A Study on Field Emission Characteristics of Planar Graphene Layers Obtained from a Highly Oriented Pyrolyzed Graphite Block
© to the authors 2009
Received: 23 April 2009
Accepted: 1 July 2009
Published: 12 July 2009
This paper describes an experimental study on field emission characteristics of individual graphene layers for vacuum nanoelectronics. Graphene layers were prepared by mechanical exfoliation from a highly oriented pyrolyzed graphite block and placed on an insulating substrate, with the resulting field emission behavior investigated using a nanomanipulator operating inside a scanning electron microscope. A pair of tungsten tips controlled by the nanomanipulator enabled electric connection with the graphene layers without postfabrication. The maximum emitted current from the graphene layers was 170 nA and the turn-on voltage was 12.1 V.
Field emission is a quantum mechanical tunneling phenomenon in which electrons escape from a solid surface into vacuum, as explained theoretically by R. H. Fowler and L. Nordheim in 1928. Field emission is widely used in many kinds of vacuum electronic applications such as flat panel displays, microwave power tubes, electron sources, and electron-beam lithography. Over the past decade, research groups worldwide have shown that carbon nanotubes (CNTs) are excellent candidates for electron emission [1, 2]. CNTs possess advantages in aspect ratios, tip radius of curvature, chemical stability, and mechanical strength. However, issues related to the placement and throughput of CNT arrays has hampered the development of such arrays for commercial applications. Here, we use graphene for field emission.
Graphene is a two-dimensional honeycomb-structured single crystal showing ballistic transport, zero band gap, and electric spin transport characteristics [3–5]. In previous studies, graphene layers were randomly distributed on cathode electrodes for field emission display applications [6, 7]. However, further field emission studies are required using high-quality, planar graphene structure (e.g. obtained from a highly oriented pyrolyzed graphite (HOPG) block). In order to understand the fundamental behavior of graphene field emission and expand its application into vacuum nanoelectronics beyond the field emission display, the characterization and analysis of field emission from an individual graphene sheet is necessary.
where I: current, E: electric field (V/d), β: field-enhancement factor, φ: work function, A: area, ħ: reduced Planck constant, and m: electron mass. Assuming the work function of graphene is 5 eV and the gap between the graphene sheet and the nanomanipulator tip is 1 μm, the estimated field-enhancement factor, β, is 3519. It is found that the measured field-enhancement factor is comparable with previous results of graphene film prepared by electrophoresis , and the field emission efficiency of graphene is twice as high as other carbon nanomaterials such as CNT and diamond film [10, 11].
This field-emitting nanodevice based on the planar form of graphene potentially allows for top-down CMOS compatible process flows, an advantage for potential industrial fabrication of electronic devices. For applications where high field emission currents or low turn-on voltages are required, nanodevices based on graphene would inherently provide the necessary alignment based on its crystallographic nature.
This work has partially been supported by Exchange Student Program by Brain Korea 21, Award No KUK-F1-038-02 made by King Abdullah University of Science and Technology (KAUST) and National Science Foundation (Major Research Instrumentation Program, Award No. DMI-0619762).
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