Ultraviolet Ozone Treatment Research Articles

Effect of UV-induce ozone treatment on physics and morphological properties of hydrothermally grown Ga-F-codoped ZnO nanostructure

The effects of ultraviolet ozone treatment (UVO treatment) on the physical and morphological structure of Ga/F co-doped Zn Onanorods. The ZnO seeding layers were prepared by sol-gel dip coating method based on zinc acetate dehydrate (CH3COO)2Zn•2H2O and diethanolamine ((HOCH2CH2)2NH, DEA) into absolute ethanol (C2H5OH) with concentration of 0.5 M. The seeding solution was dip-coated onto the cleaned glass substrates. The G/F co-doped ZnO nanorods were synthesized by hydrothermal process. The G/F co-doped ZnO nanorods were grown on seed layer with varied ultraviolet ozone treatment at 2, 4, 6, 8, 10, 12, 14, 16 and18 min. The influence of ultraviolet ozone treatment on physical, optical and morphological of G/F co-doped ZnO nanorods have been extensively scrutinized by X-ray diffraction (XRD) and optical spectroscopy, UV-Visible Spectrophotometer (UV-vis) and Field emission scanning electron microscope (FE-SEM). The effects of ultraviolet ozone treatment on different density of Ga/F co-doped ZnO nanorods were obtained as different ultraviolet ozone treatment were introduced.

Enhanced performance of perovskite solar cells by ultraviolet-ozone treatment of mesoporous TiO2

The performance of a semiconductor electronic or photonic device depends greatly on the properties of the interface. In a typical perovskite solar cell (PSC), the interface between electron transport layer (ETL) and perovskites is found to significantly influence the power conversion efficiency (PCE). Herein, Ultraviolet-ozone (UVO) treatment, a technique commonly used to clean a device substrate, is applied on ETL, specially, mesoporous/compact TiO2 layer. This treatment increases the conductivity of ETL and removes the residual organics at the surface. Consequently, an improved interface between mesoporous TiO2 and perovskite is achieved to enhance the performance of PSC. For example, the fill factor (FF) increases by ∼13%, the short-circuit current density (Jsc) and open-circuit voltage (Voc) increase by ∼2%, and the PCE finally enhances by ∼20% with 15 min of UVO treatment. With this method, the PCE of the best cell reaches to 20.43% under the illumination of AM 1.5 (100 mW cm−2) simulated sunlight.

Bright prospect of using alcohol-soluble Nb2O5 as anode buffer layer for efficient polymer solar cells based on fullerene and non-fullerene acceptors

New breakthroughs are expecting to be achieved based on the discovery of novel interfacial materials for polymer solar cells (PSCs). Herein, the simple and facial approach of spin-coating technology with post heat and ultraviolet-ozone treatment is performed on niobium oxalate to prepare Nb2O5 interfacial layer with ultra-high transmittance. The ultraviolet photoemission spectroscopy results confirm that Nb2O5 with a work function of 4.85 eV is suitable for employing as anode buffer layer (ABL). The average power conversion efficiencies (PCEs) of the P3HT:PCBM-based fullerene devices with Nb2O5 ABL reaches to 4.01%, surpassing that (3.69%) of the control devices with ITO/PEDOT:PSS ABL. Further investigations on the PBDB-T:ITIC-based non-fullerene PSCs with Nb2O5 ABL demonstrate that a PCE as high as 8.67% can be reached, which is superior to that of device modified by PEDOT:PSS ABL (8.03%). Namely, 8% efficiency improvement in PSCs based on fullerene and non-fullerene acceptors realized as compared to the control devices with PEDOT:PSS ABL.

Mechanical and thermal properties of hybrid carbon fibre–phenolic matrix composites containing graphene nanoplatelets and graphite powder

ABSTRACTCarbon fibre–phenolic matrix (CF–P) composites containing graphene nanoplatelets (GNPs) were manufactured for improved mechanical and thermal properties. For comparison, micrometer-size pyrolytic graphite powder (GP) was also incorporated in CF–P composites. The loading of carbon fibres was kept constant at 60 wt-% while the quantity of GNPs was varied from 0.1 wt-% to 0.3 wt-% and GP from 1.0 wt-% to 3.0 wt-%. Only GNPs were functionalised by ultraviolet-ozone treatment to improve their dispersion in the matrix while all the composites were manufactured by hand layup method and characterised by scanning electron microscopy, impact, flexural, thermogravimetry and ablation tests. The composite containing 0.3 wt-% GNPs showed considerable improvement in ablation, flexural and impact testing as compared to CF-P composites containing GP. Finally, the ablation mechanisms of post-ablated composites were discussed in the light of available data in the literature.

Simple InCl3 Doped PEDOT:PSS and UV-Ozone Treatment Strategy: External Quantum Efficiency up to 21% for Solution-Processed Organic Light-Emitting Devices with a Thermally Activated Delayed Fluorescence Emitter.

A low-cost and easy-process scheme for solution-processed organic light-emitting devices (OLEDs) was provided to overcome the flaws of poly(styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiphene) (PEDOT:PSS) together with the indium tin oxide anode. The modified PEDOT:PSS with higher work function (5.66 eV) and more efficient hole injecting ability was obtained by simply mixing the aqueous PEDOT:PSS with InCl3 and then consecutive ultraviolet-ozone treatment. The simply structured and solution-processed OLEDs with our modified PEDOT:PSS achieved avery high external quantum efficiency of 21.0% using a classic thermally activated delayed fluorescence emitter, 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenzene. The origin of this great promotion was explored through photoelectron spectroscopy, Fourier transform infrared reflection spectroscopy, and atomic force microscopy, from which we inferred that InCl3 itself, the losing of insulting PSS outer shell, and transformation to quinoid structure of PEDOT chains accounted for this improvement. Our modification method of PEDOT:PSS is beneficial for promoting solution-processed organic semiconducting devices.

Effects of dry oxidation treatments on monolayer graphene

Ultraviolet–ozone (UVO) and oxygen plasma are widely used to modify the surface of materials because these processes are facile and accessible. These dry oxidation treatments are also commonly applied to 2D graphene and are presumed to induce similar oxidation effects on the graphene surface. However, in this work, these treatments are revealed to induce the formation of different types of defects on the surface of graphene because the UVO treatment causes a chemical reaction, whereas the oxygen plasma treatment causes both physical and chemical reactions. The oxygen plasma treatment results mainly in topological defects, which effectively induce the attachment of oxygen atoms onto the treated surface; by contrast, the UVO treatment induces only the attachment of oxygen atoms onto the treated surface, without inducing lattice distortion. These results are confirmed mainly by atomic-resolution transmission electron microscopy imaging and electron energy loss spectroscopy. Using such facile dry oxidation treatments, we experimentally modified the surface states of graphene at the atomic scale.

Highly selective immobilized bimetallic Ni-Au nanoparticle catalyst for the partial hydrogenation of m-dinitrobenzene

Transition metal nanoparticles (NPs) are extensively used as catalysts for a wide and diverse range of organic transformations when immobilized on appropriate solid supports. We describe the development of a highly active and highly selective heterogeneous catalyst based on Ni-Au NPs supported on activated carbon fibers (ACFs) for the partial reduction of m-dinitrobenzene (m-DNB) to m-nitroaniline (m-NAN), an important platform chemical used in the synthesis of dyes and polymers. Initially, Ni NPs with narrow size distribution and ranging from 2 to 14nm were prepared with poly-N-vinyl-2-pyrrolidone (PVP) as a stabilizer. Evaluation of the NPs as catalysts in the liquid-phase hydrogenation of m-dinitrobenzene led to the establishment of an antipathetic structure sensitivity, i.e. the larger NPs displayed a 6-fold higher turnover frequency than the smaller NPs. The selectivity to the target m-NAN product is independent of the size of the Ni NPs, possibly due to preferential PVP absorption of the NP edges and vertices. Consequently, Ni NPs of 2nm were supported on ACFs and residual PVP was removed by a ultra-violet ozone (UVO) treatment, rendering a highly selective structured catalyst that affords m-NAN in almost 96% yield. A two-site (plane vs. edge Ni-atoms) Langmuir–Hinshelwood kinetic model is consistent with the experimental kinetic data confirming that low-coordination atoms (edges and vertices) are responsible for selective reaction. Consequently, we prepared bimetallic Ni-Au NPs (Ni:Au=1:1) aiming to generate Ni surface sites mimicking the properties of edge and vertex atoms. The resulting UVO-treated Ni-Au NPs of 3nm immobilized on ACFs afford m-NAN with a yield exceeding 98%. Such a high yield appears to be unprecedented and shows how careful nanocatalyst design, guided by detailed structural characterization and mechanistic studied, can lead to highly selective catalysts of industrial relevance.

Optimization of ultraviolet ozone treatment process for improvement of polycaprolactone (PCL) microcarrier performance.

Growing cells on microcarriers may have overcome the limitation of conventional cell culture system. However, the surface functionality of certain polymeric microcarriers for effective cell attachment and growth remains a challenge. Polycaprolactone (PCL), a biodegradable polymer has received considerable attention due to its good mechanical properties and degradation rate. The drawback is the non-polar hydrocarbon moiety which makes it not readily suitable for cell attachment. This report concerns the modification of PCL microcarrier surface (introduction of functional oxygen groups) using ultraviolet irradiation and ozone (UV/O3) system and investigation of the effects of ozone concentration, the amount of PCL and exposure time; where the optimum conditions were found to be at 60,110.52ppm, 5.5g PCL and 60min, respectively. The optimum concentration of carboxyl group (COOH) absorbed on the surface was 1495.92nmol/g and the amount of gelatin immobilized was 320±0.9µg/g on UV/O3 treated microcarriers as compared to the untreated (26.83±3µg/g) microcarriers. The absorption of functional oxygen groups on the surface and the immobilized gelatin was confirmed with the attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR) and the enhancement of hydrophilicity of the surface was confirmed using water contact angle measurement which decreased (86.93°-49.34°) after UV/O3 treatment and subsequently after immobilization of gelatin. The attachment and growth kinetics for HaCaT skin keratinocyte cells showed that adhesion occurred much more rapidly for oxidized surfaces and gelatin immobilized surface as compared to untreated PCL.

EFFECTS OF VARIOUS TREATMENTS ON SILICONE RUBBER SURFACE

ABSTRACTHydroxy groups were generated on a poly(dimethylsiloxane) (PDMS) surface using different methods. Attempts were made to prepare a homogeneous film on the PDMS surface and eliminate microwrinkles from the surface. Because the hydroxylation process changes the chemical composition of the PDMS surface, resulting in a cracked surface, selecting the best method for surface treatment with minimized surface microwrinkles and cracks was attempted. The results obtained from scanning electron microscopy showed that using the pulsed ultraviolet-ozone (UVO) radiation method with a controlled duration time, ozone treatment, continuous UVO treatment using a glass filter, and water media in UVO treatment was more effective than other methods evaluated in this study to prevent microwrinkles. The results obtained from contact angle measurements and attenuated total reflectance Fourier transform infrared spectroscopy revealed that the UVO treatment in the presence of a water medium created more hydroxy groups compared with other methods.

Modulation of the effective viscosity of polymer films by ultraviolet ozone treatment

Nanoconfinement of a polymer film affords a reduction of the glass transition temperature (Tg) and effective viscosity (ηeff). Early on, Prof. Tisato Kajiyama pioneered the idea of enhanced polymer mobility at the free surface. This concept is now well established, and accounts for the Tg and ηeff reductions of thin polymer films. To pay tribute to Prof. Kajiyama's seminal contribution, it is fitting to report in this special issue the use of ultraviolet ozone (UVO) to chemically modify the surface of polymer films and thereby alter their dynamical properties for the first time. Specifically, we show that with a brief exposure time of only 1.0 s under typical UVO treatment conditions, the ηeff of polystyrene (PS) films supported by silica changes from decreasing to rapidly increasing as the film thickness is decreased upon the UVO treatment. As such, the tendency of the films to spontaneously rupture on heating is significantly lessened. Considering the simplicity and inexpensiveness of the method, our results demonstrate that UVO treatment is an attractive method to refine the dynamical properties of polymer films and improve their thermal stability.

Transferability and Adhesion of Sol-Gel-Derived Crystalline TiO2 Thin Films to Different Types of Plastic Substrates.

Anatase thin films were prepared on various plastic substrates by our recently developed sol-gel transfer technique. Polycarbonate (PC), poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polyether ether ketone (PEEK), and polyvinylidene chloride (PVDC) were employed as plastic substrates. A Si(100) substrate was first coated with a polyimide (PI)/polyvinylpyrrolidone (PVP) mixture layer, and an alkoxide-derived titania gel film was deposited on it by spin-coating. The resulting titania gel film was heated to 600 °C, during which the PI/PVP layer decomposed and the gel film was converted into a 60 nm thick anatase film. The anatase film was then transferred from the Si(100) substrate to the plastic substrate. This was achieved by heating the plastic/anatase/Si(100) stack in a near-infrared image furnace to 120-350 °C, depending on the type of plastic substrate, under unidirectional pressure. The anatase film cracked during transfer to PE, PP, PEEK, and PVDC substrates but did not crack during transfer to PC, PMMA, and PET substrates. The fraction of the total film area that was successfully transferred was assessed with the aid of image analysis. This fraction tended to be large for plastics with C═O and C-O groups and small for those without these groups. The film/substrate adhesion assessed by cross-cut tape tests also tended to be high for plastics with C═O and C-O groups and low for those without these groups. The adhesion to plastics without C═O or C-O groups could be enhanced and their transfer area fraction increased by oxidizing the native plastic surface by ultraviolet-ozone treatment prior to transfer.

Enhanced planar perovskite solar cells with efficiency exceeding 16% via reducing the oxygen vacancy defect state in titanium oxide electrode.

In this work, the influence of oxygen vacancy defect (OVD) in compact titanium oxide (c-TiO2) on the performance of planar perovskite solar cells (p-PSCs) is investigated, and the possible mechanisms are also proposed. To meet our objective, anatase c-TiO2 thin films with various OVD concentrations are prepared by changing the oxygen flux during the DC magnetron sputtering process and are characterized by the intensity of defect signals in the X-ray photoelectron spectra. We conclude that abundant OVDs can trigger an obviously increased majority carrier accumulation zone at the metal oxide/perovskite interface and enhanced capacitance, thereby greatly deteriorating photogenerated carrier collection efficiency. A detailed analysis of the study results also reveals that the presence of OVD in the bulk and surface of c-TiO2 can slow down electronic carrier transport and lower its electron quasi-Fermi level under illumination, leading to the detrimental charge recombination in p-PSCs. Furthermore, we report a remarkably enhanced p-PSC efficiency via preparing c-TiO2 using high oxygen flux and subsequent ultraviolet ozone treatment. As a consequence, repeatable power conversion efficiency (PCE) is propelled to as high as 16.62%, coupled with negligible hysteresis and increased stability. These results provide a significant implication for further perfecting efficient and stable p-PSCs for their record efficiency.

Ultraviolet-ozone anode surface treatment and its effect on organic solar cells

The effect of ultraviolet (UV)-ozone-treated indium-tin oxide (ITO, anode) on the initial parameters and degradation in small-molecule organic solar cells (OSCs) with the structure of ITO/copper phthalocyanine (CuPc, donor)/fullerene (acceptor)/bathocuproine (cathode buffer)/Ag (cathode) was experimentally investigated. A UV-ozone exposure with a UV intensity of 13.5mW/cm2 on the ITO surface was examined. The results indicated that compared with OSCs with no UV exposure, the initial short-circuit current density and power-conversion efficiency ηp increased in the OSC by 20% and 13%, respectively, after 1min of UV-ozone exposure. A repeated illumination stress comprising 3s of illumination and 12s of darkness was imposed on OSCs in air. The UV-ozone-treated OSCs showed excellent durability under the repeated illumination stress. After 10min of UV-ozone exposure, the OSCs exhibited only an 8% decrease in ηp after 100 illumination cycles. However, with no UV exposure, ηp decreased by approximately 65%, and the OSCs developed strong S-shaped kinks in their current–voltage characteristics, suggesting an increase in series resistance at the ITO–CuPc interface. The UV-ozone treatment much reduces the carbon contaminants on the ITO surface and increases the clean surface with polar components of OH functional groups and negatively charged oxygen. This generates attractive force between ITO and CuPc film. The attractive force prevents further CuPc crystal disorder and void formation at the ITO/CuPc interface, and achieves the durability against the illumination stress.

Wettability effects of graphene oxide aqueous solution in photodetectors based on graphene oxide/silicon heterojunctions via ultraviolet ozone treatment

We report the wettability effects of graphene oxide (GO) aqueous solution on the electrical and photoresponse properties of GO-silicon (Si) photodetectors via ultraviolet ozone (UVO) treatment. GO-Si vertical heterojunctions were fabricated using a spray-coating method. In the GO/p-Si heterojunctions without UVO treatment (GO/p-Si), an island-like assembly of GO sheets was formed, indicating that a GO stacking structure may have an island shape on the substrate due to partial surface coverage. In contrast, for those with UVO treatment (GO/UVO-p-Si), a relatively more close-packed GO deposition may occur due to the more hydrophilic property of the substrate surface, leading to the full surface coverage of the p-Si surface. Photodetectors based on GO/p-Si and GO/UVO-p-Si heterojunctions exhibit distinct electrical and photoresponse properties. The GO/UVO-p-Si-based devices showed a higher photo-to-dark current ratio, higher turn-on voltage, and lower ideality factor compared to the GO/p-Si-based devices. The transport mechanism in the photodetectors can be explained in terms of space-charge-limited conduction and the tunneling of charge carriers through the GO layer.

Ultraviolet-Ozone Treatment for Effectively Removing Adhesive Residue on Graphene

In this paper, we systematically investigated the influence of adhesive residue existing in deterministic transfer process upon graphene, and put forward a rapid and effective way named ultraviolet-ozone (UVO) treatment to reduce this negative effect. Results indicate that this adhesive residue may cause poor contact between metal and graphene, thus greatly degrading the performance of the device. However, this unpleasant influence could be reduced effectively by adopting UVO treatment. This work may be helpful to fabricate higher performance functional devices based on two-dimensional materials by removal of the adhesive residue.

Achieving high mobility, low-voltage operating organic field-effect transistor nonvolatile memory by an ultraviolet-ozone treating ferroelectric terpolymer.

Poly(vinylidene fluoride–trifluoroethylene) has been widely used as a dielectric of the ferroelectric organic field-effect transistor (FE-OFET) nonvolatile memory (NVM). Some critical issues, including low mobility and high operation voltage, existed in these FE-OFET NVMs, should be resolved before considering to their commercial application. In this paper, we demonstrated low-voltage operating FE-OFET NVMs based on a ferroelectric terpolymer poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] owed to its low coercive field. By applying an ultraviolet-ozone (UVO) treatment to modify the surface of P(VDF-TrFE-CTFE) films, the growth model of the pentacene film was changed, which improved the pentacene grain size and the interface morphology of the pentacene/P(VDF-TrFE-CTFE). Thus, the mobility of the FE-OFET was significantly improved. As a result, a high performance FE-OFET NVM, with a high mobility of 0.8 cm2 V−1 s−1, large memory window of 15.4~19.2, good memory on/off ratio of 103, the reliable memory endurance over 100 cycles and stable memory retention ability, was achieved at a low operation voltage of ±15 V.

Transparent, wear-resistant, superhydrophobic and superoleophobic poly(dimethylsiloxane) (PDMS) surfaces

Superoleophobic surfaces that exhibit self-cleaning, antifouling, low-drag, and anti-smudge properties with high transparency are of interest in industrial applications including optical devices, solar panels, and self-cleaning windows. In many superoleophobic surfaces created to date, the lack of mechanical durability has been an issue. In this work, for the first time, transparent, wear-resistant, superhydrophobic and superoleophobic surfaces were developed for polydimethylsiloxane (PDMS) using a simple and scalable fabrication technique. PDMS is of importance in biomedical applications as it is biocompatible, chemically stable, and transparent. PDMS was made superhydrophobic either through micropatterning or an applied coating of hydrophobic SiO2 nanoparticles with a binder of methylphenyl silicone resin. Through the addition of fluorination via fluorosilane, the nanoparticle/binder coating was made superoleophobic. Intermediate steps using ultraviolet-ozone treatment were required for improved deposition and adhesion of the coatings. The effects of surface treatments were examined through contact angle and tilt angle measurements. The coating was found to have re-entrant geometries desirable for superoleophobicity and to exhibit mechanical wear resistance and transparent properties.

Influence of Ultraviolet/Ozonolysis Treatment of Nanocarbon Filler on the Electrical Resistivity of Epoxy Composites.

In the present work, we have investigated concentration and temperature dependences of electrical conductivity of graphite nanoplatelets/epoxy resin composites. The content of nanocarbon filler is varied from 0.01 to 0.05 volume fraction. Before incorporation into the epoxy resin, the graphite nanoplatelets were subjected to ultraviolet ozone treatment at 20-min ultraviolet exposure. The electric resistance of the samples was measured by two- or four-probe method and teraohmmeter E6-13. Several characterization techniques were employed to identify the mechanisms behind the improvements in the electrical properties, including SEM and FTIR spectrum analysis.It is established that the changes of the relative intensities of the bands in FTIR spectra indicate the destruction of the carboxyl group –COOH and group –OH. Electrical conductivity of composites has percolation character and graphite nanoplatelets (ultraviolet ozone treatment for 20 min) addition which leads to a decrease of percolation threshold 0.005 volume fraction and increase values of electrical conductivity (by 2–3 orders of magnitude) above the percolation threshold in comparison with composite materials—graphite nanoplatelets/epoxy resin. The changes of the value and behavior of temperature dependences of the electrical resistivity of epoxy composites with ultraviolet/ozone-treated graphite nanoparticles have been analyzed within the model of effective electrical conductivity. The model takes into account the own electrical conductivity of the filler and the value of contact electric resistance between the filler particles of the formation of continuous conductive pathways.

Low-temperature, solution-processed indium-oxide thin-film transistors fabricated by using an ultraviolet-ozone treatment

For the fabrication of low-temperature solution-processed metal-oxide thin-film transistors (TFTs), alternative annealing processes have recently been studied for reduced fabrication cost and applications to flexible devices. Indium nitrate solution has been proposed as a precursor for the low-temperature solution-processed TFTs. However, due to its high decomposition temperature, achieving a high-performance indium-oxide (In2O3) TFT at temperatures below 200°C is still difficult. In this study, for improved metal-oxide formation in low-temperature solution-processed In2O3 TFT, indium nitrate film was exposed to UV-ozone for 30 min before annealing at 200°C. The smooth scanning electron microscopy (SEM) image of the UV-ozone treated film implies that the indium nitrates are condensed after treatment. In addition, X-ray photoemission spectroscopy (XPS) data suggest that UV-ozone decreases the number of oxygen vacancies and increases the number of metal-oxygen-metal bonds in the indium-oxide films. As a result, high electrical device performance was achieved with an improved Ion/off ratio (∼107) and mobility (1.25 cm2V −1s −1).

Multi-solution processes of small molecule for flexible white organic light-emitting diodes

Most small molecule organic light emitting diode (SM-OLED) device structures are made in one layer using solution-based processing because the solution is usually a high dissolvent material that easily attacks the layer below it. We demonstrate a simple and reliable stamping technique for fabricating multi-solution process flexible white SM-OLEDs. The structure is anode/spin-hole injection layer/spin-emitting layer/stamping-electron transport layer/cathode. Poly(di-methyl silane) (PDMS) stamp is used for transferring electron transport layer. An intermediate ultraviolet-ozone surface treatment is introduced to temporarily modify the PDMS stamp surface. Then, the solution-based electron transport layer film can therefore be uniformly formed on top of the PDMS surface. After that the electron transport layer film on the PDMS stamp is transfer-printed onto the emitting layer with suitable heating and pressing. A solution-based processing is successfully established to efficiently fabricate flexible white SM-OLEDs. The SM-OLEDs were obtained at the current density of 20mA/cm2, luminance of 1062cd/m2, current efficiency of 5.57cd/A, and Commission internationale de l'éclairage coordinate of (0.32, 0.35).