39 research outputs found
Defects, band bending and ionization rings in MoS2
Chalcogen vacancies in transition metal dichalcogenides are widely
acknowledged as both donor dopants and as a source of disorder. The electronic
structure of sulphur vacancies in MoS2 however is still controversial, with
discrepancies in the literature pertaining to the origin of the in-gap features
observed via scanning tunneling spectroscopy (STS) on single sulphur vacancies.
Here we use a combination of scanning tunnelling microscopy (STM) and STS to
study embedded sulphur vacancies in bulk MoS2 crystals. We observe
spectroscopic features dispersing in real space and in energy, which we
interpret as tip position- and bias-dependent ionization of the sulphur vacancy
donor due to tip induced band bending (TIBB). The observations indicate that
care must be taken in interpreting defect spectra as reflecting in-gap density
of states, and may explain discrepancies in the literature.Comment: 7 pages, 5 figure
Metastable polymorphic phases in monolayer TaTe2
Polymorphic phases and collective phenomena—such as charge density waves (CDWs)—in transition metal dichalcogenides (TMDs) dictate the physical and electronic properties of the material. Most TMDs naturally occur in a single given phase, but the fine-tuning of growth conditions via methods such as molecular beam epitaxy (MBE) allows to unlock otherwise inaccessible polymorphic structures. Exploring and understanding the morphological and electronic properties of new phases of TMDs is an essential step to enable their exploitation in technological applications. Here, scanning tunneling microscopy (STM) is used to map MBE-grown monolayer (ML) TaTe2. This work reports the first observation of the 1H polymorphic phase, coexisting with the 1T, and demonstrates that their relative coverage can be controlled by adjusting synthesis parameters. Several superperiodic structures, compatible with CDWs, are observed to coexist on the 1T phase. Finally, this work provides theoretical insight on the delicate balance between Te…Te and Ta–Ta interactions that dictates the stability of the different phases. The findings demonstrate that TaTe2 is an ideal platform to investigate competing interactions, and indicate that accurate tuning of growth conditions is key to accessing metastable states in TMD
Crossover from 2D ferromagnetic insulator to wide bandgap quantum anomalous Hall insulator in ultra-thin MnBi2Te4
Intrinsic magnetic topological insulators offer low disorder and large
magnetic bandgaps for robust magnetic topological phases operating at higher
temperatures. By controlling the layer thickness, emergent phenomena such as
the Quantum Anomalous Hall (QAH) effect and axion insulator phases have been
realised. These observations occur at temperatures significantly lower than the
Neel temperature of bulk MnBi2Te4, and measurement of the magnetic energy gap
at the Dirac point in ultra-thin MnBi2Te4 has yet to be achieved. Critical to
achieving the promise of this system is a direct measurement of the
layer-dependent energy gap and verifying whether the gap is magnetic in the QAH
phase. Here we utilise temperature dependent angle-resolved photoemission
spectroscopy to study epitaxial ultra-thin MnBi2Te4. We directly observe a
layer dependent crossover from a 2D ferromagnetic insulator with a bandgap
greater than 780 meV in one septuple layer (1 SL) to a QAH insulator with a
large energy gap (>100 meV) at 8 K in 3 and 5 SL MnBi2Te4. The QAH gap is
confirmed to be magnetic in origin, as it abruptly diminishes with increasing
temperature above 8 K. The direct observation of a large magnetic energy gap in
the QAH phase of few-SL MnBi2Te4 is promising for further increasing the
operating temperature of QAH materials
On-surface synthesis of polyethylenedioxythiophene
On-surface synthesis of conjugated polymers is made challenging by the need to promote the desired reaction while preventing or minimizing unwanted ancillary reactions that compromise the product integrity. We perform a comprehensive study of the reactions of 2,5-dichloro-3,4-ethylenedioxythiophene on coinage metal surfaces, and demonstrate that only on Ag(111) can we obtain a planar polymer product, polyethylenedioxythiophene (PEDOT)
High‐Temperature One‐Step Synthesis of Efficient Nanostructured Bismuth Vanadate Photoanodes for Water Oxidation
Authors acknowledge the financial supports of the Australian Research
Council (ARC) DP150101939, ARC DE160100569, Westpac 2016 Research
Fellowship, the ActewAGL Endowment Fund, and the Research School of
Engineering of the ANU. Authors also acknowledge the Centre for
Advanced Microscopy (CAM) with funding through the Australian
Microscopy and Microanalysis Research Facility (AMMRF), and the
Australian National Fabrication Facility (ANFF), ACT Node. A.N.S. acknowledges funding by the ARC through the Centre of Excellence for
Electromaterials Science (CE140100012)
Three-dimensional microporous graphene decorated with lithium
Three-dimensional (3D) graphene-based architectures can combine the two-dimensional properties of graphene with the high surface-to-volume ratio required for a large variety of technological applications. We present a spectro-microscopy study of stable microporous 3D few-layer graphene structures with a very low density of defects/edges and of unsaturated bonds, as deduced by Raman and core level photoemission spectroscopy. These qualities make these interconnected graphene networks ideal candidates to accommodate lithium adatoms, with a high density of Li per unit volume and a Li uptake per C atom higher than the value observed for graphite, as confirmed by core level photoemission spectroscopy