摘要:

A very compact, vacuum compatible charge coupled device (CCD) camera has been developed for vacuum ultraviolet and soft x-ray imaging spectroscopy. It can house any CCD frame format and two of them have been selected:385×576pixels, suitable for normal incidence spectroscopy (300–2500 Å), and256×1024pixels, for grazing incidence applications (5–300 Å). Owing to its small and lightweight package, it can be placed at the focus of vacuum spectrometers. A new concept cooling system is based on a three stage thermoelectric cooler in thermal connection with the CCD through a 30-cm-long flexible conductor, allowing the detector to have stress-free movements along the focal plane and a constant temperature. The camera head has been designed to achieve a high cooling efficiency, thus the CCD can be operated at−40 °C.This detector is well suited for applications that require high sensitivity and signal to noise ratio, wide dynamic range, good spatial and spectral resolutions. In addition, it overcomes the limits of fixed detectors and lets the optical performances of the spectrometer remain unchanged. The CCD camera has been tested during an experiment of laser produced plasma spectroscopy and some preliminary results are reported. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148818

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The extension of a continuous scan high spectral resolution(0.006 cm−1)Fourier transform spectrometer for time-resolved Fourier transform spectroscopy with a temporal resolution in the ns regime is described. The time resolution is achieved by synchronizing a laser/transient digitizer system with the interferometer. The realization of the data acquisition and the experimental setup are described. Examples of time-resolved measurements are given. Detector limited temporal resolution of<10 nsis shown by recording scattered light from a pulsed dye laser. Spectral resolution of<0.5 cm−1is demonstrated by observing the fluorescence of electronically excited CH radicals produced in the multi photon dissociation ofCHBr3.The signal-to-noise behavior of time-resolved Fourier transform apparatus is investigated as a function of spectral (0.1–4.0 cm−1unapodized) and time resolution and of the intensity of the detected light. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148819

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present a simple scanning mirror mechanism for a Fourier transform spectrometer, consisting of a voice coil actuator, a ball-bearing slide, and a single cube corner mirror or retroreflector. The use of a single cube corner reduces significantly the sensitivity of the Fourier transform spectrometer to the tilt of its moving mirror, enabling the simple mechanism. With simple velocity feedback using a linear velocity transducer, we achieve a scan speed stability of 2&percent;–5&percent; (root-mean-square) for scan speeds from 40 to 440 &mgr;m/s for a travel of 2.2 cm, corresponding to a spectral resolution of0.06 cm−1.Fringe amplitude stability is about 5&percent;. This scan mechanism was operated at standard temperature and pressure, but the relatively minute amount of lubricant in the ball-bearing slide may indicate possible operation under vacuum and/or cryogenic conditions. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148820

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A low background and almost hydrocarbon free(∼1×10−14 Torr)molecular beam apparatus with an improved universal detector, based on electron bombardment ionization, has been constructed for crossed molecular beam research. Extremely high vacuum(∼1×10−12 Torr)for the detector’s ionization region is achieved using multiple ultrahigh vacuum pumps. In addition to a home-made liquid nitrogen cryopump and a turbomolecular pump, a two stage cryogenic He cold head (∼10 K) is used to pump the detector’s ionization region. Using this arrangement, theH2background in the detector can be reduced by about two orders of magnitude in comparison with previously built similar instruments. Therefore, the signal-to-noise for detectingH2product detection sensitivity is substantially enhanced, making experimental studies ofH2elimination channels in photodissociation processes much easier. Backgrounds atm/e=28(CO+),16(CH4+,O+),15(CH3+),14(CH2+),and 13(CH+)in the ionization detection region are also significantly reduced. In this article, we will describe the new apparatus in detail and present some preliminary results of the unimolecular decomposition studies ofCH3OHat 157 nm excitation to demonstrate the capabilities of low background detectionH2using this new instrument. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148821

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A method for time-of-flight analysis of neutral cluster beams is presented. It is based on the use of a channeltron as a fast flux-sensitive detector of high-speed neutral particles in a beam. The impact of neutral clusters on the channeltron surface causes the emission of charged particles, which can be detected by the channeltron itself. We show that a channeltron can be used for the characterization of velocity distributions in analogy with fast ion gauges but without requiring any ionization device. This method has also the advantage of being selectively sensitive to the cluster component of seeded supersonic beams. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148869

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A tandem mass spectrometer consisting of a double-focusing magnetic-sector mass analyzer in series with a time-of-flight (TOF) mass analyzer has been designed and constructed. The TOF analyzer was a quadratic-field ion mirror. The method of ionization used was matrix-assisted laser desorption/ionization. Precursor ions were mass selected with the magnetic-sector analyzer, and time focused by ion bunching prior to fragmentation in a collision cell. The fragment ions were mass analyzed with the TOF analyzer, which possessed the property that residence times (i.e., times of flight) in the mirror were independent of ion velocity. The theoretical background to the instrumental design is presented. Experimental results are presented, showing resolutions of 4000 in fragment ion spectra and demonstrating effective high-energy collision-induced decomposition of peptide molecule ions. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148822

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A dual mass gate is described which allows for high resolution separation of ions under realistic laser desorption/ionization and matrix assisted laser desorption/ionization time of flight mass spectrometry conditions at 10 kV kinetic energy. The device consists of two interleaved comb units sequentially positioned in the ion beam path. This allows significant improvement in resolution relative to one unit by separation of “low pass” and “high pass” functions. Principal limits as given by mechanical dimensions of the device and electrical properties of the switches are also discussed. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148823

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A novel ion-counting method for significantly improving the spatial resolution and detection sensitivity of two-dimensional product imaging in molecular beam experiments is presented. The method makes use of real-time digital image processing to retrieve, threshold, and determine the local maximum of each ion hitting a microchannel plate assembly. The current version can process data at rates up to 3.07 Mbyte/s, and methods for accelerating this rate are proposed. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148824

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A new toroidal electrostatic analyzer (ESA) configuration for medium energy ion scattering has been designed and fabricated for structural analysis of surfaces. The present analyzer has a wide interelectrode distance of 16 mm and an energy range of 10&percent; of the pass energy at a constant applied voltage. The analyzer is mounted horizontally on a turntable and accepts ions scattered within a well defined angular range. To get a good energy resolution, we employed a photon-counting image acquisition system (PIAS: Hamamatsu Photonics) with spatial resolution of 40–50 &mgr;m, combined with a three-stage microchannel plate. The electric fields of the toroidal ESA including the fringing fields were calculated by a finite element method. Ion trajectories through the analyzer were calculated using a Monte Carlo method. In this way, the optimum conditions of the geometry and size of the entrance and exit slits were determined. Our toroidal analyzer resolved three surface peaks from the Si isotopes (28Si,29Si,and30Si) clearly in the aligned spectra from H-terminated Si(001) and Si(111) and the energy resolution(&Dgr;E/E)was estimated to be about1×10−3.We describe the notable features of the new setup of the toroidal analyzer and show direct detection of H on Si(001) and Si(111) as a typical application. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148825

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An ultrahigh vacuum spectrometer system has been designed and constructed for obtaining spatial- and time-resolved, element-specific images of atoms that are scattered and recoiled from surfaces. A pulsed noble gas ion beam in the 1–5 keV range is used to scatter and recoil atoms from a surface. A large, position-sensitive microchannel plate detector with resistive anode encoder, that is sensitive both to ions and fast neutrals records the spatial distribution patterns of the emitted atoms. The use of time-of-flight methods allows capture of these patterns in time windows as short as 10 ns. The sensitivity of these patterns to the details of surface structure provides the basis for a scattering and recoiling imaging spectrometry (SARIS). The primary ion beam current is∼0.1 nA/cm2,supplied in 20 ns pulses at a rate of 30 kHz, resulting in∼5×102 ions/pulse;images with adequate statistics can be obtained in several seconds with a total ion dose of<1010 ions/cm2.The SARIS technique can provide unique, element-specific, real-space, surface structural information at a resolution of<0.1 Åon a time scale of seconds for analysis of surface composition, structure, and dynamics. Examples provided for demonstrating the capabilities of the system are 4 keVHe+andAr+scattering and recoiling from Pt{111} and 4 keVKr+scattering and recoiling from CdS{0001}. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148826

出版商:AIP    

年代:1998

数据来源: AIP