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Type: Article × Subject: relaxation ×

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    Heteroepitaxy of group IV materials for future device application
    (Bristol : IOP Publ., 2023) Yamamoto, Yuji; Wen, Wei-Chen; Tillack, Bernd
    Heteroepitxy of group IV materials (Si, SiGe, and Ge) has great potential for boosting Si-based novel device performance because of the possibility for strain, band gap/Fermi-level engineering, and applying emerging artificial materials such as a superlattice (SL) and nanodots. In order to control group IV heteroepitaxy processes, strain, interface, and surface energies are very essential parameters. They affect dislocation formation, interface steepness, reflow of deposited layers, and also surface reaction itself during the growth. Therefore, process control and crystallinity management of SiGe heteroepitaxy are difficult especially in the case of high Ge concentrations. In this paper, we review our results of abrupt SiGe/Si interface fabrication by introducing C-delta layers and the influence of strain on the surface reaction of SiGe. Three-dimensional self-ordered SiGe and Ge nanodot fabrication by proactively using strain and surface energies by depositing SiGe/Si and Ge/SiGe SL are also reviewed.
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    Exceptionally High Blocking Temperature of 17 K in a Surface-Supported Molecular Magnet
    (Weinheim : Wiley-VCH, 2021) Paschke, Fabian; Birk, Tobias; Enenkel, Vivien; Liu, Fupin; Romankov, Vladyslav; Dreiser, Jan; Popov, Alexey A.; Fonin, Mikhail
    Single-molecule magnets (SMMs) are among the most promising building blocks for future magnetic data storage or quantum computing applications, owing to magnetic bistability and long magnetic relaxation times. The practical device integration requires realization of 2D surface assemblies of SMMs, where each magnetic unit shows magnetic relaxation being sufficiently slow at application-relevant temperatures. Using X-ray absorption spectroscopy and X-ray magnetic circular dichroism, it is shown that sub-monolayers of Dy2 @C80 (CH2 Ph) dimetallofullerenes prepared on graphene by electrospray deposition exhibit magnetic behavior fully comparable to that of the bulk. Magnetic hysteresis and relaxation time measurements show that the magnetic moment remains stable for 100 s at 17 K, marking the blocking temperature TB(100) , being not only in excellent agreement with that of the bulk sample but also representing by far the highest one detected for a surface-supported single-molecule magnet. The reported findings give a boost to the efforts to stabilize and address the spin degree of freedom in molecular magnets aiming at the realization of SMM-based spintronic units.
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    Nematic fluctuations in iron-oxychalcogenide Mott insulators
    (London : Nature Publishing Group, 2021) Freelon, B.; Sarkar, R.; Kamusella, S.; Brückner, F.; Grinenko, V.; Acharya, Swagata; Laad, Mukul; Craco, Luis; Yamani, Zahra; Flacau, Roxana; Swainson, Ian; Frandsen, Benjamin; Birgeneau, Robert; Liu, Yuhao; Karki, Bhupendra; Alfailakawi, Alaa; Neuefeind, Joerg C.; Everett, Michelle; Wang, Hangdong; Xu, Binjie; Fang, Minghu; Klauss, H.-H.
    Nematic fluctuations occur in a wide range physical systems from biological molecules to cuprates and iron pnictide high-Tc superconductors. It is unclear whether nematicity in pnictides arises from electronic spin or orbital degrees of freedom. We studied the iron-based Mott insulators La2O2Fe2OM2M = (S, Se), which are structurally similar to pnictides. Nuclear magnetic resonance revealed a critical slowing down of nematic fluctuations and complementary Mössbauerr spectroscopy data showed a change of electrical field gradient. The neutron pair distribution function technique detected local C2 fluctuations while neutron diffraction indicates that global C4 symmetry is preserved. A geometrically frustrated Heisenberg model with biquadratic and single-ion anisotropic terms provides the interpretation of the low temperature magnetic fluctuations. The nematicity is not due to spontaneous orbital order, instead it is linked to geometrically frustrated magnetism based on orbital selectivity. This study highlights the interplay between orbital order and spin fluctuations in nematicity.
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    Dynamics of Broadband Lasing Cascade from a Single Dot-in-well InGaAs Microdisk
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2019) Talalaev, Vadim; Kryzhanovskaya, Natalia; Tomm, Jens W.; Rutckaia, Viktoriia; Schilling, Joerg; Zhukov, Alexey
    The development of a fast semiconductor laser is required for the realization of next-generation telecommunication applications. Since lasers operating on quantum dot ground state transitions exhibit only limited gain due to the saturation effect, we investigate lasing from excited states and compare its corresponding static and dynamic behavior to the one from the ground state. InAs quantum dots (QDs) grown in dot-in-well (DWELL) structures allowed to obtain light emission from ground and three excited states in a spectral range of 1.0–1.3 μm. This emission was coupled to whispering gallery modes (WGMs) of a 6 μm microdisk resonator and studied at room temperature by steady-state and time-resolved micro-photoluminescence. We demonstrate a cascade development of lasing arising from the ladder of quantum dot states, and compare the lasing behavior of ground and excited state emission. While the lasing threshold is being increased from the ground state to the highest excited state, the dynamic behavior is improved: turn-on times and lifetimes of WGMs become shorter paving the way towards high frequency direct driven microlasers. © 2019, The Author(s).