Terrace Surfaces Research Articles

Thermodynamics and Kinetics of SiC CVD Epitaxy

One of the challenges in modeling epitaxial growth is to establish a connection between the experimental conditions and microstructure and epitaxial quality of the films. At the core of this problem is the need to have accurate models of the heterogeneous chemistry during epitaxy that can bridge reactor scale with atomic scale simulations and take into account the impact of film microstructure. In this work we focus on the heterogeneous chemistry models for SiC epitaxy by CVD. First, we carry out a sensitivity analysis of existing models in the literature, and we identify their limitations as well as the main reaction pathways that can be found at different experimental conditions. We then cast these models in the context of the step-flow growth. This allow us to rationalize the expected dependence of the different sticking probability values on the miscut angle and, more generally, on the surface terrace to step site ratio. Finally we show how these models can be used to bridge reactor-scale and atomistic simulations by providing sticking probabilities that depend on the surface morphology and the atomistic details of gas-surface interaction.

A new landscape metric for the identification of terraced sites: The Slope Local Length of Auto-Correlation (SLLAC)

This work presents the potential for high-resolution remote sensing data (LiDAR digital terrain models) to determine the spatial heterogeneity of terraced landscapes. The study objective is achieved through the identification of a new parameter that distinguishes this unique landscape form from more natural land formations. The morphological indicator proposed is called the Slope Local Length of Auto-Correlation (SLLAC), and it is derived from the local analysis of slope self-similarity. The SLACC is obtained over two steps: (i) calculating the correlation between a slope patch and a defined surrounding area and (ii) identifying the characteristic length of correlation for each neighbourhood. The SLLAC map texture can be measured using a surface metrology metric called the second derivative of peaks, or Spc. For the present study, we tested the algorithm for two types of landscapes: a Mediterranean and an Alpine one. The research method involved an examination of both real LiDAR DTMs and simulated ones, in which it was possible to control terrace shapes and the percentage of area covered by terraces. The results indicate that SLLAC maps exhibit a random aspect for natural surfaces. In contrast, terraced landscapes demonstrate a higher degree of order, and this behaviour is independent of the morphological context and terracing system. The outcomes of this work also prove that Spc values decrease as the area of terraced surfaces increases within the investigated region: the Spc for terraced areas is significantly different from the Spc of a natural landscape. In areas of smooth natural morphology, the Spc identifies terraced areas with a 20% minimum height range covered in terraces. In contrast, in areas of steep morphologies and vertical cliffs, the algorithm performs well when terraces cover at least 50% of the investigated surface. Given the increasing importance of terraced landscapes, the proposed procedure offers a significant and promising tool for the exploration of spatial heterogeneity in terraced sites.

Threefold atmospheric-pressure annealing for suppressing graphene nucleation on copper in chemical vapor deposition

Chemical vapor deposition (CVD) is a promising method of producing a large single-crystal graphene on a catalyst, especially on copper (Cu), and a further increase in domain size is desirable for electro/optic applications. Here, we report on threefold atmospheric-pressure (ATM) annealing for suppressing graphene nucleation in atmospheric CVD. Threefold ATM annealing formed a step and terrace surface of the underlying Cu, in contrast to ATM annealing. Atomic force microscopy and Auger electron mapping revealed that Si-containing particles existed on threefold-ATM- and ATM-annealed surfaces; particles on Cu had a lower density after threefold ATM annealing than after ATM annealing. The formation of a step and terrace surface and the lower density of particles following the threefold ATM annealing would play a role in reducing graphene nucleation. By combining threefold ATM annealing and electropolishing of Cu, the nucleation of graphene was effectively suppressed, and a submillimeter-sized hexagonal single-crystal graphene was successfully obtained.

Modifying Oxide Single Crystal Surfaces to Study Photoinduced Electron Transfer

Single crystal oxide semiconductor electrodes provide an ideal experimental system for the elucidation of the models and parameters that control light absorption, charge separation, and transport at semiconductor/liquid interfaces. Such fundamental investigations can prove very valuable in the understanding of dye sensitized nanocrystalline solar cells. The single crystal experimental system is much less complex than its nanocrystalline counterpart and the study of well-defined crystallographic surfaces allows for more definitive conclusions to be made concerning the relation between sensitizer attachment and surface structure and the sensitizer’s performance. I will report recent work on the sensitization of low index faces of both anatase and rutile forms of TiO2 and ZnO single crystals with dyes, quantum dots and polymers. We employ atomic force microscopy (AFM) to verify that atomically flat terraced oxide surfaces are prepared and to elucidate the structure of the sensitizers adsorbed on these surfaces. Photocurrent spectroscopy and attenuated reflection spectroscopy are used to correlate the photocurrent response with the optical absorption of the sensitizing species and the relative electron injection efficiencies of for instance dye monomers and aggregates. We have also recently begun to grow homoepitaxial layers on both anatase and rutile using atomic layer deposition (ALD). These layers can have superior electronic properties compared to the substrate crystal and allows us to control the doping density in the near surface region. The primary focus of this talk will be on CdSe and PbS quantum dots as sensitizers. PbS quantum dots adsorbed on anatase (001) surfaces irradiated with light of >2.5 times their band gap have been shown to produce more than one injected electron per incident photon (1), a process known as carrier multiplication or multiple exciton generation (MEG). Harnessing MEG may result in more efficient solar conversion devices.1. Justin B. Sambur, Thomas Novet and B. A. Parkinson, “Multiple Exciton Collection in a Sensitized Photovoltaic System”, Science, 330, 63-66, (2010)

Chemical stabilization and improved thermal resilience of molecular arrangements: possible formation of a surface network of bonds by multiple pulse atomic layer deposition.

In this work, we make use of an atomic layer deposition (ALD) surface reaction based on trimethyl-aluminum (TMA) and water to modify O-H terminated self-assembled layers of octadecylphosphonic acid (OPA). The structural modifications were investigated by X-ray reflectivity, X-ray diffraction, and atomic force microscopy. We observed a significant improvement in the thermal stability of ALD-modified molecules, with the existence of a supramolecular packing structure up to 500 °C. Following the experimental observations, density functional theory (DFT) calculations indicate the possibility of formation of a covalent network with aluminum atoms connecting OPA molecules at terrace surfaces. Chemical stability is also achieved on top of such a composite surface, inhibiting further ALD oxide deposition. On the other hand, in the terrace edges, where the covalent array is discontinued, the chemical conditions allow for oxide growth. Analysis of the DFT results on band structure and density of states of modified OPA molecules suggests that besides the observed thermal resilience, the dielectric character of OPA layers is preserved. This new ALD-modified OPA composite is potentially suitable for applications such as dielectric layers in organic devices, where better thermal performance is required.

Definition and origin of the dune-field pattern at White Sands, New Mexico

Abstract A LiDAR-derived digital elevation model (DEM) of a representative portion of the White Sands Dune Field, New Mexico, allows for characterization of an unprecedented range of dune-field parameters and serves as a basis for pattern analysis. Dune-field parameters were measured and statistically analyzed for populations of dunes selected at random and occurring along transects. Populations sampled by these two different methods are comparable, but highlight the sensitivity of transect placement in a dune field that has pattern heterogeneity. Based upon coefficients of variation, pattern emerges at White Sands primarily because of a strong fabric of crestline orientation, and secondarily because of the regularity of spacing between dunes of similar shape as defined by sinuosity, height and length. Linear regression of dune parameters shows that dune geometric relationships vary primarily with crestline length, but there is little correlation between other parameters, including dune spacing and height. This result highlights the sensitivity of identifying topographic heterogeneity in a LiDAR-derived DEM, given that mean ratios conform to global averages. Stripping off the dunes in Matlab shows a terraced surface, which is interpreted to represent paleo-shorelines formed during relative still stands in the overall retreat of Lake Otero. Elevated bands of higher, more closely spaced dunes occur just leeward of the paleo-shorelines. A revised model for the White Sands Dune Field consists of the basinward progradation of successive dune-field segments. Each segment is associated with a paleo-shoreline, and consists of an upwind dune ridge, represented by the elevated bands, and a leeward dune field.

A paleo-seismological study of the Dauki fault at Jaflong, Sylhet, Bangladesh: Historical seismic events and an attempted rupture segmentation model

A paleo-seismological study was conducted at Jaflong, Sylhet, Bangladesh, which is on the eastern part of the Dauki fault. The geomorphology around Jaflong is divided into the Shillong Plateau, the foothills, the lower terraces, and the alluvial plain from north to south. Because the foothills and lower terraces are considered to be uplifted tectonically, an active fault is inferred to the south of the lower terraces. This fault, which branches from the Dauki fault as a foreland migration, is known as the Jaflong fault in this paper. The trench investigation was conducted at the southern edge of the lower terrace. The angular unconformity accompanied by folding, which is thought to be the top of the growth strata, was identified in the trench. An asymmetric anticline with a steep southern limb and gentle northern limb is inferred from the back-tilted lower terrace and the folding of the gravel layer parallel to the lower terrace surface. The timing of the seismic event which formed the folding and unconformity is dated to between AD 840 and 920.The trench investigation at Gabrakhari, on the western part of the Dauki fault, revealed that the Dauki fault ruptured in AD 1548 (Morino et al., 2011). Because the 1897 great Indian earthquake (M⩾8.0; Yeats et al., 1997) was caused by the rupture of the Dauki fault (Oldham, 1899), it is clear that the Dauki fault has ruptured three times in the past one thousand years. The timing of these seismic events coincides with that of the paleo-liquefactions confirmed on the Shillong Plateau. It is essential for the paleo-seismological study of the Dauki fault to determine the surface ruptures of the 1897 earthquake. The Dauki fault might be divided into four rupture segments, the western, central, eastern, and easternmost segments. The eastern and western segments ruptured in AD 840–920 and in 1548, respectively. The 1897 earthquake might have been caused by the rupture of the central segment.

Drainage migration and out of sequence thrusting in Bhalukpong, Western Arunachal Himalaya, India

In the foreland regions of the Western Arunachal Himalaya (WAH), geological studies along the Kameng river (between Tipi village and the Himalayan Frontal Thrust (HFT)) reveal four levels of unpaired terraces and a paired terrace. In WAH, wrench deformation of HFT zone resulted in a SE propagation of the Balipara anticline and it is suggested that the Mikir high basement controls its orientation. Ages of terrace surfaces from Siwaliks suggest that since the Late Pleistocene, Kameng River migrated at a rate varying between ∼7.5cm/yr in upper reaches and ∼13.5cm/yr towards northeast due to HFT related uplift. In the Brahmaputra plains, luminescence ages of abandoned paleochannel deposits suggest eastward shifting of the Kameng river at an average rate of ∼1m/yr. Field evidences between Bhalukpong and Tipi villages show Pliocene strath and Quaternary terrace surfaces, displaced by faults that do not correspond to the mapped faults in the foreland region. We interpret them as out-of-sequence thrusts (OOSTs). This is the first such report of OOST in the NE Himalaya. Presence of active OOST is inferred by similar age (∼1ka) and differing incision rates of the surface of same terrace (T2b) in adjacent locations. This suggests that OOSTs in the western Arunachal Siwalik are <1ka. Average slip rate and horizontal shortening rate on OOST during the Holocene, are calculated as ∼12mm/yr and 7mm/yr respectively. Thus any estimation of Holocene shortening in the Siwalik therefore, needs to incorporate slip along the OOSTs given that it accommodates a significant amount of N-S compression of the Himalayan fold-and-thrust belt. The reason for OOST in the WAH Siwalik foreland is discussed in terms of the critical wedge dynamics arising from erosion via tectonics-climate interaction. We estimate a minimum slip rate of Siwalik as ∼27mm/yr during the Holocene and suggest acceleration in shortening rates east of Bhutan.

Climatically controlled formation of river terraces in a tectonically active region along the southern piedmont of the Tian Shan, NW China

Combined tectonic uplift and Quaternary climate variability control the deposition and abandonment of terraces along the southern Tian Shan in northwest China. Several preserved terraces have been deformed by an actively growing anticline within the uplifted frontal thrust system of the southern Tian Shan. We combine geomorphic mapping, topographic surveys of the deformed terrace surfaces, 10Be terrestrial cosmogenic nuclide (TCN) depth profile dating, and optically stimulated luminescence (OSL) dating to develop a new chronology for the terraces along the Huangshui He since 550ka. Our in situ 10Be dating of fluvial gravels capping strath terraces suggests a relationship between the formation and abandonment of the terraces and glacial climate cycles since the middle-late Pleistocene. These data indicate that the formation of the four terraces occurred at ~550, ~ 430, ~ 350, and ~60ka. We suggest that episodes of aggradation were facilitated by high sediment supply during glacial periods, followed by subsequent incision that led to abandonment of these terraces during deglaciation. We also estimate that tectonically induced river incision may account for about 60–70% of the total incision. However, during the intervening time between 350ka and present, only one terrace was formed and preserved. We suggest that this record might be caused by a gradually decreasing uplift rate of the anticline through time and thus has influenced the preservation of terraces. Therefore, our results demonstrate the utility of chronologic records from southern Tian Shan for deconvolving the effects of tectonics and climate on fluvial incision.

Step Terrace Tuned Anisotropic Transport Properties of Highly Epitaxial LaBaCo2O5.5+δ Thin Films on Vicinal SrTiO3 Substrates

Highly epitaxial LaBaCo2O5.5+δ (LBCO) thin films were grown on different miscut (001) SrTiO3 substrates (miscut angle of 0.5°, 3.0°, and 5.0°) to study the substrate surface step terrace effect on the in-plane electrical transport properties. The microstructure studies by X-ray diffraction and transmission electron microscopy indicate that the as-grown films are A-site disordered cubic perovskite structures with the c-axis highly oriented along the film growth direction. The four-probe scanning tunneling microscopy (STM) studies show that the LBCO thin films grown on the vicinal SrTiO3 substrates have a typical semiconductor behavior with the substrate surface terrace step inducing anisotropic electronic transport properties. These results indicate that in highly epitaxial thin films the surface terrace step induced local strains can play an important role in controlling the electronic transport properties and the anisotropic nature.

A comparison of Quaternary soil chronosequences from the Ionian and Tyrrhenian coasts of Calabria, southern Italy: Rates of soil development and geomorphic dynamics

Soil development during the Quaternary was investigated, by comparing and integrating analytical datasets of three soil chronosequences developed on different terrace staircases along the Tyrrhenian (western) and Ionian (eastern) coasts of northern Calabria, southern Italy. Two of these soil chronosequences developed on early to late Pleistocene marine terraces in two sectors of the Praia area (western coast), whereas the third one developed on fluvial terraces in the Rossano area (eastern coast) spanning from middle to late Pleistocene ages, respectively. We present and discuss both novel results and already published data related to selected morphological, physical, chemical, mineralogical and SEM analyses from the two coastal sectors. We explored the effects of time on soil development, trying to unravel the role of soil-forming processes, parent material and geomorphic dynamics on direction and rates of pedogenesis. A complex nature of parent materials was indicated by the geochemical signature, coupling certain similarities with some heterogeneity between the two study sectors but also across single soil profiles, as a response to morphodynamic processes (soil reworking, aggradation, burial and/or erosion), in turn promoting soil ageing and/or rejuvenation. These processes and lithological discontinuities were also responsible for some data scattering from calculated soil chronofunctions for peculiar soil properties and pedogenic indices plotted against estimated soil ages. Among the main outcomes, good positive correlations were obtained for the (Fed–Feo)/Fet and Fed/Fet indices, weighted on the basis of total soil profile and single horizon thicknesses to minimize the effects of soil truncation by erosion processes. Our results confirm the reliability of these indices as soil development indicators. Moreover, they suggest that: (i) rates of soil development did not change significantly over ca. 100–800 ka, despite the cyclical alternation of Pleistocene climate changes; (ii) dominant soil-forming processes tend to minimize original differences of pedogenic substrata and local (pedo)climatic conditions through time. In addition, soil chronofunctions permitted to estimate the unknown age (the time range of soil development before burial, about 200 ky) of a buried soil profile in the Rossano area, not correlated to any terrace surface of known age. The occurrence of etched quartz grains in soils of different ages for the two study sectors clearly indicates different rates of silica dissolution in the Tyrrhenian and Ionian coasts of Calabria, promoted by different climatic and pedoenvironmental conditions.

Morphological and electronic properties of epitaxial graphene on SiC

We report on the structural and electronic properties of graphene grown on SiC by high-temperature sublimation. We have studied thickness uniformity of graphene grown on 4H–SiC (0001), 6H–SiC (0001), and 3C–SiC (111) substrates and investigated in detail graphene surface morphology and electronic properties. Differences in the thickness uniformity of the graphene layers on different SiC polytypes is related mainly to the minimization of the terrace surface energy during the step bunching process. It is also shown that a lower substrate surface roughness results in more uniform step bunching and consequently better quality of the grown graphene. We have compared the three SiC polytypes with a clear conclusion in favor of 3C–SiC. Localized lateral variations in the Fermi energy of graphene are mapped by scanning Kelvin probe microscopy. It is found that the overall single-layer graphene coverage depends strongly on the surface terrace width, where a more homogeneous coverage is favored by wider terraces. It is observed that the step distance is a dominating, factor in determining the unintentional doping of graphene from the SiC substrate. Microfocal spectroscopic ellipsometry mapping of the electronic properties and thickness of epitaxial graphene on 3C–SiC (111) is also reported. Growth of one monolayer graphene is demonstrated on both Si- and C-polarity of the 3C–SiC substrates and it is shown that large area homogeneous single monolayer graphene can be achieved on the Si-face substrates. Correlations between the number of graphene monolayers on one hand and the main transition associated with an exciton enhanced van Hove singularity at ~4.5eV and the free-charge carrier scattering time, on the other are established. It is shown that the interface structure on the Si- and C-polarity of the 3C–SiC (111) differs and has a determining role for the thickness and electronic properties homogeneity of the epitaxial graphene.

Archaeological sites on large river’s islands as records of Holocene climate and fluvial changes. A geomorphological case study in the Danube river section between Komárom and Paks, Hungary

The purpose of the research is the enhanced understanding of the Late Pleistocene and Holocene variability of fluvial dynamics affected by the climate changes in Hungary and its surrounding regions. The research area includes the islands of the Danube in the river section between Komarom and Paks, it spans 71 settlements. Two big islands: the Szentendre (55 km2) and Csepel Island (242 km2) are in the studied section of the Danube. In those islands there are also floodfree terrace surfaces (last glaciation) (Mari, L. 2002, Fiar S. 2004). Beside those large islands there are more than 50 smaller or formerly existing islands in the study area. The present studies focus on those islands, naturally in connection with the large islands and with the coastal areas along the river. The geomorphological study of the smaller and lower lying islands in large rivers offers a new, less applied aspect of fluvial dynamics. The advantage of the study of islands is that they react sensitively to environmental changes, while they are less affected by the geomorphological impact of areas lying beyond the river. The history of the islands intertwines with human history, while the period of the islands’ evolution may be paralleled with human history. Traces of human inhabitation and land use from Neolithic times can be found on their surfaces despite the fact that they have been always limitedly suitable for inhabitation due to the floods. Yet they were repeatedly inhabited or used in the past, therefore historical data are readily available.

Highly textured fresnoite thin films synthesized in situ by pulsed laser deposition with CO2 laser direct heating

Fresnoite Ba2TiSi2O8 (BTS) thin films were grown and crystallized in situ using pulsed laser deposition (PLD) with CO2 laser direct heating of the a-plane sapphire (1 1 0) substrates up to 1250 °C. Starting with 775 °C growth temperature, (0 0 1)- and (1 1 0)-textured BTS and BaTiO3 phases, respectively, could be assigned in the films, and the typical fern-like BTS crystallization patterns appear. For higher process temperatures of 1100 to 1250 °C, atomically smooth, terraced surface of the films was found, accompanied by crystalline high-temperature phases of Ba–Ti–Si oxides. HAADF micrographs taken in both scanning transmission electron microscopy and energy-dispersive x-ray spectrometry mode show details of morphology and elemental distribution inside the films and at the interface. To balance the inherent Si deficiency of the BTS films, growth from glassy BTS × 2 SiO2 and BTS × 2.5 SiO2 targets was considered as well. The latter targets are ideal for PLD since the employed glasses possess 100% of the theoretical density and are homogeneous at the atomic scale.

Inferring a Thrust-Related Earthquake History from Secondary Faulting: A Long Rupture Record of La Laja Fault, San Juan, Argentina

Research Article| December 17, 2013 Inferring a Thrust‐Related Earthquake History from Secondary Faulting: A Long Rupture Record of La Laja Fault, San Juan, Argentina Thomas K. Rockwell; Thomas K. Rockwell aDepartment of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, California 92182‐102 Search for other works by this author on: GSW Google Scholar Daniel E. Ragona; Daniel E. Ragona bBP p.l.c., 1 St James’s Square, London, SW1Y 4PD, United Kingdom Search for other works by this author on: GSW Google Scholar Andrew J. Meigs; Andrew J. Meigs cCollege of Earth, Ocean, and Atmospheric Sciences, 104 CEOAS Administration Hall, Oregon State University, Corvallis, Oregon 97331‐5506 Search for other works by this author on: GSW Google Scholar Lewis A. Owen; Lewis A. Owen dDepartment of Geology, University of Cincinnati, Cincinnati, Ohio 45221 Search for other works by this author on: GSW Google Scholar Carlos H. Costa; Carlos H. Costa eDepartamento de Geología, Universidad Nacional de San Luis, 5700 San Luis, Argentina Search for other works by this author on: GSW Google Scholar Emilio A. Ahumada Emilio A. Ahumada eDepartamento de Geología, Universidad Nacional de San Luis, 5700 San Luis, Argentina Search for other works by this author on: GSW Google Scholar Author and Article Information Thomas K. Rockwell aDepartment of Geological Sciences, San Diego State University, 5500 Campanile Drive, San Diego, California 92182‐102 Daniel E. Ragona bBP p.l.c., 1 St James’s Square, London, SW1Y 4PD, United Kingdom Andrew J. Meigs cCollege of Earth, Ocean, and Atmospheric Sciences, 104 CEOAS Administration Hall, Oregon State University, Corvallis, Oregon 97331‐5506 Lewis A. Owen dDepartment of Geology, University of Cincinnati, Cincinnati, Ohio 45221 Carlos H. Costa eDepartamento de Geología, Universidad Nacional de San Luis, 5700 San Luis, Argentina Emilio A. Ahumada eDepartamento de Geología, Universidad Nacional de San Luis, 5700 San Luis, Argentina Publisher: Seismological Society of America First Online: 14 Jul 2017 Online ISSN: 1943-3573 Print ISSN: 0037-1106 Bulletin of the Seismological Society of America (2014) 104 (1): 269–284. https://doi.org/10.1785/0120110080 Article history First Online: 14 Jul 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Thomas K. Rockwell, Daniel E. Ragona, Andrew J. Meigs, Lewis A. Owen, Carlos H. Costa, Emilio A. Ahumada; Inferring a Thrust‐Related Earthquake History from Secondary Faulting: A Long Rupture Record of La Laja Fault, San Juan, Argentina. Bulletin of the Seismological Society of America 2013;; 104 (1): 269–284. doi: https://doi.org/10.1785/0120110080 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of the Seismological Society of America Search Advanced Search Abstract Trenches excavated across the surface rupture of the 15 January 1944 Mw 7 San Juan, Argentina, earthquake show evidence for repeated rupture of La Laja fault in the late Pleistocene and Holocene. The 1944 rupture extended for about 7 km striking ∼N35°E, and dipping 42° E parallel to Neogene bedding, with a maximum east‐side‐up vertical displacement of 30 cm. We interpret nine discrete colluvial wedges, each capped by a soil, as evidence for nine surface ruptures in the past ∼32–35 ka. Our topographic profile of the T3 terrace surface projected across the fault suggests these nine events collectively produced ∼10.3 m of dip displacement. We used radiocarbon and optically stimulated luminescence dating to define the timing of past events, yielding an average recurrence interval of 3.9±0.3 ka. The average estimate for displacement per event is about 1.1 m, compared with the 0.5 m of dip slip that occurred in 1944. Using a fault‐related fold model that infers ∼28 m of shortening based on the axial surface migration for the T3 terrace, along with the ∼35 ka age of the terrace, yields a shortening rate of ∼0.8 mm/yr by the 1944 source thrust fault, which is about 20% of the Global Positioning System—constrained total shortening rate across the Precordillera. Using this shortening rate and an assumed fault dip of 30° implies a fault slip rate of about 1.1 mm/yr, which combined with the average recurrence interval, implies ∼4 m of average slip per event on the causative fault at depth.Online Material: Unit descriptions from the trenches, stepwise reconstruction from trench 1, and annotated photographs of the La Laja region. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

NEW OBSERVATIONS ON THE AGE AND CONTEXT OF SOANIAN TOOLS FOUND IN POST-URBAN HARAPPAN SITES AND ALONG WTH SE ASIAN TYPE TOOLS ON THE MID-HOLOCENE TERRACES IN THE NW SUB-HIMALAYAS

ABSTRACT Most of the alluvial fan surfaces in the northwestern sub-Himalayas were laid down during terminal Pleistocene to late mid-Holocene times and so were the cusp terraces of the streams cutting through Siwaliks and the joining perennial Himalayan rivers. Though the stone tools and other prehistoric artefacts found on a surface have to be younger than the age of that surface but in the absence of any dates, almost all the earlier workers in this region determined the chronology of lithic sites by mere speculations. We have recently made surface collections from almost 30 stream-terrace sites and alluvial fan surfaces in the sub-Himalayas and have excavated two in buried state, all were in dated contexts. We have observed that the Soanian type stone implements existed in the sub-Himalayas up to late mid-Holocene times. This inference is also confirmed by the discovery of such tools from post-Urban Harappan sites and also in association with Harappan potsherds on young terrace surfaces. The discovery of many new tool-types, especially the pitted cobbles and edge-ground lithic specimens known from the mid-Holocene sites elsewhere, especially of Southeast Asia, also hints at the influence of those lithic industries in this region. We briefly present here the lithic assemblages from five sites with new evidences and conclude that the Soanian and many new tool-types were in use in the northwestern sub-Himalayas until the late mid-Holocene times.

Late Quaternary uplift rate inferred from marine terraces, Shimokita Peninsula, northeastern Japan: A preliminary investigation of the buried shoreline angle

After estimating tectonic uplift rates along the northern part of the northeast Japan forearc (the overriding plate in the northeast Japan subduction zone) by mapping the elevation of the inner edges of marine terrace surfaces, we refined this estimate through elevation measurements of the buried shoreline angle beneath well-dated marine terrace surfaces, from which we could derive more accurate paleo-sea levels. The uplift rate initially inferred from the inner edge of marine terrace T4, correlated with marine isotope stage MIS 5e by tephrochronology, increases eastward from 0.11–0.22mky−1 around the backarc volcanic front to 0.17–0.32mky−1 in the forearc on the peninsula of Shiriyazaki. We refined the uplift rates for T4, on the basis of the shoreline angle elevation, from the reconstructed profile of the paleo-sea cliff and wave-cut platform on a rocky coast and the reconstructed profile of the swash zone sediments and terrace deposits on a sandy coast. The refined uplift rates were 0.14–0.25mky−1 on the rocky coast and 0.14–0.23mky−1 on the sandy coast, slightly slower than the rates we inferred from the height of T4 and about one-half to three-fourths of previously reported rates. By extrapolation from the example of the sandy coast, the refined uplift rate around the volcanic front was 0.09–0.18mky−1. The vertical deformation across the forearc of the Shimokita Peninsula since MIS 5e is possibly associated with regional isostatic uplift of 0.09–0.18mky−1 and anticlinal deformation by an offshore fault, interpreted from acoustic profiles, of 0.05–0.07mky−1.

Promotional Effect of Carbon on Fe Catalysts for Ammonia Decomposition: A Density Functional Theory Study

Density functional theory calculations have been performed to investigate the recombinative desorption of N on terraced Fe(100) and Fe(110) as well as stepped Fe(111) and Fe(211) surfaces. The results showed that the stepped surfaces, especially the Fe(111) surface, are more active than the terraced surfaces, which could be related to the presence of so-called C7 sites for the stepped surfaces. Carbon atoms were found to stabilize the thermodynamically unstable stepped surfaces to be the energetically favored facets and thus facilitate the preferential exposure. As these carbon atoms incorporated into the stepped surfaces in the form of surface or subsurface carbon, the activation energy for the recombinative desorption of N was lowered, which was mainly ascribed to the decrease in the d band center of surface Fe atoms. In addition, a relation between the electronic and structural properties of Fe catalysts in the absence or presence of carbon and ammonia decomposition activity was also correlated.

Adsorption of NO on Pd and Pd2 supported at the regular and defective CdO (0 0 1) surfaces: Density functional theory study

The adsorption of NO on Pd atoms and homonuclear transition metal dimers, Pd2, deposited on O2− and Fs sites of the CdO (001) surface was studied by density functional calculations and an embedded cluster model. Geometrical optimization of adsorption of the molecule NO on Pd/CdO and Pd2/CdO with different spin states at particular sites was conducted. Spin polarized calculations were performed, and the systems in the most stable spin states were determined. Spin quenching occurs for Pd2 complexes at the terrace and defective surfaces. Supported Pd2 stabilized the low spin states of the adsorbed metals in comparison with free Pd2. Although the interaction of Pd and Pd2 particles with Fs sites is much stronger than with regular O2− sites, the adsorption of NO is stronger on Pd2/CdO (O2−) than on Pd2/CdO (Fs) with low spin state. Nevertheless, the greater interaction of NOPd and NOPd2 at O2− sites increases the energy required to switch from high to low spin. The variations observed in the magnetic properties of the adsorbed species at the CdO (001) surface are correlated with the energy gaps of the frontier orbitals. The adsorption properties of NO were analyzed with reference to the natural bond orbital, charge transfer, band gaps, the total charge-density contours, and pairwise and non-pairwise additivity. The binding of NO precursor is dominated by the E(i)Pdx−NO pairwise additive components, and the role of the support was not restricted to the metal or the dimer.

Effect of Hydrogen for Preservation of Reconstructed Surfaces

It is well known that a smooth surface of Si wafers can be obtained by Si surface reconstruction via high-temperature annealing. However, there remains a possibility of smooth Si surfaces deteriorating by accidental oxidation (called reflow oxidation) during the unloading process, i.e., taking out Si wafers from a vertical furnace after high-temperature annealing. Therefore, we considered it important to investigate the atomic-scale effects of oxidation on surface steps and terraces on Si wafers during the unloading process. We examined the effect of unloading temperature on oxide formation on Si (100) and Si (110) surfaces. The change in surface roughness was also measured. Our results indicated a significant improvement in the root mean square values of the surface roughness of terraces on the reconstructed surface. Moreover, this improvement was dependent on the decrease in the oxidation layer thickness in the case of low-temperature unloading. Furthermore, for suppressing reflow oxidation, we replaced the injected Ar gas with H2 in the cooling process during high-temperature Ar annealing and evaluated the thickness of the reflow oxidation layer and surface structure of Si (100) and Si (110). H2 annealing during the cooling process resulted in the formation of H-terminated Si surfaces, and this formation effectively suppressed reflow oxidation. However, the H2 atmosphere also caused etching of the reconstructed Si surfaces. Atomic force microscopy measurements revealed that in spite of the etching, Si (100) and Si (110) surface roughness drastically decreased because of subsequent roughness variation, regarded as being caused by oxidation. In the case of Si (110), characteristic line oxidation was effectively suppressed, resulting in a smooth terrace-and-step structure. In summary, the obtained results suggested that our method is effective for restraining the increase in atomic-scale surface roughness due to oxidation.