Atomic-scale imaging of insulating diamond through resonant electron injection

Abstract

The electronic properties of insulators such as diamond are of interest not only for their passive dielectric capabilities for use in electronic devices, but also for their strong electron confinement on atomic scales. However, the inherent lack of electrical conductivity in insulators usually prevents the investigation of their surfaces by atomic-scale characterization techniques such as scanning tunnelling microscopy (STM). And although atomic force microscopy could in principle be used, imaging diamond surfaces has not yet been possible. Here, we demonstrate that STM can be used in an unconventional resonant electron injection mode to image insulating diamond surfaces and to probe their electronic properties at the atomic scale. Our results reveal striking electronic features in high-purity diamond single crystals, such as the existence of one-dimensional fully delocalized electronic states and a very long diffusion length for conduction-band electrons. We expect that our method can be applied to investigate the electronic properties of other insulating materials and so help in the design of atomic-scale electronic devices.

The role of (sub)-surface oxygen on the surface electronic structure of hydrogen terminated (100) CVD diamond

“…5c shows a resonance tunneling behaviour, similar to the one observed for clean diamond surfaces in Ref. [12,13]. Nevertheless, in our case, the surface resonances are observed for the hydrogenated surface, containing also residual oxygen atoms while in ref [13], hydrogen-free, 2×1 reconstructed surfaces have been studied.…”

“…Even though similar experiments have been done before, there are several novelties in our measurements compared to previous work [12,13]. Compared to results of Dujardin and Bobrov [12,13] we use undoped H terminated CVD diamond films (in all other published cases either B-doped samples or clean surfaces with a Penney reconstructed surface have been used for STM imaging providing sufficient surface conductivity). Till now, as far as we know it was not possible to carry out STM atomic resolution imaging on annealed Hterminated undoped diamond films.…”

“…On the other hand, for sample #2 there is not sufficient conductivity and/or concentration of surface states to carry out STM experiments. Because STM imaging was possible for B-doped H-terminated diamond surfaces [12,13] (e.g. there is a sufficient density of Hrelated surface states as reported in several publications [12]), we can conclude that it is probably mainly the surface conductivity that limits the STM imaging on undoped samples hydrogenated in a pure H-plasma and subsequently UHVannealed.…”

“…[12,13]. Nevertheless, in our case, the surface resonances are observed for the hydrogenated surface, containing also residual oxygen atoms while in ref [13], hydrogen-free, 2×1 reconstructed surfaces have been studied. These resonances observed for H2/O2 mixture treated diamond surfaces are observed for the first time and will be discussed in another publication.…”

Quantum Confinement of Hot Image-Potential State Electrons

“…Because of the applied electric field between STM tip and sample, the ISs shift to higher energies and their energy spacings expand. It has been demonstrated that tunneling via ISs allows detailed visualization of the surface of insulating diamond films with atomic resolution [8]. IS dynamics has recently been investigated for various flat surfaces, including Fe [9], Au [10] and Cu surfaces [10,11].…”