Convergence of Notch and β-catenin signaling induces arterial fate in vascular progenitors

The Notch intracellular domain and β-catenin team up with RBP-J to regulate gene transcription and promote the development of arterial endothelial cells

The Photoelectrochemical Production of Hydrogen

The photoeffects on the oxygen and hydrogen evolution reactions at n- and p-type semiconductors, respectively, have been studied theoretically and experimentally in connection with the direct production of hydrogen from solar energy. The experimental techniques involved in this work include: 1. Photocurrent measurements under the illumination of a 150W or a 900 W Xe lamp, using potential sweep methods. 2. Photo current measurements under illumination by monochromatic light using a Jarrell-Ash grating monochrometer and a Xe lamp. 3. Impedance measurements, using the direct method. 4. Transient photo current measurements following light illumination and light interruption. 5. Chemical vapor deposition to make TiO2 films on other semiconductors. 6. Sintering method for metal titanates synthesis. The following novel experimental matter has been resolved: 1. The quantum efficiency of photoelectrochemical reactions involving hydrogen or oxygen evolution at several potentials and wavelengths involving TiO2, Fe2TiO5, ZnTe, CdTe, GaAs, InP, GaP, SiC and Si in alkaline and acid solution. 2. The flat band potentials of ZnTe, CdTe and SiC in alkaline and acid solution and of InP in alkaline solution at various frequencies. 3. The break down of the photoelectrodes, i.e., TiO2, Fe2TiO5, ZnTe, CdTe, GaAs, InP, GaAs, SiC and Si in alkaline solution and acid solution, as a function of time. 4. The transient behaviour of photocurrents. 5. The prevention of the anodic dissolution of CdS by the use of thin film coating transparent to light. 6. The finding of Fe2TiO5 as a stable photoanode and of CdTe as a stable photocathode. The theory of photoelectrochemical system has been developed originally in the following way. Gurney's quantum mechanical theory of charge transfer reaction was modified to account for the photoelectrochemical charge transfer reaction. The number of electrons arriving at the electrode surface per unit time per unit area at certain energy level was calculated by considering the properties of the semiconductor. The energy levels of an acceptor and a donor states in the OHP were estimated. The potential drop was at first considered to occur totally within the semiconductor. Following this model, photocurrents were calculated and compared with the experimental results. Considerable discrepancies existed between calculated and experimental results. Energy losses of excited electrons within the semiconductor and the potential drop in the electric double layer were then taken into account. Also, the potential barrier for emitted electrons was modified by considering the image interaction of the emitting electron with the semiconductor electrode. The photocurrents calculated by this modified theory agreed fairly well with the experimental results. By applying this theory, the critical potential, at which the quantum efficiency becomes significant, has been related to the flat band potential and the energy gap.A Thesis Presented for the Degree of Doctor of Philosophy in The Flinders University of South Australi

Electrochemical Metal Deposition on Top of an Organic Monolayer

Electrochemical deposition of metals (platinum or gold) only on top of an organothiolate, 1,4-benzene-dimethanethiol (BDMT) or hexanedithiol (HDT), self-assembled monolayer (SAM) on a Au(111) substrate was achieved by electrochemical reduction of PtCl4^[2-] or AuCl^[4-] ion, which was preadsorbed on one free thiol end group of the dithiol SAM formed on a Au surface, in a metal-ion-free sulfuric acid solution at potentials more negative than the reduction potential of the metal ion. Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) measurement after the reduction of preadsorbed PtCl4^[2-] ion on BDMT/Au(111) electrode showed the presence of Pt not underneath but on top of the BDMT SAM. After a negative potential scan of the Pt/BDMT/Au(111) electrode to -1.30 V in 0.1 M KOH solution, a typical cyclic voltammogram of a clean Au(111) electrode was obtained, showing that the BDMT SAM with a Pt layer was reductively desorbed. These results proved that a Pt-BDMT SAM-Au substrate sandwich structure without a short circuit between the two metals was successfully constructed by this technique. Furthermore, a decanethiol (DT) monolayer was constructed on a Au layer, which was formed by the reduction of preadsorbed AuCl4^[-] ion on HDT/Au(111) electrode. The formation of DT/Au/HDT/Au(111) structure was confirmed as two cathodic peaks corresponding to reductive desorption of DT from Au on top of the HDT/Au(111) at -0.97 V and that of Au/ HDT from Au(111) at -1.12 V were observed when potential was scanned negatively to -1.35 V

Mechanistic Study of Photoelectrochemical Reactions at a p-GaP Electrode

The photocurrent-potential relations of a p-GaP electrode in various solutions are studied potentiostatically. Both the cathodic and anodic photocurrents are observed, i.e., the sign of photocurrent changes at a certain potential which we name the potential of zero photocurrent, Vzp. The potential of zero photocurrent is close but not equal to the flatband potential. The origin of the anodic photocurrent is presented. The log (photoeurrent)-potential relations follow the Tafel line at medium bias potentials and deviate from it at large and small bias potentials. The mechanism of the cathodic reactions is proposed based on the experimental results. The rate-determining step is the supply of photoexcited electrons to the semiconductor surface at large bias potentials and is the electrochemical, i.e., surface, process at medium and small bias potentials. At the small bias potentials, the photocurrent is enhanced by the photoelectrochemical reduction of oxidized species created by holes in valence band