U.S. patent application number 12/017644 was filed with the patent office on 2008-09-11 for nanoparticles wtih grafted organic molecules.
Invention is credited to Rebecca J. Anthony, David Jurbergs, Uwe Kortshagen, Xuegeng Li, Lorenzo Mangolini, Elena Rogojina.
Application Number | 20080220175 12/017644 |
Document ID | / |
Family ID | 39471616 |
Filed Date | 2008-09-11 |
United States Patent
Application |
20080220175 |
Kind Code |
A1 |
Mangolini; Lorenzo ; et
al. |
September 11, 2008 |
NANOPARTICLES WTIH GRAFTED ORGANIC MOLECULES
Abstract
An apparatus for producing grafted Group IV nanoparticles is
provided and includes a source of Group IV nanoparticles. A chamber
is configured to carry the nanoparticles in a gas phase and has an
inlet and an exit. The inlet configured to couple to an organic
molecule source which is configured to provide organic molecules to
the chamber. A plasma source is arranged to generate a plasma. The
plasma causes the organic molecules to break down and/or activate
in the chamber and bond to the nanoparticles. A method of producing
grafted Group IV nanoparticles is also provided and includes
receiving Group IV nanoparticles in a gas phase, creating a plasma
with the nanoparticles, and allowing the organic molecules to break
down and/or become activated in the plasma and bond with the
nanoparticles.
Inventors: |
Mangolini; Lorenzo;
(Minneapolis, MN) ; Kortshagen; Uwe; (Roseville,
MN) ; Anthony; Rebecca J.; (Minneapolis, MN) ;
Jurbergs; David; (Austin, TX) ; Li; Xuegeng;
(Sunnyvale, CA) ; Rogojina; Elena; (Los Altos,
CA) |
Correspondence
Address: |
WESTMAN CHAMPLIN & KELLY, P.A.
SUITE 1400, 900 SECOND AVENUE SOUTH
MINNEAPOLIS
MN
55402-3244
US
|
Family ID: |
39471616 |
Appl. No.: |
12/017644 |
Filed: |
January 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60881663 |
Jan 22, 2007 |
|
|
|
Current U.S.
Class: |
427/430.1 ;
118/723MW |
Current CPC
Class: |
C01B 33/02 20130101;
B01J 2219/0849 20130101; B01J 2219/0869 20130101; Y10S 977/773
20130101; B01J 2219/0875 20130101; B01J 2219/0847 20130101; B01J
2219/0809 20130101; B01J 2219/0896 20130101; B01J 2219/0886
20130101; B01J 2219/0835 20130101; B01J 19/088 20130101 |
Class at
Publication: |
427/430.1 ;
118/723.MW |
International
Class: |
C23C 16/00 20060101
C23C016/00; B05D 1/18 20060101 B05D001/18 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] The United States government has certain rights in this
invention pursuant to Agency Grant No. DMI-0556163 awarded by
National Science Foundation.
Claims
1. An apparatus for producing grafted Group IV nanoparticles,
comprising: a source of Group IV nanoparticles; a chamber
configured to carry the nanoparticles in a gas phase having an
inlet and an exit; an organic molecule source coupled to the inlet
configured to provide organic molecules to the chamber; a plasma
source arranged to generate a plasma; and wherein the plasma causes
the organic molecules to break down and/or become activated in the
chamber and bond to the particles.
2. The apparatus of claim 1 including at least one electrode
coupled to the chamber and a radio frequency (RF) signal source
coupled to the electrode configured to create a plasma to break
down and/or activate organic molecules in the chamber whereby
organic molecules in the chamber bond to the nanoparticles.
3. The apparatus of claim 2 including a second electrode coupled to
the chamber and driven by the radio frequency (RF) signal
source.
4. The apparatus of claim 1 including a filter coupled to the exit
from the chamber arranged to receive particles from in the
chamber.
5. The apparatus of claim 4 wherein the filter comprises a wire
mesh.
6. The apparatus of claim 1 wherein the organic molecule source
includes a gas source.
7. The apparatus of claim 1 wherein the organic molecule source
includes a liquid precursor.
8. The apparatus of claim 1 wherein organic molecules are selected
from the group of organic molecules consisting of 1-dodecene;
Dodecane; Octyl-alcohol; 1-hexene; 1-hexyne; Hexane; Hexyl-alcohol;
Hexyl-amine; 1-pentene; Acrylic acid; Allylamine; Ethylene-Diamine;
Decyl-aldehyde (Decanal); Ethylene-glycol; compounds with saturated
carbon bonds; compounds with one or more aromatic rings; compounds
with unsaturated terminal functional group; alcohols (--OH), thiols
(--SH), amines (--NH.sub.2), aldehydes)-CH.dbd.O), carboxylic acids
(--COOH); compounds with one or more aromatic rings or unsaturated
terminal functional group and with more than one of the same
functional group present in the same molecule; compounds with one
or more aromatic rings or unsaturated terminal functional group and
with different functional groups present in the same molecule.
9. The apparatus of claim 1 wherein the organic molecule source
includes a solid precursor or a gaseous precursor.
10. The apparatus of claim 1 wherein the inlet for the organic
molecule source is positioned in an afterglow of a plasma of the
nanoparticles.
11. The apparatus of claim 1 wherein the nanoparticles are
generated from the nanoparticles sources consisting of plasmas,
thermal methods, laser pyrolysis, laser photolysis, laser ablation,
liquid phase reactions, combustion processes and flame
processes.
12. The apparatus of claim 1 wherein the Group IV nanoparticles
comprise doped nanoparticles.
13. The apparatus of claim 1 wherein the Group IV nanoparticles
comprise silicon or germanium.
14. The apparatus of claim 1 wherein the plasma also provides
electromagnetic radiation (such as visible or ultraviolet
radiation) to assist bonding of the organic molecules to the
nanoparticles.
15. The apparatus of claim 1 including a second source of
nanoparticles.
16. The apparatus of claim 1 including a second organic molecule
source.
17. A method of producing grafted Group IV nanoparticles,
comprising: receiving Group IV nanoparticles in a gas phase;
creating a plasma to immerse the nanoparticles in; providing
organic molecules to the nanoparticles; and allowing the organic
molecules to break down and/or become activated in the plasma and
bond with the nanoparticles.
18. The method of claim 18 including collecting nanoparticles in a
filter from the exit of the chamber.
19. The method of claim 18 including applying an RF signal to an
electrode to form the plasma.
20. The method of claim 18 wherein providing organic molecules
comprises providing a liquid, solid or gaseous precursor.
21. The method of claim 21 including injecting a gas into the
liquid precursor to thereby bubble the liquid precursor and provide
the organic molecules.
22. The method of claim 18 wherein the organic molecules are
acetylene or methane.
23. The method of claim 18 including injecting a gas into a liquid
precursor.
24. The method of claim 18 wherein the organic molecules are
provided in an afterglow of a plasma of the nanoparticles.
25. The method of claim 18 wherein the Group IV nanoparticles
comprises silicon or germanium.
26. The method of claim 18 including using the plasma to also
provide a source of radiation to assist bonding of the organic
molecules to the nanoparticles.
27. The method of claim 17 wherein receiving nanoparticles
comprises receiving doped nanoparticles.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is based on and claims the benefit
of U.S. provisional patent application Ser. No. 60/881,663, filed
Jan. 22, 2007, the content of which is hereby incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to grafting of molecules onto
nanoparticles. More specifically, the present invention relates to
grafting of organic molecules onto Group IV nanoparticles.
[0004] Nanoparticles have recently attracted significant attention
from researchers in a variety of disciplines, due to a wide array
of potential applications in the fabrication of nanostructured
materials and devices. Semiconductor nanoparticles, such as silicon
nanoparticles, are of special interest due to their potential uses
in photoluminescence-based devices, doped electroluminescent light
emitters, photovoltaic devices, memory devices and other
microelectronic devices, such as diodes and transistors.
[0005] In many instances, it is desirable to graft molecules onto
the surface of nanoparticles. The grafting of molecules to the
surface is sometimes called "passivation," but may also impart new
properties to the nanoparticles. In one example prior art approach
to grafting molecules, nanoparticles are collected as a powder and
then transferred into mixtures of solvents and ligands molecules
and reacted for several minutes to hours. This process can be used
to attach the ligands to the surface of the nanoparticles. The
ligand molecules should have a sufficient length such that they are
able to overcome the van der Walls forces between particles to push
agglomerated nanoparticles apart. Another example prior art
technique is the thermal gas phase method. In the thermal gas phase
method, the molecules are electrically neutral and no charge
prevents them from agglomerating. In order to passivate these
particles while avoiding agglomeration, the thermal method is
limited to relatively small particle concentrations such that the
particles remain sufficiently separated and do not agglomerate.
SUMMARY OF THE INVENTION
[0006] An apparatus for producing grafted Group IV nanoparticles is
provided and includes a source of Group IV nanoparticles. A chamber
is configured to carry the nanoparticles in a gas phase and has an
inlet and an exit. The inlet configured to couple to an organic
molecule source which is configured to provide organic molecules to
the chamber. A mixture of particles and organic molecules is formed
in the gas phase. A plasma source is arranged to generate a plasma.
The plasma causes the organic molecules to break down and/or become
activated in the chamber and bond to the nanoparticles. A method of
producing grafted Group IV nanoparticles is also provided and
includes receiving Group IV nanoparticles in a gas phase, creating
a plasma with the nanoparticles, and allowing the organic molecules
to break down and/or activate in the plasma and bond with the
nanoparticles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a simplified diagram showing a two stage plasma
reactor in accordance with one example embodiment of the present
invention.
[0008] FIG. 2 is a simplified diagram showing a single stage plasma
reactor in accordance with another example embodiment of the
present invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0009] The present invention provides an apparatus and method for
grafting organic molecules onto Group IV nanoparticles. The
grafting is performed with the nanoparticles in a gas phase. An
organic molecule source is provided and the organic molecules break
down and/or are activated in a plasma to enable their reaction with
the nanoparticle surfaces.
[0010] The grafting of molecules to the surface of nanoparticles
can be called "passivation", but it also imparts new properties to
the nanoparticles. For example, the grafting can also make the
particles soluble in various organic solvents. This is important if
one wants to make a nanoparticle ink which requires, isolated,
non-agglomerated particles in solution. Applications of such inks
are in printable electronics and solution processable solar cells.
However, the invention is not limited to this implementation.
[0011] In prior approaches to grafting molecules to particles,
particles were typically collected as a powder, transferred into
mixtures of solvents and ligand molecules and reacted for a period
of from several minutes to hours to attach the ligands to the
surface. In one example of the present invention, nanoparticles are
synthesized in a first plasma in a few milliseconds and next
transferred into a second plasma, in which the ligands are attached
within a few hundreds of milliseconds to one second. This provides
an advantage in terms of time and processing ease. Moreover, this
"in-flight" method allows attaching shorter molecules than is
typically possible in the liquid phase. In prior liquid phase
approaches, one starts with a powder of agglomerated particles. The
ligand molecules need to have a sufficient length such that they
can overcome the van der Walls forces between particles to push
agglomerated nanoparticles apart. In the plasma method of the
invention, the surface grafting is performed on individual
particles suspended in a gas stream. It is thus possible to attach
very short ligands, which may be desirable for some applications
such as in printed electronics.
[0012] In-flight passivation of particles can be achieved by
thermal gas-phase methods, for instance by flowing the mixture of
particles and organic molecules through a furnace. The plasma
method of this invention differs from the thermal gas phase method
in a number of aspects. In the plasma, particles are negatively
charged, which significantly reduces agglomeration of individual
particles. In the thermal gas-phase method, particles are
electrically neutral and are not prevented from agglomerating. In
order to passivate particles while avoiding agglomeration, the
thermal gas-phase method is typically limited to very small
particle concentrations, such that the particle agglomeration rate
is lower than the reaction rate between the particles and the
organic molecules. The plasma approach allows for much higher
particle concentrations, as the electric repulsion between
particles significantly lowers the agglomeration rate. Hence, the
plasma approach will allow much larger processing rates than the
thermal gas-phase method.
[0013] The invention provides other advantages such as the ability
to operate with a larger range of molecules than the thermal
method. Non-thermal plasma selectively heats the electrons in the
plasma but leaves the background gas cold. The energetic electrons
can dissociate and/or activate ligand molecules and produce
reactive radicals which attach to the nanoparticle surfaces. In
contrast, the thermal gas-phase method relies on thermally
activating certain bonds to initiate the reaction, requiring
heating of the entire gas stream to achieve a heating of the
particles. Further, the thermal method requires that the ligands
have certain excitable bonds, such as unsaturated C.dbd.C bonds.
The plasma approach also functions with saturated molecules such as
alkanes which do not have any unsaturated bonds. The techniques can
be used with Group IV nanoparticles including germanium and silicon
nanoparticles.
[0014] FIG. 1 is a simplified diagram showing a two stage reactor
100 in accordance with one example embodiment of the present
invention. Reactor 100 includes a first plasma chamber 102 and a
second plasma chamber 104. Plasma chamber 102 receives a gas from
gas source 106 and includes an RF power supply connected to
electrodes 110. The RF power supply 108 drives electrodes 110 with
an RF signal and creates a non-thermal plasma in the gas from gas
source 106 between electrodes 110. This causes nanoparticles to
form from the gas. For example, if the gas is
Ar--SiH.sub.4--H.sub.2, silicon nanoparticles will be formed in
plasma chamber 102. The nanoparticles then enter second stage
plasma (or passivation) chamber 104. Plasma chamber 104 includes a
second RF power supply 116 which couples between electrode 118 and
electrical ground 120. Plasma chamber 104 receives organic
molecules in accordance with the present invention. In the
configuration shown in FIG. 1, the organic molecules are from an
organic molecule source 130 which comprises a liquid precursor 132
through which a gas from gas source 134 is bubbled. For example,
gas source 134 can comprise argon. This provides a flow of
evaporated reactant which is injected into plasma chamber 104
through inlet 136. The plasma chamber 104 receives the
nanoparticles from chamber 102 through inlet 140. The pressure and
temperature of the bubbler and the flow rate from gas source 134
can be adjusted to control the organic molecule density in the
second stage chamber 104. Plasma chamber 104 comprises a parallel
plate reactor configured as a continuous flow reactor, with
particles being carried past the lower electrode plate 118 and into
an exhaust blind 150 which carries a filter 152.
[0015] The first plasma chamber 102 can form nanoparticles in
accordance with any appropriate technique. One example plasma based
technique is shown and described in co-pending application Ser. No.
11/155,340, entitled, PROCESS AND APPARATUS FOR FORMING
NANOPARTICLES USING RADIO FREQUENCY PLASMAS, by Kortshagen et al.
which is incorporated herein by reference in its entirety. As
discussed below, the nanoparticles can be formed using any
appropriate technique and are not limited to formation using a
plasma.
[0016] As discussed above, the nanoparticles are received in the
second stage 104. For example, second stage 104 can comprise a five
inch diameter parallel plate reactor having a two inch plate gap.
The nanoparticles can be received directly into chamber 104 and a
separate orifice is not required. In this example, particles are
nucleated and grown in the first stage 102 and the gas flow brings
them into the second stage through inlet 140. The organic molecules
are received into the second stage chamber through inlet 136 and
can be adjusted to have a desired density. The second RF power
supply 116 causes the molecular gas to break down and/or activate
and bond with the nanoparticles. The flow continues through exhaust
150 and the nanoparticles, with the bonded organic molecules, are
collected in a filter 152. The filter can comprise any appropriate
filter, for example, a wire mesh filter. In one configuration, a
pressure gauge 170 is provided in the exhaust 150 and can be used
to monitor the pressure in the chamber.
[0017] The organic molecules can be selected as desired. Examples
of organic molecules are shown below in Table 1. Various different
bonds are formed between the carbon molecules and the nanoparticle
and those are also shown in Table 1.
TABLE-US-00001 TABLE 1 NAME STRUCTURE BOND 1-dodecene
H.sub.3C--(CH.sub.2).sub.9--CH.dbd.CH.sub.2 G4SA-Carbon Dodecane
H.sub.3C--(CH.sub.2).sub.10--CH.sub.3 G4SA-Carbon Octyl-alcohol
H.sub.3C--(CH.sub.2).sub.7--OH G4SA-Oxygen 1-hexene
H.sub.3C--(CH.sub.2).sub.3--CH.dbd.CH.sub.2 G4SA-Carbon 1-hexyne
H.sub.3C--(CH.sub.2).sub.3--C.ident.CH.sub.2 G4SA-Carbon Hexane
H.sub.3C--(CH.sub.2).sub.4--CH.sub.3 G4SA-Carbon Hexyl-alcohol
H.sub.3C--(CH.sub.2).sub.5--OH G4SA-Oxygen Hexyl-amine
H.sub.3C--(CH.sub.2).sub.5--NH.sub.2 G4SA-Nitrogen 1-pentene
H.sub.3C--(CH.sub.2).sub.2--CH.dbd.CH.sub.2 G4SA-Carbon Acrylic
acid H.sub.2C.dbd.CH--COOH G4SA-Carbon or G4SA- Oxygen Allylamine
H.sub.2C.dbd.CH--CH.sub.2--NH.sub.2 G4SA-Carbon or G4SA- Oxygen
Ethylene-diamine H.sub.2N--CH.sub.2--CH.sub.2--NH.sub.2
G4SA-Nitrogen Ethylene-glycol HO--CH.sub.2--CH.sub.2--OH
G4SA-Oxygen
Here G4SA refers to Group IV surface atoms including Si, Ge, C or
any other Group IV element.
[0018] The list set forth in Table 1 is not exhaustive and other
materials and compounds may be used such as Decyl aldehyde
(Decanal). In general, the following compounds can be delivered
into the plasma and reacted with the particles: [0019] Compounds
with saturated carbon bonds, i.e. alkanes. [0020] Compounds with
one or more aromatic rings (benzene, toluene, mesitylene, pentacene
etc.). [0021] Compounds with unsaturated terminal functional group,
i.e. alkenes and alkynes. Examples are 1-dodecene, 1-octadecene,
1-exene, 1-pentene, propene, butene, styrene, ethylene, acetylene,
1-pentyne etc. [0022] Alcohols (--OH), thiols (--SH), amines
(--NH.sub.2), aldehydes (--CH.dbd.O), carboxylic acids (--COOH).
[0023] Compounds of point 3 and 4, but with more than one of the
same functional group present in the same molecule. Examples are
molecules such as 1,3 butadiene, ethylene glycol (ethane-1,2-diol),
ethylene diamine, divinylbenzene. [0024] Compounds of point 3 and
4, but with different functional groups present in the same
molecule. Examples are allylamine, acrylic acid, mercaptopropionic
acid. [0025] Compounds containing any of the above mentioned
functional groups but also containing one or more silicon atoms.
Such compounds are usually referred to as organisilanes.
[0026] The molecular monomer to be grafted onto the particle
surface may be solid, liquid or gaseous at room temperature. If
gaseous, it may be delivered into the reactor from a compressed gas
cylinder using any type of compatible flow meter; if liquid, a
bubbler system may be used to saturate a carrier gas with the
monomer; if solid, a sublimator may be used to saturate a carrier
gas with the monomer. The carrier gas may be an inert gas (such as
Argon, Helium etc.), a reactive gas (such as H.sub.2), or it might
be an organic monomer precursor itself (for instance, ethylene may
be bubbled through 1-dodecene to deliver monomers of different
length to the reactor, and to achieve mixed termination of the
particle surface).
[0027] More than one monomer may be delivered into the reactor.
This can be done by building a separate delivery line for each
monomer, or (if both monomers are liquid) by mixing the two liquids
and by using a bubbler to deliver the mixture to the reactor. More
than one monomer can be delivered to the reactor to achieve mixed
termination of the particle surface.
[0028] The organic molecule might contain one or more atoms of
group III and V, such as P, As, B, Sb. Examples are
triphenilphosphine, trioctylphosphine (TOP), trioctylphosphine
oxide (TOPO), tributylborane, etc.
[0029] In one example experiment, 1-dodecene was reacted and used
to bond with silicon nanoparticles. For this gas phase reaction 30
sccm of argon and 8 sccm of SiH.sub.4 (5% in He) were provided in
the first stage plasma reactor 102. Further, 15 sccm of argon was
provided through the bubbler 130 which was maintained at the same
pressure as the reactor (1.4 Torr). A power of 60 watts was used
for the RF power supply 108 of the first reactor. A relatively low
power (10-15 watts) was used for the second reactor 104 to
successfully passivate the silicon particle surfaces. The resultant
passivated nanoparticles were collected in the filter 152 and
appeared to have a compact brown layer covering a stainless steel
mesh of the filter. When the filter 152 was dipped into a solvent
(toluene), the deposited nanoparticles began to disperse in the
solvent. This dispersing occurred even without any sonication in
the solution. A clear colloidal dispersion of silicon nanoparticles
was obtained.
[0030] FIG. 2 is a simplified diagram of another configuration of
the present invention in which a single stage plasma reactor 180 is
provided. Elements in FIG. 2 which are similar to those shown in
FIG. 1 have retained that numbering. In the single stage plasma
reactor of FIG. 2, the nanoparticles are nucleated and form
nanocrystals as discussed above in the first plasma chamber 102. As
the particles leave chamber 102, they are exposed to a plasma
afterglow 190 in passivation chamber 192. Passivation chamber 192
is configured to receive the gas from an organic molecule source
130. If the plasma afterglow is sufficiently energetic to break
down and/or activate the bonds of the organic molecules in the gas,
these molecules will bond with the nanoparticles as discussed
above.
[0031] As discussed above, the nanoparticles can be formed using
any appropriate technique and are not required to be formed in a
plasma chamber. However, if a plasma chamber is employed to form
the nanoparticles, a single stage reactor may be possible in which
the nanoparticles are passivated in the afterglow plasma from the
production chamber. Although RF plasma chambers are discussed
herein, other types of plasma chambers may also be used including
DC, or microwave based plasma sources. Plasmas are desirable
because they impart a negative charge to the nanoparticles and
reduce the particle agglomeration rate.
[0032] The present application is applicable to Group IV
nanoparticles which include pure Group IV elements as well as Group
IV compounds which include other elements including doped
particles. Specific examples of Group IV elements includes silicon
and germanium. The nanoparticles may be produced just prior to
their passivation, or may be produced separately, in time and/or
location as desired. For example, the nanoparticles can be produced
using a thermal process with a furnace and subsequently injected
into a plasma chamber. The nanoparticles may be injected into the
plasma chamber using any appropriate technique including injection
in a liquid phase through an atomizer or the like, electrosprayed,
etc. During the bonding, the Group IV nanoparticles are bonded with
the organic molecules. Examples of bonds linking organic molecules
to the Group IV nanoparticles include Si-carbon, Si-oxygen,
Si-sulfur, and Si-Nitrogen bonds, or others based upon any Group IV
element. The precursor used in passivation may be any appropriate
gas, liquid or solid which may be injected into the chamber in a
dispersed form. Although argon is discussed above as a carrier gas,
the present invention is not limited to this configuration.
[0033] The passivated nanoparticles may be collected on a filter as
discussed above, or collected using other collection techniques.
One example includes bubbling the passivated nanoparticles through
a liquid solvent.
[0034] Although the discussion above describes the passivation of a
single type of nanoparticle, multiple types of nanoparticles may be
passivated at the same time. Such a configuration, nanoparticles
having desired concentrations are injected into the passivation
chamber and bond with the injected organic molecules. Similarly,
multiple types of organic molecules may be used in the bonding
process. These bonding steps may be performed in a single chamber,
or as the nanoparticles pass through multiple chambers. Any
appropriate organic molecules may be used including those set forth
above.
[0035] In one configuration, the first chamber can comprise any gas
phase method used for the synthesis of nanoparticles such as, but
not limited to, ultraviolet, thermal or plasma. Following the
synthesis of the nanoparticles, the nanoparticles are then
subjected to a passivation with organic molecules. In such a
configuration, with the gas phase nanoparticles immediately
followed by functionalization, problems associated with
agglomeration are eliminated or significantly reduced and the
resultant particles may be immediately processed in a solution
without requiring additional steps. Electromagnetic radiation
(including visible or ultraviolet) from the plasma can be used to
assist in the bonding process.
[0036] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention. As used
herein, the plasma as set forth above may be any type of plasma
including, "a gaseous medium that is partly ionized by the
applications of a DC (direct current) or AC (alternating current)
electric field. The electric field can be applied in continuous
wave (CW) mode or in a pulsed mode. In the most general case,
plasmas can be produced under gas pressures ranging from less than
1 Pa to exceeding 10.sup.6 Pa. The densities of the free charge
carriers (electrons and ions) range from smaller than 10.sup.12
m.sup.-3 to larger than 10.sup.22 m.sup.-3. The temperatures of
electrons may range from less than 0.1 electronvolt to more than 10
electronvolt. Temperatures of the heavy charge carriers (ions) may
range from the temperature of the neutral gas (nonthermal plasma)
up to temperatures equaling the electron temperature (thermal
plasma)." Another definition of plasma, includes, "Gas pressures
between 1 Pa to 10.sup.5 Pa, free charge carrier densities ranging
from 10.sup.14 m.sup.-3 to larger than 10.sup.18 m.sup.-3, electron
temperatures between 0.1 electronvolt and 10 electronvolt, and ion
temperatures between room temperature and up to .about.1000
Kelvin." Various flow rates of the materials through the reactor
may be used. The flow rates through the functionalization plasma
can range, depending on the size and throughput of the reactor to
be designed, from a few sccm (cubic centimeter per minute at
standard reference conditions) to many slm (liter per minute at
standard reference conditions). More relevant than the flow rates
are the residence times of nanoparticles in the reaction zone,
which reasonably can range from around a millisecond to several
seconds. Further, the present invention is not limited to the
specific plasma source as set forth above. In various embodiments,
reactions may be conducted in both low pressure gas environment and
at gas pressures on the order of atmospheric gas pressure. At low
pressures (1 Pa-1000 Pa) plasma can be produced through a number of
plasma sources in both continuous and pulse discharged operation:
[0037] DC glow discharges [0038] Radiofrequency (RF) capacitively
coupled plasmas [0039] Radiofrequency inductively coupled plasmas
[0040] Microwave produced plasmas in microwave resonators [0041]
Radiofrequency and microwave traveling wave produced plasmas such
as, but not limited to, surface waves, helicon waves, electron
cyclotron resonance discharges [0042] Electron beam produced
plasmas [0043] DC and RF hollow cathode discharges At pressures
closer to atmospheric pressures (1000 Pa-10.sup.6 Pa), plasmas can
be produced both in a continues wave and a pulsed discharge
operation by: [0044] DC arc discharges [0045] Radiofrequency (RF)
capacitively coupled plasmas [0046] Radiofrequency inductively
coupled plasmas [0047] Microwave produced plasmas in microwave
resonators [0048] Radiofrequency and microwave traveling wave
produced plasmas such as, but not limited to, surface waves. [0049]
Electron beam produced plasmas [0050] DC and RF microhollow cathode
discharges [0051] Corona discharges [0052] Spark discharges [0053]
Dielectric barrier discharges [0054] Atmospheric pressure glow
discharges [0055] Gliding arc discharges At both low pressures as
well as close to atmospheric pressures, nanoparticles may be
functionalized by either being directly exposed to the plasma zone
containing the molecular precursors for surface functionalization,
or by being exposed to the effluent (afterglow) of the plasma. The
plasma breaks down (disassociates) and/or activates the molecules
to achieve the desired reaction. The plasma can provide a source of
reduction to assist in the process. Various nanoparticle sources
include plasmas, thermal methods, laser pyrolysis, laser
photolysis, laser ablation, liquid phase reactions, combustion
processes and flame processes.
* * * * *