How nanocrystalline diamond films become charged in nanoscale

Electrostatic charging of oxygen-terminated nanocrystalline diamond (NCD) thin films deposited on silicon in sub-100 nm thickness and with intentionally high relative sp2 phase ratio (60%) is characterized on a microscopic level. By correlating Kelvin Force Microscopy, Current-Sensing Atomic Force Microscopy, micro-Raman spectroscopy and cross-sectional Scanning Electron Microscopy data we show that the charging is determined by both the surface topography (grains and grain boundaries) and complex sub-surface morphology (arrangement of grains and sp2 phase) on scales below 2 × 2 μm2. These microscopic data and macroscopic I(V) characteristics evidence that sp2 phase dominates over diamond grains in local electrostatic charging of NCD thin films. Moreover, the tip-surface junction quality is identified as the main factor behind large variations (0.1 to 1 V) of the overall induced electrostatic charge contrast.

► We locally charge NCD using AFM and characterize the outcome by KFM.
► Grain boundaries charge more efficiently due to their pronounced sp2 phase.
► As charging varies across the sample, we measure CS-AFM for local current determination.
► The local current profiles differ due to complex subsurface morphology seen by SEM.
► However, variations in charged potential are due to tip-surface junction issues.