Discipline: Chemistry and Chemical Sciences
Subcategory: Materials Science
Margot Dormer - Pennsylvania State University
Co-Author(s): Jason Lapano and Roman Engel-Herbert, Pennsylvania State University, University Park, PA
Introduction: Silicon semiconductors are quickly approaching their physical size limitation. In order to preserve Moore’s law, scientists are investigating new materials for next generation electronic devices. TaS2 is a 2D material that serves as a promising candidate. TaS2 demonstrates a unique metal-to-insulator transition in its 1T phase with over an order of magnitude change in resistivity1. However, growth of this material remains challenging. Achieving 2D layer by layer growth is hindered due to the low nucleation rate of TaS2 on suitable substrates, as well as its propensity to form the competing 2H phase. However, the use of nucleation sites during growth has been shown to improve the quality of films grown in other 2D systems. The objective of this research is to investigate the synthesis of 2D TaS2 utilizing TaO nucleation sites and if this atomically thin layer can be stabilized in its 1T phase. Materials and Methods: TaO nucleation sites of varying sizes and geometries are synthesized on Si wafers. TaS2 is then grown via atomic layer deposition (ALD), using TaCl5 and H2S on these wafers at high temperatures. The formula for the ALD is as follows: TaCl_5+2H_2 S→TaS_2+4HCl+1/2Cl_2 The behaviors of TaS2 at different temperatures and pressures are observed via Atomic Force Microscopy (AFM) and Raman Spectroscopy. Complete crystallization of the TaS2 films was achieved via an ex-situ anneal. Annealing conditions were optimized by tuning the annealing temperature, sulfur partial pressure, and annealing time. Results and Discussion: I will present my findings on the deposition and growth kinetics of 2D 1T-TaS2 with particular focus on the development of the two-dimensional growth mode using the nucleation sites. I will discuss the relation between the film morphology and the nucleation site geometry, as well as spacing between sites. These effects will be correlated through our findings via AFM and Raman spectroscopy. Conclusion: 1T TaS2 demonstrates great potential as a replacement for ordinary silicon semiconductors. A metal-to-insulator transition would serve to be more efficient than traditional semiconductors because of its ability to instantaneously switch from being a full insulator to a full conductor, whereas semiconductors can only achieve partial insulation and conduction making it an ideal candidate for future electronic devices.
Funder Acknowledgement(s): The Emerging Frontiers in Research Innovation Research Education and Mentorship Program is sponsored by the National Science Foundation.
Faculty Advisor: Jason Lapano, firstname.lastname@example.org
Role: I conducted the annealing of the growth parameters and the characterization of my growths via atomic force microscopy and raman spectroscopy.