Two-Step Thin Film Growth of Quasi-One-Dimensional Penta-Telluride ZrTe₅ Realized by an Amorphous-to-Crystalline Transition

Quasi-one-dimensional (quasi-1D) van der Waals (vdWs) materials, such as black phosphorus (BP) and transition metal chalcogenides (MX_3~5, M=transition metal, X=S, Se, and Te), have emerged as a forefront in materials science due to their unique electric, optical, and mechanical properties rooted in their distinctive 1D chain structures, distinct from their two-dimensional counterparts. Among these, ZrTe₅ has attracted attention due to its exceptional electrical properties as both a Dirac and Weyl semimetal, coupled with its potential for novel quantum phenomena and robust thermoelectric performance. However, the large-scale fabrication of ZrTe₅ thin films has remained a challenge, hindering its integration into practical semiconductor devices. In this study, we propose a novel approach to address this challenge by employing radio frequency (RF) magnetron sputtering, a well-established physical vapor deposition (PVD) technique, for the large-area growth of ZrTe₅ thin films.[1] Through meticulous investigation combining structural, electrical, and optical characterization techniques, we unveil a comprehensive understanding of the amorphous-to-crystalline phase transition in ZrTe₅ thin films. Our findings reveal a dramatic four-order-of-magnitude decrease in resistivity upon crystallization, accompanied by a significant change in optical properties and band structure. Detailed structural analysis using X-ray diffraction (XRD) and Raman spectroscopy elucidated the phase transition of the amorphous ZrTe₅ phase into a single orthorhombic crystalline structure. Furthermore, high-resolution hard X-ray photoelectron spectroscopy (HAXPES) has been applied for insight into the evolution of the electronic states and bonding configurations during the phase transition. We observed the phase transition from an amorphous phase characterized by Zr-Zr and Te-Te homopolar bonds to a crystalline phase dominated by Zr-Te bonds, indicating the formation of quasi-1D trigonal prismatic chains. The electrical properties, probed through Hall measurements, revealed a remarkable increase in carrier density and mobility upon crystallization, resulting in a substantial drop in resistivity. These changes are attributed to modifications in the local bonding environment and band structure, as evidenced by a valence band structure analysis and determination of the optical bandgap. The observed nearly one-order-of-magnitude change in bandgap between the amorphous and crystalline phases underscores the potential of ZrTe₅ for applications such as optical switching.[1]<br/> <br/>Our study not only contributes to the fundamental understanding of phase transition in quasi-1D materials but also presents a scalable fabrication method for large-area ZrTe₅ thin films, paving the way for their integration into advanced electronic and optical devices. These insights offer new avenues for exploring the diverse functionalities of quasi-1D materials and harnessing their unique properties for next-generation applications in materials science and beyond.<br/> <br/><b>Acknowledgments: </b>This work was supported by the JSPS KAKENHI (Grant Nos. 21H05009, 22K20474, 24K00915) and the Murata Science Foundation. This work was also supported by the Commissioned Research (JPJ012368C03701) of National Institute of Information and Communications Technology (NICT), JAPAN. The authors also acknowledge the financial support from the Hirose Foundation and Iketani Science and Technology Foundation. The HAXPES measurements were performed at beamline BL09XU at SPring-8, Japan as parts of proposals of 2022A1575, respectively.<br/> <br/>[1] Shuang, Yi, et al. "Amorphous-to-crystalline transition-induced two-step thin film growth of a quasi-one-dimensional penta-telluride ZrTe₅." <i>Journal of Materials Science & Technology</i>, In press (2024).