bluuebunny/crossref_metadata_2025 huggingface dataset:
Satellite Remote Sensing for Earth System Science: NASA's Earth Observing System (Eos)
Authors: Curran Robert J.
Published: February 2023

Environmental concerns of a global nature are influencing the development of a multidisciplinary approach to understanding the Earth as a system. In recent years these concerns have become more prominent due to a series of problems involving large geographic regions such as; understanding the effects of the increases in carbon dioxide, understanding the causes and consequences of changes in the ozone layer, and resolving the anthropogenic influence on the acidity of precipitation. Clearly the global scope of these and other problem areas requires both a multidisciplinary, as well as a multinational approach for their solution. In order to address these problems, observational capabilities must be employed ranging from in situ and laboratory measurements to satellite based global remote sensing. An Earth Observing System (Eos) is planned to meet many of these requirements for remote sensing from low Earth orbiting satellites. A number of instruments are under consideration as the payload for the sun-synchronous satellite platforms. The payload is conceptually grouped into three packages to illustrate the synergistic relationships that exist among the instruments.
Time Resolved Lidar Fluorosensor for Oil Pollution Detection
Authors: Ferrario A. , Pizzolati P.L. , Zanzottera E.
Published: February 2023

This work is based on a preliminary experimental research made by researchers of JRC-Ispra1 according to which an airborne fluorosensor system, able to jointly perform a time and spectral analysis of oil fluorescence, is useful for the detection and the characterisation of oil spills on the sea surface. They have demonstrated that while spectral analysis alone can hardly enable to distinguish between two oils of the same class (for example two crude oils), the time-spectral analysis can easily discriminate between two oils with nearly the same spectral pattern.
A Simple Optical Method of Simultaneous Measurement of Characteristic Scales and Intensity of Atmospheric Turbulence
Authors: Zhukov A.F. , Nosov V.V.
Published: February 2023

For solving a large number of problems on optical radiation propagation in the atmosphere the atmospheric turbulent characteristics should be determined. There are the inner l
0
and outer L
0
scales of turbulence, structural characteristics of fluctuations of the refractive index

C
n
2

. The value of

C
n
2

determines the turbulence intensity. All these characteristics are the parameters in the spatial spectral density φ
n
(x). The function is given as [1,2] where x
m
=5,92/l0, x
0
=2π/L
0
. In the inertial subrange (x
0
≤ x ≤ x
m
) the model (1) coincides with the Kolmogorov spectrum of turbulence.
GASCOSCAN and GASCOFIL-Remote Sensing Gas Correlation Spectrometers for Tropospheric Trace Gas Measurements
Authors: Morrow W. H. , Nicholls R. W.
Published: February 2023

Correlation spectroscopy, which is a powerful diagnostic tool for the determination and monitoring of trace atmospheric contaminants, involves a correlative comparison between the features of a "field spectrum" of a specific region of the atmosphere, and the features of a "mask function" which is representative of the spectral absorption features of the molecular species of interest. The degree of correlation between these can be interpreted quantitatively as a direct measure of the column density of the species of interest in the instrumental field of view.
Enhanced Direct-Detection of CO2 Lidar Returns Using a Laser Pre-Amplifier*
Authors: Killinger D. K. , Button J. L. , McLellan E. J.
Published: February 2023

The relative merits and technical differences between direct-detection and heterodyne-detection for CO2 lidar are well known. Direct-detection offers enhanced information concerning the average intensity of the lidar returns but at the expense of reduced signal-to-noise level. Heterodyne detection requires an increase in system complexity, provides an enhancement in the S/N ratio of 4 to 6 orders of magnitude, but is limited in its ability to scan rapidly through several CO2 laser lines.
Raman Shifted Dye Laser for DIAL Measurements of Atmospheric Temperature, Pressure and Density
Authors: Singh Upendra N. , Mahon Rita , Wilkerson Thomas D.
Published: February 2023

In recent years Differential Absorption Lidar (DIAL) measurements in the A-band of molecular oxygen have been suggested1-5 as a means of profiling atmospheric variables such as temperature, pressure, and density. Laser sources of pulsed, tunable (760 - 770 nm) and narrow-bandwidth (0.02 - 0.03 cm-1) radiation, having a high degree of spectral purity (>99%) in this region of the oxygen A-band, are thus highly desirable. This paper reports on the current state of progress in our laboratory efforts in this field.
A Portable UV-DIAL System for Ground-Based Measurements of Lower-Stratospheric Ozone Profiles: Design and Performance Simulation
Authors: Rodgers M. O. , Stickel R.E. , Asai K. , Bradshaw J.D. , Davis D.D.
Published: February 2023

Recent developments in stratospheric chemistry such as the observation of a springtime "ozone hole" over the Antarctic1, have illustrated the need for a rugged, lightweight instrument for the determination of lower stratospheric ozone profiles over remote areas. Variations of the widely-used UV-DIAL methodology2 appear to provide the most promising approach to the development of such and instrument.
CO2 Laser Pre-Amplifier for Lidar Application
Authors: Chan Kinpui , Bufton Jack L.
Published: February 2023

A laser pre-amplifier based on the multiple-pass geometry inside a low-pressure, pulsed CO2 laser discharge has been developed for lidar applications near 10 μm wavelength. The laser pre-amplifier produces a gain pulse on the order of 100 μsec duration with peak power gains as large as 1000 (30db). Design considerations, predicted preformance, and initial laboratory test results for this laser pre-amplifier have been previously presented (refs. 1 & 2). In this paper we report the results of a series of laboratory tests on the pulsed gain and gain stability when this laser pre-amplifier is used with a CO2 TEA laser source. These measurements form the basis for application of the pre-amplfier to enhanced direct-detection in a CO2 lidar.
Laser Sources and Sensitivity Calculations for a Near-Infrared Dial System
Authors: Milton Martin J T , Jolliffe Barrie W , Partridge Roger H , Woods Peter T
Published: February 2023

The applications of DIAL systems operating in the near ultraviolet and visible spectral regions are limited to the small number of species that absorb in those regions. However, the infrared spectral region offers the possibility of detecting a much larger number of gases, including most of the hydrocarbons. Although many DIAL systems have been constructed for use in the mid-infrared (at 10 μm in particular), relatively few attempts1-4 have been made to use the near-infrared despite the large number of strong absorption lines, particularly around 3 μm. The design of a direct-detection DIAL system to operate in this region involves a considerable number of differences from DIAL systems operating in other spectral regions. We consider here: the spectroscopy of target gases, possible laser sources, and the sensitivity and accuracy that might be expected from such a system, with particular consideration to its use for measuring hydrocarbon concentrations at the ppm level in the atmosphere.
A Simple System for Frequency Locking Two CO2 Lasers
Authors: Draper Douglas C. , Holmes J. Fred , Hunt John , Peacock John
Published: February 2023

An optical heterodyne system requires a local oscillator which tracks the frequency of the transmitter. Otherwise the heterodyned signal, which has a frequency equal to the difference between the transmitted and local oscillator frequencies, would drift outside the bandwidth of the receiver.
The Ionization Threshold in Intense Field Multiphoton Ionization of Atoms
Authors: Pan Liwen , Sundaram Bala , Armstrong Lloyd
Published: February 2023

In recent studies of intense field above-threshold multiphoton ionization of atoms, the ponderomotive potential is introduced to explain the suppression of lower energy photoelectrons.1 This explanation, which we will refer to as PPT (Ponderomotive Potential Theory), predicts an increase of ionization potential with increasing laser intensity. When using linearly polarized laser light with an intensity of about 1013 W/cm2, and a wavelength of 1064 nm, this increase of the ionization potential will be about an eV.
Peak suppression in Above-Threshold-Ionization
Authors: Agostini P. , Petite G. , Yergeau F.
Published: February 2023

Recently, the Above-Threshold-Ionization (ATI) phenomenon has received much attention, in particular from theoreticians bringing up models to interpret the suppression of the low-energy part of the electron energy spectrum. In this respect, the reasons why some electron peaks should be suppressed can be classified in three groups: first, intensity effects which modify, in all models, the ATI probabilities and in some of them would induce strong Stark shifts of the ionization limit. Second, polarization effects: it has been proposed that in circular polarization, the high-angular-momentum final states, which are also the high-energy part of the spectrum, should dominate over the low-angular-momentum ones. Third, space charge effects, which could prevent the low-energy electrons from escaping from the interaction region. In this paper, after a brief review of the experimental and theoretical material, we present and discuss new experimental results obtained in a regime free of space charge effects, using a magnetic collection and time-of-flight technigue. In xenon at 1064 nm, the main results are: (i) the first peak of the ATI spectrum is suppressed at 5×10−2 W.cm−2 with linear polarization and at a lower value in circular polarization. For both polarizations, the peak suppression takes place at intensities much lower than the saturation intensity. For circular polarization, the effect of the centrifugal barrier which has been proposed recently is discussed, with the conclusion that it may enhance the peak supression which remain, fundamentally an intensity effect.
Multiple Charges Creation (Up to Xe6+) from Xe atoms by An Intense CO2 Laser*
Authors: Chin S.L. , Xiong W. , Lavigne P.
Published: February 2023

Experiments in recent years have shown that using an intense laser beam of intensities of more than 1013 W/cm2 (up to 1016 W/cm2) multiply charged ions of rare gas atoms were created with relative ease. The wavelengths of the lasers ranged from the infrared1,2 through the near i.r.3 and visible3 to the u.v.4. Most of the data indicated that a step-wise multiphoton process was responsible for the multiple charge creation.
Multiply charged ions and energy spectrum of electrons in multiphoton ionization
Authors: Lompré L.-A. , Mainfray G.
Published: February 2023

The different aspects of the multiphoton ionization of one-electron atoms are now well understood. They can be described by rigourous theoretical models in the framework of perturbation theory. Recently emphasis has been given to two new developments : (1) the production of multiply charged ions from many-electron atoms, (2) the investigation of electron energy spectra produced in multiphoton ionization of atoms.
Observation and Analysis of the Autoionizing Spectra of Sr
Authors: Sufen Hu , Sen Zhang , Jie Lu , Jizhen Qiu , Jiazhen Sun
Published: February 2023

The Sr atoms are excited stepwise by means of three dye lasers. All three lasers are linearly polarized in the same direction to allow the populations of the

(5p

1
2

ns)

J
=
1

or

(5p

1
2

nd)

J=1,3

. By sweeping the wavelength of the third dye laser we are able to record the excitation spectrum of the autoionizing states.
Ezekiel's Wheels as a Complex Halo Phenomenon
Authors: Hall Freeman F.
Published: February 2023

The biblical account of wheels in the sky, seen by Ezekiel, can be explained in almost all of its detail as a complex halo phenomenon.
Light Pillars from Nearby Light Sources
Authors: Mallmann A. James , Hock Jeffrey L. , Greenler Robert G.
Published: February 2023

When light from the sun reflects off the external faces of airborne ice crystals, patterns of light may appear in the sky. The parhelic circle and sun pillar are two specific examples. In this paper we present a discussion of the light pillars that are produced when ice crystals are illuminated by nearby light sources.
Measurement of the phase function of natural snow crystals
Authors: Winchester L. W.
Published: February 2023

The degradation of contrast in a snowy atmosphere can be explained by examining the phase function of natural snow crystals. The phase function determines the apparent broadening of a source as the radiation is scattered in the atmosphere. Since the orientation of the snow crystals as well as their size and shape must be considered when calculating scattering, the phase functions of various types of snow crystals are needed in order to compute the transmission through a snowy atmosphere. The snow crystal phase functions are also of importance in problems involving radiative transfer in cloud atmospheres as high altitude clouds consist mainly of ice crystals.
Descartes, the Rainbow and the Mythical 10 000 Calculations
Authors: Barmore Frank E.
Published: February 2023

I have noticed in several places the statements that Descartes calculated an enormous number of ray paths through a raindrop in explaining the rainbow1,2. The origin of this belief is unclear. A possible source may be the comment by Taylor3 in his physics text that Descartes "…traced some ten thousand rays through a drop…" in order to find the cause of the bow. However, Boyer4 notes that Grau5 made such a claim in the 19th century. Because this mistaken belief seems widespread it seems worthwhile to point it out yet again.
A Method for Showing Polarization Effects in Optical Sky Phenomena
Authors: Greenler Robert
Published: February 2023

We can observe polarization effects in optical sky phenomena by viewing the scene through a polarizing filter. Usually two orthogonal orientations of the filter will provide the greatest difference from polarizing effects. If the scene is photographed through each of these polarizer orientations, the resulting pictures should record much of the polarization information. To observe the polarization effects we can look for the difference in the two photographs. A projection device that emphasizes this difference is demonstrated.
Skylight Polarization During a Total Solar Eclipse: A Quantitative Description
Authors: Können G.P.
Published: February 2023

Although it is known since at least 19051) that the skylight polarization changes drastically when the totality of a solar eclipse starts, it lasted till 1961 till this effect was recorded instrumentally 2). Since then, only a few more instrumental observations have become available 3-7). However, the information obtained prior to 1973 is too limited for getting a quantitative understanding of the phenomenon, since the observers restricted their measurements to one single point in the sky, located at 90° from the sun in the solar vertical 2-6). This situation changed in 1973, when Shaw recorded a very complete set of sky radiance observations during the 30 June eclipse, which is still of an unmatched quality 7). His measurements included also a polarization scan in the solar vertical, so that we got for the first time a general impression of the state of polarization at eclipse conditions. It turned out that the degree of polarization during eclipse has a symmetry with respect to the zenith, with a minimum value in the zenith and a maximum polarization rather close to the horizon. This outcome fascinated me for years and I wondered if it is possible to calculate the polarization at eclipse conditions from Shaws on-side intensity measurements and his polarization measurements outside totality by means of a simple two-step scattering model. The results of an attempt for this are rather encouraging and presented in this lecture.
Polarization Properties of Light Pillars: Brewster Angle Effects
Authors: Sassen Kenneth
Published: February 2023

Nocturnal light pillar displays are not uncommon during conditions of very light snowfall when temperatures are well below freezing.1 Like the related reflection phenomenon of the sun pillar,2 light pillar occurrences demonstrate the presence of ice crystals oriented with their reflecting faces very nearly parallel to the ground. Assemblages of simple plate crystals, with their large basal faces, constitute the best scattering medium for these displays, provided that their sizes correspond to those which display stable fall attitudes.3 Sun and light pillars, however, have quite different structures as a result of the reflection geometries from light sources positioned essentially at infinity, and locally.4 Moreover, light pillars are perhaps unique among atmospheric optical displays in that they are anthropogenic and, since the observer is actually located within the cloud of crystals, it is a simple matter to study the nature of the particles causing the display.
Multiple Scattering Effects in Halo Phenomena.
Authors: Tränkle E. , Greenler R.
Published: February 2023

Halo phenomena comprise a surprisingly large variety of arcs and spots in the sky. Most of the observed phenomena are explained in the framework of geometrical optics by a single scattering of the sunrays at hexagonal ice crystals/1/. The repeated scattering of sunrays by two or three crystals is proposed to explain a few rarely observed phenomena like the cross in the sun region and the double structure of the subsun/2/. The trouble is that in most of these cases an alternative explanation can be given; i.e. the cross may be produced by diffraction scattering/3/.
Laboratory Simulation of Inferior and Superior Mirages
Authors: Greenler Robert G.
Published: February 2023

Mirages come in a wide variety of forms. For simplicity we divide them into two classes. Over a region of space where the air temperature decreases with height (as over a hot road or heated desert floor) light rays follow curved paths that are concave upwards. Such paths yield an upright image of a distant scene that appears to be below its actual position and hence is called an inferior mirage. Where the air temperature increases with height (as when warm air flows over a cold body of water) light-ray paths are concave downward. An upright image of a distant scene, in this case, appears above its real position, which we indicate by calling it a superior mirage. Of course, more complicated mirage effects can be observed when we look through a layered atmosphere which has a positive temperature gradient at some elevations and a negative gradient at others. Such complicated mirages may not fit neatly into our two classes. I will not discuss the elementary theory of the mirages here. Two Scientific American articles1,2 describe new ways to understand mirage phenomena, and the classical treatment can be found in a variety of texts; for example, see references 3-6.
Laser Interferometry and Laser Induced Fluorescence Studies of Laser Etching
Authors: Dreyfus R.W. , Walkup R. , Jasinski J.M.
Published: February 2023

Excimer laser ablation of solids with laser power densities in the range 106 to 109 W/cm2 is becoming increasingly important in laser processing of materials for microelectronics. The ablation process produces an intense plume of gas phase material which expands rapidly away from the ablated surface. We report on real time interferometric measurements of free electron density and laser induced fluorescence studies of atoms and molecules in the plume, with the objective of understanding the dynamics of material ablation.
Direct-writing in self-developing resists using low-power, cw, ultraviolet light
Authors: Bjorkholm J. E. , Eichner L. , White J. C. , Howard R. E. , Craighead H. G.
Published: February 2023

"Direct-write" technologies for the laser processing of semiconductors use sharply focused laser beams to induce localized chemical reactions at semiconductor surfaces. Though these processes are slow compared with conventional optical printing, they are of scientific interest and they appear promising for applications involving the customizing, repairing, and testing of integrated circuits. There also has been interest in "self-developing" photoresists; these are materials that ablate during exposure to optical radiation. The use of a self-developing resist eliminates the need for a development step following exposure.
Selective Laser-stimulated Desorption of Molecules by Internal Vibration Excitation
Authors: Jedrzejek C.
Published: February 2023

A model of photodesorption due to a laser resonantly coupled to an internal vibration mode of the adsorbed molecule is considered. Contrary to works of Gortel, Kreuzer and collaborators1,2 the model accounts for an anharmonicity of the internal vibration, broadening of energy levels of a zero-order Hamiltonian, and partly for multiphonon nature of the resonant heating mechanism. The importance of these features of the model was earlier demonstrated by the author and coworkers for thermal desorption3 and laser-stimulated desorption (LSD) through the excitation of the surface bond.4
Time-Resolved Vibrational Energy Relaxation of Surface Adsorbates
Authors: Heilweil E. J. , Casassa M. P. , Cavanagh R. R. , Stephenson J. C.
Published: February 2023

Many chemical and physical processes that occur at solid interfaces may be better understood from the measurement of energy flow within adsorbate and substrate vibrational modes. In order for a chemical transformation to occur along a reaction coordinate, for example, specific molecular bond vibrational excitation followed by dissociation and reformation is required. With the advent of ultrashort optical pulse technology, we are now in a position to directly monitor the ultrafast kinetics of energy decay of vibrational modes in condensed-phase molecular systems. While such measurements have been conducted for gas and liquid phase systems, there have been no previous reports of measurements of energy relaxation in chemically relevant surface species. We have thus undertaken a course of research to directly investigate the vibrational relaxation dynamics of molecules adsorbed on high surface area metal oxides.
Electroreflectance Vibrational Spectroscopy: Theory and Measurement of the Stark Effect of CO on Ni[100]
Authors: Lambert D. K.
Published: February 2023

Electroreflectance vibrational spectroscopy1-4 (EVS) is an infrared technique for obtaining extremely high resolution spectra of adsorbed species. Light from a tunable infrared diode laser is reflected from an adsorbate covered surface to a detector. The reflected light is modulated by using a large electric field to shift adsorbate vibrational frequency - the Stark effect. Sensitivity to fractional modulation as low as 2x10−8 Hz−1/2, near the shot noise limit, is obtained. The high sensitivity and zero background nature of EVS also allow absolute measurements of the Stark tuning rate to be made.
Electronic Spectroscopy and Relaxation Dynamics of Adsorbates on Metal Surfaces
Authors: Avouris Phaedon
Published: February 2023

Information on the nature and non-radiative decay of electronically excited states of adsorbates is essential for the microscopic understanding of a variety of surface dynamical processes.
Laser Photochemical Etching of Molybdenum and Tungsten Thin Films by Surface Halogenation*
Authors: Rothschild M. , Sedlacek J. H. C. , Ehrlich D. J.
Published: February 2023

Laser direct writing techniques, employing rapidly scanned microchemical deposition and etching reactions, are of importance for advanced nonlithographic fabrication of microelectronics. One class of applications employs these techniques for fine-line in situ alteration of conducting films as a last step in fabrication. Of particular importance for these applications is laser-induced patterning of Mo and W, which are becoming widely used materials for metallization of both Si and GaAs microelectronic devices.
Thin Film Growth and Deposition by Low Energy Electron Stimulated Surface Chemistry
Authors: Kunz R. R. , Allen T. E. , Mayer T. M.
Published: February 2023

Direct materials processing by focused particle beams has received considerable attention in recent years. The electron beam, traditionally used for resist exposure in electron beam lithography applications, is among the candidates for direct materials modification. High energy electrons (>1keV) are not very chemically active due to small cross sections for inelastic scattering processes such as bond dissociation and attachment. Low energy electrons are expected to be much more efficient at stimulating chemical processes. In particular, secondary electrons produced by particle or photon bombardment of surfaces with kinetic energies of approx. 2-10 eV have large cross sections for attachment and dissociative electron attachment to many electronegative molecules. We have begun a general investigation of chemical reactivity and mechanisms of electron-adsorbate interactions leading to film growth and deposition. Prospects for applications to focussed beam, direct write materials processing are being explored.
Role of Ions in Carbon Film Deposition by a Window-less Hydrogen Lamp
Authors: Hanabusa M. , Kaneoka T.
Published: February 2023

Optically transparent and electrically resistive amorphous carbon films can be deposited by photolysis of acetylene with VUV light on a substrate kept near room temperature. However, the deposited films are characterized by low refractive indices and soft. A similar result was obtained with electron-impact dissociation of acetylene. It is known that ions play important role in producing hard carbon films with high refractive indices. Therefore, we used a window-less, microwave-excited H2 tube to dissociate acetylene. Owing to its short wavelength components and presence of active hydrogen atoms, ions are generated from the source gas injected at the exit end of the discharge tube. They are further accelerated by an applied electric field. Then, not only deposition became faster, but as expected, we could improve film quality. The films were hard and their refractive indices became as high as 2.11. The bias required to improve film quality was approximately 300 V. The substrate was silicon. The deposition rate was 700 Å/min at room temperature, and it decreased with increasing substrate temperature.
An in-situ infrared study of the interaction of oxygen and fluorine plasmas with Si and SiO2 surfaces
Authors: Claassen W.C.M. , Dieleman J.
Published: February 2023

Future technology for ultra large scale integrated semiconductor circuits will need low temperature processes for growing and etching thin films. An important thin film is that of SiO2 on top of Si. The composition and structure of this film and its interface with Si partly determines the electrical properties of the resulting devices. Detailed information about composition and structure of thin films can be obtained with the use of vibrational spectroscopy, e.g. electron energy loss- (EELS), Raman- or infrared absorption spectroscopy (IRAS). EELS features high sensitivity and a large spectral range but its disadvantages are low resolution (> 40 cm-1) the risk of electron beam induced reactions and its limitation to pressures below 10-4 Pa. (ref. l). With Raman spectroscopy enough sensitivity is obtained only when using special modified metal surfaces (SERS). Since infrared spectroscopy combines high resolution with adequate sensitivity and furthermore is not limited to low pressure environments, it is an obvious choice for the study of interaction of plasmas with thin films and interfaces. Its sensitivity however poses problems for frequencies below 800 cm-1.
UV assisted growth of GaAs
Authors: Balk P.
Published: February 2023

This contribution reviews our work on the uv stimulated growth of GaAs in the MOVPE system. These studies were performed using different metalorganic Ga compounds and AsH3 in a H2 carrier at different partial pressures and flow velocities over a range of temperatures. We compared stimulation using a low pressure Hg lamp (main output at 254 nm) and an excimer laser at different wavelengths.
Atomic Layer Growth of GaAs by Pulsed Laser MOVPE
Authors: Aoyagi Yoshinobu , Doi Atsutoshi , Iwai Sohachi , Namba Susumu
Published: February 2023

Atomic layer epitaxy has recently been interested in by many workers since the epitaxy seems to be a promising candidate for producing thin epitaxial layers and abrupt interfaces controlled in atomic scale. In this epitaxy As and Ga atoms are alternatively deposited on the GaAs substrate, layer by layer, and it is essential to realize the precise atomic layer epitaxy (SME, Stepwise Monoatomic layer Epitaxy(1)) that the deposition of Ga or As atom should be stopped automatically at the 100 % surface coverage of each atoms.
Monolayer Film Properties Measurements Using High Q Graphite Fibers
Authors: Gregory Stephen
Published: February 2023

Although the field of surface analysis continues to grow rapidly, it remains true that mechanical properties of films are not easily studied. Indeed, when the films are one to a few monolayers thick, the very definitions of mechanical properties are in question.
Deposition of Metal Lines Using an Excimer Laser
Authors: Adrian F. J. , Bohandy J. , Kim B. F. , Jette A. N. , Thompson P.
Published: February 2023

A laser-induced forward transfer (LIFT) technique for transferring metal from one substrate to another has recently been reported.1 With this method, a metal film, deposited on a transparent source substrate, is irradiated by the laser which is focused at the interface between the film and substrate, Fig. 1, so that the ablated metal is expelled outward and will deposit on a target substrate located near the source. As noted previously,1 properties of the deposited metal features such as resolution, i.e., similarity of the deposited to the ablated metal region, electrical conductivity, etc., depend on a number of parameters including laser power density, film thickness, source target distance, etc.
Multiphoton Ionization Mass Spectrometric Detection of Gas Phase Radicals Produced in the Spontaneous Etching Reaction of Silicon by XeF2
Authors: Dagata J. A. , Squire D. W. , Dulcey C. S. , Hsu D. S. Y. , Lin M. C.
Published: February 2023

We have recently demonstrated selective detection of SiF and SiF2 radicals produced in the reaction of F2 and NF3 with silicon in a flow system using multiphoton ionization mass spectrometry (MPI/MS)1. In this paper we report results for the spontaneous surface etching reaction of p-doped (110) and uncharacterized silicon single crystals by XeF2 over a wide range of temperatures (300-1000 K) and pressures (10-6 to 10-4 Torr). We have found that under single collison conditions SiF2 is the only gas phase radical produced in the surface reaction of XeF2 and silicon. The activation energy for producing gas phase SiF2, Ea[SiF2], is about 6.0 kcal/mol.
Adsorbate Interactions and Poisoning on Cr(110)
Authors: Shinn Neal D.
Published: February 2023

The chemisorption of carbon monoxide and oxygen on Cr(110) at temperatures below 150K has been studied using photoemission, vibrational and Auger spectroscopies, and low energy electron diffraction (LEED). Direct evidence for co-adsorbate interactions which induce changes in the (1) molecular CO bonding to the chromium surface and (2) the CO dissociation energetics has been found. This work provides a microscopic picture of the "poisoning" of the Cr(110) surface for CO dissociation by electronegative oxygen atoms.
Electron Energy-Loss Spectroscopy and Reflection High-Energy Electron Diffraction Studies of the Adsorption and Pyrolysis of Si2H6 on Si (100)2x1
Authors: Suda Y. , Lubben D. , Motooka T. , Greene J.E.
Published: February 2023

Disilane, Si2H6, is a promising precursor for the low-temperature deposition of Si films by chemical vapor deposition (CVD) and uv-laser-induced CVD (LCVD). It has a higher reactivity on Si surfaces and a lower decomposition temperature as well as a larger uv absorption cross section than silane (SiH4).(1) We have investigated adsorption kinetics and thermally-induced reactions of Si2H6 on Si (100)2x1 surfaces using electron energy-loss spectroscopy (EELS) and reflection high-energy electron diffraction (RHEED).
Thermal Decomposition of Ga-alkyls Adsorbed on GaAs(100) and Mechanisms of Laser Induced Pyrolysis
Authors: McCaulley J. A. , McCrary V. R. , Donnelly V. M.
Published: February 2023

Laser enhanced deposition of III-V semiconductor films is often performed under conditions where laser induced decomposition of the group HI alkyl is rate-limiting. Understanding the chemistry is important for optimizing growth rate selectivity and for reducing carbon incorporation. We report X-ray photoelectron spectroscopy (XPS) studies of thermal decomposition and excimer laser stimulated decomposition of triethylgallium (TEGa) and trimethylgallium (TMGa) adsorbed on single crystal GaAs(100) in ultrahigh vacuum. Kinetic models of thermal decomposition that relate results obtained with widely different heating rates (10-2 vs1011 K/s) are presented.
Band Bending and Oxygen-Induced Defects in a-Si:H
Authors: Winer K.
Published: February 2023

Little attention has been paid to amorphous semiconductor surfaces since the valence band photoemission spectra of amorphous Si and Ge were first measured 15 years ago. This neglect has been due, in part, to the lack of a well-defined amorphous structure and the resulting preparation-dependent nature of amorphous semiconductor properties, which has frustrated the reproducibility of both surface and bulk measurements. Persistent efforts have minimized the impact of these materials issues, but an important stumbling block has remained to further understanding the surface electronic structure of technologically-important amorphous semiconductors such as hydrogenated amorphous silicon (a-Si:H). In such materials, measurement of the distribution of gap states (typically present in densities below 1019 eV-1cm-3) is of primary importance and requires sensitivities orders of magnitude higher than those available with conventional photoemission methods. The recent development of total yield, with its high dynamic range (107: 1) and energy resolution (ΔE≦0.1 eV), as a surface gap state spectroscopy has opened up an exciting new window on the surface electronic structure of an entire class of increasingly important technological materials.1
The Passivation of Si and Ge Surfaces with Arsenic
Authors: Bringans R. D.
Published: February 2023

Many semiconductor surfaces reconstruct with substantial atomic rearrangements compared to the ideally-terminated bulk crystal structure. The use of particular monolayer films has been shown to remove surface reconstructions and to lead to a good approximation of a bulk-terminated crystal. The simplest case, in principle, is the direct saturation of dangling bonds with monovalent atoms. It has been found that hydrogen atoms bonding to Si and Ge surfaces do indeed remove the surface reconstructions and that the group VII atoms remove the reconstruction on the (111) surfaces.
A Generalized Model for the Analysis of Surface Residence Effects During Ion-Assisted Etching
Authors: O’Brien W.L. , Rhodin T.N.
Published: February 2023

A detailed understanding of the mechanisms of ion-assisted etching is important for both pure and applied scientific interpretations. For pure science the study of ion-assisted etching offers new information on radiation-induced surface reactions. For applied science the study of ion-assisted etching offers information important to understanding of the dry processing of semiconductors and metals.
Oxide Layer Growth on Gallium Arsenide Using a High Kinetic Energy Atomic Oxygen Beam
Authors: Hoffbauer M.A. , Cross J.B. , Farr J.D. , Bermudez V.M.
Published: February 2023

The inherent theoretical advantages of GaAs electronic devices over those employing Si technology are severely limited in practice by the difficulty of forming passivating oxide layers. 1 Problems encountered with oxide stoichiometry, crystallinity, interface defects, and chemical stability have been the subjects of numerous studies over the last 15 years. 2-8 One of the major factors contributing to these problems is the differing rates of oxidation of Ga and As and the volatility of the AS2O3 and AS2O5 products at temperatures above ~100 °C.
Electronically Induced Modifications of a-Si:H(P) Films by Scanning Tunneling Microscopy
Authors: Hartmann E. , Koch F. , Behm R. J.
Published: February 2023

We report local electronic modifications of phosphorus-doped, hydrogenated amorphous silicon films [a-Si:H(P)], on a nm-scale, by use of a Scanning Tunneling Microscope.
Silicon Atomic Layer Growth By Laser Beam/Si2H6 Adsorbates Interactions
Authors: Nagasawa Y. , Tanaka T. , Miyazaki S. , Hirose M.
Published: February 2023

Saturated monomo1ecular adsorption of Si2H6 on a silicon surface held at temperatures around -60°C and subsequent irradiation of a single shot of ArF excimer laser fully decomposes the adsorbed layer to promote the atomic layer growth of Si. TEA CO2 laser irradiation at 10P6 line, which selectively excites the surface SiH3 bond, significantly reduces the content of the bonded hydrogen in the silicon layer. Possible mechanisms for the silicon atomic layer growth and the hydrogen reduction are also discussed.
Adsorption and Desorption Kinetics for Si (C2H5)2H2 on Si(111) 7x7
Authors: Coon P.A. , Wise M.L. , George S.M.
Published: February 2023

Diethylsilane (DES), Si (C2H5)2H2, is a promising candidate for the atomic layer epitaxy of silicon. Alkylsilanes are advantageous because they are less toxic and flammable than silanes. The reactions of organosilanes with silicon surfaces are also important both fundamentally and technologically. This study explored the adsorption and desorption kinetics for Si (C2H5)2H2 on Si (111) 7x7 using laser induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques.
Oriented Aluminum Films on Silicon by Direct Ion Beam Deposition
Authors: Zuhr R. A. , Haynes T. E.
Published: February 2023

The formation of metal films on Si at low temperatures is of fundamental interest in thin film physics, as well as a key step in the processing of integrated circuits for microelectronics. If grain size and uniformity could be controlled in the Al metallization used in semiconductor manufacturing, the reliability of such conductors, particularly during thermal cycling, could be greatly improved. One possible way to achieve such control is through the introduction of energy in the form of energetic ions during film growth. [1] The Al on Si system is especially interesting, not only because Al is presently the conductor of choice for microelectronics fabrication, but also because the system exhibits unusual interface properties. [2] It has been demonstrated that oriented crystalline Al films can be grown on Si( 111) and Si(100) surfaces at room temperature by the technique of ionized cluster beam deposition (ICB), even though there is a large mismatch in the size of the respective lattices (25%). [3,4] It is important to determine whether similar oriented growth can be achieved by other thin film deposition techniques and to understand the significant deposition parameters. In this paper we will study the formation of oriented Al films on Si by direct deposition from a low-energy mass-analyzed ion beam.
Scanning Scattering Microscope: A Novel Optical Technique for Imaging Surface Microtopography
Authors: Marton Denes , Fine Joseph
Published: February 2023

The Scanning Scattering Microscope (SSM) [1] can produce two-dimensional, high resolution micrographs of very small surface features and surface microtopography; this optical technique is very sensitive to surface roughness, surface and near-surface damage, and individual surface defects. Its present lateral resolution of about 5 μm is augmented by an extremely high sensitivity to surface roughness of about 2 nm.
Analysis of Surface Roughness of Silicon Surfaces by Reflection Electron Energy Loss Spectroscopy
Authors: Frase H.N. , Wong S.S. , Ahn C.C. , Atwater H.A.
Published: February 2023

The quantification of semiconductor surface roughness in the 0.5 - 10 nm range is a problem of current scientific and technological interest. Surface roughness measurements are also of great technological interest, particularly for silicon, since the starting surface roughness affects the roughness and ultimate quality of transistor gate dielectrics and other reacted or deposited layers. While atomic force microscopy and other scanning probe methods are now in widespread use for ex situ surface roughness evaluation, this is considerable interest in developing in situ methods for surface roughness measurement during growth or etching. Candidate in situ roughness analysis methods currently include reflection high energy electron diffraction (RHEED) and RHEED oscillations, widely used for monolayer roughness measurements, ellipsometry, and X-ray reflectivity. In this summary, we describe another method: the use of low-loss inelastic electron scattering measurements using reflection electron energy loss spectroscopy (REELS) to investigate silicon surface roughness.
Fabrication and Properties of Ultrathin Films of Porous Silicon
Authors: Fauchet P.M.
Published: February 2023

We have manufactured thin films of light-emitting porous silicon (LEPSi) by electrochemical etching in HF and subsequently lifted them off the silicon wafer by an electropolishing step [1]. The film thickness was varied from 100 μm to 0.1 μm and the porosity ranged from < 40% to ≥ 90%. To insure the structural integrity of the thinner, higher porosity films, they were deposited on sapphire windows where they remain attached by van der Waals or electrostatic forces, in a manner reminiscent of earlier work with ultrathin film of III-V semiconductors [2]. The microstructural, chemical and optical properties of these films have been investigated using a variety of tools, including AFM, XRD, FTIR, cw and time-resolved absorption and luminescence measurements. These films are optically flat (see Fig. 1), do not scatter light, show pronounced Fabry-Perot interference fringes in the transparency region which can extend to photon energies well above the bandgap of crystalline silicon (see Fig. 2) and can have a refractive index as low as 1.2 to 1.3. The peak of the luminescence spectrum, which is determined by quantum size effects and surface chemistry, has no clear relation to the onset of absorption, which is dominated by the largest nanocrystallites. The broad luminescence spectrum splits into a few narrow peaks which are produced by multiple interference (see Fig. 3).
Abstractive vs. Dissociative Chemisorption of Molecular Halogens on the Si(111)-7x7 Surface: A Molecular Beam/STM Study
Authors: Jensen J.A. , Yan C. , Behringer E.R. , Kummel A.C.
Published: February 2023

The chemisorption of a mono-energetic molecular beams of F2 , Cl2, and Br2 onto a room temperature Si(111)-7x7 surface are examined using scanning tunneling microscopy and the resulting adsorbate structures are studied as a function of translational energy/chemisorption mechanism. For F2 chemisorption on Si(111)-7x7, there is no intrinsic physisorption state and therefore no island formation at low incident translational energy1. Instead at low translational energy (0.03eV), we observe that the dominant adsorption sites are single reacted adatoms (Si-F), while at higher translational energy (0.27eV) dimers/neighboring pairs of reacted adatoms are commonly observed. From previous work by the Ceyer2 and Carter3 groups, it is known that at low translational energy, F2 can adsorb via abstraction ( F2 collides, one F atom chemisorbs, the other is ejected into the gas phase), while at higher translational energies, dissociative chemisorption becomes the predominant adsorption mechanism. Our STM experiments, in conjunction with a simple Monte Carlo model, show that at low translational energy, the abstraction mechanism accounts for nearly all chemisorption of F2 because nearly all adsorption sites are single reacted adatoms. At higher translational energy, the dissociative chemisorption mechanism becomes important and the predominance for single site adsorption is greatly reduced while the occurrence of dimers/pairs of reacted adatoms is increased.
Electron Beam Nanolithography
Authors: Marrian Christie R.K.
Published: February 2023

Motivated by trends in the microelectronics industry and the quest to investigate electronic and material properties in the quantum effect size regime, there is a strong drive to understand and overcome the limits of the processing required for microfabrication. At the beginning of the next century, the precision required in feature sizes for microelectronics manufacturing is projected to be close to 10 nm, i.e. about 25 atomic diameters. Still smaller feature sizes are needed for nanoelectronic device research. For example, to observe effects such as lateral resonant tunneling and coulomb blockade at close to room temperature, feature sizes below 10 nm are necessary. Central to any fabrication scheme for these dimensions is a lithographic step where a pattern is defined in a radiation sensitive material, commonly called the resist, and then replicated into the substrate to define a structure or device. Due to the availability of equipment and knowledge base, the preferred means for defining the smallest possible structures involves the use of a focused high energy beam of electrons.
Kinetic Modeling of the Atomic Layer Epitaxy Window in Group IV Semiconductor Growth
Authors: Eres Gyula
Published: February 2023

Atomic layer epitaxy (ALE) is a method for epitaxial growth of semiconductor thin films that utilizes the adsorption kinetics of source gases for external control of the film growth process [1]. ALE takes advantage of the self-limiting nature of the chemisorption process for achieving layer-by-layer growth of semiconductors with uniform film thickness, ideally, 1 ML per adsorption cycle. The 1 ML/cycle film growth is a uniquely distinguishing feature, that makes ALE highly attractive for preparation of ultrathin films of precisely controlled thickness. Other unique characteristics of ALE growth are that the spatial homogeneity of thin films, and the film thickness per cycle are insensitive to small variations in the external process parameters. The parameter space in which ALE is independent of external conditions is known as the ALE window [2].
Z-scan Measurements of Porous Silicon Particles in a Colloidal Suspension
Authors: Choi S. S. , Fiddy M. A.
Published: February 2023

Since Canham's report that porous silicon (PS) exhibits efficient visible photoluminescence under UV illumination at room temperature [1], extensive investigations addressing porous silicon's pore formation, surface morphology, photo/electroluminescent mechanism(s), and applications are already well reviewed [2-5]. Although much debate still surrounds porous silicon in the aforementioned areas, the viability of porous silicon as an optoelectronic material (e.g. optical switch) is well realized [6]. Thus, the motivation for our efforts is to find a new viable optoelectronic medium, namely a colloidal suspension of porous silicon nanoparticles in some cases microparticles. Colloidal suspensions of gold and polymer composites, possibly due to quantum confinement effects, have yielded large third order nonlinearities of 10-5 to 10-8 esu [7].