W. G. Sainty

Ion-beam-assisted deposition of thin films.

Some effects on the properties of electron-beam evaporated thin films produced by ion bombardment of the growing film are reported. Substantial increases in the packing densities of SiO2 , TiO2 , and ZrO2 films have been produced as measured by the reduction in the adsorption of moisture when the films are exposed to a humid atmosphere. In a ZrO2-SiO2 multilayer interference filter, changes in the wavelength of the peak transmittance on exposure to the atmosphere have been reduced from 8 nm for films deposited without ion bombardment to <1 nm for ion-beam-assisted films.

Modification of the optical and structural properties of dielectric ZrO2 films by ion‐assisted deposition

Low‐energy bombardment by argon and oxygen ions has been used in the deposition of thin dielectric films of ZrO2. The film packing density has been improved from 0.83 to unity with a corresponding increase in the refractive index from 1.84 to 2.19. The highest stable refractive index measured was 2.23 for oxygen ion‐assisted deposition of ZrO2 on a substrate heated to 300 °C. Ion bombardment during condensation of evaporated ZrO2 on a room temperature substrate results in crystallization into the cubic phase which is consistent with previous studies of ion impact crystallization by thermal‐spike processes. At elevated substrate temperatures the monoclinic phase is also present.

Properties of CeO2 thin films prepared by oxygen-ion-assisted deposition.

Thin films have been prepared by electron-beam evaporation of CeO2, where the growing film has been bombarded with oxygen ions. The packing density of the films has been increased from ∼0.55 without ion bombardment to unity with bombardment as determined by moisture adsorption measurements. The refractive index, extinction coefficient, and scattering loss are reported for a range of ion energies from 50 to 1200 eV. The ratio of ion-current density to film growth rate required to produce films that did not adsorb moisture was found to be a minimum for ion energies in the 300–600-eV range. Absorption and scatter losses are smallest for the lower ion energies and the crystal structure of CeO2 films is relatively stable under ion bombardment although ion-assisted films tend to be less crystalline than evaporated layers.

Ion‐assisted deposition of mixed TiO2‐SiO2 films

Mixed thin films of TiO2 and SiO2 were produced by coevaporation from separate electron‐beam sources and simultaneous bombardment of the growing film with oxygen ions. The optical properties of the films were determined during growth by in situ ellipsometry and the surface composition of the deposited films studied by in situ ion scattering spectroscopy, ex situ x‐ray photoelectron spectroscopy, and energy filtered electron diffraction. The correlation between the optical and surface characterization is presented. There is evidence of local variations in the relative concentrations of TiO2 and SiO2. The position of the Si 2p binding energy depends on the TiO2 content in the film, indicating the possible formation of an intimate mixture.

Protective dielectric coatings produced by ion-assisted deposition

Optically transparent dielectric films, when prepared by thermal evaporation or sputtering, have had limited use for many applications due to their permeability and lack of stability. We report on protective dielectric films produced by ion-beam-assisted deposition which demonstrate significant improvements over films produced by conventional deposition techniques. This result can be explained in terms of the increased packing density of ion-assisted films over the porous columnar microstructure usually associated with evaporated films. In addition, ion bombardment of the metal films produced the most stable structures and also substantially improved the adhesion of the films. The endurance under chemical attack of these films was found to be limited by the surface finish of the substrates.

Characterization of growing thin films by insitu ellipsometry, spectral reflectance and transmittance measurements, and ion‐scattering spectroscopy

A versatile ultrahigh‐vacuum thin‐film deposition and analysis system is described. Films are deposited by electron beam evaporation with the possibility of ion beam bombardment of the growing film. Measurements of the reflectance and/or transmittance of the coating surface can be made simultaneously at 16 wavelengths across the visible or infrared spectrum. Ellipsometric measurements can also be made in situ, at a single wavelength and single angle of incidence, by an ellipsometer which can operate in either an automatic rotating analyzer mode or a manual nulling mode. The system is also equipped with an ion gun producing a submillimeter spot, and with a hemispherical sector, ion energy analyzer for ion scattering spectroscopy studies of the film surface. Results obtained during the deposition of a gold film are presented to demonstrate the capability of the system.

Influence of ion assistance on the optical properties of MgF(2).

The optical properties of MgF(2) films prepared by evaporation and ion-assisted deposition have been determined from transmittance and near-normal incidence reflectance measurements and also from electron-energy loss spectroscopy (EELS). The results show that oxygen-ion assistance leads to higher extinction coefficients for wavelengths <180 nm. Transmission electron microscopy studies show that the crystal grain size of MgF(2) films is not strongly affected by oxygen or argon-ion bombardment. The presence of MgO in the films is inferred from RBS measurements and proposed to be the major factor influencing VUV losses. EELS is also demonstrated to be a valuable technique for determination of optical properties from the near-infrared to x-ray regions of the spectrum.

The structure and properties of ion‐beam‐synthesized boron nitride films

Films containing boron and nitrogen were prepared by electron‐beam evaporation of boron and bombardment of the growing film with nitrogen ions of energy up to 1500 eV. Hard films of high transparency (extinction coefficient <0.01) were prepared with nitrogen‐to‐boron atomic arrival ratios greater than one. The optical constants in the visible part of the spectrum were determined as a function of B‐to‐N atomic ratio in the film and substrate temperature using optical photometry. Measurements of the optical constants were extended to 40 eV using a Kramers–Kronig analysis of electron‐energy‐loss spectra. Boron‐to‐nitrogen atomic arrival rates were determined and show that as ion energy and substrate temperature are increased ion flux must be increased to achieve the same stoichiometry. Film structure was imaged using high‐resolution electron microscopy, and the radial distribution function (RDF) was determined. The RDF of stoichiometric films showed that high substrate temperatures increased the size of the ...

Ion‐assisted deposition of bulklike ZrO2 films

Stable thin films of zirconium dioxide are produced by ion‐assisted electron beam deposition at room temperature and 300 °C. The method yields films with substantially increased packing density resulting in refractive indices close to the bulk value. The improvement in optical properties is accompanied by an amorphous to cubic crystalline transition of the film structure which is mixed with a monoclinic phase for heated films.

Optical properties of TiNx produced by reactive evaporation and reactive ion-beam sputtering

Abstract Thin films of titanium nitride are produced by activated reactive evaporation and reactive ion-beam sputtering. The optical constants n and k are calculated over the wavelength region 400–700 nm and vacuum-to-air changes are investigated. It is found that substantial modification of the optical properties occurs as a result of water sorption and oxidation in the bulk of the films.