SUPPLEMENTARY MATERIAL
Nanomechanical investigation of thin-film electroceramic/metal-organicframework multilayers
James P. Best,1* Johann Michler,1 Jianxi Liu,2 Zhengbang Wang,2 Manuel Tsotsalas,2
Xavier Maeder,1 Silvana Röse,3,4 Vanessa Oberst,5 Jinxuan Liu,2 Stefan Walheim,6
Hartmut Gliemann,2 Peter G. Weidler,2 Engelbert Redel2* and Christof Wöll2*
Dr. J. P. Best*, Dr. X. Maeder, Dr. J. Michler
1
Empa, Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkerstrasse 39
3602 Thun, Switzerland
J. Liu, Z. Wang, Dr. M. Tsotsalas, Dr. J. Liu, Dr. H. Gliemann, Dr. P. G. Weidler, Dr. E. Redel*,
Prof. Dr. C. Wöll*
2
Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1,
76344 Eggenstein-Leopoldshafen, Germany
S. Röse
3Preparative
Macromolecular Chemistry, Institute for Chemical Technology and Polymer Chemistry (ICTP), Karlsruhe Institute
of Technology (KIT), Engesserstr. 18, 76128 Karlsruhe, Germany
4Institute for Biological Interfaces (IBG), Karlsruhe Institute of Technology (KIT), Herrmann-von-Helmholtz-Platz 1, 76344
Eggenstein-Leopoldshafen, Germany
V. Oberst
5
Institute of Applied Mechanics (IAM), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1,
76344 Eggenstein-Leopoldshafen, Germany
Dr. S. Walheim
6
Institute of Nanotechnology (INT), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1,
76344 Eggenstein-Leopoldshafen, Germany
E-Mail: james.best@empa.ch, engelbert.redel@kit.edu, christof.woell@kit.edu
Keywords: (Indentation, MOFs, Photonic Sensors, Thin Films, Hybrid Materials, Mechanical Properties)
Experimental Section
All chemicals used in this work are commercially available from different sources and
suppliers. Single-component HKUST-1 films were grown on pretreated/modified Si wafers
(orientation (100), polished, thickness: 525 ± 20 μm, specific resistivity: 8−12 Ω/cm; from
Silchem Handelsgesellschaft GmbH, DE). All other films were grown on (111) orientation Si
wafers. The Si wafers were treated by oxygen plasma (Diener Plasma; gas flow: 50 sccm,
mixture: pure O2) for 30 min to remove impurities as well as increase the number of OH
functional groups and the hydrophilicity on the Si surface before growing the SURMOFs. The
HKUST-1 SURMOFs for the multilayered thin films were epitaxially grown on the pretreated Si
substrate using the LPE spray method described elsewhere [1], in which the metal-containing
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solution (1 mmol Cu(OAc)2) and the linker solution (0.1 mmol BTC) are sprayed sequentially on
the substrate. Single-component HKUST-1 films were grown on COOH terminated selfassembled monolayers as described in reference [1]. The desired thickness can be adjusted
through the number of distinct LPE spray cycles applied; e.g., 20 spray cycles for HKUST-1
results in a total thickness from LPE spraying of 80 nm, 34 spray cycles for HKUST-1 results in
a total thickness of 115 nm, and 40 spray cycles for HKUST-1 results in a total thickness of 135
nm (see also Figure S1 below).
Figure S1: Thickness of multilayered ITO/HKUST-1 devices for blue (left), green (middle) and
yellow (right) formed using sputtering and spraying processes.
Thin film ITO (SnO2/In2O3) as the high Refractive Index (n) component was sputtered
describing a top down approach from an ITO sputter substrate (with 10 wt% SnO2, Kurt J
Lesker, UK) in a self-built UHV-sputtering chamber. The film was deposited using a r.f.
sputtering setup with a 3″ION’X planar magnetron source (TFC, Grafenberg, DE) mounted on a
standard double-cross recipient equipped with pre-sputter shutter and a sample positioner
allowing for various working distances (150–200 mm) between magnetron and substrate.
2
The crystallographic texture of the ITO films was determined from Bragg-Brentano theta-2theta
diffractograms, using the Harris method [2]. A texture coefficient (TC) is calculated from the
relative intensities of the (hkl) reflections in the diffractograms:
TC( hkl ) 
I ( hkl ) / I 0 ( hkl )
(1)
1 / n I ( hkl ) / I 0 ( hkl )
where I0(hkl) and I(hkl) represent the relative intensity of the (hkl) reflection of a randomly oriented
powder sample (In2O3 COD number 1010341) and that of the measured thin film specimen,
respectively, and n is the number of reflections. Figure S2 shows the 2Theta-theta
diffractograms with the texture coefficients of the different ITO films for the (211), (222), (400)
and (440) reflections. The results show an increase of the In2O3 (440) preferred orientation with
an increase in film thickness. The grain size have been estimated form the full width at half
maximum of the (222) and (440) peaks using the Scherrer equation. Values range between 30
and 50 nm, but no consistent trend could be recognized with an increase of the film thickness.
3
Figure S2: a) 2Theta-theta diffractograms (Bragg-Brentano set-up) of the 5 ITO samples
(artificial y-offset between the samples). b) Texture coefficient (TC) calculations for the (211),
(222), (400) and (440) reflections for the ITO samples. Samples 1-5 correspond to ITO films
with thickness 70 - 1013 nm as per Figure 2.
XRD measurements were also made on the multilayered samples. As shown in Figure S3 the
XRD patterns, a refractive peak at around 21.5° belongs to sputtered ITO (211) thin film [3], and
the intensity of HKUST-1 thin films is increased depending on the increase of film thickness. It
shows that epitaxial growth of crystalline HKUST-1 retains a similar orientation. Figure S3(c-d)
shows the XRD patterns of various layers of HKUST-1 and ITO thin film for the ITO/HKUST-1
system. By analyzing the peak intensity of HKUST-1 (222) and ITO (211), it was found that the
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intensity increase between ITO and HKUST-1 had a gradient of approximately 7.09 (Figure
S3(e)), which corresponds to the density gradient for ITO/HKUST-1 (~ 7.24). Comparing the
coherent scattering domain size of the various layers of HKUST-1, homogeneous thin films were
confirmed which calculated by both Scherrer equation (average of all refractive peaks) and
Williamson-Hall plot by analyzing all of the (002), (220) and (222) reflections [4]. Since the
instrumental contribution to the line broadening has been considered, but no stress/strain
contributions were added, the calculated domain size by Scherrer equation represents a lower
limit. The scattering domain size of HKUST-1 analyzed by Williamson Hall plot shows a quite
similar value of ~ 58 nm for all the different layers.
( B  b) cos 
K
 4 0 sin 
Lvol
(2)
Where B(2θ) is the integral breadth, b the instrumental width, θ the diffraction angle, k is the
Scherrer constant (0.89), λ is 0.15406 nm (Cu Kα1), Lvol the domain Size, and ε0 is the lattice
constant mismatch.
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Figure S3: Out-of-plane XRD analysis of the ITO/HKUST-1 multilayered thin-films: XRD
patterns of (a) various thickness of HKUST-1 SURMOF thin films deposited on ITO substrate
(5th layer), and (b) sputtered ITO and Si substrate; XRD patterns of various layers of (c)
HKUST-1 and (d) ITO thin film for the ITO/HKUST-1 system; (e) comparing the intensity of
the various layers of HKUST-1 and ITO thin film which were taken from (c)-(d), the lines are
corresponding to the linear fit of the intensity respectively; (f) coherent scattering domain size
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Lvol of the various layers of HKUST-1 thin films calculated by the Scherrer equation and
Williamson-Hall plot.
Spectroscopic ellipsometry (SE) analyses have been performed using a Woollam M-44
ellipsometer at a fixed incidence angle of 75.0° on Au-wafer substrates, in the range 400–800
nm. Modeling, fitting, and regression of the ellipsometric data were performed using the VASE
software provided by the manufacturer. Table S1 compares the refined data for the optical
thickness from SE measurements with SEM measurements in regard to the used thickness from
LPE spraying of 10, 20, 30, 40 and 60 layers of HKUST-1.
Table S1: OT (optical thickness) from SE measurements where MSE is the mean squared error,
and PT (physical thickness) from SEM images, for determination of the HKUST-1 film
thickness.
HKUST-1 samples
OT (SE)
SE MSE
PT (SEM)
10 layers
37.8 nm
6.1
40.9 nm
20 layers
75.0 nm
5.8
-
30 layers
105.6 nm
5.0
108.8 nm
40 layers
130.0 nm
5.2
-
60 layers
192.6 nm
3.3
195.6 nm
Morphology studies were performed to check the continuity, compactness, and homogeneity of
the single layered as well as multi-layered SURMOF thin films, as well as to detect possible
meso/macro porosity within the epitaxial grown SURMOF coatings. Therefore a ZEISS
(Gemini®-Series) SEM operated at 3.5-5 kV for SURMOF and ITO thin films on silicon
substrates on an Al-SEM cross-section holder was utilized for SEM imaging (Figure 1, S4 and
S7). The SEM images in Figure 3 were obtained using a Hitachi S4800 high-resolution
microscope at 1.5 kV. AFM investigations (Figure S5) of ITO and HKUST-1 films were
performed using tapping mode cantilevers (Mikromasch, Estonia) with a commercial AFM
system (NT-MDT, Moscow). RMS roughness values are provided in Table S2.
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Figure S4. HR-SEM micrographs of single layered HKUST-1 thin films; (a) 10 layers HKUST1 = 40.9 nm, (b) 30 layers HKUST-1 108.8 nm and (c) 60 layers HKUST-1 195.6 nm.
Nanoindentation measurements were performed using a Ubi-1 nanoindenter (Hysitron,
Minneapolis) under load control. For indentation measurements at applied forces less than 500
μN a ramped load function was used with load, hold, and unload segment times each of 5 s. For
10 mN indents, a constant strain rate (0.05 s-1) loading segment was used, with hold time of 10 s,
and unloading time of 5 s. For all measurements transducer drift at a pre-load value of 2 μN was
taken into account through 60 s monitoring and 30 s drift analysis. A diamond Berkovich probe
(Synton-MDP AG, Nidau, Switzerland) was calibrated prior to use using both reciprocal imaging
using an TGT1 test grating (NT-MDT) and indentation calibration with a fused-quartz standard
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sample (CSM Instruments SA, Peseux, Switzerland). The calibration procedure was then
replicated after the measurement set to check for any damage at the tip apex.
Figure S5. AFM tapping mode images of ITO (top and middle) and HKUST-1 (bottom). Scans
show increasing film thickness (samples 01 to 05) from left to right.
Table S2: RMS roughness (nm) for AFM images in Figure S5. Values generated using a cut-off
of 0.02, line length 10 μm, line thickness 128 pixels, and BSpline interpolation.
01
02
03
04
05
ITO (10х10μm2)
0.3
0.3
0.5
0.7
0.8
ITO (1х1μm2)
0.5
0.6
0.8
0.8
1.1
HKUST-1 (10х10μm2)
2.0
2.2
2.0
1.4
2.3
The elastic indentation of multilayered coatings was simulated using commercially available
FilmDoctor software (Sächsisches Institut für Oberflächenmechanik, Ummanz, Germany). Both
500 μN and 10 mN Berkovich indents were simulated using a conical indenter with an equivalent
cone angle of 70.3° in order to appropriately model the contact area for a Berkovich indenter as
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previously discussed in literature [5]. Experimentally determined inputs (film thickness and
elastic modulus) were utilized, along with Poisson’s ratios from literature as described in the
main text. For all simulations, 250 points were utilized in both x and z directions.
Figure S6. Scatter plot of reduced Young’s modulus plot against normalized contact depth for
hybrid multilayer (ML) films with 5 bilayers (a). Simulations for the elastic indentation of multilayered samples at applied load of 500 μN (b). Shown are von Mises stress distributions, and
strain distributions normal to the indentation axis (inset).
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Figure S7. SEM micrographs for 5 bilayers 1D-PBG HKUST-1/ITO blue (top), green (middle),
and yellow (bottom).
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References
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H.K. Arslan, O. Shekhah, J. Wohlgemuth, M. Franzreb, R.A. Fischer, and C. Wöll, Adv. Funct. Mater. 21,
4228 (2011).
2.
G.D. Harris, Philos.Mag. 43, 113 (1952).
3.
E. Terzini, P. Thilakan, and C. Minarini, Mater. Sci. Eng., B 77, 110 (2000).
4.
H.P. Klug, L.E. Alexander, X-Ray Diffraction Procedures, Wiley, New York, (1954).
5.
A.C. Fischer-Cripps, J. Mater. Res. 25, 927 (2011).
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