Ultrathin Metal–Organic Framework Nanosheets with Ultrahigh Loading of Single Pt Atoms for Efficient Visible‐Light‐Driven Photocatalytic H2 Evolution

A surfactant‐stabilized coordination strategy is used to make two‐dimensional (2D) single‐atom catalysts (SACs) with an ultrahigh Pt loading of 12.0 wt %, by assembly of pre‐formed single Pt atom coordinated porphyrin precursors into free‐standing metal–organic framework (MOF) nanosheets with an ultrathin thickness of 2.4±0.9 nm. This is the first example of 2D MOF‐based SACs. Remarkably, the 2D SACs exhibit a record‐high photocatalytic H₂ evolution rate of 11 320 μmol g^?1 h^?1 via water splitting under visible light irradiation (λ>420 nm) compared with those of reported MOF‐based photocatalysts. Moreover, the MOF nanosheets can be readily drop‐casted onto solid substrates, forming thin films while still retaining their photocatalytic activity, which is highly desirable for practical solar H₂ production.     

Synthesis and structure of some substituted 2-amino-4-aryl-7-propargyloxy-4H-chromene-3-carbonitriles

A series of 2-amino-7-hydroxy-4H-chromene-3-carbonitriles 4a–l were synthesized through three-component reaction using sodium carbonate as a catalyst. The reaction was carried out in 96% ethanol-water medium (1:20 ratio in volume). Propargyl ether compounds 5a–l of these chromene-3-carbonitriles were successfully synthesized from corresponding hydroxyl chromene derivatives by reaction with propargyl bromide. Two different procedures were applied in this process: the procedure that used potassium carbonate in dried acetone and the procedure that used sodium hydride in dried DMF. The latter gave the ethers 5a–l in higher yields. The single-crystal X-ray structure of propargyl ether 5g has been recorded.     

Characteristics of pulse fiber amplifier with China-made LMA fiber and (6+1)×1 multimode combiner

A pulse master-oscillator fiber power amplifier system with china-made large-mode-area fiber and a (6+1)×1 multimode combiner is demonstrated. The system generates up to 4.8 W of amplified radiation (100 kHz) at a wavelength of 1064 nm with a near-diffraction-limited beam quality (M²=1.2), and the overall slope efficiency with respect to the launched pump power is 50%. Some basic characteristics of this system, including the pulse-amplification characteristics, the gain characteristics, as well as the emission spectrum characteristics are investigated in detail.     

Performance analysis of a thermosize micro/nano heat engine

In a recent paper [A. Sisman, I. Muller, Phys. Lett. A 320 (2004) 360] the thermodynamic properties of ideal gases confined in a narrow box were examined theoretically. The so-called “thermosize effects” similar to thermoelectric effects, such as Seebeck-like thermosize effect, Peltier-like thermosize effect and Thomson-like thermosize effect, were analyzed. Like the thermoelectric generator, based on the thermosize effects we have established a model of micro/nano scaled ideal gas heat engine cycle which includes two isothermal and two isobaric processes. The expressions of power output and efficiency of this cycle in the two cases of reversible and irreversible heat exchange are derived and the optimal performance characteristics of the heat engine is discussed by some numerical example. The results obtained here will provide theoretical guidance for the design of micro/nano scaled device.     

Aperture based Raman spectroscopy on SiGe film structures with high spatial resolution

We have investigated silicon–germanium (SiGe) line structures employing metallic apertures in combination with Raman spectroscopy to obtain high‐spatial strain resolution below the diffraction limit. The apertures were cut into specifically shaped electrochemically etched tungsten tips, which were adjusted within the Raman laser beam on the sample surface by a tuning fork atomic force microscope. With this setup, line structures on patterned SiGe films with a center‐to‐center distance down to 200 nm were resolved in the Raman scans, evidently indicating a resolution clearly below the far‐field Raman resolution of about 600 nm for the used instrument. This setup allows improved local strain analysis by Raman spectroscopy and shows potential for further near‐field Raman applications. Copyright © 2008 John Wiley & Sons, Ltd.     

C60LB薄膜覆盖离子交换玻璃波导的光功率限制

集成光学光波导是光学非线性相互作用的理想结构,与块状结构相比,波导结构能够把光束限制在微米量级的尺寸范围,形成了光束在光波导中无衍射传播并造成作用在波导媒质上的光功率密度成数量级增长,使非线性相互作用所要求的长相互作用距离和高功率密度二因素得到满足.     

Singular boundary value problems for the one-dimension p-Laplacian

The singular boundary value problem

where φ(s)=|s|^p−2s, p>1, is studied in this paper. The singularity may appear at u=0, t=0 and t=1, and the function g may change sign. The existence of solutions is obtained via an upper and lower solution method.