Letteratura scientifica selezionata sul tema "Localized GaN growth"

AbstractThe crystal structure of a-plane GaN/ZnO heterostructures on r-plane sapphire was investigated by using the XRD and TEM measurment. It was found the formation of (220) ZnGa2O4 and crystal orientation of semipolar (10$\bar 1$3) GaN at GaN/ZnO interface. The epitaxial relation of normal surface direction are the sapphire (1$\bar 1$02) // a-GaN (11$\bar 2$0) and ZnGa2O4 (220) // semi-polar GaN (10$\bar 1$$\bar 3$). Beside, the emission peak energy of ZnO appears shift about 60 meV in the GaN/ZnO/GaN heterostructures due to the re-crystallization of ZnO layer with Ga or N atom and the formation of the localized state.

GaN cap layer with different thicknesses was grown on each InGaN well layer during MOCVD growth for InGaN/GaN multiple quantum well (MQW) samples to study the influence of the cap layer on the photoluminescence (PL) characteristics of MQWs. Through the temperature-dependent (TD) PL spectra, it was found that when the cap layer was too thick, the localized states of the quantum wells were relatively non-uniform. The thicker the well layer, the worse the uniformity of the localized states. Furthermore, through micro-area fluorescence imaging tests, it was found that when the cap layer was too thick, the luminescence quality of the quantum well was worse. In summary, the uniformity of the localized states in the quantum wells and the luminescence characteristics of the quantum wells could be improved when a relatively thin cap layer of the quantum well was prepared during the growth. These results could facilitate high efficiency QW preparation, especially for green LEDs.

The review of the results of growth of bulk Al and Ga nitride crystals on foreign substrates by the sublimation sandwich method (SSM) is presented. The kinetics and the mechanism of sublimation and condensation nitrides depending on the growth conditions, structure of the vapor phase, crystal orientation and the distance between the source and the seed are analyzed. It is experimentally established that by joint annealing of AlN and SiC the rate of AlN sublimation significantly increases due to formation of a liquid phase on the crystal surface. Non-uniform distribution of the liquid phase localized mainly near structural and morphological defects results in the selective nature of the surface etching, and also is the reason of deterioration of the growing crystal quality. The process of bulk AlN crystals growth with simultaneous evaporation of the seed allowing to grow crystals without cracks and with the improved parameters is realized. On SiC seeds bulk AlN crystals from 0.5 to 2 inch in diameter are grown.

Single crystal GaN films with a wurtzite structure were grown on the basal plane of sapphire. A high density of threading dislocations parallel to the c-axis crossed the film from the interface to the film surface. They were found to have a predominantly edge character with a Burgers vector. In addition, dislocation hal-loops, elongated along the c-axis of GaN, were also found on the prism planes. These dislocations had a mostly screw character with a [0001] Burgers vector. Substrate surface steps with a height of were found to be accommodated by localized elastic bending of GaN (0001)GaN planes in the vicinity of the film/substrate interface. Observations show that the region of the film, with a thickness of ∼100 nm, adjacent to the interface is highly defective. This region is thought to correspond to the low-temperature GaN “buffer” layer which is initially grown on the sapphire substrate. Based on the experimental observations, a model for the formation of the majority threading dislocations in the film is proposed. The analysis of the results leads us to conclude that the film is under residual biaxial compression.

In this study, GaN-based blue InGaN/GaN light-emitting diodes (LEDs) with different growth rates of the quantum barriers were fabricated and investigated. The LEDs with quantum barriers grown with a higher growth rate exhibit a lower leakage current and less non-radiative recombination centers in the multiple quantum wells (MQWs). Therefore, the LED with a higher barrier growth rate achieves a better light output power by 18.4% at 120 mA, which is attributed to weaker indium fluctuation effect in the QWs. On the other hand, the localized states created by indium fluctuation lead to a higher local carrier density, and Auger recombination in the QWs. Thus, the efficiency droop ratio of the LEDs with a higher barrier growth rate was only 28.6%, which was superior to that with a lower barrier growth rate (39.3%).

This study explores the effects of growth temperature of InGaN/GaN quantum well (QW) layers on indium migration, structural quality, and luminescence properties. It is found that within a specific range, the growth temperature can control the efficiency of In incorporation into QWs and strain energy accumulated in the QW structure, modulating the luminescence efficiency. Temperature-dependent photoluminescence (TDPL) measurements revealed a more pronounced localized state effect in QW samples grown at higher temperatures. Moreover, a too high annealing temperature will enhance indium migration, leading to an increased density of non-radiative recombination centers and a more pronounced quantum-confined Stark effect (QCSE), thereby reducing luminescence intensity. These findings highlight the critical role of thermal management in optimizing the performance of InGaN/GaN MQWs in LEDs and other photoelectronic devices.

In this work, a GaN-on-Si quasi-vertical Schottky diode was demonstrated on a locally grown n-GaN drift layer using Selective Area Growth (SAG). The diode achieved a current density of 2.5 kA/cm2, a specific on-resistance RON,sp of 1.9 mΩ cm2 despite the current crowding effect in quasi-vertical structures, and an on/off current ratio (Ion/Ioff) of 1010. Temperature-dependent current–voltage characteristics were measured in the range of 313–433 K to investigate the mechanisms of leakage conduction in the device. At near-zero bias, thermionic emission (TE) was found to dominate. By increasing up to 10 V, electrons gained enough energy to excite into trap states, leading to the dominance of Frenkel–Poole emission (FPE). For a higher voltage range (−10 V to −40 V), the increased electric field facilitated the hopping of electrons along the continuum threading dislocations in the “bulk” GaN layers, and thus, variable range hopping became the main mechanism for the whole temperature range. This work provides an in-depth insight into the leakage conduction transport on pseudo-vertical GaN-on-Si Schottky barrier diodes (SBDs) grown by localized epitaxy.

90 Shockley partial dislocations in GaN are investigated by first-principles calculations. This work is focussed on the electrical properties of dislocation cores, and on investigating the electrical fields around these defects. The band structure analysis shows that both the and core partials possess a midgap state. The -core dislocations give rise to a donor level Ev +0:87 eV that might explain the absorption peak at 2.4 eV revealed by energy loss spectroscopy measurements. The acceptor level Ev + 1:11 eV localized at the -core dislocations might contribute to the yellow luminescence. These dislocations experience a substantial charge polarization along the [0001] growth axis. In addition, we show that these dislocations tend to charge in a high stress field.

70 MeV Si ions irradiation at the liquid nitrogen temperature (77 K) induced nanoclustering on GaN epilayers grown by Metal Organic Chemical Vapor Deposition (MOCVD) are reported. HRXRD rocking curves show that there are no localized amorphization due to irradiation. Atomic force microscopy images reveal the formation of nanoclusters on the surface of the irradiated samples. On increasing the fluence the number of modified regions on the surface increases and resulted in three dimensional growth of nanocluster due to overlapping and coalescence. X-ray photoelectron spectroscopy (XPS) studies confirm that the surface features are composed of GaN . The variation of carrier concentration and hall mobility with respect to ion fluence are also studied. The effects of ion-beam induced modifications on the structural, surface characteristics and electrical properties of GaN are studied and possible mechanisms responsible for the modifications are discussed.

Despite a high lateral breakdown voltage above 10 kV for large contact distances and a breakdown field of 5 MV cm−1 for short contact distances, an Al0.9Ga0.1N/GaN heterostructure with an 8 nm strained GaN channel grown on an AlN/sapphire template suffers from a low and anisotropic mobility. This work deals with a material study to elucidate this issue. Threading dislocations were observed along the growth direction in transmission electron microscopy pictures and are more in number in the (11−20) plane. Steps were also detected in this plane at the GaN channel interfaces. With the help of device simulations and static characterizations, the deep level transient spectroscopy technique allowed five traps located in the GaN channel to be identified. Most of them are associated with nitrogen- or gallium-vacancy-related defects and are expected to be localized at the interfaces of GaN with the buffer and the barrier. It is likely that these electrically active defects contribute to reduce the mobility in the two-dimensional electron gas. In addition, a link was established between the mobility and the dependence of the quality of the channel interfaces on the crystallographic orientation.

Le nitrure de gallium (GaN) est un semiconducteur prometteur pour les microLEDs, mais lacroissance hétéroépitaxiale du GaN génère des dislocations qui réduisent leur efficacitéd’émission. Afin d’améliorer la qualité du GaN épitaxiée, on propose une approche qui consisteà faire la croissance des pyramides de GaN au-dessus de nanopiliers de GaN/AlN/Si(111)/SiO2.L’excès d’énergie à l'interface de chaque pyramide permettra aux piliers de subir une rotationdurant la coalescence des pyramides de GaN qui sont au-dessus afin que ceux-ci se coalescenten s’alignant cristallographiquement. Les objectifs de cette thèse sont de comprendre lesphénomènes qui ont lieu durant la coalescence, déterminer la qualité des couches GaNobtenues, étudier la rotation des piliers et proposer un modèle de piliers optimales. Ainsi,différents échantillons ont été caractérisés par la diffraction d'électrons rétrodiffusés, lacathodoluminescence et différentes techniques avancées de diffraction des rayons X réalisées àl’European Synchrotron Radiation Facility. Les résultats ont confirmé la rotation des piliers de0.1° après coalescence ainsi que la réalisation des lignes de GaN très homogènes (densité dedislocations ≈1.2 x 107 cm-2). Nous avons pu suivre le comportement du GaN au début de lacoalescence ; les piliers de GaN initialement désorientés sont transformés en gros îlots de GaNbien définis et bien orientés en eux-mêmes. La présence des dislocations au niveau des jointsde grains a été confirmé. De plus, nous avons constaté que tant que l'inclinaison entre les piliersvoisins ne dépasse pas 0.1°, les piliers voisins contribuent à former des domaines cristallinssimilaire en taille à ceux formés au début de la coalescence. Des simulations éléments finis etdes calculs analytiques ont permis d’optimiser les différents paramètres des piliers. Le rayon(r) du pilier a été identifié comme le paramètre ayant le plus grand impact sur l'énergienécessaire à la rotation car cette dernière a été trouvé proportionnelle à r4. Ces résultats ontpermis la réalisation d'un nouveau modèle de piliers optimisé qui a montré des résultatsprometteurs et permettra la fabrication d'îlots GaN de haute qualité adaptés aux microLEDs<br>Gallium nitride (GaN) is a promising semiconductor for microLEDs, but heteroepitaxial growthof GaN generates dislocations that reduce their emission efficiency. To improve the quality ofthe GaN, we propose novel approach based on growing GaN pyramids on top ofGaN/AlN/Si(111)/SiO2 nano-pillars. The approach relies on the excess surface energy at eachpyramid's interface to allow the pillars to tilt/twist, coalescing and aligning the GaN on top. Themain objective of this work is to gain a physical understanding of the processes operating duringcoalescence, determine the GaN quality, investigate the tilt/twist of the pillars and propose anoptimal pillars pattern. Therefore, different samples were studied by electron backscatterdiffraction, cathodoluminescence and advanced X-ray diffraction techniques at the EuropeanSynchrotron Radiation Facility. The results demonstrated the rotation of pillars by 0.1°. Weshowed that achievement of homogenous GaN layers in lines of pillars (dislocation density ≈1.2 x 107 cm-2). We were able to follow the behavior of the GaN at the early stage ofcoalescence, in fact, the initially misoriented GaN pillars, were found to coalesce into largerwell-defined GaN domains with a unique orientation distribution within each domain and a tiltlimit of 0.1° between neighboring pillars was found. Geometrically necessary dislocations werefound at the grain boundaries of the GaN domains. To complete the work, finite elementsimulations and analytical calculations are performed to identify the optimal parameters thatmake the pillars rotation energetically feasible; the radius (r) of the pillar was identified as theparameter with the greatest impact as the energy required to rotate is proportional to r4. Theseresults allowed the realization of new optimized pillars pattern that showed promising resultsand will allow the fabrication of high quality GaN islands suitable for microLEDs

AbstractIn this chapter, important research results for the development of a robust and damage-tolerant multimaterial tunnel lining are presented. This includes the production, design and optimization of fiber-reinforced hybrid segmental lining systems based on numerical models and experimental investigations under tunneling loads. In addition, novel tail void grouting materials are developed and optimized regarding their infiltration and hardening behavior while taking the interaction with the surrounding ground into account. In order to expand the applicability of mechanized tunneling regarding soils characterized by significant swelling potential due to water uptake by clay minerals, a deformable segmental lining system is presented. The risk of damage due to high localized loads is reduced by the integration of additional radial protective layers on the lining segments and a compressible annular gap grout, which protect the tunnel structure by undergoing high deformations after reaching a certain yielding load. However, the deformability of such support systems affects the distribution of the stresses around the tunnel which governs the magnitude and buildup of the swelling pressure in the soil. Therefore, the development of damage tolerant lining systems requires a material and structural design which ensures an optimal soil-structure interaction through a synergy of computational and experimental techniques.

Abstract So far, all the materials physics and devices have used single-crystal multilayer semiconductor structures. Great effort has been made in the growth to achieve precise single-crystal properties and sharp interfaces between adjacent layers. During the fabrication of devices, the process steps attempt to preserve the crystalline integrity. In the past 20 years, hydrogenated amorphous Si has developed rapidly from a research material (first doped to make p-n junction devices in 1976) to the host material for the electronics of displays, with a $4 billion turnover in 1991-1992 (Le Comber 1992). It is now possible to obtain photocells for powering calculators, watches, etc., photoconductors for a wide range of sensing applications, thin-film transistors for driving liquid-crystal displays, and high-voltage thin-film transistors for driving printers. The films of amorphous Si suitable for devices are prepared by plasma-enhanced chemical vapour deposition from SiH4. In the early days, the role of hydrogen was underestimated in this device-grade material, but it is now known to constitute anywhere in the 2-16 at. % range (Street 1991) (this reference is a comprehensive introduction to hydrogenated amorphous Si, including an introduction to multilayers). The role of hydrogen is to saturate all the unsatisfied dangling bonds in a continuous random network. Studies of ideal random networks (shown schematically in Fig. 20.1) indicate that a dangling bond is electronically active with energy levels in and near the gap. The formation of Si-H bonds saturates these bonds and moves the relevant states far from the gap. Only states associated with unsatisfied Si-H bonds and with traditional donors and acceptors remain in the gap, and the behaviour of the latter is similar to that in crystalline semiconductors. The nearest-neighbour distance between Si atoms is the same as in the crystal, and the density of amorphous Si is only a few per cent less than that of single-crystal Si. There is some evidence that the Si-H bonds are metastable, and that movement of hydrogen takes place between different bonds (Street 1991). The electronic structure of an amorphous semiconductor differs from its crystalline counterpart; despite the absence of long-range order, and a band structure in the conventional sense, there is still a principal bandgap. The band-edge densities of states do not have the sharp E energy dependence, but rather an exponential tail brought about by electron states localized in regions of lower potential energy within the amorphous network; these states are spread over a range with an energy scale E0 ∼ 0.1 eV associated with it (Fig. 20.l(b)).

Growing concerns about climate-change pollutants, the widening gap between the rich and the poor, resource shortages, and the world’s gamut of ecological problems have placed new pressures on sustainists. Creating a sustainable society that thrives within its biophysical limits is no longer seen as a distant and utopian objective; it’s now an urgent matter that, if neglected or mismanaged, will bring devastating consequences for the planet and the human economy that lives off of it. The increased political attention, institutional support, and financial commitment to the cause of sustainability means heightened expectations for immediate, tangible results. The public doesn’t want idle chatter; it wants workable solutions to very real problems. Can sustainists seize the moment and lead the transition to the sustainable future? The quest to create a sustainable society faces a host of obstacles, and many pressing questions remain unanswered: How can the entrenched political and corporate interests that perpetuate unsustainability be overcome? How can society willingly transform itself? Where will the money and political will come from to coordinate the transition? Will this sustainable society be “industrialized” or “post-industrial,” “globalized” or “localized”? Will the changes be top–down, bottom–up, or both? By charting the growth and development of sustainability since 1700, this book has not meant to imply that ecotopia is an inevitable end point. Even optimists concede that it’s quite possible that the task is too tall, that industrial society could drive itself straight into the ground, that collapse is a real threat, and that the Industrial Revolution was the first phase of humanity’s protracted extinction event. If sustainability does succeed in undoing the many harms that have caused our ecological predicament, it will only do so with the broad support of the public and through a cooperative effort to adapt and transform. At the risk of bombast, it will have to change the course of human history, and that’s no easy task. This book ends with a discussion of 10 challenges faced by the sustainability movement.

Abstract The Ticha Project is a digital endeavor focused on knowledge repatriation and language reclamation, guided by a Zapotec agenda that centers Zapotec goals and authority. This decolonial practice forges a collaborative, reciprocal scholarship where Zapotec and non-Native experts work together in pursuit of overlapping goals, forming an interdisciplinary community which resists the individualism of academia and draws strength from an inclusive Zapotec collective. In this chapter the authors detail Ticha’s working philosophy through two interrelated projects: (1) Caseidyneën Saën, an e-book of pedagogical materials focused on Colonial Zapotec documents, and (2) the Conversatorios, workshops led by and for Zapotec individuals that serve as important sites of Indigenous knowledge production. The authors challenge readers to find their own community-centered agenda and to grow a bigger linguistics by embracing deeply localized research. Ticha Project na teiby zeiny guieb lo bi (ni na “digital”) ni yzicy xcal nanën quën xtizhën na. Rcazën gyenën teiby ni izhiu par ra Bunyza, ra ni bsanne ra xauzanën, Bunyzado, danoën. Rcazën gyicy ni nanën ni bzuca Dizhtily loën, chiru danoën Bunyza gyieneën gualnezh quën ra buny nan ni queity na ra Bunyza gacneën saën gyenën ropta rseinyën, chiru gyeinychieën teiby guezh nan ni sutyep lo ni rseidyrëng yu rseidy sutyepneën saën rataën. Lo teiby xnez gyets xte Ticha re rniën xa na xjab xtenën, chiru ygwiën lo styop ra zeiny ni cagyienyën ni ngabne sani: (1) Caseidyneën Saën na teiby gyets rseidy ni na teiby xnez gyets guieb lo bi (ni na “e-book”) ni rseidy nazh ra gyets Dizhzado, chiru (2) chi bdop ra Bunyza bgwe dizh nii bzub xliet xa na gal nan xte ra Bunyza. Ra ni cagyual nde rnabën load ual gacbe xii rcaz lazhad ganad tyen chile subru guecy ni racbe buny yu rseidy nezbag laty gunyberuad xai na lazhad.

Vertically aligned single-walled carbon nanotubes (VA-SWNTs) is expected to be an extra-ordinal material for various optical, electrical, energy, and thermal devices. The recent progress in growth control and characterization techniques will be discussed. The CVD growth mechanism of VA-SWNTs is discussed based on the in-situ growth monitoring by laser absorption during CVD. The growth curves are characterized by an exponential decay of the growth rate from the initial rate determined by ethanol pressure. The initial growth rate and decay of it are discussed with carbon over-coat on metal catalysts and gas phase thermal decomposition of precursor ethanol. For the precisely patterned growth of SWNTs, we recently propose a surface-energy-difference driven selective deposition of catalyst for localized growth of SWNTs. For a self assembled monolayer (SAM) patterned Si surface, catalyst particles deposit and SWNTs grow only on the hydrophilic regions. The proposed all-liquid-based approach possesses significant advantages in scalability and resolution over state-to-the-art techniques, which we believe can greatly advance the fabrication of nano-devices using high-quality as-grown SWNTs. The optical characterization of the VA-SWNT film using polarized absorption, polarized Raman, and photoluminescence spectroscopy will be discussed. Laser-excitation of a vertically aligned film from top means that each nanotube is excited perpendicular to its axis. Because of this predominant perpendicular excitation, interesting cross-polarized absorption and confusing and practically important Raman features are observed. The extremely high and peculiar thermal conductivity of single-walled carbon nanotubes has been explored by non-equilibrium molecular dynamics simulation approaches. The thermal properties of the vertically aligned film and composite materials are studied by several experimental techniques and Monte Carlo simulations based on molecular dynamics inputs of thermal conductivity and thermal boundary resistance. Current understanding of thermal properties of the film is discussed.

Abstract The growth of silica particles in coflow diffusion flames has been studied experimentally using light scattering and local thermophoretic sampling techniques. The number densities and volume fractions of both aggregates and spherical particles have been determined calculated by a novel method of using the scattering cross section measured from 90° light scattering with the combination of particle sizes and morphology measured from the localized sampling and TEM image analysis under the assumption of monodisperse distribution of primary particles in an aggregate. Rayleigh-Debye-Gans and Mie theories have been applied to the calculations for fractal aggregates and spherical particles, respectively. Of particular interests are the effects of carrier gas flow rates on the evolution of silica particles and the roles of radial heat and H2O diffusion have been studied when using N2 or O2 as a carrier gas.

Recent developments on ultrafine submonolayer epitaxy on vicinal substrates1 by molecular beam epitaxy (MBE)2 or metalorganic chemical vapor deposition (MQCVD)3,4 made it possible to fabricate arrays of quantum wires named tilted superlattices (TSL) and serpentine superlattices (SSL).2,5 Figure 1 (a) and (b) show the cross sectional profile of a TSL and a SSL. A TSL or a SSL is directly grown on an off axis or vicinal GaAs substrate by alternating deposition of two materials of different compositions by either MBE or MOCVD. The end result is an array of quantum well wires (QWW) shown in figure 1 with a period T, which is determined by the tilt angle, α of the substrate. Such QWW are considered to be superior to bulk and quantum well structures in laser applications due to a larger temperature coefficient, larger relaxation frequency, and smaller threshold current. Furthermore, these structures have several significant advantages in comparison with the arrays of QWW fabricated with the fine line lithography techniques. The lateral dimensions are in the low nanometer range which is suitable for obtaining sufficient quantum size effect, they are obtained processing free, hence is free from processing damage. There is one practical difficulty in the fabrication of a TSL, however. To keep the growth interface vertical one has to know the exact growth rates and keep them constant throughout the growth. Any deviation from the correct value would tilt the growth interface. This difficulty can be circumvented if one deliberately varies the growth rate from less than the correct value to greater than the correct value.5 Then one grows a superlattice with a curved growth interface and somewhere within the grown layer one obtains a vertical interface, hence two dimensional confinement as shown in figure 1 (b). In this paper a study of the optical properties of the SSL for quantum wire laser applications is undertaken. The most important criteria for this application is a large subband spacing, larger than the thermal energy and broadening of the energy levels due to unavoidable imperfections, and narrow subband widths to create well localized and sharp gain peaks.

Energetic beams provide nonthermal conditions for film synthesis in order to achieve growth processes and material properties that cannot be obtained by using a thermal flux. However, a detailed understanding of the gas phase and surface chemistry responsible for film growth and the resulting material properties has not been achieved for the complex reaction and transport processes involved. In the following it will be shown how the deposition chemistry can be studied using localized initiation of the deposition chemistry by a VUV laser.

Abstract Hydrogen energy and hydrogen fuel cell vehicles have become the key development directions of countries around the world, and high-pressure hydrogen storage technology is the most widely used hydrogen storage method in hydrogen fuel cell vehicles. The on-board Type 4 hydrogen storage cylinders are an important hydrogen storage component of hydrogen fuel cell vehicles, and the storage medium is flammable and explosive high-pressure hydrogen. Therefore, the on-board Type 4 hydrogen storage cylinders determine the safety of the hydrogen fuel cell vehicles. When a hydrogen fuel cell vehicle accidentally catches fire, the high-pressure hydrogen storage cylinder may be exposed to localized fire, and gas cylinders are at risk of explosion before the pressure relief device (TPRD) operates. In this paper, the computational fluid dynamics method was used to establish the numerical calculation model of the on-board Type 4 hydrogen storage cylinders under localized fire, and the accuracy of the numerical calculation model was verified by the fire test results. Using the established numerical calculation model, the heat transfer characteristics of the 35MPa on-board Type 4 hydrogen storage cylinders after localized fire for 600s was analyzed, the effect of different filling media on the heat transfer characteristics of Type 4 hydrogen storage cylinder was studied. The results show: The temperature of the burning area of gas cylinder was significantly higher than that of other areas. The temperature growth rate of the gas in cylinder remained basically unchanged, and the maximum temperature of the gas reached 353K at 600s. As the burning time goes on, the growth rate of the gas pressure increased continuously, and the gas pressure reached 36.3MPa at 600s. And different filling mediums have little effect on the heat transfer characteristics of on-board Type 4 hydrogen storage cylinders.

External corrosion growth rate is an essential parameter to establish the time interval between successive pipe integrity evaluations. Actual corrosion rates are difficult to measure or predict. NACE Standard RP0502 [1] recommends several methods including comparison with historical data, buried coupons, electrical resistance (ER), and Linear Polarization Resistance (LPR) measurements. This paper presents a testing program and procedure to validate the use of the LPR and ER methods to enhance the estimation of corrosion growth rates and improve the selection of reassessment intervals of gas transmission pipelines. Laboratory and field tests were performed using the LPR and ER technologies. The evaluation of soil parameters that affect localized corrosion included its type, moisture content, pH, resistivity, drainage characteristics, chloride and sulfite levels, and soil Redox potential. The results show that the LPR device provides instantaneous measurement of corrosion potential and it may be used to reflect the variations of corrosion rates with the changes of soil conditions, moisture, and temperature. However, LPR measurements are more efficient in saturated soils with uncertainty about its validity in partially and totally dry soils. Consequently, seasonal changes in soil conditions make it difficult to estimate total corrosion growth rate. On the other hand, the measurements using the ER method provided consistent estimates for long-term corrosion growth rates. Corrosion growth rates were also evaluated from a previous study by the National Institute of Standards (NIST) [2]. A procedure was developed to correlate soil properties to corrosion rates from the ER measurements and NIST data. The procedure was implemented in a computer program to provide an estimate of corrosion rate based on the soil input data and allows the operator to use the ER probes to improve the reliability of corrosion rate estimates.

The research in Japan on the wide-bandgap materials for short-wavelength light emitting devices based on modem growth techniques of MOVPE and MBE started in early 1980s. The first attempt to organize a cooperative research system for wide-gap semiconductors in Japan can be traced back to the year 1984, when about 20 university research groups which had already been engaged in research on wide-gap II-VI materials gathered and started to make plans for joint research. This was followed by a three-year period research project on the property control of compound semiconductors, especially of II-VI, wide-gap III-V and I-III-VI2 materials, within a priority area research program for "New Functionality Materials - Design, Preparation and Control", which started in 1987 under support of the Ministry of Education, Science and Culture. It was renewed in 1990 as an advanced project for additional three years, and since then it has been running with emphasis on atomic-scale control of crystal growth, control of localized electronic states, creation of new optical functionality, quantum structures and new properties, and control of material properties for new optical devices. Under the project, the growth of wide-gap II-VIs, especially of ZnSe and related alloys and superlattices has been very actively studied in many university laboratories.

The use of high performance ceramic thermal barrier coatings in stationary gas turbines requires fundamental knowledge of their fatigue behavior under high temperature gradients and thermal cycling. An experimental method based on rapid laser heating complemented with finite-element calculations was developed in order to identify the major damage mechanisms and to obtain a data set for reliability assessment of thermal barrier coatings for temperature and stress fields similar to gas turbine conditions. The observed failures are strongly related to the pretreatment procedures such as annealing under high temperature gradients and isothermal long-term oxidation. The vertical crack patterns observed close to the top surface of the Zirconia coating are generated at the moment of rapid cooling. These cracks are induced by high biaxial tensile stresses caused by the temperature gradient and the stress reversion after relaxation of compressive stresses at high temperatures. The long-term fatigue behavior is decisively determined by two processes: (i) The porous Zirconia loses its damage tolerant properties by densification. (ii) The growth of an oxide layer at the bond coat degrades adhesion and produces localized stress fields at the interface. Cyclic loads increase the length of existing in-plane cracks and delaminations rather than enlarging their number. Misfit of the crack flanks and wedge effects are the driving forces for continued crack propagation. These experimental results are discussed in terms of fracture mechanics.

The War in the Pacific National Historical Park (WAPA), a protected area managed by the National Park Service (NPS), was established "to commemorate the bravery and sacrifice of those participating in the campaigns of the Pacific Theater of World War II and to conserve and interpret outstanding natural, scenic, and historic values on the island of Guam." Coral reef systems present in the park represent a vital element of Guam?s cultural, traditional, and economical heritage, and as such, are precious and in need of conservation. To facilitate the management of these resources, NPS determined that a scleractinian (stony coral) species survey was necessary to establish a baseline for existing coral communities and other important factors for conservation. EnviroScience, Inc. performed a survey of stony coral species, coral habitat, and current evidence of stressors at WAPA?s H?gat and Asan Units in 2022. This report summarizes these findings from a management perspective and compares its findings to previous survey data from 1977 and 1999 (Eldridge et al. 1977; Amesbury et al. 1999). WAPA is located on the tropical island of Guam, located on the west-central coast of the island, and encompasses 2,037 acres. Underwater resources are a significant component of the park, as 1,002 acres consists of water acres. The park is comprised of seven units, of which two of these, the H?gat and Asan Beach Units, include all the oceanic water acres for the park. The H?gat Beach Unit (local spelling, formerly known as ?Agat?) is located at the south-west portion of the park and consists of 38 land acres and 557 water acres (NPS 2003). The Asan Beach Unit consists of 109 acres of land and 445 water acres (NPS 2003). A current baseline for existing coral communities and other important factors for conservation necessitates the need for up-to-date data on the location, presence, relative abundance, and present health of corals. Park managers need this updated data to determine where and how to best focus conservation priorities and identify restoration opportunities. Management actions in park reef areas informed by this inventory included identifying locations where there were: high rates of sedimentation; high coral biomass; rare or threatened species, with a priority given to species endemic to Guam and listed as ?threatened? under the U.S. Endangered Species Act (ESA; Acropora globiceps, A. retusa, A. speciosa, and Seriatopora aculeata); coral persistence and decline, disease and/or nuisance species, including the crown-of-thorns starfish (Acanthaster cf. solaris, ?COTS?) and the sponge Terpios hoshinota; and bleached areas. All work carried out was in accordance with the NPS statement of work (SOW) requirements, which involved a quantitative inventory using both new and pre-existing transects. The resulting transects totaled 61 (including the four from the 1999 study), each measuring 50 meters in length and distributed across depths of up to 50 feet. Divers took photo-quadrat samples covering an area of approximately 9 m?, encompassing 50 photo-quadrats of dimensions 0.50 m x 0.36 m (n=50). The collective area surveyed across all 61 transects amounted to ~549 m?. Additionally, a qualitative search was conducted to enhance documentation of coral species that have limited distribution and might not be captured by transects, along with identifying harmful species and stressors. Timed roving diver coral diversity surveys were carried out at a total of 20 sites occurring within the waters of WAPA, including eight sites at the H?gat unit and 12 sites at the Asan unit. The findings from this report reveal significant disparities in benthic cover compositions between H?gat and Asan units. The H?gat unit exhibits high abundances of turf algae and unconsolidated sediment while the Asan beach unit presents a different scenario, with hard coral as the dominant benthic cover, followed closely by crustose coralline algae (CCA). The Asan unit is also more difficult to access from shore or boat relative to H?gat which provides that unit some protection from human influences. The Asan beach unit's prevalence of hard coral, CCA, and colonizable substrate suggests a more favorable environment for reef growth and the potential benefits of maintaining robust coral cover in the area. These distinct differences in benthic communities highlight the contrasting ecological dynamics and habitats of the two study areas. Across both H?gat and Asan beach unit transects, a total of 56 hard coral species were recorded from 27 genera, with 44 species recorded from the H?gat unit and 48 species recorded from the Asan unit. Of the four historical transects surveyed in the Asan unit from 1999, three experienced declines in percent coral cover (17.38-78.72%), while the fourth had an increase (10.98%). During the timed roving diver coral diversity surveys, a total of 245 hard coral species, including 241 scleractinian coral species representing 49 genera and 4 non-scleractinian coral species representing 4 genera were recorded. Uncertainties related to coral identification, unresolved boundaries between morphospecies, differences in taxonomists' perspectives, and the rapidly evolving state of coral taxonomy have significant implications for species determinations during coral diversity surveys. While the recent surveys have provided valuable insights into coral diversity in WAPA waters, ongoing taxonomic research and collaboration among experts will be essential to obtain a more comprehensive and accurate understanding of coral biodiversity in the region. Of the several ESA coral species that were searched for among the H?gat and Asan beach units, Acropora retusa was the only coral species found among quantitative transects (n=2) and A. globiceps was observed during coral diversity surveys. Acropora speciosa, which was dominant in the upper seaward slopes in 1977, is now conspicuously absent from all the surveys conducted in 2022 (Eldredge et al., 1977). The disappearance and reduction of these once-dominant species underscores the urgency of implementing conservation measures to safeguard the delicate balance of Guam's coral reefs and preserve the diversity and ecological integrity of these invaluable marine ecosystems. Other formerly common or locally abundant species were infrequently encountered during the diversity surveys, including Acropora monticulosa, A. sp. ?obtusicaulis?, A. palmerae, Stylophora sp. ?mordax?, Montipora sp. ?pagoensis?, and Millepora dichotoma. Significant bleaching-associated mortality was recorded for these species, most of which are restricted to reef front/margin zones exposed to moderate-to-high levels of wave energy. Sedimentation was present in both H?gat and the Asan units, though it was more commonly encountered in H?gat transects. While significant portions of the reef area within the WAPA H?gat unit are in poor condition due to a variety of stressors, some areas still hosted notable coral communities, which should be a potential focus for park management to prevent further degradation. There is a need for more effective management of point source pollution concerns, particularly when subpar wastewater treatment or runoff from areas with potential pollution or sediment-laden water is flowing from nearby terrestrial environments. Future monitoring efforts should aim to establish a framework that facilitates a deeper understanding of potential point source pollution incidents. This would empower park managers to collaborate with adjacent communities, both within and outside of park boundaries, to mitigate the localized impacts of pollution (McCutcheon and McKenna, 2021). COTS were encountered during transect surveys as well as in coral diversity surveys. including along the upper reef front/reef margin at site Agat-CS-2. The frequency of these observations, particularly in the WAPA H?gat unit and where stress-susceptible corals are already uncommonly encountered, raise concern about the ability of the populations of these coral species to recover following acute disturbance events, and calls in to question the ability of some of these species to persist in WAPA waters, and in Guam?s waters more broadly. More frequent crown-of-thorns control efforts, even if only a handful of sea stars are removed during a single effort, may be required to prevent further loss to vulnerable species. There were several documented incidents of Terpios hoshinota covering large sections of branching coral in the reef flat along transects, but it is still unclear how detrimental this sponge is to the overall reef system. There is a concern that elevated levels of organic matter and nutrients in the water, such as those resulting from sewage discharge or stormwater runoff, could lead to increased Terpios populations (De Voogd et al. 2013). Consequently, it is important to track populations in known areas of sedimentation and poor water quality. The presence of unique species at single survey sites within the study areas underscores the ecological importance of certain locations. Some species are known to occur in other locations in Guam, while a few may be limited to specific sites within WAPA waters. These differences are likely influenced by environmental and biological factors such as poor water quality, severe heat stress events, chronic predation by crown-of-thorns sea stars, disease, and reduced herbivore populations. These factors collectively shape the condition of the benthic community, leading to variations in species distribution and abundance across the study sites. Documenting coral stress and identifying potentially harmful species allows for proactive management strategies to prevent the establishment of nuisance or detrimental species while populations are still manageable. Updated data on the location, presence, relative abundance, and health of corals is essential for park managers to prioritize conservation efforts and identify restoration opportunities effectively. Observations from this report raise concerns about the health and resilience of coral ecosystems in the H?gat unit and emphasize the need for knowledge of local factors that shape benthic community structure. Understanding the drivers responsible for these variations is crucial for effective conservation and management strategies to preserve the ecological balance and overall health of coral reefs in both units. Continued monitoring efforts will be critical in assessing long-term trends and changes in benthic cover and enabling adaptive management approaches to safeguard these valuable marine ecosystems in the face of ongoing environmental challenges.