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The amino group of proline is part of a pyrrolidine ring, which makes it unique among the proteinogenic amino acids. To unravel its full electronic structure, proline in solid state and aqueous solution is investigated using X-ray emission spectroscopy and resonant inelastic soft X-ray scattering. By controlling the pH value of the solution, proline is studied in its cationic, zwitterionic, and anionic configurations. The spectra are analyzed within a "building-block principle" by comparing with suitable reference molecules, i.e., acetic acid, cysteine, and pyrrolidine, as well as with spectral calculations based on density functional theory. We find that the electronic structure of the carboxyl group of proline is very similar to that of other amino acids as well as acetic acid. In contrast, the electronic structure of the amino group is significantly different and strongly influenced by the ring structure of proline.

Cyanide monolayers on Au{111} restructure from a hexagonal close-packed lattice to a mixed-orientation "ribbon" structure through thermal annealing. The new surface structure loses most of the observed surface features characterizing the initial as-adsorbed system with "ribbon" domain boundaries isolating rotationally offset surface regions where the orientation is guided by the underlying gold lattice. A blue shift to higher frequencies of the CN vibration to 2235 cm-1 with respect to the as-adsorbed CN/Au{111} vibration at 2146 cm-1 is observed. In addition, a new low-frequency mode is observed at 145 cm-1, suggesting a chemical environment change similar to gold-cyanide crystallization. We discuss this new structure with respect to a mixed cyanide/isocyanide monolayer and propose a bonding scheme consisting of Au-CN and Au-NC bound molecules that are oriented normal to the Au{111} surface.

A vibronic resonance between Au{111} surface states and adsorbed CN vibrations has been predicted, which we target for study. We have formed stable monolayers of cyanide on Au{111} and observe a hexagonal close-packed lattice with a nearest neighbor distance of 3.8 ± 0.5 Å. Cyanide orients normal to the surface attached via a Au-C bond. We show that the substrate-molecule coupling is particularly strong, leading to ultrafast electron transfer from the cyanide molecules to the Au{111} substrate as measured by resonant Auger spectroscopy using the core-hole clock method. The CN/Au{111} system is a simple example of a strongly interacting adsorbate-substrate system and will be the subject of a number of further studies, as discussed.

Amorphous oxide thin-film transistors (TFTs), including a-InGaZnO (IGZO) in particular, are promising devices for display and other applications. For commercial fabrication, IGZO is typically fabricated using vacuum-based methods, involving high costs and complex equipment. These drawbacks are overcome by cost-effective, solution-based processes, which, however, do not deliver the IGZO layer of the same quality as vacuum-based methods. This results in a trade-off between mobility and stability of the respective devices, diminishing their overall performance. The compromise between mobility and stability in these devices arises from defects, notably oxygen vacancies, during solution-based fabrication. Here, we suggest a solution to this problem by the introduction of a MgO or AlOx interlayer between the IGZO semiconductor and polymer insulator in a top-gate, bottom-contact TFT. The Mg and Al ions, originating from such an interlayer, suppress the appearance of the interfacial oxygen vacancies, serving as the major source of device instability, preserving at the same time bulk oxygen vacancies, promoting the mobility. In addition to this favorable function, the MgO/AlOx interlayer, characterized by a wide band gap, improves the performance of the joint dielectric layer by reducing the leakage current. As the result of both these favorable properties within the proposed strategy, a stable, hysteresis-free, and considerably performing device with a mobility of 4.6 cm2 V−1 s−1, an ON/OFF ratio exceeding >106.5, and a shift of the threshold voltage of 0.6 V could be fabricated, with all these parameters being superior as compared to the standard TFTs. [ABSTRACT FROM AUTHOR]

Whereas monopodal self-assembling monolayers (SAMs) are most frequently used for surface and interface engineering, tripodal SAMs are less popular due to the difficulty in achieving a reliable and homogeneous bonding configuration. In this context, in the present study, the potential of phosphonic acid (PA) decorated triptycene (TripPA) for formation of SAMs on oxide substrates was studied, using indium tin oxide (ITO) as a representative and application-relevant test support. A combination of several complementary experimental techniques was applied and a suitable monopodal reference system, benzylphosphonic acid (PPA), was used. The resulting data consistently show that TripPA forms well-defined, densely packed, and nearly contamination-free tripodal SAMs on ITO, with the similar parameters and properties as the monopodal reference system. Modification of wetting properties and work function of ITO by non-substituted and cyano-decorated TripPA SAMs was demonstrated, showing a potential of this tripodal system for surface engineering of oxide substrates. [ABSTRACT FROM AUTHOR]

Metal‐organic frameworks (MOFs) are a specific class of hybrid, crystalline, nano‐porous materials made of metal‐ion‐based 'nodes' and organic linkers. Most of the studies on MOFs largely focused on porosity, chemical and structural diversity, gas sorption, sensing, drug delivery, catalysis, and separation applications. In contrast, much less reports paid attention to understanding and tuning the electrical properties of MOFs. Poor electrical conductivity of MOFs (~10−7–10−10 S cm−1), reported in earlier studies, impeded their applications in electronics, optoelectronics, and renewable energy storage. To overcome this drawback, the MOF community has adopted several intriguing strategies for electronic applications. The present review focuses on creatively designed bulk MOFs and surface‐anchored MOFs (SURMOFs) with different metal nodes (from transition metals to lanthanides), ligand functionalities, and doping entities, allowing tuning and enhancement of electrical conductivity. Diverse platforms for MOFs‐based electronic device fabrications, conductivity measurements, and underlying charge transport mechanisms are also addressed. Overall, the review highlights the pros and cons of MOFs‐based electronics (MOFtronics), followed by an analysis of the future directions of research, including optimization of the MOF compositions, heterostructures, electrical contacts, device stacking, and further relevant options which can be of interest for MOF researchers and result in improved devices performance. [ABSTRACT FROM AUTHOR]

Aryl-substituted alkanethiolate (AT) self-assembled monolayers (SAMs) exhibit typically so-called odd–even effects, viz. systematic variations in the film structure, packing density, and molecular inclination depending on the parity of the number of the methylene units in the alkyl linker, n. As an exception to this rule, ATs carrying an anthracen-2-yl group (Ant-n) as tail group were reported to have different behavior due the non-symmetric attachment of the anthracene unit to the AT linker, providing additional degree of freedom for the molecular organization and allowing for partial compensation of the odd–even effects. In this context, the structure of SAMs formed by adsorption of anthracene-substituted ATs (Ant-n; n = 1–6) at room temperature on Au(111) substrate was investigated by high-resolution scanning tunnelling microscopy (STM). Most of these SAMs exhibit a coexistence of two different ordered phases, some of which are common for either n = odd or n = even while other vary over the series, showing a broad variety of different structures. The average packing density of the Ant-n SAMs, derived from the analysis of the STM data, varies by 7.5–10% depending on the parity of n, being, as expected, higher for n = odd. The respective extent of the odd–even effects is noticeably lower than that usually observed for other aryl-substituted monolayers (∼25%), which goes in line with the previous findings and emphasizes the impact of the non-symmetric attachment of the aromatic unit. [ABSTRACT FROM AUTHOR]

This work describes the effects of dodecavanadate anions and phthalocyanine ligands as well as the identity of lanthanide centers on the charge transport characteristics of heterometallic complexes (nBu4N)3[HV12O32Cl-(LnPc)] and (nBu4N)2[HV12O32Cl-(LnPc)2] for SmIII–ErIII, LuIII, and YIII on gold surfaces. In molecular ensemble junctions with eutectic Ga–In top contacts, the complexes containing two phthalocyanine ligands are highly conductive but show no clear effect of varying the lanthanide. By contrast, the complexes that omit phthalocyanine but include 4f-functionalized dodecavanadate building blocks show clear trends in conductance, rectification, and transition voltages. Density functional theory calculations show that the occupied and unoccupied frontier orbitals in the heterometallic complexes are delocalized on the phthalocyanine ligand and dodecavanadate anion, respectively, suggesting strong lanthanide–ligand electronic coupling. Near-edge X-ray absorption fine structure spectroscopy on these complexes further suggests that the phthalocyanine ligands are arranged such that their edges are in contact with the electrodes, creating tunneling transmission channels that bypass the lanthanide, effectively obviating the electronic contributions of the lanthanide centers to charge transport. These results separate the influence of the individual constituents of these metal–ligand complexes on the tunneling charge-transport properties. These results demonstrate how strongly coupled ligands such as phthalocyanine can dominate charge transport, from which we construct design rules for harnessing the properties of f-block elements in redox-active molecular heterojunctions. [ABSTRACT FROM AUTHOR]

The effective detection of hydrogen peroxide (H2O2) in different environments and, above all, in biological media, is an important practical issue. To this end, we designed a novel electrochemical sensor for H2O2 detection by introducing gold nanoparticles (AuNPs) into the porous poly(ethylene glycol) (PEG) matrix formed by the thermally activated crosslinking of amino- and epoxy-decorated STAR-PEG precursors. The respective composite PEG-AuNP films could be readily prepared on oxidized Si substrates, separated from them as free-standing nanosheets, and transferred as H2O2 sensing elements onto the working electrode of the electrochemical cell, with the performance of the sensing element relied on the established catalytic activity of AuNPs with respect to H2O2 decomposition. The sensitivity, detection limit, and the operation range of the composite PEG-AuNP sensors were estimated at ~3.4 × 102 μA mM−1 cm−2, 0.17 μM of H2O2, and 20 μM–3.5 mM of H2O2, respectively, which are well comparable with the best values for other types of H2O2 sensors reported recently in literature. The particular advantages of the composite PEG-AuNP sensors are commercial source materials, a simple fabrication procedure, the bioinert character of the PEG matrix, the 3D character of the AuNP assembly, and the possibility of transferring the nanosheet sensing element to any secondary substrate, including the glassy carbon electrode of the electrochemical cell. In particular, the bioinert character of the PEG matrix can be of importance for potential biological and biomedical applications of the designed sensing platform. [ABSTRACT FROM AUTHOR]

This study introduces an alternative approach to immobilize thiolated single-stranded DNA (ssDNA) for the DNA sensing. In contrast to the standard, monomolecular assembly of such moieties on gold substrate, over the thiolate–gold anchors, we propose to use bioinert, porous polyethylene glycol (PEG) films as a 3D template for ssDNA immobilization. The latter process relies on the reaction between the thiol group of the respectively decorated ssDNA and the epoxy groups in the epoxy-rich PEG matrix. The immobilization process and subsequent hybridization ability of the resulting sensing assembly were monitored using cyclic voltammetry and electrochemical impedance spectroscopy, with the latter tool proving itself as the most suitable transduction technique. Electrochemical data confirmed the successful immobilization of thiol-decorated ssDNA probes into the PEG matrix over the thiol–epoxy linkage as well as high hybridization efficiency, selectivity, and sensitivity of the resulting DNA sensor. Whereas this sensor was equivalent to the direct ssDNA assembly in terms of the efficiency, it exhibited a better selectivity and bioinert properties in view of the bioinert character of the PEG matrix. The above findings place PEG films as a promising platform for highly selective ssDNA sensing, leveraging their flexible chemistry, 3D character, and bioinert properties. [ABSTRACT FROM AUTHOR]

Modification of source and drain electrodes in organic thin film transistors (OTFTs) by dipolar self-assembled monolayers (SAMs) is frequently used to reduce the charge injection barrier at the interface between the electrodes and the organic semiconductor (OSC). However, such a modification can also affect the morphology and crystallinity of the OSC. Here, we show that the latter effect can be particularly strong and even decisive for the OTFT performance if the modification by SAMs not only involves the electrodes but, due to the specific affinity of the SAM-forming molecules, includes also the common OTFT substrate, usually exposed to these molecules as well, during the respective fabrication step. For this purpose, we fabricated and characterized in detail a series of model OTFTs with a top-gate-bottom-contact configuration and poly(3-hexylthiophene-2,5-diyl) OSCs. For the modification, we used binary dipolar SAMs with either carboxylic acid or silane anchoring groups, deposited either exclusively onto the electrodes (indium tin oxide) or both onto the electrodes and OTFT substrate (glass). The composition of the SAMs was varied, allowing us to tune the charge injection barrier gradually. The morphology and crystallinity of the OSC were monitored. [ABSTRACT FROM AUTHOR]

A series of molecules with oligophenylene backbone, thiolate anchoring group, and pentafluoro-λ6-sulfanyl (−SF5) tail group was synthesized and used as precursors to form self-assembled monolayers (SAMs) on Au(111) substrates. The resulting SAMs feature dense molecular packing, upright molecular orientation, and chemically homogeneous SAM-ambient interface, comprised entirely of the −SF5 moieties. These SAMs exhibit exceptional wetting and electrostatic properties, showing advancing water contact angles up to 103° and work function values up to 5.96 eV—probably the highest values reported for any aromatic monolayers on gold. They also feature a comparably low value of the tunnelling decay coefficient (0.38 ± 0.07 Å−1), typical of oligophenylene backbone, which is not affected by the introduction of the −SF5 group. The latter also hardly affects the current densities at a specific bias compared to analogous monolayers with other electronegative tail groups. The superior electrostatic and good charge transport properties of the designed, SF5-terminated SAMs make them potentially useful for interface engineering in organic electronics and photovoltaics. [ABSTRACT FROM AUTHOR]

A series of ultrathin (80–100 nm) poly-(ethylene glycol)–fullerene (PEG-C60) composite films were fabricated by three different methods, denoted immersion, one-pot, and reflux. These films are composed of cross-linked amine-/epoxy-decorated STAR-PEGs and disk-shaped C60 clusters with an average diameter of 314–329 nm and narrow size distribution. The clusters are located either on the surface of the films (immersion) or embedded in their bulk, coupling either physically (one-pot) or chemically (reflux) to the PEG network. The content of C60 in the composite films varies depending on the preparation method and is highest (∼30%) in the case of reflux, featuring also a shift of the lowest unoccupied molecular orbital energy of C60 by ∼70 meV compared to the immersion case. These films exhibit distinct optical and electrochemical properties of C60, merged with some favorable characteristics of the PEG matrix and resulting, in particular, in good electrochemical conductivity and high elasticity. The films can be separated from the substrate, forming composite nanosheets, which can be either used as free-standing ones or transferred to a secondary substrate with the preservation of the original properties. Potential applications of PEG-C60 films and nanosheets include flexible electronic devices, photodetectors, and electrochemical sensors, including biosensors in particular. [ABSTRACT FROM AUTHOR]

Electrostatic effects in charge transport across the molecular framework, including those imposed by halogen atoms, have recently attracted noticeable attention of the molecular-electronics community. In this context, in the present work, we studied the effect of tail group (R) substitution on the charge transport properties of oligophenylenethiolate self-assembled monolayers (SAMs) on Au(111), with R = H, F, CH3, and CF3. The length of the molecular backbone was varied from one to three rings and the quality, basic parameters, and electrostatic properties of the SAMs were monitored. For a given length of the molecular backbone, the current density showed a strong dependence on R, being the highest for R = CH3, and then successively lower for R = H, R = CF3, and R = F. This tendency correlated neither with the molecular length of the precursors nor with the work function of the SAMs and was, therefore, exclusively ascribed to the identity of the tail group. In contrast to the current density, the tunneling decay coefficient, describing its dependence on the molecular length, was found to be independent of the identity of the tail group. The reasons behind the observed behavior are discussed and rationalized within the available experimental data and reasonable assumptions. [ABSTRACT FROM AUTHOR]