Articles you may be interested inScanning tunneling microscopy observations of hafnium carbide thin films as a field emission material J. Vac. Sci. Technol. B 23, 741 (2005); 10.1116/1.1849192 Current image tunneling spectroscopy of boron-doped nanodiamonds J. Appl. Phys. 97, 044312 (2005); 10.1063/1.1834722 Development of an in situ ultra-high-vacuum scanning tunneling microscope in the beamline of the 15 MV tandem accelerator for studies of surface modification by a swift heavy ion beam Rev. Sci. Instrum. 72, 3884 (2001);

Scanning tunnelling microscopy (STM) and current imaging tunnelling current spectroscopy (CITS) methods were performed on polycrystalline diamond films grown on silicon substrates grown by microwave plasma-enhanced chemical vapour deposition. Large tunnelling currents were observed at some grain boundaries and crystal surfaces with secondary grains. Following atomic force microscopy (AFM) measurements, we performed scanning probe contact current (SPCC) measurements to investigate the spatial variation of electrical resistance on the surface by using an AFM cantilever in contact mode. The conducting grain boundaries and facets were observed on both boron-doped and undoped samples. For microscale characterization of the field emission properties, we performed scanning probe field emission current (SPFEC) measurements. From the results of STM/CITS, AFM/SPCC and SPFEC, it is concluded that the specific grain boundaries and facets on polycrystalline diamonds work as initial points of electron emission and cause high field emission current through a conducting pass formed in the bulk.

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Electron emission from a polycrystalline diamond coated silicon field emitter surface was studied using in situ exposure to various gas species during its operation. Significant enhancement of the electron emission was found after the emitting surface was exposed to hydrogen at pressures in the range 5×10−4 to 10−3 Torr. Introducing other gases such as Ne and He only suppressed the emission current. A continuous emission current was measured from such a hydrogen-exposed surface even after the electric field was reduced to below the initial threshold for electron emission. No similar result was found for pure silicon surface when identical conditions applied. This phenomenon was interpreted as the formation of a dynamically vacuum-stable layer by polarized hydrogen and the diamond surface. Such a surface layer may significantly lower the surface barrier and exhibit the negative electron affinity property.

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