U.S. patent application number 11/320515 was filed with the patent office on 2007-05-24 for multi-pixel electron microbeam irradiator systems and methods for selectively irradiating predetermined locations.
This patent application is currently assigned to The University of North Carolina at Chapel Hill. Invention is credited to Sha X. Chang, Otto Z. Zhou.
Application Number | 20070114434 11/320515 |
Document ID | / |
Family ID | 38049553 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070114434 |
Kind Code |
A1 |
Chang; Sha X. ; et
al. |
May 24, 2007 |
MULTI-PIXEL ELECTRON MICROBEAM IRRADIATOR SYSTEMS AND METHODS FOR
SELECTIVELY IRRADIATING PREDETERMINED LOCATIONS
Abstract
Multi-pixel electron microbeam irradiator systems and methods
are provided with particular applicability for selectively
irradiating predetermined cells or cell locations. A multi-pixel
electron microbeam irradiator system can include a plurality of
individually addressable electron field emitters sealed in a
vacuum. The multi-pixel electron microbeam irradiator system can
include an anode comprising one or more electron permeable portions
corresponding to the plurality of electron field emitters. Further,
the multi-pixel electron microbeam irradiator system can include a
controller operable to individually control electron extraction
from each of the electron field emitters for selectively
irradiating predetermined locations such as cells or cell
locations.
Inventors: |
Chang; Sha X.; (Chapel Hill,
NC) ; Zhou; Otto Z.; (Chapel Hill, NC) |
Correspondence
Address: |
JENKINS, WILSON, TAYLOR & HUNT, P. A.
3100 TOWER BLVD
SUITE 1200
DURHAM
NC
27707
US
|
Assignee: |
The University of North Carolina at
Chapel Hill
|
Family ID: |
38049553 |
Appl. No.: |
11/320515 |
Filed: |
December 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60639958 |
Dec 29, 2004 |
|
|
|
Current U.S.
Class: |
250/400 |
Current CPC
Class: |
H01J 37/317 20130101;
H01J 2201/30469 20130101; H01J 33/02 20130101; H01J 2237/2006
20130101; H01J 37/302 20130101; H01J 2237/316 20130101; H01J 33/04
20130101; H01J 2237/0635 20130101; H01J 2237/2004 20130101; G21K
5/04 20130101; H01J 37/304 20130101 |
Class at
Publication: |
250/400 |
International
Class: |
G01K 1/08 20060101
G01K001/08 |
Claims
1-36. (canceled)
37. A method for selectively irradiating target biological cells,
the method comprising: (a) providing a plurality of individually
controllable electron field emitters; (b) providing an electrode
operable to extract electrons from the electron field emitters; (c)
determining target biological cells for irradiation; (d)
identifying locations of the determined target biological cells;
and (e) individually controlling electron extraction from each of
the electron field emitters to selectively irradiate the identified
locations for irradiating the determined target biological
cells.
38. The method of claim 37 wherein the electron field emitters
comprise components selected from the group consisting of a
nanotube, a nanorod, a Spindt tip, and nanoparticles of
diamond.
39. The method of claim 37 wherein the electron field emitters
comprise carbon nanotubes.
40. The method of claim 37 wherein individually controlling
electron extraction includes individually controlling a supply of
voltages between each of the electron field emitters and the
electrode.
41. The method of claim 37 comprising focusing the electrons
emitted from the electron field emitters into a plurality of
focused electron beams for irradiating the identified
locations.
42. The method of claim 37 comprising: (a) providing an anode
comprising a plurality of electron permeable portions corresponding
to the plurality of electron field emitters; and (b) applying a
voltage between the electron permeable portions and the electrode
for accelerating the extracted electrons through the electron
permeable portions.
43. The method of claim 37 comprising determining relative
coordinates of locations that can be irradiated by the electron
field emitters.
44. The method of claim 43 comprising matching at least one of the
identified locations of the determined target biological cells with
at least one of the relative coordinates.
45. The method of claim 44 wherein individually controlling
electron extraction comprises controlling electron extraction from
the electron field emitters corresponding to the at least one of
the identified relative coordinates matched to the at least one of
the identified locations of the determined target biological
cells.
46. A method for selectively irradiating predetermined locations on
biological cells, the method comprising: (a) providing a plurality
of individually addressable electron field emitters; (b) providing
an electrode operable to extract electrons from the electron field
emitters; (c) providing an anode comprising one or more electron
permeable portions corresponding to the plurality of electron field
emitters; and (d) individually controlling electron extraction from
each of the electron field emitters to selectively irradiate a
plurality of predetermined locations on biological cells through
the one or more electron permeable portions.
47. A method for manufacturing a multi-pixel electron microbeam
biological cell irradiator system, the method comprising: (a)
depositing a plurality of conductive contacts on a substrate,
wherein the conductive contacts are spaced apart and electrically
isolated from one another; (b) depositing a plurality of electron
field emitters on the conductive contacts; (c) depositing a
non-conductive spacer on the substrate; (d) depositing an electrode
on the non-conductive spacer; and (e) providing a plurality of
transistors operable to be individually controlled to apply
different voltages between the conductive contacts and the
electrode for individually extracting electrons from each of the
electron field emitters for selectively irradiating a plurality of
predetermined locations on biological cells.
48. The method of claim 47 wherein the conductive contacts comprise
conductive lines.
49. The method of claim 47 wherein the substrate comprises material
selected from the group consisting of silicon and glass.
50. (canceled)
51. A method for selectively irradiating target cells, the method
comprising: (a) providing a plurality of individually controllable
electron field emitters; (b) providing an electrode operable to
extract electrons from the electron field emitters; (c) determining
target cells for irradiation; (d) identifying locations of the
determined target cells; (e) individually controlling electron
extraction from each of the electron field emitters to selectively
irradiate the identified locations for irradiating the determined
target cells; (f) depositing a second non-conductive spacer on the
electrode; (g) depositing a focusing electrode on the second
non-conductive spacer; (h) depositing a third non-conductive spacer
on the focusing electrode; and (i) depositing a collimator on the
third non-conductive spacer.
52. The method of claim 51 comprising: (a) depositing a fourth
non-conductive spacer on the focusing electrode; and (b) providing
an anode on the third non-conductive spacer, wherein the anode
includes at least one electron permeable portion.
53. (canceled)
54. A method for selectively irradiating target cells, the method
comprising: (a) depositing a plurality of conductive contacts on a
substrate, wherein the conductive contacts are spaced apart and
electrically isolated from one another; (b) depositing a plurality
of electron field emitters on the conductive contacts; (c)
depositing a non-conductive spacer on the substrate; (d) depositing
an electrode on the non-conductive spacer; and (e) providing a
plurality of transistors operable to be individually controlled to
apply different voltages between the conductive contacts and the
electrode for individually extracting electrons from each of the
electron field emitters for selectively irradiating predetermined
locations; and (f) providing an anode on the substrate, wherein
providing an anode comprises: (i) providing a substrate including
an electron permeable layer on a surface thereof; and (ii) etching
through the substrate to the electron permeable layer from a
surface opposing the electron permeable layer.
55. A method for selectively irradiating target biological cells,
the method comprising: (a) identifying a plurality of target
locations of target cells on biological cells; (b) determining
dosage to be used for each target location; and (c) programming a
controller of a multi-pixel electron microbeam cell irradiator
system to set an amplitude and duration of a gate voltage to be
applied to electron field emitters on one or more cathodes such
that each electron field emitter provides a predetermined amount of
electrons to corresponding target locations.
56. A multi-pixel array microbeam irradiator for ex-vivo cellular
irradiation of a biological sample, the microbeam irradiator
comprising: (a) an array of individually addressable electron
microbeam pixels; and (b) a controller operable to individually
control electron microbeam emission from each of the electron
microbeam emitters for selectively irradiating a biological sample
at predetermined microscopic locations with respective microbeams
at controlled radiation doses and dose rates.
57. The microbeam irradiator of claim 56 wherein the biological
sample comprises a plurality of biological cells contained in a
Petri dish, wherein specific cells of the biological cells are
selected under a microscope, wherein the controller of the
microbeam irradiator is configured to individually control the
microbeam pixels to irradiate the selected cells with the
microbeams, and wherein the controller of the microbeam irradiator
is configured to control the microbeam pixels to irradiate
corresponding selected cells by a respective microbeam with
controlled dose and dose rate.
58. The microbeam irradiator of claim 56 wherein the biological
sample comprises a plurality of biological cells, wherein the
microbeam irradiator comprises an optical imaging device configured
to image the biological cells before, during, and after cell
irradiation for investigation of cellular and subcellular responses
to high spatial and temporal resolution irradiation.
59. The microbeam irradiator of claim 56 comprising an
electron-transparent window configured to vacuum-seal the microbeam
irradiator and configured to allow the microbeams escape through
the window to the ambient to irradiate the biological sample.
60. The microbeam irradiator of claim 59 wherein the biological
sample is positioned outside the electron-transparent window in the
ambient for receiving the microbeams.
61. The microbeam irradiator of claim 56 comprising a multi-pixel
microbeam collimator configured to define the cross-sectional area
of each microbeam.
62. The microbeam irradiator of claim 56 wherein the diameter of
each microbeam escaping from the electron-transparent window is on
the order of 1-100 microns.
63. The microbeam irradiator of claim 56 wherein the array of
individually addressable electron microbeam pixels comprises: (i) a
two-dimensional cathode array with a plurality of individually
addressable electron field emitters; and (ii) an anode comprising
one or more electron permeable portions corresponding to the
plurality of electron field emitters; and wherein the controller is
operable to individually control electron extraction from each of
the electron field emitters for selectively irradiating
predetermined cells or cell locations of the biological sample.
64. The microbeam irradiator of claim 63 wherein the anode is
coupled to ground and the cathode is operated at a high
voltage.
65. The microbeam irradiator of claim 63 comprising an electron
transparent window comprising silicon nitride.
66. The microbeam irradiator of claim 63 wherein the electron field
emitters comprise carbon nanotubes.
67. The microbeam irradiator of claim 63 wherein the electron field
emitters comprise components selected from the group consisting of
a nanotube, a carbon nanotube, a nanorod, a Spindt tip, and
nanoparticles of diamond.
68. The microbeam irradiator of claim 63 comprising a gate
electrode including a plurality of apertures through which
electrons travel.
69. The microbeam irradiator of claim 63 comprising a focusing
electrode configured to focus the electrons emitted from the
electron field emitters into a plurality of focused electron beams
for irradiating the predetermined microscopic locations.
70. The microbeam irradiator of claim 63 wherein a cross section of
one of the electron beams is less than about 20 microns in
diameter.
71. The microbeam irradiator of claim 63 wherein energy of the
electrons irradiating the predetermined microscopic locations is
greater than about 10 KeV.
72. The microbeam irradiator of claim 63 comprising: (a) an
electrode; and (b) a power source operable to apply a voltage
between the electron permeable portions and the electrode for
accelerating electrons through the electron permeable portions.
73. The microbeam irradiator of claim 63 wherein the one or more
electron permeable portions comprise a thin layer of nitride.
74. The microbeam irradiator of claim 63 wherein the one or more
electron permeable portions comprise a thin layer of boride.
75. The microbeam irradiator of claim 63 wherein the one or more
electron permeable portions comprise a thin layer of polymer.
76. A method for ex-vivo cellular irradiation of a biological
sample, the microbeam irradiator comprising: (a) providing an array
of individually addressable electron microbeam pixels; and (b)
individually controlling electron microbeam emission from each of
the electron microbeam emitters to selectively irradiate a
biological sample at predetermined microscopic locations with
respective microbeams at controlled radiation doses and dose
rates.
77. The method of claim 76 wherein the biological sample comprises
a plurality of biological cells contained in a Petri dish, and the
method comprises: (a) selecting specific cells of the biological
cells under a microscope; (b) individually controlling the
microbeam pixels to irradiate the selected cells with the
microbeams; and (c) controlling the microbeam pixels to irradiate
corresponding selected cells by a respective microbeam with
controlled dose and dose rate.
78. The method of claim 76 wherein the biological sample comprises
a plurality of biological cells, and the method comprises imaging
the biological cells with an optical imaging device before, during,
and after cell irradiation for investigation of cellular and
subcellular responses to high spatial and temporal resolution
irradiation.
79. The method of claim 76 comprising providing an
electron-transparent window configured to vacuum-seal the microbeam
irradiator and configured to allow the microbeams escape through
the window to the ambient to irradiate the biological sample.
80. The method of claim 79 comprising positioning the biological
sample outside the electron-transparent window in the ambient for
receiving the microbeams.
81. The method of claim 76 comprising providing a multi-pixel
microbeam collimator configured to define the cross-sectional area
of each microbeam.
82. The method of claim 76 wherein the diameter of each microbeam
escaping from the electron-transparent window is on the order of
1-100 microns.
83. The method of claim 76 wherein providing an array of
individually addressable electron microbeam pixels includes
providing: (i) a two-dimensional cathode array with a plurality of
individually addressable electron field emitters; and (ii) an anode
comprising one or more electron permeable portions corresponding to
the plurality of electron field emitters; and wherein the method
comprises individually controlling electron extraction from each of
the electron field emitters to selectively irradiate predetermined
cells or cell locations of the biological sample.
84. The method of claim 83 wherein the anode is coupled to ground
and the cathode is operated at a high voltage.
85. The method of claim 83 comprising providing an electron
transparent window comprising silicon nitride.
86. The method of claim 83 wherein the electron field emitters
comprise carbon nanotubes.
87. The method of claim 83 wherein the electron field emitters
comprise components selected from the group consisting of a
nanotube, a carbon nanotube, a nanorod, a Spindt tip, and
nanoparticles of diamond.
88. The method of claim 83 comprising providing a gate electrode
including a plurality of apertures through which electrons
travel.
89. The method of claim 83 comprising providing a focusing
electrode configured to focus the electrons emitted from the
electron field emitters into a plurality of focused electron beams
for irradiating the predetermined microscopic locations.
90. The method of claim 83 wherein a cross section of one of the
electron beams is less than about 20 microns in diameter.
91. The method of claim 83 wherein energy of the electrons
irradiating the predetermined microscopic locations is greater than
about 10 KeV.
92. The method of claim 83 comprising: (a) providing an electrode;
and (b) providing a power source operable to apply a voltage
between the electron permeable portions and the electrode for
accelerating electrons through the electron permeable portions.
93. The method of claim 83 wherein the one or more electron
permeable portions comprise a thin layer of nitride.
94. The method of claim 83 wherein the one or more electron
permeable portions comprise a thin layer of boride.
95. The method of claim 83 wherein the one or more electron
permeable portions comprise a thin layer of polymer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional patent application claims the benefit
of U.S. Provisional Application No. 60/639,958, filed Dec. 29,
2004, the disclosure of which is incorporated by reference herein
in its entirety.
TECHNICAL FIELD
[0002] The subject matter disclosed herein relates to electron
irradiation devices and methods using electron field emission
technology. More particularly, the subject matter disclosed herein
relates to multi-pixel cell irradiator systems and methods for
selectively irradiating cells at predetermined locations.
BACKGROUND ART
[0003] Microbeam irradiators can be utilized for studying the
microscopic biological effects of radiation in the cellular and
sub-cellular level. Such devices can be utilized to bombard one or
more cells with charged particles or photons for predetermined
radiation dose and dose rate. An understanding of radiobiology at
the cellular and sub-cellular level is important for improvements
of cancer treatment and for an understanding of low dose radiation
risk. Cellular micro-radiation is recognized as a powerful
technique for this endeavor. One of the most active areas of
research using a microbeam irradiator is the "bystander effect",
which involves the response of "unhit" cells to the radiation
deposited in their neighboring cells. "Bystander effect" studies
using microbeam devices have revealed the complicated
intra-cellular and inter-cellular response to radiation that may
have significant impact on the policy making of radiation
protection for general public and for the space program.
[0004] Cell irradiation can include exposing cells to alpha
particles, electrons, or X-rays. Recently, there has been interest
in low-linear energy transfer (LET) microbeams using electrons and
ultrasoft X-rays. Thermionic emission and field emission are two
mechanisms for generating electrons. Although field emission is a
sometimes preferred mechanism to extract electrons, many currently
available vacuum electronic devices utilize thermionic electron
sources. The wide use of thermionic electron sources may be partly
due to the lack of effective electron field emitters. Recent
studies have shown that carbon nanotubes have promising electron
emission properties with high emission current, low turn-on field,
and lifetime that can be required for device applications. A
typical field emission device can include a cathode having a
plurality of electron field emitters (e.g., carbon nanotubes) and
an anode spaced from the cathode. A voltage applied between the
anode and the cathode can induce the emission of electrons from the
electron field emitters towards the anode.
[0005] A few large research institutions in the world are capable
of delivering microbeam irradiation at the cellular level. These
microbeam devices require major resources to develop and maintain.
Further, in currently available microbeam irradiators, there is
only a single microbeam port. One exemplary single port electron
microbeam having a thermionic electron source includes an electron
gun consisting of a heated filament and electron optics for
accelerating and collimating a broad electron beam. The electron
optics includes a suppression aperture that allows pulsing of the
beam with sub-microsecond time resolution. The final spatial
resolution of an electron microbeam can be achieved either by
focusing or collimation. The electron microbeam can be used to
target individual cells without significant scattering to
neighboring cells. Target cells or sub-cellular regions designated
for irradiation in a population must be irradiated one at a time by
physically aligning the microbeam with each of the target cells.
Some research experiments require the irradiation of a large number
of individually selected cells, as many as 10,000, to obtain
statistically significant results. This requirement makes it
difficult to utilize single port microbeam devices for experiments
requiring irradiation of a large number of cells and, especially,
if real-time observation is also required.
[0006] Most cell irradiations in research labs today use
irradiators that cannot deliver radiation beams much smaller than a
centimeter. Therefore, researchers often have to deduce conclusions
about microscale activities of a cell from macroscopic studies of
irradiating a group of cells. The lack of microscale radiation
manipulation ability can be especially detrimental when studying a
minority cell type in a large cell population because of the low
signal to noise ratio in the experimental data.
[0007] Accordingly, in light of desired improvements associated
with microbeam cellular irradiators, there exists a need for
improved microbeam irradiator functionality and availability and
related methods.
SUMMARY
[0008] In accordance with this disclosure, novel multi-pixel
electron microbeam irradiator systems and methods for selectively
irradiating predetermined locations are provided.
[0009] It is an object of the present disclosure therefore to
provide novel microbeam irradiator systems and methods for
selectively irradiating predetermined locations. This and other
objects as may become apparent from the present disclosure are
achieved, at least in whole or in part, by the subject matter
described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Preferred embodiments of the subject matter described herein
will now be described with reference to the accompanying drawings,
of which:
[0011] FIG. 1A is a schematic, cross-sectional side view of a
multi-pixel electron microbeam irradiator system and a Petri dish
in a cell irradiation setup according to one embodiment of the
subject matter described herein;
[0012] FIG. 1B is a schematic top view of predetermined locations
that can be individually irradiated by the electron field emitters
of the multi-pixel electron microbeam irradiator system shown in
FIG. 1A in accordance with one embodiment of the subject matter
described herein;
[0013] FIG. 2 is a schematic, cross-sectional side view of another
multi-pixel electron microbeam irradiator system including a
plurality of individually addressable electron field emitters for
selectively irradiating predetermined locations according to one
embodiment of the subject matter described herein;
[0014] FIGS. 3A-3F are steps of a method for fabricating multiple
electron field emitters, a gate electrode, and a focusing electrode
according to one embodiment of the subject matter described
herein;
[0015] FIGS. 4A-4E are steps of a method for fabricating a gate
electrode according to one embodiment of the subject matter
described herein;
[0016] FIGS. 5A-5D are steps of a method for fabricating an anode
including a plurality of electron transparent windows according to
one embodiment of the subject matter described herein;
[0017] FIG. 6 is an optical image of an individually addressable
electron field emitter structure; and
[0018] FIG. 7 is an optical image of a top view of three electron
field emitters after carbon nanotube deposition and removal of a
photoresist.
DETAILED DESCRIPTION
[0019] In accordance with the present disclosure, multi-pixel,
electron microbeam irradiator systems and methods are provided. The
systems and methods described herein can have particular
application for use in selectively irradiating predetermined
locations such as cells or cellular locations as described herein.
An electron microbeam irradiator system according to the present
disclosure can include a plurality of individually addressable
electron field emitters sealed in a vacuum. Further, an electron
microbeam irradiator system can include an anode comprising one or
more electron permeable portions corresponding to the plurality of
electron field emitters. A controller can be operable to
individually control electron extraction from each of the electron
field emitters for selectively irradiating predetermined locations.
The electron emitters can be individually turned on and off for
individually irradiating the predetermined locations for a
predetermined time duration and radiation dosage using a
predetermined sequence.
[0020] The electron field emitters can be any suitable conductive
structure and can have a sharp tip or protrusion for electron
emission under an electrical field. Exemplary electron field
emitters can include "Spindt" tips and other suitable
nanostructures. "Spindt" tips and related processes are described
in the publication "Vacuum Microelectronics," I. Brodie and C. A.
Spindt, Advances in Electronics and Electron Physics, 83: 1-106
(1992), the disclosure of which is incorporated by reference
herein. Exemplary materials of electron field emitter tips can
include molybdenum (Mo), silicon (Si), diamond (e.g., defective CVD
diamond, amorphic diamond, cesium-coated diamond, a nano-diamond),
and graphite powders.
[0021] Nanostructures suitable for electron emission can include
nanotube and nanowires/nanorods composed of either single or
multiple elements, such as carbon nanotubes. A single carbon
nanotube can have a diameter in the range of about 0.5-500 nm and a
length on the order of about 0.1-100 microns.
[0022] Carbon nanotubes readily emit large fluxes of electrons with
small angular divergence. A carbon nanotube can include a single
graphene shell, which is termed a single-wall carbon nanotube, or
multiple concentric graphene shells, which is termed a multi-wall
carbon nanotube. Carbon nanotubes, nanowires and nanorods can be
fabricated by techniques such as laser ablation, arc discharge, and
chemical vapor deposition (CVD) methods. Further, carbon nanotubes
can be made via solution or electrochemical synthesis. An exemplary
process for fabricating carbon nanotubes is described in the
publication "Materials Science of Carbon Nanotubes: Fabrication,
Integration, and Properties of Macroscopic Structures of Carbon
Nanotubes," Zhou et al., Acc. Chem. Res., 35: 1045-1053 (2002), the
disclosure of which is incorporated herein by reference. A single
carbon nanotube or a nanotube bundle can produce a current of about
0.1-10 .mu.A.
[0023] Table 1 below summarizes the threshold field required to
obtain a current density of 10 mA/cm.sup.2 for several electron
field emitter/cathode materials. TABLE-US-00001 TABLE 1 Emission
Threshold Field of Different Field Emitter/Cathode Material
Electron Field Emitter/Cathode Threshold Field (V/.mu.m) for
Material 10 mA/cm.sup.2 Mo Tips 50-100 Si Tips 50-100 p-type
Diamond 160 Defective CVD Diamond 30-120 Amorphic Diamond 20-40
Cesium-coated Diamond 20-30 Graphite Powders 10-20 Nano-Diamond 3-5
(unstable >30 mA/cm.sup.2) Assorted Carbon Nanotubes 1-2 (stable
>4000 mA/cm.sup.2)
[0024] In one embodiment, a multi-pixel electron microbeam
irradiator system in accordance with the subject matter disclosed
herein can include electron field emitters for irradiation of an
area, such as, for example, 10.sup.3-10.sup.6 (per square
centimeter of area) individually selected cells or sub-cellular
regions in a Petri dish. This radiation can be simultaneous,
sequential, or of any predetermined temporal pattern. The radiation
to each selected region can be controlled (i.e., individually
turned on or off). The radiation can be controlled with high
spatial (micrometer scale) and/or temporal (microsecond scale)
resolution. Further, the radiation dose rate can be controlled and
it can produce low to ultra-high dose rate (about 10.sup.3
Gy/sec.sup.3). The physical size of a multi-pixel electron
microbeam irradiator system according to the present disclosure can
be small and portable. It is envisioned that the device can be
placed directly under an optical microscope for in-situ observation
during the irradiation process.
[0025] FIGS. 1A and 1B illustrate views of a multi-pixel electron
microbeam irradiator system having a plurality of locations that
can be selectively irradiated by the multi-pixel electron microbeam
irradiator system according to one embodiment of the subject matter
described herein. FIG. 1A is a schematic, cross-sectional side view
of a multi-pixel electron microbeam irradiator system generally
designated 100 and a Petri dish PD in a cellular irradiation setup.
System 100 can include a plurality of individually addressable and
controllable electron field emitters FE (also referred to herein as
"pixels") for selectively irradiating predetermined locations L in
Petri dish PD. FIG. 1B is a schematic top view showing
predetermined locations L that can be individually and selectively
irradiated by electron field emitters FE of system 100. Referring
now to FIG. 1A, each electron field emitter FE can comprise one or
more carbon nanotubes and/or other suitable electron field emission
materials. Electron field emitters FE can be attached to a surface
of a cathode, conductive or contact line, or other suitable
conductive material. The cathodes can be attached to a suitable
non-conductive substrate such that the electron field emitters are
electrically isolated.
[0026] Electron field emitters FE can be individually controlled
(i.e., turned on and off) to emit electrons for selectively
irradiating predetermined locations L (shown in FIG. 1B). In one
embodiment, a controller CTR can control a voltage source VS to
individually apply voltages between each electron field emitter FE
and a gate electrode (not shown) to generate electric fields for
extracting electrons from electron field emitters FE. Controller
CTR can include hardware, software, and/or firmware, such as memory
(e.g., RAM, ROM, and computer-readable disks), transistors,
capacitors, resistors, inductors, logic circuitry, and other
components suitable for individually controlling electron emission
from electron field emitters FE. Controller CTR can also control
the intensity, timing, and duration of electron emission for each
of the electron field emitters FE.
[0027] Controller CTR can execute instructions for performing a
sequence by which locations L are irradiated with electron beams
generated by electron field emitter FE. The executable instructions
can be implemented as a computer program product embodied in a
computer readable medium. Exemplary computer readable media can
include disk memory devices, chip memory devices, application
specific integrated circuits, programmable logic devices,
downloadable electrical signals, and/or any other suitable computer
readable media.
[0028] Electron field emitters FE can be oriented such that
extracted electrons are directed towards respective predetermined
locations L. Further, a voltage can be applied between the gate
electrode and an anode A for accelerating the extracted electrodes
towards anode A. The voltage for accelerating the extracted
electrodes can be between about 20-60 kV and adjusted such that
electrons reach a desired energy for delivering radiation to
predetermined locations L. The energy of a beam of electrons at
anode A can be about 10 KV or greater. System 100 can also include
a collimator and/or focusing electrode for collimating and focusing
electrons extracted from electron field emitters FE and thus
reducing the size of electron microbeams EM.
[0029] A vacuum chamber VC can include a sealed interior for
containing electron field emitters FE and the gate electrode. The
interior of vacuum chamber VC can be evacuated to achieve a desired
interior pressure. An exemplary interior pressure of vacuum chamber
VC can be about 10.sup.-7 Torr. Predetermined locations L can be
positioned on an exterior of vacuum chamber VC. Extracted electrons
can travel from the interior of vacuum chamber VC to its exterior
through electron permeable portions, such as one or more thin
Si.sub.4N.sub.3 or polymer exit windows. The electron permeable
portions can be made of any suitable material having sufficient
thickness for permitting electrons to pass and having sufficient
robustness for withstanding a pressure difference between the
interior and exterior of vacuum chamber VC.
[0030] In one embodiment, Petri dish PD can be positioned to
receive electron microbeams EM emitted from microbeam irradiator
system 100. Petri dish PD can include a bottom component comprising
a polyester film such as a Mylar.RTM. brand film F for allowing
minimal attenuation of electron microbeams EM before the beams
reach locations L. Referring now to FIG. 1B, Petri dish PD can
include a monolayer of cells C that can be selectively irradiated
by system 100 (shown in FIG. 1A). In one embodiment, a reflective
microscope (not shown) can be used to image the cell population and
identify the target cells or regions and their locations, as well
as for real-time observation of cells C during and after radiation.
Using available cellular imaging and image analysis packages, an
operator can quickly identify target cells TC for irradiation.
Automated cellular microscope image analysis software as utilized
are understood by those of skill in the art.
[0031] In one exemplary process for irradiating target cells TC
using microbeam irradiator system 100, all of electron field
emitters FE can be turned on for identifying all positions P that
can be irradiated by system 100. The position identification
process can occur without Petri dish PD in position to receive
radiation. Next, while all of electron field emitters FE are turned
on, an image capture device having control and imaging equipment
suitable for capturing microscopic images and relative positions
can be used to capture an image of the positions irradiated by the
emitted electrons. Next, the imaging equipment can determine the
relative coordinates of the positions. When system 100 is placed in
a position for irradiating cells C in dish PD, two or more
"calibration" electron field emitters FE can be turned on and
imaged in the same coordinate system where target cells TC are
identified.
[0032] Subsequent to a determination of the coordinates of the
"calibration" electron field emitters FE, the coordinates of other
"non-calibration" electron field emitters FE can be determined.
Next, electron field emitters FE can be selected that correspond to
locations of respective target cells TC. The electron field
emitters FE corresponding to respective target cells TC can be
activated and controlled to deliver a predetermined radiation
dosage to target cells TC. Controller CTR can be programmed to
control the intensity, timing, and duration of electron emission by
electron field emitters FE to target cells TC. Further, one or more
images of the cells in dish PD can be captured during and
subsequent to exposure for obtaining information for radiation
biology research.
[0033] FIG. 2 illustrates a schematic, cross-sectional side view of
a multi-pixel electron microbeam irradiator system 200 including a
plurality of individually addressable electron field emitters FE
for selectively irradiating predetermined locations L according to
one embodiment of the subject matter described herein. Referring to
FIG. 2, system 200 can include a gate electrode GE operable to
extract electrons from field emitters FE on generation of an
electric field between gate electrode GE and field emitters FE.
After extraction from field emitters FE, the electrons can be
formed as electron microbeams and directed by generated electrical
fields to travel along pathways P. Field emitters FE may be spaced
apart in an array or grid such that different locations may be
irradiated by the emitted electrons. A controller CTR may be
operable to individually control electron emission from each field
emitter FE for selectively irradiating locations L along pathways
P.
[0034] In one embodiment, controller CTR can individually operate a
plurality of metal-oxide-semiconductor field-effect transistors
(MOSFETs) T for individually addressing field emitters FE to emit
electrons. In one embodiment, controller CTR can be a digital I/O
board. Controller CTR can include a field emitter addressing
function AF that can individually switch on and off transistors T.
The drains of field emitters FE can be connected to a corresponding
one of a plurality cathodes C. Each cathode C can be connected to a
respective field emitter FE via a resistor such as a 100 kilo ohm
protection resistor R. Function AF can control power supply PS to
individually turn on and off power to the sources of transistors T
for individually turning transistors T on and off. Transistors T
can be turned on and off by the individual application of a high
signal (e.g., 5 V) and a low signal (e.g., 0 V), respectively, to
the gates of the transistors T. When a high signal is applied to
the gate of a transistor, a drain-to-source channel of the
transistor is turned on to apply a voltage difference between a
respective cathode C and gate electrode GE. A voltage difference
exceeding a threshold can generate an electric field between
cathode C and gate electrode GE such that electrons are extracted
from respective electron field emitters FE. Conversely, when a low
voltage (e.g. 0 V) is applied to the gate of a transistor, a
corresponding drain-to-source channel is turned off such that the
voltage at electron field emitter FE is electrically floating and
the voltage difference between a respective cathode C and gate
electrode GE cannot generate an electric field of sufficient
strength to extract electrons from the respective electron field
emitter. Function F is operable to individually control the
voltages applied to the gates of transistors T. Thus, function F
can individually address and control the extraction of electrons
from field emitters FE.
[0035] Cathodes C can be attached to a substrate S in an array or
grid-like spacing. Substrate S can be made of silicon or any other
suitable non-conductive substrate material for electrically
isolating cathodes C. A spacer S1 can be disposed between substrate
S and gate electrode G for suitably spacing electron field emitters
FE and gate electrode G. Spacer S1 can be made of an insulation
material for electrically insulating substrate S and gate electrode
GE.
[0036] A vacuum chamber VC can include a sealed and evacuated
interior between anode A and electron field emitters FE. The
interior of vacuum chamber VC can have a pressure differential with
its exterior.
[0037] Further, microbeam array system 200 can include an anode A
having a plurality of electron permeable portions EPP through which
emitted electrons can pass. Each electron permeable portion EPP can
be positioned for passing electrons from a respective electron
field emitter FE. Further, electron permeable portions EPP can be
made of silicon nitride (Si.sub.3N.sub.4) or any other suitable
material that is permeable to electrons. Silicon nitride has a high
permeability to electrons and is mechanically robust for supporting
a pressure differential of the interior and exterior of vacuum
chamber VC, which can be one or more atmospheres.
[0038] An voltage difference can be applied between anode A and
gate electrode GE such that respective fields are generated for
accelerating elections emitted by respective electron field
emitters FE towards respective electron permeable portions EPP. In
one embodiment, anode A and electron permeable portions EPP can be
electrically connected to a ground G. Further, the energy of the
electrons can be adjusted by adjusting the electrical field applied
between gate electrode GE and cathode C. The voltage between gate
electrode GE and cathode C can be adjusted to change the electrical
field generated therebetween.
[0039] Microbeam array system 200 can include a plurality of
focusing electrodes FEL for at least partially focusing electrons
emitted by respective electron field emitters FE. The electrons can
be focused in a direction substantially towards respective
locations L. A focusing electron voltage (V.sub.f) can be applied
to focusing electrode FEL by power supply PS. Focusing electrode
FEL can be made of any suitable conductive material, such as Al,
Fe, Cu, and Mo. Focusing electrode FEL can be spaced from gate
electrode GE by a spacer S2 made of a suitable material for
electrically isolating focusing electrode FEL and gate electrode
GE.
[0040] A plurality of collimators CL can be positioned between
respective electron permeable portions EPP and electron field
emitters FE. Collimators CL can collimate and tune the beam profile
of the emitted electrons before the electrons pass through electron
permeable portions EPP. Collimators CL can be electrically isolated
from electron permeable portions EPP and anode A by a spacer S3
made of insulation material. Further, collimators CL can be spaced
from focusing electrode FEL by a spacer S4 made of insulation
material.
[0041] Collimators CL, focusing electrodes FEL, and gate electrodes
GE can be each formed of a single layer of conductive material. For
example, collimators CL can be formed of a single layer of metal.
Further, collimators CL, focusing electrodes FEL, and gate
electrodes GE can each include apertures for providing a pathway
for emitted electrons to travel from respective electron field
emitters FE.
[0042] Gate electrodes, focusing electrodes, collimators, anodes
having electron permeable portions, spacers and other components of
the multi-pixel electron microbeam irradiator systems described
herein can be fabricated by either bulk or surface micromachining
techniques. Bulk micromachining generally involves sculpting one or
more sides of a substrate to form desired three dimensional
structures in the same substrate material. The substrate can be
made of a material that is readily available in bulk form, such as
silicon or glass. Wet and/or dry etching techniques can be employed
in association with etch masks and etch stops to form
microstructures and apertures within the material. Etching can be
performed through the backside of the substrate. The etching
technique can be either isotropic or anisotropic in nature. Etch
masks and etch stops are used to prevent predetermined regions of
the substrate from being etched.
[0043] Conventional lithographic techniques can be employed in
accordance with micromachining of the gate electrodes, focusing
electrodes, collimators, anodes having electron permeable portions,
spacers and other components of the multi-pixel electron microbeam
irradiator systems described herein. Accordingly, basic
lithographic process steps such as photoresist application, optical
exposure, and the use of developers are not described in detail
herein.
[0044] Similarly, generally known-etching processes can be employed
to selectively remove material or regions of material. An imaged
photoresist layer is ordinarily used as a masking template. A
pattern can be etched directly into the bulk of a substrate, or
into a thin film or layer that is then used as a mask for
subsequent etching steps.
[0045] The type of etching process employed in a particular
fabrication step (e.g., wet, dry, isotropic, anisotropic,
anisotropic-orientation dependent), the etch rate, and the type of
etchant used will depend on the composition of material to be
removed, the composition of any masking or etch-stop layer to be
used, and the profile of the etched region to be formed. As
examples, poly-etch (HF:HNO.sub.3:CH.sub.3COOH) can generally be
used for isotropic wet etching. Hydroxides of alkali metals (e.g.,
KOH), simple ammonium hydroxide (NH.sub.4OH), quaternary
(tetramethl) ammonium hydroxide ((CH.sub.3).sub.4 NOH, also known
commercially as TMAH), and ethylenediamine mixed with pyrochatechol
in water (EDP) can be used for anisotropic wet etching to fabricate
V-shaped or tapered grooves, trenches or cavities. Silicon nitride
is typically used as the masking material against etching by KOH,
and thus can be used in conjunction with the selective etching of
silicon. Silicon dioxide is slowly etched by KOH, and thus can be
used as a masking layer if the etch time is short. While KOH will
etch undoped silicon, heavily doped (p++) silicon can be used as an
etch-stop against KOH as well as the alkaline etchants and EDP. A
metal that can be used to form contacts and interconnects is gold,
which is resistant to EDP. The adhesion layer applied in connection
with forming a gold component (e.g., chromium) is also resistant to
EDP.
[0046] It will be appreciated that electrochemical etching in
hydroxide solution can be performed instead of timed wet etching.
For example, if a p-type silicon wafer is used as a substrate, an
etch-stop can be created by epitaxially growing an n-type silicon
end layer to form a p-n junction diode. A voltage is applied
between the n-type layer and an electrode disposed in the solution
to reverse-bias the p-n junction. As a result, the bulk p-type
silicon is etched through a mask down to the p-n junction, stopping
at the n-type layer. Furthermore, photovoltaic and galvanic
etch-stop techniques are also suitable.
[0047] Dry etching techniques such as plasma-phase etching and
reactive ion etching (RIE) can also be used to remove silicon and
its oxides and nitrides, as well as various metals. Deep reactive
ion etching (DRIE) can be used to anisotropically etch deep,
vertical trenches in bulk layers. Silicon dioxide can be used as an
etch-stop against DRIE, and thus structures containing a buried
silicon dioxide layer, such as silicon-on-insulator (SOI) wafers,
can be used as starting substrates for the fabrication of
microstructures.
[0048] An alternative patterning process to etching is the lift-off
process. In this case, the conventional photolithography techniques
are used for the negative image of the desired pattern. This
process can be used to pattern metals, which are deposited as a
continuous film or films when adhesion layers and diffusion
barriers are needed. The metal can be deposited on the regions
where it is to be patterned and on top of the photoresist mask
(negative image). The photoresist and metal on top can be removed
to leave behind the desired pattern of metal, such as the
patterning of contact lines.
[0049] Suitable electron field emitters, such as carbon nanotubes,
can be formed on conductive or semiconductive surfaces, such as
contact lines and cathodes, described herein by electrophoretic
deposition techniques and any other suitable techniques known to
those of skill in the art, such as screen printing, chemical vapor
deposition, and spraying. Generally, for example, carbon nanotubes
can be electrophoretically deposited on a surface by a combination
of some or all of the following steps: (1) forming a solution or
suspension containing the carbon nanotubes; (2) selectively adding
"chargers" to the solution; (3) immersing electrodes in the
solution, with the surface upon which the carbon nanotubes are to
be deposited acting as one of the electrodes; (4) applying a direct
and/or alternating current for creating an electrical field between
the electrodes for a predetermined period of time to thereby cause
the carbon nanotubes in the solution to migrate toward and attach
themselves to the conductive or semiconductive surface; and (5)
optional subsequent processing of the coated surface.
[0050] The components of multi-pixel electron microbeam irradiator
systems described herein can be assembled by a variety of methods.
Generally, for example, electron field emitters, a gate electrode,
focusing electrodes, collimators, an anode having electron
permeable portions, spacers and other components of a multi-pixel
electron microbeam irradiator system can be positioned together as
described herein to form a vacuum chamber. The electron field
emitters can be positioned within the interior of the chamber along
with other components, such as a gate electrode and anode, for
generating electric fields for extracting electrons from the
electron field emitters and accelerating the electrons through
electron permeable portions of the anode. The vacuum chamber can be
subsequently sealed and evacuated to a predetermined minimum
pressure, or back-filled with an inert atmosphere, for preparation
of generating electron beams.
[0051] According to one embodiment, an array of electron field
emitters, a gate electrode, and a focusing electrode can be
fabricated on a substrate by combination of electrophoresis and
photolithography processes. Referring to FIGS. 3A-3F, a method for
fabricating multiple electron field emitters, a gate electrode, and
a focusing electrode according to one embodiment of the subject
matter described herein is illustrated. Referring to FIG. 3A, a
substrate 300 can be provided, which can be a 3'' silicon wafer,
glass, or other suitable substrate. A thermal oxide layer 302 can
be disposed on a top surface of substrate 300. Further,
electrically-isolated conductive contact lines 304 can be disposed
on a top surface of layer 302. Contact lines 304 can be parallel
electrode lines made of silver (Ag). Further, in one embodiment,
contact lines 304 can be 150 .mu.m in width and spaced by 100
.mu.m.
[0052] Referring to FIG. 3B, electron field emitters FE can be
deposited on a top surface of lines 304 by a
photolithography/electrophoresis process. In one embodiment, a
release/photoresist layer 306 can be deposited on portions of layer
302 that are not to be covered by electron field emitters FE.
Further, in one embodiment, electron field emitters FE can be
carbon nanotubes. Next, Referring to FIG. 3C, layer 306 can be
removed without disturbing electron field emitters FE. An exemplary
lithography and electrophoresis process for patterning carbon
nanotubes is described in the publication "Liquid-Phase Fabrication
of Patterned Carbon Nanotube Field Emission Cathodes," Oh et al.,
Appl. Phys. Lett., 87(19): 3738 (2004), the disclosure of which is
incorporated herein by reference in its entirety.
[0053] Referring to FIG. 3D, a dielectric insulation layer or
spacer 308 comprising a plurality of apertures corresponding to
electron field emitters FE can be disposed on the top surface of
layer 302 between electron field emitters FE. Insulation layer 308
can be aligned using a mask aligner. In one embodiment, insulation
layer 308 can be made of glass or any other suitable insulation
material. Insulation layer 308 can be about 15 .mu.m in thickness
and patterned with an opening for exposing contact lines 304.
[0054] Referring to FIG. 3E, a gate electrode GE comprising a
plurality of apertures corresponding to electron field emitters FE
can be disposed on insulation layer 308. Next, referring to FIG.
3F, another insulation layer 310 and a focusing electrode FEL can
be disposed on gate electrode GE. Insulation layer 310 and focusing
electrode FEL can include a plurality of apertures corresponding to
electron field emitters FE. An anode including a plurality of
electron transparent windows can be fabricated. Each of the windows
can correspond to one of electron field emitters FE. Alignment can
be accomplished using alignment marks under a mask aligner and
bonded together using a suitable wafer bonding technique.
[0055] According to one embodiment, electron field emitters FE can
be about 50-100 .mu.m in diameter. Further, electron field emitters
FE can be electrically insulated from one another so that they can
be individually addressed or controlled. Spacing between gate
electrode GE and electron field emitters FE can be about 100 .mu.m
or any suitable distance such that a desired current can be reached
with 1-2 kV driving voltage on gate electrode GE. Focusing
electrode FEL can focus the field-emitted electrons on the electron
transparent windows of the anode.
[0056] In an alternate embodiment, insulation layer or spacer 308
and gate electrode GE can be deposited on the top surface of layer
302 prior to the deposition of electron field emitters FE. Next,
insulation layer 308 and gate electrode GE can be covered by layers
of resist and release materials. For example, contact lines 304,
insulation layer 308, and gate electrode GE can be spin-coated with
a uniform layer of OMNICOAT.TM. release (available from MicroChem,
Inc. of Newton, Me.). Next, contact lines 304, insulation layer
308, and gate electrode GE can be spin-coated with a uniform layer
of epoxy-based SU-8 negative photoresist product (available from
MicroChem, Inc.) of about 10-20 mm in thickness. Depending on the
desired SU-8 thickness, spin speed and viscosity of SU-8 can be
controlled. The photoresist can be insoluble in alcohol. Next, the
photoresist can be patterned by contact-mode UV photolithography
and developed such that the area contact lines 304 to be deposited
with electron field emitters FE is removed while the other surfaces
are covered with cross-linked SU-8. Subsequently, the exposed
OMNICOAT.TM. release can be chemically removed to reveal contact
lines 304. Next, electron field emitters FE (in this example,
carbon nanotubes) can be electrophoretically deposited onto contact
lines 304 by applying a DC voltage between contact lines 304 and a
counter-electrode submerged in alcohol containing carbon nanotubes.
Further, MgCl.sub.2 "chargers" can be added to the solution and a
voltage applied between contact lines 304 and counter-electrode to
cause the carbon nanotubes to deposit on contact lines 304. After
deposition of the carbon nanotubes, the photoresist can be stripped
using a release such as an OMNICOAT.TM. release.
[0057] According to one embodiment, a gate electrode can be
fabricated by combination of photolithography and deep reactive ion
etch (DRIE) processes. Referring to FIGS. 4A-4E, a method for
fabricating a gate electrode according to one embodiment of the
subject matter described herein is illustrated. Referring to FIG.
4A, a substrate 400 can be provided, which can be a silicon wafer
or other suitable substrate. Next, substrate 400 can patterned with
an etch mask 402 for forming a metal mesh structure. Referring to
FIG. 4B, a mesh structure MS can be formed by performing a deep
reactive ion etch. The etch can be about 50 .mu.m deep. Referring
to FIG. 4C, mesh structure MS can be covered with a photoresist 404
and an opposing side of substrate 400 covered with an etch mask
406. Next, referring to FIG. 4D, a deep reactive ion etch can be
performed from the opposing side until an aperture is formed to
mesh structure MS. Referring to 4E, photoresist 404 and etch mask
406 can be removed for completing the fabrication of gate electrode
GE.
[0058] According to one embodiment, an anode including a plurality
of electron transparent windows can be fabricated by combination of
lithography, anisotropic silicon etching, and DRIE processes.
Referring to FIGS. 5A-5D, a method for fabricating an anode
including a plurality of electron transparent windows according to
one embodiment of the subject matter described herein is
illustrated. Referring to FIG. 5A, a substrate 500 can be provided,
which can be a silicon wafer, ITO-coated glass, or other suitable
substrate. Electron permeable layers 502 and 504 can be deposited
on opposing sides of substrate 500. Layers 502 can be made of
silicon nitride (Si.sub.3N.sub.4) or any other suitable material
that is permeable to electrons. Silicon nitride has a high
permeability to electrons and is mechanically robust for supporting
a pressure differential of at least one atmosphere. In one
embodiment, layer 502 may be a layer of silicon nitride having a
thickness between about 500-1000 A, which can function as an etch
mask for an etching process. Layer 504 can be a 2500 A layer of
silicon nitride, a portion of which can function as electron
transparent windows.
[0059] Referring to FIG. 5B, areas on layer 502 can be defined for
etching. For example, layer 502 can be patterned with a photoresist
506. Referring to FIG. 5C, a reactive ion etching process can be
applied to remove the portions of layer 502 left uncovered by
photoresist 506. Next, photoresist 506 can be removed. Referring to
FIG. 5D, exposed portions of substrate 500 are removed by an
anisotropic hot KOH etch. Trenches T can be formed by etching
through substrate 500 to form electron transparent windows TW. In
one example, transparent windows TW can be about 20 .mu.m.times.20
.mu.m. Transparent windows TW can be positioned for intercepting
electron beams emitted from electron field emitters (such as
electron field emitters FE shown in FIGS. 1 and 2). Alignment marks
can be patterned on the wafer to assist subsequent assembly with
the electron field emitters. The resulting structure can function
as a collimator of the electron beams when substrate 500 is of a
material and thickness for preventing the penetration of electrons
therethrough. For example, a silicon wafer having a thickness of
400 .mu.m can prevent electrons from penetrating through.
[0060] In one embodiment, the nitride can be unaffected by the etch
process. After completion of the KOH anisotropic etching, a metal
layer can be deposited onto the resulting wafer. The metal can be
deposited onto the areas of the wafer not covered by a photoresist.
The photoresist can be lifted off in a solvent. The metal layer can
serve as an anode component in a multi-pixel electron microbeam
irradiator system according to one embodiment of the subject matter
described herein.
[0061] FIGS. 6 and 7 are representations of optical images of
actual electron field emitter structures. In particular, FIG. 6 is
an optical image of an individually addressable electron field
emitter structure. The image shows a cathode electrode 600, a gate
electrode 602, and an active area 604.
[0062] FIG. 7 is an optical image of a top view of three electron
field emitters after carbon nanotube deposition (dark areas) and
removal of a photoresist. The image shows carbon nanotubes 700 on
cathode lines and a gate electrode 702.
[0063] A multi-pixel electron microbeam irradiator system according
to the subject matter described herein can be used for individually
irradiating a selected single cell or a subcellular region in a
cell population in vitro, without depositing radiation doses to
adjacent cells and regions. Further, multi-pixel electron microbeam
cell irradiator systems according to the subject matter described
herein can be used by researchers for studying microscopic
processes activated by particular cellular or sub-cellular
components of interest following radiation.
[0064] The above-described components and techniques can be applied
to devices and systems having electron field emitters and related
methods. In addition to uses described above, exemplary devices and
systems that can be used with the subject matter described herein
can include flat-panel displays, microwave vacuum tubes, portable
X-ray devices, and gas discharge tubes.
[0065] It will be understood that various details of the subject
matter described herein may be changed without departing from the
scope of the subject matter described herein. Furthermore, the
foregoing description is for the purpose of illustration only, and
not for the purpose of limitation, as the subject matter described
herein is defined by the claims as set forth hereinafter.
* * * * *