摘要:

In this article, we describe an ultrahigh vacuum (UHV) compatible superconducting quantum interference device (SQUID) magnetometer system for investigations of surface, interface, and thin film magnetism. This system provides a new capability for a commercial SQUID magnetometer to characterize freshly deposited thin film samples transported from a separate molecular‐beam epitaxy deposition facility without breaking vacuum. Magnetic measurements can be performed over a wide range of temperatures down to 4.2 K in applied magnetic fields as high as 1 T, and under a variable vacuum environment in which pressures as low as 10−10Torr can be achieved. The combination of the extremely high sensitivity of the SQUID for magnetic measurements with UHV analysis techniques offers the unique capability for films to be prepared, processed, and characterized repeatedly without substantial contamination. The capabilities of the UHV‐SQUID magnetometer system are demonstrated byinsitumeasurements of the magnetic properties of Co/CoO bilayered thin films grown on Si(100) single‐crystal substrates by electron‐beam evaporation. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146023

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new technique, MICROTHERM, has been developed for noncontact sheet resistance measurements of semiconductor wafers. It is based on the application of microwave energy to the wafer, and simultaneous detection of the infrared radiation resulting from ohmic heating. The pattern of the emitted radiation corresponds to the sheet resistance distribution across the wafer. This method is nondestructive, noncontact, and allows for measurements of very small areas (several square microns) of the wafer. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146474

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thin film stress gauges for the measurement of stress waves in solids are calibrated in a uniaxial strain field where the lateral strain components are zero. Frequently, measurements of stress are needed in situations where the lateral strain components are nonzero. The analysis of data often becomes that of best guess, or whatever seems most reasonable. This work is an attempt to quantify the effect of strain on stress gauge output, and to present a technique for strain compensation. To accomplish this, the theories of piezoresistive and piezoelectric films are used to develop equations of the gauge output in terms of normal stress and two components of lateral strain. Thus, with two strain gauges and one gauge that reads stress plus strain, a time‐resolved stress history can be accurately determined. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146024

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A new method of measuring the free‐surface velocity via soft x‐ray shadowgraphy is presented. Using that method, the shock‐wave pressure was deduced. In addition, a new method of measuring the Mie scattering of the debris from laser‐induced spall in aluminum is also presented. The data have yielded the distribution of the debris radii in the range of 1–7 &mgr;m. Furthermore, it was shown that the smaller particles are the faster ones. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146025

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A cryostatic setup is described to perform photothermal deflection measurements from room temperature to 77 K. The setup uses gaseous nitrogen as a medium where the photodeflection is produced. The ability of the system to work is demonstrated presenting some measurements of thermal diffusivity of high‐temperature superconductor samples and of yttrium‐iron garnets with variable aluminum content. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146026

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A two‐dimensional shear viscometer has been constructed and tested using free‐standing liquid soap films. The viscometer, which is an analog of a three‐dimensional Couette cell, consists of an inner rotating disk and an outer stationary ring. The viscosity of the liquid films can be reliably obtained by measuring either the transient response of the disk upon a stepwise increment of the applied stress on the disk, or by measuring the strain‐stress relation in the steady state. The design can be easily modified to accommodate other types of flow which are useful for investigating hydrodynamic and rheological behavior in a variety of thin films, such as liquid crystal and polymer films. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146027

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have developed a fast and precise thermoregulation system incorporated within a physiological experiment on a brain slice. The thermoregulation system is used to control the temperature of a recording chamber in which the brain slice is placed. It consists of a single‐chip microcomputer, a set command module, a display module, and an FLC module. A fuzzy control algorithm was developed and a fuzzy logic controller then designed for achieving fast, smooth thermostatic performance and providing precise temperature control with accuracy to 0.1 °C, from room temperature through 42 °C (experimental temperature range). The fuzzy logic controller is implemented by microcomputer software and related peripheral hardware circuits. Six operating modes of thermoregulation are offered with the system and this can be further extended according to experimental needs. The test results of this study demonstrate that the fuzzy control method is easily implemented by a microcomputer and also verifies that this method provides a simple way to achieve fast and precise high‐performance control of a nonlinear thermoregulation system in a physiological brain slice experiment. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146423

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe a simple near‐infrared hygrometer based on a broadband light‐emitting diode (LED) centered at 1320 nm. Light from the LED is collimated and passes through a rotating optical‐filter assembly and a sample cell. The water vapor concentration is measured using a synchronous detection scheme. This compact and robust instrument has a response time of 0.15 s and can reliably detect short‐term absolute humidity changes as small as 0.6 mg/L (which equate to 0.02% absorption); the long‐term stability of the absolute humidity measurement over a period of 4 days is approximately 1 mg/L. These performance characteristics are particularly well suited to measurements associated with human respiration, and we present results in this humidity regime. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146028

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Aqueous‐electrolyte resistors were developed for use as dummy loads in pulsed power systems. These resistors are simple, robust, low‐inductance devices capable of operation at high voltage and high current, and may be used to dissipate large pulse energies without catastrophic failure. The resistivity and temperature coefficient of resistivity were measured for several candidate electrolytes, including aqueous solutions of copper sulfate, potassium and aluminum sulfate, potassium dichromate, silver nitrate, sodium dichromate, and sodium thiosulfate. The resistivity of potassium dichromate solution is expressed by the power law &rgr;(&OHgr; cm)=1640C−1.0942for electrolyte concentrations in the rangeC=0.025–25 g/l. The temperature coefficient of resistivity is in the range (1/&rgr;)(∂&rgr;/∂Ts)=−(0.01–0.03)/°C for typical aqueous metal–salt electrolytes and is dependent on the solution temperatureTsand, to a lesser extent, on the electrolyte concentration. Aqueous solutions of potassium dichromate are compatible with brass, copper, and stainless‐steel electrodes and polycarbonate and polymethylmethacrylate insulators, even at high concentration and elevated temperature. Such resistors give long shelf and operational lifetimes. If the maximum allowable resistance change (decrease) during the pulse is 10%, then the energy deposition per unit volume of electrolyte solution is limited to approximately 20 J/cm3for resistors initially at room temperature. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146029

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

In order to obtain low uncertainty levels in computer‐controlled electrical precision measurements, the controlling system must not interfere with the measurement system. The optical interface described here provides the two systems with an insulation resistance higher than 1014&OHgr; using two optical fibers, which also allow the systems to be remotely located. The interface treats two dc voltage signals: one of them is used to drive the measuring system, and the other is the result of the measurement and can be read with a relative accuracy of 1×10−4. The interface can be used to automatically drive dc resistance bridges and will be applied to a cryogenic setup having a superconducting quantum interference device as a detector. ©1995 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146030

出版商:AIP    

年代:1995

数据来源: AIP