Room-temperature epitaxial growth of NiO(1 1 1) thin films by pulsed laser deposition

doi:10.1016/S0022-0248(01)01964-9

Journal of Crystal Growth

Volumes 237–239, Part 1, April 2002, Pages 591-595

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Abstract

The room-temperature epitaxial growth of NiO(1 1 1) thin films was successfully achieved on α-Al₂O₃(0 0 0 1) substrates using a pulsed laser deposition method. The epitaxial growth mechanism and the effect of oxygen pressure on the film quality were investigated using X-ray diffraction, X-ray pole figure, reflection high-energy electron diffraction and atomic force microscopy. The orientation relationships of the films with respect to the substrates were $NiO [1 1 1]∥ α-Al_{2} O_{3} [0 0 0 1]$ , $NiO [1 0 1 ̄]∥ α-Al_{2} O_{3} [1 0 1 ̄ 0]$ , and $NiO [2 1 ̄ 1 ̄]∥ α-Al_{2} O_{3} [1 1 2 ̄ 0]$ . The films consisted of a lot of domains and showed sixfold symmetry. These results can be explained by the higher-order epitaxy mechanism enabling the fourfold longer in-plane lattice parameters of NiO(1 1 1) to match the threefold longer parameters of α-Al₂O₃(0 0 0 1) with <4.5% misfit. The crystallinity of the epitaxial films was significantly improved by expanding the in-plane lattice parameter. This is due to the relaxation of the lattice misfit between the film and the substrate at the initial growth.

Introduction

Nickel oxide (NiO) is an antiferromagnetic material whose Néel temperature is 523 K. It has a NaCl-type crystalline structure, and becomes a p-type wide-gap semiconductor when its composition deviates from stoichiometry or when monovalent atoms such as Li⁺ are doped. NiO thin films are very useful as the exchange-biased layers of spin-valve giant magnetoresistance sensors [1], p-type transparent conducting films [2], and electrochromic devices [3].

On the other hand, NiO epitaxial films have been used as the epitaxial layers of artificial oxide superlattices with some very interesting structural and magnetic properties [4], [5]. In preparing superlattices consisting of epitaxial layers, the substrate temperature is a very important factor. It should be as low as possible to avoid interdiffusion between layers. Among the various deposition methods available today, pulsed laser deposition (PLD) has an advantage in preparing high-quality thin films at relatively low substrate temperatures, because of the generation of highly excited species through photochemical ablation [6]. It has been reported that oxide thin films on lattice-matched substrates, such as the CeO₂(1 1 1) film/Si(1 1 1) substrate [7] and NiO(1 0 0) film/MgO(1 0 0) substrate [8], could be grown epitaxially at room temperature by a PLD method.An epitaxial thin film of NiO(1 1 1) has a layered structure in which nickel ions and oxygen ions are alternately stacked along the 〈1 1 1〉 direction. It has been generally prepared on an α-Al₂O₃(0 0 0 1) substrate at a substrate temperature above 100°C. The in-plane lattice parameters of NiO(1 1 1) are 0.2952 nm for d_(1 1 0) and 0.1705 nm for d_(2 1 1), and those of α-Al₂O₃(0001) are 0.4122 nm for $d_{(101̄0)}$ and 0.2379 nm for $d_{(112̄0)}$ . The lattice misfit between d_(1 1 0) of NiO(1 1 1) and $d_{(112̄0)}$ of α-Al₂O₃(0 0 0 1) is as large as 24%. It is suspected that this large lattice misfit makes the film surface rougher due to the effect of three-dimensional island growth when the substrate temperature increases and significantly influences both the epitaxial growth and film quality of the deposited films. Accordingly, it is very important that the substrate temperature is as low as possible for the epitaxial growth of NiO(1 1 1) films on α-Al₂O₃(0 0 0 1) substrates. However, there are few reports on the epitaxial growth at room temperature and the film quality of NiO(1 1 1) thin films on α-Al₂O₃(0 0 0 1) substrates. Recently, we found that NiO(1 1 1) thin films could be grown epitaxially on α-Al₂O₃(0 0 0 1) substrates at room temperature using a PLD method, and that the crystallinity of epitaxial films was drastically improved by expanding the in-plane lattice parameter of the films. In this paper, we describe the room-temperature epitaxy of NiO(1 1 1) films on α-Al₂O₃(0 0 0 1) substrates, and discuss the epitaxial growth mechanism and the effect of oxygen pressure on the film quality.

Section snippets

Experimental procedure

NiO films were fabricated using a PLD apparatus with an rf-radical source [9]. A KrF excimer laser beam was focused on the target, which was prepared by sintering NiO powder in air at 1200°C for 72 h. Substrates were α-Al₂O₃(0 0 0 1) single crystals and were annealed in an oxygen atmosphere at 1000°C before deposition to obtain atomically flat surfaces [10]. NiO films were prepared on the substrates at room temperature (30°C) under a repetition frequency of 1 Hz. The distance from the target to the

Results and discussion

Fig. 1 shows the XRD patterns of NiO thin films deposited at various oxygen pressures. With increasing oxygen pressure, the intensities from NiO(1 1 1) and (2 2 2) became stronger. These peaks disappeared when the oxygen pressure exceeded 1.3 Pa.

The RHEED patterns of NiO thin films prepared at various oxygen pressures are shown in Fig. 2. The electron beam was incident along the $〈1 0 1 ̄ 〉$ and $〈2 1 ̄ 1 ̄ 〉$ azimuths. Clear streak RHEED patterns were observed below an oxygen pressure of 1.3 Pa, and showed

Conclusion

The room-temperature epitaxial growth of NiO(1 1 1) thin films was successfully achieved on α-Al₂O₃(0 0 0 1) substrates using a PLD method. The epitaxial growth mechanism and the effect of oxygen pressure on the film quality were investigated. The epitaxial orientation relationships between the films and the substrates were $NiO[1 1 1]∥ α-Al_{2} O_{3} [0 0 0 1]$ , $NiO[1 0 1 ̄] ∥ α-Al_{2} O_{3} [1 0 1 ̄ 0]$ , and $NiO[2 1 ̄ 1 ̄]∥ α-Al_{2} O_{3} [1 1 2 ̄ 0]$ . A lot of domains were observed on the film surface by AFM, and the symmetry of the film was

Acknowledgements

We would like to thank Prof. Taichiro Ito, Dr. Norifumi Fujimura and Dr. Atsushi Ashida of Osaka Prefecture University for their useful discussions. We also appreciate the kind support of Dr. Hirofumi Chikakiyo of Rigaku Co. who evaluated the NiO(1 1 1) film using X-ray pole figure measurements.

References (11)

M.J. Carey et al.
J. Appl. Phys.
(1993)
H. Sato et al.
Thin Solid Films
(1993)
S. Yamada et al.
J. Appl. Phys.
(1988)
T. Terashima et al.
J. Appl. Phys.
(1984)
G. Chern et al.
Appl. Phys. Lett.
(1991)

There are more references available in the full text version of this article.

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Room-temperature epitaxial growth of NiO(1 1 1) thin films by pulsed laser deposition

Abstract

Introduction

Section snippets

Experimental procedure

Results and discussion

Conclusion

Acknowledgements

J. Appl. Phys.

Thin Solid Films

J. Appl. Phys.

J. Appl. Phys.

Appl. Phys. Lett.