139 results on '"Joseph G. Tischler"'
Search Results
2. Cu2-xS/PbS Core/Shell Nanocrystals with Improved Chemical Stability
- Author
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Rhonda M. Stroud, Janice E. Boercker, Nadeemullah A. Mahadik, Sarah Brittman, Patrick Y. Yee, Peter C. Sercel, Alexander L. Efros, and Joseph G. Tischler
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Core shell ,Materials science ,Nanocrystal ,Chemical engineering ,General Chemical Engineering ,Materials Chemistry ,Chemical stability ,General Chemistry - Abstract
Nanocrystals of doped semiconductors, such as Cu_(2-x)S, hold much promise for near infrared active devices because, unlike in noble metals, their tunable infrared plasmon can exist in nanocrystals with diameters
- Published
- 2021
3. Tuning of Phonons and Surface Phonon Polaritons
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Vanessa M. Breslin, Andrea B. Grafton, Daniel C. Ratchford, Alexander J. Giles, Kenan P. Fears, Christopher R. So, D. Scott Katzer, Chase T. Ellis, Joseph G. Tischler, Joshua D. Caldwell, Adam D. Dunkelberger, and Jeffrey C. Owrutsky
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- 2022
4. Ultrafast Active Tuning of the Berreman Mode
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Alexander J. Giles, Kenan P. Fears, Vanessa M. Breslin, Igor Vurgaftman, D. Scott Katzer, Jeffrey C. Owrutsky, Chase T. Ellis, Andrea B. Grafton, Joseph G. Tischler, Daniel Ratchford, Adam D. Dunkelberger, R. Joseph Weiblen, Joshua D. Caldwell, and Elizabeth S. Ryland
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Materials science ,genetic structures ,Condensed matter physics ,Phonon ,Mode (statistics) ,Physics::Optics ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,eye diseases ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,010309 optics ,Phonon polariton ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,0103 physical sciences ,Polar ,sense organs ,Electrical and Electronic Engineering ,Thin film ,0210 nano-technology ,Ultrashort pulse ,Biotechnology - Abstract
The Berreman effect, by which thin films of polar dielectric materials exhibit strong, narrow resonances near their longitudinal optic (LO) phonon frequency, results in strong material interactions...
- Published
- 2019
5. Enhanced Infrared Photodiodes Based on PbS/PbCl
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Adam E, Colbert, Diogenes, Placencia, Erin L, Ratcliff, Janice E, Boercker, Paul, Lee, Edward H, Aifer, and Joseph G, Tischler
- Abstract
Improved passivation strategies to address the more complex surface structure of large-diameter nanocrystals are critical to the advancement of infrared photodetectors based on colloidal PbS. In this contribution, the performance of short-wave infrared (SWIR) photodiodes fabricated with PbS/PbCl
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- 2021
6. Rapid Bimolecular and Defect-Assisted Carrier Recombination in Hexagonal Boron Nitride
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Alexander J. Giles, James C. Culbertson, Daniel Ratchford, Adam D. Dunkelberger, Jeffrey C. Owrutsky, Chase T. Ellis, Roderick B. Davidson, Andrea B. Grafton, Joshua D. Caldwell, Ioannis Chatzakis, Joseph G. Tischler, James H. Edgar, Song Liu, and Jaime A. Freitas
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Materials science ,Band gap ,Physics::Optics ,Hexagonal boron nitride ,Astrophysics::Cosmology and Extragalactic Astrophysics ,02 engineering and technology ,010402 general chemistry ,medicine.disease_cause ,01 natural sciences ,Condensed Matter::Materials Science ,medicine ,Physical and Theoretical Chemistry ,Nonlinear Sciences::Pattern Formation and Solitons ,Astrophysics::Galaxy Astrophysics ,business.industry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Semiconductor ,Optoelectronics ,0210 nano-technology ,business ,Recombination ,Ultraviolet - Abstract
Hexagonal boron nitride (hBN) is a wide, indirect bandgap semiconductor that holds great promise for optoelectronic devices in the ultraviolet and mid-infrared spectral regimes. The efficiency of o...
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- 2019
7. Intrinsic Gap States in Semiconductors with Inverted Band Structure: Comparison of SnTe vs PbTe Nanocrystals
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Roman Vaxenburg, C. Stephen Hellberg, Chase T. Ellis, Janice E. Boercker, Joseph G. Tischler, Danielle L. Woodall, and Alexander L. Efros
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Materials science ,Photoluminescence ,Valence (chemistry) ,Condensed matter physics ,business.industry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermal conduction ,01 natural sciences ,Spectral line ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,General Energy ,Semiconductor ,Nanocrystal ,Physical and Theoretical Chemistry ,0210 nano-technology ,Electronic band structure ,business ,Quantum - Abstract
In this contribution we compare size-dependent optical properties of PbTe and SnTe nanocrystals (NCs). We demonstrate that the size dependence of the band edge absorption line and the photoluminescence (PL) of PbTe NCs can be quantitatively described by optical transitions between the lowest quantum confined states of conduction and valence bands. In contrast, the optical properties of SnTe NCs are strongly influenced by intrinsic gap states that arise from the inverted band structure that can be described by introducing a negative energy gap Eg < 0. In principle, these intrinsic gap states could be observed directly in PL and absorption of small size SnTe NCs, where the wave functions of these states are spread over the entire NC volume. In our samples, however, these transitions are not observed due to self-doping of SnTe NCs by holes created from negatively charged Sn vacancies. As a result, the absorption is blue-shifted due to filling of the gap states and confined valence band levels by holes (pheno...
- Published
- 2019
8. Plasmonic nanoarcs: a versatile platform with tunable localized surface plasmon resonances in octave intervals
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Matthew S. Davis, Chase T. Ellis, Joseph G. Tischler, Kunyi Zhang, Oded Rabin, Andrew P. Lawson, Thomas E. Murphy, and Hans A. Bechtel
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Physics ,Communications Technologies ,business.industry ,Surface plasmon ,Physics::Optics ,Nonlinear optics ,Optics ,Optical Physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Polarization (waves) ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,010309 optics ,0103 physical sciences ,High harmonic generation ,Electrical and Electronic Engineering ,Surface plasmon resonance ,0210 nano-technology ,business ,Magnetic dipole ,Plasmon ,Localized surface plasmon - Abstract
The tunability of the longitudinal localized surface plasmon resonances (LSPRs) of metallic nanoarcs is demonstrated with key relationships identified between geometric parameters of the arcs and their resonances in the infrared. The wavelength of the LSPRs is tuned by the mid-arc length of the nanoarc. The ratio between the attenuation of the fundamental and second order LSPRs is governed by the nanoarc central angle. Beneficial for plasmonic enhancement of harmonic generation, these two resonances can be tuned independently to obtain octave intervals through the design of a non-uniform arc-width profile. Because the character of the fundamental LSPR mode in nanoarcs combines an electric and a magnetic dipole, plasmonic nanoarcs with tunable resonances can serve as versatile building blocks for chiroptical and nonlinear optical devices.
- Published
- 2020
9. Tailoring phonon-polaritons with new materials and active modulation
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Alexander J. Giles, Chase T. Ellis, Joseph G. Tischler, Vanessa M. Breslin, Joshua D. Caldwell, Igor Vurgaftman, D. Scott Katzer, Adam D. Dunkelberger, Jeffrey C. Owrutsky, and Daniel Ratchford
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Range (particle radiation) ,Materials science ,Phonon ,business.industry ,Nanophotonics ,Physics::Optics ,Spectral line ,Condensed Matter::Materials Science ,Modulation ,Polariton ,Optoelectronics ,Polar ,Thin film ,business - Abstract
The mid-infrared spectra of many polar materials are dominated by highly reflective reststrahlen bands that occur between the transverse and longitudinal optical phonons. Within the reststrahlen bands, light can couple with optical phonons to support phonon-polariton modes. These modes enhance light-matter interactions through the concentration of light to nanoscale dimensions, and therefore, are particularly promising for mid-infrared nanophotonic applications. Here, we discuss our work on expanding the spectral range over which phonon-polaritons are supported by using new material systems, as well as active tuning of the modes via carrier photoinjection. In particular, we report on the confinement of hyperbolic phonon-polaritons in calcite, a ubiquitous polar material. We also report the use of the LO-phonon-plasmon-coupling (LOPC) effect to actively tune the Berreman mode of a GaN thin film.
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- 2020
10. Binary Superlattices of Infrared Plasmonic and Excitonic Nanocrystals
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Patrick Y. Yee, Janice E. Boercker, Syed B. Qadri, Joseph G. Tischler, Sarah Brittman, and Nadeemullah A. Mahadik
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Condensed Matter::Quantum Gases ,Coupling ,Materials science ,Infrared ,business.industry ,Superlattice ,Physics::Optics ,Binary number ,Metamaterial ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Condensed Matter::Materials Science ,Nanocrystal ,Physics::Atomic and Molecular Clusters ,Optoelectronics ,General Materials Science ,Self-assembly ,0210 nano-technology ,business ,Plasmon - Abstract
Self-assembled superlattices of nanocrystals offer exceptional control over the coupling between nanocrystals, similar to how solid-state crystals tailor the bonding between atoms. By assembling nanocrystals of different properties (e.g., plasmonic, excitonic, dielectric, or magnetic), we can form a wealth of binary superlattice metamaterials with new functionalities. Here, we introduce infrared plasmonic Cu
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- 2020
11. Synthesis and Characterization of PbS/ZnS Core/Shell Nanocrystals
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Rhonda M. Stroud, Todd Brintlinger, Danielle L. Woodall, Diogenes Placencia, Chase T. Ellis, Michael H. Stewart, Joseph G. Tischler, Paul D. Cunningham, and Janice E. Boercker
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Materials science ,General Chemical Engineering ,Shell (structure) ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Sulfur ,Dark field microscopy ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Nanocrystal ,Chemical engineering ,Monolayer ,Scanning transmission electron microscopy ,Materials Chemistry ,Thioacetamide ,0210 nano-technology - Abstract
We demonstrate a synthetic method to add a ZnS shell, with controlled thickness, to PbS nanocrystals using Zn oleate and thioacetamide as Zn and S precursors. The ZnS shell reaction is self-limiting and deposits approximately a monolayer of ZnS per shell reaction without causing the PbS nanocrystals to Ostwald ripen. The reaction is self-limiting because the sulfur precursor, thioacetamide, is less reactive toward the PbS/ZnS core/shell nanocrystal surface as compared to the Zn oleate precursor present in the reaction solution. To increase the ZnS shell thickness beyond a monolayer, subsequent ZnS shell reactions are modified by adding the thioacetamide 10 minutes before the Zn oleate. This gives the thioacetamide time to react at the PbS/ZnS core/shell nanocrystal surface before the Zn oleate is added. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) shows most ZnS shells lack crystalline order. However, select core/shell nanocrystals have epitaxial crystalline (zinc-b...
- Published
- 2018
12. Active tuning of surface phonon polariton resonances via carrier photoinjection
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Mijin Kim, Chase T. Ellis, James Long, Joshua D. Caldwell, Joseph G. Tischler, Bryan T. Spann, O. J. Glembocki, Daniel Ratchford, Adam D. Dunkelberger, I. Vurgaftman, Jeffrey C. Owrutsky, Chul Soo Kim, and Alexander J. Giles
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010302 applied physics ,Condensed Matter - Materials Science ,Materials science ,business.industry ,Phonon ,Nanophotonics ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Physics::Optics ,02 engineering and technology ,Surface phonon ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Blueshift ,Condensed Matter::Materials Science ,Laser linewidth ,Semiconductor ,0103 physical sciences ,Polariton ,Optoelectronics ,0210 nano-technology ,business ,Plasmon - Abstract
Surface phonon polaritons (SPhPs) are attractive alternatives to infrared plasmonics for subdiffractional confinement of infrared light. Localized SPhP resonances in semiconductor nanoresonators are narrow, but that linewidth and the limited extent of the Reststrahlen band limit spectral coverage. To address this limitation, we report active tuning of SPhP resonances in InP and 4H-SiC by photoinjecting free carriers into nanoresonators, taking advantage of the coupling between the carrier plasma and optic phonons to blueshift SPhP resonances. We demonstrate state-of-the-art tuning figures of merit upon continuous-wave excitation (in InP) or pulsed excitation (in 4H-SiC). Lifetime effects cause the tuning to saturate in InP, and carrier redistribution leads to rapid (
- Published
- 2017
13. Natural hyperbolicity in bulk calcite
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Thomas L. Reinecke, Saikat Mukhopadhyay, Chase T. Ellis, Daniel Ratchford, Michelle Johannes, Joseph G. Tischler, and Eric M. Jackson
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Crystal ,Calcite ,chemistry.chemical_compound ,Materials science ,chemistry ,Chemical physics ,business.industry ,General Physics and Astronomy ,Photonics ,business ,Reflectivity ,Natural (archaeology) - Abstract
Naturally occurring materials with hyperbolic optical properties are attracting considerable interest due to their ability to confine light in small volumes and their resulting potential for applications in photonics. This paper uses a first-principles theoretical approach without adjustable parameters to investigate the hyperbolic optical properties of bulk calcite (CaCO3). This material exhibits natural hyperbolic behavior within its Reststrahlen bands at 1403–1552 and 864–887 cm−1. The calculated results are shown to be in good agreement with our reflectance data obtained from frequency- and polarization-dependent measurements. These results show that calcite is an attractive natural hyperbolic material; in addition, it has the advantage of low losses and is available commercially in a variety of crystal orientations.
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- 2021
14. The effect and nature of N–H complexes in the control of the dominant photoluminescence transitions in UV-hydrogenated GaInNAs
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Khalid Hossain, N. J. Estes, Bin Wang, M. Al Khalfioui, Mathieu Leroux, Evan R. Glaser, C. R. Brown, Joseph G. Tischler, Terry Golding, Ian R. Sellers, Chase T. Ellis, and V. R. Whiteside
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010302 applied physics ,Photoluminescence ,Materials science ,Passivation ,Band gap ,business.industry ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Materials Science ,Lattice constant ,Impurity ,Chemical physics ,0103 physical sciences ,Optoelectronics ,Density functional theory ,Spontaneous emission ,0210 nano-technology ,business ,Electronic band structure - Abstract
Due to its 1 eV band gap and GaAs-matched lattice constant, GaInNAs has long been considered for use in four-junction multi-junction solar cells; but, material quality issues have impeded its use in highly efficient devices. Here, we present an analysis of GaInNAs samples partially hydrogenated via a UV-activated process in which nitrogen-related alloy fluctuations, impurities, and defects have been passivated; remarkably, removing completely the ‘s-shape’ dependence of the photoluminescence while keeping intact the effects of nitrogen substitution, i.e., the band gap of the alloy prior to passivation. Hydrogenation of the optical samples by a UV-activated process has resulted in GaInNAs photoluminescence dominated by the free-excitonic band gap transition, rather than radiative recombination processes from the shallow localized centers that result due to unavoidable alloy fluctuations. This behavior is unique since these centers dominate the low temperature photoluminescence even in the highest quality dilute nitrides. Density functional theory calculations show that the hydrogenation of the N and Ga atoms eliminates the defect levels from the band gap through the formation of H–N centers that act as donors; while at high concentration of hydrogen, Ga–H2–N complexes reside within the continuum. The formation of these hydrogen complexes, along with the incumbent change of the band structure, explains the reduction of emission from the localized centers upon hydrogenation.
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- 2017
15. Controlling dissolution of PbTe nanoparticles in organic solvents during liquid cell transmission electron microscopy
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Todd Brintlinger, Danielle L. Woodall, Nabraj Bhattarai, Joseph G. Tischler, and Janice E. Boercker
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Materials science ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Chemical engineering ,Transmission electron microscopy ,Etching (microfabrication) ,Liquid cell ,Radiolysis ,Electron dose ,Cathode ray ,General Materials Science ,0210 nano-technology ,Dissolution - Abstract
We present direct visualization of the dynamics of oleic-acid-capped PbTe nanoparticles suspended in different organic solvents using liquid cell transmission electron microscopy. Liquid cell transmission electron microscopy is a powerful tool to directly observe the behavior of a variety of nanoparticles in liquids, but requires careful consideration and quantification of how the electron beam affects the systems being investigated. We find that etching and dissolution of PbTe nanoparticles occurs with a strong dependence on electron dose rate ranging from no perceivable effect on the nanoparticles with lower dose rates (50 e− A−2 s−1) to complete dissolution within seconds or minutes at higher dose rates (100 and 200 e− A−2 s−1). We propose that oxidative etching, resulting from the radiolysis of small amounts of water, causes the PbTe nanoparticles to dissolve after exposure to a threshold electron dose rate of 50 e− A−2 s−1.
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- 2019
16. Controlling the Infrared Dielectric Function through Atomic-Scale Heterostructures
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Christopher J. Winta, Rhonda M. Stroud, Pratibha Dev, Alexander J. Giles, Thomas L. Reinecke, D. Scott Katzer, Ilya Razdolski, Jonathan P. Winterstein, Joshua R. Nolen, Nikolai Christian Passler, Igor Vurgaftman, Alexander Paarmann, Martin Wolf, Joseph G. Tischler, Neeraj Nepal, Joseph R. Matson, Juan Carlos Idrobo, Nabil Bassim, Ioannis Chatzakis, Daniel Ratchford, Jordan A. Hachtel, Michael B. Katz, Joshua D. Caldwell, Matthew T. Hardy, and Chase T. Ellis
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Materials science ,Phonon ,Infrared ,Superlattice ,General Physics and Astronomy ,FOS: Physical sciences ,Physics::Optics ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Atomic units ,Article ,Condensed Matter::Materials Science ,interface phonon ,Condensed Matter::Superconductivity ,Polariton ,General Materials Science ,Condensed Matter - Materials Science ,business.industry ,Scattering ,second harmonic generation ,optic phonons ,General Engineering ,Materials Science (cond-mat.mtrl-sci) ,superlattice ,Surface phonon ,polar semiconductor ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Surface plasmon polariton ,surface phonon polaritons ,0104 chemical sciences ,infrared ,Optoelectronics ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,business - Abstract
Surface phonon polaritons (SPhPs), the surface-bound electromagnetic modes of a polar material resulting from the coupling of light with optic phonons, offer immense technological opportunities for nanophotonics in the infrared (IR) spectral region. However, once a particular material is chosen, the SPhP characteristics are fixed by the spectral positions of the optic phonon frequencies. Here, we provide a demonstration of how the frequency of these optic phonons can be altered by employing atomic-scale superlattices (SLs) of polar semiconductors using AlN/GaN SLs as an example. Using second harmonic generation (SHG) spectroscopy, we show that the optic phonon frequencies of the SLs exhibit a strong dependence on the layer thicknesses of the constituent materials. Furthermore, new vibrational modes emerge that are confined to the layers, while others are centered at the AlN/GaN interfaces. As the IR dielectric function is governed by the optic phonon behavior in polar materials, controlling the optic phonons provides a means to induce and potentially design a dielectric function distinct from the constituent materials and from the effective-medium approximation of the SL. We show that atomic-scale AlN/GaN SLs instead have multiple Reststrahlen bands featuring spectral regions that exhibit either normal or extreme hyperbolic dispersion with both positive and negative permittivities dispersing rapidly with frequency. Apart from the ability to engineer the SPhP properties, SL structures may also lead to multifunctional devices that combine the mechanical, electrical, thermal, or optoelectronic functionality of the constituent layers. We propose that this effort is another step toward realizing user-defined, actively tunable IR optics and sources.
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- 2019
17. Ultralow Loss Polaritons in Isotopically Pure Hexagonal Boron Nitride
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James H. Edgar, Dimitri Basov, Joshua D. Caldwell, Thomas G. Folland, Ganjigunte R. S. Iyer, Chase T. Ellis, Joseph G. Tischler, Song Liu, Alexander J. Giles, Jeffrey C. Owrutsky, and Sai Sunku
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Materials science ,Infrared ,business.industry ,Resolution (electron density) ,Nanophotonics ,Hexagonal boron nitride ,Lambda ,Standing wave ,chemistry.chemical_compound ,chemistry ,Boron nitride ,Polariton ,Optoelectronics ,business - Abstract
We experimentally observe a significant improvements in polariton lifetime through isotopic enrichment of hexagonal boron nitride (hBN). Commensurate increases in the polariton propagation length are demonstrated via direct imaging of polaritonic standing waves by means of infrared nano-optics, with resolution greater than $\lambda/125$ observed in a preliminary hyperlens design. Our results provide the foundation for a materials-growth-directed approach aimed at realizing the loss control necessary for the development of next generation PhP-based nanophotonic devices.
- Published
- 2019
18. Effects of a Lead Chloride Shell on Lead Sulfide Quantum Dots
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Michael H. Stewart, Todd Brintlinger, Sarah Brittman, Adam E. Colbert, William B. Heuer, Janice E. Boercker, Rhonda M. Stroud, Paul D. Cunningham, and Joseph G. Tischler
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Photoluminescence ,Materials science ,Lead chloride ,Physics::Optics ,Photodetector ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Condensed Matter::Materials Science ,Monatomic ion ,chemistry.chemical_compound ,Nanocrystal ,chemistry ,Quantum dot ,Chemical physics ,General Materials Science ,Lead sulfide ,Physical and Theoretical Chemistry ,0210 nano-technology ,Absorption (electromagnetic radiation) - Abstract
The size of a quantum-confined nanocrystal determines the energies of its excitonic transitions. Previous work has correlated the diameters of PbS nanocrystals to their excitonic absorption; however, we observe that PbS quantum dots synthesized in saturated dispersions of PbCl2 can deviate from the previous 1Sh-1Se energy vs diameter curve by 0.8 nm. In addition, their surface differs chemically from that of PbS quantum dots produced via other syntheses. We find that these nanocrystals are coated in a shell that is measurable in transmission electron micrographs and contains lead and chlorine, beyond the monatomic chlorine termination previously proposed. This finding has implications for understanding the growth mechanism of this reaction, the line width of these quantum dots' photoluminescence, and electronic transport within films of these nanocrystals. Such fundamental knowledge is critical to applications of PbS quantum dots such as single-photon sources, photodetectors, solar cells, light-emitting diodes, lasers, and biological labels.
- Published
- 2019
19. Giant magneto-optical Kerr enhancement from films on SiC due to the optical properties of the substrate
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Alok Mukherjee, Chase T. Ellis, Guandong Wang, D. Kurt Gaskill, M. M. Arik, Youyan Liu, Joseph G. Tischler, C. R. Eddy, P. Fowler, Hao Zeng, E. Oliverio, Evan R. Glaser, Joseph L. Tedesco, R. L. Myers-Ward, Payam Taheri, and J. Cerne
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Condensed Matter - Materials Science ,Kerr effect ,Materials science ,Condensed matter physics ,Graphene ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Infrared spectroscopy ,Metamaterial ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,Polarization (waves) ,01 natural sciences ,law.invention ,law ,0103 physical sciences ,Thin film ,010306 general physics ,0210 nano-technology ,Refractive index - Abstract
We report a giant enhancement of the mid-infrared (MIR) magneto-optical complex Kerr angle (polarization change of reflected light) in a variety of materials grown on SiC. In epitaxially-grown multilayer graphene, the Kerr angle is enhanced by a factor of 68, which is in good agreement with Kerr signal modeling. Strong Kerr enhancement is also observed in Fe films grown on SiC and Al-doped bulk SiC. Our experiments and modelling indicate that the enhancement occurs at the high-energy edge of the SiC reststrahlen band where the real component of the complex refractive index n passes through unity. Furthermore, since the signal is greatly enhanced when n=1, the enhancement is predicted to exist over the entire visible/infrared (IR) spectrum for a free-standing film. We also predict similar giant enhancement in both Faraday (transmission) and Kerr rotation for thin films on a metamaterial substrate with refractive index n=-1. This work demonstrates that the substrate used in MOKE measurements must be carefully chosen when investigating magneto-optical materials with weak MOKE signals or when designing MOKE-based optoelectronic devices., 15 pages, 4 figures
- Published
- 2019
20. 3D-printed infrared metamaterials
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Nicholas Sharac, Joseph G. Tischler, and Ganjigunte R. S. Iyer
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Semiconductor ,Materials science ,business.industry ,Etching (microfabrication) ,Nanophotonics ,Metamaterial ,Optoelectronics ,Dielectric ,Reactive-ion etching ,Thin film ,business ,Plasmon - Abstract
Dielectric and semiconductor structures at the nanoscale are increasingly being applied in nanophotonic applications such as enhanced sensing, magnetic field enhancements, and metasurfaces. In contrast to their traditional metal plasmon counterparts -- such as Au and Ag -- dielectric materials benefit from low losses and CMOS compatibility. Here we explore of 3D dielectric structures on the nanometer and micron scales via a new patterning method, which employs both 3D, direct laser write (DLW) and reactive ion etching (RIE). Polymer structures, which are controlled down to the submicron scale both laterally and in height are printed using DLW onto various dielectric materials and are sub sequentially, etched using RIE. By tuning the etch ratio of the dielectric and polymer, the 3D printed pattern is transferred into the dielectric. By patterning a range of different 3D geometries onto Si, SiC, and hBN, we show that this method is applicable to a range of dielectric and semiconductor materials and to a range of different microstructures and nanostructures. Further, we show the possibility of selectively removing the polymer mask without damaging the underlying dielectric material, which enables the possibility of additional fabrication methods, such as for etching thin films.
- Published
- 2019
21. Implementation of plasmonic band structure to understand polariton hybridization within metamaterials
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Nicholas Sharac, Keith Perkins, Francisco J. Bezares, Alexander J. Giles, Sharka M. Prokes, Orest J. Glembocki, Thomas G. Folland, Joseph G. Tischler, and Joshua D. Caldwell
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Physics ,Photon ,business.industry ,Surface plasmon ,Physics::Optics ,Metamaterial ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,010309 optics ,Optics ,0103 physical sciences ,Polariton ,Antenna (radio) ,0210 nano-technology ,business ,Electronic band structure ,Plasmon ,Photonic crystal - Abstract
Gap surface plasmons (GSPs) serve a diverse range of plasmonic applications, including energy harvesting, communications, molecular sensing, and optical detection. GSPs may be realized where tightly spaced plasmonic structures exhibit strong spatial overlap between the evanescent fields. We demonstrate that within similar, nested geometries that the near-fields of the GSPs within the individual nanostructures are hybridized. This creates two or more distinct resonances exhibiting near-field distributions extended over adjacent spatial regions. In contrast, dissimilar, nested structures exhibit two distinct resonances with nominally uncoupled near-fields, resulting in two or more individual antenna resonance modes. We deploy plasmonic band structure calculations to provide insight into the type and degree of hybridization within these systems, comparing the individual components. This understanding can be used in the optimized design of polaritonic metamaterial structures for desired applications.
- Published
- 2018
22. Atomic-scale photonic hybrids for mid-infrared and terahertz nanophotonics
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Joseph G. Tischler, Joshua D. Caldwell, Thomas L. Reinecke, O. J. Glembocki, Jeffrey C. Owrutsky, and Igor Vurgaftman
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Terahertz radiation ,business.industry ,Biomedical Engineering ,Nanophotonics ,Physics::Optics ,Metamaterial ,Bioengineering ,Nanotechnology ,02 engineering and technology ,Surface phonon ,Dielectric ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surface plasmon polariton ,Atomic and Molecular Physics, and Optics ,010309 optics ,0103 physical sciences ,Polariton ,General Materials Science ,Electrical and Electronic Engineering ,Photonics ,0210 nano-technology ,business - Abstract
The field of nanophotonics focuses on the ability to confine light to nanoscale dimensions, typically much smaller than the wavelength of light. The goal is to develop light-based technologies that are impossible with traditional optics. Subdiffractional confinement can be achieved using either surface plasmon polaritons (SPPs) or surface phonon polaritons (SPhPs). SPPs can provide a gate-tunable, broad-bandwidth response, but suffer from high optical losses; whereas SPhPs offer a relatively low-loss, crystal-dependent optical response, but only over a narrow spectral range, with limited opportunities for active tunability. Here, motivated by the recent results from monolayer graphene and multilayer hexagonal boron nitride heterostructures, we discuss the potential of electromagnetic hybrids--materials incorporating mixtures of SPPs and SPhPs--for overcoming the limitations of the individual polaritons. Furthermore, we also propose a new type of atomic-scale hybrid--the crystalline hybrid--where mixtures of two or more atomic-scale (∼3 nm or less) polar dielectric materials lead to the creation of a new material resulting from hybridized optic phonon behaviour of the constituents, potentially allowing direct control over the dielectric function. These atomic-scale hybrids expand the toolkit of materials for mid-infrared to terahertz nanophotonics and could enable the creation of novel actively tunable, yet low-loss optics at the nanoscale.
- Published
- 2016
23. Ultra low-loss polaritons in hexagonal boron nitride (Conference Presentation)
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Joshua D. Caldwell, Timothy B. Hoffman, Thomas L. Reinecke, Lucas Lindsay, Michael M. Fogler, Dmitri Basov, Song Liu, Chase T. Ellis, Siyuan Dai, Igor Vurgaftman, James H. Edgar, Alexander J. Giles, Nathaniel Assefa, Ioannis Chatzakis, and Joseph G. Tischler
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Standing wave ,Wavelength ,Optical path ,Materials science ,business.industry ,Phonon ,Infrared ,Polariton ,Nanophotonics ,Physics::Optics ,Optoelectronics ,business ,Polarization (waves) - Abstract
Conventional optical components are limited to size-scales much larger than the wavelength of light, as changes to the amplitude, phase and polarization of the electromagnetic fields are accrued gradually along an optical path. However, advances in nanophotonics have produced ultrathin, so-called “flat” optical components that beget abrupt changes in these properties over distances significantly shorter than the free space wavelength. While high optical losses still plague many approaches, phonon polariton materials have demonstrated long lifetimes for localized modes in comparison to plasmon-polariton based nanophotonics. Our work predicts a further 14-fold increase in the optic phonon lifetime and we experimentally report a ~3-fold improvement through isotopic enrichment of hexagonal boron nitride (hBN). We establish commensurate increases in the phonon polariton propagation length via direct imaging of polaritonic standing waves by means of infrared nano-optics. Our results provide the foundation for a materials-growth-directed approach towards realizing the loss control necessary for the development of phonon polariton based nanophotonic devices.
- Published
- 2018
24. Approaches towards actively tunable mid- to far-infrared nanophotonics (Conference Presentation)
- Author
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Joseph G. Tischler, Daniel Ratchford, Chase T. Ellis, Chul Soo Kim, Kyle P. Kelley, Mijin Kim, Evan L. Runnerstrom, Adam D. Dunkelberger, Jeffrey C. Owrutsky, Virginia D. Wheeler, Jon-Paul Maria, Joshua D. Caldwell, J. Ryan Nolen, Thomas G. Folland, and Igor Vurgaftman
- Subjects
Presentation ,Engineering ,Far infrared ,business.industry ,media_common.quotation_subject ,Nanophotonics ,business ,Engineering physics ,media_common - Published
- 2018
25. Localized phonon-polariton modes in periodic GaN nanowire arrays grown by selective area epitaxy (Conference Presentation)
- Author
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Chase T. Ellis, Joseph G. Tischler, Bryan T. Spann, Todd E. Harvey, Kris A. Bertness, Joshua R. Nolen, Matthew D. Brubaker, Joshua D. Caldwell, and Thomas G. Folland
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Materials science ,business.industry ,Terahertz radiation ,Nanowire ,Physics::Optics ,Condensed Matter::Materials Science ,symbols.namesake ,Semiconductor ,Selective area epitaxy ,symbols ,Optoelectronics ,Photonics ,business ,Raman spectroscopy ,Plasmon ,Molecular beam epitaxy - Abstract
Localized surface phonon-polariton (SPhP) resonances in polar semiconductor nanostructures can provide highly sub-diffractional electromagnetic fields. Furthermore, SPhP resonances offer enhanced resonant quality factors when compared to plasmon-polariton based systems. The various material platforms and nanostructure geometries achievable in polar semiconductors suggest they would be ideal platforms for tunable, long-wavelength photonics applications. Moreover, the constituent atomic basis defines the operating frequency regime for SPhP resonances; tunable from the mid-infrared to THz. Here, we investigate Raman active aspects of SPhP modes in GaN nanowire arrays that are grown via selective area molecular beam epitaxy. We detect strong Raman peaks within the Reststrahlen band of GaN that are not found in the bulk GaN Raman spectrum. These SPhP modes occur around 700 cm^-1 (~ 14.3 microns), offering a spectral region for device applications which is currently not accessible by plasmonic based systems or other SPhP enabled materials. Utilizing selective area epitaxy, we created GaN nanowire arrays with various diameters and pitches, from which the Raman spectra showed tuning of the apparent SPhP resonances. Infrared reflectance measurements were also performed with an FTIR microscope to further establish the physical properties of the resonances. Finally, computational studies of the structures’ reflectance were used to solidify our understanding of the geometry/SPhP-resonance-tuning relationship.
- Published
- 2018
26. Hybrid longitudinal-transverse phonon polaritons
- Author
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Christopher R. Gubbin, Rodrigo Berte, Michael A. Meeker, Alexander J. Giles, Chase T. Ellis, Joseph G. Tischler, Virginia D. Wheeler, Stefan A. Maier, Joshua D. Caldwell, and Simone De Liberato
- Subjects
0301 basic medicine ,Phonon ,Science ,FOS: Physical sciences ,General Physics and Astronomy ,Physics::Optics ,Near and far field ,02 engineering and technology ,Resonance (particle physics) ,General Biochemistry, Genetics and Molecular Biology ,Article ,03 medical and health sciences ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Polariton ,lcsh:Science ,Astrophysics::Galaxy Astrophysics ,Nanopillar ,Physics ,Multidisciplinary ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,General Chemistry ,021001 nanoscience & nanotechnology ,3. Good health ,Transverse plane ,030104 developmental biology ,Quasiparticle ,Physics::Accelerator Physics ,lcsh:Q ,Condensed Matter::Strongly Correlated Electrons ,Microscopic theory ,0210 nano-technology ,Optics (physics.optics) ,Physics - Optics - Abstract
Phonon polaritons, hybrid light-matter quasiparticles resulting from strong coupling of the electromagnetic field with the lattice vibrations of polar crystals are a promising platform for mid-infrared photonics but for the moment there has been no proposal allowing for their electrical pumping. Electrical currents in fact mainly generate longitudinal optical phonons, while only transverse ones participate in the creation of phonon polaritons. We demonstrate how to exploit long-cell polytypes of silicon carbide to achieve strong coupling between transverse phonon polaritons and zone-folded longitudinal optical phonons. We develop a microscopic theory predicting the existence of the resulting hybrid longitudinal-transverse excitations. We then provide an experimental observation by tuning the resonance of a nanopillar array through the folded longitudinal optical mode, obtaining a clear spectral anti-crossing. The hybridisation of phonon polaritons with longitudinal phonons could represent an important step toward the development of phonon polariton-based electrically pumped mid-infrared emitters., Phonon polaritons are promising for mid-infrared photonics but only longitudinal optical phonons are directly accessed by electrical currents. Here, the authors predict and experimentally confirm hybrid longitudinal-transverse excitations. This could lead to phonon polariton-based electrically pumped mid-infrared emitters.
- Published
- 2018
27. The effect of excited state occupation and phonon broadening in the determination of the non-equilibrium hot-carrier temperature in InGaAsP quantum-well absorbers (Conference Presentation)
- Author
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Louise C. Hirst, Vincent R. Whiteside, Hamidreza Esmaielpour, Joseph G. Tischler, Ian R. Sellers, and Robert J. Walters
- Subjects
Laser linewidth ,Photoluminescence ,Materials science ,Condensed matter physics ,Phonon ,Excited state ,Energy conversion efficiency ,Continuous wave ,Excitation ,Quantum well - Abstract
Hot carrier solar cells (HCSCs) have been proposed as potential systems to increase the conversion efficiency of single gap solar cells beyond the Shockley-Queisser limit. Despite a great deal of recent progress in HCSCs, designing an effective and efficient hot carrier absorber remains challenging. To evaluate the efficiency of any proposed absorber accurate determination of the carrier temperature is required. This can be non-trivial, particularly in the quantum wells (QW) where state-filling effects can complicate the simple extraction of carrier temperature from photoluminescence (PL) spectra. Specifically, the PL may be distorted if there are other linewidth broadening mechanisms prevalent in addition to non-equilibrium carriers. These may include; in addition to state filling, the effects of phonons and system inhomogeneities, all of which serve to perturb the PL linewidth. In this study, an InGaAsP QW with a type-II band alignment is investigated using continuous wave power and temperature dependent PL to evaluate the effects of broadening on the extraction of the true carrier temperature in the system [1]. Since there is a relatively small energy separation between the ground and first excited state transitions in the QW studied, state filling effects can be controlled and their contribution to the linewidth evaluated, using various conditions and combinations of excitation power and lattice temperature. The role of phonons is also presented, and supported within the framework of a theoretical model that includes the various phononic processes and their temperature dependent contribution to the PL. This work is supported by the National Science Foundation Grant ECCS #1610062 [1] Esmaielpour, Hamidreza, Vincent R. Whiteside, Louise C. Hirst, Joseph G. Tischler, Chase T. Ellis, Matthew P. Lumb, David V. Forbes, Robert J. Walters, and Ian R. Sellers. Progress in Photovoltaics: Research and Applications (2017).
- Published
- 2018
28. Strong Coupling Effects Between IR-Inactive Zone Folded LO Phonon and Localized Surface Phonon Polariton Modes in SiC Nanopillars
- Author
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Joshua D. Caldwell, Francisco J. Bezares, Joseph G. Tischler, Loretta M. Shirey, Chase T. Ellis, Dmitry N. Chigrin, Alexander J. Giles, Richard Kasica, M. A. Meeker, and Orest J. Glemboki
- Subjects
Materials science ,Infrared ,Phonon ,Polariton ,Physics::Optics ,Resonance ,Surface phonon ,Dielectric ,Molecular physics ,Plasmon ,Nanopillar - Abstract
While plasmonics have a broad range of technological applications including infrared photovoltaics and photodetectors, plasmonic metals are subject to high optical losses in the long-wave infrared spectral regime. In order to reduce optical losses in the infrared, alternatives to plasmonic metals are being explored. One promising alternative employs polar dielectric materials, which exhibit a highly-reflective, optically-metallic spectral band (Reststrahlen band), bounded by the LO and TO optical phonons, and are capable of supporting plasmonic-like resonance in the infrared. In polar dielectrics, plasmonic-like resonances, known as surface phonon polariton (SPhP) resonances, arise from a coupling between incident light and collective oscillations of bound lattice charges, which are mediated by the optical phonons. In this study, we have examined the SPhP resonances of SiC nanopillars with constant height of 950 nm and width in the range of 200–400 nm, as a function of their aspect ratio (AR=Length/Width=0.5–16). As the nanopillar width is decreased, we have found that localized SPhP resonances redshift towards the zone folded LO (ZFLO) phonon that is normally not infrared active. However, as localized SPhP resonances are spectrally tuned through the ZFLO mode, we have found that the latter mode becomes infrared active. Furthermore, reflectance measurements have revealed strong coupling between the ZFLO and both the monopolar and dipolar localized SPhP resonances.
- Published
- 2018
29. Synthesis and Optical Properties of PbSe Nanorods with Controlled Diameter and Length
- Author
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Diogenes Placencia, Janice E. Boercker, Joseph G. Tischler, and Edward E. Foos
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Nanotubes ,Materials science ,Photoluminescence ,Analytical chemistry ,Nanowire ,Nanotechnology ,Branching (polymer chemistry) ,Electronic states ,Absorbance ,Lead ,Microscopy, Electron, Transmission ,Nanocrystal ,General Materials Science ,Nanorod ,Physical and Theoretical Chemistry ,Selenium Compounds - Abstract
The synthesis of PbSe nanorods with low branching (
- Published
- 2015
30. Safer salts for CdTe nanocrystal solution processed solar cells: the dual roles of ligand exchange and grain growth
- Author
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Woojun Yoon, Edward E. Foos, Joseph G. Tischler, William B. Heuer, Eric Kowalski, and Troy K. Townsend
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,Open-circuit voltage ,Annealing (metallurgy) ,Inorganic chemistry ,Halide ,Heterojunction ,General Chemistry ,Cadmium chloride ,Cadmium telluride photovoltaics ,chemistry.chemical_compound ,Grain growth ,chemistry ,Nanocrystal ,General Materials Science - Abstract
Inorganic CdSe/CdTe nanocrystals for solid-state photovoltaic devices are typically sintered into a bulk-like material after annealing in the presence of solid cadmium chloride. As in commercial CdTe devices, this salt exposure is a key component to improve device performance by promoting grain growth. However, in contrast to vapor depositions, we demonstrate that the role of the salt treatment also involves crucial ligand removal reactions, which are a unique challenge facing nanocrystal ink depositions. After testing other salts such as CdF2, CdCl2, CdBr2, CdI2 and Cd(NO3)2 for oleate ligand removal as determined by FTIR, SEM imaging of CdTe grain growth revealed the largest grains were observed from reactions with CdCl2 (142 ± 26 nm) and, to a lesser extent, CdBr2 (131 ± 19 nm). These results were used to identify cadmium-free alternatives. Trimethylsilyl chloride (28.0 ± 5.1 nm), NH4Br (75.5 ± 31 nm) and NH4Cl (136 ± 39 nm) were also tested, demonstrating comparable ligand removal and grain growth to the cadmium halides. In order to validate these observations, heterojunction photovoltaic devices were fabricated from CdSe/CdTe nanocrystals treated with non-toxic NH4Cl in place of the conventional CdCl2. Under AM 1.5G illumination, open circuit voltages (Voc), short circuit currents (Jsc) and efficiencies (η) of solar cells processed with evaporated Au and commercial ITO were found to be Voc = 0.46 ± 0.02 V, Jsc = 9.27 ± 0.6 mA cm−2, and η = 1.73 ± 0.24 demonstrating minimal differences in film morphology and device performance compared to those fabricated using cadmium chloride. Specific properties of the salts (solubility, reactivity, melting point and the identity of both the cation and the anion) were found to have a profound impact on grain growth and consequently device performance, suggesting the need for further investigation of additional non-toxic metal halide salts for this reaction.
- Published
- 2015
31. Reply to comments on 'An extended hardness limit in bulk nanoceramics', Acta Materialia 69 (2014) 9–16
- Author
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Ramasis Goswami, Boris N. Feigelson, R.K. Everett, Chase T. Ellis, Dat D. Nguyen, Syed B. Qadri, Joseph G. Tischler, Fritz J. Kub, Edward P. Gorzkowski, and James A. Wollmershauser
- Subjects
Materials science ,Mechanical Engineering ,Metallurgy ,Spinel ,Metals and Alloys ,engineering.material ,Condensed Matter Physics ,Nanoceramic ,Nanocrystalline material ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,engineering ,General Materials Science ,Ceramic ,Limit (mathematics) ,Grain boundary strengthening - Abstract
A response is provided to comments by Krell concerning the validity of the Hall–Petch relationship and the optical transmission in nanocrystalline ceramics discussed in a recent Acta Materialia paper.
- Published
- 2014
32. Enhanced Hot-Carrier Effects in InAlAs/InGaAs Quantum Wells
- Author
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Markus Fuhrer, Michael K. Yakes, Louise C. Hirst, Christopher G. Bailey, Joseph G. Tischler, María Ujué González, Matthew P. Lumb, Nicholas J. Ekins-Daukes, and Robert J. Walters
- Subjects
Thermal equilibrium ,education.field_of_study ,Materials science ,Photoluminescence ,business.industry ,Q value ,Population ,Heterojunction ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,Thermalisation ,law ,Solar cell ,Optoelectronics ,Electrical and Electronic Engineering ,business ,education ,Quantum well - Abstract
Hot-carrier solar cells require absorber materials with restricted carrier thermalization pathways, in order to slow the rate of heat energy dissipation from the carrier population to the lattice, relative to the rate of carrier extraction. Absorber suitability can be characterized in terms of carrier thermalization coefficient (Q). Materials with lower Q generate steady-state hot-carrier populations at lower levels of incident solar power and, therefore, are better able to perform as hot-carrier absorbers. In this study, we evaluate Q = 2.5±0.2 W·K -1 · cm -2 for a In 0.52 AlAs/In 0.53 GaAs single-quantum-well(QW) heterostructure using photoluminescence spectroscopy. This is the lowest experimentally determined Q value for any material system studied to date. Hot-carrier solar cell simulations, using this material as an absorber yield efficiency ~39% at 2000X, which corresponds to a >5% enhancement over an equivalent single-junction thermal equilibrium device.
- Published
- 2014
33. Effect of occupation of the excited states and phonon broadening on the determination of the hot carrier temperature from continuous wave photoluminescence in InGaAsP quantum well absorbers
- Author
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Vincent R. Whiteside, Hamidreza Esmaielpour, Robert J. Walters, Chase T. Ellis, Matthew P. Lumb, Louise C. Hirst, Joseph G. Tischler, Ian R. Sellers, David V. Forbes, Institut Photovoltaïque d’Ile-de-France (UMR) (IPVF), École polytechnique (X)-Ecole Nationale Supérieure de Chimie de Paris - Chimie ParisTech-PSL (ENSCP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-TOTAL FINA ELF-EDF (EDF)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut Photovoltaïque d’Ile-de-France (ITE) (IPVF)-Air Liquide [Siège Social], and University of Southampton
- Subjects
Photoluminescence ,Materials science ,Phonon ,02 engineering and technology ,01 natural sciences ,7. Clean energy ,0103 physical sciences ,Electrical and Electronic Engineering ,[SPI.NANO]Engineering Sciences [physics]/Micro and nanotechnologies/Microelectronics ,Spectroscopy ,Quantum well ,ComputingMilieux_MISCELLANEOUS ,010302 applied physics ,[PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics] ,Condensed matter physics ,Renewable Energy, Sustainability and the Environment ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Excited state ,[SPI.OPTI]Engineering Sciences [physics]/Optics / Photonic ,Continuous wave ,Atomic physics ,0210 nano-technology ,Ground state ,[SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing ,Excitation - Abstract
An InGaAsP quantum well with a type-II band alignment is studied using continuous wave power and temperature dependent photoluminescence (PL) spectroscopy. The small energy separation between the ground state and first excited state results in significant thermal carrier redistribution and excited state occupation, particularly, with increasing excitation power and temperature. This state filling is evident as a high-energy shoulder in the PL spectra, the same energy region where in the simplest Planck-description the gradient is considered inversely proportional to carrier temperature. The outcome of an excited state occupation in broadening the high-energy PL tail is to perturb the temperature extracted using this analysis; therefore, the true temperature of carriers is not properly evaluated when significant state filling occurs. In addition, broadening of the PL due to phonons at higher temperatures also distorts (or falsely increases) the non-equilibrium “hot” carrier temperature and as such should be considered when using Planck's relation. The role of these two effects is considered and their mutual effect on the analysis of the extracted hot carrier temperature discussed. Copyright © 2017 John Wiley & Sons, Ltd.
- Published
- 2017
34. Economic Analysis of Transfer Printed III–V Virtual Substrates
- Author
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Shawn Mack, S. I. Maximenko, M. A. Meeker, Chase T. Ellis, Matthew Meitl, Matthew P. Lumb, Michael K. Yakes, Laura B. Ruppalt, Kenneth J. Schmieder, Robert J. Walters, Joseph G. Tischler, and Mitchell F. Bennet
- Subjects
Cost reduction ,Materials science ,Etching (microfabrication) ,business.industry ,Transfer (computing) ,Hardware_INTEGRATEDCIRCUITS ,Process (computing) ,Economic analysis ,Polishing ,Optoelectronics ,Substrate (printing) ,business ,Layer (electronics) - Abstract
We propose a novel methodology for III-V substrate cost reduction that does not rely on chemical-mechanical polishing (CMP) or low-throughput release layer etching. The details of this process are provided, and results of an economic model for GaAs and InP virtual substrates dictate 20x and 34x reductions to substrate cost, respectively. The impact of modeled assumptions are quantified in order to better understand the potential range of end-goal virtual substrate cost.
- Published
- 2017
35. The role of N-H complexes in the control of localized center recombination in hydrogenated GaInNAs (Conference Presentation)
- Author
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Joseph G. Tischler, Mathieu Leroux, Vincent R. Whiteside, Khalid Hossain, Bin Wang, Mohamed Al Khalfioui, Evan R. Glaser, M. Fukuda, Nicholas J. Estes, Collin R. Brown, Chase T. Ellis, Ian R. Sellers, and Terry Golding
- Subjects
010302 applied physics ,Materials science ,Photoluminescence ,Applied physics ,Passivation ,Hydrogen ,business.industry ,Annealing (metallurgy) ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,Nitride ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,chemistry ,law ,0103 physical sciences ,Solar cell ,Optoelectronics ,0210 nano-technology ,business ,Luminescence - Abstract
A significant improvement in the quality of dilute nitrides has recently led to the ability to reveal depletion widths in excess of 1 μm at 1 eV [1]. The real viability of dilute nitrides for PV has been recently demonstrated with the reporting of a record efficiency of 43.5% from a 4J MJSC including GaInNAs(Sb) [2]. Despite the progress made, these materials remain poorly understood and work continues to improve their lifetime and reproducibility. We have investigated the possibility of improving the functionality of GaInNAs using hydrogenation to selectively passivate mid-gap defects, while preserving the substitutional nitrogen. Temperature dependent photoluminescence measurements of the intrinsic region of a GaInNAs p-i-n solar cell show a classic “s-shape” associated with localization prior to hydrogenation. No sign of this “s-shape” is evident after hydrogenation, despite the retention of substitutional nitrogen as evidenced by the band absorption of 1 eV. The absence of an “s-shape” at low-temperature in hydrogenated GaInNAs is rather curious since, even in high quality nitrides this behavior is due to the emission of isoelectronic centers created via N-As substitution [3]. The potential origins of this behavior will be discussed. The promise of this process for GaInNAs solar cells was demonstrated by a three-fold improvement in the performance of a hydrogenated device with respect to an as-grown reference [4]. [1] “Wide-depletion width GaInNAs solar cells by thermal annealing,” I. R. Sellers, W-S. Tan, K. Smith, S. Hooper, S. Day and M. Kauer, Applied Physics Letters 99, 151111 (2011) [2] “43.5% efficient lattice matched solar cells,” M. Wiemer, V. Sabnis, and H. Yuen, Proc. SPIE 8108, 810804 (2011) [3]“Probing the nature of carrier localization in GaInNAs, epilayers using optical methods,” T. Ysai, B. Barman, T. Scarce, G. Lindberg, M. Fukuda, V. R. Whiteside, J. C. Keay, M. B. Johnson, I. R. Sellers, M. Al Khalfioui, M. Leroux, B. A. Weinstein and A. Petrou. Applied Physics Letters 103, 012104 (2013) [4] “Improved performance in GaInNAs solar cells by hydrogen passivation by hydrogen passivation,” M. Fukuda, V. R. Whiteside, J. C. Keay, A. Meleco, I. R. Sellers, K. Hossain, T. D. Golding, M. Leroux, and M. Al Khalfioui, Applied Physics Letters 106, 141904 (2015)
- Published
- 2017
36. Low-Loss Phonon Polaritons in Nanostructured Dielectrics
- Author
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Jeffrey C. Owrutsky, Orest J. Glembocki, Alexander J. Giles, Francisco J. Bezares, Siyuan Dai, Joseph G. Tischler, Joshua D. Caldwell, Dimitri Basov, Richard Kasica, Chase T. Ellis, Loretta M. Shirey, and Michael M. Fogler
- Subjects
Materials science ,business.industry ,Scattering ,Phonon ,Polariton ,Nanophotonics ,Physics::Optics ,Optoelectronics ,Dielectric ,business ,Refractive index ,Plasmon ,Nanopillar - Abstract
Plasmonics provides great promise for nanophotonic applications. However, the high optical losses inherent in metal-based plasmonic systems have limited progress. Thus, it is critical to identify alternative low-loss materials. One alternative is polar dielectrics that support surface phonon polariton (SPhP) modes, where the confinement of infrared light is aided by optical phonons. SiC nanopillar arrays support such modes, exhibiting a dipolar resonance transverse to the nanopillar axis and a monopolar resonance associated with the longitudinal axis dependent upon the SiC substrate. Both exhibit exceptionally narrow linewidths (7–24 cm−1), with quality factors of 40–135, which exceed the theoretical limit of plasmonic systems, with extreme subwavelength confinement of (λres3/Veff)1/3 = 50–200. These observations promise to reinvigorate research in SPhP phenomena and their use for nanophotonic applications. Another approach is the use of hyperbolic materials, which have been a focus of the nanophotonics community for their potential to realize sub-diffractional imaging and focusing of light, and novel optical properties, such as a negative index of refraction. The recent observation that hexagonal boron nitride (hBN) is a natural, high efficiency hyperbolic material has led to a surge in research within this field. Due to the low-loss nature, van der Waals bonding and extreme crystal anisotropy, the hyperbolic polaritons within hBN are not only promising for novel applications within the mid-infrared, but is also extremely well suited for fundamental investigations into their resonant behaviors. We have used scattering near-field optical microscopy (s-SNOM) to directly probe the local surface electromagnetic fields of three-dimensionally confined nanostructures of hBN, reporting the first experimental observation of frequency dependent internal angular reflection within a hyperbolic nanostructure, a phenomenon previously theoretically predicted.
- Published
- 2017
37. High-Order Multipole Resonances in Cuboidal Surface Phonon Polariton Nanoresonators
- Author
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Joseph G. Tischler, Francisco J. Bezares, Joshua D. Caldwell, Dmitry N. Chigrin, Loretta M. Shirey, Richard Kasica, Orest J. Glembocki, Jeffrey C. Owrutsky, and Chase T. Ellis
- Subjects
Physics ,Condensed matter physics ,Infrared ,Phonon ,Polariton ,Nanophotonics ,Physics::Optics ,Surface phonon ,Dielectric ,Multipole expansion ,Plasmon - Abstract
It has been demonstrated that nanoresonators fabricated on the surface of polar dielectric materials, such as silicon carbide, are able to sustain plasmonic-like effects in the mid- to long- wave infrared spectral range with impressive figures of merit (Hillenbrand R, Taubner T, Keilmann F, Nature 418:159–162, 2002; Caldwell JD, Glembocki OJ, et al., Nano Lett 13:3690–3697, 2013; Wang T, Li P, et al., Nano Lett 13:5051–5055, 2013). Such phenomena is achieved by exploiting the TO and LO phonons to resonantly excite collective oscillations of bound lattice (Caldwell JD, Lindsay L, et al., Nanophotonics 4:2192–8614, 2015). The fact that these excitations are mediated by bound charges, rather than free charges - such as the case with plasmonic metals, results in extremely low optical losses and enhanced resonant phenomena. As such, polar dielectric nanoresonators may play a role in improving infrared nanophotonic technologies, such as waveguides, sources, near-field optics, solar cells, chemical sensors, biosensors, and photonic circuitry. However, fully realizing this potential, hinges on the ability to precisely control the near-field behavior of polar dielectric nanoresonators. In this work, we use a combination of optical measurements and finite element method simulations to investigate the far- and near-field resonant behavior of structurally-asymmetric, cuboidally-shaped, 4H-SiC nanoresonators with fixed height (\( h=950\ \mathrm{nm} \)), fixed length (\( l=400\ \mathrm{nm} \)), and varying width (\( w=400-6400\ \mathrm{nm} \)). Overall, we observe over 12 polarization-sensitive resonances that can be tuned across the Reststrahlen band of 4H-SiC (\( 796-964\ {\mathrm{cm}}^{-1} \)) (Ellis, C.T. et al. Scientific Reports 6:32959, 2016) by changing the nanopillar aspect ratio (\( AR=w/l=1-16 \)). Futhermore, we find that these resonances exhibit a wide range of near-field radiation patterns that vary from a simple transverse dipole mode that is preserved for all ARs to complex, high-order multipoles with modal profiles that evolve with aspect ratio.
- Published
- 2017
38. Bulk properties of InN films determined by experiments and theory
- Author
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Joelson André de Freitas, Gustavo Baldissera, M. Matsuoka, Mukesh Kumar, D. David, Clas Persson, A. Ferreira da Silva, Jose Fernando Diniz Chubaci, M.V.S. da Silva, and Joseph G. Tischler
- Subjects
GW approximation ,Materials science ,Photoluminescence ,Exciton ,Analytical chemistry ,Condensed Matter Physics ,Molecular physics ,Inorganic Chemistry ,Condensed Matter::Materials Science ,Absorption edge ,Attenuation coefficient ,Materials Chemistry ,Density of states ,Ion beam-assisted deposition ,Absorption (electromagnetic radiation) - Abstract
Bulk properties of InN are determined by combining experimental and theoretical studies. In this work, we produced high quality InN film deposited on GaN templates by a modified ion beam assisted deposition technique confirmed by low temperature photoluminescence and absorption. The density of states, real and imaginary parts of the complex dielectric function and the absorption coefficient are calculated by means of first-principles beyond density-functional theory. The quasi-particle aspect is described in the framework of a quasi-particle method (the GW approximation). The calculated band-gap energy is ~0.8 eV whereas significance in the optical absorption occurs at ~1.2 eV, which are consistent with both luminescence and absorption results. The Bethe–Salpeter equation is utilized to model the two-particle exciton interactions, revealing a strong excitonic peak just below the absorption edge of InN.
- Published
- 2014
39. Step graded buffer for (110) InSb quantum wells grown by molecular beam epitaxy
- Author
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Adrian Podpirka, Brian R. Bennett, Mark E. Twigg, Joseph G. Tischler, and R. Magno
- Subjects
Materials science ,business.industry ,Annealing (metallurgy) ,Condensed Matter Physics ,Buffer (optical fiber) ,Inorganic Chemistry ,Crystallography ,Transmission electron microscopy ,Lattice (order) ,Materials Chemistry ,Surface roughness ,Optoelectronics ,Growth rate ,business ,Quantum well ,Molecular beam epitaxy - Abstract
We report on a two step buffer layer preparation for the growth of InSb quantum wells on a (110) GaAs surface. At each buffer layer step, layer conditions were optimized to produce smooth surfaces compatible with InSb quantum wells. Through varying growth rate, group V/III flux ratio, substrate temperature, and the addition of in situ annealing, we are able to grow In0.85Al0.15Sb on a GaAs substrate with an RMS surface roughness of approximately 2 nm. Surface morphology and cross-sectional transmission electron microscopy (TEM) were analyzed to understand the formation of threading dislocations, inclusions and dislocation filtering. This work presents an initial study for the growth of large lattice mismatched III-V materials on the (110) surface.
- Published
- 2014
40. Impact of Nanocrystal Spray Deposition on Inorganic Solar Cells
- Author
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Joseph G. Tischler, Woojun Yoon, Edward E. Foos, and Troy K. Townsend
- Subjects
Materials science ,Annealing (metallurgy) ,business.industry ,Band gap ,Oxide ,Nanotechnology ,Cadmium telluride photovoltaics ,chemistry.chemical_compound ,Nanocrystal ,chemistry ,Chemical engineering ,Photovoltaics ,Surface roughness ,General Materials Science ,Thin film ,business - Abstract
Solution-synthesized inorganic cadmium telluride nanocrystals (∼4 nm; 1.45 eV band gap) are attractive elements for the fabrication of thin-film-based low-cost photovoltaic (PV) devices. Their encapsulating organic ligand shell enables them to be easily dissolved in organic solvents, and the resulting solutions can be spray-cast onto indium-tin oxide (ITO)-coated glass under ambient conditions to produce photoactive thin films of CdTe. Following annealing at 380 °C in the presence of CdCl2(s) and evaporation of metal electrode contacts (glass/ITO/CdTe/Ca/Al), Schottky-junction PV devices were tested under simulated 1 sun conditions. An improved PV performance was found to be directly tied to control over the film morphology obtained by the adjustment of spray parameters such as the solution concentration, delivery pressure, substrate distance, and surface temperature. Higher spray pressures produced thinner layers (60 nm) with lower surface roughness (200 nm), leading to devices with improved open-circuit voltages (Voc) due to decreased surface roughness and higher short-circuit current (Jsc) as a result of enhanced annealing conditions. After process optimization, spray-cast Schottky devices rivaled those prepared by conventional spin-coating, showing Jsc = 14.6 ± 2.7 mA cm(-2), Voc = 428 ± 11 mV, FF = 42.8 ± 1.4%, and Eff. = 2.7 ± 0.5% under 1 sun illumination. This optimized condition of CdTe spray deposition was then applied to heterojunction devices (ITO/CdTe/ZnO/Al) to reach 3.0% efficiency after light soaking under forward bias. The film thickness, surface morphology, and light absorption were examined with scanning electron microscopy, optical profilometry, and UV/vis spectroscopy.
- Published
- 2014
41. An extended hardness limit in bulk nanoceramics
- Author
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James A. Wollmershauser, R.K. Everett, Joseph G. Tischler, Chase T. Ellis, Syed B. Qadri, Ramasis Goswami, Edward P. Gorzkowski, Fritz J. Kub, and Boris N. Feigelson
- Subjects
Materials science ,Polymers and Plastics ,Metallurgy ,Metals and Alloys ,Microstructure ,Nanoceramic ,Grain size ,Nanocrystalline material ,Electronic, Optical and Magnetic Materials ,visual_art ,Ceramics and Composites ,visual_art.visual_art_medium ,Grain boundary ,Crystallite ,Ceramic ,Grain boundary strengthening - Abstract
Mechanical strengthening by grain refinement is a method whereby a material’s strength and hardness can be increased by decreasing the average crystallite grain size. The empirical Hall–Petch relationship mathematically describes grain boundary strengthening and provides guidance for a straightforward way to produce stronger materials. While the phenomenon has been widely explored in nanocrystalline metals, the difficulty associated with fabricating high-quality dense nanocrystalline ceramics has left unanswered the question of the validity and extent of the relationship in ceramics. Prior studies suggest the occurrence of an inverse Hall–Petch response in ceramics with grain sizes
- Published
- 2014
42. Sintered CdTe Nanocrystal Thin Films: Determination of Optical Constants and Application in Novel Inverted Heterojunction Solar Cells
- Author
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Matthew P. Lumb, Joseph G. Tischler, Woojun Yoon, Troy K. Townsend, and Edward E. Foos
- Subjects
Spin coating ,Materials science ,business.industry ,Heterojunction ,Quantum dot solar cell ,Cadmium telluride photovoltaics ,Computer Science Applications ,law.invention ,Indium tin oxide ,Nanocrystal ,law ,Solar cell ,Optoelectronics ,Electrical and Electronic Engineering ,Thin film ,business - Abstract
In this paper, we report a novel heterojunction solar cell based on sintered CdTe and CdSe nanocrystal thin films using solution-based deposition. For the absorber layer, CdTe thin films were made using a layer-by-layer deposition process consisting of spin coating colloidal CdTe nanocrystals followed by a sintering step. The optical constants for these sintered CdTe films were accurately determined through a combination of optical modeling and measurements. For the all-solution processed p–n heterojunction, we focus on CdSe nanocrystal thin films due to their excellent compatibility with solution processing. For the optimized inverted structure (glass/ITO/CdSe/CdTe/Cr/Au), a high open-circuit voltage $(V_{\rm oc})$ of 593 ± 32 mV with an efficiency of 1.9 ± 0.2% was obtained under simulated one sun illumination. These preliminary results demonstrate that this novel inverted heterojunction structure has the potential to produce a high-quality CdSe/CdTe junction for utilization in heterojunction solar cells.
- Published
- 2014
43. Improved theoretical model of InN optical properties
- Author
-
Joelson André de Freitas, M. Matsuoka, Gustavo Baldissera, Jose Fernando Diniz Chubaci, Clas Persson, Joseph G. Tischler, and A. Ferreira da Silva
- Subjects
Photoluminescence ,Ion beam deposition ,Condensed matter physics ,Band gap ,Chemistry ,Local-density approximation ,Thin film ,Condensed Matter Physics ,Luminescence ,Ion beam-assisted deposition ,Electronic band structure ,Molecular physics - Abstract
The optical properties of InN are investigated theoretically by employing the projector augmented wave (PAW) method within Green's function and the screened Coulomb interaction approximation (GWo). The calculated results are compared to previously reported calculations which use local density approximation combined with the scissors-operator approximation. The results of the present calculation are compared with reported values of the InN bandgap and with low temperature near infrared luminescence measurements of InN films deposited by a modified Ion Beam Assisted Deposition technique. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
- Published
- 2014
44. Author Correction: Ultralow-loss polaritons in isotopically pure boron nitride
- Author
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Alexander J. Giles, Igor Vurgaftman, Nathanael Assefa, James H. Edgar, Ioannis Chatzakis, Dimitri Basov, Joseph G. Tischler, Siyuan Dai, Thomas L. Reinecke, Lucas Lindsay, Michael M. Fogler, Joshua D. Caldwell, Timothy B. Hoffman, Chase T. Ellis, and Song Liu
- Subjects
chemistry.chemical_compound ,Materials science ,chemistry ,Mechanics of Materials ,business.industry ,Boron nitride ,Mechanical Engineering ,Polariton ,Optoelectronics ,General Materials Science ,General Chemistry ,Condensed Matter Physics ,business - Published
- 2019
45. Probing hyperbolic polaritons
- Author
-
Joshua D. Caldwell, Joseph G. Tischler, and Igor Vurgaftman
- Subjects
Physics ,Scanning probe microscopy ,Optics ,Phonon ,business.industry ,Polariton ,Nanophotonics ,Mid infrared ,Physics::Optics ,business ,Atomic and Molecular Physics, and Optics ,Interference microscopy ,Electronic, Optical and Magnetic Materials - Abstract
Hyperbolic phonon polaritons confined to the subdiffraction limit exhibit encouragingly long lifetimes and group velocities as slow as 0.002c. Researchers use a time-resolved set-up sensitive to nanometre-scale optical fields to shed light on the exciting optical properties of hyperbolic materials.
- Published
- 2015
46. Electrical Measurement Under Atmospheric Conditions of PbSe Nanocrystal Thin Films Passivated by Remote Plasma Atomic Layer Deposition of Al$_{\bf 2}$O $_{\bf 3}$
- Author
-
Joseph G. Tischler, Edward E. Foos, William B. Heuer, Woojun Yoon, Janice E. Boercker, and Anthony R. Smith
- Subjects
Materials science ,Passivation ,business.industry ,Nanotechnology ,Computer Science Applications ,Atomic layer deposition ,Nanocrystal ,Thin-film transistor ,Remote plasma ,Optoelectronics ,Electrical and Electronic Engineering ,Thin film ,business ,Layer (electronics) ,Deposition (law) - Abstract
PbSe nanocrystal thin-film transistors (TFTs) were passivated using remote plasma atomic layer deposition (ALD) of a ~10 nm thick Al2O3 film at 150 °C. By using a highly reactive remote oxygen plasma source, the time for one complete ALD cycle was about 15 s with growth rates of ~1.1 A/cycle. The effective mobilities measured under atmospheric condition from AlO-passivated PbSe nanocrystal TFTs were comparable to the values reported previously for air-free PbSe nanocrystal TFTs, demonstrating that ALD Al2O3 layers prevent oxidation and degradation of nanocrystal films from air exposure. The variation in the effective mobility of passivated devices was also found to be negligible under ambient conditions over a period of 30 days. The results show that remote plasma ALD processing of Al2O3 is capable of producing an effective passivation layer on air-sensitive nanocrystals with high deposition rates at reduced temperature.
- Published
- 2013
47. Aspect-ratio driven evolution of high-order resonant modes and near-field distributions in localized surface phonon polariton nanostructures
- Author
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Chase T. Ellis, Dmitry N. Chigrin, Jeffrey C. Owrutsky, Alexander J. Giles, Joshua D. Caldwell, Loretta M. Shirey, Joseph G. Tischler, Francisco J. Bezares, Richard Kasica, and Orest J. Glembocki
- Subjects
Multidisciplinary ,Materials science ,business.industry ,Nanophotonics ,Physics::Optics ,Metamaterial ,02 engineering and technology ,Dielectric ,Surface phonon ,021001 nanoscience & nanotechnology ,Polarization (waves) ,01 natural sciences ,Article ,Resonator ,0103 physical sciences ,Polariton ,Optoelectronics ,010306 general physics ,0210 nano-technology ,business ,Plasmon - Abstract
Polar dielectrics have garnered much attention as an alternative to plasmonic metals in the mid- to long-wave infrared spectral regime due to their low optical losses. As such, nanoscale resonators composed of these materials demonstrate figures of merit beyond those achievable in plasmonic equivalents. However, until now, only low-order, phonon-mediated, localized polariton resonances, known as surface phonon polaritons (SPhPs), have been observed in polar dielectric optical resonators. In the present work, we investigate the excitation of 16 distinct high-order, multipolar, localized surface phonon polariton resonances that are optically excited in rectangular pillars etched into a semi-insulating silicon carbide substrate. By elongating a single pillar axis we are able to significantly modify the far- and near-field properties of localized SPhP resonances, opening the door to realizing narrow-band infrared sources with tailored radiation patterns. Such control of the near-field behavior of resonances can also impact surface enhanced infrared optical sensing, which is mediated by polarization selection rules, as well as the morphology and strength of resonator hot spots. Furthermore, through the careful choice of polar dielectric material, these results can also serve as the guiding principles for the generalized design of optical devices that operate from the mid- to far-infrared.
- Published
- 2016
48. Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices
- Author
-
Troy K. Townsend, Woojun Yoon, William B. Heuer, Edward E. Foos, Dario Durastanti, and Joseph G. Tischler
- Subjects
General Chemical Engineering ,chemistry.chemical_element ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,Indium ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,law.invention ,Engineering ,law ,Solar cell ,Spin coating ,General Immunology and Microbiology ,General Neuroscience ,Temperature ,021001 nanoscience & nanotechnology ,Cadmium telluride photovoltaics ,0104 chemical sciences ,Indium tin oxide ,chemistry ,Nanocrystal ,Chemical engineering ,Nanoparticles ,Glass ,0210 nano-technology ,Tin - Abstract
We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 °C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl(-) anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136±39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.
- Published
- 2016
49. Size and Temperature Dependence of Band-Edge Excitons in PbSe Nanowires
- Author
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Rhonda M. Stroud, Janice E. Boercker, Thomas J. Zega, Emily M. Clifton, Mark E. Twigg, Joseph G. Tischler, and Edward E. Foos
- Subjects
Photoluminescence ,Materials science ,Condensed matter physics ,Exciton ,Nanowire ,Nanotechnology ,Edge (geometry) ,Spectral line ,symbols.namesake ,Nanocrystal ,Stokes shift ,symbols ,General Materials Science ,Physical and Theoretical Chemistry ,Absorption (electromagnetic radiation) - Abstract
We report the attenuance and temperature-dependent photoluminescence spectra of PbSe nanowires with diameters between 5.6 and 26.4 nm (12−23% relative standard deviation) and lengths greater than 1...
- Published
- 2011
50. Optical probing of low-pressure solution grown GaN crystal properties
- Author
-
Joseph G. Tischler, N.Y. Garces, Boris N. Feigelson, and Jaime A. Freitas
- Subjects
Photoluminescence ,Atmospheric pressure ,business.industry ,Gallium nitride ,Crystal growth ,Condensed Matter Physics ,Acceptor ,Inorganic Chemistry ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,symbols.namesake ,Optics ,chemistry ,Impurity ,Chemical physics ,Materials Chemistry ,symbols ,business ,Recombination ,Raman scattering - Abstract
The structural and optical properties of self-nucleated crystals grown by a near atmospheric pressure solution growth method are presented. High-resolution room temperature Raman scattering studies demonstrate that stress-free crystals with low free-electron background have been produced. Low and room temperature photoluminescence experiments confirm the presence of shallow donors and an unknown shallow acceptor. Large relative intensity variations of the emission bands assigned to recombination process involving donors and acceptor, resulting from significant changes in the incorporation and/or activation of defect associated with each recombination channel, reflect major changes in the intrinsic material properties.
- Published
- 2010
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