Electrical Properties of Amorphous Rh Oxide Thin Films Prepared by Reactive Sputtering

Abstract

Conducting Rh oxide thin films were prepared by sputtering a Rh target in an Ar and O2 mixed gas. Effects of the oxygen gas flow ratio on the crystallinity, chemical bonding state and resistivity were studied. Amorphous Rh2O3 films were prepared at an O2 flow ratio of 20%. The Rh2O3 films had a relatively high resistivity of 2 mΩcm and a negative temperature coefficient of resistance (TCR) of -1000 ppm/°C, which indicated semiconducting characteristics. On the other hand, amorphous RhOx films with a composition of 1.5 ≤x ≤1.7 were prepared at O2 flow ratios above 40%. Resistivity of these RhOx films were 800 µΩcm and had almost no temperature dependence. Metallic conduction characteristics of RhO2 were assumed to be revealed by the decrease in the oxygen deficiency.

XPS Study of Nanostructured Rhodium Oxide Film Comprising Rh4+ Species

“…In other works 38,43,67,68 RhO 2 oxide were interpreted mainly based on XPS data, moreover authors analyzed supported Rh nanoparticles synthesized with chemical methods where the influence of contaminations might be crucial. We therefore tend to believe that the results reported by Kato and coauthors 39,40,70 should be more reliable. In our experiments no additional peaks in Rh 3d spectra were detected around 309 eV even after a long-term plasma exposure.…”

“…The binding energy of these peaks is 1.5–2 eV higher than the one for atomic oxygen in Rh oxide lattice that implies less charged oxygen species like hydroxides, carbonates, low coordinated oxygen in the lattice, and molecular-like oxygen species (peroxides, superoxides, ozonides). The peak at 531.0 eV might be related to the RhOOH species. , The carbonate like species should give impact at ∼532.0 eV. , The peak with 533.6 eV could originate from adsorbed/capsulated H 2 O species. ,, The total oxygen-to-rhodium ratio calculated based on XPS data was ∼1.7. Correlation of the main O 1s peak intensity ( I (O Ox ), E b (O 1s) = 529.6 eV)) with the Rh 3d intensity of oxidized rhodium peaks ( I (Rh Ox ), E b (Rh 3d 5/2 ) = 308.2 eV)) yielded an O/Rh ratio of 1.5:1, which is in line with Rh 2 O 3 stoichiometry.…”

“…9,65 The peak with 533.6 eV could originate from adsorbed/capsulated H 2 O species. 9,39,60 The total oxygen-to-rhodium ratio calculated based on XPS data was ∼1. Plasma Oxidation of Rh Foil.…”

“…RhO 2 oxide was synthesized and characterized by X-ray diffraction many years ago. − Formation of RhO 2 species was shown for supported rhodium systems by temperature-programmed reduction (TPR) experiments and calorimetric study . However, catalytic properties of Rh 4+ species and its spectroscopic characteristics are still debatable and need clarificatio ,− Usually, the Rh 3+ species in RhO x oxides or mixed Rh-support oxides (for instance, a solid solution of Rh x Ce 1– x O 2−δ in Rh/CeO x systems) can be observed in rhodium-based catalytic systems using X-ray photoelectron spectroscopy (XPS) data. ,, However, some authors discuss presence of Rh 4+ O 2 species in Rh/Al 2 O 3 and Rh/CeO 2 catalysts as well. , The reference data on Rh 4+ spectroscopic characteristics obtained in model Rh–O systems needs to be collected to help resolve confusion in the interpretation of XPS data.…”

Preparation of RhO2 Thin Films by Reactive Sputtering and Their Characterizations

“…We have reported preliminary results on the formation of amorphous Rh oxide thin films by reactive sputtering in a previous paper, however, low-resistivity RhO 2 films could not be realized. 14) In this study, therefore, we examined the influences of sputtering parameters, such as rf power and substrate temperature, and postdeposition annealing on structural and electrical properties of deposited thin films, in order to obtain low-resistivity RhO 2 thin films.…”