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Green H 2 production by solar water splitting relies entirely on the intrinsic properties of the photocatalyst. In this study the impact of these intrinsic properties on the photocatalytic activity of anatase TiO 2 , the quintessential component of state of the art photocatalytic systems was explored at the nanoscale. The exploration involved a holistic microstructural and optical characterization of fully crystallized anatase thin films synthetized by metalorganic chemical vapor deposition. A combination of electron microscopy, spectroscopic ellipsometry, and infrared spectroscopy revealed that when the deposition temperature increased, the morphology evolved from dense to porous and columnar nanostructures. Interestingly, the columns with a complex, tree-like nanostructure photogenerated 18 times more H 2 than the densest sample. This result shows that the beneficial effect of the morphological nano-complexification and crystallographic diversification of the exchange facets on the photocatalytic performance outweighs the detrimental aspects inherent to this evolution, namely the drop of the charge carrier transport and the increase of residual stress. 1. Introduction Research on renewable energy is vital in the current context of global warming and societies that rely on high energy consumption. Hydrogen is a promising source of renewable energy and catalyzed solar water splitting (SWS) is a carbon-free method to produce it. Numerous materials have been tested to catalyze this reaction [1,2]. Among them, TiO 2-because it is non-toxic, chemically stable, abundant and affordable has been widely investigated as a photocatalytic material since Fujishima and Honda's seminal work [3-8]. Despite its high energy band-gap (3.2 eV), crystalline anatase TiO 2 shows attractive opto-electronic properties. It is an indirect semiconductor with a long exciton lifetime [9,10]; it has a conduction band minimum energy level below the redox potential of H+/H 2 (0 V vs. NHE) and a valence band maximum energy level above the redox potential of O 2 /H 2 O (+1.23 V vs. NHE) [11,12].

For a lab-on-chip application, we fabricate a blue bottom emitting strong microcavity organic light emitting diode (OLED), using very smooth and optically thin (25 nm) silver film as anode on a glass substrate. To improve the hole injection in the OLED device, PEDOT-PSS (poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonic acid)) has been used, so the silver anode must present not only a very smooth surface but also a strong adherence on the glass and a high wettability to allow a good PEDOT-PSS spin coating deposition. To obtain these physical properties, different 5 nm thick nucleation layers (germanium, chromium, and hydrogenated amorphous carbon) have been used to grow the silver thin films by e-beam deposition. The Ge/Ag bilayer presents all the desired properties: this bilayer, investigated by ellipsometry, optical profilometry, contact angle measurements, and XPS analysis, highlights an ultrasmooth surface correlated with the film growth mode and a high wettability related to its surface chemical composition.