Littérature scientifique sur le sujet « Colloidal NC »

A method of colloidal synthesis of monodisperse nanocrystals (NC) with high stability, narrow bands of photoluminescence (PL) and high quantum yield has been developed. The process of colloidal synthesis took place at room temperature and for the passivation of NC used a variety of surfactants. The surface of NC CdTe was modified by introducing them into a matrix, organic or crystalline. In our case, the matrix was porous Silicon (PS), that is a composite structure was formed on the basis of the matrix and NC semiconductor. Nanocomposite structures of PS – NC CdTe were obtained by introducing colloidal solutions of NC CdTe into the solid matrix of PS and subsequent processing at a certain temperature regime. The photoluminescent properties of a composite system in which the matrix is microcrystalline PS and the second component is NC CdTe deposited from a colloidal solution of NC CdTe have been studied. The peculiarity of this system is that both components have PL of different intensities.The large difference in PL intensities and different positions of the radiation bands allowed, comparing the PL spectra of the colloidal solution of NC CdTe, PS and NC CdTe – PS at different stages of introduction of CdTe nanoparticles into the porous Silicon surface, to identify the interaction and mutual influence of the two constituent materials. The main disadvantages of the method are its relative novelty, which leads to the need for empirical selection of some parameters of the synthesis. The planned change of properties of PS and colloidal solutions of NC CdTe by variation of technological methods of synthesis and processing methods will allow to control the physical properties of this composite system and use it to develop new principles of design and creation of new generation sensor devices.

Over the last few decades, a tremendous research effort has been dedicated to realizing colloidal nanocrystals (NCs) as useful devices. Contrary to the well-established synthesis of colloidal NCs, the fabrication method to transfer the NCs to a nanostructured film has not studied well, despite the importance of using NCs as integrated devices. Especially, an advanced fabrication technique is crucial for further improving device performance along with the fine colloidal synthesis and NC device applications. As an advanced technique, electrophoretic deposition (EPD) can be introduced to mitigate the limitations of traditional tools, such as spin-coating, drop-casting, and spray coating, by creating desirable NC thin films from colloidal solutions using an electric field. We found several key controllable parameters such as solvent, surfactant ligand, and voltage, to tune the NC film’s morphology as well as the mechanism of the NC deposition. To clearly understand the mechanism of the deposition, in-situ technique was also developed by utilizing a light scattering method, which can provide the real time tracking analysis.

We consider a system consisting of very small colloidal particles clothed each by f end-grafted flexible polymer chains we regarded as star polymers, and hard spherical colloidal particles in a good solvent. Our main objective is to determine the expression of the interaction force between a spherical colloid and a star polymer as a function of distance between them. We limit ourselves to the case where the star polymer is smaller than the colloid. In the first part, the system is dissolved in a melt of short linear chains of polymerization degree P<N, where N denotes the polymerization degree of grafted chains. To compute the expected force, we consider two regimes: (1) high-grafting density [Formula: see text] and (2) small-grafting density (f < f*). For (f > f*), we show that the expression of the expected force coincides exactly with that of the case of a small molecular weight solvent. For (f < f*), we show that there is a change in behavior. In the second part, we assume that the lengths of the f grafted chains were randomly distributed and there is talk of a polydisperse star polymer. We show that the computation of the expected force depends on the relative values of the polymerization degree of longest grafted chain, N, when it is compared to the typical one Nc ~ f1/(α-1). Here α is the polydispersity exponent. We distinguish two regimes depending on whether N < Nc or N > Nc. For the regime with N < Nc, and comparing the expression of the force obtained for the monodisperse case, we can say that the polydispersity of grafted chains induce a drastic change of the force expression. For the regime with N > Nc, we found the existence of two distance-ranges. For small distances, the effective force expression is identical to that relative to the above case (N < Nc). But for high distances, the effective force expression is similar to the monodisperse case.

Analytical ultracentrifugation (AUC) is a powerful technique to observe colloidal nanocrystals (NCs) directly in solution and obtain critical information about their physical-chemical properties. Nevertheless, a more comprehensive implementation of AUC for the characterisation of such a class of crystalline colloids has been traditionally impaired by the requirement of having a priori knowledge of the complex, multilayered structure formed by NC in solution. This includes the nature (density and mass) of the surface ligands (SLs) that provide NC colloidal stability and the shell of solvent molecules formed on it. Herein, we propose a methodology to determine the NCs size by using SLs with a density equal to that of the solvent. Thereby, the buoyancy force of the SL shell is neutral, and the density of the NCs is sufficient a priori knowledge to calculate their related mass and size distributions. The simplicity and reliability of the method are evaluated with cetyltrimethylammonium bromide (CTAB) stabilized spherical gold NCs (AuNCs) of dimensions ranging from 1 to 17 nm. The proposed method has great potential to be transferred to any non-crystalline and crystalline colloids of different nature and composition, which have a density that is equal to the bulk and can be stabilized by SLs having a density that matches that of the solvent.

The physicochemical properties of low-dimensional structures based on CdTe obtained are investigated by the method of colloidal synthesis. The analysis of the optical absorption spectra and the luminescence intensity of the CdTe colloidal NCs showed that the nature of the dispersion medium significantly affects their optical properties. The optical absorption spectra of the CdTe NK fractions obtained by dissolving the flocs in deionized water and in deionized water with the addition of NaOH have been shown to have the same character. However, the addition of NaOH results in a shift of the absorption maximum by 8-12 nm into the longwave region. This suggested that the addition of NaOH to the colloidal solution of NK CdTe during sedimentation deposition leads to the aggregation of cadmium telluride particles. The addition of NaOH results in the quenching of photoluminescence. It can be assumed that during the sedimentation deposition there is a leaching of THC to a critical concentration, therefore, due to insufficient stabilization of the surface of the NC CdTe, a rapid aggregation of particles occurs and a loss of sedimentation stability of the solution is observed, which causes the PL quenching. The analysis of the optical absorption and photoluminescence spectra of the fractions of the colloidal solution of NC CdTe obtained by using DMF as a dispersion medium during the sedimentation deposition leads to the conclusion that the nature of the dispersion medium significantly affects the optical properties of CdTe NC. The maxima of the OP spectra corresponding to the first exciton transition of all fractions are shifted to the longwave region and change their shape compared to the corresponding spectra for the aqueous fractions. In this case, the PL intensity of the first and second fractions of CdTe NC in DMF is approximately 100 ppm. exceeds the PL intensity of the aqueous fractions, which can be explained by the fact that DMF, unlike deionized water, does not wash out THC from the surface of the CdTe NC.

We report on preparation process and optical characterization of a nanocomposite material obtained dispersing colloidal semiconductor nanocrystals (NCs), namely CdS and CdSe@ZnS core–shell system in poly(methyl methacrylate) (PMMA). Such method allows a large flexibility on nanocrystal materials and on the choice of the polymer characteristics. Nanocomposite thin films were extensively investigated by means optical and morphological techniques. The effects on NC composition, concentration, size, and surface chemistry on the spectroscopical and structural behaviour of the nanocomposite properties were studied. The NC size dependent optical properties of the nanocomposites are mainly accounted by the NC composition and size, while the morphology of the films is explained on the base of the NC surface characteristics and their concentration in the nanocomposites.

A continuous synthetic method in a micro-tubular reactor is introduced for synthesizing mono-disperse and solution-stable chalcopyrite colloidal copper indium diselenide nanocrystal (CuInSe₂ NC) inks with potential scalability.

We report a hot-injection colloidal method for the synthesis of nanocrystalline (NC) iron diselenide (FeSe₂), and iron ditelluride (FeTe₂) derived from iron(ii) bromide as the iron (Fe) precursor.

The Radford Army Ammunition Plant (RAAP) produces nitrocellulose (NC) as a major ingredient in tank and artillery ammunition propellant. Through the process of NC production, wastewater is generated which contains large quantities of NC in the micron and sub-micron size range. These suspended and colloidal particles are collectively called NC fines. Under the impetus of a proposed Ammunition Procurement and Supply Agency suspended solids effluent limit of 25 mg/l and a greater emphasis on pollution prevention, significant research has been conducted into the areas of waste minimization and NC fine removal at the RAAP. One aspect of the current research involved a field study at the RAAP. The purpose of the field study was to inspect and discuss the entire NC production process with the operators, foremen, and NC production supervisor. With the information collected at the RAAP, it was possible to propose several waste minimization schemes and NC fines removal alternatives. From existing data, it was calculated that the proposed pollution prevention ideas could save the RAAP approximately $1,500,000 annually.

I nanocristalli colloidali a semiconduttore (NC), grazie alle loro proprietà ottiche regolabili tramite la dimensione ed alla processabilità in soluzione, sono state a lungo proposte come alternative versatili e sintetizzate chimicamente per numerose tecnologie fotoniche, optoelettroniche e quanto-computazionali, nonché come building-blocks funzionali e superatomici per metamateriali artificiali assemblati con approcci bottom-up. Dalla loro scoperta oltre 30 anni fa, enormi progressi nella chimica colloidale e superficiale, nella fisica dei NC e nelle applicazioni nei dispostivi, hanno portato queste proposte sempre più vicine alla realtà. In questo lavoro esploro i fenomeni fotofisici di quattro diversi sistemi di NC, differenziati dalla composizione chimica e dalla loro forma. Ho studiato i più promettenti NC ternari intrinseci di CuInS2 che in modo innato offrono alternative senza metalli pesanti e non tossiche ai materiali esistenti a base di Cd e Pb, caratterizzate da un ampio Stokes shift e lunghi tempi di decadimento di fotoluminescenza. L’origine di queste proprietà ottiche nei NC di CuInS2 non era però stata compresa, con teorie contrastanti che le descrivono. Qui, dopo aver confermato sperimentalmente l’origine della PL dovuta alla struttura fine della banda di valenza, abbiamo ottimizzato i NC per fabbricare un concentratore solare luminescente ad ampia area (30x30 cm2) con una efficienza di potenza ottica record del 6.8%. In seguito, discuto gli effetti del drogaggio ad impurezza elettronica in NC di calcogenuri binari sintetizzati tramite una innovativa procedura di crescita “a seme” che risulta in un numero preciso di droganti in ogni NC, quindi superando il limite poissoniano per le loro proprietà di semiconduttori magnetici diluiti (DMS). Studi strutturali, spettroscopici e magneto-ottici descrivono in dettaglio i processi fisici coinvolti, dovuti al livello di drogaggio esatto dei NC. Gli atomi d’oro, inseriti come droganti per la prima volta all’interno di NC II-VI, sono incorporati come specie non magnetica Au+ ed attivano una PL intensa e variabile con la dimensione all’interno del gap del semiconduttore, modificando artificialmente l’occupazione della banda di valenza. Fondamentalmente, la conversione transiente degli Au+ in Au2+ paramagnetici (configurazione 5d9) sotto eccitazione ottica genera sia un forte magnetismo che un comportamento da DMS che dimostrano il contributo delle singole impurezze paramagnetiche al magnetismo macroscopico dei NC, sbloccando il loro potenziale applicativo in dispositivi quantici e di spintronica. Inoltre, riporto gli effetti del drogaggio sostituzionale con atomi paramagnetici in NC di perovskite CsPbCl3 drogati con Mn2+ e rivelo il meccanismo di trasferimento di energia specifico che coinvolge stati di difetto poco profondi che risultano nella duplice emissione di PL e inducono uno Stokes shift vantaggioso per tecnologie di gestione fotonica. Infine, concludo mostrando gli effetti della anisotropia di forma in sistemi di NC colloidali con la sintesi e lo studio di nanoplateles bidimensionali di CdTe. Inoltre, mostro alcuni dati spettroscopici preliminari che rendono questi sistemi molto attraenti per applicazioni nella tecnologia laser e di rilevamento di radiazione ultraveloce. Nel corso di questo lavoro, ho lavorato sulla sintesi colloidale delle nanostrutture e studiato i sistemi nanocristallini menzionati usando tecniche di caratterizzazione strutturale come la diffrazione di raggi X e la microscopia a trasmissione elettronica. Tecniche spettroscopiche tra cui l’assorbimento transiente ultraveloce, la PL a stato stazionario e risolta in tempo a temperature criogeniche, il dicroismo circolare magnetico e la risonanza paramagnetica di elettroni sono state usate per investigare queste nanostrutture, chiarendo la loro fotofisica fondamentale e sfruttando i loro potenziali applicativi in tecnologie moderne e di nuova generazione.
Colloidal semiconductor nanocrystals (NCs), owing to their size-tuneable electronic properties and solution processability, have long been proposed as versatile chemically synthesized alternatives for many photonic, optoelectronic, and quantum computational technologies as well as super-atomic functional building blocks for bottom-up assembled artificial metamaterials. Since their original discovery over 30 years ago, tremendous advancements in colloidal and surface chemistry, NC physics, and device application have brought this vision closer to reality. In this work I explore these photophysical phenomena in four different NC systems diversified by chemical composition and shapes. I studied the most favorable intrinsic ternary CuInS2 NCs which inherently offers heavy metal free, non-toxic alternatives to the existing Cd and Pb based materials with a large Stokes shift and long photoluminescence decay time. The origin of these optical properties in CuInS2 NCs were however not fully understood with conflicting theories describing its characteristic aforementioned properties. Here, subsequential to experimentally confirming the valence band fine structure origin of luminescence in these nanostructures, we utilized the optimized NCs and fabricated a large area Luminescent solar concentrator of 30ˣ30 cm2 area with record Optical Power Efficiency of 6.8% to the date. Then, I discuss the effects of electronic impurity doping in binary chalcogenide NCs synthesized by a novel seeded growth procedure resulting in quantized dopants in each NC thus overcoming the Poissionian bottleneck for their diluted magnetic semiconductor properties. Structural, spectroscopic, and magneto-optical investigations trace a comprehensive picture of the physical processes involved, resulting from the exact doping level of the NCs. Gold atoms, doped here for the first time through the reaction protocol into II−VI NCs, are found to incorporate as non-magnetic Au+ species activating intense size-tuneable intragap photoluminescence and artificially offsetting the hole occupancy of valence band states. Fundamentally, the transient conversion of Au+ to paramagnetic Au2+ (5d9 configuration) under optical excitation results in strong photoinduced magnetism and diluted magnetic semiconductor behaviour revealing the contribution of individual paramagnetic impurities to the macroscopic magnetism of the NCs unlocking their potential to be exploited for applications in quantum and spintronic devices. Moreover, I communicate the effects of substitutional doping with paramagnetic atoms in Manganese doped CsPbCl3 perovskite NCs and reveal a peculiar energy transfer mechanism involving shallow defects states subsequently resulting in dual emission and inducing Stokes shift desirable for photon management technologies. Finally, I conclude by talking about the effect of shape anisotropy in colloidal NC systems by synthesizing and studying two-dimensional colloidal CdTe nanoplatelets. Moreover, I report some very interesting preliminary spectroscopic data that presents these NC systems at great heed with respect to their application in lasing technology and in Ultrafast radiation detection applications. Through the course of my PhD, I worked on the colloidal synthesis of nanostructures, and studied the aforementioned NC systems using structural characterization techniques like X-Ray diffractions and transmission electron microscopy. Spectroscopic techniques including ultrafast transient absorption, steady state and time resolved photoluminescence spectroscopy at cryogenic temperatures, magnetic circular dichroism and electron paramagnetic resonance were used to study and report these nanostructures, thus elucidating their fundamental photophysics and exploit their applicative potential in modern, next generation technologies.

Emulsification is an important process in various fields including foods, pharmaceuticals, cosmetics, and chemicals. Emulsification operation is commonly conducted using conventional emulsification devices, such as high-speed blenders, colloid mills, high-pressure homogenizers, and ultrasonic homogenizers. However, these emulsification devices result in the production of polydisperse emulsions with wide droplet size distributions and poor controllability in droplet size and its distribution. In contrast, monodisperse emulsions consisting of monosize droplets have received a great deal of attentions over the past decade due to their high-tech applications, e.g., monosize microparticles as spacers for electronic devices and monosize micro-carriers for drug delivery systems (DDS). Our group proposed microchannel (MC) emulsification as a promising technique to produce monodisperse emulsions in the mid 1990s. Micro/Nanochannel (MNC) emulsification enables generating monosize droplets with the smallest coefficient of variation (CV) of below 5% using MC and nanochannel (NC) arrays of unique geometry. The resultant droplet size, which ranged from 0.5 to 200 μm, can be precisely controlled by channel geometry. Droplet generation for MNC emulsification is very mild and does not require any external shear stress; a dispersed phase that passed through channels is transformed spontaneously into monosize droplets inside a continuous-phase domain. The aim of this paper is to present recent developments in MNC emulsification chips, particularly focusing on asymmetric straight-through MC arrays for large-scale production of monodisperse emulsions. Asymmetric straight-through MC array chips were fabricated using a silicon-on-insulator wafer. Numerous asymmetric straight-through MCs each consisting of a microslot and a narrow MC were positioned in the central region of the chip. Monosize droplets were stably generated via asymmetric straight-through MCs at high production rates. Below a critical droplet production rate, monosize droplets were generated via asymmetric straight-through MCs, with droplet size and size distribution independent of the droplet productivity. The use of a large asymmetric straight-through MC array chip achieved the mass production of monosize tetradecane oil droplets at ∼1 L/h. The simulation results using CFD (computational fluid dynamics) agreed well with the experimental results and provided useful information, such as the movement of the oil-water interface during droplet generation. Monosize submicron droplets were also obtained using NC emulsification chips made of single-crystal silicon.