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We report measurements of the terahertz (THz) refractive index and absorption in 5 mol% MgO-doped congruent lithium niobate (MCLN) over 15-340 K and 0.25-2.3 THz, using narrowband THz emission from periodically poled lithium niobate (PPLN) crystals. Both THz-phase and optical group refractive indices along the extraordinary axis are extracted with a self-referenced emission-based approach. Temperature-and frequency-dependent absorption coefficients are obtained from both time-domain field decay and frequency-domain analysis; the time-domain method is found to be more robust, particularly at higher absorption. We derive empirical models for n(f,T) and alpha(f,T); the refractive index model reproduces the full dataset and all measured central frequencies with sub-percent relative error, while the absorption model recovers the measured absorption coefficients with a mean absolute error of about 0.5 cm-1, and both show good agreement with earlier QPM-based measurements. Taken together, the extended dataset and direct benchmarking provide a consistent and reliable foundation for modeling THz propagation, dispersion, and phase matching in MCLN, especially under cryogenic conditions where literature data are sparse or inconsistent. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
When subjected to a highly strained environment, N-substituted alkyl chain perylene diimides, PDI-Cn (n) = 5-8), reveal a combination of structural and optoelectronic responses directed by the odd-even alkyl chain effect. Their phase transitions, absorption and emission properties have been systematically analyzed using synchrotron and in-lab X-ray diffraction, UV-vis absorption, and photoluminescence spectroscopy, complemented by theoretical calculations. Their packing interactions, dominated by pi-stacking and weak C-H & ctdot;O interactions, lead to strikingly similar crystal structures, all belonging to the triclinic space group P1. Their distinct polymorphic behavior under high pressure is regulated by the alkyl chain length and conformations, and at high temperatures by the scissor-like movements of parallel pi-stacked molecules. The most susceptible to external stimuli are the even-PDIs, PDI-C6 and PDI-C8, which transform between three phases under high pressure. Compression of pi-stacking distances induces a significant bathochromic shift in absorption and emission spectra, most prominently red-shifting the absorption edge in PDI-C8 by 84.4 nm GPa-1. These findings provide valuable insights into the mechanism behind structure-property relationships for one of the most promising classes of organic semiconductors and underscore the role of the odd-even effect in organic semiconductors combined with the potential of strain engineering for optimizing material performance.
This work investigates the formation of extra-framework aluminum Lewis acid sites (EFAl LAS) in Y zeolite via aluminum ion-exchange (Al-IE) as a function of parent zeolite Si/Al ratio, treatment conditions, i.e., with and without heating and stirring, and the presence of cocations, i.e., proton, ammonium, and sodium. High-silica Y zeolites (Si/Al >= 15) facilitate efficient EFAl incorporation via silanol-assisted anchoring while maintaining framework integrity and microporosity, as verified by 27Al NMR, ICP-OES, XRD, and N2 physisorption. The incorporated EFAl, octahedral under NMR conditions, served as LAS without affecting the Br & oslash;nsted acidity, as demonstrated by pyridine-probed FTIR spectroscopy, and showed a strong correlation with enhanced catalytic activity in the Meerwein-Ponndorf-Verley (MPV) reduction of 4-tert-butylcyclohexanone. In very low silica Y zeolites, however, EFAl are incorporated at the expense of BAS, along with significant changes in framework integrity and microporosity. Under optimized Al-IE conditions, particularly ambient temperature Al-IE with moderate stirring, maximum generation of EFAl LAS and the respective MPV catalytic activity was achieved. Conversely, Al-IE under heating resulted in a lower number of LAS and reduced MPV rates, with LAS content and MPV activity being lowest due to Al-IE under combined heating and stirring despite maximum overall aluminum content. Minimal LAS formation and respective catalytic activity were observed in sodium-exchanged samples, underscoring the inhibitive effect of Na+ on the EFAl formation. In contrast, zeolites in their protonic and ammonium forms equally favor the efficient formation of catalytically active EFAl LAS. These results outline approaches for modulating LAS in zeolites via nonframework aluminum modification without compromising Br & oslash;nsted acidity and crystallinity.
Mechanical strain can be used to control physical properties in materials. The experimental investigation of strain-induced effects at the nanoscale is of importance not only for its fundamental aspects but also for the development of device applications. Transmission x-ray microscopy is a particularly well-suited technique for nanoscale imaging of magnetic materials, but its compatibility with in situ mechanical straining of samples is limited. In this work, we present a setup for applying tailored in situ mechanical strains to freestanding thin films by means of a microelectromechanical system (MEMS) actuator. We then present a proof-of-concept experiment in which a freestanding 80-nm-thick (001) BiFeO3 multiferroic thin film is strained with the MEMS device, allowing us to control the coupled ferroelectric/spin cycloidal configuration.
ABSTRACT The introduction of magnetic microbeads has greatly advanced biomedical research by enabling high‐precision methods for cell sorting, biomolecule transport, and cell force analysis. Applications extend to molecular isolation, diagnostic assays, and targeted drug delivery. Torques observed on superparamagnetic microbeads during cell experiments indicate spatial variations in the microbead properties. A high degree of internal magnetic structure complexity is revealed by nanoscale 3D imaging of superparamagnetic microbeads via soft X‐ray laminography. Microbeads are found to have an uneven distribution of magnetic magnetite nanoparticles. The effects of this on the hydrodynamic behavior of the microbeads are analyzed by semi‐numerical simulations using the laminography data. The calculated magnitudes of magnetic torque are consistent with the data from microbead transport experiments, involving fibroblast cells. By this, a structural basis for magnetic torques observed in experiments with superparamagnetic microbeads has been identified. Soft X‐ray laminography is proven to be a powerful technique for revealing structural details important to lab‐on‐a‐chip technologies. The findings indicate that magnetic microbeads deviate considerably from the theoretical model of uniform spheres. The identified structural heterogeneities hold significant implications for lab‐on‐chip experiments.
