A high-pressure atomic force microscope for imaging in supercritical carbon dioxide

A high-pressure atomic force microscope (AFM) that enables in situ, atomic scale measurements of topography of solid surfaces in contact with supercritical CO(2) (scCO(2)) fluids has been developed. This apparatus overcomes the pressure limitations of the hydrothermal AFM and is designed to handle pressures up to 100 atm at temperatures up to ～350 K. A standard optically-based cantilever deflection detection system was chosen. When imaging in compressible supercritical fluids such as scCO(2), precise control of pressure and temperature in the fluid cell is the primary technical challenge. Noise levels and imaging resolution depend on minimization of fluid density fluctuations that change the fluid refractive index and hence the laser path. We demonstrate with our apparatus in situ atomic scale imaging of a calcite (CaCO(3)) mineral surface in scCO(2); both single, monatomic steps and dynamic processes occurring on the (1014) surface are presented. This new AFM provides unprecedented in situ access to interfacial phenomena at solid-fluid interfaces under pressure.     

Design of a continuous-flow reactor for in situ x-ray absorption spectroscopy of solids in supercritical fluids

This paper presents the design and performance of a novel high-temperature and high-pressure continuous-flow reactor, which allows for x-ray absorption spectroscopy or diffraction in supercritical water and other fluids under high pressure and temperature. The in situ cell consists of a tube of sintered, polycrystalline aluminum nitride, which is tolerant to corrosive chemical media, and was designed to be stable at temperatures up to 500 °C and pressures up to 30 MPa. The performance of the reactor is demonstrated by the measurement of extended x-ray absorption fine structure spectra of a carbon-supported ruthenium catalyst during the continuous hydrothermal gasification of ethanol in supercritical water at 400 °C and 24 MPa.     

激光刻蚀金银合金胶体的制备及其SERS应用

金属胶体是一种新兴的表面增强拉曼散射(SERS)活性衬底,利用激光液相刻蚀技术制备了金银合金胶体,并通过透射电镜、吸收光谱、表面增强拉曼散射光谱等手段对其特性进行表征。结果表明,合金粒子多数为球形颗粒,颗粒大小在5nm左右,并且有很好的分散性,等离子体共振吸收峰位于428nm。此外,该胶体表现出很好的表面增强拉曼散射活性,且性能稳定可在室温下长时间保存。     

Studies on laser ablation of low temperature co-fired ceramics (LTCC)

LTCC material is introduced as an excellent alternative to silicon, glass or plastic materials for the fabrication of miniaturised analytical devices, though it is most widely used in the automotive industry and microwave industry. Laser ablation of LTCC material was studied in this report. This kind of green tape material is mechanised by excimer laser (KrF, 248 nm) and UV laser (Nd:YAG, 355 nm) and, for the first time, by infrared laser (1,090 nm). The optical photos and the SEM photos of the LTCC ablated by different kinds of laser sources are given in this paper. For the first time, we discuss the laser ablation of LTCC by optical fibre sources. When using the excimer laser, the tapered structure can be easily seen from the SEM photo. However, a kind of clear and perfect ablation of LTCC can be seen for the first time by the 1,090-nm infrared laser ablation.     

An optical high-pressure cell for transient grating measurements of biological substance with a high reproducibility

We describe a high-pressure optical cell that can be used for time-resolved transient grating measurements to determine the thermodynamic properties of transient species under high pressure. This high-pressure cell enables us to compare the grating signal intensities of different samples quantitatively. Using this high-pressure cell with an inner sample cell, one can measure various thermodynamic properties of a biological substance in time domain. The stability and reproducibility of this apparatus are described.     

Time-resolved near-field optics: exciton transport in semiconductor nanostructures

We present a systematic, temperature-dependent study of excitonic real-space transfer into single GaAs quantum wires using time-resolved low-temperature near-field luminescence spectroscopy. Excitons generated by local short pulse optical excitation in a 250 nm spot undergo diffusive transport over a length of several micrometres and are subsequently trapped into the quantum wire by optical phonon emission. The effect of local energy barriers in the vicinity of the quantum wire on the real-space transfer dynamics is monitored directly by mapping the time-resolved quantum wire luminescence. Experiments at variable temperatures are compared to numerical simulations based on drift-diffusive model calculations, and the spatio-temporal evolution of the two-dimensional exciton distribution within the nanostructure is visualized.     

基于皮秒激光烧蚀的氧化铟锡纳米颗粒制备系统

液相脉冲激光烧蚀法合成纳米颗粒是一种绿色环保的制备方法。基于该方法搭建了一套氧化铟锡(ITO)纳米颗粒制备系统,该系统采用皮秒激光作为光源辐照去离子水中的氧化铟锡固体靶材,最终合成出ITO纳米颗粒。随着入射脉冲能量的增加及激光辐照时间的增长,激光烧蚀效率明显增大,ITO产量增多。采用扫描电子显微镜(SEM)及X射线能谱仪(EDS)对制备的ITO纳米颗粒进行表征,所制备的纳米颗粒不含除铟(In)、锡(Sn)之外的杂质成分,纯度较高且72%的ITO纳米颗粒粒径大小在20～50 nm之间。     

激光溅射离子源垂直引入式飞行时间质谱仪的研制

介绍了两台自行研制的激光溅射离子源垂直引入式飞行时间质谱仪(LAI-oa-TOFMS),相比于其他固体样品直接分析法,该仪器具有样品预处理简单、样品更换速度快(数分钟)、可进行微区分析、谱图干扰峰少和绝对灵敏度高(10-15g级)等众多优点。两台质谱仪的最佳质量分辨率分别达到7 000和4 000(FWHM)。重点对比分析了不同样品的电离方式和离子传输系统对仪器性能的影响。     

New large volume hydrothermal reaction cell for studying chemical processes under supercritical hydrothermal conditions using time-resolved in situ neutron diffraction

The design and testing of a new large volume Inconel pressure cell for the in situ study of supercritical hydrothermal syntheses using time-resolved neutron diffraction is introduced for the first time. The commissioning of this new cell is demonstrated by the measurement of the time-of-flight neutron diffraction pattern for TiO(2) (Anatase) in supercritical D(2)O on the POLARIS diffractometer at the United Kingdom's pulsed spallation neutron source, ISIS, Rutherford Appleton Laboratory. The sample can be studied over a wide range of temperatures (25-450 °C) and pressures (1-355 bar). This novel apparatus will now enable us to study the kinetics and mechanisms of chemical syntheses under extreme environments such as supercritical water, and in particular to study the crystallization of a variety of technologically important inorganic materials.     

Ultrasensitive ultraviolet-visible 20 fs absorption spectroscopy of low vapor pressure molecules in the gas phase

We describe an ultrasensitive pump-probe spectrometer for transient absorption measurements in the gas phase and in solution. The tunable UV pump and the visible (450-740 nm) probe pulses are generated by two independently tunable noncollinear optical parametric amplifiers, providing a temporal resolution of 20 fs. A homebuilt low gain photodetector is used to accommodate strong probe pulses with a shot noise significantly lower than the overall measurement noise. A matched digitizing scheme for single shot analysis of the light pulses at kilohertz repetition rates that minimizes the electronic noise contributions to the transient absorption signal is developed. The data processing scheme is optimized to yield best suppression of the laser excess noise and thereby transient absorbance changes down to 1.1 x 10(-6) can be resolved. A collinear focusing geometry optimized for a 50 mm interaction length combined with a heatable gas cell allows us to perform measurements on substances with low vapor pressures, e.g., on medium sized molecules which are crystalline at room temperature. As an application example highlighting the capability of this instrument, we present the direct time-domain observation of the ultrafast excited state intramolecular proton transfer of 2-(2(')-hydroxyphenyl)benzothiazole in the gas phase. We are able to compare the resulting dynamics in the gas phase and in solution with a temporal precision of better than 5 fs.     

Impurities removal by laser blow-off from in-vacuum optical surfaces on RFX-mod experiment

An in situ window cleaning system by laser blow-off through optical fiber has been developed on the basis of a feasibility study previously presented. The beam generated by a Q-switched Nd:YAG laser is launched in a vacuum box into a high damage threshold optical fiber through a lens. The fiber output is focused on the impurities-coated surface of a vacuum window exposed to the plasma of the RFX-mod experiment, and it is remotely controlled with an xy motion system to scan the entire surface. We first investigate the energy density threshold necessary to ablate the deposited impurity substrate on removed dirty windows: above threshold, a single laser pulse recovers ～95% of the window transmission before its exposure to the plasma, while below it the efficiency of the cleaning process is too poor. The system so conceived was then used to clean the three collection windows of the Main Thomson scattering diagnostic on RFX-mod. We also present results obtained applying the same technique to the SiO-protected Al mirror used for the Z(eff) diagnostic: an energy threshold for efficient impurity removal without mirror damage is first identified, then ablation tests are executed and analyzed in terms of recovered reflectivity. The SIMS technique is used both with windows and mirror to study the composition of surfaces before and after the ablation.     

High-pressure cell for neutron reflectometry of supercritical and subcritical fluids at solid interfaces

A new high-pressure cell design for use in neutron reflectometry (NR) for pressures up to 50 MPa and a temperature range of 300-473 K is described. The cell design guides the neutron beam through the working crystal without passing through additional windows or the bulk fluid, which provides for a high neutron transmission, low scattering background, and low beam distortion. The o-ring seal is suitable for a wide range of subcritical and supercritical fluids and ensures high chemical and pressure stability. Wafers with a diameter of 5.08 cm (2 in.) and 5 mm or 10 mm thickness can be used with the cells, depending on the required pressure and momentum transfer range. The fluid volume in the sample cell is very small at about 0.1 ml, which minimizes scattering background and stored energy. The cell design and pressure setup for measurements with supercritical fluids are described. NR data are shown for silicon/silicon oxide and quartz wafers measured against air and subsequently within the high-pressure cell to demonstrate the neutron characteristics of the high-pressure cell. Neutron reflectivity data for supercritical CO(2) in contact with quartz and Si/SiO(2) wafers are also shown.     

X-ray diffraction in the pulsed laser heated diamond anvil cell

We have developed in situ x-ray synchrotron diffraction measurements of samples heated by a pulsed laser in the diamond anvil cell at pressure up to 60 GPa. We used an electronically modulated 2-10 kHz repetition rate, 1064-1075 nm fiber laser with 1-100 μs pulse width synchronized with a gated x-ray detector (Pilatus) and time-resolved radiometric temperature measurements. This enables the time domain measurements as a function of temperature in a microsecond time scale (averaged over many events, typically more than 10,000). X-ray diffraction data, temperature measurements, and finite element calculations with realistic geometric and thermochemical parameters show that in the present experimental configuration, samples 4 μm thick can be continuously temperature monitored (up to 3000 K in our experiments) with the same level of axial and radial temperature uniformities as with continuous heating. We find that this novel technique offers a new and convenient way of fine tuning the maximum sample temperature by changing the pulse width of the laser. This delicate control, which may also prevent chemical reactivity and diffusion, enables accurate measurement of melting curves, phase changes, and thermal equations of state.     

An integrated laser Raman optical sensor for fast detection of nitrogen and oxygen in a cryogenic mixture

An integrated fiber optic Raman sensor was designed for real-time, nonintrusive detection of liquid nitrogen (LN(2)) in liquid oxygen (LO(2)) at high pressures and high flow rates. This was intended to monitor the quality of LO(2) in oxidizer feed lines during the ground testing of rocket engines. Various issues related to optical diagnosis of cryogenic fluids (LN(2)/LO(2)) in supercritical environment of rocket engine test facility, such as fluorescence from impurity in optical window of feed line, signal-noise ratio, and fast data acquisition time, etc., are well addressed. The integrated sensor employed a frequency doubled 532-nm continuous wave Nd:YAG laser as an excitation light source. The other optical components included were InPhotonics Raman probes, spectrometers, and photomultiplier tubes (PMTs). The spectrometer was used to collect the Raman spectrum of LN(2) and LO(2). The PMT detection unit was integrated with home-built LABVIEW software for fast monitoring of concentration ratios LN(2) and LO(2). Prior to designing an integrated sensor system, its optical components were also tested with gaseous nitrogen (GN(2)) and oxygen (GO(2)).     

A High-Sensitivity System for Cathodoluminescent Studies with the Camebax Electron Probe Microanalyzer

Our system for cathodoluminescent studies incorporates two optical spectrometers for the near UV, visible, and IR regions; an optical system for cathodoluminescent imaging; an electron-beam deflection system; and a sample-stage cooler. The optical spectrometers are integrated with a Camebax electron probe microanalyzer. Cathodoluminescent spectrometers are substituted for the binocular viewer. They are similar in optical arrangement and differ only in their diffraction-grating parameters. The spectrometers have high spectral resolution (0.1 nm) and sensitivity, are compact (40 × 30 cm) and lightweight (5 kg), and may therefore be mounted directly on the microanalyzer column. The system is able to record spectra by modulating the electron beam and in the time-resolving mode, and to analyze changes in the intensity of emission bands with a time resolution as high as 2 s. A photographic attachment is used to form an image (in natural colors) of the distribution of structuraldefects and other inhomogeneities in a sample with a magnification of 100 to 600 power. The use of a sample-stage cooler allows measurements to be made at temperatures ranging from 80 K to room temperature.     

Note: simple means for selective removal of the 365 nm line from the Hg spectrum using Dy

The emission spectrum of mercury has a notable line at about 365 nm under both low and medium-high pressure conditions. A simple filter based on a solution of dysprosium ions, Dy(3+), is shown to be very useful for applications of Hg-light sources where this line is unwanted. The presented filter is cheap, robust, and stable towards degradation or bleaching - even under intense irradiation. The absorption spectrum for the Dy-filter is presented along with emission spectra from both low-pressure and high-pressure Hg-lamps to illustrate the utility of the technique under best-case and worst-case conditions. Attenuation of the 365 nm spectral line is almost total for the low-pressure source whereas for the high-pressure source the attenuation is about a factor of three.     

Controlled Synthesis and Optical Properties of Pure Gold Nanoparticles

Abstract

Gold nanoparticles were synthesized by laser ablation of a gold metallic disc at wavelengths of 532 nm and 355 nm with 7 ns pulse duration in the pure water. The colloidal gold nanoparticles were characterized by ultraviolet-visible absorption spectroscopy, transmission electron microscopy, and fluorescence spectrometry. The presence of a surface plasmon resonance peak around ～ 524 nm indicates the formation of gold nanoparticles. The formation efficiencies of gold nanoparticles in colloids were found to increase when ablating the gold metallic disc with a laser having a longer wavelength. The size distributions of the gold nanoparticles thus produced were measured by transmission electron microscopy. A reduction in mean diameter of the particles was observed with a decrease in the laser wavelength under the irradiation at a high fluence of 25 mJ/pulse. The fluorescence spectroscopy demonstrated that these gold nanoparticles are fluorescent, showing a strong blue emission intensity at 458 nm.     

Density measurements of noncrystalline materials at high pressure with diamond anvil cell

We describe an x-ray absorption method for in situ density measurement of non-crystalline materials in the diamond anvil cell using a monochromatic synchrotron x-ray microbeam. Sample thickness, which is indispensable in the absorption method, can be determined precisely by extrapolating the thickness profile of the gasket obtained by x-ray absorption and diffraction measurements. Diamond deformation across the sample chamber becomes noticeable at high pressures above 10 GPa, which can be monitored with a precision better than 1%, as demonstrated by measurements on crystalline Ag. We have applied the developed method to measure densities of the classic network-forming GeO(2) glass in octahedral form at pressures up to 56 GPa. The fit to the pressure-volume data with the Birch-Murnaghan equation from 13 to 56 GPa gives parameters of V(0)=23.2+/-0.4 cm(3)mol and K=35.8+/-3.0 GPa, assuming that K(')=4. This method could be applicable for in situ determination of the density of liquids and other noncrystalline materials using a diamond anvil cell up to ultrahigh pressures.     

三光束激光干涉诱导向后转移制备金纳米结构及其SERS特性

为了提高激光诱导向后转移制备微纳阵列结构的效率,本文提出三光束激光干涉诱导向后转移(LIIBT)技术,为激光干涉技术与激光诱导向后转移的有机结合。本文以ITO玻璃为接收衬底,金薄膜为靶材,LIIBT过程中采用三光束激光干涉进行加工。SEM结果表明,在激光能量密度为25 mJ/cm^2,金膜厚度为50 nm条件下,获得了较好的阵列结构,周期为5μm,金纳米粒子均匀分布在其表面,尺寸小于100 nm的粒子达到80%以上。EDX分析结果表明微米尺度点阵由大量的In元素组成,该结构的形成源于激光与ITO层相互作用。将1.0×10^-5,1.0×10^-7和1.0×10^-9 M的罗丹明6G溶液,旋涂于微结构表面并进行拉曼光谱研究,在612 cm^-1,773 cm^-1,1190 cm^-1,1319 cm^-1和1511 cm^-1处发现了罗丹明6G的特征峰,说明制备的金纳米结构对微量的罗丹明6G有明显的SERS效应。本文提出的LIIBT技术将大大提高激光诱导向后转移制备微纳阵列结构的效率,在超灵敏检测、光电子器件、微流控等领域均具有广泛的应用前景。     

Detection of dust on JET with the high resolution Thomson scattering system

Dust particles have been observed with Thomson scattering systems on several tokamaks. We present here the first evidence of dust particles observed by the new high resolution Thomson scattering system on JET. The system consists of filter spectrometers that analyze the Thomson scattering spectrum from 670 to 1050 nm in four spectral channels. The laser source is a 5 J Q-switched Nd:YAG laser. Without a spectral channel at the laser wavelength, only dust particles that emit broadband light could be detected; these particles have been observed on JET after disruptions. The timing of their emission is clearly different from that expected for a Thomson scattering pulse. The light pulse from dust happens after the peak of the laser light and has a long tail.