Saburo Nagata

Behaviour of impurity atoms and adsorbed oxygen atoms on (001) face of iron epitaxial film

Abstract The behaviour of impurity atoms and adsorbed oxygen atoms on a (001) iron face were studied by a four-grid type LEED-AES system. The (001) iron face was prepared by deposition; that is, the iron atoms were evaporated from an iron wire (99.9 per cent) which was heated directly by electric current, and the iron film was grown epitaxially on the (001) face of an MgO substrate under wide ranges of experimental conditions. The orientations, (001)Fe//(001)MgO, [100]Fe//[110]MgO, were identified. No impurity atoms were detected during the film formation by AES. When the film was heated at temperatures higher than 500°C, extra spots appeared in the LEED pattern and a distinct sulphur peak appeared in the AES curve. They indicate that a super structure, Fe(001)C(2×2)S, was formed. This structure was stable but when it was treated in an oxygen atmosphere (1×10−6torr) at 500°C, the sulphur peak vanished and another super structure, Fe(001)P(2×2)0, was formed. When the substrate was kept at a high temperature during the film formation, it seems that a super-structure, Fe(001)C(2×2)C was formed.

Structure of Film Prepared by Low Energy Sputtering of Molybdenum

Dependence of the structure and electrical resistivity of sputtered molybdenum films on residual gas pressure, ion energy, ion current density and substrate temperature are investigated in detail. Fcc structure is obtained when the residual gas pressure is high and the deposition rate is low. The film structure is bcc on substrates at 500°C, while the film of fcc structure does not transform to bcc when it is heated up to 700°C in vacuum. The lattice constant of fcc structure coincides with that of γ-Mo2N obtained by reactive sputtering. From these results, it is concluded that the film of fcc structure is γ-Mo2N.

Structure and Deposition Mechanism of Molybdenum Nitride Films Prepared by Reactive Sputtering

The structure and deposition mechanism of reactively sputtered films prepared by sputtering molybdenum metal in argon gas mixed with nitrogen are investigated. In argon alone, a b.c.c. Mo film is deposited on the glass, carbon film and NaCl substrates. In a mixed atmosphere of argon and nitrogen, f.c.c. γ-Mo2N and hex. δ-MoN films are obtained on carbon film substrates. The lattice constant of γ-Mo2N shows a considerable change in the range from 4.14 to 4.28 A as the partial pressure of nitrogen increases. A correlation between the product at the surface of the molybdenum target formed during sputtering and the structure of the films on various substrates, and the effect of the substrate temperature on the structure of the films show that the molybdenum nitrides are formed by the combination of sputtered molybdenum atoms with nitrogen at the substrate surface irrespective of the partial pressure of nitrogen.

Recovery Process and Metastable Crystals in Vacuum Co-Deposited Mn–Al Films

Metastable crystals are often found in the recovery process of vacuum co-deposited alloy films. In order to explore this possibility in the Mn-Al system, the films with various compositions were prepared and investigated in a hot stage of an electron microscope. Change of their electric resistance was also measured. The films with 100–35 at.%Mn showed only grain growth of the crystals which were found at the corresponding compositions in the equilibrium phase diagram. The films with 30–25 at.%Mn showed discrete nucleation of leaf-formed crystals which were not found in the phase diagram. Further raising up of the temperature gave a transformation of the crystals into the one-dimensionally disordered δ(Mn-Al) phase, which also did not exist in the phase diagram. The films with 15–8 at.%Mn showed discrete nucleation of circular crystals, which were mainly identified as MnAl6. Resistance of the last films showed anomalous oscillation which started just before the nucleation.

Microstructure in MnAl(r) Alloy Phase

In order to express reciprocal vectors of the crystal lattice with lower symmetry than cubic or orthorhombic, a standard lattice with exact cubic symmetry is used as the reference axes of coordinates. General formula for the reciprocal vectors of a crystal twinned on any crystallographic plane, (pqr), is then derived. The formula has a wide applicability to any one of the Bravais lattices with low symmetry. Expressions for the splits of the diffraction spots due to the twinning in the pseudo-cubic lattice of MnAl(r) alloy phase are derived from the above formula and diffraction patterns of the alloy taken by the selected area diffraction method are analyzed using these expressions. The results show that the microstructure in MnAl(r) phase is composed of crystals twinned on {100} and {110}. Boundaries between the main bands and those between the parallel sub-bands are {100} and {110} twin planes, respectively. Arrangement of atoms in the unit cell is assumed to be the same as that of Cr5Al8 Calculated intensities of the diffraction spots agree fairly well with the observed ones.

LEED-AES Study of Clean (001) Iron Surface

Iron atoms were deposited on a clean MgO (001) surface kept at room temperature in UHV. The height of the Mg(L1M1M1, 26 eV) peak decreased rapidly and became very small when the average thickness was about 7 angstroms. Therefore, only several layers of iron atoms must have been distributed on the face without any naked area. The height of the Fe (L3M2,3M4,5, 648 eV) peak increased smoothly with deposition, but the Fe (M2,3M4,5M4,5, 42 eV) peak was not detected in the early stage. In the following stages no anomalous phenomena were observed, and a clean epitaxial film was formed. The behaviours of impurity atoms and adsorbed atoms are described also.

Internal Stress and Growth of Evaporated Gold Films in U.H.V.

A sensitive bending beam device having a lever system coupled with the capacitive sensor is constructed for measuring the stress in evaporated films in U.H.V. It is capable of high temperature bakeout. The internal stress in gold film on the glass substrate is measured continuously during and after the deposition. A pressure of ≤5×10-8 Torr can be maintained during the deposition. The large tensile stress is generated at an early stage of the film growth and is related with the growth process of the film observed by transmission electron microscope. The origin of the stress in the early stage of the film growth is discussed.