This application note explains how SWCNT enables low-power sensing by forming a percolation network that converts adsorption- or strain-driven microstructural changes into measurable resistance shifts in films and composites.
SWCNT enables gas/strain/wearable sensors by forming a percolation network where junction tunneling resistance shifts with adsorption, strain, and microcrack evolution, converting small stimuli into a stable electrical signal at low loading.
SWCNT behaves as a one-dimensional sp² carbon conductor whose network conductivity is dominated by junction density, tube alignment, and defect/functionalization state.
For sensor architectures, the key advantage is not “maximum conductivity,” but a network that is:
Network conduction (percolation): Electrical pathways emerge when tube–tube contacts form a connected cluster; conductivity is governed by the number and quality of junctions rather than tube intrinsic conductivity alone.
Junction/contact modulation: Mechanical strain changes junction count, contact area, and tunneling distance, shifting resistance (piezoresistive response).
Surface charge transfer: Adsorbed molecules and functional groups modulate carrier density and local barriers at tube surfaces and junctions, shifting resistance (chemiresistive response).
Activation: Triggered by the stimulus domain—electrochemical potential (electrochemical sensors), applied strain (wearables), or adsorption environment (gas/vapor).
Suggested for evaluation — application-specific testing required
Non-Applicability: In air-exposed processes requiring sustained temperatures above ~200 °C, SWCNT performance can degrade due to oxidative attack; consider sealed/inert or alternative conductors for that regime.
Unknown/Unverified: Long-duration baseline stability under combined humidity + cyclic strain is application-dependent and often dominated by packaging/encapsulation; this must be validated per device stack.
Activation Boundary: Meaningful sensor response typically requires operation near the percolation regime; if loading is far above percolation (dense conductive film), small adsorption/strain perturbations may not measurably change resistance.
Mechanism statements follow established nanotube transport concepts (percolation, junction/tunneling resistance, surface charge transfer). Device-level outcomes (drift, hysteresis, humidity coupling) remain formulation- and packaging-dependent.
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