Abstract

Recent developments in radio frequency (RF) electronics motivate the interest in developing multi-functional materials which have effective electrical properties with increasing frequency that minimize the conventional skin effect. Carbon nanotubes (CNTs) are emerging as a candidate material due to high direct current (DC) electrical conductivity, flexure tolerance, corrosion resistance, and low density. The DC electrical conductivity of CNT networks is affected by the high resistance junctions between individual or bundled CNTs. Strategies to modify the properties of these junctions have included chemical doping, nano-metal deposition, and physical densification. Alternating current (AC) conductivity measurements of bulk CNT materials to date have shown constant or even increasing values up to 120 GHz. Thus, this dissertation focuses on applying doping and metallization strategies for improving DC electrical properties to altering the AC conductivity of bulk CNTs. AC conductivity measurements were performed using a rectangular waveguide-based technique up to 40 GHz. Initially, a comparison of purified and KAuBr4-doped commercial MWCNT sheet was made to the as-received material. The as-received MWCNT sheet showed a decrease with frequency, whereas the purified sample (with reduced iron impurities) provided a stable AC conductivity. Laser ablation-based thinning of the purified MWCNT sheet produced increased transmission, which was shown to improve measurement accuracy. The laser-thinned purified MWCNT sheet was subsequently doped with KAuBr4 and demonstrated a 3-4× AC conductivity enhancement. The purified MWCNT sheet was also deposited with varying weight loadings (% w/w) of platinum using a Joule heating-driven chemical vapor deposition (CVD) technique. Platinum overcoating of the MWCNT network was observed, consistent with previous studies, resulting in a 1.4× increase in AC conductivity. A high frequency modeling technique using the generalized Drude conduction theory was applied to the experimental measurements from purified, KAuBr4-doped, or platinum-deposited MWCNT sheet to better understand the high frequency effects of each process. The fit results showed that inclusion of KAuBr4 or platinum nano-metal to the MWCNT network increased the material’s plasma frequency, which is attributed to higher carrier density in the material leading to enhanced AC conductivity. Finally, a demonstration of the enhanced RF properties for CNTs was performed using free-standing thin films to directly measure the EMI shielding effectiveness using the rectangular waveguide setup from 10 GHz to 15 GHz. Thus, the work exhibits a practical application of the CNT conductive materials that combines thin film optical transparency and surface conformability with favorable RF shielding properties.

Publication Date

8-13-2024

Document Type

Dissertation

Student Type

Graduate

Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microsystems Engineering

College

Kate Gleason College of Engineering

Advisor

Brian J. Landi

Advisor/Committee Member

Ivan Puchades

Campus

RIT – Main Campus

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