Large-Area, Highly Sensitive SERS Substrates with Silver Nanowire Thin Films Coated by Microliter-Scale Solution Process

A microliter-scale solution process was used to fabricate large-area, uniform films of silver nanowires (AgNWs). These thin films with cross-AgNWs were deposited onto Au substrates by dragging the meniscus of a microliter drop of a coating solution trapped between two plates. The hot spot density was tuned by controlling simple experimental parameters, which changed the optical properties of the resulting films. The cross-AgNW films on the Au surface served as excellent substrates for surface-enhanced Raman spectroscopy, with substantial electromagnetic field enhancement and good reproducibility

Anisotropic nanomaterials: structure, growth, assembly, and functions

Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications

Effect of experimental parameters on optimal reflection of light from opaque media

Previously we considered the effect of experimental parameters on optimized transmission through opaque media using spatial light modulator (SLM)-based wavefront shaping. In this study we consider the opposite geometry, in whichwe optimize reflection from an opaque surface such that the backscattered light is focused onto a spot on an imaging detector. By systematically varying different experimental parameters (genetic algorithm iterations, bin size, SLM active area, target area, spot size, and sample angle with respect to the optical axis) and optimizing the reflected light we determine how each parameter affects the intensity enhancement. We find that the effects of the experimental parameters on the enhancement are similar to those measured for a transmissive geometry, but with the exact functional forms changed due to the different geometry and the use of a genetic algorithm instead of an iterative algorithm. Additionally, we find preliminary evidence of greater enhancements than predicted by random matrix theory, suggesting a possibly new physical mechanism to be investigated in future work

Initial tamper tests of novel tamper-indicating optical physical unclonable functions

Optical physical unclonable functions (O-PUFs) are materials containing a large number of randomly distributed degrees of freedom that can be probed optically. We develop tamper-indicating O-PUF seals using polyurethane adhesives with dispersed nanoparticles, where authentication is performed by use of wavefront-shaping controlled reflection. We test the material's and authentication method's tamper-indicating ability using tampering attacks including: mechanical, thermal, and chemical attacks, with the results demonstrating the material/method's robust tamper-indicating ability. Additionally, we demonstrate that authentication depends strongly on the microscopic distribution of nanoparticles within the polymer, which is unfeasibly difficult to clone. These results are the first demonstration of the validity of this technique for use as tamper-indicating seals. (C) 2017 Optical Society of Americ