Mário A. Bica de Moraes

Mechanisms of polymer film deposition from r.f. discharges of acetylene, nitrogen and helium mixtures☆

Mixtures of C2H2, He and N2 were polymerized in an r.f. discharge. Quantitative optical emission spectroscopy was used to determine relative concentrations of the key species CH and CN in the plasma as a function of the proportions of monomer gases in the feed, and to delineate the behavior of the electron mean energy and number density in the discharge. Transmission IR spectroscopy (IRS) and electron spectroscopy for chemical analysis (ESCA) of films deposited from discharges containing different proportions of nitrogen revealed the incorporation of both CH and CN in the deposited material. Deposition rates were also determined and their connection with deposition mechanisms via gas-phase and surface reactions is outlined.

Relationships between the plasma environment and the composition and optical properties of plasma‐polymerized thin films produced in rf discharges of C2H2‐SF6 mixtures

Polymer films were grown in rf discharges containing different proportions of C2H2 and SF6. Quantitative optical emission spectrometry (actinometry) was used to follow the trends in the plasma concentrations of the species H and F, and more tentatively, of CH, CF, and CF2, as a function of the feed composition. Infrared spectroscopy revealed the density of CH and CF bonds in the deposited material. As the partial pressure of SF6 in the feed was increased, the degree of fluorination of the polymer also rose. The form of the dependency of the deposition rate on the proportion of SF6 in the feed was in good qualitative agreement with the activated growth model. From transmission ultraviolet visible spectroscopy data the refractive index and the absorption coefficient of the polymers were calculated as a function of the deposition parameters. Since the optical gap depended to some extent upon the degree of fluorination, it could, within limits, be determined by a suitable choice of the proportion of SF6 in the feed. A qualitative explanation of this relationship is given.

Properties of titanium oxide films obtained by PECVD

Abstract Amorphous TiO 2 films containing carbon and excess oxygen were deposited from glow discharge plasmas of titanium tetraisopropoxide Ti(OC 3 H 7 ) 4 , helium, oxygen and argon mixtures. The discharge was generated in a stainless steel vacuum chamber by two parallel-plate electrodes connected to a 13.56 MHz power supply. A substrate holder, to which a d.c. bias voltage could be applied, was positioned outside the region between the two electrodes, i.e. in a region of lower plasma density. The substrate voltage bias, V B , and the ratio of the partial pressures of O 2 to Ti(OC 3 H 7 ) 4 [oxygen to precursor (OTP) ratio] in the chamber were adopted as the principal deposition parameters. Details of the molecular structure of the films were investigated by infrared spectroscopy and X-ray photoelectron spectroscopy. The latter was also used to determine the O/Ti and C/Ti atomic ratios at the film surface. The total (surface and bulk) O/Ti and C/Ti atomic ratios were determined using Rutherford backscattering spectroscopy. While neither the surface nor the total O/Ti ratio varied significantly with V B and the OTP ratio, both the surface and total C/Ti ratios varied strongly with these parameters. The refractive index, determined by ultraviolet-visible spectroscopy, and the electrical conductivity, measured by a two-point probe, were influenced by the polarity and magnitude of V B .

HMDSO plasma polymerization and thin film optical properties

Departamento de Fisica e Quimica Faculdade de Engenharia UNESP, 12500-000 Guaratingueta, SP

Amorphous oxygen‐containing hydrogenated carbon films formed by plasma enhanced chemical vapor deposition

Films were deposited from glow discharge plasmas of acetylene–oxygen–argon mixtures in a deposition system fed with radio frequency power. The principal variable was the proportion of oxygen in the gas feed, Xox. The chemical structure and elemental composition of the films were investigated by transmission infrared spectrophotometry and x‐ray photoelectron spectroscopy. Optical properties—refractive index, absorption coefficient, and optical gap—were determined from transmission ultraviolet‐visible spectroscopy data. The latter also allowed the determination of film thicknesses and hence deposition rates. It was found that the oxygen content of the films and, within limits, the refractive index are controllable by the selection of Xox.

Fluorinated polymer films from r.f. plasmas containing benzene and sulfur hexafluorine

Mixtures of C6H6 and SF6 were polymerized in an r.f. discharge. Actinometry (quantitative optical emission spectroscopy) was used to determine trends in the plasma concentrations of the species F, H and CH as a function of the proportion of SF6 in the feed. Infrared spectroscopy and electron spectroscopy for chemical analysis were employed to characterize the deposited material. Increasing proportions of SF6 in the feed produced increased fragmentation of the benzene molecules and greater fluorination of the deposited material. The deposition rate, as determined by optical interferometry, was found to be enhanced about 4 times by the presence of 10–20% SF6 in the feed. At 50% SF6 in the feed, deposition rates were greater than in pure C6H6 plasmas despite the (probably large) etching effect of atomic fluorine from the discharge. Relationships between the plasma composition, electron density and temperature, film composition and growth rate are discussed.

Optical emission study of reaction mechanisms in the deposition of nitrogen‐containing amorphous hydrogenated carbon films

The reaction mechanisms taking place in a film‐forming radio frequency discharge of a mixture of acetylene, nitrogen, and helium have been investigated using optical emission spectroscopy. A transient actinometric method was employed, based on the interruption of the flow of one of the feed gases (either C2H2 or N2), and the subsequent observation of the time‐dependent changes in the discharge environment, specifically of the concentrations of CH and CN species, two possible precursors of film formation. Both N2 and C2H2 affect the CH and CN concentrations. Nitrogen strongly enhances the rate of formation of CH, very probably via gas phase reactions between atomic nitrogen and C2H2 or other species containing carbon and hydrogen. On the other hand, the relatively high CH concentration observed in discharges without nitrogen is taken to indicate that fragmentation of the C2H2 molecules by the discharge is another important mechanism of formation of the CH species. For the CN species, gas phase reactions be...

Influence of Ar+ ion irradiation on the properties of plasma polymerized acetylene films

Abstract Plasma polymerized acetylene is an amorphous material whose properties can be significantly changed upon ion irradiation. In this work, the modification of the structural, optical, electrical and mechanical properties of PPA films by 150-keV Ar+ ions is investigated. The ion fluence varied from 1018 to 1021 m−2 at a constant current of 100 μA. Structural and optical properties were analyzed using infrared and ultraviolet-visible spectroscopies, respectively. From oxygen plasma etching experiments, further structural information was obtained. A two-point probe was employed to measure the electrical resistivity. Hardness measurements were made using a nanoindenter. The infrared spectra showed depletion of hydrogen and increased concentration of carbon double bonds with increasing ion fluence. As a consequence, the optical, electrical and mechanical properties were also modified. The optical transmission in the UV and visible regions were diminished with increasing ion fluence, reflecting a narrowing of the optical gap. The electrical resistivity decreased with increasing fluence; a decrease of 11 orders of magnitude with respect to the pristine film was measured for the highest fluence (1021 m−2). A strong increase of hardness was observed as the ion fluence was increased. A hardness of 10.6 GPa was measured after irradiation at the fluence of 1021 m−2. The oxygen-etching rate decreased significantly as the fluence was increased. Both the hardness and etching results strongly indicate that a highly cross-linked structure was formed at high ion fluences.

Structural and optical properties of amorphous hydrogenated fluorinated carbon films produced by PECVD

Fluorinated films were deposited from radiofrequency discharges of toluene/trifluorotoluene and toluene/sulfur hexafluoride mixtures. Actinometric optical emission spectroscopy was used to determine trends in the concentrations of the plasma species H, CH, and F as a function of the partial pressure of trifluorotoluene or sulfur hexafluoride present (expressed as a percentage of the total chamber pressure) designated RT and Rs, respectively. Transmission infrared spectrophotometry and electron spectroscopy for chemical analysis revealed that the films contain various fluorine-containing functionalities and that the degree of fluorination increases as RT or Rs is increased. Ultraviolet-visible spectrophotometry of films deposited at various values of RT and of Rs allowed the determination of the absorption coefficients α of the films. From plots of α as a function of photon energy it was possible to calculate the optical gap (E04). An intriguing result was a decline and subsequent rise in E04 as Rs was increased. Molecular modelling using ZINDO/PM3 calculations provided a semi-quantitative explanation of the dependence of E04 on Rs.

Li diffusion and electrochromism in amorphous and crystalline vanadium oxide thin film electrodes

Amorphous vanadium oxide films were synthesized onto ITO-coated glass substrates by the hot filament metal oxide deposition technique. The as-deposited samples were heat-treated in an argon atmosphere. X-ray diffraction analysis revealed that the films treated at 200 and 300 oC were still amorphous, while those treated at 400 and 500 oC were crystalline, with a V2O5 structure. All electrodes were electrochemically reversible for Li+ intercalation, exhibiting the electrochromic effect, observed from optical transmittance measurements at 632.8 nm. The Li-diffusion coefficient, DC, was measured by the galvanostatic intermittent titration technique (GITT) as function of the inserted charge. For the crystalline films it was observed that the optical absorbance and the DC increase with increasing Li insertion in the single-phase regions of crystalline LixV2O5 and decrease in the two-phase regions. For the latter, an effective DC was considered. The presence of other vanadium oxides mixed to the V2O5 matrix was inferred for the crystalline films from the chronopotentiometric and DC measurements.