Electrolysis: processes – compositions used therein – and methods – Electrolytic coating – Depositing predominantly single metal or alloy coating on...
Reexamination Certificate
2001-06-04
2004-06-29
King, Roy (Department: 1742)
Electrolysis: processes, compositions used therein, and methods
Electrolytic coating
Depositing predominantly single metal or alloy coating on...
C205S118000, C205S122000, C205S194000, C427S249100, C427S577000, C423S447300
Reexamination Certificate
active
06755956
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to carbon nanostructures and methods of growing the same, and more particularly to carbon nanostructures that are attached to catalyst dots, and catalyst-induced methods of growing carbon nanostructures, especially on the tips of cantilevers, nanowires, wafers, conductive micro
anostructures, and the like.
BACKGROUND OF THE INVENTION
Programmable Nanometer-Scale Electrolytic Metal Deposition and Depletion
A previous invention, referenced hereinabove, describes nanometer-scale deposition and/or depletion of nanostructures in liquids at preferably ambient temperature and preferably neutral pH through electric field-directed, programmable, pulsed electrolytic metal deposition or depletion.
Application of a programmable and short (ns—ms time scale) pulsing direct current source is used to control the number of atoms being deposited by the electrolytic metal reduction and deposition process. As shown in the following platinum deposition reaction at a cathode using water-soluble hexachloroplatinate, the number of electrons supplied can control the formation of metallic platinum. In electrolytic deposition, electric current and the duration of the current can control the number of electrons.
[PtCl
6
]
2−
+4e
−
→Pt↓+6Cl
−
Other water-soluble metal compounds that have been shown to be applicable include, but are not limited to: PtCl
4
, OsCl
3
, Na
2
[PtCl
6
], Na
2
[OsCl
6
], (NH
4
)
2
RuCl
6
, K
3
RuCl
6
, Na
2
IrCl
6
, (NH
4
)
3
IrCl
6
, (NH
4
)
3
RhCl
6
, K
2
PdCl
4
, (NH
4
)
2
PdCl
4
, Pd(NH
3
)
4
Cl
2
, ReCl
3
, NiCl
2
, CoCl
2
, PtO
2
, PtCl
2
, Pt(NH
3
)
4
Cl
2
, (NH
4
)
6
Mo
7
O
24
, NaAuCl
4
, KAu(CN)
2
K
2
[PtCl
4
],and K
3
Fe(CN)
6
. Combinations of two or more water-soluble metal compounds can be used sequentially or simultaneously.
As illustrated in
FIG. 1
, a programmable current source
18
is used to precisely control the number of electrons used to achieve the desired nanometer-scale electrolytic metal deposition. A non-conductive substrate
10
supports nanometer sized electrodes, also called nanowires and nanoelectrodes—cathode
12
and anode
14
—which are usually comprised of gold but can be other metals or conductive materials. Spacing between the nanoelectrode tips
13
,
15
in the range of 1-10 &mgr;m produces results that are suitable for many applications.
A preselected metal
16
is deposited onto the tip of the cathode
12
. The metal
16
is usually Pt, but can be any metal that can be deposited electrolytically. A programmable, pulsable current source
18
has electrical connections
20
,
22
to the respective nanoelectrodes
12
,
14
. A bypass circuit
24
is shown, which includes a bypass selector switch
26
and a variable resistor
28
.
Nanoelectrodes
12
,
14
represent a subset of microscopic sized structures (nanostructures) that are suitable for use. Nanostructures acting as electrodes can be of various sizes and shapes. Spacing between the two nanostructures should not exceed 50 &mgr;m, preferably 20 &mgr;m, more preferably, 10 &mgr;m, most preferably, 5 &mgr;m.
The programmable, pulsable current source
18
can be of any suitable construction. Keithley Model 220 programmable current source or the latest Keithley Model 2400 series of Source Meters (available from Keithley Instruments, Inc., 28775 Aurora Road, Cleveland, Ohio 44139, or on the Internet at www.keithley.com) are already capable of supplying a minimum of about 9400 electrons per pulse [500 fA×3 ms×electron/(1.60×10
−19
C)], which could translate to a deposition of 2350 platinum atoms per pulse based on the stoichiometry of the deposition reaction. If this amount of platinum is deposited on the end of a nanowire with a 10 nm×10 nm cross section, 2350 platinum atoms per pulse can translate into about 1 nm of metal deposition (2.6 layers of platinum atoms) per pulse. The programmable, pulsable current source
18
should be capable of controlling the process so that nanometer metal deposition or depletion as precise as about 1500 metal atoms per pulse can be achieved. A preferable range is contemplated to be 1500×10
14
atoms per pulse, although the skilled artisan will recognize that the method can operate well beyond this range.
The bypass circuit
24
is preferably added to fine-tune the electron flow for even more precise control of deposition or depletion—the addition or removal of monolayers or submonolayers of atoms—that can be achieved. The bypass circuit
24
is used to divert some of the electricity away from the nanoelectrodes
12
,
14
in order to deposit or deplete fewer metal atoms per pulse. For example, when the impedance of the variable resistor
28
is adjusted to 50% of the impedance between the two nanoelectrodes
12
,
14
, two thirds of the 9400 electrons per pulse can be drained through the bypass circuit
24
. In this case, the electrolytic metal deposition can be controlled to a step as precise as 780 platinum atoms (3130 electrons) per pulse, which can be translated to a deposition of 0.87 layer of platinum atoms
16
on a 10- by 10-nm surface at the tip of the cathodic nanoelectrode
12
. By allowing a greater portion of the current to flow through the bypass circuit
24
, it is possible to control deposition of metal 16 atoms as precise as 100 atoms per pulse. A preferable range for this extremely finely controlled deposition is contemplated to be 100-2500 atoms per pulse, although the skilled artisan will recognize that the method can operate well beyond this ultrafine deposition range.
The bypass circuit
24
can also protect the nanometer structure from electrostatic damage, especially when the structure is dry. For example, after desired programmable electrolytic metal deposition is achieved as illustrated in
FIG. 1
, the bypass circuit
24
should remain connected with the nanostructures
12
and
14
while the programmable pulsing current source can then be removed. As long as the bypass circuit remains connected with the nanostructures
12
and
14
, any electrostatic charges that might be created during wash and dry of the nanostructures will be able to flow through the bypass circuit
24
that, in this case, comprises the closed switch
26
, the variable resistor
28
, and wires that connect the switch
26
and the variable resistor
28
with the nanoelectrodes
12
,
14
. This prevents accumulation of electrostatic charges at any one of electrodes against the other electrode from occurring, thus eliminating the possibility of electrostatic damage at the nanometer gap between the tips
13
,
15
of the nanoelectrodes
12
,
14
.
A special nanostructural arrangement can be used to control the initiation point(s) of nanometer bonding. Special structural arrangements of the nanowire electrodes can be made by various lithographic techniques (e.g., photolithography and electron-beam lithography) to control the initiation point(s) of the electrolytic metal deposition. As shown in
FIG. 2
, multiple nanowire cathodes
12
,
12
′ should have respective tips
13
,
13
′ pointing to the respective tips
15
,
15
′ of nanowire anode
14
so that the strongest electric field is therebetween. Spacing of the multiple nanowire cathodes
12
,
12
′ should be regulated to ensure deposition of metal
16
,
16
′ at the desired cathode location, because the electric field (E) is a vector that is strongly dependent on distance (r):
E∝r
−2
Electrolytic metal-dissolving reactions are applied to deplete metal—open nanometer gaps and control gap size as shown in FIG.
3
. By conducting the reversal of the metal deposition reaction with sodium chloride solution instead of hexachloroplatinate as an electrolytic substrate, metallic platinum at the anode tip(s)
16
can be electrolytically depleted via dissolution in a controllable way according to the following reaction:
Pt+6Cl
−
→[PtCl
6
]
2−
+4e
−
This metal-di
Eres Gyula
Greenbaum Elias
Lee Ida
Lee James Weifu
Lowndes Douglas H.
King Roy
Leader William T.
Marasco Joseph A.
UT-Battelle LLC
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