Alkanethiolates (ATs) forming self-assembled monolayers (SAMs) on coinage metal and semiconductor substrates have been used successfully for decades for tailoring the properties of these surfaces. Here, we provide a detailed analysis of a highly promising class of AT-based systems, which are modified by one or more dipolar carboxylic acid ester groups embedded into the alkyl backbone. To obtain comprehensive insight, we study nine different embedded-dipole monolayers and five reference non-substituted SAMs. We systematically varied chain lengths, ester group orientations, and number of ester groups contained in the chain. To understand the structural and electronic properties of the SAMs, we employ a variety of complementary experimental techniques, namely infrared reflection absorption spectroscopy (IRS), highresolution X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), atomic force microscopy (AFM), and Kelvin probe (KP) AFM. These experiments are complemented with state-of-the-art electronic band-structure calculations. We find intriguing electronic properties like large and variable SAM-induced work function modifications and dipole induced shifts of the electrostatic potential within the layers. These observations are analyzed in detail by joining the results of the different experimental techniques with the atomistic insight provided by the quantum-mechanical simulations.orientation of this group in the backbone, the work function of the system can be changed by either +0.57 or −0.42 eV relative to a reference oligophenylene SAM. This variation is achieved without changing the chemistry for docking to the substrate or the chemical composition of the SAMambient interface. 28 Tuning the work function is, however, not the only effect of the embedded pyrimidine group in these systems, since it also induces a potential discontinuity inside the monolayer. This effect significantly changes the transport properties of the SAM, shifting the transition voltage and resulting in current rectification. 30,31 The potential discontinuity also shifts the core-level energies in the regions above and below the embedded dipoles relative to each other. These shifts can be observed directly by X-ray photoelectron spectroscopy (XPS), reflected as different binding energies (BEs) for the photoemission peaks associated with both regions. This observation, along with others, [32][33][34][35] lead us to question the generally accepted chemical shift model that assumes that shifts in the core-level BEs in monomolecular films are solely a consequence of different chemical environments of the respective atoms, 36 with the energy referenced to the Fermi level of the substrate. In contrast, it suggests that electrostatic shifts not related to the immediate chemical environment of an atom are similarly important. Generally, such electrostatic shifts are superimposed on the chemical ones and can under certain circumstances even play a dominant role. 37 The respective electrostatic effects in photoemiss...

TiO2 thin film based, chemiresistive sensors for NO2 gas which operate at room temperature under ultraviolet (UV) illumination have been demonstrated in this work. The rf-sputter deposited and post-annealed TiO2 thin films have been characterized by atomic force microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction to obtain surface morphology, chemical state, and crystal structure, respectively. UV-vis absorption spectroscopy and Tauc plots show the optical properties of the TiO2 films. Under UV illumination, the NO2 sensing performance of the TiO2 films shows a reversible change in resistance at room-temperature. The observed change in electrical resistivity can be explained by the modulation of surface-adsorbed oxygen. This work is the first demonstration of a facile TiO2 sensor for NO2 analyte that operates at room-temperature under UV illumination.

Solution-processed high-efficiency p–n heterojunction photodetectors have been developed using transition metal oxides.

Thin films of hydrogenated amorphous silicon can be produced at MPa pressures from silane without the use of plasma at temperatures as low as 345 °C. High pressure chemical vapor deposition may open a new way to low cost deposition of amorphous silicon solar cells and other thin film structures over very large areas in very compact, simple reactors.