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Yellow, green, and blue plasmonic nanofluids were produced without wet chemistry by direct deposition of Ag, Cu, and simultaneous co-deposition of Ag + Cu nanoparticles from sputter-based gas aggregation cluster sources in liquid polyethylene glycol.

We report on the growth of metal- and metal-oxide based nanoparticles (NPs) in heated polyol solutions. For this purpose, NPs are produced by the sputtering of a silver, gold, or a copper target to produce either silver, gold, or copper oxide NPs in pentaerythritol ethoxylate (PEEL) which has been annealed up to 200 °C. The objective of the annealing step is the fine modulation of their size. Thus, the evolution of the NP size and shape after thermal annealing is explained according to collision/coalescence kinetics and the affinity between the metal-/metal-oxide and PEEL molecule. Moreover, highlights of few phenomena arising from the annealing step are described such as (i) the reduction of copper oxide into copper by the polyol process and (ii) the effective formation of carbon dots after annealing at 200 °C.

Ag thin films are widely used in Low-E glass. High conductivity and low emissivity require a film thickness of at least 10 nm, which is costly for the industry. The cost of Low-E coating could be drastically reduced by lowering the amount of Ag without decreasing the conductivity. For that purpose, it is necessary to understand Ag film growth and related macroscopic properties. This can be studied by thin film growth simulations. In this work, we present results of Ag growth on ZnO by magnetron sputtering and related properties with multiscale simulations (DFT, Molecular Dynamics, and kinetic Monte Carlo). A new method to take into account defects generated by magnetron sputtering has been developed. Simulated conductivity has been compared with experiments and shows the same trend with a difference attributed to electron scattering at grain boundaries. To go further, we propose patterned substrates with and without defects to find an original tuneable process to increase the conductivity of ultrathin metallic films. We show that a patterned substrate does not increase the conductivity. Instead, it leads to a controlled growth of small islands which could be used for other applications requiring plasmonic properties. Finally, conductivity is higher for the same deposited thickness when the substrate has a higher defect density.

N-doped TiO2 materials have recently attracted a considerable amount of interest due to their enhanced photoelectrochemical properties compared to pristine TiO2. However, this improvement is still ...

The rise of van der Waals hetero-structures based on transition metal dichalcogenides (TMDs) opens the door to a new generation of optoelectronic devices. A key factor controlling the operation and performance of such devices is the relative alignment of the band edges of the components. The electronic properties of the layers can be further modulated by chemical doping, typically leading to the introduction of gap states. However, it is not clear whether the impact of doping in a given layer is preserved when building vertical stacks incorporating it. This has motivated the present study aiming at shedding light by means of first-principles calculations on the electronic properties of heterogeneous bilayers containing one doped layer. Doping has been achieved based on the experimental literature by inserting the dopants by substitution in the 2D layer, by covalently attaching adatoms or functional groups on the surface, or by physisorbing electroactive molecules. Interestingly, very different scenarios can be encountered depending on the two materials present and the nature of doping. The impact of doping is preserved when the trap levels associated with the dopants lie in the bandgap of the bilayer. On the other hand, the pristine neutral layer can get doped to an extent depending on how its electrons can fill the trap levels associated with the other component. Altogether, the present theoretical work demonstrates that the properties of the bilayers are not simply defined by additive rules of the components.

Magnetron sputter deposition of metal targets over liquids allows producing colloidal solutions of small metal nanoparticles (NPs) without any additional reducing or stabilizing reagents. Despite that this synthetic approach is known for almost 15 years, the detailed mechanism of NP formation is still unclear. Detailed investigations must be carried out to better understand the growth mechanism and, ultimately, control the properties of the NPs. Here, the combination of the gold (Au) target and castor oil, a highly available green solvent, was chosen as a model system to investigate how different experimental parameters affect the growth of NPs. The effect of deposition time, applied sputter power, working gas pressure, and type of sputter plasma (direct current magnetron sputtering (DC-MS) vs. high-power impulse magnetron sputtering (HiPIMS)) on properties of Au NPs has been studied by UV-vis spectroscopy and transmission electron microscopy (TEM), and further supported by quantum-chemistry calculations and mass-spectrometry analysis. The mechanism of the Au NP formation includes the production of primary NPs and their subsequent aggregative growth limited by diffusion in the viscous castor oil medium. Final Au NPs have a narrow size distribution and a medium diameter of 2.4–3.2 nm when produced in DC-MS mode. The NP size can be increased up to 5.2 ± 0.8 nm by depositing in HiPIMS mode which, therefore, mimics energy and time-consuming post synthesis annealing.

Graphdiyne (GDY), which features a highly π-conjugated structure, direct bandgap, and high charge carrier mobility, presents the major requirements for photocatalysis. Up to now, all photocatalytic studies are performed without paying too much attention on the GDY bandgap (1.1 eV at the GW many-body theory level). Such a narrow bandgap is not suitable for the band alignment between GDY and other semiconductors, making it difficult to achieve efficient photogenerated charge carrier separation. Herein, for the first time, it is demonstrated that tuning the electronic bandgap of GDY via H-substitution (H-GDY) promotes interfacial charge separation and improves photocatalytic H evolution. The H-GDY exhibits an increased bandgap energy (≈2.5 eV) and exploitable conduction band minimum and valence band maximum edges. As a representative semiconductor, TiO is hybridized with both H-GDY and GDY to fabricate a heterojunction. Compared to the GDY/TiO, the H-GDY/TiO heterojunction leads to a remarkable enhancement of the photocatalytic H generation by 1.35 times under UV–visible illumination (6200 µmol h g) and four times under visible light (670 µmol h g). Such enhancement is attributed to the suitable band alignment between H-GDY and TiO, which efficiently promotes the photogenerated electron and hole separation, as supported by density functional theory calculations., The work in Mons was supported by the Belgian National Fund for Scientific Research (FRS-FNRS). Computational resources were provided by the Consortium des Équipements de Calcul Intensif (CÉCI) funded by F.R.S.-FNRS under Grant No. 2.5020.11. J.C. is an FNRS research director. ICN2 acknowledges funding from Generalitat de Catalunya 2017 SGR 327 and the Spanish MINECO project ENE2017-85087-C3. ICN2 was supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706) and was funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work was performed in the framework of Universitat Autònoma de Barcelona Materials Science Ph.D. program. X.H. thanks China Scholarship Council for scholarship support (201804910551).

The chemical engineering of chalcogens' defects (either selenium or sulfur) on the surfaces of Nonprecious transition metal chalcogenides provides an effective route to enhance their electrocatalytic activity. Yet, the precise role of such defects during the OER is not fully understood, which in turn precludes an efficient optimization of their catalytic activity. Herein, CoNiSe2 film, representing a multi-transition metal selenide model with selenium defects, is electro-deposited on a carbon cloth to investigate and optimize the intrinsic and dynamic behavior of selenium vacancies during the OER process. Interestingly, the defective CoNiSe2 with the optimized amount of selenium vacancies exhibits an advanced OER performance, including low overpotential (252 mV at 10 mA cm−2) and high stability for 30 h. The ex-situ XPS and Raman spectroscopies also indicate that the optimized amount of selenium vacancies can facilitate the pre-oxidation of Co and Ni sites. The latter leads to a rapid adsorption of OH− ions and a further stabilization of Co/NiOOH, which in turn mediates the efficiency of OER. The density functional theory (DFT) calculations show that the introduction of a Se-vacancy on CoNiSe2 surface enables to adjust the changes in Gibbs free energy between different OER steps and thereby, significantly reduce the overpotential.

Large contact resistance at metal-substrate/ZnO heterostructure interfaces prevents achieving highly efficient device performance. Herein, we present a systematic study on the effect of Ni-doping in the reduction of the Schottky contact barrier at metal-substrate/ZnO heterostructure. To this end, Ni-doped zinc oxide (Ni:ZnO) thin films were deposited on glass substrate by a spray technique with different Ni-doping concentrations. X-ray Diffraction and Atomic Force Microscopy (AFM) measurements showed that Ni-doping enhances the surface uniformity as compared to the undoped-ZnO films and significantly decreases the roughness (RMS) from 35 to 17 nm. Conductive Atomic Force Microscopy (C-AFM) with a Bruker's platinum coated probe (Pt-Ir) tip results in the stabilization of a p-type Schottky contact with a small height barrier of ~0.4 eV, which is among the smallest values reported in literature for ZnO thin films. Our first principle calculations, which are based on the relative alignment of the band edges of the components, also confirm the reduction in the Schottky barrier height by Ni-doping in line with the experimental tendency. Both experimental and theoretical results provide a robust evidence of the potential of stabilization of a small p-type Schottky contact at metallic-substrate/ZnO interface through a Ni-doping.

Effective methods for the synthesis of high-purity nanoparticles (NPs) have been extensively studied for a few decades. Among others, cold plasma-based sputtering metals onto a liquid substrate appears to be a very promising technique for the synthesis of high-purity NPs. The process enables the production of very small NPs without using any toxic reagents and complex chemical synthesis routes, and enables the synthesis of alloy NPs which can be the first step towards the formation of porous NPs. In this paper, the synthesis of gold-copper alloy NPs has been performed by co-sputtering gold and copper targets over pentaerythritol ethoxylate. The resulting solutions contain a mixture of gold, copper oxide, and alloy NPs having a radius of few angstroms. The annealing of these NPs, inside the solution, has been performed in order to increase their size and further induce the dealloying of the Au-Cu NPs. The resulting NPs exhibit either a nanoporous structure or are self-organized in an agglomerate of small NPs.

Al-doped ZnO is well known as an alternative Transparent Conductive Oxide (TCO) to Indium Tin Oxide (ITO). Recently, co-doped ZnO with Ti and Al (TAZO) have been explored to improve the conductivity while maintaining moisture durability and opto-electronic properties. In this context, the structural, morphological, and optical properties of TAZO films deposited by reactive magnetron are investigated by experiments and Density Functional Theory (DFT) simulations. The results show that TiO2 units substitute Zn atoms in the ZnO wurtzite structure and, whatever the concentration of Ti, the formation of Al2O3 is taking place. In addition, a three-regime model as a function of Ti content is proposed to explain the evolution of the properties. First, for Ti content 〈 2.2 at%, TiO2 is incorporated by substitution of Zn by TiO2 units in the ZnO network leading to a more oxidized Zn state and a hybridization between Zn4s and Ti3d orbitals. This opens the bandgap and increases the compressive stress of TAZO films. Between 2.2 at% and 7.0 at% of Ti content, cauliflower shape grains appear due to the compressive stress induced by small clusters of TiO2. For Ti content 〉 7.0 at%, amorphous TAZO films are observed and are composed of TiO2, Al2O3 and ZnO.

Low-emissivity glasses rely on multistacked architectures with a thin silver layer sandwiched between oxide layers. The mechanical stability of the silver/oxide interfaces is a critical parameter that must be maximized. Here, we demonstrate by means of quantum-chemical calculations that a low work of adhesion at interfaces can be significantly increased via doping and by introducing vacancies in the oxide layer. For the sake of illustration, we focus on the ZrO2(111)/Ag(111) interface exhibiting a poor adhesion in the pristine state and quantify the impact of introducing n-type dopants or p-type dopants in ZrO2 and vacancies in oxygen atoms (nVO; with n = 1, 2, 4, 8, 10, 16), zirconium atoms (mVZr; with m = 1, 2, 4, 8), or both (nVO + mVZr; with m/n = 1:2, 1:4, 2:2, 2:4). In the case of doping, interfacial electron transfer promotes an increase in the work of adhesion, from initially 0.16 to ∼0.8 J m-2 (n-type) and ∼2.0 J m-2 (p-type) at 10% doping. A similar increase in the work of adhesion is obtained by introducing vacancies, e.g., VO [VZr] in the oxide layer yields a work of adhesion of ∼1.5-2.0 J m-2 at 10% vacancies. An increase is also observed when mixing VO and VZr vacancies in a nonstoichiometric ratio (nVO + mVZr; with 2n ≠ m), while a stoichiometric ratio of VO and VZr has no impact on the interfacial properties.

For many applications, as for example tandem dye-sensitized solar cells (DSSCs), the development of transparent p-type semiconductor with good charge transport properties is crucial. In this work, a nitrogen-doped TiO2 material is transformed by ion implantation into an efficient hole transport layer that could reduce the electron-hole recombination processes in the devices. Theoretical calculations allowed to demonstrate that the position of nitrogen species as well as their respective ratio impact the optical and electrical properties of N-doped TiO2 materials. The chemical composition was therefore tuned by the ion implantation parameters, achieving a high transparency in the UV–visible region while generating delocalized states near the top of the valence band that do not act as traps. In terms of electrical properties, beyond the possibility to tune the electrical behavior of TiO2 from n-type to p-type upon nitrogen doping, we succeed to increase the conductivity by a higher electron mobility without change in their density, which is of prime interest for charge transport application.

Magnetron sputter deposition of metals onto low vapor pressure liquids is a clean and straightforward method of nanoparticle (NP) production. Herein, we discuss the production of silver nanoparticles (Ag NPs) via magnetron sputtering of a silver target onto castor oil, a biocompatible and highly available liquid. A state-of-the-Art (bipolar) high-power impulse magnetron sputtering (HiPIMS) was used for the first time for the sputtering onto liquid procedure. The effect of several parameters such as sputter time, applied power, working gas pressure, and type of sputtering plasma (direct current magnetron sputtering (DC-MS) vs. HiPIMS and bipolar HiPIMS) onto NP properties has been studied by UV–vis spectroscopy and transmission electron microscopy (TEM). The scenario of Ag NPs formation is inferred from these analyses, and further supported by mass-spectrometry and quantum-chemistry calculations. Initial Ag NPs formed in castor oil have a diameter ranging from 0.8 nm to 4 nm, its stability is discussed in terms of the plasma-liquid surface interaction and the quantum chemistry data.

Understanding the phase formation in zirconia (ZrO2) has triggered a great debate over the last couple of decades, with several mechanisms proposed so far. In the present letter, we demonstrate by well-optimized experimental measurements supported by Density Functional Theory (DFT) calculations that only O vacancies allow for the stabilization of the cubic (c) phase at room temperature. These vacancies distort the zirconia lattice, forcing the crystal to arrange itself in a high symmetric c structure.

There is a growing interest in utilizing the distinctive material properties of organic semiconductors for spintronic applications. Here, we explore the injection of pure spin current from Permalloy into a small molecule system based on dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) at ferromagnetic resonance. The unique tunability of organic materials by molecular design allows us to study the impact of interfacial properties on the spin injection efficiency systematically. We show that both the spin injection efficiency at the interface and the spin diffusion length can be tuned sensitively by the interfacial molecular structure and side chain substitution of the molecule., info:eu-repo/semantics/published

Titanium and silver atoms were magnetron-sputtered either onto pentaerythritol ethoxylate (PEEL) or 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIMTFSI) ionic liquid (IL), and the formation of nanoparticles (NPs) is discussed based on the chemical interaction between the metal atoms and the host liquid. In the case of PEEL, our data reveal that titanium atoms sputtered in low-pressure argon plasma first form a film over the liquid surface. However, the latter dissolves as the film gets oxidized when vented to the air; asymmetric and faceted titanium dioxide NPs are finally obtained as if they were originating from a dismantled polycrystalline thin film. In the case of silver sputtered on PEEL, a film forms and solvation never occurs even after exposing the sample to air because the oxidation of silver is thermodynamically much less favorable than titanium. Quantum-chemical calculations confirm that the chemical interaction of TiO2 with PEEL molecules is favored as compared to metallic...

A new empirical potential has been derived to model an Ag–Zn–O system. Additional parameters have been included into the reactive force field (ReaxFF) parameter set established for ZnO to describe the interaction between Ag and ZnO for use in molecular dynamics (MD) simulations. The reactive force field parameters have been fitted to density functional theory (DFT) calculations performed on both bulk crystal and surface structures. ReaxFF accurately reproduces the equations of state determined for silver, silver zinc alloy and silver oxide crystals via DFT. It also compares well to DFT binding energies and works of separation for Ag on a ZnO surface. The potential was then used to model single point Ag deposition on polar (000View the MathML source1¯) and non-polar (10View the MathML source1¯0) orientations of a ZnO wurtzite substrate, at different energies. Simulation results then predict that maximum Ag adsorption on a ZnO surface requires deposition energies of ≤ 10 eV.

The functionality of interfaces in hybrid inorganic/organic (opto)electronic devices is determined by the alignment of the respective frontier energy levels at both sides of the heterojunctions. Controlling the interface electronic landscape is a key element for achieving favourable level alignment for energy and charge transfer processes. Here, we show that the electronic properties of polar ZnO surfaces can be reversibly modified using organic photochromic switches. By employing a range of surface characterization techniques combined with density functional theory (DFT) calculations, we demonstrate that self-assembled monolayers (SAMs) of photochromic phosphonic acid diarylethenes (PA-DAE) can be employed to reversibly change the electronic properties of polar ZnO/SAM structures by light stimulus. The highest occupied molecular orbital level of PA-DAE is raised by 0.7 eV and the lowest unoccupied one lowered by 0.9 eV, respectively, upon illumination by ultraviolet light and the levels shift back to their original position upon illumination by green light. Our results thus provide a pathway to tailor hybrid interface electronic properties in a dynamic manner upon simple light illumination, which can be exploited to reversibly tune the electrical properties of photo-switchable (opto)electronic devices.

We report (time-dependent) density functional theory calculations characterizing the changes in the electronic and optical properties of oligothiophene dyes when grafted on a titania surface via a carboxylic acid or catechol moiety as anchoring group, in relation to their use in dye-sensitized solar cells. The broadening of the LUMO level of the compounds upon adsorption has been extracted from the computed electronic structures and used to estimate electron injection times into the conduction band of the oxide. The strongly coupled carboxylic-containing dyes lead to faster electron injection times compared to catechol-substituted dyes. This difference is ascribed to the electron-donating character of the catechol moiety that polarizes the dye LUMO away from the dye@titania interface. The absorption spectra simulated at the TD-DFT level indicate that the grafted carboxylic-thiophene dyes undergo an indirect injection mechanism (type I) in which an intramolecular excitation is created before the charge is transferred to titania. In contrast, catechol dyes with a short conjugation length for the thiophene backbone are type II sensitizers exhibiting a direct injection mechanism leading to a direct photoexcitation from the dye HOMO to the titania conduction band. A mixed character prevails for the injection in the case of catechol dyes containing a longer oligothiophene chain.

Density functional theory (DFT) calculations were performed to assess the work of adhesion of silver layers deposited on metal oxide surfaces differing by their chemical nature (ZnO, TiO2, SnO2, and ZrO2) and their crystallographic face. The calculated work of adhesion values range from ∼0 to 3 J m–2 and are shown to originate from the interplay between ionic (associated with charge transfer at the interface) and covalent (as probed by atomic bond orders between silver and the metal oxide atoms) interactions. The results are discussed in the context of the design of silver/metal oxide interfaces for low-emissivity glasses.

The performance of organic nanostructures is closely related to the organization of the functional molecules. Frequently, molecular chirality plays a central role in the way molecules assemble at the supramolecular level. Herein we report the hierarchical self-assembly of benzo-fused tetrathia[7]helicenes on solid surfaces, from a single surface-bound molecule to well-defined microstructures, using a combination of various characterization techniques assisted by molecular modeling simulations. Similarities as well as discrepancies are revealed between homochiral and heterochiral aggregations by monitoring the hierarchical nucleation of helicenes on surfaces, where the impact of enantiopurity, concentration and adsorbate-substrate interaction on molecular organization are disclosed. ispartof: Nanoscale vol:9 issue:45 pages:18075-18080 ispartof: location:England status: published

The electronic structure of the hybrid interface between ZnO and the prototypical organic semiconductor PTCDI is investigated via a combination of ultraviolet and X-ray photoelectron spectroscopy (UPS/XPS) and density functional theory (DFT) calculations. The interfacial electronic interactions lead to a large interface dipole due to substantial charge transfer from ZnO to 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI), which can be properly described only when accounting for surface defects that confer ZnO its n-type properties.

The modification in the work-function of the (1 1 1) gold surface upon deposition of self-assembled monolayers (SAMs) based on alkanethiol derivatives has been characterized at the Density Functional Theory level when introducing chemical derivatizations. Chemical derivatizations have been introduced by: (i) replacing thiol as anchoring group by selenol or isocyanide functionalities; and (ii) introducing terminal electroactive substituents varying by their electron donor versus acceptor character. Changes in the anchoring group have shown that substitution of S by Se has no significant impact on the total work-function shift. Consideration of various terminal substituents has also pointed to the key role played by internal restructuration of the SAM geometry on the work-function. These results contribute in establishing guidelines toward a fine control of interface engineering in opto-electronic devices.

The interaction between 2,2′-bithiophene-5-carboxylic acid (PT2) sublimed under ultra-high vacuum conditions and anatase (101) and rutile (110) TiO2 single crystal surfaces is investigated by studying the electronic spectral density near the Fermi level with synchrotron-based spectroscopy. The experimental results are compared to density functional theory calculations of the isolated PT2 molecule and of the molecule adsorbed on an anatase TiO2 (101) cluster. The relative concentrations of Ti, C, and S atoms indicate that the adsorbed molecule remains intact upon deposition, which is typical of a Stranski-Krastanov growth mode. The analysis of the O1s spectrum suggests a predominant bidentate geometry of the adsorption with both rutile and anatase surfaces, as supported by previous theoretical simulations. It is also theoretically and experimentally demonstrated that the PT2 adsorption causes the appearance of new electronic states in the gap near the TiO2 valence band. A pinning effect of the LUMO level o...

Chiral recognition of enantiomers by host compounds is one of the most challenging topics in modern host-guest chemistry. Amongst the well-established methods, mass spectrometry (MS) is increasingly used nowadays, due to its low detection limit, short analysis time, and suitability for analyzing mixtures and for studying chiral effects in the gas phase. The development of electrospray-ionization (ESI) techniques provides an invaluable tool to study, in the gas phase, diastereoisomeric complex ions prepared from enantiomer ions and a chiral selector. This paper reports on an ESIMS and ESIMSMS study of the molecular mechanisms that intervene in the chiral-recognition phenomena observed between amino acids and a chiral crown ether. The modified crown ether, namely (+)-([18]crown-6)-2,3,11,12-tetracarboxylic acid, is used as the chiral selector when covalently bound on a stationary phase in liquid chromatography. This study was stimulated by the fact that, except with threonine and proline, consistent elution orders were observed, which indicates that the D enantiomers interact more strongly with the chiral selector than the L enantiomers. For proline, the lack of a primary amino group is likely to be responsible for the nonresolution of the two forms, whereas the second stereogenic center on threonine could explain the reversed elution order. In light of those observations, we performed mass spectrometry experiments to understand more deeply the enantiomeric recognition phenomena, both in solution by the enantiomer-labeled guest method and in the gas phase by gas-phase ligand-exchange ion/molecule reactions. The results have been further supported by quantum chemical calculations. One of the most interesting features of this work is the identification of a nonspecific interaction between proline and the crown ether upon ESIMS analysis.

Many recent experimental studies have demonstrated that the deposition of a self-assembled monolayer (SAM) made of polar molecules on a metal surface can significantly modulate its work function and hence the barrier for hole and electron injection in optoelectronic devices. The permanent dipole moment associated with the backbone of the molecules plays a key role in defining the amplitude and direction of the work-function shift. We illustrate here via quantum-chemical calculations performed on model systems that the dipole moment of molecules is significantly reduced going from the isolated state to the SAM. Such depolarization effects that are most often neglected thus reduce the work-function shift and have to be taken in account to control and understand charge-injection barriers in devices at a quantitative level.

Many recent experimental studies have demonstrated that the deposition of self-assembled monolayers on a metal electrode can significantly modulate its work function and hence charge injection properties in organic-based devices. In this context, we model here by means of Density Functional Theory (DFT) calculations the deposition of long saturated and partially fluorinated alkanethiol chains on the gold (111) surface and explore the shift in the work function while changing the size and degree of fluorination of the molecular backbone in order to contribute to the definition of design rules. Among all the derivatization schemes, only the introduction of a terminal fluoromethyl unit leads to an appreciable change in the work function shift, further accompanied by a reversal of its sign. The results show pronounced odd–even effects with different origins.

We have characterized theoretically the work-function modifications of the (111) surfaces of gold and silver upon deposition of self-assembled monolayers based on methanethiol and trifluoromethanethiol. A comparative analysis is made between the experimental results and those obtained from two widely used approaches based on density functional theory. The contributions to the total work-function modifications are estimated on the basis of two decomposition schemes of the thiol molecules that have been proposed in the literature. The contributions are found to differ significantly between the two approaches, as do the corresponding adsorption energies.

STM brings to light chirality aspects of the self-assembly of a functionalized helicene at the interface between a liquid and the solid substrates, gold and graphite. This reveals conditions for conglomerate formation.

Chemisorption of self-assembled monolayers (SAMs) is a universal method to modify numerous surface properties, which allows interfaces to be optimized for the application of choice. [ 1 ] Because of this reason SAMs are currently widely used as key components in the fabrication of various optoelectronic devices, such as organic thin-fi lm transistors (OTFTs), [ 2 ] organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) and organic memory (OMEM) cells. [ 3 ]

Graphene-based two-dimensional (2D) materials are promising candidates for a number of different energy applications. A particularly interesting one is in next generation supercapacitors, where graphene is being explored as an electrode material in combination with room temperature ionic liquids (ILs) as electrolytes. Because the amount of energy that can be stored in such supercapacitors critically depends on the electrode-electrolyte interface, there is considerable interest in understanding the structure and properties of the graphene/IL interface. Here, we report the changes in the properties of graphene upon adsorption of a homologous series of alkyl imidazolium tetrafluoroborate ILs using a combination of experimental and theoretical tools. Raman spectroscopy reveals that these ILs cause n-type doping of graphene, and the magnitude of doping increases with increasing cation chain length despite the expected decrease in the density of surface-adsorbed ions. Molecular modeling simulations show that doping originates from the changes in the electrostatic potential at the graphene/IL interface. The findings described here represent an important step in developing a comprehensive understanding of the graphene/IL interface. ispartof: ACS NANO vol:13 issue:3 pages:3512-3521 ispartof: location:United States status: published

Transistors operate by controlling the current flowing from a source to a drain electrode via a third electrode (gate), thus giving access to a binary treatment (ON/OFF or 0/1) of the signal currently exploited in microelectronics. Introducing a second independent lever to modulate the current would allow for more complex logic functions amenable to a single electronic component and hence to new opportunities for advanced electrical signal processing. One avenue is to add this second dimension with light by incorporating photochromic molecules in current organic-based electronic devices. In this Spotlight, we describe different concepts that have been implemented in organic thin films and in molecular junctions as well as some pitfalls that have been highlighted thanks to theoretical modeling.

Charge injection barriers at metal/organic interfaces can be tuned by modifying the work function of metallic electrodes using self‐assembled monolayers (SAMs) of polar molecules. An interesting example of polar molecules is offered by donor–acceptor (D–A) dyads based on ferrocene (Fc) as electron‐donor unit and either a polychlorotriphenylmethyl radical or a polychlorotriphenylmethane as electron‐acceptor units, connected by a π‐conjugated vinylene bridge. The D–A radical exhibits high chemical and thermal stability and presents different electronic, optical, and magnetic properties with respect to the closed‐shell form. The magnitude of the shift in the charge injection barriers for these two D–A systems is estimated by means of surface potential measurements performed by Kelvin probe force microscopy. The experimental data are compared with density functional theory calculations, which evidence the importance of the molecular dipole moments and polarizabilities to understand the experimental values. In order to achieve high work function shifts of metals upon SAM formation, the molecules forming the SAM have to exhibit both a high permanent dipole moment and a low polarizability along the direction normal to the substrate. In presence of polarizable molecules, the work function shifts can be enhanced by reducing the intermolecular interactions; by using mixed SAMs with active molecules embedded into a passive matrix., This work was financially supported by the EC through the Marie Curie project ITN iSwitch (Grant Agreement No. 642196). Computational resources were provided by the Consortium des Équipements de Calcul Intensif (CÉCI) funded by the Belgian National Fund for Scientific Research (F.R.S.‐FNRS) under Grant No. 2.5020.11. J.C. is an FNRS research director. The authors also acknowledge the financial support from Instituto de Salud Carlos III, through “Acciones CIBER.” The Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER‐BBN), an initiative funded by the VI National R&D&I Plan 2008e2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions and financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund. The authors also appreciate the financial support through projects: BE‐WELL (CTQ2013e40480‐R), FANCY (CTQ2016‐80030‐R), MOTHER (MAT2016‐80826‐R), and OPTIMODE (MAT2016‐77852‐C2‐1‐R), granted by DGI (Spain), GenCat (2017‐SGR‐918 and 2017‐SGR‐668), financed by DGR (Catalunya), and Severo Ochoa Program Grant No. SEV‐2015‐0496, financed by Mineico (Spain). M.P. thanks the Spanish Government for financial support through BES‐2008‐003588 FPI and PTA2014‐09788‐I fellowships.