Topotactic Metal–Insulator Transition in Epitaxial SrFeOx Thin Films

Topotactic phase transformation enables structural transition without losing the crystalline symmetry of the parental phase and provides an effective platform for elucidating the redox reaction and oxygen diffusion within transition metal oxides. In addition, it enables tuning of the emergent physical properties of complex oxides, through strong interaction between the lattice and electronic degrees of freedom. In this communication, the electronic structure evolution of SrFeO_x epitaxial thin films is identified in real‐time, during the progress of reversible topotactic phase transformation. Using real‐time optical spectroscopy, the phase transition between the two structurally distinct phases (i.e., brownmillerite and perovskite) is quantitatively monitored, and a pressure–temperature phase diagram of the topotactic transformation is constructed for the first time. The transformation at relatively low temperatures is attributed to a markedly small difference in Gibbs free energy compared to the known similar class of materials to date. This study highlights the phase stability and reversibility of SrFeO_x thin films, which is highly relevant for energy and environmental applications exploiting the redox reactions.     

Physics of Thin Films

The formulae for the reflection of a periodic system of thin films (S-polarization) valid in the soft X-ray region, based on Ewald's dynamical theory of diffraction, are presented. Model caluclations for some mirrors are presented and the results compared with the classical (Fresnel) formulae.     

Use of Thin Films for High-sensitivity Angle Measurement.

We propose to use thin films to provide a drastic improvement of measurement sensitivity in the recently developed small-angle measurement method, namely, angle measurement based on the internal-reflection effect. By designing the thin films (single layer or multiple layers) so that they provide an antireflection effect in the vicinity of the critical angle, we show that the sensitivity of angle measurement can be increased exponentially with the increase of the number of thin-film layers. This method provides a new means of designing angle sensors with increased sensitivities without having to increase the number of reflections and therefore the physical size and the required fabrication accuracy of the reflection prisms. We describe the design of the thin films for this particular application and the analysis of measurement sensitivity and range as determined by the material and the number of layers of the thin films. Selection of the optimal initial angle for high linearity performance is also discussed.     

Nanoindentation of Ni-Ti Thin Films

Ni-Ti thin films of various compositions were sputtered-deposited on silicon substrates. Their mechanical properties (hardness and Young's modulus) were then determined using a nanoindenter equipped with a Berkovich tip. This paper examines the effects of composition on the mechanical properties (hardness and Young's modulus) of the sputter deposited Ni-Ti thin films. This is of particular interest since the actuation properties of these shape memory alloy films are compositionally sensitive. The surface-induced deformation is revealed via Atomic Force Microscopy (AFM) images of the indented surfaces. Which show evidence of material pile-up that increases with increasing load. The measured Young's moduli are also shown to provide qualitative measures of the extent of stress-induced phase transformation in small volumes of Ni-Ti films.     

Properties of Optical Thin Films

In this review an attempt is made to look shortly into the fundamentals of optical thin films at first and to describe them more detailed by examples and applications in the second part of the paper.     

Measuring Thin Transparent Films Precisely

Fast Fourier transform (FTT) and nonlinear regression analysis are established analysis methods in the context of reflectometric layer thickness determination on thin transparent films. Where applicable, FFT is a very fast method for determining film thickness, but with limitations in resolution. The far more complex nonlinear regression analysis provides more accurate results. But it also has its problems which are discussed here.     

纳米尺度的磁电复合薄膜

纳米尺度的磁电复合薄膜具有优良的铁电铁磁耦合特性,其在下一代新型多功能器件中具有大的应用潜力,从而引起了广泛关注.介绍了纳米尺度磁电复合薄膜的实验制备和性能,重点论述了磁电复合薄膜中的铁电相和铁磁相材料,最后指出了磁电复合薄膜中尚待进一步研究的问题.