Differences In Deposition Rates Research Articles

Influence of magnetic field strength on plasma, microstructure, and mechanical properties of Cr thin films deposited by MPPMS and DOMS

Magnetic field strength plays a vital role in determining the discharge behavior in magnetron sputtering. It enables the customization of discharge plasma and thin film properties. This study aims to compare the discharge behavior and investigate the potential effects on Cr thin films deposited using modulated pulsed power magnetron sputtering (MPPMS) and deep oscillation magnetron sputtering (DOMS) at different magnetic field strengths. The magnetic field strength in the target center increased from 67 to 91 mT tuning by the target thickness from 8 to 3 mm, and the average electron temperature was higher in a DOMS discharge than that in a MPPMS discharge. For both MPPMS and DOMS deposited Cr thin films, the refractive index and mechanical properties have been promoted with the increase in magnetic field strength, and almost all Cr thin films showed a Cr(110) preferred orientation. The hardness and modulus increased from 11.3 and 275.6 to 13.8 to 285.1 GPa for MPPMS deposited thin films, while the hardness and modulus for DOMS Cr thin films were much higher, increasing from 11.2 and 283.6 to 17.3 to 297.2 GPa. The possible differences between MPPMS and DOMS were analyzed based on the plasma global model and empirical equations. The analysis revealed that the high discharge current of DOMS is primarily caused by the possibility of back-attraction ion difference between MPPMS and DOMS. The voltage oscillation in a DOMS discharge provides sufficient time for ionized ions to escape from cathode attraction. Regarding the difference in deposition rate, it should at least be the cooperative results of the target back-attraction effect and ion evacuation time difference in plasma.

Improvement of SiC deposition uniformity in CVD reactor by showerhead with baffle

The growth uniformity of silicon carbide (SiC) by halide chemical vapour deposition (HCVD) is influenced by equipment configuration, and a uniform film can be obtained by optimising the chamber structure. An SiC deposition kinetics model is studied in this work, and a detailed chemical reaction mechanism is incorporated into a model reaction chamber to verify the deposition kinetics model. We studied the influence of hole size of showerhead, baffle size, and baffle positioning on the growth uniformity. Further, we then optimised the process parameters using an orthogonal experimental method. Reducing the hole size of showerhead led to a “double peak” in the deposition rate across the substrate from the edge to both sides, which first increased and then decreased. The “double peak” disappeared upon reduction of hole size. With an increase in baffle size, the growth uniformity first increased and then decreased. Moreover, the baffle displacement had little effect on the deposition rate when the baffle-to-showerhead distance was at least 45 mm. Meanwhile, the growth uniformity gradually worsened when the baffle distance was reduced. The showerhead and baffle reduced the extreme difference in deposition rate across the effective deposition area by improving the spatial velocity distribution within the reaction chamber. A uniform SiC film could be obtained using the proposed optimisation method. Furthermore, the results of the orthogonal experimental method showed that the deposition rate increased by 57.8%, and the uniformity of growth standard deviation decreased by 18% compared with the ground state. This study provides theoretical guidance for future optimisations of CVD chambers.

Sea level rise and marsh surface elevation change in the Meadowlands of New Jersey

The marshlands of the Meadowlands of New Jersey are valuable wetland ecosystems in a highly developed urban area and provide a natural habitat to more than 285 species of birds, a great variety of fishes, and many other living organisms. It is not clear if these ecosystems and their associated ecological services will persist under conditions of accelerated sea level rise (SLR), in geography where space for a landward retreat of marshlands is limited. In this study, we used the deep rod surface elevation table method and feldspar marker horizons to measure surface elevation change and vertical accretion rate in five marshland sites over 11 years. The controlling parameters of the accretion rate were explored. The results showed that sediments were not limited for vertical accretion. About 16% of the total suspended solids reaching the marsh via the tide was trapped by the marsh surface. Hydraulic duty alone cannot explain differences in deposition rates between low and high marsh. Precipitation, snow accumulation, and sea surge from storms were the main drivers influencing subsidence. The overall subsidence rate was 1.5 ± 1.3 mm/year. All sites combined showed increases in surface elevation of 4.0 ± 0.7 mm/year. This rate of increase is not enough to keep up with the 8 mm/year SLR prediction. There is a 50% chance that in 80 years, 7% of current marshlands will be underwater or will convert to unvegetated mudflats, and most high marsh habitats will disappear.

Host plants influence susceptibility of whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) to the entomopathogenic fungus Isaria fumosorosea (Hypocreales: Cordycipitaceae)

ABSTRACTWe quantified the tritrophic effect of host plant on the susceptibility of the sweetpotato whitefly Bemisia tabaci (Genn.) to a fungal pathogen in the laboratory. Second-instar whiteflies reared on cucumber, eggplant, tomato and bean plants for six generations were exposed to conidial suspensions of Isaria fumosorosea isolate IF-1106. Our results did not detect differences in response (proportional survival or median lethal time, LT50 days) among insect populations derived from different plants that were treated with 107 conidia/ml. However, at concentrations ≤ 5×106 conidia/ml, whiteflies reared on bean and tomato died significantly more quickly (i.e. LT50 of 4–5 days) compared with cucumber and eggplant reared populations (5–7 days). Bean and tomato-reared populations were also more susceptible to mycosis (LC50 ≈ 6 × 105 conidia/ml) compared with those reared on cucumber (1.9 × 106 conidia/ml) and eggplant (1.5 × 106 conidia/ml). A separate study confirmed that this differential response of whitefly populations to I. fumosorosea was not explained by differences in deposition rate of conidia on leaf surfaces (i.e. a dosage effect). Our findings show that host plants affect the pathogenicity and virulence of a herbivore pathogen, but depend on the rate of exposure (inoculum) applied.

我国南方红壤区氮磷湿沉降对森林流域氮磷输出及水质的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 我国南方红壤区氮磷湿沉降对森林流域氮磷输出及水质的影响 DOI: 10.5846/stxb201503030415 作者: 作者单位: 西南林业大学环境科学与工程学院,中国科学院地理科学与资源研究所,西南林业大学环境科学与工程学院,中国科学院地理科学与资源研究所,中国科学院地理科学与资源研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31570465）；中国科学院青年创新促进会资助项目 Impact of atmospheric nitrogen and phosphorus wet deposition on nitrogen and phosphorus export and associated water quality: a case study of forest watershed in the red soil area, Southern China Author: Affiliation: College of Forestry, Southwest University of environmental science and engineering,Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:持续高通量的氮、磷输入导致水体富营养化的问题已引起广泛关注。通过对江西省千烟洲香溪流域水样（常规水样，降雨后的地表径流以及雨水水样）的季节性监测，研究大气氮、磷湿沉降对森林流域氮、磷输出动态及水质的影响。结果表明：从2013年6月至2014年5月，香溪流域内氮、磷湿沉降通量分别为11.86 kg/hm2和0.38 kg/hm2，其中氮湿沉降主要集中在夏秋两季，占全年输入量的64%，而磷沉降主要集中在夏季，占全年输入量的43%，表现出明显的季节性差异；水体pH值（6.22-8.89）的变化范围较大，而且氮、磷的输出受土地管理（施肥方式）及降雨事件的影响较为明显，尤其在耕作期，总氮的输出量占全年氮输出总量的96.2%，而总磷的输出量占全年磷输出总量的61.4%；对4场不同强度降雨（按降雨强度从大到小）的氮、磷输出动态过程分析，发现不同强度的降雨对水体氮、磷的输出过程影响不同，在径流未形成前以及降雨强度达到暴雨级别时，降雨对流域水体氮、磷的稀释作用明显，而在大雨强度下水体磷的输出量明显高于其他降雨；研究期间，香溪流域内氮湿沉降对水体的贡献量为101.97 kg，磷湿沉降的贡献量为0.60 kg，4场降雨氮对流域水体的贡献量为4.46kg，占流域氮输出负荷的15.22%，磷对水体的贡献量为0.032kg，占流域磷输出负荷的0.85%。同时，根据营养状态指数（EI），发现流域水体全年处于中至富营养状态，而且研究期间水体氮、磷浓度均超过水体富营养化阈值（氮1.5 mg/L，磷0.15 mg/L），存在爆发水体富营养化的威胁。 Abstract:Continuously high flux of nitrogen (N) and phosphorus (P) input into rivers leading to water eutrophication has attracted public concern. The aim of the study was to determine the impact of N and P wet deposition on N and P transport in the forest watershed in Qianyanzhou, Jiangxi Province, China, based on the monitoring data from long-term sample and analysis. The results showed that from June 2013 to May 2014, the N and P wet deposition flux for the monitored watershed reached 11.86 kg/hm2 and 0.38 kg/hm2, respectively. There was a seasonal difference in deposition rates, wherein the N wet deposition mainly focus on the summer and autumn, accounting for 64% of total N wet deposition, whereas the P deposition mainly occurred in summer, accounting for 43% of total P wet deposition input. The pH fluctuation for watershed was large and the impact of land management (e.g., fertilizing) and rainfall events on N and P output were pronounced. The output of N and P mainly focus on the cultivation period, accounting for 96.2% and 61.4% of the total output from June 2013 to May 2014, respectively, which is because exogenous input of N and P from chemical fertilizers was large in this period. By analyzing the dynamic processes of N and P output during four rainfall events, we found that the impact of different intensities of rain events on the output process was different. The dilution effect on N and P output during rainfall process was significant before becoming runoff or rain intensity reached the storm level. Under heavy rain, P output was higher than that under other rainfall intensities. The contribution of N and P wet deposition to water were 101.97 kg and 0.60 kg, respectively. The N and P wet deposition in four rain events reached 4.46 kg and 0.032 kg, respectively, accounting for 15.22% of total N and 0.85% of total P output. According to the Eutrophication Index for the Xiangxi watershed, the water quality of the Xiangxi watershed is at moderate to severe degree of eutrophication state, especially during the cultivation period. We also analyzed that the N and P concentration in water during study period all exceeded the eutrophication threshold (N 1.5 mg/L, P 0.15 mg/L), which have the potential risk of water eutrophication. 参考文献 相似文献 引证文献

Indoor particle dynamics in schools: Determination of air exchange rate, size-resolved particle deposition rate and penetration factor in real-life conditions

Indoor and outdoor airborne particles, CO, CO2 levels and comfort parameters were monitored at two naturally ventilated elementary schools (S1 and S2). This paper studies the variation of ventilation rate during lectures, recreations, lunchtime and after class. Additionally, mass balance equations were used to estimate the particle deposition rates and penetration factors for different particle size fractions. The originality of the present work resides in taking advantage of occupants’ activities as sources of indoor particles and tracer gas CO2 used to simultaneously estimate the above-mentioned parameters in different scenarios. This simple approach makes the determination of indoor particle dynamics more effective, and allows reducing the cost of indoor air quality studies. During the class, the ventilation rates at S1 and S2 fluctuated largely from day to day, with respective average values of 10.08 m3/h/p and 7.92 m3/h/p, significantly lower than the ASHRAE acceptable value (18 m3/h/p) in classrooms. The particle deposition loss rate coefficients for 0.3–10 µm particles dramatically increased from 0.16–0.18 h−1 for the 0.3–0.5 µm fraction to 1.81–2.31 h−1 for the 7.5–10 µm fraction, while their corresponding penetration factors declined from 0.94 to 0.30, respectively. The difference in deposition rate between schools was probably associated to discrepancies in particle density.

Deposit Formation in a Grate–Kiln Plant for Iron-Ore Pellet Production. Part 2: Characterization of Deposits

Buildup of deposit material in chunks on refractory linings caused by combustion of various fuels is a well-known problem. This study characterizes the short-term deposits on refractory material in a grate–kiln process, carried out through in situ measurements using a water-cooled probe with a part of a refractory brick mounted in its end. Sampling was carried out during combustion of both oil and coal. A significant difference in deposition rates was observed; deposition during oil firing was negligible compared to coal firing. The deposits are mainly hematite particles embedded in bonding phase, mainly comprising Si, Al, Fe, Ca, and O. Moreover, it was found that the prevailing flue-gas direction determines the formation of the deposits on the probe and that inertial impaction controls the deposition rate. However, this rate can also be affected by the amount of air-borne particles present in the kiln.

Spheres vs. rods: The shape of gold nanoparticles influences aggregation and deposition behavior

The influence of shape on nanomaterial aggregation and deposition was systematically studied with poly-acrylic acid (PAA) coated uniform-sized gold nanospheres (AuNSs) and nanorods (AuNRs). Time resolved dynamic light scattering was employed to study their aggregation kinetics in a wide range of mono- and di-valent electrolyte conditions. Results indicated that PAA coated AuNSs have higher aggregation propensity compared to anisotropic PAA coated AuNRs, as observed through critical coagulation concentration (CCC). The CCC values were estimated as 50mM NaCl and 1.8mM CaCl2 for AuNS, which showed substantial increase to 250mM NaCl and 7mM CaCl2 for anisotropic AuNRs. Though electrokinetic behavior showed similar surface potential for the spherical and rod-shaped materials, the geometric differences between the samples have likely resulted in unique conformation of the PAA coatings, leading to different magnitudes of steric hindrances and hence yielding the observed aggregation behavior. The deposition kinetics was monitored using the quartz crystal microbalance with dissipation technique. AuNRs showed relatively slower deposition compared to AuNSs for low electrolytes concentrations. With the increase in electrolyte concentration, the differences in deposition rates between spheres and rods diminished. The results from this study showed that the shape of nanomaterials can influence interfacial properties and result in unique aggregation and deposition behavior under typical aquatic conditions.

Atmospheric deposition and storm induced runoff of heavy metals from different impermeable urban surfaces

Contaminants deposited on impermeable surfaces migrate to stormwater following rainfall events, but accurately quantifying their spatial and temporal yields useful for mitigation purposes is challenging. To overcome limitations in current sampling methods, a system was developed for rapid quantification of contaminant build-up and wash-off dynamics from different impervious surfaces. Thin boards constructed of concrete and two types of asphalt were deployed at different locations of a large carpark to capture spatially distributed contaminants from dry atmospheric deposition over specified periods of time. Following experimental exposure time, the boards were then placed under a rainfall simulator in the laboratory to generate contaminant runoff under controlled conditions. Single parameter effects including surface roughness and material composition, number of antecedent dry days, rain intensity, and water quality on contaminant build-up and wash-off yields could be investigated. The method was applied to quantify spatial differences in deposition rates of contaminants (TSS, zinc, copper and lead) at two locations varying in their distance to vehicle traffic. Results showed that boards exposed at an unused part of the carpark >50 m from vehicular traffic captured similar amounts of contaminants compared with boards that were exposed directly adjacent to the access route, indicating substantial atmospheric contaminant transport. Furthermore, differences in contaminant accumulation as a function of surface composition were observed. Runoff from asphalt boards yielded higher zinc loads compared with concrete surfaces, whereas runoff from concrete surfaces resulted in higher TSS concentrations attributed to its smoother surfaces. The application of this method enables relationships between individual contaminant behaviour and specific catchment characteristics to be investigated and provides a technique to derive site-specific build-up and wash-off functions required for modelling contaminant loads from impermeable surfaces.

Atmospheric deposition contributes little nutrient and sediment to stream flow from an agricultural watershed

Atmospheric deposition of nutrients within agricultural watersheds has received scant attention and is poorly understood compared to nutrient transport in surface and subsurface water flow pathways. Thus, we determined the deposition of phosphorus (P), nitrogen (N), and sediment in a mixed land use watershed in south-central Pennsylvania (39.5 ha; 50% corn–wheat–soybean rotation, 20% pasture, and 30% woodland), in comparison with stream loads at several locations along its reach between 2004 and 2006. There was a significant difference in deposition rates among land uses ( P < 0.05) with more P and N deposited on cropland (1.93 kg P and 10.71 kg N ha −1 yr −1) than pasture (1.10 kg P and 8.06 kg N ha −1 yr −1) and woodland (0.36 and 2.33 kg N ha −1 yr −1). Although not significant, sediment showed the same trends among land uses. A significant relationship was found between P in deposition and P in soil <10-m away from the samplers suggesting much of the deposited sample was derived from local soil. Samplers adjacent to the stream channel showed deposition rates (1.64 kg P and 8.83 kg N ha −1 yr −1) similar to those on cropland. However, accounting for the surface area of the stream, direct deposition of P, N, and sediment probably accounted for <3% of P and <1% of N and sediment load in stream flow from the watershed (1.41 kg P, 27.09 kg N, and 1343 kg sediment ha −1 yr −1 at the outlet). This suggests that strategies to mitigate nutrient and sediment loss in this mixed-land use watershed should focus on runoff pathways.

A comparison of lead pollution record in Sphagnum peat with known historical Pb emission rates in the British Isles and the Czech Republic

Vertical Pb concentration gradients and isotope ratios ( 206Pb/ 207Pb, 208Pb/ 207Pb) are reported for five 210Pb-dated Sphagnum peat profiles. The studied peat bogs are in the British Isles (Thorne Moors, England; Mull, Scotland; and Connemara, Eire) and central Europe (Ocean, northern Czech Republic; Rybarenska slat, southern Czech Republic). Both the U.K. and the Czech Republic experienced maximum Pb emissions from Ag–Pb smelting around 1880. Pb emissions from coal burning peaked in 1955 in the U.K. and in the 1980s in the Czech Republic. In both countries, use of alkyl-lead additives to gasoline resulted in large Pb emissions between 1950 and 2000. We hypothesized that peaks in Pb emissions from smelting, coal burning and gasoline burning, respectively, should be mirrored in the peat profiles. However, a more complicated pattern emerged. Maximum annual Pb accumulation rates occurred in 1870 at Ocean, 1940 at Thorne Moors, 1988 at Rybarenska slat, and 1990 at Mull and Connemara. Atmospheric Pb inputs decreased in the order Thorne Moors ≥ Ocean > Rybarenska slat > Mull > Connemara. The Ocean bog was unique in the central European region in that its maximum Pb pollution dated back to the 19th century and coincided with maximum Pb smelting at Freiberg and Pribram. In contrast, numerous previously studied sites showed no Pb accumulation maximum in the 19th century, but increasing pollution until the 1980s. It remains unclear why Ocean did not record the regional peak in Pb emissions caused by high coal and gasoline burning around 1980, while an array of nearby bogs studied previously did record the 1980 coal/gasoline peak, but no 1880 smelting peak. Mean 206Pb/ 207Pb ratios of potential pollution sources were 1.07 and 1.11 for gasoline, 1.17 and 1.17 for local ores, and 1.18 and 1.19 for coal in the U.K. and the Czech Republic, respectively. The calculated percentages of gasoline-derived Pb in peat (≤55% for the British Isles and ≤63% for the Czech Republic) were surprisingly low. An explanation for the low percentage of gasoline-derived Pb in peat can be more easily found for the Czech sites (until 1989 Czechoslovakia was the third largest lignite producer in the world). Regional differences in deposition rates of gasoline-derived Pb in the U.K. need further study.

Photothermal CVD of Carbon Thin Films using CH2I2 as the Precursor

AbstractThin carbon films are deposited via CVD from the precursor methylene iodide (CH2I2) using two different activation sources; a broadband IR lamp and a thermal plate. Large differences in deposition rates are observed when comparing the two sources of activation. The characteristics of the deposition kinetics of the highly sensitive system are also investigated by employing a split, symmetric reactor, and by using a qualitative model. Raman spectroscopy (RS) is used for microstructural characterization of the films. The lamp technique allows a simple and low‐cost experimental setup, for deposition of disordered carbon thin films at relatively low temperatures and high rates.

Modeling deposition of particles in typical horizontal ventilation duct flows

Particles carried by airflows through ventilation ducts in heating, ventilation and air-conditioning (HVAC) systems have adverse effects on human health. Knowledge of particle deposition rates in ventilation ducts is useful for modeling exposures to particles within buildings and more completely understanding particle fates. To meet these objectives, deposition rates of particles to various internal surfaces in a smooth horizontal square ventilation duct are predicted by Reynolds-Averaged Navier-Stokes (RANS)-Lagrangian simulation at all three air speeds of 3.0 m/s, 7.0 m/s and 9.0 m/s. Drag, lift force, gravity, inertial force and turbulent diffusions are considered in the computation of particle motion. The influences of relaxation time, particle size, air speed, turbulent flow development profiles and surface orientations on predicted deposition rates (dimensionless deposition velocities) of particles is discussed. For particles larger than 10 μm, it is shown that vertical wall deposition rates in a smooth horizontal square ventilation duct where the turbulent flow profiles is fully developed first increase with dimensionless relaxation time increase and then slightly decrease with dimensionless relaxation time increasing at three different air speeds. The maximum of the sidewall deposition rates is 0.12. Floor deposition rates increase with dimensionless relaxing time increase and attain the maximum value of 9.6. Ceiling deposition rates firstly gradually decrease and then rapidly decrease to zero with dimensionless relaxing time increasing at different air speeds. The maximum of the ceiling deposition rates is 0.054. Particle deposition rates to the ceiling, wall and floor in the horizontal duct with a fully developed turbulent flow profile are all lower than that in the horizontal duct with a developing turbulent flow profile. Particle deposition rates are mainly dependent on friction velocity (air speed) and particle size. The differences in deposition rates to the duct floor, wall and ceiling decrease with increasing air speed. The results of Lagrangian simulations in this work are valuable for more accurately predicting and understanding particle deposition in typical ventilation ducts.

Illumination-Modulated Electrodeposition of Various Kinds of Noble Metal on p-Type Silicon

We report on the control of photo-assisted electrodeposition of several kinds of noble metal on p-type Si by adjusting the illumination condition. In the case of Pt and Cu, the deposition rate and the particle density of metal deposits under illumination were considerably higher than those obtained in the dark, because illumination produces photo-excited electrons and enables another channel through the conduction band for charge transfer in addition to the channel through the valence band which is used in the dark. Using this difference in deposition rate between these two conditions, we have succeeded in control of the morphology of Cu layer on p-type Si without changing applied potential, as well as the Pt system. The nucleation of metal particles could be controlled by modulating illumination duration and light intensity, and the nuclei could be grown in the dark. On the other hand, it was difficult to control the deposition of Pd and Au by modulating illumination, because they were spontaneously deposited even in the dark by their rapid immersion plating rate on p-type Si.

Surface selective chemical deposition of polyanilines

We report on chemical in situ deposition of poly( o-anisidine) and polyaniline on bare and thiol-modified gold. It is shown that the process of o-anisidine polymerization is initiated on the metal surface and in consequence it is very sensitive to modifications of the coating substrate. Polyaniline deposited under the same conditions does not reveal such sensitivity as the polymer is forming in the polymerization solution and is subsequently physisorbed on the surface. Thus, the substrate itself has little effect on the polymer deposition rate. The large differences in deposition rates of poly( o-anisidine) make this material promising in preparation of polymeric patterns using lithographic methods.

Redeposition of etch products on sidewalls during SiO2 etching in a fluorocarbon plasma. IV. Effects of substrate temperature in a CF4 plasma

Effects of substrate temperature on the redeposition of bottom-emitted particles to the sidewall surface and the resulting changes in the sidewall properties during SiO2 etching in a CF4 plasma were investigated. A Faraday cage and specially designed, step-shaped substrates located in a plasma etcher allowed us to observe lateral and vertical etch rates, the temperature dependence of redeposition, and resulting changes in the chemical composition of the sidewall surface. We conducted two sets of experiments under different process conditions to observe changes in the temperature effect with ion energy and plasma density. Process (I), which was carried out with a 200 W source power and a −400 V bias voltage, represented a typical reactive ion etching condition for low plasma density and high ion energy, and process (II), with 500 W and −200 V, represented an inductively coupled plasma condition of high plasma density and low ion energy. Lateral etching was more sensitive to substrate temperature than vertical etching. As the substrate temperature was raised, the redep-effect, which was defined as the difference in deposition rates between two sidewalls, either affected by bottom-emitted particles or not, was slightly decreased in process (I) but was significantly increased in process (II). The chemical composition of the sidewall surface was highly dependent on substrate temperature. The carbon content and the F/C ratio of the surface carbon-containing layer formed on the sidewall increased and decreased, respectively, with substrate temperature. The O/Si ratio of the redep-etch combined layer formed beneath the surface carbon-containing layer decreased when the substrate temperature was increased.

Millennial-scale records of atmospheric mercury deposition obtained from ombrotrophic and minerotrophic peatlands in the Swiss Jura Mountains.

Peat cores from two bogs were used to reconstruct changes in net atmospheric mercury deposition in Switzerland for the past 2-3 millennia. The two records were compared to assess the reliability of peat cores as archives of atmospheric mercury deposition. Net mercury accumulation rates and Hg(ex), an indicator of significant anthropogenic mercury contamination, were calculated for both cores. Both records showed stable background values (0.5-1.9 and 1.0-3.0 microg of Hg m(-2) yr(-1)). In both profiles, mercury accumulation rates began to increase during the 12th century, and Hg(ex) appeared during the 14th century. The late 19th and early 20th centuries have been studied in detail. The profiles match well with the history of local and global mercury emissions. The magnitude of increase from the pre-anthropogenic to anthropogenic period was also very similar in both records. Although the two sites are botanically very similar and lie only 3.5 km apart, accumulation rates at TGE were generally higher than those at EGR. This indicates that, although such records can be used to determine the chronologies of and relative changes in rates of atmospheric mercury deposition, differences in rates of mercury accumulation rates between sites do not necessarily indicate differences in deposition rates of mercury from the atmosphere.

Chemical vapor deposition of undoped and in-situ boron- and arsenic-doped epitaxial and polycrystalline silicon films grown using silane at reduced pressure

A nonselective epitaxial growth process for heterojunction bipolar transistors has been studied. The difference in growth rates for epitaxial and polycrystalline films could be used to monitor the thickness of the intrinsic and extrinsic base layers. The films were grown using chemical vapor deposition on Si 〈100〉 (epitaxy) and on silicon dioxide (polycrystalline) at reduced pressure (20–80 Torr) for undoped and in situ B or As doping. The depositions were carried out using silane diluted in hydrogen. Diborane and arsine were used as the source gas for dopants. For the undoped Si films, the deposition of polycrystalline films had a substantially higher rate than that of epitaxial ones. The growth rate of both epitaxial and polycrystalline depositions decreased with increasing total pressure. It was, however, linearly proportional to the silane partial pressure, pSiH4. The dependence of the growth rate on the hydrogen partial pressure was proportional to pH2−0.82 for epitaxial and to pH2−0.60 for polycrystalline depositions. The apparent activation energy was 2.1 and 1.6 eV for the epitaxial and polycrystalline depositions, respectively. A growth mechanism assuming the dissociative adsorption of silane on the Si surface, in combination with first-order hydrogen desorption kinetics, was employed to describe the experimental observations, including the differences in deposition rates, dependency on the hydrogen partial pressure as well as apparent activation energy. In situ B doping influenced neither the epitaxial nor polycrystalline depositions. In situ As doping, on the other hand, largely reduced the growth rate compared to the undoped films to such an extent that there was no appreciable difference in growth rate between the epitaxial and polycrystalline Si. The doping concentration in the epitaxial B and As films were of the order of 1018 cm−3, identical deposition conditions yielded a 5 and 20 times larger dopant incorporation in the B and As doped polycrystalline films, respectively.

Depositional and post‐depositional controls on magnetic signals from saltmarshes on the north‐west coast of Ireland

Magnetic measurements were carried out on samples from two saltmarshes deposited during the last century on the north‐west coast of Ireland. Based on profiles from cliffed saltmarsh edge, mid‐marsh and supratidal locations, the processes that affect the generation and persistence of magnetic properties in environments were investigated. This was done to help in understanding the geochemical processes affecting north‐west Irish coast saltmarshes and to determine the frequency and provenance of sediment‐laden flooding events; hence, disentangling the importance of clastic and organic contributions to saltmarsh growth. Magnetic properties indicate depositional and post‐depositional effects varying on both temporal and spatial scales. The interpretations presented here suggest that both biogenic and diagenetic processes have a strong effect on the magnetic properties recorded: in the former case, the growth of magnetotactic bacteria is the main process; in the latter case, it is reductive diagenesis, associated with organic matter decomposition, that is important. The biogenic and diagenetic effects overprint and degrade the detrital magnetic signatures respectively. This suggests that magnetic measurements within the context of north‐west Irish coast saltmarshes can provide limited information on clastic sediment input to these environments. Comparisons between sites on the north‐west coast of Ireland show similar magnetic properties, despite differences in deposition rates, implying that significant post‐depositional alteration of magnetic properties occurs within the first 20–40 years after deposition. Magnetic properties of north‐west coast Irish saltmarshes are put into a regional context by comparison with magnetic profiles from similar sites.

Effect of Diluent Gases on Growth Behavior and Characteristics of Chemically Vapor Deposited Silicon Carbide Films

SiC films were chemically vapor deposited onto graphite substrates using methyltrichlorosilane (MTS, CH3SiCl3) as a source and argon or hydrogen as diluent gases to investigate the effect of each diluent gas on growth behavior and characteristics. Each diluent gas used had a relative difference in deposition rate within a certain temperature region. Such growth characteristics of the SiC films as preferred orientation, microstructure, and chemical composition varied remarkably with the diluent gas used. Microhardness and surface roughness were compared for SiC films prepared using the different diluent gases.