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Archimedean Tilings and Hierarchical Lamellar Morphology Formed by Semicrystalline Miktoarm Star Terpolymer Thin Films Karim Aissou, Wonsang Kwon, muhammad mumtaz, Segolene Antoine, Mireille Maret, Giuseppe Portale, Guillaume Fleury, and Georges Hadziioannou ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.5b06728 • Publication Date (Web): 29 Mar 2016 Downloaded from http://pubs.acs.org on March 30, 2016

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Archimedean Tilings and Hierarchical Lamellar Morphology Formed by Semicrystalline Miktoarm Star Terpolymer Thin Films

Karim Aissou,1*# Wonsang Kwon,1# Muhammad Mumtaz,1,2 Ségolène Antoine,1 Mireille Maret,3 Giuseppe Portale,4 Guillaume Fleury,1* and Georges Hadziioannou1 1

Laboratoire de Chimie des Polymères Organiques, CNRS - ENSCPB - Université de Bordeaux, 16 Avenue Pey-Berland, F-33607 Pessac Cedex, France

2

ARKEMA, Groupement de Recherches de Lacq, RN 117, BP 34, F-64170 Lacq Cedex, France

3

Laboratoire de Science et Ingénierie des Matériaux et Procédés, CNRS - IPB, F-38000, France 4

#

Macromolecular Chemistry & New Polymeric Materials, Zernike Institute for Advanced Materials, Nijenborgh 4, NL-9747 AG Groningen, the Netherlands

These two authors contributed equally to this work.

E-mail: [email protected], [email protected] Keywords: 3-miktoarm star terpolymer, directed self-assembly, hierarchical lamellar pattern, Archimedean tiling, topographical substrate.

Abstract: 3-Miktoarm star terpolymer architecture provides a window of opportunity in the design of complex “three-colored” patterns at the nanometer scale. Here, the directed selfassembly (DSA) of 3-miktoarm star terpolymer (poly(1,1-dimethyl silacyclobutane)-armpolystyrene-arm-poly(D,L lactide acid)) (PDMSB-arm-PS-arm-PLA, noted hereafter 3µDSL) into a hierarchical lamellar morphology is described. Excellent orientational order has been achieved by templating the asymmetric hierarchical lamellar morphology with topographical substrates. Increasing the PLA volume fraction leads to the formation of a hexagonal [6.6.6] Archimedean tiling which coexists with a metastable square symmetry [4.8.8] tiling stabilized by the step between terraces. Stability of the [6.6.6] tiling over the [4.8.8] one is also demonstrated with GISAXS measurements.

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Since the first synthesis of 3-miktoarm star terpolymers (3 µ-ABC) with three immiscible blocks in 1992,1 several 3 µ-ABC terpolymers have been prepared using various controlled polymerization techniques, including chlorosilane2 and macromonomer3 methods or midfunctionalized diblock copolymers4 and heterofunctional core molecules5 strategies. The 3miktoarm star terpolymer material is one of the rare materials which gives access to 2D Archimedean tiling patterns consisting of one or more type of regular polygon filling the plane without gaps. In bulk, several Archimedean tilings obtained from 3 µ-ABC have been reported6–11 such as [6.6.6], [4.8.8], [4.6.12] and [3.3.4.3.4] (where the numbers denote the number of edges of the polygonal tiles meeting at each vertex) while there are only few studies on 2D Archimedean tiling patterns produced from microphase-separated 3 µ-ABC thin films.12,13 Although the ternary phase diagram of 3 µ-ABC is dominated by Archimedean tilling structures, this material gives also access to several hierarchical lamellar morphologies including lamellae and alternating spheres or cylinders.14 The knitting pattern morphology which consists of undulating lamellae and alternating cylinders is the only one thin film hierarchical lamellar morphology reported in the literature.15 In this work, we demonstrate the formation of another thin film hierarchical lamellar morphology resulted from the self-assembly of 3 µ-DSL prepared via a mid-functionalized semicrystalline16,17 PDMSB-b-PS precursor. This asymmetric hierarchical microstructure with a p2mm symmetry can be described as cylinders-within-lamellae where the most incompatible domains (PDMSB and PLA) are efficiently separated by a shell of PS domain. Here, the star junction point resides at the interface between PLA cylinders and their host PS lamellae as proposed for the bulk morphology.7 We also show highly-oriented hierarchical lamellar pattern by templating the self-assembled three colored structure in thin films. Finally, by increasing the size of the PLA block attached to a mid-functionalized PDMSB-b-PS, a thin


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film [6.6.6] Archimedean tiling with a p6mm symmetry was produced. This three-colored hexagonal pattern coexists with a metastable square symmetry [4.8.8] tiling stabilized by the steps between terraces.

Results and discussion The library of 3 µ-DSL star terpolymers used in this study was built via a semicrystalline mid-functional PDMSB-b-PS (Mn = 36 kg.mol-1, ΦPDMSB = 0.32). To this aim, the midfunctional PDMSB-b-PS was first synthetized by sequential anionic polymerization using a 1,1-diphenylethylene (DPE) derivative bearing a tert-butyldimethylsilyl-protected hydroxyl functionality. The third arm was subsequently prepared by triazabicyclodecene (TBD) catalyzed ring opening polymerization of D,L-lactide monomer using the deprotected hydroxyl function as initiator. The molecular structure of 3 µ-DSL star terpolymers is depicted on Scheme 1. Bulk morphology of the mid-functional PDMSB-b-PS sample annealed at 120°C during 12h is consistent with a hexagonal close-packed (HCP) cylindrical phase with a period, p, of 34.3 nm (q* = 0.21 nm-1) as revealed by the synchrotron small-angle X-ray scattering pattern performed at room temperature (see Fig. S1). In addition to higherorder peaks of the p6mm symmetry located at q/q* = 31/2, 41/2 and 71/2, a well-defined PDMSB crystallization peak located at q** = 0.66 nm-1 (PDMSB fold length, pfl = 9.5 nm) is clearly observable. This result indicates that PDMSB chains are partially crystalized within cylindrical domains with a diameter, dcyl, of about 19 nm (dcyl ~ 2 pfl). From this SAXS pattern and using a PDMSB statistical segment length, aPDMSB, of 11 Å, the Flory-Huggins interaction parameter, χDS, between PDMSB and PS was estimated to be 0.07 from a strong segregation theory (SST) calculation described previously.18 Mid-functional PDMSB-b-PS and 3 µ-DSL thin films were deposited on templated and smooth silicon substrates by spin-coating a tetrahydrofuran (THF) diluted solution (1% wt.).


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The film thickness, t, was controlled by varying the spin-coating speed (1.5-3 krpm). The selfassembly of PDMSB-b-PS and 3 µ-DSL thin films was achieved by exposing samples during 3h to a continuous stream of THF vapor produced by bubbling nitrogen gas through the liquid solvent as described previously.19 This continuous flow system was used to control the THF vapor pressure in the chamber by dilution with a separate N2 stream so that the solvent vapor consisted to 8 sccm THF vapor and 2 sccm N2 (total 10 sccm) swelled the films without causing their dewetting. Solvent-annealed PDMSB-b-PS and 3 µ-DSL thin films were quenched in air by quickly removing the lid of the chamber. PDMSB-b-PS and 3 µ-DSL thin films were imaged by AFM and SEM after etching preferentially PDMSB domains with a CF4/O2 reactive ion etch (RIE) treatment (plasma conditions are 40 W, 17 sccm CF4 and 3 sccm O2). In parallel, several 3 µ-DSL thin films were also imaged by AFM after an O2-rich RIE (plasma conditions are 90 W, 10 sccm O2 and 5 sccm Ar) which oxidizes the lowest Tg PDMSB block and thus, enhances the PLA domain contrast on AFM phase images. Out-of-plane PDMSB cylinders (dark) with p ∼ 34 nm are produced from a solventannealed mid-functional PDMSB-b-PS thin film (t ~ 50 nm) as revealed by the AFM topographic view presented in Figure S1 after etching preferentially the PDMSB phase with a CF4/O2 RIE plasma. This result is in accordance with the morphology and the period observed in bulk from SAXS data (see Fig. S1). AFM topographic view presented in Figure 1 shows a solvent-annealed 3 µ-DSL thin film (t ~ 45 nm) consisting of PDMSB (D, ΦPDMSB = 0.22), PS (S, ΦPs = 0.46) and PLA (L, Mn = 21 kg.mol-1, ΦPLA = 0.32) after a CF4/O2 RIE etching plasma treatment. This 3 µ-DSL thin film includes two morphologies with p6mm or p4mm symmetry and the dashed line on the figure delimits the regions occupied by the different phases. The use of a fluorine rich RIE plasma to preferentially remove PDMSB microdomains reveals the square symmetry pattern (right of the image) with a period of ~ 32 nm could be a [4.8.8] tiling consisting of PDMSB (dark) located on square positions while PS and PLA


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(bright) are positioned on octagon sites as showed on the schematic model. The hexagonal symmetry pattern (left of the image) with a period of ~ 32 nm could be assigned to a [6.6.6] tiling having prismatic microdomains which are not of equal size. To support that these two structures that are Archimedean tilings with columnar domains oriented normal to the substrate, GISAXS measurements were performed on samples etched with a CF4/O2 RIE plasma (see Fig. 2). GISAXS pattern features a first-order scattering rod (noted q*) characteristic of a columnar phase oriented normal to the substrate and an additional less intense first-order Bragg rod (noted q**) confirming the coexistence of another out-of-plane columnar phases within the thin film. The minority structure with a period of 31 nm (p = 2π/q**, q**= 0.203 nm-1) could be assigned to the p4mm phase which is a [4.8.8] tiling since incompatible 3 µ-ABC terpolymer chains give access to only one Archimedean tiling with a square symmetry. The majority structure has a first-order peak located at q*= 0.223 nm-1 (p = 2π/q* (4/3)1/2 = 32.5 nm) and higher-order peaks in the ratio 31/2, 41/2 and 71/2 which are characteristic of a 2D hexagonal lattice and can be labelled as 10, 11, 20 and 21. Several tilings like the [6.6.6], [4.6.12] and more complex ones have a hexagonal lattice. Therefore, to know more about this phase, some samples were etched with an O2/Ar RIE plasma which enables a partial oxidization of the PDMSB block and thus, improves the PLA contrast on AFM phase images (see Fig. S2a-b). As both PLA and PDMSB microdomain arrays are ordered into a hexagonal phase with the same period of ~ 32 nm, we conclude the 2D Archimedean tilling pattern produced from the self-assembled 3 µ-DSL (D:S:L = 22:46:32) thin film is a [6.6.6] tiling. To definitely assert this point, the [6.6.6] tiling pattern was also evidenced from the SEM image presented in Figure 3. The use of a fluorine rich RIE plasma to etch preferentially PDMSB blocks revealed that PS (bright), PLA (gray) and PDMSB (dark) microdomains are arranged on hexagonal lattices with a similar period around 32 nm, so that a [6.6.6] Archimedean tiling is formed.


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As indicated by the GISAXS pattern, the [4.8.8] Archimedean tiling is not the dominant phase within the films since it coexists with a more intense p6mm structure. Lower magnification AFM images reveal that the p4mm structure is often observed in the step between terraces as showed on the representative AFM topographic view presented in Figure 4a. Solvent-annealed 3 µ-DSL (D:S:L = 22:46:32) thin films split into terraces where the upper and lower terraces are occupied by the p6mm structure while the step between terraces stabilizes the p4mm structure. The height differences between terraces were found to have a value of ~ 5 nm (see Fig. 4b). Stabilization of another phase by the effect of the film thickness has been reported for ABA triblock copolymer20 as well as for 3-miktoarm star terpolymer.13 Here, it is noteworthy that the contrast observed from the p6mm phase located on lower terraces is equivalent than the one produced when the duration of the CF4/O2 RIE plasma is increased. This result suggests that PDMSB is partially depleted from the interior of lower terraces to form a layer at the air interface due to its lower surface energy. In addition, the height difference between lower and upper terraces (~ 5 nm) after CF4/O2 RIE plasma is consistent with the formation of a PDMSB top layer. The use of topographical substrates to guide the grain orientation of the [6.6.6] tiling reveals the p4mm phase is also stabilized by the periodic steps of silica templates consisting of 250 nm wide and 50 nm deep trenches separated by 250 nm wide mesas. This phenomenon is illustrated by the 3D-AFM topographic image presented in Figure S3 showing a continuous 3 µ-DSL thin film with well-ordered outof-plane columns having a p6mm symmetry (p ∼ 32 nm) in trenches while steps (areas close to walls) and mesas are occupied by a poorly-ordered p4mm phase (p ∼ 31 nm). Interestingly, in spite of the presence of the poorly-ordered p4mm phase on mesas, the hexagonal phase exhibits a single grain orientation (area of 2 µm2) as indicated by the 2D-FFT, which shows six first-order spots.


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Thin films fabricated from a solvent-annealed 3 µ-DSL consisting of PDMSB (ΦPDMSB = 0.27), PS (ΦPs = 0.56) and PLA (Mn = 9 kg.mol-1, ΦPLA = 0.17) (t ~ 45 nm) were etched with two consecutive RIE plasma treatments having different chemistries (fluorine- or argon-rich plasma) to localize the position of PDMSB and PLA within the microphase-separated morphology (see Fig. 5). The use of a RIE plasma with a fluorinated chemistry to remove PDMSB microdomains reveals the formation of asymmetric lamellae where the PDMSB domain size is about 13 nm while lamellae occupied by PS and PLA domains have a domain size of ~25 nm (see Fig. 5a). GISAXS data obtained from thin films prepared with similar conditions indicate that the lamellar interfaces present undulations as depicted on the Fig. 5a (inset) since the scattering rod (located at q* = 0.176 nm-1, p ∼ 36 nm) curves inwards to form a partial ring (see Fig. S4).21 A further Ar/O2 plasma (40 W, Ar (45 sccm), O2 (5 sccm)) used to improve the contrast between PS and PLA domains reveals that PS lamellae enclose PLA cylinders which are not perfectly-distributed within the lamellae (see Fig. 5b). In parallel, some samples, etched with an O2 rich RIE plasma to partially oxidize PDMSB block, reveal the formation of discontinuous lines which are due to the alignment of PLA microdomains within PS lamellae (see Fig. S2c-d). The AFM phase presented on Fig. S2d confirms that PLA domains are not well-distributed within PS lamellae. However, the SEM image taken after etching a solvent-annealed 3 µ-DSL (D:S:L = 27:56:17) thin film with a CF4/O2 then a subsequent Ar/O2 RIE plasma treatments shows that PLA domains can be locally ordered into a well-defined rectangular structure (p2mm) as revealed from the SEM FTT and its associated profile (see Fig. 6). In this case, the intra-lamellar distance of PLA (gray) columns (i.e. within the same PS lamellar domain) is ∼ 50 nm (red arrow on FFT profile) while the (inter-lamellar) distance between PLA domains located on two distinct PS (bright) lamellae separated by a PDMSB (dark) domain is about 38 nm (black arrow on FFT profile) in accordance with AFM images presented in Figure 5.


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All the results show that the hierarchical microstructure presents no interface between PDMSB and PLA domains making this lamellar morphology stable since the Flory-Huggins interaction parameter between this two components is expected to be higher than that of the two other pairs (χDS < χLS < χDL). Crystallization, acting as second force, may also account to drive the microphase separation into this asymmetric lamellar structure.16 Similar bulk morphology consisting of lamellae of poly(2-vinyl pyridine) (noted V) and PS with polybutadiene (noted B) cylinders have been previously obtained from 3 µ-VSB thin films with volume fractions V:S:B = 59:22:19.7 This morphology is different from the knitting pattern observed experimentally from solvent-annealed polyisoprene-arm-polystyrene-armpolyferrocenylethylmethylsilane (3 µ-ISF, I:S:F = 34:43:23) thin films15 and obtained theoretically from SCFT calculations (A:B:C = 50:30:20) where the longest arm form undulating lamellae in which the other two blocks are embedded.22 The control of the long-range order of the hierarchical morphology has been achieved by using topographical grating in silica with a period of 500 nm consisting of 300 nm wide and 50 nm deep trenches separated by 200 nm wide mesas (see Fig. 7). Well-ordered out-of-plane lamellae confined in trenches were produced when the polymer layer thickness (t ~ 25 nm) is not enough thick to generate a continuous film after the solvent-annealing process (see Fig. 7a). The templated asymmetric lamellar phase, oriented along the groove direction, has a period (p ~ 37.5 nm) similar than the one obtained on a smooth substrate (p ~ 38 nm). Increasing the polymer layer thickness induces the formation of a continuous film (tmesa ~ 20 nm and ttrench ~ 60 nm) where four unit cells with a period of ~ 50 nm are observed on the mesas and eight in the trenches (p ~ 37.5 nm) (see Fig. 7b). This indicates an increase of the lamellar period of ~ 30% on mesas which is driven by the incommensurability of the mesa wide with the lamellar period. It is noteworthy that untemplated thin films can also selfassemble into a lamellar structure having a similar large period close to specific topological


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defect like the so-called chevron morphology where p is found to be about 51 nm (see Fig. S5).

Conclusion In summary, self-assembly of 3 µ-DSL thin films into ordered 2D Archimedean tilings and hierarchical lamellar pattern is demonstrated. Excellent orientational order has been achieved by templating the hierarchical lamellar morphology with topographical substrate. The asymmetric lamellae produced from 3 µ-ABC provide a great convenience in lithography application since many asymmetric lithographic line and space patterns are required and, cannot be straightforwardly achieved by conventional block copolymer self-assembly. In addition, the blending of the hierarchical lamellar structure with another 3 µ-DSL can be used to tailor the periodicity of asymmetric lines. For instance, blending of 3 µ-DSL thin films (D:S:L = 27:56:17) with 30 % wt. of 3 µ-DSL (D:S:L = 22:46:32) leads to a periodicity change of the hierarchical lamellar pattern (pneat ~ 38 nm, pblend ~ 30 nm). A [6.6.6] tiling with a period of 32 nm has been also produced from 3 µ-ABC. This “three-colored” pattern, which cannot be obtained from a linear terpolymer, could be useful to produce dense array of nanoobjects such as dots, pillars or holes with utility in microelectronic patterning.

Experimental Section Directed self-assembly of 3 µ-DSL thin films: Untemplated and templated 3 µ-DSL thin films were spin-coated from THF solutions (1% wt.) and the film thickness was controlled by varying the spin-coating speed (1.5-3 krpm). The self-assembly of 3 µ-DSL thin films was promoted by exposing samples 3h to a continuous stream of THF vapor produced by bubbling


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nitrogen gas through the liquid solvent as described previously.19 Untemplated film thickness has been determined by AFM from scratched polymer area while templated film thickness has been indirectly deduced from the mesa and trench height difference. Topographical grating fabrication: The periodic topographical gratings were fabricated using a Lloyd’s mirror interferometer with a 325 nm He-Cd laser beam. To transfer the interference lithography pattern into the Si/50nm SiO2 layer, a trilayer resist stack methodology was used. This trilayer was obtained by inserting a hard mask layer consisting of a SiO2 thick film between a chemically-amplified negative resist resin and an anti-reflection coating (ARC) layer. After development of the resist, the pattern was transferred into the hard mask then into the ARC and finally into the SiO2 by a series of RIE steps to form a grating. SEM and AFM Characterizations: Atomic force microscopy (AFM Dimension FastScan, Bruker) was used in tapping mode to characterize the surface morphology of 3 µ-DSL thin films. Silicon cantilevers (Fastcsan-A) with a typical tip radius of ∼ 5 nm were used. The resonance frequency of the cantilevers was about 1.25 kHz. Prior to AFM measurement, 3 µDSL thin films were etched with fluorine- or oxygen-rich RIE treatments in order to remove the PDMSD phase or to enhance contrast of PLA domains on AFM phase images (plasma conditions are: 40 W, 17 sccm CF4 and 3 sccm O2 or 90 W, 10 sccm O2 and 5 sccm Ar). Scanning electron microscopy (SEM, JEOL 7800) was used in GBSH mode at an accelerating voltage of 1 kV to take 3 µ-DSL thin films images. GISAXS and SAXS Measurement: GISAXS measurements were performed on CRBBM02 beamline at the European Synchrotron Radiation Facilities (ESRF) in Grenoble using a photon energy of 11 keV. The samples were positioned on a kappa-goniometer, for an accurate control of the incident angle versus the film surface, chosen between the critical angles of the polymer and the Si substrate. Horizontal and vertical widths of the beam focused at the sample position were equal to 300 and 150 µm, respectively. GISAXS patterns were


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recorded on a XPAD 2D pixel detector (960 × 560 pixels, 130 µm pixel size) placed at a distance of 3080 mm from the sample.23 The intense incident and reflected beams were stopped by a 2 mm wide Ta strip. To minimize air scattering the whole path of the scattered beam was under vacuum apart from the nearest region around sample. With the incident beam propagating along the x direction, the GISAXS images were recorded in the (qy, qz) plane where qy and qz are the components of the scattering vector, related to the in-plane angle 2θf and out-plane angle αf. GISAXS pattern, shown hereafter, was normalized with respect to the incident beam intensity monitored by a front photomultiplier. SAXS experiments were performed on the Dutch-Belgian Beamline (DUBBLE) at the European Synchrotron Radiation Facility (ESRF) station BM26B in Grenoble.24 The energy of the x-ray beam was 11 keV, which corresponds to a wavelength of 1.127 Å. The 2D images were radially averaged around the center of the primary beam in order to obtain the isotropic SAXS intensity profiles. The scattering pattern from a specimen of silver behenate was used for the calibration of the wavevector scale of the scattering curves. Finally, the data were normalized to the intensity of the incident beam in order to correct for primary beam intensity fluctuations.

Acknowledgements The authors acknowledge support from Arkema and the Région Aquitaine. The ESRF and NWO are acknowledged for allocating beamtime at the Dutch-Belgian beamline (DUBBLE) for the SAXS experiments. D2AM French CRG Beamline is also acknowledged for allocating GISAXS beamtime. K. A. thanks Prof. C. A. Ross from MIT who provided topographical gratings. This work was performed within the framework of the Equipex ELORPrintTec ANR-10-EQPX-28-01 and the LabEx AMADEUS ANR-10-LABEX-0042-AMADEUS with the help of the French state Initiative d’Excellence IdEx ANR-10-IDEX-003-02 and the LCPO-Arkema INDUSTRIAL CHAIR “HOMERIC” ANR-13-CHIN-0002-01.

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Scheme 1. Molecular formula of the 3 µ-DSL star terpolymers used in this work where m and n have constant values of 100 and 240 as they correspond to those of the mid-functional PDMSB-b-PS while p is equal to 125 for the 3 µ-DSL (D:S:L = 27:56:17) or 292 for the 3 µDSL (D:S:L = 22:46:32).


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Figure 1. AFM topographic view of a solvent-annealed 3 µ-DSL (D:S:L = 22:46:32) thin film (t ~ 45 nm) treated by a CF4/O2 RIE plasma which includes two columnar morphologies indexed with a p6mm or p4mm symmetry. The dashed line delimits the regions occupied by the different phases. Schematic models showing (top) the p4mm and (bottom) the p6mm microstructures corresponding to the [4.8.8] and [6.6.6] tilings, respectively. Scale bar: 250 nm.

Figure 2. GISAXS pattern of a solvent-annealed 3 µ-DSL (D:S:L = 22:46:32) thin film (t ~ 45 nm) treated by a CF4/O2 RIE plasma. Black and red arrows on the GISAXS pattern indicate the first-peak order position of the p6mm and p4mm phases and are noted q* and q**, respectively. Higher-order peaks of the p6mm phase are also indexed.


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Figure 3. SEM image of a solvent-annealed 3 µ-DSL (D:S:L = 22:46:32) thin film (t ~ 45 nm). A CF4/O2 RIE plasma was used to reveal a “three colored” pattern where PS (bright), PLA (gray) and PDMSB (dark) domains were arranged in a [6.6.6] tiling with a p6mm symmetry. Inset: high magnification SEM image of the [6.6.6] tiling.


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Figure 4. (a) AFM topographic view of a solvent-annealed 3 µ-DSL (D:S:L = 22:46:32) thin film (t ~ 37 nm measured at the lower terrace) treated by a CF4/O2 RIE plasma and (b) AFM height profile along the blue line shown in (a). Dashed lines delimit the regions occupied by the different phases. Scale bar: 250 nm.


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Figure 5. AFM topographic views of solvent-annealed 3 µ-DSL (D:S:L = 27:56:17) thin films (t ~ 45) taken after: (a) a CF4/O2 RIE treatment and (b) a subsequent Ar/O2 RIE plasma. Insets: high magnification AFM topographic images and schematic of the hierarchical lamellae structure. Scale bars: 250 nm.


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Figure 6. (a) SEM image of a solvent-annealed 3 µ-DSL (D:S:L = 27:56:17) thin film (t ~ 45 nm). A CF4/O2 followed by a subsequent Ar/O2 RIE plasma treatments were used to reveal asymmetric lamellae where PDMSB (dark) domains are separated by PS (bright) and PLA (gray) domains. (b) The SEM FFT and its corresponding intensity profile demonstrate the presence of a well-ordered rectangular (p2mm) phase formed by PLA domains with intra- and inter-lamellar distances of ∼ 50 and 38 nm, respectively, indicated by red and black arrows.


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Figure 7. AFM topographic views of solvent-annealed 3 µ-DSL (D:S:L = 27:56:17) thin films deposited on topographical substrates followed by a CF4/O2 RIE treatment. Sample thicknesses are: (a) ttrench ~ 25 nm and (b) tmesa ~ 20 nm and ttrench ~ 60 nm. Scale bars: 250 nm.


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Archimedean Tilings and Hierarchical Lamellar ... - ACS Publications

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