Effect of reinforcement particle size on the tribological properties of nano-diamond filled polytetrafluoroethylene based coating.

The tribological properties of PTFE composite coatings reinforced by nano-diamonds were investigated. Mechanical particle size reduction and dispersion of nano-diamond aggregates were performed by milling with ceramic beads in an organic solvent. Particle size was controlled by the milling time. Pastes comprising a PTFE solution mixed with nano-diamond having various sizes were coated on the aluminum substrate. Ball-on-plate type wear test was performed to investigate the friction and wear behavior. The results indicated that the addition of nano-diamonds effectively improved tribological performance of the PTFE coating. The reduction in nano-diamond sizes were not always improved the wear resistance of PTFE coating. This unexpected behavior was explained by observation on the worn surfaces and wear debris.

Coil Knotting during Endovascular Coil Embolization for Ruptured MCA Aneurysm. A Case Report.

SUMMARY: Complications during coil embolization of cerebral aneurysms include thromboembolic events, hemorrhagic complications related to procedural aneurysmal rupture and parent vessel perforation, and coil-related complications. The present report describes a rare coil-related complication involving spontaneous coil knotting.

Oxidation of step edges on Si(001)-c(4x2).

The initial oxidation process of the ultraclean Si(001)-c(4x2) surface is studied using scanning tunneling microscopy at low temperature. At the early stage of oxygen adsorption, reactions with Si atoms at SB steps are dominant over those at terraces by more than 2 orders of magnitude, and they proceed in two distinct stages to high oxidation states. Guided by the ab initio calculations, the oxidation structures at each stage are proposed. The extreme reactivity of the step edge is due to the presence of rebonded adatoms with dangling bonds and weak rebonds, and their proximity allows the formation of -Si-O- chain structures along the step edge, unlike those on the Si(111) surface.

Atomic-scale phase coexistence and fluctuation at the quasi-one-dimensional metal-insulator transition.

Scanning tunneling microscopy of a quasi-one-dimensional (1D) metal-insulator transition in an In nanowire array on the Si(111) surface reveals unprecedented details in the transition dynamics. The transition proceeds in microscopic first order, namely, through the domain-by-domain conversion at the nanoscale, from the metallic to the insulating phase or vice versa. The definition of domains and their effective transition temperatures (Tc) are strongly correlated with the distribution of defects. Below Tc, the condensation and the fluctuation of 1D charge density waves are observed within the isolated metallic domains, as well as at the domain boundaries. The appearance of such isolated condensates suggests a strong intrawire coupling: a manifestation of the 1D nature of the critical fluctuation, as well as the origin of the first-order transition.

Direct evidence of the charge ordered phase transition of indium nanowires on Si111.

A controversial issue of the driving force for the phase transition of the one-dimensional (1D) metallic In wires on Si(111) is studied by low-temperature scanning tunneling microscopy and spectroscopy. The energy gap opening and the longitudinal charge ordering through charge transfer at the Fermi level are unambiguously observed. The vacancy defects induce a local charge ordering decoupled from a lattice distortion above T(c), and pin the phase of charge order below T(c). All these results below and above T(c) including the detailed features such as local fluctuations strongly support the 1D charge-density-wave mechanism for the phase transition.

Novel electronic structure of inhomogeneous quantum wires on a Si surface.

A one-dimensional system of Si(111)-(5 x 2)-Au is explored using scanning tunneling microscopy and spectroscopy. The chain of Si adatoms called bright protrusions (BP's) is found to be semiconducting with an evanescent state in the gap, which originates from adjoining metallic BP-free segments. A quantitative analysis shows that the evanescent state decays in inverse-Gaussian form, leading to an appearance of a parabolic BP chain, and scales to its chain length. Spatial decay of the state suggests a quadratic band bending and the existence of a Schottky-like potential barrier at the interface driven by charge transfer.

Metal-insulator transition in Au atomic chains on Si with two proximal bands.

One-dimensional atomic chains on Au/Si(557) feature two proximal 1D bands near the Fermi level, which were controversially attributed as a spinon-holon pair of a Luttinger liquid. Angle-resolved photoemission shows that only one band is metallic with the neighboring one gapped at room temperature. Furthermore, even the metallic branch is found to undergo a metal-insulator transition upon cooling, which follows a mean-field-type behavior. Scanning tunneling microscopy observes two apparently unequivocal chains on the surface, one of which exhibits periodicity doubling accompanying the metal-insulator transition. The surface 1D structure is thus concluded to be insulating at low temperature with a Peierls-type instability.

Observation of Quantum-Size Effects at Room Temperature on Metal Surfaces With STM.

Surface steps act as confining barriers for electrons in metal-surface states. Thus, narrow terraces and small single-atom-high metal islands act as low-dimensional, electron-confining structures. In sufficiently small structures, quantum-size effects are observable even at room temperature. Scanning tunneling spectroscopy is used to image the probability amplitude distributions and discrete spectra of the confined states. Examination of the electronic structure of the steps provides evidence for electron-density smoothing and the formation of step-edge states. Estimates of the electron-confining barriers are obtained.

Field-Induced Nanometer- to Atomic-Scale Manipulation of Silicon Surfaces with the STM.

The controlled manipulation of silicon at the nanometer scale will facilitate the fabrication of new types of electronic devices. The scanning tunneling microscope (STM) can be used to manipulate strongly bound silicon atoms or clusters at room temperature. Specifically, by using a combination of electrostatic and chemical forces, surface atoms can be removed and deposited on the STM tip. The tip can then move to a predetermined surface site, and the atom or cluster can be redeposited. The magnitude of such forces and the amount of material removed can be controlled by applying voltage pulses at different tip-surface separations.

Negative differential resistance on the atomic scale: implications for atomic scale devices.

Negative differential resistance (NDR) is the essential property that allows fast switching in certain types of electronic devices. With scanning tunneling microscopy (STM) and scanning tunneling spectroscopy, it is shown that the current-voltage characteristics of a diode configuration consisting of an STM tip over specific sites of a boron-exposed silicon(111) surface exhibit NDR. These NDR-active sites are of atomic dimensions ( approximately 1 nanometer). NDR in this case is the result of tunneling through localized, atomic-like states. Thus, desirable device characteristics can be obtained even on the atomic scale.