Excellent photocatalytic and photoelectrochemical activities from 1D/2D FeSe2/SnSe heterojunction photocatalysts constructed by FeSe2 nanorods and SnSe nanosheets

In this work, FeSe₂ nanorods have been employed to be loaded on SnSe nanosheets to develop 1D/2D FeSe₂/SnSe heterojunction photocatalysts. These test results of XRD, SEM, HRTEM and XPS fully confirm the successful construction of FeSe₂/SnSe heterojunction. These results of photocatalytic and photoelectrochemical test further reveal that FeSe₂/SnSe heterojunction photocatalysts have excellent photocatalytic and photoelectrochemical activities. In comparison to the SnSe, the highest photocurrent density of the 1D/2D FeSe₂/SnSe heterojunction photocatalyst is 19.2 μA/cm², which has 123% promotion. Besides, the biggest degradation rates k of the 1D/2D FeSe₂/SnSe heterojunction photocatalyst is 0.00612 nearly 297% enhancement than the SnSe. Further analysis indicated that as for 1D/2D FeSe₂/SnSe heterojunction photocatalyst, its internal resistance was largely reduced and carrier separation efficiency was significantly improved with the recombination of FeSe₂. This work confirmed that FeSe₂/SnSe is an ideal composite system with great potential in photocatalysis.     

Co dopant drives surface smooth and improves power factor of evaporated SnSe films

Unstable nanosheet morphology of polycrystalline SnSe film becomes a limitation for its application in the field of waste heat recovery. This study dopes Co into the evaporated SnSe film to smooth the surface and to improve power factor. The results show that Co dopant makes the rough nanosheet change to surface densely packed structure. The dopant Co forms Co particles distributing around SnSe grain boundary, which suppress SnSe (011) plane growth and subsequent reduce nanosheet formation. In addition, Co dopant increases electric conductivity through increasing the carrier concentration, but the magnetism of Co particles decreases carrier mobility due to spin-charge coupling and also affects the Seebeck coefficient. The power factor thus is improved after doped Co. This study presents a method to fabricate polycrystalline SnSe film with smooth surface morphology and high power factor.     

Multipoint Defect Synergy Realizing the Excellent Thermoelectric Performance of n‐Type Polycrystalline SnSe via Re Doping

SnSe has attracted much attention due to the excellent thermoelectric (TE) properties of both p‐ and n‐type single crystals. However, the TE performance of polycrystalline SnSe is still low, especially in n‐type materials, because SnSe is an intrinsic p‐type semiconductor. In this work, a three‐step doping process is employed on polycrystalline SnSe to make it n‐type and enhance its TE properties. It is found that the Sn_0.97Re_0.03Se_0.93Cl_0.02 sample achieves a peak ZT value of ≈1.5 at 798 K, which is the highest ZT reported, to date, in n‐type polycrystalline SnSe. This is attributed to the synergistic effects of a series of point defects: $V_{\mathrm{Se}}^{\mathrm{..}},{\mathrm{Cl}}_{\mathrm{Se}}^{.},V_{\mathrm{Sn}}^{,,},{\mathrm{Re}}_{\mathrm{Sn}}^{\times },{\mathrm{Re}}_{}^0$. In those defects, the $V_{\mathrm{Se}}^{\mathrm{..}}$ compensates for the intrinsic Sn vacancies in SnSe, the ${\mathrm{Cl}}_{\mathrm{Se}}^{.}$ acts as a donor, the $V_{\mathrm{Sn}}^{,,}$acts as an acceptor, all of which contribute to optimizing the carrier concentration. Rhenium (Re) doping surprisingly plays dual‐roles, in that it both significantly enhances the electrical transport properties and largely reduces the thermal conductivity by introducing the point defects, ${\mathrm{Re}}_{\mathrm{Sn}}^{\times },{\mathrm{Re}}_{}^0$. The method paves the way for obtaining high‐performance TE properties in SnSe crystals using multipoint‐defect synergy via a step‐by‐step multielement doping methodology.     

Highly sensitive triethylamine sensor with ppb level detection limit based on SnSe nanofibers

To overcome the high-power consumption and poor selectivity of gas sensors and achieve ppb level low concentration gas sensing is an urgent need to widely deploy sensors to establish an air quality monitoring application network. In this paper, a fish-mesh SnSe nanofibers with diameter of 100 nm prepared by uniaxial electrospinning was introduced and its gas sensitivity was studied. The gas sensor based on SnSe nanofibers showed excellent selectivity and high sensitivity (31.07) for low concentration (10 ppm) triethylamine at low temperature (160 °C), and a low detection base limit (500 ppb). Therefore, fish-mesh SnSe nanofibers provide a new strategy for the preparation of high-performance triethylamine sensors.     

Crystal structure modulation of SnSe thermoelectric material by AgBiSe2 solid solution

Although low thermal conductivity and high band degeneracy bring promising thermoelectric performance to cubic SnSe, its preparation strategies remain elusive. Here, a series of Sn_1–2x(AgBi)_xSe samples are synthesized using the vacuum melting (1173 K) and spark plasma sintering (723 K) methods. Owing to the increased configurational entropy caused by AgBiSe₂ solid solution, the cubic structure is obtained when x exceeds 0.2. The optimized carrier concentration significantly enhances electrical conductivity (σ), and maximal σ of 350 Scm⁻¹ is obtained in Sn_0.5(AgBi)_0.25Se. Combined with the low lattice thermal conductivity caused by the small sound velocity and strong anharmonicity, the figure of merit of 0.08 is reached in Sn_0.6(AgBi)_0.2Se at 500 K. The mechanical performances are also improved, and a high Vicker hardness of 1.5 GPa is obtained in Sn_0.4(AgBi)_0.3Se. This work demonstrates the importance of the configurational entropy in phase regulation and provides insights into the design of new thermoelectrics.     

Achieving weak anisotropy in N-type I-doped SnSe polycrystalline thermoelectric materials

SnSe is a very strong anisotropic material; sometimes, strong anisotropy is unenviable for producing parts of thermoelectric (TE) devices. In order to study the efficient preparation of high-performance n-type polycrystalline SnSe with weak anisotropy, in this work, we combine mechanical alloying at 450 RPM for 10 h and spark plasma sintering at 773 K under 50 MPa pressure for the preparation of polycrystalline SnSe _0.95-xI_x (x = 0,0.01,0.02,0.03) samples, and investigate the TE properties. The prepared samples show very weak anisotropy. With iodine doping, increased carrier concentration is observed, in agreement with DFT calculations. A peak ZT ≈ 1.02 at 723 K is observed with I-doping of x = 0.02, which is about 225% higher than that of undoped sample with ZT ≈ 0.31 at 723 K in parallel direction, mainly attributed to the enhanced power factor and about 56% reduced thermal conductivity from 0.68 Wm^?1K^?1 to 0.30 Wm^?1K^?1. TE properties in both directions are not much different, and the ratios of electrical and thermal conductivities in both directions are very close to unity.     

Investigation of inter-diffusion in bilayer GeTe/SnSe phase change memory films

A metal-chalcogenide layer, SnSe, is inserted between the memory layer GeTe and the top electrode to form a phase change memory cell. The GeTe layer exhibits ovonic threshold switching at a threshold field of ~ 110 V/μm. For subsequent implementation into applications and reliability, material inter-diffusion and sublimation are examined in bilayer phase change films of GeTe/SnSe. Transmission electron microscopy and parallel electron energy loss spectroscopy analyses reveal Sn migration to the GeTe layer, which is responsible for lowering the rhombohedral to cubic structural transformation temperature in GeTe. Incongruent sublimation of SnSe and GeTe is observed at temperatures higher than 500 °C. Severe volatilization of Se results in the separation of a metallic Sn phase. The use of Al₂O₃ as a capping layer has been found to mitigate these effects.     

自供能Ag/SnSe纳米管红外探测器的制备和性能研究

采用光沉积法在SnSe纳米管表面沉积Ag纳米粒子,在室温下制备了Ag修饰的SnSe纳米管(Ag/SnSe),通过SEM、EDS、TEM和XRD等手段表征其表面形貌、元素组成和晶体结构。随后,将Ag/SnSe纳米管旋涂在FTO导电面作为工作电极并以Pt电极为对电极组装了Ag/SnSe纳米管红外探测器,使用830 nm的光作为红外模拟光源研究了红外探测性能。结果表明,Ag/SnSe纳米管的平均直径约为100~200 nm,Ag纳米颗粒负载在SnSe纳米管表面。与SnSe纳米管红外探测器相比,Ag修饰的SnSe纳米管红外探测器的最大光电流密度提高到120 nA/cm²,上升时间和下降时间分别缩短到0.109和0.086 s。同时,Ag修饰的SnSe纳米管红外探测器的稳定性较高,可循环使用。     

The effects of S-doping concentration on the photocatalytic performance of SnSe/S-GO nanocomposites

The effects of S-doped graphene oxide (S-GO) on the photocatalytic performance of SnSe nanostructures have been investigated. Different concentrations of S-doping as 2S-GO, 4S-GO, and 6S-GO (2, 4, and 6% in weight) have been synthesized. Characterization results indicated sulfur not only has successfully placed in the GO structure and a part of the GO sheet has been changed into reduced GO (rGO) by sulfur doping but also the surface morphology of the GO sheets has been changed from a smooth surface to fractured crack surfaces. The results showed that the increase of sulfur content caused the morphology of the SnSe nanostructures was changed from nanoparticles (NPs) into nanorods (NRs). The photocatalytic activity of the samples to degrade dyes under the visible-light irradiation conditions was carried out and it was observed an enhancement photocatalytic performance for the SnSe/2S-rGO nanocomposites in comparison to the other samples. More than 95% of dyes were degraded by the SnSe/2S-rGO nanocomposites for only 60 min. Brunauer–Emmett–Teller (BET) and electrical measurement results indicated the textural properties and conductivity of GO sheets were improved by sulfur doping. In addition, the photogenerated electron lifetime (τ_r) of the SnSe/rGO and SnSe/S-rGO nanocomposites has been measured by the Bode phase plot and it was observed a lifetime of τ_r = 71.1 and 31.7 μs for the SnSe/S-rGO and SnSe/rGO nanocomposites, respectively.