Todd G. Ruskell

Driven nonlinear atomic force microscopy cantilevers: From noncontact to tapping modes of operation

A numerical model of the operation of an atomic force microscope with a driven cantilever is presented. This model takes into account the attractive van der Waals and repulsive indentation forces acting between tip and sample. The time‐dependent displacement amplitude and phase of the tip oscillations, and the magnitude, duration, and sign of the short bursts of tip–sample force are derived. It is shown that the stiffness of the tip and sample materials is an important factor in determining the magnitude and duration of the tip–sample repulsive force and the magnitude of sample indentation. The model covers typical operating ranges of vibrating cantilever atomic force microscopes, from the noncontact to the tapping modes.

High resolution Fowler‐Nordheim field emission maps of thin silicon oxide layers

An improved method for characterizing thin oxide films using Fowler‐Nordheim field emission is reported. The method uses a conducting‐tip atomic force microscope with dual feedback systems, one for the topography and a second for the field emission bias voltage. Images of the voltage required to maintain a 10 pA emission current through a 3 nm oxide film thermally grown on p‐type Si(100) demonstrate a spatial resolution of 8 nm.

Scanning tunneling microscopy and spectroscopy of individual C60 molecules on Si(100)-(2×1) surfaces

Abstract Individual C 60 molecules chemisorbed on Si(100)-(2 × 1) surfaces have been studied by scanning tunneling microscopy and spectroscopy. Chemisorption was realized by annealing the samples with room-temperature deposited adsorbates to 600°C. Spectroscopic results on individual adsorbates reveal a transition of their electronic structure from that of a near-free adsorbate to that of SiC, as the adsorbate-substrate interaction increases.

Intramolecular features of individual C60 molecules on Si(100) observed by STM

Abstract Intramolecular features (IMF) of a variety of individual C 60 molecules adsorbed on an Si(100)-(2 × 1) surface have been imaged by scanning tunneling microscopy under ultrahigh vacuum conditions. Features of individual C 60 molecules clearly show the local density of states superimposed on their cage structure. Both physisorbed (pre-annealed) and chemisorbed (post-annealed) species have been imaged on the same surface, exhibiting characteristics that depend on their bonding nature. Intramolecular features of a physisorbed C 60 molecule and of two chemisorbed molecules are presented.

Growth of silicon nitride by scanned probe lithography

Scanning probe lithography has been used for the first time to grow silicon nitride nanostructures on silicon substrates. The lithography was performed by an atomic force microscope (AFM) placed in an evacuated chamber with a partial pressure of annhydrous ammonia. The silicon nitride nanostructures were grown by negatively biasing the silicon tip with respect to the sample. By changing the environment of the AFM, both silicon oxide and silicon nitride can be grown and subsequently processed.

NANOSECOND TIME-SCALE SEMICONDUCTOR PHOTOEXCITATIONS PROBED BY A SCANNING TUNNELING MICROSCOPE

The high‐frequency response of scanning tunneling microscopy of a semiconductor is demonstrated by using the beat frequencies of the longitudinal modes of a HeNe laser at the tunneling junction. We present a comparison of the slow and fast optical response of photoexcited charge carriers in the layered structure semiconductors n‐type MoS2 and p‐type WSe2 using this method.