Bulk ReSe2: record high refractive index and biaxially anisotropic material for all-dielectric nanophotonics. (arXiv:2212.01501v1 [cond-mat.mes-hall])

2022-12-06T04:30:24+00:00December 6th, 2022|Categories: Publications|Tags: |

We show that bulk rhenium diselenide, ReSe2 is characterized by record high value of the refractive index exceeding 5 in near-infrared frequency range. We use back focal plane reflection spectroscopy to extract the components of the ReSe2 permittivity tensor and reveal its extreme biaxial anisotropy. We also demonstrate the good agreement between the experimental data and the predictions of the density functional theory. The combination of the large refractive index and giant optical anisotropy makes ReSe2 a perspective material for all-dielectric nanophotonics in the near-infrared frequency range.

Published : "arXiv Mesoscale and Nanoscale Physics".

Growth of Transition Metal Dichalcogenides by Solvent Evaporation Technique. (arXiv:2007.14167v1 [cond-mat.mtrl-sci])

2020-07-29T02:29:23+00:00July 29th, 2020|Categories: Publications|Tags: , , , , , , |

Due to their outstanding properties and promises for future technology in energy generation, transition metal dichalcogenides (TMDs) have gathered a lot of interest in recent years. Amongst this class of materials TMDs based on molybdenum, tungsten, sulfur and selenium gathered a lot attention because of their semiconducting properties and the possibility to be synthesized by bottom up techniques. Here, using an evaporation of metal-saturated chalcogen melt at 850-655 deg., we were able to obtain, from their solid solutions, a high quality crystals of transition metal diselenide and ditelluride crystals like (PtTe2, PdTe2, NiTe2, TaTe2, TiTe2, RuTe2, PtSe2, PdSe2, NbSe2, TiSe2, VSe2, ReSe2). Additionally, we show the possibility to synthesize crystals of rare-earth metal polychalcogenides and NbS2. Most of the obtained crystals have a layered CdI2 structure. We, further, have investigated the basic physical properties of some selected obtained crystals. These investigations reflect the good quality of the obtained crystals. Remarkably, the charge density wave transition in both 1T-TiSe2 and 2H-NbSe2 crystals shows a clear sign at 200 K and 33 K, respectively. Angle-resolved photoemission spectroscopy and electron diffractions techniques are used to directly access the electronic and crystalline properties of PtTe2 single crystals.

Published in: "arXiv Material Science".

High refractive index and extreme biaxial opticalanisotropy of rhenium diselenide for applicationsin all-dielectric nanophotonics. (arXiv:2007.06287v1 [cond-mat.mes-hall])

2020-07-14T04:30:34+00:00July 14th, 2020|Categories: Publications|Tags: |

We establish simple quantitative criterium for the search of new dielectric materials with high values of the refractive index in the visible range. It is demonstrated, that for light frequencies below the band gap the latter is determined by the dimensionless parameter $eta$ calculated as the ratio of the sum of the widths of conduction and valence bands and the band gap. Small values of this parameter, which can be achieved in materials with almost flat bands, lead to dramatic increase of the refractive index. We illustrate this rule with a particular example of rhenium dichalcogenides, for which we perform ab-initio calculations of the band structure and optical susceptibility and predict the values of the refractive index > 5 in a wide frequency range around 1 eV together with compratively low losses. Our findings open new perspectives in the search for the new high-index/low loss materials for all-dielectric nanophotonics.

Published : "arXiv Mesoscale and Nanoscale Physics".

The optical signature of few-layer ReSe$_2$. (arXiv:2005.12878v1 [cond-mat.mes-hall])

2020-05-27T02:29:38+00:00May 27th, 2020|Categories: Publications|Tags: , |

Optical properties of thin layers of rhenium diselenide (ReSe$_2$) with thickness ranging from mono- (1~ML) to nona-layer (9~MLs) are demonstrated. The photoluminescence (PL) and Raman scattering were measured at low ($T$=5~K) and room ($T$=300~K) temperature, respectively. The PL spectra of ReSe$_2$ layers display two well-resolved emission lines, which blueshift by about 60~meV when the layer thickness decreases from 9~MLs to a bilayer. A rich structure of the observed low-energy Raman scattering modes can be explained within a linear chain model. The two phonon modes of intralayer vibrations, observed in Raman scattering spectra at about 120~cm$^{-1}$, exhibit very sensitive and opposite evolution as a function of layer thickness. It is shown that their energy difference can serve as a convenient and reliable tool to determine the thickness of ReSe$_2$ flakes in the few-layer limit.

Published in: "arXiv Material Science".

N2 Electroreduction to NH3 via Selenium Vacancy‐Rich ReSe2 Catalysis at an Abrupt Interface

2020-05-20T13:07:50+00:00May 20th, 2020|Categories: Publications|Tags: |

Vacancy engineering has been proved repeatedly as an adoptable strategy to boost electrocatalysis, while its poor selectivity restricts the usage in nitrogen reduction reaction (NRR) as overwhelming competition from hydrogen evolution reaction (HER). Revealed by density functional theory calculations, the selenium vacancy in ReSe 2 crystal can enhance its electroactivity for both NRR and HER by shifting the d ‐band from ‐2.91 to ‐2.33 eV. To restrict the HER, we report a novel method by burying selenium vacancy‐rich ReSe 2 @carbonized bacterial cellulose (V r ‐ReSe 2 @CBC) nanofibers between two CBC layers, leading to boosted Faradaic efficiency of 42.5% and ammonia yield of 28.3 μg h ‐1 cm ‐2 at a potential of ‐0.25 V at an abrupt interface. As demonstrated by the nitrogen bubble adhesive force, superhydrophilic measurements, and COMSOL Multiphysics simulations, the hydrophobic and porous CBC layers can keep the internal V r ‐ReSe 2 @CBC nanofibers away from water coverage, leaving more unoccupied active sites for the N 2 reduction (especially for the potential determining step of proton‐electron coupling and transferring processes as *HNNH 2 → *H 2 NNH 2 ).

Published in: "Angewandte Chemie International Edition".

High mobility ReSe 2 field effect transistors: Schottky-barrier-height-dependent photoresponsivity and broadband light detection with Co decoration

2019-11-04T14:35:19+00:00November 4th, 2019|Categories: Publications|Tags: |

2D transition metal dichalcogenides are promising in various electronics and optoelectronics applications and have gained popularity owing to their carrier transport and strong light–matter interactions. To fully realize their potential in field-effect transistors (FETs) and photodetectors, high mobility and high responsivity are imperative. Here, we demonstrate the highest mobility of ~166 cm 2 V −1 s −1 at 200 K for single-layer rhenium diselenide (ReSe 2 ) FETs encapsulated between h-BN flakes at V g   =  47 V. The high mobility is attributed to low-resistance contacts of scandium/gold (Sc/Au), with a low Schottky barrier height and reduced charge scattering platform of h-BN. Further, we elucidated the Schottky-barrier-height dependent high photoresponsivity (~3.2  ×  10 6 A W −1 ) of few-layer ReSe 2 (FL-ReSe 2 ) at 532 nm-wavelength laser light on an h-BN substrate with Sc/Au conta…

Published in: "2DMaterials".

THz polarization-sensitive characterization of a large-area multilayer rhenium diselenide nanofilm

2019-09-30T10:34:15+00:00September 30th, 2019|Categories: Publications|Tags: |

Recently, rhenium diselenide (ReSe 2 ) has attracted considerable attention due to its high anisotropy in the layer plane, which makes it a promising candidate for wide applications in electronics and optoelectronics. In this paper, we focus on the polarization-sensitive characteristics of a large-area multilayer ReSe 2 nanofilm in the terahertz (THz) region under passive and active conditions by means of THz time-domain spectroscopy. We demonstrate the passive ReSe 2 nanofilm with intrinsic THz polarization anisotropy. Maximum transmittance occurs only when the polarization direction of the incident THz wave is along the Re-chains direction. More importantly, THz polarization properties of the active ReSe 2 nanofilm by an external electric field applied in a selected directions are also demonstrated. The modulation depth of the THz transmission is up to 16% and the response time is on the order of picoseconds. In addition, a comparative ex…

Published in: "Nanotechnology".

Complete determination of crystallographic orientation of ReX2 (X=S, Se) by polarized Raman spectroscopy. (arXiv:1909.11423v1 [cond-mat.mes-hall])

2019-09-26T04:30:45+00:00September 26th, 2019|Categories: Publications|Tags: , |

Polarized Raman spectroscopy on few-layer ReS2 and ReSe2 was carried out to determine the crystallographic orientations. Since monolayer ReX2 (X=S or Se) has a distorted trigonal structure with only an inversion center, there is in-plane anisotropy and the two faces of a monolayer crystal are not equivalent. Since many physical properties vary sensitively depending on the crystallographic orientation, it is important to develop a reliable method to determine the crystal axes of ReX2. By comparing the relative polarization dependences of some representative Raman modes measured with three different excitation laser energies with high-resolution scanning transmission electron microscopy, we established a reliable procedure to determine the all three principal directions of few-layer ReX2 including a way to distinguish the two types of faces: a 2.41-eV laser for ReS2 or a 1.96-eV laser for ReSe2 should be chosen as the excitation source of polarized Raman measurements; then the relative directions of the maximum intensity polarization of the Raman modes at 151 and 212 cm-1 (124 and 161 cm-1) of ReS2 (ReSe2) can be used to determine the face types and the Re-chain direction unambiguously.

Published : "arXiv Mesoscale and Nanoscale Physics".

Giant gate-tunable bandgap renormalization and excitonic effects in a 2D semiconductor

2019-07-19T22:47:19+00:00July 19th, 2019|Categories: Publications|Tags: , |

Understanding the remarkable excitonic effects and controlling the exciton binding energies in two-dimensional (2D) semiconductors are crucial in unlocking their full potential for use in future photonic and optoelectronic devices. Here, we demonstrate large excitonic effects and gate-tunable exciton binding energies in single-layer rhenium diselenide (ReSe2) on a back-gated graphene

Published in: "Science Advances".

The energy band structure analysis and 2 μm Q-switched laser application of layered rhenium diselenide

2019-05-08T10:33:24+00:00May 8th, 2019|Categories: Publications|Tags: , |

RSC Adv., 2019, 9,14417-14421DOI: 10.1039/C9RA02311A, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Yongping Yao, Xiaowen Li, Rengang Song, Na Cui, Shande Liu, Huiyun Zhang, Dehua Li, Qiangguo Wang, Yan Xu, Jingliang HeIn this paper, we

Published in: "RSC Advances".

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".

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