An accurate description of the evolution of organic aerosol in the Earth's atmosphere is essential for climate models. However, the complexity of multiphase chemical and physical transformations has ...been challenging to describe at the level required to predict aerosol lifetimes and changes in chemical composition. In this work a model is presented that reproduces experimental data for the early stages of oxidative aging of squalane aerosol by hydroxyl radical (OH), a process governed by reactive uptake of gas phase species onto the particle surface. Simulations coupling free radical reactions and Fickian diffusion are used to elucidate how the measured uptake coefficient reflects the elementary steps of sticking of OH to the aerosol as a result of a gas-surface collision, followed by very rapid abstraction of hydrogen and subsequent free radical reactions. It is found that the uptake coefficient is not equivalent to a sticking coefficient or an accommodation coefficient: it is an intrinsically emergent process that depends upon particle size, viscosity, and OH concentration. An expression is derived to examine how these factors control reactive uptake over a broad range of atmospheric and laboratory conditions, and is shown to be consistent with simulation results. Well-mixed, liquid behavior is found to depend on the reaction conditions in addition to the nature of the organic species in the aerosol particle.
Reactive uptake of OH by organic aerosol particles is situational and related to internal diffusion distances between OH sticking events.
The heterogeneous oxidation of organic aerosol by hydroxyl radicals (OH) can proceed through two general pathways: functionalization, in which oxygen functional groups are added to the carbon ...skeleton, and fragmentation, in which carbon-carbon bonds are broken, producing higher volatility, lower molecular weight products. An ongoing challenge is to develop a quantitative molecular description of these pathways that connects the oxidative evolution of the average aerosol properties (e.g. size and hygroscopicity) to the transformation of free radical intermediates. In order to investigate the underlying molecular mechanism of aerosol oxidation, a relatively compact kinetics model is developed for the heterogeneous oxidation of squalane particles by OH using free radical intermediates that convert reactive hydrogen sites into oxygen functional groups. Stochastic simulation techniques are used to compare calculated system properties over ten oxidation lifetimes with the same properties measured in experiment. The time-dependent average squalane aerosol mass, volume, density, carbon number distribution of scission products, and the average elemental composition are predicted using known rate coefficients. For functionalization, the calculations reveal that the distribution of alcohol and carbonyl groups is controlled primarily by the initial OH abstraction rate and to lesser extent by the branching ratio between secondary peroxy radical product channels. For fragmentation, the calculations reveal that the formation of activated alkoxy radicals with neighboring functional groups controls the molecular decomposition, particularly at high O/C ratios. This kinetic scheme provides a framework for understanding the oxidation chemistry of a model organic aerosol and informs parameterizations of more complex systems.
Dissolution and swelling of thin films of ionizable polymers in contact with aqueous alkaline solutions are examined using a quartz crystal microbalance, while simultaneously recording the visible ...reflectivity and infrared absorption of the evolving films. From these data changes in the thickness, depth structure, composition, mass, and mechanical properties of the polymer film during its interaction with the aqueous solution can be detected. Analysis of these provides evidence for the formation of interfacial gel layers resulting from acid−base reaction of the polymer with the hydroxide solution and yields information on the kinetics of transport and chemical reaction that control the overall process. Kinetics simulations indicate that the most important factors influencing observed behaviors are the intrinsic reactivity of ionizable groups on the polymer and the response of the film's mechanical properties, which determine the ability of small molecules to move through it, to incorporation of water.
Chemically amplified (CA) resists are in widespread use for the fabrication of leading-edge microelectronic devices, and it is anticipated that they will see use well into the future. The refinement ...and optimization of these materials to allow routine imaging at dimensions that will utlimately approach the molecular scale will depend on an improved in-depth understanding of the materials and their processing.
The dissolution of exposed regions of polymeric resists in aqueous base to form a pattern is a complex reactive process. It has recently been proposed that a critical level of ionization is required ...for a polymer chain to move from the film into solution. That model successfully predicts many of the features of polymer dissolution such as dependence on chain length and solution pH but has not been used to describe the detailed kinetics of the dissolution process. In this work we use the critical ionization model as a framework for a simple reaction scheme that describes the coupled reversible ionization−relaxation steps that transform a polymer chain from an unsolvated form into a solvated one. Simulations of the dissolution process are used to predict line shapes as a function of local extent of polymer deprotection in chemically amplified positive tone photoresists and examine chemical factors that lead to roughening. The results show that nonlinearities inherent in the dissolution kinetics are responsible for resist imaging. The kinetics also lead to increased roughening as the aerial image contrast is decreased. Implications of these results for current models of resist development and roughening are discussed. A kinetic criterion connecting critical ionization to the state of the materials in solid and solvated phases is proposed.
Males and females of dioecious plant species often differ in their reproductive investment. Such differences frequently result in differential demographic costs represented by lower growth, survival, ...and/or frequency of reproduction, and/or by more variable reproductive effort through time for females. We present the results of a study on Corema conradii, a rare dioecious shrub of the coastal dune heathlands of northeastern North America. We estimated the reproductive investment of both males and females, determined their age structure, and compared their spatial patterns in a population at Îles-de-la-Madeleine, Quebec. We also determined the sex ratio of the four populations known to occur on the islands. Males invested more in reproduction at flowering, but when fruit production was considered, female reproductive investment was higher in terms of biomass, Mg, and Ca, but not in terms of N, P, and K. The age frequency distribution of males and females did not differ significantly from one another. The population dispersion pattern was contagious, with patches of similar-age individuals. There was no spatial segregation between males and females, although the sex ratio varied somewhat spatially. Females did not start reproducing at a later age than males and did not appear to have a shorter longevity. However, the crown and radial growth rates of females were lower than those of males. When estimated by the crown intercept method, the sex ratio of all four populations was male biased. However, because males had a higher crown growth rate, genet sex ratio was in fact balanced. Higher investment in reproduction was associated with a lower growth rate, which represents a differential cost of reproduction according to sex in this species.
A photochemical path for formation of volatile S and acidolytic paths for formation of volatile Si and/or C during exposure to ultraviolet light have been identified for two silicon-containing ...bilayer photoresists using atmospheric pressure ionization mass spectrometry (API MS) and secondary ion mass spectrometry (SIMS). Si and S are of particular concern because of their potential for irreversible adsorption onto nearby optical coatings inside a lithographic tool, causing permanent detuning. We describe the analytical techniques used and report estimates for absolute numbers of Si and S atoms lost from the resists. The data show that Si bound through oxygen is easily cleaved from the polymer by photogenerated acid while Si bound through carbon is not. Photodissociation of perfluorosulfonic acid from the photoacid generators results in significant loss of S. The data are compared to previous studies, and the advantages and limitations of these techniques for photoresist chemistry characterization are discussed.
Nanoimprint Materials Systems Houle, F. A.; Miller, D. C.; Fornof, A. ...
Journal of Photopolymer Science and Technology,
01/2008, Letnik:
21, Številka:
4
Journal Article
Odprti dostop
In UV cure nanoimprint lithography the interfaces as well as the resist composition play an important role in determining the characteristics of the resulting patterned material, which can be used ...for subsequent pattern transfer, or be functional. It is important for applications that there be only rare defects, and that template release always be a clean process. In this paper fundamental physical and chemical aspects of the resist template interface are discussed, with a particular focus on how they influence the process of template removal.
The heterogeneous oxidation of organic aerosol by hydroxyl radicals (OH) can proceed through two general pathways: functionalization, in which oxygen functional groups are added to the carbon ...skeleton, and fragmentation, in which carbon-carbon bonds are broken, producing higher volatility, lower molecular weight products. An ongoing challenge is to develop a quantitative molecular description of these pathways that connects the oxidative evolution of the average aerosol properties (
e.g.
size and hygroscopicity) to the transformation of free radical intermediates. In order to investigate the underlying molecular mechanism of aerosol oxidation, a relatively compact kinetics model is developed for the heterogeneous oxidation of squalane particles by OH using free radical intermediates that convert reactive hydrogen sites into oxygen functional groups. Stochastic simulation techniques are used to compare calculated system properties over ten oxidation lifetimes with the same properties measured in experiment. The time-dependent average squalane aerosol mass, volume, density, carbon number distribution of scission products, and the average elemental composition are predicted using known rate coefficients. For functionalization, the calculations reveal that the distribution of alcohol and carbonyl groups is controlled primarily by the initial OH abstraction rate and to lesser extent by the branching ratio between secondary peroxy radical product channels. For fragmentation, the calculations reveal that the formation of activated alkoxy radicals with neighboring functional groups controls the molecular decomposition, particularly at high O/C ratios. This kinetic scheme provides a framework for understanding the oxidation chemistry of a model organic aerosol and informs parameterizations of more complex systems.
A compact, experimentally validated model of organic aerosol oxidation enables the ageing process to be connected to specific chemical reactions.
Numerous preclinical studies support the role of spinal neuroimmune activation in the pathogenesis of chronic pain, and targeting glia (eg, microglia/astrocyte)- or macrophage-mediated ...neuroinflammatory responses effectively prevents or reverses the establishment of persistent nocifensive behaviors in laboratory animals. However, thus far, the translation of those findings into novel treatments for clinical use has been hindered by the scarcity of data supporting the role of neuroinflammation in human pain. Here, we show that patients suffering from a common chronic pain disorder (lumbar radiculopathy), compared with healthy volunteers, exhibit elevated levels of the neuroinflammation marker 18 kDa translocator protein, in both the neuroforamina (containing dorsal root ganglion and nerve roots) and spinal cord. These elevations demonstrated a pattern of spatial specificity correlating with the patients' clinical presentation, as they were observed in the neuroforamen ipsilateral to the symptomatic leg (compared with both contralateral neuroforamen in the same patients as well as to healthy controls) and in the most caudal spinal cord segments, which are known to process sensory information from the lumbosacral nerve roots affected in these patients (compared with more superior segments). Furthermore, the neuroforaminal translocator protein signal was associated with responses to fluoroscopy-guided epidural steroid injections, supporting its role as an imaging marker of neuroinflammation, and highlighting the clinical significance of these observations. These results implicate immunoactivation at multiple levels of the nervous system as a potentially important and clinically relevant mechanism in human radicular pain, and suggest that therapies targeting immune cell activation may be beneficial for chronic pain patients.
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