist and dry bands across this full range of temperatures. As convection aggregates, we find a decrease in upper tropospheric cloud fraction but an increase in lower tropospheric cloud fraction; this sensitivity of clouds to aggregation agrees with observations in the upper troposphere but not in the lower troposphere. An advantage of the channel geometry is that a separation distance between convectively active regions can be defined; we present a theory for this distance based on boundary layer. We find that surface fluxes and radiative heating act as positive feedback mechanisms, favouring self‐aggregation, but advection of moist static energy acts as a negative feedback, opposing self‐aggregation, for nearly all temperatures and times. Early in the process of self‐aggregation, surface fluxes are a positive feedback at all temperatures, shortwave radiation is a strong positive feedback at low surface temperatures but weakens at higher temperatures and longwave radiation is a negative feedback at low temperatures but becomes a positive feedback for temperatures greater than 295–300 K. Clouds contribute strongly to the radiative feedback, especially at low temperatures.

International Round-Robin Study of the Thermoelectric Transport Properties of an n-Type Half-Heusler Compound from 300 K to 773 K

International transport property-measurement round-robins have been conducted by the thermoelectric annex under the International Energy Agency (IEA) Implementing Agreement on Advanced Materials for Transportation (AMT). Two previous round-robins used commercially available bismuth telluride as the test material, with the objectives of understanding measurement issues and developing standard testing procedures. This round-robin extended the measurement temperature range to 773 K. It was designed to meet the increasing demands for reliable transport data for thermoelectric materials used for power-generation applications. Eleven laboratories from six IEA-AMT member countries participated in the study. A half-Heusler (n-type) material prepared by GMZ Energy was selected for the round-robin. The measured transport properties had a narrower distribution of uncertainty than previous round-robin results. The study intentionally included multiple testing methods and instrument types. Over the full temperature range, the measurement discrepancies for the figure of merit, ZT, in this round-robin were ±11.5 to ±16.4% from the averages.

Test Station for Frequency-Domain Dielectric Spectroscopy of Nanocomposites and Semiconductors

An upgraded test station is described for determining the electrophysical properties of materials by frequency-domain dielectric spectroscopy. As a result of the upgrade, the range of measurable temperatures is expanded (the full range of measurable temperatures is 10–450 K) and also better accuracy of the measurement and temperature control is achieved. The test station is controlled using a new special computer program. The upgraded test station makes it possible to simultaneously study two samples in the a.c. frequency range from 50 Hz to 5 MHz. Results of studies of the electrical properties (resistance Rp, capacitance Cp, phase shift angle θ, and dielectric loss tangent or dissipation factor tan δ) are presented for the metal–dielectric nanocomposite (FeCoZr)x(CaF2)(100–x).

Entropy and thermopower in the 2D t-J model

The entropy of the two-dimensional t-J model is investigated using its 12th order high temperature series. A direct Padé extrapolation of the entropy series doesn't converge well for temperatures below T ∼ J. The series coefficients are exact polynomials so the series convergence can be improved by modifying the series that is extrapolated. By subtracting a scaled version of the series for the entropy of the Heisenberg antiferromagnet from the t-J entropy series the low temperature convergence is greatly improved. Using this technique results are obtained for the full range of electron densities and temperatures. The electron density is an adjustable parameter in the series coefficients allowing the density dependence of the entropy and the density derivative at fixed temperature ∂S/∂n|T to be determined accurately. The density derivative depends strongly on temperature, unlike noninteracting models. The density derivative is also an approximation to the experimentally measured thermopower.

Comparative physiological studies on the growth of cryptic species of Bostrychia intricata (Rhodomelaceae, Rhodophyta) in various salinity and temperature conditions

SummaryInter‐ and intra‐specific physiological variations of intertidal macroalgae have been well investigated. However, studies on physiological responses of cryptic algal species have been poorly documented. Bostrychia intricata is a widespread marine red alga in the Southern Hemisphere, and has many cryptic species. We investigated the effect of different salinities and temperatures on the specific growth rate of three cryptic species (N2, N4 and N5) of B. intricata from New Zealand. Our data indicated that all cryptic species grew at the full range of salinities and temperatures tested, but exhibited a significant difference in their specific growth rates. Cryptic species N4 had a higher growth rate than the other two cryptic species under all experimental conditions, whereas cryptic species N2 occasionally showed a higher growth rate than cryptic species N5 at high salinities and lower temperatures. The distinct physiological properties of these cryptic species may explain their distribution pattern (a wider distribution of cryptic species N4 than N2 and N5) in New Zealand. The physiological divergence between the cryptic species could be related to their levels of evolutionary divergence, with more similar physiology between cryptic species, which share a more recent common ancestor (N2 and N5). Our findings underline that morphologically indistinguishable cryptic algal species are different in many other aspects and are truly independent entities.

The continuous strength method for steel cross-section design at elevated temperatures

When subjected to elevated temperatures, steel displays a reduction in both strength and stiffness, its yield plateau vanishes and its response becomes increasingly nonlinear with pronounced strain hardening. For steel sections subjected to compressive stresses, the extent to which strain hardening can be exploited (i.e. the strain at which failure occurs) depends on the susceptibility to local buckling. This is reflected in the European guidance for structural fire design EN1993-1-2 [1], which specifies different effective yield strengths for different cross-section classes. Given the continuous rounded nature of the stress–strain curve of structural steel at elevated temperatures, this approach seems overly simplistic and improved accuracy can be obtained if strain-based approaches are employed [2]. Similar observations have been previously made for structural stainless steel design at ambient temperatures and the continuous strength method (CSM) was developed as a rational means to exploit strain hardening at room temperature. This paper extends the CSM to the structural fire design of steel cross-sections. The accuracy of the method is verified by comparing the ultimate capacity predictions with test results extracted from the literature. It is shown that the CSM offers more accurate ultimate capacity predictions than current design methods throughout the full temperature range that steel structures are likely to be exposed to during a fire. Moreover due to its strain-based nature, the proposed methodology can readily account for the effect of restrained thermal expansion on the structural response at cross-sectional level.

Thermal effects on the development of Naranga aenescens Moore (Lepidoptera: Noctuidae)

Naranga aenescens Moore is an important insect pest found in rice paddy field. We investigated the development periods of N. aenescens egg, larva, pupa, and total immature insects at eight constant temperatures: 15.0°C, 17.5°C, 20.0°C, 22.5°C, 25.0°C, 27.5°C, 30.0°C, and 32.5°C. N. aenescens developed successfully from the egg stage to the adult stage at all the tested temperatures except 15.0°C. The developmental time of each life stage was significantly influenced by temperatures. The developmental rate of N. aenescens increased as the temperature increased from 15.0°C to 30.0°C but declined at 32.5°C, except in the pupa stage. The lower developmental threshold (LDT) and the thermal constant (K) was estimated using linear regression. The higher temperature threshold and the lower temperature threshold were calculated using two nonlinear functions. LDT and K from egg to adult emergence were 12.01°C and 330.84 degree days, respectively. The temperature range of N. aenescens from the lower developmental threshold to the higher developmental threshold using a performance model (24.03) was wider than that determined using the Sharpe–Schoolfield–Ikemoto model (19.77). Developmental completion of N. aenescens was described using a two-parameter Weibull distribution model. Adult emergence frequency of N. aenescens over a full range of constant temperatures was simulated using developmental rate functions and the Weibull function. Biological characteristics of N. aenescens populations from different geographic areas were discussed.

Healing and sliding stability of simulated anhydrite fault gouge: Effects of water, temperature and CO2

Anhydrite-bearing faults are currently of interest to 1) CO2-storage sites capped by anhydrite caprocks (such as those found in the North Sea) and 2) seismically active faults in evaporite formations (such as the Italian Apennines). In order to assess the likelihood of fault reactivation, the mode of fault slip and/or fault leakage, it is important to understand the evolution of frictional strength during periods of no slip and upon reloading (healing and relaxation behavior) and of the velocity dependence of friction of anhydrite fault gouge. Therefore, we performed slide–hold–slide experiments combined with a velocity-stepping sequence using simulated anhydrite fault gouge (>95wt.% CaSO4). Vacuum-dry and water-wet experiments were performed at temperatures ranging from 20 to 150°C, and at an effective normal stress of 25MPa. We also performed tests using dry CO2, water-wetted CO2 and CO2-saturated water as pore fluid, but only at 120°C. If pore fluid was present, a fluid pressure of 15MPa was present. Vacuum-dry samples exhibit similar frictional healing to samples containing lab-air, but healing is significantly enhanced in wet samples. Dry samples exhibit velocity-weakening behavior at T ≥120°C, and wet samples exhibit velocity-strengthening behavior over the full temperature range. The presence of CO2 does not influence the healing behavior or the velocity-dependence of friction. Samples containing water-wetted CO2 exhibit behavior similar to wet samples. We infer that the healing in dry samples is controlled by plastic asperity creep (Dieterich-type), possibly through dislocation creep and/or twinning. In wet samples healing is inferred to be controlled by increases in contact area and cohesion by pressure solution. Using a pressure solution rate model to extrapolate healing by contact area growth indicates that the maximum re-strengthening through such a mechanism will only take days to tens of days.

Capacitance behavior of InAlN Schottky diodes in presence of large concentrations of shallow and deep states related to oxygen

The capacitance-voltage-temperature characteristics of nonintentionally doped In0.16Al0.84 N/n+-GaN Schottky diodes were measured at 1 MHz and in the 90–400 K range. They are discussed in the framework of existing theories, which properly treat the Poisson's equation, especially near the edge of the space-charge region, the so-called transition region. The concentration of a shallow donor and of a deep DX-like center, previously reported, is properly determined. The key parameter to discuss the temperature dependence of the capacitance is the ratio between the frequency of the small ac modulating signal and the temperature-dependent emission rate associated to each level. The capacitance-voltage C-Va curves were successfully fitted using a three parameters expression over the full range of temperatures. The concentration of both shallow and deep levels exceeds a few 1018 cm−3. Based on secondary ion mass spectrometry profiling, we assign both levels to the dominant oxygen impurity. This result supports our previous assignment of the shallow donor to a substitutional oxygen atom on a nitrogen site and the deep state to an O-related DX center, naturally explaining its high concentration. The sluggish kinetics at low temperatures, associated to the large concentration of deep levels located near the transition region, is illustrated by hysteresis loops in the C-Va curves below 270 K. Furthermore, the contribution of free carriers to the capacitance is revealed below 150 K, when both shallow and deep donors cannot respond anymore due to an emission rate lower than the 1 MHz modulating frequency. Finally, the presence of a highly doped thin surface barrier, as already reported in other III-nitrides, finds further support.

Spatially resolved x-ray studies of liquid crystals with strongly developed bond-orientational order.

We present an x-ray study of freely suspended hexatic films of the liquid crystal 3(10)OBC. Our results reveal spatial inhomogeneities of the bond-orientational (BO) order in the vicinity of the hexatic-smectic phase transition and the formation of large-scale hexatic domains at lower temperatures. Deep in the hexatic phase up to 25 successive sixfold BO order parameters have been directly determined by means of angular x-ray cross-correlation analysis (XCCA). Such strongly developed hexatic order allowed us to determine higher order correction terms in the scaling relation predicted by the multicritical scaling theory over a full temperature range of the hexatic phase existence.

Influence of inherent structure shear stress of supercooled liquids on their shear moduli.

Configurations of supercooled liquids residing in their local potential minimum (i.e., in their inherent structure, IS) were found to support a non-zero shear stress. This IS stress was attributed to the constraint to the energy minimization imposed by boundary conditions, which keep size and shape of the simulation cell fixed. In this paper, we further investigate the influence of these boundary conditions on the IS stress. We investigate its importance for the computation of the low frequency shear modulus of a glass obtaining a consistent picture for the low- and high frequency shear moduli over the full temperature range. Hence, we find that the IS stress corresponds to a non-thermal contribution to the fluctuation term in the Born-Green expression. This leads to an unphysical divergence of the moduli in the low temperature limit if no proper correction for this term is applied. Furthermore, we clarify the IS stress dependence on the system size and put its origin on a more formal basis.

A MEMS Vibratory Gyroscope With Real-Time Mode-Matching and Robust Control for the Sense Mode

This paper presents a method to accomplish automatic and real-time mode-matching control for a microelectromechanical systems vibratory gyroscope based on improved fuzzy algorithm and neural network algorithm. Meanwhile, robust control for the sense mode is applied to enhance the reliability of the closed-loop system. Experimental results demonstrate that it only needs ~8 s to achieve mode-matching intelligently in the improved fuzzy control system. In addition, a mismatching error <;0.32 Hz is achieved over the temperature range from -40 °C to 80 °C in the neural network real-time control system, which is improved by more than one order of magnitude compared with that of once-time control system. In addition, the temperature coefficient of the zero bias is also improved to be 0.5°/h/°C in the real-time mode-matching control system. Experimental results of phase margin, gain margin, and sensitivity margin indicate that the closed-loop system is stable and robust enough over the full temperature range. Moreover, the bandwidth and bias instability of the mode-matching gyroscope with closed-loop controlled sense mode are >85 Hz and <;5°/h, respectively.

On the interplay between phonon-boundary scattering and phonon-point-defect scattering in SiGe thin films

This paper provides theoretical understanding of the interplay between the scattering of phonons by the boundaries and point-defects in SiGe thin films. It also provides a tool for the design of SiGe-based high-efficiency thermoelectric devices. The contributions of the alloy composition, grain size, and film thickness to the phonon scattering rate are described by a model for the thermal conductivity based on the single-mode relaxation time approximation. The exact Boltzmann equation including spatial dependence of phonon distribution function is solved to yield an expression for the rate at which phonons scatter by the thin film boundaries in the presence of the other phonon scattering mechanisms. The rates at which phonons scatter via normal and resistive three-phonon processes are calculated by using perturbation theories with taking into account dispersion of confined acoustic phonons in a two dimensional structure. The vibrational parameters of the model are deduced from the dispersion of confined acoustic phonons as functions of temperature and crystallographic direction. The accuracy of the model is demonstrated with reference to recent experimental investigations regarding the thermal conductivity of single-crystal and polycrystalline SiGe films. The paper describes the strength of each of the phonon scattering mechanisms in the full temperature range. Furthermore, it predicts the alloy composition and film thickness that lead to minimum thermal conductivity in a single-crystal SiGe film, and the alloy composition and grain size that lead to minimum thermal conductivity in a polycrystalline SiGe film.

Effect of the anisotropy of monocrystalline silicon mechanical properties on the dynamic characteristics of a micromechanical gyroscope

The aim of the research was to determine the effect of temperature on mechanical properties of a micromechanical gyroscope with the sensing element mounted on a silicon wafer, with the crystallographic orientation of (100) (110) (111). The research is of current relevancy since the metrological characteristics that depend on the eigenfrequencies over the full temperature range are to be controlled. The temperature-modal analysis of the micromechanical gyroscope model was performed with ANSYS program. The temperature dependence for eigenfrequencies was obtained. The dependence of the scale factor on temperature for the most temperature-independent variant of sensor positioning on the wafer was determined. The developed mathematical model was used to find the forms of the output oscillations of the gyroscope.

Solubility of Methane in Propylene Carbonate

The solubility of methane in propylene carbonate was measured at the temperatures (244.26, 248.14, 255.37.37, 266.48, 273.15, 298.15, 333.15, and 373.15) K. Pressures ranged from (101 to 11200) kPa. The Peng–Robinson equation of state was used to correlate the data over the full temperature and pressure range. A linearly temperature dependent binary interaction parameter was found to correlate the experimental data the best. The correlation reproduces the experimental data with an overall average percent deviation in the mole fraction of 6.9 %. The Krichevsky–Ilinskaya equation combined with the Peng–Robinson equation of state was used to obtain Henry’s constants of methane in propylene carbonate.

Temperature dependent thermal conductivity of a suspended submicron graphene ribbon

Thermophysical characterization of graphene is very important for both fundamental and technological research. While most of the existing thermal conductivity measurements are for graphene sheets with sizes larger than 1 μm, the thermal conductivities for suspended submicron graphene ribbons are still very few, although the thermal conductivity of graphene ribbons at the submicron scale is predicted to be much smaller than large graphene and strongly size dependent for both length and width due to the 2D nature of phonon transport. Here, we report the temperature dependent thermal conductivity of a 169-nm wide and 846-nm long graphene ribbon measured by the electrical self-heating method. The measured thermal conductivities range from (12.7 ± 2.95) W/m/K at 80 K to (932 ± 333) W/m/K at 380 K, being (349 ± 63) W/m/K at 300 K, following a ∼ T2.79 law for the full temperature range of 80 K to 380 K and a ∼ T1.23 law at low temperatures. The comparison of the measured thermal conductance with the ballistic transport limit indicates diffusive transport in this narrow and short ribbon due to phonon-edge as well as phonon-defect scattering. The data were also combined with an empirical model to predict possible width dependence of thermal conductivity for suspended graphene ribbons. These results help understand the 2D phonon transport in suspended submicron graphene ribbons and provide knowledge for controlling thermophysical properties of suspended graphene nanoribbons through size manipulation.

The origin of the antiferromagnetic behaviour of the charge-transfer compound (HMTTF)[Ni(mnt)2

The charge-transfer (HMTTF)[Ni(mnt)2] material (1) was the first mixed-stack compound reported to present ferromagnetic (FM) interactions between the donor (D) and acceptor (A) units within each mixed-stack. Despite the presence of a dominant FM interaction, its magnetic susceptibility curve, χ(T), corresponded to that of an antiferromagnetic (AFM) compound at low temperatures, a fact that was tentatively explained in terms of a FM-to-AFM magnetic transition. In this work, the First-Principles Bottom-Up procedure has been applied to rationalize the magnetic properties of 1. The results presented herein indicate the presence of up to five sizeable JAB magnetic exchange interactions (26.0, -1.7, 1.9, 0.1, and -99.3 cm(-1)) that create a complex 2D magnetic network. This magnetic topology not only produces a calculated χ(T) curve that is in excellent agreement with the experimental measurements, but also allows us to understand the magnetic behaviour of 1, in the full range of temperatures, solely in terms of the different Boltzmann population of diamagnetic and paramagnetic spin states as the temperature changes. Our data thus provide a plausible explanation for the AFM behaviour of 1 at low temperatures that does not involve a phase transition.

Irradiation and temperature influence on the Bi-doped silica fiber

We report Bi-doped fibers prepared by modified chemical vapor deposition combination with solution doping process. The fibers are divided into three groups under 60Co radiations with different doses. The absorption spectra and fluorescence spectra of the fiber before and after irradiation are investigated. The dependence of fluorescence intensity of the fiber on temperature (-40-70 ℃) are measured. Experimental results show that the radiation-induced absorptions (RIAs) of the fibers increase significantly at 700 nm and 800 nm with the increase of the irradiation dose. We ascribe the great enhancement of the RIA of the fiber to the generation of more Bi near-infrared (NIR) active centers. Because near infrared nonluminous valance state like Bi3+ captures free electrons and converts into Bi2+, and further into Bi+under the 60Co radiations with different doses. We also find that the NIR fluorescence spectra are stable before and after irradiation under 976 nm LD excitation. The possibility of communication in a radiation environment is proved, such as in outer space is proved. In addition, the fluorescence intensity dependence on temperature in a full-temperature range is analyzed, and we find that the fluorescence intensity decreases with the increase of temperature. It is contributed to the Bi active center that Bi+ may gradually turn into nonluminous Bi metallic colloids during thermal activation. The variation law of fluorescence intensity is analyzed in the whole range of temperature. We believe that the variation law of fluorescence intensity provides data and basis for the stable operation of bismuth-doped fiber laser in the future.

Development of a Stress Compensation Layer for 3-D Assembly of Thin Pixel Modules

Pixel modules are the fundamental building blocks of the ATLAS pixel detector system used in the CERN LHC facility. In their basic form, they consist of a silicon sensor that is flip-chip bonded to a CMOS read-out integrated chip (ROIC). One of the main objectives for the ATLAS experiment is to develop an approach toward low-mass modules, thus reducing radiation length. From the module perspective, this can be achieved by using advanced 3-D technology processes that include the formation of copper and solder microbumps on top of the ROIC front side, the thinning of both the sensor and the CMOS ROIC, and, finally, the flip-chip assembly of the two chips. The thinning of the silicon chips leads to low bump yield at the solder reflow stage, due to bad coplanarity of the two chips creating dead zones within the pixel array. In the case of the ROIC, which is thinned to 100 μm, the chip bow varies from −100 μm at room temperature to +175 μm at reflow temperature, resulting in CTE mismatch between materials in the CMOS stack and the silicon substrate. Our objective was to compensate dynamically for the stress of the front-side stack by adding a compensating layer to the back side of the wafer. Using our material thermomechanical database coupled with a proprietary analytical simulator, and measuring the bow of the ROIC at die level, we were able to reduce the bow magnitude by approximately a factor of 3 by introducing the compensating layer. We show that it is possible to change the sign of the bow at room temperature after deposition of a SiN/Al:Si stack. The amplitude of the correction can be manipulated by the deposition conditions of the SiN/Al:Si stack. Further development of the back-side deposition conditions are ongoing, where the target is to control the room temperature bow close to zero and reduce the bow magnitude throughout the full solder reflow temperature range, hence conserving bump yield. In keeping with a 3-D process, the materials used are compatible with through-silicon via (TSV) technology with a TSV-last approach in mind, should we integrate this technology in the future.