Etude de l'autodiffusion superficielle du cuivre

Perraillon, B.; Torrens, Ian M.; Levy, V.

doi:10.1016/0036-9748(72)90100-7

Cited by 10 publications

(2 citation statements)

References 5 publications

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“…First, at 400 ± C, surface diffusion is estimated as 10 29 cm 2 ͞sec [12], which can transfer components over distances greater than 10 23 cm during 10 4 sec of growth. Second, a force capable of driving Cu onto the free surface is present in the difference between the surface energies of Co and Cu, which are, respectively, 2.7 and 1.9 J͞m 2 [13,14].…”

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confidence: 99%

Epitaxial Growth of Metastable Co-Cu Alloys by a Surface Pump Mechanism

1996

Phys. Rev. Lett.

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We report the operation for Co-Cu alloys of a surface pump mechanism whereby bulk metastable alloys are formed during epitaxial growth. This happens when a material with a larger surface energy (Co) is grown on a film with a lesser surface energy (Cu). The specific pathway transports Cu through pinholes by surface diffusion at temperatures which are too low for the metastable alloy to decompose by bulk diffusion. [S0031-9007(96)01717-6] PACS numbers: 68.55. -a, 81.05.Bx, 81.15.HiNanostructures of successive Cu and Co layers have attracted attention as spin valve systems with giant magnetoresistances (GMR) and consequent technical potential [1]. Both as thin films and nanophases formed by mechanical milling their structural characteristics have proved interesting from a much wider perspective for the marked departures from the equilibrium phase diagram they exhibit [2][3][4][5][6]. Curious new alloying effects have also been observed in monolayer systems with Co and Cu components [6]. All these behaviors are of interest both for understanding the rich growth-related magnetic properties [1] of this system, and for the opportunities they reveal for the synthesis of new and metastable materials. The Co-Cu phase diagram [7], reproduced for the reader's convenience in Fig. 1, is of limited promise, showing only small solubilities of the components all the way from low temperatures to the solidus. Cu is fcc at all temperatures, but Co has a hcp to fcc transition near 400 ± C. The components remain largely unmixed because the bulk free energy G rises towards the 50-50 alloy as indicated in the inset [2] of Fig. 1, where the chemical potentials for both Co and Cu are also shown. Despite these clearly documented energetics, Co-Cu alloys, near 50% in composition, have been observed to form during mechanical milling [2,3], as epitaxial monolayers [6,8], and during the epitaxial growth of attempted multilayer nanostructures at temperatures above 300 ± C [4,5]. Our own attention was focused on the system by quite extraordinary observations on their epitaxial films, described immediately in what follows. This Letter reports a study of novel growth behavior and proposes an explanation for the observations. In our initial work, about 1000 Å of fcc Cu(111) was grown by molecular beam epitaxy on bcc Nb(110) near 200 ± C, using sapphire ͑1120͒ as a substrate and with equipment that is described in other publications [9]. A 500 Å layer of hcp Co (0001) was then grown on top of the Cu at the same temperature. The materials were of reasonable quality, exhibiting streaky reflection high energy electron diffraction (RHEED) characteristic of single crystals with flat surfaces. X-ray diffraction from the Cu films revealed Bragg scans ϳ0.1 ± wide and rocking curves ϳ0.3 ± wide for (111) reflections, which indicate structural coherence lengths ¿10 2 atomic spacings.After the initial Co growth the sample was then heated to 500 ± C and a further 500 Å of Co deposited. X-ray analysis quickly revealed that what had grown on top of the first, pur...

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confidence: 99%

Epitaxial Growth of Metastable Co-Cu Alloys by a Surface Pump Mechanism

1996

Phys. Rev. Lett.

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“…3, as a solid line, are the values for D that were used in the study. We have also reviewed other data for Xe diffusion in U and found that the values used in this study are at the upper limits of the experimental data [41][42][43][44][45]. If the actual diffusivities are less than the values used in this study, the experimental constraints for temperature, dose, and dose rate that are discussed in Section 5 would be significantly relaxed, that is, then a successful experiment would become more likely.…”

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confidence: 87%