Magnetic Field-assisted Chemical Vapor Deposition of Transition Metal Oxides and in situ Investigations on Electronic Structure by X-ray

与化学气相沉积（CVD）的常规实验参数（如温度、压力和前驱体化学）相比，对外在参数（如磁场）影响的研究较少。在过渡金属CVD的SPP初始相中获得的结果表明，外加磁场对相组成、晶粒生长和致密化过程有很强的影响，显著改变了所获得薄膜的形貌、化学形貌和功能特性。Cr(OBut)4的磁场辅助CVD （mfCVD）显示出从反铁磁性Cr2O3（零场）到铁磁性Cr3C2 （1.0 Tesla）的显著调制。同样，氧化铁在mfCVD中的生长表现出强烈的各向异性效应，从而增强了薄膜的光电化学性能。该应用程序的科学目标是：(i)通过使用更高的场强（高达4特斯拉）和更高的前驱体通量（科隆大学）将场效应与均匀和非均匀成核联系起来；（ii）通过基于同步加速器的operando x射线光谱学（PGI-6, j<s:1>利希研究中心）在原子水平上了解生长过程和磁场效应。为此，将系统地研究含有d-和p-嵌段元素的尖晶石前驱分子([CoAl2（OR)8] vs. [CoFe2(OR)8]）转化为固体薄膜的相偏析和相变现象。这将把分子离子和粒子的内在特性（如磁性）与它们的宏观表现（晶粒尺寸和晶体结构）联系起来。mfCVD实验与薄膜生长过程中的operando x射线吸收光谱将揭示外加磁场如何影响成核、表面扩散、氧化还原过程和晶格级相互作用，从而全面了解生长中的氧化物的表面化学和沉淀现象。本研究将证明外磁场是否可以扩大CVD的实验空间，并为影响生长薄膜的特性提供额外的控制参数。此外，磁场辅助相偏析和界面反应的过渡金属尖晶石携带顺磁性和反磁性中心原子（CoFe2O4 vs. CoAl2O4）将被研究。为了验证化学形貌和表面性质的变化，将在场增强和零场条件下生长的薄膜上进行小分子（例如H2O， CO2）活化的operando x射线光谱。项目活动得到了SPP成员在mfCVD样品的高级磁化测量（RG Gutfleisch），固体核磁共振研究（RG Wurmehl）薄膜样品的磁有序（RG Volkert）和高分辨率SEM/TEM微结构变化（RG Volkert）领域的互补专业知识的支持。

Compared to conventional experimental parameters of chemical vapor deposition (CVD) such as temperature, pressure and precursor chemistry, investigations on effects of extrinsic parameters (e.g., magnetic field) are less studied. The results obtained in the initial phase of the SPP on the CVD of transition metal demonstrated strong effects of external magnetic fields on the phase composition, grain growth and densification processes significantly altering the morphology, chemical topography and functional properties of the obtained films. Magnetic field-assisted CVD (mfCVD) of Cr(OBut)4 showed a remarkable modulation of the chemical composition from antiferromagnetic Cr2O3 (zero field) to ferromagnetic Cr3C2 (1.0 Tesla). Similarly, the growth of iron oxide in mfCVD showed strong anisotropy effects in films responsible for enhanced photoelectrochemical properties. The scientific objectives of this application is to (i) correlate the field effects to homogeneous and heterogeneous nucleation by using higher field strengths (up to 4 Tesla) and higher precursor fluxes (University of Cologne) and (ii) understand the growth process and magnetic field effect on an atomistic level by synchrotron based operando X-Ray spectroscopy (PGI-6, Research Center Jülich). For this purpose, conversion of spinel precursor molecules containing both d- and p-block elements ([CoAl2(OR)8] vs. [CoFe2(OR)8] into solid films will be systematically studied with respect to phase segregation and transformation phenomena. This will link the intrinsic properties (e.g., magnetism) of molecular ions and particles to their macroscopic manifestation (grain size and crystallographic structure). The mfCVD experiments together with operando X-ray absorption spectroscopy during film growth will decipher how nucleation, surface diffusion, redox processes and lattice-level interactions are influenced by applied magnetic fields and thus provide a holistic understanding of surface chemistry and precipitation phenomena in growing oxides. This research will demonstrate whether external magnetic fields can expand the experimental space of CVD and provide an additional control parameter for influencing the characteristics of as-grown thin films. Moreover, magnetic field-assisted phase segregation and interfacial reactions in transition metal spinels carrying paramagnetic and diamagnetic central atoms (CoFe2O4 vs. CoAl2O4) will be investigated. For the validation of changes in the chemical topography and surface properties, operando X-Ray spectroscopy of the activation of small molecules (e.g., H2O, CO2) will be performed on films grown in field-enhanced and zero-field conditions. The project activities are supported by the complementary expertise of the SPP members in the field of advanced magnetization measurements of mfCVD samples (RG Gutfleisch), magnetic ordering in thin film samples by solid-state NMR studies (RG Wurmehl) and microstructural changes via high-resolution SEM/TEM (RG Volkert).