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Keysight Technologies
Imaging Graphene via Low Voltage Field
Emission Scanning Electron Microscopy
Application Note
Introduction conductivity suggests graphene as graphene, a SEM must have a small
an excellent transparent conductive beam spot size corresponding to a high
Pursuing novel materials with intriguing electrode in flat panel displays, touch spatial resolution.
properties is always an active field screens and cathode ray tubes [4]. In
on the horizon of materials science. order for graphene to fulfill this promise 2) Low beam energy
One paradigm is graphene which has in large-scale manufacturing of high- The ultra-thin graphene film is
attracted enormous passions and performance electronics, high-quality "transparent" to high energy electron
stimulated extensive research efforts graphene with large dimensions is beams. Since the preferred imaging
all over the world since its discovery needed. Among several techniques for information for SEM is the secondary
in 2004 [1]. With a monolayer of sp2- graphene synthesis, chemical vapor electrons generated by the primary
bonded carbon atoms arranged in a deposition (CVD) is the most promising beam in the sample, low beam energy is
honeycomb crystal lattice, graphene is approach for this purpose owing to the required to image ultra-thin materials.
a basic building block for all graphitic high quality of CVD graphene on large Furthermore, low energy SEMs
materials, from wrapping up into 0D surface as well as the compatibility minimize beam induced sample damage
fullerenes, or rolling into 1D nanotubes, of CVD with current standard wafer- and sample charging of exposed
to stacking into 3D graphite. For quite scale lithography and integrated circuit non-conducting materials, which is
a long time, such a 2D graphitic layer fabrication processes. ideal for imaging graphene films on
had been described as a vintage model insulating substrates.
because this structure is not stable in Characterization of graphene films
theory [2]. The success of obtaining is essential for the quality control 3) High contrast imaging
free-standing graphene, for the first purposes. Common techniques include Many features in graphene are difficult
time, by mechanical exfoliation of highly optical microscopy, atomic force to image because of poor contrasts.
oriented pyrolytic graphite (HOPG) has microscopy, Raman spectroscopy, A perfect graphene monolayer is
immediately entranced both scientists transmission electron microscopy, smooth and featureless making it a
in academia trying to understand the Auger electron spectroscopy, etc. challenging surface for SEM imaging.
basic behavior of matter and those Scanning electron microscopy (SEM) A SEM with inherently high contrast
working in industry trying to explore is getting more popular for imaging and with the ability to enhance the
novel applications. Predicted by graphene because it is a rapid, non- contrast using multiple detection
theories and followed by experimental invasive and effective imaging technique techniques is advantageous.
demonstrations, graphene possesses which is complimentary to most other
unique electrical, mechanical and techniques. However, challenges still 4) High performance detector
optical properties. Currently graphene- exist in SEM imaging of graphene An efficient, high performance electron
based nanoelectronics are the subject films. To effectively image graphene, detector is required for detecting low
of intense focus. For instance, the high SEM needs to meet the following energy electrons which provide the
intrinsic mobility in graphene makes it requirements: best surface contrast and topographic
an attractive material for high-speed sensitivity.
electronics [3], and its high optical 1) High spatial resolution
transmittance coupled with high Graphene films usually have nanoscale Fortunately, the low voltage field
features. To resolve the morphology of emission scanning electron microscopy
(LV FE-SEM) can meet all the above
requirements, hence it is potentially an
ideal technique for graphene imaging.
In this study, different graphene
samples were imaged by using a
Keysight Technologies, Inc. 8500
compact FE-SEM. All samples were
directly mounted on double carbon
tapes without any other sample
preparation followed by loading into the
sample chamber for imaging. With an
innovative miniature all-electrostatic
electron beam column design, Keysight
8500 can achieve high resolutions at
low beam voltages (500 V