Optical properties and microstructure of plasma deposited Ta2O5 and Nb2O5 films

Abstract

Advanced optical filter applications require an appropriate control of the optical constants, as well as of other suitable film properties such as mechanical performance, thermal and environmental stability, absence of refractive index inhomogeneities, and others. In the present work we studied the characteristics of two high index optical materials, namely amorphous tantalum pentoxide (Ta2O5) and niobium pentoxide (Nb2O5) prepared by plasma enhanced chemical vapor deposition, using penta-ethoxy tantalum Ta(OC2H5)5 and penta-ethoxy niobium, Nb(OC2H5)5, precursors. We particularly investigated the effect of energetic conditions on the film growth by using different modes of plasma excitation, namely rf, microwave, and dual-mode microwave/radio frequency discharges. Under sufficient ion bombardment, controlled by the rf-induced negative substrate bias, the dense Ta2O5 and Nb2O5 films exhibited a refractive index of 2.16 and 2.26 (at 550nm), respectively, while the extinction coefficient was below 10−5, as determined by spectroscopic ellipsometry, and spectrophotometry. We found that increasing ion bombardment during the film growth leads to an appreciable increase of carbon concentration, as indicated by a strong double peak at 1400 and 1500cm−1 in the Fourier transform infrared spectra. Elastic recoil detection measurements revealed an atomic concentration of 2.5% and 5.5% of carbon in the bulk of the Ta2O5 and Nb2O5 films. The presence of carbon did not appear to negatively affect the film optical and mechanical performance and stability. We discuss the relationship between the optical properties and microstructure, and the possible mechanism of carbon bonding in the form of chelate and bridging groups.

High temperature annealing effect on structure, optical property and laser-induced damage threshold of Ta2O5 films

“…5 shows the Ta 4f spectra from the asdeposited and annealed Ta 2 O 5 films. The spectra reveal two 4f 7/2 and 4f 5/2 peaks at 26.4 and 28.2 eV, respectively, which shows composition of the films is Ta 5+ [21,22]. The O/Ta ratio is estimated from the XPS peak area together with their relative sensitivity factors.…”

Electronic structures, elastic and optical properties of M2O5 (M = V, Nb, Ta)

“…Balog et al [7] performed further studies on V 2 O 5 at high temperature and pressure conditions (1500°C, 29 GPa) and confirmed that HPP1 and HPP2 are β-V 2 O 5 and B-V 2 O 5 , respectively. Moreover, the numerous excellent electrical, optical, and physical-chemical properties of M 2 O 5 have encouraged theoretical and experimental investigations of these compounds [8][9][10][11][12][13][14][15][16][17][18][19]. Given its large flux of ion implantation and outlet, large lithium-ion storage density, and stable properties in the polymer electrolyte, V 2 O 5 film might be applied in the electrode layer [8,9].…”

“…This film has been widely applied in various fields [11,12]. attention from researchers [13][14][15]; they have been applied in various optical thin films and photoelectronic devices [16][17][18][19].…”

Plasma enhanced aerosol–gel method: a new way of preparing ceramic coatings

“…It can be observed in the form of strong absorption bands at approximately 1,500 cm -1 . A detailed analysis of these new bands shows that they can originate from chelate complexes [16] presented in Fig. 7.…”