SnSe2 Nanosheets for Subpicosecond Harmonic Mode‐Locked Pulse Generation

Tin diselenide (SnSe₂) nanosheets as novel 2D layered materials have excellent optical properties with many promising application prospects, such as photoelectric detectors, nonlinear optics, infrared photoelectric devices, and ultrafast photonics. Among them, ultrafast photonics has attracted much attention due to its enormous advantages; for instance, extremely fast pulse, strong peak power, and narrow bandwidth. In this work, SnSe₂ nanosheets are fabricated by using solvothermal treatment, and the characteristics of SnSe₂ are systemically investigated. In addition, the solution of SnSe₂ nanosheets is successfully prepared as a fiber‐based saturable absorber by utilizing the evanescent field effect, which can bear a high pump power. 31st‐order subpicosecond harmonic mode locking is generated in an Er‐doped fiber laser, corresponding to the maximum repetition rate of 257.3 MHz and pulse duration of 887 fs. The results show that SnSe₂ can be used as an excellent nonlinear photonic device in many fields, such as frequency comb, lasers, photodetectors, etc.     

Ag掺杂Cu2SnSe3致相反热电性能及其复合提升

热电材料可有效回收废热并将其转化为电能, 然而转换效率受复杂耦合热电参数的限制。高效热电材料需要具有优异的电传输和良好的隔热性能。具有类金刚石结构的Cu₂SnSe₃是一种潜在的中温区热电材料, 本研究通过在Sn位和Cu引入Ag离子, 分别获得了高电传输相Cu₂Sn_0.93Ag_0.07Se₃和低热传输相Cu_1.91Ag_0.09SnSe₃, 然后通过机械混合和烧结制备了Cu₂Sn_0.93Ag_0.07Se₃和Cu_1.91Ag_0.09SnSe₃两相复合的材料。利用两相材料的晶体结构相同和晶格常数匹配的特点, 在高温段有效地协同调控了Cu₂SnSe₃材料的电输运和热输运性能, 从而使材料的高温热电性能得到优化, 用有效介质理论很好地描述了高性能的两相复合材料的电和热传输行为。     

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.     

Doping engineering: Highly improving hydrogen evolution reaction performance of monolayer SnSe

By using the first-principles approach, we explore the hydrogen evolution reaction (HER) performance of SnSe monolayer. It is found that the SnSe monolayer with or without intrinsic defects is not good HER catalyst. By doping eighteen different elements at Sn or Se sites of the SnSe monolayer, we find that the elements P and In can effectively reduce the free energies of hydrogen (H) adsorption (ΔG) to −0.1 eV and 0.21 eV, much lower than 1.45 eV of perfect monolayer SnSe. This is attributed to great dispersion of electronic density of states of absorbed hydrogen atom having small interactions with doping elements. However, strong hybridizations between H and doping elements (K and Te) increase the ΔG values of doping systems (ΔG = 2.84 eV and ΔG = 1.77 eV).     

Ultrasonic spray pyrolysis deposition of SnSe and SnSe2 using a single spray solution

Thin films of SnSe and SnSe2 have been deposited using the ultrasonic spray pyrolysis(USP) technique.To the best of our knowledge this is the first report of the deposition of SnSe and SnSe2 thin films using a single spray solution.The use of a single spray solution for obtaining both a p-type material,SnSe,and an n-type material,SnSe2,simplifies the deposition technique.The SnSe2 thin films have a bandgap of 1.1 eV and the SnSe thin films have a band gap of 0.9 eV.The Hall measurements were used to determine the resistivity of the thin films.The SnSe2 thin films show a resistivity of 36.73 Ωcm and n-type conductivity while the SnSe thin films show a resistivity of 180 Ωcm and p-type conductivity.     

SnSe_2纳米片的制备及结构表征

用溶剂热法制备了SnSe2纳米片,用XRD、EDS、SEM等手段对SnSe2纳米片的结构进行了表征。结果表明,采用亚硒酸钠为硒源,以乙二醇为溶剂,乙二胺为辅助溶剂,在180℃反应3 h制得花瓣状的厚度约为30 nm的SnSe2纳米片。随着反应时间的延长,纳米片的厚度增加;而采用硒粉为硒源,在180℃反应5 h制得厚度达60 nm的SnSe2纳米片;反应温度对合成晶体的形貌有重要影响,在180℃反应有利于形成结晶良好的纳米片。     

花状SnSe0.5S0.5@N-C复合材料的制备及其在钠离子电池中的应用

为了设计具有高容量和循环稳定性的钠离子电池负极材料,合成了有序花状SnSe,在其表面进行氮碳掺杂,并进一步硫化,得到有序花状SnSe0.5S0.5@N-C复合材料.采用SEM、TEM、XRD、XPS对复合材料的结构和形貌进行了表征,并将其作为钠离子电池负极进行了性能测试.结果表明,当SnSe0.5S0.5@N-C作为钠离子电池负极时,表现出较高的可逆容量和优异的循环性能.在0.2 A/g电流密度下,复合材料在循环100圈后的可逆比容量仍可高达430.7 mA·h/g.     

Ultrahigh Power Factor and Ultralow Thermal Conductivity at Room Temperature in PbSe/SnSe Superlattice: Role of Quantum-Well Effect

Reduced dimension is one of the effective strategies to modulate thermoelectric properties. In this work, n-type PbSe/SnSe superlattices with quantum-well (QW) structure are fabricated by pulsed laser deposition. Here, it is demonstrated that the PbSe/SnSe multiple QW (MQW) shows a high power factor of ≈25.7 µW cm^?1 K^?2 at 300 K, four times larger than that of PbSe single layers. In addition, thermal conductivity falls below 0.32 ± 0.06 W m^?1 K^?1 due to the phonon scattering at interface when the PbSe well thickness is confined within the scale of phonon mean free path (1.8 nm). Featured with ultrahigh power factor and ultralow thermal conductivity, ZT at room temperature is significantly increased from 0.14 for PbSe single layer to 1.6 for PbSe/SnSe MQW.     

Cu Intercalation and Br Doping to Thermoelectric SnSe2 Lead to Ultrahigh Electron Mobility and Temperature‐Independent Power Factor

Due to its single conduction band nature, it is highly challenging to enhance the power factor of SnSe₂ by band convergence. Here, it is reported that simultaneous Cu intercalation and Br doping induce strong Cu–Br interaction to connect SnSe₂ layers, otherwise isolated, via “electrical bridges.” Atom probe tomography analysis confirms a strong attraction between Cu intercalants and Br dopants in the SnSe₂ lattice. Density functional theory calculations reveal that this interaction delocalizes electrons confined around Sn? Se covalent bonds and enhances charge transfer across the SnSe₂ slabs. These effects dramatically increase electron mobility and concentration. Polycrystalline SnCu_0.005Se_1.98Br_0.02 shows even higher electron mobility than pristine SnSe₂ single crystal and the theoretical expectation. This results in significantly improved electrical conductivity without reducing effective mass and Seebeck coefficient, thereby leading to the highest power factor of ≈12 µW cm^?1 K^?2 to date for polycrystalline SnSe₂ and SnSe. It even surpasses the value for the state‐of‐the‐art n‐type SnSe_0.985Br_0.015 single crystal at elevated temperatures. Surprisingly, the achieved power factor is nearly independent of temperature ranging from 300 to 773 K. The engineering thermoelectric figure of merit ZT_eng for SnCu_0.005Se_1.98Br_0.02 is ≈0.25 between 773 and 300 K, the highest ZT_eng ever reported for any form of SnSe₂‐based thermoelectric materials.