Dominant Moving Species in the Formation of Amorphous HfNi by Solid-State Reaction
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Y.-T. CHENG, M.-A. NICOLET AND W. L. JOHNSON California Institute of Technology, Pasadena, California 91125.
ABSTRACT: The displacements of Mo, Zr and Pd markers have been monitored by backscattering of MeV He4 to study the growth of the amorphous HfNi phase by solid-state reaction. We find that the Ni is the dominant moving species in this reaction.
INTRODUCTION: Amorphous metallic alloys have been traditionally produced by rapid quenching from the melt or by sputtering [1]. Recently, however, it has been demonstrated that the amorphous metallic phase can also be produced The energetic and kinetic by solid-state reaction (SSR)[2-11]. requirements for such a reaction to occur seem to be a compromise between a lowering of the free-energy, and a mode of growth that favors the amorphous phase over the crystalline ones[6]. Detailed growth kinetics of such reactions have been the subject of several studies[5,7,10,11]. In a previous paper we have reported that Ni is the dominated moving species in the amorphous NiZr phase formation by SSR[11]. This conclusion was drawn from a set of marker experiment in which the growth of the amorphous NiZr layer and the movement of the "markers" were monitored by using Mev He+ backscatering spectrometry. In this paper, we extend the study to the HfThe amorphization of Ni/Hf by SSR has been reported Ni system. previously[5]. One classical example of marker experiments in determining dominant moving species was provided by Kirkendall and Smigelskas (Kirkendall effect)[12]. In their experiments Mo wires (- 10 pm in diameter) were used as markers between two bulk metals, to determine which of the latter had In thin-film diffusion the greater intrinsic diffusion coefficient[12]. studies, with film thicknesses of the order 1000 A, markers that fulfill an equivalent function must be very thin (- 10 A). They can be realized by either evaporation or ion implantation. The positional change of the marker as well as the thickness of the growing amorphous layer may be Thus the dominant monitored by MeV backscattering spectrometry (BS)[13]. moving species is determined by studying such small scale Kirkendell effect. Details of this kind of marker experiments may be found in the literature relating to silicide formation[14-18].
Mat. Res. Soc. Symp. Proc. Vol. 54. c 1986 Materials Research Society
176
E[PERIMENTS: The sample configuration is shown in Fig.l( insert ). Mo, Zr and Pd were selected as markers because their atomic mass were such that their BS Mo may signals separate easily from those of Hf and Ni. Furthermore, be considered an "inert" marker, whereas Zr (Pd) may be viewed as an "isotope" of Hf (Ni) (detailed discussion below). About 6 to 15 A of marker material were deposited. The top Hf layer thickness was 900- 1500 A. The Ni layer thickness was about 2000 A. The thin layers of Ni and Hf ( -25 A) on either side of the marker were used so as to position the marker within amorphous NiHf after an initial short thermal annealing step. This configuration is advantageous to minimize the p
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