Fractional coverage of defects in self-assembled thiol monolayers on gold

Au electrodes are alkylated by self-assembled organic monolayers of octadecanethiol from alcohol solution. The electron tunnelling resistance of a monolayer-coated gold electrode has been investigated by ac impedance. The relation between the fractional coverage of different defects and the corresponding film thickness at these ‘collapsed’ sites has been deduced from electron tunnelling theory. By using the concepts of average film thickness at defect (d_a) and average fractional coverage of defect (θ_a), we have obtained the θ_ad_a plot. The influence of the apparent standard rate constant on the shape of the θ_ad_a plot has been discussed. In our experiments, Fe(CN)₆^3−/4− is used as a redox probe to study the θ_ad_a plot of an octadecanethiol monolayer. The θ_a versus d_a plot indicates that the defects with d_a<6 methylene groups and θ_a<0.1 can increase the apparent standard rate constant from 1.9×10⁻¹⁰ cm s⁻¹, which is the theoretical value calculated from electron tunnelling theory, to 2.9×10⁻⁷ cm s⁻¹. The average thickness of the whole monolayer (ATWM), which is obtained from the θ_a versus d_a plot and which can indicate the blocking property of the monolayer, is 11 methylene groups.     

基于聚合物支撑形貌液晶/聚合物光栅的低阈值分布反馈式激光器

利用低光强曝光进行全息液晶/聚合物光栅(HPDLC)的制备,获得了内部无液晶微滴具有聚合物支撑形貌的低散射透射光栅结构.分别研究了染料PM567,DCM,DCJTI的放大的自发辐射(ASE)阈值及相对出射光强等性质,得到三种染料中DCJIT的ASE阈值最低,相对出射光强最高,表明DCJTI更适于制备低阈值、高转化效率激光器.分别采用这三种染料制备基于聚合物支撑形貌光栅的分布反馈式激光器,通过改变光栅周期得到不同出射波长的激光.其中,以DCJTI为工作物质,得到中心波长为648 nm,阈值为0.65μJ/pulse,转化效率为1.6%,线宽为0.3 nm的高性能激光.与国内外同类激光器相比,在阈值、转化效率、线宽三个方面均有不同程度的提高.     

Bounded and compact Toeplitz operators on the weighted Bergman space over the bidisk

Forα1,let dvαdenote the weighted Lebesgue measure on the bidisk andμa complex measure satisfying some Carleson-type conditions.In this paper,we show a sufcient and necessary condition for the Toeplitz operatorTαˉμto be bounded or compact on weighted Bergman spaceL1a(dvα).     

Carrier-envelope phase effects on high-harmonic generation driven by mid-infrared laser field

The influence of the carrier-envelope phase on high-harmonic generation is investigated, both experimentally and theoretically, for three different interaction gas media, driven by mid-infrared, few-cycle and CEP-stabiUzed laser pulses. Different patterns of harmonic spectra with varying CEP for the three interaction gas media are observed. Furthermore, in comparing our experiment results to the previous works driven by near-infrared laser pulses, different phenomena are found. Through numerical simulation, we find that for the two different kinds of driving fields, i.e. mid-infrared and near-infrared laser pulses, different kinds of electron trajectories contribute to the generation of high harmonics.     

Preparation, characterization of carboxylated bamboo fibers and their adsorption for lead(II) ions in aqueous solution

The present study was conducted to develop a simple and versatile method to prepare carboxylated bamboo fibers which can be applied as potential bio-adsorbent for metal ions removal due to the high content of carboxyl groups. The chemical modification of bamboo fibers with citric acid (CA) was carried out by friendly semi-dry oven method. The resulting products with carboxyl group content between 1.99 and 4.13 mmol/g were accessible by changing ultrasonic pretreatment time, reaction temperature, reaction time and the amounts of catalyst and citric acid in order to minimize cross-linking reaction and thereby maximize carboxyl groups content. The characterization of the resulting products confirmed that carboxyl groups were successfully grafted onto surface of bamboo fibers. Moreover, the carboxylated bamboo fibers could be applied as bio-adsorbent for the removal of lead(II) ions from aqueous solution. Results showed that the adsorption capacity of Pd²⁺ could reach 127.1 mg/g for carboxylated bamboo fibers with 4.13 mmol/g carboxyl group content prepared under the ultrasonic pretreatment for 20 min at the CA/bamboo fibers weight ratio of 4.0 in the catalyst amount of 30 wt% at 120 °C for 90 min and the carboxylated bamboo fibers exhibited highly efficient regeneration with no significant loss of adsorption capacity of lead ion after five repeated adsorption/desorption cycles.