Epitaxial Growth of Complex Metal Oxides

Gertjan Koster, Mark Huijben, Guus Rijnders

• Publisher: Woodhead Publishing
• Year: 2015
• ISBN:
  9781782422556
• Topic: Technology & Engineering
• Subtopic: Mining Engineering
• Index: Technology & Engineering

The atomic arrangement and subsequent properties of a material are determined by the type and conditions of growth leading to epitaxy, making control of these conditions key to the fabrication of higher quality materials. Epitaxial Growth of Complex Metal Oxides reviews the techniques involved in such processes and highlights recent developments in fabrication quality which are facilitating advances in applications for electronic, magnetic and optical purposes.

Part One reviews the key techniques involved in the epitaxial growth of complex metal oxides, including growth studies using reflection high-energy electron diffraction, pulsed laser deposition, hybrid molecular beam epitaxy, sputtering processes and chemical solution deposition techniques for the growth of oxide thin films. Part Two goes on to explore the effects of strain and stoichiometry on crystal structure and related properties, in thin film oxides. Finally, the book concludes by discussing selected examples of important applications of complex metal oxide thin films in Part Three.

• Provides valuable information on the improvements in epitaxial growth processes that have resulted in higher quality films of complex metal oxides and further advances in applications for electronic and optical purposes
• Examines the techniques used in epitaxial thin film growth
• Describes the epitaxial growth and functional properties of complex metal oxides and explores the effects of strain and defects

Part One

Epitaxial growth of complex metal oxides

Outline

1. Growth studies of heteroepitaxial oxide thin films using reflection high-energy electron diffraction (RHEED)

2. Sputtering techniques for epitaxial growth of complex oxides

3. Hybrid molecular beam epitaxy for the growth of complex oxide materials

4. Chemical solution deposition techniques for epitaxial growth of complex oxides

5. Epitaxial growth of superconducting oxides

6. Epitaxial growth of magnetic-oxide thin films

1

Growth studies of heteroepitaxial oxide thin films using reflection high-energy electron diffraction (RHEED)

G. Koster, M. Huijben, A. Janssen, and G. Rijnders MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands

Abstract

In this chapter, reflection high-energy electron diffraction (RHEED) in combination with pulsed laser deposition (PLD) is described. Both the use of RHEED as a real-time rate-monitoring technique and methods to study nucleation and growth during PLD are discussed. After a brief introduction of RHEED, a case is made for the step density model to describe the intensity variations encountered during deposition. An overview of these intensity variations, the intensity response during an RHEED experiment as a result of various kinetic growth modes, is given.

Keywords

Electron diffraction; Step density model; Thin film growth modes

1.1. Introduction: reflection high-energy electron diffraction and pulsed laser deposition

Reflection high-energy electron diffraction (RHEED) was limited to low background pressures until the development of high-pressure RHEED, which makes it possible to monitor in situ surface structure during deposition of oxides at higher pressures, opened new possibilities (Rijnders, Koster, Blank, & Rogalla, 1997). In addition to intensity oscillations caused by layer-by-layer growth, enabling accurate control of the growth rate, it became clear that intensity relaxation caused by typical pulsed deposition leads to a wealth of information about growth parameters (Blank, Rijnders, Koster, & Rogalla, 1998).

Pulsed laser deposition (PLD) has become an important technique in the fabrication of novel materials. Although use of PLD started in the mid-1960s (Ready, 1963), when initial attempts to produce high-quality thin films showed the promise of this technique, it was not until the discovery of high-T_c superconductors that PLD became widespread. The main benefits of PLD that are often quoted in literature are the relative easy stoichiometric transfer of material from target to the substrate, the flexibility of choice of materials and an almost free choice of (relatively high) background pressure. For instance, during the deposition of oxides, an oxygen background pressure up to 1 mbar is usually used.

Here, we demonstrate the use of RHEED during PLD by means of four examples showing how the effect of initial growth on the recorded RHEED signal leads to information on factors such as crystal termination on growth kinetics. For an extensive overview of the various growth models that apply to highly kinetic deposition, refer to the article by Christen and Eres (2008) or Rijnders and Blank (2007).

1.2. Basic principles of RHEED¹

In a typical RHEED system, a high-energy electron beam (10–50 keV) arrives at a surface under a grazing incident angle (0.1°–5°) (Figure 1.1(a)). At these energies the electrons penetrate any material for several hundreds of nanometers. Because of a grazing angle of incidence, however, the electrons interact with only the topmost layer of atoms (1–2 nm) at the surface, which makes the technique very surface sensitive. (By contrast, low-energy electron diffraction is surface sensitive because of the shallow penetration depth of low-energy electrons [100–500 eV].) The scattered electrons collected on a phosphorus screen form a diffraction pattern characteristic of the crystal structure of the surface and also contain information concerning the morphology of the surface. As we will see, RHEED is remarkably sensitive to variations in morphology and roughness during thin film growth and therefore is often used as a method to monitor thickness in real time.

Figure 1.1 Typical setup for a reflection high-energy electron diffraction experiment in real space (a) and reciprocal space (b).

1.3. Variations of the specular intensity during deposition

Here we briefly discuss the variations of specular intensity as a function of the variation of the surface roughness during deposition and growth of thin films, considering basic kinetics in the case of homoepitaxial growth (e.g., strontium titanate [SrTiO₃] on SrTiO₃ [001]). For an in-depth review of the use of RHEED during PLD, see Koster et al. (2011).

Figure 1.2 (a) Intensity oscillations during homoepitaxial growth of strontium titanate (SrTiO₃) at 850 °C and 3 Pa, indicating true layer-by-layer growth. (d) Calculated intensity oscillations using the diffraction model (b) (a schematic representation of which is given in (e)), and a step-density model (c) (a schematic representation of which is given in (f)). The number of pulses needed to complete one unit cell layer is estimated to be 27.

1.3.1. Specular intensity oscillations

The intensity oscillations recorded for homoepitaxy of SrTiO₃ are depicted in Figure 1.2(a), together with the intensities calculated using two diffe...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• List of Contributors
• Woodhead Publishing Series in Electronic and Optical Materials
• Part One. Epitaxial growth of complex metal oxides
• Part Two. Properties and analytical techniques
• Part Three. Applications of complex metal oxides
• Index