Photoresists comparative analysis using soft X-ray synchrotron radiation and time-of-flight mass spectrometry

Positive photoresists are widely used in lithographic process for the fabrication of relief components. When exposed to UV radiation they suffer chemical reactions modifying their chemical and physical properties. Aiming to follow molecular modifications among two different photoresists unexposed and previously exposed to ultraviolet light we have employed spectroscopic techniques coupled with mass spectrometry in the study of the AZ-1518 and AZ-4620 photoresists. The photon stimulated ion desorption (PSID) technique following the S K-edge NEXAFS spectrum was employed at the brazilian synchrotron light source (LNLS), during single-bunch operation and using time-of-flight mass spectrometry (TOF-MS) for ion analysis. NEXAFS and PSID mass spectra on both AZ-1518 and AZ-4620 photoresists (unexposed and exposed) were obtained and relative desorption ion yield curves determined for the main fragments as a function of the photon energy. They present marked different PSID spectra. Fragments related to the photochemical decomposition of the AZ-1518 photoresist could be clearly identified differently from the AZ-4620. Studies on the hardness of both photoresists were performed using O₂ plasma reactive ion etching (RIE) technique, analyzed by scanning electron microscopy (SEM) and used to explain different desorption yields in the PSID spectra. These results show that the PSID technique is adequate to investigate structural changes in molecular level in different unexposed and exposed photoresists, which is crucial for improving our knowledge about the breakup process.     

THE ROLES OF REACTION INHOMOGENEITY IN PHASE SEPARATION KINETICS AND MORPHOLOGY OF REACTIVE POLYMER BLENDS

 The roles of reaction inhomogeneity in phase separation of polymer mixtures were described and summarized via two examples: photocross-link of polymer mixtures in the bulk state and photopolymerization of monomer in the liquid state. The reaction kinetics, the reaction-induced elastic strain and the phase separation kinetics were monitored respectively by UV-Vis spectroscopy, Mach-Zehnder interferometry and laser-scanning confocal microscopy. It was found that phase separation in the bulk state was strongly influenced by the elastic strain associated with the intrinsic inhomogeneity of the reaction, whereas the autocatalytic behavior of the polymerization plays an important role in the resulting morphology in the liquid state. These experimental results are discussed in conjunction with the morphology control of polymer mixtures by using chemical reactions.     

Kinetics studies of the degradation of sirolimus in solid state and in liquid medium

The use of sirolimus and its analogs has been evaluated for the treatment of different cancer types. The stability studies of sirolimus enabled to determine the kinetics of its chemical reactions in solid state and in the liquid medium. During intrinsic stability tests in a liquid medium, sirolimus showed a lack of stability when exposed to heat, neutral and basic hydrolysis. Analysis by high-performance liquid chromatography detected: two degradation products after exposure to heat; one degradation product for both basic and neutral hydrolyses; and all degradation products exhibited UV spectra similar to the drug’s spectrum. Kinetics studies in a liquid medium revealed low drug stability in methanolic solution; this instability may be exacerbated in the presence of water or high pH. The application of solid-state kinetic models showed that the drug degrades in accordance with the diffusion dimensional model, with greater stability and an expiration date equal to 6 years, demonstrating that sirolimus has satisfactory stability in the solid state. Through this understanding, it is possible to develop more stable pharmaceutical formulations using sirolimus.

     

THE ROLES OF REACTION INHOMOGENEITY IN PHASE SEPARATION KINETICS AND MORPHOLOGY OF REACTIVE POLYMER BLENDS

The roles of reaction inhomogeneity in phase separation of polymer mixtures were described and summarized via two examples:photocross-link of polymer mixtures in the bulk state and photopolymerization of monomer in the liquid state. The reaction kinetics,the reaction-induced elastic strain and the phase separation kinetics were monitored respectively by UV-Vis spectroscopy,Mach-Zehnder interferometry and laser-scanning confocal microscopy.It was found that phase separation in the bulk state was strongly ...     

聚苯撑苯并二噻唑的甲基磺酸溶液的相转变过程及其动力学研究

用退偏振光强度法及偏光显微镜研究了溶致性液晶高分子聚苯撑苯并二噻唑的甲基磺酸溶液(PBT/MSA)由液晶相至各向同性相(N→I转变),及由各向同性相至液晶相(I→N转变)的相变过程.液晶相的形成(I→N)服从Av-rami方程,Avrami指数为1左右,表明该体系的液晶相是以一维棒状方式形成的.相转变温度与浓度有关,提高温度可加速在应力下液晶相长程有序结构的形成.     

TiO2光催化反应机理及动力学研究进展

光催化处理环境污染物是基于催化反应过程中的一些自由基对污染物的氧化或还原作用，反应途径通常是HO·攻击或穴直接攻击，对可见光敏感的化合物也可能通过激发态来分解。动力学的表述多数符合L－H模式，广泛研究了L－H模式下的吸附与催化活性的关系，对动力学的研究也是了解其反应机理的重要途径。     

Characterization of the Simultaneous Decay Kinetics of Metarhodopsin States II and III in Rhodopsin by Solution‐State NMR Spectroscopy

The mammalian visual dim‐light photoreceptor rhodopsin is considered a prototype G protein‐coupled receptor. Here, we characterize the kinetics of its light‐activation process. Milligram quantities of α,ε‐¹⁵N‐labeled tryptophan rhodopsin were produced in stably transfected HEK293 cells. Assignment of the chemical shifts of the indole signals was achieved by generating the single‐point‐tryptophan to phenylalanine mutants, and the kinetics of each of the five tryptophan residues were recorded. We find kinetic partitioning in rhodopsin decay, including three half‐lives, that reveal two parallel processes subsequent to rhodopsin activation that are related to the photocycle. The meta II and meta III states emerge in parallel with a relative ratio of about 3:1. Transient formation of the meta III state was confirmed by flash photolysis experiments. From analysis of the site‐resolved kinetic data we propose the involvement of the E₂‐loop in the formation of the meta III state.     

Biogenic internal standards for duall-label radiochemical detection of metabolites in liquid chromatography

Dual-label radiochemical methods for liquid chromatography are described. Two sets of compounds are used, each set with a different isotopic label. The procedures decrease quantitative uncertainties by as much as 30% for samples in which chemical reactions have altered a test compound in compared biological systems. This advantage is especially useful in toxicologic metabolism studies. Determinations or comparisons of several conjugated and unconjugated metabolites are achieved by extraction and high-performance liquid chromatography based on these procedures. Quantitative procedures that include an internal standard, biologically generated by rats exposed to radiolabeled compounds, are used. By means of these internal standards, metabolite concentrations are compared for test organisms, and results are obtained for metabolites common to both organisms. Effects of impurities, isotope exchange, or chemical kinetics are also evaluated utilizing a modification of the technique.     

Die Kerze

In this paper we discuss the physical chemistry of the candle light, which has shown to encompass thermodynamics, chemical kinetics, transport processes and quantum chemistry and physics. In a candle light all states of matter (solid, liquid, gas and plasma) are present. Solid wax is molten by the heat radiation of the flame and subsequently pumped through the wick by capillary forces to the interior of the flame, where the liquid wax is evaporated and ignited. Oxygen cannot penetrate deeply into the flame so that inside the flame reducing reaction conditions prevail. In the flame the wax molecules are pyrolized to small molecule fragments (including ions: plasma), which are the starting point for building up poly‐aromatic rings and finally soot particles. The almond‐shape of the candle light is the result of convection of the hot air around the flame. The candle light serves as a flow reactor with luminous effect where molecular oxygen from the atmosphere oxidized ultimately the wax molecules to CO₂ and water. Only a very small percentage (0.5 %) of the released heat in the combustion reaction is transformed into visible light, rendering the candle light an incredibly inefficient albeit romantic light source.     

Phototunable Liquid‐Crystalline Phases Made of Nanoparticles

The properties of liquid‐crystalline (LC) hybrid systems made of inorganic nanoparticles grafted with photosensitive azo compounds are presented. For materials with a large density of azo ligands at the surface, the LC structure can be reversibly melted by UV light, and the return to the LC state does not require the absorption of visible light. For systems with a lower density of azo ligands, UV light causes shortening of the distance between metal sublayers in the lamellar phase. Interestingly, the azo derivatives attached to the nanoparticle surface show very different kinetics of cis/trans conformational change as compared to the free molecules. The cis form of free ligands in solution is stable for days, whereas the isomerization of molecules attached to the nanoparticle surface to the trans form takes only a few minutes. Apparently, owing to the crowded environment, azo ligands immobilized at a metal surface behave as they would in the condensed state.     

Period-four Modulation of Photosystem II Primary Quinone Acceptor (QA) Reduction/Oxidation Kinetics in Thylakoid Membranes

Photosystem II (PSII), a multiprotein complex mainly coded by the chloroplast genome in higher plants and algae, contains the oxygen-evolving complex with four manganese atoms responsible for the oxidation of water. After each absorption of a light quantum by pigment molecules in the light harvesting complexes of PSII, the Mn cluster advances in its oxidation states denoted from S₀ to S₄. The S₄ state decays to S₀ in the dark with the concurrent release of molecular oxygen. Therefore, the oxygen production in PSII exposed to successive single turnover excitations follows a period-four oscillation pattern. The intensity of chlorophyll a fluorescence of PSII is also known to be influenced by the oxidation state of the Mn cluster. In the present work, fluorescence induction kinetics was measured in isolated thylakoids with various initial S-state populations settled by preflashes. The shape of the fluorescence induction traces was strongly affected by preflashes. O-J and J-I phases of the induction followed a period-four oscillation pattern. The results indicate that these changes reflect the influence of the oxidation rate of the Mn cluster on the reduction/oxidation kinetics of the primary quinone acceptor (Q_A) of PSII.     

EXCITED STATES IN PHOTODIMERIZATION OF AQUEOUS TYROSINE AT ROOM TEMPERATURE

Abstract— The photoionization of tyrosine in aqueous solution in the liquid state was studied at room temperature by analyzing the kinetics of formation of bityrosine upon irradiation of tyrosine, and the external heavy-atom effect on the formation of bityrosine. The relative number of bityrosine molecules was determined by measuring the fluorescence intensity at 400 nm. A kinetic model for the formation of bityrosine was formulated on the assumption that the rate constants were first-order for production of radicals and for recombination with ejected electrons. The applicability of this model to the present case was confirmed by the experimental data. On the basis of the model, we found that the electronic process of photoionization of tyrosine at room temperature is different in acidic and alkaline media. In acidic media a tyrosine molecule absorbs one light quantum and photoionizes through a singlet excited state, while in alkaline media a tyrosinate ion photoionizes after absorption of two light quanta. The intermediate product that absorbs the second photon is in a triplet excited state.     

Ion transfer across liquidliquid interfaces from transition-state theory and stochastic molecular dynamics simulations

We investigate the kinetics and dynamics of ion transfer across liquidliquid interfaces. We calculate the potential of mean force (pmf) of ion transfer from Monte Carlo simulations of a lattice–gas model, assuming independent chemical and electrostatic contributions. The shape of the pmf justifies considering the transfer as activated. The kinetics are obtained from transition-state theory and independently from stochastic molecular dynamics simulations. Both methods yield consistent results, with straight Tafel plots and friction effects in line with Kramers’ theory, but stronger than for a diffusing particle. A higher friction makes barrier recrossing more likely.     

A High-Performance Liquid Chromatography Study of D-Cellobiose Degradation Under Fenton Conditions

Abstract

Cellobiose was used to model chemical processes taking place during the weathering of cotton fiber cellulose. High-performance liquid chromatography (HPLC) showed that the products of cellobiose degradation were D-glucose and organic acids under Fenton-type conditions (ferrous ion plus H₂0₂). Hydrogen peroxide was added directly or photochemically generated in situ by the action of UV light upon aqueous ferrous ammonium sulfate. Effects on D-cellobiose degradation caused by added peroxide or ferrous ion were nonitored at varying concentrations and under UV light and dark conditions. Increasing concentrations of peroxide or ferrous ion resulted in greater degradation. Samples exposed to UV light (350 nm) experienced greater degradation than those not exposed.     

Subliminal light control of dark adaptation kinetics in Phycomyces phototropism

The dark adaptation kinetics of Phycomyces phototropism depend critically on the experimental protocol. When sporangiophores that had been light-adapted to a fluence rate of 1 W m-2 at 447 nm were exposed to dim unilateral light, the adaptation kinetics showed exponential decay (6 min time constant). However, when light-adapted sporangiophores were kept for variable intervals in darkness (i.e. in presence of traditional red safelight) and then exposed to dim unilateral test light, the decay kinetics of adaptation were biexponential with a rapid decay during the first minute (1 min time constant), followed by a slow recovery (11 min time constant). Thus, the dim subliminal light given after the sporangiophores had been adapted to 1 W m-2, was actually perceived, and exerted control over the dark-adaptation process. The observed acceleration of dark-adaptation kinetics constitutes a novel light effect of the sporangiophore. At wavelength 383 nm this effect was not observed. Because a beta-carotene lacking mutant, L91 (genotype carB), was unmodified in dark-adaptation kinetics measured in the presence or absence of subliminal light, it appears that beta-carotene is not involved in the photocontrol of adaptation.     

聚苯撑苯并二噻唑的甲基磺酸溶液的相转变过程及其动力学研究

 用退偏振光强度法及偏光显微镜研究了溶致性液晶高分子聚苯撑苯并二噻唑的甲基磺酸溶液(PBT/MSA)由液晶相至各向同性相(N→I转变),及由各向同性相至液晶相(I→N转变)的相变过程.液晶相的形成(I→N)服从Av-rami方程,Avrami指数为1左右,表明该体系的液晶相是以一维棒状方式形成的.相转变温度与浓度有关,提高温度可加速在应力下液晶相长程有序结构的形成.     

Rate kernel theory for pseudo-first-order kinetics of diffusion-influenced reactions and application to fluorescence quenching kinetics

Theoretical foundation of rate kernel equation approaches for diffusion-influenced chemical reactions is presented and applied to explain the kinetics of fluorescence quenching reactions. A many-body master equation is constructed by introducing stochastic terms, which characterize the rates of chemical reactions, into the many-body Smoluchowski equation. A Langevin-type of memory equation for the density fields of reactants evolving under the influence of time-independent perturbation is derived. This equation should be useful in predicting the time evolution of reactant concentrations approaching the steady state attained by the perturbation as well as the steady-state concentrations. The dynamics of fluctuation occurring in equilibrium state can be predicted by the memory equation by turning the perturbation off and consequently may be useful in obtaining the linear response to a time-dependent perturbation. It is found that unimolecular decay processes including the time-independent perturbation can be incorporated into bimolecular reaction kinetics as a Laplace transform variable. As a result, a theory for bimolecular reactions along with the unimolecular process turned off is sufficient to predict overall reaction kinetics including the effects of unimolecular reactions and perturbation. As the present formulation is applied to steady-state kinetics of fluorescence quenching reactions, the exact relation between fluorophore concentrations and the intensity of excitation light is derived.     

Morphology control of liquid crystalline composite gels based on molecular self-assembling kinetics

Liquid crystalline composite gels consisting of a low molecular mass gelator and a low molecular mass liquid crystal were prepared by two types of gelation method (continuous cooling and isothermal gelating), which provide different molecular self-assembling kinetics of the low molecular mass gelator as gelation proceeds. Optical microscopy and atomic force microscopy revealed that numerous fine strands of the one-dimensionally assembled low molecular mass gelators were formed in the composite gels for both the continuous cooling method and the isothermal gelating method. However, the thinner strands were more homogeneously dispersed in the isothermal gelation product at an appropriate temperature, than in the continuous cooling process. This difference in dispersion state of the strands was shown (by polarizing optical microscopy) to have a significant influence on the molecular alignment of the low molecular mass liquid crystal in the liquid crystalline composite gel. The electro-optical response and light scattering–transmitting switching, of the liquid crystalline composite gel in an applied electric field was extremely dependent on the morphology of the gelators. High contrast light switching was achieved for the composite prepared by isothermal gelation. The response time of electro-optical switching was less than 100?µs under 30?V_rms.     

Morphology control of liquid crystalline composite gels based on molecular self-assembling kinetics

Liquid crystalline composite gels consisting of a low molecular mass gelator and a low molecular mass liquid crystal were prepared by two types of gelation method (continuous cooling and isothermal gelating), which provide different molecular self-assembling kinetics of the low molecular mass gelator as gelation proceeds. Optical microscopy and atomic force microscopy revealed that numerous fine strands of the one-dimensionally assembled low molecular mass gelators were formed in the composite gels for both the continuous cooling method and the isothermal gelating method. However, the thinner strands were more homogeneously dispersed in the isothermal gelation product at an appropriate temperature, than in the continuous cooling process. This difference in dispersion state of the strands was shown (by polarizing optical microscopy) to have a significant influence on the molecular alignment of the low molecular mass liquid crystal in the liquid crystalline composite gel. The electro-optical response and light scattering-transmitting switching, of the liquid crystalline composite gel in an applied electric field was extremely dependent on the morphology of the gelators. High contrast light switching was achieved for the composite prepared by isothermal gelation. The response time of electro-optical switching was less than 100 µs under 30 V_rms.     

Kinetics of evaporation of some liquids by thermogravimetry

Latent heat of evaporation is one of the decisive factors in the design and operation of chemical plants [1], Brennan et al. [2] have shown that the heat of evaporation of a liquid and the activation energy of evaporation, E^evap_act are found, as expected, to be numerically similar. We present here some results on the kinetics of evaporation of five liquids (selected at random) based on TG data.