Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

Colloidal inorganic nanocrystals, free-standing crystalline nanostructures generated and processed in solution phase, represent an important class of advanced nanoscale materials owing to the flexibility with which their physical–chemical properties can be controlled through synthetic tailoring of their compositional, structural and geometric features and the versatility with which they can be integrated in technological fields as diverse as optoelectronics, energy storage/ conversion/production, catalysis and biomedicine. In recent years, building upon mechanistic knowledge acquired on the thermodynamic and kinetic processes that underlie nanocrystal evolution in liquid media, synthetic nanochemistry research has made impressive advances, opening new possibilities for the design, creation and mastering of increasingly complex “colloidal molecules”, in which nanocrystal modules of different materials are clustered together via solid-state bonding interfaces into free-standing, easily processable multifunctional nanocomposite systems. This Review will provide a glimpse into this fast-growing research field by illustrating progress achieved in the wet-chemical development of last-generation breeds of all-inorganic heterostructured nanocrystals (HNCs) in asymmetric non-onionlike geometries, inorganic analogues of polyfunctional organic molecules, in which distinct nanoscale crystalline modules are interconnected in hetero-dimer, hetero-oligomer and anisotropic multidomain architectures via epitaxial heterointerfaces of limited extension. The focus will be on modular HNCs entailing at least one magnetic material component combined with semiconductors and/or metals, which hold potential for generating enhanced or unconventional magnetic properties, while offering diversified or even new chemical-physical properties and functional capabilities. The available toolkit of synthetic strategies, all based on the manipulation of seeded-growth techniques, will be described, revisited and critically interpreted within the framework of the currently understood mechanisms of colloidal heteroepitaxy

Self assembly of highly fluorescent semiconductor nanorods into large scale smectic liquid crystal structures by coffee stain evaporation dynamics

We deposit droplets of nanorods dispersed in solvents on substrate surfaces and let the solvent evaporate. We find that strong contact line pinning leads to dense nanorod deposition inside coffee stain fringes, where we observe large-scale lateral ordering of the nanorods with the long axis of the rods oriented parallel to the contact line. We observe birefringence of these coffee stain fringes by polarized microscopy and we find the direction of the extraordinary refractive index parallel to the long axis of the nanorods.Comment: 11 pages, 6 figures and supporting informatio

Graded vertical phase separation of donor/acceptor species for polymer solar cells

The donor/acceptor inter-mixing in bulk heterojunction (BHJ) solar cells is a critical parameter, often leading to irreproducible performance of the finished device. An alternative solution-processed device fabrication strategy towards a better control of the micro/nano-structured morphology consists of a sequential coating of the donor (e.g., poly-(3-hexylthiophene), P3HT) and the acceptor (e.g., [6,6]-phenyl-C61-butyric acid methyl ester, PCBM) from orthogonal solvents. We demonstrate that, in spite of the solvent orthogonality, this technique does not lead to a well-defined bilayer with a sharp interface, but it rather results in a graded vertical phase-separated junction, resulting from the diffusion of the PCBM in the P3HT bottom layer. We are able to control the diffusion of PCBM, which occurs preferentially in the amorphous P3HT domains, by easily varying the ratio between crystalline/amorphous domains in the P3HT. Such a ratio can be simply modified by changing the solvent for P3HT. We show that the donor–acceptor diffused bilayer (DB) junction is an intermediate structure which combines both advantages of the well-defined bilayer and conventional BHJ configurations. Indeed, the DB device geometry ensures the good reproducibility and charge percolation, like the well-defined bilayer, while preserving the interpenetration of the donor and acceptor species, resulting in an efficient charge separation, characteristic of the BHJ. Overall the annealed DB device geometry can be assimilated to a graded BHJ with an improved reproducibility and mean power conversion efficiency (PCE) of 3.45%, higher than that of the standard BHJ devices of 3.07%. Furthermore, we demonstrate the highest performance for the as-cast DB device with a PCE of 2.58%. It is worthy to note that our DB device exhibits improved open circuit voltage, fill factor, series and shunt resistances, which denote that the vertically phase separated DB junction ensures improved charge percolation

Control of colloidal CaCO3 suspension by using biodegradable polymers during fabrication

Fabrication of homogenous CaCO3 particles is a significant step in assembling polyelectrolyte capsules. It is crucial to control the dimensions, the shape and the charge of the calcium carbonate particles in order to have homogenously separated and charged templates as final result. For this reason, previously. hey have been deeply investigated. Recently, crystallization of CaCO3 was done by adding poly (sodium 4-styrenesulfonate) (PSS) as negatively charged polymer and poly (allylamine hydrochloride) (PAH) as positively charged polymer and the results were surprising. The homogenous particles were separated and they carried the same charge of the used polymer. The aim of this work was to investigate the synthesis process of CaCO3 particles in different experimental conditions: calcium carbonate was produced in presence and in absence of water and with addition of appropriate polymers. In particular, chitosan (CHI) and poly acrylic acid (PAA) were chosen as biodegradable polymers whereas PSS and PAH were chosen as non-biodegradable polymers. Shape and diameter of particles were investigated by using transmission and scanning electron microscopy, elemental composition was inferred by energy dispersive X-ray analyses whereas their charges were explored by using zeta potential

Reversible wettability of hybrid organic/inorganic surfaces of systems upon light irradiation/storage cycles

In this work we present hybrid organic/inorganic structures that can exhibit reversible surface wettability, altered in a controllable manner. In particular, we use the method of photo-patterning to produce polymeric SU-8 pillars of specific geometries, onto which we subsequently deposit colloidal TiO2 nanorods. In this way, we combine the microroughness of the polymeric pillars with the nanoroughness of the nanorod-coating to create highly hydrophobic surfaces. The hydrophobicity of these systems can be changed reversibly into hydrophilicity upon irradiation of the hybrid structures with pulsed UV laser light. This behaviour is due to the well-known property of TiO2, that becomes superhydrophilic upon UV light irradiation. This property is reversible and we monitor the recovery of our hybrid polymeric/inorganic-nanorods structures to their initial hydrophobic character upon dark storage and heating. The wetting behaviour has been modelled and analysed according to the surface geometry. The direct implementation of such structures into microfluidics devices is demonstrated. Copyright © 2010 Inderscience Enterprises Ltd

Determination of surface properties of various substrates using TiO2 nanorod coatings with tunable characteristics

We present a novel approach to cover different substrates with thin light-sensitive layers that consist of organic-capped TiO2 nanorods (NRs). Such NR-based coatings exhibit an increasing initial hydrophobicity with increasing NR length, and they demonstrate a surface transition from this highly hydrophobic state to a highly hydrophilic one under selective UV–laser irradiation. This behaviour is reversed under long dark storage. Infrared spectroscopy measurements reveal that light-driven wettability changes are accompanied by a progressive hydroxylation of the TiO2 surface. The surfactant molecules that cover the NRs do not appear to suffer for any significant photocatalytic degradation

Probe Tips Functionalized with Colloidal Nanocrystal Tetrapods for High-Resolution Atomic Force Microscopy Imaging

The performance and resolution of atomic force microscopy (AFM) imaging depends mainly on the quality and shape of the probe tip, since the obtained AFM image is a convolution of the tip profile and the sample structure. Therefore, tip radii that are smaller and aspect ratios that are higher than the sample features are desirable in order to obtain good images. Progress in the ability to design, fabricate, and assemble nanostructures in the size range of a few nanometers has raised the demand for probe tips with a corresponding resolution. Standard commercially available tips made of Si or SiN have a pyramidal shape with a tip radius of the order of 10 nm or larger and therefore do not image nanostructures with features in the few nanometer range adequately. One solution to this problem is the commercially available super-sharp Si probes with tip radius of 2 nm, which, however, obtain their high resolution at a price: the sharp tip can break easily during an experiment. These limitations have stimulated many efforts to enhance the resolution of AFMby functionalizing the probe tips with high-aspect-ratio nanostructures. Carbon nanotubes have demonstrated excellent properties in this respect. Different approaches for the attachment of the carbon nanotubes to the AFM cantilever have been developed, and a spatial resolution of only a few nanometers has been demonstrated. However, the attachment of carbon nanotubes to theAFM tip is still a time consuming and very difficult task, and often results in non-reproducible nanotube configuration and placement. The optimal attachment geometry, with the tip perpendicular to the sample under investigation, is particularly hard to realize. Also, the inherent thermal vibration of long nanotubes can cause difficulties when they are used for AFM imaging. Recent approaches to overcome these difficulties comprise the growth of multiwalled carbon nanotubes and the electron beam induced deposition of carbon nanocones on tipless cantilevers. For a recent review on AFM probes see elsewhere. Shape-controlled semiconductor nanocrystals are another very interesting family of nanostructures that can enhance the spatial resolution of AFM. Tetrapod-shaped nanocrystals are especially appealing for functionalizing AFM tips. Their ability to align on a surface with three supporting base arms, and the fourth arm pointing straight up, resembles an optimal geometry for the sensing of topography with the fourth, vertical arm. Recent advances in colloidal chemical synthesis have led to tetrapod samples with arm lengths of the order of several hundred nanometers and a diameter at the arm extremity well below 10 nm. Moreover, the optoelectronic properties of shape-controlled nanocrystals can extend the functionality of AFM beyond the probing of topography. Banin and coworkers, for example, showed that AFM probes functionalized with spherical core/shell nanocrystals can be used for near field optical imaging. Here, we report the positioning of single CdTe tetrapods on flattenedAFM tips and demonstrate the feasibility of these tips, via the vertical tetrapod arm, for high resolution AFM imaging. Withour tippreparationweachieve anoptimal probingangle of 908, due to the use of contactmode scanning for the preparation of the tip flat. This inherently leads to a tip geometrywith the flat parallel to thesampleplane,which, combinedwiththecapability of tetrapods to self-align with three arms contacting the surface and the fourth pointing vertically upward, results in a geometry where the vertical arm probes the topography at a 908 angle to the sample surface. The high aspect ratio shape of the tetrapod arms, with diameters ranging from 5 to 10nm and lengths ranging from 100 to 300 nm, provides excellent properties for high-resolution topography scanning. In particular, we find that the tetrapod-functionalized tips work very well for imaging surfaces that are covered with nanocrystal samples. Furthermore, our tip fabrication technique could open the way for the fabrication of high aspect ratio optically and electronically sensitive probe tips due to the semiconductor properties of the tetrapods. Large aspect ratio colloidal nanocrystal CdTe tetrapods with arm lengths ranging from 100 to 300 nm and diameters around 10 nm were fabricated by chemical synthesis as reported elsewhere and dissolved in toluene (see Supporting Information Fig. S2 for a TEM image of these very large tetrapods). The rapid growth of the tetrapod arms led to a pointed shape (i.e., to a decreasing arm diameter toward the arm extremity), which is advantageous for our purpose of high spatial resolution imaging (see Fig. 1b). Figure 1(b and c) show transmission electron microscopy (TEM) images of tetrapods deposited by drop casting onto a carbon coated TEM grid. The images show that the tetrapods self-align, with three arms contacting the substrate and the fourth arm pointing straight upward, appearing as a dark circular spot in the image. A sketch of the tetrapod-functionalized AFM probe is shown in Figure 1a. [!] Dr. R. Krahne, C. Nobile, A. Fiore, R. Mastria, Prof. R. Cingolani, Dr. L. Manna National Nanotechnology Laboratory of CNR-INFM Distretto Tecnologico ISUFI Via per Arnesano, Lecce 73100 (Italy) E-mail: [email protected]

Polarized light emitting diode by long-range nanorod self-assembling on a water surface.

We demonstrate a straightforward strategy to fabricate a multilayer inorganic/organic polarized light-emitting diode device based on highly ordered arrays of rod-shaped nanocrystals as the active species. We have developed a simple and effective method that allows colloidal CdSe/CdS core/shell nanorods to be laterally aligned in smectic or nematic phases on the surface of water. A floating film of such ordered nanorods has been collected by a poly(dimethylsiloxane) (PDMS) stamp pad and transferred by contact printing onto previously evaporated organic layers. Thanks to the lateral nanorod alignment the as-prepared film exhibited strong polarized photoluminescence and it has been used as emissive layer in the polarized electroluminescent device

Confinement effects on optical phonons in spherical, rod-, and tetrapod-shaped nanocrystals detected by Raman spectroscopy

Spherical, rod- and tetrapod shaped CdSe nanocrystals are investigated by Raman spectroscopy and the longitudinal-optical and surface optical phonons are observed. We find that the position of the longitudinal-optical phonon slightly red-shifts with decreasing diameter, whereas the position of the surface optical phonon depends significantly on diameter and length of the rods or the tetrapod arms

Sonication-Assisted Production of Fosetyl-Al Nanocrystals: Investigation of Human Toxicity and In Vitro Antibacterial Efficacy against Xylella Fastidiosa

none10Recently, there is a growing demand in sustainable phytopathogens control research. Nanotechnology provides several tools such as new pesticides formulations, antibacterial nanomaterials and smart delivery systems. Metal nano-oxides and different biopolymers have been exploited in order to develop nanopesticides which can offer a targeted solution minimizing side effects on environment and human health. This work proposed a nanotechnological approach to obtain a new formulation of systemic fungicide fosetyl-Al employing ultrasonication assisted production of water dispersible nanocrystals. Moreover, chitosan was applicated as a coating agent aiming a synergistic antimicrobial effect between biopolymer and fungicide. Fosetyl-Al nanocrystals have been characterized by morphological and physical-chemical analysis. Nanotoxicological investigation was carried out on human keratinocytes cells through cells viability test and ultrastructural analysis. In vitro planktonic growth, biofilm production and agar dilution assays have been conducted on twoXylella fastidiosasubspecies. Fosetyl-Al nanocrystals resulted very stable over time and less toxic respect to conventional formulation. Finally, chitosan-based fosetyl-Al nanocrystals showed an interesting antibacterial activity againstXylella fastidiosasubsp.paucaandXylella fastidiosasubsp.fastidiosa.Regione Puglia, Deliberazione della Giunta Regionale n. 1410 del 12/06/2015 “Linee guida per il parco della ricerca e sperimentazione finalizzata alla prevenzione e al contenimento del complesso del disseccamento rapido dell’olivo (CODIRO)” Project FATA- “Trattamenti fitoterapici innovativi a base di vettori di chitosano” MIPAAFT, Project Oli.Di.X.I.It-“OLIvicoltura e Difesa da Xylella fastidiosa e da Insetti vettori in Italia”, D.M. 23773 del 6/09/2017.openFrancesca Baldassarre; Giuseppe Tatulli; Viviana Vergaro; Stefania Mariano; Valeria Scala; Concetta Nobile; Nicoletta Pucci; Luciana Dini; Stefania Loreti; Giuseppe CiccarellaBaldassarre, Francesca; Tatulli, Giuseppe; Vergaro, Viviana; Mariano, Stefania; Scala, Valeria; Nobile, Concetta; Pucci, Nicoletta; Dini, Luciana; Loreti, Stefania; Ciccarella, Giusepp