Abstract
The temperature coefficient of resistivity ( θ T ) of carbon-based materials is a critical property that directly determines their electrical response upon thermal impulses. It could have metal- (positive) or semiconductor-like (negative) behavior, depending on the combined temperature dependence of electron density and electron scattering. Its distribution in space is very difficult to measure and is rarely studied. Here, for the first time, we report that carbon-based micro/nanoscale structures have a strong non-uniform spatial distribution of θ T . This distribution is probed by measuring the transient electro-thermal response of the material under extremely localized step laser heating and scanning, which magnifies the local θ T effect in the measured transient voltage evolution. For carbon microfibers (CMFs), after electrical current annealing, θ T varies from negative to positive from the sample end to the center with a magnitude change of >130% over <1 mm. This θ T sign change is confirmed by directly testing smaller segments from different regions of an annealed CMF. For micro-thick carbon nanotube bundles, θ T is found to have a relative change of >125% within a length of ∼2 mm, uncovering strong metallic to semiconductive behavior change in space. Our θ T scanning technique can be readily extended to nm-thick samples with μm scanning resolution to explore the distribution of θ T and provide a deep insight into the local electron conduction.
Original language | English |
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Article number | 085102 |
Journal | Journal of Applied Physics |
Volume | 134 |
Issue number | 8 |
DOIs | |
State | Published - Aug 28 2023 |
Funding
This work was partially supported by the US National Science Foundation (Nos. CBET1930866 and CMMI2032464 for X.W.), Guangdong Basic and Applied Basic Research Foundation (No. 2023A1515012684 for C.D.), and National Natural Science Foundation of China (No. 52106220 for S.X.). The contribution by G.E. was supported by the Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division.