Plasma-molten Metal and/or Liquid Interactions for Materials/Chemical Processing

Several grand challenges in energy storage and conversion need the discovery of functional materials that many agree will be composed of complex compositions at nanoscale. In this regard, plasma based materials processing has been shown to be promising for combinatorial techniques and scalable processing. The use of plasma oxidation of liquid precursors allows for creation of metastable complex oxide particles with compositional control.1 A number of examples will be discussed in which the above two techniques are currently being used for accelerating the development of a variety of catalysts including electrocatalysts and materials for storage applications. This talk will highlight our efforts to understand the role of plasmas under two categories: (a) the synergistic effects hydrogen and nitrogen plasma interactions with molten metals;2 and (b) the oxygen plasma-liquid droplet interactions.3 To gain insights into these mechanisms we have studied the interaction of hydrogen and nitrogen plasmas with low melting point metals, primarily with gallium. Absorption/desorption experiments as well as theoretical-computational calculations were performed. Experiments have shown an increment of adsorbed gaseous species into the molten metal in the presence of plasmas. In the case of oxygen plasma-liquid droplet interactions for creating complex oxides, the role of solvated electrons, oxygen radicals and heating effects will be discussed. Finally, the use of plasmas for achieving liquid phase epitaxial growth of GaN and related materials will be discussed.4 Author acknowledge primary funding support from NSF Solar Project (DMS 1125909), and NSF EPSCoR (1355438). References 1. P. Ajayi, S. Kumari, D. Jaramillo-Cabanzo, J. Spurgeon, J. Jasinski and M.K. Sunkara, “A rapid and scalable method for making mixed metal oxide alloys for enabling accelerated materials discovery”, J. of Materials Research, 31 (11), 1596-1607(2016) 2. L. Carreon, D.F. Jaramillo-Cabanzo, I. Chaudhuri, M. Menon and M.K. Sunkara, “Synergistic interactions of H2 and N2 with molten gallium in the presence of plasma”, Journal of Vacuum Science and Technology A, 36, 021303 (2018). 3. P. Ajayi, M. Z. Akram, W. H. Paxton, J. B. Jasinski and M. K. Sunkara, “Nucleation and Growth Mechanisms During Complex Oxide Formation Using Plasma Oxidation of Liquid Precursors”, Submitted (2019) 4. Jaramillo, J. Jasinski and M. Sunkara, “Liquid Phase Epitaxial Growth of Gallium Nitride”, Crystal Growth and Design, 19, 11, 6577-6585(2019)

Synthesis of a mesoporous titania thin film with a pseudo-single-crystal framework by liquid-phase epitaxial growth, and enhancement of photocatalytic activity

An anatase-phase mesoporous titania thin film with a pseudo-single-crystal framework was facilely synthesized by an inexpensive chemical process.

Electrochemical Epitaxial Growth of TiO2/CdS/PbS Nanocables

Electrochemical deposition as a liquid phase epitaxial growth method is widely used to fabricate different kinds of hierarchical structures. As a typical heterostructure, TiO2/PbS is widely utilized in the areas of photovoltaics and photocatalysis. Oriented TiO2 nanorod (NR) arrays can provide direct pathways for the electron transport of photoanode. However, the lattice mismatch between TiO2 NR sides and PbS is very large; PbS nanoparticles (NPs) only formed on the top of TiO2 NRs. To solve this problem, TiO2/CdS core/shell nanocables were firstly prepared electrochemically because the lattice ratio between TiO2 and CdS was 0.916; and then, PbS NPs were successfully deposited over CdS shells (the lattice ratio between CdS and PbS was 0.697) to form TiO2/CdS/PbS hierarchical heterostructures. Experimental results demonstrated that the CdS interlayer could effectively promote the growth of PbS NPs on the surface and improve the fill factor and short current density of the photoanodes.

Liquid-Phase Epitaxial Growth and Characterization of Nd:YAl3(BO3)4 Optical Waveguides

We investigated the fabrication of neodymium doped thin film optical waveguide-based devices as potential active sources for planar integrated optics. Liquid-phase epitaxial growth was used to fabricate neodymium-doped yttrium aluminum borate films on compatible lattice-matched, un-doped yttrium aluminum borate substrates. We observed the refractive index contrast of the doped and un-doped crystal layers via differential interference contrast microscopy. In addition, characterization by X-ray powder diffraction, optical absorption and luminescence spectra demonstrated the crystal quality, uniformity and optical guiding of the resulting thin films.

Liquid-Phase Epitaxial Growth and Characterization of Nd:YAl3(BO3)4 Optical Waveguides

We investigated fabrication of neodymium doped thin film optical waveguide-based devices as potential active sources for planar integrated optics. Liquid-phase epitaxial growth was used to fabricate neodymium-doped yttrium aluminum borate films on compatible lattice-matched un-doped yttrium aluminum borate substrates. We observed the refractive index contrast of the doped and un-doped crystal layers by differential interference contrast microscopy. In addition, characterization by X-ray powder diffraction, optical absorption and luminescence spectra demonstrated the crystal quality and uniformity and optical guiding of the resulting thin films.   

Theory and experiments of liquid phase epitaxial growth Part 1

Characterization of the liquid phase epitaxial growth is in the scope of the present paper. The determination of the main parameters of the process such as the stationary growth rate, the time constant, the stationary supercooling, the kinetic coefficient, the initial growth rate, the crystallization mechanism are under consideration. Pursuing this aim a differential equation has been obtained which allows obtaining the dependences of the supersaturation, the growth rate and the growth layer thickness on the duration of growth. These dependences allow the determination of the above mentioned process parameters. Two mechanisms of crystallization are considered - the normal growth and the growth assisted by the screw dislocations. The two dimensional nuclei growth has not been considered because an analytical solution of the equation was not possible. Some of the theoretical contentions are confirmed by the experiments. Using the obtained values of the parameters dependences are defined. Good agreement between theory and experimental results is observed.