Development of laser deposited multilayer zone plate structures for soft X-ray radiation

As a novel approach, the combination of pulsed laser deposition and focused ion beam was applied to fabricate different types of multilayer zone plate structures for soft X-ray applications. For this purpose, high quality non-periodic ZrO₂/Ti multilayers were deposited by pulsed laser deposition on planar Si substrates and on rotating steel wires with layer thicknesses according to the Fresnel zone plate law. Linear focusing optics were fabricated by cutting slices out of the multilayers by focused ion beam and placing them directly over pinholes within Si₃N₄ substrates. Additionally, it was shown that laser deposition of depth-graded multilayers on a wire is also a promising way for building up multilayer zone plates with point focus. First experiments using a table-top X-ray source based on a laser-induced plasma show that the determined focal length and spatial resolution of the fabricated multilayer Laue lens corresponds to the designed optic.     

Uniformity study of wafer-scale InP-to-silicon hybrid integration

β-SiC nanowires were synthesized by a simple carbothermal reduction of carbonaceous silica xerogel. The morphology and structure of the nanowires were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results showed that the nanowires were hexagonal prism-shaped hierarchical nanostructures. The typical stacking faults and twin defects of SiC nanowires were also observed. Band-gap characterization and photoluminescence properties of SiC nanowires were investigated by UV-vis absorption spectroscopy and fluorescence photometry, respectively. The results showed the SiC nanowire was an indirect transition semiconductor and the band gap energy for the SiC nanowires was 2.85 eV. The photoluminescence peak value at 470 nm (2.64 eV) originating from the SiC nanowires was a little higher than the value of band-gap energy.     

Conductive,Monodisperse Polyaniline Nanofibers of Controlled Length Using Well‐Defined Cylindrical Block Copolymer Micelles as Templates

Stable colloidal dispersions of polyaniline (PAni) nanofibers with controlled lengths from about 200 nm–1.1 μm and narrow length distributions (L_w/L_n<1.04; L_w=weight average micelle length, L_n=number average micelle length) were prepared through the template‐directed synthesis of PAni using monodisperse, solution‐self‐assembled, cylindrical, block copolymer micelles as nanoscale templates. These micelles were prepared through a crystallization‐driven living self‐assembly method from a poly(ferrocenyldimethylsilane)‐b‐poly(2‐vinylpyridine) block copolymer (PFS₂₅‐b‐P2VP₄₂₅). This material was initially self‐assembled in iPrOH to form cylindrical micelles with a crystalline PFS core and a P2VP corona and lengths of up to several micrometers. Sonication of this sample then yielded short cylinders with average lengths of 90 nm and a broad length distribution (L_w/L_n=1.32). Cylindrical micelles of PFS₂₅‐b‐P2VP₄₂₅ with controlled lengths and narrow length distributions (L_w/L_n<1.04) were subsequently prepared using thermal treatment at specific temperatures between 83.5 and 92.0 °C using a 1D self‐seeding process. These samples were then employed in the template‐directed synthesis of PAni nanofibers through a two‐step procedure, where the micellar template was initially stabilised by deposition of an oligoaniline coating followed by addition of a polymeric acid dopant, resulting in PAni nanofibers in the emeraldine salt (ES) state. The ES–PAni nanofibers were shown to be conductive by scanning conductance microscopy, whereas the precursor PFS₂₅‐b‐P2VP₄₂₅ micelle templates were found to be dielectric in character.     

An Efficient Route to 2-(Formylmethyl)-Cyclopenten-3-one and Its 1-methyl-Congener

We describe a five-step synthesis of 2-(formylmethyl) - cyclopenten-3-one (1a) and its 1-methyl congener (1b) from 6-methylhept-5-ene-2-one by way of the respective 2-(3-methylbut-2-enyl)-cyclopenten-3-ones (5) and selective ozonolysis of these intermediates.     

WHAT ARE THE DIFFERENCES OF POLYMER SURFACE RELAXATION FROM THE BULK?

The polymer surface relaxation in thin films has been a long debating issue.We report a new method on studying surface relaxation behaviors of polymer thin films on a solid substrate.This method involved utilizing a rubbed polyimide surface with a pretilting angle in a liquid crystalline cell.Due to the surface alignment,the liquid crystals were aligned along the rubbing direction.During heating the liquid crystalline cell,we continuously monitored the change of orientation of the liquid crystals.It is u...     

Cosmic rays through the Higgs portal

We consider electroweak singlet dark matter with a mass comparable to the Higgs mass. The singlet is assumed to couple to standard matter through a perturbative coupling to the Higgs particle. The annihilation of a singlet in the mass range m_Sm_h is dominated by proximity to the W, Z and Higgs peaks in the annihilation cross section. We find that the continuous photon spectrum from annihilation of perturbatively coupled singlets in the galactic halo can reach a level of several per mil of the EGRET diffuse γ ray flux.     

Nanosecond laser-induced surface damage of optical multimode fibers and their preforms

High-power optical multimode fibers are essential components for materials processing and surgery and can limit the performance of expensive systems due to breakdown at the end faces. The aim of this paper is the determination of laser-induced damage thresholds (LIDT) of fibers (FiberTech) and preforms (Heraeus Suprasil F300). Preforms served as models. They were heated up to maximum temperatures of 1100, 1300 and 1500°C and cooled down to room temperature at rates of 10 K min⁻¹ (oven) and ∼10⁵ K min⁻¹ (quenched in air) to freeze in various structural states simulating different conditions similar to a drawing process during the production of fibers. Single- and multi-pulse LIDT measurements were done in accordance with the relevant ISO standards. Nd:YAG laser pulses with durations of 15 ns (1064 nm wavelength) and 8.5 ns (532 nm) at a repetition rate of 10 Hz were used. For the preforms, LIDT values (1-on-1) ranged from 220 to 350 J/cm² (1064 nm) and from 80 to 110 J/cm² (532 nm), respectively. A multi-pulse impact changed the thresholds to lower values. The LIDT (1064 nm wavelength) of the preforms can be regarded as a lower limit for those of the fibers.     

原子尺度的欧姆表

一种高度稳定的扫描隧道显微镜(STM)可以在小于原子尺度范围精密测量金属的电学性能。扫描隧道显微镜可以在表面对单个原子成像,或者移动单个原子。研究人员最近进一步提高了这个仪器的精确性,可以对铅表面单个原子附近不同位置的电导进行测量。这个结果或许有助于揭示金属和超导体的性质的差异,未来或许可以用于纳米加工技术。一台STM的探针非常尖锐,尖端只有一个原子,将探针在真空中操控到距离表面极近的位置。电子可以在加有电势的间隙之间越过,或者称隧穿。当探针在表面运动时,记录通过探针的电流可以对表面成像。另外一种STM技术是将探针保持与表面接触,使得探针原子与样品表面形成化学键。研究人员使用这种被称为点接触技术,可以测量一种材料原子尺度的电导性质,了解在量子物理中电流是如何流动的,此时传统的欧姆定律不再成立。     

Defect orientation on the chain folded surfaces of two-arm poly(ethylene oxide) lamellar crystals

Two-arm poly(ethylene oxide) fractions (PEOs) with arm lengths of 2 220 g/mol were synthesized via a reaction using terephthaloyl (1,4-), isophthaloyl (1,3-) and phthaloyl (1,2-) dichorides as coupling agents. The center of each molecule thus includes a phenylene group as a configurational defect, and they are excluded to the crystal folded basal surfaces. In the lamellar crystals with the once-folded overall molecular conformation, observations of surface-enhanced Raman scattering experiments show that only the in-plane vibration modes are selectively enhanced. This implies that the arrangement of phenylene groups adopts a “stand-up” orientation on the basal surface, i. e., the π plane of phenylene groups in the defects is perpendicular to the lamellar basal surface.