Formation Of Such Nanostructures Research Articles

Multiphysics approaches for modeling nanostructural evolution during physical vapor deposition of phase-separating alloy films

Physical vapor deposition of phase-separating alloy films yields a rich variety of distinct self-assembled nanostructures depending on the deposition rate and temperature. However, the role of grain boundaries, elastic imhomogeneity, and anisotropy, and surface tension, in the formation of such nanostructures is currently not well understood. Here, we employ a phase-field approach that couples the multiphysics of elemental diffusion, elastic misfit and anisotropy, surface tension, and grain boundaries with processing parameters, namely deposition rate and temperature, to investigate phase separation and grain boundary evolution in binary alloy films. We develop phase-field deposition models of increasing complexity to isolate and analyze the influence of processing parameters on nanostructural transitions in vapor co-deposited films. While it is found that such transitions are primarily guided by a minimization of total free energy, our simulation-based insights strongly indicate the phenomena of nanostructure selection at faster deposition rates. It is anticipated that the insights gained from this study will provide the much-required knowledgebase for establishing nanostructure-level control in the physical vapor deposition of alloy films.

Evolution in the formation of graphene nanocapsules from coal tar pitch

It has recently been reported that coal tar pitch (CTP) can be utilised as raw material for the production of graphene nanocapsules (GNCs) because it is formed by a great quantity of aromatic organic compounds (which promote the rearrangement of double bonds by a process of polymerisation). Due to the importance of graphene and the search for a non-expensive methodology to produce it, this work used CTP to synthesise GNCs using an in situ activation technique at low temperatures and evaluating the effect of the working temperature on the formation of such nanostructures. In other words, analysing the form of the particle as the temperature rises from 600 to 900 °C. As result of the experimentation, powders were obtained and analysed by the techniques of X-Ray Diffraction, Raman Spectroscopy and Microscopy, employing Field Emission Scanning Electron Microscopy by normal mode as well as by Scanning Transmission Electron Microscopy and a High-Resolution Scanning Electron Microscopy. The results show that working with temperatures between 800 and 850 °C promotes the production of GNCs, considering that their size reduces as the working temperature rises.

Assembly of Protein Stacks With in Situ Synthesized Nanoparticle Cargo.

The ability of proteins to form hierarchical structures through self-assembly provides an opportunity to synthesize and organize nanoparticles. Ordered nanoparticle assemblies are a subject of widespread interest due to the potential to harness their emergent functions. In this work, the toroidal-shaped form of the protein peroxiredoxin, which has a pore size of 7 nm, was used to organize iron oxyhydroxide nanoparticles. Iron in the form of Fe2+ was sequestered into the central cavity of the toroid ring using metal-binding sites engineered there and then hydrolyzed to form iron oxyhydroxide particles bound into the protein pore. By precise manipulation of the pH, the mineralized toroids were organized into stacks confining one-dimensional nanoparticle assemblies. We report the formation and the procedures leading to the formation of such nanostructures and their characterization by chromatography and microscopy. Electrostatic force microscopy clearly revealed the formation of iron-containing nanorods as a result of the self-assembly of the iron-loaded protein. This research bodes well for the use of peroxiredoxin as a template with which to form nanowires and structures for electronic and magnetic applications.

Study of Compression-Induced Supramolecular Nanostructures of an Imidazole Derivative by Langmuir-Blodgett Technique.

In this communication, we report the design and synthesis as well as the supramolecular assembly behavior of a 2,4,5-triaryl imidazole derivative (compound 1) at the air-water interface and in thin films using Langmuir-Blodgett (LB) technique. The main idea for such a chemical structure is that the long alkyl chain and N-H of the imidazole core may help to form supramolecular architecture through the hydrophobic-hydrophobic interaction and hydrogen bonding, respectively. Accordingly, the interfacial behavior as well as morphology of 1 in thin films were studied through a series of characterization methods such as surface pressure-area (π-A) isotherm, hysteresis analysis, ultraviolet-visible (UV-vis) absorption and steady-state fluorescence spectroscopies, Fourier transform infrared, X-ray diffraction, Brewster angle microscopy (BAM), and atomic force microscopy (AFM) measurements, and so forth. Pressure-area isotherm is an indication toward the formation of supramolecular nanostructures instead of an ideal monolayer at the air-water interface. This has been confirmed by the hysteresis analysis and BAM measurement at the air-water interface. AFM images of 1 in the LB monolayer exhibits the formation of supramolecular nanowires as well as nanorods. By controlling different film-forming parameters, it becomes possible to manipulate these nanostructures. With the passage of time, the nanowires come close to each other and become straight. Similarly, nanorods come close to each other and form bundles of several rods in the LB films. H-bonding, J-aggregation, as well as compression during film formation might play a key role in the formation of such nanostructures. Electrical switching behavior of compound 1 was also observed because of the presence of an electron donor-acceptor system in 1. This type of organic switching behavior may be promising for next-generation organic electronics.

Metal oxide nanostructures by a simple hot water treatment

Surfaces with metal oxide nanostructures have gained considerable interest in applications such as sensors, detectors, energy harvesting cells, and batteries. However, conventional fabrication techniques suffer from challenges that hinder wide and effective applications of such surfaces. Most of the metal oxide nanostructure synthesis methods are costly, complicated, non-scalable, environmentally hazardous, or applicable to only certain few materials. Therefore, it is crucial to develop a simple metal oxide nanostructure fabrication method that can overcome all these limitations and pave the way to the industrial application of such surfaces. Here, we demonstrate that a wide variety of metals can form metal oxide nanostructures on their surfaces after simply interacting with hot water. This method, what we call hot water treatment, offers the ability to grow metal oxide nanostructures on most of the metals in the periodic table, their compounds, or alloys by a one-step, scalable, low-cost, and eco-friendly process. In addition, our findings reveal that a “plugging” mechanism along with surface diffusion is critical in the formation of such nanostructures. This work is believed to be of importance especially for researchers working on the growth of metal oxide nanostructures and their application in functional devices.

In vitro degradation behavior and cytocompatibility of a bioceramic anodization films on the biodegradable magnesium alloy

Abstract Magnesium (Mg), and its alloys have good potential for using in biomedical applications due to its good mechanical properties and biodegradability. However, the poor corrosion resistance and insufficient mechanical stability of Mg in biological fluids have limited its clinical applicability. As a result, surface modification techniques are being investigated to improve corrosion resistance for biomedical applications. In this study, a bioactive CaP film were deposited on the surface of the AZ31B magnesium alloy via anodization with SBF solution used as the electrolyte with and without ZrO 2 Nanoparticles (NPs). The samples were evaluated and characterized in vitro to assess their degradation and cytocompatability behaviour via FE-SEM, electrochemical corrosion test, immersion test, and cell culture tests. The results indicate that the AZ31B Mg alloy surface anodized in SBF with and without ZrO 2 NPs consists of CaP nanoplate leaf-like apatite structures and porous 3-D structures, respectively. The nanomorphology showed uniform growth on the anodized surface that had created the porous layer on the surface of the samples three days after immersion in the SBF solution. The formation of such nanostructures on the anodized sample could provide the implant materials with extra biocompatibility. Moreover, this unique deposited layer can improve the corrosion resistance and cytocompatability of the Mg alloys, which make it a promising material for use in biomedical applications.

Star-shaped tetrathiafulvalene oligomers towards the construction of conducting supramolecular assembly.

The construction of redox-active supramolecular assemblies based on star-shaped and radially expanded tetrathiafulvalene (TTF) oligomers with divergent and extended conjugation is summarized. Star-shaped TTF oligomers easily self-aggregate with a nanophase separation to produce supramolecular structures, and their TTF units stack face-to-face to form columnar structures using the fastener effect. Based on redox-active self-organizing supramolecular structures, conducting nanoobjects are constructed by doping of TTF oligomers with oxidants after the formation of such nanostructures. Although radical cations derived from TTF oligomers strongly interact in solution to produce a mixed-valence dimer and π-dimer, it seems to be difficult to produce nanoobjects of radical cations different from those of neutral TTF oligomers. In some cases, however, radical cations form nanostructured fibers and rods by controlling the supramolecular assembly, oxidation states, and counter anions employed.

Framed carbon nanostructures: synthesis and applications in functional SPM tips.

We present a synthesis method to fabricate framed carbon-based nanostructures having highly anisotropic shapes, in particular, the nanofork and nanoscalpel structures which are obtained systematically under optimized growth conditions. A theoretical model is developed to explain the formation of such nanostructures on Si cantilevers and W etched wires exposed to a focused electron beam. We then demonstrate the potentials of these nanostructures as functional tips for scanning probe microscopy. Owing to their anisotropic shapes, such tips can be very useful for nanolithography, nanosurgery of biological objects, and precise manipulation with surface particles. Overall, our method provides a simple and robust way to produce functional scanning probe microscopy tips with variable shapes and enhanced capabilities for different applications compared to standard cantilevers.

Exploiting oriented attachment in stabilizing La3+-doped gallium oxide nano-spindles

The morphology of the single crystalline gallium oxide nano-spindles remained conserved even after doping them with >1.4 at% of La3+ ions and formation of such nanostructures could be explained by invoking the mechanism of oriented attachment.

Templateless electrogeneration of polypyrrole nanostructures: impact of the anionic composition and pH of the monomer solution

Different superhydrophilic polypyrrole nanostructures can be electrosynthezised in the presence of anions of weak acid (monohydrogenophosphate) and non-acidic anions (perchlorate) without the need for templates. Actually the type of nanostructures formed depends both on the concentration of anions at the electrode and on the interfacial pH. Depending on the anion composition of the pyrrole aqueous solution the film electrogenerated under a given applied potential is either a very thin membrane (10–20 nm) consisting of overoxidized polypyrrole or a tridimensional film with oriented nanowire array or a network of more or less interconnected nanofibers. The formation of such nanostructures is explained by a side reaction which is water oxidation. Since this reaction is pH-dependent, the pH of the pyrrole solution is one of the key parameter for the synthesis of such nanostructures. The reaction mechanism is discussed and compared to those proposed in the literature for nanofiber network electrosynthesis. Actually in the monomer solution, the role of the anions of weak acid is twofold. On the one hand they allow to limit the decrease of the interfacial pH during pyrrole oxidation and on the other hand to decrease the interfacial anion concentration, so that water oxidation takes place with formation of hydroxyl radicals and dioxygen nanobubbles.

In Situ Hydrothermal Synthesis of Mn3O4 Nanoparticles on Nitrogen-doped Graphene as High-Performance Anode materials for Lithium Ion Batteries

Developing new electrode materials with high specific capacity for excellent lithium ion storage properties is very desirable. In this paper, we introduce a simple hydrothermal method for the growth of Mn3O4 nanoparticles onto nitrogen-doped graphene (N-doped graphene) for high-performance lithium ion battery (LIB) anodes. Hydrazine plays a fundamental role in the formation of such nanostructures as it can act both as a reducing agent and as a nitrogen source. In the synthesized composite, highly crystalline Mn3O4 nanoparticles with average sizes of 20–50nm are homogeneously dispersed on both sides of the N-doped graphene. The nitrogen content in the doped graphene is confirmed by elemental analyzer, and 2 wt% of the sample is found to be composed of nitrogen element. The as-prepared Mn3O4/N-doped graphene composites exhibit remarkable electrochemical performance, including high reversible specific capacity, outstanding cycling stability, and excellent rate capability (approximately 400mA h g−1 at 2.0 A g−1) when used as the anode material for LIBs. The improvement in the electrochemical properties of the material can be attributed to graphene, which acts as both an electron conductor and a volume buffer layer, and nitrogen doping allows for fast electron and ion transfer by decreasing the energy barrier. This type of metal oxide/N-doped graphene composites can be promising candidates for high-performance anode materials for LIBs.

Temperature effects in carbon monoxide and methanol electrooxidation on platinum–ruthenium: influence of grain boundaries

The temperature dependence of methanol and CO monolayer oxidation is studied on carbon-supported PtRu (1:1 atomic ratio) electrodes with different metal percentages (5, 30, and 60 wt.%) in an aqueous H2SO4 electrolyte. High-resolution transmission microscopy confirms that at high (30 or 60 wt.%) metal percentage PtRu nanostructures with a high concentration of intercrystalline boundaries are formed. These nanostructures comprise multiple-twinned particles, particles with intersecting randomly oriented intergrain boundaries, or particles with parallel intergrain boundaries. Formation of such nanostructures leads to a decrease of the apparent activation energy of the methanol and CO monolayer oxidation, while the Tafel slope and the reaction order in methanol show minor dependence on the type of nanostructure. Materials with a high concentration of grain boundary regions may be of interest for practical applications in direct methanol or proton exchange fuel cells fed with reformate.

Formation of plasma-generated nanostructures on polymer surfaces for various polymer types

To produce functional elements for optical applications, the components often have to be coated or joined together. Low adhesion is usually caused by different polarity or surface chemistry of the individual components. Therefore, measures have to be taken to modify the respective interfaces to improve the adhesion. In the case of highly transparent polymers (e.g. PC, PMMA, COC, PA) this turns out to be problematic due to the demands on the optical properties. Many methods for adhesion promotion, as etching with chemicals or mechanical roughening, lead to a significant deterioration in the transparency of such components. In many cases a plasma treatment alone has no sufficient effect on improving the adhesion. The Fraunhofer Institute in Jena (IOF) is working several years now on the nano-structuring of polymer surfaces by plasma etching. Except for antireflection purposes, such a structure can also be used to promote adhesion. However, large structure depths and high aspect ratios are necessary therefore. In the experiments carried out here the self-organizing formation of such nanostructures on various polymer types was studied.

Thermally oxidized formation of new Ge dots over as-grown Ge dots in the Si capping layer

A Si-capped Ge quantum dot sample was self-assembly grown via Stranski-Krastanov mode in a molecular beam epitaxy system with the Si capping layer deposited at 300 °C. After annealing the sample in an oxygen atmosphere at 1000 °C, a structure, namely two layers of quantum dots, was formed with the newly formed Ge-rich quantum dots embedded in the oxidized matrix with the position accurately located upon the as-grown quantum dots. It has been found that the formation of such nanostructures strongly depends upon the growth temperature and oxygen atmosphere. A growth mechanism was proposed to explain the formation of the nanostructure based on the Ge diffusion from the as-grown quantum dots, Ge segregation from the growing oxide, and subsequent migration/agglomeration.

ChemInform Abstract: Conducting Supramolecular Nanofibers and Nanorods

AbstractReview: 58 refs.

Controllable fabrication of platinum nanospheres with a polyoxometalate-assisted process

Pt nanospheres with an average diameter of 60±10 nm have been successfully synthesized at room temperature through a facile polyoxometalate(POM)-assisted process. Characterization by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) clearly showed that these Pt nanospheres consisted of 2–7 nm Pt nanodots. During the formation of such unique nanostructures, POMs were found to serve as both catalyst and stabilizer. The size of the as-synthesized Pt nanospheres could be controlled solely by adjusting the molar ratio of POMs to H 2PtCl 6. A possible formation mechanism based on POMs-mediated electron transfer from ascorbic acid (AA) to PtCl 6 2− and AA-assisted aggregation was tentatively proposed to rationalize the formation of such nanostructures. Importantly, these specific Pt nanospheres exhibited good electrocatalytic activity towards the oxidation of methanol, making them promising for applications in direct methanol fuel cells.

Conducting supramolecular nanofibers and nanorods

Recent progress in the study of electroconducting nanomaterials such as nanofibers, nanorods and other nanostructures based on the supramolecular self-assembly of hexabenzocoronenes, oligo(thiophene)s, tetrathiafulvalenes and perylene-3,4,9,10-tetracarboxylic diimides is described in this tutorial review. Conducting nanofibers and nanorods are constructed by doping pi-donors or pi-acceptors with oxidants or reductants before/after the formation of such nanostructures; however, some nanofibers show electric conductivity without any doping in the neutral state. Although cation radicals and anion radicals seem to be difficult to form nanofibers and nanorods, a limited number of cation radicals produce conducting nanofibers. For nanofibers and nanorods composed of weak pi-donors and pi-acceptors, their conductivities are measured by time-resolved microwave conductivity techniques.

Facile Production of Self-Assembly Hierarchical Dumbbell-Like CoOOH Nanostructures and Their Room-Temperature CO-Gas-Sensing Properties

In this paper, we report a simple and novel coordination compound precursor route to synthesize the hierarchical dumbbell-like CoOOH nanostructures in high yield. A possible growth mechanism governing the formation of such nanostructures is discussed. The CO-gas-sensing properties of the as-synthesized nanostructures are investigated in detail. The dumbbell-like CoOOH nanostructures have a large active surface area of {110} facets, which can provide sufficient space for the interaction between CoOOH and the detected gases. As a result, the as-prepared dumbbell-like CoOOH nanostructures exhibit a superior sensitivity to CO at room temperature, as well as good reproducibility and short response/recovery times. The as-prepared CoOOH nanostructures could have potential applications in nanosensors.

Hydrothermal Growth of ZnO Nanorods Aligned Parallel to the Substrate Surface

Hydrothermal growth of ZnO nanorods with their c-axis aligned parallel to the surface of a Si (100) wafer substrate is demonstrated. With appropriate choice of process conditions (precursor concentrations, solution temperature, growth time), the (002) face of such nanorods is seen to support the emergence of as many as 10−20 aligned ZnO nanowires, with diameters of ∼50 nm and lengths that can extend to several micrometers. Similar growth of parallel nanorods/nanowires is observed on an amorphous carbon film surface. The influence of the substrate surface on the formation of such nanostructures is discussed. Such demonstrations of nanorod/nanowire growth parallel to a substrate surface could prove helpful in future nanodevice fabrication strategies.

A facile coordination compound precursor route to controlled synthesis of Co3O4 nanostructures and their room-temperature gas sensing properties

We report a simple and novel coordination compound precursor route to synthesize shape-controlled Co3O4 nanostructures. The resultant morphologies of the nanostructures can be tailored by controlling the reaction temperature and the sodium hydroxide concentrations during the growth process. Temperature was found to play an important role in the formation of CoOOH nanosheets and Co3O4 nanooctahedra. A too low temperature (<100 °C) is disadvantageous for the formation of regular hexagonal CoOOH nanosheets and a too high temperature (>200 °C) is unfavourable for the formation of Co3O4 nanooctahedra. At a certain temperature, sodium hydroxide concentration is also crucial for the formation of different shapes of Co3O4 nanostructures. A possible growth mechanism governing the formation of such nanostructures is discussed. The gas sensing properties of the as-synthesized nanostructures are investigated in detail, which reveals that the as-prepared Co3O4 nanostructures exhibit superior sensitivity to CO and CH4 relative to bulk Co3O4 at room temperature, as well as good reproducibility and short response/recovery times. The as-prepared Co3O4 nanostructures could have potential applications in nanosensors.