Pattern formation of metal–oxide hybrid nanostructures via the self-assembly of di-block copolymer blends

Dae Soo Jung a, Jiwon Bang a, Tae Wan Park a, Seung Hyup Lee a, Yun Kyung Jung b, Myunghwan Byun c, Young-Rae Cho d, Kwang Ho Kim *de, Gi Hun Seong *f and Woon Ik Park *a
aElectronic Convergence Materials Division, Korea Institute of Ceramic Engineering & Technology (KICET), 101 Soho-ro, Jinju 52851, Republic of Korea. E-mail: thane0428@kicet.re.kr; thane0428@gmail.com
bDepartment of Biomedical Engineering, Inje University, 197 Inje-ro, Nam-Gu, Kimhae, Republic of Korea
cDepartment of Advanced Materials Engineering, Keimyung University, 1095 Dalgubeol-daero, Daegu 42601, Republic of Korea
dDepartment of Materials Science and Engineering, Pusan National University (PNU), Pusan 46241, Republic of Korea
eGlobal Frontier R&D Center for Hybrid Interface Materials, Busan 46241, Republic of Korea. E-mail: kwhokim@pusan.ac.kr
fDepartment of Bionano Engineering, Hanyang University, Ansan 15588, Republic of Korea. E-mail: ghseong@hanyang.ac.kr

Received 12th May 2019 , Accepted 15th July 2019

First published on 19th July 2019


The templated self-assembly of block copolymers (BCPs) with a high Flory–Huggins interaction parameter (χ) can effectively create ultrafine, well-ordered nanostructures in the range of 5–30 nm. However, the self-assembled BCP patterns remain limited to possible morphological geometries and materials. Here, we introduce a novel and useful self-assembly method of di-BCP blends capable of generating diverse hybrid nanostructures consisting of oxide and metal materials through the rapid microphase separation of A–B/B–C BCP blends. We successfully obtained various hybridized BCP morphologies which cannot be acquired from a single di-BCP, such as hexagonally arranged hybrid dot and dot-in-hole patterns by controlling the mixing ratios of the solvents with a binary solvent annealing process. Furthermore, we demonstrate how the binary solvent vapor annealing process can provide a wide range of pattern geometries to di-BCP blends, showing a well-defined spontaneous one-to-one accommodation in dot-in-hole nanostructures. Specifically, we show clearly how the self-assembled BCPs can be functionalized via selective reduction and/or an oxidation process, resulting in the excellent positioning of confined silica nanodots into each nanospace of a Pt mesh. These results suggest a new method to achieve the pattern formation of more diverse and complex hybrid nanostructures using various blended BCPs.


Introduction

During the past few decades, the directed self-assembly (DSA) of diblock copolymers (di-BCPs) with a high Flory–Huggins interaction parameter (χ) has attracted considerable attention as one of the promising candidates for scalable nanofabrication due to its excellent pattern resolution, low process cost, and short process time.1–14 Self-assembled di-BCPs present various nanoscale structures in the range of 5–30 nm, such as spheres, cylinders, gyroids and lamellae, through the strong microphase separation between two blocks or the minimization of the Gibbs free energy.9,15–22 Furthermore, high-χ BCPs self-assemble into periodic nanostructures with better line edge roughness (LER) and lower defect density levels compared to low-χ BCPs, stemming from the high segregation strength (χN, N = degree of polymerization).23–26 These high-χ BCPs are typically annealed by a pure or mixed solvent vapor annealing (SVA) process to provide sufficient chain mobility, as high-χ BCPs generally show slow self-assembly kinetics owing to their poor polymer chain diffusivity (D), which exponentially decreases in proportion to the χ value.27,28 In the SVA system, the use of a binary solvent which consists of two preferential or swelling solvents for each block of the A-b-B BCP induces both rapid self-assembly kinetics to obtain highly ordered nanostructures and excellent morphological or size tunability.29,30 However, the sets of self-assembled BCP morphologies available and their functionalities remain limited to pure di-BCPs owing to the restricted number of blocks in di-BCPs than tri-BCPs.25,31,32

To extend these limited di-BCP geometries, many BCP research groups have recently suggested various innovative approaches. For example, the formation of non-regular and complex di-BCP patterns was achieved by employing dense chemical and/or topographic guiding templates formed by e-beam lithography.33,34 The double-templated self-assembly of high-χ BCPs to obtain hierarchical nanostructures was also introduced as a BCP double-patterning process. Unusual and novel nanostructures formed by the self-assembly of A–B–C tri-BCP thin films have also been extensively explored.35 As another strategy, the self-assembly of blended di-BCPs to produce various two-dimensional (2D) and/or 3D nanostructures has also been widely investigated due to the advantage of the outstanding ability and extension capability of the BCP morphology range. BCP technologies which effectively manipulate BCP geometries by controlling key parameters such as the mixing composition, volume fraction and molecular weight (MW) of BCPs have also been comprehensively studied.36–40 Hierarchical self-assembly for a blend of A–B and B–C di-BCPs based on supramolecular (H-bonding) interactions was also reported, showing highly ordered square arrays of cylinders.16 Recently, we also demonstrated a host–guest self-assembly of a blend of high-χ and low-χ BCPs, showing spontaneous positioning between host and guest BCP microdomains without any H-bond linkages.41,42 However, despite these great efforts, uniform long-range order for two functional high-χ di-BCP blends through microphase separation still has not been achieved in the absence of supramolecular interactions between the two di-BCPs.

Here, we present a method which efficiently produces diverse hybrid nanostructures consisting of oxide and metal through the rapid microphase separation of di-BCP blends. We also show a sequential, selective reduction and/or oxidation process of several self-assembled BCP microdomains. More specifically, we demonstrate the successful realization of the functional pattern generation of hexagonally arranged hybrid dot (metal–oxide) and dot-in-hole (oxide-in-oxide and oxide-in-metal) nanostructures in a short period of annealing time (≤10 min) by controlling the mixing ratio of the annealing solvents in a binary SVA system. In addition, we explain how the controlled binary SVA process can provide both geometric variability and rapid self-assembly kinetics of di-BCP blends, presenting an example of well-defined spontaneous one-to-one accommodation in dot-in-hole nanostructures. In addition, with a mixture of two di-BCPs with high χ parameters, we show the successful pattern formation of confined spherical SiOx nanodots within the designated nanospaces of a Pt mesh while also minimizing the free energy.

Results and discussion

Microphase separation for various di-BCP blends

Fig. 1 schematically presents the concept of the three di-BCP blends used to obtain well-ordered hybrid nanostructures consisting of metal and oxide; in this case, hexagonally arranged dot and dot-in-hole patterns. For the demonstration of the microphase separation of various di-BCP blends, we initially chose four di-BCPs: cylinder-forming poly(2-vinylpyridine-b-styrene) (P2VP-b-PS) with a high χ (∼0.18), sphere-forming poly(styrene-b-ferrocenyldimethylsilane) (PS-b-PFS) with a low χ (∼0.06), cylinder-forming poly(dimethylsiloxane-b-styrene) (PDMS-b-PS) with a high χ (∼0.26), and sphere-forming PS-b-PDMS with a high χ (∼0.26). Fig. 1a shows the polymer chains and molecular formulas of the three di-BCP blends. Blend 1, Blend 2, and Blend 3 are mixtures of P2VP-b-PS and PS-b-PFS, PDMS-b-PS and PS-b-PFS, and P2VP-b-PS and PS-b-PDMS di-BCP solutions, respectively. The schematic images in the upper part of Fig. 1b show the microphase-separated microdomains of the blended BCP thin films after a binary SVA process. The drawings at the bottom of Fig. 1b are diverse hybrid nanostructures composed of metal and oxide obtained from Blend 1, Blend 2, and Blend 3 after an oxidization and/or reduction process using a reactive ion etching (RIE) system. Blend 1, a blend of P2VP-b-PS and PS-b-PFS BCPs, forms hexagonally arranged spherical P2VP and PFS microdomains in a PS matrix after annealing, showing a self-assembled hybrid dot pattern composed of metal and nonmetal materials (oxidized PFS, ox-PFS, and SiFexOy) after an O2 plasma treatment. Blend 2, which is a blend of PDMS-b-PS and PS-b-PFS, shows the specific one-to-one accommodation of PFS nanospheres in hexagonally perforated lamella (HPL) PDMS microdomain via uniform microphase separation, resulting in the formation of a novel hybrid dot-in-hole pattern which shows organized ox-PFS dots in the oxidized PDMS (ox-PDMS, SiOx) hole structure after a two-step sequential plasma treatment of CF4 and oxygen to remove the top-PDMS layer and PS matrix, respectively. Blend 3, a blend of P2VP-b-PS and PS-b-PDMS, forms a dot-in-hole hybrid nanostructure consisting of SiOx and metal through the minimization of the free energy after a sequential process of metal ion incorporation and an O2 plasma treatment.
image file: c9nr04038b-f1.tif
Fig. 1 Microphase separation of various di-BCP blends. (a) Blends of P2VP-b-PS and PS-b-PFS di-BCPs (Blend 1), PDMS-b-PS and PS-b-PFS di-BCPs (Blend 2), and P2VP-b-PS and PS-b-PDMS di-BCPs (Blend 3) for the pattern formation of diverse hybrid nanostructures. (b) Self-assembled morphologies of Blend 1, Blend 2, and Blend 3 before/after the RIE process. Blend 1 shows a hexagonally arranged dot pattern consisting of oxide (Ox-PFS, SiFexOy) and metal. Blend 2 shows a dot-in-hole nanostructure composed of two different oxides (Ox-PFS and Ox-PDMS) via host–guest self-assembly. Blend 3 shows a dot-in-hole hybrid nanostructure, showing one-to-one accommodation of oxide (Ox-PDMS, SiOx) nanodots in a metal mesh. The P2VP blocks are selectively incorporated with metal ions before an O2 plasma treatment.

Morphological tunability of cylinder-forming di-BCPs

First, we investigated the morphological tunability of a cylinder-forming PS-b-P2VP (SV42) BCP with a MW of 42 kg mol−1 and a minority volume fraction (fdryP2VP) of 25% and a cylinder-forming PDMS-b-PS (DS45) BCP with a MW of 45.5 kg mol−1 and a minority volume fraction (fdryPDMS) of 33.7% in the dry state. To control the SV42 BCP morphology, we selected a binary solvent composed of dimethylformamide (DMF) and toluene, which are preferential for P2VP and PS blocks, respectively. During the solvent annealing step, the effective volume fraction of the P2VP block (feffP2VP) varied depending on the volume ratio between the DMF and toluene (vDMF/vTOL), as DMF selectively swells the P2VP block. Fig. 2a shows the morphological transition of the SV42 BCP when the vDMF/vTOL ratio is varied at an annealing time of 10 min. Although a line structure with a line width of 12 nm was observed in pure toluene (vDMF/vTOL = 0), as the vDMF/vTOL ratio was increased, feffP2VP also increased due to the selective swelling of P2VP caused by the DMF vapor. As shown in Fig. 2a and b, the area fraction of the HPL in the self-assembled VS42 increased in proportion to the vDMF/vTOL ratio, showing a well-ordered Pt hole structure with a diameter of ∼36 nm at a vDMF/vTOL ratio of 0.7. The inset images (FFT, fast Fourier transform) in the scanning electron microscope (SEM) data indicate the good ordering of the self-assembled hole patterns. For the DS45 BCP, we used a mixed solvent of heptane and toluene, which are preferred for PDMS and PS blocks, respectively. As shown in Fig. 2c–d and in Fig. S1 in the ESI, the DS45 BCP thin film also presents a 16 nm-line structure when annealed with pure toluene (vHEP/vTOL = 0), whereas a binary solvent induces a morphological change from a cylinder to an HPL structure depending on the vHEP/vTOL ratio, through the selective swelling of PDMS by heptane vapor. Under the best annealing conditions, a highly ordered SiOx hole structure with a diameter of ∼36 nm with vHEP/vTOL = 1.2 was achieved after annealing for 30 min. This outstanding morphological variability of high-χ BCPs can provide confined spaces for self-assembled tiny nanoparticles through the spontaneous one-to-one accommodation of BCP blends, resulting in the effective pattern generation of novel hybrid nanostructures.
image file: c9nr04038b-f2.tif
Fig. 2 Geometrical evolution of cylinder-forming VS42 and DS45 BCPs when annealed with binary solvents. (a) Morphological evolution of VS42 at varying mixing ratios of DMF and toluene. (b) Graph of the area fraction of HPL vs. the vDMF/vTOL ratio. (c) Pattern evolution of DS45 at varying mixing ratios of DMF and toluene. (d) Graph for the area fraction of HPL vs. the vHEP/vTOL ratio. The area fraction of HPL in the self-assembled VS42 and DS45 increases in proportion to the vDMF/vTOL and vHEP/vTOL ratio, respectively. The annealing time for VS42 and DS45 was fixed at 10 min and 30 min, respectively.

Hexagonally arranged hybrid nanodot pattern

To obtain a hybrid nanoparticle array, a blend (Blend 1) of cylinder-forming high-χ VS42 BCP and sphere-forming low-χ PS-b-PFS (SF35) with a MW of 35 kg mol−1 and a minority volume fraction (fdryPFS) of 11.5% was employed. When selecting two BCPs for self-assembly of the blend, the two BCPs with a similar MW of majority block (e.g. PS block) is helpful to lead to the microphase separation of the blend. A solution of VS42 and SF35 dissolved in toluene was physically mixed together at a mixing ratio (vVS42/vSF35) of 1.0, as shown in Fig. S2. After the blending of the two di-BCPs, the volume fraction of P2VP and PFS block decreases depending on the arithmetical calculation of the total volume of the blend, resulting in the formation of dual spherical microdomains consisting of P2VP and PFS blocks. Fig. 3 shows a hexagonally organized hybrid dot pattern through the microphase separation of Blend 1. The blended BCP thin film was solvent-annealed under a binary solvent consisting of propylene glycol and toluene for ten minutes. To form spherical microdomains, the propylene glycol, which is not preferential for either the P2VP or PFS blocks, was chosen. After the SVA process, the P2VP block was selectively incorporated with metal ions (Pt+) followed by dry-etching by O2 plasma, as shown in Fig. 3a. When the PS matrix is removed, spherical P2VP and PFS blocks are reduced and oxidized, respectively, realizing in the well-defined metal–nonmetal hybridization of Pt and SiFexOy, as shown in Fig. 3b. The ordering of the hexagonally arranged, hybrid dot pattern may be improved by increasing the annealing time. Here, it should be noted that controlling the mixing ratios of the di-BCP solutions and annealing solvents can suppress macrophase separation in favor of microphase separation for physically blended BCPs, thereby creating hybridized BCP morphologies that cannot be obtained from a single di-BCP.
image file: c9nr04038b-f3.tif
Fig. 3 Hexagonally arranged hybrid dot pattern through the microphase separation of the blended VS42 and SF35 BCPs. (a) The procedure used for the pattern formation of a hybrid nanodot structure consisting of metal (Pt) and oxide (SiFexOy). After the P2VP block of self-assembled blended BCP thin film is selectively incorporated with metal ions, the blended BCP is dry-etched by O2 plasma. When the PS matrix is removed, the PFS and P2VP blocks are oxidized and reduced, respectively, resulting in the generation of a SiFexOy and Pt nanodot structure. (b) The self-assembled dot pattern of the blended VS42 and SF35 BCPs over a large area (left) with vP.G/vTOL = 2.0 when vVS42/vSF35 = 1. The magnified image (right) clearly shows a well-defined, hexagonally arranged hybrid dot pattern consisting of a metal (Pt) and an oxide (SiFexOy).

Pattern formation of a dual-oxide nanostructure

Fig. 4 shows the novel pattern formation of a dot-in-hole dual-oxide nanostructure with the blended BCP consisting of high-χ DS45 and low-χ SF35 BCPs (Blend 2). The morphologies of the self-assembled BCP blend can be observed after a two-step sequential plasma treatment of CF4 and oxygen by an RIE system. After removing the top-PDMS block of the self-assembled blended BCP thin film by CF4 plasma, both the PDMS and PFS blocks are oxidized as SiOx and SiFexOy materials by the O2 plasma treatment, respectively, as shown in Fig. 4a. Fig. 4b shows the morphological evolution of the blended BCP monolayer depending on the vHEP/vTOL ratio at an annealing time of five minutes. This rapid pattern formation can be achieved by using a mixed solvent in that binary SVA can plasticize both blocks of di-BCPs (P2VP and PS), resulting in faster self-assembly kinetics compared to a single-component SVA process, as we previously reported. As mentioned with regard to Fig. 2, the pure DS45 BCP forms cylindrical and HPL morphologies when annealed with pure toluene and a binary solvent of heptane and toluene, respectively. For the blended BCP, the spherical PFS microdomains can be located within the nanospaces of the PDMS HPL structure via the controlled incorporation of a preferential solvent (heptane) by precisely controlling the vHEP/vTOL ratio without the occurrence of macrophase separation between the two di-BCPs. This is possible because when positioning spherical nanoparticles at the center of the space in the HPL, minimization of the free energy can be achieved, as we previously found by means of theoretical calculations using self-consistent field theory (SCFT).39 As shown in Fig. 4b and c, the area of the PDMS microdomain increased in proportion to the vHEP/vTOL ratio due to the selective swelling of PDMS by heptane, whereas the PFS microdomain preserved its morphology regardless of the vHEP/vTOL conditions due to the small difference in the solubility parameters between PS (δ = 18.5) and PFS (δ = 18.6). The vHEP/vTOL ratio which led to one-to-one accommodation, showing each sub-20 nm SiFexOy nanoparticle confined in each SiOx hole (diameter: ∼55 nm), was 1.2, whereas spatially nonuniform microphase separation occurred due to the mismatch in the area fraction between the PDMS and PFS microdomains when vHEP/vTOL < 1.2 or vHEP/vTOL > 1.2. These results suggest that microphase separation can be induced using a controlled binary SVA process based on selective tunability for di-BCP blends consisting of high-χ and low-χ BCPs, showing a unique, well-defined hybrid dual-oxide dot-in-hole nanostructure.
image file: c9nr04038b-f4.tif
Fig. 4 Pattern formation of the dot-in-hole hybrid oxide nanostructure with the blended BCP with high-χ DS45 and low-χ SF35 BCPs. (a) The procedure for the pattern generation of the hybrid dot-in-hole nanostructure consisting of SiFexOy and SiOx. After removing the top-PDMS block of the self-assembled blended BCP (DS45 and SF35) thin film, the BCP is treated with O2 plasma. When the PS matrix is etched out, both the PDMS and the PFS microdomains are oxidized, resulting in conversions to SiOx and SiFexOy, respectively. (b) Morphological evolution of the blended BCP monolayer depending on the vHEP/vTOL ratio. (c) Graph of the number of dot-in-hole structures vs. the vHEP/vTOL ratio. The PDMS increases in proportion to the vHEP/vTOL ratio through the selective swelling of PDMS, showing spontaneous one-to-one accommodation at vHEP/vTOL = 2.0.

Pattern formation of the dot-in-hole hybrid nanostructure

We now demonstrate the method used to induce the microphase separation of a blend (Blend 3) composed of two high-χ di-BCPs. To encourage the host–guest self-assembly with the A–B/B–C blend of two high-χ di-BCPs, for which the χA/C > χB/C > χA/B relationship holds, the selection of the di-BCP is very important to prevent macrophase separation stemming from the strong incompatibility between the two di-BCPs. Accordingly, we chose a cylinder-forming VS42 BCP and a sphere-forming PS-b-PDMS (SD28) BCP with a MW of 28 kg mol−1 and a minority volume fraction of fdryPDMS = 9.8% to obtain a hybrid metal-nonmetal dot-in-hole nanostructure. The blend of SV42 and SD28 was annealed with a binary solvent of DMF and heptane for ten minutes. During the SVA process, feffP2VP increased in proportion to the vDMF/vTOL ratio due to the selective swelling of the P2VP block by DMF vapor. To provide the functionality to the self-assembled blended BCPs, a three-step sequential process is required, as shown in Fig. 5a. After removing the segregated top-PDMS at the air/polymer interface by means of CF4 plasma, the P2VP block in the PS matrix was selectively incorporated with Pt ions. Then, both the P2VP and PDMS microdomains were reduced and oxidized by O2 plasma, respectively, while the PS block was removed, leading to the formation of a dot (SiOx)-in-hole (Pt) hybrid pattern. Fig. 5b shows the morphological change of the blended BCP monolayer depending on the vDMF/vTOL ratio. As noted in Fig. 1, the effective volume fraction of the P2VP microdomain increases in proportion to the vDMF/vTOL ratio through the selective swelling of the P2VP block, showing well-defined host–guest self-assembly when vDMF/vTOL = 2.0 at a fixed vVS42/vSD28 of 1.0. Fig. 5c shows a graph of the number of dot-in-hole structures (one-to-one) vs. vDMF/vTOL ratio. Fig. 5d shows the uniform hybridization of the metal (Pt) and nonmetal (SiOx) materials over a large area. In this case, it should also be emphasized that the composition of the di-BCPs can be widely designed depending on the desirable device applications, and the components of the annealing solvents can be optimized to obtain well-ordered hybrid nanostructures.
image file: c9nr04038b-f5.tif
Fig. 5 Self-assembled dot-in-hole hybrid nanostructure with a blended BCP thin film of two high-χ BCPs (VS42 and SD28). (a) Procedure of the pattern generation of the dot-in-hole hybrid nanostructure consisting of Pt (holes) and SiOx (dots). After removing the top-PDMS block of the self-assembled blended BCP (VS42 and SD28) thin film, the P2VP microdomain is selectively incorporated with Pt ions. When the PS matrix is removed as the blended BCP is exposed to O2 plasma, the P2VP and PDMS microdomains are reduced and oxidized, respectively, resulting in the creation of a dot (SiOx)-in-hole (Pt) nanostructure. (b) Morphological evolution of the blended BCP monolayer depending on the vDMF/vTOL ratio. (c) Graph of the number of dot-in-hole unit structures vs. the vHEP/vTOL ratio. The effective volume fraction of the P2VP microdomain increases in proportion to the vDMF/vTOL ratio through the selective swelling of the P2VP block, showing spontaneous one-to-one accommodation at vDMF/vTOL = 2.0. (d) Self-assembled dot-in-hole structure over a large area at vDMF/vTOL = 2.0 when vVS42/vSD28 = 1.0.

Experimental section

Block copolymer (BCP) self-assembly

Before the annealing of the single and blended di-BCPs, the bare Si substrates were washed with ethanol and isopropyl alcohol (IPA). The Si substrates were then surface-modified with a hydroxyl-terminated PS (OH-PS) homopolymer with a MW of 42 kg mol−1 at 150 °C for two hours in a vacuum oven to promote the self-assembly of BCPs. All of the BCPs were dissolved at ∼1.2 wt% in toluene and were then spin-coated onto the Si substrates at 5000 rpm for 20 seconds. The OH-PS homopolymer and the di-BCPs (VS42, DS45, SF35, and SD28) were purchased from Polymer Source Inc. in Canada. The BCP thin films were annealed by pure toluene vapor or a mixed solvent vapor in a stainless steel chamber at 85 °C. After annealing, the samples were plasma-treated with CF4 (20 s at 50 W) and/or O2 (30 s at 60 W) using a reactive ion etching (RIE) system.

Metal ion incorporation

The self-assembled PS-b-P2VP or SV42-blended BCP thin films were immersed in the aqueous metal salt (Na2PtCl4) solution with acid in a beaker. The immersion solutions were prepared by mixing 1 mL of the metal salt solution with a concentration of 100 mM, and 9 mL 1% HF (aq.) for one hour. After metal ion incorporation, the sample was rinsed with deionized (DI) water and dried using a N2 spray gun. O2 (30 s at 60 W) plasma was used to remove the PS block and reduce the metal ions using a reactive ion etching (RIE) system.

Characterization

The various nanostructures of self-assembled single and blended BCPs were observed using a field-emission scanning electron microscope (FE-SEM: Hitachi S-4800) after the RIE process. All SEM images were obtained at a high acceleration voltage (Vacc ∼ 5–10 kV) and a working distance of 3–5 mm.

Conclusions

In summary, we presented a method which effectively creates various hybrid nanostructures composed of oxide and metal which cannot be obtained from a single di-BCP through the uniform microphase separation of di-BCP blends and their functionalization. We successfully achieved a pattern generation of a hexagonally arranged hybrid sub-20 nm dot (Pt-SiFexOy) nanostructure from a blend of cylinder-forming P2VP-b-PS and sphere-forming PS-PFS BCPs. We also showed a microphase-separated dot-in-hole dual-oxide (SiFexOy-in-SiOx) nanostructure created with a short annealing time (≤10 min) from a blend of PDMS-b-PS and PS-b-PFS BCPs using a binary solvent based on the SVA method, showing well-defined spontaneous one-to-one accommodation. In addition, we obtained a dot-in-hole (SiOx-in-Pt) hybrid nanostructure which has minimum free energy via the host–guest self-assembly of the two high-χ di-BCPs (P2VP-b-PDMS and PS-b-PDMS) by controlling the mixing ratio of two annealing solvents. This unique and useful approach is widely applicable to many other BCP blends, contributing to the diversification of BCP geometries and the easy fabrication of functional and complex nanostructures for device applications.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This research was mainly supported by the Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) and Basic Private Research Program of the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (No. 2013M3A6B1078874 & NRF-2017R1D1A1B03034490). This work was also supported by the Industrial Core Technology Development Program (10080656) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea).

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Footnotes

Electronic supplementary information (ESI) available: Detailed description of additional self-assembled BCP patterns and size distribution of SiOx dot patterns at various RTA temperatures. See DOI: 10.1039/c9nr04038b
These authors contributed equally to this work.

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