54 results on '"Nuri Yazdani"'
Search Results
2. Dynamic lattice distortions driven by surface trapping in semiconductor nanocrystals
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Burak Guzelturk, Benjamin L. Cotts, Dipti Jasrasaria, John P. Philbin, David A. Hanifi, Brent A. Koscher, Arunima D. Balan, Ethan Curling, Marc Zajac, Suji Park, Nuri Yazdani, Clara Nyby, Vladislav Kamysbayev, Stefan Fischer, Zach Nett, Xiaozhe Shen, Michael E. Kozina, Ming-Fu Lin, Alexander H. Reid, Stephen P. Weathersby, Richard D. Schaller, Vanessa Wood, Xijie Wang, Jennifer A. Dionne, Dmitri V. Talapin, A. Paul Alivisatos, Alberto Salleo, Eran Rabani, and Aaron M. Lindenberg
- Subjects
Science - Abstract
Charge trapping can lead to severe nonradiative losses in colloidal semiconductor nanocrystals (NCs). The authors report femtosecond electron diffraction measurements on photoexcited NCs to reveal atomic-scale insights into how localization of charges at trap sites induce surface deformations.
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- 2021
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3. Charge transport in semiconductors assembled from nanocrystal quantum dots
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Nuri Yazdani, Samuel Andermatt, Maksym Yarema, Vasco Farto, Mohammad Hossein Bani-Hashemian, Sebastian Volk, Weyde M. M. Lin, Olesya Yarema, Mathieu Luisier, and Vanessa Wood
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Science - Abstract
While efficiency of nanocrystal-based devices has improved, charge transport within semiconductors assembled from nanocrystal quantum dots has remained unclear. Here, the authors use ab initio calculations to develop a predictive model for charge transport that also explains the origin of deep electronic traps and validate it experimentally.
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- 2020
- Full Text
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4. Bulk and Nanocrystalline Cesium Lead-Halide Perovskites as Seen by Halide Magnetic Resonance
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Laura Piveteau, Marcel Aebli, Nuri Yazdani, Marthe Millen, Lukas Korosec, Franziska Krieg, Bogdan M. Benin, Viktoriia Morad, Christophe Piveteau, Toni Shiroka, Aleix Comas-Vives, Christophe Copéret, Aaron M. Lindenberg, Vanessa Wood, René Verel, and Maksym V. Kovalenko
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Chemistry ,QD1-999 - Published
- 2020
- Full Text
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5. Nanocrystal superlattices as phonon-engineered solids and acoustic metamaterials
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Nuri Yazdani, Maximilian Jansen, Deniz Bozyigit, Weyde M. M. Lin, Sebastian Volk, Olesya Yarema, Maksym Yarema, Fanni Juranyi, Sebastian D. Huber, and Vanessa Wood
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Science - Abstract
Phonon engineering enables tailored heat-transfer properties, controlled elastic and acoustic vibration propagation, and custom phonon-electron and phonon-photon interactions. Here, the authors present an approach for the observation and tunability of vibrational modes of nanocrystal superlattices.
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- 2019
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6. Phonon-engineered solids constructed from nanocrystals
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Maximilian Jansen, Nuri Yazdani, and Vanessa Wood
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Biotechnology ,TP248.13-248.65 ,Physics ,QC1-999 - Abstract
Here, we present the concept of colloidal nanocrystal-based solids as solution-processed, phonon-engineered materials. In particular, we discuss superlattice phonons, the vibrational modes associated with the motion of the nanocrystals away from their equilibrium positions in the nanocrystal solid (or superlattice). We calculate the characteristic energies and density of states of these superlattice phonons by modeling the nanocrystal solids as three-dimensional mass-spring networks. In this model, the nanocrystals correspond to the masses and their surface terminating organic or inorganic moieties (i.e., ligands) act as springs. We parameterize this model by determining nanocrystals masses based on crystal size and material density and by using density functional theory to determine the spring constant associated with ligand-mediated bonding between the nanocrystals. We show that by varying the type of nanocrystals, their ligands, and the topology of the nanocrystal superlattice, it is possible to systematically tune the density of states of the superlattice phonons in the energy range of 0.01 meV–10 meV. We then highlight how the construction of binary nanocrystals superlattices can be used, for example, to introduce phononic bandgaps at specific energies. Finally, we show that even with disorder stemming from finite nanocrystal size distributions and variations in the bonding between the nanocrystals and the ligands, distinct superlattice phonons modes will still be present.
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- 2019
- Full Text
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7. Modeling and optimization of atomic layer deposition processes on vertically aligned carbon nanotubes
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Nuri Yazdani, Vipin Chawla, Eve Edwards, Vanessa Wood, Hyung Gyu Park, and Ivo Utke
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atomic layer deposition ,vertically aligned carbon nanotubes ,continuum diffusion model ,conformal coating guidelines ,titania, TiO2 ,Technology ,Chemical technology ,TP1-1185 ,Science ,Physics ,QC1-999 - Abstract
Many energy conversion and storage devices exploit structured ceramics with large interfacial surface areas. Vertically aligned carbon nanotube (VACNT) arrays have emerged as possible scaffolds to support large surface area ceramic layers. However, obtaining conformal and uniform coatings of ceramics on structures with high aspect ratio morphologies is non-trivial, even with atomic layer deposition (ALD). Here we implement a diffusion model to investigate the effect of the ALD parameters on coating kinetics and use it to develop a guideline for achieving conformal and uniform thickness coatings throughout the depth of ultra-high aspect ratio structures. We validate the model predictions with experimental data from ALD coatings of VACNT arrays. However, the approach can be applied to predict film conformality as a function of depth for any porous topology, including nanopores and nanowire arrays.
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- 2014
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8. Effect of Positional Disorders on Charge Transport in Nanocrystal Quantum Dot Thin Films
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Yunhua Xing, Nuri Yazdani, Weyde M. M. Lin, Maksym Yarema, Raphael Zahn, and Vanessa Wood
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deep electronic trap state ,density functional theory (DFT) ,nanocrystals ,PbS ,positional and energetic disorder ,charge transport ,time-of-flight (ToF) ,kinetic Monte Carlo (KMC) simulation ,Materials Chemistry ,Electrochemistry ,Electronic, Optical and Magnetic Materials - Abstract
Understanding the impact of positional and energetic disorders in nanocrystal (NC) quantum dot thin films on charge transport is crucial to determine what to prioritize in terms of the synthesis and fabrication of these materials and to accelerate their development for electronics. Here, we computationally construct realistic NC thin films with different types of disorders and apply a density functional theory (DFT)-parameterized, kinetic Monte Carlo simulation to systematically study the effects of disorders on transport. We obtain statistics on the carrier transit pathways through the NC films and carrier residence times on individual NCs. This provides insights into the distribution of transit times across the thin films and the effective mobility. We conclude that the impact of positional disorders on charge transport depends on the type of disorder and how it affects the spacing between neighboring NCs. The formation of transport paths with short inter-NC distances can enhance mobility. Meanwhile, random packing (RP) of NCs and energetic disorders due to a distribution of NC sizes decreases mobility 2- to 4-fold. Because of the large reorganization energy of small NCs, increasing the electric field has little influence on the median residence time of a charge carrier on an NC; however, an electric field straightens the transport path of the charge carrier and reduces the average number of hops a carrier makes, which can slightly enhance mobility. Deep electronic trap states are especially detrimental to carrier mobility, particularly at low fields and when the films are otherwise highly ordered., ACS Applied Electronic Materials, 4 (2), ISSN:2637-6113
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- 2022
9. Metasurface Colloidal Quantum Dot Photodetectors
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Nikola Đorđević, Raphael Schwanninger, Maksym Yarema, Stefan Koepfli, Olesya Yarema, Yannick Salamin, Nolan Lassaline, Bojun Cheng, Nuri Yazdani, Alexander Dorodnyy, Yuriy Myronovych Fedoryshyn, Vanessa Wood, and Juerg Leuthold
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Electrical and Electronic Engineering ,metamaterials ,photodetectors ,plasmonics ,quantum dots ,Atomic and Molecular Physics, and Optics ,Biotechnology ,Electronic, Optical and Magnetic Materials - Abstract
Efficient photodetectors that can be easily engineered for a specific spectral window are of high interest. Here, we report on the design, fabrication, and characterization of metasurface-enhanced photodetectors and photodiodes using colloidal quantum dots. We fabricate photoconductors optimized for the wavelength range around 1550 nm featuring responsivities of up to 8000 A/W with low noise equivalent powers on the order of tens of pW/Hz. Further, we produce photodiodes with responsivities of ∼5 mA/W that offer faster responses (14 μs rise time). The high responsivities are due to the metasurface, which increases the absorption by a factor of 10 compared to that of a quantum dot thin film of the same thickness and a structure that enables a photo-gain. We introduce a metasurface to detect either of the two orthogonal polarizations. The fabricated photoconductors operate at low voltages (1-5 V), making them compatible with the complementary metal-oxide-semiconductor (CMOS) read-out circuitry. ISSN:2330-4022
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- 2022
10. Measuring Electron-Phonon Coupling induced Lattice Reorganization in Lead Halide Perovskite Nanocrystals through Femto-Second Resolved Optical-pump Diffraction-probe experiments
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Nuri Yazdani, Maryna Bodnarchuk, Federica Bertolotti, Norberto Masciocchi, Antonietta Guagliardi, Maksym Kovalenko, Vanessa Wood, and Aaron Lindenberg
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- 2022
11. Manipulating Electronic Structure from the Bottom-Up: Colloidal Nanocrystal-Based Semiconductors
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Sebastian Volk, Vanessa Wood, and Nuri Yazdani
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Materials science ,business.industry ,Doping ,02 engineering and technology ,Electronic structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermal conduction ,01 natural sciences ,0104 chemical sciences ,Colloid ,Semiconductor ,Nanocrystal ,Valence band ,Optoelectronics ,General Materials Science ,Physical and Theoretical Chemistry ,Thin film ,0210 nano-technology ,business - Abstract
Semiconductors assembled from colloidal nanocrystals (NCs) are often described in the same terms as their single-crystalline counterparts with references to conduction and valence band edges, doping densities, and electronic defects; however, how and why semiconductor properties manifest in these bottom-up fabricated thin films can be fundamentally different. In this Perspective, we describe the factors that determine the electronic structure in colloidal NC-based semiconductors, and comment on approaches for measuring or calculating this electronic structure. Finally, we discuss future directions for these semiconductors and highlight their potential to bridge the divide between localized quantum effects and long-range transport in thin films., The Journal of Physical Chemistry Letters, 11 (21), ISSN:1948-7185
- Published
- 2020
12. Phonon-Mediated and Weakly Size-Dependent Electron and Hole Cooling in CsPbBr3 Nanocrystals Revealed by Atomistic Simulations and Ultrafast Spectroscopy
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Kai Chen, Ivan Infante, Pieter Geiregat, Jorick Maes, Felipe Zapata, Justin M. Hodgkiss, Vanessa Wood, Simon C. Boehme, Nuri Yazdani, Stephanie ten Brinck, Zeger Hens, AIMMS, and Theoretical Chemistry
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Photoluminescence ,Materials science ,Absorption spectroscopy ,Phonon ,Ab initio ,nonadiabatic molecular dynamics ,Bioengineering ,02 engineering and technology ,Electron ,Polaron ,Molecular physics ,Condensed Matter::Materials Science ,General Materials Science ,SDG 7 - Affordable and Clean Energy ,Spectroscopy ,lead-halide perovskite nanocrystal ,Charge-carrier cooling ,Mechanical Engineering ,excited-states dynamics ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Charge carrier ,hot carriers ,electron-phonon coupling ,0210 nano-technology - Abstract
We combine state-of-the-art ultrafast photoluminescence and absorption spectroscopy and nonadiabatic molecular dynamics simulations to investigate charge-carrier cooling in CsPbBr3 nanocrystals over a very broad size regime, from 0.8 to 12 nm. Contrary to the prevailing notion that polaron formation slows down charge-carrier cooling in lead-halide perovskites, no suppression of carrier cooling is observed in CsPbBr3 nanocrystals except for a slow cooling (over ∼10 ps) of "warm" electrons in the vicinity (within ∼0.1 eV) of the conduction band edge. At higher excess energies, electrons and holes cool with similar rates, on the order of 1 eV ps-1 carrier-1, increasing weakly with size. Our ab initio simulations suggest that cooling proceeds via fast phonon-mediated intraband transitions driven by strong and size-dependent electron-phonon coupling. The presented experimental and computational methods yield the spectrum of involved phonons and may guide the development of devices utilizing hot charge carriers.
- Published
- 2020
13. Non-Equilibrium Lattice Dynamics in Photo-Excited Two-Dimensional Perovskites
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Shelby A. Cuthriell, Shobhana Panuganti, Craig C. Laing, Michael A. Quintero, Burak Guzelturk, Nuri Yazdani, Boubacar Traore, Alexandra Brumberg, Christos D. Malliakas, Aaron M. Lindenberg, Vanessa Wood, Claudine Katan, Jacky Even, Xiaoyi Zhang, Mercouri G. Kanatzidis, Richard D. Schaller
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- 2022
- Full Text
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14. Recombination Dynamics in PbS Nanocrystal Quantum Dot Solar Cells Studied through Drift–Diffusion Simulations
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Vanessa Wood, Nuri Yazdani, Weyde M. M. Lin, Edward H. Sargent, Mengxia Liu, Maksym Yarema, Olesya Yarema, and Thomas Kirchartz
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Materials science ,nanocrystal ,quantum dot ,lead sulfide ,solar cell ,simulation ,device architecture ,Dynamics (mechanics) ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Nanocrystal ,Quantum dot ,Chemical physics ,Materials Chemistry ,Electrochemistry ,Diffusion (business) ,ddc:620 ,0210 nano-technology ,Recombination ,Elektrotechnik - Abstract
The significant performance increase in nanocrystal (NC)-based solar cells over the last decade is very encouraging. However, many of these gains have been achieved by trial-and-error optimization, and a systematic understanding of what limits the device performance is lacking. In parallel, experimental and computational techniques provide increasing insights into the electronic properties of individual NCs and their assemblies in thin films. Here, we utilize these insights to parameterize drift–diffusion simulations of PbS NC solar cells, which enable us to track the distribution of charge carriers in the device and quantify recombination dynamics, which limit the device performance. We simulate both Schottky- and heterojunction-type devices and, through temperature-dependent measurements in the light and dark, experimentally validate the appropriateness of the parameterization. The results reveal that Schottky-type devices are limited by surface recombination between the PbS and aluminum contact, while heterojunction devices are currently limited by NC dopants and electronic defects in the PbS layer. The simulations highlight a number of opportunities for further performance enhancement, including the reduction of dopants in the nanocrystal active layer, the control over doping and electronic structure in electron- and hole-blocking layers (e.g., ZnO), and the optimization of the interfaces to improve the band alignment and reduce surface recombination. For example, reduction in the percentage of p-type NCs from the current 1–0.01% in the heterojunction device can lead to a 25% percent increase in the power conversion efficiency. ISSN:2637-6113
- Published
- 2021
15. Ultra-narrow room-temperature emission from single CsPbBr
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Gabriele, Rainò, Nuri, Yazdani, Simon C, Boehme, Manuel, Kober-Czerny, Chenglian, Zhu, Franziska, Krieg, Marta D, Rossell, Rolf, Erni, Vanessa, Wood, Ivan, Infante, and Maksym V, Kovalenko
- Abstract
Semiconductor quantum dots have long been considered artificial atoms, but despite the overarching analogies in the strong energy-level quantization and the single-photon emission capability, their emission spectrum is far broader than typical atomic emission lines. Here, by using ab-initio molecular dynamics for simulating exciton-surface-phonon interactions in structurally dynamic CsPbBr
- Published
- 2021
16. Dynamic lattice distortions driven by surface trapping in semiconductor nanocrystals
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Ethan Curling, Stephen Weathersby, Jennifer A. Dionne, Stefan Fischer, Benjamin L. Cotts, Arunima D. Balan, A. Paul Alivisatos, Alexander H. Reid, John P. Philbin, Marc Zajac, Dipti Jasrasaria, David Hanifi, Burak Guzelturk, Vladislav Kamysbayev, Alberto Salleo, Ming-Fu Lin, Eran Rabani, Vanessa Wood, Michael Kozina, Dmitri V. Talapin, Nuri Yazdani, Xiaozhe Shen, Zach Nett, Brent A. Koscher, Xijie Wang, Aaron M. Lindenberg, Suji Park, Richard D. Schaller, and Clara Nyby
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Materials science ,Band gap ,Science ,General Physics and Astronomy ,Physics::Optics ,FOS: Physical sciences ,macromolecular substances ,02 engineering and technology ,Photon energy ,010402 general chemistry ,behavioral disciplines and activities ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Auger ,Condensed Matter::Materials Science ,mental disorders ,cond-mat.mes-hall ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Physics::Atomic and Molecular Clusters ,Optical materials and structures ,Colloids ,Physics::Atomic Physics ,Condensed Matter::Quantum Gases ,Multidisciplinary ,Condensed Matter - Mesoscale and Nanoscale Physics ,Quantum dots ,technology, industry, and agriculture ,General Chemistry ,equipment and supplies ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Nanocrystal ,Electron diffraction ,Chemical physics ,Picosecond ,Femtosecond ,Atomistic models ,0210 nano-technology ,Excitation ,Materials for optics - Abstract
Nonradiative processes limit optoelectronic functionality of nanocrystals and curb their device performance. Nevertheless, the dynamic structural origins of nonradiative relaxations in such materials are not understood. Here, femtosecond electron diffraction measurements corroborated by atomistic simulations uncover transient lattice deformations accompanying radiationless electronic processes in colloidal semiconductor nanocrystals. Investigation of the excitation energy dependence in a core/shell system shows that hot carriers created by a photon energy considerably larger than the bandgap induce structural distortions at nanocrystal surfaces on few picosecond timescales associated with the localization of trapped holes. On the other hand, carriers created by a photon energy close to the bandgap of the core in the same system result in transient lattice heating that occurs on a much longer 200 picosecond timescale, dominated by an Auger heating mechanism. Elucidation of the structural deformations associated with the surface trapping of hot holes provides atomic-scale insights into the mechanisms deteriorating optoelectronic performance and a pathway towards minimizing these losses in nanocrystal devices., Nature Communications, 12 (1), ISSN:2041-1723
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- 2021
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17. Magnetic Resonance Spectroscopy of Bulk and Nanocrystalline Cesium Lead Halide Perovskites
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Franziska Krieg, Nuri Yazdani, Maksym V. Kovalenko, Marcel Aebli, René Verel, and Laura Piveteau
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Lead (geology) ,Materials science ,chemistry ,Caesium ,Inorganic chemistry ,chemistry.chemical_element ,Halide ,Nuclear magnetic resonance spectroscopy ,Nanocrystalline material - Published
- 2020
18. Size, Ligand, and Defect-Dependent Electron-Phonon Coupling in Chalcogenide and Perovskite Nanocrystals and Its Impact on Luminescence Line Widths
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Olesya Yarema, Vanessa Wood, Nuri Yazdani, Maksym Yarema, and Sebastian Volk
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Materials science ,Chalcogenide ,Ligand ,02 engineering and technology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,010309 optics ,Coupling (electronics) ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,chemistry ,Nanocrystal ,Quantum dot ,Condensed Matter::Superconductivity ,0103 physical sciences ,Electrical and Electronic Engineering ,0210 nano-technology ,Luminescence ,Biotechnology ,Line (formation) ,Perovskite (structure) - Abstract
ACS Photonics, 7 (5), ISSN:2330-4022
- Published
- 2020
19. Bulk and Nanocrystalline Cesium Lead-Halide Perovskites as Seen by Halide Magnetic Resonance
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Marthe Millen, Bogdan M. Benin, Viktoriia Morad, Aaron M. Lindenberg, René Verel, Christophe Copéret, Vanessa Wood, Christophe Piveteau, Aleix Comas-Vives, Laura Piveteau, Marcel Aebli, Franziska Krieg, Nuri Yazdani, Lukas Korosec, Toni Shiroka, and Maksym V. Kovalenko
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Materials science ,010405 organic chemistry ,Scattering ,General Chemical Engineering ,Relaxation (NMR) ,Ab initio ,General Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Characterization (materials science) ,Chemistry ,Molecular dynamics ,Chemical physics ,Quadrupole ,Nuclear quadrupole resonance ,Spectroscopy ,QD1-999 ,Research Article - Abstract
Lead-halide perovskites increasingly mesmerize researchers because they exhibit a high degree of structural defects and dynamics yet nonetheless offer an outstanding (opto)electronic performance on par with the best examples of structurally stable and defect-free semiconductors. This highly unusual feature necessitates the adoption of an experimental and theoretical mindset and the reexamination of techniques that may be uniquely suited to understand these materials. Surprisingly, the suite of methods for the structural characterization of these materials does not commonly include nuclear magnetic resonance (NMR) spectroscopy. The present study showcases both the utility and versatility of halide NMR and NQR (nuclear quadrupole resonance) for probing the structure and structural dynamics of CsPbX3 (X = Cl, Br, I), in both bulk and nanocrystalline forms. The strong quadrupole couplings, which originate from the interaction between the large quadrupole moments of, e.g., the 35Cl, 79Br, and 127I nuclei, and the local electric-field gradients, are highly sensitive to subtle structural variations, both static and dynamic. The quadrupole interaction can resolve structural changes with accuracies commensurate with synchrotron X-ray diffraction and scattering. It is shown that space-averaged site-disorder is greatly enhanced in the nanocrystals compared to the bulk, while the dynamics of nuclear spin relaxation indicates enhanced structural dynamics in the nanocrystals. The findings from NMR and NQR were corroborated by ab initio molecular dynamics, which point to the role of the surface in causing the radial strain distribution and disorder. These findings showcase a great synergy between solid-state NMR or NQR and molecular dynamics simulations in shedding light on the structure of soft lead-halide semiconductors., ACS Central Science, 6 (7), ISSN:2374-7951
- Published
- 2020
20. Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering Microscopy
- Author
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Ming-Fu Lin, Vanessa Wood, Aaron M. Lindenberg, Eric M. Janke, Alberto Salleo, Xijie Wang, Igor Coropceanu, Suji Park, Nuri Yazdani, Benjamin L. Cotts, Dmitri V. Talapin, Alexander H. Reid, James K. Utterback, Vladislav Kamysbayev, Marc Zajac, Michael Kozina, Aditya Sood, Stephen Weathersby, Naomi S. Ginsberg, Xiaozhe Shen, Burak Guzelturk, Standford University, University of Colorado [Boulder], University of Chicago, Stanford University, Laboratory of Nanoelectronics [ETH Zürich], Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich] (ETH Zürich), University of California [Berkeley], and University of California
- Subjects
Materials science ,General Physics and Astronomy ,Physics::Optics ,02 engineering and technology ,time-resolved microscopy ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,Light scattering ,Condensed Matter::Materials Science ,electron−phonon coupling ,General Materials Science ,Thin film ,Nanoscience & Nanotechnology ,ComputingMilieux_MISCELLANEOUS ,ligands ,Ultrafast electron diffraction ,General Engineering ,colloidal nanocrystals ,ultra fast electron diffraction ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,0104 chemical sciences ,Photoexcitation ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Nanocrystal ,Electron diffraction ,thermal transport ,Chemical physics ,Colloidal gold ,Femtosecond ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,[SPI.MECA.THER]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Thermics [physics.class-ph] ,hot carriers ,electron-phonon coupling ,0210 nano-technology ,ultrafast electron diffraction - Abstract
Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.
- Published
- 2020
21. Quantifying Diffusion through Interfaces of Lithium-Ion Battery Active Materials
- Author
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Yasmine Sassa, Nami Matsubara, Peter Benedek, Mark T. F. Telling, Ola Kenji Forslund, Fanni Juranyi, Martin Månsson, Marisa Medarde, Elisabetta Nocerino, Nuri Yazdani, and Vanessa Wood
- Subjects
Battery (electricity) ,Materials science ,02 engineering and technology ,Electrolyte ,Surface engineering ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,Lithium-ion battery ,0104 chemical sciences ,Atomic diffusion ,Chemical physics ,Particle ,General Materials Science ,Diffusion (business) ,Cyclic voltammetry ,0210 nano-technology - Abstract
Detailed understanding of charge diffusion processes in a lithium-ion battery is crucial to enable its systematic improvement. Experimental investigation of diffusion at the interface between active particles and the electrolyte is challenging but warrants investigation as it can introduce resistances that, for example, limit the charge and discharge rates. Here, we show an approach to study diffusion at interfaces using muon spin spectroscopy. By performing measurements on LiFePO4 platelets with different sizes, we determine how diffusion through the LiFePO4 (010) interface differs from that in the center of the particle (i.e., bulk diffusion). We perform ab initio calculations to aid the understanding of the results and show the relevance of our interfacial diffusion measurement to electrochemical performance through cyclic voltammetry measurements. These results indicate that surface engineering can be used to improve the performance of lithium-ion batteries.
- Published
- 2020
22. Dopants and Traps in Nanocrystal-Based Semiconductor Thin Films: Origins and Measurement of Electronic Midgap States
- Author
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Olesya Yarema, Maksym Yarema, Sebastian Volk, Nuri Yazdani, and Vanessa Wood
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Semiconductor thin films ,energy-resolved electrochemical impedance spectroscopy ,Materials science ,computer.internet_protocol ,trap state ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Nanocrystal thin films ,Materials Chemistry ,Electrochemistry ,Thin film ,Dopant ,business.industry ,PbS ,electronic midgap state ,Fourier transform photocurrent spectroscopy ,FTPS ,ER-EIS ,Charge (physics) ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Nanocrystal ,Optoelectronics ,0210 nano-technology ,business ,computer - Abstract
ACS Applied Electronic Materials, 2 (2), ISSN:2637-6113
- Published
- 2020
23. Phonon-Mediated and Weakly Size-Dependent Electron and Hole Cooling in CsPbBr
- Author
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Simon C, Boehme, Stephanie Ten, Brinck, Jorick, Maes, Nuri, Yazdani, Felipe, Zapata, Kai, Chen, Vanessa, Wood, Justin M, Hodgkiss, Zeger, Hens, Pieter, Geiregat, and Ivan, Infante
- Subjects
Condensed Matter::Materials Science ,Letter ,electron−phonon coupling ,Charge-carrier cooling ,excited-states dynamics ,nonadiabatic molecular dynamics ,hot carriers ,lead-halide perovskite nanocrystal - Abstract
We combine state-of-the-art ultrafast photoluminescence and absorption spectroscopy and nonadiabatic molecular dynamics simulations to investigate charge-carrier cooling in CsPbBr3 nanocrystals over a very broad size regime, from 0.8 to 12 nm. Contrary to the prevailing notion that polaron formation slows down charge-carrier cooling in lead-halide perovskites, no suppression of carrier cooling is observed in CsPbBr3 nanocrystals except for a slow cooling (over ∼10 ps) of “warm” electrons in the vicinity (within ∼0.1 eV) of the conduction band edge. At higher excess energies, electrons and holes cool with similar rates, on the order of 1 eV ps–1 carrier–1, increasing weakly with size. Our ab initio simulations suggest that cooling proceeds via fast phonon-mediated intraband transitions driven by strong and size-dependent electron–phonon coupling. The presented experimental and computational methods yield the spectrum of involved phonons and may guide the development of devices utilizing hot charge carriers.
- Published
- 2020
24. Simulating nanocrystal-based solar cells: A lead sulfide case study
- Author
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Sebastian Volk, Thomas Kirchartz, Olesya Yarema, Maksym Yarema, Weyde M. M. Lin, Vanessa Wood, and Nuri Yazdani
- Subjects
010304 chemical physics ,business.industry ,Photovoltaic system ,Energy conversion efficiency ,General Physics and Astronomy ,Quantum dot solar cell ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Semiconductor ,Solar cell efficiency ,Nanocrystal ,chemistry ,law ,0103 physical sciences ,Solar cell ,Optoelectronics ,ddc:530 ,Lead sulfide ,Physical and Theoretical Chemistry ,business ,Elektrotechnik - Abstract
The Journal of Chemical Physics, 151 (24), ISSN:0021-9606, ISSN:1089-7690
- Published
- 2019
25. Measuring the Electronic Structure of Nanocrystal Thin Films Using Energy-Resolved Electrochemical Impedance Spectroscopy
- Author
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Sebastian Volk, Nuri Yazdani, Maksym Yarema, Emir Sanusoglu, Olesya Yarema, and Vanessa Wood
- Subjects
energy-resolved electrochemical impedance spectroscopy ,Materials science ,quantum dots ,02 engineering and technology ,Electronic structure ,ligand ,010402 general chemistry ,01 natural sciences ,chemistry.chemical_compound ,General Materials Science ,Lead sulfide ,Physical and Theoretical Chemistry ,Thin film ,EIS ,density of states ,nanocrystal thin films ,PbS ,photovoltaics ,nanocrystal doping ,ER-EIS ,Dopant ,business.industry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Dielectric spectroscopy ,Nanocrystal ,chemistry ,Quantum dot ,Density of states ,Optoelectronics ,0210 nano-technology ,business - Abstract
The Journal of Physical Chemistry Letters, 9 (6), ISSN:1948-7185
- Published
- 2018
26. In Situ Monitoring of Cation-Exchange Reaction Shell Growth on Nanocrystals
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Nuri Yazdani, Olesya Yarema, Annina Moser, Weyde M. M. Lin, Vanessa Wood, and Maksym Yarema
- Subjects
Materials science ,Nanostructure ,Photoluminescence ,Diffusion ,Shell (structure) ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Colloid ,General Energy ,Chemical engineering ,Nanocrystal ,Monolayer ,Physical and Theoretical Chemistry ,0210 nano-technology ,Layer (electronics) - Abstract
We demonstrate how in situ monitoring of the photoluminescence during shell growth around colloidal nanocrystals (NCs) can be used to develop a detailed and quantitative model for this process. We apply it here to study cation-exchange based growth of ZnS on a Cu–In–Se NC to form Cu–In–Se/ZnSe1–xSx alloyed NCs. We determine that this process begins with the Zn precursor binding to the outer layer of the NC followed by diffusion of Zn cations into successive atomic monolayers of the NC. At temperatures below 100 °C, Zn cations can only diffuse into the outermost atomic monolayer of the Cu–In–Se NCs. At growth temperatures above 100 °C, the second monolayer also becomes thermally accessible and can be filled with Zn cations. Our results provide an understanding of cation-exchange shell growth at the atomic level via optical analysis. The approach and mathematical model described here can be applied to other core/shell nanostructures and allows selection of optimal synthesis conditions to achieve desired cor...
- Published
- 2017
27. Upscaling Colloidal Nanocrystal Hot-Injection Syntheses via Reactor Underpressure
- Author
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Olesya Yarema, Deniz Bozyigit, Vanessa Wood, Weyde M. M. Lin, Nuri Yazdani, Maksym Yarema, and Sebastian Volk
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Materials science ,business.industry ,General Chemical Engineering ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Orders of magnitude (numbers) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Colloid ,Semiconductor ,Nanocrystal ,Materials Chemistry ,0210 nano-technology ,business - Abstract
We report an approach to linearly upscale hot-injection syntheses of colloidal nanocrystals by applying mild underpressure to the flask reactor prior to the injection such that rapid addition of large volumes of the precursor is facilitated. We apply this underpressure-assisted approach to successfully upscale synthetic protocols for metallic (Sn) and semiconductor (PbS, CsPbBr3, and Cu3In5Se9) nanocrystals by 1–2 orders of magnitude to obtain tens of grams of nanocrystals per synthesis. Here, we provide the technical details of how to perform underpressure-assisted upscaling and demonstrate that nanocrystal quality is maintained for the large-batch syntheses by characterizing the size, size distribution, composition, optical properties, and ligand coverage of the nanocrystals for both small- and large-scale syntheses. This work shows that fast addition of large injection volumes does not intrinsically limit upscaling of hot-injection-based colloidal syntheses.
- Published
- 2017
28. Nanocrystal superlattices as phonon-engineered solids and acoustic metamaterials
- Author
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Deniz Bozyigit, Olesya Yarema, Vanessa Wood, Sebastian Volk, Sebastian D. Huber, Fanni Juranyi, Maximilian Jansen, Weyde M. M. Lin, Nuri Yazdani, and Maksym Yarema
- Subjects
Materials for devices ,Materials science ,Phonon ,Science ,Superlattice ,Physics::Optics ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Inelastic neutron scattering ,Condensed Matter::Materials Science ,Condensed Matter::Superconductivity ,Acoustic metamaterials ,lcsh:Science ,Topology (chemistry) ,Multidisciplinary ,business.industry ,Electronics, photonics and device physics ,Metamaterial ,General Chemistry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Mechanical engineering ,0104 chemical sciences ,Nanocrystal ,Optoelectronics ,lcsh:Q ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,business ,Acoustic vibration - Abstract
Phonon engineering of solids enables the creation of materials with tailored heat-transfer properties, controlled elastic and acoustic vibration propagation, and custom phonon–electron and phonon–photon interactions. These can be leveraged for energy transport, harvesting, or isolation applications and in the creation of novel phonon-based devices, including photoacoustic systems and phonon-communication networks. Here we introduce nanocrystal superlattices as a platform for phonon engineering. Using a combination of inelastic neutron scattering and modeling, we characterize superlattice-phonons in assemblies of colloidal nanocrystals and demonstrate that they can be systematically engineered by tailoring the constituent nanocrystals, their surfaces, and the topology of superlattice. This highlights that phonon engineering can be effectively carried out within nanocrystal-based devices to enhance functionality, and that solution processed nanocrystal assemblies hold promise not only as engineered electronic and optical materials, but also as functional metamaterials with phonon energy and length scales that are unreachable by traditional architectures., Nature Communications, 10 (1), ISSN:2041-1723
- Published
- 2019
29. Phonon-engineered solids constructed from nanocrystals
- Author
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Nuri Yazdani, Maximilian Jansen, and Vanessa Wood
- Subjects
Materials science ,Phonon ,lcsh:Biotechnology ,Superlattice ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,Crystal ,Condensed Matter::Materials Science ,lcsh:TP248.13-248.65 ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Topology (chemistry) ,010302 applied physics ,Condensed matter physics ,Condensed Matter::Other ,General Engineering ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,lcsh:QC1-999 ,Nanocrystal ,Molecular vibration ,Density of states ,Density functional theory ,Software_PROGRAMMINGLANGUAGES ,0210 nano-technology ,lcsh:Physics - Abstract
APL Materials, 7 (8), ISSN:2166-532X
- Published
- 2019
- Full Text
- View/download PDF
30. Soft surfaces of nanomaterials enable strong phonon interactions
- Author
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Deniz Bozyigit, Maksym Yarema, Fanni Juranyi, Vanessa Wood, Sebastian Volk, Kantawong Vuttivorakulchai, Weyde M. M. Lin, Mathieu Luisier, Olesya Yarema, and Nuri Yazdani
- Subjects
Multidisciplinary ,Materials science ,Condensed matter physics ,Phonon ,business.industry ,Exciton ,Nanotechnology ,02 engineering and technology ,Semiconductor device ,Electron ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,7. Clean energy ,Inelastic neutron scattering ,0104 chemical sciences ,Nanomaterials ,Condensed Matter::Materials Science ,Semiconductor ,Condensed Matter::Superconductivity ,Condensed Matter::Strongly Correlated Electrons ,Charge carrier ,0210 nano-technology ,business - Abstract
Phonons and their interactions with other phonons electrons or photons drive energy gain loss and transport in materials. Although the phonon density of states has been measured and calculated in bulk crystalline semiconductors1 phonons remain poorly understood in nanomaterials2 3 4 5 despite the increasing prevalence of bottom up fabrication of semiconductors from nanomaterials and the integration of nanometre sized components into devices6 7 8. Here we quantify the phononic properties of bottom up fabricated semiconductors as a function of crystallite size using inelastic neutron scattering measurements and ab initio molecular dynamics simulations. We show that unlike in microcrystalline semiconductors the phonon modes of semiconductors with nanocrystalline domains exhibit both reduced symmetry and low energy owing to mechanical softness at the surface of those domains. These properties become important when phonons couple to electrons in semiconductor devices. Although it was initially believed that the coupling between electrons and phonons is suppressed in nanocrystalline materials owing to the scarcity of electronic states and their large energy separation9 it has since been shown that the electron–phonon coupling is large and allows high energy dissipation rates exceeding one electronvolt per picosecond (refs 10 11 12 13). Despite detailed investigations into the role of phonons in exciton dynamics leading to a variety of suggestions as to the origins of these fast transition rates14 15 and including attempts to numerically calculate them12 13 16 fundamental questions surrounding electron–phonon interactions in nanomaterials remain unresolved. By combining the microscopic and thermodynamic theories of phonons1 17 18 19 and our findings on the phononic properties of nanomaterials we are able to explain and then experimentally confirm the strong electron–phonon coupling and fast multi phonon transition rates of charge carriers to trap states. This improved understanding of phonon processes permits the rational selection of nanomaterials their surface treatments and the design of devices incorporating them.
- Published
- 2016
31. Probing Solvent-Ligand Interactions in Colloidal Nanocrystals by the NMR Line Broadening
- Author
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Ivan Infante, Jonathan S. Owen, Alessandro Lauria, Markus Niederberger, Zeger Hens, Isabel Van Driessche, Jonathan De Roo, Emile Drijvers, Nuri Yazdani, Vanessa Wood, Jorick Maes, José C. Martins, AIMMS, and Theoretical Chemistry
- Subjects
Solid-state chemistry ,General Chemical Engineering ,Nanoparticle ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Nanomaterials ,chemistry.chemical_compound ,SURFACE-CHEMISTRY ,Selenide ,BINDING ,Materials Chemistry ,NANOPARTICLES ,OXIDE NANOCRYSTALS ,EXCHANGE ,NANOMATERIALS ,Ligand ,SUPERLATTICES ,Solvation ,General Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Chemistry ,PBS QUANTUM DOTS ,SIZE ,chemistry ,Nanocrystal ,Chemical physics ,METAL-SELENIDE NANOCRYSTALS ,Proton NMR ,0210 nano-technology ,SDG 6 - Clean Water and Sanitation - Abstract
Although solvent-ligand interactions play a major role in nanocrystal synthesis, dispersion formulation, and assembly, there is currently no direct method to study this. Here we examine the broadening of 1H NMR resonances associated with bound ligands and turn this poorly understood descriptor into a tool to assess solvent-ligand interactions. We show that the line broadening has both a homogeneous and a heterogeneous component. The former is nanocrystal-size dependent, and the latter results from solvent-ligand interactions. Our model is supported by experimental and theoretical evidence that correlates broad NMR lines with poor ligand solvation. This correlation is found across a wide range of solvents, extending from water to hexane, for both hydrophobic and hydrophilic ligand types, and for a multitude of oxide, sulfide, and selenide nanocrystals. Our findings thus put forward NMR line-shape analysis as an indispensable tool to form, investigate, and manipulate nanocolloids.
- Published
- 2018
32. Solvent-Ligand Interactions in Colloidal Nanocrystals
- Author
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Jonathan De Roo, Nuri Yazdani, Emile Drijvers, Alessandro Lauria, Jorick Maes, Isabel Van Driessche, Markus Niederberger, Vanessa Wood, José C. Martins, Ivan Infante, and Zeger Hens
- Abstract
Although solvent-ligand interactions play a major role in nanocrystal synthesis, dispersion formulation and assembly, there is currently no direct method to study this. Here we examine the broadening of 1H NMR resonances associated with bound ligands, and turn this poorly understood descriptor into a tool to assess solvent-ligand interactions. We show that the line broadening has both a homogeneous and a heterogeneous component. The former is nanocrystal-size dependent and the latter results from solvent-ligand interactions. Our model is supported by experimental and theoretical evidence that correlates broad NMR lines with poor ligand solvation. This correlation is found across a wide range of solvents, extending from water to hexane, for both hydrophobic and hydrophilic ligand types, and for a multitude of oxide, sulfide and selenide nanocrystals. Our findings thus put forward NMR line shape analysis as an indispensable tool to form, investigate and manipulate nanocolloids.
- Published
- 2018
33. Tuning Electron-Phonon Interactions in Nanocrystals through Surface Termination
- Author
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Ivan Infante, Deniz Bozyigit, Kantawong Vuttivorakulchai, Nuri Yazdani, Vanessa Wood, Mathieu Luisier, AIMMS, and Theoretical Chemistry
- Subjects
Materials science ,Phonon ,carrier cooling ,phonons ,Nanocrystals ,quantum dots ,electron−phonon coupling ,thermal broadening ,Bioengineering ,02 engineering and technology ,Electronic structure ,Surface engineering ,010402 general chemistry ,01 natural sciences ,Ion ,chemistry.chemical_compound ,Condensed Matter::Materials Science ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Lead sulfide ,Mechanical Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Nanocrystal ,chemistry ,Chemical physics ,Quantum dot ,Charge carrier ,electron-phonon coupling ,0210 nano-technology ,SDG 6 - Clean Water and Sanitation - Abstract
Nano Letters, 18 (4), ISSN:1530-6984, ISSN:1530-6992
- Published
- 2018
34. Measuring the Vibrational Density of States of Nanocrystal-Based Thin Films with Inelastic X-ray Scattering
- Author
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Vanessa Wood, Weyde M. M. Lin, Olesya Yarema, Ramon Gao, Alexey Bosak, Tra Nguyen-Thanh, Nuri Yazdani, and Maksym Yarema
- Subjects
Materials science ,Scattering ,business.industry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,0104 chemical sciences ,Nanomaterials ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Semiconductor ,chemistry ,Nanocrystal ,Quantum dot ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Lead sulfide ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Thin film ,0210 nano-technology ,business ,Perovskite (structure) - Abstract
The Journal of Physical Chemistry Letters, 9 (7), ISSN:1948-7185
- Published
- 2018
35. Machine Learning for Analysis of Time-Resolved Luminescence Data
- Author
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Juerg Leuthold, Arnulf Rosspeintner, Vanessa Wood, Eric Vauthey, Olesya Yarema, Maksym Yarema, Joseph Beckwith, Nuri Yazdani, and Nikola Đorđević
- Subjects
Materials science ,Photoluminescence ,business.industry ,Condensed Matter::Other ,Physics::Optics ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Nanocrystal ,Optical materials ,ddc:540 ,Time resolved luminescence ,Optoelectronics ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,Luminescence ,Biotechnology - Abstract
Time-resolved photoluminescence is one of the most standard techniques to understand and systematically optimize the performance of optical materials and optoelectronic devices. Here, we present a machine learning code to analyze time-resolved photoluminescence data and determine the decay rate distribution of an arbitrary emitter without any a priori assumptions. To demonstrate and validate our approach, we analyze computer-generated time-resolved photoluminescence data sets and show its benefits for studying the photo- luminescence of novel semiconductor nanocrystals (quantum dots), where it quickly provides insight into the possible physical mechanisms of luminescence without the need for educated guessing and fitting.
- Published
- 2018
36. In Situ Measurement and Control of the Fermi Level in Colloidal Nanocrystal Thin Films during Their Fabrication
- Author
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Vanessa Wood, Maksym Yarema, Nuri Yazdani, Deniz Bozyigit, Sebastian Volk, and Olesya Yarema
- Subjects
Materials science ,Fabrication ,quantum dots ,02 engineering and technology ,Electronic structure ,010402 general chemistry ,01 natural sciences ,symbols.namesake ,nanocrystals ,General Materials Science ,Physical and Theoretical Chemistry ,Thin film ,business.industry ,Fermi level ,in-situ measurement ,Semiconductor device ,021001 nanoscience & nanotechnology ,electronic structure ,0104 chemical sciences ,Dipole ,Nanocrystal ,Quantum dot ,symbols ,Optoelectronics ,0210 nano-technology ,business - Abstract
The Journal of Physical Chemistry Letters, 9 (24), ISSN:1948-7185
- Published
- 2018
- Full Text
- View/download PDF
37. Efficient Machine Learning Algorithms to Analyze Time-Resolved Luminescence Data
- Author
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Juerg Leuthold, Eric Vauthey, Arnulf Rosspeintner, Olesya Yarema, Nikola Đorđević, Maksym Yarema, Joseph Beckwith, Nuri Yazdani, and Vanessa Wood
- Subjects
Photoluminescence ,Materials science ,Distribution (number theory) ,business.industry ,Machine learning ,computer.software_genre ,Fluorescence spectroscopy ,Condensed Matter::Materials Science ,Time resolved luminescence ,A priori and a posteriori ,Artificial intelligence ,business ,Luminescence ,computer ,Algorithm - Abstract
A machine learning algorithm is applied to analyze decay rate distribution in time-resolved photoemission data without a priori assumptions. We show that our approach is efficient in identifying physical processes in colloidal nanocrystals.
- Published
- 2018
38. Modeling and optimization of atomic layer deposition processes on vertically aligned carbon nanotubes
- Author
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Hyung Gyu Park, Eve Edwards, Vipin Chawla, Vanessa Wood, Ivo Utke, and Nuri Yazdani
- Subjects
conformal coating guidelines ,Titania ,Materials science ,Nanowire ,General Physics and Astronomy ,Nanotechnology ,Carbon nanotube ,engineering.material ,lcsh:Chemical technology ,lcsh:Technology ,Full Research Paper ,law.invention ,Atomic layer deposition ,Coating ,law ,Energy transformation ,TiO2 ,vertically aligned carbon nanotubes ,General Materials Science ,lcsh:TP1-1185 ,Ceramic ,Electrical and Electronic Engineering ,Porosity ,lcsh:Science ,continuum diffusion model ,lcsh:T ,titania, TiO2 ,lcsh:QC1-999 ,Nanopore ,Nanoscience ,visual_art ,Vertically aligned carbon nanotubes ,Continuum diffusion model ,Conformal coating guidelines ,atomic layer deposition ,engineering ,visual_art.visual_art_medium ,lcsh:Q ,lcsh:Physics - Abstract
Many energy conversion and storage devices exploit structured ceramics with large interfacial surface areas. Vertically aligned carbon nanotube (VACNT) arrays have emerged as possible scaffolds to support large surface area ceramic layers. However, obtaining conformal and uniform coatings of ceramics on structures with high aspect ratio morphologies is non-trivial, even with atomic layer deposition (ALD). Here we implement a diffusion model to investigate the effect of the ALD parameters on coating kinetics and use it to develop a guideline for achieving conformal and uniform thickness coatings throughout the depth of ultra-high aspect ratio structures. We validate the model predictions with experimental data from ALD coatings of VACNT arrays. However, the approach can be applied to predict film conformality as a function of depth for any porous topology, including nanopores and nanowire arrays., Beilstein Journal of Nanotechnology, 5, ISSN:2190-4286
- Published
- 2014
- Full Text
- View/download PDF
39. Bulk and Nanocrystalline Cesium Lead-Halide Perovskites as Seen by Halide Magnetic Resonance.
- Author
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Piveteau, Laura, Aebli, Marcel, Nuri Yazdani, Millen, Marthe, Korosec, Lukas, Krieg, Franziska, Benin, Bogdan M., Viktoriia Morad, Piveteau, Christophe, Shiroka, Toni, Comas-Vives, Aleix, Copéret, Christophe, Lindenberg, Aaron M., Wood, Vanessa, Verel, René, and Kovalenko, Maksym V.
- Published
- 2020
- Full Text
- View/download PDF
40. Facile diameter control of vertically aligned, narrow single-walled carbon nanotubes
- Author
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Hyung Gyu Park, Seul Ki Youn, Jörg Patscheider, and Nuri Yazdani
- Subjects
Ostwald ripening ,Materials science ,Hydrogen ,Economies of agglomeration ,General Chemical Engineering ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,Partial pressure ,Carbon nanotube ,Catalysis ,law.invention ,chemistry.chemical_compound ,symbols.namesake ,Acetylene ,chemistry ,Chemical engineering ,law ,symbols ,Nanometre - Abstract
Here, we report a diameter-controlled synthesis of vertically aligned (VA) single-walled carbon nanotubes (SWNTs) via catalytic chemical vapor deposition (CVD), enabled by ultrathin iron (Fe) catalysts on alumina (Al2O3) and low acetylene (C2H2) partial pressure. A long forest of sub-3-nm SWNTs up to one millimeter in height could be obtained without addition of hydrogen or moisture, and precise control of the SWNT diameters was successfully established. Key for the efficient growth of such arrays of narrow SWNTs is threefold: (a) growth temperature low enough to suppress catalyst agglomeration and Ostwald ripening, (b) C2H2 partial pressure below a certain level to extend the catalyst lifetime, and (c) size-matching at nanometer scale between Fe catalyst seeds and Al2O3 support asperities in order to mitigate the surface migration and undesirable enlargement of catalyst particles. Our findings can contribute to the facile achievement of uniform, dense arrays of high quality VA-SWNTs with narrow diameter distributions desirable for advanced nanofiltration and electronic applications.
- Published
- 2013
41. Hole Mobility in Nanocrystal Solids as a Function of Constituent Nanocrystal Size
- Author
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Deniz Bozyigit, Vanessa Wood, Olesya Yarema, Maksym Yarema, and Nuri Yazdani
- Subjects
Electron mobility ,Chemistry ,Band gap ,business.industry ,Monte Carlo method ,Nanotechnology ,Context (language use) ,Radius ,Semiconductor ,Nanocrystal ,Chemical physics ,Quantum dot ,General Materials Science ,Physical and Theoretical Chemistry ,business - Abstract
Solids of semiconductor nanocrystals (NCs) are semiconductors in which the band gap can be controlled by changing the size of the constituent NCs. To date, nontrivial dependencies of the carrier mobility on the NC size have been reported. We use the time-of-flight (TOF) technique to measure the carrier mobility as a function of the NC size and find that the hole mobility of the NC solid increases dramatically with decreasing NC radius. We show that this result is in agreement with an analytic model for carrier mobility in NC solids. We further implement Monte Carlo simulations to aid in understanding the transient measurements in the context of models of dispersive transport. This work highlights that changing NC size in a device has important implications for charge transport.
- Published
- 2015
42. A quantitative model for charge carrier transport, trapping and recombination in nanocrystal-based solar cells
- Author
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Deniz Bozyigit, Olesya Yarema, Nuri Yazdani, Vanessa Wood, and Weyde M. M. Lin
- Subjects
Multidisciplinary ,Materials science ,Physics::Optics ,General Physics and Astronomy ,Charge (physics) ,02 engineering and technology ,General Chemistry ,Trapping ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Bioinformatics ,7. Clean energy ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Quantitative model ,0104 chemical sciences ,Condensed Matter::Materials Science ,Nanocrystal ,Chemical physics ,Charge carrier ,0210 nano-technology ,Recombination - Abstract
Improving devices incorporating solution-processed nanocrystal-based semiconductors requires a better understanding of charge transport in these complex, inorganic–organic materials. Here we perform a systematic study on PbS nanocrystal-based diodes using temperature-dependent current–voltage characterization and thermal admittance spectroscopy to develop a model for charge transport that is applicable to different nanocrystal-solids and device architectures. Our analysis confirms that charge transport occurs in states that derive from the quantum-confined electronic levels of the individual nanocrystals and is governed by diffusion-controlled trap-assisted recombination. The current is limited not by the Schottky effect, but by Fermi-level pinning because of trap states that is independent of the electrode–nanocrystal interface. Our model successfully explains the non-trivial trends in charge transport as a function of nanocrystal size and the origins of the trade-offs facing the optimization of nanocrystal-based solar cells. We use the insights from our charge transport model to formulate design guidelines for engineering higher-performance nanocrystal-based devices., Colloidal nanocrystals could help improve the performance of the next generation of solar cells, but a model that fully describes the electronic behaviour of such devices is missing. Bozyigit et al. now develop a quantitative model for charge transport in these solar cells.
- Published
- 2015
43. SWIMRT: A graphical user interface using the sliding window algorithm to construct a fluence map machine file
- Author
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Nuri Yazdani, Grigor N. Grigorov, and James C.L. Chow
- Subjects
Computer science ,sliding window algorithm ,Radiation Dosage ,User-Computer Interface ,Sliding window protocol ,Dosimetry ,Radiation Oncology Physics ,Humans ,Radiology, Nuclear Medicine and imaging ,IMRT ,MATLAB ,Instrumentation ,Graphical user interface ,computer.programming_language ,Radiation ,Computer program ,business.industry ,Radiotherapy Planning, Computer-Assisted ,fluence map ,File format ,Multileaf collimator ,computer programming ,Calibration ,Trimming ,Female ,Radiotherapy, Intensity-Modulated ,Particle Accelerators ,business ,computer ,Algorithm ,Algorithms ,MLC - Abstract
A custom‐made computer program, SWIMRT, to construct “multileaf collimator (MLC) machine” file for intensity‐modulated radiotherapy (IMRT) fluence maps was developed using MATLAB® and the sliding window algorithm. The user can either import a fluence map with a graphical file format created by an external treatment‐planning system such as Pinnacle3 or create his or her own fluence map using the matrix editor in the program. Through comprehensive calibrations of the dose and the dimension of the imported fluence field, the user can use associated image‐processing tools such as field resizing and edge trimming to modify the imported map. When the processed fluence map is suitable, a “MLC machine” file is generated for our Varian 21 EX linear accelerator with a 120‐leaf Millennium MLC. This machine file is transferred to the MLC console of the LINAC to control the continuous motions of the leaves during beam irradiation. An IMRT field is then irradiated with the 2D intensity profiles, and the irradiated profiles are compared to the imported or modified fluence map. This program was verified and tested using film dosimetry to address the following uncertainties: (1) the mechanical limitation due to the leaf width and maximum traveling speed, and (2) the dosimetric limitation due to the leaf leakage/transmission and penumbra effect. Because the fluence map can be edited, resized, and processed according to the requirement of a study, SWIMRT is essential in studying and investigating the IMRT technique using the sliding window algorithm. Using this program, future work on the algorithm may include redistributing the time space between segmental fields to enhance the fluence resolution, and readjusting the timing of each leaf during delivery to avoid small fields. Possible clinical utilities and examples for SWIMRT are given in this paper. PACS numbers: 87.53.Kn, 87.53.St, 87.53.Uv
- Published
- 2006
44. Enhanced charge transport kinetics in anisotropic, stratified photoanodes
- Author
-
Ivo Utke, Jakob Buchheim, Jörg Patscheider, Deniz Bozyigit, Hyung Gyu Park, Nuri Yazdani, Vanessa Wood, and Seul Ki Youn
- Subjects
Materials science ,Diffusion ,Kinetics ,Charge (physics) ,Carbon nanotube ,Photochemistry ,7. Clean energy ,law.invention ,Dye-sensitized solar cell ,Chemical engineering ,law ,General Materials Science ,Anisotropy ,Mesoporous material ,Order of magnitude - Abstract
The kinetics of charge transport in mesoporous photoanodes strongly constrains the design and power conversion efficiencies of dye sensitized solar cells (DSSCs). Here, we report a stratified photoanode design with enhanced kinetics achieved through the incorporation of a fast charge transport intermediary between the titania and charge collector. Proof of concept photoanodes demonstrate that the inclusion of the intermediary not only enhances effective diffusion coefficients but also significantly suppresses charge recombination, leading to diffusion lengths two orders of magnitude greater than in standard mesoporous titania photoanodes. The intermediary concept holds promise for higher-efficiency DSSCs.
- Published
- 2014
45. Towards designing robust coupled networks
- Author
-
Shlomo Havlin, Christian Schneider, Nuno A. M. Araújo, Hans J. Herrmann, Nuri Yazdani, Massachusetts Institute of Technology. Department of Civil and Environmental Engineering, and Schneider, Christian Michael
- Subjects
Mathematical optimization ,Computer science ,media_common.quotation_subject ,Blackout ,Framework ,Complex networks ,FOS: Physical sciences ,01 natural sciences ,Article ,010305 fluids & plasmas ,Betweenness centrality ,Statistics ,Computational science ,Applied physics ,Robustness (computer science) ,0103 physical sciences ,medicine ,FOS: Mathematics ,010306 general physics ,Scaling ,Condensed Matter - Statistical Mechanics ,media_common ,Multidisciplinary ,Statistical Mechanics (cond-mat.stat-mech) ,Telecommunication systems ,Probability and statistics ,Disordered Systems and Neural Networks (cond-mat.dis-nn) ,Condensed Matter - Disordered Systems and Neural Networks ,Computational Physics (physics.comp-ph) ,Cascading failure ,Interdependence ,Physics - Data Analysis, Statistics and Probability ,Disconnection ,medicine.symptom ,Networks ,Physics - Computational Physics ,Data Analysis, Statistics and Probability (physics.data-an) - Abstract
Natural and technological interdependent systems have been shown to be highly vulnerable due to cascading failures and an abrupt collapse of global connectivity under initial failure. Mitigating the risk by partial disconnection endangers their functionality. Here we propose a systematic strategy of selecting a minimum number of autonomous nodes that guarantee a smooth transition in robustness. Our method which is based on betweenness is tested on various examples including the famous 2003 electrical blackout of Italy. We show that, with this strategy, the necessary number of autonomous nodes can be reduced by a factor of five compared to a random choice. We also find that the transition to abrupt collapse follows tricritical scaling characterized by a set of exponents which is independent on the protection strategy., Scientific Reports, 3, ISSN:2045-2322
- Published
- 2013
46. Metal-dielectric-CNT nanowires for femtomolar chemical detection by surface enhanced Raman spectroscopy
- Author
-
Hyung Gyu Park, Tiziana C. Bond, Ali Ozhan Altun, Seul Ki Youn, and Nuri Yazdani
- Subjects
Materials science ,Pyridines ,Surface Properties ,Nanowire ,Analytical chemistry ,Carbon nanotube ,Dielectric ,Spectrum Analysis, Raman ,law.invention ,Metal ,law ,General Materials Science ,Plasmon ,biology ,business.industry ,Nanotubes, Carbon ,Nanowires ,Mechanical Engineering ,Substrate (chemistry) ,Surface-enhanced Raman spectroscopy ,Ethylenes ,Hafnia ,biology.organism_classification ,Mechanics of Materials ,visual_art ,visual_art.visual_art_medium ,Optoelectronics ,Gold ,business - Abstract
A highly sensitive substrate for surface enhanced Raman spectroscopy (SERS) is formed by arrays of gold-coated metallic carbon nanotubes having a nanoinsert of high-k dielectric (hafnia) as an energy coupling barrier. Repeated femtomolar detection of 1,2 bis-(4-pyridyl)-ethylene in solution demonstrates the critical contribution of this plasmonic energy coupling barrier to the enhanced chemical sensitivity.
- Published
- 2013
47. Erratum: Enhanced ferromagnetism from electron-electron interactions in double-exchange-type models [Phys. Rev. B83, 134405 (2011)]
- Author
-
Nuri Yazdani and Malcolm P. Kennett
- Subjects
Physics ,Colossal magnetoresistance ,Ferromagnetism ,Condensed matter physics ,Monte Carlo method ,Electron ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Published
- 2012
48. Enhanced ferromagnetism from electron-electron interactions in double exchange type models
- Author
-
Nuri Yazdani and Malcolm P. Kennett
- Subjects
Physics ,Work (thermodynamics) ,Spins ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Quantum Monte Carlo ,Monte Carlo method ,FOS: Physical sciences ,02 engineering and technology ,Fermion ,Electron ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,3. Good health ,Electronic, Optical and Magnetic Materials ,Condensed Matter - Strongly Correlated Electrons ,Ferromagnetism ,0103 physical sciences ,Curie temperature ,010306 general physics ,0210 nano-technology - Abstract
The magnetic properties of a variety of materials with promise for technological applications have been described by models in which fermions are coupled to local moment spins. Monte Carlo studies of such models usually ignore electron-electron interactions, even though the energy scale corresponding to these interactions may be comparable to or larger than other relevant energy scales. In this work we add on-site interactions between fermions to the double exchange model which we study with a Monte Carlo scheme in which temporal fluctuations of local moment spins are fully accounted for and electron-electron interactions are treated at a mean field level. We show that when the number of fermions is considerably less than the number of local moments even moderate interactions can lead to significant enhancement of ferromagnetism and the Curie temperature., Comment: 4 + epsilon pages, 3 figures
- Published
- 2010
- Full Text
- View/download PDF
49. Nanowires: Metal-Dielectric-CNT Nanowires for Femtomolar Chemical Detection by Surface Enhanced Raman Spectroscopy (Adv. Mater. 32/2013)
- Author
-
Tiziana C. Bond, Nuri Yazdani, Seul Ki Youn, Hyung Gyu Park, and Ali Ozhan Altun
- Subjects
Metal ,Materials science ,Mechanics of Materials ,Mechanical Engineering ,visual_art ,visual_art.visual_art_medium ,Nanowire ,General Materials Science ,Nanotechnology ,Dielectric ,Surface-enhanced Raman spectroscopy - Published
- 2013
50. Sci-Thurs PM: Delivery-01: Sliding Window IMRT: Uncertainties of the leading edge and plateau of the beam profile
- Author
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Grigor N. Grigorov, Nuri Yazdani, R Barnett, and James C. L. Chow
- Subjects
Physics ,Leading edge ,Optics ,Photon ,business.industry ,Sliding window protocol ,Dose profile ,General Medicine ,Irradiation ,business ,Plateau (mathematics) ,Beam (structure) ,Linear particle accelerator - Abstract
The aim of this work is to analyze the dependence of the dose profile uncertainties for the sliding window IMRT (SW-IMRT) beams under the condition of an extreme dose rate (DR) and leaf velocity (LV). The deviations of the edges and plateau for the beam profiles of small number of MUs delivered using the dynamic MLC were studied. Field sizes with lengths of 5 and 10 cm were irradiated by photon beams of 2-8 MU/beam, DR = 100-600 MU/min and LS = 1-5 cm/s. Kodak TL radiographic films were used in the measurement. The photon beams (6 and 15 MV) were produced by a Varian 21EX Linac with a 120-leaf MLC. It is found that the MLC cannot keep the leaves moving with a proper speed continuously under a stable DR when beam of small MUs are irradiated. For example, the dynamic MLC needs 1.2 s and 12 MU to irradiate a field of 5 cm length with 2 MU using DR = 600 MU/min and LC = 5 cm/s. The plateau of the beam profile has several sinusoidal periods of about 150 ms. The magnitude of the plateau uncertainties was about 7% and 15% for the dose of the beam with DR = 400 and 600 MU/min (2 MU/beam), respectively. It is concluded that SW-IMRT beams of more than 10 MUs, delivered with 1 cm/s ⩽ LV ⩽ 5 cm/s and 100 MU/min ⩽ DR ⩽ 600 MU/min, have a good agreement between the delivered and planned dose profiles.
- Published
- 2008
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