摘要:

A description is given of a digital data‐recording and control system that has been used with a high resolution low energy electron scattering apparatus for the measurement of characteristic electron energy‐loss spectra and Auger‐electron spectra of solids (at room and elevated temperatures) and liquids. This system is based on a multichannel analyzer and has the following features: (a) Specimens can be prepared many times with data accumulated in arbitrarily short times after preparation (prior to specimen contamination), and final spectra of high precision can be obtained by summation of individual runs; (b) the voltage sweep applied to the electron energy analyzer can be calibrated dynamically; and (c) data can be accumulated and the target heated by electron bombardment in a cyclic manner with variable accumulation and heating periods. Characteristic loss spectra of tungsten at 800 °C and of liquid aluminum are presented as examples of operation of the system.

ISSN:0034-6748    

DOI:10.1063/1.1686294

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A novel atom probe is described which can determine the mass‐to‐charge ratios of all ion species produced during a single desorption event or of individual species at several preselected crystallographic locations during each desorption event. This is accomplished without tip movement in an instrument no larger than a conventional field ion microscope by using a new channel plate photomultiplier detector. Alignment, aiming, and pulse stability problems common to all previous designs have been eliminated. Although the present mass resolution is 4 amu atm/n= 184/3, single isotope resolution, if desired, seems possible.

ISSN:0034-6748    

DOI:10.1063/1.1686295

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A description is given of an electron impact spectrometer developed particularly for characterizing different gaseous molecules on the basis of the differences in the term scheme of the excited molecular electronic states over the energy range from 3.0 to 20 eV. A beam of monoenergetic (100 mV FWHM) electrons is incident upon a gas target within a constant potential region defined by an extremely electron‐transparent tungsten wire grid wound over the six faces of an insulating cubical frame. Electrons emerging from this region are analyzed in energy by observing the variation in current to an enclosing collector electrode as a function of its electrical potential. A spectrum over the energy range 3–11 eV with a signal‐to‐noise ratio of better than 500, and an over‐all resolution of 180 mV, of sufficient quality to discriminate between closely similar molecules, such as the isomers of chlorotoluene, is obtained in 20 sec at 100 nA exciting beam current and a sample pressure of 10−4Torr.

ISSN:0034-6748    

DOI:10.1063/1.1686296

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Measurements and interpretation of ultrasonic velocities in complex media place requirements upon the measurements techniques which cannot be met by conventional ultrasonic equipment. The widely used high resolution echo and pulse overlap techniques are not generally applicable to such materials, especially in composites where the pulse is often severely distorted. A new high time resolution method based upon the pulse transmission technique is described to meet these applications. This approach is well suited to the measurement of ultrasonic velocities and velocity changes in media which are highly dispersive and/or highly attenuating. By using a crossover‐point detecting circuit, time measurements may be made at asinglereference point in the received acoustic pulse with a resolution of better than 1 nsec. If the pulse is distorted, such measurements at more than one crossover‐point are useful in performing a mathematical analysis upon the rf pulse. In single crystal aluminum, where echo measurements can be used for comparison, a timing accuracy of 2 nsec is demonstrated for the technique. Also, the unusually wide frequency capability of the method is demonstrated with measurements of the dispersion curve for high purity polymethylmethacrylate (PMMA).

ISSN:0034-6748    

DOI:10.1063/1.1686297

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Four basic configurations suitable for recording low frequency noise from two‐terminal devices‐single voltage and single current amplifiers, dual voltage and dual current amplifiers with cross‐correlation‐are reviewed. Simple signal‐to‐noise ratio comparisons form the basis for the practical selection of the configuration which achieves the best match between the characteristics of the source (including its electrical access) and those of available amplifiers.

ISSN:0034-6748    

DOI:10.1063/1.1686298

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A modification of a scanning x‐ray topographic camera is described which automatically plots the lattice curvature of single crystal substrates strained by thin films or surface treatments such as diffusion and ion implantation. Film and substrate stresses are calculated from the radius of curvature. The unit operates as an electromechanical feedback system which maintains the orientation of a wafer such that the diffracted x‐ray intensity remains within preset limits while a finely collimated x‐ray beam traverses the wafer. Anx‐yrecorder continuously plots the changes in orientation as a function of position yielding a trace whose slope is proportional to the radius of curvature of the substrate lattice. The sensitivity of the apparatus is such that radii of curvature of 2000 m can be measured. In addition, the lateral spatial resolution is such that the local substrate lattice curvature can be determined under alternating and overlapping 2.5 mm wide stripes of metal and oxide films. It is also shown that both the curvature and uniformly exposed x‐ray topographs can be obtained simultaneously even though the wafers are severely warped due to the processing steps.

ISSN:0034-6748    

DOI:10.1063/1.1686299

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A comparison is made of the line source (LS) method and the differential line source (DLS) method of measuring thermal conductivity of particulate materials in vacuum. The DLS method requires more instrumentation in the measuring circuitry (an additional amplifier and a differentiating circuit), but since it does not require a stable temperature to initiate a test, it does not need a sample temperature control system. DLS tests can be taken as the temperature in the samples is rising from liquid nitrogen temperature to room temperature. This eliminates the practice of extrapolating thermal conductivity over this large temperature range. Also, the advantages of reduced test time, data reduction time, and small sample temperature rise enable the experimenter to take about 7–12 DLS tests in the time of 2 LS tests. Test data from the two methods agree very well. The DLS method gives slightly lower conductivity values for the small particles tested. The difference between the two methods is smaller at low temperatures than at high temperatures. The agreement in the large particle tests at room temperature is good. An error analysis shows that the LS and the DLS have total relative errors of 18 and 20%, respectively.

ISSN:0034-6748    

DOI:10.1063/1.1686300

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper describes a new type of system for displaying slow scan video signals from a scanning electron microscope. The system uses digital buffering so that an image can be viewed on a TV monitor while it is being accumulated in a storage tube. The display system can simultaneously record two images and hold up to four images in storage. These images may be overlaid on one another in different colors. [A. V. Crewe and V. Beck, Proceedings of the 29th Annual Meeting of the Electron Microscopy Society of America (1971) p. 40]. The display system is also well suited for interfacing the microscope to a computer. A Nova 800 computer and a Kennedy 8000 series tape system are used with the display system to simultaneously record and analyze two channels of digitized data.

ISSN:0034-6748    

DOI:10.1063/1.1686301

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

A method for determining the average grain size and the specific resistivity temperature dependence of a metallic powder sample is presented. The method utilizes the change in the rf Q value of a coil, caused by placing the sample in it.

ISSN:0034-6748    

DOI:10.1063/1.1686302

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This paper describes an optimal design of a transformer‐coupled matching stage for use in a high‐power pulsed rf amplifier and the practical considerations for obtaining a rapid fall of the rf pulse. It also describes a high‐power stage for use in pulsed NMR experiments, and presents a passive quenching technique for achieving rapid termination of the rf pulse.

ISSN:0034-6748    

DOI:10.1063/1.1686303

出版商:AIP    

年代:1973

数据来源: AIP