Constant Incidence Angle Research Articles

The three-step model in electron spectroscopy revisited I. Angular distribution of Auger electron emission from non-crystalline Al, Si and Cu surfaces

Measurements are presented of the Auger electron intensity emitted from non-crystalline Al, Si and Cu samples as a function of the emission angle, for a constant angle of incidence of the primary electrons. For this particular geometry, all features in the experimental angular distribution are completely attributable to the processes playing a role in the electron escape. It is found that surface roughness and electron refraction at the potential barrier do not affect the shape of the angular distribution. The angular distribution of the high energy core lines (CCC) are perfectly described by a cosine distribution. A distinct deviation of this behaviour is observed for the low energy valence band (CVV) transitions that is caused by the influence of surface excitations. Analysis of reflection electron energy loss spectra (REELS) demonstrates that for energies≳1000 eV, the increase of surface excitations when going to more oblique emission angles is compensated by a decrease in the probability for bulk excitations. This complementarity of surface and bulk excitations is not perfect at lower energies and leads to a significant net effect of surface excitations. In particular, it is empirically found that the CVV angular distribution is consistent with the simple model in which it is assumed that bulk inelastic collisions occur homogeneously throughout the semi-infinite solid.

Variable-azimuth laser ablation: principles and application for film deposition on long tubes and tapes

A new development of the pulsed laser ablation (PLA) technique based on variable azimuth ablation (VAA) is reported. The VAA itself is based on periodic variations of the azimuth of the laser beam relative to the target at a constant angle of beam incidence. Such variations result in a suppression of cone–valley surface structures which tend to develop in the case of a fixed azimuth. VAA leads to high-level stabilization of the laser plume during a long-term deposition process. As a result, the VAA method stabilizes the deposition rate with a tolerance of only 3–6% instead of a 90% decrease in the rate as in conventional PLA. Different possibilities for the realization of the VAA technique based on 2- and 3-way target scans are discussed. In the case of large areas, VAA technique with a meander beam target scan is capable of the deposition of high-quality multicompositional superconducting films on tubes and tapes more than 1 m in length.

Aspheric collimator for a point source x-ray lithography system

X-ray point sources are an interesting alternative to synchrotrons for small to medium scale production. These sources are by nature highly divergent, and thus require the use of collimation for delivering an acceptable lithographic illumination. We present the design of an aspheric collimator for a point source such as a dense plasma focus system. Designing a collimating mirror for a point source presents different challenges than designing one for a synchrotron source, although both cases require that the radiation be condensed and collimated to deliver the radiation with 1%–2% uniformity and acceptable runout over a large field area. The collimator is 3 cm wide and 31 cm long, accepts 20 mrad in the vertical and 70 mrad in the horizontal, and delivers the x-ray flux to a 3 cm×3 cm field on a mask located 3 m from the source with a runout of 6 mrad. The figure is an asphere, not dissimilar to those developed previously. The scanning mechanism, however, is radically different, since the virtual rotation point is located at the source, rather than at the mirror pole. This design provides excellent uniformity since the mirror is always scanned inside the radiation cone while maintaining a constant nominal incidence angle. The design principles and predicted performance are discussed in detail, together with a consideration of the manufacturing challenge for such a mirror. The collimator design presented has the capability of delivering the required power density and collimation from an x-ray point source to satisfy the requirements of x-ray lithography.

Multitemporal Land-Cover Classification Using SIR-C/X-SAR Imagery

The dual-flight program (April and October) for the SIR-C/X-SAR instrument aboard the shuttle Endeavor was designed expressly to acquire Synthetic Aperture Radar (SAR) imagery at two significantly different seasons. At the Michigan Forests Test Site (MFTS), the April mission occurred at the beginning of the spring thaw and the October mission occurred just prior to and during the fall color change. Four scenes are evaluated at a constant incidence angle. Seven features are extracted from the SAR data for potential use in classification using powers at different frequencies and polarizations. Given multiseason SIR-C/X-SAR imagery, there are three possible approaches in the classifier development: 1) Under the assumption that the scene does not change significantly as a function of time, develop one classification for a set of x scenes using n features, with x times the number of samples per feature; 2) ignore the multiseason availability and develop independent classifications for each scene using n features; 3) develop a true multitemporal classification where N of features equals n (number of features) times x (number of scenes). Each of these is applied using a combination knowledge-based and Bayesian classifier. Level II (roughly forest community) results show that the true multitemporal April/October classification works very well (97%), as do those for the individual scenes (>90%). A pooled classifier works poorly (April=90%, October=77%) and shows that temporal changes in phenology and moisture conditions contribute significant noise in terrain classification.

Comparison between cross-track and conical scanning microwave window channels near 90 GHz

The principal objective of this study was to determine the angular characteristics of the cross-track 92-GHz window channel of the SSM/T-2 microwave water vapor radiometer (T-2) over the ocean surface and to relate measurements from this instrument to corresponding 85-GHz window channel measurements from the conical scanning SSM/I imager. The conical scanner views at constant incidence angle and fixed polarizations, whereas the cross-track instrument scans across incidence angles with changing polarization. A model, based on radiative transfer calculations and Fresnel surface parameterization, successfully interrelated signals from the two radiometers as a function of T-2 scan angle for a significant fraction of the oceanic measurements. This confirmed the angular dependence model and provided a general relationship between 92-GHz SSM/T-2 and 85-GHz SSM/I signals, which is applicable in the absence of depolarization by rain, clouds, or severe sea surface roughness. Intercomparison between instruments, based on surface modeling, may be useful for instrumental calibration, it may assist in evaluation of microwave transmission models, and it does provide a validity test for ocean surface emissivity parameterization and cloud clearing procedures.

Chirp-improvement of optical intersecting-waveguide switch/modulators by electrode curvature

Introduction of slight exponential curvature into the electrode shape of optical intersecting-waveguide switch/modulators is proposed as the means of improving their frequency-chirping behavior. The improvement is achieved by adjusting the electrode curvature to make it pose a constant angle of incidence to all plane-wave spatial components of the guided mode. This results in reduction of the phase disturbances associated with the total reflection process and the frequency-chirping is, consequently, lowered.

Exit traverse study of mixed-flow turbines with inlet incidence variation

This paper reports a traverse survey of the flow conditions at the exhaust pipe of two mixed-flow turbines. The experimental method is described and the results discussed. It shows that for both turbines, a shroud-hub flow migration might be generated within the blades at higher pressure ratios, which relieves the high blade loading at the shroud, and a flow separation from the suction side of the hub might occur at the lower pressure ratios. The turbine with ‘constant incidence angle’ rotor design suffered from greater swirl loss and a possible internal flow separation than the one with a constant blade inlet angle.

Atomic Force Microscopy Investigation of Noble Gas Ion Bombardment on InP: Effect of Ion Energy

Mirror-polished InP(100) samples, n-doped with S atoms to 4×1018 cm−3, were bombarded with neon, argon and krypton ions. The energy of the ions was varied from 0.5–5 keV at a constant angle of incidence at 41° with respect to the sample normal. The ion dose density for Ne+ was 1.8×1016 ions cm−2 and for Ar+ and Kr+ was 5×1016 ions cm−2. A low ion current density of 5×1013 ions cm−2 s−1 was used to minimize sample heating. The resulting topography development was investigated by atomic force microscopy (AFM). The topography development was quantified in terms of RMS (root-mean-square) roughness using the software of the AFM and analysed as a function of the energy of the bombarded ions. Atomic force micrographs showing various types of topography for some specific ion energies are presented. For each ion species there is a critical energy for which the surface roughness attains a maximum value.

Variations of LEED intensities with angle of incidence and the influence on spot profiles.

We have performed a systematic theoretical study of the effects of variations in the direction of the incoming electron beam on low-energy electron-diffraction (LEED) intensities for the surfaces Ni{111} and p(2\ifmmode\times\else\texttimes\fi{}2)C-Ni{111}. Large intensity modulations are observed for variations of the order of 5\ifmmode^\circ\else\textdegree\fi{} in the polar angle of incidence, and the R factor comparison between theoretical I-V curves rise to 1.0 (i.e., no correlation) after varying the polar angle by about 10\ifmmode^\circ\else\textdegree\fi{}--15\ifmmode^\circ\else\textdegree\fi{}. Such data can be used as an independent set of I-V curves to increase the energy range of LEED analyses. Another benefit of collecting data at off-normal incidence directions is that multiple R-factor minima can be shifted or eliminated by changes of 20\ifmmode^\circ\else\textdegree\fi{}--30\ifmmode^\circ\else\textdegree\fi{} in the polar angle. However, we could not see a clear improvement in the sensitivity towards the lateral positions of surface atoms for polar angles below 40\ifmmode^\circ\else\textdegree\fi{}. We have also studied possible effects on measured spot profiles for data taken by scanning through the incidence direction. Serious differences in the relative satellite intensities of split spots which are equal at constant incident angle and additional broadening and distortions of spot shapes could be found for certain angular scan ranges and energies.

Argon bombardment‐induced topography development on InP

AbstractInP (100) samples, n‐doped with S atoms to 4 × 1018 cm−3 and to 6 × 1018 cm−3, were bombarded by low energy (0.5 to 5 keV) argon ions. After bombardment, the surfaces exhibited the formation of small protrusions on the surface. These sputter cones appeared after an ion dose of the order of 1015 Ar+ cm−2. These cones grow slowly with increasing ion dose. At a constant dose, the sizes and density of these cones depended on the angle of incidence of the argon ions. At an ion incidence angle of approximately 41°, a maximum was obtained in the topography development. The sputter‐induced morphology had, at a constant dose density and angle of incidence, only a slight dependence on the energy of ions in the 0.5 to 5 keV range. Sputtering at the two lower energies (0.5 and 1 keV) resulted in an increase in the surface roughness compared to the higher ion energies. No synergic effects of simultaneous electron and ion bombardment were observed in the as‐factory received samples. When the angle of incidence of the bombarding ions was kept fixed, the degree of sputter‐induced surface topography remained constant for different relative orientations of the (100) InP substrates. Seeding cones were observed under appropriate conditions, but were not systematically investigated.

Matrix‐assisted laser desorption/ionization: Dependence of the ion yield on the laser beam incidence angle

AbstractSome basic properties of matrix‐assisted laser desorption/ionization (MALDI) have been investigated by varying the angle between the pulsed UV‐laser beam and the target surface, thus determining its influence on the MALDI process. The minimum deposited laser energy needed for protein ion production (the threshold energy) and the protein‐yield dependence on the laser energy have been determined for incidence angles between 35° and 60° with respect to the target surface normal. The measurements demonstrate that neither the threshold energy nor the dependence of the protein yield on the laser energy vary with the incidence angle within the range studied. Hence the corresponding parameters that involve the area of irradiation, namely the threshold laser fluence as well as the ion‐yield dependence on fluence have a cosine dependence on the incidence angle. Furthermore, the threshold energy at constant incidence angle scales with the mass of the analyte molecule for proteins in the range from 5700 to 66 000 u.

Band effects in the 5p levels of Ho(0001)

Recent band structure calculations have indicated that the 5 p core levels of the lanthanide metals may influence the bonding significantly. The authors have investigated this possibility with angle-resolved UV photoemission from the 5 p levels of Ho(0001), using synchrotron radiation. Spectra taken at normal and off-normal emission show a changeover in the relative intensities of the 5p1/2 and 5p3/2 peaks, and the spectra taken at equal emission angles either side of the surface normal (for a constant photon incidence angle) are found to differ significantly. As these phenomena would not occur if the 5 p levels were 'true' core levels, i.e. showing negligible dispersion, the authors conclude that they must have a significant bandwidth.

Direct visualization of monolayers at the air-water interface by Brewster angle microscopy

No light is reflected from the air-water interface under Brewster angle incidence if p-polarized light is used. With constant angle of incidence, the formation of a monolayer on the water surface modifies the Brewster angle condition, and light reflection is observed. Reflectivity-area isotherms of arachidic acid monolayers on pure water and on aqueous solution of different pH have been measured. Areas of different brightness due to different molecular density and/or refractive index in the monolayer have been recorded with a video system as micrographic pictures. This Brewster angle microscopy enables us also to detect monolayer inhomogeneities and the reversible formation of solid-phase domains upon compression of monolayers of DMPE

NV-6208: A midcurrent ion implanter with constant beam angle of incidence

Several ion implantation applications achieve superior yields when the ion beam strikes the wafer with a constant angle of incidence across the entire surface of the wafer. Batch end stations with mechanically scanned disks provide implants with constant incident angle, but may not be economical for low dose implants. A midcurrent implanter having a pick-and-place serial endstation has been designed to provide constant implant angle. The equipment utilizes a novel combination of electrostatic X– Y raster scanning with small mechanical movements of the target to achieve a constant beam incident angle. Scanning and target motion are servoed to beam current variations. Wafers of 200 mm diameter can be implanted at a rate of 250 per hour. A system description and performance measurement results are presented.

A Multiple Beam Synthetic Aperture Radar Design Concept for Geoscience Applications

The multiple beam synthetic aperture radar (SAR) has been presented as a superior alternative to conventional side-looking SAR designs for mapping earth resources from space. The multiple beam approach provides wide swath coverage at nearly constant incident angle while conserving peak power. These desirable system characteristics, however, are realized at the expense of additional signal processing. A design example illustrates the attributes of the multiple beam SAR in comparison to a conventional side-looking system. A novel beam formation processing architecture is shown which can provide simultaneous range compression while forming the beams. A configuration for the image formation processor is proposed and analyzed in terms of an analog implementation which can perform Doppler compression at speeds faster than real time. These implementation schemes indicate that on-board processing for the multiple beam SAR is possible.

Current Research in Geological Applications of Remote Sensing Techniques and Implications for Petroleum Geology: ABSTRACT

Exploration geologists have made extensive use of aerial photography and orbital Landsat imagery, primarily for purposes of structural mapping. The Landsat 4 spacecraft launched in July 1982 is carrying a new imaging instrument called the Thematic Mapper which represents a significant advance over earlier Landsat sensors. The Thematic Mapper possesses improved End_Page 546------------------------------ spectral resolution (seven spectral channels distributed throughout the visible and infrared portions of the electromagnetic spectrum), improved spatial resolution (30 × 30 m [98 × 98 ft] ground resolution), and improved sensitivity (256 gray levels in each spectral channel). Experimental studies with airborne Thematic Mapper simulators tentatively indicate that these measurement capabilities will have a major payoff in terms of our ability to detect variations in clay mineralogy and abundance, to map bleaching effects in surficial rocks and soils that may be produced by hydrocarbon seepage, and to detect variations in the distribution and vigor of natural vegetation that are also related to seepage phenomena. The improved spatial resolution of the Thematic Mapper will enabl photogeologists to identify smaller scale landforms and drainage features which will also contribute to improved structural mapping capabilities. Research is currently underway to determine the utility of Thematic Mapper measurements for geologic mapping in complex areas characterized by large relief and extensive vegetation. Recent experimental results have underscored the need for improved spectral resolution in the next generation of visible and infrared sensors. Radar imaging techniques also represent an important source of information concerning geological conditions at the earth's surface. Imaging radars artificially illuminate the earth at an angle of incidence and azimuthal direction that can be controlled by the radar operator. Variations in radar backscatter intensity observed at different angles of incidence are largely governed by areal variations in surface relief and roughness. Exploration geologists have made extensive use of airborne radar surveys for terrain analysis and structural mapping, particularly in tropical environments. However, it is difficult to obtain quantitative information on surface roughness conditions from airborne surveys because of the large variation in incidence angle that occurs across the radar's ground sw th. Spaceborne radar systems offer the unique advantage of being able to illuminate large areas at a nearly constant angle of incidence due to their much greater elevation above the earth's surface. A Shuttle Imaging Radar Experiment (SIR-B), which will be conducted in August 1984, is designed to acquire multiple images of selected regions at different radar incidence angles. In principle, the coregistration of these images will enable researchers to differentiate surficial materials on the basis of their roughness characteristics in much the same way that multispectral measurements at visible wave-lengths are used to detect variations in surface pigmentation. Experimental studies tentatively indicate that variations in surface roughness detected in orbital radar surveys can be related t subtle differences in the lithology of sedimentary rock units. Orbital radar techniques may provide an important new tool for mapping facies variations within sedimentary basins. Additional orbital experiments are being planned during the latter 1980s to evaluate the geological utility of radar imagery obtained at multiple frequencies and multiple polarizations. End_of_Article - Last_Page 547------------

The total reflection of light at smooth and rough silver films and surface plasmons

Measurements of the reflection of thin silver films are reported which have been performed with the ATR method at constant wavelength λ as well as at constant angle of incidence θ. The backbending of the reflection minimum as a function of θ at constant λ is discussed. The influence of the interband absorption determines the R(θ,λ) dependence. Surface roughness displaces the turning point in the backbending curve.

Influence of surface roughness on the reflection of gold films in the region of surface plasmon excitation

The reflection ( R) of light at rough gold films has been measured in the region of surface plasmon (SP) excitation and compared with a smooth gold film. The SP resonance minima are shifted to larger wavevectors and their halfwidth is enlarged with increasing surface roughness. Different positions of the reflection minima were observed measuring R(Θ) at constant wavelength λ, and measuring R(λ) at constant angle of incidence Θ. The calculated values prove this observation.

Medium energy electron diffraction on aluminum

Measurements of the specular beam intensity in the medium range of energy (645 eV and 980 eV) are presented for the aluminum (001) and (110) surfaces. They have been performed with a LEED goniometer allowing to achieve high accuracy in the determination of the angular parameters of the diffraction experiment. The experimental results are displayed in the form of iso-intensity maps in (θ, φ) coordinates at a constant primary beam energy. θ denotes the colatitude angle of incidence and is varied in the range 30° to 80°. φ denotes the azimuth and is varied between 0° and 360°. Sections of the maps at constant angle of incidence are known as rotation diagrams. A model calculation ignoring intra-layer multiple scattering, but incorporating inter-layer multiple scattering processes shows the prominent role of the latter, in many cases, and the non-negligible contribution of the former in other cases. Sections of the maps at constant azimuth are called incidence-profiles. They are very sensitive to the azimuth and very hard to compute. Using the preceding model calculation, average incidence profiles have been computed, using as input parameters the refractive and absorptive potentials and the surface normal relaxation parameter obtained by a pseudo-kinematic analysis of experimental average incidence profiles as explained in another paper. The peak position and width have been compared to those obtained from the pseudo-kinematic calculation. From the result, it is shown that if averaging is performed according to a specific set of restrictive rules, the pseudokinematic analysis of the data has a semi-quantitative meaning.

The QMG/2, a magnetic spectrograph for nuclear research

A new magnetic spectrograph, the QMG/2, has been designed for the Kernfysisch Versneller Instituut, Groningen. It is similar to the Q3D spectrographs in use at several nuclear physics laboratories but includes some new features. Among these are a second multipole, a straight focal plane, constant dispersion, constant angle of incidence (45°) on the detector, and a device called a “snake” used to adjust mechanically the effective shape of the field boundaries after manufacture.