Browsing by Author "Chen, Wei"

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Bandgap tunability at single-layer molybdenum disulphide grain boundaries
(2015-02-01)
Huang, Yu Li
;
Chen, Yifeng
;
Zhang, Wenjing
;
Quek, Su Ying
;
Chen, Chang-Hsiao
Two-dimensional transition metal dichalcogenides have emerged as a new class of semiconductor materials with novel electronic and optical properties of interest to future nanoelectronics technology. Single-layer molybdenum disulphide, which represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle energy gap to be 2.40 +/- 0.05 eV for single-layer, 2.10 +/- 0.05 eV for bilayer and 1.75 +/- 0.05 eV for trilayer molybdenum disulphide, which were directly grown on a graphite substrate by chemical vapour deposition method. More interestingly, we report an unexpected bandgap tunability (as large as 0.85 +/- 0.05 eV) with distance from the grain boundary in single-layer molybdenum disulphide, which also depends on the grain misorientation angle. This work opens up new possibilities for flexible electronic and optoelectronic devices with tunable bandgaps that utilize both the control of two-dimensional layer thickness and the grain boundary engineering.
Enhanced bioconjugation on sputtered palladium nano-thin-film electrode
(2019-03-04)
Chang, Chia-Yu
;
Chen, Wei
;
Su, Chien-Hao
;
Chang, Pang-Chia
;
Huang, Yun-Tzu
A highly reactive surface with an enhanced ability for chemical bonding relies on the presence of specifically coordinated atoms and step edges at the surface. In this study, an electrode with a unique Stranski-Krastanov-like thin film, with an epitaxial sputtering of a palladium (Pd) nanoparticle double layer on the polyethylene terephthalate substrate, was developed. On the surface of this flexible Pd-nano-thin-film (NTF) electrode with a (1 1 1) containing surface, DNA probes can be quickly immobilized in as short a period as 20 min, which is 24 times faster than that on the gold electrode. A DNA-based anticancer compound (ACC) sensing and screening process that would use the DNA functionalized Pd-NTF electrode as the biosensor was then proposed. Interestingly, the developed biosensor could detect DNA and ACCs, such as doxorubicin, tetra-O-methyl nordihydroguaiaretic acid, and Taxol via interactions with solutions containing 1 mu l ACCs within 11 min, and the sensitivity of the ACC solution is similar to 0.1 mu M (similar to 36 pg per-test), as detected by electrochemical impedance spectroscopy. Moreover, this highly reactive surface can be used in regular sensors and other interfaces, in scientific applications. (C) 2019 Author(s).
Highly flexible, robust, stable and high efficiency perovskite solar cells enabled by van der Waals epitaxy on mica substrate
(2019-06-01)
Jia, Chunmei
;
Zhao, Xingyu
;
Lai, Yu-Hong
;
Zhao, Jinjin
;
Wang, Pei-Chun
Flexible and lightweight solar cells are promising for numerous emerging applications, and organometallic halide perovskites are particularly suitable for flexible solar cell applications. Transferring state of art high efficiency perovskite solar cells (PSCs) processing onto a flexible substrate, however, is challenging, requiring substantial redevelopment of materials compositions, device architectures, and processing conditions. In this work, highly flexible, robust, stable, and high efficiency PSCs based on mica substrate have been successfully developed, exhibiting a champion photovoltaic conversion efficiency (PCE) of 18.0%, retaining more than 91.7% of the original PCE after 5000 cycles of large deformation bending, and being relatively stable against humidity under elevated temperature. Key to such excellent performance is the inorganic and transparent mica substrate that is chemically inert and stable under high temperature, so that processing developed for glass-based high efficiency perovskite solar cells (PSCs) can be readily applied without modification. Furthermore, the layered mica substrate is highly flexible, and van der Waals epitaxial growth of transparent conducing ITO relaxes the mechanical constraint on the PSCs substantially, reducing the strain in the device even under large bending deformation. We believe inorganic flexible mica substrate can be used as a platform for high efficiency PSCs compatible to glass substrate, speeding up the development of flexible PSCs substantially.
Meta-analysis of Dense Genecentric Association Studies Reveals Common and Uncommon Variants Associated with Height
(2011-01-07)
Lanktree, Matthew B.
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Guo, Yiran
;
Murtaza, Muhammed
;
Glessner, Joseph T.
;
Bailey, Swneke D.
Height is a classic complex trait with common variants in a growing list of genes known to contribute to the phenotype. Using a genecentric genotyping array targeted toward cardiovascular-related loci, comprising 49,320 SNPs across approximately 2000 loci, we evaluated the association of common and uncommon SNPs with adult height in 114,223 individuals from 47 studies and six ethnicities. A total of 64 loci contained a SNP associated with height at array-wide significance (p < 2.4 x 10(-6)), with 42 loci surpassing the conventional genome-wide significance threshold (p < 5 x 10(-8)). Common variants with minor allele frequencies greater than 5% were observed to be associated with height in 37 previously reported loci. In individuals of European ancestry, uncommon SNPs in IL11 and SMAD3, which would not be genotyped with the use of standard genome-wide genotyping arrays, were strongly associated with height (p < 3 x 10(-11)). Conditional analysis within associated regions revealed five additional variants associated with height independent of lead SNPs within the locus, suggesting allelic heterogeneity. Although underpowered to replicate findings from individuals of European ancestry, the direction of effect of associated variants was largely consistent in African American, South Asian, and Hispanic populations. Overall, we show that dense coverage of genes for uncommon SNPs, coupled with large-scale meta-analysis, can successfully identify additional variants associated with a common complex trait.
Synthesis of Photoisomerizable Block Copolymers by Atom Transfer Radical Polymerization
(2009-09-22)
Huang, Chih-Feng
;
Chen, Wei
;
Russell, Thomas P.
;
Balazs, Anna C.
;
Chang, Feng-Chih
A series of polystyrene-block-poly(n-butyl methacrylate) (PS-b-PnBMA) diblock copolymers (di-BCPs) with an azobenzene moiety [trans-4-methacryloyloxyazobenzene (MOAB)] in the PnBMA segment was prepared by atom transfer radical polymerization (ATRP). P(nBMA-co-MOAB) macroinitiators were prepared by activators regenerated by electron transfer (ARGET) ATRP. The MOAB was slightly more reactive than nBMA, resulting in a weak gradient fashion of copolymer. The macroinitiators were subsequently chain-extended with styrene. Acceleration of the ATRP rate was observed in the presence of a reducing agent. P(nBMA-co-MOAB)-b-PS di-BCPs were obtained with relatively narrow molecular weight distributions ((M) over bar (w)(M) over bar (n) = 1.16-1.49) and the molecular weights were in good agreement with the theoretical values. The efficiency of photoisomerization of the MOAB units was above 80%. DSC traces showed a single T(g) suggesting the block copolymers were miscible before UV irradiation. After UV irradiation, the X-ray reflectivity measurements showed the beating of two frequencies, indicating the formation of island-hole structure.