Understanding the dynamics of charge carriers at nanoscale interfaces is an important field of research both from the fundamental science and technological applications perspective. Interactions between semiconductor quantum dots (QD), a prototypical 0D system, and 2D van der Waals materials have been getting a lot of attention in recent research2,3. Here, we report the observation of efficient non-radiative energy transfer (NRET) from core-shell QD to graphene and MoS2 via photoluminescence quenching of single QD emission on monolayer materials and direct measurement of decay rates through time-resolved photoluminescence on single layer to bulk 2D crystals1. Our measurements reveal opposite trends with thickness of the 2D materials for the rate of NRET to graphene and MoS2. The contrasting behaviours are explained in terms of the competition between the screening of the QD dipole and the dissipation of the electric field in the 2D material.

Johanna Zultak is a PhD student at DTU Nanotech working on stacks of various 2D materials for electronic devices fabrication and characterization. She received his Master degree in Physics from EPFL in 2014.

We study electromagnetic scattering and subsequent plasmonic excitations in periodic grids of graphene ribbons. To address this problem, we develop an analytical method to describe the plasmon-assisted absorption of electromagnetic radiation by a periodic structure of graphene ribbons forming a diffraction grating for THz and mid-IR light. The major advantage of this method lies in its ability to accurately describe the excitation of graphene surface plasmons (GSPs) in one-dimensional (1D) graphene gratings without the use of both time-consuming, and computationally-demanding full-wave numerical simulations. We thus provide analytical expressions for the reflectance, transmittance and plasmon-enhanced absorbance spectra, which can be readily evaluated in any personal laptop with little-to-none programming. We also introduce a semi-analytical method to benchmark our previous results and further compare the theoretical data with spectra taken from experiments, to which we observe a very good agreement. These theoretical tools may therefore be applied to design new experiments and cutting-edge nanophotonic devices based on graphene plasmonics.

[1] Book: P. A. D. Gonçalves and N. M. R. Peres, "An Introduction to Graphene Plasmonics" (World Scientific, Singapore, 2016).

P. André Gonçalves is currently a PhD student at Structured Electromagnetic Materials Group, DTU Fotonik, at Technical University of Denmark. Lately he has been doing research on the plasmonic properties of graphene and related 2D materials in several nanoengineered landscapes. He holds BSc in Physics from the University of Minho (2011, Portugal) and a MSc in Theoretical Physics from the University of Porto (2014, Portugal). 

Observed features in combination with other observations testify that the CTL is morphologically anisotropic through the layer thickness; sp2 phase of turbostratic bi-layer grapheme is formed at the top, and thicker sp3 allotrope sub-layer is formed beneath it. 

Aram Mailian is a senior researcher at the Institute for Informatics and at the Laboratory of Solar Engineering at State Engineering University, Yerevan, Armenia. He got his PhD degree in 1987 from Yerevan State University, Armenia. He is experienced in experimental investigation of surface properties of semiconductors, especially optical transitions at semiconductor surface. During recent years he deals with the carbon layers developed by rubbing. 

We discuss the significance of the screening tensor of a two-dimensional material (e.g. graphene) that is either suspended or surrounded by a non-dispersive medium. This quantity, which is defined as the ratio of the applied electrical field and the total field (which includes the material's response), determines the screening of space and time dependent fields. By solving the Maxwell equations, we are able to determine the relation between the components of such a tensor and those of the space and time dependent conductivity. We also review the question of the relation between the conductivity tensor and the response functions obtained from linear response. The RPA approximation is also reviewed is such a context. Finally, a simple application of such results is discussed.

Jaime E. Santos is a post-doctoral research fellow at the Centre of Physics of the University of Minho. Most recently, he was an invited researcher at the DTU Nanotech, during 2015, and before that he was a Assistant Research Professor at the University of Minho from 2012-2014. He has also been a visitor to the Max Planck Institute for the Physics of Complex Systems and the Max Planck Institute for the Chemical Physics of Solids, both in Dresden. He was also a post-doc at the HMI in Berlin and at the TUM in Munich.

Spyros Yannopoulos obtained his PhD from the University of Patras (1997) on the structure and dynamics of non-crystalline solids. He is currently a Principal Researcher at FORTH/ICE-HT specializing on advanced amorphous materials and nanomaterials. His research activities are focused on a molecular-based level understanding of materials’ properties and phenomena in hard and soft condensed matter employing experimental and (recently) computational methods. Main research activities include studies of disordered solids (glasses, amorphous films), photonic applications of amorphous semiconductors, nanostructured materials with specific functionalities (nanostructured oxides for nanophotonics, hydrogen evolution, energy conversion applications and gas sensing). He has been involved in the exploration of laser-assisted methods for graphene synthesis using a variety of organic and inorganic (carbides) substances. Recent activities include also the fabrication of 2-D crystals (TMDChs) and the study of their catalytic activities in solar cell devices. He has published 118 papers in peer-reviewd journals and 12 chapters in international books.

Spyros Yannopoulos obtained his PhD from the University of Patras (1997) on the structure and dynamics of non-crystalline solids. He is currently a Principal Researcher at FORTH/ICE-HT specializing on advanced amorphous materials and nanomaterials. His research activities are focused on a molecular-based level understanding of materials’ properties and phenomena in hard and soft condensed matter employing experimental and (recently) computational methods. Main research activities include studies of disordered solids (glasses, amorphous films), photonic applications of amorphous semiconductors, nanostructured materials with specific functionalities (nanostructured oxides for nanophotonics, hydrogen evolution, energy conversion applications and gas sensing). He has been involved in the exploration of laser-assisted methods for graphene synthesis using a variety of organic and inorganic (carbides) substances. Recent activities include also the fabrication of 2-D crystals (TMDChs) and the study of their catalytic activities in solar cell devices. He has published 118 papers in peer-reviewd journals and 12 chapters in international books.

[1] J. R. Hauptmann, T. Li, S. Petersen, J. Nygard, P. Hedegard, T. Bjornholm, B. W. Laursen, K. Norgaard, Phys Chem Chem Phys 2012, 14, 14277-14281

Martin Kühnel is a PhD student at the University of Copenhagen, supervised by Kasper Nørgaard, working mainly with chemical derived graphene and molecular electronics. He received his M.Sc. degree in Nano Science from the University of Copehagen in 2013. His PhD project is part of the Danish Alliance of Graphene Application Technology and Engineering (DA-GATE).

In this master thesis study, a van der Waals heterostructure with partially a clean and partially a contaminated interface was assembled. This heterostructure was used for studying the contamination's influence on the electronic properties of the encapsulated graphene. By applying the van der Pauw strategy for 4-terminal electrical characterization of sheet resistance, two square shaped devices with corner terminals were fabricated using Electron Beam Lithography. The devices were subsequently characterized by Raman spectroscopy, which indicated a difference in extrinsic doping of the graphene in the two device regions. A system with lock-in amplification, allowed accurate measurements of the device resistance while the devices were cooled in a cryostat. Measurements were performed from 300K to 2K in 9 steps. In the 2-50K range, the measurements showed negative resistances and large retraceable fluctuations at high carrier densities, indicating the onset of quasi-ballistic transport. Measurements at 50K exhibited carrier mobilities at n ± 10^(12) cm^(-2) up to 40,000 cm^(2)/Vs for the cleaner device and up to 22,000 cm^(2)/Vs for the more contaminated device. Analysis of the carrier mobility temperature dependence showed a temperature dependence for the clean device down to 150K, while the carrier concentration of the more contaminated exhibited temperature independence.

Martin Bjergfelt is a recent graduate (June 2016) from the Technical University of Denmark. He performed his thesis study at the Nanocarbon Group at DTU Nanotech on van der Waals heterostructure devices. He has primarily had experimental work with 2D materials, and has an interest in bringing the technological advancements in the field closer to industrial applications. Within 2D material technology, he has experience with mechanical exfoliation, van der Waals heterostructure assembly, Electron Beam Lithography, dry etching, metalization, as well as characterization experience with 4-terminal measurements, Raman spectroscopy, AFM, SEM and TEM.

Nanomaterials based on graphene are highly important because of their unique properties for example high contact surface area, high electrical conductivity and their enormous stability. Graphene and graphene related materials have been used as promising catalyst supports in energy conversion and storage applications. However, in order to produce more efficient catalyst supports, in our research we successfully modify graphene with various active functional groups for example amine, thiophene, fluorosilane, and RGD peptide mono and multifunctionalization of graphene oxide. Then, these modified graphene has been used as efficient supports for Platinum (Pt) catalyst nanoparticles. The dispersion of Pt deposited on modified graphene has been enhanced and stable optimized dispersions were obtained in organic solvents. The cyclic voltametry (CV) results of Pt on mono functional graphene showed a high electrochemical surface area (ECSA) of 147 m2/g for Pt/GO-RGD compared to Pt/carbon black (Pt/C, 80 m2/gPt) and Pt/GO (99 m2/gPt). The efficiency of multifunctional graphene oxide will also be discussed in details. These modified graphene nanomaterials will be used in proton exchange membrane fuel cell (PEMFC) electrodes and their efficiency will be evaluated in details by means of fuel cell performance.

Here, we describe a novel type of graphene oxide linking layer for highly sensitive biosensing based on surface plasmon resonance (SPR), which has become an indispesible tool for scientific research and drug development [1]. During the last three decades, researchers have used only two technologies of linking layers for SPR biosensors, which are based on self-assembled monolayers of thiol molecules and on hydrogel layers. Using graphene and its derivatives, we developed biosensor chips for existing commercial biosensors, whose sensitivity is higher than for commercial sensor chips available on the market [2] (Fig. 1). Modification of carboxyl groups to N-hydroxysuccinimide esters in the flow cell of SPR biosensor demonstrated that the num-ber of carboxyl groups, which can be used for molecule immobilization, is more than 20 times higher in the graphene oxide linking layer than in the linking layer of commercial hydrogel-based sensor chip. In addition, the graphene oxide sensor chip was demonstrated to be 3 times more sensitive comparing to the commercial hydrogel chips when using in the standard biosensing protocol based on streptavidin-biotin interaction with streptavi-din immobilized on the GO surface via pi-stacking. This will enable us to investigate interactions of protein targets with small ligands and will broaden and accelerate academic and pharmaceutical research.