Negative-charge-functionalized carbon nanodot: a low-cost smart cold emitter

Cold emission properties of carbon nanodots (CNDs) evaluated using ANSYS Maxwell software are predicted to be size-dependent and then verified experimentally. In order to correlate the electron emission properties with the size of CNDs, the work function values were determined using ultraviolet photoelectron spectroscopy. This is the first report on theoretical calculations based on density functional theory and experimental results that confirm the work function dependency on the charge state of the functional group attached on the particle surface. The smallest CND (2.5 nm) has the highest percentage of negatively charged groups as well as the lowest work function (5.18 eV). The smallest dimension with the lowest work function assures that this sample is the best suited for field emission. It shows excellent field emission properties with a high current density of ∼1.45 mA cm−2 at 2 V m−1 electric field, turn-on field as low as 0.04 V m−1, very high field enhancement factor of 2.7 × 105 and high stability. Overall, the zero-dimensional CNDs showed superior field emission activity as compared to the higher dimensional carbon nanomaterials.