Greatly increased electrical conductivity of PBTTT-C14 thin film via controllable single precursor vapor phase infiltration.

Doping is an important strategy for effectively regulating the charge carrier concentration of semiconducting materials. In this study, the electronic properties of organic-inorganic hybrid semiconducting polymers, synthesized viain situcontrolled vapor phase infiltration (VPI) of poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) with the metal precursors molybdenum pentachloride (MoCl5) and titanium tetrachloride (TiCl4), were altered and characterized. The conductivities of the infiltration-doped PBTTT-C14 thin films were enhanced by up to 9 and 4 orders of magnitude, respectively. The significantly improved electrical properties may result from interactions between metal atoms in the metal precursors and sulfur of the thiophene rings, thus forming new chemical bonds. Importantly, VPI doping has little influence on the structure of the PBTTT-C14 thin films. Even if various dopant molecules infiltrate the polymer matrix, the interlayer spacing of the films will inevitably expand, but it has negligible effects on the overall morphology and structure of the film. Also, Lewis acid-doped PBTTT-C14 thin films exhibited excellent environmental stability. Therefore, the VPI-based doping process has great potential for use in processing high-quality conductive polymer films.

Entropy-Driven Self-Healing of Metal Oxides Assisted by Polymer-Inorganic Hybrid Materials.

Enabling self-healing of materials is crucially important for saving resources and energy in numerous emerging applications. While strategies for the self-healing of polymers are advanced, mechanisms for semiconducting inorganic materials are scarce due to the lack of suitable healing agents. Here a concept for the self-healing of metal oxides is developed. This concept consists of metal oxide nanoparticle growth inside the bulk of halogenated polymers and their subsequent entropy-driven migration to externally induced defect sites, leading to recovery of the defect. Herein, it is demonstrated that the pool of self-healing materials is expanded to include semiconductors, thereby increasing the reliability and sustainability of functional materials through the use of metal oxides. It is revealed that electrical properties of tin-doped indium oxide can be partially restored upon healing. Such properties are of immediate interest for the further development of transparent flexible electrodes.

Facile Fabrication of Gold Nanorods@Polystyrenesulfonate Yolk-Shell Nanoparticles for Spaser Applications.

We present a method for producing gold nanorods surrounded by a hollow polymeric shell of polystyrenesulfonate and show that the cavities of such particles can be filled with various organic dyes. The approach consists of covering gold nanorods with silica, followed by its slow hydrolysis in an aqueous medium in the presence of the polymer thin layer permeable for dye molecules. The proposed method enables the yolk-shell nanoparticles to be obtained and loaded with organic dyes without a need to use thermal treatment and/or chemical etching, which makes it suitable for use in the creation of spasers.

Amorphous AlN films grown by ALD from trimethylaluminum and monomethylhydrazine.

The great interest in aluminium nitride thin films has been attributed to their excellent dielectric, thermal and mechanical properties. Here we present the results of amorphous AlN films obtained by atomic layer deposition. We used trimethylaluminum and monomethylhydrazine as the precursors at a deposition temperature of 375-475 °C. The structural and mechanical properties and chemical composition of the synthesized films were investigated in detail by X-ray diffraction, X-ray photoelectron spectroscopy, electron and probe microscopy and nanoindentation. The obtained films were compact and continuous, exhibiting amorphous nature with homogeneous in-depth composition, at an oxygen content of as low as 4 at%. The mechanical properties were comparable to those of AlN films produced by other techniques.

Lasing Spaser in Photonic Crystals.

Plasmonic nanolasers (spasers) are of intense interest, attributable to their ability to generate a high-intensity coherent radiation. We infiltrated a three-dimensional silica-based photonic crystal (PhC) film with spasers, composed of spherical gold cores, surrounded by silica shells with dye molecules. In spasers, the gold nanospheres supported the surface plasmons and the dye molecules transferred incoming optical energy to the surface plasmons. Our experiments show that such a structure, consisting of a PhC, which acts as an external distributed feedback resonator, and spasers, can serve as a coherent source of electromagnetic radiation. Spasers were locked in phase by the common radiation causing a phenomenon called the lasing spaser: the emission of spatially and temporarily coherent light normal to the surface of the PhC film. The far-field radiation patterns appeared in the shape of the Star-of-David, which is due to the dispersion along the Brillouin zone boundary. The infiltration of the spasers into the PhC led to drastic narrowing of the emission peak and an 80-fold decrease in the spaser generation threshold with respect to the same spasers in a suspension at room temperature.

Radical-triggered cross-linking for molecular layer deposition of SiAlCOH hybrid thin films.

Here, we report on a simultaneous growth and radical-initiated cross-linking of a hybrid thin film in a layer-by-layer manner via molecular layer deposition (MLD). The cross-linked film exhibited a self-limiting MLD growth behavior and improved properties like 12% higher film density and enhanced stability compared to the non-cross-linked film.

ALD coating of centrifugally spun polymeric fibers and postannealing: case study for nanotubular TiO2 photocatalyst.

This work describes the synthesis of highly photocatalytically active TiO2 tubes (TiTBs) by combining centrifugal spinning and atomic layer deposition (ALD). Poly(vinyl pyrrolidone) (PVP) fibers were first produced by centrifugal spinning and subsequently coated with TiO2 with various film thicknesses in a fluidized bed ALD reactor. After annealing of the TiO2 ALD coated PVP fibers, TiO2 tubes (TiTBs) with excellent textural properties and diameters in the range from approx. 170 to 430 nm were obtained. The morphology and structure of all TiTBs were investigated by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), and Brunauer-Emmett-Teller analysis (BET). Liquid phase photocatalysis was conducted to determine the photocatalytic activity of the TiTBs. The photocatalytic activity of the TiTBs obtained after 50 TiO2 ALD cycles (degradation rate 0.123 min-1) was twice that of the reference TiO2 P25. The underlying reasons for the remarkable photocatalytic performance were textural properties of the resulting tubes along with suitable crystallinity, embedded within the 1D tubular morphology. The herein presented proof-of-concept approach paves a way for the processing of various polymeric fibers into various tubular nanostructures.

Omniphobic Etched Aluminum Surfaces with Anti-Icing Ability.

In this work, omniphobic surfaces are developed by combining chemical etching and surface modification of aluminum. In the first step, hierarchical micro/nanostructuring is carried out by chemical etching. Thereafter, a perfluoropolyether is grafted onto the corrugated aluminum substrate, decreasing its surface free energy and turning the system omniphobic. The morphology and chemical composition of the developed surfaces are characterized. We observed a low affinity toward liquids, regardless of their chemical nature and surface tension. The surface shows superhydrophobic properties with a water contact angle of 160° and simultaneously strong oleophobic properties with a hexadecane contact angle of 141°. Furthermore, these omniphobic surfaces significantly delay the freezing time of water droplets to 5100 s, which is about 20-fold of the freezing time on pristine aluminum (260 s), and they even inhibit ice growth by repelling the incoming droplets prior to ice nucleation.

Molecular layer deposition of hybrid siloxane thin films by ring opening of cyclic trisiloxane (V3D3) and azasilane.

In this work, we report the first ring opening vapor to solid polymerization of cyclotrisiloxane and N-methyl-aza-2,2,4-trimethylsilacyclopentane by molecular layer deposition (MLD). This process was studied in situ with a quartz crystal microbalance and the thin film was characterized by X-ray photoelectron spectroscopy, ATR-FTIR and high-resolution transmission electron microscopy.

'Sandwich'-like hybrid ZnO thin films produced by a combination of atomic layer deposition and wet-chemistry using a mercapto silane as single organic precursor.

This study describes a straightforward preparation of hybrid organic-inorganic thin films containing a stable 'sandwich'-like structure of two atomic layer deposited (ALD) ZnO layers separated by a thin organosilane phase, which is built from a single organic component (3-mercaptopropyl)trimethoxysilane (MPTMS). Grafting of MPTMS on the first ALD ZnO layer was performed in solution and driven by the strong affinity of the terminal thiol functionality (-SH) towards ZnO. We demonstrate that under different reaction conditions, either MPTMS monolayers are prepared or a 5 nm thick cross-linked polymeric network is formed due to the self-condensation of silane, which covers the ALD ZnO surface. This film served as a soft template for the nucleation of an ALD ZnO top layer by creation of S-Zn and Si-O-Zn bonds at the upper interface, as confirmed by XPS measurements. An increase in surface roughness, as compared to the initial ZnO film, is observed after removal of the organic layer from the hybrid structure by calcination, which is accompanied by an improvement in UVA photocatalytic activity towards the degradation of methyl orange dye. Thus, MPTMS can be used as a sacrificial agent in combination with low temperature ALD processes for building rougher and photocatalytically efficient ZnO coatings.

SCIP: a new simultaneous vapor phase coating and infiltration process for tougher and UV-resistant polymer fibers.

The physical properties of polymers can be significantly altered by blending them with inorganic components. This can be done during the polymerization process, but also by post-processing of already shaped materials, for example through coating by atomic layer deposition (ALD) or hybridizing through vapor phase infiltration (VPI), both of which are beneficial in their own way. Here, a new processing strategy is presented, which allows distinct control of the coating and infiltration. The process is a hybrid VPI and ALD process, allowing separate control of infiltrated and coated components. This new simultaneous vapor phase coating and infiltration process (SCIP) enhances the degrees of freedom for optimizing the properties of polymers, as shown on the example of Kevlar 29 fibers. The SCIP treated fibers show an increase of 17% of their modulus of toughness (MOT) in comparison to native Kevlar, through the nanoscale coating with alumina. At the same time their intrinsic sensitivity to 24 hours UV-irradiation was completely suppressed through another infiltrated material, zinc oxide, which absorbs the UV irradiation in the subsurface area of the fibers.

Building organosilica hybrid nanohemispheres via thiol-ene click reaction on alumina thin films deposited by atomic layer deposition (ALD).

The present work shows a surface-induced preparation of sub-100 nm organosilica nanohemispheres on atomic layer deposited (ALD) Al2O3 thin films, which was achieved by cooperative condensation/hydrolysis and thiol-ene click chemical reactions. The two-step synthetic approach consists of an initial silanization of the Al2O3 film with vinyltrimethoxysilane (VTMS), followed by a photo-promoted growth of surface-bound nanoparticles in the presence of (3-mercaptopropyl)trimethoxysilane (MPTMS). Characterization by means of FE-SEM, XPS and EDS points towards the growth of the nanohemispherical structures being governed by an initial nucleation of thiolated organosilica seeds in solution as a result of self-condensation of MPTMS and oxidation of thiols to disulfides. Once bound to the vinyl terminated Al2O3via photo-assisted thiol-ene coupling, these seeds promote area-selective growth of the nanoparticles through binding of further MPTMS from the solution. After an additional ALD deposition of ZnO, the resulting thin hybrid film exhibits enhanced hydrophobicity when compared to ZnO films deposited directly on Al2O3 under the same processing conditions.

Ligand-induced reduction concerted with coating by atomic layer deposition on the example of TiO2-coated magnetite nanoparticles.

Atomic layer deposition is a chemical deposition technology that provides ultimate control over the conformality of films and their thickness, even down to Ångström-scale precision. Based on the marked superficial character and gas phase process of the technique, metal sources and their ligands shall ideally be highly volatile. However, in numerous cases those ligands corrode the substrate or compete for adsorption sites, well-known as side reactions of these processes. Therefore, the ability to control such side reactions might be of great interest, since it could achieve synchronous coating and alteration of a substrate in one process, saving time and energy otherwise needed for a post-treatment of the sample. Consequently, advances in this way must require understanding and control of the chemical processes that occur during the coating. In this work, we show how choosing an appropriate ligand of the metal source can unveil a novel approach to concertedly coat and reduce γ-Fe2O3 nanoparticles to form a final product composed of Fe3O4/TiO2 core/shell nanoparticles. To this aim, we envisage that appropriate design of precursors and selection of substrates will pave the way for numerous new compositions, while the ALD process itself allows for easy upscaling to large amounts of coated and reduced particles for industrial use.

Introducing the concept of pulsed vapor phase copper-free surface click-chemistry using the ALD technique.

We report for the first time on a pulsed vapor phase copper-free azide-alkyne click reaction on ZnO by using the atomic layer deposition (ALD) process technology. This reproducible and fast method is based on an in situ two-step reaction consisting of sequential exposures of ZnO to propiolic acid and benzyl azide.

Laponite-Based Surfaces with Holistic Self-Cleaning Functionality by Combining Antistatics and Omniphobicity.

In the present work, perfluoroalkylated laponite nanoparticles with a high degree of functionalization (60 wt %) have been prepared and a methodology to prepare transparent, antistatic, and omniphobic laponite-based films with holistic self-cleaning properties against liquids, solids and liquid-solid mixtures has been developed. The intrinsic electrical and ionic conductivities observed in unmodified laponite coatings are combined with perfluoroalkyl-modified laponite clays. As a result, films with improved self-cleaning functionality based on dust-repellency and omniphobic liquid-repellence (sheet resistance in the range of 107 Ω/□ and contact angles of 106° (H2O) and 93° (oil)) were obtained. These unique films, being capable to repel dust and liquids, were applied to a variety of substrates (i.e., glass and plastics) and tested against solids and liquids of different nature with excellent performance. Bending tests of these holistic self-cleaning films deposited over flexible substrates showed better mechanical performance than unmodified laponite films.

Conductive Polymer-Inorganic Hybrid Materials through Synergistic Mutual Doping of the Constituents.

Polymer-matrix-based inorganic-organic hybrid materials are at the cutting edge of current research for their great promise of merging properties of soft and hard solids in one material. Infiltration of polymers with vapors of reactive metal organics is a pathway for postsynthetic blending of the polymer with inorganic materials. Here, we show that this process is also an excellent method for fabricating conductive hybrid materials. Polyaniline (PANI) was infiltrated with ZnO and the initially insulating polymer was converted to a PANI/ZnO hybrid with conductivities as high as 18.42 S/cm. The conductivity is based on a synergistic effect of the constituting materials, where the inorganic and the polymeric fractions mutually act as dopants for the counterpart. The process temperature is a very important factor for successful infiltration, and the number of applied infiltration cycles allows tuning the level of conductivity of the resulting PANI/ZnO.

Ferritin-mediated siRNA delivery and gene silencing in human tumor and primary cells.

We demonstrate a straightforward method to encapsulate siRNA into naturally available and unmodified human apoferritin. The encapsulation into apoferritin is independent of the sequence of the siRNA and provides superior protection for those sensitive molecules. High efficiency in transfection can be achieved in human tumorigenic cells, human primary mesenchymal stem cells (hMSC) and peripheral blood mononuclear cells (PBMCs). In contrast to Lipofectamine, highly effective gene silencing can be achieved with ferritin as the delivery agent in both tumor cells and PBMCs at low siRNA concentrations (10 nM). As an endogenous delivery agent, apoferritin does not induce immune activation of T- and B-cells in human PBMCs. Apoferritin shows intrinsic anti-inflammatory effects and apoferritin-mediated delivery shows a preference for immune-activated T- and B-cells, a natural selectivity which may turn useful for drug delivery in case of infections or inflammatory diseases.

Comparison of two endogenous delivery agents in cancer therapy: Exosomes and ferritin.

Exosomes and ferritin: Two biomacromolecules from our human bodies both draw increasing interest for advanced drug delivery due to their endogenous origin and their morphology, the cage-like structures. They possess perfect naturally designed structures for loading and shielding of cargo. Their intrinsic biological functions enable a natural delivery of the load and specific targeting. More and more evidences point towards the evolution of a new era of drug delivery strategies with exosomes and ferritin, even for potential personalized therapy. This review focuses on the advantages as well as limits of exosomes and ferritin as endogenous carriers for cancer therapy. We compare their structure-specific cargo loading and their intrinsic cancer-related biological functions. Remaining challenges and promising perspectives for future development to use these two endogenous agents are discussed.

Functionalization of Defect Sites in Graphene with RuO2 for High Capacitive Performance.

Graphene is an attractive material for its physicochemical properties, but for many applications only chemically synthesized forms such as graphene oxide (GO) and reduced graphene oxide (rGO) can be produced in sufficient amounts. If considered as electrode material, the intrinsic defects of GO or rGO may have negative influence on the conductivity and electrochemical properties. Such defects are commonly oxidized sites that offer the possibility to be functionalized with other materials in order to improve performance. In this work, we demonstrate how such ultimately efficient functionalization can be achieved: namely, through controlled binding of very small amount of materials such as RuO2 to rGO by atomic layer deposition (ALD), in this way substituting the native defect sites with RuO2 defects. For the example of a supercapacitor, we show that defect functionalization results in significantly enhanced specific capacitance of the electrode and that its energy density can be stabilized even at high consumption rates.