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Graphene Coated Nanoparticles and Nanograins

Periodic Reporting for period 2 - GRANN (Graphene Coated Nanoparticles and Nanograins)

Reporting period: 2017-01-01 to 2018-06-30

Under GRANN we aim to bring our knowledge and expertise with graphene synthesis, graphene coatings and control of graphenes’ electronic properties on macroscopic samples into the realm of nanoparticles and nano-grains. We aim to exploit the remarkable properties of graphene by designing and synthesizing a new family of high quality monolayer graphene coated metal nanoparticles and by chemically functionalizing these graphene coated nanoparticles to tune their chemical and electronic properties. Furthermore, we aim to synthesize graphene coated SiC nano-grains and amorphous carbon nanoparticles - model systems for interstellar dust grains – and explore their catalytic activity in key interstellar reactions under a range of interstellar conditions.

This will allow us to address a series of questions of both fundamental scientific nature and of relevance to industrial applications. Specific questions that we will address include: Can we protect metallic nanoparticles from oxidation and/or sintering, while retaining their optical and/or catalytic properties? If not – how are these properties changed by the graphene coating. How does chemical reactivity of graphene layers change with size and curvature and what is the effect of a metal core on the reactivity of the outer graphene shell? What are the catalytic properties of graphene coated SiC nano-grains under interstellar conditions? What happens to the plasmonic properties of nanoparticles when they become graphene coated and can we tune these properties by chemical functionalization? What are the chemical, optical and plasmonic properties of graphene nano-shells? Are graphene coated nanoparticles, nanograins and nano-shells photocatalyticaly active?

The output of this high-risk, high gain research project could potentially be a family of chemically stable, graphene coated nano-particles with tunable optical, electronic and possibly even chemical properties, which could find use in a wide range of applications, including industrial catalysis, as components in solar cells and possibly even in conductive inks. The intellectual legacy of the project will be i) an increased atomic-scale understanding of the basic chemical and physical properties of graphene nano-structures, which will guide future research in graphene nano-science; ii) insight into the role played by carbon-coated interstellar dust-grains in interstellar catalysis and into finite size effects for surface reactions in low temperature and low pressure regimes, thereby resulting in improved understanding of the development of interstellar chemical complexity; iii) new methods to control electronic and chemical properties of graphene coated nanoparticles of use both in basic research and for application, and finally, iv) the necessary knowledge to gauge the applicability of graphene coated nanoparticles in industrial applications, thus feeding directly into the R&D knowledge base of European industry via ongoing and future industrial collaborations.
We have investigated chemical vapour deposition and molecular beam epitaxy synthesis routes to graphene formation on Pt and Ag nanoparticles of varying sizes and shapes and deposited on varying substrates.

We have developed new methods to control the electronic properties of graphene by: 1) Controlling the symmetry of the chemical functionalization structures of graphene on metal substrates allowing for band gap engineering. For more detail see J. H. Jørgensen, A. G. Čabo, R. Balog, L. Kyhl, M. N. Groves, A. Cassidy, A. Bruix, M. Bianchi, M. Dendzik, M. A. Arman, L. Lammich, J. I. Pascual, J. Knudsen, B. Hammer, P. Hofmann, and L. Hornekær, Symmetry Driven Band Gap Engineering in Hydrogen Functionalized Graphene, ACS Nano 10, 10798 (2016). 2) Growing ordered arrays of graphene nanodots in a BCN alloy matrix. The periodicity of the graphene nanodots can be tuned by altering the synthesis conditions. For more detail see L. Camilli, J. H. Jorgensen, J. Tersoff, A. C. Stoot, R. Balog, A. Cassidy, J. T. Sadowski, T. Jerzy, P. Boggild, and L. Hornekær, Self-assembly of ordered graphene nanodot arrays. Nat. Comm. 8, 47 (2017).

We have developed a novel method to produce highly vibrationally excited molecular hydrogen and have demonstrated the catalytic activity of graphene coated metal substrates towards dissociative adsoprtion of these molecules. For more detail see L. Kyhl, R. Bisson, R. Balog, M. N. Groves, E. L. Kolsbjerg, A. M. Cassidy, J. H. Jørgensen, S. Halkjær, J. A. Miwa, A. G. Čabo, T. Angot, P. Hofmann, M. A. Arman, S. Urpelainen, P. Lacovig, L. Bignardi, H. Bluhm, J. Knudsen, B. Hammer, and L. Hornekaer, Exciting H2 Molecules for Graphene Functionalization, ACS Nano 12, 513 (2018).

We have demonstrated a novel way to increase graphene coating performance by chemically functionalizing graphene with hydrogen to achieve a stronger graphene-metal bond. The increased binding between graphene and the metal results in prevention of intercalation of reactive species at the graphene-metal interface. Specifically, using the model system of graphene on Ir, we have demonstrated that the coating protects against intecalation of CO at at least 10 times higher pressures and 70 times higher fluences than un-functionalized graphene coatings. A manuscript detailing these results is presently under review.

We plan to translate these finding to improve coating properties and control of electronic and plasmonic properties of graphene coated nanoparticles.
We have demonstrated a novel way to increase graphene coating performance by chemically functionalizing graphene with hydrogen to achieve a stronger graphene-metal bond. The increased binding between graphene and the metal results in prevention of intercalation of reactive species at the graphene-metal interface.

We have developed new methods to control the electronic properties of graphene by Controlling the symmetry of the chemical functionalization structures of graphene on metal substrates allowing for band gap engineering.

We have developed a novel method to produce highly vibrationally excited molecular hydrogen and have demonstrated that the catalytic activity of graphene covered metal substrates allows for their functionalization by these molecules.

The deposition of nanoparticles on non-metallic substrates such as semiconductors is important for possible technological applications. During the characterization of metallic nanoparticles on a GaN substrate, one has to take into account the Schottky barrier effects taking place at the interface between a semiconductor and a metal, which makes the STM characterization more difficult. We have reduced these undesired effects by adding an interface layer below the nanoparticles. Thus, the STM characterization of large Pt nanoparticles on GaN has been achieved.

The output of this high-risk, high gain research project could potentially be a family of chemically stable, graphene coated nano-particles with tunable optical, electronic and possibly even chemical properties, which could find use in a wide range of applications, including industrial catalysis, as components in solar cells and possibly even in conductive inks. The intellectual legacy of the project will be i) an increased atomic-scale understanding of the basic chemical and physical properties of graphene nano-structures, which will guide future research in graphene nano-science; ii) insight into the role played by carbon-coated interstellar dust-grains in interstellar catalysis and into finite size effects for surface reactions in low temperature and low pressure regimes, thereby resulting in improved understanding of the development of interstellar chemical complexity; iii) new methods to control electronic and chemical properties of graphene coated nanoparticles of use both in basic research and for application, and finally, iv) the necessary knowledge to gauge the applicability of graphene coated nanoparticles in industrial applications, thus feeding directly into the R&D knowledge base of European industry via ongoing and future industrial collaborations.
Scanning Tunneling Microscopy Image of Hydrogen Functionalized Graphene
STM images and XPS spectra of amorphous and crystalline Pt Nanoparticles on Au.