Supporting Online Material
Angle and Polarization-Resolved Absorption Spectral Mapping of
Organic Single Rubrene Nanoplates
Hyun Soo Lee1, Ji Hyun Kim1, Krishna P. Dhakal1, Jin Woo Lee2, Jin Sun Jung2,
Jinsoo Joo2* and Jeongyong Kim1*
1
Department of Physics, University of Incheon, Incheon 406-772, Korea
2
Department of Physics, Korea University, Seoul 136-713, Korea
*Corresponding authors. E-mail: jeongyong@incheon.ac.kr (J. Kim) and jjoo@korea.ac.kr (J.
Joo); Fax: +82-2-766-8018; Tel: +82-32-835-8222
I. Preparation of Rubrene Nanoplate and Thin film
II. Experimental Setup of Absorption Spectral Mapping
Supplementary Figure 1
III. Estimation of Average Incidence Angle Corresponding to NA of
Illumination Objective Lens
Supplementary Figure 2 and Table I
IV. Estimation of lateral resolution
Supplementary Figure 3
I. Preparation of Rubrene Nanoplate and Thin film
We used physical vapor deposition method for the growth of rubrene nanoplates [1].
The rubrene powder, purchased from Sigma-Aldrich Co. without further purification
was placed on the heating zone in the middle of a furnace used for vaporization.
Rubrene nanoplates were obtained by controlling the gas flow rate and vaporizing
temperature. The source temperature was ~ 310℃ and the flow rate of N2 gas was
~400 cm3/min. The temperature of the sample growth zone was 200 ~ 250℃. Pure
nitrogen gas was continuously flowed during the growth and cooling process to
prevent the oxidation of the sample. Gold (Au) nanoparticles with dodecanethiolatefunctionalized groups (diameter 2 ~ 20 nm) which played the role of a seed for the
growth of the 2-dimensional rubrene nanostructure were spin or drop-casted on the
SiO2 growth substrate. Prepared rubrene nanoplates were dispersed on the glass
substrate.
The rubrene thin film was prepared by organic molecule beam deposition (OMBD)
method [2].
The thin film was deposited onto cover glass substrate at temperatures
varying from 120℃ to 135℃ in vacuum of 3.1  10-7 torr for 27 hours. The distance
between the source and the target substrate was 15 cm. The thickness of the rubrene
thin film measured by atomic force microscope (AFM) was ~500 nm.
II.
Experimental Setup of Absorption Spectral Mapping
Fig. S-1. A schematic diagram of an experimental arrangement to measure absorption
spectra in the wavelength range 400-900 nm using a spectrometer.
Absorption spectral mapping is carried out using the AFM (Park Systems XE120) mounted on an inverted optical microscope (Axiovert200, Zeiss) coupled
with a spectrometer. The light source (1) to generate the broadband wavelength
light required for absorption spectra was a halogen-tungsten bulb, which was
focused using the condenser objective lens (OL) (2) onto the sample on the stage
(4) of the microscope. Here, four condenser OLs with different numerical apertures
(NAs) of 0.28, 0.6, 0.90 and 0.95 were used to vary the incidence angle to the
sample. The collection OL (5) below the sample having the NA of 1.4 was used to
image the sample on the focal plane of a microscope output port, where a
multimode optical fiber (7) is placed to collect the transmitted light. In this scheme,
all the light originated from the location which the optical fiber end is imaged on
by the collection OL are collected by the optical fiber. The lateral size of the
collection volume on the sample is mainly determined by the powers of the
objective lens and the ‘tube lens’ (6) in the microscope and the core size of the
collecting optical fiber. The other end of the optical fiber is connected to the input
of the spectrometer (8), equipped with a cooled CCD to take the transmission
spectra. Experimental setup for laser confocal PL measurement is described in
previous literature [3].
To generate two-dimensional absorption mapping image, we used the data
acquisition system of the AFM which was synchronized with the spectrometer
CCD and the local transmission spectra at each pixel position are taken while
doing raster scanning by the AFM sample stage. The scanning area are typically
tens of m large squares and consist of 128 by 128 pixels containing 16384 spectra
at one mapping image. First, the background transmission spectra were obtained
from the transparent area on the glass substrate and were used to divide all the
transmission spectra. If necessary, we obtained an AFM image of the same rubrene
nanoplate to estimate the local absorption coefficient. Experimental setup for laser
confocal PL mapping is the same as the same as absorption spectral mapping
except that the light source is the 488 nm line of an argon ion laser and the
collection OL of absorption experiment was also used to focus the laser on the
sample.
V. Estimation of Average Incidence Angle Corresponding to NA of
Illumination Objective Lens
The illumination light focused by the OL with NA possesses a range of incidence
angle from 0° to med= sin-1 NA. Considering the circular illumination and the area
weighting factor, average incidence angle to the sample, med is give by,
 tan  max 

2 

 med  tan 1 
Here one should consider the refraction by Snell’s Law at the boundary of the air
(n1=1) and the rubrene nanoplate (n2=1.7) then the actual incidence angle that rubrene
molecule would experience is given by
 sin  med
 n2
 av  n1 sin 1 



Fig. S-2 Estimation of average incidence angle that rubrene molecule in rubrene
nanoplate experience.
Using above relation, the average incidence angle corresponding to the NA of the
illumination objective lens are estimated as following,
Table S-I The average incidence angle depending on NA
Numerical Aperture (N.A.)
0.28
0.6
0.9
0.95
Refraction Angle(  av )
6.8°
16.0°
29.0°
32.2°
III. Estimation of Lateral Resolution of Absorption Spectral
Mapping
Light Intensity (a.u.)
450
400
350
mean value=387.3±6.7
I0.88=355.6
300
250
200
150
I0.12=154.9
0.982m
mean value=123.2±11.6
100
0
2
4
6
8
10
12
Spatial Position (m)
Fig. S-3 (a) Spectral absorption mapping image of Rubrene thin film grown by
OMBD (b) The band averaged line profile extracted from the shaded area in the
absorption spectral mapping image.
Lateral resolution of absorption spectral mapping was measured from the obtained
absorption spectral mapping image of the rubrene thin film deposited by organic
molecular beam deposition (OMBD) method. The image in Fig. S-3 (a) shows the
boundary of two different domains observed in absorption image of OMBD rubrene
film. We selected a rectangular area across this boundary and obtained averaged line
profile which is displayed in Fig. S-3 (b). This line profile consists of three sections,
lower plateau, upper plateau and the adjoining slope. The x-coordinates corresponding
to 12 % and 88 % of the slope were selected and their distance was measured to be
0.98 μm which was determined as the spatial lateral resolution of the absorption
spectral mapping.
References
[S1] J. W. Lee, K. H. Kim, D. H. Park, M. Y. Cho, Y. B. Lee, J. S. Jung, D. -C. Kim,
J. Y. Kim, and J. Joo, Adv. Funct. Mater. 19, 704 (2009)
[S2] K.H. Kim, T. H. Kwak, M. Y. Cho, J.W. Lee, J. Joo, Synthetic Met. 158, 553
(2008)
[S3] D. H. Park, H. S. Kim, M. -Y. Jeong, Y. B. Lee, H.-J. Kim, D.-C. Kim, J. Y. Kim,
J. Joo, Adv. Funct. Mater. 20, 2526 (2008)