Beam Induced Reactions in Metal-Film Systems
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BEAM INDUCED REACTIONS IN METAL-FILM SYSTEMS
S. S. LAU Dept. of Electrical Engineering and Computer Science, UCSD, La Jolla, Ca. MARTTI MAENPXX Electrical Engineering Dept., Caltech, Pasadena, Ca. 91125 JAMES W. MAYER Dept. of Materials Science, Bard Hall, Cornell, Ithaca, N.Y. 14853
92093
ABSTRACT Pulsed beams (laser, electron, or ion) and ion beams (ion beam mixing) have been used to induce structural and compositional changes in metal-metal and metal-semiconductor thinMetastable crystalline and amorphous phases film structures. Although ultra fast quenching occurs with have been formed. both techniques, metastable phases are formed by quenching from the liquid with pulsed beams and from the solid-phase With both techniques metastable with ion-induced reactions. phases can be formed over a broader compositional range than with conventional melt-quench methods.
INTRODUCTION A variety of beam techniques--ion, electron and laser beams in pulsed or continuous modes--have been used to induce structural and compositional changes Metain thin-film systems and in the near-surface region of bulk materials. stable phases, crystalline and amorphous, are often formed as a result of the The technological importance of beam techniques extremely fast quench rates. in surface alloying and directed energy deposition is reflected in the recent publications in the field [1-5]. Since the first demonstration of metallic glasses made by splat cooling, a multitude of metastable phases have been obtained by rapid quenching of melts [6]. However, the cooling rates (105-107 °K/sec) available with splat cooling techniques were found sufficient for metallic glass formation only for selected Faster cooling systems and only for compositions close to a deep eutectic [7]. rates (109-1010 °K/sec) can be achieved with pulsed (10-8-10-7 sec) beams where Such energy sufficient for melting is deposited in the near surface region. fast cooling rates resulted in metastable phase formation in laser-irradiated thin-film [8, 9] and ion-implanted Ni [10] and Cu [11] single crystals as well as in pulsed electron beam irradiation of ion-implanted Cu [12] and Al [13] single crystals. Intense pulsed ion beams have also been used to anneal ionimplanted semiconductors [14]. The composition of the near-surface region of metals can be changed in a 2 controlled manner by high-dose (t 1017 ions/cm ) implantations of selected ionThis implantation-metallurgy process with obvious surface-alloying species. applications in fields [2,4,5] such as corrosion, wear, and hardness has also been used for formation of metastable alloys [15-17] and amorphous metals [18]. Sputtering effects set a limit on the maximum obtainable concentration of imHigher concentrations can be obtained by depositing a planted species [19]. layer of material on the substrate and then mixing the layer and substrate by implanting with ions of sufficient energy to penetrate through the deposited layer [20]. A direct comparison of the two processes showed that ion-induced atomic mixing produced
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