Supporting Information
Chemically Functionalized Graphene for Bipolar Electronics
Bernard R. Matis1, Felipe A. Bulat2, Adam L. Friedman3, Brian H. Houston4, and Jeffrey W.
Baldwin4,*
1
NRC Postdoctoral Associate, NRL, Washington, DC 20375, United States
2
Sotera Defense Solutions Inc., Crofton, Maryland 21114, United States
3
Naval Research Laboratory, Code 6361, Washington, DC 20375, United States
4
Naval Research Laboratory, Code 7130, Washington, DC 20375, United States
*Correspondence to: jeffrey.baldwin@nrl.navy.mil
Hydrogenation procedure:
Hydrogenation of graphene is performed in an Oxford Instruments plasma enhanced
chemical vapor deposition (PECVD) reactor according to Reference 11 in the main text and
under the conditions: 30W RF, 100 SCCM H2, 1.5 Torr, 30s. The PECVD was at 30 degrees
Celsius before transferring the sample into the chamber on the center of a blank, clean, and
undoped silicon wafer. The maximum chamber temperature reached during the hydrogenation
process was ~40 degrees Celsius.
Upon hydrogenation, the sample is removed from the PECVD and characterized using
Raman spectroscopy to confirm the presence of single layer graphene by measuring of the shape
of the 2D peak (2679 cm-1, 2nd order D-mode), and to quantify the degree of hydrogenation using
a measure of the relative defect density in each film by the D/G ratio, a ratio of the D-mode
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intensity (1345 cm-1, appearing due to symmetry breaking at defect sites) to the G-mode intensity
(1588 cm-1, E2g phonon mode). The D/G ratio is related to the defect-free domain size of
graphitic materials in this case caused by the addition of hydrogen to the graphene sheet.S1, S2
Raman spectra were collected under ambient conditions using a Renishaw MicroRaman
Spectrometer with a 514nm laser excitation.
De-hydrogenation procedure:
We annealed the exfoliated device PN2 at 220 oC in argon for 24 hours in order to show
that the effects measured in this device are due to the hydrogenation, and not due to unintentional
defects. Raman spectra were collected immediately before and after annealing the sample, and
the spectra are shown in Fig. S6. This data clearly shows that the hydrogenation process is
reversible at a temperature well below the temperature at which vacancies are mobilized in
graphene (>725 oC).S3,S4 After the 220 oC heat treatment, the device PN2 was cooled to 4.2K
and the resistance across the now missing interface was characterized. The inset to Figure 4a of
the manuscript displays this post heat treatment data set. Here we show that the post heat-treated
sample recovers from the high resistance state to its original state before hydrogenation, as can
be seen by the overlap of the black and blue traces within the inset. The black trace within the
inset is the same black trace plotted within the main figure. The blue trace corresponds to the
data for Rjct following the 220 oC heat treatment. The return of the junction resistance to the prefunctionalized data supports our argument that the increase in Rjct is due specifically to the
hydrogenation of the graphene, and not due to defects as these would not be removed at such low
temperatures. S3,S4,S5,S6
The low temperature of desorption of hydrogen from the hydrogenated
graphene surface is consistent with what has been calculated S5 and experimentally determined S4
2
and has been shown to be due to the strained bonds S5, S6 that are generated from the partially
hydrogenated lattice.
Supporting References:
S1
F. Tuinstra and J. L. Koenig, J. Chem. Phys. 53, 1126-1130 (1970).
S2
J.-H. Chen, W. G. Cullen, C. Jang, M. S. Fuhrer, and E. D. Williams, Phys. Rev. Lett. 102,
236805 (2009).
S3
Physics of Graphite, B.T. Kelly, Applied Science Publishers, London, 1981 p.405.
S4
M. Wojtaszek, N. Tombros, A. Caretta, P.H.M. van Loosdrecht, B.J. van Wees, Journal of
Applied Physics 110, 063715, (2011).
S5
K.S. Subrahmanyam, P. Kumar, U. Maitra, A. Govindaraj, K.P.S.S. Hembram, U.V.
Waghmare, C.N.R. Rao, Proc. Natl. Acad. Sci. 108, 2674-2677, (2011).
S6
M.Z. Hossain, J.E. Johns, K.H. Bevan, H.J. Karmel, Y.T. Liang, S. Yoshimoto, K. Mukai, T.
Koitaya, J. Yoshinobu, M. Kawai, et al., Nature Chem. 4, 305-309 (2012).
3
Supporting Figures:
SFig. 1. Charge neutrality points of the initial graphene for devices (a) PN1 and (b) PN2.
Measurements were performed using an AC current excitation and at B=0T. In these cases no
PMMA covered any portion of the graphene. Note that the locations of the CNP’s here do not
significantly change once the PMMA is added in order to protect a region of the graphene from
exposure to the hydrogen plasma. The Drude mobility’s listed in the main text were extracted
from the high carrier density limits of these traces.
SFig. 2. (a) AC transport and Raman spectra for the graphene/hydrogenated graphene p-n
interface, PN2. (a) CNPs for device PN2. The graph depicts the four wire resistance R as a
function of Vg at temperature T and at B=0T showing the CNPs for each side of the interface.
(b) Raman spectra of the two sides of the interface for device PN2 normalized to the G-mode
intensity.
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SFig. 3. AC transport and Raman spectra of a third graphene/hydrogenated graphene p-n
interface, PN3. (a) CNPs for device PN3. The graph depicts the four wire resistance R as a
function of Vg at temperature T and at B=0T showing the CNPs for each side of the interface.
(b) Raman spectra of the two sides of the interface for device PN3 normalized to the G-mode
intensity.
SFig. 4. AC transport and Raman spectra of a fourth graphene/hydrogenated graphene p-n
interface, PN4. (a) CNPs for device PN4. The graph depicts the four wire resistance R as a
function of Vg at temperature T and at B=0T showing the CNPs for each side of the interface.
(b) Raman spectra of the two sides of the interface for device PN4 normalized to the G-mode
intensity.
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SFig. 5. DC VI curves for device PN2 from which the data shown in Fig. 4(a) of the main text
was extracted.
SFig. 6. Raman spectra of the hydrogenated graphene side of the interface for device PN2 before
and after the 24 hour heat treatment at 220 oC. The spectra have been normalized to the G-mode
intensity, and show the recovery of the graphene Raman signature.
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