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Dielectric properties and frequency response of self-assembled monolayers of alkanethiols 总被引:1,自引:0,他引:1
Wang B Luo J Wang X Wang H Hou JG 《Langmuir : the ACS journal of surfaces and colloids》2004,20(12):5007-5012
This paper presents dielectric properties of alkanethiol self-assembled monolayers (SAMs) under an ac electric field. Using a Hg-SAM/SAM-Hg junction, we measured the ac impedance of alkanethiol SAMs using a sinusoidal perturbation of 30 mV (peak-to-peak) with frequency ranging from 1 Hz to 1 MHz at zero bias. Semicircles at higher frequencies and at middle frequencies along with Warburg lines at lower frequencies were observed in complex plane impedance plots, that is, Nyquist plots. The frequency response of SAMs was analyzed by modeling the junction using an equivalent circuit and fitting the Nyquist plots. The semicircles at higher frequencies are attributed to the effect of the SAM/SAM interfaces, and the ones at middle frequencies are attributed to the effect of alkanethiol SAMs. The comparison in the plots of the imaginary part of the impedance Z against frequency for the bare Hg electrodes (in pure ethanal) and the SAM-covered Hg electrodes (in alkanethiol solution) supports the analysis. The Warburg lines are attributed to a certain ionic impurity. The dielectric loss spectra are further analyzed. Chain-length-dependent peaks, which correspond to different relaxation mechanisms, at higher frequencies and middle frequencies were observed in the spectra of the dissipation factor (tan delta vs frequency). The peaks move to small frequency with the increase of chain length of alkanethiols. Using a correlation of peak position with the chain length, we then derived active energies of 39-99 meV for alkanethiol SAMs of C7-C18 under an ac electric field. 相似文献
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Lu Tian Arash Tahmasebi Jianglong Yu 《Journal of Thermal Analysis and Calorimetry》2014,118(3):1577-1584
Thermal decomposition of magnesite is investigated by using a TG–MS. Different kinetic methods including Coats–Redfern, Flynn–Wall–Ozawa, and Kissinger–Akahira–Sunose are used to investigate the thermal decomposition kinetics of magnesite. It was observed that the activation energy values obtained by these methods are similar. The average apparent activation energy is found to be about 203 kJ mol?1. The raw magnesite and its decomposition products obtained at different temperatures are analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscope (SEM). The concentration of functional groups, crystal structure and composition, and apparent morphology of decomposition products were studied in detail. The FTIR, XRD, and SEM analyses showed that magnesite was completely decomposed at 973 K to form MgO. 相似文献
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Shufang Wang Huiling Li Kun Zhao Songqing Zhao Mingjing Chen Jingchun Chen Jianglong Wang Guangsheng Fu 《Applied Physics A: Materials Science & Processing》2011,105(2):407-410
A heterojunction was fabricated by growing a layer of Bi2Sr2Co2O
y
thin film on the 0.7 wt% Nb-doped SrTiO3 substrate. Such heterojunction showed good rectifying characteristics over a wide temperature range, and its transport mechanism
under the forward bias can be attributed to a space charge limited conduction mechanism via defects near the interface of
the heterojunction. Photovoltaic properties of the heterojunction were studied by using both continuous-wave and pulsed irradiations
and the results can be well explained by the photovoltaic effect of a p–n junction. 相似文献
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Wang P Li X Zhu J Chen J Yuan Y Wu X Danishefsky SJ 《Journal of the American Chemical Society》2011,133(5):1597-1602
Described herein is a method for the joining of complex peptides to complex oligosaccharides via an N-linkage. The ω-aspartylation is conducted by coupling fully deprotected glycosylamine with a peptide containing a unique thioacid at the ω-aspartate carboxyl. In the presence of HOBT, under conditions that, in principle, allow for oxidation, complex components are combined in encouraging yields to produce structurally and stereochemically defined N-linked glycopolypeptides wherein the carbohydrate domain can be quite complex. Various mechanisms for oxidative coupling are proposed. 相似文献
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Influencing factors on bioaccumulation of Ni by Synechcoccus were studied in this paper. The equilibration time of Ni bioaccumulation was about 80 min in aqueous solution. Bioaccumulation quantity reached maximum when mass ratio of Ni to dry weight concentration of Synechcoccus was 16-18%. Bioaccumulation quantity increased with increasing pH. The optimum pH was 9-10 and higher pH led to precipitation of Ni(OH)2. Bioaccumulation quantity was also influenced by temperature and light intensity reaching their optima at 35℃ and 3 000 lx respectively. Bioaccumulation of nonliving algae was larger than that of living algae. 相似文献
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在对超高能区宇宙线产生的广延大气簇射的模拟计算中注意到,质子—空气核碰撞中的受伤核子数分布和非弹性截面对于簇射的纵向发展有着重要的影响.本文依据符合现有加速器能区的有关质子—质子作用截面的经验公式,对超高能区的质子与空气核碰撞的受伤核子数分布和非弹性截面做了计算. 相似文献