WO2007040672A2

WO2007040672A2 - Ultra-small resonating charged particle beam modulator

Info

Publication number: WO2007040672A2
Application number: PCT/US2006/022779
Authority: WO
Inventors: Jonathan Gorrell; Mark Davidson; Michael E. Maines; Paul Hart
Original assignee: Virgin Islands Microsystems, Inc.
Priority date: 2005-09-30
Filing date: 2006-06-12
Publication date: 2007-04-12
Also published as: TW200714122A; US7253426B2; US20070075263A1; TW200713383A; US7791291B2; US20070085039A1; US7791290B2; US20070075326A1; TW200713381A; WO2007040672A3

Abstract

A method and apparatus for modulating a beam of charged particles is described in which a beam of charged particles is produced by a particle source and a varying electric field is induced within an ultra-small resonant structure. The beam of charged particles is modulated by the interaction of the varying electric field with the beam of charged particles.

Description

ULTRA-SMALL RESONATING CHARGED PARTICLE BEAM MODULATOR 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 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, filed on August 15, 2005, entitled "Method Of

Patterning Ultra-Small Structures," filed on August 15, 2005, both 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 the modulation of a beam of charged particles.

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 P a^ι|t: r;:aτdi,/o y fresquoeniEckie/s,e foer e7xa:;7mgptle, i .s re ,lat .i.ve ,ly easy t .o generat .e usi .ng re ,lat .i.ve ,ly , 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. p. -,|p, ^. I jj ,_;q. ,₍..J₁1»^, y »3 jj3 ■^»;!(■ y ig_|

[000&] ^{" '"}" ^' We nave 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 (RP) 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 *C T/ US 06 / B E!! 779 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 P¹ C IV U S OS / K B 77 '9 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 m the grating at a frequency m 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, P C T,/ IJ S O 6 / ≡ 277^1Qi the ability to transfer energy to the electrons wilhin 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 nm 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 NJ. 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. T/ US QB /SE 779

[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] A new structure for producing electromagnetic radiation is now described

in which a source produces a beam of charged particles that is modulated by interaction

with a varying electric field induced by a ultra-small resonant structure.

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 is a schematic of a charged particle modulator that velocity

modulates a beam of charged particles according to embodiments of the present

invention.

[0051] FIG. 3 is an electron microscope photograph illustrating an example ultra-

small resonant structure according to embodiments of the present invention.

[0052] FIG. 4 is an electron microscope photograph illustrating the very small and

very vertical walls for the resonant cavity structures according to embodiments of the

present invention.

[0053] FIG. 5 shows a schematic of a charged particle modulator that angularly

modulates a beam of charged particles according to embodiments of the present

invention. [0054] FIGS. 6(a)-6(c) are electron microscope photographs illustrating various

exemplary structures according to embodiments of the present invention.

DESCRIPTION

[0055] FIG. 2 depicts a charged particle modulator 200 that velocity modulates a

beam of charged particles according to embodiments of the present invention. As shown

in FIG. 2, a source of charged particles 202 is shown producing a beam 204 consisting of

one or more charged particles. The charged particles can be electrons, protons or ions

and can be produced by any source of charged particles including cathodes, tungsten

filaments, planar vacuum triodes, ion guns, electron- impact ionizers, laser ionizers,

chemical ionizers, thermal ionizers, or ion impact ionizers. The artisan will recognize

that many well-known means and methods exist to provide a suitable source of charged

particles beyond the means and methods listed.

[0056] Beam 204 accelerates as it passes through bias structure 206. The source of

charged particles 202 and accretion bias structure 206 are connected across a voltage.

Beam 204 then traverses excited ultra-small resonant structures 208 and 210.

[0057] An example of an accretion bias structure is an anode, but the artisan will

recognize that other means exist for creating an accretion bias structure for a beam of

charged particles.

[0058] Ultra-small resonant structures 208 and 210 represent a simple form of

ultra-small resonant structure fabrication in a planar device structure. Other more

complex structures are also envisioned but for purposes of illustration of the principles ^;:ι'C T/ If J S O G / S 5779 involved the simple structure of Fig. 2 is described. There is no requirement that ultra-

small resonant structures 208 and 210 have a simple or set shape or form. Ultra-small

resonant structures 208 and 210 encompass a semi-circular shaped cavity having wall 212

with inside surface 214, outside surface 216 and opening 218. The artisan will recognize

that there is no requirement that the cavity have a semi-circular shape but that the shape

can be any other type of suitable arrangement.

[0059] Ultra-small resonant structures 208 and 210 may have identical shapes and

symmetry, but there is no requirement that they be identical or symmetrical in shape or

size. There is no requirement that ultra-small resonant structures 208 and 210 be

positioned with any symmetry relating to the other. An exemplary embodiment can

include two ultra-small resonant structures; however there is no requirement that there be

more than one ultra-small resonant structure nor less than any number of ultra-small

resonant structures. The number, size and symmetry are design choices once the

inventions are understood.

[0060] In one exemplary embodiment, wall 212 is thin with an inside surface 214

and outside surface 216. There is, however, no requirement that the wall 212 have some

minimal thickness. In alternative embodiments, wall 212 can be thick or thin. Wall 212

can also be single sided or have multiple sides.

[0061] In some exemplary embodiments, ultra-small resonant structure 208

encompasses a cavity circumscribing a vacuum environment. There is, however, no

requirement that ultra-small resonant structure 208 encompass a cavity circumscribing a vacuum environment. Ultra-small resonant structure 208 can confine a cavity

accommodating other environments, including dielectric environments.

[0062] In some exemplary embodiments, a current is excited within ultra-small

resonant structures 208 and 210. When ultra-small resonant structure 208 becomes

excited, a current oscillates around the surface or through the bulk of the ultra-small

structure. If wall 212 is sufficiently thin, then the charge of the current will oscillate on

both inside surface 214 and outside surface 216. The induced oscillating current

engenders a varying electric field across the opening 218.

[0063] In some exemplary embodiments, ultra-small resonant structures 208

and 210 are positioned such that some component of the varying electric field induced

across opening 218 exists parallel to the propagation direction of beam 204. The varying

electric field across opening 218 modulates beam 204. The most effective modulation or

energy transfer generally occurs when the charged electrons of beam 204 traverse the gap

in the cavity in less time then one cycle of the oscillation of the ultra-small resonant

structure.

[0064] In some exemplary embodiments, the varying electric field generated at

opening 218 of ultra-small resonant structures 208 and 210 are parallel to beam 204. The

varying electric field modulates the axial motion of beam 204 as beam 204 passes by

ultra-small resonant structures 208 and 210. Beam 204 becomes a space-charge wave or

a charge modulated beam at some distance from the resonant structure. [0065] Ultra-small resonant structures can be built in many different shapes. The

shape of the ultra-small resonant structure affects its effective inductance and

capacitance. (Although traditional inductance an capacitance can be undefined at some

of the frequencies anticipated, effective values can be measured or calculated.) The

effective inductance and capacitance of the structure primarily determine the resonant

frequency.

[0066] Ultra-small resonant structures 208 and 210 can be constructed with many

types of materials. The resistivity of the material used to construct the ultra-small

resonant structure may affect the quality factor of the ultra-small resonant structure.

Examples of suitable fabrication materials include silver, high conductivity metals, and

superconducting materials. The artisan will recognize that there are many suitable

materials from which ultra-small resonant structure 208 may be constructed, including

dielectric and semi-conducting materials.

[0067] An exemplary embodiment of a charged particle beam modulating ultra-

small resonant structure is a planar structure, but there is no requirement that the

modulator be fabricated as a planar structure. The structure could be non-planar.

[0068] Example methods of producing such structures from, for example, a thin

metal are described in commonly-owned U.S. Patent Application No. 10/917,511

(""Patterning Thin Metal Film by Dry Reactive Ion Etching"). In that application,

etching techniques are described that can produce the cavity structure. There, fabrication techniques are described that result in thin metal surfaces suitable for the ultra-small

resonant structures 208 and 210.

[0069] Other example methods of producing ultra-small resonant structures are

described in commonly-owned U.S. Application No. 11/203,407, filed on August 15,

2005 and entitled "Method of Patterning Ultra-Small Structures." Applications of the

fabrication techniques described therein result in microscopic cavities and other

structures suitable for high-frequency resonance (above microwave frequencies)

including frequencies in and above the range of visible light.

[0070] Such techniques can be used to produce, for example, the klystron ultra-

small resonant structure shown in FIG. 3. In FIG. 3, the ultra-small resonant klystron is

shown as a very small device with smooth and vertical exterior walls. Such smooth

vertical walls can also create the internal resonant cavities (examples shown in FIG. 4)

within the klystron. The slot in the front of the photo illustrates an entry point for a

charged particle beam such as an electron beam. Example cavity structures are shown in

FIG. 4, and can be created from the fabrication techniques described in the above-

mentioned patent applications. The microscopic size of the resulting cavities is

illustrated by the thickness of the cavity walls shown in FIG. 4. In the top right corner,

for example, a cavity wall of 16.5 nm is shown with very smooth surfaces and very

vertical structure. Such cavity structures can provide electron beam modulation suitable

for higher-frequency (above microwave) applications in extremely small structural

profiles. IP' C T /"U S O B /¹" S E! 77" 9 [0071] FIGS. 4 and 5 are provided by way of illustration and example only. The

present invention is not limited to the exact structures, kinds of structures, or sizes of

structures shown. Nor is the present invention limited to the exact fabrication techniques

shown in the above-mentioned patent applications. A lift-off technique, for example,

may be an alternative to the etching technique described in the above-mentioned patent

application. The particular technique employed to obtain the ultra-small resonant

structure is not restrictive. Rather, we envision ultra-small resonant structures of all types

and microscopic sizes for use in the production of electromagnetic radiation and do not

presently envision limiting our inventions otherwise.

[0072] FIG. 5 shows another exemplary embodiment of a charged particle beam

modulator 220 according to embodiments of the present invention. In these

embodiments, the source of charged particles 222 produces beam 224, consisting of one

or more charged particles, which passes through bias structure 226.

[0073] Beam 224 passes by excited ultra-small resonant structure 228 positioned

along the path of beam 224 such that some component of the varying electric field

induced by the excitation of excited ultra-small resonant structure 228 is perpendicular to

the propagation direction of beam 224.

[0074] The angular trajectory of beam 224 is modulated as it passes by ultra-small

resonant structure 228. As a result, the angular trajectory of beam 224 at some distance

beyond ultra-small resonant structure 228 oscillates over a range of values, represented

by the array of multiple charged particle beams (denoted 230). [0075] FIGS. 6(a)-6(c) are electron microscope photographs illustrating various

exemplary structures operable according to embodiments of the present invention. Each

of the figures shows a number of U-shaped cavity structures formed on a substrate. The

structures may be formed, e.g., according to the methods and systems described in related

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,

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.

[0076] Thus are described ultra-small resonating charged particle beam modulators

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. An device comprising:

a source producing a beam of charged particles; and

an ultra-small resonant structure inducing a varying electric field interacting

with incoming electromagnetic radiation, whereby said beam of charged particles is

modulated by interacting with said varying electric field.

2. The device of claim 1 wherein said ultra-small resonant structure is a

cavity.

3. The device of claim 1 wherein said ultra-small resonant structure is a

surface plasmon resonant structure.

4. The device of claim 1 wherein said ultra-small resonant structure is a

plasmon resonating structure.

5. The device of claim 1 wherein said ultra-small resonant structure has

a semi-circular shape.

6. The device of claim 1 wherein said ultra-small resonant structure is

symmetric.

7. The device of claim 1 wherein said varying electric field of said

resonant structure modulates the electrons of said electron beam angular trajectory.

8. The device of claim 1 wherein said varying electric field of said

ultra-small resonant structure modulates the axial motion of said electron beam.

9. The device of claim 1 wherein said resonant structure is a cavity

filled with a dielectric material.

10. The device of claim 1 wherein said charged particles are selected

from the group comprising: electrons, protons, and ions.

11. The device of claim 1 wherein said source of charged particles is a

source selected from the group comprising: 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.

12. The device of claim 1 wherein said ultra-small resonant structure is

constructed of a material selected from the group comprising: silver (Ag), copper (Cu), a

conductive material, a dielectric, a transparent conductor; and a high temperature

superconducting material.

13. A method of modulating a beam of charged particles comprising:

providing an ultra-small resonant structure;

inducing a varying electric field within the ultra-small resonant structure by

interacting with incoming electromagnetic radiation; and

modulating said beam of charged particles by the interaction of said

varying electric field with said beam of charged particles.

14. The method of modulating a beam of charged particles of claim 13

wherein said step of inducing includes inducing the varying electric field within a cavity.

15. The method of modulating a beam of charged particles of claim 13

wherein said step of inducing includes inducing the varying electric field within a surface

plasmon resonant structure.

16. The method of modulating a beam of charged particles of claim 13

wherein said step of inducing includes inducing the varying electric field within a semi¬

circular shaped structure.

17. The method of modulating a beam of charged particles of claim 13

wherein said step of inducing includes inducing the varying electric field within a

symmetrical structure.

18. The method of modulating a beam of charged particles of claim 13

wherein said step of inducing includes inducing the varying electric field within an

asymmetrical structure.

19. The method of modulating a beam of charged particles of claim 13

wherein said varying electric field of said resonant structure modulates the electrons of

said electron beam angular trajectory.

20. The method of modulating a beam of charged particles of claim 13

wherein said varying electric field of said ultra-small resonant structure modulates the

axial motion of said electron beam.

21. The method of modulating a beam of charged particles of claim 13

wherein said step of inducing includes inducing the varying electric field within a cavity

filled with a dielectric material.

22. The method of modulating a beam of charged particles of claim 13

wherein said beam of charged particles comprises a beam of electrons.

23. The method of modulating a beam of charged particles of claim 13

wherein said beam of charged particles comprises a beam of protons.

24. The method of modulating a beam of charged particles of claim 13

wherein said beam of charged particles comprises a beam of ions.

25. The method of modulating a beam of charged particles of claim 13

wherein said beam of charged particles is produced by a device selected from the group

comprising: an ion gun; a tungsten filament; a cathode; a planar vacuum triode having a

large parasitic capacitance; an electron-impact ionizer; a laser ionizer; a chemical ionizer;

a thermal ionizer; and an ion-impact ionizer.

26. The method of modulating a beam of charged particles of claim 13

wherein said step of inducing includes the step of providing a ultra-small resonant

structure constructed of silver.

27. The method of modulating a beam of charged particles of claim 13

structure constructed of high temperature superconducting material.