Thermal activation and reaction of allyl alcohol on Ni(100)

The thermal chemistry of allyl alcohol (CH₂CHCH₂OH) on a Ni(100) single-crystal surface was studied by the temperature programmed desorption (TPD) and the X-ray photoelectron spectroscopy (XPS). The allyl alcohol adsorbs molecularly on the metal surface at 100 K. Intact molecular desorption from the surface occurs at temperatures around 180 K, but some molecules exhibit chemical reactivity on the surface: activation of the OH, CC, and CO bonds produces η¹(O)-allyloxy CH₂CHCH₂O_(a), η²(C, C) allyl alcohol (C_(a)H₂C_(a)HCH₂OH), and η³(C, C, O)-alkoxide (C_(a)H₂C_(a)CH₂ O_(a)) intermediates. Further thermal activation of allyl alcohol on the surface yields propylene (CH₂CHCH₃), 1-propanol (CH₃CH₂CH₂OH), propanal (CH₃CH₂CHO), and combustion and dehydrogenation products (H₂O, H₂, and CO). Propylene desorbs from the surface at temperatures of around 270 K. Hydrogenation to the η³(C, C, O)-alkoxide intermediate leads to the production of propanal which desorbs from the surface around 320 K, while hydrogenation of the η²(C, C) allyl alcohol intermediate produces 1-propanol, which desorbs at around 310 K. The co-adsorption of hydrogen atoms on the surface enhances the formation of the saturated alcohol, while co-adsorption of oxygen enhances the formation of both the saturated alcohol and the saturated aldehydes.     

2D planar field emission devices based on individual ZnO nanowires

2D planar field emission devices based on individual ZnO nanowires were achieved on Si/SiO₂ substrate via a standard e-beam lithography method. The anode, cathode and ZnO nanowires were on the same substrate; so the electron field emission is changed to 2D. Using e-beam lithography, the emitter (cathode) to anode distance could be precisely controlled. Real time, in situ observation of the planar field emission was realized in a scanning electron microscope. For individual ZnO nanowires, an onset voltage of 200 V was obtained at 1 nA. This innovative approach provides a viable and practical methodology to directly implement into the integrated field emission electrical devices for achieving “on-chip” fabrication.     

Control the revisit time of the electron wave packet

Ionization of molecules by strong laser fields launches an electron wave packet. This electron wave packet, which can be driven back by the field to recollide with the parent ion, has been widely explored to probe the ultrafast nuclear dynamics. We numerically demonstrate the precise control of the temporal characteristic of the recolliding electron wave packet (REWP) by orthogonally polarized two-color fields. Through changing the relative phase of the two fields, the revisit time of REWP can be manipulated with a resolution of less than 200 attos, thus significantly improving the resolution of the well known molecular clock. This provides an efficient method for real-time observation of the ultrafast molecular dynamics with attosecond resolution.     

High spatial resolution distributed strain sensor based on linear chirped fiber Bragg grating and fiber loop ringdown spectroscopy

A simple sensor system for high spatial resolution distributed strain field measurement is proposed and demonstrated experimentally. The fiber loop ringdown technique combined with a linear chirped fiber Bragg grating is used to realize the high spatial resolution. A proof-of-concept distributed strain sensor with 2?mm spatial resolution is realized. The sensor network is also explored and researched experimentally. The proposed technique suggests a broad range of applications for real-time distributed physical parameter sensing, such as strain or temperature.     

Enhanced optical absorption in nanopatterned silicon thin films with a nano-cone-hole structure for photovoltaic applications

In this paper, the optical properties of the silicon nano-cone-hole (NCH) structure array are studied. The ultimate efficiency of the optimized NCH array is enhanced by 23.11% compared to an optimized nanohole array of the same thickness. The absorptance enhancement of the NCH arrays is attributed to its lowered reflectance, more supported resonant modes, and enhanced mode interaction. The angular dependence of ultimate efficiency is also investigated.     

Development of long-life-cycle tablet ceramic adsorbent for geosmin removal from water solution

In this study, the tablet ceramic adsorbent (TCA), a silica/iron(III) oxide composite material, has been developed for geosmin (GSM) removal from the water solution. The physicochemical characteristics of TCA were examined with XRD, SEM, EDX and BET analyses. The sorption characteristics of GSM on TCA were investigated in a batch system. Attempts have been made to understand the adsorption kinetics, the effect of initial GSM concentration, solution pH, and reaction time.The batch experiments equilibrium data were well fitted to the Lagergren kinetic equation, which indicate the first-order nature adsorption. Over 82% of the GSM was removed by the TCA within 600 min at an initial concentration of 200 ng/L with 20 g/L of TCA dose. The batch and regeneration study indicated that the TCA is a cost-effective GSM adsorbent with sufficient mechanical strength to retain its physical integrity after long-time adsorption, and high regeneration performance for long-life-cycle application. Almost no second contamination (toxic sludge or leached iron) was observed after adsorption, and the gas resultant of thermal regeneration is harmless to atmospheric environment.     

Two-dimensional self-assembly of esters with different configurations at the liquid-solid interface

Self-assembled monolayers of hexadecyl palmitate (HP) and 3,3′-thiodipropionic acid di-n-octadecyl ester (TADE) physisorbed on highly oriented pyrolytic graphite (HOPG) are investigated using scanning tunneling microscope (STM) and computer simulation. Both molecules form alkane-like linear shapes to maximize the interactions with substrate when they adsorb on HOPG surface. The HP molecules self-assemble into lamellae with the chain-trough angle of 48°, which is the result of a shifting 3/2 units from the adjacent molecule in a lamella. Based on the simulation insights combined with STM images, we confirm that a perpendicular orientation appears in which the HP molecular backbone is rotated 90° with respect to the substrate such that the carbonyl points away from the HOPG surface. TADE molecules form three kinds of configurations with chain-trough angles of 90°, 72° and 60° by shifting 0, 1/2 and 1 units from their adjacent molecules, respectively. The bright stripes in STM images reveal the electron density distribution of the part between two ester groups. The energy differences of three TADE adsorption configurations by molecular mechanics (MM) simulation are used to explain the structural coexistence phenomenon. It is also shown that lattice match between alkyl chain of molecules and HOPG substrate could change molecular conformation upon self-assembly.     

航天鱼眼相机光学系统设计的研究

充分考虑鱼眼相机应用的空间环境特点,设计了一款基于1/3inch(1inch=25.4mm)CCD的航天鱼眼相机光学系统,系统焦距2.1mm,F数为4,视场角为210°,工作温度-40℃～+60℃。重点研究了环境因素对鱼眼相机光学系统成像质量的影响,分别从抗空间带电粒子、抗紫外辐照、温度和气压适应性方面进行了分析和研究,给出了相应的解决思路和方法。相机在严峻的空间环境下具有良好的环境适应性,为在轨获得超广角空域信息提供了保证。     

Study of radiation background at the north crossing point of the BEPCⅡ in collision mode

Understanding the radiation background at the north crossing point (NCP) in the tunnel of BEPCII is crucial for the performance safety of the High Purity Germanium (HPGe) detector, and in turn of great significance for long-term stable running of the energy measurement system. Therefore, as the first step, a NaI(Tl) detector is constructed to continuously measure the radiation level of photons as background for future experiments. Furthermore, gamma and neutron dosimeters are utilized to explore the radiation distribution in the vicinity of the NCP where the HPGe detector will be located. Synthesizing all obtained information, the shielding for neutron irradiation is studied based on model-dependent theoretical analysis.