Nanoscopic Morphologies in Block Copolymer Nanorods as Templates for Atomic‐Layer Deposition of Semiconductors

Abstract

Block copolymers (BCPs) self-assemble into ordered arrays of nanoscopic domains, the nature of which depends on the constituents of the BCPs and their molecular architecture.[1] BCPs have been exploited as precursors for nanoporous materials [2] and as templates for the rational design of nanoscopic architectures with periods from below 10 nm up to the 100-nm-range in thin-film configurations.[3] Whereas molds containing arrays of aligned cylindrical nanochannels with hard confining walls, such as self-ordered anodic aluminum oxide (AAO), [4] have been used to fabricate one-dimensional nanostructures from a plethora of materials, [5] the self-assembly of BCPs in cylindrical confinement has only recently emerged as an access to nanorods exhibiting ordered nanoscopic fine structures.[6] Sol-gels containing precursors for inorganic scaffold materials and BCPs as structuredirecting soft templates were infiltrated into AAO. Subsequent gelation and calcination yielded nanorods consisting of various inorganic oxides and amorphous carbon exhibiting ordered mesoporous fine structures. [7] However, direct infiltration of microphase-separated BCP melts into AAO [8] has received much less attention, mainly because of a lack of obvious applications of the solid BCP nanorods thus obtained. Only recently, BCP nanorods have been converted into mesoporous polymeric nanorods by degrading sacrificial blocks [9] and by selective swelling.[10]BCPs confined to AAO with pore diameters about one order of magnitude larger than their characteristic bulk periods have been reported to retain bulk-like morphologies, such as cylinders oriented along the pore axes and concentric-cylindrical lamellae.Nanoscopic domain structures substantially different from those obtained in the absence of geometric constraints form if BCPs self-assemble within cylindrical pores having diameters of the same order of magnitude than their characteristic periods. [11][12][13] Wu et al. synthesized silica nanorods containing helical and circular-cylindrical ''stacked-doughnuts'' mesopore structures by gelation and calcination of sol-gels containing poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) and tetraethyl orthosilicate infiltrated into AAO with pore diameters below 70 nm, [11] and prepared metal replicas of helical mesopores by electrochemical deposition.[14] However, only little effort has been directed to the experimental study of BCP melts selfassembling under strong cylindrical confinement, [12] even though the formation of a broad variety of unprecedented confinementinduced nanoscopic domain structures has been predicted. [15] Thus, only a small range of the potentially accessible morphologies has been realized, and their exploitation for the generation of functional nanostructures has not yet been addressed.Here, we report the fabrication of hierarchical one-dimensional semiconductor nanostructures containing structural motifs, such as helices and stacked doughnuts, that mimic unconventional, confinement-induced nanoscopic...

Gyroid-Forming Diblock Copolymers Confined in Cylindrical Geometry: A Case of Extreme Makeover for Domain Morphology

“…Similarly, for the sphere-forming PS-b-PB, one observes that large pores (D/L 0 > 3.2) lead to spherical PB domains aligned along the pore axis, whereas in pores with smaller diameters (D/L 0 < 3.2), core-shell cylindrical morphologies, single columns of spherical microdomains, and spirals of doubly and triply paired spherical microdomains are observed [9,10]. Helical and stacked toroidal structures have also been observed by Wang and coworkers in the study of asymmetric poly(styrene-b-2-vinylpyridine) DBCPs confined in anodic aluminum oxide nanopores [12]. Concentric lamellar (CL) structures have been observed by Sun and coworkers in the study of symmetric poly(styrene-b-methyl methacrylate) DBCPs confined in alumina nanopores [13].…”

Templated self‐assembly of block copolymers – Toward the rational design of plasmonic nanorods

“…2) by selective swelling the blocks making up the helices. Inorganic functional materials, such as ZnO, could be deposited on the walls of the internal mesopores [20] using atomic layer deposition [37]. Extraction of the BCP soft template yielded helical semiconductor nanostructures (Fig.…”

Strategies for Inorganic Incorporation using Neat Block Copolymer Thin Films for Etch Mask Function and Nanotechnological Application

“…Such approaches allow tuning and interface engineering to precisely modify nanoscale BCP features on a large scale. This review focuses on techniques that modify nanolithography relevant self-assembled BCP templates (spheres, cylinders, lamella) as opposed to methods that coat or infi ltrate kinetically trapped structures like micelles, [ 92 ] nanorods, [ 93 ] etc. It could be argued that ALD alone is not a true "infi ltration" technique however it warrants highlighting due it possible impact for feature size alteration, density multiplication potential, and close relationship with SIS (Section 3.3).…”