Bismuth telluride (Bi 2 Te 3 )-based thermoelectric materials are well-known for their high figure-of-merit (zT value) in the low-temperature region. Stable joints in the module are essential for creating a reliable device for long-term applications. This study used electroless Co−P to prevent a severe interfacial reaction between the joints of solder and Bi 2 Te 3 . A thick and brittle SnTe intermetallic compound layer was successfully inhibited. The strength of the joints improved, and the fracture mode became more ductile; furthermore, there was no significant degradation of thermoelectric properties after depositing the Co−P layer after long-term aging. The result suggests that electroless Co−P could enhance the interfacial stability of the joints and be an effective diffusion barrier for Bi 2 Te 3 thermoelectric modules.

Properly selecting electrode materials for antimony telluride (Sb 2 Te 3 ) thermoelectric (TE) thin film enhances the power factor. This study analyzed the compositional variation and measured the TE properties of pristine antimony telluride (Sb 2 Te 3 ), Ni/Sb 2 Te 3 / Ni, and Cu/Sb 2 Te 3 /Cu thin films that were aged to simulate real applications. The rapid diffusion of Cu in the Cu/Sb 2 Te 3 /Cu film resulted in the massive growth of the CuTe intermetallic compound (IMC), which led to Te deficiency. Te deficiency causes the formation of antisite Sb Te ′ and reduces the power factor. Antisite Te Sb• increases the power factor because the growth of Sb 2 O 3 on the pristine Sb 2 Te 3 and Ni/Sb 2 Te 3 /Ni films, in which almost no Ni diffusion occurs, results in Sb deficiency. The formation of oxides and IMCs alters the stoichiometry of the films. The formation of the NiTe reaction layer at the interface becomes a self-barrier that inhibits Ni diffusion to the Sb 2 Te 3 film. Herein, a defect reaction is proposed to explain the effects of such changes on the TE properties and the relationship between the stoichiometry of the films and the concentrations of the antisites.

In order to confirm the superconductivity observed in hexagonal ϵ-NbN reported recently, we have deposited NbN film on (0001) 4H-SiC substrate, with good lattice match, intentionally to grow hexagonal NbN phase. The detailed structural analysis show that the deposited films are (111)-orientated δ-NbN phase with dense rotational (60°) twins. Double diffraction effect in selected area electron diffraction and Moiré fringes in high resolution transmission electron microscope images confirm the existence of rotational twins in nanometer scale. The growth of highly twined film results from no energy preference for the two rotational twins of (111)-orientated δ-NbN to bond with the Si-faced (0001) 4H-SiC substrate. These highly twined δ-NbN epitaxial films exhibit high normal state resistivity, lower T C, but good spatial uniformity of superconducting energy gap. No ϵ-NbN phase was observed in this study which is might due to a low growth temperature of thin film.

No abstract

No abstract

No abstract

For thin-film thermoelectric modules with electrodes deposited on the sides of the thermoelectric material, the diffusion of atoms from the electrode affects the module's performance. Long-term aging is crucial when the module is for practical applications. In this study, Bi 2 Te 3 thin films with a highly preferred orientation were fabricated by a co-sputtering deposition method. Cu was used as the electrode because of its high electrical conductivity; it migrates through the Bi 2 Te 3 film via surface and grain boundary diffusion. The diffusing Cu segregates at grain boundaries and forms a Cu 2−x Te intermetallic compound on the sample surface. Contact resistivity at the interface between the Cu electrode and Bi 2 Te 3 thin films substantially increases with aging time. Long-term aging unavoidably degrades the power factor (PF) of the pristine Bi 2 Te 3 since n-type Bi 2 Te 3 converts into p-type by the formation of antisite defects. The study shows that the diffusing Cu from the electrodes of the Cu/Bi 2 Te 3 /Cu module significantly mitigates the degradation of the PF after long-term aging.