Epitaxy, electrical transport and phase transitions in charge ordered Ruddlesden-Popper perovskite oxide layers

在本项目中，我们要研究半掺杂外延Pr-Ca-Mn-O（PCMO）Ruddlesden-Popper（RP）薄膜的生长机制和结构-性能关系的n=1和n=2。锰氧化物的RP相代表具有极化子准粒子的准二维高度相关电子系统，它可以结晶为电荷有序相。电荷序可以被外部刺激“熔化”，并具有长寿命的电子空穴对激发。这使得迷人的新功能，特别是在光电子学，传感器技术和微电子。该项目的主要目标是了解决定外延层生长方向的机制。这些不仅由与衬底的失配决定，而且还由表面/界面的化学性质决定。此外，将确定应力松弛导致的缺陷，并研究它们对有序化温度的影响。作为薄膜的合成提供了通过外延、应变和缺陷来控制膜的性质以影响异质结中的功能的可能性。通过脉冲激光沉积（PLD）进行沉积。表征的主要焦点是外延和应变（X射线衍射，TEM），生长过程（AFM，SEM）和弹性应力（梁弯曲法）的调查。这是结合在磁场和电场中的温度相关的电输运测量。通过高分辨率透射电子显微镜（HRTEM）对缺陷和电荷有序进行研究。在该项目第一阶段的基础上，重点是n=1阶的Ruddlesden-Popper-Manganese薄膜，Tc=320 K，第二阶段将扩展到n=2阶及更高，其具有高达370 K的更高转变温度。

In this project we want to investigate growth mechanisms and structure-property relationships of semi-doped epitaxial Pr-Ca-Mn-O (PCMO) Ruddlesden-Popper (RP) films of order n=1 and n=2. The RP phases of the manganates represent quasi two-dimensional highly correlated electron systems with polaron quasi-particles, which can crystallize to a charge-ordered phase. The charge order can be "melted" by external stimuli and has long-lived electron-hole-pair excitations. This enables fascinating new functions, especially in photovoltaics, sensor technology and microelectronics. The main goal of the project is to gain an understanding of the mechanisms that determine the growth orientation of epitaxial layers. These are not only determined by the mismatch to the substrate, but also by the chemistry of the surface / interface. Furthermore, the defects resulting from stress relaxation will be determined and their effect on the ordering temperature will be investigated. The synthesis as thin films offers the possibility to control the properties of the films by epitaxy, strain and defects in order to influence the functionalities in heterojunctions. The deposition is performed by pulsed laser deposition (PLD). The main focus of the characterization is the investigation of epitaxy and strains (X-ray diffraction, TEM), the growth process (AFM, SEM) and elastic stresses (beam bending method). This is done in combination with temperature dependent electrical transport measurements in magnetic and electric fields. The investigation of defects and charge order is performed by means of high-resolution transmission electron microscopy (HRTEM). Based on the first phase of the project, which is focused on Ruddlesden-Popper-Manganate films of order n=1 with a Tc=320 K, the second phase will be extended to the order n=2 and higher, which have higher transition temperatures of up to 370 K.