The application of graphene for large-area electronics requires controllable growth of single crystalline quasi-freestanding graphene films. Controllable growth of graphene films on gold foils at various temperatures using molecular beam epitaxy is shown. Film quality and electrical characteristics probed using Hall measurement, Raman spectroscopy, and Rutherford backscattering spectrometry are shown to improve at lower temperature possibly peaking at ~825˚C. Further experiments are required to assess a stronger correlation between growth parameters and film characteristics. In particular, varying carbon flux and increasing the number of growths are discussed.
Table of Contents
I. Introduction
II. Theory
A. Graphene
i. Properties
ii. Graphene Growth and Kinetics
B. Characterization
i. Surface Topology Analysis using Atomic Force Microscopy (AFM)
ii. Vibrational Energy States Using Raman Spectroscopy
iii. Chemical Composition using Rutherford Backscattering Spectrometry
iv. Electrical Carrier Concentration and Mobility using Hall Measurement
III. Experimental Methods
A. Growth Process
B. Transfer Process
C. Electrical Characterization
D. Material Characterization
IV. Results
V. Discussion
A. Explanation of AFM Images
B. Explanation of Raman Spectra
C. Explanation of Rutherford Backscattering Spectra
D. Explanation of Hall Measurements
E. Growth Parameters vs. Film Characteristic Trends
VI. Conclusion
VII. References
VIII. Appendix
Research Objectives and Themes
This work investigates the physical vapor deposition (molecular beam epitaxy) of elemental carbon on polycrystalline gold foils to achieve controllable, high-quality graphene growth. The study aims to explore the correlation between growth temperatures and the resulting electronic and structural properties of the films, while characterizing mobility and carrier concentration through Hall measurements and spectroscopic analysis.
- Molecular Beam Epitaxy (MBE) of graphene on gold substrates.
- Characterization of film morphology, chemical composition, and electrical transport properties.
- Evaluation of growth temperature effects on film quality and crystallinity.
- Comparison of experimental results with established benchmark data for single-layer graphene.
- Optimization of transfer processes for device integration.
Excerpt from the Book
i. Properties
Monolayer graphene has attracted great attention for its robust thermal, mechanical, optical, electronic, and magnetic properties REF. Most useful and perplexing property is its Dirac-like band diagram which deviates from traditional materials. Graphene's bands follow the Dirac band dispersion as opposed to the Schrodinger dispersion relation, resulting in a linear dispersion relation and essentially no bandgap.
Electrons and holes act like massless Dirac fermions and the conduction and valence bands meet at a single point, called the Dirac point, making the effective bandgap zero. Graphene is a 2D material; more specifically, its electronic characteristics are unique. Carbon has six electrons and four valence electrons, which occupy the 2s, 2px, 2py, 2pz orbitals. The 2px and 2py orbitals combine with the 2s orbital to form 3 sp2 hybridized orbitals while the 2pz orbital mixes with 2pz orbitals of adjacent atoms to form π bonds. Various models exist to describe the electronic structure of graphene from first principles including the tight-binding model and Landau theory[21]. Although the tight-binding model only considers first order bonding (π bonds), it explains both the band structure and the formation of a bandgap due to multiple layers and various external factors [22]. Please refer to [21], [23] for further reading.
Summary of Chapters
I. Introduction: Discusses the significance of graphene for modern electronics and provides a literature review of growth methods on various metal surfaces.
II. Theory: Explains the electronic properties of graphene and the fundamental physics behind characterization techniques like AFM, Raman spectroscopy, and Hall measurements.
III. Experimental Methods: Details the growth process of graphene on gold foils and the subsequent transfer methods to silicon dioxide substrates.
IV. Results: Presents the raw data obtained from AFM imaging, Raman spectroscopy, and electrical measurements across different growth temperatures.
V. Discussion: Analyzes the gathered data, linking film characteristics like surface roughness, defect density, and carrier mobility to the specific growth parameters used.
VI. Conclusion: Summarizes the findings regarding optimal growth temperature ranges and suggests future work to further improve film crystallinity.
Keywords
Graphene, Molecular Beam Epitaxy, Gold Foils, Raman Spectroscopy, Atomic Force Microscopy, Hall Effect, Carrier Mobility, Carrier Concentration, Thin Film Growth, Carbon Deposition, Nanomaterials, Material Characterization, Electronic Structure, Surface Topology, Epitaxial Growth
Frequently Asked Questions
What is the core subject of this research paper?
This paper focuses on the controllable growth of single-crystalline graphene films on gold foils using physical vapor deposition (molecular beam epitaxy) and the subsequent characterization of these films.
What are the primary themes investigated in the study?
The study examines growth kinetics, structural topology, chemical composition via backscattering spectrometry, and electrical transport properties such as carrier concentration and mobility.
What is the main objective of the research?
The primary goal is to determine the optimal growth temperature for producing high-quality, quasi-freestanding graphene films and to establish correlations between growth parameters and electronic characteristics.
Which scientific methods are utilized to analyze the graphene films?
The author employs Atomic Force Microscopy (AFM) for surface analysis, Raman Spectroscopy for evaluating film quality and defect density, and Hall measurements to extract carrier concentration and mobility.
What does the main body of the work cover?
The main body covers the theoretical background of graphene, detailed experimental procedures for growth and transfer, the presentation of spectroscopic and electrical results, and a comprehensive discussion of observed trends.
Which keywords best describe this research?
Key terms include Graphene, Molecular Beam Epitaxy, Gold Foils, Raman Spectroscopy, AFM, and Hall Effect.
Why are gold foils used as the growth substrate?
Gold is chosen due to its inertness, which mitigates oxide-related effects and prevents significant strain in the graphene, offering a promising substrate for obtaining films with properties close to free-standing graphene.
How is the film quality assessed after transfer?
Quality is assessed by comparing Raman spectra of the transferred films against a commercial standard, looking specifically at peak ratios like 2D/G and the presence of D peaks to quantify disorder.
- Quote paper
- Anand Sampat (Author), 2012, Molecular Beam Epitaxy of Graphene on Gold Foils: Growth and Characterization, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/207041
