Low-energy properties of electrons and holes in CuFeS2

The antiferromagnetic semiconductor CuFeS2 belongs to a magnetic symmetry class that is of interest for spintronics applications. In addition, its crystal lattice is compatible with Si, making it possible to integrate it with nonmagnetic semiconducting structures. Therefore, we investigate this material by finding the effective k⋅p Hamiltonian for the electron and hole bands. We base this description on ab initio calculations and classify the electronic bands by their symmetry. As a result, we find that CuFeS2 exhibits spin-polarized bands. We also find that the crystal symmetry allows for the anomalous Hall effect. Finally, we suggest using cyclotron resonance to verify our proposed effective mass tensors at the conduction band minimum and valence band maximum.acceptedVersio

Epitaxial antiperovskite/perovskite heterostructures for materials design

We demonstrate fabrication of atomically sharp interfaces between nitride antiperovskite Mn$_{3}$GaN and oxide perovskites (La$_{0.3}$Sr$_{0.7}$)(Al$_{0.65}$Ta$_{0.35}$)O$_{3}$ (LSAT) and SrTiO$_{3}$ as paradigms of nitride-antiperovskite/oxide-perovskite heterostructures. Using a combination of scanning transmission electron microscopy (STEM), atomic-resolution spectroscopic techniques, and first-principle calculations, we investigated the atomic-scale structure, composition, and boding at the interface. We show that the epitaxial growth between the antiperovskite and perovskite compounds is mediated by a coherent interfacial monolayer that connects the two anti-structures. We anticipate our results to be a major step for the development of functional antiperovskite/perovskite heterostructures opening to harness a combination of their functional properties including topological properties for ultra low power applications

Performance and reliability of PZT-based piezoelectric micromirrors operated in realistic environments

The number of application areas for piezoelectric micro electromechanical systems based on PZT have increased rapidly over the years. Thus, to continue the development towards commercial deployment, characterizing lifetime and reliability during operation in realistic and harsh environments is important. Such environments are demanding for piezoMEMS devices since they often involve high humidity levels and elevated temperatures which gives rise to complex degradation. To address how such conditions affects device performance we combined optical and electrical measurements to elucidate the degradation of a PZT-based thin-film piezoelectric MEMS micromirror during temperature-humidity-cycling tests. As a test structure, 1 μm PbZr 0.40 Ti 0.60 O 3 on a 10 nm LaNiO 3 buffer-layer, were deposited by pulsed laser deposition on platinized Silicon-on-Insulator wafers. A 250 nm Au/TiW top electrode was deposited by DC-sputtering before structuring the final device. The micro mirrors were unipolarly actuated with a signal of 20 V peak-to-peak at a frequency of 1.5 kHz in an ambient with constant vapor concentration of 22 g/m 3 for device temperatures between 25 o C and 175 o C. Humidity-related degradation was manifested as local breakdown events and pinholes on top of and along the edges of the used electrodes. This had a strong effect on device performance and preceded degradation due to polarization-fatigue at all temperatures. Also, both the initial piezoelectric response and number of cycles to device failure increased with increasing substrate temperature in humid ambient.Performance and reliability of PZT-based piezoelectric micromirrors operated in realistic environmentsacceptedVersio

Structural investigation of epitaxial LaFeO_3 thin films on (111) oriented SrTiO_3 by transmission electron microscopy

We report on structural domains in LaFeO3 epitaxial thin films on (111) oriented SrTiO3 observed by transmission electron microscopy using low magnification dark field imaging and high resolution transmission electron microscopy techniques. The films were grown by pulsed laser deposition and had a thickness ≈ 20 nm. Three domain orientations are found, in accordance with the orthorhombic structure of LaFeO3. The domains themselves are of irregular shapes, and vary in size from tens to thousands of nm2. Regions of reduced Bragg scattering are observed as straight lines along , hinting at a complex domain structure.publishedVersio

Spatially Confined Spin Polarization and magnetic sublattice control in (La,Sr)MnO3−δ Thin Films by Oxygen Vacancy Ordering

Perovskite oxides are known for their strong structure property coupling and functional properties such as ferromagntism, ferroelectricity and high temperature superconductivity. While the effect of ordered cation vacancies on functional properties have been much studied, the possibility of tuning the functionality through anion vacancy ordering has received much less attention. Oxygen vacancies in ferromagnetic La0.7Sr0.3MnO3−δ thin films have recently been shown to accumulate close to interfaces and form a brownmillerite structure (ABO2.5). This structure has alternating oxygen octahedral and tetrahedral layers along the stacking direction, making it a basis for a family of ordered anion defect controlled materials. We use density functional theory to study how structure and properties depend on oxygen stoichiometry, relying on a block-by-block approach by including additional octahedral layers in-between each tetrahedral layer. It is found that the magnetic and electronic structures follow the layers enforced by the ordered oxygen vacancies. This results in spatially confined electronic conduction in the octahedral layers, and decoupling of the magnetic sub-lattices in the octahedral and tetrahedral layers. These results demonstrate that anion defect engineering is a promising tool to tune the properties of functional oxides, adding a new avenue for developing functional oxide device technology

Octahedral coupling in (111)- and (001)-oriented La0.7Sr0.3MnO3/SrTiO3 heterostructures

Rotations and distortions of oxygen octahedra in perovskites play a key role in determining their functional properties. Here, we investigate how octahedral rotations can couple from one material to another in La2/3Sr1/3MnO3/SrTiO3 epitaxial heterostructures by first principles density functional theory calculations, emphasizing the important differences between systems oriented perpendicular to the (111)- and (001)-facets. We find that the coupling length of out-of-phase octahedral rotations is independent of the crystalline facet, pointing toward a steric effect. However, the detailed octahedral structure across the interface is significantly different between the (111)- and (001)-orientations. For (001)-oriented interfaces, there is a clear difference whether the rotation axis in SrTiO3 is parallel or perpendicular to the interface plane, while for the (111)-interface, the different rotations' axes in SrTiO3 are symmetry equivalent. Finally, we show that octahedral coupling across the interface can be used to control the spatial distribution of the spin density

Performance and reliability of PZT-based piezoelectric micromirrors operated in realistic environments

The number of application areas for piezoelectric micro electromechanical systems based on PZT have increased rapidly over the years. Thus, to continue the development towards commercial deployment, characterizing lifetime and reliability during operation in realistic and harsh environments is important. Such environments are demanding for piezoMEMS devices since they often involve high humidity levels and elevated temperatures which gives rise to complex degradation. To address how such conditions affects device performance we combined optical and electrical measurements to elucidate the degradation of a PZT-based thin-film piezoelectric MEMS micromirror during temperature-humidity-cycling tests. As a test structure, 1 μm PbZr 0.40 Ti 0.60 O 3 on a 10 nm LaNiO 3 buffer-layer, were deposited by pulsed laser deposition on platinized Silicon-on-Insulator wafers. A 250 nm Au/TiW top electrode was deposited by DC-sputtering before structuring the final device. The micro mirrors were unipolarly actuated with a signal of 20 V peak-to-peak at a frequency of 1.5 kHz in an ambient with constant vapor concentration of 22 g/m 3 for device temperatures between 25 o C and 175 o C. Humidity-related degradation was manifested as local breakdown events and pinholes on top of and along the edges of the used electrodes. This had a strong effect on device performance and preceded degradation due to polarization-fatigue at all temperatures. Also, both the initial piezoelectric response and number of cycles to device failure increased with increasing substrate temperature in humid ambient

Performance and reliability of PZT-based piezoelectric micromirrors operated in realistic environments

The number of application areas for piezoelectric micro electromechanical systems based on PZT have increased rapidly over the years. Thus, to continue the development towards commercial deployment, characterizing lifetime and reliability during operation in realistic and harsh environments is important. Such environments are demanding for piezoMEMS devices since they often involve high humidity levels and elevated temperatures which gives rise to complex degradation. To address how such conditions affects device performance we combined optical and electrical measurements to elucidate the degradation of a PZT-based thin-film piezoelectric MEMS micromirror during temperature-humidity-cycling tests. As a test structure, 1 μm PbZr 0.40 Ti 0.60 O 3 on a 10 nm LaNiO 3 buffer-layer, were deposited by pulsed laser deposition on platinized Silicon-on-Insulator wafers. A 250 nm Au/TiW top electrode was deposited by DC-sputtering before structuring the final device. The micro mirrors were unipolarly actuated with a signal of 20 V peak-to-peak at a frequency of 1.5 kHz in an ambient with constant vapor concentration of 22 g/m 3 for device temperatures between 25 o C and 175 o C. Humidity-related degradation was manifested as local breakdown events and pinholes on top of and along the edges of the used electrodes. This had a strong effect on device performance and preceded degradation due to polarization-fatigue at all temperatures. Also, both the initial piezoelectric response and number of cycles to device failure increased with increasing substrate temperature in humid ambient.Performance and reliability of PZT-based piezoelectric micromirrors operated in realistic environmentsacceptedVersio