Maesoon Im

Self-cleaning effect of highly water-repellent microshell structures for solar cell applications

A self-cleaning effect developed through the use of a superhydrophobic and water-repellent surface was demonstrated for solar cell applications. A perfectly ordered microshell array was fabricated on a transparent and flexible polydimethylsiloxane (PDMS) elastomer surface. This microshell PDMS showed an excellent water-repellent property with a contact angle (CA) higher than 150° and a hysteresis of lower than 20°, even without the aid of a low surface energy chemical coating. Fabricated superhydrophobic microshell PDMS showed a superior dust cleaning effect compared to that of flat PDMS, preventing the degradation by dust particles of solar cell efficiency. This transparent, flexible and superhydrophobic microshell PDMS surface provides feasibility for a practical application of superhydrophobic surfaces in solar cells.

An implantable neural probe with monolithically integrated dielectric waveguide and recording electrodes for optogenetics applications

OBJECTIVE Optogenetics promises exciting neuroscience research by offering optical stimulation of neurons with unprecedented temporal resolution, cell-type specificity and the ability to excite as well as to silence neurons. This work provides the technical solution to deliver light to local neurons and record neural potentials, facilitating local circuit analysis and bridging the gap between optogenetics and neurophysiology research. APPROACH We have designed and obtained the first in vivo validation of a neural probe with monolithically integrated electrodes and waveguide. High spatial precision enables optical excitation of targeted neurons with minimal power and recording of single-units in dense cortical and subcortical regions. MAIN RESULTS The total coupling and transmission loss through the dielectric waveguide at 473 nm was 10.5 ± 1.9 dB, corresponding to an average output intensity of 9400 mW mm(-2) when coupled to a 7 mW optical fiber. Spontaneous field potentials and spiking activities of multiple Channelrhodopsin-2 expressing neurons were recorded in the hippocampus CA1 region of an anesthetized rat. Blue light stimulation at intensity of 51 mW mm(-2) induced robust spiking activities in the physiologically identified local populations. SIGNIFICANCE This minimally invasive, complete monolithic integration provides unmatched spatial precision and scalability for future optogenetics studies at deep brain regions with high neuronal density.

Lock-and-key geometry effect of patterned surfaces: wettability and switching of adhesive force.

A rough surface can be a regular (engineered surface), a random (irregular rough surface), or an intermediate case (hierarchical rough surface). Whichever case is used for wettability, a truly superhydrophobic surface exhibits not only a high contact angle (>150 8) but also a low-contact-angle hysteresis (sliding angle). Quere et al. theoretically described how contact-angle hysteresis generates an adhesive force and the contact angle and hysteresis can be controlled by tailoring the surface topography of the solid substrate. Researchers have since attempted to capture these properties in synthetic materials with nanoscale surface features or changes of surface topography. For flexibility in adapting to rough surfaces, poly (dimethylsiloxane) (PDMS) elastomer, an ideal elastic material in terms of its stress–strain response, has attracted great attention. Particular interest has focused on introducing nanoscale structures onto microscale surfaces using surface treatments to reach a hydrophobic state, such as mechanically assembled monolayers, CO2 pulsed-laser etching, [8–10] UV/ ozone surface treatments, SF6 plasmas, [12] oxygen plasma and chemical surface treatments, and laser etching. Besides these, Hang et al. created an artificial lotus leaf by

Partially Depleted SONOS FinFET for Unified RAM (URAM)—Unified Function for High-Speed 1T DRAM and Nonvolatile Memory

Unified random access memory (URAM) is demonstrated for the first time. The novel partially depleted (PD) SONOS FinFET provides unified function of a high-speed capacitorless 1T DRAM and a nonvolatile memory (NVM). The combination of an oxide/nitride/oxide (O/N/O) layer and a floating-body facilitates URAM operation in PD SONOS FinFETs. An NVM function is achieved by FN tunneling into the O/N/O stack and, a 1T-DRAM function is achieved by excessive-hole accumulation in the PD body. The fabricated PD SONOS FinFET shows retention time exceeding 10 years for NVM operation and program/erase time below 6 ns for 1T-DRAM in a single-cell transistor. These two memory functions are guaranteed without disturbance between them.

Multiple-Gate CMOS Thin-Film Transistor With Polysilicon Nanowire

An ultimately scaled multiple-gate CMOS thin-film transistor with a polysilicon (poly-Si) nanowire demonstrates feasibility for vertical integration using multiple active layers for application in the terabit memory era. The short-channel effects are suppressed using a multiple gate to wrap around the nanowire in devices with a size of a few tenths of a nanometer. The switching and output characteristics show high device performance without a crystallization process for the poly-Si nanowire.

A flexible fish-bone-shaped neural probe strengthened by biodegradable silk coating for enhanced biocompatibility

This paper reports a fish-bone-shaped polyimide neural probe for chronic recording applications. This unique design aims to minimize tissue reaction by having flexible substrate, small dimensions, large separation distance between electrodes and the probe shank, as well as large substrate openings. A biodegradable silk polymer is coated around the polyimide structure to provide temporary mechanical strength during insertion. The time required for the complete degradation of silk can be controlled within the range of 30 minutes to 25 hours by water annealing process. In-vitro insertion of the fabricated silk-coated probe into brain tissue has been successfully demonstrated.

Integration of field effect transistor-based biosensors with a digital microfluidic device for a lab-on-a-chip application.

A new platform for lab-on-a-chip system is suggested that utilizes a biosensor array embedded in a digital microfluidic device. With field effect transistor (FET)-based biosensors embedded in the middle of droplet-driving electrodes, the proposed digital microfluidic device can electrically detect avian influenza antibody (anti-AI) in real time by tracing the drain current of the FET-based biosensor without a labeling process. Digitized transport of a target droplet enclosing anti-AI from an inlet to the embedded sensor is enabled by the actuation of electrowetting-on-dielectrics (EWOD). A reduction of the drain current is observed when the target droplet is merged with a pre-existing droplet on the embedded sensor. This reduction of the drain current is attributed to the specific binding of the antigen and the antibody of the AI. The proposed hybrid device consisting of the FET-based sensor and an EWOD device, built on a coplanar substrate by monolithic integration, is fully compatible with current fabrication technology for control and read-out circuitry. Such a completely electrical manner of inducing the transport of bio-molecules, the detection of bio-molecules, the recording of signals, signal processing, and the data transmission process does not require a pump, a fluidic channel, or a bulky transducer. Thus, the proposed platform can contribute to the construction of an all-in-one chip.

An Underlap Channel-Embedded Field-Effect Transistor for Biosensor Application in Watery and Dry Environment

An underlap channel-embedded FET is proposed for electrical, label-free biosensor in both watery and dry environments, and current-voltage characteristics measured under each environment are compared. To investigate the effectiveness of the underlap device as a biosensor for both environments, antigen-antibody binding of an avian influenza (AI) is used. Antibody of AI binding on antigen-immobilized surface provides additional negative charge on underlap surface, and they give rise to channel potential increasing and result in drain current reduction. In this study, we have verified that the biosensor characteristics measured under dry environment is valid as much as they are valid for watery environment.

Neural probes integrated with optical mixer/splitter waveguides and multiple stimulation sites

This paper reports new neural probe schemes incorporating various optical waveguides for optogenetic applications. A photodefinable polymer (SU-8) has been patterned to form optical mixer and splitter waveguides for advanced optical functions with multiple light sources and easy delivery of light to multiple shanks, respectively. Also, multiple stimulation sites have been implemented by step-wise patterning in a single waveguide. In addition to SU-8 waveguides, iridium electrodes have been integrated for recording of neural signals from optically stimulated neurons with light of specific wavelengths. Single mode optical fibers have been coupled in grooves etched in the probe body. We have successfully demonstrated transmissions of blue light, 473 nm in wavelength, through the waveguides that are integrated on the fabricated devices.

Electrowetting on a Polymer Microlens Array

This paper reports on the electrowetting behavior of a flexible poly(dimethylsiloxane) (PDMS) microlens array. A Cr and Au double-layered electrode was formed on an array of microlenses with diameters of 10 microm and heights of 13 microm. A deposition of parylene and a coating of Teflon were followed for electrical insulation as well as for enhancement of the hydrophobicity. On the nearly superhydrophobic microlens array surface, the electrowetting of a deionized water droplet was observed over the contact angle range of approximately 140 degrees to approximately 58 degrees by applying 0-200 V, respectively. The electrowetting phenomenon was reversible even in air environment with applied voltages of less than 100 V. The electrowetting on the microlens array surface lost its reversibility after the microlens array surface was completely wetted when the water meniscus touched the bottom of the microlens array. Analysis of meniscus shapes and net force direction follows to elucidate the reversibility. The convex curvature of the microlens caused gradual rather than abrupt impalement of water into the gap among the microlenses.