Makoto Kitabatake

Microscopic study of field emission from diamond particles

The field emission properties and microscopic characteristics of diamond particles (DPs) are studied by scanning electron microscopy (SEM), secondary electron spectroscopy (SES), scanning tunneling microscopy/spectroscopy (STM/STS), scanning field emission microscopy (SFEM) and field emission electron microscopy (FEEM). DPs with an average size of 1 μm were spin-coated onto a tungsten substrate. After the spin-coat process, an undoped thin diamond layer was grown on the DP surfaces by the conventional microwave plasma-assisted CVD method. Consequently, the total emission current measured on the DP-seeded substrate (1 X 1 cm 2 ) was approximately 1 mA under an electric field of 3.5 kV/mm. The DPs with the CVD diamond overcoat have facet edges of diamond, which are sometimes covered with small crystallites. The SES spectrum for these samples showed that the surface of DPs with a CVD diamond overcoat has essentially a NEA surface. The SFEM was able to image the distribution of field emission sites by scanning the STM tip with fixed tip height. The SFEM and FEEM images suggest that some particular DPs contribute to field emission and the emission occurs from the top site of the DP. The modification of surface property and electric field at the top site or edge of the DP affects the effective field emission.

Secondary-electron and field-emission spectroscopy/ microscopy studies of chemical vapor deposition grown diamond particles

Abstract High-pressure synthetic diamond particles (DPs) were first seeded over a high-conductive n-type Si(0xa00xa01) wafer and non-doped diamond layers were then grown onto the DP surfaces by chemical vapor deposition. This sample had good field emission (FE) characteristics. For comparison, a poor FE sample was made from the DP-seeded substrate. We have characterized several important factors of these samples using secondary-electron spectroscopy (SES), field emission spectroscopy (FES) and field emission microscopy (FEM). SES measurements showed that the surface electron affinity of the samples with good FE characteristics is negative but that with poor FE characteristics is positive. FES measurements for a good FE sample showed that a FES peak starts at the substrate Fermi level and moves downward in kinetic energy together with increase of the full-width at half-maximum of peak as the electric field is increased. FEM measurements showed that there are “hot spots” that strongly field-emit electrons. A plausible model of FE for isolated DPs on conducting substrate is proposed under which a key factor of FE is a resistive interface between DPs and the substrate.

Field emission from diamond particles studied by scanning field emission microscopy

Field emission properties from diamond particles (DPs) are studied. The DPs with thin chemically vapor deposited (CVD) diamond overcoat, dispersed onto metal substrate, essentially exhibit negative electron affinity (NEA). Field emission, approximately 1mA/cm(2) under a macroscopic electric field of 3.5kV/mm are observed. Microscopic electrical properties were studied by scanning tunneling microscopy/spectroscopy. Most parts of the DP surface exhibit narrow gap and p-type characteristics. The localized regions, which have wide gap like bulk diamond properties, are randomly distributed near the top of DP. The field emission current distribution depicted by scanning field emission microscopy (SFEM) show that the electron emission is originating from a localized region on the selected DPs. We found, through SFEM measurement, some favorable field emission spots (hot spots) where measured emission current is several orders higher than that of the other DPs (normal spots). Field emission spectroscopy (FES) results suggest that a poorly conducting layer is present along the electron path from the metal electrode to vacuum.We propose two models for field emission from hot spots, which involve two main mechanisms. One is electron injection from the metal substrate to the DP, which is attributed to the electric field enhancement at intrinsic non-doped diamond (i-diamond) layer sandwiched between the metal substrate and the surface conductive layer (p-diamond) of the CVD diamond overcoat on the DP. The other is electron emission at the top site of NEA DP through the local i-diamond region or the depletion region of the p-diamond, which is caused by the applied electric field.