Sulfur-incorporated nanocrystalline carbon (n-C:S) thin films were deposited in a custom-built hot-filament chemical vapor deposition (HFCVD) using CH_4/H_2/H_2S gas feedstocks [1]. The modification of the surface morphology due to sulfur addition was revealed using scanning electron microscopy, a typical example of which is shown in Fig. 1. The rms surface roughness (σ) estimated from AFM (not shown) becomes reduced from 74 nm (for no sulfur) to 25 nm (for S-assisted). The corresponding average grain size goes from around 100 nm to 20-30 nm. The I-V characteristics obtained for the n-C:S thin films grown with respect to substrate temperature (T_S) are shown in Fig. 2. Two interesting features can immediately be seen: (i) a systematic decrease of turn-on field (E_c), and (ii) an exponential increase of current amplitude, with increasing T_S. The lowest E_C values were around 4.0 V/μ for 900 °C, WHICH INCREASES TO 13.5-14.0 v/μm as the substrate temperature goes down to 500 °C [1]. Sulfur thus induced changes in the microstructure and in the electronic structure of the material that play key roles in the enhancement of the field emission properties [1]. This synthesis-specific material has a strong potential for cold cathode applications.
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