Nanophotoactivity of Porphyrin Functionalized Polycrystalline ZnO Films

Abstract

Kelvin probe force microscopy in darkness and under illumination is reported to provide nanoscale-resolved surface photovoltage maps of hybrid materials. In particular, nanoscale charge injection and charge recombination mechanisms occurring in ZnO polycrystalline surfaces functionalized with Protoporphyrin IX (H2PPIX) are analyzed. Local surface potential and surface photovoltage maps not only reveal that upon molecular adsorption the bare ZnO work function increases, but also they allow study of its local dependence. Nanometer-sized regions not correlated with apparent topographic features were identified, presenting values significantly different from the average work function. Depending on the region, the response to the light excitation is different, distinguishing two relaxation processes, one faster than the other. This behavior can be explained in terms of electrons trapped closed to the molecule-semiconductor interface or electrons pushed into the ZnO bulk, respectively. Moreover, the origin of these differences is correlated with the H2PPIX-ZnO bonding and molecules configuration and aggregation. The chenodeoxycholic acid (CDCA) coadsorption leads to a more homogeneous surface potential distribution, confirming the antiaggregate effect of this additive, while the surface photovoltage is mostly dominated by the slow relaxation component. This work reveals the complexity of real device architectures with ill-defined surfaces even in a relatively simple system with only one type of dye molecule and hightlights the importance of nanoscale characterization with appropriate tools.

Adsorption, Ordering, and Metalation of Porphyrins on MgO Nanocube Surfaces: The Directional Role of Carboxylic Anchoring Groups

“…There is general agreement that the functional properties of metal oxide/porphyrin hybrids are subject to the hierarchy of different interaction types, to surface bonding and to the geometry of the molecular layer. , In devices, the complex microscopic architecture, however, makes it very demanding to establish firm correlations between the specific oxide/porphyrin geometries and the macroscopic material properties. One possible approximation to this problem is the use of novel nanoscale characterization techniques. , On the other hand, appropriate model systems for adsorption and charge transfer studies are needed. Gas-phase engineered and aggregate-free MgO nanocube powders feature a high definition with respect to surface composition and structural properties. , The present study shows consistently that the metalation of 2HTPP on MgO nanocubes is associated with the formation of a monolayer of flat-lying molecules .…”

“…One possible approximation to this problem is the use of novel nanoscale characterization techniques. 53,55 On the other hand, appropriate model systems for adsorption and charge transfer studies are needed. Gas-phase engineered and aggregate-free MgO nanocube powders feature a high definition with respect to surface composition and structural properties.…”

A Functionalized Tetrakis(4-Nitrophenyl)Porphyrin Film Optical Waveguide Sensor for Detection of H2S and Ethanediamine Gases

“…The surface of the Nf-TNPP thin film exhibits higher molecular ordering when compared to that of the TNPP thin film; the average surface roughnesses of the Nf-TNPP and TNPP sensing films were determined to be 9.97 nm and 20.4 nm, respectively. In addition, the peaks of the Nf-TNPP film are less high and the valleys less deep (i.e., the film is flatter, Figure 2 a) than those of the TNPP film ( Figure 2 b), owing to the presence of functional groups on the film surface [ 48 , 49 , 50 , 51 ]. The strong interactions between the Nf and TNPP are recognizable by a noticeable conformational change in the morphology of the film layer, which highlights the inclusion of TNPP molecules into the Nf structure; this also indicates that the TNPP molecules are well distributed across the surface of the Nf film.…”

Nanoscale J-aggregates of poly(3-hexylthiophene): key to electronic interface interactions with graphene oxide as revealed by KPFM

“…the photogenerated charges do not have enough time to relax during the "off" part of the two-pass method. 33 It should be mentioned that in the in situ sample, a few particles present an ex situ-like behaviour (marked with a red arrow in Fig. 2(d), (f ) and (g)).…”