WO2007064358A2 - Structures and methods for coupling energy from an electromagnetic wave - Google Patents

Abstract

A device couples energy from an electromagnetic wave to charged particles in a beam. The device includes a micro-resonant structure and a cathode for providing electrons along a path. The micro-resonant structure, on receiving the electromagnetic wave, generates a varying field in a space including a portion of the path. Electrons are deflected or angularly modulated to a second path.

Description

STRUCTURES AND METHODS FOR COUPLING ENERGY FROM AN ELECTROMAGNETIC WAVE

COPYRIGHT NOTICE

[0001] A portion of the disclosure of this patent document contains material which is subject to copyright or mask work protection. The copyright or mask work owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright or mask work rights whatsoever.

RELATED APPLICATIONS

[0002] This application is related to and claims priority from U.S. Patent

Application No. __/__, , [atty. docket 2549-0003], titled "Ultra-Small Resonating

Charged Particle Beam Modulator," and filed September 30, 2005, the entire contents of

which are incorporated herein by reference. This application is related to U.S. Patent

Application No. 10/917,511, filed on August 13, 2004, entitled "Patterning Thin Metal

Film by Dry Reactive Ion Etching," and U.S. Application No. 11/203,407, entitled

"Method Of Patterning Ultra-Small Structures," filed on August 15, 2005, and U.S.

Application No. __/__, [atty. docket 2549-0059], titled "Electron Beam Induced

Resonance," and filed on even date herewith, all of which are commonly owned with the

present application at the time of filing, and the entire contents of each of which are

incorporated herein by reference.

FIELD OF INVENTION

[0003] This disclosure relates to coupling energy from an electromagnetic wave. INTRODUCTION AND BACKGROUND Electromagnetic Radiation & Waves [0004] Electromagnetic radiation is produced by the motion of electrically charged

particles. Oscillating electrons produce electromagnetic radiation commensurate in

frequency with the frequency of the oscillations. Electromagnetic radiation is essentially

energy transmitted through space or through a material medium in the form of

electromagnetic waves. The term can also refer to the emission and propagation of such

energy. Whenever an electric charge oscillates or is accelerated, a disturbance

characterized by the existence of electric and magnetic fields propagates outward from it.

This disturbance is called an electromagnetic wave. Electromagnetic radiation falls into

categories of wave types depending upon their frequency, and the frequency range of

such waves is tremendous, as is shown by the electromagnetic spectrum in the following

chart (which categorizes waves into types depending upon their frequency):

[0005] The ability to generate (or detect) electromagnetic radiation of a particular

type (e.g., radio, microwave, etc.) depends upon the ability to create a structure suitable

for electron oscillation or excitation at the frequency desired. Electromagnetic radiation

at radio frequencies, for example, is relatively easy to generate using relatively large or

even somewhat small structures.

ELECTROMAGNETIC WAVE GENERATION

[0006] There are many traditional ways to produce high-frequency radiation in

ranges at and above the visible spectrum, for example, up to high hundreds of Terahertz.

There,are also many traditional and anticipated applications that use such high frequency

radiation. As frequencies increase, however, the kinds of structures needed to create the

electromagnetic radiation at a desired frequency become generally smaller and harder to

manufacture. We have discovered ultra-small-scale devices that obtain multiple different

frequencies of radiation from the same operative layer.

[0007] Resonant structures have been the basis for much of the presently known

high frequency electronics. Devices like klystrons and magnetrons had electronics that

moved frequencies of emission up to the megahertz range by the 1930s and 1940s. By

around 1960, people were trying to reduce the size of resonant structures to get even

higher frequencies, but had limited success because the Q of the devices went down due

to the resistivity of the walls of the resonant structures. At about the same time, Smith

and Purcell saw the first signs that free electrons could cause the emission of

electromagnetic radiation in the visible range by running an electron beam past a diffraction grating. Since then, there has been much speculation as to what the physical

basis for the Smith-Purcell radiation really is.

[0008] We have shown that some of the theory of resonant structures applies to

certain nano structures that we have built. It is assumed that at high enough frequencies,

plasmons conduct the energy as opposed to the bulk transport of electrons in the material,

although our inventions are not dependent upon such an explanation. Under that theory,

the electrical resistance decreases to the point where resonance can effectively occur

again, and makes the devices efficient enough to be commercially viable.

[0009] Some of the more detailed background sections that follow provide

background for the earlier technologies (some of which are introduced above), and

provide a framework for understanding why the present inventions are so remarkable

compared to the present state-of-the-art.

Microwaves

[0010] As previously introduced, microwaves were first generated in so-called

"klystrons" in the 1930s by the Varian brothers. Klystrons are now well-known

structures for oscillating electrons and creating electromagnetic radiation in the

microwave frequency. The structure and operation of klystrons has been well-studied

and documented and will be readily understood by the artisan. However, for the purpose

of background, the operation of the klystron will be described at a high level, leaving the

particularities of such devices to the artisan's present understanding. [0011] Klystrons are a type of linear beam microwave tube. A basic structure of a

klystron is shown by way of example in Figure l(a). In the late 1930s, a klystron

structure was described that involved a direct current stream of electrons within a vacuum

cavity passing through an oscillating electric field. In the example of Figure l(a), a

klystron 100 is shown as a high-vacuum device with a cathode 102 that emits a well-

focused electron beam 104 past a number of cavities 106 that the beam traverses as it

travels down a linear tube 108 to anode 103. The cavities are sized and designed to

resonate at or near the operating frequency of the tube. The principle, in essence,

involves conversion of the kinetic energy in the beam, imparted by a high accelerating

voltage, to microwave energy. That conversion takes place as a result of the amplified

RF (radio frequency) input signal causing the electrons in the beam to "bunch up" into

so-called "bunches" (denoted 110) along the beam path as they pass the various cavities

106. These bunches then give up their energy to the high-level induced RF fields at the

output cavity.

[0012] The electron bunches are formed when an oscillating electric field causes

the electron stream to be velocity modulated so that some number of electrons increase in

speed within the stream and some number of electrons decrease in speed within the

stream. As the electrons travel through the drift tube of the vacuum cavity the bunches

that are formed create a space-charge wave or charge-modulated electron beam. As the

electron bunches pass the mouth of the output cavity, the bunches induce a large current, much larger than the input current. The induced current can then generate

electromagnetic radiation.

Traveling Wave Tubes

[0013] Traveling wave tubes (TWT) - first described in 1942 - are another well-

known type of linear microwave tube. A TWT includes a source of electrons that travels

the length of a microwave electronic tube, an attenuator, a helix delay line, radio

frequency (RF) input and output, and an electron collector. In the TWT, an electrical

current was sent along the helical delay line to interact with the electron stream.

Backwards Wave Devices

[0014] Backwards wave devices are also known and differ from TWTs in that they

use a wave in which the power flow is opposite in direction from that of the electron

beam. A backwards wave device uses the concept of a backward group velocity with a

forward phase velocity. In this case, the RF power comes out at the cathode end of the

device. Backward wave devices could be amplifiers or oscillators.

Magnetrons

[0015] Magnetrons are another type of well-known resonance cavity structure

developed in the 1920s to produce microwave radiation. While their external

configurations can differ, each magnetron includes an anode, a cathode, a particular wave

tube and a strong magnet. Figure l(b) shows an exemplary magnetron 112. In the

example magnetron 112 of Figure l(b), the anode is shown as the (typically iron) external

structure of the circular wave tube 114 and is interrupted by a number of cavities 116 interspersed around the tube 114. The cathode 118 is in the center of the magnetron, as

shown. Absent a magnetic field, the cathode would send electrons directly outward

toward the anode portions forming the tube 114. With a magnetic field present and in

parallel to the cathode, electrons emitted from the cathode take a circular path 118 around

the tube as they emerge from the cathode and move toward the anode. The magnetic

field from the magnet (not shown) is thus used to cause the electrons of the electron beam

to spiral around the cathode, passing the various cavities 116 as they travel around the

tube. As with the linear klystron, if the cavities are tuned correctly, they cause the

electrons to bunch as they pass by. The bunching and unbunching electrons set up a

resonant oscillation within the tube and transfer their oscillating energy to an output

cavity at a microwave frequency.

Reflex Klystron

[0016] Multiple cavities are not necessarily required to produce microwave

radiation. In the reflex klystron, a single cavity, through which the electron beam is

passed, can produce the required microwave frequency oscillations. An example reflex

klystron 120 is shown in Figure l(c). There, the cathode 122 emits electrons toward the

reflector plate 124 via an accelerator grid 126 and grids 128. The reflex klystron 120 has

a single cavity 130. In this device, the electron beam is modulated (as in other klystrons)

by passing by the cavity 130 on its way away from the cathode 122 to the plate 124.

Unlike other klystrons, however, the electron beam is not terminated at an output cavity, but instead is reflected by the reflector plate 124. The reflection provides the feedback

necessary to maintain electron oscillations within the tube.

[0017] In each of the resonant cavity devices described above, the characteristic

frequency of electron oscillation depends upon the size, structure, and tuning of the

resonant cavities. To date, structures have been discovered that create relatively low

frequency radiation (radio and microwave levels), up to, for example, GHz levels, using

these resonant structures. Higher levels of radiation are generally thought to be

prohibitive because resistance in the cavity walls will dominate with smaller sizes and

will not allow oscillation. Also, using current techniques, aluminum and other metals

cannot be machined down to sufficiently small sizes to form the cavities desired. Thus,

for example, visible light radiation in the range of 400 Terahertz - 750 Terahertz is not

known to be created by klystron-type structures.

[0018] U.S. Patent No. 6,373, 194 to Small illustrates the difficulty in obtaining

small, high-frequency radiation sources. Small suggests a method of fabricating a micro-

magnetron. In a magnetron, the bunched electron beam passes the opening of the

resonance cavity. But to realize an amplified signal, the bunches of electrons must pass

the opening of the resonance cavity in less time than the desired output frequency. Thus

at a frequency of around 500 THz, the electrons must travel at very high speed and still

remain confined. There is no practical magnetic field strong enough to keep the electron

spinning in that small of a diameter at those speeds. Small recognizes this issue but does

not disclose a solution to it. [0019] Surface plasmons can be excited at a metal dielectric interface by a

monochromatic light beam. The energy of the light is bound to the surface and

propagates as an electromagnetic wave. Surface plasmons can propagate on the surface

of a metal as well as on the interface between a metal and dielectric material. Bulk

plasmons can propagate beneath the surface, although they are typically not energetically

favored.

[0020] Free electron lasers offer intense beams of any wavelength because the

electrons are free of any atomic structure. In U.S. Patent No. 4,740,973, Madey et al.

disclose a free electron laser. The free electron laser includes a charged particle

accelerator, a cavity with a straight section and an undulator. The accelerator injects a

relativistic electron or positron beam into said straight section past an undulator mounted

coaxially along said straight section. The undulator periodically modulates in space the

acceleration of the electrons passing through it inducing the electrons to produce a light

beam that is practically collinear with the axis of undulator. An optical cavity is defined

by two mirrors mounted facing each other on either side of the undulator to permit the

circulation of light thus emitted. Laser amplification occurs when the period of said

circulation of light coincides with the period of passage of the electron packets and the

optical gain per passage exceeds the light losses that occur in the optical cavity.

Smith-Purcell

[0021] Smith-Purcell radiation occurs when a charged particle passes close to a

periodically varying metallic surface, as depicted in Figure l(d). [0022] Known Smith-Purcell devices produce visible light by passing an electron

beam close to the surface of a diffraction grating. Using the Smith-Purcell diffraction

grating, electrons are deflected by image charges in the grating at a frequency in the

visible spectrum. In some cases, the effect may be a single electron event, but some

devices can exhibit a change in slope of the output intensity versus current. In Smith-

Purcell devices, only the energy of the electron beam and the period of the grating affect

the frequency of the visible light emission. The beam current is generally, but not

always, small. Vermont Photonics notice an increase in output with their devices above a

certain current density limit. Because of the nature of diffraction physics, the period of

the grating must exceed the wavelength of light.

[0023] Koops, et al., U.S. Patent No. 6,909,104, published November 30, 2000,

(§ 102(e) date May 24, 2002) describe a miniaturized coherent terahertz free electron

laser using a periodic grating for the undulator (sometimes referred to as the wiggler).

Koops et al. describe a free electron laser using a periodic structure grating for the

undulator (also referred to as the wiggler). Koops proposes using standard electronics to

bunch the electrons before they enter the undulator. The apparent object of this is to

create coherent terahertz radiation. In one instance, Koops, et al. describe a given

standard electron beam source that produces up to approximately 20,000 volts

accelerating voltage and an electron beam of 20 microns diameter over a grating of 100

to 300 microns period to achieve infrared radiation between 100 and 1000 microns in

wavelength. For terahertz radiation, the diffraction grating has a length of approximately 1 mm to 1 cm, with grating periods of 0.5 to 10 microns, "depending on the wavelength

of the terahertz radiation to be emitted." Koops proposes using standard electronics to

bunch the electrons before they enter the undulator.

[0024] Potylitsin, "Resonant Diffraction Radiation and Smith-Purcell Effect," 13

April 1998, described an emission of electrons moving close to a periodic structure

treated as the resonant diffraction radiation. Potylitsin 's grating had "perfectly

conducting strips spaced by a vacuum gap."

[0025] Smith-Purcell devices are inefficient. Their production of light is weak

compared to their input power, and they cannot be optimized. Current Smith-Purcell

devices are not suitable for true visible light applications due at least in part to their

inefficiency and inability to effectively produce sufficient photon density to be detectible

without specialized equipment.

[0026] We realized that the Smith-Purcell devices yielded poor light production

efficiency. Rather than deflect the passing electron beam as Smith-Purcell devices do,

we created devices that resonated at the frequency of light as the electron beam passes by.

In this way, the device resonance matches the system resonance with resulting higher

output. Our discovery has proven to produce visible light (or even higher or lower

frequency radiation) at higher yields from optimized ultra-small physical structures.

COUPLING ENERGY FROM ELECTROMAGNETIC WAVES

[0027] Coupling energy from electromagnetic waves in the terahertz range from

0.1 THz (about 3000 microns) to 700 THz (about 0.4 microns) is finding use in numerous new applications. These applications include improved detection of concealed weapons

and explosives, improved medical imaging, finding biological materials, better

characterization of semiconductors; and broadening the available bandwidth for wireless

communications.

[0028] In solid materials the interaction between an electromagnetic wave and a

charged particle, namely an electron, can occur via three basic processes: absorption,

spontaneous emission and stimulated emission. The interaction can provide a transfer of

energy between the electromagnetic wave and the electron. For example, photoconductor

semiconductor devices use the absorption process to receive the electromagnetic wave

and transfer energy to electron-hole pairs by band-to-band transitions. Electromagnetic

waves having an energy level greater than a material's characteristic binding energy can

create electrons that move when connected across a voltage source to provide a current.

In addition, extrinsic photoconductor devices operate having transitions across forbidden-

gap energy levels use the absorption process (S.M., Sze, "Semiconductor Devices

Physics and Technology," 2002).

[0029] A measure of the energy coupled from an electromagnetic wave for the

material is referred to as an absorption coefficient. A point where the absorption

coefficient decreases rapidly is called a cutoff wavelength. The absorption coefficient is

dependant on the particular material used to make a device. For example, gallium

arsenide (GaAs) absorbs electromagnetic wave energy from about 0.6 microns and has a

cutoff wavelength of about 0.87 microns. In another example, silicon (Si) can absorb energy from about 0.4 microns and has a cutoff wavelength of about 1.1 microns. Thus,

the ability to transfer energy to the electrons within the material for making the device is

a function of the wavelength or frequency of the electromagnetic wave. This means the

device can work to couple the electromagnetic wave's energy only over a particular

segment of the terahertz range. At the very high end of the terahertz spectrum a Charge

Coupled Device (CCD) — an intrinsic photoconductor device — can successfully be

employed. If there is a need to couple energy at the lower end of the terahertz spectrum

certain extrinsic semiconductors devices can provide for coupling energy at increasing

wavelengths by increasing the doping levels.

SURFACE ENHANCED RAMAN SPECTROSCOPY (SERS)

[0030] Raman spectroscopy is a well-known means to measure the characteristics

of molecule vibrations using laser radiation as the excitation source. A molecule to be

analyzed is illuminated with laser radiation and the resulting scattered frequencies are

collected in a detector and analyzed.

[0031] Analysis of the scattered frequencies permits the chemical nature of the

molecules to be explored. Fleischmann et al. (M. Fleischmann, P. J. Hendra and A. J.

McQuillan, Chem. Phys. Lett., 1974, 26, 163) first reported the increased scattering

intensities that result from Surface Enhanced Raman Spectroscopy (SERS), though

without realizing the cause of the increased intensity.

[0032] In SERS, laser radiation is used to excite molecules adsorbed or deposited

onto a roughened or porous metallic surface, or a surface having metallic nano-sized features or structures. The largest increase in scattering intensity is realized with surfaces

with features that are 10-100 run in size. Research into the mechanisms of SERS over the

past 25 years suggests that both chemical and electromagnetic factors contribute to the

enhancing the Raman effect. (See, e.g., A. Campion and P. Kambhampati, Chem. Soc.

Rev., 1998, 27 241.)

[0033] The electromagnetic contribution occurs when the laser radiation excites

plasmon resonances in the metallic surface structures. These plasmons induce local

fields of electromagnetic radiation which extend and decay at the rate defined by the

dipole decay rate. These local fields contribute to enhancement of the Raman scattering

at an overall rate of E4.

[0034] Recent research has shown that changes in the shape and composition of

nano-sized features of the substrate cause variation in the intensity and shape of the local

fields created by the plasmons. Jackson and Halas (J.B. Jackson and N.J. Halas, PNAS,

2004, 101 17930) used nano-shells of gold to tune the plasmon resonance to different

frequencies.

[0035] Variation in the local electric field strength provided by the induced

plasmon is known in SERS-based devices. In U.S. Patent application 2004/0174521 Al,

Drachev et al. describe a Raman imaging and sensing device employing nanoantennas.

The antennas are metal structures deposited onto a surface. The structures are

illuminated with laser radiation. The radiation excites a plasmon in the antennas that

enhances the Raman scatter of the sample molecule. [0036] The electric field intensity surrounding the antennas varies as a function of

distance from the antennas, as well as the size of the antennas. The intensity of the local

electric field increases as the distance between the antennas decreases.

Advantages & Benefits

[0037] Myriad benefits and advantages can be obtained by a ultra-small resonant

structure that emits varying electromagnetic radiation at higher radiation frequencies such

as infrared, visible, UV and X-ray. For example, if the varying electromagnetic radiation

is in a visible light frequency, the micro resonant structure can be used for visible light

applications that currently employ prior art semiconductor light emitters (such as LCDs,

LEDs, and the like that employ electroluminescence or other light-emitting principals). If

small enough, such micro-resonance structures can rival semiconductor devices in size,

and provide more intense, variable, and efficient light sources. Such micro resonant

structures can also be used in place of (or in some cases, in addition to) any application

employing non-semiconductor illuminators (such as incandescent, fluorescent, or other

light sources). Those applications can include displays for personal or commercial use,

home or business illumination, illumination for private display such as on computers,

televisions or other screens, and for public display such as on signs, street lights, or other

indoor or outdoor illumination. Visible frequency radiation from ultra-small resonant

structures also has application in fiber optic communication, chip-to-chip signal coupling,

other electronic signal coupling, and any other light-using applications. [0038] Applications can also be envisioned for ultra-small resonant structures that

emit in frequencies other than in the visible spectrum, such as for high frequency data

carriers. Ultra-small resonant structures that emit at frequencies such as a few tens of

terahertz can penetrate walls, making them invisible to a transceiver, which is

exceedingly valuable for security applications. The ability to penetrate walls can also be

used for imaging objects beyond the walls, which is also useful in, for example, security

applications. X-ray frequencies can also be produced for use in medicine, diagnostics,

security, construction or any other application where X-ray sources are currently used.

Terahertz radiation from ultra-small resonant structures can be used in many of the

known applications which now utilize x-rays, with the added advantage that the resulting

radiation can be coherent and is non-ionizing.

[0039] The use of radiation per se in each of the above applications is not new.

But, obtaining that radiation from particular kinds of increasingly small ultra-small

resonant structures revolutionizes the way electromagnetic radiation is used in electronic

and other devices. For example, the smaller the radiation emitting structure is, the less

"real estate" is required to employ it in a commercial device. Since such real estate on a

semiconductor, for example, is expensive, an ultra-small resonant structure that provides

the myriad application benefits of radiation emission without consuming excessive real

estate is valuable. Second, with the kinds of ultra-small resonant structures that we

describe, the frequency of the radiation can be high enough to produce visible light of any

color and low enough to extend into the terahertz levels (and conceivably even petahertz or exahertz levels with additional advances). Thus, the devices may be tunable to obtain

any kind of white light transmission or any frequency or combination of frequencies

desired without changing or stacking "bulbs," or other radiation emitters (visible or

invisible).

[0040] Currently, LEDs and Solid State Lasers (SSLs) cannot be integrated onto

silicon (although much effort has been spent trying). Further, even when LEDs and SSLs

are mounted on a wafer, they produce only electromagnetic radiation at a single color.

The present devices are easily integrated onto even an existing silicon microchip and can

produce many frequencies of electromagnetic radiation at the same time.

[0041] Hence, there is a need for a device having a single basic construction that

can couple energy from an electromagnetic wave over the full terahertz portion of the

electromagnetic spectrum.

GLOSSARY [0042] As used throughout this document:

[0043] The phrase "ultra-small resonant structure" shall mean any structure of any

material, type or microscopic size that by its characteristics causes electrons to resonate at

a frequency in excess of the microwave frequency.

[0044] The term "ultra-small" within the phrase "ultra-small resonant structure"

shall mean microscopic structural dimensions and shall include so-called "micro"

structures, "nano" structures, or any other very small structures that will produce

resonance at frequencies in excess of microwave frequencies. DESCRIPTION OF PRESENTLY PREFERRED EXEMPLARY EMBODIMENTS OF THE

INVENTION

BRIEF DESCRIPTION OF FIGURES

[0045] The invention is better understood by reading the following detailed

description with reference to the accompanying drawings in which:

[0046] FIG. l(a) shows a prior art example klystron.

[0047] FIG. l(b) shows a prior art example magnetron.

[0048] FIG. l(c) shows a prior art example reflex klystron.

[0049] FIG. l(d) depicts aspects of the Smith-Purcell theory.

[0050] FIG. 2(a) is a highly-enlarged perspective view of an energy coupling

device showing an ultra-small micro-resonant structure in accordance with embodiments

of the present invention;

[0051] FIG. 2(b) is a side view of the ultra-small micro-resonant structure of

FIG. 2(a);

[0052] FIG. 3 is a highly- enlarged side view of the energy coupling device of

FIG. 2(a);

[0053] FIG. 4 is a highly-enlarged perspective view of an energy coupling device

illustrating the ultra-small micro- resonant structure according to alternate embodiments

of the present invention; [0054] FIG. 5 is a highly-enlarged perspective view of an energy coupling device

illustrating of the ultra-small micro-resonant structure according to alternate

embodiments the present invention;

[0055] FIG. 6 is a highly-enlarged top view of an energy coupling device

illustrating of the ultra-small micro- resonant structure according to alternate

embodiments the present invention; and

[0056] FIG. 7 is a highly-enlarged top view of an energy coupling device showing

of the ultra-small micro- resonant structure according to alternate embodiments of the

present invention.

DESCRIPTION

[0057] Generally, the present invention includes devices and methods for coupling

energy from an electromagnetic wave to charged particles. A surface of a micro-resonant

structure is excited by energy from an electromagnetic wave, causing it to resonate. This

resonant energy interacts as a varying field. A highly intensified electric field component

of the varying field is coupled from the surface. A source of charged particles, referred to

herein as a beam, is provided. The beam can include ions (positive or negative),

electrons, protons and the like. The beam may be produced by any source, including,

e.g., without limitation an ion gun, a tungsten filament, a cathode, a planar vacuum

triode, an electron-impact ionizer, a laser ionizer, a chemical ionizer, a thermal ionizer, an

ion-impact ionizer. The beam travels on a path approaching the varying field. The beam

s deflected or angularly modulated upon interacting with a varying field coupled from the surface. Hence, energy from the varying field is transferred to the charged particles

of the beam. In accordance with some embodiments of the present invention,

characteristics of the micro-resonant structure including shape, size and type of material

disposed on the micro-resonant structure can affect the intensity and wavelength of the

varying field. Further, the intensity of the varying field can be increased by using

features of the micro-resonant structure referred to as intensifiers. Further, the micro-

resonant structure may include structures, nano-structures, sub-wavelength structures and

the like. The device can include a plurality of micro-resonant structures having various

orientations with respect to one another.

[0058] FIG. 2(a) is a highly-enlarged perspective- view of an energy coupling

device or device 200 showing an ultra-small micro-resonant structure (MRS) 202 having

surfaces 204 for coupling energy of an electromagnetic wave 206 (also denoted E) to the

MRS 202 in accordance with embodiments of the present invention. The MRS 202 is

formed on a major surface 208 of a substrate 210, and, in the embodiments depicted in

the drawing, is substantially C-shaped with a cavity 212 having a gap 216, shown also in

FIG. 2(b). The MRS 202 can be scaled in accordance with the (anticipated and/or

desired) received wavelength of the electromagnetic wave 206. The MRS 202 is referred

to as a sub-wavelength structure 214 when the size of the MRS 202 is on the order of

one-quarter wavelength of the electromagnetic wave 206. For example, the height H of

the MRS 202 can be about 125 nanometers where the frequency of the electromagnetic

wave 206 is about 600 terahertz. In other embodiments, the MRS 202 can be sized on the order of a quarter-wavelength multiple of the incident electromagnetic wave 206. The

surface 204 on the MRS 202 is generally electrically conductive. For example, materials

such as gold (Au), copper (Cu), silver (Ag), and the like can be disposed on the surface

204 of the MRS 202 (or the MRS 202 can be formed substantially of such materials).

Conductive alloys can also be used for these applications.

[0059] Energy from electromagnetic wave 206 is transferred to the surface 204 of

the MRS 202. The energy from the wave 218 can be transferred to waves of electrons

within the atomic structure on and adjacent to the surface 204 referred to as surface

plasmons 220 (also denoted "P" in the drawing). The MRS 202 stores the energy and

resonates, thereby generating a varying field (denoted generally 222). The varying field

222 can couple through a space 224 adjacent to the MRS 202 including the space 224

within the cavity 212.

[0060] A charged particle source 228 emits a beam 226 of charged particles

comprising, e.g., ions or electrons or positrons or the like. The charged particle source

shown in FIG. 2(a) is a cathode 228 for emitting the beam 226 comprising electrons 230.

Those skilled in the art will realize that other types and sources of charged particles can

be used and are contemplated herein. The charged particle source, i.e., cathode 228, can

be formed on the major surface 208 with the MRS 202 and, for example, can be coupled

to a potential of minus V_Cc- Those skilled in the art will realize that the charged particle

source need not be formed on the same surface or structure as the MRS. The cathode 228

can be made using a field emission tip, a thermionic source, and the like. The type and/or source of charged particle employed should not be considered a limitation of the present

invention.

[0061] A control electrode 232, preferably grounded, is typically positioned

between the cathode 228 and the MRS 202. When the beam 226 is emitted from the

cathode 228, there can be a slight attraction by the electrons 230 to the control electrode

232. A portion of the electrons 230 travel through an opening 234 near the center of the

control electrode 232. Hence, the control electrode 232 provides a narrow distribution of

the beam 226 of electrons 230 that journey through the space 224 along a straight path

236. The space 224 should preferably be under a sufficient vacuum to prevent scattering

of the electrons 230.

[0062] As shown in FIG. 2(a), the electrons 230 travel toward the cavity 212

along the straight path 236. If no electromagnetic wave 206 is received on surface 204,

no varying field 222 is generated, and the electrons 230 travel generally along the straight

path 236 undisturbed through the cavity 212. In contrast, when an electromagnetic wave

206 is received, varying field 222 is generated. The varying field 222 couples through

the space 224 within the cavity 212. Hence, electrons 230 approaching the varying field

222 in the cavity 212 are deflected or angularly modulated from the straight path 236 to a

plurality of paths (generally denoted 238, not all shown). The varying field 222 can

comprise electric and magnetic field components (denoted E and B in FIG. 2(a)). It

should be noted that varying electric and magnetic fields inherently occur together as

taught by the well-known Maxwell's equations. The magnetic and electric fields within the cavity 212 are generally along the X and Y axes of the coordinate system,

respectively. An intensifier is used to increase the magnitude of the varying field 222 and

particularly the electric field component of the varying field 222. For example, as the

distance across the gap 216 decreases, the electric field intensity typically increases

across the gap 216. Since the electric field across the gap 216 is intensified, there is a

force (given by the equation F = qE ) on the electrons 230 that is generally transverse to

the straight path 236. It should be noted that the cavity 212 is a particular form of an

intensifier used to increase the magnitude of the varying field 222. The force from the

magnetic field B (given by the equation F = qv χ B ) can act on the electrons 230 in a

direction perpendicular to both the velocity v of the electrons 230 arid the direction of

the magnetic field B . For example, in one embodiment where the electric and magnetic

fields are generally in phase, the force from the magnetic field acts on the electrons 230

generally in the same direction as the force from the electric field. Hence, the transverse

force, given by the equation F = g(E + v x B) , angularly modulating the electrons 230 can

be contributed by both the electric and magnetic field components of the varying field

222.

[0063] FIG. 3 is a highly-enlarged side-view of the device 200 from the exposed

cavity 212 side of FIG. 2(A) illustrating angularly modulated electrons 230 in

accordance with embodiments of the present invention. The cavity 212, as shown, can

extend the full length L of the MRS 202 and is exposed to the space 224. The cavity 212 ^'

can include a variety of shapes such as semi-circular, rectangular, triangular and the like. [0064] When electrons 230 are in the cavity 212, the varying field 222 formed

across the gap 216 provides a changing transverse force F on the electrons. Depending

on the frequency of the varying field 222 in relation to the length (L) of the cavity 212,

the electrons 230 traveling through the cavity 212 can angularly modulate a plurality of

times, thereby frequently changing directions from the forces of the varying field 222.

Once the electrons 230 are angularly modulated, the electrons can travel on any one of

the plurality of paths generally denoted 238, including a generally sinusoidal path

referred to as an oscillating path 242. After exiting the cavity 212, the electrons 230 can

travel on another one of the plurality of paths 238 referred to as a new path 244, which is

generally straight. Since the forces for angularly modulating the electrons 230 from the

varying field 222 are generally within the cavity 212, the electrons 230 typically no

longer change direction after exiting the cavity 212. The location of the new path 244 at

a point in time can be indicative of the amount of energy coupled from the

electromagnetic wave 206. For example, the further the beam 226 deflects from the

straight path 236, the greater the amount of energy from the electromagnetic wave 206

transferred to the beam 226. The straight path 236 is extended in the drawing to show an

angle (denoted α) with respect to the new path 244. Hence, the larger the angle α the

greater the magnitude of energy transferred to the beam 226.

[0065] Angular modulation can cause a portion of electrons 230 traveling in the

cavity 212 to collide with the MRS 202 causing a charge to build up on the MRS 202. If

electrons 230 accumulate on the MRS 202 in sufficient number, the beam 226 can offset or bend away from the MRS 202 and from the varying field 222 coupled from the MRS

202. This can diminish the interaction between the varying field 222 and the electrons

230. For this reason, the MRS 202 is typically coupled to ground via a low resistive path

to prevent any charge build-up on the MRS 202. The grounding of the MRS 202 should

not be considered a limitation of the present invention.

[0066] FIG. 4 is a highly-enlarged perspective- view illustrating a device 400

including alternate embodiments of a micro-resonant structure 402. In a manner as

mentioned with reference to FIG. 2(A), an electromagnetic wave 206 (also denoted E)

incident to a surface 404 of the MRS 402 transfers energy to the MRS 402, which

generates a varying field 406. In the embodiments shown in FIG. 4, a gap 410 formed by

ledge portions 412 can act as an intensifϊer. The varying field 406 is shown across the

gap 410 with the electric and magnetic field components (denoted E and B ) generally

along the X and Y axes of the coordinate system, respectively. Since a portion of the

varying field can be intensified across the gap 410, the ledge portions 412 can be sized

during fabrication to provide a particular magnitude or wavelength of the varying field

406.

[0067] An external charged particle source 414 targets a beam 416 of charged

particles (e.g., electrons) along a straight path 420 through an opening 422 on a sidewall

424 of the device 400. The charged particles travel through a space 426 within the gap

410. On interacting with the varying field 426, the charged particles are shown angularly

modulated, deflected or scattered from the straight path 420. Generally, the charged particles travel on an oscillating path 428 within the gap 410. After passing through the

gap 410, the charged particles are angularly modulated on a new path 430. An angle β

illustrates the deviation between the new path 430 and the straight path 420.

[0068] FIG. 5 is a highly-enlarged perspective- view illustrating a device 500

according to alternate embodiments of the invention. The device 500 includes a micro-

resonant structure 502. The MRS 502 is formed by a wall 504 and is generally a semi¬

circular shape. The wall 504 is connected to base portions 506 formed on a major surface

508. In the manner described with respect to the embodiments of FIG. 2(A), energy is

coupled from an electromagnetic wave (denoted E), and the MRS 502 resonates

generating a varying field. An intensifier in the form here of a gap 512 increases the

magnitude of the varying field. A source of charged particles, e.g., cathode 514 targets a

beam 516 of electrons 518 on a straight path 520. Interaction with the varying field

causes the beam 516 of electrons 518 to angularly modulate on exiting the cavity 522 to

the new path 524 or any one of a plurality of paths generally denoted 526 (not all shown).

[0069] FIG. 6 is a highly-enlarged top-view illustrating a device 600 including yet

another alternate embodiment of a micro-resonant structure 602. The MRS 602 shown in

the figure is generally a cube shaped structure, however those skilled in the art will

immediately realize that the MRS need not be cube shaped and the invention is not

limited by the shape of the MRS structure 602. The MRS should have some area to

absorb the incoming photons and it should have some part of the structure having

relatively sharp point, corner or cusp to concentrate the electric field near where the electron beam is traveling. Thus, those skilled in the art will realize that the MRS 602

may be shaped as a rectangle or triangle or needle or other shapes having the appropriate

surface(s) and point(s). As described above with reference to FIG. 2(A)₅ energy from an

electromagnetic wave (denoted E) is coupled to the MRS 602. The MRS 602 resonates

and generates a varying field. The varying field can be magnified by an intensifier. For

example, the device 600 may include a cathode 608 formed on the surface 610 for

providing a beam 612 of electrons 614 along a path. In some embodiments, the cathode

608 directs the electrons 614 on a straight path 616 near an edge 618 of the MRS 602,

thereby providing an edge 618 for the intensifier. The electrons 614 approaching a space

620 near the edge 618 are angularly modulated from the straight path 616 and form a new

path 622. In other embodiments, the intensifier can be a corner 624 of the MRS 602,

because the cathode 608 targets the beam 612 on a straight path 616 near the corner 624

of the MRS 602. The electrons 614 approaching the corner 624 are angularly modulated

from the straight path 616, thereby forming a new path 626. The new paths 622 and 626

can be any one path of the plurality of paths formed by the electrons on interacting with

the varying field. In yet other embodiments, (not shown) the intensifier may be a

protuberance or boss that protrudes or is generally elevated above a surface 628 of the

MRS 602.

[0070] FIG. 7 is a highly-enlarged view illustrating a device 700 including yet

other alternate embodiments of micro-resonant structures according to the present

invention. The MRS 702 comprises a plurality of structures 704 and 706, which are, in preferred embodiments, generally triangular shaped, although the shape of the structures

704 and 706 can include a variety of shapes including rectangular, spherical, cylindrical,

cubic and the like. The invention is not limited by the shape of the structures 704 and

706.

[0071] Surfaces of the structures 704, 706 receive the electromagnetic wave 712

(also denoted E). As described with respect to FIG. 2(A), the MRS generates a varying

field (denoted 716) that is magnified using an intensifier. In some embodiments, the

intensifier includes corners 720 and 722 of the structure 704 and corner 724 of the

structure 706. The cathode 726 provides a beam 728 of electrons 704 approaching the

varying field 716 along the straight path 708. The electrons 704 are deflected or

angularly modulated from a straight path 708 at corners 720, 722 and 724, to travel along

one of a plurality of paths (denoted 730), e.g., along the path referred to as a new path

732. In other embodiments, the intensifier of the varying field may be a gap between

structures 704 and 706. The varying field across the gap angularly modulates the beam

728 to a new path 736, which is one of the plurality of paths generally denoted 730 (not

all shown).

[0072] It should be appreciated that devices having a micro-resonant structure and

that couple energy from electromagnetic waves have been provided. Further, methods of

angularly modulating charged particles on receiving an electromagnetic wave have been

provided. Energy from the electromagnetic wave is coupled to the micro-resonant

structure and a varying field is generated. A charged particle source provides a first path of electrons that travel toward a cavity of the micro-resonant structure containing the

varying field. The electrons are deflected or angularly modulated from the first path to a

second path on Interacting with the varying field. The micro-resonant structure can

include a range of shapes and sizes. Further, the micro-resonant structure can include

structures, nano-structures, sub-wavelength structures and the like. The device provides

the advantage of using the same basic structure to cover the full terahertz frequency

spectrum.

[0073] Although various particular particle sources and types have been shown and

described for the embodiments disclosed herein, those skilled in the art will realize that

other sources and/or types of charged particles are contemplated. Additionally, those

skilled in the art will realize that the embodiments are not limited by the location of the

sources of charged particles. In particular, those skilled in the art will realize that the

location or source of charged particles need not be on formed on the same substrate or

surface as the other structures.

[0074] The various devices and their components described herein may be

manufactured using the methods and systems described in related U.S. Patent Application

No. 10/917,571, filed on August 13, 2004, entitled "Patterning Thin Metal Film by Dry

Reactive Ion Etching," and U.S. Application No. 11/203,407, filed on August 15, 2005,

entitled "Method Of Patterning Ultra-Small Structures," both of which are commonly

owned with the present application at the time of filing, and the entire contents of each of

have been incorporated herein by reference. [0075] Thus are described structures and methods for coupling energy from an

electromagnetic wave and the manner of making and using same. While the invention

has been described in connection with what is presently considered to be the most

practical and preferred embodiment, it is to be understood that the invention is not to be

limited to the disclosed embodiment, but on the contrary, is intended to cover various

modifications and equivalent arrangements included within the spirit and scope of the

appended claims.

Claims

WE CLAIM

1. A device for coupling energy from an electromagnetic wave to a

charged particle beam, the device comprising:

an ultra-small micro-resonant structure having a surface for receiving the

electromagnetic wave, said ultra-small micro-resonant structure constructed and adapted

to generate a varying field on receiving the electromagnetic wave, and to cause a charged

particle beam approaching the varying field to be modulated; and

a source providing the charged particle beam, wherein the charged particle

beam comprises particles selected from the group comprising: electrons, positive ions,

negative ions, and protons, said particle beam being provided along a generally-straight

first path toward the varying field,

wherein the micro-resonant structure includes a region with varying field,

wherein the charged particle beam exits the cavity along a generally-straight second path

distinct from the first path, wherein an angle between the first path and the second path is

related, at least in part, to a magnitude of the energy coupled from the electromagnetic

wave to the charge particle beam.

2. A device for coupling energy from an electromagnetic wave to a

charged particle beam, the device comprising: an ultra-small micro-resonant structure constructed and adapted to generate

a varying field on receiving the electromagnetic wave, and to cause a charged particle

beam approaching the varying field to be angularly modulated.

3. A device as in claim 2 further comprising:

a source providing the charged particle beam.

4. A device as in claim 2 wherein the charged particle beam comprises

particles selected from the group comprising: electrons, positive ions, negative ions,

positrons and protons.

5. A device as in claim 2 wherein said particle beam is provided along

a first path toward the varying field.

6. A device as in claim 5, wherein the first path is generally straight.

7. A device as in claim 2 wherein the micro-resonant structure

comprises a surface for receiving the electromagnetic wave.

8. A device as in claim 7 wherein the surface comprises a metal

selected from the group comprising: silver (Ag), gold (Au), copper (Cu) and alloys.

9. A device as in claim 3 further comprising a substrate on which the

micro-resonant structure is formed.

10. A device as in claim 9 where said source is formed on said substrate.

11. A device as in claim 2, further comprising an intensifϊer for

increasing the magnitude of the varying field.

12. A device as in claim 11, wherein the intensifier comprises a cavity in

said micro-resonant structure having a gap.

13. A device as in claim 12 wherein the cavity has a semi-circular shape.

14. A device as in claim 12 wherein the cavity has a rectangular shape.

15. A device as in claim 12, wherein the varying field across the gap is

intensified.

16. A device as in claim 12, wherein the charged particle beam enters

the cavity transverse to the gap.

17. A device as in claim 12, wherein the charged particle beam is

angularly modulated by the varying field across the gap.

18. A device as in claim 12 wherein the charged particle beam exits the

cavity along a second path distinct from the first path.

19. A device as in claim 18, wherein the second path is generally

straight.

20. A device as in claim 19, wherein an angle between the first path and

the second path is related, at least in part, to a magnitude of the energy coupled from the

electromagnetic wave to the charge particle beam.

21. A device as in claim 11, wherein the intensifier comprises an edge of

said micro-resonant structure having an adjacent space.

22. A device as in claim 21 wherein the charged particle beam traverses

the space adjacent to the edge and is angularly modulated by the varying field.

23. A device as in claim 21 wherein the charged particle beam travels

from the space adjacent to the edge on the second path, distinct from said first path, when

the charged particle beam has been angularly modulated.

24. A device as in claim 11, wherein the intensifier comprises a corner

of the micro-resonant structure.

25. A device as in claim 24, wherein the charged particle beam travels to

the space adjacent to the corner and is angularly modulated by the varying field.

26. A device as in claim 25, wherein the charged particle beam travels

from the space adjacent to the corner on a second path, distinct from the first path, when

the charged particle beam has been angularly modulated.

27. A device as in claim 11 wherein a height of the micro-resonant

structure is about a one-quarter wavelength multiple of the wavelength of the

electromagnetic wave.

28. A device as in claim 27, wherein the micro-resonant structure

comprises a sub-wavelength structure.

29. A device as in claim 28, wherein the micro-resonant structure

comprises a nano-scale structure.

30. A device as in claim 29, wherein said micro-resonant structure

further comprises a coupler.

31. A device as in claim 30, wherein the coupler comprises an antenna.

32. A method of coupling energy from an electromagnetic wave to a

charged particle beam, the method comprising: providing an ultra-small micro-resonant structure having at least one

surface;

receiving energy from the electromagnetic wave on the at least one surface;

generating a varying field around the ultra-small micro-resonant structure;

providing a charged particle beam that approaches the varying field; and

angularly modulating the charged particle beam using the varying field.

33. The method of claim 32, wherein receiving energy from the

electromagnetic wave comprises:

receiving the electromagnetic wave on the surface; and

generating a charge density wave on and adjacent to the surface.

34. The method of claim 33, wherein generating the charge density wave

comprises exciting plasmons on the surface using the evanescent waves.

35. The method of claim 34, wherein angularly modulating the charged

particle beam comprises transversely coupling energy from the varying field to the

charged particle beam.

36. The method of claim 35, further comprising intensifying the varying

field.

37. The method of claim 36, wherein intensifying the varying field

comprises coupling the varying field across a gap of a cavity of the ultra-small micro-

resonant structure.

38. The method of claim 37, wherein intensifying the varying field

comprises coupling the varying field around a corner of the ultra-small micro-resonant

structure.

39. The method of claim 38, wherein intensifying the varying field

comprises coupling the varying field around an edge of the micro-resonant structure.

40. The method of claim 39, wherein intensifying the varying field

comprises coupling the varying field across a gap between nano-structures.

41. A device comprising: an ultra-small micro-resonant structure constructed and adapted to receive

energy from an electromagnetic wave, and having a field intensifier associated therewith,

wherein

a charged particle beam approaching the intensifier on a first path continues

on the first path when the ultra-small micro-resonant structure is not receiving energy

from an electromagnetic wave, and wherein the charged particle beam approaching the

intensifier on the first path continues on a second path, distinct from the first path, when

the ultra-small micro-resonant structure is receiving energy from an electromagnetic

wave.

42. A device as in claim 41, wherein the size of an angle between said

first path and said second path is related, at least in part, to a magnitude of the energy

from the electromagnetic wave.

43. A device as in claim 41 wherein, responsive to an electromagnetic

wave incident thereon, the ultra-small micro-resonant structure produces a varying field

that angularly modulates the charged particle beam to a path distinct from the first path.

44. The device of claim 41 , wherein the shape of the ultra-small micro-

resonant structure is selected from the group of shapes comprising: triangles, cubes,

rectangles, cylinders and spheres.

45. The device of claim 42, wherein the ultra-small micro-resonant

structure comprises a cavity having a gap.

46. The device of claim 45, wherein the charged particle beam

approaches the cavity on the first path transverse to the gap.

47. The device of claim 46, wherein the cavity is semi-circular.

48. The device of claim 45, wherein the gap intensifies the varying field.