摘要:

A PARC174A polarographic analyzer has been transformed into a comprehensive microcomputer controlled electroanalytical system by interfacing it with an IBM PC equipped with a Tecmar LabMaster data acquisition subsystem. Techniques implemented include square wave voltammetry, chronoamperometry, cyclic voltammetry, differential pulse, normal pulse, and sampled dc polarography, and stripping voltammetry which can be used with either linear sweep, differential pulse, or square‐wave techniques. The PARC174A functions only as a potentiostat and current to voltage converter. All the potential waveforms are generated by theD/Aconverter of the LabMaster and the current data are sampled by theA/Dconverter. The software developed should be easily adaptable to most potentiostats with minor modification. Because no extra circuitry is desired to complicate the system, a small‐step staircase waveform is used to approximate the linear dc ramp in cyclic voltammetry, differential pulse, and sampled dc techniques. The discrepancy in results obtained using linear dc ramp and small‐step staircase waveforms was carefully examined and proven to be negligible. All the techniques implemented have been shown to give theoretically predicted results. The results are also found essentially the same as those obtained using a conventional PARC174A. This computer controlled system makes available the use of square wave voltammetry, which was otherwise not available on the original machine. Experimental data showed that 4.76×10−8M Cd2+could be quantitatively analyzed by square wave voltammetry when a dropping mercury electrode was used.

ISSN:0034-6748    

DOI:10.1063/1.1144015

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A high‐sensitivity computer‐controlled infrared polariscope has been developed to measure a small amount of phase retardation, and the principal axes of birefringence induced by residual strains in commercial III‐V compound wafers with standard dimensions. In order to check the performance of the polariscope, semi‐insulating LEC‐grown GaAs (100) wafers, currently used for high‐speed integrated circuits, were examined. The residual strain components of ‖Sr−St‖, ‖Syy−Szz‖, and ‖Syz‖ were evaluated from the measured values of the phase retardation and the principal axes of birefringence. It was found that the polariscope developed here was highly sensitive enough to characterize the residual strain components to the order of 10−7in thin commercial GaAs wafers.

ISSN:0034-6748    

DOI:10.1063/1.1144016

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new optical method is established to measure the crack length and its velocity in transparent crystals by utilizing the total reflection of light beam at the cleavage crack plane. The optical system is constructed by using a laser, aPINphotodiode sensor, and a wave memory. With the apparatus the crack propagation velocity can be measured at any desired position inside the specimen with a time resolution of less than 1 &mgr;s. The measurement on a cleavage crack in NaCl reveals that the maximum speed of the crack is about 800 m/s and the fluctuation of the velocity occurs prior to the arrest.

ISSN:0034-6748    

DOI:10.1063/1.1144017

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We made a new polarization analyzing system for measuring a rotation of major axis of elliptical polarization in x‐ray magnetic resonant scattering. This system, based on a two‐axis diffractometer, is characterized by introducing a 45° linearly polarized x‐ray incident beam. Design and performance of the system are described. The rotation can be measured with precision of 0.2°–0.3° at the vicinity of GdL3‐absorption edge where the maximum rotation is about −2°.

ISSN:0034-6748    

DOI:10.1063/1.1144453

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new experimental geometry for simultaneously mapping the rocking curves of a sample over a one‐ or two‐dimensional array of points on the sample has been developed. The 422 asymmetric diffraction of Cu K&agr;1radiation with a monolithic channel‐cut silicon crystal angularly collimates and spatially expands the x‐ray beam. A cooled Reticon linear photodiode array with 25‐&mgr;m spatial resolution was used for the one‐dimensional detector. Compared with the commonly used double‐crystal diffractometer method, more information can be obtained from the present method, for example, characterization of the minute local misorientation of subgrains and the precise determination of the curvature of a crystal. The uniformity of the crystal quality and the local variation of the curvature of the crystal planes over a sample can also be revealed from the contour map of the rocking curves. Maps of the rocking curves of several samples have been collected using this method.

ISSN:0034-6748    

DOI:10.1063/1.1144018

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe a differential absorption spectrometer that measures the energy spectrum (from 20 to 800 keV) of flash x rays whose intensity precludes pulse‐height analysis methods. The spectrometer uses individually calibrated thermoluminescent dosimeters, each inside its own spherical absorber, to accommodate isotropic radiation from pulsed bremsstrahlung sources. An iterative perturbation unfolding code determines the spectrum from the detector responses and the computed energy response functions. Unfolding works best with a good guess for the initial spectrum, and data with less than a few percent error.

ISSN:0034-6748    

DOI:10.1063/1.1144019

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The radio‐frequency coil sensitivity for NMR signal detection can be defined asB1/&sqrt;P, which is the magnetic field that the coil induces at a given point per unit supplied power. We propose a new method, based on the reciprocity theorem, to quickly evaluate the sensitivity of a tuned coil. The only requirement of the method is a voltage gain measurement with a small dual‐loop probe, without mobilization of the NMR unit. The probe can be used to gauge and map the sensitivity of the coil with good accuracy, while monitoring its tuning frequency &ohgr;0and its quality factorQ. Our method is particularly convenient for development and maintenance of coils for MR imaging, and more generally could be applied to other fields involving radio‐frequency characterization of inductive circuits.

ISSN:0034-6748    

DOI:10.1063/1.1144020

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new Fourier transform ion cyclotron resonance mass spectrometer is described in three sections: magnet, vacuum system, and electronics/data system. Each component is described in detail (e.g., manufacturer’s part numbers, drawings, circuit schematics, etc.). Of special interest is the high‐frequency signal generation and processing required to extend the lower‐mass limit for singly charged ions to 1 u. In particular, two new multiple heterodyne techniques for high‐frequency measurements are described, as well as a method for producing a long‐duration electron beam, and the implementation ofz‐axis ejection for selective removal of unwanted ions of various mass‐to‐charge ratios.

ISSN:0034-6748    

DOI:10.1063/1.1144021

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A time domain magnetic spectrometer based on a pick‐up coil is presented for the study of spin‐lattice relaxation rates in paramagnetic samples at high magnetic fields and at liquid‐helium temperatures. The equilibrium between the spin system and the lattice is disturbed either by heating the spin system under the electron spin resonance condition (using far‐infrared laser pulses) or by heating the lattice (using nonresonant laser pulses). Resulting magnetization changes induce a voltage in a pick‐up coil oriented parallel to the field. By measuring the temporal evolution of this voltage, one can observe the spin‐lattice relaxation directly. The spin‐lattice relaxation in the diluted magnetic semiconductor CdMnTe is measured in order to demonstrate the performance of the spectrometer. The two methods of disturbing the equilibrium between the spin system and the lattice are compared.

ISSN:0034-6748    

DOI:10.1063/1.1143968

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have developed a simple method of collecting the thermal derivative spectra of solids. In this method, a sample’s reflectance is measured at two specific temperatures and the thermal difference of the material’s reflectance is calculated. By digitally averaging these differences, we obtain spectra equivalent to thermal modulation spectra. Since this is not a modulation technique we have named it thermal difference spectroscopy. Using the thermal difference spectrometer we have achieved a base line noise level in the normalized thermal difference reflectance spectrum (&Dgr;R/R) of approximately 5×10−5. To demonstrate the technique’s utility as a truly noncontact derivative spectroscopy we have collected thermal difference spectra of both thin‐film and bulk samples.

ISSN:0034-6748    

DOI:10.1063/1.1143969

出版商:AIP    

年代:1993

数据来源: AIP