Abstract:
A system and method for bonding and unbonding of small objects using small adhesive particles. The system and method includes the use of a plurality of optical tweezers to manipulate objects to be bonded and adhesive particles suspended in a fluid. The objects to be bonded (or unbonded) and the adhesive particles are positioned by lower power optical tweezers and then an intense bonding optical tweezer is activated to cause the adhesive to join the objects together (or used to unbond objects).

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
       [0001]     The present application claims priority to U.S. Provisional Application No. 60/693,876, filed on Jun. 24, 2005 and incorporated herein by reference in its entirety. 
     
    
       [0002]     This work was supported by the National Science Foundation through Grant Number DBI-0233971 and DMR-0451589. 
     
    
     FIELD OF THE INVENTION  
       [0003]     The invention relates generally to a method and system for bonding small particles and objects using nanometer to micrometer-sized adhesive particles which are controlled by light beams such as holographic optical tweezers to perform the bonding operation. More particularly, the invention relates to the use of holographic optical tweezers to manipulate, chemically modify and cure small adhesive particles for bonding and other joining operations for small objects.  
       BACKGROUND OF THE INVENTION  
       [0004]     Dramatic progress has recently been made in the field of nanotechnology which has created greatly increased demand in the manipulation of small particles on nanometer to micrometer-sized geometries. For example, it is frequently desirable to form temporary and also permanent bonds which are on a very small scale. This can, for example, be problematic simply because of the small size scale or where the objects to be joined do not normally adhere, or where fusing the objects to establish a bond would involve undesirable chemical or physical changes of state.  
       SUMMARY OF THE INVENTION  
       [0005]     It is therefore an object of the invention to provide an improved system and method for bonding together and unbonding small particles.  
         [0006]     It is another object of the invention to provide an improved system and method for applying small adhesive particles to small objects for selectively bonding and unbending them.  
         [0007]     It is yet a further object of the invention to provide an improved system and method using a light beam, such as optical tweezers, to manipulate objects and adhesive particles to bond and/or unbond the objects.  
         [0008]     It is also an object of the invention to provide an improved system and method using holographic optical tweezers to manipulate, and at least one of chemically transform or heat selected objects and/or adhesive particles to enable bonding and/or unbonding operations.  
         [0009]     It is an additional object of the invention to provide an improved system and method for bonding similar or dissimilar objects without need for any special surface preparation.  
         [0010]     It is yet another object of the invention to provide an improved system and method for forming permanent bonds and/or temporary bonds among fluid dispersed microscopic objects manipulated by light beams such as holographic optical tweezers or other forms of optical tweezers.  
         [0011]     In accordance with the above objects and others explained hereinafter, as well as examples provided, the present invention involves a system and method for forming bonds (and unbending) using adhesive particles manipulated by optical tweezers. Various types of microscopic objects, from nanometer to micrometer size, can be readily bonded together (and unbonded) by judicious manipulation of adhesive particles relative to the objects to be bonded. This system and method also allow co-dispersal of small particles or objects and the adhesive in the same fluid medium.  
         [0012]     These and other objects, advantages and features of the invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the several drawings described below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1 ( a ) illustrates two objects suspended in a fluid with adhesive particles;  FIG. 1 ( b ) illustrates the two objects of  FIG. 1 ( a ) positioned against one another by using optical tweezers and adhesive particles are also collected at the junction by optical tweezers;  FIG. 1 ( c ) illustrates the system of  FIG. 1 ( b ) after turning off the optical tweezers used to position and activate the adhesive particles; and  FIG. 1 ( d ) illustrates a finally bonded object.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     A system and method illustrative of a preferred form of the invention is illustrated in FIGS.  1 ( a )- 1 ( d ). In  FIG. 1 ( a ) two objects  100  are trapped by the action of a plurality of light beams, such as optical tweezers  110 . Adhesive particles  120 , along with the objects  100 , are suspended in a fluid medium  130  which typically is a gel or liquid, but could also be any fluid environment capable of suspending the objects  100  and the adhesive particles  120 . As shown in  FIG. 1 ( a ) the objects  100  are not interacting in any substantial way with the adhesive particles  120 , and the optical tweezers  110  are also not interacting with the adhesive particles  120 . In an alternative embodiment the adhesive particles  120  and the objects  100  can be manipulated also with the use of optical field gradients, electrical fields and other photonic forces. Such forces can be adjusted to enable movement of the objects  100  and bonding with the adhesive particles  120  and also can be unbonded.  
         [0015]     In a preferred embodiment, the adhesive used for the particles  120  should be selected so that the adhesive particles  120  remain stably dispersed in the fluid medium  130  over at least the course of the assembly process and so that they do not ordinarily interact strongly with the objects  100  to be assembled. In the case that the objects  100  are to be manipulated by the optical traps  110 , it can be desirable to make the adhesive particles  120  interact only weakly with the optical traps  110 , so that they do not interfere with normal manipulation. Once the objects  100  are arranged in the desired configuration, one or more of the particularly intense light beams, such as optical tweezers  140 , are trained on the intended junction. This intense illumination forms a bond through any combination of the following described processes.  
         [0016]     In another embodiment the optical traps  110  and/or the above-referenced alternative sources for manipulation, bonding and unbonding can be used to initiate chemical changes, chemical bonding, shape rearrangement and other manipulations of the objects  100 . The adhesive particles  120  can also be selected to act as dissolving agents for debonding purposes. In addition, the user can have available a mixture of different types of adhesive particles  120 , such as particles for etching objects, for debonding and particles for constructing particular electronic, chemical, biological, mechanical and optical structures.  
         [0017]      FIG. 1 ( b ) shows the objects  100  brought into proximity in the desired configuration, and an additional bright or bonding optical tweezer  140  can be trained on the intended junction or joint area. The adhesive particles  120  stream to the junction or joint area, which also is heated by the intense illumination of the tweezer  140 . This causes the adhesive particles  120  to fuse to each other and to the objects  100 .  FIG. 1 ( c ) shows the system after the intense optical tweezer  140  is turned off, and a final bonding joint  150  has been formed. The completed object  160  is shown still localized by the optical tweezers  1   10 , which can be used to manipulate the combined object  160  for other processing, including additional gluing. Once the intense optical tweezer  140  is removed and the bonding joint  150  has cooled, no additional interaction between the adhesive particles  120  and the completed object  160  occurs.  FIG. 1 ( d ) shows the completed object  160  without applying the optical tweezers  110  and thus is floating freely in the suspending fluid medium  130 .  
         [0018]     Whereas an ordinary optical trap, such as the tweezers  110 , may not be effective at trapping one of the adhesive particles  120 , the intense tweezer  140  may either trap the adhesive particles  120  at the junction or else create a controllable rate of a flux of the adhesive particles  120  flowing toward the junction area. In the case that either the objects  100  to be joined, the adhesive particles  120 , or both, absorb some portion of the optical tweezer&#39;s incident photon flux. The resulting heating can be used to melt or otherwise fuse the adhesive particles  120  to each other and to the objects  100  to be joined, thereby forming the bonding or “glue” joint  150 . Similarly, the intense illumination at the tweezer&#39;s  140  focus can be used to excite photochemical transformations that achieve this bonding. In either case, the wavelength and power of laser light and the composition of the adhesive particles  120  can be selected to minimize undesirable transformations in the adhesive particles  120  and objects  100  before bonding and to optimize the final bond after. The resulting bond formed by the adhesive particles  120  can be predetermined such that the bond material can have a desired property, chemically or electrically, such as being a metallic bond, a non-conductor or a semiconductor.  
         [0019]     The following non-limiting description provides examples of preferred forms of the invention.  
       EXAMPLE 1  
       [0020]     As a practical demonstration of this system and method, we dispersed vacuum-grown GaN nanowires in a 5:1 mixture of tetrahydrofuran (THF) in water. These cylindrical nanowires, typically measuring 50 nanometers in diameter and 10 micrometers in length are stably dispersed in this solvent for at least several days. Thermoplastic colloidal spheres were codispersed by allowing the solvent to make contact with Norland Type 88 adhesive under ultraviolet illumination at room temperature. The resulting partially photocured plastic spheres are also stably dispersed in this solvent, and do not appear to interact with the nanowires. The fully cured adhesive is thermoplastic with a transition temperature around 50° C. Pairs of nanowires were manipulated into contact with holographic optical tweezers (HOTS), whose intensity was subsequently increased. Increased fluorescence from the nanowires suggests local heating at the wires&#39; ends. The observed formation of bubbles at slightly laser power suggests a steady-state temperature of around 50° C. under experimental conditions. Increasing the trapping laser&#39;s intensity also induced a streaming flow of adhesive particles past the junction, leading to a buildup of plastic material as the particles collided with the hot nanowire ends, presumably because the particles melted and stuck. The laser illumination was removed after a visible joint was formed, and the resulting free-floating assembly retained its structure, demonstrating that a rigid bond had been formed.  
       EXAMPLE 2  
       [0021]     As another demonstration of an example of a preferred embodiment, we trained an intense optical tweezer at the edge of a gold electrode evaporated onto the surface of a sapphire substrate in the same solution. Once again, adhesive particles streamed to the. locally heated spot, where they formed a rigid structure. Translating the optical tweezer to the edge of the deposited structure permitted further adhesive deposition. Meltflow growth of adhesive structures under optical tweezer control can be used to create three-dimensional structures with features comparable in size to the scale of the adhesive particles and the wavelength of light.  
         [0022]     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.