Search

The carbon nanotube (CNT) field emitter was fabricated using a thin free-standing CNT film, indicating a line-shape CNT field emitter. Field emission properties of the CNT field emitter were investigated in both diode and triode configurations. The CNT field emitter showed a low turn-on electric field of 1.8 V/ $\mu$ m and a high emission current of 40.3 mA, corresponding to the emission current density of 96 A/cm2 in the diode configuration. It also exhibited a high anode current of 40 mA, corresponding to the anode current density of 95.2 A/cm2 in the triode configuration. In addition, the CNT field emitter showed a good electron beam transmittance of 86.4% and excellent emission stability without degradation for 15 h. The main reason for the high performance of our CNT field emitter is caused by the high density of emission sites at the edge of the CNT film.

Textile electronics are ideal for novel electronic devices owing to their flexibility, light weight, and wearability. In this work, wearable organic field-effect transistors (OFETs) with all-graphene electrodes, fabricated using hot pressing, are described. First, highly conductive and flexible electrodes consisting of a cotton textile substrate and electrochemically exfoliated graphene (EEG) were prepared via hot pressing. The EEG/textile electrodes exhibited a low sheet resistance of 1.3 Ω sq−1 and high flexibility; these were used as gate electrodes in the wearable OFETs. In addition, spray-coated EEG was also used as the source/drain (S/D) electrodes of the wearable OFETs, which recorded a sheet resistance of 14.8 Ω sq−1 after hot pressing. The wearable OFETs exhibited stable electrical performance, a field-effect mobility of 13.8 cm2 V−1 s−1, and an on–off current ratio of ~103 during 1000 cycles of bending. Consequently, the fabrication method for wearable transistors developed using textiles and hot-pressed graphene electrodes has potential applications in next-generation wearable devices.

Graphite nanoplatelet (GNP) paste field emitters fabricated using all-carbon-based materials, such as GNPs, graphite nanoparticles, graphite binders, and a graphite rod substrate have been demonstrated. The GNP field emitters on the graphite rod substrate showed an emission current density of 84.3 mA/cm2 and good emission stability with a degradation rate of less than 10%, indicating higher emission performance than other GNP field emitters. The enhanced field emission performance of the GNP field emitter is attributed to a low work function barrier between carbon materials, low contact resistance between GNPs and the graphite rod substrate, and good GNP paste bulk electrical conductivity. The new approach to fabricate GNP field emitters using all-carbon-based materials can be useful for various field emission devices.

We demonstrate that using nanocomposite thin films consisting of semiconducting polymer, poly(3-hexylthiophene) (P3HT), and electrochemically exfoliated graphene (EEG) for the active channel layer of organic field-effect transistors (OFETs) improves both device performances and mechanical properties. The nanocomposite film was developed by directly blending P3HT solution with a dispersion of EEG at various weight proportions and simply transferring to an Si/SiO2 substrate by the solution floating method. The OFET based on P3HT/EEG nanocomposite film showed approximately twice higher field-effect mobility of 0.0391 cm2·V−1·s−1 and one order of magnitude greater on/off ratio of ~104 compared with the OFET based on pristine P3HT. We also measured the mechanical properties of P3HT/EEG nanocomposite film via film-on-elastomer methods, which confirms that the P3HT/EEG nanocomposite film exhibited approximately 2.4 times higher modulus (3.29 GPa) than that of the P3HT film (1.38 GPa), while maintaining the good bending flexibility and durability over 10.0% of bending strain and bending cycles (1000 cycles). It was proved that the polymer hybridization technique, which involves adding EEG to a conjugated polymer, is a powerful route for enhancing both device performances and mechanical properties while maintaining the flexible characteristics of OFET devices.

We investigated the dependence of electron mobility on the thickness of MoS2 nanosheets by fabricating bottom-gate single and few-layer MoS2 thin-film transistors with SiO2 gate dielectrics and Au electrodes. All the fabricated MoS2 transistors showed on/off-current ratio of ∼107 and saturated output characteristics without high-k capping layers. As the MoS2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS2 transistors increased from ∼10 to ∼18 cm2V−1s−1. The increased subthreshold swing of the fabricated transistors with MoS2 thickness suggests that the increase of MoS2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS2 layer on its thickness.

Diameters and crystallinity of multi-walled carbon nanotubes (MWCNTs) dependent on reduction temperature of the Fe–Co/MgO catalyst were investigated. MWCNTs were synthesized by catalytic chemical vapor depositing and the Fe–Co/MgO catalyst was fabricated by using a sol-gel method. According to Raman analysis, transmission electron microscopy and thermogravimetric analysis, the diameter distribution of MWCNTs was broadened with increasing reduction temperature of the Fe–Co/MgO catalyst and crystallinity was improved. The above results are attributed to an increased size and enhanced crystallinity of metal catalyst particles by increasing reduction temperature.

BackgroundThe administration of a single dose of propofol is reported to be effective in decreasing the incidence and severity of emergence agitation (EA) in children following sevoflurane anesthesia. The aim of this study was to investigate the clinical usefulness of a single dose of propofol 1 mg/kg at the end of adenotonsillectomy for reducing the incidence of EA after sevoflurane anesthesia.MethodsNinety children, aged 3-8 years, undergoing adenotonsillectomy were randomized into two groups: the propofol group (n = 45) and the saline group (n = 45), of which 88 children completed the study. Anesthesia was maintained with sevoflurane 2-2.5 vol% and nitrous oxide/oxygen (50%/50%). At the completion of adenotonsillectomy, the propofol group patients were given 1 mg/kg of propofol and the saline group patients were given saline 0.1 ml/kg in the same volume. The incidence of EA was assessed with Aono's four point scale and the severity of EA was assessed with pediatric anesthesia emergence delirium (PAED) scale at 5 min (T5), 15 min (T15) and 30 min (T30) after emergence.ResultsOf the 88 patients, the incidence of EA at T5, T15 and T30 was 61.4%, 27.3%, and 4.5% in the propofol group while in the saline group was 68.2%, 29.5%, and 9.1%, respectively. The incidence and severity of EA were not found to be significantly different between the two groups, but the scales in each group decreased significantly over time.ConclusionsThe administration of propofol 1 mg/kg at the end of surgery did not have any significant effect in reducing the incidence and severity of EA in children undergoing adenotonsillectomy under sevoflurane anesthesia.

There are many causes of prolonged postoperative muscle weakness, including drugs, residual anesthetics, cerebrovascular events, electrolyte imbalance, hypothermia, and neuromuscular disease. Neuromuscular diseases are relatively rare, with the most common being myasthenia gravis and Lambert-Eaton myasthenic syndrome (LEMS). We report an unusual case in which a patient who was given a muscle relaxant during mediastinoscopy developed postoperative muscle weakness that was ultimately diagnosed as secondary to LEMS.

We have doped manganese-oxide onto graphene by an electrochemical method. Graphene showed a clear ferromagnetic semiconductor behavior after doping of manganese-oxide. The manganese-oxide doped graphene has a coercive field (Hc) of 232 Oe at 10 K, and has the Curie temperature of 270 K from the temperature-dependent resistivity using transport measurement system. The ferromagnetism of manganese-oxide doped graphene attributes to the double-exchange from the coexistence of Mn3+ and Mn4+ on the surface of graphene. In addition, the semiconducting behavior is caused by the formation of manganese-oxide on graphene.

The carbon nanotube (CNT) field emitters have been fabricated by attaching a CNT film on a graphite rod using graphite adhesive material. The CNT field emitters showed much improved field emission properties due to increasing crystallinity and decreasing defects in CNTs after the high temperature thermal annealing at 900 °C in vacuum ambient. The CNT field emitters showed the low turn-on electric field of 1.15 V/μm, the low threshold electric field of 1.62 V/μm, and the high emission current of 5.9 mA which corresponds to a current density of 8.5 A/cm2. In addition, the CNT field emitters indicated the enhanced field emission properties due to the multi-stage effect when the length of the graphite rod increases. The CNT field emitter showed good field emission stability after the high temperature thermal annealing. The CNT field emitter revealed a focused electron beam spot without any focusing electrodes and also showed good field emission repeatability.

The relationship between the field emission and the density of states (DOS) of single-walled carbon nanotubes (SWCNTs) synthesized by hydrogen arc-discharge method is investigated. The results have shown that the field emission of SWCNTs can be closely related to the DOS of SWCNTs near the Fermi level.

The electronic structure of multiwalled carbon nanotubes (CNTs) was investigated, depending on the growth temperature, using synchrotron X-ray photoelectron spectroscopy (XPS) and field emission measurements. Field emission from the as-grown CNTs exhibits a large enhancement of current density with growth temperature, strongly correlated with the electronic structure revealed by XPS.

The synthesis of thin single-crystalline gallium nitride (GaN) nanowires and their optical and field emission properties are demonstrated. The synthesized GaN nanowires are shown to be single-crystalline wurtzite structures.

The hydrogen storage capacity of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) in ambient conditions is studied by means of the volumetric method, and compared with those of the single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs). Results indicate that the herringbone carbon nanotube structure is more capable of hydrogen storage than the herringbone graphite nanofiber structure.

A nanoindenter XP with scanning capabilities was used to perform nanoindentations on GaN and ZnO nanowires with radii in the range of 20–50 nm, positioned on a silicon substrate and bonded to the substrate at their ends with platinum. Since the geometry of indentation of a nanowire differs significantly from the indentation of a half-space, the standard Oliver-Pharr method [W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)] of analysis may not be used. A two interface contact model has been developed for the nanoindentation of a nanowire on a flat substrate, with the two interfaces, indenter/nanowire and nanowire/substrate, being in a series. The contact at the indenter/nanowire interface is modeled as an elliptical contact at the sphere (indenter)/cylinder interface. The contact at the nanowire/substrate interface is modeled as a contact at the cylinder/half-space interface under some concentrated forces applied on top of the cylinder. Under these latter conditions the cylinder may be expected to recede from the half-space when the load is applied. In order to predict the contact stiffness for the two interfaces, the theories of Hertzian contacts and receding contacts have been reviewed, generalized, and used. Considering the possible adhesion at the nanowire/substrate interface and the fixed ends of the nanowire, we have considered two limits for the contact at the nanowire/substrate interface: one with and one without separation at the interface; thus, we obtain two bounds for the contact stiffness and hardness. The model has been used to analyze the nanoindentation data for GaN and ZnO nanowires. We found that the hardness of the GaN nanowire is 46.7±5.6 GPa, which is much higher than that of the ZnO nanowire, 3.4±0.9 GPa. We also found that the Oliver-Pharr hardness [W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)] may be the rough lower bound of the hardness and the Joslin-Oliver hardness [D. L. Joslin and W. C. Oliver, J. Mater. Res. 5, 123 (1990)] may be the rough upper bound of the hardness. [ABSTRACT FROM AUTHOR]

The synthesis of saw-like nanostructures composed of ZnO nanobelts and ZnS nanowires by a simple thermal evaporation process is reported. The formation of saw-like heterostructures is induced by the polar surfaces of wurtzite ZnO and ZnS and their photoluminescence properties are studied at room temperature.

The controlled growth of novel hierarchical nanoarchitectures is reported, using a simple atmospheric pressure thermal vapor deposition method. In the process, both the morphology and the construction units could be efficiently controlled by a simple adjustment of the weight ratio of In/In2S3.

Delicate hollow ZnO urchins are fabricated by thermal evaporation of metallic zinc powders in a tube furnace without the use of additive, high temperature, or low pressure. Studies indicated that the growth of hollow ZnO urchins involves the vaporization of Zn powder, solidification of liquid droplets, surface oxidation, sublimation, and self-catalytic growth of one-dimensional nanowires.

Large-scale synthesis of single-crystal CdS micro belts as achieved by modifying thermal evaporation method, in which an adiabatic layer was used to provide abrupt temperature decrease and high gas concentration for the microbelt growth. Studies found that the adiabatic layer has great influence on the formation of CdS microbelts.

S-doped ZnO nanostructures such as nanonails and nanowires are synthesized through a simple one-step catalyst-free thermal evaporation process on a large scale. Studies found out that the S-doped ZnO nanonails and nanowires were single-crystalline wurtzite structure and grew along the (001) direction.

Thermal chemical vapor deposition of acetylene (C2H2) is employed for growing the vertically aligned carbon nanotubes (CNTs) on iron (Fe) deposited silicon oxide (SiO2) substrate in a wide temperature range of 550 to 950 degree Celsius. Images obtained from transmission electron microscope reveal that all the CNTs had a bamboolike structure in which the curvature of compartment layers was directed to the tip, independently of growth temperature.

Diameters and crystallinity of multi-walled carbon nanotubes (MWCNTs) dependent on reduction temperature of the Fe--Co/MgO catalyst were investigated. MWCNTs were synthesized by catalytic chemical vapor depositing and the Fe--Co/MgO catalyst was fabricated by using a sol-gel method. According to Raman analysis, transmission electron microscopy and thermogravimetric analysis, the diameter distribution of MWCNTs was broadened with increasing reduction temperature of the Fe--Co/MgO catalyst and crystallinity was improved. The above results are attributed to an increased size and enhanced crystallinity of metal catalyst particles by increasing reduction temperature. [ABSTRACT FROM AUTHOR]

Back-gated MoSe2 thin-film transistors (TFTs) with an Al2O3-capping layer were fabricated, and the device characteristics of the MoSe2 TFTs that are dependent on the Al2O3-capping-layer passivation were investigated. The output drain current was doubled, the fluctuation of the output current was suppressed, and the threshold voltage of the MoSe2 TFTs was negatively shifted with the Al2O3-capping layer. The on/off-current ratio of the MoSe2 TFTs is approximately six decades regardless of the Al2O3-capping layer, but the field-effect mobility was greatly increased from 2.86 cm2/Vs to 10.26 cm2/Vs after the deposition of the Al2O3-capping layer. According to the results of this study, the Al2O3-capping layer can enhance the device characteristics of MoSe2 TFTs. [ABSTRACT FROM AUTHOR]

We investigated the dependence of electron mobility on the thickness of MoS2 nanosheets by fabricating bottom-gate single and few-layer MoS2 thin-film transistors with SiO2 gate dielectrics and Au electrodes. All the fabricated MoS2 transistors showed on/off-current ratio of ~107 and saturated output characteristics without high-k capping layers. As the MoS2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS2 transistors increased from ~10 to ~18 cm2V-1s-1. The increased subthreshold swing of the fabricated transistors with MoS2 thickness suggests that the increase of MoS2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS2 layer on its thickness. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes (SWCNTs) are promising materials as active channels for flexible transistors owing to their excellent electrical and mechanical properties. However, flexible SWCNT transistors have never been realized on paper substrates, which are widely used, inexpensive, and recyclable. In this study, we fabricated SWCNT thin-film transistors on photo paper substrates. The devices exhibited a high on/off current ratio of more than 106 and a field-effect mobility of approximately 3cm²/V·s. The proof-of-concept demonstration indicates that SWCNT transistors on flexible paper substrates could be applied as low-cost and recyclable flexible electronics. [ABSTRACT FROM AUTHOR]

Boron nitride nanotubes (BNNTs) are considered as a promising cold electron emission material owing to their negative electron affinity. BNNT field emitters show excellent oxidation endurance after high temperature thermal annealing of 600°C in air ambient. There is no damage to the BNNTs after thermal annealing at a temperature of 600°C and also no degradation of field emission properties. The thermally annealed BNNTs exhibit a high maximum emission current density of 8.39mA/cm² and show very robust emission stability. The BNNTs can be a promising emitter material for field emission devices under harsh oxygen environments. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) emitters with small emission area were fabricated on graphite rods using CNT films. By introducing the edge polishing process, the field emission performance of the CNT emitter was much improved, which showed a very high emission current of 6.34mA (1.6 A/cm2) under an applied electric field of 5.3V/μm. It also indicates good long-term emission stability, which reveals no degradation in the emission current for 20 h. The emission patterns demonstrate uniform and well-focused electron beam spots. The enhanced field emission performance is mainly attributed to the suppressed edge emission after the edge polishing process. [ABSTRACT FROM AUTHOR]

A micro-scale metal grid based on a silicon frame for application to electron field emission devices is introduced and experimentally demonstrated. A silicon lattice containing aperture holes with an area of 80 × 80 &mgr;m2 and a thickness of 10 µm is precisely manufactured by dry etching the silicon on one side of a double-polished silicon wafer and by wet etching the opposite side. Because a silicon lattice is more rigid than a pure metal lattice, a thin layer of Au/Ti deposited on the silicon lattice for voltage application can be more resistant to the geometric stress caused by the applied electric field. The micro-fabrication process, the images of the fabricated grid with 88% geometric transparency and the surface profile measurement after thermal feasibility testing up to 700 °C are presented. [ABSTRACT FROM AUTHOR]

We highlight the significance of multiwall carbon nanotube (MWCNT) shape on the electrical percolation. For rodlike MWCNTs, percolation threshold depends on aspect ratio (L/d). For random coil-like MWCNTs, the percolation threshold does not depend on L/d but depends on the shape factor of MWCNTs represented by the ratio between static bending persistence length and diameter. Surface resistivities of various MWCNTs converge into single curve when we plot their dimensionless surface concentration versus surface resistivity. The surface resistivity of MWCNT films decrease with increasing temperature, particularly at low concentrations, indicating the films can be used as a negative temperature coefficient thermistor. [ABSTRACT FROM AUTHOR]

Vertically aligned Fe2O3 nanowire arrays were synthesized by the thermal oxidation of Fe foil. They consist of single-crystalline rhombohedral α-Fe2O3 nanocrystals grown along the [1120] direction. Most of the nanowires have a sharp tip (diameter=50 nm) and beltlike base. The magnetization measurement reveals a Morin temperature of 125 K and unique magnetic anisotropy due to the easy axis of the magnetocrystalline anisotropy perpendicular to the nanowire axis. [ABSTRACT FROM AUTHOR]

We have investigated nitrogen doping effects on the structure and crystallinity of bamboo-shaped multiwalled carbon nanotubes (BS-MWNTs) by means of x-ray photoemission spectroscopy (XPS) and transmission electron microscopy. By controlling the NH3/C2H2 flow ratio during the chemical vapor deposition, the nitrogen concentrations of 0.4% to 2.4% were obtained. According to the XPS measurements, the increasing nitrogen concentration gave rise to an increase of the N-sp3 C bonds as well as the deterioration of the crystallinity of the BS-MWNTs. Besides, the N-sp3 C bonds were found to prevail over the N-sp2 C bonds above 5% nitrogen concentration. At higher nitrogen concentrations, the BS-MWNTs showed shorter compartment distances, presumably due to the suppressed surface diffusion of carbon on the catalyst particles. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the synthesis of carbon nanotubes by thermal chemical vapor deposition of C[sub 2]H[sub 2] on transition metal-coated silicon substrates. Relevance of the surface modification of transition metals deposited on substrates to nanotube growth; Control of the diameters of carbon nanotubes by applying different transition metals.

The field emission properties of boron nitride nanotube (BNNT) field emitters according to vacuum pressure were demonstrated. During the short-term emission operation, the field emission behaviors were almost similar, regardless of the vacuum pressure, even though the turn-on electric field of the BNNT field emitter was slightly increased as the vacuum pressure increased. On the other hand, during the long-term emission operation, both the degradation and fluctuations of the emission current of the BNNT field emitters were dramatically increased as the vacuum pressure increased. The degradation of field emission properties of the BNNT emitters according to vacuum pressure is mainly attributed to the ion bombardment effect, rather than the oxidation effect. The field emission behavior under Ar ambient also strongly demonstrates that the degradation and the fluctuation of the emission current are largely dependent on the ion bombardment effect. [ABSTRACT FROM AUTHOR]