FeCl3-Intercalated Few-Layer Graphene: Opto-Electronics Properties and Applications (Graphene Europe 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

8:8

= 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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