Overview: Our research focuses on the exploration of novel oxide materials – both thin film heterostructures and nanostructures – in pursuit of two major research thrusts: multiferroic and multifunctional materials and devices and solar energy conversion, specifically oxide materials for photovoltaics and photocatalysis of water. The foundation of the research is based on the controlled growth of oxide thin film heterostructures and nanostructures via pulsed laser deposition and molecular beam epitaxy.  Aided by state-of-the-art in-situ characterization methods such as reflection high energy electron diffraction (RHEED) we can achieve atomic-scale control of these oxide materials. We augment these growth capabilities with detailed characterization (structural and physical) – including extensive utilization of scanning probe- and synchrotron-based experiments – while leveraging strong collaborations both at UIUC and around the world to gain fundamental insight and understanding of these materials.

Multiferroics: Driven by recent advances in the production of high quality thin films of such complex oxide materials, great attention has been given to understand order, coupling, and possible applications of multiferroic materials that simultaneously possess multiple ferroic order parameters (i.e., ferroelectricity, ferromagnetism, and/or ferroelasticity).  Researchers have been drawn by the promise of strong coupling between order parameters and the possibility for new functionalities in materials and what this may mean for the next generation of memory, sensing, and logic devices.  This work falls into a number of major programs:

Focus I – Search for New Multiferroics: The search for and characterization of new candidate multiferroic materials.  By utilizing thin film epitaxy it may be possible to stabilize the first room temperature ferroelectric-ferromagnet or to create magnetic ferroelectrics via atomically controlled growth of artificial heterostructures.

Focus II – Interfacial Functionality in Complex Oxides: It is widely known that interfaces in materials can vary quite drastically from the bulk of a material.  Our work includes the study of metallic ferromagnet interactions with multiferroics, coupling between complex oxide materials in epitaxially grown heterostructures, and probing novel states of low dimensional matter.

Oxides for Energy Applications: Driven by the ever increasing need for alternative energy, our research group is working to answer the rising energy needs of the world by investigating a new set of materials – oxide materials – that are abundant, require little post-mining processing, and offer an exciting set of properties that make them interesting for further study in parallel with traditional semiconducting materials.  Many materials studied to date suffer from a number of drawbacks including abundance, toxicity, cost, and stability issues.  Our group aims to work with widely available oxide materials to find an alternative path to energy sustainability around the world.  This work falls into a number of major programs:

Focus I – Solar Energy Conversion: Our group is working on the creation of oxide-based photovoltaic devices.  Key to this work is being able to tune properties (i.e., band gap, carrier mobility, and absorptivity), probe in detail the electronic structure of these materials, and utilize novel functionality in materials to achieve advances in energy applications.

Focus II – Photocatalysis of Water: Our research focuses on the search for new candidate oxide materials possessing smaller band gaps and the careful study of the electronic structure of these and other materials. Additionally we are working to utilize oxide materials, which are typically very stable in solution, as either passive protective or active absorbing layers capable of transporting charge to and from the solution/oxide interface to a buried oxide/semiconductor interface in traditional semiconductor-based systems.

L. W. Martin, et al., Advances in the growth and characterization of magnetic, ferroelectric, and multiferroic oxide thin films, Invited review in Mater. Sci. Eng. R-Rep to appear Fall 2009.

S. Y. Yang, J. Seidel, S. J. Byrnes, P. Shafer, C.-H. Yang, M. D. Rossell, J. W. Ager III, L. W. Martin, R. Ramesh, Domain wall driven anomalous photovoltaic effects in a complex oxide, submitted to Nature, June 2009.

R. J. Zeches, M. D. Rossell, J. X. Zhang, A. J. Hatt, C. H. Yang, A. Kumar, A. Melville, J. F. Ihlefeld, R. Erni, C. Ederer, V. Gopalan, D. G. Schlom, N. A. Spaldin, L. W. Martin, R. Ramesh, A strain-driven morphotropic phase boundary in BiFeO3, submitted to Science, May 2009.

S.-Y. Yang, L. W. Martin, et al., Photovoltaic effects in BiFeO3 Thin Films, under review at Appl. Phys. Lett., May 2009.

M. Huijben, L. W. Martin, et al., Electrically controlled magnetization in an oxide multiferroic/ferromagnet heterostructure, under review at Nature Mater., May 2009.
M.B. Holcomb, L.W. Martin, et al., Probing the evolution of antiferromagnetism in multiferroics, under review at Phys. Rev. B, May 2009.

M. O. Ramirez, A. Kumar, S. A. Denev, N. J. Podraza, X. S. Xu, R. C. Rai, Y.-H. Chu, J. Seidel, L. W. Martin, et al., Phys. Rev. B 79, 224106 (2009).

M. C. Langer, C. L. S. Kantner, Y.-H. Chu, L. W. Martin, et al., Observation of ferromagnetic resonance in SrRuO3 by the time-resolved magneto-optical Kerr effect, Phys. Rev. Lett. 102, 177601 (2009).

C.H. Yang, J. Seidel, S.-Y. Kim, P. Rossen, P. Yu, M. Gajek, Y.-H. Chu, L. W. Martin, et al., Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films, Nature Mater. 8, 485 (2009).

M. O. Ramirez, A. Kumar, S. A. Denev, Y.-H. Chu, J. Seidel, L. W. Martin, et al., Spin-charge-lattice coupling through resonant multimagnon excitations in multiferroic BiFeO3, Appl. Phys. Lett. 94, 161905 (2009).

Y.-H. Chu, Q. He, C.-H. Yang, P. Yu, L. W. Martin, et al., Nanoscale control of domain architectures in BiFeO3 Thin Films, Nano Lett. 9, 1726 (2009).

J. Seidel*, L.W. Martin*, et al., Conducting ferroelectric domain walls in oxide multiferroics, Nature Mater. 8, 229 (2009).

L.W. Martin, Multiferroics, Invited chapter, McGraw-Hill 2009 Yearbook of Science and Technology, McGraw-Hill: Columbus (2009).

L.W. Martin, et al., Multiferroics: Thin films and nanostructures, (Invited review paper) J. Phys. Condens. Matter 20, 434220 (2008).

M. Huijben, L.W. Martin, et al., Critical thickness and orbital ordering in ultrathin La0.7Sr0.3MnO3 films, Phys. Rev. B 78, 094413 (2008).

L.W. Martin, et al., Nanoscale control of exchange bias with BiFeO3 thin films, Nano Lett. 8, 2050 (2008).

A. Kumar, N.J. Podraza, S. Denev, J. Li, L.W. Martin, et al., Linear and nonlinear optical properties of multifunctional PbVO3 thin films, Appl. Phys. Lett. 92, 231915 (2008).

Y.-H. Chu*, L.W. Martin*, et al., Electric-field control of local ferromagnetism using a magnetoelectric multiferroic, Nature Mater. 7, 478 (2008).

A. Kumar, N. Podraza, S. Denev, M. Ramirez, Y.-H. Chu, L.W. Martin, et al., Linear and Nonlinear Optical Properties of BiFeO3, Appl. Phys. Lett. 92, 121915 (2008).

Y.-H. Chu, Q. Zhan, C.-H. Yang, M. Cruz, L.W. Martin, et al., Low voltage performance of epitaxial BiFeO3 films on Si substrates through lanthanum-substitution, Appl. Phys. Lett. 92, 102909 (2008).

S. Basu, L.W. Martin, et al., Photoconductivity in BiFeO3 thin films, Appl. Phys. Lett. 92, 091905 (2008).

L.W. Martin, et al., Room temperature exchange bias and spin valves based on BiFeO3/SrRuO3/SrTiO3/Si(001) heterostructures, Appl. Phys. Lett. 91, 172513 (2007).
Y.-H. Chu, L. W. Martin, et al., Controlling magnetism with multiferroics, Mater. Today 10, 16 (2007).

Y.-H. Chu, M.P. Cruz, C.-H. Yang, L.W. Martin, et al. Domain control in multiferroic BiFeO3 through substrate vicinality, Adv. Mater. 19, 2662 (2007).

J.F. Ihlefeld, A. Kumar, L.W. Martin, et al., Adsorption-controlled molecular-beam epitaxial growth of BiFeO3, Appl. Phys. Lett. 91, 071922 (2007).

Y.-H. Chu, T. Zhao, M.P. Cruz, Q. Zhan, P.L. Yang, L.W. Martin, et al., Ferroelectric size effects in multiferroic BiFeO3 thin films, Appl. Phys. Lett. 90, 252906 (2007).

Y.-H. Chu, L.W. Martin, et al., Epitaxial multiferroic BiFeO3 thin films: Progress and future directions, Ferroelectrics 354, 167 (2007).

R. Ramesh, F. Zavaliche, Y.-H. Chu, L.W. Martin, et al., Magnetoelectric complex-oxide heterostructures, Phil. Mag. Lett. 87, 155 (2007).

G.P. Pabst, L.W. Martin, et al., Leakage mechanisms in BiFeO3 thin films, Appl. Phys. Lett. 90, 072902 (2007).

A. Kumar, L.W. Martin, et al., Polar and magnetic properties of PbVO3 thin films, Phys. Rev. B 75, 060101(R) (2007).

L.W. Martin, et al., Growth and structure of PbVO3 thin films, Appl. Phys. Lett. 90, 062903 (2007).

Y.-H. Chu, Q. Zhan, L.W. Martin, et al., Nanoscale domain control in multiferroic BiFeO3 thin films, Adv. Mater. 18, 2307 (2006).

• Berkeley Summer Institute for Preparing Future Faculty - Institute Fellow (Summer 2008)
• Intel Robert Noyce Fellow in Microelectronics (August 2007-March 2008)
• National Science Foundation IGERT Fellow in Nanoscience and Engineering (August 2004-August 2007)
• Sapphire Award Winner, Graduate Excellence in Materials Science (GEMS), Materials Science and Technology Meeting (Fall 2006, Cincinnati, OH)
• Gold Medal Award Winner, Materials Research Society Graduate Student Award (Spring 2006)
• William T. Lankford Jr. Memorial Scholarship (May 2003, Carnegie Mellon University)