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Volume 53, Issue 6, 01 June 1982

Charge collection scanning electron microscopy
View Description Hide DescriptionThis review encompasses the application of the scanning electron microscope to the study and characterization of semiconductor materials and devices by the Electron Beam Induced Conductivity (EBIC) method. In this technique, the charge carriersgenerated by the electron beam of the microscope are collected by an electric field within the material and sensed as a current in an external circuit. When employed as the video signal of the SEM, this collected current image reveals inhomogeneities in the electrical properties of the material. The technique has been used to determine carrier lifetime, diffusion length, defect energy levels, and surface recombination velocities. Charge collection images reveal the location of p‐n junctions, recombination sites such as dislocations and precipitates, and the presence of doping level inhomogeneities. Both the theoretical foundation and the practical aspects of these effects are discussed in a tutorial fashion in this review.

Estimation of wavenumber and frequency spectra using fixed probe pairs
View Description Hide DescriptionWe introduce the concept of the local wavenumber and frequency spectral density, which can be estimated using spatially fixed, point data sources (’’fixed probe pairs’’), and discuss the relationship of this spectral density to the conventional wavenumber and frequency spectral density and the cross‐power spectral density. The local wavenumber and frequency spectral density is shown to be equivalent to the conventional wavenumber and frequency spectral density when the fluctuation is stationary and homogeneous and consists of a superposition of wave packets; such a fluctuation is the basic model used in many turbulence theories. A digital method for estimating the local wavenumber spectrum is described and applied to the study of drift‐wave turbulence in an rf‐excited discharge. The statistical dispersion relation and wavenumber spectral width, computed from the local wavenumber and frequency spectrum of the drift‐wave turbulence, are compared with the conventional spectral moments computed using the correlation method of Iwama and Tsukishima; good agreement is found over a wide range of frequency. A frequency‐integrated wavenumber spectrum is computed; both frequency and wavenumber spectral indices are found independently. The local wavenumber and frequency spectrum is a completely new approach to the use of fixed‐probe data, and we believe it can greatly extend the quantity of information available from fixed probes, which are the principle tools in many, if not most, fluctuation experiments.

Electrically resonant transducer for a gravitational wave antenna
View Description Hide DescriptionOne of the leading problems in gravitational wave detection is the construction of an optimized transducer capable of reaching the predicted sensitivity limit set by the amplifiernoise. Existing transducers, when used with ultra‐low noiseamplifiers, are far from this limit. In this paper, electrical tuning is proposed to improve the match between the mechanical oscillator and the amplifier in the case of an inductively coupled electromechanical transducer. A detailed calculation of the sensitivity of this device is carried out. This calculation shows substantial improvement over the untuned system. The requirement on the tuning is shown to be noncritical. The most severe requirement is the one imposed by the electrical losses in the resonating capacitor.

Measurement of thermal diffusivity using a pyroelectric detector
View Description Hide DescriptionA new method of measuring the thermal diffusivity of thin layers has been developed and applied to the characterization of laminated structures. The thermal diffusivity is measured using pyroelectric detection of a laser generated thermal pulse propagating through the sample. The shape of this pulse is governed by the thermal properties of both the sample and the detector. However, the thermal diffusivity of the sample can be determined from the position of the peak in the pyroelectric signal and the sample thickness. This method can be applied to thermal diffusivity measurements of thin or thick films, laminates, and thermal greases.

Studies of three‐cylinder electrostatic mirrors and lenses
View Description Hide DescriptionWith the aim of using it in mass spectrometry, we have tried to find an axisymmetric electrostatic system with very particular characteristics, viz. reduced spherical and chromatic aberrations. We chose a system made up of three coaxial cylinders of radius ρ. The inner electrode is 0.90 ρ long and is separated from the outer cylinders (which are taken to be of infinite length) by two identical gaps of 0.40 ρ. This system has been studied from both the mirror and the lens point of view. The mirror is studied using two electrostatic parameters. The potentials of the three cylinders are reffered to as V _{1}, V _{2}, and V _{3}. The first parameter used is R _{ d }=100 (V _{1}−V _{2})/(V _{1}−V _{3}) and the second is V _{3}/V _{1}. For six values of R _{ d }, ranging from 100 to 74, we examine the paraxial characteristics and the coefficients of spherical and chromatic aberration as a function of V _{3}/V _{1}. We only deal with the area where the mirrors are convergent and where the radii of curvature do not exceed 10ρ. For the values of R _{ d } studied, other than 100, we use a field of variation from −0.10 to −0.50 for V _{3}/V _{1}. When we study the lens, we deal with the area where the outer potentials V _{1} and V _{3} are identical. There is thus only one variable, the ratio V _{2}/V _{1} of the potentials of the first two cylinders. We consider two cases: V _{2}/V _{1}≳1 and V _{2}/V _{1}<1. Among the results obtained, we have chosen two groups of mirrors for which the chromatic aberration coefficient C _{ c } is null and whose radii of curvature are greater than 6.60 ρ, a group of mirrors for which the spherical aberration coefficient C _{ s } is null and where C _{ c } is greatly reduced (here the radii of curvature are greater than 4.00 ρ), and a mirror for which both C _{ c } and C _{ s } are null and which has a radius of curvature of 7.28 ρ.

Knock‐on particle preheat in ion beam fusion targets
View Description Hide DescriptionThe elasticscattering of beam ions is shown to cause a potentially damaging flux of penetrating secondary knock‐on particles. These secondary particles will be more penetrating than the primary ions if the atomic mass of the primary is larger than the secondary. A calculation, using the specific example of helium ions incident on an absorbing material containing hydrogen, reveals that the knock‐on protons have a range greater than five times the range of the primary helium ions, and can cause a preheat problem. Thus, this effect is shown to be an important design consideration.

Concept for energy‐storage rings at 10–100 MJ
View Description Hide DescriptionA concept is considered for storing 10–100 MJ of electrical energy in a relatively lightweight and compact device. Energy is stored as electron kinetic energy confined in the vertical betatron field of a toroidal ring. Electrons are injected into a ring at full voltage but low current and low power. The stored electron energy is released on a fast time scale. Synchrotron radiation, wall fields, and instabilities constrain the energy that can be stored in each ring.

Motional side‐band resonances in the microwave spectrum of stored ions
View Description Hide DescriptionSide‐band resonances were investigated in the radio‐frequency (rf) spectrum of free ions stored in a radio‐frequency quadrupoleion trap. The magnetic resonance signals occur at the center frequency and at the center frequency plus or minus integral multiples of the characteristic ion macromotion frequencies. The experiment was performed on ^{3}He^{+} using the ion storage exchange collision technique. Contributions of the side‐band intensity arose predominantly from the standing microwave field inside the cavity. The effect of a small traveling wave component was also included. The microwave field was fed into the trap structure which, in addition to being used for trapping, was also employed as a broad band cavity in the TE_{013} mode. The dependence of the intensity distribution of the side‐band spectrum on different ion motion temperatures and energy distributions of the ions was studied numerically. It was demonstrated experimentally that initially the stored ions have a uniform energy distribution. Since the stored ion cloud samples different microwave fields at different times, the induced perturbation of the microwave field is spread out in frequency and a correlation function approach is suitable to interpret the side‐band spectra. The present experiment was carried out in the microwave region where narrow‐band coherent radiation fields are readily available. However, the same side bands should also occur in the optical spectrum of stored ions and are of interest to laser cooling experiments.

Motion of ions in the Kingdon trap
View Description Hide DescriptionThe classical and quantum motion of ions in a Kingdon trap (Orbitron) is studied for nearly circular orbits. The frequencies of small axial and radial oscillations are derived for both the logarithmic potential and the actual potential. A numerical comparison with the asymptotic approximation and with exact energy eigenvalues shows that the small oscillation method is adequate for most purposes.

Magnetic induction of ferromagnetic spherical bodies and current bands
View Description Hide DescriptionThe method of separation of variables has been applied to derive the magnetic fields of four magnetostatic field problems. Three problems consist of infinitesimally thin spherical current bands and a ferromagnetic spherical shell. Two of these configurations have a magnetic spherical shell with an internal or external current band and the third has a spherical shell with both internal and external current bands. A fourth problem consists of a magnetic sphere with an external current band of finite width. Calculations of the magnetic field for sample problems are presented. The solutions are intended for analysis of the magnetizing behavior of ferromagnetic substances and have applicability in electrical machinery and magnet design.

Magnetic induction of ferromagnetic prolate spheroidal bodies and infinitesimally thin current bands
View Description Hide DescriptionThis paper discusses the solution of the vector Laplace’s equation using the method of separation of variables to determine the magnetic field of three systems consisting of infinitesimally thin prolate spheroidal current bands and a ferromagnetic prolate spheroidal shell. Two configurations consist of a ferromagnetic spheroidal shell with an internal or external current band. The third configuration consists of a spheroidal shell with both internal and external current bands. The solutions are limited to dc currents and linear shell materials. They provide a method for calculating the interaction between the ferromagnetic material and the current band for symmetric and nonsymmetric current bands and a prolate spheroidal shell.

Ion beam exposure characteristics of resists: Experimental results
View Description Hide DescriptionThe exposure characteristics of six polymer resists to 1.5 MeV H^{+}, He^{+}, and O^{+} ions and to 20 keV electrons were measured. The resists used were polystyrene (PS), polymethyl methacrylate (PMMA), PMMA mixed with 20% of a copolymer of vinyl acetate and vinyl chloride (VMCC), poly(glycidyl methacrylate‐co‐3‐chlorostyrene) (GMC), poly(butene‐1‐sulfone) (PBS), and a novolac. The deposited energy per unit volume required to expose a resist was found to be a function of the spatialenergy dissipation rate of the ion in the resist. This has been accounted for in terms of the nature of the energy distribution around the primary particle track in conjunction with whether the resist requires the activation of a single site or two adjacent sites to produce exposure.

Amplification of frequency upshifted radiation by cold relativistic guided electron beams
View Description Hide DescriptionAn amplifier on cold, relativistic, guided electron beams is considered. The problem is reduced to a set of first‐order, linear, ordinary differential equations. The dispersion relation governing the stability of the system is derived and its solutions are studied numerically. The results of the calculations show that in the submillimeter regime, the spatial growth rates in the system may be comparable to those predicted for Raman‐free electron lasers.

The dependence of transversely excited atmospheric CO_{2} laser performance on circuit configuration
View Description Hide DescriptionThe dependence of pulsed CO_{2} laser performance, in terms of efficiency and power output, on circuit configuration has been investigated. It has been shown that the type of circuit used to excite the laser can significantly affect its performance. The variation of laser output with circuit has been shown to be consistent with a change in the value of E/N at which energy is transferred into the glow discharge.

Plasma conditions required for attainment of maximum gain in resonantly photo‐pumped aluminum XII and neon IX
View Description Hide DescriptionWe present a detailed analysis of the plasma conditions required to optimize gain in two proposed x‐ray lasing schemes using resonant photo‐pumping. In one proposed configuration, the Si XIII line 1s ^{2}‐1s2p ^{1} P at 6.650 Å pumps Al XII 1s ^{2}−1s3p ^{1} P at 6.635 Å, inverting the Al XII n = 3 and n = 2 levels which are separated by 44 Å. A similar approach which utilizes the Na X 1s ^{2}‐1s2p ^{1} P line at 11.00 Å would invert the n = 4, 3, and 2 levels of Ne IX. Conditions in the pumped neon and aluminumplasmas, and in the pumpingsiliconplasma, are calculated using a multistage, multilevel atomic model with multifrequency radiation transport. For modeling the pumpingsodium line we have inferred the intensity from a spectrum of a neon filled, laser‐imploded glass microballoon containing sodium impurities obtained at Rochester. The pump line intensities calculated for Si and inferred for Na are equivalent to blackbodies of 252 and 227 eV, respectively. It is found that peak gain for the 3‐2 lines of about 100 cm^{−1} occurs at ion densities of 10^{20} cm^{−3} and 4×10^{20} cm^{−3} in the pumped neon and aluminumplasmas, respectively. Temperatures required to maximize gain in the pumped plasmas are found to be 50 and 100 eV, for neon and aluminum, respectively. Finally, since the silicon and aluminum lines are slightly off resonance, we have investigated the effect of streaming the plasmas toward each other at various velocities to offset some or all of the wavelength difference. It is found that a streaming velocity of 6.8×10^{7} cm sec^{−1}—fully offsetting the wavelength difference—will approximately triple the achieved gain compared to the zero velocity case. Lesser increases in gain occur with partial velocity offsets.

Accelerated facet degradation of InGaAsP/InP double‐heterostructure lasers in water
View Description Hide DescriptionFacet degradation of InGaAsP/InP double‐heterostructure (DH) lasers in accelerating environment of water was studied from the standpoint of quantitative comparison with GaAlAs DH lasers. Facet degradation of InGaAsP/InP DH lasers proceeds by oxidation mechanism and its degradation rate is 2–3 orders below that of GaAlAs DH lasers. The difference of oxidation behavior between InGaAsP/InP and GaAlAs DH lasers was examined by using large wafers having the same composition as lasers. The following results were obtained: the oxidation proceeds with the inward diffusion of molecule water through the oxide film, the oxidation rate of n‐InP is more than two orders of magnitude lower than that of n‐GaAs, In oxide and P oxide were uniformly distributed in the depth profile of the oxide for InP and InGaAsP, and As oxide has the abnormally depleted distribution in the front layer of the oxide for GaAs and GaAlAs. The facet degradation rate is influenced by some experimental factors, i.e., the optical output power, the injection current in dc‐biased experiment, and the water temperature in unbiased experiment. To explain the degradation behavior caused in dc‐biased and unbiased experiment under identical mechanism, we attempted to evaluate the degradation rate as a function of the facet temperature; the optical output power and the injection current in dc‐biased experiment were assumed to contribute to the supplying source of carriers, which rapidly recombine nonradiatively, raise the facet temperature, and finally promote the diffusion of molecule water through oxides and the reaction rate at oxide‐facet interface. Combining these results with the fact that the oxidation rate varies in proportion to the partial pressure of a molecule water in the operation environment, we estimated the degradation rate of InGaAsP/InP DH lasers operated under 6.7 mW/μm^{2} at 70 °C in a nearly dry nitrogen environment (relative humidity of 1–10%).

The coupling of continuous‐wave laser radiation into painted aluminum‐alloy plates
View Description Hide DescriptionThis paper describes a model for the physical behavior of a painted surface when irradiated by a high‐energy laser. The model proposes that the paint degrades to a residue which adheres to the surface and whose optical and thermal propertiescontrol the coupling of the radiation to that surface Experimental observations are presented which confirm the theoretical predictions of the model. Measurements of the intensity‐dependent absorptance of the surface of painted A12024 alloy plates agree with calculated values when appropriate values of the thermophysical properties of the paint residue are chosen.

Plasma KrF laser pulse compressor
View Description Hide DescriptionThe use of a plasma medium for the compression of KrF laser light to pulse widths suitable for laser‐driven fusion applications is described. The results indicate that efficient pulse compression can be realized. A particular feature is the absence of the troublesome backward second‐Stokes wave found in gas cell compressors.

Temperature dependence of the refractive index of strontium titanate and prism coupling to lithium niobate optical waveguides
View Description Hide DescriptionThe temperature dependence of the refractive index of SrTiO_{3}, near room temperature, has been found to be −5.1×10^{−5} °C^{−1} at 632.8 nm by a variation of the minimum deviation prism method. We found that this temperature dependence had to be included to account correctly for the observed temperature sensitivity of coupling light to lithium niobateoptical waveguides with strontiumtitanateprisms.

Characterization of surfaces by deconvolution of ultrasonic echoes using extended bandwidth
View Description Hide DescriptionFrom deconvolution of the echo scattered by a surface, it is theoretically possible to obtain the impulse response of this scatterer. In some cases, this response can be closely related to the geometry of the scatterer and can be used for its characterization. In practice, even in the field of ultrasonic spectroscopy, the transducers always exhibit a finite bandwidth. We suggest a method for extending the Fourier spectrum which leads to better results after deconvolution. The experiments are performed with targets consisting either of small plane surfaces with various shapes, or of large randomly rough surfaces. The results are in good agreement with those expected using the Kirchhoff‐Helmholtz approximation.