Yuh-Lin Wang

Highly Active and Stable Hybrid Catalyst of Cobalt-Doped FeS2 Nanosheets–Carbon Nanotubes for Hydrogen Evolution Reaction

Hydrogen evolution reaction (HER) from water through electrocatalysis using cost-effective materials to replace precious Pt catalysts holds great promise for clean energy technologies. In this work we developed a highly active and stable catalyst containing Co doped earth abundant iron pyrite FeS(2) nanosheets hybridized with carbon nanotubes (Fe(1-x)CoxS(2)/CNT hybrid catalysts) for HER in acidic solutions. The pyrite phase of Fe(1-x)CoxS(2)/CNT was characterized by powder X-ray diffraction and absorption spectroscopy. Electrochemical measurements showed a low overpotential of ∼0.12 V at 20 mA/cm(2), small Tafel slope of ∼46 mV/decade, and long-term durability over 40 h of HER operation using bulk quantities of Fe(0.9)Co(0.1)S(2)/CNT hybrid catalysts at high loadings (∼7 mg/cm(2)). Density functional theory calculation revealed that the origin of high catalytic activity stemmed from a large reduction of the kinetic energy barrier of H atom adsorption on FeS(2) surface upon Co doping in the iron pyrite structure. It is also found that the high HER catalytic activity of Fe(0.9)Co(0.1)S(2) hinges on the hybridization with CNTs to impart strong heteroatomic interactions between CNT and Fe(0.9)Co(0.1)S(2). This work produces the most active HER catalyst based on iron pyrite, suggesting a scalable, low cost, and highly efficient catalyst for hydrogen generation.

Enhanced performance and stability of a polymer solar cell by incorporation of vertically aligned, cross-linked fullerene nanorods.

Research on polymer solar cells (PSC) using organic p-type (donor) and n-type (acceptor) semiconductors has attracted tremendous scientific and industrial interest in recent years. The charge generation and charge transport play equally important roles in determining the device efficiency. To dramatically increase the area of the donor–acceptor interface for efficient charge separation, a bulk heterojunction (BHJ) is adopted to form an interpenetrating network of donor and acceptor materials. This configuration decreases the distance that excitons need to travel to reach the heterojunction interface, thus reducing exciton recombination. However, the donor and acceptor are randomly interspersed; pathways for charges to reach the electrodes through the active layer are disordered. Free charges are likely to encounter an opposite charge, resulting in charge recombination and reduced current. 4] Moreover, space charge may be built up if charges are locally trapped on isolated domains. Furthermore, an increase in the thickness of the BHJ layer to enhance absorption is usually accompanied by deteriorated charge collection. Consequently, controlling phase separation toward optimal morphology in BHJ by external treatments, such as thermal or solvent annealing, is an important but challenging task. To provide a direct path for charge transport while maintaining a large interfacial area, the ideal architecture of the donor and acceptor is the periodic, vertically aligned, and interpenetrating ordered bulk heterojunction (OBHJ). The electrons and holes have straight and independent pathways to the electrodes to shorten the carrier transport length and reduce the probability of charge recombination. Several elegant studies have attempted to demonstrate this conceptual architecture, for example by a template-assisted strategy or self-assembly of block copolymer. However, realization of high-performance OBHJ devices has not been successful. We envision that designing a system that combines a BHJ for efficient charge generation with an OBHJ for efficient charge transport and collection would be a more practical strategy. Such a configuration is specifically suitable for solar cells with inverted architecture, because an electron-selective layer is required at the bottom of the active layer for electron extraction and hole blocking. For instance, the upper BHJ active layer of an inverted solar cell is infiltrated into vertically aligned nanorods extending from a bottom layer of an inorganic semiconductor (e.g. ZnO or TiO2). [18–20] However, owing to the poor electrical coherence at the organic/inorganic interface, the improvement in efficiency is moderate (PCE ranges from 2.1 to 2.7%). Recently, we reported a cross-linkable fullerene material, [6,6]-phenyl-C61-butyric styryl dendron ester (PCBSD). The formation of a cross-linked PCBSD (C-PCBSD, Figure 1a) planar layer allows realization of a multilayer inverted device by all-solution processing. By using indene–C60 bisadduct (ICBA, Figure 1a) with a higher-lying lowest unoccupied molecular orbital (LUMO) energy level to serve as the acceptor in the blend, an inverted solar cell device based on the ITO/ZnO/C-PCBSD/ICBA:P3HT/PEDOT:PSS/Ag configuration achieved an enhanced power conversion efficiency

Functionalized arrays of Raman-enhancing nanoparticles for capture and culture-free analysis of bacteria in human blood

Summary form only given. Detecting bacteria in clinical samples without the time-consuming culture process is most desired for rapid diagnosis. Such a culture-free detection needs to capture and analyze bacteria from a body fluid usually containing complicate constituents. Here we show that vancomycin (Van) coating of a special substrate with arrays of Ag-nanoparticles, which can provide label-free analysis of bacteria via surface enhanced Raman spectroscopy (SERS), leads to 1000 folds increase in its capability to capture bacteria without introducing significant spectral interference. Bacteria spiked in human blood can be concentrated onto a microscopic Van-coated area while blood cells are excluded. Furthermore, A Van-coated substrate provides distinctly different SERS spectra of Van-susceptible and Van-resistant Enterococcus, indicating its potential use for drug-resistance test. Our results represent a critical step towards the creation of SERS-based multifunctional biochips for rapid culture/label-free detection and drug-resistant testing of microorganisms in clinical samples.

Ordered anodic alumina nanochannels on focused-ion-beam-prepatterned aluminum surfaces

A combined process of electropolishing, focused-ion-beam lithography, and controlled anodization is used to fabricate anodic alumina films with ordered nanochannels. The ion beam is used to create a hexagonally close-packed lattice of concaves on a polished aluminum surface and the concaves act as pinning points for guiding the growth of nanochannels in the following anodization step. By carefully matching the lattice constant (100 nm) with the anodization voltage, ordered nanochannels with aspect ratio of ∼100 are fabricated. The effects of the ion dose and its corresponding depth of the concaves on the ordering of the nanochannel array are investigated and a minimum depth of 3 nm is found to be necessary for effective guidance of the growth of ordered nanochannels.

A High Speed Detection Platform Based on Surface-Enhanced Raman Scattering for Monitoring Antibiotic-Induced Chemical Changes in Bacteria Cell Wall

Rapid and accurate diagnosis for pathogens and their antibiotic susceptibility is critical for controlling bacterial infections. Conventional methods for determining bacteriums sensitivity to antibiotic depend mostly on measuring the change of microbial proliferation in response to the drug. Such “biological assay” inevitably takes time, ranging from days for fast-growing bacteria to weeks for slow-growers. Here, a novel tool has been developed to detect the “chemical features” of bacterial cell wall that enables rapid identification of drug resistant bacteria within hours. The surface-enhanced Raman scattering (SERS) technique based on our newly developed SERS-active substrate was applied to assess the fine structures of the bacterial cell wall. The SERS profiles recorded by such a platform are sensitive and stable, that could readily reflect different bacterial cell walls found in Gram-positive, Gram-negative, or mycobacteria groups. Moreover, characteristic changes in SERS profile were noticed in the drug-sensitive bacteria at the early period (i.e., ∼1 hr) of antibiotic exposure, which could be used to differentiate them from the drug-resistant ones. The SERS-based diagnosis could be applied to a single bacterium. The high-speed SERS detection represents a novel approach for microbial diagnostics. The single-bacterium detection capability of SERS makes possible analyses directly on clinical specimen instead of pure cultured bacteria.

Ultra-High-Responsivity Broadband Detection of Si Metal–Semiconductor–Metal Schottky Photodetectors Improved by ZnO Nanorod Arrays

This study describes a strategy for developing ultra-high-responsivity broadband Si-based photodetectors (PDs) using ZnO nanorod arrays (NRAs). The ZnO NRAs grown by a low-temperature hydrothermal method with large growth area and high growth rate absorb the photons effectively in the UV region and provide refractive index matching between Si and air for the long-wavelength region, leading to 3 and 2 orders of magnitude increase in the responsivity of Si metal-semiconductor-metal PDs in the UV and visible/NIR regions, respectively. Significantly enhanced performances agree with the theoretical analysis based on the finite-difference time-domain method. These results clearly demonstrate that Si PDs combined with ZnO NRAs hold high potential in next-generation broadband PDs.

The Antarctic Impulsive Transient Antenna ultra-high energy neutrino detector: Design, performance, and sensitivity for the 2006–2007 balloon flight

Abstract We present a comprehensive report on the experimental details of the Antarctic Impulsive Transient Antenna (ANITA) long-duration balloon payload, including the design philosophy and realization, physics simulations, performance of the instrument during its first Antarctic flight completed in January of 2007, and expectations for the limiting neutrino detection sensitivity.

New Limits on the Ultrahigh Energy Cosmic Neutrino Flux from the ANITA Experiment

We report initial results of the first flight of the Antarctic Impulsive Transient Antenna (ANITA-1) 2006-2007 Long Duration Balloon flight, which searched for evidence of a diffuse flux of cosmic neutrinos above energies of E(nu) approximately 3 x 10(18) eV. ANITA-1 flew for 35 days looking for radio impulses due to the Askaryan effect in neutrino-induced electromagnetic showers within the Antarctic ice sheets. We report here on our initial analysis, which was performed as a blind search of the data. No neutrino candidates are seen, with no detected physics background. We set model-independent limits based on this result. Upper limits derived from our analysis rule out the highest cosmogenic neutrino models. In a background horizontal-polarization channel, we also detect six events consistent with radio impulses from ultrahigh energy extensive air showers.

High-speed focused-ion-beam patterning for guiding the growth of anodic alumina nanochannel arrays

Long-range ordered arrays of anodic alumina nanochannels are grown by anodizing an aluminum covered with a patterned layer of polymethylmethacrylate (PMMA) resist. The two-dimensional hexagonal-closed-packed pattern is created by focused ion beam (FIB) exposure of the PMMA and transferred onto the aluminum surface by phosphoric acid etching. The required exposure time per channel is only ∼20 μs, more than two orders of magnitude reduction in comparison with the previous method employing FIB direct sputtering of the aluminum surface.

Faceting phase transitions of Mo(111) induced by Pd, Au and oxygen overlayers

Abstract The influence of about a monolayer coverage of Pd, Au and oxygen on the structural stability of the Mo(111) surface has been studied under ultrahigh vacuum (UHV) using X-ray photoemission spectroscopy (XPS), Auger electron spectroscopy (AES), temperature programmed thermal desorption spectroscopy (TDS) and low energy electron diffraction (LEED). Pd and oxygen are found to induce the formation of [lcub]112[rcub] and [lcub]447[rcub] oriented facets respectively on the substrate surface. Both surfaces undergo a reversible “faceted/planar” phase transition at higher temperatures and the transition shows intrinsic hysteresis in both cases. With Au coverage, the precisely oriented Mo(111) surface is stable, whereas the vicinal surfaces can be induced to form a mixture of [lcub]112[rcub] facets and the original (111) surface. The implication of these results to the existing conjectures about the mechanism of adsorbate-induced faceting is discussed.