52 results on '"Yaakov R. Tischler"'
Search Results
2. New Method to Study the Vibrational Modes of Biomolecules in the Terahertz Range Based on a Single-Stage Raman Spectrometer
- Author
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Basanth S. Kalanoor, Maria Ronen, Ziv Oren, Doron Gerber, and Yaakov R. Tischler
- Subjects
Chemistry ,QD1-999 - Published
- 2017
- Full Text
- View/download PDF
3. Microcavity Enhanced Raman Spectroscopy of Fullerene C60 Bucky Balls
- Author
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Vinayaka H. Damle, Miri Sinwani, Hagit Aviv, and Yaakov R. Tischler
- Subjects
cers ,fullerene c60 ,dft ,Chemical technology ,TP1-1185 - Abstract
Raman spectroscopy is a widely used characterization technique in material science. It is a non-destructive tool with relatively simple instrumentation, and provides intrinsic qualitative information of analytes by probing their vibrational modes. In many cases, Raman enhancement is essential for detecting low-intensity signals in high-noise environments, spectrally unresolved features, and hidden modes. Here we present optical and Raman spectroscopic characterization of fullerene C 60 in a gold microcavity. The fabrication of single-layered gold mirrors is facile, low cost and direct but was proven to give considerably significant enhancement. The findings of this work demonstrate the cavity resonance as a powerful tool in obtaining tunability over individual peak for selective enhancement in the tuned spectral range. The PL of the material within the cavity has demonstrated a red shift assumed to be caused by the low-energy transitions. These transitions are induced by virtual low-energy states generated by the cavity. We further observe that adopting this principle enables resolution of active Raman modes that until now were unobserved. Finally, we assigned the new experimentally observed modes to the corresponding motions calculated by DFT.
- Published
- 2020
- Full Text
- View/download PDF
4. Polarization Dependence of Low-Frequency Vibrations from Multiple Faces in an Organic Single Crystal
- Author
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Irena Nemtsov, Hagit Aviv, Yitzhak Mastai, and Yaakov R. Tischler
- Subjects
microcrystal ,low frequency Raman ,crystal orientation ,intermolecular interactions ,Crystallography ,QD901-999 - Abstract
Recent developments in optical filters have enabled the facile use of Raman spectroscopy for detection of low frequency (LF) vibrational modes. LF-Raman spectroscopy offers fast and sensitive characterization of LF vibrations, and enables the measurement of single microcrystals and detection of defects. It is useful for probing intermolecular interactions in crystals, which are lower in energy, such as hydrogen bonds, shear modes, and breathing modes. Crystal excitation from multiple faces allows learning the orientation of intermolecular interactions, as polarization dependence varies with the polarizability of the interactions along the planes. Elucidating the orientations of the intermolecular interactions in organic crystals is essential for guiding the reactions or adsorption to a specific crystal face. In this study, we investigated the dependence of the LF-Raman signal intensity on the orientation of an organic single microcrystal of L-alanine. Three incident beam directions provided the orientations of the intermolecular interactions by analyzing the corresponding LF-Raman spectra. The signal intensity correlated well with the proximity between the incident beam’s direction and the orientations of the intermolecular interactions. Excellent compatibility was found between the spectra and simulated orientations based on structural information.
- Published
- 2019
- Full Text
- View/download PDF
5. Low-frequency Raman spectroscopy – a versatile technique for material characterization and detection
- Author
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Hagit Aviv, Vinayaka Harshothama Damle, and Yaakov R. Tischler
- Published
- 2023
6. Higher Ultrasonic Frequency Liquid Phase Exfoliation Leads to Larger and Monolayer to Few-Layer Flakes of 2D Layered Materials
- Author
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Ilana Perelshtein, Rajashree Konar, Hagit Aviv, Olga Girshevitz, Madina Telkhozhayeva, Yaakov R. Tischler, Gilbert Daniel Nessim, and Eti Teblum
- Subjects
Materials science ,Silver sulfide ,Sonication ,02 engineering and technology ,engineering.material ,010402 general chemistry ,Digenite ,01 natural sciences ,law.invention ,chemistry.chemical_compound ,Transition metal ,law ,Monolayer ,Electrochemistry ,General Materials Science ,Graphite ,Composite material ,Spectroscopy ,Graphene ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Exfoliation joint ,0104 chemical sciences ,chemistry ,engineering ,0210 nano-technology - Abstract
Among the most reliable techniques for exfoliation of two-dimensional (2D) layered materials, sonication-assisted liquid-phase exfoliation (LPE) is considered as a cost-effective and straightforward method for preparing graphene and its 2D inorganic counterparts at reasonable sizes and acceptable levels of defects. Although there were rapid advances in this field, the effect and outcome of the sonication frequency are poorly understood and often ignored, resulting in a low exfoliation efficiency. Here, we demonstrate that simple mild bath sonication at a higher frequency and low power positively contributes to the thickness, size, and quality of the final exfoliated products. We show that monolayer graphene flakes can be directly exfoliated from graphite using ethanol as a solvent by increasing the frequency of the bath sonication from 37 to 80 kHz. The statistical analysis shows that ∼77% of the measured graphene flakes have a thickness below three layers with an average lateral size of 13 μm. We demonstrate that this approach works for digenite (Cu9S5) and silver sulfide (Ag2S), thus indicating that this exfoliation technique can be applied to other inorganic 2D materials to obtain high-quality few-layered flakes. This simple and effective method facilitates the formation of monolayer/few layers of graphene and transition metal chalcogenides for a wide range of applications.
- Published
- 2021
7. Combining polarized low-frequency Raman with XRD to identify directional structural motifs in a pyrolysis precursor
- Author
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Hagit Aviv, Eliyahu M. Farber, Yaakov R. Tischler, Tal Ben Uliel, David Eisenberg, Marilena Farbinteanu, and Wowa Stroek
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Materials science ,Coordination polymer ,Catalysis ,Physics::Geophysics ,law.invention ,Coordination complex ,chemistry.chemical_compound ,symbols.namesake ,law ,Materials Chemistry ,Physics::Chemical Physics ,Crystallization ,Porosity ,chemistry.chemical_classification ,Hydrogen bond ,Metals and Alloys ,General Chemistry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Crystallography ,chemistry ,Ceramics and Composites ,symbols ,Raman spectroscopy ,Pyrolysis ,Single crystal - Abstract
Long-range structures and dynamics are central to coordination chemistry, yet are hard to identify experimentally. By combining polarized low-frequency Raman spectroscopy with single crystal XRD to study barium nitrilotriacetate, a metal-organic coordination polymer and a useful pyrolysis precursor, we could assign Raman peaks experimentally to layer shear motions and perpendicular hydrogen bond vibrations. These directional long-range interactions further determined the preferred fracture directions during crystallization, establishing an important link between structural motifs in the precursor, and the porosity of the carbon it yields upon pyrolysis.
- Published
- 2021
8. New aqueous energy storage devices comprising graphite cathodes, MXene anodes and concentrated sulfuric acid solutions
- Author
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Gil Bergman, Yury Gogotsi, Doron Aurbach, Yaakov R. Tischler, Fyodor Malchik, Michal Weitman, Hagit Aviv, Bar Gavriel, Nicole Leifer, Reut Cohen, Mikhael D. Levi, Netanel Shpigel, Shay Tirosh, and Gil Goobes
- Subjects
Materials science ,Renewable Energy, Sustainability and the Environment ,Intercalation (chemistry) ,Energy Engineering and Power Technology ,Sulfuric acid ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Cathode ,Energy storage ,0104 chemical sciences ,law.invention ,Anode ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,law ,Electrode ,General Materials Science ,Graphite ,Cyclic voltammetry ,0210 nano-technology - Abstract
The newly emerging demand for ‘beyond-lithium’ electrochemical energy storage systems necessitates the development of alternative options in providing sustainable cost-effective storage capabilities. In pursuit of discovering such a solution, the intercalation of bisulfate anions into graphite in 17 M H2SO4 solutions has been revaluated. Although the insertion process of bisulfate into graphite was extensively studied many years ago, only poor electrochemical performance has been demonstrated. In this work, we discovered the superior performance of the graphite bisulfate system, associated with the electrodes’ fabrication method which presents a high energy density of more than 80 mW h/g and a surprising rate capability (75 mW h/g was obtained at 15 C) alongside impressive long-term stability of more than 1500 cycles with only 5% capacity fading. Potentiostatic intermittent titration technique followed by slow-scan-rate cyclic voltammetry (SSCV) was used to shed light on the bisulfate intercalation process. Combining the bisulfate intercalation into the graphite with a highly reversible proton insertion process into Ti3C2 MXene in such a concentrated acidic environment allows the development of a dual-ion device composed of graphite positive electrode (cathode) and MXene negative electrode (anode). This asymmetric system shows a high energy density of 35 mW h/g, good cyclability and an extended potential window of 1.5 V, demonstrating new opportunities for further developments of intercalation electrodes for large energy storage.
- Published
- 2020
9. Identification of Enantiomers Using Low-Frequency Raman Spectroscopy
- Author
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Vinayaka Harshothama Damle, Hagit Aviv, and Yaakov R. Tischler
- Subjects
Stereoisomerism ,Spectrum Analysis, Raman ,Vibration ,Analytical Chemistry - Abstract
Distinguishing between d and l enantiomers is of important scientific interest, especially for the pharmaceutical industry. Enantiomeric differentiation in the solid form is repeatedly presented as a challenge in the research community. Raman spectroscopy is a nondestructive tool, widely used for the characterization of different materials by probing their vibrational modes. The low-frequency region of the Raman spectrum reveals lattice-level interactions and global fluctuations in the molecule. Lower frequencies correspond to vibrations arising from weaker bonds and long-range interactions and hence are very susceptible to polarization changes. This work presents low-frequency Raman (LFR) spectroscopy as a facile technique to identify enantiomers. The optical setup of conventional Raman spectroscopy is engineered such that the excitation and collection geometries use an asymmetrical focal cone. In addition, a half-wave retarder is added to the excitation path and a Glan-Taylor polarizer is added to the collection path, and these modifications allow us to select the polarization plane for both excitation and collection geometries. The asymmetry in the foci when using a polarized beam for excitation provides different intensities of the collected signal for each polarization plane. In a calibrated system, one can define the chirality of an analyte by comparing the intensity of the LFR signal along orthogonal sets of polarization planes. For nonchiral molecules, the spectral intensity is always higher in the co-polarized plane when compared to the orthogonally depolarized plane, as expected. This contrast in the intensity of Raman spectra serves as a distinct tool for identifying enantiomers.
- Published
- 2022
10. Microcavity enhancement of low‐frequency Raman scattering from a CsPbI 3 thin film
- Author
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Anat Itzhak, Laxman Gouda, Tal Ben Uliel, Hagit Aviv, and Yaakov R. Tischler
- Subjects
Signal enhancement ,symbols.namesake ,Materials science ,business.industry ,symbols ,Optoelectronics ,General Materials Science ,Low frequency ,Thin film ,business ,Raman spectroscopy ,Spectroscopy ,Raman scattering - Published
- 2019
11. Structural Characterization and Room Temperature Low-Frequency Raman Scattering from MAPbI3 Halide Perovskite Films Rigidized by Cesium Incorporation
- Author
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Vinayaka H. Damle, Yaakov R. Tischler, Shay Tirosh, and Laxman Gouda
- Subjects
Materials science ,Absorption spectroscopy ,Analytical chemistry ,Energy Engineering and Power Technology ,Halide ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Ion ,symbols.namesake ,Phase (matter) ,Materials Chemistry ,Electrochemistry ,symbols ,Chemical Engineering (miscellaneous) ,Electrical and Electronic Engineering ,Thin film ,0210 nano-technology ,Raman spectroscopy ,Raman scattering ,Perovskite (structure) - Abstract
The structural instability of organometal halide perovskites (OHP) is one of the major issues concerning commercialization of perovskite solar cells. Probing this intrinsic instability is one of the major milestones and challenging tasks toward enhancing the lifespan of the material. Here we have incorporated Cs ions into methylammonium lead iodide (MAPbI3) films and studied the thin film structural and optical properties. Incorporation of Cs into MAPbI3 leads to formation of both α-CsPbI3 and ∂-CsPbI3 phases, black and yellow, respectively, as indicated by the evolution of the optical band edge and X-ray diffraction (XRD) spectrum. At a concentration of 20% Cs ions, we observe the existence of a stable α-CsPbI3 phase. Incorporating 59% or more Cs ions yields the yellow phase of CsPbI3, due to alloying of Cs with the MAPbI3 matrix. The structural transformations observed in absorption spectra and XRD are confirmed by low-frequency Raman spectroscopy. The thermally induced structural fluctuations in pure M...
- Published
- 2018
12. Unravelling Defect Passivation Mechanisms in Sulfur-treated Sb2Se3
- Author
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Laxman Gouda, Marinus Kunst, Cui W, Friedrich D, Rajiv Ramanujam Prabhakar, Thomas Moehl, Sebastian Siol, van de Krol R, Jihye Suh, Damilola Adeleye, Vinayaka H. Damle, Yaakov R. Tischler, Sudhanshu Shukla, and Tilley D
- Subjects
Materials science ,Photoluminescence ,Passivation ,business.industry ,chemistry.chemical_element ,Carrier lifetime ,Sulfur ,symbols.namesake ,chemistry ,symbols ,Optoelectronics ,Charge carrier ,Spontaneous emission ,business ,Raman spectroscopy ,Spectroscopy - Abstract
Sb2Se3 has emerged as an important photoelectrochemical (PEC) and photovoltaic (PV) material due to its rapid rise in photoconversion efficiencies. However, despite its binary nature, Sb2Se3 has a complex defect chemistry, which reduces the maximum photovoltage that can be obtained. Thus, it is important to understand these defects and to develop passivation strategies in order to further improve this material. In this work, a comprehensive investigation of the charge carrier dynamics of Sb2Se3 and the influence of sulfur treatment on its optoelectronic properties was performed using time resolved microwave conductivity (TRMC), photoluminescence (PL) spectroscopy and low frequency Raman spectroscopy (LFRS). The key finding in this work is that upon sulfur treatment of Sb2Se3, the carrier lifetime is increased by the passivation of deep defects in Sb2Se3 in both the surface region and the bulk, which is evidenced by increased charge carrier lifetime of TRMC decay dynamics, increased radiative recombination efficiency and decreased deep defect level emission (PL), and improved long-range order in the material (LFRS). These findings provide crucial insights into the defect passivation mechanisms in Sb2Se3 paving the way for developing highly efficient PEC and PV devices.
- Published
- 2021
13. Sulfur Treatment Passivates Bulk Defects in Sb 2 Se 3 Photocathodes for Water Splitting
- Author
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Rajiv Ramanujam Prabhakar, Thomas Moehl, Dennis Friedrich, Marinus Kunst, Sudhanshu Shukla, Damilola Adeleye, Vinayaka H. Damle, Sebastian Siol, Wei Cui, Laxman Gouda, Jihye Suh, Yaakov R. Tischler, Roel van de Krol, and S. David Tilley
- Subjects
Biomaterials ,charge carrier dynamics ,Sb2Se3 ,Physique [G04] [Physique, chimie, mathématiques & sciences de la terre] ,photoluminescence spectroscopy ,low‐frequency Raman spectroscopy ,water splitting ,photocathode ,photoelectrochemistry ,TRMC ,Physics [G04] [Physical, chemical, mathematical & earth Sciences] ,Electrochemistry ,time‐resolved microwave conductivity ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Abstract
Sb2Se3 has emerged as an important photoelectrochemical PEC and photovoltaic PV material due to its rapid rise in photoconversion efficiencies. However, Sb2Se3 has a complex defect chemistry, which reduces the maximum photovoltage. Thus, it is important to understand these defects and develop defect passivation strategies in Sb2Se3. A comprehensive investigation of the charge carrier dynamics of Sb2Se3 and the influence of sulfur treatment on its optoelectronic properties is performed using time resolved microwave conductivity TRMC , photoluminescence PL spectroscopy, and low frequency Raman spectroscopy LFR . The key finding in this work is that upon sulfur treatment of Sb2Se3, the carrier lifetime is increased by the passivation of deep defects in Sb2Se3 in both the surface region and the bulk, which is evidenced by increased charge carrier lifetime of TRMC decay dynamics, increased radiative recombination efficiency, decreased deep defect level emission PL , and the emergence of new vibration modes by LFR
- Published
- 2022
14. Microcavity Enhanced Raman Spectroscopy of Fullerene C60 Bucky Balls
- Author
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Yaakov R. Tischler, Hagit Aviv, Miri Sinwani, and Vinayaka H. Damle
- Subjects
Materials science ,Fabrication ,Fullerene ,Instrumentation ,02 engineering and technology ,010402 general chemistry ,lcsh:Chemical technology ,01 natural sciences ,Biochemistry ,Article ,Analytical Chemistry ,symbols.namesake ,lcsh:TP1-1185 ,Electrical and Electronic Engineering ,fullerene C60 ,Range (particle radiation) ,business.industry ,Resolution (electron density) ,021001 nanoscience & nanotechnology ,cers ,dft ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Characterization (materials science) ,Molecular vibration ,symbols ,Optoelectronics ,0210 nano-technology ,business ,Raman spectroscopy ,fullerene c60 - Abstract
Raman spectroscopy is a widely used characterization technique in material science. It is a non-destructive tool with relatively simple instrumentation, and provides intrinsic qualitative information of analytes by probing their vibrational modes. In many cases, Raman enhancement is essential for detecting low-intensity signals in high-noise environments, spectrally unresolved features, and hidden modes. Here we present optical and Raman spectroscopic characterization of fullerene C 60 in a gold microcavity. The fabrication of single-layered gold mirrors is facile, low cost and direct but was proven to give considerably significant enhancement. The findings of this work demonstrate the cavity resonance as a powerful tool in obtaining tunability over individual peak for selective enhancement in the tuned spectral range. The PL of the material within the cavity has demonstrated a red shift assumed to be caused by the low-energy transitions. These transitions are induced by virtual low-energy states generated by the cavity. We further observe that adopting this principle enables resolution of active Raman modes that until now were unobserved. Finally, we assigned the new experimentally observed modes to the corresponding motions calculated by DFT.
- Published
- 2020
15. Synthesis through 3D printing: formation of 3D coordination polymers
- Author
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Gurunathan Thangavel, Shlomo Magdassi, Yaakov R. Tischler, Samuel A. Morris, Pooi See Lee, Oded Halevi, Jingwei Chen, Tal Ben Uliel, and School of Materials Science and Engineering
- Subjects
chemistry.chemical_classification ,3d printed ,Materials science ,Materials [Engineering] ,business.industry ,Coordination polymer ,General Chemical Engineering ,3D printing ,Nanotechnology ,General Chemistry ,Polymer ,Amides ,Complex Networks ,3d printer ,chemistry.chemical_compound ,Monomer ,chemistry ,Coordination network ,business - Abstract
Coordination polymers (CPs) and coordination network solids such as metal–organic frameworks (MOFs) have gained increasing interest during recent years due to their unique properties and potential applications. Preparing 3D printed structures using CP would provide many advantages towards utilization in fields such as catalysis and sensing. So far, functional 3D structures were printed mostly by dispersing pre-synthesized particles of CPs and MOFs within a polymerizable carrier. This resulted in a CP active material dispersed within a 3D polymeric object, which may obstruct or impede the intrinsic properties of the CP. Here, we present a new concept for obtaining 3D free-standing objects solely composed of CP material, starting from coordination metal complexes as the monomeric building blocks, and utilizing the 3D printer itself as a tool to in situ synthesize a coordination polymer during printing, and to shape it into a 3D object, simultaneously. To demonstrate this, a 3D-shaped nickel tetra-acrylamide monomeric complex composed solely of the CP without a binder was successfully prepared using our direct print-and-form approach. We expect that this work will open new directions and unlimited potential in additive manufacturing and utilization of CPs. National Research Foundation (NRF) Published version This research was supported by the grants from the National Research Foundation, Prime Minister's Office, Singapore under its Campus of Research Excellence and Technological Enterprise (CREATE) Programme, Nanomaterials for Energy and Water-Energy Nexus, and by the Hebrew university fund for PhD students.
- Published
- 2020
16. Chiral Purity of Crystals Using Low-Frequency Raman Spectroscopy
- Author
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Hagit Aviv, Yaakov R. Tischler, Yitzhak Mastai, and Irena Nemtsov
- Subjects
Quantitative Biology::Biomolecules ,Circular dichroism ,Materials science ,Hydrogen bond ,Analytical chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,symbols.namesake ,Enantiopure drug ,X-ray crystallography ,symbols ,Physical and Theoretical Chemistry ,Enantiomer ,0210 nano-technology ,Enantiomeric excess ,Chirality (chemistry) ,Raman spectroscopy - Abstract
The pharmaceutical industry is in need of new techniques to identify the chirality of solids due to regulatory and safety concerns regarding the biological activity of enantiomers. In this study, we present for the first time the application of low-frequency Raman spectroscopy as a new and sensitive method for analyzing the chiral purity of crystals. Using this method, we were able to identify small amounts, as low as 1 % w/w, of an enantiomer in racemic crystals. To demonstrate the capabilities of the method, we used a model system based on chiral crystals of enantiopure, racemic crystals and their mixtures in various ratios. We found that the low-frequency Raman spectra of racemic and enantiopure crystals are significantly different, reflecting the different hydrogen bond networks. Moreover, a comparison of the sensitivity of enantiomeric excess in chiral crystals to that of circular dichroism and X-ray diffraction measurements showed that low-frequency Raman attains high sensitivity comparable to chiral optical methods used for solutions. Overall, our proposed approach of using Raman spectroscopy for determining enantiomeric excess in crystals is simple, fast, and offers a high degree of chiral sensitivity.
- Published
- 2018
17. Vibrational Strong Light–Matter Coupling Using a Wavelength-Tunable Mid-infrared Open Microcavity
- Author
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Yaakov R. Tischler, Alexander Palatnik, Rena Yitzhari, and Omree Kapon
- Subjects
Materials science ,Mid infrared ,Physics::Optics ,02 engineering and technology ,01 natural sciences ,chemistry.chemical_compound ,0103 physical sciences ,Physical and Theoretical Chemistry ,Methyl methacrylate ,Thin film ,Fourier transform infrared spectroscopy ,010306 general physics ,Absorption (electromagnetic radiation) ,Astrophysics::Galaxy Astrophysics ,Coupling ,business.industry ,Resonance ,021001 nanoscience & nanotechnology ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Wavelength ,General Energy ,chemistry ,Optoelectronics ,0210 nano-technology ,business - Abstract
An open microcavity (OMC) is an optical system that is composed of two mirrors, where one is fixed and the second is on a movable stage. OMCs enable tuning the optical resonances of the system and insertion of different materials between the mirrors and are therefore of large scientific interest due to their many potential applications. Strong light–matter coupling of the vibrational transitions of organic molecules with the optical modes of a microcavity generates new polaritonic states in the mid-infrared (mid-IR) spectral region. Here we achieve strong light–matter coupling in the mid-IR using a low optical-loss OMC that is wavelength-tunable via a piezoelectric actuator. A thin film of poly(methyl methacrylate) (PMMA) was deposited onto one of the mirrors to couple the narrow and intense absorption peak of the carbonyl stretch mode at 1731 cm–1 to the OMC. Polaritonic states are observed in FTIR transmission measurements when an OMC resonance is matched to the carbonyl stretch. By dynamically varying ...
- Published
- 2017
18. Replacing a Century Old Technique – Modern Spectroscopy Can Supplant Gram Staining
- Author
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Elad Goldberg, Yaron Aviv, Yaakov R. Tischler, Hagit Aviv, and Shirly Berezin
- Subjects
Gram-negative bacteria ,Gram-positive bacteria ,Science ,02 engineering and technology ,010402 general chemistry ,Tip-enhanced Raman spectroscopy ,Gram-Positive Bacteria ,Spectrum Analysis, Raman ,01 natural sciences ,Article ,Microbiology ,law.invention ,law ,Gram-Negative Bacteria ,Spectroscopy ,Pathogen ,Gram ,Multidisciplinary ,biology ,Cell Membrane ,021001 nanoscience & nanotechnology ,biology.organism_classification ,0104 chemical sciences ,Gram staining ,Biochemistry ,Phenazines ,Medicine ,Gentian Violet ,0210 nano-technology ,Bacteria - Abstract
Rapid and accurate Gram differentiation is paramount as the first step of pathogen identification and antibiotics administration. However, the current method requires additional reagents, is time-consuming, and is operator dependent. Here we show the principle of tip enhanced Raman spectroscopy (TERS) can differentiate between Gram negative and positive species, by detecting the changes in tip-enhancement in the Raman scattering from the bacteria’s lipid-bilayer membrane, which specifically enhances Gram negative bacteria.
- Published
- 2017
19. Low Cost Method for Generating Periodic Nanostructures by Interference Lithography Without the Use of an Anti-Reflection Coating
- Author
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Hagit Aviv, Merav Muallem, Omree Kapon, Alex Palatnik, and Yaakov R. Tischler
- Subjects
Materials science ,Holography ,Nanotechnology ,02 engineering and technology ,Substrate (printing) ,engineering.material ,Photoresist ,01 natural sciences ,law.invention ,Interference lithography ,010309 optics ,Coating ,Interference (communication) ,law ,0103 physical sciences ,General Materials Science ,business.industry ,Mechanical Engineering ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Laser ,Mechanics of Materials ,engineering ,Optoelectronics ,0210 nano-technology ,business ,Layer (electronics) - Abstract
Interference lithography has proven to be a useful technique for generating periodic sub-diffraction limited nanostructures. Interference lithography can be implemented by exposing a photoresist polymer to laser light using a two-beam arrangement or a one-beam configuration based on a Lloyd’s Mirror Interferometer. For typical photoresist layers, an anti-reflection coating must be deposited on the substrate to prevent adverse reflections from cancelling the holographic pattern of the interfering beams. For silicon substrates, such coatings are typically multilayered and complex in composition. By thinning the photoresist layer to a thickness well below the quarter wavelength of the exposing beam, we demonstrate that interference gratings can be generated without an anti-reflection coating on the substrate. We used ammonium dichromate doped polyvinyl alcohol as the positive photoresist because it provides excellent pinhole free layers down to thicknesses of 40 nm, and can be cross-linked by a low-cost single mode 457 nm laser and etched in water. Gratings with a period of 320 nm and depth of 4 nm were realized, as well as a variety of morphologies depending on the photoresist thickness. This simplified interference lithography technique promises to be useful for generating periodic nanostructures with high fidelity and minimal substrate treatments.
- Published
- 2017
20. Spectroscopic gas identification using piezo tuned micro-cavity enhanced Raman scattering (Conference Presentation)
- Author
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Omree Kapon, Roman Yasinov, Alan Feinstein, Nir Karasikov, Vinayaka H. Damle, Yaakov R. Tischler, and Tal Ben Uliel
- Subjects
Materials science ,Spectrometer ,Scattering ,business.industry ,Infrared spectroscopy ,Laser ,Signal ,Collimated light ,law.invention ,symbols.namesake ,law ,symbols ,Optoelectronics ,Raman spectroscopy ,business ,Astrophysics::Galaxy Astrophysics ,Raman scattering - Abstract
Raman spectroscopy has been shown to be a powerful spectroscopic approach for detecting gases. It is capable of detecting gases that possess no infrared absorption feature, such as diatomics, and it also does not suffer from signal saturation as can be the case for transmission measurements. However, the Achilles heel of Raman based gas detection is the low scattering cross section. Here we show that introducing gas into an optical open micro-cavity (OMC) can greatly enhance the Raman signal. The enhancement comes from 2 factors: namely confining the light longer in the gas containing volume, hence strengthening the light-matter interaction, and also directing the Raman scattering in a more collimated fashion towards the detector. The OMC has been designed such that the separation between the mirrors is piezo controlled, hence it is possible to scan the micro-cavity resonances and tune the OMC to a particular Raman transition. Using the OMC, with laser excitation at 532 nm, we show detection of several gases simultaneously such as nitrogen and oxygen, and discuss prospects for boosting the limit of detection. The presentation will cover the design consideration of the Tip, Tilt, Z microcavity having a range of 40 micron and a positioning resolution of 10 nm. The design comprises an intrinsic position to allow close loop operation. Response time is in the msec range to facilitate fast scanning. The spectrometer set up will be presented as well as representative experimental results.
- Published
- 2019
21. 2D Transition Metal Dichalcogenides for Solution-Processed Organic and Perovskite Solar Cells
- Author
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K. Petridis, G. Kakavelakis, I. Kaliakatsos, Yaakov R. Tischler, and Laxman Gouda
- Subjects
Materials science ,Silicon ,business.industry ,Graphene ,chemistry.chemical_element ,Nanotechnology ,Energy storage ,Solution processed ,law.invention ,Transition metal ,chemistry ,law ,Photovoltaics ,Photonics ,business ,Perovskite (structure) - Abstract
The construction of low cost, printable compatible, solution processed, of high performance, stable solar cells is one of the scientific milestones of the next ten years. The discovery of graphene launched a new era in the materials science, and the research implemented in the exceptional properties of the two-dimensional (2D) materials. The chemical, physical, electrical and mechanical properties of 2D materials match with the requirements that the various building blocks of the third-generation photovoltaics should have in order for these devices to deliver exceptional performance and become attractive alternatives to silicon-based solar cells. The 2D library of materials expands in a very high pace and nowadays includes 150 exotic layered materials. Among them are the transition metal dichalcogenides (2D-TMDs). Recent advances in atomically thin 2D-TMDs (e.g., MoS2, WS2, MoSe2 and WSe2) have introduced numerous promising technologies in nanotechnologies, photonics, sensing, energy storage and solar cells to name few. This chapter highlights the contributions of 2D-TMDs toward the construction of high efficiency and of long lifetime, solution-processed organic and perovskite solar cells.
- Published
- 2019
22. Solid-State Rhodamine 6G Microcavity Laser
- Author
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Alexander Palatnik and Yaakov R. Tischler
- Subjects
Materials science ,Physics::Optics ,02 engineering and technology ,Dielectric ,010402 general chemistry ,01 natural sciences ,law.invention ,Vertical-cavity surface-emitting laser ,Rhodamine 6G ,chemistry.chemical_compound ,law ,Dielectric mirror ,Electrical and Electronic Engineering ,Dye laser ,business.industry ,021001 nanoscience & nanotechnology ,Laser ,Optical microcavity ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,chemistry ,Optoelectronics ,0210 nano-technology ,business ,Lasing threshold - Abstract
In this letter, we demonstrate lasing from Rhodamine 6G in a microcavity organic vertical cavity surface emitting laser (VCSEL) in solid state. We adopted an original approach to forming thin films of Rhodamine 6G doped into a poly(methyl methacrylate) (PMMA) host matrix and to integrating them in a dielectric microcavity architecture. We dissolved the materials in dimethylformamide and then spin coated the gain layer onto a planar dielectric mirror in an anhydrous environment to prevent premature precipitation of the PMMA. The second dielectric mirror was positively curved and was positioned on top of the gain layer to form a VCSEL with a tunable cavity resonance and a quality factor exceeding $Q = 1500$ . We optically excited the device through one of the cavity resonances using femtosecond pulses and observed lasing above a threshold of $17 \pm 3 ~\mu \text{J}$ /cm2 of absorbed energy. The lasing emission followed the polarization of the pump and narrowed from 0.85 to 0.05 nm.
- Published
- 2016
23. Strong Light-Matter Coupling and Hybridization of Molecular Vibrations in a Low-Loss Infrared Microcavity
- Author
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Merav Muallem, Alexander Palatnik, Yaakov R. Tischler, and Gilbert Daniel Nessim
- Subjects
Materials science ,Light ,Spectrophotometry, Infrared ,Infrared ,Physics::Optics ,02 engineering and technology ,Methylmethacrylate ,Vibration ,01 natural sciences ,Molecular physics ,law.invention ,law ,Dispersion relation ,0103 physical sciences ,Polariton ,General Materials Science ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,010306 general physics ,Absorption (electromagnetic radiation) ,Condensed Matter::Quantum Gases ,Condensed Matter::Other ,business.industry ,Resonance ,Dimethylformamide ,021001 nanoscience & nanotechnology ,Distributed Bragg reflector ,Optical microcavity ,Molecular vibration ,Solvents ,Optoelectronics ,0210 nano-technology ,business - Abstract
Hybridized polaritons are generated by simultaneously coupling two vibrational modes of two different organic materials to the resonance of a low-loss infrared optical microcavity. A thin film of poly methyl methacrylate with solvent molecules of dimethylformamide trapped inside provided two spectrally narrow, closely spaced carbonyl stretches with absorption peaks at 1731 and 1678 cm(-1). Situating this film in a microcavity based on Ge/ZnS distributed Bragg reflector mirrors produced three distinct polariton branches in the dispersion relation due to hybridization of the vibrational resonances. Two anticrossings were observed with Rabi splittings of 9.6 and 5.2 meV, between the upper-to-middle and middle-to-lower polariton branches, respectively. This system marks the first demonstration of polariton hybridization between a solid and solvent molecules and can open new paths toward chemical reaction modification and energy transfer studies in the mid-infrared spectral range.
- Published
- 2016
24. Third-Order Optical Nonlinearities in Organometallic Methylammonium Lead Iodide Perovskite Thin Films
- Author
-
Basanth S. Kalanoor, Laxman Gouda, Yaakov R. Tischler, Ronen Gottesman, Shay Tirosh, Eynav Haltzi, and Arie Zaban
- Subjects
Materials science ,Kerr effect ,Physics::Optics ,02 engineering and technology ,010402 general chemistry ,7. Clean energy ,01 natural sciences ,law.invention ,Optics ,law ,Solar cell ,Z-scan technique ,Electrical and Electronic Engineering ,Thin film ,Perovskite (structure) ,business.industry ,Nonlinear optics ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Optoelectronics ,sense organs ,0210 nano-technology ,business ,Lasing threshold ,Refractive index ,Biotechnology - Abstract
With solar conversion efficiencies surpassing 20%, organometallic perovskites show tremendous promise for solar cell technology. Their high brightness has also led to demonstrations of lasing and power-efficient electroluminescence. Here we show that thin films of methylammonium lead iodide, prepared by solution processing at temperatures not exceeding 100 °C, exhibit a highly nonlinear intensity-dependent refractive index due to changes in the free-carrier concentration and for femtosecond excitation at higher intensities undergo saturation that can be attributed to the Pauli blocking effect. Nonlinear refractive index and nonlinear absorption coefficients were obtained by the Z-scan technique, performed simultaneously in open- and closed-aperture configurations. Both nanosecond- and femtosecond-pulsed lasers at multiple wavelengths were used in order to distinguish between the mechanisms inducing the nonlinearities. The magnitude and sign of the nonlinear refractive index n2 were determined. For resonan...
- Published
- 2016
25. Strong light-matter coupling between a molecular vibrational mode in a PMMA film and a low-loss mid-IR microcavity
- Author
-
Yaakov R. Tischler, Merav Muallem, Gilbert Daniel Nessim, and Alex Palatnik
- Subjects
Condensed Matter::Quantum Gases ,Materials science ,Condensed Matter::Other ,business.industry ,Infrared ,Physics::Optics ,General Physics and Astronomy ,Resonance ,02 engineering and technology ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,Wavelength ,Laser linewidth ,0103 physical sciences ,Polariton ,Optoelectronics ,Photonics ,010306 general physics ,0210 nano-technology ,business ,Absorption (electromagnetic radiation) ,Astrophysics::Galaxy Astrophysics - Abstract
Microcavity devices exhibiting strong light-matter coupling in the mid-infrared spectral range offer the potential to explore exciting open physical questions pertaining to energy transfer between heat and light and can lead to a new generation of efficient wavelength tunable mid-infrared sources of coherent light based on polariton Bose-Einstein Condensation. Vibrational transitions of organic molecules, which often have strong absorption peaks in the infrared and considerably narrower linewidths than organic excitonic resonances, can generate polaritonic states in the mid-infrared spectral range using microcavity devices. Here, narrow linewidth polaritonic resonances are exhibited in the mid-infrared by coupling the carbonyl stretch vibrational transition of a polymethyl methacrylate film to the photonic resonance of a low optical-loss mid-infrared microcavity, which consisted of two Ge/ZnS dielectric Bragg reflectors. Rabi-splitting of 14.3 meV is observed, with a 4.4 meV polariton linewidth at anti-crossing. The large Rabi-splitting relative to linewidth indicates efficient impedance-matching between the bare vibrational and photonic states, and suggests molecular-vibration polaritons incorporated in dielectric microcavities can be an enabling step towards realizing polariton optical switching and polariton condensation in the mid-infrared spectral range.
- Published
- 2015
26. Raman scattering obtained from laser excitation of MAPbI3 single crystal
- Author
-
Shalom Avadyayev, Omree Kapon, Vinayaka H. Damle, Chenyi Yi, Minghao Li, Hagit Aviv, Junjie Zhou, Tal Ben-Uliel, and Yaakov R. Tischler
- Subjects
Materials science ,business.industry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,0104 chemical sciences ,law.invention ,symbols.namesake ,Tetragonal crystal system ,law ,symbols ,Optoelectronics ,General Materials Science ,Orthorhombic crystal system ,Laser power scaling ,0210 nano-technology ,business ,Raman spectroscopy ,Single crystal ,Raman scattering ,Perovskite (structure) - Abstract
Finding renewable energy sources is of paramount importance to meet the increasing global energy demand whilst minimizing the impact on the environment. The research community has focused on solar energy as it is endlessly available, and have ranked the methylammonium lead iodide (MAPbI3) as one of the most promising candidate amongst perovskite solar cells. Despite its high efficiency, the MAPbI3 is sensitive to humidity, light, and temperature, its instability affects primarily on the crystalline structure and eventually leads to degradation. Three crystalline structures are known for this material, orthorhombic, tetragonal, and cubic which exist in different temperatures. Here we report on several processes detected from laser excitation of MAPbI3 single crystal at ambient conditions. A phase transition from tetragonal to cubic phase was induced by excitation of over 15 mW laser power. The phases were characterized by LF-Raman and photoluminescence, taken simultaneously with the increase of exciting laser power and the spectral changes were assigned to the structural differences. In addition, Raman stimulation of iodine vapors signal was observed, those vapors were generated from the core of the focus wherein the highest temperature led to degradation. The stimulated Raman phenomenon was enabled due to the unique properties of the MAPbI3 single crystal and revealed viability to use this material for additional applications in other research fields.
- Published
- 2020
27. Characterization of peptides self-assembly by low frequency Raman spectroscopy
- Author
-
Yaakov R. Tischler, Maria Ronen, Izhar Ron, Basanth S. Kalanoor, Ziv Oren, and Doron Gerber
- Subjects
chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Materials science ,Hydrogen bond ,General Chemical Engineering ,010401 analytical chemistry ,Peptide ,General Chemistry ,Low frequency ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Hydrophobic effect ,Crystallography ,symbols.namesake ,Dynamic light scattering ,chemistry ,symbols ,Self-assembly ,Spectroscopy ,Raman spectroscopy - Abstract
Low Frequency Vibrational (LFV) modes of peptides and proteins are attributed to the lattice vibrations and are dependent on their structural organization and self-assembly. Studies taken in order to assign specific absorption bands in the low frequency range to self-assembly behavior of peptides and proteins have been challenging. Here we used a single stage Low Frequency Raman (LF-Raman) spectrometer to study a series of diastereomeric analogue peptides to investigate the effect of peptides self-assembly on the LF-Raman modes. The structural variation of the diastereomeric analogues resulted in distinct self-assembly groups, as confirmed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) data. Using LF-Raman spectroscopy, we consistently observed discrete peaks for each of the self-assembly groups. The correlation between the spectral features and structural morphologies was further supported by principal component analysis (PCA). The LFV modes provide further information on the degrees of freedom of the entire peptide within the higher order organization, reflecting the different arrangement of its hydrogen bonding and hydrophobic interactions. Thus, our approach provides a simple and robust complementary method to structural characterization of peptides assemblies.
- Published
- 2018
28. Synthesis and characterization of a J-aggregating TDBC derivative in solution and in Langmuir–Blodgett films
- Author
-
Yaakov R. Tischler and Hagit Aviv
- Subjects
Photoluminescence ,Absorption spectroscopy ,Biophysics ,Analytical chemistry ,General Chemistry ,Condensed Matter Physics ,Biochemistry ,Fluorescence ,Langmuir–Blodgett film ,Atomic and Molecular Physics, and Optics ,symbols.namesake ,chemistry.chemical_compound ,chemistry ,Stokes shift ,Monolayer ,symbols ,Cyanine ,J-aggregate - Abstract
Here we present the synthesis and optical characterization of a new amphiphilic cyanine dye, 1,1′-dioctadecane-3,3′-di(4-sulfobutyl)-5,5′,6,6′-tetrachloro-benzimidazolocarbo-cyanine (C18S4). C18S4 is a derivative of the heavily studied J-aggregating cyanine dye TDBC that was designed specifically for creating stable amphiphilic monolayers when spread at an air–water interface. Unlike TDBC, which readily J-aggregates in water, we show that C18S4 introduced into water tends to produce micelles with monomeric spectral properties and only exhibits strong J-aggregation after an emulsification procedure and a week of dye reorganization. When deposited on a Langmuir Blodgett (LB) trough, C18S4 forms a stable monolayer with a repeatable isotherm. Layers transferred via LB deposition to a functionalized glass substrate show pronounced J-aggregation, depending on the surface transfer pressure. Layers transferred at 35 mN/m present an intense narrow absorption spectrum peaked at λ =589 nm with FWHM=523 cm −1 (18 nm). The accompanying fluorescence shows a narrow spectrum with FWHM=332 cm −1 (11.5 nm) and a Stokes shift less than 1 nm. The ability to create J-aggregates of C18S4 via LB deposition provides control over the J-aggregation process of TDBC-like molecules and can ultimately lead to tuning the J-aggregate coupling for specific experiments and applications.
- Published
- 2015
29. Super-Resolved Raman Spectra of Toluene and Toluene–Chlorobenzene Mixture
- Author
-
Dror Malka, Garry Berkovic, Yaakov R. Tischler, and Zeev Zalevsky
- Subjects
Resolution (mass spectrometry) ,Chemistry ,Analytical chemistry ,Physics::Optics ,Toluene ,Atomic and Molecular Physics, and Optics ,Spectral line ,Analytical Chemistry ,Filter (large eddy simulation) ,Laser linewidth ,symbols.namesake ,chemistry.chemical_compound ,Chlorobenzene ,symbols ,Physics::Chemical Physics ,Raman spectroscopy ,Spectroscopy ,Fabry–Pérot interferometer - Abstract
In this paper, we present a method for “super-resolved” Raman spectroscopy which improves the resolution of obtained spectra. Experimental investigations were carried out on the spectra of toluene and a toluene–chlorobenzene mixture. A tunable Fabry–Perot filter is added to the detection channel and by measuring the spectra for several states of the filter a spectrum of higher resolution can be obtained after a decoding process. We demonstrate both a reduced linewidth in the pure toluene spectra and partial separation of the two overlapping peaks in the mixture.
- Published
- 2015
30. Characterization of Crystal Chirality in Amino Acids Using Low-Frequency Raman Spectroscopy
- Author
-
Hagit Aviv, Irena Nemtsov, Yitzhak Mastai, and Yaakov R. Tischler
- Subjects
Chemistry ,Scattering ,02 engineering and technology ,Crystal structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Spectral line ,0104 chemical sciences ,Crystal ,Crystallography ,symbols.namesake ,Enantiopure drug ,symbols ,Side chain ,Physical and Theoretical Chemistry ,0210 nano-technology ,Chirality (chemistry) ,Raman spectroscopy - Abstract
We present a new method for differentiating racemic crystals from enantiopure crystals. Recently, developments in optical filters have enabled the facile use of Raman spectroscopy to detect low-frequency vibrational (LFV) modes. Here, for the first time, we use Raman spectroscopy to characterize the LFV modes for crystalline organic materials composed of chiral molecules. The LF-Raman spectra of racemic and enantiopure crystals exhibit a significant variation, which we attribute to different hydrogen-bond networks in the chiral crystal structures. Across a representative set of amino acids, we observed that when comparing racemic versus enantiopure crystals, the available LFV modes and their relative scattering intensity are strong functions of side chain polarity. Thus, LF-Raman can be used as a method that is complementary to the currently used methods for characterizing crystal chirality due to simpler, faster, and more sensitive measurements, along with the small sample size required, which is limited by the laser-beam diameter in the focus.
- Published
- 2017
31. Microcavity Laser Based on a Single Molecule Thick High Gain Layer
- Author
-
Alexander Palatnik, Yaakov R. Tischler, and Hagit Aviv
- Subjects
Dye laser ,Materials science ,business.industry ,Exciton ,General Engineering ,Physics::Optics ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,Optical microcavity ,0104 chemical sciences ,law.invention ,Vertical-cavity surface-emitting laser ,law ,Monolayer ,Optoelectronics ,General Materials Science ,Photonics ,0210 nano-technology ,business ,Lasing threshold - Abstract
The ability to confine excitons within monolayers has led to fundamental investigations of nonradiative energy transfer, super-radiance, strong light–matter coupling, high-efficiency light-emitting diodes, and recently lasers in lateral resonator architectures. Vertical cavity surface emitting lasers (VCSELs), in which lasing occurs perpendicular to the device plane, are critical for telecommunications and large-scale photonics integration, however strong optical self-absorption and low fluorescence quantum yields have thus far prevented coherent emission from a monolayer microcavity device. Here we show lasing from a monolayer VCSEL using a single molecule thick film of amphiphilic fluorescent dye, assembled via Langmuir–Blodgett deposition, as the gain layer. Threshold was observed when 5% of the molecules were excited (4.4 μJ/cm2). At this level of excitation, the optical gain in the monolayer exceeds 1056 cm–1. High localization of the excitons in the VCSEL gain layer can enhance their collective emis...
- Published
- 2017
32. Deposition and Characterization of Roughened Surfaces
- Author
-
Hagit Aviv, Shirly Berezin, Miri Sinwani, Ortal Agai, and Yaakov R. Tischler
- Subjects
Materials science ,02 engineering and technology ,01 natural sciences ,symbols.namesake ,chemistry.chemical_compound ,0103 physical sciences ,Polymer chemistry ,Electrochemistry ,General Materials Science ,Thin film ,010306 general physics ,Porosity ,Spectroscopy ,chemistry.chemical_classification ,Spin coating ,Polyvinyl acetate ,Surfaces and Interfaces ,Polymer ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,chemistry ,Chemical engineering ,symbols ,Polystyrene ,Polymer blend ,0210 nano-technology ,Raman spectroscopy - Abstract
Phase separation occurs whenever a solvent leaves a solution of strongly incompatible polymers. This can happen in bulk and in films. Films can be tailored as substrates for multiple applications such as solar cells, surface catalysis, and antireflection coatings. In this study, polystyrene (PS) was dissolved with polyvinyl acetate (PVAc) in different ratios using chlorobenzene as the solvent. Thin films of different ratios of PS and PVAc were deposited on glass via spin coating. The deposited films were investigated for their morphology, strain, surface area, and Raman scattering. The incompatibility between the two polymers leads to the growth of roughened PVAc islands supported by the PS matrix. A down shift in the Raman PVAc signal was observed in the combined film as compared with a 100% PVAc film, which was attributed to the high strain of PVAc that grew as tips. As the PVAc concentration in the polymer blend increases, the porous regions in the film expand and the amount and height of PVAc tips increase as well, up to the point where the pores merge to create a uniform surface. The optimal ratio for the deposition of a uniformly roughened surface is 75% PVAc and 25% PS. For demonstrating a possible application, we applied the partially roughened surface as a substrate for surface-enhanced Raman scattering and demonstrated at least 500% increase in the signal intensity measured in roughened areas. This is explained by the rod effect from the PVAc tips.
- Published
- 2017
33. Millimeter-Tall Carpets of Vertically Aligned Crystalline Carbon Nanotubes Synthesized on Copper Substrates for Electrical Applications
- Author
-
Eti Teblum, Malachi Noked, Judith Grinblat, Yaakov R. Tischler, Anna Kremen, Merav Muallem, Doron Aurbach, Gilbert Daniel Nessim, and Yafit Fleger
- Subjects
Materials science ,Diffusion ,chemistry.chemical_element ,Nanotechnology ,Chemical vapor deposition ,Carbon nanotube ,Copper ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,law.invention ,General Energy ,chemistry ,Chemical engineering ,Electrical resistivity and conductivity ,law ,Physical and Theoretical Chemistry ,Layer (electronics) ,Water vapor - Abstract
We synthesized millimeter-tall, dense carpets of crystalline CNTs on nonpolished copper substrates with a thin Al2O3 (below 10 nm) underlayer and Fe (1.2 nm) layer as a catalyst using chemical vapor deposition (CVD). Preheating of the hydrocarbon precursor gases and in-situ formation of controlled amounts of water vapor were critical process parameters. High-resolution microscopy showed that the CNTs were crystalline with lengths up to a millimeter. Electrical conduction between the CNTs and the copper substrate was demonstrated using multiple methods (probe station, electrodeposition, and hydrolysis of water). Through TEM characterizations of cross sections, we demonstrated that copper diffusion into the alumina layer during the thermal process was the key to explain the observed electrical conductivity. Additionally, the high electrical conductivity of a thermally processed sample compared to the insulating behavior of a pristine sample confirmed the mechanistic hypothesis. Adsorption isotherm measureme...
- Published
- 2014
34. Synthesis of an amphiphilic rhodamine derivative and characterization of its solution and thin film properties
- Author
-
Yoni Ramon, Yaakov R. Tischler, Hagit Aviv, Sivan Harazi, and Dillon Schiff
- Subjects
Sulfonyl ,chemistry.chemical_classification ,Materials science ,Metals and Alloys ,Quantum yield ,Surfaces and Interfaces ,Photochemistry ,Micelle ,Langmuir–Blodgett film ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Rhodamine ,chemistry.chemical_compound ,chemistry ,Amphiphile ,Monolayer ,Materials Chemistry ,Polystyrene - Abstract
Here we present characterization of solution and thin film properties of Lissamine rhodamine B sulfonyl didodecyl amine (LRSD), an amphiphilic derivative of rhodamine. LRSD was synthesized by functionalizing Lissamine rhodamine B sulfonyl chloride (LRSC) with didodecylamine via a straightforward sulfonylation reaction. LRSD's long alkane chains make it highly soluble in chloroform, with a marked increase in brightness compared to the starting material. LRSD is shown to form well-defined robust micelles in water, without the addition of a co-surfactant and stable monolayers at the air–water interface. The greater lipophilicity of LRSD also enables doping into non-polar polymeric host matrices such as polystyrene with less aggregation and hence higher fluorescence quantum yield than LRSC or even rhodamine B. The monolayers of LRSD were prepared via Langmuir–Blodgett deposition and showed shifts in the photoluminescence peak from 575 nm to 595 nm, as the surface pressure is varied from 3 mN/m to 11 mN/m.
- Published
- 2014
35. Raman and Photoluminescence Properties of Red and Yellow Rubrene Crystals
- Author
-
Miri Sinwani and Yaakov R. Tischler
- Subjects
Diffraction ,Materials science ,Photoluminescence ,Crystal orientation ,Physics::Optics ,Polarization Microscopy ,Spectral line ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,Crystallography ,chemistry.chemical_compound ,General Energy ,chemistry ,Condensed Matter::Superconductivity ,symbols ,Astrophysics::Solar and Stellar Astrophysics ,Physical and Theoretical Chemistry ,Raman spectroscopy ,Rubrene - Abstract
In this article, we use a combination of micro-Raman and microphotoluminescence measurements to demonstrate that rubrene single crystals, which appear as yellow platelets and red needles, are two distinct orientations of the same crystallographic unit cell. As confirmed by X-ray diffraction and polarization microscopy, we show that red and yellow crystals represent the crystallographic orientations (020) and (002), respectively, with the crystallographic c-axis being the optically activated orientation in red crystals and the b-axis in yellow crystals. Raman measurements of red crystals are characterized by a pronounced Raman shift at 217 cm–1, which to the best of our knowledge is the first report of this peak at its predicted spectral position. The Raman and photoluminescence spectra obtained from yellow crystals change abruptly at their borders into the spectra of red crystals, confirming the distinct spectroscopic properties of each crystal orientation. The combination of Raman and photoluminescence m...
- Published
- 2014
36. Multiprobe NSOM fluorescence
- Author
-
Shirly Berezin, Basanth S. Kalanoor, Yaakov R. Tischler, Yuval Garini, and Hesham Taha
- Subjects
spm ,Materials science ,business.industry ,multiprobe ,Physics ,QC1-999 ,fret ,nsom ,tuning fork probe ,Fluorescence ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,lumogen ,Förster resonance energy transfer ,Optoelectronics ,Near-field scanning optical microscope ,Electrical and Electronic Engineering ,business ,Biotechnology - Abstract
In this paper, we demonstrate simultaneous AFM/NSOM using a dual-tip normal tuning-fork based scanning probe microscope. By scanning two SPM probes simultaneously, one dedicated for AFM with a standard tip diameter of 20 nm, and the second having a 150 nm aperture NSOM fiber with 200 nm thick gold coating, we combine the benefits of ∼20 nm spatial resolution from the AFM tip with the spectral information of a near-field optical probe. The combination of simultaneous dual-tip scanning enables us to decouple the requirements for high resolution topography and probe functionality. Our method represents a marked shift from previous applications of multi-probe SPM where essentially a pump-probe methodology is implemented in which one tip scans the area around the second. As a model system, we apply dual-tip AFM/NSOM scanning to a sample of spin-cast nano-clustered Lumogen dyes, which show remarkable brightness and photochemical stability. We observe morphology features with a resolution of 20 nm, and a near-field optical resolution of 150 nm, validating our approach.
- Published
- 2014
37. Quantum Efficiency and Bandgap Analysis for Combinatorial Photovoltaics: Sorting Activity of Cu–O Compounds in All-Oxide Device Libraries
- Author
-
Assaf Y. Anderson, Arie Zaban, Yaniv Bouhadana, Benjamin Kupfer, Hagit Aviv, Yaakov R. Tischler, Hannah-Noa Barad, Sven Rühle, and Eli Rosh-Hodesh
- Subjects
Chemical substance ,heterojunction ,Band gap ,Photovoltaics ,Combinatorial Chemistry Techniques ,Thin film ,photophysics ,photochemistry ,nanotechnology ,business.industry ,Chemistry ,Lasers ,Heterojunction ,Oxides ,General Chemistry ,General Medicine ,Photochemical Processes ,thin films ,continuous compositional spread ,Optoelectronics ,Quantum Theory ,Quantum efficiency ,business ,Science, technology and society ,Copper ,Research Article - Abstract
All-oxide-based photovoltaics (PVs) encompass the potential for extremely low cost solar cells, provided they can obtain an order of magnitude improvement in their power conversion efficiencies. To achieve this goal, we perform a combinatorial materials study of metal oxide based light absorbers, charge transporters, junctions between them, and PV devices. Here we report the development of a combinatorial internal quantum efficiency (IQE) method. IQE measures the efficiency associated with the charge separation and collection processes, and thus is a proxy for PV activity of materials once placed into devices, discarding optical properties that cause uncontrolled light harvesting. The IQE is supported by high-throughput techniques for bandgap fitting, composition analysis, and thickness mapping, which are also crucial parameters for the combinatorial investigation cycle of photovoltaics. As a model system we use a library of 169 solar cells with a varying thickness of sprayed titanium dioxide (TiO2) as the window layer, and covarying thickness and composition of binary compounds of copper oxides (Cu-O) as the light absorber, fabricated by Pulsed Laser Deposition (PLD). The analysis on the combinatorial devices shows the correlation between compositions and bandgap, and their effect on PV activity within several device configurations. The analysis suggests that the presence of Cu4O3 plays a significant role in the PV activity of binary Cu-O compounds.
- Published
- 2014
38. New Method to Study the Vibrational Modes of Biomolecules in the Terahertz Range Based on a Single-Stage Raman Spectrometer
- Author
-
Ziv Oren, Maria Ronen, Yaakov R. Tischler, Doron Gerber, and Basanth S. Kalanoor
- Subjects
chemistry.chemical_classification ,Spectrometer ,Terahertz radiation ,General Chemical Engineering ,Biomolecule ,010401 analytical chemistry ,Intermolecular force ,Analytical chemistry ,02 engineering and technology ,General Chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Spectral line ,Article ,0104 chemical sciences ,lcsh:Chemistry ,symbols.namesake ,chemistry ,lcsh:QD1-999 ,Chemical physics ,Molecular vibration ,Intramolecular force ,symbols ,0210 nano-technology ,Raman spectroscopy - Abstract
The low-frequency vibrational (LFV) modes of biomolecules reflect specific intramolecular and intermolecular thermally induced fluctuations that are driven by external perturbations, such as ligand binding, protein interaction, electron transfer, and enzymatic activity. Large efforts have been invested over the years to develop methods to access the LFV modes due to their importance in the studies of the mechanisms and biological functions of biomolecules. Here, we present a method to measure the LFV modes of biomolecules based on Raman spectroscopy that combines volume holographic filters with a single-stage spectrometer, to obtain high signal-to-noise-ratio spectra in short acquisition times. We show that this method enables LFV mode characterization of biomolecules even in a hydrated environment. The measured spectra exhibit distinct features originating from intra- and/or intermolecular collective motion and lattice modes. The observed modes are highly sensitive to the overall structure, size, long-range order, and configuration of the molecules, as well as to their environment. Thus, the LFV Raman spectrum acts as a fingerprint of the molecular structure and conformational state of a biomolecule. The comprehensive method we present here is widely applicable, thus enabling high-throughput study of LFV modes of biomolecules.
- Published
- 2016
39. Polarization Dependence of Low-Frequency Vibrations from Multiple Faces in an Organic Single Crystal
- Author
-
Yitzhak Mastai, Yaakov R. Tischler, Irena Nemtsov, and Hagit Aviv
- Subjects
Materials science ,General Chemical Engineering ,02 engineering and technology ,010402 general chemistry ,microcrystal ,01 natural sciences ,Molecular physics ,Inorganic Chemistry ,Crystal ,symbols.namesake ,crystal orientation ,Polarizability ,lcsh:QD901-999 ,General Materials Science ,Spectroscopy ,intermolecular interactions ,Intermolecular force ,low frequency Raman ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Polarization (waves) ,0104 chemical sciences ,Molecular vibration ,symbols ,lcsh:Crystallography ,0210 nano-technology ,Raman spectroscopy ,Single crystal - Abstract
Recent developments in optical filters have enabled the facile use of Raman spectroscopy for detection of low frequency (LF) vibrational modes. LF-Raman spectroscopy offers fast and sensitive characterization of LF vibrations, and enables the measurement of single microcrystals and detection of defects. It is useful for probing intermolecular interactions in crystals, which are lower in energy, such as hydrogen bonds, shear modes, and breathing modes. Crystal excitation from multiple faces allows learning the orientation of intermolecular interactions, as polarization dependence varies with the polarizability of the interactions along the planes. Elucidating the orientations of the intermolecular interactions in organic crystals is essential for guiding the reactions or adsorption to a specific crystal face. In this study, we investigated the dependence of the LF-Raman signal intensity on the orientation of an organic single microcrystal of L-alanine. Three incident beam directions provided the orientations of the intermolecular interactions by analyzing the corresponding LF-Raman spectra. The signal intensity correlated well with the proximity between the incident beam&rsquo, s direction and the orientations of the intermolecular interactions. Excellent compatibility was found between the spectra and simulated orientations based on structural information.
- Published
- 2019
40. Improving Raman spectra of pure silicon using super-resolved method
- Author
-
Yaakov R. Tischler, Zeev Zalevsky, Dror Malka, and Binyamin Adler Berke
- Subjects
Materials science ,Silicon ,business.industry ,chemistry.chemical_element ,Superresolution ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,symbols.namesake ,Optics ,chemistry ,symbols ,Optoelectronics ,business ,Raman spectroscopy - Published
- 2019
41. Basic model of absorption depth and injection levels in silicon under intermediate illumination levels
- Author
-
Moshe Sinvani, Zeev Zalevsky, Yaakov R. Tischler, and Ran Aharoni
- Subjects
Materials science ,Photon ,Extended X-ray absorption fine structure ,High power lasers ,Silicon ,business.industry ,ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION ,Physics::Optics ,chemistry.chemical_element ,Two-photon absorption ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Power (physics) ,Wavelength ,Optics ,chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,business ,Absorption (electromagnetic radiation) ,ComputingMethodologies_COMPUTERGRAPHICS - Abstract
In this paper we present a novel model that connects the absorption depth of photons into silicon with the power of the applied illumination. So far in the literature the absorption depth was solely dependent on the wavelength of the illuminating photons. The new relation is important for better designing silicon based devices that are illuminated with high power lasers. Experimental results validate the proposed modeling.
- Published
- 2013
42. Spectroscopic Method for Fast and Accurate Group A Streptococcus Bacteria Detection
- Author
-
Hagit Aviv, Yaakov R. Tischler, Efraim Rosenbaum, and Dillon Schiff
- Subjects
0301 basic medicine ,Time Factors ,Streptococcus pyogenes ,Analytical chemistry ,02 engineering and technology ,medicine.disease_cause ,Spectrum Analysis, Raman ,Group A ,Analytical Chemistry ,03 medical and health sciences ,Antigen ,Streptococcus bacteria ,In vivo ,medicine ,biology ,Chemistry ,021001 nanoscience & nanotechnology ,biology.organism_classification ,Fluorescence ,030104 developmental biology ,Biochemistry ,biology.protein ,Antibody ,0210 nano-technology ,Bacteria - Abstract
Rapid and accurate detection of pathogens is paramount to human health. Spectroscopic techniques have been shown to be viable methods for detecting various pathogens. Enhanced methods of Raman spectroscopy can discriminate unique bacterial signatures; however, many of these require precise conditions and do not have in vivo replicability. Common biological detection methods such as rapid antigen detection tests have high specificity but do not have high sensitivity. Here we developed a new method of bacteria detection that is both highly specific and highly sensitive by combining the specificity of antibody staining and the sensitivity of spectroscopic characterization. Bacteria samples, treated with a fluorescent antibody complex specific to Streptococcus pyogenes, were volumetrically normalized according to their Raman bacterial signal intensity and characterized for fluorescence, eliciting a positive result for samples containing Streptococcus pyogenes and a negative result for those without. The normalized fluorescence intensity of the Streptococcus pyogenes gave a signal that is up to 16.4 times higher than that of other bacteria samples for bacteria stained in solution and up to 12.7 times higher in solid state. This method can be very easily replicated for other bacteria species using suitable antibody-dye complexes. In addition, this method shows viability for in vivo detection as it requires minute amounts of bacteria, low laser excitation power, and short integration times in order to achieve high signal.
- Published
- 2016
43. Utilizing pulsed laser deposition lateral inhomogeneity as a tool in combinatorial material science
- Author
-
Arie Zaban, Eli Rosh-Hodesh, Adam Ginsburg, Yaakov R. Tischler, Hannah-Noa Barad, David A. Keller, Hagit Aviv, Assaf Y. Anderson, Klimentiy Shimanovich, Yaniv Bouhadana, and Ichiro Takeuchi
- Subjects
Fabrication ,Chemistry ,business.industry ,Lasers ,Nanotechnology ,General Chemistry ,General Medicine ,Substrate (electronics) ,Orders of magnitude (numbers) ,Pulsed laser deposition ,Small Molecule Libraries ,Electrical resistivity and conductivity ,Materials Testing ,Deposition (phase transition) ,Optoelectronics ,Combinatorial Chemistry Techniques ,Thin film ,business ,Layer (electronics) ,Iron Compounds - Abstract
Pulsed laser deposition (PLD) is widely used in combinatorial material science, as it enables rapid fabrication of different composite materials. Nevertheless, this method was usually limited to small substrates, since PLD deposition on large substrate areas results in severe lateral inhomogeneity. A few technical solutions for this problem have been suggested, including the use of different designs of masks, which were meant to prevent inhomogeneity in the thickness, density, and oxidation state of a layer, while only the composition is allowed to be changed. In this study, a possible way to take advantage of the large scale deposition inhomogeneity is demonstrated, choosing an iron oxide PLD-deposited library with continuous compositional spread (CCS) as a model system. An Fe₂O₃-Nb₂O₅ library was fabricated using PLD, without any mask between the targets and the substrate. The library was measured using high-throughput scanners for electrical, structural, and optical properties. A decrease in electrical resistivity that is several orders of magnitude lower than pure α-Fe₂O₃ was achieved at ∼20% Nb-O (measured at 47 and 267 °C) but only at points that are distanced from the center of the PLD plasma plume. Using hierarchical clustering analysis, we show that the PLD inhomogeneity can be used as an additional degree of freedom, helping, in this case, to achieve iron oxide with much lower resistivity.
- Published
- 2015
44. FRET-based Scanning Probe Microscopy with a Donor Dye Coated AFM Tip
- Author
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Shirly Berezin, Omree Kapon, Yaakov R. Tischler, and Basanth S. Kalanoor
- Subjects
Fluorescence-lifetime imaging microscopy ,Scanning probe microscopy ,Materials science ,Förster resonance energy transfer ,Light sheet fluorescence microscopy ,biological sciences ,Microscopy ,technology, industry, and agriculture ,Scanning ion-conductance microscopy ,Nanotechnology ,Near-field scanning optical microscope ,macromolecular substances ,Scanning capacitance microscopy - Abstract
A FRET-based method of near-field fluorescence lifetime imaging is developed. Lumogen dye attached to the apex of an AFM tip acts as a nanometeric light source for exciting the sample via non-radiative energy transfer.
- Published
- 2015
45. Photoinduced Reversible Structural Transformations in Free-Standing CH3NH3PbI3 Perovskite Films
- Author
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Claudio Quarti, Shay Tirosh, Yaakov R. Tischler, Laxman Gouda, Filippo De Angelis, Arie Zaban, Ronen Gottesman, Eli Rosh-Hodesh, Eynav Haltzi, Edoardo Mosconi, and Basanth S. Kalanoor
- Subjects
Photoluminescence ,thin film ,Nanotechnology ,Substrate (electronics) ,7. Clean energy ,law.invention ,Thin glass ,symbols.namesake ,law ,TheoryofComputation_ANALYSISOFALGORITHMSANDPROBLEMCOMPLEXITY ,Solar cell ,ComputingMethodologies_SYMBOLICANDALGEBRAICMANIPULATION ,Raman ,illumination ,photoluminescence ,solar cell ,General Materials Science ,Physical and Theoretical Chemistry ,Thin film ,Perovskite (structure) ,Chemistry ,Chemical physics ,symbols ,sense organs ,Raman spectroscopy ,MathematicsofComputing_DISCRETEMATHEMATICS - Abstract
In the pursuit to better understand the mechanisms of perovskite solar cells we performed Raman and photoluminescence measurements of free-standing CH3NH3PbI3 films, comparing dark with working conditions. The films, grown on a glass substrate and sealed by a thin glass coverslip, were measured subsequent to dark and white-light pretreatments. The extremely slow changes we observe in both the Raman and photoluminescence cannot be regarded as electronic processes, which are much faster. Thus, the most probable explanation is of slow photoinduced structural changes. The CH3NH3PbI3 transformation between the dark and the light structures is reversible, with faster rates for the changes under illumination. The results seem to clarify several common observations associated with solar cell mechanisms, like performance improvement under light soaking. More important is the call for solar-cell-related investigation of CH3NH3PbI3 to take the photoinduced structural changes into consideration when measuring and interpreting the results.
- Published
- 2015
46. Room temperature fabrication of dielectric Bragg reflectors composed of a CaF2/ZnS multilayered coating
- Author
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Alex Palatnik, Gilbert Daniel Nessim, Yaakov R. Tischler, and Merav Muallem
- Subjects
Fabrication ,Materials science ,business.industry ,High-refractive-index polymer ,Substrate (electronics) ,engineering.material ,Zinc sulfide ,Rhodamine 6G ,chemistry.chemical_compound ,Optics ,chemistry ,Coating ,engineering ,Optoelectronics ,General Materials Science ,Thin film ,business ,Layer (electronics) - Abstract
We describe the design, fabrication, and characterization of mechanically stable, reproducible, and highly reflecting distributed Bragg reflectors (DBR) composed of thermally evaporated thin films of calcium fluoride (CaF2) and zinc sulfide (ZnS). CaF2 and ZnS were chosen as the low and high refractive index components of the multilayer DBR structures, with n = 1.43 and n = 2.38 respectively, because neither material requires substrate heating during the deposition process in order to produce optical quality thin films. DBRs consisting of seven pairs of CaF2 and ZnS layers, were fabricated with thicknesses of 96 and 58 nm, respectively, as characterized by high-resolution scanning electron microscopy (HR-SEM), and exhibited a center wavelength of λc = 550 nm and peak reflectance exceeding 99%. The layers showed good adhesion to each other and to the glass substrate, resulting in mechanically stable DBR coatings. Complete optical microcavities consisting of two such DBR coatings and a CaF2 spacer layer between them could be fabricated in a single deposition run. Optically, these structures exhibited a resonator quality factor of Q > 160. When a CaF2/ZnS DBR was grown, without heating the substrate during deposition, on top of a thin film containing the fluorescent dye Rhodamine 6G, the fluorescence intensity showed no degradation compared to an uncoated film, in contrast to a MgF2/ZnS DBR coating grown with substrate heating which showed a 92% reduction in signal. The ability to fabricate optical quality CaF2/ZnS DBRs without substrate heating, as introduced here, can therefore enable formation of low-loss high-reflectivity coatings on top of more delicate heat-sensitive materials such as organics and other nanostructured emitters, and hence facilitate the development of nanoemitter-based microcavity device applications.
- Published
- 2014
47. Reduced lasing threshold from organic dye microcavities
- Author
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Alex Palatnik, Gleb M. Akselrod, Katherine W. Stone, Elizabeth R. Young, Vladimir Bulovic, and Yaakov R. Tischler
- Subjects
Materials science ,Dye laser ,Condensed Matter::Other ,business.industry ,Exciton ,Relaxation (NMR) ,Physics::Optics ,Context (language use) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Gain-switching ,Semiconductor laser theory ,law.invention ,Solid-state lighting ,law ,Optoelectronics ,Atomic physics ,business ,Lasing threshold - Abstract
We demonstrate an unexpected tenfold reduction in the lasing threshold of an organic vertical microcavity under subpicosecond optical excitation. In contrast to conventional theory of lasing, we find that the lasing threshold depends on the rate at which excitons are created rather than the total energy delivered within the exciton lifetime. The threshold reduction is discussed in the context of microcavity-enhanced super-radiant coupling between the excitons. The interpretation of super-radiance is supported by the temporal relaxation dynamics of the microcavity emission, which follows the super-radiance time rather than the cavity lifetime. This demonstration suggests that room-temperature super-radiant effects could generally lower the threshold in four-level lasing systems of similar relaxation dynamics.
- Published
- 2014
48. Influence of gain material concentration on an organic DFB laser
- Author
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Hagit Aviv, Alexander Palatnik, Yaakov R. Tischler, and Ora Bitton
- Subjects
Distributed feedback laser ,Dye laser ,Materials science ,business.industry ,Slope efficiency ,02 engineering and technology ,Nanosecond ,021001 nanoscience & nanotechnology ,Laser ,01 natural sciences ,Waveguide (optics) ,Electronic, Optical and Magnetic Materials ,law.invention ,010309 optics ,law ,Excited state ,0103 physical sciences ,Optoelectronics ,0210 nano-technology ,business ,Lasing threshold - Abstract
In this work, we investigate the properties of an organic distributed feedback laser as the concentration of the gain material in the waveguide core is varied across two orders of magnitude, from 5% down to 0.025%. The laser dye DCJTB (4-(Dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-9-enyl-vinyl)-4H-pyran) incorporated into a PVK (poly(9-vinylcarbazole)) host matrix provided the gain. The composite layer of PVK:DCJTB was spin-cast onto a silica grating with second order periodicity, and upon nanosecond optical excitation lasing was generated in the wavelength range of 600 nm. The threshold pulse energy for achieving lasing increased as the concentration of DCJTB was reduced, however the threshold excitation density quantified in terms of number of excited molecules per unit area remained nearly constant at 1.3×1013 molecules/cm2. In contrast, the relative slope efficiency for lasing decreased considerably as the gain concentration was reduced. We show that this effect can not be explained by a standard 4-level lasing model, but rather that it is due to optically induced charge separation for the DCJTB molecules situated in the PVK host matrix. Our findings suggest that fast charge separation and long back recombination times can be a significant factor in limiting further reduction of the gain concentration in organic DFB lasers.
- Published
- 2016
49. A simplified method for generating periodic nanostructures by interference lithography without the use of an anti-reflection coating
- Author
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Merav Muallem, Hagit Aviv, Omree Kapon, Yaakov R. Tischler, and Alex Palatnik
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Holography ,Photoresist ,engineering.material ,law.invention ,Interference lithography ,Nanolithography ,Optics ,Coating ,Interference (communication) ,law ,engineering ,X-ray lithography ,Photolithography ,business - Abstract
Interference lithography has proven to be a useful technique for generating periodic sub-diffraction limited nanostructures. Interference lithography can be implemented by exposing a photoresist polymer to laser light using a two-beam arrangement or more simply a one beam configuration based on a Lloyd's Mirror Interferometer. For typical photoresist layers, an anti-reflection coating must be deposited on the substrate to prevent adverse reflections from cancelling the holographic pattern of the interfering beams. For silicon substrates, such coatings are typically multilayered and complex in composition. By thinning the photoresist layer to a thickness well below the quarter wavelength of the exposing beam, we demonstrate that interference gratings can be generated without an anti-reflection coating on the substrate. We used ammonium dichromate doped polyvinyl alcohol as the positive photoresist because it provides excellent pinhole free layers down to thicknesses of 40 nm, and can be cross-linked by a l...
- Published
- 2015
50. Resonant Cavity Colloidal Quantum Dot LEDs
- Author
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Geoffrey J. Supran, Vladimir Bulovic, Yasuhiro Shirasaki, Vanessa Wood, and Yaakov R. Tischler
- Subjects
Materials science ,Physics::Instrumentation and Detectors ,business.industry ,Physics::Optics ,Electroluminescence ,law.invention ,Nanomaterials ,law ,Quantum dot ,Quantum dot laser ,Optoelectronics ,Spontaneous emission ,business ,Diode ,Light-emitting diode ,Spectral purity - Abstract
We demonstrate resonant-cavity colloidal quantum dot light-emitting diodes that exhibit electroluminescence with enhanced spectral purity and directionality and show that the enhancement is due to modification of the optical modes of the system.
- Published
- 2011
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