Chiral thin solid films of dielectric materials have been deposited using the Glancing Angle Deposition (GLAD) process¹. This new technique utilizes oblique incidence deposition and computer controlled substrate motion to fabricate films with helical or vertical microstructures and with porosities from 10 to 94%. Refractive indices of porous films were found to correlate with film density according to standard linear mixing rules. The film porosity may be changed continuously during growth, leading to controlled variation of refractive index with film thickness. This has been accomplished while maintaining vertical film microstructures and has been applied to the fabrication of a 22-layer, 50 nm bandpass rugate filter consisting of MgF₂ of refractive index ranging from 1.11 to 1.34². Chiral films have been fabricated with GLAD with helical pitches of 50 nm to 11 micrometers in metal oxides and fluorides. Films with a chiral microstructure have been found to rotate the plane of polarization of light (340 degrees/mm) in a manner similar to cholesteric liquid crystals (CLCs). It is expected that these films will exhibit circular Bragg reflection (utilized in CLC displays) where one incident circular polarization state is preferentially reflected while the other is transmitted. The large range of control over film microstructure may prove advantageous in applications for which CLC's are currently used.

¹K. Robbie and M.J. Brett, Journal of Vacuum Science and Technology A15, 1460 (1997).

²K. Robbie, A.Hnatiw, M. Brett, R. MacDonald and J. McMullin, Electronics Letters 33, 1213 (1997).

Enhanced electronic conductivity in II-VI semiconductors is achieved by introducing defect levels in close proximity to the conduction band. These levels, which derive from localized impurities or intentionally introduced dopants, become populated upon reduction of the materials and serve as source electronic states from which free carriers are generated. The chemical state of the film, which is dependent upon deposition conditions and post deposition processing, is associated with an increase in film conductivity and infrared reflectivity. In many cases, these impurity levels are prone to reoxidation leading to time dependent properties variations. The introduction of dopants such as Pt or Au, which tend to resist oxidation, is but one means by which the conductivity can be stabilized in both spin cast or rf sputtered films.

Following post deposition reduction in hydrogen or cathodic reaction in an electrochemical cell, partial reduction of resident cations in the lattice results which leads to gross changes in the Raman allowed E1 mode frequency, linewidth, and intensity. The extent of reduction also is manifested by alteration of dopant chemical state as determined from XPS traces. Current voltage measurements obtained in an electrochemical cell (pH 7 aqueous buffer solution) also show changes in resident oxidation state upon polarization of the electrode. Results indicate a reversible charge state transformation for certain cations but contrast with experiments on films containing more noble cation dopants which show little tendency to reoxidize once they have been reduced. Work reported here has implications for stabilizing film conductivity and for the development of new sensor materials.

Overcoated gold surfaces are used in a variety of applications where broad band high reflectance is desired. Such reflectors are often required to exhibit durability in challenging environments which expose the reflectors to severe temperature cycles and abrasion. Commonly used oxides such as HfO₂ and Y₂O₃ exhibit moderate adhesion to gold. Gold reflectors overcoated with PVD films of these oxides show some durability after deposition but fail abrasion and adhesion tests after exposure to temperature and time.

An alternative structure for overcoating the gold reflectors is achieved by using a very thin layer of a metallic binder (5 to 12 angstroms of chrome or tantalum) between the gold and the subsequent oxide layers (patent pending). A structure incorporating the thin binder layer and the oxide films is extremely stable and shows superb adhesion and abrasion resistance even after exposure to multiple rapid thermal cycles and long term exposure to temperature and humidity. Metal films with thickness of the order of 5 to 12 angstroms are substantially transparent and cause minimal degradation of the reflectivity of the underlying gold. Thes structures have been reliably reproduced in volume produciton.

Nitrogen-containing diamond like carbon films (a-C:H:N) deposited by rf (13,56 MHz) plasma decompositions of CH₄-H₂-N₂ gas mixture were studied. Nitrogen content in the gas mixture was changed from 0 to 45% that led to change of relative nitrogen content in the film measured by Auger electron spectroscopy from 0 to 8 at.%.

The time-resolved photoluminescence (PL) spectroscopy has been used to investigate the luminescent properties of the nitrogen containing DLC films. It was found that increasing of nitrogen content in the gas mixture in the range of 20-45% results in downshift of main luminecsent band from 450 to 600 nm and in drastic increasing of the main PL band intensity.

On the other hand, PL spectra of the nitrogen containing DLC films measured from the lateral face of the the film reveal dramatic narrowing and increasing of intensity of the PL bands. The mechanisms of the effects observed are also discussed. The results obtained show that nitrogen containing DLC films can be used for development of new light-emitting devices.