Talanta 78 (2009) 964–969 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Fabrication and nanoindentation properties of TiN/NiTi thin films and their applications in electrochemical sensing Ashvani Kumar a , Devendra Singh b , Rajendra N. Goyal c,∗ , Davinder Kaur a a Department of Physics and Center of Nanotechnology, Indian Institute of Technology Roorkee, Roorkee 247667, India b Metallurgy and Materials Engineering Department, Indian Institute of Technology Roorkee, Roorkee 247667, India c Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India article info Article history: Received 13 October 2008 Received in revised form 5 January 2009 Accepted 5 January 2009 Available online 20 January 2009 Keywords: TiN/NiTi heterostructures Nanoindentation Sensors Corrosion resistance abstract Nanocrystalline TiN/NiTi thin films have been grown on silicon substrate by dc magnetron sputtering to improve the corrosion and mechanical properties of NiTi based shape memory alloys without sacrificing the phase transformation effect. Interestingly, the preferential orientation of the TiN films was observed to change from (1 1 1) to (2 0 0) with change in nature of sputtering gas from 70% Ar + 30% N 2 to 100% N 2 . In present study the influence of crystallographic orientation of TiN on mechanical and corrosion prop- erties of TiN/NiTi thin films was investigated. TiN (2 0 0)/NiTi films were found to exhibit high hardness, high elastic modulus, and thereby better wear resistance as compared to pure NiTi and TiN (1 1 1)/NiTi films. Electrochemical test revealed that TiN coated NiTi film exhibits better corrosion resistance in 1M NaCl solution as compared to uncoated NiTi film. The application of TiN/NiTi films in the electrochemi- cal sensing of dopamine, which has a critical physiological importance in Parkinson’s disease, has been demonstrated. A comparison of voltammetric response of dopamine at silicon based electrodes modified with different nanocrystalline coatings indicated that these films catalyze the oxidation of dopamine. © 2009 Elsevier B.V. All rights reserved. 1. Introduction It has been demonstrated that NiTi shape memory alloy (SMA) thin films are promising materials to fabricate micro devices for micro-electro-mechanical systems (MEMS) and bio-MEMS such as micropumps, microwrappers and stents for neurovascular blood vessels [1–3]. However, there are still some concerns for the wide application of SMA thin films because of their unsatisfactory mechanical and tribological performances, chemical resistance and biological reliability. High nickel content in NiTi alloys often stim- ulated suspicion for their medical use because of nickel toxicity [4,5]. The limited hardness and wear resistance of NiTi make it dif- ficult to be used in orthodontic and MEMS applications. In order to improve surface properties, corrosion resistance and suppression of Ni ions release of NiTi shape memory alloys, many techniques such as nitrogen ion implantation [6], laser surface treatment [7], thermal and anodic oxidation [8,9], have been employed. The prob- lems of these surface treatments are high cost, possible surface or ion induced damage, amorphous phase formation, or degradation of shape memory effects. The magnetron sputtering has impor- tant specific advantages such as low levels of impurities and easy control of the deposition rate and also enables the production of ∗ Corresponding author. Tel.: +91 1332 285794. E-mail address: rngcyfcy@iitr.ernet.in (R.N. Goyal). thin films of various morphology and crystallographic structure. The deposition of nanocrystalline and nanocomposite thin films via magnetron sputtering has been reported in literature [10,11]. The present study explored the insitu deposition of hard and adherent nanocrystalline titanium nitride (TiN) protective coating on NiTi thin films by dc magnetron sputtering. TiN is chosen for passivation layer due to its superior mechanical properties, excel- lent corrosion, wear resistance and good biocompatibility and TiN coatings are often used to modify the orthopedic implant mate- rials to extend their life span [12,13]. The purpose of the present study is to examine the effect of crystallographic orientation of TiN on mechanical and corrosion properties of TiN/NiTi heterostructure thin films. The investigation revealed better mechanical and corro- sion properties in case of TiN (2 0 0)/NiTi films as compared to TiN (1 1 1)/NiTi and pure NiTi films. The present study also explores the utility of TiN (2 0 0), TiN (2 0 0)/NiTi, TiN (1 1 1)/NiTi nanocrystalline coatings over Si (1 0 0) substrate as working electrode material for electroanalytical purpose. In recent years the electrodes modified with various nanomate- rials have been used for the electrochemical sensing of biologically important compounds as the surface modification has been found to exhibit electrocatalytic effect [14–18]. As electrochemical meth- ods have distinct advantages [19,20] over other conventional methods for determination of dopamine (DA), a catecholamine neurotransmitter generated in various parts of central and periph- eral nervous system, hence, careful monitoring of dopamine 0039-9140/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2009.01.005