紫外/臭氧法PDMS表面亲水改性机理研究

紫外/臭氧改性法是一种操作简单、成本低廉的PDMS表面亲水改性方法。采用该方法对PDMS表面进行亲水改性,利用接触角测量仪对改性效果进行评价,并与PDMS无臭氧紫外法进行了比较。测试表明PDMS表面经紫外/臭氧法处理12小时后,表面接触角达到60°左右,在空气中放置两周后仍保持较好的亲水性。其改性机理可以通过多种表征手段进行分析。红外光谱测试可以看出,PDMS在经过紫外/臭氧改性后,其表面官能团变化明显,随改性时间延长,疏水基团—CH₃逐渐减少,亲水基团Si—OH和—OH逐步增加,二氧化硅典型红外光谱峰也同时出现。通过扫描电镜和能谱测试可以看出,PDMS表面经过改性产生了二氧化硅为主的硅的氧化物。综合上述结果,紫外/臭氧处理法能够使PDMS表面亲水基团增多,同时生成类玻璃态SiO_x薄层,既改善了PDMS表面的亲水性,又阻止了PDMS表面疏水性的完全恢复,亲水性可以长时间保持。     

臭氧修饰(001)晶面TiO2纳米片及其光催化降解甲苯研究

本文系统研究了臭氧修饰对(001)主导晶面锐钛矿型TiO₂光催化剂降解甲苯性能的影响. 利用自行搭建的光催化VOCs降解装置对催化剂光降解甲苯的性能进行了测试. 通过多种表征手段,结合原位DRIFTS和DFT计算研究了臭氧表面修饰及甲苯吸附和降解机理. 结果表明,用臭氧进行表面修饰可以显著提高(001)主导晶面TiO₂光催化降解甲苯的性能. (001)晶面上丰富的5c-Ti不饱和配位是臭氧分子的吸附位点,其解离后形成的Ti-O键与H₂O分子结合,在表面生成大量孤立的Ti_5c-OH. Ti_5c-OH 是甲苯分子的吸附位,它的形成显著提高了对甲苯分子的吸附能力. 在光照下Ti_5c-OH与光生空穴结合能形成·OH自由基. 通过臭氧解离产生的O₂也可以与光生电子结合形成超氧自由基. 这些具有强氧化性活性自由基的形成促进了对气相甲苯的光催化降解速率.     

Improvement of the high-κ/Ge interface thermal stability using an in-situ ozone treatment characterized by conductive atomic force microscopy

In this work, an in-situ ozone treatment is carried out to improve the interface thermal stability of HfO₂/Al₂O₃ gate stack on germanium (Ge) substrate. The micrometer scale level of HfO₂/Al₂O₃ gate stack on Ge is studied using conductive atomic force microscopy (AFM) with a conductive tip. The initial results indicate that comparing with a non in-situ ozone treated sample, the interface thermal stability of the sample with an in-situ ozone treatment can be substantially improved after annealing. As a result, void-free surface, low conductive spots, low leakage current density, and relative high breakdown voltage high-κ/Ge are obtained. A detailed analysis is performed to confirm the origins of the changes. All results indicate that in-situ ozone treatment is a promising method to improve the interface properties of Ge-based three-dimensional (3D) devices in future technology nodes.     

Effective ozone generation utilizing a meshed-plate electrode in a dielectric-barrier discharge type ozone generator

A meshed-plate electrode, an alternative to the conventional plate electrode of the dielectric-barrier discharge (DBD) ozone generator, has been studied in order to show the effectiveness of the meshed-plate electrode in improving ozone generation. A DBD ozone generator with mesh electrode is shown to have the following two advantages: First, such a device produces corona at its thin, sharp edges, thereby decreasing corona onset voltage for a given gap spacing. Second, by utilizing the air-voids of the meshed-plate electrode, the dense ozone produced in the small, high temperature gap region of the DBD can escape rapidly to the low temperature region. As a result, decomposition of the ozone can be reduced. In this study, surface discharge, meshed-plate electrode, and conventional DBD ozone generators are studied and compared experimentally. The maximum ozone generation concentration and ozone generation efficiency are obtained with the meshed-plate type electrode.     

The reinforcement ability of ozone-treated CNFs on mechanical properties of C–epoxy composites

Carbon nanofibers (CNFs) are ozone-treated for different time durations (45 and 90 min). Changes in surface characteristics of CNFs due to ozone treatment were studied with BET surface area analyzer and Raman spectroscopy. Raman spectroscopic studies showed that ozone treatment is imparting enhanced degree of disorder for CNFs. Changes in surface functional groups of CNFs due to ozone treatment were estimated using elemental analysis and thermogravimetric analysis. The influence of ozone-treated CNFs on the mechanical properties of laminated (2D) carbon fiber-reinforced epoxy matrix (CFRP) composites has been studied. Results indicate that ozone-treated CNFs can improve the mechanical properties of CFRPs significantly as compared to untreated CNFs due to enhanced interface compatibility between the ozone-treated CNFs to the matrix. Ozone treatment of CNFs proposed in this study has the potential to overcome the limitations of the conventional methods of generating functional groups.     

Hydrophobic recovery of UV/ozone treated poly(dimethylsiloxane): adhesion studies by contact mechanics and mechanism of surface modification

Silicone elastomers (Sylgard 184 and 170), based on poly(dimethylsiloxane) (PDMS), were surface treated by a combined exposure to UV and ozone. The effects of the treatments were analyzed as a function of time elapsed after stopping the treatments using different standard surface characterization techniques, such as water contact angle measurements, XPS and atomic force microscopy (AFM). However, the primary focus of this study was to apply the Johnson–Kendall–Roberts (JKR) contact mechanics approach to investigate PDMS samples prior to and following UV/ozone surface treatment. A gradual formation of a hydrophilic, silica-like surface layer with increasing modulus was observed with increasing UV/ozone exposure. A subsequent hydrophobic recovery after UV/ozone exposure was observed, as indicated by increasing contact angles. This supports the hypothesis that the hydrophobic recovery is mainly caused by the gradual coverage of a permanent silica-like structure with free siloxanes and/or reorientation of polar groups. PDMS containing a homogenously dispersed filler (Sylgard 184), exhibited a decreasing surface roughness (by AFM) when the oxidized surface region “collapsed” into a smooth SiO_x layer (final surface roughness <2 nm). PDMS containing heterogeneously distributed, aggregated filler particles (Sylgard 170), exhibited an increasing surface roughness with treatment dose, which was attributed to the “collapse” of the oxidized surface region thus exposing the contours of the underlying filler aggregates (final surface roughness ∼140 nm). A dedicated device was designed and built to study the contact mechanics behavior of PDMS prior to, and following surface treatment. The value of the combined elastic modulus obtained for PDMS lens and semi-infinite flat surface system showed an increase in full agreement with the formation of a silica-like layer exhibiting a high elastic modulus (compared with untreated PDMS). The work of adhesion observed in JKR experiments exhibited an increasing trend as a function of treatment done in agreement with contact angle data. JKR experiments showed hydrophobic recovery behavior as anticipated from contact angle measurements. Single pull-off force measurements by JKR and numerical analysis of full-approach JKR curves were in quantitative agreement regarding practical work of adhesion values.     

A comparison of variational and discrete ordinate methods for solving radiative transfer problems

In this paper, we compare the variational and discrete ordinate methods applied to their simplest representative cases: the 2-step function variational method and the 2-stream approach. It is shown that both methods require minimal computational time. Numerical results of the source functions, intensities and fluxes for the problem of diffuse reflection by different plane-parallel isotropic atmospheres are compared between the two methods. Limitations of both approaches for different single scattering albedos and optical depths are discussed. It is also shown that the variational technique is a more efficient algorithm in handling multi-layer cloud conditions for radiative transfer problems.     

Surface modification and adhesion of wood-plastic composite (WPC) treated with UV/ozone

Because of the surfaces of wood-plastic composite (WPC) materials are enriched in polymers of low surface energy, they exhibit low adhesion properties. UV/ozone is proposed as surface treatment for increasing the surface energy and adhesion of WPC materials made with different polymers (polyethylene, polypropylene and polyvinyl chloride). UV lamp-WPC surface distance and time of UV exposure were varied for optimizing UV/ozone treatment of WPC, and UV dose used ranged between 2.02 × 10^?14 and 5.05 × 10^?12 J·s/m². UV/ozone treatment created new carbon-oxygen polar groups in WPC surfaces and increased their surface energy, mainly their polar component. Furthermore, ablation of the outermost WPC surface was produced, more noticeably by reducing the distance between WPC surface and UV lamp and by increasing the duration of the treatment. Noticeable increase in 180° peel adhesion was obtained in the joints made with UV/ozone treated WPC at 10–30 mm distance during 1–5 min (i.e., UV dose between 5.61 × 10^?14 and 2.53 × 10^?12 J·s/m²). Although 180° peel strength of joints made with acrylic adhesive tape and UV/ozone treated WPC for 10 min and 10 mm distance (UV dose: 5.05 × 10^?12 J·s/m²) was not increased because of dominant effect of ablation over creation of polar groups, the cross-hatch adhesion to different coatings was highly improved, irrespective of the polymer used and the wood content of WPC; however, the surface modifications and adhesion of UV/ozone treated WPC were more marked when its wood content was higher and by using UV dose between 0.10 × 10^?12 and 2.53 × 10^?12 J·s/m².     

Positive Trend of Surface Ozone in the North of the Privolzhskii Federal Region of the Russian Federation

The results of long-term continuous measurements of surface ozone concentrations, performed in 2010–2016 in the relatively low-urbanized region in the north of the Privolzhskii Federal Region of the Russian Federation (Vyatskie Polyany, Kirov oblast) are presented. A regular increase in the amplitude of diurnal variations of yearly average surface ozone concentrations is detected. The possible causes of this phenomenon can be both an increase in the atmospheric concentration of pollutants, i.e., precursors of tropospheric ozone, and climatic changes.     

Theoretical investigation of ozone production in negative corona discharge

The purpose of this work is to highlight the chemical kinetics in plasma of pure oxygen. A comprehensive model of ozone generation in wire-to-cylinder negative corona discharge is presented. The model combines the physical processes in the discharge with the chemistry of ozone formation. It is based on an extensive reaction scheme including the major electronic and ionic processes. The importance of excited atomic and molecular states is demonstrated. The obtained results show clearly that the surface material affect quite well the ozone decomposition.     

Etching-enhanced surface stress relaxation during initial ozone oxidation

Initial oxidation via ozone on the Si(1 0 0) surface is investigated by measuring surface stress and observing atomic structure via a scanning tunneling microscopy (STM). A similar investigation is also carried out for molecular oxygen and the results are compared. As a result, monotonic increase of the surface stress to the compressive stress side is obtained up to 0.33 N/m for ozone oxidation at room temperature, while molecular oxygen shows only tiny surface stress growth. From the STM observations, it is found that the difference between ozone and molecular oxygen oxidation is the existence of surface etching. As the origin of the surface stress, therefore, the reduction of the intrinsic tensile surface stress due to the reconstructed surface by the etching process is proposed.     

Constraints on the dynamical and chemical theories of the ?Ozone Hole?

Summary We report calculation results which could impose some constraints for the proposed chemical and dynamical theories on the ozone hole. One set of calculations is about the consistency between the observed optical thickness of polar stratospheric clouds (PSC) and the surface required for the heterogeneous reactions by the chemical theories. Assuming a reaction rate for ClNO₃+H₂O we find the sticking coefficient to be larger than 0.1 for consistency with observed PSC extinctions. The other set of calculations is about the perturbation to the residual circulation due to the presence of additional heating produced by PSCs. The perturbed residual circulation is of the opposite sign (i.e. downward) with respect to that necessary for the dynamical generation of an ozone hole.     

Dynamical studies and product analysis of O(1D) + H2/D2 reactions

The aim of this study was to analyse the dynamics of O(¹D)?+?H₂/D₂ reactions using quasiclassical trajectory calculations on a double-valued potential energy surface for H₂O. Produced on the photodissociation of stratospheric ozone, the excited oxygen atom is a highly reactive species whose chemistry plays a key role in the ozone depletion cycle. In order to make comparisons with experiment, we studied these reactions at fixed translational collision energies. In particular, we consider the reactive cross sections, the thermal rate constants, the opacity function, and the differential cross sections. In addition, we also study the energy distribution of the products and compare the results with experiment and calculations based on phase space statistical theory. Results for the rotational population of the OH products are also compared with experimental results. The agreement between our results and experiment reinforces the accuracy of the H₂O potential energy surface used.     

Surface control of CdSe nanocrystals by UV-exposure in air and successive thermal treatment under ultra high vacuum

Colloidal CdSe nanocrystals were synthesized through a solution process. The CdSe nanocrystals coated on Si(1 0 0) wafers were UV-exposed in either an air or argon atmosphere to distinguish the effect of generated ozone from UV-radiation at 365 nm on the removal of surface capping pyridine molecules. The pyridine on the CdSe nanocrystal's surface could be effectively removed by the ozone generated during UV-exposure with an accompanying highly oxidized surface state of the CdSe nanocrystals. For the removal of surface oxides of CdSe nanocrystals, a successive thermal treatment under ultra high vacuum (UHV) was adopted. The optical energy bandgap measured by using UV-vis absorption spectroscopy showed a red shift with treatment with an increase of annealing temperature. The electronic energy structure of UHV-annealed CdSe nanocrystals film was analyzed in situ using X-ray absorption and photoelectron spectroscopy. A great resemblance was found between the values of the optical and electron energy bandgaps of effectively surface-treated CdSe nanocrystals film after UHV-annealing at 400 °C.     

Preparation and ozone-surface modification of activated carbon. Thermal stability of oxygen surface groups

The control of the surface chemistry of activated carbon by ozone and heat treatment is investigated. Using cherry stones, activated carbons were prepared by carbonization at 900 °C and activation in CO₂ or steam at 850 °C. The obtained products were ozone-treated at room temperature. After their thermogravimetric analysis, the samples were heat-treated to 300, 500, 700 or 900 °C. The textural characterization was carried out by N₂ adsorption at 77 K, mercury porosimetry, and density measurements. The surface analysis was performed by the Bohem method and pH of the point of zero charge (pH_pzc). It has been found that the treatment of activated carbon with ozone combined with heat treatment enables one to control the acidic-basic character and strength of the carbon surface. Whereas the treatment with ozone yields acidic carbons, carbon dioxide and steam activations of the carbonized product and the heat treatment of the ozone-treated products result in basic carbons; the strength of a base which increases with the increasing heat treatment temperature. pH_pzc ranges between 3.6 and 10.3.     

Zur O2-Dissoziation in der Gleichstromglimmentladung. Teil I Bestimmung des Dissoziationsgrades mittels der O3-Bildung an gekühlten Oberflächen

The synthesis of ozone on the surface S cooled with liquid nitrogen O + O₂·S→O₃·S[1] was used to measure the concentration of atoms in a flow tube downstream of a d.c. discharge. The flow tube was constructed in the form of a U-tube. The ozone was deposited as a blue liquid film in the neighbourhood of the surface of the liquid nitrogen on the walls of the part of the U-tube, which was connected with the discharge tube. The oxygen atom decay in the U-tube was observed by measuring the production of ozone as the distance between the discharge tube (diameter: 5,2 cm) and the surface of the liquid nitrogen was varied. The decay is first order in atom concentration for the pressures p > 1 torr. But for the pressures below p = 1 torr near by the discharge tube we observed deviations from the law of decay In [O]₀/[O] = k·t for the currents of about i = 100 mA. This effect was attributed to the process From the extrapolation of an ozone production curve atom concentrations in the discharge have been obtained. The transition from the ?H”? form to the ?T”? form (striated, low average electric field) of the discharge [2] caused the dissociation to decrease rapidly. The highest dissociation (10%) was obtained in the ?H”? form at high currents (i = 120 mA) and low pressures (p = 0,60 torr). The yield of atomic oxygen per kilowatt hour of energy was measured as functions of pressure and gas flow rate for i = 100 mA and i = 50 mA.     

Influence of reactive oxygen species on the sterilization of microbes

The influence of reactive oxygen species on living cells, including various microbes, is discussed. A sterilization experiment with bacterial endospores reveals that an argon–oxygen plasma jet very effectively kills endospores of Bacillus atrophaeus (ATCC 9372), thereby indicating that oxygen radicals are the key element of sterilization. Ozone in acidic water also kills endospores of B. atrophaeus very effectively, demonstrating the capability of cleaning a large surface area contaminated by toxic biological agents. The viable microbe numbers after the contact with acidic ozone water directly correlate with increase in the ozone decay time in water after lowering the pH value of water from pH = 7 to 4 indicating that acidic ozone water is an effective means of sterilizing microbes. However, advanced cells such as fertilized eggs were not greatly influenced by the acidic ozone water. Also, both human and canine cells after treatment with the acidic ozone water prospered without showing signs of stress due to ozone in acidic water. This study suggests that antioxidant enzymes such as superoxide dismutase can be developed in the advanced cells to protect themselves from attacks by reactive oxygen species. Meanwhile, the advanced cells utilize oxygen by certain enzymes, proliferating life on earth.     

Stratospheric ozone descent into the troposphere: Case studies

Summary The penetration of stratospheric air into the troposphere, revealed by high ozone concentrations measured both by an aircraft (Electra) and at a mountain station (Mt. Cimone) during a lee cyclogenesis event (April 24–25, 1982), is investigated. A detailed analysis of the meteorological fields and the application of the isentropic-trajectory method allowed us to reveal the dynamical processes responsible for the ozone transport into the troposphere. We show that the two episodes of high ozone concentrations have to be attributed to the evolution of two distinct upper vortexes, only one of which was associated with surface lee cyclone development. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 19–22, 1984, Rome.     

Extraction of tight binding parameters from in-situ ARPES on the continuously doped surface of cuprates

Recently we developed a technique of ozone/vacuum annealing to continuously change the doping level of the surface of Bi_2Sr_2CaCu_2O_(8+x)and measured a nearly whole superconducting dome on one surface by in-situ angle-resolved photoemission spectroscopy [arXiv: 1805.06450]. Here we study the evolution of the electronic structures of Bi_2Sr_2CaCu_2O_(8+)xusing this technique together with tight binding fits. The tight binding parameters are extracted to study their evolution with doping.     

Carbon nanohorn sensor to detect ozone in water

A sensor to detect ozone in water was fabricated using coating film of single-wall carbon nanohorns (CNHs). This sensor is based on the phenomena that the electric resistance of the CNH-film decreased with the adsorption of ozone molecules thereon due to charge transfer from the surface of CNHs to O₃ molecules. The shift of the electric resistance of the CNH-film was monitored with varied concentrations of aqueous ozone at several temperatures. The shift of the electric resistance of the CNH-film was correlated with the ozone concentration and temperature based on monolayer adsorption model with consideration of activation energies of the relevant adsorption, desorption, and sensitivity of charge transfer.