The pulsed-laser induced photochemical production of metallic Ga islands on the surface of GaAs cleaved, irradiated, and studied in ultrahigh vacuum (UHV) is documented through photoelectron spectroscopy and subsequent scanning electron microscopy. Ga islands are detected for laser fluences as low as 1 mJ/cm2, far below those previously reported for modification of GaAs, and for which the temperature rise is negligible.

Oxide films of ZrO2, Y2O3, yttria stabilized zirconia (YSZ), and high Tc superconducting YBa2Cu3O7-x and Bi-Sr-Ca-Cu-O films were produced by spin coating metallo-organic precursors onto Si, ZrO2 and MgO single crystal substrates. Densification of these oxide films, after pyrolysis of organic constituents, was achieved by scanning a Nd:YAG laser beam across the film surface. Surface morphology, microstructures, spatial grain size distribution, compositional variations, defects and physical properties of laser sintered films were characterized using SEM, EDS, TEM, SIMS, XRD and 4-point electrical resistivity probe. Laser processing parameters, deposited film thickness and organic burn-off showed strong influences on the film densification behavior. This paper focuses on pursuing optimum conditions for obtaining dense, uniform sintered patterns in oxide films and on understanding the film-substrate interaction and dynamics of nucleation and growth via the laser rapid sintering process.

Excimer laser processing results in very rapid solidification of metal surfaces. In addition to mixing or segregation processes, rapid heat treatment can result in phase transformations which yield beneficial surface properties. We have investigated the effect of pulsed excimer laser radiation on the microstructure and surface hardness of Ti-6A1-4V. This material undergoes a well defined martensite transformation during rapid quenching from temperatures in the β phase field. The depth of the transformed layer is thus a marker for the temperature profile during processing. We find that the depth of the transformed layer agrees well with a simple 1-D calculation of heat flow following the laser pulse. As measured by the nanoindenter, we find that the surface martensite is softer than the mechanically polished alloy. Multiple pulse processing at high fluences results in an increase in surface hardness, but at a depth much less than that of the martensite, suggesting an independent mechanism.

It is shown that the composition and structure of CdTe and CdS surfaces can be reversibly controlled by excimer laser irradiation at fluences below the melting threshold. The removal rate is observed to depend exponentially on laser fluence up to the melting threshold. The translational energies of products desorbed from laser-irradiated CdTe surfaces were determined using time-of-flight spectrometry and are well-described by a Maxwellian velocity distribution. The dynamics of the photo-stimulated desorption process are correlated with the laser-induced changes in composition, and it is shown that the data are consistent with a thermal mechanism for desorption. A model is introduced which describes the reversible, fluence-dependent changes in composition and structure in terms of the kinetic competition between formation and desorption processes at the semiconductor surface.

The propagation of the laser-induced plasma formed by KrF irradiation of Y1Ba2Cu3O7 has been characterized in background pressures of oxygen and argon typically used for thin film growth. The ion current transmitted through the background gases was recorded along the normal to the irradiated pellet as a function of distance in order to measure the decreasing velocity and magnitude of the expanding plasma current due to collisional slowing and attenuation of the laser plume. The integrated ion charge delivered to a substrate at low pressures can be described by elastic scattering giving a general integral cross sections of σc[O2] = 3.2 × 10−16 cm2 and σc[Ar] = 2.7 × 10−16 cm2. At higher pressures, inelastic-scattering leads to increased recombination and reactive conversion of ions indicated by increased fluorescence of all the species, which becomes dominated by fluorescence of YO and BaO. Spatially resolved fluorescence measurements indicate that the luminous boundary to the plasma follows a weak shock front which coincides with the ion flux propagation. The ion transmission is found to drop exponentially with distance and background pressure, in agreement with a simple scattering model which yields general scattering cross sections for ion-argon σi-Ar = 2.1 × 10−16 cm2 and ion-oxygen σi-O2 = 2.3 × 10−16 cm2 interactions in background pressures up to 300 mTorr. The general features of the plume deceleration are described in terms of a drag force model.

Optical probing of laser-assisted chemical reactions on surfaces in real time can help explain and control these processes. Raman microprobe spectroscopy and micro laser induced fluorescence are the two optical probes employed here to investigate several examples of localized laser surface reactions. Raman microprobe analysis is used to monitor in real time the CuCl and CuCl2 products on the surface during local laser etching of copper films by Cl2 and the concomitant loss of the Cu2O passivation layer. It is also used to follow the production of Cu2O during the laser oxidation of Cu. Polarization Raman analysis is utilized to identify and analyze partially molten silicon during laser heating in vacuum and during the etching of silicon by chlorine. Laser induced fluorescence is used as a real time microprobe of desorbed products during local laser-assisted etching of Si and Al surfaces.

We have conducted an experiment which measures the product population and kinetic energy (KE) distributions from the UV laser induced decomposition of crystalline Bi2Sr2Ca1Cu2O8. We have measured these distributions at two laser wavelengths 248, 351. At a third wavelength (355 nm) we have measured the photoejected mass spectra from both a single crystal Bi2Sr2Ca1Cu2O8 sample and a polycrystalline Bi2Sr2Ca2Cu3O10 sample. For all the experiments, the laser fluence is maintained near the threshold for ion formation. The laser fluences are well below the level for instigating a laser induced above surface plasma. Our results show that the ejected products are not the consequence of a laser surface evaporation process. We measure a wavelength dependence in the ejected species population distribution and the ejected kinetic energy distribution (< KE > = 5 ± 1 eV.2eV FWHM) is indicative of an electronic excitation process. The measured ion mass spectra show atomic, diatomic (e.g. Sr2+), and oxide (e.g. SrO+, CaO+) species with lesser quantities of the complex oxides (e.g. S2O+). Distinctly absent from the mass spectra are the oxide compounds BiO+, CuO+, and the atomic species O+. Furthermore, the mass spectrum shows that at 248 nm laser excitation, the Bi+ species is the abundant photopro-duct. However, for both the 351 nm and 355 nm excitations, the Sr+ and SrO+ ions are measured as more abundant. Also, comparing the 355 nm laser excitation of the single and polycrystalline samples, there is very little difference in the photoejected species mass spectrum.

Carrier-driven photochemical etching of semiconductors can be selectively suppressed by altering the near-surface region to enhance carrier recombination, thereby reducing the supply of carriers that drive the surface etching reaction. Two methods for enhancing recombination and decreasing the etch rate at a given phonon flux include ion implantation and localized Zn diffusion. Raman spectroscopy can be employed to determine whether sufficient alteration of electronic properties has occurred to suppress etching.

Carrier-driven photochemical reactions, which require direct participation of free carriers for the chemical reaction to proceed, can be selectively suppressed by increasing the minority carrier recombination rate, thereby reducing the supply of carriers that drive the surface etching reaction. Two methods for enhancing recombination and decreasing the etching quantum yield, which is the number of atoms removed per incident photon, include ion implantation and localized Zn diffusion. For ion implantation, recombination-promoting defect concentrations depend on ion species, fluence, and annealing both during and after the implantation process. Other recombination processes related to carrier scattering from ionized impurities from in-diffusion of dopants or following implant activation can control etching.

Raman spectroscopy can be employed to detect changes in electronic properties that correlate with etching suppression. Changes that occur in the LO-phonon lineshape, such as those associated with phonon confinement and ionized impurity scattering, can be diagnostic of the carrier-driven etching behavior following a specific treatment. We have demonstrated two applications of Raman spectroscopy as a diagnostic for suppression of the carrier-driven photochemical etching of GaAs.

Atomic absorption spectroscopy (AAS) has been used as an in situ diagnostic tool to study sputtering of high-temperature superconductors. Hollow-cathode lamps were used as line sources to measure relative atomic species concentrations during sputtering of Y-Ba-Cu-oxide targets using a Kaufman ion gun. The AAS measurements showed that the fluxes of ground state Ba and Cu ejected from a composite target during argon- and oxygen-ion bombardment varied greatly with sputtering parameters. Measurements were made of the effects of changes in ion-beam energy, ion flux to the target, and target temperature. In addition, the variation in atomic densities of Ba and Cu with distance from the target were measured. For comparison, AAS measurements during argon- and oxygen-ion sputtering of a pure copper target were also performed. The AAS results were verified by measuring stoichiometry variations of thin films deposited under identical conditions.

Emission spectra resulting from ion beam sputtering an Y-Ba-Cu-O target were observed as a function of beam voltage and time using an optical multichannel analyser. The observed spectra were clean with several peaks attributed to each of Y, Ba, and Ar. A well defined O peak and a weak CuO peak were available for comparison. The intensities of the cation peaks were linear with respect to beam voltage above 450 V. Presputtering of a previously stored target was characterized by the diminishment of an initially large H peak as the cation peaks emerged.

A variety of electron-beam-induced effects, including oxidation, reduction and surface rearrangements are observed to occur at surfaces of oxides, fluorides and compound semiconductors during electron irradiation within the electron microscope. The extent and type of surface modifications observed are shown to depend upon the irradiation level, the residual microscope vacuum and the specimen temperature. For example, ex situ annealing of compound semiconductors leads to different end-products compared with in situ irradiation, thus showing that residual gas components can have a strong influence on the surface reactions. Electron irradiation of rutile during annealing at high temperature under ultrahigh vacuum conditions caused the rapid development of well-facetted holes without the usual intermediary phase seen at room temperature in conventional vacuum.

Aluminum thin films were photodeposited on silicon wafer from dimethyl-aluminum hydride under illumination of the ultraviolet photons generated by a deuterium lamp with a distinguished wavelength dependence. Namely, the growth rates increase linearly with vapor pressure under illumination of the l60-nm vacuum ultraviolet band from the lamp, while the growth starts above 0.3 mTorr only with the 240-nm band. To study the early stage of photo-deposition of Al, we constructed a scanning tunneling microscope and observed Al, islands. Steep sides were observed on islands with the distinguished boundary between vertical and horizontal growth. The shape of islands formed in the illuminated region and in the dark area was identical, thus indicating the absence of photo-induced migration effects.

Ion scattering spectroscopy (ISS) has been used to directly monitor the nitrogen coverage of a niobium target during ion-beam reactive sputtering. This measurement shows that the fully reacted target is nearly completely covered with nitrogen. The functional dependence of the nitrogen coverage on the N2 pressure has also been obtained. By taking the fractional target coverage to be a steady-state equilibrium between nitrogen sputter removal and thermal N2 arrival, the measured target coverage has been accurately modeled. The results indicate that the nitridation reaction is controlled by the thermal N2 molecules, which stick to the target with a high probability. This firmly establishes the fact that the molecular N2 flux can control the target reaction. This target coverage model has also been applied to fit the measured deposition rate as a function of the N2 pressure and shows that the deposition rate does not accurately reflect the target coverage. By modifying an existing reactive sputtering model, we show that the deposition rate can be modeled accurately by taking into account both the gettering reaction at the growing film and the target reaction.

The Secondary Electron Emission (SEE) spectra of type Ha diamond, highly oriented pyrolytic graphite (HOPG), amorphous carbon (e-beam evaporated), glassy carbon and amorphic-diamond (filtered arc evaporated) were measured in the 0–80 eV electron kinetic energy range, and found to be very distinctive for the different carbon allotropcs. The sensitivity of SEE spectroscopy to crystal damage for the type Ha diamond surface was studied by performing SEE measurements as function of 1 keV argon ion irradiation dose. Two examples of the use of SEE in the characterization of diamond surfaces are presented. In the first, the crystalline quality of the back and front surfaces of a chemically vapour deposited diamond thin film which had dclaminated from a fused quartz substrate were compared using SEE and, in the second, SEE was used to provide a qualitative estimate of the damage induced by mechanical polishing of a natural diamond surface.

The deposition of titanium lines by KrF excimer laser direct writing on lithium niobate (LiNbO3) has been investigated. A detailled study of the line profile has been performed since this is critical in the fabrication of Ti:LiNbO3 optical waveguides. We show that at a low power density E, the maximum thickness t is proportional to E, while increasing E leads to the diffusion of Ti into LiNbO3 resulting in a saturation and even a decrease in thickness. Preliminary results on Ti:LiNbO3 optical waveguides show that their characteristics are similar to those made by conventional methods.