Carbon Nanotube Fiber Pretreatments for Electrodeposition of Copper

Abstract

ere is increasing interest towards developing carbon nanotube-copper (CNT-Cu) composites due to potentially improved properties. Carbon nanotube macroscopic materials typically exhibit high resistivity, low electrochemical reactivity, and the presence of impurities, which impede its use as a substrate for electrochemical deposition of metals. In this research, different CNT fiber pretreatment methods, such as heat treatment, immersion in Watts bath, anodization, and exposure to boric acid (H 3 BO 3 ), were investigated to improve the electrochemical response for copper deposition. It was shown that these treatments affect the surface activity of CNTs, including electrical resistivity, polarization resistance, and active surface area, which influence the electrodeposition process of copper. Properties of CNT structures and CNT-Cu composites were researched by electrochemical impedance spectroscopy (EIS), galvanostatic copper deposition, scanning electron microscope (SEM), and four-point electrical resistance measurements. Heat treatment, Watts bath, anodization, and boric acid treatments were shown to be effective for modifying the CNT surface reactivity for subsequent electrochemical deposition of copper.

Copper/carbon nanotube composites: research trends and outlook

“…In addition, electrodeposition affords Cu/CNT fabrication at various scales and in different configurations (figure 4 b ). Both microscale Cu/CNT, such as pillars [52,59] and patterns [3,6,60] on Si substrates (for device application) and macroscale samples, such as sheets/films [55,57,62,65] and wires [53,54,56,63,64,66,67] (for power lines, motor windings, etc.) have been reported.…”

“… Increasing CNT template hydrophilicity: CNTs have been functionalized with oxygen-containing groups to improve hydrophilicity and, thereby, wetting by aqueous Cu electrolytes. Usual functionalization methods are anodization [54,66], heat-treatment in oxygen atmosphere [66], etc. Besides facilitating Cu deposition, using oxygen-functionalized templates is also reported to improve CNT–Cu interaction in the composites, leading to better properties than composites obtained from non-functionalized templates.…”

“…This two-stage process has shown success in fabricating Cu-matrix composites embedding a high vol% of CNTs (45–50 vol%) at both microscale (planar and vertical interconnects) [3,6,59,60] and macroscale (sheets and wires) [3,63,64,67]. The two-stage process overcomes the limitation of CNT template direct aqueous electrodeposition that invariably leads to Cu-coated composites (laminates or core–shell structures) [53–57,61,62,65,66] regardless of template functionalization.The major achievement of electrodeposition has been in revealing the potential of Cu/CNT as a Cu alternative by producing lightweight composites with electrical, thermal and mechanical performances rivalling that of Cu. As mentioned before, electrodeposition succeeded in breaking the CNT vol% limit posed by powder-processing.…”

“…( b ) Achieving uniform CNT and Cu distribution by template electrodeposition: CNT–Cu phase separation manifests as [CNT-core/Cu-sheath] structures in composites fabricated by aqueous-medium Cu electrodeposition of CNT templates [53–57,61,62,65,66]. Alternative protocols using organic solutions of Cu 2+ as electrolytes (two-stage electrodeposition [3,6,59,60,63,64,67]) have been successful in obtaining Cu-matrix composites instead of core-sheath structures (as seen in §2.2).…”

“…Synthesizing CNT templates is now fairly well-established. CNT materials of various configurations, such as macro wires and sheets or micropillars with controlled CNT orientation and structures are now readily available [73][74][75] and even produced commercially [54,66], heat-treatment in oxygen atmosphere [66], etc. Besides facilitating Cu deposition, using oxygen-functionalized templates is also reported to improve CNT -Cu interaction in the composites, leading to better properties than composites obtained from nonfunctionalized templates.…”