Combination Of Ellipsometry Research Articles

Growth and electrochemical behaviour of a poly [tricarbonyl(vinylbipyridyl)rhenium chloride] film. Heterogeneous reduction of CO2

The mechanism of anionic electropolymerisation of [(vbpy)Re(CO)3Cl], where vbpy is 4-vinyl-4′-methyl-2,2′-bipyridyl, has been studied with ellipsometry, and the nature of the film formed established. The chemical transformations of this film on reduction to – 1.9 V have been studied by in situ FTIR spectroscopy in the presence and absence of CO2, and the spectra assigned using Timney's ligand effect parameters. This analysis shows that the reduction chemistry is somewhat simplified as compared to the homogeneous case studied earlier, with dimerisation of the reduction products much less prevalent. The films are highly active for CO2 reduction but show long-term degradation, and one possible mechanism for this is explored with a combination of ellipsometry and FTIR.

Ellipsometry of metal deposition

The initial stages during galvanic deposition were monitored by ellipsometry in combination with cyclic voltammetry for the growth of Bi, Cu and Ge films on polycrystalline Au, Pd and Pt substrates. The upd of Bi on Au, of Ge on Pt and of Cu on Au could be detected ellipsometrically but not for Bi on Pd or Pt. The refractive index of the upd film of Bi on Au changes with increasing coverage. The bulk deposit film of Bi on Au and of Cu on Au grows at constant refractive index.

Optical studies of PdO thin films

Palladium oxide thin films are studied by ellipsometry, optical transmission, and Raman scattering. The PdO films are made by completely oxidizing Pd films sputtered onto fused silica substrates, and their optical constants determined using a combination of ellipsometry and transmission measurements. Oxidation kinetics experiments are performed on thick Pd substrates at temperatures of 300–500 °C. The optical properties of the films show a thickness dependence suggesting an increased absorption at the PdO-Pd interface. Ellipsometry on oriented single crystals of PdO yields the anisotropic optical constants at 632.8 nm. These results are combined with an effective medium theory to show that the oxidized films have a void density of 20–25%. Raman scattering is demonstrated to be a very sensitive probe for detecting the presence of PdO on Pd. An oxide only a few Å thick is readily detectable, despite the absence of any surface enhanced Raman effect.

Investigation of metal deposition with ellipsometry

The underpotential and bulk deposition of a metal onto a foreign metal substrate was monitored with ellipsometry in combination with cyclic voltammetry. Deposit—substrate systems were investigated for which the refractive index of the bulk deposit is respectively larger, about equal and smaller than N substrate, viz lead deposition on gold and platinum and copper deposition on platinum. The refractive index of the Pb—UPD film on au was found to be intermediate between N Pb and N Au. Bulk lead is deposited already when the coverage is about three monolayers; furthermore alloy formation was established at longer deposition times. Also for the Cu—UPD flm on Pt, a refractive index was obtained in between the values of substrate and bulk deposit. Homogeneous deposition of bulk Cu occurs if E < −0.60 V vs mse. For the PbPt system the refractive indices of the UPD layer and the bulk deposit do not differ much.

An ellipsometric investigation of nickel oxide films in alkaline solution: The multilayer film approach

The properties of anodic oxide films formed on polycrystalline nickel electrodes in alkaline solution under potentiodynamic conditions were studied by means of cyclic voltammetry and combined ellipsometry and reflectometry. The oxide film grown on a Ni surface during the potential scan between hydrogen and oxygen evolution was revealed to be optically inhomogeneous. In this paper a reliable model for two- or three-layer oxide films with different refractive indices is demonstrated. It has been found that Ni(II) oxides form a bottom thin solid state film (final thickness of about 3 nm) of n ̂ 3=2.50(±0.15) -0i (the mean value for λ=632.8 nm) composed of NiO and Ni(OH) 2 phases. At higher anodic potentials a further oxidation of Ni(II) oxides and the formation of thick layers of Ni(III) and Ni(IV) phases on top of the passive film occurs, most probably, due to a defect mechanism. The obtained values of the refractive indices are: n ̂ 2=1.41(±0.01)−0.073(±0.005)i and n ̂ 1=1.38(±0.01)−0.06(±0.01)i for oxide film layers containing socalled β-NiOOH and γ-NiOOH hydrous nickel oxide species, respectively.

An ellipsometric investigation of nickel oxide films in alkaline solution: The multilayer film approach

Abstract The properties of anodic oxide films formed on polycrystalline nickel electrodes in alkaline solution under potentiodynamic conditions were studied by means of cyclic voltammetry and combined ellipsometry and reflectometry. The oxide film grown on a Ni surface during the potential scan between hydrogen and oxygen evolution was revealed to be optically inhomogeneous. In this paper a reliable model for two- or three-layer oxide films with different refractive indices is demonstrated. It has been found that Ni(II) oxides form a bottom thin solid state film (final thickness of about 3 nm) of n 3 =2.50(±0.15) -0i (the mean value for λ=632.8 nm) composed of NiO and Ni(OH)2 phases. At higher anodic potentials a further oxidation of Ni(II) oxides and the formation of thick layers of Ni(III) and Ni(IV) phases on top of the passive film occurs, most probably, due to a defect mechanism. The obtained values of the refractive indices are: n 2 =1.41(±0.01)−0.073(±0.005)i and n 1 =1.38(±0.01)−0.06(±0.01)i for oxide film layers containing socalled β-NiOOH and γ-NiOOH hydrous nickel oxide species, respectively.

Optical and electrical properties of single-crystalline zirconium carbide.

Optical and electrical properties are reported for single-crystalline ${\mathrm{ZrC}}_{0.89}$. The specular reflectance was measured between 0.025 and 6.5 eV, and ellipsometry measurements were made between 1.2 and 4.5 eV. The combination of ellipsometry with reflectance allows optical functions to be computed reliably between 0 and 6.5 eV and also provides a check on the consistency of the measurements. The van der Pauw technique was used to measure the electrical resistivity of the samples at temperatures between 4.2 and 300 K and the Hall coefficient at room temperature. Drude parameters obtained from the electrical measurements are in good agreement with those obtained from the optical data. Both the optical and electrical results are compared to other experimental results and to theory.

Optical analysis of absorbing double layers by combined reflection and transmission ellipsometry

A method known as combined ellipsometry, which utilizes the simultaneous interpretation of the ellipsometric parameters determined for light reflected and transmitted by the air side and by the substrate side of thin films, was used to obtain an optical analysis of absorbing double layers deposited onto a non-absorbing substrate. It is shown that the use of this method enables the evaluation of all the optical parameters characterizing absorbing double layers consisting of a non- absorbing and an absorbing thin film. Combined ellipsometry can be used for analysing the double layers formed by two highly absorbing thin films in a reasonable way if this method is complemented by a precise auxiliary method, e.g. the Fizeau method. These conclusions are demonstrated by experimental results obtained for samples of the following double layers: MgF 2/Al, Al/MgF 2, TiO/Au and Au/Ni. The ellipsometric parameters were measured at a wavelength λ of 632.8 nm.

Ellipsometric studies of film formation on tooth enamel and hydrophilic silicon surfaces.

The uptake of salivary substances onto hydrophilic negatively charged surfaces of silicon or onto enamel surfaces was studied in vitro with ellipsometry. There was a rapid initial uptake of substances followed by a slow but continuous uptake probably of other substances, which could be removed from saliva by absorption with a S. mutans serotype c strain. the kinetics for the uptake onto enamel and silicon surfaces and the thicknesses of the layers were similar. The combination of ellipsometry and silicon surfaces is suggested as a model for obtaining increased information on dental pellicle formation.

Ellipsometric investigation of black soap films

Thin soap films of sodium dodecyl sulphate and sodium dodecyl benzenesulphonate have been studied with a combination of ellipsometry and reflectometry. It is demonstrated that an optical three-layer model is superior to a one-layer model for the interpretation of the ellipsometric data. The refractive indices of the film core and the surface layers are determined, and it is found that the index for the surface is higher than that for the film core. The composition of the Newton type of film is discussed on the basis of these data.

Gas adsorption studies by ellipsometry in combination with low energy electron diffraction and mass spectrometry

Isotherms for physical adsorption on a silver single crystal surface from ultrahigh vacuum have been determined by ellipsometry. Molecular volumes, derived from the optically determined monolayer film thickness, indicate that the classical macroscopic theory of ellipsometry for film covered surfaces is surprisingly well suited for physically adsorbed coverages of molecular dimensions. For a fractional monolayer coverage, the electron diffraction pattern has been found to remain characteristic of the clean substrate surface. The results also show the difficulties in the preparation and definition of clean solid surfaces, and indicate a sensitivity of the ellipsometer to surface roughness on an atomic level.