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Three new ionic salts containing [M(CN)8]4− (M = MoIV and WIV) were prepared using large complex cations based on a non-conventional motif built with the tris(2-aminoethyl)amine (noted hereafter tren) ligand, [{M’(tren)}3(μ-tren)]6+ (M’ = CuII and ZnII). The crystal structures of the three compounds show that the atomic arrangement is formed by relatively isolated anionic and cationic entities. The three compounds were irradiated with a blue light at low temperature, and show a significant photomagnetic effect. The remarkable properties of these compounds are (i) the long-lived photomagnetic metastable states for the [Mo(CN)8]4−-based compounds well above 200 K and (ii) the rare efficient photomagnetic properties of the [W(CN)8]4−-based compound. These photomagnetic properties are compared with the singlet-triplet conversion recently reported for the K4[Mo(CN)8]·2H2O compound. [ABSTRACT FROM AUTHOR]

The superiority of the electronic transport properties of single-walled carbon nanotube (SWNT) ropes over SWNT mats is verified from low temperature and frequency-dependent transport. The overall change of resistance versus in nanotube mats shows that 3D variable range hopping is the dominant conduction mechanism within the 2-300K range. The magneto-resistance (MR) is found to be predominantly negative with a parabolic nature, which can also be described by the hopping model. Although the positive upturn of the MR at low temperatures establishes the contribution from quantum interference, the inherent quantum transport in individual tubes is suppressed at elevated temperatures. Therefore, to minimize multi-channel effects from inter-tube interactions and other defects, two-terminal devices were fabricated from aligned SWNT (extracted from a mat) for low temperature transport as well as high-frequency measurements. In contrast to the mat, the aligned ropes exhibit step-like features in the differential conductance within the 80-300K temperature range. The effects of plasmon propagation, unique to one dimension, were identified in electronic transport as a non-universal power-law dependence of the differential conductance on temperature and source-drain voltage. The complex impedance showed high power transmission capabilities up to 65 GHz as well as oscillations in the frequency range up to 30 GHz. The measurements suggest that aligned SWNT ropes have a realistic potential for high-speed device applications. [ABSTRACT FROM AUTHOR]

While carbon nanotubes (CNT) have been suggested as thermal management material for integrated circuits, the thermal properties, and, especially, the thermal boundary resistance (TBR) of as-grown CNT fabricated at low temperature have hardly been investigated. Here, the thermal resistance of CNT vias, with different bundle lengths and diameters fabricated at 500°C using chemical vapour deposition, are investigated using the 3ω-method. It was found that the thermal resistance hardly changes with length except for the smallest bundle diameter of 2 μm, indicating that the TBR (109-1010K/W per tube) dominates the thermal conduction. This is in contrast to the electrical resistance and temperature coefficient of resistance, both of which clearly increase with length. From the slope of the thermal resistance versus length of the 2 lm wide bundles, the thermal conductivity of the CNT was estimated to be 1.4-2.8 W/mK. This low thermal conductivity is attributed to the low quality of the samples as determined by Raman spectroscopy. [ABSTRACT FROM AUTHOR]

In the present study, the total oxidation of n-butanol and carbon monoxide (CO) was investigated on 1 wt% Pd/γ-Al2O3 catalysts which were prepared via the dielectric-barrier discharge (DBD) and wet-impregnation (WI) methods. All catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and Brunauer-Emmett-Teller method (BET). The catalytic activities in the total oxidation of VOCs (n-butanol) and CO under gas-phase conditions was measured. The results showed that the palladium catalysts prepared from DBD method exhibited higher activity in total oxidation of n-butanol and CO than catalysts prepared by WI method. This difference is due to better physicochemical properties of catalysts prepared by DBD method. For 1 wt% Pd loading, total oxidation of n-butanol and CO was achieved at 300 °C and 175 °C with the DBD method. Meanwhile, oxidation efficiency of the catalysts prepared by WI method is only approximately 90 % in two cases. [ABSTRACT FROM AUTHOR]

We evaluate the phase diagram of the Kern–Frenkel patchy model with four interaction sites for four different values of the radial interaction range (all in the single-bond-per-patch regime) keeping the area of the interaction patches fixed. Four stable crystal phases are investigated, namely diamond cubic (DC), bcc, fcc, and plastic fcc. The DC is favored at low temperatures and pressures, while the bcc is favored at low temperatures and intermediate to high pressures. At low temperatures and very high pressures an ordered fcc phase is found, while—as expected—at high temperatures, the only stable crystal is a plastic fcc phase. We find a rich phase diagram with several re-entrant coexistence lines, which can be brought in the equilibrium phase diagram by a proper choice of the range. We also show that the gas-liquid phase separation becomes metastable as the range narrows, and it takes place in a region of the phase diagram where the low density diamond crystal is the thermodynamically stable phase. [ABSTRACT FROM AUTHOR]

The effect of electric field on the thermal expansion of the TlGaSe2 ferroelectric-semiconductor with a layer crystalline structure has been investigated. A strong transformation of negative linear expansion coefficient in the layer plane has been observed as a result of the applied electric field. It was concluded that internal electric fields created by local polarized states in the ferroelectric- semiconductor are responsible for a negative thermal expansion and its behavior under the electric field. Predominantly, the electrostriction effect is the driving mechanism of the lattice deformation of TlGaSe2 crystals at low temperatures. [ABSTRACT FROM AUTHOR]

The effect of electric field on the thermal expansion of the TlGaSe2 ferroelectric-semiconductor with a layer crystalline structure has been investigated. A strong transformation of negative linear expansion coefficient in the layer plane has been observed as a result of the applied electric field. It was concluded that internal electric fields created by local polarized states in the ferroelectric- semiconductor are responsible for a negative thermal expansion and its behavior under the electric field. Predominantly, the electrostriction effect is the driving mechanism of the lattice deformation of TlGaSe2 crystals at low temperatures. [ABSTRACT FROM AUTHOR]

The whispering gallery mode technique applied to single-crystal quartz has been used as a precise method to determine the dependence of the dielectric permittivity of pure single-crystal quartz on temperature-induced dimensional changes at cryogenic temperatures. The anisotropic temperature coefficients of permittivity (TCP) perpendicular and parallel to the crystal axis have been determined between 4.7 and 280 K. The difference between TCPs perpendicular and parallel to the crystal axis, near 17 GHz, between 160 and 300 K is approximately half the thermal expansion coefficient perpendicular to the crystal axis. Over this temperature range, the fractional change in the relative permittivity values perpendicular and parallel to the crystal axis, as a result of thermal expansion of the perpendicular dimension of the crystal, only differs by a small constant value. [ABSTRACT FROM AUTHOR]

In this paper, the photonic band diagram and the density of states in finite photonic structures are analyzed and optimized for broad bandwidths using the apodization method. Based on the effective propagation constant, the group refractive index can be computed for the finite structures, which is adopted to reveal the physical explanation on the optimal band gaps. The surface states of the finite photonic crystal and the mode matching at the interfaces are also considered. It is found that the high group index of the photonic structures can obtain broad bandwidths and also enhance the mode matching at the interfaces. By slowly varying the radii of the cylinders monotonously in two dimensions, the first band gap can be increased from 10.6% to 20.04%. This work provides a useful tool for the optimal design of finite photonic crystals. [ABSTRACT FROM AUTHOR]

Ice III is a hydrogen bond disordered crystal which when cooled 1 K/min or faster transforms to an antiferroelectric hydrogen bond ordered structure, ice IX. Throughout its region of stability, experiments indicate that the H bonds in ice III are, in fact, partially ordered, i.e., some proton arrangements are preferred. In addition, there has been evidence that the structure of ice IX retains some residual disorder after the transition. Diffraction experiments and calorimetry apparently conflict with regard to the degree of ordering at the ice III/IX transition. Mean field statistical mechanical theories have been used to link partial occupations from diffraction data with thermodynamics. In this work, we investigate the ice III/IX proton ordering phase transition using electronic density functional theory calculations for small unit cells, extended to simulate the phase transition in a large unit cell using graph invariants. In agreement with experiment, we observe partial ordering over a wide range of temperatures as ice III transforms to partially disordered ice IX, near 126 K, which becomes fully ordered at lower temperatures. We compare our results from full statistical mechanical simulations with mean field models, finding small errors for the low-temperature ice IX phase and much larger errors for the high-temperature ice III phase. The failure of mean field theories may explain the apparent conflict between diffraction experiments and calorimetry. [ABSTRACT FROM AUTHOR]

We have grown In0.25Ga0.75N films on nearly lattice-matched ZnO(0001) substrates with atomically flat surfaces at low substrate temperatures using pulsed laser deposition. We have found that InGaN having a stepped and terraced structure on its surface grows at low substrate temperatures. We have also found that InGaN grows in the layer-by-layer mode, even at room temperature (RT), while maintaining straight steps and atomically flat terraces from the first monolayer. This phenomenon exhibits a singular contrast to the case of RT epitaxy of GaN on ZnO, where a considerable number of defects are observed on the stepped structure of the first several layers. This difference can be attributed to a smaller lattice mismatch between InGaN and ZnO. [ABSTRACT FROM AUTHOR]

Good quality Ca3Sc2Ge3O12 garnet crystals activated with Yb3+ have been grown by means of the flux growth method and characterized using optical spectroscopy techniques. The low-temperature absorption and emission spectra give evidence of the presence of nonequivalent optical centers, as a consequence of the distribution of the Yb3+ ions in different lattice sites. The effect of codoping with Na+ or Mg2+ on the Yb3+ site distribution has been investigated. The energy-level schemes of the most important centers have been determined on the basis of site-selective spectroscopy experiments. Cooperative luminescence has also been observed and reliably compared with the self-convolution of the NIR luminescence. [ABSTRACT FROM AUTHOR]

Magnetoresistance and magnetic hysteresis loop measurements have been used to investigate the strong interfacial coupling in cobalt oxide/ferromagnet bilayers at low temperatures. For the biased state, an asymmetry in the magnetization reversal processes has been found. It is characterized by domain wall motion as the dominant mechanism for the decreasing field branch and an appreciable amount of magnetization rotation for the increasing field branch. The observed behavior is different from other exchange bias systems. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the synthesis of MgB[sub 2] with bulk superconducting properties by conventional solid state methods at temperatures as low as 550 °C. Mg deficiencies of the type Mg[sub 1-x]B[sub 2] were tested. T[sub c] was found to decrease by about 1 K at large x, though the amount of nonstoichiometry, if any, is likely to be very small. For specific processing conditions, indications of the 25–30 K transition often seen in thin films were seen in the bulk materials. The lower temperature transition may be associated with the grain boundaries. These results indicate that it should be possible to fabricate MgB[sub 2] with bulk properties in in situ thin films at temperatures of 600 °C or less. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which focused on the low-temperature dynamic properties of photorefractive gratings in cobalt-doped potassium-strontium-sodium-barium-niobate crystals. Experiment details; Results and discussion; conclusions.

This paper reports a method for producing α-Al2O3 at low temperatures by using a hydrothermal process and a seeding technique. White aluminum hydroxide precipitate prepared through a homogeneous precipitation method using aluminum nitrate and urea was peptized by using formic acid at room temperature to transform it into a transparent alumina sol. After the sol was hydrothermally treated, α-Al2O3 nanoparticle seeds were added to the sol. The sol containing the α-Al2O3 nanoparticles was transformed into an α-Al2O3-seeded alumina gel by drying at room temperature. The non-seeded alumina gel began to crystallize into α-Al2O3 at 500 °C. The α-Al2O3-seeding promoted the crystallization of the alumina gel to α-Al2O3. A remarkable α-Al2O3 crystallinity was achieved with an increase in α-Al2O3 content by weight in the final seeded alumina gel. Even with a content as low as 1%, the seeded alumina gel was partially crystallized to α-Al2O3 at a temperature as low as 400 °C. [ABSTRACT FROM AUTHOR]

Sintering of nanosized powder mixtures occurs at relatively low temperatures and is accompanied by interdiffusion between the powders and low-temperature homogenization or formation of new phases. The kinetics of interdiffusion depends on the grain size of the structure being formed in the powder compacts. We consider size effects of interdiffusion during sintering at sufficiently low temperatures when bulk diffusion is completely frozen and homogenization or formation of other phases occurs due to diffusion-induced motion of grain boundaries. These effects take place both in the mixtures of mutually soluble powder materials and materials that form intermetallic compounds. We analyze mainly the results obtained as development of the studies that were initiated by Professor Yakov Yevseevich Geguzin. [ABSTRACT FROM AUTHOR]

The processes of vibrational relaxation (VR) and vibrational cooling (VC) are investigated in low temperature crystals of complex molecules, specifically benzene, naphthalene, anthracene, and durene. In the VR process, a vibration is deexcited, while VC consists of many sequential and parallel VR steps which return the crystal to thermal equilibrium. A theoretical model is developed which relates the VR rate to the excess vibrational energy, the molecular structure, and the crystal structure. Specific relations are derived for the vibrational lifetime T1 in each of three regimes of excess vibrational energy. The regimes are the following: Low frequency regime I where VR occurs by emission of two phonons, intermediate frequency regime II where VR occurs by emission of one phonon and one vibration, and high frequency regime III where VR occurs by evolution into a dense bath of vibrational combinations. The VR rate in each regime depends on a particular multiphonon density of states and a few averaged anharmonic coefficients. The appropriate densities of states are calculated from spectroscopic data, and together with available VR data and new infrared and ps Raman data, the values of the anharmonic coefficients are determined for each material. The relationship between these parameters and the material properties is discussed. We then describe VC in a master equation formalism. The transition rate matrix for naphthalene is found using the empirically determined parameters of the above model, and the time dependent redistribution in each mode is calculated. [ABSTRACT FROM AUTHOR]

Negative differential resistance (NDR) in current-voltage (I-V) characteristics and apparent colossal electroresistance were observed in Gd0.5Sr0.5MnO3 single crystals at low temperatures. The continuous dc I-V measurements showed a marked thermal drift. In addition, temperature of the sample surface was found to be significantly higher than that of the base at high applied currents. Two different strategies namely estimation and diminution of the Joule heating (pulsed I-V measurements) were employed to investigate its role in the electric transport properties. Our experiments reveal that the NDR in Gd0.5Sr0.5MnO3 is a consequence of Joule heating rather than the melting of charge order. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic properties of EuMnxGa3-x intermetallics have been investigated using powder x-ray diffraction and magnetic measurement. EuMnxGa3-x crystallizes in an orthorhombic structure with a space group of Cmcm, and Z=4. The lattice parameters are a=4.294(1)–4.287(1) Å, b=18.50(3)–18.57(3) Å, and c=4.384(6)–4.372(9) Å. In each unit cell, there are four nonequivalent 4c crystal positions for 4Eu, 4GaI, 4(GaII,Mn), and 4GaIII. EuMnxGa3-x (x<0.27) intermetallic compounds are antiferromagnetic at low temperature. A magnetic transition from the paramagnetic to the ferromagnetic occurs in EuMn0.3Ga2.7 at room temperature when applying a low field of 40 Oe. Moreover, this ferromagnetic order is very weak and sensitive to the applied field. With increasing the applied field, the ferromagnetic order tends to vanish. This phenomenon might be interpreted as the Mn spin state change induced by charge balance at low field. [ABSTRACT FROM AUTHOR]

We present evidence that low temperature atmosphere annealing of Co/Pd magnetic multilayers reduces both the dipolar and exchange interactions, but the dipolar interaction decreases very rapidly at the lowest temperatures. We also infer cobalt oxide formation at grain boundaries. This results in a reduction of the exchange between grains, reduces the length scale of ordering in the ac demagnetized state of the films. We demonstrate that this is the result of the decoupling the grains. [ABSTRACT FROM AUTHOR]

The crystal structure and magnetic properties of EuMnxGa3-x intermetallics have been investigated using powder x-ray diffraction and magnetic measurement. EuMnxGa3-x crystallizes in an orthorhombic structure with a space group of Cmcm, and Z=4. The lattice parameters are a=4.294(1)–4.287(1) Å, b=18.50(3)–18.57(3) Å, and c=4.384(6)–4.372(9) Å. In each unit cell, there are four nonequivalent 4c crystal positions for 4Eu, 4GaI, 4(GaII,Mn), and 4GaIII. EuMnxGa3-x (x<0.27) intermetallic compounds are antiferromagnetic at low temperature. A magnetic transition from the paramagnetic to the ferromagnetic occurs in EuMn0.3Ga2.7 at room temperature when applying a low field of 40 Oe. Moreover, this ferromagnetic order is very weak and sensitive to the applied field. With increasing the applied field, the ferromagnetic order tends to vanish. This phenomenon might be interpreted as the Mn spin state change induced by charge balance at low field. [ABSTRACT FROM AUTHOR]

We reported the low-temperature high performance IGZO TFTs by solution processing. The influence of IGZO composition over broad range on thin films and devices properties were investigated by a wide range of characterization techniques. The schematic of TFT solution-processed IGZO TFTs mobility with different compositions has been obtained. In order to achieve decent TFT performance, the In content should be much high for solution-processed IGZO TFTs. The optimal solution-processed IGZO TFTs with In:Ga:Zn = 5:1:1 composition exhibited a large mobility of 9.1 cm 2  V −1  s −1 , low subthreshold swing of 0.22 V/decade, and high on/off ratio of 10 6 at 300 °C processing temperature. [ABSTRACT FROM AUTHOR]

The crystal structure of Cu5FeS4 (bornite) has been investigated using synchrotron X‐ray powder diffraction at temperatures between 10 and 275 K. Diffraction data confirm that bornite crystallizes in the orthorhombic space group Pbca at 275 K. The unit‐cell volume decreases continuously on cooling, but undergoes an abrupt contraction below ∼65 K, where a first‐order Pbca→Pca21 structural transition takes place. The primary active mode yielding the observed ordered structure corresponds to the irreducible representation Γ2−, with wavevector (0,0,0). Pair distribution function analysis shows strong discrepancies between the local and the average structure. The average Fe—S bond length obtained through the EXAFS local probe is consistent with the values independently provided by X‐ray powder diffraction data, strongly supporting the preferred location of Fe. Several studies have focused on the positions of cations in bornite; however there is still a lack of definitive proof on the ordering of iron. Comparison between high‐resolution diffraction data and EXAFS strongly suggests that the preferred location of iron is on two specific sites. Moreover, the high‐resolution X‐ray powder diffraction revealed that a low‐temperature first transition occurs towards a even more puzzling structure, studied on the basis of the room‐temperature structure. [ABSTRACT FROM AUTHOR]

Nanocrystalline multilayer thin-films are manufactured in configurations of alternating porous ceramic (TiN) layers of relatively high thickness (hceramic) with metal (Ti) layers of low thicknesses (0.8 nm < hmetal < 34 nm) and keeping a constant modulation ratio (η ∼ hceramic/hmetal ∼ 17.5). As hmetal decreases, the overall co-deformation mechanism in the multilayer films bifurcates into the dislocation dominant confined layer slip (CLS) mechanism in the metal and diffusional creep dominant processes in the porous ceramic layer at hmetal ∼ 6.7 nm. This bifurcation leads to simultaneously achieving the highest strain hardening rate due to the CLS mechanism in one layer and the highest strain rate sensitivity value due to the diffusional flow in the other and overcoming the strength-ductility paradox in multilayer thin-film materials at low temperatures. [ABSTRACT FROM AUTHOR]

The room-temperature photoluminescence intensity and conductivity of GaN films grown by reactive rf sputtering were improved by the addition of hydrogen during growth. The differential resistivity decreased by two orders of magnitude when 2.4% H2 was added to the deposition gas. The improvement in the photoluminescence intensity occurred together with an increase in the level of oxygen contamination and an apparent increase in the structural disorder. At 0 and 20% H2, respectively, the refractive indices were 2.45 and 1.98, and the bandgaps were 3.06 and 3.64 eV, with the change attributed to oxygenation. [ABSTRACT FROM AUTHOR]

Er 3+ doped (95 -x )B 2 O 3 - x ZnO-5TiO 2 ( x = 45, 50 and 55 mol%) bulk glasses were prepared by conventional melt quenching method and investigated by transmission and photoluminescence (PL) spectroscopy. Transmission spectra exhibit sharp absorption bands at 364, 377, 406, 441, 448, 488, 521, 541, 651, 792, 974, and 1530 nm, that correspond to absorption on Er 3+ ions and they are attributed to the optical transitions from the ground state 4 I 15/2 to the excited states 4 G 9/2 , 4 G 11/2 , 4 F 9/2 , 4 F 3/2 , 4 F 5/2 , 4 F 7/2 , 2 H 11/2 , 4 S 3/2 , 4 F 9/2 , 4 I 9/2 , 4 I 11/2 and 4 I 13/2 , respectively. The optical gap has been estimated around 3.5 eV with a tendency to increase with increasing ZnO content. Low-temperature PL properties of the Er 3+ doped glasses and of the host glass itself were investigated. To achieve this goal, two different wavelengths (325 and 514.5 nm) were used for PL excitation. PL spectra excited by He-Cd laser at 325 nm were dominated by the host glass broad-band luminescence centred at around 570 nm. Simultaneously we observed narrow emission and absorption features due to 4 f- 4 f electronic transitions in Er 3+ ions superposed on the broad band host glass luminescence. We argue that these superposed narrow absorption dips represent a direct evidence of the energy transfer from the electronic structure of the host to 4 f states of Er 3+ ions. Fine structure of Er 3+ emission bands at 980 and 1530 nm, corresponding to radiative transitions from the two lowest excited states of Er 3+ ions to the ground state manifold have been investigated at room temperature and at 4 K, and a schematic energy diagram of Stark levels of 4 I 11/2 , 4 I 13/2 and 4 I 15/2 manifolds has been deduced. [ABSTRACT FROM AUTHOR]

Yb-doped Al[sub x]Ga[sub 1-x]As (x=0–1) was fabricated by low temperature epitaxial growth using a molecular beam epitaxy method. Photoluminescence (PL) measurements were performed in a temperature range between 1.6 and 150 K. Three sharp PL peaks due to intra-4f transition of Yb were observed around λ=1 μm in samples with x>=0.3, whereas samples with x<0.3 show no PL peak in this region. Irrespective of wide variety of the Al contents x, PL intensities of these peaks show a similar rapid thermal quenching above 100 K. Furthermore, a broad and intense PL band was found at around 1.4 eV. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Low-temperature molten-salt method and the NH 4 NO 3 flux were developed to synthesize quasi-spherical cubic BaGdF 5 :Ce 3+ /Er 3+ /Yb 3+ nanocrystals with the average diameter of 30 nm. The optimum doping concentrations of Er 3+ and Yb 3+ are determined to 2 and 20 mol%, respectively. The introduction of Ce 3+ in BaGdF 5 : Er 3+ /Yb 3+ nanocrystals deduced a huge variation of the profile of the UC emission under 976 nm laser irradiation. The strong ultraviolet UC emission of 330–380 nm is due to the overlap of 4 G 7/2 , 2 K 15/2 , 4 G 9/2 → 4 I 15/2 transitions of Er 3+ , and strong blue one locating at 440–480 nm is attributed to the overlap of 4 F 3/2, 4 F 5/2 → 4 I 15/2 and 4 G 7/2 , 2 K 15/2 , 4 G 9/2 → 4 I 13/2 transitions of Er 3+ , respectively. The UC emission mechanism and energy transfer process of BaGdF 5 :Ce 3+ /Er 3+ /Yb 3+ nanocrystals were provided in detail and demonstrated by the fluorescence decay curves and pumping power dependent UC emission spectra. This work not only demonstrates a rational approach to tailor UC emission (red, blue and ultraviolet) by tuning doping ions and concentration, but also for better understanding of their essential UC luminescence properties. [ABSTRACT FROM AUTHOR]

By the hydrothermal method, two new mixed alkali carbonates, LiRbCO3 and LiCsCO3 were synthesized for the first time. Both compounds crystallize in the monoclinic space group P21/n, and exhibit similar wave like [LiCO3]∞ layers connected by Rb–O and Cs–O bonds, respectively. They not only possess low melt temperature and wide spectral transmittance range, but also have relatively large birefringence confirmed by first principles calculations. In the mixed alkali carbonates system of LiMCO3 (M = K, Rb, Cs), with the increase of atomic radius of the alkali metal, the birefringence is reduced from 0.11 in LiKCO3 to 0.09 in LiCsCO3, while the refractivity is increasing. The increasing refractivity and decreasing birefringence can be interpreted by the enhancement of orbital hybridization resulting from the reduced C–O bond length and weakened structural anisotropy, respectively. [ABSTRACT FROM AUTHOR]

We report a low-temperature transmission high-energy electron diffraction study of solid carbon dioxide films in the temperature range 15-87 K. The precise analysis of the experimental diffraction intensities shows that molecular axes noticeably deviate from the cubic space diagonals of the $$Pa\overline{3}$$ structure. The molecular tips tend to be oriented toward the empty spaces between two molecules in the nearest basal planes. Nevertheless, the crystal structure is still identified as $$Pa\overline{3}$$ but with 24 equivalent positions for oxygen atoms instead of 8 positions as it was thought before. We have shown that the relevant maximal angle deviations in the selected directions could be as big as $${\sim } 30^{\circ }$$ at the lowest temperatures and they decrease at higher temperature. This results in hopping precession of molecules instead of simple librations. [ABSTRACT FROM AUTHOR]

The present study deals with the development of a chemical sensor for the detection of liquefied petroleum gas (LPG) at a low operating temperature using Zinc ferrite (ZnFeO)/ Bacillus subtilis ( B. subtilis) hybrid nanostructures. The nanostructure ZnFeO and B. subtilis powder, taken in equal proportion was made into films using the spin coating technique. X-ray diffraction, thermal analysis, scanning electron microscopy, and transmission electron microscopy were used to study morphology, structure and crystallite size. The sensing properties of the hybrid structure were studied and excellent response was observed in the temperature range of 50-55°C for 400 ppm LPG, when compared to the individual components of the hybrid. The signal output of the proposed sensor were extremely stable for more than 30 days. This method proposes the usage of the biomolecule/metal oxide composites in electronics and helps to reduce the metal oxide usage. [ABSTRACT FROM AUTHOR]

A newly developed self-consistent CALPHAD thermodynamic database involving Al, Am, Ga, Pu, and U is presented. A first optimization of the slightly characterized Am-Al and completely unknown Am-Ga phase diagrams is proposed. To this end, phase diagram features as crystal structures, stoichiometric compounds, solubility limits, and melting temperatures have been studied along the U-Al → Pu-Al → Am-Al, and U-Ga → Pu-Ga → Am-Ga series, and the thermodynamic assessments involving Al and Ga alloying are compared. In addition, two distinct optimizations of the Pu-Al phase diagram are proposed to account for the low temperature and Pu-rich region controversy. The previously assessed thermodynamics of the other binary systems (Am-Pu, Am-U, Pu-U, and Al-Ga) is also included in the database and is briefly described in the present work. Finally, predictions on phase stability of ternary and quaternary systems of interest are reported to check the consistency of the database. [ABSTRACT FROM AUTHOR]

Phononic crystal (PnC) membranes are a promising solution to improve sensitivity of bolometric sensor devices operating at low temperatures. Previous work has concentrated only on tuning thermal conductance, but significant changes to the heat capacity are also expected due to the modification of the phonon modes. Here, we calculate the area-specific heat capacity for thin (37.5 - 300 nm) silicon and silicon nitride PnC membranes with cylindrical hole patterns of varying period, in the temperature range 1 - 350 mK. We compare the results to two- and three-dimensional Debye models, as the 3D Debye model is known to give an accurate estimate for the low-temperature heat capacity of a bulk sample. We found that thin PnC membranes do not obey the 3D Debye T³ law, nor the 2D T² law, but have a weaker, approximately linear temperature dependence in the low temperature limit. We also found that depending on the design, the PnC patterning can either enhance or reduce the heat capacity compared to an unpatterned membrane of the same thickness. At temperatures below ~ 100 mK, reducing the membrane thickness unintuitively increases the heat capacity for all samples studied. These observations can have significance when designing calorimetric detectors, as heat capacity is a critical parameter for the speed and sensitivity of a device. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) was synthesized by carbothermal reduction and nitridation method from a mixture of various transition alumina powders and carbon black using 2.45 GHz microwave irradiation in N2 atmosphere. We achieved the synthesis of AlN at 1300-1400°C using 2.45 GHz microwave irradiation for 60 min. Our results suggest that θ-Al2O3 is more easily nitrided than γ-, δ-, and α-Al2O3. On the other hand, nitridation ratio of samples synthesized in a conventional furnace under nitrogen atmosphere were zero or very low. These results show that 2.45 GHz microwave irradiation enhanced the reduction and nitridation reaction of alumina. [ABSTRACT FROM AUTHOR]

We report here the effect of a controlled modification of the shell microstructure around the crystalline core of a silicon nanowire (SiNW) grown at a low (320 °C) temperature by the hot wire chemical vapor processing (HWCVP) method. We demonstrate these effects through the evaluation of the performance of a micro-supercapacitor (µ-SC) device fabricated with these SiNWs having different shell structures. It is to be emphasized that the shell microstructure could be modified through a controlled interplay of the process parameters during the growth. A careful optimization of the shell microstructure in these nanowires during its low-temperature deposition has led to a µ-SC with capacitance value of 94 µF/cm. This result opens up exciting opportunities for HWCVP-grown SiNWs to be employed for on-chip µ-SC and other low-temperature applications. [ABSTRACT FROM AUTHOR]

To synthesize nitrogen-doped carbon nanofibers (N-CNFs) at high growth rates and low temperatures less than 673 K, nickel species (metallic nickel and nickel oxide) supported on alumina particles were used as the catalysts for an acetonitrile catalytic chemical vapor deposition (CVD) process. The nickel:alumina mass ratio in the catalysts was fixed at 0.05:1. The catalyst precursors were prepared from various nickel salts (nitrate, chloride, sulfate, acetate, and lactate) and then calcined at 1073 K for 1 h in oxidative (air), reductive (hydrogen-containing argon), or inert (pure argon) atmospheres to activate the nickel-based catalysts. The effects of precursors and calcination atmosphere on the catalyst activity at low temperatures were studied. We found that the catalysts derived from nickel nitrate had relatively small crystallite sizes of nickel species and provided N-CNFs at high growth rates of 57 ± 4 g-CNF/g-Ni/h at 673 K in the CVD process using 10 vol% hydrogen-containing argon as the carrier gas of acetonitrile vapor, which were approximately 4 times larger than that of a conventional CVD process. The obtained results reveal that nitrate ions in the catalyst precursor and hydrogen in the carrier gas can contribute effectively to the activation of catalysts in low-temperature CVD. The fiber diameter and nitrogen content of N-CNFs synthesized at high growth rates were several tens of nanometers and 3.5 ± 0.3 at.%, respectively. Our catalysts and CVD process may lead to cost reductions in the production of N-CNFs. [ABSTRACT FROM AUTHOR]

Presents information on a study which measured the low-temperature mobility of high-quality two-dimensional hole systems confined at a heterostructure. Background of the study; Methodology of the study; Results and discussion.

ABSTRACT Synthetic l-lactide random copolymers can be employed as controlled release materials when prepared using supercritical carbon dioxide (scCO2), since they are biodegradable via hydrolysis. To determine the effects of thermal properties on polymer performance following scCO2 processing, three types of poly( l-lactide) having different properties were assessed. The Tm of one poly( l-lactide) sample (H-100) was found to be approximately 170 °C over the processing pressure range from 8 to 18 MPa, while a second sample (H-440) also showed a constant value of approximately 152 °C. In contrast, the poly( l-lactide) REVODE exhibited a Tm of 146 °C prior to processing but a higher value of 147 °C following treatment at 8 MPa. Unlike the H-100 and H-440, the Tm value of the REVODE tended to decrease with increasing pressure. The Tg values increased greatly under mild conditions of 8 MPa pressure and a temperature of 40 °C. In particular, the Tg values for the H-440 and REVODE increased by 4 °C and 5 °C, respectively. All Tg values were lowest at 12 MPa and increased with increasing processing pressure, although the effect of processing temperature was minimal. The Χc DSC of the H-100 was 18% initially but increased to 20% upon scCO2 processing at 40 °C and 14 MPa, and showed further increases at higher processing temperatures. Although the relationship between processing temperature and Χc DSC values for the H-440 showed the same trend as observed with the H-100, a different trend was seen for the REVODE. The Χc XRD values obtained from the XRD analyses differed from the values generated by DSC analysis, and showed a maximum degree of crystallinity following processing at 80 °C both with and without scCO2 treatment. ATR FT-IR analyses identified peaks due to semicrystalline regions in poly( l-lactide) samples treated with scCO2, even when applying low temperatures. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44006. [ABSTRACT FROM AUTHOR]

Low temperature crystallization of oil is employed in the production of omega-3 which are a product of interest in the food industry. The aim of this work was to model the influence of temperature and time in the mass of the solid and liquid phases. The model developed enabled the estimation of polyunsaturated fatty acids (PUFA), eicosapentaenoic acid and docosahexaenoic acids (EPA and DHA) contents in the liquid phase. Solutions of sardine oil in hexane were crystallized at several temperatures (−55, −65, −75 and −85 °C) and times (1–24 h). The transient variation of liquid phase mass at a given temperature was modeled employing two parameters: the equilibrium mass of the phase (m eq , g) and the overall mass transfer coefficient (K G·A , h −1 ). The results showed that the highest PUFA concentrates (>80%) were produced at −85 °C and 24 h. The model proposed is a useful tool for estimating the composition and total mass of winterized oils (r 2 > 0.83). [ABSTRACT FROM AUTHOR]

Several works have reported that haematite has non-linear initial susceptibility at room temperature, like pyrrhotite or titanomagnetite, but there is no explanation for the observed behaviours yet. This study sets out to determine which physical property (grain size, foreign cations content and domain walls displacements) controls the initial susceptibility. The performed measurements include microprobe analysis to determine magnetic phases different to haematite; initial susceptibility (300 K); hysteresis loops, SIRM and backfield curves at 77 and 300K to calculate magnetic parameters and minor loops at 77 K, to analyse initial susceptibility and magnetization behaviours below Morin transition. The magnetic moment study at low temperature is completed with measurements of zero field cooled--field cooled and AC susceptibility in a range from 5 to 300 K. The minor loops show that the non-linearity of initial susceptibility is closely related to Barkhausen jumps. Because of initial magnetic susceptibility is controlled by domain structure it is difficult to establish a mathematical model to separate magnetic subfabrics in haematite-bearing rocks. [ABSTRACT FROM AUTHOR]

A novel heterometallic cluster, Dy12Na6, has been prepared and characterized. It represents an unprecedented high-nuclearity alkali-metal-Ln cluster with a cage-like shape. In situ generated ligands participated in the formation of the heterometallic cluster. Magnetic measurements suggest that Dy12Na6 shows slow magnetic relaxation at low temperature. [ABSTRACT FROM AUTHOR]

A2M3O12 materials (A = Al, Sc, Fe, In, Ga, Y; M = Mo, W) were synthesized using the non-hydrolytic sol-gel process. In contrast to previous studies, in which amorphous materials were recovered that required heating to 500-700 °C to induce crystallization, several compounds could be crystallized in a temperature range compatible with low temperature processing of devices and composites. Under certain reaction conditions, crystalline Sc2Mo3O12, Fe2Mo3O12, and In2Mo3O12 were obtained at temperatures as low as 230 °C. This may allow use of these materials for in-situ composite formation, which could result in new practical applications. [ABSTRACT FROM AUTHOR]

Photoelectrical response in CuInS2–ZnIn2S4alloys single crystals was analysed in the low temperature region from 30 K up to 100 K. The molar ratio of ZnIn2S4in the alloys was varied in the range 0 mol%−16 mol%. The crystals with up to 12 mol% were the single-crystalline, meanwhile those with 16 mol% were the two phase ones. We have analysed spectral distribution of their photocurrent at different temperatures and the following relaxation towards the stationary values. The photo-induced photoconductivity phenomena were identified. Moreover the long-lasting relaxations with characteristic times exceeding 1.5×103 sec were observed at lowest temperatures. They used to shorten exponentially with increasing temperature showing thermally activated behaviour. The main parameters of the photoconductivity kinetics and their temperature dependencies were determined. The observed behaviour was explained by the slow multicenter recombination due to the combined effect of different trapping and recombination centers. The effects of both – “fast” and “slow” recombination centers were taken into account. [ABSTRACT FROM AUTHOR]

A novel Zr 1- x Fe x V 2- x Mo x O 7 (0 ≤ x ≤ 0.9) material is developed and the effect substitutions of Fe 3+ /Mo 6+ for Zr 4+ /V 5+ in ZrV 2 O 7 on the thermal expansion property are investigated. For the smaller x value ( x ≤ 0.5), their crystal structures remain cubic. The one of x = 0.5 is much higher than recent reports about uni-substitution of P 5+ for V 5+ and dual-substitution of Cu 2+ /P 5+ for Zr 4+ /V 5+ . For a substitution more than 0.5, crystal lattice appears distorted and 3 × 3 × 3 superstructure disappears gradually. For the substitution of x = 0.9, low thermal expansion is obtained from 140 to 700 K, which holds great potential applications in low temperature field. The mechanism of low thermal expansion of Zr 1- x Fe x V 2- x Mo x O 7 (0 ≤ x ≤ 0.9) is discussed around the distortion of crystal structure due to the substitutions of Fe 3+ /Mo 6+ for Zr 4+ /V 5+ in ZrV 2 O 7 . [ABSTRACT FROM AUTHOR]

Divalent Ni2+ ion and tetravalent Ti4+ ion equiatomic co-substituted two trivalent Fe3+ ions of M-type barium ferrite in the form of Ba(NiTi)xFe12-2xO19 with x = 1.0, 1.1, 1.2, 1.3. The samples were prepared using solid state reaction route and added 2.5 wt% Bi2O3 to lower sintering temperature. The samples were sintered at 925℃ and 950℃ for 6 h. As the Ni–Ti molar content changed from 1.0 to 1.3, all XRD patterns showed the single phase of the M-type barium ferrite without other intermediate phase. The microstructures were analyzed with scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The saturation magnetization Ms (49.74–29.58 emu/g) and the coercivity Hc (426.44–329.63 Oe) decreased with increasing Ni–Ti composition x and indicated that a decrease of magnetic moment and anisotropy was achieved by substitution of Ni–Ti. These properties attribute to Ni and Ti occupancies at different sites in the barium ferrite crystalline structure. [ABSTRACT FROM AUTHOR]

We present the susceptibility and neutron diffraction data on multiferroic Ni 3− x Co x V 2 O 8 with x =0.1 and 0.5. The temperature dependence of the susceptibility indicates that the magnetic order–disorder transition occurs at T HTI =8.5 K in both samples. Below T HTI , the high-temperature incommensurate magnetic structure is realized, which undergoes a transition to the low-temperature incommensurate phase when the sample is cooled. The temperature evolution of the propagation vector k for x =0.1 is very weak, which confirms previous studies showing that substitution of 3.5% Ni ions by Co ions suppresses the explicit temperature dependence of k that is observed in the parent compound. On the other hand, we found that the vector k for x =0.5 exhibits a definite temperature dependence, which differs from the case of the undoped sample ( x =0). [ABSTRACT FROM AUTHOR]

B 2 O 3 –Bi 2 O 3 –SiO 2 –ZnO glass modified Li 2 MgTi 3 O 8 (BBSZ-LMT) ceramics were fabricated via a solid–state reaction route. Pure phases and dense crystal morphology were obtained. Experimental results indicated that the BBSZ glass can not only lower the sintering temperature of the LMT ceramic to 950 °C, but also promote its densification and grain growth, which was beneficial for the enhanced microwave dielectric performance. Among all the BBSZ modified LMT samples, the 2 wt.% of BBSZ doped LMT ceramic (marked as LB3 in this article) possessed good microwave dielectric properties: ε r = 27.1, Q × f = 16,000 GHz (7.95 GHz), τ f =(−)1.3 ppm/ ° C. It is suggested that the BBSZ glass is an effective additive for LMT ceramic as a suitable candidate for LTCC applications in microwave devices. [ABSTRACT FROM AUTHOR]