Phonons And Excitons In ZrSe2 – ZrS2 Alloys

What Has Been Achieved:

ZrS2 has been previously explored in the literature for photodetection and photovoltaic applications, and has recently gained increased attention due to predictions of an indirect-to-direct band gap transition with application of strain. These properties may be further enhanced by alloying with ZrSe2 to produce ZrSxSe2-x (x=0...2). While these alloys show promise for novel optoelectronic applications, previous studies of this system are limited and have only focused on growth, theoretical calculations of electronic and thermoelectric properties, angle-resolved photoemission spectroscopy, and absorption measurements. No studies exist that explore the alloy-dependence of basic properties such as the phonon mode energies and exciton states. Therefore, we have partnered with the 2DCC to conduct a comprehensive investigation of the ZrSxSe2-x alloy system using density functional theory, Raman spectroscopy, and spectroscopic ellipsometry.

Importance of Achievement:

Our study reveals that long-range Coulomb interactions activate infrared phonons which are otherwise optically silent. In some cases, this results in unique Raman spectra that are completely dominated by infrared phonons. We also find from our spectroscopic ellipsometry measurements that the ZrSxSe2-x alloys host strong light-matter interactions with low optical losses in the near-infrared. This study suggests that these materials are highly attractive for atomically-thin photodetector and photovoltaic applications tunable across visible to near-infrared wavelengths.

Unique Features of the MIP That Enabled Project:

The MIP was able to provide our collaboration with high quality crystal growth of the full range of alloy compositions necessary for this work using the chemical vapor transport technique. These efforts led to the unexpected synthesis of trichalcogenide alloys that have spurred an entirely new area of investigation for the members of this project. Publication Oliver et al. represents a collaboration between two separate user projects that arose from relationships formed through the Graphene and Beyond workshop, knowledge sharing efforts and the user committee collaboration sessions among active users.

Publications:

Sean M. Oliver, Joshua J. Fox, Arsalan Hashemi, Akshay Singh, Randal L. Cavalero, Sam Yee, David W. Snyder, Rafael Jaramillo, Hannu-Pekka Komsa, and Patrick M. Vora. Phonons and excitons in ZrSe2 – ZrS2 alloys. J. Mater. Chem. C 20–22 (2020).

Joshua J Fox, Saiphaneendra Bachu, Randal L Cavalero, Robert M Lavelle, Sean M Oliver, Sam Yee, Patrick M Vora, Nasim Alem, David W Snyder. Chemical Vapor Transport Synthesis, Characterization and Compositional Tuning of ZrSxSe2-x for Optoelectronic Applications. Journal of Crystal Growth. 125609 (2020).

Seong Soon Jo, Akshay Singh, Maria Gabriela Sales, L. Cavalero, David W. Snyder, Patrick M. Vora, Stephen J. McDonnell, Aiichiro Nakano, R. Jaramillo. Tape-time processing: Kinetics and mechanisms of native oxidation of transition metal dichalcogenides ZrSxSe2-x and MoS2. In preparation. (2020)