Experimental details

Carbon nanotube films are commonly prepared by float catalyst chemical vapor deposition. An ethanol solution containing 2% ferrocene and 1% thiophene was injected by a programmable syringe into a tubular reactor as a carbon source and catalyst for the growth of carbon nanotubes. Hydrogen gas (2000 sccm) was injected as a carrier gas. The growth of the carbon nanotubes occurred at a temperature around 800°C. Ethanol, thiophene, and ferrocene were used as raw materials. The carbon nanotubes were organized into a thin aerogel hollow tube, blown out of the reactor tube with the help of flowing gas, and then continuously collected on a roller.

To create a series of CNTFs with different thickness, we compressed the carbon nanotube aerogel to obtain the CNTFs and sprayed alcohol on the surface to compact them. We then placed them in a FW-4/4A press machine for further densification processing by applying different pressures, resulting in densified carbon nanotube films with thicknesses of 10 μm, 15 μm, 20 μm, and 30 μm. To clarify the discussion in Section 3, we denoted these samples with different densified thicknesses as CNTF-10, CNTF-15, CNTF-20, and CNTF-30, respectively.

The roll of CNTF with densified thickness was first placed in a plasma cleaner at a power of 70 W for 120 s after pretreatment to avoid the dispersion or corrosion of carbon nanotubes during electrolysis. Copper nanoparticle layers were grown on the surface of the pretreated carbon nanotube film. The electrolyte was an aqueous solution of copper sulfate CuSO₄ (0.03 M), sodium citrate Na₃C₆H₅O₇ (0.05 M), boric acid H₃BO₃ (0.5 M), and polyethylene glycol (6 g/L). The electrochemical deposition temperature was 75°C, the constant potential was -0.92 V, and the pH was adjusted to 8 with NaOH. The electrochemical deposition lasted for 20, 40, 60 or 80 min. To clarify the discussion in Section 3, we denoted these samples with different decomposition times as CNTF/Cu-20, CNTF/Cu-40, CNTF/Cu-60, and CNTF/Cu-80, respectively (with the same thickness of CNTF). The electrolyte was continuously stirred at a speed of 200 rpm throughout the reaction. The electrochemical deposition potential could be adjusted by an electrochemical workstation (CHI 660E, Chenhua, China). A three-electrode system was used, with the carbon nanotube film as the working electrode, a platinum plate as the counter electrode, and Ag/AgCl as the reference electrode. After the reaction, the sample surface was rinsed with deionized water to remove any possible solvent residues, and then dried with argon gas and placed in an oven at 60°C for 30 min to remove the residual moisture in the gap of the sample.

To exploit the influence of metal materials on EMI shielding efficiency. we also prepared Ni nanoparticle layers on CNTF for comparison with copper nanoparticle layers. The roll of CNTF was first placed in a plasma cleaner at a power of 70 W for 120 s after pretreatment to avoid the dispersion or corrosion of carbon nanotubes during electrolysis. Nickel nanoparticle layers were grown on the surface of the pretreated carbon nanotube film. The electrolyte was an aqueous solution of nickel sulfate NiSO4 (0.05 M) and boric acid H3BO3 (0.2 M). The electrochemical deposition temperature was 60°C, the constant potential was -1.7 V, and the electrochemical deposition lasted for 20, 40, 60 or 80 min. The electrolyte was continuously stirred at a speed of 200 rpm throughout the reaction. The electrochemical deposition potential could be adjusted by an electrochemical workstation (CHI 660E, Chenhua, China). A three-electrode system was used, with the carbon nanotube film as the working electrode, a platinum plate as the counter electrode, and Ag/AgCl as the reference electrode. After the reaction, the sample surface was rinsed with deionized water to remove any possible solvent residues, and then dried with argon gas and placed in an oven at 60°C for 30 min to remove the residual moisture in the gap of the sample. For clear discussions, we have denoted these samples with different decomposition time as CNTF/Ni-20, CNTF/Ni-40, CNTF/Ni-60, CNTF/Ni-80, respectively.