Effect of interlayer thickness on electrochemical properties and corrosion resistance of sputtered TiNxnm/Tixnm multilayer thin films

Abstract

Three multilayers [TiNxnm/Tixnm/p-type Si (100)] (x = 2.5, 5, 10) were fabricated using a dc-magnetron sputtering to evaluate surface and interfacial effect on electrochemical properties for possible application in supercapacitor electrode materials. The (111) and (101) planes of TiN and Ti were observed at 36.50° and 40.19° respectively. TA, LA, and TO phonon modes were found at 254.12, 306.15, and 637.94 cm−1, respectively. The defect state distribution of Ti, N, and O was investigated from PL. XPS confirmed the Ti at. % of TiNxnm/Tixnm multilayers decreased from 43.07 to 12.04 and N at. % increased from 42.79 to 72.53 % as the x value decreased from 10 nm to 2.5 nm. The areal specific capacitance (Ca) and energy density (E) of the TiNxnm/Tixnm multilayer electrode increased with decreasing multilayer thickness. E varied from 0.27 to 1.37 mWhcm−2 and the power density (P) from 5.04 to 25.4 mWcm−2 for the multilayers. The diffusion coefficient (D) and total accumulated charge (Qin) decreased from 6.48 × 10−17 to 1.56 × 10−18 cm2/s and 1.82 to 1.64 C/cm2, respectively, for TiNxnm/Tixnm multilayers. The capacitive contribution was the highest in x = 10 (2.181 Av−1s). However, the diffusion-limited contribution was maximum in x = 5 (3.541 Av−1/2s1/2). The cyclic stability maintained at 85.4 % capacitive retention over 1000 cycles and the expansive potential window (up to 0.8 V in 1 M H2SO4) makes the multilayer thin films ideal for supercapacitor electrodes. Among all the samples, the TiN2.5nm/Ti2.5nm exhibited the highest Ca, E, and diffusion coefficient, originating from the smaller layer thickness, leading to more ohmic conductivity and facilitating the supercapacitive performance.