Fabrication Of Novel Nanostructures Research Articles

Nanodiamond driven structure evolution of ZnO nanorods

Spontaneous growth in ambient environment has become an exciting topic issue for nanostructured materials. Here, hydrothermally synthesized zinc oxide (ZnO) nanorods loaded with detonation nanodiamonds (DNDs) enable a spontaneous structure evolution related to a catalytic reduction of solid phase carbon of DNDs, being different from the traditional carbonaceous carbon dioxide gas (CO2). Exposed to ambient environment from days to weeks, the original ZnO nanorods placed on silicon substrate transfer to a concentric core–shell structure of ZnCO3/ZnO including abundant Zn/DND nanoparticles. A coaxial configuration with periodical multi-layered walls is formed, when the surrounding CO2 concentration is increased arising from supporting amorphous carbon film beneath. Importantly, the ZnO/DND nanorods are directly dissociated into DND@Zn core–shell nanoparticles in CO2-rich environment. The structural evolution from ZnO nanorods is attributed to DND having catalytic, reducibility, and hydrophilic hierarchical porosity structure with the participations of CO2 and H2O in air. This work demonstrates that based on the combination of ZnO and DNDs, a spontaneous growth process occurs, which provides a strategy for fabrication of novel nanostructures (not limited to ZnO nanorods). Furthermore, it offers a possibility for degradation of greenhouse gases by enhancing capture and decomposition of CO2 in ambient environment for carbon neutral.

Self-assembly of graphene sheets actuated by surface topological defects: Toward the fabrication of novel nanostructures and drug delivery devices

This paper focuses on self-assembly behaviors of graphene with surface topological defects using the atomistic simulation. The self-assembly graphene models are proposed based on three design principles. The systematic self-assembly simulations are performed and compared to achieve their dynamic nature and time dependence based on various design variables. It is found that the constructed self-assembly phase diagrams contain four distinct modes including polygon nanoscroll, polygon nanotube, breathing oscillation and damping vibration, which can be influenced by the number of unit cell along y-direction. Based on surface engineering consideration and reverse design paradigm, a target geometry such as polygon nanotube can be approximated by a graphene surface with programmable ripples and topological defects. Finally, the fundamental building block of self-assembly graphene is analyzed to reflect the self-assembly capacity. The results in this paper can be used to achieve the novel nanostructures and develop the design space of all-graphene-based drug delivery devices.

Review on DFT calculation of s‐triazine‐based carbon nitride

AbstractTo improve the photocatalytic performance of pristine photocatalysts, element doping, construction of composites and fabrication of novel nanostructures are recognized as universal modification methods. These methods have been experimentally verified to be effective in manifold photocatalytic application over various photocatalysts. Density functional theory (DFT) calculation is a powerful and fundamental tool to pinpoint the intrinsic mechanism of the enhanced photocatalytic activity. And it holds the degree of precision ranging from atoms, molecules to unit cells. Herein, recent DFT calculation research progress of modified s‐triazine‐based graphitic carbon nitride (g–C3N4) systems as photocatalysts is summarized. To specify, we collected information of doping site, formation energy, geometric, and electronic properties. We also discussed the synergistic effect of work function, Fermi level and band edge position on the built‐in electric field, transfer route of photogenerated charge carriers and photocatalytic mechanism (traditional type II or direct Z‐scheme heterostructure). Moreover, we analyzed the geometric configuration, band structure, and stability of g–C3N4 nanocluster, nanoribbon, and nanotube. Finally, future perspective in the further theoretical revelation of g–C3N4‐based photocatalysts is proposed.

Interfacial Defects Dictated In Situ Fabrication of Yolk-Shell Upconversion Nanoparticles by Electron-Beam Irradiation.

Homogeneous core–shell structured nanoparticles (NPs) are prevailingly designed to accommodate lanthanide emitters, and such an epitaxial shell deposited on core NP is generally believed to help eliminate surface traps or defects on the as‐prepared core. However, upon electron‐beam irradiation to core–shell–shell NaLuF4:Gd/Yb/Er@NaLuF4:Nd/Yb@NaLuF4 upconversion NPs (UCNPs), it is revealed that interfacial defects actually exist at the core–shell and shell–shell interfaces, even with a higher density than the bulk‐phase defects in inner core. Because of such higher density of interfacial defects, the kinetic energies transferred from energetic electrons to atoms may trigger the faster Na/F atom ejections and outward atom migrations in the coating layers than in the inner core of NPs, which ultimately results in the in situ formation of novel yolk–shell UCNPs. These findings provide new insights into interfacial defects in homogeneous core–shell structured NaLnF4 NPs, and pave the way toward utilizing the interactions of high‐energy particles with materials for in situ fabrication of novel nanostructures.

Coating strategies for atomic layer deposition

AbstractAtomic layer deposition (ALD) is a vapor phase technique capable of producing a variety of materials. It consists of the alternation of separate self-limiting surface reactions, which enables accurate control of film thickness at the Angstrom level. ALD becomes a powerful tool for a lot of industrial and research applications. Coating strategies are the key for ALD; however, there are few systematic reviews concerning coating strategies for ALD. This review provides a detailed summary of state-of-the-art coating strategies in ALD, emphasizing the recent progress in the fabrication of novel nanostructures. The progress in coating strategies is reviewed in three parts: template-assisted preparation of low-dimensional nanomaterials and complex nanostructures; surface treatments, including the surface activation and the surface blocking ways; enhanced reactor, such as plasma and fluid bed reactor, and improved growth method such as the ABC-type model. In addition, we also discussed the challenges facing the coating method for ALD.

Electron-Irradiated Polymer Brushes for Hollow Carbon Nanosphere Arrays.

A thermally stable 2D array of spheres and their morphology control become important for the fabrication of novel nanostructures. Here, a simple method is presented for fabrication of large-area and well-ordered arrays of carbonized polystyrene (PS) hollow spheres with a controlled (close-packed or non-close-packed hexagonal) morphology, prepared by combining the self-assembly of PS-grafted silica nanoparticles, etching, electron irradiation, and subsequent thermal annealing. Fine control in the 2D or 3D nanostructure of carbon materials can open up new opportunities for high-performance nanoscale applications that require an efficient fabrication method for preparation of the porous carbon array.

Opto-Microfluidic Immunosensors: From Colorimetric to Plasmonic.

Optical detection has long been the most popular technique in immunosensing. Recent developments in the synthesis of luminescent probes and the fabrication of novel nanostructures enable more sensitive and efficient optical detection, which can be miniaturized and integrated with microfluidics to realize compact lab-on-a-chip immunosensors. These immunosensors are portable, economical and automated, but their sensitivity is not compromised. This review focuses on the incorporation and implementation of optical detection and microfluidics in immunosensors; it introduces the working principles of each optical detection technique and how it can be exploited in immunosensing. The recent progress in various opto-microfluidic immunosensor designs is described. Instead of being comprehensive to include all opto-microfluidic platforms, the report centers on the designs that are promising for point-of-care immunosensing diagnostics, in which ease of use, stability and cost-effective fabrication are emphasized.

Dense Plasma Focus-Based Nanofabrication of III-V Semiconductors: Unique Features and Recent Advances.

The hot and dense plasma formed in modified dense plasma focus (DPF) device has been used worldwide for the nanofabrication of several materials. In this paper, we summarize the fabrication of III–V semiconductor nanostructures using the high fluence material ions produced by hot, dense and extremely non-equilibrium plasma generated in a modified DPF device. In addition, we present the recent results on the fabrication of porous nano-gallium arsenide (GaAs). The details of morphological, structural and optical properties of the fabricated nano-GaAs are provided. The effect of rapid thermal annealing on the above properties of porous nano-GaAs is studied. The study reveals that it is possible to tailor the size of pores with annealing temperature. The optical properties of these porous nano-GaAs also confirm the possibility to tailor the pore sizes upon annealing. Possible applications of the fabricated and subsequently annealed porous nano-GaAs in transmission-type photo-cathodes and visible optoelectronic devices are discussed. These results suggest that the modified DPF is an effective tool for nanofabrication of continuous and porous III–V semiconductor nanomaterials. Further opportunities for using the modified DPF device for the fabrication of novel nanostructures are discussed as well.

Formation of Carbonized Polystyrene Sphere/hemisphere Shell Arrays by Ion Beam Irradiation and Subsequent Annealing or Chloroform Treatment.

Heat-resistant two-dimensional (2D) sphere/hemisphere shell array is significant for the fabrication of novel nanostructures. Here large-area, well-ordered arrays of carbonized polystyrene (PS) hollow sphere/hemisphere with controlled size and morphology are prepared by combining the nanosphere self-assembly, kV Ag ion beam modification, and subsequent annealing or chloroform treatment. Potential mechanisms for the formation and evolution of the heat-resistant carbonized PS spherical shell with increasing ion fluence and energy are discussed. Combined with noble metal or semiconductor, these modified PS sphere arrays should open up new possibilities for high-performance nanoscale optical sensors or photoelectric devices.

Homogenous Core–Shell Nitrogen‐Doped Carbon Nanotubes for the Oxygen Reduction Reaction

AbstractNanoarchitectures provide a new impulse to develop highly efficient electrocatalysts for the oxygen reduction reaction (ORR). Nitrogen‐doped 1D or 2D carbon‐based catalysts exhibit highly catalytic performances, owing to their distinctive features. Of great interest is the fabrication of novel nanostructures combining the advantages of 1D and 2D materials. To achieve this challenge, homogenous core–shell nitrogen‐doped carbon nanotubes were successfully prepared by using a simple one‐pot method. The unique structure possesses the features of common carbon nanotubes (core) and standing graphite (shell). The novel structure with a synergistic effect of 1D and 2D materials contributes to enhanced ORR activity. Moreover, the core–shell catalysts exhibit long‐term stability and high tolerance to methanol‐poisoning effects, which are shortfalls for commercial Pt/C electrocatalysts.

Flattened Multiwalled Carbon Nanotube with Multi-Layered Structure.

Fabrication of novel nanostructures based on carbon nanotubes has been a focus of recent interest since they are expected to inherit excellent properties of carbon nanotube. To find new nanotube-based nanostructures, it is important to find a new growth mode or process. This paper reports the formation of a multiwalled carbon nanotube that has bi-layered structure and is partly flattened. Transmission electron microscopy observations suggest that the outer multiwalled layer was formed first from a Fe catalyst nanoparticle, and was partly flattened during the growth. Then the catalyst nanoparticle worked again to form the inner multiwalled tube moving inside the outer tube and became flattened at the same position of the outer tube. It is likely that the inner growth gave an expansion stress against the flattened outer tube; nevertheless, the flattened part of the outer tube remained. This observation evidences that the flattening of the nanotube occurred simultaneously during the growth and was stabilized by structural defect.

Silver Ions Induce Lateral Etching of Gold Nanorods by K2PtCl4.

Selective etching is significant for fabrication of novel nanostructures. Here silver ions are introduced to control the lateral etching of gold nanorods by K2PtCl4 in a hot solution, producing a number of dumbbell-like PtAu-Au thin gold nanorods. Silver ions control the selective deposition of the reduced Pt(0) atoms, causing the selective etching of the unprotected Au. The middle diameter of the obtained dumbbell-like nanorods can be adjusted from 12 nm to <10 nm. It is believed that this is an effective method to reduce the diameter of gold nanorods.

Amorphous carbon nanotube–polyaniline core–shell nanostructures for efficient cold cathode applications

The general challenge to improve the field emission properties of conducting polymers depends on the fabrication of novel nanostructures from their polymeric aggregates and/or the synthesis of novel nanocomposites. Here we report amorphous carbon nanotube (aCNT)–polyaniline (PANI) core–shell hierarchical structures for the first time, which exhibit high field emission properties. The aCNT–PANI hierarchical nanostructures were prepared using a facile and cost effective method, which involved a simple in situ oxidative polymerization of aniline in the presence of aCNTs at three different temperatures. The as-synthesized samples were characterized using X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy and Raman spectroscopy. The field emission characteristics of the pristine aCNT sample were compared with the composites synthesized at different temperatures. The turn-on fields of the aCNT–PANI composites in comparison with the pristine aCNTs decreased from 9.13 to 2.57 V μm−1 and the emission current density increased from 0.031 to 1.27 mA cm−2 at an electric field of 11.50 V μm−1. The improvement in the field emission properties of the aCNT–PANI composites can be explained in terms of both a higher enhancement factor and a lower work function of the composite. This research gives a new perception towards the radical improvement of field emission properties of conducting polymers, based on unique hierarchical core–shell nanostructures.

Simple Holographic Patterning for High‐Aspect‐Ratio Three‐Dimensional Nanostructures with Large Coverage Area

AbstractUsing the vertical standing wave phenomena commonly regarded as a deterrent in holographic lithography, multifaceted three‐dimensional (3D) nanostructures are fabricated on polymeric photoresist materials using a simple two‐beam interferometer. Large‐area 3D nanostructures with high aspect ratios (greater than 10) are readily produced using this methodology, including grating, pillar and pore patterns. Furthermore, manipulation of the lithography process conditions results in unique sidewall profiles of the nanostructures. Such 3D holographic control even produces highly porous polymer membranes composed of 3D interconnected pore networks, which resembles the 3D photonic crystal compound nanostructures that were previously attainable only with limited pattern coverage area using complex multibeam holographic lithography processes. Such well‐tailored high‐aspect‐ratio 3D nanostructures with large pattern coverage area further enable the fabrication of novel nanostructures for functionalized materials via various additive and subtractive pattern transfer techniques such as etching, deposition, and molding. In particular, direct molding followed by thermal decomposition process leads to the synthesis of hierarchical titanium oxide nanostructures of tunable 3D geometry, which would be of great significance in applications of photonic crystals, photovoltaic solar cells, and photocatalyst in water decontamination.

From nanocrystal synthesis to functional nanostructure fabrication: laser ablation in liquid

Although nanomaterials investigations have been carried over the recent decades, researchers still face a fundamental challenge: how to control the phase, size and shape of nanocrystals in the synthesis of nanomaterials, i.e., how to achieve the transformation from nanocrytsal synthesis to functional nanostructure fabrication. For this issue, we, in this review, introduce recent developments in laser ablation in liquid (LAL) for the synthesis and fabrication of novel nanostructures with metastable phases and shapes. Laser ablation of solid targets in liquid has actually opened a door toward to synthesize nanocrystals and fabricate nanostructures due to these advantages as follows: (i) LAL is a chemically "simple and clean" synthesis due to the process with reduced byproduct formation, simpler starting materials, no need for catalyst, etc. (ii) Under ambient conditions, not extreme temperature and pressure, a variety of metastable phases that may not usually be attainable, can be generated by mild preparation methods. (iii) New phase formation involves in both liquid and solid upon LAL, which allows researchers to choose and combine interesting solid target and liquid to synthesize nanocrystals and fabricate nanostructures of new compounds for purpose of fundamental research and potential applications. (iv) The phase, size and shape of the synthesized nanocrystals can be readily controlled by tuning laser parameters and applying assistances such as inorganic salts or electrical field upon LAL. For example, we have synthesized the micro- and nanocubes of carbon with C(8)-like structures by the inorganic salts assisted LAL, and the micro- and nanocubes and spindles of GeO(2) by the electrical field assisted LAL. Additionally, we have developed a new technique to fabricate functional nanopatterns on the basis of the pulsed-laser deposition in liquid. Accordingly, LAL could greatly extend its application in fabrication of functional nanostructures in the future.

Electrochemical fabrication of novel nanostructures based on anodic alumina

A novel nanostructured sandwich PAA/Al/PAA (PAA: porous anodic alumina) wassuccessfully designed and fabricated by anodic oxidation on both sides of an Al foil. Thepore size of the PAA membranes was controlled by choosing appropriate voltage, lengthof anodic oxidization time, temperature and electrolytes. The thickness of thecentral Al layer was varied by changing the anodic oxidization time. We showthat the nanostructured sandwich PAA/Al/PAA can be used as a template infabricating homogeneous or heterogeneous nanostructured sandwiches by depositingthe same kind of material or different materials into the PAA membranes of thesandwich. We also show that it can be used to prepare nanowires and bipolarelectrodes. In addition, Al nanosheets or Al nanowalls were produced by removingthe PAA films completely or partially. Nanogaps between the PAA films werealso formed by etching away the centre Al layer of the sandwich structures. Thethickness of these nanosheets, nanowalls and nanogaps was controlled by choosingappropriate electrolytes and electrochemical parameters during the anodic oxidationof Al. All these nanostructures offer novel opportunities for both fundamentalresearch and technological applications of low dimensional nanostructure systems.

Silicon-on-insulator processes for the fabrication of novel nanostructures

In this brief report, we discuss novel single crystal structures for electronic device and microelectromechanical system applications using processes that employ selective epitaxial growth (SEG) and silicon-on-insulator (SOI) wafers. Selective epitaxial growth of silicon is used to provide robust, reliable mechanical and electrical contacts between the SOI layer and the substrate. Subsequent removal of the buried oxide results in single crystal structures suspended in air. The films can then be thinned using wet or dry etching or thinned using sacrificial oxidation steps with the possibility of forming ultrathin SOI layers. Diodes formed at the substrate–SEG junction demonstrate high breakdowns and low leakage indicating good electrical isolation between the SOI layer and the substrate. The silicon on air regions can be used for dual-gate metal–oxide–semiconductor devices, quantum wires, cantilevers, as a substrate for lattice mismatched epitaxy, ultrathin SOIs, and lateral field emission tips.

Electrophoretic Isolation of Discrete Au Nanocrystal/DNA Conjugates

Colloidal nanocrystal/DNA conjugates hold the promise of becoming powerful probes for biological diagnostics as well as versatile building blocks for nanotechnology. To fully realize this potential, it is important to precisely control the number of oligonucleotides bound to the nanocrystal. Here we demonstrate electrophoretic isolation of 5 and 10 nm gold nanocrystals bearing discrete numbers of single-stranded DNA (1−5). The potential use of these discrete conjugates in the fabrication of novel nanostructures is discussed.