Bi3.25La0.75Ti3O12 (BLT) nanotube capacitors for semiconductor memories

We report results of fabrication and examination of Bi_3.25La_0.75Ti₃O₁₂ (BLT) ferroelectric nanotubes. BLT nanotubes are suggested for developing 3D ferroelectric nanotube capacitors which could be used in high-density memory applications. BLT nanotubes were prepared by template-wetting process using polymeric sources where anodic aluminum oxide had been used as a template. After annealing, tubular BLT structures were crystallized inside the pores of the template. By selective etching of the template, released BLT nanotubes have been obtained. Crystallization and nucleation of the nanotubes were analyzed by XRD and FE-SEM techniques.     

Synthesis, characterization and electrochemical behavior of polypyrrole/carbon nanotube composites using organometallic-functionalized carbon nanotubes

Thorn-like, organometallic-functionalized carbon nanotubes were successfully developed via a novel microwave hydrothermal route. The organometallic complex with methyl orange and iron (III) chloride served as reactive seed template, resulting in the oriented polymerization of pyrrole on the modified carbon nanotubes without the assistance of other oxidants. Morphological and structural characterizations of the carbon nanotube/methyl orange-iron (III) chloride and polypyrrole/carbon nanotube composites were examined using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), infrared spectroscopy and X-ray diffraction (XRD). The electrochemical property of the polypyrrole/carbon nanotube composite was elucidated by cyclic voltammetry and galvanostatic charge-discharge. A specific capacitance of 304 F g⁻¹ was obtained within the potential range of −0.5-0.5 V in 1 M KCl solution.     

Fe nanowire encapsulated in boron nitride nanotubes

Boron nitride (BN) nanotubes, nanohorns, nanocoils were synthesized by annealing Fe₄N and B powders at 1000 °C for 1 h in nitrogen gas atmosphere. Especially, Fe-filled BN nanotubes were produced, and investigated by high-resolution electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy, which indicates that the [110] of Fe is parallel to the BN nanotube axis. Formation mechanism of Fe-filled BN nanotube was speculated based on these results.     

Theoretical investigation of CO adsorption on TM-doped (MgO)12 (TM = Ni, Pd, Pt) nanotubes

CO adsorption on TM-doped magnesia nanotubes (TM = Ni, Pd and Pt) have been studied by using density functional theory. Our calculation results show that CO favors adsorption on TM-doped magnesia nanotubes in the form of C atom bonding with TM atom. Fukui indices analysis clearly exhibits that doping of impurity TM atom allows for a noticeably enhancement of nucleophilic reactivity ability of magnesia nanotube. The adsorption energies demonstrate that CO molecule is more strongly bound on the 3-fold TM atoms than the 4-fold TM atoms. This finding is well confirmed by TM-C bond length, charge transfer and C-O vibrational frequency. The high adsorption energy of 2.55 eV is found when CO adsorbs on 3-fold Pt in Pt-doped magnesia nanotubes, implying the kind of the doping TM atom has a significant influence on the chemical reactivity.     

NMR strategies to study the local magnetic properties of carbon nanotubes

The local magnetic properties of the one dimensional inner space of the nanotubes are investigated using ¹³C nuclear magnetic resonance spectroscopy of encapsulated fullerene molecules inside single walled carbon nanotubes. Isotope engineering and magnetically purified nanotubes have been advantageously used on our study to discriminate between the different diamagnetic and paramagnetic shifts of the resonances. Ring currents originating from the π electrons circulating on the nanotube, are found to actively screen the applied magnetic field by −36.9 ppm. Defects and holes in the nanotube walls cancel this screening locally. What is interesting, that at high magnetic fields, the modifications of the NMR resonances of the molecules from free to encapsulated can be exploited to determine some structural characteristics of the surrounding nanotubes, never observed experimentally.     

Physico-chemical properties of titania nanotubes synthesized via hydrothermal and annealing treatment

Titania nanotubes are synthesized via hydrothermal treatment of TiO₂ powders in NaOH solution at 110 °C for 90 h, followed by annealing at 400 °C. The morphology of nanotubes is characterized by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Microscopic observations on the transformation process indicate that the nanotubes retain their shapes after the annealing process. The crystalline structure and composition are examined by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX). The results confirm the absence of impurity peaks and the crystal structure change from nanotubes to anatase phase after annealing treatment. The average specific surface area of the particles is probed using gas adsorption-desorption measurements. The prepared tubular samples exhibit greater specific surface areas and higher pore volumes than the precursor. Moreover, it is apparent that the hydrothermal treatment modifies the optical properties of the titania samples and red-shifts the UV absorption to a band gap energy of 3.04 eV after annealing treatment.     

Recovery properties of hydrogen gas sensor with Pd/titanate and Pt/titanate nanotubes photo-catalyst by UV radiation from catalytic poisoning of H2S

Recovery properties after H₂S catalytic poisoning of catalytic-type gas sensor with photo-catalysts and UV radiation have been examined. Each sensing material of the sensor consists of Pd, Pt supported on γ-Al₂O₃ and Pd/titanate, Pt/titanate nanotubes or TiO₂ particles. Pd/titanate and Pt/titanate nanotubes photo-catalyst were synthesized by hydrothermal synthesis method. All the sensors were deactivated after 500 ppm H₂S exposure for 20 h. The sensors with Pd/titanate or Pt/titanate nanotubes showed regenerated voltage response under UV radiation. However the sensor with TiO₂ particles showed negligible regenerated voltage response. Regenerated voltage response with Pd/titanate or Pt/titanate nanotubes may stem from location of Pd or Pt catalyst on the titanate nanotube photo-catalyst.     

A preservation study of carbon nanotubes in alumina-based nanocomposites via Raman spectroscopy and nuclear magnetic resonance

Raman spectroscopy was used to study the preservation of the carbon nanotube structure in nanotube-reinforced alumina nanocomposites consolidated via spark plasma sintering (SPS). A series of Raman spectroscopy experiments was used to identify the thermal breakdown temperature of single-walled carbon nanotubes (SWCNTs) embedded in nanocrystalline alumina. It was found that the carbon nanotube structure remains intact after sintering at 1150 °C, but almost completely breaks down by 1350 °C after only 5 min. Also, ²⁷Al nuclear magnetic resonance (NMR) was used to study the chemical and structural effects of high-energy ball milling (HEBM) and SPS consolidation on pure alumina and SWCNT-alumina nanocomposites. HEBM does not change the mixed coordination number of the as-received alumina, but slight peak shifts indicate residual stresses. No Al₄C₃ was detected in any of the consolidated samples – even up to 1550 °C for 10 min. Thus, it is concluded that consolidation of carbon nanotube-reinforced composites should be completed at temperatures below ∼1250 °C in order to preserve the carbon nanotube structure. PACS 61.18.Fs; 61.46.Fg; 61.82.Rx; 62.25.+g; 76.60.-k     

GaS multi-walled nanotubes from the lamellar precursor

Inorganic fullerene-like (IF) nanotubes constructed from layered metal chalcogenides are of particular significance because of their excellent physical properties and potential application in wide fields. But very few previous studies were focused on the IF nanotubes of layered III-VI semiconductor. Therefore we investigate the preparation, structure and photoluminescence (PL) properties of GaS nanotube (an important III-VI semiconductor IF nanotube). A simple method is introduced to prepare GaS multi-walled nanotubes for the first time by annealing the natural lamellar precursor in Ar. The reaction temperature is crucial for the formation of nanotube. A suitable temperature range is 500–850 °C. Bulk quantities of GaS nanotubes with diameters of 30–150 nm and lengths up to ten micrometers were produced. Some of these nanotubes show corrugated and interlinked structure and form many segments, demonstrating a bamboo-like structure. As compared to bulk materials, the obvious distinction of the products in PL spectra at liquid nitrogen temperature of 77 K was due to the structure variety. PACS 61.46.+w; 81.07.De; 81.16.Be     

Synthesis of multi-wall carbon nanotubes by the pyrolysis of ethanol on Fe/MCM-41 mesoporous molecular sieves

Ordered hexagonal arrangement MCM-41 mesoporous molecular sieves were synthesized by the traditional hydrothermal method, and Fe-loaded MCM-41 mesoporous molecular sieves (Fe/MCM-41) were prepared by the wet impregnation method. Their mesoporous structures were testified by X-ray diffraction (XRD) and the N₂ physical adsorption technique. Carbon nanotubes (CNTs) were synthesized by the chemical vapor deposition (CVD) method via the pyrolysis of ethanol at atmospheric pressure using Fe/MCM-41 as a catalytic template. The effect of different reaction temperatures ranging from 600 to 800 ^°C on the formation of CNTs was investigated. The resulting carbon materials were characterized by various physicochemical techniques such as transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The results show that multi-wall carbon nanotubes (MWCNTs) with an internal diameter of ca. 7.7 nm and an external diameter of ca. 16.9 nm were successfully obtained by the pyrolysis of ethanol at 800 ^°C utilizing Fe/MCM-41 as a catalytic template.