Block Copolymer-Templated Chemistry on Si, Ge, InP, and GaAs Surfaces

Abstract

Patterning of semiconductor surfaces is an area of intense interest, not only for technological applications, such as molecular electronics, sensing, cellular recognition, and others, but also for fundamental understanding of surface reactivity, general control over surface properties, and development of new surface reactivity. In this communication, we describe the use of self-assembling block copolymers to direct semiconductor surface chemistry in a spatially defined manner, on the nanoscale. The proof-of-principle class of reactions evaluated here is galvanic displacement, in which a metal ion, M+, is reduced to M0 by the semiconductor, including Si, Ge, InP, and GaAs. The block copolymer chosen has a polypyridine block which binds to the metal ions and brings them into close proximity with the surface, at which point they undergo reaction; the pattern of resulting surface chemistry, therefore, mirrors the nanoscale structure of the parent block copolymer. This chemistry has the added advantage of forming metal nanostructures that result in an alloy or intermetallic at the interface, leading to strongly bound metal nanoparticles that may have interesting electronic properties. This approach has been shown to be very general, functioning on a variety of semiconductor substrates for both silver and gold deposition, and is being extended to organic and inorganic reactions on a variety of conducting, semiconducting, and insulating substrates.

Tuning the Dimensions and Periodicities of Nanostructures Starting from the Same Polystyrene‐block‐poly(2‐vinylpyridine) Diblock Copolymer

“…[22,31,32,34,50] Post-loading implies that the inorganic salts are loaded after the formation of the micellar film, while preloading implies that the micelles are loaded in solution and …”

Synthesis and SERS Properties of Nanocrystalline Gold Octahedra Generated from Thermal Decomposition of HAuCl4 in Block Copolymers

“…At Au III /pyridyl loadings of 0.1, 0.5, and 0.7, the average density of nanoparticles is approximately 36, 32, and 19 lm -2 , respectively; these numbers indicate that the block copolymer is not mediating spacing because the heating melts the block copolymers and thus the average distances between the block copolymer cores become independent of the observed room-temperature patterning. [18] To investigate the scalability of the synthesis of gold octahedra, a bulk preparation was carried out with a thick film (5-8 lm, as determined by SEM) prepared by evaporation deposition of a 0.5 wt % polymer solution in toluene on a silicon substrate, followed by thermal treatment at 250°C for 5 min in air. The ratio of HAuCl 4 /PS-b-P2VP was kept constant at 0.5 Au III /pyridyl-group.…”

“…S2) that showed a substantially enhanced gold signal at 350°C over 250°C, pointing to less interference by the polymer, a result of its apparent thermal degradation. [18] Since the polymer inhibited 2-NAT contact with the gold nanoparticle film, PS-b-P2VP was removed by a brief, 1.5 min room-temperature treatment with oxygen plasma. Nanoparticle shapes and average spacing remained unchanged upon plasma treatment (Fig.…”

Organic-Free Au-Pd Alloys on Germanium Substrate via Spontaneous Galvanic Displacement Reaction

“…[8][9][10][11][12][13] The galvanic displacement, a mechanism-based nomenclature for the spontaneous metal nanocrystal formation, involves direct electron transfer from metal or semiconductor substrates (electron donors) to metallic precursor cations (electron acceptors) at room temperature according to their relative electrochemical redox potentials. A representative example of metal nanocrystals synthesized by the galvanic displacement is Au nanoparticles on germanium (Ge) surface.…”

“…To take the best advantage of its simplicity, the galvanic displacement process has been mostly applied to synthesize monometallic noble metal nanocrystals such as Au, Ag, Pd, Pt, and etc. [8][9][10][11][12][13] on Ge or other semiconductors such as GaAs, InP substrate, of which cations generally have significantly large positive standard reduction potential values. On the contrary, there is not much report about the formation of composite alloys which are of great interest from scientific and technological perspectives owing to their composition-dependent optical, catalytic, electronic, and magnetic properties.…”