Symmetric Reflection Research Articles

Exploiting Friedel pairs to interpret scanning 3DXRD data from complex geological materials.

The present study introduces a processing strategy for synchrotron scanning 3D X-ray diffraction (s3DXRD) data, aimed at addressing the challenges posed by large, highly deformed, polyphase materials such as crystalline rocks. Leveraging symmetric Bragg reflections known as Friedel pairs, our method enables diffraction events to be precisely located within the sample volume. This method allows for fitting the phase, crystal structure and unit-cell parameters at the intra-grain scale on a voxel grid. The processing workflow incorporates several new modules, designed to (i) efficiently match Friedel pairs in large s3DXRD datasets containing up to 108 diffraction peaks; (ii) assign phases to each pixel or voxel, resolving potential ambiguities arising from overlap in scattering angles between different crystallographic phases; and (iii) fit the crystal orientation and unit cell locally on a point-by-point basis. We demonstrate the effectiveness of our technique on fractured granite samples, highlighting the ability of the method to characterize complex geological materials and show their internal structure and mineral composition. Additionally, we include the characterization of a metal gasket made of a commercial aluminium alloy, which surrounded the granite sample during experiments. The results show the effectiveness of the technique in recovering information about the internal texture and residual strain of materials that have undergone high levels of plastic deformation.

Willis coupling in one-dimensional poroelastic laminates

We employ the Baker–Campbell–Hausdorff formula to derive closed-form expressions for the effective properties, including emergent Willis coupling, of a one-dimensional heterogeneous poroelastic medium consisting of a periodically repeating two-layer unit-cell. In contrast to the elastic and fluidic analogs, the Willis coupling of this periodic poroelastic medium does not vanish in the low-frequency limit. However, the effective wavenumber and impedance of this asymmetric lamellar material demonstrate symmetric reflection and absorption behavior that is indicative of symmetric structures in the low-frequency limit due to the effect of Darcy’s law on the dynamic effective density, which is inversely proportional to frequency. These closed-form expressions are validated against results obtained by direct numerical evaluation. The scattering coefficients, particularly the two reflection coefficients for incidence from either side of a finite length asymmetric structure, are different at non-zero frequencies but still in the metamaterial limit and are correct when the Willis coupling is included. The results show that asymmetry in poroelastic layers results in direction-dependent absorption coefficients, one of which could be optimized based on layer properties and asymmetry factors. As a consequence, the frequency range of validity of these scattering coefficients is wider when the Willis coupling matrix is accounted for than in its absence. This work paves the way for better control of elastic and acoustic waves in multiphase materials by considering poroelastic behavior.

Probe-Type Multi-Core Fiber Optic Sensor for Simultaneous Measurement of Seawater Salinity, Pressure, and Temperature.

In this article, we propose and demonstrate a probe-type multi-core fiber (MCF) sensor for the multi-parameter measurement of seawater. The sensor comprises an MCF and two capillary optical fibers (COFs) with distinct inner diameters, in which a 45° symmetric core reflection (SCR) structure and a step-like inner diameter capillary (SIDC) structure filled with polydimethylsiloxane (PDMS) are fabricated at the fiber end. The sensor is equipped with three channels for different measurements. The surface plasmon resonance (SPR) channel (CHSPR) based on the side-polished MCF is utilized for salinity measurement. The fiber end air cavity, forming the Fabry-Pérot interference (FPI) channel (CHFPI), is utilized for pressure and temperature measurement. Additionally, the fiber Bragg grating (FBG) channel (CHFBG), which is inscribed in the central core, serves as temperature compensation for the measurement results. By combining three sensing principles with space division multiplexing (SDM) technology, the sensor overcomes the common challenges faced by multi-parameter sensors, such as channel crosstalk and signal demodulation difficulties. The experimental results indicate that the sensor has sensitivities of 0.36 nm/‱, -10.62 nm/MPa, and -0.19 nm/°C for salinity, pressure, and temperature, respectively. As a highly integrated and easily demodulated probe-type optical fiber sensor, it can serve as a valuable reference for the development of multi-parameter fiber optic sensors.

High-speed planar laser-induced fluorescence investigation of nitric oxide generated by hypersonic Mach reflections for computational fluid dynamics validation

In this article, the authors present an experimental investigation of the thermochemical relaxation regions downstream of symmetric Mach reflections generated in Mach 8.5 flows with stagnation enthalpies from 7 to 10 MJ/kg. The experiment was performed in the Hypervelocity Expansion Tunnel at the National Aerothermochemistry and Hypersonics Laboratory of Texas A&M University. The investigation focused on studying the nitric oxide morphology in the vicinity of a strong normal shock wave and shear layers. Experimental planar laser-induced fluorescence measurements at 250 kHz repetition rate with a quasi-simultaneous natural emission photography demonstrate a sufficient rejection of natural emission and reveal intricate flow structures in the shock vicinity. Steady computational fluid dynamics (CFD) flow solutions obtained with the US3D software were used to simulate laser-induced fluorescence signal levels for quantitative comparison against the experimentally acquired data. The investigation accomplished four objectives: complex flowfield visualization in the vicinity of the Mach stem with 4 μs temporal resolution, evaluation of the level of high-temperature chemistry effects introduced to the freestream by the expansion tunnel, both qualitative and quantitative CFD simulation validation, and cross-checking or introduction of fundamental properties of nitric oxide laser-induced fluorescence including absorption cross section for vibrationally excited states of nitric oxide and a collisional quenching cross section of nitric oxide by atomic nitrogen.

Visualizing local bending of lattice planes by extending two-azimuth synchrotron X-ray diffraction datasets to asymmetric reflection

Synchrotron X-ray rocking curve imaging (RCI) is modified to visualize local bending of lattice planes of a single crystal substrate (XR-V-LBLP). This method uses two-azimuth RCI datasets of asymmetric reflection or symmetric reflection. The analysis algorithm is described and a Python software code is provided in the Supplementary material. The two symmetrically equivalent 112¯4 datasets obtained from a GaN (0001) 4-inch wafer are reanalyzed using this software. The normal vector, reciprocal-lattice vector, of the local lattice planes, which is approximately parallel to the sample surface, is formulated as the product of two rotation matrices. This vector is written in polar coordinates using the length and two declination angles, newly introduced in this article. The spatial and probability distributions of the declination angles are also presented. The proposed method enables visualization of the local shape or orientation of the lattice planes of the entire wafer. The limits of application of the method are examined for the samples studied. The sample is found to satisfy two conditions regarding the relative d-spacing difference and the curvature of the lattice planes at all 50 adjacent μm positions.

X-ray scattering study of GaN nanowires grown on Ti/Al2O3 by molecular beam epitaxy.

GaN nanowires (NWs) grown by molecular beam epitaxy on Ti films sputtered on Al2O3 are studied by X-ray diffraction (XRD) and grazing-incidence small-angle X-ray scattering (GISAXS). XRD, performed both in symmetric Bragg reflection mode and at grazing incidence, reveals Ti, TiN, Ti3O, Ti3Al and Ga2O3 crystallites with in-plane and out-of-plane lattice parameters intermediate between those of Al2O3 and GaN. These topotaxial crystallites in the Ti film, formed as a result of interfacial reactions and N exposure, possess little misorientation with respect to Al2O3. As a result, GaN NWs grow on the top TiN layer, possessing a high degree of epitaxial orientation with respect to the substrate. The measured GISAXS intensity distributions are modelled by the Monte Carlo method, taking into account the orientational distributions of NWs, the variety of their cross-sectional shapes and sizes, and the roughness of their side facets. The cross-sectional size distributions of the NWs and the relative fractions of the {1100} and {1120} side facets are determined.

On Some Reflections of Profit and Loss Functions

This article is about the symmetrical reflections of profit and loss functions and the functions obtained from them, which are widely used in economic, economic and financial applications of mathematics. It is seen that the applications in the literature are calculated according to the profit and loss accounts alone. Since the occurrence of loss in an economic activity negatively affects the result of the profit, as a result of the loss, economic activity bankruptcy, etc. decisions are finalized. This has irreversible consequences. The controllability of these two interactive events poses reassuring risks. In short, it enables the manageability of the activity. Applications in life take place on a more real axis. To control, to see the whole event, thus providing the possibility of intervention. Therefore, it started with linear functions in the plane. Evaluations were made on the graphics here.
 The system concepts existing in Mathematical Science, their results in applications, especially in economic activities in the market were examined and their symmetrical reflections with respect to each other were examined. Starting from the reflections of the known profit and loss functions, their interactions with each other were investigated [4]. How the break-even point was reflected according to these reflections, and therefore what they did was examined. The reflection of profit and loss functions according to another function was discussed. This makes it necessary for the control, planning and implementation of the situations observed in an economic activity, which are known in market economies. Therefore, it was emphasized that when the price will change in an economic activity, it will be more important to monitor and manage, and even at what stage the advertisements will be made, as a result of reflections. The loss curve is negatively sloping due to price, reflecting new information on the condition of its slope. It was emphasized that the reflections of the determining factors in marketing vary so much. As is known, prices simultaneously reflect both the value for the buyer of the next (or marginal) unit and the cost for the seller of that unit.

Terahertz multibeam modulation reflection-coded metasurface

Most of reported coding metasurfaces only use phase encoding or amplitude encoding to regulate electromagnetic waves, which limits the flexibility of terahertz wave regulation. In this work, a metasurface element structure is proposed. The metasurface element is composed of three layers, i.e. metal pattern structure layer, intermediate medium layer, and metal base layer. According to the geometric phase principle, the phase coverage in the 2π range can be achieved by rotating the metal pattern structure layer under the incidence of the circular-polarized terahertz wave. The metasurface element structure is arranged reasonably by using the phase coding, and the 1-bit and 2-bit phase coding metasurface are designed. First of all, the coding metasurface with interlacing “0” and “1” is designed to generate a double beam reflection under the vertical incidence of circular polarized terahertz waves, while the two-dimensional checkerboard coding metasurface with “0” and “1” generates a symmetrical four-beam reflection. In addition, the metasurface is designed to deflect the reflected beam, and the coding period is changed to design the metasurface to deflect the reflected beam to the specified angle, showing good flexibility. Finally, the convolutional operation is introduced to flexibly regulate the circular polarized beam, and the functions of beam splitting and reflection beam deflection are obtained. The amplitude coded metasurface is designed under theincidence of the online polarized terahertz wave, and the near-field imaging effect can be realized by the amplitude differentiation of polarization reflection. The designed amplitude coded metasurface realizes the function of imaging in space, presenting the designed “CJLU” pattern, which has different imaging effects at different observation locations. When the observation plane distance is 80 μm at the observation frequency of 1.22 THz, the near-field imaging effect is best. In conclusion, we propose a terahertz multibeam modulation reflection-coded metasurface, which combines geometric phase and amplitude variation to achieve different terahertz wave modulation functions under different polarization incident terahertz waves. The results from the simulated near-field radiation model and the far-field radiation model are both in agreement with the theoretical calculation predictions. The designed metasurface provides a degree of freedom method for terahertz wave polarization and phase manipulation, which greatly improves the efficiency of terahertz wave manipulation and has potential applications in terahertz systems.

Crystalline Quality and Surface Morphology Improvement of Face-to-Face Annealed MBE-Grown AlN on h-BN

In this study, AlN epilayers were grown by ammonia-assisted molecular beam epitaxy on 3 nm h-BN grown on c-sapphire substrates. Their structural properties were investigated by comparing as-grown and postgrowth annealed layers. The role of annealing on the crystalline quality and surface morphology was studied as a function of AlN thickness and the annealing duration and temperature. Optimum annealing conditions were identified. The results of X-ray diffraction showed that optimization of the annealing recipe led to a significant reduction in the symmetric (0 0 0 2) and skew symmetric (1 0 -1 1) reflections, which was associated with a reduction in edge and mixed threading dislocation densities (TDDs). Furthermore, the impact on the crystalline structure of AlN and its surface was studied, and the results showed a transition from a surface with high roughness to a smoother surface morphology with a significant reduction in roughness. In addition, the annealing duration was increased at 1650 °C to further understand the impact on both AlN and h-BN, and the results showed a diffusion interplay between AlN and h-BN. Finally, an AlN layer was regrown on the top of an annealed template, which led to large terraces with atomic steps and low roughness.

Effects of sapphire substrate orientation on Sn-doped α-Ga2O3 grown by halide vapor phase epitaxy using α-Cr2O3 buffers

Heavily Sn-doped films of α-Ga2O3 were grown by halide vapor phase epitaxy (HVPE) on basal plane c-sapphire and on (10-12) r-sapphire substrates with and without α-Cr2O3 thin buffers prepared by magnetron sputtering and annealing in air at 500 °C for 3 h. For both substrate orientations, the use of α-Cr2O3 buffers led to three major effects. The first was a substantial decrease of the half-width of the symmetric and asymmetric x-ray reflections. The second was an order of magnitude decrease of the net donor concentration produced by flowing the same amounts of Sn into the reactor. Third, there was a reduction in the concentration of the major electron trap in the films near E c − 1 eV by more than a factor of two. These results show the major influence of sapphire substrate orientation on the electrical and structural properties of α-Ga2O3 grown by HVPE.

RAD@home citizen science discovery of an active galactic nucleus spewing a large unipolar radio bubble on to its merging companion galaxy

ABSTRACT Active galactic nucleus (AGN) feedback during galaxy merger has been the most favoured model to explain black hole–galaxy co-evolution. However, how the AGN-driven jet/wind/radiation is coupled with the gas of the merging galaxies, which leads to positive feedback, momentarily enhanced star formation, and subsequently negative feedback, a decline in star formation, is poorly understood. Only a few cases are known where the jet and companion galaxy interaction leads to minor off-axis distortions in the jets and enhanced star formation in the gas-rich minor companions. Here, we briefly report one extraordinary case, RAD12, discovered by RAD@home citizen science collaboratory, where for the first time a radio jet–driven bubble (∼ 137 kpc) is showing a symmetric reflection after hitting the incoming galaxy which is not a gas-rich minor but a gas-poor early-type galaxy in a major merger. Surprisingly, neither positive feedback nor any radio lobe on the counter jet side, if any, is detected. It is puzzling if RAD12 is a genuine one-sided jet or a case of radio lobe trapped, compressed and re-accelerated by shocks during the merger. This is the first imaging study of RAD12 presenting follow-up with the Giant Metrewave Radio Telescope, archival MeerKAT radio data and Canada-France-Hawaii Telescope optical data.

Low Temperature Selective Epitaxy of Group-IV Semiconductors for Nanoelectronics

Continuous improvement of device performance is becoming very challenging as the transistor dimension approaches the physical limits of scalability. In particular, the source/drain (S/D) layer resistivity and contact resistance at the S/D region became major components for further parasitic resistance reduction [1]. Therefore, layers with high active doping concertation is required for future technology nodes. From another side, novel architectures such as 3D-stacked devices constraints the allowed thermal budget for epitaxy processes [2]. In this work, we will review our recent achievements on LT epitaxy for both Si:P and SiGe:B layers to enable (i) parasitic resistance reduction and (ii) novel integration schemes.All layers were grown in a 300 mm ASM reduced pressure chemical vapor deposition reactor on Si(001) substrates and patterned substrates.Firstly, we will discuss the benefits of SiP growth at low temperature leading to high active doping concentrations (~1.1×1021 cm-3), as reported in our previous work [3]. Figure 1 shows the omega-2theta scans around the symmetric (004) reflections of the Si:P/Si stacks. As expected, reducing the Si precursor flow leads to a higher substitutional P (~7.5%) incorporation in the layer. The good crystallinity of the SiP layer is attested by the well-defined thickness fringes. Figure 2a represents the XRR scans of non-selective SiP process and selective SiP process compared to 100 nm bare SiO2 on Si substrate. The presence of fringes (red curve) indicates that a 2D amorphous SiP layer is deposited on SiO2. To confirm the full selectivity of the process and the absence of nuclei on the SiO2 surface, top view SEM was performed (cf. Figure 2b).Afterwards, we will focus on the SiGe:B epitaxy at low temperature. Figure 3a shows omega-2theta scans around the symmetric (004) reflections of the SiGe:B/Si stacks for various B flows. The apparent Ge content drops from 52.1% to around 41.3% when B flow was multiplied by 16. The inset represents the reciprocal space map (RSM) around the asymmetric (224) peak of SiGe:B layers grown on Si(001) substrates with the highest B flow. The RSM clearly indicates high quality and fully strained SiGe:B layer. Figure 3b depicts the apparent Ge drop vs B flow. This reduction in Ge content is attributed to B strain compensation effect leading to artificially lower Ge content [4]. Figure 3c represents SiGe:B layer resistivity vs B flow. Resistivity drops until a critical B flow and then increases with increasing B flow. Figure 4 shows active doping concentration and Hall mobility as function of the B flow. The Hall measurements were performed on a cleaved wafer edge and assume a Hall scattering factor of 1. Active carrier concertation increases with increased B flow. As a side effect of the higher activation, the Hall mobility is lowered likely due to an increase in ionized impurity scattering which is the reason why the resistivity does not decrease substantially below a certain value for higher B flows at current growth conditions. Layers with similar physical properties have resulted in S/D metal contact resistivity of ~5×10-10 Ohm.cm2 [5]. Figure 5 depicts the selective process on advanced patterned nanosheet test structures. Figure 5a illustrates the selectivity towards several nanosheet structures, Figure 5b shows a zoomed in image indicating selective process towards inner SiN spacers and SiO2. Figure 5c is a FFT of the SiGe:B area indicated by red square and Figure 5d is an EDS map of the key elements (Si, Ge, O, C, Cl, F, N). Figure 6a and 6b show the selective process stability over 20 runs. The HR-XRD measurements at wafer center are represented in Figure 6a. Figure 6b represents the resistivity at the wafer center. Thickness uniformity across one of the wafer is illustrated in Figure 6c. The results indicate excellent wafer to wafer and within wafer uniformities despite low temperature processing.LT epitaxy offers several advantages to reach high active doping concentrations and enable novel integration schemes. Despite challenges associated to LT epitaxy, in this work we showed the possibility to grow selective layers while maintaining the excellent physical layer properties, within wafer uniformity and wafer to wafer reproducibility.[1] H. Wu et al. EEE International Electron Devices Meeting (IEDM), (2018), pp. 35.4.1.[2] A. Vandooren et al. IEEE Symposium on VLSI Technology, (2018), pp. 69-70.[3] R. Khazaka et al. ECS Meeting s, MA2020-02(24), (2020) 1734-1734.[4] J.M. Hartmann et al. ECS JSST, 3(11) (2014) 382.[5] H. Xu et al. IEEE Symposium on VLSI Technology, (2022), (to be published). Figure 1

Switching between symmetric and asymmetric separation-induced shock reflections in an oscillatory duct flow

Separation-induced shock reflections in straight ducts are generally considered asymmetric for Mach numbers beyond 2.2, but our experiment shows that this is not always the case. A symmetric shock pattern, a proven outcome of following the free-interaction theory (FIT), is observed to appear in an oscillatory duct flow at a Mach number of 2.47. Interestingly, its existence is restricted to the period when the shocks move forward. Once a full retreat starts, it changes suddenly into an utterly asymmetric style that conforms to the past observation. This behavior indicates that the FIT fundamentally plays a limited role in supersonic duct flows.

Structural and electrical properties of thick κ-Ga2O3 grown on GaN/sapphire templates

Thick (23 µm) films of κ-Ga2O3 were grown by Halide Vapor Phase Epitaxy (HVPE) on GaN/sapphire templates at 630 °C. X-ray analysis confirmed the formation of single-phase κ-Ga2O3 with half-widths of the high-resolution x-ray diffraction (004), (006), and (008) symmetric reflections of 4.5 arc min and asymmetric (027) reflection of 14 arc min. Orthorhombic κ-Ga2O3 polymorph formation was confirmed from analysis of the Kikuchi diffraction pattern in electron backscattering diffraction. Secondary electron imaging indicated a reasonably flat surface morphology with a few (area density ∼103 cm−2) approximately circular (diameter ∼50–100 µm) uncoalesced regions, containing κ-Ga2O3 columns with in-plane dimensions and a height of about 10 µm. Micro-cathodoluminescence (MCL) spectra showed a wide 2–3.5 eV band that could be deconvoluted into narrower bands peaked at 2.59, 2.66, 2.86, and 3.12 eV. Ni Schottky diodes prepared on the films showed good rectification but a high series resistance. The films had a thin near-surface region dominated by Ec − 0.7 eV deep centers and a deeper region (∼2 µm from the surface) dominated by shallow donors with concentrations of ≤1016 cm−3. Photocurrent and photocapacitance spectra showed the presence of deep compensating acceptors with optical ionization energies of ∼1.35 and 2.3 eV, the latter being close to the energy of one of the MCL bands. Deep level transient spectroscopy revealed deep traps with energies near 0.3, 0.6, 0.7, 0.8, and 1 eV from the conduction band edge. The results show the potential of HVPE to grow very thick κ-Ga2O3 on GaN/sapphire templates.

Two-Inch Aluminum Nitride (AIN) Single Crystal Growth for Commercial Applications

Aluminum Nitride (AlN) is an Ultra-wide Bandgap (UWBG) semiconductor that attracts significant interest for its potential application for high power switches, high power density, high frequency and high operating temperature for rf. Currently, AlN substrates are being used for ultraviolet (UV) light emitters at wavelengths shorter than 300nm including UVC Light Emitting Diodes (UVC LED) as well as laser diodes. Successful commercialization of the aluminum nitride as an UWBG substrate depends on several factors such as substrate availability, size, quality, and cost. Here we report on the current status of the bulk growth of AlN single-crystals as well as their subsequent processing for making substrates.The AlN crystals are grown using a proprietary physical vapor transport (PVT) technique where a sublimation-recondensation approach is utilized. This method shows very high potential in terms of growing large (> 2-in in diameter) bulk AlN crystals. However, some challenges have yet to be resolved en route to 100 mm diameter crystals. The crystal growth is carried out in a Tungsten crucible that contains the AlN seed and the source material. The AlN source material sublimes and decomposes into Aluminum atoms and Nitrogen molecules. These species are then transported to the seed where they form AlN and incorporate into the growing crystal along the c-axis. Aluminum nitride is used as a native seed utilizing the Al-polar face. Increasing the crystal dimensions demands careful tailoring of thermal gradients to lower the thermally induced stresses and achieve high crystalline quality. Currently, AlN single crystals with diameters > 2 inch are grown using the method described above and larger diameters are possible with appropriate furnace design. Large bulk crystals could be beneficial for production of non-polar and semi-polar substrates which are used to reduce the internal electric fields due to polarization.The AlN crystals are sliced into c-face oriented wafers and subsequently polished. Several substrate parameters are tracked such as the wafer bow, thickness variation, surface roughness, and sub-surface damage. The two-inch AlN wafers have a radius of curvature ≥ 20 m, RMS ≤ 5 Å, and zero sub-surface damage. The crystalline quality is measured by X-ray diffractometry (XRD) rocking curves, etch pit density, and photo-elastic birefringence pattern (cross-polar imaging). Narrow rocking curves for both symmetric and asymmetric reflections with full width at half maximum (FWHM) of 6 - 10 arcsec are measured across the whole the wafer area. The AlN wafers are transparent in the UV region. The graph shows a 52-point map of the absorption coefficient values 8 – 10 cm-1 at 265nm wavelength for a 2-in AlN substrate. The very low UV absorption is linked to the material purity measured by Secondary Ion Mass Spectrometry (SIMS) and Glow Discharge Mass Spectrometry (GDMS). Excellent material purity ensures achievement of high thermal conductivity, a crucial parameter for an UWBG substrate. We measure the thermal conductivity using a Xenon flash method conforming to the ASTM E1461-01 or ASTM E1461-13 standards. Using this method directly on 2-inch AlN substrate we obtain room temperature thermal conductivity 293 W/m*K at room temperature (RT) and with very high slope of about -1.6 for the temperature range from RT to 300°C suggesting minimal phonon scattering.AlN substrates made using the above described methods are used to fabricate high performance, long lifetime UVC LEDs for air purification, water disinfection, surface cleaning, and environmental sensing. High quality pseudomorphic epitaxial layers are grown using Metal-Organic Chemical Vapor Deposition (MOCVD) process to form the device structure. Commercially available WD product (Klaran™) achieve germicidal power outputs that exceed 80 mW with drive currents up to 700 mA at a nominal wavelength of 265 nm. The devices feature long lifetimes exceeding 6000 hours at L50B10 as well as a wide radiation pattern with a viewing angle of 130°. Figure 1

Growth of lattice-relaxed InGaN thick films on patterned sapphire substrates by tri-halide vapor phase epitaxy

Lattice-relaxed thick InGaN films could be obtained using patterned sapphire substrates (PSSs) by tri-halide vapor phase epitaxy. Furthermore, by inserting the GaN intermediate layer between the InGaN epilayer and the PSS, the crystalline quality of the InGaN epilayer was drastically improved. According to the X-ray diffraction ω-rocking curve measurements, the full width at half maximum of the InGaN epilayer was 850 arcsec around the symmetrical reflection and 967 arcsec around the skew-symmetrical reflection. It was also found that the thickness of the GaN intermediate layer influences the crystalline quality of the InGaN epilayer. As the thickness of the GaN intermediate layer increases, the crystalline quality of the GaN intermediate layer gets higher, resulting in the crystalline quality of the InGaN epilayer was improved.

A Study of Defects in InAs/GaSb Type-II Superlattices Using High-Resolution Reciprocal Space Mapping.

In this paper, the study of defects in InAs/GaSb type-II superlattices using high-resolution an x-ray diffraction method as well as scanning (SEM) and transmission (TEM) electron microscopy is presented. The investigated superlattices had 200 (#SL200), 300 (#SL300), and 400 (#SL400) periods and were grown using molecular beam epitaxy. The growth conditions differed only in growth temperature, which was 370 °C for #SL400 and #SL200, and 390 °C for #SL300. A wings-like diffuse scattering was observed in reciprocal space maps of symmetrical (004) GaSb reflection. The micrometer-sized defect conglomerates comprised of stacking faults, and linear dislocations were revealed by the analysis of diffuse scattering intensity in combination with SEM and TEM imaging. The following defect-related parameters were obtained: (1) integrated diffuse scattering intensity of 0.1480 for #SL400, 0.1208 for #SL300, and 0.0882 for #SL200; (2) defect size: (2.5–3) μm × (2.5–3) μm –#SL400 and #SL200, (3.2–3.4) μm × (3.7–3.9) μm –#SL300; (3) defect diameter: ~1.84 μm –#SL400, ~2.45 μm –#SL300 and ~2.01 μm –#SL200; (4) defect density: 1.42 × 106 cm−2 –#SL400, 1.01 × 106 cm−2 –#SL300, 0.51 × 106 cm−2 –#SL200; (5) diameter of stacking faults: 0.14 μm and 0.13 μm for #SL400 and #SL200, 0.30 μm for #SL300.

Four-dimensional tracer flow reconstruction in fractured rock through borehole ground-penetrating radar (GPR) monitoring

Abstract. Two borehole ground-penetrating radar (GPR) surveys were conducted during saline tracer injection experiments in fully saturated crystalline rock at the Grimsel Test Site in Switzerland. The saline tracer is characterized by an increased electrical conductivity in comparison to formation water. It was injected under steady-state flow conditions into the rock mass that features sub-millimeter fracture apertures. The GPR surveys were designed as time-lapse reflection GPR from separate boreholes and a time-lapse transmission survey between the two boreholes. The local increase in conductivity, introduced by the injected tracer, was captured by GPR in terms of reflectivity increase for the reflection surveys, and attenuation increase for the transmission survey. Data processing and difference imaging was used to extract the tracer signal in the reflection surveys, despite the presence of multiple static reflectors that could shadow the tracer reflection. The transmission survey was analyzed by a difference attenuation inversion scheme, targeting conductivity changes in the tomography plane. By combining the time-lapse difference reflection images, it was possible to reconstruct and visualize the tracer propagation in 3D. This was achieved by calculating the potential radially symmetric tracer reflection locations in each survey and determining their intersections, to delineate the possible tracer locations. Localization ambiguity imposed by the lack of a third borehole for a full triangulation was reduced by including the attenuation tomography results in the analysis. The resulting tracer flow reconstruction was found to be in good agreement with data from conductivity sensors in multiple observation locations in the experiment volume and gave a realistic visualization of the hydrological processes during the tracer experiments. Our methodology was demonstrated to be applicable for monitoring tracer flow and transport and characterizing flow paths related to geothermal reservoirs in crystalline rocks, but it can be transferred in a straightforward manner to other applications, such as radioactive repository monitoring or civil engineering projects.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP at BESSY II.

The time-resolved hard X-ray diffraction endstation KMC-3 XPP for optical pump/X-ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four-circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non-linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time-resolution of 17 ps is achieved with the `low-α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X-ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time-resolved detection of the diffracted hard X-ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields arepresented.

Microstructure of epitaxial Mg3N2 thin films grown by MBE

The epitaxial growth of Mg3N2 thin films by molecular beam epitaxy has been recently achieved. This work presents the structural properties of the films, including grain sizes and lattice rotations, as assessed by x-ray diffraction and transmission electron microscopy. The films’ microstructure consists of well-aligned columnar grains 10 nm in diameter that nucleate at the film/substrate interface and display a significant column twist, in the order of 2.5°. As growth proceeds, tilted and twisted mosaic blocks overgrow these columns, as observed in many other epitaxial semiconductors. Yet, the rocking curves on symmetric reflections display extremely narrow peaks (∼50 arc sec), revealing a long-range spatial correlation between structural defects that should not be mistakenly considered a proof of high crystalline quality.