Correlating atomic structure and transport in single-nanometer scale graphene devices / Zhengqing John Qi.

Format:

Book

Manuscript

Thesis/Dissertation

Author/Creator:

Qi, Zhengqing John, author.

Contributor:

Johnson, A. T. Charlie, degree supervisor, degree committee member.

Drndić, Marija, degree committee member.

Mele, Eugene, degree committee member.

Heiney, Paul, degree committee member.

Bernardi, Mariangela, degree committee member.

University of Pennsylvania. Department of Physics and Astronomy.

Language:

English

Subjects (All):

Penn dissertations--Physics and astronomy.

Physics and astronomy--Penn dissertations.

Local Subjects:

Penn dissertations--Physics and astronomy.

Physics and astronomy--Penn dissertations.

Physical Description:

xi, 188 leaves ; 29 cm

Production:

[Philadelphia, Pennsylvania] : [University of Pennsylvania], 2014.

Summary:

Graphene nanoribbons (GNRs) are promising candidates for next-generation integrated circuit (IC) components, a fact that motivated the exploration of the relationship between atomic structure and transport in graphene patterned at IC-relevant length scales (<10 nm). We first demonstrated superior low- and high-field transport in heterostructures of chemical vapor deposited graphene and hexagonal boron nitride, presenting a scalable methodology for high-quality graphene device integration. To investigate IC-relevance, we introduced a set of novel patterning techniques used to fabricate freestanding GNR devices to widths as small as 0.7 nm, concurrent with simultaneous high-resolution imaging and electrical transport characterization, all conducted within an aberration-corrected transmission electron microscope. We found that sub-10 nm GNRs were inherently disordered and semi-amorphous immediately after patterning. Current-induced Joule heat motivated the structural recrystallization process, resulting in faceted, highly crystalline GNRs with atomically sharp edges. Intrinsic conductance doubled to roughly 2.7 e² /h after the recrystallization process, where e is the electron charge and h is Plank's constant, despite an almost three times reduction in device width, attributed in part to the enhanced carrier transport from the higher structural crystallinity. Current annealing enabled the controlled fabrication of crystalline mono- and few-layer GNR devices. We found that the intrinsic conductance of sub-10 nm ribbons scaled with width as G (w) [approximate] 0.75 (e² /h)w [nm] for few-layer GNRs, where w is the width (measured in nm), while monolayer GNRs were roughly five times less conductive. Few-layer GNRs consistently formed bonded-bilayers and were robust structures that sustained currents in excess of 1.5 μA per carbon bond across a 5 atom-wide ribbon. Nanosculpted, crystalline monolayer GNRs exhibited armchair-terminated edges after current annealing, presenting a pathway for the controlled fabrication of semiconducting GNRs with known edge geometry. A third terminal was introduced to allow for in situ modulation of the chemical potential. An electrically isolated graphene electrode was patterned to be in close proximity to sub-10 nm GNR devices, acting as a local side-gate. We found that gating efficiency increased for narrower channels, attributed to the greater field coupling between the GNR and gate. The methodology presented here offers a unique platform to study the interplay between the atomic structure and three-terminal transport properties of single-nanometer scale GNR devices.

Notes:

Ph. D. University of Pennsylvania 2014.

Department: Physics and Astronomy.

Supervisor: A.T. Charlie Johnson.

Includes bibliographical references.