Hsieh-Cheng Han

Label free sub-picomole level DNA detection with Ag nanoparticle decorated Au nanotip arrays as surface enhanced Raman spectroscopy platform.

Label free optical sensing of adenine and thymine oligonucleotides has been achieved at the sub-picomole level using self assembled silver nanoparticles (AgNPs) decorated gold nanotip (AuNT) arrays. The platform consisting of the AuNTs not only aids in efficient bio-immobilization, but also packs AgNPs in a three dimensional high surface area workspace, assisting in surface enhanced Raman scattering (SERS). The use of sub-10 nm AgNPs with optimum inter-particle distance ensures amplification of the chemically specific Raman signals of the adsorbed adenine, thymine, cytosine and guanine molecules in SERS experiments. High temporal stability of the Raman signals ensured reliable and repeatable DNA detection even after three weeks of ambient desk-top conservation. This facile architecture, being three dimensional and non-lithographic, differs from conventional SERS platforms.

Application of parylene-coated quartz crystal microbalance for on-line real-time detection of microbial populations

A novel technique of applying a quartz crystal microbalance (QCM) sensor to the on-line real-time detection of microbial populations is described. The pQCM sensor was fabricated by depositing di-para-xylene (parylene) over the entire surface of a QCM sensor through a chemical vapor deposition (CVD) process. An electrically insulated film of parylene on the QCM sensor enabled the operation of the sensor in the liquid environment, and the resonance frequency of the pQCM sensor set in the medium of a cultivation flask shifted in response to the microbial population. The effects of pH, conductivity, and viscosity of the medium on the frequency shift of the pQCM sensor were investigated. Ignorable responses (less than 1% at 10(3)cells) were obtained during an incubation cycle. The detection limit of the pQCM sensor was identified as 10(2) cells ml(-1) with a frequency shift of around 2 x 10(3)Hz. The cell numbers of Escherichia coli cultivated in both the YEM medium and whole milk were detected. A satisfactory correlation (r(2)=0.95) was obtained between the cell number and the response of the pQCM sensor. Experimental results suggest that the pQCM described here is applicable to the continuous long-term detection of microbial populations during a fermentation process.

Enhancing efficiency with fluorinated interlayers in small molecule organic solar cells

This study presents a simple approach to improve the performance of small molecule based organic solar cells (OSCs) by inserting a fluorinated buffer layer (e.g., PFAS) at the hetero-interface of bilayer devices. As demonstrated in this work, the PFAS modification reduces the surface energy of the conventional PEDOT : PSS photoanode and results in a significant improvement in the pentacene based OSC. The passivated PEDOT : PSS surface after PFAS modification has a lower interface energy with pentacene and facilitates 3D single crystalline (dendritic-like) phase pentacene growth. Concurrently, the accumulated negative charges of the fluorinated PFAS layer result in the development of interfacial dipole moments that in turn lead to an enhanced built-in potential across the devices, and consequently enhanced hole transport efficiency. Improved performance of the modified OSCs is evident from the ∼97% enhancement in efficiency from 0.88% to 1.73%, along with the open-circuit voltage improvement from 0.29 to 0.42 V. As well as improving the photovoltaic performance, the PFAS treatment also enhances the stability of the device under high temperature annealing, which is essential in the fabrication process.

High K Nanophase Zinc Oxide on Biomimetic Silicon Nanotip Array as Supercapacitors

A 3D trenched-structure metal-insulator-metal (MIM) nanocapacitor array with an ultrahigh equivalent planar capacitance (EPC) of ~300 μF cm(-2) is demonstrated. Zinc oxide (ZnO) and aluminum oxide (Al2O3) bilayer dielectric is deposited on 1 μm high biomimetic silicon nanotip (SiNT) substrate using the atomic layer deposition method. The large EPC is achieved by utilizing the large surface area of the densely packed SiNT (!5 × 10(10) cm(-2)) coated conformally with an ultrahigh dielectric constant of ZnO. The EPC value is 30 times higher than those previously reported in metal-insulator-metal or metal-insulator-semiconductor nanocapacitors using similar porosity dimensions of the support materials.

Gold nanoparticle-modulated conductivity in gold peapodded silica nanowires.

We report the enhanced electrical conductivity properties of single gold-peapodded amorphous silica nanowires synthesized using microwave plasma enhanced chemical vapor deposition. Dark conductivity of the gold-peapodded silica nanowires can be adjusted by controlling the number of incorporated metal nanoparticles. The temperature-dependent conductivity measurement reveals that the band tail hopping mechanism dominates the electron transport in the gold-peapodded silica nanowires. The high conductivity in the nano-peapodded nanowires with more embedded gold-nanoparticles can be explained by the higher density of hopping states and shorter hopping distance. These Au-embedded amorphous silica nanowires have provided a new approach to enhance not only the electron conduction, but also the chemical-sensor response/sensitivity.

Giant room temperature electric-field-assisted magnetoresistance in La0.7Sr0.3MnO3/n-Si nanotip heterojunctions

An on-chip approach for fabricating ferromagnetic/semiconductor-nanotip heterojunctions is demonstrated. The high-density array of Si nanotips (SiNTs) is employed as a template for depositing La(0.7)Sr(0.3)MnO(3) (LSMO) rods with a pulsed-laser deposition method. Compared with the planar LSMO/Si thin film, the heterojunction shows a large enhancement of room temperature magnetoresistance (MR) ratio up to 20% under 0.5 T and a bias current of 20 µA. The MR ratio is found to be tunable, which increases with increasing external bias and the aspect ratios of the nanotips. Electric-field-induced metallization, in conjunction with nanotip geometry, is proposed to be the origin for the giant MR ratio.

The Effects of Fluorine-Contained Molecules on Improving the Polymer Solar Cell by Curing the Anomalous S-Shaped I–V Curve

In this study, we investigate the effects of fluorinated poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) buffer layer on the performance of polymer photovoltaic cells. We demonstrate for the first time, the deterioration of the device performance can be effectively mended by modifying the interface between the active layer and buffer layer with heptadecafluoro-1,1,2,2-tetra-hydro-decyl trimethoxysilane (PFDS) and perfluorononane. Device performance shows a substantial enhancement of short-circuit current from 7.90 to 9.39 mA/cm(2) and fill factor from 27% to 53%. The overall device efficiency was improved from 0.98% to 3.12% for PFDS modified device. The mechanism of S-shape curing is also discussed. In addition, the stability of modified devices shows significant improvement than those without modification. The efficiency of the modified devices retains about half (1.88%) of its initial efficiency (4.1%) after 30 d compared to the unmodified ones (0.61%), under air atmosphere.

Dye sensitized solar cells with carbon and cobalt derivatives as counter electrodes

In this report, we use series of cobalt derivatives, conducting polymer and carbon materials as the counter electrodes to replace the conventional platinum in dye sensitized solar cells. The basic cobalt derivatives, Co12 and Co15, showed the capability as the counter electrode with proper short-circuit current (JSC) and open-circuit voltage (VOC), but the poor conductivity and redox ability result in bad fill factor of the device. After mixing Co12 and Co15 with carbon black, the device performances were enhanced obviously. The further improve was done by combine Co derivative and carbon black to form the new type material CoCB as the counter electrode. The great conductivity and redox ability enhanced both JSC and VOC, the optimized device show the power conversion efficiency of 7.13%, similar to the control device with conventional Pt electrode. The result showed the potential of cobalt derivatives as the counter electrode of DSSCs.

Ultra-thick wetting layer induced phase separations in P3HT/fullerene solar cells: The femtosecond time-resolved photo-luminescence and the transient absorption

Control over morphology in polymer solar cell of conjugated polymer:fullerene active layer has gained experimental interest as the phase separation will change vertical and lateral composition and enhance the optical and electrical properties. While the vertical composition, lateral morphology with electrical or optical charateristics have been observed to support the speculation that surface energy is the driving force for phase separation, the interplay of phase separation and substrate surface energy is elusive. Although researches have suggested the surface-directed spinodal decomposition can be found in polymer:fullerene blends and leads to ideal phase morphology in bulk composition, it is still miscible for the comprehensive analysis for bulk phase morphology, crystallinity acceleration and electronic properties in the device, as well as the dynamic and interplay of phase separation for top surface, bulk domain and wetting area near the substrate. Based on the previous studies, we hypothesize that the formation of wetting layer can be facilitated by controlling the surface energy of substrate, so we design the standard structure device composed of P3HT:PCBM active layer with fluorinated compounds (PFDS) spin-coated on PEDOT: PSS. Experiments designed are to investigate the presence of wetting layer and to observe the vertical composition and lateral phase separation via depth profiling and top surface images. Finally, the time resolved photoluminescence and transient absorption were used to investigate the charge separation and exciton generation and so on.