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The Vietnamese Mekong Delta (VMD) has been affected by environmental challenges for several decades, including coastal erosion and land subsidence. Subsidence rates of several cm/yr have been reported in parts of the delta, which are one order larger than the regional sea level rise of 3.3 mm/yr. The precise monitoring of subsidence with high spatial and temporal resolution is essential to understand its causes and associated risks, and to support the development and monitoring of countermeasures. Here, we present subsidence estimates between 2017 and 2022 derived from advanced persistent scatterer interferometry (PSI) applied to Sentinel-1 data. The PSI approach fully integrates temporary persistent scatterers, in order to derive the best possible persistent scatterer network for long time series. Furthermore, we adapted a method to optimally integrate reference points with known displacement to suppress spatially correlated nuisance (SCN) in the derived displacement time series. Due to a lack of geodetic references, we built an infrastructural reference network based on large bridges with piled foundations of about 70 m depth, which are only affected by compaction in deeper soil layers. We compare the method with the standard referencing approach in PSI, and show that referencing to the selected reference bridges with our method enables to measure the largest part of the subsidence while reducing the SCN considerably. We find the highest subsidence rates of more than 7 cm/yr mainly in urban areas, and various kinds of temporal nonlinearities.

Direct epitaxial growth of III-V on Si for optical emitters and detectors remains a challenge. Here, the authors demonstrate in-plane monolithic integration of an InGaAs nanostructure p-i-n photodetector on Si capable of high-speed optical data reception at 32 Gbps enabled by a 3 dB bandwidth exceeding 25 GHz.

We employ self-consistently coupled opto-electrical simulations to explore the design strategy for a proposed electrically pumped metallic coaxial ring cavity nanolaser. With the optical cavity optimized to the physical size of 1.4(λ/n)3, the lasing ability using two gain medium schemes, bulk InGaAs and InGaAs/InP multiple quantum wells (MQWs), are compared. It is shown that the device with the bulk gain medium lases at 1568 nm, while the gain fails to overcome the optical loss in the case of the MQW gain medium due to its lower modal confinement ratio. Variations in material parameters like carrier mobility and Auger coefficient in the bulk laser or carrier capture time in the MQW laser are found to hardly change the lasing ability, although they do impact lasing threshold and efficiency in the bulk case. To study the possibility of further device down-scaling, the lasing feasibility of a smaller cavity with a size of 0.23(λ/n)3 is investigated. We demonstrate that neither including the Purcell effect nor using a metallic substrate for better mode confinement improves the lasing behavior.

The Mekong delta, like many deltas around the world, is subsiding at a relatively high rate, predominately due to natural compaction and groundwater overexploitation. Land subsidence influences many urbanized areas in the delta. Loading, differences in infrastructural foundation depths, land-use history, and subsurface heterogeneity cause a high spatial variability in subsidence rates. While overall subsidence of a city increases its exposure to flooding and reduces the ability to drain excess surface water, differential subsidence results in damage to buildings and above-ground and underground infrastructure. However, the exact contribution of different processes driving differential subsidence within cities in the Mekong delta has not been quantified yet. In this study we aim to identify and quantify drivers of processes causing differential subsidence within three major cities in the Vietnamese Mekong delta: Can Tho, Ca Mau and Long Xuyen. Satellite-based PS-InSAR (Persistent Scatterer Interferometric Synthetic Aperture Radar) vertical velocity datasets were used to identify structures that moved at vertical velocities different from their surroundings. The selected buildings were surveyed in the field to measure vertical offsets between their foundation and the surface level of their surroundings. Additionally, building specific information, such as construction year and piling depth, were collected to investigate the effect of piling depth and time since construction on differential vertical subsidence. Analysis of the PS-InSAR-based velocities from the individual buildings revealed that most buildings in this survey showed less vertical movement compared to their surroundings. Most of these buildings have a piled foundation, which seems to give them more stability. The difference in subsidence rate can be up to 30 mm/year, revealing the contribution of shallow compaction processes above the piled foundation level (up to 20 m depth). This way, piling depths can be used to quantify depth-dependent subsidence. Other local factors such as previous land use, loading of structures without a piled foundation and variation in piling depth, i.e., which subsurface layer the structures are founded on, are proposed as important factors determining urban differential subsidence. PS-InSAR data, in combination with field observations and site-specific information (e.g., piling depths, land use, loading), provides an excellent opportunity to study urban differential subsidence and quantify depth-dependent subsidence rates. Knowing the magnitude of differential subsidence in urban areas helps to differentiate between local and delta wide subsidence patterns in InSAR-based velocity data and to further improve estimates of future subsidence.

In this paper a simulation study of the effect of conduction and valence band offsets on the subthreshold swing (SS) of a double-gate tunnel field-effect transistor (TFET) with gate-overlapped source is presented. The simulations show that if the pn-junction and the hetero-junction coincide, the band offsets can significantly improve the SS by suppressing the so-called point tunneling at the pn-junction. It turns out that the performance of an n-channel TFET is determined by the direct conduction band offset whereas that of a p-channel TFET is mainly effected by the energy difference between the light hole bands of the two materials. Thus, the performance of the hetero-junction TFET can be improved by selecting material systems with high conduction or valence band offsets. The misalignment between the pn-junction and the hetero-junction is shown to degrade the SS. The above-described band-offset engineering has been applied to the GeSn/SiGeSn hetero-structure system with and without strain. Simulations of GeSn/SiGeSn hetero-TFETs with band-to-band-tunneling parameters determined from pseudopotential calculations show that compressive strain in GeSn widens the design space for TFET application while tensile strain reduces it.

Knowledge about the existing materials in urban areas has, in recent times, increased in importance. With the use of imaging spectroscopy and hyperspectral remote sensing techniques, it is possible to measure and collect the spectra of urban materials. Most spectral libraries consist of either spectra acquired indoors in a controlled lab environment or of spectra from afar using airborne systems accompanied with in situ measurements. Furthermore, most publicly available spectral libraries have, so far, not focused on facade materials but on roofing materials, roads, and pavements. In this study, we present an urban spectral library consisting of collected in situ material spectra with imaging spectroscopy techniques in the visible and near-infrared (VNIR) and short-wave infrared (SWIR) spectral range, with particular focus on facade materials and material variation. The spectral library consists of building materials, such as facade and roofing materials, in addition to surrounding ground material, but with a focus on facades. This novelty is beneficial to the community as there is a shift to oblique-viewed Unmanned Aerial Vehicle (UAV)-based remote sensing and thus, there is a need for new types of spectral libraries. The post-processing consists partly of an intra-set solar irradiance correction and recalculation of reference spectra caused by signal clipping. Furthermore, the clustering of the acquired spectra was performed and evaluated using spectral measures, including Spectral Angle and a modified Spectral Gradient Angle. To confirm and compare the material classes, we used samples from publicly available spectral libraries. The final material classification scheme is based on a hierarchy with subclasses, which enables a spectral library with a larger material variation and offers the possibility to perform a more refined material analysis. The analysis reveals that the color and the surface structure, texture or coating of a material plays a significantly larger role than what has been presented so far. The samples and their corresponding detailed metadata can be found in the Karlsruhe Library of Urban Materials (KLUM) archive.