/Tag: ReSe2

Pressure dependence of direct optical transitions in ReS2 and ReSe2. (arXiv:1812.02995v1 [cond-mat.mtrl-sci])

2018-12-10T02:29:26+00:00December 10th, 2018|Categories: Publications|Tags: , |

We present an experimental and theoretical study of the electronic band structure of ReS2 and ReSe2 at high hydrostatic pressures. The experiments are performed by photoreflectance spectroscopy and are analyzed in terms of ab initio calculations within the density functional theory. Experimental pressure coefficients for the two most dominant excitonic transitions are obtained and compared with those predicted by the calculations. We assign the transitions to the Z k-point of the Brillouin zone and other k-points located away from highsymmetry points. The origin of the pressure coefficients of the measured direct transitions is discussed in terms of orbital analysis of the electronic structure and van der Waals interlayer interaction. The anisotropic optical properties are studied at high pressure by means of polarization-resolved photoreflectance measurements.

Published in: "arXiv Material Science".

Diverse Atomically Sharp Interfaces and Linear Dichroism of 1T’ ReS2‐ReSe2 Lateral p–n Heterojunctions

2018-11-28T22:32:07+00:00November 28th, 2018|Categories: Publications|Tags: , , , |

2D distorted octahedral (1T’) ReS2‐ReSe2 lateral heterojunctions with atomically sharp interfaces are synthesized by using two‐step epitaxial growth. Diverse interface structures and polarization‐sensitive photodiode properties are achieved in the 1T’ heterojunctions, which open up new prospects for transition‐metal dichalcogenides in building multi‐functional electronic and optoelectronic devices. Abstract Creating heterojunctions between different 2D transition‐metal dichalcogenides (TMDs) would enable on‐demand tuning of electronic and optoelectronic properties in this new class of materials. However, the studies to date are mainly focused on hexagonal (2H) structure TMD‐based heterojunctions, and little attention is paid on the distorted octahedral (1T’) structure TMD‐based heterojunctions. This study reports the large‐scale synthesis of monolayer 1T’ ReS2‐ReSe2 lateral heterojunction with domain size up to 100 µm by using two‐step epitaxial growth. Atomic‐resolution scanning transmission electron microscopy reveals high crystal quality of the heterojunction with atomically sharp interfaces. Interestingly, three types of epitaxial growth modes accompanying formation of three different interface structures are revealed in the growth of 1T’ heterojunction, where the angle between the b‐axis of ReS2 and ReSe2 is 0°, 120°, and 180°, respectively. The 0° and 180° interface structures are both found to be more abundant than the 120° interface structure owing to their relative lower formation energy. Electrical transport demonstrates that the as‐grown heterostructure forms lateral p–n junction with intrinsic rectification characteristics and exhibits polarization‐dependent photodiode properties. This is the first time the linear dichroism is achieved in 2D lateral heterostructure, which is important for the development of new devices with multi‐functionality.

Published in: "Advanced Functional Materials".

Phase Modulators Based on High Mobility Ambipolar ReSe2 Field-Effect Transistors. (arXiv:1808.03621v1 [cond-mat.mes-hall])

2018-08-13T00:30:27+00:00August 13th, 2018|Categories: Publications|Tags: |

We fabricated ambipolar field-effect transistors (FETs) from multi-layered triclinic ReSe2, mechanically exfoliated onto a SiO2 layer grown on p-doped Si. In contrast to previous reports on thin layers (~2 to 3 layers), we extract field-effect carrier mobilities in excess of 10^2 cm^2/Vs at room temperature in crystals with nearly ~10 atomic layers. These thicker FETs also show nearly zero threshold gate voltage for conduction and high ON to OFF current ratios when compared to the FETs built from thinner layers. We also demonstrate that it is possible to utilize this ambipolarity to fabricate logical elements or digital synthesizers. For instance, we demonstrate that one can produce simple, gate-voltage tunable phase modulators with the ability to shift the phase of the input signal by either 90^o or nearly 180^o. Given that it is possible to engineer these same elements with improved architectures, for example on h-BN in order to decrease the threshold gate voltage and increase the carrier mobilities, it is possible to improve their characteristics in order to engineer ultra-thin layered logic elements based on ReSe2.

Published : "arXiv Mesoscale and Nanoscale Physics".

Modulation of Photothermal Anisotropy using Black Phosphorus/ Rhenium Diselenide Heterostructures

2018-05-16T14:24:35+00:00May 16th, 2018|Categories: Publications|Tags: , , |

Nanoscale, 2018, Accepted ManuscriptDOI: 10.1039/C8NR02229A, CommunicationXiao-Guang Gao, Guo-Xing Chen, De-Kang Li, Xiao-Kuan Li, Zhibo Liu, Jianguo TianManipulating the polarization of an incident beam using two-dimensional materials has become an important research direction towards the development of nano-optical devices. Black phosphorus (BP) and rhenium

Published in: "RSC Nanoscale".

Temperature-dependent Raman spectroscopy studies of the interface coupling effect of monolayer ReSe 2 single crystals on Au foils

2018-03-23T12:31:09+00:00March 23rd, 2018|Categories: Publications|Tags: |

Rhenium diselenide (ReSe 2 ), which bears in-plane anisotropic optical and electrical properties, is of considerable interest for its excellent applications in novel devices, such as polarization-sensitive photodetectors and integrated polarization-controllers. However, great challenges to date in the controllable synthesis of high-quality ReSe 2 have hindered its in-depth investigations and practical applications. Herein, we report a feasible synthesis of monolayer single-crystal ReSe 2 flakes on the Au foil substrate by using a chemical vapor deposition route. Particularly, we focus on the temperature-dependent Raman spectroscopy investigations of monolayer ReSe 2 grown on Au foils, which present concurrent red shifts of E g -like and A g -like modes with increasing measurement temperature from 77–290 K. Linear temperature dependences of both modes are revealed and explained from the anharmonic vibration of the ReSe …

Published in: "Nanotechnology".

Tuning the Electronic and Photonic Properties of Monolayer MoS2 via In Situ Rhenium Substitutional Doping

2018-02-16T08:28:40+00:00February 16th, 2018|Categories: Publications|Tags: , , , |

Abstract Doping is a fundamental requirement for tuning and improving the properties of conventional semiconductors. Recent doping studies including niobium (Nb) doping of molybdenum disulfide (MoS2) and tungsten (W) doping of molybdenum diselenide (MoSe2) have suggested that substitutional doping may provide an efficient route to tune the doping type and suppress deep trap levels of 2D materials. To date, the impact of the doping on the structural, electronic, and photonic properties of in situ-doped monolayers remains unanswered due to challenges including strong film substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Here, in situ rhenium (Re) doping of synthetic monolayer MoS2 with ≈1 at% Re is demonstrated. To limit substrate film charge transfer, r-plane sapphire is used. Electronic measurements demonstrate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Moreover, low-temperature photoluminescence indicates a significant quench of the defect-bound emission when Re is introduced, which is attributed to the MoO bond and sulfur vacancies passivation and reduction in gap states due to the presence of Re. The work presented here demonstrates that Re doping of MoS2 is a promising route toward electronic and photonic engineering of 2D materials. This work demonstrates in situ rhenium (Re) doping of synthetic monolayer MoS2 with ≈1 at% Re on r-plane sapphire. Electronic measurements elucidate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Low-temperature photoluminescence measurements reveal suppression of defect emission induced by Re

Published in: "Advanced Functional Materials".

Electronic band structure of rhenium dichalcogenides. (arXiv:1801.02933v1 [cond-mat.mes-hall])

2018-01-10T19:58:54+00:00January 10th, 2018|Categories: Publications|Tags: , , |

Calculated band structures of bulk transition metal dichalcogenides ReS2 and ReSe2 are presented, showing the complicated nature of the interband transitions in these materials, with several close-lying band gaps. Three-dimensional plots of constant energy surfaces in the Brillouin zone at energies near the band extrema are used to show that the valence band maximum and conduction band minimum are not located at any special high symmetry points. We show that, at the level of approximation of our calculations, both materials are indirect gap materials and that one must be careful to consider the whole Brillouin zone volume in addressing this question.

Published : "arXiv Mesoscale and Nanoscale Physics".

Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe<sub>2</sub> and MoSe<sub>2</sub>

2017-11-23T09:09:09+00:00November 23rd, 2017|Categories: Publications|Tags: , |

Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe2 and MoSe2Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe<sub>2</sub> and MoSe<sub>2</sub> , Published online: 22 November 2017; doi:10.1038/s41699-017-0043-1The Raman spectra of ReSe2-xSx alloys allows investigation of the distribution of substitutional sulfur atoms within the lattice of ReSe2. A team led by Lewis S. Hart at the University of Bath performed a combination of Raman spectroscopy at visible excitation wavelengths and density functional perturbation theory on ternary ReSe2-xSx alloys obtained by chemical vapor transport. The combination of a traditional normal incidence configuration and an “edge-on” geometry allowed identification of in-plane and out-of-plane Raman features, optically active in the respective experiments owing to their specific selection rules. The frequencies of the observed local vibrational modes arising from sulfur and oxygen atoms were observed to change as a function of the stoichiometric composition of the alloy, thus providing a means of monitoring such impurities. A similar effect was predicted for MoSe2-xSx alloys.

Published in: "NPJ 2D Materials and Applications".

Synthesis of Large-Size 1T′ ReS2xSe2(1−x) Alloy Monolayer with Tunable Bandgap and Carrier Type

2017-10-23T12:31:26+00:00October 23rd, 2017|Categories: Publications|Tags: , |

Abstract Chemical vapor deposition growth of 1T′ ReS2xSe2(1−x) alloy monolayers is reported for the first time. The composition and the corresponding bandgap of the alloy can be continuously tuned from ReSe2 (1.32 eV) to ReS2 (1.62 eV) by precisely controlling the growth conditions. Atomic-resolution scanning transmission electron microscopy reveals an interesting local atomic distribution in ReS2xSe2(1−x) alloy, where S and Se atoms are selectively occupied at different X sites in each Re-X6 octahedral unit cell with perfect matching between their atomic radius and space size of each X site. This structure is much attractive as it can induce the generation of highly desired localized electronic states in the 2D surface. The carrier type, threshold voltage, and carrier mobility of the alloy-based field effect transistors can be systematically modulated by tuning the alloy composition. Especially, for the first time the fully tunable conductivity of ReS2xSe2(1−x) alloys from n-type to bipolar and p-type is realized. Owing to the 1T′ structure of ReS2xSe2(1−x) alloys, they exhibit strong anisotropic optical, electrical, and photoelectric properties. The controllable growth of monolayer ReS2xSe2(1−x) alloy with tunable bandgaps and electrical properties as well as superior anisotropic feature provides the feasibility for designing multifunctional 2D optoelectronic devices. 2D 1T′ ReS2xSe2(1−x) semiconductor alloy with tunable composition is synthesized by using chemical vapor deposition growth. The tunable bandgap and carrier type combined with the strong anisotropic feature realized within a monolayer alloy open up new prospects for transition metal dichalcogenides in building multifunctional electronic and optoelectronic devices.

Published in: "Advanced Materials".

Temperature dependence of Raman shifts in layered ReSe2 and SnSe2 semiconductor nanosheets

2016-10-15T11:37:50+00:00July 8th, 2015|Categories: Publications|Tags: |

By A. Taube, A. Łapińska, J. Judek and M. Zdrojek Transition metal dichalcogenides (TMDCs) are attractive for variety of nanoscale electronics and optoelectronics devices due to their unique properties. Despite growing progress in the research field of TMDCs, many of their properties are still unknown. In this letter, we report measurements of Raman spectra of rhenium diselenide (ReSe2) and tin …read more

Published in: Applied Physics Letters

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