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Atom lithography
Atom lithography
2009
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Efficient sub-Doppler laser cooling of an Indium atomic beam, Opt. Express 17, 21216-21221 (2009)BibTeX
ABSTRACT »We have realized efficient transverse cooling of an Indium atomic beam by combining optical pumping with a closed cycle UV laser cooling transition at 325.6 nm. The transverse velocity of the atomic beam is reduced to 13.5 ±3.8 cm/s, well below the Doppler cooling limit. The fraction of laser-cooled In atoms is enhanced to 12±3 % by optical pumping in the present experiment. It can be scaled up to approach 100% efficiency in cooling, providing high brightness atomic beams for further applications. Our results establish In on the map of elements suitable for applications involving laser cooling.
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Strong effective saturation by optical pumping in three-level systems, Phys. Rev. A 80, 063801 (2009)BibTeXABSTRACT »We have studied nonlinear absorption from the In P1/2,3/2 ground-state doublet in a resistively heated high-temperature cell and a hollow cathode lamp. Using probe and pump lasers at 410 and 451 nm, respectively, absorption spectra with nonlinear properties caused by saturated absorption, coherent dark resonances, and optical pumping are observed. A theoretical description in terms of a density-matrix theory agrees very well with the observed spectra and identifies optical pumping as a dominating process of broadening in the stepwise contribution rather than velocity-changing collisions. Our experiments suggest that the theory used here is widely applicable in saturation spectroscopy on three-level Λ systems.
2008
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Continuous-wave coherent ultraviolet source at 326 nm based on frequency trippling of fiber amplifiers, Opt. Express 16, 16803-16808 (2008)BibTeXABSTRACT »We have demonstrated a tunable single frequency source of continuous-wave (CW) coherent ultraviolet (UV) radiation at λ_3ω = 326 nm. Laser light of a tunable diode laser at λ_ω = 977 nm was split and injected into two independent fiber amplifiers yielding 1 W and 0.4 W, respectively. The 1 W branch was resonantly frequency doubled, resulting in 120 mW of useful power at λ_2ω = 488 nm. The third harmonic was generated by summation of the second branch of λ_ω and λ_2ω which were enhanced by a doubly resonant cavity. This light source has TEM_00 character and can be continuously tuned over more than 18 GHz. It is of interest for efficient laser cooling of In and potentially other applications.
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Laser cooling of an indium atomic beam enabled by magnetic fields, Phys. Rev. A 77, 033402 (2008)BibTeXABSTRACT »We demonstrate magnetic field enabled optical forces on a neutral indium atomic beam in a light field consisting of five frequencies. The role of dark magnetic ground state sublevels is studied and enables us to cool the atomic beam transversely to near the Doppler limit with laser frequencies tuned above the atomic resonance. The effect of laser cooling can be explained with transient effects in the light potential created by the standing wave light field where the atoms are optically pumped into the dark states and recycled by Larmor precession.
2006
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Resist-assisted atom lithography with group III elements, Appl. Phys. B 85, 487-491 (2006)BibTeXABSTRACT »Resist-assisted atom lithography with group III elements, specifically with gallium and indium, is demonstrated. Self-assembled monolayers (SAM) of nonanethiols prepared on thin sputtered gold films were exposed to a beam of neutral gallium and indium atoms through a physical mask. The interaction of the Ga and In atoms with the nonanethiol layer, followed by a wet etching process, creates well defined structures on the gold film, with features below 100 nm. The threshold of the lithographic process was estimated by optical methods and found to be around 3 gallium atoms and 12 indium atoms per thiol molecule. Our experiments suggest that resist-assisted atom lithography can be realized with group III elements and possibly extended to new neutral atomic species.
2005
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Complex Light-Mask Generation for Atom Guiding by Time and Frequency Domain Intensity Superposition, Laser Physics 15, 95 (2005)BibTeXABSTRACT »We propose to generate a complex light mask for atom nanofabrication by multiplexing light fields sequentially in the time domain or synchronously in the frequency domain. The method effectively superposes intensities rather than electric fields and may be useful for atomic beams at thermal velocity and also at very slow velocities.
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The atom pencil: serial writing in the sub-micrometre domain, Appl. Phys. B 80, 941 (2005)BibTeXABSTRACT »The atom pencil we describe here is a versatile tool that writes arbitrary structures by atomic deposition in a serial lithographic process. This device consists of a transversely laser-cooled and collimated cesium atomic beam that passes through a 4-pole atom-flux concentrator and impinges on to micron- and sub-micron-sized apertures. The aperture translates above a fixed substrate and enables the writing of sharp features with sizes down to 280 nm. We have investigated the writing and clogging properties of an atom pencil tip fabricated from silicon oxide pyramids perforated at the tip apex with a sub-micron aperture.
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Atomic nanofabrication: perspectives for serial and parallel deposition , J. Phys.: Conference Series 19, 118 (2005)BibTeXABSTRACT »Recent advances in atomic nanofabrication with laser manipulated atomic beams are discussed with regard to the creation of arbitrary structures.
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Advancing atomic nanolithography: cold atomic Cs beam exposure of alkanethiol self-assembled monolayers, J. Phys.: Conference Series 119, 109 (2005)BibTeXABSTRACT »We report the results of a study into the quality of functionalized surfaces for nanolithographic imaging. Self-assembled monolayer (SAM) coverage, subsequent post-etch pattern definition and minimum feature size all depend on the quality of the Au substrate used in atomic nanolithographic experiments. We find sputtered Au substrates yield much smoother surfaces and a higher density of {111} oriented grains than evaporated Au surfaces. A detailed study of the self-assembly mechanism using molecular resolution AFM and STM has shown that the monolayer is composed of domains with sizes typically of 5-25 nm, and multiple molecular domains can exist within one Au grain. Exposure of the SAM to an optically-cooled atomic Cs beam traversing a two-dimensional array of submicron material masks ans also standing wave optical masks allowed determination of the minimum average Cs dose (2 Cs atoms per SAM molecule) and the realization of
2004
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One- and two-color laser spectroscopy of indium vapor in an all-sapphire cell, Phys. Rev. A 70, 033810 (2004)BibTeXABSTRACT »We present saturation and polarization laser spectroscopy experiments of indium vapor with a single color on the 410 nm transition and with two colors at 410 and 451 nm. The spectra observed by polarization spectroscopy are discussed in terms of a quantitative model. The line shapes observed with two-color spectroscopy can phenomenologically be described taking into account hyperfine changing collisions, velocity changing collisions, and dark resonances. As an application, we actively stabilized a 410 nm diode laser on the resonances of saturation and polarization spectroscopy, and obtained long term frequency stabilities in the 100 kHz–1 MHz range.
2003
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Atom lithography, Yearbook of Science and Technology, McGraw-Hill, (2003)BibTeXABSTRACT »Atom lithography designates a physical method where the forces exerted by interfering laser beams on the atoms of an atomic beam are used to steer the atoms into nanostructures fabricated on a plane surface. While atom lithography is the most frequently used term, the method is also known as light-force lithography and atomic nanofabrication (ANF).
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Atomic nanofabrication with complex light fields, Appl. Phys. B 77, 1-9 (2003)BibTeXABSTRACT »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.
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Atomic nanofabrication: atomic deposition and lithography by laser and magnetic forces, J. Phys. D: Appl. Phys. 36, R17-R38 (2003)BibTeXABSTRACT »Atomic deposition on a surface can be controlled at the nanometre scale by means of optical and magnetic forces. Impingement of atoms on the surface can lead to growth of a structured array (direct deposition) or to chemical modifications of the surface (neutral atom lithography). In this report we survey requirements, present the current results, and explore the potential applications of this method of nanofabrication.
2002
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Atom Lithography with a Holographic Light Mask, Phys. Rev. Lett. 88, 083601 (2002)BibTeXABSTRACT »In atom lithography with optical masks, deposition of an atomic beam on a given substrate is controlled by a standing light-wave field. The lateral intensity distribution of the light field is transferred to the substrate with nanometer scale. We have tailored a complex pattern of this intensity distribution through diffraction of a laser beam from a hologram that is stored in a photorefractive crystal. This method can be extended to superpose 1000 or more laser beams. The method is furthermore applicable during growth processes and thus allows full 3D structuring of suitable materials with periodic and nonperiodic patterns at nanometer scales.
2001
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Magnetic whispering-gallery mirror for atoms, Phys. Rev. A 63, 053405 (2001)BibTeXABSTRACT »Videotape with a sinusoidal magnetization of 31 μm wavelength is used to reflect Cs atoms with unit reflectivity in a 75 m/s atomic beam. The atoms serve as a probe, allowing us to measure the magnetic field at the surface. A technique is presented for mounting the videotape so that its surface can be curved to a specific shape or made flexible. We show that such a reflector provides high-quality grazing-incidence atom optics and we demonstrate deflections as large as 23° in a whispering-gallery geometry.
2000
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Nanoscale focusing of atoms with a pulsed standing wave, Appl. Phys. B 70, 689 (2000)BibTeXABSTRACT »We have theoretically and experimentally investigated the focusing properties of a detuned pulsed standing wave onto a beam of neutral atoms. In close analogy to the continuous-wave situation the dipole force leads to a periodic focusing of atoms with a period of λ/2, provided an adiabatic condition is fulfilled. Pulsed laser light is conveniently converted to short wavelengths and hence offers advantages in the application of atom lithography with elements of technological interest having blue or UV resonance lines.
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High-brilliance Zeeman-slowed cesium atomic beam, Phys. Rev. A 61, 013405 (2000)BibTeXABSTRACT »We have built a Zeeman-slower apparatus which produces a slow and cold cesium atomic beam. The atomic beam has a mean velocity in the range 35–120 m/s and a high atomic current of more than 2×10^10 cold atoms/s. A small longitudinal velocity spread was achieved by optimizing the termination of the slowing process. The measured value of less than 1 m/s is consistent with a numerical simulation of the slowing process. With a magnetic lens and a tilted two-dimensional optical molasses stage, the slow atomic beam is transversely compressed, collimated, and deflected. We achieve a transverse temperature below the Doppler limit. The brilliance of this beam has been determined to be 7×10^23 atoms s^-1 m^-2 sr^-1. By optical pumping the slow atomic beam can be polarized in the outermost magnetic substates F=4,mF=±4, of the cesium ground state. This brilliant beam is an ideal source for experiments in atom optics and atom lithography.
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GaN blue diode lasers: a spectroscopist's view, Appl. Phys. B 70, 567 (2000)BibTeXABSTRACT »We have characterized the spectroscopic properties of one of the first samples of blue-emitting diode lasers based on GaN. With such a laser diode operated inside a standard extended cavity arrangement we find a mode-hop free tuning range of more than 20 GHz and a linewidth of 10 MHz. Doppler-free spectroscopy on an indium atomic beam reveals the isotope shift between the two major indium isotopes as well as efficient optical pumping.
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Reflection of cold atoms by a cobalt single crystal, Appl. Phys. B 70, 661 (2000)BibTeXABSTRACT »We have demonstrated that a cobalt single crystal can be used to make a remarkably smooth retro-reflector for cold paramagnetic atoms. The crystal is cut so that its surface lies in the (0001) plane and the atoms are reflected by the magnetic field above the surface due to the self-organized pattern of magnetic domains in the material. We find that the reflectivity for suitably polarized atoms exceeds 90% and may well be unity. We use the angular spread of a reflected atom cloud to measure the roughness of the mirror. We find that the angular variation of the equivalent hard reflecting surface is (3.1±0.3°)rms for atoms dropped onto the mirror from a height of 2 cm.
1999
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Reflection of a slow cesium atomic beam from a naturally magnetized Nd-Fe-B surface, Appl. Phys. B 69, 501 (1999)BibTeXABSTRACT »We have demonstrated the partly directed reflection of a slow cesium atomic beam by using the natural magnetic stray field above a Nd-Fe-B surface. From these experiments we determine the reflectivity and a minimum value for the magnetic stray field directly at the surface.
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Efficient magnetic guiding and deflection of atomic beams with moderate velocities, Appl. Phys. B 69, 217 (1999)BibTeXABSTRACT »We have studied guidance and deflection of a beam of cesium atoms by a strong toroidal magnetic quadrupole field. The beam guide is made from permanent magnets sustaining a radial field gradient of 2.8 T/cm. Atoms with moderate longitudinal velocities ranging from 30 m/s to 70 m/s were inserted across the 10-mm-diameter aperture of a 24.5° arc with radius 300 mm. We have measured transmission and beam divergence and find good agreement with ray-tracing calculations and analytical estimates. The magnetic beam guide allows for 100% transmission of heavy atoms over large angles.
1997
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Atomlithographie, Phys. J. 53, 523 (1997)BibTeXABSTRACT »Grofitechnisch angewandte optische Lithographieverfahrenstofien bei Auflosungen unter 100 nm auf eine prinzipielle Grenze. Die Lithographie mit neutralen Atomstrahlen bietet dazu insbesondere beim parallelen Schreiben periodischer Strukturen eine interessante, noch junge Alternative. Indem man die Wechselwirkung der Atome mit Lichtmasken ausnutzt, gelingt es, grofiflachig periodische Linienmuster und verschiedene zweidimensional periodische Strukturen mit einer Auflosung unter 100 nm zu erzeugen. Dabei werden Atome entweder direkt auf einem Substrat deponiert oder zur Modifikation organischer Resists genutzt. Der folgende Beitrag gibt einen herblick iiber den Stand der Lithographie mit Atomstrahlen.
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Nanoscale atomic lithography with a cesium atomic beam, Appl. Phys. B 65, 419 (1997)BibTeXABSTRACT »We have demonstrated the lithographic production of a periodic nanostructure by focusing a transversely laser cooled cesium atomic beam with a standing-wave light field. With a self-assembled monolayer used as the resist on a gold surface, exposure to cesium atoms locally changes the wetability. Subsequently a wet-etching process transfers the pattern to the underlying gold film. We have generated lines with a separation of half the wavelength of the cesium D2 line (852 nm) and a width of about 120 nm and covering a large area of approximately 1 mm^2.
1996
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Pattern generation with cesium atomic beams at nanometer scales, Appl. Phys. B 63, 649 (1996)BibTeXABSTRACT »We have demonstrated that a cesium atomic beam can be used to pattern a gold surface using a self assembling monolayer (SAM) as a resist. A 12.5 µm period mesh was used as a proximity mask for the atomic beam. The cesium atoms locally change the wetability of the SAM, which allows a wet etching reagent to remove the underlying gold in the exposed regions. An edge resolution of better than 100 nm was obtained. The experiment suggests that this method can either be used as a sensitive position detector with nanometer resolution in atom optics, or for nanostructuring in a resist technique.
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