Correction: Self-limiting stoichiometry in SnSe thin films
Correction for ‘Self-limiting stoichiometry in SnSe thin films’ by Jonathan R. Chin et al. , Nanoscale , 2023, 15 , 9973–9984, https://doi.org/10.1039/D3NR00645J.
Chin, Jonathan R.↗
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Synthesis, redox exfoliation, and magnetic nanoparticle decoration of VSe 2 and SnSe 2 nanosheets
2H SnSe 2 and 1T VSe 2 van der Waals materials were synthesized and then subjected to redox exfoliation. Decoration of these 2D sheets with iron oxide nanoparticles produced a synergistic magnetization response that exceeded that of iron oxide alone.
Chemistry↗
Onset of anharmonicity and thermal conductivity in SnSe
The anharmonicity in SnSe is investigated through the analysis of moments of 119Sn nuclear resonant inelastic x-ray scattering and ab initio molecular dynamics calculations. Experimental evidences show that the anharmonic behavior started around 300 K, substantially lower than the usually suggested structural transition at 800 K. Both theory and experiments reveal substantial lifetime broadening and frequency renormalization of the optical phonons. Additionally, thermal conductivities calculated from the temporal energy moment using the Einstein diffusion equation are in good agreement with previous experiments. The abrupt increase of the thermal power near 800 K is driven by an electronic factor and not by the enhanced anharmonicity due to structural change.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Nonthermal Bonding Origin of a Novel Photoexcited Lattice Instability in SnSe
Lattice dynamics measurements are often crucial tools for understanding how materials transform between different structures. Here, we report time-resolved x-ray scattering-based measurements of the nonequilibrium lattice dynamics in SnSe, a monochalcogenide reported to host a novel photoinduced lattice instability. By fitting interatomic force models to the fluence dependent excited-state dispersion, we determine the nonthermal origin of the lattice instability to be dominated by changes of interatomic interactions along a bilayer-connecting bond, rather than of an intralayer bonding network that is of primary importance to the lattice instability in thermal equilibrium.
36 MATERIALS SCIENCE↗
Direct observation of multiple conduction-band minima in high-performance thermoelectric SnSe
Not Available
Okawa, Mario (ORCID:0000000165408988)↗
Observation of a Novel Lattice Instability in Ultrafast Photoexcited SnSe
Not Available
36 MATERIALS SCIENCE↗
Directing Charge Carriers and Ferroelectric Domains at Lateral Interfaces in van der Waals Heterostructures
Emergent phenomena in traditional ferroelectrics are frequently observed at heterointerfaces. Accessing such functionalities in van der Waals ferroelectrics requires the formation of layered heterostructures, either vertically stacked (similar to oxide ferroelectrics) or laterally stitched (without equivalent in 3D-crystals). Here, we investigate lateral heterostructures of the ferroelectric van der Waals semiconductors SnSe and SnS. A two-step process produces ultrathin crystals comprising an SnSe core laterally joined to an SnS edge-band, as confirmed by Raman spectroscopy, transmission electron microscopy (TEM) imaging, and electron diffraction. TEM shows a moiré pattern across the SnSe core due to coverage by an ultrathin SnS layer. The ability of the lateral interface (IF) to direct excited carriers, probed by cathodoluminescence, shows electron transfer over 560 nm diffusion length from the SnS edge-band. Large, thin flakes supporting ferroelectricity allow investigating domains and domain wall interactions in uniform crystals and lateral heterostructures. Polarized optical microscopy of sub-20 nm flakes consistently shows ⟨110⟩ oriented stripe domains with mirror-twin domain walls. Heterostructures adopt two domain configurations, with domains either constrained to the SnSe core or propagating across the entire SnSe–SnS flakes. Furthermore, the combined results demonstrate multifunctional van der Waals heterostructures with high-quality IFs presenting extraordinary opportunities for manipulating carrier flows and ferroelectric domain patterns.
2D ferroelectrics↗
Giant Nonlinear Optical Response via Coherent Stacking of In-Plane Ferroelectric Layers
Thin ferroelectric materials hold great promise for compact nonvolatile memory and nonlinear optical and optoelectronic devices. Herein, an ultrathin in-plane ferroelectric material that exhibits a giant nonlinear optical effect, group-IV monochalcogenide SnSe, is reported. Nanometer-scale ferroelectric domains with ≈90°/270° twin boundaries or ≈180° domain walls are revealed in physical-vapor-deposited SnSe by lateral piezoresponse force microscopy. Atomic structure characterization reveals both parallel and antiparallel stacking of neighboring van der Waals ferroelectric layers, leading to ferroelectric or antiferroelectric ordering. Ferroelectric domains exhibit giant nonlinear optical activity due to coherent enhancement of second-harmonic fields and the as-resulted second-harmonic generation was observed to be 100 times more intense than monolayer WS 2 . This work demonstrates in-plane ferroelectric ordering and giant nonlinear optical activity in SnSe, which paves the way for applications in on-chip nonlinear optical components and nonvolatile memory devices.
36 MATERIALS SCIENCE↗
Pure spin current injection of single-layer monochalcogenides
We compute the spectrum of pure spin current injection in ferroelectric single-layer SnS, SnSe, GeS, and GeSe. The formalism takes into account the coherent spin dynamics of optically excited conduction states split in energy by spin–orbit coupling. The velocity of the electron's spins is calculated as a function of incoming photon energy and angle of linearly polarized light within a full electronic band structure scheme using density functional theory. We find peak speeds of 520, 360, 270 and 370 Km s -1 for SnS, SnSe, GeS and GeSe, respectively which are an order of magnitude larger than those found in bulk semiconductors, e.g., GaAs and CdSe. Interestingly, the spin velocity is almost independent of the direction of polarization of light in a range of photon energies. Our results demonstrate that single-layer SnS, SnSe, GeS and GeSe are candidates to produce on demand spin-current in spintronics applications.
2D-monochalcogenides↗
Materials Data on Sn4TeSe3 by Materials Project
(SnSe)2Sn2TeSe crystallizes in the monoclinic Pm space group. The structure is two-dimensional and consists of one Sn2TeSe sheet oriented in the (0, 0, 1) direction and one SnSe sheet oriented in the (0, 0, 1) direction. In the Sn2TeSe sheet, there are two inequivalent Sn2+ sites. In the first Sn2+ site, Sn2+ is bonded to four equivalent Te2- and one Se2- atom to form a mixture of distorted edge and corner-sharing SnTe4Se square pyramids. There are two shorter (2.96 Å) and two longer (3.43 Å) Sn–Te bond lengths. The Sn–Se bond length is 2.79 Å. In the second Sn2+ site, Sn2+ is bonded in a 3-coordinate geometry to one Te2- and two equivalent Se2- atoms. The Sn–Te bond length is 2.97 Å. Both Sn–Se bond lengths are 2.82 Å. Te2- is bonded in a 5-coordinate geometry to five Sn2+ atoms. Se2- is bonded in a trigonal non-coplanar geometry to three Sn2+ atoms. In the SnSe sheet, there are two inequivalent Sn2+ sites. In the first Sn2+ site, Sn2+ is bonded in a distorted T-shaped geometry to three Se2- atoms. There are one shorter (2.77 Å) and two longer (2.82 Å) Sn–Se bond lengths. In the second Sn2+ site, Sn2+ is bonded in a 3-coordinate geometry to three Se2- atoms. There are one shorter (2.78 Å) and two longer (2.82 Å) Sn–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to three Sn2+ atoms. In the second Se2- site, Se2- is bonded in a trigonal non-coplanar geometry to three Sn2+ atoms.
36 MATERIALS SCIENCE↗
Materials Data on InSn3Se4 by Materials Project
InSnSe2(SnSe)2 crystallizes in the monoclinic Pm space group. The structure is two-dimensional and consists of one InSnSe2 sheet oriented in the (0, 0, 1) direction and one SnSe sheet oriented in the (0, 0, 1) direction. In the InSnSe2 sheet, In2+ is bonded in a 5-coordinate geometry to five Se2- atoms. There are a spread of In–Se bond distances ranging from 2.80–3.41 Å. Sn2+ is bonded in a 3-coordinate geometry to three Se2- atoms. There are two shorter (2.79 Å) and one longer (2.82 Å) Sn–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a distorted trigonal non-coplanar geometry to one In2+ and two equivalent Sn2+ atoms. In the second Se2- site, Se2- is bonded in a 5-coordinate geometry to four equivalent In2+ and one Sn2+ atom. In the SnSe sheet, there are two inequivalent Sn2+ sites. In the first Sn2+ site, Sn2+ is bonded in a 3-coordinate geometry to three Se2- atoms. There are one shorter (2.77 Å) and two longer (2.81 Å) Sn–Se bond lengths. In the second Sn2+ site, Sn2+ is bonded in a 3-coordinate geometry to three Se2- atoms. There are one shorter (2.80 Å) and two longer (2.81 Å) Sn–Se bond lengths. There are two inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a distorted trigonal non-coplanar geometry to three Sn2+ atoms. In the second Se2- site, Se2- is bonded in a distorted trigonal non-coplanar geometry to three Sn2+ atoms.
36 MATERIALS SCIENCE↗
Epitaxial Growth of 2D Core‐Crown SnS 2 /SnSe 2 Heterostructure Through Interfacial Modification with Polyvinylpyrrolidone
Abstract Developing generalized strategies for controlled synthesis of 2D heterostructures remains a significant challenge because the existing approaches often suffer from poor reproducibility and scalability. In this study, a solution synthesis approach for epitaxial core‐crown heterostructures with controlled band alignment, that overcomes these challenges is reported. Polyvinylpyrrolidone (PVP) is used as a structure‐directing agent to reduce lattice mismatch between SnS 2 and SnSe 2 (10‐10) surfaces and direct epitaxial growth of SnSe 2 crown on SnS 2 seed. Additionally, PVP adsorption to the basal plane prevents van der Waals stacking and stabilizes 2D heterostructures during synthesis. Driven by interfacial thermodynamics, the formation of the core‐crown heterostructure is highly reproducible and the size of the 2D heterostructure and relative areas of the core and the crown can be precisely controlled in a two‐step process by varying synthesis times for the seed and the crown. The identified growth pathway for 2D heterostructures can be generalized to other combinations of van der Waals materials to provide a platform for synthesizing micron‐size epitaxial heterostructures with a desired electronic structure for catalysis and microelectronics.
Liu, Lili [Physical and Computational Sciences Dir↗
Heteroepitaxial control of thickness, strain, and domain architecture in few-layer ferroelectric tin monochalcogenides
Thin-film epitaxy and epitaxial strain have been widely exploited to tune domain configurations, switching behavior, and ferroic properties in conventional three-dimensional ferroelectric thin films; however, its application to controlling the properties of two-dimensional (2D) ferroelectrics has remained largely unexplored. Here, using SnX (X = Se, S) as a model system, we demonstrate heteroepitaxial control of thickness, strain state, and domain architecture in few-layer ferroelectric SnX via growth on monolayer MoS2 van der Waals (vdW) templates. Compared with conventional growth, MoS2-templated heteroepitaxy promotes epitaxial alignment, yielding ultrathin SnSe films with improved crystalline quality, full areal coverage, and enlarged lateral dimensions. Strong interfacial epitaxial coupling induces pronounced in-plane strain and stabilizes a hierarchical ferroelastic domain architecture, in which long-range 90° stripe domains are further subdivided into nanoscale rotational variants, as revealed by scanning transmission electron microscopy and synchrotron X-ray microscopy. Piezoresponse force microscopy and second-harmonic polarimetry confirm robust in-plane polarization, while ferroelectricity in SnSe is established through polarization-electric field hysteresis and nonvolatile ferroelectric resistive switching with on/off ratios approaching 1000. A nonvolatile, switchable ferroelectric diode effect further evidences direct coupling between polarization and charge transport. Notably, ferroelectric switchability exhibits a strong thickness dependence and is preserved only below ∼10 layers. This vdW heteroepitaxial strategy is further extended to ferroelectric SnS. The seamless heteroepitaxial integration of 2D ferroelectrics with CMOS-compatible, wafer-scale MoS2 templates provides a general and scalable route for strain-enabled structural and ferroelectric engineering in emerging memory and low-power optoelectronic applications.
Wang, Yueyin↗
Macroscopic Monochalcogenide van der Waals Ferroics: Growth, Domain Structures, and Curie Temperature
Two-dimensional and layered van der Waals materials promise to overcome the limitations of conventional ferroelectrics in terms of miniaturization and material integration, but synthesis has produced only small (up to few micrometer-sized) ferroic crystals. Here, we report the realization of in-plane ferroelectric few-layer crystals of the monochalcogenides tin(II) sulfide and selenide (SnS, SnSe) whose linear dimensions exceed the current state of the art by up to 1 order of magnitude. Such large crystals allow the investigation of ferroic domain patterns that are unaffected by edges and finite-size effects. Analysis of the abundant stripe domains by electron microscopy and nanobeam electron diffraction shows two distinct domain types: twin domains separated by positively charged walls with alternating head-to-head and tail-to-tail polarization as well as not previously observed purely rotational domains connected by neutral domain walls with head-to-tail dipoles. Access to large crystals allowed the determination of the Curie temperature of few-layer SnSe van der Waals ferroelectrics, and it enables the investigation of this class of ferroelectrics by widely available methods such as polarized optical microscopy. Furthermore, the combination with layer transfer protocols promises uniform materials for exploring fundamentals and for implementing devices for information processing and energy conversion.
36 MATERIALS SCIENCE↗
Domain-dependent strain and stacking in two-dimensional van der Waals ferroelectrics
Van der Waals (vdW) ferroelectrics have attracted significant attention for their potential in next-generation nano-electronics. Two-dimensional (2D) group-IV monochalcogenides have emerged as a promising candidate due to their strong room temperature in-plane polarization down to a monolayer limit. However, their polarization is strongly coupled with the lattice strain and stacking orders, which impact their electronic properties. Here, we utilize four-dimensional scanning transmission electron microscopy (4D-STEM) to simultaneously probe the in-plane strain and out-of-plane stacking in vdW SnSe. Specifically, we observe large lattice strain up to 4% with a gradient across ~50 nm to compensate lattice mismatch at domain walls, mitigating defects initiation. Additionally, we discover the unusual ferroelectric-to-antiferroelectric domain walls stabilized by vdW force and may lead to anisotropic nonlinear optical responses. Our findings provide a comprehensive understanding of in-plane and out-of-plane structures affecting domain properties in vdW SnSe, laying the foundation for domain wall engineering in vdW ferroelectrics.
42 ENGINEERING↗