Moir\'e patterns on STM images of graphite from surface and subsurface rotated layer

We have observed with STM moir\'e patterns corresponding to the rotation of one graphene layer on HOPG surface. The moir\'e patterns were characterized by rotation angle and extension in the plane. Additionally, by identifying border domains and defects we can discriminate between moir\'e patterns due to rotation on the surface or subsurface layer. For a better understanding of moir\'e patterns formation we have studied by first principles an array of three graphene layers where the top or the middle layer appears rotated around the stacking axis. We compare the experimental and theoretical results and we show the strong influence of rotations both in surface and subsurface layers for moir\'e patterns formation in corresponding STM images.Comment: 5 pages, 6 figure

STM observation of electronic wave interference effect in finite-sized graphite with dislocation-network structures

Superperiodic patterns near a step edge were observed by STM on several-layer-thick graphite sheets on a highly oriented pyrolitic graphite substrate, where a dislocation network is generated at the interface between the graphite overlayer and the substrate. Triangular- and rhombic-shaped periodic patterns whose periodicities are around 100 nm were observed on the upper terrace near the step edge. In contrast, only outlines of the patterns similar to those on the upper terrace were observed on the lower terrace. On the upper terrace, their geometrical patterns gradually disappeared and became similar to those on the lower terrace without any changes of their periodicity in increasing a bias voltage. By assuming a periodic scattering potential at the interface due to dislocations, the varying corrugation amplitudes of the patterns can be understood as changes in LDOS as a result of the beat of perturbed and unperturbed waves, i.e. the interference in an overlayer. The observed changes in the image depending on an overlayer height and a bias voltage can be explained by the electronic wave interference in the ultra-thin overlayer distorted under the influence of dislocation-network structures.Comment: 8 pages; 6 figures; Paper which a part of cond-mat/0311068 is disscussed in detai

Transition metals on the (0001) surface of graphite: Fundamental aspects of adsorption, diffusion, and morphology

In this article, we review basic information about the interaction of transition metal atoms with the (0001) surface of graphite, especially fundamental phenomena related to growth. Those phenomena involve adatom-surface bonding, diffusion, morphology of metal clusters, interactions with steps and sputter-induced defects, condensation, and desorption. General traits emerge which have not been summarized previously. Some of these features are rather surprising when compared with metal-on-metal adsorption and growth. Opportunities for future work are pointed out

Supported metal clusters and cluster-substrate interaction studied by scanning tunneling microscopy

Thesis (Ph. D.)--University of Hawaii at Manoa, 1992.Includes bibliographical references.Microfiche.xiii, 80 leaves, bound ill. 29 cmThis PhD dissertation is concerned with an experimental study of supported metal clusters and cluster-substrate interaction. The geometric and electronic structures of platinum and cobalt clusters on graphite, the effects of clusters on the graphite substrate, and the influences from the substrate to clusters were investigated by scanning tunneling microscopy. A topographic study of adatoms and small clusters of platinum and cobalt on highly-oriented pyrolytic graphite was performed both in air and in ultra-high vacuum. The samples were prepared by vapor deposition on the graphite surface. Stable images of adatoms and small clusters on graphite were obtained with atomic resolution showing their atomic structures. Taking the graphite lattice as reference, the adsorption sites of adatoms and clusters on the surface as well as the bond lengths and bond angles of clusters were determined. Various superstructures on graphite were found near the adsorbed clusters, or generally near defects. The superstructures are localized in small areas near the clusters and decay within a distance of 2 - 5 nm into the graphite lattice. Detailed analyses show that they were due to periodic charge-density modulations superimposed onto the graphite lattice. The different periodic modulations have the same period of 1.5a (a =0.245 nm, is the lattice constant of graphite) and exist in three possible directions, each rotated 30° relative to the graphite lattice. They are generated by adsorbed clusters which act as a scattering center and perturb the surface charge-density. Among many graphite substrates being studied, anomalous giant lattices were observed on three of the samples. They exhibited hexagonal symmetry with lattice constants of 1.7 nm, 2.8 nm, 3.8 nm and 6.6 nm. Atomic resolution of graphite was obtained simultaneously. By introducing small rotations of the top graphite layer relative to the underlying single crystal, a complete description is developed to account for all the features displayed by the STM images. In addition to the giant and atomic lattices, a supergiant lattice was observed. Cobalt particles on the surface were also imaged and were found on the top sites of the giant lattice

FORMATION OF OUTGROWTHS AT THE INITIAL GROWING STAGE OF YBA2CU3OX ULTRATHIN FILMS ON ZRO2 SUBSTRATES

Ultrathin films of YBa2Cu3Ox with good crystallinity and superconductivity were prepared by a modified off-axis sputtering. The microstructure, with emphasis on surface morphology and formation of outgrowths, was studied by using atomic force microscopy and electron microscopy, It was found that many outgrowths were formed at the initial growing stage. Therefore it is important to suppress the nucleation of outgrowths at a very early growing step to obtain a smooth film. The nucleation of outgrowths is significantly influenced by surface defects on the substrate. Discussion is also made in correlation with the occurrence of an intermediate layer commonly observed on ZrO2. From our observation, YBa2Cu3Ox might be grown directly on the surface of ZrO2 without forming any intermediate layer, if the film thickness is very small. (C) 1995 American Institute of Physics

Characterization of nanostructures micromachined with Focused Ion Beams (FIB)

Focused Ion Beam (FIB) technology has been demonstrated to be a powerful technique in micro-machining and microfabrication. As the critical dimensions of the device migrate towards the nanometre regime, FIB becomes an important tool in the construction of these devices. In machining and fabrication with FIB in the deep submicron dimensions, an important consideration is the ability to correlate the structures with the processes of deposition or milling so that the instrumental parameters can be optimized. Effects such redeposition during milling in such fine dimensions will have to be controlled. However, since feature size of these structures fabricated with the FIB often have profiles of a few 10's of nanometres, it is increasingly difficult to use standard analytical techniques such as scanning electron microscopy (SEM) to resolve such features. At the same time, atomic force microscopy (AFM) with it's near atomic resolution is now a standard metrology tool in semiconductor manufacturing. In this paper the authors would like to demonstrate, using Atomic force Microscopy (AFM), the effects of parameters such as probe current on the micromachined profiles produced by FIB. We will compare these results obtained with AFM with those using SEM. Control of these parameters in the fabrication of nanostructures on different substrate materials such as metals and semiconductors will also be demonstrated

Imaging of sub-surface nano particles by tapping-mode atomic force microscopy

Time-of-Right secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), and tapping mode atomic force microscopy (TM-AFM) were used to study the surface of a poly(N-vinyl-2-pyrrolidone) thin film containing nano silica particles. ToF-SIMS results illustrate that the topmost layer of the thin film consists of PVP and a small amount of poly(dimethyl siloxane) (PDMS). Nano silica particles are localized underneath this layer. XPS results suggest that the concentration of the silica particles increases as the sampling depth increases from 5.3 to 7.2 nm. TM-AFM phase imaging is shown to be capable of detecting the presence of these sub-surface nano silica particles. (C) 2000 Elsevier Science Ltd. All rights reserved