High Power Laser Effects on Unimplanted and Implanted Aluminium Single Crystals
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HIGH POWER LASER EFFECTS ON UNIMPLANTED AND IMPLANTED ALUMINIUM SINGLE CRYSTALS
G.BATTAGLIN, A.CARNERA, G.DELLA MEA AND P.MAZZOLDI Unita GNSM-CNR, Institute of Physics, UniversitA di Padova,
ITALY
A.K.JAIN, V.N.KULKARNI* AND D.K.SOOD Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay-4000 85, *Visiting Research Fellow, Marathwada University, Aurangabad, INDIA
IN4DIA
INTRODUCTION Mechanisms involved in laser processing of ion implanted semiconductors have been extensively investigated (1,2). Relatively little work has been done on implanted metals (3,10). The liquid solid interface (melt front) velocity in metals (11,12) is much larger than that in Si. Therefore several nonequilibrium effects on recrystallization (6) solute segregation (9) and metastable phase formation (4,6,7) are observed. Such effects would depend on the melt front velocity, equilibrium phase diagram considerations (such as equilibrium segregation coefficient Ko, miscibility in licuid phase, intermediate phases etc.) and also on the as implanted nonequilibrium phase and defect structure. In this paper we present a study of the influence of some of these parameters during laser treatment of sincle crystals of virgin Al and dilute implanted alloys of Mo and Cd in Al. These alloys were chosen because a) the as implanted nonequilibrium phase and defect structure are already well established (13). Mo forms a metastable substitutional solid solution whereas Cd is nonsubstitutional, b) equilibrium phase diagrams are widely different; Cd-Al system (14) is almost completely immiscible in liquid phase with a monotectic at 1.5 at % Cd at 649 0 C, Ko %0 and the Vo-Al system (15) has miscibility in liquid phase, several intermediate phases, Kon 7 at Presently used composition. EXPERIMENTAL
Aluminium single crystals were electropolished in an electrolyte containing 90% methanol and 10% perchloric acid, to produce a mirror finish. Such a polishing method determines a reflectance value, measured at A=1.06jm of 0.94 (i0), in excellent agreement with the best reported ones (16). The expected R value for 0.69pm wavelength is then 0.89 (17). The surface finishing is a crucial parameter for the reproducibility and comparison of both measurements performed on different samples and calculation with experiments. Indeed a variation of about 10%in Rcauses an increasing of a factor 2 in the melting threshold (11). The absorbed laser energy density affects the solid-liquid interface velocity during the rapid self-quenching following the laser pulse (11) thus determining the dopant redistribution (5) and the crystal regrowth (3,61. Some samples were implanted with 150 Key Mo ions at 150 0 C and some with 300 Key Cd ions at room 2 2 6 temoerature. Implantation doses were 1.lx101 mo ions/cm and 1.7x1016Cd ions/cm respectively. Specimens were irradiated in air at room temperature by a 0-switched ruby laser operating in multimode. Energy densities ranged between 1 2 and 12 J/cm . The pulse duration was 15 ns (FWHIP) and the effective spot size 2 was about
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