U.S. patent application number 12/958224 was filed with the patent office on 2011-06-02 for extreme synthesis of crystalline aerogel materials from amorphous aerogel precursors.
This patent application is currently assigned to Lawrence Livermore National Security, LLC. Invention is credited to Jonathan C. Crowhurst, Peter J. Pauzauskie, Joe H. Satcher, JR., Marcus A. Worsley.
Application Number | 20110129614 12/958224 |
Document ID | / |
Family ID | 44069099 |
Filed Date | 2011-06-02 |
United States Patent
Application |
20110129614 |
Kind Code |
A1 |
Pauzauskie; Peter J. ; et
al. |
June 2, 2011 |
EXTREME SYNTHESIS OF CRYSTALLINE AEROGEL MATERIALS FROM AMORPHOUS
AEROGEL PRECURSORS
Abstract
In one embodiment, a system includes a pressure cell adapted for
enclosing a porous structure; an inert pressure medium within the
pressure cell; and a heat source for heating the porous structure.
In another embodiment, a composition of matter includes a
crystalline porous structure having a density of about 30 to about
50 mg/cm.sup.3. A method according to one embodiment includes
positioning an amorphous porous structure in a pressure cell;
injecting an inert pressure medium within the pressure cell; and
pressurizing the pressure cell to a pressure that thermodynamically
favors a crystalline phase of the porous structure over an
amorphous phase of the porous structure to transition the amorphous
porous structure into a crystalline porous structure. Additional
embodiments are also presented.
Inventors: |
Pauzauskie; Peter J.;
(Seattle, WA) ; Crowhurst; Jonathan C.;
(Livermore, CA) ; Worsley; Marcus A.; (Hayward,
CA) ; Satcher, JR.; Joe H.; (Patterson, CA) |
Assignee: |
Lawrence Livermore National
Security, LLC
Livermore
CA
|
Family ID: |
44069099 |
Appl. No.: |
12/958224 |
Filed: |
December 1, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61265638 |
Dec 1, 2009 |
|
|
|
Current U.S.
Class: |
427/554 ; 118/50;
118/50.1; 252/182.11; 252/500 |
Current CPC
Class: |
C01B 13/322 20130101;
C01P 2006/12 20130101; C01P 2002/84 20130101; C01P 2006/10
20130101; C01P 2004/03 20130101; C01P 2002/02 20130101; C09K 11/65
20130101; C01P 2002/72 20130101; C09C 1/44 20130101; C01B 33/1585
20130101; C01P 2004/04 20130101 |
Class at
Publication: |
427/554 ;
118/50.1; 118/50; 252/500; 252/182.11 |
International
Class: |
B05D 3/06 20060101
B05D003/06; H01B 1/00 20060101 H01B001/00; C09K 3/00 20060101
C09K003/00 |
Goverment Interests
[0002] The United States Government has rights in this invention
pursuant to Contract No. DE-AC52-07NA27344 between the United
States Department of Energy and Lawrence Livermore National
Security, LLC for the operation of Lawrence Livermore National
Laboratory.
Claims
1. A system, comprising: a pressure cell adapted for enclosing a
porous structure; an inert pressure medium within the pressure
cell; and a heat source for heating the porous structure.
2. The system as recited in claim 1, wherein the pressure cell is a
diamond anvil cell, the diamond anvil cell comprising: a gasket
having a front side and a back side; a first diamond having at
least one flat, smooth face; and a second diamond having at least
one flat, smooth face, wherein the at least one flat, smooth face
of the first diamond has a surface area greater than a surface area
of the front side of the gasket and is capable of completely
covering a perimeter of the front side of the gasket, wherein the
at least one flat, smooth face of the second diamond has a surface
area greater than the surface area of the front side of the gasket
and is capable of completely covering a perimeter of the back side
of the gasket, wherein the flat, smooth face of the first diamond
is in contact with the front side of the gasket, and wherein the
flat, smooth face of the second diamond is in contact with the back
side of the gasket.
3. The system as recited in claim 2, wherein the first diamond and
the second diamond are ultralow fluorescence diamonds.
4. The system as recited in claim 1, wherein the heat source is a
laser.
5. The system as recited in claim 4, wherein the inert pressure
medium has a low photon absorption cross section at an operational
wavelength and intensity of the laser and low chemical reactivity
with the porous structure such that chemical reactions and
background absorption are reduced during heating of the porous
structure at high pressure.
6. The system as recited in claim 1, wherein the inert pressure
medium comprises supercritical neon gas.
7. The system as recited in claim 1, wherein the inert pressure
medium comprises at least one of: neon gas, argon gas, helium gas,
krypton gas, xenon gas, and carbon dioxide gas.
8. The system as recited in claim 1, wherein the porous structure
comprises a carbonized resorcinol-formaldehyde aerogel that has a
specific density of about 30 to 50 mg/cm.sup.3.
9. The system as recited in claim 1, wherein the porous structure
comprises one of: amorphous silica aerogel, amorphous alumina
aerogel, and amorphous titania aerogel.
10. A composition of matter, comprising: a crystalline porous
structure having a density of about 30 to about 50 mg/cm.sup.3.
11. The composition of matter as recited in claim 10, wherein the
porous structure comprises carbonized resorcinol-formaldehyde
aerogel that has a specific density of about 40 mg/cm.sup.3.
12. The composition of matter as recited in claim 10, wherein the
crystalline porous structure comprises one of: silica aerogel,
alumina aerogel, and titania aerogel.
13. The composition of matter as recited in claim 10, wherein the
crystalline porous structure has characteristics of being
phase-transitioned from an amorphous porous structure.
14. The composition of matter as recited in claim 10, further
comprising one or more dopant elements.
15. The composition of matter as recited in claim 10, wherein the
one or more dopant elements comprise dopant elements that impart at
least one of: optical and electrical properties to the porous
structure.
16. A method, comprising: positioning an amorphous porous structure
in a pressure cell; injecting an inert pressure medium within the
pressure cell; and pressurizing the pressure cell to a pressure
that thermodynamically favors a crystalline phase of the porous
structure over an amorphous phase of the porous structure to
transition the amorphous porous structure into a crystalline porous
structure.
17. The method as recited in claim 16, further comprising heating
the amorphous porous structure to accelerate transition to the
crystalline phase and to overcome a corresponding phase change
barrier.
18. The method as recited in claim 17, wherein a laser is
selectively applied according to a user-defined pattern to heat one
or more selected regions of the amorphous porous structure.
19. The method as recited in claim 17, wherein the amorphous porous
structure is heated to a temperature of greater than about
500.degree. C.
20. The method as recited in claim 16, further comprising returning
the pressure and temperature in the pressure cell to ambient
conditions.
21. The method as recited in claim 16, wherein the amorphous porous
structure comprises one of silica aerogel, alumina aerogel, and
titania aerogel.
22. The method as recited in claim 16, wherein the amorphous porous
structure is an aerogel of carbonized resorcinol-formaldehyde that
has a specific density of about 30 to 50 mg/cm.sup.3.
23. The method as recited in claim 16, wherein the amorphous porous
structure comprises carbon aerogel and has a specific density of
about 40 mg/cm.sup.3.
24. The method as recited in claim 16, wherein the inert pressure
medium conformally and homogeneously occupies a void volume of the
pressure cell and a void volume of pores of the amorphous porous
structure without disturbing pore morphology of the amorphous
porous structure.
25. The method as recited in claim 16, wherein the pressure cell is
pressurized to a pressure of about 21.times.10.sup.9 Pa, wherein
the amorphous porous structure comprises an amorphous-phase
carbonized resorcinol-formaldehyde aerogel.
26. The method as recited in claim 16, wherein the inert pressure
medium comprises at least one of: neon gas, argon gas, helium gas,
krypton gas, xenon gas, and carbon dioxide gas.
Description
RELATED APPLICATIONS
[0001] The present application claims priority to a U.S.
Provisional Patent Application filed Dec. 1, 2009, under Appl. No.
61/265,638, which is incorporated herein by reference.
FIELD OF THE INVENTION
[0003] The present invention relates to aerogels, and more
particularly to extreme synthesis of crystalline aerogel materials
from amorphous aerogel precursors.
BACKGROUND
[0004] Aerogels are a fascinating class of high surface-area,
mechanically-robust materials with a broad range of both commercial
and fundamental scientific applications. Owing to its highly porous
mass-fractal nanostructure, amorphous silica aerogel has been used
as a capture agent in NASA's cometary-dust retrieval missions, to
control disorder in .sup.3He-superfluid phase transitions, in the
fabrication of targets for laser inertial confinement fusion, in
low-k microelectromechanical (MEMS) devices, and in Cherenkov
nucleonic particle detectors.
[0005] In particular, amorphous carbon aerogel has received a
considerable amount of attention in recent years owing to its low
cost, electrical conductivity, mechanical strength, and thermal
stability. Numerous applications have been explored for this
material including water desalination, electrochemical
supercapacitors, and thermal insulation.
[0006] Impressive advances have been made in the synthesis of
polycrystalline aerogels through the oxidative aggregation of
chalcogenide quantum dots that preserve spectral signatures of
quantum confinement. Also, silicon divacancies in nanodiamond have
also been shown to be bright single-photon-emitters at room
temperature (Jelezko, Phys. Stat. Sol. A, 2006), as well as being
photostable near-infrared biocompatible fluorophores (Lu, PNAS,
2007).
[0007] Furthermore, recent high-pressure, high temperature (HPHT)
experiments with mesoporous silica have been employed to produce
mesoporous coesite phase after oxidative removal of the carbon
pressure medium. However, the achievement of an amorphous to
crystalline phase transition in an aerogel material has remained an
outstanding challenge, largely due to the difficulty in preventing
pore collapse in the high surface area aerogel starting
material.
[0008] In addition, thermal, electrical, optical, mechanical, and
chemical properties of low-density amorphous aerogels can change
profoundly through conversion from an amorphous to a crystalline
phase, opening up new horizons for applications of this material in
fundamental science.
[0009] Therefore, a method and system capable of synthesizing
crystalline aerogel materials from amorphous aerogel precursors
would have great utility in basic science and commercial
applications.
SUMMARY
[0010] In one embodiment, a system includes a pressure cell adapted
for enclosing a porous structure; an inert pressure medium within
the pressure cell; and a heat source for heating the porous
structure.
[0011] In another embodiment, a composition of matter includes a
crystalline porous structure having a density of about 30 to about
50 mg/cm.sup.3.
[0012] A method according to one embodiment includes positioning an
amorphous porous structure in a pressure cell; injecting an inert
pressure medium within the pressure cell; and pressurizing the
pressure cell to a pressure that thermodynamically favors a
crystalline phase of the porous structure over an amorphous phase
of the porous structure to transition the amorphous porous
structure into a crystalline porous structure.
[0013] Other aspects and embodiments of the present invention will
become apparent from the following detailed description, which,
when taken in conjunction with the drawings, illustrate by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1A shows a schematic diagram of an apparatus for
extreme synthesis of crystalline aerogel from amorphous aerogel,
according to one embodiment.
[0015] FIG. 1B shows a schematic diagram of a diamond-anvil-cell
(DAC), according to one embodiment.
[0016] FIG. 2 shows a Raman spectroscopy profile of a crystalline
diamond aerogel, according to one embodiment.
[0017] FIG. 3 shows comparative scanning transmission X-ray
absorption profiles of an amorphous carbon and a crystalline
diamond aerogel, according to one embodiment.
[0018] FIG. 4A shows a schematic example of a point vacancy in a
crystalline structure, according to one embodiment.
[0019] FIG. 4B shows a visible fluorescence profile of point
vacancies in a crystalline structure, according to one
embodiment.
[0020] FIG. 5 shows a comparison of time-correlated single photon
counting profiles of a 100 nm grain, a crystalline diamond aerogel,
and lacy carbon, according to one embodiment.
[0021] FIG. 6 shows a confocal fluorescence transmission electron
microscopy (TEM) image of a crystalline diamond aerogel, according
to one embodiment.
[0022] FIG. 7 shows a scanning electron microscopy (SEM) image of a
crystalline diamond aerogel, according to one embodiment.
[0023] FIG. 8 shows: A) a bright-field TEM image of an amorphous
carbon aerogel, according to one embodiment, B) a bright-field TEM
image of crystalline diamond aerogel, according to one embodiment,
C) an electron diffraction TEM image of an amorphous carbon
aerogel, according to one embodiment, and D) an electron
diffraction TEM image of crystalline diamond aerogel, according to
one embodiment.
[0024] FIG. 9 depicts a method for synthesizing a crystalline
diamond aerogel, according to one embodiment.
[0025] FIG. 10A shows a high-resolution TEM image of an amorphous
carbon aerogel, according to one embodiment.
[0026] FIG. 10B shows a high-resolution TEM image of a crystalline
diamond aerogel, according to one embodiment.
DETAILED DESCRIPTION
[0027] The following description is made for the purpose of
illustrating the general principles of the present invention and is
not meant to limit the inventive concepts claimed herein. Further,
particular features described herein can be used in combination
with other described features in each of the various possible
combinations and permutations.
[0028] Unless otherwise specifically defined herein, all terms are
to be given their broadest possible interpretation including
meanings implied from the specification as well as meanings
understood by those skilled in the art and/or as defined in
dictionaries, treatises, etc.
[0029] It must also be noted that, as used in the specification and
the appended claims, the singular forms "a," "an" and "the" include
plural referents unless otherwise specified.
[0030] In one general embodiment, a system includes a pressure cell
adapted for enclosing a porous structure; an inert pressure medium
within the pressure cell; and a heat source for heating the porous
structure.
[0031] In another general embodiment, a composition of matter
includes a crystalline porous structure having a density of about
30 to about 50 mg/cm.sup.3.
[0032] In yet another general embodiment, a method includes
positioning an amorphous porous structure in a pressure cell;
injecting an inert pressure medium within the pressure cell; and
pressurizing the pressure cell to a pressure that thermodynamically
favors a crystalline phase of the porous structure over an
amorphous phase of the porous structure to transition the amorphous
porous structure into a crystalline porous structure.
[0033] Referring now to the figures, FIG. 1A shows a schematic
representation of one exemplary embodiment of an apparatus 100,
which includes a diamond anvil cell (DAC) 101, which is also shown
separately in FIG. 1B. The DAC 101 includes two diamonds 102 with
flat, smooth faces positioned parallel to one another, in flush
contact with a metallic gasket 104 so as to form a hollow sample
chamber 106. In a preferred embodiment, the DAC 101 may be built
with ultralow fluorescence diamonds to allow for optical access
through the sample chamber 106.
[0034] According to more embodiments, any pressurized chamber
capable of maintaining pressures sufficient to transition a porous
structure (such as an aerogel) from an amorphous phase to a
crystalline phase may be used, such as a piston operated pressure
chamber, hydraulic pressure chamber, etc.
[0035] In one approach, a porous structure 108, such as an aerogel
of carbonized resorcinol-formaldehyde that has a specific density
of about 40 mg/cm.sup.3, may be loaded into the sample chamber 106.
While a carbonized resorcinol-formaldehyde aerogel is employed as
the porous structure in a preferred embodiment, any amorphous
aerogel or amorphous porous structure, exhibiting appropriate
physical properties may be used, as would be understood by one of
skill in the art upon reading the present descriptions, for
example, aerogels of silica, alumina, titania, etc.
[0036] For the sake of clarity and simplicity, for the remainder of
this description, the porous structure will be referred to as an
aerogel. However, the descriptions and embodiments herein are not
meant to be limited to only aerogels, as any suitable porous
structures may be used.
[0037] The sample chamber 106 is then filled with an inert pressure
medium 110. The inert pressure medium 110 conformally and
homogeneously occupies a void volume of the sample chamber 106 and
the void volume of the pores of the aerogel 108 without disturbing
the pore morphology of the aerogel 108, in one embodiment.
[0038] According to one exemplary embodiment, the inert pressure
medium 110 may be neon. Neon's low critical point (44.4 K, 27.2
atm) and moderate freezing pressure near room-temperature (4.70 Pa
at 293 K) permit conformal, homogenous filling of the void volume
of the highly-porous carbon aerogel starting material with solid
cubic-close-packed (ccp) neon. Furthermore, neon's low chemical
reactivity and low photon absorption cross section at 1064 nm
reduce undesirable chemical reactions and background absorption
during laser heating at high pressure.
[0039] The inert pressure medium 110 preferably has low chemical
reactivity with the compounds comprising the aerogel 108, as well
as a low photon absorption cross section at the operational
wavelength and intensity of a heating laser 118. While
supercritical neon gas is employed in the exemplary embodiment, any
gas exhibiting appropriate physical properties may be used as would
be apparent to one of skill in the art upon reading the present
descriptions, for example, supercritical argon, helium, krypton,
xenon, carbon dioxide, etc.
[0040] The aerogel 108 and inert pressure medium 110 are then
pressurized in the sample chamber 106, significantly restricting
mechanical deformation and atomic diffusion at high pressures and
temperatures, in one approach. Further compression ultimately
produces pressure conditions that thermodynamically favor a
crystalline phase, as opposed to the amorphous phase, of the
aerogel 108. The pressure necessary to create conditions that
thermodynamically favor a particular compositional state of matter
may vary with the physical properties of the aerogel 108 and the
desired phase change, and these parameters may generally be
inferred from the physical phase diagram of the aerogel material,
as would be known by one having ordinary skill in the art.
[0041] Once thermodynamically favorable pressure is achieved,
kinetic barriers inhibit the amorphous-to-crystalline phase change
reaction, in one embodiment. In a preferred approach, applying heat
to the pressurized aerogel 108 may facilitate the phase change
reaction by providing the atoms comprising the aerogel material
with kinetic energy sufficient to overcome the corresponding phase
change barrier. Heating may be accomplished via any controlled
method as known in the art, and may preferably be homogeneous.
[0042] In one exemplary embodiment, a heating laser 118 may be used
as a controlled heating source that passes through e.g., a wp
filter 116 and is reflected toward the sample chamber 106 by, e.g.,
a pbc element 114. The laser is focused into the sample chamber 106
with an objective lens 112, and heats the aerogel 108 to a final
temperature determined by the aerogel material's optical absorption
cross section at the wavelength and intensity of the laser. In a
preferred embodiment, controlled application of heat by a laser
allows precise control over the spatial sites where phase
transition from amorphous to crystalline occur. This allows for a
crystalline aerogel to systematically be sculpted from starting
amorphous materials.
[0043] In one exemplary approach, while converting amorphous-phase
carbonized resorcinol-formaldehyde aerogel to a crystalline-phase,
an upper limit of the pressure used to create thermodynamically
favorable conditions was approximately 21.times.10.sup.9 Pa.
Furthermore, heating the carbonized resorcinol-formaldehyde aerogel
with an infrared, approximately 100 W continuous Nd:YAG laser
operating at 1064 nm and focused onto the sample chamber with a
Mitutoyo objective lens having about 50.times. magnification
produced final temperatures above about 500.degree. C.
[0044] After completion of the phase-change reaction, pressure and
temperature may be reduced to ambient conditions, allowing the
inert pressure medium 110 to escape the aerogel 108 by diffusion,
possibly with atmospheric air, while maintaining the porosity of
the crystalline aerogel 108. This crystalline aerogel 108 may be
recovered with standard extraction equipment as known by one having
ordinary skill in the art. Properties of the aerogel 108 may be
discovered via a suite of techniques including
Raman/photoluminescence spectroscopy, time-correlated single photon
counting, scanning/transmission electron microscopy imaging,
electron diffraction, electron energy loss spectroscopy, and
synchrotron scanning transmission x-ray absorption microscopy.
[0045] Aerogel Properties
[0046] The amorphous carbon aerogel may have a low density of
approximately 40 mg/cm.sup.3, which is retained in the resulting
crystalline diamond aerogel because the inert pressure medium
homogeneously and conformally supports each pore within the
amorphous structure during phase transition and preserves the
three-dimensional structure of the starting material. FIG. 7 shows
an SEM image of a crystalline diamond aerogel, according to one
embodiment.
[0047] The amorphous carbon aerogel strongly absorbs incident
energy from the heating laser and is observed to glow while
heating. This thermal radiation has been observed to reach a local
temperature greater than about 500.degree. C. for a carbon aerogel.
As observed by visible microscopy, during heating the resulting
material becomes significantly more transparent, scattering rather
than absorbing a large amount of incident light.
[0048] Raman spectroscopy was employed to probe this translucent
material further resulting in a spectrum as shown in FIG. 2. In
contrast with the amorphous carbon aerogel, a sharp new Raman mode
is visible in the laser-heated regions with both a frequency and
pressure-dependence consistent with a phase transition to
crystalline diamond. In particular, while the starting carbon
aerogel exhibits sp.sup.2 and sp.sup.3 bonding and vibrational
properties characteristic of graphite, the new Raman mode informs a
change in vibrational mode of bonding consistent with inelastic
cubic diamond sp.sup.3 bonding. Similarly consistent results have
been observed in silica-based aerogels, where amorphous starting
material exhibits no crystal structure and crystalline aerogel
exhibits new vibrational modes consistent with crystalline bonding
of the sp.sup.3 variety.
[0049] Furthermore, intense fluorescence is visible from
laser-heat, as shown in FIG. 6, and retained at ambient conditions,
suggesting formation of luminescent point defects in the newly
formed diamond phase.
[0050] In one embodiment, point defects may be controlled by doping
the starting aerogel material with an element of interest and
subsequently performing the conversion process in order to
incorporate desired features into the crystalline aerogel. In one
approach, dopants may have optical and/or electrical properties of
interest to facilitate downstream applications, for example:
fluorophore doping for fluorescent labeling, nitrogen doping for
quantum computing, nitrogen doping for optical sensors, etc.
[0051] Following release of pressure, the material may be recovered
from the DAC chamber with motorized probes (such as those from
Marzhauser Wetzlar) and prepared for further analysis with
transmission electron microscopy (TEM). Low magnification
brightfield images (as shown in FIG. 8) reveal similarities in the
microstructure between the amorphous carbon starting materials and
the recovered diamond aerogel. FIG. 8 shows: A) a bright-field TEM
image of an amorphous carbon aerogel, according to one embodiment,
B) a bright-field TEM image of crystalline diamond aerogel,
according to one embodiment, C) an electron diffraction TEM image
of an amorphous carbon aerogel, according to one embodiment, and D)
an electron diffraction TEM image of crystalline diamond aerogel,
according to one embodiment.
[0052] The highly porous aerogel morphology of the starting
materials appears well preserved in the recovered material
following laser heating at 20 GPa due to support provided from
solid neon which is a soft, hydrostatic, and chemically inert
pressure medium. Electron diffraction of the starting material
shows characteristic amorphous graphitic ring patterns while the
recovered material shows several new diffraction rings which can be
indexed to the cubic diamond crystal lattice, as shown in FIG.
8.
[0053] The presence of a new diamond phase is confirmed further
through high-resolution TEM images. High-resolution TEM images,
shown in FIGS. 10A and 10B, reveal the amorphous starting materials
include interconnected graphitic domains with grain sizes less than
about 10 nm, as expected for a carbon aerogel and shown in FIG.
10A. In contrast, the recovered diamond aerogel material appears to
include ultrananocrystalline grains connected through thin surface
coatings of graphitic carbon. Individual grains range in size from
about 1 nm to about 100 nm and high-resolution imaging, as shown in
FIG. 10B, shows sharp lattice fringes with a d-spacing of about
2.06 .ANG., corresponding to the (1,1,1) plane of cubic diamond.
The diamond grain-size distribution depends largely on the dwell
time and intensity of the heating laser used to overcome kinetic
barriers to the thermodynamically favorable amorphous-to-diamond
phase transition.
[0054] Electron energy loss (EELS) spectra, as shown in FIG. 3,
agrees well with this observed microstructure, showing a small
graphitic .pi.* antibonding absorption peak at 285.5 eV as well as
the characteristic second gap of diamond at 302.5 eV.
[0055] Integration of the area under the .pi.* absorption peak
indicates greater than 90% phase purity of the crystalline diamond
aerogel material. Electron diffraction of the material following
x-ray absorption shows that the ultrananocrystalline diamond phase
is still present after a 100 meV resolution scanning transmission
x-ray absorption microscopy measurement.
[0056] One dramatic and unanticipated new feature in the recovered
diamond aerogel is the presence of extremely bright and photostable
luminescence, as observed in time-correlated single photon counting
profiles shown in FIG. 5. In one approach, small fragments of
recovered material may be supported on either silicon nanowires,
lacy-carbon TEM grids, etc., for subsequent optical analysis.
[0057] FIG. 8 shows a bright-field TEM image from a segment of
recovered diamond aerogel material that includes several different
diamond grain sizes, from about 1 nm to about 100 nm, resulting
from different dwell times during laser heating, in image B. The
material may be excited with about a 488 nm continuous wave Ar+-ion
laser, and the emission may be dispersed with a spectrometer for
further analysis. Two sharp spectral features are observed, one at
about 639 nm and another at about 739 nm, as shown in FIG. 4B,
corresponding to the negatively charged nitrogen vacancy (NV-) and
silicon divacancy centers, respectively, as shown in FIG. 4A. The
NV- center has been shown to exhibit a fascinating array of
properties, including bright, stable single photon emission with
long (ms) coherence lifetimes at room temperature, making it a
prime candidate for optically addressable quantum bits.
[0058] Time-correlated single photon counting may be used to probe
the luminescence from this recovered material. Significant
differences in luminescence intensity are observed across the
material, correlating with grain size, as shown in FIG. 4A.
Analysis of the emission lifetime from both large diamond grains
and diffuse material shows a characteristic long component of
approximately 10 ns corresponding with reports for the NV-
center.
[0059] In addition, the chemically and physically robust
characteristics of diamond enable utilization of materials
comprised of crystalline diamond aerogel in a broad range of
operational conditions, including extreme temperature and chemical
reactivity such as acidity/basicity.
[0060] When the crystalline aerogel comprises carbon, it may have
characteristics of diamond or graphite, depending on an extent of
crystallinity. When the crystalline aerogel comprises silica, it
may have characteristics of glass or quartz, depending on an extent
of crystallinity. Other aerogel materials may have characteristics
of other crystalline structures, as would be apparent to one of
skill in the art upon reading the present descriptions.
[0061] In one approach, defects within diamond crystals may produce
differing emission wavelengths as a function of isotopic identity
of the atomic point defect. Taking advantage of this isotopic
sensitivity, diamond aerogel may be employed as a detector for
isotopic distribution of environmental or experimental samples
including, for example, atmospheric and cosmic debris, debris from
detonation events, etc.
[0062] Now referring to FIG. 9, a method 900 is shown according to
one embodiment. The method 900 may be implemented in any desired
environment, including those shown in FIGS. 1A-1B, according to
various embodiments.
[0063] In operation 902, an amorphous aerogel is positioned in a
pressure cell. The pressure cell and the amorphous aerogel may be
of any type, such as those described previously according to
various embodiments.
[0064] In operation 904, an inert pressure medium is injected
within the pressure cell.
[0065] In operation 906, the pressure cell is pressurized to a
pressure that thermodynamically favors a crystalline phase of the
aerogel over an amorphous phase of the aerogel to transition the
amorphous aerogel into a crystalline aerogel.
[0066] In optional operation 908, the amorphous aerogel is heated
to accelerate transition to the crystalline phase and overcome a
corresponding phase change barrier. According to one embodiment, a
laser may be selectively applied according to a user-defined
pattern to heat one or more selected regions of the amorphous
aerogel. This allows for the aerogel to be precisely formed
according to a predefined structure, shape, pattern, etc., and
sizes, thicknesses, and extent of crystallinity may be
controlled.
[0067] According to one embodiment, the amorphous aerogel may be
heated to a temperature of greater than about 500.degree. C.
[0068] In optional operation 910, the pressure and temperature in
the pressure cell are returned to ambient conditions, e.g., the
conditions in the pressure cell prior to heating and pressurizing,
for example, about 25.degree. C. and about 1 atm.
[0069] In one approach, the amorphous aerogel may include one of:
silica, alumina, titania, and/or combinations thereof, among
others.
[0070] In another approach, the amorphous aerogel may be an aerogel
of carbonized resorcinol-formaldehyde that has a specific density
of about 30 to 50 mg/cm.sup.3.
[0071] In yet another approach, the amorphous aerogel may include
carbon and may have a specific density of about 40 mg/cm.sup.3.
[0072] In a further embodiment, the inert pressure medium may
conformally and homogeneously occupy a void volume of the pressure
cell and a void volume of pores of the amorphous aerogel without
disturbing pore morphology of the amorphous aerogel. This allows
the aerogel to maintain its shape through the transition from
amorphous to crystalline.
[0073] According to another embodiment, the pressure cell may be
pressurized to a pressure of about 21.times.10.sup.9 Pa, when the
amorphous aerogel includes an amorphous-phase carbonized
resorcinol-formaldehyde aerogel. Other pressures may be used that
correspond to other aerogel materials as would be apparent to one
of skill in the art upon reading the present descriptions.
[0074] In another approach, the inert pressure medium may include
at least one of: neon gas, argon gas, helium gas, krypton gas,
xenon gas, carbon dioxide gas, and mixtures thereof, among
others.
[0075] The methods and embodiments described herein may be extended
to produce unknown crystalline aerogel materials with previously
unachievable phases with relevance towards discovery-class
fundamental science targeted at new materials with enhanced energy
conversion or storage capacities. The fabrication of diamond
aerogel thin films could find potential use in high-current field
emission applications, among others.
[0076] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. Thus, the breadth and scope of a
preferred embodiment should not be limited by any of the
above-described exemplary embodiments, but should be defined only
in accordance with the following claims and their equivalents.
* * * * *