Clifton W. Draper

Laser irradiation of nickel single crystals

The effect of Q‐switched Nd:YAG laser beam irradiation on virgin and ion‐implanted Ni 〈110〉 single crystals has been studied. Rutherford backscattering and channeling have been used to establish crystal quality and to determine depth distributions and lattice locations of the implanted species (Au, Ag, and Ta) before and after laser treatment. Chanelling and Nomarski optical microscopy show that the Ni surface melts during the irradiation, followed by an epitaxial lattice regrowth resulting in (i) a formation of defects even in samples, (ii) a redistribution of the implanted atoms, and (iii) implanted atoms residing on substitutional lattice sites to form metastable solid solutions.

Laser surface alloying of gold films on nickel

Abstract Au-Ni surface alloys have been made by the laser induced melting of Au films on Ni substrates. By optimizing the laser parameters or by depositing Au-Ni sandwich structures it has been possible to produce concentrated substitutional alloys extending to depths of some thousands of Angstroms. These Au-Ni surface alloys are probably epitaxial with the underlying Ni single crystal substrates.

Laser surface alloying for passivation of TiPd

Abstract Q-switched laser surface alloying of 150 A palladium vacuum deposits onto polycrystalline titanium is shown to be an effective way of passivating titanium against corrosion by acid environments. Rutherford backscattering is utilized to measure near-surface concentration profiles. The surface palladium enrichment that occurs during initial corrosion was monitored as a function of time in boiling HCl solutions. The post-laser-alloying precorrosion level of 4 at.% increases to a steady state concentration of 15 at.% after 3 h. The corrosion rates observed are comparable with those for bulk alloyed material. Laser surface alloying has advantages over both thermal diffusion and ion implantation, which have also been used to make surface alloys in order to reduce noble metal consumption.

Laser surface alloying: a bibliography

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 ALLOYING OF DEPOSITED METAL FILMS ON NICKEL

Laser irradiation offers unique possibilities for surface alloying. Results are presented for liquid phase alloying of deposited metal films of Ag, Au, Pd, Sn, and Ta on both polycrystalline and single crystal nickel by both CW CO 2 and Q-switched Nd-YAG lasers. The structure and composition of the surface alloys are characterized by Rutherford backscattering (RBS) and channeling, by optical and scanning electron microscopy, Auger electron spectroscopy (AES), and electron spectroscopy for chemical analysis (ESCA). The corrosion properties and microhardness of some of the surface alloys have been characterized.

Analysis of Laser Alloyed Surfaces

Surface alloys of Au-Ni with a wide range of concentrations have been produced by laser irradiation of thin Au films on Ni. These films have been analyzed using Rutherford backscattering (RBS) and channeling. Many thin film metals other than Au have also been successfully alloyed using these methods. An example of a potential application is the laser surface alloying of Pd to Ti for corrosion passivation.

THE NATURE OF RESIDUES FOLLOWING THE ASHING OF ARSENIC IMPLANTED PHOTORESIST

Extensive analytical characterization indicates that the most significant contaminant following dry processing of As-implanted photoresist is not a carbon-based residue, but is in fact arsenic itself. The arsenic residue is an amorphous form of elemental arsenic, relatively free of oxygen or carbon, that is stable for long periods of time. Since arsenic is not particularly soluble in sulfuric acid, hydrogen peroxide, or their mixtures, it makes sense to pose questions regarding the optimum choice for post-dry processing wet chemical cleans.

Microstructures of CuZr phases formed by laser surface treatment

Abstract Pulsed laser irradiation of thin copper deposits sputtered onto polycrystalline zirconium sheet produces a variety of near-surface phases, as shown by transmission electron microscopy and X-ray diffraction. The most prominent phases are amorphous CuZr alloys of various compositions, including those which are richer in zirconium than achievable by splat quenching, and a copper-free zirconium glass stabilized by oxygen. Thermal annealing of the irradiated samples in the temperature range 200–700 °C leads to the formation of crystalline ZrO 2 , CuZr 2 and Cu 46 Zr 54 as a result of devitrification of the metastable glasses.

Hafnium-implanted nickel studied with TDPAC and RBS/channeling before and after laser surface melting and thermal annealing

Abstract The Hf implanted Ni system has been studied by the time-differential perturbed angular correlation (TDPAC) technique and by Rutherford backscattering (RBS)/channeling. Low fluence implants were thermally annealed in vacuum at increasing temperature in order to study the evolution of substitutional and defect-associated solutes using TDPAC. Both detrapping and precipitation (or segregation) effects have been observed. Higher fluence implants were studied by both TDPAC and RBS/channeling in as-implanted as well as laser surface-melted regimes.

AES and RBS analysis of laser mixed Cr and Ni multilayer films on Cu alloys

Abstract The chemical analysis of Cr and Ni multilayer films laser mixed with Cu alloy substrates has been carried out with Auger electron and Rutherford backscattering spectroscopies. For multilayer transition metal on metal systems, such as Cu/Cr/Ni, the complementary use of both AES and RBS results in a more detailed understanding of the laser mixed compositional profiles than would result from the application of either technique alone. The relative strengths and weaknesses of both analytical methods are pointed out.