Atom Lithography Research Articles

Controllable visibility and resolution of Nth-order Talbot imaging with pseudo-thermal light.

The theoretical proposal for an improved Talbot imaging technique has been analyzed in a periodic object illuminated by a pseudo-thermal light source and detected only by two detectors in two imaging schemes. The improved effect of lensless grating ghost image and Talbot image quality (fringe resolution and visibility) can be attributed to the higher correlation orders N. While at a certain order N, the spatial resolution of Talbot carpet patterns is determined by two-photon bunching effect, which depends on the positions of the periodic object and two detectors and different detection methods. Moreover, the sub wavelength of spatial correlation peaks and Talbot images obtained, when we use two asynchronous scanning detectors or an accelerated scanning detector. The present imaging schemes have the characteristic of the controllable image visibility and resolution, which has a potential application in periodic image reconstructions, sub wavelength resolution microscopy and sub wavelength atom lithography.

Creation of polarization gradients from superposition of counter propagating vector LG beams.

We present a detailed theoretical analysis of the formation of standing waves using cylindrically polarized vector Laguerre-Gaussian (LG) beams. It is shown that complex interplay between the radial and azimuthal polarization state can be used to realize different kinds of polarization gradients with cylindrically symmetric polarization distribution. Expressions for four different cases are presented and local dynamics of spatial polarization distribution is studied. We show cylindrically symmetric Sisyphus and corkscrew type polarization gradients can be obtained from vector LG beams. The optical landscape presented here with spatially periodic polarization patterns may find important applications in the field of atom optics, atom interferometry, atom lithography, and optical trapping.

Fabrication and measurement of traceable pitch standard with a big area at trans-scale

Atom lithography with chromium can be utilized to fabricate a pitch standard, which is directly traceable to the wavelength of the laser standing waves. The result of a calibrated commercial AFM measurement demonstrates that the pitch standard is (212.8±0.1) nm with a peak-to-valley-height (PTVH) better than 20 nm. The measurement results show the high period accuracy of traceability with the standing laser wavelength (λ/2 = 212.78 nm). The Cr nano-grating covers a 1000 μm×500 μm area, with a PTVH better than 10 nm. The feature width broadening of the Cr nanostructure has been experimentally observed along the direction of the standing waves. The PTVH along the Gaussian laser direction is similar to a Gaussian distribution. Highly uniform periodic nanostructures with a big area at the millimeter scale, and the surface growth uniformity of the Cr nano-grating, show its great potential in the application of a traceable pitch standard at trans-scales.

An Atom Laser over Optical Lasers

An atom laser is a coherent state of propagating atoms. They are created out of a Bose Einstein Condensation (BEC) of atoms which are output coupled using various techniques. An optical laser or conventional laser generates a coherent beam of light waves where as an atom laser produces a coherent beam of matter waves. An atom laser will have a major impact on the fields of atom optics, atom lithography and precision measurements.The Himalayan Physics Vol. 4, No. 4, 2013 Page: 99-101 Uploaded date: 12/23/2013

Coherent atom lithography with nanometer resolution

The resolution of optical lithography and the spacing of atom lithography are limited by about half of the wavelength due to the Rayleigh limit. Here we propose a coherent atom lithography experiment which can print nanometer structures. In this proposal, we show that subwavelength spatial distribution of the atoms in the excited state can be achieved by inducing spatially modulated Rabi oscillations in two-level atoms. We use the internal energy of the atoms to excite the photoresist and it can then print the subwavelength structure into the photoresist. For the peak Rabi frequency of about 2 GHz and the recoil limited collimation, we show that sub-$10\text{-nm}$ spacing in both one- and two-dimensional space is possible.

Atom lithography with subwavelength resolution via Rabi oscillations

We propose two atom lithography techniques with subwavelength resolution based on position-dependent Rabi oscillations. Our method either uses neutral or ionized atoms to write subwavelength patterns. We illustrate our proposal by numerical simulations of an experimental setup using rubidium Rydberg atoms. We show that, for a microwave wavelength of 1.4 cm, a spacing of a few hundred nanometers is possible.

Structured mirror array for two-dimensional collimation of a chromium beam in atom lithography

Direct-write atom lithography, one of the potential nanofabrication techniques, is restricted by some difficulties in producing optical masks for the deposition of complex structures. In order to make further progress, a structured mirror array is developed to transversely collimate the chromium atomic beam in two dimensions. The best collimation is obtained when the laser red detunes by natural line-width of transition 7S3 → 7P04 of the chromium atom. The collimation ratio is 0.45 vertically (in x axis), and it is 0.55 horizontally (in y axis). The theoretical model is also simulated, and success of our structured mirror array is achieved.

Generation of surface optical vortices by evanescent Bessel beams

We present that a set of high order Bessel beams when internally reflected at a dielectric/vacuum interface can create distinct evanescent light modes in each of which the intensity distribution is restricted to a sub-wavelength region near the interface outside the dielectric. We believe that this could really facilitate lateral optical manipulation of nano-particles and neutral atoms along the interface. Similarly, the set-up could lead to the formation of two-dimensional surface optical vortices that possibly will give rise to attractive phenomena, including pattern rotation liken to a surface optical Ferris wheel. Applications are envisaged to be in atom lithography, optical surface tweezers, and spanners. Key words: Bessel beam, optical surface tweezers, optical surface spanners.

Method of identifying the relative position between standing wave of laser light and substrate in atom lithography

Standing wave of laser light acts as an array of lenses to focus the moving atoms in atom lithography. The position between standing wave and substrate plays an important role in determining the quality of depositional nanometer lines. Using the rule of Gaussian beam, a method of accurately identifying the position of standing wave of laser light is reported. By adjusting accurately the displacement stage which carries the beam focus lens and reflective mirror, the laser beam is subsequently shielded by depositional substrate. Signal of photoelectric detector is changed because of shielding the standing wave, so we can convert the displacement of standing wave into electrical signal. Positioning the standing wave against substrate is achieved by using the value of waist diameter of standing wave of laser light. Theoretical model is developed according to the experimental process. The result of numerical computation coincides well with the experimental record. This method realizes accurately positioning standing wave of laser light against substrate, and it provides the experimental basic for deeply studying the influence of the distance between standing wave and substrate on the quality of depositional nanometer lines.

Feature width miniaturization in atom nanolithography with double standing wave layers

Periodic nanostructures spaced by half of the wavelength can be obtained by the technology of laser-focused atomic deposition. Experimental result with single standing wave layer is presented, with a periodicity of 213 ± 0.1 nm, a height of 4 nm, and a feature width of 64 ±6 nm. To further minimize the feature width,focusing and depositing characteristics of double standing wave layers are numerically simulated with optimized particle optics model. It is shown that the spherical aberration is reduced significantly. The predicted feature width is 18.2 nm and the height is approximately 12.6 nm when the powers of the two standing wave layers are 6 and 14 mW, respectively. Well-defined line occurs even when the full-width at half-maximum (FWHM) of transverse angular spread reaches 0.5 mrad. OCIS codes: 140.3325, 220.3740, 220.4241. doi: 10.3788/COL201210.S21403. The fabrication of nanoscale structures by neutral atom lithography has the potential to significantly put forward the nanotechnology, ranging from device miniaturization in electronic industry to nanometrology. Over the last two decades, one-dimensional (1D) structures with this direct deposition technique have been grown with sodium [1] , chromium [2,3] , cesium [4,5] , aluminum [6] , ytterbium [7] , iron [8] , barium [9] , and metastable helium [10] . Focusing and depositing char

Structure formation in atom lithography using geometric collimation

Atom lithography uses standing wave light fields as arrays of lenses to focus neutral atom beams into line patterns on a substrate. Laser cooled atom beams are commonly used, but an atom beam source with a small opening placed at a large distance from a substrate creates atom beams which are locally geometrically collimated on the substrate. These beams have local offset angles with respect to the substrate. We show that this affects the height, width, shape, and position of the created structures. We find that simulated effects are partially obscured in experiments by substrate-dependent diffusion of atoms, while scattering and interference just above the substrate limit the quality of the standing wave lens. We find that in atom lithography without laser cooling the atom beam source geometry is imaged onto the substrate by the standing wave lens. We therefore propose using structured atom beam sources to image more complex patterns on subwavelength scales in a massively parallel way.

Simulation of Two-Dimensional Transverse Laser Cooling of Cesium Beam from Pyramidal Magneto-Optical Trap Atom Funnel

Simulation of two-dimensional (2D) transverse laser cooling of Cs atomic beam from pyramidal magneto-optical trap atom funnel (PMOTAF) conceived for atom lithography is presented. The results show that both the minimum full width at half maximum (FWHM) and the maximum peak value of the spatial profile of the atomic beam occur at the frequency detuning of optical molasses equals to -0.5 Г. Moreover, for each frequency detuning, an increase in the intensity of the optical molasses leads to smaller FWHM and higher peak value. The not negligible role of gravity on the atomic beam of sub-thermal longitudinal velocity along the horizontal direction is that every atomic trajectory possesses a parabolic motion either before or after laser cooling which leads to a noticeable displacement of the peak value at the observation plane with respect to the starting point.

一维原子光刻经典模型的优化

一维原子光刻经典模型的优化

The research of motorial characteristic of sodiumatoms in standing wave field

Direct write atom lithography is a new technique in which resonant light is used to pattern an atomic beam and the nanostructures are formed when the atoms deposit on the substrate. The motion of sodium atoms in standing wave filed is discussed. Based on the semi-classical model, this paper analyses the motion equation of sodium atom in the laser standing wave field, and then gets the trajectory of the atoms in the standing wave field by analytical simulation for different longitudinal and transverse velocities. The simulative results show that the FWHM width of stripes was 2.78 nm and the contrast was 38.5 ∶1 for the optimal longitudinal velocity, while that of the stripes was 29.1 nm and the contrast was 15 ∶1 for non-optimal longitudinal velocities. At the same time, the results show that the FWHM width of stripes was 4.2 nm and the contrast was 20 ∶1 when the divergence of atomic beam was 0.15 mrad. Whereas, the stripes presented Multi-peaked configuration and the quality deteriorated with the divergence of atomic beam increased to 1.5 mrad.

Chromium atom deposition in elliptical standing wave filed

Direct-write atom lithography is a new technique in which resonant light is used to pattern an atomic beam and the nanostructures are formed when the atoms deposit on a substrate. The motorial characteristics of chromium atoms in an elliptical standing wave filed are discussed, and the simulation results are given with different deflective angles of elliptical standing wave. The full width at half maximum (FWHM) is 3.2 nm and the contrast is 36 ∶1 with a deflective angle of 0. The FWHM is 6.5nm and the contrast is 24 ∶1 with a deflective angel of 15, but when the deflective angle reaches 30, the stripe splits and two-peak configuration is formed.

Nanofabrication by magnetic focusing of supersonic beams

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 microns, are predicted. This scheme is applicable both to precision patterning of surfaces with metastable atomic beams and to direct deposition of material.

Atom lithography with near-resonant standing waves

We study the optimal focusing of two-level atoms with a near-resonant standing wave light, using both classical and quantum treatments of the problem in the thin- and thick-lens regimes. It is found that the near-resonant standing wave focuses the atoms with a reduced background in comparison with far-detuned light fields. For some parameters, the quantum atomic distribution shows even better localization than the classical one. Spontaneous emission effects are included via the technique of quantum Monte Carlo wave function simulations. We investigate the extent to which nonadiabatic and spontaneous emission effects limit the achievable minimal size of the deposited structures.

An ellipsoidal mirror for focusing neutral atomic and molecular beams

Manipulation of atomic and molecular beams is essential to atom optics applications including atom lasers, atom lithography, atom interferometry and neutral atom microscopy. The manipulation of charge-neutral beams of limited polarizability, spin or excitation states remains problematic, but may be overcome by the development of novel diffractive or reflective optical elements. In this paper, we present the first experimental demonstration of atom focusing using an ellipsoidal mirror. The ellipsoidal mirror enables stigmatic off-axis focusing for the first time and we demonstrate focusing of a beam of neutral, ground-state helium atoms down to an approximately circular spot, (26.8±0.5) μm×(31.4±0.8) μm in size. The spot area is two orders of magnitude smaller than previous reflective focusing of atomic beams and is a critical milestone towards the construction of a high-intensity scanning helium microscope.

Atom lithography with metastable helium

A bright metastable helium (He∗) beam is collimated sequentially with the bichromatic force and three optical molasses velocity compression stages. Each He∗ atom in the beam has 20 eV of internal energy that can destroy a molecular resist assembled on a gold coated silicon wafer. Patterns in the resist are imprinted onto the gold layer with a standard selective etch. Patterning of the wafer with the He∗ was demonstrated with two methods. First, a mesh was used to protect parts of the wafer making an array of grid lines. Second, a standing wave of λ=1083 nm light was used to channel and focus the He∗ atoms into lines separated by λ/2. The patterns were measured with an atomic force microscope establishing an edge resolution of 80 nm. Our results are reliable and repeatable.

Atom lithography without laser cooling

Using direct-write atom lithography, Fe nanolines are deposited with a pitch of 186 nm, a full width at half maximum (FWHM) of 50 nm, and a height of up to 6 nm. These values are achieved by relying on geometrical collimation of the atomic beam, thus without using laser collimation techniques. This opens the way for applying direct-write atom lithography to a wide variety of elements.