Abstract:
A method and system for assembling a quasicrystalline heterostructure. A plurality of particles is provided with desirable predetermined character. The particles are suspended in a medium, and holographic optical traps are used to position the particles in a way to achieve an arrangement which provides a desired property.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     The present application claims priority to U.S. Provisional Application No. 60/697,872, filed on Jul. 8, 2005 and incorporated herein by reference in its entirety. 
     
    
       [0002]     This work was supported by the National Science Foundation through Grant Numbers DMR0451589, DMR021306 and DMR0243001, and US Department of Energy grant DE-FG02-91ER40671. 
     
    
     FIELD OF THE INVENTION  
       [0003]     This invention relates generally to the field of quasicrystalline heterostructures. More particularly the invention relates to the assembly of quasicrystalline photonic heterostructures with specified orientational symmetry in two dimensions, or along any two dimensions in a three-dimensional structure, or with any specified three-dimensional quasicrystalline symmetry, and also the use of holographic optical traps (HOTS) to perform that assembly and to the use of those HOTS assembled structures for a variety of uses.  
       BACKGROUND OF THE INVENTION  
       [0004]     Crystalline materials have long been exploited in many optical and electronic applications for physical properties arising from their crystalline symmetry. Although such crystalline materials allow many technological applications to be fulfilled, there are limitations imposed by such crystalline symmetry. For example, ordered arrangements of dielectric materials with alternating domains of high and low index of refraction are known to exhibit a property for the transmission of light known as a photonic bandgap. The optical properties of a photonic bandgap material are characterized by a range of frequencies of light for which light cannot propagate, nor is it absorbed. This property is analogous to the electronic bandgaps that arise in semiconductors for the transport of electrons, and should result in a similarly broad spectrum of applications. The extent of a material&#39;s photonic bandgap depends both on the dielectric properties of the constituent dielectric materials and also on the symmetries of their three-dimensional arrangement. The limited set of distinct symmetries available for crystalline arrangements require a very large contrast in dielectric constant to achieve a full photonic bandgap, and these symmetries result in optical materials whose optical properties are very sensitive to structural and chemical defects. By contrast, quasicrystals are known that have far higher rotational symmetries than is possible for crystals. They consequently should exhibit larger and more uniform photonic bandgaps than any crystalline arrangement of the same materials, and should have optical properties that are more robust against defects and disorder. Two-dimensional and three-dimensional quasicrystalline arrangements of materials therefore should have a wide range of technological applications based on their optical and other physical properties.  
       SUMMARY OF THE INVENTION  
       [0005]     It is therefore an object of the invention to provide an improved system and method for fabricating quasicrystalline structures.  
         [0006]     It is another object of the invention to provide an improved system and method for fabricating quasicrystalline photonic heterostructures using holographic optical traps.  
         [0007]     It is also an object of the invention to provide an improved article of manufacture of a three dimensional quasicrystalline photonic heterostructure.  
         [0008]     It is a further object of the invention to provide an improved system and method for constructing materials having photonic band gaps forbidden in crystalline materials.  
         [0009]     It is yet another object of the invention to provide an improved system and method for constructing rotationally symmetric heterostructures having optical, mechanical, chemical, biological, electrical and magnetic properties unachievable by crystalline materials.  
         [0010]     It is an additional object of the invention to provide an improved quasicrystalline heterostructure having programmable optical, mechanical, biological, electrical, magnetic and chemical properties.  
         [0011]     It is also another object of the invention to provide an improved system and method for constructing a quasicrystalline structure with specified Brillouin zones for selected technological applications.  
         [0012]     It is also a further object of the invention to provide an improved system and method for constructing a quasicrystalline material with a substantially spherical Brillouin zones.  
         [0013]     It is yet an additional object of the invention to provide an improved system and method for constructing a quasicrystalline material having long range orientational order without transitional periodicity and constructed to operate in a predetermined manner responsive to at least one of an electrical field, a magnetic field and electromagnetic radiation.  
         [0014]     It is also a further object of the invention to provide an improved system and method for constructing quasicrystalline heterostructures which can be switched from one structural state to another state by repositioning particles to thereby modify physical, biological, and chemical properties of the arrangement.  
         [0015]     It is still another object of the invention to provide an improved system and method for constructing quasicrystalline heterostructures by use of holographic optical traps to dynamically modify chemical and physical properties in accordance with time sensitive requirements.  
         [0016]     It is another object of the invention to provide an improved system and method for constructing quasicrystalline heterostructures having holographic optical traps to form engineered features which enable creation of narrow band waveguides and frequency selective filters of electromagnetic radiation.  
         [0017]     It is yet another object of the invention to provide an improved system and method for organizing disparate components using holographic optical traps to position selectable components in a quasicrystalline heterostructure for establishing chemical, biological and physical properties for a desired technological application.  
         [0018]     It is also an object of the invention to provide an improved system, method of manufacture and article of manufacture with deliberately incorporated defects for programmably achieving a variety of electrical, optical, magnetic, mechanical, biological and chemical properties and applications.  
         [0019]     It is yet an additional object of the invention to provide an improved method and article of manufacture of a quasicrystal with replaced spheres or other components of different size or shape to modify local photonic characteristics of the quasicrystal.  
         [0020]     It is a further object of the invention to provide an improved method and article of manufacture with selective replacement of one or more spheres on other molecular component geometries of different chemical composition or at different sites than a given quasicrystalline site to create new properties or break the quasicrystalline symmetry to create new properties for a variety of applications.  
         [0021]     It is another object of the invention to provide an improved method and article of manufacture of a quasicrystal with a particular domain having a topological defect, such as a phase slip, like a grain boundary in ordinary crystalline molecules, thereby giving rise to new useful properties.  
         [0022]     It is another object of the invention to provide an improved method and article of manufacture of two or more quasicrystalline domains created by holographic trap manipulation to create higher order structures with the resulting combination having optical properties selected from each component domain.  
         [0023]     It is still an additional object of the invention to provide an improved method and article of manufacture for creating combinations of one or more quasicrystalline domains with one or more crystalline domains to create useful higher order structures.  
         [0024]     It is a further object of the invention to provide an improved method and article of manufacture involving assembly of crystalline and quasicrystalline domains using optical tweezers and/or other particle force assembly methodologies including self assembly, electropheresis, and optical gradient fields to create useful combination structures.  
         [0025]     These and other objects, advantages and features of the invention, together with the organization and manner of operations thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings described below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1 ( a ) illustrates a view of silica spheres organized by holographic optical tweezers into a planar pentagonal quasicrystal (the scale bar indicates 5 micrometers);  FIG. 1 ( b ) illustrates a heptagonal quasicrystalline domain;  FIG. 1 ( c ) illustrates an octagonal quasicrystalline domain arrangement; and  FIG. 1 ( d ) illustrates an octagonal quasicrystalline domain with an embedded waveguide;  
         [0027]      FIG. 2 ( a ) illustrates a first of four views of an icosahedron assembled from dielectric colloidal spheres using holographic optical traps;  FIG. 2 ( b ) illustrates a second view with a 2-fold symmetry axis;  FIG. 2 ( c ) illustrates a third view with a 5-fold symmetry axis and  FIG. 2 ( d ) illustrates a fourth view midplane;  FIG. 2 ( e ) illustrates the progressive assembly of the colloidal quasicrystal illustrated in  FIG. 2 ( a )-( d ); and  
         [0028]      FIG. 3 ( a ) shows a holographic assembly of a three dimensional colloidal quasicrystal with the particles trapped in a two dimensional projection of a three dimensional icosahedron quasicrystalline lattice;  FIG. 3 ( b ) shows particles displaced into the fully three dimensional configuration with the shaded region the one embedded icosahedron;  FIG. 3 ( c ) shows reducing the lattice constant to create a compact three dimensional quasicrystal; and  FIG. 3 ( d ) illustrates a measured optical diffraction pattern displaying 10-fold symmetric peaks for the constructed quasicrystal; and  FIG. 3 ( e ) illustrates the progressive assembly of the colloidal quasicrystal illustrated in  FIG. 3 ( a )-( d ). 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0029]     A system and method have been developed for the construction of quasicrystalline heterostructures for a wide variety of technological applications. Various articles of manufacture and compositions of matter can be prepared. In a most preferred embodiment, holographic optical traps are used as the starting tool to position a selected particle in a given position. Therefore, in the preferred embodiment the approach is based on the well known holographic optical trapping technique in which computer-generated holograms are projected through a high numerical aperture microscope objective lens to create large three dimensional arrays of optical traps. In our implementation, light at 532 nm from a frequency doubled diode-pumped solid state laser (Coherent Verdi) is imprinted with phase only holograms using a liquid crystal spatial light modulator (SLM) (Hamamatsu X8267 PPM). The modified laser beam is relayed to the input pupil of a 100× NA 1.4 SPlan Apo oil immersion objective mounted in an inverted optical microscope (Nikon TE2000U), which focuses it into optical traps. The same objective lens is used to form images of trapped objects by using the microscope&#39;s conventional imaging train. As a soft fabrication technique, holographic assembly requires substantially less processing than conventional methods such as electron beam lithography and can be applied to a wider range of materials. Assembly with holographic optical traps lends itself readily to creating nonuniform architectures (e.g., microstructural arrangements, articles of manufacture and compositions of matter) with specifically engineered features, such as the channel embedded in the octagonal domain in  FIG. 1 ( d ). Such structures can, for example, act as narrowband waveguides and frequency-selective filters for visible light.  
         [0030]     Holographic trapping&#39;s ability to assemble free-form heterostructures extends also to three dimensions. The sequence of images of a rolling icosahedron in  FIG. 2 ( a )-( d ) show how the colloidal spheres&#39; appearance changes with distance from the focal plane. This sequence demonstrates that holographic trapping with a single laser beam can successfully organize spheres into vertical stacks along the optical axis, while maintaining one sphere in each trap.  
         [0031]     The icosahedron itself is the fundamental building block of a class of three dimensional quasicrystals, such as the example in FIGS.  3 ( a )-( d ). Building upon our earlier work on holographic assembly, we assemble a three dimensional quasicrystalline domain by first creating a two dimensional arrangement of spheres corresponding to the planar projection of the planned quasicrystalline domain (see  FIG. 3 ( a )). Next, we translate the spheres along the optical axis to their final three dimensional coordinates in the quasicrystalline domain, as shown in  FIG. 3 ( b ). One icosahedral unit is highlighted in FIGS.  3 ( a ) and ( b ) to clarify this process. Finally, the separation between the traps is decreased in  FIG. 3 ( c ) to create an optically dense structure. This particular domain consists of 173 spheres in 7 layers, with typical interparticle separations of 3 μm.  
         [0032]     The completed quasicrystal was gelled and its optical diffraction pattern recorded at a wavelength of 632 nm by illuminating the sample with a collimated beam from a HeNe laser, collecting the diffracted light with the microscope&#39;s objective lens and projecting it onto a charge-coupled device (CCD) camera with a Bertrand lens. The well defined diffraction spots clearly reflect the quasicrystal&#39;s five-fold rotational symmetry in the projected plane.  
         [0033]     Holographic assembly of colloidal silica quasicrystals in water is easily generalized to other materials having selectable optical, electrical, magnetic, chemical and mechanical properties for a wide variety of technological applications. Deterministic organization of disparate components under holographic control can be used to embed gain media in photonic band gap (PBG) cavities, to install materials with nonlinear optical properties within waveguides to form switches, and to create domains with distinct chemical functionalization. The comparatively small domains we have created can be combined into larger heterostructures through sequential assembly and spatially localized photopolymerization. In all cases, this soft fabrication process results in mechanically and environmentally stable materials that can be integrated readily into larger systems.  
         [0034]     Beyond the immediate application of holographic trapping to fabricating quasicrystalline materials, the ability to create and continuously optimize such a variety of articles of manufacture and compositions of matter enables new opportunities for achieving heretofore unattainable products and perform processes not possible. Many other functionalities can be performed, such as evaluating the dynamics and statistical mechanics of colloidal quasicrystals. The optically generated quasiperiodic potential energy landscapes described herein also can provide a flexible model system for experimental studies of transport through aperiodically modulated environments.  
         [0035]     In other embodiments, the above described methods of fabricating and manipulating quasicrystalline structures can further be employed to manipulate compositions of matter to introduce a variety of particular defects which can establish useful electrical, optical, biological, mechanical, magnetic and chemical attributes. Due to the many degrees of freedom available by virtue of the ability to establish these quasicrystalline structures and associated defects, one can achieve numerous different physical, mechanical and chemical properties, many of which are unachievable with crystalline or amorphous structures. These properties can be used in a wide variety of commercial areas spanning the electronics, computer, biological, chemical, optical, mechanical properties and magnetics fields.  
         [0036]     The technique further permits the manufacture of quasicrystals with replacement of spheres, or other components, with different size or shape spheres or different size or shape components, enabling modification of properties, such as, for example, photonic characteristics. This concept can also be applied to replace spheres or other size and shape component groups at selected locations with constituents of different chemical, mechanical, electrical, magnetic or optical character, thereby allowing controlled designs of quasicrystalline arrangements with different selectable properties useful in many commercial fields.  
         [0037]     In other embodiments domains of quasicrystals can be selectively modified to introduce phase slip boundaries, similar to grain boundaries in crystalline materials, to develop properties of interest for commercial exploitation. In addition, two or more quasicrystalline domains can be created by optical trap manipulation of particles to generate higher order structural components with physical and/or chemical properties characteristic of the properties of each component domain. In addition, such combinations can be integrated with crystalline domains to create further higher order structures for selectable commercial applications.  
         [0038]     The assembly of all these structures can be accomplished not only by use of optical tweezers but also by other particle force movement force sources. These other force movement sources can be used alone or in combination with the optical tweezers and these other particle force sources can include at least one of self assembly, other photonic methodologies and controllable electrical and magnetic fields. These methodologies allow controlled construction of virtually any desired structure exhibiting a wide range of programmed physical, biological or chemical properties.  
         [0039]     The following non-limiting example describes one method of assembling colloidal particles as a quasicrystal.  
       EXAMPLE  
       [0040]     Colloidal silica microspheres 1.53 μm in diameter (Duke Scientific Lot 5238) can be organized by first being dispersed in an aqueous solution of 180:12:1 (wt/wt) acrylamide, N,N methylenebisacrylamide and diethoxyacetophenone (all Aldrich electrophoresis grade). This solution rapidly photopolymerizes into a transparent polyacrylamide hydrogel under ultraviolet illumination, and is stable otherwise. Fluid dispersions were imbibed into 30 μm thick slit pores formed by bonding the edges of #1 coverslips to the faces of glass microscope slides. The sealed samples were then mounted on the microscope&#39;s stage for processing and analysis.  
         [0041]     Silica spheres are roughly twice as dense as water and sediment rapidly into a monolayer above the coverslip. A dilute layer of spheres is readily organized by holographic optical tweezers into arbitrary two dimensional configurations, including the quasicrystalline examples in FIGS.  1 ( a )-( d ). FIGS.  1 ( a ), ( b ) and ( c ) show planar pentagonal, heptagonal and octagonal quasicrystalline domains, respectively, each consisting of more than 100 particles. Highlighted spheres emphasize each domain&#39;s symmetry. These structures all have been shown to act as two dimensional PBG materials in microfabricated arrays of posts and holes.  FIG. 1  ( d ) shows an octagonal quasicrystalline domain with an embedded waveguide.  
         [0042]     While preferred embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with one of ordinary skill in the art without departing from the invention in its broader aspects. Various features of the invention are defined in the following claims.