Salawu Yusuff Adeyemi, Lee Nam-Suk, Kim Heon-Jung
Department of Physics, College of Natural and Life Science and Department of Materials-Energy Science and Engineering, College of Engineering, Daegu University, Gyeongbuk 38453, Republic of Korea.
National Institute for Nanomaterials Technology (NINT), Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea.
ACS Omega. 2019 Aug 8;4(8):13330-13337. doi: 10.1021/acsomega.9b01497. eCollection 2019 Aug 20.
This study reports the key ingredients that influence the orientation and stability of a α-FeO layer that grows on a metastable ε-FeO during pulsed laser deposition. Depending on the substrate temperature, two different α-FeO orientations arise on the ε-FeO (004) surface. At 800 °C, (2-10)-oriented α-FeO is stabilized, whereas at 700 °C, (006) orientation occurs. The (2-10)-oriented α-FeO layer possesses an interface with densely packed Fe ions with presumably considerable number of oxygen vacancies. On the other hand, the (006)-oriented α-FeO layer is stabilized, as in the case of the YSZ (100) substrate, due to the domain pattern with an in-plane rhombic shape, which is known to become an effective nucleation site. Growth with the unexpected (2-10) orientation can be understood based on a model that takes into account the surface energy as the dominant factor, which mainly stems from the presence of dangling bonds on the surface and the atomic vibration of the surface atoms. As the surface is one of the critical elements related to the specific functionality of a material, the present study will offer valuable insights into the designs of functional devices with novel surface properties.
本研究报告了在脉冲激光沉积过程中，影响在亚稳ε-FeO上生长的α-FeO层取向和稳定性的关键因素。根据衬底温度的不同，在ε-FeO（004）表面会出现两种不同取向的α-FeO。在800℃时，（2-10）取向的α-FeO得以稳定，而在700℃时，则出现（006）取向。（2-10）取向的α-FeO层与紧密堆积的Fe离子形成界面，可能存在大量氧空位。另一方面，（006）取向的α-FeO层得以稳定，就像在YSZ（100）衬底的情况一样，这是由于具有面内菱形形状的畴图案，已知其会成为有效的成核位点。基于一个将表面能作为主导因素的模型，可以理解出现意外（2-10）取向的生长情况，表面能主要源于表面悬键的存在以及表面原子的振动。由于表面是与材料特定功能相关的关键要素之一，本研究将为具有新颖表面特性的功能器件设计提供有价值的见解。
