R. O. Dillon

Deposition of diamond-like carbon on a titanium biomedical alloy

Abstract Much of the orthopedic community now believe that the long-term failure of total hip and knee prostheses is directly or indirectly due to the production of wear particles, particularly polyethylene wear particles which are produced at the articulating interface between the metal component and the high molecular weight plastic component. Therefore, a friction and wear reducing coating on the metal component, which is also biocompatible, should reduce the production of the polyethylene wear particles and dramatically extend hip-implant life. Diamond-like carbon (DLC), with its extreme smoothness, hardness, low coefficient of friction, and biocompatibility is an excellent candidate for such an application. One of the key issues that may limit the utility of DLC in this application is the adhesion of this material to common biomedical alloys. We will show that high adhesion strength between sputter-deposited DLC and a silicon-coated titanium biomedical alloy can be easily achieved.

Growth of diamond films on stainless steel

Abstract Continuous diamond films have been deposited on 304 stainless steel with a silicon intermediate layer by means of hot-filament chemical vapor deposition. The most serious problems for growing diamond films on ferrous metals are a long nucleation period, the catalytic effect of iron, and thermal expansion mismatch. In order to reduce these unwanted effects, three approaches have been adopted. First, an intermediate layer was used to block carbon diffusion, enhance adhesion and suppress sp 2 carbon formation. Second, oxygen-assisted low temperature deposition was used to minimized the thermal expansion effect and also avoid the phase transition of iron alloys. Third, initial and secondary nucleation was enhanced to yield small grain sizes in the continuous film. The morphology and quality of the deposited films were characterized by scanning electron microscopy and Raman spectroscopy respectively. Pull-off adhesion tests showed that the intermediate layer was strongly bonded to both the steel substrate and diamond film.

Thermochromic VO2 sputtered by control of a vanadium-oxygen emission ratio

Abstract The objective of this work is to deposit and characterize coatings containing primarily the VO 2 phase. This phase has a thermochromic semiconductor to metal transition at 68°C. The VO 2 thus becomes more reflective and conductive above the transition temperature. One application uses the change in infrared optical properties for thermal switches near room temperature. Precise stoichiometry is required to deposit VO 2 coatings because of competition from other oxide phases. To achieve this stoichiometric control we deposited VO 2 by controlling a plasma emission ratio of vanadium and oxygen. The emission ratio was processed in real time for feedback control. The feedback involved increasing or decreasing the oxygen flow to maintain a desired ratio. Direct current reactive magnetron sputtering was used with a constant current power supply. We varied the deposition temperature between 350 and 650°C and the amount of oxygen injected into the system from 3.0–3.8 sccm. X-Ray, resistance and reflectance measurements verified that the majority phase of the coatings was VO 2 . The resistance results showed a change of about three orders of magnitude due to the semiconductor to metal transition. The reflectance results showed emittance changes in the infrared between 61.2 and 90%, so this is an excellent material for a thermal switch. Space simulation exposures showed that these films could withstand between 3.7 and 37.2 years in space without forming other phases but that their emittance would degrade during this time.

Radio-frequency plasma chemical vapor deposition growth of diamond

Plasma chemical vapor deposition (CVD) at 13.56 MHz has been used to produce diamond particles in two different inductively coupled systems with a mixture of methane and hydrogen. The effect of a diamondlike carbon (DLC) overcoating on silicon, niobium, and stainless‐steel substrates has been investigated and in the case of silicon has been found to enhance particle formation as compared to uncoated polished silicon. In addition the use of carbon monoxide in hydrogen has been found to produce well‐defined individual faceted particles as well as polycrystalline films on quartz and DLC coated silicon substrates. Plasma CVD is a competitive approach to production of diamond films. It has the advantage over microwave systems of being easily scaled to large volume and high power.

Optical properties of photochromic organic–inorganic composites

Abstract We prepared several photochromic composite films based on a hybrid organic–inorganic matrix in which metal heteropolyoxometallates are entrapped. Infrared Fourier transform and UV-Visible spectroscopic ellipsometry methods have been used for the first time to study the coloring/bleaching process of the composite films. Data on all samples were acquired using a J.A. Woollam Co. VASE instrument and WVASE software. The optical absorption of these spin-coated films changed markedly by a reversible process, in the presence or absence of UV irradiation. The VIS-NIR transmission data showed that the films containing tungsten heteropolyoxometallate (HPOM) had strong absorptions at about 720 nm, 1108 nm and the films containing molybdenum HPOM had a strong absorption at 720 nm. We have also extracted for the first time the visible and infrared optical functions of the films. For the colored films, the Lorentz and Gaussian oscillators were used to describe the optical behavior in the 400–1700 nm wavelength range and 700–4000 cm −1 wavenumber range, respectively. The composite films containing tungsten heteropolyoxometallate (HPOM) showed faster coloration and bleaching than pure tungsten oxide films. The composite films with molybdenum HPOM showed faster coloration and much slower bleaching than tungsten HPOM.

Optical and interfacial electronic properties of diamond-like carbon films

Abstract We have been preparing hard semitransparent carbon films on oriented polished crystal wafers of silicon, indium phosphide and gallium arsenide, as well as on KBr and quartz. Properties of the films were determined using IR and visible absorption spectroscopy, ellipsometry, conductance-capacitance spectroscopy and α particle-proton recoil spectroscopy. Preparation techniques include r.f. plasma decomposition of methane (and other hydrocarbons), ion beam sputtering and dual-ion-beam sputter deposition. Optical energy band gaps as large as 2.7 eV and extinction coefficients lower than 0.1 at long wavelengths are found. Electronic state densities at the interface with silicon as low as 10 10 states eV -1 cm -2 were found.

Spectroscopic analysis of photochromic films

Sol-gel processing was used to dope photochromic dyes into three matrices: metal alkoxide, metal alkoxide-polymer, and pure polymeric materials. The films on silicon and quartz substrates were examined, with and without ultraviolet (UV) irradiation, by ellipsometry, UV-visible transmission spectroscopy, and Fourier transform infrared (FTIR) transmission spectroscopy. Variable angle spectroscopic ellipsometry (VASE) data were analyzed for film thickness and optical constants, and in some cases thickness nonuniformity. A modified Cauchy and a combined Cauchy–Lorentz model were used to fit the unirradiated and irradiated film optical constants, respectively. The optical constants of the films showed significant changes upon irradiation. This means that the absorption coefficient and hence the emissivity of the films is being modulated with UV irradiation. The VASE-fitted thicknesses of the films were in the range of 1–6 μm. In the FTIR spectra, the spiropyran doped samples have shown IR transmission changes ...

Visible and infrared photochromic properties of amorphous WO3−x films

The photochromic properties of sputtered amorphous tungsten oxide (a-WO3−x) films have been studied. The a-WO3−x films, prepared under different oxygen partial pressures, were irradiated with ultraviolet (UV) light at room temperature, and the transmission decrease of the films was measured. We used ellipsometry for the first time with and without UV irradiation to extract the optical indices n and k of magnetron direct-current sputtered films in the VIS/IR wavelength region. We have applied for the first time the Cauchy–Lorentz model for simulating the photochromic properties of the irradiated a-WO3−x films. The results are consistent with previous reports showing that oxygen deficiency is very important in determining the photochromic properties of the a-WO3−x films.

Sound velocity and Young’s modulus in plasma deposited amorphous hydrogenated carbon

The first carbon-film sound velocities obtained with the piezoelectric method are given. The a-C:H films were deposited from methane using rf plasma chemical vapor deposition at different substrate biases and thus contain varying hydrogen concentrations. Measurements of density allowed the Young’s modulii of the films to be calculated. Both the sound velocity and the Young’s modulus reached a maximum as the substrate bias changed from −47 to −175 V. The film with the maximal properties occurred at a bias of −76 V and had a sound velocity of 16.4 km/s, a Young’s modulus of 589 GPa, an optical gap of 2.16 eV and a density of 2.19 g/cm3. Although the modulus is 52% that of the directionally averaged value of diamond, it produced a sound velocity 91% that of diamond due to the lower film density. The film densities were in the range of 1.81–2.43 g/cm3 with the densest films occurring at the highest bias magnitudes. Optical gap measurements were taken with a photospectrometer and yielded a gap that decreased f...

Effect of antenna porphyrins and phthalocyanines on the photochromism of benzospiropyrans in poly(methyl methacrylate) films

Photochromic materials have optical properties that change reversibly in response to irradiation. The benzospiropyran used in this work undergoes a transmission change of approximately 90% at 550 nm; however, a reasonable reaction rate for both the forward and reverse reaction is necessary for applications such as smart windows in buildings. The time constant for colorless spiropyrans to darken to the merocyanine form under ultraviolet radiation is of the order of 10 min, but the reverse reaction is very much slower. The objective of this work was to increase the reaction rate for the reverse bleaching reaction. This was achieved by modifying the benzospiropyran in a poly(methyl methacrylate) matrix by the addition of one of seven porphyrins or phthalocyanines. We report second-order rate constants obtained from the slope of the reciprocal of the maximum absorption amplitude vs. time. These constants characterize the initial reaction rate. Data taken with an FTIR spectrometer showed that every porphyrin increased the initial reaction rate, with phthalocyanine showing the fastest reversion rate, 21-fold that of the unmodified benzospiropyran. One vanadyl phthalocyanine showed an eight-fold increase. The effect on the visible reaction rate was determined using vanadyl phthalocyanines, and a particular vanadyl phthalocyanine increased the initial reaction rate by a factor of approximately three.