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.

Two-dimensional (2D) indium selenide (InSe) has been widely studied for applications in transistors and photodetectors, benefitting from its excellent optoelectronic properties. Among the three specific polytypes (γ-, ϵ- and β-phase) of InSe, only the crystal lattice of InSe in β-phase (β-InSe) belongs to a nonsymmetry point group of $D_{6h}^4$, which indicates a stronger anisotropic transport behavior and a potential in the polarized photodetection of β-InSe based optoelectronic devices. Therefore, we prepare the stable p-type 2D layered β-InSe via temperature gradient method. The anisotropic Raman, transport and photoresponse properties of β-InSe have been experimentally and theoretically proved. It shows that the β-InSe based device has a ratio of 3.76 for the maximum to minimum dark current and a high photocurrent anisotropic ratio of 0.70 at 1 V bias voltage, respectively. The appealing anisotropic properties demonstrated in this work clearly identify β-InSe as a competitive candidate for filter-free polarization sensitive photodetectors.

Lanthanum (La)-doped zinc oxide nanoparticles were synthesized with different La concentrations by employing a gel combustion method using poly(vinyl alcohol) (PVA). The as-synthesized photocatalysts were characterized using various techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), photoluminescence (PL) spectroscopy, and UV–visible absorption spectroscopy. The average size of ZnO nanoparticles decreased from 34.3 to 10.3 nm with increasing concentrations of La, and the band gap, as evaluated by linear fitting, decreased from 3.10 to 2.78 eV. Additionally, it was found that the photocatalytic activity of doped samples, as investigated by using methyl orange dye under visible lights, improved in response to the increase in La concentration. The decomposition of methyl orange reached 85.86% after 150 min in visible light using La0.1Zn0.9O as the photocatalyst.

ᅟWe report on the successful preparation of Bi-doped n-type polycrystalline SnSe by hot-press method. We observed anisotropic transport properties due to the (h00) preferred orientation of grains along the pressing direction. The electrical conductivity perpendicular to the pressing direction is higher than that parallel to the pressing direction, 12.85 and 6.46 S cm−1 at 773 K for SnSe:Bi 8% sample, respectively, while thermal conductivity perpendicular to the pressing direction is higher than that parallel to the pressing direction, 0.81 and 0.60 W m−1 K−1 at 773 K for SnSe:Bi 8% sample, respectively. We observed a bipolar conducting mechanism in our samples leading to n- to p-type transition, whose transition temperature increases with Bi concentration. Our work addressed a possibility to dope polycrystalline SnSe by a hot-pressing process, which may be applied to module applications.Highlights We have successfully achieved Bi-doped n-type polycrystalline SnSe by the hot-press method.We observed anisotropic transport properties due to the [h00] preferred orientation of grains along pressing direction.We observed a bipolar conducting mechanism in our samples leading to n- to p-type transition. Electronic supplementary materialThe online version of this article (10.1186/s11671-018-2500-y) contains supplementary material, which is available to authorized users.

We have realized a magnetic tensor gradiometer by interferometrically measuring the relative phase between two spatially separated Bose-Einstein condensates (BECs). We perform simultaneous Ramsey interferometry of the proximate 87 Rb spin-1 condensates in freefall and infer their relative Larmor phase -and thus the differential magnetic field strength -with a common-mode phase noise suppression exceeding 50 dB. By appropriately biasing the magnetic field and separating the BECs along orthogonal directions, we measure the magnetic field gradient tensor of ambient and applied magnetic fields with a nominal precision of 0.30 nT mm −1 and a sensor volume of 2 × 10 −5 mm 3 . We predict a spin-projection noise limited magnetic energy resolution of order ∼ 10 for typical Zeeman coherence times of trapped condensates with this scheme, even with the low measurement duty cycle of current BEC experiments.