Between approximately 17,500 and 15,000 years ago, the Atlantic meridional overturning circulation weakened substantially in response to meltwater discharges from disintegrating Northern Hemispheric ...glacial ice sheets. The global effects of this reorganization of poleward heat flow in the North Atlantic extended to Antarctica and the North Pacific. Here we present evidence from North Pacific paleo surface proxy data, a compilation of marine radiocarbon age ventilation records, and global climate model simulations to suggest that during the early stages of the Last Glacial Termination, deep water extending to a depth of approximately 2500 to 3000 meters was formed in the North Pacific. A switch of deepwater formation between the North Atlantic and the North Pacific played a key role in regulating poleward oceanic heat transport during the Last Glacial Termination.
A continuous composite oxygen isotope (δ18O) stratigraphy from benthic foraminifera in the Bering Sea was reconstructed in order to provide insight into understanding sea-ice evolution in response to ...Northern Hemisphere Glaciation. Oxygen isotope records from multiple species of benthic foraminifera at Integrated Ocean Drilling Program (IODP) Expedition 323 Site U1343 (54°33.4′N, 176°49.0′E, water depth 1950m) yield a highly refined orbital-scale age model spanning the last 1.2Ma, and a refined age model between 1.2 and 2.4Ma. An inter-species calibration was used to define species offsets and to successfully obtain a continuous composite benthic δ18O record, correlated with the global composite benthic δ18O stack curve LR04 to construct an orbital-scale age model. The consistency of the benthic δ18O stratigraphy with biostratigraphy and magnetostratigraphy confirms the reliability of both methods for constraining age. The time difference between cyclic changes in sedimentary physical properties and glacial–interglacial cycles since 0.8Ma is notable, and suggests that physical properties alone cannot be used to construct an orbital-scale age model. Amplitude changes in physical properties and a significant drop in the linear sedimentation rate during glacials after 0.9Ma indicate that the glacial sea-ice edge extended beyond the Bering Sea Slope (Site U1343) at this time.
Step-by-step change of growth temperature was investigated to control GaN nanorod diameter in the molecular-beam epitaxy. It was found that when the growth temperature is decreased, the GaN nanorod ...diameter gradually increases with the progress of lower temperature growth. On the contrary, opposite change of the diameter was observed when the growth temperature is increased during nanorod growth. The Ga adatom density on the GaN surface and the dissociation in the GaN nanorods play an important role on the shape variation of nanorods and we can control the diameter of GaN nanorods by regulating the growth temperature.
•The self-assembled GaN nanorods were grown under a nitrogen-rich condition.•The variation of nanorod diameter was observed by the change of growth temperature.•The mechanism of the diameter variation was explained in terms of Ga adatom density.
We reconstructed the ventilation record of deep water at 2100 m depth in the mid-latitude western North Pacific over the past 25 kyr from radiocarbon measurements of coexisting planktic and benthic ...foraminiferal shells in sediment with a high sedimentation rate. The 14C data on fragile and robust planktic foraminiferal shells were concordant with each other, ensuring high quality of the reconstructed ventilation record. The radiocarbon activity changes were consistent with the atmospheric record, suggesting that no massive mixing of old carbon from the abyssal reservoir occurred throughout the glacial to deglacial periods.
Hydrogen-induced cracking (HIC) tests were performed on fourteen types of X65 line pipe steels in various environments in which the hydrogen sulfide (H2S) partial pressures (PH2S) were in the range ...from 1 × 10/5 MPa to 0.1 MPa and pH was in the range from 2 to 5. The conditions governing HIC occurrence were investigated and the following results were obtained: —Hydrogen permeability in steel (PerFe) was formulated as a function of PH2S and pH (PerFe) = 7.1 + 0.96 × (1.4logPH2S − 0.51 pH), where 0.1 MPa ≥ PH2S ≥ 1 × 10−3 MPa and 5 ≥ pH; PerFe = 3.3 + 0.75 × (0.3logPH2S − 0.51 pH), where 1 × 10−3 MPa > PH2S ≥ 1 × 10−5 MPa and 5 ≥ pH. —Critical hydrogen permeability in steel (Percrit) was expressed as a function of the critical length of inclusions (acrit) and the maximum hardness of the center-segregation zone (Hvmax) for the investigated thermomechanical-controlled process (TMCP) steels and the controlled rolled and air-cooled (CR) steels (log Percrit = 1.7 − 0.0030 Hv − 1/4logacrit). —If the maximum hardness of the center-segregation zone (Hvmax) and the size of inclusions—such as manganese sulfide (MnS) in TMCP steels and CR steels—are given, the occurrence of HIC can be predicted for a given environmental condition. The prediction model indicates how the sour-resistant line pipe steels should be produced, reducing the elongated inclusion length and the hardness in the center-segregation zone.
X-ray photoemission spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED) have been used to investigate the initial stages of InP growth on H-terminated Si and native Si oxide ...surfaces. By annealing at 800°C, the H-terminated Si surface exhibits a (2×1) RHEED pattern while the native oxide surface just shows a halo RHEED pattern. After exposing them to P2 flux, the Si(2×1) clean surface exhibits a (2×1) RHEED pattern while the native Si oxide layer always shows the halo RHEED pattern. XPS measurement reveals that while P atoms adsorb on the Si(2×1) surface, the adsorption of P atoms does not take place on the native Si oxide surfaces. In consequence of the difference in the adsorption of P atoms between the clean Si and Si oxide surfaces, InP does not grow on the Si oxides at temperatures above 450°C while InP grows on the clean Si substrates. Based on the findings, we will discuss the mechanism of the selective area growth of InP on patterned Si substrates with Si oxide mask in terms of desorption of In and P.
► We discuss the mechanism of the selective area growth of InP on Si. ► P atoms adsorb on the Si(2×1) surface. ► P atoms do not adsorb on the native Si oxide surfaces. ► InP does not grow on the Si oxides at temperatures above 450°C.
GaDyN/GaN double-barrier magnetic tunneling junctions (DB-MTJs) structures are grown on GaN templates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). X-ray diffraction (XRD) θ/2θ ...scan curves exhibited a clear peak of GaDyN at low angle side of the GaN (0002) diffraction peak. From analyzing extended x-ray absorption fine structure (EXAFS), majority of Dy atoms are found to be incorporated into substituting the Ga sites in GaN with wurtzite structure, and GaDyN has longer bond length than that of GaN. From XRD and EXAFS results, the lattice constant of the GaDyN is larger than that of GaN due to large radius of Dy ion. Photoluminescence from GaDyN DB-MTJs structure was found, which is related to the Dy ions. Ferromagnetism is confirmed in the magnetization versus magnetic field curves at room temperature for the all samples. It is found that the magnetization per unit volume and the coercivity show change with increasing the thickness of the middle GaDyN layer. This implies that the interlayer interaction exists between the GaDyN layers.
► GaDyN/GaN double-barrier magnetic tunneling junctions (DB-MTJs) structures are grown by the MBE method. ► Ferromagnetism is confirmed at room temperature for the GaDyN quantum wells. ► It is found that the interlayer interaction exists between the GaDyN quantumwells.
The growth parameter dependence of structural, electrical and magnetic properties in Gd-doped GaN layers grown by plasma-assisted molecular beam epitaxy has been investigated. The structural and ...magnetic properties of Gd-doped GaN films grown on GaN templates strongly depend on the MBE growth condition. While Gd-doped GaN grown under relatively high Ga fluxes consist of wurtzite GaGdN layers without Gd-related precipitates, Gd-incorporated GaN films grown under low Ga fluxes contain a lot of nanoparticles ranging from several nm to several tens nm in size. The samples with Gd-related nanoparticles exhibit hysteresis in the magnetization–magnetic field curves at 10K. The separation between the field-cooled and zero-field-cooled magnetization–temperature curves is observed at around 30K. This behavior is understood in terms of super-paramagnetism originating from the ferromagnetic nanoparticles observed in the cross-sectional transmission electron microscopy images.
► Gd-doped GaN thin films were grown by varying Ga BEP using PA-MBE. ► Gd-doped GaN films grown under low Ga fluxes contain a lot of nanoparticles. ► Gd-doped GaN films grown under low Ga fluxes have super-paramagnetic property.
GaDyN/GaN double-barrier magnetic tunneling junctions (DB-MTJs) structures are grown on GaN templates by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). X-ray diffraction (XRD) theta .../2 theta scan curves exhibited a clear peak of GaDyN at low angle side of the GaN (0002) diffraction peak. From analyzing extended x-ray absorption fine structure (EXAFS), majority of Dy atoms are found to be incorporated into substituting the Ga sites in GaN with wurtzite structure, and GaDyN has longer bond length than that of GaN. From XRD and EXAFS results, the lattice constant of the GaDyN is larger than that of GaN due to large radius of Dy ion. Photoluminescence from GaDyN DB-MTJs structure was found, which is related to the Dy ions. Ferromagnetism is confirmed in the magnetization versus magnetic field curves at room temperature for the all samples. It is found that the magnetization per unit volume and the coercivity show change with increasing the thickness of the middle GaDyN layer. This implies that the interlayer interaction exists between the GaDyN layers.
We have investigated optical property of GaGdN grown on GaN template by radio-frequency plasma-assisted molecular beam epitaxy by varying the concentration of Gd. All the samples exhibit ...photoluminescence emission at the near band edge of 356nm, a blue luminescence (BL) band around 420nm and a green luminescence (GL) band around 500nm, instead of yellow luminescence (YL) band around 550nm frequently observed in n-GaN layer. The band edge emission is independent of the Gd concentration. This shows that the values of band gap for the GaGdN layers are the same as that of GaN. The temperature dependencies of the GL band intensity and peak wavelength are very similar to those of the YL band observed in the GaN epitaxial layers on the GaN templates. On the other hand, with increasing the Gd concentration, the BL bands observed in the GaGdN layers are red-shifted and their intensities decrease. The BL band intensity remains unchanged in the temperature range of 20–60K. It rapidly decreases at temperature above 100K, and disappears at 200K. The BL band is red-shifted in the temperature range of 4–200K and its value is about twice larger than that of the GL band.
► We have investigated optical property of GaGdN grown on GaN(0001) by PA-MBE. ► GaGdN exhibits PL emission at the band edge, BL and GL bands, instead of YL band. ► The origin of the GL bands was considered as Ga vacancy. ► The BL band observed in GaGdN is closely related to the incorporation of Gd atoms.
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