Atomistic Modeling of Colloidal Nanoparticles with Active Ligands: Solvation, Electroactivity, pH-Activity, and Bio-Activity
Dec 1, 2014 11:15am ‐ Dec 1, 2014 11:30am
Identification: E1.08
We present our recent collaborative studies of colloidal nanoparticles with active ligands that can control the nanoparticle behavior. In particular, we show that 1) nanoparticles of different sizes can have different solvation properties, 2) self-assembly and positioning of nanoparticles at the interfaces of different ionic solvents can be controlled by electric fields, 3) pH can control the self-assembly of nanoparticles into exotic superstructures, and 4) ligands can determine the biological responses or nanoparticles. We use atomistic molecular dynamics simulations to capture the unique characteristics of these novel systems and explain their properties through the physical, chemical, and biological processes taking part at their ligands.
Oxygen Delivery Scaffolds for Tissue Engineering and Tissue Preservation
Dec 1, 2014 11:15am ‐ Dec 1, 2014 11:30am
Identification: H2.04
Multiexciton Generation and Decay in Two-Dimensional Nanosheets
Dec 1, 2014 11:15am ‐ Dec 1, 2014 11:30am
Identification: II1.07
We have determined the Auger recombination kinetics of electrons and holes in colloidal CdSe-only and CdSe/CdS/ZnS core/shell nanoplatelets by time-resolved photoluminescence measurements.(1) At high excitation density Auger recombination can be described by second-order kinetics. From this we infer that the majority of electrons and holes are bound in the form of neutral excitons, while the fraction of free charges is much smaller, in agreement with our terahertz conductivity measurements. The biexciton Auger recombination is not diffusion-controlled and is more than one order of magnitude smaller than for quantum dots and nanorods of equal volume. The latter is of advantage for application in lasers, light-emitting diodes and photovoltaics.
The generation of two or more electron-hole pairs for the absorption of a single energetic photon is of interest for development of highly efficient (up to 44%) solar cells. The efficiency of this carrier multiplication (CM) process depends on several factors, including the competition with cooling, the Coulomb interaction between the hot charge carrier and the final trion density of states. All these factors depend on nanocrystal dimensionality. Previously carrier multiplication has been investigated in lead chalcogenide quantum dots (0D), nanorods (1D) and bulk (3D).
We investigated the efficiency of carrier multiplication in two-dimensional PbS nanosheets of 4 to 7 nm thickness using ultrafast optical pump-probe spectroscopy.(2) The efficiency of carrier multiplication in nanosheets is much higher than for quantum dots, nanorods and bulk material. in thin PbS nanosheets virtually the entire excess photon energy above the CM threshold is used for CM, in contrast to quantum dots, nanorods and bulk lead chalcogenide materials.
References:
(1) Kunneman, L. T.; Tessier, M. D.; Heuclin, H.; Dubertret, B.; Aulin, Y. V.; Grozema, F. C.; Schins, J. M.; Siebbeles, L. D. A. J. Phys. Chem. Lett. 2013, 4, 3574.
(2) Aerts, M.; Bielewicz, T.; Klinke, C.; Grozema, F. C.; Houtepen, A. J.; Schins, J. M.; Siebbeles, L. D. A. Nature Commun. 2014, 5, 3789.
The generation of two or more electron-hole pairs for the absorption of a single energetic photon is of interest for development of highly efficient (up to 44%) solar cells. The efficiency of this carrier multiplication (CM) process depends on several factors, including the competition with cooling, the Coulomb interaction between the hot charge carrier and the final trion density of states. All these factors depend on nanocrystal dimensionality. Previously carrier multiplication has been investigated in lead chalcogenide quantum dots (0D), nanorods (1D) and bulk (3D).
We investigated the efficiency of carrier multiplication in two-dimensional PbS nanosheets of 4 to 7 nm thickness using ultrafast optical pump-probe spectroscopy.(2) The efficiency of carrier multiplication in nanosheets is much higher than for quantum dots, nanorods and bulk material. in thin PbS nanosheets virtually the entire excess photon energy above the CM threshold is used for CM, in contrast to quantum dots, nanorods and bulk lead chalcogenide materials.
References:
(1) Kunneman, L. T.; Tessier, M. D.; Heuclin, H.; Dubertret, B.; Aulin, Y. V.; Grozema, F. C.; Schins, J. M.; Siebbeles, L. D. A. J. Phys. Chem. Lett. 2013, 4, 3574.
(2) Aerts, M.; Bielewicz, T.; Klinke, C.; Grozema, F. C.; Houtepen, A. J.; Schins, J. M.; Siebbeles, L. D. A. Nature Commun. 2014, 5, 3789.
Refractory Metals for High Temperature Metamaterial Thermal Emitters
Dec 1, 2014 11:15am ‐ Dec 1, 2014 11:30am
Identification: L1.08
Thermophotovoltaic (TPV) devices can enhance the efficiency of existing energy generation infrastructure by reclaiming heat lost during production processes. In order to maximize the efficiency of these devices, the conversion efficiency of the TPV system needs to be optimized. Most TPV systems consist of three discrete stages: a thermal emitter, a filter, and a TPV diode. One avenue to increase TPV efficiency is to replace the wide-band emitters presently in use with a selective thermal emitter. The selective emitter would absorb wide-band radiation from a heat source and convert it into narrow bandwidth peaks of radiation tailored to the rest of the system. This would dramatically reduce energy loss due to reflection, diode heating, and carrier relaxation. In recent years, metamaterials (MM) have emerged as the ideal medium for the development of engineerable, narrowband selective emitters for such applications.
Most research into metamaterials has utilized gold as the conducting metal. With a bulk melting point of 1064 °C, nano-sized gold patterns will completely degrade at, if not before, the operating temperature of most TPV cells. The most common TPV cells in use today are bulk GaSb diodes. The band gap of this material is 0.7eV, which corresponds to a light wavelength of 1.7μm. According to Wien's Law, to achieve a blackbody radiation curve with this wavelength at the peak intensity the radiating body would have to be at a temperature of 1400 °C, well above the melting point of gold. Exploring alternate materials and their viability for use in emitters will lead to great advances in current achievable efficiencies.
To operate at the high temperatures required to optimize the efficiency of such photodiodes, traditional MM conductors, such as gold and copper, need to be replaced with more thermally robust metals. Our research consists of a thorough study of potential materials and looks at the design and response of metamaterial selective emitters with emission peaks at 1, 2, 3, 4, 6, 8, and 10 microns, respectively. Designs were made using gold, to compare with current literature, as well as platinum, tungsten, and irridium. Testing will consist of absorption measurements at room temperature and emission testing at increasingly higher temperatures until breakdown is achieved.
Most research into metamaterials has utilized gold as the conducting metal. With a bulk melting point of 1064 °C, nano-sized gold patterns will completely degrade at, if not before, the operating temperature of most TPV cells. The most common TPV cells in use today are bulk GaSb diodes. The band gap of this material is 0.7eV, which corresponds to a light wavelength of 1.7μm. According to Wien's Law, to achieve a blackbody radiation curve with this wavelength at the peak intensity the radiating body would have to be at a temperature of 1400 °C, well above the melting point of gold. Exploring alternate materials and their viability for use in emitters will lead to great advances in current achievable efficiencies.
To operate at the high temperatures required to optimize the efficiency of such photodiodes, traditional MM conductors, such as gold and copper, need to be replaced with more thermally robust metals. Our research consists of a thorough study of potential materials and looks at the design and response of metamaterial selective emitters with emission peaks at 1, 2, 3, 4, 6, 8, and 10 microns, respectively. Designs were made using gold, to compare with current literature, as well as platinum, tungsten, and irridium. Testing will consist of absorption measurements at room temperature and emission testing at increasingly higher temperatures until breakdown is achieved.
Measuring the Young Measure Using EBSD
Dec 1, 2014 11:15am ‐ Dec 1, 2014 11:30am
Identification: NN1.08
EBSD is a method of measuring the local orientation of crystals at the scale down to nanometer, while Young measure is a mathematical tool of analyzing deformation with fine microstructure at the continuum scale (often larger than micrometer). For martensitic materials without external stressing, local crystal orientation is sufficient to determine the local deformation, given the transformation stretch tensor and the assignment of variants to regions of homogeneous deformation. Therefore, EBSD is potentially a tool of accurately measuring the deformation distribution in a small (at the continuum scale) neighborhood of a point in such materials. The distribution can be further utilized to construct the Young measure field.
This manuscript discusses a scheme for measuring the Young measure using EBSD in a material that undergoes a martensitic phase transformation. The scheme is based on the (weak) Cauchy-Born rule. The scheme first includes an algorithm of determining the transformation stretch metric. Then by assigning phases or variants for regions in the EBSD images, the distribution of deformation gradients in a small neighborhood of a point in the sample is measured. Besides, the scheme also includes specific algorithms to check whether certain zero elastic energy microstructures, which have been associated with low hysteresis and enhanced reversibility, are present in the sample. The treatment is geometrically exact: no assumptions of smallness of the deformation are made in the interpretation of the measurements.
We acknowledge the financial support of MURI project FA9550-12-1-0458 (administered by AFOSR). This research also benefited from the support of NSF-PIRE grant number OISE-0967140.
Sub-Microsecond In-Situ X-Ray Diffraction of Bulk Polycrystalline Metals under Dynamic Compression
Dec 1, 2014 11:15am ‐ Dec 1, 2014 11:30am
Identification: TT1.06
Time-resolved x-ray diffraction can provide important insights into the evolution of the structure of a material during dynamic loading, such as the elastic strains in individual phases, crystallographic texture, and the development of new (possibly metastable) phases. We performed time-resolved x-ray diffraction on bulk polycrystalline metals and alloys undergoing dynamic compressive loading in a split Hopkinson (Kolsky) bar apparatus at strain rates of approximately 2500 s−1 with exposures as short as 70 ns. The diffraction patterns were recorded in transmission onto the Cornell Keck-PAD, a high-speed analog pixel array detector, using 10 keV x-rays from the Cornell High Energy Synchrotron Source (CHESS). Varying the orientation of the Kolsky bar with respect to the incident x-rays and the position of the detector allowed us vary the orientation of the scattering vector with respect to the loading direction.
As an example we discuss texture evolution of magnesium alloy AZ31 under dynamic compression. We observed a decrease in scattering from the (0002) planes and a corresponding increase in scattering from the (10-10) planes with the scattering vector perpendicular to the loading axis, while the opposite behavior was observed with the scattering vector approximately parallel to the loading axis. This is consistent with texture evolution in the form of a reorientation of the magnesium lattice due to activation of {10-11}<10-1-2> compression twins in response to dynamic deformation. Finally, we will discuss prospects for future developments in experiments of this kind, taking advantage of new detectors and x-ray sources.
Structure-Property Relationship in Biologically-Derived Eumelanin Cathodes Electrochemical Energy Storage
Dec 1, 2014 11:30am ‐ Dec 1, 2014 11:45am
Identification: A1.10
Organic compounds represent promising alternatives to inorganic materials for renewable and sustainable energy storage devices. Organic molecules can be processed into non-conventional form factors, are cost-effective, and exhibit reduced toxicity compared to other exotic inorganic materials. Carbonyls, carboxylates, amines are the attractive redox-active chemical signatures of organic compounds that could potentially be utilized as electrode materials by reversible binding of cations. While these redox-active organic compounds enable the novel pathway as charge storage devices, there are many persistent challenges that may limit the prospective utility of organic electrodes. Major challenges include low charge collection abilities and high solubility in electrolytes.
Here we introduce the use of biologically-derived eumelanin pigments as cathode materials in aqueous sodium-ion electrochemical storage devices. Eulemanin, a sub-class of melanin, exhibits redox-active signatures including pendant carboxylates, aromatic amines, and catechols that can support reversible cation binding. Eulemanins are ideal electrode materials because they are stable in aqueous electrolytes and are composed of nanostructured granules. Homogeneous microstructures overcome kinetic limitations of organic electrodes. Current collection in semiconducting melanins can be improved by incorporating conducting silver nanowire (AgNW) networks. Full cells are composed of sodium titanium phosphate (NaTi2(PO4)3) anodes and eumelanin cathodes. Galvanostatic full cell discharge exhibits a stable working potential of 0.5 V. Specific capacities of full cells discharged at 0.05 Ag-1 contain 49 and 78 mAhg-1 for natural (NatMel) and synthetic melanin (SynMel) respectively. FT-IR and Raman spectra corroborate that Na+ associates with pendant carboxylates of eumelanins during discharge. Natural melanins exhibit unique potential plateaus during discharge that are not present in synthetic melanins. These data support the presence of porphyrin structures in natural melanins, which are largely absent in synthetic melanins. The details regarding the structure-property relationships will be discussed.
Taken together, eumelanin-based cathodes represent a material that is compatible with broader strategies of sustainable and renewable energy storage. Melanins are a class of organic molecules that exhibit suitable performance, cost-effectiveness, and limited processing to produce electrochemical storage devices.
Here we introduce the use of biologically-derived eumelanin pigments as cathode materials in aqueous sodium-ion electrochemical storage devices. Eulemanin, a sub-class of melanin, exhibits redox-active signatures including pendant carboxylates, aromatic amines, and catechols that can support reversible cation binding. Eulemanins are ideal electrode materials because they are stable in aqueous electrolytes and are composed of nanostructured granules. Homogeneous microstructures overcome kinetic limitations of organic electrodes. Current collection in semiconducting melanins can be improved by incorporating conducting silver nanowire (AgNW) networks. Full cells are composed of sodium titanium phosphate (NaTi2(PO4)3) anodes and eumelanin cathodes. Galvanostatic full cell discharge exhibits a stable working potential of 0.5 V. Specific capacities of full cells discharged at 0.05 Ag-1 contain 49 and 78 mAhg-1 for natural (NatMel) and synthetic melanin (SynMel) respectively. FT-IR and Raman spectra corroborate that Na+ associates with pendant carboxylates of eumelanins during discharge. Natural melanins exhibit unique potential plateaus during discharge that are not present in synthetic melanins. These data support the presence of porphyrin structures in natural melanins, which are largely absent in synthetic melanins. The details regarding the structure-property relationships will be discussed.
Taken together, eumelanin-based cathodes represent a material that is compatible with broader strategies of sustainable and renewable energy storage. Melanins are a class of organic molecules that exhibit suitable performance, cost-effectiveness, and limited processing to produce electrochemical storage devices.
Label Free Plasmonic Biosensing of Cardiac Biomarker, Troponin Using Aptamer Conjugated Nanoparticles
Dec 1, 2014 11:30am ‐ Dec 1, 2014 11:45am
Identification: D2.04
Acute myocardial infarction (MI) remains a leading cause of morbidity and mortality worldwide. Cardiac biomarker, troponin, is the most specific and sensitive test for detection and risk stratification of myocardial damage. However, existing immunoassay techniques are too expensive and not ideal for point-of-care and resource-limited settings. The use of label-free plasmonic biosensing is an attractive alternative to the existing immunoassay techniques. Metal nanostructures conjugated with antibody can be used to capture and detect protein biomarkers owing to refractive index sensitivity of the localized surface plasmon resonance of these nanostructures. Although natural antibodies exhibit good specificity, they suffer from poor shelf life, limited pH and temperature stability and excessive cost, making them non-ideal for point-of-care diagnostics.
Here we design and demonstrate a protein aptamer-based plasmonic biosensor to quantitatively detect troponin in physiological fluids. Considering the remarkable stability (chemical, temporal and environmental) of the aptamers, plasmonic biochips based on aptamers as recognition elements enable facile handling and storage. Furthermore, the use of protein aptamers as recognition elements results in higher sensitivity compared to antibodies considering the smaller size of the aptamers and the exponential decay in refractive index sensitivity from the surface of the nanotransducers. Finally, the plasmonic biosensing is implemented on a flexible and ubiquitous paper substrate enabling the easy translation of this technology to point-of-care and resource-limited settings.
Here we design and demonstrate a protein aptamer-based plasmonic biosensor to quantitatively detect troponin in physiological fluids. Considering the remarkable stability (chemical, temporal and environmental) of the aptamers, plasmonic biochips based on aptamers as recognition elements enable facile handling and storage. Furthermore, the use of protein aptamers as recognition elements results in higher sensitivity compared to antibodies considering the smaller size of the aptamers and the exponential decay in refractive index sensitivity from the surface of the nanotransducers. Finally, the plasmonic biosensing is implemented on a flexible and ubiquitous paper substrate enabling the easy translation of this technology to point-of-care and resource-limited settings.
Amplified Spontaneous Emission and Lasing in Colloidal Quantum Wells
Dec 1, 2014 11:30am ‐ Dec 1, 2014 11:45am
Identification: II1.08
Colloidal quantum wells (CQWs), which are also known as colloidal nanoplatelets, are appealing light-emitting materials exhibiting unique optical properties. These include narrow photoluminescence full-width at half-maxima, quantum-well like density of states and absence of inhomogeneous broadening which make these CQWs as promising optical gain materials. However, there was no demonstration of lasing in the CQWs to date.
In this work, we demonstrate ultrahigh efficiency amplified spontaneous emission (ASE) and lasing in CdSe core and CdSe/CdS core/crown CQWs.[1] Core/crown CQWs, which have been recently introduced, show enhanced optical properties owing to the laterally grown CdS layer that also acts as a light-absorbing antenna boosting the absorption cross-section.[2, 3] Here, we synthesize various core/crown CQWs having varying lateral crown size, then we study single- and two-photon absorption pumped ASE in these CQWs. Core/crown CQWs exhibit enhanced optical gain performance as compared to the only core CQWs thanks to the increased absorption cross-section and enhanced passivation by the crown layer. We achieve single-photon absorption (?exc = 400 nm) pumped ASE with a threshold as low as 41 ?J/cm2 in the core/crown CQWs, which represents the best reported ASE threshold among the colloidal nanocrystals emitting in the green region of the visible spectrum.[1] Then, we also investigate two-photon absorption (?exc = 800 nm) pumped ASE in these CQWs exhibiting a record low threshold of 4.5 mJ/cm2 better than that of the best reported threshold in quantum dots and rods.[1] Moreover, we measure the gain coefficient via variable stripe length technique, using which the gain coefficient of the core/crown CQWs is found to be as high as 650 cm-1. This represents more than 2- and 4-fold enhancement over the best reported gain coefficient in colloidal quantum rods and dots.[4, 5]
Finally, we develop an all solution processed vertical cavity surface emitting laser (VCSEL) of the CQWs that are sandwiched between two distributed Bragg reflectors, which were fabricated by colloidal nanoparticles of SiO2 and TiO2. The VCSELs exhibit surpassing two-photon absorption pumped lasing performance with a lasing threshold of 2.5 mJ/cm2 with a Q-factor of 300.[1] Overall, these remarkable results of ultralow threshold ASE and extremely high optical gain coefficient make these CQWs highly promising materials as colloidal optical gain media for lasers.
References:
[1] B. Guzelturk et al., ACS Nano (2014) DOI: 10.1021/nn5022296.
[2] M. D. Tessier et al., Nano Lett. 14, 207-213 (2014).
[3] A. Prudnikau et al., JACS 135, 14476-14479 (2013).
[4] A. V. Malko et al., Appl. Phys. Lett. 81, 1303 (2002).
[5] M. Kazes et al., J. Phys. Chem. C 111, 7898-7905 (2007).
In this work, we demonstrate ultrahigh efficiency amplified spontaneous emission (ASE) and lasing in CdSe core and CdSe/CdS core/crown CQWs.[1] Core/crown CQWs, which have been recently introduced, show enhanced optical properties owing to the laterally grown CdS layer that also acts as a light-absorbing antenna boosting the absorption cross-section.[2, 3] Here, we synthesize various core/crown CQWs having varying lateral crown size, then we study single- and two-photon absorption pumped ASE in these CQWs. Core/crown CQWs exhibit enhanced optical gain performance as compared to the only core CQWs thanks to the increased absorption cross-section and enhanced passivation by the crown layer. We achieve single-photon absorption (?exc = 400 nm) pumped ASE with a threshold as low as 41 ?J/cm2 in the core/crown CQWs, which represents the best reported ASE threshold among the colloidal nanocrystals emitting in the green region of the visible spectrum.[1] Then, we also investigate two-photon absorption (?exc = 800 nm) pumped ASE in these CQWs exhibiting a record low threshold of 4.5 mJ/cm2 better than that of the best reported threshold in quantum dots and rods.[1] Moreover, we measure the gain coefficient via variable stripe length technique, using which the gain coefficient of the core/crown CQWs is found to be as high as 650 cm-1. This represents more than 2- and 4-fold enhancement over the best reported gain coefficient in colloidal quantum rods and dots.[4, 5]
Finally, we develop an all solution processed vertical cavity surface emitting laser (VCSEL) of the CQWs that are sandwiched between two distributed Bragg reflectors, which were fabricated by colloidal nanoparticles of SiO2 and TiO2. The VCSELs exhibit surpassing two-photon absorption pumped lasing performance with a lasing threshold of 2.5 mJ/cm2 with a Q-factor of 300.[1] Overall, these remarkable results of ultralow threshold ASE and extremely high optical gain coefficient make these CQWs highly promising materials as colloidal optical gain media for lasers.
References:
[1] B. Guzelturk et al., ACS Nano (2014) DOI: 10.1021/nn5022296.
[2] M. D. Tessier et al., Nano Lett. 14, 207-213 (2014).
[3] A. Prudnikau et al., JACS 135, 14476-14479 (2013).
[4] A. V. Malko et al., Appl. Phys. Lett. 81, 1303 (2002).
[5] M. Kazes et al., J. Phys. Chem. C 111, 7898-7905 (2007).
Engineered Infrared Plasmonic Metamaterials for Molecular Vibration Enhancement and Suppression Observed by Photothermal Spectral-Microscopy
Dec 1, 2014 11:30am ‐ Dec 1, 2014 11:45am
Identification: L1.09
Recently, the interaction between plasmonic metamaterials and vibrational modes of a molecule has been studied as a potential method for ultrasensitive light-matter interaction. It has been shown that coupling of radiative modes of plasmonic metamaterials can mimic electromagnetically induced transparency behavior as observed in atomic and molecular interference effects. In this work, we demonstrate coupling between a narrow molecular vibrational mode with a broad plasmonic resonance that enhances or suppresses the molecular resonance. At critical coupling it cancels out the absorption band entirely. The observed phenomenon is investigated by direct absorption using the FTIR and photothermal spectral-microscopy. Plasmonic metamaterials were fabricated using a liftoff process and e-beam lithography. A thin layer of liquid crystal was placed on top of the structures with a weak combinational band at 1912cm-1. By tuning the length and the periodicity of the plasmonic nano-antennae array we were able to suppress, enhance and cancel out the molecular vibrational mode. A home-built mid-IR photothermal setup is used in combination with a tunable QCL, a plasmonic substrate, an inexpensive silicon photodetector and lock-in detection to measure the sensitivity and specificity of performing vibrational infrared spectroscopy on biomolecules. Mid-IR photothermal spectroscopy combined with plasmonic metamaterials has the potential to detect ultralow concentration of absorbers using low-cost photodetectors and bright tunable QCLs.