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301.
Zhenhua Zhang Chao Guo Denise Jeng Kwong Jie Li Xiaoqing Deng Zhiqiang Fan 《Advanced functional materials》2013,23(21):2765-2774
The donor–acceptor molecule is the only molecule that features a real intrinsic rectification. However, all investigations in the last decades showed that rectification behaviors of such molecules are not promising since their rectification ratio is only on the order of 10. Use of carbon chains Cn to serve as spacers is reported, along with attempts to modulate electrical behavior of the donor–acceptor molecule. Calculations using the first‐principles method show that electrical behavior is indeed altered substantively, and a particular regularity can be clearly observed, i.e., a dramatic odd–even oscillation for electronic behavior with increasing carbon‐chain length n. For models with even‐n carbon chains, the rectification ratio is small (30), and no negative differential resistance (NDR) behavior is detected, but the rectifying performance of models with odd‐n carbon chains is tremendously improved and rectification ratios on the order of 50 to 400 can be achieved, alongside a large NDR. This study thus suggests that using a suitable spacer might be an effective way to significantly boost electrical characteristics, including rectifying performance, of the donor–acceptor molecule. 相似文献
302.
Wireless sensor networks provide a wide range of applications, such as environment surveillance, hazard monitoring, traffic
control, and other commercial or military applications. The quality of service provided by a sensor network relies on its
coverage, i.e., how well an event can be tracked by sensors. This paper studies how to optimally deploy new sensors in order
to improve the coverage of an existing network. The best- and worst-case coverage problems that are related to the observability
of a path are addressed and formulated into computational geometry problems. We prove that there exists a duality between
the two coverage problems, and then solve the two problems together. The presented placement algorithm is shown to deploy
new nodes optimally in polynomial time. 相似文献
303.
Macrocyclic polyethers, e.g., crown ethers and cryptands, were prepared and employed as phase transfer catalysts for free radical polymerization of acrolein, a vinyl monomer, with persulfates (S2O82–) as initiators. The catalytic abilities of various macrocyclic polyethers as catalysts for the free radical polymerization of acrolein were found to be in the order: benzo‐15‐crown‐5 > dibenzo‐18‐crown‐6 > 12‐crown‐4 > 15‐crown‐5 > 18‐crown‐6 > cryptand‐22 with sodium persulfate (Na2S2O8) as initiator. Sodium persulfate proved to be a better initiator than ammonium persulfate or potassium persulfate with benzo‐15‐crown‐5 as a catalyst. Effects of solvents and temperature on the catalytic polymerization were also investigated. The polymerization rates in various solvents were in the order: dioxane > benzene > acetonitrile > acetone > dichloromethane > hexane > water. Comparison between bulk polymerization and solution polymerization was also made. Higher polymerization rate was observed at higher temperature. The molecular weights of polyacrolein and the conversion of monomer in reaction period were determined with gel permeation chromatography and ultra‐violet spectrophotometry, respectively. Concentration effects of crown ether and initiator were also investigated and discussed. 相似文献
304.
Ming‐Shan Tsai U. Narasimha Rao Jeng‐Rong Wang Chung‐Hao Liang Ming‐Chang P. Yeh 《中国化学会会志》2001,48(5):869-876
Semihydrogenation of α,β‐unsaturated ynoates and ‐ynones bearing a γ‐alkoxy group can be performed using triphenylphosphine and water. α,β‐Unsaturated ynoates were reduced to a mixture of cis and trans α,β‐unsaturated enoates, whereas, ynones were reduced to trans α,β‐unsaturated enones as the only products. 相似文献
305.
Jeng‐Hun Lee Jungmo Kim Dan Liu Fengmei Guo Xi Shen Qingbin Zheng Seokwoo Jeon Jang‐Kyo Kim 《Advanced functional materials》2019,29(29)
Realization of sensing multidirectional strains is essential to understanding the nature of complex motions. Traditional uniaxial strain sensors lack the capability to detect motions working in different directions, limiting their applications in unconventional sensing technology areas, like sophisticated human–machine interface and real‐time monitoring of dynamic body movements. Herein, a stretchable multidirectional strain sensor is developed using highly aligned, anisotropic carbon nanofiber (ACNF) films via a facile, low‐cost, and scalable electrospinning approach. The fabricated strain sensor exhibits semitransparency, good stretchability of over 30%, outstanding durability for over 2500 cycles, and remarkable anisotropic strain sensing performance with maximum gauge factors of 180 and 0.3 for loads applied parallel and perpendicular to fiber alignment, respectively. Cross‐plied ACNF strain sensors are fabricated by orthogonally stacking two single‐layer ACNFs, which present a unique capability to distinguish the directions and magnitudes of strains with a remarkable selectivity of 3.84, highest among all stretchable multidirectional strain sensors reported so far. Their unconventional applications are demonstrated by detecting multi‐degrees‐of‐freedom synovial joint movements of the human body and monitoring wrist movements for systematic improvement of golf performance. The potential applications of novel multidirectional sensors reported here may shed new light into future development of next‐generation soft, flexible electronics. 相似文献
306.
Tsun-Lai Hsu Denny Duan-Lee Tang Jeng Gong 《Electron Device Letters, IEEE》1999,20(10):532-534
This paper shows that MOSFET operated in dynamic-threshold (DT) mode (Vbody=Vgate) is more suitable for low-noise RF/analog applications than those operated in conventional mode (Vbody=Vsource). Detailed low-frequency noise properties of these two modes of device operation were compared for 0.31-μm gate MOSFET's, in which NMOS's are surface-channel devices (S.C.) and PMOS's are buried-channel (B.C.) devices. Experimental data show that when the devices are biased at same transconductance, the low-frequency noise in DT mode is 30 times lower (at gm=2.2×10-3 S) than that in the conventional mode for the B.C. devices and ten times (at gm=2.0×10 -3 S) lower for the S.C. devices 相似文献
307.
Ging-Ho Hsiue Rong-Ho Lee Ru-Jong Jeng 《Journal of polymer science. Part A, Polymer chemistry》1999,37(14):2503-2510
A series of all organic nonlinear optical (NLO) sol-gel materials based on melamines and an azobenzene dye (Disperse Orange 3; DO3) have been investigated. Different contents of DO3 were covalently bonded with the melamine-based organic network via condensation of amino and methylol groups. The optically clear samples exhibited second-order optical nonlinearity (second-harmonic coefficient d33) = 35.4 and 11.5 pm/V at 1064 and 1542 nm, respectively) after poling and curing at 220°C for 1 h. Thermal behavior of these organic NLO sol-gel systems was studied by temperature-dependent dielectric relaxation. The results indicate that the incorporation of rigid NLO-active chromophore into the melamine-based matrix leads to high rigidity and dense packing of the organic network. Subsequently, higher glass transition temperatures were obtained for the organic NLO sol-gel material with higher DO3 content. The influence of composition on the temporal stability at 100°C was also investigated. Temporal stability at 100°C was studied as a function of system composition. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2503–2510, 1999 相似文献
308.
Chung‐Yao Lin Shao‐Sian Li Je‐Wei Chang Hao‐Chung Chia Yu‐Yun Hsiao Chun‐Jen Su Bing‐Jun Lian Cheng‐Yen Wen Shao‐Ku Huang Wei‐Ru Wu Di‐Yan Wang An‐Chung Su Chun‐Wei Chen U‐Ser Jeng 《Advanced functional materials》2019,29(36)
Recently, a new seeding growth approach for perovskite thin films is reported to significantly enhance the device performance of perovskite solar cells. This work unveils the intermediate structures and the corresponding growth kinetics during conversion to perovskite crystal thin films assisted by seeding PbS nanocrystals (NCs), using time‐resolved grazing‐incidence X‐ray scattering. Through analyses of time‐resolved crystal formation kinetics obtained from synchrotron X‐rays with a fast subsecond probing time resolution, an important “catalytic” role of the seed‐like PbS NCs is clearly elucidated. The perovskite precursor‐capped PbS NCs are found to not only accelerate the nucleation of a highly oriented intermediate phase, but also catalyze the conversion of the intermediate phase into perovskite crystals with a reduced activation energy Ea = 47 (±5) kJ mol?1, compared to 145 (±38) kJ mol?1 for the pristine perovskite thin film. The reduced Ea is attributed to a designated crystal lattice alignment of the perovskite nanocrystals with perovskite cubic crystals; the pivotal heterointerface alignment of the perovskite crystals coordinated by the Pb NCs leads to an improved film surface morphology with less pinholes and enhanced crystal texture and thermal stability. These together contribute to the significantly improved photovoltaic performance of the corresponding devices. 相似文献
309.
Tai-Sing Wu Leng-You Syu Shih-Chang Weng Horng-Tay Jeng Shih-Lin Chang Yun-Liang Soo 《Journal of synchrotron radiation》2018,25(5):1395-1399
This work reports an unconventional defect engineering approach using synchrotron‐radiation‐based X‐rays on ceria nanocrystal catalysts of particle sizes 4.4–10.6 nm. The generation of a large number of oxygen‐vacancy defects (OVDs), and therefore an effective reduction of cations, has been found in CeO2 catalytic materials bombarded by high‐intensity synchrotron X‐ray beams of beam size 1.5 mm × 0.5 mm, photon energies of 5.5–7.8 keV and photon fluxes up to 1.53 × 1012 photons s?1. The experimentally observed cation reduction was theoretically explained by a first‐principles formation‐energy calculation for oxygen vacancy defects. The results clearly indicate that OVD formation is mainly a result of X‐ray‐excited core holes that give rise to valence holes through electron down conversion in the material. Thermal annealing and subvalent Y‐doping were also employed to modulate the efficiency of oxygen escape, providing extra control on the X‐ray‐induced OVD generating process. Both the core‐hole‐dominated bond breaking and oxygen escape mechanisms play pivotal roles for efficient OVD formation. This X‐ray irradiation approach, as an alternative defect engineering method, can be applied to a wide variety of nanostructured materials for physical‐property modification. 相似文献
310.
Huw Waters Noel Bristow Omar Moudam Shu-Wei Chang Chun-Jen Su Wei-Ru Wu U.-Ser Jeng Masaki Horie Jeff Kettle 《Organic Electronics》2014,15(10):2433-2438
The effect that processing additives have upon the lifetime of PCPDTBT-based OPVs has been investigated. The results show conclusively that whilst ODT processing additive enhances the initial performance of PCPDTBT:PCBM OPVs, it is detrimental to their long term performance, when measured under light soaking at 1 Sun of irradiance. Results are shown for both encapsulated and non-encapsulated devices. Topographical and morphological measurements made using AFM and small- and wide-angle X-ray scattering of active layers show that there are greater morphological changes of devices fabricated with the 1,8-octanedithiol upon light soaking, revealing a relatively venerable morphology of the active layer processed with the additive, when subject to light soaking. 相似文献