摘要:

The advantages of the cross‐correlation time of flight (TOF) method when applied to surface scattering experiments under ultrahigh vacuum conditions are demonstrated in comparison with the conventional TOF method. The principle of the cross‐correlation TOF technique including the deconvolution procedure and statistical accuracy given by this method is discussed. The main parts of the spectrometer: chopper blade, magnetic rotor suspension and drive, and data acquisition system are described followed by the test of the TOF spectrometer, and by an illustration of the efficiency of this technique by means of TOF distributions measured for hydrogen molecules desorbing from metal surfaces.

ISSN:0034-6748    

DOI:10.1063/1.1136697

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A source of polarized He (23S) metastable atoms is described that provides a thermal energy beam with a flux of the order of ∼1014metastables s−1steradian−1at a polarizationPz∼50%. The polarization of the beam can be simply reversed, or modulated, without changing the beam trajectory or flux. The beam contains no significant admixtures of He(21S) atoms, photons, or fast neutrals and is suitable for use in a wide variety of collision and surface physics experiments.

ISSN:0034-6748    

DOI:10.1063/1.1136698

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The construction of a multipass device for laser‐molecular beam spectroscopy is described. The device increases signal to noise ratios by a factor of 10 does not contribute to the width of the signal, and in addition provides an indication of the orthogonality of laser and molecular beams.

ISSN:0034-6748    

DOI:10.1063/1.1136699

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A new analytical instrument has been developed to give real‐time chemical composition and size data on individual aerosol particles. It separates the particles from the entraining gases by means of aerodynamic nozzles and differential pumping, so that they enter the high vacuum region as a collimated beam. Each arriving particle is flash vaporized, the vapor ionized, and the ions analyzed by a quadrupole mass spectrometer. The instrument has been tested with several inorganic and organic aerosols and has yielded mass spectral peaks corresponding to a series of fragment ions. The more stable compounds yielded the parent ion as well. Particles 0.9 &mgr;m in diameter are readily detected with signal‐to‐noise ratios of 12:1 on the dominant peak. On this basis, the small‐size sensitivity limit is well under 0.5 &mgr;m diameter and, with design improvements, can probably be extended to 0.1 &mgr;m or smaller.

ISSN:0034-6748    

DOI:10.1063/1.1136700

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Detectability and mass resolution of a newly built high mass resolution time‐of‐flight atom probe were examined. In order to maximize the detectability, the specimen tip apex, the probe hole, and the entering side of the energy‐compensating deflector were aligned by a laser beam. Transmittance of ions through the deflector and mass resolution were optimized varying the combinations of deflector electrode voltages. The detectability, defined as the ratio of the number of all atoms in the area aimed by the probe hole to the number of field evaporated ions arriving at the detector, was found to be dependent on the crystallographic plane and its aimed area, possibly due to the rolling motion of the field evaporating atoms in a certain preferable direction. The observed detectability ranges from only 10% at the central area of the W (011) plane, which is dark in a multiatom‐layer desorption image, to 91% at the (011) plane side of the W(114) plane, which is significantly higher than the maximum detectability limited by the effective area of a chevron detector, 55%. Thus, the overall detectability might be as high as 50% and the transmittance would be nearly 100%. The mass resolution &Dgr;m/mwas 1/1100 at half peak height which was comparable to the theoretically expected mass resolution limited by the pulse width and the time resolution of the timer, 5 ns, and each of the detected W ions was clearly discriminated corresponding to each W isotope. The atom probe also successfully demonstrated its unique capability of the atomic layer‐by‐layer mass analysis providing the ultimately fine depth profile.

ISSN:0034-6748    

DOI:10.1063/1.1136701

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

High speed circuitry for measurement of particle flight times over the range from 15 ns to <1 &mgr;s with event rates as high as 105 s−1was developed for use in a time‐of‐flight field‐ionization mass spectrometer for neutral particles. The circuits were designed for space flight applications and have low power consumption (∼2 W), low weight (<50 g), and small physical size (6×13 cm). The circuitry is easily interfaced with standard pulse height analysis equipment or a microprocessor.

ISSN:0034-6748    

DOI:10.1063/1.1136702

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The mirror technique provides a promising new soft x‐ray, energy‐resolving capability. Mirrors have the uncommon but very useful characteristic of behaving as low‐pass filters. If x‐ray absorption is low, then the change in reflection across the critical cutoff energy at a particular mirror angle is quite sharp and can be used to resolve x‐ray spectra with energy resolution comparable to solid‐state detectors. The properties of mirrors that enable them to resolve x‐ray spectra have been incorporated into a two‐mirror intermediate‐resolution x‐ray spectrometer, which is described here. The instrument is capable of measuring pulsed‐source x‐ray spectra between a few tenths and about 8 keV.

ISSN:0034-6748    

DOI:10.1063/1.1136703

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A simple procedure has been developed in laser fusion diagnostics to calibrate,insitu, a copper‐activation detector for 14.1 MeV DT neutrons. By mounting thin solid state track detectors in front of the copper‐activation detector, one can measure the fluence of DT alpha particles and thus also determine the neutron fluence. An inferred alpha particle yield from this measurement can then be utilized to calibrate the copper‐activation detector.

ISSN:0034-6748    

DOI:10.1063/1.1136704

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

We present a novel electrostatic, energy‐dispersive particle analyzer whose astigmatism can be used to measure the polar angle distribution of charged particles originating in a sample spot, in a multichanneling mode. The analyzer consists of a toroidal prism and a truncated conical lens, both coaxial on an axis through the particle source. The toroidal prism is used in an unusual way, in that the axial radius of the central equipotential surface varies from infinity to a certain minimal value for varying deflection angles in the prism. We develop design criteria for an analyzer using this principle, suitable for measurements on solid samples. The energy resolution of the analyzer lies between those of a 127 ° cylindrical and of a 180 ° spherical analyzer. Angular resolutions of <2.6 ° (FWHM) can be achieved.

ISSN:0034-6748    

DOI:10.1063/1.1136705

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The Fast Digital Data Acquisition System (FDDAS) links a Vacuum Generator’s HB5 Scanning Transmission Electron Microscope and a PDP‐11/34 minicomputer, to enable high‐speed collection and storage of digitized images for analysis, processing, and display, either in real time (using hardware) or later (via software). The FDDAS hardware consists of a digital scan generator, a programmable quad scaler with quad discriminator, an on‐line processor with digital gray level generator, an analog to digital converter, and a joystick. These devices are interconnected as addressable locations on the FDDAS bus line, the ’’System Bus,’’ on which they can act as data sources or sinks. The FDDAS also contains the circuitry for interfacing the system bus to the PDP‐11 UNIBUS, allowing it to read or write image data into the computer at memory cycle speeds. The FDDAS software consists of data transfer, data reformatting, and test pattern generation modules which are linked in an overlay structure and designed to execute under Digital Equipment Corporation’s RT11 operating system.

ISSN:0034-6748    

DOI:10.1063/1.1136679

出版商:AIP    

年代:1981

数据来源: AIP