Delineating the pathways for the site-directed synthesis of individual nanoparticles on surfaces

Abstract

Although nanoparticles with exquisite properties have been synthesized for a variety of applications, their incorporation into functional devices is challenging owing to the difficulty in positioning them at specified sites on surfaces. In contrast with the conventional synthesis-then-assembly paradigm, scanning probe block copolymer lithography can pattern precursor materials embedded in a polymer matrix and synthesize desired nanoparticles on site, offering great promise for incorporating nanoparticles into devices. This technique, however, is extremely limited from a materials standpoint. To develop a materials-general method for synthesizing nanoparticles on surfaces for broader applications, a mechanistic understanding of polymer-mediated nanoparticle formation is crucial. Here, we design a four-step synthetic process that enables independent study of the two most critical steps for synthesizing single nanoparticles on surfaces: phase separation of precursors and particle formation. Using this process, we elucidate the importance of the polymer matrix in the diffusion of metal precursors to form a single nanoparticle and the three pathways that the precursors undergo to form nanoparticles. Based on this mechanistic understanding, the synthetic process is generalized to create metal (Au, Ag, Pt, and Pd), metal oxide (Fe 2 O 3 , Co 2 O 3 , NiO, and CuO), and alloy (AuAg) nanoparticles. This mechanistic understanding and resulting process represent a major advance in scanning probe lithography as a tool to generate patterns of tailored nanoparticles for integration with solid-state devices.T he integration of nanoparticles into devices has enabled applications spanning sensing (1, 2), catalysis (3), electronics (2), photonics (4), and plasmonics (5, 6), but synthesizing individual nanoparticles with control over size, composition, and placement on substrates is challenging (1-3, 6, 7). With conventional approaches, nanoparticles are synthesized and subsequently positioned on a surface using techniques such as parallel printing (8), surface dewetting (9, 10), microdroplet molding (7), nanoparticle sliding (11), direct writing (4, 12, 13), and self-assembly (2, 14, 15). However, it is difficult and in most cases, impossible to use these methods to reliably make and position a single particle on a surface with nanometer-scale control.In contrast with the conventional synthesis-then-positioning paradigm, which is the basis for most single-particle device incorporation schemes, scanning probe block copolymer lithography (SPBCL) is an example of precursor positioning-then-synthesis. The technique uses concepts from the block copolymer community (16) and the positional control offered by dip-pen nanolithography (DPN) (17) to deliver attoliter volumes of a metalcoordinated block copolymer onto a surface, which then can be used to synthesize individual nanoparticles (18,19). Importantly, SPBCL allows one to directly synthesize arbitrary patterns of single nanoparticles over large areas on a surface, which has been usef...

Preparation of IrO2 nanoparticles with SBA-15 template and its supported Pt nanocomposite as bifunctional oxygen catalyst

“…As reported by Liu and Mirkin [28], individual nanoparticles were successfully synthesized at specified sites on surface by scanning probe block copolymer lithography, where the nanoparticles were artificially controlled by amount of the precursor loaded in each patterned polymer feature. Here, we control IrO 2 particles by SBA-15 pore channels, where IrO 2 are restrictively grown.…”

The Structural Fate of Individual Multicomponent Metal‐Oxide Nanoparticles in Polymer Nanoreactors

“…SPBCL enables the synthesis of individual metal, [7] oxide, [7b] and sulfide [8] NPs at predefined locations on a substrate. Unlike other techniques that enable localized delivery of NPs, such as sol-gel deposition of oxide nanostructures via dip-pen nanolithography (DPN), [9] or printing of preformed NPs, [10] with SPBCL, metal-coordinated block copolymers are deposited onto a substrate in the form of attoliter hemispherical domes (polymer nanoreactors).…”

“…Each reactor, when heated under the appropriate environment, results in the formation of a single NP. [7] Significantly, this process allows one to directly control the stoichiometry and thermal processing while synthesizing on substrates compatible with electron microscopy. These properties make SPBCL a powerful tool for synthesizing NPs with precise control over composition and size, making it an ideal platform for the systematic study of crystal structure and elemental composition and distribution with correlated electron microscopy.…”

“…Although SPBCL has been used to study oxide NPs containing a single metal element, [7b] it has not been extended to multicomponent metal oxide formation. To reliably make a given multicomponent particle with a relatively well-defined structure and stoichiometry, the synthesis of each particle must be studied over a range of temperatures and compositions.…”

“…Moreover, these complex nanostructures can be readily generated en masse with large area lithographic techniques such as polymer pen lithography. [7a, 18] Taken together, all of these observations should lead to an enhanced understanding of the conditions that yield complex oxide NPs with emergent properties.…”