Denzel Bridges

High-rate in-plane micro-supercapacitors scribed onto photo paper using in situ femtolaser-reduced graphene oxide/Au nanoparticle microelectrodes

Direct laser-reduction of graphene oxide (GO), as a lithography-free approach, has been proven effective in manufacturing in-plane micro-supercapacitors (MSCs) with fast ion diffusion. However, the power density and the charge/discharge rate are still limited by the relatively low conductivity of electrodes. Here, we report a facile approach by exploiting femtolaser in situ reduction of the hydrated GO and chloroauric acid (HAuCl4) nanocomposite simultaneously, which incorporates both the patterning of rGO electrodes and the fabrication of Au current collectors in a single step. These flexible MSCs boast achievements of one-hundred fold increase in electrode conductivities of up to 1.1 × 106 S m−1, which provide superior rate capability (50% for the charging rate increase from 0.1 V s−1 to 100 V s−1), sufficiently high frequency responses (362 Hz, 2.76 ms time constant), and large specific capacitances of 0.77 mF cm−2 (17.2 F cm−3 for volumetric capacitance) at 1 V s−1, and 0.46 mF cm−2 (10.2 F cm−3) at 100 V s−1. The use of photo paper substrates enables the flexibility of this fabrication protocol. Moreover, proof-of-concept 3D MSCs are demonstrated with enhanced areal capacitance (up to 3.84 mF cm−2 at 1 V s−1) while keeping high rate capabilities. This prototype of all solid-state MSCs demonstrates the broad range of potentials of thin-film based energy storage device applications for flexible, portable, and wearable electronic devices that require a fast charge/discharge rate and high power density.

Electrospinning of nanofibers and their applications for energy devices

With the depletion of fossil fuels and the increasing demand of energy for economic development, it is urgent to develop renewable energy technologies to sustain the economic growth. Electrospinning is a versatile and efficient fabrication method for one-dimensional (1D) nanostructured fibers of metals, metal oxides, hydrocarbons, composites, and so forth. The resulting nanofibers (NFs) with controllable diameters ranging from nanometer to micrometer scale possess unique properties such as a high surface-area-to-volume and aspect ratio, low density, and high pore volume. These properties make 1D nanomaterials more advantageous than conventional materials in energy harvesting, conversion, and storage devices. In this review, the key parameters for e-spinning are discussed and the properties of electrospun NFs and applications in solar cells, fuel cells, nanogenerators, hydrogen energy harvesting and storage, lithium-ion batteries, and supercapacitors are reviewed. The advantages and disadvantages of electrospinning and an outlook on the possible future directions are also discussed.

Fabrication, characterization, and applications of microlenses.

Microlenses (MLs) and microlens arrays (MLAs) are assuming an increasingly important role in optical devices. In response to this rapid evolution in technology, emphasis is being placed on research into new manufacturing methods for these devices as well as the characterization of their performance. This paper provides an overview of the fabrication of MLs and MLAs by electrical, mechanical, chemical, and optical methods. As each processing method has distinct advantages and limitations, the most significant characteristic parameters and the measurement of these parameters are discussed for each method. These parameters are then used as indices to evaluate and improve each of the processing methods. Some examples of practical applications of MLAs, especially for micromechanical optoelectronic devices, are also given. This paper aims to summarize the present development and the state of the art in processing technology of MLs and MLAs.

Anisotropic optical properties of large-scale aligned silver nanowire films via controlled coffee ring effects

Thin films with one-dimensional nanostructures and unique physical properties are potential candidates for next-generation high-performance electronic, optoelectronic, and electromechanical systems. Here we report that large-scale oriented silver nanowire films can be prepared by controlling the coffee-ring effect through tilting the substrates during the film deposition. The anisotropic optical properties of the orientated silver nanowire film are researched here. Surface enhanced Raman scattering (SERS) spectra were recorded from Rhodamine 6G adsorbed on the silver nanowire films. The SERS spectra showed striking polarization dependence according to the angle between the long axes of the nanowires and the light polarization. At the vertical excitation (i.e., light polarization forms a 90° angle to the long axes of the nanowires), the SERS intensity reaches a maximum. Minimum intensities were obtained at a parallel excitation. The three-dimensional finite element method was used to give an in-depth explanation of these properties. Angular resolution fluorescence is also studied. The fluorescence displays an angle-dependence similar to the Raman activities. Optical properties were also investigated through the polarization of reflectivity spectra. The reflectivity is smaller when the incident light is polarized parallel to the orientation direction. As the wavelength increases, the reflectivity increases when the polarization of incident light is perpendicular to the orientation direction. When the wavelength is greater than 870 nm, the amplitude can be up to doubled. Our study indicates that this technique is promising in the production of large-scale orientated silver nanowire films with anisotropic optical properties for high-performance electronic, optoelectronic, and electromechanical systems.

Zero-dimensional to three-dimensional nanojoining: current status and potential applications

The continuing miniaturization of microelectronics is pushing advanced manufacturing into nanomanufacturing. Nanojoining is a bottom-up assembly technique that enables functional nanodevice fabrication with dissimilar nanoscopic building blocks and/or molecular components. Various conventional joining techniques have been modified and re-invented for joining nanomaterials. This review surveys recent progress in nanojoining methods, as compared to conventional joining processes. Examples of nanojoining are given and classified by the dimensionality of the joining materials. At each classification, nanojoining is reviewed and discussed according to materials specialties, low dimensional processing features, energy input mechanisms and potential applications. The preparation of new intermetallic materials by reactive nanoscale multilayer foils based on self-propagating high-temperature synthesis is highlighted. This review will provide insight into nanojoining fundamentals and innovative applications in power electronics packaging, plasmonic devices, nanosoldering for printable electronics, 3D printing and space manufacturing.

Fabrication of embedded microball lens in PMMA with high repetition rate femtosecond fiber laser

Embedded microball lenses with superior optical properties function as convex microball lens (VMBL) and concave microball lens (CMBL) were fabricated inside a PMMA substrate with a high repetition rate femtosecond fiber laser. The VMBL was created by femtosecond laser-induced refractive index change, while the CMBL was fabricated due to the heat accumulation effect of the successive laser pulses irradiation at a high repetition rate. The processing window for both types of the lenses was studied and optimized, and the optical properties were also tested by imaging a remote object with an inverted microscope. In order to obtain the microball lenses with adjustable focal lengths and suppressed optical aberration, a shape control method was thus proposed and examined with experiments and ZEMAX® simulations. Applying the optimized fabrication conditions, two types of the embedded microball lenses arrays were fabricated and then tested with imaging experiments. This technology allows the direct fabrication of microlens inside transparent bulk polymer material which has great application potential in multi-function integrated microfluidic devices.

Photonic nanomanufacturing of high performance energy devices on flexible substrates

The authors have investigated various photonic processing for various energy devices on flexible substrates with nanoinks. For printable electronics, different conducting nanoinks are developed, including silver nanowires, silver nanoplates, Cu-Ag core-shell nanoparticles, graphene oxide, and graphene. The authors showed that these inks are enabling for direct writing of antenna on paper for radio frequency (RF) energy harvesting, potentially for wireless charging application. For curing printed nanoinks and nanopastes, the authors compared four kinds of methods: chemical activated self-sintering, thermal sintering, photonic sintering with flash light, and athermal sintering with ultrafast fiber laser irradiation. The authors also developed an innovative and facile approach to fabricate supercapacitors on flexible substrates with femtosecond laser writing and photonic reduction. Au-reduced graphene oxide nanocomposite is used for electrical electrodes and collectors. Unlike previous studies, collectors ar...

High performance hybrid supercapacitors on flexible polyimide sheets using femtosecond laser 3D writing

The authors successfully demonstrated flexible hybrid supercapacitors on polyimide sheets by integrating femtosecond laser direct writing, Au coating, and MnO2 electrodeposition. Scanning electron microscope images display that focused pulsed laser irradiation rapidly converts the polyimide surface into an electrically conductive porous carbon structure. After Au coating and thermal sintering of Au nanoparticles, these flexible supercapacitors achieved an enhanced rate capability. Compared to the in-plane supercapacitors, the specific capacitance of hybrid supercapacitors with MnO2 electrodeposition increase from 20 to 300 mF/cm2 at 0.5 mA/cm2 charge/discharge current. These high performance supercapacitors can be potentially integrated with applications for portable and wearable electronic devices, solar cells, chemical and biomedical sensors, display devices, and other on-chip level devices.The authors successfully demonstrated flexible hybrid supercapacitors on polyimide sheets by integrating femtosecond laser direct writing, Au coating, and MnO2 electrodeposition. Scanning electron microscope images display that focused pulsed laser irradiation rapidly converts the polyimide surface into an electrically conductive porous carbon structure. After Au coating and thermal sintering of Au nanoparticles, these flexible supercapacitors achieved an enhanced rate capability. Compared to the in-plane supercapacitors, the specific capacitance of hybrid supercapacitors with MnO2 electrodeposition increase from 20 to 300 mF/cm2 at 0.5 mA/cm2 charge/discharge current. These high performance supercapacitors can be potentially integrated with applications for portable and wearable electronic devices, solar cells, chemical and biomedical sensors, display devices, and other on-chip level devices.