Skin-Inspired Tactile Sensor on Cellulose Fiber Substrates with Interfacial Microstructure for Health Monitoring and Guitar Posture Feedback.

Skin-inspired flexible tactile sensors, with interfacial microstructure, are developed on cellulose fiber substrates for subtle pressure applications. Our device is made of two cellulose fiber substrates with conductive microscale structures, which emulate the randomly distributed spinosum in between the dermis and epidermis layers of the human skin. The microstructures not only permit a higher stress concentration at the tips but also generate electrical contact points and change contact resistance between the top and bottom substrates when the pressure is applied. Meanwhile, cellulose fibers possessing viscoelastic and biocompatible properties are utilized as substrates to mimic the dermis and epidermis layers of the skin. The electrical contact resistances (ECR) are then measured to quantify the tactile information. The microstructures and the substrate properties are studied to enhance the sensors' sensitivity. A very high sensitivity (14.4 kPa-1) and fast recovery time (approx. 2.5 ms) are achieved in the subtle pressure range (approx. 0-0.05 kPa). The device can detect subtle pressures from the human body due to breathing patterns and voice activity showing its potential for healthcare. Further, the guitar strumming and chord progression of the players with different skill levels are assessed to monitor the muscle strain during guitar playing, showing its potential for posture feedback in playing guitar or another musical instrument.

Au-Based Thin-Film Metallic Glasses for Propagating Surface Plasmon Resonance-Based Sensor Applications.

We deposited Au-Cu-Si, an Au-based thin-film metallic glass (TFMG) of ∼50 nm thickness, as the activation layer for propagating surface plasmon resonance (PSPR)-based sensors on a BK7 glass substrate to substitute the commonly used gold layer. The film composition was tuned to yield the maximum Au content (∼65 at %), while the structure remained amorphous. The results showed that the Au-based TFMG could support surface plasmon resonance and gave rise to the extinction in the angle-resolved reflection spectrum. Using deionized water and ethyl alcohol with the refractive index difference of ∼0.03 as the analytes, the angle shift given by Au-based TFMG was 4° compared to 5° given by the Au film. Hence, Au-based TFMG is feasible to be used as the activation layer in PSPR-based sensors. Compared to the Au film, Au-based TFMG has the advantages of being less expensive, lacking grain boundary scattering, better adhesion to the substrate, and higher resistance to scratch and corrosion because of its amorphous structure with excellent mechanical properties.

Structural and Optical Properties of Textured Silicon Substrates by Three-Step Chemical Etching.

We implemented the fabrication of hybrid structures, including pyramids, etching holes, and inverted pyramidal cavities on silicon substrates, by three-step chemical etching. To achieve this, we utilized anisotropic wet etching as the first-step etching to form pyramids of various sizes. Subsequently, metal-assisted chemical etching was performed to develop aligned etching holes on the pyramidal structure. Ultimately, anisotropic wet etching was used again as the third-step etching for the etchant to penetrate holes to form inverted pyramidal cavities. Optimizing the three-step etching treatments, large-scale textured structures with low reflectance could be obtained, and they show potential for applications in sensors, solar cells, photovoltaics, and surface-enhanced Raman scattering (SERS). Examples of using the textured silicon substrates for SERS applications were given.

Surface plasmons excited by multiple layer grating.

The surface plasmons that are excited by the multiple layer grating structures on the gold thin film are studied using the finite-difference time-domain method in this paper. The structure parameters' effects on the coupling enhancement of surface plasmons are examined, and the structure design guidelines are given. It is found that the distance between the grating layers and the distance between the gratings and gold thin film are the key structure parameters for better cavity resonances. To have the stronger field enhancements of the excited surface plasmons for the multilayer grating structures, it is found that the width of the gratings should be smaller for the lower grating layers. The multiple layer gratings with proper structure designs can have better performances than single layer grating structure because the cavity effects can enhance the light coupling and more light can be coupled into the surface plasmons by more layers of grating. It is found that the maximum electric field intensity for five layer grating structures can be 163% of the case of the single layer grating structure in our simulations.

Effects of Al Addition on Microstructures and Mechanical Properties of CoCrFeMnNiAlx High Entropy Alloy Films.

CoCrFeMnNiAlx (x = 0, 0.07, 0.3, 0.6, 1.0, 1.3) high-entropy alloy films (HEAFs) were processed by co-sputtering of CoCrFeMnNi alloy and Al targets. The effects of Al content on the microstructures and mechanical properties of HEAFs were studied. The XRD results indicated that the crystalline structure changed from the single face-centered cubic (FCC) phase for x = 0 and 0.07 to duplex FCC + body-centered cubic (BCC) phases for x = 0.3 and 0.6, and eventually, to a single BCC phase for x = 1.0 and 1.3, which agreed with the corresponding selected-area electron diffraction patterns. Also, nanotwins were observed in the FCC phase. Mechanical properties of films were studied using nanoindentation and micropillar compression tests. The hardness increased from 5.71 GPa at x = 0 to 8.74 GPa at x = 1.3. The compressive yield strength increased from 1.59 GPa to 3.73 GPa; however, the fracture strain decreased from 20.91% (no fracture) to 13.78% with the increasing Al content. Both nanotwins and BCC phase contributed to the strengthening effects for CoCrFeMnNiAlx HEAFs. Also, compared to the bulk CoCrFeMnNiAlx counterpart, the film exhibited much higher hardness and strength because of the much smaller grain size and the presence of nanotwins.

Far-field and near-field monitoring of hybridized optical modes from Au nanoprisms suspended on a graphene/Si nanopillar array.

The optical hybridization of localized surface plasmons and photonic modes of dielectric nanostructures provides us wide arenas of opportunities for designing tunable nanophotonics with excellent spectral selectivity, signal enhancement, and light harvesting for many optical applications. Graphene-supported Au nanoprisms on a periodic Si nanopillar array will be an ideal model system for examining such an optical hybridization effect between plasmonic modes and photonic modes. Here, through the measurement of the reflectance spectra as well as graphene phonons by surface-enhanced Raman scattering (SERS), we investigated both the far-field and near-field properties of these optically hybridized modes. The effects of photonic modes and Mie resonances of the Si nanopillars on the localized surface plasmons of the Au nanoprisms and on their near-field enhancement were experimentally elucidated through the measurements of graphene phonons using two excitation lasers with wavelengths of 532 and 785 nm. The wavelength-dependent SERS intensities of monolayer graphene are clearly understood in terms of the optical hybridization, and the SERS enhancement factor estimated from finite-difference time-domain simulations exhibited good agreement with the measurements. The elucidated spectral tunability in the near-field light-matter interaction would be useful for potential applications in various types of graphene-based photonics.

Gold-rich ligament nanostructure by dealloying Au-based metallic glass ribbon for surface-enhanced Raman scattering.

A new method to fabricate an Au-rich interconnected ligament substrate by dealloying the Au-based metallic glass ribbon for surface-enhanced Raman scattering (SERS) applications was investigated in this study. Specifically, three substrates, Au film, Au-based metallic glass ribbon, and dealloyed Au-based metallic glass ribbon, were studied. The dealloyed surface showed ligament nanostructure with protruding micro-islands. Based on the field emission scanning electron microscopy, reflection and scattering measurements, the dealloyed Au-based metallic glass provided a large surface area, multiple reflections, and numerous fine interstices to produce hot spots for SERS enhancements. The SERS signal of analyte, p-aminothiophenol, in the micro-island region of dealloyed Au-based metallic glass was about 2 orders of magnitude larger than the flat Au film. Our work provides a new method to fabricate the inexpensive and high SERS enhancements substrates.

Effects of the rotation angle on surface plasmon coupling of nanoprisms.

We studied the effects of relative orientation of bowtie nanostructures on the plasmon resonance both experimentally and theoretically in this work. Specifically, we fabricated gold bowtie nanoantennas with rotated nanoprisms, measured the near-field and the far-field resonance behaviors using Raman spectroscopy and scattering microspectroscopy, and simulated the effects of the rotation angle on the localized surface plasmonic resonance using finite-difference time-domain simulations. In addition to the widely-discussed dipolar resonance in regular bowtie nanostructures, defined as tip-mode resonance in the present study, the excitations of edge-mode resonance were discovered under certain rotation angles of nanoprisms. Because of the resonances of different modes at different wavelengths, two different incident laser sources were used to measure the Raman spectra to provide evidence for the evolution of different resonance modes. Also, both the tip-mode and edge-mode resonances were verified by the simulated charge density distribution and their trends were discussed. Based on the discovered trend, a plasmon protractor was created with a near-exponential decay relationship between the relative resonance wavelength shift and cosine of the rotation angle. A plasmon hybridization model was also proposed for rotated bowties to explain the coupling between nanoprisms during rotation.

Optical control of fluorescence through plasmonic eigenmode extinction.

We introduce the concept of optical control of the fluorescence yield of CdSe quantum dots through plasmon-induced structural changes in random semicontinuous nanostructured gold films. We demonstrate that the wavelength- and polarization dependent coupling between quantum dots and the semicontinuous films, and thus the fluorescent emission spectrum, can be controlled and significantly increased through the optical extinction of a selective band of eigenmodes in the films. This optical method of effecting controlled changes in the metal nanostructure allows for versatile functionality in a single sample and opens a pathway to in situ control over the fluorescence spectrum.

Electric field enhancement and far-field radiation pattern of the nanoantenna with concentric rings.

The optical antennas have the potential in various applications because of their field enhancement and directivity control. The directivity of a dipole antenna can be improved by directivity-enhanced Raman scattering structure, which is a combination of a dipole antenna and a ring reflector layer on a ground plane. The concentric rings can collect the light into the center hole. Depending upon the geometry of the antenna inside the hole, different electric field enhancements can be achieved. In this paper, we propose to combine the concentric rings with the directivity-enhanced Raman scattering structure in order to study its electric field enhancement and the far-field radiation pattern by finite-difference time-domain simulations. Compared with the structure without the concentric rings over the ground plane, it is found that our proposed structure can obtain stronger electric field enhancements and narrower radiation beams because the gold rings can help to couple the light into the nanoantenna and they also scatter light into the far field and modify the far-field radiation pattern. The designed structures were fabricated and the chemical molecules of thiophenol were attached on the structures for surface-enhanced Raman scattering (SERS) measurements. The measured results show that the structure with concentric rings can have stronger SERS signals. The effects of the dielectric layer thickness in our proposed structure on the near-field enhancements and far-field radiation are also investigated. The proposed structure can be useful for several nanoantenna applications, such as sensing or detecting.

PRAP: an ab initio software package for automated genome-wide analysis of DNA repeats for prokaryotes.

MOTIVATION: Prokaryotic genome annotation has been focused mainly on identifying all genes and their protein functions. However, <30% of the prokaryotic genomes submitted to GenBank contain partial repeat features of specific types and none of the genomes contain complete repeat annotations. Deciphering all repeats in DNA sequences is an important and open task in genome annotation and bioinformatics. Hence, there is an immediate need of a tool capable of identifying full spectrum repeats in the whole genome. RESULTS: We report the PRAP (Prokaryotic Repeats Annotation Program software package to automate the analysis of repeats in both finished and draft genomes. It is aimed at identifying full spectrum repeats at the scale of the prokaryotic genome. Compared with the major existing repeat finding tools, PRAP exhibits competitive or better results. The results are consistent with manually curated and experimental data. Repeats can be identified and grouped into families to define their relevant types. The final output is parsed into the European Molecular Biology Laboratory (EMBL)/GenBank feature table format for reading and displaying in Artemis, where it can be combined or compared with other genome data. It is currently the most complete repeat finder for prokaryotes and is a valuable tool for genome annotation. AVAILABILITY: https://sites.google.com/site/prapsoftware/ CONTACT: hsuehc@ntu.edu.tw. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Resonance modes, cavity field enhancements, and long-range collective photonic effects in periodic bowtie nanostructures.

The discovery of single-molecule sensitivity via surface-enhanced Raman scattering on resonantly excited noble metal nanoparticles has brought an increasing interest in its applications to the molecule detection and identification. Periodic gold bowtie nanostructures have recently been shown to give a large enhancement factor sufficient for single molecule detection. In this work, we simulate the plasmon resonance for periodic gold bowtie nanostructures. The difference between the dipole and the quadrupole resonances is described by examining the magnitude and phase of electric field, the bound surface charge, and the polarization. The gap size dependence of the field enhancement can be interpreted by considering cavity field enhancement. Also, additional enhancement is obtained through the long-range collective photonic effect when the bowtie array periodicity matches the resonance wavelength.

High tunability of the surface-enhanced Raman scattering response with a metal-multiferroic composite.

We demonstrate active control of the plasmonic response from Au nanostructures by the use of a novel multiferroic substrate-LuFe(2)O(4) (LFO)-to tune the surface-enhanced Raman scattering (SERS) response in real time. From both experiments and numerical simulations based on the finite-difference time-domain method, a threshold field is observed, above which the optical response of the metal nanostructure can be strongly altered through changes in the dielectric properties of LFO. This offers the potential of optimizing the SERS detection sensitivity in real time as well as the unique functionality of detecting multiple species of Raman active molecules with the same template.

Free-standing optical gold bowtie nanoantenna with variable gap size for enhanced Raman spectroscopy.

We describe plasmonic interactions in suspended gold bowtie nanoantenna leading to strong electromagnetic field (E) enhancements. Surface-enhanced Raman scattering (SERS) was used to demonstrate the performance of the nanoantenna. In addition to the well-known gap size dependence, up to 2 orders of magnitude additional enhancement is observed with elevated bowties. The overall behavior is described by a SERS enhancement factor exceeding 10(11) along with an anomalously weak power law dependence of E on the gap size in a range from 8 to 50 nm that is attributed to a plasmonic nanocavity effect occurring when the plasmonic interactions enter a strongly coupled regime.

Analyses of multilayered dental ceramics subjected to biaxial flexure tests.

OBJECTIVES: The purpose of this study was to formulate explicitly the equation to relate the biaxial strength of multilayered dental ceramics to the fracture load for multilayered discs subjected to biaxial flexure tests. METHODS: Analytical modeling showed that the solutions for multilayered discs subjected to biaxial flexure tests could be obtained from the existing solutions for monolayered systems by replacing the neutral surface position and the flexural rigidity of monolayers with those of multilayers. Finite element analyses were performed on porcelain/zirconia bilayered discs subjected to piston-on-ring and ring-on-ring tests to verify the analytical results. RESULTS: Good agreement was obtained between (i) present analytical results and Roark's formulas for stresses at the top and the bottom surfaces of bimetallic discs subjected to bending, and (ii) present analytical and finite element results for porcelain/zirconia bilayered discs subjected to piston-on-ring and ring-on-ring tests. SIGNIFICANCE: The present closed-form solutions provide a basis for evaluating the biaxial strength of multilayered dental ceramics. Depending upon the strength of the individual layers and the stress distribution through the thickness of the multilayer during tests, cracking can initiate from any layer under tension.