Enhancing thermoelectric properties of Sb2Te3 flexible thin film through microstructure control and crystal preferential orientation engineering

A thermoelectric thin-film device consisting of n-type Bi2Te3 and p-type Sb2Te3 thin-film legs was prepared on a glass substrate by using co-evaporation and annealing process. The Seebeck coefficient and the power factor of the co-evaporated Bi2Te3 film were 130μV/K and 0.7 © 1014W/K2·m, respectively, and became substantially improved to 1160μV/K and 16 © 1014W/K2·m by annealing at 400°C for 20min. While the Seebeck coefficient of the co-evaporated Sb2Te3 thin film was 72 μV/K, it increased significantly to 165­142μV/K by annealing at 200­400°C for 20min. A maximum power factor of 25 © 1014W/K2·m was achieved for the co-evaporated Sb2Te3 film by annealing at 400°C for 20min. A thermopile sensor consisting of 10 pairs of n-type Bi2Te3 and p-type Sb2Te3 thin-film legs exhibited a sensitivity of 2.7mV/K. [doi:10.2320/matertrans.M2013010]

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Thermoelectric Characteristics of n-Type Bi2Te3 and p-Type Sb2Te3 Thin Films Prepared by Co-Evaporation and Annealing for Thermopile Sensor Applications

Enhanced thermoelectric properties of Sb2Te3 and Bi2Te3 films for flexible thermal sensors

The chemical bond is one of the most powerful, yet much debated concepts in chemistry, explaining property trends in solids. Recently, a novel type of chemical bonding was identified in several higher chalcogenides, characterized by a unique property portfolio, unconventional bond breaking, and sharing of about one electron between adjacent atoms. This metavalent bond is a fundamental type of bonding in solids, besides covalent, ionic, and metallic bonding, raising the pertinent question as to whether there is a well-defined transition between metavalent and covalent bonds. Here, three different pseudo-binary lines, namely, GeTe1-x Sex , Sb2 Te3(1-x) Se3x , and Bi2-2x Sb2x Se3 , are studied, and a sudden change in several properties, including optical absorption e2 (ω), optical dielectric constant e∞ , Born effective charge Z*, electrical conductivity, as well as bond breaking behavior for a critical Se or Sb concentration, is evidenced. These findings provide a blueprint to experimentally explore the influence of metavalent bonding on attractive properties of phase-change materials and thermoelectrics. Particularly important is its impact on optical properties, which can be tailored by the amount of electrons shared between adjacent atoms. This correlation can be used to design optoelectronic materials and to explore systematic changes in chemical bonding with stoichiometry and atomic arrangement.

Metavalent Bonding in Crystalline Solids: How Does It Collapse?

Layered Sb2Te3 films were grown by a MOCVD process on Al2O3(0001) substrates at 400 °C by use of i-Pr3Sb and Et2Te2 and characterized by SEM, AFM, XRD, EDX and Auger spectroscopy. The electrical sheet resistivity was measured in the range of 4 to 400 K, showing a monotonic increase with increasing temperature. The valence band structure probed by angle-resolved photoemission shows the detailed dispersions of the bulk valence band and the topological surface state of a quality no less than for optimized bulk single crystals. The surface state dispersion gives a Dirac point roughly 30 meV above the Fermi level leading to hole doping and the presence of bulk valence states at the Fermi energy.

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Deposition of topological insulator Sb2Te3 films by an MOCVD process

Antimony telluride (Sb2Te3) thin films were deposited on silicon substrates at room temperature (300 K) by radio frequency magnetron sputtering method. The effects of annealing in N2 atmosphere on their thermoelectric properties were investigated. The microstructure and composition of these films were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The electrical transport properties of the thin films, in terms of electrical conductivity and Seebeck coefficient were determined at room temperature. The carrier concentration and mobility were calculated from the Hall coefficient measurement. Both of the Seebeck coefficient and Hall coefficient measurement showed that the prepared Sb2Te3 thin films were p-type semiconductor materials. By optimizing the annealing temperature, the power factor achieved a maximum value of 18.02 μW cm−1 K−2 when the annealing temperature was increased to 523 K for 6 h with a maximum electrical conductivity (1.17 × 103 S/cm) and moderate Seebeck coefficient (123.9 μV/K).

Effects of annealing on thermoelectric properties of Sb2Te3 thin films prepared by radio frequency magnetron sputtering

Bi0.5Sb1.5Te3.0 thin films were deposited on silicon substrates at room temperature by co-sputtering and the effects of annealing temperatures on structure and thermoelectric properties were investigated. The composition, crystallinity, and microstructure of these thin films were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, and scanning electron microscopy. The crystalline quality of the thin films was enhanced with a rising annealing temperature. When annealed at 573 K, the layered structure of the Bi0.5Sb1.5Te3.0 thin films with a preferred orientation along the (00l) plane was formed. However, excessive high annealing temperature caused the thin films to become porous due to the separation of substantial Sb-rich precipitates. The electrical transport properties of the thin films, in terms of electrical conductivity and Seebeck coefficient were determined at room temperature. The carrier concentration and mobility were calculated from the Hall coefficient measurement. By optimizing the annealing temperature and time to 573 K for 6 h, the thermoelectric power factor was enhanced to 22.54 μW/(cm K2) at its maximum with a moderate electrical conductivity of 6.21 × 102 S/cm and a maximum Seebeck coefficient of 190.6 μV/K.

Bo Fang

Papers

Effects of annealing on thermoelectric properties of Sb2Te3 thin films prepared by radio frequency magnetron sputtering

Influence of annealing on the structural and electrical transport properties of Bi0.5Sb1.5Te3.0 thin films deposited by co-sputtering