Single-crystalline Nanotubes Research Articles

Array of single crystalline anatase TiO2 nanotubes with significant enhancement of photoresponse

Anatase TiO2 nanotubes array (ATONA) has attracted tremendous attention owing to its promising applications in solar cells, water splitting and organic pollutants photocatalytic degradation. However, the activity of ATONAs was greatly suppressed by the grain boundaries existed in the tube walls, which acted as carrier scattering and recombination centers. Herein, we report a novel strategy to prepare array of single crystalline anatase TiO2 nanotubes (SC-ATONAs) with significant enhancement of the photocatalytic activity and UV photo response performance compared to the polycrystalline counterparts. The growth of SC-ATONAs was achieved by establishing a crystallization temperature gradient along the tube wall, which ensured the crystallization started from the nucleation of a single nucleus at the bottom of amorphous TiO2 nanotubes prepared by Ti anodization. These findings pave the way to prepare single-crystalline nanotubes with superior performance for other materials.

Design Hierarchical Electrodes with Highly Conductive NiCo2S4 Nanotube Arrays Grown on Carbon Fiber Paper for High-Performance Pseudocapacitors

We report on the development of highly conductive NiCo2S4 single crystalline nanotube arrays grown on a flexible carbon fiber paper (CFP), which can serve not only as a good pseudocapacitive material but also as a three-dimensional (3D) conductive scaffold for loading additional electroactive materials. The resulting pseudocapacitive electrode is found to be superior to that based on the sibling NiCo2O4 nanorod arrays, which are currently used in supercapacitor research due to the much higher electrical conductivity of NiCo2S4. A series of electroactive metal oxide materials, including CoxNi1-x(OH)2, MnO2, and FeOOH, were deposited on the NiCo2S4 nanotube arrays by facile electrodeposition and their pseudocapacitive properties were explored. Remarkably, the as-formed CoxNi1-x(OH)2/NiCo2S4 nanotube array electrodes showed the highest discharge areal capacitance (2.86 F cm(-2) at 4 mA cm(-2)), good rate capability (still 2.41 F cm(-2) at 20 mA cm(-2)), and excellent cycling stability (∼ 4% loss after the repetitive 2000 cycles at a charge-discharge current density of 10 mA cm(-2)).

Single-crystalline nanotubes of spinel lithium nickel manganese oxide with lithium titanate anode for high-rate lithium ion batteries

Single-crystalline nanotubes of LiNi0.473Mn1.473Al0.054O4 (LNMAO-NT) have been synthesized and evaluated as cathode using LNMAO-NT/Li half cell and LNMAO-NT/Li4Ti5O12 (LTO) full cell, respectively. Galvanostatic charge/discharge tests show that the LNMAO-NT half cell exhibits discharge capacity of 118 mAh g−1 and specific energy (calculated only based on the cathode material) of 508 Wh kg−1 at 5 C. Two types of full cells (LTO-limited and LNMAO-NT-limited cell) are constructed using three-electrode configuration. Measurement results reveal that LTO-limited full cell has a lower cathode potential vs. Li metal than LNMAO-NT-limited one at the end of cutoff voltage. The LNMAO-NT/LTO full cell exhibits discharge capacity of 158 mAh g−1 at 0.5 C and 120 mAh g−1 at 10 C, respectively, showing superior high-rate capability of LNMAO-NT. In addition, 87% of capacity retention of the LNMAO-NT/LTO full cell can be achieved after 200 cycles at 5 C, indicating good structural stability of one dimensional LNMAO-NT. Moreover, study of in situ Raman spectra at different potentials reveals good structural reversibility during charging and discharging process, indicating that LNMAO-NT would be one of the most promising high-voltage cathodes for high power lithium ion batteries.

Synthesis, structural and magnetic characterization of highly ordered single crystalline BiFeO3 nanotubes

In this work, we report on the fabrication of highly ordered single crystalline BiFeO3 (BFO) nanotubes by a sol–gel technique using two-step anodic aluminum oxide (AAO) as template. We prepared BFO nanotubes with dimensions of 65nm in diameter and 3μm in length, as confirmed by scanning electron microscopy (SEM) measurements. The obtained single crystalline nanotubes present the expected pure phase (BiFeO3) as confirmed by energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). In addition to the antiferromagnetic behavior, the magnetization curves of the BFO nanotubes also present a ferromagnetic response, which holds from 2 to 300K. This desirable behavior is associated to the break of the antiferromagnetic helical spin ordering of the BFO nanotubes. Besides the magnetocrystalline anisotropy, the large length-to-diameter ratio induced an uniaxial shape anisotropy, attested by the applied magnetic field angle measurements.

First-Principles Study on Transport Properties of Saturated Single Crystalline GaN Nanotubes

Electronic structures and transport properties of the saturated single crystalline GaN nanotubes with 0.92 nm inner diameter and different wall thickness have been investigated by using first-principles and non-equilibrium green's function (NEGF). The result shows, the energy gap of the saturated single crystalline nanotubes changed from 0.2933 to 2.8442 eV. The saturated single crystalline GaN nanotubes have the direct band gap and the band gap decreases with the increase of wall thickness of nanotubes. The electronic density of state and the electronic transmission spectra of two-probe system have pulse-type sharp peak, the change of electronic density of state is in accord with electronic transmission rate. I-V characteristics of two-probe systems reflect that the saturated single-wall GaN nanotube and the saturated single-layer GaN nanotube are semiconducting properties, and the saturated double-layer GaN nanotube appears metallic behavior.

Single-Crystalline LiMn2O4 Nanotubes Synthesized Via Template-Engaged Reaction as Cathodes for High-Power Lithium Ion Batteries

Single-crystalline nanotubes of spinel LiMn2O4 with a diameter of about 600 nm, a wall thickness of about 200 nm and a length of 1–4 μm have been synthesized via a template-engaged reaction using β-MnO2 nanotubes as a self-sacrifice template. In this fabrication, a minimal structural reorganization can be responsible for the chemical transformation from [001]-oriented β-MnO2 template to [110]-oriented LiMn2O4. Galvanostatic charge/discharge measurements indicate that the nanotubes exhibit superior high-rate capabilities and good cycling stability. About 70% of its initial capacity can be retained after 1500 cycles at 5 C rate. Importantly, the tubular nanostructures and the single-crystalline nature of the most LiMn2O4 nanotubes are also well preserved after prolonged charge/discharge cycling at a relatively high current density, indicating good structural stability of the single-crystalline nanotubes during lithium intercalation/deintercalation process. As is confirmed from Raman spectra analyses, no evident microstructural changes occur upon long-term cycling. These results reveal that single-crystalline nanotubes of LiMn2O4 will be one of the most promising cathode materials for high-power lithium ion batteries.

Synthesis of ZnO nanotubes and nanotube-nanorod hybrid hexagonal networks using a hexagonally close-packed colloidal monolayer template

We present a new synthetic approach, via hydrothermal process with the use of polystyrene (PS) colloids, to fabricate vertically aligned, single crystalline ZnO nanotube arrays. Electron microscopy images revealed that single crystalline nanotubes with inner diameters of ∼15–20 nm and wall thicknesses of ∼10–15 nm were formed just below the PS colloids, whereas solid nanorods were grown in the absence of PS colloids. In addition, nanorods enclosing the PS colloids exhibited much faster growth rates than those on the area not covered with PS colloids. These results indicate that the introduction of PS colloids affected the formation and diffusion of adatoms. The growth behavior of ZnO crystals with regards to the PS colloids was exploited to convert the ZnO nanostructures from solid to nanotube-nanorod hybrid networks by introducing hexagonally close-packed PS colloidal monolayers. Moreover, we demonstrated further conversion to complete tubular forms by reducing the aperture size between adjacent PS colloids with thermal annealing.

Thiol-Capped ZnO Nanowire/Nanotube Arrays with Tunable Magnetic Properties at Room Temperature

The present study reports room-temperature ferromagnetic behaviors in three-dimensional (3D)-aligned thiol-capped single-crystalline ZnO nanowire (NW) and nanotube (NT) arrays as well as polycrystalline ZnO NT arrays. Besides the observation of height-dependent saturation magnetization, a much higher M(s) of 166 microemu cm(-2) has been found in NTs compared to NWs (36 microemu cm(-2)) due to larger surface area in ZnO NTs, indicating morphology-dependent magnetic properties in ZnO NW/NT systems. Density functional calculations have revealed that the origin of ferromagnetism is mainly attributed to spin-polarized 3p electrons in S sites and, therefore, has a strong correlation with Zn-S bond anisotropy. The preferential magnetization direction of both single-crystalline NTs and NWs lies perpendicular to the tube/wire axis due to the aligned high anisotropy orientation of the Zn-S bonds on the lateral (100) face of ZnO NWs and NTs. Polycrystalline ZnO NTs, however, exhibit a preferential magnetization direction parallel to the tube axis which is ascribed to shape anisotropy dominating the magnetic response. Our results demonstrate the interplay of morphology, dimensions, and crystallinity on spin alignment and magnetic anisotropy in a 3D semiconductor nanosystem with interfacial magnetism.

Room temperature fabrication of single crystal nanotubes of CaSn(OH) 6 through sonochemical precipitation

CaSn(OH) 6 nanotubes were fabricated by sonochemical precipitation method at room temperature. A direct rolling process from nanosheets to nanotubes was expected for the synthesis of CaSn(OH) 6 nanotubes. The transient CaSn(OH) 6 nanosheets are formed as intermediates produced by the spontaneous self-assembly and transformation of amorphous colloid clusters. During the crystallization process of intermediate nanosheets, the relaxation of surface strain in the nanosheet interfaces can induce the nanosheets to roll up to form nanotubes under ultrasonic conditions. In this synthesis, the addition of Na 2CO 3 seems to play an important role in the formation, size, and shape control of the nanotubes. Investigations into the stability performance of the nanotubes indicate that the morphologies are very sensitive to pH and temperature. The method suggests a general strategy for the design and fabrication of functional single-crystalline nanotubes through an intermediate nanosheet rolling process. The in vitro fabrication of such single crystal nanotubes could shed light on fundamental mechanisms for closed hollow nanostructures. Furthermore, nanotubes produced in high yield and at low cost are envisioned to have applications in areas ranging from medicine to pharmaceuticals through to materials science.

Synthesis and Analysis of New Inorganic Single-Crystalline Nanotubes and Nanowires

Synthesis and Analysis of New Inorganic Single-Crystalline Nanotubes and Nanowires

Mechanistic Investigations of PEG-Directed Assembly of One-Dimensional ZnO Nanostructures

Mechanistic investigation on spherical assembly of the unique one-dimensional ZnO nanorods, solid nanocones, or hollow prisms with the closed -c end, directed by poly ethylene glycol (PEG) with different molecular weights, has been carried out using spectroscopic methods. The single crystalline ZnO nanoprisms, hollow along the c axis but closed at the -c end, aggregate to urchin-type globules in the microscale when PEG 2000 is used as directing reagent, while spherical aggregates of single crystalline ZnO nanocones are obtained under the direction of PEG 200. Studies reveal that both the PEG molecules aggregate to globules by interacting with zinc species in suitable solvents and englobe the zinc species. By the short time of ultrasonic pretreatment on the solution, a kind of flagellum structure is induced around the globules, in long tubular shapes for PEG 2000 but as shorter wedges for PEG 200. The globules with flagellums are templates for the assembly of the ZnO nanotubes or ZnO nanocones in the hydrothermal treatment. The tiny ZnO crystallites, produced in the hydrothermal process, stack to the templates and amalgamate to single crystalline nanotubes or nanocones, similar to the oriented attachment mechanism. The PEG 2000 template is included in the ZnO cavity of nanotubes, while PEG 200 is excluded from the ZnO nanocones due to the different intertwist properties between the two PEG molecules. Both the urchin-type assemblies, possessing the same external crystalline plane, compose a isotropic powder and emit very strong yellow light, centered at approximately 2.1 eV, under the excitation of the He-Cd laser at 325 nm, which has been correlated to the specific crystal plane. The special powders will be easily coated onto any type of surface for the decoration of a large area of surfaces for future applications.

Formation of Crystalline SrAl2O4 Nanotubes by a Roll‐Up and Post‐Annealing Approach

On a roll: Nanotubes of SrAl2O4, an important phosphorescent host material, are prepared. Nanoscrolls are first formed through the roll-up of an artificial lamellar precursor in solution. The layer interfaces are then removed by high-temperature annealing, resulting in single-crystalline nanotubes.

One‐Step Preparation of Single‐Crystalline β‐MnO2 Nanotubes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Self‐Assembled Highly Faceted Wurtzite‐Type ZnS Single‐Crystalline Nanotubes with Hexagonal Cross‐Sections.

AbstractFor Abstract see ChemInform Abstract in Full Text.

One-Step Preparation of Single-Crystalline β-MnO2 Nanotubes

Single-crystal beta-MnO(2) nanotubes with diameters in the range 200-500 nm and lengths up to several micrometers were successfully prepared by a simple hydrothermal method through oxidizing MnSO(4) with NaClO(3) in the presence of poly(vinyl pyrrolidone) (PVP). It was found that the formation process of beta-MnO(2) nanotubes included two primary evolution stages over time: (1) the MnOOH nanoparticles initially formed in the hydrothermal system and anisotropic growth to nanorods and nanorod aggregates, and (2) the MnOOH nanorods transformed into beta-MnO(2) tubular structure and grown into beta-MnO(2) nanotubes due to continuous growth through a dissolution-recrystallization process eventually. Based on a series of experimental analysis, the formation mechanism of these nanostructures was discussed briefly. The present study has enlarged the family of nanotubes available and offers a possible new, general route to one-dimensional single-crystalline nanotubes of other materials.

Self‐Assembled Highly Faceted Wurtzite‐Type ZnS Single‐Crystalline Nanotubes with Hexagonal Cross‐Sections

The synthesis of self-assembled highly faceted wurtzite-type ZnS single crystalline nanotubes with hexagonal cross-section was studied. A high temperature thermal-chemical reaction route to self-assemble highly faceted ZnS nanotubes with hexagonal cross-sections. It was studied that the formation of ZnS is actually a self-assisted growth process. The self-assembly growth along the c-axis to highly hexagonal-faceted ZnS single-crystalline nanotubes is associated with its crystallographic structural characteristics. Field-emission scanning electron microscopy (FE-SEM) was used to examine the morphologies of the products.

Inside Front Cover: Self‐Assembled Highly Faceted Wurtzite‐Type ZnS Single‐Crystalline Nanotubes with Hexagonal Cross‐Sections (Adv. Mater. 16/2005)

AbstractHighly faceted wurtzite‐type ZnS nanotubes with hexagonal cross‐section morphologies have been self‐assembled via a controllable high‐temperature thermal‐chemical reaction route in work reported by Yin and co‐workers on p. 1972. The self‐assembly growth along c‐axis to highly hexagonal‐faceted ZnS single‐crystalline nanotubes is associated with the crystallographic characteristics, such as the non‐central and polar surfaces of the wurtzite‐type ZnS structure. The faceted ZnS nanotubes grow along the <0001> direction, and are closed by low‐index faces of non‐polar {1000} faces. The inside cover and insets show electron microscopy and scanning electron microscopy images of the faceted ZnS nanotubes.

A Facile Route to Fabricate Single-crystalline Antimony Nanotube Arrays

Abstract Single-crystalline antimony nanotube arrays are fabricated in the anodic alumina membranes using the pulsed electrodeposition technique for the first time. The thickness of Au layer sputtered on the anodic alumina membrane and the pulsed electrodeposition technique are two key factors to produce single-crystalline nanotubes.

Template-free synthesis on single-crystalline InP nanotubes

A simple template-free thermal chemical route has been developed to prepare InP nanotubes with zinc blende structure by controlling the reaction temperature and flowing gas. The synthesized InP nanotubes are single-crystalline, free from defects and dislocations, and partially filled with In. The presence of metallic indium at tips of and within the synthesized InP nanotubes indicated a vapor–liquid–solid mechanism for the formation of InP nanotubes. The synthesized InP single-crystalline nanotubes grew along [1¯10] direction. The synthesized InP nanotubes have a uniform outer diameter of 50–60 nm and a wall thickness of 7–10 nm. The photoluminescence spectrum at room temperature exhibits a great shift from the bulk band gap of 1.35 eV to high energy of 1.49 eV.

Growth of Well Aligned IrO2 Nanotubes on LiTaO3(012) Substrate

Self-assembled and well-aligned IrO2 nanotubes have been grown on LiTaO3 (LTO) (012) substrates via metal-organic chemical vapor deposition (MOCVD), using (methylcyclopentadienyl)(1,5-cyclooctadiene)iridium(I) as the source reagent. The surface morphology, structural, and spectroscopic properties of the as-deposited nanotubes were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and micro-Raman spectroscopy. FESEM and TEM micrographs revealed that the single-crystalline nanotubes were grown with a tilt angle of ∼35° from the normal to the substrate. The IrO2 nanotubes showed square cross-sections and open-end morphology with the long axis toward the [001] direction. The analysis of selected area diffraction (SAD) and XRD patterns indicated the epitaxial growth of IrO2 nanotubes on LTO (012) with the orientation relationship given by IrO2(101)//LTO(012) and IrO2[01̄0]//LTO[100]. The probable mechanism for the formation of nanotubes has been discussed. Micro-Raman spectrum shows the red-shift and peak broadening of the IrO2 signatures with respect to that of the bulk counterpart which may be indicative of a phonon confinement effect for these nanotubes.