Unilamellar vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) with varying 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio) propionate] (DSPE-PEG-PDP) concentration between 0 mol % and 24 mol % were assembled on atomically flat template-stripped gold (TS Au) surfaces. Force spectroscopy, using an atomic force microscope (AFM), of the resulting tethered lipid bilayer membranes (tLBMs) in buffer provided information regarding mechanical response as a function of tethering molecule, DSPE-PEG-PDP, concentration. Young’s modulus was determined by fitting the force–indentation curve with a recently modified Sneddon model that corrects for contributions from the substrate underneath. At low concentrations, Young’s modulus is lower than that of a supported POPC LBM, i.e., directly sitting on a solid substrate. The decrease in modulus is attributed to increased membrane fluidity as coupling between the tLBM and solid substrate is reduced by the incorporation of DSPE-PEG-PDP tethering groups. From the determined Young’s modulus values, the PEG chain conformation is found to dominate tLBM rigidity at concentrations above 6 mol %. Analysis of AFM force spectroscopy data indicates that the poly(ethylene glycol) (PEG) mushroom to brush transition occurs near 6 mol %, and this leads to first softening and then abrupt stiffening of tLBMs at higher DSPE-PEG-PDP concentration associated with the transition. When DSPE-PEG-PDP concentration is increased to 24 mol %, AFM topography and Young’s modulus appear correlated with another phase transition; AFM topography images are consistent with a bilayer disk structure with DSPE-PEG-PDP segregated at the rim of the disk.

We investigate for the first time the capacity of a two-dimensional periodic array (a metasurface) of circular nanoclusters (CNCs) of plasmonic nanoparticles to support magnetic Fano resonances. These resonances are characterized by narrow angular and/or spectral features in the reflection/transmission/absorption coefficients associated with a circular disposition of nanoparticles’ dipole moments (forming a current loop) under oblique TE-polarized plane wave incidence illumination. We find that these narrow resonant features are either array-induced or single-CNC-induced, as shown by using a theoretical analysis based on the single dipole approximation and full-wave simulations, leading to enhanced magnetic and electric fields. In particular, array-induced resonances are narrower than single-CNC-induced ones and also provide even larger field enhancements, in particular generating a magnetic field enhancement of about 10-fold and an electric field enhancement of about 40-fold for a representative metasurface. We suggest that the novel results pertaining to metasurfaces made of CNCs shown here may be used for the development of sensors based on enhanced magnetic fields and for the enhancement of magnetic nonlinearities.Keywords: circular nanoclusters; Fano resonances; metasurfaces; plasmonic nanoparticles

Metallic nanoparticles (MNP) are utilized as electrocatalysts, cocatalysts, and photon absorbers in heterostructures that harvest solar energy. In such systems, the interface formed should be stable over a wide range of pH values and electrolytes. Many current nonthermal processing strategies rely on physical interactions to bind the MNP to the semiconductor. In this work, we demonstrate a generic chemical approach for fabricating highly stable electrochemically/photocatalytically active monolayers and tailored multilayered nanoparticle structures using azide/alkyne-modified Au, TiO2, and SiO2 nanoparticles on alkyne/azide-modified silicon, indium tin oxide, titania, stainless steel, and glass substrates via click chemistry. The stability, electrical, electrochemical, and photocatalytic properties of the interface are shown via electrochemical water splitting, methanol oxidation, and photocatalytic degradation of Rhodamine B (RhB) dye. The results suggest that the proposed approach can be extended for the large-scale fabrication of highly stable heterostructure materials for electrochemical and photoelectrocatalytic devices.Keywords: click chemistry; heterostructures; layer-by-layer; methanol oxidation; tailored mono/multilayers; water splitting;

Discrete clusters of closely spaced Au nanoparticles can be utilized in devices from photovoltaics to molecular sensors because of the formation of strong local electromagnetic field enhancements when illuminated near their plasmon resonance. In this study, scalable, chemical self-organization methods are shown to produce Au nanoparticle clusters with uniform nanometer interparticle spacing. The performance of two different methods, namely electrophoresis and diffusion, for driving the attachment of Au nanoparticles using a chemical cross-linker on chemically patterned domains of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films are evaluated. Significantly, electrophoresis is found to produce similar surface coverage as diffusion in 1/6th of the processing time with an ∼2-fold increase in the number of Au nanoparticles forming clusters. Furthermore, average interparticle spacing within Au nanoparticle clusters was found to decrease from 2–7 nm for diffusion deposition to approximately 1–2 nm for electrophoresis deposition, and the latter method exhibited better uniformity with most clusters appearing to have about 1 nm spacing between nanoparticles. The advantage of such fabrication capability is supported by calculations of local electric field enhancements using electromagnetic full-wave simulations from which we can estimate surface-enhanced Raman scattering (SERS) enhancements. In particular, full-wave results show that the maximum SERS enhancement, as estimated here as the fourth power of the local electric field, increases by a factor of 100 when the gap goes from 2 to 1 nm, reaching values as large as 1010, strengthening the usage of electrophoresis versus diffusion for the development of molecular sensors.

Atomic force microscopy (AFM) studies under aqueous buffer probed the role of chemical affinity between liposomes, consisting of large unilamellar vesicles, and substrate surfaces in driving vesicle rupture and tethered lipid bilayer membrane (tLBM) formation on Au surfaces. 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio) propionate] (DSPE-PEG-PDP) was added to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) vesicles to promote interactions via Au–thiolate bond formation. Forces induced by an AFM tip leading to vesicle rupture on Au were quantified as a function of DSPE-PEG-PDP composition with and without osmotic pressure. The critical forces needed to initiate rupture of vesicles with 2.5, 5, and 10 mol % DSPE-PEG-PDP are approximately 1.1, 0.8, and 0.5 nN, respectively. The critical force needed for tLBM formation decreases from 1.1 nN (without osmotic pressure) to 0.6 nN (with an osmotic pressure due to 5 mM of CaCl2) for vesicles having 2.5 mol % DSPE-PEG-PDP. Forces as high as 5 nN did not lead to LBM formation from pure POPC vesicles on Au. DSPE-PEG-PDP appears to be important to anchor and deform vesicles on Au surfaces. This study demonstrates how functional lipids can be used to tune vesicle–surface interactions and elucidates the role of vesicle–substrate interactions in vesicle rupture.

Driving forces are investigated for assembling low dimensional, metallic, erbium and dysprosium disilicide nanowires on Si(001), using both scanning probe microscopy and density functional theory. Side-by-side comparison between emulated and measured scanning tunneling microscopy images allows establishment of reliable atomic models for complex adatom surface reconstructions of Er/Si(001) and Dy/Si(001) that are precursors to high aspect ratio disilicide nanowires. Peculiar surface reconstructions and relaxation of Si bonds are identified as the key factors for nucleation of these disilicide nanowires in parallel arrays on vicinal Si(001). Stable nanowire widths and heights are calculated with predicted atomic models that are consistent with experimental observations. A clear understanding of the nanowire–substrate interface is determined by correlating adatom reconstruction patterns with nanowire formation that is imperative to the development of unique procedures for massive fabrication of monodisperse nanosystems.

Lipid vesicles are designed with functional chemical groups to promote vesicle fusion on template-stripped gold (TS Au) surfaces that does not spontaneously occur on unfunctionalized Au surfaces. Three types of vesicles were exposed to TS Au surfaces: (1) vesicles composed of only 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipids; (2) vesicles composed of lipid mixtures of 2.5 mol % of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-poly(ethylene glycol)-2000-N-[3-(2-pyridyldithio)propionate] (DSPE-PEG-PDP) and 97.5 mol % of POPC; and (3) vesicles composed of 2.5 mol % of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(poly(ethylene glycol))-2000] (DSPE-PEG) and 97.5 mol % POPC. Atomic force microscopy (AFM) topography and force spectroscopy measurements acquired in a fluid environment confirmed tethered lipid bilayer membrane (tLBM) formation only for vesicles composed of 2.5 mol % DSPE-PEG-PDP/97.5 mol % POPC, thus indicating that the sulfur-containing PDP group is necessary to achieve tLBM formation on TS Au via Au-thiolate bonds. Analysis of force−distance curves for 2.5 mol % DSPE-PEG-PDP/97.5 mol % POPC tLBMs on TS Au yielded a breakthrough distance of 4.8 ± 0.4 nm, which is about 1.7 nm thicker than that of POPC lipid bilayer membrane formed on mica. Thus, the PEG group serves as a spacer layer between the tLBM and the TS Au surface. Fluorescence microscopy results indicate that these tLBMs also have greater mechanical stability than solid-supported lipid bilayer membranes made from the same vesicles on mica. The described process for assembling stable tLBMs on Au surfaces is compatible with microdispensing used in array fabrication.

Template stripping of Au films in ultrahigh vacuum (UHV) produces atomically flat and pristine surfaces that serve as substrates for highly ordered self-assembled monolayer (SAM) formation. Atomic resolution scanning tunneling microscopy of template-stripped (TS) Au stripped in UHV confirms that the stripping process produces a flat, predominantly 〈111〉 textured, atomically clean surface. Octanethiol SAMs vapor deposited in situ onto UHV TS Au show a c(4 × 2) superlattice with (√3 × √3)R30° basic molecular structure having an ordered domain size up to 100 nm wide. These UHV results validate the TS Au surface as a simple, clean and high-quality surface preparation method for SAMs deposited from both vapor phase and solution phase.