Particle guidance system

INTRODUCTION

The title of the invention is

Particle Guidance System.

The inventor is Michael J. Renn of 9634 MacAllan Road NE, Albuquerque, N. Mex. 87109. The inventor is a citizen of the United States of America.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

FIELD OF THE INVENTION

The present invention relates generally to the field of optical guides. More specifically, one embodiment of the present invention relates to methods and apparatus for confining a non-atomic particle in a laser beam. The particle, which is confined in the laser beam, is guided through a hollow core optical fiber for study, measurement or deposition. The process is used to produce three-dimensional structures.

BACKGROUND OF THE INVENTION

Methods for transporting atomic sized particles using radiation and pressure-based processes are known in the art, and have been used to precisely and non-mechanically manipulate particles. An atom placed in an optical beam is attracted to or repelled from regions of high intensity, depending whether the atom can be polarized at the optical frequency. Laser-induced optical forces arise when particles are polarized in intense optical fields. Laser guidance of non-atomic particles utilizes these optical forces arising generally from the deflection and scattering of light. These forces have been used in a number of optical traps. For example, “optical tweezers” allow dielectric particles to be trapped near the focal point of a tightly focused, high-power laser beam. These optical tweezers are used to manipulate biological particles, such as viruses, bacteria, micro-organisms, blood cells, plant cells, and chromosomes. Optical tweezers also allow a user to manipulate small, particles in an aqueous medium, though they do not allow the user to perform the same manipulation in the air. Optical traps for atoms are used in investigations of ultra-cold collisions and of the collective effects of trapped atoms.

Most known techniques for trapping atoms in a tightly focused laser beam, and for transporting atoms together with the laser beam have limitations, since the trapping occurs only in a small region near the focal point of the laser. As a result, imaging and detecting devices utilizing optical traps must be built around a sample chamber, which often limits the size of the chamber in the devices. Since trapping and transporting particles occurs inside the chamber, then these imaging and detection devices require the laser beam to be steered from outside the chamber. Moreover, optical trapping forces are typically not large enough to trap particles in the laser beam if the background medium in the chamber is turbulent or convective. Furthermore, when conventional optical tweezers are employed, only a substantially transparent particle possesses the optical qualities that are required to enable the axial force exerted on the particle in the laser beam to trap the particle inside the beam.

The technique of guiding atoms through a hollow core optical fiber was devised to improve previous procedures for manipulating particles through various media over long distances, and for transporting cold atoms from one vacuum system to another. Fiber-guided atoms are deflected from the inner surface of the fiber by light also guided in the fiber. Optical forces induced by the laser light guided in a fiber may be used to reflect atoms from the inner wall of a hollow core optical fiber. In this setting, laser light is coupled to the lowest-order grazing incidence mode, and the laser frequency is tuned to the red side. Atoms are attracted to the high intensity region at the center of the fiber. Atoms guided in a fiber this way undergo a series of loss-less oscillations in a transverse plane, and unconstrained motion in an axial direction.

While the method of guiding atoms through optical fibers was a step forward in developing means for manipulating and transporting particles from a source to a desired destination, an inherent limitation of this previous method was the atomic size of a manipulated particle. Because of an atom's size, the wavelength of the guiding laser beam had to be close to that of an atomic transition, and the manipulation itself could be performed only in a vacuum, requiring a special vacuum chamber. The process of atomic particle transportation is limited to moving a few kinds of materials, essentially ruling out manipulating and guiding atoms of a broad range of materials. In previous nano-fabrication processes, those which guide atoms and precisely deposit them on a substrate to form nanometer size features, high throughput is not achieved.

It is desirable in industrially-applicable techniques to achieve high-rate depositions of a wide range of materials having particle sizes many times greater than single atoms. The need exists to provide a method and apparatus for manipulating and guiding microscopic (non-atomic) particles through a suitable medium along straight and bent trajectories. It is also desirable to provide a method and apparatus capable of guiding particles of a wide range of materials in non-vacuum environment and depositing the particles on various kinds and shapes of substrates.

The problem of providing a method and apparatus for optimal control of diverse material particles ranging in size from individual or groups of atoms to microscopic particles used to fabricate articles having fully dense, complex shapes has presented a major challenge to the manufacturing industry. Creating complex objects with desirable material properties, cheaply, accurately and rapidly has been a continuing problem for designers. Producing such objects with gradient or compound materials could provide manufacturers with wide-ranging commercial opportunities. Solving these problems would constitute a major technological advance, and would satisfy a long felt need in the part fabrication industry.

SUMMARY OF THE INVENTION

The present invention provides a solution to the problems encountered by previous particle manipulation methods. The present invention provides methods and apparatus for laser guidance of micron-sized and mesoscopic particles. The invention also furnishes methods and apparatus which use laser light to trap particles within the hollow region of a hollow-core optical fiber. This embodiment of the invention enables the transportation of particles along the fiber over long distances. The present invention also includes processes for guiding a wide variety of material particles, including solids and aerosol particles, along an optical fiber to a desired destination.

The present invention further includes methods and apparatus for guiding particles in ambient, aqueous or gaseous environments, including an inert gas environment, which may be desirable for the fabrication of objects.

The invention may also be employed to deliver liquid and solid particles to a substrate using a laser to guide particles in hollow-core optical fibers after extracting the particles from source backgrounds. This method allows a user to fabricate micron-size surface structures, such as electrical circuits and micro-electronic-mechanical devices, on a virtually unlimited variety of substrates, including semiconductors, plastics, metals and alloys, ceramics and glasses. The particles deposited on such substrates can be metals or alloys, semiconductors, plastics, glasses, liquid chemical droplets and liquid droplets containing dissolved materials or colloidal particles.

Another embodiment of the invention may be used as a fiber optic particle guide for non-contact, non-mechanical manipulation of mesoscopic particles. Such particles include those of biological origin such as bacteria, viruses, genes, proteins, living cells and DNA macromolecules. The particles can also be inorganic, such as glasses, polymers and liquid droplets.

Another embodiment of the present invention provides a method of controlling and manipulating non-atomic particles by trapping them within an optical fiber anywhere along the length of the fiber. A laser beam may be directed to an entrance of a hollow-core optical fiber by a focusing lens. A source of particles to be guided through the fiber provides a certain number of particles near the entrance to the fiber. The particles are then drawn into the hollow core of the fiber by the focused laser beam, propagating along a grazing incidence path inside the fiber. Laser induced optical forces, generated by scattering, absorption and refraction of the laser light by a particle, trap the particle close to the center of the fiber and propels it along. Virtually any micron-size material, including solid dielectric, semiconductor and solid particles as well as liquid solvent droplets, can be trapped in laser beams, and transported along optical fibers due to the net effect of exertion of these optical forces. After traveling through the length of the fiber, the particles can be either deposited on a desired substrate or in an analytical chamber, or subjected to other processes depending on the goal of a particular application.

In another embodiment of the present invention, the particle manipulation methods are used to levitate particles inside a hollow-core fiber. In this method, particles or liquid droplets captured by a tightly focused laser beam are drawn into a vertically positioned fiber. After a certain distance inside the fiber, the propelling axial optical force pulling the particle up is balanced by the gravitational force acting on the particle. Such a balance of forces makes the particle levitate in an equilibrium position, allowing the estimation of the magnitude of the propelling force. Similarly, if a particle is trapped in a horizontally positioned optical fiber by two laser beams entering the fiber from two opposing ends of the fiber, the particle will levitate in a certain equilibrium position inside the fiber. Varying the intensity of the lasers allows one to estimate the magnitude of the force confining the particle in the center of the fiber.

The invention may also be utilized to transport and pattern aerosol particles on a substrate. By directing particles along the fiber and onto the substrate, micron-size features of desirable shape can be fabricated by directed material deposition (DMD) of these particles. Such features are built up by continual addition of particles, which are fused together on the substrate by various techniques including “in-flight” melting of the particles and subsequent coalescence of molten droplets on the substrate. This embodiment also offers the ability to simultaneously deposit solid particles and liquid “precursors,” where the liquids serve to fill the gaps between solid particles. A precursor is any material that can be decomposed thermally or chemically to yield a desired final product. Coalescence of liquid precursors on the substrate and subsequent decomposition by laser heating to form a final product on the substrate and sintering of the deposited material by laser, or chemical binding are additional techniques made possible by the invention. Another technique that is enabled by the invention is the heating of a substrate, as in conventional CVD processes.

An appreciation of other aims and objectives of the present invention may be achieved by studying the following description of preferred and alternate embodiments and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a schematic representation of optical forces exerted on a particle by a laser beam.

FIG. 2

is a side view of a hollow-core optical fiber.

FIG. 3

is a graph showing the dependence of optical forces on a radial position of a particle from the center of a laser beam.

FIG. 4

is a schematic representation of a laser guidance apparatus.

FIG. 5

is a microscopic picture of a sodium chloride (NaCl) deposition example.

FIGS.

6

(

a

)-(

e

) are microscopic pictures of crystal deposition for barium titanate (BaTiO

3

), indium oxide (In

2

O

3

), silver (Ag), aluminum nitrate (Al(NO

3

)

3

) and aluminum oxide (Al

2

O

3

), respectively.

FIGS.

7

(

a

)-(

d

) are photographs showing levitation of a water droplet in a curved section of an air-filled optical fiber.

FIG. 8

is a schematic representation of a two-laser trapping apparatus.

FIG. 9

is a schematic representation of another embodiment of a two-laser trapping apparatus.

FIG. 10

is a schematic sketch of a particle deposition apparatus using a laser and co-flowing air column to propel the particles.

FIG. 11

is a schematic, side elevation view of an aerosol-jetting deposition apparatus for material depositions.

FIG. 12

is a perspective view, schematically shown, of a general method of laser light treatment of deposited particulates.

FIG. 13

is a perspective view of another apparatus for treating deposited particulates.

FIG. 14

is a schematic of an aerosol jetting, particle deposition apparatus revealing treatment of the deposition by an integral laser.

FIG. 15

is a side elevation view of a method of direct writing and treating of materials on a temporary substrate or support.

FIG. 16

is a schematic perspective view of a method of controlling the energy required to treat materials deposited to form three-dimensional structures.

FIG. 17

is an elevation schematic rendering of apparatus for forming structures using laser guidance and liquid jetting, particularly useful in transporting living cells to a substrate.

A DETAILED DESCRIPTION OF PREFERRED & ALTERNATIVE EMBODIMENTS

Background of the Invention

Optical forces arise when particles are polarized in intense optical fields. These forces result from the reflection and refraction of light at the interface of a particle's surface and its environment. When the size of a particle is large compared to the wavelength of the incident light, the forces acting on the particle can be described in a geometrical ray approximation.

The following symbols and abbreviations used throughout this Specification are explained below:

mW — milliwatt (laser power)

μm — micrometer (length)

mm — millimeter (length, wavelength)

λ — wavelength

nm — nanometer (length)

η — index of refraction

As shown in

FIG. 1

, a single optical laser ray

10

from a laser beam is shown striking a sphere

12

having a refractive index ηs larger than a refractive index ηm of the surrounding medium. In this example, sphere

12

is a dielectric sphere made of an optically transparent material, so it is transparent to ray

10

. Incident on a surface interface

14

, ray

10

undergoes partial reflection and refraction. A portion of incident ray

10

reflected at interface

14

is known as radiation pressure. The first time a portion of ray

10

is reflected is when ray

10

enters sphere

12

at an entrance point

16

, creating radiation pressure force F

2

, perpendicular to the surface of sphere

12

and directed toward the center of the sphere. The second time a portion of ray

10

is reflected is when the ray exits sphere

12

at an exit point

18

, creating radiation pressure force F

4

, also perpendicular to the surface of sphere

12

, but directed outwardly. Portions of ray

10

which are refracted at the surface of sphere

12

when the ray enters and exits the sphere at points

16

and

18

create forces F

1

, and F

3

respectively. Force F

1

is perpendicular to the direction of the refracted ray

10

as it propagates inside sphere

12

. Similarly, force F

3

is perpendicular to the direction of the once-again refracted ray

10

as it propagates after exiting the sphere

12

. The sum of the forces F

1

through F

4

, in addition to forces arising from multiple reflections inside the sphere, gives the total force acting on sphere

12

from the ray

10

.

If total forces from all possible rays incident on sphere

12

are calculated and added up, the summation will give the two resulting net forces. The first net force is a confinement force, also known as a gradient force, acting in a radial direction. This direction is toward an increase of laser beam intensity. The second net force, known as a radiation pressure force, acts along the axis z of the laser beam and results in propelling sphere

12

along the direction of laser propagation. Consequently, optical forces exerted by a laser beam on sphere

12

simultaneously pull the sphere toward the center of the laser beam and accelerate the sphere along the direction of propagation of the beam. It is important to note that the mechanism of guiding non-atomic particles through optical fibers utilized in the present invention is different from that of guiding atoms. Most notably, optical forces causing confinement and propulsion of a non-atomic particle in a fiber are based on non-resonant scattering of light, as described with regard to FIG.

1

. To the contrary, atomic laser guidance is based on resonant interactions between the laser field and the atom.

Optical Forces Acting on a Particle in a Laser Field

To obtain a magnitude of radiation pressure and gradient forces sufficient to propel a particle, high intensity laser fields are required. These are normally achieved in highly focused laser beams. As a result, optical forces, sufficient to trap and propel particles occur only near the laser beam “waist” (w

0

) in a hollow core of an optical fiber. The beam waist (w

0

) is the radial distance from the center of the beam to where the beam energy declines to 1/e. Within the hollow core, a high intensity region of the beam extends along the length of the fiber, providing for propulsion as well as confinement of the particles inside the hollow fiber. When a laser beam propagates along the fiber, the beam does not stray but travels along the length of the fiber, making it possible to carry the particle along the fiber. Although one of the preferred embodiments of the invention utilizes a laser to guide particles, any high intensity field of controllable radiation or beam of energy may be used to practice the invention.

The radial profile of the lowest order optical mode coupled to a hollow fiber is represented by a zero

th

order Bessel function J

0

(Xρ), where X=2.4/ρ

0

, where ρ

0

is the radius of a hollow core region

24

of the fiber as shown in FIG.

2

. The lowest loss grazing-incidence mode has an intensity I at radial distance ρ from fiber centerline and axial distance z along the fiber given by the following equation:

I

(ρ,

z

)=

I

0

(

J

0

(

X

ρ))

2

exp(−

z/z

0

) Equation (1)

where I

0

is the peak intensity of the laser field at the fiber center where ρ=0, and z

0

is a beam decay length, given by:

z

0

=6.8 (ρ

0

3

/λ

2

)((ν

2

−1)

−½

/(ν

2

+1)) Equation (2)

where ν is the ratio of fiber wall refractive index ηf to the hollow core refractive index ηm of the medium in the hollow core region, λ is the laser wave length in the hollow region, z is the distance from the beginning of the fiber. It follows from equation (1), that the intensity of the laser field has a maximum at the center of the fiber where ρ=0 and slowly decreases along the length of the fiber as exp(−z/z

0

). Beam decay length z sets the limit of the distance which particles can be guided. In general, z is calculated using equation (2) for a specific fiber geometry, laser wave length, and refractive indices of the fiber core and walls. An estimate of equation (2) provides a practical limit to a guidance distance of up to 100 inches.

A chart

30

of optical forces

41

in units of 10

−11

Newtons on a dielectric particle having a radius r larger than the wavelength λ of a laser is shown in FIG.

3

. The graph depicts radial dependence of the axial scattering force

40

and radial gradient force

42

on a 7 μm diameter polystyrene sphere (ηs=1.59) near the entrance of a water-filled fiber using geometric ray formalism and equation (1) for the intensity profile calculations.

The experimental conditions were the following: A 3.6 mm diameter, 240 milliwatt (mW) laser beam was coupled with 90% efficiency into a 20 μm diameter fiber. As seen in

FIG. 3

, a radial gradient force

40

increases nearly linearly with small displacements

43

from the fiber center indicating a restoring force drawing the particle toward the high intensity central region of the fiber. An axial force

42

in

FIG. 3

is nearly constant for small displacements

43

from the center.

From a theoretical basis and experimental results described above, it follows that if an intense laser beam inside a hollow core fiber has a proper profile and if the trapped particle is damped by the fluid inside the fiber, the particle is confined inside the laser beam and can be transported with the beam without bouncing off the inside walls of the fiber. The size of the particles capable of being guided that way can vary from about 50 nanometers (nm) diameter to about 10 micrometers (μm) diameter. The higher the refractive index of a particle, the larger optical forces are exerted on the particle, and, consequently, the easier it is to manipulate and transport such a particle.

Materials Manipulated

Besides polystyrene spheres and water droplets, other substances guided through the fibers were salt, sugar, potassium iodide (KI), cadmium telluride (CdTe), silicon (Si) and germanium (Ge) crystals, gold (Au) and silver (Ag) particles with sizes ranging from about 10 nm to about 10 μm. A 0.5 watt laser and a 17 μm inner-diameter, air-filled fiber were used. Listed in Table 1 and 2 are the materials manipulated by laser guidance on a variety of substrates. Since metal particles, such as Au and Ag, for example, usually reflect light well and absorb very little light, larger metal particles can be transported along the hollow-core fibers faster than less reflective materials.

TABLE ONE

Materials Manipulated

Metals

Au, Ag, Pd, Rh, Pt

Dielectrics

Glass, BaTiO

3

, Al

2

O

3

Semiconductors

Si, Ge, CdS, In

2

O

3

Liquids

H

2

O, acids, bases, solvents, salt

solutions,

Plastics

Polystyrene

Biological

Embryonic nerve and glial cells,

bacteria, microtubules

Substrates used:

Glass, Ceramic, Plastic, Paper, Si,

Polyimide

Line Dimensions: 3 μm ± 0.5 μm

The use of hollow core fibers allows manipulation of a wide variety of particles and virtually opens up a non-contact, non-mechanical way of transporting numerous materials. Living cells can be manipulated and guided through the fibers in liquid environments. Examples of the results of fiber guiding for several types of dielectric particles are shown in

FIGS. 7

a-d

and discussed later. Each image of a short section of fiber in

FIGS. 7

a

-

7

d

is captured on a CCD camera.

FIGS. 7

a

-

7

c

show snapshots of polystyrene spheres guided in a water-filled fiber.

FIG. 7

d

shows an example of a particle guided in an air-filled fiber. The track of scattered light in

FIG. 7

d

indicates the trajectory of a 1 μm water droplet in a 20 μm diameter fiber.

Direct-Write Patterning of Surfaces

One of the many applications of particle laser guidance is direct-write patterning of surfaces, in which optical forces transport particles through hollow core optical fibers and deposit the transported particles on surfaces. In the laser guidance and surface patterning apparatus

44

depicted in

FIG. 4

, laser light

46

is focused into the hollow region

48

of a hollow core fiber

50

and guided in a low order grazing incidence mode. Aerosol particles

52

created by a “nebulizer”

54

(a device which reduces a liquid to fine mist) and situated near the fiber entrance

56

are funneled into the hollow region

48

by optical gradient and scattering forces, and then guided to a substrate

58

. For best results, substrate

58

is usually placed between 10 μm and 300 μm from the end of the fiber, because at larger distances the optical forces decrease rapidly and cannot continue to confine the particles.

The material used for surface patterning is usually either dissolved or suspended in a liquid

60

, such as sodium chloride (NaCl) dissolved in water (H

2

O) in the experiment of FIG.

4

. The material can be a crystalline substance, for example barium titanate (BaTiO

3

), a common capacitor material for electronic applications. It may be a dissolved precursor material, such as silver nitrate, which can be decomposed to silver as the deposited material by heating while inside the laser beam during transportation. It is contemplated that many other materials are capable of being transported to a surface and deposited on the surface. When an aerosol mist

62

is generated by the nebulizer

54

, the mist is directed into the laser beam

46

near an entrance

56

of the hollow fiber

50

. Laser axial scattering forces and radial gradient forces at the entrance

56

draw the aerosol particles

52

toward the center of the laser beam

46

and propel them into the fiber

50

. As the aerosol particles travel through the fiber

50

, excess solvent evaporates, leaving behind solid crystal particles

59

. Such drawing technique has general application. A wide variety of materials can be drawn into a laser beam

46

. Precursors for virtually every material used in electronics are known and available.

Coupling the laser beam

46

into the fiber

50

is accomplished with the help of a lens

64

that matches the fiber mode radius to the Gaussian beam waist. In one of the embodiments of the apparatus

44

, for a fiber having an inner diameter of 20 μm, a 0.05 numerical aperture (NA) lens gives a coupling efficiency better than 90% into the lowest order mode. It is possible to use lenses with a larger NA, which lenses excite rapidly decaying high-order modes. Considerable care must be given to angular alignment of the incident laser light to the fiber. A misalignment of about 1 degree excites high-order modes and results in the guided particles hitting the inside wall of the fiber.

As shown in

FIG. 5

, experimental patterning results are shown for salt (NaCl) crystallites guided by a diode laser onto a glass cover slip by the apparatus described above and depicted in FIG.

4

. In that experiment, a 250 mW laser beam at 800 nm wavelength (λ) was coupled into an fiber 8 mm long, having an inner hollow core diameter of 20 μm. In other successful direct writing experiments, a 400 mW laser beam, λ=800 μm was used. NaCl crystals were dissolved in distilled water to form a saturated solution

60

. The droplets of the solution

60

were launched into the laser beam

46

by the nebulizer

54

. Since optical forces are a strong function of particle size, scaling approximately as the square of particle size, the largest droplets

52

are preferentially captured and guided into the fiber

50

. As the droplets begin to propagate along the fiber

50

, the water in the droplets evaporates after about 2 mm of travel into the fiber

50

, so the solid NaCl crystals

59

are formed and then guided along the rest of the fiber

50

onto the glass cover slip

58

.

Direct “Writing” of Micron-Size Features On Substrates with Laser-Guided Particles

As seen in

FIG. 5

, the first two patterns

66

&

68

, respectively correspond to a single NaCl crystallite guided and delivered to the glass surface of substrate

58

in FIG.

4

. The other three patterns

70

,

72

&

74

in

FIG. 5

correspond to structural features formed by multiple NaCl crystallites

59

. The spot diameter of each pattern is about 5 μm, which is significantly smaller than the 20 μm diameter of the inner hollow core of the guiding fiber. This observation confirms the fact that the radial optical forces confine the crystallites

59

to the center of the hollow core

48

. It was estimated that the size of each crystallite

59

is about 1 μm for a saturated NaCl solution

60

. The size of a crystallite

59

on a substrate

58

can be reduced by reducing the concentration of NaCl in the initial solution

60

.

Another experimental example of direct writing presents patterns of BaTiO

3

In

2

O

3

, Ag, aluminum nitrate (Al(NO

3

)

3

), and aluminum oxide (AL

2

O

3

) crystal depositions, which are shown in

FIGS. 6

a

through

6

e,

respectively. The lines of crystals in

FIGS. 6

a

through

6

e

were drawn at various micrometer translation rates during the deposition. The BaTiO

3

crystals were guided by a 1 Watt laser at λ=532 nm, transported through a 14 μm diameter fiber, four millimeters long.

Fabrication by Directed Particle Deposition

By directing particles along the fiber

50

onto the substrate

58

shown in

FIG. 4

, micron-size features of desirable shape can be fabricated. As noted above, the direct deposition of nanometer-size particles, called “nano-fabrication,” allows a user to build features of dimensions less than 100 nm on a substrate, which is currently the smallest feature achievable in photo-lithographic processes. Such features are built up by continued addition of particles, which can be fused together on substrate

58

by various techniques. These include 1) in-flight melting of the particles and subsequent coalescence of molten droplets on the substrate, 2) simultaneous deposition of solid particles and liquid precursors, wherein the liquids serve to fill the gaps between solid particles, 3) coalescence of liquid precursors on the substrate and subsequent decomposition by laser treatment to form the final product on the substrate, 4) sintering of the deposited material by laser, and 5) chemical binding. The structural features can be composed of a wide variety of materials, such as metals, semiconductors, and insulators.

The current invention makes it possible to create surface structural features less than a micron in size. It is, therefore, possible to increases the density of electrical circuits on a printed board by means of the invention. Circuitry can be “written” on substrates made of plastics, metals, ceramics and semiconductors with the wide range of materials described above. Circuits can be deposited on such substrates with high throughput. Another implementation of laser-guided directed material deposition is the direct-write process on an arbitrary shaped substrate. This process allows the circuitry to conform to the shape of the substrate. Direct writing of micron-sized structural features can be used to print unique identification markers. Manufacturing prototype micro-electronic mechanical devices in the rapidly growing micro-electronic mechanical systems (MEMS) industry is a further use of the invention. Since the direct writing technique can be used to print electrical circuits on a virtually unlimited variety of substrates, the products for which the technique can be used include wireless communication devices, “smart” credit cards, and embedded circuitry in biological implants.

Electrical circuit fabrication which calls for fully dense, continuous, micron-size patterns, can be achieved by the present invention using the direct-write laser-guidance method. In one preferred embodiment, particles melt during laser transportation, so the molten particles flowing together onto the substrate are deposited there as fully dense patterns. A high laser intensity of 10

12

Watts per square meter (W/m

2

) at the fiber entrance can melt nearly any material by laser light absorption. Strongly absorbing materials, such as metals and alloys will melt at a lower power of about 100 mW within the first 100 μm of the fiber entrance. To melt weakly absorbent materials, such as transparent glasses and ceramics, a laser emitting in the material's absorption band or a more intense laser is usually required. In the apparatus depicted in

FIG. 4

, the length of fiber

50

or the optical coupling mode can be adjusted, so that entering particles

52

melt at fiber entrance

56

, but the laser intensity at a fiber exit such as at substrate

58

, is sufficiently low to minimize heating of substrate

58

. Such low exiting intensity can be achieved by the appropriate choice of the length and diameter of the guiding fiber.

Depositions Using Precursors

An alternate method of depositing materials onto a substrate is by use of precursors in depositions. In the laser material deposition method of the present invention, the desired product is a material to be deposited on the substrate. For example, silver nitrate is a salt that dissolves in water. Therefore, laser guiding the droplets of the silver nitrate inside an optical fiber heats the droplets confined in the laser beam, yields the final material, silver. The silver is then deposited on the substrate. Alternatively, heating of the droplets can be accomplished by any other conventional means. Heating and decomposing indium nitrate is another example of using precursors in laser deposition. Guiding and heating indium nitrate in the laser beam inside an optical fiber decomposes to a transparent semiconductor, indium oxide.

Yet another way of depositing a desired material on a substrate is by laser guidance of a liquid droplet which transports a small, solid particle. During transportation, the liquid droplet evaporates, exposing the small solid particle, which is then deposited onto the substrate. In many cases it is easier to guide and deposit precursors rather than the final desired materials.

A list of preferred precursor materials for electronic applications appears in Table Two.

TABLE TWO

Material

Precursor

Cu

Copper formate

Pt

Platinum tetrachloride

Au

Gold chloride, gold thiolate

Ag

Silver trifluoroacetate

Ni

Nickel formate

Zn

Zinc formate

Rh

Rhodium chloride

Laser Levitation of Particles

The same principle on which apparatus

44

in

FIG. 4

is based is used to provide an apparatus and method for laser levitation of individual crystallites. If a particle

52

is guided along the vertically disposed fiber

50

in

FIG. 4

, the force of gravity pulls the particle

52

down. while the axial optical force pushes the particle up the length of the fiber

50

. Since the axial force becomes smaller with distance along the fiber, the two forces eventually balance each other and the particle remains levitated at an equilibrium height. When the particle is in equilibrium, the magnitude of the axial force propelling the particle

52

upward is equal to the magnitude of the gravitational force pulling the particle down. The apparatus

44

can serve as a device for measuring the axial force of propulsion since the magnitude of the gravitational force is easily calculated.

The photographs in

FIGS. 7

(

a

)-(

d

) show the levitation of a five micrometer water droplet in a five millimeter curved section of an air-filled fiber. A 240-milliwatt laser operating at a wavelength of 800 nanometers is coupled with 90% efficiency to the fiber in the lowest-loss mode. Five micrometer diameter water droplets, (whose size is estimated by optical microscopy), are funneled into the fiber by the laser light radiating through a fog of droplets. The scattered light from the droplet is easily seen by the naked eye in

FIGS. 7

a-d,

as the droplet travels through the fiber.

Laser Traps

Another embodiment of a laser levitation apparatus is shown in FIG.

8

. In that embodiment, laser beams

80

&

82

are focused through lenses

81

into entrance faces

84

&

86

at opposite ends, respectively, of a fiber

88

. The axial forces exerted on a particle

90

from laser beams

80

and

82

inside a hollow core

92

of fiber

88

are opposite, creating an equilibrium point on a particle

90

inside the fiber. At the same point, the force confining the particle

90

to the center of hollow core

92

doubles in magnitude. By reducing the laser intensity, particle

90

is pulled down by the gravitational force toward the lower part of the hollow core

92

. Since the gravitational force can be easily calculated, measurements of the particle's downward displacement provides a measure of the radial confinement force.

Laser traps for confining liquids, salts, glasses and metals, similar to the kind depicted in

FIG. 8

, have been constructed and tested for several hours while monitoring the particles' dynamic behavior and light scattering. By mixing droplets in such traps, chemical reactions were observed during the mixing process. Such an apparatus is useful for “container-less” processing of chemicals. Droplets are mixed by laser-heating or coalescence while confined in the laser beam.

Another application of a two-beam laser trap is an apparatus

100

for recording the emission spectrum of trapped particles. The apparatus is shown schematically in FIG.

9

. The trap is formed by laser beams

92

&

95

directed into opposite ends

94

&

96

of a hollow fiber

98

. The laser beams

92

&

95

are formed by a beam splitter

93

, which splits a laser beam generated by a source

91

. The beams

92

&

95

are redirected by folding mirrors

102

and focused on the fiber ends

94

&

96

by lenses

110

&

112

. A particle mist

108

is generated in chamber

104

, which contains a solution of the material of interest. At a point inside fiber

98

, optical forces from laser beams

92

and

95

balance and the laser field confines and heats the particles

97

inside the fiber

98

. Optical emission spectrum of the trapped particles

97

is then recorded by a low light spectrophotometer

99

.

Two-beam, laser trap apparatus

100

can be a useful tool in controlling fully-dense, direct writing and adhesion of particles to a substrate. The combined use of emission spectrum and light-scattering patterns of a particle will distinctly determine the melting temperature and conditions for controlling direct laser writing. The conditions for melting are determined by measuring the particle's temperature from its radiative emission and by measuring the temperature's dependence on material, particle size, laser power and hollow fiber dimensions. The particle's phase transition between solid and liquid is determined from the changes in optical scattering patterns.

Fabrication by Laser Depositions of Particles Using a Hybrid System

FIG. 10

reveals a hybrid apparatus

120

for low-cost fabrication of micro-electronic-mechanical systems using fluid-guided particles in a cytometeric-type flow in a hollow container

143

. Fluid forces propel a flow of aerosol particles

136

axially through the apparatus

120

. The fluid forces are higher than optical forces produced by a laser beam

122

. However, the optical forces on the particles

142

move them toward the center of the laser beam

122

. The forces are great enough to keep the particles

136

from reaching the walls of the chamber

143

, precluding clogging. In this apparatus

120

, the flow of aerosol droplets

136

, carrying particulate or precursor material, is admitted into the chamber

143

through inlets

142

at the chamber top. The laser beam

122

is passed through the chamber

143

, focused by a lens

124

on a nozzle orifice

144

of a variable nozzle

128

in the outlet of the chamber

143

. As earlier described, the aerosol droplets

136

are drawn into the laser beam but propelled with high velocity through the nozzle orifice

144

toward a substrate

134

by the entraining fluid. The nozzle orifice

144

is adjustable, preferably electrostatically, depending on the size of a feature to be deposited on the substrate

134

. On the way to the substrate

134

, the aerosol particles

136

are treated by laser heating. The laser beam

122

evaporates the aerosol droplets

136

, leaving crystals or thermally coalesced particles

140

which are subsequently deposited on the substrate

134

. The laser beam

122

can be used to treat the particles

140

“on the fly” or after deposition on the substrate

134

. This technique is further discussed below. The deposition continues according to a desired pattern to create useful three-dimensional structure.

A hollow column of co-flowing air

138

surrounds the stream of particles

140

in a sheath, forming a barrier

130

and focusing the particles

140

on a second nozzle

132

orifice. The second, adjustable orifice

132

is placed near the substrate to control the flow of particles

140

to the substrate for deposition and divert air flow away from the deposition. The co-flowing air

138

is led away from the deposition through air outlets

146

. The flow rates of the aerosol droplets

136

and the co-flowing air

138

are adjusted so their velocities are the same at and below the nozzle orifice

144

.

Laser-Guided Depositions Using Liquid/Aerosol Jetting Technique

FIG. 11

illustrates an aerosol-jetting deposition apparatus

150

for material depositions. The apparatus

150

is particularly useful in transporting living cells to a substrate where they can be nurtured and grown. Container

154

is filled with aerosol material or particles suspended in a liquid (

156

). When transporting living cells to a substrate

164

, a laser beam

152

is unable to apply much force to a cell. This is because living cells usually have small light deflection. A desirable speed for the particle stream is of the order of 1 meter per second at the substrate

164

, but a laser beam

152

intense enough to achieve this velocity would likely destroy or damage the cells. Therefore, to move such cells at a high velocity and speed-up the deposition process, a co-flowing fluid (

156

) is needed. Additionally, living cells should be constantly immersed in a life-supporting fluid even after deposition on the substrate

164

.

FIG. 17

also illustrates this process.

The laser beam

152

is useful in guiding living cells and similar particles to the center of the channel

158

which directs them to the substrate

164

. The beam

152

is also used to hold the cells to the substrate long enough for them to adhere at the surface

166

, else they would be swept away in escaping fluid.

In

FIG. 11

, the fluid flow

156

is forced through a pinhole

162

in an orifice plate

160

at the bottom of the container

154

. Fluid forces propel the particulates in the fluid toward the substrate

164

. The orifice plate

160

is transparent to the laser beam

152

so the beam

152

can treat the particles on the fly or after deposition on the substrate

164

.

Laser-Guided Material Deposition Methods Using Treatable and Treated Particles

Laser guided manipulation methods for depositing materials on a substrate disclosed in the present invention can be further extended by treating the deposited particles with an energy source. The energy source may be a heat source, another laser beam or the deposition laser beam itself.

FIG. 12

depicts a method of treating deposited materials

172

on a substrate

171

with a laser beam

174

, after an original deposition

172

by, for example, direct writing as described above. Laser beam

174

is directed through a focusing lens

176

onto the treatable, deposited material

172

. A line of treated material

178

is created by scanning the laser beam

174

in a desired pattern. Untreated, deposited material

172

is then removed by a solvent or mechanical means. Repeating the deposition, treatment and removal of material produces three-dimensional structures. These structures may be formed from a plurality of different materials.

FIG. 13

depicts an alternative method of treating deposited materials

188

on a substrate

190

. In this alternative, particles

192

are deposited by means of an aerosol jet from an aerosol jetting apparatus

182

, such as described above, conventional spin coating, jetting or similar techniques. As in

FIG. 12

, an intense optical source, such as a focused laser beam

184

, is scanned over the treatable, deposited material

188

following deposition. The substrate

190

may be composed of ceramic, polymer, paper, circuit board, glass, semiconductor, metals, to name a few materials. The deposition particle

192

may be a metal salt, a metal salt dissolved in solvent, a solid particulate such as a metal, a dielectric, a semiconductor, a polymer or a solid particulate suspended in a liquid, or a liquid polymer incorporating particulates. Solvent evaporation, leaving the treated particulate

189

, is facilitated by the laser

184

heating the deposited material

188

. Alternatively, thermally-initiated cross-linking forms the treated material

189

.

Simultaneous Deposition and Treatment of Particulate Material

By use of the apparatus

200

described in

FIG. 14

, a large step is eliminated in the process of depositing particles on a substrate for fabrication of three-dimensional structures. With this apparatus

200

, the deposition of particles from an aerosol source

208

is guided to the substrate

212

by aerosol deposition apparatus

206

, similar to that first described above and presented in FIG.

11

. The laser beam

202

, focused by lens

204

on the orifice

210

of the aerosol deposition apparatus

206

, not only keeps the aerosol droplets

216

centered in the beam on the way to the substrate

212

, but the laser beam

202

is also used to treat the deposited material

214

. Such treatment can take place while the particles

216

are “on the fly” or when they impact on the substrate

212

surface. Treatment may be particle melting, decomposition, sintering or other chemical and mechanical reactions caused by the laser's interaction with the particle

216

. The resulting, treated depositions have desirable mechanical and electrical properties for electronics and micro-electronic mechanical system applications.

Direct-Writing and Treating Materials Using Temporary Support

FIG. 15

provides an illustration of a method of direct writing and treating of materials on a temporary substrate or support. A laser particle deposition apparatus

120

, such as described in

FIG. 10

may be used to form a structure

224

which is used as base for new depositions of treatable material

226

and a container for a soluble support material

230

. The support material

230

may be deposited by conventional or laser-guided means, then solidified by chemical, thermal, or optical means. A support material

230

may be an ice, a crystalized salt, or a solidified liquid polymer, among many other possible types. The treatable material

226

is deposited on the support material

230

. Then, using laser

22

focused by lens

228

, the treatable material

226

is laser treated as described earlier to form dense, connected and/or ductile material structures

227

. The support material

230

is then removed by a suitable solvent or procedure.

Controlling the Energy Required to Treat Materials Deposited to Form Three-Dimensional Structures

In forming three-dimensional structures of laser-deposited materials, it is sometimes useful to reduce the laser power needed to treat the deposited material during or after deposition. For example, an inexpensive laser diode might be used for the treatment process if most of the energy necessary for such treatment were supplied by another means. An apparatus

240

for doing that is described by FIG.

16

. In this alternative embodiment of the laser-manipulation invention, a stream

244

of aerosol droplets

246

is introduced into the laser deposition apparatus

242

after passing through a heater

246

which pre-treats the aerosol droplets

245

, drying and or partially decomposing them. The laser-deposition apparatus

242

is patterned after the one shown in

FIG. 11

which employs a co-flow fluid to propel the particles

245

through a small orifice toward a substrate

254

. A pre-treated deposit

248

is therefore laid on the substrate

248

. The substrate

254

is itself conditioned with a substrate heater

250

. Because the deposition

248

is heated to a pre-treatment state and temperature conditioned by the substrate heater

250

, an infrared lamp or a high power diode laser, only light from a low energy laser beam

241

is needed for completion of the treatment. Fully treated material

252

is formed by scanning the laser beam

241

over the substrate

248

in a desired pattern. The steps are repeated to produce a structure in three dimensions. In the example shown in

FIG. 16

, a treatable platinum deposition is prepared from water-soluble platinum tetrachloride. By pre-heating droplets

245

of platinum tetrachloride as they enter the deposition apparatus

242

, and then raising the temperature of the deposited material to near 580 degrees Celsius with the substrate heater

250

, a low-power, diode laser can complete the decomposition of a desired deposition pattern

252

to pure platinum.

In electronics applications, besides platinum tetrachloride, preferred laser-treatable materials are: gold tetrachloride, copper formate, silver acetate, silver nitrate, barium titanate and aluminum oxide. The minimum size of a treated region is about one micrometer.

Forming Deposited Structures Using Laser Guidance and Liquid Jetting

In previous discussion above, it was noted that certain cells, among them living tissue, should be constantly immersed in a supporting fluid even after deposition on a substrate. The apparatus

260

shown schematically in

FIG. 17

is designed to fill this need. An inner chamber

264

is disposed in a fluid-filled, outer chamber

266

.

The outer chamber

266

contains fluid media

267

, including in the case of deposited living cells, nutrients necessary for growth. Other fluids may be selected to treat inorganic materials such as metals or plastics. The inner chamber

264

contains a fluid containing dissolved or suspended particulates

263

. Pressurization of the inner chamber

264

with air or other fluid flow propels a stream containing particulates

272

through a small orifice

269

in the inner chamber toward substrate

268

which is immersed in the first chamber fluid media

267

. A laser beam

261

holds the particles

272

in place on the deposition footprint

274

, on the substrate

264

and treats them as needed by decomposition or other chemical and mechanical reactions possible with laser-particle interaction.

CONCLUSION

Although the present invention has been described in detail with reference to particular preferred and alternative embodiments, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements may be made without departing from the spirit and scope of the Claims that follow. The various configurations that have been disclosed above are intended to educate the reader about preferred and alternative embodiments, and are not intended to constrain the limits of the invention or the scope of the Claims. The List of Reference Characters which follows is intended to provide the reader with a convenient means of identifying elements of the invention in the Specification and Drawings. This list is not intended to delineate or narrow the scope of the Claims.

LIST OF REFERENCE CHARACTERS

FIGS. 1 & 2

10

Laser beam ray

12

Dielectric, spherical particle

14

Surface of the sphere

16

Point on the surface of the sphere at which ray enters

18

Point on the surface of the sphere at which ray exits

20

Centerline of laser beam incident on a hollow optical fiber

22

Hollow optical fiber

24

Bore of the optical fiber

r Radius of sphere

ρ Radial distance from laser beam center line to center of sphere

ρ

0

Radius of the bore of a hollow optical fiber

F

1

Optical force due to refraction of ray when entering sphere

F

2

Optical (radiation pressure) force due to reflection of ray when entering sphere

F

3

Optical force due to refraction of ray when leaving sphere

F

4

Optical force due to reflection of ray when leaving sphere

η

f

Index of refraction of the hollow optical fiber

η

m

Index of refraction of medium surrounding sphere

η

s

Index of refraction of sphere

FIG. 3

30

Chart of optical forces on a dielectric particle having a radius larger than the wavelength of an illuminating laser

40

Radial gradient force

41

Optical force in 10

−11

Newtons

42

Axial force in 10

−11

Newtons

43

Radial position of the dielectric particle in micrometers

FIG. 4

44

Laser guidance of particles and surface patterning apparatus

46

Laser beam

48

Bore of hollow optical fiber

50

Hollow optical fiber

52

Particle

54

Nebulizer

56

Entrance aperture of hollow fiber

57

Shield

58

Substrate

59

Solid crystallite particles

60

Sodium chloride (NaCl) dissolved in water (H

2

O)

62

Aerosol mist

64

Focusing lens

FIG. 5

66

,

68

Single NaCl crystal laser-guided to a glass substrate

70

,

72

Structural feature formed by multiple NaCl crystals

74

Structural feature formed by multiple NaCl crystals

FIG. 8

80

First laser beam

81

Focusing lens

82

Second laser beam

84

L. H. entrance face of hollow optical fiber

86

R. H. entrance face of hollow optical fiber

88

Hollow optical fiber

90

“Levitated” particle

92

Bore of hollow optical fiber

FIG. 9

91

Laser source

92

R. H. Laser beam

93

Beam splitter

94

L. H. entrance face of hollow optical fiber

95

L. H. Laser beam

96

R. H. entrance face of hollow optical fiber

97

“Levitated” particle

98

Hollow optical fiber

99

Spectrophotometer

100

Two-beam laser trap apparatus

102

Folding mirror

104

Aerosol chamber

106

Liquid with dissolved or suspended particles

108

Aerosol mist

110

R. H. Focusing lens

112

L. H. focusing lens

FIG. 10

120

Laser particle deposition apparatus with co-flowing air

122

Laser beam

124

Focusing lens

126

Co-flowing air outer chamber

128

First variable nozzle

130

Air barrier

132

Second variable nozzle

134

Substrate

136

Aerosol droplet flow

138

Co-flowing air

140

Particle

142

Aerosol droplet flow

143

Inner chamber

144

First, variable nozzle orifice

146

Outlet air ducts

FIG. 11

150

Aerosol-jetting deposition apparatus for material depositions

152

Laser beam

153

Focusing lens

154

Container may be filled with

156

Aerosol material or suspended particles in a liquid flow

158

Guide channel

160

Orifice plate

162

Orifice

164

Substrate

166

Deposition surface

FIG. 12

170

Method of laser treating deposited materials

171

Substrate

172

Treatable material deposition

174

Laser beam

176

Focusing lens

178

Laser-treated material

FIG. 13

180

Alternative method of treating deposited materials

181

Flow of aerosol particles

182

Aerosol jetting apparatus

184

Laser beam

188

Treatable material

189

Laser treated material

190

Substrate

192

Particle flow

FIG. 14

200

Apparatus for simultaneous deposition and treatment of particulate material

202

Laser beam

204

Focusing lens

206

Aerosol deposition apparatus

208

Aerosol source

210

Orifice

212

Substrate

214

Treated, deposited material

216

Particle stream

FIG. 15

220

Apparatus for direct-writing and treating materials using temporary support

222

Laser beam

223

Focusing lens

224

Deposited structure

226

Treatable material

230

Support material

232

Substrate

FIG. 16

240

Apparatus for controlling energy required to treat deposited materials

241

Laser beam

242

Aerosol deposition apparatus

243

Particles

244

Stream of aerosol droplets

245

Aerosol droplets

246

Aerosol pre-heater

248

Treatable deposited material

250

Substrate heater

252

Treated material

254

Substrate

FIG. 17

260

Apparatus for forming structures using laser guidance and liquid jetting

261

Laser beam

262

Focusing lens

263

Dissolved or suspended particulates

264

Inner chamber

266

Outer chamber

267

Fluid media

268

Substrate

269

Orifice

272

Particle stream

274

Deposition footprint

Number	Name	Date	Kind
3808432	Ashkin	Apr 1974	A
3808550	Ashkin	Apr 1974	A
4016417	Benton	Apr 1977	A
4810658	Shanks et al.	Mar 1989	A
4909080	Kikuta et al.	Mar 1990	A
5009102	Afromowitz	Apr 1991	A
5170890	Wilson et al.	Dec 1992	A
5677196	Herron et al.	Oct 1997	A

	Number	Date	Country
Parent	09/408621	Sep 1999	US
Child	09/584997		US

Particle guidance system

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims

CROSS-REFERENCES TO RELATED PATENT APPLICATIONS & CLAIMS FOR PRIORITY

Government Interests

US Referenced Citations (8)

Non-Patent Literature Citations (4)

Provisional Applications (1)

Continuation in Parts (1)

Entry
Ashkin, A., “Acceleration and Trapping of Particles by Radiation Pressure”, Physical Review Letters, Jan. 26, 1970, pp. 156-159, vol. 24, No. 4, The American Physical Society.
Ashkin, A., et al., “Optical trapping and manipulation of single cells using infrared laser beams”, Nature, Dec. 24/31, 1987, pp. 769-771, vol. 330, London, Great Britain.
Renn, M.J., et al., “Laser Guidance and Trapping of Mesoscale Particles in Hollow-Core Optical Fibers”, Physical Review Letters, Feb. 15, 1999, pp. 1574-1577, vol. 82, No. 7, The American Physical Society.
Renn, M.J., et al., “Particle manipulation and surface patterning by laser guidance”, Journal of Vacuum Science & Technology B, Nov./Dec. 1998, pp. 3859-3863, vol. 16, No. 6, American Vacuum Society.