2021 Bill Sproul Award and Honorary ICMCTF Lecture Recipient

Purpose

The Bill Sproul Award and Honorary ICMCTF lectureship is to recognize the achievements of a mid-career researcher who has made outstanding scientific and/or technological contributions in areas of interest to the Advanced Surface Engineering Division (ASED) of the AVS, with emphasis in the fields of surface engineering, thin films, and related topics.

2021 Bill Sproul Award and Honorary Lecture Recipient
Daniel Gall, Rensselaer Polytechnic Institute, USA

Biography

Daniel Gall holds a professor position in Materials Science and Engineering at the Rensselaer Polytechnic Institute, USA. He received his Diploma from the University of Basel in 1994 and his Ph.D. from the University of Illinois at Urbana-Champaign in 2000. Prof. Gall’s research focuses on the development of an atomistic understanding of thin film growth and on the electronic and optical properties of materials, with a particular interest in the epitaxial growth of transition-metal nitrides and their mechanical and opto-electronic properties. Daniel Gall has served in many positions within the ICMCTF, ASED, and AVS. He is a Fellow of the American Vacuum Society, and has won numerous awards from NSF, DoE, RPI, IBM, and LAM for his work on transition metal nitrides and on high-conductivity interconnects. Professor Gall has authored over 160 peer-reviewed journal articles. His students won over 60 best poster and paper awards. http://www.rpi.edu/~galld

Abstract

“Transition Metal Nitride Layers: New Phases and New Properties”
Daniel Gall, Rensselaer Polytechnic Institute, USA

We explore new transition metal nitride compounds using a combination of epitaxial layer growth, first-principles calculations, and measurements of electronic, optical, and mechanical properties as a function of composition and structure. Rock-salt structure nitrides are both mechanically and thermodynamically stable for group 3 transition metals. However, increasing the valence electron concentration by moving towards the right in the periodic table increases the strength of metal-metal bonds leading to a brittle-to-ductile transition and enhanced toughness, but also decreases the vacancy formation energy on both cation and anion sublattices, resulting in vacancy-stabilized compounds like cubic WN with a dramatically reduced elastic modulus, and new thermodynamically stable phases like a 5-fold coordinated base-centered monoclinic stoichiometric MoN. Conversely, reducing the valence electron concentration to reach a vanishing density of states at the Fermi level results in transition metal nitride semiconductors with promising properties for high-temperature electronic, thermoelectric, opto-electric, piezo-electric, plasmonic and magnetoresistive devices. Examples include ScN, Ti_0.5Mg_0.5N and CrN with 0.92, 0.7-1.7 and  0.2+/-0.4 eV bandgaps, respectively. The carrier concentrations are controlled by F and O doping, the bandgap is engineered by alloying with Al to form Cr_1-xAl_xN, (Ti_0.5Mg_0.5)_1-xAl_xN, and Sc_1-xAl_xN, the piezoelectric response is enhanced by the intentional introduction of local bonding instabilities in the wurtzite phase, and a two-dimensional electron gas is formed at the oxygen-exposed CrN(001) surface.