Fabrication and characterization of graphene-superconductor devices
Doktorsavhandling, 2015

Graphene is the first single-atom-thick two-dimensional material and exhibits a large set of interesting properties. This thesis consists of two parts. The first regards the growth of large-area graphene using chemical vapor deposition (CVD). Graphene is grown using CVD on copper catalyst showing high quality with charge carrier mobility exceeding 3000 cm2/Vs. Wet chemical etching is used to transfer graphene to insulating substrates. Cu is removed using either diluted HNO3 or diluted HCl with a small amount of added H2O2. To allow for faster transfer and avoid consuming copper, a hydrogen-bubbling method is developed to delaminate graphene from Cu. Graphene transferred this way shows properties similar to those of graphene transferred using wet etching. To avoid transfer-related issues, graphene is grown non-catalytically directly on insulating substrates such as SiO2, Al2O3, and Si3N4. The grain size is only ~10 nm due to the lack of catalytic activity during growth. Such graphene shows inferior electronic properties with mobility in the order of ~tens of cm2/Vs. Despite that, sheet resistance around kΩ, the possibility to grow several layer thick films, and optical properties similar to those of pristine graphene make it an interesting material. A method for cleaning graphene mechanically using atomic force microscopy (AFM) is developed. By appropriate choice of the applied force, atomically smooth (roughness < 0.2 nm) graphene with improved mobility and reduced doping is achieved. The second part of this thesis considers experiments combining graphene and superconductors. A graphene-based cold-electron bolometer is realized using graphene as absorber material. It shows response to 100 GHz radiation at 300 mK and a temperature responsivity of ~0.4 µV/mK at 300 mK. The Aharonov-Bohm effect is studied in graphene having superconducting or normal metal mirrors. The mirrors improve the visibility of the Aharonov-Bohm oscillations, and up to third order oscillations are observed. Weak localization in inhomogeneous magnetic fields is studied in graphene by putting it in close proximity to a type-II superconductor. A deviation from the homogeneous result is observed for fields smaller than the characteristic field Bφ.

Synthesis

Atomic force microscopy

Aharonov-Bohm effect

Graphene

Bolometer

Chemical vapor deposition

Mechanical cleaning

Weak localization

A423 (Kollektorn), MC2
Opponent: Prof. Saverio Russo

Författare

Niclas Lindvall

Chalmers, Mikroteknologi och nanovetenskap (MC2), Kvantkomponentfysik

Low Partial Pressure Chemical Vapor Deposition of Graphene on Copper

IEEE Transactions on Nanotechnology,; Vol. 11(2012)p. 255-260

Artikel i vetenskaplig tidskrift

Large-area uniform graphene-like thin films grown by chemical vapor deposition directly on silicon nitride

Applied Physics Letters,; Vol. 98(2011)

Artikel i vetenskaplig tidskrift

Cleaning graphene using atomic force microscope

Journal of Applied Physics,; Vol. 111(2012)p. Article Number: 064904-

Artikel i vetenskaplig tidskrift

Family of graphene-based superconducting devices

JETP Letters,; Vol. 94(2011)p. 329-332

Artikel i vetenskaplig tidskrift

Towards transfer-free fabrication of graphene NEMS grown by chemical vapour deposition

Micro and Nano Letters,; Vol. 7(2012)p. 749-752

Artikel i vetenskaplig tidskrift

The Aharonov-Bohm effect in graphene rings with metal mirrors

Carbon,; Vol. 50(2012)p. 5562-5568

Artikel i vetenskaplig tidskrift

Styrkeområden

Nanovetenskap och nanoteknik

Ämneskategorier

Nanoteknik

Den kondenserade materiens fysik

Infrastruktur

Nanotekniklaboratoriet

ISBN

978-91-7597-248-0

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie

A423 (Kollektorn), MC2

Opponent: Prof. Saverio Russo