Direct observation and mechanism for enhanced electron emission in hydrogen plasma-treated diamond nanowire films

The effect of hydrogen plasma treatment on the electrical conductivity and electron field emission (EFE) properties for diamond nanowire (DNW) films were systematically investigated. The DNW films were deposited on silicon substrate by N2-based microwave plasma-enhanced chemical vapor deposition process. Transmission electron microscopy depicted that DNW films mainly consist of wirelike diamond nanocrystals encased in a nanographitic sheath, which formed conduction channels for efficient electron transport and hence lead to excellent electrical conductivity and EFE properties for these films. Hydrogen plasma treatment initially enhanced the electrical conductivity and EFE properties of DNW films and then degraded with an increase in treatment time. Scanning tunneling spectroscopy in current imaging tunneling spectroscopy mode clearly shows significant increase in local emission sites in 10 min hydrogen plasma treated diamond nanowire (DNW10) films as compared to the pristine films that is ascribed to the formation of graphitic phase around the DNWs due to the hydrogen plasma treatment process. The degradation in EFE properties of extended (15 min) hydrogen plasma-treated DNW films was explained by the removal of nanographitic phase surrounding the DNWs. The EFE process of DNW10 films can be turned on at a low field of 4.2 V/μm and achieved a high EFE current density of 5.1 mA/cm(2) at an applied field of 8.5 V/μm. Moreover, DNW10 films with high electrical conductivity of 216 (Ω cm)(-1) overwhelm that of other kinds of UNCD films and will create a remarkable impact to diamond-based electronics.