Arbitrary Two-dimensional Patterns Research Articles

Negative index metamaterial at ultraviolet range for subwavelength photolithography

Abstract A negative index metamaterial (NIM) at ultraviolet range is constructed with stacked plasmonic waveguides. Based on the waveguides performing antisymmetric modes, the negative refractions of both wavevector and energy flow are realized when a TM-polarized light with a wavelength of 365 nm incidents on the plane of the layers. It is proved that the NIM could be introduced into subwavelength photolithography for extending working distance. Both theoretical and experimental results indicate that the patterns with a feature size of 160 nm can be reproduced in photoresist with a 100 nm-thick air working distance. Moreover, arbitrary two-dimensional patterns with a depth reach 160 nm can be obtained without diffraction fringe by employing a nonpolarized light. This design gives new insights into the manipulation of light. The improved working distance, well-shaped patterns over large area present an innovative method for improving subwavelength photolithography.

A Versatile Platform for Mass Spectrometry Imaging of Arbitrary Spatial Patterns.

A vision-system driven platform, RastirX, has been constructed for mass spectrometry imaging (MSI) of arbitrary two-dimensional patterns. The user identifies a region of interest (ROI) by drawing on a live video image of the sample with the computer mouse. Motion commands are automatically generated to move the sample to acquire scan data for the pixels in the ROI. Synchronization of sample stage motion with laser firing and mass spectrometer (MS) scan acquisition is fully automated. RastirX saves a co-registered optical image and the scan location information needed to convert raw MS data into imzML format. Imaging an arbitrarily shaped ROI instead of the minimal enclosing rectangle reduces contamination from off-sample material and significantly reduces acquisition time.

Mask-free construction of three-dimensional silicon structures by dry etching assisted gray-scale femtosecond laser direct writing

A mask-free micro/nano fabrication method is proposed for constructing arbitrary gradient height structures on silicon, combining gray-scale femtosecond laser direct writing (GS-FsLDW) with subsequent dry etching. Arbitrary two-dimensional patterns with a gradient concentration of oxygen atoms can be fabricated on the surface of undoped silicon wafer by FsLDW in air. After dry etching, various three-dimensional (3D) gradient height silicon structures are fabricated by controlling the laser power, scanning step, etching time, and etching power. As an example, a well-defined 3D Fresnel zone plate was fabricated on silicon wafer, which shows excellent focusing and imaging properties. The combination of high precision from dry etching and 3D fabrication ability on non-planar substrates of FsLDW, may broaden its applications in microelectronics, micro-optics, and microelectromechanical systems.

Charge sensor and particle trap based on z-cut lithium niobate

The generation of adhesive regions on a z-cut lithium niobate crystal without an additional voltage supply is demonstrated. We show that the origin of the attractive force in the respective solvent is electrophoresis, which can selectively trap charged particles in illuminated regions. Using digital holographic microscopy to measure the space-charge field in a y-cut crystal, we demonstrate the difference between electrophoretic and dielectrophoretic particle manipulation. The suggested method enables the creation of arbitrary two-dimensional patterns, circumventing restrictions originating from the crystal asymmetry. Furthermore, it allows the discrimination between charged particles of different signs, thus acting as a charge sensor.

Multiplexing and switching of virtual electrodes in optoelectronic tweezers based on lithium niobate

We introduce a method for trapping and arranging microparticles in arbitrary two-dimensional patterns with high flexibility. For this purpose, optoelectronic tweezers based on lithium niobate as photoconductor are used to create virtual electrodes through modulated illumination. The evolving field gradients arrange microparticles due to dielectrophoretic (DEP) forces and enable an all-optical approach for DEP. In order to increase flexibility further, we investigate multiplexed electrode structures for in situ reconfiguration of particle arrangements. Using the all-optical erasure of previously written virtual electrodes, we demonstrate electrode switching and sequential particle trapping in a microchannel for microfluidic applications.

Laser-directed hierarchical assembly of liquid crystal defects and control of optical phase singularities

Topological defect lines are ubiquitous and important in a wide variety of fascinating phenomena and theories in many fields ranging from materials science to early-universe cosmology, and to engineering of laser beams. However, they are typically hard to control in a reliable manner. Here we describe facile erasable “optical drawing” of self-assembled defect clusters in liquid crystals. These quadrupolar defect clusters, stabilized by the medium's chirality and the tendency to form twisted configurations, are shaped into arbitrary two-dimensional patterns, including reconfigurable phase gratings capable of generating and controlling optical phase singularities in laser beams. Our findings bridge the studies of defects in condensed matter physics and optics and may enable applications in data storage, singular optics, displays, electro-optic devices, diffraction gratings, as well as in both optically- and electrically-addressed pixel-free spatial light modulators.

Generation of super-resolution atomic state density distribution based on temporallycascaded multiple light exposures

We propose a novel approach to optical generation of superresolution atomic state density distribution based on interaction between Lambda- type atoms and temporally-cascaded driving fields. The scheme effectively inscribes multiplication of optical intensity profiles on atomic state density distribution, which can produce arbitrary patterns beyond the diffraction limit. The degree of resolution enhancement can be increased, not depending on the intrinsic nonlinearity of the photographic medium or the number of simultaneously interacting fields unlike the previous schemes. Procedures for drawing arbitrary two-dimensional patterns and effects of atomic state decoherence are described.

Nonlinear interferometric lithography for arbitrary two-dimensional patterns

A new, relatively simple experimental technique for generating arbitrary, two-dimensional patterns with high visibility and higher resolution than allowed by the Rayleigh criterion has been developed. The theoretical and experimental details of the method, based on repeated phase-coherent interference of four beams on a multiphoton absorber, are described. A sample pattern generated by numerical computer simulation of the technique is also shown.

In situ monitoring and control of material growth for high resolution electron beam induced deposition

During electron beam induced deposition on electron transparent membranes, the transmitted annular dark field (ADF) signal can be monitored. A method was developed to use the ADF signal to obtain insight into the growth process and to control the mass of individual nanometer-sized deposits. Arbitrary two-dimensional patterns can be defined. The smallest sampling time of the ADF signal monitoring is presently about 40ms. For arrays of dots that were deposited, the growth of each individual dot was monitored. It is observed that the growth is different for each dot, although the average deposit growth rate is linear with the dwell time. Apart from monitoring the ADF signal during the growth, the amount of deposited mass can be controlled for individual deposits by terminating the growth process when the ADF signal exceeds a threshold value. The dynamic ADF feedback control was applied to reduce variations in deposit mass. This attempt did not succeed, but the method was successfully applied to prevent the occurrence of a proximity effect. When the electron beam irradiates the side of an already existing structure, the amount of deposited material is higher than if the electron beam irradiates an area that is under normal incidence. With the dynamic ADF feedback control, this effect can be compensated in situ and the amount of deposited material that is probed by the beam is constant regardless of the local growth rate. The mass deposition resolution of the feedback system is estimated by assuming a volume and a density of the deposits. It is estimated that the ultimate mass resolution is a single molecule.

Two-dimensional atomic lithography by submicrometer focusing of atomic beams

We analyze a method for serial writing of arbitrary two-dimensional patterns using optical focusing of a collimated atomic beam. A spatial light modulator is used in a side illumination geometry to create a localized optical spot with secondary maxima that are well separated from the central peak. Numerical simulation of a lithography experiment using a magneto-optical trap as a source of cold Cs atoms, collimation and cooling in a magnetic guide, and optical focusing predicts full width at half maximum pixel sizes of 110 x 110 nm and writing times of about $20 \rm ms$ per pixel.

Quantum-interferometric optical lithography: Towards arbitrary two-dimensional patterns

As demonstrated by Boto et al. [Phys. Rev. Lett. 85, 2733 (2000)], quantum lithography offers an increase in resolution below the diffraction limit. Here, we generalize this procedure in order to create patterns in one and two dimensions. This renders quantum lithography a potentially useful tool in nanotechnology.

Decomposition of two-dimensional microlaser patterns

For an ordinary individually addressable microlaser array, a separate control line is used for each microlaser, which requires a large number of control lines for even a small array. An organization that reduces the width of the control stream and simplifies packaging is matrix addressing, in which microlasers are arranged at the crossings of horizontal and vertical control lines. We consider the problem of decomposing arbitrary two-dimensional microlaser patterns into matrix-addressable patterns that are applied time sequentially to realize the target pattern. We present a mathematical model for the decomposition process and present an algorithm for optimal decomposition. We also consider bake factor, in which no more than N microlasers in a neighborhood of M (where N < M) are enabled, which avoids thermal overload by limiting the density of enabled microlasers. We conclude with a case study and show that, for completely arbitrary two-dimensional patterns, the average number of time-sequential patterns is less than the number of rows in a square array.

Phase-shifting masks for microlithography: automated design and mask requirements

The problem of automated design of phase-shifting masks for enhanced-resolution optical lithography is examined. We propose a computationally viable algorithm for the rapid design of phase-shifting masks for arbitrary two-dimensional patterns. Our approach is based on the use of a class of optimal coherent approximations to partially coherent imaging systems described by the Hopkins model. These approximations lead to substantial computational and analytical benefits, and, in addition, the resultant approximation error can be quite small for imaging systems with coherence factor σ ≤ 0.5. These approximate models allow us to reduce the mask-design problem to the classical phase-retrieval problem in optics. A fast iterative algorithm, closely related to the Gerchberg–Saxton algorithm, is then applied to generate (suboptimal) phase-shifting masks. Analytical results related to practical requirements for phase-shifting masks are also presented. These results address questions related to the number of discrete phase levels required for arbitrary patterns and provide some insight into alternative strategies for the use of phase-shifting masks. A number of simulated phase-shifting mask-design examples are provided to illustrate the methods and ideas presented.