Spontaneous Vertical Ordering and Pyrolytic Formation of Nanoscopic Ceramic Patterns from Poly(styrene‐b‐ferrocenylsilane)

Abstract

The patterning of surfaces on the nanometer scale is desirable for a variety of applications ranging from membranes to magnetic data storage.[1±4] Block copolymers provide a very promising route to this goal since they self-assemble into ordered arrays of nanostructures, [5±10] where the size is dictated by the molecular weight, and the type of morphology depends on the volume fractions of the blocks. However, control over domain orientation and lateral order of these arrays in thin films has been a challenge. Preferential wetting of a surface by one of the blocks typically results in the orientation of the copolymer microdomains parallel to the substrate, and the film thickness is quantized by the equilibrium period, L 0 . As the film thickness (D) approaches L 0 , the orientation of the microdomains becomes increasingly dictated by the strength of interfacial interactions and the commensurability of L 0 in relation to D. [11] In the case of a confined thin film, incommensurability of L 0 causes either a stretching or compression of the period or a reorientation of the structure normal to the surface. In thin films where the surface is not confined, control over the interfacial interactions has provided a simple route to control the orientation.[12] For thicker films, external fields (i.e., an electric field) have proven to be very effective in controlling the orientation of the microdomains. [13,14] Here, the spontaneous ordering of cylindrical microdomains in thin films of a metal-containing polyferrocene block copolymer perpendicular to a substrate surface is demonstrated. In addition, the pyrolysis of the ordered films to generate patterned arrays of ceramic nanostructures is described.Most studies of block copolymer self-assembly performed to date have focused on organic materials. Metal-containing block copolymers offer additional opportunities for the creation of functional nanostructured materials. [15,16] In this study, the microphase separation in thin films of an amorphous organic±organometallic block copolymer is discussed. Asymmetric poly(styrene-b-ferrocenylethylmethylsilane) block copolymers (PS 374 -b-PFS 45 , number average molecular weight, M n = 52 000 g mol ±1 , polydispersity index (PDI) = 1.21, PS volume fraction of 0.806) having cylindrical domains of PFS block in a PS matrix were studied. The copolymers were prepared by sequential anionic ring-opening polymerization (ROP) as described previously. [17,18] The T g of the PFS block is 19 C, whereas the T g of the PS block is~100 C. This contrasts with symmetrically substituted polyferrocenylsilanes, where the T g of the PFS block is significantly higher and the PFS block crystallizes. Both perturb microphase separation. [19±21] Small-angle X-ray scattering (SAXS) studies of a thermally annealed bulk sample of PS 374 -b-PFS 45 gave a scattering pattern consistent with a cylindrical morphology with a period of 33 nm, as shown in Figure 1. A series of PS 374 -b-PFS 45 films were prepared by spin coating the diblock copolymer onto silicon waf...

Block Copolymer Nanolithography: Translation of Molecular Level Control to Nanoscale Patterns

“…[198,204] Calcination of PS-b-PFS BCP thin films with spherical PFS microdomains was also shown to be an effective strategy for producing arrays of magnetic dots. [205] In a similar way to the formation of metal nanoparticles by reduction of small molecule precursors, sol-gel processes has been widely employed to prepare metal oxide nanoparticles, nanowires, and thin films. The small molecule precursors can be selectively nucleated in hydrophilic domains, which allows spatial localization in amphiphilic BCP thin films.…”

Polyferrocenylsilane‐Based Polymer Systems

“…Self-assembled PI-b-PFS [156] and PS-b-PFS [157] thin films on silicon substrate were used for onestep lithography induced by RIE and pyrolysis, respectively. Remarkably, the former organometallic domains retain their original structure and no change in domain spacing occurs.…”

Pattern transfer using block copolymers

“…O 2 RIE was employed to remove the PI blocks and thereby produce an inorganic oxide mask [121]. Besides O 2 RIE, heating the sample to more than 600 • C was also used to degrade the BCP and to remove the organic components [122,123]. Prior to the heat treatment, the BCP was exposed to UV light to cross-link the PS matrix and thus to prevent the flow of the matrix.…”