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All-optical control of exciton flow in a colloidal quantum well complex

Light(Science & Applications) 2020年第1期9卷 1749-1756页

作者： Junhong Yu Manoj Sharma Ashma Sharma Savas Delikanli Hilmi volkan demir Cuong Dang LUMINOUS Centre of Excellence for Semiconductor Lighting and DisplaysSchool of Electrical and Electronic EngineeringThe Photonics Institute(TPI)Nanyang Technological University50 Nanyang Avenue639798 SingaporeSingapore Department of Electrical and Electronics Engineering and Department of Physics UNAM-Institute of Materials Science and NanotechnologyBilkent UniversityBilkent06800 AnkaraTurkey School of Physical and Mathematical Sciences Division of Physics and Applied PhysicsNanyang Technological University639798 SingaporeSingapore CINTRA UMI CNRS/NTU/THALES 3288 Research Techno Plaza50 Nanyang DriveBorder X BlockLevel 6637553 SingaporeSingapore

Excitonics,an alternative to romising for processing information since semiconductor electronics is rapidly approaching the end of Moore’s ***,the development of excitonic devices,where exciton flow is controlled,is mainly focused on electric-field modulation or exciton polaritons in high-Q ***,we show an alloptical strategy to manipulate the exciton flow in a binary colloidal quantum well complex through mediation of the Förster resonance energy transfer(FRET)by stimulated *** the spontaneous emission regime,FRET naturally occurs between a donor and an *** contrast,upon stronger excitation,the ultrafast consumption of excitons by stimulated emission effectively engineers the excitonic flow from the donors to the ***,the acceptors’stimulated emission significantly accelerates the exciton flow,while the donors’stimulated emission almost stops this *** this basis,a FRET-coupled rate equation model is derived to understand the controllable exciton flow using the density of the excited donors and the unexcited *** results will provide an effective alloptical route for realizing excitonic devices under room temperature operation.

关键词： process flow quantum

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Mechanosynthesis of polymer-stabilized lead bromide perovskites:Insight into the formation and phase conversion of nanoparticles

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Nano Research 2021年第4期14卷 1078-1086页

作者： Guocan Jiang Onur Erdem Rene Hubner Maximilian Georgi Wei Wei Xuelin Fan Jin Wang Hilmi volkan demir Nikolai Gaponik Physical Chemistry Technische Universitat DresdenZellescher Weg 1901069 DresdenGermany Department of Physics Department of Electrical and Electronics Engineeringand UN A M-Institute of Materials Science and NanotechnologyBilkent University06800 AnkaraTurkey LUMINOUS Center of Excellence for Semiconductor Lighting and DisplaysSchool of Electrical and Electronic EngineeringSchool of Mathematical and Physical SciencesSchool of Materials Science and EngineeringNanyang Technological UniversityNanyang AvenueSingapore 639798Singapore Helmholtz-Zentrum Dresden-Rossendorf Institute of Ion Beam Physics and Materials ResearchBautzner Landstrasse 40001328 DresdenGermany Key Laboratory of the Ministry of Education for Advanced Catalysis Materials Zhejiang Normal UniversityJinhua 321004China

The application of polymers to replace oleylamine(OLA)and oleic acid(OA)as ligands for perovskite nanocrystals is an effective strategy to improve their stability and durability especially for the solution-based ***,we report a mechanosynthesis of lead bromide perovskite nanoparticles(NPs)stabilized by partially hydrolyzed poly(methyl methacrylate)(h-PMMA)and highmolecular-weight highly-branched poly(ethylenimine)(PEI-25K).The as-synthesized NP solutions exhibited green emission centered at 516 nm,possessing a narrow full-width at half-maximum of 17 nm and as high photoluminescence quantum yield(PL QY)as 85%,while showing excellent durability and resistance to polar solvents,e.g.,*** colloids of polymer-stabilized NPs were directly processable toform stable and strongly-emitting thin films and solids,making them attractive as gain ***,the roles of h-PMMA and PEI-25K in the grinding process were studied in *** h-PMMA can form micelles in the grinding solvent of dichloromethane to act as size-regulating templates for the growth of *** PEI-25K with large amounts of amino groups induced significant enrichment of PbBr_(2)in the reaction mixture,which in turn caused the formation of CsPb_(2)Br_(5)-mPbBr_(2)and CsPbBr_(3)-Cs_(4)PbBr_(6)-nCsBr *** presence of CsPbBr_(3)-Cs_(4)PbBr_(6)-nCsBr NPs was responsible for the high PL QY,as the Cs_(4)PbBr_(6)phase with a wide energy bandgap can passivate the surface defects of the CsPbBr_(3)*** work describes a direct and facile mechanosynthesis of polymer-coordinated perovskite NPs and promotes in-depth understanding of the formation and phase conversion for perovskite NPs in the grinding process.

关键词： lead bromide perovskites mechanosynthesis polymer ligands polymer micelles poly(ethyleneimine)-induced phase conversion

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Exciton dynamics in luminescent carbon nanodots： Electron-hole exchange interaction

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Nano Research 2016年第2期9卷 549-559页

作者： Bo Peng Xin Lu Shi Chen Cheng Hon Alfred Huan Qihua Xiong Evren Mutlugun Hilmi volkan demir Siu Fung Yu Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Singapore 637371 Singapore NOVITAS Nanoelectronics Centre of Excellence School of Electrical and Electronic Engineering Nanyang Technological UniversitySingapore 639798 Singapore LUMINOUS Centre of Excellence for Semiconductor Lighting and Displays School of Electrical and Electronic Engineering NanyangTechnological University Singapore 639798 Singapore Department of Applied Physics the Hong Kong Polytechnic University Hong Hum Hong Kong SAR China

The electron-hole exchange interaction significantly influences the optical properties of excitons and radiative decay. However, exciton dynamics in luminescent carbon dots （Cdots） is still not clear. In this study, we have developed a simple and efficient one-step strategy to synthesize luminescent Cdots using the pyrolysis of oleylamine. The sp^2 clusters of a few aromatic rings are responsible for the observed blue photoluminescence. The size of these clusters can be tuned by controlling the reaction time, and the energy gap between the π-π＊ states of the sp^2 domains decreases as the sp^2 cluster size increases. More importantly, the strong electron-hole exchange interaction results in the splitting of the exciton states of the sp^2 clusters into the singlet-bright and triplet-dark states with an energy difference ΔE, which decreases with increasing sp^2 cluster size owing to the reduction of the confinement energy and the suppression of the electron-hole exchange interaction.

关键词： carbon dots photoluminescence pyrolysis electron-hole exchange interaction energy splitting

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High-efficiency CdTe/CdS core/shell nanocrystals in water enabled by photo-induced colloidal hetero-epitaxy of CdS shelling at room temperature

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Nano Research 2015年第7期8卷 2317-2328页

作者： Hakimeh Zare Maziar Marandi Somayeh Fardindoost Vijay Kumar Sharma Aydan Yeltik Omid Akhavan Hilmi volkan demir Nima Taghavinia Institute for Nanoscience and Nanotechnology Shafif University of Technology Tehran 14588 Iran Department of Physics Faculty of Sciences Arak University Arak 38156-8-8349 Iran Department of Physics Department of Electrical and Electronics Engineering and UNAM-Institute of Materials Science and Nanotechnology Bilkent University Ankara Turkey Luminous Center of Excellence for Semiconductor Lighting and Displays Microelectronics Division School of Electrical and Electronics Engineering and Physics and Applied Physics Division School of Physical and Mathematical Sciences Nanyang Technological University Singapore 639798 Singapore Physics Department ShafifUniversity of Technology Tehran 14588 Iran

We report high-efficiency CdTe/CdS core/shell nanocrystals synthesized in water by epitaxially growing CdS shells on aqueous CdTe cores at room temperature, enabled by the controlled release of S species under low-intensity ultraviolet （UV） light illumination. The resulting photo-induced dissociation of S2O2- ions conveniently triggers the formation of critical two-dimensional CdS epitaxy on the CdTe surface at room temperature, as opposed to initiating the growth of individual CdS core-only nanocrystals. This controlled colloidal hetero-epitaxy leads to a substantial increase in the photoluminescence （PL） quantum yield （QY） of the shelled nanocrystals in water （reaching 64%）. With a systematic set of studies, the maximum PL QY is found to be almost independent of the illuminating UV intensity, while the shell formation kinetics required for reaching the maximum QY linearly depends on the illuminating UV intensity. A stability study of the QD films in air at various temperatures shows highly improved thermal stability of the shelled QDs （up to 120 ℃ in ambient air）. These results indicate that the proposed aqueous CdTe/CdS core/shell nanocrystals hold great promise for applications requiring efficiency and stability.

关键词： CdTe/CDs,core/shell nanocrystal thermal stability photochemical

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Sweet plasmonics： Sucrose macrocrystals of metal nanoparticles

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Nano Research 2015年第3期8卷 860-869页

作者： Talha Erdem Zeliha Soran-Erdem Pedro Ludwig Hernandez-Martinez Vijay Kumar Sharma Halil Akcali Ibrahim Akcali Nikolai Gaponik Alexander Eychmeller Hilmi volkan demir Departments of Electrical and Electronics Engineering Physics UNAM-National Nanotechnology Research Center and Institute ot Materials Science and Nanotechnology Bilkent University Ankara 06800 Turkey School of Electrical and Electronic Engineering and School of Physical and Mathematical Sciences Nanyang Technological University Singapore 639798 Singapore Physical Chemistry TU Dresden Bergstrasse 66b D-O 1062 Dresden Germany

The realization of plasmonic structures generally necessitates expensive fabrication techniques, such as electron beam and focused ion beam lithography, allowing for the top-down fabrication of low-dimensional structures. Another approach to make plasmonic structures in a bottom-up fashion is colloidal synthesis, which is convenient for liquid-state applications or very thin solid films where aggregation problems are an important challenge. The architectures prepared using these methods are typically not robust enough for easy handling and convenient integration. Therefore, developing a new plasmonic robust platform having large-scale dimensions without adversely affecting the plasmonic features is in high demand. As a solution, here we present a new plasmonic composite structure consisting of gold nanoparticles （Au NPs） incorporated into sucrose macrocrystals on a large scale, while preserving the plasmonic nature of the Au NPs and providing robustness in handling at the same time. As a proof of concept demonstration, we present the fluorescence enhancement of green CdTe quantum dots （QDs） via plasmonic coupling with these Au NPs in the sucrose crystals. The obtained composite material exhibits centimeter scale dimensions and the resulting quantum efficiency （QE） is enhanced via the interplay between the Au NPs and CdTe QDs by 58% （from 24% to 38%）. Moreover, a shortening in the photoluminescence lifetime from 11.0 to 7.40 ns, which corresponds to a field enhancement factor of 2.4, is observed upon the introduction of Au NPs into the QD incorporated macrocrystals. These results suggest that such ＂sweet＂ plasmonic crystals are promising for large-scale robust platforms to embed plasmonic nanoparticles.

关键词： plasmonics macrocrystals metal nanoparticles metal enhancedfluorescence colloidal quantum dots

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Interfacial charge and energy transfer in van der Waals heterojunctions

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InfoMat 2022年第3期4卷 64-84页

作者： Zehua Hu Xue Liu Pedro Ludwig Hernandez-Martínez Shishu Zhang Peng Gu Wei Du Weigao Xu Hilmi volkan demir Haiyun Liu Qihua Xiong Division of Physics and Applied Physics School of Physical and Mathematical SciencesNanyang Technological UniversitySingaporeSingapore Institutes of Physical Science and Information Technology Anhui UniversityHefeiP.R.China LUMINOUS Center of Excellence for Semiconductor Lighting and DisplaySchool of Electrical and Electronics EngineeringNanyang Technological UniversitySingaporeSingapore State Key Laboratory of Low-Dimensional Quantum Physics Department of PhysicsTsinghua UniversityBeijingP.R.China Beijing Academy of Quantum Information Sciences BeijingP.R.China Institute of Functional Nano and Soft Materials(FUNSOM) Soochow UniversitySuzhouP.R.China Key Laboratory of Mesoscopic Chemistry of MOE School of Chemistry and Chemical EngineeringNanjing UniversityNanjingP.R.China Department of Physics Department of Electrical and Electronics EngineeringUNAM-National Nanotechnology Research Center and Institute of Materials Science and NanotechnologyBilkent UniversityAnkaraTurkey Beijing Innovation Center for Future Chips Tsinghua UniversityBeijingP.R.China

Van der Waals heterojunctions are fast-emerging quantum structures fabricated by the controlled stacking of two-dimensional(2D)*** to the atomically thin thickness,their carrier properties are not only determined by the host material itself,but also defined by the interlayer interactions,including dielectric environment,charge trapping centers,and stacking *** abundant constituents without the limitation of lattice constant matching enable fascinating electrical,optical,and magnetic properties in van der Waals heterojunctions toward next-generation devices in photonics,optoelectronics,and information *** review focuses on the charge and energy transfer processes and their dynamics in transition metal dichalcogenides(TMDCs),a family of quantum materials with strong excitonic effects and unique valley properties,and other related 2D materials such as graphene and hexagonalboron *** the first part,we summarize the ultrafast charge transfer processes in van der Waals heterojunctions,including its experimental evidence and theoretical understanding,the interlayer excitons at the TMDC interfaces,and the hot carrier injection at the graphene/TMDCs *** the second part,the energy transfer,including both Förster and Dexter types,are reviewed from both experimental and theoretical ***,we highlight the typical charge and energy transfer applications in photodetectors and summarize the challenges and opportunities for future development in this field.

关键词： 2-dimensional semiconductors carrier dynamics charge and energy transfer optical spectroscopy optoelectronics

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High-performance AlGaInP light-emitting diodes integrated on silicon through a superior quality germanium-on-insulator

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Photonics Research 2018年第4期6卷 290-295页

作者： YUE WANG BING WANG WARDHANA A. SASANGKA SHUYU BAO YIPING ZHANG HILMI volkan demir JURGEN MICHEL KENNETH ENG KIAN LEE SOON FATT YOON EUGENE A. FITZGERALD CHUAN SENG TAN KWANG HONG LEE Low Energy Electronic Systems (LEES) Singapore-MIT Alliance for Research and Technology (SMART) 1 CREATE Way #10-01 CREATE Tower Singapore 138602 Singapore School of Electrical and Electronic Engineenng Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore Department of Materials Science and Engineerng Massachusetts Institute of Technology Cambridge Massachusetts 02139 USA

High-performance GaInP/AlGaInP multi-quantum well light-emitting diodes(LEDs) grown on a low threading dislocation density(TDD) germanium-on-insulator(GOI) substrate have been demonstrated. The low TDD of the GOI substrate is realized through Ge epitaxial growth, wafer bonding, and layer transfer processes on 200 mm wafers. With O_2 annealing, the TDD of the GOI substrate can be reduced to ~1.2 × 10~6 cm^(-2). LEDs fabricated on this GOI substrate exhibit record-high optical output power of 1.3 mW at a 670 nm peak wavelength under 280 mA current injection. This output power level is at least 2 times higher compared to other reports of similar devices on a silicon(Si) substrate without degrading the electrical performance. These results demonstrate great promise for the monolithic integration of visible-band optical sources with Si-based electronic circuitry and realization of high-density RGB(red, green, and blue) micro-LED arrays with control circuitry.

关键词：绝缘体发光二极管通讯技术发展现状

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Cultivable Sponge-Associated Actinobacteria from Coastal Area of Eastern Mediterranean Sea

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Advances in Microbiology 2014年第6期4卷 306-316页

作者： Ozlem Oner Güner Ekiz E.Esin Hames volkan demir Ozkan Gübe F.Can Ozkaya M.Baki Yokes Atac Uzel Erdal Bedir Department of Biotechnology Graduate School of Natural and Applied SciencesEge UniversityBornovaIzmirTurkey Department of Bioengineering Faculty of EngineeringEge UniversityBornovaIzmirTurkey Institute of Marine Sciences and Management İstanbul UniversityVefaİstanbulTurkey Department of Molecular Biology and Genetics Faculty of Arts and SciencesHalic UniversitySıracevizler Cd.No:29 BomontisisliIstanbulTurkey Department of Biology Faculty of ScienceEge UniversityBornovaIzmirTurkey

In this study, 16 marine sponge samples collected from Eastern Mediterranean Sea were used for the isolation of sponge-associated Actinobacteria. Different media and pre-treatment methods were applied for the isolation experiments. In total, 7578 actinomycetes colonies were observed on the primary isolation plates, and 20 representative isolates were selected for further studies based on their morphologies and chemical profiles. These isolates were investigated for their antimicrobial activities, seawater requirements and 16S rRNA gene sequences. The phylogenetic analysis revealed that 80% of the isolated Actinobacteria was a member of the Streptomyces genus. All the isolates showed no absolute requirement for seawater. Fifteen of the selected isolates exhibited antimicrobial activity against methicillin resistant Staphylococcus aureus and vancomycin resistant Enterococcus faecium, whereas 3 isolates were active against Candida albicans.

关键词： Sponge-Associated Actinobacteria Streptomyces Nocardiopsis Antimicrobial Activity

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