A new model for low pressure chemical vapor deposition of SiO2 films by ozone augmented tetraethoxysilane

A simple model has been developed to analyze the low pressure chemical vapor deposition (LPCVD) of SiO₂ films from tetraethoxysilane (TEOS) and ozone. It is found that the model correlates well the experimental data taken at 30 to 90 Torr which is the range of the Applied Materials 5000 reactor. The model shows from correlations of experimental data that gas phase reaction reduces the deposition rate and that this effect becomes more significant at temperatures above about 365°C. The model also explains successfully the trend in experimental data on Arrhenius plots for pressures from 30 to 90 Torr. These data indicate that the temperature, T_m, at which the deposition rate is a maximum, decreases as the pressure is increased. This occurs because the effect of parasitic gas phase reactions becomes more important at higher pressure. Furthermore, thetrends predicted buy our model are consistent with the experimental data taken under atmospheric pressure chemical vapor deposition (APCVD), even though these conditions are outside the range of applicability of this model which assumes low pressure and therefore very high rates of diffusion.     

Volatility of radioactive iodine under gamma irradiation: effects of H2O2 and NaOH on the decomposition rate of volatile molecular iodine dissolved in aqueous solutions

Journal of Radioanalytical and Nuclear Chemistry - The decomposition of molecular iodine by hydrogen peroxide and sodium hydroxide was kinetically studied in aqueous solutions at ambient...     

Die Kinetik polymerer Aldehyde

Zusammenfassung Auf Grund einer Theorie über den Aufbaumechanismus der Polyoxymethylene ist es gelungen, ketteneinheitliche Produkte in Abhängigkeit von Temperatur, Katalysator und Konzentration darzustellen.Die Unterscheidung der verschiedenen Produkte kann durch die Bestimmung ihrer Lösungsgeschwindigkeits-Konstanten erfolgen.     

Defects and microvoids in a-Si and a-Si:H

We report the first measurements of positron-annihilation spectra of samples of both pure and hydrogenated amorphous silicon. Comparison of these spectra with that of crystalline silicon indicates that the lowest-lifetime component can be identified as the contribution mainly from valence-band electrons. Both the pure (a-Si) and the hydrogenated (a-Si:H) samples exhibit a component with intermediate lifetime, which we attribute to small vacancies consisting of about 4 missing atoms. Finally, only a-Si:H shows a significant long-lived line (τ > 5 ns), which arises from large microvoids, with ～ 100 missing atoms. The existence of these microvoids in a-Si:H is consistent with recent reports of the presence of occluded H₂ gas under high pressure in such films.     

Facile synthesis of cis-2-Alkyl-3-trialkylsilyloxycycloalkanones via the non-aldol aldol rearrangement of 2,3-epoxycycloalkanols

Silyl triflate-promoted rearrangement of cis-2,3-epoxycycloalkanols A, prepared by epoxidation of the cyclic allylic alcohol and then silylation, afforded good yields ( approximately 70-75%) of the cis-2-alkyl-3-silyloxycycloalkanones B, presumably via the intermediates C and D, even with quite large alpha-substituents, e.g., tert-butyl. Finally, it has been shown that the stereochemistry of the epoxy alcohol is crucial as one would expect from the mechanism.     

Uncertainties of method performance statistics based on a balanced completely randomized model interlaboratory study

Using exact and asymptotic distributions, formulas were developed to derive population variances and uncertainties, and their corresponding unbiased estimates, for the method performance statistics, i.e., the sample mean (y..), the repeatability variance and standard deviation and (s2r and sr), and the reproducibility variance and standard deviation (s2R and sR) and obtained from collaborative study of an analytical method.     

Nanoparticle assisted magnetic resonance imaging of the early reversible stages of amyloid beta self-assembly

Co@Pt-Au nanoparticles, which have enhanced magnetism and high stability in aqueous media, are utilized in conjunction with MRI to monitor the structural evolution of Abeta assemblies, especially Abeta protofibrils in the early reversible stages.     

Structure and conductance of aromatic and aliphatic dithioacetamide monolayers on Au(111)

The structure and electrical properties of self-assembled monolayers of cyclic aromatic and aliphatic dithioacetamides (1,4-bis(mercaptoacetamido)benzene and 1,4-bis(mercaptoacetamido)cyclohexane) and of mixed dithioacetamide/alkanethiol monolayers are characterized by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM) and contact angle goniometry. Both dithioacetamides are found to pack densely on Au(111), however the monolayers are poorly ordered as a result of hydrogen bond formation between the amide groups. The coassembly and the insertion method are compared for the formation of mixed dithioacetamide/alkanethiol monolayers. By coassembly, islands of dithioacetamides in a dodecanethiol matrix can only be obtained at a low dithioacetamide/dodecanethiol concentration ratio in solution (1/10) and by thermal annealing of the resulting monolayers. Small and well defined dithioacetamide domains are realized by insertion of dithioacetamides into defect sites of closely packed octanethiol monolayers. These domains are used to determine the molecular conductance by means of STM height profiles and molecular lengths resulting from density functional theory (DFT) calculations. The difference in the tunneling decay constant beta measured for aromatic dithioacetamides (beta = 0.74-0.76/A) and for aliphatic dithioacetamides (beta = 0.84-0.91/A) highlights the influence of the conjugation within the cyclic core on molecular conductance.     

Nanoaggregate of thermosensitive chitosan-Pluronic for sustained release of hydrophobic drug

A thermo-sensitive chitosan-Pluronic copolymer (CP) was prepared by grafting mono-carboxyl Pluronic onto the chitosan using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) and N-hydroxysuccinimide (NHS). Indomethacin (IMC)-loaded nanoaggregate (NA) was prepared using the synthesized CP by the direct dissolution method. The critical aggregate concentration (CAC), hydrodynamic size and surface morphology of the prepared CP nanoaggregate (CPNA) were characterized by fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM), respectively. The resulting CAC and the average diameter of CPNA were about 0.31 g/l and 120 nm, indicating high structural stability of CPNA and size favorable for intravenous delivery of drugs. In vitro release test of the IMC encapsulated into CPNA showed sustained release rate of IMC as compared with that from Pluronic micelle. Therefore, we can conclude that our CPNA can be a novel type of superior drug carrier for sustained delivery of hydrophobic drugs.