Date of Final Oral Examination (Defense)
Type of Culminating Activity
Doctor of Philosophy in Materials Science and Engineering
Materials Science and Engineering
Brian J. Jaques, Ph.D.
David Estrada, Ph.D.
Dmitri Tenne, Ph.D.
Joshua Wood, Ph.D.
As society continues to create new digital content, the telecommunications industry is seeking new technologies to enable higher bandwidth and lower costs to keep pace with the growing demand. Two-dimensional black phosphorus is proposed as a replacement for III-V compound semiconductors as the optically active material in next-generation silicon photonics as it can enable device scaling with lower power consumption. Therefore, the primary motivation of this dissertation was to investigate BP synthesis and chemical doping using an industrially scalable process, high energy ball milling. Initially, the work focused on understanding the ball mill conversion kinetics of red to black phosphorus, hitherto unknown, and is detailed in Chapter 2. The process follows a nucleation and growth dominated mechanism whose rate is controlled by the collision energy and milling intensity. Photoluminescence on mechanochemically synthesized BP showed visible and infrared emissions at the few-layer limit, indicating this process route provides optically viable BP suitable for silicon photonics. To address feasibility of doping, arsenic alloys with phosphorus were subsequently produced by ball milling in order to better understand how the crystal structure changes with substitutional doping; this work is described in Chapter 3. A similar conversion kinetics study was also performed showing a two-step mechanism. First, within a few minutes of milling, the trigonal PAs structure forms followed by a much slower phase transformation to the orthorhombic structure. This work provided a solid benchmark for how substitutional atoms affects the crystal structure, vibrational modes, binding energies, and photoluminescence. Candidate dopants for BP beyond arsenic included germanium, sulfur, selenium, and tellurium. Milling results for germanium phosphides are presented in Chapter 4 and results for phosphorus with sulfur, selenium, and tellurium are presented in Chapter 5. Germanium appears to dope BP (< 1 > at% Ge) as do sulfur (< 10 >at%) and selenium (< 10 > at%). Tellurium does not appear to form a stable dopant with black phosphorus via ball milling. Higher concentrations produced layered trigonal and monoclinic Ge-P crystals, while several crystalline and amorphous phosphorus sulfides and selenides are synthesized by this novel route. Together, Chapters 3-5 indicated that mechanochemical doping of BP with arsenic, germanium, sulfur and selenium is feasible with future work to explore electrical measurements. Finally, within the appendix, a discussion is presented challenges for ball mill doping of BP including milling material, red phosphorus purity, and candidate dopants; limited structural characterization of BP doped with germanium and selenium are included. Less comprehensive work on ball mill reactions of phosphorus with boron, tin, antimony, and bismuth are also reported in the appendix. These results confirmed inability to form phosphorus antimonides while several of the known tin phosphides were successfully synthesized. Independent of the black phosphorus work, a separate study on the synthesis of several intermetallic half-Heuslers for thermoelectric applications is also included in the Appendix. The half-Heusler work shows the versatility of ball milling to synthesize a wide range of intermetallic compounds and revealed nuances regarding challenges of milling together high temperature refractory metals, transition metals, and soft metalloids, in terms of particle size reduction, single phase synthesis, and milling media contamination.
Pedersen, Samuel Vladimir, "Mechanochemical Synthesis of Functional Layered Materials" (2022). Boise State University Theses and Dissertations. 1947.