Nanofabrication of hybrid nanomaterials: Macroscopically aligned nanoparticles pattern via directed self-assembly of block copolymers

Periodic hybrid nanostructured materials based on aligned inorganic nanoparticles within self-assembled copolymer matrixes aimed to harness the collective properties of generated functional nanomaterials. The nanoparticles are desirable for their useful magnetic, optical, catalytic, and electronic properties owed to the quantum confinement effect. For instance, gold, palladium and platinum as nanoparticles, have shown significant change in the physiochemical properties in comparison to their bulk materials. If the nanoparticles are aligned into well-defined macroscopic periodic nanostructures in diverse of morphologies, the unique collective properties are significantly enhanced. These unique properties can be transformed to improve the performance of storage media, multi-contact tracks solar panels and optoelectronic devices. Within this review, the nanofabrication tools will be presented as an alternative route to conventional top-down methods for the fabrication of periodic nanostructured hybrid materials. A simple approach is reviewed to fabricate periodic nanostructured hybrid systems based on the directed assembly of inorganic nanoparticles into well-defined periodic three-dimensional nanostructures provided by the self-assembling ability of block copolymers. The fabrications of varieties morphologies and the formation mechanism at different dimensions will be discussed as well as the characterization techniques. Finally, several applications of the proposed hybrid nanostructures are highlighted for the next generation of miniaturized devices.     

Conducting Electroactive Polymers via Photopolymerization: A Review on Synthesis and Applications

Photopolymerization can be considered as an appropriate method in synthesis of conducting electroactive polymers. This paper presents a survey on the major principles of photopolymerization method, then reviews performed researches on photopolymerization leading to conducting electroactive polymer-based materials, and thereby reveals the significant information relevant to their structures and properties. The main focus of this state-of-the-art review is classification of the photoinduced synthesis of conducting electroactive polymers according to predominant mechanism in detail. Furthermore, practical applications of photopolymerization to fabrication of conducting polymeric structures such as films and nanostructures are surveyed from different publications.     

固态离子学法制备金属纳米材料的研究进展

金属纳米材料具有优于相应块体材料的优良特性,由于合成方法所限,很难实现宏观量级尺度金属纳米材料的定向生长。固态离子学法能够有效控制纳米材料的形貌、长度、排列有序度和粗糙度,制备宏观尺寸的纳米材料。该文详细介绍了固态离子学法的制备机理;分别综述了单一金属纳米材料的制备过程及电场强度、电流和快离子导体薄膜的种类对材料的形貌和排列有序度的影响,并介绍了不同合金纳米材料和复合纳米材料的制备工艺,通过对比单一金属纳米材料、合金及复合纳米材料分别作为表面增强拉曼散射基底时的极限浓度,总结了影响检测灵敏度的因素;最后总结了该领域面临的问题,并对该方法未来的发展趋势进行展望。     

氧化亚铜在太阳能电池、光催化领域的研究进展

作为半导体光电功能材料,Cu2O薄膜和纳米材料由于具有独特的能带结构和优异的性能,在电子信息、能源、环境保护等领域具有重要的应用前景。介绍了Cu2O薄膜与纳米材料的制备方法及其在太阳能电池和光催化领域的应用。分析了目前存在的问题,并提出今后研究的对策。     

Broadband antireflective silicon nanostructures produced by spin-coated Ag nanoparticles

We report the fabrication of broadband antireflective silicon (Si) nanostructures fabricated using spin-coated silver (Ag) nanoparticles as an etch mask followed by inductively coupled plasma (ICP) etching process. This fabrication technique is a simple, fast, cost-effective, and high-throughput method, making it highly suitable for mass production. Prior to the fabrication of Si nanostructures, theoretical investigations were carried out using a rigorous coupled-wave analysis method in order to determine the effects of variations in the geometrical features of Si nanostructures to obtain antireflection over a broad wavelength range. The Ag ink ratio and ICP etching conditions, which can affect the distribution, distance between the adjacent nanostructures, and height of the resulting Si nanostructures, were carefully adjusted to determine the optimal experimental conditions for obtaining desirable Si nanostructures for practical applications. The Si nanostructures fabricated using the optimal experimental conditions showed a very low average reflectance of 8.3%, which is much lower than that of bulk Si (36.8%), as well as a very low reflectance for a wide range of incident angles and different polarizations over a broad wavelength range of 300 to 1,100 nm. These results indicate that the fabrication technique is highly beneficial to produce antireflective structures for Si-based device applications requiring low light reflection.     

Towards nano-organic chemistry: perspectives for a bottom-up approach to the synthesis of low-dimensional carbon nanostructures

Low-dimensional carbon nanostructures, such as nanotubes and graphenes, represent one of the most promising classes of materials, in view of their potential use in nanotechnology. However, their exploitation in applications is often hindered by difficulties in their synthesis and purification. Despite the huge efforts by the research community, the production of nanostructured carbon materials with controlled properties is still beyond reach. Nonetheless, this step is nowadays mandatory for significant progresses in the realization of advanced applications and devices based on low-dimensional carbon nanostructures. Although promising alternative routes for the fabrication of nanostructured carbon materials have recently been proposed, a comprehensive understanding of the key factors governing the bottom-up assembly of simple precursors to form complex systems with tailored properties is still at its early stages. In this paper, following a survey of recent experimental efforts in the bottom-up synthesis of carbon nanostructures, we attempt to clarify generalized criteria for the design of suitable precursors that can be used as building blocks in the production of complex systems based on sp(2) carbon atoms and discuss potential synthetic strategies. In particular, the approaches presented in this feature article are based on the application of concepts borrowed from traditional organic chemistry, such as valence-bond theory and Clar sextet theory, and on their extension to the case of complex carbon nanomaterials. We also present and discuss a validation of these approaches through first-principle calculations on prototypical systems. Detailed studies on the processes involved in the bottom-up fabrication of low-dimensional carbon nanostructures are expected to pave the way for the design and optimization of precursors and efficient synthetic routes, thus allowing the development of novel materials with controlled morphology and properties that can be used in technological applications.     

Multimaterial Fibers

Recent progress in combining multiple materials with disparate optical, electronic, and thermomechanical properties monolithically in the same fiber drawn from a preform is paving the way to a new generation of multimaterial fibers endowed with unique functionalities delivered at optical fiber length scales and costs. A wide range of unique devices have been developed to date in fiber form-factor using this strategy, such as transversely emitting fiber lasers, fibers that detect light, heat, or sound impinging on their external surfaces, and fibers containing crystalline semiconductor cores. Incorporating such fibers in future fabrics will lead to textiles with sophisticated functionality. Additionally, long-standing issues in traditional applications of optical fibers have been addressed by multimaterial fibers, such as photonic bandgap guidance in hollow-core all-solid-cladding fibers and imparting mechanical robustness to soft-glass mid-infrared fibers. We review recent progress in this nascent but rapidly growing field and highlight areas where growth is anticipated. Furthermore, the insights emerging from this research are pointing to new ways that the fiber drawing process itself may be leveraged as a fabrication methodology. In particular, we describe recent efforts directed at appropriating multimaterial-fiber drawing for chemical synthesis and the fabrication of nanostructures such as nanowire arrays and structured nanoparticles.     

Langmuir-Blodgettry of nanocrystals and nanowires

Although nanocrystals and nanowires have proliferated new scientific avenues in the study of their physics and chemistries, the bottom-up assembly of these small-scale building blocks remains a formidable challenge for device fabrication and processing. An attractive nanoscale assembly strategy should be cheap, fast, defect tolerant, compatible with a variety of materials, and parallel in nature, ideally utilizing the self-assembly to generate the core of a device, such as a memory chip or optical display. Langmuir-Blodgett (LB) assembly is a good candidate for arranging vast numbers of nanostructures on solid surfaces. In the LB technique, uniaxial compression of a nanocrystal or nanowire monolayer floating on an aqueous subphase causes the nanostructures to assemble and pack over a large area. The ordered monolayer can then be transferred to a solid surface en masse and with fidelity. In this Account, we present the Langmuir-Blodgett technique as a low-cost method for the massively parallel, controlled organization of nanostructures. The isothermal compression of fluid-supported nanoparticles or nanowires is unique in its ability to achieve control over nanoscale assembly by tuning a macroscopic property such as surface pressure. Under optimized conditions (e.g., surface pressure, substrate hydrophobicity, and pulling speed), it allows continuous variation of particle density, spacing, and even arrangement. For practical application and device fabrication, LB compression is ideal for forming highly dense assemblies of nanowires and nanocrystals over unprecedented surface areas. In addition, the dewetting properties of LB monolayers can be used to further achieve patterning within the range of micrometers to tens of nanometers without a predefined template. The LB method should allow for easy integration of nanomaterials into current manufacturing schemes, in addition to fast device prototyping and multiplexing capability.     

Generation of charged nanoparticles during the synthesis of carbon nanotubes by chemical vapor deposition

Generation of charged nanoparticles in the gas phase has been frequently reported during the synthesis of thin films and nanostructures, such as nanowires, using chemical vapor deposition (CVD). In an effort to confirm whether charged carbon nanoparticles were also generated during the synthesis of carbon nanotubes (CNTs) by CVD, a differential mobility analyzer combined with a Faraday cup electrometer was connected to an atmospheric-pressure CVD reactor under typical conditions for CNT growth. The size distribution of positively and negatively charged nanoparticles abundantly generated in the gas phase could be measured. Under conditions in which charged nanoparticles were not generated, no nanotubes could be grown.     

A novel method for designing carbon nanostructures: Tailoring-induced self-scrolling of graphene flakes

Design and fabrication of functional carbon nanostructures is a challenging but meaningful mission for scientists to propel the development of nanotechnology, such as nanopharmacology, nanobiology and nanofluidic manipulation. In order to fabricate the carbon nanostructures, using forced-field-based molecular dynamics simulations, we proposed a feasible method to obtain the carbon nanostructures through tailoring-induced self-scrolling of graphene flakes. And the shapes of the carbon nanostructures could be regulated by controlling the tailoring patterns. We also analyzed the mechanism for the tailoring-induced self-scrolling of graphene flakes. By analyzing the scrolling process in detail, it was found that the van der Waals interactions were responsible for the formation of the carbon nanostructures. In addition, we also found that the tailoring could also induce the scrolling of Boron Nitride flakes, and this indicates that the tailoring might provide an universal method for self-assembly of two dimensional materials. This work is expected to trigger further studies on the design of nanostructures and the applications of these nanostructures in functional nanodevices.     

Fabrication and characteristics of Pd nanoparticles/nanofilms on ceramics toward catalytic electrodes

We report an approach of fabricating various palladium nanostructures with tailored morphologies in nanoparticles (Ø80-300 nm), nanoporous films (Ø50-200 nm), and integrated nanotubules arrays (Ø300 nm and 5 μm long) on different ceramic materials. Microporous titanate ceramics or nanoporous alumina films were first prepared through a solid-state synthesis or an anodic oxidization of aluminum sheets. The micro- and nanoporous ceramics were then used as supporting materials in an electroless deposition to deposit Pd nanoparticles or nanofilms over the porous substrates, thus leading to various Pd nanostructures with large surface areas and high corrosion resistance for many applications. EDX and EPMA analysis disclosed that the phosphor co-deposition in 5-11 at.% P occurred in the palladium electroless deposition. XRD analysis showed that the as-deposited Pd-P alloys were polycrystalline with a preferential orientation of (1 1 1) facet. The phosphor included in the Pd-P alloy films existed as a solid solution form, rendering as a single phase Pd-P alloy with nanocrystals (∼5 nm across) of cubic palladium.     

Multifunctional Magnetic-fluorescent Nanocomposites for Biomedical Applications

Nanotechnology is a fast-growing area, involving the fabrication and use of nano-sized materials and devices. Various nanocomposite materials play a number of important roles in modern science and technology. Magnetic and fluorescent inorganic nanoparticles are of particular importance due to their broad range of potential applications. It is expected that the combination of magnetic and fluorescent properties in one nanocomposite would enable the engineering of unique multifunctional nanoscale devices, which could be manipulated using external magnetic fields. The aim of this review is to present an overview of bimodal “two-in-one” magnetic-fluorescent nanocomposite materials which combine both magnetic and fluorescent properties in one entity, in particular those with potential applications in biotechnology and nanomedicine. There is a great necessity for the development of these multifunctional nanocomposites, but there are some difficulties and challenges to overcome in their fabrication such as quenching of the fluorescent entity by the magnetic core. Fluorescent-magnetic nanocomposites include a variety of materials including silica-based, dye-functionalised magnetic nanoparticles and quantum dots-magnetic nanoparticle composites. The classification and main synthesis strategies, along with approaches for the fabrication of fluorescent-magnetic nanocomposites, are considered. The current and potential biomedical uses, including biological imaging, cell tracking, magnetic bioseparation, nanomedicine and bio- and chemo-sensoring, of magnetic-fluorescent nanocomposites are also discussed.     

Template-free fabrication of silicon micropillar/nanowire composite structure by one-step etching

A template-free fabrication method for silicon nanostructures, such as silicon micropillar (MP)/nanowire (NW) composite structure is presented. Utilizing an improved metal-assisted electroless etching (MAEE) of silicon in KMnO₄/AgNO₃/HF solution and silicon composite nanostructure of the long MPs erected in the short NWs arrays were generated on the silicon substrate. The morphology evolution of the MP/NW composite nanostructure and the role of self-growing K₂SiF₆ particles as the templates during the MAEE process were investigated in detail. Meanwhile, a fabrication mechanism based on the etching of silver nanoparticles (catalyzed) and the masking of K₂SiF₆ particles is proposed, which gives guidance for fabricating different silicon nanostructures, such as NW and MP arrays. This one-step method provides a simple and cost-effective way to fabricate silicon nanostructures.     

Direct Deposit of Fiber Reinforced Energetic NanoComposites

The ideal situation of assembling an energetic nanoparticles‐polymer matrix is obtaining materials with high particle loading while still maintaining mechanical integrity. In this paper, we introduced a direct deposition approach to create a reactive polymer fiber reinforced composite with aluminum (Al‐NPs) and copper oxide nanoparticles (CuO‐NPs) in a polyvinylidene fluoride (PVDF) reactive binder. Even with up to 70 wt % thermite, these films still maintain a uniform morphology and considerable flexibility. With the same overall material composition, both the reactive and mechanical properties of fiber reinforced films shown marked improvement over the corresponding non‐nanofiber films. The combustion propagation velocity of fiber reinforced films is up to 1.8 times faster than the corresponding non‐nanofiber films. For the mechanical properties, the films with 110 nm diameter fibers were 2.3, 23 and 5.8 times superior in tensile strength, strain and toughness respectively, as compared to films with the same mass loading but with no fibers. The results suggest deploying a fiber reinforced structure enables fabrication of nanocomposite with high loadings of energetic materials. These result imply that a 3‐D printing approach may demonstrate significant advantages in developing advanced propulsion systems.     

Synthesis of hermetically-sealed graphite-encapsulated metallic cobalt (alloy) core/shell nanostructures

Hermetically-sealed graphite encapsulated cobalt core/shell nanostructures have been prepared by the CO Boudouard reaction using in situ generated cobalt as the catalyst. Only core/shell nanostructures were obtained, rather than a mixture of cobalt nanoparticles with carbon nanotubes or nanofibers. The magnetic cobalt nanoparticles are highly crystallized with a hexagonal-close packed crystal phase (average diameter of ca. 25 nm) and coated with an 8–9 nm thick graphitic shell. The nanostructures have a high saturation magnetization of 85 emu/g and can be easily separated by an external magnet. The creation of the hermetically-sealed graphitic shell not only keeps the magnetic cobalt nanoparticles from reacting with strong mineral acids, but also has biocompatibility and makes further functionalization easy. A pseudo-planar aromatic molecule, xylenol orange, was used as the model molecule because it can be absorbed on the graphitic shell mainly by π–π stacking interaction. This was confirmed by Raman and ultraviolet–visible spectroscopy. Graphite encapsulated Fe₂Co and Fe_0.64Ni_0.36 alloy core/shell nanostructures were also fabricated by this method.     

Multifunctional mesoporous silica nanocomposite nanoparticles for theranostic applications

Clever combinations of different types of functional nanostructured materials will enable the development of multifunctional nanomedical platforms for multimodal imaging or simultaneous diagnosis and therapy. Mesoporous silica nanoparticles (MSNs) possess unique structural features such as their large surface areas, tunable nanometer-scale pore sizes, and well-defined surface properties. Therefore, they are ideal platforms for constructing multifunctional materials that incorporate a variety of functional nanostructured materials. In this Account, we discuss recent progress by our group and other researchers in the design and fabrication of multifunctional nanocomposite nanoparticles based on mesoporous silica nanostructures for applications to simultaneous diagnosis and therapy. Versatile mesoporous silica-based nanocomposite nanoparticles were fabricated using various methods. Here, we highlight two synthetic approaches: the encapsulation of functional nanoparticles within a mesoporous silica shell and the assembly of nanoparticles on the surface of silica nanostructures. Various nanoparticles were encapsulated in MSNs using surfactants as both phase transfer agents and pore-generating templates. Using MSNs as a scaffold, functional components such as magnetic nanoparticles and fluorescent dyes have been integrated within these systems to generate multifunctional nanocomposite systems that maintain their individual functional characteristics. For example, uniform mesoporous dye-doped silica nanoparticles immobilized with multiple magnetite nanocrystals on their surfaces have been fabricated for their use as a vehicle capable of simultaneous magnetic resonance (MR) and fluorescence imaging and drug delivery. The resulting nanoparticle-incorporated MSNs were then tested in mice with tumors. These in vivo experiments revealed that these multifunctional nanocomposite nanoparticles were delivered to the tumor sites via passive targeting. These nanocomposite nanoparticles served as successful multimodal imaging probes and also delivered anticancer drugs to the tumor site. With innumerable combinations of imaging modalities and drug delivery available within these vehicles, multifunctional nanocomposite nanoparticles provide new opportunities for clinical diagnostics and therapeutics.     

A composite CdS thin film/TiO2 nanotube structure by ultrafast successive electrochemical deposition toward photovoltaic application

Fabricating functional compounds on substrates with complicated morphology has been an important topic in material science and technology, which remains a challenging issue to simultaneously achieve a high growth rate for a complex nanostructure with simple controlling factors. Here, we present a novel simple and successive method based on chemical reactions in an open reaction system manipulated by an electric field. A uniform CdS/TiO₂ composite tubular structure has been fabricated in highly ordered TiO₂ nanotube arrays in a very short time period (~90 s) under room temperature (RT). The content of CdS in the resultant and its crystalline structure was tuned by the form and magnitude of external voltage. The as-formed structure has shown a quite broad and bulk-like light absorption spectrum with the absorption of photon energy even below that of the bulk CdS. The as-fabricated-sensitized solar cell based on this composite structure has achieved an efficiency of 1.43% without any chemical doping or co-sensitizing, 210% higher than quantum dot-sensitized solar cell (QDSSC) under a similar condition. Hopefully, this method can also easily grow nanostructures based on a wide range of compound materials for energy science and electronic technologies, especially for fast-deploying devices.     

Lithography-free fabrication of silicon nanowire and nanohole arrays by metal-assisted chemical etching

We demonstrated a novel, simple, and low-cost method to fabricate silicon nanowire (SiNW) arrays and silicon nanohole (SiNH) arrays based on thin silver (Ag) film dewetting process combined with metal-assisted chemical etching. Ag mesh with holes and semispherical Ag nanoparticles can be prepared by simple thermal annealing of Ag thin film on a silicon substrate. Both the diameter and the distribution of mesh holes as well as the nanoparticles can be manipulated by the film thickness and the annealing temperature. The silicon underneath Ag coverage was etched off with the catalysis of metal in an aqueous solution containing HF and an oxidant, which form silicon nanostructures (either SiNW or SiNH arrays). The morphologies of the corresponding etched SiNW and SiNH arrays matched well with that of Ag holes and nanoparticles. This novel method allows lithography-free fabrication of the SiNW and SiNH arrays with control of the size and distribution.     

Nanoskiving: a new method to produce arrays of nanostructures

This Account reviews nanoskiving--a new technique that combines thin-film deposition of metal on a topographically contoured substrate with sectioning using an ultramicrotome--as a method of fabricating nanostructures that could replace conventional top-down techniques in selected applications. Photolithography and scanning beam lithography, conventional top-down techniques to generate nanoscale structures and nanostructured materials, are useful, versatile, and highly developed, but they also have limitations: high capital and operating costs, limited availability of the facilities required to use them, an inability to fabricate structures on nonplanar surfaces, and restrictions on certain classes of materials. Nanoscience and nanotechnology would benefit from new, low-cost techniques to fabricate electrically and optically functional structures with dimensions of tens of nanometers, even if (or perhaps especially if) these techniques have a different range of application than does photolithography or scanning beam lithography. Nanoskiving provides a simple and convenient procedure to produce arrays of structures with cross-sectional dimensions in the 30-nm regime. The dimensions of the structures are determined by (i) the thickness of the deposited thin film (tens of nanometers), (ii) the topography (submicrometer, using soft lithography) of the surface onto which the thin film is deposited, and (iii) the thickness of the section cut by the microtome (> or =30 nm by ultramicrotomy). The ability to control the dimensions of nanostructures, combined with the ability to manipulate and position them, enables the fabrication of nanostructures with geometries that are difficult to prepare by other methods. The nanostructures produced by nanoskiving are embedded in a thin epoxy matrix. These epoxy slabs, although fragile, have sufficient mechanical strength to be manipulated and positioned; this mechanical integrity allows the nanostructures to be stacked in layers, draped over curved surfaces, and suspended across gaps, while retaining the in-plane geometry of the nanostructures embedded in the epoxy. After removal of the polymer matrix by plasma oxidation, these structures generate suspended and draped nanostructures and nanostructures on curved surfaces. Two classes of applications, in optics and in electronics, demonstrate the utility of nanostructures fabricated by nanoskiving. This technique will be of primary interest to researchers who wish to generate simple nanostructures, singly or in arrays, more simply and quickly than can be accomplished in the clean-room. It is easily accessible to those not trained in top-down procedures for fabrication and those with limited or no access to the equipment and facilities needed for photolithography or scanning-beam fabrication. This Account discusses a new fabrication method (nanoskiving) that produces arrays of metal nanostructures. The defining process in nanoskiving is cutting slabs from a polymeric matrix containing embedded, more extended metal structures.     

Carbon nanocages grown by gold templating

A method for growing carbon cages using gold nanoparticles as templates is reported. Gold nanoparticles were deposited on carbon nanotubes (CNTs). The nanocages were grown on the gold particles by electrical Joule heating of the CNT. The gold was subsequently evaporated, leaving the cages intact. A special in situ TEM-holder equipped with a small scanning tunneling microscope was used as an electrical probe to drive current through the CNT, while the TEM was used for imaging of the entire growth process. The method might provide a general way for making carbon structures limited only by the shapes allowed by the fabrication methods of the gold nanostructures.