摘要:

A thermally compensated tube scanner scanning tunneling microscope (STM) has been constructed and successfully tested. This design utilizes two concentric piezoelectric tubes, one for scanning and one for thermal compensation and inertial sample translation (over several mm), as well as fine adjustment of sample position while in tunneling range. This design eliminates the need for mechanical components such as springs, levers, gears, or stepper motors that are known to result in considerable vibration sensitivity, thermal drift, and low‐resonance frequencies. This new design demonstrates continuously variable‐temperature operation as well as atomic resolution without vibration isolation for the first time in a STM. Thermal drift of less than 1 A˚/h and less than 10 A˚/K have been determined. Also, the lowest mechanical resonance frequency of 21 kHz makes this new design suitable for high‐speed applications such as video rate scanning.

ISSN:0034-6748    

DOI:10.1063/1.1140047

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An inelastic electron tunneling spectrometer is described which is capable of providing constant‐resolution spectra over the 0 to greater than 16 000‐cm−1range. Constant‐resolution data acquisition is especially beneficial in the case of electronic transitions studied by tunneling spectroscopy. Data acquired asd2V/dI2, (d2V/dI2)/(dV/dI)2, and in constant‐resolution mode are compared. At intermediate and at high bias, either of the two latter data‐acquisition methods is superior to the first. At high bias voltage, constant‐resolution spectra are superior.

ISSN:0034-6748    

DOI:10.1063/1.1140048

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A scanning microscope stage has been developed for use at cryogenic temperatures. The stage uses a piezoelectric driving element and circular flexure hinges to achieve a slow scan travel of greater than 10 &mgr;m and a near‐resonance travel of 100 &mgr;m while immersed in liquid helium at 4.2 K. The scanner has been operated inside a pressure cell in a dilution refrigerator, where it dissipates less than 150 &mgr;W of heat at 100 mK.

ISSN:0034-6748    

DOI:10.1063/1.1140049

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

An eight‐beam receiver system for millimeter‐wave radio astronomy is described. The receiver is designed to map spatially extended radio sources in both spectral line and continuum emission at a wavelength of 1.2 mm. This receiver is now in use on the 12‐m radio telescope on Kitt Peak in Arizona.

ISSN:0034-6748    

DOI:10.1063/1.1140050

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Procedures for the rapid and precise control by electromechanical means of the reference beam phase shift during differential holography are described. Phase shift is created with the use of a piezoelectric ceramic translator that is driven by a two‐step voltage pulse to minimize mechanical ringing. The resultant suppression of resonant vibration permits an order of magnitude reduction in the time interval between the exposures. The adjustment of the phase shift signal is assisted by use of feedback control arrangement to stabilize an interferometer.

ISSN:0034-6748    

DOI:10.1063/1.1140051

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have designed and built a low‐cost current–voltage converter with a bandwidth larger than 200 MHz and a fixed ac insertion gain of 20 dB for use in multiple‐frequency phase fluorometry (MFPF). We describe its application with the Hamamatsu R928 photomultiplier (PMT) and discuss problems of radio‐frequency (rf) interference, signal‐to‐noise ratio (S/N), PMT nonlinearity, and overall frequency bandwidth. The separation of ac and dc signal paths introduces the possibility of direct determination of relative modulation in two simultaneous measurements. We demonstrate that systematic errors such as PMT nonlinearity can be completely eliminated in MFPF by an appropriate experimental procedure and report an accuracy of our dual‐beam instrument of 5 ps.

ISSN:0034-6748    

DOI:10.1063/1.1140052

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The usefulness and limitations of the Becton–Dickinson fluorescence‐activated cell sorter FACS IV for fluorescence polarization measurements were examined. A set of tests to determine the characteristics of the detection geometry, the optical properties of the beam splitter, and the capability to process fluorescence polarization data is presented. Recommendations are provided for correcting instrumental deficiencies.

ISSN:0034-6748    

DOI:10.1063/1.1140053

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The design and operating properties of a GaAs polarized electron source are presented. An electron optical system is described that passes more than 80% of the emitted electrons at 10 &mgr;A to the target under low‐energy (7–20 eV) parallel beam conditions. Laser excitation can give rise to abnormal energy distributions of the photoemitted electron beam. The existence of longitudinal modes gives a possible explanation for this behavior, which can be avoided using a mode stabilized light source. The overall performance of the polarized electron source is demonstrated by inverse photoemission spectra from Ni(110).

ISSN:0034-6748    

DOI:10.1063/1.1140054

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

This article describes a laser‐based source and detection scheme for performing time‐resolved photoemission studies of materials. The pulsed laser source produces intense picosecond pulses of coherent radiation that are nearly continuously tunable from the near infrared to photon energies up to 13 eV. To achieve high sensitivity, a novel multianode time‐of‐flight spectrometer has been built that generates an angularly resolved intensity versus kinetic energy spectrum with better than 100‐meV resolution. The source and detector provide an opportunity to study the electronic dynamics of excited systems on a picosecond time scale.

ISSN:0034-6748    

DOI:10.1063/1.1140055

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Mass resolution of a time‐of‐flight mass spectrometer with a two‐stage electrostatic reflector is calculated for secondary neutral mass spectrometry. The instrument parameters are optimized for energy and space focusing: correcting the flight time difference due to the energy width &Dgr;Eof sputtered particles and the spatial width &Dgr;sof an ionizing laser beam. The effect of &Dgr;scan be compensated by applying an acceleration field to the ionizing region, and the maximum resolution becomes about 1000 for &Dgr;E=10 eV and &Dgr;s=1.0 mm.

ISSN:0034-6748    

DOI:10.1063/1.1140056

出版商:AIP    

年代:1988

数据来源: AIP