/Tag: PtSe2

Topological Type-II Dirac Fermions Approaching the Fermi Level in a Transition Metal Dichalcogenide NiTe2. (arXiv:1808.07610v1 [cond-mat.str-el])

2018-08-24T02:29:25+00:00August 24th, 2018|Categories: Publications|Tags: |

Type-II Dirac/Weyl semimetals are characterized by strongly tilted Dirac cones such that the Dirac/Weyl node emerges at the boundary of electron and hole pockets as a new state of quantum matter, distinct from the standard Dirac/Weyl points with a point-like Fermi surface which are referred to as type-I nodes. The type-II Dirac fermions were recently predicted by theory and have since been confirmed in experiments in the PtSe2-class of transition metal dichal-cogenides. However, the Dirac nodes observed in PtSe2, PdTe2 and PtTe2 candidates are quite far away from the Fermi level, making the signature of topological fermions obscure as the physical properties are still dominated by the non-Dirac quasiparticles. Here we report the synthesis of a new type-II Dirac semimetal NiTe2 in which a pair of type-II Dirac nodes are located very close to the Fermi level. The quantum oscillations in this material reveal a nontrivial Berry’s phase associated with these Dirac fermions. Our first principles calculations further unveil a topological Dirac cone in its surface states. Therefore, NiTe2 may not only represent an improved system to formulate the theoretical understanding of the exotic consequences of type-II Dirac fermions, it also facilitates possible applications based on these topological carriers.

Published in: "arXiv Material Science".

Intrinsic Point Defects in Ultrathin 1T-PtSe2 Layers. (arXiv:1808.04719v1 [cond-mat.mes-hall])

2018-08-15T04:30:22+00:00August 15th, 2018|Categories: Publications|Tags: , , |

Among two dimensional (2D) transition metal dichalcogenides (TMDs), platinum diselenide (PtSe2) stands at a unique place in the sense that it undergoes a phase transition from type-II Dirac semimetal to indirect-gap semiconductor as thickness decreases. Defects in 2D TMDs are ubiquitous and they play crucial roles in understanding electronic, optical, and magnetic properties and tailoring them for desirable applications. Here we investigate intrinsic point defects in ultrathin 1T-PtSe2 layers grown on mica through the chemical vapor transport method, using scanning tunneling microscopy (STM) and first-principles calculations. We found five distinct defects from STM topography images and obtained the local density of states of the defects. By combining the STM results with the first-principles calculations, we identified the types and characteristics of these defects, which are Pt vacancies at the topmost and next monolayers, Se vacancies in the topmost monolayer, and Se antisites at Pt sites within the topmost monolayer. Interestingly, our study shows that the Se antisite defects are the most abundant with the lowest formation energy in a Se-rich growth condition, in contrast to cases of 2D TMD MoS2 family. Our findings will directly influence tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or growth condition in thin semiconductor PtSe2 layers.

Published : "arXiv Mesoscale and Nanoscale Physics".

Atomically thin noble metal dichalcogenide: a broadband mid-infrared semiconductor

2018-04-18T10:31:25+00:00April 18th, 2018|Categories: Publications|Tags: |

Atomically thin noble metal dichalcogenide: a broadband mid-infrared semiconductorAtomically thin noble metal dichalcogenide: a broadband mid-infrared semiconductor, Published online: 18 April 2018; doi:10.1038/s41467-018-03935-0The mid-infrared technologies are essential to various applications but suffer from limited materials with suitable bandgap. Here the authors demonstrate that two-dimensional atomically thin PtSe2 with variable bandgaps in the mid-infrared via layer and defect engineering is highly promising for mid-infrared optoelectronics.

Published in: "Nature Communications".

Highly sensitive electromechanical piezoresistive pressure sensors based on large-area layered PtSe$_{2}$ films. (arXiv:1803.07151v1 [cond-mat.mtrl-sci])

2018-03-21T19:58:56+00:00March 21st, 2018|Categories: Publications|Tags: |

Two-dimensional (2D) layered materials are ideal for micro- and nanoelectromechanical systems (MEMS/NEMS) due to their ultimate thinness. Platinum diselenide (PtSe$_{2}$), an exciting and unexplored 2D transition metal dichalcogenides (TMD) material, is particularly interesting because its scalable and low temperature growth process is compatible with silicon technology. Here, we explore the potential of thin PtSe$_{2}$ films as electromechanical piezoresistive sensors. All experiments have been conducted with semimetallic PtSe$_{2}$ films grown by thermally assisted conversion of Pt at a CMOS-compatible temperature of 400{deg}C. We report high negative gauge factors of up to -84.8 obtained experimentally from PtSe$_{2}$ strain gauges in a bending cantilever beam setup. Integrated NEMS piezoresistive pressure sensors with freestanding PMMA/PtSe$_{2}$ membranes confirm the negative gauge factor and exhibit very high sensitivity, outperforming previously reported values by orders of magnitude. We employ density functional theory (DFT) calculations to understand the origin of the measured negative gauge factor. Our results suggest PtSe$_{2}$ as a very promising candidate for future NEMS applications, including integration into CMOS production lines.

Published : "arXiv Mesoscale and Nanoscale Physics".

Wafer-scale fabrication of 2D van der Waals heterojunctions for efficient and broadband photodetection. (arXiv:1803.04695v1 [cond-mat.mes-hall])

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

A variety of fabrication methods for van der Waals heterostructures have been demonstrated; however, their wafer-scale deposition remains a challenge. Here we report few-layer van der Waals PtS2/PtSe2 heterojunction photodiodes fabricated on a 2″ SiO2/Si substrate that is only limited by the size of work chamber of the growth equipment, offering throughputs necessary for practical applications. Theoretical simulation results show that the bandgap of PtS2 is shrunk to half of its original size in the PtS2/PtSe2 heterostructures, while PtSe2 exhibits a limited response to the coupling. Both PtSe2 and PtS2 layers in the coupled system are still semiconductors. Dynamic photovoltaic switching in the heterojunctions is observed at zero-volt state under laser illuminations of 532 to 2200 nm wavelengths. The PtS2/PtSe2 photodiodes show excellent characteristics in terms of a high photoresponsivity of 361 mAW-1, an external quantum efficiency (EQE) of 84%, and a fast response speed (66 ms). The wafer-scale production of 2D photodiodes in this work accelerates the possibility of 2D materials for practical applications in the next-generation energy-efficient electronics.

Published : "arXiv Mesoscale and Nanoscale Physics".

Thickness-modulated metal-to-semiconductor transformation in a transition metal dichalcogenide

2018-03-02T10:32:00+00:00March 2nd, 2018|Categories: Publications|Tags: |

Thickness-modulated metal-to-semiconductor transformation in a transition metal dichalcogenideThickness-modulated metal-to-semiconductor transformation in a transition metal dichalcogenide, Published online: 02 March 2018; doi:10.1038/s41467-018-03436-0The electronic band structure of van der Waals crystals is strongly sensitive to the number of layers. Here, the authors observe a thickness-dependent metal-to-semiconductor transition in layered PtSe2 by means of electrical transport measurements.

Published in: "Nature Communications".

Electrical devices from top-down structured platinum diselenide films

2018-03-02T09:09:09+00:00March 2nd, 2018|Categories: Publications|Tags: |

Electrical devices from top-down structured platinum diselenide filmsElectrical devices from top-down structured platinum diselenide films, Published online: 28 February 2018; doi:10.1038/s41699-018-0051-9Transport measurements on channels of layered PtSe2 give insight into the realization of high-performance nanoelectronic PtSe2 devices. A team led by Niall McEvoy at Trinity College Dublin investigated the electrical contact properties of PtSe2 channels with controlled dimensions and thicknesses. Electron beam lithography was used to fabricate structures with different contact metals and different PtSe2 film thicknesses, and the corresponding contact resistivity and sheet resistance of the PtSe2 devices were extracted from transmission line method measurements. The charge-transport characteristics of the PtSe2 devices revealed that edge-contacted structures are able reduce the contact resistivity when compared to conventional devices with top contacts, thanks to enhancement of the carrier injection at the contacts. These results may pave the way to optimal design of PtSe2 nanoelectronic devices.

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

Fast, Self-Driven, Air-Stable, and Broadband Photodetector Based on Vertically Aligned PtSe2/GaAs Heterojunction

2018-02-16T08:28:42+00:00February 16th, 2018|Categories: Publications|Tags: , |

Abstract Group-10 layered transitional metal dichalcogenides including PtS2, PtSe2, and PtTe2 are excellent potential candidates for optoelectronic devices due to their unique properties such as high carrier mobility, tunable bandgap, stability, and flexibility. Large-area platinum diselenide (PtSe2) with semiconducting characteristics is far scarcely investigated. Here, the development of a high-performance photodetector based on vertically aligned PtSe2-GaAs heterojunction which exhibits a broadband sensitivity from deep ultraviolet to near-infrared light, with peak sensitivity from 650 to 810 nm, is reported. The Ilight/Idark ratio and responsivity of photodetector are 3 × 104 and 262 mA W−1 measured at 808 nm under zero bias voltage. The response speed of τr/τf is 5.5/6.5 µs, which represents the best result achieved for Group-10 TMDs based optoelectronic device thus far. According to first-principle density functional theory, the broad photoresponse ranging from visible to near-infrared region is associated with the semiconducting characteristics of PtSe2 which has interstitial Se atoms within the PtSe2 layers. It is also revealed that the PtSe2/GaAs photodetector does not exhibit performance degradation after six weeks in air. The generality of the above good results suggests that the vertically aligned PtSe2 is an ideal material for high-performance optoelectronic systems in the future. This work shows the large-area growth of high-quality vertically aligned PtSe2, and its application to photodetectors based on PtSe2-GaAs heterojunctions which exhibit a broadband sensitivity to illumination ranging from deep ultraviolet to near-infrared light, with a peak sensitivity in the region from 650 to 810 nm. The high-performance broadband photodetector will develop the

Published in: "Advanced Functional Materials".

Approaching the Type-II Dirac Point and Concomitant Superconductivity in Pt-doping Stabilized Metastable 1T-phase IrTe2. (arXiv:1711.10909v1 [cond-mat.mtrl-sci])

2017-11-30T19:59:01+00:00November 30th, 2017|Categories: Publications|Tags: , |

Topological semimetal is a topic of general interest in material science. Recently, a new kind of topological semimetal called type-II Dirac semimetal with tilted Dirac cones is discovered in PtSe2 family. However, the further investigation is hindered due to the huge energy difference from Dirac points to Fermi level and the irrelevant conducting pockets at Fermi surface. Here we characterize the optimized type-II Dirac dispersions in a metastable 1T phase of IrTe2. Our strategy of Pt doping protects the metastable 1T phase in low temperature and tunes the Fermi level to the Dirac point. As demonstrated by angle-resolved photoemission spectra and first principle calculations, the Fermi surface of Ir1-xPtxTe2 is formed by only a single band with type-II Dirac cone which is tilted strongly along kz momentum direction. Interesting superconductivity is observed in samples for Dirac point close to Fermi level and even survives when Fermi level aligns with the Dirac point as finite density of states created by the tilted cone dispersion. This advantage offers opportunities for possible topological superconductivity and versatile Majorana devices in type-II Dirac semimetals.

Published in: "arXiv Material Science".

Band gap opening of graphene by forming a graphene/PtSe2 van der Waals heterojunction

2017-09-22T12:28:47+00:00September 22nd, 2017|Categories: Publications|Tags: , |

RSC Adv., 2017, 7,45393-45399DOI: 10.1039/C7RA06865D, Paper Open Access &nbsp This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.Zhaoyong Guan, Shuang Ni, Shuanglin HuAs a promising high performance FET, the graphene/PtSe2 vdW heterojunction has a band gap of 0.264[space]eV.The content of

Published in: "RSC Advances".

Experimental evidence for type-II Dirac semimetal in ${mathrm{PtSe}}_{2}$

2017-09-01T20:30:15+00:00September 1st, 2017|Categories: Publications|Tags: |

Author(s): Kenan Zhang, Mingzhe Yan, Haoxiong Zhang, Huaqing Huang, Masashi Arita, Zhe Sun, Wenhui Duan, Yang Wu, and Shuyun ZhouWhile a monolayer PtSe2 film is a semiconductor with interesting spin structure, bulk PtSe2 crystal has been predicted to be a topological Dirac semimetal that can host a new type of Lorentz-violating Dirac fermions. Despite the intriguing predictions, experimental progress on the electronic structu…[Phys. Rev. B 96, 125102] Published Fri Sep 01, 2017

Published in: "Physical Review B".

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