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Op Pp of Gp oo ; Tow

Gp OpooAma! Kasryl,2 George Tuevski2 Marceo Kuroda2,3 Ageeth Bo12 Genn Martyna2 Behard Menges4

Soshi Oid Mostafa E Ashryl,2 Matthew Cop Libor ick

IEgypt-BM Nnotechnoogy Research Center (EGNC) Smar Viage Buing 11 Cairo-Aexndria DeserRoad 177 Egypt

2BM T. Watson Research Center 111 Kitchawn Rd Yorktown Heights NY 18 USA3Department of Computer Science Unversity of inois at Urbna-Champign Urbna 181 USA

4Max Panck stitute for Poymer Reserch Ackermnnweg 1 18 Mainz Germny

Graphene, a newly discovered material with unusual electrical and optical properies, hasattracted interest for a number of potential applications. One of the most actively pursued

applications is using graphene as a transparent conducting electrode for use in solar cells, diplays

or touch screens. In this work, two studies are pursued in parallel to explore the electrical and

optical properties of graphene. Graphene was prepared on copper by the standard chemical vapor

deposition (CVD) method [l], the preparation procedure and conditions are described in [2]. The

effect of chemical p-type doping on graphene stacks was studied in order to reduce the sheet

resistance of graphene. The doping decreases the sheet resistance by a factor of 3 elding lmscomprised of eight stacked layers with a sheet resistance of 90 QJ at a transmittance of80% [2].

A theoretical model that accurately describes the stacked graphene film system as a resistor

network was also developed [2]. The experimental data shows a line increase in conductivity

with the number of graphene layers, indicating that each layer provides an additional transport

channel, in good agreement with the theoretical model (Fig. 1)

t d ," f dp

i: ,' . E '

M

_

g

Fig. 1 (a) An AFM image of one graphene ayer prepared by the CVD method (b) A scheme of the two dopingmethod (c) rhen bd stcture befoe nd e doing (d) epmnt and hoic ine

increase in the graphene conducti ty by increasing the number of tacked ayers fore nd aer doping.

In order to study the optical properties, the growth conditions were irst optimized to yield a

smooth and clean graphene lm. The effects of annealing and growth time on the quality of the

lm was studied with a variety of characterization techniques including X-ray photoelectron

spectroscopy (S), Raman Spectroscopy, Medium Energy Ion Scattering (MEIS), ellipsometer

and Surface Plasmon Resonance (SPR). These techniques were used to obtain information on the

thickness and the refractive index of the graphene mono layers and stacked multilayers. Graphene

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grown under the following conditions, 10 minute Cu anneal and 10 minute carbon exposure,

gave the smoothest and cleanest lms as confirmed by SEM and AFM imaging. Although the

electrical properties are similar under different growth conditions, the shorter annealing and

growth time decreased the surface roughness and, consequently, the scattering leading to easier

optical measurements. The results of the MEIS (thickness) and the ellipsometry (n and k) were

used to fit the SPR data as a starting point to study the plasmon propagation in graphene.

Studying the combination of the electrical and optical properties can be of great value for

developing graphene-based optoelectronic devices.

-Graphene o Cu fil (30 mi Aea/30 mi Gowt)Graphene o Cu foi (10 mi Aeal/ 0 i Gowt) Aeal mi Gwh-Gaphene ansfered o SO

0 n Annea/0 Gow AeaU mi Grwh

-Graphene ransferred o SO

0 i Annea/0 i Gow 6 AeaU mi Grwh

:

>'is:

Msurt Fitting

(c)

8 Bndg Ey ev

! (b)

01.-

, . . n k

M E v Wv m

1 Ram Sh "

.9OB

?0.6

o:

3

- 50 Au I layer Graphee 50 Au 2 Layers Graphee

24

Fig. (a) e XPS resuts of graphene prepared at different conditions (b) Rmn measurements of the grapheneprepared at dierent conditions (c) e tting of the MES measurements gives a l graphene ayers 8 nm) (d)the eipsometer measurements of n nd k of1 ayer graphene using the thickness expoited from the MES to t edata (e) Surface pasmon measurements (SPR) of one and two ayers graphene on god showing the shi in the

resonnce the data expoited from MES and eipsometer are used to t e SPR data.

This work was conducted under and partially funded by the 2008 joint development agreementetwe M Rearch ad he Govemet o th Arab Repulic o Egt throgh the Eg

Nanotechnology Center EGNC;

Reference

[1] X. Li, Y Zhu, W. Cai, M. Borysiak, B. Han, D. Chen, R. D. Piner, L. Colombo, R. Ruoff,Nano Lett., 2009, 435-4363

[2] A. Kasry, M. A. Kuroda, G. J. Martna, G. S. Tulevski, A. A. Bol, ACS Nano, ASAP, July

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