2D SnSe Research Articles

Local probe of the interlayer coupling strength of few-layers SnSe by contact-resonance atomic force microscopy

The interlayer bonding in two-dimensional (2D) materials is particularly important because it is not only related to their physical and chemical stability but also affects their mechanical, thermal, electronic, optical, and other properties. To address this issue, we report the direct characterization of the interlayer bonding in 2D SnSe using contact-resonance atomic force microscopy (CR-AFM) in this study. Site-specific CR spectroscopy and CR force spectroscopy measurements are performed on both SnSe and its supporting SiO2/Si substrate comparatively. Based on the cantilever and contact mechanic models, the contact stiffness and vertical Young’s modulus are evaluated in comparison with SiO2/Si as a reference material. The interlayer bonding of SnSe is further analyzed in combination with the semi-analytical model and density functional theory calculations. The direct characterization of interlayer interactions using this non-destructive methodology of CR-AFM would facilitate a better understanding of the physical and chemical properties of 2D layered materials, specifically for interlayer intercalation and vertical heterostructures.

Pd-decorated 2D SnSe ultrathin film on SiO2/Si for room-temperature hydrogen detection with ultrahigh response

Developing hydrogen sensors with high integration and high performance is still a great challenge. Herein, two dimensional (2D) layered tin monoselenide (SnSe) ultrathin films are deposited on SiO2-buffered silicon substrates via a scalable sputtering method. Then, a 15-nm-thickness Pd layer is decorated on the SnSe film. Due to the anisotropic van der Waals force from 2D SnSe surface, large quantities of nanoscaled Pd grains are formed, largely enhancing the active area when exposed in gas molecules. Benefiting from the unique surficial structure and abrupt interfacial properties with a large built-in electrical field, the fabricated Pd-decorated SnSe/SiO2/Si heterojunction exhibits excellent room-temperature H2 sensing performance with an ultrahigh response of ∼3225, 2–3 orders of magnitude higher than other 2D-based sensors. The sensor device also achieves fast response/recovery speed (73.1/23.7 s), ultralow detecting limit (∼0.91 ppb), as well as good selectivity. These findings promise the great potential of Pd-decorated SnSe/SiO2/Si heterostructures for high-performance sensor applications.

Enhancement of the Thermoelectric Performance of 2D SnSe Nanoplates through Incorporation of Magnetic Nanoprecipitates

Single crystals of tin selenide (SnSe), a layered material, have recently drawn massive attention in the field of thermoelectrics for its low thermal conductivity and high thermoelectric figure of ...

Tin Selenide Molecular Precursor for the Solution Processing of Thermoelectric Materials and Devices.

In the present work, we report a solution-based strategy to produce crystallographically textured SnSe bulk nanomaterials and printed layers with optimized thermoelectric performance in the direction normal to the substrate. Our strategy is based on the formulation of a molecular precursor that can be continuously decomposed to produce a SnSe powder or printed into predefined patterns. The precursor formulation and decomposition conditions are optimized to produce pure phase 2D SnSe nanoplates. The printed layer and the bulk material obtained after hot press displays a clear preferential orientation of the crystallographic domains, resulting in an ultralow thermal conductivity of 0.55 W m-1 K-1 in the direction normal to the substrate. Such textured nanomaterials present highly anisotropic properties with the best thermoelectric performance in plane, i.e., in the directions parallel to the substrate, which coincide with the crystallographic bc plane of SnSe. This is an unfortunate characteristic because thermoelectric devices are designed to create/harvest temperature gradients in the direction normal to the substrate. We further demonstrate that this limitation can be overcome with the introduction of small amounts of tellurium in the precursor. The presence of tellurium allows one to reduce the band gap and increase both the charge carrier concentration and the mobility, especially the cross plane, with a minimal decrease of the Seebeck coefficient. These effects translate into record out of plane ZT values at 800 K.

Two-Dimensional Tin Selenide (SnSe) Nanosheets Capable of Mimicking Key Dehydrogenases in Cellular Metabolism.

While dehydrogenases play crucial roles in tricarboxylic acid (TCA) cycle of cell metabolism, which are extensively explored for biomedical and chemical engineering uses, it is a big challenge to overcome the shortcomings (low stability and high costs) of recombinant dehydrogenases. Herein, it is shown that two-dimensional (2D) SnSe is capable of mimicking native dehydrogenases to efficiently catalyze hydrogen transfer from 1-(R)-2-(R')-ethanol groups. In contrary to susceptible native dehydrogenases, lactic dehydrogenase (LDH) for instance, SnSe is extremely tolerant to reaction condition changes (pH, temperature, and organic solvents) and displays extraordinary reusable capability. Structure-activity analysis indicates that the single-atom structure, Sn vacancy, and hydrogen binding affinity of SnSe may be responsible for their catalytic activity. Overall, this is the first report of a 2D SnSe nanozyme to mimic key dehydrogenases in cell metabolism.

Two‐Dimensional Tin Selenide (SnSe) Nanosheets Capable of Mimicking Key Dehydrogenases in Cellular Metabolism

AbstractWhile dehydrogenases play crucial roles in tricarboxylic acid (TCA) cycle of cell metabolism, which are extensively explored for biomedical and chemical engineering uses, it is a big challenge to overcome the shortcomings (low stability and high costs) of recombinant dehydrogenases. Herein, it is shown that two‐dimensional (2D) SnSe is capable of mimicking native dehydrogenases to efficiently catalyze hydrogen transfer from 1‐(R)‐2‐(R′)‐ethanol groups. In contrary to susceptible native dehydrogenases, lactic dehydrogenase (LDH) for instance, SnSe is extremely tolerant to reaction condition changes (pH, temperature, and organic solvents) and displays extraordinary reusable capability. Structure–activity analysis indicates that the single‐atom structure, Sn vacancy, and hydrogen binding affinity of SnSe may be responsible for their catalytic activity. Overall, this is the first report of a 2D SnSe nanozyme to mimic key dehydrogenases in cell metabolism.

Nanoscale Thermal Behavior of 2D SnSe Nanosheets

The thickness‐dependent nanoscale thermal behaviors of 2D SnSe nanosheets are studied via 3ω thermal mode atomic force microscopy and local Raman spectra. It is found that the 2D SnSe nanosheets demonstrate a decreasing thermal behavior with the reduction of thickness in the range of 6–40 nm. The unique thermal behavior is ascribed to the nonharmonic interlayer coupling along the armchair direction of SnSe crystal structure, in which the redshift of in‐plane vibration (, ) gives rise to phonon softening and finally the thickness‐dependent thermal behavior of SnSe nanosheets. Such nanoscale thermal behavior provides a new insight to understand the local thermal transport of 2D materials and their applications in energy consumption.

2D SnSe/Si heterojunction for self-driven broadband photodetectors

Van der Waals heterojunctions based on atomically thin 2D materials have opened up new realms in modern semiconductor industry. However, it is still challenging to fabricate large-area ultrathin 2D films. Herein, we successfully fabricate wafer-size 2D SnSe films on Si substrate by magnetron sputtering technique, enabling the formation of SnSe/Si van der Waals (vdWs) heterojunction device. The high-resolution transmission electron microscopy is employed to character the structure of SnSe film and SnSe/Si heterojunction with ideal orthorhombic structure and atomically abrupt interface, respectively. The energy diagram of SnSe/Si heterojunction is constructed, exhibiting similar barrier heights for electron and hole carrier. The SnSe/Si heterojunction shows obvious diode behavior with rectification ratio of ~1.6 × 104, forward current of ~194.5 mA cm−2 at ±1.0 V. Furthermore, owing to the high crystalline orientation, specific energy-band alignment, as well as the strong built-in electrical field, the SnSe/Si heterojunction illustrates a broadband photodetecting properties with the wavelength ranging from ultraviolet to near-infrared light, showing a high detectivity of 4.4 × 1012 cmHz1/2 W−1, a high responsivity of 566.4 mA mW−1 and an ultrafast response/recovery time of ~1.6/47.7 µs under zero external bias. This work provides a new strategy for fabrication of low cost 2D optoelectronic devices with high-performance.

Realization of High Thermoelectric Figure of Merit in Solution Synthesized 2D SnSe Nanoplates via Ge Alloying.

Recently single crystals of layered SnSe have created a paramount importance in thermoelectrics owing to their ultralow lattice thermal conductivity and high thermoelectric figure of merit ( zT). However, nanocrystalline or polycrystalline SnSe offers a wide range of thermoelectric applications for the ease of its synthesis and machinability. Here, we demonstrate high zT of ∼2.1 at 873 K in two-dimensional nanoplates of Ge-doped SnSe synthesized by a simple hydrothermal route followed by spark plasma sintering (SPS). Anisotropic measurements also show a high zT of ∼1.75 at 873 K parallel to the SPS pressing direction. Ge doping (3 mol %) in SnSe nanoplates significantly enhances the p-type carrier concentration, which results in high electrical conductivity and power factor of ∼5.10 μW/cm K2 at 873 K. High lattice anharmonicity, nanoscale grain boundaries, and Ge precipitates in the SnSe matrix synergistically give rise to the ultralow lattice thermal conductivity of ∼0.18 W/mK at 873 K.

Stability and magnetic properties of SnSe monolayer doped by transition metal atom (Mn, Fe, and Co): a first-principles study

Two dimensional (2D) tin selenium (SnSe) is an intriguing material with desired thermal and electric properties in nanoelectronics. In this paper, we carry on a density functional theory study on the stability and dilute magnetism of the 3d TM (Mn, Fe, and Co) doped 2D SnSe. Both the adsorption and substitution are in consideration here. We find that all the defects are electrically active and the cation substitutional doping (TM@Sn) is energetically favorable. The TM@Sn prefers to act as accepters and exhibits high-spin state with nonzero magnetic moment. The magnetic moment is mainly contributed by the spin-polarized charge density of the TM impurities. The magnetism is determined by the arrangement of the TM-3d orbitals, which is the result of the crystal field splitting and spin exchange splitting under specific symmetry. The magnetic and electronic properties of the TM@Sn are effectively modulated by external electric field (Eext) and charge doping. The Eext shifts the TM impurities relative to the SnSe host and then modifies the crystal field splitting. In particular, the magnetic moment is sensitive to the Eext in the Fe@Sn because the Eext induces distinct structure transformation. Based on the formation energy, doping electrons is a viable way to modulate the magnetic moment of TM@Sn. Doping electrons shift the 3d states towards low energy level, which induces the occupation of more 3d states and then the reduction of magnetism. These results render SnSe monolayer a promising 2D material for applications in future spintronics.

Phonon-driven electron scattering and magnetothermoelectric effect in two-dimensional tin selenide

The bulk tin selenide (SnSe) is the best thermoelectric material currently with the highest figure-of-merit due to strong phonon–phonon interactions. We investigate the effect of electron–phonon coupling (EPC) on the transport properties of a two-dimensional (2D) SnSe sheet. We demonstrate that EPC plays a key role in the scattering rate when the constant relaxation time approximation is deficient. The EPC strength is especially large in contrast to that of pristine graphene. The scattering rate depends sensitively on the system temperatures and the carrier densities when the Fermi energy approaches the band edge. We also investigate the magnetothermoelectric effect of the 2D SnSe. It is found that at low temperatures there is enormous magnetoelectrical resistivity and magnetothermal resistivity above 200%, suggesting possible potential applications in device design. Our results agree qualitatively well with the experimental data.

2D SnSe-based vdW heterojunctions: tuning the Schottky barrier by reducing Fermi level pinning.

Two-dimensional (2D) SnSe is a very promising material for semiconducting devices due to its novel properties. However, the contact behavior between a 2D SnSe sheet and a three-dimensional (3D) metal surface shows an un-tunable Schottky barrier because of the metallization of the SnSe sheet induced by strong Fermi level pinning at the contact interface. In this work, we use graphene rather than 3D metals as the metal electrode which comes into contact with a single-layer SnSe sheet to form a van der Waals (vdW) heterojunction. Based on state-of-the-art theoretical calculations, we find that the intrinsic properties of the SnSe sheet are preserved and the Fermi level pinning is weakened because of the vdW interaction between the SnSe sheet and graphene. We further demonstrate that an Ohmic contact can be realized by doping graphene with boron or nitrogen atoms or using other high-work-function 2D metals such as ZT-MoSe2, ZT-MoS2, or H-NbS2 sheet as the electrode to reduce the Fermi level pinning, leading to a spontaneous hole injection from the electrode to the channel material. This study sheds light on how to tune the Schottky barrier height for better device performance.