Overview

Our understanding of physical reality remains incomplete. Studies on the behavior of ions and electrons in solids possessing complex crystal structures and strong Coulomb interactions will improve our knowledge of collective emergent behavior of matter. Materials synthesis therefore forms a foundational aspect and brings a collaborative dimension to scholarship. Themes we work on include:

  • Correlated semiconductors for neuroscience and intelligence
  • Evolutionary biology inspired adaptive matter
  • Physics of ion conductors
Programs

Organismic Materials and Intelligence

Adapting evolutionary knowledge from the natural world and the corresponding plasticity displayed by living beings into the physical world may lead to paradigm shift in designing artificial brains, haptic intelligence and human-machine interfaces. We are interested in exploring the use of correlated semiconductors as model systems (‘organismoids’) to design tunable electronic states via learning and adaptation. Materials synthesis, discovery of new adaptive phase change systems and understanding electronic structure of orbitally non-degenerate semiconductor lattices under various environmental stimuli form an important aspect of scholarship in this program. Long term vision of this program includes advancing physical analogs of evolutionary and haptic intelligence.

VO2 field effect switch


Stable phase transition in VO2

Stable phase transition in VO2


Nickelate brain-inspired circuits with ionic liquid gates

Nickelate brain-inspired circuits with ionic liquid gates

Epitaxial SmNiO3 films

Epitaxial SmNiO3 films


VO2 carrier density change w/ phase transition

VO2 carrier density change w/ phase transition

Physics of ion conductors and complex fluid interfaces

Ion injection and transport under extreme chemical potentials offers an elegant non-thermal route to design properties in functional materials and ion-selective membranes to mimic natural entities. Understanding the thermodynamic (with condensed matter theorists) and kinetic (dynamical relaxation) aspects of these processes combined with in-situ diagnostics (with DOE collaborators) is of interest. A related question is whether glassy dynamics in liquid gated systems can be probed in freestanding membranes directly via ionic-electronic coupling measurements?

Electrical conductivity relaxation in nanoscale ceria films at high temperatures

Electrical conductivity relaxation in nanoscale ceria films at high temperatures


Ultra-thin YSZ films for SOFCs

Ultra-thin YSZ films for SOFCs

Test chips to study ionic conductivity

Test chips to study ionic conductivity


Chip scale SOFCs

Chip scale SOFCs


Fabrication of integrated fuel cell devices for portable energy

Fabrication of integrated fuel cell devices for portable energy


Materials Discovery: Experimental Techniques

Experimental realization of oxide-based neural circuits require advances in materials synthesis and test structures that allow interrogation of the intrinsic properties. Two problems in this regard are of particular interest: (1) experimental techniques to advance crystalline materials synthesis via extreme thermodynamic environments and (2) methods to study phase formation in-operando in a dynamic environment. A significant part of this research is conducted in close collaboration with researchers at national laboratories.

Oxide growth mechanisms under e-fields

Oxide growth mechanisms under e-fields


Ultra-high pressure metastable phase synthesis

Suspended channel oxide FETs

Suspended channel oxide FETs


Laboratory and Instrumentation

We have custom thin film growth chambers (physical vapor deposition) to synthesize a variety of multi-component oxides and metal electrodes, oxidation systems to controllably vary non-stoichiometry, several unique probe stations to perform electrical, electrochemical measurements at high temperature (over 1000 degC) and controlled environment (over 30 decades in oxygen pressure).

Most of the equipment has been designed and built in-house by group members including undergraduate students allowing for unique transport property measurements in designer environments.

Research Sponsors

We are grateful to our sponsors: National Academy of Sciences, National Science Foundation, Department of Defense, ARPA-E, Semiconductor Research Corporation, as well as others in industry for supporting our research.

Collaborations

We collaborate extensively with academic researchers in fields spanning Condensed Matter Physics, Photonics, Physical Chemistry, Biology and Computational Science and Electrical Engineering, as well as at industrial and DoD labs. This is not surprising since we invest many years learning to synthesize a few materials systems. Please contact Shriram at shriram@purdue.edu if you are interested in exploring collaborative studies.