Andrew J. Mayne

Formation of one-dimensional self-assembled silicon nanoribbons on Au(110)-(2 × 1)

We report results on the self-assembly of silicon nanoribbons (NRs) on the (2 × 1) reconstructed Au(110) surface under ultra-high vacuum conditions. Upon adsorption of 0.2 monolayer (ML) of silicon, the (2 × 1) reconstruction of Au(110) is replaced by an ordered surface alloy. Above this coverage, a new superstructure is revealed by low energy electron diffraction (LEED), which becomes sharper at 0.3 Si ML. This superstructure corresponds to Si nanoribbons all oriented along the [1¯10] direction as revealed by LEED and scanning tunneling microscopy (STM). STM and high-resolution photoemission spectroscopy indicate that the nanoribbons are flat and predominantly 1.6 nm wide. In addition, the silicon atoms show signatures of two chemical environments corresponding to the edge and center of the ribbons.

Quantum Interference Channeling at Graphene Edges

Electron scattering at graphene edges is expected to make a crucial contribution to the electron transport in graphene nanodevices by producing quantum interferences. Atomic-scale scanning tunneling microscopy (STM) topographies of different edge structures of monolayer graphene show that the localization of the electronic density of states along the C-C bonds, a property unique to monolayer graphene, results in quantum interference patterns along the graphene carbon bond network, whose shapes depend only on the edge structure and not on the electron energy.

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.

Difficulty for oxygen to incorporate into the silicon network during initial O2 oxidation of Si(100)-(2×1)

First principles calculations and scanning tunneling microscopy studies of the oxidation of Si(100)-(2x1) surfaces by molecular oxygen reveal that the surface silanone (O)(Si=O) species is remarkably stable, constituting the key intermediate for initial oxidation. The propensity for oxygen to remain within the top surface layer as opposed to incorporating within Si-Si backbonds is surprisingly high. This resistance to incorporation into a cubic lattice even at higher coverages could be a factor to facilitate surface amorphization in subsequent steps.

Formation of unconventional standing waves at graphene edges by valley mixing and pseudospin rotation

We investigate the roles of the pseudospin and the valley degeneracy in electron scattering at graphene edges. It is found that they are strongly correlated with charge density modulations of short-wavelength oscillations and slowly decaying beat patterns in the electronic density profile. Theoretical analyses using nearest-neighbor tight-binding methods and first-principles density-functional theory calculations agree well with our experimental data from scanning tunneling microscopy. The armchair edge shows almost perfect intervalley scattering with pseudospin invariance regardless of the presence of the hydrogen atom at the edge, whereas the zigzag edge only allows for intravalley scattering with the change in the pseudospin orientation. The effect of structural defects at the graphene edges is also discussed.Changwon Park, Heejun Yang, Andrew J. Mayne, Gérald Dujardin, Sunae Seo, Young Kuk, Jisoon Ihm, and Gunn Kim ∗ Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea Semiconductor Devices Lab, Samsung Advanced Institute of Technology, Yongin, Gyeonggi-Do 449-712, Korea Laboratoire de Photophysique Moléculaire, CNRS, Bât. 210, Univ Paris Sud, 91405 Orsay, France Department of Physics, Sejong University, Seoul 143-747, Korea (Dated: January 11, 2013)

Imaging and spectroscopy of individual CdSe nanocrystals on atomically resolved surfaces

Imaging and spectroscopy of individual CdSe nanocrystals have been performed with the scanning tunneling microscope (STM) on atomically resolved hydrogenated Si(100) surfaces. The CdSe nanocrystals have been deposited under vacuum onto the surface by using the pulse valve method. Two different types of CdSe nanocrystals, capped either with trioctylphosphine oxide ligands or with cadmium stearate ligands, have been studied to optimize their anchoring to the surface. The I(V) spectroscopy shows a characteristic resonant excitation spectrum through the unoccupied levels of the nanocrystals with no significant charging effect. This suggests that the nanocrystals are weakly coupled to the surface, thus requiring a stronger coupling with the STM tip to achieve a measurable tunnel current. These results demonstrate the importance of depositing nanocrystals on clean and atomically well-defined surfaces for reliable measurement of their properties.

Adsorption of silicon on Au(110): An ordered two dimensional surface alloy

We report on experimental evidence for the formation of a two dimensional Si/Au(110) surface alloy. In this study, we have used a combination of scanning tunneling microscopy, low energy electron diffraction, Auger electron spectroscopy, and ab initio calculations based on density functional theory. A highly ordered and stable Si-Au surface alloy is observed subsequent to growth of a sub-monolayer of silicon on an Au(110) substrate kept above the eutectic temperature.

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.

Inelastic interactions of tunnel electrons with surfaces

Inelastic interactions of electrons emitted from the tip of a scanning tunnelling microscope (STM) are used to desorb individual hydrogen atoms from a Ge(111) surface. It is observed that the inelastic interactions depend not only on the electron energy and the current intensity but also on the electron emission regime of the STM tip. Quite surprisingly, it is found that tunnel electrons interact inelastically much less efficiently than field emitted electrons even though the electrons are in resonance with the Ge-H unoccuppied orbital.

Adsorption of ethylene on Si(111)7×7 by synchrotron radiation photoemission

Abstract Ethylene adsorption on Si(111)7×7 was studied by valence band and Si2p core line synchrotron radiation photoemission. Experiments were performed at room temperature, as a function of coverage. The simultaneous quenching of the S 1 and S 2 silicon surface states upon adsorption shows that ethylene adsorbs in a molecular form, on a bridging site between a silicon adatom and rest atom. An electron donation from silicon to ethylene, which indicates a rather strong SiC bond, induces an upward shift of the shallower molecular orbitals. The CC double bond is stretched and becomes intermediate between single and double bond.