Influence of Momentary Annealing on the Nanoscale Surface Morphology of Room Temperature Pulsed Laser Deposited NiO(111)
- PDF / 52,784,944 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 34 Downloads / 161 Views
Influence of Momentary Annealing on the Nanoscale Surface Morphology of Room Temperature Pulsed Laser Deposited NiO(111) Epitaxial Thin Films on Atomically Stepped Sapphire (0001) Substrates Ryosuke Yamauchi1, Geng Tan1, Daishi Shiojiri1, Nobuo Tsuchimine2, Koji Koyama3, Satoru Kaneko1,4, Akifumi Matsuda1, and Mamoru Yoshimoto1 1 Department of Innovative and Engineered Materials, Tokyo Institute of Technology, Yokohama 226-8502, Japan 2 Toshima Manufacturing Co., Ltd., Higashimatsuyama, Saitama 355-0036, Japan 3 Namiki Precision Jewel Co., Ltd., Adachi, Tokyo 123-8511, Japan 4 Kanagawa Industrial Technology Center, Ebina, Kanagawa 243-0435, Japan ABSTRACT We examined the influence of momentary annealing on the nanoscale surface morphology of NiO(111) epitaxial thin films deposited on atomically stepped sapphire (0001) substrates at room temperature in O2 at 1.3 × 10−3 and 1.3 × 10−6 Pa using a pulsed laser deposition (PLD) technique. The NiO films have atomically flat surfaces (RMS roughness: approximately 0.1–0.2 nm) reflecting the step-and-terrace structures of the substrates, regardless of the O2 deposition pressure. After rapid thermal annealing (RTA) of the NiO(111) epitaxial film deposited at 1.3 × 10−3 Pa O2, a periodic straight nanogroove array related to the atomic steps of the substrate was formed on the film surface for 60 s. In contrast, the fabrication of a transient state in the nanogroove array formation was achieved with RTA of less than 1 s. However, when the O2 atmosphere during PLD was 1.3 × 10−6 Pa, random crystal growth was observed and resulted in a disordered rough surface nanostructure after RTA. INTRODUCTION Nickel oxide (NiO) with an NaCl-type structure is an antiferromagnetic semiconductor [1-3]. NiO has numerous applications as electrode materials for lithium ion batteries [4,5] and electrochemical supercapacitors [6,7], catalysts for carbon nanotube formation [8,9], and resistive switching memories [10,11] owing to its high performance, abundance, and low cost. In addition, NiO films have various interesting properties, such as excellent chemical stability, good crystallinity, and transparency. The band gap of NiO was determined to be approximately 3.5– 4.0 eV by optical measurement [3,12,13]. A recent trend in NiO research is the development of nanostructured materials [4-9,14-16]. Effectively controlling the size, morphology, and structure of NiO nanomaterials is important for applications involving morphology-dependent properties. Therefore, many efforts have been made to prepare various NiO nanostructures such as nanowalls [4], nanosheets [5,14], nanoflake arrays [15], nanocubes [16], etc. We previously reported the self-organizing formation of a periodic straight nanogroove array by postannealing an NiO(111) epitaxial thin film grown at room temperature on an atomically stepped sapphire (0001) substrate using rapid thermal annealing (RTA) [17]. RTA is a nonequilibrium thermodynamic process that is expected to lead to the formation of transient states and the generation of novel mate
