CD Variation Research Articles

Cd and Zn concentration in hybrid poplar foliage and leaf beetles grown on polluted sediment-derived soils.

Foliar Cd and Zn concentrations of hybrid poplars commonly planted on sediment-derived soils were assessed in field circumstances. Selected sites covered a range of soil types and plantation characteristics. Reference data for foliar concentrations were established from samples taken in a tree-nursery. Even in the reference situation a large variation in foliar Cd and Zn concentrations was observed, with relative standard deviations in the order of 15%. Foliar concentrations of Cd and Zn in poplars growing on sediment-derived soils increased during the growing season. The accumulation rate was markedly higher on polluted sediment-derived soils than in the reference situation. Poplars grown on polluted sediment derived soils showed elevated and deviating foliar Cd and Zn concentrations (>7.5 mg Cd kg(-1) DW and 320 mg Zn kg(-1) DW). A thin unpolluted covering layer did not influence foliar concentrations. Regardless of site characteristics, poplar age, species or clone, a significant positive relation was found between soil and foliar concentration for Zn and to a lesser extent for Cd. Bioconcentration factors for Cd and Zn were higher than one in baseline situations, but mostly lower than one on polluted sediment-derived soils. Cd:Zn ratio was on the average twice as high as in the soil. Leaf beetles showed normal body concentrations for Zn, but higher Cd concentrations than in reference situations. BCFs were lower than one on sediment-derived soils. Foliar results indicated a possible threat in long-term habitat development of poplar plantations. This conclusion was confirmed by the significant higher Cd concentrations in leaf beetles grown on poplars with deviant foliar concentrations. However, litter decomposition rates were generally evaluated as normal.

Cypress tree ( Cupressus semervirens L.) bark as an indicator for heavy metal pollution in the atmosphere of Amman City, Jordan

Bio-monitoring of air quality in Amman City was investigated by analyzing 36 cypress tree ( Cupressus semervirens L.) bark samples from three sites of different anthropogenic activities at the end of summer season 2001. Cypress barks were found to be a good bio-indicator for air pollution in arid regions. Variation in Pb, Zn, Mn, Cr, Ni, Cd, and Cu contents between sites was observed due to different types of activities. Traffic emissions were found to be the main source of heavy metal pollution in the atmosphere of Amman. Lead content was found to be the highest in highly traffic density areas. The industrial part of the city was characterized by high Zn, Mn, Cr, Ni, and Co contents. No significance variations were found in pH values of the bark between the sites. This was attributed to buffering effect of carbonate in the atmosphere originated from soil of the area.

Manufacturability of single and double-gate ultrathin silicon film fully depleted SOI technologies

Of several possible devices that can be used for sub-70 nm node technologies, two are built on ultra thin SOI layers. Scaling of such thin silicon layer SOI devices is constrained by the severe short channel control problem. To alleviate this, double-gate structures have been proposed by Wong et al. (1999), Chang et al. (2000), and Ieong et al. (2000). In this paper, we assess the manufacturability of single-gate (SG) and symmetric double-gate (DG) devices for gate lengths between 15 and 70 nm. Our results show that SG devices are not only manufacturable but also have tighter distributions than DG devices; inverter ring oscillator (RO) stage delays and power consumption are also better for SG devices. Besides gate length we find two additional major sources of variation: silicon thickness and encapsulation width. We show that for an optimized double-gate device with minimized parasitic resistance, CD variations become a dominant factor at 20-nm gate lengths despite superior electrostatic integrity. Also, the work function of metal gates must be controlled to better than /spl plusmn/0.1 eV (3/spl sigma/) to avoid severe manufacturability problems.

Cadmium accumulation by willow clones used for soil conservation, stock fodder, and phytoremediation

Elevated levels of cadmium are often found in the soil of New Zealand pasturelands due to the long-term use of Cd-contaminated fertilisers. The accumulation of Cd in willow biomass used as stock fodder could therefore adversely affect agricultural productivity and human health. Alternatively, willows may be used for phytoremediation of Cd-contaminated soil at polluted sites. An investigation was carried out to determine the variation in Cd as well as Zn, Mn, and Fe accumulation in 15 willow clones that had been bred for soil conservation purposes. These clones were grown under controlled conditions in 20-L pots of soil containing Cd, Zn, Mn, and Fe at concentrations of 0.3, 64, 597, and 56 000 mg/kg, respectively. Daily water use was measured over the final 2 weeks of the experiment and biomass accumulation was determined at the end of the experiment. We found that shrub willows had significantly higher leaf and stem Cd, Mn, and Zn concentrations than tree willows. Average leaf Cd concentrations varied widely between clones from 1.5 to 10 mg/kg. Clones with a high Cd accumulation capacity may be selected to improve the efficacy of Cd-phytoremediation, whereas clones that accumulated lower Cd concentrations may be used for stock fodder. Metal concentrations were not significantly correlated with plant water-use, or biomass production.

Embedded Control Solutions

QCS (Quality Control System) and CD actuator suppliers have been focused on providing solutions for the existing paper machine market for the last 30 years. These systems have proved to be highly effective at reducing MD and CD variations, resulting in significant increases in production, savings in raw material and energy, and improvements in sheet quality. Almost all paper machines are now equipped with QCS and CD actuator systems. A closer examination of QCS and CD actuator systems reveals their past and present limitations.

Cadmium accumulation and metallothionein synthesis in freshwater bivalves ( Pyganodon grandis): relative influence of the metal exposure gradient versus limnological variability

The relative influence of limnological confounding factors on cadmium (Cd) bioaccumulation and metallothionein (MT) synthesis was quantified in natural populations of freshwater bivalves ( Pyganodon grandis) living in lakes along a Cd concentration gradient. During the ice-free period, we measured 15 environmental variables in the water compartment and determined total concentrations of Cd and MT in the gills of bivalves at 37 littoral stations in 20 lakes distributed across the mining area of Rouyn-Noranda in northwestern Québec. A multiple linear regression model including pH (+), dissolved Ca concentrations (−) and free Cd 2+ concentrations at the sediment–water interface (+) explained 74% of the variability in Cd concentrations in the bivalve gills. Dissolved Ca (−) and free Cd 2+ (+) together explained 62% of the variation in MT concentrations in the bivalve gills. Partial linear regression analyses indicated that the limnological factors' pure and shared effects together accounted for 48 and 45% of the total variation in Cd and MT concentrations in the gills, respectively. A lake selection procedure that could be applied in monitoring programs is proposed to minimise the relative influence of these confounding variables.

Hepatic metallothionein as a biomarker for metal contamination: age effects and seasonal variation in European flounders ( Pleuronectes flesus) from the Severn Estuary and Bristol Channel

Hepatic concentrations of metallothionein [MT] and three metals (Cu, Zn, Cd) were determined in 242 European flounders ( Pleuronectes flesus) collected from power stations at Oldbury-upon-Severn and Hinkley Point, located in Severn Estuary and Bristol Channel, UK, respectively, between March 1996 and February 1998. A model involving three-factor analysis of variance (ANOVA) was used to examine variation in MT and metal concentrations with respect to season, year and site; with age-class included as a covariate in the analysis. Hepatic concentrations of MT and Cd (and to some degree, Cu, but not Zn) increased significantly with age. The model explained 38, 25, 17 and 26% of the variation in MT, Cu, Zn and Cd, respectively, with significant effects due to season, and to a lesser extent, to year. Site was only a significant factor for Cd which was higher in fish from Hinkley. Correlation between the individual concentration of MT and each metal alone, or in combination, was poor, and explained only an additional 3.0% of the residual variation in MT, most of which was attributable to Cu (2.7%). Compared to other industrialised estuaries, Cd concentrations were high (>20 μg g −1 in some individuals). The study emphasises the importance of seasonal variation and other factors in biomonitoring programmes and highlights the limitations of using [MT] as a biomarker for metal contamination in flounders from the Severn Estuary.

High-throughput high-density mapping and spectrum analysis of transistor gate length variations in SRAM circuits

High-throughput high-density mapping of gate length variations using static random-access memory (SRAM) as electronic test structures is reported. In the experiments, direct measurements of bit-line currents revealed the individual transistor gate length variations within every memory cell. With SRAM and its fast addressing circuits we can measure CD variations with measurement time as fast as 5 /spl mu/s per data point and spatial periodicities down to 6 /spl mu/m. Layout-dependent periodic errors were found to take up 30% to 90% of the total observed error variance, depending on the spatial frequency range and specific measurement grid used. Peaks in the error spectrum were found to be related to the periodicities existing in the circuit layout. Lithography simulations were done as efforts to identify the periodic error sources. It was found that proximity effects and pattern-dependent coma effects contributed to a large percentage of the high spatial frequency errors observed. By independent optical measurements of the poly mask, it was found that the CD error contributions from the mask are very small, and are negligible when compared to the stepper-lens-induced CD errors.

A study of multiple scattering effect with 10 kV e-beam system

Multiple scattering effect is discussed with a low voltage e-beam system. A test layout is designed to figure out the multiple scattering effect. A dark erosion is studied to identify the scattering range. The range is found to be as far as ∼15mm with our 10kV e-beam system. The effective scattering doses are 5.6% an 5.3% in terms of CD variation for beam spot sizes of 0.15um and 0.3um, respectively. CD variation between features in non-multiple scattered area and those in multiple scattered is 22nm–31nm that is not negligible for small features.

Speciation and phytoavailability of cadmium in selected surface soils of South Australia

A modified sequential extraction scheme was developed for partitioning the particulate-bound cadmium (Cd) into 9 fractions: exchangeable, carbonate-bound/specifically adsorbed, metal–fulvic acid-complex-bound, metal–humic acid-complex-bound, easily reducible metal oxide-bound, organic-bound, amorphous mineral colloid-bound, crystalline Fe oxide-bound, and detrital (bound to mineral lattices). Results on 11 surface soils showed that Cd in these soils was predominantly present in detrital form, bound to the mineral lattices, accounting for 15.8–61.9%, with an average of 33.4%, of the total Cd in the soils. The average relative abundance of Cd bound to the different particulate forms in the soils is in the order: detrital (0.077 mg/kg) > specifically adsorbed/carbonate-bound (0.066 mg/kg) > organic-bound (0.033 mg/kg) > metal–fulvic acid-complex-bound (0.031 mg/kg) > easily reducible metal oxide-bound (0.019 mg/kg) > exchangeable (0.013 mg/kg) > metal–humic acid-complex-bound (0.011 mg/kg) > crystalline Fe oxide-bound (0.001 mg/kg) =amorphous mineral colloid-bound (0.001 mg/kg). The phytoavailable Cd content was determined as Cd concentration in the shoot and leaf of durum wheat plants grown on the soils in a greenhouse study. Statistical treatment of the data showed that the exchangeable Cd (r = 0.735, P = 0.01) and the metal–fulvic acid-complex-bound Cd (r = 0.824, P = 0.002) correlated significantly with the plant-available Cd, compared with other species. The exchangeable and fulvic acid fraction of the metal–organic-complex-bound Cd contents, together, could explain 91.5% of the variation in plant-available Cd, determined as Cd concentration in leaf and stem of the durum wheat plants (r = 0.956, P = 0.0001). The significance of metal–fulvic acid complexes on Cd phytoavailability has not been reported so far and needs in-depth research in explaining the toxicity and food chain contamination of Cd in the environment.

Genotypic variation in cadmium accumulation by seed of linseed, and comparison with seeds of some other crop species

The accumulation of cadmium (Cd) in plants is a health issue because a range of grain and vegetable crops can accumulate levels of Cd that are in excess of limits set by the World Health Organization and individual countries. Many Australian agricultural soils used to produce confectionery linseed have a history of intensive use of Cd-contaminated phosphatic fertilisers and this, combined with soil properties such as high chloride salinity, can result in enhanced availability of Cd to crops. We investigated genotypic variation in Cd accumulation in seed of 17 linseed and Linola (termed linseed) lines from Australia and elsewhere in a glasshouse study using a soil from southern Australia that had a history of the application of Cd-contaminated phosphatic fertiliser. Canola, Indian mustard, lupins, and wheat were also included in the study for comparison. Under the experimental conditions, Cd concentrations in seed of all but one of the linseed lines exceeded the maximum permitted concentration (MPC) of 250 µg/kg for confectionery linseed traded on the international market. There was a 2.3-fold variation in seed Cd concentrations between all the linseed lines (range, 233–545 µg/kg). Linseed lines from Australia and overseas were equally capable of accumulating Cd in seed. Brown-seeded and golden-seeded lines accumulated similar concentrations of Cd. Canola, Indian mustard, lupins, and wheat accumulated about 10-fold lower concentrations of Cd in seed than linseed, and did not exceed Australian or other MPCs. There was little difference in Cd concentrations between the seed and de-seeded capsules of linseed, but a large difference in Cd concentration between the seed and de-seeded fruit parts of the other crops. The mean seed to de-seeded fruit part Cd concentration ratio for linseed was 0.87 : 1 compared with a ratio of 0.35 : 1 for the other crops, suggesting that linseed has comparatively ineffective barriers discriminating against the transport of Cd to seed. Analysis of seed lots of confectionery linseed sampled from a grain receival depot showed that seed lots from farms in Victoria (range 140–560 µg Cd/kg) had 5-fold greater Cd concentrations than those from farms in New South Wales (range 20–160 µg/kg). This is presumably due to a more intensive history of the application of Cd-contaminated phosphatic fertiliser to pastures and crops in Victoria, as well as differences in environmental and soil conditions.

Understanding CD variations in optical lithography using predictive modeling techniques

Understanding CD variations in optical lithography using predictive modeling techniques

CD control using SiON BARL processing for sub-0.25 μm lithography

In this paper, various contributions to the reflection variation at the resist/BARL interface are investigated. Not only deviations in the optical parameters (n, k, thickness T) of the BARL are causing variations in reflectivity, but also thickness variations of transparent layers underneath the BARL. Furthermore, the impact of substrate reflectivity on CD variation for 0.2@mm features is investigated, using various SiON layers. Since substrate reflectivity has to be very low for good CD control, and since some reflectivity variations can be unavoidable, the use of a TAR layer in combination with BARL is proposed as a simple solution to maintain good CD control on real product wafers.

Temporal changes of 210Po in temperate coastal waters

The temporal variation of Polonium-210 ( 210Po) was examined in coastal sea water, the mussel Mytilus edulis, the winkle Littorina littorea and green alga Ulva lactuca in order to investigate the entry of 210Po into the marine food chain. More than 99% of 210Po in the water column occurred in the particulate phase. Dissolved 210Po concentrations peaked during the spring phytoplankton bloom and it is suggested this is related to preferential scavenging of 210Po by the increased numbers of bacteria, viruses and small dissolved particulates. Changes in L. littorea 210Po specific activity are thought not to be related to food, but to a drop in body weight following spawning. Much of the 210Po accumulated by M. edulis was located in the digestive gland. The specific activity of 210Po in the digestive gland of M. edulis was shown to be strongly correlated with changes in sea water suspended particulate specific activity. Examination of other trace metal (Ag, Al, As, Ca, Cd, Cr, Co, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Sb, Se, Sn and Zn) variations in the digestive gland revealed that class B and borderline metals had a strong positive correlation with 210Po. On-going work is investigating whether the accumulation and loss of 210Po is affected by the presence of metallothioneins.

Natural Cd and Pb variations in Mytilus californianus during the upwelling season

The short term variability of Cd and Pb in Mytilus californianus in relation to upwelling events was studied. Sea water and mussel samples were taken daily for 4 weeks during the upwelling season (late summer) on the west coast of Vancouver Island. Upwelling indicators (PO 4, T and S) were measured and related to the variations in dissolved Cd and Pb in sea water. High variability in Cd and Pb mussel concentrations were detected, with significant differences found from one day to another. After normalizing, to account for the variability due to the condition of the mussel, significant differences among samples were still detected. The differences in mussel Cd were associated with the variations in dissolved Cd due to upwelling. Mussel Pb, however, was not related to variations in dissolved Pb. Principal component analysis was used to unravel patterns of variation among all variables measured. Parallel to the sampling of natural mussel beds, a transplant experiment was performed to compare the variability of intertidal vs. subtidal mussels. The transplanted mussels exhibited a less variable condition index and revealed more clearly the relation of dissolved Cd with the concentrations in the mussels. Lead in mussels, again, did not show a relationship with dissolved Pb. In addition, the mantle edge (from 3 days with highest and lowest Cd concentrations) was analyzed as an alternative indicator which could exhibit less variability. The Cd variability in the mantle edge was compared with that of the gills and the remainder. The mantle edge, even though it showed less variability than the gills and the remainder, still exhibited significant differences between days.

Optimization of optical density and planarization of an anti-reflectant

A series of ARC's have been prepared with optical densities ranging from 6–13/μ. Conformality of the ARC films was measured from 64% to 72%, and was not independent of optical density. Good line width control (less than 25 nm for 0.23 m lines) was obtained for ARC's over smooth reflective topography. CD variation over more severe topographies (a transparent topography and vertical edged topography) was poor for quarter micron lines. The more conformal ARC's gave the best CD variation over transparent topography and over smooth reflective topography. There was no observed correlation between optical density and CD variation.

Uniformity of Cd 1 − xZn xTe grown by high-pressure Bridgman

We have employed both low-temperature photoluminescence (PL) spectroscopy and high-spatial-resolution, room-temperature PL mapping to determine composition variation in Cd 1 − x Zn x Te grown by high-pressure Bridgman. Composition variations Δx of approximately 5–10% are observed between tip and heel of an approximately 13 cm long boule, while fluctuations of 1–2% are observed within a single, detector-scale sample. We also show that there are great discrepancies in the calculated zinc concentration, depending on which expression for E g( x) is chosen from the literature. We have performed high-resolution, triaxial X-ray analysis on selected samples to determine which of the published relations is most accurate for our material. We have also examined the relationship between the low-temperature PL spectrum and detector performance, and found that the line width of the donor-bound-exciton peak can be used as a predictor of performance.

Laboratory study of cd and hg uptake by two freshwater molluscs in relation to concentration, age and exposure time

To assess the potential of two molluscs species as bioindicators of Cd and Hg pollution in aquatic ecosystems, a laboratory study was conducted on the short-lived gastropod Viviparus georgianus and the pelecypod Elliptio complanata. Using analysis of covariance (ANCOVA), we have evaluated the contribution of the aqueous trace metal concentration, the size of the molluscs and the exposure time to explain the Cd and Hg body concentration. Results show that all the parameters analyzed have a significant effect on Cd and Hg body variation in the gastropod except for the time of exposure and the interaction time of exposure-height of the individuals. The same results are observed for the pelecypod, except that the length of the individuals has not a significant influence on Cd and Hg variation. The major part of the variability of the body metal concentration seems to be explained by these three parameters: the water metal concentration, the interaction of water metal concentration with time of exposure and the interaction of water metal concentration with time of exposure and the size of the individuals.

Strategies to Improve Linewidth Control for 0.25.MU.m and 0.18.MU.m devices.

Linewidth control in the 0.25μm-0.18μm range will be one of the biggest challenges for future optical lithography. Various parameters contribute to CD variations: stepper parameters, lens errors, mask imperfections, resist processing, wafer topography, proximity effects and operator errors. The goal of this paper is to elaborate on the most important contributors to CD variations. Linewidth control is studied directly, characterised by the 3σ variation of the CD spread. Our investigations are based on simulations and on experimental work. CD control for 0.25μm applications is compared for four resist strategies: negative tone resist with TAR, negative tone resist on BARC, positive tone resist on BARC and top surface imaging (TSI) in combination with dry development. Proximity correction is taken into account. Best results are obtained with the negative tone process on BARC and with TSI. Concerning CD-control for 0.18μm devices, a feasibility study is carried out, based on simulations. NA and σ optimisation will be required for sufficient CD control, as well as proximity correction on the mask. This feasibility study is illustrated with various experimental results obtained using TSI (Desire process).

Effect of Reticle Erros on Systematic Intrafield Line Width Variations

We have studied the contributions of reticle line width ( CD) errors to systematic intrafield CD variations for 0.35 µ m i-line lithography by measuring electrical resistance of lines patterned in polysilicon films. Reticle errors were determined by independent measurements, and their effects on final printed dimensions were analyzed. Both reticles and steppers contribute to the systematic intrafield variation. In some cases, the total variance exceeds the sum of the variances individually associated with steppers and reticles. Because aberrations and reticle errors are not random, analysis of variance must take their correlation into consideration. We have observed cases in which this correlation and nonlinear imaging contribute significantly to total line width variance.