This paper describes a parallel method to generate polymer nanowrinkles over large areas with wavelengths that were continuously tuned down to 30 nm. Reactive ion etching using fluorinated gases was used to chemically treat thermoplastic polystyrene films, which resulted in a stiff skin layer. Upon heating, the treated thermoplastic, microscale, and nanoscale wrinkles were formed. We used variable-angle spectroscopic ellipsometry to characterize the thickness of the skin layer; this thickness could then be used to predict and control the nanowrinkle wavelength. Because the properties of these nanotextured polymer surfaces can be tuned over a large range of wrinkle wavelengths, they are promising for a broad range of applications, especially those that require large-area and uniform surface patterning.

This paper describes how delamination-free, hierarchical patterning of graphene can be achieved on prestrained thermoplastic sheets by surface wrinkling. Conformal contact between graphene and the substrate during strain relief was maintained by the presence of a soft skin layer, resulting in the uniform patterning of three-dimensional wrinkles over large areas (>cm). The graphene wrinkle wavelength was tuned from the microscale to the nanoscale by controlling the thickness of the skin layer with 1 nm accuracy to realize a degree of control not possible by crumpling, which relies on delamination. Hierarchical patterning of the skin layers with varying thicknesses enabled multiscale graphene wrinkles with predetermined orientations to be formed. Significantly, hierarchical graphene wrinkles exhibited tunable mechanical stiffness at the nanoscale without compromising the macroscale electrical conductivity.

This paper describes how a memory-based, sequential wrinkling process can transform flat polystyrene sheets into multiscale, three-dimensional hierarchical textures. Multiple cycles of plasma-mediated skin growth followed by directional strain relief of the substrate resulted in hierarchical architectures with characteristic generational (G) features. Independent control over wrinkle wavelength and wrinkle orientation for each G was achieved by tuning plasma treatment time and strain-relief direction for each cycle. Lotus-type superhydrophobicity was demonstrated on three-dimensional G1-G2-G3 hierarchical wrinkles as well as tunable superhydrophilicity on these same substrates after oxygen plasma. This materials system provides a general approach for nanomanufacturing based on bottom-up sequential wrinkling that will benefit a diverse range of applications and especially those that require large area (>cm(2)), multiscale, three-dimensional patterns.

This paper reports the manipulation of surface plasmon polaritons (SPPs) in a liquid plasmonic metal by changing its physical phase. Dynamic properties were controlled by solid-to-liquid phase transitions in 1D Ga gratings that were fabricated using a simple molding process. Solid and liquid phases were found to exhibit different plasmonic properties, where light coupled to SPPs more efficiently in the liquid phase. We exploited the supercooling characteristics of Ga to access plasmonic properties associated with the liquid phase over a wider temperature range (up to 30 °C below the melting point of bulk Ga). Ab initio density functional theory-molecular dynamic calculations showed that the broadening of the solid-state electronic band structure was responsible for the superior plasmonic properties of the liquid metal.

We describe herein how to control the orientation of polymer nanowrinkles and nanofolds with large amplitudes. Nanowrinkles were created by chemically treating thermoplastic polystyrene sheets to form a thin skin layer and then heating the substrate to relieve strain. By manipulating the strain globally and locally in the skin layer, we could tune whether wrinkles or folds formed, as well as the distances over which these structures could be produced. This unique materials system provided access to high strain regimes, which enabled mechanisms behind the spontaneous formation of complex structures to be explored.

Porous p-Cu 2 O films were prepared on transparent conductive glass from a dispersion of Cu 2 O powder in ethanol. Upon illumination with a 100 W tungsten lamp, the photocurrent of the porous Cu 2 O film was appreciably greater when compared to electrodeposited Cu 2 O films. The enhancement is attributed to the increased interfacial area between the film and the solution due to the three-dimensional nature of the Cu 2 O film. No chemical change was detected by visual examination and X-ray diffraction of the porous Cu 2 O film after illumination for 2 h in the aqueous solution at −0.4 V vs saturated calomel electrode. The reported stability of electrodeposited Cu 2 O films is attributed to the effect of Cu + -terminated ͑111͒ surface, where the H + -assisted photoreduction of Cu 2 O is less likely to occur. The well-known instability of single-crystal Cu 2 O is hypothesized to be due to the predominating ͑211͒ and ͑311͒ surfaces, where the photodecomposition to Cu is inevitable at the exposed O 2− sites.

Nanostructured surfaces with quasi-random geometries can manipulate light over broadband wavelengths and wide ranges of angles. Optimization and realization of stochastic patterns have typically relied on serial, direct-write fabrication methods combined with real-space design. However, this approach is not suitable for customizable features or scalable nanomanufacturing. Moreover, trial-and-error processing cannot guarantee fabrication feasibility because processing-structure relations are not included in conventional designs. Here, we report wrinkle lithography integrated with concurrent design to produce quasi-random nanostructures in amorphous silicon at wafer scales that achieved over 160% light absorption enhancement from 800 to 1,200 nm. The quasi-periodicity of patterns, materials filling ratio, and feature depths could be independently controlled. We statistically represented the quasi-random patterns by Fourier spectral density functions (SDFs) that could bridge the processing-structure and structure-performance relations. Iterative search of the optimal structure via the SDF representation enabled concurrent design of nanostructures and processing.wrinkles | light trapping | silicon photonics | spectral density function | pattern transfer Q uasi-random structures with neither periodic nor fully disordered geometries are useful in the design of superhydrophobic substrates (1, 2), stretchable electronics (3-6), and sensors (7,8). In particular, these nanostructured systems support rich Fourier spectra that enable light manipulation over broadband wavelengths and over wide collection angles (9, 10). Independent control over the relative degree of order vs. disorder, materials filling ratio, and feature size is critical to generate patterns with a diverse range of optical responses (11). For example, quasi-random nanostructures in photonic materials such as amorphous silicon (a-Si) are being increasingly used in photovoltaics and light-emitting diodes (9, 12-18). To enhance device performance from the patterns, optimization of nanoscale structure is crucial. However, most efforts to control quasirandom patterns have relied on serial processes such as electron-beam lithography (9,12,16,18,19). Although such approaches enable precise pattern placement and maximum control over the nanostructured features, the tools are not scalable and are cost prohibitive for large-area fabrication (>1 cm 2 ). Furthermore, most work has focused on the traditional, sequential strategy for pattern generation: (i) design nanostructures in real space for a target performance and then (ii) fabricate structures by trial-and-error processing optimization (9, 20). Without considering the fabrication conditions as part of the overall design strategy, however, conventional methods cannot ensure manufacturing feasibility of the optimized nanostructures. Trial-and-error experiments to achieve optimal designs are usually time-consuming. Hence, development of a concurrent design approach can establish the phase space of target quasi-rand...

We describe herein how to control the orientation of polymer nanowrinkles and nanofolds with large amplitudes. Nanowrinkles were created by chemically treating thermoplastic polystyrene sheets to form a thin skin layer and then heating the substrate to relieve strain. By manipulating the strain globally and locally in the skin layer, we could tune whether wrinkles or folds formed, as well as the distances over which these structures could be produced. This unique materials system provided access to high strain regimes, which enabled mechanisms behind the spontaneous formation of complex structures to be explored.Over every length scale, wrinkles form when a compressive strain is applied to a stiff skin on a soft substrate.[1] The average wrinkle periodicity (l) can be predicted from the skin thickness (h) and the ratio of the Young modulus of the skin (E S ) and substrate (E B ). [1][2][3] For microscale and nanoscale wrinkles, the skin layer is typically a stiffened polymer or deposited metal film, whereas substrate examples include compressible polymers or fluids. [2,[4][5][6][7] Wrinkling has emerged as a way to control the mechanical, electrical, and optical properties of a substrate without changing the bulk properties of the material. [3,4] For example, polymer microwrinkles can increase hydrophobicity while maintaining mechanical flexibility.[8] We previously reported how the wavelengths of nanowrinkles (l < 500 nm) could be tuned down to 30 nm by creating a skin layer on thermoplastic polystyrene (PS) sheets through plasma treatment with fluorinated gases.[9] This chemical patterning method enabled access to wrinkle wavelengths much smaller than those accessible with other systems [1,9] because of the low Youngs modulus ratio (E S / E B < 10) and thin skin layers (h < 20 nm).Besides l, wrinkle amplitude (A) is another important parameter that defines the properties of a substrate. Uniformly distributed 2D strain results in randomly oriented nanowrinkles with a value A that depends on the amount of applied strain (e) until a critical threshold is reached. In this strain regime, A has been limited to less than 10 nm for nanowrinkles. [1,4] Above this threshold, strain is relieved by the formation of a second generation of wrinkles with a larger periodicity [4] or by a wrinkle-to-fold transition, [5,10] whereby strain is concentrated into periodic folds. [7,11] Such structures that form under high strain may enable additional tuning of surface properties; however, the materials characteristics that lead to these structures are not well understood.[3] Patterning of the local strain distribution in the skin layer at the microscale is another strategy to create ordered structures from inherently disordered patterns. [2,[12][13][14][15][16] For example, etched features in a gold skin layer on a poly(dimethylsiloxane) substrate have been used to orient microwrinkles over distances up to 17 times the wrinkle wavelength. [2,12] Although micro-and nanoscale patterns [17] have been used to control the ampli...