Atomic Nanofabrication Research Articles

Neutral particles pushed or pulled by laser pulses.

Acceleration of neutral particles is of great importance in many areas, such as controlled chemical reactions, atomic nanofabrication, and atom optics. Recent experimental studies have shown that pulsed lasers can be used to push neutral Rydberg atoms forward [Nature 461, 1261 (2009)10.1038/nature08481; Nat. Photonics 6, 386 (2012)10.1038/nphoton.2012.87]. Our simulation shows that pulsed lasers can also be used to pull Rydberg atoms back toward a light source. In particular, we proposed a method of using two laser pulses on a neutral atom, then selective operations on the neutral atom (pushing or pulling) can be performed by adjusting the delay time between the two laser pulses.

Polarization-gradient laser cooling as a way to create strongly localized structures for atom lithography

Generally, the conditions for deep sub-Doppler laser cooling do not match the conditions for the strong atomic localization that takes a place in deeper optical potential and, in consequence, leads to larger temperature. Moreover, for a given detuning in a deep optical potential the secular approximation which is usually used for quantum description of laser cooling becomes no more valid. Here we perform an analysis of atomic localization in optical potential based on a full quantum approach for atomic density matrix. We also show that the laser cooling in a deep far-off detuned optical potential, created by a light field with a polarization gradient, can be used as an alternative method for forming high contrast spatially localized structures of atoms for the purposes of atom lithography and atomic nanofabrication. Finally, we perform an analysis of the possible limits for the width and the contrast of localized atomic structures that can in principle be reached by this type of the light mask.

Nanopatterning by atomic nanofabrication: Interaction of laser cooled atoms with surfaces

By using laser manipulation techniques, we have produced a cesium beam with sub-thermal velocity; atoms of the beam have then been deposited onto graphite substrates. Analyses of the samples, carried out in vacuum by tunneling microscopy, demonstrate that, at reduced surface coverage rates, isolated atom-sized structures are formed on the substrate. Results are of interest for the development of an atomic nanofabrication approach exploitable also with soft materials.

Magnetic induced dichroism and frequency stabilization of violet-blue diode lasers on gallium atomic transitions

We study the magnetic-field-induced dichroism on a sample of gallium neutral atoms created in a hollow cathode lamp and describe a method for robust stabilization of violet-blue diode lasers tuned on gallium atomic transitions for an atom nanofabrication experiment. We compare the experimental dichroic signals with theoretical simulations obtained by the solving of the exact atom-field interaction Hamiltonian. We find excellent agreement when considering the magnetic field shielding from the hollow cathode. This method allows for a wide range of frequency tuning, modulation-free locking, and long-term stability of external-cavity diode lasers. From analysis of a square root Allan variance we have achieved a stability of 1 MHz at 1-s average time.

Talbot-Lau effect for atomic de Broglie waves manipulated with light

We have demonstrated the Talbot-Lau effect for atomic de Broglie waves in the time domain. This effect is based on Fresnel diffraction of matter waves from an incoherent source. In the experiment, de Broglie waves of atoms in a particular internal state have been manipulated and the resulting density directly imaged by resonant optical fields. These experiments allow us to probe the quantum dynamics of the atomic center of mass. We have also used this effect to create patterns in the density of the atoms with period as small as $1∕10$ of the optical wavelength, demonstrating the potential application of this technique for atom nanofabrication.

Atomic nanofabrication: perspectives for serial and parallel deposition

Recent advances in atomic nanofabrication with laser manipulated atomic beams are discussed with regard to the creation of arbitrary structures.

Quantum Features in Atomic Nanofabrication using Exactly Resonant Standing Waves

We report on the first fabrication of nanostructures with exactly resonant light revealing the quantum character of the atom-light interaction. Classically the formation of nanostructures is not expected; thus, the observed formation of complex periodic line patterns can be explained only by treating atom-light interaction and propagation of the atoms quantum mechanically. Our numerical quantum calculations are in quantitative agreement with this experimental finding. Moreover, the theory predicts that for small detunings nanostructures with lambda/4 period can be produced, which beats the standard nanofabrication limit of lambda/2. Our experiments confirm this prediction.

Towards fabrication of ordered gallium nanostructures by laser manipulation of neutral atoms: study of self-assembling phenomena

Surface diffusion has an impact on the lateral resolution of nanostructures in bottom-up atom nanofabrication. In this paper we study the effects of the gallium atoms self-assembled on silicon surfaces (100) patterned with trenches at different slopes. These particular substrate morphologies have been made to enable an effective deposition rate variation along the surface. In this way we experimentally mimic the effect of the atomic flux modulation created by standing wave during an atom nanofabrication experiment. Even if we observe self-organization of gallium atoms on the surface, we conclude that the nano-islands are not affected by surface diffusion processes and the effective variation of the deposition rate per unit area is the dominant factor affecting the growth differences along the surface. This result demonstrates that the self-organization of gallium atoms should not prevent the observation of a periodic nano-patterning created by atom nano-fabrication techniques.

Atomic nanofabrication using an ytterbium atomic beam

Highly parallel and periodically narrow lines of ytterbium (Yb) atoms were successfully produced on a substrate using a near resonant laser light and direct-write atomic nanofabrication. Yb atoms are a promising material for nanofabrication using atom optics particularly due to their electric conductivity, the laser wavelength required for their manipulation, and the vapor pressure required for their fabrication. Collimated 174Yb atoms were channeled into the nodes of an optical standing wave with dipole force and then deposited onto a substrate. We clearly observed a grating pattern of Yb atoms fabricated on a substrate with a line separation of approximately 200 nm after examining the surface of the substrate with an atomic force microscope. This is the first demonstration of nanofabrication using the atom-optical approach with Yb atoms.

Atomic nanofabrication by laser manipulation of a neutral cesium beam

In this work, we report on the results of a nanolithography experiment with a cold cesium beam. We have realized a brilliant and collimated cesium beam with a low longitudinal velocity (10 m/s) exploiting laser cooling techniques, in particular a pyramidal atomic funnel. The cesium atomic beam has been utilized to pattern gold substrates, using Self Assembled Monolayers (SAM) of thiols as resist, and a wet etching process. The pattern generated by a light mask, a one-dimensional standing e.m. wave, was characterized by diffraction and Atomic Force Microscopy (AFM) measurements, showing the presence of lines spaced half the wavelength of the standing wave (426 nm) with lateral size well below 100 nm.

Atomic nanofabrication with complex light fields

The method of neutral atom lithography allows one to transfer to a substrate a 2D intensity modulation of an atomic beam imposed by an inhomogeneous light field. The complexity of the pattern depends on the properties of the light field constructed from the superposition of multiple laser beams. For the design of suitable light fields we present a mathematical model with a corresponding numerical simulation of the so-called inverse problem. Furthermore, details of an experiment carried out with a holographically reconstructed light field are discussed.

Spherical correction lens array for atom nanofabrication

A simple means to realize conservative, all-optical atomic array illuminators is proposed. We show that, in the atom nanofabrication context, such devices can be used to substantially reduce imaging problems caused by spherical lens imperfections. Both one- and two-dimensional focusing setups are considered.