Surface Smoothing by Gas Cluster Ion Beam Using Decreasing Three-Step Energy Treatment

Funding Information: This work was supported by the Hubei Provincial and Municipal Double First-class Talent Construction Start-up Fund in 2022 (Project No. 600460045), the Key R&D program of Hubei Province (Grant No. 2022BAA049), the Science and Technology Planning Project of Shenzhen Municipality (Grant Nos. 2019N032, JCYJ20220530140605011), and the National Key Research and Development Program of China (Grant No. 2022YFB4601000). Publisher Copyright: © 2023 by the authors.A three-step treatment of Si wafers by gas cluster ion beam with decreasing energy was used to improve the performance of surface smoothing. First, a high energy treatment at 15 keV and an ion fluence of 2 × 1016 cm−2 was used to remove initial surface features (scratches). Next, treatments at 8 and 5 keV with the same fluences reduced the roughness that arose due to the formation of morphological features induced by the surface sputtering at the first high energy step. The surface morphology was characterized by the atomic force microscopy. The root mean square roughness Rq and 2D isotropic power spectral density functions were analyzed. For comparison, the smoothing performances of single-step treatments at 15, 8, and 5 keV were also studied. The lowest roughness values achieved for the single and three-step treatments were 1.06 and 0.65 nm, respectively.publishersversionpublishe

Growth and Magnetooptical Properties of Anisotropic TbF3 Single Crystals

The present paper investigates the Faraday effect and absorption and luminescence spectra of single-crystal TbF3 measured at 90 K and 300 K. The optical-quality single-phase TbF3 crystals (structural type β-YF3) were grown by the Bridgman technique. Faraday rotation angles were measured at remagnetization along the [100] crystallographic axis. Low temperature optical measurements were carried out along the [100] axis. “Quasi-doublet” sublevels with energy at 0 cm-1, 65 cm-1 and 190 cm-1, and also a singlet sublevel with energy at 114 cm-1 located in the ground 7F6 multiplet were determined from the low temperature luminescence spectra. The Van-Vleck behavior of the magnetic susceptibility χb can be satisfactorily explained by the magnetic mixing of wave functions belonging to the ground and first excited “quasi-doublet” sublevels at 0 and 65 cm-1, respectively. Analysis of the oscillation dependences of the rotation angle showed that the value of the natural birefringence (Δn ≈ 0.0186) remains nearly constant within the wavelength and temperature ranges under investigation. As the temperature decreases, we find significant increases in the oscillation amplitude of the rotation angle and in the Verdet constant V. The spectral dependences V(χ) are linear throughout the temperature range. The magnetooptical activity of TbF3 can be explained by means of the spin- and parity-allowed electric-dipole 4f→5d transitions in the Tb3+ ions

Formation of nanoripples on ZnO flat substrates and nanorods by gas cluster ion bombardment

Funding Information: This work was supported by the National Natural Science Foundation of China under grant 11875210, the Science and Technology Planning Project of Guangdong Province under grant 2018A050506082, China Postdoctoral Science Foundation under grant 2019M652687, and by the grant RFBR No.19-05-00554 in the part of the development of advanced approach to analysis of geochemical objects.In the present study Ar+ cluster ions accelerated by voltages in the range of 5-10 kV are used to irradiate single crystal ZnO substrates and nanorods to fabricate self-assembled surface nanoripple arrays. The ripple formation is observed when the incidence angle of the cluster beam is in the range of 30-70°. The influence of incidence angle, accelerating voltage, and fluence on the ripple formation is studied. Wavelength and height of the nanoripples increase with increasing accelerating voltage and fluence for both targets. The nanoripples formed on the flat substrates remind of aeolian sand ripples. The ripples formed at high ion fluences on the nanorod facets resemble well-ordered parallel steps or ribs. The more ordered ripple formation on nanorods can be associated with the confinement of the nanorod facets in comparison with the quasi-infinite surface of the flat substrates.publishersversionpublishe

Magnetooptics of non-Kramers Eu3+ ions in garnets: analysis complemented by crystal-field splitting modeling calculations

Spectra of absorption, luminescence, magnetic circular dichroism (MCD), and magnetic circular polarization of luminescence (MCPL) in Gd3Ga5O12:Eu3+ and Eu3Ga5O12 garnets were studied within the visible spectral range at 300 K. Analysis of the spectral and temperature dependences of the magnetooptical and optical spectra made it possible to identify the magneto-dipole (MD) and electro-dipole (ED) 4f→4f transitions occurring between Stark sublevels of the 7FJ (J=1, 2) and 5D0 multiplets in Eu3+-containing garnet structures. Quantum mechanical “mixing” had significant influence on quasi-degenerate states of the non-Kramers rare-earth Eu3+ ion for Eu3Ga5O12 in MCD due to forbidden MD transition 7F1→5D0 and for Gd3Ga5O12:Eu3+ in MCPL due to MD 4f→4f transition 5D0→7F1 and forced ED-transition 5D0→7F2. A parameterized Hamiltonian defined to operate within the entire 4f(6) ground electronic configuration of Eu3+ ion was used to model the experimental Stark levels, including their irreducible representations and wavefunctions. The crystal-field parameters were determined through a Monte-Carlo method in which nine independent crystal-field parameters, Bkq, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental levels was 0.73 meV

Magnetooptics of magnetic-dipole transitions in the rare-earth paramagnetic garnets

The Faraday effect (FE) of the rare-earth (RE) paramagnetic garnet crystals associated with magnetic-dipole (MD) transitions has been investigated theoretically over a wide temperature range 80 to 300 K. Over this temperature range, the “gyromagnetic” Verdet V gm (m) of the Eu3Ga5O12 (EuGG) is not a linear function of the magnetic susceptibility χ measured along the [111] axis. We find that the nontrivial character of the temperature dependence of the MD Verdet constant V gm (m) is associated with the presence of a contribution to the Faraday rotation of the Van Vleck “mixing” by an external magnetic field of the Eu3+ electronic states. The optical absorption and magnetic circular dichroism (MCD) of Eu3+ ion in EuGG at 85 K for the MD transition 7 F 0 → 5 D 1 were measured along the [111] axis. We show that the appearance of the MCD feature observed for the absorption line near 526.6 nm for the 7 F 0 → 5 D 1 MD absorption band may be well-explained by the contribution of Van Vleck “mixing” between the Stark singlet states from the 7 F 0 and 7 F 1 multiplet manifolds mixed by the external magnetic field H

Study on velocity mode of 57Fe Mӧssbauer spectroscopy and determination of lattice dynamics in Fe3S4

57Fe Mӧssbauer spectroscopy studies on chemically synthesized greigite Fe3S4 have been conducted with a unique velocity mode, known as constant velocity with slope, which allows detection of subtle changes and in-depth details of sextets in the spectra. Accurate determination of the overlapped sub-spectra corresponding to tetrahedral Fe3+ (A) and octahedral Fe2.5+ (B) sub-lattices has been made based on the special velocity mode. Estimation of Debye temperature θD from the temperature dependent central shift (CS) values gives the values: 805 ± 10 K and 760 ± 10 K for A- and B-sites, respectively. The discrepancy of two θD values reveals different lattice vibration between A- and B-sites. The Lamb-Mӧssbauer factor ratio fB/fA is found to be 0.98 at room temperature. The different low-temperature behaviors of hyperfine magnetic field for tetrahedral A- and octahedral B-sites are observed. Keywords: Spinel structure, Mӧssbauer, Spectroscopy, Lattice dynamics, Debye temperatur

Specific features of Eu3+ and Tb3+ magnetooptics in gadolinium-gallium garnet (Gd3Ga5O12)

We reported magnetooptical properties of Eu3+(4f(6)) and Tb3+(4f(8)) in single crystals of Gd3Ga5O12 (GGG), Y3Ga5O12 (YGG), and Eu3+(4f(6)) in Eu3Ga5O12 (EuGG) for both ions occupying sites of D2 symmetry in the garnet structure. Absorption, luminescence, and magnetic circular polarization of luminescence (MCPL) spectra of Tb3+ in GGG and YGG and absorption and magnetic circular dichroism (MCD) of Eu3+ in EuGG were studied. The data were obtained at 85 K and room temperature (RT). Magnetic susceptibility of Eu3+ in EuGG was also measured between 85 K and RT. The magnetooptical and magnetic susceptibility data were modeled using the wavefunctions of the crystal-field split energy (Stark) levels of Eu3+ and Tb3+ occupying D2 sites in the same garnets. The results reported gave a precise determination of these Stark level assignments and confirmed the symmetry labels (irreducible representations) of the closely-spaced Stark levels (quasi-doublets) found in the 5D1 (Eu3+) and 5D4 (Tb3+) multiplets. Ultraviolet (UV) excitation (\u3c300 nm) of the 6PJ and 6IJ states of Gd3+ in the doped GGG crystals led to emission from 5D4 (Tb3+) and 5D1 and 5D0 (Eu3+) through radiationless energy transfer to the 4f(n−1)5d band of Tb3+ and to UV quintet states of Eu3+. The temperature-dependent emission line shapes and line shifts of the magnetooptical transitions excited by UV radiation suggested a novel way to explore energy transfer mechanisms in this rare-earth doped garnet system

Tb3+ Ion Optical and Magneto-Optical Properties in the Cubic Crystals KTb3F10

The optical and magneto-optical characteristics of KTb3F10 crystals in the transition region of 5D4 → 7F6 4f8 configurations of the Tb3+ ion at temperatures of 90 and 300 K were studied. The schemes of the optical transitions in the KTb3F10 crystals were constructed, and the energies of most of the Stark sublevels of the ground 7F6 and excited 5D4 multiplets of the Tb3+ ion split by the C4v symmetry crystal environment were determined. The presence of three- and two-doublet states in the energy spectra of the Tb3+ion multiplets 7F6 and 5D4, respectively, was established, which is in good agreement with theoretical predictions. The use of the wavefunctions of the Stark sublevels of multiplets split by a tetragonal crystal field and combining in the studied optical transition made it possible to explain some of the magnetic and magneto-optical features observed in the KTb3F10 single crystals