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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.

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.

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.

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.

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.

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...

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.

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 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...

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.