U.S. patent application number 13/181631 was filed with the patent office on 2011-11-03 for synthesis of pb alloy and core/shell nanowires.
This patent application is currently assigned to The Regents of the University of California. Invention is credited to Taleb Mokari, Peidong Yang, Minjuan Zhang.
Application Number | 20110268968 13/181631 |
Document ID | / |
Family ID | 40781619 |
Filed Date | 2011-11-03 |
United States Patent
Application |
20110268968 |
Kind Code |
A1 |
Mokari; Taleb ; et
al. |
November 3, 2011 |
SYNTHESIS OF Pb ALLOY AND CORE/SHELL NANOWIRES
Abstract
Embodiments of the present invention are directed to methods of
producing nanowires comprising a PbSe core and a PbS shell, and
methods of producing nanowires comprising a PbSe core and a PbTe
shell. The method for producing the PbSe core/PbS shell nanowires
comprise the steps of providing a core/shell growth solution
comprising PbSe nanowires, heating the core/shell growth solution
to a temperature sufficient to produce a PbS shell over the PbSe
nanowires, adding a Pb precursor solution to the core/shell growth
solution, and adding an S precursor solution to the core/shell
growth solution after the addition of the Pb precursor to produce
nanowires comprising a PbSe core and a PbS shell.
Inventors: |
Mokari; Taleb; (Berkeley,
CA) ; Zhang; Minjuan; (Ann Arbor, MI) ; Yang;
Peidong; (Berkeley, CA) |
Assignee: |
The Regents of the University of
California
Oakland
CA
Toyota Motor Engineering and Manufacturing North America,
Inc.
Erlanger
KY
|
Family ID: |
40781619 |
Appl. No.: |
13/181631 |
Filed: |
July 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11937225 |
Nov 8, 2007 |
8003021 |
|
|
13181631 |
|
|
|
|
Current U.S.
Class: |
428/373 ;
427/215; 977/892 |
Current CPC
Class: |
C01B 19/007 20130101;
Y10S 977/762 20130101; B82Y 30/00 20130101; C01P 2004/04 20130101;
C01P 2002/72 20130101; Y10T 428/2929 20150115; C01P 2004/16
20130101 |
Class at
Publication: |
428/373 ;
427/215; 977/892 |
International
Class: |
B32B 9/00 20060101
B32B009/00; B05D 7/00 20060101 B05D007/00; B05D 5/00 20060101
B05D005/00 |
Claims
1. A method for producing nanowires comprising a PbSe core and a
PbS shell comprising the steps of: providing a core/shell growth
solution comprising PbSe nanowires; heating the core/shell growth
solution to a temperature sufficient to produce a PbS shell over
the PbSe nanowires; adding a Pb precursor solution to the
core/shell growth solution; and adding an S precursor solution to
the core/shell growth solution after the addition of the Pb
precursor to produce nanowires comprising a PbSe core and a PbS
shell.
2. The method of claim 1 wherein the core/shell growth solution
comprises tri-octyl phosphine (TOP) and diphenyl ether (DPE).
3. The method of claim 1 wherein the S precursor solution comprises
S and TOP.
4. The method of claim 1 wherein the core/shell growth solution was
heated to a temperature of about 130.degree. C.
5. The method of claim 1 further comprising heating the core/shell
growth solution after the addition of the PbSe nanowires to a
temperature of about 130.degree. C.
6. The method of claim 1 wherein the nanowire comprising a PbSe
core and a PbS shell comprise a thickness of about 11 nm.
7. A PbSe core/PbS shell nanowire produced by the method of claim
1.
8. A method for producing nanowires comprising a PbSe core and a
PbTe shell comprising the steps of: providing a Pb precursor
solution; adding a Te precursor solution to the Pb precursor
solution to produce a PbTe solution; providing a core/shell growth
solution heated to a temperature of about 150.degree. C., wherein
the core/shell growth solution comprises PbSe nanowires; and adding
the PbTe solution to the core/shell growth solution to form
nanowires comprising a PbSe core and a PbTe shell.
9. The method of claim 8 further comprising the step of reheating
the core/shell growth solution after the addition of the PbTe
solution to a temperature of about 130.degree. C.
10. The method of claim 8 further comprising isolating the
PbSe/PbTe core/shell nanowires from the core/shell growth solution
by centrifugation in the presence of toluene or ethanol.
11. The method of claim 8 wherein the core/shell growth solution is
heated to a temperature of about 190.degree. C. prior to the
addition of the PbTe solution.
12. The method of claim 8 wherein the Te precursor comprises Te and
TOP.
13. The method of claim 8 wherein the Te precursor is added
dropwise to the Pb precursor solution.
14. The method of claim 8 wherein the core/shell growth solution
comprises TOP and DPE.
15. The method of claim 8 wherein the PbTe shell comprises a
thickness of about 5 to about 30 nm.
16. The method of claim 8 wherein the nanowire comprising the PbSe
core and PbTe shell comprises a thickness of about 10 to about 45
nm.
17. A PbSe core/PbTe shell nanowire produced by the method of claim
1
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional application of U.S. patent
application Ser. No. 11/937,225 filed Nov. 8, 2007, which is
incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0002] Embodiments of the present invention are generally related
to the synthesis of nanoalloys and core/shell nanowires, and are
specifically related to methods of making PbSe.sub.xY.sub.1-x
nanoalloys and PbSe/PbY core/shell (Y.dbd.S, Te) nanowires.
BACKGROUND
[0003] Nanostructures (e.g., semiconductor nanostructures) provide
unique optical, physical and electrical properties, which makes
them the main building blocks in various devices such as
electronic, photonic, thermoelectric and sensor based devices. Due
to the numerous benefits provided, continual efforts are being made
develop new structures (e.g., semiconductor nanostructures) with
nanoscale dimensions; however, controlling the dimensions and the
shape of the nanostructures remains a challenge. When controlled,
the nanostructures may improve the optical and physical properties
of semiconductors by changing the band gap in the strong
confinement region, where one of the dimensions is smaller than the
corresponding excitonic Bohr diameter.
[0004] Semiconductor nanowires in the form of alloys or core/shell
systems may be utilized as materials for semiconductors and be
operable to yield various band gap energies. Also, Pb-chalcogenide
materials have been identified as effective nanostructures. For
example, Pb-chalcogenide materials are often utilized in
thermoelectric devices because of their low heat conductivity.
[0005] Accordingly, improved nanoalloys, as well as improved
methods of making these nanoalloys are desirable for use in
semiconductor nanostructures.
SUMMARY
[0006] According to one embodiment, a method for producing
nanowires comprising a PbSe core and a PbS shell is provided. The
method comprises providing a core/shell growth solution comprising
PbSe nanowires, heating the core/shell growth solution to a
temperature sufficient to produce a PbS shell over the PbSe
nanowires, adding a Pb precursor solution to the core/shell growth
solution; and adding an S precursor solution to the core/shell
growth solution after the addition of the Pb precursor to produce
nanowires comprising a PbSe core and a PbS shell.
[0007] According to yet another embodiment, a method for producing
nanowires comprising a PbSe core and a PbTe shell is provided. The
method comprises the steps of providing a Pb precursor solution,
adding a Te precursor solution to the Pb precursor solution to
produce a PbTe solution, providing a core/shell growth solution
heated to a temperature of about 150.degree. C., wherein the
core/shell growth solution comprises PbSe nanowires, and adding the
PbTe solution to the core/shell growth solution to form nanowires
comprising a PbSe core and a PbTe shell.
[0008] These and additional features provided by the embodiments of
the present invention will be more fully understood in view of the
following detailed description, in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The following detailed description of specific embodiments
of the present invention can be best understood when read in
conjunction with the drawings enclosed herewith.
[0010] FIG. 1A is a Transmission Electron Microscopy (TEM)
micrograph illustrating a PbSe core nanowire prior to the formation
of a ternary PbSe.sub.0.4S.sub.0.6 alloy shown in FIG. 1B,
according to one or more embodiments of the present invention;
[0011] FIG. 1B is a TEM micrograph illustrating a
PbSe.sub.0.4S.sub.0.6 alloy, according to one or more embodiments
of the present invention;
[0012] FIG. 2A is a TEM micrograph illustrating a PbSe core
nanowire prior to the coating of a PbS shell as shown in FIG. 2B,
according to one or more embodiments of the present invention;
[0013] FIG. 2B is a TEM micrograph illustrating a PbSe core with a
PbS shell thereon, according to one or more embodiments of the
present invention;
[0014] FIG. 3 is a High Resolution Transmission Electron Microscopy
(HRTEM) micrograph illustrating a PbSe core with a PbTe shell,
according to one or more embodiments of the present invention;
[0015] FIG. 4 is a powder X-Ray Diffraction (XRD) pattern of a
portion of the PbSe.sub.0.4S.sub.0.6 alloy of FIG. 1B, according to
one or more embodiments of the present invention;
[0016] FIG. 5 is an Electron Energy Loss Spectroscopy (EELS)
spectrum of a portion of the PbSe.sub.0.4S.sub.0.6 alloy of FIG.
1B, according to one or more embodiments of the present
invention;
[0017] FIG. 6 is a powder (XRD) pattern of the PbSe/PbS core/shell
of FIG. 2B, according to one or more embodiments of the present
invention;
[0018] FIG. 7 is a flow chart illustrating the method of producing
PbSe nanowires;
[0019] FIG. 8 is a flow chart illustrating the method of producing
PbSe.sub.xY.sub.1-x (Y.dbd.Te or S) alloys, according to one or
more embodiments of the present invention.
[0020] FIG. 9 is a flow chart illustrating the method of producing
PbSe/PbS core/shell alloys, according to one or more embodiments of
the present invention.
[0021] FIG. 10 is a flow chart illustrating the method of producing
PbSe/PbTe core/shell alloys, according to one or more embodiments
of the present invention.
[0022] The embodiments set forth in the drawings are illustrative
in nature and not intended to be limiting of the invention defined
by the claims. Moreover, individual features of the invention will
be more fully apparent and understood in view of the detailed
description.
DETAILED DESCRIPTION
[0023] Embodiments of the present invention are directed to methods
of making PbSe.sub.xY.sub.1-x alloy nanowire and PbSe/PbY
core/shell nanowires, where Y.dbd.S or Te. As used herein, an
"alloy" is a structure comprising a mixture of one or more metal
elements. As used herein, a "core/shell" is a structure comprising
a "core" metal based material and at least one separate coating
layer ("the shell") thereon, wherein the shell may comprise the
same or a different composition than the core composition. As will
be shown below, the processing steps can dictate whether the
product is in the form of an alloy nanowire or in the form of a
core/shell nanowire.
[0024] Referring generally to the flow charts of FIGS. 7 and 8, the
methods for producing PbSe.sub.xY.sub.1-x alloys can include the
initial steps of preparing a PbSe nanowire and a PbY solution
(Y.dbd.S or Te). As shown in FIG. 8, PbSe nanowires may be produced
by mixing a Pb precursor solution with a Se precursor solution, in
conjunction with additional treatment steps.
[0025] Referring to FIG. 7, the PbSe nanowire synthesis may include
a Pb precursor solution comprised of 0.76 g of lead acetate
trihydrate and 2 mL of oleic acid dissolved in 10 mL of diphenyl
ether (DPE). This Pb precursor solution can be heated to
150.degree. C. for at least 30 minutes in argon atmosphere to form
a lead oleate complex. Then, the solution can be then dried. After
about 30-40 min, the solution can be cooled to 60.degree. C., and
mixed with a selenium (Se) solution comprising, for example, 4 mL
of 0.167 M TOPSe solution in tri-octyl phosphine (TOP). The Se
solution can be added slowly to prevent PbSe nucleation. The PbSe
solution can then be injected under vigorous stirring into a heated
growth solution (e.g., 250.degree. C.) containing 0.2 g of
Tetradecyl phosphonic acid (TDPA) dissolved in 15 mL of DPE. The
growth solution can be purified by heating to 180.degree. C. After
about 50 s of heating, the reaction mixture can be cooled to room
temperature using a water bath. The crude solution can then be
mixed with an equal volume of hexane. The nanowires can then be
isolated by centrifugation at 6000 rpm for 5 min. The precipitated
product from the centrifuge can be re-dispersed in chloroform or
toluene for further characterization. FIG. 1A provides a TEM
micrograph illustration of the PbSe nanowires produced by the
foregoing synthesis method. The diameter of produced PbSe nanowires
can vary from 4 nm up to 15 nm, with a length of up to 50
micrometers. It should be understood, however, that the foregoing
embodiment for preparing the PbSe nanowires is exemplary and other
methods are contemplated for producing PbSe nanowires.
[0026] To prepare the PbY solution as shown in FIG. 8, a Pb
precursor solution is mixed with a Y precursor solution. Like
above, the Pb precursor solution may comprise a lead oleate complex
formed from a mixture of lead acetate trihydrate, oleic acid, and
diphenyl ether (DPE). The Y precursor solution may include S or Te
in a solution comprising tri-octyl phosphine (TOP), or suitable
solvents such as Octadecene, Tributyl phospine, Triphenyl
phosphine. In an experimental example, an S precursor solution can
be prepared by dissolving 0.1 g of S in 0.5 ml of TOP and heating
the solution to 50.degree. C. for 10 minutes before cooling to room
temperature. The Pb precursor solution can be prepared using 0.2 g
of lead acetate trihydrate, 2 ml of TOP, 2 ml of DPE and 1.5 ml of
oleic acid. The Pb solution can be heated to 150.degree. C. for 30
minutes and then cooled to room temperature. At room temperature,
the S precursor solution can be added to the Pb precursor solution
under stirring. Other compositions and processing steps for the
production of Pb and Y precursor solutions are contemplated
herein.
[0027] After the PbSe nanowires are prepared, the PbSe nanowires
can be delivered to an growth solution. They can act as a medium
for the reaction of the PbSe nanowires and the PbY solution. The
growth solution may comprise TOP and DPE, or other suitable
materials. As mentioned before, the trialkyl phosphine, or trialkyl
amine may be used as solvents. These solvents are compatible to the
nanowire surface (via a Lewis acid/base reaction mechanism) and can
also dissolve the chalcogenide metals. When adding the PbSe
nanowires, the growth solution may be maintained at ambient
temperature; however, other suitable temperatures are contemplated
herein. In one experimental example, the growth solution may
comprise 2 ml of DPE and 2 ml TOP, which is heated at 180.degree.
C. for 20-25 minutes and then cooled to room temperature before
adding 30 mg of PbSe nanowires.
[0028] After the PbSe nanowires are added to the growth solution,
the growth solution is heated to a temperature of at least
150.degree. C., (e.g., the PbY solution described above) or in one
embodiment, between about 190 to about 200.degree. C. Subsequently,
the PbY solution is added. The PbY may be added slowly to prevent
self-nucleation, or the formation of undesirable crystal
structures. In one embodiment, a PbS solution was added dropwise at
a rate of about 0.25 ml/min.
[0029] Additional treatment steps are contemplated for the
formation of the PbSe.sub.xY.sub.1-x alloy. For example, the growth
solution can be annealed for 10 minutes and then cooled to room
temperature. The alloy product can then be separated by adding
hexane and centrifuging at 6000 rpm for 5 min.
[0030] In accordance with the exemplary methods provided above, a
ternary PbSe.sub.xY.sub.1-x alloy may be formed and may comprise a
composition of PbSe.sub.0.4S.sub.0.6, such as shown in the TEM
micrograph of FIG. 1B. Other suitable compositions of
PbSe.sub.xY.sub.1-x are also contemplated. The inventors have
recognized that the above described processing steps facilitate
diffusion between the PbSe core and the PbY shell, and thus produce
a ternary nanoalloy, not a core/shell nanowire. The diffusion
process may be divided into two stages. In the first stage,
addition of the PbY (e.g., Y.dbd.S) solution to the PbSe nanowire
solution results in the growth of the PbS as a shell. In the second
stage, multiple factors (i.e. high temperature, small diameter of
the PbSe core and the small lattice mismatch between the PbSe core
and PbY) facilitate diffusion between the core and shell to form
the alloy. For example, heating the growth solution prior to
addition of the PbS solution facilitates greater particle movement
between the PbSe nanowire core and PbS shell. Since smaller
diameter nanowires are more reactive and less energetically stable,
minimizing the diameter of the PbSe nanowires also aids diffusion.
In one embodiment, such as that described above, the PbSe nanowires
have a diameter between about 4 and 15 nm. Furthermore, the small
lattice mismatch between the PbSe core and the PbY shell
(D.sub.PbSe/D.sub.PbS.about.3% and D.sub.PbSe/D.sub.PbTe.about.5%;
where D is the lattice constant of the crystals) facilitates
further diffusion.
[0031] To demonstrate the alloys formed by methods described
herein, such as the PbSe.sub.0.4S.sub.0.6 alloy, FIGS. 4 and 5 are
provided. As illustrated in the EDX (Energy Dispersive X-ray
Spectroscopy) spectrum of FIG. 4, the intensity pattern differs
from both cubic PbSe and cubic PbS, and is disposed between the
peaks of the cubic PbSe and cubic PbS. This pattern demonstrates
that the alloy product does not comprise distinct PbSe and PbS
compositions, which would be present in core/shell configuration.
As shown in the Electron Energy Loss Spectroscopy (EELS) spectrum
of FIG. 5, S was identified at 165 eV. Furthermore, as the PbSe
nanowires were converted into PbSe.sub.0.4S.sub.0.6 alloys, a
change in diameter from 6 nm to about 10 nm was observed due to the
addition of the PbS materials.
[0032] In addition to the methods of forming alloys, the present
invention is also directed to core/shell synthesis, for example,
methods for producing core/shell nanowires comprising a PbSe core
and a PbS shell are contemplated. Referring to FIG. 9, the shell
synthesis is based on the Successive Ion Layer Adsorption and
Reaction (SILAR) approach, an approach for growing shells over core
materials with nanoscale dimensions. In the SILAR approach, growth
of the shell is designed to grow one monolayer at a time by
alternating the addition of cationic (Pb precursor solution) and
anionic (S precursor solution) precursors into a core/shell growth
solution comprising PbSe nanowires. The core/shell growth solution
may also comprise solvents such as tri-octyl phosphine (TOP) and
diphenyl ether (DPE). In accordance with the methods, Pb precursor
solution is added to the core/shell growth solution Like the above
methods of forming the alloy, the Pb precursor solution may
comprise a lead oleate complex. Subsequently, an S precursor
solution (e.g., S in a TOP solution) is added to the core/shell
growth solution which contains the PbSe nanowires and Pb precursor
solution. Then, the core/shell growth solution is heated to a
temperature sufficient to produce the PbS shell. In one embodiment,
the PbS shell can be produced by heating the core/shell growth
solution to a temperature of about 130.degree. C. By using lower
heating temperatures than the methods of forming the alloys
described above, the amount of diffusion between core and shell is
minimized and the core/shell configuration is thereby maintained.
In further embodiments, the addition of Pb and S precursor solution
may be repeated multiple to increase the thickness of the PbS
shell. Other treatment steps are contemplated herein.
[0033] In an experimental example, the synthesis of PbSe/PbS
core/shell nanowires was carried out by slowly adding 0.3 ml of a
Pb precursor solution and 0.1 ml of an S precursor solution (0.063
g/2 ml TOP) to a core/shell growth solution comprising PbSe
nanowires. The Pb precursor solution is added first and then the S
precursor solution is added at a rate of 0.3 ml/min after a waiting
time of three minutes. In addition to PbSe nanowires, the
core/shell growth solution contained 2 ml of DPE and 2 ml of TOP
and was purified by heating to 200.degree. C. for 25 minutes. After
addition of the Pb and S precursors, the solution was reheated to
130.degree. C. The PbSe/PbS core/shell nanowire product, as shown
in FIG. 2B, had a thickness of about 11 nm. The inventors recognize
that the thickness of the shell, and thereby the thickness of the
nanowire may be adjusted by modifying the concentration of the
precursors.
[0034] FIG. 6 is an XRD spectrum of core/shell nanowire
manufactured pursuant the forgoing example. As shown, two sets of
peaks are identified in the XRD pattern thus indicating the
existence of two different crystal structures (i.e., the PbSe and
PbS crystal structures). The XRD measurement was carried out after
purifying the sample and extracting the PbSe/PbS core/shell
nanowires. The sample was washed and purified by size selective
precipitation (PbS nanocrystals were formed in the shell
growth).
[0035] Furthermore, the methods of the present invention are also
directed to producing core/shell nanowires comprising a PbSe core
and a PbTe shell. Referring to FIG. 10, the synthesis of the
PbSe/PbTe core/shell materials is essentially a two-step synthesis,
wherein the PbSe nanowires were prepared first and the shell was
grown in a second stage. The PbSe nanowire core may be prepared
according to the synthesis method described above and as shown in
FIG. 7. To prepare the PbTe shell, a Pb precursor solution is
prepared and then a Te precursor is added to the Pb precursor to
produce a PbTe solution. Similar to above, the Pb precursor
solution may comprise a lead oleate complex, and the Te precursor
may comprise Te and TOP. The Te precursor may be added dropwise, or
in low concentration to prevent self-nucleation i.e. the formation
of PbTe nanocrystals instead of a PbTe shell. As described below,
self-nucleation is a more significant problem for PbSe nanowires of
greater surface area.
[0036] After forming the PbTe solution, the PbTe solution is added
to a core/shell growth solution comprising PbSe nanowires in order
to form PbTe shells over the PbSe nanowires. The core/shell growth
solution may be heated to a temperature above 150.degree. C., or
specifically about 190.degree. C. Like the above methods, the
core/shell growth solution may comprise TOP and DPE.
[0037] In an experimental example, the growth of the shell was
carried out by addition of 0.07 mg of Pb (the same Pb precursor
solution used for the alloy) and 0.063 g of Te in 2 ml TOP. The Pb
solution was dried by heating to 140.degree. C. for 10 minutes, and
then cooled. After cooling to room temperature, the Te solution was
added dropwise. This PbTe solution was then slowly added to the
core/shell growth solution (at 190.degree. C.), which contained 2
ml of TOP, 2 ml of DPE and 20 mg of PbSe nanowires. After adding
all of the precursors, the reaction was annealed at 130.degree. C.
for another 7 minutes before cooling to room temperature. To
separate the product, 2 ml of toluene and 2 ml of ethanol were
added to the solution, which was then centrifuged for 5
minutes.
[0038] The experimental example above produced a PbSe/PbTe
core/shell nanowire as shown in FIG. 3. The PbSe/PbTe core/shell
nanowire comprised a final thickness of 40 nm, whereas the
thickness prior to the addition of the PbTe shell coating is
.about.8 nm. The shell thickness may be adjusted by changing the
concentrations of the Pb and Te precursor solutions. Consequently,
the PbTe shell may comprise a thickness of about 5 to about 30 nm,
and the core/shell nanowire may comprise a thickness of about 10 to
about 45 nm. Shell thickness impacts the physical and optical
properties of the PbSe cores, thus the shell thickness may be
optimized to produce the best nanowire performance.
[0039] As discussed above, the coating of the PbTe shell material
on the PbSe is carried out at higher temperature compared with the
PbS shell. In specific examples, the PbS shell is formed in a
core/shell growth solution heated to 130.degree. C., whereas the
PbTe shell is formed in a core/shell growth solution heated to
190.degree. C. This is due in part to the higher lattice mismatch
for PbTe (PbTe, 5.5% vs. PbS 3.0%). Due to this higher lattice
mismatch, higher temperatures are required to grow a uniform PbTe
shell over the PbSe core. The processing steps are also optimized
to combat unwanted side reactions (e.g., self-nucleation of the
PbTe). When PbSe nanowires have a large surface area, shell
formation may be difficult, due to the possibility of forming
clusters and islands of the shell material on the core surface. In
the foregoing experimental example, the inventor minimized
potential unwanted cluster formation by annealing the solution for
7 minutes in 130.degree. C. to form a uniform and single
crystalline shell coating.
[0040] For the purposes of describing and defining the present
invention it is noted that the terms "substantially" and "about"
are utilized herein to represent the inherent degree of uncertainty
that may be attributed to any quantitative comparison, value,
measurement, or other representation. The terms "substantially" and
"about" are also utilized herein to represent the degree by which a
quantitative representation may vary from a stated reference
without resulting in a change in the basic function of the subject
matter at issue.
[0041] Having described the invention in detail and by reference to
specific embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims. More
specifically, although some aspects of the present invention are
identified herein and illustrated in the figures, it is
contemplated that the present invention is not necessarily limited
to these aspects of the invention.
* * * * *