No abstract

Scanning probe microscope tip-induced local oxidation is a promising tool for the fabrication of nanometre-scale structures and devices. In this study, oxide line patterns were fabricated on the surface of a titanium thin film using a conductive atomic force microscope (AFM). Geometrical characters of the oxide line patterns and their dependence on the exposure parameters in fabricating, i.e. the applied voltage amplitude and duration, ambient humidity, AFM set point value, and the mode of applied voltage, are investigated. The dependence of the oxide width on the applied voltage duration was found to have two distinct growth rates and a two-stage growth model was proposed to account for it. Application of pulsed voltages was proved to be an efficient method for suppressing the growth of oxide width by repeatedly breaking the directional transport of OH − ions in the process of oxidation. A line-width of 8 nm was achieved with an optimized pulsed voltage. Based on the experimental results, optimal controlling of exposure parameters to improve the fabricating resolution and reliability are discussed.

Recently, unusual and strikingly beautiful seahorse-like growth patterns have been observed under conditions of quasitwo-dimensional growth. These 'S'-shaped patterns strongly break two-dimensional inversion symmetry; however such broken symmetry occurs only at the level of overall morphology, as the clusters are formed from achiral molecules with an achiral unit cell. Here we describe a mechanism which gives rise to chiral growth morphologies without invoking microscopic chirality. This mechanism involves trapped electrostatic charge on the growing cluster, and the enhancement of growth in regions of large electric field. We illustrate the mechanism with a tree growth model, with a continuum model for the motion of the one-dimensional boundary, and with microscopic Monte Carlo simulations. Our most dramatic results are found using the continuum model, which strongly exhibits spontaneous chiral symmetry breaking, and in particular finned 'S' shapes like those seen in the experiments.

The electrical properties of C,,-tetracyanoquinodimethane (TCNQ) thin films fabricated by using an ionized-cluster-beam method in a high vacuum system were investigated. The films werc characterized by transmission electron microscopy (TEM) and electronic spectroscopy. The spectroscopic results evidenced the formatjon of the charge-transfer complex system in C,,-TCNQ thin films and the TEM results revealed the microstructure of the films. The film thickness is of about 100nm. The elcctromotive intensity a t the transition point is a few IO' V/m. The possible meclianism of the electrical phenomena of the films is discussed in the paper.

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