Figure 2

Characterization and stability tests in air. (a) Infrared absorption spectra of an uncoated micro-hotplate (black line) compared to that of a CNT-coated plate (red line) absorbing almost all light. (b) Emission spectra measured at 600 \(^{\circ }\)C for an uncoated (black line), CNT-coated (blue line), and encapsulated (red line) micro-hotplate, respectively. CNT-coated devices show a \(\sim\) 8-fold emission increase when compared to uncoated devices at equivalent temperature, however, unencapsulated CNTs burn-off within minutes, resulting in their emission spectrum (blue line) falling from an initial value close to that of an encapsulated device (red line) to that of an uncoated device (black line). Optical inspection (inset) shows CNTs have almost entirely burned-off. (c) Emission spectra measured at 600 \(^{\circ }\)C over a 10-day period, for a device with encapsulated NH\(_3\):C\(_2\)H\(_2\)-synthesised CNTs (shown in Fig. 1f). Optical images recorded at respective times show encapsulated CNTs are not affected by the high temperature operation. An optical image of a test sample after operating at a much higher, 850 \(^{\circ }\)C, temperature for 4 hours is presented in the bottom-right corner, showing the CNTs are intact. (d) (bottom two lines) Raman spectra measured at 532 nm before and after the operation stability test presented in (c). As a comparison, the top two lines show the Raman spectra measured for the same test (not shown) done with H\(_2\):C\(_2\)H\(_2\)-synthesised CNTs (shown in Fig. 1h) instead, showing both samples remain stable.