Patent Application
20150024289
The invention generally relates to novel materials comprising a metallic element and TiSi2 and methods of their preparation. More particularly, the invention relates to novel compositions and hierarchical nanostructures comprising a metallic element (e.g., Pt, Ru, Pd) and TiSi2, and their gas-phase preparation (e.g., via an atomic layer deposition (ALD) process) and applications in energy storage (e.g., fuel cells, lithium oxygen batteries).
Novel compositions or material morphologies play important roles in diverse technologies and applications such as in the field of electrical energy storage. (Bruce, et al. 2008 Angew. Chem. Int. Ed. 47, 2930-2946; Goodenough, et al. 2010 Chem. Mater. 22, 587-603; Yang, et al. 2012 Nat. Mater. 11, 560-3.) The key challenges encountered in advancing these technologies are often associated with material designs, particularly on the nanoscale. Single component nanostructures, for example, experience inherent limitations as they face diverse functional needs in more and more complex systems. While heteronanostructures show great promise by delivering multiple functionalities simultaneously, they encounter various challenges in terms of preparation, for example, the lack of precise control of deposition sites at small dimension but large scale. As a result, a wider use of fine hierarchical nanostructures has been hampered by high cost of equipment and process complexity (e.g., advanced soft lithography and precise surface treatment).
For instance, electrode design for proton exchange membrane fuel cells is one such area where such issues are critical. (Markovic, et al. 2001 Fuel Cells 1, 105-116; Gasteiger, et al. 2005 Appl. Catal. B 56, 9-35; Stamenkovic, et al. 2007 Science 315, 493-497; Gasteiger, et al. 2009 Science 324, 48-49; Stephens, et al. 2011 J. Am. Chem. Soc. 133, 5485-5491.) To afford high current density, conductive frameworks with high surface area are desired for the electrode's construction. Porous carbon, especially those with nanoscale pores, is popularly used as a scaffold, onto which catalysts for oxygen reduction reaction (ORR) and/or hydrogen oxidation reaction (HOR) are dispersed. The choice of porous carbon could limit the performance of fuel cells, including poor stability and reduced catalytic activities. Another example is in lithium oxygen batteries where carbon support electrodes have been discovered as a main failing mechanism due to its instability during operation. (Wang, et al. 2007 J. Power Sources 171, 331-339; Adzic, et al. 2007 Top. Catal. 46, 249-262; Stamenkovic, et al. 2007 Nat. Mater. 6, 241-247; Strasser, et al. 2010 Nat. Chem. 2, 454-460.) To date, examples of low-cost, non-carbon-based porous conductive frameworks remain rare other than those involving precious metals. (Ding, et al. 2004 Adv. Mater. 16, 1897-1900; Peng, et al. 2012 Science 337, 563-566.)
Thus, it remains critically important to develop conductive, porous materials that are inexpensive and carbon free. Such materials have the potential to enable significant advances in diverse fields such as in electrical energy storage.
The invention provides novel materials and compositions achieved from a highly selective growth of a metallic element (e.g., a transition metal such as Pt, Pd and Ru) on the b planes of TiSi2 nanonets by atomic layer deposition. In the case of Pt, as-grown Pt nanoparticles exhibit an unusual 5-fold twinned structure that preferably exposes {111} surfaces of Pt. The resulting material showed high activity toward ORR reactions and great potentials as a promising air cathode for applications like fuel cells. Similarly, another composition, Ru/TiSi2, showed promising performance as air cathode for lithium oxygen batteries. The open structures allow high current densities, a highly coveted feature for applications such as electric transportation.
For many electrochemical reactions such as oxygen reduction, catalyst supports are of critical importance as they provide large surface area for catalyst loading and pathways for electron and mass transfer. Presently, porous carbon is the most commonly employed, the application of which has been recently recognized to be a potential source of concerns.
The invention provides a conductive, two-dimensional material of the TiSi2 nanonet, a unique supporting material to replace carbon. Metal nanoparticles were grown onto TiSi2 by atomic layer deposition. Surprisingly, the growth exhibited a unique selectivity, for example, with Pt deposited only on the top/bottom surfaces of the nanonets in nanoscale without mask or patterning. The materials showed great promise in catalyzing oxygen reduction reactions as one of the key challenges in both fuel cells and metal air batteries.
In one aspect, the invention generally relates to a catalytic system. The catalytic system includes nanoparticles of a metallic element grown onto one or more two-dimensional conductive nanostructures of TiSi2, wherein the catalyst system does not comprise carbon.
In another aspect, the invention generally relates to nanoparticles of a metallic element grown on a surface of a two-dimensional conductive nanostructure of TiSi2.
In yet another aspect, the invention generally relates to catalytic system comprising the nanoparticles according to the invention.
In yet another aspect, the invention generally relates to a fuel cell comprising a catalytic system according to the invention.
In yet another aspect, the invention generally relates to a battery comprising a catalytic system according to the invention.
In yet another aspect, the invention generally relates to a method for growing a metallic element on a surface of substrate. The method includes: providing one or more precursors of a metallic element; providing TiSi2 having one or more conductive nanostructures (e.g., two-dimensional nanonets); generating the metallic element in the gaseous phase; and depositing the metallic element on the two-dimensional conductive nanostructures of TiSi2. The metallic element exhibits a pre-select crystalline surface.
This invention provides a unique class of materials comprising a metallic element, such as a transition metal, and TiSi2 and methods of their preparation. More particularly, the invention relates to novel compositions of hierarchical nanostructures comprising a metallic element and TiSi2, and their gas-phase preparation (e.g., via an ALD process). The invention employs a novel gas-phase ALD technique for heteronanostructure fabrication on anisotropic substrates with site selectivity. The invention offers a much-needed methodology for site selective deposition, which is superior to the traditional expensive and complex photolithography techniques. Such heteronanostructure may find wide applications in energy storage and energy conversions.
The effective surface energy control allows site selective deposition. By using the anisotropic surfaces of a substrate, the invention does not rely on patterning. Furthermore, the rich chemistries of atomic layer deposition facilitate the control of various functional materials to be deposited on different types of substrates even with high aspect ratio.
For example, inexpensive and easy to prepare TiSi2 nanonets are employed. (Zhou, et al. 2008 Angew. Chem. Int. Ed. 47, 7681-7684; Zhou, et al. 2009 Chem. Mater. 21, 1023-1027; Zhou, et al. 2011 ACS Nano 5, 4205-4210.) When used to grow Pt, a highly unusual selective deposition is obtained, resulting in 5-fold twinned Pt nanoparticles whose {111} planes are preferably exposed. The Pt/TiSi2 combination exhibits ORR activities in aqueous solutions comparable to that of optimized commercial Pt/C catalyst, establishing the nanonet as a promising candidate for air electrode design and construction.
The invention provides unconventional heterostructure functional materials and a novel approach to material fabrication via ALD. First, the invention offers a unique combination of Pt and TiSi2. TiSi2 (titanium silicide) has a high surface area and high conductivity, a perfect candidate as a scaffold for electrocatalysts. Pt (Platinum) is one of the most widely used catalysts in diverse industrial applications. The combination of Pt/TiSi2 as disclosed herein has a potential to replace currently used Pt/C (carbon) catalyst. Second, the invention employs an improved ALD process that not only provides conformal deposition, but also selective deposition. In certain embodiments, ALD precursors are selectively adsorbed and decomposed on certain crystal faces with crystal growth taking place at the reactive sites in a layer-by-layer growth fashion. This technique exhibits advantages in high efficient deposition, precise site control cost effective and capability of coating on complex nanostructures with high aspect ratios.
An exemplary application of the hierarchical nanostructures of Pt/TiSi2 is for use as an electrocatalyst for fuel cells. The deposition of Pt particles showed a high concentration of twinning and {111} surface termination. As a result, the Pt/TiSi2 of the invention has an improved specific activity and mass activity compared to the traditional Pt/C catalyst for oxygen reduction reaction in aqueous media.
The invention offers various advantages over existing technologies. For example, the selective gas-phase deposition of functional materials on TiSi2 does not require complex photolithography or electron beam lithography processes. The site selective deposition originates from the anisotropic surface of TiSi2 nanostructures. Thus, the selective deposition process of the invention offers cost benefits in production and is also amenable to large-scale production. The selective deposition also offers precision control superior over many lithography techniques and can reach down to nm range (e.g., 20 nm). In addition, the materials prepared by gas-phase synthesis may avoid serious contaminations or ligand passivation common in liquid phase synthesis.
In one aspect, the invention generally relates to a catalytic system. The catalytic system includes nanoparticles of a metallic element grown onto one or more conductive nanostructures (e.g., two-dimensional nanonets) of TiSi2, wherein the catalyst system does not comprise carbon.
In another aspect, the invention generally relates to nanoparticles of a metallic element grown on a surface of a two-dimensional conductive nanostructure of TiSi2.
The metallic element may be any suitable metallic element, for example, a transition metal element such as Pt, Ru, Pd
In certain preferred embodiments, the nanoparticles of a metallic element are grown onto the one or more two-dimensional conductive nanostructures of TiSi2 by atomic layer deposition.
In certain preferred embodiments, the nanoparticles of a metallic element are grown onto the one or more two-dimensional conductive nanostructures of TiSi2 without mask or patterning.
In certain preferred embodiments, the nanoparticles of a metallic element are selectively grown only on the top and/or bottom surfaces of the one or more two-dimensional conductive nanostructures of TiSi2.
In certain preferred embodiments, the nanoparticles of a metallic element are crystalline.
In certain preferred embodiments, the nanostructures of TiSi2 are selected from nanonets and nanowires of TiSi2.
In certain preferred embodiments, the nanonets of TiSi2 have dimensions from about 0.1 μm to about 50 μm (e.g., from about 0.5 μm to about 25 μm, from about 1.0 μm to about 10 μm).
In certain preferred embodiments, the metallic element is Pt and the nanoparticles selectively exhibit a 5-fold twinned structure exposing {111} surfaces of Pt.
In certain preferred embodiments, the nanoparticles are selectively grown on one or more (020) planes of TiSi2 nanonets.
In yet another aspect, the invention generally relates to a method for growing a metallic element on a surface of substrate. The method includes: providing one or more (e.g., 1, 2, 3) precursors of a metallic element; providing TiSi2 having one or more two-dimensional conductive nanostructures; generating the metallic element in the gaseous phase; and depositing the metallic element on the two-dimensional conductive nanostructures of TiSi2. The metallic element exhibits a pre-select crystalline surface.
The one or more precursors may be selected from organometallic compounds. For example, Pt may be generated from precursors such as Trimethyl(methylcyclopentadienyl)platinum(IV) (MeCpPtMe3). Ru may be generated from precursors such as Bis(ethylcyclopentadienyl)ruthenium(II) (Ru(EtCp)2). Pd may be generated from precursors such as Palladium(II) hexafluoroacetylacetonate (Pd(hfac)2).
In yet another aspect, the invention generally relates to catalytic system comprising the nanoparticles according to the invention.
In yet another aspect, the invention generally relates to a fuel cell comprising a catalytic system according to the invention.
In yet another aspect, the invention generally relates to a battery comprising a catalytic system according to the invention.
Performance of the Pt/TiSi2 nanonet combination was compared with Pt/C-based system. (Zhou, et al. 2011 Chem. Soc. Rev. 40, 4167-4185; Bing, et al. 2010 Chem. Soc. Rev. 39, 2184-2202.) To obtain uniform coverage of Pt nanoparticles on the surface of TiSi2 nanonets, which is important for electrochemical ORR reactions, atomic layer deposition was adopted as the preparation method. (Christensen, et al. 2009 Small 5, 750-757.) A highly selective deposition was obtained, with Pt nanoparticles only growing on the (020) planes of TiSi2 nanonets (
Although selective growth of nanoparticles such as Ag and Pt on the tips of ZnO and CdS nanorods, respectively, have been reported, similar selectivity of gas-phase deposited nanoparticles on a nanostructured substrate is not known. (Pacholski, et al. 2004 Angew. Chem. Int. Ed. 43, 4774-4777; Habas, et al. 2008 J. Am. Chem. Soc. 130, 3294-3295; Amirav, et al. 2010 J. Phys. Chem. Lett. 1, 1051-1054.)
Regarding the nanonet form of TiSi2, it is of a layered structure known as C49 and different from its bulk and nanowire counterparts (C54). The top and bottom surfaces of TiSi2 nanonets are the b planes which are made of Si atoms only. (Zhou, et al. 2008 Angew. Chem. Int. Ed. 47, 7681-7684.)
A number of control experiments were carried out to demonstrate that the growth is indeed specific to TiSi2 nanonets.
First, Pt deposition on TiSi2 nanowires was studied. As schematically shown in
To understand whether the nanonet morphology played a role in the selective deposition, a thin layer (10 ALD cycles) of TiO2 was grown by ALD on TiSi2 nanonets, converting the surfaces (top, bottom and sides) to a non-distinguishable TiO2 coverage. (Lin, et al. 2009 J. Am. Chem. Soc. 131, 2772-2773.) Subsequent ALD growth resulted in a uniform deposition of Pt nanoparticles (
Taken as a whole, the results establish that the selective deposition of Pt nanoparticles was specific to TiSi2 nanonets, and the surfaces are the key reason for the selectivity. It is worth noting that TiSi2 nanonets exhibit a resistivity of ca. ˜10 ˜Ωcm, which is approximately 10 times better than bulk C49 TiSi2 and comparable to the more conductive C54. Previous studies suggest that the improved conductivity is due to the lack of stacking faults along the b direction in the nanonets. (Zhou, et al. 2008 Angew. Chem. Int. Ed. 47, 7681-7684.)
The surface energy difference is believed to be an important factor that governs the selective growth. The selective deposition disclosed herein is highly reproducible. (Lin, et al. 2009 J. Am. Chem. Soc. 131, 2772-2773; Liu, et al. 2011 Angew. Chem. Int. Ed. 50, 499-502; Lin, et al. 2011 J. Am. Chem. Soc. 133, 2398-2401.) For C49 TiSi2, theoretical studies show that b planes are more stable than a and c planes by up to 20% in surface energies; the difference between various planes of C54 TiSi2 is much less pronounced. (Wang, et al. 2006 Appl. Surf Sci. 252, 4943-4950.)
a shows dependence of Pt nanoparticle sizes and mass loading (relative to the total mass of Pt and TiSi2 nanonet support) on ALD cycle numbers.
The resulting Pt nanoparticles are crystalline in nature. Representative high magnification TEM images of multiple-twinned Pt nanoparticles deposited on TiSi2 by ALD are shown in
The nanonet-substrate was of critical importance to the high yield of the twinned Pt nanoparticles. When the nanonet was replaced by TiSi2 nanowires or TiO2-coated nanonets, the yield of twinned Pt nanoparticles dropped dramatically to <5%, although the total number of particles deposited remained comparable. It is believed that the interaction between Pt and the TiSi2 nanonet b planes plays a key role to the formation of twinned Pt nanoparticles.
Catalytic activity for ORR in aqueous solution was studies.
As shown in
Cyclic voltammetry (CV) of both TiSi2/Pt and Pt/C was first obtained in 0.1 M KOH at 25° C., and the purpose was to measure their electrochemically active surface area (ESA). The data was collected in alkaline solutions because our later characterizations were performed in solutions of the same conditions. As shown in
By comparison, the CV features of Pt/C were consistent with those of Pt (110) and (100) surfaces. A Pt ESA of 27.9 m2 g−1 was obtained on Pt/C while Pt/TiSi2 exhibited a slightly higher value of 35.1 m2 g−1. Note that the areal densities in terms of Pt mass loading for both were comparable (ca. 50 μgPt cmdisk−2). As such, the ESA difference is significant. One cause contributing to this difference may come from the multiple-twinned nature of Pt in Pt/TiSi2, which exposes more (111) surface atoms. (Yang, et al. 2012 ACS Nano 6, 9373-9382.) Another reason may be found in the relatively simple interface between Pt/TiSi2, which ensures more Pt exposure; by comparison, in Pt/C mixture, carbon may wrap around Pt to reduce the effective surface areas.
To study the ORR catalytic activity, measurements were carried out in O2 saturated alkaline solution (0.1 M KOH, 25° C.) by the rotating disk electrode (RDE) technique. ORR polarization curves of both Pt/TiSi2 and Pt/C at all rotating rates showed a diffusion- or mass-transfer-controlled region at voltages below 0.6-0.7 V vs. RHE (reversible hydrogen electrode), and diffusion-kinetic combined region above 0.7-0.8 V vs. RHE. The limiting currents at diffusion-controlled region are well defined as the current densities increase with ω1/2. As shown in
The 5-fold twinned nature of the Pt nanoparticles is an important reason for the performance difference. It was also noticed that Pt/TiSi2 and Pt/C samples had slightly different slopes of 80.2 mV/decade and 110.9 mV/decade, respectively, which is in agreement with literature reports of pure Pt (111) and Pt (100) surfaces in 0.1 M KOH. (Ross, P. N., Oxygen Reduction Reaction on Smooth Single Crystal Electrodes. In Handbook of Fuel Cells, John Wiley & Sons, Ltd: 2010.)
To optimize the properties of Pt/TiSi2 for further improvement of the catalytic activities as shown in
A saturation current density of 19.3 mA cmgeo−2 was measured (
ESA was determined from Pt—H adsorption/desorption region between 0.05-0.45 V vs. RHE. A surface charge density of 210 μC/cm2 for a monolayer adsorption/desorption of hydrogen on Pt surface was employed for estimation. For similar sizes of Pt particles on TiSi2 nanonets and Vulcan carbon, the calculated surface areas normalized to per gram of Pt were 35.1 m2 g−1 and 27.9 m2 g−1, respectively.
The CV of Pt/C sample in 0.1 M KOH has been reported by some of our previous papers. (Sheng, et al. 2010 J. Electrochem. Soc. 157, B1529-B1536.) Briefly, it showed the typical Pt—H underpotential deposition region, double-layer region, and Pt-oxide region. The Pt—H peaks at 0.2-0.3 V and 0.3-0.4 V can be attributed to the Pt—H interaction on Pt (110) and Pt (100) planes, respectively, based on the CVs of Pt single-crystal surfaces. However, the CV recorded on Pt/TiSi2 showed a dramatically different pattern, with suppressed peaks from Pt—H interaction on Pt (110) and Pt (100) surfaces. Combining with the structure characterization data and the factor of low growth kinetics of ALD process, Pt on TiSi2 has a higher Pt (111) surface concentration than Pt on C.
It has also been demonstrated that uniform and selective deposition of Ru NPs on TiSi2 nanonets can be achieved by atomic layer deposition. The resulting materials (Ru/TiSi2) showed promising performance in lithium oxygen batteries as an air cathode.
Ru deposition on TiSi2 was found to be site selective (same as Pt ALD deposition on TiSi2). The Ru nanoparticles were only grown on the top and bottom surfaces of a nanonet.
Ru/TiSi2 showed excellent performance as an air cathode in lithium oxygen batteries. The capacity reached 1000 mAh/gRu and good stability was demonstrated for 60 cycles.
Scanning electron microscope (SEM) characterization indicated a layer of Li2O2 product formed during discharge, which coated the entire Ru/TiSi2 nanostructure. The Li2O2 product can be reversibly removed by charging the cathode, and the entire nanostructure remains integrity even after 60 repeated cycles.
TiSi2 nanonets were synthesized by a chemical vapor deposition method. A Ti foil (Simga-Aldrich, 0.127 mm thick, purity: 99.7%) was placed in a home-built reaction chamber and heated to 675° C. Then, SiH4 (10% in He, Voltaix; at 50 standard cubic centimeter per minute, or sccm), TiCl4 (98%, Sigma-Aldrich; 2 sccm), and H2 (Industrial grade, Airgas; 60 sccm) were introduced to the chamber, and the pressure was maintained constant at 5 Torr. The growth duration was typically 10-120 min for varying sizes and densities of nanonets.
TiO2 was deposited in a Cambridge nanotech (Savannah 100) ALD system following procedures we previously reported. (Lin, et al. 2009 J. Am. Chem. Soc. 131, 2772-2773.) In brief, the reaction took place at 275° C. with a constant flow of N2 at 20 sccm. Titanium (IV) isopropoxide (Ti(iPrO)4, heated to 75° C.) and deionized H2O (room temperature) were used as reaction precursors. The pulse and purge times for Ti(iPrO)4 and H2O were 50 ms & 10 s, 15 ms & 10 s, respectively. A 10-cycle growth of TiO2 (estimated thickness: 0.5 nm) was applied to the TiSi2 nanonets to modify the surface.
The preparation of Si NWs was reported previously. (Yuan, et al. 2011 Angew. Chem. Int. Ed. 50, 2334-2338.) Briefly, Si (100) substrate (Wafernet) was cleaned with acetone, methanol, and isopropanol sequentially. The substrate was then oxidized in H2O2/H2SO4 (1:3 vol:vol) solution at 90° C. for 10 min to remove heavy metals and organic residue, and then rinsed by deionized water. Finally, the cleaned substrate was immersed into an HF/AgNO3 solution (4 M HF and 0.02 M AgNO3) for 30 min at 50° C. to produce Si NWs.
Pt nanoparticles were deposited in an Arradiance (Gemstar) atomic layer deposition system. The growth temperature was 250° C., with trimethyl-methylcyclopentadienyl platinum (IV) (MeCpPtMe3, heated to 75° C.) and compressed air (room temperature) as reaction precursors. Each cycle consisted of four repeated pulse/purges of MeCpPtMe3 for sufficient surface adsorption and one pulse/purge of O2 to decompose MeCpPtMe3. The purge gas was N2, and its flow rate was 90 sccm.
In conducting Ru ALD, Ru nanoparticles were deposited on TiSi2 nanonets in an Arradiance (Gemstar) atomic layer deposition system. The growth temperature was 290° C., with Bis(ethylcyclopentadienyl)ruthenium(II) (Ru(EtCp)2, heated to 110° C.) and compressed air (room temperature) as reaction precursors. Each cycle consisted of four repeated pulse/purge sub-cycles of Ru(EtCp)2 for sufficient surface adsorption and one pulse/purge of O2 to decompose Ru(EtCp)2. The purge gas was N2, and its flow rate was 90 sccm.
As-grown samples were imaged using a transmission electron microscope (TEM, JEOL 2010F) and a scanning electron microscope (SEM, JEOL 6340F). The TEM was operated at an acceleration voltage of 200 kV, and the SEM was at 10 kV. Elemental analysis was conducted using an energy dispersive spectroscopy (EDS) attachment to the TEM.
Pt/TiSi2 on flat Ti foil was attached onto the rotating disk electrode (glassy carbon electrode, 5 mm in diameter, Pine Instrument) for electrochemical measurements. The Pt/C electrode in the control experiment was prepared by first ultrasonicating the Pt/C nanoparticles (46 wt % supported by Vulcan carbon, Tanaka Kikinzoku (TKK), average diameter of Pt nanoparticles is 3.5 nm) in deionized water (Millipore, 18.2 MΩ) for 1 hour to make the ink, and then drop-casting the catalyst ink onto the same type of rotating disk electrode. The loading of nanoparticles was 50 μgPt/cm2disk.
Measurement of effective surface area (ESA): Cyclic voltammetry (CV) were collected in 0.1 M KOH solutions at a temperature maintained at 25° C. A Pt wire sealed in glass tubing and an Ag/AgCl electrode (4 M KCl, Pine Instruments) were used as counter and reference electrode, respectively. The electrolyte was purged with N2 (ultra high purity, Airgas) for 30 min before measurements. CVs were recorded at a scan rate of 50 mV s−1 between 0.05 and 1.10 V vs. RHE until they were stabilized. CVs were then recorded and presented at a scan rate of 10 mV s−1 in the same voltage range for ESA measurements.
Characterization of oxygen reduction activities: After ESA measurements, electrolyte was purged with O2 (ultra high purity, Airgas) for 30 minutes before evaluating ORR activities of Pt/TiSi2 and Pt/C samples. Polarization curves were recorded at various rotating rates (2500 rpm, 1600 rpm, 900 rpm, 400 rpm, 100 rpm) at a scan rate of 10 mV s−1 between 0.05 and 1.10 V vs. RHE. To correct for capacitance contribution, oxygen reduction currents were obtained by subtracting the polarization curve in N2 from the corresponding curve in O2.
ORR Activities in this Study and among Literature Reports
The kinetic current density in this study was calculated by Koutecky-Levich equation
1/i=1/ik+i/iD Equation (1)
where i is the measured current density, ik is the kinetic current density, and iD is the diffusion limited current density. (Bard, A. J.; Faulkner, L. R., Electrochemical Methods: Fundamentals and Applications. 2000.) The specific activity or mass activity of Pt on carbon showed in
In this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural reference, unless the context clearly dictates otherwise.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described. Methods recited herein may be carried out in any order that is logically possible, in addition to a particular order disclosed.
References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made in this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material explicitly set forth herein is only incorporated to the extent that no conflict arises between that incorporated material and the present disclosure material. In the event of a conflict, the conflict is to be resolved in favor of the present disclosure as the preferred disclosure.
The representative examples are intended to help illustrate the invention, and are not intended to, nor should they be construed to, limit the scope of the invention. Indeed, various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including the examples and the references to the scientific and patent literature included herein. The examples contain important additional information, exemplification and guidance that can be adapted to the practice of this invention in its various embodiments and equivalents thereof.
This application claims the benefit of U.S. Provisional Application No. 61/766,511, filed Feb. 19, 2013, the entire content of which is incorporated herein by reference in its entirety.
The United States Government has certain rights to the invention pursuant to Grant No. 1055762 from the National Science Foundation to Boston College.
| Number | Date | Country | |
|---|---|---|---|
| 61766511 | Feb 2013 | US |
