Organic-inorganic Systems Research Articles

Hybrid organic-inorganic systems formed by self-assembled gold nanoparticles in CuPcF4 molecular crystal

In this work we have fabricated and studied hybrid organic-inorganic nanocomposite system formed by gold nanoparticles self-assembled in organic semiconductor thin film - copper tetrafluorophthalocyanine (CuPcF4). By means of Photoelectron Spectroscopy and Transmission Electron Microscopy (TEM) the evolution of the morphology and electronic structure of the system as a function of nominal gold content have been investigated. The gold atoms, deposited onto the CuPcF4 surface, diffuse into the organic matrix and self-assemble to nanoparticles in a well-defined manner with a narrow size distribution, which depends on the amount of deposited gold. Using High-Resolution TEM, we were able to observe the atomic planes of single gold nanoparticles and their coalescence processes. Photoelectron spectroscopy has not revealed any detectable chemical reaction between gold and organic. However, the strong upward band bending, induced by gold nanoparticles in the organic film, takes place.

Treatment of non-ideality in the SPACCIM multiphase model – Part 1: Model development

Abstract. Ambient tropospheric deliquesced particles generally comprise a complex mixture of electrolytes, organic compounds, and water. Dynamic modeling of physical and chemical processes in this complex matrix is challenging. Thus, up-to-date multiphase chemistry models generally do not consider non-ideal solution effects. Therefore, the present study was aimed at presenting further development of the SPACCIM (Spectral Aerosol Cloud Chemistry Interaction Model) through treatment of solution non-ideality, which has not been considered before. The present paper firstly describes the model developments including (i) the implementation of solution non-ideality in aqueous-phase reaction kinetics in the SPACCIM framework, (ii) the advancements in the coupling scheme of microphysics and multiphase chemistry and (iii) the required adjustments of the numerical schemes, especially in the sparse linear solver and the calculation of the Jacobian. Secondly, results of sensitivity investigations are outlined, aiming at the evaluation of different activity coefficient modules and the examination of the contributions of different intermolecular forces to the overall activity coefficients. Finally, first results obtained with the new model framework are presented. The SPACCIM parcel model was developed and, so far, applied for the description of aerosol–cloud interactions. To advance SPACCIM also for modeling physical and chemical processes in deliquesced particles, the solution non-ideality has to be taken into account by utilizing activities in reaction terms instead of aqueous concentrations. The main goal of the extended approach was to provide appropriate activity coefficients for solved species. Therefore, an activity coefficient module was incorporated into the kinetic model framework of SPACCIM. Based on an intercomparison of different activity coefficient models and the comparison with experimental data, the AIOMFAC approach was implemented and extended by additional interaction parameters from the literature for mixed organic–inorganic systems. Moreover, the performance and the capability of the applied activity coefficient module were evaluated by means of water activity measurements, literature data and results of other activity coefficient models. Comprehensive comparison studies showed that the SpactMod (SPACCIM activity coefficient module) is valuable for predicting the thermodynamic behavior of complex mixtures of multicomponent atmospheric aerosol particles. First simulations with a detailed chemical mechanism have demonstrated the applicability of SPACCIM-SpactMod. The simulations indicate that the treatment of solution non-ideality might be needed for modeling multiphase chemistry processes in deliquesced particles. The modeled activity coefficients imply that chemical reaction fluxes of chemical processes in deliquesced particles can be both decreased and increased depending on the particular species involved in the reactions. For key ions, activity coefficients on the order of 0.1–0.8 and a strong dependency on the charge state as well as the RH conditions are modeled, implying a lowered chemical processing of ions in concentrated solutions. In contrast, modeled activity coefficients of organic compounds are in some cases larger than 1 under deliquesced particle conditions and suggest the possibility of an increased chemical processing of organic compounds. Moreover, the model runs have shown noticeable differences in the pH values calculated with and without consideration of solution non-ideality. On average, the predicted pH values of the simulations considering solution non-ideality are −0.27 and −0.44 pH units lower under 90 and 70 % RH conditions, respectively. More comprehensive results of detailed SPACCIM-SpactMod studies on the multiphase processing in organic–inorganic mixtures of deliquesced particles are described in a companion paper.

Modulating Optoelectronic Properties of Two-Dimensional Transition Metal Dichalcogenide Semiconductors by Photoinduced Charge Transfer.

Atomically thin transition metal dichalcogenides (TMDCs) have attracted great interest as a new class of two-dimensional (2D) direct band gap semiconducting materials. The controllable modulation of optical and electrical properties of TMDCs is of fundamental importance to enable a wide range of future optoelectronic devices. Here we demonstrate a modulation of the optoelectronic properties of 2D TMDCs, including MoS2, MoSe2, and WSe2, by interfacing them with two metal-centered phthalocyanine (MPc) molecules: nickel Pc (NiPc) and magnesium Pc (MgPc). We show that the photoluminescence (PL) emission can be selectively and reversibly engineered through energetically favorable electron transfer from photoexcited TMDCs to MPcs. NiPc molecules, whose reduction potential is positioned below the conduction band minima (CBM) of monolayer MoSe2 and WSe2, but is higher than that of MoS2, quench the PL signatures of MoSe2 and WSe2, but not MoS2. Similarly, MgPc quenches only WSe2, as its reduction potential is situated below the CBM of WSe2, but above those of MoS2 and MoSe2. The quenched PL emission can be fully recovered when MPc molecules are removed from the TMDC surfaces, which may be refunctionalized and recycled multiple times. We also find that photocurrents from TMDCs, probed by photoconductive atomic force microscopy, increase over 2-fold only when the PL is quenched by MPcs, further supporting the photoinduced charge transfer mechanism. Our results should benefit design strategies for 2D inorganic-organic optoelectronic devices and systems with tunable properties and improved performances.

Organised chaos: entropy in hybrid inorganic-organic systems and other materials.

Entropy is one of the fundamental quantities which links emerging research areas like flexibility and defect engineering in inorganic-organic hybrid materials. Additionally, a delicate balance between entropy and enthalpy can lead to intriguing temperature-driven transitions in such materials. Here, we briefly overview traditional material design principles, highlight the role of entropy in the past and discuss how computational methods can help us to understand and quantify entropic effects in inorganic-organic hybrid materials in the future.

Analysis of Resistive Switching Characteristics in Surface Anchored Metal Organic Framework (SURMOF) Films

In the quest for new nonvolatile memory devices many new device concepts and materials systems have emerged in recent years. Notably MRAMs, FeRAMs, STTRAMs and RRAMs have attracted considerable attention and research efforts. Particularly in RRAM, the majority of these new developments are focusing on inorganic materials systems and very little work has been reported on organic or hybrid organic-inorganic memory related materials systems. Here we report on the resistive switching characteristics of a class of hybrid designer solids HKUST-1(Hong Kong University of Technology1) (or [Cu3(BTC)2]) SURMOF porous conductors which were loaded with ferrocene. SURMOF films are also referred to as porous coordination polymers (PCPs). The electrical conductivity of SURMOF films can be modulated by loading the pores with appropriate organic semiconductors. Loading with ferrocene or TCNQ can enable ion transport in addition to electron transport thus change the electrical conductivity. The SURMOF samples for this study have been grown on surface-functionalized Au-substrates by employing a layer-by-layer, liquid-phase epitaxial method. Device fabrication was carried out by depositing top electrodes from either Cu or Au using a commercial e-beam deposition system. Two different device stacks were fabricated and tested. The first device consisted of an Au/SURMOF/Cu/Au stack with SURMOF film thickness of around 75nm. The Cu/Au top electrode was deposited by e-beam evaporation with a thicknesses of 200nm and 25nm respectively and patterned with a shadow mask to produce disks of 200µm in diameter. The second device consisted of an Au/SURMOF/Al/Au stack with a SURMOF thickness of 10nm, 20nm and 50nm. The Al/Au top electrode was deposited by e-beam evaporation with a thicknesses of 700nm and 100nm respectively, and patterned with a shadow mask to yield disks of 150µm in diameter. A slow voltage ramp typically between -1.5V to +1.5V was used. Measurements have been performed on pristine samples directly after synthesis. Initially pristine SURMOF switching devices are in a high resistance state. In our device configuration the bottom electrode is grounded and the voltage is applied to the top electrode. In devices with Cu/Au as top electrode, ON was observed on negative voltage sweeps and OFF was observed on positive voltage sweeps. In devices with Al/Au top electrodes, ON was observed on positive voltage sweeps and OFF was observed on negative voltage sweeps. After increasing the voltage from 0 V to max. 0.75 V, a transition to a low resistance state is observed. The voltage was swept in the reverse polarity to switch from low to high resistance state. Current as high as 50mA was required to switch the device from low to high resistance state. Measurements were also performed on the unloaded SURMOF devices. Compared to the loaded device, the switching characteristics are quite poor. The observed phenomena are crucially dependent on ferrocene loading. Ferrocene loading increased the conductivity within the MOF layer and therefore lowers the resistance. The devices could be switched using pulse width longer than 20 ns. Although the device switched within tens of nanoseconds, the time of switching could not be established due to large device capacitance values. The polarity of the SET and RESET in the devices with the Cu as the top electrode rules out the possibility of Cu ion migration being the reason for formation and dissolution of the low resistance path during switching. Additionally, devices with Al top electrode were also measured. Similar to the Cu top electrode, the Al top electrode devices also showed resistive switching.

SBA-15 Mesoporous Silica Modified with Gallic Acid and Evaluation of Its Cytotoxic Activity

Gallic acid has been covalently conjugated to SBA-15 mesoporous silica surface through different linkers. Cytotoxic activity of the hybrid organic-inorganic systems against HeLa and KB cell lines has been analyzed. Up to 67% of HeLa or KB tumor cells growth inhibition has been achieved at low silica concentration used (10 μg mL-1).

Many-body dispersion effects in the binding of adsorbates on metal surfaces

A correct description of electronic exchange and correlation effects for molecules in contact with extended (metal) surfaces is a challenging task for first-principles modeling. In this work, we demonstrate the importance of collective van der Waals dispersion effects beyond the pairwise approximation for organic-inorganic systems on the example of atoms, molecules, and nanostructures adsorbed on metals. We use the recently developed many-body dispersion (MBD) approach in the context of density-functional theory [Tkatchenko et al., Phys. Rev. Lett. 108, 236402 (2012) and Ambrosetti et al., J. Chem. Phys. 140, 18A508 (2014)] and assess its ability to correctly describe the binding of adsorbates on metal surfaces. We briefly review the MBD method and highlight its similarities to quantum-chemical approaches to electron correlation in a quasiparticle picture. In particular, we study the binding properties of xenon, 3,4,9,10-perylene-tetracarboxylic acid, and a graphene sheet adsorbed on the Ag(111) surface. Accounting for MBD effects, we are able to describe changes in the anisotropic polarizability tensor, improve the description of adsorbate vibrations, and correctly capture the adsorbate-surface interaction screening. Comparison to other methods and experiment reveals that inclusion of MBD effects improves adsorption energies and geometries, by reducing the overbinding typically found in pairwise additive dispersion-correction approaches.

Immobilization of Zidovudine Derivatives on the SBA-15 Mesoporous Silica and Evaluation of Their Cytotoxic Activity.

Novel zidovudine derivatives, able to be covalently conjugated to silica surface, have been obtained and grafted to SBA-15 mesoporous silica. Cytotoxic activity of the hybrid organic-inorganic (zidovudine derivatives-silica) systems against HeLa and KB cell lines has been analyzed. Addition of folic acid had a positive influence on the cytotoxicity. Up to 69% of HeLa and 65% of KB tumor cells growth inhibition has been achieved at low silica concentration used (10 μg/mL).

Commensurism at electronically weakly interacting phthalocyanine/PTCDA heterointerfaces

Interfaces in multilayered electronic devices are of paramount importance, especially for layer thicknesses in the nanometer range. Among the interfacial processes are charge injection or extraction and excitonic dissociation, the latter being particularly relevant if molecular components are involved. Highly ordered superstructures are preferable to prevent undesired losses of charge carriers and/or excitons. Epitaxial organic-inorganic systems have already received eminent attention, but only few studies have dealt with organic-organic heterointerfaces so far. Here, we focus on the adsorption of metal-phthalocyanines (MePc, Me = Sn or Cu) on 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) in the form of stacked monolayers (ML) on Ag(111). Using scanning tunneling microscopy and low-energy electron diffraction we reveal an initial nonordered growth for dilute SnPc submonolayers and consecutively three condensed phases at coverages ranging up to $1\phantom{\rule{0.16em}{0ex}}\mathrm{ML}$---each possessing a distinct commensurate registry with the underlying PTCDA. By applying in situ optical differential reflectance spectroscopy and photoelectron spectroscopy we find that neither the SnPc nor the CuPc phases exhibit significant electronic or optical coupling with the PTCDA interlayer. Therefore, our results demonstrate that commensurism does not necessarily imply chemisorption, as stated previously in the literature, but that physisorption may be accompanied by commensurate superstructures.

Engineering nanostructures by binding single molecules to single-walled carbon nanotubes.

Organic and hybrid organic-inorganic systems are promising candidates for low cost photovoltaics. Recently, perovskite-based systems have been attracting a large amount of research attention, where the highest performing devices employ a small molecule (2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene) (Spiro-OMeTAD) hole transporter. Here, we demonstrate the production of single-walled carbon nanotube (SWNT)/single molecule nanostructures using a simple solution processing technique for effective and strong binding of Spiro-OMeTAD to individual polymer-wrapped SWNTs. These small molecules bind very strongly, which causes both large mechanical strain of the nanotubes and also improves the separation of individual SWNTs, thus improving the nanotube photoluminescence quantum efficiency by 1 order of magnitude compared to simple polymer-nanotube nanohybrids. Using absorption and photoluminescence measurements, we show that there is a dramatic variation in the electronic properties of the polymer-NT nanocomposites due to the band alignment formed with Spiro-OMeTAD. These self-assembled nanocomposites offer the potential for integration into high performance optoelectronic such as photovoltaic cells and light emission devices.

Organic-inorganic mixed-valence systems with strongly-coupled triarylamine and cyclometalated osmium.

Organic-inorganic mixed-valence systems with strongly-coupled triarylamine and cyclometalated osmium have been developed. They display two well-separated redox couples at low potentials. Each of the three readily accessible oxidation states can be distinguished by the absorbance at three different wavelengths.

FTIR Measurements of SiO2 Glass Prepared by Sol-Gel Technique

The sol gel route allows powder-less processing of glasses and ceramics. Sol gel chemistry provides mild conditions so that organic species can be mixed with the inorganic precursors, leading to the formation of hybrid organic-inorganic systems. In the present work silica glasses were prepared by sol gel technique. The structural properties of silica glasses has been investigated with Fourier Transform Infrared Spectroscopy (FTIR), since Infrared spectroscopy may probe the nature of the bond between the metal cation and its surrounding oxygens and can distinguish the bonding between metal cations with oxygen.

Biodegradable poly(glycerol sebacate)/poly(3-hydroxybutyrate)-TiO2 nanocomposites: fabrication and characterisation

Novel Nanocomposite films containing TiO2 nanoparticles incorporated in blend matrices of biocompatible and bioresorbable polymers, namely poly(glycerol sebacate) (PGS) and poly(3-hydroxybutyrate) P(3HB), were developed. The samples were fabricated via a sequential step of solvent casting followed by cross-linking. PGS/P(3HB) blends (controls) were fabricated in two different ratios, i.e. 7∶1 and 8∶1. Varying amounts of TiO2 nanoparticles (1 and 2 vol.-%) were incorporated into the matrices. SEM studies revealed that the TiO2 particles were distributed both within the matrix and on the surface of the films thus imparting surface nanotopography and increasing the surface roughness. These microstructural features combined with the cumulative effect of blending of the two polymeric systems influenced the wettability, chemical and mechanical properties of the films. In vitro degradation of the fabricated matrices in PBS medium over a 30 day period confirmed that the composites undergo weight loss and mechanical, chemical and surface topography changes. The nanocomposites constitute model biodegradable organic–inorganic systems suitable for tissue engineering applications.

Visualization Experimental Study on Organic-Inorganic Crosslinked Plugging System Plugging

As a compound modifying and flooding agent, the organic-inorganic crosslinked plugging system which is mixed by gel and silicide according our experimental study, formed integral crosslinked system at high temperature and varied in a broad range gelling time by regulate concentration of organic-inorganic crosslinked plugging system. It exhibits excellent thermostability, shear properties, plugging performance and washable characteristic. In this visual experiment, the organic-inorganic crosslinked plugging systems injection, waterflooding effect and sealing capacity on homogeneous reservoir and heterogeneous reservoir are all exhibited clearly. The results of experiment show that organic-inorganic crosslinked plugging system has a good injectivity and water plugging performance. Depth of injection has an important effect on water-flooding situation, further influencing the increasement of recovery factor. Before the injection of Organic-Inorganic Crosslinked Plugging System, we inject some viscosity reducer, such as foam solution which reducing the deep oil viscosity, keeping the high recovery efficiency and preventing the mistaken plugging.

Cross-sectional TEM preparation of hybrid inorganic/organic materials systems by ultramicrotomy

Preparation of hybrid inorganic-organic systems (HIOS) for transmission electron microscopy (TEM) in cross sectional view is the key for understanding the interfacial structure. Strikingly different materials properties like hardness, cleavability and heat sensitivity limit the number of applicable preparation strategies. Successful preparation of a HIOS system combining ZnO and para-sexiphenyl (6P) is realized by ultramicrotomy. It is shown that the alignment of the cutting plane with respect to the (0001) cleavage plane of ZnO plays a decisive role for successful preparation of extended TEM lamellae and the preservation of the HIOS structure. In particular, for (0001) oriented ZnO substrates the optimum cut direction is parallel to the HIOS interface. In cross-sectional high-resolution TEM images (100) lattice planes of 6P are observed proving the appropriate preparation strategy.

Space-Charge Transfer in Hybrid Inorganic-Organic Systems

We discuss density functional theory calculations of hybrid inorganic-organic systems that explicitly include the global effects of doping (i.e., position of the Fermi level) and the formation of a space-charge layer. For the example of tetrafluoro-tetracyanoquinodimethane on the ZnO(0001[over ¯]) surface we show that the adsorption energy and electron transfer depend strongly on the ZnO doping. The associated work function changes are large, for which the formation of space-charge layers is the main driving force. The prominent doping effects are expected to be quite general for charge-transfer interfaces in hybrid inorganic-organic systems and important for device design.

Modeling the surface tension of complex, reactive organic–inorganic mixtures

Abstract. Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as heterogeneous reactivity, ice nucleation, and cloud droplet formation. We present new experimental data for the surface tension of complex, reactive organic–inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2–6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two semi-empirical surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well described by a weighted Szyszkowski–Langmuir (S-L) model which was first presented by Henning et al. (2005). Two approaches for modeling the effects of salt were tested: (1) the Tuckermann approach (an extension of the Henning model with an additional explicit salt term), and (2) a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2) for surface tension modeling of aerosol systems because the Henning model (using data obtained from organic–inorganic systems) and Tuckermann approach provide similar modeling results and goodness-of-fit (χ2) values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.

Competition between Förster Resonance Energy Transfer and Electron Transfer in Stoichiometrically Assembled Semiconductor Quantum Dot–Fullerene Conjugates

Understanding how semiconductor quantum dots (QDs) engage in photoinduced energy transfer with carbon allotropes is necessary for enhanced performance in solar cells and other optoelectronic devices along with the potential to create new types of (bio)sensors. Here, we systematically investigate energy transfer interactions between C60 fullerenes and four different QDs, composed of CdSe/ZnS (type I) and CdSe/CdS/ZnS (quasi type II), with emission maxima ranging from 530 to 630 nm. C60-pyrrolidine tris-acid was first coupled to the N-terminus of a hexahistidine-terminated peptide via carbodiimide chemistry to yield a C60-labeled peptide (pepC60). This peptide provided the critical means to achieve ratiometric self-assembly of the QD-(pepC60) nanoheterostructures by exploiting metal affinity coordination to the QD surface. Controlled QD-(pepC60)N bioconjugates were prepared by discretely increasing the ratio (N) of pepC60 assembled per QD in mixtures of dimethyl sulfoxide and buffer; this mixed organic/aqueous approach helped alleviate issues of C60 solubility. An extensive set of control experiments were initially performed to verify the specific and ratiometric nature of QD-(pepC60)N assembly. Photoinitiated energy transfer in these hybrid organic-inorganic systems was then interrogated using steady-state and time-resolved fluorescence along with ultrafast transient absorption spectroscopy. Coordination of pepC60 to the QD results in QD PL quenching that directly tracks with the number of peptides displayed around the QD. A detailed photophysical analysis suggests a competition between electron transfer and Förster resonance energy transfer from the QD to the C60 that is dependent upon a complex interplay of pepC60 ratio per QD, the presence of underlying spectral overlap, and contributions from QD size. These results highlight several important factors that must be considered when designing QD-donor/C60-acceptor systems for potential optoelectronic and biosensing applications.

Modification of Abiotic–Biotic Interfaces with Small Molecules and Nanomaterials for Improved Bioelectronics

Low efficiency of charge extraction (and conversely charge injection) across biotic–abiotic interfaces constitutes an obstacle to the integration of biological and electronic systems in high-performance bioelectronic devices. Advances in the promotion of charge transport across these typically nonconductive interfaces will have far-reaching implications in important applications such as alternative energy generation, bioelectrosynthesis, diagnostics, and environmental monitoring. This review highlights the use of synthetic materials to improve electrical interfacing between biological systems and electrodes, focusing specifically on whole cell bioelectrochemical systems. By taking advantage of a rich variety of materials chemistry and synthetic methodologies, significant improvements to the facilitation of charge transport across abiotic–biotic interfaces have been realized. The modifications of the bioelectronic interfaces presented herein include the use of organic small molecules, semiconducting and redox active polymers, inorganic nanoparticles, carbon nanotubes, graphene, hybrid organic–inorganic systems, and micro-/nanoelectrodes. However, design rules to guide material selection and choices regarding device architecture remain ambiguous. Establishment of a clearer understanding of bioelectronic charge transfer phenomena, their constituent pathways, and means of stimulating or selecting for different pathways is still work in progress. As such, great opportunities exist for materials scientists to contribute to these topics through design and implementation.

Porous silica as host for PEG-supported coumarin molecules

The design of novel organic–inorganic systems made of poly(ethyleneglycol) (PEG)-supported coumarin loaded into porous silica is presented. The hybrid system was obtained by impregnation of a xerogel silica matrix with a PEG-supported coumarin ethanolic solution. The chemical and physical properties of the hybrid systems are evaluated by means of infrared spectroscopy and thermo-gravimetric analysis, and correlated to UV–Vis optical absorption and time-resolved photoluminescence. It was found that the optical properties of the coumarin, which are not affected by the polymeric PEG support, are preserved upon loading into the silica porous support. The hybrid material obtained may represent a tool for drug delivery as the release of the PEG-supported coumarin from the silica xerogel into water media takes place.