Supporting Information
Nanopatterning of diarylethene films via
selective dissolution of one photoisomer
Precious Cantu1, Trisha L. Andrew2, and Rajesh Menon1
1
Department of Electrical and Computer Engineering, University of Utah, Salt Lake City, UT
84112, USA.
2
Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
1. Sample Preparation
The silicon substrates were cleaned by immersion in diluted hydrofluoric acid (HF:H 2O =
1:50) to etch away the native oxide layer and dried with N 2. To remove any hydrophobic
adsorbed contaminents, the surface was cleaned using Reactive Ion Etching (RIE) (Oxford
Plasma Lab 80 Plus RIE). Oxygen gases were injected into the chamber through mass flow
controllers with 200 W RIE chuck power, 20mT chamber pressure, and flow rates of 50
standard cubic centimeters per minute (sccm). After 1 minute etching, the surface was blown
with nitrogen gas. The photochromic molecule was then thermally evaporated from an Al2O3
boat at 100 degrees Celsius using a custom built low temperature thermal evaporator with a
base pressure of 1x10-6 Torr and a deposition rate of ~1.32 Å/second. After evaporation, the
films were illuminated with short-wavelength UV lamp (UVGL-25, Analytika Jena AG) for
3 minutes to fully convert the samples to the closed-ring isomer, 1c. The film thicknesses
were then measured with a Tencor P-10 Profilometer measuring ~29nm.
2. Demonstration of effectiveness of dissolution method
To demonstrate the effectiveness of our method, we produced 1D-grating patterns fabricated
by interference lithography. Figure S1 shows the characterization of different development
times and exposure times as illustrated by the atomic-force micrographs for a ~22nm-thick
film of compound 1 that was exposed to a standing wave 2 = 633nm wavelength (CW 05-
1
LHP-151, Melles-Griot) of period 600 nm for 240 minutes and 314 minutes with an output
laser power of ~2.7mW. As exposure to the polar solvent (100%(wt) ethylene glycol) is
increased from 15 seconds to 60 seconds, one can clearly see the increased contrast. The lines
are well defined with a width of about /2.4 (265 nm) for an immersion time of 60 seconds
for the 314 minutes exposure. As the immersion time is reduced to 30 seconds, the linewidth
decreases slightly. When the immersion time is 15 seconds, it is clear that not all the closedring isomer, 1c, has been removed, which significantly reduces the contrast of the printed
lines.
30 secs
60 secs
Increasing development time
240 minutes
15 secs
314 minutes
6nm
6nm
0nm
6nm
0nm
6nm
0nm
6nm
0nm
6nm
0nm
0nm
Fig. S1: Atomic force micrographs of isolated lines after various development times for
exposure times of 240mins and 314mins.
3. Density Functional Theory Calculations
The results of the density functional theory calculations of the two photochromic isomers
is illustrated in Scheme S1.
open-ring isomer
5.65 Debye
closed-ring isomer
13.39 Debye
Scheme S1: Dipole moments of the open (1o) and closed (1c) ring isomers of
photochrome BTE. The dipole moment vectors are superimposed on the geometryoptimized molecular structures of the respective isomers. Calculations were performed
with the Gaussian software interface [1] using the B3LYP functional and a standard 631G(d) basis set.
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4. Dissolution Characterization
A schematic of the experiment to characterize the macro-scale dissolution of compound 1
is shown in Fig. S2.
1o
1c
1o
1c
100% (wt)
ethylene glycol
Fig. S2: Schematic of setup for dissolution of compound 1 in 100%(wt) ethylene glycol.
The resulting plot showing the thickness of the layer remaining as a function of
immersion time is shown in Fig. S3.
Fig. S3: Plot of thickness remaining of the closed-ring, 1c, and open-ring, 1o, forms as a
function of dissolution time in 100%(wt) ethylene glycol.
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References
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Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A.
Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino,
G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M.
Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,J. A. Montgomery, Jr., J.
E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N.
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