Lattice Transformation from 2-D to Quasi 1-D and Phonon Properties of Exfoliated ZrS2 and ZrSe2. (arXiv:2210.00631v1 [cond-mat.mtrl-sci])

2022-10-04T02:29:19+00:00October 4th, 2022|Categories: Publications|Tags: , |

We investigate the thermal properties of these Zirconium based materials using confocal Raman spectroscopy. We observed 2 different and distinctive Raman signatures for exfoliated ZrX2 (where X = S or Se). These Raman modes generally depend on the shape of the exfoliated nanosheets, regardless of the incident laser polarization. These 2 shapes are divided into 2D- ZrX2 and quasi 1D- ZrX2. For 2D- ZrX2, Raman modes are in alignment with those reported in literature. However, for quasi 1D-ZrX2, we show that Raman modes are identical to exfoliated ZrX3 nanosheets, indicating a major lattice transformation from 2D to quasi-1D. We also measure thermal properties of each resonant Raman mode for each ZrX2 shape. Based on our measurements, most Raman modes exhibit a linear downshift dependence with temperature. However, for ZrS2, we see an upshift (blueshift) with temperature for A1g mode, which is attributed to non-harmonic effects caused by dipolar coupling with IR-active modes. Moreover, the observed temperature dependence coefficient for some phonon modes of quasi 1D-ZrX2 differ dramatically, which can be caused by the quasi 1D lattice. Finally, we measure phonon dynamics under optical heating for each of 2D-ZrX2 and quasi 1D-ZrX2 and show phonon confinement in quasi 1D-ZrX2 nanosheets. We extract the thermal conductivity and the interfacial thermal conductance for each of 2D-ZrX2 and quasi 1D-ZrX2 nanosheets. Our calculations indicate lower interfacial thermal conductance for quasi 1D-ZrX2 compared to 2D-ZrX2, which can be attributed to the phonon confinement in 1D. Based on our model, we show low thermal conductivity for

Published in: "arXiv Material Science".

Charge qubit in van der Waals heterostructures

2019-09-27T14:38:05+00:00September 27th, 2019|Categories: Publications|Tags: , , |

Author(s): Bruno Lucatto, Daniel S. Koda, Friedhelm Bechstedt, Marcelo Marques, and Lara K. TelesIn this Rapid Communication, we develop the concept of charge qubits in van der Waals heterostructures. A theoretical proof of concept is provided for the ZrSe2/SnSe2 system, in which a framework connecting the electronic structure with quantum information is described. The quantum state is prepared…[Phys. Rev. B 100, 121406(R)] Published Fri Sep 27, 2019

Published in: "Physical Review B".

Electrical Conduction at the Interface between Insulating van der Waals Materials

2019-03-13T12:32:48+00:00March 13th, 2019|Categories: Publications|Tags: , , , , , |

Highly conducting interfaces between insulating 2D materials are demonstrated in van der Waals heterostructures fabricated by molecular‐beam epitaxy. In situ growth monitoring by reflection high energy electron diffraction confirms layer‐by‐layer fabrication of the heterostructures and the formation of abrupt interfaces. Hall effect measurements reveal that the conducting carriers are holes, and their densities are as large as 1014 cm−2. Abstract Emergent properties of 2D materials attract considerable interest in condensed matter physics and materials science due to their distinguished features that are missing in their bulk counterparts. A mainstream in this research field is to broaden the scope of material to expand the horizons of the research area, while developing functional interfaces between different 2D materials is another indispensable research direction. Here, the emergence of electrical conduction at the interface between insulating 2D materials is demonstrated. A new class of van der Waals heterostructures consisting of two sets of insulating transition‐metal dichalcogenides, group‐VI WSe2 and group‐IV TMSe2 (TM = Zr, Hf), is developed via molecular‐beam epitaxy, and it is found that those heterostructures are highly conducting although all the constituent materials are highly insulating. The WSe2/ZrSe2 interface exhibits more conducting behavior than the WSe2/HfSe2 interface, which can be understood by considering the band alignments between constituent materials. Moreover, by increasing Se flux during heterostructure fabrication, the WSe2/ZrSe2 interface becomes more conducting, reaching nearly metallic behavior. Further improvement of the crystalline quality as well as exploring different material combinations are expected to lead to metallic conduction, providing a novel functionality emerging

Published in: "Advanced Functional Materials".

Electrical Conduction at the Interface between Insulating van der Waals Materials

2019-03-10T20:32:47+00:00March 10th, 2019|Categories: Publications|Tags: , , , , , |

Highly conducting interfaces between insulating 2D materials are demonstrated in van der Waals heterostructures fabricated by molecular‐beam epitaxy. In situ growth monitoring by reflection high energy electron diffraction confirms layer‐by‐layer fabrication of the heterostructures and the formation of abrupt interfaces. Hall effect measurements reveal that the conducting carriers are holes, and their densities are as large as 1014 cm−2. Abstract Emergent properties of 2D materials attract considerable interest in condensed matter physics and materials science due to their distinguished features that are missing in their bulk counterparts. A mainstream in this research field is to broaden the scope of material to expand the horizons of the research area, while developing functional interfaces between different 2D materials is another indispensable research direction. Here, the emergence of electrical conduction at the interface between insulating 2D materials is demonstrated. A new class of van der Waals heterostructures consisting of two sets of insulating transition‐metal dichalcogenides, group‐VI WSe2 and group‐IV TMSe2 (TM = Zr, Hf), is developed via molecular‐beam epitaxy, and it is found that those heterostructures are highly conducting although all the constituent materials are highly insulating. The WSe2/ZrSe2 interface exhibits more conducting behavior than the WSe2/HfSe2 interface, which can be understood by considering the band alignments between constituent materials. Moreover, by increasing Se flux during heterostructure fabrication, the WSe2/ZrSe2 interface becomes more conducting, reaching nearly metallic behavior. Further improvement of the crystalline quality as well as exploring different material combinations are expected to lead to metallic conduction, providing a novel functionality emerging

Published in: "Advanced Functional Materials".

Electrical Conduction at the Interface between Insulating van der Waals Materials

2019-03-07T10:32:37+00:00March 7th, 2019|Categories: Publications|Tags: , , , , , |

Highly conducting interfaces between insulating 2D materials are demonstrated in van der Waals heterostructures fabricated by molecular‐beam epitaxy. In situ growth monitoring by reflection high energy electron diffraction confirms layer‐by‐layer fabrication of the heterostructures and the formation of abrupt interfaces. Hall effect measurements reveal that the conducting carriers are holes, and their densities are as large as 1014 cm−2. Abstract Emergent properties of 2D materials attract considerable interest in condensed matter physics and materials science due to their distinguished features that are missing in their bulk counterparts. A mainstream in this research field is to broaden the scope of material to expand the horizons of the research area, while developing functional interfaces between different 2D materials is another indispensable research direction. Here, the emergence of electrical conduction at the interface between insulating 2D materials is demonstrated. A new class of van der Waals heterostructures consisting of two sets of insulating transition‐metal dichalcogenides, group‐VI WSe2 and group‐IV TMSe2 (TM = Zr, Hf), is developed via molecular‐beam epitaxy, and it is found that those heterostructures are highly conducting although all the constituent materials are highly insulating. The WSe2/ZrSe2 interface exhibits more conducting behavior than the WSe2/HfSe2 interface, which can be understood by considering the band alignments between constituent materials. Moreover, by increasing Se flux during heterostructure fabrication, the WSe2/ZrSe2 interface becomes more conducting, reaching nearly metallic behavior. Further improvement of the crystalline quality as well as exploring different material combinations are expected to lead to metallic conduction, providing a novel functionality emerging

Published in: "Advanced Functional Materials".

Emergence of conduction band-induced semiconductor-to-metal transition in ZrSe2 through Hf substitution. (arXiv:1812.00157v1 [cond-mat.mtrl-sci])

2018-12-04T02:29:16+00:00December 4th, 2018|Categories: Publications|Tags: , |

Two-dimensional (2D) layered materials are very important and versatile platform for exploring novel electronic properties in different phases. The chemical doping in two-dimensional (2D) layered materials can engineer the electronic structure with useful physical properties which are distinct in comparison with the pristine one. Herein, we employed angle-resolved photoemission spectroscopy (ARPES) combined with first-principles density functional theory (DFT) calculations, to show the possible phase engineering of ZrSe2 via Hafnium (Hf) atoms substitution, which manifests a semiconducting-to-metallic transition. The emergence of conduction band at high symmetry M point around the Brillouin zone boundary due to extra charge doping, clearly demonstrates the conceivable evidence of semiconductor to metal transition in ZrSe2, through Hf substitution (about 12.5 percent) at room temperature. Similarly, the electrical resistance measurements further revealed the decrease of resistance with increasing temperature for ZrSe2 that confirms the semiconducting behavior, while the resistance increases with increasing temperature for Hf doped ZrSe2 that in an indication of the metallic behavior. This study further demonstrates the possibility of the band gap engineering through heavily doped metal in 2D materials thereby modulating the electronic properties of layered materials for next-generation electronic applications.

Published in: "arXiv Material Science".

Localized Surface Plasmon Resonance on Two-Dimensional HfSe2 and ZrSe2. (arXiv:1810.04829v1 [cond-mat.mtrl-sci])

2018-10-12T02:29:39+00:00October 12th, 2018|Categories: Publications|Tags: , , , |

HfSe2 and ZrSe2 are newly discovered two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) with promising properties for future nanoelectronics and optoelectronics. We theoretically revealed the electronic and optical properties of these two emerging 2D semiconductors, and evaluated their performance for the application of localized surface plasmon resonance (LSPR) at extreme conditions: in-plane direction versus out-of-plane direction and monolayer versus multilayer. First, the energy band structure and dielectric constants were calculated for both the monolayer and multilayer structures using Kohn-Sham density functional theory (KS-DFT) with van der Waals (vdW) corrections. A parallel-band effect observed in the monolayer band structure indicates a strong light-matter interaction. Then, based on the calculated dielectric constants, the performance of the LSPR excited by Au sphere nanoparticles (NPs) was quantitatively characterized, including polarizability, scattering and absorption cross-sections, and radiative efficiency using Mie theory. For the multilayer HfSe2 and ZrSe2, the LSPR showed very comparable intensities in both the in-plane and out-of-plane directions, suggesting an isotropy-like light-matter interaction. In a comparison, the LSPR excited on the monolayer HfSe2 and ZrSe2 was clearly observed in the in-plane direction but effectively suppressed in the out-of-plane direction due to the unique anisotropic nature. In addition to this extraordinary anisotropy-to-isotropy transition as the layer number increases, a red-shift of the LSPR wavelength was also found. Our work has predicated the thickness-dependent anisotropic light-matter interaction on the emerging 2D semiconducting HfSe2 and ZrSe2, which holds great potential for broad optoelectronic applications such as sensing and energy conversion.

Published in: "arXiv Material Science".

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