bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed-Laser Atom-Probe Study of H3, N3 and NH3 Formation on Metal Surfaces
Authors: Tsong T. T. , Ai C. F. , Liu Wu
Published: February 2023

The surface field must play an important role in the reactivity of a surface. This effect can be probed in field ion emission experiments. First, the applied field in these experiments is an adjustable parameter and it is of the same order of magnitude as the surface field. Second, the size of a field ion emitter resembles well a dispersed catalytically active metallic particle. We report here a study of surface catalyzed formation of H3, N3 and NH3 on various crystal planes of about 20 transition metals using pulsed-laser stimulated field desorption technique. In pulsed-laser stimulated field desorption, adsorbed surface species are first thermally desorbed by pulsed-laser heating of the surface. They are subsequently field ionized and detected.
Technique for Measuring Surface Diffusion by Laser-Beam-Localized Surface Photochemistry*
Authors: Zeiger H. J. , Tsao J. Y. , Ehrlich D. J.
Published: February 2023

The surface migration of adsorbed species is a fundamental kinetic step in most surface chemical reactions, e.g., those involved in heterogeneous catalysis, thin-film growth, and etching. Consequently, numerous techniques have been developed over the years for measuring surface-migration rates. Most of these techniques, however, are only applicable to strongly bound or robust adsorbates, such as atoms and some diatomic molecules, since they involve subjecting the surface to extreme environmental conditions, such as large electric fields or electron bombardment. An ultrahigh vacuum is usually also a requirement.
Studies of Laser Chemical Vapor Deposition Using Surface Sensitive Infrared Photoacoustic Spectroscopy
Authors: Higashi G. S. , Rothberg L. J. , Fleming C. G.
Published: February 2023

We report vibrational spectra of surface adsorbates during KrF laser assisted chemical vapor deposition (CVD) of Al films from trimethylaluminum (TMA) on single crystal sapphire substrates. The pulsed optoacoustic technique used has submonolayer sensitivity to O-H and C-H infrared active stretching vibrations and allows studies of the interactions between adsorbed H2O and TMA on surfaces prior to deposition. It also provides information about film composition during the early stages of laser stimulated growth. In addition, because surface Al-CH3 groups can be observed directly, the role of surface phase photochemistry in laser CVD can be investigated.
Laser-Initiated Dry Etching of SiO2
Authors: Chu Jack O. , Flynn George W. , Brewer Peter D. , Osgood Richard M.
Published: February 2023

In general photochemical (drying etching) process of thin films based on (UV) laser-initiated chemistry is difficult to investigate both mechanistically and kinetically. Some of the most important questions are concerned with the photo-formation of the reactive species and their (reactive) chemical interaction with the surface. The UV-laser assisted etching of SiO2 from photolysis of CH2 CHF is quite attractive for mechanistic studies of the etching process because of the relative simple (in-situ) application of IR (time-resolved) fluorescence and absorption techniques to monitor both the HF etchant and the SiF4 products within the gas-surface system. The strong oscillator and absorption strength of the HF molecules makes it possible to monitor its photo-production and follow the subsequent etching reaction with the SiO2 surface. Moreover, high resolution and sensitive diode laser absorption probes can be used to investigate the surface products (SiF4, SiF3, SiF2 and SiF) in the gas phase.
Interface Studies by Optical Second Harmonic Generation
Authors: Shen Y. R.
Published: February 2023

Optical second harmonic generation has recently been shown to be an effective probe for surface studies. Its surface specificity derives from the fact that the process is generally forbidden in a bulk with inversion symmetry but always allowed at a surface or interface. As an optical technique, the method has the advantages of being non-destructive, capable of ultrafast time resolution, and applicable to interfaces between condensed media. We consider here only applications of the method to studies of molecular adsorption at interfaces.
Real-time Monitoring of Surface Reactions on Si(111) by Optical Second-Harmonic Generation
Authors: Heinz T. F. , Loy M.M.T. , Thompson W. A.
Published: February 2023

The sensitivity of optical second-harmonic generation (SHG) to atomic and molecular monolayers absorbed on surfaces of centrosymmetric media has now been well established.1 Recent work has also demonstrated the dependence of the SHG process on the ordering and symmetry of the surface region.2 In this paper, we apply the surface SHG technique to follow in real time some widely studied and technologically important reactions occurring on clean, well-defined Si(111)-7x7 surfaces. We discuss here both the oxidation of the Si surface and the formation of thin layers of disordered and epitaxial Pd silicide.
Second Harmonic Generation Studies of Adsorption and Reorientation at Electrode Surfaces
Authors: Voss D.F. , Bunding K.A. , Nagumo M. , Goldberg L.S.
Published: February 2023

Second harmonic generation at surfaces (SSHG) has recently been the subject of increasing interest among researchers who require a probe of interfacial phenomena that is both surface-specific and can be utilized in condensed phase studies (see [1] and references therein). SSHG belongs to a larger class of second order nonlinear optical processes that includes optical rectification, sum and difference frequency mixing, and the Pockles effect, all of which are symmetry forbidden in isotropic media (at least in the electric dipole approximation [1]). At an interface between dissimilar media the isotropy which may be present in the bulk material is disturbed, and processes such as second harmonic generation can occur. This property is attractive for probing surface phenomena because only very weak electric quadrupole and magnetic dipole signals are generated in the bulk material. Furthermore, SSHG is an optical effect and requires only transparency of the media at the fundamental and harmonic wavelength, rather than the more stringent condition of ultrahigh vacuum imposed by electron and ion probes.
Survival of Vibrationally-Excited Nitric Oxide Scattered from LiF(100) Surface: Angular and Velocity Analysis
Authors: Misewich J. , Zacharias H. , Loy M. M. T.
Published: February 2023

The role of internal energy in the scattering of molecular beams from surfaces has recently attracted much attention.1-3 Most of these experiments however are confined to the scattering of molecules distributed over the lowest few rotational levels of the ground vibrational state. In the experiments presented here, laser spectroscopic techniques are utilized to perform state-to-state molecular beam scattering experiments. Two laser beams intersect the molecular beam: tunable infrared laser radiation excites the incident molecular beam to a single vibrational-rotational state then tunable ultraviolet laser radiation state-selectively probes the molecular beam through two photon resonance enhanced ionization. The beam of vibrationally excited molecules is well defined in time allowing the direct determination of velocity distributions for a laser-selected state by taking time-of-flight spectra at various probe laser positions. We report here the angular and velocity distribution of vibrationally excited molecules that we have observed surviving the collision with a freshly cleaved LiF(100) surface.
Study of Molecule Surface Interaction Dynamics by Laser
Authors: Walther Herbert
Published: February 2023

During the last decade atomic and molecular beam techniques have been of great help for investigating the dynamics of atom or molecule-surface interaction. As long as atoms are involved in the interaction process, the measurements of angular and velocity distributions provide sufficient insight. When molecules are scattered, however, additional information on changes of the internal energy is necessary. Recently, the laser-induced fluorescence method and resonance ionization in combination with time-of-flight measurements were successfully used to determine the influence of surface interaction on the energy distribution between translational, rotational, vibrational and electronic excitation (see references [1,2] for a survey on the published work). The laser experiments lead to a complete description of the dynamics of the molecule-surface interaction.
Optical and Electron Probes of the Structure of Surfactant Coated Surfaces
Authors: Garoff S. , Hall R. B. , Deckman D. W.
Published: February 2023

The absorption of a monolayer of amphiphilic or surfactant molecules onto a surface can dramatically affect a number of the macroscopic properties of that surface. These properties, such as wetting by a fluid, lubrication of the solid, or chemical reactions of the surface, are of fundamental as well as technological importance. Our studies have focussed on the molecular scale structure of these monolayers and have attempted to probe how the structure depends on the deposition process used to absorb the monolayers. Further, by studying the molecular aspects of surfactant coated surfaces, we hope to gain insight into the nature of wetting and the other macroscopic phenomena which are profoundly affected by the presence of the surfactant monolayer.
Above-Bandgap Polarization Anisotropies in Cubic Semiconductors: A Visible-Near uv Probe of Surfaces
Authors: Aspnes D. E.
Published: February 2023

Recent work on the 0.5 eV below-bandgap surface state on 2x1-<111> Si cleaved in ultrahigh vacuum showed strong polarization anisotropy in near-normal incidence absorptance and reflectance measurements.1,2 The present work describes the first experiments undertaken to systematically study anisotropies in the above-bandgap reflectance of cubic semiconductors. An experimentally simple configuration is used, wherein the sample is rotated while being illuminated with near-normal-incidence linearly polarized light and the second harmonic of the mechanical rotation frequency in the reflected beam is phase-sensitively detected and determined as a function of photon energy.
Chlorine Surface Interactions and Laser Induced Surface Etching Reactions
Authors: Sesselmann W. , Chuang T.J.
Published: February 2023

It is by now quite well established that photon beams, in particular lasers, can be used to induce or enhance chemical reactions between a gas and a solid surface [1]. Also, recent advances in applications of lasers to perform chemical etching and vapor deposition have raised firm expectation that the laser technique may have significant impact on processing materials for microelectronics [2]. In laser induced chemical etching of solids, the fundamental surface processes include the reaction between the adsorbate and substrate and the vaporization of product species. In order to better understand the radiation-gas-surface interaction mechanisms, we have carried out experiments with ESCA and Auger depth profiling, and time-resolved mass spectrometry in conjunction with laser irradiation of solid surfaces. Specifically, we have investigated Si/Cl2, Ni-Fe/Cl2, and Ag/Cl2 systems.
Mechanism of Trimethylaluminum Chemical Vapor Deposition Studied by Multiphoton Ionization Mass Spectrometric Detection
Authors: Squire D.W. , Dulcey C.S. , Lin M.C.
Published: February 2023

Recent mechanistic studies of organometallic chemical vapor deposition (MOCVD) have suggested that organometallic cleavage and organic radical recombination take place on or above the heated substrate.1 We have employed the method of multiphoton ionization (MPI) in conjunction with conventional mass spectrometry to probe radical2 as well as stable products to elucidate the mechanisms of CVD processes.
Quantum Model of Dephasing-Enhanced Laser Desorption
Authors: Lin Jui-teng , Huang Xi-Yi , George Thomas F.
Published: February 2023

Existing theories of laser-induced and/or phonon-assisted desorption are based upon one-dimensional (1D) surface potential analyses, which include a truncated harmonic potential (THP), 1D Morse potential (1MP) and master equation treatment with multiphonon transitions [1]. One of the severe limitations of these models is that any two-dimensional (2D) features of the excited adspecies are completely ignored, causing some unrealistic results. For example, THP over-estimates the transition rate, while the rate is underestimated by 1MP. In the present paper, we propose a qualitatively correct physical model which is able to effectively take into account the 2D features by introducing a dephasing factor into an anharmonic master equation.
Photochemical Processes in Deposition and Etching: The Interdependence of Excitation and Reaction
Authors: Houle F. A.
Published: February 2023

Deposition and etching reactions induced by a laser beam incident on a surface are uniquely influenced by the nature of the excitation source. For example, considerable effort has been made to clarify the relative importance of reactions from the ground and electronically excited states in decomposition and desorption. In order to use results of such studies to understand real systems, however, the fact that the level of optical excitation may vary in time must be explicitly considered. Indeed, as a surface reaction proceeds substantial changes in the chemical nature of the system, and hence its optical and thermal properties, may take place. These changes directly affect the amount of excitation coupled into the system, feeding back into the chemistry. This circular interdependence of excitation and reaction can lead to considerable complexity in apparently simple processes. For this reason caution must be exercised in deriving mechanistic information from macroscopic rate measurements during etching and deposition reactions.
Chemical Etching of Silicon by CO2 Laser Induced Dissociation of NF3
Authors: Brannon James H.
Published: February 2023

Surface studies have established that radicals frequently react with surfaces which are inert to the parent molecule. Dissociation of the parent molecule provides a reaction channel which avoids the often large activation barrier inherent in parent molecule-surface interactions. The interaction of gaseous NF3 with amorphous silicon is an excellent example of this type of behavior. While NF3 does not measurably chemically react with silicon at ambient temperatures, the fluorine containing radicals produced from laser dissociated NF3 readily do so. Some fraction of the fluorosilyl reaction products spontaneously desorb, resulting in silicon removal (etching). In this study parallel incident dissociating radiation did not contact the silicon surface, indicating that the observed etching reactions result from purely chemical effects. Effects due to transient surface heating or physical ablation can be discounted.
Surface Interaction of Electronically Excited Molecules
Authors: Schröder H. , Rager B. , Kompa K.L.
Published: February 2023

We have experimentally studied the survival probability of electronically excited molecules in collisions with solid surfaces. The molecular beam was produced by a pulsed nozzle. A fast ion gauge, a QMS, a pyroelectric foil (bolometer) and special light collecting optics were utilized as diagnostic tools. The QMS and the light detector could be rotated around the scattering center, thus allowing for angularly resolved measurements. Scattering from the foil directly revealed the free energy change involved in the scattering process. The molecules tested were Ni(CO)4 and SO2. XeCl laser (308 nm) excitation of Ni(CO)4 yields the electronically excited fragment

Ni

(

CO

)

3
*

with unit efficiency. The radiative lifetime of

Ni

(

CO

)

3
*

is =17μs, that of SO2 is > 55 μs for XeCl laser excitation. A long lifetime is essential for the experimental purpose because the excited portion of the beam must be monitored over a sufficiently long distance in front of and behind the scattering centre.
Effects of Ar+ angle-of-incidence on chemical sputtering of Si with Cl2
Authors: van Zwol J. , Kolfschoten A.W. , van Laar J. , Dieleman J.
Published: February 2023

Studies of chemical sputtering of silicon by simultaneous exposure to Cl2 and low-energy Ar+ ions, using mass spectroscopy and time-of-flight techniques, have shown that the main products are atomic Si and Cl and molcular SiCl and SiCl2. The largest fractions of the time-of-flight distributions of these products have collision cascade-like distributions with a binding energy range characteristic for each of these four products. The model explaining these and some other observations ascribes a central role to Ar+ ion-induced amorphization and Ar+ ion-induced mixing of adsorbed Cl into the top atomic layers of the Si, which is accompanied by formation of molecular SiCl and SiCl2 trapped in the bulk without further chemical binding to the surrounding bulk network. The largest part of the four main products is removed from the solid by physical sputtering. The chemical enhancement is ascribed to mainly two factors, first the formation of large amounts of trapped SiCl and SiCl2 molecules with a low binding energy range and second a reduction in the binding energy of the Si in the binding network by the mixing with Cl. This was demonstrated, among other things, by the observation that for flux ratios of Cl2 to Ar+ increasing from about 1 to about 100 the relative amount of SiCl and SiCl2 with respect to Si is enhanced and the binding energies reduced (ref. 1).
Ion and Laser Interactions as Encountered in Synthesis and Utilization of Metal Containing Polymer Films
Authors: Kay Eric
Published: February 2023

We have previously reported how simultaneous chemical sputtering and plasma polymerization in a capacitively coupled r.f. plasma diode system can lead to polymer films in which small metal clusters (10Å-100 Å) are uniformly dispersed throughout. Post deposition laser irradiation of such a metal containing polymer film leads to migration and coalescence of gold clusters as soon as a second order phase transition associated with the polymer glass transition temperature, Tg, is surpassed. Starting with such a metal containing dielectric polymer film having a metal volume fraction below electrical percolation and then subjecting it to laser irradiation brings about metal coalescence into a continuous metal medium within spatial dimensions controlled by the laser beam and showing bulk conductivity. Likewise, laser induced cluster coalescence can lead to controlled growth in cluster size and shape accompanied by dramatic changes in optical transmission/reflection characteristics in keeping with predictions by Effective Medium Theories.(1,2) Using a pulsed Kr+ laser at 647 nm with pulse width of 150 nsec gave sharp optical contrast threshold at 4 mW laser power. Using an unfocused Kr+ laser adjusted to deliver 2x104 watts/cm2 induces changes in electrical conductivity by greater than 10 orders of magnitude.
Cluster emission from a Molybdenum surface
Authors: Husinsky W. , Pellin M. , Calaway W. , Burnett J. , Schweitzer E. , Young C. , Gruen D.
Published: February 2023

The emission process of polyatomic species, in particular the sputtering of metal-adsorbate molecules and metal clusters, has very recently been studied to an increasing extent theoretically and experimentally [1-5]. However, due to the small fraction of sputttered clusters, relatively few experimental data are available at present. The interest in metal clusters arises primarily because metal clusters exhibit a strong potential as catalysts and they represent an intermediate state between atoms and metals. Often already metal clusters, build up of relatively few constituents, show features close to metals.
MBE Growth Mechanisms on GaAs (100)
Authors: Farrell H.H. , Harbison J. P. , Peterson L.
Published: February 2023

Molecular beam epitaxy (MBE) growth on III-V(100) substrates is a very Comolex process as it involves 16 atoms per unit cell for each bilayer cycle. This relatively large unit cell leads to a truly astronomical number of possible intermediate steos. It is the purpose of this work to suggest a detailed mechanism that may be formally characterized by four major intermediate stages that are typified by staple surface structures having both surface dimers (as initially proposed by A. Y. Cho (1) ) and dimer vacancies. These stages occur at the chemisorption of 0.25, 0.5, 0.75 and 1.0 of a monolayer of Ga during the growth cycle.
Lateral Migration of CO on Ni (100) in the Presence and Absence of Concentration Gradients
Authors: Roop B. , Mullins D. R. , Costello S. A. , White J. M.
Published: February 2023

Laser induced desorption (LID) has been recently employed by several groups to determine the diffusion coefficients of small molecules on metal surfaces. The LID method uses a pulsed laser to deplete a well-defined region of the adsorbate-covered surface, thereby setting up a concentration gradient. By refilling the originally depleted area with an isotopically labelled molecule, we are able to compare the diffusion rate of CO/Ni (100) at saturation coverage with and without a concentration gradient.
Electronic Excitation of Sputtered Atoms
Authors: Husinsky W. , Wurz P. , Strehl B. , Betz G.
Published: February 2023

The existence of sputtered electronically excited atoms and molecules is a well known fact and has been studied for quite some time. Nonetheless, up to this point a deeper understanding of excitation processes is lacking. In addition, even more puzzels have been created when first measurements by Doppler-Shift-Laser-Fluorescence-Spectroscopy (DSLFS) of the energy distribution of sputtered excited metastable atoms[1-3] showed results contradicting those theories[4,5] which had been proposed based on Light-versus-Distance (LvD)[6,7] and Line-Profile Studies[8,9] of the emitted light of sputtered short-lived excited atoms.
Formation of TiN on Si and SiO2 by Rapid Processing Using a Large Area Electron Beam
Authors: Die-chi SUN , Zeng-qi Yu , Fu-ming Li , Yuan-cheng Du , Hai Wang , Guo-bao Jiang
Published: February 2023

The increasing challenge in reducing the vertical dimension in modern VLSI. A multilayer metallization system has been used conventionally. It comprises three parts, Al used as a last layer to offer electrical interconnects, the metalloid silicide chosen as ohmic contact to Si, an intermediate layer inserted between them as diffusion barrier. So-called nitrides of transition metal may be suggested as suitable diffusion barrier,/1/ as we know, TiN film can be produced by nitrogen ion implanted onto evaporated Ti film and formed during nitrogen annealing of magnetron sputtered Ti film /2/ or nitrogen ion implanted and annealed TiN film with a thermal treatment by an electron beam /3/. However, a suitable TiN diffusion barrier layer, as most previous papers have reported, either a relative high annealing temperature or longer enough treating time was required. We describe here a new method of TiN film on crystalline Si and SiO2 substrate respectively using a wide area electron beam. The Ti film was deposited in a standard vaccum system, the thickness of Ti film was 1000 Å. The rapid nitride processing was performed by a large area plasma electron beam, the cross section of electron beam is 50 mm in diameter and the uniformity better than 4% over cross section of EB. It was operated in 10°–10−2 Torr of N2 and He gas enviroment. In experiment, the processing time, ratio of the mixture of N2 and He, the pressure and flow rate of gases and power density of EB were varied. After 5-50 seconds nitridation processing TiN were formed, the surface of thin film turned gold like colour.
Adsorption of Disilane and Hydrogen on Si (111)-7x7 Studied by Multiple Internal Reflection Infrared Spectroscopy
Authors: Uram K.J. , Jansson U.
Published: February 2023

The chemisorption of Si2H6 and atomic hydrogen on a Si (111)-7x7 surface has been studied over a temperature range of 100K-500K using multiple internal reflection infrared spectroscopy. The high resolution and polarization selection rules enable us to identify specific adsorbed SiHx species. The characterization and comparison of surface species derived from the adsorption of Si2H6 and hydrogen give insight into the effect of local geometry on vibrational frequency and also increases our understanding of the chemical vapor deposition of silicon from silanes.
Adsorbate-induced Surface States and Fermi-level Pinning at Semiconductor Surfaces
Authors: Mönch Winfried
Published: February 2023

Adatoms on semiconductors are inducing surface states and surface dipoles. For the observation of adatom-induced surface states, cleaved surfaces of III-V compound semiconductors are especially suited since they contain no intrinsic surface states within the bulk band gap. At such surfaces, the bands are thus flat up to the surface and adsorbate-induced surface band-bending is thus easily attributed to extrinsic surface states. Such adatom-induced surface states are responsible for the pinning of the Fermi level at adsorbate-covered semiconductor surfaces. Adatom-induced surface dipoles, on the other hand, are changing the ionization energy of the surface. Variations of the work function, finally, are including both changes of the surface band-bending and of the ionization energy.
Electron, Ion, and Photon Beam Induced Reduction of SnO2(110): Power Dissipation Thresholds
Authors: Erickson J. W.
Published: February 2023

Incident electrons, ions, and photons stimulate oxygen desorption from SnO2 (110). Power absorption thresholds characterize other surface and near-surface processes.
A New Technique for Quantitative Elemental Analysis of the Near Surface Region (<3nm) of Planar Solids
Authors: Hockett R. S.
Published: February 2023

The effective study of molecular physics of beam-activated chemical reactions would benefit from measuring the near surface (<3nm) elemental composition. Ideally, the quantitative composition would provide not only the major and minor constituents, as is done by ESCA and AES, but also the trace constituents which may contribute to catalytic or inhibitor effects for the reaction of interest. An example of a possible catalytic effect is the role of Fe on the reaction of nitrogen with the silicon surface [1]. A new analytical technique, Total Reflection X-Ray Fluorescence (TXRF) analysis, may non-destructively provide some of this information (elements with atomic number above 13) when the sample is planar. An example application related to beam/surface interactions would be the pre- and post-processing measurement of trace heavy metals on silicon wafers where the cleaning process uses UV-irradiation to activate the removal of trace metals [2].
UV Photoetching of Copper
Authors: Brannon James H. , Brannon Karen W.
Published: February 2023

Pulsed laser etching of copper using chlorine has been demonstrated and investigated (1-3). Chlorine, however, strongly corrodes copper even in the absence of light. To avoid this problem, we have examined UV photoetching of copper using the vapor of two room temperature liquids, CF2Br2 and CCl4. Both species are inert towards copper in the dark, but will undergo gas-phase photolysis with near unit quantum efficiency to produce Br or Cl atoms. At 248 nm, the gas-phase absorption of CF2Br2 is some 3 orders larger than CCl4 Yet surprisingly, the 248 nm etch rate is similar for both over the range 1-10 torr. At 351 nm, where the gas-phase absorption for both species becomes vanishingly small, CCI4 is observed to etch copper with the same rate as at 248 nm, while CF2Br2 does not cause etching. These results suggest that gas-phase photolysis of CF2Br2, but not CCI4, is important in initiating copper etching.
Adsorbed Layers in the Process of Chemical Vapor Deposition
Authors: Nishizawa Jun-ichi
Published: February 2023

In chemical vapor deposition, surface migration of adsorbed species is an important factor which limit the minimum crystal growth temperature, since high substrate temperature enhances the surface migration of the adsorbate. But, high temperature process produces defects in the crystal. Concerning this problem, photoepitaxy was proposed by the author in 1961 (1). It has been applied to Si (2) and GaAs vapor phase epitaxy (3), resulting in higher crystal quality at a lower growth temperature. Photochemical processes allow the possibility that each elemental process can be individually controlled among the competitive processes by using a specific wavelength.
The Absorption of 1.17 eV Photons by Al2O3 ( 11 2 ¯ 0 )
Authors: Schildbach M. A. , Hamza A. V.
Published: February 2023

Recently, it has been proposed that multiphoton absorption by wide band gap materials is an important mechanism for energy absorption on surfaces ultimately leading to laser-induced surface damage. Many authors have observed non-thermal, photon-stimulated desorption of particles with radiation at energies less than the band gap of the solid material sample.1 The multiphoton nature of the process was gleaned either from the dependence of the particle yield on photon fluence or by the fact that the single photon energy was insufficient to excite electrons across the band gap. In cases where the number of photons required in the process is large (>3), the assistance of surface or defect states in the band gap has been proposed as the origin of photon absorption or as states that resonantly enhance the multiphoton absorption. However, the surfaces studied have not been sufficiently well-characterized to confirm the proposed mechanism.
Chemical Imaging of Surfaces Using the Surface Analysis by Laser Ionization (SALI) Technique
Authors: Moro Lorenza , Mouncey Simon P. , Becker Christopher H.
Published: February 2023

The determination of the lateral distributions of chemical species on surfaces is of constantly increasing technological importance in many applications, such as integrated circuit manufacturing. The only two tools which have been available are scanning Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS) (in scanning or microscope modes). The AES technique is the most widespread but generally is considered to be of lesser sensitivity than SIMS, at least for spatial resolutions (defined by the primary beam diameter, d) of approximately ≥ 0.1 µm. Nominal sensitivities for AES are ~2 to 3% concentrations for d ≥1 µm, and 3 to 10 % for d ranging from 1.0 µm to 0.1 µm, respectively.1 Also, scanning AES can be very problematic for insulators and electron sensitive materials, although it undoubtedly will continue to be a major tool.
Etching of SiO2 film by synchrotron radiation in hydrogen and its application to low-temperature surface cleaning
Authors: Nara Yasuo , Sugita Yoshihiro , Nakayama Noriaki , Ito Takashi
Published: February 2023

In order to grow silicon films with good crystal quality, it is important to remove oxygen and carbon contaminants on the surface and to obtain clean substrate surface immediately before growth. In conventional surface cleaning process, silicon substrate is heated up to about 1000°C and the surface contaminants are evaporated or gas-etched from the substrate surface. However, such high temperature treatment causes the redistribution of impurity atoms in the substrates and it makes difficult to fabricate fine structures. Recently, synchrotron radiation (SR) stimulated evaporation of SiO2 film and its application to surface cleaning at 650°C have been reported1), and the usefulness of SR induced reactions for low-temperature process is being recognized.
Electronic Energy Transfer Between Donor and Acceptor Adlayers on Single-Crystal Surfaces: Distance and Coverage Dependence
Authors: Haynes D.R. , Tokmakoff A. , George S.M.
Published: February 2023

Electronic energy transfer in surface adlayers is a mechanism of fundamental importance to surface photochemical processes. In this study, the electronic energy transfer from a donor p-terphenyl (TP) adlayer to an acceptor 9,10-diphenylanthracene (DPA) adlayer was studied using quantum yield measurements at 30 K and 85 K. These investigations employed an Al2O3(0001) crystal surface as a two-dimensional support on which donor, spacer and acceptor adlayers could be sequentially adsorbed. The quantum yield measurements were performed in ultra high vacuum (UHV) utilizing laser induced fluorescence techniques.
A Study of Structural Properties of Non-stoichiometric Zinc Oxide Films Deposited by e-Beam Evaporation Technique
Authors: Chen Rui-yu , Yuan Chang-sheng , Wang Qi-he
Published: February 2023

In this paper, we discuss the effects of various temperatures of substrates and annealings on the structural properties of non-stoichiometric zinc oxide films.
Formation of Submicrometer Carbonaceous Islands During SEM Examination of Thin GaAs Layers on Si Substrates
Authors: Turner G.W. , Nitishin P.M.
Published: February 2023

Carbonaceous islands with controllable diameters up to ~ 2500 Å have been formed during SEM examination of very thin GaAs layers deposited by molecular beam epitaxy on Si substrates.
Excitonic Mechanism of Photon-Stimulated Desorption of Excited Alkali Atoms from Alkali Halides
Authors: Bunton Patrick H. , Haglund Richard F. , Liu Dengfa , Tolk Norman H.
Published: February 2023

The mechanism leading to photon-stimulated desorption (PSD) of excited atoms from the surfaces of alkali halides has been a subject of controversy since it was first discussed a decade ago [1]. We have recently carried out a systematic experimental study of PSD from alkali halides under both valence-band [2] and core-level [3] excitation. Our data demonstrate that the desorption yields for excited alkali atoms track the excitonic optical response of these crystals even at photon energies below the bulk band gap. Secondary electron measurements, taken simultaneously, implicate the formation of excess metal in the time and dose dependence of PSD yields. These results suggest a unified picture of PSD in which the ion motion initiating desorption is pictured as the decay of a localized, highly deformed vibrational mode of the crystal. Plausible mechanisms for creation of the excited atomic state include relaxation of excited F-centers and resonant neutralization into the excited state on metallic microclusters.
Atomic Layer Growth of SiO2 on Si(100) using SiCl4 and H2O in a Binary Reaction Sequence
Authors: Sneh Ofer , Wise Michael L. , George Steven M.
Published: February 2023

Future silicon microelectronics technology will require nanoscale components to achieve ultra large scale integration. The reduction to nanometer scale sizes will be dependent on processing that can be controlled at the atomic level and conformally deposit into high aspect ratio structures. The Si/SiO2 interface is central in silicon technology. Controlled and conformal deposition of SiO2 dielectric layers will be crucial for the fabrication of MOS gate oxides as thin as 50 Å and high aspect ratio trench capacitors in DRAM. Both requirements can be inherently achieved by the technique known as atomic layer epitaxy (ALE)1 or atomic layer processing (ALP) if the deposited film is not epitaxial.
Optical Properties of Silcon Nanoclusters
Authors: Brus Louis E.
Published: February 2023

Summary not available.
Coincident product distributions and vector correlations in the 193 nm photodissociation of NCCN
Authors: Wu Ming , Hall Gregory E.
Published: February 2023

The theory of unimolecular decomposition has played a central role in the history of chemical kinetics and molecular dynamics. Energy-dependent rate constants, product final state distributions, and photofragment excitation spectra have provided experimental tests for simple and complex unimolecular theories. The use of Doppler spectroscopy to measure correlated velocity and angular momentum distributions can frequently provide a more complete picture of the dissociation process than other, more integrated measurements. The 193 nm dissociation of cyanogen (NCCN) has been considered a classic case of a barrierless dissociation, well described by simple phase space theory, where all asymptotic product states that conserve total energy and angular momentum are considered equally likely.
Molecular Beam Optical Stark and PPMODR Spectroscopy of Pt Containing Molecules
Authors: Steimle Timothy C. , Li Boa-Zhong , Jung Kook Young
Published: February 2023

Ligated platinum compounds are important in many homogeneous catalytic processes yet there is very little experimental information about the Pt-ligand bond. The most detailed information about bonding comes from the analysis of gas phase spectra recorded at a resolution sufficient to resolve the fine and hyperfine structure and shifts in spectral features caused by the application of static electric and magnetic fields. The advent of the supersonic laser ablation/reaction source (1-4) has eliminated many of the problems associated with the generation molecules containing refractory elements, such as Pt. In our laboratory we use such a molecular beam source in the optical Stark and pump/probe microwave optical double resonance (PPMODR)studies. In both techniques the detected signal is single mode cw-dye laser induced fluorescence (LIF).
Degenerate Four Wave Mixing Spectroscopy of Free Radicals in Low-Pressure Plasmas
Authors: Hudgens Jeffrey W. , Green David S.
Published: February 2023

Four wave mixing spectroscopies offer new ways to measure chemical species in extremely hostile environments. Among the most demanding of these applications is the measurement of radical chemistry within plasmas. Most plasmas are highly luminous and are characterized by steep gradients in temperature and concentration. These hostile properties thwart fluorescence and absorption diagnostics. In addition, in many useful plasma reactors the electrodes and associated electronics impose cumbersome optical geometries. We are using degenerate four-wave mixing (DFWM) spectroscopy to sidestep these impediments and to provide sensitive and spatially resolved measurements of concentration and temperature. In conjunction with computer simulations this data will lead to a better understanding of fundamental chemistry within plasma environments. In this paper we describe proof-of-principal experiments that use NH radical spectra to profile the evolution of gas mixtures containing ammonia, hydrogen (or fluorine) and argon passed through a microwave discharge. We will also present data from similar experiments in which hydrocarbon radicals are the important reaction intermediates produced by the plasma chemistry.
High Resolution CCD Spectrography of the Visible Night Airglow
Authors: James J F
Published: February 2023

Using iterative optical ray-tracing, two plane-grating spectrographs have been designed and constructed which work at F/1.4 with a refrigerated CCD camera having a 1152 × 289 pixel CCD chip, to make spectra of the night airglow. There is a marked gain (about ×50) in sensitivity over current instrumentation.
Vibrational Dynamics in Liquids and Glasses: Picosecond Infrared Vibrational Photon Echoes and Other IR Experiments
Authors: Fayer Michael D.
Published: February 2023

The first vibrational photon echo experiments conducted in the liquid and solid phases [1,2] are used to examine the vibrational dynamics of solute molecules in liquids and glasses. . These experiments are performed using the Stanford superconducting linac pumped free electron laser which provides a source of tunable ~0.7 psec IR pulses. The psec IR vibrational photon echo experiment directly examines the interactions of a particular vibration with phonons and other vibrational modes of the system. In an IR vibrational echo experiment, the laser is tuned to the vibration of interest. Two pulses, one delayed in time, excite the sample. The echo is a third pulse of light that emerges from the sample in a unique direction. The intensity of the echo pulse is measured as a function of the delay between the two excitation pulses. The decay of the echo is a direct measure of the homogeneous dephasing of the vibration. In condensed matter systems, vibrational lines are generally inhomogeneously broadened. Therefore, taking a spectrum does not provide the dynamical information that is available from analysis of the homogeneous spectrum. The echo decay is the Fourier transform of the homogeneous vibrational line. The echo pulse sequence removes inhomogeneous broadening and permits the dynamical information that is contained in the homogeneous line to be obtained.
Vibrational Dynamics in Electron Transfer
Authors: Spears Kenneth G. , Wen Xiaoning
Published: February 2023

Electron transfer is a widely studied and important phenomena with an extensive literature. The measurement of electron transfer (ET) rates as a function of vibrational state has been a long sought goal for testing the vibrational reorganization component of electron transfer. Prior insight into vibrational effects has been indirect, initially through correlations of rate versus exothermicity for a variety of compounds, and more recently through Raman spectroscopic identification of important vibrational modes. A direct electron transfer rate measurement for two vibrational states and subsequent identification of the final vibrational quantum numbers following electron transfer have been measured in our recent work for the first time.1
Vibrational Dynamics of CO Bound to Myoglobin and Metallo-porphyrins
Authors: Peterson Kristen A. , Hill Jeffrey R. , Diott Dana D. , Fayer Michael D.
Published: February 2023

We have made direct measurements of the vibrational lifetimes of carbonmonoxide (CO) bound at the active site of wildtype myoglobin [1] and myoglobin with single residue mutations in the binding pocket. Measurements were also made for CO bound to water soluble metalloporphyrins with differing metals and peripheral substituents. A pump-probe technique using tunable microjoule pulses from an infrared free-electron laser was used to monitor the loss of vibrational energy from the CO ligand with 2 picosecond time resolution. Recovery to the CO vibrational ground state in both the protein and soluble porphyrin systems occurs in the range from 10 to 30 picoseconds. The vibrational lifetime of CO bound to myoglobin is essentially independent of temperature from 20 to 300 K.
Time Resolved Photochemistry in Ionic Clusters
Authors: Lineberger W. Carl
Published: February 2023

Ultrafast pump-probe studies of photodissociation and the subsequent recombination or photochemistry in size-selected ionic clusters (ICI-(CO2)n, I-2(CO2)n, (O2)-n) will be discussed. The experiments provide direct measurements of the effect of partial solvation on the electronic structure of the solute.
Microcavities for Ultrasensitive Spectroscopy
Authors: Olmsted Brian L. , Jones Michieal L.
Published: February 2023

Spectroscopy is often performed on emission or absorption centers that due to sample preparation are located within a thin film or located in proximity to a dielectric interface. However, locating emission or absorption centers near reflecting interfaces can strongly effect their interaction with the electromagnetic field. In recent years, there have been several reports of the observation of a change in the angular distribution of emission due to cavity confinement. In addition, changes in the radiative lifetime have also been reported. A review of spontaneous emission from planar microstructures has recently been presented by Deppe et. al.1 The perturbation of the radiative properties of centers can be predicted using quantum electrodynamics for the electromagnetic modes of the discontinuous media. In fact, it is possible to design a specific structure to enhance the mode amplitude, and therefore, the interaction at the position of a radiative center. This approach can be used for ultrasensitive spectroscopy. Furthermore, emission or excitation angle can be used to selectivity cause enhancement at a particular frequency or position within a planar structure.
Infrared Kinetic Spectroscopy Applied to Radical Reaction Yields: Propargyl from the Reaction of Singlet Methylene with Acetylene
Authors: Adamson J. D. , Morter C. L. , Glass G. P. , Curl R. F.
Published: February 2023

Infrared kinetic spectroscopy is a powerful tool for quantitative investigation of radical reaction rates and reaction branching ratios. Here it is applied to determine the rate and yield of the reaction between singlet methylene and acetylene, This reaction is believed1 to be the main reaction forming propargyl, C3H3, in hydrocarbon flames. The dimerization of the propargyl produced is proposed1 to be the principal pathway for the formation of benzene, C6H6. A series of subsequent reactions starting with benzene ultimately yields the soot and fullerenes formed in flames.
Femtosecond nonlinear optical studies of molecular and structural dynamics in condensed phases
Authors: Lotshaw William T. , Staver P. Randall
Published: February 2023

The information content of femtosecond time-resolved nonlinear optical transients can be fully exploited by combining conventional kinetic analyses of the transient waveforms with a spectral analysis of the discreet Fourier transform (FFT) of the same. Qualitative and quantitative constraints on the sample systems and time-resolved data format must be observed to generate rigorously defensible and verifiable data interpretations.
Diode laser spectroscopy of a fast-axial-flow CO2 laser active medium: vibrational distributions and plasma-chemical reactions
Authors: Spiridonov Maxim , Toebaert David
Published: February 2023

The diode laser spectrometer operating in the 4.5 μm region with a spectral resolution of about 10-4cm-1 was applied to investigate the active medium of a DC-excited fast-axial-flow CO2 laser. Detailed distributions of the CO2 molecules over the rotational and vibrational levels in a glow discharge plasma have been obtained, and corresponding temperatures have been derived. The vibrational distribution involves more than 30 levels from all vibrational modes of CO2. The bending and symmetric stretch temperatures were found to be equal, and approximately equal (within experimental error of 2-4%) to the rotational temperature.
Image Sequence Segmentation in Time†
Authors: Yang Y.H. , Fichter J.M.
Published: February 2023

In this paper, we will present a technique that addresses the following question: Given an image sequence, how to partition this sequence into meaningful subsequences? The technique developed is based on statistical analysis of an encoding scheme of difference images. Results on some simulation sequences will be presented. To the best of our knowledge, this problem has never been raised nor addressed in published literature.
VLSI Architectures for Real-Time Image Processing
Authors: Narendra Pat
Published: February 2023

Real-time image processing has come of age in numerous industrial and military applications. Now is the opportune moment to define architectures which can yield low cost generic VLSI building blocks spanning the various algorithm and system requirements. In this paper, we summarize typical sensor formats and algorithms to identify common data flow and computational structures required for their real-time VLSI implementation. A set of criteria for evaluating architectures for VLSI is developed and used to examine several representative architectures. Recommendations for common VLSI building blocks are made for the representative architectures.
Integrated Sensors for Robotic Applications
Authors: Hackwood Susan
Published: February 2023

Summary not available