Kirill Bobrov

Atomic-scale imaging of insulating diamond through resonant electron injection.

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.

Atomic-scale desorption of hydrogen from hydrogenated diamond surfaces using the STM

Abstract Diamond has a number of unique chemical and physical properties. In particular, when covered with hydrogen, diamond surfaces acquire a negative electron affinity (NEA). This NEA property has already been used to fabricate high-efficiency diamond-based light detectors and/or electron emitters. We have used the scanning tunnelling microscope for (i) atomic-scale visualisation of the hydrogenated diamond surface, (ii) probing the surface electronic structure and (iii) atomic-scale desorption of hydrogen atoms. Desorption of individual hydrogen atoms has been used to pattern pre-selected areas on the hydrogenated diamond surface. This is considered to be a promising way to fabricate atomic-scale photon detectors and/or electron emitters. The feasibility of the tip-induced atomic-scale desorption of hydrogen from the diamond surface is discussed in comparison with the similar studies on hydrogenated silicon and germanium surfaces performed previously.

Molecular oxygen adsorption on partially hydrogenated diamond (100) surfaces

Molecular oxygen has been found to be easily adsorbed on the partially hydrogenated diamond C(100)-(2×1):H surfaces, whereas the clean and fully hydrogenated C(100) surfaces are completely inert to molecular oxygen. The partially hydrogenated diamond C(100)-(2×1) surfaces have been prepared by (i) in situ hydrogen photodesorption from the fully hydrogenated surface and (ii) in situ hydrogen adsorption on the clean surface. The surface reactivity has been monitored through the changes of the valence band photoemission spectra upon molecular oxygen exposure. These results suggest that oxygen adsorption occurs on the isolated carbon dangling bonds produced, on partially hydrogenated surfaces, from the breaking of the π-bonding of paired dangling bonds.

Initial stage of NO adsorption on Si(100)-(2×1) studied by synchrotron radiation photoemission and photodesorption

The NO adsorption on the Si(100)-(2 x 1) surface was investigated by synchrotron radiation photoemission and photodesorption in the energy ranges including the valence band and the Si 2p, N 1s and O 1s core levels. The study was performed both ass function of NO exposure and as a function of temperature in the range 20-300 K. The photoemission experiments show clear evidence of a dissociative adsorption process both at room temperature as well as at temperatures as low as 20 K. Furthermore, the silicon surface states are involved in the adsorption process. The core level spectroscopy shows a complex adsorption pattern of the atomic species, which might involve a sub-surface migration of nitrogen atoms. The photodesorption yields only O+ in the Si 2p and O Is energy ranges. No nitrogen ion desorption is detected. In the Si 2p energy range the O+ photodesorption pattern follows the enhanced secondary electron yield when crossing the ionization threshold. In the O Is energy range the O+ photodesorption pattern is interpreted in terms of a partial sub-surface migration of oxygen atoms

Low temperature electron transport on semiconductor surfaces

The low-temperature electron transport on semiconductor surfaces has been studied using an ultrahigh-vacuum, variable temperature scanning tunneling microscope (STM). The STM I(V) spectroscopy performed at various temperatures has made it possible to investigate the temperature dependence (300 K to 35 K) of the surface conductivity of three different semiconductor surfaces: highly doped n-type Si(100), p-type Si(100), and hydrogenated C(100). Low temperature freezing of specific surface electronic channels on the highly doped n-type Si(100) and moderately doped p-type Si(100) surfaces could be achieved, whereas the total surface conductivity on the hydrogenated C(100) surface can be frozen below only 180 K.