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In this study, we present a fabrication process of thermoelectric (TE) power generator modules (TEGs) using the Ag sinter bonding technique for assembling the TE legs with their interconnecting bridges. As TE material, we use commercial half-Heusler (HH) compounds (p-type Hf0.5Zr0.5CoSn0.2Sb0.8 and n-type Hf0.6Zr0.4NiSn0.98Sb0.02), which offer high TE figures of merit in the medium-to-high temperature range. Magnetron-sputtered bilayers of Au and TiW are deposited on top of the TE legs as metallization and diffusion barriers, respectively. Stability of the sinter-bonded joints is investigated by application of external tensile stress and thermal stress by cyclic temperature change followed by an analysis of the fracture surfaces. As the main cause of failure, we reveal a mixed pattern of near-surface cracking in the HH compounds and adhesion fractures between the sinter layer and the thin-film metallizations. Fabricated two-leg and four-leg unicouple TEGs are operated at maximum temperature differences of 325 K and 400 K across the TE legs, respectively, and maximum hot-side temperatures of 375°C and 510°C, respectively. The resulting maximum power densities amount to 1.0 W cm−2 (two-leg) and 1.9 W cm−2 (four-leg), and for the TE figures of merit, we calculate 2.6 × 10−4 K−1 (two-leg) and 3.4 × 10−4 K−1 (four-leg). [ABSTRACT FROM AUTHOR]

This paper presents experimental results on the preparation and investigation of the carbon nanotubes–copper composite material. Carbon nanotubes (CNTs) were synthesized on silicon substrates by the chemical vapor deposition (CVD) method and then filled with copper by evaporation from a melting pot in a vacuum. Copper evenly covered both the surface of the entangled tubes and the free substrate surface between the tubes. To improve the adhesion of tubes and matrix material, a carbon substructure was grown on the surface of tubes by adding working gas plasma to the CNT synthesis area. It is proposed to use a copper coating as a diffusion barrier upon subsequent filling of the reinforcing CNT frame by a carbide-forming materials matrix with predetermined physico-mechanical and tribological properties. [ABSTRACT FROM AUTHOR]

Four specimen patterns with the microstructure of a microcopper wire are deposited on the Si-wafer substrate plus thermal oxide (SiO2) film as the top layer. Each pattern was prepared to have two kinds of specimens, including with and without ultrathin carbon film between the copper wire and the top layer (SiO2). The effect of carbon film on electrical properties is evaluated via the measurements of the I (current)–V (voltage) curve, sheet electrical resistance, current leakage, and its ratio and effective permittivity. A rapid thermal annealing (RTA) technique is provided as an economic and efficient method to grow the ultrathin carbon film rapidly as the interlayer. Appropriate choices of 900 °C and 3 min as the annealing temperature and time can produce ultrathin carbon film with nearly 100% coverage of the copper surface. The sheet resistance of specimen demonstrates the behavior exactly opposite to that of the carbon film coverage of wire surface. The combined effect of elevating the voltage and annealing temperature of the specimen with carbon film on the current leakage is much lower than that arising in the specimen without carbon film, so long as the carbon films operating at that temperature (between 350 and 500 °C) are still sustainable. The differences in current leakage and effective permittivity between these two kinds of specimen are significantly increased by raising the temperature. The intensity (IC) of copper diffusions into the SiO2 layer in the specimens with the carbon film demonstrates behavior similar to that of current leakage (CL). The IC and CL values for the temperatures ≦ 350 °C are much lower than those obtained at 500 °C. [ABSTRACT FROM AUTHOR]

The diffusion barrier property of Co-P film as a buffer layer between SiC-dispersed BiTe bulk material and In-48Sn solder was investigated. A Co-P film with thickness of ~6 µm was electroplated on SiC-dispersed BiTe substrate, joined with In-48Sn solder by a reflow process, and annealed at 100°C for up to 625 h. The formation and growth kinetics of intermetallic compounds (IMCs) at the interface between the In-48Sn and substrate were studied using transmission electron microscopy and scanning electron microscopy with energy-dispersive x-ray spectroscopy. The results showed that crystalline Co(In,Sn) formed as an irregular layer adjacent to the solder side at the solder/Co-P interface due to diffusion of Co towards the solder, and a small amount of amorphous CoPInSn appeared at the Co-P side because of diffusion of In and Sn into Co-P. The growth of Co(In,Sn) and CoPInSn during solid-state aging was slow, being controlled by interfacial reaction and diffusion, respectively. For comparison, In-48Sn/BiTe-SiC joints were prepared and the IMCs in the joints analyzed. Without a diffusion barrier, In penetrated rapidly into the substrate, which led to the formation of amorphous InBi phase in crystalline InTe matrix. These IMCs grew quickly with prolongation of the annealing time, and their growth was governed by volume diffusion of elements. The experimental data demonstrate that electroplated Co-P film is an effective diffusion barrier for use in BiTe-based thermoelectric modules. [ABSTRACT FROM AUTHOR]

U-Mo alloys are being developed as low enrichment monolithic fuel under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Diffusional interactions between the U-Mo fuel alloy and Al-alloy cladding within the monolithic fuel plate construct necessitate incorporation of a barrier layer. Fundamentally, a diffusion barrier candidate must have good thermal conductivity, high melting point, minimal metallurgical interaction, and good irradiation performance. Refractory metals, Zr, Mo, and Nb are considered based on their physical properties, and the diffusion behavior must be carefully examined first with U-Mo fuel alloy. Solid-to-solid U-10 wt.%Mo versus Mo, Zr, or Nb diffusion couples were assembled and annealed at 600, 700, 800, 900 and 1000 °C for various times. The interdiffusion microstructures and chemical composition were examined via scanning electron microscopy and electron probe microanalysis, respectively. For all three systems, the growth rate of interdiffusion zone were calculated at 1000, 900 and 800 °C under the assumption of parabolic growth, and calculated for lower temperature of 700, 600 and 500 °C according to Arrhenius relationship. The growth rate was determined to be about 10 times slower for Zr, 10 times slower for Mo and 10 times slower for Nb, than the growth rates reported for the interaction between the U-Mo fuel alloy and pure Al or Al-Si cladding alloys. Zr, however was selected as the barrier metal due to a concern for thermo-mechanical behavior of UMo/Nb interface observed from diffusion couples, and for ductile-to-brittle transition of Mo near room temperature. [ABSTRACT FROM AUTHOR]

Tungsten-titanium (WTi) thin films are known as potential adhesion promoters and diffusion barriers. The barrier efficiency of WTi thin films against indium (In) diffusion was experimentally studied by x-ray diffraction (XRD) measurements during in situ annealing. Specific multilayered samples were designed to estimate the diffusion barrier properties using the Ni/In system. These diffusion samples were made up of a 100-nm-thick WTi layer prepared by magnetron sputtering from an alloyed target (W:Ti ≈ 70:30 at.%), sandwiched between Ni and Au/In layers. WTi film microstructures were observed to depend on the working pressure. Diffusion barrier breakdown was monitored upon annealing by the formation of intermetallic compounds (IMC) (intermixing between Ni and In). Annealing was performed at temperatures of 573 K, 623 K, and 673 K (homologous temperatures $$T/T_{\rm m}^{\rm In} \simeq 1.34, 1.45$$ , and 1.57, respectively) and under primary vacuum. The diffusion coefficients of In in WTi were determined. The correlation between WTi film microstructure and diffusion barrier efficiency was established. Better diffusion barrier performance was obtained for WTi films with dense microstructure associated with a compressive residual stress state. Hence, tuning the sputtering conditions allows significant improvement of barrier performance against diffusion through a change of the film microstructure. [ABSTRACT FROM AUTHOR]

The suitability of P-doped g-C3N4 for sodium storage was assessed using density functional theory. The electronic structure of P-doped g-C3N4 was calculated and the results indicate that the presence of the P atom causes the band gap of g-C3N4 to narrow. Na adsorption on a P-g-C3N4 sheet was investigated. Projected density of states (PDOS) analysis revealed that pyridinic nitrogen atoms in g-C3N4 play the main role in Na adsorption. High binding energies were calculated for Na storage on g-C3N4, leading to a high voltage range (1–3 V) and a high Na diffusion barrier (2.3 eV). Doping the substrate with more P atoms resulted in lower voltages (below 2.2 V), easier Na diffusion (with a barrier of 1.2 eV), and therefore a material that was better suited than g-C3N4 for use in anodes. [ABSTRACT FROM AUTHOR]