Characterization of Niobium Oxide Films Prepared by Reactive DC Magnetron Sputtering

Abstract

Niobium oxide films have been prepared on glass and Si(100) substrates by reactive dc magnetron sputtering of a metallic Nb target in an argon-oxygen atmosphere. The properties of the films as a function of oxygen partial pressure have been studied systematically by Rutherford backscattering spectroscopy, X-ray diffraction, X-ray reflectometry and optical spectroscopy. Rutherford backscattering studies show that the films are substoichiometric at lower oxygen flow while stoichiometric films can be formed above 7.5 sccm O 2 flow. Grazing incidence X-ray diffraction studies show that the films are amorphous. X-ray reflectometry was used to determine the sputter rate, density and surface roughness of the films. The films prepared at lower oxygen flow rates had a higher density than those prepared at higher oxygen flow rates. For appropriate oxygen flow rates fully transparent niobium oxide films can be grown with rates up to 0.5 nm/s for a constant cathode current of 900 mA. From optical spectroscopy measurements of reflectance and transmittance we have determined the optical constants such as the refractive index (n), extinction coefficient (k) and band gap (E g ) as well as the film thickness. For the fully transparent films prepared above 7.5 sccm O 2 flow rate a band gap of 3.5 to 3.6 eV is obtained. Optical spectroscopy measurements show that the refractive index of the films decreases upon increasing oxygen flow rate and this finding is related to a decrease of density upon increasing oxygen flow.

Ellipsometric Selective Sensitivity to Magnetic Nanostructures

“…On the surface we supposed an oxidation layer with refractive index n = 2.1 (the refractive index of Nb 2 O 5 [14]). …”

Influence of ionisation zone motion in high power impulse magnetron sputtering on angular ion flux and NbOxfilm growth

“…Since NbO x or Nb 2 O 5 films are frequently used as optical thin films due to their high transmittance, high refractive index and chemical stability [28][29][30][31], we performed a brief characterisation of their optical properties. As shown in Fig.…”

Influence of air oxidation on the properties of decorative NbOxNy coatings prepared by reactive gas pulsing

“…It means that, even if the oxygen contents in the three as-deposited films are not very different (Table 1), the presence of Nb-O bonds strongly depends on the duty cycle. After annealing at 600°C and for all duty cycles, the spectra exhibited the same diffuse bands and a pronounced one at 800 cm − 1 , which is typical from a Nb 2 O 5 feature [18].…”

“…Moreover, at 500 and 600°C, the indentation occurs in the oxidised layer (the maximum indentation depth was close to 500 nm for a total thickness around 2.2 μm) since almost half or all the coating are oxidised [2]. Therefore the measured hardness value is close to the value for a homogeneous Nb 2 O 5 coating, close to 6 GPa [18]. The Young modulus values of these niobium oxynitride coatings exhibited a tendency similar to that of the hardness, with E ≈ 20 × H. It puts in evidence the fragility and brittleness of these coatings, since this proportional law is deducted from the Griffith's theory applied to brittle materials [19].…”