In this study 3-aminopropyltrimethoxysilane (APTMS) was used for the modification of single-crystal silicon wafers (111). We deposited the self-assembled layers from a solution of APTMS in five solvents with different polarities under various reaction conditions. The influence of the different solvents on the morphology of the modified surfaces was studied, since the possible heterogeneity may significantly influence the application of such surfaces. Our results show that the amount of coatings and the morphology of the modified surface strongly depend on the type of solvent. Silanization carried out in acetonitrile and toluene leads to the formation of a rough surface with a large density of APTMS polymerized molecules in the form of islands. The surfaces modified in N,N-dimethylformamide were smoother, with a lower density of APTMS islands. When using acetone and ethanol as a solvent we prepared a smooth, thin, modified surface, with a very low density of the APTMS islands. We discuss the influence of the polarity of the solvents on the morphology of the modified surfaces.
COBISS.SI-ID: 1715759
While the demonstrated power conversion effi ciency of organic photovoltaics (OPVs) now exceeds 10%, new design rules are required to tailor interfaces at the molecular level for optimal exciton dissociation and charge transport in higher efficiency devices. We show that molecular shape-complementarity between donors and acceptors can drive performance in OPV devices. Using core hole clock (CHC) X-ray spectroscopy and density functional theory (DFT), we compare the electronic coupling, assembly, and charge transfer rates at the interface between C60 acceptors and flat- or contorted-hexabenzocorone (HBC) donors. The HBC donors have similar optoelectronic properties but differ in molecular contortion and shape matching to the fullerene acceptors. We show that shape-complementarity drives self-assembly of an intermixed morphology with a donor/acceptor (D/A) ball-and-socket interface, which enables faster electron transfer from HBC to C60 . The supramolecular assembly and faster electron transfer rates in the shape complementary heterojunction lead to a larger active volume and enhanced exciton dissociation rate. This work provides fundamental mechanistic insights on the improved efficiency of organic photovoltaic devices that incorporate these concave/convex D/A materials.
COBISS.SI-ID: 2547556
Understanding the role of intermolecular interaction on charge transfer characteristics in π-stacked molecular systems is central to the rational design of hybrid electronic materials. However, a quantitative study of charge transfer in such systems is often difficult because of poor control over molecular morphology. Using resonant photoemission spectroscopy we studied the femtosecond charge-transfer dynamics in cyclophanes, which consist of two precisely stacked pi-systems. We attributed difference in charge transfer to the decreased inter-ring electronic coupling.
COBISS.SI-ID: 26125351
Charge transfer through non-covalent interactions is crucial to a variety of chemical phenomena. Being weak and nonspecific these interactions often coexist with stronger covalent ones, making it difficult to isolate the transfer efficiency of one type of bond versus another. Within our studies of carrier transport over empty molecular orbitals in adsorbed aromatic molecules we succeeded to map out the preferred pathways of ultrafast carrier transport from organic molecules to the underlying substrate and to relate them with specific type of molecular bonding. With the use of X-ray resonant spectroscopy we studied a model aromatic system, 1,4-benzenediamine (BDA) molecules bound on Au surface through an Au–N donor–acceptor (D/A) bond, as these are known to provide a pathway for electronic conduction in molecular devices. We show that charge delocalization across the D/A bond occurs in less than 500 as. Furthermore, the Au–N bond also enhances delocalization to the substrate from the neighboring carbon sites, demonstrating that fast charge transfer across a metal–organic interface does not require a covalently bonded system.
COBISS.SI-ID: 26934567
This work describes the preparation and characterization of a silicon surface modified by different self-assembled aminopropylsilanes (APS) with the purpose of using them in sensor applications. Single-crystal silicon wafers were modified with aminosilanes that have different numbers of bonding sites: 3-aminopropyltrimethoxysilane (APTMS), 3-aminopropyldiethoxymethylsilane (APRDMS) and 3-aminopropylethoxydimethylsilane (APREMS). We deposited the self-assembled layers from a solution of aminosilanes in toluene under various reaction conditions. The surface composition and the chemical bonding were determined using X-ray photoelectron spectroscopy (XPS). Furthermore, the surface morphology was investigated using atomic force microscopy (AFM). Our results show that the reactivity with the Si-oxide layer and the polymerization of aminosilanes depend on the number of possible bonding sites. The APTMS reacted the most intensively with the Si-oxide layer; a less intensive reaction was observed for the APRDMS; and the least intensive reaction was observed for the APREMS.
COBISS.SI-ID: 36892165