2013 IR&D Annual Report

Large-Area Synthesis of Graphene for Electronic Devices, 18-R8303

Principal Investigators
Vasiliki Z. Poenitzsch
Thomas Booker
John Harrison

Inclusive Dates: 04/01/12 – 10/01/13

Background — At present, graphene is one of the hottest topics in condensed-matter physics and materials science. Graphene is a monolayer, thick planar sheet of sp2-bonded carbon atoms packed in a two-dimensional (2D) honeycomb lattice. The unique structure of graphene yields extraordinary thermal, mechanical and electrical properties. In 2004, Novoselov and Geim first isolated graphene by cleaving graphite with adhesive tape. Research on graphene has since been a fast-developing field, with exciting properties being confirmed and new concepts and applications appearing at an incredible rate.

Potential applications include field-effect transistors, interconnects, sensors, conducting films, clean energy devices, and conductive reinforced composites. Because of the promising and versatile properties of graphene, Novoselov and Geim were awarded the 2010 Nobel Prize in Physics. Despite intense interest and remarkably rapid progress in the field of graphene-related research, there is still a long way to go for the widespread implementation of graphene. It is primarily due to the difficulty of reliably producing high quality samples, especially in a scalable fashion. This project seeks to help close the chasm between graphene manufacturability and its application. Developing graphene deposition technologies will enable SwRI to provide applied research and development on graphene to a range of clients.

Approach — The primary objective of this project is to establish graphene deposition technologies at SwRI®. The immediate aims of this project are to establish a graphene thermal chemical vapor deposition (CVD) processing technology, develop a novel graphene plasma enhanced CVD (PECVD) processing technology and investigate their electronic application specific performance of produced graphene films. Facilities and expertise to deposit large-area (≥1 in.2), high-quality graphene films at SwRI (Figure 1) were established. This new capability will significantly strengthen SwRI’s position to provide applied research and development on graphene to a range of clients. An in-house graphene thermal chemical vapor deposition (CVD) technology was developed.

Figure 1: Photographs (a,b) of new thermal CVD chamber running process experiments for producing graphene films and of (c) as-grown film on Cu foil from a graphene deposition process experiment.
 Figure 1. Photographs (a,b) of new thermal CVD chamber running process experiments for producing graphene films and of (c) as-grown film on Cu foil from a graphene deposition process experiment.

Accomplishments — The technology was used successfully to grow pristine, single-to-few layer graphene films using Raman spectroscopy, transmission electron microscopy (TEM), and scanning tunneling microscopy (STM) (Figure 2). The large area graphene films were successfully transferred from Cu growth substrates to glass and Si wafer substrates (Figure 3). The performance was measured of 94 percent transmittance and 900 to 1,300 ohms/square for transferred SwRI graphene films, which matches that of current state-of-art CVD graphene films. A plasma-enhanced chemical vapor deposition (PECVD) technology was developed using a plasma jet and heating stage (not shown). PECVD growth of graphene films was investigated, but resulted only in the deposition of thin, amorphous carbon films. A PECVD process for growth of vertically aligned carbon nanotubes (CNTs), however, was developed. Preliminary evidence was also obtained for higher pressure PECVD deposition of diamond-like carbon (DLC) films. Altogether, SwRI has built a portfolio that will enable entry into the graphene research arena. While this project focused on graphene, the real benefit of the project was establishing thermal CVD and PECVD processes that have expanded and diversified SwRI’s current unique coating capabilities and efforts in nanotechnology.

Figure 2: Images of single-to-few layer graphene films grown
Figure 2. (a) Transmission electron microscopy image showing atomic resolution, (b) diffractogram showing crystalline structure, and c) scanning tunneling microscopy image showing atomic resolution of pristine, single layer graphene film.
Figure 3: Image of large area graphene films successfully transferred
Figure 3. Photograph of 2 in. x 2 in. pristine graphene film transferred to glass substrate. Measured performance of 94 percent transmittance and 900 to 1,300 ohms/square for transferred SwRI graphene films.
Benefiting government, industry and the public through innovative science and technology
Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.
04/15/14