Croissance et transfert de graphene pour la fabrication d'electrodes transparentes

This master's thesis focuses on the characterization and optimization of transparent and conductive electrodes made from graphene layers. We used a low pressure CVD method, with methane as the carbon source and copper as a catalyst and growth support, to synthesize graphene. Scanning electron microscopy and Raman spectroscopy were used to demonstrate that the graphene layers are complete and uniform.;A method using a polymer (PMMA) as a mechanical support has been optimized for the transfer of graphene films onto various substrates, such as glass or silicon dioxide on silicon. Characterization of transferred samples by optical and scanning electron microscopy and Raman spectroscopy reveals that transferred films are undamaged and that the surface is free of visible residues. The intensity of the defect-related peak in Raman mapping measurements is low, indicating that the as-grown and transferred graphene layers are of high quality.;This transfer process has been applied to fabricate transparent electrodes with one to four layers of graphene. The electrodes were characterized by Raman spectroscopy, optical transmission analyses and electrical resistance measurements using the van der Pauw method. Raman results indicate that the average doping level of the samples decreases with an increasing number of graphene layers. The optical measurements yield transparency values ranging from 97.5 to 90 % for wavelengths between 400 and 1000 nm, depending on the number of stacked layers. The sheet resistance of the electrodes varies between 560 and 360 Ω/□, which is an equivalent or superior performance to that of graphene electrodes reported in the literature.;An electrochemical method was used to dope the samples in an ionic liquid to vary the Fermi level and to decrease the sheet resistance down to 260 Ω/□ for a monolayer graphene electrode. This doping allows to vary the work function of graphene between 3.9 and 5.6 eV. Taken together, these results demonstrate that graphene appears as an ideal material to be used as transparent electrode given its excellent optical and electrical properties as well as the ability to easily modify its work function and thus minimize the contact resistance with various semiconductor materials.