Applied Surface Science 274 (2013) 282–287 Contents lists available at SciVerse ScienceDirect Applied Surface Science jou rn al h omepa g e: www.elsevier.com/locate/apsusc Role of base pressure on the structural and nano-mechanical properties of metal/diamond-like carbon bilayers Neeraj Dwivedi a,b , Sushil Kumar a,∗ , Hitendra K. Malik b a National Physical Laboratory (CSIR), K.S. Krishnan Road, New Delhi 110012, India b Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India a r t i c l e i n f o Article history: Received 18 January 2013 Received in revised form 6 March 2013 Accepted 8 March 2013 Available online 15 March 2013 Keywords: DLC Nano-mechanical properties, Nanoindentation a b s t r a c t The influence of base pressure on the structural and nano-mechanical properties of plasma produced metal (Cu and Ti)/diamond-like carbon (DLC) bilayers is reported. All of these samples show the for- mation of micro and nano-structured morphology with very low average roughness (less than 1 nm). The Cu/DLC and Ti/DLC bilayers deposited at low base pressure exhibit comparatively higher hardness and better nano-mechanical properties than the ones grown at higher base pressure. Highest hardness as ∼49 GPa is obtained in Ti/DLC bilayer grown at low base pressure condition. Several other nano- mechanical parameters are also examined and correlated with each other. Present investigation will be useful to understand the role of base pressure on the properties of DLC coatings and may enhance its industrial application in term of hard and protective coatings. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Diamond-like carbon (DLC) is an interesting form of carbon as it contains multiple phases including diamond-like sp 3 and graphite- like sp 2 phases. It is a metastable material and has high degree of disorder owing to distortion in bond angle and bond length. Despite having high degree of disorder, DLC films have shown excellent mechanical, electrical and optical properties [1–9]. The properties of DLC films strongly depend on sp 3 /sp 2 ratio, which is predominantly controlled by deposition parameters. By varying sp 3 /sp 2 ratio, its hardness, optical band gap and conductivity can be tuned over wide range. Recently, Dwivedi et al. [10] have explored the correlation of sp 3 /sp 2 ratio with electrical, optical and nano- mechanical properties of DLC films. The DLC films can be deposited at low temperature, even room temperature, which allows its depo- sition on glass and flexible plastic substrates. Hence, DLC has been considered as an excellent engineering material for the past few years. There are several parameters for the deposition of DLC thin films including ion energy or self bias, gas pressures, deposition tem- perature, gas flow rates, etc. All of these parameters influence the sp 3 /sp 2 ratio, structure and bonding environment of DLC film and tailor its properties. Singh et al. [11] have evaluated the effect of bias on properties of DLC films. Piazza et al. [12] have examined ∗ Corresponding author. Tel.: +91 11 4560 8650; fax: +91 11 4560 9310. E-mail addresses: neerajdwivedi6@gmail.com (N. Dwivedi), skumar@nplindia.org (S. Kumar). the properties of DLC films as a function of acetylene gas pressure. Fallon et al. [13] and Maitre et al. [14] have explored the influence of bias on the properties of amorphous carbon films. Recently, we have also examined the properties of DLC and modified DLC films as the function of pressure and bias [15–17]. So, all these parame- ters have already been widely explored for the deposition of DLC films. Apart from these parameters, the base pressure is also found to be a crucial parameter that can directly affect the properties of DLC films. The base pressure influences the gas phase kinetics and structure of the deposited films. Under a high base pressure con- dition, atmospheric oxygen added into the structure. However, an amount of atmospheric oxygen gets reduced when the base pres- sure becomes lower. So it would be very exciting to see how the nano-mechanical properties of DLC gets change upon changing the base pressure from high to low base pressure regimes, as DLC is hard material. It would be worth mentioning that despite of this important parameter no significant research pertaining to evalua- tion of properties of DLC films as a function of base pressure has been conducted. Although DLC films have excellent properties, they also show poor adhesion to the substrates due to high residual stress. In order to solve stress issue, various foreign elements have been incorpo- rated in DLC matrix. Damasceno et al. [18] have incorporated Si into DLC to minimize stress. Freire [19] has reduced the stress of amorphous carbon film by adding nitrogen. Chen and Hong [7] have minimized the stress of carbon films by copper incorporation. All of these foreign elements although lowers the stress, they also reduce the hardness. Hence, alternative approach is required to reduce the stress and improve the adhesion of DLC film without affecting its 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.03.037