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Semiconductor nanowires (NWs) capped with metal nanoparticles (NPs) show multifunctional and synergistic properties, which are important for applications in the fields of catalysis, photonics, and electronics. Conventional colloidal syntheses of this class of hybrid structures require complex sequential seeded growth, where each section requires its own set of growth conditions, and methods for preparing such wires are not universal. Here, we report a new and general method for synthesizing metal–semiconductor nanohybrids based on particle catalysts, prepared by scanning probe block copolymer lithography, and chemical vapor deposition. In this process, metallic heterodimer NPs were used as catalysts for NW growth to form semiconductor NWs capped with metallic particles (Au, Ag, Co, Ni). Interestingly, the growth processes for NWs on NPs are regioselective and controlled by the chemical composition of the metallic heterodimer used. Using a systematic experimental approach, paired with density functional theory calculations, we were able to postulate three different growth modes, one without precedent.

Multimetallic heterostructured nanoparticles with high-index facets potentially represent an important class of highly efficient catalysts. However, due to their complexity, they are often difficult to synthesize. Herein, a library of heterostructured, multimetallic (Pt, Pd, Rh, and Au) tetrahexahedral nanoparticles was synthesized through alloying/dealloying with Bi in a tube furnace at 900–1000 °C. Electron microscopy and selected area diffraction measurements show that the domains of the heterostructured nanoparticles are epitaxially aligned. Although nanoparticles formed from Au alone exhibit low-index facets, Pt and Au form PtAu heterostructured nanoparticles with high-index facets, including domains that are primarily made of Au. Furthermore, the alloying/dealloying of Bi occurs at different rates and under different conditions within the heterostructured nanoparticles. This influences the types of architectures observed en route to the final high-index state, a phenomenon clearly observable in the case of PdRhAu nanoparticles. Finally, scanning probe block copolymer lithography was used in combination with this synthetic strategy to control nanoparticle composition in the context of PtAu nanoparticles (1:4 to 4:1 ratio range) and size (15 to 45 nm range).

Realizing nanostructured interfaces with precise architectural control enables one to access properties unattainable using bulk materials. In particular, a nanostructured interface (e.g., a core–shell nanowire) between two semiconductors leads to a short charge separation distance, such that photoexcited charge carriers can be more quickly and efficiently collected. While vapor-phase growth methods are used to synthesize uniform core–shell nanowire arrays of semiconductors such as Si and InP, more general strategies are required to produce related structures composed of a broader range of materials. Herein, we employ anodic aluminum oxide templates to synthesize CH3NH3PbI3perovskite core–copper thiocyanate shell nanowire arrays employing a combination of electrodeposition and solution casting methods. Using scanning electron microscopy, powder X-ray diffraction, and time-resolved photoluminescence spectroscopy, we confirm the target structure and show that adopting a core–shell nanowire architecture accelerates the rate of charge quenching by nearly 3 orders of magnitude compared to samples with only an axial junction. Subsequently, we fit decay curves to a triexponential function to attribute fast quenching in core–shell nanowires to charge extraction by the copper thiocyanate nanotubes, as opposed to recombination within the perovskite nanowires. Dramatic improvements to charge extraction speed and efficiency result from the substantially reduced charge separation distance and increased interfacial area achieved viathe core–shell nanowire array architecture.

Patterning nanoscale features across macroscopic areas is challenging due to the vast range of length scales that must be addressed. With polymer pen lithography, arrays of thousands of elastomeric pyramidal pens can be used to write features across centimeter-scales, but deformation of the soft pens limits resolution and minimum feature pitch, especially with polymeric inks. Here, we show that by coating polymer pen arrays with a ∼175 nm silica layer, the resulting hard transparent arrays exhibit a force-independent contact area that improves their patterning capability by reducing the minimum feature size (∼40 nm), minimum feature pitch (<200 nm for polymers), and pen to pen variation. With these new arrays, patterns with as many as 5.9 billion features in a 14.5 cm2area were written using a four hundred thousand pyramid pen array. Furthermore, a new method is demonstrated for patterning macroscopic feature size gradients that vary in feature diameter by a factor of 4. Ultimately, this form of polymer pen lithography allows for patterning with the resolution of dip-pen nanolithography across centimeter scales using simple and inexpensive pen arrays. The high resolution and density afforded by this technique position it as a broad-based discovery tool for the field of nanocombinatorics.

Nanoparticle on mirror (NPoM) architectures are attractive for optical applications–particularly for sensing–due to their simplicity and reliability of their multicomponent plasmonic interactions. However, to date, work has predominantly focused on monometallic nanoparticles on different metallic films. While these studies have investigated the effect of geometry on the optical responses of NPoM structures, understanding the effect of nanoparticle composition is needed to gain a full understanding and complete control over these systems. To elucidate the role of composition on localized plasmonic resonances, a surface-based nanoparticle synthetic method, scanning block copolymer lithography (SPBCL), was used to synthesize and characterize single Au0.5Ag0.5particles on a five-layer, thermally stable plasmonic mirror substrate. The use of SPBCL is important because it can easily be extended to almost a limitless number of polyelemental systems. We demonstrate the potential of the approach by using surface-enhanced Raman spectroscopy to detect benzene-1,4-dithiol adsorbed onto individual alloyed AuAg NPs in an NPoM geometry.