A stable, single-photon emitter in a thin organic crystal for application to quantum-photonic devices

Single organic molecules offer great promise as bright, reliable sources of identical single photons on demand, capable of integration into solid-state devices. It has been proposed that such molecules in a crystalline organic matrix might be placed close to an optical waveguide for this purpose, but so far there have been no demonstrations of sufficiently thin crystals, with a controlled concentration of suitable dopant molecules. Here we present a method for growing very thin anthracene crystals from super-saturated vapour, which produces crystals of extreme flatness and controlled thickness. We show how this crystal can be doped with a widely adjustable concentration of dibenzoterrylene (DBT) molecules and we examine the optical properties of these molecules to demonstrate their suitability as quantum emitters in nanophotonic devices. Our measurements show that the molecules are available in the crystal as single quantum emitters, with a well-defined polarisation relative to the crystal axes, making them amenable to alignment with optical nanostructures. We find that the radiative lifetime and saturation intensity vary little within the crystal and are not in any way compromised by the unusual matrix environment. We show that a large fraction of these emitters are able to deliver more than $10^{12}$ photons without photo-bleaching, making them suitable for real applications.Comment: 12 pages, 10 figures, comments welcom

Nanostructured PbS-doped inorganic film synthesized by sol-gel route

IV-VI semiconductor quantum dots embedded into an inorganic matrix represent nanostructured composite materials with potential application in temperature sensor systems. This study explores the optical, structural, and morphological properties of a novel PbS quantum dots (QDs)- doped inorganic thin film belonging to the Al2O3 -SiO2 -P2O5 system. The film was synthesized by the sol-gel method, spin coating technique, starting from a precursor solution deposited on a glass substrate in a multilayer process, followed by drying of each deposited layer. Crystalline PbS QDs embedded in the inorganic vitreous host matrix formed a nanocomposite material. Specific investigations such as X-ray diffraction (XRD), optical absorbance in the ultraviolet (UV)-visible (Vis)-near infrared (NIR) domain, NIR luminescence, Raman spectroscopy, scanning electron microscopy– energy dispersive X-ray (SEM-EDX), and atomic force microscopy (AFM) were used to obtain a comprehensive characterization of the deposited film. The dimensions of the PbS nanocrystallite phase were corroborated by XRD, SEM-EDX, and AFM results. The luminescence band from 1400 nm follows the luminescence peak of the precursor solution and that of the dopant solution. The emission of the PbS-doped film in the NIR domain is a premise for potential application in temperature sensing systems.This study was funded by a grant of the Romanian National Authority for Scientific Research and Innovation, CCCDI–UEFISCDI, project ERANET-MANUNET-TEMSENSOPT, MNET20/ NMCS3732, within PNCDI III, contract 213/02.12.2020; Ministry of Research, Innovation and Digitalization (MRID), Core Program, contracts no. 16N/2019, 18N/2019 and 21N/2019; MRID through Program I—Development of the National R & D System, Subprogram 1.2–Institutional Performance– Projects for Excellence Financing in RDI, contracts no. 13PFE/2021, 18PFE/2021 and 35PFE/2021; CCCDI-UEFISCDI project PN-III-P2-2.1-PED-2021-2541. Support from the Public University of Navarre for Research Groups is also acknowledged

Biomimetic route to hybrid nano-Composite scaffold for tissue engineering

Hydroxyapatite-poly(vinyl) alcohol-protein composites have been prepared by a biomimetic route at ambient conditions, aged for a fortnight at 30±2°C and given a shape in the form of blocks by thermal cycling. The structural characterizations reveal a good control over the morphology mainly the size and shape of the particles. Initial mechanical studies are very encouraging. Three biocompatibility tests, i.e., hemocompatibility, cell adhesion, and toxicity have been done from Shree Chitra Tirunal, Trivandrum and the results qualify their standards. Samples are being sent for more biocompatibility tests. Optimization of the blocks in terms of hydroxyapatite and polymer composition w.r.t the applications and its affect on the mechanical strength have been initiated. Rapid prototyping and a β-tricalcium – hydroxyapatite combination in composites are in the offing

Photoluminescent diamond nanoparticles for cell labeling: study of the uptake mechanism in mammalian cells

Diamond nanoparticles (nanodiamonds) have been recently proposed as new labels for cellular imaging. For small nanodiamonds (size <40 nm) resonant laser scattering and Raman scattering cross-sections are too small to allow single nanoparticle observation. Nanodiamonds can however be rendered photoluminescent with a perfect photostability at room temperature. Such a remarkable property allows easier single-particle tracking over long time-scales. In this work we use photoluminescent nanodiamonds of size <50 nm for intracellular labeling and investigate the mechanism of their uptake by living cells . By blocking selectively different uptake processes we show that nanodiamonds enter cells mainly by endocytosis and converging data indicate that it is clathrin mediated. We also examine nanodiamonds intracellular localization in endocytic vesicles using immunofluorescence and transmission electron microscopy. We find a high degree of colocalization between vesicles and the biggest nanoparticles or aggregates, while the smallest particles appear free in the cytosol. Our results pave the way for the use of photoluminescent nanodiamonds in targeted intracellular labeling or biomolecule deliver

Functional 2D nanoparticle/polymer array : interfacial assembly, transfer, characterization, and coupling to photonic crystal cavities

We developed a universal, facile and robust method to prepare free-standing, ordered and patternable nanoparticle/polymer monolayer arrays by evaporation-induced self-assembly at a fluid interface. The ultra-thin monolayer nanoparticle/polymer arrays are sufficiently robust that they can be transferred to arbitrary substrates, even with complex topographies. More importantly, the Poly (methyl methacrylate) (PMMA) in the system serves as a photoresist enabling two modes of electron beam (e-beam) nanoparticle patterning. These ultra-thin films of monolayer nanoparticle arrays are of fundamental interest as 2D artificial solids for electronic, magnetic and optical properties and are also of technological interest for a diverse range of applications in micro- and macro-scale devices including photovoltaics, sensors, catalysis, and magnetic storage. By co-assembly with block co-polymers, the nanoparticles were selectively positioned in one specific phase, representing a high throughput route for creating nanoparticle patterns. The self-assembly process was investigated by combined in-situ grazing incidence small angle x-ray scattering (GISAXS) and numerical simulation. By e-beam irradiation of free-standing 2D NP/polymer arrays, anisotropic nanowire arrays have been fabricated. Additionally, preliminary investigation on assembly of binary nanoparticle arrays has also been introduced, serving as promising future directions of interfacial assembly. viii Controlling the rate of spontaneous emission and thus promoting the photon generation efficiency is a key step toward fabrication of Quantum dot based single-photon sources, and harnessing of light energy from emitters with a broad emitting spectrum. Coupling of photo emitters to photonic cavities without perturbing the optical performance of cavities remains as a challenge in study of Purcell effect based on quantum electrodynamics. Taking advantage of interfacial assembly and transfer, we have achieved controlled deposition of quantum dots into high Q photonic microcavities and studied the modification of their optical properties. Anomalous enhanced spontaneous emission and Fabry-Perot resonance have been observed

Electrospray deposition of chalcogenide glass films for gradient refractive index and quantum dot incorporation

Chalcogenide glasses (ChGs) are well-known for their optical properties, making them ideal candidates for emerging applications of mid-infrared microphotonic devices, such as lab-on-a-chip chemical sensing devices, which currently demand additional flexibility in processing and materials available to realize new device designs. Solution-derived processing of ChG films, initially developed in the 1980s by Chern and Lauks, has consisted mainly of spin-coating and offers unique advantages over the more traditional physical vapor deposition techniques. In the present effort, the nanoparticles of interest are luminescent quantum dots (QDs), which can be used as an on-chip source of light for a planar chemical sensing device. Prior efforts of QD incorporation have exposed limitations of spin-coating of ChG solutions, namely QD aggregation and material waste, along with incompatibility with larger scale manufacturing methods such roll-to-roll processing. This dissertation has evaluated electrospray (ES) as an alternative method of solution-derived chalcogenide glass film deposition. While employed in other materials systems, deposition of optical quality ChG films via electrospray has not been previously attempted, nor have parameters until now, been defined. This study has defined pre-cursor solution chemistry, electrospray jet process parameters required for formation of stable films, annealing protocols and resulting film attributes, yielding important correlations needed to realize high optical quality films. Electrosprayed films attributes were compared to those seen for spin coating and trade-offs in processing route and resulting quality, were identified. Optical properties of importance to device applications were defined, including surface roughness, refractive index, and infrared transmission. The use of a serpentine path of the spray over the substrate was demonstrated to obtain uniform thickness, blanket films, and demonstrates process compatibility with roll-to-roll processing whereby (theoretically) 100% of starting solution can be utilized in a continuous process. The present effort has shown that electrospray offers the advantage of spatially defined, localized deposition, which enables direct 2-D and 3-D printing, though with limited (unoptimized) spatial resolution on the order of millimeters. Knowledge of processing protocols were exploited to fabricate multi-layer films from two different glass compositions to yield an effective refractive index gradient (GRIN). GRIN coatings were fabricated and refractive index variations were predicted. The advantages of electrospray deposition were also explored for the enhancement of quantum dot doping in ChG films. A hypothesis whereby electrospray would enable deposition of films based on consolidation of many, single QD doped aerosol droplets was developed and evaluated. Experimental validation of this premise in CdSe and PbS doped ChG films was shown, indicating that electrospray offers a kinetic barrier to QD movement preventing aggregation from occurring, not seen in spin-coating. Two types of organic ligands were found to enhance dispersion of QDs in amine solvents, octadecylamine and mercaptopropionic acid. Utilizing TEM characterization, evidence that electrospray may be more suitable than spin-coating for the dispersion of QDs in solution-derived ChG films was confirmed. However, the ultimate effectiveness of this approach was limited due to the ability to quantify direct loading levels of the QD and surrounding glass matrix. This work demonstrates that electrospray offers additional flexibility over spin-coating and other evaporation methods for the deposition of ChG coatings. Electrospray processing of doped and undoped ChG solutions for microphotonic applications has been shown as a viable alternative in the processing and material toolbox where spatially defined index and dopant control is required

The effect of surface structure on the optical and electronic properties of nanomaterials

Surface passivation of semiconductor quantum dots is essential to preserve their efficient and robust light emitting properties. By using a lattice matched (mismatch = 0.5%) lead halide perovskite matrix, we achieve shell-like passivation of lead sulfide QDs in crystalline films, leading to efficient infrared light emission. These structures are made from a simple one-step spin coating process of an electrostatically stabilized colloidal suspension. Photoluminescence and transient absorption spectroscopy indicate rapid energy transfer between the perovskite matrix and the QDs, suggesting an interface with few trap states. In addition to housing the efficient infrared QD emitters, lead halide perovskites themselves have good carrier mobilities and low trap densities, making these solution-processable heterostructures an attractive option for electrically pumped light emitting devices. The highest performing quantum dots for visible light applications are CdE (E=chalcogenide) core/shell heterostructures. Again, surface passivation plays a huge role in determining the brightness and robustness of visible QD emitters. Multilayer shell passivation is usually used to produce the highest quantum yield particles. Surface trap states are shown to be detrimental to luminescence output, even in thick-shelled particles. Spherical quantum wells allow for thicker shells and with good surface passivation, show promising reduction of biexciton auger recombination, as measured by a time correlated single photon counting (TCSPC) microscope. TCSPC methods were used to diagnose and identify QD architectures for LED applications and explore fundamental recombination dynamics using photon antibunching measurements, and statistical analysis of blinking traces.Introducing new surfaces onto graphitic substrates can be a useful for introducing new electronic properties, patterning device-specific geometries, or appending molecular catalysts. Metal nanoparticles were used to act as a catalyst for the gasification and etching of graphite and graphene. Several methods of controlling the initiation, propagation, and density of these trenches were explored. Patterning defects helped control where initiation occurred, while faceting existing defect sites could also enable more facile initiation and control the direction at the beginning of etching, due to the wetting mechanism of particle movement. Patterning the metal also was shown as a promising avenue to limit unwanted gasification and promote etching in specific, patterned regions. Surface functionalization using reactive gases was performed and characterized with outlook for future experiments

量子ドット太陽電池とペロブスカイト太陽電池における界面エンジニアリングと界面電荷移動ダイナミクス

電気通信大学201

Surface Optochemical Sensors

The objective of my research is to develop new surface optochemical sensors for studying cellular processes by investigating techniques to modify surface properties. The spectral characteristics of the modified surfaces and coatings are designed to show remarkable changes after interaction with analytes from biological fluids and cells. My studies focused on pancreatic cells and addressed the need for improved techniques to measure zinc release from pancreatic cells (chapter 3, 4) and to measure the metastasis potential of cancerous pancreatic cells (chapter 5). Chapter 3 describes the development of zinc sensing glass slides by conjugating a carboxylmodified ZnAF-2 to an amino functionalized glass surface. The sensor was used for the measurement of glucose-stimulated zinc ion release from cultured beta pancreatic cells with impact in diabetes research. In chapter 4 is described conjugation of the carboxyl-modified ZnAF-2 to antibody molecules (A2B5) that specifically recognize pancreatic cells. This enabled for the first time the use of targeted zinc sensors to monitor zinc release events from pancreatic cells. Chapter 5 describes development for the first time of a fluorescence sensor to measure the proteolysis activity of pancreatic cancer cells in microfluidic systems. The sensor was fabricated using a Layer by layer (LbL) deposition of polyelectrolyte. The sensor was based on Fluorescence Resonance Energy Transfer (FRET) between luminescent quantum dots (serve as donors) and rhodamine molecules (serve as acceptors) that are separated by multi-layers of polyelectrolytes. The microfluidic platform enables precise delivery of reactants to assemble the sensor and facilitate unique cellular assays of enzymatic activity and enzymatic expression on pancreatic cancer cells