This review deals with the use of solution processing approaches for organic electronics with a focus on material ink formulations as well as on their applicability. The solution processing techniques include methods like gravure printing, screen printing and ink-jet printing. Basic principles of each approach are understood and fundamental correlations between material (metals, semiconductors, and dielectrics) ink properties and final device performances can be drawn. Nevertheless, solution processing methods have the potential to evolve as the most promising tools in organic device fabrication techniques and have already been applied successfully in the fields of organic thin film transistors, solar cells and biosensing devices

Metal oxides are versatile substrates for the design of a wide range of SAM-based organic−inorganic materials among which ZnO nanostructures modified with phosphonic SAM are promising semiconducting systems for applications in technological fields such as biosensing, photonics, and field-effect transistors (FET). Despite previous studies reported on various successful grafting approaches, issues regarding preferred anchoring modes of phosphonic acids and the role of a second reactive group (i.e., a carboxylic group) are still a matter of controversial interpretations. This paper reports on an experimental and theoretical study on the functionalization of ZnO nanorods with monofunctional alkylphosphonic and bifunctional carboxyalkylphosphonic acids. X-ray photoelectron and infrared spectroscopies have been combined with DFT modeling to explain and understand the interactions that drive the surface anchoring of phosphonic acids on ZnO surface. It was found that both monofunctional and bifunctional acids anchor on ZnO through a multidentate bonding which involves both PO and P−O moieties of the phosphonic group. Moreover, anchored bifunctional acids bend to the surface, promoting a further interaction between surface hydroxyl groups and carboxylic terminations. This secondary interaction can be limited by increasing the surface density of the anchored molecules. ■ INTRODUCTIONFunctionalization of metal oxides with self-assembled monolayers (SAMs) is nowadays a field of great interest since it is a powerful and low-cost method to form stable and flexible surfaces with controlled properties. 1−3 Possible applications range from protective coatings which enhance mechanical properties (such as adhesion, friction, and corrosion resistance) 4−6 to functional layers in specific electronics devices such as field-effect transistors, 7,8 sensors, 9−12 or dye-sensitized solar cells (DSSCs). 13 Therefore, the present decade has seen a surge of interest in the modification of metal oxides (TiO 2 , AgO, Al 2 O 3 , ZrO, ZnO, ITO) with SAM having various anchoring groups, among which phosphonic moieties were proven to be an efficient alternative to the more often adopted carboxylic and siloxane tethering functionalities. 14−17 Among mentioned metal oxides, nanostructured ZnO, a wide-band-gap semiconductor (E g = 3.37 eV at room temperature) 18 used in sensors, 19 electronic devices, 20,21 and solar cells, 22−24 is a promising substrate for the design of SAM-based organic− inorganic materials of technological relevance. 25−32 Examples of SAM-functionalized ZnO nanostructures include nanorods modified either with carboxyalkylphosphonic acids (HOOC-(CH 2 ) n P(O)(OH) 2 (n = 2, 9)) for biosensing 25 or with C60-functionalized phosphonic linkers for photonic devices 26 and nanowire-based ZnO field-effect transistors (FET) which use long-chain alkylphosphonic acids as gate dielectrics. 27 Despite various studies reported on a wide range of successful anchoring approaches, issues regarding preferred anchoring modes (monodenta...

Zn-doped TiO 2 nanofibers shelled with ZnO hierarchical nanoarchitectures have been fabricated combining electrospinning of TiO 2 (anatase) nanofibers and metal-organic chemical vapor deposition (MOCVD) of ZnO. The proposed hybrid approach has proven suitable for tailoring both the morphology of the ZnO external shell as well as the crystal structure of the Zn-doped TiO 2 core. It has been found that the Zn dopant is incorporated in calcined electrospun nanofibers without any evidence of ZnO aggregates. Effects of different Zn doping levels of Zn-doped TiO 2 fibers have been scrutinized and morphological, structural, physico-chemical and optical properties evaluated before and after the hierarchical growth of the external ZnO shell over the electrospun nanofibers. Moreover, doping promotes the incipient transition from the anatase to rutile phase in the core-shell Zn-doped TiO 2-ZnO nanostructures at lower temperature than that observed for pure TiO 2. Finally, the present core-shell hierarchical nanofibers possess a very large surface to volume ratio and exhibit a marked cathodoluminescence with a strong UV and visible emission.

Well aligned, long and uniform ZnO nanorods have been reproducibly fabricated adopting a two-steps Metal-Organic Chemical Vapour Deposition (MOCVD) and Chemical Bath Deposition (CBD) fabrication approaches. Thin (<100 nm) ZnO buffer layers have been seeded on silicon substrates by MOCVD and ZnO layers have been subsequently grown, in form of well textured nanorods, using CBD. It has been found that the structure and thickness of the seed layer strongly influence the final morphology and the crystal texturing of ZnO nanorods as well as the CBD growth rate. There is, in addition, a strong correlation between morphologies of CBD grown ZnO nanorods and those of the seed layer underneath. Thus, nanorods deposited over low temperature MOCVD buffer layers are less homogeneous in lateral dimensions and poorly vertically oriented. On the contrary, higher temperature nano-dimensional ZnO seeds favour the CBD growth of almost mono-dimensional homologue nanorods, with an adequate control of the lateral transport of matter. The nanorod aspect ratio values decrease upon increasing the deposition temperatures of the seed layers. Moreover, the nanorods length can be tailored either by adjusting the CBD growth time or by changing concentration of the N,N,N',N'-tetramethylethylenediamine ligand used in the CBD process. In particular, at high concentrations, the CBD process is faster with a greater global aspect ratio in agreement with a preferential one-dimensional growth of the ZnO nanostructures. Finally, these ZnO nanorod arrays possess good optical quality in accordance to the photoluminescence properties

a b s t r a c tA new ligand, N, N, N , N -tetramethylethylenediamine, has been used to grow ZnO nanorods on silicon substrates via a two steps approach. A preliminary seeding on silicon substrates has been combined with chemical bath deposition using a Zinc acetate -N, N, N , N -tetramethylethylenediamine aqueous solution. The used diamino ligand has been selected as Zn 2+ complexing agent and the related hydrolysis generates the reacting ions (Zn 2+ and OH − ) responsible for the ZnO growth. The seed layer has been annealed at low temperature (<200°C) and the ZnO nanorods have been grown on this ZnO amorphous layer. There is experimental evidence that the ligand concentration (ranging from 5 to 50 mM) strongly affects the alignment of ZnO nanorods on the substrate, their lateral dimension and the related surface density. Length and diameter of ZnO nanorods increase upon increasing the ligand concentration, while the nanorod density decreases. Even more important, it has been demonstrated, as proof of concept, that chemical bath deposition can be usefully combined with colloidal lithography for selective ZnO nanorod deposition. Thus, by patterning the ZnO seeded substrate with polystyrene microsphere colloidal lithography, regular Si hole arrays, spatially defined by hexagonal ZnO nanorods, have been successfully obtained.

Solution-based printing approaches permit digital designs to be converted into physical objects by depositing materials in a layer-by-layer additive fashion from microscale to nanoscale resolution. The extraordinary adaptability of this technology to different inks and substrates has received substantial interest in the recent literature. In such a context, this review specifically focuses on the realization of inks for the deposition of ZnO, a well-known wide bandgap semiconductor inorganic material showing an impressive number of applications in electronic, optoelectronic, and piezoelectric devices. Herein, we present an updated review of the latest advancements on the ink formulations and printing techniques for ZnO-based nanocrystalline inks, as well as of the major applications which have been demonstrated. The most relevant ink-processing conditions so far explored will be correlated with the resulting film morphologies, showing the possibility to tune the ZnO ink composition to achieve facile, versatile, and scalable fabrication of devices of different natures.

Focusing on the interplay between interface chem-1 istry, electrochemistry, and integrated electronics, we show a 2 novel low-cost and flexible biosensing platform for continuous 3 glucose monitoring. The amperometric biosensing system features 4 a planar three-electrode structure on a plastic substrate, and 5 a wireless NFC-powered electronic system performing sensor AQ:1 6 analog front-end, A/D conversion, digital control, and display 7 tasks. The working electrode is made of electropolymerized poly 8 (3,4-ethylenedioxythiophene) film onto a polyethylene terephtha-9 late/gold electrode followed by immobilization of cross-linked 10 glucose oxidase by glutaraldehyde. The advantages offered by 11 such a device, including low-cost materials and instrumentation 12 as well as the good sensitivity of 9.24 µA/(mM • cm 2) are 13 promising tools for point-of-care monitoring. It is demonstrated 14 that the devices are good candidates for the development of 15 advanced sensing approaches based on the investigation of the 16 noise produced during operation (fluctuation-enhanced sensing).

a b s t r a c tThe fluorescence-based sensing capability of ultrathin ZnO-SiO 2 nanoplatforms, deposited by an integrated approach of colloidal lithography and metal organic chemical vapor deposition, has been investigated upon adsorption of fluorescein-labeled albumin, used as model analyte biomolecule. The protein immobilization process after spontaneous adsorption/desorption significantly enhances the green emission of the different ZnO-based films, as evidenced by scanning confocal microscopy, corresponding to a comparable protein coverage detected by X-ray photoelectron spectroscopy. Moreover, experiments of fluorescence recovery after photobleaching evidence that the protein lateral diffusion at the biointerface is affected by the chemical and/or topographical patterning of hybrid ZnO-SiO 2 surfaces. The used approach is very promising for biomolecular detection applications of these ZnO-SiO 2 nanoplatforms, by simple sizing of the 2D vs. 3D patterning design, which in turn is accomplished by the fine tuning of the integrated colloidal lithography-chemical vapor deposition processes.