The surface stress induced during the formation of alkanethiol self-assembled monolayers (SAMs) on gold from the vapor phase was measured using a micromechanical cantilever-based chemical sensor. Simultaneous in situ thickness measurements were carried out using ellipsometry. Ex situ scanning tunneling microscopy was performed in air to ascertain the final monolayer structure. The evolution of the surface stress induced during coverage-dependent structural phase transitions reveals features not apparent in average ellipsometric thickness measurements. These results show that both the kinetics of SAM formation and the resulting SAM structure are strongly influenced both by the surface structure of the underlying gold substrate and by the impingement rate of the alkanethiol onto the gold surface. In particular, the adsorption onto gold surfaces having large, flat grains produces high-quality self-assembled monolayers. An induced compressive surface stress of 15.9 ± 0.6 N/m results when a c(4×2) dodecanethiol SAM forms on gold. However, the SAMs formed on small-grained gold are incomplete and an induced surface stress of only 0.51 ± 0.02 N/m results. The progression to a fully formed SAM whose alkyl chains adopt a vertical (standing-up) orientation is clearly inhibited in the case of a small-grained gold substrate and is promoted in the case of a large-grained gold substrate.

SUMMARYAn apparatus has been developed for investigation of hydraulic conductivity of frozen soils. The test procedure is isothermal and involves the passage of water from one reservoir into the frozen sample and out of the frozen sample into a second reservoir. The water in the reservoirs remains unkozen because it contains dissolved lactose. The concentration of lactose is such that, initially, the water in the reservoirs is in thermodynamic equilibrium with the water in the sod. On application of pressure to one reservoir a known hydraulic gradient is established and flow takes place. Flow is shown to vary linearly witb hydraulic gradient. The hydraulic conductivity coefficient depends on soil type and temperature and is related to the unfrozen water content. At temperatures within a few tenths of 0°C the coefficient apparently ranges from lo-' to cm sec-', and decreases only slowly below about -05°C. Soils known to be susceptible to frost heave are shown to have significant hydraulic conductivities well below 0°C.

Many interactions drive the adsorption of molecules on surfaces, all of which can result in a measurable change in surface stress. This article compares the contributions of various possible interactions to the overall induced surface stress for cantilever-based sensing applications. The surface stress resulting from adsorption-induced changes in the electronic density of the underlying surface is up to 2-4 orders of magnitude larger than that resulting from intermolecular electrostatic or Lennard-Jones interactions. We reveal that the surface stress associated with the formation of high quality alkanethiol self-assembled monolayers on gold surfaces is independent of the molecular chain length, supporting our theoretical findings. This provides a foundation for the development of new strategies for increasing the sensitivity of cantilever-based sensors for various applications.

For groundwater-surface water interactions to be understood in complex wetland settings, the architecture of the underlying deposits requires investigation at a spatial resolution sufficient to characterize significant hydraulic pathways. Discrete intrusive sampling using conventional approaches provides insufficient sample density and can be difficult to deploy on soft ground. Here a noninvasive geophysical imaging approach combining three-dimensional electrical resistivity tomography (ERT) and the novel application of gradient and isosurface-based edge detectors is considered as a means of illuminating wetland deposit architecture. The performance of three edge detectors were compared and evaluated against ground truth data, using a lowland riparian wetland demonstration site. Isosurface-based methods correlated well with intrusive data and were useful for defining the geometries of key geological interfaces (i.e., peat/gravels and gravels/ Chalk). The use of gradient detectors approach was unsuccessful, indicating that the assumption that the steepest resistivity gradient coincides with the associated geological interface can be incorrect. These findings are relevant to the application of this approach in settings with a broadly layered geology with strata of contrasting resistivities. In addition, ERT revealed substantial structures in the gravels related to the depositional environment (i.e., braided fluvial system) and a complex distribution of low-permeability putty Chalk at the bedrock surface-with implications for preferential flow and variable exchange between river and groundwater systems. These results demonstrate that a combined approach using ERT and edge detectors can provide valuable information to support targeted monitoring and inform hydrological modeling of wetlands.

10Eutrophication is a globally significant challenge facing aquatic ecosystems, associated with human 11 induced enrichment of these ecosystems with nitrogen (N) and phosphorus (P). However, the limited 12 availability of inherent labels for P and N has constrained understanding of the triggers for 13 eutrophication in natural ecosystems and appropriate targeting of management responses. This paper 14 proposes and evaluates a new multi-stable isotope framework that offers inherent labels to track 15 biogeochemical reactions governing both P and N in natural ecosystems. importance of abiotic and metabolic processes for the in-river fate of N and P are also explored 27 through the stable isotope framework. Microbial uptake of ammonium to meet metabolic demand for 28 N is suggested by substantial enrichment of δ 15 N NH4 (by 10.2‰ over a 100m reach) under summer 29 low flow conditions. Whilst the concentration of both nitrate and phosphate decreased substantially 30 along the same reach, the stable isotope composition of these ions did not vary significantly, 31indicating that concentration changes are likely driven by abiotic processes of dilution or sorption. 32The in-river stable isotope composition and the concentration of P and N were also largely constant 33 downstream of the waste water treatment works, indicating that effluent-derived nutrients were not 34 strongly coupled to metabolism along this in-river transect. Combined with in-situ and laboratory 35 hydrochemical data, we believe that a multi-stable isotope framework presents a powerful approach 36 for understanding and managing eutrophication in natural aquatic ecosystems. 37 38

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A method for calculating the surface stress associated with the deflection of a micromechanical cantilever is presented. This method overcomes some of the limitations associated with Stoney’s formula by circumventing the need to know the cantilever’s Young’s modulus, which can have a high level of uncertainty, especially for silicon nitride cantilevers. The surface stress is calculated using readily measurable cantilever properties, such as its geometry, spring constant, and deflection. The method is applicable to both rectangular and triangular cantilevers. A calibration of the deflection measurement is also presented. The surface stress measurement is accurate to within 4%–7%. © 2001 American Institute of Physics

Creative remediation schemes have been implemented with success at petroleum-contaminated sites in Alaska and Canada during the past decade. Contaminated media have been landfarmed, amended with fertilizers, augmented with microbial products, and manipulated with engineered systems. Phytoremediation developments and use of biodegradable synthetic and polymeric resins for potential use with petroleum and xenobiotic contaminants are on the horizon. Treatment of supra-permafrost water and melt-water runoff with permeable reactive barriers and partitioning bioreactors is now possible. Cost and time limitations will likely continue to drive remediation decisions in the Arctic. Environmental policy, environmental constraints, and cost will dictate what technologies are appropriate for Antarctic clean-up, although the pressure of time is less acute because land transfer and liability are not drivers. This paper discusses some recent advances in remediation engineering for use in polar regions. Conceptual models are presented, and case study treatment costs and durations are highlighted to aid environmental decision-making.