<p>Vertical cavity lasers (VCLs) are of great interest aslow-cost, high-performance light sources for fiber-opticcommunication systems. They have a number of advantages overconventional edge-emitting lasers, including low powerconsumption, efficient fiber coupling and wafer scalemanufacturing/testing. For high-speed data transmission overdistances up to a few hundred meters, VCLs (or arrays of VCLs)operating at 850 nm wavelength is today the technology ofchoice. While multimode fibers are successfully used in theseapplications, higher transmission bandwidth and longerdistances require single-mode fibres and longer wavelengths(1.3-1.55 µm). However, long-wavelength VCLs are as yetnot commercially available since no traditional materialssystem offers the required combination of bothhigh-index-contrast distributed Bragg reflectors (DBRs) andhigh-gain active regions. Earlier work on long-wavelength VCLshas therefore focused on hybrid techniques, such as waferfusion between InP-based QWs and AlGaAs DBRs, but more recentlythe main interest in this field has shifted towardsall-epitaxial GaAs-based devices employing novel 1.3-µmactive materials. Among these, strained GaInNAs/GaAs QWs aregenerally considered one of the most promising approaches andhave received a great deal of interest.</p><p>The aim of this thesis is to investigate monolithicGaAs-based long-wavelength (>1.2 µm) VCLs with InGaAsor GaInNAs QW active regions. Laser structures - or partsthereof - have been grown by metal-organic vapor phase epitaxy(MOVPE) and characterized by various techniques, such ashigh-resolution x-ray diffraction (XRD), photoluminescence(PL), atomic force microscopy, and secondary ion massspectroscopy (SIMS). High accuracy reflectance measurementsrevealed that n-type doping is much more detrimental to theperformance of AlGaAs DBRs than previously anticipated. Asystematic investigation was also made of the deleteriouseffects of buried Al-containing layers, such as AlGaAs DBRs, onthe optical and structural properties of subsequently grownGaInNAs QWs. Both these problems, with their potential bearingon VCL fabrication, are reduced by lowering the DBR growthtemperature.</p><p>Record-long emission wavelength InGaAs VCLs were fabricatedusing an extensive gain-cavity detuning. The cavity resonancecondition just below 1270 nm wavelength occurs at the farlong-wavelength side of the gain curve. Still, the gain is highenough to yield threshold currents in the low mA-regime and amaximum output power exceeding 1 mW, depending on devicediameter. Direct modulation experiments were performed on1260-nm devices at 10 Gb/s in a back-to-back configuration withopen, symmetric eye diagrams, indicating their potential foruse in high-speed transmission applications. These devices arein compliance with the wavelength requirements of emerging10-Gb/s Ethernet and SONET OC-192 standards and may turn out tobe a viable alternative to GaInNAs VCLs.</p><p><b>Keywords:</b>GaInNAs, InGaAs, quantum wells, MOVPE, MOCVD,vertical cavity laser, VCSEL, long-wavelength, epitaxy, XRD,DBR</p>

Thin films become more and more important in science and industry. The main objective of this work was the expanding of the measurement capabilities of the XRD 3000PTS to the field of thin films. The success of the changes was documented by maesurements on TiC thin films. / Dünne Schichten gewinnen in Forschung und Industrie zunehmend an Bedeutung. Ziel der Arbeit war es deshalb, den Einsatzbereich des vorhandenen Diffraktometers XRD 3000PTS auf Untersuchungen an dünnen Schichten zu erweitern. Der Erfolg der Veränderungen konnte mit Messungen an einer TiC Probenserie bestätigt werden.

Because of the anticipated high demand for Indium, ongoing growth of CIGS technology may be limited. Kesterite materials, which replace In with a Zn/Sn couple, are thought to be a solution to this issue. However, efficiencies are still below the 10% level, and these materials are proving to be complex. Even determination of the bandgap is not settled because of the occurrence of secondary phases. We use a film growth process, 2SSS, which we believe helps control the formation of secondary phases. Under the right growth conditions we find 1/1 Zn/Sn ratios and XRD signatures for Cu2ZnSnSe4 with no evidence of secondary phases. The optical absorption profile of our films is also a good match to the CIS profile even for films annealed at 500° C. We see no evidence of phase separation. The effect of intentional variation of the Zn/Sn ratio on material and device properties is also presented.

Η υδροχλωρική δονεπεζίλη (Donepezil.HCl, DPZ) είναι ένα φάρμακο που λαμβάνεται για τη θεραπεία της νόσου Altzheimer. Δρα ως ανασολέας της ακετυλοχοληστερινάσης, ενός ενζύμου υπεύθυνου για την καταστροφή του νευροδιαβιβαστή ακετυλοχολίνη, αυξάνοντας το ποσό της ακετυλοχολίνης στον εγκέφαλο. Παρουσιάζει διάφορες κρυσταλλικές μορφές, συμπεριλαμβανομένων δύο ένυδρων, καθώς και μια άμορφη φάση. Τα δισκία Υδροχλωρικής Δονεπεζίλης λαμβάνονται από το στόμα και μπορεί να αποθηκευθούν για κάποιο χρονικό διάστημα πριν χρησιμοποιηθούν. Τα δισκία DPZ ισχύος 10 mg περιέχουν 3.6 % API, ενώ στις περιπτώσεις όπου λαμβάνει χώρα πολυμορφική μετατροπή, η επιμέρους περιεκτικότητα κάθε πολυμόρφου είναι ακόμα μικρότερη. Η ταυτοποίηση και ποσοτική ανάλυση των πολυμόρφων ή ένυδρων μορφών είναι δυνατή μόνο με τη χρήση περίθλασης ακτίνων Χ και δονητικών φασματοσκοπικών τεχνικών. Λόγω του μικρού ποσοστού της δραστικής ουσίας στα δισκία και της πιθανής παρουσίας περισσοτέρων του ενός πολυμόρφου αλλά και του μεγάλου σχετικά ορίου ανίχνευσης αυτών των τεχνικών η ταυτοποίηση και ποσοτική ανάλυση είναι μια αναλυτική πρόκληση. Στην παρούσα εργασία έγινε προσπάθεια ταυτοποίησης των κρυσταλλικών μορφών του DPZ σε δισκία και έλεγχος της σταθερότητάς τους μετά από διάφορες διαδικασίες παρασκευής των δισκίων, καθώς και μετά από αποθήκευση σε διάφορες συνθήκες υγρασίας και θερμοκρασίας, χρησιμοποιώντας τις πειραματικές τεχνικές XRD, FT-IR και FT-Raman. Παρατηρήθηκε ότι η προέλευση του API, οι συνθήκες αποθήκευσης και κυρίως η μέθοδος παρασκευής των δισκίων επηρεάζουν τη σταθερότητα των φαρμακευτικών σκευασμάτων. Με στόχο τη διερεύνηση της δυνατότητας ανάπτυξης ποσοτικών αναλυτικών μεθόδων προσδιορισμού των πολυμόρφων Ι και ΙΙΙ του DPZ σε δισκία, οι παραπάνω τεχνικές χρησιμοποιήθηκαν για τον υπολογισμό των ορίων ανίχνευσης των δύο πολυμόρφων (0.35% κ.β. για το πολύμορφο Ι και 0.44 % κ.β. για το πολύμορφο ΙΙΙ με την τεχνική Raman, 0.95% κ.β. για το πολύμορφο Ι και 1.3 % κ.β. για το πολύμορφο ΙΙΙ με την τεχνική XRD, 1.2% κ.β. για τη μορφή Ι και 1.0 % κ.β. για τη μορφή ΙΙΙ με την τεχνική IR, όπως προέκυψαν μετά από στατιστική επεξεργασία των πειραματικών δεδομένων των διαφόρων τεχνικών), καθώς και για τον ποσοτικό τους προσδιορισμό. Η τεχνική Raman φαίνεται να μπορεί χρησιμοποιηθεί για ποσοτική ανάλυση των πολυμόρφων Ι και ΙΙΙ του DPZ σε δισκία, ενώ επιπλέον η ποσοτική μέθοδος που παρουσιάσθηκε εδώ είναι απλή και μη καταστροφική για τα δείγματα. Η μέθοδος XRD μπορεί πιθανόν να χρησιμοποιηθεί για την ποσοτική ανάλυση δισκίων DPZ, με μεγαλύτερο όμως σφάλμα σε σύγκριση με την τεχνική Raman, ενώ η μέθοδος FT-IR ATR, παρέχει τα λιγότερο καλά ποσοτικά αποτελέσματα, ακόμα και στην περίπτωση που το δισκίο περιέχει αποκλειστικά το ένα από τα δύο πολύμορφα. Τέλος, με στόχο την ερμηνεία των φασμάτων δόνησης που καταγράφησαν στην παρούσα εργασία, υπολογίστηκαν η σταθερή δομή του μορίου της Δονεπεζίλης και της ένυδρης Δονεπεζίλης (με ένα μόριο νερού ανά μόριο Δονεπεζίλης) και τα φάσματα δόνησης (IR και Raman) με τις μεθόδους Hartree-Fock ab-initio και DFT (Density Functional Theory) και χρήση του υπολογιστικού πακέτου Gaussian09. / Donepezil hydrochloride (DPZ) is a medication used to treat Altzheimer’s disease. It acts as an inhibitor of acetylcholisterinase, an enzyme responsible for the destruction of the neurotransmitter acetylcholine, thus increasing the level of acetylcholine in the brain. As most of the pharmaceutical solids, DPZ exhibits polymorphism. Donepezil hydrochloride has different crystalline forms, including two hydrates, as well as an amorphous phase. DPZ is available for oral administration in tablets which can be stored for some time before use. In the present study, an effort was made to identify the crystal form of DPZ in tablets, as well as to test its stability against time, temperature and humidity, after various manufacturing processes, using XRD, FT-IR and FT-Raman techniques. The data showed that the origin of the API, the storing conditions and mainly the manufacturing process of the tablets affect the stability of the API. Quantitative determination of polymorphs I and III of DPZ in tablets was also attempted using the above experimental methods. Calibration models were constructed and applied in DPZ tablets. The detection limits of polymorphs I and III of DPZ for each technique, derived after statistical treatment of the experimental data, were calculated. Raman spectroscopy exhibited the lower detection limit (0.35 weigh % for polymorph Ι and 0.44 % weigh % for polymorph ΙΙΙ) compared with XRD (0.95% weigh % for polymorph Ι and 1.3 % weigh % for polymorph ΙΙΙ) and IR spectroscopy (1.2% weigh % for polymorph Ι and 1.0 % weigh % for polymorph ΙΙΙ). The data suggest that Raman spectroscopy could be applied to quantify polymorphs I and III in DPZ tablets; moreover, the Raman quantitative method presented in this work is simple and non-destructive for the tablets. The application of the X ray diffraction method for the quantitative analysis of polymorphs I and III in tablets yielded larger errors compared with Raman spectroscopy, while the FT-IR ATR technique yielded poor quantitative results, even in the case that only one polymorph was present in DPZ tablets. Finaly, in order to facilitate the assignment of the vibrational spectra recorded in this study, the optimized structure and the vibrational spectra (IR and Raman) of Donepezil and Donepezil hydrate (Donepezil:H20 = 1:1) molecules were calculated at the Hartree-Fock and DFT (Density Functional Theory) level of theory using the Gaussian 09 program package. The weigh % of the API in the tablets containing 10 mg of DPZ is 3.6 %. In cases where two or more polymorphs are present, the weigh % of each polymorphic form is lower. The difficulty in the identification and quantification of the crystal phase of DPZ is stemming from the small percentage of the API in the tablets, the considerable overlapping of DPZ XRPD patterns and IR and Raman spectra of the polymorphs and the excipients and the availability of various polymorphs.

Aluminum (Al) powder metallurgy (PM) provides a cost effective and environmentally friendly means of creating lightweight, high performance, near net shape components, relative to conventional casting/die casting technology. Unfortunately, the current lack of commercially available Al alloy powder blends has hindered development in this field as a result of the limited scope of mechanical properties available; especially under elevated temperature conditions common to many automotive applications. As such, the objective of this research was to attempt to improve the versatility of current Al PM technology through the incorporation of Fe and Ni transition metal additions into an emerging Al- 4.4Cu-1.5Mg-0.2Sn alloy, as this technique is known to enhance the elevated temperature stability of wrought/cast Al alloys through the formation of stable, Fe/Ni aluminide dispersoids. Initial experimentation consisted of evaluating the feasibility of incorporating Fe and Ni both elementally and pre-alloyed, through a series of tests related to their PM processing behaviour (compressibility, sintering response) and sintered product performance (ambient tensile properties). Results confirmed that pre-alloying of the base Al powder was the most effective means of incorporating Fe and Ni as all such specimens achieved properties similar or slightly superior to the unmodified alloy. Of the pre-alloyed systems considered, that containing 1%Fe+1%Ni displayed the most desirable results in terms of mechanical performance and microstructural homogeneity of the Fe/Ni dispersoid phases present in the sintered product. Bars of the baseline system and that modified with pre-alloyed additions of 1Fe/1Ni were then sintered industrially to gain a preliminary sense of commercial viability and obtain additional specimens for elevated temperature exposure tests. Results confirmed that the sintering response, tensile properties and microstructures were essentially identical in both alloys whether they were sintered in a controlled laboratory setting or an industrial production environment. Furthermore, DSC data indicated that S (Al2CuMg)-type phases were the dominant precipitates formed during heat treatment. The effects of elevated temperature exposure were assessed in the final stage of research. Both alloys were found to exhibit comparable behaviour when exposed to the lowest (120°C) and highest (280°C) temperatures considered. Here, the alloys showed no obvious degradation at 120°C. Conversely, exposure at 280°C prompted a steady decline in yield strength for both alloys with significant precipitate coarsening noted as well. Despite these similarities, differences emerged during isochronal tests at intermediate temperatures. Here, DSC data indicated that the precipitates present in the pre-alloyed material were stable at temperatures up to 160°C while those in the unmodified alloy had begun to overage under the same exposure conditions. These differences were accompanied by increased stability in tensile yield strength for the pre-alloyed material. In all, this study has indicated that the use of Al powder pre-alloyed with Fe/Ni additions is feasible for press-and-sinter PM technology and that the sintered product exhibits improved elevated temperature stability under certain conditions.

No description available.

This research is part of an ongoing project to create gypsum wallboards with enhanced fire resistance. The main goal of this research is to better understand the dehydration properties of calcium sulfate dihydrate, and the hydration of calcium sulfate hemihydrate as well as anhydrous calcium sulfate. The lab-scale kinetics of these processes were studied using thermogravimetric analysis and sorption analysis. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the products from different processes. In addition to the instrumental studies, small batches were handled in ovens and liquid slurries to better mimic the real world processing of these materials. The effects of temperature, time and humidity were investigated to determine their influence on the kinetics of dehydration/hydration of different hydration forms of calcium sulfate.

Sodium hydroxide can cause cellulose to swell and can even dissolve cellulose in a narrow range of the phase diagram. It was found that for cellulose with low to moderate degree of polymerization, the maximal solubility occurs with 8~10% soda solution. In recent years, researchers found that sodium hydroxide with urea at cold temperature can dissolve cellulose better than sodium hydroxide alone. However, the lack of sufficient understanding of the NaOH and NaOH/urea dissolution process significantly constrains its applications. In order to fully understand the cellulose dissolution in alkali system, there are several aspects of problems that need to be addressed. Our focus in this study is in the interaction of cellulose with alkali solution at low temperatures, the improvement of its solubility, and the effect of hemicellulose and lignin.

Polymer/clay nanocomposites consisting of an epoxy resin matrix filled with organoclays have been investigated. The main objective of this study was to determine which combination of components led to the greatest enhancement in properties of the epoxy resin. Exfoliation of the clay was desired, as exfoliated nanocomposites are known to exhibit great improvements in mechanical properties [1]. The epoxy resins studied were di-functional DGEBA and tetra-functional TGDDM. The epoxy resin was cured with three different hardeners, these included: the high functionality amine hardener, TETA, and two anhydride hardeners, accelerated MTHPA and pure HHPA. The three organoclays used, contained alkylammonium cations and were also compared to the unmodified clay. Morphology was investigated by XRD and TEM, and the flexural properties of the resulting nanocomposites were studied. The effect that the addition of an organoclay has on the cure of the epoxy resin was investigated using MDSC. Both the temperatures required to cure the resin with, and without, the clay, and any changes in the total heat flow that occurred were studied. The Tg++ of the cured nanocomposites was also measured using MDSC. The heat flow results indicated that the clays added to the epoxy resins act as a physical barrier, which prevents the resin from reaching full cure. In the higher functional resin, the addition of clay resulted in a significant decrease in the total heat flow, suggesting that a large amount of epoxy remains uncured, and, as a result, there should be a reduction in the amount of cross-linking. The lower cross-link density led to a significantly lower Tg and the mechanical properties were also poorer. The reactivity of the hardener towards the resin was found to have the greatest impact on the cured nanocomposite morphology. Intragallery polymerisation occurring at a faster rate than the extragallery polymerisation causes exfoliation. In order to achieve a balance that favours intragallery polymerisation, it was found that the curing reaction was required to be catalysed by the alkylammonium cation of the organoclay, and not catalysed by other means. The DGEBA cured with HHPA provided the largest layer expansion in the clay structure due to the alkylammonium cation catalysing the anhydride ring-opening reaction. The effect was not seen with TGDDM due to the tertiary amine in its structure. The accelerator within the MTHPA assisted extragallery polymerisation of the resin and the TETA cured readily without additional catalysis.

Electrochemical behavior of electrolytic manganese dioxide (EMD), chemically prepared battery grade manganese dioxide (BGM), titanium dioxide (TiO2), lithium iron phosphate (LiFePO4) and lithium manganese phosphate (LiMnPO4) in aqueous lithium hydroxide electrolyte has been investigated. These materials are commonly used as cathodes in non-aqueous electrolyte lithium batteries. The main aim of the work was to determine how the electroreduction/oxidation behavior of these materials in aqueous LiOH compares with that reported in the literature in non-aqueous electrolytes in connection with lithium batteries. An objective was to establish whether these materials could also be used to develop other battery systems using aqueous LiOH as electrolyte. The electrochemical characteristics of the above materials were investigated by subjecting them to slow scan cyclic voltammetry and determining the charge/discharge characteristics of Zn/cathode material-aqueous LiOH batteries. The products of electroreduction/oxidation were characterized by physical techniques using X-ray diffraction (XRD), scanning electron micrography (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), Thermogravimetric analysis (TG) and infra-red spectrometry (IR). The reduction of ã-MnO2 (EMD) in aqueous lithium hydroxide electrolyte is found to result in intercalation of Li+ into the host structure of ã-MnO2. The process was found to be reversible for many cycles. This is similar to what is known to occur for ã-MnO2 in non-aqueous electrolytes. The mechanism, however, differs from that for reduction/oxidation of ã-MnO2 in aqueous potassium hydroxide electrolyte. KOH electrolyte is used in the state-of-art aqueous alkaline Zn/MnO2 batteries. Alkaline batteries based on aqueous KOH as the electrolyte rely upon a mechanism other than K+ intercalation into MnO2. This mechanism is not reversible. This is explained in terms of the relative ionic sizes of Li+ and K+. The lithium-intercalated MnO2 lattice is stable because Li+ and Mn4+ are of approximately the same size and hence Li+ is accommodated nicely into the host lattice of MnO2. The K+ ion which has almost double the size of Li+ cannot be appropriately accommodated into the host structure and hence the K+ -intercalated MnO2 phase is not stable. Chemically prepared battery grade MnO2 (BGM) is found to undergo electroreduction/oxidation in aqueous LiOH via the same Li+ intercalation mechanism as for the EMD. While the Zn/BGM- aqueous LiOH cell discharges at a voltage higher than that for the Zn/EMD- aqueous LiOH cell under similar conditions, the rechargeability and the material utilization of the BGM cell is poorer. The cathodic behavior of TiO2 (anatase phase) in the presence of aqueous LiOH is not reversible. In addition to LiTiO2, Ti2O3 is also formed. The discharge voltage of the Zn/TiO2- aqueous LiOH cell and material utilization of the TiO2 as cathode are very low. Hence TiO2 is not suitable for use in any aqueous LiOH electrolyte battery. LiFePO4 (olivine-type structure) as a cathode undergoes electrooxidation in aqueous LiOH forming FePO4. However the subsequent reduction forms not only the original LiFePO4 but also Fe3O4. Thus the process is not completely reversible and hence LiFePO4 is not a suitable material for use as a cathode in aqueous battery systems. LiMnPO4 (olivine-type structure) undergoes reversible electrooxidation in aqueous LiOH forming MnPO4. The charge/discharge voltage profile of the Zn/MnPO4-aqueous LiOH cell, its coulombic efficiency and rechargeability are comparable to that of the cell using ã-MnO2. EMD and LiMnPO4 both have the potential for use in rechargeable batteries using aqueous LiOH as the electrolyte. Recommendations for further developmental work for such batteries are made.