Context.
Neptune’s incomplete ring arcs have been stable since their discovery in 1984 by stellar occultation. Although these structures should be destroyed within a few months through differential ...Keplerian motion, imaging data over the past couple of decades have shown that these structures remain stable.
Aims.
We present the first SPHERE near-infrared observations of Neptune’s ring arcs taken at 2.2 μm (broadband
Ks
) with the IRDIS camera at the Very Large Telescope (VLT) in August 2016.
Methods.
The images were aligned using the ephemerides of the satellite Proteus and were suitably co-added to enhance ring and satellite signals.
Results.
We analyse high-angular-resolution near-infrared images of Neptune’s ring arcs obtained in 2016 at the ESO VLT-UT3 with the adaptive-optics-fed camera SPHERE-IRDIS. We derive accurate mean motion values for the arcs and the nearby satellite Galatea. The trailing arcs Fraternité and Égalité have been stable since they were last observed in 2007. Furthermore, we confirm the fading away of the leading arcs Courage and Liberté. Finally, we confirm the mismatch between the arcs’ position and the 42:43 inclined and eccentric corotation resonances with Galatea, thus demonstrating that no 42:43 corotation model works to explain the azimuthal confinement of the arcs’ materiel.
Neptune's incomplete ring arcs have been stable since their discovery in 1984 by stellar occultation. Although these structures should be destroyed within a few months through differential Keplerian ...motion, imaging data over the past couple of decades has shown that these structures are persistent. We present here the first SPHERE near-infrared observations of Neptune's ring arcs taken at 2.2 \(\mu\)m (BB-Ks) with the IRDIS camera at the Very Large Telescope in August 2016. The images were aligned using the ephemerides of the satellite Proteus and were suitably co-added to enhance ring and satellite signals. We analyse high-angular resolution near-infrared images of Neptune's ring arcs obtained in 2016 at the ESO VLT-UT3 with the adaptive-optics fed camera SPHERE-IRDIS. We derive here accurate mean motion values for the arcs and the nearby satellite Galatea. The trailing arcs Fraternité and Egalité are stable since they were last observed in 2007. Furthermore, we confirm the fading away of the leading arcs Courage and Liberté. Finally, we confirm the mismatch between the arcs' position and 42:43 inclined and eccentric corotation resonances with Galatea; thus demonstrating that no 42:43 corotation model works to explain the azimuthal confinement of the arcs' materiel.
The fabrication of low-resistance and thermal stable ohmic contacts is important for realization of reliable SiC devices. For the n-type SiC, Ni-based metallization is most commonly used for Schottky ...and ohmic contacts. Many experimental studies have been performed in order to understand the mechanism of ohmic contact formation and different models were proposed to explain the Schottky to ohmic transition for Ni/SiC contacts. In the present review, we summarize the last key results on the matter and post open questions concerning the unclear issues of ohmic contacts to n-type SiC. Analysis of the literature data and our own experimental observations have led to the conclusion that the annealing at high temperature leads to the preferential orientation of silicide at the heterointerface (0001)SiC//(013)δ-Ni2Si. Moreover, we may conclude that only δ-Ni2Si grains play a key role in determining electrical transport properties at the contact/SiC interface. Finally, we show that the diffusion barriers with free diffusion path microstructure can improve thermal stability of metal-SiC ohmic contacts for high-temperature electronics.
•Growth conditions for strain-compensated cascade lasers grown by MBE are elaborated.•It is shown that a step-flow growth mode is desirable for growth of QCL structures.•The MBE technology has been ...verified by fabrication of state-of-the-art devices.
We investigate growth conditions for strain-compensated In0.67Ga0.33As/In0.36Al0.64As/InP quantum cascade lasers (QCLs) by solid-source molecular beam epitaxy (SSMBE). The extensive discussion of growth procedures is presented. The technology was first elaborated for In0.53Ga0.47As/In0.52Al0.48As material system lattice matched to InP. After that QCLs with lattice matched active region were grown for validation of design and obtained material quality. The next step was elaboration of growth process and especially growth preparation procedures for strain compensated active regions. The grown structures were examined by HRXRD, AFM, and TEM techniques. The on-line implementation of obtained results in subsequent growth runs was crucial for achieving room temperature operating 4.4-μm lasers. For uncoated devices with Fabry-Perrot resonator up to 250mW of optical power per facet at 300K was obtained under pulsed conditions. The paper focuses on MBE technology and presents developed algorithm for strain-compensated QCL growth.
Copper (Cu) is an essential element involved in various metabolic processes in plants, but at concentrations above the threshold level, it becomes a potential stress factor. The effects of two ...different cytokinins, kinetin (KIN) and 6-benzylaminopurine (BAP), on chlorophyll a fluorescence parameters, stomatal responses and antioxidation mechanisms in castor (Ricinus communis L.) under Cu2+ toxicity was investigated. Ricinus communis plants were exposed to 80 and 160 μM CuSO4 added to the growth medium. Foliar spraying of 15 μM KIN and BAP was carried out on these seedlings. The application of these cytokinins enhanced the tissue water status, chlorophyll contents, stomatal opening and photosynthetic efficiency in the castor plants subjected to Cu2+ stress. The fluorescence parameters, such as Fm, Fv/Fo, Sm, photochemical and non-photochemical quantum yields, energy absorbed, energy trapped and electron transport per cross-sections, were more efficiently modulated by BAP application than KIN under Cu2+ toxicity. There was also effective alleviation of reactive oxygen species by enzymatic and non-enzymatic antioxidation systems, reducing the membrane lipid peroxidation, which brought about a relative enhancement in the membrane stability index. Of the various treatments, 80 µM CuSO4 + BAP recorded the highest increase in photosynthetic efficiency compared to other cytokinin treatments. Therefore, it can be concluded that BAP could effectively alleviate the detrimental effects of Cu2+toxicity in cotyledonary leaves of R. communis by effectively modulating stomatal responses and antioxidation mechanisms, thereby enhancing the photosynthetic apparatus’ functioning.
In order to fabricate the AlGaN/GaN-on-Si HEMTs on existing Si-CMOS production lines, manufacturing processes must meet the rigors of Si-CMOS technology eliminating Au. One of the requirements is ...formation of Au-free, low resistivity ohmic contacts to AlGaN/GaN heterostructures. In this work we report structural and electrical studies of Ti/Al-based ohmic contacts to AlGaN/GaN HEMTs with TiN/Cu cover layers. Ohmic contacts have been observed after annealing of Ti/Al/TiN/Cu or Ti/Al/Ti/TiN/Cu/TiN multilayers on recessed AlGaN/GaN structure at temperature of 550 °C, specific contact resistance is about 2.3 × 10−4 Ω cm2, however, lower value was obtained after annealing at 750 °C. The XRD and TEM studies reveal formation of additional phases during annealing, namely Al3Ti and Ti2AlN inside the volume of the metallization stack and AlN at metal/GaN interface. Measured dependence of contact resistance on temperature suggests a “metal-like” carrier transport mechanism in partially recessed Ti/Al/Ti/TiN/Cu ohmic contact to 2D electron gas.
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The paper presents the results of investigations of zinc oxide (ZnO) layers as a potential sensing material, being affected by certain selected gaseous environments. The investigations concerned the ...optical transmission through thin ZnO layers in wide spectral ranges from ultraviolet to the near infrared. The effect of the gaseous environment on the optical properties of zinc oxide layers with a thickness of ~ 400 nm was analyzed applying various technologies of ZnO manufacturing. Three kinds of ZnO layers were exposed to the effect of the gaseous environment, viz.: layers with relatively slight roughness (RMS several nm), layers with a considerable surface roughness (RMS some score of nm) and layers characterized by porous ZnO structures. The investigations concerned spectral changes in the transmission properties of the ZnO layers due to the effect of such gases as: ammonia (NH
), hydrogen (H
), and nitrogen dioxide (NO
) in the atmosphere of synthetic air. The obtained results indicated the possibility of applying porous ZnO layered structures in optical gas sensors.
Switchable, double wavelength generation is demonstrated from a single vertical external cavity surface-emitting laser chip. Power of ~0.5 W for two wavelengths λ≈967 nm and 1,018 nm i.e. within the ...spectral distance of 51 nm were registered. In the semiconductor heterostructure a single set of nominally identical quantum wells was enclosed in a single, two-mode resonant microcavity. The wavelength switching was induced by the change of the pump power. The increase or decrease of the pump power changes the active region temperature and thus tunes spectrally the gain spectrum to the one of two modes.
Nickel-based contacts with additional interfacial layer of carbon, deposited on n-type 4H-SiC, were annealed at temperatures ranging from 600 to 1000°C and the evolution of the electrical and ...structural properties were analyzed by I-V measurements, SIMS, TEM, and Raman spectroscopy. Ohmic contact is formed after annealing at 800°C and minimal specific contact resistance of about 2.0×10-4 Ω cm2 has been achieved after annealing at 1000°C. The interfacial carbon is amorphous in as-deposited state and rapidly diffuses and dissolves in nickel forming graphitized carbon. This process activates interfacial reaction between Ni and SiC at lower temperature than usual and causes the formation of ohmic contact at relatively low temperature. However, our results show that the specific contact resistance as well as interface quality of contacts was not improved, if additional layer of carbon is placed between Ni and SiC.
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