Narrow Terraces Research Articles

Study on Functional Effectiveness of Soil and Water Conservation Measures in Rubber Plantations on Hainan Island

In rubber plantations, understory coverage is often disrupted by human activities, which increases the risk of soil erosion under intense rainfall typical of tropical islands. Evaluating the effectiveness of soil and water conservation measures (SWCMs) is crucial for effectively conserving subcanopy resources. This study focused on Hainan Island’s rubber plantations, where nine different SWCMs were implemented, and the runoff and sediment yield were monitored during the rainy season using runoff plots. Through correlation analysis, we identified the primary rainfall characteristic factors leading to soil and water loss on rubber plantation slopes. Path analysis was then used to quantify the impacts of these characteristic factors. The results showed that the SWCMs were significantly more effective in erosion reduction (68.55%) than in runoff reduction (58.95%). Of all the measures, comprehensive SWCMs proved most effective in controlling runoff (71.34%), followed by engineering SWCMs (62.03%) and biological SWCMs (43.51%). Comprehensive SWCMs were also found to be effective in erosion reduction, with a rate of 77.84%, surpassing engineering and biological SWCMs by 7.23% and 20.66%, respectively. Notably, the combination of narrow terraces, contour trenches, and grass planting was the most effective, achieving runoff-reduction rates of 80.94% and erosion-reduction rates of 85.27%. This combination is recommended as a primary prevention method. Rainfall and maximum 30-min intensity (I30) were identified as key variables affecting the efficacy of SWCMs, with rainfall positively correlating with runoff yield and I30 being more closely linked to sediment production. This study provides valuable insights for developing erosion control strategies for sloping garden lands in similar regions and lays theoretical foundations for future ecological restoration projects.

Effective removal of global tilt from atomically-resolved topography images of vicinal surfaces with narrow terraces

The main feature of vicinal surfaces of crystals characterized by the Miller indices (hhm) is rather small width (less than 10 nm) and substantially large length (more than 200 nm) of atomically-flat terraces. This makes difficult to apply standard methods of image processing and correct visualization of crystalline lattices at the terraces and multiatomic steps. Here we consider two procedures allowing us to minimize effects of both small-scale noise and global tilt of sample: (i) analysis of the difference of two Gaussian blurred images, and (ii) subtraction of the plane, whose parameters are determined by optimization of the histogram of the visible heights, from raw topography image. It is shown that both methods provide nondistorted images demonstrating atomic structures on vicinal Si(556) and Si(557) surfaces.

Variable downcanyon morphology controlling the recent activity of shelf-incised submarine canyons (Alboran Sea, western Mediterranean)

This research aims to distinguish genetic sedimentary processes building canyon geomorphological patterns and the factors driving different sedimentary activities in two nearby Mediterranean shelf-incised submarine canyons (Carchuna and Motril) that exhibit different degrees of incision on the narrow margin of the northern Alboran Sea.The straight Carchuna Canyon incises the shelf up to 200 m off the coastline and exhibit steep canyon walls featuring narrow terraces, muddy sands with high contents of organic matter along the thalweg, and transported shelf benthic foraminifera in distal settings. The Motril Canyon head is wider and incises the shelf edge, ca. 2 km off the coastline. It exhibits a sinuous morphology and less steep walls, wider terraces, and higher sedimentation rates with muddy sediments along the thalweg. In both canyons, cross-section relief, width, incision, and area decrease downslope, although these parameters increase locally.The downslope variations of geomorphological parameters are attributed to enhanced erosional/depositional processes promoted by tectonically controlled abrupt changes of the axial channel orientation. The degree of shelf incision, the location of the canyon heads in relation with the local sediment sources, and the seasonally variable hydrodynamic regimes determine the different degrees of recent canyon activity. The Motril Canyon is interpreted as a mature system that reflects episodic activity, collecting fine-grained sediments from the nearby Guadalfeo River. The Carchuna Canyon exhibits a youthful developmental stage whose activity is more continuous and involves sediment trapping of littoral cells and continuous downslope sand transport.

Enhancing microstructure and device performance of InGaN quantum dot micro-LEDs through substrate off-cut angle modulation

InGaN quantum dots (QDs) are regarded as a compelling candidate material for the fabrication of high-quality GaN-based micro-LEDs. In this work, to study the impact of a substrate structure on InGaN QDs and QD-based micro-LEDs, GaN-on-sapphire substrates with off-cut angles toward the a-axis of 0.2°, 0.4°, and 0.7° were utilized as templates for the fabrication of InGaN QDs and InGaN QDs-based micro-LEDs. Experimental results show that GaN template with 0.4° off-cut angle exhibits the narrowest terrace width and enables InGaN QDs to be higher and more uniform. The InGaN QD sample grown on 0.4° substrate has a very small wavelength shift of 2.5 nm with temperature increasing and owns the longest photoluminescence peak wavelength implying the highest In content. Furthermore, electroluminescence (EL) spectra demonstrate that QD-based micro-LED array has excellent wavelength stability under various injection currents, and the stability can be improved further on a GaN template with narrower terraces. The results indicate that altering the terrace width of GaN template is a feasible scheme for improving the properties of GaN-based micro-LEDs.

Manipulation of BiFeO3 nanostructure by substrate terrace morphology

Topological domain structures, such as vortex and center domain have been found in BiFeO3 nanoislands fabricated by self-assemble approaches, which exhibit great application potential in nonvolatile storage. However, how to control the self-assembled nanostructure during preparation process is still an open question. Here, we successfully grew BiFeO3 films with nano-stripe, nano-maze and dense nanoisland structures on LaAlO3 (001) substrate by pulsed laser deposition. We found the formation of different nanostructures is related to the terrace morphology of the substrate. Nano-stripe structure with strip domain and high conduction tail-to-tail domain wall preferred to form on wide terrace, nano-maze structure with three-fold or four-fold center-type domain usually form on bunched terrace, while dense nanoisland structure with two/three-fold domain preferred to from on the narrow or rough terrace LaAlO3 substrate. These findings provide guidance for manipulating the ferroelectric topological domain structure during film preparation process.

Soils of Agricultural Terraces on Clay Shales in the Mid-Mountain Zone of the Eastern Caucasus

The article considers the chemical properties and biological activity of soils of agricultural terraces on clay shales in the mid-mountain zone of the Eastern Caucasus. It is established that the area of terraced plots in the southern zone of Shale Dagestan is about 264 km2 of the territory. These soils are currently in a fallow state but represent a significant reserve of highly fertile erosion-resistant soils, the cultivation of which, unlike soils on consolidated rocks, is possible with the help of modern technology. The influence of slope exposure, steepness, terrace size, duration of the plowing period on the chemical properties and biological activity of soils has been studied. It is shown that for background soils outside the terracing zone, the slope exposure has a decisive influence. For terraced areas, the impact of exposure is less pronounced. The formation of a vertical terraced surface led to a change in the thermal regime, as a result of which the differences in chemical and microbiological properties of soils on the slopes of the northern and southern exposures became less pronounced. The leveling effect of terracing is most noticeable on relatively gentle slopes (12°–18°), where the width of the terraced canvas is greatest. On steep slopes (20°) with narrow terraces, the influence of slope exposure on soil properties remains. At the same time, factors such as the duration of soil functioning and the features of agricultural technology have no less significant impact on soil properties. The regularities of changes in soil properties within the body of any single terrace have been established. The most fertile area within one terrace is the instrument part, where the profile depth is greatest. As we approach the rear seam of the terrace, a natural decrease in a number of biological and chemical indicators is observed.

Modulation of the LaFeO3 film growth by the terrace width of SrTiO3 substrates

We have investigated the growth of polar LaFeO3 thin films on SrTiO3 (001) substrates with various terrace widths by pulsed laser deposition. It is found that the growth of LaFeO3 films undergoes a transition from a two-dimensional (2D) mode to a three-dimensional (3D) mode due to polarity compensation. Notably, however, the critical thickness of the growth mode transition from 2D to 3D can be modulated by the terrace width of the substrate, i.e., when the film is 30 monolayers thick, it becomes 3D growth on the substrates with narrow terrace width (∼100 nm) while it maintains 2D growth on those with wide terrace width (∼400 nm). Combined with dynamic and kinetic models, we have found that the modulation of the critical thickness from 2D to 3D is rationalized as a result of competition between the dynamic process and the kinetic process. These findings highlight the key influence of substrate surface morphology on the epitaxial growth of complex oxide films, shedding light on the construction of multifunctional artificial low-dimensional structures with polar stackings.

Israelite Plain, southwestern Australia, a siliciclastic, late Quaternary Coorong analogue, without dolomite

The Israelite Plain, a narrow terrace at the western edge of the Great Australian Bight, is characterised by a series of schizohaline, ephemeral lakes leeward of a marginal marine eolianite dune complex that has many similarities to the Coorong Coastal Plain (CCP). The late Pleistocene and Holocene sediments are a mixture of dominantly quartzose sand and lesser carbonate components. Paleolagoon to shallow marine MIS 5e, mollusc-rich quartzose deposits are capped by calcrete or karst and contain a biota similar to the well-documented, coeval Glanville Formation on the CCP. Holocene sands with minor carbonate are also lagoonal and resemble many modern Coorong Lagoon deposits. Both deposits are interpreted to reflect marine accumulation during sea-level highstands. Lakes today range from dry to water-filled with most floored by calcareous quartzose sand. Microbial influenced sedimentary structures in the form of pustular to laminated mats veneer lake margin bedrock and sediment. Carbonate minerals are mostly calcite with abundant accessory magnesium-calcite, aragonite and traces of magnesite, monohydrocalcite and halite. Gypsum is minor but ubiquitous and floors one of the smaller, marginal-marine lakes. Although having a similar evaporative climate and evidence of groundwater resurgence like Coorong lakes, there is no significant synsedimentary dolomite. This aspect is interpreted to reflect the narrow width of the plain, and the Mg-poor source of groundwater from the nearby karst Nullarbor Plain to the north. The Israelite Plain, together with other coeval, young successions marginal to the Southern Ocean under a semiarid climate now illustrate the depositional variations and early diagenetic differences that can occur in similar environments adjacent to a cool ocean. KEY POINTS The Israelite Plain is a narrow, marginal marine terrace covered by Quaternary, lagoonal, eolian to lacustrine, calcareous siliciclastic sands, similar to several other calcareous terraces along the southern Australia coast. The interpreted sediment ages are late Pleistocene stage MIS 5e with the deposit sporadically overlain by similar Holocene deposits. Most 14C age dates are suspicious because of interpreted diagenesis or MIS 5e age, whereas U/Th age dates appear correct or altered by diagenesis. Pleistocene biota is dominated by the bivalve Anadara trapezia, whereas Holocene deposits contain a varied array of cooler water molluscs. The carbonates are similar to those on the Coorong Coastal Plain but do not contain any dolomite likely because of climate and lack of Mg-groundwater flow.

Surface structure-sensitivity dependence and mechanistic study of the glucose electro-oxidation on Pt stepped surfaces in neutral solution (pH 7)

• Glucose electro-oxidation in neutral solution is a sensitive-structure reaction. • On Pt-[( n )(1 1 1)x(1 0 0)]: when n ≥ 9 , [1 0 0] steps favor more energetic reactions pathways. • As higher the [1 0 0] steps density on (1 1 1) terraces, lower is the catalytic activity. • On narrow (1 0 0) terraces, [1 1 1] steps conduce the reaction through less poisoned path. • [1 1 0] steps sites favor the CO L adsorption, especially as narrower as the surface is. The electro-oxidation of glucose (0.01 M) in a neutral solution phosphate buffer solution – pH ∼ 7 (0.1 M) is strongly sensitive to the surface structure. On surfaces containing (1 0 0) terraces domains the reaction occurs mainly into these sites due to their higher activity. Higher (1 1 1) step density into (1 0 0) terrace domains conducts the reaction through a less poisoned and energetic pathway because steps inhibit the cyclic carbonate formation. On surfaces containing (1 1 1) terrace sites, on large atom-wide terrace ( n ≥ 9 ) the reactivity of the (1 0 0) steps seems to be mainly associated to the anticipation of the formation of glucuronic acid and favor its oxidation to glucaric acid and/or xylonic acid + CO, that are more energetic reactions. On the other hand, when the step density is increased, the catalytic activity decreases as result of adsorption of intermediates and/products generated during the reaction on (1 0 0) steps. Lower and medium (1 1 0) density steps favor the adsorption of glucose on surfaces containing (1 1 1) terraces symmetry, but independently of the terrace step symmetry, as the (1 1 0) step density is increased the electrocatalytic activity is reduced because the reaction takes place through a more poisoned pathway, with the formation of a greater amount of species that adsorb strongly on the (1 1 0) sites and block the surface.

Evaluation of traditional rain-fed agricultural terraces for soil erosion control through UAV observation in the middle mountain of Nepal

The livelihood of most people in the mountainous region of Nepal depends on traditional farming practices. Farmers modify their lands by constructing narrow outward sloping terraces to control soil erosion in the mountain and hill of Nepal. However, preliminary observation reveals that farmers adopt different strategies to manage outward sloping terraces according to the amount of rainfall so as to avoid the impact from soil erosion due to excessive rainfall. Thus, this study aims to evaluate the effectiveness of the traditional practice of topographic management of outward sloping rain-fed terraces to control soil erosion. The study makes a comparative analysis of topographic values of terraces and the estimated rates of soil erosion in different rainfall regions. Topographic values were derived from high spatial resolution (20 cm) Digital Elevation Model (DEM) data acquired by Unmanned Aerial Vehicle (UAV). Revised Universal Soil Loss Equation (RUSLE) was used to estimate the rate of soil erosion based on this high-resolution DEM together with other required variables. The research revealed that the traditional practice of topographic modification is highly effective to control soil erosion, as no significant differences in the rates of soil erosion were found even though the amount of rainfall considerably varies at different sites.

Platinum Catalyst Degradation: Unusual Nucleation and Growth of Nanoislands

The longevity of a catalyst plays a crucial role for many industrial scale applications. Platinum is the best candidate to be used in electrochemical energy conversion systems due to its high activity. However, platinum catalysts degrade during fuel cell operation. The origin of this degradation, the loss of material, is very likely rooted in the roughening of the surface: the nucleation and growth of nanoislands [1, 2, 3, 4]. It is known that the extend of this roughening can be tuned by additives, change of the electrolyte pH, or operation within different potential windows [5, 6, 7]. In this work, we study the degradation of different platinum stepped surfaces under potential cycling to oxidative potentials. Interestingly, we quantify significantly less degradation on surfaces with narrower terraces: Ra(Pt(111)) > Ra(Pt(15 15 14)) > Ra(Pt(554)) > Ra(Pt(553)) > Ra(Pt(533)). We present here a model that explains this trend, in which steps act like sinks for both adatoms and vacancies, slowing down the nucleation and growth of the above mentioned nanoislands. We support our results, which were derived until now solely on electrochemical measurements, with in-operando Electrochemical Scanning Tunneling Microscopy (EC-STM) images.

In Situ/Operando STM of the Fischer–Tropsch Synthesis on a Co(101̅15) Surface─A Study to Bridge the Materials Gap between Single-Crystal Models and Supported Catalysts

Co(101̅15), a vicinal surface of the Co(0001) surface, has a similar density of steps as the supported Co catalysts used in the industrial Fischer–Tropsch synthesis. We have investigated whether this surface can serve as a model system to bridge the materials gap between single crystals and supported catalysts. Experiments on the Co(101̅15) surface were performed by scanning tunneling microscopy (STM) under in situ/operando conditions and by gas chromatography (GC) with the same sample under the same conditions. X-ray photoelectron spectroscopy (XPS) was used for postreaction surface analysis. In the experiments, 2:1 mixtures of H2 and CO (syngas) were applied at a total pressure of 950 mbar and at a sample temperature of 503 K. The morphology resolved by STM under these conditions showed long, narrow terraces as expected for the Co(101̅15) surface but also step bunching. GC showed the formation of C1 to C4 hydrocarbons in considerably higher amounts compared to reference experiments with a Co(0001) sample. The activity of the Co(101̅15) sample was higher than that of the Co(0001) sample by a factor approximately proportional to the density of atomic steps. It is concluded that atomic steps are the active sites on this highly stepped surface. An analysis of literature data of supported Co catalysts shows that the activities reported in the majority of these studies are comparable to those of the Co(101̅15) sample.

Atomistic mechanisms of the initial oxidation of stepped Cu3Au(100)

Alloy oxidation is complex and involves several critical processes that lack understanding on the atomic level. Here, we report an atomistic picture of the initial-stage oxidation of stepped ${\mathrm{Cu}}_{3}\mathrm{Au}(100)$ using a combination of surface science tools and modeling to illuminate the microscopic processes underlying oxygen-adsorption-induced structural and compositional changes. Pristine ${\mathrm{Cu}}_{3}\mathrm{Au}(100)$ consists of wide CuAu-terminated terraces and narrow Cu-terminated terraces separated by monatomic steps. Counterintuitive to the common expectations of the adsorbate-induced surface segregation of the more reactive alloy component, our observations demonstrate that the oxygen adsorption leads to the exfoliation of the outermost CuAu layer, thereby exposing the inner Cu plane to O attack. This occurs via the oxygen-assisted abstraction of Au and Cu atoms from step edges and CuAu terraces, which generates many Cu adatoms aggregating into Cu clusters and Au adatoms dissolving into the bulk. The oxygen adsorption onto fourfold hollow sites of the exposed Cu plane results in nucleation and growth of the $c(2\ifmmode\times\else\texttimes\fi{}2)\text{\ensuremath{-}}\mathrm{O}$ superstructure, which can be fit well by the Johnson-Mehl-Avrami-Kolmogorov theory with a site-saturated nucleation mechanism.

Syn‐rift sediment gravity flow deposition on a Late Jurassic fault‐terraced slope, northern North Sea

AbstractStructurally controlled bathymetry in rifts has a significant influence on sediment routing pathways and depositional architecture of sediment gravity flow deposits. In contrast to rift segments characterized by crustal‐scale half‐grabens, the tectono‐stratigraphic evolution of deep‐water rift domains characterised by distributed faulting on narrow fault terraces has received little attention. We use 3D broadband seismic data, calibrated by boreholes, from the Lomre and Uer terraces in the northern North Sea rift to investigate Late Jurassic syn‐rift sediment gravity flow systems on fault‐terraced slopes. The sediment gravity flow fairways were sourced from hinterland drainages via basin margin deltaic systems on the Horda Platform to the southeast. The deep‐water sedimentary systems evolve from initial, widespread submarine channelized lobe complexes, through submarine channels, to incised submarine canyons. This progressive confinement of the sediment gravity flow system was concomitant with progressive localization of strain onto the main terrace‐bounding faults. Although the normal fault network on the terraces has local impact on deep‐water sediment transport and the architecture of gravity flow deposits, it is the regional basin margin to rift axis gradient that dominantly controls deep‐water sediment routing. Furthermore, the gravity flow deposits on the Lomre and Uer terraces were predominantly sourced by rift margin deltaic systems, not from erosion of local uplifted footwall crests, emphasising the significance of hinterland catchments in the development of volumetrically significant deep‐water syn‐rift depositional systems.

Enhanced critical magnetic field for monoatomic-layer superconductor by Josephson junction steps

We have studied the monoatomic-layer superconductors formed on semiconducting substrates and investigated the role of steps in superconducting properties. In the present study we found that the steps of the Si(111)-\ensuremath{\surd}3\ifmmode\times\else\texttimes\fi{}\ensuremath{\surd}43 Pb reconstructed structure significantly disrupt the electronic states of the superconducting atomic layer and hold Josephson-like vortices under the out-of-plane magnetic field. Because of the strong decoupling, narrow terraces whose width is less than three times the coherence length behave like superconducting nano stripes and exhibit large critical field against the out-of-plane magnetic field. Since monolayer superconductors are intrinsically strong against in-plane magnetic field, superconducting materials highly tolerant against magnetic fields in all directions might be tailored by controlling the step arrangement in the atomic-layer superconductors.

Структурные свойства тонких пленок кристаллического топологического изолятора Pb-=SUB=-0.7-=/SUB=-Sn-=SUB=-0.3-=/SUB=-Te на Si(111)

In this work, the selection and optimization of technological growth parameters of thin Pb0.7Sn0.3Te layers up to 300 nm thick, grown on the Si(111) surface at temperatures of 230−400◦C by the method of molecular beam epitaxy was carried out. The surface morphology of the films was studied, and the epitaxial relations were determined. It was shown that, depending on the growth temperature, the surface morphology ranges from relatively narrow terraces to smooth micrometer-sized islands with monoatomic steps on their surface.

Seismic Site Condition of Mainland China from Geology

AbstractWe use geology as a proxy to produce a site condition map of mainland China for seismic hazard assessment. The geology is from a 1:1,000,000-scale digital database and a 1:2,500,000-scale Quaternary map. We use the lithological descriptions and ages to assign the site condition for each geologic unit. Published site condition data are used to evaluate our mapping results. Our results agree well for the strong-motion stations in Gansu–Sichuan area, except in the mountainous area. There, the mismatches are due to our geological map scales missing narrow river terrace deposits. Our results also match well in the Shandong and Beijing Plain areas, except in thin fluvial and alluvial deposits fringing bedrock mountains. Our site-response categories match well-published average VS–depth profiles from microzonation studies of 14 major urban areas.

Platinum additive impacts on vapor-liquid-solid growth chemical interface for high-quality SiC single crystal films

Pt additive to Si-based flux in the vapor-liquid-solid (VLS) process for 4H–SiC epitaxial films has been successful in suppressing the step bunching as well as in promoting the step-flow growth mode at growth temperatures much lower than 2000 °C, as evidenced by in situ laser microscope observation of a model solution growth chemical interface. As a result, the SiC film surface became remarkably flat, exhibiting well-regulated step-and-terrace structures with narrow terrace widths and straight step lines; the polytype of 4H–SiC was much more stabilized in the grown SiC films even at a growth temperature of 1250 °C. Furthermore, there is little concern about incorporation of Pt atoms as an impurity into the grown SiC films so that their Schottky junction properties are almost as excellent as those of 4H–SiC single crystals.

Step-edge guided growth of nanowires on three-fold symmetric vicinal Si(111) surfaces

Clean vicinal surfaces exhibit a stepped pattern due to the presence of narrow terraces formed on a clean surface. Therefore, this provides a platform for the aligned growth of nanowires. Using this type of surface as a template, we have grown nanowires of iron di-silicide, which are preferentially directed along the length of the terraces and are following the step-edges. These nanowires do not follow underlying three-fold symmetry of the substrate. We have thus shown two-fold symmetric growth on a three-fold symmetric surface, where diffusion barrier energy plays an important role in determining the shape of the islands. The orientations of nanowires are governed primarily by the presence of step-edges. However, the crystallographic symmetry properties of the underlying substrate have also played its role in controlling the nanowire orientation. The system was grown by molecular beam epitaxy and analysed by scanning tunneling microscopy.

Morphology of Palladium Thin Film Deposited on a Two-Dimensional Bilayer Aluminosilicate

The morphology of a thin palladium film deposited on bilayer Al0.35Si0.65O2/Ru(0001), previously proposed as a two-dimensional zeolite model, is investigated using a set of complementary spectroscopy and microscopy tools. Pd single atoms are known to penetrate the bilayer silica, but when a thick Pd film is deposited on the aluminosilicate case some of the metal remains on top of the bilayer oxide. Annealing this surface results in a decrease in the Pd/Si ratio seen in X-ray photoelectron spectroscopy, indicating either further permeation of Pd, or dewetting of surface Pd to form nanoparticles and leave aluminosilicate exposed. An interesting observation is that two very distinct morphologies are obtained for the film. On small narrow terraces, flat wetting films are produced, while on larger terraces Pd particles leaving a partially exposed bilayer aluminosilicate framework are obtained.