WO2007040676A2 - Electron beam induced resonance - Google Patents

Abstract

We describe an ultra-small structure that produces visible light of varying frequency, from a single metallic layer. In one example, a row of metallic posts are etched or plated on a substrate according to a particular geometry. When a charged particle beam passed close by the row of posts, the posts and cavities between them cooperate to resonate and produce radiation in the visible spectrum (or even higher). A plurality of such rows of different geometries can be etched or plated from a single metal layer such that the charged particle beam will yield different visible light frequencies (i.e., different colors) using different ones of the rows.

Description

ELECTRONBEAMINDUCEDRESONANCE

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 to U.S. Application No. 11/203,407, filed on August 15, 2005, entitled "Method Of Patterning Ultra-Small Structures," and to U.S. Application No. _/__,___ [Atty. Docket 2549-0058], titled "Structures And Methods For Coupling Energy From An Electromagnetic Wave," 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 resonance induced in ultra-small metal-layer

structures by a charged particle beam. Atty. Docket 25 -0 59 / UB OG/ E 3 Eu S O

INTRODUCTIONANDBACKGROUND

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 P C T/^* IJl S O B / H 3 iΞ 3 O 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. ^;;;" C T/ U S O IB ,/ 532 B O

[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. ^■■»cτ/ysoe/Ξ3Eeo

[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 . ... CTZ USOBZEiIB EBO 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 terror materials, better TV^' U S Oi IB /^'Ei! 3EiISO 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 nm in size. Research into the mechanisms of SERS over the

past 25 years suggests that both chemical and electromagnetic factors contribute to the C T,,-" IJ S OB /^' E 3 iΞ 8 O 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. C T/" 1,1 S O B / Ξ 3 ≡ S O 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 IPC T/U SOB /^'S BS B O 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] There is thus a need for a device having a single layer 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 EXAMPLES OF THE INVENTION [0045] Figure l(a) shows a prior art example klystron.

[0046] Figure l(b) shows a prior art example magnetron.

[0047] Figure l(c) shows a prior art example reflex klystron.

[0048] Figure l(d) depicts aspects of the Smith-Pufcell theory. ^[CT/^"USOB/ 53E! 80l

[0049] Figure 2 is schematic representation of an example embodiment of the

invention;

[0050] Figure 3 is another schematic representation of certain parameters

associated with light emission from exemplary embodiments of the present invention;

[0051] Figure 4 is a microscopic photograph of an example light-emitting comb

structure;

[0052] Figure 5 is a microscopic photograph of a series of example light-emitting

comb structures;

[0053] Figure 6 is a microscopic photograph of a series of example light-emitting

comb structures;

[0054] Figure 7 is a microscopic photograph of a side view of example series of

comb structures;

[0055] Figures 8 and 9 are closer version microscopic photographs of example

light-emitting comb structures;

[0056] Figure 10 is an example substrate pattern used for testing the effect of comb

length variations;

[0057] Figure 11 is a microscopic photograph of a side view of an example comb

structure;

[0058] Figure 12 is a microscopic photograph of a series of frequency sensitive

comb structures;

[0059] Figure 13 is a graph showing example intensity and wavelength versus

finger length for some of the series of comb teeth of Figure 10; [0060] Figure 14 is a graph showing intensity versus post length for the series of

comb teeth of Figure 10;

[0061] Figures 15 and 16 are microscopic photographs of dual rows of comb teeth;

[0062] Figure 17 is an example substrate with example dual rows of comb teeth

and single rows of comb teeth;

[0063] Figures 18-20 are further examples of dual rows of comb teeth; and

[0064] Figures 21-24 are further examples of dual rows of C-shaped structures.

[0065] As shown in Figure 2, a single layer of metal, such as silver or other thin

metal, is produced with the desired pattern or otherwise processed to create a number of

individual resonant elements. Although sometimes referred to herein as a "layer" of

metal, the metal need not be a contiguous layer, but can be a series of elements

individually present on a substrate. The metal with the individual elements can be

produced by a variety of methods, such as by pulse plating, depositing or etching.

Preferred methods for doing so are described in co-pending U.S. Application No.

10/917,571, filed on August 13, 2004, entitled "Patterning Thin Metal Film by Dry

Reactive Ion Etching," and in co-pending U.S. Application No. 11/203,407, filed on

August 15, 2005, entitled "Method of Patterning Ultra-small Structures."

[0066] The etching does not need to remove the metal between posts all the way

down to the substrate level, nor does the plating have to place the metal posts directly on

the substrate (they can be on a silver layer on top of the substrate, for example). That is,

the posts may be etched or plated in a manner so a small layer of conductor remains ^»CT/usoe/B35eo beneath, between and connecting the posts. Alternatively, the posts can be conductively

isolated from each other by removing the entire metal layer between the posts. In one

embodiment, the metal can be silver, although other metal conductors and even

dielectrics are envisioned as well.

[0067] A charged particle beam, such as an electron beam 12 produced by an

electron microscope, cathode, or any other electron source 10 and passing closely by a

series of appropriately-sized structures, causes the electrons in the structures to resonate

and produce visible light. In Figure 2, resonance occurs within the metal posts 14 and in

the spaces between the metal posts 14 on a substrate and with the passing electron beam.

The metal posts 14 include individual post members 15a, 15b,...15n. The number of post

members 15a...15n can be as few as one and as many as the available real estate permits.

We note that theoretically the present resonance effect can occur in as few as only a

single post, but from our practically laboratory experience, we have not measured

radiation from either a one post or two post structure. That is, more than two posts have

been used to create measurable radiation using current instrumentation.

[0068] The spaces between the post members 15 a, 15b, ...15n (Figure 2) create

individual cavities. The post members and/or cavities resonate when the electron beam

12 passes by them. By choosing different geometries of the posts and resonant cavities,

and the energy (velocity) of the electron beam, one can produce visible light (or non-

visible EMR) of a variety of different frequencies (for example, a variety of different

colors in the case of visible emissions) from just a single patterned metal layer. C T/ U S O G /" iS 3 ig S O

[0069] That resonance is occurring can be seen in Figure 14. There, the average

results of a set of experiments in which the photon radiation from an example of the

present invention was plotted (in the y-axis, labeled "counts" of photons, and measured

by a photo multiplier tube as detected current pulses) versus the length of the length of

the posts 14 that are resonating (in the x-axis, labeled as "finger length"). The intensity

versus finger length average plot shows two peaks (and in some experimental results, a

third peak was perhaps, though not conclusively, present) of radiation intensity at

particular finger lengths. We conclude that certain finger lengths produce more intensity

at certain multiple lengths due to the resonance effect occurring within the post 14 itself.

[0070] For completeness, the substrate used in the above finger length resonance

tests is shown in Figure 10. There, the lines of posts in the vertical direction correspond

to posts of different length from "0" length to 700nm length. As described in more detail

below, the experiment is conducted by passing an electron beam near the rows of posts

and generally perpendicular to them (that is, the electron beam passes vertically with

respect to Figure 10). The specifications for the experiment were: a period between

posts of 156nm, a 15kV beam energy from an electron microscope at 90 degrees to the

length of the posts. In that test, a continuous conductive silver substrate layer was

beneath the posts. When we repeated the tests, we found that there was some variation in

terms of actual intensities seen by the different finger lengths, which we attribute to slight

variations in the proximity of the electron beam to the post runs, but the resonance effect

was generally apparent in each case. ^■C T/ySOB / E 3ΞE*O

[0071] Notably, the resonance effect described in Figure 14 appears to occur in the

individual posts themselves. That is, it appears that we are recording an effect that occurs

from oscillations that are on the surface (including perhaps within) the posts themselves.

That resonance is supplementing system resonance, namely the resonance that occurs

between adjacent posts. Although these theories do not limit our inventions, we believe

that the supplemental resonance occurring within the posts is amplifying the system

resonance such that new, substantial levels of intensity are being recognized. As the

electron beam passes by the posts, charged particles in the posts begin to resonate

between adjacent posts. That resonance produces electromagnetic radiation-and is

predominantly responsible for the first peak in Figure 14. What we have now seen is that

we can, by choosing finger length, demonstrate further resonance within the fingers

themselves (as opposed to between adjacent fingers) that is predominantly responsible for

the second peak and is also responsible for amplifying the intensity of the system

resonance. We have seen, for example, that without system resonance, then the electron

beam cannot be made intense enough to excite the in-post resonance to a detectible level.

But, with the system resonance, both the system resonance and the in-post resonance

excite the others to further excitation.

[0072] We have also detected with angle periodic structures that running the beam

one way over the angled teeth produces an effective output while running the beam the

other way decreases the output dramatically.

[0073] We have also detected that, unlike the general theory on Smith-Purcell,

which states that frequency is only dependant on period and electron beam characteristics (such as beam intensity), some of the frequencies of our detected beam change with the

finger length. Thus, as shown in Figure 13, the frequency of the electromagnetic wave

produced by the system on a row of 220nm fingers (posts) has a recorded intensity and

wavelength greater than at the lesser shown finger lengths. With Smith-Purcell, the

frequency is related to the period of the grating (recalling that Smith-Purcell is produced

by a diffraction grating) and beam intensity according to:

where λ is the frequency of the resonance, L is the period of the grating, n is a constant, β is related to the speed of the electron beam, and θ is the angle of diffraction of the electron. [0074] It is reasonable to suggest, that if the other modes are aligned to the

operating frequency, the Q of the device will be improved. A sweep of the duty cycle of

the space width s (shown in Figure 3) and post width (1-s) indicates that the space width s

and period length 1 have relevance to the center frequency of the resultant radiation. By

sweeping the geometries d, 1, and s of Figure 3 and the length of the posts (shown in

Figure 2 and variously at Figure 10), at given electron velocity v and current density,

while evaluating the characteristic harmonics during each sweep, one can ascertain a

predictable design model and equation set for a particular metal layer type and

construction. With such, a series of posts can be constructed that output substantial EMR

in the visible spectrum (or higher) and which can be optimized based on alterations of the

geometry, electron velocity and density, and metal type.

[0075] Using the above-described sweeps, one can also find the point of maximum

Q for given posts 14 as shown in Figure 14. Additional options also exist to widen the F" C T/ U S O IB /Ξ! 3 iΞ 8 O bandwidth or even have multiple frequency points on a single device. Such options

include irregularly shaped posts and spacing, series arrays of non-uniform periods,

asymmetrical post orientation, multiple beam configurations, etc.

[0076] Some example geometries are described herein and are shown in the

associated figures. Those geometries do not limit the present inventions, but are

described in order to provide illustrative examples of geometries that work for the

intended purpose. In Figure 3, an example representation of our posts is shown with

dimensional variables labeled for clarity. As described above, in our devices, for

example, as the post length d was swept in length, the intensity of the radiation was

oscillatory in nature, aligning very near to the second and third harmonic lengths.

[0077] In Figure 4, a microscopic photograph depicts a set of actual single metal-

layer posts, of the kind generally referred to in Figure 3. In the Figure 4 example, the

metal layer is silver. The metal is pulse plated to provide the posts 14 shown. The posts

may be constructed according to the techniques described in the applications identified

above under "Related Applications."

[0078] In Figure 4, the post length is about 698nm. The space width, s, is about

51.5nm. The post and space width, 1, is about 155nm. The electron beam runs

perpendicular to the length of the posts and spaces, as shown in Figure 2. Unlike a

Smith-Purcell device, the resultant radiation from a structure such as shown in Figure 4 is

actually intense enough to be visible to the human eye without the use of a relativistic

electron beam. Another example set of the structures of Figure 4 in which the post length

was altered to determine the effect on harmonic lengths is shown in Figure 5. There, four =^»CT/ USOB/ia358O different example post lengths are shown, 303 nm, 349 nm, 373 run, and 396 nm. The

example of Figure 5 realizes harmonic oscillation aligning near the second and third

harmonic lengths

[0079] As described previously, by altering the combined length, period 1, spaces

s, and post members 15a...15n, the center frequency of the radiation changes. It is thus

valuable to size a row of posts 14 such that a desired frequency of visible light is emitted

when the charged particle beam is passed near it. Figure 6 illustrates an alternative

example embodiment in which we produce a variety of frequencies by modifying the post

lengths in multiple rows of differently configured posts. By etching, plating or otherwise

producing multiple rows of posts, each of which is tuned to a produce a different

frequency, multiple colors of visible light can be produced by directing an injected

charged particle beam parallel and close to appropriate ones of the rows.

[0080] Indeed, we can envision a row of posts having varying lengths within the

row itself, such that different frequencies of radiation are excited by different ones or

combinations of posts. The result could be a mixed, multiple wavelength light.

[0081] Different frequency outputs can also be obtained by directing multiple

charged particle beams at different rows of posts etched from or plated on the same metal

layer. Thus, one can obtain any color of visible light from a single layer metal nano- or

micro- structure. Because the rows are only about a few micrometers or less apart,

directing multiple electron beams simultaneously at different ones of the rows could also

mix the visible light to yield to the human eye essentially any color frequency in the

visible spectrum. The breadth and sensitivity of color options available in such a system CT/' U SO G / ΪG* 3 E O O is limited only by the number and geometries of the rows, and the number of electron

beam sources available to stimulate the rows into resonance.

[0082] Figure 7 illustrates a side view of a set of rows of posts. As shown, each

row has a different geometry to produce a different radiation. Various period, space

distances, and depths are shown. The lengths of the posts, a dimension clearly shown in

the example of Figure 6, are not clearly identifiable in Figure 7. In Figure 7, the period

of the second row is 210nm while the period of the third row is 175nm. The space of the

first row is 123nm, while the space of the fourth row is 57nm. Depths and lengths can

also be varied. Each of the rows can exhibit different post geometries (although there

may be reasons for including some or all rows of duplicate geometries).

[0083] As shown in Figure 6, the post elements 14 do not necessarily have to have

the backbone portion connecting the posts, as shown in Figure 4. The posts on the

substrate can resemble a comb with a backbone connecting all of the teeth, as in Figure 4,

or can resemble be just the teeth without the comb backbone, as in Figure 6. Each post

can also be freestanding and physically unconnected to adjacent posts except by the

portion of metal layer remaining beneath the posts or by the substrate if the metal layer is

completely removed from around the posts. Alternatively, the posts can be connected by

remaining metal layer in the form of the backbone shown in Figure 3 or by a top layer

shown in Figure 11, or by a connecting conductive substrate beneath the posts. In Figure

11, the posts have period length 1 of 213 nm, a post width (I - s) of 67.6 nm and a height

(d) of 184 nm. The posts are covered by a layer of silver, which can provide advantageous — though not necessary — coupling between the posts (such coupling can

also or alternatively be provided by contiguous metal layer left beneath the posts).

[0084] Figures 8 and 9 illustrate still further example geometries of non-backboned

posts 14 are shown. In each case, just two rows are shown, although any number of rows

can be employed, from one to any. The number of rows is limited by available real estate

on the substrate, except that multiple substrates can also be employed proximate (side-by-

side or atop) each other. The specific dimensions shown in Figures 8 and 9, like the other

examples described herein are just illustrative and not limiting. Sizes and geometries of

the posts, numbers of the posts, sequences of the posts, and arrangements of the posts can

also be changed and remain within the concepts of the present inventions.

[0085] When the backbone is removed, for certain wavelengths, radiation can emit

from both sides of the device. Depending on the spacing and the XY-dimensions of the

post members, it may be possible that there is a blocking mode that negates the photon

emission from that side. The emissions are thus altered by the presence/absence of the

backbone, but the existence of resonance remains.

[0086] The direction of the radiation can also be adjusted. We have noted that

radiation has been detected outwardly from the row (essentially parallel to the long

dimension of the posts and spaces), as well as upwardly (relative, for example, to the

plane of Figure 6). It thus appears that some directionality can be advantageously

employed for the radiation's initial direction.

[0087] Given that plasmon velocity is material dependent, it can be advantageous

to build devices using conductive materials other than silver. We expect that less

conductive materials would have a lower emission wavelength due to the slower plasmon

velocity. Similarly, more conductive material would have higher emission wavelengths.

Thus, metal or other conductive layers of different types can be employed. As described

above, we envision single metal or alloy layers of different row geometries producing

different frequencies. We also envision different metal layer types with the same or

different row geometries to produce different frequencies.

[0088] Figure 12 illustrates anther set of post rows (similar to Figure 10). The

rows in Figure 12 have no backbones on the posts. As can be seen, the different rows are

formed of a common metal layer and have different lengths so as to produce different

frequencies and intensities of radiation when a charge particle beam passes close to (and

generally parallel to) a selected row.

[0089] Figures 15-17 are still further example configurations of the rows of posts

14. In Figures 15 and 16, two rows are provided in proximity, so an electron beam 12

can be passed between the two rows, exciting resonance in each row simultaneously.

Each row can have posts of the same geometry or each row can have posts of different

geometries. Further, as between the two rows, the geometries of the posts can be entirely

the same, some different, or entirely different. If the rows have uniform posts within the

row and different posts as between the two rows, then the different rows produce

different wavelengths of radiation from a common electron beam.

[0090] With the two row embodiments of Figures 15-16, detectable light output

was increased at least 20% (the increase is likely much more than 20% due to the

inability to detect light going in undetected directions from the two rows. »C T/ U S O B / E BB 80

[0091] Figure 17 is a substrate with some two row embodiments, as in Figures 15

and.16, with other single row and multiple row example embodiments. In Figure 17, the

dual row embodiments on the left side produced light of two different colors. Figures 18-

20 show some additional details of the dual row embodiments. It is worth noting that

simultaneous dual frequency outputs from two rows, like those shown in Figure 18-20,

are not realized with devices operating according to diffraction theory, such as Smith-

Purcell devices.

[0092] As should be understood from these descriptions, there is a wide variety of

geometries of posts, geometries of rows, orientations of posts and rows, kinds of posts,

kinds of metal, kinds of substrates, backbones, electron beam characteristics and other

criteria that we envision within the framework of our inventions. We envision within our

inventions deviations from the above criteria, whether or not specifically described

herein. For example, Figures 21-24 show still further example resonant structures by

which an electron beam can pass to induce resonance in and between. In Figure 21, the

structures are not in the form of straight posts (as in Figure 1), but are instead C-shaped

cavities which can form a type of waveguide. The electron beam passes down the middle

of the facing Cs, perpendicular to the arms of the Cs. As in Figure 1, the electron beam

induces resonance in the structures, both within the structures (including surface

resonance) and among the structures (system resonance) to produce electromagnetic

radiation at superior intensities and optimizable wavelengths.

[0093] Figure 21 also illustrates a device that exhibits higher order of harmonics

by alternating "half-stubs" between the full stubs. The same kind of idea in which half- ^::;"C T / U S O B / E!! 3 Ξ Θ O stubs are alternated with full stubs can be incorporated into any of the other embodiments

(such as the several post embodiments) described earlier in this document. In the case of

Figure 21, the half-stubs are actually half-Cs nestled into the full-Cs, with the electron

beam passing near and perpendicular to the arms of each. Resonance occurs within each

C, between the nestled and nestling Cs, and between adjacent large Cs. As in previously

described embodiments, the period of the repeating Cs is less than the wavelength of

light, so the light is not being diffracted because the period spacing is so small that the

arms of the Cs (or in the case of the posts, the ends of the posts) appear essentially as a

solid "surface" to the wave. In the case of Figure 21, the period of the respective arms of

the Cs is 117nm. The distance from the end of one arm of a big-C to the other arm of the

same big-C is about 797nm (i.e., it can be greater than the wavelength of light) The

length of each big-C arm is about 515nm.

[0094] Figure 22 illustrates a double rowed, single-C embodiment in which offset,

facing Cs are provided with the electron beam running between them. As shown, the

period of the repeating arms is about 427nm. The space within which the electron beam

runs is about 40nm. The width of the C is about 122nm. The entire length of two facing

Cs and the space between is 802nm.

[0095] Figure 23 illustrates a number of example light-producing embodiments,

including nestled-C embodiments and post embodiments. Figure 24 is a hybrid of the Cs

and posts, in which a post is nestled into each C. The posts and C-arms have a period of

about 225nm, with a spacing between the arms of adjacent Cs of about 83nm. Again, the electron runs down the middle slit to induce resonance in the proximate posts and ends of

the C-arms.

[0096] All of the structures described operate under vacuum conditions. Our

invention does not require any particular kind of evacuation structure. Many known

hermetic sealing techniques can be employed to ensure the vacuum condition remains

during a reasonable lifespan of operation. We anticipate that the devices can be operated

in a pressure up to atmospheric pressure if the mean free path of the electrons is longer

than the device length at the operating pressure.

[0097] The conductive structures described herein are preferably comprised of

silver, but may be any conductive metal or may be any non-metallic conductor such as an

ionic conductor. Dielectrics are also envisioned as layer materials in the alternative to

conductive layers, or in combination with them.

[0098] We have thus described electron beam induced resonance that can be used

to produce visible light of optimized frequencies from a single metal layer. Such devices

have application in such fields as ultra high-speed data communications and in any light

producing application.

[0099] The various devices and their components described herein may be

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

No. 10/917,511, 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.

[00100] Thus are described electron beam induced resonance and methods and

devices for 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 series of one or more structures arranged in a continuum on a single

substrate to emit electromagnetic radiation at a output wavelength, the series having a

period between the structures less than the wavelength of the emitted electromagnetic

radiation, the series emitting said electromagnetic radiation when a charged particle beam

is directed generally along and proximate the series of structures.

2. A series according to claim 1, wherein the structures have a length to

induce resonance on the surface of, or within, the structures as the charged particle beam

passes the structures to emit said electromagnetic radiation.

3. A series according to claim 2, wherein the structures have a length to

induce resonance among the respective structures as the charged particle beam passes the

structures to emit said electromagnetic radiation.

4. A series of structures according to claim 1, wherein the series is a first

series, and further including:

a second series of structures geometrically different from the first series and

arranged near the first series to emit electromagnetic radiation when said charged particle

different frequency than the first series.

5. A series of structures according to claim 1, wherein the series is a first

series, and further including:

a plurality of series of one or more structures geometrically different from the first

series and arranged on a common substrate in respective and different continuums to emit

electromagnetic radiation at one or more different frequencies than the first series when

said charged particle beam is directed generally along and proximate the plurality any of

the series of structures.

6. A series according to claim 5, wherein each one of the plurality of

additional series of structures is geometrically different from every other series of one or

more structures.

7. A series according to claim 6, wherein each of the plurality of additional

series of one or more structures emits electromagnetic radiation at a frequency different

from every other series of one or more structures.

8. A series according to claim 1, wherein the structures are posts.

. ,

,,,_{u r} .,.„„. ,, „

9...... J..,..p_;.A,se|ieβ-§<jCiQ-_jding to claim 1, wherein the structures are arms of C-shaped

structures.

10. A series according to claim I₅ wherein the structures are arms of nested C-

shaped structures.

11. A series according to claim 1, wherein the structures are arms of C-shaped

structures and nested posts.

12. Periodic structures arranged in rows on a single substrate and having at

least two different structure geometries inducing electromagnetic radiation in at least two

different frequencies corresponding at least in part to the two different structure

geometries when a charged particle beam is directed generally along the structures.

13. Periodic structures according to claim 12, wherein two of the rows having

the at least two different structure geometries are proximate to one another such that a

common charged particle beam simultaneously induces the electromagnetic radiation

from both rows.

14. Periodic structures according to claim 13, wherein the structures are offset,

facing C-shaped structures. P if T _■'■'" IM ' il B^WH^W^^^ ^according ^{t0 c}l^aim H wherein the C-shaped structures are nested.

16. Periodic structures according to claim 12, wherein the electromagnetic

radiation is in the visible light spectrum.

17. Periodic structures according to claim 12, wherein a periodicity of each of

the periodic structures is less than the wavelength of the electromagnetic radiation

induced thereby.

18. Periodic structures according to claim 12, wherein the structures are posts

arranged on a substrate.

19. Periodic structures according to claim 12, wherein the structures in a given

row are conductively connected to one another.

20. Periodic structures according to claim 12, wherein the structures are

composed of one from the group of: metals, alloys, non-metallic conductors and

dielectrics.

21. A method of producing electromagnetic radiation, comprising the steps of: p _jj J- / i_j ptffiβφig gsjtøfp@iodic structures on a substrate, the set of structures having an

arm length in a direction generally parallel to the plane of the substrate;

directing a beam of charged particles near and perpendicular to the arm length of

said structures so as to induce resonance in the structures and thereby emit

electromagnetic radiation at a particular wavelength greater than a period of said periodic

structures.

22. A series according to claim 1, wherein the structures are composed of one

from the group of: metals, alloys, non-metallic conductors and dielectrics.