Absorption and Transmission Power Coefficients for Millimeter Waves in a Weakly Ionised Vegetation Fire

A vegetation fire plume is a weakly ionised gaseous medium. Electrons in the plume are mainly due to thermal ionisation of incumbent alkali impurities. The medium is highly collisional with free electron - neutral particle been the dominant particle interaction mechanism. Signal strength of an incident millimetre wave (MM-Wave) may be significantly attenuated in the plume depending on the extent of ionisation. A numerical experiment was set to investigate signal power loss of a MM-Wave incident on a simulated weakly ionised fire plume with flame maximum (seat) temperature ranging from 1000–1150 K. The simulated fire plume had alkali impurities (potassium) content of 1.0% per unit volume. MM-Wave frequency range investigated in the experiment is from 30–60 GHz. The simulation has application in the prediction of MM-Wave propagation in a crown forest fire and may also be applied in remote sensing studies of forest fire environments. Simulated attenuation per unit path length for the MM-Wave frequencies ranged from 0.06–24.00 dBm^?1. Phase change per unit path length was simulated to range from 2.97–306.17°m^?1 while transmission power coefficients ranged from maximum of 0.9996 for a fire plume at 1000 K to a minimum value of 0.8265 for a plume at a temperature of 1150 K over a plume depth of 1.20 m. Absorption power coefficient ranged from a minimum value of 0.0004 to maximum value of 0.1585 at a seat temperature of 1150 K over the plume depth.     

Terahertz Frequency-Domain Spectroscopy of Low-Pressure Acetonitrile Gas by a Photomixing Terahertz Synthesizer Referenced to Dual Optical Frequency Combs

A terahertz (THz) frequency synthesizer based on photomixing of two near-infrared lasers with a sub-THz to THz frequency offset is a powerful tool for spectroscopy of polar gas molecules due to its broad spectral coverage; however, its frequency accuracy and resolution are relatively low. To tune the output frequency continuously and widely while maintaining its traceability to a frequency standard, we developed a photomixing THz synthesizer phase-locked to dual optical frequency combs (OFCs). While the phase-locking to dual OFCs ensured continuous tuning within a spectral range of 120 GHz, in addition to the traceability to the frequency standard, use of a broadband uni-traveling carrier photodiode for photomixing enabled the generation of CW-THz radiation within a frequency range from 0.2 to 1.5 THz. We demonstrated THz frequency-domain spectroscopy of gas-phase acetonitrile CH₃CN and its isotope CH₃ ¹³CN in the frequency range of 0.600–0.720 THz using this THz synthesizer. Their rotational transitions were assigned with a frequency accuracy of 8.42?×?10^?8 and a frequency resolution of 520 kHz. Furthermore, the concentration of the CH₃CN gas at 20 Pa was determined to be (5.41?±?0.05)?×?10¹⁴ molecules/cm³ by curve fitting analysis of the measured absorbance spectrum, and the mixture ratio of the mixed CH₃CN/CH₃ ¹³CN gas was determined to be 1:2.26 with a gas concentration of 10¹⁴–10¹⁵ molecules/cm³. The developed THz synthesizer is highly promising for high-precision THz-FDS of low-pressure molecular gases and will enable the qualitative and quantitative analyses of multiple gases.     

DLTS Analysis and Interface Engineering of Solution Route Fabricated Zirconia Based MIS Devices Using Plasma Treatment

In this work, we have fabricated low-temperature sol–gel spin-coated and oxygen (O₂) plasma treated ZrO₂ thin film-based metal–insulator–semiconductor devices. To understand the impact of plasma treatment on the Si/ZrO₂ interface, deep level transient spectroscopy measurements were performed. It is reported that the interface state density (D _it) comes down to 7.1 × 10¹⁰ eV^?1 cm^?2 from 4 × 10¹¹ eV^?1 cm^?2, after plasma treatment. The reduction in D _it is around five times and can be attributed to the passivation of oxygen vacancies near the Si/ZrO₂ interface, as they try to relocate near the interface. The energy level position (E _T) of interfacial traps is estimated to be 0.36 eV below the conduction band edge. The untreated ZrO₂ film displayed poor leakage behavior due to the presence of several traps within the film and at the interface; O₂ plasma treated films show improved leakage current density as they have been reduced from 5.4 × 10^?8 A/cm² to 1.98 × 10^?9 A/cm² for gate injection mode and 6.4 × 10^?8 A/cm² to 6.3 × 10^?10 A/cm² for substrate injection mode at 1 V. Hence, we suggest that plasma treatment might be useful in future device fabrication technology.     

Far-infrared cyclotron resonance study of neutral impurity scattering in GaAs

Far-infrared laser cyclotron resonance with the help of photoexcitation enables us to separate the electron-neutral donor and electron-neutral acceptor scattering rates in GaAs. Allowing for the complication due to the coexistence of donors and acceptors, inaccuracy due to unknown contribution of phonon scatterings etc., one finds that the electron-neutral donor scattering cross-section is 2.9×10^?11 cm² at 4.2 K, that is 23 times as large as the electron-acceptor scattering cross-section.     

Thermoelectric Properties of p-Type Mg2Si0.25Sn0.75 Doped with Sodium Acetate and Metallic Sodium

We have investigated the thermoelectric properties of p-type Na-doped Mg₂ Si_0.25Sn_0.75 solid solutions prepared by liquid–solid reaction and hot-pressing methods. Na was introduced into Mg₂Si_0.25Sn_0.75 by using either sodium acetate (CH₃COONa) or metallic sodium (2 N). The samples doped with sodium acetate consisted of phases with antifluorite structure and a small amount of MgO as revealed by x-ray diffraction, whereas the sample doped with metallic sodium contained the Sn, MgO, and Mg₂SiSn phases. The hole concentrations of Mg_1.975Na_0.025Si_0.25Sn_0.75 doped by sodium acetate and metallic sodium were 1.84 × 10²⁵ m^?3 and 1.22 × 10²⁵ m^?3, respectively, resulting in resistivities of 4.96 × 10^?5 Ω m (sodium acetate) and 1.09 × 10^?5 Ω m (metallic sodium). The Seebeck coefficients were 198 μV K^?1 (sodium acetate) and 241 μV K^?1 (metallic sodium). The figures of merit for Mg_1.975Na_0.025Si_0.25Sn_0.75 were 0.40 × 10^?3 K^?1 (sodium acetate) and 0.25 × 10^?3 K^?1 (metallic sodium) at 400 K. Thus, sodium acetate is a suitable Na dopant for Mg₂Si_1?x Sn _x .     

Interaction of microwaves with atmospheric pressure plasmas

In this paper, the interaction of microwaves with a plasma, generated at atmospheric pressure, is studied. The refractive index, attenuation index, skin depth, attenuation coefficient, phase coefficient, and reflectivity are investigated as functions of the plasma number density, the wave frequency and type of polarization, and the grazing angle. It is found that two frequency regimes characterize these type of plasmas. The first is a range where the phase velocity and attenuation of the wave both increase with frequency. The second is a frequency range in which the phase velocity and attenuation of the wave remain constant. It is also found that to have a shallow skin depth, the plasma number density has to be in the 10¹³ cm^?3 range. The reflectivity is found to be an increasing function of the number density. In horizontal polarization, the reflectivity is a decreasing function of the grazing angle. But in vertical polarization and for grazing angle less than 20°, the reflectivity has a maximum at a frequency $f = f_s = \frac{{2\pi f_{pe}^2 }}{\nu }$ , where f_pe is the electron plasma frequency and v is the collision frequency.     

Effects of Rapid Thermal Annealing on Electrical Transport in Heavily Doped ZnO Thin Films Deposited at Different Substrate Temperatures

In this work, heavily doped ZnO thin films with carrier concentrations of 1.7 × 10²⁰–1.1 × 10²¹ cm^?3 were prepared on glass substrates using direct current magnetron sputtering combined with rapid thermal annealing (RTA). The effects of RTA on the electrical transport properties of the thin films were investigated. Results showed that the resistivities of the thin films deposited at low temperatures were markedly improved due to the increased mobilities and/or carrier concentrations. Temperature-dependent Hall measurements and theoretical calculations suggested that the influence of grain boundary scattering was negligible for all the samples and the mobility was mainly determined by ionized impurity scattering. The influence of crystallographic defects on the mobility could be effectively reduced via RTA when the carrier concentration was above 4.0 × 10²⁰ cm^?3, resulting in a mobility and resistivity close to the ionized impurity scattering theoretical estimation. The highest mobility of 46 cm² V^?1 s^?1 at the resistivity of 2.8 × 10^?4 Ω cm and the lowest resistivity of 2.6 × 10^?4 Ω cm were achieved for the RTA-treated 1 wt.% Al-doped ZnO and 5 wt.% Ga-doped ZnO thin films, respectively.     

Thermal Conductivity Variation with Temperature for Lead-Free Ternary Eutectic Solders

The variations of the thermal conductivity with temperature for the lead-free ternary eutectic solders Bi-42.73 wt.%Sn-1.03 wt.%Ag (Bi-Sn-Ag), Sn-3.5 wt.%Ag-0.9 wt.%Cu (Sn-Ag-Cu), Sn-6 wt.%Sb-5 wt.%Ag (Sn-Sb-Ag), Sn-42.8 wt.%Bi-0.04 wt.%Cu (Sn-Bi-Cu), and In-48.4 wt.%Sn-2.31 wt.%Ag (In-Sn-Ag) were measured using a linear heat flow apparatus. It was observed that the thermal conductivities of solid phases for the Bi-Sn-Ag, Sn-Ag-Cu, Sn-Sb-Ag, Sn-Bi-Cu, and In-Sn-Ag solders decrease linearly with increasing temperature. The thermal conductivities of the Bi-Sn-Ag, Sn-Ag-Cu, Sn-Sb-Ag, Sn-Bi-Cu, and In-Sn-Ag solders at their melting temperature were obtained as 17.89 ± 1.6 W/K-m, 49.89 ± 4.5 W/K-m, 41.96 ± 3.8 W/K-m, 20.03 ± 1.8 W/K-m, and 70.21 ± 6.3 W/K-m, respectively. The thermal temperature coefficients for the Bi-Sn-Ag, Sn-Ag-Cu, Sn-Sb-Ag, Sn-Bi-Cu, and In-Sn-Ag solders were also determined to be ?2.894 × 10^?3 K^?1, ?0.907 × 10^?3 K^?1, ?1.246 × 10^?3 K^?1, ?2.638 × 10^?3 K^?1, and ?1.250 × 10^?3 K^?1, respectively, from plots of thermal conductivity versus temperature.     

Frequency-Dependent Low Cycle Fatigue of Sn1Ag0.1Cu(In/Ni) Solder Joints Subjected to High-Frequency Loading

The low-cycle-fatigue characteristics of solder joints, formed by reflowing Sn98.8/Ag1.0/Cu0.1/In0.05/Ni0.02 solder over electroless nickel immersion gold-plated copper pads, were investigated by dynamic cyclic bending of printed circuit boards (PCBs). The PCB strain amplitudes were varied from 1.2 × 10^?3 to 2.4 × 10^?3 and the flexural frequencies ranged from 30 Hz to 150 Hz, to simulate drop impact-induced PCB resonant frequencies. A trend of drastically decreasing fatigue life with cyclic frequency was observed, in contrast with previous reports indicating the reverse; this is attributed to the different failure mechanisms activated. A systematic procedure involving optimization followed by transformation was used to condense the strain–frequency–life data into a master curve expressed in strain–life space.     

A Thermally Conductive Composite with a Silica Gel Matrix and Carbon-Encapsulated Copper Nanoparticles as Filler

Core–shell-structured nanocapsules with a copper core encapsulated in a carbon shell (Cu-C) were synthesized by a direct-current arc-discharge method. Morphological and microstructural characterization showed that the Cu-C consisted of a nanosized Cu core and carbon shell, with the carbon shells containing 6 to 15 ordered graphitic layers and amorphous carbon that effectively shield the metallic Cu core from oxidation. A thermally conductive composite was successfully fabricated using a silica gel matrix incorporated with Cu-C filler. The Cu-C nanoparticles were homogeneously dispersed in the silica gel. The effects of Cu-C on the thermal conductivity, electrical resistivity, and coefficient of thermal expansion (CTE) of the composite were investigated. For composites with 6.16 vol.%, 11.04 vol.%, 16.70 vol.%, and 23.34 vol.% Cu-C content, the thermal conductivity at 50°C was 0.32 W/(m K) to 0.77 W/(m K), the electrical resistivity was 1.98 × 10⁹, 3.48 × 10⁷, 302, and 1 Ω m, respectively, while the CTE at 200°C was 3.79 × 10^?4 K^?1 to 3.44 × 10^?4 K^?1. The results reveal that the ordered graphitic shells in the Cu-C increased both the thermal and electrical conduction, but decreased the CTE by preventing the Cu cores from expanding.     

Carrier Lifetimes of Iodine-Doped CdMgTe/CdSeTe Double Heterostructures Grown by Molecular Beam Epitaxy

Iodine-doped CdMgTe/CdSeTe double heterostructures (DHs) have been grown by molecular beam epitaxy and studied using time-resolved photoluminescence (PL), focusing on absorber layer thickness of 2 μm. The n-type free carrier concentration was varied to ～7 × 10¹⁵ cm^?3, 8.4 × 10¹⁶ cm^?3, and 8.4 × 10¹⁷ cm^?3 using iodine as dopant in DHs. Optical injection at 1 × 10¹⁰ photons/pulse/cm² to 3 × 10¹¹ photons/pulse/cm², corresponding to initial injection of photocarriers up to ～8 × 10¹⁵ cm^?3, was applied to examine the effects of excess carrier concentration on the PL lifetimes. Iodine-doped DHs exhibited an initial rapid decay followed by a slower decay at free carrier concentration of 7 × 10¹⁵ cm^?3 and 8.4 × 10¹⁶ cm^?3. The optical injection dependence of the carrier lifetimes for DHs was interpreted based on the Shockley–Read–Hall model. The observed decrease in lifetime with increasing n is consistent with growing importance of radiative recombination.     

The Synthesis and Characterization of Cerium Carbonate Hydroxide Nanorods as an Anode for Lithium-Ion Batteries

Nanorods cerium carbonate hydroxide, CeCO₃OH, was synthesized through a low-temperature reaction route. The data of x-ray diffraction and scanning electron microscopy revealed that the as-prepared samples were CeCO₃OH nanorods. The diameters of the nanorods were in the range of 50–100 nm, and the lengths were around 300–500 nm. As an anode of a lithium ion battery, the charge–discharge capacity, cyclability and lithium-ion diffusion kinetics of CeCO₃OH nanorods were investigated. The calculated lithium ion diffusion coefficient was 1.36 × 10^?19 cm² s^?1. The initial discharge capacity was about 621.6 mA h g^?1 at 0.2 mA cm^?2 in 0.05–2.5 V. After 100 cycles, the discharge capacity stabilized at about 362 mA h g^?1 and the Coulombic efficiency was nearly 98%, indicating the potential application in anodes of lithium-ion batteries.     

Characterization of Strain Due to Nitrogen Doping Concentration Variations in Heavy Doped 4H-SiC

Highly doped 4H-SiC will show a significant lattice parameter difference with respect to the undoped material. We have applied the recently developed monochromatic contour mapping technique for 4H-SiC crystals to a 4H-SiC wafer crystal characterized by nitrogen doping concentration variation across the whole sample surface using a synchrotron monochromatic x-ray beam. Strain maps of 0008 and ? 2203 planes were derived by deconvoluting the lattice parameter variations from the lattice tilt. Analysis reveals markedly different strain values within and out of the basal plane indicating the strain induced by nitrogen doping is anisotropic in the 4H-SiC hexagonal crystal structure. The highest strain calculated along growth direction [0001] and along [1-100] on the closed packed basal plane is up to ? 4 × 10^?4 and ? 2.7 × 10^?3, respectively. Using an anisotropic elasticity model by separating the whole bulk crystal into numerous identical rectangular prism units, the measured strain was related to the doping concentration and the calculated highest nitrogen level inside wafer crystal was determined to be 1.5 × 10²⁰ cm^?3. This is in agreement with observation of double Shockley stacking faults in the highly doped region that are predicted to nucleate at nitrogen levels above 2 × 10¹⁹ cm^?3.     

Electrical Conductivity of V2O5–TeO2–Sb Glasses at Low Temperatures

Semiconducting glasses of the type 40TeO₂–(60 ? x) V₂O₅–xSb were prepared by rapid melt quenching and their dc electrical conductivity was measured in the temperature range 180–296 K. For these glassy samples, the dc electrical conductivity ranged from 2.26 × 10^?7  S cm^?1 to 1.11 × 10^?5 S cm^?1 at 296 K, indicating the conductivity is enhanced by increasing the V₂O₅ content. These experimental results could be explained on the basis of different mechanisms (based on polaron-hopping theory) in the different temperature regions. At temperatures above Θ _D/2 (where Θ _D is the Debye temperature), the non-adiabatic small polaron hopping (NASPH) model is consistent with the data, whereas at temperatures below Θ _D/2, a T ^?1/4 dependence of the conductivity indicative of the variable range hopping (VRH) mechanism is dominant. For all these glasses crossover from SPH to VRH conduction was observed at a characteristic temperature T _R ≤ Θ _D/2. In this study, the hopping carrier density and carrier mobility were determined at different temperatures. N (E _F), the density of states at (or near) the Fermi level, was also determined from the Mott variables; the results were dependent on V₂O₅ content.     

Dielectric Measurements of CVD Diamonds at Millimeter Wavelength Using a Fabry-Perot Open Resonator

Precise dielectric property measurements at a millimeter wave frequency band are attractive. A Fabry-Perot open resonator consisting of hemispherical and plane mirrors, coupling holes is designed by the use of analytic theories and a numerical simulation code. HFSS. Dielectric constant measurements on CVD diamonds are performed by a frequency variation method. Measurements show that permittivity and loss tangent range from 5.59 to 6.46, and from 1.1 × 10^?3, to 5.3 × 10^?2. respectively, in the frequency range of 95–100 GHz depending on sample preparation of the CVD diamonds.     

Thermoelectric Properties of Al-Doped ZnO Thin Films

We have prepared 2 % Al-doped ZnO (AZO) thin films on SrTiO₃ substrates by a pulsed laser deposition technique at various deposition temperatures (T _dep = 300–600 °C). The thermoelectric properties of AZO thin films were studied in a low temperature range (300–600 K). Thin film deposited at 300 °C is fully c-axis-oriented and presents electrical conductivity 310 S/cm with Seebeck coefficient ?65 μV/K and power factor 0.13 × 10^?3 Wm^?1 K^?2 at 300 K. The performance of thin films increases with temperature. For instance, the power factor is enhanced up to 0.55 × 10^?3 Wm^?1 K^?2 at 600 K, surpassing the best AZO film previously reported in the literature.     

Effects of Al/Sb Double Doping on the Thermoelectric Properties of Mg2Si0.75Sn0.25

Al/Sb double-doped Mg₂Si_0.75Sn_0.25 materials were prepared by liquid–solid reaction synthesis and the hot-pressing technique. The effects of Al/Sb double doping on the thermoelectric properties were investigated at temperatures between room temperature and 900 K, and the resistivity and Hall coefficient were investigated at 80 K to 900 K. Al/Sb double-doped samples were found to be n-type semiconductors in the investigated temperature range. The absolute Seebeck coefficient (α), resistivity (ρ), and thermal conductivity (κ) for Al/Sb double-doped samples at room temperature were in the ranges of 152.5 μV K^?1 to 109.2 μV K^?1, 2.92 × 10^?5 Ω m to 1.29 × 10^?5 Ω m, and 2.50 W K^?1 m^?1 to 2.86 W K^?1 m^?1, respectively. The absolute values of α increased with increasing temperature up to a maximum, and decreased thereafter. This could be attributed to mixed carrier conduction in the intrinsic region. κ decreased linearly with increasing temperature to a minimum near the intrinsic region, then increased rapidly because of bipolar components. The highest ZT value measured was 0.94 at 850 K for Mg_1.9975Al_0.0025Si_0.75Sn_0.2425Sb_0.0075. Sb doping was effective for enhancement of ZT, because of a remarkable increase in the carrier concentration. However, Al doping was almost ineffective for enhancing ZT.     

Generation of High-Power Sub-THz Waves in Magnetized Turbulent Electron Beam Plasmas

Sub-THz radiation can be generated by conversion of plasma waves into electromagnetic (EM) radiation in a plasma with strong Langmuir (LT) turbulence produced via a two-stream instability of a high current relativistic electron beam (REB). Nonlinear plasmon-plasmon merging results in the generation of photons nearby the 2^nd harmonic of the plasma frequency 2ω _p (“2ω _p -process”). For plasma densities of 10¹⁴???10¹⁵?cm^?3, these frequencies are in the range of sub-THz waves at 370–570 GHz. The specific power density of sub-THz-wave emission from plasmas in the multi-mirror magnetic trap GOL-3 (at BINP) during injection of a 10-μs-REB with a current density of about 1 kA/cm² at plasma densities n _e ?≈?5?10¹⁴?cm^?3, electron temperatures T _e ?≈?1.5 keV and magnetic induction B?≈?4 T was measured to be approx. 1 kW/cm³ in the frequency band around 300 GHz. In the case of a weakly relativistic 100-μs-electron beam (90 keV) with 250 A/cm² the corresponding results are 700 W/cm³ around 90 GHz with an efficiency of 1–2 % at n _e ?≈?3?10¹³?cm^?3 (total power?≈?30 kW). Theoretical investigations show that at a density of n _e ?≈?3?10¹⁵?cm^?3 and a turbulence level of 5 % the generated sub-THz power can reach?≈?1 MW/cm³.     

Incorporation and Activation of Arsenic Dopant in Single-Crystal CdTe Grown on Si by Molecular Beam Epitaxy

We report the use of molecular beam epitaxy to achieve p-type doping of CdTe grown on Si(211) substrates, by use of an arsenic cracker and post-growth annealing. A high hole density in CdTe is crucial for high efficiency II–VI-based solar cells. We measured the density of As in single-crystal CdTe by secondary ion mass spectroscopy; this showed that high As incorporation is achieved at low growth temperatures. Progressively higher incorporation was observed during low-temperature growth, presumably because of degradation of crystal quality with incorporation of As at such defect sites as dislocations and defect complexes. After As activation annealing under Hg overpressure, hole concentrations were obtained from Hall measurements. The highest doping level was ～2.3 × 10¹⁶ cm^?3, and near-10¹⁶ cm^?3 doping was readily reproduced. The activation efficiency was ～50%, but further optimization of the growth and annealing conditions is likely to improve this value.     

Tunnel Junction with Autodoped AlGaAs on InP

We describe the low resistance of tunnel junction structures with a p ⁺-AlGaAs layer grown on an InP substrate using the autodoping technique. An Al_0.4Ga_0.6As layer showed a hole concentration of 2.4 × 10²⁰ cm^?3 without additional material sources. We demonstrated that the proposed tunnel junction structure with a p ⁺-Al_0.4Ga_0.6As/In_0.52Al_0.48As multiple-quantum-well layer on an InP substrate exhibited a low resistance of 2.5 × 10^?5 Ω cm², as estimated from reverse current–voltage characteristics, and a tunnel peak current density of 170 A/cm².