/Tag: In2Se3

InSe: a two-dimensional material with strong interlayer coupling. (arXiv:1803.09919v1 [cond-mat.mtrl-sci])

2018-03-28T19:58:56+00:00March 28th, 2018|Categories: Publications|Tags: , |

Atomically thin, two-dimensional (2D) indium selenide (InSe) has attracted considerable attention due to large tunability in the band gap (from 1.4 to 2.6 eV) and high carrier mobility. The intriguingly high dependence of band gap on layer thickness may lead to novel device applications, although its origin remains poorly understood, and generally attributed to quantum confinement effect. In this work, we demonstrate via first-principles calculations that strong interlayer coupling may be mainly responsible for this phenomenon, especially in the fewer-layer region, and it could also be an essential factor influencing other material properties of {beta}-InSe and {gamma}-InSe. Existence of strong interlayer coupling manifests itself in three aspects: (i) indirect-to-direct band gap transitions with increasing layer thickness; (ii) fan-like frequency diagrams of the shear and breathing modes of few-layer flakes; (iii) strong layer-dependent carrier mobilities. Our results indicate that multiple-layer InSe may be deserving of attention from FET-based technologies and also an ideal system to study interlayer coupling, possibly inherent in other 2D materials.

Published : "arXiv Mesoscale and Nanoscale Physics".

InSe monolayer: synthesis, structure and ultra-high second-harmonic generation

2018-03-20T16:31:38+00:00March 20th, 2018|Categories: Publications|Tags: , |

III–IV layered materials such as indium selenide have excellent photoelectronic properties. However, synthesis of materials in such group, especially with a controlled thickness down to monolayer, still remains challenging. Herein, we demonstrate the successful synthesis of monolayer InSe by physical vapor deposition (PVD) method. The high quality of the sample was confirmed by complementary characterization techniques such as Raman spectroscopy, atomic force microscopy (AFM) and high resolution annular dark field scanning transmission electron microscopy (ADF-STEM). We found the co-existence of different stacking sequence ( β – and γ -InSe) in the same flake with a sharp grain boundary in few-layered InSe. Edge reconstruction is also observed in monolayer InSe, which has a distinct atomic structure from the bulk lattice. Moreover, we discovered that the second-harmonic generation (SHG) signal from monolayer InSe shows large optical second-order susceptibility that is…

Published in: "2DMaterials".

A switchable diode based on room-temperature two-dimensional ferroelectric {alpha}-In2Se3 thin layers. (arXiv:1803.04664v1 [cond-mat.mtrl-sci])

2018-03-14T19:59:05+00:00March 14th, 2018|Categories: Publications|Tags: , |

Nanoscaled room-temperature ferroelectricity is ideal for developing advanced non-volatile high-density memories. However, reaching the thin film limit in conventional ferroelectrics is a long-standing challenge due to the possible critical thickness effect. Van der Waals materials, thanks to their stable layered structure, saturate interfacial chemistry and weak interlayer couplings, are promising for exploring ultra-thin two-dimensional (2D) ferroelectrics and device applications. Here, we demonstrate a switchable room-temperature ferroelectric diode built upon a 2D ferroelectric {alpha}-In2Se3 layer as thin as 5 nm in the form of graphene/{alpha}-In2Se3 heterojunction. The intrinsic out-of-plane ferroelectricity of the {alpha}-In2Se3 thin layers is evidenced by the observation of reversible spontaneous electric polarization with a relative low coercive electric field of ~$2 X 10^5 V/cm$ and a typical ferroelectric domain size of around tens ${mu}m^2$. Owing to the out-of-plane ferroelectricity of the {alpha}-In2Se3 layer, the Schottky barrier at the graphene/{alpha}-In2Se3 interface can be effectively tuned by switching the electric polarization with an applied voltage, leading to a pronounced switchable double diode effect with an on/off ratio of ~$10^4$. Our results offer a new way for developing novel nanoelectronic devices based on 2D ferroelectrics.

Published in: "arXiv Material Science".

InSe: a two-dimensional material with strong interlayer coupling

2018-03-07T02:24:17+00:00March 7th, 2018|Categories: Publications|Tags: , |

Nanoscale, 2018, Accepted ManuscriptDOI: 10.1039/C7NR09486H, PaperYuanhui Sun, shulin Luo, Xin-Gang Zhao, Koushik Biswas, Songlin Li, Lijun ZhangAtomically thin, two-dimensional (2D) indium selenide (InSe) has attracted considerable attention due to large tunability in the band gap (from 1.4 to 2.6 eV) and high carrier

Published in: "RSC Nanoscale".

Characterization, optical properties and electron(exciton)-phonon interaction in bulk In2Se3 crystals and InSe nanocrystals in In2nSe3 confinement. (arXiv:1802.02781v1 [cond-mat.mtrl-sci])

2018-02-09T19:59:20+00:00February 9th, 2018|Categories: Publications|Tags: , , |

Complex electron-microscopic, energy-dispersed and wide-temperature optical absorption and photoluminescence (PL) investigations are carried out into Bridgeman-grown layered In2Se3 crystals. It is shown that In2Se3 crystals as a whole have a homogeneous concentration of In and Se atoms, corresponding with In2Se3 stoichiometry. Nevertheless, In2Se3 crystals contain a significant amount of dislocations, on which nano-sized interspersions of crystal phases of pure InSe, In6Se7 and monoclinic red Se settle down. Optical wide-temperature investigations of In2Se3 allow us to do the following: establish the width of the band-gap, the exciton binding energy; determine the frequency of a half-layer A-phonon, which takes part in electron (exciton)-phonon interaction; and to evaluate the effective masses of carriers and the dielectric permeability. Finally, blue shift of the band-gap and character of the electron (exciton)-phonon interaction of nano-sized 3D InSe crystals confined in an In2Se3 crystal matrix; influence of an InSe nanocrystal radius and of an ensemble of 3D InSe nanocrystals with different radii for an increase of the exciton emission/absorption half-width line with temperature and radii of InSe nanocrystals are discussed.

Published in: "arXiv Material Science".

High-Performance Photo-Electrochemical Photodetector Based on Liquid-Exfoliated Few-Layered InSe Nanosheets with Enhanced Stability

2017-12-19T18:30:00+00:00December 19th, 2017|Categories: Publications|Tags: , |

Abstract The band gap of few-layered 2D material is one of the significant issues for the application of practical devices. Due to the outstanding electrical transport property and excellent photoresponse, 2D InSe has recently attracted rising attention. Herein, few-layered InSe nanosheets with direct band gap are delivered by a facile liquid-phase exfoliation approach. We have synthesized a photoelectrochemical (PEC)-type few-layered InSe photodetector that exhibits high photocurrent density, responsivity, and stable cycling ability in KOH solution under the irradiation of sunlight. The detective ability of such PEC InSe photodetector can be conveniently tuned by varying the concentration of KOH and applied potential suggesting that the present device can be a fitting candidate as an excellent photodetector. Moreover, extendable optimization of the photodetection performance on InSe nanosheets would further enhance the potential of the prepared InSe in other PEC-type devices such as dye-sensitized solar cells, water splitting systems, and solar tracking equipment. A photoelectrochemical photodetector fabricated from indium selenide nanosheets with preferable adjustable response performances to sunlight is presented. Specifically, the detection ability of such a detector can be conveniently regulated by tuning the concentration of electrolyte and the applied potential. The as-fabricated InSe detector responds to sunlight and its photocurrent density can reach 300 nA cm−2 with no degeneration.

Published in: "Advanced Functional Materials".

Atomic-scale mechanisms of defect- and light-induced oxidation and degradation of InSe. (arXiv:1712.04662v1 [cond-mat.mtrl-sci])

2017-12-14T19:59:24+00:00December 14th, 2017|Categories: Publications|Tags: , , , , |

Layered indium selenide (InSe), a new two-dimensional (2D) material with a hexagonal structure and semiconducting characteristic, is gaining increasing attention owing to its intriguing electronic properties. Here, by using first-principles calculations, we reveal that perfect InSe possesses a high chemical stability against oxidation, superior to MoS2. However, the presence of intrinsic Se vacancy (VSe) and light illumination can markedly affect the surface activity. In particular, the excess electrons associated with the exposed In atoms at the VSe site under illumination are able to remarkably reduce the dissociation barrier of O2 to ~0.2 eV. Moreover, at ambient conditions, the splitting of O2 enables the formation of substitutional (apical) oxygen atomic species, which further cause the trapping and subsequent rapid splitting of H2O molecules and ultimately the formation of hydroxyl groups. Our findings uncover the causes and underlying mechanisms of InSe surface degradation via the defect-photo promoted oxidations. Such results will be beneficial in developing strategies for the storage of InSe material and its applications for surface passivation with boron nitride, graphene or In-based oxide layers.

Published in: "arXiv Material Science".

Unusual phonon behavior and ultra-low thermal conductance of monolayer InSe

2017-11-29T14:26:19+00:00November 29th, 2017|Categories: Publications|Tags: , |

Nanoscale, 2017, Accepted ManuscriptDOI: 10.1039/C7NR07779C, PaperHangbo Zhou, Yongqing Cai, Gang Zhang, Yong-Wei ZhangMonolayer indium selenide (InSe) has shown many fascinating properties, such as high electron mobility, quantum Hall effect and anomalous optical response. However, its phonon properties, thermal transport properties and its…The content

Published in: "RSC Nanoscale".

Electrically Driven Reversible Phase Changes in Layered In2Se3 Crystalline Film

2017-10-04T18:30:18+00:00October 4th, 2017|Categories: Publications|Tags: , , |

Abstract An unconventional phase-change memory (PCM) made of In2Se3, which utilizes reversible phase changes between a low-resistance crystalline β phase and a high-resistance crystalline γ phase is reported for the first time. Using a PCM with a layered crystalline film exfoliated from In2Se3 crystals on a graphene bottom electrode, it is shown that SET/RESET programmed states form via the formation/annihilation of periodic van der Waals’ (vdW) gaps (i.e., virtual vacancy layers) in the stack of atomic layers and the concurrent reconfiguration of In and Se atoms across the layers. From density functional theory calculations, β and γ phases, characterized by octahedral bonding with vdW gaps and tetrahedral bonding without vdW gaps, respectively, are shown to have energy bandgap value of 0.78 and 1.86 eV, consistent with a metal-to-insulator transition accompanying the β-to-γ phase change. The monolithic In2Se3 layered film reported here provides a novel means to achieving a PCM based on melting-free, low-entropy phase changes in contrast with the GeTe–Sb2Te3 superlattice film adopted in interfacial phase-change memory. Reversible crystalline–crystalline phase-change memories are developed by stacking In2Se3 on the bottom graphene electrode. This shows SET and RESET programmed states via formation and annihilation of periodic van der Waals’ gaps. The reversible transition of monolithic In2Se3 layered film demonstrates the potential of melting-free and low-entropy phase-change memories.

Published in: "Advanced Materials".

Fast photoresponse and high detectivity in copper indium selenide (CuIn 7 Se 11 ) phototransistors

2017-10-03T14:31:20+00:00October 3rd, 2017|Categories: Publications|Tags: , |

The fast and sensitive detection of light can lead to a variety of optoelectronics and/or photonic-based applications in fields ranging from fast optical switching devices to health and environmental monitoring systems. Although several systems based on organic and inorganic materials show high sensitivity to visible light, in general they suffer from slow response times. Here we show that phototransistors fabricated using multilayers of CuIn 7 Se 11 exhibit response times of ~ tens of µ s with responsivity ( R ) values  >  10 AW −1 and with external quantum efficiencies reaching beyond 10 3 % when excited with a 658 nm wavelength laser. These devices also show high specific detectivity ( D * ) values of ~10 12 Jones. The responsivity and detectivity exhibited by these phototransistors are at least an order of magnitude better than commercially available conventional Si-based photodetectors, coupled w…

Published in: "2DMaterials".

Memristive behavior in In2Se3 asymmetrical hetero-structures

2017-09-29T18:29:22+00:00September 29th, 2017|Categories: Publications|Tags: |

RSC Adv., 2017, 7,46431-46435DOI: 10.1039/C7RA08438B, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Yafei Yuan, Xinran Cao, Yan Sun, Jing Su, Chunmin Liu, Ling Cheng, Lihua Yuan, Hao Zhang, Jing LiBased on Ag/In2Se3/ITO and Ta/In2Se3/ITO asymmetrical

Published in: "RSC Advances".

A flexible, transparent and high-performance gas sensor based on layer-materials for wearable technology

2017-09-13T12:29:17+00:00September 13th, 2017|Categories: Publications|Tags: , , |

Gas sensors play a vital role among a wide range of practical applications. Recently, propelled by the development of layered materials, gas sensors have gained much progress. However, the high operation temperature has restricted their further application. Herein, via a facile pulsed laser deposition (PLD) method, we demonstrate a flexible, transparent and high-performance gas sensor made of highly-crystalline indium selenide (In 2 Se 3 ) film. Under UV–vis-NIR light or even solar energy activation, the constructed gas sensors exhibit superior properties for detecting acetylene (C 2 H 2 ) gas at room temperature. We attribute these properties to the photo-induced charger transfer mechanism upon C 2 H 2 molecule adsorption. Moreover, no apparent degradation in the device properties is observed even after 100 bending cycles. In addition, we can also fabricate this device on rigid substrates, which is also capable to detect ga…

Published in: "Nanotechnology".

Out-of-plane Piezoelectricity and Ferroelectricity in Layered ${alpha}$-In2Se3 Nano-flakes. (arXiv:1708.09049v1 [cond-mat.mtrl-sci])

2017-08-31T19:59:09+00:00August 31st, 2017|Categories: Publications|Tags: |

Piezoelectric and ferroelectric properties in the two dimensional (2D) limit are highly desired for nanoelectronic, electromechanical, and optoelectronic applications. Here we report the first experimental evidence of out-of-plane piezoelectricity and ferroelectricity in van der Waals layered ${alpha}$-In2Se3 nano-flakes. The non-centrosymmetric R3m symmetry of the ${alpha}$-In2Se3 samples is confirmed by scanning transmission electron microscopy, second-harmonic generation, and Raman spectroscopy measurements. Domains with opposite polarizations are visualized by piezo-response force microscopy. Single-point poling experiments suggest that the polarization is potentially switchable for ${alpha}$-In2Se3 nano-flakes with thicknesses down to ~ 10 nm. The piezotronic effect is demonstrated in two-terminal devices, where the Schottky barrier can be modulated by the strain-induced piezopotential. Our work on polar ${alpha}$-In2Se3, one of the model 2D piezoelectrics and ferroelectrics with simple crystal structures, shows its great potential in electronic and photonic applications.

Published in: "arXiv Material Science".

Defects and oxidation resilience in InSe

2017-08-22T14:30:02+00:00August 22nd, 2017|Categories: Publications|Tags: , , |

Author(s): K. J. Xiao, A. Carvalho, and A. H. Castro NetoWe use density functional theory to study intrinsic defects and oxygen related defects in indium selenide. We find that InSe is prone to oxidation, but however not reacting with oxygen as strongly as phosphorene. The dominant intrinsic defects in In-rich material are the In interstitial, a shallow d…[Phys. Rev. B 96, 054112] Published Thu Aug 17, 2017

Published in: "Physical Review B".

Defects and oxidation resilience in $InSe$. (arXiv:1705.05519v2 [cond-mat.mtrl-sci] UPDATED)

2017-08-02T19:59:42+00:00August 2nd, 2017|Categories: Publications|Tags: , , |

We use density functional theory to study intrinsic defects and oxygen related defects in indium selenide. We find that ${InSe}$ is prone to oxidation, but however not reacting with oxygen as strongly as phosphorene. The dominant intrinsic defects in ${In}$-rich material are the ${In}$ interstitial, a shallow donor, and the ${Se}$ vacancy, which introduces deep traps. The latter can be passivated by oxygen, which is isoelectronic with ${Se}$. The dominant intrinsic defects in ${Se}$-rich material have comparatively higher formation energies.

Published in: "arXiv Material Science".

Two-dimensional InSe as a potential thermoelectric material. (arXiv:1705.06688v3 [cond-mat.mtrl-sci] UPDATED)

2017-07-25T19:59:02+00:00July 25th, 2017|Categories: Publications|Tags: , , |

Thermoelectric properties of monolayer indium selenide (InSe) are investigated by using Boltzman transport theory and first-principles calculations as a function of Fermi energy and crystal orientation. We find that the maximum power factor of p-type (n-type) monolayer InSe can be as large as 0.049 (0.043) W/K$^2$m at 300 K in the armchair direction. The excellent thermoelectric performance of monolayer InSe is attributed to both of its Seebeck coefficient and electrical conductivity. The large Seebeck coefficient originates from the moderate (about 2 eV) band gap of monolayer InSe as an indirect gap semiconductor, while its large electrical conductivity is due to its unique two-dimensional density of states (DOS), which consists of an almost constant DOS near the conduction band bottom and a sharp peak near the valence band top.

Published in: "arXiv Material Science".

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