Background Slope Research Articles

Geophysical Research on an Open Pit Mine for Geotechnical Planning and Future Land Reclamation: A Case Study from NW Macedonia, Greece

In open pit mining areas, knowledge of geotechnical conditions (e.g., overburden thickness, background slope, and fault locations) ensures geotechnical safety during exploitation as well as reclamation planning. The Greek Public Power Corporation initiated a research program after stability issues emerged on the southern side of the Mavropigi open pit mine in NW Macedonia. Geotechnical wells revealed steeply dipping bedrock and thin tectonic contact, indicating the need for the detailed imaging of the subsurface for future stability measures. For this purpose, a geophysical investigation aimed to extract information mostly for the dip of the interface between schist bedrock and overlaying Neogene sediments and/or limestones. Based on the high contrast of electrical properties between schists and limestones, as well as the differences in acoustic impedance and formation thickness, the seismic reflection and electrical resistivity tomography (ERT) methods were selected. The suitability of the seismic reflection for its application in this area was checked by generating synthetic seismic data, which resulted from the simulation of seismic wave propagation for geological models of the area. The acquisition parameters were determined after the noise test. Field seismic data processing produced a depth-migrated section, which revealed the existence of a fault. The use of dipole–dipole and gradient arrays, in 2D and 3D electrical resistivity measurements, ensured both the lateral and vertical mapping of schist bedrock and detected limestone bodies within the overburden. Also, the tectonic contact zone between limestone and schist formations was properly imaged. The comparison between geoelectrical and seismic sections indicated that the seismic reflection method provided a more accurate estimate of fault inclination. Finally, the geophysical survey enriched the geotechnical models necessary for sustainable mining (e.g., rational exploitation, the optimization of productivity, and zero accidents) including the planning of future reclamation.

Deep-water channels in the lower Congo basin: Evolution of the geomorphology and depositional environment during the Miocene

Abstract Deep-water channel systems are an important component of the “source to sink” system from continental slope to deep-sea basin. They are also the critical reservoir type in deep-water hydrocarbon exploration. The study of geomorphology evolution, filling processes and controlling factors of the Miocene deep-water channel in the Lower Congo Basin is conducive to deepening our understanding of basin dynamics, and to improving the prediction accuracy of deep-water reservoirs. Based on 3D seismic data, cores, thin sections, well logging data, we study the Miocene seismic stratigraphic characteristics, deep-water sedimentary units, lithofacies and channel types. Using the techniques and means of seismic geomorphology, we discuss the occurrence, development, recession and extinction processes of channel complexes and controlling factors. The Miocene was divided into seven 3rd-order sequences. Each 3rd-order sequence is subdivided into two (lower/upper) seismic stratigraphy units, with initial flooding surface (FS) as the separated boundary. The seismic characteristics of the lower/upper unit suggest the occurrence of alternating turbidite/hemipelagic sedimentary units. Seismic units such as erosional surface, filling channel, levee, lobe, MTD and background slope deposits are described. Fifteen deep-water lithofacies are identified and they are determined to be composed of clay, silt, fine-coarse sand, gravel, and conglomerate. The deep-water channels in the study area are interpreted four types: single-stage erosional channel, single-stage aggradational channel, vertical aggradational channel complexes and lateral migration channel complexes. The different types of channel are the results of interaction of flow energy and accommodation space. On this basis, we propose that tectonic uplift is the driving force for the formation of the deep-water sandy channel system, and that high frequency sea-level fluctuation in West Africa controls the development of third-order sequences and restricts the scale of the deep-water sandstone accumulation. In addition, the avulsion processes controlled by climate variations are the main factors to influence channel complex filling process.

Architecture, process, and environmental diversity in a late Cretaceous slope channel system

ABSTRACT Arroyo San Fernando, on the Pacific coast of Baja California, Mexico, provides a superb view of the architecture of a Maastrichtian active margin slope channel system and the record of its evolution through a third-order sea-level cycle. The succession is organized into architectural building blocks (channel-complex sets) consisting of a channel belt with an axial region and a channel-belt margin of terraces and internal levees. The channel belt is confined by an external levee on one side and by an erosion surface into the slope on the other. Each channel-complex set can be subdivided into three stages of evolution: Stage I consists of highly amalgamated coarse-grained channel complexes, Stage II consists of gravelly meander belts with marginal and stratigraphically intervening thin-bedded turbidites, and Stage III consists of mudstones representing abandonment. This succession is associated with repeated and therefore predictable changes in architecture, facies distribution, inferred seafloor morphology, and sedimentary process. We describe variability in the sedimentology, ichnology, palynology, provenance, and inferred sedimentary processes between and within these architectural elements. Channel formation and fill are attributed to erosion, sediment transport, and deposition by turbidity currents and lesser debris flows. Ichnology indicates enhanced oxygenation and supply of organic material, substrate type, and turbidity within the channel belt; the axial region can be differentiated from the terraces by differing response to turbidity-current intensity. Levee environments show ichnological gradients away from the channel towards background slope. Palynology reflects confinement of the supply of terrigenous material to the channel belt, but is also indicative of stratification within the turbidity-currents, as is the distribution of heavy minerals. Provenance is from the extinct part of the continental-margin arc to the east, via high-gradient gravelly streams and across a steep shoreline, with direct supply of coastal material to deep water. Architectural hierarchy bears comparison with other slope channel systems, but in common with them the fill represents only a small fraction of the time that the system was active.

Coupled External‐Internal Dynamics of Layered Circulation in the South China Sea: A Modeling Study

AbstractThe external inflow/outflow through straits on the periphery of the South China Sea (SCS) and the associated internal response of vertical transport over the broad continental slope form and sustain a cyclonic‐anticyclonic‐cyclonic (CAC) circulation in the upper‐middle‐lower layer in the SCS. We conduct a process‐oriented numerical study to investigate the underlying coupled external‐internal dynamics that remains unknown, despite that the dynamics plays a critical role in forming and sustaining the CAC circulation. External sandwich‐like inflow‐outflow‐inflow in the water column through the Luzon Strait forms a three‐dimensional CAC slope current over the curving slope topography in the SCS basin, in which the downward/upward transport associated with the cross‐slope motion is established. The along‐slope current over the basin provides vorticity through the beta effect and accounts for the most external planetary vorticity input through the strait in the upper layer of the SCS, while the vorticity induced by the vertical transport is the major response to the external vorticity flux in the middle and lower layers. We illustrate the critical role of the vertical transport in linking the vorticity among the different layers for the development and sustenance of the CAC circulation. The vertical transport is associated with the cross‐slope motion due to slope current‐topography interaction, which involves mainly in bottom frictional transport and geostrophic cross‐isobath transport by the pressure gradient force in the along‐slope direction. Pressure gradient force is generated by nonlinear vorticity advection and the beta effect of the background slope current.

Development of a partially-avulsed submarine channel on the Niger Delta continental slope: Architecture and controlling factors

On the Niger Delta slope a partially-avulsed channel, named Tombia Channel (TC), was recognized. This work used high-resolution 3D seismic data to investigate its external morphology, internal architecture and the detailed association with the feeder channel, i.e. Bukuma Channel System (BCS). TC emanated from a slope transition zone of BCS where a sharp bend as well as the channel-floor aggradation increased the instability of BCS and triggered by an outsize flow event, the avulsion happened. The initial flow path of TC appeared to follow discontinuous linear trains of small scours and residual pockmarks; as it evolved, TC developed a very low sinuosity and did not have levees. Preserved cross-sectional profiles of TC changed from dish, deep-U, V to shallow-U shape downstream, which was mainly controlled by increasing then decreasing background slope. Three channel forms were recognized within TC, forming a fining upward sequence, which may be associated with the progressive abandonment of BCS; each channel form also showed a trend of increasing grain size along the flow direction. TC evolved through four stages: Stage 1 was characterized by the interaction of overspilling flow stripped off from BCS with the inherited overbank topography; Stage 2 was featured by the full establishment of a channelized flow pathway and then by deposition of early Channel form 1; Stage 3 was dominated firstly by further development of the flow pathway and then by deposition of latter Channel form 2; Stage 4 occurred in the abandonment phase and referred to the hemipelagic draping on the residual negative relief (Channel form 3). If TC commonly develops so as to fully capture the sediment gravity flows from BCS, architectural records of this type would have low preservation potential. However, the shut-down of BCS make that preservation possible and it provides potentially important insights into submarine channel avulsion processes.

Comparing reach scale hyporheic exchange and denitrification induced by instream restoration structures and natural streambed morphology

Excess nutrients commonly lead to eutrophication and harmful algal blooms. Stream restoration is increasingly popular for nutrient removal enhancing exchange with the reactive hyporheic zone. Hyporheic reactions such as denitrification are often transport-limited and instream restoration structures have been proposed to enhance hyporheic exchange and nutrient removal. However, the comparative effects of instream structure types and watershed setting (i.e. environmental characteristics such as sediment hydraulic conductivity, stream slope) are still poorly understood. Here we used MIKE SHE to model groundwater and surface water interaction and nitrate removal (denitrification) in a 200 m second order stream reach. We simulated various in-stream structures (channel-spanning weirs, partially spanning structures such as cross veins, buried structures) and investigated the effect of controlling environmental characteristics that vary with watershed setting. We found that the environmental characteristics had the greatest effect on surface water-groundwater exchange and therefore denitrification, including streambed hydraulic conductivity, natural or background stream topography and slope, and groundwater levels. Type and number of instream structures also influenced surface water-groundwater exchange and denitrification, but to a lesser degree. Human effects at the watershed scale from agriculture and urbanization likely play a role in whether reach-scale restoration practices succeed in achieving water quality goals both through effect on exchange itself (e.g., altering bed sediment texture) and on nitrate sources. More broadly, restoration efforts at the watershed scale itself, such as reducing fertilizer use or improving stormwater management, may be necessary to achieve ambitious water quality goals. Nevertheless, reach-scale restoration efforts such as in-stream structures may play a useful role in certain watershed settings, for example where groundwater conditions induce neither strong gaining nor strong losing conditions. The interaction of reach-scale modifications and watershed setting must be understood to optimize nutrient removal from stream restoration through enhanced hyporheic exchange.

A Raman spectroscopy study of the effect of thermal treatment on structural and photoluminescence properties of CVD diamond films

Micro- Raman spectroscopic technique is employed to investigate structural and micro-photoluminescence (μ-PL) properties of diamond films obtained by chemical vapour deposition (CVD) on silicon substrate. Information on the behaviour of PL centred at 2eV upon annealing to 300°C and cooling is obtained from background slope and G band intensity in the Raman spectra (the so-called S parameter). The results show that PL is thermally quenched and this process has a character of continuous of energy distribution due to point defects for temperatures below 100°C. Additionally, the distribution of hydrogen concentration at the diamond films surface of different structures is estimated for room temperature and compared with the results obtained from atomic force microscopy (AFM). The obtained data indicate a correlation between the size and character of the grain boundaries and the hydrogen concentration.

Q-LAVHA: A flexible GIS plugin to simulate lava flows

Q-LavHA is a freeware plugin which simulates lava flow inundation probability from one or regularly distributed eruptive vents on a Digital Elevation Model (DEM). It combines existing probabilistic and deterministic models and proposes some improvements to calculate the probability of lava flow spatial propagation and terminal length. Spatial propagation is constrained by the probabilistic steepest slope. Corrective factors are included to allow the flow simulation to overcome small topographical obstacles and to fill pits. The terminal length of the flow simulation can be determined based on a fixed length value, a statistical length probability function or based on the thermo-rheological properties of an open-channel lava flow. The impact of model parameters, background slope and DEM resolution on the accuracy of the simulations are discussed. The user-friendly interface and the flexibility of Q-LavHA makes it a tool applicable from long-term volcanic hazard assessment to short-term hazard forecasting.

DETECTION OF SLOPE MOVEMENT BY COMPARING POINT CLOUDS CREATED BY SFM SOFTWARE

This paper proposes movement detection method between point clouds created by SFM software, without setting any onsite georeferenced points. SfM software, like Smart3DCaputure, PhotoScan, and Pix4D, are convenient for non-professional operator of photogrammetry, because these systems require simply specification of sequence of photos and output point clouds with colour index which corresponds to the colour of original image pixel where the point is projected. SfM software can execute aerial triangulation and create dense point clouds fully automatically. This is useful when monitoring motion of unstable slopes, or loos rocks in slopes along roads or railroads. Most of existing method, however, uses mesh-based DSM for comparing point clouds before/after movement and it cannot be applied in such cases that part of slopes forms overhangs. And in some cases movement is smaller than precision of ground control points and registering two point clouds with GCP is not appropriate. Change detection method in this paper adopts CCICP (Classification and Combined ICP) algorithm for registering point clouds before / after movement. The CCICP algorithm is a type of ICP (Iterative Closest Points) which minimizes point-to-plane, and point-to-point distances, simultaneously, and also reject incorrect correspondences based on point classification by PCA (Principle Component Analysis). Precision test shows that CCICP method can register two point clouds up to the 1 pixel size order in original images. Ground control points set in site are useful for initial setting of two point clouds. If there are no GCPs in site of slopes, initial setting is achieved by measuring feature points as ground control points in the point clouds before movement, and creating point clouds after movement with these ground control points. When the motion is rigid transformation, in case that a loose Rock is moving in slope, motion including rotation can be analysed by executing CCICP for a loose rock and background slope independently.

DETECTION OF SLOPE MOVEMENT BY COMPARING POINT CLOUDS CREATED BY SFM SOFTWARE

Abstract. This paper proposes movement detection method between point clouds created by SFM software, without setting any onsite georeferenced points. SfM software, like Smart3DCaputure, PhotoScan, and Pix4D, are convenient for non-professional operator of photogrammetry, because these systems require simply specification of sequence of photos and output point clouds with colour index which corresponds to the colour of original image pixel where the point is projected. SfM software can execute aerial triangulation and create dense point clouds fully automatically. This is useful when monitoring motion of unstable slopes, or loos rocks in slopes along roads or railroads. Most of existing method, however, uses mesh-based DSM for comparing point clouds before/after movement and it cannot be applied in such cases that part of slopes forms overhangs. And in some cases movement is smaller than precision of ground control points and registering two point clouds with GCP is not appropriate. Change detection method in this paper adopts CCICP (Classification and Combined ICP) algorithm for registering point clouds before / after movement. The CCICP algorithm is a type of ICP (Iterative Closest Points) which minimizes point-to-plane, and point-to-point distances, simultaneously, and also reject incorrect correspondences based on point classification by PCA (Principle Component Analysis). Precision test shows that CCICP method can register two point clouds up to the 1 pixel size order in original images. Ground control points set in site are useful for initial setting of two point clouds. If there are no GCPs in site of slopes, initial setting is achieved by measuring feature points as ground control points in the point clouds before movement, and creating point clouds after movement with these ground control points. When the motion is rigid transformation, in case that a loose Rock is moving in slope, motion including rotation can be analysed by executing CCICP for a loose rock and background slope independently.

Statistical properties of coastal long waves analysed through sea-level time-gradient functions: exemplary analysis of the Siracusa, Italy, tide-gauge data

Abstract. This study presents a new method to analyse the properties of the sea-level signal recorded by coastal tide gauges in the long wave range that is in a window between wind/storm waves and tides and is typical of several phenomena like local seiches, coastal shelf resonances and tsunamis. The method consists of computing four specific functions based on the time gradient (slope) of the recorded sea level oscillations, namely the instantaneous slope (IS) as well as three more functions based on IS, namely the reconstructed sea level (RSL), the background slope (BS) and the control function (CF). These functions are examined through a traditional spectral fast Fourier transform (FFT) analysis and also through a statistical analysis, showing that they can be characterised by probability distribution functions PDFs such as the Student's t distribution (IS and RSL) and the beta distribution (CF). As an example, the method has been applied to data from the tide-gauge station of Siracusa, Italy.

X-RAY PROPERTIES OF THE NORTHERN GALACTIC CAP SOURCES IN THE 58 MONTHSWIFT/BAT CATALOG

We present a detailed X-ray spectral analysis of a complete sample of hard X-ray selected AGN in the Northern Galactic Cap of the 58-month Swift Burst Alert Telescope (Swift/BAT) catalog, consisting of 100 AGN with b>50deg. This region has excellent potential for further study due to the availability of a wide range of archival multi-wavelength data, and we propose it as a low-redshift analog to the `deep fields' work on AGN at higher redshifts. We present distributions of luminosity, absorption, and other key quantities, from fitting new and archival X-ray data gathered from XMM-Newton, Swift/XRT, ASCA and Swift/BAT. We probe to deeper redshifts than the 9-month BAT catalog (<z>=0.043), and uncover a broader absorbing column density distribution. The fraction of obscured (log N_H >= 22) objects in the sample is ~60%, and 43--56% of the sample exhibits `complex' 0.4--10keV spectra. The soft excess is either well-detected in AGN or undetected, suggesting that the process responsible for producing the soft excess is not ubiquitous. The fraction of Compton-thick sources in our sample is ~9%, and `hidden/buried AGN' constitute ~14% of our sample. Compton reflection is found to be important in a large fraction of our sample using joint XMM-Newton+BAT fits (reflection amplitude <R> = 2.7 +/- 0.75), indicating light bending or extremely complex absorption. The average 1--10keV spectrum for the sample reproduces the 1--10keV X-ray background slope as found for the 9-month BAT AGN sample. The completeness limit for the sample is ~4 times fainter than that for the 9-month catalog (abridged).

Numerical experiments on the dynamics of channelised lava flows at Mount Cameroon volcano with the FLOWGO thermo-rheological model

As for many other effusive volcanoes, Mount Cameroon (MC) is a volcano for which only limited information exists on lava flow properties and emplacement dynamics for recent eruptions. This study provides new quantitative constraints for rheological and dynamic characteristics of lava flow effusion for the 1982 and 2000 eruptive events, used to calibrate the FLOWGO thermo-rheological model for these lava flows. The FLOWGO 1-D physical model is used to simulate down-flow evolution of the geometry and rheology of channel-contained cooling-limited lava flows. Morphometric data from historical lava flows were acquired from the field, e.g. channel geometry, levee and background slope, in order to estimate lava yield strength, velocity and effusion rate. Lava density and viscosity were also estimated from compositional data and laboratory methods. To account for uncertainty in the input rheological and geometrical data, three end-member scenarios were used to bracket the potential range in lava channel initial dimension, initial lava temperature and phenocryst content. For each of these scenarios, two crustal growth models were used: one assuming strong insulation due to lava flow surface crusting, the other a much lower crusting rate. Twelve numerical simulations were made per flow and the results were compared against the channel geometry, microlite content, yield strength and viscosity estimates from field and laboratory investigations. Best-fit models where obtained for both the 1982 and 2000 lava flows using a low rate of surface crusting, high initial temperature and low phenocryst content. Model-predicted lengths were within 5% of the actual lengths. Modelled mean effusion rates for the 1982 (52–64m3s−1) and 2000 (10m3s−1) flows closely matched field data derived estimations (26–68 and 9.5m3s−1 respectively). FLOWGO model results are highly sensitive to initial channel dimensions, phenocryst content and the FLOWGO model is unable to reproduce the observed rapid near-vent increase in microlite content. Near-vent rapid cooling induced by lava degassing is yet to be fully documented and integrated into numerical lava flow models such as FLOWGO, but obtained results already provide valuable insights for lava flow hazard assessment at Mount Cameroon.

Raman Scattering Study of Hydrogen Storage Material LiNH2

Raman scattering spectra of LiNH 2 have been measured from 3.4 to 673 K. Precise polarization dependence of the single crystalline LiNH 2 and first principles calculation have successfully assigned all observed peaks. Li vibration with the lowest energy at 133 cm -1 shows the anomaly, where its energy decreases with decreasing temperature. This anomaly shows that the Li vibration is highly anharmonic with large amplitude. In addition, the energy of 133 cm -1 gives the very small force constant of 0.05 mdyn/Å between Li and NH 2 in the diatomic model. This weak interaction suggests that LiNH 2 easily decomposes to Li and NH 2 . Below 100 K, we have found new peaks in the energy range from 100 to 700 cm -1 . No additional degrees of freedom for vibrations conclude that rotational motion of NH 2 molecule freezes below 100 K. With increasing temperature, the bond angle of H–N–H and bond length N–H in NH 2 become narrow and long, respectively. At the reaction temperature region, the correlation between the integrated intensity of N–H vibration in Li 2 NH and back ground slope has been observed and the background change is originated from the desorption of NH 3 molecules. Final materials due to chemical reactions are different between single crystal and powder samples. In the single crystal, the spectrum similar with that at room temperature appears at 673 K and this suggests that the reaction finishes only at the thin surface layer, not entire volume. However, the powder sample of LiNH 2 decomposes to Li 2 NH and finally change to the Li 3 N for the sake of NH 3 desorption.

Dynamics of a dense gravity current flowing over a corrugation

In this study, we investigate the dynamics of a dense gravity currents over different sizes of ridges and canyons. We employ a high resolution idealized isopycnal model and perform a large number of experiments changing the aspect ratio of a ridge/canyon, the Coriolis parameter, the reduced gravity, the background slope and initial overflow thickness. The control run (smooth topography) is in an eddy-regime and the frequencies of the eddies coincide with those of the Filchner overflow ( Darelius et al., 2009). Our idealized corrugation experiments show that corrugations steer the plume downslope, and that ridges are more effective than canyons in transporting the overflow to the deep ocean. We find that a corrugation Burger number ( Bu c ) can be used as a parameter to describe the flow over topography. Bu c is a combination of a Froude number and the aspect ratio. The maximum downslope transport of a corrugation can be increased when the height of the corrugation increases ( Bu c increases) or when the width of the corrugation decreases ( Bu c increases). In addition, we propose a new parameterization of mixing as a function of Bu c that can be used to account for unresolved shear in coarse resolution models. The new parameterization captures the increased local shear, thus increasing the turbulent kinetic energy and decreasing the gradient Richardson number. We find reasonable agreement in the overflow thickness and transport between the models with this parameterization and the high resolution models. We conclude that mixing effects of corrugations can be implemented as unresolved shear in an eddy diffusivity formulation and this parameterization can be used in coarse resolution models.

Influence of the wavelength-dependence of fiber couplers on the background signal in wavelength modulation spectroscopy with RAM-nulling

Recently a technique to optically eliminate the background residual amplitude modulation in 1f wavelength modulation spectroscopy was demonstrated, where perfect elimination throughout the scan range was not achieved due to the wavelength-dependence of couplers and that of the laser intensity modulation. This paper theoretically analyzes the technique and experimentally demonstrates that the elimination can be perfect for one of three possible experimental configurations, making this important for potential applications with some recently-developed laser sources. For the other configurations a non-zero background slope is predicted, experimentally verified, and the anomalous nature of signals is thereby explained. A common signal normalization method is devised that is independent of the signal slope, a fact that is important for industrial deployment of such systems.

Hydrogen content estimation of hydrogenated amorphous carbon by visible Raman spectroscopy

In the present study, we report the hydrogen content estimation of the hydrogenated amorphous carbon (a-C:H) films using visible Raman spectroscopy in a fast and nondestructive way. Hydrogenated diamondlike carbon films were deposited by the plasma enhanced chemical vapor deposition, plasma beam source, and integrated distributed electron cyclotron resonance techniques. Methane and acetylene were used as source gases resulting in different hydrogen content and sp2∕sp3 fraction. Ultraviolet-visible (UV-Vis) spectroscopic ellipsometry (1.5–5eV) as well as UV-Vis spectroscopy were provided with the optical band gap (Tauc gap). The sp2∕sp3 fraction and the hydrogen content were independently estimated by electron energy loss spectroscopy and elastic recoil detection analysis-Rutherford back scattering, respectively. The Raman spectra that were acquired in the visible region using the 488nm line shows the superposition of Raman features on a photoluminescence (PL) background. The direct relationship of the sp2 content and the optical band gap has been confirmed. The difference in the PL background for samples of the same optical band gap (sp2 content) and different hydrogen content was demonstrated and an empirical relationship between the visible Raman spectra PL background slope and the corresponding hydrogen content was extracted.

Entrainment in bottom gravity currents over complex topography from three‐dimensional nonhydrostatic simulations

By recognizing that oceanic overflows follow the seafloor morphology, which shows a self‐similar structure at spatial scales ranging from 100 km to 1 m, the impact of topographic bumps on entrainment in gravity currents is investigated using a 3D nonhydrostatic spectral element model. It is found that a bumpy surface can lead to a significant enhancement of entrainment compared to a smooth surface. The change in entrainment is parameterized as a function of statistical estimates of the amplitude and wavenumber parameters of bumps with respect to the background slope.

A study of ta-C, a-C:H and Si-a:C:H thin films on polymer substrates as a gas barrier

Two types of diamond-like carbon (DLC) films were grown on Poly (ethylene terepthalate) (PET) substrates have been investigated for density, internal stress, gas permeability and structural properties by an X-ray reflectometry, surface profilometer, Raman spectroscopy and water vapour permeation analysis system, respectively. The high density tetrahedral amorphous carbon (ta-C) films (3.27 g/cm 3) prepared by filtered vacuum cathodic arc (FCVA) showed unexpected high water vapour transmission rate (WVTR) (1.3 g/m 2 day) and a surface covered by a network of deep micro-cracks, which is due to intrinsic stress inside the ta-C films (up to 12 GPa). The soft Si doped hydrogenated amorphous carbon (Si-a:C:H) films prepared by plasma enhanced chemical vapour deposition (PECVD) exhibited low transmission rate (0.03 g/m 2 day) with a water vapour reduction factor up to 98% and a surface almost completely free of micro-cracks. Si incorporation in the a-C:H films reduced both the film density from 2.3 g/cm 3 to 1.85 g/cm 3 and the compressive stress to <0.5 GPa. This could be understood by two possibilities. Firstly, the increasing in the hydrogen content within the films (as indicated by increasing the Raman background slope) developed more polymer–like bonds, which weakens the microstructure. Second, replacing the stronger CC bonds (3.7 eV) by CSi (3.21 eV) bonds where the relaxation of residual stress would occur with large strains in the CSi bonds.

Inelastic electron scattering observation using energy filtered transmission electron microscopy for silicon–germanium nanostructures imaging

This paper presents a new technique using energy filtered TEM (EFTEM) for inelastic electron scattering contrast imaging of Germanium distribution in Si–SiGe nanostructures. Comparing electron energy loss spectra (EELS) obtained in both SiGe and Si single crystals, we found a spectrum area strongly sensitive to the presence of Ge in the range [50–100eV]. In this energy loss window, EELS spectrum shows a smooth steeply shaped background strongly depending on Ge concentration. Germanium mapping inside SiGe can thus be performed through imaging of the EELS background slope variation, obtained by processing the ratio of two energy filtered TEM images, respectively, acquired at 90 and 60eV. This technique gives contrasted images strongly similar to those obtained using STEM Z-contrast, but presenting some advantages: elastic interaction (diffraction) is eliminated, and contrast is insensitive to polycrystalline grains orientation or specimen thickness. Moreover, since the extracted signal is a spectral signature (inelastic energy loss) we demonstrate that it can be used for observation and quantification of Ge concentration depth profile of SiGe buried layers.