The 100 nm cutoff is a standard convention in the field of nanotechnology. Remembering this specific value is key to correctly answering definitional questions about nanomaterials.
Step 1: Nano-materials Defined:
Nano-materials are materials structured at the nanometer scale (nano- = \(1 \text{ nm} = 10^{-9} \text{ m}\)). Their properties differ from bulk materials due to quantum effects or high surface-area-to-volume ratio. Step 2: Nanoscale Dimensions:
Internationally (ISO/TS 80004), a nanomaterial has at least one external dimension, or an internal/surface structure, between approximately 1 to 100 nanometers.
Thus, a "nano-material" has at least one dimension typically less than 100 nm. Larger scales are in the micro- or sub-micron range, where bulk properties prevail. Step 3: Conclusion:
The generally accepted characteristic length for nano-materials is less than 100 nm.