TUNABLE ELECTRONIC COMPOSITES WITH PHASE CHANGE MATERIALS AND CONTROLLED DISORDER

TUNABLE ELECTRONIC COMPOSITES WITH PHASE CHANGE MATERIALS AND CONTROLLED DISORDERCode 31 form for Ramanathan (29 Feb 2016)Objective:The objective of this proposal is to combine the distinct insulating and metallic states in correlated oxides such as NbO2, V2O3 and VO2 dispersed in insulating matrices, to control the ground state via induced defects, and hence create artificial electronic composites whose properties can be tuned in the GHz frequency range.Approach:Thin film oxides and composites will be grown by physical vapor deposition. To grow embeddedcomposites, there will be two approaches taken. One is to grow 3D islands of the inclusions in the insulating matrix by sequential deposition and thickness control. Oxides like VO2 and NbO2 can grow in clustered 3D form on surfaces and we can exploit this to make islands. A second approach that leads to better control over the periodicity is to grow sequential layers followed by reactive ion etching of the inclusion layers to create patterned dispersions. Once a layer is patterned, further deposition followed by patterning will lead to another layer of inclusions. To create the disordered phases, two methods will be employed. One is to perform ion irradiation on the oxide layers to create locally metallic regions and the second approach is to anneal the films in highly reducing environments that are setup in the Ramanathan laboratory at Purdue. Ion irradiation experiments on representative samples will be conducted at University of Jena by C. Ronning. The rate of reduction of the correlated oxides is much faster than that of the insulating matrix such as silica and hence it is possible to create the composite structures at near-ambient temperatures. The electrodes used in the study will primarily be noble metals such as Pt to serve as electrical contacts. In order to design high-performance microwave components, a complete characterization of the microwave properties is required. This data will inform materials development and compositional optimization. The microwave parameters of interest are the real part of the dielectric permittivity, the loss tangent, dispersion, linearity and power handling. Dielectric characterization can be performed using Draper~s Keysight 10-GHz Split Cylinder Resonator. This is an industry standard test for microwave materials characterization. Merit/Naval Relevance:The materials studies and high frequency measurements combined will provide insights into the fundamental understanding of tunable electronic composites using oxide systems that undergo insulator-metal transitions. These insights will inform the potential of phase-change composites in frequency-tunable electromagnetic devices of interest to the ONR Electromagnetic Materials Program and the naval mission in areas such as electronic maneuver warfare.Prof. Ramanathan has established a strong group in the School of Materials Engineering at Purdue University following a faculty position at Harvard University and work at Intel Corporation. He has made advances in the understanding of metal-insulator transitions in correlated oxides, the physics of solid-state fuel cells, and the role of point defects in long- range carrier transport. His background and facilities will be complemented by Dr. Amy Duwel~s expertise in microwave measurements at Draper Laboratories. The result is likely to be significant advances in basic science and engineering with transition opportunities to more applied work of interest to DON.SOW:Base Period (12 months):Purdue will perform materials growth, fabrication and structural/compositional characterization to develop composite structures that will be suited for the microwave measurements. Ion irradiation experiments on representative samples will be carried out at Institute of Solid State Physics ~ Jena and will be characterized at Purdue and properties compared to that of low oxygen pressure annealed samples. Initial measurements of dielectric properties of representa