Thermal Conductivity of Indium–Graphene and Indium-Gallium–Graphene Composites

Samples of graphene composites with a matrix of indium or indium-gallium alloy were prepared in the form of foils using exfoliated graphene dispersions. The thermal conductivity of the composite samples with different thicknesses was determined using the three-omega method. Indium–graphene composite samples with a thickness of 430 μm exhibited a twofold increase in thermal conductivity, whereas indium-gallium–graphene composite samples with a thickness of 330 μm exhibited a threefold improvement in thermal conductivity over that of the matrix at 300 K. The effective medium approximation (EMA) was used to model the thermal conductivity of the composite samples. The graphene platelet size distribution was used to determine the average thermal conductivity of graphene in the composite samples. The interfacial thermal conductance between graphene and indium or indium-gallium alloy determined from EMA was not the limiting factor in the improvement of the thermal conductivity of the composite samples, although the increase in thermal conductivity was found to be slightly lower than predicted theoretically using acoustic and diffuse mismatch models. The smaller size of the graphene platelets obtained by exfoliation prior to dispersion in the matrix appears to be the limiting factor.     

Thermal Conductivity of InAs/GaSb Type?II Superlattice

The cross-plane thermal conductivity of a type?II InAs/GaSb superlattice (T2SL) is measured from 13?K to 300?K using the 3?? method. Thermal conductivity is reduced by up to two orders of magnitude relative to the GaSb bulk substrate. The low thermal conductivity of around 1?W/m?K to 8?W/m?K may serve as an advantage for thermoelectric applications at low temperatures, while presenting a challenge for T2SL interband cascade lasers and high-power photodiodes. We describe a power-law approximation to model nonlinearities in the thermal conductivity, resulting in increased or decreased peak temperature for negative or positive exponents, respectively.     

Thermal Expansion and Thermal Conductivity of (In2S3)x(AgIn5S8)1 – x Alloys

Semiconductors - The thermal expansion and thermal conductivity of In2S3 and AgIn5S8 single-crystal compounds and (In2S3)x(AgIn5S8)1 – x alloys grown by the Bridgman method are studied. It is...     

Thermal Conductivity in Bi1−x Sb x Solid Solutions

Bi_1?x Sb _x solid solutions have attracted much attention as promising low-temperature thermoelectric materials. Previously, we observed distinct extrema in the isotherms of the transport and mechanical properties of polycrystalline Bi_1?x Sb _x and attributed their presence to the transition from diluted to concentrated solid solutions and to the reconstruction of the energy band structure under increasing Sb concentration. The goal of the present work is a detailed study of the concentration dependences of the thermal conductivity λ for Bi_1?x Sb _x polycrystalline solid solutions (x = 0 to 0.09) in the temperature range of 170 K to 300 K. It is established that the λ(x) dependences exhibit a nonmonotonic behavior: in certain concentration ranges an anomalous increase in λ with increasing x is observed. It is shown that the concentration dependences of the thermoelectric figure of merit calculated on the basis of the measured λ values are also nonmonotonic. The obtained data represent additional evidence in favor of our assumptions stated earlier about a significant effect of electronic phase transitions observed in Bi_1?x Sb _x solid solutions on the concentration dependences of their thermoelectric properties. These results should be taken into account when developing new Bi_1?x Sb _x -based materials.     

Effect of Nonlinearity of the Phonon Spectrum on the Thermal Conductivity of Nanostructured Materials Based on Bi–Sb–Te

A theoretical investigation of the lattice thermal conductivity of nanostructured materials based on Bi–Sb–Te is presented. The calculations were based on relaxation time approximation and took into account both the real phonon spectra, obtained from first-principles by use of density functional theory, and the anisotropy of phonon relaxation time. Phonon relaxation time data were determined from experimental values of the lattice thermal conductivity. The decrease of the thermal conductivity caused by the nanostructure was compared with results from calculations based on the linear Debye approach. Estimation showed that phonon boundary scattering can lead to a 55% decrease of thermal conductivity for a grain size of ~20 nm in the Debye approximation. Taking the nonlinearity of the acoustic phonon spectrum into account leads to a 20% larger decrease of the thermal conductivity because of boundary scattering. The reason is that consideration of the real phonon spectrum increases the relative contribution to thermal conductivity of acoustic phonons with low frequencies that are scattered more strongly at nanograin boundaries. Similarly, estimation of lattice thermal conductivity reduction as a result of phonon scattering by nanoinclusions gave an 8% larger decrease when the real phonon spectrum was used rather than the linear Debye approximation. For such a substantial decrease of lattice thermal conductivity, the effect of the optical phonons was estimated; it was shown that optical phonons can reduce the change of thermal conductivity as a result of grain boundary scattering by no more than 10%. Finally, the minimum lattice thermal conductivity was estimated to be 0.07 W/m K because of acoustic modes (0.09 W/m K in the Debye approach) and 0.14 W/m K when the contribution of optical modes was also taken into consideration.     

Design and Analysis of Ring Resonator with Thermal Tuning

A type of waveguide ring resonator, based on Er^3＋/Yb^3＋ co-doped phosphate glass and using thermal-optical effect as tuning manner, is brought up. The ring resonator is composed of two straight waveguides and a ring waveguide with radius of 400 μm. Electrode is evaporated on the top of the waveguide to achieve thermal tuning. Firstly, the filtering scheme of the ring resonator is analyzed, then how parameters of the electrode influence the filtering characteristics is discussed.     

Frequency Dependent Capacitance and Conductance–Voltage Characteristics of Nitride GaAs Schottky Diode

Semiconductors - A nitride GaAs Schottky diode have been fabricated by nitridation of GaAs substrates with thickness 0.7 nm of GaN layer. The capacitance–voltage C(V) and...     

Thermal Characteristics of Optoelectronic Modules with DIP and BGA Package

In order to meet the electrical and thermal performance requirements of current high performance optoelectronics, two package types with dual-in-line package（DIP） and ball grid array（BGA） for optoelectronics are modeled and thermally simulated, their thermal characterizations are compared and discussed by using the temperature contours and the simulated heating characterization curves in free air and forced air ambient. The results show that BGA has superior inside and outside total performances, and has the promising future in the highly integrated optoelectronics.     

Effect of Chemical Doping and Ion Implantation on Conductivity of Poly （p-phenylene vinylene） Derivatives

The surface conductivity of poly [2-methoxy-5-(3 '-methyl)butoxy]-p-phenylene vinylene (PMOMBOPV) films doped with FeCl3 and H2 SO4 by chemical method and implanted by N ions was studied and the comparison of environmental stability of conductive behavior was also investigated. The energy and dose of N ions were in the rang 15～35 kev and 3. 8× 1015 ～9. 6× 1016 ions/cm2, respectively. The conductivity of PMOMBOPV film was enhanced remarkably with the increases of the energy and dose of N ions. For example, the conductivity of PMOMBOPV film was 3.2 × 10-2 S/cm when ion implantation was performed with an energy of 35 kev at a dose of 9. 6 × 1016 ions/cm2 , which was almost seven orders of magnitude higher than that of film unimplanted. The environmental stability of conductive behavior for ionimplanted film was much better than that of chemical doped films. Moreover, the conductive activation energy of ion-implanted films was measured to be about 0.17 eV.     

Thermal Conductivities of III-V Antimonides

Thermal parameters of various III-V antimonides,especially the quaternary lattice matched to GaSb or InAs substrates as well as some strained ternaries,have been investigated theoretically.Results show that at most composition region many ternary and quaternary antimonides exhibit rather lower thermal conductivity compared to related binaries,and the reason has been discussed.The thermal designing rule of the lasers and other power devices using those antimonides also has been discussed.     

Nerve-Fiber-Inspired Construction of 3D Graphene “Tracks” Supported by Wood Fibers for Multifunctional Biocomposite with Metal-Level Thermal Conductivity

Given the rapid developments in modern electronics, there is an urgent need for polymer composites with excellent heat-dissipating capabilities to address the cooling problem of these devices. However, designing a highly thermally conductive polymer composite that can outperform metals and ceramics while also exhibiting high processability and low cost remains a challenge. Herein, inspired by the fibrous pathway of human nervous system, natural wood fibers (WFs) are used as the template and coated with graphene nanoplates (GNPs) via a simple electrostatic self-assembly approach. Subsequent hot-pressing process yields “core-sheath” microstructured fibers, wherein the GNPs are compactly contacted face to face and arranged along the surfaces of the fibrous WF “cores”. This WF@G biocomposite consists of highly efficient 3D fibrous “tracks” for heat transmission, resulting in an extremely high thermal conductivity of 134 W (m K)⁻¹, which is at par with those of many metals. It also exhibits several other desirable properties and functionalities, including high mechanical strength and excellent flame resistance as well as remarkable electromagnetic shielding and Joule heating performances, which has significant potential for use as a functional thermal management material (TMM). Hence, this study describes a simple yet scalable manufacturing technique for the development of advanced metal-level biomass-based TMMs.     

Synthesis Method and Absorption Application of Nanocrystalline Alloy Flakes

The soft magnetic Fe-Si-B nanocrystalline/ amorphous flakes were fabricated by ball milling from the elemental powders and annealing the amorphous precursor, respectively. The microstructure, magnetic and microwave properties were evaluated by different synthesis methods. By computation, ball-milled Fe78Si13B9 flakes demonstrated potential appfication in absorption.     

Synthesis and characterization of sol-processed α-MnO2 nanostructures

Nanostructure of α-MnO₂ was prepared by air oxidation of manganese chloride (MnCl₂) via sol processing by adding N, N-Dimethylformamide (DMF) as surface active material. The obtained material was conventionally annealed at 400 °C for 2 h. The product was characterized by X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The chemical reaction involved in the synthesis of α-MnO₂ nanostructure was proposed and discussed. From XRD pattern, the purity and crystallinity of final product was observed. The synthesized α-MnO₂ nanostructure showed an average crystallite size of 17 nm.     

Electrical and Thermal Transport Properties of Ge1–xPbxCuySbyTeSe2y

Balancing the contradictory relationship between thermoelectric parameters, such as effective mass and carrier mobility, is a challenge to optimize thermoelectric performance. Herein, the exceptional thermoelectric performance is realized in GeTe through collaboratively optimizing the carrier and phonon transport via stepwise alloying Pb and CuSbSe₂. The formation energy of Ge vacancy is efficiently bolstered by alloying Pb, which reduces carrier density and carrier scattering to maintain superior carrier mobility in GeTe. Additionally, CuSbSe₂, acting as an n-type dopant, further modulates carrier density and validly equilibrates carrier mobility and effective mass. Accordingly, the promising power factor of 45 µW cm⁻¹ K⁻² is achieved at 723 K. Meanwhile, point defects are found to significantly suppress phonons transport to descend lattice thermal conductivity by Pb and CuSbSe₂ alloying, which barely impacts the carrier mobility. A combination with superior carrier mobility and lower lattice thermal conductivity, a maximum ZT of 2.2 is attained in Ge_0.925Pb_0.075Cu_0.005Sb_0.005TeSe_0.01, which corresponds to a 100% promotion compared with that of intrinsic GeTe. This study provides a new indicator for optimizing carrier and phonon transport properties by balancing interrelated thermoelectric parameters.     

Effect of Ultraviolet Radiation and Electric Field on the Conductivity of Structures Based on α- and ε-Ga2O3

Semiconductors - The effect of ultraviolet radiation and a strong electric field on the conductivity of structures based on two types of polymorphic gallium-oxide films is studied. Both types of...     

Studies on Dielectric Properties of Silicon Nitride at High Temperature

In this paper, the dielectric properties of silicon nitride are studied using the dielectric polarization theories. According to the developed dielectric models, the temperature dependence of dielectric constant and loss of silicon nitride is mainly analyzed. In addition, the impact of Li^＋, K^＋, Ca^2＋, Al^3＋ and Mg^2＋ doping on the dielectric properties of silicon nitride are also estimated.     

Graphene-Based Ultralight Compartmentalized Isotropic Foams with an Extremely Low Thermal Conductivity of 5.75 mW m−1 K−1

The importance of high-performance thermal insulation materials is rapidly emerging due to energy conservation and the management of temperature-sensitive device perspectives. Recent thermal insulation materials including complex structures have been developed either by reducing the structural connectivity to mitigate thermal transport through solid conduction or forming directionally aligned confined inner pores to suppress the internal gas convection. In this study, to create a highly efficient thermal insulating material that suppresses thermal transport in all directions, graphene-based anisotropic closed-cellular structures (CCS) are devised with a highly ordered assembly of hollow compartments with extremely thin walls (≈50 nm). This uniquely designed CCS made from microfluidically synthesized graphene solid bubbles exhibited a remarkably low thermal conductivity of 5.75 mW m⁻¹ K⁻¹ thanks to effective suppression of both solid conduction and gas conduction/convection. Therefore, the proposed strategy in this work offers a novel toolkit for implementing next-generation high-performance insulation materials.     

Electrical Conductivity of Parylene F at High Temperature

The electrical conductivity of both as-deposited and annealed poly(α,α,α′,α′-tetrafluoro-p-xylylene) (PA-F) films has been investigated up to 400°C. The static conductivity (σ _DC) values of PA-F measured between 200°C and 340°C appear to be ∼2.5 orders of magnitude lower for annealed films than for as-deposited ones. This change is attributed to a strong increase in the crystallinity of the material occurring above 340°C. After annealing at 400°C in N₂, the σ _DC value measured at 300°C, for instance, decreased from 3.8 × 10⁻¹² Ω⁻¹ cm⁻¹ to 7.5 × 10⁻¹⁵ Ω⁻¹ cm⁻¹. Physical interpretations of such an improvement are offered.     

Synthesis of metal oxide composite nanosheets and their pressure sensing properties

This study presents the synthesis of metal oxides composite nanosheets(oxides of cobalt, zinc and iron) and their pressure sensing properties. A transducer has been fabricated to directly measure the resistance–pressure and impedance–pressure relationships of pristine nanopowder. At the initial stage, a nanopowder sample of 10 mm diameter and 1 mm height was placed in the transducer and by applying pressure of up to 8.15 kN/m2;the DC resistance and the impedance are reduced by 44% on average. It can be explained by the densification of the samples and a decrease in porosity due to the effect of pressure. It was also observed that the DC resistance increases with time and saturated within 8 min. It is considered that this phenomenon is based on the effect of displacement currents of bound charges. The dependences of the impedance phase(θ) on frequency and pressure have also been investigated.     

Analysis and Design of a ΔΣ Modulator for Fractional-N Frequency Synthesis

提出了一种适用于分数分频锁相环频率综合器的全数字噪声整型 ΔΣ调制器电路结构新的设计方法,并将其最终实现. 采用了流水线技术和新的CST算法优化多位输入加法器结构，从而降低了整体的复杂度和功耗. 这种电路结构通过了Matlab的行为级仿真，ASIC全定制实现并流片，该结构也通过VHDL综合实现验证，最后给出的测试结果表明该电路具有良好的性能，可应用于单片千兆赫兹级低功耗CMOS频率综合器中.