Karl K. Berggren

Microlithography by using neutral metastable atoms and self-assembled monolayers.

Lithography can be performed with beams of neutral atoms in metastable excited states to pattern self-assembled monolayers (SAMs) of alkanethiolates on gold. An estimated exposure of a SAM of dodecanethiolate (DDT) to 15 to 20 metastable argon atoms per DDT molecule damaged the SAM sufficiently to allow penetration of an aqueous solution of ferricyanide to the surface of the gold. This solution etched the gold and transformed the patterns in the SAMs into structures of gold; these structures had edge resolution of less than 100 nanometers. Regions of SAMs as large as 2 square centimeters were patterned by exposure to a beam of metastable argon atoms. These observations suggest that this system may be useful in new forms of micro- and nanolithography.

NANOSTRUCTURE FABRICATION IN SILICON USING CESIUM TO PATTERN A SELF-ASSEMBLED MONOLAYER

This letter describes the formation of nanometer-scale features in a silicon substrate using a self-assembled monolayer (SAM) of octylsiloxane on silicon dioxide as a resist sensitive to a patterned beam of neutral cesium atoms. The mask that patterned the atomic beam was a silicon nitride membrane perforated with nm and μm scale holes, in contact with the substrate surface. In a two-step wet-chemical etching process, the pattern formed in the SAM was transferred first into the SiO2 layer and then into an underlying silicon substrate. This process demonstrated the formation of silicon features with diameter ∼60u2009nm.

Self-assembled monolayers exposed by metastable argon and metastable helium for neutral atom lithography and atomic beam imaging

We used a beam of noble gas atoms in a metastable excited state to expose a thin (1.5 nm) self-assembled monolayer resist applied over a gold-coated silicon wafer. We determined exposure damage as a function of dose of metastable atoms by processing the samples in a wet-chemical etch to remove the gold from unprotected regions and then measuring the reflectivity with a laser and observing the microstructure with an atomic force microscope. We found that the minimum dose required to damage the resist substantially was 1.7(3)×1015 atoms/cm2 for metastable helium, and 25(7)×1015 atoms/cm2 for metastable argon.

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.

Demonstration of a nonmagnetic blazed-grating atomic beam splitter.

We demonstrate a coherent atomic beam splitter for metastable helium atoms, based on the diffraction of atomic matter waves from a blazed phase grating. The beam splitter is created by driving the two transitions of a three-level V system with differentially detuned standing light waves that have a relative spatial phase shift of pi/2. The light f ields create a potential that is approximately triangular as a function of position in the laser field. Splittings of 38 times the photon momentum have been observed.

Nanofabrication using neutral atomic beams

We present a survey of neutral atom lithography. The combination of nm-scale features, large-area parallel deposition, and effective resists demonstrates the promise of atoms as a lithographic element. We demonstrate the transfer of 70-nm-wide features from a neutral atomic beam into a substrate using several resists, including self-assembled monolayers of alkanethiolates on Au and of alkylsiloxanes on SiO2, and “contamination” resists deposited from vapor. Unlike photons and electrons, noble gas atoms in energetic metastable states have an internal state structure that is easily manipulable, introducing the possibility of novel lithographic schemes based on the optical quenching of internal energy.

A virtual slit for atom optics and nanolithography

We propose a simple `virtual slit for atoms based on the position- and velocity-dependent optical pumping of atoms into an undetected internal state. We show how this slit can be used as a nanometre scale, high-contrast tool for atom lithography as well as a subrecoil collimator for atomic beams.

Demonstration of a blazed grating beam splitter for two-level atoms

Abstract We experimentally demonstrate a coherent beam splitter for metastable helium atoms based on the diffraction of atomic matter waves from a blazed phase grating. The blazed grating is based on an optical potential and is formed when a two-level atomic system interacts with two standing light waves. The standing waves are detuned symmetrically about the atomic resonance and have a relative spatial phase shift of π 2 . We show theoretically that splittings beyond the Raman-Nath regime are possible. We have observed experimentally momentum splittings of 28 times the photon momentum.

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.

Atom lithography using standing-wave quenching

We used spatially dependent optical pumping in a standing wave to create nanostructures using metastable argon and resist-based atom lithography. Although the localization is caused by spontaneous emission, the matter wave diffraction and the mechanical effects of the light affect the resulting atomic localization. We investigate the role of the spontaneous emission.