The discovery of chirality-induced spin selectivity (CISS), resulting from an interaction between the electron spin and handedness of chiral molecules, has sparked interest in surface-adsorbed chiral molecules due to potential applications in spintronics, enantioseparation, and enantioselective chemical or biological processes. We study the deposition of chiral heptahelicene by sublimation under ultra-high vacuum onto bare Cu(111), Co bilayer nanoislands on Cu(111), and Fe bilayers on W(110) by low-temperature spin-polarized scanning tunneling microscopy/spectroscopy (STM/STS). In all cases, the molecules remain intact and adsorb with the proximal phenanthrene group aligned parallel to the surface. Three degenerate in-plane orientations on Cu(111) and Co(111), reflecting substrate symmetry, and only two on Fe(110), i.e., fewer than symmetry permits, indicate a specific adsorption site for each substrate. Heptahelicene physisorbs on Cu(111) but chemisorbs on Co(111) and Fe(110) bilayers, which nevertheless remain for the sub-monolayer coverage ferromagnetic and magnetized out-of-plane. We are able to determine the handedness of individual molecules chemisorbed on Fe(110) and Co(111), as previously reported for less reactive Cu(111). The demonstrated deposition control and STM/STS imaging capabilities for heptahelicene on Co/Cu(111) and Fe/W(110) substrate systems lay the foundation for studying CISS in ultra-high vacuum and on the microscopic level of single molecules in controlled atomic configurations.

• Klíčová slova
• STM, adsorption geometry, chiral molecules, ferromagnetic surfaces, molecular deposition,
• Publikační typ
• časopisecké články MeSH

Thin films of bismuth and iron oxides were obtained by atomic layer deposition (ALD) on the surface of a flexible substrate poly(4,4'-oxydiphenylene-pyromellitimide) (Kapton) at a temperature of 250°C. The layer thickness was 50 nm. The samples were examined by secondary-ion mass spectrometry, and uniform distribution of elements in the film layer was observed. Surface morphology, electrical polarization, and mechanical properties were investigated by atomic force microscope, piezoelectric force microscopy, and force modulation microscopy. The values of current in the near-surface layer varied in the range of ±80 pA when a potential of 5 V was applied. Chemical analysis was performed by X-ray photoelectron spectroscopy, where the formation of Bi2 O3 and Fe2 O3 phases, as well as intermediate phases in the Bi-Fe-O system, was observed. Magnetic measurements were carried out by a vibrating sample magnetometer that showed a ferromagnetic response. The low-temperature method of functionalization of the Kapton surface with bismuth and iron oxides will make it possible to adapt the Bi-Fe-O system to flexible electronics.

• Klíčová slova
• Bi2O3, BiFeO3, Fe2O3, atomic layer deposition, flexible substrate, functionalized surface, multiferroic,
• Publikační typ
• časopisecké články MeSH

Magnetism in two dimensions is traditionally considered an exotic phase mediated by spin fluctuations, but far from collinearly ordered in the ground state. Recently, 2D magnetic states have been discovered in layered van der Waals compounds. Their robust and tunable magnetic state by material composition, combined with reduced dimensionality, foresee a strong potential as a key element in magnetic devices. Here, a class of 2D magnets based on metallic chlorides is presented. The magnetic order survives on top of a metallic substrate, even down to the monolayer limit, and can be switched from perpendicular to in-plane by substituting the metal ion from iron to nickel. Using functionalized STM tips as magnetic sensors, local exchange fields are identified, even in the absence of an external magnetic field. Since the compounds are processable by molecular beam epitaxy techniques, they provide a platform with large potential for incorporation into current device technologies.

• Klíčová slova
• 2D material, XMCD, ferromagnetism, nickelocene, transition metal halides, van der waals material,
• Publikační typ
• časopisecké články MeSH

The interplay between chirality and magnetism is a source of fascination among scientists for over a century. In recent years, chirality-induced spin selectivity (CISS) has attracted renewed interest. It is observed that electron transport through layers of homochiral molecules leads to a significant spin polarization of several tens of percent. Despite the abundant experimental evidence gathered through mesoscopic transport measurements, the exact mechanism behind CISS remains elusive. This study reports spin-selective electron transport through single helical aromatic hydrocarbons that are sublimed in vacuo onto ferromagnetic cobalt surfaces and examined with spin-polarized scanning tunneling microscopy (SP-STM) at a temperature of 5 K. Direct comparison of two enantiomers under otherwise identical conditions revealed magnetochiral conductance asymmetries of up to 50% when either the molecular handedness is exchanged or the magnetization direction of the STM tip or Co substrate is reversed. Importantly, the results rule out electron-phonon coupling and ensemble effects as primary mechanisms responsible for CISS.

• Klíčová slova
• CISS effect, chirality, ferromagnetic substrate, scanning probe microscopy, single‐molecule studies,
• Publikační typ
• časopisecké články MeSH

Metal-organic frameworks (MOFs) represent an interesting class of versatile materials with important properties, including magnetism. However, the synthesis of atomically precise large-scale 2D MOFs with nontrivial strong magnetic coupling represents a current research challenge. In this regard, we report on the synthesis of a high-quality large-scale 2D MOF, with strong π-d magnetic exchange coupling. To this aim, we present a new two-step synthetic approach that consists of the initial formation of an extended supramolecular organic framework on a Au(111) surface, establishing the large-scale order of organic ligands and their subsequent metalation by single cobalt atoms assisted by annealing. Moreover, we show that the usage of radical asymmetric organic ligands enables us to form a magnetic 2D MOF with strong π-d electron interactions. According to the multireference calculations, the 2D MOF shows complex spin interactions beyond the traditional superexchange mechanism, with the interplay between antiferromagnetic and ferromagnetic couplings. We anticipate that this synthetic strategy can be adapted to different approaches, such as liquid interfaces or insulating substrates, to synthesize high-quality 2D MOFs. Accompanied by the high control with atomic precision over the magnetic properties of the ligands and metals, this approach enables the formation of large-scale 2D MOFs with complex spin interactions, which will open new avenues in the field of 2D magnetic materials.

• Publikační typ
• časopisecké články MeSH

BiFeO3 (BFO) films on highly oriented pyrolytic graphite (HOPG) substrate were obtained by the atomic layer deposition (ALD) method. The oxidation of HOPG leads to the formation of bubble regions creating defective regions with active centers. Chemisorption occurs at these active sites in ALD. Additionally, carbon interacts with ozone and releases carbon oxides (CO, CO2). Further annealing during the in situ XPS process up to a temperature of 923 K showed a redox reaction and the formation of oxygen vacancies (Vo) in the BFO crystal lattice. Bubble delamination creates flakes of BiFeO3-x/rGO heterostructures. Magnetic measurements (M-H) showed ferromagnetism (FM) at room temperature Ms ~ 120 emu/cm3. The contribution to magnetization is influenced by the factor of charge redistribution on Vo causing the distortion of the lattice as well as by the superstructure formed at the boundary of two phases, which causes strong hybridization due to the superexchange interaction of the BFO film with the FM sublattice of the interface region. The development of a method for obtaining multiferroic structures with high FM values (at room temperature) is promising for magnetically controlled applications.

• Klíčová slova
• BiFeO3, atomic layer deposition, ferromagnetic properties, graphite surface, perovskite structure,
• Publikační typ
• časopisecké články MeSH

Quantum magnonics investigates the quantum-mechanical properties of magnons, such as quantum coherence or entanglement for solid-state quantum information technologies at the nanoscale. The most promising material for quantum magnonics is the ferrimagnetic yttrium iron garnet (YIG), which hosts magnons with the longest lifetimes. YIG films of the highest quality are grown on a paramagnetic gadolinium gallium garnet (GGG) substrate. The literature has reported that ferromagnetic resonance (FMR) frequencies of YIG/GGG decrease at temperatures below 50 K despite the increase in YIG magnetization. We investigated a 97 nm-thick YIG film grown on 500 μm-thick GGG substrate through a series of experiments conducted at temperatures as low as 30 mK, and using both analytical and numerical methods. Our findings suggest that the primary factor contributing to the FMR frequency shift is the stray magnetic field created by the partially magnetized GGG substrate. This stray field is antiparallel to the applied external field and is highly inhomogeneous, reaching up to 40 mT in the center of the sample. At temperatures below 500 mK, the GGG field exhibits a saturation that cannot be described by the standard Brillouin function for a paramagnet. Including the calculated GGG field in the analysis of the FMR frequency versus temperature dependence allowed the determination of the cubic and uniaxial anisotropies. We find that the total crystallographic anisotropy increases more than three times with the decrease in temperature down to 2 K. Our findings enable accurate predictions of the YIG/GGG magnetic systems behavior at low and ultralow millikelvin temperatures, crucial for developing quantum magnonic devices.

• Klíčová slova
• Magnetic properties and materials, Spintronics, Surfaces, interfaces and thin films,
• Publikační typ
• časopisecké články MeSH

Nanocomposite films of BiFeO3-Bi2Fe4O9 were fabricated on a sapphire substrate Al2O3 using the method of gas discharge high-frequency cathodic sputtering of a ceramic target with a stoichiometric composition in an oxygen atmosphere. The results of the film analysis using X-ray structural analysis, Raman scattering, XPS, and atomic force microscopy are presented. The lattice parameters, surface topography, chemical composition of the films, concentration, and average sizes of the crystallites for each phase were determined. It was shown that the ratio of the BiFeO3 to Bi2Fe4O9 phases in the obtained film is approximately 1:2. The sizes of the crystallites range from 15 to 17 nm. The optical and magnetic properties of the nanocomposite layers were studied, and the band gap width and magnetization hysteresis characteristic of ferromagnetic behavior were observed. The band gap width was found to be 1.9 eV for the indirect and 2.6 eV for the direct interband transitions. The magnetic properties are characterized by a hysteresis loop resembling a "wasp-waist" shape, indicating the presence of magnetic anisotropy.

• Klíčová slova
• Bi2Fe4O9, BiFeO3, film, multiferroics, nanocomposite,
• Publikační typ
• časopisecké články MeSH

Pulse laser deposited La2/3Sr1/3MnO3 ultrathin films on SrTiO3 substrates were characterized by polar and longitudinal Kerr magneto-optical spectroscopy. Experimental data were confronted with theoretical simulations based on the transfer matrix formalism. An excellent agreement was achieved for a 10.7 nm thick film, while a distinction in the Kerr effect amplitudes was obtained for a 5 nm thick film. This demonstrated the suppression of ferromagnetism due to the layer/substrate interface effects. A revised, depth-sensitive theoretical model with monolayer resolution described the experimental data well, and provided clear cross-section information about the evolution of ferromagnetism inside the film. It was found that the full restoration of the double-exchange mechanism, responsible for the ferromagnetic ordering in La2/3Sr1/3MnO3, occurs within the first nine monolayers of the film. Moreover, all the studied films exhibited magneto-optical properties similar to bulk crystals and thick films. This confirmed a fully developed perovskite structure down to 5 nm.

• Klíčová slova
• Interface effects, Magneto-optical Kerr effect, Magneto-optics, Manganites, Ultrathin films,
• Publikační typ
• časopisecké články MeSH

A new fluorescent, non-cytotoxic perylene diimide derivative with two biotins at the peri position, PDI2B, has been synthesized. This molecule is able to interact selectively with G-quadruplexes with scarce or no affinity towards single- or double-stranded DNA. These features have made it possible to design a simple, effective, safe, cheap, and selective method for fishing G-quadruplex structures in solution by use of PDI2B and streptavidin coated magnetic beads. The new cyclic method reported leads to the recovery of more than 80 % of G-quadruplex structures from solution, even in the presence of an excess of single-stranded or duplex DNA as competitors. Moreover, PDI2B is a G4 ligand that can display higher thermal stabilization and greater affinity for 2- over 3-tetrad quadruplexes, which constitutes a novel type of behavior.

• Klíčová slova
• DNA, G-quadruplexes, biophysics, nucleic acids, perilene,
• MeSH
• biotin chemie   MeSH
• DNA chemie   MeSH
• fluorescenční barviva chemie   MeSH
• G-kvadruplexy * MeSH
• imidy chemická syntéza   MeSH
• jednovláknová DNA chemie   MeSH
• ligandy MeSH
• magnety MeSH
• perilipin 1 chemie   MeSH
• perylen analogy a deriváty   chemická syntéza   MeSH
• povrchové vlastnosti MeSH
• roztoky MeSH
• streptavidin chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• biotin MeSH
• DNA MeSH
• fluorescenční barviva MeSH
• imidy MeSH
• jednovláknová DNA MeSH
• ligandy MeSH
• perilipin 1 MeSH
• perylen MeSH
• perylenediimide MeSH Prohlížeč
• roztoky MeSH
• streptavidin MeSH