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Development of Rocksalt Nitride Metal/Semiconductor Superlattices and Metamaterials

Superlattices are periodic stacking of two different materials aimed at achieving unprecedented functionalities utilizing the anisotropy in structure which otherwise are not exhibited by either of the individual materials. As the demand for different types of functionality in the same material is growing, we are forced to explore artificially engineered materials like superlattices and heterostructure. However we cannot just engineer any two materials to make a superlattice, there are certain basic physics and materials science guidelines that have to be followed. These include (a) similarity in material’s class (like oxides or nitrides), (b) similarity in lattice constant, (c) low excess surface energy and others. Fortunately nitride family does allow some room to engineer superlattices and our work focuses here.

Our approach is to grow rocksalt nitride metal/semiconducotor superlattices that show desirable functionality ranging from thermoelectricity, plasmonics, thermal heat transport and others.Over the past few years, we have developed two family of superlattices namely (Zr,Hf)N/(Sc,Y)N and (Ti,W)N/(Al,Sc)N. The rocksalt crystal structure of the constituent metals (ZrN,HfN,TiN,WN) and semiconductors (ScN,YN, and rocksalt (Al,Sc)N)) have allowed us to grow epitaxial, pseudomorphic, coherant superlattices having cube-on-cube crystal growth. We characterize these superlatices with a range of spectroscopic and microscopic techniques that includes but not limited to XRD, XRR, RBS, SEM, HRTEM, STEM and others. We also do first-principles based calculations and develop models to understand their physical properties.




1. First-principles analysis of thermoelectric ZrN/ScN metal/semiconductor superlattices. Bivas Saha, Timothy D. Sands and Umesh V. Waghmare. Journal of Applied Physics 109, 073720 (2011).

2. Electronic Structure, Vibrational spectra and Thermal Properties of HfN/ScN Metal/semiconductor superlattices:  A first-principles Study: Bivas Saha, Timothy D. Sands and Umesh V. Waghmare. Journal of Physics: Condensed Matter, 24 415303, (2012).

Collaborators: Jeremy Schroeder (Linkoping University), Sammy Saber(Purdue), Eric Stach (Brookhaven)