TaSe2

/Tag: TaSe2

Potential 2D Materials with Phase Transitions: Structure, Synthesis, and Device Applications

2018-11-10T22:34:17+00:00November 10th, 2018|Categories: Publications|Tags: , |

2D materials with phase transitions, such as charge density wave and magnetic and dipole orderings, are an important subfamily of 2D materials. Strong charge–spin–lattice couplings in the materials enable vast potentials for new‐concept and new‐structure devices. Recent experimental progress on the synthesis and device demonstration based 2D phase‐transition materials, such as 1T‐TaS2, CrI3, and Cr2Ge2Te6 monolayers, is reviewed. Abstract Layered materials with phase transitions, such as charge density wave (CDW) and magnetic and dipole ordering, have potential to be exfoliated into monolayers and few‐layers and then become a large and important subfamily of two‐dimensional (2D) materials. Benefitting from enriched physical properties from the collective interactions, long‐range ordering, and related phase transitions, as well as the atomic thickness yet having nondangling bonds on the surface, 2D phase‐transition materials have vast potential for use in new‐concept and functional devices. Here, potential 2D phase‐transition materials with CDWs and magnetic and dipole ordering, including transition metal dichalcogenides, transition metal halides, metal thio/selenophosphates, chromium silicon/germanium tellurides, and more, are introduced. The structures and experimental phase‐transition properties are summarized for the bulk materials and some of the obtained monolayers. In addition, recent experimental progress on the synthesis and measurement of monolayers, such as 1T‐TaS2, CrI3, and Cr2Ge2Te6, is reviewed.

Published in: "Advanced Materials".

Potential 2D Materials with Phase Transitions: Structure, Synthesis, and Device Applications

2018-11-07T08:35:31+00:00November 7th, 2018|Categories: Publications|Tags: , |

2D materials with phase transitions, such as charge density wave and magnetic and dipole orderings, are an important subfamily of 2D materials. Strong charge–spin–lattice couplings in the materials enable vast potentials for new‐concept and new‐structure devices. Recent experimental progress on the synthesis and device demonstration based 2D phase‐transition materials, such as 1T‐TaS2, CrI3, and Cr2Ge2Te6 monolayers, is reviewed. Abstract Layered materials with phase transitions, such as charge density wave (CDW) and magnetic and dipole ordering, have potential to be exfoliated into monolayers and few‐layers and then become a large and important subfamily of two‐dimensional (2D) materials. Benefitting from enriched physical properties from the collective interactions, long‐range ordering, and related phase transitions, as well as the atomic thickness yet having nondangling bonds on the surface, 2D phase‐transition materials have vast potential for use in new‐concept and functional devices. Here, potential 2D phase‐transition materials with CDWs and magnetic and dipole ordering, including transition metal dichalcogenides, transition metal halides, metal thio/selenophosphates, chromium silicon/germanium tellurides, and more, are introduced. The structures and experimental phase‐transition properties are summarized for the bulk materials and some of the obtained monolayers. In addition, recent experimental progress on the synthesis and measurement of monolayers, such as 1T‐TaS2, CrI3, and Cr2Ge2Te6, is reviewed.

Published in: "Advanced Materials".

Lithium ion intercalation in thin crystals of hexagonal TaSe2 gated by a polymer electrolyte. (arXiv:1810.10683v1 [cond-mat.mtrl-sci])

2018-10-26T02:29:19+00:00October 26th, 2018|Categories: Publications|Tags: |

Ionic liquid gating has been used to modify properties of layered transition metal dichalcogenides (TMDCs), including two-dimensional (2D) crystals of TMDCs used extensively recently in the device work, which has led to observations of properties not seen in the bulk. The main effect comes from the electrostatic gating due to strong electric field at the interface. In addition, ionic liquid gating also leads to ion intercalation when the ion size of gate electrolyte is small compared to the interlayer spacing of TMDCs. However, the microscopic processes of ion intercalation have rarely been explored in layered TMDCs. Here, we employed a technique combining photolithography device fabrication and electrical transport measurements on the thin crystals of hexagonal TaSe2 using multiple channel devices gated by a polymer electrolyte LiClO4/PEO. The gate voltage and time dependent source-drain resistances of these thin crystals were used to obtain information on the intercalation process, the effect of ion intercalation, and the correlation between the ion occupation of allowed interstitial sites and the device characteristics. We found a gate voltage controlled modulation of the charge density waves and scattering rate of charge carriers. Our work suggests that ion intercalation can be a useful tool for layered materials engineering and 2D crystal device design.

Published in: "arXiv Material Science".

Thermally Oxidized Two-dimensional TaS2 as a High-k{appa} Gate Dielectric for MoS2 Field-Effect Transistors. (arXiv:1808.08303v1 [physics.app-ph])

2018-08-28T04:30:21+00:00August 28th, 2018|Categories: Publications|Tags: , , |

We report a new approach to integrating high-k{appa} dielectrics in both bottom- and top-gated MoS2 field-effect transistors (FETs) through thermal oxidation and mechanical assembly of layered twodimensional (2D) TaS2. Combined X-ray photoelectron spectroscopy (XPS), optical microscopy, atomic force microscopy (AFM), and capacitance-voltage (C-V) measurements confirm that multilayer TaS2 flakes can be uniformly transformed to Ta2O5 with a high dielectric constant of ~ 15.5 via thermal oxidation, while preserving the geometry and ultra-smooth surfaces of 2D TMDs. Top-gated MoS2 FETs fabricated using the thermally oxidized Ta2O5 as gate dielectric demonstrate a high current on/off ratio approaching 106, a subthreshold swing (SS) down to 61 mV/dec, and a field-effect mobility exceeding 60 cm2V-1 s-1 at room temperature, indicating high dielectric quality and low interface trap density.

Published : "arXiv Mesoscale and Nanoscale Physics".

Hidden CDW states and insulator-to-metal transition after a pulsed femtosecond laser excitation in layered chalcogenide 1T-TaS2-xSex

2018-07-20T18:36:21+00:00July 20th, 2018|Categories: Publications|Tags: , |

The hidden (H) quantum state in 1T-TaS2 has sparked considerable interest in the field of correlated electron systems. Here, we investigate ultrafast switches to stable H charge density wave (H-CDW) states observed in 1T-TaS2–xSex, with x = 0 and 0.5 crystals, upon excitation with a single femtosecond laser pulse. In

Published in: "Science Advances".

Charge density wave controlled carrier injection in gated 1T-TaS2/2H-MoS2 heterojunction. (arXiv:1807.01652v1 [cond-mat.mes-hall])

2018-07-05T00:30:22+00:00July 5th, 2018|Categories: Publications|Tags: , , |

An efficient electrical contact between a highly conducting van der Waals (vdW) material to another semiconducting vdW channel is an important step towards achieving “all-2D” flexible electronics. 1T-TaS2 is a layered material that exhibits distinct electrical conductivity phases owing to the interaction between charge density wave and the underlying lattice. Here we demonstrate a low-Schottky barrier height (SBH) vdW contact between 1T-TaS2 source and 2H-MoS2 channel in a back gated structure exhibiting characteristic transport features. With an increase in the temperature, as the phase of TaS2 changes from commensurate (C) charge density wave (CDW) to triclinic (T), under ON condition, the drive current of the transistor enhances by ~40% owing to the phase transition induced suppression of TaS2 series resistance. On the contrary, the SBH between TaS2 and MoS2 increases during the C-T phase transition, which can be directly correlated with the collapse of the Mott gap in TaS2. The change in SBH allows us to estimate an electrical Mott gap opening of ~71 +/- 7 meV in the C phase of TaS2, providing an independent verification of the results obtained from different optical techniques.

Published : "arXiv Mesoscale and Nanoscale Physics".

Ultrabroadband photosensitivity from visible to terahertz at room temperature. (arXiv:1806.08952v1 [cond-mat.mtrl-sci])

2018-06-26T02:29:19+00:00June 26th, 2018|Categories: Publications|Tags: , |

Charge-density wave (CDW) is one of the most fundamental quantum phenomena in solids. Different from ordinary metals in which only single particle excitations exist, CDW also has collective excitations and can carry electric current in a collective fashion. Manipulating this collective condensation for applications has long been a goal in the condensed matter and materials community. Here we show that the CDW system of 1T-TaS2 is highly sensitive to light directly from visible down to terahertz, with current responsivities around the order of ~1 AW-1 at room temperature. Our findings open a new avenue for realizing uncooled, ultrabroadband and sensitive photoelectronics continuously down to terahertz spectral range.

Published in: "arXiv Material Science".

Interlayer coupling and the phase transition mechanism of stacked MoS2/TaS2 heterostructures discovered using temperature dependent Raman and photoluminescence spectroscopy

2018-06-14T14:32:24+00:00June 14th, 2018|Categories: Publications|Tags: , , , |

RSC Adv., 2018, 8,21968-21974DOI: 10.1039/C8RA03436B, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Miao Chen, Bin Zhou, Fang Wang, Liping Xu, Kai Jiang, Liyan Shang, Zhigao Hu, Junhao ChuThe important interlayer coupling of the MoS2-TaS2 heterostructure

Published in: "RSC Advances".

Tuning Ising superconductivity with layer and spin–orbit coupling in two-dimensional transition-metal dichalcogenides

2018-04-12T10:32:03+00:00April 12th, 2018|Categories: Publications|Tags: , , |

Tuning Ising superconductivity with layer and spin–orbit coupling in two-dimensional transition-metal dichalcogenidesTuning Ising superconductivity with layer and spin–orbit coupling in two-dimensional transition-metal dichalcogenides, Published online: 12 April 2018; doi:10.1038/s41467-018-03888-4Monolayer transition-metal dichalcogenide (TMD) is promising to host features of topological superconductivity. Here, de la Barrera et al. study layered compounds, 2H-TaS2 and 2H-NbSe2, in their atomic layer limit and find a largest upper critical field for an intrinsic TMD superconductor.

Published in: "Nature Communications".

Vertical 1T-TaS2 Synthesis on Nanoporous Gold for High-Performance Electrocatalytic Applications

2018-03-07T08:31:50+00:00March 7th, 2018|Categories: Publications|Tags: , , |

Abstract 2D metallic TaS2 is acting as an ideal platform for exploring fundamental physical issues (superconductivity, charge-density wave, etc.) and for engineering novel applications in energy-related fields. The batch synthesis of high-quality TaS2 nanosheets with a specific phase is crucial for such issues. Herein, the successful synthesis of novel vertically oriented 1T-TaS2 nanosheets on nanoporous gold substrates is reported, via a facile chemical vapor deposition route. By virtue of the abundant edge sites and excellent electrical transport property, such vertical 1T-TaS2 is employed as high-efficiency electrocatalysts in the hydrogen evolution reaction, featured with rather low Tafel slopes ≈67–82 mV dec−1 and an ultrahigh exchange current density ≈67.61 µA cm−2. The influence of phase states of 1T- and 2H-TaS2 on the catalytic activity is also discussed with the combination of density functional theory calculations. This work hereby provides fundamental insights into the controllable syntheses and electrocatalytic applications of vertical 1T-TaS2 nanosheets achieved through the substrate engineering. Vertically oriented 1T-TaS2 nanosheets are first synthesized on nanoporous gold (NPG) substrates, via the chemical vapor deposition route. By virtue of the abundant edge sites and excellent electrical transport property, such vertical 1T-TaS2/NPG are employed as high-efficiency electrocatalysts in the hydrogen evolution reaction. The influence of the phase states of TaS2 on the catalytic activity is also explored according to theoretical calculations.

Published in: "Advanced Materials".

Low-Frequency Noise and Sliding of the Charge Density Waves in Two-Dimensional Materials. (arXiv:1802.02536v1 [cond-mat.mes-hall])

2018-02-08T19:58:45+00:00February 8th, 2018|Categories: Publications|Tags: , |

There has been a recent renewal of interest in charge-density-wave (CDW) phenomena, primarily driven by the emergence of two-dimensional (2D) layered CDW materials, such as 1T-TaS2, characterized by very high transition temperatures to CDW phases. In the extensively studied classical bulk CDW materials with quasi-1D crystal structure, the charge carrier transport exhibits intriguing sliding behavior, which reveals itself in the frequency domain as “narrowband” and “broadband” noise. Despite the increasing attention on physics of 2D CDWs, there have been few reports of CDW sliding, specifically in quasi-2D rare-earth tritellurides and none on the noise in any of 2D CDW systems. Here we report the results of low-frequency noise (LFN) measurements on 1T-TaS2 thin films – archetypal 2D CDW systems, as they are driven from the nearly commensurate (NC) to incommensurate (IC) CDW phases by voltage and temperature stimuli. We have found that noise in 1T-TaS2 devices has two pronounced maxima at the bias voltages, which correspond to the onset of CDW sliding and the NC-to-IC phase transition. We observed unusual Lorentzian noise features and exceptionally strong noise dependence on electric bias and temperature. We argue that LFN in 2D CDW systems has unique physical origin, different from known fundamental noise types. The specifics of LFN in 2D CDW materials can be explained by invoking the concept of interacting discrete fluctuators in the NC-CDW phase. Noise spectroscopy can serve as a useful tool for understanding electronic transport phenomena in 2D CDW materials characterized by coexistence of different phases and strong CDW

Published : "arXiv Mesoscale and Nanoscale Physics".

Infrared nanoimaging of the metal-insulator transition in the charge-density-wave van der Waals material $1Ttext{−}{mathrm{TaS}}_{2}$

2018-01-08T16:30:57+00:00January 8th, 2018|Categories: Publications|Tags: , |

Author(s): Alex J. Frenzel, Alexander S. McLeod, Dennis Zi-Ren Wang, Yu Liu, Wenjian Lu, Guangxin Ni, Adam W. Tsen, Yuping Sun, Abhay N. Pasupathy, and D. N. BasovUsing scanning near-field optical microscopy at cryogenic temperatures, we explored the first-order metal-insulator transition of exfoliated 1T−TaS2 microcrystals on a SiO2/Si substrate. We clearly observed spatially separated metallic and insulating states during the transition between commensurate…[Phys. Rev. B 97, 035111] Published Mon Jan 08, 2018

Published in: "Physical Review B".

Unusual enhancements of B_{c2} and T_c in the restacked TaS_2 nanosheets. (arXiv:1712.07763v1 [cond-mat.supr-con])

2017-12-22T19:59:26+00:00December 22nd, 2017|Categories: Publications|Tags: , |

Recently we reported an enhanced superconductivity in restacked monolayer TaS_2 nanosheets compared with the bulk TaS2, pointing to the exotic physical properties of low dimensional systems. Here we tune the superconducting properties of this system with magnetic field along different directions, where a strong Pauli paramagnetic spin-splitting effects is found in this system. Importantly, an unusual enhancement as high as 3.8 times of the upper critical field B_{c2} is observed under the inclined external magnetic field. Moreover, with the vertical field fixed, we find that the superconducting transition temperature T_c can be enhanced by increasing the transverse field and forms a dome-shaped phase diagram. We argue that the restacked crystal structure without inversion center along with the strong spin-orbit coupling may play a key role for our observations. The present findings are significant in the viewpoint of fundamental physics and may also facilitate the applications of low-dimensional superconductors in the environment of high field.

Published in: "arXiv Material Science".

Raman spectroscopy of optical phonon and incommensurate charge density wave modes in 2H-TaSe2 exfoliated flakes. (arXiv:1712.01514v1 [cond-mat.mtrl-sci])

2017-12-06T19:59:30+00:00December 6th, 2017|Categories: Publications|Tags: |

2H-TaSe2 is a model transition metal dichalcogenide material that develops charge density waves (CDWs).Here we present variable-temperature Raman spectroscopy study on both incommensurate charge density waves (ICDW) and optical phonon modes of 2H-TaSe2 thin layers exfoliated onto SiO2 substrate. Raman scattering intensities of all modes reach a maximum when the sample thickness is about 11 nm. This phenomenon can be explained by optical interference effect between the sample and the substrate. The E2gICDW amplitude modes experience redshift as temperature increases. We extract ICDW transition temperature (TICDW) from temperature dependence of the frequency of E2gICDW mode. We find that TICDW increases in thinner flakes,which could be due to a result of significantly enhanced electron-phonon interactions. Our results open up a new window for search and control of CDW of two-dimensional matter.

Published in: "arXiv Material Science".

Total Ionizing Dose Effects on Threshold Switching in 1T-Tantalum Disulfide Charge-Density-Wave Devices. (arXiv:1712.01354v1 [physics.app-ph])

2017-12-06T19:58:52+00:00December 6th, 2017|Categories: Publications|Tags: , |

The 1T polytype of TaS2 exhibits voltage-triggered threshold switching as a result of a phase transition from nearly commensurate to incommensurate charge density wave states. Threshold switching, persistent above room temperature, can be utilized in a variety of electronic devices, e.g., voltage controlled oscillators. We evaluated the total-ionizing-dose response of thin film 1T-TaS2 at doses up to 1 Mrad(SiO2). The threshold voltage changed by less than 2% after irradiation, with persistent self-sustained oscillations observed through the full irradiation sequence. The radiation hardness is attributed to the high intrinsic carrier concentration of 1T-TaS2 in both of the phases that lead to threshold switching. These results suggest that charge density wave devices, implemented with thin films of 1T-TaS2, are promising for applications in high radiation environments.

Published : "arXiv Mesoscale and Nanoscale Physics".

Total-Ionizing-Dose Effects on Threshold Switching in $1{T}$ -TaS2 Charge Density Wave Devices

2017-11-24T01:21:23+00:00November 24th, 2017|Categories: Publications|Tags: , |

The $1{T}$ polytype of TaS2 exhibits voltage-triggered threshold switching as a result of a phase transition from nearly commensurate to incommensurate charge density wave states. Threshold switching, persistent above room temperature, can be utilized in a variety of electronic devices, e.g., voltage controlled oscillators. We evaluated the total-ionizing-dose response of thin film $1{T}$ -TaS2 at doses up to 1 Mrad (SiO2). The threshold voltage changed by less than 2% after irradiation, with persistent self-sustained oscillations observed through the full irradiation sequence. The radiation hardness is attributed to the high intrinsic carrier concentration of $1{T}$ -TaS2 in both of the phases that lead to threshold switching. These results suggest that charge density wave devices, implemented with thin films of $1{T}$ -TaS2, are promising for applications in high radiation environments.

Published in: "IEEE Electron Device Letters".

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