In2Se3

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Room‐Temperature Ferroelectricity in Hexagonally Layered α‐In2Se3 Nanoflakes down to the Monolayer Limit

2018-11-11T04:32:19+00:00November 11th, 2018|Categories: Publications|Tags: , |

The thinnest layered ferroelectric is demonstrated for the first time at room temperature. The semiconducting hexagonal α‐In2Se3 nanoflakes exhibit out‐of‐plane and in‐plane ferroelectricity that are closely intercorrelated. The polarization switching and hysteresis loops can be realized in the thickness as thin as ≈2.3 nm (bilayer) and ≈1.2 nm (monolayer). Two types of ferroelectric switchable devices are proposed to show the potential application in nonvolatile memories. Abstract 2D ferroelectric material has emerged as an attractive building block for high‐density data storage nanodevices. Although monolayer van der Waals ferroelectrics have been theoretically predicted, a key experimental breakthrough for such calculations is still not realized. Here, hexagonally stacking α‐In2Se3 nanoflake, a rarely studied van der Waals polymorph, is reported to exhibit out‐of‐plane (OOP) and in‐plane (IP) ferroelectricity at room temperature. Ferroelectric multidomain states in a hexagonal α‐In2Se3 nanoflake with uniform thickness can survive to 6 nm. Most strikingly, the electric‐field‐induced polarization switching and hysteresis loop are, respectively, observed down to the bilayer and monolayer (≈1.2 nm) thicknesses, which designates it as the thinnest layered ferroelectric and verifies the corresponding theoretical calculation. In addition, two types of ferroelectric nanodevices employing the OOP and IP polarizations in 2H α‐In2Se3 are developed, which are applicable for nonvolatile memories and heterostructure‐based nanoelectronics/optoelectronics.

Published in: "Advanced Functional Materials".

High Mobilities in Layered InSe Transistors with Indium‐Encapsulation‐Induced Surface Charge Doping

2018-11-10T22:34:25+00:00November 10th, 2018|Categories: Publications|Tags: , |

A robust layered indium selenide (InSe) field‐effect transistor (FET) with superior high mobility (3700 cm2 V−1 s−1 at room temperature) is demonstrated by depositing an indium doping layer. With tunable carrier transport, the surface‐doped InSe FETs present flexible operations to realize various logic circuits, such as inverters and not‐or and not‐and gates. Abstract Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field‐effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm2 V−1 s−1 at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron‐doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low‐frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature‐dependent mobility. Finally, the flexible functionalities of the logic‐circuit applications, for instance, inverter and not‐and (NAND)/not‐or (NOR) gates, are determined with these surface‐doping InSe FETs, which establish a paradigm for 2D‐based materials to overcome the bottleneck in the development of electronic devices.

Published in: "Advanced Materials".

High Mobilities in Layered InSe Transistors with Indium‐Encapsulation‐Induced Surface Charge Doping

2018-11-07T10:34:02+00:00November 7th, 2018|Categories: Publications|Tags: , |

A robust layered indium selenide (InSe) field‐effect transistor (FET) with superior high mobility (3700 cm2 V−1 s−1 at room temperature) is demonstrated by depositing an indium doping layer. With tunable carrier transport, the surface‐doped InSe FETs present flexible operations to realize various logic circuits, such as inverters and not‐or and not‐and gates. Abstract Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field‐effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm2 V−1 s−1 at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron‐doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low‐frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature‐dependent mobility. Finally, the flexible functionalities of the logic‐circuit applications, for instance, inverter and not‐and (NAND)/not‐or (NOR) gates, are determined with these surface‐doping InSe FETs, which establish a paradigm for 2D‐based materials to overcome the bottleneck in the development of electronic devices.

Published in: "Advanced Materials".

High Mobilities in Layered InSe Transistors with Indium‐Encapsulation‐Induced Surface Charge Doping

2018-11-07T00:35:18+00:00November 6th, 2018|Categories: Publications|Tags: , |

A robust layered indium selenide (InSe) field‐effect transistor (FET) with superior high mobility (3700 cm2 V−1 s−1 at room temperature) is demonstrated by depositing an indium doping layer. With tunable carrier transport, the surface‐doped InSe FETs present flexible operations to realize various logic circuits, such as inverters and not‐or and not‐and gates. Abstract Tunability and stability in the electrical properties of 2D semiconductors pave the way for their practical applications in logic devices. A robust layered indium selenide (InSe) field‐effect transistor (FET) with superior controlled stability is demonstrated by depositing an indium (In) doping layer. The optimized InSe FETs deliver an unprecedented high electron mobility up to 3700 cm2 V−1 s−1 at room temperature, which can be retained with 60% after 1 month. Further insight into the evolution of the position of the Fermi level and the microscopic device structure with different In thicknesses demonstrates an enhanced electron‐doping behavior at the In/InSe interface. Furthermore, the contact resistance is also improved through the In insertion between InSe and Au electrodes, which coincides with the analysis of the low‐frequency noise. The carrier fluctuation is attributed to the dominance of the phonon scattering events, which agrees with the observation of the temperature‐dependent mobility. Finally, the flexible functionalities of the logic‐circuit applications, for instance, inverter and not‐and (NAND)/not‐or (NOR) gates, are determined with these surface‐doping InSe FETs, which establish a paradigm for 2D‐based materials to overcome the bottleneck in the development of electronic devices.

Published in: "Advanced Materials".

Room‐Temperature Ferroelectricity in Hexagonally Layered α‐In2Se3 Nanoflakes down to the Monolayer Limit

2018-11-07T00:32:16+00:00November 6th, 2018|Categories: Publications|Tags: , |

The thinnest layered ferroelectric is demonstrated for the first time at room temperature. The semiconducting hexagonal α‐In2Se3 nanoflakes exhibit out‐of‐plane and in‐plane ferroelectricity that are closely intercorrelated. The polarization switching and hysteresis loops can be realized in the thickness as thin as ≈2.3 nm (bilayer) and ≈1.2 nm (monolayer). Two types of ferroelectric switchable devices are proposed to show the potential application in nonvolatile memories. Abstract 2D ferroelectric material has emerged as an attractive building block for high‐density data storage nanodevices. Although monolayer van der Waals ferroelectrics have been theoretically predicted, a key experimental breakthrough for such calculations is still not realized. Here, hexagonally stacking α‐In2Se3 nanoflake, a rarely studied van der Waals polymorph, is reported to exhibit out‐of‐plane (OOP) and in‐plane (IP) ferroelectricity at room temperature. Ferroelectric multidomain states in a hexagonal α‐In2Se3 nanoflake with uniform thickness can survive to 6 nm. Most strikingly, the electric‐field‐induced polarization switching and hysteresis loop are, respectively, observed down to the bilayer and monolayer (≈1.2 nm) thicknesses, which designates it as the thinnest layered ferroelectric and verifies the corresponding theoretical calculation. In addition, two types of ferroelectric nanodevices employing the OOP and IP polarizations in 2H α‐In2Se3 are developed, which are applicable for nonvolatile memories and heterostructure‐based nanoelectronics/optoelectronics.

Published in: "Advanced Functional Materials".

CuInS2–In2Se3 quantum dots – a novel material via a green synthesis approach

2018-11-05T14:36:30+00:00November 5th, 2018|Categories: Publications|Tags: |

RSC Adv., 2018, 8,37146-37150DOI: 10.1039/C8RA07389A, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.N. J. Simi, Libin Kuriakose, R. Vinayakan, V. V. IsonNovel CuInS2–In2Se3 QDs prepared by a two stage organometallic colloidal synthesis.The content of this

Published in: "RSC Advances".

CuInS2–In2Se3 quantum dots – a novel material via a green synthesis approach

2018-11-05T14:36:30+00:00November 5th, 2018|Categories: Publications|Tags: |

RSC Adv., 2018, 8,37146-37150DOI: 10.1039/C8RA07389A, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.N. J. Simi, Libin Kuriakose, R. Vinayakan, V. V. IsonNovel CuInS2–In2Se3 QDs prepared by a two stage organometallic colloidal synthesis.The content of this

Published in: "RSC Advances".

Non-volatile ferroelectric memory effect in ultrathin {alpha}-In2Se3. (arXiv:1810.05328v1 [cond-mat.mtrl-sci])

2018-10-15T02:29:33+00:00October 15th, 2018|Categories: Publications|Tags: , |

Recent experiments on layered {alpha}-In2Se3 have confirmed its room-temperature ferroelectricity under ambient condition. This observation renders {alpha}-In2Se3 an excellent platform for developing two-dimensional (2D) layered-material based electronics with nonvolatile functionality. In this letter, we demonstrate non-volatile memory effect in a hybrid 2D ferroelectric field effect transistor (FeFET) made of ultrathin {alpha}-In2Se3 and graphene. The resistance of graphene channel in the FeFET is tunable and retentive due to the electrostatic doping, which stems from the electric polarization of the ferroelectric {alpha}-In2Se3. The electronic logic bit can be represented and stored with different orientations of electric dipoles in the top-gate ferroelectric. The 2D FeFET can be randomly re-written over more than $10^5$ cycles without losing the non-volatility. Our approach demonstrates a protype of re-writable non-volatile memory with ferroelectricity in van de Waals 2D materials.

Published in: "arXiv Material Science".

Transformation of 2D group-III selenides to ultra-thin nitrides: enabling epitaxy on amorphous substrates

2018-09-28T10:33:37+00:00September 28th, 2018|Categories: Publications|Tags: , , |

The experimental realization of two-dimensional (2D) gallium nitride (GaN) has enabled the exploration of 2D nitride materials beyond boron nitride. Here we demonstrate one possible pathway to realizing ultra-thin nitride layers through a two-step process involving the synthesis of naturally layered, group-III chalcogenides (GIIIC) and subsequent annealing in ammonia (ammonolysis) that leads to an atomic-exchange of the chalcogen and nitrogen species in the 2D-GIIICs. The effect of nitridation differs for gallium and indium selenide, where gallium selenide undergoes structural changes and eventual formation of ultra-thin GaN, while indium selenide layers are primarily etched rather than transformed by nitridation. Further investigation of the resulting GaN films indicates that ultra-thin GaN layers grown on silicon dioxide act as effective ‘seed layers’ for the growth of 3D GaN on amorphous substrates.

Published in: "Nanotechnology".

Band offset and an ultra-fast response UV-VIS photodetector in γ-In2Se3/p-Si heterojunction heterostructures

2018-08-21T08:32:45+00:00August 21st, 2018|Categories: Publications|Tags: , |

RSC Adv., 2018, 8,29555-29561DOI: 10.1039/C8RA05677C, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Y. X. Fang, H. Zhang, F. Azad, S. P. Wang, F. C. C. Ling, S. C. SuHigh-quality γ-In2Se3 thin films and a γ-In2Se3/p-Si

Published in: "RSC Advances".

Optical second harmonic generation in encapsulated single-layer InSe. (arXiv:1808.05874v1 [physics.optics])

2018-08-20T04:30:23+00:00August 20th, 2018|Categories: Publications|Tags: , , |

We report the observation of optical second harmonic generation (SHG) in single-layer indium selenide (InSe). We measure a second harmonic signal of $>10^3$ $textrm{cts/s}$ under nonresonant excitation using a home-built confocal microscope and a standard pulsed pico-second laser. We demonstrate that polarization-resolved SHG serves as a fast, non-invasive tool to determine the crystal axes in single-layer InSe and to relate the sharp edges of the flake to the armchair and zigzag edges of the crystal structure. Our experiment determines these angles to an accuracy better than $pm$ $0.2^{circ}$. Treating the two-dimensional material as a nonlinear polarizable sheet, we determine a second-order nonlinear sheet polarizability $| chi_{textrm{sheet}}^{(2)}|=(17.9 pm 11.0)times 10^{-20}$ $textrm{m}^2 textrm{V}^{-1}$ for single-layer InSe, corresponding to an effective nonlinear susceptibility value of $| chi_textrm{eff}^{(2)}| approx (223 pm 138) times 10^{-12}$ $textrm{m} textrm{V}^{-1}$ accounting for the sheet thickness ($textrm{d} approx 0.8$ $textrm{nm}$). We demonstrate that the SHG technique can also be applied to encapsulated samples to probe their crystal orientations. The method is therefore suitable for creating high quality van der Waals heterostructures with control over the crystal directions.

Published : "arXiv Mesoscale and Nanoscale Physics".

Room temperature in-plane ferroelectricity in van der Waals In2Se3

2018-07-14T02:36:22+00:00July 14th, 2018|Categories: Publications|Tags: |

Van der Waals (vdW) assembly of layered materials is a promising paradigm for creating electronic and optoelectronic devices with novel properties. Ferroelectricity in vdW layered materials could enable nonvolatile memory and low-power electronic and optoelectronic switches, but to date, few vdW ferroelectrics have been reported, and few in-plane vdW ferroelectrics

Published in: "Science Advances".

Magnetotransport and lateral confinement in an InSe van der Waals Heterostructure

2018-06-21T10:34:16+00:00June 21st, 2018|Categories: Publications|Tags: , , , |

In the last six years, indium selenide (InSe) has appeared as a new van der Waals heterostructure platform which has been extensively studied due to its unique electronic and optical properties. Such as transition metal dichalcogenides (TMDCs), the considerable bandgap and high electron mobility can provide a potential optoelectronic application. Here we present low-temperature transport measurements on a few-layer InSe van der Waals heterostructure with graphene-gated contacts. For high magnetic fields, we observe magnetoresistance minima at even filling factors related to two-fold spin degeneracy. By electrostatic gating with negatively biased split gates, a one-dimensional channel is realized. Close to pinch-off, transport through the constriction is dominated by localized states with charging energies ranging from 2 to 5 meV. This work opens new possibility to explore the low-dimensional physics including quantum point contact and quantum dot.

Published in: "2DMaterials".

Large Disparity Between Optical and Fundamental Band Gaps in Layered In2Se3. (arXiv:1806.01251v1 [cond-mat.mtrl-sci])

2018-06-05T02:29:26+00:00June 5th, 2018|Categories: Publications|Tags: |

In$_2$Se$_3$ is a semiconductor material that can be stabilized in different crystal structures (at least one 3D and several 2D layered structures have been reported) with diverse electrical and optical properties. This feature has plagued its characterization over the years, with reported band gaps varying in an unacceptable range of 1 eV. Using first-principles calculations based on density functional theory and the HSE06 hybrid functional, we investigated the structural and electronic properties of four layered phases of In$_2$Se$_3$, addressing their relative stability and the nature of their fundamental band gaps, i.e., direct {em versus} indirect. Our results show large disparities between fundamental and optical gaps. The absorption coefficients are found to be as high as that in direct-gap III-V semiconductors. The band alignment with respect to conventional semiconductors indicate a tendency to $n$-type conductivity, explaining recent experimental observations.

Published in: "arXiv Material Science".

Gate-Defined Quantum Confinement in InSe-based van der Waals Heterostructures. (arXiv:1805.05896v1 [cond-mat.mes-hall])

2018-05-16T19:58:54+00:00May 16th, 2018|Categories: Publications|Tags: , , |

Indium selenide, a post-transition metal chalcogenide, is a novel two-dimensional (2D) semiconductor with interesting electronic properties. Its tunable band gap and high electron mobility have already attracted considerable research interest. Here we demonstrate strong quantum confinement and manipulation of single electrons in devices made from few-layer crystals of InSe using electrostatic gating. We report on gate-controlled quantum dots in the Coulomb blockade regime as well as one-dimensional quantization in point contacts, revealing multiple plateaus. The work represents an important milestone in the development of quality devices based on 2D materials and makes InSe a prime candidate for relevant electronic and optoelectronic applications.

Published : "arXiv Mesoscale and Nanoscale Physics".

The role of surface chemical reactivity in the stability of electronic nanodevices based on two-dimensional materials “beyond graphene” and topological insulators. (arXiv:1805.00729v1 [cond-mat.mtrl-sci])

2018-05-03T19:58:49+00:00May 3rd, 2018|Categories: Publications|Tags: , , , , |

Here, we examine the influence of surface chemical reactivity toward ambient gases on the performance of nanodevices based on two-dimensional materials “beyond graphene” and novel topological phases of matter. While surface oxidation in ambient conditions was observed for silicene and phosphorene with subsequent reduction of the mobility of charge carriers, nanodevices with active channels of indium selenide, bismuth chalcogenides and transition-metal dichalcogenides are stable in air. However, air-exposed indium selenide suffers of p-type doping due to water decomposition on Se vacancies, whereas the low mobility of charge carriers in transition-metal dichalcogenides increases the response time of nanodevices. Conversely, bismuth chalcogenides require a control of crystalline quality, which could represent a serious hurdle for up scaling.

Published : "arXiv Mesoscale and Nanoscale Physics".

Effects of Graphene/BN Encapsulation, Surface Functionalization and Molecular Adsorption on the Electronic Properties of Layered InSe: A First-Principles Study. (arXiv:1804.05180v1 [cond-mat.mtrl-sci])

2018-04-17T19:59:37+00:00April 17th, 2018|Categories: Publications|Tags: , , , , , |

By using first-principles calculations, we investigated the effects of graphene/boron nitride (BN) encapsulation, surface functionalization by metallic elements (K, Al, Mg and typical transition metals) and molecules (tetracyanoquinodimethane (TCNQ) and tetracyanoethylene (TCNE)) on the electronic properties of layered indium selenide (InSe). It was found that an opposite trend of charge transfer is possible for graphene (donor) and BN (acceptor), which is dramatically different from phosphorene where both graphene and BN play the same role (donor). For InSe/BN heterostructure, a change of the interlayer distance due to an out-of-plane compression can effectively modulate the band gap. Strong acceptor abilities to InSe were found for the TCNE and TCNQ molecules. For K, Al and Mg-doped monolayer InSe, the charge transfer from K and Al atoms to the InSe surface was observed, causing an n-type conduction of InSe, while p-type conduction of InSe observed in case of the Mg-doping. The atomically thin structure of InSe enables the possible observation and utilization of the dopant-induced vertical electric field across the interface. A proper adoption of the n- or p-type dopants allows for the modulation of the work function, the Fermi level pinning, the band bending, and the photo-adsorbing efficiency near the InSe surface/interface. Investigation on the adsorption of transition metal atoms on InSe showed that Ti-, V-, Cr-, Mn-, Co-adsorbed InSe are spin-polarized, while Ni-, Cu-, Pd-, Ag- and Au-adsorbed InSe are non-spin-polarized. Our results shed lights on the possible ways to protect InSe structure and modulate its electronic properties for nanoelectronics and electrochemical

Published in: "arXiv Material Science".

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