Chlorine Precursors Research Articles

Investigation of silicon nitride for spacer via plasma-enhanced atomic layer deposition using a (tert-butylamino)dimethylsilane precursor

Silicon nitride (SiNx) has attracted considerable attention as a spacer in advanced semiconductor devices, owing to its superior barrier performance. However, the fabrication of SiNx films remains challenging, because of the corrosive byproducts generated when using chlorine precursors and impurities associated with the redeposition species of precursor ligands. The selection of precursor and optimization of the process parameters influence the film growth and improve the film properties. In this study, the (tert-butylamino)dimethylsilane (TBADMS) precursor and N2 plasma were introduced for the first time by plasma-enhanced atomic layer deposition (PEALD) to deposit SiNx films. We attempted to improve the film properties by adjusting the substrate temperature and investigated different growth mechanisms. The film deposited at 300 °C exhibited the most superior film properties, with an N/Si ratio close to ideal Si3N4, high film density, smooth surface, and low wet etch rate. The proposed growth mechanism demonstrates the influence of the initial surfaces and residual redeposition species removal within the film. Additionally, dielectric characterization indicates that films deposited at a higher temperature exhibit enhanced dielectric constant and reduced hysteresis (k = 7.2, ΔV = 0.6 V) in comparison to those (k = 4.9, ΔV = 1.2 V) deposited at lower temperature.

Improved Performance of Air-Processed Perovskite Solar Cells via the Combination of Chlorine Precursors and Potassium Thiocyanate.

Due to their low cost and high efficiency, hybrid perovskite solar cells (PSCs) have shown the most outstanding competitiveness among third-generation photovoltaic (PV) devices. However, several challenges remain unresolved, among which the limited stability is arguably the main. Chlorine (Cl) has been widely employed to yield PV performances, but the Cl-doping mechanism and its role in mixed-halide PSCs are not entirely understood. Here, we investigate the effect of Cl-doping using different precursors such as formamidinium chloride (FACl), cesium chloride (CsCl), and lead chloride (PbCl2), which lead to the incorporation of Cl at different sites of the perovskite crystal. We demonstrate that the stability and efficiency of air-processed PSCs are strongly affected by Cl bonding into the cationic chloride precursor. Furthermore, adding potassium thiocyanate (KSCN) leads to the maximum efficiency of 18.1%, improving the operational stability with only 18% PCE loss after 520 h, stored under ambient conditions. Incorporating CsCl and KSCN presents an effective approach to further boost the performance and thermal stability of PSCs by tailoring the composition of the perovskite's composition. Finally, we used the slot-die method to demonstrate that our strategy is scalable for large-area devices that have shown similar performance. Our results show that fully air-processed and stable PSCs with high efficiency for large production and commercialization are achievable.

An Updated Anthropogenic Emission Inventory of Reactive Chlorine Precursors in China

An Updated Anthropogenic Emission Inventory of Reactive Chlorine Precursors in China

Properties and improvements of chlorine-doped methylamine-based perovskites

Metal halide perovskite (MHP) has been widely used in optoelectronic devices such as solar cells in recent years due to their high absorption coefficients, long-range charge carrier diffusion lengths, and adjustable band gap, which is expected to achieve commercial application. Methylammonium lead iodide (MAPbI<sub>3</sub>) has been fully investigated as a standard perovskite component, however, due to the low formation energy of polycrystalline films fabricated by wet chemical method, crystal defects (including interface and grain boundary defects) are generally inevitable, which is a principal factor leading to phase transition. Therefore, reducing the defect density of perovskite is a prominent approach to improve the stability of perovskite. Although defect passivation is one of the most commonly used methods to fabricate efficient perovskite solar cells (PSCs), the relatively weak secondary bond between molecular passivation group and perovskite crystal may bring difficulties to the application of practical devices, particularly when operating under harsh environments, such as high temperature, humidity, and ultraviolet light. Therefore, improving the intrinsic structure stability of the perovskite via changing its composition can be an effective way. Although perovskites containing chlorine precursors have been empolyed in solar cells device, how chloride ions affect the structural and electronic properties of these films was not understood yet. In this work, two-phase perovskite (MAPbI<sub>2</sub>Cl) was fabricated by one-step spin coating with methylamine chloride (MACl) and lead iodide (PbI<sub>2</sub>) as precursors. As a result, chloride (Cl) doping can superiorly induce perovskite crystallization and thus stabilize the MAPbI<sub>3</sub> lattice. The Cl doped perovskite layer shows lower defect density, and compared with the original MAPbI<sub>3</sub> film, the carrier lifetime of MAPbI<sub>2</sub>Cl is increased by 7 times. Simultaneously, both of PCE and operational stability have been largely improved with PCE increased from 11.41% to 13.68%. There is no obvious degradation in the maximum power point output for nearly 8000 seconds in ambient conditions.

Anthropogenic emissions of atomic chlorine precursors in the Yangtze River Delta region, China

Chlorine radical plays an important role in the formation of ozone and secondary aerosols in the troposphere. It is hence important to develop comprehensive emissions inventory of chlorine precursors in order to enhance our understanding of the role of chlorine chemistry in ozone and secondary pollution issues. Based on a bottom-up methodology, this study presents a comprehensive emission inventory for major atomic chlorine precursors in the Yangtze River Delta (YRD) region of China for the year 2017. Four primary chlorine precursors are considered in this study: hydrogen chloride (HCl), fine particulate chloride (Cl−) (Cl− in PM2.5), chlorine gas (Cl2), and hypochlorous acid (HClO) with emissions estimated for twelve source categories. The total emissions of these four species in the YRD region are estimated to be 20,424 t, 15,719 t, 1556 and 9331 t, respectively. The emissions of HCl are substantial, with major emissions from biomass burning and coal combustion, together accounting for 68% of the total HCl emissions. Fine particulate Cl− is mainly emitted from industrial processing, biomass burning and waste incineration. The emissions of Cl2 and HClO are mainly associated with usage of chlorine-containing disinfectants, for example, water treatment, wastewater treatment, and swimming pools. Emissions of each chlorine precursor are spatially allocated based on the characteristics of individual source category. This study provides important basic dataset for further studies with respect to the effects of chlorine chemistry on the formation of air pollution complex in the YRD region.

Effects of domestic handling of drinking water on halogenated acetaldehydes

Halogenated acetaldehydes (HALs) are widely considered to be the third largest group of identified disinfection by-products (DBPs) by weight in drinking water. In this study, we evaluated various scenarios for the domestic handling of drinking water and their effects on HALs. Two drinking water systems (DS1 and DS2) were selected for this case study. First, tap water samples that were collected in DS1 at different time and from different locations were subjected to three domestic handling scenarios: boiling, domestic filtration using a point-of-use device with a new filter followed by refrigeration, and refrigeration in a covered glass pitcher. In the last two scenarios, the maximum storage (refrigeration) time was 24 h. Second, two water samples each from DS1 and DS2 were collected to investigate the effects that heating water to different temperatures has on HALs. According to the results, boiling the water effectively removed most HALs except dichloroacetaldehyde (DCAL), which increased. In contrast to the variable behaviors of HALs after boiling, all HALs were consistently and significantly reduced by domestic filtration. However, the overall removal efficiency of HALs from filtration (65%) was considerably lower than that from boiling (85%). Finally, refrigeration had no significant impact on the overall concentration of total HALs. However, chloral hydrate levels increased in unfiltered water after refrigeration, likely due to the reaction of chlorine residuals and precursors present in water. Therefore, boiling and domestic filtering of tap water may be recommended for the removal of HALs prior to consuming tap water.

An emission inventory for Cl2 and HOCl in Shanghai, 2017

Chlorine radical plays an important role in ozone formation. However, it has not generally been included in air quality modelling in China. In this study, an emission inventory for atomic chlorine precursors was developed for Shanghai in the year 2017. Total emissions of chlorine radical precursors were estimated at 8650 tons/year. The main source sectors of chlorine precursors in Shanghai include the volatilization of disinfectants, including in water treatment (850 tons/year, accounting for 9.8% among total emissions), in cooling towers (4,000 tons/year, 46.2%), in wastewater treatment (2,700 tons/year, 31.2%), in tap water (310 tons/year, 3.6%), in swimming pools (280 tons/year, 3.2%), and in the usage of chlorine-containing disinfectants (210 tons/year, 2.4%). The contribution of sea salt heterogeneous reactions with ozone to chlorine radical precursors is estimated as 90 tons/year; this represents a lower bound on the emissions from sea salt because of other reaction pathways (e.g., the reaction of particulate chloride with N2O5). Local emissions from coal combustion and chemical manufacturing were estimated to be relatively small. This study provides a basis for further study regarding the influence of chlorine chemistry on ozone formation in Shanghai.

Disinfection By-Products in Swimming Pool Water and Possibilities of Limiting Their Impact on Health of Swimmers

The presence of water disinfection by-products (DBPs) in the pool environment is a threat to the health of the users of swimming pools. Due to the mechanism of DBP formation, we are not able to prevent their presence. However, there are several ways to prevent the harmful effects of DBPs on the health of pool users; among these, various kinds of methods that result in the reduction of combined chlorine and DBPs precursors should be mentioned. And last but not least, a new approach to the design of the ventilation system for indoor swimming pools seems to be crucial for the above-mentioned purpose.

Room‐Temperature Synthesis and Enhanced Photocatalytic Performance of BiOCl Microsphere

AbstractHierarchical BiOCl microspheres assembled from nanosheets with predominated (110) facets were facilely fabricated by precipitation at room temperature and characterized systematically. The effects of the solvents, chlorine precursors and reaction time on the growth of the BiOCl microspheres have been investigated in detail. Rhodamine B (RhB) was selected to evaluate the photocatalytic activity of the as‐obtained samples under visible‐light irradiation, and the results revealed that the BiOCl microspheres synthesized with WCl6 exhibited superior RhB removal efficiency through a photosensitization process, and the degradation efficiency was 99% within 25 min and was still kept over 97% after five runs. The enhanced photocatalytic activities were mainly attributed to their hierarchical structure, high specific surface area as well as more exposed (110) facet. The superoxide radicals (•O2−) were demonstrated to be the main active species in the photodegradation process. Additionally, photocatalysis mechanism was proposed based on experimental results.

Controlled synthesis of core-shell carbide-derived carbons through in situ generated chlorine

Core-shell porous carbon represents an innovative concept for optimizing performances of carbon materials in a wide range application. Here, a novel route to produce carbons with spatially varying pore and microstructure is presented. Following the carbide-derived carbon method, a homogeneous and adjustable shell generation is achieved through mixing a limited amount of solid chlorine precursors with titanium carbide raw material. Chlorine is released in situ when reaching approx. 600 °C and consumed subsequently directly, resulting in the aspired materials. Various characterization methods proved that the amount of solid chlorine precursor directly adjusts the share of the shell for the core-shell material, while a range of 5–80% was studied. The amorphous, microporous shell can be converted to a mesoporous and graphitic shell (crystal sizes 20 nm), through a subsequent vacuum annealing, allowing to control the properties of the carbon shell. The carbon core results after a subsequent second chlorination step, where directly gaseous chlorine is used. The materials were characterized in detail after every step of this novel route. Adjusting the share between mesoporous/graphitic shell and microporous/amorphous core for these new materials is of interest in applications where competing processes like mass transfer and surface interaction need to be optimized.

Texture of MAPbI3 Layers Assisted by Chloride on Flat TiO2 Substrates

In this paper, we use X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy to investigate the structural and morphological properties of methylammonium lead iodide (MAPbI3) thin films deposited on flat TiO2 substrates, as obtained with and without the use of chlorine precursors. We demonstrate that the presence of Cl precursors assists the growth of oriented MAPbI3 domains along a specific growth direction. Such features are attributed to the proximity of the Cl species to the interface with the TiO2 substrate.

Chlorosulfonamide Salts Are Superior Electrophilic Chlorine Precursors for the Organocatalytic Asymmetric Chlorocyclization of Unsaturated Amides

Chloramine-T·3H(2)O and other chlorosulfonamide salts can serve as readily available, stable, and inexpensive precursors of electrophilic chlorine in the organocatalytic asymmetric chlorofunctionalization of olefins. In conjunction with commercially available organocatalysts, they can be utilized in the asymmetric chlorocyclization of unsaturated amides to yield products with unprecedented levels of stereoselectivity even at ambient temperatures and high concentrations.

Observations of gas phase hydrochloric acid in the polluted marine boundary layer

AbstractShip‐based measurements of gas phase hydrochloric acid (HCl), particulate chloride (pCl−), and reactive nitrogen oxides (NOy) were made in the polluted marine boundary layer along the California coastline during spring 2010. These observations are used to assess both the rate of Cl atom production from HCl and the role of direct HCl emissions and subsequent partitioning as a source for pCl−. Observations of HCl made in coastal Southern California are broadly correlated with NOz (NOz ≡ NOy – NOx), peaking at 11 A.M. The observed median HCl mixing ratio in Southern California is 1.3 ppb (interquartile range: 0.53–2.7 ppb), as compared to 0.19 ppb (interquartile range: 0.10–0.38 ppb) measured along the Sacramento River between San Francisco and Sacramento. Concurrent measurements of aerosol ion chemistry indicate that aerosol particles sampled in Northern California are heavily depleted in Cl−, corresponding to a mean pCl− deficit of 0.05 ± 0.03 (1σ) ppb for sub‐10 µm aerosol particles. In comparison, aerosols measured in Southern California indicate that over 25% of particles showed an addition of Cl− to the particle population. Observations presented here suggest that primary sources of HCl, or gas phase chlorine precursors to HCl, are likely underestimated in the California Air Resource Board emissions inventory. These results highlight the need for future field observations designed to better constrain direct reactive halogen emissions.

Photolysis of inorganic chloramines and efficiency of trichloramine abatement by UV treatment of swimming pool water

Trichloramine, one of the three inorganic chloramines (mono-, di- and trichloramine), is a problematic disinfection by-product in recreational pool water since it causes skin and eye irritations as well as irritations of the respiratory tract. The most commonly used chloramine mitigation strategy in pool water is UV treatment. Experiments with membrane inlet mass spectrometry (MIMS) confirmed that inorganic chloramines are effectively degraded by UV irradiation with low-pressure (LP) and medium-pressure (MP) mercury lamps (apparent quantum yields (QY): NH2Cl = 0.50 (LP) and 0.31 (MP) mol einstein−1, NHCl2: 1.06 (LP) and 0.85 (MP) mol einstein−1). Trichloramine showed the fastest depletion with a quantum yield slightly above 2 mol einstein−1 in purified (LP and MP) and pool water (MP). This high quantum yield can partly be explained by reactions involving OH radicals (purified water) and the reaction of trichloramine with moieties formed during UV irradiation of pool water. The presence of free chlorine affects trichloramine degradation (QY: ∼1.5 mol einstein−1) since it scavenges OH radicals and competes with trichloramine for reactive species (e.g. organic amines).Measurements in a pool facility revealed that the installed UV reactors degraded trichloramine by 40–50% as expected from laboratory experiments. However, trichloramine reduction in the pools was less pronounced than in the UV reactors. Model calculations combining pool hydraulics with formation/abatement of trichloramine showed that there was a fast trichloramine formation in the pool from the residual chlorine and nitrogenous precursors. The main factors influencing trichloramine concentrations in pool water are the free chlorine concentration and the UV treatment in combination with the recirculation rate through the water treatment system.

Silicon structuring by etching with liquid chlorine and fluorine precursors using femtosecond laser pulses

The aim of this study is to investigate the micrometer and submicrometer scale structuring of silicon by liquid chlorine and fluorine precursors with 200 fs laser pulses working at both fundamental (775 nm) and frequency doubled (387 nm) wavelengths. The silicon surface was irradiated at normal incidence by immersing the Si (111) substrates in a glass container filled with liquid chlorine (CCl4) and fluorine (C2Cl3F3) precursors. We report that silicon surfaces develop an array of spikes with single step irradiation processes at 775 nm and equally at 387 nm. When irradiating the Si surface with 400 pulses at 330 mJ/cm2 laser fluence and a 775 nm wavelength, the average height of the formed Si spikes in the case of fluorine precursors is 4.2 μm, with a full width at half maximum of 890 nm. At the same irradiation wavelength chlorine precursors develop Si spikes 4 μm in height and with a full width at half maximum of 2.3 μm with irradiation of 700 pulses at 560 mJ/cm2 laser fluence. Well ordered areas of submicrometer spikes with an average height of about 500 nm and a width of 300 nm have been created by irradiation at 387 nm by chlorine precursors, whereas the fluorine precursors fabricate spikes with an average height of 700 nm and a width of about 200 nm. Atomic force microscopy and scanning electron microscopy of the surface show that the formation of the micrometer and sub-micrometer spikes involves a combination of capillary waves on the molten silicon surface and laser-induced etching of silicon, at both 775 nm and 387 nm wavelength irradiation. The energy-dispersive x-ray measurements indicate the presence of chlorine and fluorine precursors on the structured surface. The fluorine precursors create a more ordered area of Si spikes at both micrometer and sub-micrometer scales. The potential use of patterned Si substrates with gradient topography as model scaffolds for the systematic exploration of the role of 3D micro/nano morphology on cell adhesion and growth is envisaged.

The Structure and Vibrational Spectrum of the Si(111)−H/Cl Surface

In this work, the vibrations of mixed coverage Si(111)−H/Cl surfaces are determined using quantum chemical calculations and Fourier transform infrared spectroscopy. The structure and symmetry considerations of the modes are used to assign the vibrational frequencies for varying coverages of both hydrogen and chlorine on the surface. Significant shifts in the Si−H and Si−Cl stretching frequencies are found as a function of coverage, while the bending modes are shifted very slightly. Our results suggest that Si−H stretching shifts can be used as a probe for chlorine coverage during the reaction of chlorine precursors with the hydrogen-terminated Si(111) surface. Finally, an analysis of coverage dependence suggests that a chemical inductive effect is the dominant origin of the resulting stretching frequency shifts, though a small contribution from the lone pairs interacting with the surface is also possible.

Formation and fate of haloacetic acids (HAAs) within the water treatment plant

Most research on the occurrence of chlorinated disinfection by-products (DBPs) in drinking water has focused on trihalomethane (THM) formation and evolution, in particular within distribution systems. In this research, we investigated the variability of the occurrence of haloacetic acids (HAAs) during the treatment process in two facilities where surface water is pre-chlorinated before being treated by conventional physico-chemical processes. The investigation focused on both seasonal and point-to-point fluctuations of HAAs. In both facilities, samples were collected weekly during 1 complete year at four points in order to generate robust data on HAAs and on complementary parameters. The results showed that the initial formation of HAAs was the highest and the most variable in the plant where levels of DBP precursor indicators and the pre-chlorination dose were both higher and more variable. Subsequent formation of HAAs from the pre-chlorination point until the settled water occurred due to remaining levels of residual chlorine and DBP precursors. However, HAA levels and in particular dichloroacetic acid (DCAA) (the preponderant HAA species in the waters under study) decreased dramatically during filtration, very probably because of biodegradation within the filter. The effect of filtration on DCAA fate was season-dependant, with the highest degradation in warm water periods and practically no variation during winter. Statistical modeling was applied to empirically identify the operational factors responsible for HAA formation and fate. Model performance to identify HAA variability in waters following pre-chlorination was much better than for water following filtration, which is due to the lack of information on mechanisms and conditions favoring DCAA degradation.

Photochemical formation of perchlorate from aqueous oxychlorine anions

Evidence of atmospherically produced perchlorate is being accumulated, yet information regarding its formation process is largely unknown. For the first time, the present study demonstrates that perchlorate can be generated as an end-product of photochemical transformation reactions of chlorine precursors such as aqueous salt solutions of hypochlorite, chlorite, and chlorate upon exposure to ultraviolet (UV) radiation. For example, under exposure to UV light from photochemical reactor lamps at a peak wavelength of 253.7 nm for 7 days, the observed perchlorate concentrations were 5, 25, and 626 μg/L at initial chlorite concentrations of 100, 1000, and 10,000 mg/L, respectively. In addition, perchlorate was generated within 7 days from aqueous chlorite solutions at mid-latitude (33°59′N, 101°89′W) spring and summer solar radiation. Via UV radiation from the artificial lamps and sunlight, chlorite was converted to chloride (68%) and chlorate (32%) as end-products on the basis of molar percentage. However, perchlorate was not detected from aqueous chloride solutions at initial concentrations up to 10,000 mg/L under the experimental conditions. Relevant mechanistic pathways were proposed based on the fact that chlorine dioxide (as a primary intermediate) may play a significant role in phototransformation of the precursors leading to perchlorate.

Spectroscopic and Structural Characterization of Chlorine Loading Effects on Mo/Si:Ti Catalysts in Oxidative Dehydrogenation of Ethane

The structural changes induced in a silica-titania mixed-oxide support (1:1 molar ratio) by chlorine addition at different loading levels, their relation to the structural characteristics of supported MoOx species over the support, and their correlation with ethane oxidative dehydrogenation (ODH) activity have been examined. The molybdenum and chlorine precursors are incorporated into the Si/Ti support network as it forms during gelation by using a "one-pot" modified sol-gel/coprecipitation technique. In situ X-ray diffraction during calcination shows the Si/Ti 1:1 mixed-oxide support is in a state of nanodispersed anatase titania over amorphous silica. With the addition of molybdenum and chlorine modifier, this anatase feature becomes more pronounced, indicating a decreased dispersion of titania. The effective titania surface area on the chlorine-doped Si:Ti support obtained from 2-propanol temperature-programmed reaction supports this observation. Raman spectra of dehydrated samples point to an enhanced interaction of MoOx species with silica at the expense of titania. X-ray photoelectron spectroscopic results show that, without forming a molybdenum chloride, the presence of chlorine significantly alters the relative surface concentration of Si vs Ti, the electronic structure of the surface MoOx species, and the oxygen environment around supported MoOx species in the Si/Ti network. Secondary ion mass spectrometry detected the existence of SiCl fragments from the mass spectra, which provides molecular insight into the location of chlorine in Mo/Si:Ti catalysts. The observed increase in ethane ODH selectivity with chlorine modification may be ascribed to the MoOx species sharing more complex ligands with silica and titania with the indirect participation of chlorine. Steady-state isotopic transient kinetic analysis (SSITKA) is used to to examine the oxygen insertion and exchange mechanisms. The catalysts show very little oxygen exchange with the gas phase in the absence of a reaction medium. During the steady-state ODH reaction, lattice oxygen appears to be the primary source of oxygen in the formation of water and CO2.

Modification of styrene–butadiene rubber surfaces by plasma chlorination

Chlorination with halogenating agents in organic solutions is a common surface treatment for styrene–butadiene rubber materials to improve their adhesion to polyurethane adhesives. An attempt to replace this wet chemical method with a clean plasma technique has been undertaken. Styrene–butadiene rubbers (both model elastomers, such as Finaprene 435 and Finaprene 507 and a typical composite vulcanised rubber) were exposed to the action of plasma generated in various reactive mixtures containing chlorine moieties. As chlorine precursors, trichloromethane (CHCl 3), tetrachloromethane (CCl 4), and chlorine (Cl 2) were used. These compounds were supplied to the reactors as a pure agent or in a mixture with argon or oxygen. Pure argon and air were also tested. The process was performed both in RF (13.56 MHz) and AF (20 kHz) glow discharges, utilising electrode reactors working at low pressure. FTIR spectroscopy, contact angle measurements, and T-peel tests (before and after plasma treatment) characterised the elastomer surfaces. It has been found that for the pure CHCl 3 and CCl 4 plasmas with a relatively low power, the peel strength of the treated rubber surfaces is approximately 56% higher than that for the materials chemically chlorinated, and two to three times higher in comparison with the non-treated surfaces.