Ultra Low Specific Contact Resistivity in Metal-Graphene Junctions via Atomic Orbital Engineering

A systematic investigation of graphene edge contacts is provided. Intentionally patterning monolayer graphene at the contact region creates well-defined edge contacts that lead to a 67% enhancement in current injection from a gold contact. Specific contact resistivity is reduced from 1372 {\Omega}m for a device with surface contacts to 456 {\Omega}m when contacts are patterned with holes. Electrostatic doping of the graphene further reduces contact resistivity from 519 {\Omega}m to 45 {\Omega}m, a substantial decrease of 91%. The experimental results are supported and understood via a multi-scale numerical model, based on density-functional-theory calculations and transport simulations. The data is analyzed with regards to the edge perimeter and hole-to-graphene ratio, which provides insights into optimized contact geometries. The current work thus indicates a reliable and reproducible approach for fabricating low resistance contacts in graphene devices. We provide a simple guideline for contact design that can be exploited to guide graphene and 2D material contact engineering.Comment: 26 page

Theoretical Analysis of a 2D Metallic/Semiconducting Transition-Metal Dichalcogenide NbS2//WSe2 Hybrid Interface

A first-principles theoretical study of a monolayer-thick lateral heterostructure (LH) joining two different transition metal dichalcogenides, NbS2 and WSe2, is reported. The NbS2//WSe2 LH can be considered a prototypical example of a metal (NbS2)/semiconductor (WSe2) 2D hybrid heterojunction. First, realistic atomistic models of the NbS2//WSe2 LH are generated and validated, its band structure is derived, and it is subjected to a fragment decomposition and electrostatic potential analysis to extract a simple but quantitative model of this interfacial system. Stoichiometric fluctuations models are also investigated and found not to alter the qualitative picture. Then, electron transport simulations are conducted and they are analyzed via band alignment analysis. It is concluded that the NbS2//WSe2 LH appears as a robust seamless in-plane 2D modular junction for potential use in optoelectronic devices going beyond the present miniaturization technology

Simulation of contact resistance in patterned graphene

While trying to exploit graphene in Radio Frequency applications, the reduction of the contact resistance (Rc) is probably one of the most challenging technological issues to be solved. Graphene patterning under the metal has been demonstrated to be a promising solution, leading to a reduction of Rc by up to a factor of 20, probably due to an increased conductivity at the borders of the patterns of graphene. This technology is still at the early stage and a complete understanding of the physical mechanisms at play is lacking. To this purpose we propose a multi- scale approach based on first-principle calculations, and the solution of the continuity equation to compute Rc in the considered patterned contacts

A high resolution wind&wave forecast model chain for the Mediterranean and Adriatic Sea

DHI (Danish Hydraulic Institute) and HyMOLab (Hydrodynamics and Met-Ocean Laboratory of the Dept. of Engineering and Architecture of the University of Trieste) have undertaken a joint applied research project with the aim to develop a state-of-art wind-wave forecast service at mid resolution for the Mediterranean Sea and at very high resolution for the Adriatic Sea. Weather routing, civil protection, coastal engineering, oil&gas and renewable energy fields, the planning of operations at sea, ... are just few among the multiple potential applications of this service. The meteorological model used in this study is WRF-ARW, one of the most widely used state-of-the-art open-source non-hydrostatic model. Global Forecast System (GFS) dataset provides the boundary and initial conditions. MIKE21-Spectral Waves is used as wave model with resolution ranging from 0.1 to 0.03 approximately. The use of a local area meteorological model guarantees higher levels of resolution and accuracy in an area such as the Mediterranean Sea where the complex orography and coastline induce short-time/small-space weather scales. The model chain runs daily (or twice a day on demand) on the High Performance Computing (HPC) infrastructure of HyMOLab. The validation of the entire model chain and specifically the forecast data obtained for the sea state is continuously updated according to new available data from satellites and buoys. Anyway, a major verification of the performance of the model chain against historic data (hindcast) is almost mandatory. For this aim, we performed a multi-decade test obtaining very good statistical parameters for the entire model chain performance. In this context the hindcast dataset developed by DHI and HyMOLab consists of 35 years of hourly data for the period 1979-2013, with the same model chain. The CFSR d093.0 hourly dataset with a spatial resolution of 0.5 provides the boundary and initial conditions. The atmospheric and wave models performance is checked against six satellite datasets, missions Envisat, ERS-2, Geosat FO, Jason-1, Jason-2, Topex-Poseidon, using a moving window technique procedure. Wave data close to coast are compared with available data from more than 20 buoys. The paper describes the validation procedure adopted for the hindcasted data. Furthermore the forecast service is described too, with specific emphasis to the very high resolution adopted in the Adriatic Sea

First heterogeneously Pd-catalysed C3-arylation of free indoles

internationa

First heterogeneously palladium-catalysed fully selective C3-arylation of free NH-indoles

International audienceA simple heterogeneously palladium-catalysed procedure for the selective C3-arylation of indoles is reported. Under relatively standard reaction conditions (Pd-catalyst, K2CO3, dioxane, reflux), using only 1 mol % [Pd(NH3)4]/NaY as the catalyst, indoles substituted or not at position 2 gave up to 92% conversion (i.e., 85% isolated yield) towards the expected C3-arylated indole

Innovative one-pot heterogeneous Pd-catalysed synthesis of stylbenes, bibenzyls and bis(bibenzyls).

internationa

Efficient Heterogeneously Palladium-Catalysed Synthesis of Stilbenes and Bibenzyls

Cusati, Giuseppe Wedig, Anja Djakovitch, LaurentAn alternative heterogeneously palladium catalysed procedure for the synthesis of functional stilbenes and bibenzyls is reported. Starting from aryl bromides and using simple commercially available Pd/C catalyst at a low catalytic rate (1 mol%), stilbenes are obtained with 30-100% GC-yields and bibenzyls are produced in a one-pot fashion with 27-100% GC-yields. The procedure showed, however, some limitations when applied to strongly deactivated aryl bromides that could be in some extent overcome by using corresponding iodo derivatives

Theoretical study of metal-graphene contact resistance

One of the main technological issues to be solved in graphene technology is the realization of graphene/metal contacts with very low contact resistance. Unfortunately, the values reported in literature are not completely consistent and the mechanisms at play at the interfaces are not fully understood. The principal aim of our work is to understand the nature of the mechanisms involved in the metal-graphene interface, through an in-depth multiscale theoretical study at the fundamental level, exploiting ab-initio simulations. We have considered two different categories of metals, based on the binding energy and the metal-graphene distance, i.e., physisorbed and chemisorbed metals. We have performed electronic calculations and detailed analysis of the electrostatic potential at the interface region of the system and computed transport through the interface, so to accurately calculate the contact resistance. Our approach is able to explain experimental results available in the literature, and it can be used in order to engineer contact resistance (i.e., giving hints so to obtain optimized interfaces), and to eventually obtain high performance devices based on graphene