摘要:

It is important to be able to measure accurately theQfactor of an open resonator to compute loss tangent of low‐loss dielectric materials. In this paper, we report the results of the heterodyne detection technique used to measure theQfactor of an open resonator in theW‐band frequency range. A more general algorithm is used for determining theQfactor. This algorithm offers some advantages over the commonly used ‘‘half‐power frequencies’’ method of measurement of theQfactor. The effect of signal/noise ratio on the accuracy of measurement of theQfactor is experimentally studied. It is shown that with the set up used, it is possible to measure theQfactor to an accuracy of better than 1%.

ISSN:0034-6748    

DOI:10.1063/1.1143287

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This article describes systems in which the precession of a single particle spin is magnetically coupled to the excitation of an oscillator. The behavior of such systems resembles that of a ‘‘folded’’ Stern–Gerlach experiment, in which the linear spatial trajectory of the original Stern–Gerlach experiment is folded into the cyclic trajectory of an oscillator. Both quantum and semiclassical solutions to the equations of motion are derived. The results encompass any kind of oscillator which couples to a magnetic field. Examples include mechanical cantilevers with a magnetic source affixed to them, as well as inductor‐capacitor resonant circuits. One potential application of oscillator‐coupled magnetic resonance is the imaging of biological molecules. Some design issues relevant to molecular imaging are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143837

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Impressed by the high resolution and easy operation of the new generation scanning tunneling microscopes (STMs), we built a pocket‐size high‐stability atomic force microscope (AFM) with deflection measurement by tunneling. It was our aim to reach high mechanical and thermal stability of the tunnel junction as well as full compatibility with our existing STM system. Our first AFM scanhead, designed for large scan ranges up to 15 &mgr;m, stably measured an artificial grid structure on SiO2, reproducibly showing details of less than 1 nm in size. On this well‐defined sample we compared constant force with variable deflection measurements.

ISSN:0034-6748    

DOI:10.1063/1.1143288

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The performance of an atomic force microscope using a laser diode interferometer has been improved to the point where its resolution is comparable to that of laser beam deflection systems. We describe the structure of this microscope, present a model that takes into account the main parameters associated with its operation, and demonstrate its sensitivity by showing images of a small area scan with atomic resolution as well as a large area scan in a stand‐alone configuration.

ISSN:0034-6748    

DOI:10.1063/1.1143289

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A piezoelectric inertial stepping motor for multiple rotations of small optical or mechanical components has been developed. The spherical rotor can be rotated about two or three orthogonal axes. Angular step resolution of 1 arcsec is achieved and the maximum speed lies in the range of degrees per second. The design is compact and eliminates mechanical backlash. Simple electronic control is achieved with only one wire per rotational axis. Low‐voltage signals between 15 and 30 V are sufficient for driving the motor. No voltage is necessary for maintaining the rotor in a static position. A first application is described with laser optics as they are used in the detector of a scanning force microscope, offering the advantage of remote controlled adjustment.

ISSN:0034-6748    

DOI:10.1063/1.1143290

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Characteristics of an ultrahigh vacuum (UHV) stepping motor have been examined for practical use. The temperature rise of the motor in the energized‐and‐rest condition was measured as a function of the coil current. The result showed that it is approximately proportional to the electric power fed to the coil. The outgassing from the motor increased significantly at temperatures above 100 °C. The components of the released gas were the usual species in vacuum such as H2, H2O, CO, CO2, and hydrocarbons. Initially a small amount of NH3was also observed at temperatures higher than 150 °C. This gas might originate from a small amount of the epoxy resin used for bonding the rotor and the permanent magnets. It decreased rapidly during the test operation. In the running mode, the outgassing of H2, CH4, H2O, CO, and CO2increased with the revolution rate. The amount of the H2released from the motor with the silver‐ion plated ball bearings was larger than that with the MoS2coated ball bearings. The lifetime of the MoS2‐coated ball bearings was longer than that of the Ag ion plated ones.

ISSN:0034-6748    

DOI:10.1063/1.1143291

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We present an optical technique for the measurement of semiconductor surface electric fields. The measurement technique uses the Kerr electro‐optic effect in nitrobenzene, a phase sensitive interferometer, and associated data acquisition units to measure the surface electric fields between the contacts of a planar semiconductor device. This technique was used to measure the surface fields on silicon devices used in pulsed power applications, but has the potential for use as an electric field probe for any device having high surface electric fields, both pulsed and dc. The measurement technique showed a temporal resolution of 100 ns, which can be easily reduced to a few nanoseconds using superior data acquisition and detection systems. The spatial resolution was about 50 &mgr;m for devices that had a typical contact separation of about 500 &mgr;m (power devices). This technique can be applied to measure the surface fields on devices commonly used in microelectronic applications. In this paper we discuss in detail the measurement technique and present the results obtained for silicon photoconductive power switches.

ISSN:0034-6748    

DOI:10.1063/1.1143292

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Gundestrup is a Langmuir/Mach probe array which measures the flow velocity in the scrape‐off layer of Tokamak de Varennes (TdeV). It is based on the concept of a Mach probe where presheaths extending upstream and downstream from the probe, parallel to the magnetic field, attract charge to a circular array of collecting pins. The polar distribution of ion saturation currents to the circular array is used to compute the components of flow velocity in the plasma. With Gundestrup, there is an assumed flow perpendicular to the magnetic field as well as parallel to it. Equations representing the collection of charge by individual pins on the probe are presented and sample flow patterns from the scrape‐off layer are shown.

ISSN:0034-6748    

DOI:10.1063/1.1143239

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A methyl radical source has been developed for use in high vacuum. Methyl radicals are produced through azomethane pyrolysis in a tubular reactor located inside an ultrahigh vacuum chamber. Other gas products include nitrogen from azomethane pyrolysis, and methane, ethane plus hydrogen from the reactions of methyl radicals on the walls of the reactor. Methyl yields as high as 42% have been observed.

ISSN:0034-6748    

DOI:10.1063/1.1143240

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A supersonic sodium cluster beam source with a refilling system is described in detail. Due to the external refilling system a new loading of the oven, which is designed for high‐temperature application at 800 °C, is accomplished very fast and interrupts the measuring process only for 1–2 h. Additional purification of the alkali metal in the reservoir allows the usage of standard quality sodium samples.

ISSN:0034-6748    

DOI:10.1063/1.1143241

出版商:AIP    

年代:1992

数据来源: AIP