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BackgroundLarge size aspherical mirrors have been widely used in space communication systems because of their high angular resolution and energy harvesting ability.PurposeThis study aims to develop a high energy and high flux argon (Ar) ion gun for the rapid polishing of modified silicon layer on the surface of large size SiC aspherical mirror.MethodsFirst of all, Ar ionization was realized by filament and anode grid. Ar+ energy was determined by anode voltage whilst the extractor and electrostatic lenses were employed to achieve Ar+ emission and focusing. The high transmittance of argon ions was realized by adjusting the voltage between the filament and the anode grid to maximize the ionization rate, and adjusting the size and relative position of the electrostatic focusing lens. The materials in the Ar ion gun were selected not only suitable for ultra-high vacuum, but also preventing from vacuum discharge. Then, the parameters of the main components of argon ion gun were determined by theoretical calculation and simulation of the trajectory of argon ion beam. Finally, preliminary experimental tests were carried out to verify its performance.ResultsThe test results show that the Ar+ energy and beam flux can reach 20 keV and 50 μA, respectively, at 30 mm working distance and Ar partial pressure of 1.2×10-2 Pa. The beam size can be continuously adjusted from 19 mm to 24 mm.ConclusionsThis developed argon ion gun with small size, high energy and high flux, can be installed on a vacuum multi-dimensional displacement table for a wide range of movement to achieve high vacuum surface polishing of large aperture optical elements.

Temperature and dosage-dependent reactions of NH3 on the Si(111)-(7 × 7) surface have been studied by low-temperature scanning tunneling microscopy. It was found that the surface reaction exhibited three different dissociative adsorption channels as the temperature increases at low exposure. Under the condition of high exposure, the amorphous structure of silicon nitride film gradually transformed into an ordered phase, with the increase of substrate temperature, and finally presented an 8/3 × 8/3 structure. This means that both exposure and temperature are critical for forming an ordered surface structure. Furthermore, many adsorbates were observed on the nitride region during the growth process, which is believed to be the intermediate reactants in the nitridation reaction and consumed in the subsequent annealing process to form an orderly and clean surface morphology. [ABSTRACT FROM AUTHOR]

Spin Seebeck effect (SSE) for an yttrium iron garnet (YIG)/nickel oxide (NiO)/platinum (Pt) trilayer device was studied in a wide temperature range. It is found that the SSE signal is nonmonotonic in the temperature domain and shows a maximum around the Néel temperature of the NiO layer, which is similar to the temperature dependence of the spin pumping signal in the same device. This result identified that the thermal-excited incoherent spin currents are also sensitive to the fluctuation of an antiferromagnetic system and can be used to probe the antiferromagnetic phase transition. Furthermore, the antiferromagnetic NiO layer is considered to be valuable for the optimization of spin transport efficiency at YIG/Pt interface, which enhances the SSE signal around room temperature. [ABSTRACT FROM AUTHOR]

Perfect surfaces can upgrade the quality of the films grown on them and ensure that their physical properties do not deteriorate. Here, an atomically flattened surface is homogeneously formed over an entire MgO(001) substrate by an original chemical polishing technique. The atomically flattened substrate enabled a nondeteriorating Verwey transition to be induced in a 50 nm thick Fe3O4 thin film on the substrate because of the extremely low defect density and high homogeneity of the film. The maximum relative change in resistivity was ∼6, which is almost a one-order improvement, which was due to the atomically flattened substrate. Additionally, a statistical evaluation shows that the changes in resistivity and transition temperatures across the Verwey transition shift toward higher values. The result clearly shows the effectiveness of a substrate surface with both atomic flatness and high crystallinity in suppressing the variation in a characteristic among samples, leading to the development of high-performance magnetoresistive devices to manifest the materials' potential physical properties. [ABSTRACT FROM AUTHOR]

The domain structure of antiferromagnetic (AFM) NiO( 100) has been investigated by nonmagnetic x-ray linear dichroism (XLD) at the O K edge using photoemission electron microscopy and linearly polarized x-ray light. The evolution of XLD image contrast as the function of the angle between the crystal orientation and the incident 5- or p-polarized light is clearly observed. The angular dependence of the XLD contrast is in good agreement with the calculated x-ray absorption cross section of O Is to 2p orbital that is deformed anisotropically by the strong hybridization with Ni 3d Orbitals. This agreement strongly supports the conclusion that the observed XLD contrast reflects the twin-domain (T-domain) structure of the NiO crystal. By comparing the experimental data with the calculation, it is possible to assign each domain contrast to a specific r-domain in the quantitative manner. The proposed simple and clear way of T-domain assignment will be useful for investigating the magnetic domain structures of NiO and other oxide AFM materials such as FeO, CoO, and CuO, and will be important for understanding the magnetic properties of AFM materials, such as the exchange bias effect. [ABSTRACT FROM AUTHOR]

Abstract: The electronic properties of p- and n-type Ba8Ga16Ge30 (BGG) are studied using soft X-ray photoelectron spectroscopy at a high-energy facility. Three bands are resolved in the valence band region. The first band for n-type BGG is sensitive to temperature, while the second band is sensitive for p-type BGG. The change in the ratio of Ba to Ga, from which the carrier type is controlled in this system, modifies the positions of Ga residing at the larger (Ga–CGe)24 cage. This modification in the host network is responsible for the large differences observed in electronic properties of p- and n-BGGs in this clathrate family. [Copyright &y& Elsevier]

Abstract: The solid solutions BaAl1−x Si1+x (0⩽ x ⩽0.5) were prepared. The compound with the stoichiometric composition (x =0) did not show superconductivity as reported by other investigators, but the solid solutions with x >0 became superconductors with a transition temperature T c =2.8K. The comparison of the lattice parameters with those of the other isotypic ternary superconductors MAlSi (M=Ca,Sr) suggested that the superconductivity could be related to the lattice parameter within the (AlSi) plane rather than the interlayer spacing. The band structures near the Fermi level of MAlSi (M=Ca,Sr,Ba) were measured using soft X-ray photoelectron spectroscopy, which were in good agreement with the calculated ones, confirming that the contribution of the d orbitals of the alkaline-earth metals were predominant in the conduction bands. [Copyright &y& Elsevier]

Extensive soft x-ray photoelectron spectroscopy studies are performed on Ba 8 Ga 16 Ge 30 (BGG) and Sr 8 Ga 16 Ge 30 (SGG) single crystals ranging from Fermi to core levels, at a high-energy facility. Valence band x-ray photoelectron spectroscopy (XPS) experiments with theoretical calculations revealed that the valence band is mainly constructed by the Ge/Ga 4s and 4p wave functions with little contribution of the Ba/Sr atomic orbitals. Surprisingly, unexpected features evidencing the different shift for the 2a- and 6d- sites between Ba 4d and Sr 3d are observed. The detailed analyses including theoretical support by first-principles band-structure calculations lead to the conclusion that the component distributions of the larger tetrakaidecahedral cage are different depending on the endohedral atoms, which contrasts with the past consensus that BGG and SGG have the same framework structure. This may give thorough reconsiderations on earlier interpretations of experimental data.