A5004939650- Quantum Dots Synthesis And Properties
- Chalcogenide Semiconductor Thin Films
- Perovskite Materials and Applications
- Nanocluster Synthesis and Applications
- Semiconductor Quantum Structures and Devices
- 2D Materials and Applications
- Molecular Junctions and Nanostructures
- Electronic and Structural Properties of Oxides
- Intellectual Capital and Performance Analysis
- Neuroscience and Neural Engineering
- Strong Light-Matter Interactions
- ZnO doping and properties
- Magnetic and transport properties of perovskites and related materials
- Catalytic Cross-Coupling Reactions
- Graphene research and applications
- Random lasers and scattering media
- Copper-based nanomaterials and applications
- Solid-state spectroscopy and crystallography
- Nanowire Synthesis and Applications
- Organic Light-Emitting Diodes Research
- Covalent Organic Framework Applications
- Impact of AI and Big Data on Business and Society
- Quantum-Dot Cellular Automata
- Organic and Molecular Conductors Research
University of Duisburg-Essen
2014-2025
University of Washington
2020-2021
Princeton University
2013
We study the effect of carbon to oxygen ratio (C/O) on electrical resistance functionalized graphene sheets prepared by thermal exfoliation and reduction graphite oxide at various temperatures. Using a 2-probe technique in conjunction with Kelvin probe force microscopy, we observe transition from high-resistance (>400 kΩ/sq) nonlinear current/voltage characteristics low C/O low-resistance (<10 linear behavior high C/O, indicating hopping diffusive electron transport....
Doping semiconductor nanocrystals with magnetic transition-metal ions has attracted fundamental interest to obtain a nanoscale dilute semiconductor, which unique spin exchange interaction between and exciton. So far, the study on doped NCs usually been conducted larger than 2 nm because of synthetic challenges. Herein, we report synthesis characterization Mn(2+)-doped (CdSe)13 clusters, smallest semiconductors. In this study, single-sized clusters are produced in large scale. Despite their...
Nanoclusters are important prenucleation intermediates for colloidal nanocrystal synthesis. In addition, they exhibit many intriguing properties originating from their extremely small size lying between molecules and typical nanocrystals. However, synthetic control of multicomponent semiconductor nanoclusters remains a daunting goal. Here, we report on the synthesis, doping, transformation multielement magic-sized clusters, generating smallest alloys. We use Lewis acid–base reactions at room...
Magic-sized semiconductor clusters represent an exciting class of materials located at the boundary between quantum dots and molecules. It is expected that replacing single atoms host crystal with individual dopants in a one-by-one fashion can lead to unique modifications material properties. Here, we demonstrate dependence magneto-optical response (CdSe)13 on discrete number Mn2+ ion dopants. Using time-of-flight mass spectrometry, are able distinguish undoped, monodoped, bidoped cluster...
Abstract The fundamental bandgap E g of a semiconductor—often determined by means optical spectroscopy—represents its characteristic fingerprint and changes distinctively with temperature. Here, we demonstrate that in magic sized II-VI clusters containing only 26 atoms, pronounced weakening the bonds occurs upon excitation, which results strong exciton-driven shift phonon spectrum. As consequence, drastic increase d /d T (up to factor 2) respect bulk material or nanocrystals typical size is...
In two-dimensional (2D) colloidal semiconductor nanoplatelets, which are atomically flat nanocrystals, the precise control of thickness and composition on atomic scale allows for synthesis heterostructures with well-defined electron hole wave function distributions. Introducing transition metal dopants a monolayer precision enables tailored magnetic exchange interactions between band states. Here, we use absorption based technique circular dichroism (MCD) to directly prove coupling charge...
We study ion migration in 2D lead halide perovskites of varying dimensionality using scanning Kelvin probe microscopy (SKPM). perform potentiometry on micrometer-scale lateral junctions the absence injected charge, and we compare how motion varies between prototypical two-dimensional n-butylammonium iodide (BA2PbI4, n = 1), methylammonium-incorporated quasi-2D (BA2MA3Pb4I13, ∼⟨n⟩ 4) under effects illumination temperature. attribute observed slow dynamics to relaxation bias-induced ionic...
Magic-sized clusters represent materials with unique properties at the border between molecules and solids provide important insights into nanocrystal formation process. However, synthesis, doping, especially structural characterization become more challenging decreasing cluster size. Herein, we report successful introduction of Co2+ ions extremely small-sized CdSe intention using internal ligand field transitions to obtain insights. Despite huge mismatch radii Cd2+ (>21%), can be...
The impact of quantum confinement on the exchange interaction between charge carriers and magnetic dopants in semiconductor nanomaterials has been controversially discussed for more than a decade. We developed manganese-doped CdSe well nanoribbons with strong perpendicular to c-axis, showing distinct heavy hole light resonances up 300 K. This allows separate study s-d p-d interactions all way room temperature. Taking into account optical selection rules statistical distribution orientation...
Electrical spin manipulation remains a central challenge for the realization of diverse spin-based information processing technologies. Motivated by demonstration confinement-enhanced sp-d exchange interactions in colloidal diluted magnetic semiconductor (DMS) quantum dots (QDs), such materials are considered promising candidates future spintronic or spin-photonic applications. Despite intense research into DMS QDs, electrical control their and magneto-optical properties daunting goal. Here,...
As easy-to-grow quantum wells with narrow excitonic features at room temperature, two-dimensional (2D) Ruddleson-Popper perovskites are promising for realizing novel nanophotonic devices based on exciton-photon interactions. Here, we demonstrate a distinct hybrid Fano resonance in (C4H9NH3)2PbI4 thin films prepared via spin coating. Using classical coupled-oscillator model and finite-difference time-domain simulations, link the interference to coupling of exciton Rayleigh-like scattering...
We present an experimental study of the magneto-optical activity multiple excited excitonic states manganese-doped CdSe quantum dots chemically prepared by diffusion doping method. Giant Zeeman splittings each these can be extracted for a series dot sizes and are found to depend on radial number hole envelope function involved in transition. As seven out eight transitions involve same electron energy state, 1Se, dominant character transition identified, making use fact that g-factor pure...
Abstract CsPbBr 3 represents a highly attractive material for perovskite light-emitting diodes (PeLEDs) in the green spectral range. However, lack of deposition tools reproducible and scalable growth films is one major obstacles hindering PeLED commercialization. Here, we employ showerhead-assisted chemical vapor (CVD) method to produce uniform pinhole-free application. The precursors CsBr PbBr 2 are evaporated under low vacuum N carrier gas. By adjusting sublimation temperature, process...
Two-dimensional (2D) van der Waals (vdW) semiconductors such as transition metal dichalcogenides (TMDCs) or 2D halide perovskites receive increasing attention active materials in photosensing applications due to their high oscillator strength, large electronic mobility, and mechanical flexibility. For triggering an efficient separation of optically generated charge carriers hence improving the photodetectivity, different vdW are combined into functional heterostructures, i.e., TMDCs...
In the last decade, organic-inorganic hybrid halide perovskite materials have developed into a very large research area in photovoltaics and optoelectronics as promising light harvesters. Lead-free double perovskites recently been investigated an environmentally friendly alternative to lead-containing compositions. However, lead-free so far rarely produced due certain complexity their synthesis. A number of small molecular cations investigated, but compositions containing azetidinium, which...
Filter-less, wavelength-selective photodetectors made of perovskite usually rely on the charge collection narrowing mechanism, which intrinsically limits response times. Using narrow excitonic peak of, e.g., two-dimensional (2D) Ruddlesden–Popper perovskites as direct absorbers to realize color-selective photodetectivity promises faster responses. However, one major challenge in realizing such devices remains separation and carrier extraction tightly bound excitons. Here, we report...
Abstract Magic-sized (CdSe) 13 clusters (MSCs) represent a material class at the boundary between molecules and quantum dots that exhibit pronounced well separated excitonic fine structure. The characteristic photoluminescence is composed of exciton bandgap emission spectrally broad mid-gap related to surface defects. Here, we report on thermally activated energy transfer from fine-structure split states by using temperature dependent excitation spectroscopy. We demonstrate can be suppressed...