Papers by Keyword: Columnar

Abstract: Visible-light enabled titanium oxide (TiO2) films deposited on indium tin oxide (ITO) substrates are investigated for their capabilities to both pollution control and splitting water on hydrogen production. Three types of TiO2 films are prepared at different levels of doping nitrogen (N) and carbon (C) and sputtering power. All three samples are similar in morphological and microstructural features, but differ in their interfacial phase and dopants. For the N,C-codoped TiO2 film prepared at a higher sputtering power, tin ions can permeate into the growing TiO2 film from the ITO substrate and promote the formation of crystalline Ti1-xSnxO2 layer. It shows the highest photocatalytic oxidation rate over methylene blue (MB) solution under ultraviolet and blue light irradiation, respectively. This is ascribed to the photosensitized carbon on the columnar grains, leading an increase in the MB adsorption capacity and light harvesting efficiency. Conversely, the N-TiO2 film prepared at a lower power exhibits the highest photocurrent density of which a higher Schottky barrier formed at the TiO2/ITO interface. A hydrogen yield rate of 0.25 μmol/cm2 h is obtained under blue light irradiation. These suggest that the interfacial properties of TiO2/ITO film and C-doping truly control its photocatalytic capabilities in addition to the well-known surface states.

Abstract: Simulations of several laboratory experiments developed for the study of structure and segregation in casting are presented. Interaction between the development of dendritic grain structure and segregation due to the transport of heat and mass by diffusion and convection is modeled using a Cellular Automaton - Finite Element model. The model includes a detailed treatment of diffusion of species in both the solid and liquid phases as presented elsewhere in this volume [1]. Applications deal with prediction of columnar and equiaxed grain structures, as well as inter-dendritic and inter-granular segregations induced by diffusion and macrosegregation induced by thermosolutal buoyancy forces.

Abstract: We have fabricated columnar nano-porous SiC by photo-electrochemical etching on the C-face of n-type 6H SiC at constant voltage. SEM images reveal that the pores are long, straight and parallel with diameters of about 20 nm. We have produced such layers up to 250 μm thick. The pore morphologies for both Si and C-face SiC samples are compared and discussed as a part of the effort to understand the growth mechanism. It is found that the constant voltage etching condition on C-face SiC is crucial for this nano-columnar pore formation.

Abstract: A hybrid columnar and dendritic porous structure has been developed in n-type 6H SiC using photoelectrochemical etching with proper control of the applied voltage and current density. The diameter of the formed columnar pores is around 200-500 nm. A possible formation mechanism due to the spatial distribution of holes and the HF concentration gradient in the pores is proposed. A self-supporting film with this morphology is a promising candidate for protein dialysis.