50 results on '"Aycan Yurtsever"'
Search Results
2. Exploring the Remarkably High Photocatalytic Efficiency of Ultra-Thin Porous Graphitic Carbon Nitride Nanosheets
- Author
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Zahra Kalantari Bolaghi, Cristina Rodriguez-Seco, Aycan Yurtsever, and Dongling Ma
- Subjects
photodegradation ,hydrogen evolution reaction ,porous carbon nitride ,exfoliation ,Chemistry ,QD1-999 - Abstract
Graphitic carbon nitride (g-C3N4) is a metal-free photocatalyst used for visible-driven hydrogen production, CO2 reduction, and organic pollutant degradation. In addition to the most attractive feature of visible photoactivity, its other benefits include thermal and photochemical stability, cost-effectiveness, and simple and easy-scale-up synthesis. However, its performance is still limited due to its low absorption at longer wavelengths in the visible range, and high charge recombination. In addition, the exfoliated nanosheets easily aggregate, causing the reduction in specific surface area, and thus its photoactivity. Herein, we propose the use of ultra-thin porous g-C3N4 nanosheets to overcome these limitations and improve its photocatalytic performance. Through the optimization of a novel multi-step synthetic protocol, based on an initial thermal treatment, the use of nitric acid (HNO3), and an ultrasonication step, we were able to obtain very thin and well-tuned material that yielded exceptional photodegradation performance of methyl orange (MO) under visible light irradiation, without the need for any co-catalyst. About 96% of MO was degraded in as short as 30 min, achieving a normalized apparent reaction rate constant (k) of 1.1 × 10−2 min−1mg−1. This represents the highest k value ever reported using C3N4-based photocatalysts for MO degradation, based on our thorough literature search. Ultrasonication in acid not only prevents agglomeration of g-C3N4 nanosheets but also tunes pore size distribution and plays a key role in this achievement. We also studied their performance in a photocatalytic hydrogen evolution reaction (HER), achieving a production of 1842 µmol h−1 g−1. Through a profound analysis of all the samples’ structure, morphology, and optical properties, we provide physical insight into the improved performance of our optimized porous g-C3N4 sample for both photocatalytic reactions. This research may serve as a guide for improving the photocatalytic activity of porous two-dimensional (2D) semiconductors under visible light irradiation.
- Published
- 2024
- Full Text
- View/download PDF
3. Versatile metal-wire waveguides for broadband terahertz signal processing and multiplexing
- Author
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Junliang Dong, Alessandro Tomasino, Giacomo Balistreri, Pei You, Anton Vorobiov, Étienne Charette, Boris Le Drogoff, Mohamed Chaker, Aycan Yurtsever, Salvatore Stivala, Maria A. Vincenti, Costantino De Angelis, Detlef Kip, José Azaña, and Roberto Morandotti
- Subjects
Science - Abstract
Waveguides that can provide complex signal-processing functionalities while guiding terahertz signals are desired. Here, the authors report the independent processing of multiplexed signals by engineering the metal surface of a four-wire waveguide.
- Published
- 2022
- Full Text
- View/download PDF
4. Phase-enabled metal-organic framework homojunction for highly selective CO2 photoreduction
- Author
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Yannan Liu, Chuanshuang Chen, Jesus Valdez, Debora Motta Meira, Wanting He, Yong Wang, Catalin Harnagea, Qiongqiong Lu, Tugrul Guner, Hao Wang, Cheng-Hao Liu, Qingzhe Zhang, Shengyun Huang, Aycan Yurtsever, Mohamed Chaker, and Dongling Ma
- Subjects
Science - Abstract
Homojunctions are very promising in photocatalysis, but challenging to achieve. Herein, authors report a well-defined hierarchical metal–organic framework-based homojunction, formed via a one-pot synthesis route directed by hollow transition metal nanoparticles, as photocatalysts for CO2 reduction.
- Published
- 2021
- Full Text
- View/download PDF
5. Homodyne Solid-State Biased Coherent Detection of Ultra-Broadband Terahertz Pulses with Static Electric Fields
- Author
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Alessandro Tomasino, Riccardo Piccoli, Yoann Jestin, Boris Le Drogoff, Mohamed Chaker, Aycan Yurtsever, Alessandro Busacca, Luca Razzari, and Roberto Morandotti
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THz pulse detection ,solid-state device ,four-wave mixing ,Chemistry ,QD1-999 - Abstract
We present an innovative implementation of the solid-state-biased coherent detection (SSBCD) technique, which we have recently introduced for the reconstruction of both amplitude and phase of ultra-broadband terahertz pulses. In our previous works, the SSBCD method has been operated via a heterodyne scheme, which involves demanding square-wave voltage amplifiers, phase-locked to the THz pulse train, as well as an electronic circuit for the demodulation of the readout signal. Here, we demonstrate that the SSBCD technique can be operated via a very simple homodyne scheme, exploiting plain static bias voltages. We show that the homodyne SSBCD signal turns into a bipolar transient when the static field overcomes the THz field strength, without the requirement of an additional demodulating circuit. Moreover, we introduce a differential configuration, which extends the applicability of the homodyne scheme to higher THz field strengths, also leading a two-fold improvement of the dynamic range compared to the heterodyne counterpart. Finally, we demonstrate that, by reversing the sign of the static voltage, it is possible to directly retrieve the absolute THz pulse polarity. The homodyne configuration makes the SSBCD technique of much easier access, leading to a vast range of field-resolved applications.
- Published
- 2021
- Full Text
- View/download PDF
6. Enhancing Efficiency of Nonfullerene Organic Solar Cells via Using Polyelectrolyte-Coated Plasmonic Gold Nanorods as Rear Interfacial Modifiers
- Author
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Zhonglin Du, Ting Yu, Wanting He, Aycan Yurtsever, Ricardo Izquierdo, Maziar Jafari, Mohamed Siaj, and Dongling Ma
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General Materials Science - Abstract
Sufficient sunlight absorption and exciton generation are critical for developing efficient nonfullerene organic solar cells (OSCs). In this work, polyelectrolyte polystyrenesulfonate (PSS)-coated plasmonic gold nanorods (GNRs@PSS) were incorporated, for the first time, into the inverted nonfullerene OSCs as rear interfacial modifiers to improve sunlight absorption and charge generation via the near-field plasmonic and backscattering effects. The plasmonic GNRs effectively improved the sunlight absorption and enhanced the charge generation. Meanwhile, the negatively charged PSS shell ensured the uniform dispersion of the GNRs on the surface of the photoactive layer, optimized the interfacial contact, and further promoted the hole transport to the electrode. These concerted synergistic effects augmented the efficiency (10.11%) by nearly 20% relative to the control device (8.47%). Remarkably, the ultrathin (∼2.2 nm) organic layer on the surface of GNRs was closely examined by acquiring the carbon contrast image through energy-filtered transmission electron microscopy (EF-TEM), which clearly confirmed the coating uniformity from the side to end-cap of GNRs. The surface plasmon resonance (SPR) effect of the GNRs@PSS on the surface of the photoactive layer was unprecedentedly mapped by photoinduced force microscopy (PiFM) under the illumination of a tunable wavelength supercontinuum laser mimicking sunlight. Furthermore, investigations into the effect of size, surface coverage, and incorporation location of GNRs@PSS on the performance of OSCs revealed that the appropriate design and incorporation of the plasmonic nanostructures are crucial, otherwise the performance can be decreased, as evidenced in the case of front interface integration.
- Published
- 2022
7. Role of Interfacial Engineering of 'Giant' Core–Shell Quantum Dots
- Author
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Gurpreet Singh Selopal, Omar Abdelkarim, Pawan Kumar, Lei Jin, Jiabin Liu, Haiguang Zhao, Aycan Yurtsever, Francois Vidal, Zhiming M. Wang, and Federico Rosei
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Materials Chemistry ,Electrochemistry ,Energy Engineering and Power Technology ,Chemical Engineering (miscellaneous) ,Electrical and Electronic Engineering - Published
- 2022
8. Imaging Photon-Induced Near-Field Distributions of a Plasmonic, Self-Assembled Vesicle by a Laser-Integrated Electron Microscope
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Wanting He, Chuanshuang Chen, Yannan Liu, Alessandro Tomasino, S. Shayan Mousavi Masouleh, Jesus Valdez, Tugrul Guner, Roberto Morandotti, Audrey Moores, Gianluigi A. Botton, Yongfeng Zhou, Aycan Yurtsever, and Dongling Ma
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Mechanical Engineering ,General Materials Science ,Bioengineering ,General Chemistry ,Condensed Matter Physics - Abstract
Plasmonic polymeric nanoassemblies offer valuable opportunities in photoconversion applications. Localized surface plasmon mechanisms behind such nanoassemblies govern their functionalities under light illumination. However, an in-depth investigation at the single nanoparticle (NP) level is still challenging, especially when the buried interface is involved, due to the availability of suitable techniques. Here, we synthesized an anisotropic heterodimer composed of a self-assembled polymer vesicle (THPG) capped with a single gold NP, enabling an 8-fold enhancement in hydrogen generation compared to the nonplasmonic THPG vesicle. We explored the anisotropic heterodimer at the single particle level by employing advanced transmission electron microscopes, including one equipped with a femtosecond pulsed laser, which allows us to visualize the polarization- and frequency-dependent distribution of the enhanced electric near fields at the vicinity of Au cap and Au–polymer interface. These elaborated fundamental findings may guide designing new hybrid nanostructures tailored for plasmon-related applications.
- Published
- 2022
9. Two-dimensional functionalized hexagonal boron nitride for quantum dot photoelectrochemical hydrogen generation
- Author
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Ghada Bassioni, Gurpreet Singh Selopal, Zhiming Wang, Hadis Zarrin, Omar Abdelkarim, Fabiola Navarro-Pardo, Jasneet Kaur, Jiabin Liu, Federico Rosei, and Aycan Yurtsever
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Materials science ,Hydrogen ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,Carbon nanotube ,Electrolyte ,010402 general chemistry ,01 natural sciences ,7. Clean energy ,law.invention ,chemistry.chemical_compound ,law ,General Materials Science ,Photocurrent ,Renewable Energy, Sustainability and the Environment ,business.industry ,Heterojunction ,General Chemistry ,Photoelectrochemical cell ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Quantum dot ,Optoelectronics ,0210 nano-technology ,business - Abstract
We report the design and fabrication of a heterojunction photoanode consisting of two-dimensional (2D) functionalized hexagonal boron nitride (F-h-BN) nanoflakes, introduced at the interface between SnO2 and quantum dots (QDs) (e.g. CdS and CdS–CdSe), used as a photoanode in a photoelectrochemical cell (PEC) for hydrogen (H2) generation. We highlight the effect of 2D F-h-BN nanoflakes on the carrier recombination and performance of the PEC system. In addition, the tailoring of SnO2 film thickness and incorporation of multi-walled carbon nanotubes (MWCNTs) were investigated for their effect on carrier dynamics and overall device performance. Our results show that a PEC device based on SnO2/F-h-BN/CdS QDs exhibits a 60% improvement in the saturated photocurrent density (at 1.0 V vs. RHE) compared to the control device, due to improved electron injection and reduced carrier recombination at the metal oxide/QDs/electrolyte interface. The highest saturated photocurrent density value reached 6.35 mA cm−2 (at 1.0 V vs. RHE), after thickness optimization of the SnO2 film, incorporation (0.015 wt%) of MWCNTs, and cascade CdS–CdSe QDs. In addition, the PEC system maintains 98% of the initial value of photocurrent density after four hours of continuous one sun illumination (AM 1.5G, 100 mW cm−2). Our results offer a simple yet cost-effective and efficient strategy to enhance the performance of QD based PEC H2 generation and potentially other optoelectronic devices.
- Published
- 2020
10. Broadband Terahertz Signal Processing and Multiplexing with Four-wire Waveguides
- Author
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Junliang Dong, Alessandro Tomasino, Giacomo Balistreri, Pei You, Anton Vorobiov, Aycan Yurtsever, Salvatore Stivala, Maria A. Vincenti, Costantino De Angelis, Detlef Kip, José Azaña, and Roberto Morandotti
- Abstract
We demonstrate a new waveguide geometry, namely a four-wire waveguide, which acts as a terahertz polarization-division multiplexer and a novel platform to realize versatile signal-processing functionalities into independent channels over a broadband terahertz frequency range.
- Published
- 2022
11. Constructing quantum dots sensitized TiO2 nanotube p-n heterojunction for photoelectrochemical hydrogen generation
- Author
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Omar Abdelkarim, Amir Mirzaei, Gurpreet S. Selopal, Aycan Yurtsever, Ghada Bassioni, Zhiming M. Wang, Mohamed Chaker, and Federico Rosei
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General Chemical Engineering ,Environmental Chemistry ,General Chemistry ,Industrial and Manufacturing Engineering - Published
- 2022
12. Versatile metal-wire waveguides for broadband terahertz signal processing and multiplexing
- Author
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Junliang Dong, Alessandro Tomasino, Giacomo Balistreri, Pei You, Anton Vorobiov, Étienne Charette, Boris Le Drogoff, Mohamed Chaker, Aycan Yurtsever, Salvatore Stivala, Maria A. Vincenti, Costantino De Angelis, Detlef Kip, José Azaña, Roberto Morandotti, Dong J., Tomasino A., Balistreri G., You P., Vorobiov A., Charette E., Le Drogoff B., Chaker M., Yurtsever A., Stivala S., Vincenti M.A., De Angelis C., Kip D., Azana J., and Morandotti R.
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Multidisciplinary ,Science ,Physics::Optics ,General Physics and Astronomy ,General Chemistry ,Terahertz signal processing, Terahertz multiplexing, Waveguides ,Settore ING-INF/01 - Elettronica ,General Biochemistry, Genetics and Molecular Biology - Abstract
Waveguides play a pivotal role in the full deployment of terahertz communication systems. Besides signal transporting, innovative terahertz waveguides are required to provide versatile signal-processing functionalities. Despite fundamental components, such as Bragg gratings, have been recently realized, they typically rely on complex hybridization, in turn making it extremely challenging to go beyond the most elementary functions. Here, we propose a universal approach, in which multiscale-structured Bragg gratings can be directly etched on metal-wires. Such an approach, in combination with diverse waveguide designs, allows for the realization of a unique platform with remarkable structural simplicity, yet featuring unprecedented signal-processing capabilities. As an example, we introduce a four-wire waveguide geometry, amenable to support the low-loss and low-dispersion propagation of polarization-division multiplexed terahertz signals. Furthermore, by engraving on the wires judiciously designed Bragg gratings based on multiscale structures, it is possible to independently manipulate two polarization-division multiplexed terahertz signals. This platform opens up new exciting perspectives for exploiting the polarization degree of freedom and ultimately boosting the capacity and spectral efficiency of future terahertz networks.
- Published
- 2021
13. Single-shot real-time sub-nanosecond electron imaging aided by compressed sensing: Analytical modeling and simulation
- Author
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Aycan Yurtsever, Jinyang Liang, Xianglei Liu, and Shian Zhang
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010302 applied physics ,Physics ,Ground truth ,business.industry ,General Physics and Astronomy ,02 engineering and technology ,Cell Biology ,Nanosecond ,021001 nanoscience & nanotechnology ,01 natural sciences ,Streaking ,Data cube ,Modeling and simulation ,Compressed sensing ,Optics ,Structural Biology ,Temporal resolution ,0103 physical sciences ,General Materials Science ,0210 nano-technology ,business ,Ultrashort pulse - Abstract
Bringing ultrafast (nanosecond and below) temporal resolution to transmission electron microscopy (TEM) has historically been challenging. Despite significant recent progress in this direction, it remains difficult to achieve sub-nanosecond temporal resolution with a single electron pulse, in real-time (i.e., duration in which the event occurs) imaging. To address this limitation, here, we propose a methodology that combines laser-assisted TEM with computational imaging methodologies based on compressed sensing (CS). In this technique, a two-dimensional (2D) transient event [i.e. (x,y) frames that vary in time] is recorded through a CS paradigm, which consists of spatial encoding, temporal shearing via streaking, and spatiotemporal integration of an electron pulse. The 2D image generated on a camera is used to reconstruct the datacube of the ultrafast event, with two spatial and one temporal dimensions, via a CS-based image reconstruction algorithm. Using numerical simulation, we find that the reconstructed results are in good agreement with the ground truth, which demonstrates the applicability of CS-based computational imaging methodologies to laser-assisted TEM. Our proposed method, complementing the existing ultrafast stroboscopic and nanosecond single-shot techniques, opens up the possibility for single-shot, real-time, spatiotemporal imaging of irreversible structural phenomena with sub-nanosecond temporal resolution.
- Published
- 2019
14. Optical resonances of hollow nanocubes controlled with sub-particle structural morphologies
- Author
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Aycan Yurtsever, Zackaria Mahfoud, Jesus Valdez, Lucas V. Besteiro, and Tugrul Guner
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Materials science ,business.industry ,Physics::Optics ,Nanoparticle ,02 engineering and technology ,Pinhole ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Spectral line ,Symmetry (physics) ,0104 chemical sciences ,law.invention ,Breakage ,law ,Galvanic cell ,Optoelectronics ,Particle ,General Materials Science ,Electron microscope ,0210 nano-technology ,business - Abstract
The structural details of nanoparticles at the sub-particle level are critical for our understanding of their functionalities and the basic mechanisms involved in their formation. In particular, the geometries of such features determine the particle's overall optical response. Hollow metallic nanoparticles (hollow-MNPs) that have cubic geometries, with varying morphologies on their walls and voids in their body, offer a platform to study the effects of such structural features on the properties of single nanoparticles and their ensemble. Here, we report the control over sub-particle pinholes and voids by modifying the dynamics of the galvanic reaction, and we connect these structures to the optical response of the hollow nanocubes. We observe that symmetry breakage in individual particles, caused by pinholes and voids, has a drastic effect on the plasmon-resonance peak positions in their UV-Vis-NIR spectra. Via electron microscopy imaging, statistical analyses, and electromagnetic simulations, we observe that enlargement in a pinhole's diameter and an increase in their number produce a redshift in the resonance absorption peak of the ensemble. Our results outline nanoparticle design avenues via sub-particle morphologies for several applications, including those operating in the biological window and those carrying chemical payloads in organisms.
- Published
- 2019
15. Phase-enabled metal-organic framework homojunction for highly selective CO2 photoreduction
- Author
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Hao Wang, Yong Wang, Wanting He, Tugrul Guner, Mohamed Chaker, Qiongqiong Lu, Huang Shengyun, Dongling Ma, Catalin Harnagea, Yannan Liu, Jesus Valdez, Aycan Yurtsever, Cheng-Hao Liu, Qingzhe Zhang, Chuanshuang Chen, and Debora Motta Meira
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Materials science ,Surface photovoltage ,Science ,General Physics and Astronomy ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Article ,Crystal ,Phase (matter) ,Homojunction ,Photocatalysis ,Electrochemical reduction of carbon dioxide ,Composites ,Multidisciplinary ,Nanoscale materials ,General Chemistry ,Metal-organic frameworks ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Charge carrier ,Metal-organic framework ,0210 nano-technology - Abstract
Conversion of clean solar energy to chemical fuels is one of the promising and up-and-coming applications of metal–organic frameworks. However, fast recombination of photogenerated charge carriers in these frameworks remains the most significant limitation for their photocatalytic application. Although the construction of homojunctions is a promising solution, it remains very challenging to synthesize them. Herein, we report a well-defined hierarchical homojunction based on metal–organic frameworks via a facile one-pot synthesis route directed by hollow transition metal nanoparticles. The homojunction is enabled by two concentric stacked nanoplates with slightly different crystal phases. The enhanced charge separation in the homojunction was visualized by in-situ surface photovoltage microscopy. Moreover, the as-prepared nanostacks displayed a visible-light-driven carbon dioxide reduction with very high carbon monooxide selectivity, and excellent stability. Our work provides a powerful platform to synthesize capable metal–organic framework complexes and sheds light on the hierarchical structure-function relationships of metal–organic frameworks., Homojunctions are very promising in photocatalysis, but challenging to achieve. Herein, authors report a well-defined hierarchical metal–organic framework-based homojunction, formed via a one-pot synthesis route directed by hollow transition metal nanoparticles, as photocatalysts for CO2 reduction.
- Published
- 2021
16. Time-Domain Integration of Terahertz pulses
- Author
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Aycan Yurtsever, Roberto Morandotti, Alessandro Tomasino, Junliang Dong, Salvatore Stivala, Giacomo Balistreri, José Azaña, Tomasino A., Balistreri G., Dong J., Yurtsever A., Stivala S., Azana J., and Morandotti R.
- Subjects
Physics ,Waveguide (electromagnetism) ,business.industry ,Terahertz radiation ,Physics::Optics ,Electromagnetic radiation ,Settore ING-INF/01 - Elettronica ,Terahertz spectroscopy and technology ,Terahertz, Time-Domain Integration ,symbols.namesake ,Optical rectification ,Fourier transform ,symbols ,Optoelectronics ,Heterodyne detection ,Time domain ,business - Abstract
We report on the time-domain integration of terahertz pulses obtained via the tight confinement of the radiation in a tapered two-wire waveguide. Both simulation and experimental results prove the time integration capability of this structure.
- Published
- 2021
17. Tapered Two-Wire Waveguide for Time-Domain Integration of Broadband Terahertz Pulses
- Author
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Salvatore Stivala, Junliang Dong, José Azaña, Aycan Yurtsever, Alessandro Tomasino, Giacomo Balistreri, Roberto Morandotti, Tomasino A., Balistreri G., Dong J., Yurtsever A., Stivala S., Azana J., and Morandotti R.
- Subjects
Physics ,business.industry ,Terahertz radiation ,Physics::Optics ,Topology (electrical circuits) ,Terahertz spectroscopy and technology ,symbols.namesake ,Fourier transform ,Broadband ,symbols ,Optoelectronics ,Waveguide (acoustics) ,Time domain ,Heterodyne detection ,Terahertz, Time-domain integration, Waveguides ,business ,Nonlinear Sciences::Pattern Formation and Solitons - Abstract
We show the time-domain integration of terahertz pulses achieved in a sub-wavelength, tapered two-wire waveguide. Both simulation and experimental results prove the time integration functionality of this waveguide topology.
- Published
- 2021
18. Homodyne Solid-State Biased Coherent Detection of Ultra-Broadband Terahertz Pulses with Static Electric Fields
- Author
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Boris Le Drogoff, Riccardo Piccoli, Alessandro Tomasino, Alessandro Busacca, Yoann Jestin, Aycan Yurtsever, Roberto Morandotti, Mohamed Chaker, Luca Razzari, Tomasino A., Piccoli R., Jestin Y., Drogoff B.L., Chaker M., Yurtsever A., Busacca A., Razzari L., and Morandotti R.
- Subjects
Heterodyne ,Four-wave mixing, Solid-state device, THz pulse detection ,Terahertz radiation ,THz pulse detection ,General Chemical Engineering ,02 engineering and technology ,01 natural sciences ,Signal ,Settore ING-INF/01 - Elettronica ,Article ,lcsh:Chemistry ,010309 optics ,Optics ,0103 physical sciences ,Demodulation ,General Materials Science ,solid-state device ,Electronic circuit ,Physics ,business.industry ,Amplifier ,Settore ING-INF/02 - Campi Elettromagnetici ,021001 nanoscience & nanotechnology ,Direct-conversion receiver ,lcsh:QD1-999 ,four-wave mixing ,0210 nano-technology ,business ,Voltage - Abstract
We present an innovative implementation of the solid-state-biased coherent detection (SSBCD) technique, which we have recently introduced for the reconstruction of both amplitude and phase of ultra-broadband terahertz pulses. In our previous works, the SSBCD method has been operated via a heterodyne scheme, which involves demanding square-wave voltage amplifiers, phase-locked to the THz pulse train, as well as an electronic circuit for the demodulation of the readout signal. Here, we demonstrate that the SSBCD technique can be operated via a very simple homodyne scheme, exploiting plain static bias voltages. We show that the homodyne SSBCD signal turns into a bipolar transient when the static field overcomes the THz field strength, without the requirement of an additional demodulating circuit. Moreover, we introduce a differential configuration, which extends the applicability of the homodyne scheme to higher THz field strengths, also leading a two-fold improvement of the dynamic range compared to the heterodyne counterpart. Finally, we demonstrate that, by reversing the sign of the static voltage, it is possible to directly retrieve the absolute THz pulse polarity. The homodyne configuration makes the SSBCD technique of much easier access, leading to a vast range of field-resolved applications.
- Published
- 2020
19. Homodyne Coherent Detection of THz Pulses via DC-biased Solid-State Devices
- Author
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Roberto Morandotti, Yoann Jestin, Mohamed Chaker, B. Le Drogoff, Luca Razzari, Alessandro Busacca, Alessandro Tomasino, Riccardo Piccoli, and Aycan Yurtsever
- Subjects
Direct-conversion receiver ,Materials science ,business.industry ,Terahertz radiation ,Solid-state ,Optoelectronics ,business - Abstract
We present the solid-state-biased coherent detection technique for ultra-broadband THz pulses operated via a homodyne configuration. This makes our detection method of easy implementation, suitable for cost-effective and portable THz systems.
- Published
- 2020
20. Role of surface engineering of hybrid structure for high performance quantum dots based photoelectrochemical hydrogen generation
- Author
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Federico Rosei, Ghada Bassioni, Pawan Kumar, Zhiming Wang, Karthik Suresh, Omar Abdelkarim, Aycan Yurtsever, Kulbir Kaur Ghuman, Fabiola Navarro-Pardo, and Gurpreet Singh Selopal
- Subjects
Photocurrent ,Materials science ,business.industry ,General Chemical Engineering ,Nanoparticle ,02 engineering and technology ,General Chemistry ,Surface engineering ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Industrial and Manufacturing Engineering ,0104 chemical sciences ,Quantum dot ,Environmental Chemistry ,Optoelectronics ,Water splitting ,Nanorod ,Density functional theory ,0210 nano-technology ,business ,Hydrogen production - Abstract
We report the synthesis of a TiO2 hybrid structure, consisting of a combination of nanorods and nanoparticles, subsequently treated with hydrazine to enhance the performance of photoelectrochemical (PEC) hydrogen (H2) generation. The optimized TiO2 hybrid photoanode sensitized with Quantum dots (QDs), yields a saturated photocurrent density of 4.25 mA cm−2 (at 0.8 V vs RHE), which is 172% higher than that of the reference sample. The optimized hybrid photoanode treated with hydrazine exhibits an additional 28% increase in the saturated photocurrent density, reaching 5.43 mA cm−2 with CdS QDs, and 8.12 mA cm−2 with CdS/CdSe QDs (at 0.8 V vs RHE), while maintaining 80% of the initial value of photocurrent density, after 2 h of continuous one sun illumination (AM 1.5 G, 100 mW cm−2). We used Density Functional Theory with Hubbard energy correction (DFT + U) calculations to describe the mechanism that underpins this significant improvement. DFT + U results highlighted that the concentration of the hydrazine treatment plays a crucial role and affects the sites (surface or interstitial) where nitrogen may be present. This eventually affects the recombination centers within the hybrid photoanode. Thus, the results of this work define a promising strategy to optimize the morphology of the hybrid photoanodes via hydrazine surface engineering to fabricate efficient and stable PEC water splitting devices for H2 generation.
- Published
- 2022
21. Steady-state voltammetric characterization and simulation-aided study of the mass transfer enhancement at conical W/WO2 ultramicroelectrodes
- Author
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Uriel Bruno-Mota, Patrick Soucy, Fabiola Navarro-Pardo, Ingrid Nayeli Rodriguez-Hernández, Aycan Yurtsever, Ana C. Tavares, Germán Orozco, and Rasool Doostkam
- Subjects
Scanning electron microscope ,General Chemical Engineering ,Analytical chemistry ,02 engineering and technology ,Conical surface ,Electrolyte ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Focused ion beam ,0104 chemical sciences ,Radius of curvature (optics) ,Mass transfer ,Electrode ,Electrochemistry ,Cyclic voltammetry ,0210 nano-technology - Abstract
Ultramicroelectrodes (UMEs) have demonstrated their utility in different applications, ranging from probing chemistry to high-resolution electrochemical imaging. Conical UMEs with the apex in the nanometer range are of special interest because their geometrical features may allow the study of single/few nanoparticles, single entities, or electrochemical reactions occurring in the inner structures of living cells which are difficult to access with other types of UMEs. However, there is a lack of experimental studies with individual unshielded conical electrodes aiming at quantifying the impact of the geometry and dimensions on their electrochemical response. In this work, W / WO2 conical UMEs with aspect ratios ranging from 6.6 to 22 and apexes with nm-size dimensions were prepared by electrochemical etching of tungsten wires through an induced dynamic meniscus regime, and in one case followed by focused ion beam milling. The electrodes were characterized by scanning electron microscopy and by cyclic voltammetry in 5 mM [Fe (CN)6]3− and 5 mM [Fe (CN)6]4− in 0.5 M KCl as a function of the depth of the UME immersed in the electrolyte solution. Computational fluid dynamics simulations were used to investigate the mass transfer of the electroactive species at the vicinity of the electrodes. Analytical expressions to predict the steady-state current of conical electrodes with aspect ratios from 3 to 22 and radius of curvature below 110 nm were also derived. It was found that the ratio of the electrochemical surface area to the geometric one rapidly increases when the depth of the UME's in solution is lower than 15 µm, in agreement with a rapid increase of the magnitude of the total flux towards the UMEs apex. Both experimental and simulation studies point to the radius of curvature as the most important parameter determining the rate of the oxidation / reduction of the [Fe (CN)6]3−/ [Fe (CN)6]4− species at non-insulated conical UMEs with high aspect ratio.
- Published
- 2022
22. Diameter dependent transparency changes of nanorod-based large-area flexible smart window devices
- Author
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Fuqiang Ren, Dongling Ma, Huang Shengyun, Aycan Yurtsever, and Fan Yang
- Subjects
Atmosphere (unit) ,Fabrication ,Renewable Energy, Sustainability and the Environment ,Computer science ,Window (computing) ,02 engineering and technology ,General Chemistry ,Transparency (human–computer interaction) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,7. Clean energy ,01 natural sciences ,Environmentally friendly ,Engineering physics ,0104 chemical sciences ,Modulation ,General Materials Science ,Nanorod ,Electronics ,0210 nano-technology - Abstract
Saving energy and designing an environmentally friendly atmosphere in modern buildings will require smart windows that can adapt to a variety of conditions and requirements, such as weather, human load and personal desire. The key element of such windows is the material system that transmits light in and out of the building in a controlled manner. To address the need for such a system, here we report the fabrication of novel, flexible, large-area devices that are based on suspended organometallic nanorods. As a result of the detailed characterization and extensive optimization of nanorod synthesis and device fabrication, our fabricated devices achieve superior optical and stability performances, with optical modulation as high as 73.7% (the highest value reported to date) and bending capability up to ∼180 degrees without any structural damage. This performance is further reinforced by repeated switching testing between high (“on”) and low (“off”) optical transmittance states over 500 cycles. Finally, we are able to scale up the fabrication of such devices to large areas (24 cm by 9 cm, size limited by our laboratory-scale doctor blade), underlining the possibility of adopting the results reported herein for future flexible smart windows and electronics. An interesting finding that the eventual SPD performance is indeed largely dependent on the diameter of the nanorods instead of their aspect ratios provides useful guidelines for future development.
- Published
- 2018
23. 3D Nanoscale Morphology Characterization of Ternary Organic Solar Cells
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Ting Yu, Wanting He, Maziar Jafari, Tugrul Guner, Pandeng Li, Mohamed Siaj, Ricardo Izquierdo, Baoquan Sun, Gregory C. Welch, Aycan Yurtsever, and Dongling Ma
- Subjects
General Materials Science ,General Chemistry - Abstract
It is highly desired to develop advanced characterization techniques to explore the 3D nanoscale morphology of the complicated blend film of ternary organic solar cells (OSCs). Here, ternary OSCs are constructed by incorporating the nonfullerene acceptor perylenediimide (PDI)-diketopyrrolopyrrole (DPP)-PDI and their morphology is characterized in depth to understand the performance variation. In particular, photoinduced force microscopy (PiFM) coupled with infrared laser spectroscopy is conducted to qualitatively study the distribution of donor and acceptors in the blend film by chemical identification and to quantitatively probe the segmentation of domains and the domain size distribution after PDI-DPP-PDI acceptor incorporation by PiFM imaging and data processing. In addition, the energy-filtered transmission electron microscopy with energy loss spectra is utilized to visualize the nanoscale morphology of ultrathin cross-sections in the configuration of the real ternary device for the first time in the field of photovoltaics. These measurements allow to "view" the surface and cross-sectional morphology and provide strong evidence that the PDI-DPP-PDI acceptor can suppress the aggregation of the fullerene molecules and generate the homogenous morphology with a higher-level of the molecularly mixed phase, which can prevent the charge recombination and stabilize the morphology of photoactive layer.
- Published
- 2021
24. Time‐Domain Integration of Broadband Terahertz Pulses in a Tapered Two‐Wire Waveguide
- Author
-
José Azaña, Junliang Dong, Giacomo Balistreri, Salvatore Stivala, Alessandro Tomasino, Aycan Yurtsever, Roberto Morandotti, Balistreri G., Tomasino A., Dong J., Yurtsever A., Stivala S., Azana J., and Morandotti R.
- Subjects
Materials science ,ultrafast optics ,Terahertz radiation ,business.industry ,nonlinear optics ,Ultrafast optics ,Nonlinear optics ,Condensed Matter Physics ,THz radiation ,Settore ING-INF/01 - Elettronica ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Optics ,All-optical signal processing ,Thz radiation ,Broadband ,Waveguide (acoustics) ,Time domain ,THz waveguides ,business - Abstract
In this work, the time-domain integration of broadband terahertz (THz) pulses via a tapered two-wire waveguide (TTWWG) is reported. Such a guiding structure consists of two metallic wires separated by a variable air gap that shrinks down to a subwavelength size as the movement takes from the waveguide input to its output. It is shown that while an input THz pulse propagates toward the subwavelength output gap, it is reshaped into its first-order time integral waveform. In order to prove the TTWWG time integration functionality, the THz pulse is detected directly within the output gap of the waveguide, so as to prevent the outcoupling diffraction from altering the shape of the time-integrated THz transient. Since the time-domain integration is due to the tight geometrical confinement of the THz radiation in a subwavelength gap volume, the TTWWG operational spectral range can easily be tuned by judiciously changing both the output gap size and the tapering angle. The results lead to the physical realization of a broadband, analog THz time integrator device, which is envisioned to serve as a key building block for the implementation of complex and ultrahigh-speed analog signal processing operations in THz communication systems.
- Published
- 2021
25. Compressed ultrafast transmission electron microscopy: a simulation study
- Author
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Jinyang Liang, Shian Zhang, Xianglei Liu, and Aycan Yurtsever
- Subjects
Data cube ,Physics ,Ground truth ,Optics ,Compressed sensing ,Computer simulation ,business.industry ,Temporal resolution ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Streak ,Nanosecond ,business ,Ultrashort pulse - Abstract
Bringing ultrafast temporal resolution to transmission electron microscopy (TEM) has historically been challenging. Despite significant recent progress in this direction, it remains difficult to achieve sub-nanosecond temporal resolution with a single electron pulse imaging. To address this limitation, here, we propose a methodology that combines laserassisted TEM with computational imaging methodologies based on compressed sensing (CS). In this technique, a twodimensional (2D) transient event [i.e. (x, y) frames that vary in time] is recorded through a CS paradigm. The 2D streak image generated on a camera is used to reconstruct the datacube of the ultrafast event, with two spatial and one temporal dimensions, via a CS-based image reconstruction algorithm. Using numerical simulation, we find that the reconstructed results are in good agreement with the ground truth, which demonstrates the applicability of CS-based computational imaging methodologies to laser-assisted TEM. Our proposed method, complementing the existing ultrafast stroboscopic and nanosecond single-shot techniques, opens up the possibility for single-shot, spatiotemporal imaging of irreversible structural phenomena with sub-nanosecond temporal resolution.
- Published
- 2019
26. Electrochemistry at Tungsten Conical Sharp Tip Electrodes
- Author
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Ana C. Tavares, Uriel Bruno-Mota, Aycan Yurtsever, and Jesus Valdez
- Subjects
Materials science ,chemistry ,Electrode ,chemistry.chemical_element ,Conical surface ,Tungsten ,Composite material ,Electrochemistry - Abstract
Most of the electrochemical studies are performed with macroscopic, bulk electrodes. The materials of interest are placed on centimeter sized electrodes and the current originating from large macroscopic areas are measured. Although, this traditional approach produces strong signals that are perfect for quantitative analyses it lacks the capability to resolve individual entities or sub-micron structural heterogeneities, that contribute to the electrochemical signal. It averages-out different structures and hence, it becomes impossible to perform in depth studies of chemical reactions occurring at different sites. With modern developments in nanofabrication, simulations and computer aided design, as well as in state of the art potentiostats, the doors were open for the rapid development of a highly active field of research in the last years: The electrochemistry at the nanoscale, which has allowed to achieve electrochemical measurements from submicron entities [1], [2], and it’s leading the way to the development of single molecule electrochemistry. In this work we will present our approach to the study of electrochemical reactions on single entities, which includes the fabrication of very sharp conical tips to be used as working electrodes and to achieve high spatial resolution. Figure A shows a scanning electron microscope image of a tungsten tip prepared by electrochemical etching of a tungsten wire in KOH solution, with a radius of curvature of 100 nm. Two main oxides are formed during the anodic polarization of the tungsten electrodes, passivating their surface [3], [4]. However, cyclic voltammetry studies in acid and neutral electrolytes, revealed a potential window and scan rate where a conductive oxide is formed and thus suitable to be used as electrode material. As a result, the tungsten tips were further characterized electrochemically by cyclic voltammetry in presence of a redox probe and as a function of the exposed surface area in the electrolyte solution. An electrochemical response characteristic of ultramicroelectrodes was recorded for tip lengths below 70 µm, Figure B. It was also found that the electroactive area is higher than the geometric one [5], Figure C. The contribution of the roughness of the electrode, the meniscus effect and a possible field enhancement due to the geometry of the electrodes to the electrochemical surface area will be quantified. This work represents thus, a step ahead towards a better understanding of the electrochemical processes in increasingly smaller structures to eventually reach the ultimate goal of the use of nanometer-sized electrodes: single molecule electrochemistry. Acknowledgements To Consejo Nacional de Ciencia y Tecnología (CONACYT) for the financial support with the scholarship 739820 for graduate studies abroad. References [1] L. A. Baker, “Perspective and Prospectus on Single-Entity Electrochemistry,” J. Am. Chem. Soc., vol. 140, pp. 15549–15559, 2018. [2] Y. Wang, X. Shan, and N. Tao, “Emerging tools for studying single entity electrochemistry,” Faraday Discuss., vol. 193, pp. 9–39, 2016. [3] M. Anik and K. Osseo-Asare, “Effect of pH on the anodic behavior of tungsten,” J. Electrochem. Soc., vol. 149, no. 6, 2002. [4] M. Anik, “pH-dependent anodic reaction behavior of tungsten in acidic phosphate solutions,” Electrochim. Acta, vol. 54, no. 15, pp. 3943–3951, 2009. [5] C. G. Zoski and M. V. Mirkin, “Steady-state limiting currents at finite conical microelectrodes,” Anal. Chem., vol. 74, no. 9, pp. 1986–1992, 2002. Figure 1
- Published
- 2020
27. Niobium Pentoxide Nanoparticles and Their Self-Assembled in Building Blocks for Gas Sensors
- Author
-
Ana C. Tavares, Marcos R.V. Lanza, Hela Kammoun, and Aycan Yurtsever
- Subjects
chemistry.chemical_compound ,Materials science ,chemistry ,Nanoparticle ,Nanotechnology ,Niobium pentoxide ,Self assembled - Abstract
Niobium pentoxide (Nb2O5) is characterized by an outstanding chemical stability, high corrosion resistance and color changing chemistry. Nb2O5 can adopt different crystal structures (pseudohexagonal, orthorhombic and monoclinic), depending on the temperature [1]. Still, it is one of the least studied metal oxides. [2], [3]. Thus, exploring new synthetic methods and the physicochemical properties of the resulting oxide nanoparticles (NPs) could open new opportunities in different applications such as electrocatalysis, electrochromic displays, Surface-enhanced Raman spectroscopy and gas, humidity, and biological/chemical sensing. For gas sensing applications, nanostructured individual NPs of Nb2O5 with uniform shape, narrow size distribution along with high surface area are required to facilitate the adsorption of the target gas molecules. [1], [3], [4], [5]. Hydrothermal and solvothermal methods are widely used to produce metal oxides NPs with various morphologies. [1] These methods are easily scaled up and produce materials with high purity. Due to the high autogenous pressure inside the reactor, the nanoparticles are usually crystalline; and depending on the temperature and the time of reaction, the crystal phase can be controlled. However, the control of the size and the shape of the NPs with hydrothermal synthesis is a challenge because after nucleation, the nuclei precipitate and agglomerate forming microstructures with ill-defined shapes. [3] ,[5] In this work, we report the synthesis of spherical-like niobium oxide nanoparticles by one-pot hydrothermal synthesis using as a precursor ammonium niobium oxalate aqueous solution, Figures 1.A and 1.B. The kinetics of the NPs growth was investigated by Dynamic Light Scattering (DLS), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). Figure 1.B. shows that the Nb2O5 NP grow according to the Oswald ripening mechanism, with the size of the nanoparticles increasing from 2 nm to 80 nm with the reaction time. However, the nanoparticles tend to coalesce forming larger nanostructures with uncontrollable size landing to unstable suspensions. A comparative study between different charged ligands, revealed citric acid as the best ligand to ensure the stability of the Nb2O5 suspensions and to control the nanoparticles’ size. Indeed, using citric acid the size of the size of the aggregates in the suspensions is reduced by the factor of 10, from 200 to around 20 nm of diameter. The control of the size and shape of the NPs was found to be critical to form 3D superlattices and to maximize the surface area once the nanoparticles form thin films, Figure 1.C. The kinetic of the NPs growth and the physicochemical properties of the NPs and films will be discussed in detail. Acknowledgements The authors would like to thank the funding from NSERC (Strategic partnership program, Canada). References [1] YD Wang, LF Yang, ZL Zhou, YF Li, XH Wu. Materials Letters, 49 (5), 277-281 (2001). [2] I. C. M. S. Santos, L. H. Loureiro, M. F. P. Silva and A. M. V. Cavaleiro, Polyhedron. 21,2009-42015 (2002). [3] J.F. Carneiro, M.J. Paulo, M. Siaj, A.C. Tavares, and M.R.V. Lanza, J. Catal. 332, 51–61 (2015). [4] A. K.Rosmalini, A. R. Rozina, M. M. Y. A. Alsaif, & al, ACS Appl. Mater. Interfaces, 7, 8, 4751-4758 (2015). [5] J. A. Darr, J. Zhang, N. M. Makwana, X. Weng, Chem. Rev., 117, 17, 11125-11238 (2017). Figure 1
- Published
- 2020
28. 1D/2D Cobalt‐Based Nanohybrids as Electrocatalysts for Hydrogen Generation
- Author
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Federico Rosei, Zhiming Wang, Aycan Yurtsever, Omar Abdelkarim, Haiguang Zhao, Jiabin Liu, Gurpreet Singh Selopal, Ana C. Tavares, and Fabiola Navarro-Pardo
- Subjects
Materials science ,chemistry.chemical_element ,02 engineering and technology ,Carbon nanotube ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Biomaterials ,chemistry ,Chemical engineering ,law ,Electrode ,Electrochemistry ,Hydrogen evolution ,0210 nano-technology ,Cobalt ,Hydrogen production - Published
- 2020
29. (Invited) Oxygen Evolution and Reduction on La0.5Sr0.5Co0.8Fe0.2O3- Δ Perovskites with Tunable Structural Features
- Author
-
Ana C Tavares, Francesca Deganello, Jose Guadalupe Rivera, Jesus Valdez, German Orozco Gamboa, and Aycan Yurtsever
- Abstract
Oxygen evolution (OER) and oxygen reduction (ORR) reactions are the fundamental processes occurring at the air electrode of metal-air batteries and fuel cells. Presently, large overpotentials are required for these reactions to occur at an appreciable rate. Therefore, development of catalysts capable of reducing the activation losses at the oxygen electrode is highly desirable. Perovskite oxides are one of the most interesting low-cost electrocatalysts for air electrodes, because they can adopt a wide variety of chemical compositions and crystal structures, thereby enabling correlative studies between the electrocatalytic activity and their electronic structure (1, 2). Recently, we reported a possible relation between the cell volume of La0.6Sr0.4Fe0.6Mn0.4O3-δ perovskites and their ORR activity and selectivity (2 e- vs ‘’2+2’’ e- pathway), with lower cell volumes corresponding to higher number of exchanged electrons (3). It was also reported by others that some structural features in the perovskite influence the activity of these mixed oxides for both ORR and OER (4-6). In this presentation, we will discuss our recent studies on the ORR and OER activity of a series of La0.5Sr0.5Co0.8Fe0.2O3- δ electrocatalysts prepared by solution combustion synthesis. The choice of diverse experimental conditions allowed us to tune oxygen deficiency, microstrain and other structural properties. As exemplified in Figure 1, for one of the investigated electrocatalysts, thermal annealing in argon reduces the bond angle between the oxygen atom and the two B-site metal cations, resulting in a higher electrocatalytic activity for both OER and ORR. In addition to structure–electrocatalytic activity correlations, we will complement our comparative studies with analytical scanning electron microscopy and spatially resolved elemental mapping of selected electrode surfaces subjected to accelerated stability tests. Figure 1. Crystal structures of La0.5Sr0.5Co0.8Fe0.2O3- δ prepared from solution combustion using citrate as fuel and thermal annealed in Ar (top right) and in Air (bottom left). Differences in the Co-O-Co bond angle are highlighted. Oxygen evolution (OER, top left) and oxygen reduction (ORR, bottom right) polarization curves recorded in 0.1 M KOH at 5 mVs-1 and 1600 rpm. References 1. J. Suntivich, H. A. Gasteiger, N. Yabuuchi, H. Nakanishi, J. B. Goodenough and Y. Shao-Horn, Nat Chem, 3, 546 (2011). 2. J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough and Y. Shao-Horn, Science, 334, 1383 (2011). 3. F. Deganello, D. N. Oko, M. L. Testa, V. La Parola, M. L. Tummino, C. O. Soares, J. G. Rivera, G. Orozco, D. Guay and A. C. Tavares, ACS Applied Energy Materials, 1, 2565 (2018). 4. Y. Sun, Z. Liu, W. Zhang, X. Chu, Y. Cong, K. Huang and S. Feng, Small, 0, 1803513. 5. X. Xu, Y. Chen, W. Zhou, Y. Zhong, D. Guan and Z. Shao, Advanced Materials Interfaces, 5, 1701693 (2018). 6. W. Zhou and J. Sunarso, The Journal of Physical Chemistry Letters, 4, 2982 (2013). Figure 1
- Published
- 2019
30. (Invited) Nanohybrids for Manipulating Solar Energy
- Author
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Aycan Yurtsever and Dongling Ma
- Abstract
With unique physical and chemical properties, and high potential for many important applications, nanomaterials have attracted extensive attention in the past two decades. For instance, due to their unique, size- and shape-tunable surface plasmon resonance, plasmonic nanostructures have recently been explored for increasing the efficiency of solar cells and photocatalysis. Essentially they enhance and/or broaden solar photon harvesting via improved light scattering, strong near field effect and/or hot electron injection. Combination of different nanomaterials into a single architecture leads to greatly enhanced properties, or even better, promising, multifunctional nanomaterials. In this talk, I will present our recent work on the synthesis of hybrid nanomaterials (the assemblies of different types of nanoscale materials) as well as their applications in smart windows, solar cells, solar fuel, photocatalysis, etc. [1-8]. Rational design of hybrid nanomaterials, which is the key to maximize the benefits from respective nano-components, is highlighted. References: 1. Am. Chem. Soc., 2013, 135, 9616; 2. Adv. Energy Mater. 2018, 1703658; 3. Adv. Funct. Mater. 2018, 1706235; 4. ACS Catalysis, 2017, 7, 6225; 5. Adv. Funct. Mater, 2015, 25, 2950; 6. Adv. Funct. Mater. 2015, 25, 6650; 7. Adv. Funct. Mater., 2012, 22, 3914; 8. Adv. Mater., 2012, 24, 6289.
- Published
- 2019
31. Graphene-layered steps and their fields visualized by 4D electron microscopy
- Author
-
John Spencer Baskin, Ahmed H. Zewail, Sang Tae Park, and Aycan Yurtsever
- Subjects
Photons ,Multidisciplinary ,Materials science ,Graphene ,business.industry ,Electrons ,STRIPS ,Electron ,Substrate (electronics) ,Light scattering ,Nanostructures ,law.invention ,Microscopy, Electron ,Optics ,law ,Transmission electron microscopy ,Electric field ,Physical Sciences ,Femtosecond ,Optoelectronics ,Graphite ,business - Abstract
Enhanced image contrast has been seen at graphene-layered steps a few nanometers in height by means of photon-induced near-field electron microscopy (PINEM) using synchronous femtosecond pulses of light and electrons. The observed steps are formed by the edges of graphene strips lying on the surface of a graphene substrate, where the strips are hundreds of nanometers in width and many micrometers in length. PINEM measurements reflect the interaction of imaging electrons and induced (near) electric fields at the steps, and this leads to a much higher contrast than that achieved in bright-field transmission electron microscopy imaging of the same strips. Theory and numerical simulations support the experimental PINEM findings and elucidate the nature of the electric field at the steps formed by the graphene layers. These results extend the range of applications of the experimental PINEM methodology, which has previously been demonstrated for spherical, cylindrical, and triangular nanostructures, to shapes of high aspect ratio (rectangular strips), as well as into the regime of atomic layer thicknesses.
- Published
- 2013
32. Subparticle Ultrafast Spectrum Imaging in 4D Electron Microscopy
- Author
-
Ahmed H. Zewail, Renske M. van der Veen, and Aycan Yurtsever
- Subjects
Photons ,Silver ,Multidisciplinary ,Photon ,Light ,Vacuum ,Chemistry ,Scanning electron microscope ,business.industry ,Resolution (electron density) ,Metal Nanoparticles ,Nanoparticle ,Time ,Microscopy, Electron ,Optics ,Microscopy ,business ,Ultrashort pulse ,Nanoscopic scale ,Copper ,Plasmon - Abstract
Plasmon Probe When light of certain wavelengths strikes a metal surface, it sets the metal's electrons in motion along trajectories termed “plasmon modes.” Yurtsever et al. (p. 59 ; see the Perspective by Batson ) constructed a type of electron microscope that can probe the electric fields associated with this process by measuring the energy of a separate pulse of electrons that is bounced off the surface immediately (less than trillionths of a second) after the light strikes. The spatial resolution was sufficient to map intensities in distinct regions of a single silver nanoparticle.
- Published
- 2012
33. High-Performance Suspended Particle Devices Based on Copper-Reduced Graphene Oxide Core-Shell Nanowire Electrodes
- Author
-
Dongling Ma, Huang Shengyun, Aycan Yurtsever, Fuqiang Ren, Qingzhe Zhang, and Pandeng Li
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,Graphene ,business.industry ,Nanowire ,Oxide ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Copper ,0104 chemical sciences ,law.invention ,Core shell ,chemistry.chemical_compound ,chemistry ,law ,Electrode ,Optoelectronics ,Particle ,General Materials Science ,0210 nano-technology ,business - Published
- 2018
34. 4D Nanoscale Diffraction Observed by Convergent-Beam Ultrafast Electron Microscopy
- Author
-
Ahmed H. Zewail and Aycan Yurtsever
- Subjects
Diffraction ,Multidisciplinary ,Nanostructure ,Reflection high-energy electron diffraction ,business.industry ,Chemistry ,Gas electron diffraction ,Molecular physics ,Optics ,Orders of magnitude (time) ,Electron diffraction ,Energy filtered transmission electron microscopy ,business ,Electron backscatter diffraction - Abstract
Converging on Dynamics Electron diffraction is a versatile technique for discerning atomic-level structure, but the data emerge averaged over the micron–scale area sampled by the electrons, and so blur local distinctions in systems that aren't strictly periodic. A recent approach to minimizing this problem has been to focus the electron beam impinging on the sample. Yurtsever and Zewail (p. 708 ) have now applied convergent focusing to an ultrafast electron diffraction apparatus and were thus able to resolve picosecond structural dynamics in local regions tens of nanometers across. The technique was used to probe heterogeneous temperature changes in laser-heated silicon.
- Published
- 2009
35. Thickness measurements using photonic modes in monochromated electron energy-loss spectroscopy
- Author
-
Aycan Yurtsever, Jerome K. Hyun, Martin Couillard, and David A. Muller
- Subjects
Materials science ,Infrared ,business.industry ,Electron energy loss spectroscopy ,Physics::Optics ,Electron ,Gallium arsenide ,law.invention ,chemistry.chemical_compound ,Condensed Matter::Materials Science ,chemistry ,law ,Optoelectronics ,Photonics ,Spectroscopy ,business ,Instrumentation ,Waveguide ,Cherenkov radiation - Abstract
Characteristic energies of photonic modes are a sensitive function of a nanostructures’ geometrical parameters. In the case of translationally invariant planar waveguides, the eigen-energies reside in the infrared to ultraviolet parts of the optical spectrum and they sensitively depend on the thickness of the waveguide. Using swift electrons and the inherent Cherenkov radiation in dielectrics, the energies of such photonic states can be effectively probed via monochromated electron energy-loss spectroscopy (EELS). Here, by exploiting the strong photonic signals in EELS with 200 keV electrons, we correlate the energies of waveguide peaks in the 0.5–3.5 eV range with planar thicknesses of the samples. This procedure enables us to measure the thicknesses of cross-sectional transmission electron microscopy samples over a 1–500 nm range and with best-case accuracies below ±2%. The measurements are absolute with the only requirement being the optical dielectric function of the material. Furthermore, we provide empirical formulation for rapid and direct thickness estimations for a 50–500 nm range. We demonstrate the methodology for two semiconducting materials, silicon and gallium arsenide, and discuss how it can be applied to other dielectrics that produce strong optical fingerprints in EELS. The asymptotic form of the loss function for two-dimensional materials is also discussed.
- Published
- 2014
36. Nanoscale Probes in Ultrafast Transmission Electron Microscopy
- Author
-
Aycan Yurtsever
- Subjects
Materials science ,business.industry ,Transmission electron microscopy ,Scanning confocal electron microscopy ,Optoelectronics ,business ,Instrumentation ,Nanoscopic scale ,Ultrashort pulse - Published
- 2015
37. Entangled Nanoparticles: Discovery by Visualization in 4D Electron Microscopy
- Author
-
J. Spencer Baskin, Ahmed H. Zewail, and Aycan Yurtsever
- Subjects
Titanium ,Silver ,Materials science ,Surface Properties ,Mechanical Engineering ,Metal Nanoparticles ,Nanoparticle ,Bioengineering ,Nanotechnology ,General Chemistry ,Quantum entanglement ,Condensed Matter Physics ,Polarization (waves) ,Nanostructures ,Nanomaterials ,Microscopy, Electron ,Wavelength ,Imaging, Three-Dimensional ,Materials Testing ,General Materials Science ,Particle size ,Particle Size ,Nanoscopic scale ,Plasmon - Abstract
Particle interactions are fundamental to our understanding of nanomaterials and biological assemblies. Here, we report on the visualization of entangled particles, separated by as large as 70 nm, and the discovery of channels in their near-fields. For silver nanoparticles, the induced field of each particle extends to 50-100 nm, but when particles are brought close in separation we observe channels as narrow as 6 nm, a width that is 2 orders of magnitude smaller than the incident field wavelength. The channels' directions can be controlled by the polarization of the incident field, particle size, and separation. For this direct visualization of these nanoscopic near-fields, the high spatial, temporal, and energy resolutions needed were hitherto not possible without the methodology given here. This methodology, we anticipate, paves the way for further fundamental studies of particle entanglement and for possible applications spanning materials and macromolecular assemblies.
- Published
- 2012
38. Ultrafast Kikuchi Diffraction: Nanoscale Stress−Strain Dynamics of Wave-Guiding Structures
- Author
-
Sascha Schaefer, Aycan Yurtsever, and Ahmed H. Zewail
- Subjects
Diffraction ,Materials science ,Reflection high-energy electron diffraction ,Gas electron diffraction ,business.industry ,Mechanical Engineering ,Physics::Optics ,Bragg's law ,Bioengineering ,General Chemistry ,Condensed Matter Physics ,Optics ,Electron diffraction ,General Materials Science ,Wave vector ,business ,Kikuchi line ,Envelope (waves) - Abstract
Complex structural dynamics at the nanoscale requires sufficiently small probes to be visualized. In conventional imaging using electron microscopy, the dimension of the probe is large enough to cause averaging over the structures present. However, by converging ultrafast electron bunches, it is possible to select a single nanoscale structure and study the dynamics, either in the image or using electron diffraction. Moreover, the span of incident wave vectors in a convergent beam enables sensitivity levels and information contents beyond those of parallel-beam illumination with a single wave vector Bragg diffraction. Here, we report the observation of propagating strain waves using ultrafast Kikuchi diffraction from nanoscale volumes within a wedge-shaped silicon single crystal. It is found that the heterogeneity of the strain in the lateral direction is only 100 nm. The transient elastic wave gives rise to a coherent oscillation with a period of 30 ps and with an envelope that has a width of 140 ps. The origin of this elastic deformation is theoretically examined using finite element analysis; it is identified as propagating shear waves. The wedge-shaped structure, unlike parallel-plate structure, is the key behind the traveling nature of the waves as its angle permits "transverse" propagation; the parallel-plate structure only exhibits the "longitudinal" motion. The studies reported suggest extension to a range of applications for nanostructures of different shapes and for exploring their ultrafast eigen-modes of stress-strain profiles.
- Published
- 2012
39. Direct visualization of near-fields in nanoplasmonics and nanophotonics
- Author
-
Ahmed H. Zewail and Aycan Yurtsever
- Subjects
Materials science ,Silver ,Nanophotonics ,Physics::Optics ,Nanoparticle ,Metal Nanoparticles ,Bioengineering ,Nanotechnology ,Photometry ,Electric field ,Materials Testing ,General Materials Science ,Plasmon ,business.industry ,Mechanical Engineering ,General Chemistry ,Equipment Design ,Surface Plasmon Resonance ,Condensed Matter Physics ,Equipment Failure Analysis ,Optoelectronics ,Particle size ,Photonics ,business ,Ultrashort pulse ,Excitation - Abstract
Electric fields of nanoscale particles are fundamental to our understanding of nanoplasmonics and nanophotonics. Success has been made in developing methods to probe the effect of their presence, but it remains difficult to directly image optically induced electric fields at the nanoscale and especially when ensembles of particles are involved. Here, using ultrafast electron microscopy, we report the space-time visualization of photon-induced electric fields for ensembles of silver nanoparticles having different sizes, shapes, and separations. The high-field-of-view measurements enable parallel processing of many particles in the ensemble with high throughput of information. Directly in the image, the evanescent fields are observed and visualized when the particles are polarized with the optical excitation. Because the particle size is smaller than the wavelength of light, the near-fields are those of nanoplasmonics and are precursors of far-field nanophotonics. The reported results pave the way for quantitative studies of fields in ensembles of complex morphologies with the nanoparticles being embedded or interfacial.
- Published
- 2012
40. Kikuchi ultrafast nanodiffraction in four-dimensional electron microscopy
- Author
-
Ahmed H. Zewail and Aycan Yurtsever
- Subjects
Diffraction ,Multidisciplinary ,Materials science ,Wave packet ,Resonance ,Bragg's law ,Electron ,Polarization (waves) ,Molecular physics ,Kinetics ,Microscopy, Electron ,Nuclear magnetic resonance ,Microscopy, Electron, Transmission ,X-Ray Diffraction ,Normal mode ,Commentaries ,Nanotechnology ,Kikuchi line - Abstract
Coherent atomic motions in materials can be revealed using time-resolved X-ray and electron Bragg diffraction. Because of the size of the beam used, typically on the micron scale, the detection of nanoscale propagating waves in extended structures hitherto has not been reported. For elastic waves of complex motions, Bragg intensities contain all polarizations and they are not straightforward to disentangle. Here, we introduce Kikuchi diffraction dynamics, using convergent-beam geometry in an ultrafast electron microscope, to selectively probe propagating transverse elastic waves with nanoscale resolution. It is shown that Kikuchi band shifts, which are sensitive only to the tilting of atomic planes, reveal the resonance oscillations, unit cell angular amplitudes, and the polarization directions. For silicon, the observed wave packet temporal envelope (resonance frequency of 33 GHz), the out-of-phase temporal behavior of Kikuchi’s edges, and the magnitude of angular amplitude (0.3 mrad) and polarization elucidate the nature of the motion: one that preserves the mass density (i.e., no compression or expansion) but leads to sliding of planes in the antisymmetric shear eigenmode of the elastic waveguide. As such, the method of Kikuchi diffraction dynamics, which is unique to electron imaging, can be used to characterize the atomic motions of propagating waves and their interactions with interfaces, defects, and grain boundaries at the nanoscale.
- Published
- 2011
41. Visualizing the Optically Induced Near-fields of Nanoplasmonics with Ultrafast Transmission Electron Microscopy
- Author
-
Aycan Yurtsever
- Subjects
Materials science ,Photon ,business.industry ,Physics::Optics ,Electron ,symbols.namesake ,Optics ,Transmission electron microscopy ,Electric field ,symbols ,business ,Instrumentation ,Ultrashort pulse ,Excitation ,Raman scattering ,Measured quantity - Abstract
Localized electric fields that are induced optically exhibit unique phenomena of fundamental importance to nanoplasmonics. In recent years, they have been considered for efficient photovoltaic and light harvesting devices, single molecule detection, biomolecular labeling and manipulation, and surface enhanced Raman scattering [1]. Several methodologies have been utilized for probing the near-fields, and these include optical methods, cathodoluminesce and transmission electron microscopy [2]. The latter probes the fields with sub-nanometer precision but the measured quantity is the dielectric response of the system to an impinging swift electron, and not to a photon excitation.
- Published
- 2014
42. Interference effects on guided Cherenkov emission in silicon from perpendicular, oblique, and parallel boundaries
- Author
-
Aycan Yurtsever, Martin Couillard, and David A. Muller
- Subjects
Physics ,Waveguide (electromagnetism) ,Electron energy loss spectroscopy ,Excited state ,Physics::Optics ,Electron ,Atomic physics ,Condensed Matter Physics ,Electromagnetic radiation ,Spectral line ,Excitation ,Cherenkov radiation ,Electronic, Optical and Magnetic Materials - Abstract
Waveguide electromagnetic modes excited by swift electrons traversing Si slabs at normal and oblique incidence are analyzed using monochromated electron energy-loss spectroscopy and interpreted using a local dielectric theory that includes relativistic effects. At normal incidence, sharp spectral features in the visible/near-infrared optical domain are directly assigned to $p$-polarized modes. When the specimen is tilted, $s$-polarized modes, which are completely absent at normal incidence, become visible in the loss spectra. In the tilted configuration, the dispersion of $p$-polarized modes is also modified. For tilt angles higher than $\ensuremath{\sim}50\ifmmode^\circ\else\textdegree\fi{}$, Cherenkov radiation, the phenomenon responsible for the excitation of waveguide modes, is expected to partially escape the silicon slab and the influence of this effect on experimental measurements is discussed. Finally, we find evidence for an interference effect at parallel $\text{Si}/{\text{SiO}}_{2}$ interfaces, as well as a delocalized excitation of guided Cherenkov modes.
- Published
- 2010
43. Nanomechanical motions of cantilevers: direct imaging in real space and time with 4D electron microscopy
- Author
-
David J. Flannigan, Ahmed H. Zewail, Peter C. Samartzis, and Aycan Yurtsever
- Subjects
Models, Molecular ,Diffraction ,Time Factors ,Cantilever ,Modulus ,Bioengineering ,Young's modulus ,Molecular physics ,Motion ,symbols.namesake ,Optics ,Nano ,Image Processing, Computer-Assisted ,General Materials Science ,Elastic modulus ,Microscale chemistry ,Physics ,business.industry ,Mechanical Engineering ,General Chemistry ,Condensed Matter Physics ,Organic semiconductor ,Microscopy, Electron ,symbols ,Nanoparticles ,Stress, Mechanical ,business - Abstract
The function of many nano- and microscale systems is revealed when they are visualized in both space and time. Here, we report our first observation, using four-dimensional (4D) electron microscopy, of the nanomechanical motions of cantilevers. From the observed oscillations of nanometer displacements as a function of time, for free-standing beams, we are able to measure the frequency of modes of motion and determine Young's elastic modulus and the force and energy stored during the optomechanical expansions. The motion of the cantilever is triggered by molecular charge redistribution as the material, single-crystal organic semiconductor, switches from the equilibrium to the expanded structure. For these material structures, the expansion is colossal, typically reaching the micrometer scale, the modulus is 2 GPa, the force is 600 microN, and the energy is 200 pJ. These values translate to a large optomechanical efficiency (minimum of 1% and up to 10% or more) and a pressure of nearly 1,500 atm. We note that the observables here are real material changes in time, in contrast to those based on changes of optical/contrast intensity or diffraction.
- Published
- 2009
44. Formation of Guided Cherenkov Radiation in Silicon-Based Nanocomposites
- Author
-
Aycan Yurtsever, Martin Couillard, and David A. Muller
- Subjects
Materials science ,Silicon ,Infrared ,business.industry ,Electron energy loss spectroscopy ,Physics::Optics ,General Physics and Astronomy ,chemistry.chemical_element ,medicine.disease_cause ,Electromagnetic radiation ,Semimetal ,chemistry ,medicine ,Density of states ,Optoelectronics ,Atomic physics ,business ,Astrophysics::Galaxy Astrophysics ,Cherenkov radiation ,Ultraviolet - Abstract
We use a monochromated 200 keV electron beam as a nanometer-resolution probe of the photonic density of states in bulk and nanoparticle $\mathrm{Si}/{\mathrm{SiO}}_{2}$ systems, observing infrared to ultraviolet waveguided Cherenkov modes in Si slabs, but none in ${\mathrm{SiO}}_{2}$. While isolated Si nanoparticles are too small to support Cherenkov radiation, we find high densities of Si nanoparticles in ${\mathrm{SiO}}_{2}$ support a damped form of the radiation, with the modes determined by the effective medium of the $\mathrm{Si}/{\mathrm{SiO}}_{2}$ mixture. The guided nature of the radiation is confirmed by the presence of a thickness-dependent cutoff.
- Published
- 2008
45. Competition between bulk and interface plasmonic modes in valence electron energy-loss spectroscopy of ultrathinSiO2gate stacks
- Author
-
Aycan Yurtsever, Martin Couillard, and David A. Muller
- Subjects
Materials science ,Reflection high-energy electron diffraction ,Electron diffraction ,Electron energy loss spectroscopy ,Energy filtered transmission electron microscopy ,Atomic physics ,Condensed Matter Physics ,Valence electron ,Spectroscopy ,Electron spectroscopy ,Molecular physics ,Plasmon ,Electronic, Optical and Magnetic Materials - Published
- 2008
46. Competition between Interface and Bulk Modes in Valence EELS of Thin Films
- Author
-
Aycan Yurtsever, Martin Couillard, and David A. Muller
- Subjects
Materials science ,Valence (chemistry) ,Condensed matter physics ,Thin film ,Instrumentation - Published
- 2007
47. 3-D Imaging of Non-Spherical Silicon Nanoparticles Embedded in Silicon Oxide by Plasmon Tomography
- Author
-
Aycan Yurtsever, David A. Muller, and Matthew Weyland
- Subjects
Materials science ,Silicon ,chemistry ,Hybrid silicon laser ,chemistry.chemical_element ,Nanoparticle ,Nanotechnology ,Tomography ,Silicon oxide ,Instrumentation ,Plasmon ,3 d imaging - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005
- Published
- 2006
48. Uncovering Nanoscale Chemical Variations in the Third Dimension; Electron Tomography in the Analytical Mode
- Author
-
Matthew Weyland, Aycan Yurtsever, David A. Muller, and Peter Ercius
- Subjects
Optics ,Materials science ,Electron tomography ,Dimension (vector space) ,business.industry ,Mode (statistics) ,business ,Instrumentation ,Nanoscopic scale - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006
- Published
- 2006
49. Three-dimensional imaging of nonspherical silicon nanoparticles embedded in silicon oxide by plasmon tomography
- Author
-
David A. Muller, Matthew Weyland, and Aycan Yurtsever
- Subjects
Photoluminescence ,Materials science ,Physics and Astronomy (miscellaneous) ,Silicon ,business.industry ,Physics::Optics ,Nanoparticle ,chemistry.chemical_element ,Nanotechnology ,chemistry ,Electron tomography ,Quantum dot ,Density of states ,Optoelectronics ,Silicon oxide ,business ,Plasmon - Abstract
Silicon nanoparticles embedded in silica show promising optoelectronic properties, due to quantum confinement and/or radiative interface states that should correlate with the particles’ average size and shape. Here the authors report the combination of electron tomography with plasmon-filtered microscopy in order to reconstruct the three-dimensional morphology of silicon nanoparticles. They find that particles with complex morphologies and high surface to volume ratios are dominant, rather than the commonly assumed near-spherical structures. These results should affect quantum-confined excitons and the interface density of states. Their findings may help to explain the physical origin of the unusually broad photoluminescence bands and efficiencies.
- Published
- 2006
50. Nanomechanical Motions of Cantilevers: Direct Imaging in Real Space and Time with 4D Electron Microscopy.
- Author
-
David J. Flannigan, Peter C. Samartzis, Aycan Yurtsever, and Ahmed H. Zewail
- Published
- 2009
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