Nanocrystalline Diamond-Like Carbon Coatings Boost Field-Emission Efficiency of Silicon Nanowires

Nanocrystalline diamond-like carbon (nc-DLC) films were synthesized using CH₄ and H₂ precursor gases in a capacitively coupled plasma chemical vapor deposition (CCP-CVD) system at 450 °C and 250 W RF power. Plasma pressure optimization (1–7 Torr) identified 4 Torr as optimal, yielding films with intensity ratios, with a ratio of disordered to graphitic structures (I_D/I_G) of 0.63, diamond-like to graphitic structures (I_Dia/I_G) of 0.69, diamond to the disordered structures (I_Dia/I_D) of 1.09, and a high sp³ content of 66.75%. These films were coated on vertically oriented Si nanowire (SiNW) arrays, previously optimized via a metal-assisted chemical etching (MACE) process, to investigate the impact of coating time (T_DLC = 10–60 min) on field emission (FE) performance. At T_DLC = 40 min, Raman and XPS analyses revealed an I_D/I_G ratio of ~0.67 and an sp³ content of 68.73%, correlating with enhanced FE properties, including a reduced turn-on field (E_ON) of 4.60 V/µm, increased current density (J), and an elevated field enhancement factor (β) of 1676.01, compared to uncoated SiNWs (E_ON = 5.80 V/µm, β = 1107.93). Heating the hybrids to 150 °C further improved performance, reducing E_ON to 3.2 V/µm and increasing J to 4500.67 µA/cm². The DLC layer at T_DLC = 40 min, featuring ~5 nm diamond <111> nanocrystals and ~68% sp³ content, significantly lowered the potential barrier for electron emission, demonstrating SiNW/nc-DLC hybrid structures have a strong potential for applications in flat-panel displays and advanced electron emitters, such as electron microscopes.