摘要:

We have designed and constructed a torsional oscillator magnetometer for use in magnetic fields up to 25 T. The anisotropic component of the magnetization is detected by measuring the shift in the resonant frequency of the oscillator, which is fabricated from a single‐crystal silicon wafer using micromachining techniques. The frequencies for the oscillators described here are between 100 Hz and 1 kHz and can be measured with a resolution of order 1 part in 108in a 10 s averaging time, allowing for the detection of magnetic moments of 2×10−11J/T at 1 T. Our oscillators are optimized for experiments on GaAs‐AlGaAs heterostructures, but the method is suitable for any sample with an anisotropic susceptibility. We have applied the technique to two systems, a quasi‐one‐dimensional spin chain and a two‐dimensional electron gas. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147562

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A computer‐controlled system for measuringM‐Hhysteresis loops of soft magnetic materials is described. It overcomes many of the problems associated with these kinds of measurements of low coercivity materials. The combination of ‘‘low drift’’ hardware and measurement procedure makes software correction unnecessary. At every field step, the homemade integrator is reset in order to minimize the drift and to provide a way of separating the sample contribution to the signal from the field contribution and, consequently, to allowM‐Hplots. Furthermore, to avoid the residual drift of the hardware, the method of ‘‘two‐way measurement’’ is applied, giving drifts of 0.01% per hour. Results obtained for a FINEMET alloy film annealed at different temperatures are presented, illustrating the ability of the system to measure soft magnetic materials. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147563

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have fabricated a Josephson–Fraunhofer magnetometer based on the shrinking of the Fraunhofer pattern exhibited by high‐Tcgrain boundaries Josephson (GBJ) junctions. It is obtained using flux focuser and GBJ junction directly patterned on a single chip. The device is actively voltage biased and operates in a field locked loop as conventional superconducting quantum interference device systems. The amplitude of the auxiliary modulation field is adjusted to obtain the maximal sensitivity; the coupling between the feedback coil and the flux focuser has been studied to evaluate the magnetometer performances. The system bandwidth is 1 kHz and the measured noise level is 40 pT/&sqrt;Hz above 10 Hz. The slew rate and the dynamic range of the magnetometer are 2 mT/s and 112 dB (1 Hz bandwidth), respectively. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147564

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The current dependence of the forward voltage of a cryogenic silicon diode temperature sensor (CRYO Industries of America, Inc.) is reported here in the temperature range 10–300 K. The current values are varied from 10 nA to 0.1 A. The sensitivity of the diode is observed to increase for lower current values in the high temperature range. The rapid increase of the forward voltage at low temperatures is observed to be suppressed considerably by reducing the current. This study helps us to conclude that for all practical purposes such commercial diodes (prescribed for a particular current value of 10 &mgr;A) can be operated for a wider range of current values, with suitable calibration data. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147565

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

In many scientific and industrial applications the permeating flow through a membrane separating two fluid phases must be kept constant, either because the flow is feeding another system which requires a constant in‐flow, or because membrane fouling is being studied and it is necessary to know what must be done to maintain the flow. We describe a digital proportional‐integral controller which makes it possible to maintain a constant permeating flow through a Nuclepore membrane with 8 &mgr;m mean pore radius. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147566

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have developed a multifunctional surface analysis system based on a scanning electron beam for nanofabrication and characterization of surface reactions for fabrication processes. The system performs scanning electron microscopy (SEM), scanning reflection electron microscopy (SREM), Auger electron spectroscopy (AES), and x‐ray photoelectron spectroscopy. Nanometer scale resolution is obtained for ultrahigh vacuum (UHV)‐SEM while the mechanical pumping instruments are operated. Single atomic steps on Si(111) surfaces are observed through SREM. Surface sensitive AES measurement is achieved with SREM geometry; this has a great advantage for investigating atomic step related surface reactions. High spatial resolution AES analysis is also achieved by using a nanometer scale probe beam. Auger electron signals from a hundred Ag atoms on a Si(111) surface are successfully detected with high sensitivity. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147567

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A modification of commercially manufactured atomic force microscopy cantilevers which reduces the bending of the V‐shaped legs due to changes in temperature is described. Gold‐coated silicon nitride cantilevers are a bimorph system in which the different thermal expansion coefficients of the materials comprising the system can produce a temperature‐dependent change in curvature. Other stress‐related effects might also be responsible for the observed bending. By removing the gold film and redepositing gold only at the end of the V‐shaped legs, a reduction in the bending of the cantilever is accomplished while the required optical reflectivity for the laser deflection system is retained. Imaging x‐ray photoelectron spectroscopy, scanning electron microscopy, and changes in the detector photodiode signal related to bending of the cantilever are shown for modified and unmodified tips. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147568

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new method for height calibration of scanning probe microscopes (SPMs), applicable for any height from 0.3 nm to beyond 100 nm, is presented. A previously calibrated piezo is set in a SPM instead of a sample. A definite time‐periodic elongation at a corresponding voltage can serve as height standard. The method is easy to use, tuneable in a wide range and exact to the limits of the SPM itself. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147569

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a scanning force microscope working in the repulsive force mode designed for fluid–cell measurements and tip–sample interaction studies. The instrument uses the optical beam deflection principle to measure cantilever motion and is compatible with commercially available microfabricated cantilevers. The instrument is designed to accommodate tube scanners with lengths up to 2 in. In order to minimize memory effects in the piezoelectric scanner, we have introduced a technique of pre‐ and postscanning to get reproducible force versus distance curves. Different linearizing algorithms to decrease the unlinearities of the scanner motions are demonstrated. As examples of the performance, we present an image of a mica surface obtained in air showing atomic scale stick–slip features, and a force measurement using the fluid cell with NaCl electrolyte showing the double layer interaction between a glass sphere and a mica surface. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147545

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A microscope has been constructed in which a high‐transition temperature dc superconducting quantum interference device (SQUID) in vacuum is brought to within 140 &mgr;m of samples at room temperature and pressure. The SQUID is mounted on the upper end of a sapphire rod, cooled to liquid nitrogen temperature, below a 75‐&mgr;m thick sapphire window. Samples can either be placed directly on the window or scanned over the SQUID to produce magnetic images. A square‐washer SQUID with inner and outer dimensions of 30 and 50 &mgr;m can resolve 130 &mgr;m magnetic features. The instrument is intended primarily for biological applications. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147570

出版商:AIP    

年代:1996

数据来源: AIP