Annealing effect on electron field-emission properties of diamond-like nanocomposite films

The field-emission properties of a Si-O bond-containing diamond-like nanocomposite (DLN) film were investigated as a function of annealing temperature (T_a). It was found that with increasing T_a the emission threshold voltage decreased gradually. After annealing at T_a = 500°C, the emission current decreased significantly. At T_a = 700°C, however, the field-emission properties of the DLN film improved greatly, the threshold field became very low (∼1.5 V/μm), and the emission current rather high (e.g., ∼2.3 μA/mm² at an electric field of 22 V/μm). The structural variation of the film after annealing at different temperatures was monitored by ultraviolet Raman spectroscopy, spectroscopic ellipsometry, atomic-force microscopy, and electrical resistivity measurements. By using a three-step model: (i) electron injection from the substrate, (ii) electron transport through the film, and (iii) electron emission at the film surface, the annealing effect on field-emission properties of the DLN film were qualitatively interpreted. It is believed that the threshold electric field is determined by the local electron affinity on the film surface, while the emission current is mainly limited by electron injection and transport processes.