Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Coating
Patent
1996-07-08
1998-10-27
Beck, Shrive
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Coating
427 8, 4271263, 427250, 4272553, 4272557, 427377, 117108, H01L 3924
Patent
active
058278028
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of vacuum depositing a monomolecular layer on a host surface, this monomolecular layer including at least one element chosen from groups IIa, IIIa, IVa, VIIIa, Ib, IIb, IIIb, Vb of the Periodic Table of the Elements or an element capable of exhibiting a mixed valency, said method including the steps consisting in heating the host surface to a predetermined temperature below 600.degree. C. and in vacuum evaporating at least the abovementioned element in order to deposit it on the host surface, the total atomic flux of the abovementioned element or elements arriving on said surface being adjusted between 10.sup.12 and 10.sup.15 atoms/cm.sup.2. s.
As used in this context, the term "monomolecular layer" indicates a layer consisting of a single thickness of the atoms or molecules constituting said layer.
BACKGROUND OF THE INVENTION
A method as defined above has been described, in particular, by Schuhl et
It has been found in practice that the formation of a strictly monomolecular layer is extremely difficult because the element which is deposited on the host surface naturally tends to form three-dimensional aggregates, that is to say aggregates having a thickness consisting of a plurality of superposed layers of the chemical species which normally constitute the monomolecular layer. This is because three-dimensional aggregates are energetically more stable than a strictly monomolecular layer.
The formation of such aggregates is in general irreversible and it has detrimental consequences on the properties of the material formed by deposition on the host surface, in particular, but not exclusively, when said material is a superconducting material.
Furthermore, when a plurality of monomolecular layers are deposited successively one on top of the other, the formation of a three-dimensional aggregate on one layer also promotes the appearance of such aggregates on the following layers, so that the properties of the following layers are also interfered with.
The object of the present invention is, in particular, to avoid these drawbacks.
SUMMARY OF THE INVENTION
Thus, according to the present invention, a method of the type in question is essentially characterized in that the formation of the monomolecular layer is monitored in real time, and in that the evaporation of the element is stopped when the complete formation of the monomolecular layer is detected.
Of course, this method makes it possible to successively deposit a plurality of identical monomolecular layers, in which case the evaporation of the element deposited is only stopped when the deposition of the last monomolecular layer is stopped, this last layer constituting the abovementioned monomolecular layer.
Controlling the temperature of the host surface and the flux of the deposited element arriving on this host surface makes it possible to avoid the appearance of three-dimensional atom aggregates during the formation of the monomolecular layer.
The atom flux of the element deposited on the host surface should in general be between a minimum value, below which a monoatomic layer cannot be formed, and a maximum value above which the formation of three-dimensional atom aggregates which prevent the formation of a strictly monoatomic layer is unavoidable. These minimum and maximum values are experimentally determined for each element to be deposited, in accordance with its particular growth mechanism.
Furthermore, stopping the evaporation of the element deposited as soon as the monomolecular layer is completed makes it possible to avoid the formation of three-dimensional atomic aggregates due to an excess of said deposited element.
In advantageous embodiments, one and/or other of the following arrangements is/are employed: high-energy electron diffraction (RHEED), while measuring the intensity of the electron diffraction lines, the complete formation of the monomolecular layer being detected when said intensity reaches a second extremum after passing through a first extremum during the for
REFERENCES:
patent: 4988670 (1991-01-01), Itozaki et al.
Schuhl et al., Physica C, vol. 162-164, Dec. 1989, pp. 627-628.
Lagues et al., Physics and Chemistry of Molecular and Oxide Superconductors. Satellite Conference to LT20, Eugene, OR, Jul. 27-31, 1993, as disclosed in Journal of Superconductivity, Feb. 1994, pp. 221-225 .
Beck Shrive
Meeks Timothy
Ufinnova
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