Scanning tunnelling microscopy of carbon nanotubes

This paper briefly reviews how scanning tunnelling microscopy (STM) and spectroscopy (STS) are used to analyse the atomic structure and the electronic properties of individual single-wall carbon nanotubes. In this area, the progress accomplished over the past several years has been spectacular. As this paper demonstrates, all the effects predicted by theory have been verified experimentally. Geometrical and electronic effects specific to carbon nanotubes are illustrated by analysing a series of STM images and STS spectra computed using a tight-binding theory. The simulations include a catalogue of images of 27 single-wall nanotubes, Stone-Wales defects in semiconducting nanotubes, and a symmetric Y-junction.     

Scanning tunnelling microscopy and tunnelling spectroscopy of titanium before and afterin vitro immersion

In an effort to understand thein vivo interactions of titanium and its alloys with a biological environment, surface science methods have been used on specimens retrieved fromin vitro andin vivo experiments. A relatively new technique that has the potential to further our knowledge of the oxide-solution interface is scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (TS). This work documents the use of STM/TS in the study of titanium thin films before and after immersion in anin vitro solution. Titanium thin films were fabricated using a procedure which produced an oxide that had minimal contaminants. Half of the thin films were immersed in an electrolyte. STM/TS was performed immediately after the immersion period. Constant current images were obtained. Current-voltage characteristics were recorded at regions of interest. The topography of the nonimmersed films revealed that the surface was qualitatively the same as other sputter deposited metal films. I–V curves showed little spatial variation. The topography of the immersed film showed little change from the nonimmersed ones. However, significant spatial variation of the local electronic structure was noted. This indicates that titanium surface-fluid interactions do not occur uniformly on the film.     

Scanning tunnelling microscopy studies of nucleation and growth of silver films

Different stages of nucleation and growth of silver films grown on gold-coated mica by vacuum evaporation have been studied by using scanning tunnelling microscopy. These studies reveal a complete picture of the sequence of events from initial island formation to a fairly smooth film surface. The surface roughness pattern matches the growth process. The angle of contact of the cap-shaped silver islands formed during the initial stages of growth was found to be about 12°, confirming three-dimensional island type of growth.     

Scanning tunnelling microscopy and spectroscopy of ultra-flat graphene on hexagonal boron nitride

Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy-momentum dispersion relations which cross at the Dirac point. However, accessing the physics of the low-density region at the Dirac point has been difficult because of disorder that leaves the graphene with local microscopic electron and hole puddles. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance. Here we use scanning tunnelling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moiré patterns. However, contrary to predictions, this conformation does not lead to a sizeable band gap because of the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron-hole charge fluctuations are reduced by two orders of magnitude as compared with those on silicon oxide. This leads to charge fluctuations that are as small as in suspended graphene, opening up Dirac point physics to more diverse experiments.     

Scanning tunnelling microscopy imaging of symmetry-breaking structural distortion in the bismuth-based cuprate superconductors

A complicating factor in unravelling the theory of high-temperature (high-T(c)) superconductivity is the presence of a 'pseudogap' in the density of states, the origin of which has been debated since its discovery. Some believe the pseudogap is a broken symmetry state distinct from superconductivity, whereas others believe it arises from short-range correlations without symmetry breaking. A number of broken symmetries have been imaged and identified with the pseudogap state, but it remains crucial to disentangle any electronic symmetry breaking from the pre-existing structural symmetry of the crystal. We use scanning tunnelling microscopy to observe an orthorhombic structural distortion across the cuprate superconducting Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4+x) (BSCCO) family tree, which breaks two-dimensional inversion symmetry in the surface BiO layer. Although this inversion-symmetry-breaking structure can impact electronic measurements, we show from its insensitivity to temperature, magnetic field and doping, that it cannot be the long-sought pseudogap state. To detect this picometre-scale variation in lattice structure, we have implemented a new algorithm that will serve as a powerful tool in the search for broken symmetry electronic states in cuprates, as well as in other materials.     

Scanning tunnelling microscopy of diamond deposition at the nanometre scale holes on highly orientated pyrolytic graphite

Abstracts are not published in this journal     

Scanning electron microscopy imaging of single-walled carbon nanotubes on substrates

Scanning electron microscopy (SEM) plays an indispensable role in nanoscience and nanotechnology because of its high efficiency and high spatial resolution in characterizing nanomaterials.Recent progress indicates that the contrast arising from different conductivities or bandgaps can be observed in SEM images if single-walled carbon nanotubes (SWCNTs) are placed on a substrate.In this study,we use SWCNTs on different substrates as model systems to perform SEM imaging of nanomaterials.Substantial SEM observations are conducted at both high and low acceleration voltages,leading to a comprehensive understanding of the effects of the imaging parameters and substrates on the material and surface-charge signals,as well as the SEM imaging.This unified picture of SEM imaging not only furthers our understanding of SEM images of SWCNTs on a variety of substrates but also provides a basis for developing new imaging recipes for other important nanomaterials used in nanoelectronics and nanophotonics.     

Electron microscopy study of mesophase pitch-based graphite fibres

A comprehensive electron microscopic investigation of the structure of the graphitic sheet in mesophase pitch-based fibres is presented.In situ brightfield and (00l) darkfield observation of the sheets in sub micrometre fibres reveals a finely striated structure, associated with three-dimensional order. (hkl) darkfield imaging of the sheets in their edge-on and face-on orientations indicates that the striations correspond to the edge view of a mosaic of graphite grains. The grains have lateral dimensions of 100 to 200 nm on average but are only a few atomic layers thick.In situ lattice imaging of the fibre edges indicates a very high level of lattice perfection of the (00l) domains below the fibre surface, quite in line with the outstanding mechanical and thermal properties of this type of fibres. A variety of surface defects are revealed. Preferential orientation effects of the sheet texture on the fibre electron diffraction pattern are described.     

Non-invasive study of nerve fibres using laser interference microscopy

This paper presents the results of a laser interference microscopy study of the morphology and dynamical properties of myelinated nerve fibres. We describe the principles of operation of the phase-modulated laser interference microscope and show how this novel technique allows us to obtain information non-invasively about the internal structure of different regions of a nerve fibre. We also analyse the temporal variations in the internal optical properties in order to detect the rhythmic activity in the nerve fibre at different time scales and to shed light on the underlying biological processes. We observe pronounced frequencies in the dynamics of the optical properties and suggest that the oscillatory modes have similar origin in different regions, but different strengths and mutual modulation properties.