Inexpensive, reliable temperature and pressure sensors are a crucial part in most manufacturing processes. Moreover, the current demand for increasingly more integrated consumer products has created a strong need for low cost materials with exceptional sensitivity and mechanical or thermal stability. At present, temperature and pressure sensing relies on advanced spinel-type metal oxides. Here, we use reducing flame spray synthesis for the large-scale production (10g h-1) of carbon coated metallic copper nanoparticles (10 to 20 nm). The carbon coating protected the zero-valent copper particles from oxidation in air. However the preparation of different carbon layers resulted in a carbon metal composite with distinctly different electrical properties. Bulk pills of pressed carbon/copper nanoparticles exhibiting a predominantly insulating carbon layer (left) displayed a highly pressure- and temperature dependent electrical resistivity. The negative temperature coefficient (NTC) behavior of the material revealed a similar or greater material constant (β= 4790K, right) than commercial sensing materials. On the other hand copper nanoparticles with a graphene layer of a predominant sp2 character showed an ill-defined band gap and weak conducting properties with low sensitivity (middle). This contribution investigates a novel, core-shell structured metal / carbon nanomaterial with exceptional sensitivity. A theoretical analysis suggested a tunneling based conduction mechanism for these metallic core / insulating shell materials.
Fig. 1: Transmission electron micrograph of as prepared insulating (left) and conducting (middle) C/Cu nanocomposites. The insulating nanomaterial showed a strong NTC behavior comparable to applied ceramic sensing materials (right).
References: E.K. Athanassiou, R.N. Grass and W.J. Stark, Nanotechnology, 2006, 17, 1668.
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