Van Quang Nguyen

Achieving ZT=2.2 with Bi-doped n-type SnSe single crystals

Recently SnSe, a layered chalcogenide material, has attracted a great deal of attention for its excellent p-type thermoelectric property showing a remarkable ZT value of 2.6 at 923 K. For thermoelectric device applications, it is necessary to have n-type materials with comparable ZT value. Here, we report that n-type SnSe single crystals were successfully synthesized by substituting Bi at Sn sites. In addition, it was found that the carrier concentration increases with Bi content, which has a great influence on the thermoelectric properties of n-type SnSe single crystals. Indeed, we achieved the maximum ZT value of 2.2 along b axis at 733 K in the most highly doped n-type SnSe with a carrier density of −2.1 × 1019 cm−3 at 773 K.

New synthesis of MnSi2 thin film and its thermoelectric properties

The authors report the formation of a new manganese silicide phase, MnSi2, using an intermixing method that involves evaporating a manganese thin film on a silicon substrate at a high temperature of 600 °C. The crystal structure of MnSi2 is tetragonal with lattice constants of a = 5.518 A and c = 17.449 A, identical to that of Mn4Si7. Analysis of the film using high-angle annular dark-field imaging confirmed that the composition ratio of Mn and Si was 1:2. The electric resistivity and Seebeck coefficient of the film were 2.08 × 10−3 Ω cm and 107.84 μV/K at 410 K, respectively, which resulted in a maximum power factor of 5.60 × 10−4 W/K2m.

Magneto-transport and thermoelectric properties of epitaxial FeSb2 thin film on MgO substrate

We report magneto-transport and thermoelectric properties of FeSb2 thin film epitaxially grown on the MgO substrate using molecular beam epitaxy. The film exhibits compressive strain of 1.74% owing to large lattice mismatch, whose physical consequences are nontrivial. Magnetic phase has been changed from diamagnetic in bulk, as evidenced by anomalous Hall effect (AHE) and negative magneto-resistance (MR). The FeSb2 film is semiconducting without any metallic transition unlike the bulk counterpart. In particular, hysteresis in MR with distinct feature of AHE is evident with coercive field of 500 and 110 Oe for T = 20 and 50 K, respectively. Furthermore, from the Seebeck coefficients and temperature dependence of the resistivity, it is evident that the film is semiconducting with small band gap: 3.76 meV for T   40 K, respectively, where maximum thermoelectric power factor of 12 μV/cm·K at T = 50 K.

Magneto-transport and thermoelectric properties of MnP thin film on GaAs (100)

This study investigates the magneto-transport and thermoelectric properties of MnP thin films grown on GaAs (100) substrate using molecular beam epitaxy at 300 and 400°C. The MnP thin films exhibit ferromagnetic ordering, as evidenced by anomalous Hall effect and negative magneto-resistance. XRD patterns show orthorhombic structure of the thin film. Hysteresis loops are also observed which strongly suggest ferri-/ferro-magnetic ordering. Temperature dependent resistivities show metallic behavior.