A concept of a scanning positron microscope

The concept of a scanning positron microscope which is under construction in München and Trento will be shown. A beam with a variable energy from 1 to 30 keV and a spot diameter of 1 m, which can be scanned over an area of (0.6×0.6) mm², is formed after a double stage stochastic cooling of the positrons emitted from a radioactive source. Additionally, the beam will be pulsed to have a well-defined time base for positron lifetime measurements. The design of the microscope is dominated by special demands of positron physics. Therefore, the microscope contains electron optical elements which are well known but rarely used. These are the through the lens reflection remoderator and the optical column with a magnetic side gap lens as probe forming lens.     

Analysis of solids with a secondary-neutral microprobe based on electron-gas post-ionization

The detection sensitivity and the lateral resolution in electron-gas SNMS have been improved in a newly developed secondary-neutral microprobe. This instrument combines the high post-ionization efficiency provided by the electron component of an rf-plasma (post-ionization probability alpha(0) of some 10(-2)) with a high-transmission magnetic mass spectrometer. Using the plasma as an effective primary ion source, secondary-neutral intensities of up to 10(9) cps can be realized for 1 keV Ar(+) ion bombardment and a primary current density of 1 mA/cm(2). To obtain laterally resolved secondary-neutral micrographs, a 20 keV-Ga(+)-ion beam produced in a liquid-metal ion source (LMIS) is utilized for sputter excitation. At Ga(+)-ion-beam currents of about 6 nA a spot size on the target of 1 microm is possible. The detection sensitivity in this operation mode is on the order of 相似文献   

High-resolution, low-voltage SEM for true surface imaging and analysis

A novel design concept for the electron optical column has been implemented in the realization of a new ultra-high performance SEM. A compound magnetic/ electrostatic objective lens is at the heart of the high-performance column: the imaging aberrations of this new lens type decrease with decreasing beam energy. Any beam cross-over between the electron source (Schottky FE-gun) and the sample has been eliminated in order to avoid broadening of the beam energy spread (Boersch effect). A high beam energy is maintained throughout the column regardless of the electron probe energy selected by the operator. This protects the beam against the effect of stray fields and minimizes any loss of beam brigthness due to stochastic electron-electron interactions. The new SEM achieves outstanding resolution, particularly at the low beam energies (3 nm achievable at E_PE = 1 keV). The secondary electrons emitted by the sample are detected with very high efficiency by an internal annular detector situated above the final lens. Due to the low imaging aberration level, a high current can easily be focused in a very small probe, thus making the new SEM ideally suited for high-resolution, quantitative X-ray analysis.     

Automatic F positron source supply system for a monoenergetic positron beam

A system which supplies an intense ¹⁸F (half life 110 min) positron source produced by an AVF cyclotron through ¹⁸O(p,n)¹⁸F reaction has been constructed. Produced ¹⁸F is transferred to a low background experiment hall through a capillary. It is electro-deposited on a graphite rod and used for a source of a slow positron beam. In the meantime the next batch of target ¹⁸O water is loaded and proton irradiation proceeds. This system makes it possible to perform continuous positron beam experiments using the ¹⁸F positron source.     

A wide-angle secondary ion probe for organic ion imaging

A secondary ion source has been developed for an organic ion microprobe capable of imaging samples up to 2 em in diameter. The source uses a focused 5 keY Cs⁺ ion beam which is rastered across the sample surface, and secondary ions from each point on the sample are collected and formed into a low energy beam to be analyzed by a quadrupole mass filter. Dynamic emittance matching is employed to deflect ions from off-axis points on the sample back onto the mass analyzer axis. Rastering and dynamic emittance matching are rapidly controlled by assembly language programs using an IBM/AT (80286) type computer. A low energy ion monitor was used to tune and evaluate the secondary ion source by providing a magnified cross-sectional image of the ion beam at the source exit aperture. A well-focused and centered secondary ion beam was obtained from each point on the sample, indicating that large-scale dynamic emittance matching with high collection efficiency is possible. Mass resolved images of grids and glycerol samples are shown to demonstrate the performance of the integrated secondary ion source mass analyzer and control system.     

Effect of silver nano particles on the fluorescence quantum yield of Rhodamine 6G determined using dual beam thermal lens method

Nano structured noble metals have very important applications in diverse fields as photovoltaics, catalysis, electronic and magnetic devices, etc. Here, we report the application of dual beam thermal lens technique for the determination of the effect of silver sol on the absolute fluorescence quantum yield (FQY) of the laser dye rhodamine 6G. A 532 nm radiation from a diode pumped solid state laser was used as the excitation source. It has been observed that the presence of silver sol decreases the fluorescence quantum efficiency. This is expected to have a very important consequence in enhancing Raman scattering which is an important spectrochemical tool that provides information on molecular structures. We have also observed that the presence of silver sol can enhance the thermal lens signal which makes the detection of the signal easier at any concentration.     

A supersonic beam ion cyclotron resonance instrument for the study of van der Waals cluster ions

For the study of ionized van der Waals cluster ions an instrument is presented, which consists of a supersonic beam cluster source coupled to an ICR spectrometer with external ion source. The neutral van der Waals clusters are generated by supersonic expansion and ionized by electron impact in the external source. The cluster ions are extracted at right angle to the neutral cluster beam and fly collision-free parallel to the magnetic field direction into the differentially pumped ICR cell. For the ion transfer, an improved lens system is presented. The cluster ion transfer lens system is capable of focusing ions with energies of a few eV perpendicular to the magnetic field direction through the differential pumping orifice. The ions are injected into the ICR cell with a trap barrier pulse, ion accumulation is possible. With this system the first ICR spectra of small cluster ions of carbon dioxide are obtained.     

The design of a spin-polarized slow positron beam

Spin-polarized low-energy positrons were considered as useful probes for studying electron spin states of both surface and bulk materials. Due to the spin-dependent interactions between electrons and positrons, the formation of positronium (Ps), an electron-positron bound system, can be distinguished from different electron spin states. Recently, a positron source of ¹⁸F has been developed for a spin polarized slow positron beam at the institute of physical and chemical research (RIKEN). The design of an electrostatic positron beam will be discussed in conjunction with a spin rotator.     

A secondary ion microprobe ion trap mass spectrometer

An ion trap mass analyzer has been attached to an organic secondary ion microprobe. A pressure differential >100 can be maintained between the ion trap and microprobe. The well-focused secondary ion beam can transit a small (2 mm) diameter tube, but gas flow from ion trap to microprobe is impeded. This pressure differential allows the microprobe to retain imaging capability. Ion trap and microprobe data systems are integrated by taking advantage of the highly reproducible periodicity of the ion trap operating in resonant ejection mode and asynchronous signal and data acquisition afforded by commercially available interface cards. Secondary ion mass spectra and images obtained indicate an approximately 10-fold improvement in sensitivity, although preliminary evidence indicates low (<1%) trapping efficiency. Image data acquisition using the ion trap for mass analysis requires at least 10 times as much time compared to using a quadrupole mass filter because the mass-selected instability mode is used for mass analysis, i.e., mass resolution in the ion trap is not continuous as it is in the quadrupole.     

Analysis of solids with a secondary-neutral microprobe based on electron-gas post-ionization

The detection sensitivity and the lateral resolution in electron-gas SNMS have been improved in a newly developed secondary-neutral microprobe. This instrument combines the high post-ionization efficiency provided by the electron component of an rf-plasma (post-ionization probability ⁰ of some 10^–2) with a high-transmission magnetic mass spectrometer. Using the plasma as an effective primary ion source, secondary-neutral intensities of up to 10⁹ cps can be realized for 1 keV Ar⁺ ion bombardment and a primary current density of 1 mA/cm². To obtain laterally resolved secondary-neutral micrographs, a 20 keV-Ga⁺-ion beam produced in a liquid-metal ion source (LMIS) is utilized for sputter excitation. At Ga⁺-ion-beam currents of about 6 nA a spot size on the target of 1 m is possible. The detection sensitivity in this operation mode is on the order of 10^–2. Mass spectra and laterally resolved images recorded with this microprobe instrument highlight its capacity as a surface analytical tool.     

Development of positron annihilation spectroscopy to test accelerated weathering of protective polymer coatings

A variable mono-energetic positron beam with a computer-controlled system has recently been constructed at the University of Missouri–Kansas City for weathering studies of polymeric coatings. The beam is designed to measure the S-parameter from Doppler-broadening energy spectra and the sub-nanometer defect properties from positron annihilation lifetimes (PAL). Significant variations of S-parameter and ortho-positronium intensity in coatings, as obtained from the newly built beam and from the Electrotechnical Laboratory’s beam, respectively, are observed as a function of depth and exposure time due to the Xe-light irradiation. A high sensitivity of positron annihilation signal response to the early stage of degradation is observed. Development of positron annihilation spectroscopy to test accelerated weathering of polymeric coatings is discussed.     

基于自由曲面的LED准直透镜设计

本文基于准直光束照明的自由曲面透镜设计方法,设计了一种以单颗LED为光源的准直透镜,其可应用于投影仪的照明系统。根据几何光学原理构造自由曲面,该方法无需求解复杂的偏微分方程,计算简单。准直透镜由内自由曲面折射面、球面、抛物面全反射曲面以及平面组成,利用Matlab编程求出自由曲面轮廓曲线的离散数据点,导入Solidworks中进行曲线拟合,建立透镜的实体模型。为探讨LED光源尺寸对准直透镜光斑影像的影响,在Tracepro中对透镜进行非序列光线追迹,模拟结果表明:当光源半径不大于1 mm时,其光学效率达到86.26%以上,视场半角达到3.3度以内。     

Positronium formation in NaY-zeolites studied by lifetime, positron beam Doppler broadening and 3-gamma detection techniques

Results of positron annihilation measurements on NaY pressed powders and deposited thin films using slow positron beam and conventional fast positron techniques are presented. In lifetime experiments using an external ²²Na source an averaged long lifetime of 1.8 ns with a sum intensity of 27% was observed in pressed powders in the presence of air at room temperature (RT). In literature this lifetime is ascribed to positrons annihilating in water filled or β cages Habrowska, A.M., Popiel, E.S., 1987. Positron annihilation in zeolite 13X. J. Appl. Phys. 62, 2419. By means of isotopic exchange some of the Na was replaced by ²²Na. These powders showed a long lifetime component of 7–8 ns with an intensity increasing from 1 to 12% when heated under normal atmosphere from RT to 200°C. No significant increase of the shorter (1.5 ns) lifetime was observed, while its intensity dropped from 13.4 to 6.6%. Both effects are ascribed to the loss of water from cages only. The beam experiments revealed a high fraction of 3-gamma annihilations in the pressed powder and thin film samples, indicating the annihilation of o-Ps and thereby the existence of large open volumes.     

Long-term lens organ culture system with a method for monitoring lens optical quality

The Scan Tox System is a method for monitoring lens optical quality (focus or lack of focus) in culture conditions, which mimic conditions inside the eye. The ocular lens is an ideal organ for long-term culture experiments because it has no direct blood supply and no connection to the nervous system. The Scan Tox System makes it possible to keep lenses for long-term studies of up to a few weeks. The use of cultured lenses, mainly bovine, replaces the need for testing the effects of potentially damaging agents on live animals. This optical monitoring apparatus uses a computer-operated scanning laser beam, a video-camera system and a video frame analyzer to record the focal length and transmittance of the cultured lens. The scanner is designed to measure the focal length at points across the diameter of the lens. The lens container permits the lens to be exposed to a vertical laser beam from below. The laser source projects its light onto a plain mirror, which is mounted at 45 degrees C on a carriage assembly. The mirror reflects the laser beam directly up through the test lens. The mirror carriage is connected to a positioning motor, which moves the laser beam across the lens. The camera sees the cross section of the beams and, by examining the image at each position of the mirror, Scan Tox software is able to measure the quality of the lens by calculating the back vertex distance for each beam position. The cultured lenses continue to maintain their original refractive function. When foreign substances are introduced to a cultured lens, the Scan Tox System measures the resulting optical response. This provides a very sensitive means to follow early damage to the eye lens. Because the lens is maintained in an intact state in solutions that are similar to those inside the eye, the lens retains its normal recuperative powers. So in addition to measuring early damage, this system allows measurement of recovery from damage.     

Raman microprobe spectrometer installed in a super-conducting magnet.

A Raman microprobe spectrometer that could be installed in the bore of a cryogen free super-conducting magnet (10 T) was designed and constructed for the investigation of the external magnetic field effect on the Raman spectra of molecular aggregates in solutions and at interfaces. The performance of the present instrument was demonstrated by measuring the magnetic field effect (0 - 10 T) on the resonance Raman spectra of diprotonated meso-tetra-(sulfonatophenyl)porphine aggregates in an acidic solution. The Raman shifts of the aggregates were not significantly influenced even in 10 T. However, the relative intensity of 1123 cm(-1) peak (nu(C(a)-N)) was interestingly enhanced about 20% under the magnetic fields higher than 2.5 T.     

Enhancement of ion transmission at low collision energies via modifications to the interface region of a spectrometer

The transmission efficiency of precursor and product ions decreases significantly at lower collision energies in a four-sector tandem mass spectrometer. In an effort to improve the overall ion transmission in this energy regime three modifications were made in the interface region between the two stages of mass analysis. An einzel lens was inserted prior to the deceleration lens of the collision cell block to reduce the precursor ion beam diameter. The collision cel1 block was reduced in thickness while maintaining the collision path length, thus increasing the number of ions which entered and exited the gas chamber, while removing any stray electrical fields. Finally, a second active focusing element was incorporated after the collision cell block to enhance the collection efficiency of the product ions. A tandem mass spectrum of angiotensin I obtained with this interface, at a collision cell block potential of 9200 volts, exhibited classical high energy collision-induced dissociation (CID) fragmentation patterns, a precursor ion transmission of 92% and an overall CID efficiency of approximately 7.5%. These improvements have resulted in a dramatically higher overall ion transmission at high collision cell potentials as well as sufficient sensitivity in acquiring good quality CID spectra in the lower collision energy regime (i.e., 60 eV). (460-469)     

Mass‐selective axial ejection from a linear ion trap with a direct current extraction field

We have developed a new mass‐selective axial ejection method from a linear ion trap (LIT). In this method, a set consisting of a trap wire lens and an extraction wire lens positioned orthogonally to each other was placed between quadrupole rods. The trap wire lens confines the ions inside the trap, and the extraction wire axially extracts ions from the trap. Ions introduced into the LIT are trapped between the inlet lens and the trap wire lens. In addition to the wire lenses, a set of excitation lenses, which are aligned orthogonally to the trap wire lens, are inserted between rods. The ions are resonantly excited in the direction perpendicular to the trap wire lens by applying a supplemental alternating current (AC) to the excitation lenses. Excited ions with a large motion pass over the trap wire lens, while unexcited ions remain trapped inside. Ions that have passed over the trap wire lens are then extracted by the extraction wire lens. The characteristics of the mass‐selective ejection with a direct current (DC) extraction field were investigated by both simulation and experiment. A mass resolving power of m/Δm = 1300 was achieved at a scan rate of 500 Th/s. The dependence of the ejection efficiency on trap wire lens bias was measured, and an ejection efficiency of 20% at a scan rate of 500 Th/s was achieved by optimizing the DC bias on the trap wire lens. Copyright © 2009 John Wiley & Sons, Ltd.     

A wavelength dispersive X–ray spectrometer for small area X–ray fluorescence spectroscopy at SPring–8 BL39XU

A wavelength dispersive X–ray spectrometer is designed and developed for X–ray fluorescence analysis and spectroscopy using an X–ray microprobe at SPring–8 BL39XU. The spectrometer uses a flat analyzer crystal, and X–rays from a small beam spot are dispersed by the crystal onto a position sensitive proportional counter. The energy resolution of the spectrometer is determined by the spatial resolution of the position sensitive proportional counter, and the additional use of the slit–scan can improve the energy resolution if necessary. Performance of the spectrometer is evaluated by using a conventional X–ray source, and preliminary experimental results of the X–ray microprobe by using brilliant hard X–rays from an X–ray undulator are reported.     

A novel imaging-enhancement-based inspection method for transparent aesthetic defects in a polymeric polarizer

The transparent aesthetic defects of polymeric polarizers are difficult to image and characterize using conventional illumination. To inspect such special defects, an automated inspection method was studied that employs the structured lighting technique to markedly enhance defect imaging. The defect was modelled as a microscale plano-convex lens, which has a slight difference in refractive index within its normal region. The imaging enhancement mechanism of the defect was simulated with a model in which the binary stripe patterns of the structured-light source are equivalent to a one-dimensional diaphragm. The experimental results were in agreement with the simulation, suggesting that the model and mechanism are feasible. A novel spatial texture filtering algorithm with higher speed and higher accuracy is proposed to process the structured light images. Approximately 200 samples with defects were successfully imaged, processed and characterized. This inspection method was verified by the final experimental results and has potential for real-time and in situ testing of defects in other polymer films and products.     

Thermal lens spectrophotometry of nitrogen dioxide using an excimer-laser-pumped dye laser

A thermal lens spectrophotometer based on a pulsed dye laser pumped by an excimer laser was constructed. A thermal lens spectrum was measured for nitrogen dioxide by scanning the dye laser wavelength, which was well correlated with an absorption spectrum. A linear calibration graph was obtained in the nl 1^?1 range, the detection limit being 4 nl 1^?1, which is similar to the best value achieved by other laser spectrometric methods. The enhancement factor achieved was 16, which is much smaller than the theoretical value of 292 calculated by assuming an exciting laser with a single transverse mode (beam waist radius 0.12 mm). However, the observed enhancement factor agrees fairly well with the theoretical value of 17 calculated from the observed beam radius (0.5 mm) at the waist. Hence the observed small enhancement factor is ascribed to poor beam quality of the dye laser used. Pulsed thermal lens spectrophotometry is shown to be useful especially for the analysis of gaseous samples at elevated temperatures.