摘要:

A varied line‐spacing plane grating monochromator is installed at an undulator beamline BL‐19B of the Photon Factory. Small contribution of aberrations to image sizes at a focal plane of the varied line‐spacing plane grating is calculated with use of an optical path function. The largest resolving power obtained from a ray tracing is estimated to be 4600 at a photon energy of 1239.85 eV and 10 000 at 91.2 eV. Gas absorption spectra show the similar extent of resolution obtained by the ray tracing. A high brightness with a high resolution may be realized in this monochromator. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146621

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A variable exit beam height double‐crystal monochromator for high‐power insertion devices was built and tested at the Photon Factory. The second crystal is mounted on a high‐precisionXYtranslational stage and its position in the parallel and perpendicular direction to the reflecting plane (x,y) is computer controlled. In this design, the exit beam height (y) and geometrically required positioning of the second crystal (x) are separately controlled. Either a fixed or variable exit beam height is obtained over the Bragg angle (&thgr;) range from 6° to 25°. A systematic noise caused by degraded parallelity between the two crystals is observed in extended x‐ray absorption fine structure spectra whenxandyare simultaneously controlled. This noise is significantly reduced by a versatile control of (x,y): for a typical scan (∼1 keV) onlyyis allowed to vary while both coordinates are controlled when a monochromator is tuned over a wider energy range. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146622

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present the design and performance of a magnetic circuit suitable for magnetizing solid samples in the measurements of soft x‐ray emission dichroism excited by synchrotron radiation. The system allows a variety of samples to be magnetized and satisfies the rather stringent geometrical constraints due to the need for minimizing the effect of photon self‐absorption by the sample. The magnetic circuit is ultrahigh vacuum compatible, can reach about 2800 G, and allows fine adjustment of sample position. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146594

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In this paper we show and discuss new results on the dissociation of N2O after core (N 1s) excitation and ionization. We have developed an experimental setup combining an electrostatic electron analyzer with a time‐of‐flight mass spectrometer without angular discrimination, operated with a strong pulsed extraction field. Taking advantage of the pulsed character of the synchrotron radiation light, we have been able to efficiently remove fortuitous coincidences, without perturbing the electron energy analysis. We relate in detail the experimental setup and show new results obtained on14N15NO. A selective fragmentation is shown depending on the excited site (central or terminal nitrogen) and the influence of the electronic excited state of the ion on the fragmentation pattern is pointed out. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146595

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe a real‐time, fast Fourier transform digital spectrometer, based on the new Sharp LH9124 chip. The system is fully programable, and in the present configuration it can measure the power spectrum of an incoming signal with a bandwidth of up to 20 MHz, a time resolution of 30 ms, a frequency resolution of up to 128 K channels, and a temporal duty cycle of 45% at 6 MHz bandwidth. An upgrade of the spectrometer is in progress, which will allow a duty cycle (efficiency) of 100% at 12 MHz bandwidth (single channel) or 6 MHz (dual channel). This new approach to the spectrum analysis will open new observational capabilities in radio astronomy and other fields. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146596

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A novel method for the calibration of spectral line intensities measured by photoacoustic spectroscopy is presented. This technique uses an electrically heated wire to mimic the acoustic signal generated by the laser absorption of a sample gas. A model was devised to describe the acoustic signal generated by both sources and to calibrate the cell. The transition dipole moment of theR(7) transition of the &ngr;2+3&ngr;3vibrational overtone band of acetylene was measured and found to be in good agreement with the literature value. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146597

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report here on the focusing properties of a two‐electrode electrostatic immersion lens of micron dimensions that is combined with the electron point source. Depending on the mode of operation of the lens, the resulting focused electron beam can have an energy as low as 15 eV if the lens is used in the decelerating mode, or an energy of typically 200 eV if the lens is used in the accelerating mode. We will also present results of using the focused beam in a TEM setup as well as in the scanning mode. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146598

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have developed a video low‐energy electron diffraction (LEED) system on the basis of a slow scan charge coupled device (CCD) camera which is capable of collecting LEED IV data at very low electron doses quickly and therefore enables us to study extremely beam sensitive surface structures which have not been accessible to LEED IV analysis before. The slow scan CCD camera allows separating the relatively short data acquisition process from the more lengthy digitizing, storage, and data analysis processes. Typical total effective exposure times can therefore be reduced to about 200–300 s (1 s per energy point) at a primary beam current of 100 nA which corresponds to a total dose of about 12eper adsorbate particle; further decrease is possible. The total measurement time for collecting a complete set of LEED images is of the order of 30–40 min which assures the exclusion of contamination effects, even for sensitive layers. The IV curves are then extracted from the digitally stored images off‐line which allows collecting the intensities of all visible spots simultaneously with a high reliability in tracing beams, even for very dense LEED patterns. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146599

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A compact scanning tunneling microscope (STM) with a novel rotary piezoelectric stepping motor for coarse positioning has been developed. An inertial method for rotating of the rotor by the pair of piezoplates has been used in the piezomotor. Minimal angular step size was about several arcsec with the spindle working torque up to 1 N×cm. Design of the STM was noticeably simplified by utilization of the piezomotor with such small step size. A shaft eccentrically attached to the piezomotor spindle made it possible to push and pull back the cylindrical bush with the tubular piezoscanner. A linear step of coarse positioning was about 50 nm. STM resolution in vertical direction was better than 0.1 nm without an external vibration isolation. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146600

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Tapping mode capabilities are successfully implemented on a commercial contact mode atomic force microscope. In our setup, standard Si3N4cantilevers are vibrated by an acoustic wave from a small piezo speaker. The minor changes needed in the measurement electronics are presented. Experiments performed both in air and under liquid, on hard as well as on soft samples, clearly demonstrate improvements in image quality, contrast, and resolution. Especially on soft biological samples, such as microtubules, the common problems of smearing and irreversible sample damage by scanning seem to be alleviated. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146601

出版商:AIP    

年代:1996

数据来源: AIP