Electrostatic charging of surfaces is widely used in a variety of technological processes. It improves wetting of plastics for painting, it is employed in electronics, e.g., in detectors or memory devices, and it is used in printers and copiers for toner positioning on paper. In this context electrostatic charging has been also explored as an effective method for guiding self-assembly of micro- and nanosized elements on insulating materials [1–3]. Electrostatic charging can be generated by various methods (laser, ion, or electron beam illumination, diverse electrodes, etc.). Charged patterns of sub-micrometer dimensions can be created using nanometer-sized probes, such as those employed in atomic force microscopy (AFM) [4, 5].
A large variety of materials have been applied for electrostatic charge storage: semiconductors  including amorphous silicon  as well as dielectric materials such as polytetrafluoroethylene and poly(methyl methacrylate) . Detection and understanding of electrostatic charging of diamond is crucial for many diamond-based electronic applications from detectors to field-effect transistors, batteries, silicon on diamond systems as well as for electrostatically guided assembly. This is because diamond as a semiconductor material can, for instance, be used for device fabrication , for passive and active bio-interfaces [8, 9], and can be deposited on diverse substrates in nanocrystalline form . From the electronic point of view, diamond is a wide band gap semiconductor (5.5 eV). Nevertheless, it can be transformed into p- or n-type semiconductor by boron  or phosphorus  doping, respectively. Intrinsic diamond is generally electrically insulating and transparent for visible light. Only when the intrinsic diamond is hydrogen-terminated (H-diamond), a thin (<10 nm) conductive layer is formed close to the diamond surface (surface conductivity) under ambient conditions . While this feature attracted considerable interest and research effort in the past , research on electronic properties of highly resistive oxygen-terminated intrinsic diamond (O-diamond) has been limited. It was related mostly to applications in radiation detectors , UV detectors , or field-effect transistors [17, 18].
As regards local and intentional electrostatic charging, diamond has been only little investigated [19–21] even though it exhibits a unique set of properties for applications as described above. Both positive and negative persistent potential changes were observed on nanocrystalline diamond (NCD) , unlike in silicon thin films . This has been attributed to the capacitor-like behavior of the NCD films . Comparing charging of NCD films prepared on gold  and silicon  substrates demonstrates that the charging is not due to the substrate itself as could be argued in the case of silicon substrates. The charging has been also shown to be more effective when the NCD films contain more sp2 phase . Surprisingly, the charging is spatially homogeneous and not confined to grain boundaries where most of the sp2 is localized . Yet maximal induced electrostatic potential contrast has been reported to be varying by up to 400 mV depending on a position on the sample . This may depend on the local material properties as well as actual tip condition.
In this article, we apply local electrostatic charging of oxygen-terminated NCD films to induce electrostatically driven self-assembly of colloidal nanoparticles into micro-patterns. Considering possible capacitive, sp2 phase, and spatially related contributions to charging, we employ films with sub-100 nm thickness, and about 60% relative sp2 content, probe their material uniformity, and repeat experiments at various positions across the films to induce as much potential contrast as needed for the self-assembly.