U.S. patent application number 12/011353 was filed with the patent office on 2010-11-18 for printable composition with nanostructures of first and second types.
Invention is credited to Scott T. Haubrich, Alfred I-Tsung Pan.
Application Number | 20100288534 12/011353 |
Document ID | / |
Family ID | 36943271 |
Filed Date | 2010-11-18 |
United States Patent
Application |
20100288534 |
Kind Code |
A1 |
Pan; Alfred I-Tsung ; et
al. |
November 18, 2010 |
Printable composition with nanostructures of first and second
types
Abstract
A printable composition for use in forming a printed element by
printing and curing is described. The printable composition
comprises a plurality of nanostructures of a first type that, upon
printing and curing, form an arrangement defining intermediate
volumes thereamong. The printable composition further comprises a
plurality of nanostructures of a second type that, upon printing
and curing, at least partially fill the intermediate volumes to
promote smooth surface topography and reduced porosity in the
printed element.
Inventors: |
Pan; Alfred I-Tsung;
(Sunnyvale, CA) ; Haubrich; Scott T.;
(Albuquerque, NM) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY;Intellectual Property Administration
3404 E. Harmony Road, Mail Stop 35
FORT COLLINS
CO
80528
US
|
Family ID: |
36943271 |
Appl. No.: |
12/011353 |
Filed: |
January 24, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11070657 |
Mar 2, 2005 |
7341680 |
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12011353 |
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Current U.S.
Class: |
174/250 ; 118/44;
977/932 |
Current CPC
Class: |
H05K 1/097 20130101;
H01B 1/24 20130101; H05K 2201/0272 20130101; H01L 29/7869 20130101;
H01B 1/22 20130101; H05K 2201/0323 20130101; H01L 21/288 20130101;
H01L 21/76801 20130101; H05K 2201/0248 20130101; Y10T 428/2982
20150115; H01L 29/78681 20130101 |
Class at
Publication: |
174/250 ; 118/44;
977/932 |
International
Class: |
H05K 1/00 20060101
H05K001/00; B05C 11/00 20060101 B05C011/00 |
Claims
1-21. (canceled)
22. A printed circuit element, comprising: a plurality of
nanostructures of a first type in an arrangement defining
intermediate volumes thereamong; and a plurality of nanostructures
of a second type at least partially filling said intermediate
volumes, said printed circuit element being formed by a transfer of
an ink solution comprising said nanostructures of the first and
second types to a surface according to a printing process and by a
curing of the transferred ink solution.
23. The printed circuit element of claim 22, wherein said
nanostructures of the first type are elongate nanostructures, and
wherein said nanostructures of the second type are compact
nanostructures.
24. The printed circuit element of claim 23, said elongate
nanostructures generally having aspect ratios greater than about
3:1, said compact nanostructures generally having aspect ratios
less than about 2:1, and wherein a ratio by weight of said compact
nanostructures to said elongate nanostructures in said printed
circuit element is between about 0.2 and 20.
25. The printed circuit element of claim 24, wherein said compact
nanostructures are generally globular with a major dimension less
than a minor dimension of said elongate nanostructures.
26. The printed circuit element of claim 25, wherein said minor
dimension of said elongate nanostructures is between about 2 nm and
100 nm.
27. The printed circuit element of claim 23, wherein said elongate
nanostructures comprise an inorganic semiconductor material, and
wherein the printed circuit element is operable as a semiconductor
circuit element having a carrier mobility greater than about 1
cm.sup.2/V-s.
28-33. (canceled)
34. An apparatus comprising means for transferring a printable
composition to a surface, said printable composition comprising a
plurality of nanostructures of a first type that, upon transfer to
a surface and curing, form an arrangement defining intermediate
volumes thereamong, said printable composition further comprising a
plurality of nanostructures of a second type that, upon said
transfer and curing, at least partially fill said intermediate
volumes to promote smooth surface topography and reduced porosity
in a resultant printed element.
35. The apparatus of claim 34, wherein said nanostructures of the
first type are elongate nanostructures, and wherein said
nanostructures of the second type are compact nanostructures.
36. The apparatus of claim 35, wherein said elongate nanostructures
generally have aspect ratios greater than about 3:1, wherein said
compact nanostructures generally have aspect ratios less than about
2:1, and wherein a ratio by weight of said compact nanostructures
to said elongate nanostructures in said printable composition is
between about 0.2 and 100.
37. The apparatus of claim 36, said printable composition further
comprising a molecular precursor that, upon said transfer and
curing, forms decomposed precursor solids further filling said
intermediate volumes.
38. The apparatus of claim 37, said elongate nanostructures
comprising a crystalline version of a compound, said decomposed
precursor solids comprising an amorphous version of said compound,
a polycrystalline version of said compound, or an epitaxially grown
single-crystal version of said compound.
Description
FIELD
[0001] This patent specification relates to printable compositions
having nanostructural ingredients and the printing of functional
materials therewith.
BACKGROUND
[0002] The field of printed electronics, and more generally the
field of printed functional materials, represents a promising
avenue toward a new world of devices ranging from flexible,
low-cost computer displays to lightweight, high-capacity storage
batteries. Using printing technologies traditionally associated
with the creation of human-readable text or graphics, special
printable compositions or "inks" are transferred to surfaces and
cured into functional elements such as conductors, semiconductors,
and dielectrics. Multilayer structures can be built in an additive
process, i.e., by printing additional layers of elements on top of
previously-cured elements, to create more complex structures such
as thin-film transistors.
[0003] Although several advantages can be brought about in terms of
device flexibility, cost, durability, and the like, the electrical
performance offered by today's printed semiconductors is generally
inferior to the performance of single-crystal semiconductors used
in most of today's high-speed electronics and computing equipment.
Whereas single-crystal silicon semiconductors may offer mobilities
in the range of 800-1000 cm.sup.2/V-s, which can facilitate device
switching speeds in the MHz and GHz range, printed semiconductor
elements such as pentacene, a p-type organic semiconductor, may
only offer mobilities on the order of 2-3 cm.sup.2/V-s.
[0004] One issue can arise in the fabrication of functional printed
elements when the printable composition contains nanostructures
intended to impart certain characteristics to the cured printed
element, such as certain electrical characteristics (e.g.,
conductive, semiconductive, dielectric, etc.). Upon thermal
treatment or other curing method, and due at least in part to a
volume shrinkage of a molecular precursor accompanying the
nanostructures in the printable composition, the morphology of the
resulting printed element can be porous, and the surface of the
resulting printed element can be rough. This, in turn, can bring
about difficulty in properly printing a subsequent layer on top of
the printed element. It would be desirable to provide for reduced
porosity and smoother surface topography in the printed
element.
SUMMARY
[0005] In accordance with an embodiment, a printable composition
for use in forming a printed element is provided. The printable
composition comprises a plurality of nanostructures of a first type
that, upon printing and curing, form an arrangement defining
intermediate volumes thereamong. The printable composition further
comprises a plurality of nanostructures of a second type that, upon
printing and curing, at least partially fill the intermediate
volumes to promote smooth surface topography and reduced porosity
in the printed element.
[0006] Also provided is a method for fabricating a printed element,
in which a composition is transferred onto a surface according to a
printing process and cured to form the printed element. The
composition comprises a plurality of nanostructures of a first type
and a plurality of nanostructures of a second type, the
nanostructures of the second type at least partially filling space
between the nanostructures of the first type in the printed
element.
[0007] Also provided is a printed circuit element comprising a
plurality of nanostructures of a first type in an arrangement
defining intermediate volumes thereamong, and a plurality of
nanostructures of a second type at least partially filling the
intermediate volumes. The printed circuit element is formed by a
transfer of an ink solution comprising the nanostructures of the
first and second types to a surface according to a printing process
and by a curing of the transferred ink solution.
[0008] Also provided is an ink formulation for a printer,
comprising a first percentage by weight of elongate nanostructures
having an aspect ratio above about 3:1, and a second percentage by
weight of compact nanostructures having an aspect ratio below about
2:1. The second percentage is between about 0.2 and 100 times the
first percentage.
[0009] Also provided is an apparatus comprising means for
transferring a printable composition to a surface, the printable
composition comprising a plurality of nanostructures of a first
type that, upon transfer to a surface and curing, form an
arrangement defining intermediate volumes thereamong. The printable
composition further comprises a plurality of nanostructures of a
second type that, upon transfer to the surface and curing, at least
partially fill the intermediate volumes to promote smooth surface
topography and reduced porosity in the resultant printed
element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 illustrates a printable composition according to an
embodiment;
[0011] FIG. 2 illustrates examples of elongate nanostructures
according to one or more embodiments;
[0012] FIG. 3 illustrates examples of compact nanostructures
according to one or more embodiments;
[0013] FIG. 4 illustrates fabricating a printed element according
to an embodiment;
[0014] FIG. 5 illustrates a surface upon which a printable
composition is being transferred by an inkjet printer according to
an embodiment;
[0015] FIG. 6 illustrates transferred and cured printable
composition having elongate nanostructures but not having compact
nanostructures;
[0016] FIG. 7 illustrates transferred and cured printable
composition according to an embodiment; and
[0017] FIG. 8 illustrates transferred and cured printable
composition according to an embodiment.
DETAILED DESCRIPTION
[0018] FIG. 1 illustrates a printable composition 102 according to
an embodiment, comprising a carrier solution 104, a plurality of
nanostructures of a first type, and a plurality of nanostructures
of a second type. By way of non-limiting example, the
nanostructures of the first type can be similar to elongate
nanostructures 106, while the nanostructures of the second type can
be similar to compact nanostructures 108. However, other types of
nanostructures can be used in other embodiments. Printable
composition 102 further comprises a molecular precursor
substantially dissolved in the carrier solution 104, the molecular
precursor being selected such that it decomposes into a desired
solid material upon transfer and curing. In one embodiment, the
molecular precursor is selected such that the decomposed precursor
solid comprises amorphous or polycrystalline versions of the
material used for the elongate nanostructures 106. In another
embodiment, the molecular precursor is selected such that, upon
transfer to a surface in conjunction with the carrier solution 104,
a saturation condition occurs that facilitates in situ growth of
crystalline or polycrystalline versions of the elongate
nanostructural material.
[0019] FIG. 2 illustrates examples 202-212 of elongate
nanostructures 106 that may be used in the printable composition
102 of FIG. 1. The elongate nanostructures 106 may comprise
nanowires, nanorods, nanodiscs, nanoplates, or any of a variety of
other anisometric nanostructures having major dimensions D1 that
are substantially greater than their minor dimensions D2, as
illustrated in FIG. 2. Depending on the particular application, the
elongate nanostructures 106 can comprise conductive, a
semiconductive, or dielectric material. Other examples can include
phosphorus. In one embodiment, the elongate nanostructures 106 have
an aspect ratio (the ratio of their major dimension D1 to their
minor dimension D2) that is greater than 3:1. In another
embodiment, the elongate nanostructures 106 have an aspect ratio
that is greater than 5:1.
[0020] It is to be appreciated that FIG. 2 illustrates only a few
examples of the many types of elongate nanostructures that may be
used in accordance with the present teachings. Moreover, different
shapes of elongate nanostructures can be mixed together without
departing from the scope of the present teachings. For example,
half of the elongate nanostructures 106 may comprise nanowires
similar to element 202 of FIG. 2, while the other half may comprise
nanodiscs similar to element 208 of FIG. 2. Although the particular
elements 202-212 illustrated in FIG. 2 are solid throughout, in
other embodiments the elongate nanostructures 106 can comprise
hollow nanocylinders or other shapes that are not solid
throughout.
[0021] FIG. 3 illustrates examples 302-308 of compact
nanostructures 108 that may be used in the printable composition
102 of FIG. 1. The compact nanostructures 108 may comprise any of a
variety of compact shapes in which a major dimension D1 is
generally comparable to a minor dimension D2. For example, the
compact nanostructures 108 may be generally globular, as
illustrated by the spheroid shape 302 or the ellipsoid shape 306 in
FIG. 3. Alternatively, the compact nanostructures 108 may comprise
truncated nanowires 308 as illustrated in FIG. 3, or other shapes
such as the pyramidal shape 304. In one embodiment, the compact
nanostructures 108 have an aspect ratio that is less than 3:1. In
another embodiment, the compact nanostructures 108 have an aspect
ratio that is less than 2:1.
[0022] The compact nanostructures 108 can comprise conductive,
semiconductive, or dielectric material. Other examples can include
phosphorus. In one embodiment, the compact nanostructures 108
comprise a material identical to the material used for elongate
nanostructures 106, while in other embodiments, the materials can
be different. As with the elongate nanostructures 106, the compact
nanostructures 108 can be mixed and matched from among different
shapes, e.g., half of the compact nanostructures can be similar to
the spheroid shape 302 of FIG. 3, while the other half can be
similar to the truncated nanowire shape 308 of FIG. 3. As with the
elongate nanostructures 106, the compact nanostructures 108 can
comprise shapes that are solid throughout, or that are not solid
throughout.
[0023] FIG. 4 illustrates fabricating a printed element according
to an embodiment. At step 402, the printable composition 102 is
prepared including elongate nanostructures 106 and compact
nanostructures 108. At step 404, the printable composition 102 is
transferred to a surface according to a printing process.
[0024] FIG. 5 illustrates a surface 504 to which a printable
composition is being transferred according to an inkjet printing
process. An inkjet printhead 502 containing the ink, i.e., the
printable composition 102, is swept across the surface 504 in a
manner analogous to the way black or colored ink is deposited on
paper by a commercially available inkjet printer, such that printed
elements 506 are formed. The example of FIG. 5 simply shows the
printed elements 506 as being parallel straight lines, it being
appreciated that specific layouts are programmed into the printer
drivers for the inkjet printing apparatus to form various circuit
elements such as electrical conductors, resistors, capacitor
plates, capacitor dielectrics, transistor sources/gates/drains,
etc. Any of a wide variety of printing processes can be used at
step 404 including, but not limited to, inkjet printing,
drop-on-demand printing, screen printing, micro-contact printing,
gravure printing, flexography printing, letterpress printing, and
electrostatic printing.
[0025] At step 406, the printed elements 506 are cured, such as by
a sintering process. In one embodiment, the sintering temperature
is low enough such that the elongate and compact nanostructures are
not melted, but high enough such that the liquid content in the
printable composition will evaporate and the molecular precursor
will decompose into the desired solid material. At step 408, upon
curing, the compact nanostructures 108 fill spaces between the
elongate nanostructures 106 to promote less porous morphology and
smoother surface topography in the printed elements 506. Subsequent
layers of printed elements can then be applied as needed to form
the desired functional device.
[0026] FIG. 6 illustrates, for purposes of clarity and comparison,
a hypothetical cross-section of a printed element near a surface
thereof for a circumstance in which elongate nanostructures 602 are
present in the printable composition but compact nanostructures are
not present. The elongate nanostructures 602 form a haystack-like
arrangement, with decomposed molecular precursor 604 also being
present and acting as a kind of physical and electrical "glue" for
proximal elongate nanostructures 602. Intermediate regions lying
among the elongate nanostructures 602, as represented by the
intermediate region 610 lying among the elongate nanostructures
602a, 602b, and 602c, can be substantially unoccupied, being only
partially filled with material such as the decomposed molecular
precursor 604. As illustrated, the morphology of the printed
element can be porous, and the surface can be rough. Notably,
depending on the particular substances and environments of the
printing process, the elongate nanostructures could alternatively
become arranged in a parallel fashion. However, even in this case
the printed element can have substantial porosity and/or surface
roughness.
[0027] FIG. 7 illustrates, for purposes of clarity and comparison,
a hypothetical cross-section of a printed element near a surface
thereof for a circumstance in which both compact nanostructures 704
and elongate nanostructures 702 are present in the printable
composition according to an embodiment. The elongate nanostructures
702 form a generally random arrangement that defines intermediate
volumes thereamong, as represented by the intermediate volume 710
positioned among the elongate nanostructures 702a, 702b, and 702c.
As illustrated, the presence of the compact nanostructures 704 in
the intermediate volumes 710 promotes reduced porosity and a
smoother surface in the resultant printed element. Moreover, the
electrical properties of the printed element can be substantially
enhanced, because electrical connectedness of the elongate
nanostructures 702 is also promoted. The present teachings are also
applicable where the elongate nanostructures become arranged in a
parallel fashion, the compact nanostructures promoting smoother
surfaces and reduced porosity in that arrangement as well.
[0028] In one particularly advantageous embodiment, the elongate
nanostructures 702 and the compact nanostructures 704 each comprise
an identical semiconducting material, and the resultant printed
element is a semiconducting element having a carrier mobility
substantially improved by the presence of the compact
nanostructures in the intermediate volumes 710. In another
particularly advantageous embodiment, the elongate nanostructures
702 and the compact nanostructures 704 each comprise an identical
conductor, and the resultant printed element is a conductor with a
conductance that is substantially improved by the presence of the
compact nanostructures in the intermediate volumes 710.
[0029] Various details relating to the above description, FIGS.
1-7, and the present teachings are presented hereinbelow, but
should not be construed as limiting the scope of the present
teachings. In one embodiment, the elongate nanostructures are
nanorods having a length of roughly 200 nm and a diameter of
roughly 10 nm. In other embodiments, the elongate nanostructures
may be substantially thinner or thicker, having a minor dimension
(i.e., diameter) between 2 nm and 100 nm, for example. Upon
transfer and cure without the compact nanostructures of the present
teachings, the nanorods would form a generally random arrangement
similar to that of FIG. 6. Some degree of electrical connectivity
among the nanorods could be achieved solely by virtue of this
haystack-like arrangement, and the overall printed element could
achieve some degree of electrical utility. However, in accordance
with an embodiment, compact nanostructures having a generally
globular shape are included in the printable composition. The
resulting printed element, also referred to as a thin film, enjoys
reduced porosity, smoother topography, and a high degree of
physical and electrical connectedness to yield improved overall
physical and electrical performance. In one example, which is
presented by way of example and not by way of limitation, the
compact nanostructures are roughly spherical (D1=D2) and have a
diameter of 7 nm where the elongate nanostructures are nanorods
having a length of roughly 200 nm and a diameter of roughly 10
nm.
[0030] In one embodiment, a major dimension of the compact
nanostructures is less than a minor dimension of the elongate
nanostructures, as with the preceding example. In other
embodiments, a major dimension of the compact nanostructures can be
comparable to a minor dimension of the elongate nanostructures. In
still other embodiments, a major dimension of the compact
nanostructures can be substantially greater than a minor dimension
of the elongate nanostructures, provided that the compact
nanostructures are small enough to populate the intermediate
volumes among the elongate nanostructures in the cured printed
element in a manner that facilitates smooth surface topography and
reduced porosity.
[0031] Elongate and compact nanostructures that may be used in
accordance with the present teachings may be fabricated in any of a
variety of ways. For example, single crystal nanowires may be grown
using methods such as vapor-liquid-solid (VLS) catalytic growth,
solution-liquid-solid (SLS) catalytic growth, and non-catalytic
vapor-phase epitaxy. Other methods for producing nanowires include
template-assisted synthesis, nanoimprint lithography, dip-pen
nanolithography, self-assembly of nanoparticles, solution phase
methods based on capping reagents, and solvothermal methods.
[0032] In one embodiment in which the elongate nanostructures are
nanorods 200 nm in length and 10 nm in diameter, and in which the
compact nanostructures are approximately 7 nm globes, the printable
composition comprises 2.0% by weight of the nanorods and 3.0% by
weight of the compact nanostructures. The ratio by weight of
compact nanostructures to elongate nanostructures in the printable
composition can generally range between about 0.2 to 100 without
departing from the scope of the present teachings. The appropriate
ratio by weight of compact nanostructures to elongate
nanostructures for a particular circumstance will be highly
dependent on the particular sizes and contours of the elongate
nanostructures, which affects how tightly or loosely they will
arrange, and also on the particular sizes and shapes of the compact
nanostructures, which will affect how efficiently they can fill the
intermediate volumes among the elongate nanostructures. Where the
elongate nanostructures are straight nanowires and the compact
nanostructures are globular, a ratio by weight of compact
nanostructures to elongate nanostructures between about 0.5 to 2
often provides for good morphology and smooth surface
topography.
[0033] A wide range of viscosities for the printable composition
are within the scope of the present teachings. In some embodiments,
the printable composition comprises a highly non-viscous solution
in which the solid content (primarily the elongate and compact
nanostructures) is relatively low, e.g. 3 percent or less. In other
embodiments, the printable composition can comprise a highly
viscous solution, even approaching 90 percent. In some embodiments,
the printable composition can have a relatively low viscosity on
the order of 10-20 centipoise, while in other embodiments the
printable composition can have a relatively high viscosity on the
order of 200 centipoise or greater.
[0034] Among other advantages according to the present teachings,
desirable electrical characteristics such as high conductivity and
high mobility can be achieved without requiring a melting or
liquid-phase fusing of the nanostructural material during the
curing/sintering process. This provides an ability to cure/sinter
at relatively low temperatures, including "plastic-friendly"
temperatures, thereby widening the choice of available substrates
(surfaces) and the variety of devices that can be fabricated.
[0035] In the particular context of semiconducting devices, while
certain known organic printed semiconductors might be cured at
relatively low temperatures, such organic semiconductors generally
suffer from relatively low carrier mobilities, as in the pentacene
example supra. When implemented in the context of inorganic
semiconductor materials, the present teachings can provide for the
higher-mobilities associated with inorganic semiconductors, while
at the same time providing for relatively low curing/sintering
temperatures including "plastic-friendly" temperatures. In one
embodiment, the sintering temperature using a printable composition
containing inorganic semiconductors according to the present
teachings can be about 500 degrees Celsius or less, while the
resultant printed element can have carrier mobilities greater than
about 10 cm.sup.2/V-s. In some embodiments, the resultant printed
element can have carrier mobilities greater than about 1
cm.sup.2/V-s. Yet another advantage according to the present
teachings is reduced shrinkage of the printed element during the
sintering process, which can thereby reduce lateral and vertical
stresses on device components during and after the curing
process.
[0036] Where a conducting printed element is desired, examples of
conducting materials for the elongate and compact nanostructures
include gold, silver, platinum, or other highly conductive metals.
Where a dielectric printed element is desired, examples of
(non-air) dielectric materials for the elongate and compact
nanostructures include Ta.sub.2O.sub.5, SiO.sub.2, and
Al.sub.2O.sub.3. Where a semiconducting printed element is desired,
examples of semiconducting materials for the elongate and compact
nanostructures include ZnO, CdS, CdSe, ZnS, PbS, GaAs, InP, InO,
InSnO, and InZnO. The semiconducting materials can be pre-doped for
negative or positive carriers, i.e., the p-doping or n-doping can
be performed in conjunction with the fabrication of the elongate
and/or compact nanostructures prior to formation of the printable
composition.
[0037] For a nanostructure material of ZnO in which the elongate
nanostructures are 2.0 percent by weight of the printable
composition and the compact nanostructures are 3.0 percent by
weight of the printable composition, one suitable molecular
precursor comprises zinc 2-ethylhexanoate (1.0 percent of the
printable composition by weight) and 2-ethylhexanoic acid (0.2
percent of the printable composition by weight). In this
embodiment, the carrier solution can comprise isopropanol (93.8
percent of the printable composition by weight).
[0038] More generally, the carrier solution can comprise solvent,
surfactants and/or other additives that will further aid in film
formation and good film morphology. By way of example and not by
way of limitation, the carrier solution can comprise solvents such
as water or isopropanol with or without a surfactant or other
additives to assist with suspension and/or distribution of the
suspended nanostructures. The surfactant can serve as a wetting
agent and/or an encapsulation agent for the nanostructures in the
carrier solution. In some embodiments, ionic surfactants are used
that have either water soluble or hydrophilic functional groups.
Examples of anionic surfactants that can be used include, but are
not limited to, sodium dodecylsulfate (SDS), sodium deoxycholate
(DOC), and N-lauroylsarcosine sodium salt. Examples of cationic
surfactants that can be used include, but are not limited to,
lauryldimethylamine oxide (LDAO), cetyltrimethylammonium bromide
(CTAB), and bis(2-ethlyhexyl)sulfosuccinate sodium salt. Any of the
above sodium salts may alternatively be a lithium salt or a
potassium salt.
[0039] In some embodiments, the carrier solution can comprise pH
modifiers. Examples of pH modifiers for the above-described example
include bases, such as sodium hydroxide (NaOH), potassium hydroxide
(KOH), ammonia (NH.sub.3), and methaneamine (CH.sub.3NH.sub.2), and
acids, such as hydrochloric acid (HCl), sulfuric acid
(H.sub.2SO.sub.4), and acetic acid (CH.sub.3COOH). Certain buffers
also may be employed as pH modifiers.
[0040] For a nanostructure material of ZnO, the molecular precursor
can comprise one or more of ZnO, Zn(NO.sub.3).sub.2, ZnSO.sub.4,
ZnCl.sub.2, and Zn(C.sub.2H.sub.3O.sub.2).sub.2 within an aqueous
carrier solution. For a nanostructure material of CdS, the
molecular precursor can comprise one or more of cadmium citrate,
cadmium chloride, and thioreau. For a nanostructure material of
CdSe, the molecular precursor can comprise one or more of cadmium
citrate and N,N-dimithyl-selenourea. For a nanostructure material
of ZnS, the molecular precursor can comprise one or more of
ZnSO.sub.4 and SC(NH.sub.2).sub.2. For a nanostructure material of
PbS, the molecular precursor can comprise one or more of
Pb(NO.sub.3) and SC(NH.sub.2).sub.2.
[0041] FIG. 8 illustrates a hypothetical cross-section of a printed
element near a surface thereof where a printable composition is
transferred and cured according to an embodiment, the printable
composition comprising a plurality of nanostructures of a first
type in an arrangement defining intermediate volumes thereamong,
the printable composition further comprising a plurality of
nanostructures of a second type at least partially filling the
intermediate volumes. By way of example, the nanostructures of the
first type can be similar to the larger nanostructures 802 of FIG.
8, while the nanostructures of the second type can be similar to
the smaller nanostructures 804. It is to be appreciated that while
the larger nanostructures 802 and smaller nanostructures 804 of
FIG. 8 are shown to be spherical, in other embodiments they can be
pyramidal, cubical, or otherwise comprising multi-sided volumes. It
still other embodiments, they can be elliptical or otherwise
oddly-shaped. The larger nanostructures 802 form an arrangement
that defines intermediate volumes thereamong, as represented by the
intermediate volume 810 positioned among the larger nanostructures
802a, 802b, 802c, and 802d. Decomposed molecular precursor 806
further fills part of the intermediate volumes 810. As illustrated,
the presence of the smaller nanostructures 804 in the intermediate
volumes 810 promotes reduced porosity and a smoother surface in the
resultant printed element. Moreover, the electrical properties of
the printed element can be substantially enhanced, because
electrical connectedness of the larger nanostructures 802 is also
promoted. While the larger nanostructures 802 are shown in FIG. 8
as forming a generally random arrangement, in other embodiments
they can become arranged in a more regular fashion, the smaller
nanostructures 804 promoting smoother surfaces and reduced porosity
in that arrangement as well.
[0042] Whereas many alterations and modifications of the
embodiments will no doubt become apparent to a person of ordinary
skill in the art after having read the foregoing description, it is
to be understood that the particular embodiments shown and
described by way of illustration are in no way intended to be
considered limiting. By way of example, although some embodiments
supra are described as having all of the elongate nanostructures
made from the same material (i.e., all conducting, all
semiconducting, all dielectric), it is not outside the scope of the
present teachings to mix conducting and semiconducting elongate
nanostructures, or to mix conducting and dielectric elongate
nanostructures, and so on, depending on the particular resultant
electrical properties desired. Likewise, the compact nanostructures
can comprise mixtures of conducting, semiconducting, and dielectric
materials without departing from the scope of the present
teachings.
[0043] By way of further example, although some embodiments supra
are described in terms of the elongate nanostructures being
randomly oriented in the cured printed element, in other
embodiments the elongate nanostructures can be uniformly or
quasi-uniformly oriented without departing from the scope of the
present teachings. By way of still further example, while certain
embodiments supra are particularly advantageous when the
nanostructures are inorganic semiconductors and the molecular
precursor is configured to decompose into amorphous or
polycrystalline versions of that inorganic material, one or more of
the elongate nanostructures, compact nanostructures, molecular
precursors, carrier solution, and decomposed molecular precursors
can comprise organic semiconductor compounds or other organic
compounds without departing from the scope of the present
teachings.
[0044] By way of still further example, while the molecular
precursor supra is described as decomposing into amorphous or
polycrystalline structures, often of the same material as the
nanostructures, the molecular precursor could alternatively form
epitaxially grown single-crystal extensions of the nanostructure
crystals, or otherwise form epitaxially grown single-crystal
versions of the nanostructural material or other material, without
departing from the scope of the present teachings. By way of even
further example, although one or more embodiments supra is
particularly advantageous where the elongate nanostructures form a
generally random arrangement upon printing and curing, in other
preferred embodiments the elongate nanostructures form a generally
ordered arrangement, e.g., generally parallel to each other, with
the compact nanostructures occupying space between the elongate
nanostructures for reducing porosity and/or surface smoothness in
the cured printed element. Thus, reference to the details of the
described embodiments are not intended to limit their scope.
* * * * *