Thèses sur le sujet « GE11 »

Il polilattide (PLA) e il suo co-polimero con l’acido glicolico (PLGA) appartengono alla famiglia dei poli-esteri alifatici, polimeri di sintesi frequentemente utilizzati in ambito farmaceutico per la loro biocompatibilità e scarsa citotossicità, approvati FDA per la somministrazione parenterale. Esistono però alcune limitazioni nell’uso del PLA e derivati nella realizzazione di sistemi di rilascio controllato dei farmaci, come nanoparticelle (NP). In particolare, il PLA è caratterizzato da un’elevata idrofobicità e da un elevato grado di cristallinità che rendono il profilo di degradazione della matrice polimerica piuttosto lento e, di conseguenza, anche la cessione dell’attivo in essi incapsulato. Per queste ragioni è necessario realizzare derivati del PLA per renderlo più adatto all’applicazione farmaceutica. Inoltre, in relazione alla patologia di interesse, è auspicabile che le NP possano essere indirizzate in maniera selettiva alla cellula bersaglio, esponendo sulla superficie delle NP di un agente di targeting attivo. Il progetto di ricerca della dottoranda è stato finalizzato alla realizzazione di NP per il trattamento di diverse patologie ossee ed è stato organizzato in due filoni: nel primo, la dottoranda ha studiato l’impiego di derivati del PLA ottenuti dalla funzionalizzazione con residui gommosi, scelti come probabile alternativa ai derivati PEGilati di uso comune, per la realizzazione di sistemi nanoparticellari, mentre nella seconda parte della ricerca la dottoranda si è focalizzata sulla realizzazione di smart nanoparticles a partire da PLGA derivatizzato con agenti di targeting attivo. Nel primo caso il polimero selezionato è il PCNL, polimero sintetizzato nel laboratorio del prof. Hillmyer dell’Università del Minnesota: la presenza di una porzione gommosa dovrebbe rendere più veloce il profilo di degradazione delle NP. Innanzitutto, la dottoranda ha valutato la citocompatibilità del nuovo polimero che ha manifestato una scarsa tossicità e quindi il polimero si presenta come buon candidato per la realizzazione di sistemi nanoparticellari. Successivamente, il polimero è stato utilizzato per la realizzazione di NP. Il metodo utilizzato e le condizioni di processo sono state ottimizzate utilizzando un PLA di peso molecolare paragonabile al PLA utilizzato per la sintesi del PCNL. Nonostante gli sforzi per individuare una metodica opportuna, le NP ottenute con PCNL mediante la tecnica della nanoprecipitazione non hanno dimostrato le caratteristiche dimensionali desiderate, probabilmente a causa del peso molecolare e della Tg del residuo gommoso. Per cui il polimero è stato momentaneamente accantonato. Per quanto riguarda la seconda parte della ricerca sono state realizzate NP intelligenti a base di PLGA funzionalizzato con un piccolo peptide che riconosce in maniera selettiva il recettore EGFR. L’obiettivo della dottoranda è stato quello di realizzare sistemi terapeutici destinati al trattamento di patologie dell’osso caratterizzate da una sovraespressione del EGFR, cioè tumori e artrite reumatoide. Il ligando selezionato come oggetto della ricerca è il GE11, dodecapeptide che funge da ligando allosterico del recettore EGFR. Nello specifico, questo filone del lavoro di ricerca è stato diviso in due parti, una parte chimica di sintesi e una parte di realizzazione dei sistemi nanoparticellari. La prima parte del lavoro è stata condotta presso il dipartimento di Chimica dell’Università di Milano, nel laboratorio della prof.ssa Speranza, dove la dottoranda si è concentrata sulla sintesi del peptide GE11 e del coniugato GE11-PLGA. Il peptide è stato sintetizzato con la tecnica della sintesi in fase solida, con una resa di processo del 45% e una purezza del peptide >95%. Successivamente, il GE11 è stato legato covalentemente al PLGA mediante la chimica della carbodiimmide. Il processo ha avuto una resa del 50-60%; dall’analisi NMR si può ricavare un’efficienza di funzionalizzazione del polimero pari al 70-80%. Nella seconda parte del lavoro, la dottoranda si è occupata della realizzazione di sistemi nanoparticellari: la metodica di preparazione è stata ottimizzata inizialmente con i polimeri puri, PLGA ed un suo derivato coniugato al polietilenglicole (PEG-PLGA), al fine di settare le condizioni di processo migliori ad ottenere NP con le dimensioni adatte ad una somministrazione sistemica e locale. Prima di passare alla realizzazione delle NP con il coniugato GE11-PLGA, sono state realizzate NP modello: infatti in questa fase è stato utilizzato un tetrapeptide modello (FQPV) per indagare le criticità della sintesi di smart nanoparticles, per poi utilizzare il coniugato di interesse GE11-PLGA in una fase successiva. Il coniugato FQPV-PLGA è stato ottenuto con la stessa metodica del coniugato GE11-PLGA. Le NP con il coniugato FQPV-PLGA sono state realizzate secondo due metodiche differenti: la nanoprecipitazione, utilizzando DMSO come solvente, e una metodica “ibrida”, utilizzando una miscela 80:20 acetone-CH2Cl2, come selezionato mediante disegno sperimentale (DoE). Le NP hanno mostrato dimensioni intorno ai 200 nm con entrambe le metodiche. Inoltre, sono state sviluppate altre due strategie complementari a quelle descritte, al fine di aumentare l’entità di caricamento del peptide FQPV nelle NP di PLGA. A questo scopo, sono stati realizzati lotti in cui il peptide FQPV è stato adsorbito sulle NP di PLGA: con questa metodica è stato ottenuto un buon caricamento (1:29.9 FQPV:PLGA p:p) che però si è dimostrato instabile nel tempo. La seconda metodica ha previsto l’incapsulazione del peptide FQPV ma i risultati non sono stati ottimali: il metodo ha permesso una scarsa incapsulazione del peptide (1:150 FQPV:PLGA p:p). Per la realizzazione delle NP di GE11-PLGA solo la metodica della nanoprecipitazione utilizzando il DMSO come solvente è stata utilizzata, a causa della insolubilità del coniugato negli altri solventi comunemente utilizzati (acetone, diclorometano). Le formulazioni considerate e caratterizzate sono due: una in cui la matrice delle nanoparticelle è formata solo dal coniugato GE11-PLGA e la seconda in cui il coniugato è in miscela 1:1 p:p con un PEG-PLGA di uguale peso molecolare. Entrambe le formulazioni realizzate presentano una dimensione intorno a 140 nm e un potenziale zeta negativo (-20 mV). Di entrambe le formulazioni è stata valutata anche la citotossicità mediante MTS test su cellule caratterizzate da una sovraespressione del EGFR (A549, carcinoma polmonare, e Caki1, carcinoma renale): entrambe hanno dimostrato un’ottima citocompatibilità sulle linee cellulari selezionate in un ampio range di concentrazioni (0,1µg/ml to 1mg/ml). Le NP sono state caratterizzate mediante DSC per valutarne il comportamento termico rispetto al polimero puro. Le NP di GE11-PLGA hanno manifestato una Tg intorno a 50°C, del tutto paragonabile al comportamento del coniugato (49,33°C). Invece, le NP di GE11-PLGA/PEG-PLGA hanno una Tg a 21°C, dovuta al contributo del coniugato e del polimero PEGilato che invece ha una Tg sub-ambiente. Questo comportamento potrebbe influenzare la cinetica di rilascio del farmaco veicolato. Tutti i sistemi nanoparticellari realizzati hanno un’ottima stabilità a 4°C in acqua per 30 giorni, a simulare una possibile forma di stoccaggio prima della somministrazione al paziente. Il test di stabilità a 37°C a pH 5 e pH 7,4, per simulare un’infiammazione e il pH fisiologico, invece ha evidenziato una tendenza all’aggregazione delle NP dopo 15-20 giorni in entrambe le condizioni di pH, come se la presenza del peptide creasse instabilità alle NP. Successivamente, la dottoranda ha valutato la stabilità delle NP nei fluidi biologici, in particolare in plasma umano e in liquido sinoviale umano. Questa parte del lavoro è stata condotta presso il gruppo del prof. Braeckmans dell’Università di Gent (BE). Gli esperimenti sono stati condotti con fSPT (fluorescence Single Particle Tracking) su NP di GE11-PLGA/ PEG-PLGA marcate con RhB. Da questi test si osserva che le NP sono stabili in entrambi i mezzi considerati: solamente in plasma umano si osserva un aumento della dimensione dovuto alla formazione di una corona proteica attorno alle NP. Le dimensioni restano comunque entro valori accettabili per la loro applicazione in vivo. Sempre durante il periodo di ricerca all’estero, la dottoranda si è occupata degli studi di uptake al fine di valutare il profilo di captazione delle NP in cellule caratterizzate da una sovraespressione del EGFR nel tempo. Il test è stato condotto con microscopia confocale, andando a quantificare la fluorescenza delle NP marcate con RhB all’intero delle cellule. Il test ha dimostrato una internalizzazione attiva delle NP con il coniugato GE11-PLGA che è risultata veloce e prolungata nel tempo, visto che dopo 24 ore le NP erano ancora presenti all’interno delle cellule. Anche le NP di solo PLGA, utilizzate come controllo, sono captate dalle cellule con un meccanismo attivo anche se il profilo è differente rispetto alle NP con il peptide GE11: l’uptake è più lento e dopo 24 ore le NP non sono più all’interno delle cellule. Le NP selezionate sono state quindi caricate con Desametasone, farmaco utilizzato per il trattamento di numerose patologie reumatiche. Diverse strategie sono state considerate al fine di aumentare il grado di incapsulazione; i risultati migliori sono stati ottenuti utilizzando Etilacetato come solvente insieme al DMSO (300 µg/100 mg polimero). I risultati raccolti relativi alle nanoparticelle di GE11-PLGA sono promettenti, se si pensa alla mancanza di aggregazione nei fluidi biologici e alla buona captazione all’interno delle cellule che sovraesprimono EGFR. Sono in corso studi mirati allo studio dei meccanismi di uptake cellulare e trafficking intracellulare delle NP e alla valutazione dell’uso di uno spaziatore tra PLGA e GE11, alternativo al PEG, al fine di migliorare l’esposizione superficiale del peptide.

Descripción: La situación empresarial del mundo en la actualidad está cambiando rápidamente, se está dando paso a la incorporación de nuevos competidores, el aumento de alianzas, fusiones y adquisiciones, la mayor demanda de calidad y servicio, los grandes avances tecnológicos y la creación de una estructura global de los mercados. Dada esa coyuntura, el mercado laboral necesita cada vez más profesionales capaces de gestionar empresas, creando nuevas o conduciendo eficientemente las existentes hacia el éxito. En este sentido, el curso proporciona al alumno los conocimientos y habilidades para poder comprender las funciones y estructuras del contexto empresarial y no sólo será capaz de identificar esos cambios en su entorno, sino que podrá transformarlos en oportunidades, planificando e implementando negocios o proyectos, de manera tal que se obtenga la mayor rentabilidad a largo plazo. Propósito: El Curso de Fundamentos de Ingeniería de Gestión Empresarial es un curso de especialidad del programa de Ingeniería de Gestión Empresarial, de carácter teórico, dirigido a los estudiantes del primer ciclo, que busca desarrollar la competencia general Pensamiento innovador (Nivel 1) y la competencia específica: (e) Resolución de problemas de Ingeniería (Nivel 1). Tiene como prerrequisito el curso de Nivelación de Matemáticas. Tiene el propósito de identificar conceptos básicos relacionados al mundo empresarial, pudiendo detectar necesidades y oportunidades cuya solución se relaciona a temas de emprendimiento e innovación, todo desde una perspectiva ingenieril.

Microtubules perform essential functions in eukaryotic cells and, with other cytoskeletal elements, are involved in diverse cellular processes. Plant cells construct four microtubule arrays; There are two cortical arrays, the interphase cortical array, and the preprophase band, the mitotic spindle and the cytokinetic phragmoplast. The control and rearrangement of these arrays through the cell cycle is coordinated by Microtubule Associated Proteins or MAPs. These proteins have diverse functions including anchoring & crosslinking microtubules or otherwise regulating microtubule formation and destruction within the cell. MOR1/GEM1 is the Arabidopsis member of the conserved XMAP215/TOGp family of proteins which are microtubule stablising MAPs and promote microtubule polymerization in vitro. In many organisms such stabilization is opposed by Kinl catastrophic kinesins, which depolymerise and destabilize microtubules. In addition to the further characterization of MOR1/GEM1, here in this thesis, two putative KinI kinesins are identified in the Arabidopsis genome, a subfamily of kinesins previously uncharacterized in plants, AtCMK1 & AtCMK2. Immunolocalisation shows that MOR1/GEM1 associates with all plant microtubule arrays throughout the cell cycle and Is found to concentrate at the plus end of microtubules In the spindle next to chromosomes and the midline of the phragmoplast where oppositely orientated microtubules overlap. Furthermore, consistent with this localization, we show that a C-terminal fragment of MOR1/GEM1 which Is absent in the pollen cytokinesis mutant, gem1 can bind microtubules and as such we propose that the defects in the phragmoplast In gem1 mutant is a result of the reduction of the MOR1/GEM1 protein to bind microtubules. Further studies indicate that unlike its budding yeast homologue Stu2, MOR1/GEM1 does not for dimers.Immunolocalisation shows that AtCMK2 associates with all the plant microtubule arrays throughout the cell cycle, particularly the metaphase spindle. However in our experiments, AtCMKI does not, but rather locates to structures within the cytoplasm, such as golgi vesicles or organelles. Here we also show that AtCMK kinesins form homodimers and do not physically Interact with MOR1/GEM1 suggesting that these factors may be genetic interactors instead. Over-expression of AtCMK2 as a GPP fusion protein results in the disruption of microtubules, leaving short microtubule fragments and tubulin oligomers or aggregates, suggesting that AtCMK2 Is a true Arabidopsis catastrophic kinesin. In addition, GUS promoter fusions show that the expression patterns of these two kinesins are very different.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1986.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING
Bibliography: leaves 173-175.
by Francis X. Dunn.
M.S.

Le gène Gec1/Gabarapl1 a été identifié au sein de notre laboratoire comme un gène régulé par les estrogènes. Il appartient à la famille Gabarap incluant les gènes Gabarap, gabarap/2 et Gabarapl3 qui codent des protéines présentant de fortes homologies de séquences. L'étude fonctionnelle de Gabarapl 1 a montré que cette protéine est impliquée dans le transport des récepteurs et particulièrement les récepteurs Gabaₐ et des κ-opioïdes via son interaction avec la tubuline et la protéine NSF. Cependant, il a été décrit que certaines protéines de la famille Atg8 sont impliquées dans l' autophagie, un mécanisme de dégradation et de survie cellulaire, qui se caractérise par la formation de doubles membranes appelées autophagosomes. Les objectifs de mon travail étaient, d'une part, de caractériser le rôle de la protéine GABARAPL1 au cours de !'autophagie et, d'autre part, de caractériser son expression dans des lignées et tissus cancéreux et sa régulation en réponse à des composés anti-cancéreux. Tout d'abord, nous avons montré que Gabarapl1 est clivée par la protéase Atg4B au niveau de sa glycine 116 avant sa conjugaison à des phopholipides. Cette forme modifiée, lipidée, est localisée à la surface des autophagosomes et des lysosomes. Nous avons ensuite montré que Gabarapl1 est faiblement exprimée dans de nombreuses lignées cancéreuses, que son expression est altérée dans les méningiomes et qu'elle est régulée par des inhibiteurs du protéasome. Ces travaux ont montré, pour la première fois, que la protéine Gabarapl1 est associée à des vésicules autophagiques et permettront de poser les hypothèses de nos futurs travaux
The Gec1 / Gabarapl1 gene was identified in our laboratory as an early estrogen regulated gene. Gabarapl1 belongs to the Gabarap family, also including Gabarap, Gabarapl2 and Gabarapl3 genes, that encode proteins which present high sequence homology with each other. A functional study of the Gabarapl 1 protein showed that this protein is involved in the transport of receptors such as the Gabaₐ and κ-opioid receptors via its interaction with tubulin and NSF. It has been reported that the Atg8 family proteins are involved in autophagy, a mechanism of degradation and cell survival that is charactenzed by the formation of double membranes called autophagosomes. The aims of my research were, firstly, to characterize the role of the Gabarapl1 protein during autophagy and, secondly, to study its expression in cancer cell lines and cancerous tissues and its regulation in response to anti-cancer drugs. First, we showed that Gabarapl1 is cleaved in the cells by the protease Atg4B at its 116 glycine residue prior to its conjugation to phospholipids. This modified form, lipidated, is located on the surface of autophagosomes and lysosomes. We then showed that Gabarapl1 expression is reduced in many cancer cell lines, and that its expression is also altered in meningiomas. Finally, we showed that Gabarapl1 expression is regulated by proteasom€: inhibitors. Thus, our results demonstrated for the first time that the Gabarapl1 protein is associatec with autophagie vesicles and allow us to propose hypothesis for future work

Notre équipe a montré une expression préférentielle de gec1 dans le Système Nerveux Central (SNC) et une faible expression dans diverses lignées cancéreuses. Nos objectifs ont été d'étudier: l'expression de gec1 dans le cerveau de rat ; le rôle de gec1 dans !'oncogenèse ; l'effet des estrogènes, in vivo et in vitro, sur l'expression de gec1. Tout d'abord, nous avons montré que gec1 est fortement exprimé dans le SNC de rat, et plus particulièrement dans les neurones impliqués dans les fonctions somesthèsiques, motrices et neuroendocrines. Au cours de !'oncogenèse, dans les méningiomes, une diminution de l'expression de gec1 est observée dans le type psammomateux. Les données cliniques ont permis de mettre en évidence une diminution du taux de messagers gec1 dans les méningiomes provenant de patientes âgées de plus de 52 ans. Puis, nous avons étudié l'impact de la surexpression de GEC1 sur la croissance de cellules de cancer du sein. La prolifération des cellules surexprimant GEC1 diminue d'un facteur voisin de 2. Enfin, nous avons étudié la régulation de l'expression de gec1 par les estrogènes. Ln vivo, nous avons montré que le taux de messagers gec1 augmente en présence de E2 dans trois aires cérébrales. Ln vitro, dans des cellules PC12 différenciées par le NGF, l'expression de gec1 est induite par Ez. Nos travaux ont ainsi permis de confirmer l'estrogéno-dépendance de gec1 à la fois in vivo et in vitro, mais également suggèrent des implications potentielles de GEC1 dans des fonctions neuronales normales et au cours de !'oncogenèse. Ces résultats ouvrent de nouvelles perspectives et renforcent l'intérêt de l'étude de GEC1 dans le SNC et au cours de !'oncogenèse
Our research team has shown that gec1 is more expressed in the Central Nervous System (CNS) and weakly expressed in various cancerous cells lines. Our objectives were to study: the expression of gec1 in the rat brain; the role of gec1 in the oncogenesis; the effect of estrogens, in vivo and in vitro, on the gec1 expression. First of all, we have showed that gec1 is strongly expressed in the rat SNC, more precisely in neurons involved in somatomotor and neuroendocrine functions. During oncogenesis, in meningiomas, a reduction of the gec1 expression is observed in psammomatous meningiomas. The clinical data highlighted a reduction in the rate of gec1 messengers in meningiomas coming from patients of more than 52 years old. Then, we studied the impact of the GEC1 over-expression on the cells growth of breast cancer. The proliferation of GEC1 over-expression cells line decreases by 2 fold compared to controls. Lastly, we studied the regulation of the gec1 expression by estrogens. Ln vivo, we showed that the rate of gec1 messengers increases in presence of E2 in the pons, the cerebellum and the diencephalon. Ln vitro, in PC12 cells differentiated by the NGF, the gec1 expression is induced by E2 alone. Our works enabled to confirm the estrogeno-dependance of gec1 in vitro and in vivo, and also suggests potential implications of GEC1 in normal neuronal functions and during the oncogenesis. These results open new prospects and reinforce the interest of GEC1 study in the CNS and during the oncogenesis

Thesis (B.Sc)--University of Hong Kong, 2007.
"A dissertation submitted in partial fulfilment of the requirements for the Bachelor of Science (Speech and Hearing Sciences), The University of Hong Kong, June 30, 2007." Includes bibliographical references (p. 28-30). Also available in print.

Thesis (M. S.)--Biology, Georgia Institute of Technology, 2008.
Committee Chair: Chernoff,Yury; Committee Member: Cairney,John; Committee Member: Choi,Jung; Committee Member: Doyle,Donald; Committee Member: Lobachev,Kirill. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Ce manuscrit de thèse est organisé en deux parties. Une première partie théorique porte sur l'étude du processus d'amplification paramétrique de signaux faibles dans les fibres optiques, conventionnelles ou non linéaires, afin de concevoir des amplificateurs optiques à ultra-larges bandes spectrales et à profil de gain plat, deux critères essentiels permettant d'accroître les débits des transmissions multiplexées en longueur d'onde. Un second volet s'intéresse à une nouvelle génération de fibre en silice, la fibre microstructurée. Les propriétés optiques peu communes de ces fibres ont été étudiées en développant un outil de modélisation original, basé sur la méthode de Galerkin vectorielle. La génération de supercontinuums spectraux dans ces fibres a été également démontrée à la fois en régimes nanoseconde et femtoseconde et analysée à partir de concepts théoriques analytiques et numériques. Enfin, les propriétés de maintien de polarisation de la fibre microstructurée ont été étudiées
This PhD thesis manuscript is organized into two parts. The first, theoretical, part deals with fibre optical parametric amplification in conventional and highly nonlinear fibres. New amplifier schemes aimed at increasing the transmission rates of wavelength-division-multiplexed systems are proposed and characterized. Flat gain spectra over very large bandwidths are obtained using two pumps in a single fibre, or a single pump in a multi-section, dispersion-tailored fibre arrangement. The second part studies air-silica microstructured fibres. An efficient modelling tool based on the vectorial Galerkin method is developed in order to study their novel guiding and dispersion properties. Supercontinuum generation in these fibres is also demonstrated, both in the nanosecond and femtosecond pulse pumping regimes, and explained through analytical and numerical calculations. Finally, polarisation mode dispersion and vectorial modulational instability in the microstructured fibre are studied

Les propriétés électroniques de (Ga,Mn)N ont été étudiées par spectroscopie d'absorption des rayons X au seuil K du Mn. Des calculs ab-initio ont été utilisés pour interpréter les spectres d'absorption de (Ga,Mn)N. Deux pré-pics sont présents dans le seuil du Mn: le premier pré-pic est attribué aux transitions électronique vers les états 3d du Mn de spin up, tandis que le second pré-pic correspond aux transitions vers les états 3d du Mn de spin down. Cette interprétation nous permet de déterminer que l'état électronique du Mn dans (Ga,Mn)N est Mn3+: deux pré-pics sont présents dans les spectres d'absorption du Mn3+ et un seul pré-pic reste dans les spectres du Mn2+. Ce changement des spectres a été vérifié expérimentalement sur des échantillons de (Zn,Mn2+)Te et (Ga,Mn2+)As. De plus, cette interprétation permet d'étudier la distribution du Mn dans (Ga,Mn)N: la forme des spectres d'absorption suggère que la distribution du Mn est homogène dans nos échantillons de (Ga,Mn)N
Electronic properties of the diluted magnetic semiconductor (Ga,Mn)N were studied by x-ray absorption spectroscopy at the K-edge of Mn. The measured x-ray absorption spectra were further interpreted using the ab-initio calculations. Two pre-edge absorption lines are observed in the x-ray absorption spectra: the first line was attributed to electronic transitions into 3d states of Mn of spin up, while the second line corresponds to transitions into 3d states of Mn of spin down. This interpretation allows us to determine the valence state of Mn: two absorption lines are present in the pre-edge structure of Mn3+ and only one line remains in case of Mn2+. Such a change of the pre-edge structure was checked experimentally on (Zn,Mn2+)Te and on (Ga,Mn2+)As. In addition, the distribution of Mn in (Ga,Mn)N can be studied using the interpretation: the shape of the spectra points to a homogeneous distribution of Mn in our (Ga,Mn)N samples

Ge1-xSnx alloys are among a small class of benign semiconductors with composition tunable bandgaps in the near-infrared spectrum. As the amount of Sn is increased the band energy decreases and a transition from indirect to direct band structure occurs. Hence, they are prime candidates for fabrication of Si-compatible electronic and photonic devices, field effect transistors, and novel charge storage device applications. Success has been achieved with the growth of Ge1-xSnx thin film alloys with Sn compositions up to 34%. However, the synthesis of nanocrystalline alloys has proven difficult due to larger discrepancies (~14%) in lattice constants. Moreover, little is known about the chemical factors that govern the growth of Ge1-xSnx nanoalloys and the effects of quantum confinement on structure and optical properties. A synthesis has been developed to produce phase pure Ge1-xSnx nanoalloys which provides control over both size and composition. Three sets of Ge1-xSnx nanocrystals have been studied, 15–23 nm, 3.4–4.6 nm and 1.5–2.5 nm with Sn compositions from x = 0.000–0.279. Synthetic parameters were explored to control the nucleation and growth as well as the factors that have led to the elimination of undesired metallic impurities. The structural analysis of all nanocrystals suggests the diamond cubic structure typically reported for Ge1-xSnx thin films and nanocrystalline alloys. As-synthesized Ge1-xSnx nanoalloys exhibit high thermal stability and moderate resistance against sintering up to 400–500 °C and are devoid of crystalline and amorphous elemental Sn impurities.

This thesis conducts a critical analysis of editorials and columns in mainstream newspapers during Malaysia's 13th General Election (GE13) campaign. In a country that practises parliamentary democracy but simultaneously observes a close cooperation (Mustafa, 2010, p. 51) between the ruling party and the mainstream press, this study explores the links between the two. The thesis demonstrates the continuing power of the mainstream press in the country. It also explores how a so-called parliamentary democracy can lead to authoritarian rule, as well as the role of the press in this process. Adhering to Critical Discourse Analysis (CDA) principles, the thesis describes and explains how particular relations of power are enacted, reproduced and legitimized within government-owned media, in this case Malaysia where control is institutionalized. This study specifically focuses on the discursive strategies of legitimation in editorials and columns, and how they present particular narratives or arguments in the interests of the powerful. The thesis offers a greater understanding of the deep ideological structures of mainstream newspapers and, in particular, their construction and (de)legitimisation of the government and opposition during the GE13 campaign. This investigation draws on various methods, from quantitative content analysis to the Discourse-historical Approach (DHA), and insights from a range of disciplines, to examine the discursive features of mainstream newspapers discourse during the GE13 campaign. The main contributions of the thesis are on theoretical, methodological and empirical grounds. It contributes to the body of knowledge on political communication research by focusing on the Asian-Malaysian context and moving away from Western-centric models that often overlook the key element of culture. The application of the DHA provides a novel and valuable contribution to the understanding of Malaysian election communication discourse through its interdisciplinary methods and analyses. The empirical investigation provides conclusive evidence that revolves around the issues of the perversion of developmental journalism, race/ethnicity, Islam and its abuses, as well as change and time. This thesis also reviews and reveals the extent to which the press in Malaysia is controlled, dominated and manipulated, thereby challenging those, including the ruling elite, who have claimed that Malaysia is a democratizing nation state.

Nanomaterials, typically less than 100 nm size in any direction have gained noteworthy interest from scientific community owing to their significantly different and often improved physical properties compared to their bulk counterparts. Semiconductor nanoparticles (NPs) are of great interest to study their tunable optical properties, primarily as a function of size and shape. Accordingly, there has been a lot of attention paid to synthesize discrete semiconducting nanoparticles, of where Group III-V and II-VI materials have been studied extensively. In contrast, Group IV and Group IV-V based nanocrystals as earth abundant and less-non-toxic semiconductors have not been studied thoroughly. From the class of Group IV, Ge1-xSnx alloys are prime candidates for the fabrication of Si-compatible applications in the field of electronic and photonic devices, transistors, and charge storage devices. In addition, Ge1-xSnx alloys are potentials candidates for bio-sensing applications as alternative to toxic materials. Tin phosphides, a class of Group IV-V materials with their promising applications in thermoelectric, photocatalytic, and charge storage devices. However, both aforementioned semiconductors have not been studied thoroughly for their full potential in visible (Vis) to near infrared (NIR) optoelectronic applications. In this dissertation research, we have successfully developed unique synthetic strategies to produce Ge1-xSnx alloy quantum dots (QDs) and tin phosphide (Sn3P4, SnP, and Sn4P3) nanoparticles with tunable physical properties and crystal structures for potential applications in IR technologies. Low-cost, less-non-toxic, and abundantly-produced Ge1-xSnx alloys are an interesting class of narrow energy-gap semiconductors that received noteworthy interest in optical technologies. Admixing of α-Sn into Ge results in an indirect-to-direct bandgap crossover significantly improving light absorption and emission relative to indirect-gap Ge. However, the narrow energy-gaps reported for bulk Ge1-xSnx alloys have become a major impediment for their widespread application in optoelectronics. Herein, we report the first colloidal synthesis of Ge1-xSnx alloy quantum dots (QDs) with narrow size dispersity (3.3±0.5 – 5.9±0.8 nm), wide range of Sn compositions (0–20.6%), and composition-tunable energy-gaps and near infrared (IR) photoluminescence (PL). The structural analysis of alloy QDs indicates linear expansion of cubic Ge lattice with increasing Sn, suggesting the formation of strain-free nanoalloys. The successful incorporation of α-Sn into crystalline Ge has been confirmed by electron microscopy, which suggests the homogeneous solid solution behavior of QDs. The quantum confinement effects have resulted in energy gaps that are significantly blue-shifted from bulk Ge for Ge1-xSnx alloy QDs with composition-tunable absorption onsets (1.72–0.84 eV for x=1.5–20.6%) and PL peaks (1.62–1.31 eV for x=1.5–5.6%). Time-resolved PL (TRPL) spectroscopy revealed microsecond and nanosecond timescale decays at 15 K and 295 K, respectively owing to radiative recombination of dark and bright excitons as well as the interplay of surface traps and core electronic states. Realization of low-to-non-toxic and silicon-compatible Ge1-xSnx QDs with composition-tunable near IR PL allows the unprecedented expansion of direct-gap Group IV semiconductors to a wide range of biomedical and advanced technological studies. Tin phosphides are a class of materials that received noteworthy interest in photocatalysis, charge storage and thermoelectric devices. Dual stable oxidation states of tin (Sn2+ and Sn4+) enable tin phosphides to exhibit different stoichiometries and crystal phases. However, the synthesis of such nanostructures with control over morphology and crystal structure has proven a challenging task. Herein, we report the first colloidal synthesis of size, shape, and phase controlled, narrowly disperse rhombohedral Sn4P3, hexagonal SnP, and amorphous tin phosphide nanoparticles (NPs) displaying tunable morphologies and size dependent physical properties. The control over NP morphology and crystal phase was achieved by tuning the nucleation/growth temperature, molar ratio of Sn/P, and incorporation of additional coordinating solvents (alkylphosphines). The absorption spectra of smaller NPs exhibit size-dependent blue shifts in energy gaps (0.88–1.38 eV) compared to the theoretical value of bulk Sn3P4 (0.83 eV), consistent with quantum confinement effects. The amorphous NPs adopt rhombohedral Sn4P3 and hexagonal SnP crystal structures at 180 and 250 °C, respectively. Structural and surface analysis indicates consistent bond energies for phosphorus across different crystal phases, whereas the rhombohedral Sn4P3 NPs demonstrate Sn oxidation states distinctive from those of the hexagonal and amorphous NPs owing to complex chemical structure. All phases exhibit N(1s) and ʋ(N-H) energies suggestive of alkylamine surface functionalization and are devoid of tetragonal Sn impurities.

Dans la recherche de nouveaux matériaux piézoélectriques pour capteurs haute température (T > 600°C), nous nous sommes intéressés au matériau α-GeO2 dont le domaine de stabilité structurale en température et l'activité piézoélectrique seraient les plus importants parmi les composés isotypes du quartz-α. La littérature rapporte quelques limitations de ces deux propriétés dans le cas de monocristaux de α-GeO2 provenant de synthèses sous pression en milieu aqueux dues notamment à la présence de groupements hydroxyles au sein de la structure. Afin de remédier à cette contamination, une autre voie de croissance a été appliquée à GeO2 ; la méthode du flux par nucléation spontanée et à partir d'un germe monocristallin. Pour faciliter la croissance de la phase quartz-α de GeO2, métastable dans les conditions ambiantes, nous avons envisagé de substituer une faible partie des cations Ge4+ par des cations Si4+ (environ 10 % atomique). Après optimisation des différents paramètres expérimentaux, les cristaux synthétisés lors de ce travail ont été analysés par plusieurs techniques de caractérisation complémentaires (spectroscopies infrarouge et Raman, analyse E.D.X., D.R.X sur monocristal et sur poudre et D.S.C.) qui ont démontré leur excellente qualité cristalline, l'absence de contamination chimique (dans la limite de détection des techniques de caractérisation) et l'absence de transition de phase de la structure quartz-α, de la température ambiante à la fusion de ces matériaux (proche de 1100°C). L'approche de l'activité piézoélectrique de α-GeO2 en fonction de la température a été réalisée via l'étude de ses propriétés électromécaniques par spectroscopie d'impédance et spectroscopie Brillouin. Nous avons ainsi démontré que le matériau de structure quartz-α de GeO2 résonnait à très haute température (≈ 900°C) avec cependant une intensité diminuée par rapport à celle enregistrée à température ambiante
In the research of new piezoelectric materials for high temperature sensors (T > 600°C), we have been interested in α-GeO2 material which would exhibit the most important piezoelectric activity and structural stability domain with temperature among the α-quartz isotype compounds. Some limitations are described in the literature concerning those two properties in the case of hydrothermally-grown α-GeO2 single crystals mainly due to the presence of hydroxyl groups in their structure. To prevent this contamination, another growth approach was applied to GeO2: flux-growth method by spontaneous nucleation and from a crystalline seed. To facilitate the growth of the α-quartz phase of GeO2, metastable in ambient conditions, we have thought to substitute a part of Ge4+ cations by Si4+ cations (around 10 atomic per cent). After optimization of the different experimental parameters, flux-grown single-crystals were analyzed by several complementary characterization techniques (infrared and Raman spectroscopies, E.D.X. analyses, single-crystal and powder X-R.D. and D.S.C.) which have demonstrated their excellent crystalline quality, the absence of chemical contamination (inside the detection limit of characterization techniques) and the absence of phase transition of the α-quartz structure, from ambient temperature to the fusion of those materials (around 1100°C). The observation of piezoelectric activity of α-GeO2 as a function of temperature was realized from the study of its electromechanical properties by impedance spectroscopy and Brillouin spectroscopy. By these means, we have demonstrated that the α-quartz structure of GeO2 still resonate at very high temperature (≈ 900°C) with a weaker intensity compared to that recorded at ambient temperature

碩士
中國文化大學
化學系應用化學碩士班
103
We have used the B3LYP of density functional theory (DFT) and a simple basis set 6-31G* to optimize the structures of the hybrid clusters formed by adsorptions of alkaline earth metal(AEM) on Ge11 and Ge12 . Generally, Be has the best capability of forming covalent bonds with Ge among Be、Mg、Ca. Geometric relaxations//single point energies were carried out at the B3LYP/6-31G*//B3LYP/6-311++G(3df) level; the same method was applied to transition-state search.Our results showed that Be is commonly hypervalent with MTV > 3, higher than the expected value 2, especially in those endohedrons. Hirshfeld charges(HCs) and molecular orbitals indicated that back-donation from hosts facilitated such hypervalency. In CaGe11 and CaGe12 ,Ca-Ge bonds have small Mayer bond orders(MBO) but metal adsorption energies (Ead) are higher than in MgGe11 and MgGe12 because MBOs underestimate the bond ionicities, which are revealed by the obviously positive HCs of Ca atoms. The binding energies (BE) in MGen are comparable with different M and the same n , meaning the contribution of metal adsorption is not significant to the complete dissociation, but the greater stability of Ge12 than Ge11 . However, Eads in MGen (also different M and same n) imply that Be adsorbs strongly on Gen, then in Ca, and then in Mg. Mg-Ge has less covalency than Be-Ge and less iconicity than Ca-Ge that make Mg the weakest adsorbate.

Polymeric systems near their glass transition are known to exhibit heterogeneous dynamics that evolve both over space and time, yet many of the underlying principles of these dynamics are still poorly understood. In this thesis, experimental single molecule studies aimed at uncovering the dynamics of polystyrene near its glass transition temperature are described. In a first approach, the influence of temperature on the timescales associated with dynamic heterogeneity – also referred to as exchange times – are identified by following the dynamics of a fluorescent perylene diimide probe embedded in a high-molecular weight polystyrene host. No clear influence on the lifetime of dynamics is found in the temperature regime Tg to Tg + 10 K. In a second study, heterogeneous dynamics are investigated in the context of molecular weight and fragility. In a similar experimental approach to that of the first study, two fluorescent dyes are utilized to report on the rotational dynamics of low- to high-molecular weight polystyrene hosts. In accordance with previous reports, the stretching exponent, β, is found to be correlated with the system’s molecular weight, even on a single molecule level. However, no clear correlation with the system’s exchange time was found. In a final study, several single molecule approaches aimed at uncovering the dynamics in confined polystyrene films are described. As no evidence for previously-described mobile surface molecules has been found, this final chapter is meant to provide a basis for future single molecule studies in confined systems.

abstract: Group-IV semiconductor alloys are of interest for Si-integrated optoelectronic applications due to the band gap tunability and enhanced optical capabilities that can be achieved through compositional tuning. This work advances the field by presenting a systematic study of the optical and electronic properties of Ge1-ySny and analogous Ge1-x-ySixSny alloys. The fundamental direct and indirect band gaps of Ge1-ySny materials are measured by room temperature photoluminescence in samples containing 0 ≤ y ≤ 0.11 and a transition to direct gap materials is found to occur at yc = 0.087. This result is enabled by the development of sample growth and processing protocols that produce high-quality materials epitaxially on Ge-buffered Si(100) substrates. Strategies to optimize the optical performance are explored by varying the film thickness, thermal and surface treatments, and n-type doping. The electrical and optical properties of diodes based on these materials are characterized by current-voltage, optical responsivity, and electroluminescence measurements. These show improved optical performance near yc with tunable emission out to 2500 nm. Measuring the carrier lifetimes in devices with strain relaxed and fully strained interfaces show significantly longer lifetimes in the fully strained case. The direct and indirect band gaps of Sn-rich (y > x) Ge1-x-ySixSny materials are measured by room temperature photoluminescence on optimized samples. These data confirm a transition to direct gap materials occurs for the ternary alloy as well. Devices based on compositions 0.02 ≤ x ≤ 0.10 and 0.03 ≤ y ≤ 0.11 are characterized by current-voltage, optical responsivity, and electroluminescence measurements and show competitive performance with analogous devices based on Ge1-ySny materials. A detailed study of the direct gap in Ge1-xSix alloys gives parameters crucial en route to a global description of the Ge1-x-ySixSny fundamental band gaps. Archetypal laser device designs on Si are explored by fabricating degenerate pn junction diodes and highly doped waveguide devices based on high-quality Ge1-ySny materials. The diodes showed tunnel-like current-voltage characteristics and tailored electroluminescence based on the doping profile. The waveguides demonstrate emission under optical stimulation.
Dissertation/Thesis
Doctoral Dissertation Physics 2015

碩士
中國文化大學
化學系應用化學碩士班
100
We have used the B3LYP density functional theory (DFT) and a simple basis set 6-31G* to optimize the structures of the hybrid clusters formed by adsorptions of alkaline earth metal (AEM) on Ge9 and Ge10. Generally, Be has the best capability of forming covalent bonds with Ge among Be、Mg、Ca. Such covalency is reflected in the trivially positive Hirshfeld charges (Hirshfield charge, HC) of Be atoms and large Mayer bond order (Mayer bond order, MBO) of Be-Ge bonds. The covalency decreases as metal atoms move down in the AEM group. In CaGe9 and CaGe10 , Ca-Ge bonds have small MBO but their metal adsorption energies (Ead) are higher than in MgGe9 and MgGe10 because MBOs underestimate the bond ionicity, which are revealed by the obviously positive HCs of Ca atoms. The binding energies (BE) in MGen are comparable with different M for the same n, meaning the contribution of metal adsorption is not significant to the complete dissociation into separated atoms and it is mainly due to the greater stability of Ge10 than Ge9 . However, Eads in MGen (also different M and same n) imply that Be adsorbs strongly on Gen, then in Ca, and then in Mg. Mg-Ge has less covalency than Be-Ge and less iconicity than Ca-Ge that make Mg the weakest adsorbate. The trends of metal HCs and MTVs are opposite with each other. Beside CaGe9 and CaGe10, the ΔEg, Ead, and BE of ground state BeGe9,10 and MgGe9,10 vary in the similar trend.

碩士
國立東華大學
材料科學與工程學系
96
A series of ternary compounds Ge1-xSnxTe with x = 0, 0.2 , 0.4, 0.6, 0.8, 1.0 were successfully synthesized by the vertical Bridgman method. These materials all have excellent crystallinity with either rhombohedral structure（x = 0 – 0.6）or face centered structure（x = 0.8 – 1.0）at room temperatures, according to XRD and AEM. In the materials with x = 0 – 0.6, subgrain boundaries and micro-twins, characteristics of a martensitic type transformation from high temperature fcc structure to low temperature rhombohedral structure, were observed by OM, SEM and TEM. Despite the presence of ample high-angle grain boundaries, no subgrains and twins were observed in the materials with x = 0.8 – 1.0 lack of such transformation upon cooling. Thermoelectric properties of these materials were characterized at 50 – 400 K. Experimental results reveal that the thermal conductivities of these materials have been successfully reduced either by the presence of subgrains and twins in the materials with x = 0 – 0.6 by the presence of high-angle boundaries in the material with x = 0.8 – 1.0. Among all synthesized materials, the one with x = 0.4 has the lowest conductivity of 28.28（mW/cm-K）at 50K. This same material also exhibit the highest ZT value of 0.038 at 400 K, which is about 10 times higher than those of GeTe and SnTe commonly used as thermoelectric material at middle temperatures.

碩士
國立東華大學
材料科學與工程學系
94
In this study, Ge1-xSnxTe(x=0,0.8,0.9,1) crystals have been grown by vertical Bridgman method. The crystallinity and composition were investigated by X-Ray diffraction, SEM , EPMA and Raman spectroscopy techniques. The Seebeck coefficient, thermal conductivity, and resistivity measurement were carried out between 50K and 400K. The Hall measurement were completed at room temperature. The Figure of merit (ZT) for these semiconductor alloys were determined from these experimental results. The composition and temperature dependence of the thermoelectric properties for Ge1-xSnxTe(x=0,0.8,0.9,1) crystals were discussed.

碩士
國立清華大學
光電工程研究所
104
Germanium-Tin (GeSn) semiconductor alloy has been considered as a candidate for implementing active Group IV optoelectronics. In this thesis, a Ge1-xSnx metal-semiconductor-metal (MSM) photodetector fabricated on Si substrate by rapid melt growth method with graded Sn concentration up to 5-10 %, which is higher than the solid solubility (~ 1 %) of Sn in Ge is demonstrated. The crystal orientation and elemental composition of the GeSn alloy are characterized by selected area diffraction (SAD) pattern and energy dispersion spectroscopy (EDS), showing a monocrystalline semiconductor quality and Sn concentration profile. This crystal quality of GeSn alloy is also investigated by Raman spectroscopy. Finally, we measure the photocurrent of the device and verify the GeSn MSM photodetector has a mid-IR photoresponse at wavelength of 2 μm.

碩士
國立臺灣大學
電子工程學研究所
99
We report on experimental investigations of the growth of Ge1-xSnx film with thickness above the critical thickness using Molecular Beam Epitaxy. A series of Ge1-xSnx films with various Sn compositions up to 14% are deposited on a Ge buffer layer for growth at low temperatures close to the melting point of Sn. Especially, a low temperature Ge buffer layer was grown between GeSn film and Ge substrate for trapping defects. Analysis of various measurements shows that the Ge1-xSnx film is defect free in the XTEM image and that Sn is distributed almost uniformly in the film for Sn compositions up to 9.3%. The Sn composition of the films is higher than the Sn composition that is theoretically predicted to cause the energy band of Ge to change from an indirect to a direct bandgap; thus, the present nvestigation provides a method for growing direct bandgap GeSn film, which is desired for use in applications involving optoelectronic devices.

碩士
國立臺灣海洋大學
電機工程學系
107
In the modern competitive consumer electronic market, a viable feature for Notebook is compactness in term of ultra-lightness and thinness. Therefore, the available space inside a Notebook is extremely limited. The spacing between the antenna and USB 3.1(Gen1) needs to be reduced to accommodate housing of other peripherals, rendering the antenna susceptible to electromagnetic interference (EMI). The generated EMI will have adverse impact on 2.4 GHz Wireless Network and wireless devices such as wireless keyboards, mice, 802.11b/g/n and Bluetooth manifested as time-lagged in response and intermittent or complete disconnection in data transmission. Therefore, the suppression technology of EMI played an ever increasing role in the wellbeing of the Notebook industry. This thesis focuses on the EMI issue between the USB 3.1(Gen1) device and Wireless Local Area Network of a Convertible Notebook. The electromagnetic field is measured to identify the interference source and the interference path. The electromagnetic noise suppression measures adopted in this study including making changes in circuit board layout, the using of different electronic filters to filter out the spurious signals, implementing common mode chokes, and the use of electromagnetic shielding materials and absorber materials. The effectiveness of the countermeasures in alleviating the EMI with the Notebook in different operating modes were studied by using the hard disk speed test software (CrystalDiskMark) to analyze the signal quality (Eye Diagram) and data throughput to ascertain the satisfaction of consumer specifications on good data transmission quality of the USB3.1 device.

碩士
國立中興大學
精密工程學系所
99
We conduct first-principles total-energy density functional calculations to study the band structures in Ge1-xSnx infrared semiconductor alloys. The sX-LDA(Screened exchange local density approximation) and HSE06(Heyd scuseria ernzerhof hybrid functional) calculations to study the band structure in Ge1-xSnx semiconductor alloys. The norm-conserving optimized pseudopotentials of Ge and Sn have been constructed for lattice constant, band-gap, electronic structure calculations. Our findings show band gap that are predicted to undergo an indirect-to-direct transition for x close to 0.125. The composition-bandgap relationships in Ge1-xSnx lattice are evaluated by a detailed comparison of bonding, electronic, structural properties. The atomic structures play a key role in the indirect-gap to direct-gap transition.

abstract: This thesis describes the fabrication of several new classes of Ge1-x-ySixSny materials with the required compositions and crystal quality to engineer the band gaps above and below that of elemental Ge (0.8 eV) in the near IR. The work initially focused on Ge1-x-ySixSny (1-5% Sn, 4-20% Si) materials grown on Ge(100) via gas-source epitaxy of Ge4H10, Si4H10 and SnD4. Both intrinsic and doped layers were produced with defect-free microstructure and viable thickness, allowing the fabrication of high-performance photodetectors. These exhibited low ideality factors, state-of-the-art dark current densities and adjustable absorption edges between 0.87 and 1.03 eV, indicating that the band gaps span a significant range above that of Ge. Next Sn-rich Ge1-x-ySixSny alloys (2-4% Si and 4-10% Sn) were fabricated directly on Si and were found to show significant optical emission using photoluminescence measurements, indicating that the alloys have direct band gaps below that of pure Ge in the range of 0.7-0.55 eV. A series of Sn-rich Ge1-x-ySixSny analogues (y>x) with fixed 3-4% Si content and progressively increasing Sn content in the 4-10% range were then grown on Ge buffered Si platforms for the purpose of improving the material's crystal quality. The films in this case exhibited lower defect densities than those grown on Si, allowing a meaningful study of both the direct and indirect gaps. The results show that the separation of the direct and indirect edges can be made smaller than in Ge even for non-negligible 3-4% Si content, confirming that with a suitable choice of Sn compositions the ternary Ge1-x-ySixSny reproduces all features of the electronic structure of binary Ge1-ySny, including the sought-after indirect-to-direct gap cross over. The above synthesis of optical quality Ge1-x-ySixSny on virtual Ge was made possible by the development of high quality Ge-on-Si buffers via chemical vapor deposition of Ge4H10. The resultant films exhibited structural and electrical properties significantly improved relative to state-of-the-art results obtained using conventional approaches. It was found that pure Ge4H10 facilitates the control of residual doping and enables p-i-n devices whose dark currents are not entirely determined by defects and whose zero-bias collection efficiencies are higher than those obtained from samples fabricated using alternative Ge-on-Si approaches.
Dissertation/Thesis
Ph.D. Physics 2013

碩士
國立臺灣大學
電子工程學研究所
100
In a recent development, tin (Sn)-based group-IV semiconductor compounds has attracted research attention for new electronic and photonic devices. The incorporation of Sn modulates the bandgap of the host IV-IV compounds, and, above a certain Sn composition, the energy band of the IV-IV compounds changes from an indirect to a direct band gap. Here, we investigate a series of Ge1-xSnx alloy with various Sn compositions up to 14% and 17% grown on Ge and Si wafer respectively using low-temperature Molecular Beam Epitaxy. To characterize band structure and optical properties of these GeSn samples, we performed spectroscopic Fourier Transform Infra-Red (FTIR), ellipsometer, and photoluminescence (PL) measurements. The Γ-to-Γ optical energy gap of Ge1-xSnx alloys can be determined by FTIR. Several critical point features, corresponding to E1, E1+Δ1, and E0’ transitions, are observed in ε1 and ε2. The positions of E1 and E1+Δ1 shift toward to lower energy as Sn composition increases. Furthermore, the optoelectronic and electronic devices can be designed for applications by those analyzed. We propose a new design of Sn-based group-IV structure for resonant tunneling diode (RTD). The proposed RTD is composed of direct-bandgap Ge1-xSnx/SiyGezSn1-y-z quantum well which can be directly grown on Si. By optimizing the composition and strain in the quantum well, a high peak-to-valley ratio of 7.69 is obtained. Those results suggest our proposed RTD design can be integrated into CMOS circuits for useful applications.

碩士
國立臺灣大學
電子工程學研究所
101
We report the characteristics of Ge1-xSnx/Ge strained layer superlattices ( ) pseudomorphically grown on Ge-buffered on Si(001) wafers by molecular beam epitaxy at low temperature. The crystal quality of the Ge1-xSnx/Ge superlattices was characterized by transmission electron microscopy, atomic force microscopy, and reflection high-energy electron diffraction. The composition and strain states were analyzed by x-ray diffraction and Raman microscopy. The optical spectra were measured by Fourier transform infrared spectroscopy, Photoluminescence, and Photoreflectance to determine the lowest direct-gap transition energies. The observed blue shifts of lowest direct-gap transition energies are attributed to the quantum confinement effect and strain effect, confirmed by our theoretical results using DFT theory. In addition, we also fit the conduction band offset ratio of GeSn/Ge heterostructure by the results of the optical experiments. In this thesis, low dimensional heterostructure of newly group IV material system is investigated. Ge1-xSnx/Ge superlattices are demonstrated by technique of low temperature growth using by Molecular Beam Epitaxy, and presenting characteristics of strained Ge1-xSnx/Ge superlattices (SLs) on Si substrates with x up to 6.96 %. Move a step forward toward the low dimensional Sn-based group IV photonic devices.

碩士
國立臺灣大學
森林環境暨資源學研究所
105
Taiwania (Taiwania cryptomerioides Hayata) is a conifer species native to Taiwan, which is known for several bioactive secondary metabolites from it. Studying terpene synthases is the key way to understand the pathway of terpene biosynthesis. In this study, Tc-Lon, Tc-Ced/Ger, Tc-αCub/Ger, Tc-Ger1 and Tc-Ger2 were isolated from Taiwania by using polymerase chain reaction (PCR) and rapid amplification of cDNA ends (RACE) methods. Tc-Lon is a sequiterpene synthase and it can synthesize longifolene. Tc-Ced/Ger and Tc-αCub/Ger are bifunctional terpene synthases, which can produce monoterpenes and sesquiterpenes simultaneously. Tc-Ced/Ger can produce sesquiterpene cedrol and monoterpene geraniol. Tc-αCub/Ger can produce sesquiterpene α-cubebene and monoterpene geraniol. DDXXD motif is absent in Tc-Ger1, so the two mutants A359D and A359D/H363D were made to clarify these two residues how them work. Interestingly, A359D and A359D/H363D have the same function like the wild type of Tc-Ger1, and it was confirmed that Tc-Ger1 and Tc-Ger2 can produce geraniol. In this study, terpene synthesis pathways were built by using metabolic engineering. Using the strategy of the metabolic engineering for terpene overproduction should also work in other synthetic pathways in the future.