Shuping Pang

Graphene as Transparent Electrode Material for Organic Electronics

Graphene, a two-dimensional atomically thick carbon atom arranged in a honeycomb lattice, was recently isolated by repeatedly peeling highly oriented pyrolytic graphite (HOPG) using sticky tape. [ 1 ] Since then, outstanding physical properties predicted and measured for graphene have been explored for practical applications such as fi eld-effect transistors, [ 1–4 ] chemical sensors [ 5–7 ] and composite reinforcement. [ 8–10 ] Monolayer graphene possesses high crystallographic quality and ballistic electron transport on the micrometer scale with only 2.3% of light absorption. [ 11 , 12 ] Moreover, the combination of its high chemical and thermal stability, [ 13 , 14 ] high stretchability, [ 15–17 ]

Layer-by-Layer Assembly and UV Photoreduction of Graphene–Polyoxometalate Composite Films for Electronics

Graphene oxide (GO) nanosheets and polyoxometalate clusters, H(3)PW(12)O(40) (PW), were co-assembled into multilayer films via electrostatic layer-by-layer assembly. Under UV irradiation, a photoreduction reaction took place in the films which converted GO to reduced GO (rGO) due to the photocatalytic activity of PW clusters. By this means, uniform and large-area composite films based on rGO were fabricated with precisely controlled thickness on various substrates such as quartz, silicon, and plastic supports. We further fabricated field effect transistors based on the composite films, which exhibited typical ambipolar features and good transport properties for both holes and electrons. The on/off ratios and the charge carrier mobilities of the transistors depend on the number of deposited layers and can be controlled easily. Furthermore, we used photomasks to produce conductive patterns of rGO domains on the films, which served as efficient microelectrodes for photodetector devices.

Synthesis of direct white-light emitting carbogenic quantum dots

A facile chemical method has been developed to synthesise highly efficient functionalized carbon dots; when illuminated with 407 nm light, both the solution and film emitted white-light directly.

Extrinsic corrugation-assisted mechanical exfoliation of monolayer graphene.

Figure 1 . a) The optical microscopy (OM) image of ≈ 100 nm thick graphite fl akes on silicon substrate after thermal annealing at 350 ° C for 2 h. b) The OM image of the same position after the reverse exfoliation [∗] S. Pang , Dr. H. N. Tsao , Dr. Y. Hernandez , Dr. X. Feng , Prof. K. Mullen Max Planck Institute for Polymer Research Ackermannweg 10, D-55128 Mainz (Germany) E-mail: feng@mpip-mainz.mpg.de; muellen@mpip-mainz.mpg.de J. M. Englert , Prof. A. Hirsch Zentralinstitut fur Neue Materialien und Prozesstechnik Dr.-Mack Str. 81 D-90762 Furth (Germany) Since the reports of the fi rst isolation and observation of the exceptional electronic, mechanical, and chemical properties, single layer graphene has attracted intense interest from both academic and industrial communities. [ 1–3 ] While the mechanical exfoliation method led to many exciting discoveries, several promising approaches have been reported for the preparation of monolayer graphene including solution exfoliation of graphite, [ 4 , 5 ] epitaxial growth from SiC, [ 6 , 7 ] reduction of graphene oxide, [ 8–10 ] and chemical vapor deposition (CVD) on metal surfaces. [ 11–13 ] Up to now, the CVD growth method seems to be the most promising technique for the production of large-scale few layer graphene fi lms. [ 13 , 14 ] However, this surface-mediated process requires very high temperatures, and tedious additional steps involving etching and transfer, thus rendering the production of graphene-based electronic devices diffi cult. Ultra-large monolayer graphene [ 15–17 ] and patterned graphene structures [ 18–22 ] constitute two important aspects for graphene fabrication technology. A simple way to directly “print” a high-quality graphene monolayer on insulating substrates from a graphite stamp would be particularly appealing for electronic applications. Covalent immobilization [ 23 , 24 ] and electrostatic forces [ 18 , 25 ] have been devised for the modifi cation of mechanical exfoliation, with the aim to improve the yield of monolayer graphene or to achieve patterned graphene structures. Despite the success in deposition of graphene patterns over a large area, these procedures suffer from a low monolayer yield ( < 10%). [ 18 , 19 , 26 ] Here, we describe an extrinsic corrugationassisted mechanical exfoliation (ECAME) for synthesizing monolayer graphene on substrates. This strategy involves a simple thermal treatment of deposited graphite on a silicon wafer in association with a wafer processing tape peeling process. This work reveals that underlayer graphene sheets can corrugate following the rough SiO 2 surface when the thick graphite fl ake is thermally annealed. Such a surface-mediated extrinsic corrugation process thus serves as the key driving force for exfoliation leading to more than 60% high-quality monolayer graphene. This protocol can be further employed to fabricate graphene patterns on the surface, a technique that may be explored for graphene-based electronic device fabrication.

Coplanar Asymmetrical Reduced Graphene Oxide–Titanium Electrodes for Polymer Photodetectors

Narrow gaps and a built-in potential originating from the different work functions of reduced graphene oxide (RGO) and titanium electrodes are used to explain the improved photosensitivity of the poly(3-hexylthiophene) photodetectors with asymmetrical RGO-Ti electrodes presented here compared to those based on symmetrical electrodes. Easy processing, high photosensitivity, high on/off ratio, and low energy consumption contribute to the promising potential of coplanar asymmetrical electrodes in the field of photoelectric devices.

Graphene and Its Synthesis

Since the isolation and identification of graphene it has become clear that in order to exploit its outstanding physical properties, high-quality samples must be produced in a reproducible and scalable way. In this chapter, we discuss a number of paths undertaken by several groups around the world to produce high-yield graphene in liquid phase by both exfoliation, and subsequent reduction, of graphite oxide and by direct exfoliation of graphite in liquid phase. Furthermore, the synthesis of nanographenes in solution and on the surface is discussed as the chemist approach to produce atomically tailored graphene from polyphenelyne precursors.