eV For Temperatures Research Articles

DFT study of Ag-X (X = Pd, Pt, Ag) decorated (8,0) single wall carbon nanotube for spintronic applications

The main purpose of the present article is an investigation of the electronic and magnetic properties of (8,0) single-wall carbon nanotube (CNT80) decorated with a diatomic configuration of Ag and X (X = Pd, Pt, and Ag). Density functional theory and the Grimme-D2 approach in spin polarization mode are employed. It is concluded that Ag and X are adsorbed on CNT80 in the dimer form rather than singly atomic adsorption. The spin-distinct electronic band structure and the densities of states are also calculated. The calculations show that Ag-Pd/CNT80 is a bipolar semiconductor with an energy gap of 0.27 eV for spin-up, 0.47 eV for spin-down, and 0.15 eV for spin-flip electrons. Ag-Pt/CNT80 is an anti-ferromagnetic p-type indirect semiconductor with a gap of 0.187 eV for temperatures below 188 K. After 188 K up to around 330 K, this structure converts to an indirect bipolar semiconductor, with an energy gap of 0.31 eV (0.37 eV) for the spin-up (down) channel. Adsorption of Ag dimer onto CNT80 leads to the p-type nonmagnetic semiconductor. As an application of the proposed materials, the absorption of CO as a polar molecule on the Ag-Pd/CNT80 structure is also investigated, and a proposed structure as a spintronic CO sensor is introduced.

Evidence for multiple liquid–liquid phase transitions in carbon, and the Friedel ordering of its liquid state

Carbon, the fourth most abundant element in the universe, forms a metallic fluid with transient covalent bonds on melting. Its liquid–liquid phase transitions, intensely sought using simulations, had been elusive. Here, we use density functional theory (DFT) simulations with up to 108 atoms using molecular dynamics, as well as one-atom DFT as implemented in the neutral pseudo-atom method where multi-atom effects are treated by ion–ion correlation functionals. Both methods use electron–electron exchange correlation functionals for electron many-body effects. Here, we show using both methods that liquid carbon displays multiple liquid–liquid transitions linked to changes in coordination number in the density range 3–6 g/cm3 when a coordination number of 12 is reached. The transitions disappear by 4 eV in temperature. The calculated pressures and transition densities are shown to be sensitive to the exchange-correlation functionals used. Significantly, we find that a simple metallic model yields the structure factors and thermodynamics with quantitative accuracy, without invoking any covalent-bonding features. The ion–ion structure factor for these densities and temperatures is found to have a subpeak tied to twice the Fermi wavevector, constraining the fluid in momentum space. The dominant Friedel oscillations forming the pair interactions correlate the ions and drive the multiple liquid–liquid phase transitions. Our results suggest that liquid carbon typifies a class of fluids whose structure is ordered by the long-ranged Friedel oscillations in the pair-potentials. These results are critical to terrestrial and astrophysical studies, inertial fusion using carbon drivers, refined shock experiments, and in seeking new carbon-based materials.

Work function performance of a C12A7 electride surface exposed to low pressure low temperature hydrogen plasmas

The calcium aluminate electride [Ca24Al28O64]4+(e−)4 (C12A7:e−) is chemically and thermally stable in ambient atmosphere, offers strong electron donating capabilities and exhibits an intrinsic work function of 2.4 eV. Thus, it is an attractive material for electron emitter and low work function applications. For an implementation in negative hydrogen ion sources, where the electride could serve as a converter surface for the H− production, compatibility with moderate vacuum conditions and exposure to low pressure low temperature hydrogen plasmas must be ensured. Hence, the stability and work function performance of a polycrystalline C12A7:e− sample are investigated under ion source relevant vacuum (∼10−6 mbar) and plasma conditions (electron temperature ∼2 eV, electron density ∼1016m−3). The work function is measured via the photoelectric effect, showing that long-term hydrogen plasma exposure results in a steady-state surface work function of 2.75±0.10 eV. Since the electride is very sensitive to surface contaminations, an increase of the surface work function occurs as soon as the plasma is switched off. Vacuum heat treatment of the degraded C12A7:e− surface after plasma activation leads to a work function minimum of 2.9 eV for temperatures in the range of 670–770 K. Exceeding a temperature of ∼770 K leads to an increase of the C12A7:e− surface work function. The sample is stable during long-term hydrogen plasma exposure (up to 10 h total plasma-on time tested) and no plasma-induced erosion is observed.

Unexpected late-time temperature increase observed in the two neutron star crust-cooling sources XTE J1701−462 and EXO 0748−676

Transient low-mass X-ray binaries (LMXBs) that host neutron stars (NSs) provide excellent laboratories for probing the dense matter physics present in NS crusts. During accretion outbursts in LMXBs, exothermic reactions may heat the NS crust, disrupting the crust-core equilibrium. When the outburst ceases, the crust cools to restore thermal equilibrium with the core. Monitoring this cooling evolution allows us to probe the dense matter physics in the crust. Properties of the deeper crustal layers can be probed at later times after the end of the outburst. We report on the unexpected late-time temperature evolution (≳2000 days after the end of their outbursts) of two NSs in LMXBs, XTE J1701−462 and EXO 0748−676. Although both these sources exhibited very different outbursts (in terms of duration and the average accretion rate), they exhibit an unusually steep decay of ∼7 eV in the observed effective temperature (occurring in a time span of ∼700 days) around ∼2000 days after the end of their outbursts. Furthermore, they both showed an even more unexpected rise of ∼3 eV in temperature (over a time period of ∼500–2000 days) after this steep decay. This rise was significant at the 2.4σ and 8.5σ level for XTE J1701−462 and EXO 0748−676, respectively. The physical explanation for such behaviour is unknown and cannot be straightforwardly be explained within the cooling hypothesis. In addition, this observed evolution cannot be well explained by low-level accretion either without invoking many assumptions. We investigate the potential pathways in the theoretical heating and cooling models that could reproduce this unusual behaviour, which so far has been observed in two crust-cooling sources. Such a temperature increase has not been observed in the other NS crust-cooling sources at similarly late times, although it cannot be excluded that this might be a result of the inadequate sampling obtained at such late times.

Tabular electrical conductivity for aluminium

AbstractA new Sesame‐type table for the electrical conductivity of aluminium is described. The table is based on density functional theory calculations and ranges from 10−3 to 1 times solid density (2.7 g/cm3), and from 10−2 to 103 eV in temperature. The table is compared with other those of simulations and to experiments and is generally in good agreement. The high‐temperature, classical limit of the conductivity is recovered for the highest temperatures and lowest densities. The table is critically evaluated, and directions for improvements are discussed.

Temperature dependence of the dielectric function of thin film CuI in the spectral range (0.6–8.3) eV

We determined the dielectric function of CuI by means of spectroscopic ellipsometry in the spectral range from 0.6 eV up to 8.3 eV for temperatures from 10 K to 300 K. Features observed in the dielectric function are attributed to electronic transitions in the Brillouin zone. The observed spin-orbit splitting of the top valence band of 630 meV at the Γ-point and 330 meV at the L-point are in good agreement with theoretical band structure calculations. From the temperature evolution of the critical point energies, we deduced the electron-phonon coupling constants as well as the typical phonon energies. The electron-phonon coupling for the lowest transitions at the Γ-point is found to be smaller than for high energy transitions at other symmetry points in the Brillouin zone.

Temperature controlled properties of sub-micron thin SnS films

Tin sulphide (SnS) thin films deposited by thermal evaporation on glass substrates are studied for different substrate temperatures. The increase in substrate temperature results in the increase of the crystallite size and change in orientation of the films. The crystal structure of the films is that of SnS only and for temperatures ≤300 °C the films are of random orientation, whereas for higher temperatures the films become (040) oriented. The variation of Sn/S composition was accompanied by a reduction in optical energy bandgap from 1.47 to 1.31 eV as the substrate temperature increases. The Urbach energy was found stable at 0.169 ± 0.002 eV for temperature up to 350 °C. Photoluminescence emission was observed only for films exhibiting stoichiometric properties and shows that a precise control of the film composition is critical to fabricate devices while an increase in grain size will be essential to achieve high efficiency.

Analytic determination of the dielectric function of InSb at energies from 0.74 to 6.42 eV at temperatures from 31 to 675 K

Dielectric functions as analytic functions of temperature are useful for nondestructive in-situ monitoring of material deposition and for device design. We present an analytic expression that accurately represents the dielectric function ɛ = ɛ 1 + iɛ 2 of InSb at energies from 0.74 to 6.42 eV for temperatures from 31 to 675 K. The original e spectra were obtained by using rotating-compensator spectroscopic ellipsometry. We used the parametric model (PM), which can accommodate the asymmetric nature of critical-point features. The InSb data are successfully reconstructed with nine PM components and yield e as a continuous function of both energy and temperature within the limits given above. Our results should be useful in a number of contexts, including device design and in-situ monitoring of deposition. A representative deposition example is discussed.

Reflectance anisotropy spectroscopy of magnetite (110) surfaces

Reflectance anisotropy spectroscopy (RAS) has been used to measure the optical anisotropies of bulk and thin-film Fe3O4(110) surfaces. The spectra indicate that small shifts in energy of the optical transitions, associated with anisotropic strain or electric field gradients caused by the (110) surface termination or a native oxide layer, are responsible for the strong signal observed. The RAS response was then measured as a function of temperature. A distinct change in the RAS line-shape amplitude was observed in the spectral range from 0.8 to 1.6 eV for temperatures below the Verwey transition of the crystal. Finally, thin-film magnetite was grown by molecular beam epitaxy on MgO(110) substrates. Changes in the RAS spectra were found for different film thickness, suggesting that RAS can be used to monitor the growth of magnetite (110) films in situ. The thickness dependence of the RAS is discussed in terms of various models for the origin of the RAS signal.

Dielectric relaxation studies on two-dimensional nanocomposites of NiS and Na-4 mica

Na-4 mica template has been used to grow NiS nanosheets within the nanochannels with thickness ~0.6 nm. DC and ac electrical properties of the nanocomposite in a pellet-form have been measured over temperature range 313–473 K at frequencies from 102 to 106 Hz. The dc resistivity variation as a function of temperature has been explained as arising due to a parallel combination of NiS nanosheets and Na-4 mica grains. The activation energies of conduction have been found to be 0.23 and 0.45 eV in temperature ranges 323–363 K and 363–424 K, respectively. The frequency exponent s obtained from ac data has a value 0.7 which signifies a three-dimensional movement of the charge carriers involved. The dielectric modulus has been analyzed by two phase laminar conductor model proposed by Isard. The activation energies of dc resistivity and relaxation time are in reasonable agreement with each other in the different temperature ranges measured.

Parametric model dielectric functions of InAs for temperatures from 22 to 675 K

Dielectric functions as continuous functions of temperature are useful for nondestructive in-situ monitoring of deposition and device design. Here, we present an analytic expression that accurately represents the dielectric function ɛ = ɛ1 + iɛ2 of InAs from 0.74 to 6.54 eV for temperatures from 22 to 675 K. We use the parametric model, which is known to accurately portray ɛ without unphysical assumptions. The parameters are obtained from ɛ spectra obtained on an InAs substrate by using spectroscopic ellipsometry. The dielectric function was successfully parameterized by using seven Gaussian-broadened polynomials.

Parameterization of the dielectric function of InP from 1.19 to 6.57 eV for temperatures from 25 to 700 K

We present an analytic expression that accurately represents the dielectric function ɛ = ɛ1 + iɛ2 of InP from 1.19 to 6.57 eV for temperatures from 25 to 700 K. The original data were obtained on a InP substrate by spectroscopic ellipsometry. The analytic representation is based on the parametric model, which is known to accurately portray ɛ without unphysical assumptions. The ɛ data are successfully reconstructed by eight Gaussian-broadened polynomials and a pole and can be used to determine ɛ as a continuous function of energy and temperature within the limits given above. Our results should be useful in a number of contexts, including device design and in situ monitoring of deposition. A representative deposition example is discussed.

Influence of solution rate and substrate temperature on the properties of lead iodide films deposited by spray pyrolysis

Polycrystalline lead iodide (PbI2) thin films have been deposited by spray pyrolysis method using N,N-dimethylformamide (DMF) as solvent as a function of several deposition parameters. DMF is used as an alternative to water due to the larger solubility limit of PbI2 in this solvent. In this work, the solution rate during the deposition time of 3 h was varied in the range of 0.11 cm3/min up to 0.30 cm3/min. A growth rate varying from 19 A s−1 up to 47 A s−1 was obtained as a function of solution rate. Dark current as a function of temperature for the final films reveals that for larger solution rates smaller values of electrical resistivity is obtained. For a solution rate of 0.30 cm3/min, an electrical transport activation energy (E a) of about 0.65 eV was measured for the whole temperature range. On the other hand, for the sample deposited with a solution rate of 0.11 cm3/min, two main transport mechanisms can be observed with an activation energy of about 1.23 eV for temperatures above 50 °C. The effect of substrate temperature is also discussed. Samples were deposited in the temperature range of 170 °C up to 250 °C with a fixed solution rate of 0.16 cm3/min. In addition, the films were exposed to X-ray irradiation in the mammography diagnosis region, using a molybdenum (Mo) anode and a peak tube potential between 26 and 36 kV (equivalent photon energies between 10 keV and 15 keV).

Characterization of InP Based SAGCM Avalanche Photodetector for Single Photon Fiber Optic Communications

This paper presents fabrication and characterization of InP-based separate absorp- tion, grading, charge, and InP/InAlAs hetro-multiplication (SAGCM) single photon avalanche photo-detectors (SPADs) for application of single photon flber optic communications. The dark current (ID) of SPAD at 90% of the breakdown voltage (VBR) was 37.8pA and 18.8nA at 200K and 300K, respectively. Under i40 - C and gate repetition frequency of 10kHz with pulse width of 2ns, the performance of dark count probability Pdc = 0:02, single-photon detection e-ciency ·det = 11:5%, noise equivalent power NEP = 5£10 i14 W/(Hz) 1=2 , a factor of quantum bit-error rate of Pdc=·det = 0:16 were simultaneously achieved. In addition, both the dark current and the dark count exhibited activation energy of 0.24eV in temperature below 240K which shown the dominant generation sources were band-to-band tunneling and fleld-enhanced band-traps-band tunneling.

Study of the Au/In Reaction for Transient Liquid-Phase Bonding and 3D Chip Stacking

The latest three-dimensional (3D) chip-stacking technology requires the repeated stacking of additional layers without remelting the joints that have been formed at lower levels of the stack. This can be achieved by transient liquid-phase (TLP) bonding whereby intermetallic joints can be formed at a lower temperature and withstand subsequent higher-temperature processes. In order to develop a robust low-temperature Au/In TLP bonding process during which all solder is transformed into intermetallic compounds, we studied the Au/In reaction at different temperatures. It was shown that the formation kinetics of intermetallic compounds is diffusion controlled, and that the activation energy of Au/In reaction is temperature dependent, being 0.46 eV and 0.23 eV for temperatures above and below 150°C, respectively. Moreover, a thin Ti layer between Au and In was found to be an effective diffusion barrier at low temperature, while it did not inhibit joint formation at elevated temperatures during flip-chip bonding. This allowed us to control the intermetallic formation during the distinct stages of the TLP bonding process. In addition, a minimal indium thickness of 0.5 μm is required in order to enable TLP bonding. Finally, Au/In TLP joints of ∅40 μm to 60 μm were successfully fabricated at 180°C with very small solder volume (1 μm thickness).

STUDY OF COPPER DIFFUSION IN LOW-k THIN FILM USING SIMS

The aim of this paper is to study Cu diffusion in polymethylsiloxane (LKD-5109) low-k dielectric material manufactured by JSR Micro with respect to applied thermal energy acting alone. Previous study on low-k dielectric thin film uses a combination of electrical and thermal stress to study Cu diffusion producing a combined activation energy. In this paper, a secondary-ion mass spectrometry (SIMS) was used to determine copper diffusion into LKD-5109 thin film on samples baked/annealed at different temperatures ranging from 373K to 573K in forming gas (7% H 2/93% N 2). The results showed that the thermal activation energy (Ea) of Cu thermal diffusion is approximately 0.14eV for baking/annealing temperature ranging from 373K to 523K. The Ea will increase to greater than 0.58eV for temperature above 523K with Cu oxidation. The increase in Ea suggests a transport mechanism due to Cu oxidation where oxidized Cu is a source of copper ions that diffused through the low-k dielectric film.

Dielectric relaxation of BaTiO 3 (BTO)–CaCu 3Ti 4O 12 (CCTO) composite screen-printed thick films at low temperatures

In this work, we report electrical measurements of CaCu 3Ti 4O 12 (CCTO) and (BaTiO 3–barium titanate, BTO) thick films. The dielectric constant ( K) measurements shows that the BTO thick film present a higher K compared to CCTO compound, in the range of frequencies under study. However, for the composite film (CCTO50 and CCTO50T films), one has an unexpected result; the dielectric constant is higher for all the frequencies under study. The BTO–CCTO composite films do not obey the empirical mixing rule. These electric properties were also studied in the temperature range of 80–300 K. For the CCTO film, two relaxation processes were detected. The calculated activation energy was around 0.51 eV for temperatures above 200 K. One second relaxation process was observed on cooling below 200 K with activation energy around 0.061 eV. For the composite film CCTO50T, both relaxation processes are still present. Therefore, these measurements confirm the potential use of such materials for small high dielectric planar devices. These films are also attractive for capacitor applications and certainly for microelectronics, microwave devices (cell mobile phones, for example), where the miniaturization of the devices is crucial.

Detailed diagnostics for a hot bromine plasma by the openM-shell opacity

The experimental transmission spectrum of a hot bromine plasma [J. E. Bailey, J. Quant. Spectrosc. Radiat. Transf. 81, 31 (2003)] has been simulated by using a detailed level accounting model (DLA). With assumption of the local thermodynamic equilibrium, the major absorption lines of the experimental spectrum are well reproduced by the present DLA calculation, and the details of the absorption line shapes are used to determine the temperature of the plasma. In contrast to the results of two former statistical models, where the temperature was determined via a global fitting to the experimental data, the present DLA diagnoses the plasma temperature by the line ratios of different charge states in the 2p-->3d transition groups resulting in a temperature of 37 eV . It is shown that a change of 1 eV in temperature could cause perceptible changes in the simulated spectrum. It is also shown that the 2 p1/2 -->3 d3/2 absorptions have been overestimated by the statistical models.

Low Resistivity p[sup +] Polycrystalline Silicon Deposition at Low Temperatures with SiH[sub 4]/BCl[sub 3

The deposition of p + polycrystalline silicon films on SiO 2 substrates by SiH 4 /BCl 3 gases has been characterized. Films were deposited at temperatures as low as 460°C with an as-deposited resistivity of 3560 ′ 130 μΩ cm with good step coverage in oxide trenches. The extracted activation energy for silicon deposition was 0.6 eV for temperatures between 490 and 580°C and boron concentration of 2.0 ′ 0.4 X 10 2 1 /cm 3 , compared with 0.2 eV for p + silicon deposition by SiH 4 /B 2 H 6 for similar conditions. Silicon films deposited by SiH 4 /BCl 3 are polycrystalline with low resistivities as-deposited at 460°C, whereas films deposited by SiH 4 /B 2 H 6 are amorphous at deposition temperatures <520°C.

Snow as a foam of ice: plasticity, fracture and the brittle-to-ductile transition

Abstract At strain rates lower than 10−4 s−1. snow deforms plastically and fractures in a ductile manner; at higher strain rates it is brittle. The brittle-to-ductile transition has an activation energy of 0.6 ± 0.1 eV. Plasticity preceding fracture is characterized by an activation energy of 0.6 ± 0.05 eV for temperatures below –6°C. and about 2.7 ± 0.4eV above. The basic deformation mechanism of snow. an ice foam, is power-law creep of ice. As in silicon, the activation energy of the brittle-to-ductile transition is the lowest of the activation energies of all deformation processes available, but in ice these are the same, 0.6eV, for dislocation glide diffusion and sublimation.