C. T. Black

GATE-VOLTAGE STUDIES OF DISCRETE ELECTRONIC STATES IN ALUMINUM NANOPARTICLES

We have investigated the spectrum of discrete electronic states in single, nm-scale Al particles incorporated into new tunneling transistors, complete with a gate electrode. The addition of the gate has allowed (a) measurements of the electronic spectra for different numbers of electrons in the same particle, (b) greatly improved resolution and qualitatively new results for spectra within superconducting particles, and (c) detailed studies of the gate-voltage dependence of the resonance level widths, which have directly demonstrated the effects of nonequilibrium excitations.

Using neutral metastable argon atoms and contamination lithography to form nanostructures in silicon, silicon dioxide, and gold

This letter describes the fabrication of ∼80 nm structures in silicon, silicon dioxide, and gold substrates by exposing the substrates to a beam of metastable argon atoms in the presence of dilute vapors of trimethylpentaphenyltrisiloxane, the dominant constituent of diffusion pump oil used in these experiments. The atoms release their internal energy upon contacting the siloxanes physisorbed on the surface of the substrate, and this release causes the formation of a carbon‐based resist. The atomic beam was patterned by a silicon nitride membrane, and the pattern formed in the resist material was transferred to the substrates by chemical etching. Simultaneous exposure of large areas (44 cm2) was also demonstrated.

Studies of electron energy levels in single metal particles

Abstract We describe the fabrication of point-contact tunnel junctions containing a single Al particle of diameter

Tunneling Through Metallic Quantum Dots

We discuss single-electron tunneling measurements at dilutionrefrigerator temperatures on metallic grains, sufficientlysmall that the quantum levels of the conduction electrons canbe resolved. These measurements directly reveal the energyeigenvalues of the electrons in a grain that typicallycontains a few thousand conduction electrons. Suchmeasurements were first carried out a few years ago by Ralph,et al. on nanograins of Al. More recently, this workhas been extended to measurements on nanoparticles of theheavy metal Au by Davidović and on nanoparticles ofalloys of Al and Au by Salinas, et al. This morerecent work has pointed up the need to go beyond the simplestindependent-electron model, to include the Coulomb interactionbetween electrons and also nonequilibrium electronpopulations. These interactions cause the energy levels tomerge into a continuum above the Thouless energy and can causea single quasiparticle level to show up as a cluster ofresonances. The strong spin-orbit interaction in Au cancause levels to split in magnetic fields with a g-factor of∼0.3, instead of the free electron g=2. In addition,there is evidence for a proliferation of low-lying energylevels suggestive of system spin values greater than1/2 induced by the exchangeinteraction. This paper will review the evolving progress thathas been made in interpreting these observations.

Discrete energy levels and superconductivity in nanometer-scale Al particles

We have fabricated single-electron tunneling transistors in which the central island is an aluminum grain with radius in the range 2–10 nm. The corresponding spacing between electron-in-a-box levels is in the range ∼0.01 to ∼1 meV. Using tunneling spectroscopy at 50 mK, we have, for the first time, resolved these discrete levels in a metallic grain. By observing the Zeeman spin splitting in a magnetic field, we can distinguish grains with even vs. odd numbers of electrons. A superconducting energy gap can be seen if the grain is large enough so that the level spacing is smaller than the energy gap. This gap is reduced continuously to zero by a magnetic field of 3–4 Tesla. While the superconducting gap adds to the Coulomb gap in determining the threshold voltage for tunneling into a grain with an initially even number of electrons, it subtracts from the Coulomb gap for a grain with an initially odd number of electrons because the tunneling electron can pair with the odd electron, forming a lower-energy fully-paired state.

Demonstration of a nanolithographic system using a self-assembled monolayer resist for neutral atomic cesium

This paper describes the formation of nanometer-scale features in gold and silicon substrates. The features in gold were made by using a self-assembled monolayer (SAM) of nonanethiolate on gold as a resist damaged by neutral cesium atoms. A SAM resist of octyltrichlorosilane on silicon dioxide was used as a resist sensitive to cesium atoms in order to fabricate features in silicon. A silicon nitride membrane perforated with nm- and micrometers -scale holes was used to pattern the atomic beam. Etching transferred the pattern formed in the SAM layer into the underlying substrate. Features of < 100-nm size were etched into the gold and silicon substrates. Investigations of the reflectivity of samples of nonanethiolate on gold, exposed to the atomic beam without a mask and subsequently etched, revealed that the resist-etch system exhibited a minimum threshold dose of cesium for damage; at doses lower than approximately 3 monolayers, the damage was insufficient to allow penetration of the SAM by the etching solution. The threshold dose for damage of the octyltrichlorosilane SAM on silicon dioxide is under investigation.