Two-dimensional Tin Research Articles

Oxidation-induced graded bandgap narrowing in Two-dimensional tin sulfide for high-sensitivity broadband photodetection

Two-dimensional (2D) layered group-IV monochalcogenides with large surface-to-volume ratio and high surface activity make that their structural and optoelectronic properties are sensitive to air oxidation. Here, we report the utilization of oxidation-induced gradient doping to modulate electronic structures and optoelectronic properties of 2D group-IV monochalcogenides by using SnS nanoplates grown by physical vapor deposition as a model system. By a precise control of oxidation time and temperature, the structural transition from SnS to SnSOx could be driven by the layer-by-layer oxygen doping and intercalation. The resulting SnSOx with a graded narrowing bandgap exhibits the enhanced optical absorption and photocurrent, leading to the fabricated SnSOx photodetector with remarkable photoresponsivity and fast response speed (<64 μs) at a broadband spectrum range of 520–1550 nm. The peak responsivity (7294 A/W) and detectivity (9.54 × 109 Jones) of SnSOx device are at least two orders of magnitude larger than those of SnS photodetector. Moreover, its photodetection performance can be competed with state-of-the-art of 2D materials-based photodetectors. This work suggests that the air oxidation could be utilized as an efficient strategy to engineer the electronic and optical properties of SnS and other 2D group-IV monochalcogenides for the development of high-performance broadband photodetectors.

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.

Photo-excited carrier behaviors of two-dimensional tin halide perovskite single crystals

Photo-excited carrier behaviors of two-dimensional tin halide perovskite single crystals

Research of Photodetectors Based On Two-Dimensional Materials

With the discovery of graphene, people have discovered that two-dimensional materials have unique properties and significance. Therefore, two-dimensional material-based photodetectors are also very valuable for research. This article first discusses the excellent properties of photodetectors based on two-dimensional materials, including high sensitivity, high modulation frequency, and wide spectral response capability. Then, recent research results on two-dimensional SnSe2/GaP type-II heterostructure photodetectors and photodetectors utilizing two-dimensional WSe2 were introduced. Additional representative studies, including two-dimensional layered materials-based valanche photodetectors and two-dimensional tin (II) sulfide (SnS) nanoflakes-based photodetectors, were also shown. The prospects and challenges of photodetectors based on two-dimensional materials were also discussed at the end of the article. They can be applied in fields such as video imaging, gas sensing, biological imaging, safety, night vision, optical communication, and motion detection. The issues of device stability, mass production, cost, and uniformity need to be addressed and find their more ideal commercial applications.

Optical properties of two-dimensional tin nanosheets epitaxially grown on graphene

Heterostacks formed by combining two-dimensional materials show novel properties which are of great interest for new applications in electronics, photonics and even twistronics, the new emerging field born after the outstanding discoveries on twisted graphene. Here, we report the direct growth of tin nanosheets at the two-dimensional limit via molecular beam epitaxy on chemical vapor deposited graphene on Al2O3(0001). The mutual interaction between the tin nanosheets and graphene is evidenced by structural and chemical investigations. On the one hand, Raman spectroscopy indicates that graphene undergoes compressive strain after the tin growth, while no charge transfer is observed. On the other hand, chemical analysis shows that tin nanosheets interaction with sapphire is mediated by graphene avoiding the tin oxidation occurring in the direct growth on this substrate. Remarkably, optical measurements show that the absorption of tin nanosheets exhibits a graphene-like behavior with a strong absorption in the ultraviolet photon energy range, therein resulting in a different optical response compared to tin nanosheets on bare sapphire. The optical properties of ultra-thin tin films therefore represent an open and flexible playground for the absorption of light in a broad range of the electromagnetic spectrum and technologically relevant applications for photon harvesting and sensors.

Probing the Interaction between Individual Metal Nanocrystals and Two-Dimensional Metal Oxides via Electron Energy Loss Spectroscopy.

Metal nanoparticles can photosensitize two-dimensional metal oxides, facilitating their electrical connection to devices and enhancing their abilities in catalysis and sensing. In this study, we investigated how individual silver nanoparticles interact with two-dimensional tin oxide and antimony-doped indium oxide using electron energy loss spectroscopy (EELS). The measurement of the spectral line width of the longitudinal plasmon resonance of the nanoparticles in absence and presence of 2D materials allowed us to quantify the contribution of chemical interface damping to the line width. Our analysis reveals that a stronger interaction (damping) occurs with 2D antimony-doped indium oxide due to its highly homogeneous surface. The results of this study offer new insight into the interaction between metal nanoparticles and 2D materials.

Optical Characterizations for Broadening Emissions from Doping of the Two-Dimensional Tin–Lead Perovskite Films

Optical Characterizations for Broadening Emissions from Doping of the Two-Dimensional Tin–Lead Perovskite Films

NH3(CH2)4NH3]SnX4 (X = Br, I): Dion-Jacobson type 2-D perovskites with short interlayer spacing.

Two-dimensional tin(II) halide perovskites stand as an environmentally benign alternative to Pb(II) halide perovskites. However, they are often challenging to make due to the oxidation of Sn(II) ion to more stable Sn(IV) ion. Here we report hybrid tin bromide and iodide perovskites: (1,4-BDA)Sn(IV)Br6 and (1,4-BDA)Sn(II)X4 (where X = Br, I; 1,4-BDA = 1,4-diammoniumbutane) with 0D and 2D structures, respectively. Their synthesis, structural characterization and photophysical properties are reported. They show bandgaps in the 1.94-2.70 eV range.

Surface chemistry altering electronic behaviour of liquid metal-derived tin oxide nanosheets.

Possessing excellent electronic properties and high chemical stability, semiconducting n-type two-dimensional (2D) tin dioxide (SnO2) nanosheets have been featured in sensing and electrocatalysis applications recently. Derived from non-layered crystal structures, 2D SnO2 has abundant unsaturated dangling bonds existing at the surface, providing interfacial activity. How the surface chemistry alters the electronic properties of 2D SnO2 nanomaterials remains unexplored. In this study, we synthesised ultra-thin 2D SnO2 nanosheets using a liquid metal (LM) touch printing technique and investigated experimentally and theoretically how the interactions of organic solvents composed of alkyl and hydroxyl groups with the surface of LM-derived 2D SnO2 modulate the electronic properties. It was found that alkane solvents can physically absorb onto the SnO2 surface with no impact on the material conductivity. Alcohol-based solvents on the other hand interact with the SnO2 surface via chemical absorptions primarily, in which oxygen atoms of hydroxyl groups in the alcohols form bonds with the surface atoms of SnO2. The binding stability is determined by the length and configuration of the hydrocarbon chain in alcohols. As representative long-chain alcohols, 1-octanol and 1-pentanol attach onto the SnO2 surface strongly, lowering the binding energy of Sn4+ and reducing the electron transfer ability of SnO2 nanosheets. Consequently, the electronic properties, i.e. conductivity and electronic mobility of SnO2 nanosheet-based electronic devices are decreased significantly.

Unveiling the role of linear alkyl organic cations in 2D layered tin halide perovskite field-effect transistors.

Two-dimensional (2D) tin halide perovskites are promising semiconductors for field-effect transistors (FETs) owing to their fascinating electronic properties. However, the correlation between the chemical nature of organic cations and charge carrier transport is still far from understanding. In this study, the influence of chain length of linear alkyl ammonium cations on film morphology, crystallinity, and charge transport in 2D tin halide perovskites is investigated. The carbon chain lengths of the organic spacers vary from propylammonium to heptanammonium. The increase of alkyl chain length leads to enhanced local charge carrier transport in the perovskite film with mobilities of up to 8 cm2 V-1 s-1, as confirmed by optical-pump terahertz spectroscopy. A similar improved macroscopic charge transport is also observed in FETs, only to the chain length of HA, due to the synergistic enhancement of film morphology and molecular organization. While the mobility increases with the temperature rise from 100 K to 200 K due to the thermally activated transport mechanism, the device performance decreases in the temperature range of 200 K to 295 K because of ion migration. These results provide guidelines on rational design principles of organic spacer cations for 2D tin halide perovskites and contribute to other optoelectronic applications.

Anisotropic properties of two-dimensional (2D) tin dihalide (SnX2, X = Cl, Br, I) monolayer binary materials

This paper investigated the electronic properties and photoresponse of two-dimensional SnX2 (X = Cl, Br, I) monolayer binary materials using computational techniques. The calculated band structure and density of states indicate that these are large band gap semiconducting materials with an indirect band gap. The studied chemical bonding mechanism shows the existence of the hybrid bonding of ionic and covalent bonds in these dihalide materials. The valence band (VB) and conduction band (CB) edge positions are also estimated, using the concept of electronegativity and band gap, to investigate the photocatalytic activity of SnX2. Next, we investigated the polarization and energy-dependent dielectric and optical functions along the crystallographic axes of these materials in the linear response approach of the perturbing incident oscillating light field. These materials exhibit an anisotropic behavior of these functions, especially in the high-energy visible and low-energy ultraviolet (UV) regions. The absorption of incident light photons is very fast in SnI2 than SnBr2 and SnCl2 in the low-energy UV region. It demonstrates the higher absorption coefficient and optical conductivity in Snl2. The obtained average static refractive index of SnCl2 is comparable to that of glass (1.5), showing its application as transparent material. The low reflection coefficient, less than 20%, makes them superior for antireflection coating materials in the infrared and visible regions. The prominent energy loss peaks show the existence of plasmon resonances in these materials. The most of losses occur in the UV region. The investigated electronic and photoresponse properties indicate that these Sn-based dihalide materials are excellent for electronic devices and optoelectronic applications. Also, the calculated VB and CB edge positions with respect to the normal hydrogen electrode show the favorable water-splitting capability of these materials.

Two-dimensional tin diselenide as the saturable absorber for passively Q-switched Er:YAP 3 μm solid-state laser

A passively Q-switched (PQS) Er:YAP laser at ∼3 μm with the two-dimensional saturable absorber (SA) tin diselenide (SnSe2) nanosheet as SA was successfully demonstrated for the first time. Under the maximum absorbed pump power of 4.0 W, the obtained continuous-wave maximum output power of Er:YAP laser was 258 mW with a corresponding slop efficiency of 7.18%. In the PQS experiment, laser pulses with the shortest pulse duration of 198 ns were yielded with a repetition rate of 317 kHz under the maximum absorbed pump power of 4.0 W, and the corresponding single pulse energy and pulse peak power were 0.66 µJ and 3.3 W, respectively. The investigation indicates that SnSe2 has the potential to be an outstanding laser modulator for PQS solid-state laser at 3 μm wavelength.

Effect of alloying Li on lithium-ion batteries applicability of two-dimensional TiN and TiC as novel electrode materials: a first principle study

The two-dimensional structures of transition metal nitride and carbide, TiN, and TiC have been alloyed with lithium (Li) in replacement of Ti, and their Li-ion applicability has been investigated using density functional theory and general gradient approximation. The alloy composition of x=0.125, 0.25, 0.375, and 0.5 have been considered and the stability of the alloys has been proved by cohesive energy and phonon density of states results. Moreover, the bond lengths between atoms as structural properties have been studied for these alloy structures. The largest peak of quantum capacitance and the largest negative value of surface storage charge are for alloy composition of TiC with x=0.125 with the values of 909.79 upmu F/cm^{2} and -,1819.58,upmu C/cm^{2}, respectively. Moreover, the results of the quantum capacitance and surface storage charge as a function of voltage for all Li alloy compounds are in the range of excellent supercapacitors and could have good potential to use as an electrode in the capacitor of Li-ion batteries. Furthermore, the electronic density of states of this group of alloys represents metallic behavior and therefore electrode material. In addition, the diffusion coefficient at temperatures of 77 and 300 K has been calculated using molecular dynamic calculations, and its lowest and largest values are 8times 10^{-8} cm^2/s (at 77 K) and 5.6times 10^{-7} cm^2/s (at 300), respectively. Plus, the largest value of electrical conductivity per relaxation time at 300 K belongs to Li_{0.25}Ti_{0.75}C with a value of 9.8times 10^{19}/(Omega m s).

Fermi level depinning via insertion of a graphene buffer layer at the gold–2D tin monoxide contact

Two-dimensional (2D) tin monoxide (SnO) has attracted much attention owing to its distinctive electronic and optical properties, which render itself suitable as a channel material in field effect transistors (FETs). However, upon contact with metals for such applications, the Fermi level pinning effect may occur, where states are induced in its band gap by the metal, hindering its intrinsic semiconducting properties. We propose the insertion of graphene at the contact interface to alleviate the metal-induced gap states. By using gold (Au) as the electrode material and monolayer SnO (mSnO) as the channel material, the geometry, bonding strength, charge transfer and tunnel barriers of charges, and electronic properties including the work function, band structure, density of states, and Schottky barriers are thoroughly investigated using first-principles calculations for the structures with and without graphene to reveal the contact behaviours and Fermi level depinning mechanism. It has been demonstrated that strong covalent bonding is formed between gold and mSnO, while the graphene interlayer forms weak van der Waals interaction with both materials, which minimises the perturbance to the band structure of mSnO. The effects of out-of-plane compression are also analysed to assess the performance of the contact under mechanical deformation, and a feasible fabrication route for the heterostructure with graphene is proposed. This work systematically explores the properties of the Au–mSnO contact for applications in FETs and provides thorough guidance for future exploitation of 2D materials in various electronic applications and for selection of buffer layers to improve metal–semiconductor contact.

High-Pressure Synthesis of Single-Crystalline SnS Nanoribbons.

Two-dimensional tin monosulfide (SnS) is attractive for the development of electronic and optoelectronic devices with anisotropic characteristics. However, its shape-controlled synthesis with an atomic thickness and high quality remains challenging. Here, we show that highly crystalline SnS nanoribbons can be produced via high-pressure (0.5 GPa) and thermal treatment (400 °C). These SnS nanoribbons have a length of several tens of micrometers and a thickness down to 5.8 nm, giving an average aspect ratio of ∼30.6. The crystal orientation along the zigzag direction and the in-plane structural anisotropy of the SnS nanoribbons are identified by transmission electron microscopy and polarized Raman spectroscopy, respectively. An ionic liquid-gated field-effect transistor fabricated using the SnS nanoribbon exhibits an on/off current ratio of >103 and a field-effect mobility of ∼0.7 cm2 V-1 s-1. This work provides a unique way to achieve one-dimensional growth of SnS.

Vibrational and Structural Properties of Two-Dimensional Tin Mixed-Halide Perovskites

The emergence of two-dimensional (2D) hybrid metal-halide perovskites has garnered significant attentions for optoelectronic devices and light-emitting applications. Since the toxicity of lead-based perovskites could potentially be harmful to the environment, several works have attempted to change the active metal to tin (Sn). Here, we investigate the characterization of (PEA)2SnBrxI4-x mixed halide perovskites using X-ray fluorescence (XRF), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. Qualitative XRF analysis suggests the presence of tin, bromine and iodine emissions under the mid-Z and high-Z ranges. In mid-Z range, Br-Kα peak appeared on 11.96 keV and Br-Kβ was detected on 13.3 keV. Meanwhile Sn-Kα, I-Kα, I-Kβ1, and I-Kβ2 peaks were detected in high-Z range on 25.24 keV, 28.6 keV, 32.35 keV and 33.11 keV, respectively. Thus, the elemental composition of mixed halide components exhibits an indicative control that bromine-rich or iodine-rich can be synthesized via rational chemical design. XRD pattern display a systematic progression at the peak 5.18° (corresponds to (002) plane), which unambiguously demonstrated the feasibility to tune halide composition in tin-based hybrid perovskite. It also confirms that (2D) hybrid metal-halide with tunable halide have identical structure for both bromine-rich and iodine-rich composition. Furthermore, the 2θ peaks slightly shifted to lower angle with increasing bromine composition. The presence of C−I bonding on ~500 cm-1 and C-Br bond on ~600 cm-1 in FTIR spectra highlights the functional group of organic cations. These experimental results promote a foundation to implement compositional engineering on 2D-tin mixed-halide perovskites for optoelectronics and scintillators.

Reduction of Hole Carriers by van der Waals Contact for Enhanced Photoluminescence Quantum Yield in Two-Dimensional Tin Halide Perovskite

Reduction of Hole Carriers by van der Waals Contact for Enhanced Photoluminescence Quantum Yield in Two-Dimensional Tin Halide Perovskite

Precursor Solution Aging: A Universal Strategy Modulating Crystallization of Two-Dimensional Tin Halide Perovskite Films

Two-dimensional (2D) tin (Sn2+)-based perovskites have achieved remarkable advancements in (opto)electronic devices. However, fabricating high-quality and reproducible Sn halide perovskite thin films remains challenging due to uncontrollably fast crystallization. To overcome this issue, dimethyl sulfoxide has been incorporated as an indispensable strategy to form Lewis acid–base adducts but also has been proven to induce an irreversible Sn2+ oxidization effect. As the crystalline films grow directly from solution, a better understanding of precursor colloidal chemistry and the film formation process is critical. In this study, we report a universal solution aging approach to fabricate high-quality and reliable 2D Ruddlesden–Popper and Dion–Jacobson Sn2+ perovskite films and devices. The proper solution aging stabilizes the precursor colloids by eliminating aggregated complex and unreacted precursor clusters in the fresh precursor, leading to homogeneous nucleation/crystallization and film growth. The precursor aging reduced film defect density by nearly 2 orders of magnitude and improved charge transport mobility by over 5 times. This study can inspire the community to understand the deposition mechanism for high-quality Sn2+ perovskite thin films and promote the development of high-performance and reproducible Sn2+ perovskite based (opto)electronic devices.

High efficacy of substrate dimensionality control in optimizing the specific capacitance and phase stability of hybridized nanostructures

The hybridization with conductive nanostructures has attracted intense research interest because of its high efficiency in the exploration of efficient energy-functional materials. In this study, we reported a high efficacy of substrate dimensionality control in optimizing the specific capacitance and phase stability of hybridized nanostructures. Employing defective holey TiN nanostructures as substrates was found to enhance the interfacial interactions with a hybridized layered double hydroxide (LDH). A comparative investigation of two-dimensional TiN-LDH nanohybrids with zero-dimensional/one-dimensional TiN-LDH homologs demonstrated that hybridization with holey two-dimensional TiN nanosheets led to a much greater specific capacitance of 2127 F g−1, which is one of the best performances among LDH-based electrodes ever-reported. In situ Raman analysis during electrochemical cycling clearly demonstrated that holey nanosheet morphology of TiN substrate is quite crucial in promoting the phase transition of hybridized Ni-Fe-LDH to NiOOH/FeOOH with the maximization of cation redox activities. These advantages of atomically thin holey TiN nanosheets could be ascribed to intimate electronic coupling at the bilateral interfaces of the two-dimensional LDH nanosheets, in addition to optimized porosity and improved mass transport.

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.