R. Messier

Revised structure zone model for thin film physical structure

Thin films prepared under conditions of low adatom mobility are characterized by a highly anisotropic physical structure with a wide range of systematically varying column and void sizes. The structure zone models, previously developed to classify the larger sized physical structures, are revised to account for the evolutionary growth stages of structure development as well as the separate effects of thermal‐ and bombardment‐induced mobility. The zone T introduced by Thornton is shown to be a subzone within zone 1.

Current Issues and Problems in the Chemical Vapor Deposition of Diamond

Current issues and problems in the chemical vapor deposition (CVD) of diamond are those which relate to its characterization, its nucleation on foreign surfaces, the question of its formation in preference to the other phases of solid carbon (for example, graphite, chaoite, or lonsdaleite), why different morphologies and crystallographic orientations (textures) are seen in different experiments or with different parameters in the same experiment, and finally whether well-crystallized metastable phases can be obtained by CVD in other material systems or are only a peculiarity of carbon chemistry. Whether a given carbon coating is justly described as diamond has been such an issue, and coatings should clearly show evidence for diamond by x-ray diffraction and Raman spectroscopy before the claim of diamond is made. Experimental results have not been consistent in many cases, and much work remains to be done before an accurate assessment can be made of the technological impact of the development.

Phase control of cubic boron nitride thin films

Ion beam assisted evaporation was used to deposit cubic and hexagonal boron nitride thin films. Boron was evaporated and bombardment was by argon and nitrogen ions. The effect of preparation conditions on the resulting phase was studied, and the relationship between the phase and the energy and momentum transferred into the film through ion bombardment was examined. It is shown that for a given temperature, the controlling factor in the resulting thin film phase is the momentum transferred into the film per depositing boron atom. At 300–400 °C a sharp threshold value of momentum‐per‐atom exists below which films are hexagonal and above which they are cubic. For 400 °C this threshold occurred at 200 (eV×amu)1/2 which is equal to 3.3×10−21 m kg s−1. Depositions performed using krypton and xenon instead of argon as the second bombarding gas confirmed this momentum‐per‐atom value. A second threshold was also observed, which was bombarding species dependent, above which either complete resputtering of the depo...

Origin and evolution of sculptured thin films

Sculptured thin films (STFs) are a new class of engineered columnar thin films in which their shapes can resemble oblique matchsticks, chevrons, multiple zigzags, S’s, C’s, helices, and even superhelices. They can have densities as low as 10%–30% of the bulk material and can be made of virtually any material. The origin and evolution of columnar thin films are reviewed in the context of structure zone models in which both thermally induced and ion bombardment-induced adatom mobility effects are considered. Since STFs are prepared under low adatom mobility and oblique angle of vapor incidence conditions, the columns are the result of clustering at the 1–10 nm level, with atomic self-shadowing controlling their growth evolution. The distribution functions of the cluster sizes, shapes, and relative heights are shown to be critical for any quantitative understanding of columnar growth, especially for achieving and maintaining steady state column diameters for oblique incidence where the self-shadowing is anis...

Optical absorption spectrum of hematite, αFe2O3 near IR to UV

Optical absorption spectra have been measured on thin (011) single crystal platelets and on highly oriented (110) thin films of αFe2O3. We have observed and assigned some of the absorption bands predicted by ligand field theory and SCF-Xα calculations. The temperature dependence of the 11760 cm−1 single crystal band has been fitted to the function ƒ = ƒ0(1 + exp (− θT)) with ƒ0 = 0.85 × 10−4 and θ = 200 K (139 cm−1). We have measured the photocurrent as a function of wavelength and have found several peaks that coincide with optical absorption bands.

Geometry of thin-film morphology

The columnar morphologies commonly found in all vapor‐deposited thin films prepared under low mobility conditions have been classified by several variations of what have been termed structure zone models. Such morphological structures are found to have a strong similarity in shape and form over six orders of magnitude in film thickness and three orders of magnitude in magnification for films of a given thickness. Thick (45‐mm) pyrolytic graphite films are shown to be a good demonstration of the continuous growth evolution of conical‐shaped units. Due to competition for growth each cone eventually goes through a death stage. A model based upon these general structural observations is presented and is shown to be a geometric construction similar to a Sierpinski gasket. The origin of this morphology seems to be the natural clustering which occurs due to the random process of ballistic aggregation.

Toward quantification of thin film morphology

Before any meaningful quantitative understanding of thin film growth morphology can be developed, a sufficiently detailed model must be established. For the case of films deposited under low mobility conditions, the model of the internal void networks, which are the morphology, is a fractal construction based upon the random competition for cone growth. The origin of the development of cones is a natural consequence of the random ballistic aggregation process. Both current and future approaches to quantitative measurement of this morphological model are discussed and include a series of direct (scanning electron, transmission electron, and field ion and optical microscopy) and indirect (spectroscopic ellipsometry, image enhancement and analysis of morphology photographs, small angle x‐ray and electron scattering, and computer simulations of film growth) characterization techniques. It is shown how quantitative preparation–property relations in thin films will have to first start with a quantitative descri...

Crystallization of diamond crystals and films by microwave assisted CVD (Part II)

Results of experiments on crystallization of diamond micro single crystals (∼10μm) and polycrystalline diamond films by microwave plasma assisted chemical vapor deposition are presented. Discussed are problems related to growth mechanisms from CH4H2 plasma: nucleation on different substrates (diamond, graphite, Si, βSiC, SiO2 and Ni), catalytic growth, Raman scattering from deposits and planar defects of diamond structure. Optimal conditions for diamond growth were found in relation to maximum growth rate and exceptional surface phenomena appearing at temperatures close to 1000°C.

The effect of surface treatment on the electrical properties of metal contacts to boron-doped homoepitaxial diamond film

Both doped and undoped homoepitaxial diamond films were fabricated using microwave plasma-enhanced chemical vapor deposition (CVD). The conductivity of the diamond film is strongly affected by the surface treatment. In particular, exposure of film surface to a hydrogen plasma results in the formation of a conductive layer which can be used to obtain linear (ohmic) I-V characteristics of the Au/diamond contacts, regardless of the doping level. It is shown how the proper chemical cleaning of the boron-doped homoepitaxial diamond surface allows the fabrication of Au-gate Schottky diodes with excellent rectifying characteristics at temperatures of at least 400 degrees C.<<ETX>>

Engineered sculptured nematic thin films

By controlling the angular relation of the substrate surface with respect to the incoming vapor direction in an evaporation deposition system, it is possible to engineer the morphology of thin films. Sculptured nematic thin films result under low adatom mobility conditions when the substrates are rotated about an axis perpendicular to the vapor direction. Thin films of MgF2 were deposited onto room temperature substrates to produce columnar morphologies ranging from chevron structures to continuously varied structures resembling S shapes and C shapes. The specific morphologies are virtually unlimited within the restriction that the minimum angle χM of the local columnar direction with respect to the substrate plane is about 30°.