bluuebunny/crossref_metadata_2025 huggingface dataset:
Ecological factors influencing disease risk in Eagle OwlsBubo bubo
Authors: ORTEGO JOAQUÍN , ESPADA FRANCISCO
Published: April 2007

In this study we assessed whether local habitat features and host population density influenced disease risk in Eagle OwlBubo bubofledglings. Measures of immune defence (concentrations of circulating white blood cells), prevalence of three parasite types (a blood parasiteLeucocytozoon ziemanni, an insectCarnus haemapterus, and a tickRhipicephalussp.) and total number of parasite species were used to quantify disease risk. We tested the hypotheses that disease risk in fledglings was higher in nests located in areas with higher length of and proximity to watercourses (as a higher abundance and viability of parasites and vectors occur in wetter areas), higher cover of forest (as forest moistness and humidity can favour higher vector and parasite proliferation), higher habitat diversity (as environmental heterogeneity increases the pool of potential vectors and parasites) and higher local owl population density (as disease transmission might be density‐dependent). The clearest relationship was with the proximity of freshwater, although the other hypotheses were also partially supported. Concentrations of white blood cells, the number of parasite species and, weakly, the prevalence ofCarnus haemapteruswere all higher in nests closer to watercourses. The prevalence of blood parasites increased with the cover of forested areas. Fledglings from nests located in more diverse habitats had higher white blood cell concentrations and showed higher prevalence of blood parasites. Finally, local host population density was positively correlated with the prevalence of blood parasites. The results suggest the existence of complex and interrelated links between ecological parameters and three different measures of disease risk, and highlight the importance of immunological approaches to assess disease risk at an intraspecific level.
Respiratory mechanics during exercise in endurance‐trained men and women
Authors: Guenette Jordan A. , Witt Jonathan D. , McKenzie Donald C. , Road Jeremy D. , Sheel A. William
Published: April 2007

The purpose of this study was to compare the mechanics of breathing including the measurement of expiratory flow limitation, end‐expiratory lung volume, end‐inspiratory lung volume, and the work of breathing in endurance‐trained men (n= 8) and women (n= 10) during cycle exercise. Expiratory flow limitation was assessed by applying a negative expiratory pressure at the mouth. End‐expiratory lung volume and end‐inspiratory lung volume were determined by having subjects perform inspiratory capacity manoeuvres. Transpulmonary pressure, taken as the difference between oesophageal and airway opening pressure, was plotted against volume and integrated to determine the work of breathing. Expiratory flow limitation occurred in nine females (90%) and three males (43%) during the final stage of exercise. Females had a higher relative end‐expiratory lung volume (42 ± 8 versus 35 ± 5% forced vital capacity (FVC)) and end‐inspiratory lung volume (88 ± 5 versus 82 ± 7% FVC) compared to males at maximal exercise (P < 0.05). Women also had a higher work of breathing compared to men across a range of ventilations. On average, women had a work of breathing that was twice that of men at ventilations above 90 l min−1. These data suggest that expiratory flow limitation may be more common in females and that they experience greater relative increases in end‐expiratory lung volume and end‐inspiratory lung volume at maximal exercise compared to males. The higher work of breathing in women is probably attributed to their smaller lung volumes and smaller diameter airways. Collectively, these findings suggest that women utilize a greater majority of their ventilatory reserve compared to men and this is associated with a higher cost of breathing.
Characteristics of the response of the iliac artery to wall shear stress in the anaesthetized pig
Authors: Kelly R. F. , Snow H. M.
Published: April 2007

The functional significance of shear stress‐induced vasodilatation in large conduit arteries is unclear since changes in the diameter have little effect on the resistance to blood flow. However, changes in diameter have a relatively large effect on wall shear stress which suggests that the function of flow‐mediated dilatation is to reduce wall shear stress. The mean and pulsatile components of shear stress vary widely throughout the arterial system and areas of low mean and high amplitude of wall shear stress are prone to the development of atheroma. In this study, using an in vivo model with the ability to control flow rate and amplitude of flow independently, we investigated the characteristics of the response of the iliac artery to variations in both the mean and amplitude of wall shear stress. The results of this study confirm that increases in mean wall shear stress are an important stimulus for the release of nitric oxide by the endothelium as indicated by changes in arterial diameter and show for the first time, in vivo, that increases in the amplitude of the pulsatile component of shear stress have a small but significant inhibitory effect on this response. A negative feedback mechanism was identified whereby increases in shear stress brought about by increases in blood flow are reduced by the release of nitric oxide from the endothelium causing dilatation of the artery, thus decreasing the stimulus to cell adhesion and, through a direct action of nitric oxide, inhibiting the process of cell adhesion. The results also provide an explanation for the uneven distribution of atheroma throughout the arterial system, which is related to the ratio of pulsatile to mean shear stress and consequent variability in the production of NO.
Linking lateral interactions in flicker perception to lateral geniculate nucleus cell responses
Authors: Kozyrev Vladislav , Silveira Luiz Carlos L. , Kremers Jan
Published: April 2007

The perception of flicker strength in a circular stimulus can be changed by altering the relative temporal phase of a simultaneously flickering surrounding annulus: perceived flicker is weak when the two stimuli are modulated in‐phase and strong when the two are modulated in counter‐phase. Previously, we found that responses of single neurons in the monkey lateral geniculate nucleus (LGN) to such stimuli resemble the psychophysical data. On the basis of the resemblance in data, it was proposed that the physiological basis for the flicker perception may be present as proximal as the LGN. To strengthen this hypothesis, we simulated the response of an array of LGN neurons, the receptive fields (RFs) of which are covered by the stimulus. The simulations were based upon single‐cell recordings in the LGN of anaesthetized marmosets (Callithrix jacchus) using the same stimuli as previously. The measurements were repeated for different spatial displacement between the stimulus and the RF. The responses depended upon the spatial displacement and the relative phase between centre and surround stimuli. The neuronal responses can be adequately described by a difference‐of‐Gaussians (DOG) model with a time delay in the RF surround. The model responses at different displacements can be considered to be identical to the output of an array of ideal and identical LGN cells with different RF locations. To be able to describe physiological and psychophysical data, obtained at different stimulus contrasts, it was necessary to consider previously described non‐linear interactions between the RF centres and surrounds. We applied a spatial peak‐to‐trough detector with a subsequent saturation and threshold to simulate a simple cortical decision mechanism. The output of this peak‐to‐trough detector could adequately describe the psychophysical data.
Role of CNT3 in the transepithelial flux of nucleosides and nucleoside‐derived drugs
Authors: Errasti‐Murugarren Ekaitz , Pastor‐Anglada Marçal , Casado F. Javier
Published: April 2007

We examined the role of the concentrative nucleoside transporter CNT3 in the establishment of a transepithelial flux of natural nucleosides and their pharmacologically active derivatives in renal epithelial cell lines. Murine PCT cells grown on a transwell dish showed endogenous CNT3 activity at their apical membrane that was responsible for the sodium‐dependent transepithelial flux of both purine and pyrimidine nucleosides. hCNT3 was also identified in human kidney and its role in the transport of nucleosides was tested. To this end, MDCK cells, lacking endogenous CNT3 activity, were genetically engineered to express the human orthologue of CNT3 (hCNT3‐MDCK cells). In these cells, hCNT3 was inserted into the apical membrane, thus generating, as for PCT cells, a transepithelial flux of both nucleosides and nucleoside‐derived drugs. Apical‐to‐basolateral transepithelial flux was present in all cells expressing a functional CNT3 transporter and was significantly higher than that found either in PCT cells in absence of sodium or in mock‐transfected MDCK cells. Nevertheless in all cases a significant amount of the transported nucleoside was retained and transformed inside cells. However release to the opposite compartment was CNT3 dependent, not only in terms of absolute flux (much higher when an apical CNT3 transporter was active) but also regarding metabolic transformations of the apically absorbed nucleosides. These results underline a critical role of CNT3 in the renal reabsorption of nucleosides and their derivatives as well as in their intracellular metabolism.
Astrocytic control of synaptic NMDA receptors
Authors: Lee C. Justin , Mannaioni Guido , Yuan Hongjie , Woo Dong Ho , Gingrich Melissa B. , Traynelis Stephen F.
Published: April 2007

Astrocytes express a wide range of G‐protein coupled receptors that trigger release of intracellular Ca2+, including P2Y, bradykinin and protease activated receptors (PARs). By using the highly sensitive sniffer‐patch technique, we demonstrate that the activation of P2Y receptors, bradykinin receptors and protease activated receptors all stimulate glutamate release from cultured or acutely dissociated astrocytes. Of these receptors, we have utilized PAR1 as a model system because of favourable pharmacological and molecular tools, its prominent expression in astrocytes and its high relevance to neuropathological processes. Astrocytic PAR1‐mediated glutamate releasein vitrois Ca2+dependent and activates NMDA receptors on adjacent neurones in culture. Activation of astrocytic PAR1 in hippocampal slices induces an APV‐sensitive inward current in CA1 neurones and causes APV‐sensitive neuronal depolarization in CA1 neurones, consistent with release of glutamate from astrocytes. PAR1 activation enhances the NMDA receptor‐mediated component of synaptic miniature EPSCs, evoked EPSCs and evoked EPSPs in a Mg2+‐dependent manner, which may reflect spine head depolarization and consequent reduction of NMDA receptor Mg2+block during subsequent synaptic currents. The release of glutamate from astrocytes following PAR1 activation may also lead to glutamate occupancy of some perisynaptic NMDA receptors, which pass current following relief of tonic Mg2+block during synaptic depolarization. These results suggest that astrocytic G‐protein coupled receptors that increase intracellular Ca2+can tune synaptic NMDA receptor responses.
A hydrophobic element secures S4 voltage sensor in position in resting Shaker K+ channels
Authors: Yang Ya‐Chin , Own Chia‐Jen , Kuo Chung‐Chin
Published: April 2007

The S4 transmembrane α‐helix in voltage‐gated channels contains several regularly spaced basic amino acid residues that could be protonated and moved across the membrane electric field in response to membrane potential changes. The translocation of the charge‐carrying S4 transduces membrane voltage to gating conformational changes of the channel, but how it is positioned and moved with respect to membrane lipid remains controversial. We found that hydrophilic and especially arginine and lysine substitution for L361 at the external end of S4 causes a large negative shift with shallowed slope of both activation and inactivation curves in Shaker K+ channels. Also, the macroscopic kinetics of activation and inactivation become much faster and barely voltage dependent, especially in the L361R mutant channel. These steady‐state and kinetic data suggest that the replacement of one single hydrophobic residue, leucine, with arginine may profoundly destabilize the resting conformation of S4, which therefore takes a partially extruded position (partly activated position) at resting potentials (e.g. −120 mV). Consistently, the L361R point mutation gives rise to an extracellularly exposed R365C that is readily modified by external hydrophilic sulfhydryl‐specific agents in the resting channel. Moreover, the extruded S4 in the L361R mutant channel could be retracted by strong hyperpolarizing potentials (∼−180 mV), from which the mutant channel is gated with slower kinetics but evidently stronger voltage dependence. We conclude that hydrophobic interaction involving a highly conserved residue at the top of S4 is crucial for properly securing the gating voltage sensor in the resting position and thus appropriate gating control of the voltage‐gated channels.
Structural and functional basis of amino acid specificity in the invertebrate cotransporter KAAT1
Authors: Miszner Andreea , Peres Antonio , Castagna Michela , Bettè Sara , Giovannardi Stefano , Cherubino Francesca , Bossi Elena
Published: April 2007

The substrate specificity of KAAT1, a Na+‐ and K+‐dependent neutral amino acid cotransporter cloned from the larva of the invertebrate Manduca sexta and belonging to the SLC6A gene family has been investigated using electrophysiological and radiotracer methods. The specificity of KAAT1 was compared to that of CAATCH1, a strictly related transporter with different amino acid selectivity. Competition experiments between different substrates indicate that both transporters bind leucine more strongly than threonine and proline, the difference between KAAT1 and CAATCH1 residing in the incapacity of the latter to complete the transport cycle in presence of leucine. The behaviour of CAATCH1 is mimicked by the S308T mutant form of KAAT1, constructed on the basis of the atomic structure of a leucine‐transporting bacterial member of the family, which indicates the participation of this residue in the leucine‐binding site. The reverse mutation T308S in CAATCH1 conferred to this transporter the ability to transport leucine in presence of K+. These results may be interpreted by a kinetic scheme in which, in presence of Na+, the leucine‐bound state of the transporter is relatively stable, while in presence of K+ and at negative potentials the progression of the leucine‐bound form along the cycle is favoured. In this context serine 308 appears to be important in allowing the change to the inward‐facing conformation of the transporter following substrate binding, rather than in determining the binding specificity.
Target‐specific PIP2signalling: how might it work?
Authors: Gamper Nikita , Shapiro Mark S.
Published: April 2007

Phosphatidylinositol 4,5‐bisphosphate (PIP2)‐mediated signalling is a new and rapidly developing area in the field of cellular signal transduction. With the extensive and growing list of PIP2‐sensitive membrane proteins (many of which are ion channels and transporters) and multiple signals affecting plasma membrane PIP2levels, the question arises as to the cellular mechanisms that confer specificity to PIP2‐mediated signalling. In this review we critically consider two major hypotheses for such possible mechanisms: (i) clustering of PIP2in membrane microdomains with restricted lateral diffusion, a hypothesis providing a mechanism for spatial segregation of PIP2signals and (ii) receptor‐specific buffering of the global plasma membrane PIP2pool via Ca2+‐mediated stimulation of PIP2synthesis or release, a concept allowing for receptor‐specific signalling with free lateral diffusion of PIP2. We also discuss several other technical and conceptual intricacies of PIP2‐mediated signalling.
Arrays of isolated tufts of vertically aligned carbon nanotubes for field emission cathodes
Authors: Mauger M. , Mouton R. , Hamzaoui O. , Binh Vu Thien
Published: April 2007

Vertically aligned carbon nanotubes (va-CNTs) in an array structure on a metallic surface have proved to be excellent field emission cathodes due to their high geometric field enhancement factor. In this study, coupling the experiment with numerical simulations, the authors revisited the field emission behavior and lifetime of these va-CNT based cathodes for two configurations, one is an array of individual va-CNTs and the other is an array of isolated tufts of va-CNTs. They conclude that arrays of isolated tufts are the most advantageous spatial configuration for field emission cathodes working in aggressive environment in particular, for the cathode field emission lifetime that increased by a factor of 5–10.
Measuring hydrogen-carbon gas inside high-vacuum glass panels by the comparative infrared light method
Authors: Chen Yi-Hsien , Chien Yu-Han , Fu Chuan-Hsu , Lin Wee-Yee , John Su Guo-Dung
Published: April 2007

In this article, the authors propose a comparative infrared light method for detecting the hydrogen-carbon (HC) gas inside sealed high-vacuum glass panels. Unlike traditional infrared detection, a comparative infrared light method can distinguish gas species at a relatively short distance, which makes it suitable for carbon-nanotube field-emission display applications. In principle, the comparative infrared light method makes use of a high-vacuum reference panel to determine the existence of the target gas inside a sample panel under test. The authors experimentally demonstrated that residual organic gas (HC related) existed in a 5mm gap between two glass panels at the vacuum level of 10−6torr by this method.
Integration of a dose control circuit with a vertically aligned nanofiber field emission device
Authors: Rahman T. , Islam S. K. , Vijayaraghavan R. , Gundman T. , Eliza S. A. , Hossain A. , Blalock B. , Randolph S. J. , Baylor L. R. , Bigelow T. S. , Gardner W. L. , Ericson M. N. , Moore J. A.
Published: April 2007

This article presents the integration of a dose control circuit (DCC) with vertically aligned carbon nanofiber (VACNF) field emission devices through a voltage boost up interface circuit for the implementation of the digital electrostatically focused e-beam array direct-write lithography concept. The VACNFs act as diodes with high turn on voltage (∼70V). Commercially available complementary metal-oxide-semiconductor technology is not capable of handling such magnitude of voltages. The voltage boost up interface circuit described in this article offers an efficient technique to shift the voltage level to a level adequate to start the emission of electron from the tips of the VACNFs. The integration of the DCC with the VACNF emitters via a voltage boost up interface circuit presented in this article facilitates the operation of the VACNFs for etching in maskless lithography while providing precise control of emission.
Development of compact field emission scanning electron microscope equipped with multiwalled carbon nanotube bundle cathode
Authors: Yabushita Ryosuke , Hata Koichi , Sato Hideki , Saito Yahachi
Published: April 2007

As the first stage of development of a nanofocused x-ray source for high-resolution x-ray radiography, a commercial compact scanning electron microscope (SEM) was modified by replacing the thermionic cathode and two magnetic condenser lenses with a multiwalled carbon nanotube (MWCNT) bundle field emission (FE) cathode and a special designed Butler electrostatic lens, respectively. This modification also brought about a downsizing to the electron optical system, only 192mm of distance between the cathode and the sample stage was achieved. The MWCNT bundle FE cathode continuously emitted electrons for over 9h under a base pressure of ca. 10−5Torr which was a severer pressure for steady FE. The performance of electron gun system consisted of the MWCNT bundle FE cathode and the special Butler electrostatic lens was demonstrated by SEM images taken under the poor vacuum condition at room temperature.
Interaction mechanism of a terahertz wave generator using a field emission cathode
Authors: Lin Ming-Chieh , Lu Pu-Shih
Published: April 2007

The interactions between the electrons and the terahertz waves in a vacuum electronic device based on field emission have been studied by employing the finite-difference time-domain particle-in-cell simulations. To understand the interaction mechanism, the cathode has been trimmed to emit electrons. The simulation results show that the efficiency of the case corresponding to the trimmed cathode is up to about 4% and higher than that of the original planar cathode. It is found that the interaction regions are located among the gaps between the cathode and the anode. In addition, the ac electric fields of the terahertz waves not only velocity modulate the electron beam but also cause the density modulation of the field emission current. The inertial bunching and prebunching effects provide the feedback loop as required by an oscillator.
Post-treatment of screen-printed carbon nanotube emitter by selective plasma etching
Authors: Yu Jun , Chen Jun , Deng S. Z. , She J. C. , Xu N. S.
Published: April 2007

Screen-printed carbon nanotube (CNT) emitter arrays were prepared by using slurry of mixture of multiwall CNTs, organic vehicles, and inorganic binder, i.e., silicon dioxide sol. The composition of the slurry was optimized by varying the CNT content in the mixture. It was found that only the cathode with appropriate CNT contents had low turn-on field and high emission current density. A post-treatment process was introduced to further improve the field emission properties which selectively etches away the silicon dioxide binder by inductively coupled plasma etching. The results show that the selective etching process could effectively remove the inorganic binder layer from screen-printing CNT emitters and improve field emission performances.
Fabrication and field emission properties of regular hexagonal flowerlike ZnO nanowhiskers
Authors: Li Chen , Lei Wei , Zhang Xiaobing , Wang J. X. , Sun X. W. , Tan S. T.
Published: April 2007

Regular hexagonal flowerlike zinc oxide (ZnO) whiskers have been fabricated on the indium tin oxide electrodes with glass panel. A relatively simple hydrothermal growth process of low temperature is developed. The field emission properties of the flowerlike ZnO nanowhiskers have a low field emission threshold voltage (2.2V∕μm at a current density of 0.1μA∕cm2) and a high current density of 1mA∕cm2 at an applied field of 6.3V∕μm. The hydrothermal process method and good field emission properties indicate their potential application in field emission display device with glass panels.
X-ray photoelectron spectroscopy and low-energy electron diffraction analyses on zirconium oxide modified (100) surface of molybdenum
Authors: Kawakubo Takashi , Satoh Shinya , Nakane Hideaki , Adachi Hiroshi
Published: April 2007

It has been found that the work function of Mo(100) surface can be reduced to 2.1eV by heating it with a slight layer of zirconium oxide in a vacuum condition [S. Satoh et al., J. Vac. Soc. Jpn. 47, 143 (2004)]. Here the low work function surface, which is abbreviated as ZrO∕Mo(100), was examined aiming to understand the reducing mechanism of the work function. Low-energy electron diffraction is employed to analyze the atomic arrangement at the surface and x-ray photoelectron spectroscopy to identify the surface chemical condition. The experiment gives almost the same results as for the ZrO∕W(100) low work function surface.
Emission characteristics of nanocrystalline porous silicon ballistic cold cathode in atmospheric ambience
Authors: Ohta Toshiyuki , Kojima Akira , Koshida Nobuyoshi
Published: April 2007

To make the specific feature of nanocrystalline silicon (nc-Si) cold cathode clear, its emission characteristics are investigated in various atmospheric gas ambiences. The experimental nc-Si diode is composed of a top thin Au film, a nanocrystallized polysilicon layer, an n+-type silicon wafer, and a back contact. Under operation in air, a significant current of about 1μA∕cm2 was detected at the collector electrode located at a distance of 1mm from the device surface. Judging from mean energy of emitted electrons, the observed current is due to electron attachment onto oxygen molecules in the proximity of the front surface. The operation stability in air has been enhanced by combining some surface treatments: high pressure water vapor annealing, forming gas (N2+H2) annealing, and surface bond modification. The surface-emitting nc-Si ballistic emitter is useful not only in vacuum but also in atmospheric pressures for various possible applications.
Field emission characteristics of polymethyl methacrylate polymer thin film
Authors: Huang W. Y. , Liu C. H. , Chen Jun , Deng S. Z. , Xu N. S.
Published: April 2007

Polymethyl methacrylate (PMMA) thin films were prepared by spin coating using chloroform solvent. The field emission current versus applied field characteristics were tested. Stable field emission was observed after a switch-on process. The field emission properties of PMMA film exhibit vacuum gap dependence characteristics. The scanning electron microscope inspection reveals that after emission process microwhiskers were formed at the surface. The gap dependence of the field emission properties was explained. It is proposed that the high field during the switch-on process leads to the formation of the microwhiskers.
New analysis of the energy distribution of field electrons from n-type semiconductors
Authors: Bae Hae K. , Hong Soon C. , Chung Moon S.
Published: April 2007

The energy distributions of field electrons were investigated both analytically and numerically for n-type semiconductors. The average energy ⟨ε⟩ and the standard deviation Δε of the distributions were obtained analytically using the WKB transmission coefficient. These analytic formulas are confirmed by the full numerical and exact calculations of ⟨ε⟩ and Δε. It implies that they are useful to characterize the energy distribution of field electrons.
Effect of neutral beam etching of p-GaN on the GaN device characteristics
Authors: Park B. J. , Min K. S. , Lee H. C. , Bae J. W. , Kim D. W. , Yeom G. Y.
Published: April 2007

GaN materials were etched using a CF4-based neutral beam, and its etch damage characteristics were compared with those etched with a CF4-based inductively coupled plasma (ICP). Photoluminescence data showed that the neutral beam etched GaN materials show fewer defects on the surface compared to the GaN materials etched by ICP. Also, the current–voltage characteristics of GaN light emitting diodes fabricated with p-GaN etched by the neutral beam showed less damage compared to those fabricated with p-GaN by the ICP. When a photonic crystal-like structure having 2-μm-diameter microlens array was formed using the neutral beam etching on the p-GaN of the GaN device, an increase of 20% in the optical emission intensity could be observed without significantly increasing the forward voltage (0.7V).
Effect of UV irradiation during synthesis of polypyrrole by a one-step deposition/polymerization process
Authors: Chang Sunyoung , Park Jaehong , Jang Jiyoung , Lee Jungwoo , Lee Jaeseung , Yi Whikun
Published: April 2007

Polypyrrole (PPY) nanofilms were synthesized by a one-step deposition/polymerization process in a vacuum chamber under ultraviolet photon irradiation. To realize the synthesis of PPY films, the authors measured the current through a conducting polymer connected by two electrodes. The nanofilms were characterized by atomic force microscopy and Fourier-transform infrared spectroscopy. A possible mechanism is proposed for the formation of the PPY nanostructure during the photopolymerization.
Architecture of field emission display based on a gate electrode of diabolo mode
Authors: Yang Xiaxi , Zhang Xiaobing , Lei Wei , Zhang Zichen , Chen Jing , Zhang Lifang
Published: April 2007

In the normal gate carbon nanotube field emission display (CNT-FED), the gate electrode is used to modulate and address the electron beam. This article proposes a novel gate architecture made on a glass substrate with diabololike funnels. Chemical corrosion was utilized to produce diabolo funnels in the glass dielectric layer. A metal layer was screen printed on the lower surface of the glass-mesh plate as an electron extraction gate electrode. MgO film was vaporized on the wall of the diabolo funnels. The electrons from CNT are transported in a diabolo mode via secondary electron emission over the wall of the diabolo funnel placed above the subemitters. As a result, electrons including the secondary electrons and backscatters are generated and the brightness of the diabolo mode gate architecture CNT-FED could increase obviously.
Influence of deposition pressure and rf power on the structure and electrical properties of Zr0.8Sn0.2TiO4 thin films prepared by rf magnetron sputtering
Authors: Huang Cheng-Liang , Wang Jun-Jie , Hsu Cheng-Hsing
Published: April 2007

ZnO-doped Zr0.8Sn0.2TiO4 (ZST) films deposited on n-type Si (100) substrates at different deposition pressures and rf powers were investigated. The structural and morphological characteristics analyzed by x-ray diffraction (XRD), atomic force microscopy, and scanning electron microscopy were found to be affected by deposition conditions, such as deposition pressure (2, 5, and 8mTorr) and rf power (250, 350, and 450W). Highly oriented ZST (101) and (111) perpendicular to the substrate surface were identified at a deposition pressure of 8mTorr and rf power of 450W. The XRD showed that the deposited films exhibited a polycrystalline microstructure. The grain size of the film increased with increasing rf power. From observing the surface morphology, ZST thin films exhibit a columnar structure. The electrical properties were measured using capacitance-voltage and current-voltage measurements on metal-insulator-semiconductor capacitor structures. The leakage current decreased with increasing rf power and deposition pressure. As rf power=450W and deposition pressure=8mTorr, a leakage-current density of 2.26×10−9A∕cm2 was obtained at 5V.
Reactive ion etching technique for via-hole applications in thick GaAs wafers
Authors: Wang Chih-Cheng , Lin Yu-Lu , Lin Shun-Kuan , Li Chun-Sheng , Huang Hou-Kuei , Wu Chang-Luen , Chang Chian-Sern , Wang Yeong-Her
Published: April 2007

The dry etching technique has been developed to etch via holes through a 5-mil-thick GaAs wafer by rf power and reactive gas pressures in a reactive ion etching system. The etching parameters are optimized for a slope profile suitable for power field effect transistors and monolithic microwave integrated circuit applications. The selectivity between GaAs and photoresist and the average etching rate can be higher than 30 and 1.1μm∕min, respectively. Furthermore, the slope angle measured from the vertical is larger than 11°, which is well suited for a thick GaAs via-hole etching process. Before the metal for the via-hole substrate is sputtered, the wet chemical etching solution based on HCl–H2O2∕H2O at room temperature is used to smooth the sidewall for a better connection. To probe these source pads, the via-hole resistances of the pseudomorphic high electron mobility transistors (PHEMTs) are measured to be less than 0.5Ω with more than 97.2% yield in a 4in. diameter GaAs wafer. It is found that the rf performance for low-noise and power PHEMTs can be further improved.
Effects of adsorbates on field emission reproducibility of sulfur-incorporated nanocomposite carbon films
Authors: González-Berríos Adolfo , Weiner Brad R. , Morell Gerardo
Published: April 2007

The effects of adsorbates on field emission reproducibility from sulfur-incorporated nanocomposite carbon films grown by hot filament chemical vapor deposition were studied. Adsorption was induced on the films by liquid treatment at standard conditions using polar (1-butanol), moderately polar (ethyl acetate), and nonpolar (hexane) liquids. Adsorbates caused an increase in the turn-on field that was found to depend on the polarity of the liquid used: the larger (smaller) the polarity, the smaller (larger) the increase in turn-on field. The analysis of the data indicates that the increase in turn-on field is due to an increase in work function caused by adsorbates. Moreover, the hysteresis behavior, present in the field emission measurements, changes from clockwise to counterclockwise due to the adsorbates. The results are discussed in terms of the affinity between the adsorbates and the films’ surface and the adsorption-desorption process occurring on the films’ surface during emission.
First-layer Si metallizations for thermally stable and smooth Ohmic contacts for AlGaN∕GaN high electron mobility transistors
Authors: Mohammed Fitih M. , Wang Liang , Adesida Ilesanmi
Published: April 2007

First-layer Si (FL-Si) Si∕Ti∕Al∕Mo∕Au contact metallizations are demonstrated to form low resistance and high temperature thermally stable Ohmic contacts on AlGaN∕GaN high electron mobility transistor (HEMT) structures. Electrical and surface morphology characterizations have indicated that contact behavior significantly depends on the thickness of FL-Si used, where FL-Si (5nm) scheme showed the most optimal behavior. The contact resistances of FL-Si schemes are stable for up to 300h during thermal aging at 500 and 600°C. Aging at 700°C resulted in gradual degradation of contact resistance with values less than 1Ωmm Ohmic behavior still maintained after 50h of thermal treatment. No deterioration in the sheet resistance of the heterostructure has been detected upon thermal aging. Atomic force microscopy, Auger electron spectroscopy, and transmission electron microscopy characterizations have been utilized to identify the effect of FL-Si incorporation on the nature of intermetallic and interfacial reactions. Results from this study demonstrate that FL-Si-based metallizations have the potential to meet the critical requirements of low resistance, high temperature thermal stability and smooth surface morphology for the fabrication of AlGaN∕GaN HEMTs.
Nanoscale ZrC∕ZrB2 multilayered coatings prepared by magnetron sputtering
Authors: Li D. J. , Yang J. , Zhang X. H. , Cao M.
Published: April 2007

Zr C ∕ Zr B 2 multilayers with nanoscale bilayer periods were synthesized by rf magnetron sputtering. The analysis of x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and nanoindentation indicated that multilayers possessed much higher hardness than the rule-of-mixture value of monolithic ZrC and ZrB2 coatings. A maximum hardness (over 47GPa) was observed in the multilayer with 27.7-nm-thick bilayer period deposited at 400°C. Higher residual stress built in the ZrC layer can be released by periodic insertion of ZrB2 into ZrC layer. The enhanced mechanical properties were related to the multilayered structure with mixed ZrB2(001), ZrB2(002), and ZrC(111) orientations.
Application of high spatial resolution scanning work function spectroscopy to semiconductor surfaces and interfaces
Authors: Gao Min , Brillson L. J.
Published: April 2007

Work function can be measured from the onset energy of secondary electron (SE) emission spectra in a scanning Auger microscope. In this article, the authors demonstrate the potential of such high spatial resolution work function spectroscopy in probing the Fermi-level position at semiconductor surfaces and the band bending at semiconductor interfaces. Using in situ cleaved cross-sectional GaAs and SiC p-n junctions, they show that the SE onset energy is very sensitive to the surface Fermi-level position and can also be used to measure electron affinity. By measuring the widths of the transition regions, the doping densities and built-in potential can be quantitatively obtained at a spatial resolution of ∼10nm. This technique can also be applied to a wide range of semiconductor heterojunctions. The influences of air cleaving, Ar ion sputtering, contamination, and primary electron beam are studied. They also discuss the advantages, limitations, and possible future improvements of this technique.
Improved field-emission characteristics of a multiwalled carbon-nanotube cathode by argon plasma pretreatment and krypton-fluoride laser irradiation
Authors: Kim W. S. , Honda T. , Oh C. B. , Ohsumi K. , Murakami K. , Abo S. , Wakaya F. , Takai M.
Published: April 2007

An effect of argon (Ar) plasma pretreatment, followed by krypton-fluoride (KrF) laser irradiation, of multiwalled carbon-nanotube (MWCNT) cathodes on field-emission (FE) characteristics was investigated. With an Ar plasma pretreatment of 100W, the FE current density was increased to 32.6mA∕cm2 at an electric field of 4.92V∕μm after laser irradiation, the value of which was about 30 times higher than the current density without plasma pretreatment. The emission-site density (ESD) was also increased by 25 times by a plasma pretreatment of 100W. However, the further increase in plasma power at and above 150W deteriorated both FE characteristics and ESD, which was due to the decrease in the number of MWCNT emission sites.
Cathodoluminescent properties of SrGa2S4:Eu2+ phosphor for field-emission display applications
Authors: Duan C. Y. , Chen J. , Deng S. Z. , Xu N. S. , Zhang J. H. , Liang H. B. , Su Q.
Published: April 2007

Cathodoluminescent properties of a SrGa2S4:Eu2+ phosphor, which was synthesized by a high-temperature solid-phase reaction, have been studied. Cathodoluminescent spectra, the Commission International de l’Eclairage color coordinates, and photoluminescence spectra were obtained. The cathodoluminescent intensity was measured at an operating voltage of 0–10kV and current density of 0–160μA∕cm2. The degradation of cathodoluminescence after high-current-density bombardment was observed. X-ray photoelectron-spectroscopy analysis showed the electron-bombardment-induced chemical reaction in the SrGa2S4:Eu2+ phosphor in which SrSO4 was formed. The cathodoluminescent properties were compared with commercial green phosphor ZnS:Cu,Au,Al and it was found that the properties of SrGa2S4:Eu2+ phosphor under high current bombardment were more stable.
Millimeter wave generator based on field emission cathode
Authors: Lin Ming-Chieh , Lu Pu-Shih
Published: April 2007

Millimeter waves have been extensively studied for many applications including high-resolution radars, communications, materials processing, plasma heating, high energy particle accelerators, and power transmission. The authors have developed a vacuum electronic device based on field emission mechanism for the generation of Ka-band millimeter waves by following the previous successful design of the terahertz devices. The design of the device has been carried out and verified by the numerical simulations. The cold tests and the hot tests have been done using the simulation tools SUPERFISH and MAGIC, respectively. A pure resonant frequency about 35GHz is obtained. The simulation results show that an electronic efficiency up to 9.16% can be achieved with no external magnetic fields. The success of the design for millimeter waves and terahertz waves implies that the interaction mechanism has general significance and should be further investigated.
Growth and field electron emission properties of nanostructured white carbon films
Authors: Zhang Lan , Ma Huizhong , Yao Ning , Lu Zhanling , Zhang Binglin
Published: April 2007

White carbon films were synthesized by microwave plasma chemical vapor deposition. Irregular flakiness microstructure consisting of nanocrystalline grains of the as-grown film was observed by scanning electron microscope. The films have a metallic gray to white color, with reflectivity of 12.56%–21.58% in the visible region. The diffraction line at 2θ=21.6° (d=0.4107nm), shown in x-ray diffraction spectrum of the film, corresponds to the (110) facet of β modifications of white carbon. The peak position at 283.46eV in the x-ray photoelectron spectrum represents binding energy of C1s core level of sp1 hybridization of carbon. Field electron emission characteristics of the film were tested. A turn-on field of 3.5V∕μm was obtained.
Surface modification and contamination characterization of ion-enhanced, implanted photoresist removal
Authors: Kawaguchi Mark N. , Papanu James S. , Chen Han-Wen , Su Bo , Verhaverbeke Steven
Published: April 2007

The authors study the dopant contamination removal effectiveness of blanket high-dose implanted photoresist wafers exposed to dual mode oxygen plasma, where a remote rf-plasma source is operated simultaneously with rf bias at low temperature. Based on total x-ray reflectance x-ray fluorescence spectrometry and secondary ion mass spectrometry analyses, sputtering effects are minimal during typical process times with most of the dopant remaining on the substrate after dual mode oxygen plasma processing. SC1-based (NH4OH:H2O2:H2O Standard Clean 1) wet clean treatments reduce dopant levels but 2×1013–4×1013at∕cm2 still remain unless the substrate is processed with hydrofluoric acid (HF) wet cleanings where the contamination level is less than 2×1011at∕cm2. Remote plasma low temperature fluorine post-treatments volatilize dopant residues but are less effective than HF wet cleanings. Dual mode forming gas (4%H2∕96%N2) plasma post-treatments are ineffective for dopant contamination removal. Low temperature dual mode oxygen plasma treatments followed by high temperature remote oxygen plasma treatments after wet cleaning have lower dopant levels than low temperature dual mode oxygen plasma processing alone. High temperature remote plasma forming gas post-treatments after dual temperature processing volatilize dopant residues. The increased dopant removal effectiveness with dry fluorine remote plasmas, HF wet cleanings, and dual temperature processing is consistent with the surface modification of the underlying silicon into an oxide from ion bombardment, which also drives dopant residues into the underlying oxide. The surface modification depth from exposure to dual mode oxygen plasma is about 49–53Å.
In-place fabrication of nanowire electrode arrays for vertical nanoelectronics on Si substrates
Authors: Franklin Aaron D. , Maschmann Matthew R. , DaSilva Manuel , Janes David B. , Fisher Timothy S. , Sands Timothy D.
Published: April 2007

Vertical arrays of Pd nanowire electrodes with controllable and reproducible diameters and lengths are fabricated using a porous anodic alumina (PAA) template supported on a metallized Si substrate. The process described here employs a hydrogen plasma to penetrate the alumina pore barrier oxide prior to electrodeposition, enabling direct electrical contact with the back electrode metallization, thereby eliminating the need for electrochemical processing with high current or voltage pulsing that can lead to delamination or voiding. Electrical characteristics reveal Ohmic contact between the Pd nanowires and the underlying Ti conductive layer for samples with a range of pore diameters from 30to130nm. This process enables both the fabrication of vertical nanowire arrays on prefunctionalized substrates, as well as the in situ fabrication of contacts to semiconductor nanodevices using a thin-film nanowire array. The hydrogen plasma step is particularly well suited to the fabrication of carbon nanotube arrays in PAA by plasma-enhanced chemical vapor deposition.
Local characterization of vapor-deposited electrode edges in thin film organic electronic devices
Authors: Sills S. , Unal K. , Bozano L. D. , Frommer J. , Scott J. C.
Published: April 2007

Scanning probe microscopy was used to characterize the shadow-mask-edge profiles formed during the vapor deposition of aluminum electrodes onto semiconducting polymer (poly-4,4′-4″-n-hexyl-triphenylamine) and gold substrates. Simultaneous topography and surface potential (Kelvin probe) imaging revealed a mask-edge profile with structure extending over a region much wider than the geometric penumbra behind the mask. The images of Al on polymer are interpreted in terms of an overlayer that is morphologically indistinguishable, but chemically distinct, from the polymer surface. On gold, a perforated granular metallic surface reveals coupled diffusion and kinetic processes that are consistent with growth of Al:Au intermetallic phases and void formation due to the faster diffusion of Al relative to Au, i.e., the Kirkendall effect.
Analysis of the early stages of stress-induced notch growth
Authors: Aoyagi Minoru
Published: April 2007

The early stages of preexisting small void growth into larger voids of characteristic shapes caused by stress-induced migration in aluminum lines were studied through biaxial thermal stress simulation. Preexisting small voids, referred to as notches, were assumed to be hemicylindrical, triangular, and grain boundary edge notches. The author showed that the notches have the potential to grow into voids of varying shape such as wedgelike, grainlike, and slitlike voids. The void shape depends strongly on the stress concentration and the free surface boundary conditions. The stress concentration suppresses void growth. The free surface influences not only the shape of the voids but also their size.
Carbon nanotube lateral field emitters with integrated metallic anode
Authors: Wong Y. M. , Kang W. P. , Davidson J. L. , Choi B. K. , Huang J. H.
Published: April 2007

In this study, a novel approach of fabricating lateral carbon nanotube (CNT) emitters on an insulating substrate with an integrated metallic anode utilizing a dual-mask microfabrication process is presented. The selective synthesis of lateral CNTs was achieved with a two-step microwave plasma-enhanced chemical vapor deposition involving a hydrogen plasma treatment prior to CNT synthesis. CNTs were found to grow laterally and along the edges of a trimetal layer containing a sandwiched catalytic thin film. Field emission characterization showed that the lateral CNT emitters had a turn-on field of 4.0V∕μm and current flow of 1.0μA at ∼5.5V∕μm. Overall, the present study demonstrates a viable approach for fabricating lateral emitters with high aspect ratio and integrated with a metallic anode, a device potentially useful for vacuum microelectronics applications.
Development of carbon nanotubes vacuum field emission differential amplifier integrated circuit
Authors: Wong Y. M. , Kang W. P. , Davidson J. L. , Kerns D. V. , Huang J. H.
Published: April 2007

The authors have recently presented a novel concept for the development of vacuum field emission (VFE) differential amplifier (diff-amp) based on a matched pair of carbon nanotube (CNT) triodes and reported the preliminary device characteristics. In this study, they report the development of a CNT VFE diff-amp using CNT emitter arrays with smaller gate aperture, obtaining better device performance after postsynthesis rapid thermal annealing treatment. A pair of well-matched 2μm circular triode arrays showed a gate turn-on voltage of ∼40V and displayed similar triode characteristics in the saturation region. Moreover, the proposed two-step analytical model shows that the common-mode rejection ratio (CMRR) in decibels has a linear relationship with the applied gate voltage for the improved dual-triode diff-amp. In addition, the diff-amp demonstrates high CMRR (34–58dB) over a wide operating region.
Current-voltage and electron emission characteristics of diamond particles
Authors: Yuan Guang , Gu Zhangzhi , Song Hang , Mimura Hidenori
Published: April 2007

Current-voltage (I-V) and electron emission characteristics of two types of diamond particles deposited on Mo tips were measured by using another Mo probe in a scanning electron microscopy chamber. The I-V and field emission characteristics of the diamond particles strongly depend on their quality. Ohmic current and no electron emission are observed in a high quality diamond particle, while Pool-Frenkel current and electron emission are observed in a cauliflowerlike particle. Furthermore, to make use of structural and electrical properties of a polycrystalline diamond film, a novel gated diamond cathode with a plane diode structure was fabricated.