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Development of a multi-steps CVD process to produce bi-layers graphene for anode of Organic Light Emitting Diodes

Trinsoutrot, Pierre and Brignone, Mauro and Vergnes, Hugues and Caussat, Brigitte and Pullini, Daniele Development of a multi-steps CVD process to produce bi-layers graphene for anode of Organic Light Emitting Diodes. (2014) In: Graphene 2014, 6 May 2014 - 9 May 2014 (Toulouse, France). (Unpublished)

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Abstract

Graphene is one of the most interesting candidates for the next generation of transparent conductive electrodes (TCEs) for electrical devices, because of its unique electronic structure. Furthermore, the optical transparency of graphene films surpasses that of conventional TCEs such as indium tin oxide (ITO) [1]. However, graphene anode for Organic Light Emitting Diodes (OLEDs) still presents several problems owing to its low work function and high sheet resistance [1], which may be related to a poor control of graphene quality. Chemical vapor deposition (CVD) on copper from methane seems to be the most efficient approach to form high quality transferable graphene for opto-electronic applications, due to the potential for commercially viable production at large scale. However, CVD processes need to be optimized for obtaining selective single or bilayers growth, as well as highly crystalline, full coverage, large area domains [2]. Indeed, CVD graphene films are typically composed of relatively small polycrystalline flakes. A high density of grain boundaries degrades the properties of graphene [2]. Thus, it is desirable to prepare large single-crystal graphene to minimize the impact of defects existing at grain boundaries. The most recent studies of the literature show that this objective can be met by using very low concentration of methane (<100 ppm), but in these conditions, it is difficult to obtain a full coverage of the substrate [3]. The most efficient way to obtain a continuous high quality monolayer of graphene seems to use a multi-steps process, first involving a very low methane concentration in order to form strictly monolayer graphene flakes with low nucleation density. Then, methane concentration is progressively increased, to counterbalance the decrease of the active catalytic copper surface [3]. In the present study, a two-step process then a three-steps one have been developed only differing by the third step, in order to produce graphene for OLED application. Methane diluted into hydrogen and argon was used on copper foils (25 mm thick, 99,999% Alfa Aesar) of 2x2 cm2. The operating temperature was fixed at 1,000°C and the total pressure was of 700 Torr. The hydrogen on methane inlet molar ratio was fixed to 800 for steps 1 and 2. The CH4 concentration was of 10 ppm for step 1 and 40 ppm for step 2, and their duration was of 60 min for each one. For step 3, only 5 min long, the CH4 concentration was of 9,000 ppm and the H2/CH4 ratio of 10. Optical microscope and Raman spectroscopy measurements (confocal Raman microscope Labram – Horiba Yvon Jobin) were carried out to investigate the quality and extend of graphene sheets.

Item Type:Conference or Workshop Item (Poster)
Audience (conference):International conference without published proceedings
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - INPT (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UPS (FRANCE)
Other partners > Centro Ricerche FIAT - CRF (ITALY)
Laboratory name:
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Deposited By: Brigitte CAUSSAT-BONNANS
Deposited On:15 May 2014 13:52

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