Lateral Inhomogeneities Research Articles

Combining Drift-Diffusion and Equivalent-Circuit Models for Efficient 3D Tandem Solar Cell Simulations

For upscaling silicon based tandem solar cells from small laboratory sizes to full size formats compatible with industrial production, two-dimensional (2-D) and 3-D effects like metal grid layout, perimeter design, and lateral inhomogeneities gain importance for tandem cell development. For understanding and quantifying such effects, 3-D tandem modeling is helpful, but the capabilities of existing solar cell simulation tools is limited in this respect. In this article, we describe a numerically efficient 3-D tandem modeling approach implemented in the solar cell simulation software Quokka3. It combines a 1-D equivalent-circuit (EQC) model of the top cell within the front side's boundary condition with either the quasi-neutral 3-D drift-diffusion model or an EQC model for the bottom cell's bulk carrier transport. This way the addition of a top cell to a single-junction silicon bottom cell model in Quokka3 adds little effort in terms of computational time and is thus compatible with large-area 3-D simulations up to full cell geometries. We showcase the usefulness of this approach by investigating various perimeter designs of small-area silicon-perovskite cells.

Application of Grazing-Incidence X-ray Methods to Study Terrace-Stepped SiC Surface for Graphene Growth.

The synthesis of graphene by the graphitization of SiC surface has been driven by a need to develop a way to produce graphene in large quantities. With the increased use of thermal treatments of commercial SiC substrates, a comprehension of the surface restructuring due to the formation of a terrace-stepped nanorelief is becoming a pressing challenge. The aim of this paper is to evaluate the utility of X-ray reflectometry and grazing-incidence off-specular scattering for a non-destructive estimate of depth-graded and lateral inhomogeneities on SiC wafers annealed in a vacuum at a temperature of 1400-1500 °C. It is shown that the grazing-incidence X-ray method is a powerful tool for the assessment of statistical parameters, such as effective roughness height, average terrace period and dispersion. Moreover, these methods are advantageous to local probe techniques because a broad range of spatial frequencies allows for faster inspection of the whole surface area. We have found that power spectral density functions and in-depth density profiles manifest themselves differently between the probing directions along and across a terrace edge. Finally, the X-ray scattering data demonstrate quantitative agreement with the results of atomic force microscopy.

Influence of Soret effect on the pre-solidification state in the neopentylglycol-(D)camphor system during microgravity experiments

We present results from a combined experimental and numerical approach to estimate the impact of thermodiffusion in the liquid phase of the binary system neopentylglycol-(D)camphor (NPG-DC) during the pre-solidification holding period of experiments on the International Space Station (ISS) in reduced gravity conditions. The Soret coefficient ST, diffusion coefficient D and thermodiffusion coefficient DT have been measured by means of the optical beam deflection technique using mixtures close to the eutectic composition of the alloy (0.547 wt frac. NPG) in the composition range of 0.522–0.581 wt frac. NPG and at different temperatures above their respective liquidus temperatures. Numerically, we implemented a one-dimensional time-dependent thermodiffusion equation to describe the composition evolution during the holding pre-solidification phase in the NPG-DC alloy in a given temperature gradient. The validated model was then applied to the more complex case of spatially changing thermal gradients, which are expected in the experimental facility used onboard the ISS. Numerical simulations estimating a maximum effect of thermodiffusion showed a small but clear effect. Using the previously determined transport coefficients and a holding phase of 10 hours, a change of the NPG concentration of less than 7% of the initial composition was obtained for the given set-up. Even if the real thermodiffusion effect is expected to be smaller, this lateral inhomogeneity in concentration has to be taken into consideration in the microgravity experiments.

Syn-collisional I-type granitoids linked to lateral lithospheric heterogeneity: A case study from the North Qaidam orogen, NW China

Granitoids constitute the major theme in evaluating the growth and reworking of continental crust on Earth. Here we present U-Pb geochronology, geochemistry and Sr-Nd-Hf isotopes of the early Paleozoic granitoids emplaced during pre- and syn-collisional stages in the North Qaidam orogen to gain insights on the granitoid typology, genetic mechanism, as well as the implications for the evolution of continental crust. The pre- and syn-collisional granitoids in this region all belong to I-type granite and are derived from different continental crustal sources including late Mesoproterozoic to early Neoproterozoic metamorphic crystalline basement, and juvenile continental crust formed during early Paleozoic oceanic subduction. Granitic magmas derived from the two sources underwent a series of magmatic processes such as mixing or assimilation, which lead to the transitional geochemical and isotopic features, suggesting that besides source components, magmatic processes from melt extraction to granitoid emplacement also exerted an important influence on the formation of these granitoids and crustal maturation. Although S-type granitoids are commonly taken as the fingerprint for continental collision, our study emphasizes that the role of I-type granites formed in syn-collisional setting should not be underestimated. Besides subducted slab processes such as roll-back, retreat, or break-off, we propose a novel geodynamic model which envisages that the lateral inhomogeneity in lithospheric thickness triggered by continental collision within the overriding plate above subduction zone controlled the magmatism. Both growth and reworking of continental crust occur during oceanic subduction, whereas syn-collision setting is dominated by continental crust reworking as in the North Qaidam orogen.

Hydrogel nanosheets confined 2D rhombic ice: a new platform enhancing chondrogenesis

Nanoconfinement within flexible interfaces is a key step towards exploiting confinement effects in several biological and technological systems wherein flexible 2D materials are frequently utilized but are arduous to prepare. Hitherto unreported, the synthesis of 2D hydrogel nanosheets (HNSs) using a template- and catalyst-free process is developed representing a fertile ground for fundamental structure-property investigations. In due course of time, nucleating folds propagating along the edges trigger co-operative deformations of HNS generating regions of nanoconfinement within trapped water islands. These severely constricting surfaces force water molecules to pack within the nanoscale regime of HNS almost parallel to the surface bringing about phase transition into puckered rhombic ice with AA and AB Bernal stacking pattern, which was mostly restricted to molecular dynamics studies so far. Interestingly, under high lateral pressure and spatial inhomogeneity within nanoscale confinement, bilayer rhombic ice structures were formed with an in-plane lattice spacing of 0.31 nm. In this work, a systematic exploration of rhombic ice formation within HNS has been delineated using high-resolution transmission electron microscopy, and its ultrathin morphology was examined using atomic force microscopy. Scanning electron microscopy images revealed high porosity while mechanical testing presented young’s modulus of 155 kPa with ∼84% deformation, whereas contact angle suggested high hydrophilicity. The combinations of nanosheets, porosity, nanoconfinement, hydrophilicity, and mechanical strength, motivated us to explore their application as a scaffold for cartilage regeneration, by inducing chondrogenesis of human Wharton Jelly derived mesenchymal stem cells. HNS promoted the formation of cell aggregates giving higher number of spheroid formation and a marked expression of chondrogenic markers (ColI, ColII, ColX, ACAN and S-100), thereby providing some cues for guiding chondrogenic differentiation.

Phase behaviour of C18-N-acyl sphingolipids, the prevalent species in human brain

Lipidomic analysis of the N-acyl components of sphingolipids in different mammalian tissues had revealed that brain tissue differed from all the other samples in that SM contained mainly C18:0 and C24:1N-acyl chains, and that the most abundant Cer species was C18:0. Only in the nervous system was C18:0 found in sizable proportions. The high levels of C18:0 and C16:0, respectively in brain and non-brain SM, were important because SM is by far the most abundant sphingolipid in the plasma membrane. In view of these observations, the present paper is devoted to a comparative study of the properties of C16:0 and C18:0 sphingolipids (SM and Cer) pure and in mixtures of increasing complexities, using differential scanning calorimetry, confocal microscopy of giant unilamellar vesicles, and correlative fluorescence microscopy and atomic force microscopy of supported lipid bilayers. Membrane rigidity was measured by force spectroscopy. It was found that in mixtures containing dioleoyl phosphatidylcholine, sphingomyelin and cholesterol, i.e. representing the lipids predominant in the outer monolayer of cell membranes, lateral inhomogeneities occurred, with the formation of rigid domains within a continuous fluid phase. Inclusion of saturated Cer in the system was always found to increase the rigidity of the segregated domains. C18:0-based sphingolipids exhibit hydrocarbon chain-length asymmetry, and some singularities observed with this N-acyl chain, e.g. complex calorimetric endotherms, could be attributed to this property. Moreover, C18:0-based sphingolipids, that are typical of the excitable cells, were less miscible with the fluid phase than their C16:0 counterparts. The results could be interpreted as suggesting that the predominance of C18:0 Cer in the nervous system would contribute to the tightness of its plasma membranes, thus facilitating maintenance of the ion gradients.

The role of non-homogeneous barrier on the electrical performance of 15R–SiC Schottky diodes grown by in-situ RF sputtering

In the present work, we have demonstrated the impact of barrier inhomogeneities on the electrical characteristics of silicon carbide (SiC) based Schottky barrier diodes (SBDs). Ohmic and Schottky contacts were deposited on RF sputtered 15R–SiC film under optimized growth conditions. Forward biased current-voltage (I–V) measurement in the temperature range of 300–420 K was employed to extract the diode parameters (barrier height, ideality factor, and Richardson constant), considering the thermionic emission (TE) as dominant charge transport mechanism. The obtained value of barrier height φB and ideality factor n exhibited anomalies as compared to theoretically predicted values. It was attributed to the co-existence of multiple charge transport mechanism owing to defect induced lateral barrier inhomogeneities at the metal-semiconductor interface. Further, Gaussian distribution of φB, as established by Warner and Guttler was incorporated along with TE model to analyze the temperature dependent I–V data to understand the non-ideality in diode parameters. Eventually, the obtained diode parameters as per the modified charge transport mechanism were found to be in close alignment with the predicted values.

Guiding Graphene Derivatization for the On‐Chip Multisensor Arrays: From the Synthesis to the Theoretical Background

AbstractEngineering the physics and chemistry of 2D materials is a key to unlock the potential of the advanced e‐nose technologies limited by the current semiconductor technologies. Herein, the adjustment of the graphene's morphology, physics, and gas sensing properties upon its carboxylation via the developed photochemical method is demonstrated. Formation of matrices of nanoscale holes yet with the retention of the lamellar structure of the graphene layer is signified upon the introduction of up to 9.5 at% of carboxyl groups. The impact of the applied carboxylation on the conduction mechanism and electronic structure is demonstrated. The appearance of a set of the localized states in the valence band is revealed, originating from the molecular orbitals of carboxyls as is signified by the proposed approach for the identification of electronic states in graphene chemical derivatives. Given holey structure, predominance of highly affine carboxyls, and lateral inhomogeneity, the enhanced detection and discrimination of various alcohols, acetone, and ammonia vapors at room temperature is demonstrated. The opposite chemiresistive response toward ammonia in the humid air is also experimentally revealed and justified by the performed density functional theory modeling on the effect of ammonia, water, and their mix on electronic structure, and resistivity of the carboxylated graphene.

Electrical evolution of W and WC Schottky contacts on 4H-SiC at different annealing temperatures

In this paper, we investigate the electrical evolution of tungsten (W) and tungsten carbide (WC) Schottky contacts on 4H-SiC subjected to thermal treatments at different annealing temperatures from 475 °C to 700 °C. For each annealing temperature, the uniformity of the Schottky barrier height (ΦB) and ideality factor (n) was monitored by current–voltage (I–V) measurements in forward bias, performed over sets of equivalent diodes. Good values of n (below 1.05) were found for both contacts up to thermal annealing at 700 °C. On the other hand, the barrier of the two contacts behaves differently. For the W/4H-SiC diode, the ΦB increases with the annealing temperature (from 1.14 eV at 475 °C to 1.25 eV at 700 °C), whereas the Schottky barrier in WC/4H-SiC features a slight reduction already with thermal annealing at 475 °C, remaining almost constant at around 1.06 eV up to annealing at 700 °C. A deeper characterization was performed on the 700 °C-annealed contacts by studying the temperature-dependence of the Schottky parameters by current–voltage–temperature (I–V–T) characterization. The ΦB and n behaviour with temperature indicates the presence of a nanoscale lateral inhomogeneity for both Schottky contacts, which can be described by Tung’s model. Finally, the temperature-dependence of the reverse characteristics could be described by the thermionic field emission model, accounting for the temperature dependent barrier height determined from forward characterization.

Study on the crustal velocity structure of the Dunhua-Mishan fault based on the dense seismic array by ambient noise tomography

The Dunhua-Mishan fault is a component of the Tanlu fault zone, and it is also a major regional fault structure in Liaoning area. The study area is located in Fushun area of the Dunhua-Mishan fault. In order to study the crustal velocity structure in this region, we used 60 sets of three-component short-period seismographs and lay out two temporary profiles in Fushun, Liaoning from Nov. 3 to 25, 2019. Each temporary profiles is about 12km long that is composed of 30 seismometers, which nearly vertically cross the Dunhua-Mishan fault where the survey lines are 6km apart. The installation stations spacing distance from 200 to 400m use the external GPS time service to record frequency range of 0.2 to 150Hz in the instrument. The crustal structure characteristics of the fault zone are studied by ambient noise cross-correlation method. In order to efficiently extract high and low frequency surface wave dispersion signals at the same time, we adopt the Extended Range Phase Shift (ERPS) method. Finally, we use ERPS method to process the collected data and invert the S-wave velocity structure. We initially obtained the S-wave velocity structure of the upper crust below 5 km in the area, which matches well with the local geological data. The S-wave velocity structure has significant lateral inhomogeneity of the Dunhua-Mishan fault in Fushun area. The S-wave velocity is obviously lower on the Dunhua-Mishan fault, while with the existence of ancient mixed granite the velocity on both sides of the fault is obviously higher.

Electrothermal Tristability Causes Sudden Burn‐In Phenomena in Organic LEDs

AbstractOrganic light‐emitting diodes (OLEDs) have been established as a mature display pixel technology. While introducing the same technology in a large‐area form factor to general lighting and signage applications, some key questions remain unanswered. Under high‐brightness conditions, OLED panels were reported to exhibit nonlinear electrothermal behavior causing lateral brightness inhomogeneities and even regions of switched‐back luminance. Also, the physical understanding of sudden device failure and burn‐ins is still rudimentary. A safe and stable operation of lighting tiles, therefore, requires an in‐depth understanding of these physical phenomena. Here, it is shown that the electrothermal treatment of thin‐film devices allows grasping the underlying physics. Configurations of OLEDs with different lateral dimensions are studied as a role model and it is reported that devices exceeding a certain panel size develop three stable, self heating‐induced operating branches. Switching between them causes the sudden formation of dark spots in devices without any preexisting inhomogeneities. A current‐stabilized operation mode is commonly used in the lighting industry, as it ensures degradation‐induced voltage adjustments. Here, it is demonstrated that a tristable operation always leads to destructive switching, independent of applying constant currents or voltages. With this new understanding of the effects at high operation brightness, it will be possible to adjust driving schemes accordingly, design more resilient system integrations, and develop additional failure mitigation strategies.

Schottky barrier inhomogeneity in (Pd / Au) Al0.22 Ga0.78N/GaN/SiC HEMT: Triple Gaussian distributions

The temperature dependence of electrical properties of (Au/Pd)/Al0.22 Ga0.78N/ GaN Schottky barrier diodes (SBDs) have been deeply analyzed by means of forward Igs (Vgs) measurements over the temperature range of 60-320 K. First results indicate that the barrier height (ϕb), ideality factor (n) and series resistance (Rs) have demonstrated a strongly temperature dependence which suggesting the presence of barrier inhomogeneities at the interface. The effect of spatial inhomogeneity causes fluctuations in the barrier height around an average value. The series resistances obtained from Cheung's function are increasing with increasing temperature. Werner's model consisted in the Schottky contact modeling through inhomogeneities of the barrier which induces the presence of three different average barrier heights each associated with a standard deviation σ. Such abnormal behavior is indeed due to the lateral inhomogeneity of the Schottky barrier, assuming three Gaussian distributions of the barrier height (BH) in three different temperature ranges of 220-320K, 120-200K, and 60-100K, respectively. The (Au/Pd)/ GaN Schottky barrier diode have been shown a Gaussian distribution giving mean s (ϕb) of 0.83, 0.43 and 0.20 eV and standard deviation σ of 139, 74.18 and 35.15 mV for the three temperature regions, respectively. A modified Richardson plot ln (I0/T2) − q2σ2/2k2T2 vs. 1/kT have given ϕb and A* as 0.95 eV and 10.56 A/cm2K2, 0.45 eV and 24.45A/cm2 K2, 0.20 eV and 28.18 A/cm2 K2, respectively. Moreover, the determination of the energy characteristic relating to the transmission probability by tunneling effect E00 made it possible to highlight two conduction modes: conduction by tunnel effect (FE) and a thermionic conduction assisted by field effect (TFE).

Large Eddy Simulations of the Dusty Martian Convective Boundary Layer With MarsWRF

AbstractLarge eddy simulation (LES) of the Martian convective boundary layer (CBL) with a Mars‐adapted version of the Weather Research and Forecasting model is used to examine the impact of aerosol dust radiative‐dynamical feedbacks on turbulent mixing. The LES is validated against spacecraft observations and prior modeling. To study dust redistribution by coherent dynamical structures within the CBL, two radiatively active dust distribution scenarios are used: one in which the dust distribution remains fixed and another in which dust is freely transported by CBL motions. In the fixed dust scenario, increasing atmospheric dust loading shades the surface from sunlight and weakens convection. However, a competing effect emerges in the free dust scenario, resulting from the lateral concentration of dust in updrafts. The resulting enhancement of dust radiative heating in upwelling plumes both generates horizontal thermal contrasts in the CBL and increases buoyancy production, jointly enhancing CBL convection. We define a dust inhomogeneity index (DII) to quantify how much dust is concentrated in upwelling plumes. If the DII is large enough, the destabilizing effect of lateral heating contrasts can exceed the stabilizing effect of surface shading such that the CBL depth increases with increasing dust optical depth. Thus, under certain combinations of total dust optical depth and the lateral inhomogeneity of dust, a positive feedback exists between dust optical depth, the vigor and depth of CBL mixing, and—to the extent that dust lifting is controlled by the depth and vigor of CBL mixing—the further lifting of dust from the surface.

Dynamic "Molecular Portraits" of Biomembranes Drawn by Their Lateral Nanoscale Inhomogeneities.

To date, it has been reliably shown that the lipid bilayer/water interface can be thoroughly characterized by a sophisticated so-called “dynamic molecular portrait”. The latter reflects a combination of time-dependent surface distributions of various physicochemical properties, inherent in both model lipid bilayers and natural multi-component cell membranes. One of the most important features of biomembranes is their mosaicity, which is expressed in the constant presence of lateral inhomogeneities, the sizes and lifetimes of which vary in a wide range—from 1 to 103 nm and from 0.1 ns to milliseconds. In addition to the relatively well-studied macroscopic domains (so-called “rafts”), the analysis of micro- and nanoclusters (or domains) that form an instantaneous picture of the distribution of structural, dynamic, hydrophobic, electrical, etc., properties at the membrane-water interface is attracting increasing interest. This is because such nanodomains (NDs) have been proven to be crucial for the proper membrane functioning in cells. Therefore, an understanding with atomistic details the phenomena associated with NDs is required. The present mini-review describes the recent results of experimental and in silico studies of spontaneously formed NDs in lipid membranes. The main attention is paid to the methods of ND detection, characterization of their spatiotemporal parameters, the elucidation of the molecular mechanisms of their formation. Biological role of NDs in cell membranes is briefly discussed. Understanding such effects creates the basis for rational design of new prospective drugs, therapeutic approaches, and artificial membrane materials with specified properties.

A new integrated geophysical-petrological global 3-D model of upper-mantle electrical conductivity validated by the Swarm M2 tidal magnetic field

SUMMARY A new global model of the present-day thermochemical state of the lithosphere and upper mantle based on global waveform inversion, satellite gravity and gradiometry measurements, surface elevation and heat flow data has been recently presented: WINTERC-G (Fullea et al. 2021). WINTERC-G is built within an integrated geophysical-petrological framework where the mantle seismic velocity and density fields are computed in a thermodynamically self-consistent framework, allowing for a direct parametrization in terms of the temperature, pressure and composition of the subsurface rocks. In this paper, we combine WINTERC-G thermal and compositional fields along with laboratory experiments constraining the electrical conductivity of mantle minerals, melt and water, and derive a set of new global three dimensional electrical conductivity models of the upper mantle. The new conductivity models, WINTERC-e, consist of two end-members corresponding to minimum and maximum conductivity of the in situ rock aggregate accounting for mantle melting, mineral water content and the individual conductivities of the main stable mantle mineral phases. The end-member models are validated over oceans by simulating the magnetic field induced by the ocean M2 tidal currents and comparing the predicted fields with the M2 tidal magnetic field estimated from 6-yr Swarm satellite observations. Our new conductivity model, derived independently from any surface or satellite magnetic data sets, is however able to predict tidal magnetic fields that are in good agreement with the Swarm M2 tidal magnetic field models estimated by Sabaka et al. and Grayver & Olsen. Our predicted M2 tidal magnetic fields differ in amplitudes by about 5–20 per cent from the Swarm M2 tidal magnetic field, with the high conductivity WINTERC-e end-member model accounting for mantle melt and water content capturing the structure of Swarm data better than the low conductivity end-member model. Spherically symmetric conductivity models derived by averaging new WINTERC-e conductivities over oceanic areas are slightly more conductive than the recent global conductivity models AA17 by Grayver et al. derived from Swarm and CHAMP satellite data in the 60–140 km depth range, while they are less conductive deeper in the mantle. The conductivities in WINTERC-e are about three to four times smaller than the AA17 conductivities at a depth of 400 km. Despite the differences in electrical conductivity, our spherically symmetric high conductivity end-member model WINTERC-e captures the structure of Swarm M2 tidal magnetic field almost the same as a state of the art 1-D conductivity models derived entirely from magnetic data (AA17, Grayver et al.). Moreover, we show that realistic lateral electrical conductivity inhomogeneities of the oceanic upper mantle derived from the temperature, melt and water distributions in WINTERC-e contribute to the M2 tidal magnetic field up to ±0.3 nT at 430 km altitude.

Lateral Distribution of Optical Excitation at Boundaries around Rubrene Islands Visualized by Microspot Two-Photon Photoemission Spectroscopy

The lateral distribution of optical excitation occurring at the edge part of rubrene (5,6,11,12-tetraphenyltetracene) molecular islands formed on highly oriented pyrolytic graphite (HOPG) substrate has been visualized with microspot two-photon photoemission (2PPE) spectroscopy of 0.4 µm resolution. As we reported previously [T. Ueba, et al., J. Phys. Chem. C 117 (2013) 20098–20103], an unoccupied peak labeled Ln is strongly enhanced in 2PPE spectroscopy by a resonant optical excitation between a diffuse unoccupied Ln molecular orbital and the HOMO. The strong enhancement is due to the hybridization of Ln with the image potential state (IPS) on the HOPG substrate. In this study, using the spatially-resolved microspot 2PPE method, we obtained the real space image of the area where the optical excitation occurs. One-photon photoelectron emission microscope (1PPE-PEEM) with 50 nm resolution is used to compare with the microspot 2PPE. The 1PPE-PEEM images are homogeneous for films below and above 1 monolayer (ML) coverage, indicating that the molecular density of rubrene is homogeneous within the lateral resolution. On the other hand, microspot 2PPE images for sub-ML films show inhomogeneous areas of several µm sizes. The images depend on the detected unoccupied levels of interest. The inhomogeneity is very significant when the image is recorded at the energy of Ln peak. The different appearance between 1PPE-PEEM and microspot 2PPE images is explained on the basis that the Ln excitation occurs at the edges of islands smaller than the resolution of the PEEM. Though the microspot 2PPE achieves only moderate lateral resolution, it is sensitive to the resonant excitation occurring at nm-scale boundaries of the molecular islands. The distribution of the nm-scale islands is the origin of the µm-scale lateral inhomogeneity. The microspot 2PPE images become homogeneous for films thicker than 1 ML, reflecting the quenching of the resonant excitation. These results demonstrate a possibility that spatially- and energy-resolved microspot 2PPE can be a powerful tool to clarify nanoscale geometric and electronic structures at the molecule/substrate interfaces.

Nonlinear saturation of thermal instabilities

Recent low-frequency simulations of a one-layer model with lateral buoyancy inhomogeneity have revealed circulatory motions resembling quite closely submesoscale features on the ocean surface often visible in satellite observations. This model is known to lack a high-wavenumber instability cutoff and, thus, to possibly undergo ultraviolet catastrophe. However, the numerically observed instabilities, referred to as “thermal” due the ability of the above inhomogeneous-layer model to incorporate thermodynamic processes, are not seen to grow indefinitely. In this note, I show that the presence of a convex pseudo-energy–momentum integral of motion for the inviscid, unforced dynamics can arrest their nonlinear grow in the zonally symmetric case. Our result is an application of Arnold and Shepherd's methods.

Combined depth-resolved cathodoluminescence spectroscopy and transmission electron microscopy on Al(Ga)N multi quantum well structures

A stack of five Al(Ga)N-based quantum wells is investigated by combined laterally and depth resolved cathodoluminescence (CL) spectroscopy in order to distinguish lateral and vertical inhomogeneities of these wells. Transmission electron microscopy (TEM) micrographs provide data for the real sample structure, which enters into the Monte-Carlo simulation of the depth-resolved CL measurements to refine the depth resolution. The comparison of these CL measurements to the results of electron energy loss spectra (EELS) allows to identify local thickness variations of the lower three quantum wells to be the origin of two different luminescence contributions to the overall spectrum. The differentiation of the two groups of quantum wells by depth-resolved CL is demonstrated.

Структурная характеризация короткопериодной сверхрешетки на основе гетероструктуры CdF-=SUB=-2-=/SUB=-/CaF-=SUB=-2-=/SUB=-/Si(111) методами просвечивающей электронной микроскопии и рентгеновской дифрактометрии

A detailed study of the structure of a short-period superlattice based on alternating layers of cadmium and calcium fluorides, grown by molecular beam epitaxy on a Si (111) substrate, by transmission electron microscopy and X-ray diffractometry, has been carried out. It was found that the superlattice is in a pseudomorphic state, and a lateral inhomogeneity with a fragment size of 10 - 40 nm was found. The reason for the broadening of the main and satellite peaks of the SL on the (111) diffraction curve has been clarified.

Upper crustal velocity and seismogenic environment of the <em>M</em>7.0 Jiuzhaigou earthquake region in Sichuan, China

On August 8, 2017, a magnitude 7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China. The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad. The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area; the complex tectonic background and the reason(s) for the frequent seismicity in the Jiuzhaigou earthquake region are unclear. In order to reveal the characteristics of the deep medium and the seismogenic environment of the <i>M</i>7.0 Jiuzhaigou earthquake region, and to interpret the tectonic background and genesis of the seismicity comprehensively, in this paper, we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale, dense mobile seismic array (China Array) for the northern section of the North–South Seismic Belt around Jiuzhaigou earthquake region. Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region, we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region, its deep tectonic environment, and the ongoing seismic risk in this region. We report that: the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity; the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology; the <i>M</i>7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust; the mainshock of the <i>M</i>7.0 earthquake occurred in the upper crust; the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep structural factor controlling the spatial distribution of the mainshock and its sequence. The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB (Songpan–Garzê Block) stretches into MSM (Minshan Mountain), and migrates to the northeast, but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block. Our results reveal an uneven distribution of high- and low-velocity structures around the Tazang segment of the East Kunlun fault zone. Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault, it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu–Maqên segment of the East Kunlun fault zone.