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Vertically Aligned Nanopatterns of Amine‐Functionalized Ti 3 C 2 MXene via
Soft Lithography
Article in Advanced Materials Interfaces · August 2020
DOI: 10.1002/admi.202000424
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Vertically Aligned Nanopatterns of Amine-Functionalized
Ti3C2 MXene via Soft Lithography
Tae-Eun Song, Hwajin Yun, Yong-Jae Kim, Ho Seung Jeon, Kyungryul Ha, Hee-Tae Jung,
Hee Han, Yury Gogotsi, Chi Won Ahn,* and Yonghee Lee*
ion intercalation to their full potential.[8]
When considering stacking 2D MXene
flakes, parallel alignment is preferred over
vertical alignment with respect to the supporting substrate because of the flakes’
large lateral size compared to its ultrathin
layer thickness of ≈1 nm. MXene films
with vertical alignment are warranted for
specific applications such as ones that
require high throughput with extremely
narrow pathways for ion transport, as
well as sensors and plasmonic devices.
Inducing vertical alignment of 2D sheets
remains quite challenging, but was done
by using liquid-crystalline MXene.[9]
Nanoscale patterning technology of
MXenes is necessary for microminiaturization, device integration, and maximization of device performance, beyond what
can be achieved using inkjet or other
printing methods.[10,11] Previous studies
exploring microscale thin-film patterning
of MXenes have been conducted;[12] however, studies based on nanopatterns with aligned MXene
stacking have not yet been reported. Because MXenes are difficult to etch as a consequence of their composition; technology
has not been developed for patterning MXene at the micro­meter
to nanometer scale. High-resolution and high-aspect-ratio
nanostructure patterning technology is valuable in various
fields, such as organic electronics, optoelectronics, biosensors,
energy storage, display devices, and plasmonics.[13–24] Thus,
alignment control of stacked MXene with nanoscale patterning
is critical for tuning the properties of MXene films for specific
applications. Recently, Zheng’s group published a method for
microscale patterning of MXenes with vertical alignment.[25]
They fabricated anti-T shaped random micropatterns with
vertically aligned MXene flakes via vacuum filtration utilizing
a metal screen mesh. Through this process they dramatically
enhanced the electrochemical properties of the MXene film but
were unable to fabricate high-resolution nanopatterns with vertically aligned MXene flakes.
“Soft lithography” refers to nonphotolithographic methods
when forming high-quality microstructures and nanostructures. This process is becoming an attractive approach to
fabricating microstructures and nanostructures that cannot
be prepared photolithographically. Polydimethylsiloxane
(PDMS) has emerged as the material of choice for the rapid,
low-cost fabrication of microfluidic channels because of its
numerous advantages which include high transparency and
Thin films of well-stacked two-dimensional MXene flakes have been used
in various applications, especially in sensors and microscale energy storage
devices, such as micro-supercapacitors. Miniaturization and integration of
devices, as well as maximization of device performance require nanoscale
patterning of MXene, beyond what can be achieved using inkjet or screen
printing. However, nanoscale patterning technology for MXene is yet to be
developed. In the present work, a simple fabrication method is demonstrated
for manufacturing Ti3C2Tx MXene films with vertically aligned nanopatterns
via soft lithography. This process involves polydimethylsiloxane (PDMS)
stamping with line-patterned PDMS molds. The feature size of the vertical
line patterning of MXene is controlled with the nanometers accuracy by
swelling of the PDMS mold by toluene, which also guides vertical alignment
of MXene flakes. As a result, vertically aligned MXene nanopatterns are
fabricated with a width of ridges less than 200 nm and 2-µm regular spacing
between the ridges. The oleylamine-functionalized MXene flakes are also
developed for better dispersion in toluene, providing a general protocol to
fabricate MXene dispersions in nonpolar solvents.
1. Introduction
MXenes, a large family of two-dimensional (2D) transitionmetal carbides and nitrides, are increasingly attracting attention
because of their excellent performance in energy storage,[1–3]
electromagnetic interference (EMI) shielding,[4] heating,[5] and
sensing applications.[6,7] MXene films perform well within
energy applications such as batteries and capacitors, especially where well-formed interlayer spaces can be utilized for
Dr. T.-E. Song, H. Yun, Y.-J. Kim, Dr. H. S. Jeon, K. Ha, Dr. H. Han,
Dr. C. W. Ahn, Dr. Y. Lee
National Nano Fab Center (NNFC)
Daejeon 34141, South Korea
E-mail: cwahn@nnfc.re.kr; yhlee@nnfc.re.kr
Y.-J. Kim, Prof. H.-T. Jung, Prof. Y. Gogotsi
Department of Chemical and Biomolecular Engineering (BK-21 Plus)
Korea Advanced Institute of Science and Technology (KAIST)
Daejeon 34141, South Korea
Prof. Y. Gogotsi
Department of Materials Science and Engineering
and A.J. Drexel Nanomaterials Institute
Drexel University
Philadelphia, PA 19104, USA
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/admi.202000424.
DOI: 10.1002/admi.202000424
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biocompatibility. Micromachining,[26] microcontact printing,[27]
microtransfer molding,[28] micromolding in capillaries
(MIMIC),[29] and solvent-assisted micromolding (SAMIM)[30]
are examples of methods used to fabricate structures on the
submicrometer scale. Recently, solute–solvent separation soft
lithography (3S soft lithography) has been reported.[31] Furthermore, Whitesides et al. demonstrated that the extent of PDMS
swelling in solvents is determined by the solubility of the solvent in PDMS and, in particular, by the Hildebrand solubility
parameters of the solvents and PDMS.[32] Swelling associated
with PDMS is commonly considered an undesirable characteristic in many applications. Nonpolar solvents such as toluene
and hexane swell PDMS substantially and induce deformation of the PDMS structure, degrade device performance, and
induce the use of PDMS in solvent-manipulation applications.
This swelling behavior is a noteworthy disadvantage to using
PDMS for soft lithography. However, we hypothesized that
swelling and swelling-induced deformation of a PDMS mold
could offer an opportunity to control the orientation of 2D
flakes and produce a vertical line pattern of MXene, offering a
new approach to fabricating nanopatterns.
In the present work, we demonstrate a simple and comprehensive method for fabricating high-resolution nanopatterns
with vertical alignment of Ti3C2Tx (T stand for surface terminations, such as O, OH, and F) MXene flakes. The developed
method is not based on photolithography and thus does not
require an etchant; etchants are undesirable because they can
oxidize Ti3C2Tx. Soft lithography via stamping of PDMS molds
was used to produce MXene patterns. Toluene was used to disperse MXene, enabling the MXene solution to infiltrate line patterns on the PDMS mold and induce PDMS swelling to guide
the vertical alignment of the MXene flakes into the nanoscale
space. However, because the pristine Ti3C2Tx flakes have OH−,
F−, or O-terminations on their surface,[33] they are hydrophilic
and do not disperse in toluene.[34] Besides, MXene flakes may
oxidize in aqueous solution.[5] Therefore, hydrophobic MXene
flakes that can be dispersed in nonpolar solvents are required
for nanoscale patterning by soft lithography using hydrophobic PDMS. For this purpose, we functionalized Ti3C2Tx with
oleylamine (OAm, C18H35NH2), making dispersible in nonpolar
solvents such as toluene and chloroform. As a result, vertically
aligned nanopatterns of MXene were successfully produced by
PDMS-based soft lithography. During the molding process, the
PDMS absorbs toluene and expands, resulting in a nanoscale
guide pattern in which MXene flakes are present. Because of
this guide pattern on a PDMS mold, vertically aligned nanopatterns of MXenes replicated the periodic patterns of the PDMS
mold after drying on the substrate.
2. Results and Discussion
Figure 1 illustrates the overall procedure, including the synthesis of the OAm-functionalized MXene dispersion and the
fabrication of vertically aligned nanopatterns of MXene flakes.
A soft lithography method via stamping of PDMS molds was
used to produce the highly periodic and high-resolution nanopatterns. To prepare the MXene solution for PDMS stamping,
we modified the surface properties of the MXene flakes from
Adv. Mater. Interfaces 2020, 2000424
hydrophilic to hydrophobic by functionalizing them with the
hydrophobic OAm ligand (Figure 1a); the method used to prepare the OAm-modified MXene is detailed in the Experimental
Section (Supporting Information). TEM images and an electron
diffraction (ED) pattern clearly show that the 2D morphology
of MXene was maintained after OAm modification (Figure S1,
Supporting Information). The size of MXene flakes ranged
from 500 nm to 5 µm before sonication (Figure S1a, Supporting
Information). Bigger flakes than the inner space of PDMS
mold (1 µm) are not suitable to form nanoscale patterns, and
we were not able to obtain clean vertically aligned nanopatterns
with those large flakes. Thus, we sonicated the solution for 3
h to obtain MXene flakes smaller than 1 µm (Figure S1d, Supporting Information).
After functionalization of the MXene surface, OAm-functionalized MXene (OAm@Ti3C2Tx) flakes were dispersed in
toluene. The OAm@Ti3C2Tx solution in toluene was dropped
onto a Si wafer, and the PDMS mold was then placed on top
(Figure 1b). Here, we used PDMS molds with a height of 1 µm
and line patterns with a 1 µm width. The PDMS stamp was
sufficiently soft to completely adhere to the substrate under
its own weight; no additional force was needed to achieve conformal contact. Toluene drove the MXene into the line patterns
on the PDMS mold via capillary and pressure effects after the
PDMS stamp was covered (Figure 1c, left). Toluene dissolved
or swelled the surface of the polymer of the PDMS mold.
Thereafter, the grooves of line patterns shrank to the nanoscale
dimensions as the PDMS mold pushed the MXene film horizontally (Figure 1c, center). The MXene film dried as the toluene evaporated, and the PDMS mold maintained conformal
contact with the substrate (Figure 1c, right). After the PDMS
mold was dried and removed, highly periodic and high-aspectratio MXene nanopatterns were formed on the Si wafer. The
overall morphology of the MXene patterns represents a nanostructured negative replica of the relief patterns on the PDMS
mold (Figure 1d). As expected, these MXene patterns included a
vertical alignment of MXene flakes, as shown in Figure 1e.
To prepare the toluene-dispersible MXene flakes, we produced OAm-functionalized MXene and confirmed its dispersibility in several organic solvents (Figure 2 and Figure S2,
Supporting Information). OAm@Ti3C2Tx was synthesized
via an electrostatic adsorption of positively charged amine on
the negatively charged MXene surface.[35] Pristine MXene and
10 mL of OAm were placed in a glass container and stirred at
450 rpm for 24 h at room temperature. After adsorption, excess
of OAm was washed away through centrifugation using ethanol. Toluene was then added to the OAm@Ti3C2Tx sediment.
Finally, we obtained a well-dispersed OAm@Ti3C2Tx solution in
toluene.
Pristine MXene and OAm@Ti3C2Tx films used for measurement of contact angles were prepared by drop-casting a pristine
MXene solution and OAm@Ti3C2Tx solution onto a Si wafer,
which was subsequently dried. Ten microliters of water was
then dropped onto the pristine MXene- and OAm@Ti3C2Tx
-coated wafer, and contact angles of the water drops were measured, showing a change in the hydrophobicity of MXene after
functionalization with OAm (53.1° for pristine MXene and
106.4° for OAm@Ti3C2Tx, Figure 2a,b). Pristine MXene flakes
disperse in water (Figure 2c) and polar organic solvents because
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Figure 1. Schematic of the vertical line patterns of OAm-functionalized hydrophobic 2D MXene. a) MXene combined with OAm is modified from
hydrophilic to hydrophobic because of the long carbon chains of the OAm-functionalized MXene. b) The solution of MXene dispersed in toluene is
dropped onto the substrate and the polydimethylsiloxane (PDMS) mold is placed on top. c) The PDMS mold is swollen by the toluene organic solvent
and shrinks when the toluene evaporates. The vertical MXene line patterns represent a nanostructure of MXene. d) Scanning electron microscopy
(SEM) image of the vertical MXene line patterns of the nanostructures. e) Cross-sectional schematic of the vertical MXene line patterns shown in (d).
of the hydrophilic functional groups (e.g., =O, –OH, and –F)
on their surface.[34] By contrast, OAm@Ti3C2Tx flakes became
hydrophobic because of the long hydrocarbon chains of OAm.
They disperse in toluene and chloroform (i.e., nonpolar organic
solvents), but not in water (Figure 2d, Figure S2, Supporting
Information).
To verify the properties of MXene flakes after surface modification with OAm, we characterized their surface chemistry
before fabrication of the MXene patterns (Figure 3). First, the
change of the MXene surface characteristics after functionalization was confirmed by X-ray photoelectron spectroscopy
(XPS) and Fourier transform infrared (FT-IR) spectroscopy.
These measurements were conducted on MXene films prepared from pristine MXene and OAm@Ti3C2Tx solutions. A
comparison of the XPS survey spectra of MXene and OAm@
Ti3C2Tx reveals that nitrogen (N1s 396 eV ≈403 eV) was present only in OAm@Ti3C2Tx (Figure 3a),[36] meaning that the
N of OAm was adsorbed on the surface of Ti3C2Tx MXene.
N1s intensity of OAm@Ti3C2Tx increased compared to the
Adv. Mater. Interfaces 2020, 2000424
pristine MXene (Figure 3b). It is also seen that the ratio of
N1s over other elements of OAm@Ti3C2Tx increased, while
the ratio of F1s decreased (Figure S4, Supporting Information). After modification of MXene with OAm, CH2 and CH3
bonds increased in the C1s peak (Figure S3a,b, Supporting
Information) and Ti-OH and Ti-H2O contributions to the O1s
peak decreased, suggesting the intercalation of OAm ligands
between MXene layers (Figure S3c,d, Supporting Information). It is also confirmed that the F1s intensity of OAm@
Ti3C2Tx over other elements decreased compared to the pristine MXene, indicating that detachment of fluorine occurred
during functionalization with OAm (Figures S3e,f and S4,
Supporting Information). The changes of TiO2 and Ti-X (Ti-C,
TixOy, Ti-N) bonds are seen in the Ti2p peak before and after
modification of MXene with OAm (Figures S3g,h and S4,
Supporting Information). A peak around 459 eV assigned to
TiO2 slightly increased after OAm functionalization, however,
as seen in TEM images (Figure S1, Supporting Information),
the oxidation state of the surface of MXene has not changed
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Figure 2. Contact angle of pristine MXene (a) and MXene modified
with OAm (OAm@Ti3C2Tx) (b). Dispersion test of pristine MXene and
OAm@Ti3C2Tx in water (c) and toluene (d).
much. It is known that MXene can degrade in the aqueous
dispersion, however, the oxidation process is retarded in
organic solvents. Also, passivation of the MXene surface by
OAm ligand can contribute to the protection of MXenes from
oxidation.[37]
Adsorption of OAm on the Ti3C2Tx MXene surface was confirmed by FT-IR analysis (Figure 3c).[38] The intensities of the
absorption bands corresponding to –OH groups on the MXene
surface at 3485 and 3644 cm−1 are high in the spectrum of
the pristine MXene, but decrease in the OAm-functionalized
MXene. In addition, the absorption band corresponding to N–H
at 3300 cm−1, which is not observed in the spectrum of the pristine MXene, is prominent in the spectrum of OAm@Ti3C2Tx,
showing intermolecular interactions between OAm and active
terminations on the surface of MXene by hydrogen bonding
and/or van der Waals forces.[39,40]
Lastly, X-ray diffraction (XRD) was performed to confirm the
effect of the OAm on MXene flakes on the interlayer spacing of
stacked MXene films (Figure 3d). The XRD patterns also show
the result of the functionalization of MXene with OAm.[41,42]
The shift of the (002) peak from 7.08° to 6.12° indicates that the
interlayer spacing of MXene increased from 1.25 to 1.45 nm,
due to adsorption of OAm. The OAm, which has a long hydrocarbon chain, is bound to the Ti3C2 MXene surface, leading to a
larger gap between the MXene layers.
After producing toluene-dispersible OAm@Ti3C2Tx, we
attempted fabrication of MXene patterns via stamping with
line-patterned PDMS molds. After patterning via PDMS
stamping, analyses by optical microscopy (OM), atomic force
microscopy (AFM), and scanning electron microscopy (SEM)
Figure 3. X-ray photoelectron spectroscopy (XPS) survey spectra (a), N1s region (b), Fourier transform infrared (FT-IR) spectra (c), and X-ray diffraction
(XRD) patterns (d) of MXene and OAm@Ti3C2Tx. Interlayer spacing increased from 1.25 to 1.45 nm after functionalization with OAm.
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Figure 4. Morphological analysis of MXene nanopatterns constructed on the Si substrate using polydimethylsiloxane (PDMS) stamping: a) optical
microscopy image; b) atomic force microscopy (AFM) image; c) low-magnification, and d) high-magnification scanning electron microscopy (SEM)
images of MXene nanopatterns with the 2 µm periodicity obtained by dropping and pressing; and e) low-magnification and f) high-magnification
cross-sectional SEM images of MXene nanopatterns with a height of ≈600 nm.
were conducted to confirm the morphology of the patterned
films and structural features of the MXene patterns (Figure 4).
The OM images show MXene nanopatterns on a large area
(Figure 4a). We obtained height and width profiles from the
AFM image in Figure 4b; these profiles provide information
about the feature size of the MXene nanopatterns. The height
and periodicity of the patterns are approximately 600 nm and
2 µm, respectively. SEM images were obtained using a dualbeam focused ion beam (FIB) SEM system for cross-sectional
SEM images. In the top-view observations, dark-gray regions
are the MXene film on the Si wafer and relatively bright lines
are MXene nanopatterns formed by PDMS stamping. These
images clearly show highly periodic MXene line patterns with
≈2 µm periodicity (Figure 4c) and a high-resolution MXene pattern (Figure 4d). We obtained the corresponding SEM crosssectional images to further characterize the structural features
of the MXene nanopatterns. A Pt layer was deposited to protect
the MXene patterns during the FIB process (Figure 4e,f). Dark
regions representing the MXene pattern are observed between
the Pt layer and the substrate. The cross-sectional SEM image
clearly shows MXene nanopatterns constructed on MXene films
with closely packed MXene flakes (Figure 4f). However, we
could not confirm the stacking directions of the MXene flakes
in each pattern because of the limited SEM resolution. Interestingly, the constructed MXene patterns show 100–200 nm wide
ridges with 2 µm periodicity from peak to peak in the pattern,
even though we used a 1 × 1 µm line pattern of the PDMS mold
with 2 µm of pitch from center to center of the lines. Moreover,
the overall morphology of the patterned MXene structures represents a nanostructured, negative replica of the relief pattern
Adv. Mater. Interfaces 2020, 2000424
on the PDMS mold. From these results, we inferred that the
shape resulting from swelling-induced deformation of the line
patterns in the PDMS mold was transferred to MXene nanopattern on a silicon wafer in a single step. However, no distinct nanopattern is formed in the case of the pristine MXene
dispersed in water and most of the MXene solution flows out
of the PDMS mold when the PDMS mold is placed on the
wafer. Water poorly wets PDMS[32] and the transferred pattern of MXene is therefore irregular (Figure S5, Supporting
Information).
To further investigate how MXene flakes are stacked in vertically aligned MXene patterns, TEM observations were conducted using cross-sectional thin-film samples of vertically
aligned MXene patterns (Figure 5). We prepared this crosssectional thin-film sample using a dual-beam FIB system after
cross-sectional SEM observation. A low-magnification TEM
image shows a vertically aligned MXene pattern (Figure 5a
and Figure S6, Supporting Information). It exhibits a ≈2 µm
pitch size between two peaks of the aligned MXene patterns
and a height of ≈500 nm. A high-magnification TEM image
(Figure 5b) shows that the upper region of the vertically aligned
MXene patterns have well-stacked layers, whereas bent layers
and empty spaces are formed at the bottom region of the vertically aligned MXene pattern. Well-stacked MXene flakes are
parallel to the substrate at the bottom of the vertically aligned
MXene pattern, near the Si-wafer substrate. High-magnification TEM images clearly show these well-stacked MXene layers
with bent MXene layers at the top of each ridge (Figure 5c)
and stacked parallel MXene layers at the bottom (Figure 5d).
Well-stacked layers (black dashed lines in Figure 5c) and bent
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Figure 5. Cross-sectional TEM analysis of a vertically aligned MXene pattern. a) Low-magnification TEM image of cross-sectional MXene pattern prepared by FIB. b) High-magnification TEM image of a vertically aligned MXene pattern corresponding to the white boxed region in Figure 5a (inset is
a schematic illustration). c,d) High-magnification TEM images of MXene layers in the vertically aligned MXene pattern; the images correspond to the
boxed areas in Figure 5b. e) Selected-area TEM image and f) electron diffraction (ED) pattern corresponding to the circled area in Figure 5a.
layers (red dashed lines in Figure 5c) show interlayer spacings
of approximately 3.6 and 18 nm, respectively. We assume that
the larger layer spacing than that in pristine stacked MXene
was a consequence of the long chain length of OAm (Figure S6,
Supporting Information).[43] In addition, different orientations
of stacked layers were confirmed by analysis of the ED pattern in the TEM image in Figure 5e. We observed tilted peaks
along the azimuthal angle (red arrow) of the peak in the red
circle; they likely arise from the different orientation of the
MXene layers in the vertically aligned pattern (Figure 5f). It was
expected that the ED pattern would have a circular arc shape
due to various orientations of stacked MXene layers, but we
were not able to obtain it, probably due to non-random orientation of MXene flakes relative to the beam. The patterned region
was too small for achieving good alignment between electron
beam and sample, and the TEM sample was bent during thinning by FIB (Figure S7, Supporting Information). We inferred
that the variation of the interlayer spacing in well-stacked layers
was induced by the relatively long chain length of OAm on the
MXene flakes[35] and that variation of the interlayer spacing in
bent layers was induced by the formation of empty space as a
consequence of (1) the MXene flakes being larger than the pattern size of the PDMS mold and (2) rapid solvent permeation
from the MXene solution to the PDMS mold. After the MXene
Adv. Mater. Interfaces 2020, 2000424
solution was dropped onto the substrate, large MXene flakes
were deposited; these deposited MXene flakes and dispersible
solvent infiltrated the PDMS pattern through rapid solvent
permeation from the MXene solution to the contacted PDMS
mold. We assume that the shape of the grooves in PDMS
changed from square to triangular in cross-section as a result
of PDMS swelling in toluene. Because of this shape change,
we obtained a vertically aligned pattern with decreasing ridge
width from the bottom (≈200 nm) to the top (less than 100 nm).
The height of the vertical ridges was approximately 600 nm,
which is less than the PDMS groove depth of 1 µm.
This approach can replace masking and etching when manu­
facturing arrays of posts and other patterns for plasmonic
devices,[44] EMI shielding, current collectors for batteries and
supercapacitors and other devices. It may also be applicable to
other 2D materials. Various MXene films patterned by PDMSbased soft lithography using the swelling-induced deformation
effect can be realized various shapes of PDMS stamps. Moreover, we expect that the vertically aligned patterns of MXenes can
provide a high-ionictransport channels. Thus, we anticipate that
vertical MXene layers on nanoscale active materials may lead to
more efficient electrodes, potentially opening a path for the fabrication of microelectronic circuits using MXene solutions and
accelerating the commercialization of MXene-based technology.
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3. Conclusion
Ti3C2Tx was functionalized with nonpolar OAm ligands and
subsequently dispersed in toluene to prepare ink suitable for
soft lithography. This ink was used for fabrication of nanopatterns by PDMS stamping under ambient conditions. PDMS
stamping enables the formation of patterns and micro/nanostructures with 2D MXene flakes without photolithography,
thus eliminating the use of etchants and eliminating possibility
of oxidation and degradation of MXene. Regularly spaced ridges
with vertical alignment of MXene flakes were produced using
the swelling-assisted PDMS stamping. The developed method
should be applicable to other 2D materials.
(MSIT), and this research was also supported by NRF-2015M3A7B6027973,
and NRF- 2015M3A7B7046618 of the National Research Foundation (NRF)
of Korea funded by the Ministry of Science and ICT, Korea.
Conflict of Interest
The authors declare no conflict of interest.
Keywords
MXene, nanopatterns, oleylamine, polydimethylsiloxane (PDMS), soft
lithography, swelling, vertical alignment
Received: March 9, 2020
Revised: July 4, 2020
Published online:
4. Experimental Section
Functionalization of MXene with OAm: First, pristine MXene was
synthesized by solid–liquid reaction.[45,46] The surface modification of
MXene was performed by reacting MXene with OAm. MXene (10 mg)
was dispersed in OAm (10 mL), and the mixture was vortexed for
3 min. This solution was then stirred continuously (450 rpm) for
24 h at room temperature. After modification of MXene, the obtained
OAm@Ti3C2Tx was washed with ethanol (30 mL) to remove residual
OAm. The washing solution was centrifuged at 4000 rpm for 5 min,
and the OAm@Ti3C2Tx product was collected after the supernatant was
discarded. The OAm@Ti3C2Tx was then dispersed in toluene (3 mL)
under ultrasonication for 3 h.
Preparation of Polydimethylsiloxane (PDMS) Mold Pattern: To prepare a
master pattern, we fabricated an array of line shapes with a periodicity of
2 µm and width of 1 µm in Si using e-beam lithography. A PDMS mold
was replicated from the Si master. The PDMS was prepared by mixing
a PDMS prepolymer (Sylgard 184A/B = 10:1, Dow Corning) and pouring
the mixed PDMS onto the Si master. After bubbles were removed from
the mixture, the PDMS mold was cured at 80 °C for 2 h.
Fabrication of Patterned MXene Films Using Soft Lithography: The
solution was prepared by mixing the MXene with toluene as a solvent.
The solution was then dropped onto the substrate. The cured PDMS
mold with the aforementioned topographic features was placed and
pressed onto the MXene solution. Conformal contact was maintained
under additional pressure for 2 h, which induced the formation of
MXene nanopatterned structures.
Characterization: A Helios NanoLab (FEI) dual-beam FIB/SEM
system was used for SEM imaging (surface and cross-section) and
cross-sectional TEM samples preparation. TEM images were obtained
as bright field images using a JEOL JEM-3010 microscope operating
at 300 kV. Contact angle images were obtained with a Phoenix
300 Plus (SEO Co., Ltd.). FT-IR spectra were acquired with a Bruker
Alpha spectrometer. XPS was carried out with a Kratos Axis-Supra, and
XRD patterns were obtained with a RIGAKU Smartlab.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
T.-E.S., H.Y., and Y.-J.K. contributed equally to this work. Collaboration
between NNFC and Drexel University was supported by the Global
Research and Development Center Program (NNFC-Drexel-SMU FIRST
Nano Co-op Centre, 2015K1A4A3047100), through the National Research
Foundation of Korea (NRF) funded by the Ministry of Science and ICT
Adv. Mater. Interfaces 2020, 2000424
[1] M. Naguib, M. Kurtoglu, V. Presser, J. Lu, J. Niu, M. Heon,
L. Hultman, Y. Gogotsi, M. W. Barsoum, Adv. Mater. 2011, 23, 4248.
[2] B. Anasori, M. R. Lukatskaya, Y. Gogotsi, Nat. Rev. Mater. 2017, 2,
16098.
[3] X. Zhang, Z. Zhang, Z. Zhou, J. Energy Chem. 2018, 27, 73.
[4] F. Shahzad, M. Alhabeb, C. B. Hatter, B. Anasori, S. Man Hong,
C. M. Koo, Y. Gogotsi, Science 2016, 353, 1137.
[5] Y. Lee, S. J. Kim, Y.-J. Kim, Y. Lim, Y. Chae, B.-J. Lee, Y.-T. Kim,
H. Han, Y. Gogotsi, C. W. Ahn, J. Mater. Chem. A 2020, 8, 573.
[6] S. J. Kim, H. J. Koh, C. E. Ren, O. Kwon, K. Maleski, S. Y. Cho,
B. Anasori, C. K. Kim, Y. K. Choi, J. Kim, Y. Gogotsi, H. T. Jung, ACS
Nano 2018, 12, 986.
[7] J. Liu, X. Jiang, R. Zhang, Y. Zhang, L. Wu, W. Lu, J. Li, Y. Li,
H. Zhang, Adv. Funct. Mater. 2019, 29, 1807326.
[8] J. Nan, X. Guo, J. Xiao, X. Li, W. Chen, W. Wu, H. Liu, Y. Wang,
M. Wu, G. Wang, Small 2019, 1902085, https://onlinelibrary.wiley.
com/doi/abs/10.1002/smll.201902085.
[9] Y. Xia, T. S. Mathis, M. Zhao, B. Anasori, A. Dang, Z. Zhou, H. Cho,
Y. Gogotsi, S. Yang, Nature 2018, 557, 409.
[10] X. Jiang, W. Li, T. Hai, R. Yue, Z. Chen, C. Lao, Y. Ge, G. Xie, Q. Wen,
H. Zhang, npj 2D Mater. Appl. 2019, 3, 34.
[11] Y. Zhang, X. Jiang, J. Zhang, H. Zhang, Y. Li, Biosens. Bioelectron.
2019, 130, 315.
[12] B. Xu, M. Zhu, W. Zhang, X. Zhen, Z. Pei, Q. Xue, C. Zhi, P. Shi,
Adv. Mater. 2016, 28, 3333.
[13] M. Kim, Y. Huang, K. Choi, C. H. Hidrovo, Microelectron. Eng. 2014,
124, 66.
[14] T. E. Song, C. W. Ahn, H. J. Jeon, Langmuir 2017, 33, 8260.
[15] X. Rui, H. Tan, Q. Yan, Nanoscale 2014, 6, 9889.
[16] S. Y. Cho, H. W. Yoo, J. Y. Kim, W. Bin Jung, M. L. Jin, J. S. Kim,
H. J. Jeon, H. T. Jung, Nano Lett. 2016, 16, 4508.
[17] B. Päivänranta, H. Merbold, R. Giannini, L. Büchi, S. Gorelick,
C. David, J. F. Löffler, T. Feurer, Y. Ekinci, ACS Nano 2011, 5, 6374.
[18] R. W. Siegel, Mater. Sci. Eng., B 1993, 19, 37.
[19] E. Boakye, L. R. Radovic, K. Osseo-Asare, J. Colloid Interface Sci.
1994, 163, 120.
[20] Y. Wang, A. Suna, J. McHugh, E. F. Hilinski, P. A. Lucas,
R. D. Johnson, J. Chem. Phys. 1990, 92, 6927.
[21] E. Menard, M. A. Meitl, Y. Sun, J. U. Park, D. J. L. Shir, Y. S. Nam,
S. Jeon, J. A. Rogers, Chem. Rev. 2007, 107, 1117.
[22] H. B. Lee, C. W. Bae, L. T. Duy, I. Y. Sohn, D. Il Kim, Y. J. Song,
Y. J. Kim, N. E. Lee, Adv. Mater. 2016, 28, 3069.
[23] D. A. Zuev, S. V. Makarov, I. S. Mukhin, V. A. Milichko, S. V. Starikov,
I. A. Morozov, I. I. Shishkin, A. E. Krasnok, P. A. Belov, Adv. Mater.
2016, 28, 3087.
2000424 (7 of 8)
© 2020 Wiley-VCH GmbH
www.advancedsciencenews.com
www.advmatinterfaces.de
[24] F. Gentile, L. Ferrara, M. Villani, M. Bettelli, S. Iannotta,
A. Zappettini, M. Cesarelli, E. Di Fabrizio, N. Coppedè, Sci. Rep.
2016, 6, 18992.
[25] M. Lu, W. Han, H. Li, H. Li, B. Zhang, W. Zhang, W. Zheng, Adv.
Mater. Interfaces 2019, 6, 1900160.
[26] N. L. Abbott, J. P. Folkers, G. M. Whitesides, Science 1992, 257, 1380.
[27] A. Kumar, H. A. Biebuyck, G. M. Whitesides, Langmuir 1994, 10,
1498.
[28] X.-M. Zhao, Y. Xia, G. M. Whitesides, Adv. Mater. 1996, 8, 837.
[29] E. Kim, Y. Xia, G. M. Whitesides, Nature 1995, 376, 581.
[30] E. King, Y. Xia, X. Zhao, G. M. Whitesides, Adv. Mater. 1997, 9, 651.
[31] X. Dai, H. Xie, J. Micromech. Microeng. 2015, 25, 095013.
[32] J. N. Lee, C. Park, G. M. Whitesides, Anal. Chem. 2003, 75, 6544.
[33] M. Ashton, K. Mathew, R. G. Hennig, S. B. Sinnott, J. Phys. Chem. C
2016, 120, 3550.
[34] K. Maleski, V. N. Mochalin, Y. Gogotsi, Chem. Mater. 2017, 29, 1632.
[35] M. Ghidiu, S. Kota, J. Halim, A. W. Sherwood, N. Nedfors, J. Rosen,
V. N. Mochalin, M. W. Barsoum, Chem. Mater. 2017, 29, 1099.
[36] J. Halim, K. M. Cook, M. Naguib, P. Eklund, Y. Gogotsi, J. Rosen,
M. W. Barsoum, Appl. Surf. Sci. 2016, 362, 406.
[37] X. Jiang, A. V. Kuklin, A. Baev, Y. Ge, H. Ågren, H. Zhang,
P. N. Prasad, Phys. Rep. 2020, 848, 1.
Adv. Mater. Interfaces 2020, 2000424
View publication stats
[38] A. Vahidmohammadi, J. Moncada, H. Chen, E. Kayali, J. Orangi,
C. A. Carrero, M. Beidaghi, J. Mater. Chem. A 2018, 6, 22123.
[39] Q. Xue, H. Zhang, M. Zhu, Z. Pei, H. Li, Z. Wang, Y. Huang,
Y. Huang, Q. Deng, J. Zhou, S. Du, Q. Huang, C. Zhi, Adv. Mater.
2017, 29, 1604847.
[40] L. Gao, C. Li, W. Huang, S. Mei, H. Lin, Q. Ou, Y. Zhang, J. Guo,
F. Zhang, S. Xu, H. Zhang, Chem. Mater. 2020, 32, 1703.
[41] N. C. Osti, M. Naguib, A. Ostadhossein, Y. Xie, P. R. C. Kent,
B. Dyatkin, G. Rother, W. T. Heller, A. C. T. Van Duin, Y. Gogotsi,
E. Mamontov, ACS Appl. Mater. Interfaces 2016, 8, 8859.
[42] Y. Tian, W. Que, Y. Luo, C. Yang, X. Yin, L. B. Kong, J. Mater. Chem.
A 2019, 7, 5416.
[43] Y. Dong, Z. S. Wu, S. Zheng, X. Wang, J. Qin, S. Wang, X. Shi,
X. Bao, ACS Nano 2017, 11, 4792.
[44] K. Chaudhuri, M. Alhabeb, Z. Wang, V. M. Shalaev, Y. Gogotsi,
A. Boltasseva, ACS Photonics 2018, 5, 1115.
[45] Y. Chae, S. J. Kim, S. Y. Cho, J. Choi, K. Maleski, B. J. Lee, H. T. Jung,
Y. Gogotsi, Y. Lee, C. W. Ahn, Nanoscale 2019, 11, 8387.
[46] C. J. Zhang, S. Pinilla, N. McEvoy, C. P. Cullen, B. Anasori, E. Long,
S. H. Park, A. Seral-Ascaso, A. Shmeliov, D. Krishnan, C. Morant,
X. Liu, G. S. Duesberg, Y. Gogotsi, V. Nicolosi, Chem. Mater. 2017,
29, 4848.
2000424 (8 of 8)
© 2020 Wiley-VCH GmbH