Adolfo De Sanctis,
University of Exeter
Apr 29, 2015.
Graphene, a single layer of carbon atoms with honeycomb structure, has emerged as a new paradigm
in condensed matter physics due to the breadth of unique physical properties which also make it the ideal
platform for novel transparent and flexible opto-electronic devices. These unique properties can be further tailored
to fit specific device functionalities by means of chemical bonding of a molecule or a chemical element
to the pristine graphene 1, 2. The most recent example of the potential of chemical functionalization is the
intercalation with FeCl3 of few-layer graphene (FLG). In this case a strong charge transfer occurs between the
graphene and the intercalant layers, resulting in heavy p-doping of graphene. This gives rise to a new system
which is the best known flexible and transparent material able to conduct electricity, with a sheet resistance of
= and an optical transmittance as high as 84% 2. FeCl3-FLG can be employed effectively as electrode
in atomically-thin photodetectors 3 and was used to provide the first evidence for magnetic ordering in the
extreme limit of two-dimensional systems 4.
In this contribution we report novel opto-electronic properties of FeCl3-FLG and opto-electronic devices
which can be realized using FeCl3-FLG. We present a study which shows that FeCl3-FLG can withstand
relative humidity of up to 100% at room temperature for 25 days, as well as temperatures of up to 150 C in
air or as high as 620 C in vacuum 5. The previously unknown durability to extreme conditions position
FeCl3-FLG as a viable and attractive replacement to indium tin oxide (ITO), the main conductive material
currently used in electronics, such as smart mirrors or windows, or even solar panels. Another key requirement
for flexible transparent conductors in modern electronics is that their work function needs to be at least
similar to that of ITO. We report the first study of the work function of large-area (9 mm2) FeCl3-FLG grown
by chemical vapor deposition on Nickel, which results in values as large as 5:1eV. Furthermore we report
the analysis of the Raman spectrum of this material from which a charge density of 5 1013 cm��2 can be
extrapolated as a result of the intercalation process. This large charge density is promising for the use of this
material as a platform for plasmonics applications in the near-infrared region. Finally, we show for the first
time, the ability to control the arrangement of FeCl3 molecules in the lattice of FeCl3-FLG by direct laser writing
micrometer-scale patterns and we demonstrate the use of these molecular-boundaries as opto-electronic
circuits. Hence we characterize these interfaces using Raman spectroscopy and scanning photocurrent measurements.
A charge concentration change of n 1:8 1013cm��2 in the exposed region (5m) results in a
p-p' junction and an enhanced photoresponse as large as 0:5 nA. These results pave the way to the molecular
design of integrated atomically-thin opto-electronic devices.
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The Energy Harvesting Research Group at the top 10 University of Exeter in the UK combines cutting edge academic research with a firm focus on needs of industry. We offer a fully integrated system approach to develop wearable and vibrational energy harvesting powered wireless sensing systems for a wide range of real world applications, including automotive, aerospace, transport, healthcare, military and defence, and other industrial sectors.
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