Tin Monoselenide Research Articles

Photostimulated Pyrothermoelectric Coupling in Two-Dimensional Tin Monoselenide Enabling Zero-Biased Multimodal Transducers.

Despite the advancement of the Internet of Things (IoT) and portable devices, the development of zero-biased sensing systems for the dual detection of light and gases remains a challenge. As an emerging technology, direct energy conversion driven by intriguing physical properties of two-dimensional (2D) materials can be realized in nanodevices or a zero-biased integrated system. In this study, we unprecedentedly attempted to exploit the photostimulated pyrothermoelectric coupling of two-dimensional SnSe for use in zero-biased multimodal transducers for the dual detection of light and gases. We synthesized homogeneous, large-area 6 in SnSe multilayers via a rational synthetic route based on the thermal decomposition of a solution-processed single-source precursor. Zero-biased SnSe transducers for the dual monitoring of light and gases were realized by exploiting the synergistic coupling of the photostimulated pyroelectric and thermoelectric effects of SnSe. The extracted photoresponsivity at 532 nm and NO2 gas responsivity of the SnSe-based transducers corresponded to 1.07 × 10-6 A/W and 13263.6% at 0 V, respectively. To bring universal applicability of the zero-biased SnSe transducers, the wide operation bandwidth photoelectrical properties (visible to NIR) and dynamic current responses toward two NO2/NH3 gases were systematically evaluated.

High-Performance Self-Driven SnSe/Si Heterojunction Photovoltaic Photodetector

Tin monoselenide (SnSe), which belongs to group IV–VI monochalcogenides, has obtained significant attention in the field of photodetection owing to its ultrahigh carrier mobilities. However, the great challenges of preparing high-quality films and high-performance devices still need to be conquered. Herein, high-density continuous SnSe films were deposited on a Si substrate using magnetron sputtering technology, and a self-driven photovoltaic-type broadband photodetector from the visible light range (VIS) to the near-infrared (NIR) range based on SnSe/Si heterojunction was constructed. Owing to its high carrier mobility, narrow band gap structure, and strong internal electric field, the SnSe/Si heterojunction device exhibits an ultrafast response and high responsivity (R), which achieves a wide spectral response of 405–980 nm. Under zero bias voltage, the greatest R and detectivity (D*) of the heterojunction were 704.6 mA/W and 3.36 × 1011 Jones at 405 nm. Furthermore, the device had a fast response time (rise time) of 20.4 μs at 980 nm of illumination. This work provides a new strategy for the fabrication of high-performance, low-cost, and self-driven photodetectors.

Self-biased and biased photo-sensitivity of Tin Mono-Selenide (SnSe) photonic crystal Photodetector under poly/monochromatic light

Recently, transition metal chalcogenides were found to be the most promising candidates for photosensor- and photodetector-based applications. This study reports the photodetection and response properties of tin selenide (SnSe) crystals grown by the direct vapour transport (DVT) technique. The basic properties of SnSe have been reported in a previous article. Photodetection properties are investigated using polychromatic or monochromatic light of varying intensities and bias voltages. Results depict that detectors work congenially under monochromatic sources of light. It is observed that responsivity (Rλ) is higher for red, while detectivity and sensitivity are observed to be maximum for blue light under the self-biased (no bias) condition. The results observed under varying intensity (spot size) in the absence of biassing suggest that as intensity rises, all the parameters of the photodetector are also rising, while at constant intensity (30 mW/cm2), by varying the bias voltage, the detectivity of red light is decreasing due to an increment in dark current. Photodetectors are more efficient at converting optical signals to electrical signals, and their sensitivity is colour-dependent. Mainly, it is observed that monochromatic light shows high sensitivity to low bias voltages, while polychromatic light shows high sensitivity to high voltages. Observed results point to the detection of both monochromatic and polychromatic light by the fabricated detector, which can be applied to SnSe-based devices. A device can be used to fabricate colour and intensity detection.

Direct Synthesis of Two-Dimensional SnSe and SnSe2 through Molecular Scale Preorganization.

Two-dimensional tin monoselenide (SnSe) and tin diselenide (SnSe2) materials were efficiently produced by the thermolysis of molecular compounds based on a new class of seleno-ligands. Main group metal chalcogenides are of fundamental interest due to their layered structures, thickness-dependent modulation in electronic structure, and small effective mass, which make them attractive candidates for optoelectronic applications. We demonstrate here the synthesis of stable tin selenide precursors by in situ reductive bond cleavage in the dimeric diselenide ligand (SeC2H4N(Me)C2H4Se)2 in the presence of SnCl4. New molecular precursors [SnIV(SeC2H4N(Me)C2H4Se)2], [SnIVCl2(SeC2H4N(Me)C2H4Se)], and [SnIV(SC2H4N(Me)C2H4S)(SeC2H4N(Me)C2H4Se)] were thoroughly characterized by multinuclear magnetic resonance studies and single-crystal X-ray diffraction analysis that revealed the Sn(IV) center to be octahedrally coordinated by two tridentate dianionic chelating ligands or trigonally pyramidally coordinated by one chelating ligand and two chlorido ligands. Preorganization of metal-selenium bonds in both compounds offered direct and reproducible synthetic access to two-dimensional tin chalcogenides (SnSe and SnSe2) via simple adjustment of the pyrolysis temperature. Additionally, SnSe2 and SnSxSe2-x particles could be successfully synthesized by microwave-assisted decomposition of the molecular precursors, which was unambiguously corroborated by both experimental and computational analyses that explained the formation of a selenium rich SnSxSe2-x phase from a single molecular precursor containing both Sn-Se and Sn-S bonds.

Electrical and Optical Properties of γ-SnSe: A New Ultra-narrow Band Gap Material.

We describe the unusual properties of γ-SnSe, a new orthorhombic binary phase in the tin monoselenide system. This phase exhibits an ultranarrow band gap under standard pressure and temperature conditions, leading to high conductivity under ambient conditions. Density functional calculations identified the similarity and difference between the new γ-SnSe phase and the conventional α-SnSe based on the electron localization function. Very good agreement was obtained for the band gap width between the band structure calculations and the experiment, and insight provided for the mechanism of reduction in the band gap. The unique properties of this material may render it useful for applications such as thermal imaging devices and solar cells.

Tuning band gap, structural and optical properties of tin selenide nanoparticles by alkali metal doping

The layered chalcogenide semiconductor, Tin monoselenide is an extraordinary candidate among chalcogenide materials because of their novel physical and chemical properties and tremendous applications in thermoelectrics, solar cells, energy storage devices, i.e. metal–ion batteries, supercapacitors etc. In this work, we synthesized polycrystalline SnSe by a simple hydrothermal method using sodium borohydride as a reducing agent for the single phase formation of SnSe nanostructures. X–ray diffraction spectroscopy has been done to confirm the orthorhombic structure and single phase formation. Fourier transform infrared characterization has been done to observe the linkage of groups among the precursors and solvents used. Further, Photoluminescence characterization has been done to estimate the band gap values and radiative recombination mechanism of the material. Ultraviolet–Visible (UV–Vis) spectroscopy has been used to study the optical properties of the material. Moreover, extrinsic heteroatom doping of sodium and potassium have been done to form NaxSnx-1Se and KxSnx-1Se respectively, which further decreases the band gap of the host material. The absorbance spectra, percentage of transmittance, extinction coefficient, direct band gap values depend upon photonic interactions and has been determined by UV–Vis spectroscopy. Elemental composition of each sample has been confirmed by EDX spectroscopy. All these properties have made the material a potential candidate for opto–electronic and photovoltaic applications.

Self-powered anisotropic photo-responsive properties of tin mono-selenide (SnSe) photodetector

Transition metal chalcogenides (TMCs) have been extensively investigated due to their pervasive range of properties for the fabrication of several next-generation optoelectronic devices including flexible detectors, photodetectors, and photo sensors. This article reports the growth, characterization, and photodetection and response study of crystalline tin selenide (SnSe) grown by the direct vapor transport (DVT) technique. The stoichiometric confirmation of as-grown compound tin mono-selenide (SnSe) was confirmed by EDAX spectra. Structural confirmation was carried out using powder X-Ray Diffraction (PXRD). The bandgap of the grown crystals was also calculated from Tauc's plot. Anisotropic photodetection study of the SnSe photodetector demonstrates the superior photocurrent of 0.62 μA under polychromatic light for the I-II configurations of contacts. The stability of isotropic configuration is also observed to be high compared to anisotropic configuration. The results suggest isotropic contact configuration is most preferable for the SnSe photodetector. We observed that, under zero biasing conditions, the device performance improves, which indicates that the fabricated photo-diode exhibits an adequate photosensitive nature. It is observed that the device performs wisely under the self-driven condition, which points out the adequate photo-conductive (photo-self-driven) nature of the detector.

SnSe-Coated Microfiber Resonator for All-Optical Modulation.

In this study, a tin monoselenide (SnSe)-based all-optical modulator is firstly demonstrated with high tuning efficiency, broad bandwidth, and fast response time. The SnSe nanoplates are deposited in the microfiber knot resonator (MKR) on MgF2 substrate and change its transmission spectra by the external laser irradiation. The SnSe nanoplates and the microfiber are fabricated using the liquid-phase exfoliation method and the heat-flame taper-drawing method, respectively. Due to the strong absorption and enhanced light–matter interaction of the SnSe nanoplates, the largest transmitted power tunability is approximately 0.29 dB/mW with the response time of less than 2 ms. The broad tuning bandwidth is confirmed by four external pump lights ranging from ultraviolet to near-infrared. The proposed SnSe-coated microfiber resonator holds promising potential for wide application in the fields of all-optical tuning and fiber sensors.

First-principles study of the structural, optoelectronic and thermophysical properties of the π-SnSe for thermoelectric applications.

Tin selenide (SnSe) has thermoelectric (TE) and photovoltaic (PV) applications due to its exceptional advantages, such as the remarkable figure of merit (ZT ≈ 2.6 at 923 K) and excellent optoelectronic properties. In addition, SnSe is nontoxic, inexpensive, and relatively abundant. These aspects make SnSe of great practical importance for the next generation of thermoelectric devices. Here, we report structural, optoelectronic, thermodynamic, and thermoelectric properties of the recently experimentally identified binary phase of tin monoselenide (π-SnSe) by using the density functional theory (DFT). Our DFT calculations reveal that π-SnSe features an optical bandgap of 1.41 eV and has an exceptionally large lattice constant (12.2 Å, P213). We report several thermodynamic, optical, and thermoelectric properties of this π-SnSe phase for the first time. Our finding shows that the π-SnSe alloy is exceptionally promising for the next generation of photovoltaic and thermoelectric devices at room and high temperatures.

A new binary phase in the tin monoselenide system: chemical epitaxy of orthorhombic γ-SnSe thin films

Deposition of SnSe from alkaline solution resulted in a new binary phase of tin monoselenide, γ-SnSe. TEM and electron diffraction showed that growth on PbS substrates resulted in epitaxial monoselenide films.

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.

Flexible SnSe Photodetectors with Ultrabroad Spectral Response up to 10.6 μm Enabled by Photobolometric Effect.

A broad spectral response is highly desirable for radiation detection in modern optoelectronics; however, it still remains a great challenge. Herein, we report a novel ultrabroadband photodetector based on a high-quality tin monoselenide (SnSe) thin film, which is even capable of detecting photons with energies far below its optical band gap. The wafer-size SnSe ultrathin films are epitaxially grown on sodium chloride via the 45° in-plane rotation by employing a sputtering method. The photodetector delivers sensitive detection to ultraviolet-visible-near infrared (UV-Vis-NIR) lights in the photoconductive mode and shows an anomalous response to long-wavelength infrared at room temperature. Under the mid-infrared light of 10.6 μm, the fabricated photodetector exhibits a large photoresponsivity of 0.16 A W-1 with a fast response rate, which is ∼3 orders of magnitude higher than other results. The thermally induced carriers from the photobolometric effect are responsible for the sub-bandgap response. This mechanism is confirmed by a temperature coefficient of resistance of -2.3 to 4.4% K-1 in the film, which is comparable to that of the commercial bolometric detectors. Additionally, the flexible device transferred onto polymer templates further displays high mechanical durability and stability over 200 bending cycles, indicating great potential toward developing wearable optoelectronic devices.

Tin monoselenide based saturable absorbers for the generation of ultrashort pulses

The IV-VI semiconducting compounds, a family of two-dimensional material with attractive optical and electrical properties, have received extensive attention in recent years. Here, we demonstrate that tin monoselenide (SnSe) can be utilized as a saturable absorber (SA) for erbium-doped fiber laser (EDFL). By sandwiching the film of polyvinyl alcohol (PVA) and SnSe between two fiber connectors and depositing the SnSe nanoparticles onto the side-polished fiber (SPF), two types of SnSe based SAs are fabricated. The nonlinear optical properties of these two SAs are investigated, the modulation depth of the SnSe-SPF and SnSe-PVA SAs are 19.5% and 16.8%, respectively. Stable soliton mode-locking operations with center wavelength of 1556.6 (1558.2) nm and pulse width of less than 2 ps are obtained in the EDFL based on SnSe-SPF (SnSe-PVA) SA. Furthermore, the experimental results confirm that the damage threshold of the SnSe-SPF SA is much higher than that of the SnSe-PVA SA. Numerous photonics devices may benefit from the nonlinear saturable absorption properties of SnSe, such as near-infrared pulsed lasers, modulators, and so on.

Beneficial Impurities and Phase Control in Colloidal Synthesis of Tin Monoselenide.

The effect of impurities in colloidal synthesis of SnSe in oleylamine surfactant was investigated. Specifically, it was found that impurities such as water, hydrochloric acid, and carbon dioxide stabilize the recently discovered cubic phase of tin monoselenide, π-SnSe. We describe the reaction that releases HCl to the reaction medium through reaction of SnCl2 with moisture and its subsequent reaction with oleylamine, transforming it from neutral to charged surfactant. A similar path occurs in the case of CO2, which reacts with oleylamine to give charged oleylammonium-oleylcarbamate molecular pairs. By exposing the reaction to controlled concentrations of "beneficial contaminants", hitherto a major source of irreproducibility in this synthesis, we demonstrate phase and shape control from π-SnSe cubes to α-SnSe rods.

Development of SnSe thin films through selenization of sputtered Sn-metal films

Tin monoselenide (SnSe) thin films with thickness in the range of 0.72–1.00 μm were prepared by the two-stage process (metallization by sputtering + selenization by rapid thermal annealing) using Sn target and selenium powder at different selenization temperatures in the range of 300–450 °C. The formation of single-phase orthorhombic(OR)-SnSe films at ≥ 400 °C was observed, whereas the secondary phase of SnSe2 in addition to OR-SnSe was formed when the films selenized at ≤ 350 °C. The single-phase OR-SnSe films exhibited Raman modes at 33 cm−1, 71 cm−1, 108 cm−1, 130 cm−1, and 151 cm−1. The crystallinity and grain size of the OR-SnSe films were improved with increasing of selenization temperature. The tin films selenized at 400 °C showed the composition ratio of Se/Sn = 0.99, the direct bandgap energy of 1.2 eV, and the p-type conductivity with electrical resistivity of 12.71 Ω cm, the mobility of 2.03 cm2 V−1 s−1, and carrier concentration of 2.42 × 1017 cm−3. The above opto-electronic properties of single-phase OR-SnSe films selenized at 400 °C indicated that these films could be used to attain good device efficiency of solar cells.

Effect of supercooling on the microstructural development and optimization of physical properties of melt grown SnSe crystals

The microstructural development of stoichiometric tin monoselenide (SnSe) crystals grown by vertical Bridgman–Stockbarger method using an indigenously fabricated furnace has been investigated under high vacuum (~ 10−6 mbar). The ampoule translation rate (tr) and supercooling, ΔT (= Tm − T, where Tm is the melting point and T is the crystallization temperature) were varied in the range, 12–2 mm/h and 20–100 °C respectively. Enhancement of ΔT and tr led to constitutional supercooling, inducing compositional changes and non-stoichiometry. Low ΔT (20–40 °C) and high tr (12–10 mm/h) resulted in globules, flakes and cavities. When ΔT = 60 °C and tr = 9 to 7 mm/h, mounds were formed with closed contours and ripples, due to atomically rough liquid–solid (l-β) interface. Fine tuning of ΔT (60 °C) and tr (2 mm/h) enabled smooth planar interface, so as to yield good quality crystalline structures with periodic atomic deposition promoting crystal growth, layer-by-layer. Energy dispersive analysis by X-rays and powder X-ray diffraction studies revealed appreciable crystallinity, chemical homogeneity and phase purity. The density of crystals estimated from crystallographic data (6.183 g/cm3) corroborates with that obtained utilizing Archimedes principle. Thermogravimetric and microindentation analyses established thermal and mechanical stability. The low etch pit density (~ 102 cm−2) manifests nearly perfect growth of crystals than their melt counterparts. UV–Vis–NIR and PL spectra reflected direct transition with an energy gap of 1.32 eV, validating immense potential of the grown crystals for photovoltaic applications.

Состав, структура, полупроводниковые свойства химически осажденных пленок SnSe

High adhesion tin monoselenide SnSe layers with a thickness of up to 200 ± 10 nm have been prepared by hydrochemical deposition from a trilonate reaction mixture. It was revealed by the X-ray diffraction method that the synthesized films crystallize in the orthorhombic system (S. G. Pnma). The presence of a significant amount of oxygen in the surface layers of the films is explained by partial oxidation of the samples with the formation of the SnO2 phase. The results of ion etching to a depth of 18 nm showed a sharp decrease in the oxygen content with depth and actual correspondence of the elemental composition to SnSe. According to the results of optical studies, the band gap was found to be 1.69 eV for direct type of transitions, respectively. The synthesized SnSe layers have a hole-type conductivity typical of this material.

Eco-friendly synthesis of SnSe nanoparticles: effect of reducing agents on the reactivity of a Se-precursor and phase formation of SnSe NPs

Tin monoselenide (SnSe) nanoparticles (NPs) have great potential to replace the conventional absorbers used in the fabrication of thin film solar cells.

Layered tin monoselenide as advanced photothermal conversion materials for efficient solar energy-driven water evaporation.

Solar energy-driven water evaporation lays a solid foundation for important photothermal applications such as sterilization, seawater desalination, and electricity generation. Due to the strong light-matter coupling, broad absorption wavelength range, and prominent quantum confinement effect, layered tin monoselenide (SnSe) holds a great potential to effectively harness solar irradiation and convert it to heat energy. In this study, SnSe is successfully deposited on a centimeter-scale nickel foam using a facile one-step pulsed-laser deposition approach. Importantly, the maximum evaporation rate of SnSe-coated nickel foam (SnSe@NF) reaches 0.85 kg m-2 h-1, which is even 21% larger than that obtained with the commercial super blue coating (0.7 kg m-2 h-1) under the same condition. A systematic analysis reveals that its good photothermal conversion capability is attributed to the synergetic effect of multi-scattering-induced light trapping and the optimal trade-off between light absorption and phonon emission. Finally, the SnSe@NF device is further used for seawater evaporation, demonstrating a comparable evaporation rate (0.8 kg m-2 h-1) to that of fresh water and good stability over many cycles of usage. In summary, the current contribution depicts a facile one-step scenario for the economical and efficient solar-enabled SnSe@NF evaporation devices. More importantly, an in-depth analysis of the photothermal conversion mechanism underneath the layered materials depicts a fundamental paradigm for the design and application of photothermal devices based on them in the future.

Optimized growth conditions of epitaxial SnSe films grown by pulsed laser deposition

We have grown epitaxial tin monoselenide (SnSe) films on MgO or SrTiO3 (STO) substrates by pulsed laser deposition (PLD) at Ts = 473 or 573 K, and investigated the optimized growth condition in terms of crystal orientation, crystallinity, and electrical resistivity. For the PLD procedure, a SnSex (x = 1.0–1.6) target containing excess Se was used to compensate for the vaporization of Se. The crystal orientation and crystallinity of the SnSe films changed depending on the growth conditions, and the magnitude of the electrical resistivity ρ of the films was closely related to the crystalline nature. The SnSe film grown on the MgO substrate at Ts = 573 K using the target with x = 1.4 was the most highly a-axis-oriented and highly crystalized among all of the films investigated in this study. However, the ρ of the film in the bc-plane was about one order of magnitude larger than those of the reported single crystal and the a-axis-oriented crystalline sample fabricated by spark plasma sintering. This larger ρ was suggested to result from the lattice mismatch and/or a small amount of nonstoichiometry in the film.