B. C. Trasferetti

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 .

Infrared reflection-absorption characterization of TiO2 films on ITO: detection of LO modes

Abstract By exploiting the high reflectivity of ITO substrates in the infrared and the detection of longitudinal optical (LO) modes provided by oblique incidence of radiation (Berreman effect), we showed that reflection-absorption experiments in the MID-IR can be successfully performed when thin inorganic oxide films deposited on ITO are used as samples. The samples we used were TiO 2 films deposited on ITO by a sol-gel method. After being annealed at different temperatures, the films presented different structures, which could be detected by the IR spectra. Cyclic voltammograms of the samples were also presented and correlated to the IR spectra. Since we expect that other inorganic oxides can yield similar results, this simple, non-destructive and inexpensive technique can be routinely used in an electrochemical laboratory.

Observation of the Berreman Effect in Infrared Reflection-Absorption Spectra of Amorphous Titanium Oxide Thin Films Deposited on Aluminum

Infrared reflection-absorption spectra of plasma-enhanced chemical vapor deposition (PECVD) amorphous TiO2 thin films on aluminum were obtained with s- and p-polarized light and oblique incidence angles. Such spectra were analyzed by means of spectral simulations based on a Fresnel equation for a three-layered system. The optical constants used in the simulations were obtained through the Kramers–Krönig analysis of the reflectance spectra of a pellet of powdered amorphous TiO2. LO-TO energy-loss functions were also calculated from these optical constants, and a splitting was observed. A good qualitative agreement between experimental and simulated spectra was achieved, and the Berreman effect was observed in both cases when p-polarized light was used. It was shown, therefore, that the Berreman effect makes infrared reflection-absorption spectroscopy a successful technique for the characterization of an amorphous TiO2 thin layer on aluminum.

s - and p -Polarized Infrared Specular Reflectance of Vitreous Silica at Oblique Incidences: Detection of LO Modes

Infrared (IR) specular reflectance spectra of a semi-infinite sample of vitreous silica (v-SiO2) were obtained with the use of both s- and p-polarized light and oblique incidence angles. The optical constants of the material and hence its longitudinal optic/transverse optic (LO-TO) functions were determined through the Kramers–Krönig analysis (KKA) of its s-polarized 20° off-normal reflectance spectrum. p-Polarized spectra had their reflection maxima blue-shifting as the incidence angle increased, while they remained unchanged for the s-polarized spectra. Since an LO mode generally lies at wavenumbers higher than its respective TO mode, such a blue shift may be due to the detection of the LO mode in addition to the TO mode as incidence angle increased. The only exception to this observation was the high-frequency shoulder, which underwent a sharp intensification as the incidence increased. The present work shows that it is indeed brought about by the weakly IR active asymmetrical mode (AS2) but only because it takes place immediately after the intense AS1 mode, which causes the refraction index spectrum to have a broad dip below unity. Such a dip is proven to be responsible for the sharp increase in the high-frequency shoulder of the reflectance spectra.

The effect of ion bombardment on the properties of TiOx films deposited by a modified ion-assisted PECVD technique

Abstract In this work we discuss the effect of ion bombardment on the structural, optical and electrical properties of TiO x -like films deposited by a novel ion-assisted plasma enhanced chemical vapor deposition technique. In such a technique an electrical biased substrate is positioned in a region of low ion density, outside the gap between the electrodes used to generate the discharge. Films were deposited in different conditions of substrate bias, V b , and their chemical structure and composition were analyzed by infrared reflectance absorbance (IRRAS) and Rutherford backscattering spectroscopies (RBSs), respectively. The optical constants of the films were evaluated by ultraviolet-visible (UV-Vis) spectroscopy. Furthermore, the two-probe method was employed to determine electrical resistivity. The results indicate that film properties are strongly influenced by V b , that is, by the kind and the energy of the charged species bombarding the growing film.

Introdução às técnicas de reflexão especular e reflexão-absorção no infravermelho: (1) reflexão especular

This paper is the second part of an article aimed to present theoretical basis as well as some applications of two infrared reflection techniques: specular reflection and reflection-absorption. It is emphasyzed how much spectral simulation can aid spectral analysis. The usefulness of reflection-absorption spectroscopy as a thin film caracterization technique is stressed. Optical effects such as LO-TO splittings and their observation as Berreman effect are also addressed.

Synthesis of polymer films by an electron emission CVD technique

A low-pressure chemical vapor deposition (CVD) technique based on the formation of reactive film precursors by dissociation of gas-phase reactants by electron impact is described. The electrons are emitted by a hot filament and a positive bias voltage applied to the substrate provides control of the emission current. The emitted electrons are primarily responsible for the gas dissociation, but secondary electrons resulting from electron-impact ionization of the gas molecules also produce reactive species, contributing to the deposition process. This technique was used to synthesize polymer films from C2H2–N2 mixtures at pressures ranging from 1–10 Pa. The dependencies of the current collected by the substrate, IS, on the substrate bias voltage, VS, and on the gas pressure were determined. The film deposition rate was measured as a function of several deposition variables such as IS, VS, and the N2 to C2H2 flow rate ratio. Oxygen was present in the films as a contaminant. Analyses by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) provided insight into the film molecular structure, allowing identification of various functional groups and binding states of the C- and N–atoms. From the XPS spectra, the N/C and O/C ratios were determined.