The crystallization and oxidation processes of thin, free-standing (FS), sputtered Cr films under the action of cw CO2 laser irradiation were studied by transmission electron microscopy (TEM) and transmission electron diffraction (TED). The crystallization is induced at power densities above 28.65 W cm−2, dwell time of 1 s, and the oxidation at power densities of 48.1 W cm−2 and longer dwell times.

The presence of microstructures on surfaces undergoing laser processing modifies the electromagnetic boundary conditions and can lead to dramatic changes in the intensity of the local electromagnetic fields and hence in the reaction rates and final morphologies resulting from the laser reaction. Examples are presented for periodic structures on planar surfaces — the rippling of Ag surfaces during laser oxidation; and for isolated dielectric structures — enhanced scattering (∼ 100x) due to dipolar resonances in Si particles.

The evaporation mechanism of CdTe, HgTe and HgO.7CdO.3Te under high power laser irradiation was investigated using mass spectroscopy. Results were compared to thermal evaporation. Thermal evaporation yields Te molecules and Cd(Hg) atoms. In the case of HgTe and Hgo.7Cdo.3Te, the evaporation is noncongruent. Evaporation induced by the irradiation of 1.06 μm Nd:YAG laser pulses evolves atomic Hg, Cd and Te congruently. The dissociative and congruent nature of this process makes it a very attractive technique for depositing thin films.

The heterogeneous decomposition of 2-propanol vapor in the presence of CuO solid can be induced by irradiation with a pulsed CO2 laser. The reaction produces both propene and acetone. In contrast, the homogeneous multiphoton-induced decomposition of 2-propanol vapor yields only propene. The branching ratio ([hydrocarbon]/[acetone]) in the heterogeneous experiments has been examined as a function of laser pulse energy. While the yield of acetone increases monotonically with increasing fluence, yields of hydrocarbon show two distinctly different regimes of fluence dependence. Reactions have been run with both d8 and h8 2-propanol and on 1:1 mixtures. Neither reaction channel shows significant isotopic selectivity over a range of experimental conditions. This data will be discussed in light of a model that involves energy deposition in the solid, followed by either heterogeneous reaction of adsorbed material or energy transfer and subsequent multiphoton excitation of the alcohol vapor.

We describe the use of time-resolved laser-induced fluorescence (TRLIF) and plasma-induced emission (PIE) spectroscopy in studying the dynamics of ion transport, formation, and loss in low frequency RF plasmas, used in plasma etching and deposition. N2+ and Cl2+ ions formed in N2, Cl2, and N2/Cl2 discharges were monitored as a function of both position between the electrodes and magnitude of the applied rf potential. In the discharge center, TRLIF was used to measure ground state ionic lifetimes. In N2/Cl2 mixtures, N2+ was found to charge exchange rapidly with Cl2 and Cl to form Cl2+ and Cl+. In the electrode sheaths, the ion response to the applied potential was evident from periodic depletion of the ion concentration as a result of acceleration by the field. From the spatial variation in the ion concentration time dependence, we deduce that the sheaths expand and contract with the same period as the applied potential.

A summary of the recent work on laser-enhanced gold plating is presented. The purpose of the study has been to obtain rapid maskless plating on thick metal samples. Results will be described on the plating rates for a variety of laser and electrical parameters. The most recent work on a laser-jet plating system will be discussed. With this system, rates of up to 30 μm/s have been achieved on 8 mil thick Be-Cu samples.

Desorption and evaporation from solid surfaces are induced with high yield and wavelength selectivity by excitation of internal adsorbate vibrations with resonant laser infrared. Simple rate equations describe essential features of the process and relate the photoreaction rate and yield to the intensity, the duration of laser-solid surface interaction and molecular properties of the adsorbate. The significance in photodesorption of the experimentally determined spectral widths is shown. Considering the spectral widths in the theory brings the order of the calculated photo-desorption rates for CH3 F-NaCl and the measured rates (also yields) in better concert.

An infrared laser generated from a Nd:YAG laser mixing with a dye laser has been used as a tunable coherent pulsed laser source to photodesorb ammonia from a Cu(100) surface after excitation of the ν3 mode. Timeresolved quadrupole mass spectrometry is sucessfully applied to determine the translational temperatures of the desorbing species from a monolayer coverage on the metal surface. Evidence for desorption induced by vibrational excitation has been obtained and the results are discussed in terms of rapid energy transfer mechanisms.

CdS and CdS:Ag thin films, deposited at room temperature, were irradiated using an argon-ion laser, causing them to become photoconductive in the path of the laser beam. Physical deformation of the thin films is reported, and the optical and electrical properties of the photoconductive devices thus fabricated are described. We suggest this as a means to fabricate small area, patterned photoconductors with the benefit of maskless, low temperature processing.

Semi-insulating GaAs as well as MOCVD GaAs layers have been doped in situ with Se in a MOCVD system. H2Se diluted in an H2 + AsH3 atmosphere, which avoids surface decomposition, is used as the doping source. The surface is heated locally for less than 1 μs with a 3-ns Nd-YAG-laser pulse (frequency doubled: λ = 532 nm, pulse ratio 5 s−1). During this short time adsorbed Se atoms are incorporated into the heated surface region.

This process allows us to achieve heavily doped thin layers with Se concentrations in the order of 1021 cm−3. Outside the irradiated area the crystal remains undoped.

Se concentrations measured with secondary ion mass spectroscopy (SIMS) and carrier concentrations measured with the van der Pauw method indicate the diffusion of adsorbed Se atoms into GaAs. The distribution and activation of Se depends on laser power and substrate temperature.

Primary and secondary ion deposition of epitaxial semiconductor films from laser-induced plasmas is reported Laser plasmas were generated by focusing 15 ns, 107 to 108 W/cm2 pulses of 5 eV photons from a KrF excimer laser onto Ge and Si wafer targets. Time-of-flight, current-voltage, and film thickness measurements at secondary (i.e., ion) targets indicated that the ions were emitted, with an average energy of ∼40 eV, in a distribution which was strongly peaked in the normal direction. Primary ion deposition was performed by placing substrates on an ion target/substrate heater biased to give additional ion acceleration as required. Secondary deposition was achieved by biasing the ion target, in this case a wafer of the same material as the laser target, sufficiently negative to sputter target material onto a third electrode. Epitaxial Si on (100) Si and Ge on (100) Si and (100) GaAs were obtained by both methods. Hall effect measurements on heteroepitaxial Ge grown at 1 μm/hr on GaAs substrates by primary deposition showed thatfthe films were p-type with hole concentrations of ∼1018 cm−3 and mobilities of ∼150 cm2/V-sec.

We have studied silicon incorporation in GaAs subsequent to Nd-YAG laser irradiation through high pressure silane atmospheres. The process involves SiH4 pyrolysis at contact with a laser-melted GaAs surface, and incorporation of the released Si atoms in the melt. SIMS analyses have allowed us to study silicon incorporation as a function of SiH4 pressure, laser energy density and number of laser shots. The high sheet resistance of the doped layers indicates that the silicon atoms are poorly electrically activated. A compensation mechanism is discussed based on oxygen penetration from native GaAs oxide layers.

The technique of laser evaporation for the deposition of thin films has been applied to a large class of materials including oxides, fluorides and II-VI semiconductors. The evaporations were performed in high vacuum or under O2 pressures of 10−3 Torr, on several types of substrates, by using CO2 lasers in CW and pulse modes. The thin films thus obtained have been characterized for their structural, optical and electrical properties.

Entire ranges of mixtures in several binary systems (e.g., SnO2-SiO2), have been obtained by coevaporation, using mirrors to steer the laser beam among sources.

Conditions that affect the stoichiometry and structural properties (laser parameters, background pressure, evaporation rate, substrate temperature) have been established for each material system. Differences in the evaporation behavior of materials under CW and pulsed conditions have been investigated for the case of ZnO. Present and future applications of this technique in the optical devices field are also discussed.

Surface-dressed optical Bloch equations are derived for the purpose of evaluating the resonance fluorescence spectrum of two interacting identical atoms near or adsorbed on a metal surface. The derivation takes into account the influence of reflected photons, dephasing due to atomic collisions, the linewidth of the driving laser field and the resonance excitation of surface plasmons. A unique behavior of the surfacemodified fluorescence, not seen in analogous gas cell experiments, is predicted. Under the appropriate circumstance, a photon emitted from one of the two atoms can be trapped by the two-adatom-surface system, and this is studied by means of a theory which treats the atoms and their surface images on the same footing.

Laser-induced periodic pattern formation has been observed on a variety of substances. In particular, low-power lasers have been used to deposit a pattern on a metal surface. For a relatively smooth surface grating, this pattern can be explained in terms of a perturbative solution of Maxwell's equations. However, as the surface grating is enhanced by this initial deposition, the perturbative solution breaks down. An alternate non-perturbative solution of Maxwell's equations for such rough surfaces is considered here.

We propose a model for laser-induced chemical vapor deposition in which the growth of hydrogenated amorphous silicon (a-Si:H) thin films is rate-controlled by the gas phase homogeneous thermal dissociation of SiH4 The gas temperature is determined by a steady-state balance between energy absorbed from the laser and energy lost by thermal conduction.The film properties are primarily controlled by the substrate temperature.

When aerosol particles are immersed in a gas in which a temperature gradient is present, a force proportional to this gradient moves these particles toward the lower temperature. This is the thermophoretic force.It is responsible for the deposition of aerosol particles in processes employed in the manufacture of gradient index silicon dioxide, germanium dioxide optical fiber preforms.The deposition efficiency is approximately 50%, and in order to increase this efficiency, we have examined the interaction of an absorbing silicon dioxide aerosol with carbon dioxide laser radiation.The resulting temperature profile mirrors the intensity distribution, since the aerosol temperature is proportional to the local laser intensity.The absorbed radiation thus creates a temperature gradient that results in additional thermophoretic and convective motion. A simple model of laser-induced buoyant convection and thermophoresis is presented, and it is shown how deposition efficiency can be increased with laser radiation.Theoretical and preliminary experimental results are discussed.

Near the threshold for laser-induced melting of semiconductors like Si and Ge, the resulting surface morphology is characterized by spatial inhcaogeneities. For cw illumination, several authors have observed the formation of randan, microscopic lamellae interspersed with molten regions, for incident fluences between threshold and approximately twice threshold.We demonstrate experimentally that such lamellae also form under pulsed conditions for 20nsec, 1.06μ pulses incident on Ge.Theoretically, we consider the simpler case of cw illumination on a bulk sample: We show that, although in principle it should be possible to form uniform melt layers of arbitrarily small thickness, for melt depths less than the skin depth of the radiation in the liquid any spatial modulation of the liquid-solid interface leads to instabilities in the coupled laser-material system.These instabilities would result in runaway inhamogeneous heat flow and hence to the formation of lamellae.Three distinct types of instabilities are identified for melt-front penetrations of less than ∼l000Å in Ge.