Effect of Cu content on microstructure, morphology, and antibacterial properties of Ti-Cu alloy thin films

Ti-Cu alloy thin films exhibit considerable potential for the development of advanced antibacteria lsurfaces, particularly for biomedical applications. In this research, Ti-Cu binary alloy thin films with a wide range of Cu content from 25.8 at% to 77.8 at% were deposited using magnetron co-sputtering with pure Ti and Cu as the targets. The composition of Cu in the films can be controlled by the applied power of Cu targets. This study investigated the effect of Cu content on the microstructural, morphological, and antibacterial properties using X-ray diffraction (XRD), Field emission scanning electron microscopy(FESEM), Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and plate-countmethod,respectively. Structural analysis using XRD revealed that Ti (Cu) solid solution is formed for the Ti-Cu coatings with the Cu contents of 25.8 at% and the films tended to form an amorphous structureembedded with Cu nanocrystals when the Cu content was 77.8 at%. Surface morphology showed thatthe films with higher Cu content exhibited increased surface roughness and the presence of Cu nano-granular features. Antibacterial evaluations against Escherichi coli showed that the films containing Cu in the range of 25.8 at% to 77.8 at%. This effect is attributed to both inherent antibacterial properties byCu and the microstructural modifications that enhance bacterial inhibition.1. IntroductionTitanium (Ti) has several intriguing properties, such as lightweight,a high melting point, and excellent biocompatibility, making it suitablefor use in medical materials. Additionally, its high oxidation resistanceand strength enable Ti can be used in various applications, including engine components and the automotive industry [1-3]. The addition of other metals can significantly enhance the properties of Ti. Onewell-known example is the Ti-Ni alloy, commonly referred to asNitinol. This alloy is extensively studied in the medical field due to its unique characteristics, such as super elasticity and the shape memory[4-6]. Alloying Ti with niobium (Nb) can reduce its elastic modulus. This reduction helps to minimize stress shielding, which is a commonproblem in implant materials. Ti-Nb alloys are particularly promising for orthopedic applications due to their excellent biocompatibility, low cytotoxicity, and high corrosion resistance [7,8]. Another notablealloy is Ti-Zr alloy, which has gained attention for its excellent bio-compatibility and mechanical properties. The addition of zirconium (Zr) to Ti improves its strength, corrosion resistance, and wear resistance,making it highly suitable for biomedical applications, particularly in dental and orthopedic implants [9,10].Copper (Cu) is another element widely used to improve the properties of Ti alloys. Due to its good electrical and thermal conductivity, as well as its widely recognized antibacterial properties. Therefore, combining these metals in the form of a Ti-Cu thin film integratestheir advantageous features, resulting in a multifunctional material that offers both mechanical strength and antibacterial benefits. This makes Ti-Cu alloys highly promising for medical applications [11-13].ChangBo et al. [14] prepared Ti- Cu alloys by Ar-arc melting followedby heat treatment and they showed that Ti alloyed with a small amountof Cu (1 wt% to 5 wt%) exhibits suitable mechanical properties, good biocompatibility, and excellent corrosion resistance. Additionally, Ti alloys containing at least 5 wt% Cu displayed a good antibacterialrate (over 99%) against E. coliand S. aureus. Stranak et al.[15]demonstrated that Ti-Cu films produced via high power impulsemagnetron sputtering can efficiently kill bacteria over 1 day to 10 day.The antibacterial mechanism of Ti-Cu alloys was multifaceted, involving both the released Cu ions disrupting cellular processes and physical effects from direct contact with the alloy surface[16,17].Moreover, The antibacterial capability of Ti-Cu alloys is also relatedto the formation of the Ti2Cu phase, finer Ti2Cu phases potentiallyresulted in improved antibacterial performance [18].In recent years, Ti-Cu alloys have been successfully fabricated in the form of thin films. Ti-Cu alloy thin film fabrication approach offers several advantages, particularly for the development of anti-bacterial surfaces [13,15,19]. Magnetron sputtering is frequently used