Advanced transition metal phosphide materials from single-source molecular precursors
Colson, Adam Caleb
Whitmire, Kenton H.
Doctor of Philosophy
In this thesis, the feasibility of employing organometallic single-source precursors in the preparation of advanced transition metal pnictide materials such as colloidal nanoparticles and films has been investigated. In particular, the ternary FeMnP phase was targeted as a model for preparing advanced heterobimetallic phosphide materials, and the iron-rich Fe 3 P phase was targeted due to its favorable ferromagnetic properties as well as the fact that the preparation of advanced Fe 3 P materials has been elusive by commonly used methods. Progress towards the synthesis of advanced Fe 2-x Mn x P nanomaterials and films was facilitated by the synthesis of the novel heterobimetallic complexes FeMn(CO) 8 (μ-PR 1 R 2 ) (R 1 = H, R 2 = H or R 1 = H, R 2 = Ph), which contain the relatively rare μ-PH2 and μ-PPhH functionalities. Iron rich Fe 2-x Mn x P nanoparticles were obtained by thermal decomposition of FeMn(CO) 8 (μ-PH 2 ) using solution-based synthetic methods, and empirical evidence suggested that oleic acid was responsible for manganese depletion. Films containing Fe, Mn, and P with the desired stoichiometric ratio of 1:1:1 were prepared using FeMn(CO) 8 (μ-PH 2 ) in a simple low-pressure metal-organic chemical vapor deposition (MOCVD) apparatus. Although the elemental composition of the precursor was conserved in the deposited film material, spectroscopic evidence indicated that the films were not composed of pure-phase FeMnP, but were actually mixtures of crystalline FeMnP and amorphous FeP and Mn x O y . A new method for the preparation of phase-pure ferromagnetic Fe 3 P films on quartz substrates has also been developed. This approach involved the thermal decomposition of the single-source precursors H 2 Fe 3 (CO) 9 PR (R = t Bu or Ph) at 400 °C. The films were deposited using a simple home-built MOCVD apparatus and were characterized using a variety of analytical methods. The films exhibited excellent phase purity, as evidenced by X-ray diffraction, X-ray photoelectron spectroscopy, and field-dependent magnetization measurements, the results of which were all in good agreement with measurements obtained from bulk Fe 3 P. As-deposited Fe 3 P films were found to be amorphous, and little or no magnetic hysteresis was observed in plots of magnetization versus applied field. Annealing the Fe 3 P films at 550 °C resulted in improved crystallinity as well as the observation of magnetic hysteresis.