May 11, 2017
May 3, 2017
Dr. Achim Woessner received his Master degree in Photonics Engineering, Nanophotonics and Biophotonics from Europhotonics coming from the Karlsruhe Institute of Technology (KIT), in Germany, before joining the Quantum Nano Optoelectronics research group led by ICREA Prof. at ICFO Frank Koppens. At ICFO, he centered his doctoral work in studying and understating the fundamental properties and capabilities of graphene plasmonics for the future development of new applications. Dr. Achim Woessner´s thesis, entitled “Exploring Flatland Nano-Optics with Graphene Plasmons” has been supervised by Prof. Dr. Frank Koppens.
Plasmons are charge oscillations coupled to electromagnetic radiation. One of their most intriguing properties is their deep subwavelength confinement resulting in strongly enhanced light-matter interaction. Metal plasmons have received tremendous interest over the last decades and have sparked the development of a range of new fields such as plasmonic nanophotonic components, metamaterials, metasurfaces and more exotic research areas such as quantum plasmonics. One of the main drawbacks of conventional metal plasmonics is that the plasmon lifetime is extremely short when the light is confined to deep subwavelength scales and that their wavelength is not tunable in situ. This is where graphene, a one atom thick semimetal consisting of carbon atoms arranged in a two-dimensional honeycomb lattice, comes into play. In graphene plasmons can be confined to extreme subwavelength scales while still having a long lifetime and their wavelength is tunable in situ. Graphene plasmonics is a relatively new research area but has already attracted a lot of attention. This is undoubtedly due to the fact that graphene plasmons are extremely versatile. They are a unique platform for exploring the limits of light matter interaction, two dimensional transformation optics, biosensing, and mid-infrared integrated optics.
The goal of this thesis is to explore the frontiers of graphene plasmonics both to understand the fundamental properties and limitations as well as to use the gained understanding to develop new concepts towards applications. We will mainly be using graphene encapsulated in hexagonal boron nitride (h-BN). This material has already shown that it is an excellent substrate for graphene as graphene fully encapsulated by h-BN at room temperature shows a mobility limited by the lattice vibrations of the graphene itself. Furthermore, it has very intriguing optical properties as it is a natural hyperbolic material which we will explore in the second part of the thesis. As measurement apparatus for the studies presented here we mainly used scattering-type scanning near-field optical microscopy (s-SNOM) as well as a technique based on s-SNOM we developed called near-field photocurrent nanoscopy. These techniques provide great insight into the working mechanisms of graphene optoelectronics with a nanometer resolution over a broad frequency range from the mid-infrared to the terahertz.
This thesis is split into a general introduction chapter and two main parts with experimental results. In the beginning I will give an introduction to graphene and its opto-electronic properties, graphene devices and their fabrication. I will also introduce h-BN, a dielectric layered material commonly used as substrate for graphene (Chapter 1). Then in the first main part of the thesis I will introduce the background and fundamentals of graphene plasmons (Chapter 2). In the following I will then introduce an experiment where we explore the limitations of the graphene plasmon lifetime at room temperature (Chapter 3). I will then show am optical phase modulator which is capable of tuning the phase in situ from 0 to 2? with a footprint of only 350nm exploiting the unique capability of tuning the graphene plasmon wavelength (Chapter 4). In the second part of the thesis I will give a background on photodetection with graphene (Chapter 5). I will then introduce a new measurement technique called infrared photocurrent nanoscopy (Chapter 6) and show how it can be used to study the optoelectronic properties of a variety of graphene devices in the infrared at the nanoscale (Chapter 7). Then I will show how graphene plasmons can be detected electrically using this technique (Chapter 8). Finally I will introduce a way of detecting phonon polaritons in h-BN electrically using graphene and show how this can be used to greatly enhance the photoresponse of graphene photodetectors in the mid-infrared (Chapter 9).
Prof. Dr. Harald Giessen-University of Stuttgart
Prof. Dr. Javier Garcia de Abajo- ICFO
Prof. Alexey Kuzmenko- University of Ginebra
April 24, 2017
Despite the numberless amount of investigations on graphene performed over the last years, this material still offers a variety of fascinating aspects to explore, in particular in view of its excitations. Combining density-functional theory with many-body perturbation theory provides a powerful framework for this purpose. Based on this methodology, I will address the following questions: Can we “see” orbitals in an electron microscope, and what kinds of images are to be expected? Can we introduce novel spectral features by stacking 2D materials? How are first- and second-order Raman spectra are affected by strain, that may be induced by an underlying substrate? How does graphene as a substrate, in turn, impact the photo-switching behavior of molecules?
Seminar, May 3, 2017, 12:00. Seminar Room
Hosted by Prof. Jens Biegert
April 10, 2017
The physics of graphene, outstanding through its relativistic electron dispersion, can also be studied in ’synthetic’ graphene, built from cold atoms in a honeycomb lattice. In the first part of my talk, I will present a flexible setting in which such synthetic graphene is coupled to a second atomic layer with non-relativistic band structure. Different effects of this proximity will be discussed, ranging from modifications in the free bandstructure to many-body effects, including the semimetal-to-superfluid phase transition and magnetized phases in the Mott insulating regime. In the second part of my talk, I will switch to a system of real graphene in the quantum Hall scenario. In this context, I will discuss the possibility of engineering a synthetic bilayer structure by coupling different Landau levels using light. This strategy not only allows to create bilayer quantum Hall phases, but may also be used for controlling quasiparticle excitations.
Seminar, April 24, 2017, 12:00. Seminar Room
Hosted by Prof. Maciej Lewenstein
March 28, 2017
Since its discovery, different techniques on how to grow high quality graphene over large planar area substrates have been investigated, developed and implemented. Among these techniques, processes like chemical vapor deposition (CVD) and plasma-enhanced CVD (PECVD) use transition metal foils that act as catalysts to favor the dissociation of a hydrocarbon gas. These processes have a major drawback; they require the transfer of graphene from the metal foils onto the desired substrate, in the process leaving organic residues on the substrate, reducing the performance and quality of the device.
In order to avoid contamination due to residue, research has been focused on direct growth on dielectric surfaces, using metal films as catalysts that can retract during growth, leaving the graphene on the dielectric area. Any additional residue would be removed using etching processes.
In a recent study published in 2D Materials, ICFO researchers Miriam Marchena and Josep Canet Ferrer led by ICREA Prof. Valerio Pruneri at ICFO in collaboration with researchers from Corning and Cornell University of New York, report on the use of Copper (Cu) catalytic templates for the growth of graphene onto 2D- and 3D-G structures.
To demonstrate the versatility of their proposed technique, the team of researchers investigated the growth of three graphene structures with different optical, electrical and morphological properties, by properly defining the initial catalytic Cu templates. These graphene structures were: the arrangement of non-aggregated copper nanoparticles (Cu NPs) in different layers to produce the formation of a 3D-G sponge-like (3D-GS) structure; one layer of isolated Cu NPs to produce 3D-graphene nanoballs (3D-GB), and the aggregation of Cu NPs to form larger catalytic structures that produced 2D graphene (2D-G) networks.
The growth of the graphene onto the substrate was performed in three different steps. They first created a Cu pattering by dip-coating Copper-oxide particles on the substrate¬¬ or by thermally evaporating the Cu from a Cu foil; then they grew the graphene by CVD methods and finally they removed any remaining Cu by wet etching, sublimation or both.
In all, the synthesis of the graphene structures for all three scenarios was properly achieved. Even more, a very high optical transmission was maintained while also preserving electrical properties of the material, a very promising feature for applications such as transparent electrodes and interfacial layers.
The results of this study are a major step forward towards the development of new surfaces that could be used for a wide variety of applications, such as antiglare display screens, solar cells, light-emitting diodes, and gas and biological plasmonic sensors, among others.
March 27, 2017
The Phantoms Foundation, in collaboration with ICFO and the Institut Catala de Nanociencia i Nanotecnologia (ICN2) are organizing the 7th edition of the Graphene Conference series, the largest European event in Graphene and 2D materials.
March 20, 2017
Two dimensional (2D) materials are crystalline materials with layered structures, including Graphene, h-BN, and Transition Metal Di-chalcogenides (TMD’s). Each of their layers is consisting of one or a few atomic layers and it forms van der Waals interactions with neighbouring layers. Atomically thin 2D materials range from semi-metallic graphene, semiconducting TMD’s to insulating h-BN. They have been studied intensively due to their extraordinary material properties.
We have been investigated 2D materials in two directions. One is to enhance the performance and the processibility of Si technology for near term applications. Especially, we have focused 2D materials as interface materials due to their atomically thin nature. For example, they are good candidates for diffusion barrier and interface materials between metal and Si to reduce the Schottky barrier heights and contact resistance in source and drain, which is one of the most critical issues for scaling down. We demonstrated a graphene hybrid interconnect for conventional Si semiconducting devices and demonstrated converting the Schottky nature of the M-S junctions into the Ohmic contact with 2D materials.
The other direction is to replace Si with 2D materials for post-Si technology and for functional devices that Si technology cannot cover well. We explored the possibility of 2D materials for photo detector and sub-10 nm graphene nanoribbons (GNRs) for a transistor channel. Also we demonstrated atomic layer deposition (ALD) on Graphene, one of the most fundamental challenges for the successful incorporation of 2D materials in electronic devices using physisorbed-precursor-assisted ALD.
In this talk, we will cover most of the topics listed above.
Seminar, March 27, 2017, 12:00. Seminar Room
Hosted by Prof. Valerio Pruneri
March 17, 2017
2D layered materials are like color papers: they can be glued, stacked, cut and folded to form integrated devices with atomic thickness. In this talk, I will first discuss how different 2D materials can be grown with distinct electrical and optical properties (coloring), how they can be connected laterally to form pattered circuits (stitching) and how their interaction with light can be designed by controlling the interlayer rotation and the valley degree of freedom (twisting). Then I will discuss our recent efforts to turn these 2D “papers” into 3D structures.
Seminar, March 20, 2017, 12:00. ICFO’s Seminar Room
Hosted by Prof. Adrian Bachtold
March 7, 2017
Underscoring the wealth of graphene research and development activity taking place in the Barcelona area, the 7th edition of Graphene Conference will now take place from the 28th until the 31st of March 2017 at the Barcelona International Convention Center (CCIB). This is the world’s largest graphene conference, bringing together both scientists and industry to work towards integrating new graphene technologies into current applications. Mr. Francesc Subirada, General Director for Research of the Catalan Ministry of Business and Knowledge, will participate in the event Opening.
During this 4 day-long conference, around 1000 attendees will have the opportunity to listen to approximately 100 prestigious keynote and invited talks, more than 150 oral and around 400 posters presentations. The event will also create many networking opportunities for future collaborations. The top class speakers will include Prof. Albert Fert, awarded the Nobel Prize in Physics 2007 for the discovery of giant magnetoresistance, and Prof. Andre Geim, awarded the Nobel Prize in Physics in 2010 for his ground-breaking experiments regarding the two-dimensional material graphene.
The general conference includes two parallel events focused on industry and knowledge transfer. Attendees will have the opportunity to visit the exhibition area and interact with both local and international participants, including booths where companies and research institutes like ICN2 and ICFO will be presenting their graphene-based technologies. Among the exhibitors, visitors will find Pavilions devoted to initiatives from as far away as Canada, Malaysia and China participating in this conference with a global impact.
ICFO- the Institute of Photonic Sciences and ICN2- the Catalan Institute of Nanoscience and Nanotechnology, both scientific organizers of the Conference are research centers, founding members of BIST- the Barcelona Institute of Science and Technology, world renowned for their expertise in graphene and 2D materials research and graphene related technologies. In addition, the event organizing committee includes experts from UCL – Université Catholique de Louvain and IIT – Italian Institute of Technology. The event main organizer, Phantoms Foundation, began organizing these series of events in 2011 and since then has brought together more than 3500 participants from over 60 countries.
March 3, 2017
Optical sensing in the short-wave and mid- infrared is of paramount importance for a vast number of applications including surveillance, night vision, product, process and environmental monitoring and spectroscopy.
Yet existing technologies, particu…
February 27, 2017
Organized by the Graphene Flagship, curated by ICFO, and supported by GSMA, the Graphene Experience Zone at the Mobile World Congress 2017 (MWC17), the largest Mobile Industry event, demonstrated that graphene research is indeed headed in the right direction with cutting-edge graphene based technological applications moving closer to market.
Now in its second year appearing at the MWC, this year’s Graphene Zone was divided into five large technological areas: IoT and sensors, Wearables and Health, Energy, Datacoms and Composites. During four days of non-stop activity, 26 institutes and companies showcased 20 technologies, demos and applications to a continuous stream of visitors, press and companies interested in seeing graphene at work in operational prototypes.
The exhibiting technologies ranged from IR sensors for car collision avoidance systems, wearable wellness sensing devices, flexible displays, force sensors, and super capacitors to an artificial arm, a retina- optical nerve implant, strain sensors for insoles, conductive inks and instant heating systems for extreme weather conditions, among others.
In parallel to the exhibits, two other main activities took place within this massive Mobile Industry encounter. On March 2nd, there was the workshop ‘Graphene Connect: From Datacom to IoT, Enabled by Graphene’, which opened with an address by Nobel Laureate Prof. Konstantin Novoselov. The workshop aimed to bring together academic and industry representatives with an interest in all things mobile, offering networking opportunities to facilitate possible future collaborations. Secondly, ICFO partnered with IIT, Novalia and University of Cambridge, all members of the Graphene Flagship, to create and coordinate the activity “Graphopolis”, an event that took place during the Youth Mobile Festival (YoMo) that same week. Aimed at raising awareness in young generations about the potential of graphene and its applications, this activity encouraged participants to create their own futuristic city by thinking, exploring and creating graphene-based technologies that could improve quality of urban life.
After witnessing the enthusiastic reaction of visitors to the stand, exhibitors of the Graphene Experience Zone agree that we are on the right track, moving forward into a phase of industrialization in which graphene is finally advancing from the research lab to the manufacturing plants.
February 27, 2017
Electronic and optical processes in nanoscale devices produce large concentration of heat, which can limit their performance and cause structural damage. Heat management at this scale is thus one of the main burdens in the design of nanodevices, which is typically dealt with by using conventional thermal conductivity to cool the involved material. This however is a relatively slow and harmful procedure.
In a paper entitled “Ultrafast radiative heat transfer”, published today in Nature Communications, Renwen Yu, Alejandro Manjavacas and ICREA Professor at ICFO Javier García de Abajo, leader of the Nanophotonics Theory Group, use the extraordinary optical and thermal properties of graphene to show that radiative heat transfer is a cleaner process that does not involve undesired inelastic excitations of the materials. Likewise, it occurs at a much faster pace than heating of the atomic lattice.
The extreme concentration of electromagnetic energy associated with graphene plasmons -the collective electron excitations of this material- combined with its record-low electronic heat capacity -a property arising from the unique electronic structure of graphene- allow researchers to show that more than 50% of the electronic heat accumulated by a graphene island can be transferred within a few hundred femtoseconds to a cooler neighboring island. This unexpected finding leads to an unprecedented situation, as all previous experimental and theoretical radiative heat transfer studies have claimed that radiative transfer occurs at a rate that is orders of magnitude lower than heat diffusion through the atomic lattice. Apart from its interest from a fundamental viewpoint, this discovery shows that radiative heat transfer using graphene and other atomically thin materials is bound to profoundly transform the way nanoscale devices are designed.
Graphene is back at Mobile World Congress (MWC) 2017 with the Graphene Experience Zone. Designed to showcase graphene mobile innovation in an interactive way, the Graphene Experience Zone will bring graphene to life. A wide range of demonstrations and …