Nanofabrication by magnetic focusing of supersonic beams

Abstract

We present a new method for nanoscale atom lithography. We propose the use of a supersonic atomic beam, which provides an extremely high-brightness and cold source of fast atoms. The atoms are to be focused onto a substrate using a thin magnetic film, into which apertures with widths on the order of 100 nm have been etched. Focused spot sizes near or below 10 nm, with focal lengths on the order of 10 µm, are predicted. This scheme is applicable both to precision patterning of surfaces with metastable atomic beams and to direct deposition of material.Nanoscale fabrication is a critical tool for realizing much of modern technology, including information processing, biomedical research, and photonics [1][2][3]. Optical lithography, the current method for chip mass production, is used to produce many features in parallel, but has a limited resolution due to the wavelength of light used. Electron beam (e-beam) lithography, a method for producing much smaller (order of 1 nm) features, is a serial, rather than parallel, method, meaning that it is much more time-consuming than optical lithography. Ebeam, however, is frequently used to fabricate the masks that are required by the latter. Additional methods, using vacuum ultraviolet or X-ray radiation [4], or using focused ion beams [5], are being developed in an effort to achieve high-resolution and high-throughput nanofabrication.One area of great potential for nanofabrication is atom lithography [6,7]. The deBroglie wavelength of atoms is typically much less than an optical wavelength, potentially resulting in a much smaller diffraction-limited spot size. Additionally, fabrication operations are parallelizable; much work has focused on depositing multiple lines and dots of atoms by focusing from a standing light wave [8][9][10][11][12]. In addition, atom lithography is versatile in the sense that one may either directly write structures onto a substrate [13][14][15][16][17], or may pattern a resist prior to etching, as in traditional lithography, using a beam of metastable atoms [18]. The primary limitation of optical focusing is that it is difficult to focus some of the atoms without simultaneously defocusing others, leading to significant aberrations and an unwanted underlayer of material. A method of mitigating this effect was proposed [19] and demonstrated [20], but is challenging to implement in practice. Alternative approaches, such as focusing of atoms using macroscopic magnetic lenses [21] or an "atom pinhole camera" [22] have also been explored. All the above techniques have used effusive beams, limiting atomic density to around 10 10 atoms/cm 3 , and have achieved controlled feature sizes (at best) on the order of 100 nm.In this Letter, we propose a new approach to atom lithography that should enable much smaller feature sizes and larger throughput. Our method consists of magnetic focusing of a supersonic beam through a nanofabricated magnetic mask. As nearly all atoms are paramagnetic in either the ground state or an accessible metastable state, magnetic foc...

Nanoscale Imaging of Neutral Atoms with a Pulsed Magnetic Lens

“…The method has been limited so far by the low magnetic field gradients available, which result in a large focal length, as well as by the fringe fields that the atoms experience as they enter and leave the magnets. Clark et al 14 recently proposed a parallel method to achieve focal spots with dimensions of sub-10 nm; however, that method does not enable true imaging and hence has limited applicability.…”