Chapter 1
Development of Epitaxial Oxide Ceramics Nanomaterials Based on Chemical Strategies on Semiconductor Platforms
A. Carretero-Genevrier1*, R. Bachelet1, G. Saint-Girons1, R. Moalla1, J. M. Vila-FungueiriƱo2, B. Rivas-Murias2, F. Rivadulla2, J. Rodriguez-Carvajal3, A. Gomez4, J. Gazquez4, M. Gich4 and N. Mestres4
1Institut des Nanotechnologies de Lyon (INL) CNRSāEcole Centrale de Lyon, Ecully, France
2Centro de InvestigaciĆ³n en QuĆmica BiolĆ³gica y Materiales Moleculares (CIQUS), Universidad de Santiago de Compostela, Santiago de Compostela, Spain
3Institut Laue-Langevin, Grenoble Cedex 9, France
4Institut de CiĆØncia de Materials de Barcelona ICMAB, Consejo Superior de Investigaciones CientĆficas CSIC, Campus UAB Catalonia, Spain
Abstract
The technological impact of combining substrate technologies with the properties of functional advanced oxide ceramics is colossal given its relevant role in the development of novel and more efficient devices. However, the precise control of interfaces and crystallization mechanisms of dissimilar materials at the nanoscale needs to be further developed. As an example, the integration of hybrid structures of high-quality epitaxial oxide films and nanostructures on silicon remains extremely challenging because these materials present major chemical, structural and thermal differences. This book chapter describes the main promising strategies that are being used to accommodate advanced oxide nanostructured ceramics on different technological substrates via chemical solution deposition (CSD) approaches. We will focus on novel examples separated into two main sections: (i) epitaxial ceramic nanomaterials entirely performed by soft chemistry, such as nanostructured piezoelectric quartz thin films on silicon or 1D complex oxide nanostructures epitaxially grown on silicon, and (ii) ceramic materials prepared by combining soft chemistry and physical techniques, such as epitaxial perovskite oxide thin films on silicon using the combination of soft chemistry and molecular beam epitaxy. Consequently, this chapter will cover cutting-edge strategies based on the potential of combining epitaxial growth and CSD to develop oxide ceramics nanomaterials with novel structures and improved physical properties.
Keywords: Epitaxial growth, thin-film growth, silicon, perovskites, solution chemistry, molecular beam epitaxy, oxide nanostructures, magnetic oxide nanowires, quartz thin films, octahedral molecular sieves
1.1 Introduction
Single-crystalline thin films of functional oxides exhibit a rich variety of properties such as ferroelectricity, piezoelectricity, superconductivity, ferro- and antiferro-magnetism, and nonlinear optics that are highly appealing for new electronic, opto-electronic and energy applications [1, 2]. Over the past few years, tremendous progress has been achieved in the growth of functional oxides on oxide substrates (such as LaAlO3, SrTiO3, Al2O3, MgO, and scandates) [3, 4]. As a result, to date, it is possible to control the epitaxial growth at the unit cell level, which has led to new phenomena arising from the engineering of novel interfaces [5ā8]. However, to fully exploit their properties, functional oxides should be effectively integrated on a semiconductor platform like silicon, germanium or III/V substrates, which are compatible with the electronics industry. The controlled epitaxial growth of functional oxide layers on semiconductor substrates is a challenging task as a result of the strong structural, chemical, and thermal dissimilarities existing between these materials. In spite of the difference in lattice parameters and thermal expansion coefficients, the major difficulty to engineer epitaxy is linked to the necessity of preventing the formation of an amorphous interfacial layer during the first stages of the growth (e.g. SiO2 or silicates on Si, depending of the atmosphere), which hinders any further epitaxy. Additionally, the cations of most oxide compounds can easily interdiffuse into the silicon substrate giving rise to the formation of spurious phases at the interface [9]. To overcome these major challenges, it is required to use a stable buffer layer, which can act simultaneously as a chemical barrier preventing ionic inter-diffusion and as a structural template favoring epitaxy.
In this context, McKee et al. [10] demonstrated the possibility to grow epitaxial SrTiO3 (STO) films on Si(001) by molecular beam epitaxy (MBE) with Sr passivation strategy. This work sets the basis to integrate STO and related perovskites on silicon for monolithic devices. Consequently, most of the research on crystalline functional oxides such as STO [11], lead zirconate titanate PbZr0.52Ti0.48O3(PZT) [12], BaTiO3 (BTO) [13ā17], LaCoO3 (LCO) [18], and La0.7Sr0.3MnO3 (LSMO) [19] integrated with Si has been based on an STO buffer layer epitaxially grown on Si(001) by MBE.
For decades, the integration of functional oxides onto a silicon platform has been identified as an important route to improve and widen the performances of microelectronics and nanoelectronics devices. A clear example is the successful preparation of two-dimensional electron gas at interfaces between LaAlO3 and SrTiO3 (STO) on Si(001). In this case, the STO film acts simultaneously as a buffer layer and as an active part of the functional heterostrucuture [20]. Moreover, 2D electron gases at the interface have also been demonstrated using LaTiO3 [21] and GdTiO3 [22, 23] grown on STO-buffered Si. Functional non-volatile BTO-based ferroelectric tunnel junctions (FTJ) on Si(001) substrates with a tunneling electroresistance (TER) ratio over 10,000% have been recently demonstrated by pulsed laser deposition (PLD) [24] and MBE [25] growth methods. In both cases, this was accomplished by including a thin layer of STO as an epitaxial template on silicon. In addition, concomitant ferroelectric and antiferromagnetic behaviors were demonstrated on single-crystal BiFeO3 (BFO) films grown on STO on Si(100) using PLD [26] and MBE [27].
Integration of self-assembled vertical epitaxial nanocomposites thin films on Si substrates has been reported for multiferroic or magnetic memory and logic devices. The growth of La0.7Sr0.3MnO3āZnO perovskiteāwurtzite and CeO2āBTO fluoriteāperovskite vertical nanocomposites on a Si substrate by PLD was descri...
