摘要:

A low noise soft x‐ray appearance potential spectrometer has been constructed. It consists of a liquid nitrogen‐cooled silicon surface‐barrier diode that detects the variations in the emitted photon flux. A 500 Å thick Al window acts as a discriminator for low energy photons (visible light and the tail of the bremsstrahlung). The performance of the detector arrangement has been tested on clean Ni films and chemisorbed O on these films. It is shown that the detector behavesideally, i.e., the signal‐to‐noise ratio is limited by theshot noise in the photon fluxfor primary electron beam intensities in the range tested (30–600 &mgr; A) and for electron energies, 300–900 eV.

ISSN:0034-6748    

DOI:10.1063/1.1686759

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

We have designed and constructed an autoranging scanning system to digitize the output of an infrared spectrometer and record it on magnetic tape. This system automatically scales the input signal, whose amplitude may range over ratios of 2000 to 1, to give a signal between 0.25 and 0.90 multiplied by an appropriate factor. Four noise reduction techniques compatible with the autoranging feature have been implemented. Two are a part of the electronic system itself and two utilize the computer in data processing. In particular, smoothing of data by least squares convoluting numbers and co‐addition (addition of corresponding points) of spectral scans over the same region give definite advantages when compared to narrow band amplifier methods in distinguishing and measuring real features with intensities of the order of the noise background of the system. The methods described have general applicability to scanning systems in which the profile of the curve generated is the important measurement.

ISSN:0034-6748    

DOI:10.1063/1.1686760

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A double‐clipped digital correlator is described which works in real time up to a sampling frequency of 16 MHz and can perform auto‐, cross‐, and triple‐correlation functions over 108 delays. The instrument is specifically designed to measure intensity correlations of weak light beams. A discussion of the statistical and systematic errors is given, with particular emphasis on the distortion introduced by the double‐clipping procedure. As an example of the possible applications of the correlator a measurement of the intensity autocorrelation of the light scattered by a pure fluid is reported.

ISSN:0034-6748    

DOI:10.1063/1.1686761

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Applying methods of statistics to photon counting in measuring a simple exponential decay with a time‐to‐amplitude converter and multichannel analyzer device shows that the histogram obtained is distorted due to the process of signal sampling. The distortion depends on count rate and life time. The distortion is biggest in the initial part of the histogram, whereas at times much greater than the decay time the histogram shows the real decay curve.

ISSN:0034-6748    

DOI:10.1063/1.1686762

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An approach is outlined for handling the general experimental problem of retrieving characteristic signals from the presence of large backgrounds. The method consists ofnth‐order differentiation followed by multiple integration of the same order. It is shown that this procedure results in a function which has the form of the remainder of the (n‐ 1)th‐order Taylor series for the background plus characteristic signals. If the function is one with a very large radius of convergence, then an order can be found such that the remainder is arbitrarily close to zero over the region of interest. Threshold functions, which are characterized by having very small convergence radii and which asymptotically approach zero on one or both sides of the point corresponding to the minimum radius of convergence, are shown to be accurately retrieved if the minimum convergence radius is contained in the region of integration. The particular advantages of the technique are demonstrated by its application to soft x‐ray appearance potential spectroscopy.

ISSN:0034-6748    

DOI:10.1063/1.1686763

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A transparent pressure vessel made of diamond has been used to study Raman spectra under pressure. It has the advantage that the relative displacement of the pressurizing pistons can be used to determine directly the change of density of the sample and to determine directly the Gru¨neisen parameter, and it can easily be heated or cooled over a wide temperature range by a gas stream. The relative displacement of the piston can also be used to identify the phase being examined, which is particularly valuable when a substance with a complicated phase diagram is being studied. The Raman spectra of the translational vibrations of ammonium fluoride II and of the rotational vibrations of anthracene have been studied using the cell.

ISSN:0034-6748    

DOI:10.1063/1.1686764

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

This paper reports the development of a coupled laser scanning electron microscope system that enables a laser beam to be introduced into the microscope sample cavity and permits active‐mode monitoring of surface modifications during or subsequent to laser pulsing. Instrumentation is also incorporated within the system design for measuring laser induced pressures and equivalent laser coupling coefficients in target materials.

ISSN:0034-6748    

DOI:10.1063/1.1686765

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An ultrasonic technique for precise measurement of sample length changes under pressure has been developed. The sample is immersed in mercury, and the length of the mercury column below the sample is measured by an ultrasonic interferometric method to give the length change of the sample relative to the steel container. The length change has been measured and the bulk modulus obtained for PMMA (polymethylmethacrylate) up to a pressure of 10 kilobars. An error analysis indicated that the principal sources of error are temperature changes during the experiment, and nonreproducible acoustic coupling effects at the mercury boundaries.

ISSN:0034-6748    

DOI:10.1063/1.1686766

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An understanding of the nature of the chemical processes occuring in dynamic, reactive, gaseous systems, such as hydrocarbon flames and chemical lasers, requires knowledge of the chemical species that actually exist in these systems. This paper reports the design and use of a flow‐type reactor tube which is passed through the ion source of a mass spectrometer permitting the components of a reacting gas phase system to be extracted adiabatically through a 10 &mgr; orifice into the ion source for analysis. The procedure for drilling this orifice with a focused CO2laser is presented, together with data which indicate that the reactive species extracted from a flame zone are representative of those existing within the reactive system.

ISSN:0034-6748    

DOI:10.1063/1.1686767

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

We describe an original and easy method to measure the microwave conductivity of semiconductors as a function of frequency (up to 140 GHz) and high electric field. This method does not need impedance measurements of the semiconductor and is based on the comparison of thermal and high field effects; measurements are equally possible as a function of lattice temperature. It may be used with sufficiently low‐doped semiconductor materials. In the case of silicon, measurements are possible for 1 <pDC<50 &OHgr;cm. An example of results is given for 10 &OHgr;cm n‐Si at 300 K and for frequencies equal to 10, 35, and 70 GHz.

ISSN:0034-6748    

DOI:10.1063/1.1686768

出版商:AIP    

年代:1974

数据来源: AIP