Composite epitaxial thin films: A new platform for tuning, probing, and exploiting mesoscale oxides
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tion Over the last three decades, the world of quantum nanomaterials has progressed in leaps and bounds, enabled by great advances in synthesis protocols and measurement tools.1 However, control and assembly of nanoscale objects still have a long way to go.2 Currently, applications that exploit nanoscale effects rely on relatively simple materials compositions, without a focus on assembly to higher-level structures. Key examples are binary semiconductor quantum dots for biolabeling3 and plasmonic metallic nanoparticles for biosensing.4 The problems of nanoscale materials being hard to anchor and contact to, and also, that they can have compromised thermal, chemical, and mechanical stability, are all critical issues that need to be addressed. A paradigm shift in thinking is required to create systems that fully harness low-dimensional phenomena. Spontaneous self-assembly of nanoscale building blocks to higher-level mesoscale architectures is required. Hence, we need to move beyond the reductionist concepts of small sizes and short length scales, toward a constructionist integrated approach for mesoscale practical devices.
The positive features of the mesoscale domain are that quantum effects still come into play since the allowed electronic energy levels are not yet continuous at this scale, but at the same time, the inherent advantages of larger dimensions, notably stability and contactability, can be exploited. An additional opportunity for the mesoscale domain is that as we move up the mesoscale staircase (Figure 1), collective behavior comes into force, giving new degrees of freedom that compete with one another. This leads to coupled electronic interactions (e.g., among magnetic moments, charges, and lattice distortions), resulting in great sensitivity to external stimuli, and ultimately, to high-performance multifunctional systems. Currently, much of mesoscale science is geared toward chemical and biological applications (e.g., using mesoporous silica),5 but is much less geared toward designing more complex mesoscale electronic devices. In our quest to fill the mesoscale gap, we need to assemble materials in a hierarchical way, from atoms to electronic devices, with materials architectonics (design of materials similar to the way an architect designs a building) guiding the way.6
J.L. MacManus-Driscoll, Department of Materials Science and Metallurgy, University of Cambridge, UK; [email protected] A. Suwardi, Department of Materials Science and Metallurgy, University of Cambridge, UK; [email protected] H. Wang, Department of Electrical and Computer Engineering and Department of Materials Science and Engineering, Texas A&M University, USA; [email protected] DOI: 10.1557/mrs.2015.258
© 2015 Materials Research Society
MRS BULLETIN • VOLUME 40 • NOVEMBER 2015 • www.mrs.org/bulletin
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COMPOSITE EPITAXIAL THIN FILMS: A NEW PLATFORM FOR TUNING, PROBING, AND EXPLOITING MESOSCALE OXIDES
Figure 1. Mesoscale staircase comparing self-assembly of the spiderweb with epitaxial oxide composite devices. (Top staircase, lef
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