U.S. patent number RE48,454 [Application Number 16/052,353] was granted by the patent office on 2021-03-02 for continuous flow reactor for the synthesis of nanoparticles.
The grantee listed for this patent is Shoei Electronic Materials, Inc.. Invention is credited to Thomas E. Novet, David M. Schut, George M. Williams.
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United States Patent |
RE48,454 |
Schut , et al. |
March 2, 2021 |
Continuous flow reactor for the synthesis of nanoparticles
Abstract
A continuous flow reactor for the efficient synthesis of
nanoparticles with a high degree of crystallinity, uniform particle
size, and homogenous stoichiometry throughout the crystal is
described. Disclosed embodiments include a flow reactor with an
energy source for rapid nucleation of the .[.procurors following.].
.Iadd.precursors to form nucleates followed .Iaddend.by a separate
heating source for growing the nucleates. Segmented flow may be
provided to facilitate mixing and uniform energy absorption of the
precursors, and post production quality testing in communication
with a control system allow automatic real-time adjustment of the
production parameters. The nucleation energy source can be
monomodal, multimodal, or multivariable frequency microwave energy
and tuned to allow different precursors to nucleate at
substantially the same time thereby resulting in a substantially
homogenous nanoparticle. A shell application system may also be
provided to allow one or more shell layers to be formed onto each
nanoparticle.
Inventors: |
Schut; David M. (Philomath,
OR), Novet; Thomas E. (Corvallis, OR), Williams; George
M. (Beaverton, OR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Shoei Electronic Materials, Inc. |
Corvallis |
OR |
US |
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Family
ID: |
1000005238658 |
Appl.
No.: |
16/052,353 |
Filed: |
August 1, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61949969 |
Mar 7, 2014 |
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61783911 |
Mar 14, 2013 |
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61784107 |
Mar 14, 2013 |
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61784257 |
Mar 14, 2013 |
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61784306 |
Mar 14, 2013 |
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61784358 |
Mar 14, 2013 |
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61783753 |
Mar 14, 2013 |
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61784183 |
Mar 14, 2013 |
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Reissue of: |
14214587 |
Mar 14, 2014 |
9592555 |
Mar 14, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F
1/02 (20130101); B22F 9/24 (20130101); B01J
19/126 (20130101); C01G 21/21 (20130101); B22F
1/00 (20130101); C01B 19/00 (20130101); B01J
4/02 (20130101); B01J 19/243 (20130101); C09K
11/881 (20130101); C01B 13/36 (20130101); B22F
9/16 (20130101); C01B 19/002 (20130101); B22F
9/24 (20130101); B22F 1/02 (20130101); B22F
1/0018 (20130101); B01J 19/0093 (20130101); B22F
9/16 (20130101); C01G 21/21 (20130101); C01B
19/002 (20130101); B22F 1/0062 (20130101); B22F
2999/00 (20130101); B01J 2219/00869 (20130101); B01J
2219/0097 (20130101); B01J 2219/00795 (20130101); B01J
2219/00934 (20130101); B01J 2219/00903 (20130101); B01J
2219/0086 (20130101); B01J 2219/00889 (20130101); B01J
2219/00873 (20130101); B01J 2219/00882 (20130101); B01J
2219/00957 (20130101); C01P 2004/03 (20130101); B01J
2219/00941 (20130101); B22F 2999/00 (20130101); B22F
9/24 (20130101); B22F 2202/11 (20130101) |
Current International
Class: |
B01J
19/12 (20060101); B22F 9/16 (20060101); B01J
19/00 (20060101); B22F 1/00 (20060101); B22F
9/24 (20060101); C01B 19/00 (20060101); C01G
21/21 (20060101); C09K 11/56 (20060101); B22F
1/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101589181 |
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Nov 2009 |
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CN |
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2006188666 |
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Jul 2006 |
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JP |
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200839042 |
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Oct 2008 |
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TW |
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201105585 |
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Feb 2011 |
|
TW |
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|
Primary Examiner: Xu; Ling X
Attorney, Agent or Firm: Alleman Hall Creasman & Tuttle
LLP
Parent Case Text
PRIORITY CLAIM
.[.This application.]. .Iadd.More than one reissue application has
been filed for the reissue of U.S. Pat. No. 9,592,555, including
the present application and U.S. Reissue application Ser. No.
16/159,332, filed Oct. 12, 2018, which is a continuation reissue of
U.S. Pat. No. 9,592,555. This application is an application for
reissue of U.S. Pat. No. 9,592,555, which .Iaddend.claims priority
to U.S. provisional patent application Ser. .[.No..]. .Iadd.Nos.
.Iaddend.61/783,753; 61/783,911; 61/784,107; 61/784,257;
61/784,306; 61/784,358; and 61/784,183 filed on Mar. 14, 2013, and
further this application claims priority to U.S. provisional
application Ser. No. 61/949,969 filed Mar. 7, 2014; all of the
disclosures of which are hereby incorporated by reference.
Claims
We claim:
1. A method for producing uniformly sized .Iadd.quantum dot
.Iaddend.nanoparticles comprising: blending at least a first
precursor and at least a second precursor together to form a liquid
precursor mixture; conducting the liquid precursor mixture along a
continuous flow path .Iadd.comprising one or more tubes through
which the liquid precursor mixture flows, wherein at least one of
the one or more tubes comprises an inner diameter of 1/4 inch to
1/2 inch.Iaddend.; .Iadd.introducing gas into the continuous flow
path fluidically so as to form partitions of the gas in the
continuous flow path; after introducing the gas into the continuous
flow path, .Iaddend.activating the liquid precursor mixture with
one or more of multimodal and multivariable .Iadd.frequency
.Iaddend.microwave energy from a microwave energy source along the
continuous flow path for a first duration at a first energy level
thereby allowing uniform nucleation of .Iadd.quantum dot nucleates
in .Iaddend.the mixture of precursors; heating the liquid precursor
mixture with a heating source along the continuous flow path for a
second duration at a controlled temperature, thereby promoting
uniform thermodynamic growth around .[.previously formed.].
.Iadd.the quantum dot .Iaddend.nucleates .Iadd.previously formed
.Iaddend.to form .[.desired core sized nanoparticles.]. .Iadd.core
quantum dot nanoparticles, wherein the core quantum dot
nanoparticles fluoresce with a full width half max (FWHM) of less
than 50 nm at wavelengths from 400 nm-700 nm.Iaddend.; and
quenching the growth of the .Iadd.quantum dot
.Iaddend.nanoparticles after heating.
2. The method of claim 1, wherein the microwave energy is
multimodal.
3. The method of claim 1, wherein the microwave energy is
multivariable in frequency.
4. The method of claim 1, .[.further comprising introducing gas
into the continuous flow path fluidically upstream of the microwave
energy source, so as to form partitions of.]. .Iadd.wherein
.Iaddend.the gas .[.in the.]. .Iadd.is introduced into
.Iaddend.multiple lines.[., which separate adjacent segments of the
liquid precursor mixture.]. .Iadd.of the continuous flow
path.Iaddend..
5. The method of claim 4, wherein the gas includes one or more of
nitrogen and argon.
6. The method of claim 1, wherein the first duration is less than
or equal to 60 seconds.
7. The method of claim 1, wherein the first duration is less than
or equal to 10 seconds.
8. The method of claim 1, wherein the first duration is less than
or equal to 3 seconds.
9. The method of claim 1, wherein the first duration is less than
or equal to 2 seconds.
10. The method of claim 1, further comprising monitoring a quality
of .Iadd.the quantum dot .Iaddend.nanoparticles via one or more
sensors; and adjusting the first duration, first energy level,
second duration, and temperature, via one or more actuators, in
response to the detected quality of the .Iadd.quantum dot
.Iaddend.nanoparticles.
11. The method of claim 1, wherein a mixture of two or more
precursors from Groups B or C herein, having different microwave
absorption cross sections, nucleate with a precursor from Group A
herein, at substantially equal rates upon flowing through the
microwave energy source, wherein Group A includes H.sub.2X where
X=O, S, Se, Te; R.sub.3PX where R=H, (CH.sub.2).sub.nCH.sub.3,
C.sub.6H.sub.5, C.sub.6H.sub.4R', n=3-18,
R'=(CH.sub.2).sub.mCH.sub.3, CH(CH.sub.3).sub.2, C(CH.sub.3).sub.3,
m=0-17, X=Se, Te; R.sub.3NX where R=H, (CH.sub.2).sub.nCH.sub.3,
Si(CH.sub.3).sub.3, n=0-4, X=S, Se, Te; ((CH.sub.3).sub.3Si).sub.2X
where X=S, Se, Te; HX(CH.sub.2).sub.nCH.sub.3 where X=O, S, Se, Te,
n=1-18; HO(CH.sub.2)(CH(OH)).sub.n(CH.sub.3) where n=1-50;
HO(CH.sub.2)(CH(OH)).sub.n(CH.sub.2OH) where n=1-50;
H.sub.2NNH.sub.2; NaBH.sub.4, NaCNBH.sub.3; and mixtures thereof
including anionic precursors and/or reducing agents, wherein Group
B includes ML.sub.y where M=Tl, Ag, Cu when y=1, M=Zn, Cd, Hg, Cu,
Pb, Ni when y=2, M=Al, Ga, B, In, Bi, Fe when y=3, L=O.sub.2
C(CH.sub.2).sub.nCH.sub.3,
.[.O.sub.2C(CH.sub.2).sub.mCHCH(CH.sub.2)OCH.sub.3).].
.Iadd.O.sub.2C(CH.sub.2).sub.mCH.dbd.CH(CH.sub.2).sub.oCH.sub.3.Iaddend.,
S(CH.sub.2).sub.nCH.sub.3, PR.sub.3, OPR.sub.3, n=2-24, m and
o=1-15, R=(CH.sub.2).sub.pCH.sub.3, C.sub.6H.sub.5,
C.sub.6H.sub.4R', p=0-18, R'=(CH.sub.2).sub.pCH.sub.3,
CH(CH.sub.3).sub.2, C(CH.sub.3).sub.3; and mixtures thereof, and
wherein Group C includes: ML.sub.y where M=Na, K, Rb, Cs, Ag, Cu
when y=1, M=Mg, Ca, Sr, Ba, Pd, Pt, Cu, Ni when y=2, M=La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Au when y=3, M=Ti, Zr,
Hf, Pt, Pd when y=4, L=O.sub.2CCH.sub.3, Cl, F, NO.sub.3; and
mixtures thereof.
12. The method of claim 1, wherein nucleation of the first and
second precursors over the first duration results in a
substantially homogeneous .Iadd.quantum dot
.Iaddend.nanoparticle.
13. The method of claim 1, further comprising: using a
continuous-flow process to expose the .Iadd.quantum dot
.Iaddend.nanoparticles to a mixture of at least a third precursor
from Group A herein and a fourth precursor from Group B or Group C
herein; and heating the exposed .Iadd.quantum dot
.Iaddend.nanoparticles in a heat source to form a first shell
around the .Iadd.quantum dot .Iaddend.nanoparticle, wherein Group A
includes: H.sub.2X where X=O, S, Se, Te; R.sub.3PX where R=H,
(CH.sub.2).sub.nCH.sub.3, C.sub.6H.sub.5, C.sub.6H.sub.4R', n=3-18,
R'=(CH.sub.2).sub.mCH.sub.3, CH(CH.sub.3).sub.2, C(CH.sub.3).sub.3,
m=0-17, X=Se, Te; R.sub.3NX where R=H, (CH.sub.2).sub.nCH.sub.3,
Si(CH.sub.3).sub.3, n=0-4, X=S, Se, Te; ((CH.sub.3).sub.3Si).sub.2X
where X=S, Se, Te; HX(CH.sub.2).sub.nCH.sub.3 where X=O, S, Se, Te,
n=1-18; HO(CH.sub.2)(CH(OH)).sub.n(CH.sub.3) where n=1-50;
HO(CH.sub.2)(CH(OH)).sub.n(CH.sub.2OH) where n=1-50;
H.sub.2NNH.sub.2; NaBH.sub.4, NaCNBH.sub.3; and mixtures thereof
including anionic precursors and/or reducing agents, wherein Group
B includes: ML.sub.y where M=Tl, Ag, Cu when y=1, M=Zn, Cd, Hg, Cu,
Pb, Ni when y=2, M=Al, Ga, B, In, Bi, Fe when y=3,
L=O.sub.2C(CH).sub.nCH.sub.3,
.[.O.sub.2C(CH.sub.2).sub.mCHCH(CH.sub.2)OCH.sub.3).].
.Iadd.O.sub.2C(CH.sub.2).sub.mCH.dbd.CH(CH.sub.2).sub.oCH.sub.3.Iaddend.,
S(CH.sub.2).sub.nCH.sub.3, PR.sub.3, OPR.sub.3, n=2-24, m and
o=1-15, R=(CH.sub.2).sub.nCH.sub.3, C.sub.6H.sub.5,
C.sub.6H.sub.4R', p=0-18, R'=(CH.sub.2).sub.pCH.sub.3,
CH(CH.sub.3).sub.2, C(CH.sub.3).sub.3; and mixtures thereof, and
wherein Group C includes: ML.sub.y where M=Na, K, Rb, Cs, Ag, Cu
when y=1, M=Mg, Ca, Sr, Ba, Pd, Pt, Cu, Ni when y=2, M=La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Au when y=3, M=Ti, Zr,
Hf, Pt, Pd when y=4, L=O.sub.2CCH.sub.3, Cl, F, NO.sub.3; and
mixtures thereof.
14. The method of claim 13, further comprising: using a
continuous-flow process to expose the .Iadd.quantum dot
.Iaddend.nanoparticles to a mixture of a fifth precursor and a
sixth precursor; and heating the exposed .Iadd.quantum dot
.Iaddend.nanoparticle to form a second shell around the first
shell.
15. The method of claim 13, further comprising: using a
continuous-flow process to expose the .Iadd.quantum dot
.Iaddend.nanoparticles to a mixture of a fifth precursor to from
Group A herein and a sixth precursor from Group B or Group C
herein; and heating the exposed .Iadd.quantum dot
.Iaddend.nanoparticle to form a second shell around the first
shell, wherein Group A includes: H.sub.2X where X=O, S, Se, Te;
R.sub.3PX where R=H, (CH.sub.2).sub.nCH.sub.3, C.sub.6H.sub.5,
C.sub.6H.sub.4R', n=3-18, R'=(CH.sub.2).sub.mCH.sub.3,
CH(CH.sub.3).sub.2, C(CH.sub.3).sub.3, m=0-17, X=Se, Te; R.sub.3NX
where R=H, (CH.sub.2).sub.nCH.sub.3, Si(CH.sub.3).sub.3, n=0-4,
X=S, Se, Te; ((CH.sub.3).sub.3Si).sub.2X where X=S, Se, Te;
HX(CH.sub.2).sub.nCH.sub.3 where X=O, S, Se, Te, n=1-18;
HO(CH.sub.2)(CH(OH)).sub.n(CH.sub.3) where n=1-50;
HO(CH.sub.2)(CH(OH)).sub.n(CH.sub.2OH) where n=1-50;
H.sub.2NNH.sub.2; NaBH.sub.4, NaCNBH.sub.3; and mixtures thereof
including anionic precursors and/or reducing agents, wherein Group
B includes: ML.sub.y where M=Tl, Ag, Cu when y=1, M=Zn, Cd, Hg, Cu,
Pb, Ni when y=2, M=Al, Ga, B, In, Bi, Fe when y=3,
L=O.sub.2C(CH.sub.2).sub.nCH.sub.3,
.[.O.sub.2C(CH.sub.2).sub.mCHCH(CH.sub.2)OCH.sub.3).].
.Iadd.O.sub.2C(CH.sub.2).sub.mCH.dbd.CH(CH.sub.2).sub.oCH.sub.3.Iaddend.,
S(CH.sub.2)CH.sub.3, PR.sub.3, OPR.sub.3, n=2-24, m and o=1-15,
R=(CH.sub.2).sub.pCH.sub.3, C.sub.6H.sub.5, C.sub.6H.sub.4R',
p=0-18, R'=(CH.sub.2).sub.pCH.sub.3, CH(CH.sub.3).sub.2,
C(CH.sub.3).sub.3; and mixtures thereof, and wherein Group C
includes: ML.sub.y where M=Na, K, Rb, Cs, Ag, Cu when y=1, M=Mg,
Ca, Sr, Ba, Pd, Pt, Cu, Ni when y=2, M=La, Ce, Pr, Nd, Pm, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Au when y=3, M=Ti, Zr, Hf, Pt, Pd when
y=4, L=O.sub.2CCH.sub.3, Cl, F, NO.sub.3; and mixtures thereof.
16. The method of claim 15, further comprising: using a
continuous-flow process to expose the .Iadd.quantum dot
.Iaddend.nanoparticles to a mixture of a seventh precursor from
Group A herein and .[.a.]. .Iadd.an .Iaddend.eighth precursor from
Group B or Group C herein; and heating the exposed .Iadd.quantum
dot .Iaddend.nanoparticle to form a third shell around the second
shell.
17. The method of claim 4, further including the step of separating
the gas from the .Iadd.quantum dot .Iaddend.nanoparticles following
the step of quenching the growth of the .Iadd.quantum dot
.Iaddend.nanoparticle.
18. The method of claim 1, wherein the continuous flow path
comprises multiple lines.[., and wherein one or more of the
multiple lines comprises an inner diameter between 1/16 of an inch
and 1 inch.]..
19. The method of claim 18, wherein one or more of the multiple
lines has an inner diameter between 1/4 and 1/2 inch.
20. The .[.nanoparticle.]. .Iadd.method .Iaddend.of claim 1,
wherein the microwave energy operates at frequencies that cause the
first and second precursors to nucleate at substantially the same
time thereby producing substantially homogenous .Iadd.quantum dot
.Iaddend.nanoparticles.
21. A method for producing uniformly sized .Iadd.quantum dot
.Iaddend.nanoparticles comprising: blending together a first and
second precursor to form a liquid precursor mixture; conducting the
liquid precursor mixture along multiple lines of a continuous flow
path .Iadd.comprising one or more tubes through which the liquid
precursor mixture flows, wherein at least one tube of the one or
more tubes comprises an inner diameter of 1/4 inch to 1/2
inch.Iaddend.; introducing gas into the continuous flow path
fluidically upstream of the microwave energy source, so as to form
partitions of the gas in the multiple lines, which separate
adjacent segments of the liquid precursor mixture; activating the
liquid precursor mixture with multimodal and/or multivariable
.Iadd.frequency .Iaddend.microwave energy from a microwave energy
source in the continuous flow path, the microwave energy source
configured to uniformly irradiate the multiple lines and thereby
uniformly nucleate the liquid precursor mixture, for a first
duration at a first energy level.Iadd., to form quantum dot
nucleates.Iaddend.; heating the activated liquid precursor mixture
with a heating source in the continuous flow path for a second
duration at a controlled temperature, thereby promoting uniform
thermodynamic growth around .[.previously formed.]. .Iadd.the
quantum dot .Iaddend.nucleates .Iadd.previously formed .Iaddend.to
form .[.desired core sized nanoparticles.]. .Iadd.core quantum dot
nanoparticles, wherein the core quantum dot nanoparticles fluoresce
with a full width half max (FWHM) of less than 50 nm at wavelengths
from 400 nm-700 nm.Iaddend.; and quenching the growth of the
.Iadd.quantum dot .Iaddend.nanoparticles after heating.
22. The method of claim 21, wherein first duration is less than or
equal to 10 seconds.
23. The method of claim 21, wherein the first duration is less than
or equal to 3 seconds.
24. The method of claim 21, wherein the first duration is less than
or equal to 2 seconds.
25. The method of claim 21, wherein the microwave energy is
multimodal.
26. The method of claim 21, the microwave energy is of
multivariable frequency.
27. The method of claim 21, wherein the gas includes one or more of
nitrogen and argon.
28. The method of claim 21, further comprising monitoring a quality
of .Iadd.the quantum dot .Iaddend.nanoparticles via one or more
sensors; and adjusting the first duration, first energy level,
second duration, and temperature, via one or more actuators, in
response to the detected quality of the .Iadd.quantum dot
.Iaddend.nanoparticles.
29. The method of claim 21, wherein a mixture of two or more
precursors from Groups B or C herein, having different microwave
absorption cross sections, nucleate with a precursor from Group A
herein, at substantially equal rates upon flowing through the first
energy source, wherein Group A includes: H.sub.2X where X=O, S, Se,
Te; R.sub.3PX where R=H, (CH.sub.2).sub.nCH.sub.3, C.sub.6H.sub.5,
C.sub.6H.sub.4R', n=3-18, R'=(CH.sub.2).sub.mCH.sub.3,
CH(CH.sub.3).sub.2, C(CH.sub.3).sub.3, m=0-17, X=Se, Te; R.sub.3NX
where R=H, (CH.sub.2).sub.nCH.sub.3, Si(CH.sub.3).sub.3, n=0-4,
X=S, Se, Te; ((CH.sub.3).sub.3Si).sub.2X where X=S, Se, Te;
HX(CH.sub.2).sub.nCH.sub.3 where X=O, S, Se, Te, n=1-18;
HO(CH.sub.2)(CH(OH)).sub.n(CH.sub.3) where n=1-50;
HO(CH.sub.2)(CH(OH)).sub.n(CH.sub.2OH) where n=1-50;
H.sub.2NNH.sub.2; NaBH.sub.4, NaCNBH.sub.3; and mixtures thereof
including anionic precursors and/or reducing agents, wherein Group
B includes: ML.sub.y where M=Tl, Ag, Cu when y=1, M=Zn, Cd, Hg, Cu,
Pb, Ni when y=2, M=Al, Ga, B, In, Bi, Fe when y=3,
L=O.sub.2C(CH.sub.2).sub.nCH.sub.3,
.[.O.sub.2C(CH.sub.2).sub.mCHCH(CH.sub.2)OCH.sub.3)OCH.sub.3).].
.Iadd.O.sub.2C(CH.sub.2).sub.mCH.dbd.CH(CH.sub.2).sub.oCH.sub.3.Iaddend.,
S(CH.sub.2).sub.nCH.sub.3, PR.sub.3, OPR.sub.3, n=2-24, m and
o=1-15, R=(CH.sub.2).sub.pCH.sub.3, C.sub.6H.sub.5,
C.sub.6H.sub.4R', p=0-18, R'=(CH.sub.2).sub.pCH.sub.3,
CH(CH.sub.3).sub.2, C(CH.sub.3).sub.3; and mixtures thereof, and
wherein Group C includes: ML.sub.y where M=Na, K, Rb, Cs, Ag, Cu
when y=1, M=Mg, Ca, Sr, Ba, Pd, Pt, Cu, Ni when y=2, M=La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Au when y=3, M=Ti, Zr,
Hf, Pt, Pd when y=4, L=O.sub.2CCH.sub.3, Cl, F, NO.sub.3; and
mixtures thereof.
30. The method of claim 29, wherein the nucleation of the first and
second precursors over the first duration results in substantially
homogeneous .Iadd.quantum dot .Iaddend.nanoparticles.
.[.31. The method of claim 1 wherein the first and second
precursors are blended prior to conduction along the continuous
flow path..].
.[.32. The method of claim 1 wherein the first and second
precursors are blended during conduction along the continuous flow
path..].
33. The method of claim 4, wherein .[.the continuous flow path
comprises at least one line having an inner diameter between 1/16
of an inch and 1 inch.]. .Iadd.two or more lines of the multiple
lines have an inner diameter of 1/4 inch to 1/2 inch.Iaddend..
.[.34. The method of claim 33, wherein the at least one line has an
inner diameter between 1/4 and 1/2 inch..].
.Iadd.35. The method of claim 1, wherein the continuous flow path
comprises multiple flow cell tubes that pass through a same
microwave reactor cavity..Iaddend.
.Iadd.36. The method of claim 1, wherein the multivariable
frequency microwave energy is tuned to a first frequency for the
first precursor and is tuned to a second frequency for the second
precursor..Iaddend.
Description
FIELD
The present disclosure relates to a system and method for efficient
and continuous production of uniformly-sized nanoparticles which
include metal nanoparticles and nanocrystalline quantum dots.
BACKGROUND
This section provides background information related to the present
disclosure which is not necessarily prior art.
Nanoparticles, which can be classified as nanocrystalline
materials, nanocrystallites, nanocrystals, quantum dots, and
quantum dot materials are produced and used for a wide variety of
applications. For example, semiconductor nanocrystallites emit a
visible light over a narrow range of wavelengths and are used in
the fabrication of light emitting diodes and the like.
Basic steps, materials, and processes for producing nanocrystalline
quantum dot materials are described in U.S. Pat. Nos. 6,179,912;
6,322,901; .[.6,833,019 8,101,021,.]. .Iadd.6,833,019; 8,101,021;
.Iaddend.and .[.8,420,155.]. .Iadd.8,420,155.Iaddend.; U.S. patent
application publication No. US2012-0315391, and Japanese patent
application publication No. 2006-188666, the disclosures of which
are hereby incorporated by reference. These and other known
production and synthesis systems and methods for producing
nanoparticles give rise to several problems, including, but not
limited to, inefficient production, poor particle quality,
inconsistent particles sizes, and/or excessive waste of the raw
materials used to form the particles.
SUMMARY
This invention relates to the system and chemistries needed for the
production of nanoparticles. This invention also relates to systems
and chemistries suitable for production of nanocrystalline quantum
dots of a uniform and repeatable size and size distribution on a
large scale that is both economical and efficient. Furthermore,
this invention relates to the chemistries and processes needed to
place between one or more shells over the core nanocrystalline
quantum dots--to enhance the electronic and/or optical properties
of the nanocrystalline quantum dots and also to improve durability
of these materials.
DRAWINGS
The drawings described herein are for illustrative purposes only of
selected embodiments and not all possible implementations, and are
not intended to limit the scope of the present disclosure.
FIG. 1 is an isometric schematic view of a four zone continuous
flow cell reactor for the production of nanoparticles in accordance
with a preferred embodiment of the present invention.
FIG. 2 is a schematic view of a four zone continuous flow cell
reactor of FIG. 1 showing an optional shell fabricator for
fabricating shell layers on the nanoparticles.
FIG. 3 is a schematic view of zone 1 of the continuous flow reactor
of FIG. 1 showing introduction of precursors and a possible
segmented flow.
FIG. 4A is a schematic view of zone 3 of the continuous flow
reactor of FIG. 1 showing a nanoparticle growth phase using a
heating source allowing precise temperature control over multiple
lines entering therethrough.
FIG. 4B is a top view of a rack received within the heating source
of FIG. 4A allowing for flow lines, with possible variable lengths
that can be tailored to this system, for the growth phase of the
reaction to take place.
FIG. 4C is an isometric view of multiple racks of FIG. 4B showing a
possible stacking arrangement within the heating source of FIG.
4A.
FIG. 5A is a schematic view of an alternative possible heating
system for introducing multiple lines into the growth phase heat
source of zone 3
FIG. 5B is an enlarged view of one line of the multiple lines into
the growth phase heat source of zone 3 in FIG. 5A.
FIG. 6 shows an enlarged cross-sectional view of the continuous
flow path in FIG. 1 showing a possible segmented flow of precursors
with a reactively inert gas such as nitrogen, argon, and the like
segmented therein.
FIG. 7 shows a schematic view of a separator for separating the
nanoparticles from the reactively inert gas following the growth
phase (Zone 3) and shell formation phase of the fabrication
process.
FIG. 8 shows a schematic view of a system layout with valves placed
at key locations so as to allow redundancy in the system thereby
allowing fabrication to continue if any one component in the system
fails.
FIG. 9 shows an exemplar reaction chart relating the nucleation
time and temperature or energy levels of two different
precursors.
FIG. 10 shows a schematic view of a possible baffle system for
redirecting microwave energy to a secondary growth heater thereby
improving energy efficiency of the system.
FIG. 11A (PRIOR ART) shows a sketch of a crystalline structure of a
non-homogenous nanoparticle formed by different precursors
nucleating at different times. CuInSe.sub.2 material produced using
a thermal batch process resulting in Cu rich cores around which In
is later deposited, producing an inhomogeneous nanoparticle of
CuInSe.sub.2.
FIG. 11B shows a sketch possible homogenous crystalline structure
of a homogenous nanoparticle formed by different precursors
nucleating at the same time. CuInSe.sub.2 nanoparticles produced
using a microwave flow cell reactor in which the Cu and In are
nucleated at the same rate, producing homogeneous nanoparticles
having well-defined structure.
FIG. 12A (PRIOR ART) is an actual image obtained using Transmission
Electron Microscopy (TEM) of the crystalline structure of FIG.
11A.
FIG. 12B is an actual image obtained using TEM of the crystalline
structure of FIG. 11B.
Corresponding reference numerals indicate corresponding parts
throughout the several views of the drawings.
DETAILED DESCRIPTION
Example embodiments will now be described more fully with reference
to the accompanying drawings. According to this disclosed
embodiment, the process is described in detail for synthesizing
nanoparticles such as quantum dots, among others.
A continuous flow cell reactor production system for the production
of quantum dots and its related components are shown in FIGS. 1-10,
11B and 12B.
Process Overview
A conceptual diagram of the nanoparticle production system 20 is
shown schematically in FIGS. 1 & 2 and provides a specific
example of the system. The system 20 includes a continuous flow
path 22 that passes through at least four zones (1-4,
respectively). In zone 1, two or more precursors 32, 34 are metered
and mixed together and passed through a tube 40 where a reactively
inert gas 42 such as nitrogen, argon, and the like may be inserted
therein to provide segmented flow of the mixture as it passes to
the next zone. For example, in one disclosed embodiment the two
precursors 32, 34 can be a reducing agent and one or more cationic
precursor(s). Alternatively, the two precursors 32, 34 can be one
or more anionic precursor(s) and one or more cationic
precursor(s).
In zone 2, the precursor mixture is rapidly energized by an energy
source 50, preferably by use of a microwave oven selected from
monomodal, multimodal or multivariable frequency where the
precursors 32, 34 are rapidly and uniformly nucleated. The flow of
the nucleated precursors then passes through to zone 3 where a heat
source 60 allows the nucleated precursors to enter a growth phase.
The process is quenched in zone 4, and the resulting nanoparticles
70 are separated from the reactively inert gas 42.
A nanoparticle quality testing system 72 may be provided following
the quenching that tests the quality of the nanoparticles 70 being
continuously produced by the system 20. The quality testing system
72 can be in communication with a control system 80 that is also
operably connected to the precursor deliver system 82, reactively
inert gas delivery system 84, energy source 50 in zone 2, heat
source 60 in zone 3 and the quenching system 86 to modulate the
volume of precursors 32, 34, gas injection, time, temperature,
energy level and flow rate through the energy source 50 and heat
source 60 as needed to automatically optimize nanoparticle quality
in real-time based on the detected quality of the particles being
produced.
As shown in FIG. 2, a shell fabrication system 100 may be provided
after zone 4 to allow one or more shell layers to be formed over
each nanoparticle 70.
A plurality of reductant elements of the production line may be
provided with the individual precursors and nanoparticle flow paths
interconnectable with valves or the like to allow redirection of
the flow path through alternative components should one component
become inoperable as shown in FIG. 8.
Each of these zones and their preferred related components are
discussed in greater detail below.
Zone 1--Precursor Metering and Mixing
In zone 1, at least one precursor 32 and preferably at least two
precursors 32, 34 are metered from their respective reservoirs and
metered in the proper proportion into the continuous flow path 22
that extends through zones 2-4. The flow path 22 is preferably a
tube 40 having an inner diameter between 1/16 of an inch to 1 inch,
and more preferably between 1/4 of and a 1/2 inch.
The desired concentration of precursors or a concentration greater
than that initially desired, is introduced into the flow path 22
using a metering pump 110 (syringe pump, peristaltic pump,
diaphragm pump as examples) to dispense into the flow path the
desired quantity of material (precursor). In the case where the
concentration is higher than desired for the reaction, a dilution
can take place by metering the desired solvent to dissolve the
precursor, while in the line, to the desired concentration.
A mixing of the precursors/components for the reaction can take
place using a static mixer, such as a T-mixer, to ensure complete
mixing of the precursors/components of the reaction. Alternatively,
a different type of mixer, such as an active stirrer, can be used
such that a homogenous solution is formed after exiting the mixing
area of the precursors. The precursors are preferably introduced
into a tube 40 that defines a flow path 22 through the system 20
and then mixed with the mixer prior to entering zone 2.
Alternatively, the precursors can first be mixed together and then
passed to a tube that defines the flow path through zone 2. The sum
of the precursor flows establishes the process flow rate. One or
more additional precursors 35 (FIG. 2) may also be provided.
Before advancing to zone 2 in the flow path 22, a plug of
reactively inert gas 42, such as nitrogen, argon or the like, that
is immiscible with the reactant fluid is introduced to create a
segmented flow 120 through the flow path 22 as best shown in FIGS.
1, 2 and 6. The introduction of the segmented flow has two
purposes: (1) turbulent mixing (the flow against the wall is slower
due to friction than the flow in the middle of the tube, creating
turbulence) is introduced within the precursor portion 122 of the
flow, and (2) reduction of material deposition on the sidewalls.
The latter event occurs through a combination of flow, turbulence
and surface tension to eliminate any deposition of material on the
sidewalls, which allows for sites of nucleation to occur (an
undesirable effect). If desired, mixing of the precursors can be
further enhanced by surface roughness on the interior surface of
the tube containing the mixture of precursors.
As shown in FIG. 3, a plurality of flow path 22 tubes 40 may be
used to increase the rate of production of nanoparticles. Multiple
lines are used to introduce two different precursors 32, 34
together, mix them, and then introduce the segmented flow 120 by
introducing nitrogen gas, argon gas or the like into the reaction
lines.
Zone 2--Nucleation
This zone through the flow path 22 is for the initiation of
nucleation. Rapidly increasing the energy level of the precursors
32, 34 with an energy source 50 quickly brings the solution and/or
precursors in the flow path tube 40 to the energy level (including
temperature) at which precursors will nucleate and undergo kinetic
growth within one minute, preferably being equal or less than ten
seconds, more preferably within less than 3 seconds and even more
preferably within less than 2 seconds.
This energy level increase may be done using several different
methods, such as microwave/dielectric heating, sonication, thermal
heating by induction or convection, or even breaking of bonds
through irradiation with lasers. This is the rapid breakdown of
precursors into reactive components forming a nucleate that may be
larger than the initial precursors, but much smaller than a
nanoparticle or quantum dot of interest. The formation of nucleates
is terminated rapidly in order to maintain size control. The
duration of the reaction in zone 2 of the flow cell reactor is
rapid, being less than one minute, preferably being equal to or
less than ten seconds, and more preferably within less than 3
seconds and even more preferably within less than 2 seconds.
The need for rapid temperature equilibration of the flow cell
precursor material to a given temperature through application of
energy from the energy source is necessary in order to maintain
tight control of the resultant nanoparticle size. By having short
nucleation periods, which are typically conducted at temperatures
greater than the growth temperature, growth upon the resultant
nucleates can be conducted without the formation of new nucleates
during the growth (Zone 3) stage of the nanoparticle formation. If
the nucleation period is extended, nucleates are formed throughout
this period. Additionally, because growth may also occur at this
step (an undesirable feature at this point and is minimized through
the use of short nucleation times), nucleates that form immediately
in Zone 2 will be larger than those nucleates that form towards the
end of the Zone 2.
Preferably, the energy source 50 uniformly heats or excites all
precursors 32, 34 (or increases their energy levels) passing
through it. A microwave has proven to be particularly useful at
accomplishing uniform heating to nucleate the precursors. The
microwave can be implemented in three different fashions, depending
on implementation within the flow cell reactor. Monomodal waveforms
(where a high Q-factor is obtained through
deconstructive/constructive interference effects of a standing
wave) are good for producing high intensity (high energy density)
microwave peaks that rapidly heat the reaction solution within the
flow cell reactor. However, the limit to this technology is that
multiple lines cannot be effectively heated using this method. A
second method is the use of multi-modal microwaves where a single
wavelength of microwave is used (typically 915 MHz, 2.45 GHz, or
5.8 GHz), but no standing wave is created. Instead, a baffle system
is used to route the microwaves through multiple angles, allowing
uniform energy exposure throughout the flow cell reactor cavity.
This allows uniform heating of multiple flow cell tubes through the
reactor cavity. The drawback to this method is lower intensity
(lower energy density) microwave irradiation within the flow cell
reactor cavity. Finally, a multivariable frequency microwave may be
used where microwaves of different frequencies (typically between
5.8 GHz and 7.0 GHz) are rapidly cycled in small steps (0.01 to
0.1) to produce uniform heating through the microwave flow cell
cavity by creating multiple standing waves of a given
frequency.
The flow rate of the precursor thorough the microwave, the
concentration of the precursors, the diameter of the tubing
containing the precursor mixture, the length of tubing being
exposed to microwave energy and the power of the microwave being
used are selected to provide the optimal time and energy exposure
for nucleation of the mixture.
Moreover, the frequencies of the microwave can be oscillated
rapidly on the order of microseconds over a large range. When using
an oscillating multimodal or multivariable frequency microwave in a
heating cavity, an additive heating effect is produced. While there
are many dips and peaks in the wave pattern produced, the physical
window for processing becomes much larger than with a monomodal
microwave frequency. This allows for additional sample size and
latitude for placement of the cell in the flow cell reactor.
Moreover, because each transition in a molecule for rotational,
vibrational and bending is frequency dependent, using a
multivariable frequency microwave allows for excitation of a
plurality of modes of different molecules at once. This increases
the heating efficiency of the microwave as many molecules will have
very low capture cross-sections at certain frequencies.
In addition, the microwave can be selected or tuned to excite two
or more different precursors so that they nucleate at the same
time. As shown in FIG. 9, different precursors tend to nucleate at
a different time for a substantially constant temperature. By
modulating the frequencies and/or the applied power at which the
microwave engages the precursors, the nucleating time between two
different precursors can be substantially the same. When two
different precursors nucleate at the same time the resulting
nanoparticle produced is homogenous as shown by the well-defined
crystalline structure 400 in FIG. 11B. An actual image of the
homogenous structure obtained using Transmission Electron
Microscopy (TEM) is shown in FIG. 12B. The modulation of the
frequencies and/or applied power allows the nucleation time between
different precursors to be tuned and/or optimized so as to allow
them to nucleate at substantially the same time.
In contrast, if traditional constant heating methods are used to
nucleate the precursors, they will not consistently nucleate at the
same time as shown in broken lines for exemplar precursor InP in
FIG. 9 resulting in an irregularly-defined crystalline structure
402 as shown in FIG. 11A (PRIOR ART). An actual image of the
irregularly-defined structure obtained using TEM is shown in FIG.
12A (PRIOR ART).
As an example, CuInSe.sub.2, when produced by batch processes or
non-microwave initiated processes, produces material which is
inhomogeneous in nature (Cu rich or In rich regions within a batch
of materials or in a nanoparticle itself), such as shown in FIGS.
11A (PRIOR ART) and 12A (PRIOR ART). When the microwave conditions
are set appropriately, because In has a larger d-orbital system
than Cu--and hence, more polarizable--it absorbs energy faster than
Cu does, increasing the rate of its reactivity, enabling the
resulting reaction to produce homogeneous materials such as shown
in FIGS. 11B and 12B.
This example provides an illustrative concept of an embodiment of
the invention, namely, the ability to create nanoparticle materials
having a high degree of crystallinity, uniform particle size,
homogeneous stoichiometry throughout the crystal, batch-to-batch
reproducibility as shown in FIG. 11B, and the ability to produce
such materials on a large scale as shown in FIG. 2. These
properties may be verified through several techniques or the use of
multiple techniques, such as:
Size Measurements: determination of the coefficient of variance
(COV) through the use of SAX (small angle x-ray scattering), TEM
(transmission electron microscopy), and XRD (x-ray diffraction)
using standard techniques. The COV is then defined as being:
COV=((standard deviation of particle size)/(average of particle
size))*100%
Where a COV <15% within a single run demonstrates uniform
particle size, and a COV <15% from batch-to-batch demonstrates
reproducibility.
Degree of Crystallinity and Homogeneous Stoichiometry: The degree
of crystallinity or the purity of the crystalline phase (as shown
in FIG. 11A and FIG. 11B) can be determined by TEM using
diffraction scattering patterns and performing a fourier transform
analysis to determine the crystalline structure of the material.
Another technique that may be used to determine this is XRD, where
the resultant diffraction pattern can be matched to a library of
known crystal structures and verified as to being inhomogeneous
(multiple contributions from different crystals) or homogeneous
(one contributing pattern diffraction matching the desired crystal
structure). Lack of a diffraction pattern in either XRD and/or TEM
is indicative of an amorphous material, indicating poor or
non-existent crystal structure.
Homogeneous Stoichiometry and Uniform Particle Size: This
information is obtained using either absorbance spectrophotometry
or photoluminescent emission. The absorption and photoluminescence
characteristics of a nanoparticle are determined by the FWHM (full
width half max, where the width of the absorbance or
photoluminescence peak is determined at half the height of the peak
of interest) obtained through the spectrum. An increase in the FWHM
means that one of multiple effects could be taking place, such as:
large particle size distribution (COV >15%), insufficient degree
of crystallinity resulting in trap states that have different
energies than a highly crystalline nanoparticle, and inhomogeneity
of the material--giving rise to multiple excitations or emissions
from the various regions within the nanoparticle or batch of
nanoparticles. A nanoparticle having a high degree of
crystallinity, a homogeneous stoichiometry, and being monodisperse
will give rise to absorption and/or photoluminescence peaks of:
<50 nm FWHM from 400 nm-700 nm, <150 nm FWHM from 700 nm-2000
nm, <300 nm FWHM from 2000 nm-10000 nm.
In the case of metallic nanoparticles, instead of a first exciton
excitation and emission, a surface resonance plasmon can be
observed. Using the same arguments presented above, a metallic
nanoparticle having a high degree of crystallinity will have <50
nm FWHM when excited at the surface plasmon resonance frequency
when excited between 400 nm and 700, and <150 nm FWHM when
excited in the near-infrared range (700 nm-2000 nm) when exciting
at the surface plasmon resonance frequency.
The frequency or frequencies which the microwave operates can also
be selected to excite a particular material in the process without
exciting other materials such as binders or the like. Microwave
frequencies ranging from between 300 MHz (1.24 .mu.eV) to 300 GHz
(1.24 meV), which are sufficiently low enough in energy that they
do not chemically change the substances by ionization. These
energies affect the rotational and bi-rotational energies of
molecules when absorbed by such species. These absorbances are
unique to each type of bending transition, rotation transition and
bi-rotational transition; hence, energies may be selected that
interact specifically with each transition. This property allows
the ability to select the desired microwave frequency to interact
with a specific reactant in a flow cell reactor, which allows
several capabilities.
For example, this allows temperature limitations associated with
the boiling point of solids to be overcome. By selectively
activating only the precursors associated with the synthesis of
nanoparticles, the solvent selection can be increased significantly
to allow for the solubility of precursors that would not normally
be used. Additionally, temperatures of the precursors can
effectively be much greater than the solvent, thereby allowing for
reactions that are not allowed through traditional heating of the
solvent.
The tube 40 carrying the precursors 32, 34 through the energy
source 50 can be configured with a cooling system, such as tubes
that encircle the tube and carry cooling liquid. This allows the
precursors within the tube to be heated, by microwaves or the like,
to high enough energy levels to promote nucleation without
overheating the tube itself and compromising its structural
limits.
Also, nanoparticles may be formed that are not feasible using
traditional colloidal nanoparticle synthetic techniques. For
example, the energy required for the formation of GaN nanoparticles
is great enough to surpass the boiling point of any solvent that is
available for synthetic techniques. Accordingly, the formation of
these nanoparticles is only done through high energy intensive and
expensive deposition systems such as Atomic Layer Deposition
("ALD"). This is done because only the precursors needed for the
formation of the GaN nanoparticles are heated in the microwave
initiated reaction of the present invention.
Moreover, in cases where one or more reaction pathways are
possible, the selective application of microwave frequencies allows
for the activation of a desirable reaction pathway. For example, if
a given reaction is thermodynamically dominated, the use of
selective microwave activating allows for the formation of the
kinetic product. The ability to selectively target which species
the reaction is going to absorb the microwave energy extends the
ability of the continuous flow cell reactor to deliver products
that would not normally be delivered at a cost that the microwave
continuous flow cell reactor is capable of delivering.
Another example of a possible benefit with selective frequency
microwaving involves the use of a polyol process to synthesize
nanoparticles of metallic salts. In this process, the metallic (Ni,
Co, Ag, and mixtures thereof) salts (acetate, chloride, fluoride,
nitrate) are dissolved at 1.0-3.0 mmol ethylene glycol or
polypropylene glycol (or similar polyol). At 2.45 GHz, the solvent
absorbs the microwave irradiation very strongly, heating the
solvent to the point where it then acts as the reducing agent for
the metallic precursor, allowing for the formation of metallic
nanoparticles. These types of reactions can be shown symbolically
as noted below: Ni(O.sub.2CCH.sub.3).sub.2+propylene
glycol.fwdarw.Ni(0) nanoparticles AgNO.sub.3+ethylene
glycol.fwdarw.Ag(0) nanoparticles
Another example is the microwave absorption of precursors for the
synthesis of PbS nanoparticles. The synthesis of PbS may be done in
the following manner. 1.5 mmol of lead oleate is dissolved in
1-octadecene with the addition of 3.0 mmol-12.0 mmol of oleic acid.
1.4 mmol of bis(trimethylsilyl)sulfide (TMS.sub.2S) which was
previously dissolved in the 1-octadecene. The microwave frequency
of 2.45 GHz is chosen because both the oleic acid and the
1-octadecene have very low absorption cross-sections at this
frequency. On the other hand, both the TMS.sub.2S and the lead
oleate have a relatively large absorption cross-section at this
frequency, allowing the absorption by these materials and the
selective activation. This exemplar reaction can be shown
symbolically as noted below.
Pb(oleate).sub.2+TMS.sub.2S.fwdarw.PbS(oleate) nanoparticles
Zone 3--Growth
This is the growth zone. At this point, the nucleates undergo one
of two processes: (1) combination with other nucleates to form
nanoparticles/quantum dots of the correct core size, or (2)
combination with unreacted precursors to form an epitaxial growth
system allowing for the formation of the nanoparticles/quantum dots
at a very controlled pace. The material is allowed to remain in the
growth zone for a period necessary for them to grow to the specific
desired core size, after which, the material is moved through Zone
4.
In general, in the growth phase, the nucleates are preferably
heated in a heat source 60 over a longer period of time, such as
greater than 100 seconds, at a lower energy level than what they
faced during nucleation. This allows thermodynamic growth and
Ostwald Ripening. This heating may be done using several different
systems, including, but not limited to, sand baths, convection
ovens, forced air heating, induction ovens, oil baths and column
heaters. Preferably, this heat source 60 is spaced apart from the
energy source 50 used in nucleation and is custom-tailored to
provide optimal growth of the nucleates. The length of the flow
path tube 40 extending through the heat source, diameter of the
tube, temperature of the heat source, uniform distribution of heat
within the tube, and nucleate flow rate though the heat source are
selected to optimize growth of the nucleates during this phase (as
shown in FIGS. 4A-C and 5A-B) thereby providing uniform morphology
and size among the nanoparticles produced.
Referring to FIGS. 4A-4C, the flow tube 40 may be arranged in a
serpentine arrangement within a rack 41 that is receivable within
the heat source 60. A plurality of racks may be stacked on top of
each other as shown in FIG. 4C thereby allowing effective heat
distribution to the flow tubes 40 while optimizing space within the
heat source 60. An alternative possible arrangement is shown in
FIGS. 5A & 5B where individual flow tubes are coiled to define
a heat transfer coil 43 with a plurality of heat transfer coils
received within the heat source 60
Zone 4--Quenching
The flow path continues past zone 3 to zone 4, where the reaction
is immediately terminated through a temperature reduction using a
quenching system 86 such as a quenching bath or the like. After
quenching the growth of the nanoparticle 70, the segmentation is
removed through a degassing step 150 (FIG. 7) to allow for
introduction of more material for shell growth and for ease of
in-line analysis to be performed.
If needed, increasing the pressure in the flow path 22 can increase
the boiling point of a solvent used in the process, thereby
allowing the system to operate at higher temperatures and energy
levels. One possible way to increase the pressure in the flow path
involves inserting a restrictive flow valve into the flow path
downstream of the quenching stage. The flow through the valve can
be adjusted so as to increase the pressure in the tube upstream of
the valve, thereby increasing the pressure in the tube through
zones 2 and 3, where the precursor and nucleates are activated and
grown.
Preferably and as best shown in FIG. 7, the reactively inert gas 42
is also separated from the nanoparticles 70. The flow path 22
extends into a chamber 160 where the nucleates drop downward and
exit from below while the gas escapes and is collected from a vent
162 above. Alternatively, the reactively inert gas can be separated
at a future point downstream in the flow path as needed.
Real-Time Quality Testing and System Optimization
As shown in FIG. 1, a testing system 72 can be provided following
nanoparticle production that tests the quality of the nanoparticles
produced. For example, Dynamic Light Scattering ("DLS") can be used
to test the properties of the particles produced. Other possible
in-line testing systems include spectrophotometry including UV, VIS
and IR spectra, fluorometry, and measurement of refractive
index.
The testing structure can be in communication with a control system
80 that monitors the results from the testing system 72 and can
modulate, preferably in real-time, components in zones 1-4 as
needed to optimize the quality of the nanoparticles produced. For
example, the flow of the individual precursors, the time and
temperature-heating-excitation energy applied through zone 2 and 3
and the amount of reactively inert gas segmented into the flow path
in zone 1 can be adjusted by the control system as needed to
optimize detected quality of the nanoparticles produced.
Depending on how many shells are introduced onto the surface of the
core material (which is produced in Zones 1-4), Zones 1, 3 and 4
can be repeated using a different set of materials
(precursors/components) to form core/shell, core/shell/shell and
core/shell/shell/shell type structures.
Shell Fabrication System
A post-production shell application system 100 may be provided
following the production of the nanoparticles as shown in FIG. 1.
As shown in FIG. 2, the shell fabrication system may include
structures for supplying one or more additional precursors (here
precursors 170, 172, 174, and 176 are shown) and a supplemental
heat source 61 for heating downstream therefrom. A continuous flow
loop 180 may be provided where any combination of the precursors
can be applied to any given shell layer and passed through the heat
source 61, thereby allowing multiple shell layers to be formed on
each nanoparticle. A second quality testing system 72' may be
provided following each shell layer application. With this testing
system 72' and the components of the shell fabrication system in
operable communication with the control system 80, the control
system 80 can provide real-time modulation of the shell fabrication
systems as needed to optimize quality of the shell layer on each
nanoparticle produced.
The purpose for the shell architecture surrounding the core
nanoparticle material is two-fold. First, by matching the lattice
parameters closely of the core material, a first shell can be added
which increases the quantum yield of the resultant nanoparticle
upon exposure to light. This is done by passivating the
nanoparticle core surface and eliminating dangling bonds which
contribute to non-radiative recombination events. Also, by lattice
matching the materials of the nanoparticle core and the first
shell, strain effects are reduced, which also causes an increase in
the quantum yield of the resultant nanoparticle.
This first shell may also have the added benefit of providing a
barrier against environmental degradation effects, such as
photo-bleaching and/or oxidation of the core material, which will
result in either a blue-shifting of emitted light, or provide
multiple trap sites for reduction of effective and desirable
electronic properties. However, in the event that this is not
provided by the first shell, a second and/or third shell may be
provided that will enhance the operational lifetime of nanoparticle
materials when used in applications. These second and third shells
do not necessarily have to be lattice matched to enhance optical
properties unless they interact with the wave function associated
with the nanoparticle in the excited state. The primary purpose of
the second and third shell are to provide increased operational
lifetime by providing protection to the nanoparticle core/shell
from environmental effects, which include, but are not limited to:
oxidation, photobleaching and temperature extremes.
The first shell integrity can be verified by measuring the quantum
yield of the nanoparticle after the first shell has been placed
onto the core of the nanoparticle. Poor coverage by the first
shell, or poor lattice matching by the first shell will result in
low quantum yields (<50%), whereas good coverage by the first
shell and good lattice matching between the first shell and the
core material will result in large quantum yields (>50%).
The lifetime of the materials can be evaluated by exposure to
light, preferably between 250 nm and 700 nm, and measuring the
photoluminescent response as a function of time. Increased
operational lifetime and enhancement of the stability of these
nanoparticles by inclusion of a second and, perhaps, a third shell,
will show less than 5% photodegration of a 10 wt % material in
solvent exposed to a minimum of 5 mW light source over the period
of two weeks upon continuous exposure in standard atmospheric
conditions.
System Redundancy and Redirectable Flow Paths
As shown in FIG. 8, a plurality of reductant elements of the
production line, such as two energy sources 50 and two heat sources
60 may be provided with redundant sets of the individual precursors
32, 24 and nanoparticle flow 22 paths interconnectable with valves
300 or the like to allow redirection of the flow path 22 through
alternative components should one component before inoperable.
Conservation of Excess Microwave Energy
As shown schematically in FIG. 10, in cases where the energy source
50 in zone 2 is a microwave oven, excess microwave energy may be
directed to assist with warming the growth area heating source 60
in zone 3. For example, a series of mirrors or the like can be
directed to a heat sink such as rubber or the like that collects
the excess microwaves and coverts them to heat.
The microwave energy entering the growth chamber can be controlled
through an insertable and movable baffle 310 which can attenuate
the amount of microwave energy entering the growth area heating
source. The temperature of the growth area heating source can be
monitored by the control system 72 which modulates the baffle
position as needed to maintain a desired temperature in the growth
chamber.
Exemplar precursor combinations that have may work particularly
well in this flow cell reactor include first precursors selected
from those found in "Group A" below with the second precursor is
selected from "Group B" or "Group C" below using conventional
periodic table nomenclature.
Group A--Precursors
H.sub.2X Where X=O, S, Se, Te
R.sub.3P=X Where R=--H, --(CH.sub.2).sub.n--CH.sub.3,
--C.sub.6H.sub.5, --C.sub.6H.sub.4--R' n=3-18
R'=--(CH.sub.2).sub.m--CH.sub.3, --CH(CH.sub.3).sub.2,
--C(CH.sub.3).sub.3 m=0-17 X=Se, Te
R.sub.3N=X Where R=--H, --(CH.sub.2).sub.n--CH.sub.3,
--Si(CH.sub.3).sub.3 n=0-4 X=S, Se, Te
((CH.sub.3).sub.3Si).sub.2X Where X=S, Se, Te
(((CH.sub.3).sub.3Si).sub.2N).sub.2X Where X=S, Se, Te
H--X--(CH.sub.2).sub.n--CH.sub.3 Where X=O, S, Se, Te n=1-18,
preferably n=4-12, more preferably n=8-10
HO--CH.sub.2--(CH(OH)).sub.n--CH.sub.3 n=1-50, preferably n=1-25,
more preferably n=1-5
HO--CH.sub.2--(CH(OH)).sub.n--CH.sub.2--OH n=1-50, preferably
n=1-25, more preferably n=1-5
H.sub.2NNH.sub.2
NaBH.sub.4
NaCNBH.sub.3
and mixtures thereof
including anionic precursors and/or reducing agents
Group B--Precursors
M(ligand).sub.y When y=1, M=Tl, Ag, Cu When y=2, M=Zn, Cd, Hg, Cu,
Pb, Ni When y=3, M=Al, Ga, B, In, Bi, Fe
Ligand=--(O.sub.2C--(CH.sub.2).sub.n--CH.sub.3),
--(O.sub.2C--(CH.sub.2).sub.m-- CH=CH--(CH.sub.2).sub.o--CH3),
--S--(CH.sub.2).sub.n--CH.sub.3, --PR.sub.3, --OPR.sub.3 n=2-24,
preferably n=8-20, more preferably n=12-16 m and o=1-15, preferably
n and o=12-16, more preferably n and o=7-9
R=--(CH.sub.2).sub.pCH.sub.3, --C.sub.6H.sub.5,
--C.sub.6H.sub.4--R' p=0-18 R'=--(CH.sub.2).sub.p--CH.sub.3,
--CH(CH.sub.3).sub.2, --C(CH.sub.3).sub.3
Or mixtures thereof.
Group C--Precursors
M(ligand).sub.y When y=1, M=Na, K, Rb, Cs, Ag, Cu When y=2, M=Mg,
Ca, Sr, Ba, Pd, Pt, Cu, Ni When y=3, M=La, Ce, Pr, Nd, Pm, Sm, Eu,
Gd, Tb, Dy, Ho, Er, Tm, Yb, Au When y=4, M=Ti, Zr, Hf, Pt, Pd
ligand=--O.sub.2C--CH.sub.3, --Cl, --F, --NO.sub.3
or mixtures thereof.
The invention is disclosed above and in the accompanying figures
with reference to a variety of configurations. The purpose served
by the disclosure, however, is to provide an example of the various
features and concepts related to the invention, not to limit the
scope of the invention. One skilled in the relevant art will
recognize that numerous variations and modifications may be made to
the configurations described above without departing from the scope
of the present invention, as defined by the appended claims.
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