Selective assembly of nanoparticles on block copolymer by surface modification

Abstract

Block copolymers have long been recognized as scaffolds to pattern nanoparticles to construct hybrid structures for various electronic [1], optical [2,3] and optoelectronic [4] applications. Earlier studies focused on synthesizing nanoparticles selectively on the nanoscopic elements of the block copolymer [5,6] to obtain ordered structures and fabricate nanodevices, such as nanowires [7]. In other studies, the hierarchical self-assembly of nanoparticles in a nanoparticle-block copolymer mixture was demonstrated where the particles were selectively drawn towards one of the components of the ordered block copolymer morphology [8][9][10]. Based on the possibility of coupling the thermodynamic ordering of the block copolymer and the selective interaction of nanoparticles with the components of the block copolymer, spontaneous ordering of nanoparticles is theorized [11][12][13] and experimentally demonstrated [14,15]. In this paper we describe a method to selectively deposit pre-synthesized nanoparticles on a (preformed) ordered block copolymer surface using a simple approach where one of the nanoscopic polymer domains is selectively functionalized using reactive plasma.PS-PI-PS tri-block copolymer, supplied by Dexco, was deposited on a Si (silicon) substrate as a thin film by spincasting a 1% solution in toluene. Spinning speed was 3,000 rpm and spinning time was 30 s. Initial thickness of the film is 26-28 nm as confirmed by ellipsometry. Molecular weights (MW) of the two PS and central PI blocks are 18,000 Daltons each and 64,000 Daltons, respectively. The isoprene block has 92% 1,4 addition. The molecular weight ratio of PS to PI results in cylindrical morphology [16,17]. The film was processed by the "solvent annealing" procedure [17] and then was baked for 20 min in vacuum at 50 °C. Next, the film was exposed to corona discharge performed in 85% relative humidity air under ambient pressure and temperature for 3 min (moderate etching) or 4 min (deep etching), followed by a thorough rinse with DI (deionized) water. After the film was dried with air flow, it was exposed to 45 W ammonia plasma at a pressure of 580 mTorr for 10 s. Immediately after plasma treatment, the film was immersed into 10 nm Au nanoparticle solution (purchased from BBinternational) for 8-24 h. The Au nanoparticle surface is negatively charged by ClO 4 − groups (as-received). Concentration of the Au nanoparticles is 5.7 × 10 12 particles ml −1 . Prior to use, the pH of the Au nanoparticle solution was adjusted by addition of diluted HCl solution (pH = 1.5) to a value of ~5. No salt was added. Finally, the film was vigorously washed with DI water and dried in air flow.In Figure 1, tapping mode atomic force microscope (AFM) images of the film prior to corona treatment (Figure 1(a)), after corona treatment under moderate (Figure 1(b)) and deep etching (Figure 1(c)) are compared. With moderate etching (Figure 1(b)), while the lateral morphology is intact, the height difference between the crest and trough, Δh, is 6 nm, compared AbstractWe have de...

Morphological analysis of self-assembled SIS block copolymer matrices containing silver nanoparticles

“…As shown in Fig. 1, the morphologies obtained for the unannealed SIS film present ordered cylinder structure produced by selfassembly at nanoscale level, thus confirming the micro-phase separation of PI and PS blocks [22,23]. The PS cylindrical domains appear oriented parallel to the free surface with a period of 15-20 nm.…”

The structures of thin layer formed by microphase separation of grafted Y-shaped block copolymers in solutions

“…This structure is of particular interest because it may allow the generation of periodic surface potential on nanoscales, and be used as structure guiding scaffold to control the spatial distribution of nanoobjects into ordered nanochains. 48,49 In Figs. 10(a) and 10(b), we show typical snapshots of Y-shaped copolymer brushes in nonselective good solvents and poor solvents for different α AB at σ = 1/2 2 , respectively.…”

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

“…[214,224] Nui and Saraf. [225] developed a method to selectively deposit nanoparticles on the ordered nanoscale elements of PS-b-PI-b-PS BCP thin films. They selectively modified the PS surface with amine groups to electrostatically attract negatively charged Au nanoparticles.…”