Active multilayer mirrors for reflectance tuning at extreme ultraviolet (EUV) wavelengths

We propose an active multilayer mirror structure for EUV wavelengths which can be adjusted to compensate for reflectance changes. The multilayer structure tunes the reflectance via an integrated piezoelectric layer that can change its dimension due to an externally applied voltage. Here, we present design and optimization of the mirror structure for maximum reflectance tuning. In addition, we present preliminary results showing that the deposition of piezoelectric thin films with the requisite layer smoothness and crystal structure are possible. Finally, polarization switching of the smoothest piezoelectric film is presented

Critical thickness and orbital ordering in ultrathin La0.7Sr0.3MnO3 films

Detailed analysis of transport, magnetism and x-ray absorption spectroscopy measurements on ultrathin La0.7Sr0.3MnO3 films with thicknesses from 3 to 70 unit cells resulted in the identification of a lower critical thickness for a non-metallic, non-ferromagnetic layer at the interface with the SrTiO3 (001) substrate of only 3 unit cells (~12 Angstrom). Furthermore, linear dichroism measurements demonstrate the presence of a preferred (x2-y2) in-plane orbital ordering for all layer thicknesses without any orbital reconstruction at the interface. A crucial requirement for the accurate study of these ultrathin films is a controlled growth process, offering the coexistence of layer-by-layer growth and bulk-like magnetic/transport properties.Comment: 22 pages, 6 figures, accepted for publication in Physical Review

Determination of the spin-flip time in ferromagnetic SrRuO3 from time-resolved Kerr measurements

We report time-resolved Kerr effect measurements of magnetization dynamics in ferromagnetic SrRuO3. We observe that the demagnetization time slows substantially at temperatures within 15K of the Curie temperature, which is ~ 150K. We analyze the data with a phenomenological model that relates the demagnetization time to the spin flip time. In agreement with our observations the model yields a demagnetization time that is inversely proportional to T-Tc. We also make a direct comparison of the spin flip rate and the Gilbert damping coefficient showing that their ratio very close to kBTc, indicating a common origin for these phenomena

Electronically coupled complementary interfaces between perovskite band insulators

Perovskite oxides exhibit a plethora of exceptional electronic properties, providing the basis for novel concepts of oxide-electronic devices. The interest in these materials is even extended by the remarkable characteristics of their interfaces. Studies on single epitaxial connections between the two wide-bandgap insulators LaAlO3 and SrTiO3 have revealed them to be either high-mobility electron conductors or insulating, depending on the atomic stacking sequences. In the latter case they are conceivably positively charged. For device applications, as well as for basic understanding of the interface conduction mechanism, it is important to investigate the electronic coupling of closely-spaced complementary interfaces. Here we report the successful realization of such electronically coupled complementary interfaces in SrTiO3 - LaAlO3 thin film multilayer structures, in which the atomic stacking sequence at the interfaces was confirmed by quantitative transmission electron microscopy. We found a critical separation distance of 6 perovskite unit cell layers, corresponding to approximately 2.3 nm, below which a decrease of the interface conductivity and carrier density occurs. Interestingly, the high carrier mobilities characterizing the separate electron doped interfaces are found to be maintained in coupled structures down to sub-nanometer interface spacing

Local probing of coupled interfaces between two-dimensional electron and hole gases in oxide heterostructures by variable-temperature scanning tunneling spectroscopy

The electronic structure of an epitaxial oxide heterostructure containing two spatially separated two-dimensional conducting sheets, one electronlike (2DEG) and the other holelike (2DHG), has been investigated using variable temperature scanning tunneling spectroscopy. Heterostructures of LaAlO3/SrTiO3 bilayers on (001)-oriented SrTiO3 (STO) substrates provide the unique possibility to study the coupling between subnanometer spaced conducting interfaces. The band gap increases dramatically at low temperatures due to a blocking of the transition from the conduction band of the STO substrate to the top of the valence band of the STO capping layer. This prevents the replenishment of the depleted electrons in the capping layer from the underlying 2DEG and enables charging of the 2DHG by applying a negative sample bias voltage within the band gap region. At low temperatures the 2DHG can be probed separately with the proposed experimental geometry, although the 2DEG is located less than 1 nm belo

Misfit strain dependence of ferroelectric and piezoelectric properties of clamped (001) epitaxial Pb(Zr0.52,Ti0.48)O3 thin films \ud

A study on the effects of the residual strain in Pb(Zr0.52Ti0.48)O3 (PZT) thin films on the ferroelectric and piezoelectric properties is presented. Epitaxial (001)-oriented PZT thin film capacitors are sandwiched between SrRuO3 electrodes. The thin film stacks are grown on different substrate-buffer-layer combinations by pulsed laser deposition. Compressive or tensile strain caused by the difference in thermal expansion of the PZT film and substrate influences the ferroelectric and piezoelectric properties. All the PZT stacks show ferroelectric and piezoelectric behavior that is consistent with the theoretical model for strained thin films in the ferroelectric r-phase. We conclude that clamped (001) oriented Pb(Zr0.52Ti0.48)O3 thin films strained by the substrate always show rotation of the polarization vecto