Nano-ARPES studies of novel transition metal dichalcogenides

Lead Research Organisation: University of Bath
Department Name: Physics

Abstract

An Overseas Travel Grant is sought to cover travel costs to carry out the first X-ray experiments on two new two-dimensional layered semiconductor materials (ReS2 and ReSe2) over the next six months, using the high intensity X-ray beam available at the SOLEIL synchrotron, Paris. This synchrotron is unique world-wide at present in providing a high intensity, tunable X-ray wavelength, and a focused spot which is sufficiently small that we can image and target regions of of the sample consisting of single atomic layers or multiple layers at will, thus enabling us to find out how the semiconductor properties change as the thickness increases from the ultimate 2D limit up to the 3D bulk crystal behaviour. This is a new type of experimental work for the Bath group but is part of a very exciting new research direction that it is pursuing, and its studies of ReS2 and ReSe2 by other means have attracted significant attention.

Planned Impact

In the short term, the research will impact mainly on the academic community, where there is a strong drive to develop applications for layered semiconductors and the nanoscale devices that can be fabricated from them. The present materials (ReS2 and ReSe2) offer functionality in a heterostructure device that no other transition metal dichalcogenides do and one can predict possible applications for them in sensing, catalysis, magnetic structures (though this is very speculative at present), superconductivity and opto-electronic devices. Thus longer-term beneficiaries of this work will be industrial R&D groups interested in nanoscale semiconductor devices going beyond silicon technologies. The promise of completely new device concepts based on, for example, valleytronics, is attracting academic attention and is likely to generate a new industry sector if realised. Meanwhile, some layered semiconductors are finding more mundane but still highly important roles and will have a shorter-term impact: these include composites of layered semiconductors for improved thermal conductivity, mechanical strength, or strain gauge applications, and these are already beginning to impact on a range of manufacturing industries.

Publications

10 25 50
 
Description We have mapped out for the first time the valence band structure of the transition metal dichalcogenides ReS2 and ReSe2 via the synchrotron experiments, together with associated computational modelling.

In non-specialist terms, atomically-thin semiconductors are currently a very hot topic for new types of electronics concepts, but there are many materials in this family with a variety of properties; we have focused on two examples with properties that were poorly known but expected to be untypical for this family. They thus add new dimensions to what could be achieved as combinations of these materials are assembled together. Our basic research has led to a much better understanding of the starting materials ReS2 and ReSe2 and will have a high impact in the academic community worldwide. We have now made the first ever studies of atomically thin materials derived from ReS2 and ReSe2 in order to understand the evolution of the quantum electronic states in such structures as they reach the ultimate level of 3-atom thick layers.
Exploitation Route With our current results, we have provided the basic understanding that enables researchers developing two dimensional device concepts to predict how these particular materials will behave, in what types of device they could find applications, and how they could be integrated into devices. The field of applications of 2D semiconductors is at a very early stage and fundamental research into the individual building blocks is likely to be followed by assembly of more complex combinations of materials; at that stage, our experimental techniques will continue to support research into the electronic structures that can be achieved. As we establish and publicise the usefulness of the nano-ARPES technique and the tools to interpret our present results, we will promote the growing role this technique will have in the field of 2D semiconductors, where it is ideally suited to answer some of the key questions. Our fundamental studies of layered materials down to the single layer limit paves the way for manipulation of these materials by stacking, to achieve a control over their properties beyond what is naturally available.
Sectors Chemicals,Digital/Communication/Information Technologies (including Software),Electronics,Energy,Environment,Pharmaceuticals and Medical Biotechnology

 
Description Our results provide a deep fundamental understanding of some little-studied and rather exotic members of an otherwise very intensively-studied family of atomically thin layered semiconductors. As such, we can focus the attention of the academic community on what makes these particular materials special in the context of the whole family and, it turns out, they ahve several unique and now well-understood properties that make them interesting additions to the suite of nanoscale 2D semiconductors. Publications are in preparation and so our results have not yet been used by other groups, but the promise of this work has already enabled us to secure continued synchrotron access to extend our work. This access is highly valued and highly competitive, so our success reflects the interest of the scientific community in these materials.
First Year Of Impact 2016
 
Description DIAMOND beam time (I05 beam line)
Amount £0 (GBP)
Funding ID SI15905 
Organisation Diamond Light Source 
Sector Private
Country United Kingdom
Start 02/2017 
End 07/2017
 
Title Sulfur and oxygen impurities in ReSe2: symmetry breaking and local vibrational modes 
Description This dataset supports the publication "Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe2 and MoSe2". It contains shell scripts for running Quantum Espresso code and the original spectroscopic data in Origin Project (.opj) file format. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Title Supporting information for "Valence band structure of ReS2 by Angle Resolved Photoemission Spectroscopy" 
Description Datasets contributing to the experimental figures (Figs. 2, 3, 4, 5) of the associated paper are contained here. Also included (code section) are scripts and associated C codes for running the band structure calculations (Figs 5 and 6); within these are the atomic coordinates which lead to the reciprocal space Brillouin Zone of Fig. 1. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Title Supporting information for "Valence band structure of ReSe2 investigated by angle-resolved photoemission spectroscopy" 
Description Data here represents raw computational and experimental data for the following work: ReSe2 and ReS2 are unusual compounds amongst the layered transition metal dichalcogenides as a result of their low symmetry, with a characteristic in-plane anisotropy due to in-plane rhenium 'chains'. They preserve inversion symmetry independent of the number of layers and, in contrast to more well-known transition metal dichalcogenides, bulk and few-monolayer Re-TMD compounds have been proposed to behave as electronically and vibrational decoupled layers. Here, we probe for the first time the electronic band structure of bulk ReSe2 by direct nanoscale angle-resolved photoemission spectroscopy. We find a highly anisotropic in- and out-of-plane electronic structure, with the valence band maxima located away from any particular high-symmetry direction. The effective mass doubles its value perpendicular to the Re chains and the interlayer van der Waals coupling generates significant electronic dispersion normal to the layers. Our density functional theory calculations, including spin-orbit effects, are in excellent agreement with these experimental findings. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Description ARPES at DIAMOND 
Organisation Diamond Light Source
Country United Kingdom 
Sector Private 
PI Contribution We proposed project and were granted beam time at DIAMOND
Collaborator Contribution DIAMOND staff assisted in proof of principle experiments, advised on experimental details, and are training PG and PDRA
Impact Collaboration at very early stage - we have initial data but no outputs
Start Year 2017
 
Description XPS and ARPES 
Organisation University of St Andrews
Country United Kingdom 
Sector Academic/University 
PI Contribution We provide novel semiconductor materials and characterise them by a variety of means, as well as fabricating devices based on these materials. We also model them theoreticallly.
Collaborator Contribution St Andrews will perform XPS and ARPES measurements to reveal fundamentals of the electronic band structure of these materials to test our theoretical and experimental work.
Impact None so far
Start Year 2015
 
Description nano-ARPES 
Organisation SOLEIL Synchrotron
Country France 
Sector Academic/University 
PI Contribution We proposed the experiments, shall provide the samples, and shall be responsible for the data analysis.
Collaborator Contribution SOLEIL provides the beamline (unique world-wide at present) and the support in running the experiments.
Impact None yet.
Start Year 2015
 
Description International advisory committee: International Conference on II-VI Compounds and Related Materials 2017 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Member of international advisory committee: International Conference on II-VI Compounds and Related Materials 2017
Year(s) Of Engagement Activity 2017
 
Description Invited talk: International Conference on Physics of 2D Crystals 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk: International Conference on Physics of 2D Crystals at Malta, May 2018
Year(s) Of Engagement Activity 2018
 
Description Invited talk: International Conference on Physics of 2D Crystals, 2017 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact invited talk at International Conference on Physics of 2D Crystals conference, Ha Long, Viet Nam, April 2017
Year(s) Of Engagement Activity 2017
 
Description Invited talk: Rhenium dichalcogenides: 2D layered semiconductors in a class of their own 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk: "Rhenium dichalcogenides: 2D layered semiconductors in a class of their own" at seminar in LMU Munich
Year(s) Of Engagement Activity 2018
 
Description Invited talk: Smart Nanomaterials 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk at Smart Nanomaterials 2018 conference, Paris, December 2018
Year(s) Of Engagement Activity 2018
 
Description Public lecture 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Public lecture organised by the IOP at the Bath Royal Scientific and Literary Institution, Queen Square, Bath,attended by IOP members and the general public.
Year(s) Of Engagement Activity 2016
 
Description Speaker at Photovoltaic Science, Application and Technology Conference 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Invited speaker at Photovoltaic Science, Application and Technology Conference, Bangor, April 2018.
Year(s) Of Engagement Activity 2018