Abstract
The selective hybrid formation of numerous tiny carbon nanofibers (CNFs) in carbon-based nonwoven fabrics (c-NFs), namely CNFs formed only on the surfaces of individual carbon fibers (i-CFs) constituting c-NFs and not on the surfaces of carbon microcoils (CMCs), could be formed by the incorporation of H2 gas flow into the C2H2 + SF6 gas flow in a thermal chemical vapor deposition system. On the other hand, the nonselective hybrid formation of numerous tiny CNFs in c-NFs, that is, tiny CNFs formed on the surfaces of both i-CFs and CMCs, could be achieved by simply modulating the SF6 gas flow on and off in continuous cycles during the reaction. Detailed mechanisms are suggested for the selective or nonselective formation of tiny CNFs in c-NFs. Furthermore, the electromagnetic wave shielding effectiveness (SE) values of the samples were investigated across operating frequencies in the 8.0–12.0 GHz range. Compared with previously reported total SE values, the presently measured values rank in the top tier. Although hybrid formation reduced the electrical conductivity of the native c-NFs, the total SE values of the native c-NFs greatly increased following hybrid formation. This dramatic improvement in the total SE values is ascribed to the increased thickness of c-NFs after hybrid formation and the electromagnetic wave absorption enhancement caused by the intrinsic characteristics of CMCs and the numerous intersections of tiny CNFs.
Highlights
No carbon nanofibers (CNFs)-related hybrids formed on the surfaces of either the carbon microcoils (CMCs) or individual carbon fibers (i-CFs) in sample B
High-magnification images of sample B revealed the existence of a large number of dots (0.05–0.1 μm in diameter) on the surfaces of both the CMCs and i-CFs
Numerous tiny CNFs formed on the surfaces of the i-CFs owing to the compact binding state of their surfaces
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Electromagnetic (EM) wave radiation emitted from electronic devices operating at high frequencies can interfere with the accurate function of other electronics. Electromagnetic wave interference (EMI) shielding of both electronics and radiation sources is required to prevent the malfunction of electronic devices. EM waves are composed of oscillating electric and magnetic fields. Materials with EM wave shielding capabilities are expected to interact with either one or both of these fields. For an efficient absorption loss greater than 10 dB, reflection and absorption loss are regarded as the main shielding mechanisms among the three major shielding routes (reflection, absorption, and multiple reflection) [1,2,3,4].
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