Simple chemical synthesis of porous carbon spheres and its improved field emission by water vapor adsorption

A very simple solvothermal approach for synthesizing porous carbon microspheres is reported here. The effect of water adsorption on the field emission properties of such samples was investigated experimentally as well as from first principle calculation. The as-synthesized microspheres were characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (TEM), atomic force microscopy and Fourier transformed infrared (FTIR) spectroscopy. XRD patterns as well as TEM lattice images confirmed that the spheres were graphitic in nature. From the microscopic analyses it was seen that the as-synthesized porous carbon spheres were actually composed of few layer thick carbon nanosheets. FTIR confirmed the adsorption of water in the sample. It has been found that samples with adsorbed water can act as a better field emitter compared to the pure ones. A first principle study showed that although no development of H2O-induced impurity states close to the Fermi level was observed due to water adsorption, there was a pronounced upward shift in the Fermi level, i.e. a decrease of work function, which is believed to be the main reason for the observed improved field emission performance.

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► Porous carbon micro-spheres consisting of few layer nanosheets were synthesized by solvothermal route.
► Adsorption of water molecules on carbon-spheres significantly improved field emission property.
► First principle calculation showed lowering of work function due to water adsorption.