arXiv subjects

Francesco Reale

Publications and source records attributed to Francesco Reale.

4 recordsLinked to original sources

arXiv2018

Electronic band structure of Two-Dimensional WS2/Graphene van der Waals Heterostructures

Combining single-layer two-dimensional semiconducting transition metal dichalcogenides (TMDs) with graphene layer in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these heterostructures. Here, we report the electronic and structural properties of transferred single layer WS2 on epitaxial graphene using micro-Raman spectroscopy, angle-resolved photoemission spectroscopy measurements (ARPES) and Density Functional Theory (DFT) calculations. The results show good electronic properties as well as well-defined band arising from the strong splitting of the single layer WS2 valence band at K points, with a maximum splitting of 0.44 eV. By comparing our DFT results with local and hybrid functionals, we find the top valence band of the experimental heterostructure is close to the calculations for suspended single layer WS2. . Our results provide an important reference for future studies of electronic properties of WS2 and its applications in valleytronic devices.

cond-mat.mtrl-sci↗

arXiv2017

Strong Spin-Orbit Interaction Induced in Graphene by Monolayer WS$_2$

We demonstrate strong anisotropic spin-orbit interaction (SOI) in graphene induced by monolayer WS$_2$. Direct comparison between graphene/monolayer WS$_2$ and graphene/bulk WS$_2$ system in magnetotransport measurements reveals that monolayer transition metal dichalcogenide (TMD) can induce much stronger SOI than bulk. Detailed theoretical analysis of the weak-antilocalization curves gives an estimated spin-orbit energy ($E_{\rm so}$) higher than 10 meV. The symmetry of the induced SOI is also discussed, and the dominant $z$ $\rightarrow$ $-z$ symmetric SOI can only explain the experimental results. Spin relaxation by the Elliot-Yafet (EY) mechanism and anomalous resistance increase with temperature close to the Dirac point indicates Kane-Mele (KM) SOI induced in graphene.

cond-mat.mes-hall↗

arXiv2017

High-Mobility and High-Optical Quality Atomically Thin WS2

The rise of atomically thin materials has the potential to enable a paradigm shift in modern technologies by introducing multi-functional materials in the semiconductor industry. To date the growth of high quality atomically thin semiconductors (e.g. WS2) is one of the most pressing challenges to unleash the potential of these materials and the growth of mono- or bi-layers with high crystal quality is yet to see its full realization. Here, we show that the novel use of molecular precursors in the controlled synthesis of mono- and bi-layer WS2 leads to superior material quality compared to the widely used topotactic transformation of WO3-based precursors. Record high room temperature charge carrier mobility up to 52 cm2/Vs and ultra-sharp photoluminescence linewidth of just 36 meV over submillimeter areas demonstrate that the quality of this material supersedes also that of naturally occurring materials. By exploiting surface diffusion kinetics of W and S species adsorbed onto a substrate, a deterministic layer thickness control has also been achieved promoting the design of scalable synthesis routes.

cond-mat.mtrl-sci↗

arXiv2017

Role of Charge Traps in the Performance of Atomically-Thin Transistors

Transient currents in atomically thin MoTe$_2$ field-effect transistor are measured during cycles of pulses through the gate electrode. The transients are analyzed in light of a newly proposed model for charge trapping dynamics that renders a time-dependent change in threshold voltage the dominant effect on the channel hysteretic behavior over emission currents from the charge traps. The proposed model is expected to be instrumental in understanding the fundamental physics that governs the performance of atomically thin FETs and is applicable to the entire class of atomically thin-based devices. Hence, the model is vital to the intelligent design of fast and highly efficient opto-electronic devices.

cond-mat.mes-hall↗