Zhixin Ma,Yang Qi,Xiaoguo Bi,Xu-dong Liu,Xiaodong Li,Ji-guang Li,Xudong Sun
SrTiO3 has high thermoelectric properties and excellent high-temperature stability, which makes it a promising thermoelectric material for use in harsh environments. Hence, it has potential applications in power generation and sensors through direct conversion between heat and electricity. In this study, we investigated the crystal orientations on the crystal growth plane to seek the crystal orientation that is suitable for higher thermoelectric (TE) properties. The [510], [12 5 0] and [320] directions were selected which are on the (001) crystal plane and quarterly divide the angle between the [100] and [110] directions. Two common directions [100] and [110] were selected for comparison purposes. The SrTiO3 single crystals are annealed in carbon powders at 1573 K and 1673 K to form SrTiO3−δ. With the increase in annealing temperature, the electrical conductivity of SrTiO3−δ in the [510], [12 5 0] and [320] directions decreases, which is attributed to the decreasing carrier concentrations. This agrees well with the results calculated using the first-principles calculation. After annealing at 1573 K, the SrTiO3−δ single crystal exhibits the highest ZT value of 0.19 at 873 K in the [510] direction. However, the two common directions, [100] and [110], are not suitable for high thermoelectric properties. In particular, the SrTiO3−δ single crystal in the [12 5 0] direction can always exhibit higher PF and ZT values, regardless of the variation of the annealing temperature in carbon powders. The results of this study are imperative for the design and development of perovskite TE materials.
The elaborate interface interactions can be critical in determining the achievable functionality of a semiconductor heterojunction (SH), particularly when two-dimensional material is enclosed in the system and its thickness is at an atomic extreme. In this work, we have successfully constructed a SH model system composed of typical transition-metal chalcogenide (TMDs) and transition metal oxides (TMO) by directly growing molybdenum sulfide (MoS2) nanosheets on atomically flat strontium titanate (SrTiO3) single crystal substrates through a conventional chemical vapor deposition (CVD) synthetic method. Multiple measurements have demonstrated the uniform monolayer thickness and single crystallinity of the MoS2 nanosheets as well as the atomic flatness of the heterojunction surface, both characterizing an extremely high quality of the interface. Clear evidence have been obtained for the electron transfer from the MoS2 adlayer to the SrTiO3 substrate which varies against the interface conditions. More importantly, the photoluminescence of MoS2 is significantly tailored, which is correlated with both the cleanness of the interface and the crystal orientation of the SrTiO3 substrate. These results not only shed fresh lights on the structure–property relationship of the TMDs/TMO heterostructures but also manifest the importance of the ideal interface structure for a hybridized system.
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