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Showing papers in "Advanced Materials in 2006"


Journal ArticleDOI
TL;DR: In this article, the authors presented a review of several organic photovoltaics (OPV) technologies, including conjugated polymers with high-electron-affinity molecules like C60 (as in the bulk-heterojunction solar cell).
Abstract: There has been an intensive search for cost-effective photovoltaics since the development of the first solar cells in the 1950s. [1–3] Among all alternative technologies to silicon-based pn-junction solar cells, organic solar cells could lead the most significant cost reduction. [4] The field of organic photovoltaics (OPVs) comprises organic/inorganic nanostructures like dyesensitized solar cells, multilayers of small organic molecules, and phase-separated mixtures of organic materials (the bulkheterojunction solar cell). A review of several OPV technologies has been presented recently. [5] Light absorption in organic solar cells leads to the generation of excited, bound electron– hole pairs (often called excitons). To achieve substantial energy-conversion efficiencies, these excited electron–hole pairs need to be dissociated into free charge carriers with a high yield. Excitons can be dissociated at interfaces of materials with different electron affinities or by electric fields, or the dissociation can be trap or impurity assisted. Blending conjugated polymers with high-electron-affinity molecules like C60 (as in the bulk-heterojunction solar cell) has proven to be an efficient way for rapid exciton dissociation. Conjugated polymer–C60 interpenetrating networks exhibit ultrafast charge transfer (∼40 fs). [6,7] As there is no competing decay process of the optically excited electron–hole pair located on the polymer in this time regime, an optimized mixture with C60 converts absorbed photons to electrons with an efficiency close to 100%. [8] The associated bicontinuous interpenetrating network enables efficient collection of the separated charges at the electrodes. The bulk-heterojunction solar cell has attracted a lot of attention because of its potential to be a true low-cost photovoltaic technology. A simple coating or printing process would enable roll-to-roll manufacturing of flexible, low-weight PV modules, which should permit cost-efficient production and the development of products for new markets, e.g., in the field of portable electronics. One major obstacle for the commercialization of bulk-heterojunction solar cells is the relatively small device efficiencies that have been demonstrated up to now. [5] The best energy-conversion efficiencies published for small-area devices approach 5%. [9–11] A detailed analysis of state-of-the-art bulk-heterojunction solar cells [8] reveals that the efficiency is limited by the low opencircuit voltage (Voc) delivered by these devices under illumination. Typically, organic semiconductors with a bandgap of about 2 eV are applied as photoactive materials, but the observed open-circuit voltages are only in the range of 0.5–1 V. There has long been a controversy about the origin of the Voc in conjugated polymer–fullerene solar cells. Following the classical thin-film solar-cell concept, the metal–insulator–metal (MIM) model was applied to bulk-heterojunction devices. In the MIM picture, Voc is simply equal to the work-function difference of the two metal electrodes. The model had to be modified after the observation of the strong influence of the reduction potential of the fullerene on the open-circuit volt

4,816 citations


Journal ArticleDOI
TL;DR: This work highlights recent developments in engineering uncrosslinked and crosslinked hydrophilic polymers for biomedical and biological applications and shows how such systems' intelligent behavior can be used in sensors, microarrays, and imaging.
Abstract: Hydrophilic polymers are the center of research emphasis in nanotechnology because of their perceived “intelligence”. They can be used as thin films, scaffolds, or nanoparticles in a wide range of biomedical and biological applications. Here we highlight recent developments in engineering uncrosslinked and crosslinked hydrophilic polymers for these applications. Natural, biohybrid, and synthetic hydrophilic polymers and hydrogels are analyzed and their thermodynamic responses are discussed. In addition, examples of the use of hydrogels for various therapeutic applications are given. We show how such systems’ intelligent behavior can be used in sensors, microarrays, and imaging. Finally, we outline challenges for the future in integrating hydrogels into biomedical applications.

3,524 citations


Journal ArticleDOI
TL;DR: A review of the progress made in the last ten years concerning the synthesis of porous carbon materials is summarized in this paper, where several different routes have been used to synthesize mesoporous carbon materials.
Abstract: In this review, the progress made in the last ten years concerning the synthesis of porous carbon materials is summarized. Porous carbon materials with various pore sizes and pore structures have been synthesized using several different routes. Microporous activated carbons have been synthesized through the activation process. Ordered microporous carbon materials have been synthesized using zeolites as templates. Mesoporous carbons with a disordered pore structure have been synthesized using various methods, including catalytic activation using metal species, carbonization of polymer/polymer blends, carbonization of organic aerogels, and template synthesis using silica nanoparticles. Ordered mesoporous carbons with various pore structures have been synthesized using mesoporous silica materials such as MCM-48, HMS, SBA-15, MCF, and MSU-X as templates. Ordered mesoporous carbons with graphitic pore walls have been synthesized using soft-carbon sources that can be converted to highly ordered graphite at high temperature. Hierarchically ordered mesoporous carbon materials have been synthesized using various designed silica templates. Some of these mesoporous carbon materials have successfully been used as adsorbents for bulky pollutants, as electrodes for supercapacitors and fuel cells, and as hosts for enzyme immobilization. Ordered macroporous carbon materials have been synthesized using colloidal crystals as templates. One-dimensional carbon nanostructured materials have been fabricated using anodic aluminum oxide (AAO) as a template.

1,904 citations


Journal ArticleDOI
TL;DR: In this paper, a survey of the recent achievements in the construction of surfaces with special wettabilities, such as superhydrophobicity, super-hydrophilicity and superoleophobicity, are presented.
Abstract: Recent achievements in the construction of surfaces with special wettabilities, such as superhydrophobicity, superhydrophilicity, superoleophobicity, superoleophilicity, superamphiphilicity, superamphiphobicity, superhydrophobicity/superoleophilicity, and reversible switching between superhydrophobicity and superhydrophilicity, are presented. Particular attention is paid to superhydrophobic surfaces created via various methods and surfaces with reversible superhydrophobicity and superhydrophilicity that are driven by various kinds of external stimuli. The control of the surface micro-/nanostructure and the chemical composition is critical for these special properties. These surfaces with controllable wettability are of great importance for both fundamental research and practical applications.

1,882 citations


Journal ArticleDOI
TL;DR: In this paper, an optical spacer between the active layer and the Al electrode is proposed to redistribute the light intensity inside the device by introducing an optical sensor. But the spacer is not suitable for the case of thin-film photovoltaic cells.
Abstract: reported under AM1.5 (AM: air mass) illumination, this efficiency is not sufficient to meet realistic specifications for commercialization. The need to improve the light-to-electricity conversion efficiency requires the implementation of new materials and the exploration of new device architectures. Polymer-based photovoltaic cells are thin-film devices fabricated in the metal-insulator-metal configuration sketched in Figure 1a. The absorbing and charge-separating bulk-heterojunction layer with a thickness of approximately 100 nm is sandwiched between two charge-selective electrodes; a transparent bilayer electrode comprising poly(3,4-ethylenedioxylenethiophene):polystyrene sulfonic acid (PEDOT:PSS) on indium tin oxide (ITO) glass for collecting the holes and a lower-work-function metal (here, Al) for collecting the electrons. The work-function difference between the two electrodes provides a built-in potential that breaks the symmetry, thereby providing a driving force for the photogenerated electrons and holes toward their respective electrodes. Because of optical interference between the incident (from the ITO side) and back-reflected light, the intensity of the light is zero at the metallic (Al) electrode; Figure 1a shows a schematic representation of the spatial distribution of the squared optical electric-field strength. [9–11] Thus, a relatively large fraction of the active layer is in a dead-zone in which the photogeneration of carriers is significantly reduced. Moreover, this effect causes more electron–hole pairs to be produced near the ITO/PEDOT:PSS electrode, a distribution which is known to reduce the photovoltaic conversion efficiency. [12,13] This “optical interference effect” is especially important for thin-film structures where layer thicknesses are comparable to the absorption depth and the wavelength of the incident light, as is the case for photovoltaic cells fabricated from semiconducting polymers. In order to overcome these problems, one might simply increase the thickness of the active layer to absorb more light. Because of the low mobility of the charge carriers in the polymer:C60 composites, however, the increased internal resistance of thicker films will inevitably lead to a reduced fill factor. An alternative approach is to change the device architecture with the goal of spatially redistributing the light intensity inside the device by introducing an optical spacer between the active layer and the Al electrode as sketched in Figure 1a. [11] Although this revised architecture would appear to solve the problem, the prerequisites for an ideal optical spacer limit the choice of materials: the layer must be a good acceptor and an electron-transport material with a conduction band edge lower in energy than that of the lowest unoccupied molecular orbital (LUMO) of C60; the LUMO must be above (or close to) the Fermi energy of the collecting metal electrode; and it must be transparent to light with wavelengths within the solar spectrum.

1,630 citations



Journal ArticleDOI
TL;DR: A review of the progress in the area of mechanical reinforcement of polymers using carbon nanotubes can be found in this paper, where the main methods described in the literature to produce and process polymer-nanotube composites are considered and analyzed.
Abstract: Owing to their unique mechanical properties, carbon nanotubes are considered to be ideal candidates for polymer reinforcement. However, a large amount of work must be done in order to realize their full potential. Effective processing of nanotubes and polymers to fabricate new ultra-strong composite materials is still a great challenge. This Review explores the progress that has already been made in the area of mechanical reinforcement of polymers using carbon nanotubes. First, the mechanical properties of carbon nanotubes and the system requirements to maximize reinforcement are discussed. Then, main methods described in the literature to produce and process polymer–nanotube composites are considered and analyzed. After that, mechanical properties of various nanotube–polymer composites prepared by different techniques are critically analyzed and compared. Finally, remaining problems, the achievements so far, and the research that needs to be done in the future are discussed.

1,557 citations


Journal ArticleDOI
TL;DR: In this paper, three general approaches (template assisted, anodic oxidation, and alkaline hydrothermal) for the preparation of nanostructured titanate and TiO2 are reviewed.
Abstract: Tubular and fibrous nanostructures of titanates have recently been synthesized and characterized. Three general approaches (template assisted, anodic oxidation, and alkaline hydrothermal) for the preparation of nanostructured titanate and TiO2 are reviewed. The crystal structures, morphologies, and mechanism of formation of nanostructured titanates produced by the alkaline hydrothermal method are critically discussed. The physicochemical properties of nanostructured titanates are highlighted and the links between properties and applications are emphasized. Examples of early applications of nanostructured titanates in catalysis, photocatalysis, electrocatalysis, lithium batteries, hydrogen storage, and solar-cell technologies are reviewed. The stability of titanate nanotubes at elevated temperatures and in acid media is considered.

1,543 citations


Journal ArticleDOI
TL;DR: In this paper, the synthesis of novel 3D flower-like iron oxide nanostructures by an ethylene glycol (EG)-mediated self-assembly process is reported, which can be used to further understand the mechanism of self-organization and expand the applications of IR nanomaterials.
Abstract: 3D nanostructures have attracted much attention because of their unique properties and potential applications. The simplest synthetic route to 3D nanostructures is probably selfassembly, in which ordered aggregates are formed in a spontaneous process. However, it is still a big challenge to develop simple and reliable synthetic methods for hierarchically selfassembled architectures with designed chemical components and controlled morphologies, which strongly affect the properties of nanomaterials. Iron oxides have been extensively studied in diverse fields including catalysis, environment protection, sensors, magnetic storage media, and clinical diagnosis and treatment. Various iron oxide structures, such as nanocrystals, particles, cubes, spindles, rods, wires, tubes, and flakes, have been successfully fabricated by a variety of methods. However, the self-assembly of these low-dimensional building blocks into complex 3D ordered nanostructures is still considerably more difficult. In order to further understand the mechanism of self-organization and expand the applications of iron oxide nanomaterials, self-assembled iron oxide 3D nanostructures need to be explored in more detail. Herein, we report the synthesis of novel 3D flowerlike iron oxide nanostructures by an ethylene glycol (EG)-mediated self-assembly process. Such a method has been adopted previously for the preparation of V2O5 hollow microspheres, [7]

1,508 citations


Journal ArticleDOI
TL;DR: In this article, a systematic review of current research on biomedical applications of layer-by-layer assembly is presented, where the structure and bioactivity of biomolecules in thin films fabricated by layer by layer assembly are introduced.
Abstract: The design of advanced, nanostructured materials at the molecular level is of tremendous interest for the scientific and engineering communities because of the broad application of these materials in the biomedical field. Among the available techniques, the layer-by-layer assembly method introduced by Decher and co-workers in 1992 has attracted extensive attention because it possesses extraordinary advantages for biomedical applications: ease of preparation, versatility, capability of incorporating high loadings of different types of biomolecules in the films, fine control over the materials’ structure, and robustness of the products under ambient and physiological conditions. In this context, a systematic review of current research on biomedical applications of layer-by-layer assembly is presented. The structure and bioactivity of biomolecules in thin films fabricated by layer-by-layer assembly are introduced. The applications of layer-bylayer assembly in biomimetics, biosensors, drug delivery, protein and cell adhesion, mediation of cellular functions, and implantable materials are addressed. Future developments in the field of biomedical applications of layer-by-layer assembly are also discussed.

1,248 citations




Journal ArticleDOI
TL;DR: The LPI-ARTICLE-2006-008doi:10.1002/adma.200502540View record in Web of Science Record created on 2006-05-03, modified on 2016-08-08 as discussed by the authors.
Abstract: Reference LPI-ARTICLE-2006-008doi:10.1002/adma.200502540View record in Web of Science Record created on 2006-05-03, modified on 2016-08-08


Journal ArticleDOI
Shouheng Sun1
TL;DR: In this paper, a review of recent advances in chemical synthesis, self-assembly, and potential applications of monodisperse binary FePt nanoparticles is presented. And the surface, structural, and magnetic properties of these nanoparticles are discussed, along with three potential applications in data storage, permanent magnetic nanocomposites, and biomedicine.
Abstract: This paper reviews recent advances in chemical synthesis, self-assembly, and potential applications of monodisperse binary FePt nanoparticles. After a brief introduction to nanomagnetism and conventional processes of fabricating FePt nanoparticles, the paper focuses on recent developments in solution-phase syntheses of monodisperse FePt nanoparticles and their self-assembly into nanoparticle superlattices. The paper further outlines the surface, structural, and magnetic properties of the FePt nanoparticles and gives examples of three potential applications in data storage, permanent magnetic nanocomposites, and biomedicine.

Journal ArticleDOI
TL;DR: A number of short peptide amphiphiles consisting of dipeptides linked to fluorenylmethoxycarbonyl spontaneously form fibrous hydrogels under physiological conditions, and the gels support the three-dimensional cell culture of chondrocytes.
Abstract: A number of short peptide amphiphiles consisting of dipeptides linked to fluorenylmethoxycarbonyl spontaneously form fibrous hydrogels under physiological conditions (see figure). The structural and physical properties of these gels are dictated by the amino acid sequence of the peptide building blocks, and the gels support the three-dimensional cell culture of chondrocytes.


Journal ArticleDOI
TL;DR: A method to prepare conducting-polymer nanotubes that can be used for precisely controlled drug release and significantly decrease the impedance and increase the charge capacity of the recording electrode sites on microfabricated neural prosthetic devices is reported on.
Abstract: The ability to create materials with well-controlled structures on the nanometer length scale is of intense interest for a variety of applications,[1,2] including controlled drug delivery[3] and biomedical devices.[4] Preparing nanoscale objects using self-assembly and templated growth techniques has been described in some recent reviews.[2,5] For example, porous membranes can be used to synthesize desired materials within the pores.[4,6] Conducting polymers are of considerable interest for a variety of biomedical applications.[7] Their response to electrochemical oxidation or reduction can produce a change in conductivity, color,[8,9] and volume.[10] A change in the electronic charge is accompanied by an equivalent change in the ionic charge, which requires mass transport between the polymer and electrolyte.[11] When counterions enter a polymer it expands and when they exit it contracts. The extent of expansion or contraction depends on the number and size of ions exchanged.[12] Electrochemical actuators using conducting polymers based on this principle have been developed by several investigators.[13–15] They can be doped with bioactive drugs, and can be used in actuators such as microfluidic pumps.[16,17] The precisely controlled local release of anti-inflammatory drugs at desired points in time is important for treating the inflammatory response of neural prosthetic devices in the central and peripheral nervous systems.[18] Here we report on a method to prepare conducting-polymer nanotubes that can be used for precisely controlled drug release. The fabrication process involves electrospinning of a biodegradable polymer, into which a drug has been incorporated, followed by electrochemical deposition of a conducting-polymer around the drug-loaded, electrospun biodegradable polymers. The conducting-polymer nanotubes significantly decrease the impedance and increase the charge capacity of the recording electrode sites on microfabricated neural prosthetic devices. The drugs can be released from the nanotubes in a desired fashion by electrical stimulation of the nanotubes; this process presumably proceeds by a local dilation of the tube that then promotes mass transport.


Journal ArticleDOI
TL;DR: Templated self-assembly of block copolymers as discussed by the authors provides a path towards the rational design of hierarchical device structures with periodic features that cover several length scales, and provides a promising route to control bottom-up self-organization processes through top-down lithographic templates.
Abstract: One of the key challenges in nanotechnology is to control a self-assembling system to create a specific structure. Self-organizing block copolymers offer a rich variety of periodic nanoscale patterns, and researchers have succeeded in finding conditions that lead to very long range order of the domains. However, the array of microdomains typically still contains some uncontrolled defects and lacks global registration and orientation. Recent efforts in templated self-assembly of block copolymers have demonstrated a promising route to control bottom-up self-organization processes through top-down lithographic templates. The orientation and placement of block-copolymer domains can be directed by topographically or chemically patterned templates. This templated self-assembly method provides a path towards the rational design of hierarchical device structures with periodic features that cover several length scales.


Journal ArticleDOI
TL;DR: In this article, the authors reported a strategy to simultaneously increase the ductility and strength of bulk nanostructured materials, by engineering very small second-phase particles into a nanometre Al alloy matrix, while further gaining rather than sacrificing its yield strength.
Abstract: In this paper we report a strategy to simultaneously increase the ductility and strength of bulk nanostructured materials. By engineering very small second-phase particles into a nanostructured Al alloy matrix, we were able to more than double its uniform elongation, while further gaining rather than sacrificing its yield strength. The simultaneous enhancement of ductility and strength is due to the increased dislocation accumulation and resistance to dislocation-slip by second-phase particles, respectively. Our strategy is applicable to many nanostructured alloys and composites, and paves a way for their large-scale industrial applications. The material used in this model study is 7075 Al alloy. The alloy was solution-treated to obtain a coarse-grained (CG) solid solution. The CG sample was immediately cryogenically rolled to produce nanostructures with an average grain size of ca. 100 nm (designated as NS sample). The NS sample was then aged at low temperature to introduce very small secondphase particles (designated as NS+P sample). The engineering stress–strain curves of these samples are compared in Figure 1a. The 0.2 % yield strengths (marked by circles) of the CG, NS, and NS+P samples are 145 MPa, 550 MPa, and 615 MPa, respectively. Therefore, the low-temperature aging enhanced the yield strength of the NS sample by 12 %. The uniform elongation (marked by the symbol on the curves in Fig. 1a) was determined by the Considere criterion (Eq. 1) governing the onset of localized deformation [8]

Journal ArticleDOI
TL;DR: In this paper, a new class of supercapacitors based on nanocrystalline vanadium nitride is reported, which can deliver an impressive specific capacitance of 1340 F g when tested at a scan rate of 2 mV s.
Abstract: Supercapacitors have been known for over thirty years but of late are emerging as attractive electrochemical energy-storage and conversion devices for future electrical vehicle application with complementary electrochemical characteristics to rechargeable batteries and fuel cells. Amongst the numerous materials studied to date, various forms of ruthenium oxides are clearly noteworthy, exhibiting superior electrochemical response. Unfortunately, the expensive nature of ruthenium has limited its technological viability. A new class of supercapacitors based on nanocrystalline vanadium nitride is reported here, which can deliver an impressive specific capacitance of 1340 F g when tested at a scan rate of 2 mV s. An even more impressive capacitance of 554 F g is noted at a higher scan rate of 100 mV s. Such a high capacitance, which exceeds that of RuO2·nH2O, is believed to be caused by a series of reversible redox reactions through hydroxy bonding confined to a few atomic layers of vanadium oxide on the surface of the underlying nitride nanocrystals, which exhibit a metallic electronic conductivity (rbulk = 1.67 × 10 6 X m). Such a modification of the nanocrystal surface chemistry may lead to the development of supercapacitors that exhibit very high and stable power densities. Supercapacitors are generally classified into electrical double layer capacitors (EDLCs), which build up electrical charge at the electrode/electrolyte interface as described by the Gouy–Chapman–Stern–Grahame model, and pseudocapacitors, which utilize a redox reaction at the interface at certain potentials. Both rely on the physicochemical changes that occur at the electrode/electrolyte interface. Hence, understanding the surface properties is crucial for achieving high power and energy densities. High-surface-area carbon-based materials are widely studied for EDLCs. On the other hand, crystalline RuO2 [1–3,7] and amorphous RuO2·nH2O [1,4–6] are well-known pseudocapacitors that exhibit a specific capacitance as high as 350 and 720 F g, respectively, due to the redox activity via proton adsorption in an acidic electrolyte. Despite the expensive nature of ruthenium oxide, it has been the focus of intense research since Ru offers a variety of oxidation states (II–IV) while exhibiting good electronic conductivity (rbulk = 2.8 × 10 6 X m). Vanadium also exhibits numerous oxidation states (II–V) similar to that of ruthenium in V2O5·nH2O, but its poor electronic conductivity (rbulk ≈ 1 ∼ 10 X m) renders the oxide unsuitable for use in high-rate electrochemical devices. However, exploiting the good electronic conductivity of the vanadium nitrides combined with the variety of oxidation states exhibited by V in vanadium oxides could lay the foundation for a new class of high-performance supercapacitors. The synthesis of these nanocrystalline vanadium nitrides with controlled surface oxidation (as in the present study) results in a unique class of supercapacitors without much loss in the overall electrical conductivity. Furthermore, the low cost, high molar density (≈6 g cm), and good chemical resistance of the transition metal nitrides render them excellent candidates for the next generation of supercapacitors. Although no detailed studies have been conducted, in the past Thompson and co-workers have explored transition metal nitrides and carbides for supercapacitors with moderate specific capacitances (< 226 F g). Amorphous V2O5·nH2O has also been tested for its supercapacitor response, but despite mixing a large amount of carbon (25 wt.-%) to improve its poor electronic conductivity (see above), the highest specific capacitance reported to date is 350 F g at a scan rate of 5 mV s. In this study, a low-temperature route based on a two-step ammonolysis reaction of VCl4 in anhydrous chloroform is used to synthesize nanocrystalline VN (see Experimental). The nanometer-sized crystals increase the susceptibility for surface oxidation, while the high surface area of the nitrides provides more redox-reaction sites. Such a VCl4/NH3 reaction, although known, tends to be largely influenced by the type of solvent used. X-ray diffraction (XRD) and highresolution transmission electron microscopy (HRTEM) are used to characterize the as-prepared and heat-treated VN nanocrystals. The as-prepared precursor consists of amorphous V(NH2)3Cl and crystalline NH4Cl, which transforms into the rock salt (Fm3m)-structured VN at 400 °C, which is C O M M U N IC A TI O N S

Journal ArticleDOI
TL;DR: In this article, a buffer film with a thickness of only several nanometers interposed between the electrode and electrolyte materials is proposed to improve the high-rate capability of solid-state lithium batteries.
Abstract: Rechargeable lithium batteries are widely used in portable equipment today. However, there have always been safety issues arising from their combustible organic electrolytes. These issues are becoming more serious with the increasing size of batteries for use in electric vehicle (EV) or load-leveling applications. Nonflammable solid electrolytes would be the ultimate solution to the safety issue. Despite their high safety, the energy densities and power densities of solid systems have been too low for their practical use. We have succeeded in increasing their energy densities to levels comparable to those of liquid ones. However, power densities, or high-rate capabilities, remain poor. In this communication, we report that a buffer film with a thickness of only several nanometers interposed between the electrode and electrolyte materials improves the high-rate capability of solid-state lithium batteries. Low ionic conductivities of solid electrolytes have been the reason for the poor high-rate capability of solid-state lithium batteries. Although the conductivities of recently discovered solid electrolytes (> 10 S cm) are slightly lower than those observed for liquid electrolytes, Li ionic conduction in the solid electrolytes has become as fast as that of liquid electrolytes, by taking into account the fact that the transport number of ions in inorganic electrolytes is unity. However, the high-rate capability of solid systems, including solid electrolytes, remains inferior. This fact strongly suggests that the rate-controlling step is not in the bulk of the solid electrolytes, but at the interface between the electrode and the electrolyte materials. Ionic conduction at interfaces between different kinds of ionic conductors, or heterojunctions, is characterized by the term “nanoionics”; a frontier study was done for a LiI– Al2O3 composite, [7] and a sophisticated example was presented by Sata et al. In the latter, two kinds of F ion conductors, BaF2 and CaF2, were brought into contact with each other. Part of the F ions then transferred from one side to the other to reach an equilibrium, which produced vacancies in the former and interstitial ions in the latter, both of which contributed to ionic conduction at the interface and enhanced the ionic conduction. Similar nanoionic phenomena should take place at the interface between the electrode and the electrolyte materials, forming a space-charge layer. Because the compositions and structures of solid electrolytes have been well tailored to achieve high ionic conductivities, the ionic conductivity of the space-charge layer, where the compositions deviate from the optima, should be lower than that of the bulk, increasing the interfacial resistance. For instance, the Li4GeS4–Li3PS4 (thio-LISICON) system used in the present study has a high ionic conductivity of the order of 10 S cm at its optimum composition. However, variation in the composition reduces it to 10 S cm. The detrimental increase in the interfacial resistance would be prominent in bulk-type or non-thin-film solid-state lithium batteries. Sulfide electrolytes should be used in such batteries, because the ionic conductivities of oxide solid electrolytes, for example, are so low that they are available only in thin-film systems. On the other hand, the cathode should be an oxide, such as LiCoO2, because of its high electrode potential. [10,11]



Journal ArticleDOI
TL;DR: In this article, the biodegradability and biocompatibility of ZnO nanowires were investigated in deionized water and ammonium tetroxide (AT) solution.
Abstract: Fabrication of nanoscale biosensors based on nanowires (NWs), nanotubes (NTs), and other nanomaterials has recently attracted enormous attention. In comparison to nanoparticles, 1D NWs and NTs have higher sensitivity because of depletion or accumulation of charge carriers at the surface that is caused by binding of charged biological macromolecules at the surface, and affects the entire cross-sectional conduction pathway. Among all 1D nanomaterials, Si NWs and carbon NTs are the most studied materials as biosensors. Functionalized Si NWs and carbon NTs have been demonstrated for detecting proteins, DNA and DNA sequence variations, and cancer markers. However, the biocompatibility and biodegradability of these nanostructures remain to be studied. For example, carbon NTs injected into human blood vessels might accumulate and occlude capillaries in the human brain, which could cause serious damage or be fatal. Being a key functional material with versatile properties, such as dual semiconducting and piezoelectric properties, ZnO has important applications in optoelectronic devices, sensors, lasers, transducers, and photovoltaic devices. In addition, the morphology and the dopant concentration of ZnO nanostructures can be well controlled by tuning the growth conditions, which further broadens their applications. ZnO nanoparticles are believed to be nontoxic, biosafe, and possibly biocompatible, and have been used in many applications in our daily life, such as drug carriers and cosmetics. However, no literature is available on the biodegradability and biocompatibility of ZnO nanowires or nanobelts, which is crucial for the application of ZnO nanostructure for biosensing. In this paper, we present the first study on biodegradability and biocompatibility of ZnO wires. We have conducted a systematic study on the etching and dissolving behavior of ZnO NWs in various solutions with moderate pH values, including deionized water, ammonia, NaOH solution, and horse blood serum. The result shows that ZnO can be dissolved by deionized water (pH≈ 4.5–5.0), ammonia (pH≈ 7.0–7.1, 8.7–9.0) and NaOH solution (pH≈ 7.0–7.1, 8.7–9.0). The study of the interaction of ZnO wires with horse blood serum shows that the ZnO wires can survive in the fluid for a few hours before they eventually degrade into mineral ions. The results of this study are of great significance. First, biosensors made of ZnO nonmaterial have a certain time to perform a device function. Secondly, once completing the corresponding service, the ZnO wires can eventually dissolve into ions that can be completely absorbed by the body and become part of the nutrition. The biodegradability and biocompatibility of ZnO NWs would allow their use for in vivo biosensing and biodetection. Synthesized by a vapor–solid growth process, the ZnO wires used in our study grew along the [0001] direction with a hexagonal cross section and were of high crystalline quality. We studied the dissolving behavior of ZnO wires in deionized water (pH≈ 4.5–5.0), ammonia (pH≈ 7.0–7.1, 8.7–9.0), NaOH solution (pH≈ 7.0–7.1, 8.7–9.0), horse blood serum solution (pH≈ 7.9–8.2), and pure horse blood serum (pH≈ 8.5). The two kinds of ammonia used in our study were prepared by diluting concentrated ammonia with deionized water. The two kinds of NaOH solution were prepared by dissolving solid NaOH in deionized water, and the horse blood serum solution was prepared by diluting pure horse blood serum with NaOH solution (pH≈ 7.0–7.1) with a volume ratio of 1:10. We adopted two processes to investigate the dissolving behavior of a single ZnO wire in different liquids. To study the dissolving process of ZnO wires in deionized water, ammonia, and NaOH solution, we used Process 1 illustrated in Figure 1a. Individual ZnO NWs were firstly manipulated with a pin and placed on a silicon substrate. After that, a droplet of C O M M U N IC A TI O N S

Journal ArticleDOI
TL;DR: In this article, the authors proposed to use a layer-by-layer (LbL) deposition of oppositely charged species (polyelectrolytes, nanoparticles, enzymes, dendrimers) from their solutions on the substrate surface to prepare reservoirs with regulated storage/release properties assembled with nanometer-thickness precision.
Abstract: The corrosion of metals is one of the main destructive processes that leads to huge economic losses. Polymer coating systems are normally applied on a metal surface to provide a dense barrier against the corrosive species in order to protect metal structures from corrosive attack. When the barrier is damaged and the corrosive agents penetrate to the metal surface the coating system can not stop the corrosion process. The most effective solution so far for designing anticorrosion coatings for active protection of metals is to employ chromate-containing conversion coatings. However, hexavalent chromium species are responsible for several diseases, including DNA damage and cancer, which is the main reason for banning Cr-containing anticorrosion coatings in Europe from 2007. The deposition of thin inorganic or hybrid films on metallic surfaces has been suggested as a pretreatment to provide an additional barrier against the corrosion species and mainly to improve adhesion between the metal and polymer coating system. The films are usually deposited by the plasma polymerization technique or the sol–gel route. Sol–gel-derived thin films that contain either inorganic (phosphates, vanadates, borates, and cerium and molybdenum compounds) or organic (phenylphosphonic acid, mercaptobenzothiazole, mercaptobenzoimidazole, triazole) inhibitors are investigated as substitutes for chromates. Among them, the highest activity is shown for sol–gel coatings with a cerium dopant of a critical concentration in the 0.2–0.6 wt % range. However, the negative effect of the free inhibitor occluded in the sol–gel matrix on the stability of the protective film is observed for all types of inhibitors (for instance, a higher concentration of Ce leads to the formation of microholes in the sol–gel film). This shortcoming calls for the development of nanometer-scale reservoirs to isolate an inhibitor inside and prevent its direct interaction with the sol–gel matrix. Nanoreservoirs should be homogeneously distributed in the film matrix and should possess controlled and corrosion-stimulated inhibitor release to cure corrosion defects. Mixed-oxide nanoparticles (e.g. ZrO2/CeO2), [4] b-cyclodextrin-inhibitor complexes, hollow polypropylene fibers, and conducting polyaniline have been explored as prospective reservoirs for corrosion inhibitors to be incorporated in the protective film. The common mechanism of the nanoreservoir activity is based on the slow release of inhibitor triggered by corrosion processes. Ion exchangers have also been investigated as ‘smart’ reservoirs for corrosion inhibitors. Chemically synthesized hydrocalmite behaves as an anion exchanger: adsorbing corrosive chloride ions and releasing corrosion-inhibiting nitrite anions. Despite considerable efforts devoted to the development of new, complex anticorrosion systems, practically no single solution is able to fulfill the requirements of sufficient corrosion protection while avoiding chromates in the coating, especially in the case of aluminum alloys used for aerospace applications. The recently developed technology of layer-by-layer (LbL) deposition of oppositely charged species (polyelectrolytes, nanoparticles, enzymes, dendrimers) from their solutions on the substrate surface represents an interesting approach to prepare reservoirs with regulated storage/release properties assembled with nanometer-thickness precision. LbL coatings are of practical interest in photonics (optical filters, luminescent coatings), electrocatalysis (electrodes for DNA transfer, enzyme-catalyzed oxidation), as membranes, and chemical reactors. LbL-assembled polyelectrolyte multilayers reveal controlled permeability properties. Depending on the nature of the assembled monolayers, the permeability of multilayer films can be controlled by changing pH, ionic strength, and temperature, or by applying magnetic or electromagnetic fields. Polyelectrolyte assemblies have never been used in corrosion-protection coatings, although storage of corrosion inhibitors in polyelectrolyte multilayers can confer several advantages: they can prevent a negative effect of the corrosion inhibitor on the stability of the coating, decrease the influence of the coating polymerization on the inhibitor, and provide intelligent release of the corrosion inhibitor, as the permeability C O M M U N IC A TI O N S

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TL;DR: In this article, the gallium-doped n-type ZnO with a thickness of 1.5 lm was grown on a c-Al2O3 substrate and showed excellent current-rectifying behavior with a threshold voltage of 3.2 V and an EL emission peak at 380 nm at room temperature.
Abstract: to improve the structural properties of n- and p-type ZnO compared to previous studies. [7] In addition, a thermal annealing process was carried out to activate the phosphorus dopants in p-type ZnO and improve the electrical and optical properties of the ZnO layers. The LED showed excellent current-rectifying behavior with a threshold voltage of 3.2 V and an EL emission peak at 380 nm at room temperature. The UV EL emission spectrum was in good agreement with the room-temperature photoluminescence (PL) spectrum of the p-type ZnO used in the LED. Furthermore, the near-bandedge emission was increased and the deep-level emission was decreased when (Mg,Zn)O alloy layers were introduced as energy barrier layers between n-type and p-type ZnO films to confine the carrier recombination process to the high-quality n-type ZnO film. A schematic diagram of the p–n homojunction ZnO LED is shown in Figure 1. The gallium-doped n-type ZnO with a thickness of 1.5 lm was grown on a c-Al2O3 substrate. It

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TL;DR: A review of some recent efforts to construct highly ordered assemblies of porphyrins, phthalocyanines, and perylenes by means of self-assembly in solution and on surfaces, and by attaching them to polymeric scaffolds is given in this paper.
Abstract: Porphyrins, phthalocyanines, and perylenes are compounds with great potential for serving as components of molecular materials that possess unique electronic, magnetic and photophysical properties. In general, a highly specific communication between a large number of these chromophores is required in order to express their function to a maximal level, and for this reason it is of importance to construct arrays in which the molecules are organized in well-defined geometries with respect to their neighbors. This review is an account of some recent efforts to construct highly ordered assemblies of porphyrins, phthalocyanines, and perylenes by means of self-assembly in solution and on surfaces, and by attaching them to polymeric scaffolds.