Mechanochemical Synthesis of Functional Layered Materials
Authors: Pedersen Samuel Vladimir 
Published: September 2022

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.