A study has been conducted on the effects of increasing cooling rate during rapid solidification of NiTi upon the phases that are produced. The hammer and anvil rapid solidification technique and laser melting with a nanosecond excimer laser were used, which allow the cooling rate to be varied by three to four orders of magnitude. Although 1/3 {110} superlattice reflections are seen in the selected area diffraction (SAD) patterns of the splat quenched (SQ) specimens, x-ray diffraction analyses show the presence of only B2 phase and martensite. On the other hand, laser treatment (LT) of the specimens produces a layer that has a L10 structure with a slight monoclinic distortion. This phase can be envisaged as a small distortion of a B2 unit cell with a volume per atom ~3.3% lower than the equilibrium B2 phase. Also martensite is present in the layer. SQ alloys exhibit a marked {200} texture due to columnar growth opposite to the direction of heat extraction, while LT produces epitaxial regrowth of the melted layer. No substantial disordering is obtained in NiTi rapidly solidified alloys.

This paper demonstrates that metastable compounds can be synthesized on solid surface via pulsed laser induced processes at the liquid solid interface. Specifically, it is shown that the metastable oxides of iron can be obtained when an iron foil immersed in water is treated with Ruby Laser pulses [ λ =693.4 nm, pulse width 30 ns, energy density 10 J/cm2].The oxide has been characterized by using the techniques of conversion electron Mössbauer spectroscopy, X-ray diffraction and Rutherford Backscattering Spectrometry. The oxygen concentration near the surface as well as the depth scale over which it falls to zero can be varied by changing the laser treatment parameters such as pulse to pulse overlap, energy per pulse etc. A near-surface composition of ∼50 at.% and a depth scale of oxygen incorporation of a few thousand A° can be easily achieved. The phase transformation of a metastable oxide under thermal treatment is also explored. The mechanisms which could be responsible for the observed effects are commented upon. Some iron foils have been treated in air using comparable laser pulse parameters to obtain a comparision between treatment in air and liquid. Interestingly these foils show presence of √-Fe, which is a high temperature phase of iron known to be unstable at room temperature when pure. Other possible applications of laser processing of solids in liquid media are also discussed.

Amorphous 55wt%Cr-45wt%Ni films (60 nm thick) supported on EM copper grids were irradiated in air at normal incidence with a ruby laser (λ∼, 0.694 μm) through a ≈ 1.5 mm diameter diaphragm using one single laser pulse of 60 ns (FWHM) with fluences ranging from 120 to 540 J.m−2. The structure of the irradiated films is studied by TEM and TED. As a rule due to the appearance of thermal gradients between the centre and the mesh edge of the EM grid, the crystallization took place under various conditions of reaction from liquid phase, liquid melted layers , activated diffusion in solid state, to under threshold conditions for the development of the crystalline nuclei in the amorphous matrix. Periodic resonant and unreso-nant structures also developed in the liquid melted layers.

Crystalline Fe-B alloys in the concentration range of 5–25 at. pct. boron were processed by slightly (∼5%) overlapping single pulse XeCl excimer laser. The influence of the initial microstructure and phases upon the structure that results after laser processing (LP) were studied. The specimens were made by a rapid solidification procedure that permits readily glass-forming alloys to be obtained with structures ranging from fully amorphous to fully crystalline. The technique is briefly described. Two crystalline specimens of Fe-20 pct. boron, one in the as-cast condition and the other annealed, were laser treated. While the melted layer of the former was amorphous, the latter remained crystalline, exhibiting a similar phase content as before irradiation. Observations of both samples by scanning electron microscopy (SEM) prior to LP revealed a difference in particle size of one order of magnitude. A mathematical model of diffusion is developed for studying the homogenization process. It is concluded that the time for diffusion in the liquid state in the sample containing the larger particles is insufficient for homogenization to occur. Similar results regarding the influence of particle size were obtained with all the other samples.

Thermally grown Ni2 Si and NiSi2 layers on <111> Si substrates were irradiated by 40 ns Nd laser pulses in the energy density range 0.3–2.0 J/cm2. The samples were analyzed by time-resolved reflectivity, 2.0 MeV He+ Rutherford backscattering in combination with channeling and by transmission electron microscopy. In the NiSi2/Si system the melt starts at the free surface (1280 K) and propagates towards the inside. Dissolution of substrate silicon atoms occurs when the silicon temperature reaches the liquidus temperature (1400 K). In the Ni2Si/Si samples the melt starts instead at the interface when it reaches the eutectic temperature (1250 K). The subsequent propagation towards the surface is limited by the mass transport of silicon atoms to maintain a composition near that of the eutectic. In some cases the surface may melt also at the congruent melting temperature (1570 K), giving rise after solidification to a quite complex structure. The different behaviour of the two silicides/silicon systems is explained in terms of phase diagram.

The three-dimensional hydrodynamics of laser-induced, steady state vaporization of aluminum (2024) in vacuim was investigated with the aid of both a hydrodynamic computer code and a Mach-Zender interferometer. Provided the laser beam is sufficiently intense, a vapor plasma forms, resulting in a sustained region of high pressure near the target. The pressure is distributed asymmetrically over the footprint in the case of oblique incidence.

This paper presents a comparative study of the microstructures formed in Al.59Ge.41and Al.70Ge.30 (eutectic composition) free standing films under laser irradiation. An hexagonal metastable phase located between Allamella, can be formed depending on the film composition and the laser pulse length.

Via-hole filling technique by momentarily melting an aluminum film has been developed, whereby planarization of aluminum films for multilevel interconnects on integrated circuits can be achieved. The melting is performed with an optical pulse irradiation from an ArF excimer laser without the problem of junction spiking. This technique is applicable to filling submicron-diameter vias having a diameter of 0.6μm with 0.7μm depth(aspect ratio:∼1.2). Very high aspect ratio(2.0) via-hole filling is achieved by heating the sample. During the laser irradiation, the sample substrate was kept at 300°C.

Laser-material interactions are pivotal to optical storage technology. Laser quenching and thermomagnetic processes form the memory basis for approaches based on “phase-change” materials and magneto-optical alloys respectively. Recent progress in phase-change materials indicates that compound semiconductors as well as single element materials are characterized by fast crystallization times. In this work we review, utilizing time-resolved optical and conductivity probes, the melt-kinetics and glass formation processes in Te thin films and the laser-induced crystallization of amorphous GeTe. The latter studies are complemented by x-ray diffraction and TEM analysis. Results are also presented on time-resolved Kerr rotation studies to investigate the magnetic domain formation kinetics in thermo-magnetic recording. Material research problems facing laser interactions with optical recording materials will be discussed.

Written and erased bits of the In-Sb phase change type optical disk medium were studied using transmission electron microscopy (TEN) and electron probe microanalysis (EPMA). Both the bits were separated into inner and outer areas and were composed of only rhombohedral Sb crystals and zinc blende In50Sb50 crystals. The difference between the two bits were in crystal size and atomic distribution of the inner area. Models of the writing and erasing processes were derived from these observations and the In-Sb phase diagram. With these models, the thicknesses, grain sizes and optical contrasts of the both bits were consistently explained.

Amorphous thin films of GeTe were irradiated with excimer laser pulses and the subsequent crystallization was investigated utilizing simultaneous transient reflectivity and conductivity measurements. Below a threshold fluence of 15 mJ/cm2 pure thermal behaviour was found. Above that value, nucleation and growth are observed during the cooldown process. Above a fluence of 22 mJ/cm2 the films crystallize to a large degree within 200ns. Between 15 and 22 mJ/cm2 crystallite nuclei are formed (“frustrated crystallization”), and application of a subsequent pulse over areas exposed to this fluence regime leads to extremely fast crystallization (50 ns).

A Raman microprobe and TEM have been used to analyze the resolidified region of liquid carbon generated by picosecond pulse laser radiation. From the relative intensities of the zone center Raman-allowed mode for graphite at 1582cm−1 and the disorder-induced mode at 1360cm−1 , the average graphite crystallite size in the resolidified region is determined as a function of incident pulse energy density. By comparing with Rutherford backscattering spectra and Raman spectra from nanosecond pulsed laser melting experiments, additional information about the disorder depth in picosecond pulsed laser melted graphite is obtained. Comparisons of TEM micrographs for nanosecond and picosecond pulsed laser melting experiments show that the structure of the laser disordered regions in graphite are similar and exhibit similar behavior with increasing laser pulse fluence. The similarities in the resolidified regions under both irradiation schemes discourages a determination of the properties of liquid carbon after the liquid has resolidified.

We have employed the pump-and-probe technique to perform picosecond time resolved measurements of the reflectivity changes in two archetypal layered compounds, IT-TiS2 and lT-TiSe2 probed at 1.064 μm after pumping by 20 ps, .532 μm laser pulses. At the threshold fluence, ∼ 40 mJ/cm2, the reflectivity drops sharply, marking the occurrence of a phase transformation on the surface of the sample. Above threshold, the reflectivity reaches a value as low as ∼0.1 at high fluences, strongly suggesting that, like in graphite, the high temperature phase is not metallic.

A novel method to study the effect of rapid heating on polymers is presented. Nanosecond time resolved reflectivity measurements of thermal decomposition of poly(3-butenyltrimethylsilane sulfone) (PBTMSS) and polymethylmetacrylate (PMMA) films spun on silicon wafers and irradiated by a pulsed excimer laser at 248 nm are reported. It was found that there exists a critical temperature for effective decomposition. The time scale for thermal decomposition is comparable with the time scales determined for photo-ablation processes. The results indicate that thermal effects are very important in the interaction between polymers and pulsed UV-lasers.

A study to examine beam-solid interaction as a function of the cut surfaces of pyrolytic graphite samples (0, 30, 60, and 90 degrees relative to the basal plane) was made using a high intensity, carbon dioxide laser beam operating at a wavelength of 10.6 μm.

Crystal growth of redeposited carbon and impurities in the burn area as well as a melt on the burn edge were observed and examined using Scanning Electron (SEM) and Scanning Auger Microscopy (SAM). Similarities and differences relating to the structure of the material were further investigated using X-ray diffraction. Thermal transport properties as a function of angle were also examined.

Synthesis of transition metal nitrides induced by excimer laser irradiation of metal foils immersed in liquid nitrogen was studied. Nitrogen incorporation was found by sputtering Auger Electron Spectroscopy in all six investigated metals (Ti, Zr, Hf, V, Nb and Ta). X-ray diffraction was used to determine the compounds formed. The morphologies of the irradiated surfaces often indicated that the surfaces had gone through a molten state. Micronthick mononitrides were grown on Ti, Zr and Hf, whereas Ta and Nb formed Ta2N and Nb2N respectively. The nitrides on V were not satisfactorily identified. The extent of nitridation correlates with the thermodynamic driving force, i.e. the Gibbs free energy for nitride formation.

Thin films (1–2μm) of cadmium sulphide, deposited by electrophoresis, consist of a close packed layer of randomly oriented cubic-phase microcrystalline particles with an average diameter of 30nm. A CW CO2 laser, operating at 10.6μm has been used to convert this into a polycrystalline structure with columnar crystals, of hexagonal phase, which extend through the thickness of the film and whose c-axis is perpendicular to the substrate. The recrystallised regions comprise aligned grains up to 300nm in diameter whose cathodoluminescence spectrum exhibits a narrow peak centred at 2.42eV with a half width identical to that for evaporated CdS (0.1eV).

High resolution electron microscopy has been used in conjunction with electron energy loss spectroscopy to follow the beam-induced reduction of WO3, V2 O5 and CuO, all of which are maximal valence oxides. All three oxides underwent reduction, although there are differences in the reduction pathway: WO3 is reduced directly to the metal by loss of oxygen from the surface layers; CuO is reduced to the metal via at least two intermediate oxides (Cu4 O3 and Cu2O); and V2 05 forms a reduced oxide (possibly V6 O13) and then remains stable. It was possible to drill holes in V2O5 with an intense, small electron probe (using a field-emission electron gun) provided the sample had previously only been exposed to an electron dose below a critical value (<108 e/nm2). Preliminary doses higher than this critical value rendered the oxide immune to hole drilling (but not to a subsequent reduction to the stable oxide mentioned above), suggesting that holes can only be drilled while the material retains the original V2O5 structure.

The annealing behavior of In+-implanted amorphous Si layers is reviewed. Particular attention is given to the amorphous to polycrystalline transformation for peak In concentrations > 0.5 atomic percent. New data concerning the transformation rate, associated In transport and microstructure are presented and phase transformation mechanisms are discussed.

The effects of intentionally introduced impurities on the crystallization time, nucleation rate and crystallite growth velocity during solid phase random crystallization of amorphous Si thin films have been determined. Films deposited in UHV onto oxidized Si wafers were subjected to multiple energy ion implantation to introduce uniform distributions of P, B, As, O or F at 0.1–1.0 at.%. Crystallization times and growth velocities were determined over the temperature range 650 to 850°C from time-resolved reflectivity measurements, and nucleation rates were determined from these data using a classical, steady state nucleation and growth model. Strong impurity effects are observed: P, B and As all decrease the nucleation rate but accelerate the growth of crystallites, whereas both 0 and F retard growth while enhancing nucleation. The largest effects are for P, which reduces the nucleation rate more than 100 times at 1% concentration, and F, which increases the rate by roughly the same amount.