Добірка наукової літератури з теми "High Quality Semiconductor Nanocrystals"

The following is an edited transcript of the presentation given by A. Paul Alivisatos, recipient of the Outstanding Young Investigator Award, at the 1995 MRS Spring Meeting in San Francisco.The work I will describe on semiconductor nanocrystals started with the realization that it is possible to precipitate a semiconductor out of an organic liquid. We can precipitate out a semiconductor as a colloid—a very small-sized semiconductor with reduced dimensionality—that will show large, quantum size effects. A dream at that time was to make an electronic material by such a process in a liquid beaker, by starting with an organic fluid and somehow injecting something into the fluid to make very small particles, which we could use in electronics. The materials we use in electronics today have perfect crystalline order. We are able to put in dopants very specifically, or control precisely their arrangements in space in enormously complicated ways. The level of purity of electronic materials is so high that making an electronic material in a wet chemistry approach seems almost impossible. If, in addition, we specify that the size must be controlled precisely, we recognize the project is a problem for basic research, yet not one ready for applications. Many fundamental problems arise if we try to make semiconductor particles, in a liquid, of such high quality that they can be used as electronic materials.

Epitaxially overgrowing a semiconductor material with higher bandgap around the QDs has proven to be a crucial approach for improving the PL efficiency and stability of nanocrystals. In this paper, a ZnS shell was deposited around ZnSe nanocrystal cores via a noninjection approach in aqueous media. The deposition procedure conducted at 100°C in a reaction flask in the presence of the shell precursor compounds, together with the crude ZnSe nanocrystal cores and the thiol ligand glutathione. The influences of various experimental variables, including the reaction time, amount of thiourea, as well as pH value, on the growth rate and luminescent properties of the obtained core/shell nanocrystals have been systematically investigated. In comparison with the original ZnSe nanocrystals, the PL efficiency of the obtained ZnSe/ZnS core/shell nanostructures can be improved significantly with a QY up to 62.8%.

Lead-halide perovskite nanocrystals (NCs) are receiving much attention as a potential high-quality source of photons due to their superior luminescence properties in comparison to other semiconductor NCs.

AbstractRecent advances in colloidal synthesis of nanocrystals have enabled high-quality high-efficiency light-emitting diodes, displays with significantly broader color gamut, and optically-pumped lasers spanning the whole visible regime. Here we review these colloidal platforms covering the milestone studies together with recent developments. In the review, we focus on the devices made of colloidal quantum dots (nanocrystals), colloidal quantum rods (nanorods), and colloidal quantum wells (nanoplatelets) as well as those of solution processed perovskites and phosphor nanocrystals. The review starts with an introduction to colloidal nanocrystal photonics emphasizing the importance of colloidal materials for light-emitting devices. Subsequently,we continue with the summary of important reports on light-emitting diodes, in which colloids are used as the color converters and then as the emissive layers in electroluminescent devices. Also,we review the developments in color enrichment and electroluminescent displays. Next, we present a summary of important reports on the lasing of colloidal semiconductors. Finally, we summarize and conclude the review presenting a future outlook.

A controllable aqueous oxidation reaction enabled layer-by-layer corrosion has been proposed to prepare high-quality two-dimensional (2D) semiconductor nanocrystals with single layer accuracy and well-retained hexagonal shapes.

ABSTRACTNanomaterials have broad application potential in biomedical and environmental science. Engineered nanomaterials are required to explore such potential. Among them carbon-based fluorescent nanoparticles offer promising alternative of conventionally used semiconductor nanocrystals, as they do not have heavy metals and associated toxicity issues. We are developing synthetic methods for high quality fluorescent carbon nanoparticle, suitable for biological staining and diagnostics. Here we focus on synthesis of fluorescent carbon nanoparticle from biomolecules, exploiting the conventionally used nucleation-growth conditions for synthesis of high quality nanocrystals such as quantum dot and metal oxides. We have shown that high quality fluorescent carbon nanoparticle can be synthesized from folic acid, riboflavin and lactose and they can be used as non-toxic bio-imaging probe.

Synthesis of CdS/CdCO3Core/Shell semiconductor nanocrystals potentially used for solar cell via hydrothermal route is presented. Water-soluble crystallites with wurtzite crystal structure (CdS), hexagonal structure (CdCO3) with strong photoluminescence are prepared. The synthesis is based on the separation of the nucleation and growth stages of core and shell by controlling some crucial factors such as temperature, pH, ratio and concentration of reactant mixture. Bare wurtzite structural CdS nanocrystallites were synthesized by using cadmium acetate and thiourea as precursors. Ostwald ripening process under high temperature leads to high sample quality. Photoluminescence of nanocrystals with Core/Shell Structure and bare nanocrystals was compared and analysed. Nanocrystals with Core/Shell Structure have stabler performance of photoluminescence than CdS bare nanocrystallites because of the shell. Transmission electron microscopy and X-ray powder diffraction indicate the presence of bulk structural properties in crystallites as small as 5nm in diameter. X-ray Photoelectron Spectroscopy was used to characterize core/shell structure of as-prepared NCs. Ultra-stability and super strong photoluminescence emission of as-prepared CdS/CdCO3Core/Shell semiconductor nanocrystallites indicates its potentially practical value in NCs solar cell.

New approaches for the synthesis of highly luminescent InP and InP/ZnS nanocrystals were developed by stepwise systematic investigation of the parameters during the reaction stages. The parameters, including solvents, precursors, ligands, capping agents, protic agents, Lewis acids and bases and temperature were discussed in detail in different chapters. The investigation processes helped increase understanding of understand the reaction and surface passivation mechanisms and to develop convenient synthesis approaches. Highly luminescent InP NCs were prepared with an in-situ indium chloride complex in the presence of zinc carboxylates or zinc dithiocarbamates - convenient nucleation initiators and stabilisers. The nanocrystals prepared covered a wide photoluminescence emission range from blue to the near infra-red. This synthesis method also allowed the in-situ growth of highly luminescent InP/ZnS core-shell nanocrystals as well. The principles of selection of reagents are also applicable in the synthesis of other nanocrystals. The as-prepared high-quality InP and InP/ZnS nanocrystals have been exploited in applications in the fields of light emitting diodes (LEOs) and bioimaging.

Aquesta tesi descriu la síntesi i caracterització de nanocristalls de perovskita BMO3 i la seva aplicació a millora les propietats de materials superconductors. Els protocols per la síntesi van permetre poder ajustar els nanocristalls al medi desitjat, a més d’aconseguir una alta estabilitat durant llarg períodes de temps en solucions amb contingut d’alta concentració de salts. La síntesi dels nanocristalls de BMO3 s’ha realitzat a partir d’una metodologia hibrida solvotèrmal, la qual està basada en la combinació d’una reacció aquós sol-gel i un procés solvotèrmal. Utilitzant aquesta metodologia vam reportar una síntesis general, fàcil, ràpida i reproduïble per tal d’obtenir nanocristalls de perovskites BMO3. A més, s’ha estudiat diferents condicions sintètiques, així com, el mecanisme del la formació dels nanocristalls. Considerant les aproximacions anteriors per obtenir aquest tipus de nanocristalls, la nostra metodologia proporciona una alta cristal·linitat amb una reducció dràstica en el temps de reacció. A través de l’estudi de nanocristalls de BaZrO3 vam postular el mecanisme que governa la mida dels nanocristalls. A més, el mecanisme postulat per aquest cas també és aplicable a altres perovskites. La nostra metodologia híbrida va demostrar la síntesi amb èxit de BaMO₃ M= (Ti4+, Zr4+and Hf4+), a més d’obtenir SrTiO3 al canviar el catió bivalent per Sr2+ Hem estudiat l’aplicabilitat dels nanocristalls sintetitzats, els quals millorant les propietats superconductores en nanocomposits en pel·lícules preparades per deposició de solució química utilitza solució de precursor d’Itri, Bari i sals de Coure. A més, aquests nanocristalls romanen estables durant llargs temps a altes concentracions en diferents solucions precursors de YBa2Cu3O7−δ. Per tant, estem demostrant per primer cop, que uns nanocristalls no reactius com BaMO₃ (M= Zr4+and Hf4+) són adequats per fabricar una alta qualitat de pel·lícules primes i gruixudes. També vam demostrar que la composició i mides dels nanocristalls són un factor crucial per determinar el comportament final de la fixació de vòrtex en aplicar un camp magnètic. En conclusió, no només es presenta uns nanocristalls amb una mida tunejable i una alta estabilitat al llarg del temps, sinó que també es demostra la seva efectivitat per realçar les propietats superconductores al introduïr els nanocristalls a una matriu de YBa2Cu3O7−δ. Donat la novetat i pertinència del nostre mètode híbrid aquest pot ser aplicable per sintetitzar un ampli ventall de nanocristalls.
Esta tesis describe la síntesis y caracterización de nanocristales de perovskitas BMO3 y su aplicación directa. Los protocolos de síntesis permitieron ajustar el tamaño de los nanocristales y lograr una estabilidad a largo plazo en soluciones con alto contenido de medios salinos. Estas nuevas propiedades de los nanocristales se aprovecharon para incrustarlos en un material superconductor YBa2Cu3O7−δ, mejorando las propiedades superconductoras de este material. Para sintetizar los nanocristales de BMO₃ se ha utilizado una metodología solvotermica híbrida, la cual está basada en la combinación específica de tratamientos sol-gel acuoso y un proceso solvotermal. Usando esta metodología obtenemos una ruta de síntesis general, fácil, rápida y reproducible de nanocristales de BMO₃. Además, se presenta unos estudios detallados a diferentes condiciones sintéticas, así como conocimientos sobre el mecanismo de formación de los nanocristales. Teniendo en cuenta las aproximaciones anteriores a esta familia de perovskitas, nuestra metodología proporciona nanocristales de forma definida altamente cristalina con una reducción drástica del tiempo de reacción. A través del estudio de los nanocristales de BaZrO₃, postulamos el mecanismo que gobierna el tamaño de los nanocristales. Este mecanismo propuesto resultó no ser solo específico para este caso, sino también aplicable a otros perovskitas. Nuestra metodología híbrida ha demostrado una síntesis exitosa de nanocristales en el caso de BaMO₃ M = (Ti4+, Zr4+ y Hf4+), además de obtener SrTiO3 al cambiar el catión divalente por Sr2+. Hemos estudiado las aplicaciones de los nanocristales sintetizados mejorando las propiedades superconductoras de películas de nanocompositos preparadas por deposición de solución química utilizando solución precursora de sales de itrio, bario y cobre. Además, los nanocristales muestran una alta estabilidad a largo plazo en diferentes soluciones precursoras de YBa2Cu3O7−δ incluso a altas concentraciones de nanocristales. En este documento, demostramos por primera vez que los nanocristales no reactivos de BMO₃ (M = Zr4+ y Hf4+) son adecuados para el crecimiento de películas delgadas y gruesas de alta calidad mediante la deposición de solución química. Además, también demostramos que la composición y los tamaños de los nanocristales son un factor crucial para adaptar el rendimiento de fijación de vórtices en campos magnéticos aplicados. En conclusión, no solo presentamos el logro de nanocristales de perovskita BMO₃ de tamaño fácil de ajustar y de alta estabilidad, sino que también demostramos su eficacia para mejorar las propiedades superconductoras cuando los nanocristales se mezclan en la matriz YBa2Cu3O7.
This thesis describes the synthesis and characterization of novel perovskite BMO3 nanocrystals and its application improving properties of superconducting material. The developed synthesis protocols allowed to tune nanocrystals’ size and achieve long-time stability in solutions with high salt media content. These new properties in the nanocrystals were exploited to embed them into a superconducting material, YBa2Cu3O7−δ, enhancing the superconducting properties of the material. The general trends of BMO₃ have been unravel using a hybrid solvothermal methodology based on the specific combination of aqueous sol-gel and solvothermal treatments. Using this methodology we reported a general, easy, fast and reproducible synthesis route of BMO₃ nanocrystals. Moreover, we present detailed studies of different synthetic conditions as well as insights in the mechanism of the nanocrystal’s formation. Considering previous approximations to this perovskite family, our methodology provides highly crystalline shape-defined nanocrystals with a drastic reduction on reaction time. Through the study of BaZrO₃ nanocrystals we postulated the governing mechanism tunning the sizes of the nanocrystals. This proposed mechanism proved to be not only specific to this case but also applicable to other perovskites. Our hybrid methodology demonstrated the successful synthesis of BaMO₃ M= (Ti4+, Zr4+ and Hf4+) nanocrystals, besides of, obtaining SrTiO3 when changing the divalent cation for Sr2+. We have studied the applications of the synthesized nanocrystals improving the superconducting properties of nanocomposites films prepared by chemical solution deposition using precursor solution of Yttrium, Barium and Copper salts. Additionally, the nanocrystals showed long term high stability in different YBa2Cu3O7−δ precursor solutions even at high nanocrystals concentration. Herein, we demonstrate for the first time, that non-reactive BMO₃ (M= Zr4+ and Hf4+) nanocrystals are suitable for growing high quality thin and thick films using chemical solution deposition. Furthermore, we also demonstrated that the composition and sizes of the nanocrystals are a crucial factor for tailoring vortex pinning performances in applied magnetic fields. In conclusion, we not only present the achievement of easily tunable-size and high-stable BMO₃ perovskite nanocrystals but demonstrated their effectiveness to enhance the superconducting properties when the nanocrystals are mixed into YBa2Cu3O7 matrix. Given the novelty and potential relevance of our hybrid method in a deep range of nanoscale systems.
Universitat Autònoma de Barcelona. Programa de Doctorat en Ciència de Materials

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2004.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references.
by Nathan E. Stott.
Ph.D.

This dissertation focuses on high-performance LC-tank CMOS VCO design at 2 GHz. The high-Q inductors are realized using wiring metal lines in advanced packages. Those inductors are used in the resonator of the VCO to achieve low phase noise, low power consumption, and a wide frequency tuning range. In this dissertation, a fine-pitch ball-grid array (FBGA) package, a multichip module (MCM)-L package, and a wafer-level package (WLP) are incorporated to realize the high-Q inductor. The Q-factors of inductors embedded in packages are compared to those of inductors monolithically integrated on Si and GaAs substrates. All the inductors are modeled with a physical, simple, equivalent two-port model for the VCO design as well as for phase noise analysis. The losses in an LC-tank are analyzed from the phase noise perspective. For the implementation of VCOs, the effects of the interconnection between the embedded inductor and the VCO circuit are investigated. The VCO using the on-chip inductors is designed as a reference. The performance of VCOs using the embedded inductor in a FBGA and a WLP is compared with that of a VCO using the on-chip inductor. The VCO design is optimized from the high-Q perspective to enhance performance. Through this optimization, less phase noise, lower power consumption, and a wider frequency tuning range are obtained simultaneously.

Although batch processes are “simple” in terms of equipment and operation design, it is often difficult to ensure consistently high product quality. The aim of this PhD project is the development of multivariate statistical methodologies for the realtime monitoring of quality in batch processes for the production of high value added products. Two classes of products are considered: those whose quality is determined by chemical/physical characteristics, and those where surface properties define quality. In particular, the challenges related to the instantaneous estimation of the product quality and the realtime prediction of the time required to manufacture a product in batch processes are addressed using multivariate statistical techniques. Furthermore, novel techniques are proposed to characterize the surface quality of a product using multiresolution and multivariate image analysis. For the first class of products, multivariate statistical soft sensors are proposed for the real-time estimation of the product quality and for the online prediction of the length of batch processes. It is shown that, to the purpose of realtime quality estimation, the complex series of operating steps of a batch can be simplified to a sequence of estimation phases in which linear PLS models can be applied to regress the quality from the process data available online. The resulting estimation accuracy is satisfactory, but can be substantially improved if dynamic information is included into the models. Dynamic information is provided either by augmenting the process data matrix with lagged measurements, or by averaging the process measurements values on a moving window of fixed length. The process data progressively collected from the plant can be exploited also by designing time-evolving PLS models to predict the batch length. These monitoring strategies are tested in a real-world industrial batch polymerization process for the production of resins, and prototypes of the soft sensor are implemented online. For products where surface properties define the overall quality, novel multiresolution and multivariate techniques are proposed to characterize the surface of a product from image analysis. After analyzing an image of the product surface on different levels of resolutions via wavelet decomposition, the application of multivariate statistical monitoring tools allow the in-depth examination of the product features. A two-level “nested” principal component analysis (PCA) model is used for surface roughness monitoring, while a new strategy based on “spatial moving window” PCA is proposed to analyze the shape of the surface pattern. The proposed approach identifies the abnormalities on the surface and localizes defects in a sensitive fashion. Its effectiveness is tested in the case of scanning electron microscope images of semiconductor surfaces after the photolithography process in the production of integrated circuits.
Nonostante i processi batch siano relativamente semplici da configurare e da gestire anche con un livello limitato di automazione e una conoscenza ridotta dei meccanismi che ne stanno alla base, spesso è difficile assicurare una qualità del prodotto finito riproducibile ed elevata. La strumentazione comunemente utilizzata nella pratica industriale riesce solo raramente a fornire misure in tempo reale della qualità di un prodotto. Inoltre, molte complicazioni nascono dalla natura multivariata della qualità, la quale dipende da una serie di parametri fisici, operativi o addirittura soggettivi. Sebbene le informazioni sulla qualità del prodotto non siano facilmente accessibili, esse sono racchiuse nelle variabili di processo abitualmente registrate dai calcolatori di processo e memorizzate in banche di dati storici. I metodi statistici multivariati permettono di ridurre la dimensione del problema proiettando le variabili di processo in uno spazio di dimensioni ridotte costituito di variabili fittizie che sono in grado di mantenere tutto il contenuto informativo sulla qualità, superando i problemi del rumore di misura delle variabili, della ridondanza e dell’elevato grado di correlazione. Inoltre, questi metodi sono in grado di trattare dati anomali o dati mancanti. Lo scopo di questa Tesi di Dottorato è di sviluppare dei sistemi innovativi per il monitoraggio della qualità di prodotti dall’alto valore aggiunto mediante tecniche statistiche multivariate. In particolare, i contributi scientifici di questo progetto di Dottorato sono: • l’elaborazione di tecniche per lo sviluppo di sensori virtuali per la stima in tempo reale della qualità del prodotto in sistemi produttivi di tipo batch; • l’applicazione non convenzionale di tecniche di proiezione su sottospazi latenti al fine di prevedere la durata di un batch o delle relative fasi operative; • lo sviluppo di metodiche innovative per il monitoraggio multirisoluzione e multivariato della qualità mediante l’analisi di immagini di un prodotto dall’alto valore aggiunto. Innanzi tutto, in questa Tesi vengono proposti sensori virtuali per la stima in linea della qualità del prodotto. Essi sono stati sviluppati e implementati prendendo in considerazione il caso di studio un processo industriale reale per la produzione di resine mediante polimerizzazione batch. I sensori virtuali proposti sono basati sulla tecnica statistica multivariate della proiezione su strutture latenti (PLS), che opera una regressione delle misure di processo usualmente disponibili in linea in tempo reale. Questo sistema riesce a garantire una accuratezza delle stime della qualità che è dello stesso ordine di grandezza delle misure di qualità fatte in laboratorio, col vantaggio che le stime in linea sono disponibili con altissima frequenza (sull’ordine di grandezza di s-1), cioè una frequenza centinaia di volte superiore delle misure che possono essere fatte in laboratorio (sull’ordine di grandezza di h-1). Inoltre, le stime sono accessibili in tempo reale e senza il ritardo che è tipico delle misure di laboratorio. Al fine di compensare le non linearità dei dati e i cambiamenti nella struttura di correlazione fra le variabili, la procedura adottata divide il batch in una sequenza di un numero limitato di fasi di stima, all’interno delle quali lo stimatore virtuale è in grado di dare stime molto accurate per mezzo di modelli PLS lineari. Il passaggio da una fase a quella successiva avviene in corrispondenza di alcuni “eventi” facilmente riconoscibili nelle stesse variabili di processo. La caratteristica principale del sensore virtuale proposto è che esso tiene conto di informazioni sulla dinamica del processo per mezzo di modelli a “variabili ritardate” (i quali aggiungono informazioni sulla dinamica del processo da valori passati delle variabili di processo) o modelli a media mobile. Il filtro a media mobile aggiunge una “memoria temporale” al sensore virtuale che migliora l’accuratezza di stima e, mediando le variabili di processo all’interno di una finestra temporale di dimensione fissata, riesce ad eliminare il rumore di misura, attenuare il rumore di processo, appiattire valori anomali e compensare l’effetto di temporanee mancanze di dati. L’ampiezza della finestra deve comunque essere scelta con cautela, dato che una finestra temporale troppo larga potrebbe ritardare gli allarmi sull’attendibilità della stima. Da un punto di vista operativo, il sistema proposto aiuta il personale che opera nell’impianto a rilevare delle derive sulla qualità del prodotto, suggerisce tempestivamente le correzioni da apportare alla ricetta del processo, e aiuta a minimizzare i fuori specifica del prodotto finale. Inoltre, il numero di campioni per la misura della qualità in laboratorio può essere ridotto drasticamente, la qual cosa determina un guadagno sia sul tempo totale del batch, sia sui costi relativi al laboratorio che alla manodopera e alla sua organizzazione. Anche una seconda tipologia di sensori virtuali è stata sviluppata per assistere il monitoraggio in linea della qualità del prodotto e per fornire informazioni utili per una programmazione efficace della produzione: un sensore virtuale per la previsione in tempo reale della durata del batch. Questa strategia di monitoraggio si basa su modelli PLS evolutivi che sfruttano le informazioni progressivamente raccolte nel tempo durante il batch per prevedere la durata del batch o di ciascuno dei relativi stadi operativi. Anche l’accuratezza ottenuta dalle previsioni ottenute con questo sensore virtuale è del tutto soddisfacente, dato che l’errore di previsione è molto inferiore sia alla variabilità delle durata del batch che alla durata dei turni di lavoro degli operatori. Inoltre, la parte iniziale del batch conferma di essere di importanza fondamentale per la durata, in quanto le condizioni iniziali delle attrezzature, lo stato delle materie prime, e la fase di riscaldamento iniziale del reattore esercitano una grandissima influenza sulle prestazioni del batch stesso. Le informazioni che si ricavano sulla durata con grande anticipo rispetto alla fine del batch permettono una migliore organizzazione degli interventi sull’impianto, degli operatori d’impianto e dell’utilizzazione delle apparecchiature. L’efficacia dei sensori per la stima della qualità e per la previsione della durata del batch è stata verificata applicandoli ed implementandoli in linea nel caso della produzione di resine mediante polimerizzazione batch. Infine, i metodi statistici multivariati sono stati utilizzati anche nel campo dell’analisi dell’immagine. Abitualmente, nella pratica industriale, le ispezioni di un prodotto mediante analisi dell’immagine vengono svolte con semplici misurazioni dei più importanti parametri fisici opportunamente messi in evidenza per mezzo di tecniche di filtrazione. Inoltre, queste misure vengono ottenute in modo non sistematico. Molte informazioni utili restano però “nascoste” nelle immagini. Queste permettono di identificare la natura complessa della qualità del prodotto finale. Per questo è stato sviluppato un sistema totalmente automatizzato per il monitoraggio in tempo reale da immagini di un manufatto dall’alto valore aggiunto. Questo sistema di monitoraggio basato su tecniche multirisoluzione e multivariate è stato applicato al caso della caratterizzazione della superficie di un semiconduttore dopo fotolitografia, un’operazione fra le più importanti nella fabbricazione di circuiti integrati. Tecniche avanzate di analisi multivariata dell’immagine estraggono le tracce che il processo lascia sul prodotto, aiutando sia il rilevamento di situazioni critiche nel processo che l’intervento con azioni correttive a neutralizzare eventuali problemi. L’approccio proposto in questa Tesi si basa su un filtraggio preliminare multirisoluzione dell’immagine mediante wavelet, seguito da uno schema di monitoraggio che conduce in parallelo un’analisi della rugosità superficiale e della forma della superficie di un prodotto. Ad esempio, la rugosità della superficie può essere esaminata con una analisi delle componenti principali “nidificata”. Questa è una strategia che si articola su due differenti livelli: il livello esterno che permette di discriminare parti differenti della superficie per mezzo di una analisi dei gruppi con PCA; il livello interno esegue il monitoraggio della rugosità superficiale con PCA. La forma della superficie viene analizzata per mezzo di un approccio PCA a “finestra mobile nello spazio”, il quale coglie l’informazione dell’immagine secondo il relativo ordine nello spazio e riesce anche a tener conto sia delle non linearità che delle differenze strutturali della superficie. Questo sistema è in grado di rilevare alcune delle caratteristiche qualitative del prodotto che abitualmente non sono accessibili senza richiedere l’intervento dell’uomo. Inoltre, il monitoraggio risulta essere veloce, attendibile e non ambiguo, ed esegue una scansione di un’immagine del prodotto localizzando in modo preciso difetti e anomalie e rilevando eventuali derive del processo. In conclusione, nonostante le metodologie proposte siano state testate su specifici casi di studio, esse hanno dimostrato di essere generali e vantano un grande potenziale. Per questo si ritiene sia possibile estenderle a differenti campi di ricerca e a diverse applicazioni industriali (ad esempio: ingegneria alimentare; industria farmaceutica; biotecnologie; etc…), nonché a differenti scale di indagine, dalla scala macroscopica alla microscopica o nanoscopica.

Breitstreifenlaser haben eine breite Emissionsapertur, die es ermöglicht eine hohe Ausgangsleistung zu erreichen. Gleichzeitig führt sie jedoch zu einer Verringerung der lateralen Strahlqualität und zu ihrem nicht-stationären Verhalten. Forschung in diesem Gebiet ist anwendungsgetrieben und somit ist das Hauptziel eine Erhöhung der Brillanz, die sowohl die Ausgangsleistung als auch die laterale Strahlqualität beinhaltet. Um die zugrunde liegenden raumzeitlichen Phänomene zu verstehen und dieses Wissen zu nutzen, um die Kosten der Brillanz-Optimierung zu minimieren, ist ein selbst-konsistentes Simulationstool notwendig, welches die wichtigsten Prozesse beinhaltet. Zunächst wird in dieser Arbeit ein quasi-dreidimensionales elektro-optisch-thermisches Model präsentiert, welches wesentliche qualitative Eigenschaften von realen Bauteilen gut beschreibt. Zeitabhängige Wanderwellen-Gleichungen werden genutzt, um die inhärent nicht-stationären optischen Felder zu beschreiben, welche an eine Ratengleichung für die Überschussladungsträger in der aktiven Zone gekoppelt sind. Das Model wird in dieser Arbeit um eine Injektionsstromdichte erweitert, die laterale Stromspreizung und räumliches Lochbrennen korrekt beschreibt. Des Weiteren wird ein Temperaturmodel präsentiert, das kurzzeitige lokale Aufheizungen in der Nähe der aktiven Zone und die Formierung einer stationären Temperaturverteilung beinhalten. Im zweiten Teil wird das beschriebene Modell genutzt, um die Gründe von Brillanz-Degradierung, das heißt sowohl die Ursprünge der Leistungssättigung als auch des nicht diffraktionslimitierten Fernfeldes zu untersuchen. Abschließend werden im letzten Teil Laserentwürfe besprochen, welche die laterale Brillanz verbessern. Hierzu gehört ein neuartiges “Schachbrettlaser” Design, bei dem longitudinal-laterale Gewinn-Verlust-Modulation mit zusätzlicher Phasenanpassung ausgenutzt wird, um eine sehr geringe Fernfeld-Divergenz zu erhalten.
Broad-area lasers are edge-emitting semiconductor lasers with a wide lateral emission aperture that enables high output powers, but also diminishes the lateral beam quality and results in their inherently non-stationary behavior. Research in the area is driven by application and the main objective is to increase the brightness which includes both the output power and lateral beam quality. To understand the underlying spatio-temporal phenomena and to apply this knowledge in order to reduce costs for brightness optimization, a self-consistent simulation tool taking into account all essential processes is vital. Firstly, in this work a quasi-three-dimensional opto-electronic and thermal model is presented, that describes well essential qualitative characteristics of real devices. Time-dependent traveling-wave equations are utilized to describe the inherently non-stationary optical fields, which are coupled to dynamic rate equations for the excess carriers in the active region. This model is extended by an injection current density model to accurately include lateral current spreading and spatial hole burning. Furthermore a temperature model is presented that includes short-time local heating near the active region as well as the formation of a stationary temperature profile. Secondly, the reasons of brightness degradation, i.e. the origins of power saturation and the spatially modulated field profile are investigated and lastly, designs that mitigate those effects that limit the lateral brightness under pulsed and continuous-wave operation are discussed. Amongst those designs a novel “chessboard laser” is presented that utilizes longitudinal-lateral gain-loss modulation and an additional phase tailoring to obtain a very low far-field divergence.

博士
國立臺灣大學
電子工程學研究所
99
The local melting point of a Ge thin film can be controlled by a hole-array pattern on the host Si substrate due to the variations in the stress distribution and the surface morphology induced by the pattern. A simple annealing process is developed from this effect to produce Ge NCs with a single-domain-crystal size over 20 nm, confirmed by transmission electron microscopy and Raman spectroscopy, from an electron-gun evaporated Ge thin film on the patterned Si substrate. The effect of dimensions of the hole array is also investigated. Photoluminescence observed around 1157 nm from some of the samples shows the possibility of improving the infrared emission capability by this proposed method. A non-destructive testing method based on near field scanning optical microscopy with a 1.55-

AbstractThe third intended application for the proposed dispersion-encoded low-coherence interferometry is the evaluation of thin-film characteristics on substrate materials. Due to the usage of thin-film technologies in high-volume production in e.g. the photovoltaics and semiconductor industry, process monitoring becomes relevant in order to ensure functional parameters such as solar cell efficiency, [289]. In this context, film thickness as well as film homogeneity over large areas are important criteria for quality assurance.

Incorporation of dopants efficiently in semiconductors at the nanoscale is an open challenge and is also essential to tune the conductivity. Typically, heating is a necessary step during nanomaterials’ solution growth either as pristine or doped products. Usually, conventional heating induces the diffusion of dopant atoms into host nanocrystals towards the surface at the time of doped sample growth. However, the dielectric heating by microwave irradiation minimizes this dopant diffusion problem and accelerates precursors’ reaction, which certainly improves the doping yield and reduces processing costs. The microwave radiation provides rapid and homogeneous volumetric heating due to its high penetration depth, which is crucial for the uniform distribution of dopants inside nanometer-scale semiconducting materials. This chapter discusses the effective uses of microwave heating for high-quality nanomaterials synthesis in a solution where doping is necessary to tune the electronic and optoelectronic properties for various applications.

In this work, we have discovered a method of forming ZnO thin films with high mobility, high carrier density and low resistivity on plastic (PET) films using non-equilibrium reaction fields, even when the films are deposited without heating, and we have also found a thin film formation technique using a wet process that is different from conventional deposition techniques. The field emission electron-beam irradiation treatment energetically activates the surface of ZnO particles and decomposes each ZnO particles. The energy transfer between zinc ions and ZnO surface and the oxygen present in the atmosphere around the ZnO particles induce the oxidation of zinc. In addition, the ZnO thin films obtained in this study successfully possess high functional thin films with high electrical properties, including high hole mobility of 208.6 cm2/Vs, despite being on PET film substrates. These results contribute to the discovery of a mechanism to create highly functional oxide thin films using a simple two-dimensional process without any heat treatment on the substrate or during film deposition. In addition, we have elucidated the interfacial phenomena and crosslinking mechanisms that occur during the bonding of metal oxide particles, and understood the interfacial physical properties and their effects on the electronic structure. and surface/interface control, and control of higher-order functional properties in metal/ceramics/semiconductor composites, and contribute to the provision of next-generation nanodevice components in a broad sense.

Rutile tin oxide (SnO2) is a wide band gap (3.6 eV at 300K [1]) n-type semiconductor material. It is widely used as sensing elements in gas sensors [2]. The sensing mechanism is generally attributed to the significant change in the electrical resistance of the material associated with the adsorption/desorption of oxygen on the semiconductor surface [3]. The formation of oxygen adsorbates (O2− or O−) results in an electron-depletion surface layer due to the electron transfer from the oxide surface to oxygen [4]. Recent studies [5, 6] have shown that use of tin oxide nanocrystals significantly improves the dynamic response and the sensitivity of sensors since the electron depletion may occur in the whole crystallite. Here we report on the fabrication and characterization of a miniaturized gas sensor based on tin oxide nanocrystals. A simple, convenient and low-cost mini-arc plasma source is used to synthesize high-quality tin oxide nanoparticles in aerosol phase at atmospheric pressure. The nanoparticle sensor is then fabricated by electrostatic assembly of product tin oxide nanoparticles onto e-beam lithographically patterned interdigitated electrodes. The microfabricated nanoparticle sensor exhibits good sensitivity and dynamic response to low-concentration ethanol vapor and hydrogen gas diluted in air.

Semiconductor crystallites which are 10's of Angstroms show a striking evolution of electronic properties with size.1 These particles (quantum dots) are large enough to exhibit a crystalline core, but small enough that solid state electronic and vibrational band structure is not yet developed. We use a recently developed synthetic method for the fabrication of high quality nanometer size (1-10 nm) II- VI semiconductor crystallites with narrow size distributions (σ<5%), emphasizing CdSe.2 Optical characterization of their electronic structure reveals both molecular and bulk-like characteristics as well as properties which are unique to nanometer size crystallites. We observe a number of discrete electronic transitions, assign them as coming from the creation of delocalized "particle-in-a- sphere" states using the theory of Ref. 3, and study their dependence on crystallite diameter.4