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40

nanotimes

News in Brief

10-04 :: April 2010

Graphene //

Graphene Films Clear Major Fabrication Hurdle

Energy (DOE) center for nanoscience, have taken a significant step at clearing the major hurdle with graphene.

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“Before we can fully utilize the superior electronic properties of graphene in devices, we must first de- velop a method of forming uniform single-layer gra- phene films on nonconducting substrates on a large scale,” says Yuegang Zhang, a materials scientist with the Lawrence Berkeley National Laboratory (Berkeley Lab). Current fabrication methods based on mecha- nical cleavage or ultrahigh vacuum annealing, he says, are ill-suited for commercial-scale production. Graphene films made via solution-based deposition and chemical reduction have suffered from poor or uneven quality.

The Berkeley researcher have successfully used direct chemical vapor deposition (CVD) to synthesize single-layer films of graphene on a dielectric sub- strate. Zhang and his colleagues made their graphene films by catalytically decomposing hydrocarbon precursors over thin films of copper that had been pre-deposited on the dielectric substrate. The copper films subsequently dewetted (separated into puddles or droplets) and were evaporated. The final product was a single-layer graphene film on a bare dielectric.

“This is exciting news for electronic applications because chemical vapor deposition is a technique

uegang Zhang and colleagues at Berkeley Lab’s Molecular Foundry, a U.S. Department of

already widely used in the semiconductor industry,” Zhang says.

“Also, we can learn more about the growth of gra- phene on metal catalyst surfaces by observing the evolution of the films after the evaporation of the copper. This should lay an important foundation for further control of the process and enable us to tailor the properties of these films or produce desired mor- phologies, such as graphene nanoribbons.”

In their study, Zhang and his colleagues used electron-beam evaporation to deposit copper films ranging in thickness from 100 to 450nm. Copper was chosen because as a low carbon solubility metal cata- lyst it was expected to allow better control over the number of graphene layers produced. Several diffe- rent dielectric substrates were evaluated including single-crystal quartz, sapphire, fused silica and silicon oxide wafers. CVD of the graphene was carried out at 1,000° Celsius (1,832° Fahrenheit) in durations that ranged from 15 minutes up to seven hours.

“This was done to allow us to study the effect of film thickness, substrate type and CVD growth time on the graphene formation,” Zhang says. A combinati- on of scanning Raman mapping and spectroscopy, plus scanning electron and atomic force microscopy confirmed the presence of continuous single-layer graphene films coating metal-free areas of dielectric substrate measuring tens of square micrometers. Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87