Tadaaki Tani

Electronic structures of organic-inorganic interfaces studied by UV photoemission

Abstract Electronic structures of interfaces, including electronically functional organic materials, were studied by UV photoemission spectroscopy (UPS) for the systems of zinc tetraphenylporphyrin (ZnTPP)-metals and merocyanine dyes-silver halides. At ZnTPP-metal interfaces, a constant lowering of vacuum level alignment of 0.7 eV was observed irrespective of the metal substrate, showing the formation of an interfacial electric dipole layer. The exposure to oxygen results in a drastic change of the interfacial electronic structure, which is ascribed to the change of the work function of the metals, rather than the doping of oxygen into ZnTPP. The estimated open circuit voltage of the Au ZnTPPA1 photovoltaic cell agreed with the observed value. For merocyanine dye-Ag halide interfaces, also a significant lowering of the vacuum level by dye deposition was observed. The interfacial electronic structures obtained by the combination of UPS and optical spectra showed excellent correspondence with the observed sensitizing behavior of dyes based on the electron transfer mechanism.

XANES Spectroscopic Studies of Chemical Bonding in Sulfur-Containing Organic Photographic Materials

S and N K-edge XANES spectroscopic study was performed for examining how XANES can be used for clarifying resonance and tautomerism in organic compounds containing thioamide (-NH-CS-) group used as additives in silver halide photography. The N K-edge spectra of all compounds, even N-methyl substituted ones, showed clear N1s → π\ddag peaks, giving a direct evidence of partially double bond character of the C-N bond, and suggesting thioamide structure by its excitation energy. S K-edge XANES spectra of the studied compounds also a clear peak at 2470-1 eV well separated from other peaks, and it is assigned to S1s → π\ddag resonance in thoioketone group by its polarization, effect of substitution at S site, and its energy significantly different from those of thiols. These results showed usefulness of XANES for studying resonance and tautomerism in these compounds, and indicate that all compounds studied, including extraordinarily strong antifoggant mercaptotetrazole, are in the thioamide form.

Temperature-dependent Br K-Edge EXAFS study on AgBrxCl1-x solid solutions

Local structures of AgBrxCl1-x solid solutions were investigated by means of Br K-edge EXAFS spectroscopy with the Br composition x varying from 0.05 to 1. The virtual crystal approximation did not hold as in other solid solutions investigated previously, although the Br-Ag bond distance noticeably varies with x. It was found for the first time that the x dependence of the Br-Ag distance is more significant at lower temperature than at room temperature. Such a new finding can be explained by the suppression of the long-range force with increasing temperature, compared with the short-range force.

Studies on electronic structure of interfaces between Ag and gelatin for stabilization of Ag nanoparticles

Extremely high stability of Ag nanoparticles in photographic materials has forced us to study the electronic structures of the interfaces between thin layers of Ag, Au, and Pt and their surface membranes in ambient atmosphere by photoelectron yield spectroscopy in air and Kelvin probe method. Owing to the Fermi level equalization between a metal layer and a membrane coming from air, the electron transfer took place from the membrane to Pt and Au layers and from an Ag layer to the membrane, giving the reason for poor stability of Ag nanoparticles in air. The control of the Fermi level of an Ag layer with respect to that of a gelatin membrane in air could be widely made according to Nernsts equation by changing the pH and pAg values of an aqueous gelatin solution used to form the membrane, and thus available to stabilize Ag nanoparticles in a gelatin matrix.

XANES Spectroscopic Studies of Merocyanine Dyes and Their Adsorbed States on AgCl

We studied the sulfur K-edge XANES spectra of several merocyanine dyes and an antifoggant PMTZ (phenylmercaptotetrazole) in the form of neat powder and adsorbed state on AgCl. Reflecting the localized nature of core excitations, the spectra of merocyanine dyes can be interpreted as contributions from S atoms in three chemical environments. The spectra of these dyes adsorbed on AgCl show significant change when S atom is in the thione (=S) form, while little change was observed when S is in the thia (-S-) form in the aromatic ring. This indicates that the dye in the thione form is adsorbed at the C=S group, while the dye with thia form may be adsorbed at other site than S. The deposition of PMTZ on AgCl also caused significant spectral change, which corresponds to the strong interaction of PMTZ with AgCl at the S site.

MoO x /Ag/MoO x transparent electrode by solution process

We have investigated a dielectric–metal–dielectric (DMD) multilayer film, which is unique as compared with such conventional transparent conductive oxides as indium tin oxide (ITO). In this study, we have selected MoO3 and Ag as the dielectric material and metal, respectively, and employed a nano-mist method in addition to a vacuum evaporation one. The transmission spectra of the films indicated that the Ag morphology changed from isolated islands to continuous layers with increasing Ag layer thickness, and that the morphology change was enhanced by MoO3. Then, MoO3/Ag/MoO3 (MAM) multilayer-structured transparent electrodes could be fabricated by a nano-mist method as well as by a vacuum evaporation one. Comparative examination is made on the properties of MAM films fabricated by these two methods for their application.