High-quality cvd graphene for spintronic applications

• Autores: Zewdu Gebeyehu
• Directores de la Tesis: María José Esplandiu Egido (dir. tes.), Sergio Valenzuela (dir. tes.), Marius. V Costache (codir. tes.)
• Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2019
• Idioma: español
• Tribunal Calificador de la Tesis: Enric Bertran Serra (presid.), Philippe Godignon (secret.), Monica F. Craciun (voc.)
• Programa de doctorado: Programa de Doctorado en Química por la Universidad Autónoma de Barcelona
• Materias:
  • Química
• Enlaces
  • Tesis en acceso abierto en: TESEO
• Resumen

  • This thesis has focused on tuning the synthesis and processing of graphene to achieve optimized spintronic applications. Thus the thesis is framed in two cut-edging topics: the graphene world with its richness of unique properties and the field of spintronics which explores the spin degree of freedom of the electrons for novel applications in information and communication technology (e.g. information storage and logic devices). Under this context graphene is a very promising spin channel material to transport spin with long spin diffusion lengths. To accomplish that, a high quality-graphene with minimum electron scattering centers is a key parameter and must be ensured from the moment of its production and during its processing. Accordingly, in this thesis, a lot of efforts have been invested to fine-tune the growth parameters of graphene by chemical vapor deposition (CVD). Several relevant contributions in the field have been achieved: • THE DEMONSTRATION of the importance of the graphene etching backreaction during growth which begins to dominate at long growth times due to an in-situ increase of hydrogen concentration. That is a phenomenon that has been previously ignored but very important to consider since it impacts on the graphene domain reshaping. A thorough characterization of the graphene domain shape evolution has been accomplished by tuning the growth time, the flow of gas precursors and the catalyst confinement which allows better identifying the onset of the etching process. Controlling this effect is very relevant to minimize structural defects induced by etching which can impact the electron/spin transport.

    • THE INTRODUCTION of a novel pretreatment of the copper catalyst to reduce nucleation sites for graphene growth. The suppression of nucleation sites is very important to promote a more single-crystalline growth of graphene and thus minimize electron scattering at the domain boundaries of the graphene crystal grains. The procedure is based on a photocatalyst-assisted thermal annealing process that efficiently removes carbonaceous contaminants which are active sites for graphene nucleation.

    • THE DEMONESTRATION of record-long propagation of spins over 30 micrometers at the graphene channel. Such output was achieved using high-quality CVD graphene grown on platinum foil and a newly developed device fabrication technique which minimizes contamination/structural defects during graphene processing. The spin lifetimes and relaxation lengths were the highest values reported at room temperature in CVD grown graphene on a standard substrate, SiO2/Si.