Titanium dioxide films deposited by cathodic arc for water treatment and microelectronics

ADRIANA MÁRQUEZ; DARINA MANOVA; DANIEL VEGA; CARLOS ACHA; STEPHAN MÄNDL; J M MEICHTRY; CARLOS PERALTA; ARIEL KLEIMAN; MARTA I LITTER; IGNACIO ABINZANO

Shangai

Conferencia; 14th International Conference on Plasma Based Ion Implantation & Deposition (PBII&D 2017); 2017

Introduction: Titanium dioxide is known to be non-toxic and to exhibit excellent chemical and physical properties, which make this material very attractive for a wide variety of applications. One of the recent, most active research focused on titania thin films is linked to its high hydrophilicity and excellent photocatalytic activity under UV irradiation [1]. As a consequence, actual and potential applications include purification of wastewaters, disinfection based on the bactericidal properties, and its use as self-cleaning coating. Among the different TiO2 polymorphs, anatase is considered as the most photoactive phase. Recently, the use of titania films in a metal-insulator-metal device configuration has been evaluated as an alternative for the development of resistive non-volatile memories (Re-RAM) based on the resistive switching of the insulator placed in between two-terminal electrodes [2]. Low and high resistive states can be programmed by application of voltage pulses to the metal electrodes. Stoichiometry and crystallinity of the TiO2 films influence on the switching behavior.Cathodic arc deposition (CAD) has demonstrated to be an efficient method for the deposition of TiO2 thin films with excellent adhesion to the substrate. The structure of the films can be independently controlled through different deposition parameters, among them the substrate bias and the temperature employed during the process.In this work, TiO2 films deposited by CAD were studied toward their use as photocatalyst in water decontamination treatments and as oxide layer in Re-RAM devices.Materials and Methods: TiO2 films were deposited with a cathodic arc with 100 A current on glass substrates. The photocatalytic activity of anatase films was evaluated through their efficiency in Cr(VI) reduction in an aqueous solution under UV irradiation using EDTA as sacrificial agent ([Cr(VI)]0 = 0,8 mM, [EDTA]0 = 1 mM, pH 2). The activity and the kinetic behavior were systematically studied as a function of the film thickness. TiO2 films of 100 nm thickness on a Ti layer of 200 nm were deposited by CAD at room temperature and at 400 ºC. These films in combination with a sputtered top platinum layer were tested as resistive memories of capacitive type. The resistive switching was studied by applying current?voltage cycles (I-V).Results and Discussion: The Cr(VI)-EDTA system under UV illumination in the absence of photocatalyst (blank) shows a base activity. The photocatalytic activity of TiO2 fims with thickness in the range from 100 to 1100 nm was always significantly higher than the base activity registered for the blank. The temporal evolution of normalized Cr(VI) concentration (C/C0) during photocatalytic tests could be adjusted by a first order kinetic equation -d(C/C0)/dt = k C/C0, where k is the kinetic constant. The k values obtained from the fitting of the Cr(VI) decay rate as a function of the film thickness are plotted in Figure 1. In order to compare, k values obtained for thin films synthesized by dip-coating from the reference material titania powder P25 are also included in Figure 1. Although the efficiency of P-25 films was higher than that of CAD films of thickness from 100 to 400 nm, the dip-coating method was limited to films with a maximum thickness as shown in Figure 1. Typical I-V curves of Ti/TiO2/Pt films are shown in Figure 2, Fig. 2a and Fig. 2b correspond to amorphous TiO2 grown at room temperature and to anatase TiO2 deposited at 400 ºC, respectively. For both TiO2 structures resistive switching with bipolar behavior was observed; a high resistance state (HRS) of 200 k and a low resistance state (LRS) of 7 k were obtained for the amorphous film, while the HRS and LRS resulted in 1400 and 300  for the anatase film. Conclusion: The photocatalytic tests of TiO2 films showed that the reaction efficiency increased as the thickness increased, achieving better performance than thin films synthesized from titania powder P25. The Ti/TiO2/Pt devices exhibited a bipolar resistive switching without the need of an electroforming step.