Challenges for Pulsed Laser Deposition of FeSe Thin Films

Anti-PbO-type FeSe shows an advantageous dependence of its superconducting properties with mechanical strain, which could be utilized as future sensor functionality. Although superconducting FeSe thin films can be grown by various methods, ultrathin films needed in potential sensor applications were only achieved on a few occasions. In pulsed laser deposition, the main challenges can be attributed to such factors as controlling film stoichiometry (i.e., volatile elements during the growth), nucleation, and bonding to the substrate (i.e., film/substrate interface control) and preventing the deterioration of superconducting properties (i.e., by surface oxidization). In the present study, we address various technical issues in thin film growth of FeSe by pulsed laser deposition, which pose constraints in engineering and reduce the application potential for FeSe thin films in sensor devices. The results indicate the need for sophisticated engineering protocols that include interface control and surface protection from chemical deterioration. This work provides important actual limitations for pulsed laser deposition (PLD) of FeSe thin films with the thicknesses below 30 nm

Synthesis and HRTEM Investigation of EuRbFe4As4 Superconductor

In the stoichiometric iron-based superconductor EuRbFe4As4, superconductivity coexists with a long-range magnetic ordering in Eu layers. Using high-resolution transmission electron microscopy (HRTEM), we observed an atomic structure of as-grown EuRbFe4As4 crystals. HRTEM shows that crystals have two-dimensional intrinsic nanoinclusions established to be the RbFe2As2 (122) phase with a volume fraction of ~5.6%. In contrast with the CaKFe4As4 compound, similar inclusions are not superconducting down to 2 K, and no second magnetization peak was observed in the magnetization measurements at low temperature with B ‖ ab. We show that the non-superconducting 122 phase nanoinclusions could act as 2D pinning centers

Effects of Kr and Xe ion irradiation on the structure of Y2O3 nanoprecipitates in YBCO thin film conductors

The response of Y2O3 nanoprecipitates in a 1-mu m YBa2Cu3O7-x layer from a superconducting wire Ag/YBCO/buffer metal oxides/Hastelloy to 107 MeV Kr and 167 MeV Xe ion irradiation was investigated using a combination of transmission electron microscopy, diffraction and X-ray energy-dispersive spectrometry. The direct observation of the radiation-induced tracks in Y2O3 nanocrystals is reported for the first time to the authors' best knowledge. Structureless damaged regions of 5-9 nm (average 8 nm) in diameter were observed in Y2O3 nanocrystals when the electronic stopping power S-e was about or higher than 4.7 keV/nm. This value of S-e is the upper estimate of the minimum electronic stopping power to create damage in yttria nanocrystals. The electron diffraction patterns, high-resolution transmission electron microscopy, high-resolution scanning transmission electron microscopy, Fourier transform patterns from areas extending a few nanometres around the tracks show that yttria and YBCO keep their respective cubic and orthorhombic pristine structures

Magnetically intercalated multilayer silicene

Silicene, a Si-based analogue of graphene, is predicted to exhibit topological electronic phases with exotic properties capable to revolutionize electronics. In particular, the silicene structure is highly advantageous for spintronics. However, lack of synthetic routes to free-standing and magnetically functionalized silicene compounds prevents experimental corroboration of the predictions. Here we synthesize EuSi2, multilayer silicene intercalated with inherently magnetic Eu atoms, on SrSi2/Si(001) templates. The resulting films are formed by crystallites of two mutually orthogonal orientations. The structure is firmly established with electron diffraction, X-ray diffraction and electron microscopy. The compound EuSi2 exhibits non-trivial magnetic and transport properties. The data are compared with those for EuSi2 films grown on SrSi2/Si(111) templates

Magnetically intercalated multilayer silicene

Silicene, a Si-based analogue of graphene, is predicted to exhibit topological electronic phases with exotic properties capable to revolutionize electronics. In particular, the silicene structure is highly advantageous for spintronics. However, lack of synthetic routes to free-standing and magnetically functionalized silicene compounds prevents experimental corroboration of the predictions. Here we synthesize EuSi2, multilayer silicene intercalated with inherently magnetic Eu atoms, on SrSi2/Si(001) templates. The resulting films are formed by crystallites of two mutually orthogonal orientations. The structure is firmly established with electron diffraction, X-ray diffraction and electron microscopy. The compound EuSi2 exhibits non-trivial magnetic and transport properties. The data are compared with those for EuSi2 films grown on SrSi2/Si(111) templates

BaTiO₃ Thin Films from Atomic Layer Deposition: A Superlattice Approach

A superlattice approach for the atomic layer deposition of polycrystalline BaTiO₃ thin films is presented as an example for an effective route to produce high-quality complex oxide films with excellent thickness and compositional control. This method effectively mitigates any undesirable reactions between the different precursors and allows an individual optimization of the reaction conditions for the Ba–O and the Ti–O subcycles. By growth of nanometer thick alternating Ba­(OH)₂ and TiO₂ layers, the advantages of binary oxide atomic layer deposition are transferred into the synthesis of ternary compounds, permitting extremely high control of the cation ratio and superior uniformity. Whereas the Ba­(OH)₂ layers are partially crystalline after the deposition, the TiO₂ layers remain mostly amorphous. The layers react to polycrystalline, polymorph BaTiO₃ above 500 °C, releasing H₂O. This solid-state reaction is accompanied by an abrupt decrease in film thickness. Transmission electron microscopy and Raman spectroscopy reveal the presence of hexagonal BaTiO₃ in addition to the perovskite phase in the annealed films. The microstructure with relatively small grains of ∼70 Å and different phases is a direct consequence of the abrupt formation reaction. The electrical properties transition from the initially highly insulating dielectric semiamorphous superlattice into a polycrystalline BaTiO₃ thin film with a dielectric constant of 117 and a dielectric loss of 0.001 at 1 MHz after annealing at 600 °C in air, which, together with the suppression of ferroelectricity at room temperature, are very appealing properties for voltage tunable devices