Investigation of Fundamental Processes Governing Secondary Organic Aerosol Formation in Laboratory Chambers

Our understanding of the processes and mechanisms by which secondary organic aerosol (SOA) is formed is derived from laboratory chamber studies. In the atmosphere, SOA formation is primarily driven by progressive photooxidation of SOA precursors, coupled with their gas-particle partitioning. In the chamber environment, SOA-forming vapors undergo multiple chemical and physical processes that involve production and removal via gas-phase reactions; partitioning onto suspended particles vs. particles deposited on the chamber wall; and direct deposition on the chamber wall. The main focus of this dissertation is to characterize the interactions of organic vapors with suspended particles and the chamber wall and explore how these intertwined processes in laboratory chambers govern SOA formation and evolution.

A Functional Group Oxidation Model (FGOM) that represents SOA formation and evolution in terms of the competition between functionalization and fragmentation, the extent of oxygen atom addition, and the change of volatility, is developed. The FGOM contains a set of parameters that are to be determined by fitting of the model to laboratory chamber data. The sensitivity of the model prediction to variation of the adjustable parameters allows one to assess the relative importance of various pathways involved in SOA formation.

A critical aspect of the environmental chamber is the presence of the wall, which can induce deposition of SOA-forming vapors and promote heterogeneous reactions. An experimental protocol and model framework are first developed to constrain the vapor-wall interactions. By optimal fitting the model predictions to the observed wall-induced decay profiles of 25 oxidized organic compounds, the dominant parameter governing the extent of wall deposition of a compound is identified, i.e., wall accommodation coefficient. By correlating this parameter with the molecular properties of a compound via its volatility, the wall-induced deposition rate of an organic compound can be predicted based on its carbon and oxygen numbers in the molecule.

Heterogeneous transformation of δ-hydroxycarbonyl, a major first-generation product from long-chain alkane photochemistry, is observed on the surface of particles and walls. The uniqueness of this reaction scheme is the production of substituted dihydrofuran, which is highly reactive towards ozone, OH, and NO3, thereby opening a reaction pathway that is not usually accessible to alkanes. A spectrum of highly-oxygenated products with carboxylic acid, ester, and ether functional groups is produced from the substituted dihydrofuran chemistry, thereby affecting the average oxidation state of the alkane-derived SOA.

The vapor wall loss correction is applied to several chamber-derived SOA systems generated from both anthropogenic and biogenic sources. Experimental and modeling approaches are employed to constrain the partitioning behavior of SOA-forming vapors onto suspended particles vs. chamber walls. It is demonstrated that deposition of SOA-forming vapors to the chamber wall during photooxidation experiments can lead to substantial and systematic underestimation of SOA. Therefore, it is likely that a lack of proper accounting for vapor wall losses that suppress chamber-derived SOA yields contribute substantially to the underprediction of ambient SOA concentrations in atmospheric models.

Geology of the Pacoima Area, Los Angeles County, California

The Pacoima area is located on an isolated hill in the northeast section of the San Fernando, the northeast portion of the Pacoima Quadrangle, Los Angeles County, California. Within it are exposed more than 2300 feet of Tertiary rocks, which comprise three units of Middle Miocene (?) age, and approximately 950 feet of Jurassic (?) granite basement. The formations are characterized by their mode of occurrence, marine and terrestial origin, diverse lithology, and structural features.

The basement complex is composed of intrusive granite, small masses of granodiorite and a granodiorite gneiss with the development of schistosity in sections. During the long period of erosion of the metamorphics, the granitic rocks were exposed and may have provided clastic constituents for the overlying formations.

As a result of rapid sedimentation in a transitional environment, the Middle Miocene Twin Peaks formation was laid down unconformably on the granite. This formation is essentially a large thinning bed of gray to buff pebble and cobble conglomerate grading to coarse yellow sandstone. The contact of conglomerate and granite is characterized by its faulted and depositional nature.

Beds of extrusive andesite, basalt porphyry, compact vesicular amygdaloidal basalts, andesite breccia, interbedded feldspathic sands and clays of terrestial origin, and mudflow breccia comprise the Pacoima formation which overlies the Twin Peaks formation unconformably. A transgressing shallow sea accompanied settling of the region and initiated deposition of fine clastic sediments.

The marine Topanga (?) formation is composed of brown to gray coarse sandstone grading into interbedded buff sandstones and gray shales. Intrusions of rhyolitedacite and ash beds mark continued but sporatic volcanism during this period.

The area mapped represents an arch in the Tertiary sediments. Forces that produced the uplift of the granite structural high created stresses that were relieved by jointing and faulting. Vertical and horizontal movement along these faults has displaced beds, offset contacts and complicated their structure. Uplift and erosion have exposed the present sequence of beds which dip gently to the northeast. The isolated hill is believed to be in an early stage of maturity.

Aspects of the washout of salmonid eggs. 2. Effects of drifting on development and survival of eggs of brown trout (Salmo trutta L.)

At high stream discharges salmonid eggs can he displaced from the gravel and may drift downstream. It has been suggested that developing salmonid eggs may be killed by ”physical shock”, especially during the period before ”eyeing”. Similarly, a progress report by the International Pacific Salmon Fisheries Commission (1966) states that salmonid eggs are most sensitive during the period between fertilisation and blastopore closure. However, it would seem unlikely that this sensitivity actually begins at the time of fertilisation because, in nature, a period, perhaps measured in hours, must occur during which the newly-fertilised eggs are exposed to physical shock during the deposition of gravel over them as a result of the cutting activity of the female fish. The present report describes simple channel experiments designed to answer the two questions: 1. After release of eggs from the gravel, does the process of drifting downstream, which implies some physical shock through movement and impact, decrease the survival of salmonid eggs? 2. Is the survival rate-influenced by the stage of development of the eggs?

Effects of flow regime on the young stages of salmonid fishes. Summary and conclusions based on results for 1981-1985

The main British salmonid species spawn in clean gravel in streams and rivers, many of them in the upland areas of Britain. The earliest stages of the life cycle (eggs and alevins) spend some months within the gravel of the river bed. During this period their survival rate can be strongly influenced by flow regime and by related phenomena such as movement of coarse river bed material, changes in water level and the deposition of silt. In recent years human influence upon the flow regimes of upland water courses and upon the sediment inputs to them has increased. In order to conserve and, if possible, enhance the populations of salmonid fishes a deeper understanding of the interrelationships between survival of young salmonids and flow-related phenomena is needed. The acquisition of appropriate information is the main aim of the present project, which included: Studies on silt movement and the infilling of gravel voids by fine sediments, together with initial studies on the relationship between intragravel oxygen supply rate and the survival of intragravel stages of salmonids; studies in the general field of egg washout. The latter investigated the physical background to gravel bed disruption, the examination of the physical characteristics of sites chosen for redds, dimensions of redds and burial depth of eggs relative to the size of the fish constructing the redd and a series of smaller studies on other aspects of egg washout.

Spin wave resonance in ferromagnetic films

The objective of this investigation has been a theoretical and experimental understanding of ferromagnetic resonance phenomena in ferromagnetic thin films, and a consequent understanding of several important physical properties of these films. Significant results have been obtained by ferromagnetic resonance, hysteresis, torque magnetometer, He ion backscattering, and X-ray fluorescence measurements for nickel-iron alloy films.

Taking into account all relevant magnetic fields, including the applied, demagnetizing, effective anisotropy and exchange fields, the spin wave resonance condition applicable to the thin film geometry is presented. On the basis of the simple exchange interaction model it is concluded that the normal resonance modes of an ideal film are expected to be unpinned. The possibility of nonideality near the surface of a real film was considered by means of surface anisotropy field, inhomogeneity in demagnetizing field and inhomogeneity of magnetization models. Numerical results obtained for reasonable parameters in all cases show that they negligibly perturb the resonance fields and the higher order mode shapes from those of the unpinned modes of ideal films for thicknesses greater than 1000 Å. On the other hand for films thinner than 1000 Å the resonance field deviations can be significant even though the modes are very nearly unpinned. A previously unnoticed but important feature of all three models is that the interpretation of the first resonance mode as the uniform mode of an ideal film allows an accurate measurement of the average effective demagnetizing field over the film volume. Furthermore, it is demonstrated that it is possible to choose parameters which give indistinguishable predictions for all three models, making it difficult to uniquely ascertain the source of spin pinning in real films from resonance measurements alone.

Spin wave resonance measurements of 81% Ni-19% Fe coevaporated films 30 to 9000 Å thick, at frequencies from 1 to 8 GHz, at room temperature, and with the static magnetic field parallel and perpendicular to the film plane have been performed. A self-consistent analysis of the results for films thicker than 1000 Å, in which multiple excitations can be observed, shows for the first time that a unique value of exchange constant A can only be obtained by the use of unpinned mode assignments. This evidence and the resonance behavior of films thinner than 1000 Å strongly imply that the magnetization at the surfaces of permalloy films is very weakly pinned. However, resonance measurements alone cannot determine whether this pinning is due to a surface anisotropy, an inhomogeneous demagnetizing field or an inhomogeneous magnetization. The above analysis yields a value of 4πM=10,100 Oe and A = (1.03 ± .05) x 10^-6 erg/cm for this alloy. The ability to obtain a unique value of A suggests that spin wave resonance can be used to accurately characterize the exchange interaction in a ferromagnet.

In an effort to resolve the ambiguity of the source of pinning of the magnetization, a correlation of the ratio of magnetic moment and X-ray film thickness with the value of effective demagnetizing field 4πNM as determined from resonance, for films 45 to 300 Å has been performed. The remarkable agreement of both quantities and a comparison with the predictions of five distinct models, strongly imply that the thickness dependence of both quantities is related to a thickness dependent average saturation magnetization, which is far below 10,100 Oe for very thin films. However, a series of complementary experiments shows that this large decrease of average saturation magnetization cannot be simply explained by either oxidation or interdiffusion processes. It can only be satisfactorily explained by an intrinsic decrease of the average saturation magnetization for very thin films, an effect which cannot be justified by any simple physical considerations.

Recognizing that this decrease of average saturation magnetization could be due to an oxidation process, a correlation of resonance measurements, He ion backscattering, X-ray fluorescence and torque magnetometer measurements, for films 40 to 3500 Å thick has been performed. On basis of these measurements it is unambiguously established that the oxide layer on the surface of purposefully oxidized 81% Ni-19% Fe evaporated films is predominantly Fe-oxide, and that in the oxidation process Fe atoms are removed from the bulk of the film to depths of thousands of angstroms. Extrapolation of results for pure Fe films indicates that the oxide is most likely α-Fe₂O₃. These conclusions are in agreement with results from old metallurgical studies of high temperature oxidation of bulk Fe and Ni-Fe alloys. However, X-ray fluorescence results for films oxidized at room temperature, show that although the preferential oxidation of Fe also takes place in these films, the extent of this process is by far too small to explain the large variation of their average saturation magnetization with film thickness.

Femtosecond laser-induced crystallization in amorphous Ge2Sb2Te5 films

Crystallization in amorphous Ge2Sb2Te5 films by irradiation with femtosecond laser was investigated. The reflectivity and X-ray diffraction measurements confirmed that the crystalline state has been achieved in amorphous Ge2Sb2Te5 films under the irradiation of fermosecond laser with an average power of 65 mW at a frequency of 1000 Hz and a pulsed width of 120 fs. The surface morphology before and after femtosecond laser irradiation was studied by scanning electron microscope; results showed that the surface of films with irradiation of femtosecond laser was composed of some the crystallized micro-region. (C) 2004 Elsevier B.V. All rights reserved.

Photoinduced effects in amorphous Ge-Se films

With light illumination from an Ar ion laser, the photoinduced changes in vacuum evaporated amorphous GeSe2 films; were investigated with the X-ray diffraction (XRD), infrared absorption (IR), scanning electron microscope (SEM), transmitting electron microscope (TEM) and transmittance spectra analysis. It was observed that the optical transmittance edges of films shifted to shorter wavelength according to annealing and light illumination and the shift in well-annealed films could be recovered by annealing at 200 degrees C for 1 h in Ar air. The magnitude of shift increased with the increase of the intensity of illumination light and the illumination time. By sides, photoinduced crystallization was also observed in the exposed regions of GeSe2 films and more of it was observed with stronger intensity of illumination light.

Effect of processing parameters on the optical properties of TiO2/ormosil planar waveguide

Hybrid TiO2/ormosil waveguiding films have been prepared by the sol-gel method at low thermal treatment temperature of 150° C. The influence of processing parameters including the molar ratios of titanium butoxide (Ti(OBu)(4))/3-glycidoxypropyltrimethoxysilane (GLYMO) and H2O/Ti(OBu)(4) (expressed as R), especially aging of sot on the optical properties was investigated. The optical properties of films were measured with scanning electron microscope (SEM), UV/VIS/NIR spectrophotometer (UV-Vis), m-line and the scattering-detection method. The results indicate that the film thickness increases with the increase of sol aging time, but the variation of refractive index as a function of sot aging time depends on the relative ratios of GLYMO to Ti(OBu)(4). Higher transmittance and lower attenuation of the planar waveguide can be obtained in the sol with lower Ti(OBu)(4) contents and shorter aging time.

Optical and surface properties of hybrid TiO2/ormosil planar waveguide prepared by the sol-gel process

Two kinds of silanes, 3-glycidoxypropyltrimethoxysilane (GLYMO) and 3-trimethoxysililpropylmethacrylate (TMSPM), were used to prepare ormosil waveguide films by the sol-gel method. Thirty percent Ti(OBu)(4) and 70% silane were contained in the precursor sets. The properties of films were measured by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV/VIS/NIR spectrophotometer (UV-vis), atomic force microscopy (AFM), m-line and scattering-detection method. The films from GLYMO and TMSPM precursors exhibit similar thickness (2.58 mu m for GLYMO, 2.51 mu m for TMSPM) and refractive index (1.5438 for GLYMO, 1.5392 for TMSPM, lambda=632.8 nm), but the film from TMSPM precursor has higher propagation loss (1.024 dB/cm, lambda=632.8 nm) than the film prepared from GLYMO (0.569 dB/cm, lambda=632.8 nm). Furthermore, the film prepared from TMSPM is easy to be opaque and cracks during coating whereas the same phenomenon was not found for the film prepared with GLYMO. It is confirmed that GLYMO is a better precursor than TMSPM for waveguide film preparation. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Effect of water content in sol on optical properties of hybrid sol-gel derived TiO2/SiO2/ormosil film

Sol-gel derived TiO2/SiO2/ormosil hybrid planar waveguides have been deposited on soda-lime glass slides and silicon substrates, films were heat treated at 150 degreesC for 2 h or dried at room temperature. Different amounts of water were added to sols to study their impacts on microstructures and optical properties of films. The samples were characterized by m-line spectroscopy, Fourier transform infrared spectroscopy (FT-IR), UV/VIS/NIR spectrophotometer (UV-vis), atomic force microscopy (AFM), thermal analysis instrument and scattering-detection method. The refractive index was found to have the largest value at the molar ratio H2O/OR = 1 in sol (OR means -OCH3, -OC2H5 and -OC4H9 in the sol), whereas the thickest film appears at H2O/OR = 1/2. The rms surface roughness of all the films is lower than 1.1 nm, and increases with the increase of water content in sol. Higher water content leads to higher attenuation of film. (C) 2004 Elsevier B.V. All rights reserved.

应用离子后处理技术提高薄膜激光损伤阈值

利用电子束热蒸发方法在K9玻璃基底上沉积氧化锆薄膜,并对其中一些样品用低能O2^+进行了后处理.采用表面热透镜技术测量薄膜样品表面弱吸收,采用显微镜观察样品离子后处理前后的显微缺陷密度.测试结果表明:经离子后处理样品表面的缺陷密度从18.6/mm^2降低到6.2/mm^2,且其激光损伤阈值从15.9 J/cm^2提高到23.1 J/cm^2,样品的平均吸收率从处理前的1.147×10^-4降低到处理后的9.56×10^-5.通过对处理前后样品的表面微缺陷密度、吸收率及损伤形貌等的分析发现:离子后处理可以降

Statistical approach to bulk inclusion initialized damage in films

In experiments, we have found an abnormal relationship between probability of laser induced damage and number density of surface inclusion. From results of X-ray diffraction (XRD) and laser induced damage, we have drawn a conclusion that bulk inclusion plays a key role in damage process. Combining thermo-mechanical damage process and statistics of inclusion density distribution, we have deduced an equation which reflects the relationship between probability of laser induced damage, number density of inclusion, power density of laser pulse, and thickness of films. This model reveals that relationship between critical sizes of the dangerous inclusions (dangerous inclusions refer to the inclusions which can initialize film damage), embedded depth of inclusions, thermal diffusion length and tensile strength of films. This model develops the former work which is the statistics about surface inclusion. (c) 2006 Elsevier B.V. All rights reserved.

磁控溅射不同厚度银膜的微结构及其光学常数

Ag films with different thickness from 8.2nm to 107.2nm were prepared by DC sputtering deposition and analyzed by X-ray diffraction with the help of optimization program on computer. Microstructrue analysis shows that the films are made of fcc-Ag particles. With the increase of thickness, the mean size of Ag particles increases and the interplaner spacing decreases gradually. The optical constants computed by computer program shows that n value decreases quickly with the increasing thickness below 17.5nm and k value changes in reverse, and then go steadily when the thickness is larger than 17.5nm at the wavelength of 550mn.

离子辅助沉积中离子束流密度的作用

测量了End-Hall离子源在不同条件下的离子束流密度，在不同离子束流密度下进行了心离子辅助沉积ZrO2薄膜的实验，研究了离子束流密度对薄膜折射率、晶相的影响．根据动量传递模型分析了离子束流密度对薄膜折射率的作用；根据热尖峰理论证明了一定条件下离子束流密度不会影响薄膜晶体结构。

德鲁德分布非均匀膜的光学特性模拟分析

从德鲁德理论出发，对多元共蒸法镀制的非均匀膜的折射率分布与沉积速率的关系进行了探讨；然后利用计算机辅助模拟，对德鲁德分布非均匀光学薄膜，从单周期和多周期、正变和负变、完整周期和存在半周期几个方面对其光学特性进行了系统分析．研究发现：其透射率的极小值和周期数的关系遵从周期数的三次多项式衰减规律，不同规律的德鲁德分布非均匀膜可用来设计不同功能的滤光片．