A very thin gold coating (e.g., 270 to 3,500 Angstroms) is vapor deposited on the surface of a nickel substrate. A short radiant energy pulse from a laser having a pulse length of about 130 nanoseconds is directed at the coated surface to melt portions of the gold coating and the nickel substrate therebelow. The energy pulse is removed to permit the melted material to resolidify as an alloy with a high concentration of gold at the surface thereof.

Laser surface alloying

Molecular dynamics simulations have been used to investigate the dynamics and redistribution of energy during the impact of a nanocrystal with adsorbed liquid films. Although impact of a 32-molecule NaCl cluster on a solid surface at 3 kilometers per second leads to melting, disordering, fragmentation, and rebounding, the same size cluster colliding with a liquid neon film transfers its energy efficiently to the liquid for a controlled soft landing. Impact on a higher density film (argon) leads to rapid attenuation of the cluster velocity, accompanied by fast heating. Subsequent disordering, melting, and fast cooling by evaporation of argon quench the cluster to a glassy state. These results suggest a method for the controlled growth of nanophase materials.

https://science.sciencemag.org/content/sci/260/5112/1304.full.pdf

Controlled deposition, soft landing, and glass formation in nanocluster-surface collisions.

Microstructure of rapidly solidified materials

Laser alloying is a material processing method which utilizes the high power density available from focused laser sources to melt metal coatings and a portion of the underlying substrate. Since the melting occurs in a very short time and only at the surface, the bulk of the material remains cool, thus serving as an intimate heat sink. Large temperature gradients exists across the boundary between the melted surface region and the underlying solid substrate. The result is rapid self-quenching and resolidification. Quench rates as great as 1011 K sec−1 and concomitant resolidification velocities of 20 m sec−1 have already been realized. What makes laser surface alloying both attractive and interesting is the wide variety of chemical and microstructural states that can be retained because of the rapid quench from the liquid phase. These include chemical profiles where the “alloyed” element is highly concentrated near the atomic surface and decreases in concentration over shallow depths (hundreds of nanometers), and uniform profiles where the concentration is the same throughout the entire melted region. The types of microstructures observed include extended solid solutions, metastable crystalline phases, and metallic glasses. This bibliography is a compilation of published work in this area.

Laser surface alloying: a bibliography

Intense pulsed-laser irradiation in a suitable chemical atmosphere can produce a significant incorporation of chemical species from the environment to the surface molten layer. This process has been used to produce p-n junctions in silicon and GaAs irradiated, respectively, in PCl3 and SiH4 atmospheres. A modelling of the incorporation process, taking into account the solid-liquid-solid transition of the surface layer, has been developed following both a numerical and a semi-analytical approach. The modelling of the doping process gives results in a reasonably good agreement with the experimental doping profiles, obtained by irradiating Si samples in PCl3 atmosphere.

Surface doping of semiconductors by pulsed-laser irradiation in reactive atmosphere

Formation of a Noncrystalline Phase in Aluminum Irradiated with a Pulsed Ruby Laser

Matrix atomic losses and oxygen incorporation under ruby-laser irradiation of silicon in gaseous atmospheres.

Electrochemical and corrosion behaviour of laser modified iron surfaces

La implanted Ni single crystals, irradiated with Q‐switched ruby laser pulses up to 5.2 J/cm2, have been studied by 1.8‐MeV 4He+ ion channeling. The laser induced damage is found higher in comparison with as‐implanted damage. The as‐implanted Ni(La) system shows nonsubstitutionality, which persists even after laser irradiations, whereas a substitutional solid solution would be expected. Irradiation in air above 1.5 J/cm2 shows a clear La surface peak, which is almost absent when irradiation is carried out in an ambient having reduced oxygen and water vapor content (10−2 Torr vacuum). The higher damage and La nonsubstitutionality after irradiation are shown to result from enhanced defect trapping during resolidification. The La surface peak formation is attributed to a mechanism involving oxidation and trapping of La at the surface. The experimental La profiles are then reproduced with a liquid phase diffusion analysis including such a mechanism.

Pulsed laser treatment of La-implanted Ni single crystals

A nonsubstitutional alloy of 7 at. % Cr implanted in single‐crystal aluminum has been irradiated with Q‐switched ruby laser pulses up to 6 J/cm2. Liquid phase epitaxy, resulting in enhanced substitutionality without any Cr redistribution, is observed up to 2 J/cm2 for a laser pulse duration of 25 ns. At higher energy densities and with shorter pulses, 12‐nsec duration, convection effects are observed to inhibit liquid phase epitaxy. The surface reflectance appears to reduce due to high implantation dose.

E. Jannitti

Papers

Formation of a Noncrystalline Phase in Aluminum Irradiated with a Pulsed Ruby Laser

Matrix atomic losses and oxygen incorporation under ruby-laser irradiation of silicon in gaseous atmospheres.

Electrochemical and corrosion behaviour of laser modified iron surfaces

Pulsed laser treatment of La-implanted Ni single crystals

Laser treatment of a nonsubstitutional alloy Cr implanted in aluminum