Understanding Surface Processes Research Articles

A Dual-Channel MoS2-Based Selective Gas Sensor for Volatile Organic Compounds.

Significant progress has been made in two-dimensional material-based sensing devices over the past decade. Organic vapor sensors, particularly those using graphene and transition metal dichalcogenides as key components, have demonstrated excellent sensitivity. These sensors are highly active because all the atoms in the ultra-thin layers are exposed to volatile compounds. However, their selectivity needs improvement. We propose a novel gas-sensing device that addresses this challenge. It consists of two side-by-side sensors fabricated from the same active material, few-layer molybdenum disulfide (MoS₂), for detecting volatile organic compounds like alcohol, acetone, and toluene. To create a dual-channel sensor, we introduce a simple step into the conventional 2D material sensor fabrication process. This step involves treating one-half of the few-layer MoS₂ using ultraviolet-ozone (UV-O3) treatment. The responses of pristine few-layer MoS₂ sensors to 3000 ppm of ethanol, acetone, and toluene gases are 18%, 3.5%, and 49%, respectively. The UV-O3-treated few-layer MoS₂-based sensors show responses of 13.4%, 3.1%, and 6.7%, respectively. This dual-channel sensing device demonstrates a 7-fold improvement in selectivity for toluene gas against ethanol and acetone. Our work sheds light on understanding surface processes and interaction mechanisms at the interface between transition metal dichalcogenides and volatile organic compounds, leading to enhanced sensitivity and selectivity.

The effect of interface heterogeneity on zinc metal anode cyclability.

Zinc metal batteries (ZMBs) are promising candidates for low-cost, intrinsically safe, and environmentally friendly energy storage systems. However, the anode is plagued with problems such as the parasitic hydrogen evolution reaction, surface passivation, corrosion, and a rough metal electrode morphology that is prone to short circuits. One strategy to overcome these issues is understanding surface processes to facilitate more homogeneous electrodeposition of zinc by guiding the alignment of electrodeposited zinc. Using Scanning Electrochemical Microscopy (SECM), the charge transport rate on zinc metal anodes was mapped, demonstrating that manipulating electrolyte concentration can influence zinc electrodeposition and solid electrolyte interphase (SEI) formation in ZMBs. Using XPS and Raman spectroscopy, it is demonstrated that an SEI is formed on zinc electrodes at neutral pH, composed primarily of a Zn4(OH)6SO4·xH2O species, its formation being attributed to local pH increases at the interface. This work shows that more extended high-rate cycling can be achieved using a 1 M ZnSO4 electrolyte and that these systems have a reduced tendency for soft shorts. The improved cyclability in 1 M ZnSO4 was attributed to a more homogeneous and conductive interface formed, rather than the bulk electrolyte properties. This experimental methodology for studying metal battery electrodes is transferable to lithium metal and anode-free batteries, and other sustainable battery chemistries such as sodium, magnesium, and calcium.

Organic Vapor Sensing Mechanisms by Large-Area Graphene Back-Gated Field-Effect Transistors under UV Irradiation.

The gas sensing properties of graphene back-gated field-effect transistor (GFET) sensors toward acetonitrile, tetrahydrofuran, and chloroform vapors were investigated with the focus on unfolding possible gas detection mechanisms. The FET configuration of the sensor device enabled gate voltage tuning for enhanced measurements of changes in DC electrical characteristics. Electrical measurements were combined with a fluctuation-enhanced sensing methodology and intermittent UV irradiation. Distinctly different features in 1/f noise spectra for the organic gases measured under UV irradiation and in the dark were observed. The most intense response observed for tetrahydrofuran prompted the decomposition of the DC characteristic, revealing the photoconductive and photogating effect occurring in the graphene channel with the dominance of the latter. Our observations shed light on understanding surface processes at the interface between graphene and volatile organic compounds for graphene-based sensors in ambient conditions that yield enhanced sensitivity and selectivity.

Provenance and maximum depositional ages of Upper Triassic and Jurassic sandstone, north‐eastern Mexico

AbstractUpper Triassic to lowest Upper Jurassic strata in north‐eastern Mexico record surface processes during the early rifting that led to the opening of the Gulf of Mexico. Exposed near Ciudad Victoria, Tamaulipas and northwest to Galeana, Nuevo Leon, these continental deposits are called the Huizachal Group. Several key questions about these strata hamper their integration into a regional understanding of Late Triassic and Jurassic sediment routing and deposition. First, the depositional age of the stratigraphically lowest unit, the El Alamar Formation, is less well established than the depositional ages of the stratigraphically higher parts of the succession, leading to questions about the timinig of the onset of tectonic context, and regional correlation of these strata. Second, better knowledge of provenance and sediment routing, including fluvial transport distance, can help determine whether and when the depositional basin was split into subbasins versus connected by a throughgoing river system. This study uses sandstone detrital zircon U‐Pb isotopic ages and clast compositions to constrain depositional ages and reconstruct tectonic setting and provenance. Detrital zircon U‐Pb ages yielded a maximum depositional age of 210 Ma for the part of the El Alamar Formation exposed near Galeana, younger than previously determined. Although long‐distance (>100 km) sediment transport cannot be ruled out, the sources for Huizachal Group sandstone framework grains and detrital zircon could have been entirely local, within about 100 km. Alluvial deposits and pyroclastic and lava flows likewise indicate transport of no more than 100 km. We therefore infer deposition in partitioned rift basins receiving sediment from local sources. These data and interpretations contribute to understanding surface processes during the initial rifting that eventually led to opening of the Gulf of Mexico.

Development of image texture analysis technique for boulder distribution measurements: Applications to asteroids Ryugu and Itokawa

Recent asteroid missions have revealed that many sub-kilometer asteroids are rubble piles. Large parts of their surfaces are covered with boulders larger than tens of centimeters. An evaluation of the abundance and size distribution of boulders provides clues to understand surface processes on boulder-covered asteroids. Here we report a new method that automatically measures the abundance of small boulders (sub-pixel to a few pixels), whose boundaries cannot be recognized with visual inspection, by quantifying the surface radiance variation that occurs during the spinning of the asteroid. After validating our approach with previous boulder counting data, we apply this method to images of the asteroids Ryugu and Itokawa, which were visited by JAXA's Hayabusa and Hayabusa2, and obtain a global distribution of the boulders larger than 0.75–3 ​m, which corresponds to 1.5–6 pixels. We find that the boulder number density of this size range is smaller (1) on the western bulge than on the eastern hemisphere and (2) on the equatorial ridge than on the higher latitudes, both of which exceed the number density of boulders ​> ​5 ​m by an order of magnitude. The boulder size distribution at 1.25–20 ​m shows that the boulders smaller than 1 ​m are more abundant at the equator than at mid-latitudes, while those larger than 1 ​m in diameter are more abundant at mid-latitudes than at the equator. This contrast suggests size-dependent migration of boulders in the latitudinal direction. We also find that the typical boulder size (the size reaching the cumulative areal coverage of 50%) is 1.9 ​m at the equatorial region (10°S-10°N) while it is 2.6 ​m at mid-latitudes (40°S-50°S, 40°N-50°N). The typical boulder size is also smaller in the western bulge (2.0–2.2 ​m). We construct global maps of the power-law index of the size frequency distribution of boulders and find minor variations over the entire surface of Ryugu (−2.53 ​± ​0.03) for boulders larger than 1.25 ​m. This small variation suggests homogeneous size sorting processes on Ryugu. Surface roughness does not show a significant correlation with the v-band albedo but shows a high anti-correlation (R ​= ​−0.73) with the current geological slope on the eastern hemisphere. Our method is useful enhancement of smooth area detection and boulder distribution characterization that will be applicable to other planetary explorations in the future, including those of Phobos and other asteroids.

Inversion of topographic evolution using low-T thermal history: A case study from coastal mountain system in Southeastern China

The topographic evolution of a mountain system provides key information for understanding surface processes. We present a new and relatively simple method to reconstruct two-dimensional paleotopography composed of two steps: (1) construction of thermal history using low-temperature thermochronological data and (2) conversion of the thermal history into topographic evolution. A new computer program “Low-T Topo” was developed to perform the suggested conversion of thermal history to paleotopography. This approach, when applied to the coastal mountain system (CMS) in Southeastern China, suggests an uneven topographic evolution along the Changting-Zhangzhou section since the Late Cretaceous. According to our modeling, the SE segment of the section was higher (maximum peak elevation = ~3.8 km) than the NW segment (~3.4 km) during ~80–50 Ma. The modeling also suggests that both the SE and NW segments experienced an initially higher exhumation rate of ~0.14 km/Myr at 80–70 Ma, which steadily decreased to about 0.03 km/Myr at 40 Ma. Since then, exhumation rates stayed relatively low (≤~0.05 km/Myr). The elevation reduction in the CMS since the Late Cretaceous played an important role introducing the warm and humid Pacific air to the inland.

Applying stable cosmogenic 21Ne to understand surface processes in deep geological time (107–108 yr)

This work sets out to test the applicability of stable cosmogenic 21Ne for quantifying the rates of surface processes over time scales of 107–108 yr and the potential limitations and pitfalls associated with such time spans. First, we examine several processes in addition to in-situ production during exposure that affect the final measured concentration of 21Ne. We calculate the magnitude of 21Ne produced by interaction with secondary cosmic ray particles after burial (muogenic Ne) and by non-cosmogenic sources (nucleogenic Ne). We also evaluate the fraction of 21Ne lost through diffusion out of the quartz crystal as a function of time and temperature (depth). We then apply our calculations to 21Ne concentrations measured in sediments that were deposited along the northern passive margin of Gondwana during the late Precambrian, Cambrian, and Lower Cretaceous. In light of the measured concentrations in the sediment samples, we discuss the limitations imposed by our calculations and show that 21Ne concentrations measured in Lower Cretaceous samples can be interpreted in terms of surface exposure times or average erosion rates during the time of erosion and transport. In contrast, concentrations measured in Cambrian and Precambrian samples are limited in their use as surface process indicators although they still yield valuable geological information. We conclude that this novel application of in situ stable cosmogenic nuclides holds the potential as a tool for quantifying surface processes and understanding landscape evolution during the deep geological past and provides insight into macro-scale processes that have shaped Earth over the past hundreds of millions of years.

Addressing uncertainties in interpreting soil surface changes by multitemporal high‐resolution topography data across scales

AbstractExtensive amounts of water erosion combined with the magnitude of on‐site and off‐site impacts have led to considerable reduction in soil fertility and increased production costs in agriculture. Digital elevation models are a useful and established tool to better understand surface processes and to quantify damages. Ongoing developments in camera‐based 3D reconstruction allow non‐expert users to produce high‐quality elevation models. Multitemporal surveys allow geomorphic change detection serving as a valuable tool for geomorphologists and erosion researchers. Despite various benefits, these recent developments are accompanied by novel challenges in the form of small‐scale nonerosive surface processes (e.g., swelling/shrinking, consolidation/compaction, and aggregate breakdown). If neglected, these alterations can sum up to distinct errors in soil loss quantification.However, as yet, there have been no studies discussing their influence on surface data sets in erosion research. We present an across‐scales approach of visualising and quantifying detailed soil physical changes and their influence on surface morphology at submillimetre resolution.The data sets were acquired at field scale from an unmanned airborne vehicle, at plot scale during an artificial rainfall simulation on an agricultural site, and at microplot scale in a laboratory set‐up. Resulting high‐precision data sets enable the desired insights in soil movements and surface alterations without preceding particle transport and soil loss. Surface changes sum up to 260 m3/ha on an Andalusian test site and could be falsely interpreted as soil loss (of 286 t/ha). These results recommend cautious interpretation of high‐resolution topography in soil erosion research.

Geomorphology of glaciated gorges in a granitic massif (Gredos range, central Spain)

ABSTRACTA detailed geomorphological map on a 1:10,000 scale is presented for a high mountain area in Gredos range (Iberian Central System). Only few detailed geomorphological maps of the range are available despite the wide diversity of landforms. The map was created with the aid of aerial photographs, satellite images, and 3D images and verified with field surveys. The landforms resulting were classified using the IGUL (Institute of Geography, University of Lausanne) legend system combined with the legend proposed by Peña et al. (1997). As a result, 40 landforms distributed over an area of 40 km2 have been identified. The map shows the spatial distribution of different geomorphological processes that have modeled a wide variety of landforms. This variety of processes and landforms identified demonstrated that geomorphological cartography obtained by combining traditional image interpretation and GIS technology facilitates the production of geomorphological maps and the obtaining of valuable data for identify and understand surface processes and landforms.

How does grid-resolution modulate the topographic expression of geomorphic processes?

Abstract. In many locations, our ability to study the processes which shape the Earth are greatly enhanced through the use of high-resolution digital topographic data. However, although the availability of such datasets has markedly increased in recent years, many locations of significant geomorphic interest still do not have high-resolution topographic data available. Here, we aim to constrain how well we can understand surface processes through topographic analysis performed on lower-resolution data. We generate digital elevation models from point clouds at a range of grid resolutions from 1 to 30 m, which covers the range of widely used data resolutions available globally, at three locations in the United States. Using these data, the relationship between curvature and grid resolution is explored, alongside the estimation of the hillslope sediment transport coefficient (D, in m2 yr−1) for each landscape. Curvature, and consequently D, values are shown to be generally insensitive to grid resolution, particularly in landscapes with broad hilltops and valleys. Curvature distributions, however, become increasingly condensed around the mean, and theoretical considerations suggest caution should be used when extracting curvature from landscapes with sharp ridges. The sensitivity of curvature and topographic gradient to grid resolution are also explored through analysis of one-dimensional approximations of curvature and gradient, providing a theoretical basis for the results generated using two-dimensional topographic data. Two methods of extracting channels from topographic data are tested. A geometric method of channel extraction that finds channels by detecting threshold values of planform curvature is shown to perform well at resolutions up to 30 m in all three landscapes. The landscape parameters of hillslope length and relief are both successfully extracted at the same range of resolutions. These parameters can be used to detect landscape transience and our results suggest that such work need not be confined to high-resolution topographic data. A synthesis of the results presented in this work indicates that although high-resolution (e.g., 1 m) topographic data do yield exciting possibilities for geomorphic research, many key parameters can be understood in lower-resolution data, given careful consideration of how analyses are performed.

HYDROLOGIC AND CRYOSPHERIC PROCESSES OBSERVED FROM SPACE

Abstract. Ten Dragon 3 projects deal with hydrologic and cryosphere processes, with a focus on the Himalayas and Qinghai – Tibet Plateau, but not limited to that. At the 1st Dragon 3 Progress Symposium in 2013 a significant potential for a better and deeper integration appeared very clearly and we worked out an overview of the ten projects identifying specific issues and objectives shared by at least two projects. At the Mid Term Symposium in 2014 a joint session was held over two days. As regards cryospheric processes science highlights covered: Glacier flow velocity by optical and SAR features tracking and InSAR; Patterns in space and time of glacier flow velocity; Mass change estimated with DTM-s and altimetry; Reflectance and LST used to classify glacier surface and understand surface processes, Inventory and changes in the number and area of lakes in the Qinghai – Tibet Plateau 1970, 1990, 2000 and 2010; Deformation of permafrost along the Qinghai – Tibet railway. Highlights on hydrologic processes included: Global comparison of SMOS, ASCAT and ERA soil moisture data products; Relative deviations evaluated by climate zone; Soil moisture data products improved with ancillary data; Assimilation of FY - , TRMM and GPM precipitation data products in WRF; Improved algorithm and data products on fractional snow cover; Improvement of MODIS ET with assimilation of LST; TRMM data products evaluated in the Yangtze; Calibration of river basin models using LST; System to calibrate, correct and normalize (spatial, spectral) data collected by imaging spectral radiometers; Integration of data acquired by different sensors, e.g. ET Monitor with optical and microwave (SMOS, FY – 3) data; Hydrological data products used both for forcing and evaluation of Qinghai – Tibet Plateau hydrological model; Wetlands vulnerability assessed through changes in land cover 1987 – 2013; Multi incidence angle and multi – temporal SAR to monitor water extent. In the general session a proposal for a Dragon Water Cycle Initiative was presented.

Palaeo-digital elevation models for use as boundary conditions in coupled ocean–atmosphere GCM experiments: a Maastrichtian (late Cretaceous) example

Abstract Palaeogeography (specifically palaeotopography and palaeobathymetry) provides an essential boundary condition for computer-based atmosphere and ocean modelling. It also provides the geographic context for understanding surface processes (palaeodrainage, palaeoweathering) and biotic interactions (palaeoecology, palaeobiogeography). With increased model resolution, coupled ocean–atmosphere general circulation models (GCMs) and the addition of vegetation, soil (weathering), ice and chemical modules, there is now a need for more robust, detailed palaeotopographies and palaeobathymetries that are fully integrated with the processes being modelled, especially the hydrological system. Here, we present a new geographic information system (GIS)-based, hydrologically correct, palaeo-digital elevation model (DEM) for the Maastrichtian (late Cretaceous). We describe the methods and concepts used to construct the map, and draw attention to the limits imposed by scale and uncertainty, and how these factors must be considered as part of the error analysis of derived model results. The underlying palaeogeography is one of a series of 27 global maps that represent the stages of the Cretaceous and sub-epochs of the Cenozoic. Each map is generated at a scale of 1:30 million in ArcView® GIS and ArcInfo™, using data from the lead author's own databases of lithologic, tectonic and fossil information, the lithologic databases of the Paleogeographic Atlas Project (The University of Chicago), a survey of published literature, and DSDP/ODP data. Interpretations of elevation are derived following the methods outlined in Ziegler et al. (Ziegler, A.M., Rowley, D.B., Lottes, A.L., Sahagian, D.L., Hulver, M.L., Gierlowski, T.C., 1985. Paleogeographic interpretation: with an example from the Mid-Cretaceous. Annual Review of Earth and Planetary Sciences, 13: 385–425), an understanding of the tectonic regime and evolution of each feature, and the age–depth relationship for the ocean. The global palaeo-DEM was derived using the elevation contours from the paleogeography and the suite of hydrological tools available in ArcInfo™ GRID. The palaeo-DEM has been constrained by defining areas of internal palaeodrainage, palaeoriver mouths and known palaeoriver courses. The Maastrichtian has been completed first to provide the boundary conditions for a series of coupled atmosphere–ocean experiments. When integrated with the results of the coupled ocean–atmosphere model, the result is a powerful tool for understanding surface processes and an important step towards the development of a continuous series representing a fully evolving palaeolandscape.

Palaeo-digital elevation models for use as boundary conditions in coupled ocean–atmosphere GCM experiments: a Maastrichtian (late Cretaceous) example

Palaeogeography (specifically palaeotopography and palaeobathymetry) provides an essential boundary condition for computer-based atmosphere and ocean modelling. It also provides the geographic context for understanding surface processes (palaeodrainage, palaeoweathering) and biotic interactions (palaeoecology, palaeobiogeography). With increased model resolution, coupled ocean–atmosphere general circulation models (GCMs) and the addition of vegetation, soil (weathering), ice and chemical modules, there is now a need for more robust, detailed palaeotopographies and palaeobathymetries that are fully integrated with the processes being modelled, especially the hydrological system. Here, we present a new geographic information system (GIS)-based, hydrologically correct, palaeo-digital elevation model (DEM) for the Maastrichtian (late Cretaceous). We describe the methods and concepts used to construct the map, and draw attention to the limits imposed by scale and uncertainty, and how these factors must be considered as part of the error analysis of derived model results. The underlying palaeogeography is one of a series of 27 global maps that represent the stages of the Cretaceous and sub-epochs of the Cenozoic. Each map is generated at a scale of 1:30 million in ArcView® GIS and ArcInfo™, using data from the lead author's own databases of lithologic, tectonic and fossil information, the lithologic databases of the Paleogeographic Atlas Project (The University of Chicago), a survey of published literature, and DSDP/ODP data. Interpretations of elevation are derived following the methods outlined in Ziegler et al. (Ziegler, A.M., Rowley, D.B., Lottes, A.L., Sahagian, D.L., Hulver, M.L., Gierlowski, T.C., 1985. Paleogeographic interpretation: with an example from the Mid-Cretaceous. Annual Review of Earth and Planetary Sciences, 13: 385–425), an understanding of the tectonic regime and evolution of each feature, and the age–depth relationship for the ocean. The global palaeo-DEM was derived using the elevation contours from the paleogeography and the suite of hydrological tools available in ArcInfo™ GRID. The palaeo-DEM has been constrained by defining areas of internal palaeodrainage, palaeoriver mouths and known palaeoriver courses. The Maastrichtian has been completed first to provide the boundary conditions for a series of coupled atmosphere–ocean experiments. When integrated with the results of the coupled ocean–atmosphere model, the result is a powerful tool for understanding surface processes and an important step towards the development of a continuous series representing a fully evolving palaeolandscape.

Profiles of in situ 10Be and 26Al at great depths at the Macraes Flat, East Otago, New Zealand

The production of cosmic ray-produced 10Be and 26Al in vein quartz was investigated from near the surface to 49,300 g cm −2 depth at three locations in Macraes gold mine, East Otago, New Zealand. The measured 26Al/ 10Be ratios are dependent on depth, which indicates that the production mechanisms of these nuclides change with depth. The transition from neutron-induced production to muon-induced production was observed at about 1000 g cm −2. The measured attenuation lengths of 10Be and 26Al from the surface down to 400 g cm −2 of this study are much larger than steady state apparent neutron attenuation length at near surface. The large measured attenuation lengths at shallow depths could be caused by deep erosion, which results in a large muon contribution to the production of the isotopes at all depths. Using revised production rates, the average model surface exposure age of the Macraes Flat was determined to be 25.0±3.3 kyr. The erosion rate of the sampling site was estimated to be at least 12 m Myr −1 using the depth profiles of 10Be and 26Al of this study. Production systematics below ∼5000 g cm −2 are poorly known, and a model is proposed for those depths. We emphasize the importance of using depth profiles of cosmogenic nuclides in understanding surface processes and past geological histories.

Sources of nonlinearity and complexity in geomorphic systems

Nonlinearity is common in geomorphology, though not present or relevant in every geomorphic problem. It is often ignored, sometimes to the detriment of understanding surface processes and landforms. Nonlinearity opens up possibilities for complex behavior that are not possible in linear systems, though not all nonlinear systems are complex. Complex nonlinear dynamics have been documented in a number of geomorphic systems, thus nonlinear complexity is a characteristic of real-world landscapes, not just models. In at least some cases complex nonlinear dynamics can be directly linked to specific geomorphic processes and controls. Nonlinear complexities pose obstacles for some aspects of prediction in geomorphology, but provide opportunities and tools to enhance predictability in other respects. Methods and theories based on or grounded in complex nonlinear dynamics are useful to geomorphologists. These nonlinear frameworks can explain some phenomena not otherwise explained, provide better or more appropriate analytical tools, improve the interpretation of historical evidence and usefully inform modeling, experimental design, landscape management and environmental policy. It is also clear that no nonlinear formalism (and, as of yet, no other formalism) provides a universal meta-explanation for geomorphology. The sources of nonlinearity in geomorphic systems largely represent well-known geomorphic processes, controls and relationships that can be readily observed. A typology is presented, including thresholds, storage effects, saturation and depletion, self-reinforcing feedback, self-limiting processes, competitive feedbacks, multiple modes of adjustment, self-organization and hysteresis.

New developments in the surface science approach to catalysis

The rigour and wide ranging power of experimental surface science techniques developed in recent years has transformed our ability to understand surface processes. In this brief but broad ranging review, these developments are illustrated with examples of new results in: structure determination; calorimetric measurements of adsorption heats; kinetics and dynamics of adsorption and surface catalysed reactions; and the control of surface reactions.