Graphene has shown extraordinary electronic and mechanical properties that can
be applied in a wide variety of devices and technological fields. Exploring and controlling
the different methods to obtain graphene is a crucial step for the successful
implementation of this material. Epitaxial growth of graphene on metal surfaces by
CVD processes has proven to be a reliable method to obtain graphene layers with
good quality and, most importantly, scalable for industrial processes. In this thesis
we study using Scanning Tunnel Microscopy at RT and at high temperature the
Chemical Vapor Deposition (CVD) reaction that takes place in the Ni(111).
We develop a method to grow graphene nanoislands on Ni(111) by tuning the parameters
involved in the CVD reaction such as the crystal temperature, propene dose
and reaction time. The method consist in dosing the propene at RT and heat the
sample once the dosing process is complete during a controlled time. The temperature
turns out to be the most determinant parameter. Heating the sample below 400
ºC results in the formation of Ni2C, a surface carbide that inhibits the formation of
graphene at the surface. Heating the sample above 400 ºC results in the formation
of graphene nanoislands with irregular shape. Above 500 ºC the number of islands
diminishes strongly due to gas desorption. To obtain graphene nanoislands in a reproducible
manner a minimum dose of 1 L is required, and the coverage of graphene
increase with the total dose offered to the surface until it reaches the saturation value
at 5 L. The heating time also has an effect in the formation of graphene nanoislands
and is found to be optimum for 5 min. A post-reaction thermal treatment can lead
to a shape transformaiton of the islands. Annealing at 500 ºC during 20 min forms
triangular graphene nanoislands, while annealing the sample at 650 ºC for 10 min
leads to hexagonal islands.
The structure of the islands is systematically studied paying special attention to
the stacking configuration and island edges. Most islands exhibit a 1x1 stacking, although
some islands with rotational Moiré patterns were observed. Islands obtained
after the thermal treatment have straight edges, which have a crystallographic orientation
characteristic of zigzag edges. On the Ni(111) the zigzag hollow (zzh) edges
are stable at RT but zigzag top (zzt) edges present a pentagon-heptagon reconstruction
named zzt(57). Triangular nanoislands exhibit zzh edges with a predominant
top-fcc stacking. The interaction between the substrate and the zzh edges is strong
enough to produce stacking changes in some small triangular nanoislands and islands
with top-hcp are occasionally observed. Hexagonal nanoislands have zzh and
zzt(57) edges alternated.
| Identifer | oai:union.ndltd.org:TDX_UAB/oai:www.tdx.cat:10803/116323 |
| Date | 22 April 2013 |
| Creators | Ollé Soronellas, Marc |
| Contributors | Ceballos, Gustavo, Gambardella, Pietro, Universitat Autònoma de Barcelona. Departament de Física |
| Publisher | Universitat Autònoma de Barcelona |
| Source Sets | Universitat Autònoma de Barcelona |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | 135 p., application/pdf |
| Source | TDX (Tesis Doctorals en Xarxa) |
| Rights | info:eu-repo/semantics/openAccess, ADVERTIMENT. L'accés als continguts d'aquesta tesi doctoral i la seva utilització ha de respectar els drets de la persona autora. Pot ser utilitzada per a consulta o estudi personal, així com en activitats o materials d'investigació i docència en els termes establerts a l'art. 32 del Text Refós de la Llei de Propietat Intel·lectual (RDL 1/1996). Per altres utilitzacions es requereix l'autorització prèvia i expressa de la persona autora. En qualsevol cas, en la utilització dels seus continguts caldrà indicar de forma clara el nom i cognoms de la persona autora i el títol de la tesi doctoral. No s'autoritza la seva reproducció o altres formes d'explotació efectuades amb finalitats de lucre ni la seva comunicació pública des d'un lloc aliè al servei TDX. Tampoc s'autoritza la presentació del seu contingut en una finestra o marc aliè a TDX (framing). Aquesta reserva de drets afecta tant als continguts de la tesi com als seus resums i índexs. |
Page generated in 0.0019 seconds