摘要:

This article presents a realization of electronic circuit to examine the dynamics of the rate equations for a directly modulated semiconductor laser. The dynamic transitions are characterized by observing the phase portraits and time evolutions of photon density and carrier density. Under the proper conditions of modulation depth and modulation frequency, the system reveals the period doubling route and bistability in various resonant regions. These are also confirmed by the numerical simulations.

ISSN:0034-6748    

DOI:10.1063/1.1142654

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This article reports on the high‐resolution performance of the grazing‐incidence plane grating monochromator SX700/II, installed at BESSY by the Freie Universita¨t Berlin, in the photon energy range from about 40 to 900 eV. The high resolving power up to 10 000 achieved with this monochromator is based on improving the figure error of the ellipsoidal focusing mirror, on reducing the vertical dimension of the beam source, and on employing a 5‐&mgr;m exit slit. We report on high‐resolution gas‐phase studies in the double‐excitation region of He, as well as at core‐excitation thresholds of Ne, Ar, Kr, and Xe in the photon‐energy range from &bartil;45 eV to &bartil;900 eV. In addition, high‐resolution core‐excitation spectra at theKthresholds of C, N, and O are presented for gas‐phase CO, N2, and O2. In all cases, high‐nRydberg states and/or vibrational sidebands of the electronic excitations were resolved. The various contributions to the present instrumental linewidths are discussed as well as the prospects for further improvements in resolution with this monochromator.

ISSN:0034-6748    

DOI:10.1063/1.1142615

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A preamplifier has been built for use within a cryogenic system operating at a temperature of 2 K. The input stage is a 2N6483 JFET operating near 100 K. The equivalent input noise is less than 8 nV/Hz1/2at a frequency of 10 Hz.

ISSN:0034-6748    

DOI:10.1063/1.1143776

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This article gives the results of an experimental and theoretical investigation into the use of a laser diode and an edge‐emitting light‐emitting diode for pulse‐position modulation. Major factors affecting the maximum peak power are discussed, various aspects of the failure mechanisms occurring are reviewed, and experimental results are given. A model to calculate laser diode temperature under pulse conditions is presented.

ISSN:0034-6748    

DOI:10.1063/1.1143786

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The design and construction of a dielectric cell, used in time‐domain reflectance measurements at low temperature and high frequencies, are presented. Criteria are developed for cell construction, based on a transmission line model of bilinear form, and are applied to the physical construction of the cell. Bilinear parameters are derived for the cell model and compared with parameters calculated from short circuit measurements of two cells differing in design.

ISSN:0034-6748    

DOI:10.1063/1.1143721

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A new low‐energy electron diffraction (LEED) system has been constructed with a pulse counting position sensitive detector using channel plates and a wedge and strip anode. The detector accepts diffracted electrons over a 120° angle and the LEED pattern is recorded as a 256×256 pixel image. Individual LEED spot intensities can be measured up to a maximum linear count rate of ∼5 kHz while the dark count rate is ∼0.02 Hz, yielding a dynamic range greater than 105. Incident beam currents for LEED measurements are ∼1 pA. Diffuse LEED intensities from disordered systems can be measured using the large dynamic range of this instrument. Examples of diffuse LEED measurements are presented. The low incident beam currents also allow for LEED intensity‐voltage measurements on surfaces sensitive to electron beam damage and on nonconducting surfaces.

ISSN:0034-6748    

DOI:10.1063/1.1143196

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetriesAto the values they would have for scattering from single atoms. These extrapolations involve the dependence ofAon either the gold film thicknesstor the maximum detected electron energy loss in the target &Dgr;E. Using a concentric cylindrical‐electrode Mott polarimeter, we have studied and compared these two types of extrapolations over the electron energy range 20–100 keV. The potential systematic errors which can result from such procedures are analyzed in detail, particularly with regard to the use of various fitting functions in thickness extrapolations, and the failure of perfect energy‐loss discrimination to yield accurate polarizations when thick foils are used. A critical discussion of previous work on this subject is presented.

ISSN:0034-6748    

DOI:10.1063/1.1143118

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A technique forinsitumeasurement of surface height variations in the scanning electron microscope (SEM) has been developed. Based on the comparison of images of microscopic areas obtained by tilting the electron beam, cross correlation is used to determine the image shift between like features in the stereo pair which is then used to dynamically correct the height of the tilt axis and lens focus in a feedback loop. This paper describes the principle of the method and its implementation using a commercial electron‐optical column. Experimental determination of measurement accuracy and examples of line scan profiling and three‐dimensional mapping are presented. Developments in instrumentation to further improve both accuracy and measurement speed are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143057

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A novel time‐of‐flight (TOF) mass spectrometer configuration has been designed which can be interfaced to a continuous ion beam source produced by atmospheric pressure ionization. The TOF device uses a beam deflection method to sweep the ion beam past a slit placed near the ionization source in order to generate a start pulse for TOF detection. The beam sweep technique is modeled by computer simulation and optimized for the various experimental parameters. Nonvolatile samples are injected into the TOF device using liquid injection into a glow discharge atmospheric pressure ionization source in helium. A resolution of at least 519 atm/z311 is obtained, which is limited by the experimental parameters available in our experiment. The mass resolution is computer modeled and it is shown that as the mass increases, the experimental constraints become less important, and the resolution will increase. It is predicted that using the correct experimental conditions and with the addition of an ion reflector that resolution of well over 1000 should be obtained.

ISSN:0034-6748    

DOI:10.1063/1.1143027

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The conventional tunneling spectrometer gives the uncalibrated second derivatived2V/dI2versus applied voltage (V) of the junction current‐voltage curve (I‐V). However, the calibrated second derivatived2I/dV2is more useful for accurate comparison with theory and can be applied to negative resistance devices. We report here a single electronic instrument for calibrated measurements of all relevant tunneling junction parameters, i.e., dynamic conductance (G), dynamic capacitance (C), current‐voltage curve, and its first and second calibrated derivatives. Moreover, it can measure the derivative of the dynamic capacitance (dC/dV) versus applied potential, which is useful for various types of semiconductor devices. This design is versatile enough to find many laboratory applications where current‐voltage curves are of interest. The circuit, based on a simple design, is accurate to 1% and allows spectral acquisition in about 15 min.

ISSN:0034-6748    

DOI:10.1063/1.1143003

出版商:AIP    

年代:1992

数据来源: AIP