Terrace Surfaces Research Articles

Afontova Gora II archaeological site: Geology and postdepositional deformation (Krasnoyarsk, Siberia)

The Afontova Gora II archaeological site located within two geologically and geomorphically different areas has been studied in terms of geology and Quaternary deposition history. Both areas lie upon alluvial terrace II of the Yensei River. At the time when terrace I alluvium was deposited, aeolian and slope-wash facies accumulated on the surface of terrace II and a slope-wash apron formed on the gently sloping surface of terrace III. It is at these different levels of the Yenisei River bank that the latest Paleolithic Afontov culture of Siberia has been found. At the Late Glacial-Holocene boundary, the slope-wash apron upon terrace III was involved in landsliding and thrust over terrace II, which deformed the subaerial deposits over both terraces II and III. As shown by detailed analysis, the landslide deposits are either strongly deformed to the degree of losing of their primary sedimentary textures and structures or form imbricated blocks with deformed margins but minor deformation in their interior. The preserved textures and structures of sediments inside the imbricated landslide blocks provide stratigraphic and genetic constraints and prove the in situ origin of anthropological, archaeological, and paleontological finds. This division also explains the archaeological sterility and abnormal thickness of the subaerial cover upon the landslide blocks.

The stratigraphy and chronology of the fluvial sediments at Warsash, UK: implications for the Palaeolithic archaeology of the River Test

This paper reports new fieldwork at Warsash which clarifies the terrace stratigraphic framework of the Palaeolithic archaeology of the region. Sections were recorded in former gravel pits and at coastal locations, supplemented by the use of ground penetrating radar and luminescence dating techniques. The region’s extensive borehole archive was also analysed to produce a revised terrace stratigraphy at Warsash and for the Test valley as a whole. At Warsash, some of the sediments previously identified as the Mottisfont/Lower Warsash Terrace are reassigned to the Hamble, Belbin/Upper Warsash and Ganger Wood/Mallards Moor Terraces. A luminescence dating programme, using test procedures not utilised in earlier dating studies in the region, yielded age estimates for the Hamble and Mottisfont/Lower Warsash Terraces at Warsash and also highlighted the complicated nature of the fluvial sediments of the River Test, suggesting that published luminescence ages for these deposits should be treated with some caution. This study indicates that the data used to construct terrace stratigraphies also requires careful assessment. The use of bedrock height and sediment thickness data produces more coherent long profile correlations than those produced by terrace surface data alone. The revised terrace stratigraphy provides the framework for the Palaeolithic archaeology at Warsash and clarifies correlations within and between archaeologically important sediments of the Test Valley, enabling it to contribute to discussions on the Lower-Middle Pleistocene settlement history of southern Britain.

Apparent Late Quaternary Fault‐Slip Rate Increase in the Southern Lower Rhine Graben, Central Europe

In regions of low strain, long earthquake recurrence intervals (104–106 yrs) and erosive processes limit preservation of Quaternary markers suitable for distinguishing whether faults slip at uniform or secularly varying rates. The Lower Rhine graben in the border region of Germany, The Netherlands, and Belgium provides a unique opportunity to explore Quaternary slip‐rate variations in a region of low strain using the basal (2.29±0.29 Ma) and surface (700±80 ka) contacts of the regionally extensive main terrace (“Hauptterrasse”), deposited by the Rhine and Maas Rivers. These surfaces are vertically offset 3–140 m and 0–68 m, respectively, across individual fault strands within a distributed network of northwest‐trending, slow‐slipping ( 80% of the sites record an apparent increase in slip rate for the more recent interval from 700 ka to present, which corresponds to a period of increased uplift of the nearby Rhenish Massif and regional volcanism. However, the apparent increase in slip rate could result, in part, from erosion of the footwall surface below the main terrace, leading to an apparent displacement that is smaller than the total vertical offset since the start of the Quaternary. Prior work focused on characterization of these faults as seismic sources in the Lower Rhine graben has preferentially relied on the average fault‐slip rate constrained using the base of the main terrace. We suggest that average fault‐slip rates calculated using the ∼700 ka main terrace surface are subjected to fewer uncertainties and sample a time interval that is more relevant for seismic‐hazard analysis. [Electronic Supplement:][1] Table of main terrace surface and basal contact offset measurements, figure describing an unrealistic faulting scenario, and a KML file with the fault‐trace mapping spanning the Lower Rhine graben. [1]: http://www.bssaonline.org/lookup/suppl/doi:10.1785/0120160197/-/DC1

Timing and process of river and lake terrace formation in the Kyrgyz Tien Shan

Well-preserved flights of river and lake terraces traverse an actively deforming rangefront, and form a link between glaciated mountains and a large intermontane lake in the Issyk-Kul basin of the Kyrgyz Tien Shan. We investigated the history and geometry of these lake and river terraces using geologic mapping, surveying, and radiocarbon and terrestrial cosmogenic nuclide dating. A prominent late Pleistocene highstand of the lake occurred over at least the period of 43–25 ka, followed by a period of deep regression and subsequent rise of the lake to the modern sill level in the late Holocene. Major aggradation of the most prominent latest Quaternary river terrace along the Ak-Terek and Barskaun rivers likely started at ∼70–60 ka, coincident to the local last glacial maximum in this region. In contrast to some models of aggradation and incision, the rivers appear to have stayed near the top of the fill for >20 ka, incising subtly below the top of this fill by ∼37 ka, locally. Deep incision likely did not occur until the peak deglaciation in the latest Pleistocene. Older dated terrace surfaces are consistent with one major terrace-forming event per glacial, constant deformation and incision rates, and typical fluvial gradients lower than the modern incising streams. The dating confirms regional terrace correlations for the most prominent late Quaternary terraces, but correlating higher terraces is complicated by spatially varying uplift rates and preferential terrace preservation between basins in the Tien Shan.

Active tectonics and geomorphology of the Gaenserndorf Terrace in the Central Vienna Basin (Austria)

In the central Vienna Basin, the area north of the River Danube is dominated by large river terraces consisting mainly of coarse sandy gravels and sand deposited by the Danube and the Morava River. IRSL dating for the terrace body yielded minimum ages from about 200 to 300 ka. The terrace deposits are locally covered with loess and aeolian sand of the last glacial period revealing OSL/IRSL ages of about 15 ka.The terraces are dissected by a system of normal faults. One of these faults, the Aderklaa-Bockfliess Fault, was investigated in 2014 by paleoseismological trenching. Eventually, the exact fault location and its vertical offset of 10 m were defined by combining electrical resistivity measurements and the analysis of remote sensing data.In addition, at the northern part of this so-called Gaenserndorf terrace, high-resolution digital terrain models based on LIDAR measurements show landforms comparable with relief features resulting from permafrost degradation. Large elongated and clam-shaped depressions are interpreted as basins of former thermokarst lakes. Current dry valleys are interpreted as the Pleistocene drainages of the terrace surface. The cryogenic morphology is preserved only in the elevated parts of the terrace and therefore in the footwall of the bounding normal faults. In contrast, Quaternary basins of the hanging wall are filled with up to 40 m thick Pleistocene and Holocene growth strata. Therefore, most characteristics of the recent geomorphology can be interpreted as a result of overlapping neotectonic processes and permafrost degeneration during the Pleistocene.

Scanning tunneling microscopy of the atomically smooth (001) surface of vanadium pentoxide V2O5 crystals

The (001) cleavage surface of vanadium pentoxide (V2O5) crystal has been studied by scanning tunneling spectroscopy (STM). It is shown that the surface is not reconstructed; the STM image allows geometric lattice parameters to be determined with high accuracy. The nanostructure formed on the (001) cleavage surface of crystal consists of atomically smooth steps with a height multiple of unit-cell parameter с = 4.37 A. The V2O5 crystal cleavages can be used as references in calibration of a scanning tunneling microscope under atmospheric conditions both along the (х, y) surface and normally to the sample surface (along the z axis). It is found that the terrace surface is not perfectly atomically smooth; its roughness is estimated to be ~0.5 A. This circumstance may introduce an additional error into the microscope calibration along the z coordinate.

Landscape Changes in the Southern Russian Plain in the Late Pleistocene: a Case Study of the Loess-Soil Sequence in the Azov Sea Region

Based on the complex studying 10 meter thick loess-soil sequence in the Beglitsa section (47°08° N, 38°31° E), the landscape and climate changes in the north-eastern Azov Sea Region in the Late Pleistocene were reconstructed. The intensity of loess accumulation decreased in the interglacial and interstadial conditions, when the soil-forming processes prevailed, and increased in cryoarid conditions of the glacial epoch, and especially, during the Late Valdai. As indicated by topography of palaeosoil horizons, loess layers of various ages envelope in sequence the primary fluvial (erosional-accumulative) relief. Loess accumulation resulted in general rise of the terrace surface. It preserved the major features of original topography but gradually smoothed the minor ones. During the entire Late Pleistocene the studied area belonged to the steppe zone. Participation of forbs in steppe communities, as well as the grass cover density, decreased in the cryoarid periglacial conditions and increased under warmer and less continental interstadial or interglacial climate. The role of intrazonal tree communities (pine forests with steppe elements, birch and alder wet forests) remained minor even in the most favorable climate of the Mikulino Interglacial, when the broad-leaved trees (mainly Quercus) participated in the forests. During the interstadial warm phases of the Valdai glacial epoch, the trees growing at present in the severe continental climatic conditions (Larix, Pinus sibirica) occurred in the region. As in the present time, near the shore of the Azov Sea, the areas with disturbed soil cover, including those with saline soil, were widespread due to abrasion, development of slumps and landslides, and erosion.

Magnetic Gradient Survey at the M. S. Roberts (41HE8) Site in Henderson County, Texas

The M. S. Roberts site is located in Henderson County, Texas and it represents one of the few known Caddo mound sites in the upper Neches River Basin in northeast Texas (Figure 1). The site is situated along Caddo Creek – an eastward-flowing tributary of the Neches River (Perttula et al. 2016; Perttula 2016; Perttula and Walters 2016). The site is located southeast of Athens, Texas. When first recorded, the single mound at the site was approximately 24 m long and 20 m wide and roughly 1.7 m in height (Pearce and Jackson 1931). Directly west of the mound was a large depression, which has since been mostly filled, and likely represents the borrow pit for mound fill. The mound is situated at the southern end of an elevated alluvial landform. The site was first reported to Dr. J. E. Pearce of the University of Texas in September 1931. In October of the same year, archaeologists from the University of Texas began investigating the mound and defining the extent of the associated settlement (Pearce and Jackson 1931). Researchers obtained a surface collection from the site and excavated an unknown number of trenches in the mound where portions of at least one burned and buried Caddo structure was identified. Their excavation notes document that the mound began as a 25 cm deposit of yellow sand constructed on the undisturbed brown sandy loam that defines the alluvial landform. A structure had been built on the yellow sand and then at some point had been burned. The burned structure was then covered with mound fill at least a meter in depth. Materials collected from the surface as part of the 1931 investigations indicate the presence of a Caddo habitation area surrounding the mound and suggest the site was occupied from the fourteenth to the early fifteenth centuries (Perttula et al. 2016; Perttula 2016; Perttula and Walters 2016). At that time, the landscape around the mound was a used as a cotton field and subject to extensive plowing. Today, the landscape is part of a residential ranch development where landowners are stewards of the site with a focus on preservation and research. In January 2015, with the permission of the landowners, renewed interested in the site began with a surface collection and the examination of the artifact collections from the 1931 work held by the Texas Archeological Research Laboratory (Perttula et al. 2016; Perttula 2016; Perttula and Walters 2016). A series of shovel tests and auger holes were then dug in the mound and surrounding habitation area in mid-2015. Shovel tests and auger holes documented organically-stained and charcoal-rich areas within the mound that were thought to represent the remains of several burned Caddo structures, and also identified non-mound habitation deposits at the site. An initial aerial survey was also conducted to map the landform topography, estimate the extent of the current mound dimensions and borrow pit, and to reconstruct changes in the shape and size of the mound since it was first recorded in 1931 (Perttula et al. 2016). The survey employed a small Unmanned Aerial Vehicle (UAV) to map the roughly 20-acre property surrounding the site at a 2 cm per pixel resolution. The aerial survey of the mound and surrounding landscape and the creation of a high-resolution digital elevation model reveal that the mound dimensions have changed significantly from what was reported in 1931 (Perttula et al. 2016). For example, aerial data document both the mound and borrow pit features and show that the mound measures 43 m North-South and 26 m East-West, and is roughly 1 meter above the surrounding terrace surface (Perttula et al. 2016). The aerial survey demonstrates that the mound has elongated over the last century since it was first recorded, likely related to historic landscape modification. In January 2016, the site was again revisited. The purpose of the fieldwork was to better define the spatial extent of archaeological deposits in the non-mounded habitation area and investigate the stratigraphy of mound deposits, identify cultural features in the mound, and hopefully obtain charred plant remains or unburned animal bones from these deposits for AMS dating. To help evaluate and identify the distribution of cultural features in the mound and the surrounding non-mounded habitation area, an area just over 1 hectare or 2.8 acres was surveyed using magnetic gradient and a second aerial survey was completed to refine the overall landscape topography (Figure 2). The magnetic gradient results document the subsurface location of at least two interpreted structures within the mound, the possible locations of three 1931 UT trenches, and several possible pit features proximate to the mound. The combination of aerial and geophysical data and the excavation results are revising our understanding of the archaeological remains and preservation conditions of the site.

Низькі тераси долини Стиру в середній частині Волинської височини

The paper focuses on the description of the low Pleistocene terraces (with the height of up to 20 m above the river level) of the Styr River valley that were identified in the middle part of the upland between Bilche–Krasne villages in the south and Boratyn–Pidhaitsi villages in the north. The main attention is concentrated on the mapping of the terraces and the overview of their outcrops as well as analysis of the boreholes data. The study of the geological structure of the terraces becomes the basis to determine their age. Mapping of river terraces was executed using topographic maps in scale 1:10 000. On the territory where previous researchers identified one or two terraces, we have identified five morphologically distinct cyclic (paired) terraces. The highest low terrace that is widespread territorially is named here the main terrace and the other four that are locally preserved are combined in a complex of minor low terraces. The level of the main Styr terrace has almost constant altitude of about 191–192 m. The average height of the terrace surface is gradually increasing downstream from 12–13 to 14–16 m above river level. Its surface is slightly undulating and complicated by relatively large isometric depressions with the diameter of up to 100 m and more. The slightly meandering forms similar to channels with the plan size comparable with the modern Styr channel occur on the terrace surface. The main terrace is relatively complicated and has mainly two-termed structure – the lower part of sedimentary sequence is composed of normal (perstrative) alluvium of large thickness; the upper part is composed of constrative alluvium accumulated when the river channel was laterally inactive. The terrace is overbuilt by a loess layer a few meters thick that covers floodplain alluvium without a distinct break in accumulation. Geological structure of the minor low terraces is relatively simple and recalls the floodplain structure. Absence of well-expressed paleosols in the alluvial and loess deposits of the low terraces suggests that they were formed during Late Pleniglacial (MIS 2). Key words: river terrace, alluvium, Late Pleistocene, Late Pleniglacial, Volhyn Upland, Styr River valley.

Лесові покриви на терасах нижньої течії Свічі

The Fore-Carpathians part of Svicha River valley partially covers Morshyn and Zalissia Uplands and Stryi-Zhydachiv depression. Within the Svicha and Sukil' river valleys, there are well-developed different-age terraces with thick stratified loess covers. The investigation of the last ones can help to define nomenclature and age of the terraces. The loess covers of the third (Kolodiiv) and the fourth (Mariampil) terraces, which are represented by Pidberezhzhia and Mizhrichchia sections accordingly, are characterised in detail in the article. Pidberezhzhia section represents a sequence of alluvial and covering deposits of the third (Kolodiiv) over-floodplain terrace of Svicha River, which is developed on its right bank. The terrace is stretched out in the form of a narrow (about 2 km) strip from the village Zarichchia to the village Novoselytsia. It is separated from the Svicha riverbed by the system of different-altitude floodplain levels and the first and second over-floodplain terraces. The boundaries between them are morphologically distinct, the exceeding of the surface of the Kolodiiv terrace above the water level in the riverbed of Svicha reaches 10 m or even more. Covering loess-soil series on the terrace has a capacity of more than 6 m and begins with the Horokhiv fossil soil complex. Mizhrichchia section represents the fourth (Mariampil) over-floodplain terrace, which to the north of Mizhrichchia village forms a scarp to the riverbed of the Svicha River, about 20 m in height. The terrace on this part of the valley of the river covers small areas and it is developed between the villages of Zarichchia and Mali Didushychi. Almost along its length, the terrace directly scarps to the riverbed. On the opposite side, where the rear seam is, it borders on the fifth (Galician) over-floodplain terrace, which forms a scarp about 10 m in height. Loess cover on the fourth terrace is up to 14 m thick. There are welldeveloped Dubno fossil soil (MIS 3) and Horokhiv fossil soil complex (MIS 5) and a thick sequence of hydromorphic deposits, which obviously correspond to the Korshiv fossil soil complex (MIS 7) in loesspaleosol series. The studied Pleistocene covers allow us to reliably identify Mariampil and Kolodiiv terraces of the Svicha River, as well as outline the nomenclature of the remaining terraces of the adjacent sections of the Zalissia and Morshyn Uplands and Stryi-Zhydachiv depression. Key words: river terrace, loess-soil covers, Dubno fossil soil, Horokhiv and Korshiv fossil soil complexes, Fore-Carpathians, Zalissia and Morshyn Uplands.

Exploring dynamic surface processes during silicate mineral (wollastonite) dissolution with liquid cell TEM.

Most liquid cell transmission electron microscopy (LC TEM) studies focus on nanoparticles or nanowires, in large part because the preparation and study of materials in this size range is straightforward. By contrast, this is not true for samples in the micrometre size range, in large part because of the difficulties associated with sample preparation starting from a 'bulk' material. There are also many advantages inherent to the study of micrometre-sized samples compared to their nanometre-sized counterparts. Here, we present a liquid cell transmission electron study that employed an innovative sample preparation technique using focused ion beam (FIB) milling to fabricate micrometre-sized electron transparent lamellae that were then welded to the liquid cell substrate. This technique, for which we have described in detail all of the fabrication steps, allows for samples having dimensions of several square micrometres to be observed by TEM in situ in a liquid. We applied this technique to test whether we could observe and measure in situ dissolution of a crystalline material called wollastonite, a calcium silicate mineral. More specifically, this study was used to observe and record surface dynamics associated with step and terrace edge movement, which are ultimately linked to the overall rate of dissolution. The wollastonite lamella underwent chemical reactions in pure deionized water at ambient temperature in a liquid cell with a 5-μm-spacer thickness. The movement of surface steps and terraces was measured periodically over a period of almost 5 h. Quite unexpectedly, the one-dimensional rates of retreat of these surface features were not constant, but changed over time. In addition, there were noticeable quantitative differences in retreat rates as a function crystallographic orientation, indicating that surface retreat is anisotropic. Several bulk rates of dissolution were also determined (1.6-4.2 • 10-7 mol m-2 s-1 ) using the rates of retreat of representative terraces and steps, and were found to be within one order of magnitude of dissolution rates in the literature based on aqueous chemistry data.

Comeback of epitaxial graphene for electronics: large-area growth of bilayer-free graphene on SiC

We present a new fabrication method for epitaxial graphene on SiC which enables the growth of ultra-smooth defect- and bilayer-free graphene sheets with an unprecedented reproducibility, a necessary prerequisite for wafer-scale fabrication of high quality graphene-based electronic devices. The inherent but unfavorable formation of high SiC surface terrace steps during high temperature sublimation growth is suppressed by rapid formation of the graphene buffer layer which stabilizes the SiC surface. The enhanced nucleation is enforced by decomposition of deposited polymer adsorbate which acts as a carbon source. Unique to this method are the conservation of mainly 0.25 and 0.5 nm high surface steps and the formation of bilayer-free graphene on an area only limited by the size of the sample. This makes the polymer-assisted sublimation growth technique a promising method for commercial wafer scale epitaxial graphene fabrication. The extraordinary electronic quality is evidenced by quantum resistance metrology at 4.2 K showing ultra-high precision and high electron mobility on mm scale devices comparable to state-of-the-art graphene.

Chronostratigraphic constraints on Middle Pleistocene faunal assemblages and Acheulian industries from the Cretone lacustrine basin, central Italy

ABSTRACTIntegrated40Ar/39Ar, trace‐element, stratigraphic, palaeontological and palaethnological data provide geochronological and biochronological constraints for the sedimentary and tectonic history of a Middle Pleistocene fluvial–lacustrine basin near Rome (Cretone Basin, central Italy), which has yielded a significant record of mammal fossil remains and Palaeolithic industry. This work is a case study of the interplay between tectonics and glacio‐eustacy, which strongly influenced the evolution of the Tyrrhenian Sea margin of central Italy. Dating of tephra layers interbedded within the Cretone Basin lacustrine succession and reconstruction of relict terraced surfaces allow correlation with similar, geochronologically constrained, marine isotopic stages (MIS) 15–5 terraced deposits along the coast. Coupled extensional tectonics and regional uplift over the last 600 ka caused the progressive uplifting and westward migration of the main fluvial–lacustrine basin and the formation of a smaller satellite basin at its eastern margin. Here, stable environmental conditions during MIS 13–5 indicated continuous human and large mammal frequentation, as testified by lithic industry and fossil remains ascribable to the Acheulean and later early Middle Palaeolithic technocomplexes and Galerian–Aurelian mammal faunas, respectively. In addition to providing independent age constraints to glacial sea‐level oscillations of this region, the reconstructed chronostratigraphic setting for the Cretone Basin provides evidence for one of the oldest Acheulean lithic assemblage of central Italy, as well as new biochronological and palaeobiogeographical data for some Middle Pleistocene mammal species of Italy.

A Two-Dimensional Supramolecular Carpet with Widely Uniform Interfacial Structure

Thin films composed of organic molecules are receiving much attention for their practical uses in various organic devices such as organic light-emitting diodes (OLEDs), organic thin film transistors (OTFTs), and organic photovoltaics (OPVs). Particularly, it has been recognized that interfaces between organic thin films and metal electrodes play crucial roles in operation characteristics of organic devices in recent years [1-3]. The interfaces between organic thin films and metal electrodes are where charge-carriers are injected into organic active layers, and various interactions at the interfaces (i.e., surface-molecule and intermolecular interactions) are of great importance in the formation of intermolecular networks and organic epitaxy which have a strong correlation with their electronic structures [1,3]. Both geometric and electronic structures of the interfaces between organic thin films and metal electrodes have profound effects on the performance of organic devices, and it is necessary to understand and control such interfacial structures for further development and enhancement of organic devices. Despite extensive studies, however, the formation of organic thin films with widely uniform interfacial structures on metal surfaces has been suffered from the limitation of molecular ordering imposed by irregular surface structures, due to the relatively weak intermolecular interactions between organic molecules compared to metallic, covalent, and coordinate bonds. Thus, a new approach is required to achieve the formation of widely uniform organic thin films without breaking structural integrity and to enhance the film uniformity. Here we demonstrate that well-balanced interfacial interactions, based on a careful design of the system, enable the formation of a two-dimensional supramolecular carpet with widely uniform interfacial structure and high adaptability on a metal surface, which can be extended over multiple surface steps and terraces without breaking structural integrity [4]. Strong intermolecular interactions in a planar fashion, symmetry of compounds, and localized surface-molecule interactions were considered in our strategies and principles of the system design. For this work, bis([1,2,5]thiadiazolo)-tetracyanoquinodimethane (BTDA-TCNQ) was used as a key element to form the two-dimensional supramolecular carpet [5], and its geometric and electronic structures were investigated using scanning tunneling microscopy and scanning tunneling spectroscopy under ultrahigh-vacuum conditions. Tetracyanoquinodimethane (TCNQ) is one of the strongest organic electron acceptors which is a widely used class in organic electronics, and it forms a strongly bonded donor-acceptor complex with tetrathiafulvalene (TTF). TCNQ and TTF are self-organized into ordered domains of the strongly bonded donor-acceptor complexes if TCNQ and TTF satisfy a 1:1 stoichiometry. Based on these molecular properties, we designed a model system of BTDA-TCNQ, which integrates both structural properties of TCNQ and TTF with a single molecule. The strong non-bonding intermolecular interactions induced by two electrostatically opposite symmetry axes of the molecule, balanced with surface-molecule interactions and site-specific rearrangements of the BTDA-TCNQ molecules near surface step edges, enables “seamless” growth mode for the formation of supramolecular carpet. It results in widely uniform interfacial structures covering over multiple surface steps and terraces even on the pre-annealed amorphous gold (Au) surface prepared on a glass substrate. In addition, the electronic structures projected onto the supramolecular carpet on the Au surface show different types and dimensionalities corresponding to the energy region and the local position of the system. These result suggest that the supramolecular carpet has great potential for applications in organic electronics, and also provide important guidelines to develop novel materials for seamless growth mode on various surfaces. [1] S. R. Forrest, Chem. Rev. 97, 1793 (1997). [2] H. Ishii, K. Sugiyama, E. Ito, and K. Seki, Adv. Mater. 11, 605 (1999). [3] D. E. Hooks, T. Fritz, and M. D. Ward, Adv. Mater. 13, 227 (2001). [4] J.-H. Kim, J.-C. Ribierre, Y. S. Yang, C. Adachi, M. Kawai, J. Jung, T. Fukushima, and Y. Kim, Nat. Commun. 7, 10653 (2016) [5] Y. Yamashita, T. Suzuku, T. Mukai, and G. Saito, J. Chem. Soc. Chem. Commun. 1985, 1044 (1985).

The mechanism of generating nanoporous Au by de-alloying amorphous alloys

De-alloying, i.e. selective dissolution of alloys, is currently studied to produce nanoporous gold items suited for use in catalysis, electrochemical applications, sensors and actuators. Both crystalline and amorphous alloys can be selectively etched. In the former, less noble atoms are removed from surface terraces of grains layer by layer, while noble ones form mounds. These evolve by undercutting and electrolyte percolation to form a ligament network. The mechanism of ligament development by de-alloying amorphous alloys is unknown. Here we show that for de-alloying a Au-based glass, in this case Au40Cu28Ag7Pd5Si20, percolation of the electrolyte through cracks of the native surface oxide initiates the formation of protuberances which are soon undercut. An interlayer develops, where Au crystals germinate, grow to nanometer size by diffusion and impinge. This is how ligaments start to coarsen. The interlayer is found at all stages between coarsened ligaments and amorphous phase. The ligaments are defective polycrystals, as opposed to single crystals obtained from crystalline alloys.

Morphotectonic control on Quaternary sedimentation and landscape evolution, Pachham Island, Kachchh, Western India

Pachham Island is the westernmost island in a chain of four rocky islands within the Great Rann of Kachchh that are bounded in the north by the Island Belt Fault (IBF). The island is characterized by two parallel and structurally controlled Kaladungar hill range and Goradungar hill range separated by a synclinal central valley. The central valley has acted as a sink for the Quaternary sediments. The island is transversely traversed by a N-S trending basement high termed as Median high that shows pronounced geomorphic and drainage anomaly. The Quaternary sediments comprise coarse-grained colluvio-fluvial deposits, miliolite, and sandy alluvium. The coarse-grained Quaternary deposits were primarily derived from the colluvium generated due to the uplift of the Kaladungar hill range and Goradungar hill range along the IBF and Goradunagar Fault, respectively. The colluvial debris were subsequently reworked, transported down slope and deposited in the central valley. The presence of the deeply incised valleys in Quaternary sediments, two levels of terrace surfaces over the Median high, and the raised Rann floor surrounding the island suggest a dominant role of neotectonics in the landscape evolution and Quaternary sedimentation.

Trace element-mineral associations in modern and ancient iron terraces in acid drainage environments

Iron-rich sediments commonly cover riverbeds that have been affected by acid drainage associated with sulfide-mineral oxidation. Freshly-formed precipitates correspond to poorly-crystalline oxyhydroxysulfates that recrystallize over time. This study examined the distribution and mineral association of trace elements (e.g., As, Cu, Zn) in modern and ancient (~6Ma) Fe terraces in the Tinto river basin, Spain. The mineral composition of the terraces was determined by Raman μ-spectroscopy. Chemical digestions, electron probe microanalyses, and synchrotron-based μ-X-ray fluorescence mapping were used to examine As, Cu, and Zn distribution and corresponding mineral associations. Fresh precipitates at modern terrace surfaces were dominated by schwertmannite, which contained high As, Cu, Mn, and Zn concentrations. However, schwertmannite transforms into goethite over days to weeks in the deeper part of the current terraces and into hematite over centuries. Affinity for trace elements was generally highest for schwertmannite and lowest for hematite, which suggests that their retention by Fe terraces decreases during mineral transformation. Hence, schwertmannite acts as temporary sink for contaminants, which are again released over long time periods. These findings should be considered for management and treatment of possible water resources affected by acid mine drainage.

In situ SEM/STM observations and growth control of monolayer graphene on SiC (0001) wide terraces

Thermal decomposition of silicon carbide (SiC) is frequently used for the formation of graphene on semi‐insulating substrates, but the growth mechanism is not well understood and thus the method to form monolayer graphene with larger domain size especially on step‐free or wide terrace surfaces is not known. In this work, various stages of graphene growth on SiC (0001) during annealing at 1‐atm‐Ar atmosphere were observed by in situ scanning electron microscopy and scanning tunneling microscopy. We found that a prolonged heating at 1550 °C over 1 h brought about the growth of monolayer graphene, starting from step edges and continuously across the whole terrace without pit formation. Monolayer graphene with the domain size over 3 µm was fabricated on wide terraces, which covered more than 90% areas of the sample surfaces. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of coordination number of Au catalyst on oxygen species and their catalytic roles

To explore the effects of coordination number of Au nanoparticles on oxygen species and their catalytic roles is very important in gold catalysis. Based on the systematic study of oxygen adsorption on Au(997) by density functional theory calculation, the quantitative correlation for different oxygen species with coverage and Au coordination number is established in theory. The only O adatoms near step area with relatively low Au coordination numbers exist at low coverage (<1/18ML), O adatoms adsorb at terrace areas with relatively high Au coordination numbers at medium coverage (1/18–2/9ML); while oxygen islands form at high coverage (>2/9ML). The theoretical predictions are in good agreement with the experimental observations in TDS spectrum. On the basis of Langmuir-Hinschelwood and Eley-Rideal mechanisms for NO oxidation, the activities of the three different oxygen species also exhibit correlation with Au coordination number. The oxygen island shows the highest oxidation activity, followed by the O adatom at terrace surface; while the O adatom near step area has the lowest oxidative performance. This work will shed light into the understanding of gold catalysis.

Ab initio study of interaction between 3d adatoms on the vicinal Cu(111) surface

Density functional theory is used to resolve the adatom-step and adatom–adatom interactions on vicinal Cu(111) surface. We demonstrated that the interactions between 3d adatoms appreciably depend on the distance from a surface step. Our calculations show that the magnitude of the repulsive barrier related to the surface step is larger for 3d adatoms located at the upper surface terrace than for adatoms located at the lower surface terrace.