One-dimensional ZnO nanostructures: fabrication, optoelectronic properties, and device applications

One-dimensional (1D) zinc oxide (ZnO) nanostructures have been extensively and intensively studied for several decades not only for their extraordinary chemical and physical properties, but also for their current and future different electronic and optoelectronic device applications. This review provides a brief overview of the progress of different synthesis methods and applications of 1D-ZnO nanostructures. Morphology of ZnO nanostructures grown by various methods and progress in the optical properties are briefly described. Using low-temperature photoluminescence (LTPL) study, detailed informations about the defect states and impurity of such nanostructures are reported. Improvement of field emission properties by modifying the edge of 1D-ZnO nanostructures is briefly discussed. Applications such as different sensors, field effect transistor, light-emitting diodes (LEDs), and photodetector are briefly reviewed. ZnO has large exciton binding energy (60 meV) and wide band gap (3.37 eV), which could lead to lasing action based on exciton recombination. As semiconductor devices are being aggressively scaled down, ZnO 1D nanostructures based resistive switching (RS) memory (resistance random access memory) is very attractive for nonvolatile memory applications. Switching properties and mechanisms of Ga-doped and undoped ZnO nanorods/NWs are briefly discussed. The present paper reviews the recent activities of the growth and applications of various 1D-ZnO nanostructures for sensor, LED, photodetector, laser, and RS memory devices.     

Chlorophylls derivatives: Photophysical properties,assemblies, nanostructures and biomedical applications

Chlorophylls are one of the most abundant organic pigments on the earth, which play an important role in the photosynthesis of plants, algae and bacteria. With the development of chromatography and chemical synthesis technology, many new chlorophylls from nature have been identified, and similar typical heterocyclic macrocyclic chlorophyll derivatives have also been designed and synthesized. Their chemical structures have significantly affected the absorption of light, energy transfer efficiency, excited-state lifetime, etc. Inspired by the chlorophylls interactions in chloroplasts for light-harvesting, we realized that intramolecular assembly and the resultant nanostructures played a more prominent role in their photophysical and photochemical properties, even in further biomedical applications, such as photodynamic and photothermal therapy, photocatalytic diagnosis, as well as optical, photoacoustic, magnetic resonance and nuclear medical imaging. In this review, we discuss the photo-properties of chlorophylls, overview the driving forces of assembly, and summarize biomedical-relevant advantages incorporated supramolecular nanostructures. In particular, the dynamic assembly under physiological condition provides unpredictable and interesting biological effects, such as aggregation/assembly induced drug retention in disease areas, optimized biodistribution and optimized the pharmacokinetics. The labeling on the assembly also provides a useful tool for us to observe the self-assembled nanostructures in vivo in a non-invasive way. Through the elaboration of different examples of chlorophylls, we hope to provide some inspiration for the biomedical application design of chlorophylls derivatives.     

Bismuth telluride nanostructures: preparation,thermoelectric properties and topological insulating effect

Bismuth telluride is known to wield unique properties for a wide range of device applications. However, as devices migrate to the nanometer scale, significant amount of studies are being conducted to keep up with the rapidly growing nanotechnological field. Bi₂Te₃ possesses distinctive properties at the nanometer level from its bulk material. Therefore, varying synthesis and characterization techniques are being employed for the realization of various Bi₂Te₃ nanostructures in the past years. A considerable number of these works have aimed at improving the thermoelectric (TE) figure-of-merit (ZT) of the Bi₂Te₃ nanostructures and drawing from their topological insulating properties. This paper reviews the various Bi₂Te₃ and Bi₂Te₃-based nanostructures realized via theoretical and experimental procedures. The study probes the preparation techniques, TE properties and the topological insulating effects of 0D, 1D, 2D and Bi₂Te₃ nanocomposites. With several applications as a topological insulator (TI), the topological insulating effect of the Bi₂Te₃ is reviewed in detail with the time reversal symmetry (TRS) and surface state spins which characterize TIs. Schematics and preparation methods for the various nanostructural dimensions are accordingly categorized.     

Low dimensional silver nanostructures: synthesis, growth mechanism, properties and applications

This work presents a review of the recent advances on the low-dimensional (LD) silver nanostructures (e.g., one-dimensional nanorods and nanowires, and two-dimensional nanoplates and nanodisks). First, the methods, either physical or chemical, for the synthesis of silver LD nanostructures are introduced. Then, the use is discussed of advanced experimental techniques (e.g., transmission electron microscope, high-resolution transmission electron microscope, scanning electron microscope, atomic force microscope, ultraviolet-visible and Raman spectra) and theoretical techniques at different time and length scales from quantum mechanics (e.g., ab initio simulation and density function theory) to molecular dynamics method for understanding the principles of governing particle growth, as well as discrete dipolar approximate method for understanding the optical properties of different shapes and sizes of silver LD nanostructures. Subsequently, the functional applications of the LD silver nanostructures in different areas such optical, electronic, and sensing, particularly for those related to surface plasma resonance are summarized based on the recent findings. Finally, some perspectives and comments for future investigation of silver nanostructures are also briefly discussed.     

Biphasic calcium phosphate bioceramics: preparation, properties and applications

Biphasic calcium phosphate (BCP) bioceramics belong to a group of bone substitute biomaterials that consist of an intimate mixture of hydroxyapatite (HA), Ca₁₀(PO₄)₆(OH)₂, and beta-tricalcium phosphate (-TCP), Ca₃(PO₄)₂, of varying HA/-TCP ratios. BCP is obtained when a synthetic or biologic calcium-deficient apatite is sintered at temperatures at and above 700 °C. Calcium deficiency depends on the method of preparation (precipitation, hydrolysis or mechanical mixture) including reaction pH and temperature. The HA/-TCP ratio is determined by the calcium deficiency of the unsintered apatite (the higher the deficiency, the lower the ratio) and the sintering temperature. Properties of BCP bioceramics relating to their medical applications include: macroporosity, microporosity, compressive strength, bioreactivity (associated with formation of carbonate hydroxyapatite on ceramic surfaces in vitro and in vivo), dissolution, and osteoconductivity. Due to the preferential dissolution of the -TCP component, the bioreactivity is inversely proportional to the HA/-TCP ratio. Hence, the bioreactivity of BCP bioceramics can be controled by manipulating the composition (HA/-TCP ratio) and/or the crystallinity of the BCP. Currently, BCP bioceramics is recommended for use as an alternative or additive to autogeneous bone for orthopedic and dental applications. It is available in the form of particulates, blocks, customized designs for specific applications and as an injectible biomaterial in a polymer carrier. BCP ceramic can be used also as grit-blasting abrasive for grit-blasting to modify implant substrate surfaces. Exploratory studies demonstrate the potential uses of BCP ceramic as scaffold for tissue engineering, drug delivery system and carrier of growth factors.     

CuO nanowhiskers: preparation,structure features,properties, and applications

This paper presents the results of a detailed study of the structure of nanowhiskers (NWs) of copper oxide formed in the process of thermal oxidation. It is shown that NWs have a bi- or poly-crystalline structure with a growth direction [110]. It is noted that the formation of NWs is facilitated by the cooperation of internal stresses with the defective structure of the underlying coating, and they grow owing to surface diffusion of copper cations from the depth of the coating to the top of the whisker. It is established that NWs have a good sorption and photocatalytic ability that will allow their use in the chemical industry, including the areas of catalysis and photocatalysis.     

Macroscopic carbon nanotube assemblies: preparation, properties, and potential applications

As classical 1D nanoscale structures, carbon nanotubes (CNTs) possess remarkable mechanical, electrical, thermal, and optical properties. In the past several years, considerable attention has been paid to the use of CNTs as building blocks for novel high-performance materials. In this way, the production of macroscopic architectures based on assembled CNTs with controlled orientation and configurations is an important step towards their application. So far, various forms of macroscale CNT assemblies have been produced, such as 1D CNT fibers, 2D CNT films/sheets, and 3D aligned CNT arrays or foams. These macroarchitectures, depending on the manner in which they are assembled, display a variety of fascinating features that cannot be achieved using conventional materials. This review provides an overview of various macroscopic CNT assemblies, with a focus on their preparation and mechanical properties as well as their potential applications in practical fields.     

Glow discharge polymeric films: preparation,structure, properties and applications

Glow discharge polymerization is one of the most important vacuum techniques to produce thin polymer films. Thin films made by a glow discharge have some profitable properties like being very dense without pinholes, thermally stable and highly insulating. The films can be deposited on any substrate. These and other properties promote the application of such films. The deposition parameters influence the structure and the properties of the films. In some cases the influence of the used monomer and of the deposition parameters is of the same order. The polymerization was carried out with several aromatic mononitriles and dinitriles and their structure and properties were investigated. Glow discharge polymers from the structural point of view have much in common with a polymer which was partially thermally degraded. Structure and properties of the mononitriles and dinitriles glow discharge polymers show remarkable differences. From these differences a quantumchemical calculation of the monomers provides a possible explanation. The main application of thin films made by glow discharge polymerization is to passivate surfaces. Some other applications of interest are known, but to increase this field of application more knowledge is necessary of the relationship between the polymerization process and the chemical structure.     

Luminescent CdTe and CdSe semiconductor nanocrystals: preparation, optical properties and applications

The novel optical and electrical properties of luminescent semiconductor nanocrystals are appealing for ultrasensitive multiplexing and multicolor applications in a variety of fields, such as biotechnology, nanoscale electronics, and opto-electronics. Luminescent CdSe and CdTe nanocrystals are archetypes for this dynamic research area and have gained interest from diverse research communities. In this review, we first describe the advances in preparation of size- and shape-controlled CdSe and CdTe semiconductor nanocrystals with the organometallic approach. This article gives particular focus to water soluble nanocrystals due to the increasing interest of using semiconductor nanocrystals for biological applications. Post-synthetic methods to obtain water solubility, the direct synthesis routes in aqueous medium, and the strategies to improve the photoluminescence efficiency in both organic and aqueous phase are discussed. The shape evolution in aqueous medium via self-organization of preformed nanoparticles is a versatile and powerful method for production of nanocrystals with different geometries, and some recent advances in this field are presented with a qualitative discussion on the mechanism. Some examples of CdSe and CdTe nanocrystals that have been applied successfully to problems in biosensing and bioimaging are introduced, which may profoundly impact biological and biomedical research. Finally we present the research on the use of luminescent semiconductor nanocrystals for construction of light emitting diodes, solar cells, and chemical sensors, which demonstrate that they are promising building blocks for next generation electronics.     

Temperature-dependent controlled preparation of ZnO nanostructures and their photoluminescence properties

High purity and yield of ZnO nanobelts, nanocombs and nanowires have been synthesized using a simple catalyst-free vapor transport process and their growth mechanism and photoluminescence properties have been investigated. Transmission electron microscopy and selected-area electron diffraction analyses reveal that the intrinsic growth behaviors of ZnO vary with the growth temperature, leading to the formation of nanostructures with different morphologies. These ZnO nanostructures show a UV emission at about 385 nm and a broad green emission around 500 nm in their photoluminescence spectra, and the green to UV emission intensity ratio is determined by their microstructures.     

Electrospinning preparation of LaOBr:Tb3+ nanostructures and their photoluminescence properties

Tb³⁺-doped LaOBr nanostructures including nanofibers, nanobelts, and hollow nanofibers were synthesized for the first time via calcinating the electrospun polyvinyl pyrrolidone/[La(NO₃)₃ + Tb(NO₃)₃ + NH₄Br] composites. X-ray diffraction analysis revealed that LaOBr:Tb³⁺ nanostructures are tetragonal in structure with space group of P4/nmm. The morphologies and sizes of LaOBr:Tb³⁺ nanostructures were investigated using scanning electron microscope and transmission electron microscope. Under the excitation of 254-nm ultraviolet light, LaOBr:Tb³⁺ nanostructures exhibit the green emissions of predominant peak at 543 nm, which is ascribed to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. It is found that the optimum doping concentration of Tb³⁺ ions in the LaOBr:Tb³⁺ nanofibers is 3 %. Interestingly, we found that the luminescence intensity of hollow nanofibers is obviously greater than that of nanofibers and nanobelts for LaOBr:Tb³⁺ under the same measuring conditions. Moreover, the luminescence of LaOBr:Tb³⁺ nanostructures are located in the green region in Commission Internationale de L’Eclairage chromaticity coordinates diagram. The formation mechanisms of LaOBr:Tb³⁺ nanofibers, nanobelts, and hollow nanofibers were also proposed. LaOBr:Tb³⁺ nanostructures are promising nanomaterials for applications in the fields of light display systems and optoelectronic devices.     

Synthesis and electrical properties of graphene–manganese oxide hybrid nanostructures

Journal of Materials Science: Materials in Electronics - In the present contribution, grapheme–manganese oxide hybrid nanostructures (G/MnO2) were synthesized via rapid and facile microwave...     

Studies progress of preparation,properties and applications of hyper-cross-linked polystyrene networks

Hyper-cross-linked Polystyrene (H-PS) are prepared by an extensive post-cross-linking of linear polystyrene in solution or poly(styrene-co-divinylbenzene) in a highly swollen gel state using bifunctional alkylating agents in the presence of Friedel-Crafts catalyst. H-PS resins differ from conventional porous polymer materials due to their unusual pore structure and outstanding swelling performances in thermodynamically good and poor solvent. In this paper, recent studies progress of preparation, properties especially physical properties and various applications are presented.     

Synthesis,properties, and anti-reflective applications of new colorless polyimide-inorganic hybrid optical materials

We report the synthesis, properties and anti-reflective applications of new colorless polyimide-inorganic hybrid thin films prepared from 1,4-bis(3,4-dicarboxyphenoxy)-2,5-di-tert-butylbenzene dianhydride (DDBBDA)/oxydianiline (ODA) with silica or titania precursors. The experimental results suggest that the prepared hybrid films have good thermomechanical properties, excellent transparence, tunable refractive indices of 1.550–1.847, and low optical birefringence. The nanocrystalline titania domain size analyzed form TEM and XRD is in the range of 10–20 nm in the hybrid materials. Three-layer anti-reflective films on glass or polymer substrates processed from the hybrid precursors have a relatively low reflection of less than 0.5% in the visible range. These results indicate that the newly prepared colorless polyimide-inorganic hybrid materials have potential applications for optical devices.     

Recent progress in molten salt synthesis of low-dimensional perovskite oxide nanostructures,structural characterization,properties, and functional applications: A review

Molten salt synthesis (MSS) method has advantages of the simplicity in the process equipment, versatile and large-scale synthesis, and friendly environment, which provides an excellent approach to synthesize high pure oxide powders with controllable compositions and morphologies. Among these oxides, perovskite oxides with a composition of ABO3 exhibit a broad spectrum of physical properties and functions (e.g. ferroelectric, piezoelectric, magnetic, photovoltaic and photocatalytic properties). The downscaling of the spatial geometry of perovskite oxides into nanometers result in novel properties that are different from the bulk and film counterparts. Recent interest in nanoscience and nanotechnology has led to great efforts focusing on the synthesis of low-dimensional perovskite oxide nanostructures (PONs) to better understand their novel physical properties at nanoscale. Therefore, the low-dimensional PONs such as perovskite nanoparticles, nanowires, nanorods, nanotubes, nanofibers, nanobelts, and two dimensional oxide nanostructures, play an important role in developing the next generation of oxide electronics. In the past few years, much effort has been made on the synthesis of PONs by MSS method and their structural characterizations. The functional applications of PONs are also explored in the fields of storage memory, energy harvesting, and solar energy conversion. This review summarizes the recent progress in the synthesis of low-dimensional PONs by MSS method and its modified ways. Their structural characterization and physical properties are also scrutinized. The potential applications of low-dimensional PONs in different fields such as data memory and storage, energy harvesting, solar energy conversion, are highlighted. Perspectives concerning the future research trends and challenges of low-dimensional PONs are also outlined.     

Low-dimensional SiC nanostructures: Fabrication, luminescence, and electrical properties

Nanostructured silicon carbide has unique properties that make it useful in microelectronics, optoelectronics, and biomedical engineering. In this paper, the fabrication methods as well as optical and electrical characteristics of silicon carbide nanocrystals, nanowires, nanotubes, and nanosized films are reviewed. Silicon carbide nanocrystals are generally produced using two techniques, electrochemical etching of bulk materials to form porous SiC or embedding SiC crystallites in a matrix such as Si. Luminescence from SiC crystallites prepared by these two methods is generally believed to stem from surface or defect states. Stable colloidal 3C-SiC nanocrystals which exhibit intense visible photoluminescence arising from the quantum confinement effects have recently be produced. The field electron emission and photoluminescence characteristics of silicon carbide nanostructures as well as theoretical studies of the structural and electronic properties of the materials are described.     

The preparation,mechanical and dielectric properties of PEN/HBCuPc hybrid films

Polyarylene ether nitriles (PEN)/hyperbranched copper phthalocyanine (HBCuPc) hybrid films have been successfully fabricated via PEN mixing with HBCuPc in N-methylpyrrolidone solution, solution-casting and then co-crosslinking at high temperature. The dielectric properties of the films were measured to find that dielectric constant as well as dielectric loss of the hybrid films increased linearly with the increasing HBCuPc content without sacrificing dielectric breakdown strength compared to that of the pristine polymer. These results shows PEN/HBCuPc hybrid films have a high dielectric constant and low dielectric loss at a high operational frequency (>1 kHz). The tensile strength and elongation at break of the hybrid films were increased with the increase of HBCuPc content and the thermal stability was improved with the increase of HBCuPc content.     

Meta-DNA: synthetic biology via DNA nanostructures and hybridization reactions

Can a wide range of complex biochemical behaviour arise from repeated applications of a highly reduced class of interactions? In particular, can the range of DNA manipulations achieved by protein enzymes be simulated via simple DNA hybridization chemistry? In this work, we develop a biochemical system which we call meta-DNA (abbreviated as mDNA), based on strands of DNA as the only component molecules. Various enzymatic manipulations of these mDNA molecules are simulated via toehold-mediated DNA strand displacement reactions. We provide a formal model to describe the required properties and operations of our mDNA, and show that our proposed DNA nanostructures and hybridization reactions provide these properties and functionality. Our meta-nucleotides are designed to form flexible linear assemblies (single-stranded mDNA (ssmDNA)) analogous to single-stranded DNA. We describe various isothermal hybridization reactions that manipulate our mDNA in powerful ways analogous to DNA–DNA reactions and the action of various enzymes on DNA. These operations on mDNA include (i) hybridization of ssmDNA into a double-stranded mDNA (dsmDNA) and heat denaturation of a dsmDNA into its component ssmDNA, (ii) strand displacement of one ssmDNA by another, (iii) restriction cuts on the backbones of ssmDNA and dsmDNA, (iv) polymerization reactions that extend ssmDNA on a template to form a complete dsmDNA, (v) synthesis of mDNA sequences via mDNA polymerase chain reaction, (vi) isothermal denaturation of a dsmDNA into its component ssmDNA, and (vii) an isothermal replicator reaction that exponentially amplifies ssmDNA strands and may be modified to allow for mutations.