摘要:

The operating thermal power transfer mechanisms in a thermal-wave resonant cavity were explored theoretically and experimentally. Both steady-state ac (thermal-wave) and dc temperature rise were considered, and conduction and radiation heat transfer modes were found to co-exist in the cavity. By introducing controlled variable offset dc resistive heating superposed on the fixed-amplitude thermal-wave oscillation, it was also found that the thermal-diffusivity values of the intracavity gas can vary sensitively as a function of the dc temperature rise within a thin boundary layer adjacent to the cavity thermal source (a metallic Cr–Ni alloy strip). This resulted in the measurement of the temperature dependence of the thermal diffusivity of air. Furthermore, the observed dominance of thermal-wave radiation power transfer in the phase channel of the thermal-wave signal at large cavity lengths allowed the measurement of the absolute infrared emissivity of the thin Cr–Ni strip source material:&Vegr;=0.091±0.004.©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148495

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Recombination of slow highly charged ions at the surface of a target foil can be used as a source of x rays for a projection x-ray microscope. In a first test of this concept, a low emittance beam ofAr18+andAr17+ions from an electron beam ion trap was focused with einzel lenses to a 20 &mgr;m full width at half maximum spot on a beryllium target foil. The 3 keV x rays from radiative deexcitation of the ions were used to obtain a magnified image of an electroformed nickel mesh with 20 &mgr;m resolution by projection onto a CCD camera. Prospects for substantial improvements in resolution and intensity are discussed. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148496

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Two primary parameters for an automated electrostatic mirror discharge technique are studied, namely the discharge voltage and the discharge current. It was found that using discharge voltages corresponding to the&sgr;>1region and near the first crossover point of a sample’s total yield curve gave the optimum discharge rate for the technique. Also, using discharge currents larger than the scanning current was shown to improve the rate of discharge. These optimizations ensure the feasibility of this technique as a discharge tool where repeated high and low beam voltage switching in the scanning electron microscope is needed. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148497

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The design of a battery-operated atomic force microscope (AFM) using a piezoresistive cantilever is described. The AFM is designed so that all power to drive the scanning tube and detection electronics comes from a self-contained battery. The prototype AFM uses a 6 V, Ni–Cd, camcorder battery, however, any battery that supplies between 6 and 12 V may be used. Scanner control and data acquisition are implemented using commercially available software running on an external computer. The prototype AFM achieves a scan area of 53 by 53 &mgr;m, consumes 1.8 W of power, and can scan continuously for about 7 h on a single battery charge. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148498

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present a new design of a scanning force microscope (SFM) for operation at low temperatures in an ultrahigh vacuum (UHV) system. The SFM features an all-fiber interferometer detection mechanism and can be used for contact as well as for noncontact measurements. Cooling is performed in a UHV compatible liquid helium bath cryostat. The design allowsin situcantilever and sample exchange at room temperature; the subsequent transport of the microscope into the cryostat is done by a specially designed transfer mechanism. Atomic resolution images acquired at various temperatures down to 10 K in contact as well as in noncontact mode are shown to demonstrate the performance of the microscope. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148499

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

This article gives the quantitative three-dimensional displacements of a piezoelectric tube scanner subject to arbitrary voltages. The results including the influences of the tip’s position and length are reported. The displacements are determined by the piezoelectric strain/charge constantd31and the geometrical parameters of the scanner. Experiment results show the feasibility of the proposed method to calibrate the effective piezoelectric constant of a scanner. The coupling between vertical and transverse scanning displacements is discussed. Comparison of the newly developed formulas with the previous formulas and finite element calculation is carried out. The theoretical basis of the recently proposed “circular arc bending model” is found and the exact form of the model is also derived. Numerical results show that the exact form agrees with the experimental results much better than the previous form. The formulas presented here can be used for the design, calibration, and further application of piezoelectric tube scanners in scanning probe microscopes. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148500

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A cell for biological samples that allows atomic force microscopy (AFM) observations in a controlled environment (air or gas or any liquid) is described. The cell is made of a modified Petri container and it is possible, through two inlet and outlet feedthroughs, to introduce an aqueous liquid during AFM observation thus directly visualizing the modifications induced on the biological specimen. Uncoated neurons and Escherichia Coli bacteria have been imaged in air and after introducing an aqueous liquid by contact-mode AFM: the microimages are similar and show a comparable resolution even though the force applied to the biological material is different. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148501

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Currently most electrical capacitance tomography systems employ the linear back-projection algorithm to reconstruct cross sectional images, the processing of which requires sensitivity maps for all electrode pairs. Usually these sensitivity maps are obtained by finite element analysis with accuracy limited by available data on sensor geometry. Alternatively they can be more accurately obtained by physical measurements so that the imaging accuracy can be improved. A test rig has been built at UMIST for this purpose. It can be controlled manually or by a computer. The experimental result shows the feasibility. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148502

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A modification of the one dimensional A˚ngstro¨m’s method that employs photothermal radiometry has been used to determine the longitudinal thermal diffusivity of three thin long bars of chemical vapor deposited diamond. Long bar specimens permit us to use a simple one-dimensional treatment that employs a linear least squares fitting procedure on both magnitude and phase data as a function of position, provided that the condition for ignoring end effects is fulfilled. Any differences in diffusivities obtained from magnitude data and from phase data can be attributed to surface heat losses; the values of diffusivity obtained with the two types of data showed no significant difference. The diffusivities obtained agree reasonably well with the mean values calculated from measurements made by several other laboratories on the same specimens. The heat source was the beam of an argon-ion laser focused onto the specimen surface either with a cylindrical lens to form a line focus or with a spherical lens to form a point focus. The differences in diffusivities obtained when a line source was used and when a point source was used were not statistically significant. A theoretical calculation indicates that the measurements on the specimen were made sufficiently far from the heat source for the one-dimensional treatment to be valid whether the line source or the point source were used: either source is expected to give the same result as was observed experimentally. A point source is preferable because the optical configuration of the experiment is simpler and larger signals are obtainable. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148873

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The numerical fit of deep level transient spectroscopy (DLTS) spectra, used primarily to analyze complex DLTS spectra, is evaluated in terms of the accuracy of measuring deep levels and the sensitivity to noise. It is shown that by using numerical fit of DLTS spectra, the uncertainties in the emission activation energy and the capture cross section of deep level defects can be improved by three to four times over the standard Arrhenius plot method. Two modifications of the fitting procedure are tested: a fit of a DLTS spectrum using one rate window, and a simultaneous fit using five different rate windows. It is shown that simultaneous fit of spectra using different rate windows is significantly more accurate, has noticeably larger convergence radius for the initial values of parameters, and is less sensitive to noise. The advantages of the fitting routine are demonstrated on experimentally obtained noisy DLTS spectra. ©1998 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148503

出版商:AIP    

年代:1998

数据来源: AIP