Dissertation/Thesis Abstract

Synthesis and device applications of graphitic nanomaterials
by Umair, Ahmad, Ph.D., The University of Iowa, 2013, 83; 3680098
Abstract (Summary)

This thesis is focused on two topics: (i) synthesis and characterization of bilayer graphene and pyrolytic carbon by atmospheric pressure chemical vapor deposition, and (ii) application of graphene in the fabrication of a buckyball memory device.

Monolayer and bilayer graphene are semi-metal with zero bandgap. One can induce a bandgap in bilayer graphene by applying a gate voltage in the stacking direction. Thus, bandgap and Fermi level in bilayer graphene can be controlled simultaneously with a double-gate device, making it a useful material for future semiconducting applications. Controlled synthesis of bilayer graphene would be the first step to fabricate bilayer graphene based devices. In this context, we report a uniform and low-defect synthesis of bilayer graphene on evaporated nickel films. Ultra-fast cooling is employed to control the number of layers and sample uniformity. The process is self-limiting, which leads to bilayer graphene synthesis over a wide range of growth-time and precursor flow-rate.

Pryolytic carbon is another important carbon nanomaterial, due to its diverse applications in electronic and biomedicalengineering. We employ chemical vapor deposition with ultra-fast cooling technique to synthesize pyrolytic carbon. Furthermore, we elucidate a method to calculate the in-plane crystal size by using Raman spectroscopy.

Finally, the use of bilayer graphene in a write-once read-many memory device has been demonstrated. The device showed irreversible switching from low-resistance to high-resistance state, with hysteresis in the transport characteristics. The control sample showed random switching and hysteresis due to electromigration of metal atoms into the active material of the device. We attribute the reliability and performance of the reported device to the ultra-smooth graphene contacts, which additionally inhibits electromigration from the underlying metallic film. Moreover, the memory device showed excellent endurance and retention characteristics.

Indexing (document details)
Advisor: Raza, Hassan
Commitee: Andersen, David R., Boggess, Thomas F., Prineas, John P., Wohlgenannt, Markus
School: The University of Iowa
Department: Electrical and Computer Engineering
School Location: United States -- Iowa
Source: DAI-B 76/06(E), Dissertation Abstracts International
Subjects: Electrical engineering, Nanotechnology, Materials science
Keywords: Chemical vapor deposition, Graphene, Novel memory devices, Pyrolytic carbon, Raman spectroscopy, Write-once read-many memory
Publication Number: 3680098
ISBN: 9781321518566
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