U.S. patent application number 12/590663 was filed with the patent office on 2010-03-18 for apparatus and method for making carbon nanotube array.
This patent application is currently assigned to Tsinghua University. Invention is credited to Shou-Shan Fan, Kai-Li Jiang, Kai Liu.
Application Number | 20100064973 12/590663 |
Document ID | / |
Family ID | 37001931 |
Filed Date | 2010-03-18 |
United States Patent
Application |
20100064973 |
Kind Code |
A1 |
Jiang; Kai-Li ; et
al. |
March 18, 2010 |
Apparatus and method for making carbon nanotube array
Abstract
An apparatus for making an array of carbon nanotubes includes a
reaction chamber with a gas inlet and a gas outlet, a quartz boat
disposed in the reaction chamber, a substrate with a surface
deposited with a film of first catalyst, and a second catalyst
disposed in the quartz beside the substrate. The substrate is
disposed in the quartz boat.
Inventors: |
Jiang; Kai-Li; (Beijing,
CN) ; Liu; Kai; (Beijing, CN) ; Fan;
Shou-Shan; (Beijing, CN) |
Correspondence
Address: |
PCE INDUSTRY, INC.;ATT. Steven Reiss
288 SOUTH MAYO AVENUE
CITY OF INDUSTRY
CA
91789
US
|
Assignee: |
Tsinghua University
Beijing
CN
HON HAI PRECISION INDUSTRY CO., LTD.
Tu-Cheng
TW
|
Family ID: |
37001931 |
Appl. No.: |
12/590663 |
Filed: |
November 12, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11371997 |
Mar 8, 2006 |
|
|
|
12590663 |
|
|
|
|
Current U.S.
Class: |
118/728 ;
977/843 |
Current CPC
Class: |
C30B 29/02 20130101;
C23C 16/26 20130101; Y10S 427/102 20130101; C30B 29/605 20130101;
C30B 25/02 20130101; C23C 16/0281 20130101; C23C 16/448
20130101 |
Class at
Publication: |
118/728 ;
977/843 |
International
Class: |
C23C 16/458 20060101
C23C016/458; C23C 16/00 20060101 C23C016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2005 |
CN |
200510033733.6 |
Claims
1. An apparatus for making an array of carbon nanotubes,
comprising: a reaction chamber having a gas inlet introducing a
carbon source gas and a carrier gas thereinto and a gas outlet; a
substrate having a layer of first catalyst provided thereon, the
substrate being disposed in the reaction chamber; and a second
catalyst reacting with the carbon source gas thereby producing a
resultant product promoting catalytic activity of the first
catalyst, wherein the reaction chamber defines a first carbon
source gas route towards the substrate; the second catalyst is
disposed on the route.
2. The apparatus as claimed in claim 1, further comprising a boat
supporting the substrate.
3. The apparatus as claimed in claim 2, wherein the boat is a
quartz boat.
4. The apparatus as claimed in claim 2, wherein the second catalyst
is disposed proximate to the substrate.
5. The apparatus as claimed in claim 1, wherein the second catalyst
is comprised of iron, nickel, and alumina.
6. The apparatus as claimed in claim 1, wherein the first catalyst
is comprised of iron, cobalt, nickel, and any combination alloy
thereof
7. The apparatus as claimed in claim 1, wherein the reaction
chamber is substantially tubular-shaped.
8. An apparatus for making an array of carbon nanotubes,
comprising: a reaction chamber having a gas inlet introducing a
carbon source gas and a carrier gas thereinto and a gas outlet; a
substrate having a layer of first catalyst provided thereon, the
substrate being disposed in the reaction chamber; a second catalyst
reacting with the carbon source gas thereby producing a resultant
product promoting catalytic activity of the first catalyst; and a
tubular boat receiving the substrate and the second catalyst
therein, the tubular boat having an open end introducing the carbon
source gas thereinto and an opposite closed end blocking and
directing the introduced carbon source gas in the boat to flow
toward the substrate, wherein the second catalyst is disposed in
the boat in a manner to enable the resultant product associated
with the second catalyst to forcedly flow toward the substrate.
9. The apparatus as claimed in claim 8, wherein the boat includes a
bottom and at least one sidewall extending from the bottom; the
second catalyst is disposed on the bottom and between the substrate
and the at least one sidewall of the boat.
10. An apparatus for making an array of carbon nanotubes,
comprising: a reaction chamber having a gas inlet and a gas outlet;
a hollow container disposed in the reaction chamber and having only
one opening oriented to the gas inlet; a substrate contained in the
hollow container, the substrate having a top surface, a bottom
surface contacting the hollow container, and a side surface
extending from the top surface to the bottom surface; a first
catalyst disposed on the top surface; a second catalyst contained
in the hollow container and distributed along the side surface of
the substrate except at parts of the side surface facing the gas
inlet.
11. The apparatus as claimed in claim 10, wherein the hollow
container comprises a sidewall and a peripheral wall extending from
a periphery of the sidewall towards the gas inlet.
12. The apparatus as claimed in claim 11, wherein both the bottom
surface and the second catalyst directly contact the peripheral
wall of the hollow container.
13. The apparatus as claimed in claim 12, wherein the second
catalyst contacts the side surface except at the parts of the side
surface facing the gas inlet.
14. The apparatus as claimed in claim 13, wherein the first
catalyst is comprised of iron, cobalt, nickel, and any combination
alloy thereof.
15. The apparatus as claimed in claim 13, wherein the second
catalyst is metallic powder or netting made of pure iron or
nickel.
16. The apparatus as claimed in claim 11, wherein the peripheral
wall perpendicularly extends from the periphery of the sidewall and
defines the only one opening.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of patent
application Ser. No. 11/371,997 filed on Mar. 8, 2006 from which it
claims the benefit of priority under 35 U.S.C. 120. The patent
application Ser. No. 11/371,997 in turn claims the benefit of
priority under 35 USC 119 from Chinese Patent Application
200510033733.6, filed on Mar. 8, 2005.
BACKGROUND
[0002] 1. Technical Field
[0003] The disclosure relates generally to apparatuses and methods
for making carbon nanotubes, and more particularly to an apparatus
and a method for making an array of carbon nanotubes.
[0004] 2. Discussion of Related Art
[0005] Carbon nanotubes were discovered by S. Iijima in 1991, they
are very small tube-shaped structures, each essentially having
composition similar to that of a graphite sheet rolled into a tube.
Theoretical studies showed that carbon nanotubes exhibit either
metallic or semiconductive behavior depending on the radii and
helicity of the tubules. Carbon nanotubes have interesting and
potentially useful electrical and mechanical properties, and have
many potential uses in electronic devices. Carbon nanotubes also
feature extremely high electrical conductivity, very small
diameters (much less than 100 nanometers), large aspect ratios
(i.e. length/diameter ratios greater than 1000), and a tip-surface
area near the theoretical limit (the smaller the tip-surface area,
the more concentrated the electric field, and the greater the field
enhancement factor). These features make carbon nanotubes ideal
candidates for electron field emitters, white light sources,
lithium secondary batteries, hydrogen storage cells, transistors,
and cathode ray tubes (CRTs).
[0006] Generally, there are three methods for manufacturing carbon
nanotubes. The first method is the arc discharge method, which was
first discovered and reported in an article by Sumio Iijima
entitled "Helical Microtubules of Graphitic Carbon" (Nature, Vol.
354, Nov. 7, 1991, pp. 56-58). The second method is the laser
ablation method, which was reported in an article by T. W. Ebbesen
et al. entitled "Large-scale Synthesis of Carbon Nanotubes"
(Nature, Vol. 358, 1992, pp. 220). The third method is the chemical
vapor deposition (CVD) method, which was reported in an article by
W. Z. Li entitled "Large-scale Synthesis of Aligned Carbon
Nanotubes" (Science, Vol. 274, 1996, pp. 1701).
[0007] In the arc discharge method, a carbon vapour is created by
an arc discharge between two carbon electrodes either with or
without a catalyst. Carbon nanotubes self-assemble from the
resulting carbon vapour. In the laser ablation technique,
high-powered laser pulses impinge on a volume of carbon-containing
feedstock gas (methane or carbon monoxide). Carbon nanotubes are
thus condensed by the laser ablation and are deposited on an
outside collector. However, the carbon nanotubes produced by the
arc discharge and the laser ablation vary greatly in diameter and
length, with little control over the dimensions of the resulting
product. Moreover, poor carbon nanotube yield and prohibitive cost
involved in making the device mean that the two methods difficult
to scale up to suit industrial production.
[0008] In the chemical vapour deposition (CVD) method, carbon
filaments and fibers are produced by thermal decomposition of a
hydrocarbon gas on a transition metal catalyst in a chemical vapour
deposition reaction chamber. In general, the chemical vapour
deposition process results in both multi-walled nanotubes (MWNTs)
and single-walled nanotubes (SWNTs) being produced. Compared with
the arc discharge method and laser ablation method, the chemical
vapour deposition method is a more simple process and can easily be
scaled up for industrial production. However, the carbon nanotubes
manufactured by the chemical vapour deposition process aren't
bundled to form an array, thus the CVD process can't assure both
quantity and quality of production.
[0009] In view of the above, another method, such as a thermal
chemical vapor deposition method is disclosed where an array of
carbon nanotubes are formed vertically aligned on a large-size
substrate. The thermal CVD method includes the steps of: forming a
metal catalyst layer on a substrate; etching the metal catalyst
layer to form isolated nano-sized catalytic metal particles;
growing carbon nanotubes from said isolated nano-sized catalytic
metal particles by the thermal chemical vapor deposition (CVD)
process; and purifying the carbon nanotubes in-situ.
[0010] The carbon nanotubes formed by the above-described methods
are vertically aligned on the substrate. However, the devices used
in above-described method are complicated. Several gas inlets are
disposed in the device for introducing different gases. Also the
carbon nanotubes formed by the above-described devices and methods
are generally comprised of a mix of MWNTs and SWNTs. The mixed
carbon nanotubes do not sufficiently exhibit the useful properties
of a single-type array of carbon nanotubes. Furthermore, excess
amorphous carbon lumps and metal catalyst lumps are also produced
along with the carbon nanotubes formed by the above-described
devices and methods and adhere to inner or outer sidewalls of the
carbon nanotubes. Thus, a complicated purification device and
method is required in addition to the above-described devices
methods. Moreover, the devices used in the above-described method
generally operate at temperatures in the range from 700.degree. C.
to 1000.degree. C. for growing carbon nanotubes, thus requiring a
highly heat-resistant reaction chamber. Therefore, the devices in
the above-described method for making the carbon nanotubes are
limited.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Many aspects of the embodiments can be better understood
with references to the following drawings. The components in the
drawings are not necessarily drawn to scale, the emphasis instead
being placed upon clearly illustrating the principles of the
embodiments.
[0012] FIG. 1 is a schematic, cutaway view of an apparatus for
making an array of carbon nanotubes in accordance with a first
embodiment of the present disclosure;
[0013] FIG. 2 is a top view of a quartz boat with a substrate and a
second catalyst thereon of FIG. 1;
[0014] FIG. 3 is a schematic, cutaway view of an apparatus for
making an array of carbon nanotubes in accordance with a second
embodiment of the present disclosure;
[0015] FIG. 4 is a cross-sectional, top view of a quartz boat of
FIG. 3;
[0016] FIG. 5 is a side view of the quartz boat of FIG. 3;
[0017] FIG. 6 shows a Scanning Electron Microscope (SEM) image of
the array of carbon nanotubes formed by the apparatus of FIG. 1;
and
[0018] FIG. 7 shows a Transmission Electron Microscope (TEM) image
of the array of carbon nanotubes formed by the apparatus of FIG.
1.
[0019] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set out
herein illustrate at least one preferred embodiment of the
disclosure, in one form, and such exemplifications are not to be
construed as limiting the scope of the disclosure in any
manner.
DETAILED DESCRIPTION
[0020] Reference will now be made to the drawings to describe
embodiments of the present apparatus and method for making an array
of carbon nanotubes, in detail.
[0021] Referring to FIGS. 1 and 2, an apparatus 100 in accordance
with a first embodiment of the present device is provided. The
apparatus 100 includes a reaction chamber 190, a quartz boat 150, a
substrate 110, a first catalyst 130 and a second catalyst 170. The
reaction chamber 190 can be a tubular container. A gas inlet 192
and a gas out let 194 are located at two opposite ends of the
reaction chamber 190 respectively. In the preferred embodiment, the
gas inlet 192 is for introducing a carrier gas and a carbon source
gas. The quartz boat 150 is disposed in the reaction chamber 190.
The quartz boat 150 can be opened at two opposite ends. In the
preferred embodiment, the quartz boat 150 is cymbiform.
Alternatively, the quartz boat 150 could be made by other suitable
materials. The substrate 110 is disposed on the bottom of the
quartz boat 150. The film of catalyst 130 is uniformly disposed on
the surface of the substrate 110 by means of chemical vapor
deposition, thermal deposition, electron-beam deposition, or
sputtering. The first catalyst 130 can be made of iron (Fe), cobalt
(Co), nickel (Ni), or any combination alloy thereof. In the
preferred embodiment, the first catalyst 130 is made of iron. The
second catalyst 170 is disposed proximate to the substrate 110. The
second catalyst 170 and the substrate 110 are disposed on the
bottom of the quartz boat 150. The second catalyst 170 is placed
beside one side of the substrate 110. The second catalyst 170 can
be either metallic powder or netting made of iron, nickel or
alumina. In the preferred embodiment, the second catalyst 170 is
iron powder. In the first embodiment, a first route is defined in
the reaction chamber 190 for the introduced carbon source gas flow
from the second catalyst 170 toward the substrate 110. The second
catalyst 170 is disposed on the route. The second catalyst 170 can
pyrolize the introduced carbon source gas to produce a small amount
of hydrogen gas which then flows toward the substrate 110. In the
preferred embodiment, the second catalyst 170 is disposed proximate
to one side of the substrate 110 facing the gas inlet 192. The
additional hydrogen activates the first catalyst 130 and reduces
the concentration of carbon source gas around the first catalyst
130. Therefore, the growth speed of the carbon nanotubes is
increased and the height of the array of the carbon nanotubes is
enhanced. In addition, advantageously, the hydrogen produced by the
second catalyst 170 and the carbon source gas can reach the first
catalyst 130 along the route and activate the first catalyst 130 to
improve the growing speed of the carbon nanotubes.
[0022] Referring to FIGS. 3, 4 and 5, an apparatus 200 in
accordance with a second embodiment of the present device is
provided. The apparatus 200 includes a reaction chamber 290, a
quartz boat 250, a substrate 210, a first catalyst 230 and a second
catalyst 270. The reaction chamber 290 can be a tubular container.
A gas inlet 292 and a gas out let 294 are located at two ends of
the reaction chamber 290 respectively. In the preferred embodiment,
the gas inlet 292 is for introducing a carrier gas and a carbon
source gas. The quartz boat 250 is disposed in the reaction chamber
290. The quartz boat 250 includes an open end. In the preferred
embodiment, the quartz boat 250 is tubular with one open end facing
towards the gas inlet 292. The substrate 210 is disposed in the
quartz boat 250. The film of first catalyst 230 is uniformly
disposed on the surface of the substrate 210 by means of chemical
vapor deposition, thermal deposition, electron-beam deposition, or
sputtering. The first catalyst 130 can be made of iron (Fe), cobalt
(Co), nickel (Ni), or any combination alloy thereof. In the
preferred embodiment, the first catalyst 230 is made of iron. The
second catalyst 270 is disposed proximate to the substrate 110. The
quartz boat 250 includes a bottom and at least one sidewall
extending from the bottom, the second catalyst 270 is disposed on
the bottom and between the substrate 210 and the at least one
sidewall of the quartz boat 250. The second catalyst 270 and the
substrate 210 are disposed on the bottom of the quartz boat 250.
The second catalyst 270 can be either metallic powder or metal
netting made of iron, nickel or alumina. In the preferred
embodiment, the second catalyst 270 is iron powder. In the second
embodiment, a second route is defined in the quartz boat 250 for
the introduced carbon source gas flow from the second catalyst 270
toward the substrate 210. The second catalyst 270 is disposed
beside three sides of the substrate 210 far from the gas inlet 292.
The second catalyst 270 pyrolizes the carbon source gas to produce
small quantities of hydrogen gas which flows towards the first
catalyst 230. The additional hydrogen activates the first catalyst
230 and reduces the concentration of carbon source gas around the
first catalyst 230. Therefore, the growth speed of the carbon
nanotubes is increased and the height of the array of the carbon
nanotubes is improved. In addition, advantageously, the hydrogen
produced by the second catalyst 270 and the carbon source gas can
reach the first catalyst 230 along the second route and activate
the first catalyst 230 to improve the growing speed of the carbon
nanotubes.
[0023] A preferred method for making an array of carbon nanotubes
using the present apparatus is provided. In the preferred
embodiment, the method is based on the first embodiment and
includes the following steps in no particularly order thereof.
Firstly, a substrate 110 with a surface is provided, and a film of
first catalyst 130 is formed on a surface of the substrate 110. The
film of first catalyst 130 is uniformly disposed on the substrate
110 by means of chemical vapor deposition, thermal deposition,
electron-beam deposition, or sputtering.
[0024] Secondly, a quartz boat 150 and a second catalyst 170 are
provided. The second catalyst 170 and the substrate 110 are
disposed on a bottom of the quartz boat 150. The second catalyst
170 is disposed proximate to the substrate 110.
[0025] Thirdly, a horizontal reaction chamber 190 with a gas inlet
192 and a gas outlet 194 is provided. The gas inlet 192 is for
introducing a carrier gas and a carbon source gas. The quartz boat
150 is disposed on a bottom of the reaction chamber 190. A first
route is defined in the reaction chamber 190 for the introduced
carbon source gas flow from the second catalyst 170 to the
substrate 110. The second catalyst 170 and the substrate 110 are
disposed on the route. In the preferred embodiment, the second
catalyst 170 is disposed proximate to at least one side of the
substrate 110 far from the gas outlet 194.
[0026] Fourthly, a carrier gas is continuously introduced into the
reaction chamber 190 from the gas inlet 192 at one atmosphere of
pressure. The carrier gas is used to create an atmosphere of inert
gas in the reaction chamber 190. Then, the reaction chamber 190 is
heated gradually to a predetermined temperature. A carbon source
gas which mixes with the carrier gas is introduced into the
reaction chamber 190 from the gas inlet 192. The carrier gas can be
a nitrogen (N.sub.2) gas or a noble gas. The carbon source gas can
be ethylene (C.sub.2H.sub.4), methane (CH.sub.4), acetylene
(C.sub.2H.sub.2), ethane (C.sub.2H.sub.6) or any combination
thereof. In the preferred embodiment, the carrier gas is argon
(Ar), the carbon source gas is acetylene. A ratio of the carrier
gas flow-rate to the carbon source gas flow-rate can be adjusted in
the range from 5:1 to 10:1. In the preferred embodiment, the argon
flow-rate is 300 sccm (Standard Cubic Centimeter per Minute), and
the acetylene flow-rate is 30 sccm. The predetermined temperature
used in the method can be in the range from 600 to 720.degree. C.
In the preferred embodiment, the predetermined temperature is in
the range from 620 to 690.degree. C.
[0027] Due to catalyzing by the first catalyst 130, the carbon
source gas supplied into the reaction chamber 190 is pyrolized in a
gas phase into carbon units (C.dbd.C or C) and free hydrogen
(H.sub.2). The carbon units are absorbed on a free surface of the
first catalyst 130 and diffused into the first catalyst 130. When
the first catalyst 130 is supersaturated with the dissolved carbon
units, carbon nanotube growth is initiated. As the intrusion of the
carbon units into the first catalyst 130 continues, an array of
carbon nanotubes is formed. The array of the carbon nanotubes
formed by the preferred embodiment is a multi-walled carbon
nanotube array. Density, diameter and length of the multi-walled
carbon nanotube array can be controlled by adjusting the flow rates
of the carbon source gas and the carrier gas, and by altering the
predetermined temperature and the reaction time. In addition, the
second catalyst 170 used in the first embodiment can act on the
carbon source gas. The second catalyst 170 can pyrolize the carbon
source gas to produce a small amounts of hydrogen gas which flows
to the first catalyst 130. The additional hydrogen produced by the
second catalyst 170 can activate the first catalyst 130, and
further reduce the concentration of the carbon source gas around
the first catalyst 30. As such, the growth speed of the carbon
nanotubes is increased and the height of the array of the carbon
nanotubes is enhanced. In the preferred first embodiment, the
reaction time is in the range from 30 to 60 minutes. The synthesis
method can produce carbon nanotubes with a length greater than
3-400 micrometers, and have a diameter in the range from 10 to 30
nanometers.
[0028] Referring to FIGS. 6 and 7, an SEM image and a TEM image of
the multi-walled carbon nanotube array formed by the present device
are shown. It can be seen that the-carbon nanotubes in the array of
the carbon nanotubes are highly bundled and super-aligned. The
height of the array of the carbon nanotubes is about 300
micrometers.
[0029] In the present apparatus and method, the second catalyst
170, 270 can be metallic powder or netting made of pure iron or
nickel. During the synthesis process of the array of the carbon
nanotubes, the second catalyst 170, 270 pyrolizes the carbon source
gas to produce small amounts of hydrogen. The hydrogen can activate
the first catalyst 130, 230 and reduce the consistency of the
carbon source gas around the first catalyst 130, 230. As such, the
growth speed of the carbon nanotubes is improved and the height of
the array of the carbon nanotubes can be from a few hundred
micrometers to a few millimeters.
[0030] In the preferred methods, the method for making the second
catalyst 170, 270 powder includes the following steps in no
particular order thereof Firstly, a powder of about 11.32 grams of
ferric nitrate and about 8 g of alumina are immersed in an ethanol
solution of 100 milliliters. Secondly, the mixture solution is
stirred for about eight hours, and then vaporized by a revolving
evaporator for about 12 hours at a temperature of about 80.degree.
C. Thirdly, the remainder after vaporizing is ball milled to
produce a second catalyst powder. In addition, the second catalyst
170, 270 powder used in the present apparatus and method can be
recycled. After the synthesis process of the array of the carbon
nanotubes, the second catalyst 170, 270 powder can be collected
from the quartz boat 150, 250. Then, the collected powder can be
burned in an oxygen atmosphere to remove the carbon nanotubes and
amorphous carbon which adhere to the second catalyst 170, 270. As
such, the second catalyst 170, 270 powder can be used many times
and thus the use of the second catalyst adds almost no additional
cost.
[0031] Furthermore, it is noted that, the shape of the quartz boat
of the present apparatus can be varied. The disposed place of the
second catalyst relates to the shape of the quartz boat and the
direction of the gas flowing in the quartz boat. In particularly,
when the quartz boat is cymbiform including two opposite open ends
with one end facing towards the gas inlet and the other facing
towards the gas outlet of the reaction chamber (referring to the
first embodiment of the present apparatus), the second catalyst is
disposed beside at least one side of the substrate far from the gas
outlet. Alternatively, when the quartz boat is tubular including
one open end facing to the gas inlet (referring to the second
embodiment of the present apparatus), the second catalyst is
disposed beside at least one side of the substrate far from the gas
inlet. Furthermore, because the purpose of adopting the second
catalyst in accordance with the present apparatus and method is
providing small amounts of additional hydrogen gas around the film
of first catalyst, the disposing of the second catalyst should obey
the following conditions. Firstly, that the second catalyst should
be disposed beside the substrate to assure that the produced
hydrogen by the second catalyst can act on the first catalyst
directly. Secondly, that the second catalyst should be disposed in
front of the substrate along a direction of gas flow that ensures
that the hydrogen produced by the second catalyst can reach the
first catalyst. Also, it is to be understood that the second
catalyst should be placed within the range of protection of the
present apparatus and methods.
[0032] It is noted that, the reaction chamber of the present
apparatus includes apparatuses for use in chemical vapor
deposition, such as horizontal CVD devices, vertical CVD devices
and a CVD device with a removable quartz boat. Moreover, the
present apparatus and method can synthesize massive carbon nanotube
arrays by disposing a plurality of substrate in the reaction
chamber simultaneously, and that the property of carbon nanotubes
thus produced is essentially uniform. Thus, both quality and
production of the carbon nanotubes can be controlled by the present
apparatus and method. Furthermore, the film of first catalyst of
the present apparatus and method can be patterned for growing
patterned carbon nanotube array.
[0033] Finally, it is to be understood that the above-described
embodiments are intended to illustrate rather than limit the
disclosure. Variations may be made to the embodiments without
departing from the spirit of the disclosure as claimed. The
above-described embodiments illustrate the scope of the disclosure
but do not restrict the scope of the disclosure.
* * * * *