Hong Ying Mao

Graphene: Promises, Facts, Opportunities, and Challenges in Nanomedicine

Nanomedicine Hong Ying Mao,† Sophie Laurent,‡ Wei Chen,*,†,§ Omid Akhavan, Mohammad Imani, Ali Akbar Ashkarran, and Morteza Mahmoudi* †Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore ‡Department of General, Organic, and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, Avenue Maistriau, 19, B-7000 Mons, Belgium Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore Department of Physics, Sharif University of Technology, P.O. Box 11155-9161, Tehran, Iran Institute for Nanoscience and Nanotechnology, Sharif University of Technology, P.O. Box 14588-89694, Tehran, Iran Novel Drug Delivery Systems Department, Iran Polymer and Petrochemical Institute, Tehran, Iran Department of Physics, Faculty of Basic Sciences, University of Mazandaran, Babolsar, Iran Nanotechnology Research Center, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran Department of Nanotechnology, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran

Surface transfer hole doping of epitaxial graphene using MoO3 thin film

Synchrotron-based in situ photoelectron spectroscopy investigations demonstrate effective surface transfer p-type doping of epitaxial graphene (EG) thermally grown on 4H–SiC(0001) via the deposition of MoO3 thin film on top. The large work function difference between EG and MoO3 facilitates electron transfer from EG to the MoO3 thin film. This leads to hole accumulation in the EG layer with an areal hole density of about 1.0×1013 cm−2, and places the Fermi level 0.38 eV below the graphene Dirac point.

Room temperature ferromagnetism in partially hydrogenated epitaxial graphene

We report room temperature ferromagnetism in partially hydrogenated epitaxial graphene grown on 4HSiC(0001). The presence of ferromagnetism was confirmed by superconducting quantum interference devices measurements. Synchrotron-based near-edge x-ray absorption fine structure and high resolution electron energy loss spectroscopy measurements have been used to investigate the hydrogenation mechanism on the epitaxial graphene and the origin of room temperature ferromagnetism. The partial hydrogenation induces the formation of unpaired electrons in graphene, which together with the remnant delocalized π bonding network, can explain the observed ferromagnetism in partially hydrogenated epitaxial graphene.

Hard corona composition and cellular toxicities of the graphene sheets

Graphene nanomaterials are recognized as one of the most promising nanomaterials because of their unique and highly attractive physicochemical properties (e.g., thermal conductivity, superlative mechanical strength, and ultrahigh surface-to-volume ratios). It is well established that when nanomaterials interact with biological medium, biomolecules and in particular proteins attach to their surfaces, which form a complex between surface of nanoparticles and proteins called corona. Thus, the interaction of the biological system with the nanomaterials depends on the composition of the protein layer, rather than the surface characteristics of the nanomaterials itself. Although there is a significant increase of interest in the application of graphene in medical science, there has been a little attention to the nanotoxicological aspects of these newly developed materials. For this reason, we aimed to investigate whether the effect of the interactions between graphene-sheets with various human plasma concentrations (i.e. both in vitro (cells/tissues) and in vivo simulating states) is toxic. The results showed that by increasing the human plasma concentration, the affinity of proteins with low molecular weights to graphene-sheets surface is significantly increased. Fluorescence microscopy of Hela and Panc-1 cell lines showed a reduction of nuclei number and an increase of reactive oxygen species (ROS) production respectively after a longer incubation of graphene-sheets with plasma proteins. ROS production was higher in Panc-1 cell line, when used as protein source for graphene-sheets than HeLa cell line.

Low temperature critical growth of high quality nitrogen doped graphene on dielectrics by plasma-enhanced chemical vapor deposition.

Nitrogen doping is one of the most promising routes to modulate the electronic characteristic of graphene. Plasma-enhanced chemical vapor deposition (PECVD) enables low-temperature graphene growth. However, PECVD growth of nitrogen doped graphene (NG) usually requires metal-catalysts, and to the best of our knowledge, only amorphous carbon-nitrogen films have been produced on dielectric surfaces by metal-free PECVD. Here, a critical factor for metal-free PECVD growth of NG is reported, which allows high quality NG crystals to be grown directly on dielectrics like SiO2/Si, Al2O3, h-BN, mica at 435 °C without a catalyst. Thus, the processes needed for loading the samples on dielectrics and n-type doping are realized in a simple PECVD, which would be of significance for future graphene electronics due to its compatibility with the current microelectronic processes.

Chemical vapor deposition graphene as structural template to control interfacial molecular orientation of chloroaluminium phthalocyanine

Chemical vapor deposition (CVD) graphene has been used as an effective structural template to manipulate molecular orientation of organic thin film of chloroaluminium phthalocyanine (ClAlPc) on indium tin oxide (ITO) electrode. As revealed by in-situ near-edge x-ray adsorption fine structure measurement, ClAlPc molecules on the CVD graphene modified ITO electrode adopt a well-aligned lying-down configuration with their molecular π-plane nearly parallel to the electrode surface, in contrast to the random orientation of ClAlPc molecules on the bare ITO electrode. This lying-down configuration results in an optimized stacking of the molecular π-plane perpendicular to the electrode surface and hence facilitates efficient charge transport along this direction.

Large-Size Linear and Star-Shaped Dihydropyrazine Fused Pyrazinacenes

Linear and star-shaped pyrazinacenes 1a-b and 2 were synthesized via condensation between a new building block 11 and pyrene tetraones or cyclohexaone. Compound 2 represents the largest star-shaped dihydropyrazine fused pyrazinacene reported so far. These largely expanded pyrazinacenes show good solubility and have a strong tendency to aggregate in both solution and thin films, indicating their potential applications for organic electronic devices.

Electrical measurement of non-destructively p-type doped graphene using molybdenum trioxide

We demonstrate effective non-destructive p-type doping of graphene via surface modification with molybdenum trioxide (MoO3) thin film using electrical transport measurements. The p-type doping via MoO3 modification of graphene leads to the downward shift of Fermi level towards the valence band. MoO3 modified graphene retains its high charge carrier mobility, facilitating the observation of quantum Hall effect. In-situ ultraviolet photoelectron spectroscopy studies also show that air exposure of MoO3 modified graphene reduces the doping efficiency.

CVD graphene as interfacial layer to engineer the organic donor-acceptor heterojunction interface properties.

We demonstrate the use of chemical-vapor-deposited (CVD) graphene as an effective indium-tin-oxide (ITO) electrode surface modifier to engineer the organic donor-acceptor heterojunction interface properties in an inverted organic solar cell device configuration. As revealed by in situ near-edge X-ray adsorption fine structure measurement, the organic donor-acceptor heterojunction, comprising copper-hexadecafluoro-phthalocyanine (F16CuPc) and copper phthalocyanine (CuPc), undergoes an obvious orientation transition from a standing configuration (molecular π-plane nearly perpendicular to the substrate surface) on the bare ITO electrode to a less standing configuration with the molecular π-plane stacking adopting a large projection along the direction perpendicular to the electrode surface on the CVD graphene-modified ITO electrode. Such templated less-standing configuration of the organic heterojunction could significantly enhance the efficiency of charge transport along the direction perpendicular to the electrode surface in the planar heterojunction-based devices. Compared with the typical standing organic-organic heterojunction on the bare ITO electrode, our in situ ultraviolet photoelectron spectroscopy experiments reveal that the heterojunction on the CVD graphene modified ITO electrode possesses better aligned energy levels with respective electrodes, hence facilitating effective charge collection.

Molecular-scale investigation of C60/p-sexiphenyl organic heterojunction interface.

In situ low-temperature scanning tunneling microscopy (LT-STM) and ultraviolet photoelectron spectroscopy (UPS) experiments have been carried out to investigate the interface properties at the C(60)∕p-sexiphenyl (6P) organic-organic heterojunction interface, including the interfacial energy level alignment and the supramolecular packing structures. As revealed by UPS measurements, the vacuum level is almost aligned at the C(60)∕6P interface, suggesting that the interface is dominated by weak intermolecular interactions, such as van der Waals and π-π interactions. In situ LT-STM experiments also indicate the formation of a molecularly sharp C(60)∕6P interface with hexagonally-close-packed C(60) layers nucleated atop 6P layer on graphite.