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As track behavior varies in a wide range of service lives and maintenance demands must be specified. The Standard Element Approach provides a specification based on the most important boundary conditions influencing track behavior such as transport load, alignment, superstructure components as well as substructure qualities, and last but not least the functionality of the dewatering system. These parameters show several possible values. The mix of all of these parameter values describes tracks in the entire network. This clustering helps for decision making for strategic asset management: superstructure component use for different parameter sets, calculating average maintenance and renewal demands and thus the respective budgets for a sustainable track strategy avoiding or reducing backlogs. The Standard Element Approach works for all railway infrastructure assets, this chapter focuses on track in detail.

We report on nanoscopic exploration of the luminescence from individual InP quantum dots (QDs) by means of highly spatially resolved cathodoluminescence (CL) spectroscopy directly performed in a scanning transmission electron microscope (STEM). A 7-fold layer stack with high-density InP quantum dots is embedded as an active medium membrane in an external-cavity surface-emitting laser. We characterize the vertical transfer of carriers within the periodic separate confinement heterostructure and determine the capture efficiency of carriers from the cladding layer into the quantum dot layers. Benefiting from the nanoscale resolution of our STEM-CL, we perform single-dot spectroscopy on single isolated QDs in the STEM lamella resolving the details of the excitonic structure of individual quantum dots. Executing highly spatially resolved spectrum line scans within the QD layers, we directly visualize the lateral transport

Land tenure security is increasingly recognized as a foundational element for advancing global sustainable development agendas, but questions remain about how it affects human well-being and environmental outcomes. We identify 117 studies that aimed to estimate the causal effect of land tenure security interventions on these outcomes. Approximately two-thirds of these studies reported positive links between improved tenure security and human well-being or environmental outcomes. Close to half of the studies that examined social and environmental outcomes reported positive impacts on both. The majority of studies assessed government-implemented interventions that statutorily recognized rights through land titling and formalization in the 1990s and 2000s. More research is needed to bolster the body of evidence on the effects of non-technical interventions (for example, capacity building and awareness raising) and the devolution of rights to inform future land policy efforts and accelerate sustainable development. A meta-analysis of 117 studies to determine the impacts of land tenure security on socio-environmental outcomes and sustainable development.

Track engineers face increasing cost pressure and budget restrictions in their work today. This leads to growing difficulty in legitimizing crucial maintenance and renewal measures. As a result, infrastructure managers must ensure they invest all available financial resources as sustainably and efficiently as possible. These boundary conditions require an objective tool enabling both a component-specific condition evaluation and preventive maintenance with renewal planning. The present research introduces such a tool for railway tracks based on innovative track data analyses. This tool includes time-series analyses for predicting future quality behavior. Consequently, the technical necessity of maintenance actions can be derived for every specific track section. In addition, these technical evaluations are combined with economic and operational considerations to plan reasonable maintenance lengths for different track components in the next few years. In a further step, business evaluations by means of annuity monitoring are executed to determine whether ongoing track maintenance or complete track renewal is the most economical solution. This methodology also allows calculating the economic damage caused by neglecting the ideal point in time for reinvestment. On the basis of this economic damage, it is possible to rank projects by priority in the case of insufficient budgets and to ensure that all available resources are invested in the most reasonable manner possible. Furthermore, such analyses clearly show that when a specific degradation level of railway track is reached track renewal is more economic in relation to life-cycle costs than ongoing maintenance.

The current inspection and measurement methodologies for turnouts are time driven and manual and thus based on unloaded measurements. However, these measurements are scarcely usable for behaviour prognosis. Analysis of technologies available on the market shows a possibility for a loaded and automatic inspection by combining already existing technologies. Standard Elements are currently in use as a common tool for assessing the life cycle of turnouts. Those Standard Elements include all maintenance tasks within the entire service life of turnouts, generated and based on experiences as well as on statistical data over an entire network and a long-time span. The economic justification of a maintenance task needs both, the initial investment and the remaining life span to be considered. However, the reasons for the end of service life and therefore lifetime limiting components must be analysed separately. This was done by numerous questionnaires and expert interviews, which have shown that the ballast and the sleepers are the overall reasons for the necessity of a reinvestment.

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Improving land tenure security (LTS) is a significant challenge for sustainable development. The Sustainable Development Goals and other recent global initiatives have renewed and increased the need to improve LTS to address climate change, biodiversity loss, food security, poverty reduction, and other challenges. At the same time, policymakers are increasingly interested in evidence‐based policies and decisions, creating urgency for practitioners and researchers to work together. Yet, incongruent characterizations of LTS (identifying the key components of LTS) by practitioners and researchers can limit collaboration and information flows necessary for research and effective policymaking. While there are systematic reviews of how LTS is characterized in the academic literature, no prior study has assessed how practitioners characterize LTS. We address this gap using data from 54 interviews of land tenure practitioners working in 10 countries of global importance for biodiversity and climate change mitigation. Practitioners characterize LTS as complex and multifaceted, and a majority of practitioners refer to de jure terms (e.g., titling) when characterizing it. Notably, in our data just one practitioner characterized LTS in terms of perceptions of the landholder, contrasting the recent emphasis in the academic literature on landholder perceptions in LTS characterizations. Researchers should be aware of incongruence in how LTS is characterized in the academic literature when engaging practitioners.

Indigenous and community lands, crucial for rural livelihoods, are typically held under informal customary tenure arrangements. This can leave the land vulnerable to outside commercial interests, so communities may seek to formalize their land rights in a government registry and obtain an official land document. But this process can be time-consuming and complex, and in contrast, companies can acquire land relatively quickly and find shortcuts around regulatory burdens. This article reviews and maps 19 community land formalization and 14 company land acquisition procedures is 15 countries in Africa, Asia and Latin America. Comparing community and company procedures identifies multiple sources of inequity.

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With gold prices skyrocketing and demand for other minerals on the rise, mining poses a growing threat to communities and ecosystems around the world. Conducting geospatial analysis of the Amazon biogeographic region, this report estimates, for the first time, the full extent of legal, large-scale mining concessions and illegal mining operations on Indigenous territories within the rainforest. It finds that, together, legal and illegal mining now cover more than 20% of Indigenous lands, endangering hundreds of Indigenous communities and critical ecosystems across 450,000 square kilometers. Mining, the study also shows, is polluting at least 30 Amazonian rivers and eroding communities’ proven ability to prevent deforestation. From 2000 to 2015, Indigenous lands with mining activities had higher incidences of tree cover loss than those without mining. In Bolivia, Ecuador and Peru, for example, forest loss was at least three times higher in Indigenous territories with mining operations – both legal and illegal – than those without; and one to two times higher in Colombia and Venezuela. Yet national laws often favor companies over Indigenous communities, the study’s comprehensive legal assessment of six Amazonian countries, including Bolivia, Brazil, Colombia, Ecuador, Guyana and Peru, reveals. Although these countries all grant important legal protections to communities, these land rights are insufficient and leave most Indigenous Peoples vulnerable to mining. Government oversight of mining activities across Indigenous lands, enforcement of existing legal protections and compliance with international environmental and social safeguards also remain weak in practice, creating tensions between Indigenous communities and miners that often escalate into violent conflict. Protecting Indigenous lands, including the sustainable development and environmental benefits they generate, will require a radical shift in governments’ and companies’ approaches to mining. Amazonian countries should strengthen Indigenous Peoples’ land and natural resource rights; establish and enforce social and environmental safeguards aligned with international standards; more consistently monitor mining operations across Indigenous lands; and step up efforts to identify and prosecute those who facilitate illegal mining practices. Companies, the report recommends, should comply with these stricter safeguards as well as invest in ecological restoration and reforestation of old mining sites.

Microcavities with InGaN quantum wells or GaN-based quantum dots as active medium are building blocks of electrically-driven, low-threshold surface-emitting lasers or single photon emitters in the visible-to-UV spectral range. In this chapter, we highlight essential developments in epitaxial growth techniques of such nitride-based microcavities and their active regions. Modern analytical techniques for structural and optical characterization of these complex heterostructures as presented in this chapter are essential to solve remaining challenges.

Indigenous communities (ICs) have emerged as important players in global efforts to reduce forest carbon emissions, in part because they are viewed as conscientious stewards of the forest lands to which they have legal title. Yet ICs tend to be located in remote areas where deforestation would be limited regardless of who manages them. Therefore, to determine whether IC management actually cuts forest carbon emissions, it is important to control for such confounding factors. To that end, we use propensity score matching and regression to analyze the effects on 2001–2013 deforestation and forest carbon emissions of IC management in the Amazon regions of Bolivia, Brazil, Ecuador and Colombia. We find that IC management reduces both deforestation and forest carbon emissions in Bolivia, Brazil and Colombia. We are not able to discern a statistically significant effect in Ecuador. These findings suggest that IC management can, in fact, help combat climate change.

Higher indium incorporation in self-organized triangular nanoprisms at the edges of InGaN/GaN core-shell nanorods is directly evidenced by spectral cathodoluminescence microscopy in a scanning transmission electron microscope. The nanoprisms are terminated by three 46 nm wide a-plane nanofacets with sharp interfaces forming a well-defined equilateral triangular base in the basal plane. Redshifted InGaN luminescence and brighter Z-contrast are resolved for these structures compared to the InGaN layers on the nanorod sidewalls, which is attributed to at least 4 % higher indium content. Detailed analysis of the inner optical and structural properties reveals luminescence contributions from 417 nm up to 500 nm peak wavelength proving the increasing indium concentration inside the nanoprism towards the nanorod surface.

We present a pulsed reactive magnetron sputter process for high quality AlN on Si (1 1 1) beneficially avoiding any high-temperature growth. Initially, metallic aluminium with a nominal thickness of about one monolayer is deposited at a substrate temperature around 850 °C in an Ar plasma followed by sputtering in an Ar/N plasma. For 250 nm thick AlN layers a surface roughness below 0.2 nm rms is obtained as determined by atomic force microscopy (AFM). Using an Al nucleation step prior to AlN growth substantially improves the crystalline properties of AlN. The FWHM values of the AlN (0 0 0 2) and the AlN (1 0 1 0) diffraction peaks with 0.45° and 0.86°, respectively, are comparable to state-of-the-art AlN on Si layers grown by metalorganic vapour phase epitaxy (MOVPE). Two different N-precursor gases, namely N2 and NH3, lead to distinct layer qualities as revealed by atomic force microscopy and transmission electron microscopy. Only with NH3 substantial lateral growth can be achieved at T = 850 °C which is mandatory to obtain smooth surface morphologies. In MOVPE such lateral AlN growth is typically only achieved at high growth temperatures (T > 1000 °C).

The exfoliation of graphite particles during the treatment in the vibratory disk mill containing commercial sugar was investigated. During the collision of the grinding ring with the grinding chamber wall an intensive stressing of graphite takes place. After treatment in the mill, the resulting dark paste was solved in water and subjected to 10 min sonication. The suspension was centrifuged to remove the not exfoliated multilayered particles. Analysis of Raman spectra shows the presence of graphite sheets in suspension. The represented method of exfoliation is environmentally friendly and scalable.

This work reports on compositionally graded ( 0 0 0 1 ¯ ) N-polar In x Ga 1−x N layers. The InGaN grades with different final In compositions x f up to 0.25 were grown by plasma-assisted molecular beam epitaxy on vicinal GaN base layers with a miscut angle of 4° towards the m -direction. When increasing x f the surface morphology evolved from an interlacing finger structure, attributed to the Ehrlich-Schwobel effect, towards fully strain-relaxed columnar features. Regardless of the crystal morphology and the strain state each graded sample exhibited a bright photoluminescence signal at room temperature spanning the whole visible range. Cross-sectional nanoscale cathodoluminescence evidenced a red-shift of the luminesced signal from 420 to 580 nm along the grade and also showed strong lateral emission inhomogeneities.

The dynamics of magnetic nanoparticles in rotating magnetic fields is studied both experimentally and theoretically. The experimental investigation is focused on the conversion of the magnetic forces to a mechanical torque acting on a ferrofluid confined in a spherical cavity in a rotating magnetic field. Polydispersity usually present in diluted ferrofluids is shown to play a crucial role in the torque conversion. Important features observed experimentally are reproduced theoretically in studies on the dynamics of particles with uniaxial magnetic anisotropy in the presence of thermal noise. The phase lag between the rotating magnetic field and the induced rotating magnetization, as well as the corresponding torque which is transferred to the carrier fluid because of the mutual coupling between both, is analyzed as a function of the particle size. It is shown that for large particles the magnetic moment is locked to the anisotropy axis. On lowering the particle radius, Neel relaxation becomes increasingly important. Illustrative numerical calculations demonstrating this behavior are performed for magnetic parameters typical for iron oxide.

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In this work we show successful metalorganic vapor phase epitaxy (MOVPE) of an AlN/AlGaN distributed Bragg reflector (DBR) that is wavelength matched to GaN quantum dots (QDs) in an AlGaN lambda cavity on top. Full insight into the growth of these structures enables the epitaxy of resonant cavity deep UV single photon emitters. The DBR was grown on an AlN/sapphire template. In order to obtain a high reflectivity as well as a sufficiently large stopband width, the refractive index contrast needs to be maximized. Additionally, the absorption of QD emission in the high gallium containing layer needs to be minimized. A compromise was found for nominal Al-concentration of 70 % in the AlGaN layers. The resulting DBR splits up into self-organized AlN/Al(X)Ga(1-X)N/Al(Y)Ga(1-Y)N trilayers, which add up to desired lambda/2-periods. Therefore, the stopband at 272 nm with a width of 6 nm shows a maximum reflectivity of 99.7 %. GaN QDs were obtained by growth of GaN on AlGaN for 10 s with a V/III-ratio of 30 followed by a growth interruption of 30 s. The QDs exhibit sharp emission lines with a FWHM down to 1 meV in µ-PL measurements. The main intensity of the QD ensemble emission is in the range of 250 nm to 275 nm. Finally, spatially resolved low temperature CL measurements show resonant DBR-enhanced GaN QD emission at 271 nm showing successful wavelength match between a AlN/AlGaN deep UV DBR and GaN QDs in an AlGaN lambda-cavity on top.

Anlagenmanagement versucht bei Produktionsanlagen den gesamten Lebenszyklus, beginnend mit der Planung und Beschaffung, dem anschliesenden Betrieb und der begleitenden Instandsetzung bis zum Ende der Nutzungsdauer der Anlage zu optimieren. Damit sind integrierte Instandsetzungskonzepte im Sinn von „Total Productive Maintenance“ sowie Qualitatsmanagement im Sinn von „Total Quality Management“ notwendige Bestandteile des Anlagenmanagements. Anlagenmanagement beschaftigt sich mit der Frage welche Anlagenauspragung zu wahlen sei. Daraus folgt, dass neben der Instandsetzung auch die Auswahl des Anlagentyps ein integraler Teil des Anlagenmanagements ist. Auf Lebenszykluskosten (LCC) basierende Investitionsentscheidungen und nachfolgende ebenso LCC basierte Instandsetzungsstrategien entsprechen damit weitgehend den Anforderungen des Anlagenmanagements, wobei Lebenszykluskostenbetrachtungen auf RAMS Analysen aufbauen. Erst die Beantwortung der Fragen nach Reliability (Haufigkeit und Art der Fehler), Availability (Verfugbarkeit unter Berucksichtigung der auftretenden Fehler und ihrer Instandhaltbarkeit), Maintainability (Optionen zur Instandsetzung) und Safety (Konsequenzen der Fehler) erlauben das Verhalten einer Anlage und die erforderlichen Instandsetzungsmasnahmen fur die gesamte Nutzungsdauer abzuschatzen und in Form der Lebenszykluskosten zu bewerten.

Many sustainability challenges relate to land use. Land rights frequently underlie the managementand changes in land use, often with a broad range of consequences. In this Voices piece, we inviteexperts to offer their perspectives on the importance of land rights in global sustainability andhuman well-being.

Freshly introduced a-screw dislocations in gallium nitride are an effective source of ultraviolet radiation, characterized by intense emission of narrow luminescence doublet lines in the spectral range of 3.1-3.2 eV. Furthermore, an additional narrow spectral line with an energy of 3.3 eV has been found at the points of intersection of such dislocations, where extended dislocation nodes were formed. In this communication, we report on the spectral properties of the characteristic luminescence of such nodes, which were obtained for the (0001) gallium nitride samples with dislocations introduced by nanoindentation. The spectral position of the dislocation-related luminescence doublet experiences a redshift with increasing distance from the indentation site. It follows the spectral shift of the excitonic near-bandgap emission, associated with stress relaxation. The luminescence of the intersection points exhibits a similar tendency. At certain local positions, its doublet fine structure is observed, which has a spectral linewidth of the order of or even less than that of the exciton. In this case, the spectral splitting between components of the doublet varies irregularly depending on the position of the exciton (i.e., on the mechanical stress). We see a clear indication of quantum dot-like emission. The fine structure of the luminescence of the intersection points can be easily explained by the energy dependence of emission on their size, as well as on their density, in particular, by the formation of paired nodes, which were previously observed in experiments in a transmission electron microscope.

We report on metalorganic vapor phase epitaxy (MOVPE) of distributed Bragg reflectors (DBR) applying a periodic modulation of the GaN doping concentration only. The doping modulation changes the refractive index of GaN via the Burstein-Moss-effect. MOVPE growth of highly doped GaN:Ge and modulation of the dopant concentration by at least two orders of magnitude within few nanometers is required to achieve a refractive index contrast of 2–3%. Such modulation characteristic is achieved despite the presence of Ge memory effects and incorporation delay. We realized DBRs with up to 100 layer pairs by combining GaN:Ge with a nominal doping concentration of 1.6×1020 cm−3 as low-refractive index material with unintentionally doped GaN as high-refractive index layer. Scanning transmission electron microscope images reveal DBR structures with abrupt interfaces and homogenous layer thicknesses in lateral and vertical direction. Reflectance measurements of DBRs designed for the blue and near UV-spectral region show a narrow stopband with a maximum reflectivity of 85% at 418 nm and even 95% at 370 nm. InGaN/GaN multi-quantum well structures grown on top of such DBRs exhibit narrow emission spectra with linewidths below 3 nm and significantly increased emission intensity.

A uniform array of gallium nitride core-shell microrod (MR) light-emitting diode (LED) structures was grown by metalorganic vapor phase epitaxy. Defects and the quantum well (QW) luminescence in an individual rod were investigated by scanning tunneling electron microscopy (STEM) and STEM cathodoluminescence. Luminescence with different wavelength was detected from the quantum wells on the semipolar tip facets and the nonpolar sidewalls of the MRs. Furthermore, the MR array is processed into LED chips. The electro-optical characteristics of the devices are analyzed. Two separate emission bands are distinguished, which are attributed to the QWs on the semipolar tip facets and the nonpolar sidewalls, respectively. To obtain white LEDs, micrograin phosphors were developed which fit in between individual MRs. By using electrophoretic particle deposition, these phosphors are deposited onto the MR LED chips. Color coordinates, color temperature, and device efficiency are evaluated. Blue (top) and phosphor-converted white (bottom) microrod LEDs on 4″ wafer.

We report the growth of green emitting InGaN quantum wells (QWs) by metal-organic vapor-phase epitaxy (MOVPE) on three-dimensional GaN templates. The {10 (1) over bar1} facets of GaN pyramids, fabricated by selective-area growth (SAG), reduce the influence of the quantum-confined Stark effect (QCSE) on the emission properties of the QW. The luminescence properties of a QW are a good indicator for the crystalline quality of the GaN layer beneath. Especially the presence of voids inside the pyramids, as well as stacking faults (SFs) and threading dislocations (TDs) in the wing region strongly influence the strain situation and the incorporation of In into the overlying InGaN layer. Thus, the crystal quality of the GaN pyramid has a strong influence on the efficiency and the emission properties of the active region. Therefore, a low-temperature nucleation on the GaN buffer in conjunction with a decreasing Ga-flux taking the decreasing c-plane growth surface of the pyramid into account was introduced. The low-temperature photoluminescence (PL) properties of the InGaN QW reveal the differences between the standard formation of the pyramid and this modified growth. Cathodoluminescence (CL) and transmission electron microscopy (TEM) measurements confirm the differences between the two growth modes in the crystal quality of the inner part of the pyramid. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adequate railway track condition is a prerequisite for safe and reliable railway operation. Many track quality indices (TQIs) have been developed with the aim of assessing the track condition holistically. These indices combine measurement signals of some or all relevant geometry parameters with different mathematical models. In this paper, a selection of important TQIs is evaluated. Using measurement data of a five kilometer track section, the indices are calculated and their properties are discussed. This study reveals that all indices exhibit drawbacks to varying degrees. As a consequence, a new index has been developed&mdash, the track quality index of Graz University of Technology (TUG_TQI). Its favorable characteristics are presented by means of the above-mentioned test section. The TUG_TQI combines all relevant track geometry parameters, which are normalized beforehand to eliminate over or underrepresentation of different parameters. Thus, the index reliably describes the overall geometrical track quality.

AlN/GaN/AlN quantum disks (Q-disks) embedded in self-assembled hexagonally shaped GaN nanowires have been grown on the Si (111) substrate by plasma-assisted molecular beam epitaxy. To correlate the structural and optical properties of individual Q-disks inside the nanowire, highly spatially resolved cathodoluminescence (CL) spectroscopy in a scanning transmission electron microscope has been performed at 18 K. CL spectrum linescans along a single nanowire clearly identify the emission from the GaN base around 354 nm as well as two recombination channels at 347 nm and 330 nm directly correlated with the AlN/GaN/AlN Q-disk. A detailed characterization of these individual quantum objects is presented.

Investigating closely stacked GaN/AlN multiple quantum wells (MQWs) by means of cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope, we have reached an ultimate spatial resolution of σ CL = 1.8 nm . The pseudomorphically grown MQWs with high interface quality emit in the deep ultraviolet spectral range. Demonstrating the capability of resolving the 10.8 nm separated, ultra-thin quantum wells, a cathodoluminescence profile was taken across individual ones. Applying a diffusion model of excitons generated by a Gaussian-broadened electron probe, the spatial resolution of cathodoluminescence down to the free exciton Bohr radius scale has been determined.

Mapping individual radiative recombination channels at the nanoscale in direct correlation with the underlying crystal structure and composition of III–V semiconductor nanostructures requires unprecedented highly spatially resolved spectroscopy methods. Here, we report on a direct one-by-one correlation between the complex radial structure and the distinct carrier recombination channels of single GaAs-AlGaAs core-multishell nanowire heterostructures using low temperature cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope. Based on an optimized focused ion beam fabrication of the optically active specimen, we directly visualize the radial luminescence evolution and identify four distinct emission lines, i.e., the near band edge and defect luminescence of the GaAs core (819 nm, 837 nm), the emission of the single embedded GaAs quantum well (QW, 785 nm), and the AlGaAs shell luminescence correlated with alloy fluctuations (650–674 nm). The detailed radial luminescence profiles are anticorrelated between QW luminescence and core emission, illustrating the radial carrier transport of the core-shell system. We inspected in detail the low-temperature capture of excess carriers in the quantum well and barriers.

We systematically studied the desorption induced GaN/AlN quantum dot formation using cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope (STEM). The GaN films were grown by metal organic vapor phase epitaxy (MOVPE) on top of an AlN/sapphire-template. After the deposition of a few monolayers GaN at 960°C a growth interruption (GRI) without ammonia supply was applied to allow for quantum dot formation. A sample series with GRI durations from 0 s to 60 s was prepared to analyze the temporal evolution systematically. Each quantum dot (QD) structure was capped with AlN grown at 1195°C. Without GRI the cross-sectional STEM images of the reference sample reveal a continuous GaN layer with additional hexagonally-shaped truncated pyramids of 20 nm height and ~100 nm lateral diameter covering dislocation bundles. Spatially averaged spectra exhibit a broad emission band between 260 nm and 310 nm corresponding to the continuous GaN layer. The truncated pyramids exhibit only drastically reduced CL intensity in panchromatic images. Growth interruption leads to desorption of GaN resulting in smaller islands without definite form located in close vicinity to threading dislocations. Now the emission band of the continuous GaN layer is shifted to shorter wavelengths indicating a reduction of GaN layer thickness. By applying 30 s GRI these islands exhibit quantum dot emission in the spectral range from 220 nm to 310 nm with ultra narrow line widths. For longer growth interruptions the QD ensemble luminescence is shifted to lower wavelengths accompanied by intensity reduction indicating a reduced QD density.

The optical and crystalline properties of a c-plane GaN-based LED structure with embedded semipolar InGaN quantum wells (QW) were investigated using highly spatially resolved cathodoluminescence spectroscopy (CL) directly performed in a scanning transmission electron microscope (STEM). Direct correlation of the cross-sectional STEM image with the simultaneously recorded spatially resolved CL mapping at room-temperature reveals the most intense emission coming from the semipolar InGaN QWs. We observe an inhomogeneous wavelength distribution due to local indium fluctuations and varying QW thickness. In contrast, the donor-acceptor pair recombination (DAP) becomes the dominating luminescence process at 16 K resulting in a superposition of the DAP luminescence and the InGaN QW emission.

In GaN, the basal plane stacking fault type I1 is a two-dimensional defect characterized by a cubic inclusion within the wurtzite structure. Excitons are bound at the BSF I1 similar to the localization in a quantum well heterostructure leading to an efficient radiative recombination. In this study, we present the optical and structural properties of basal plane stacking faults occurrent in silicon doped a-plane GaN layer by means of highly spatially resolved cathodoluminescence spectroscopy performed in a scanning transmission electron microscope. Drastically reduced panchromatic intensity in the vicinity of partial dislocations terminating the stacking faults, points to their non-radiative character. Originating from intersection of two-dimensional defects, the emission at 379.6 nm could be attributed to optically active stair-rod dislocations.

GaN based laser diodes with semipolar quantum wells are typically grown on free-standing pseudo-substrates of small size. We present an approach to create a distributed-feedback (DFB) laser with semipolar quantum wells (QWs) on c-oriented templates. The templates are based on 2-inch sapphire wafers, the method could easily be adapted to larger diameters which are available commercially. GaN nanostripes with triangular cross-section are grown by selective area epitaxy (SAE) and QWs are grown on their semipolar side facets. The nanostripes are completely embedded and can be sandwiched inside a waveguide. For optical pumping, open waveguide structures with only a bottom cladding are used. Using nanoimprint lithography, stripe masks with 250 nm periodicity were fabricated over the whole wafer area. The periodicity corresponds to a 3rd order DFB structure for a laser emitting in the blue wavelength regime. These samples were analyzed structurally by high-resolution transmission electron microscopy (HRTEM), and spatio-spectrally by cathodoluminescence (CL) inside a scanning transmission electron microscope (STEM). Samples with an undoped cap are pumped optically for stimulated emission. To prove the feasibility of realizing a 2nd order DFB structure with this approach, stripes with a 170 nm periodicity are fabricated by electron beam lithography and SAE.

We report on lattice-matched AlInN/GaN distributed Bragg reflectors (DBRs) with improved overgrowth of the AlInN layers. Typically, AlInN layers are exposed to high temperatures when changing to GaN growth conditions. Uncapped AlInN surfaces suffer from In desorption leading to formation of 2 nm thick AlN interface layers with micro-cracks at the AlInN surface. Capping the AlInN with 5 nm GaN at the same temperature and subsequent overgrowth with GaN at high temperatures resolves the In-desorption problem and DBRs with improved interface quality and smooth surfaces are achieved. Optical properties of high-reflectivity DBR structures such as maximum reflectivity and bandwidth are virtually unaffected whether or not unintentionally-grown AlN interlayers are present.

We report the influence of {111} stacking faults on the cathodoluminescence (CL) emission characteristics of cubic GaN (c-GaN) films and cubic GaN/AlN multi-quantum wells. Transmission electron microscopy (TEM) measurements indicate that stacking faults (SFs) on the {111} planes are the predominant crystallographic defects in epitaxial films, which were grown on 3C-SiC/Si (001) substrates by plasma-assisted molecular beam epitaxy. The correlation of the SFs and the luminescence output is evidenced with a CL setup integrated in a scanning TEM (STEM). By comparing the STEM images and the simultaneously measured CL signals it is demonstrated that SFs in these films lead to a reduced CL emission intensity. Furthermore, the CL emission intensity is shown to increase with increasing film thickness and decreasing SF density. This correlation can be connected to the reduction of the full width at half maximum of X-ray diffraction rocking curves with increasing film thickness of c-GaN films. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This paper analyzes whether national laws acknowledge indigenous peoples and other rural communities in 100 countries as owners of waters that arise within their lands. Results derive from information collected by LandMark to score the legal status of community land tenure. Findings are positive; half of all countries recognize communities as lawful possessors of water on their lands. Three quarters permit communities to manage the distribution and use of water on their lands. While 71 percent of countries declare water to be a public resource, this belies the substantial existence of privately owned water. In 29 percent of countries, private water is an identified legal category, and in many other countries obtainable rights to water are sufficiently substantial to imply lawful possession. Communities are beneficiaries mainly where customary rights are accorded status as property rights, or where ownership of public lands and water are devolved to rural collectives. However, opposite trends of nationalization and regulation of water suggest that while legal recognition of community land ownership may rise in the future, this will not necessarily include waters on the land. Irrespective of tenure, rural communities in 72 of 77 countries (93.5 percent) are legally assured access to water for domestic purposes. This is consistent with the rising definition of safe drinking water as a human right, although access does not necessarily come free of cost.

Despite the strong interest in optoelectronic devices working in the deep ultraviolet range, no suitable low cost, large-area, high-quality AlN substrates have been available up to now. The aim of this work is the selective area growth of AlN nanocolumns by plasma assisted molecular beam epitaxy on polar (0001) and semi-polar (11-22) GaN/sapphire templates. The resulting AlN nanocolumns are vertically oriented with semi-polar {1-103} top facets when grown on (0001) GaN/sapphire, or oriented at 58° from the template normal and exposing {1-100} non-polar top facets when growing on (11-22) GaN/sapphire, in both cases reaching filling factors ≥80%. In these kinds of arrays each nanostructure could function as a building block for an individual nano-device or, due to the large filling factor values, the overall array top surfaces could be seen as a quasi (semi-polar or non-polar) AlN pseudo-template.

The realization of reliable single photon emitters operating at high temperature and located at predetermined positions still presents a major challenge for the development of solid-state systems for quantum light applications. We demonstrate single-photon emission from two-dimensional ordered arrays of GaN nanowires containing InGaN nano-disks. The structures were fabricated by molecular beam epitaxy on (0001) GaN-on-sapphire templates patterned with nanohole masks prepared by colloidal lithography. Low-temperature cathodoluminescence measurements reveal the spatial distribution of light emitted from a single nanowire heterostructure. The emission originating from the topmost part of the InGaN regions covers the blue-to-green spectral range and shows intense and narrow quantum dot-like photoluminescence lines. These lines exhibit an average linear polarization ratio of 92%. Photon correlation measurements show photon antibunching with a g(2)(0) values well below the 0.5 threshold for single photon emission. The antibunching rate increases linearly with the optical excitation power, extrapolating to the exciton decay rate of ~1 ns-1 at vanishing pump power. This value is comparable with the exciton lifetime measured by time-resolved photoluminescence. Fast and efficient single photon emitters with controlled spatial position and strong linear polarization are an important step towards high-speed on-chip quantum information management., 8 pages

A pencil-like morphology of homoepitaxially grown GaN nanowires is exploited for the fabrication of thin conformal intrawire InGaN nanoshells which host quantum dots in nonpolar, semipolar and polar crystal regions. All three quantum dot types exhibit single photon emission with narrow emission line widths and high degrees of linear optical polarization. The host crystal region strongly affects both single photon wavelength and emission lifetime, reaching subnanosecond time scales for the non- and semipolar quantum dots. Localization sites in the InGaN potential landscape, most likely induced by indium fluctuations across the InGaN nanoshell, are identified as the driving mechanism for the single photon emission. The hereby reported pencil-like InGaN nanoshell is the first single nanostructure able to host all three types of single photon sources and is, thus, a promising building block for tunable quantum light devices integrated into future photonic circuits., 14 pages, 7 figures