Combining high mass resolution and velocity imaging in a time-of-flight ion spectrometer using pulsed fields and an electrostatic lens

We describe a momentum resolving time-of-flight ion mass spectrometer that combines a high mass resolution, a velocity focusing condition for improved momentum resolution, and field-free conditions in the source region for high resolution electron detection. It is used in electron-ion coincidence experiments to record multiple ionic fragments produced in breakup reactions of small to medium sized molecules, such as F(3)SiCH(2)CH(2)Si(CH(3))(3). These breakup reactions are caused by soft x rays or intense laser fields. The ion spectrometer uses pulsed extraction fields, an electrostatic lens, and a delay line detector to resolve the position. Additionally, we describe a simple analytical method for calculating the momentum from the measured hit position and the time of flight of the ions.     

Absolute photoluminescence quantum efficiency measurement of light-emitting thin films

We developed an integrated monochromatic excitation light source integrating sphere based detection system to accurately characterize the absolute photoluminescence quantum efficiency of commonly used polymer light emitting films without using a reference sample. Our methodology is similar to the method reported by de Mello et al. [Adv. Mater. 9, 230 (1997)] In this Note, we show that the absolute photoluminescence quantum efficiency might only be measured when an appropriate calibration of the spectral variation of the measurement system is done. This calibration is especially important when employing a short excitation wavelength (<400 nm) for common silicon-based detector.     

单列光源反射式光幕靶检测弹着点

为了降低弹丸着靶点检测的成本,提出了一种新的弹着点检测原理。采用单列光源,经两面条形表面反射镜反射后,形成"Z"型的三道光幕,用于实现对弹丸等飞行目标的测速及定位。弹丸的速度和着靶点水平方向的坐标可以通过对时间的测量得到,弹丸着靶点竖直方向的坐标可以通过单列光探测器获知。文中对检测原理进行了研究,对光源、探测器、信号特征、有效测试区域、射频测试能力等进行了分析,并在桌面进行了原理性试验。高速摄影机拍摄的小球坐标与"Z"型结构测量出的坐标相对位置误差为0.1～1mm,传统区截靶法与"Z"型结构测量出的小球速度相对测速误差为0.02%～0.2%,说明基于反射镜的"Z"型结构在定位和测速方面的应用具有可行性,提出的方法具有结构简单、解算方便、节省成本的特点。     

Ion source with longitudinal ionization of a molecular beam by an electron beam in a magnetic field

A high-efficiency ion source for a mass-spectrometer’s detector of molecular beams and their scattering products is described. The ion source is designed according to a scheme of impact ionization of a beam particle by a longitudinal electron beam in a magnetic field with a strength of up to 130 mT. The design of the source developed is very flexible and has no limitations for use in any experiments with molecular beams. An ionization efficiency of particles of an atomic helium beam of 10^?3 ions/atom has been achieved. The useful signal-to-background ratio in the detector’s chamber is 3 × 10⁴ during detection of ions with mass-to-charge ratio m/q = 4 amu.     

Measurement of probe displacement to the thermal resolution limit in photonic force microscopy using a miniature quadrant photodetector

A photonic force microscope comprises of an optically trapped micro-probe and a position detection system to track the motion of the probe. Signal collection for motion detection is often carried out using the backscattered light off the probe-however, this mode has problems of low S/N due to the small backscattering cross sections of the micro-probes typically used. The position sensors often used in these cases are quadrant photodetectors. To ensure maximum sensitivity of such detectors, it would help if the detector size matched with the detection beam radius after the condenser lens (which for backscattered detection would be the trapping objective itself). To suit this condition, we have used a miniature displacement sensor whose dimensions makes it ideal to work with 1:1 images of micrometer-sized trapped probes in the backscattering detection mode. The detector is based on the quadrant photo-integrated chip in the optical pick-up head of a compact disc player. Using this detector, we measured absolute displacements of an optically trapped 1.1 μm probe with a resolution of ～10 nm for a bandwidth of 10 Hz at 95% significance without any sample or laser stabilization. We characterized our optical trap for different sized probes by measuring the power spectrum for each probe to 1% accuracy, and found that for 1.1 μm diameter probes, the noise in our position measurement matched the thermal resolution limit for averaging times up to 10 ms. We also achieved a linear response range of around 385 nm with cross talk between axes ?4% for 1.1 μm diameter probes. The detector has extremely high bandwidth (few MHz) and low optical power threshold-other factors that can lead to its widespread use in photonic force microscopy.     

分析超速离心机的多波长检测系统及其应用

分析超迷离心技术应用离心力场在对样品分级分离的同时借助光学系统检测离心池内大分子分布及相互作用。本文阐述用于分析超迷离心机的新型多波长检测器（MWL-AUC）,它以现代CCD uv-vis分光仪为基础,几乎可用所有波长的光线同时检测同一半径处沉降样品的分布,通过沉降平衡和沉降速度试验能够获得更多信息源并应用于生物科学和工业多聚物的研究。     

Photon detection efficiency of a germanium semiconductor spectrometer

A mathematical model of a detector has been constructed using the comparison of calculated and experimental values of the photon detection efficiency of a gamma-spectrometer based on a high-purity germanium detector. The method and program for calculating the correction for coincidences in low-activity measurements for radionuclides with complex decay schemes have been created. This study makes it possible to calculate the photon detection efficiency in the cases, where the working standards for the considered measurement conditions are absent, and to take the correction of the experimental data for the cascade summation into account.     

Qualification of a fluorescence spectrometer for measuring true fluorescence spectra

New analytical methods using fluorescence detection are becoming increasingly quantitative and require easy-to-use material standards for fluorometer qualification and method validation. NIST is responding to this need by developing and producing such standards. Reported here is the first step in this process, which is to qualify a research-grade fluorescence spectrometer for measuring true fluorescence spectra of reference material candidates. "True" spectra are defined here as those with fluorescence intensity, either relative or absolute as required, and wavelength both being reported with high accuracy and known precision, after wavelength has been calibrated and corrections for excitation intensity and detection system response have been applied. The uncertainties determined in relative and absolute intensity-corrected fluorescence spectra using both calibrated source (CS)- and calibrated detector (CD)-based methods were compared. The CS-based method gave uncertainties, typically about +/-5% for relative spectral correction, that were about half that of the CD-based method for determining both relative and absolute spectral correction factors. Absolute spectral correction factors can be determined using either method without knowing the optical geometry of the instrument. The absolute spectral correction factors were found to have much larger uncertainties than the corresponding relative correction factors with uncertainties for the CS-based method of +/-10% to +/-15% being typical and +/-20% or more not being uncommon, particularly for excitation and emission wavelengths below 400 nm. Uncertainties arising from detection system nonlinearity and instrument polarization ratios were also explored.     

基于CCD和CsI闪烁体的硬X射线成像

根据CCD的工作特点,采用曝光控制和多帧图像叠合技术,研制了基于CCD和CsI闪烁体的硬X射线成像探测器,以提高对硬X射线的探测效率。搭建了实验平台,以微加工技术制作的镍准直器为成像目标进行了实验验证。实验中,利用55Fe放射源对CCD进行直接成像;然后利用241 Am放射源同时对CCD和硬X射线成像探测器分别进行直接成像和间接成像。最后,对图像中出现的拖影、清晰度渐变和区域亮度不同等现象进行分析。分析结果表明:相比CCD本身,这种技术不仅拓展了探测器的可响应能区,而且提高了的量子效率,并且在241 Am放射源照射下,实现了对硬X射线的高分辨成像,其空间分辨优于50μm。该器件可作为位置灵敏探测器应用于未来空间天文观测。     

A BSE scintillation detector in the (S)TEM

A single crystal YAG: Ce³⁺ annular scintillator axially placed in a movable light guide forms the essential part of a new BSE detector. Comparison of properties of this detector with those of a semiconductor detector is made. The bandwidth, signal-to-noise ratio, capacitance effects, and relative efficiency are parameters which favour the scintillation detector. Its disadvantage is that it must be equipped with a photomultiplier and a light guide. The position of the scintillator above the specimen permits efficient detection at a large collection angle of BSE. For normal beam incidence, the signal homogeneity from any area of the scintillator ensures that images are obtained without shadow effects due to signal loss in the scintillator or due to detector geometry. The same probe current as for other detection modes can be used. Resolution of details is as high as for an SE image.     

Invited article: an improved double-toroidal spectrometer for gas phase (e,2e) studies

A new spectrometer is described for measuring the momentum distributions of scattered electrons arising from electron-atom and electron-molecule ionization experiments. It incorporates and builds on elements from a number of previous designs, namely, a source of polarized electrons and two high-efficiency electrostatic electron energy analyzers. The analyzers each comprise a seven-element retarding-electrostatic lens system, four toroidal-sector electrodes, and a fast position-and-time-sensitive two-dimensional delay-line detector. Results are presented for the electron-impact-induced ionization of helium and the elastic scattering of electrons from argon and helium which demonstrate that high levels of momentum resolution and data-collection efficiency are achieved. Problematic aspects regarding variations in collection efficiency over the accepted momentum phase space are addressed and a methodology for their correction presented. Principles behind the present design and previous designs for electrostatic analyzers based around electrodes of toroidal-sector geometry are discussed and a framework is provided for optimizing future devices.     

A photoelectron-photoion coincidence imaging apparatus for femtosecond time-resolved molecular dynamics with electron time-of-flight resolution of sigma=18 ps and energy resolution Delta E/E=3.5%

We report on the construction and performance of a novel photoelectron-photoion coincidence machine in our laboratory in Amsterdam to measure the full three-dimensional momentum distribution of correlated electrons and ions in femtosecond time-resolved molecular beam experiments. We implemented sets of open electron and ion lenses to time stretch and velocity map the charged particles. Time switched voltages are operated on the particle lenses to enable optimal electric field strengths for velocity map focusing conditions of electrons and ions separately. The position and time sensitive detectors employ microchannel plates (MCPs) in front of delay line detectors. A special effort was made to obtain the time-of-flight (TOF) of the electrons at high temporal resolution using small pore (5 microm) MCPs and implementing fast timing electronics. We measured the TOF distribution of the electrons under our typical coincidence field strengths with a temporal resolution down to sigma=18 ps. We observed that our electron coincidence detector has a timing resolution better than sigma=16 ps, which is mainly determined by the residual transit time spread of the MCPs. The typical electron energy resolution appears to be nearly laser bandwidth limited with a relative resolution of DeltaE(FWHM)/E=3.5% for electrons with kinetic energy near 2 eV. The mass resolution of the ion detector for ions measured in coincidence with electrons is about Deltam(FWHM)/m=14150. The velocity map focusing of our extended source volume of particles, due to the overlap of the molecular beam with the laser beams, results in a parent ion spot on our detector focused down to sigma=115 microm.     

光电子成像电子能谱仪新一代DLD(延迟线检测器)系统

介绍新型X射线激发光电子成像电子能谱仪配置新一代DLD光电子检测系统优点、结构和在能谱和成像应用方面特点。     

Quantitative characterization of crosstalk effects for friction force microscopy with scan-by-probe SPMs

If the photodetector and cantilever of an atomic force microscope (AFM) are not properly adjusted, crosstalk effects will appear. These effects disturb measurements of the absolute vertical and horizontal cantilever deflections, which are involved in friction force microscopy (FFM). A straightforward procedure is proposed to study quantitatively crosstalk effects observed in scan-by-probe SPMs. The advantage of this simple, fast, and accurate procedure is that no hardware change or upgrade is needed. The results indicate that crosstalk effects depend not only on the alignment of the detector but also on the cantilever properties, position, and detection conditions. The measurements may provide information on the origin of the crosstalk effect. After determination of its magnitude, simple correction formulas can be applied to correct the crosstalk effects and then the single-load wedge method, using a commercially available grating, can be employed for accurate calibration of the lateral force.     

A reversible time-of-flight detector for use in pseudocontinuous resonance enhanced multiphoton (pc-REMPI) detection

A time-of-flight coincidence detector is demonstrated. This detector is optimized for use in a pseudocontinuous resonance enhanced multiphoton ionization scheme that requires photoelectrons and photoions to be detected in coincidence. The detector utilizes two simultaneously operating charged particle detectors, one for the detection of electrons and the other for the detection of ions. In order to allow for field reversal, the detectors are physically identical, differing only by the value of applied voltages. Particular attention is given to the implementation of a charge-to-voltage transducer that allows for subnanosecond detection of both electrons and ions.     

Efficiency of detection of Cs<Superscript>+</Superscript> and Cl<Superscript>−</Superscript> ions with a ВЭУ-7-2 microchannel electron multiplier

The absolute values of the efficiency of detection of Cs⁺ and Cl^- ions with energies of 1600 eV have been measured with a ВЭУ-7-2 microchannel electron multiplier. The relative detection efficiencies as functions of the potential of the input surface of the microchannel plate have been assessed. It has been revealed that the absolute values of the efficiency of detection of Cl^- and Cs⁺ ions differ significantly and amount to 36 and 6%, respectively, at input ion currents of ≤2 × 10^?14 A.     

Measurement of Mobility of Radioactive Air Ions in Atmosphere

A method for measuring the mobility of radon daughter products, ²¹⁸Po, in gas medium is described. The mobility of the daughter products was measured using the flow-through technique of air ion detection. The flow-through technique is based on precipitation of ions from Rn-containing air flow on the surface of a semiconductor detector. Precipitation occurs in an electrostatic field of a plane capacitor. Upon precipitation, alpha radiation of ²¹⁸Po is detected. The dependence of ion mobility on the absolute humidity of air was determined (the age of ions was about 1 s). It was shown that, within a range of humidity from 3.4 to 13.6 g/m³, this dependence is negligible. The mean mobility of ²¹⁸Po was found to be 1.05 ± 0.05 cm²/(sV).     

非对称三角形电极离子阱的单向出射性能模拟研究

三角形电极离子阱（triangular-electrode linear ion trap, TeLIT）是一种新型结构的线性离子阱,具有简单的电极结构和良好的分析性能。为进一步提高TeLIT的离子探测效率,本实验将离子出射方向的2个电极设置为不同角度,建立非对称结构的TeLIT,通过引入非对称场实现离子单向出射。通过分析电极角度差与其内部电场分布的关系,并模拟离子运动轨迹,获得离子出射情况和模拟质谱峰。理论模拟结果显示：当离子出射方向三角电极的角度差Δα=15°时,在优化的AC频率条件下,三角形电极离子阱的m/z 610离子单向出射率可达95%以上,且质量分辨率达到2647。经优化几何参数后的非对称三角形电极离子阱可在几乎不损失分辨率的情况下实现离子单向出射,大幅提高了单检测器模式下TeLIT的离子探测效率和仪器的灵敏度,使其在小型化质谱仪的开发中具有显著优势。     

Development of advanced x-ray imaging crystal spectrometer utilizing a large area segmented proportional counter for KSTAR

An advanced x-ray imaging crystal spectrometer (XICS) for KSTAR tokamak has been developed by utilizing a segmented two dimensional (2D) position-sensitive multiwire proportional counter. The XICS for the KSTAR tokamak provides time-resolved measurements of the radial ion and electron temperature profiles, toroidal plasma rotation velocity, and ionization equilibrium. The segmented 2D detector with delay-line readout and supporting electronics has been adopted to improve the photon count rate capability. The current fabrication status of the XICS for the KSTAR tokamak and the first performance test results of the prototype segmented 2D detector are presented.     

An improved single crystal adsorption calorimeter for determining gas adsorption and reaction energies on complex model catalysts

A new ultrahigh vacuum microcalorimeter for measuring heats of adsorption and adsorption-induced surface reactions on complex single crystal-based model surfaces is described. It has been specifically designed to study the interaction of gaseous molecules with well-defined model catalysts consisting of metal nanoparticles supported on single crystal surfaces or epitaxial thin oxide films grown on single crystals. The detection principle is based on the previously described measurement of the temperature rise upon adsorption of gaseous molecules by use of a pyroelectric polymer ribbon, which is brought into mechanical∕thermal contact with the back side of the thin single crystal. The instrument includes (i) a preparation chamber providing the required equipment to prepare supported model catalysts involving well-defined nanoparticles on clean single crystal surfaces and to characterize them using surface analysis techniques and in situ reflectivity measurements and (ii) the adsorption∕reaction chamber containing a molecular beam, a pyroelectric heat detector, and calibration tools for determining the absolute reactant fluxes and adsorption heats. The molecular beam is produced by a differentially pumped source based on a multichannel array capable of providing variable fluxes of both high and low vapor pressure gaseous molecules in the range of 0.005-1.5 × 10(15) molecules?cm(-2)?s(-1) and is modulated by means of the computer-controlled chopper with the shortest pulse length of 150 ms. The calorimetric measurements of adsorption and reaction heats can be performed in a broad temperature range from 100 to 300 K. A novel vibrational isolation method for the pyroelectric detector is introduced for the reduction of acoustic noise. The detector shows a pulse-to-pulse standard deviation ≤15 nJ when heat pulses in the range of 190-3600 nJ are applied to the sample surface with a chopped laser. Particularly for CO adsorption on Pt(111), the energy input of 15 nJ (or 120 nJ?cm(-2)) corresponds to the detection limit for adsorption of less than 1.5 × 10(12) CO molecules?cm(-2) or less than 0.1% of the monolayer coverage (with respect to the 1.5 × 10(15) surface Pt atoms?cm(-2)). The absolute accuracy in energy is within ～7%-9%. As a test of the new calorimeter, the adsorption heats of CO on Pt(111) at different temperatures were measured and compared to previously obtained calorimetric data at 300 K.