InSe Crystals Research Articles

Repair Engineering of Crystal Structure in van der Waals Materials by Probe Electron Beam.

The advancement of electronic technology has led to increasing research on performance and stability. Continuous electrical pulse stimulation can cause crystal structure changes, affecting performance and accelerating aging. Controlled repair of these defects is crucial. In this study, we investigated crystal structure changes in van der Waals (vdW) InSe crystals under continuous electric pulses by using electron beam lithography (EBL) and spherical aberration corrected transmission electron microscopy (Cs-TEM). Results show that electrical pulses induce amorphous regions in the InSe lattice, increasing the device resistance. We used Cs-STEM probe scanning for precise repair, abbreviated SPRT, to optimize device performance. SPRT is related to electric fields induced by the electron beam and can be applied to other 2D materials like α-In2Se3 and CrSe2, offering a potential approach to extend device lifespan.

Single crystalline Holmium doped InSe for optical limiting operation in Near-IR region

Single crystals possessing nonlinear absorption (NA) character are favorable optical limiter in near infrared region (NIR). The NA features of pure and 0.005%, 0.05%, 0.1% Holmium (Ho) doped single crystals of InSe were analyzed at 1200 nm wavelength within 120 fs and 1 kHz repetition rate. The open-aperture Z-scan technique was employed to determine the NA performance and optical limiting-(OL) threshold. In an attempt to determine the NA coefficients, two types of theoretical models were used. The first model takes into account only the two photon absorption-(TPA), while the second model considers one photon absorption, TPA and free carrier absorption. Based on the experimental results, the main NA mechanism of the studied single crystals is determined as sequential TPA. TPA coefficient value of the pure InSe single crystal increased from 1.41 × 10−10 to 10.7 × 10−10 cm W−1 with increasing Ho doping concentration at 398.1 GW cm−2 input intensity. The NA coefficients increased from 0.84 × 10−9 to 1.62 × 10−9 cm W−1 at the same input intensity. On the other hand, the OL threshold values were found to be 0.027, 0.025, 0.022 and 0.020 J cm−2 at 1200 nm wavelength for pure InSe and the increasing Ho concentration, respectively. The robust NA characteristics and the low OL threshold establish the Ho-doped InSe single crystal as a favorable candidate for OL applications in the NIR spectral region.

Uncovering the phonon spectra and lattice dynamics of plastically deformable InSe van der Waals crystals

Stacking two-dimensional (2D) van der Waals (vdW) materials in a layered bulk structure provides an appealing platform for the emergence of exotic physical properties. As a vdW crystal with exceptional plasticity, InSe offers the opportunity to explore various effects arising from the coupling of its peculiar mechanical behaviors and other physical properties. Here, we employ neutron scattering techniques to investigate the correlations of plastic interlayer slip, lattice anharmonicity, and thermal transport in InSe crystals. Not only are the interlayer slip direction and magnitude well captured by shifts in the Bragg reflections, but we also observe a deviation from the expected Debye behaviour in the heat capacity and lattice thermal conductivity. Combining the experimental data with first-principles calculations, we tentatively attribute the observed evidence of strong phonon-phonon interactions to a combination of a large acoustic-optical frequency resonance and a nesting effect. These findings correlate the macroscopic plastic slip and the microscopic lattice dynamics, providing insights into the mechano-thermo coupling and modulation in 2D vdW materials.

Preparation of In0.5Sn0.5Se Crystal via a Zone Melting Method and Evaluation of its Thermoelectric Properties

AbstractIndium selenides (InSe) is a promising layer‐structured semiconductor with broad potential applications in photovoltaics, diodes, and optic devices, but its thermoelectric performance is limited by the high thermal conductivity. In this work, by alloying high‐performance thermoelectric SnSe in InSe, the In0.5Sn0.5Se crystal is prepared via a zone melting method. The density of In0.5Sn0.5Se crystal is measured as 5.81 g cm−3 which is between the density of pure SnSe and InSe. The XRD measurements indicate that the grown In0.5Sn0.5Se crystal consists of InSe and SnSe crystals with a preferred orientation along (00l) and (h00) planes, respectively. SEM and EDS analysis reveal that eutectic InSe and SnSe phases interdigitate with each other. The thermogravimetry analysis shows a slow decrease at a temperature ≈700 °C. In0.5Sn0.5Se crystal displays a n‐type conduct behavior, the electrical conductivity σ is ≈0.02 Scm−1 at room temperature and increases to 8.4 Scm−1 under 820 K. The highest power factor PF is estimated to be ≈0.36 µWcmK−2 near 570 K. The InSe‐SnSe phase boundaries lead the thermal conductivity of In0.5Sn0.5Se crystal to be as low as 0.29 Wm−1K−1. Due to the low lattice thermal conductivity, In0.5Sn0.5Se crystal shows a ZT value of 0.04 at 600 K in this work.

Single‐crystalline indium selenide fibers by laser‐induced recrystallization and their tunable whispering‐gallery‐mode lasing by pressure‐modulating

AbstractIndium selenide (InSe) crystal, as an emerging Van der Waals semiconductor, showed great potential in optical and optoelectronic devices due to its remarkable electron mobility, flexible direct bandgap, and photoresponsivity. Especially, the bulk single‐crystalline InSe shows superplastic deformability with the aid of the interlayer gliding and cross‐layer dislocation slip. The extraordinary mechanical behavior brings significant opportunities and possibilities to pressure‐modulated optical devices, which, however, have not been explored sufficiently. Additionally, InSe crystals are challenged in the rapid large‐scale preparation and reproduction due to limitations, such as phase heterogeneity, dissociation risks, and chemical instability. Herein, we proposed a fiber drawing technique to create single‐crystalline InSe by the molten core drawing method combined with CO2 laser‐induced recrystallization. The fabricated InSe fiber, spanning several meters in length, shows a uniform and directional single‐crystalline InSe core encased within a 450 µm thick protective borosilicate glass cladding. The inherent core‐cladding configuration of the InSe fibers not only provides robust protection to the InSe crystals but also seamlessly creates a whispering‐gallery‐mode microcavity. Utilizing a 532 nm nanosecond pulsed laser as a pump, a tunable lasing from 1076.2 to 1111.8 nm was achieved, dictated by the controlled pressure within the InSe fiber. We present a simple and effective method for single‐crystalline InSe fabrication and first achieve a pressure‐modulated laser in a near‐infrared band based on InSe fiber, heralding an advancement for the scalable, efficient generation of tunable lasers.

New Organic Crystalline Material Close to Nodal-Line Materials: α′-STF2IBr2

Recently, topological materials (TMs) have attracted attention from various scientists. Their electronic properties are governed by relativistic particles called Dirac fermions which, in some cases, possess no masses and move in solids with the speed of light. In addition to the unique particles, such materials exhibit unprecedented electronic properties because of the quantum effects (interference between wavefunctions). Examples include nodal-line materials (NLMs), where metallic or even superconducting properties may appear only at the surface of the single crystals of insulators. Thus far, whether they be organic or inorganic compounds, TMs have hardly been discovered except for the zero-gap conductors (ZGCs), because there is no guideline on how to develop such unusual materials. In this work, we prepared a new organic charge–transfer complex, α′-STF2IBr2 (STF = bis(ethylenedithio)diselenadithiafulvalene), which measured the electrical and magnetic properties and calculated the band structure and intermolecular interactions. A close comparison with those of α-STF2I3, being established as a ZGC at p > 12–15 kbar, revealed that α′-STF2IBr2 is also closely related to it, but belongs to a different type of TMs, namely NLMs. This finding will accelerate the successive findings of NLMs to elucidate the mechanism of their unique electronic properties.

Influence of Antimony doping on electrical and photoelectrical response in Indium Selenide crystals

Indium Selenide (InSe) is the most suitable photovoltaic conversion material with narrow band gap (1.3 eV) in the layered semiconductors. The optical and transport properties of InSe offer significant potential for promising applications in the modern era of electronics and photo-electronic devices. The aim is achieved by high electric conductivity of InSe crystals, SbxIn1−xSe (x= 0.00, 0.10, 0.15, 0.20) crystals was grown by direct vapour transport (DVT) technique. The chemical compositional and surface morphology properties of grown crystals were studied by energy dispersive X-ray analysis (EDAX) and scanning electron microscope (SEM) respectively. The hexagonal crystal structure of grown crystal has revealed by X-ray diffraction (XRD) spectra. The dopant concentration of antimony (Sb) was found to have a decreasing effect on the optical band gap and activation energy as calculated through absorption spectra and Arrhenius relations respectively. The photo-response parameters: growth-decay and trap-depth parameters have been obtained using growth-decay curve. These results confirm that SbxIn1−xSe crystal was collective applicant for electronic and optoelectronic devices.

Remarkable plasticity and softness of polymorphic InSe van der Waals crystals

Indium selenide (InSe) crystals are reported to show exceptional plasticity, a new property to two-dimensional van der Waals (2D vdW) semiconductors. However, the correlation between plasticity and specific prototypes is unclear, and the understanding of detailed plastic deformation mechanisms is inadequate. Here three prototypes of InSe are predicted to be plastically deformable by calculation, and the plasticity of polymorphic crystals is verified by experiment. Moreover, distinct nanoindentation behaviors are seen on the cleavage and cross-section surfaces. The modulus and hardness of InSe are the lowest ones among a large variety of materials. The plastic deformation is further perceived from chemical interactions during the slip process. Particularly for the cross-layer slip, the initial In-Se bonds break while new In-In and Se-Se bonds are newly formed, maintaining a decent interaction strength. The remarkable plasticity and softness alongside the novel physical properties, endow InSe great promise for application in deformable and flexible electronics.

Growth and thermal properties of InSe crystal by using the ground simulation apparatus of China space station

Indium selenide (InSe) semiconductor crystal was grown by using the ground simulation apparatus of China space station in this work. The furnace was controlled at 715 °C and the temperature gradient for crystal growth was ∼30 °C/cm. The as-grown InSe crystalizes in γ-phase with space group of R3m. The average etching pits density (EPD) is estimated to be about 104/cm2. Thermal analysis indicates a positive thermal expansion at 30–500 °C and no volatilization occurred even as high as 1000 °C. This work not only establishes a reliable process for preparing large-sized InSe single crystal but also creates a foundation for further work in outer space in the future.

Photovoltaic effect in metal foils and crystals of topological insulators

Bi and Bi-based crystals of topological insulators demonstrate high surface charge transport and a change in polarity due to the photovoltaic effect.

High-throughput screening of 2D van der Waals crystals with plastic deformability

Inorganic semiconductors exhibit multifarious physical properties, but they are prevailingly brittle, impeding their application in flexible and hetero-shaped electronics. The exceptional plasticity discovered in InSe crystal indicates the existence of abundant plastically deformable two-dimensional van der Waals (2D vdW) materials, but the conventional trial-and-error method is too time-consuming and costly. Here we report on the discovery of tens of potential 2D chalcogenide crystals with plastic deformability using a nearly automated and efficient high-throughput screening methodology. Seven candidates e.g., famous MoS2, GaSe, and SnSe2 2D materials are carefully verified to show largely anisotropic plastic deformations, which are contributed by both interlayer and cross-layer slips involving continuous breaking and reconstruction of chemical interactions. The plasticity becomes a new facet of 2D materials for deformable or flexible electronics.

Optical bistability in layered InSe crystal

In this study, we experimentally study the dependence of the intensity of laser radiation incident on and transmitted through a layered InSe crystal. A picosecond YAG:Nd3+ laser with a parametric light generator was used as a light source, making it possible to generate light pulses with a duration of [Formula: see text]30 ps, tunable in frequency within the range of 0.75–1.5 μm. Optical bistability in the region of exciton resonance was detected in an InSe crystal at room-temperature under the picosecond YAG:Nd laser. It is shown that the decrease in absorption in the exciton resonance region is associated with the process of exciton–exciton interaction, shielding of excitons, and the Mott transition.

Compelling Evidence for the ε‐Phase InSe Crystal by Oblique Incident Second Harmonic Generation

AbstractIndium selenide (InSe), a layered semiconductor with direct band gap and high carrier mobility, holds promising applications in bendable electronics and ultrafast optoelectronics. Yet its crystal structure exhibits polytypism with four different stacking orders (γ‐, ε‐, β‐ and δ‐phases), arising from the weak van der Waals interlayer coupling. These phases are nearly‐degenerate in energy but are predicted to have contrasting electronic structures for versatile applications. It remains highly challenging to distinguish between these polytypes due to the lack of noninvasive tools that are sensitive enough to the interlayer structural variations. Here, the unambiguous discrimination of different InSe polytypes using symmetry‐sensitive oblique incident optical second harmonic generation (SHG) is demonstrated. Surprisingly, the ε‐phase is found to be dominant, although the samples from two popular commercial vendors (2D Semiconductors and Six Carbon Technology) are claimed to be the γ‐phase. These results would help promoting the precise application of InSe crystal for piezoelectric transducer and strain sensing, as well as showing the oblique incident SHG to be a powerful structural analytical tool for van der Waals layered materials.

Electronic transport properties of Pb(Bi1−xSbx)2(Te1−ySey)4 topological insulator

A series of Pb(Bi1−xSbx)2(Te1−ySey)4 topological insulator crystals with various Sb molar ratios x and Se molar ratios y were fabricated, and their electronic transport properties were studied. Some of the millimeter-sized samples exhibited metallic behavior, while others exhibited semiconducting behavior with a resistivity as high as 48 mΩ cm at 2 K. In addition, Hall coefficients with a large variance were observed for samples from the same ingot, indicating spatial fluctuations in the composition and/or a nonuniform defect distribution. Then, micrometer-sized samples were cut from the millimeter-sized sample with the highest resistivity, and further electrical transport measurements were performed. Some of the micrometer-sized samples exhibited an even higher resistivity than that for the millimeter-sized sample. The magnetoresistance of the semiconducting micrometer-sized samples agreed well with a three-dimensional weak antilocalization/weak localization model in the low-temperature region below 20 K.

Lamellae preparation for atomic-resolution STEM imaging from ion-beam-sensitive topological insulator crystals

Good specimen quality is a key factor in achieving successful scanning transmission electron microscope analysis. Thin and damage-free specimens are prerequisites for obtaining atomic-resolution imaging. Topological insulator single crystals and thin films in the chalcogenide family such as Sb2Te3 are sensitive to electron and ion beams. It is, therefore, challenging to prepare a lamella suitable for high-resolution imaging from these topological insulator materials using standard focused ion-beam instruments. We have developed a modified method to fabricate thin focused ion-beam (FIB) lamellae with minimal ion-beam damage and artifacts. The technique described in the current study enables the reliable preparation of high-quality transmission electron microscope (TEM) specimens necessary for studying ultra-thin surface regions. We have successfully demonstrated that the careful selection of FIB milling parameters at each stage minimizes the damage layer without the need for post-treatment.

Anisotropic thermal conductivity of layered indium selenide

Layered indium selenide (InSe) has emerged as a promising two-dimensional semiconductor due to its high electron mobility and direct optical bandgap in the few-layer limit. As InSe is integrated into high-performance electronic and optoelectronic systems, thermal management will become critical, thus motivating detailed characterization of intrinsic thermal properties. Here, we report the room-temperature thermal conductivity of exfoliated crystals of InSe along the through-plane and in-plane directions using conventional and beam offset time-domain thermoreflectance (TDTR), respectively. InSe crystals with varying thicknesses were prepared by mechanical exfoliation onto Si(100) wafers followed by immediate encapsulation with a 3-nm-thick AlOx passivation layer to prevent ambient degradation prior to coating with metal films for TDTR measurements. The measured thermal conductivity in the in-plane direction, Λin ≈ 8.5 ± 2 W/m K, is an order of magnitude higher than that in the through-plane direction, Λthrough ≈ 0.76±0.15 W/m K, which implies a high thermal anisotropy ≈11 ± 3. These relatively high anisotropy and low thermal conductivity compared to other layered semiconductors imply that InSe will require unique thermal management considerations when implemented in electronic, optoelectronic, and thermoelectric applications.

Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

The temperature effect on the Raman scattering efficiency is investigated in varepsilon-GaSe and gamma-InSe crystals. We found that varying the temperature over a broad range from 5 to 350 K permits to achieve both the resonant conditions and the antiresonance behaviour in Raman scattering of the studied materials. The resonant conditions of Raman scattering are observed at about 270 K under the 1.96 eV excitation for GaSe due to the energy proximity of the optical band gap. In the case of InSe, the resonant Raman spectra are apparent at about 50 and 270 K under correspondingly the 2.41 eV and 2.54 eV excitations as a result of the energy proximity of the so-called B transition. Interestingly, the observed resonances for both materials are followed by an antiresonance behaviour noticeable at higher temperatures than the detected resonances. The significant variations of phonon-modes intensities can be explained in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone.

InSe Crystals Obtained by Stoichiometric Fusion for Optoelectronic Device Application

InSe Crystals Obtained by Stoichiometric Fusion for Optoelectronic Device Application

The advancement of compelling Indium Selenide: synthesis, structural studies, optical properties and photoelectrical applications

Single crystals of Indium Selenide (InSe) were successfully grown by direct vapor transport method. The grown crystals were characterized by estimating their surface morphology, chemical composition, structural, optical and photoconductive properties using appropriate techniques. SEM image suggested that InSe crystal has layered-type surface without morphological defects. Also, the hexagonal structure of crystal has been confirmed by X-ray diffraction (XRD) spectra and selected area electron diffraction (SAED) pattern. The crystal exhibits high absorption coefficient (104 cm−1) in visible region and direct bandgap of 1.22 eV. The trap depth parameters and photoconductivity parameters were determined by the growth-decay curve and they depend upon illumination intensity, temperature and wavelength of incident light. The grown InSe crystals have excellent photoconductive properties and hence can be utilized in different photoelectrical applications.

A Low-Cost Digital Pulsed Coherent Spectrometer for Investigation of NQR in Layered Semiconductor GaSe and InSe Crystals

A low-cost digital pulsed nuclear quadrupole resonance (NQR) radio-spectrometer is proposed, all main modules of digital processing and synthesis of which on the field-programmable gate array (FPGA) are implemented. The input sensitivity of the device is of the order of 3 μV to 5 μV which allows conducting NQR studies in samples of relatively small dimensions. The application of the developed methods of NQR pulsed radio spectroscopy made it possible to increase spectral resolution, improve spectral shape and significantly reduce the time of research. In the case of studying InSe and GaSe crystals, spectra with signal-to-noise ratio (SNR) values of 41.9 dB were observed in samples with a volume of 0.1 cm3. As the results of the research have shown, the characteristics of the proposed spectrometer make it effective when used to observe free induction decay (FID) signals of a significant number of isotopes of elements with quadrupolar nuclei.