Classified Abstracts 1142--1148 487

Vacuum Applications

30. Evaporat ion and Sput ter ing

3 0 : 1 9 1142. Multi-dielectric reflecting layers for the ultraviolet inter- ference measurements. (France) Semi reflecting coatings with feeble absorption for the Fabr$- Perot interferometer were obtained by the stacking of alternate A/4 layers (high index-low index). Lead fluoride is used for high index layers. For the low index layers magnesium or aluminium fluoride as well as cryolite have been used. None of these are perfect, but each has certain advantages. For a 9-layer cryolite-lead fluoride mirror, the absorption is less than 4 per cent, transmission 6 per cent and reflection over 90 per cent. Unfortunately such layers deteriorate with time and after a few weeks, the reflection coefficient diminishes appreciably whilst the transparency only increases slightly. The authors investigated this change in detail by examining the structure of the resonance line of mercury (~ - 2 5 3 7 A) as revealed by a Fabry-Perot interferometer whose mirror had been treated in this manner. It appears that atmospheric moisture is largely to blame for the deterioration with age. (France)

(Authors, modified) H. Chantral, et. al., Colloque sur l 'optique des couches minces solides, Marseille, 8-15 Sept. 1963, J. Physique (in press).

3 0 : 1 9 1143. Influence of surface irregularities on the optical properties of thin layers. (France) The author assumes that the surface irregularities are small compared with the wavelength of the incident radiation and considers the general case of the diffraction of a plane wave by a grating of sinusoidal profile. The results hold for any angle of incidence and apply to both dielectric and metallic substrate. If the pitch of the grating is small enough, no diffrac- tion takes place and the reflection and transmission factors can be calculated. The author shows that surface irregularities are equivalent to an additional surface layer which modifies the values of the reflection and transmission factors at the air-layer interface without introducing any appreciable diffusion. (France)

(Author, modified)

P. Bousquet, Colloque sur l 'optique des couches minces solides, Marseille, 8-15 Sept. 1953, J. Physique (in press).

3 0 : 1 9 1144. Optical properties and structure of thin layers of magnesium fluroride. (France) Published values for the refractive index of magnesium fluoride in thin layers range from 1.33 to 1.46, whilst that of the material in bulk is 1.39. In order to elucidate this variation, the authors carried out the deposition of the layers under controlled con- ditions, the pertinent parameters be ing : (1) temperature of subs t ra te ; (2) thickness of layer ; (3) pressure in recipient ; (4) temperature of crucible ; (5) distance between crucible and substrate ; and (6) rate of deposition. The resultant layers were studied optically, by electron diffraction and by electron micro- scopy. Consistent reproducible results (n = 1.38) could be obtained with the following parameter values : (a) 30-200°C ; (b) >8000 A ; (c) l0 -~ tor t ; and (d) 50,~/sec. (France)

W . J. S,

M. Bourg and A. Bourg, Colloque sur l 'optique des couches minces solides, Marseille, 8-15 Sept. 1963, J. Physique (in press).

3 0 : 1 9 1145. Measurement of the optical constants of thin layers of fluorides in the extreme ultraviolet. (France) The experiments were carried out over the wavelength region 1000-2500A. and led to a quantitative determination of the

first absorption band of bar ium fluoride (1220A), sodium fluoride (1170), fluorine (1600/~) and magnesium fluoride (1030/~). In some cases, the intrinsic reflective power at the vacuum-layer interface varied appreciably with the thickness of the layer and this is attributed by the author to surface irregularities, which in the case of barium fluoride amount to 50 A for a film thickness of 2000 A. (France)

(Authors, modified)

D. Fabre, et al., Colloque sur l 'optique des couches minces solides, Marseille, 8-15 Sept. 1963, J. Physique (in press).

30 : 52 1146. Chemically reduced nickel substrates for the development of uniaxial anistropy in electro-deposited thin films. (France) Substrate surface characteristics are known to affect the hysterisis properties, reproducibility and development of uniaxial anistropy in vacuum or electro-deposited permalloy thin films (<2000 A). Primary requisites of a satisfactory substrate are extreme smoothness and an amorphous or microerystalline structure. Chemically deposited nickel has been reported as having these characteristics and the authors used this material as a substrate for electro-deposited permalloy films. Magnetic tests of the alloy revealed the expected high degree of anistropy. It is interesting to note that the maximum dispersion of the films is practically constant over the whole range of thicknesses (500- 2000 A) whilst vacuum deposited iron nickel cobalt films have been reported to show an increase in dispersion with thickness below 1500 A.. (U.S.A.) w . J . s .

R. D. Fisher and H. E. Haber, Nature, 199 (4889), 13 July 1963, 163-164.

3 0 : 1 9 1147. Structure and optical properties of thin solid layers (general review). (France) The general structural characteristics of thin layers obtained by evaporation or sputtering are discussed as a function of the parameters characterising the deposition. Most of the work has been carried out using either amorphous or crystalline sub- strates. Many questions will still have to be answered before the various factors controlling crystallization of the films are understood, and in general it is not possible to carry out experi- ments under strictly controlled conditions. It appears, however, to be established that a complete orientation of the deposit is not possible if the substrate is amorphous. (An exception is provided by some semiconductors which form monocrystalline layers on molten surfaces.) Complete orientation by epitaxy is, however, possible on monocrystalline substrates raised to a sufficiently high temperature. Using cathodic sputtering, germanium can be deposited on such substrates in either amor- phous, polycrystalline or monocrystalline form, depending on temperature of substrate and speed of projection. (Great Britain) (Author, modified)

O. S. Heavens, Colloque sur l 'optique des couches minces solides, Marseille, 8-15 Sept. 1963, J. Physique (in press).

3 0 : 1 9 1148. Thin reflection-free inhomogeneous layers. (France) If internal reflections in the layer are neglected and incidence normal, the minimum thickness of a reflection-free surface is given by

d = V4 X / n g ~ n a

where ng and n a are the refractive indices of the substrate and air respectively, the refractive index of the layer varying linearly over these limits. The author also considers the case when the