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To investigate the potential effects of miR-200c on proliferation and apoptosis of papillary thyroid cancer (PTC) cells.Micro ribonucleic acid-200c (miR-200c) inhibitor was transfected to down-regulate miR-200c expression. Cell counting kit-8 (CCK-8), colony formation experiment, and flow cytometry were used to detect the effects of miR-200c knockdown on proliferation and apoptosis of Butylated Hydroxytoluene 101 (BHT101) cells. The dual-luciferase reporter gene assay was conducted to detect whether miR-200c directly binds to the target gene. After knocking down miR-200c, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blotting analysis were performed to detect changes of target genes regarding messenger RNA (mRNA) and protein. Western blotting analysis was also adopted to detect gene expression of Wnt/β-catenin signaling pathway-related proteins.Compared with those in control group, the proliferation and clone formation ability of BHT101 cells in miR-200c knockdown group were significantly inhibited (p0.05), while the apoptosis rate increased markedly (p0.05). Dachshund Family Transcription Factor 1 (DACH1) was the direct target gene of miR-200c. After miR-200c knockdown, the expression levels of Wnt/β-catenin signaling pathway members (including c-Myc, β catenin and cyclin D1) all decreased.MiR-200c is a tumor suppressor miRNA, which promotes proliferation of PTC cells and activates Wnt/β-catenin signaling pathway by directly regulating the corresponding target protein, DACH1.

The ABX ternary compounds have a variety of attractive physical properties. For example, some of the half-Heusler compounds as a class of ABX compounds exhibit high thermal power factors and thus promising thermoelectric performances. This motivates a search for potential thermoelectric candidates from the ABX compound family different from the half-Heusler structures. In this study, we investigate the electronic and phononic structures of tetragonal NaMgX (X = P, Sb, As) compounds, which belong to the ABX family using first-principles calculations based on density functional theory and density functional perturbation theory. The whole set of thermoelectric properties are thus evaluated from the semi-classical Boltzmann transport calculations. It is revealed that weak electron–phonon coupling and strong bonding anharmonicity are the critical physical ingredients for promising thermoelectric performance, giving rise to the optimized figure of merit factor ZT of up to 1.38, 2.39, and 3.54 for NaMgX (X = P, Sb, As) compounds in the intermediate temperature range.

The microscopic mechanisms for higher thermoelectric performance of cost competitive rock salt compound Bi 2 SeS 2 were investigated. A low doping of Cu as an n-type dopant was conducted in order to optimize the band structure and improve the electrical conductivity. It was revealed that this compound exhibits a Seebeck coefficient higher than 300 μV K −1 , which sustains above 100 μV K −1 even with Cu doping, leading to a higher power factor. The microstructural characterizations revealed nano-scale Bi 2 S 3 precipitates in the Cu x Bi 2 SeS 2 matrix, beneficial to the lower lattice thermal conductivity that is insensitive to the Cu doping. A thermoelectric figure-of-merit factor ZT of ~0.7 at 450 °C in accompanying with the power factor of ~5.36 μW cm −1 K −2 was obtained under the optimized doping level, enabling this environmentally friendly compound interesting for thermoelectric power generation applications.

The aim of this study was to explore the associations of urinary selenium and polymorphisms in methylation related genes with breast cancer risk and the interactions on the risk. The present study involved in 240 female patients with incident breast cancer and 246 age-matched controls in two affiliated hospitals of Sun Yat-sen University in Guangzhou, China, from October 2009 to July 2010. DNMT1 rs2228611, MTHFR rs1801133, and MTR rs1805087 were genotyped using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry platform. Urinary concentration of selenium was measured by inductively coupled plasma mass spectrometry. Women with urinary selenium in the second tertile had a significant reduced breast cancer risk compared to those with urinary selenium in the lowest tertile [OR (95%CI): 0.50 (0.30, 0.81)]. DNMT1 rs2228611, MTHFR rs1801133, and MTR rs1805087 were not associated with breast cancer risk. Women with the third tertile of urinary selenium had a significant reduced breast cancer risk compared to those with the lowest tertile among women only with CC genotype [OR (95%CI): 0.55 (0.30, 1.00)] but not CT/TT genotypes [OR (95%CI): 1.58 (0.73, 3.42)] of MTHFR rs1801133 (P for interaction=0.044). Our results suggested that selenium was associated with a decreased risk of breast cancer and this beneficial effect was limited to women with CC genotype of MTHFR rs1801133.

The bipolar effect in relatively narrow band-gap thermoelectric (TE) compounds is a negative process deteriorating the TE properties particularly at higher temperatures. In this work, we investigate the TE performance of the compound CaMg2Bi2 using the first-principles calculation and semi-classical Boltzmann transport theory in combination with our experimental data. It is revealed that this compound exhibits a remarkable bipolar effect and temperature-dependent carrier concentration. The bipolar effect imposes remarkable influence on all the electron-transport related TE parameters. An effective carrier concentration neff as a function of temperature is proposed to account for the bipolar effect induced carrier excitations. The as-evaluated TE parameters then show good consistency with measured results. This work may shed light on our understanding of the bipolar effect in TE compounds.

In the present work, the authors suggest two methods using the bubble electrospinning to fabricate the aligned nanofibres by changing the collector electrode from a traditional metal plate into a single thin cylindrical metal electrode or two thin cylindrical metal electrodes respectively to collect the produced nanofibres. In the both cases, the aligned nanofibres are fabricated successfully.

The thermoelectric performance of materials relies substantially on the band structures that determine the electronic and phononic transports, while the transport behaviors compete and counter-act for the power factor PF and figure-of-merit ZT. These issues make a full-scale computation of the whole set of thermoelectric parameters particularly attractive, while a calculation scheme of the electronic and phononic contributions to thermal conductivity remains yet challenging. In this work, we present a full-scale computation scheme based on the first-principles calculations by choosing a set of doped half-Heusler compounds as examples for illustration. The electronic structure is computed using the WIEN2k code and the carrier relaxation times for electrons and holes are calculated using the Bardeen and Shockley’s deformation potential (DP) theory. The finite-temperature electronic transport is evaluated within the framework of Boltzmann transport theory. In sequence, the density functional perturbation combined with the quasi-harmonic approximation and the Klemens’ equation is implemented for calculating the lattice thermal conductivity of carrier-doped thermoelectric materials such as Ti-doped NbFeSb compounds without losing a generality. The calculated results show good agreement with experimental data. The present methodology represents an effective and powerful approach to calculate the whole set of thermoelectric properties for thermoelectric materials.

A facile dry route electrostatic-force-directed assembly (ESFDA) was used to deposit silver nanocrystals onto the external surface of vertically aligned multiwalled carbon nanotubes (MWCNTs). Charged and nonagglomerated aerosol silver nanocrystals were first produced using a mini-arc plasma source. The nanocrystals were then assembled onto the electrically biased MWCNT array through the enhanced electric field near the CNT surface. The electrostatic field plays a crucial role in the assembly process. Gradients of the nanocrystal size and the nanocrystal areal density along the length of the CNT have been observed, and these are likely due to the variation of the electric field near the CNT surface. The ESFDA technique enables the in situ coating of CNT arrays with nanocrystals to create novel hybrid nanomaterials with tailored properties.

Pr0.57Ca0.43MnO3 nanoparticles with an average particle size of similar to 20 nm have been synthesized using hydrothermal method in combination with post-annealing, and characterized using X-ray diffraction, X-ray photoelectron spectrometer, high-resolution transmission electron microscopy and superconducting quantum interference device magnetometery. The results show that the hydrothermal synthesis of Pr1-xCaxMnO3 compound below 240 degrees C is difficult. The Pr0.57Ca0.43MnO3 nanoparticles obtained by annealing the hydrothermal products at 900 degrees C for 2 h present an orthorhombic perovskite structure with the same lattice as bulk Pr0.6Sr0.4MnO3. Magnetic characterization reveals that the low-temperature antiferromagnetic and charge ordering transitions identified in bulk Pr0.57Ca0.43MnO3 are completely suppressed in the nanoparticles, while a ferromagnetic transition occurs at -110 K. The spin-freezing behavior at low temperature for the Pr0.57Ca0.43MnO3 nanoparticles is demonstrated. (c) 2006 Elsevier B.V. All rights reserved.

We investigated the temperature dependence of the normalized logarithmic relaxation rate $S(T)$ and the corresponding temperature dependence of the critical current ${I}_{c}(T)$ in high-${T}_{c}$ thin films (YBCO-123, TlBCCO-2212, -2223, and -2201, and Bi-2212). Experiments have been performed using persistent critical currents flowing in the a-b planes of ring-shaped samples. The magnitude of ${I}_{c}$ and the relaxation rate have been extracted from the measurement of the self-field of the current. The results revealed a relationship between ${I}_{c}(T)$ and $S(T).$ ${I}_{c}(T)$ in YBCO is a superposition of two universal components: an underdoped Ginzburg-Landau- (GL-) like one with ${I}_{c}(T)\ensuremath{\propto}{(T}_{c}\ensuremath{-}{T)}^{3/2}$ and ${T}_{c}$ between 40 and 60 K, and an Ambegaokar-Baratoff-like one close to an optimum doping. The results revealed that when the amount of the GL-like phase increases above a certain threshold value, a peak appears in $S(T)$ at temperatures of 20--30 K, and its height gradually increases with the magnitude of ${I}_{c}$ at 10 K for this phase. We discuss similarities between these results and those reported for YBCO crystals with columnar defects. The presence of two maxima in $S(T)$ have been observed for TlBCCO films that are composed of three different phases, at temperatures close to ${T}_{c}$ of two underdoped components. The studies imply that the filamentary phase separation on a nanometer scale level in the a-b planes is responsible for the changes in vortex dynamics.

The c-axis Josephson plasmon in optimally doped single-layer and bi-layer high Tc cuprates Tl2201 and Tl2212 have been investigated using infrared spectroscopy. We observed the plasma frequencies for these two compounds at 27.8 and 25.6 cm-1 respectively, which we interpret as a Josephson resonance across the TlO blocking layers. No maximum in the temperature dependence of the c-axis conductivity was observed below Tc, indicating that even in the superconducting state a coherent quasi-particle contribution to the c-axis conductivity is absent or very weak, in contrast to the behaviour of the ab-plane conductivity., Comment: 4 pages, 3 figures

The ${}^{99}\mathrm{Ru}$ M\"ossbauer effect has been measured in the ${\mathrm{Sr}}_{2}{\mathrm{Ru}}_{x}{\mathrm{Ir}}_{1\ensuremath{-}x}{\mathrm{O}}_{4}$ system for $x=1.0,$ 0.7, 0.5, and 0.4 at 4.2 K. The isomer shift measurements show a change of -0.05(.02) mm/s as the compound changes from a metal $(x=0.7)$ to an insulator $(x=0.5).$ This isomer shift change is the electronic signature of the metal-insulator transition. All these spectra are single line. At $x=0.4$ the compound undergoes a magnetic phase transition with the measurement of a hyperfine magnetic field of 7.2(1.5) T. The ${}^{99}\mathrm{Ru}$ M\"ossbauer effect has been measured from 1.8 to 147.5 K for ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and from these measurements the Debye temperature was estimated to be 427(50) K.

XPS core level and valence band spectra are presented for chemically etched epitaxial thin films of superconducting Tl2Ba2CuO6+δ on SrTiO3(100) substrates which are as-grown overdoped (superconducting transition temperature [Tc]=11 K) and annealed (Tc=63 K). The core levels measured from the annealed film are shifted to higher binding energies relative to those from the as-grown overdoped film, consistent with a doping-induced change in the chemical potential.

Overdoped ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ exhibits persistent photoconductivity at low temperatures. This effect has been observed before only in underdoped $R{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ $(R$=rare earth or yttrium). Contrary to $R{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$, ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ shows either a persistent increase or decrease of the carrier density with illumination, depending on doping and wavelength of the incident light. Thus it is possible to increase or decrease the superconducting transition temperature in ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CuO}}_{6+\ensuremath{\delta}}$ reversibly. These photoinduced changes can be explained by the existence of localized states in the charge reservoir layer.

From measurements of the far-infrared reflectivity at grazing angles of incidence with p-polarized light we determined the c-axis Josephson plasma frequencies of the single layer high-${\mathrm{T}}_{\mathrm{c}}$ cuprates ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CuO}}_{6}$ and ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4}$. We detected a strong plasma resonance at 50 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_{4}$ in excellent agreement with previously published results. For ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CuO}}_{6}$ we were able to determine an upper limit of the unscreened c-axis Josephson plasma frequency 100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ or a c-axis penetration depth g15 \ensuremath{\mu}m. The small value of ${\mathrm{\ensuremath{\omega}}}_{\mathrm{J}}$ stands in contrast to recent a prediction based on the interlayer tunneling mechanism of superconductivity.

The valence electronic structure and core levels of Tl2Ba2CuO(6 + delta) (Tl-2201) epitaxial films have been measured with X-ray photoelectron spectroscopy and are compared to those of Tl2Ba2CaCu2O(8 + delta) (Tl-2212). Changes in the Tl-2201 core-level binding energies with oxygen doping are consistent with a change in the chemical potential. Differences between the Tl-2201 and Tl-2212 measured densities of states are consistent with the calculated Cu 3d and Tl 6s partial densities of states.

An extremely low operating electric field has been achieved on zinc oxide (ZnO) nanowire field emitters grown on carbon cloth. Thermal vaporization and condensation was used to grow the nanowires from a mixture source of ZnO and graphite powders in a tube furnace. An emission current density of 1mA∕cm2 was obtained at an operating electric field of 0.7V∕μm. Such low field results from an extremely high field enhancement factor of 4.11×104 due to a combined effect of the high intrinsic aspect ratio of ZnO nanowires and the woven geometry of carbon cloth.

Field emission from carbon nanotubes grown on carbon cloth has been studied. An extremely low electric field of less than 0.4V∕μm is required to reach an emission current density of 1mA∕cm2. This ultralow operating electric field of carbon nanotubes grown on carbon cloth is mainly due to a very high field enhancement factor of 1.882×104, which is the result of geometrical configuration of the carbon nanotubes and the substrate. In addition to the field enhancement, the highly disordered microstructure of carbon nanotubes grown on carbon cloth plays an important role to field emission. This unexpected result indicates that the roughness of the substrates on which carbon nanotubes grow is very important. This result also brings us significantly closer to practical applications such as highly efficient lamps, field emission displays, micro vacuum electron sources, etc.

The length and the spacing of carbon nanotube (CNT) films are varied independently to investigate their effect on the field-emission characteristics of the vertically aligned CNT films grown by plasma-enhanced hot filament chemical vapor deposition using pulsed-current electrochemically deposited catalyst particles. It is shown that, in general, the macroscopic electric field Emac,1, defined as the electric field when the emission current density reaches 1 mA/cm2, can be reduced by increasing the length and the spacing of CNTs. However, for the very-high-density CNT films, the increase of length increases Emac,1 slightly, whereas for the very short CNT films, the increase of spacing does not effectively reduce Emac,1.

Epitaxial superconducting thin films Tl2Ba2CuO6+δ (Tl-2201) with a continuous range of doping levels have been synthesized. The films were made by rf magnetron sputtering and two-step postdeposition annealing, and their doping levels were controlled by varying the oxygen content through annealing in flowing argon. By annealing in flowing argon, the as-grown Tl-2201 thin films were changed continuously from the initially overdoped state, through the optimally doped state and then to the underdoped state. The normal state resistivity versus temperature curves of all the underdoped Tl-2201 thin films are convex, whereas those of the overdoped Tl-2201 thin films are all concave. Transmission electron microscopy bright-field images and selected area diffraction patterns of the 58 K underdoped Tl-2201 thin film showed neither twinning bands nor spot splitting associated with an orthorhombic crystal lattice. Therefore, it is concluded that underdoped Tl-2201 thin films are also tetragonal just like all the overd...

Epitaxial films of Tl2Ba2CuO6+δ (Tl‐2201) have been prepared on SrTiO3 by sputtering and postdeposition annealing. The films were deposited onto (100)SrTiO3 single crystal substrates by rf magnetron sputtering and then annealed using a two‐step process. The annealed films typically exhibit transition temperatures of about 11 K. Subsequent reannealing to optimize the oxygen doping in the film results in an increase in the transition temperature, and optimally reannealed films exhibit transition temperatures of about 83 K. The crystal structure of these films has been studied by x‐ray diffraction and transmission electron microscopy. These results indicate that both the annealed (Tc=11 K) and optimally reannealed samples (Tc=83 K) have a tetragonal crystal structure. This structural information is crucial in evaluating recent measurements on these films to determine the electron pairing symmetry (d wave or s wave) in high‐Tc superconductors.

We study propagation of light in square and hexagonal two-dimensional photonic crystals. We show, that slabs of these crystals focus light with subwavelength resolution. We propose a systematic way to increase this resolution, at an essentially fixed frequency, by employing a hierarchy of crystals of the same structure, and the same lattice constant, but with an increasingly complex basis., Comment: 16 Pages, 5 Figures

Ag-clad (Tl,V)(Sr,Ba)2Ca2Cu3Oy tapes were fabricated by a powder-in-tube process. The tapes exhibited no discernible favourable texture. Critical current density (Jc) values at 77 K were

Field emission cathodes based on carbon nanotubes are potential candidates for low-cost replacement of thermionic cathodes used in microwave tubes. This paper describes the technical approach for realizing and testing prototype field emission cathodes fabricated from aligned arrays of carbon nanotubes. The emission characteristics of prototype cathodes of up to 1 cm/sup 2/ area have been measured in both DC and pulse mode experiments. Turnon fields as low as 10 kV/cm, field enhancement factors greater than 10/sup 3/, and emission currents higher than 5 mA have been observed. These preliminary results indicate that high current densities on the order of I to 10 A/cm/sup 2/ at practical electric fields are achievable with optimized cathode structure and improved degassing.

In situ synthesis has been developed for the first time to fabricate the Tl‐based silver‐sheathed superconducting tapes. Tapes of Tl0.5Pb0.5Sr1.6Ba0.4Ca0.8Y0.2Cu2Oy (Tl‐1212) made by the in situ synthesis method under optimal oxygen partial pressure were found to have transport Jc of 7000 A/cm2 in the absence of external magnetic field. In low magnetic field (

Sixty-one human nasopharyngeal carcinomas (NPC) were examined by allelotype analysis for the purposes of detecting potential association between loss of heterozygosity (LOH), clinicopathological parameters and Epstein-Barr virus (EBV) infection. LOH was performed using 257 polymorphic markers on 22 chromosomes. High frequency LOH (or = 60%) was observed on 12 chromosome arms including 1p, 2p, 2q, 3p, 3q, 5q, 9p. 9q, 11q, 13q, 14q and 17q, with the highest LOH frequency of 91% on 3p. Seventy-three loci presented LOH frequencyor = 30%; most of these loci clustered on 1p36 p34, 2p25-p24, 3p14-p21, 3p24-p26, 5q11-q14, 5q31-q33, 9p21-p23, 9q33-q34, 11q23-q25, 13q12 q14, 13q31-q33, 14q13-q11, 14q32 and 19q13. On 1p36-p34, 2p25-p24, 5q13-q11, 5q31-q33 and 19q13 are reported for the first time. LOH was correlated with specific clinicopathological parameters including tumor T-stage, N-stage, TNM-stage, tumor differentiation and serum antibody titers of IgA against virus capsid antigens (VCA) and early antigen (EA) of EBV in NPC (LOH frequencyor = 30%). Significantly high LOH frequency was observed on 9p21 (56%) and 19q13 (50%) in NPC with stage T3+T4, while significantly higher LOH frequency was observed on 12p11 (65%) in NPC with stage T1 + T2. Significantly higher LOHfrequency on 19q13 was also observed in NPC with advanced TNM-stage (III+IV). High fractional allelic loss (FAL) value and high antibody titers of EBV IgA/VCA and/or IgA/EA were significantly correlated with T3 + T4-stage, distant lymph node metastasis and advanced TNM-stage of NPC. We also found that NPC patients with high titers of IgA/VCA and IgA/EA showed high LOH frequency on 16q (48%) and 19q13 (48%). These results suggest that LOH on 9p21, l6q and 19q13 may be responsible for the aggressiveness and progression of NPC; there may be an interaction between allelic loss and EBV infection in the etiology of NPC. High frequency of LOH on 4q21 and 14q11-q12 were alsofound to be correlated with WHO type III NPC histopathology, suggesting that LOH on these regions may cause poor NPC differentiation. Our data also may be useful for the development of a NPC molecular staging system, a system which may augment the use of clinical pathological features in the diagnosis and prognosis of this disease.

Fund of $200,000 was requested to pay part of a Transmission Electron Microscope (TEM) which costs about $1.35 million. The balance comes from various other sources. The machine has been scheduled for delivery in March 2001. The TEM will be used to assist all the research projects described in the original proposal and any other future DoD funded projects.

Simple geometric considerations show that to maximize the transport Jc for a given type of bulk superconductor, it is only necessary to have the individual grains in the sample oriented with maximal area of close contact with their immediate neighbors. With this guideline, a 24‐meter silver‐sheathed thallium‐containing superconductor of the 1223‐type without long‐range granular alignment has been made. It is flexible, uniform, and exhibits a transport Jc of 104 A/cm2 at 77 K in the absence of external magnetic field.

Two kinds of distinctive field emission behaviors were observed on vertically aligned multiwall carbon nanotube ~CNT! films grown by hot filament dc-plasma enhanced chemical vapor deposition. Some samples have stable emission current for more than 60 h ~type I!, while others degrade substantially in the first 16 h ~type II!. During the field emission measurement, a brief exposure to air led an abrupt decrease of emission current of all samples. But subsequent reevacuation made type I samples recover the emission current fully, whereas type II samples were damaged permanently reflecting on the irrecoverable emission current. Microstructure studies by transmission electron microscope clearly showed that the stable emission is due to a surface passivation of CNTs by a thin layer of amorphous carbon that prevents CNTs from reacting with ambient gases, e.g., oxygen, during air exposure. © 2004 American Institute of Physics. @DOI: 10.1063/1.1642272#

During the growth of carbon nanotubes (CNTs) by plasma enhanced chemical vapor deposition (PECVD), plasma etching is the crucial factor that determines the growth mode and alignment of the CNTs. Focusing on a thin catalyst coating (Ni = 5 nm), this study finds that the CNT growth by PECVD goes through three stages from randomly entangled (I-CNTs) to partially aligned (II-CNTs) to fully aligned (III-CNTs). The I-CNTs and II-CNTs are mostly etched away by the plasma as time goes by ending up with III-CNTs as the only product when growth time is long enough. However, with a thickness of the catalyst coating of 10 nm or more, neither I-CNTs nor II-CNTs are produced, but III-CNTs are the only type of CNTs grown during the whole growth process. During the growth of III-CNTs, the catalyst particles (Ni) stay on the tips of each of the aligned CNTs and act as a 'safety helmet' to protect the CNTs from plasma ion bombardment. On the other hand, it is also the plasma that limits the growth of III-CNTs, since the plasma eventually etches all the catalytic particles out and stops the growth.

Perovskite-type polycrystalline La1/3Sr2/3FeO3 particles with different sizes (80-2000 nm) were prepared using a simple sol-gel technique. In samples of nanoparticles with a diameter of less than 300 nm, weak ferromagnetism was observed at room temperature, which was attributed to the lattice distortion. The magnetic and specific heat measurements suggest that the charge ordering state was largely suppressed due to the lowering of the particle size, but the charge ordering temperature remained unaffected. (C) 2007 American Institute of Physics.

Well-aligned Ca3Co2O6 nanorods (∼300nm in length and ∼40nm in diameter) on Si substrates are prepared by pulsed laser deposition. The steplike magnetization feature as identified in bulk Ca3Co2O6 can be retained in the nanorods in spite of the enhanced distortion of the magnetically ordered spin chains due to the finite size effect. The out-of-plane magnetization value is slightly larger than the in-plane value, which shows the small magnetic anisotropy. An additional distinct transition at 54K associated with the spin frustration is revealed, different from the bulk samples.

Atomic-scale microstructure changes of carbon nanotubes under high bias∕high current conditions were studied by in situ high-resolution transmission electron microscopy. We found that high bias voltage caused significant structure changes, such as crystallization and elimination of amorphous coating on the surface of nanotube walls, removal of nanotube walls, and formation of atomic-scale kinks. These structural changes are attributed to high temperatures induced by high bias resistive heating on the nanotubes. These structural changes cause dramatic electronic property changes of the nanotubes correspondingly. The results provide an efficient route to tailor the electronic properties of nanotubes by appropriate structural modifications.

Recently, we have reported an extremely strong field emission from carbon nanotubes grown on carbon cloth, with the field-enhancement factor of up to 18 800. In this paper, we study the origins of this effect, by investigating field emission from individual carbon nanotubes, in a transmission electron microscope equipped with a piezo manipulator. Microscopic analysis reveals a multistage structure of some of the nanotubes, characterized by an order of magnitude smaller nanotubes branching off the tips of bigger nanotubes (or carbon fibers). The multistage structure causes a macroscopic enhancement of the electric field, which can match that of a single macroscopically long nanotube with length equal to the combined length of all stages, and the tip radius equal to that of the thinnest nanotube in the structure. This not only explains the observed giant field enhancement, but also provides important clues for the design of nanotube emitters for electronic applications.