A case is presented for processing of advanced materials via low fluence lasers where the incident fluence is below the ablation threshold. A processing technique is presented which may have application to nanometer scale 'machining'. The technique relies on partially offsetting the reduced incident fluence with enhancement in the efficiency of coupling energy to surface electromagnetic waves (Plasmons). Experimental results are shown that surface corrugation enhances coupling of incident laser radiation to surface plasmons. Additional results are presented in which plasmon excitation results in the nonthermal ejection of ionic species. An experimental result is presented on a composite thin-film material where a specific material plasmon excitation results in a commensurate signature in the species ejection kinetic energy.

A combination of fast plasma diagnostics are utilized to probe the propagation of laser ablation plumes in vacuum and low-pressure background gases in order to understand key gas dynamic processes relevant to film growth by pulsed laser deposition. During expansion into low-pressure background gases, the ion flux in the plasma plume splits into fast and slow components over a limited range of distances and times. This general effect is presented here for the case of yttrium ablation into argon, a single-element target into an inert gas. Time- resolved optical absorption spectroscopy and optical emission spectroscopy are employed to simultaneously view the populations of both excited and ground states of Y and Y⁺ for comparison with intensified-CCD photography of the visible plume luminescence and ion flux measurements made with fast ion probes during this phenomenon. These measurements indicate that plume-splitting in background gases is consistent with momentum transfer from an initial, vacuum velocity distribution into a second, slowed velocity distribution initiated by scattering collisions between plume and background gas atoms. The fast distribution is exponentially attenuated in accordance with Beer's law, and the second, slowed distribution coalesces into a stable, propagating shock structure.

Optical multichannel emission spectroscopy and intensified charge coupled device (ICCD) imaging have been applied to real-time, in situ gas phase species identification during the pulsed excimer or Nd/YAG laser deposition of selected thin films. A plume gasdynamic expansion model has been developed and used to predict the outer edge plume front locations for comparison with those observed in the ICCD images. Good agreement was found between the model and ICCD images, with plume temperatures indicated by the model to be typically between 10,000 K and 30,000 K. Molecular beam mass spectrometry has also been used for real- time, in situ species identification and velocity distribution determinations. The systems studied include PbZr_0.53Ti_0.47O₃ (PZT), BaTiO₃, AlN, BN, Al₂O₃, and Ag. The ICCD imaging of plumes from PZT and BN targets, in particular, revealed that particulate ejecta were present after some regions of the target surface had been modified morphologically by multiple exposures to the laser beam. These ejecta appeared long after the luminous plume had decayed. When relatively high laser fluences were used, ICCD imaging also revealed strong evidence for interactions between the laser and the near-surface plume. This interaction manifests itself as increased emission intensity in the direction of the incoming laser beam. Mass spectrometric studies showing relatively fast velocity components of both neutral and charged plume species support the imaging evidence. The laser-plume interaction results in higher kinetic energies and a much greater effective temperature for a portion of the plume species. The slower component(s) appeared to be more thermal in origin (i.e. controlled by surface vaporization), and apparently reflects the target surface temperature.

Planar laser induced fluorescence has been used to acquire time sequence images of ground-state, neutral Si and SiO during laser ablation of an Si target in vacuum and in the presence of a background gas at a fluence of 3-4 J/cm². The SiO images, taken in air, strongly suggest that the observed SiO is created through reaction of silicon with oxygen at the contact front as the plume expands.

An EXACTA 2000 Faraday-modulated fast-nulling ellipsometer operating at 6328 angstrom has been used in situ to measure the polarizer (P) and analyzer (A) angles produced by CdTe-Cd_1-xMn_xTe quantum well and superlattice structures during growth by pulsed laser evaporation and epitaxy. This ellipsometer is capable of measuring P and A with a relative accuracy of 0.003 degree(s) at a rate of 10 points per second. This makes it especially useful in monitoring the growth of quantum wells and superlattice structures. From fitting the ellipsometric data, the thicknesses of the layers in CdTe-Cd_1-xMn_xTe quantum well and superlattice structures can be determined with an accuracy of 5% for layers more than 100 angstrom thick and with an accuracy of 10% for layers less than 100 angstrom thick. However, when each layer of thickness less than 100 angstrom in a CdTe-Cd_1-xMn_xTe superlattice consists of two sublayers with different indices of refraction, then the accuracy of the thickness determination is only 20%. The possibility of using such a Faraday-modulated fast-nulling ellipsometer to control the deposition of quantum well layers and superlattices is discussed.

This paper reviews our recent work on laser processing and characterization of epitaxial TiN/Si heterostructures. Pulsed laser deposition (PLD) technique has been employed to grow TiN films on H- terminated Si(100) substrates at various temperatures in the range of 25 to 600 degree(s)C. A pulsed KrF excimer laser ((lambda) equals 248 nm, (tau) equals 25 X 10^-9 sec) was used with the deposition chamber maintained at a base pressure of 10^-7 Torr/. The films were characterized by x-ray diffraction technique, Auger electron spectroscopy, Raman spectroscopy, scanning and high resolution electron microscopy, Rutherford backscattering spectroscopy and four probe electrical resistivity. Auger and Raman spectroscopy revealed that the films were purely TiN and free from oxygen impurities. The x-ray diffraction and TEM results showed that the TiN films deposited at 600 degree(s)C were single crystal in nature with epitaxial relationship <100>TiN<100>Si. The RBS channeling yield for these films was found to be in the range of 10-13%. Four-point-probe electrical resistivity measurements showed characteristic metallic behavior of these films as a function of temperature with the lowest value of resistivity of about 15(mu) (Omega) -cm at room temperature. The epitaxial growth of TiN on Si(100) is rationalized in terms of domain matching epitaxy, where four unit cells of TiN match with three unit cells of Si with less than 4% misfit. This paper also describes the fundamental issues related to thin film growth, defect formation, atomic structure of defects and interfaces in semiconductor heterostructures.

Composed of sp³ bonded nodules of carbon, laser plasma films with the properties of diamond are deposited in vacuum onto almost any substrate by condensing carbon ions carrying keV energies. These multiply charged ions are obtained from the laser ablation of graphite at intensities in excess of 10¹¹ W cm^-2. The high energy of condensation provides both for the chemical bonding of such films to a wide variety of substrates and for low values of residual compressive stress, 0.6-0.8 GPa. On selected films hardness cannot be measured because of deformation of the diamond indenter and only a lower limit of 78 GPa can be reported. Coatings of 2-5 micrometers thicknesses have extended lifetimes of materials such as Si, Ti, ZnS, and stainless steel against the erosive wear from high-speed particles by factors to tens to thousands. The mechanical properties of amorphic diamond films are further enhanced by a low coefficient of friction of about 0.1. The combination of these mechanical properties seems to make amorphic diamond an attractive material for use as a protective coating in current industrial applications. Deposited upon silicon, quartz or sapphire, amorphic diamond films have interesting electrical properties including a very high coefficient of emissivity.

Thin films of zinc oxide, titanium oxide and nonlinear optical organic chromophores entrapped silica were all fabricated by using a new technique called laser assisted molecular beam deposition (LAMBD). In the cases of the zinc and titanium oxides, molecular oxygen was supersonically expanded into the laser ablated plasma plume of pure metallic targets and then directed towards a substrate. In the case of organic entrapped silica, a supersonic expansion of organic entrained in He carrier gas was mixed with an expansion containing gas phase aggregates of silica, and then directed toward the substrate. The gas phase aggregates of silica were produced by a supersonic expansion of He carrier gas into a laser ablated glass rod. Micron and submicron thick films were deposited on a variety of substrates which were situated in the path of the molecular beams. These films were then studied via scanning electron microscopy, energy dispersive X-ray spectroscopy, X- ray photoelectron spectroscopy and uv-visible spectroscopy. The quality of the oxide films were found to be largely dependent on the fluence of the incident laser, the expansion conditions employed and the metal target used. Comparing zinc and titanium, when ablated under identical experimental conditions, titanium produced the most homogeneous film. The binding energy of the Ti 2p_3/2 photoelectron peak and the splitting of the Ti 2p doublet indicate that the Ti in the deposited film is in the +4 oxidation state. The optical spectra of organic entrapped silica films, dissolved in chloroform, are identical to that of the pure organic compounds.

Excimer laser ablation of a polycrystalline graphite target was used to prepare amorphous carbon films. Optical properties of the films were investigated in dependence of the laser power density and the hydrogen supply during deposition. The hydrogen content of the films was 0.7 to 37.5 at % in dependence of the deposition conditions. An optical bandgap up to 1.6 eV was found for films with low hydrogen content. Applying an additional hydrogen plasma during deposition the optical bandgap increased up to 1.95 eV. The laser power density was varied between 1.5 and 3.4 X 10⁷ W/cm². Generally, the lower power densities near the ablation threshold lead to larger optical bandgaps. An additional excimer laser irradiation of the growing carbon films with a laser power density up to 10⁶ W/cm² leads to graphitization within the otherwise amorphous films. An increase of the laser power density to 2 X 10⁶ W/cm² induce the formation of microcrystallites. Those microcrystallites could be identified as cubic diamond by means of transmission electron microscopy (TEM) investigations.

Over the past decade major advances have occurred in the field of thin- film photovoltaics (PV) with many of them a direct consequence of the application of laser processing. Improved cell efficiencies have been achieved in crystalline and polycrystalline Si, in hydrogenated amorphous silicon, and in two polycrystalline thin-film materials. The use of lasers in photovoltaics includes laser hole drilling for emitter wrap-through, laser trenching for buried bus lines, and laser texturing of crystalline and polycrystalline Si cells. In thin-film devices, laser scribing is gaining increased importance for module interconnects. Pulsed laser recrystallization of boron-doped hydrogenated amorphous silicon is used to form highly conductive p-layers in p-i-n amorphous silicon cells and in thin-film transistors. Optical beam melting appears to be an attractive method for forming metal semiconductor alloys for contact formation. Finally, pulsed lasers are used for deposition of the entire semiconductor absorber layer in two types of polycrystalline thin-film cells-those based on copper indium diselenide and those based on cadmium telluride. In our lab we have prepared and studied heavily doped polycrystalline silicon thin films and also have used laser physical vapor deposition (LPVD) to prepare 'all-LPVD' CdS/CdTe solar cells on glass with efficiencies tested at NREL at 10.5%. LPVD is highly flexible and ideally suited for prototyping PV cells using ternary or quaternary alloys and for exploring new dopant combinations.

Laser ablation deposition technique was used to deposit silicon carbide thin films on both Si(100) and quartz substrates. The deposition was accomplished by ablating SiC sintered ceramic targets, using a KrF (248 nm) excimer laser. At a laser intensity of about 1 X 10⁹ W/cm², substrate temperatures in the (25-700) degree(s)C range were investigated. When the deposition temperature is varied from 27 to 650 degree(s)C, (i) the density of a-SiC films increases from 2.6 to 3.0 g cm^-3, while their mean roughness value (for a film thickness of about 1 micrometers ) slightly changes from 0.44 to 0.5 nm; (ii) the optical transmission of a-SiC films is significantly improved (the absorption coefficient at 632.8 nm wavelength was reduced by a factor of about 5); and (iii) their Si-C bond density, as determined by FTIR spectroscopy, increases from (13.1 +/- 1.3) to (23.4 +/- 2.4) 10²² bond cm^-3. The increased number of Si-C bonds is correlated to the increase of the optical transmission. Over all the investigated deposition temperature range, the a-SiC films were found to be under high compressive stress around a mean value of about 1.26 GPa. The control of the stress of a-SiC films was achieved by means of post- thermal annealings and the annealed a-SiC films were successfully used to fabricate x-ray membranes.

Hafnia, zirconia and yttria films for optical applications were prepared by laser ablation using an excimer laser at 248 nm wavelength. Films were deposited at room temperature either in an oxygen atmosphere or with additional oxygen ion bombardment of the growing films. We will show that laser ablated oxide films have a high refractive index approaching that of the corresponding bulk material and, hence, a high packing density. Moreover, the films possess high laser damage thresholds at 1.06 micrometers wavelength, though they are still somewhat lower than those of good electron beam evaporated films. Oxygen ion bombardment leads above a certain threshold of ion energy and current density to a decrease in refractive index. In the case of hafnia, for example, it decreases from 2.15 down to 1.80 at 600 nm wavelength. Experimental proof will be given that this behavior is a result of ion induced modifications of microstructure. While films with high refractive index were of amorphous structure and had a high packing density with low porosity, increasing ion bombardment of the growing films leads to increasing crystallization within the films and, finally, to polycrystalline films combined with increasing grainlike film growth. Larger voids between the grains result in lower packing density and, therefore, lower refractive index. Based on these findings multilayer systems of only one material with ion controlled refractive index variations were prepared and investigated with regard to their laterally resolved absorption and their laser damage thresholds.

We describe the deposition of Sr_xBa_1-xTiO₃ (0.5 <EQ x <EQ 0.8) thin films by pulsed laser deposition and the issues related the their application as active microwave device components. The Sr_xBa_1-xTiO₃ thin films (approximately equals 5000 angstrom) deposited at 775-850 degree(s)C in 350 mTorr of oxygen onto (100) MgO and LaAlO₃ were smooth, single phase, and epitaxial with the underlying substrate. Highly oriented Sr_0.5Ba_0.5TiO₃ films on LaAlO₃ with x- ray rocking curves of 72 arc seconds were observed. The dielectric constant of Sr_0.5Ba_0.5TiO₃ thin films, determined from the signal in patterned transmission lines between 100 kHz and 0.1 GHz, was approximately equals 20% of that observed for the bulk and the zero field temperature dependence was broad in comparison to the sharply peaked behavior seen in bulk. The dielectric loss tangent was measured as a function of stoichiometry for Sr_xBa_1-xTiO₃ (0.2 <EQ x <EQ 0.8) thin films (3-5 micrometers ) at room temperature and at 9.2 GHz. Loss tangent values were found to be highly sensitive to the Curie temperature of the film. Loss tangent values as low as 0.1% were obtained for Sr_0.8Ba_0.2TiO₃. The results for Sr_xBa_1-xTiO₃ thin films presented in this paper are encouraging for future applications in active microwave devices.

Thin films of CuInSe₂ (CIS) were deposited on soda-lime float glass with a molybdenum back contact by means of coevaporation and Pulsed Laser Deposition (PLD). The resulting films have been characterized by Raman scattering, SEM (Secondary Electron Microscopy), EDX (Energy Dispersive X-ray) and XRD (X-Ray Diffraction). Raman analysis is a versatile tool and is particularly suited for investigations of the near surface film structure and defect chemistry. Raman measurements of indium-rich coevaporated thin films indicate an ordered defect structure. Furthermore the Raman spectra are strongly influenced by texture properties. This makes it more difficult to assess the free carrier concentration in CIS films. Raman spectra of coevaporated CIS films and films deposited by PLD are compared.

One of the major advantages of pulsed laser deposition (PLD) for thin- film growth is the use of simply prepared solid targets. Especially for our work with CdTe-related materials in photovoltaics, target preparation by cold pressing from high purity powders works well, partly because the II-VI semiconductors such as CdTe, CdS, and ZnTe do not create serious problems with particulate generation in the PLD plume. Thus we have used mixtures of these binary compounds to produce ternary alloy films with good results. These alloy films are being used to produce band-gap-graded structures in PV cells. In addition, the PLD technique lends itself readily to the preparation of doped films again through appropriate target mixing such as elemental copper mixed into ZnTe or elemental indium mixed into CdS. In addition, doping from the vapor phase by reactive deposition of CdTe in the presence of small pressures of O₂ has been successful in reducing the normally very high resistivity of the polycrystalline CdTe Films. Electrical measurements, Raman and photoluminescence, x-ray diffraction, and scanning electron microscopy results from these materials will be presented.

Multiple quantum wells and superlattices of CdMnTe/CdTe were grown epitaxially on ZnCdTe using Pulsed Laser Evaporation and Epitaxy for Cd_.85Mn_.15Te doped with indium and high purity CdTe targets. Photoluminescence was measured in the 4-80 K temperature range. The use of different excitation wavelengths (488 nm and 623 nm) led to depth studies of the structures. In order to determine the degree of indium incorporation in the wells, the results from the multiple layer structures were compared with the photoluminescence from single layers deposited under similar conditions.

The authors describe a newly developed laser-induced chemical vapor deposition (LCVD) process using an argon-fluoride excimer laser. The LCVD apparatus is equipped with an ultrahigh-vacuum chamber system including an Auger electron spectroscopy (AES) analysis chamber and a focused laser-beam scanning system. Hydrogenated amorphous silicon films free from oxygen contamination are confirmed to be fabricated using the AES analysis before exposing the films to air. Silicon film oxidation process after prolonged exposure to air is also characterized using the AES analysis. Furthermore, the new LCVD process is applied to the fabrication of soft x-ray multilayer mirrors. A tungsten-silicon multilayer mirror with a laterally varying film thickness for high performance soft x-ray focusing systems is successfully obtained on the design rule.

This paper reviews the laser processing of II-VI and III-V compound semiconductors for optoelectronic devices. when a laser beam scanning system is combined with MBE or MOCVD apparatus, the resultant growth process is called laser-assisted epitaxy. Laser irradiation of the films has various effects, depending on the growth conditions: doping efficiency, film growth rate, and film composition are affected. Using these effects, laser-assisted epitaxy has been used to make photodetectors, laser diodes, and integrated devices for multiwavelength transmission.

The principles and properties of vacuum ultraviolet (VUV) and ultraviolet (UV) light generated from a new type of excimer lamp are described. Compared with other lamps, these VUV and UV light sources can provide high photon fluxes over large-areas. These VUV and UV sources have been used to initiate the photo-deposition of dielectric and metallic thin films. The photo-deposited film properties, determined using ellipsometry, FTIR spectroscopy, UV spectrophotometer, and electrical measurements, showed that good quality films could be produced. Multilayered films of silicon oxide, silicon nitride, and silicon oxynitride can also be produced at low temperatures (below 300 degree(s)C). Very high deposition rates (500 angstrom/min) have been obtained by irradiating silane and oxygen gas mixture at low temperatures. This technique being relatively inexpensive in capital outlay, simple to apply, and readily scalable to large-areas provides interesting perspectives for optical and electronic applications.

Excimer lamp deposited ultra-thin (< 250 angstrom) silicon dioxide and silicon oxynitride films were characterized using spectroscopic ellipsometry (SE) and Fourier transform infrared (FTIR) spectroscopy. SE analysis of the photo-deposited SiO₂ films revealed no variation in the refractive index (n) of the films for deposition temperatures of 200 degree(s)C and 300 degree(s)C. Using a Bruggeman effective medium approximation (EMA), SE analysis was employed to determine both the silicon oxynitride layer thicknesses and compositions as a function of deposition temperatures and gas ratio, defined as (N₂O/(N₂O + NH₃)). From this analysis the optical properties of the silicon oxynitride thin films were extracted. It was observed that the refractive index for the 200 degree(s)C and 300 degree(s)C series of samples decreased from n equals 1.81 to 1.46 and n equals 1.72 to 1.46 respectively as a function of increasing gas flow ratio. FTIR analysis revealed spectral features characteristic of Si-O, Si-N, Si-H and N-H bonding. The most significant feature in all recorded spectra was a mixed spectral absorption band ranging from 800 cm^-1 to 1300 cm^-1. Both the integrated band area and peak wavenumber of this absorption band was found to be sensitive to the degree of nitridation and layer thickness of the thin films. The N-H stretching bond density was calculated from the N-H peak at 3360 cm^-1 using appropriate calibration factors. A slight decrease in the N-H bond density with increasing gas flow rate was observed. This variation in bond density was significantly less than that observed for PECVD silicon oxynitride films.

An electron-beam method of measuring the local density of a rarefied gas is considered and ways of adapting it to the diagnostics of pulsed erosion jets, formed by intense laser evaporation of the surface of a solid, are discussed. A description is given of measurement systems and the results of the density measurements are reported for the specific case of an erosion jet formed by irradiation of a lead target with millisecond pulses.

The gas-phase processes relevant for oxidation during Nd:YAG laser ablation of YBaCuO superconductor in vacuum and in an oxygen environment are investigated by mass spectrometry used in conjunction with molecular beam technique. The dynamics of monoxides YO and BaO as well as small clusters formation are analyzed. To separate the processes involving ablated and ambient oxygen, argon ambient atmosphere is also used. In vacuum, the oxidation is caused predominantly by interaction of low velocity portions of ablated Y and Ba atoms with the ablated oxygen which is mostly realized, at the laser fluences used (3-5 J/cm²), in atomic form. In oxygen background, efficient formation of oxides and oxygen-contained clusters is observed at all expansions stages. The pressure dependence of the atomic and oxide fluxes for the high velocity species has been described as an attenuation of molecular beam due to reactive and elastic scattering, and thus the cross section for oxidation reactions have been estimated. Hydrodynamic effects are found to have a significant influence on the oxidation processes within the plume. In argon background, oxide fractions decrease with the pressure due to dilution of the ablated oxygen flux.

The ionization/recombination processes during the expansion of laser ablation products into a vacuum and into an ambient gas are investigated on the basis of gas dynamic model. The plasma is assumed to be heated immediately by laser irradiation up to the high temperature, and to reach the ionization equilibrium. The laser energy is estimated to be spent on the vaporization, dissociation and heating of an ablated material and on the ionization of evaporated particles. The plasma expansion is described in two-temperature approximation by the Euler equations. The model is used to analyze the laser ablation of YBaCuO superconductor in oxygen atmosphere under actual film deposition conditions. To understand the role of ionization, we compare the numerical results with one's computed ignoring the ionization processes and with the time-of-flight data. The computations show that only a small part of ionization energy goes away from the cloud with the radiation. The main part is converted into translation energy of expanding products at the initial stage of the expansion. As a result, the kinetic energy of the plasma is approximately doubled.

The expansion of laser-induced plume into an ambient gas under typical thin film deposition conditions is investigated. A simplified theoretical model has been developed to understand the dynamics of plume-ambient gas interaction under the gas pressure of typically a few tens Pa. The model is based upon the generation of a high-temperature and high-pressure plasma cloud which is initially confined to a sphere of irradiated spot radius and is then suddenly allowed to expand into a gas. The expansion is governed by the Euler system of nonstationary equations. The model has been applied to investigate the dynamics of laser ablation of YBaCuO in oxygen. Numerical results show that the series of density jumps following one after another are formed in the plume. The origin of these pulsations is attributed to the repeated reflections of the secondary shock wave due to the effect of plume overexpansion. Using the calculated data, the time-of-flight signal has been simulated to compare the numerical results with available experimental data. Surprisingly good quantitative agreement has been achieved.

We report the maskless holographic fabrication of submicron relief diffraction gratings with periods 230-500 nm and depth-to-spacing ratio as high as 0.5 on the surface of p- GaAs under visible laser light. The gratings were fabricated in the process of photochemical wet etching by laser-induced etch rate reduction method. The physical mechanism of laser-induced grating formation in p-type semiconductors is considered.

We report on XeCl excimer (308 nm) laser-assisted dry etching ablation (LADEA) of InP in a Cl₂/He atmosphere. The InCl_x layer produced by the chlorination process was ablated for laser fluences below 80 mJ/cm²; this was determined to be the ablation threshold of InP for our experimental conditions. We studied the influence of Cl₂/He mixture pressure, laser fluence and number of pulses on the etch rate of InP. Experiments were carried out with 5% and 10% concentrations of chlorine and at a laser repetition rate of 5 Hz. Employing linearly polarized light with an appropriate choice of experimental parameters (based on the afore mentioned studies), gratings were patterned by laser-induced coherent modulation of the beam at the semiconductor surface. We have also, for the first time, combined diffraction with LADEA to develop regular shaped features on semiconductor surfaces. Using this technique, 0.3-0.5 micrometers gratings were developed on the InP surfaces by an array of rectangular apertures. This approach offers the potential for fabrication of damage-free micro- or nano-structures, as well as substrates with patterns suitable for selective area deposition/epitaxy.

Information recording by laser ablation involves energy absorption by an active layer followed by heating at the focal point and in the immediately adjacent area. We have used various organic dyes as recording media and characterized their properties. The substrates employed were made of polymethyl methacrylate (PMMA) or polycarbonate (PC). The influence of defect in the substrate and the birefringence of it were studied. Apparatus was developed which makes it possible to study the sensitivity of the materials used. The static mode and the dynamic mode of operation were employed. The sensitivity threshold and resolution were determined. Visible checking of recorded pits was possible using the maximum possible magnification of 1500 times. For documentation purposes and to compare results achieved on different materials the track was imaged onto a silicon CCD camera which was connected to a personal computer via an interface for image processing. Degradation processes caused by long term storage and by day light were also studied.

Multiple quantum wells and superlattices of CdMnTe/CdTe were grown epitaxially on CdZnTe using Pulsed Laser Evaporation and Epitaxy from indium doped Cd_.85Mn_.15Te and high purity CdTe targets. The photoreflectance and photoluminescence spectra were collected at T equals 5-10 K. In addition to the photoreflectance signatures originating from the CdZnTe substrate, CdTe buffer layer and CdMnTe barrier layers, the spectra also display features that are attributed to optical transitions occurring within the CdTe quantum wells. The signatures were observed in several heterostructures with [001], [111], and [112] crystal orientations.

The Direct Simulation Monte Carlo (DSMC) method for simulating rarified gasdynamics has been applied to the problem of pulses laser deposition. Both 1D and 2D axisymmetric simulations were carried out. In both, a source of silicon expands into the background gas of argon in the presence of a diffusely reflecting substrate. Density, temperature, and axial flow velocity for each species are computed as functions of position and time. Particle flux and energy incident on the substrate are also monitored as functions of time. The simulation results are in good agreement with experimental plume diagnostics and film growth rates vs. pressure data.

Copper surface interactions with chlorine and carbon tetrachloride and a UV excimer laser are studied, in the context of applications to interconnects in microelectronic circuits. With Cl₂, a highly reactive gas, the etching process is governed by bulk diffusion. With CCl₄, which is less reactive, the limiting step is the creation of reactive species at the surface. The diffusion of active species in the gas phase is evidenced by a degree of nonuniformity of mm-sized etched spots.

Si_1-x-yGe_xC_y / Si heterostructures are realized by pulsed laser induced epitaxy (PLIE) from C⁺ implanted pseudomorphic Si_{0.84/Ge(subscript 0.16} films and from hydrogenated amorphous SiGeC films deposited on Si(100). The laser treated samples are examined by electron channeling, energy dispersive X-ray analysis, Rutherford backscattering spectroscopy, X-ray diffraction and Raman spectroscopy. First results show that laser induced epitaxy is effective, provided that laser fluence exceeds a threshold for which the melted depth is larger than the initial SiGeC layer. In addition, carbon incorporation in substitutional sites is demonstrated.

Pulsed laser deposition have been adapted for precursor fabrication of Hg-Ba-Ca-Cu-O thin films. The preparation involves a sequential deposition of HgO and Ba₂CaCu₂O_x thin layers at 200 degree(s)C on MgO and SrTiO₃ substrates. Processing parameters were optimized by studying surface morphology of the individual layers and by strict Hg content control. Ex-situ thermal postannealing and oxygen content have not yet been optimized. The obtained films show almost single phase HgBa₂CaCu₂O_6+(delta ) with a c-axis of 12.65 angstrom and T_c (onset) of 110 K as determined from magnetic measurements.

Pulsed laser deposition has been developed as a technique for the preparation of accurate planar models of catalysts. The procedure is exemplified by copper/copper oxide on alumina, a DENOX catalyst, ablated under dry or wet conditions. Ablation of hydrogen free oxides in moisture is a novel route for hydroxylation. The work wad done in a fully UHV compatible multichamber system and is part of a coherent research program to trace the role of different paths for NO reduction with hydrocarbons over alumina/Cu_xO.

Femtosecond-pulse laser processing in the visible spectral range ((tau) approximately equals 300 fs; 615 nm) allows precise microstructuring of metallic and semiconducting thin films on metal and glass substrates without disruption and delamination of the remnant material. Laser light couples into geometrical surface defects differently than into homogeneous surface regions. The heat affected zone (HAZ) is not controlled by the laser pulse duration, when (tau) < 0.5 ps, but by the electron-phonon relaxation time (tau) _e approximately equals 0.5-1 ps. A model is proposed which allows to calculate the ablation threshold fluence for the application of ultra-short laser pulses. Experimental results for the ablation of platinum and amorphous silicon thin films on gold and glass substrates are presented. Visible femtosecond-laser pulses can ablate metal films by a one-photon mechanism, and the indirect semiconductor silicon due to a nonlinear process. In the latter case, self-induced multiphoton absorption limits the laser interaction with the target to a small volume. Laser structuring of silicon thin films on glass substrates is supported by a intrinsic etch stop because the ablation threshold of glass (F_th approximately equals 1.2 J cm^-2) is greater than that of the amorphous silicon film (F_th approximately equals 0.2 J cm^-2). Barium borosilicate glass starts ablating by visible femtosecond-laser pulses after several incubation pulses which generate sufficient defects for efficient light coupling.

Excimer laser sources have already been used with success for a number of novel material processing procedures. Most promising of these deal effectively with challenging materials for which little can be done with ordinary tools in order to materialize their potential. In this presentation, attention is focused on excimer irradiation processing of high grade sintered alumina. On one hand, it is shown how effective and unique can be an excimer beam in transforming the surface of this heavily used material. Under specific irradiation conditions, surface melting of sintered alumina is obtained. The resulting material is then studied by low-angle X-ray diffraction which reveals in particular the eventual formation of the uncommon gamma-alumina phase within 10 nm from the material surface. On the other hand, a rather thorough investigation of the phenomenology of the gamma-phase synthesis is presented, stressing various aspects: dynamic, energetic, structural and chemical, all of them stemming from the unusual characteristics of the excimer laser beam itself. As a result, it is shown how the presence of this gamma-phase may induce direct electroless plating of the excimer- processed alumina surface, on of the many peculiarities of that phase showing potential applications.

Laser-induced surface modification of various polymers is presented as a suitable pretreatment of surfaces in a two-step metallization process. Materials such as polyamide (PA), polypropylene (PP), polystyrene (PS), polycarbonate (PC), acrylbutadienestyrene (ABS), styreneacrylnitril (SAN), polybutadieneterphtalate (PBT), and polyoxymethylen (POM) were treated by excimer laser radiation ((lambda) equals 248 nm) in air. The aim of this study is to investigate different processing regimes of surface modification. Therefore the laser processing variables fluence F, repetition rate v and pulse number N are varied and the absorption coefficient, optical penetration depth, ablation depth and ablation threshold are determined. The surface morphology and surface roughness are studied by optical surface profilometry and secondary electron microscopy (SEM). The influence of laser treatment on chemical composition of modified and ablated surfaces is analyzed by X-ray photoelectron spectroscopy (XPS). Depending on the processing parameters and materials properties different microstructures and values of surface roughness are generated on the micrometer length scale. Pretreatment for the subsequent metallization is performed with laser radiation, wet chemical and plasma etching. The metallization of polymers is investigated for different surface morphologies. The used metallization processes are electroplating and physical vapor deposition (PVD). Adhesion of the deposited films, measured with scratch and tape test methods, is used as a criterion for determining regimes of suitable surface modification for subsequent metallization.

A mathematical model of the transmission of heat by conduction was studied in a system consisting of thin layers on a solid support subjected to a laser impulse. The pulse length varied from 100 ns to 300 ns. It was shown (and confirmed by experiment) that, for a revolving disc, the heating effect has little influence on the active layer after sublimation recording is performed. The threshold temperature of this process for materials employed was in the range 180 to 200 degree(s)C. The calculated isotherms for the static mode are demonstrated and compared with experimental results for a case of an organic dye active layer with an absorption maximum at 780-850 nm.

The tailoring of chemical, morphologic, optical and mechanical properties of solid surfaces with laser radiation is described according to the understanding and control of photon-matter interaction with the melt, vapor and plasma states involved. According to the processing variables the dynamics of material removal, material deposition and light attenuation can be matched to the requirements of tailoring the 3D properties of material surfaces with laser radiation. The modification of surfaces by chemical processing technique, the removal of matter by thermal and non-thermal processes including etching and ablation, the deposition of single and multilayer thin films, the photoresistless pattering by direct and indirect processing techniques, and the machinig by surface treatment and drilling as well are examplarily reported. Keywords: laser processing, micro 3D structures

A combination of microwave excitation and a mask projection scheme is applied for laterally structured etching of silicon. The technology is based on polymerization of an inert overlayer, which protects the silicon surface from the etching gas. After ablating the polymer from the silicon surface with pulsed Excimer laser radiation the surface is exposed to an etching gas atmosphere. Different feed gases have been used, such as CF₄, either nonactivated or activated in a microwave discharge. With these etching gases well-defined structures can be achieved with etching rates of 0.1 micrometers /min. Using a gas mixture of CF₄ and CCl₄ the etching rate can be increased to 1 micrometers /min. smooth etching profiles can be achieved with laser fluences < 0.6 J/cm². Further, for the Si etching with MMA (methylmethacrylate) polymerization suitable processing variables for these competitive processes are obtained. The deposited polymer films and etched Si surfaces are characterized by ex-situ electron spectroscopies (XPS, AES) and the gas phase reactions are investigated with quadruple mass spectroscopy (QMS). The formation of ClF₃ or ClF is discussed as a critical step within the microwave-assisted laser dry etching (MALDE) process. The presence of these species correlates with high Si etch rates.

New maskless method of submicron relief diffraction gratings formation in the process of wet photochemical etching of n-A^IIIB^V semiconductors is developed. It is a combination of holographic method and method of laser-induced relief generation under resonant excitation of surface electromagnetic waves. The increments of exponential time growth of dominant relief Fourier harmonics at the initial (linear) stage are measured. It was discovered for the first time experimentally that nonlinear stage of relief time evolution is characterized by oscillations of amplitudes of first and second surface. Fourier harmonics and is accompanied by laser-stimulated effect of specular reflection suppression. The possibilities to control the profile form of laser-induced periodic relief (both for gratings with symmetrical and asymmetrical profiles) are explored.

Excimer laser microetching is applied on various substrate materials, including metals, metal alloys, semiconductors, and polymers, of arbitrary geometrical shape for fabricating surface-relief optical microstructures with very fine features (micron width/micron depth, or less). Particularly good results have been obtained with hardened photoresist, lithium niobate crystals, and stainless steel. The method is based on selective laser ablative etching achieved by projecting a mask, on a reduction basis, onto the substrate material. In addition to simple rectangular metal masks, computer generated holographic mask patterns were used. These hologram masters were optically plotted on photoresist, and then wet etched to produce chrome-on-quartz masks. A consecutive step-and-repeat method was used to replicate the mask on the substrate. Several types of surface relief holograms were directly etched on various materials. One class of holograms upon reconstruction produces an 8 X 8 square optical interconnect array. Another type reproduces a specific design pattern consisting of characters and numbers. Full automation of the microetching process in conjunction with a raster scanning method allows the fabrication of arbitrary pixellated multilevel micro-patterns. The direct nature of the etching technique appears to be very attractive since it eliminates the need for substrate material pre- or post-processing and can be applied to almost any solid material.

The effect of Laser Processing (LP) on defect complex formation and dissociation in ITC-GaAs was investigated by Surface Photovoltage (SPV), Photoluminescence (PL) and C-V profiling measurements. We propose that the reduction in hole concentration on LP samples is caused by a complexing of C_As and a laser-induced primary point defect. A clear correlation was found between the introduction of this complex and sample characteristics: these include, enhanced SPV signals, reduced C_As related PL intensities and a nonuniform distribution of ionized acceptors. In this exploratory work, we have demonstrated the unique influence of LP on the distribution of isolated acceptors and the free carrier concentration.

The time resolved photoluminescence (PL) spectra of nanocrystalline Si layers formed with the help of YAG laser ((lambda) equals 1.06 micrometers , E_p equals 0.3 J, t_p equals 2 X 10^-4 s) modification of the monocrystalline Si were investigated. PL was excited by pulse nitrogen laser ((lambda) equals 337 nm, t_p equals 7 X 10^-9 s, E_p equals 2 X 10^-5 J). It was established a prominent manifestation of the blue band ((lambda) equals 420 nm). There are two sets of time decays observed in PL relaxation spectra. The fast decays are observed in the wide band from 420 to 700 nm while the slow time decays are observed in wave range from 500 to 850 nm. An analysis of the amplitude and time characteristics of PL spectra allow to conclude that the fast time decays are determined by volume energy levels in nanocrystalline wires with a variable cross-section and with the short lengths conditioned by the laser induced high defects concentration. The slow part of PL kinetics is approximated by stretched exponent, characteristic of disordered systems, has exponential spectra dependence. This attests the predominance of the tunneling mechanism controlling the velocity of recombination. The obtained results count in favor of quantum confinement model of the porous silicon (PS) origin. From practical terms the laser assisted method proposed may be useful for the pattern designed PS layers formation despite of the methods using the photoresist of ion implantation.

Effect of periodic surface structures (PSS) formation on a laser—irradiated target surface is still of essential interest since these structures are responsible for redistribution of laser energy flux on the target and thus affect the coupling efficiency. Moreover, surface electromagnetic wave (SEW) generation is of considerable interest in opto-electronic and opto-acoustic applications. Most of the experimental studies of SEW excitation and PSS growth in the irradiated area due to the interference between incident laser wave and SEW were performed for the case of a stationary laser spot. Only few papers are available where authors reported considerable increase in coherence of surface "ripples" when the laser beam is scanned along the surface in order to cover the whole area of a substrate with a periodic relief. See1, for example. Meanwhile, theoretical 1D model developed by Dykhne and Rysev24 predicted velocity resonant effect of PSS formation. Our objective here is to present experimental evidence of the mentioned resonant phenomena and to report 2D effects of SEW/PSS generation in a resonantly moving laser spot and to compare growth efficiency and quality of structures with the results for stationaiy laser spot. Theoretical models of PSS are discussed elsewhere57. Incident laser wave can be scattered by the surface roughness with different spatial harmonics ej in different angles along the surface plane. Whenever roughness spectrum has harmonics with a wave vector q fitting the equation qk+k (k is the tangential component of the incident light wave vector and k is the wave vector of the scattered wave) the instability can occur. Periodic modulation of the energy distribution on the surface due to the interference of the incident and scattered waves can be "recorded" on the surface via vaporization or a similar process. The structure's growth increases scattered wave amplitude and hence the interference field. That, in turn, results in the further development of the relief with spatial period A2ir/q. Note that SEW excitation mechanism, which works for metals and semiconductors, can not be applied to the most of dielectrics. For the case of dielectrics the other origin of the "surface" wave is considered -- the portion of the incident laser wave, refracted by the certain harmonic of the surface roughness within the small angle with respect to the surface plane. It is a convenient way to describe the kinematics of the process with the vector diagram, which actually corresponds to conservation of momentum in the surface plane (Fig.l). Basically, for the p-polarized laser beam the maximum increment for PSS generation in a stationary spot is achieved when SEW wave vector is collinear to k. There are few exceptions though. Firstly, spectrum of surface roughness may contain dominant harmonics (consider scratches, for example). Relatively well developed initial relief forces scattering in the corresponding direction (see diagram), thus leading to the dominant PSS formation. Secondly, there are socalled degenerate structures (qo)8. These PSS are actually formed by two SEWs and due to that have a higher growth increment. This is often a case when angle of laser wave incidence on the surface 8 is large enough (in practice, 0<400), that both SEWs propagate relatively close to k. Finally, the last exception is PSS generation in a moving beam. This case we will discuss further.

Laser reflectometry is a simple technique, which is readily applied to real-time monitoring epitaxial growth of thin semiconductor films. It can be applied with a probe laser of low power to monitor normal and assisted semiconductor growth or with high power lasers to 'self monitor' laser assisted growth, for example during selective area epitaxy. In normal growth, laser reflectometry is most suitable for monitoring films having a thickness >= (lambda) /4 where (lambda) is the monitoring wavelength, although, having monolayer sensitivity, it can be used to monitor much thinner film growth. Examples of a Bragg reflector grown with the aid of laser reflectometry and a 6 nm AlGaAs/GaAs superlattice are given. Both growth rate and chemical composition of alloy semiconductors can be obtained in real-time for films of the above thickness and this is illustrated by reference to the AlGaAs system. Its high sensitivity to chemical composition has enabled the chemical beam epitaxial growth of carbon doped GaAs films to be monitored: results of a recent study of such films are presented and discussed. By aligning a low power probe laser along an excimer laser beam the assisted growth can be monitored. In addition to giving instantaneous information on the growth rate, the monitoring also provides a check on the developing surface morphology. In selective area epitaxy, via Ar⁺ laser assistance, the reflected signal contains growth information relating exactly to the laser footprint. Results of 'self-monitoring' Ar⁺ assisted CBE grown GaAs are discussed in terms of the mechanisms involved in the laser assistance.

In this paper we present recent results on laser-induce surface modifications and surface patterning by ablation. Different types of structure formation are discussed. The modeling of UV-laser ablation in nonstationary regimes is studied. Numerical calculations on the ablation rate are compared with experimental data.

We experimentally investigated the expanding CO₂ laser produced carbon plasma interaction with a substrate and the interactions occurring when two laser produced plasmas collide. The electron density and temperature of the single plasma source were measured and ion composition of plasma was determined by means of optical spectroscopy. The carbon dimers were observed near the target and substrate surfaces and during the collision of two plasmas.