bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnesium‐inhibited, TRPM6/7‐like channel in cardiac myocytes: permeation of divalent cations and pH‐mediated regulation
Authors: Gwanyanya Asfree , Amuzescu Bogdan , Zakharov Sergey I. , Macianskiene Regina , Sipido Karin R. , Bolotina Victoria M. , Vereecke Johan , Mubagwa Kanigula
Published: July 2004

Cardiac tissue expresses several TRP proteins as well as a Mg2+‐inhibited, non‐selective cation current (IMIC) that bears many characteristics of TRP channel currents. We used the whole‐cell voltage clamp technique in pig and rat ventricular myocytes to characterize the permeation, blockage properties and regulation of the cardiac IMIC channels in order to compare them with TRP channels, in particular with Mg2+‐sensitive TRPM6 and TRPM7. We show that removing extracellular divalent cations unmasks large inward and outward monovalent currents, which can be inhibited by intracellular Mg2+. Inward currents are suppressed upon replacing extracellular Na+ by NMDG+. Divalent cations block monovalent IMIC and, at 10–20 mm, carry measurable currents. Their efficacy sequence in decreasing outward IMIC (Ni2+= Mg2+ > Ca2+ > Ba2+) and in inducing inward IMIC (Ni2+≫ Mg2+= Ca2+≈ Ba2+), and their permeabilities calculated from reversal potentials are similar to those of TRPM6 and TRPM7 channels. The trivalent cations Gd3+ and Dy3+ also block IMIC in a voltage‐dependent manner (δ= 0.4–0.5). In addition they inhibit the inward current carried by divalent cations. IMIC is regulated by pH. Decreasing or increasing extracellular pH decreased and increased IMIC, respectively (pH0.5= 6.9, nH= 0.98). Qualitatively similar results were obtained on IMIC in rat basophilic leukaemia cells. These effects in cardiac myocytes were absent in the presence of high intracellular buffering by 40 mm Hepes. Our results suggest that IMIC in cardiac cells is due to TRPM channels, most probably to TRPM6 or TRPM7 channels or to their heteromultimeres.
In vivo intracellular responses of the medial geniculate neurones to acoustic stimuli in anaesthetized guinea pigs
Authors: Yu Yan‐Qin , Xiong Ying , Chan Ying‐Shing , He Jufang
Published: July 2004

In the present study, we investigated the auditory response features of the medial geniculate neurones, using in vivo intracellular recordings in anaesthetized guinea pigs. Of the 76 neurones examined, 9 showed ‘off’ or ‘on–off’ responses to an acoustic stimulus and thus were defined as ‘off’ or ‘on–off’ neurones. Among the remaining 67 neurones, 42 showed an excitatory postsynaptic potential (EPSP) to acoustic stimuli and 25 showed either a pure inhibitory postsynaptic potential (IPSP, 7 neurones), or an IPSP preceded by an EPSP (EPSP–IPSP type, 18 neurones). The EPSP responses exhibited a mean latency of 15.7 ± 6.1 ms, which was significantly shorter than that of the IPSP responses (21.3 ± 8.6 ms, P < 0.01). The IPSP responses also showed a significantly greater duration than the EPSP responses (208.5 ± 128.2 ms versus 122.4 ± 84.8 ms, P < 0.05), while there were no significant differences between the amplitudes of IPSP and EPSP (8.3 ± 3.2 mV versus 8.7 ± 5.3 mV). Of the 11 neurones that showed EPSP responses to acoustic stimuli and were histologically labelled, 7 were located in the lemniscal medial geniculate body (MGB) and 4 in the non‐lemniscal MGB. Another 6 labelled neurones that showed IPSP responses to acoustic stimuli were located in the non‐lemniscal MGB. With a membrane potential of above −72 mV, the neurones showed greater EPSP or IPSP to an acoustic stimulus when their membrane potential was depolarized. However, upon hyperpolarization to below −74 mV, the neurones shifted to low‐threshold calcium spikes (LTS)/LTS bursts. In response to auditory stimuli of different durations, ‘off’ neurones that responded to the offset of the acoustic stimulus and were located in the non‐lemniscal MGB showed different response latencies or deviations of latencies in addition to exhibiting different numbers of spikes, suggesting that the timing of the spikes could be another component utilized by thalamic neurones to encode information on the stimulus. Given that some non‐lemniscal neurones are multisensory and project to the entire auditory cortex, the selective corticofugal inhibition in the non‐lemniscal MGB would enable the ascending pathway to prepare the auditory cortex to receive subsequent auditory information, avoiding the interference of other sensory inputs.
Effects of cortical stimulation on auditory‐responsive thalamic neurones in anaesthetized guinea pigs
Authors: Xiong Ying , Yu Yan‐Qin , Chan Ying‐Shing , He Jufang
Published: July 2004

In the present study, we investigated neuronal responses to acoustic stimuli and cortical stimulation in the medial geniculate body (MGB) through in vivo intracellular recordings in anaesthetized guinea pigs. Of the 54 neurones examined with acoustic stimuli, 36 showed excitatory postsynaptic potential (EPSP) responses and 19 showed inhibitory postsynaptic potential (IPSP) responses to acoustic stimuli. Of the 36 EPSP neurones examined with corticofugal modulation, 29 received corticofugal depolarization, 3 corticofugal inhibition, and 4 showed no effect. Of the 19 IPSP neurones, 17 received corticofugal inhibition and 2 were not affected. The mean amplitude of the EPSPs evoked by acoustic stimuli was similar to that evoked by the electrical cortical stimulation (9.19 ± 5.55 mV versus 9.22 ± 5.16 mV). There was a significant correlation between the parameters of the EPSPs evoked by an acoustic stimulus and those evoked by cortical stimulation. The mean amplitude of the IPSP evoked by electrical cortical stimulation was significantly greater than that evoked by acoustic stimuli (11.6 ± 3.8 mV versus 9.1 ± 3.7 ms, P < 0.05). Seven auditory EPSP and 7 IPSP neurones were examined with corticofugal modulation and labelled with Neurobiotin. Of the 7 EPSP neurones, 5 showed excitatory responses to cortical stimulation and 2 demonstrated no effects. Four of the 5 neurones that received corticofugal depolarization were located in the lemniscal MGB and 1 in the non‐lemniscal MGB; of the remaining 2, 1 was located in the lemniscal and the other in the non‐lemniscal MGB. Of the 7 IPSP neurones, 1 received an excitatory corticofugal input followed by an inhibitory input and 4 received only an inhibitory corticofugal input, while the remainder demonstrated no corticofugal effects. All 7 neurones were located in the non‐lemniscal MGB. The result that both ascending and descending inputs caused similarly shaped EPSPs reflects a neuronal endogenous characteristic irrespective of the physical locations of the synapses. The IPSP responses to both acoustic stimuli and electrical cortical stimulation are likely to be caused by feedback from the thalamic reticular nucleus.
Principal neuron spiking: neither necessary nor sufficient for cerebral blood flow in rat cerebellum
Authors: Thomsen Kirsten , Offenhauser Nikolas , Lauritzen Martin
Published: July 2004

Neuronal activity, cerebral blood flow, and metabolic responses are all strongly coupled, although the mechanisms behind the coupling remain unclear. One of the key questions is whether or not increases in spiking activity in the stimulated neurons are sufficient to drive the activity‐dependent rises in cerebral blood flow (CBF) that form the basis of the signals used in functional neuroimaging such as the blood oxygen level‐dependent (BOLD) signal. To this end the present study examined the effect of enhanced spike activity per se on CBF in rat cerebellar cortex under conditions of disinhibition, achieved by blocking GABAA receptors using either bicuculline or picrotoxin. Purkinje cell spiking activity and local field potentials were recorded by glass microelectrodes, and laser Doppler flowmetry was used to monitor CBF. Disinhibition increased Purkinje cell spiking rate to 200–300% of control without incurring any increase in basal CBF. This demonstrates that increased spike activity per se is not sufficient to affect basal CBF. The neurovascular coupling between excitatory synaptic activity and CBF responses evoked by inferior olive (climbing fibre) stimulation was preserved during disinhibition. Thus, the unchanged basal CBF in the presence of the dramatic rise in Purkinje cell spiking rate was not explained by impaired synaptic activity–CBF coupling. On the basis of our previous and the present studies, we conclude that increased spiking activity of principal neurons is neither sufficient nor necessary to elicit CBF responses and in turn BOLD signals, and that activation‐dependent vascular signals reflect excitatory synaptic activity.
Regulation of tissue oxygen levels in the mammalian lens
Authors: McNulty Richard , Wang Huan , Mathias Richard T. , Ortwerth Beryl J. , Truscott Roger J W. , Bassnett Steven
Published: July 2004

Opacification of the lens nucleus is a major cause of blindness and is thought to result from oxidation of key cellular components. Thus, long‐term preservation of  lens clarity may depend on the maintenance of hypoxia in the lens nucleus. We mapped the distribution of dissolved oxygen within isolated bovine lenses and also measured the rate of oxygen consumption (Q̇O2) by lenses, or parts thereof. To assess the contribution of mitochondrial metabolism to the lens oxygen budget, we tested the effect of mitochondrial inhibitors on Q̇O2 and partial pressure of oxygen (PO2). The distribution of mitochondria was mapped in living lenses by 2‐photon microscopy. We found that a steep gradient of PO2 was maintained within the tissue, leading to PO2 < 2 mmHg in the core. Mitochondrial respiration accounted for approximately 90% of the oxygen consumed by the lens; however, PO2 gradients extended beyond the boundaries of the mitochondria‐containing cell layer, indicating the presence of non‐mitochondrial oxygen consumers. Time constants for oxygen consumption in various regions of the lens and an effective oxygen diffusion coefficient were calculated from a diffusion–consumption model. Typical values were 3 × 10−5 cm2 s−1 for the effective diffusion coefficient and a 5 min time constant for oxygen consumption. Surprisingly, the calculated time constants did not differ between differentiating fibres (DF) that contained mitochondria and mature fibres (MF) that did not. Based on these parameters, DF cells were responsible for approximately 88% of lens oxygen consumption. A modest reduction in tissue temperature resulted in a marked decrease in Q̇O2 and the subsequent flooding of the lens core with oxygen. This phenomenon may be of clinical relevance because cold, oxygen‐rich solutions are often infused into the eye during intraocular surgery. Such procedures are associated with a strikingly high incidence of postsurgical nuclear cataract.
Functional and molecular evidence of MaxiK channel β1 subunit decrease with coronary artery ageing in the rat
Authors: Nishimaru Kazuhide , Eghbali Mansoureh , Lu Rong , Marijic Jure , Stefani Enrico , Toro Ligia
Published: July 2004

Large‐conductance, voltage‐ and Ca2+‐activated K+ channels (MaxiK, BK) are key regulators of vascular tone. Vascular MaxiK are formed by the pore‐forming α subunit and the modulatory β1 subunit, which imprints unique kinetics, Ca2+/voltage sensitivities and pharmacology to the channel. As age progresses, α subunit functional expression and protein levels diminish in coronary myocytes. However, whether ageing modifies β1 subunit expression or the mechanism of α subunit reduction is unknown. Thus, we examined functional and pharmacological characteristics of MaxiK, as well as α and β1 transcript levels in coronary myocytes from young and old F344 rats. The mechanism of age‐dependent α subunit protein reduction involves its transcript downregulation. A corresponding loss of β1 transcripts was also detected in old myocytes, suggesting a proportional age‐dependent decrease of β1 to α subunit protein. Indeed, MaxiK channel properties, defined by coassembly of β1 and α subunits, were equivalent in young versus old, for example in terms of (i) activation kinetics, (ii) sensitivity to Ca2+ levels > 1 μm (iii) dehydrosoyasaponin‐I‐induced activation, and (iv) iberiotoxin blockade. Consistent with less MaxiK expression/function in older myocytes, the ability of iberiotoxin to contract coronary rings was reduced ∼50% with ageing confirming our previous findings. 5‐Hydroxytryptamine (5‐HT) contractile efficacy was reduced by iberiotoxin pretreatment in young > old coronary arteries (explained by larger iberiotoxin‐induced contraction and decreased dynamic range for 5‐HT contraction in young versus old) with no apparent differences in nitroglycerine‐induced relaxation. We propose that the age‐related MaxiK reduction involves a parallel decrease of α and β1 functional expression via a transcript downregulatory mechanism; a major impact on basal and possibly stimulated coronary contraction may contribute to altered coronary flow regulation and coronary morbidity in the elderly.
Non‐selective cationic channels of smooth muscle and the mammalian homologues of Drosophila TRP
Authors: Beech D. J. , Muraki K. , Flemming R.
Published: July 2004

Throughout the body there are smooth muscle cells controlling a myriad of tubes and reservoirs. The cells show enormous diversity and complexity compounded by a plasticity that is critical in physiology and disease. Over the past quarter of a century we have seen that smooth muscle cells contain – as part of a gamut of ion‐handling mechanisms – a family of cationic channels with significant permeability to calcium, potassium and sodium. Several of these channels are sensors of calcium store depletion, G‐protein‐coupled receptor activation, membrane stretch, intracellular Ca2+, pH, phospholipid signals and other factors. Progress in understanding the channels has, however, been hampered by a paucity of specific pharmacological agents and difficulty in identifying the underlying genes. In this review we summarize current knowledge of these smooth muscle cationic channels and evaluate the hypothesis that the underlying genes are homologues of Drosophila TRP (transient receptor potential). Direct evidence exists for roles of TRPC1, TRPC4/5, TRPC6, TRPV2, TRPP1 and TRPP2, and more are likely to be added soon. Some of these TRP proteins respond to a multiplicity of activation signals – promiscuity of gating that could enable a variety of context‐dependent functions. We would seem to be witnessing the first phase of the molecular delineation of these cationic channels, something that should prove a leap forward for strategies aimed at developing new selective pharmacological agents and understanding the activation mechanisms and functions of these channels in physiological systems.
Ca2+ and K+ (BK) channels in chick hair cells are clustered and colocalized with apical–basal and tonotopic gradients
Authors: Samaranayake Haresha , Saunders James C. , Greene Mark I. , Navaratnam Dhasakumar S.
Published: July 2004

Electrical resonance is a mechanism used by birds and many vertebrates to discriminate between frequencies of sound, and occurs when the intrinsic oscillation in the membrane potential of a specific hair cell corresponds to a specific stimulus sound frequency. This intrinsic oscillation results from an interplay between an inward Ca2+ current and the resultant activation of a hyperpolarizing Ca2+‐activated K+ current. These channels are predicted to lie in close proximity owing to the fast oscillation in membrane potential. The interplay of these channels is widespread in the nervous system, where they perform numerous roles including the control of synaptic release, burst frequency and circadian rhythm generation. Here, we used confocal microscopy to show that these two ion channels are clustered and colocalized in the chick hair cell membrane. The majority of Ca2+ channels were colocalized while the proportion of colocalized BK channels was markedly less. In addition, we report both an apical–basal gradient of these clusters in individual hair cells, as well as a gradient in the number of clusters between hair cells along the tonotopic axis. These results give physical confirmation of previous predictions. Since the proportion of colocalized channels was a constant function of Ca2+ channels, and not of BK channels, these results suggest that their colocalization is determined by the former. The molecular mechanisms underpinning their clustering and colocalization are likely to be common to other neuronal cells.
Dynamics of rat entorhinal cortex layer II and III cells: characteristics of membrane potential resonance at rest predict oscillation properties near threshold
Authors: Erchova I. , Kreck G. , Heinemann U. , Herz A. V. M.
Published: July 2004

Neurones generate intrinsic subthreshold membrane potential oscillations (MPOs) under various physiological and behavioural conditions. These oscillations influence neural responses and coding properties on many levels. On the single‐cell level, MPOs modulate the temporal precision of action potentials; they also have a pronounced impact on large‐scale cortical activity. Recent studies have described a close association between the MPOs of a given neurone and its electrical resonance properties. Using intracellular sharp microelectrode recordings we examine both dynamical characteristics in layers II and III of the entorhinal cortex (EC). Our data from EC layer II stellate cells show strong membrane potential resonances and oscillations, both in the range of 5–15 Hz. At the resonance maximum, the membrane impedance can be more than twice as large as the input resistance. In EC layer III cells, MPOs could not be elicited, and frequency‐resolved impedances decay monotonically with increasing frequency or has only a small peak followed by a subsequent decay. To quantify and compare the resonance and oscillation properties, we use a simple mathematical model that includes stochastic components to capture channel noise. Based on this model we demonstrate that electrical resonance is closely related though not equivalent to the occurrence of sag‐potentials and MPOs. MPO frequencies can be predicted from the membrane impedance curve for stellate cells. The model also explains the broad‐band nature of the observed MPOs. This underscores the importance of intrinsic noise sources for subthreshold phenomena and rules out a deterministic description of MPOs. In addition, our results show that the two identified cell classes in the superficial EC layers, which are known to target different areas in the hippocampus, also have different preferred frequency ranges and dynamic characteristics. Intrinsic cell properties may thus play a major role for the frequency‐dependent information flow in the hippocampal formation.
Texture orientation of glancing angle deposited copper nanowire arrays
Authors: Alouach H. , Mankey G. J.
Published: July 2004

Self-assembled copper nanowires were deposited on native oxide Si(100) substrates using glancing angle deposition with and without substrate rotation. Wire morphology, texture and crystallographic orientation are strongly dependent on the deposition parameters. A method for determining the preferred crystal orientation is described. This orientation is found to be different from what is expected from the geometric orientation of the wires. For wires deposited without substrate rotation, the face-centered-cubic (fcc)(111) crystal orientation, which corresponds to the close-packed, low surface energy (111) plane of copper, lies between the long axis of the wire and that normal to the substrate. X-ray diffraction data show that the wires exhibit bundling behavior perpendicular to the plane of incidence. For samples deposited with azimuthal rotation of the substrate, the fcc(111) directions in the wires are evenly distributed in a cone around the long axis of the wires, which point normal to the substrate. When the substrate is rotated during deposition at an angle of 75°, the wires exhibit a strong fcc(220) texture. These observations show that wires deposited with substrate rotation are highly textured and have random orientations in the plane of the substrate.
Fabrication and characterization of a capacitive micromachined shunt switch
Authors: Firebaugh Samara L. , Charles Harry K. , Edwards Richard L. , Keeney Allen C. , Wilderson Samuel F.
Published: July 2004

The design and fabrication of a capacitive shunt switch are described. The switch is based on a bridge structure that can be modulated using electrostatic actuation. The switch has two states: when the bridge is up the signal passes through with less than 0.1 dB insertion loss. When the bridge is down the signal is attenuated by 15–20 dB at 20 GHz. The residual stress of the bridge material is critical to operation of these switches. This stress was tightly controlled by varying the temperature of the plating bath. Different bridge widths and shapes are compared. “Bowtie” shaped bridges are demonstrated to have increased insertion loss and similar isolation compared to straight bridges. These devices were observed to be sensitive to packaging stress, resulting in more than doubling the actuation voltage. This work also describes the development of a test fixture that facilitates standard microwave connections for testing the devices without a probe station. The test fixture was observed to have an insertion loss of less than 3 dB up to 20 GHz.
Sub-100 nm radius of curvature wide-band gap III-nitride vacuum microelectronic field emitter structures created by inductively coupled plasma etching
Authors: Shah P. B. , Nichols B. M. , Derenge M. D. , Jones K. A.
Published: July 2004

A parametric investigation on the ability to use dry etching to form conical field emitter type structures in AlN and GaN was conducted using an inductively coupled plasma reactive ion etcher. Etched structures viewed with a scanning electron microscope demonstrate that an array of conical and wedge shaped structures, both with tip radius of curvatures less than 100 nm, can be manufactured by etching AlN and GaN using a photoresist mask. The etch gases investigated include Cl2, BCl3, SF6, HBr, and Ar. We also discuss the etch rates and sidewall profiles that result from using higher gas flows (up to 45 sccm) and higher discharge pressures (up to 24 mTorr) than previously reported in the literature.
Self-organizing processes in connection with metastable nanocluster states
Authors: Rieth Michael , Schommers Wolfram
Published: July 2004

In the past experimental as well as theoretical investigations have shown that the structure of metallic nanoclusters most often deviates significantly from those of the bulk. With the help of molecular dynamics calculations we demonstrate how the transition from bulk structured materials to nanostructured clusters might take place. In connection with such structural transitions one result is rather interesting: the occurrence of metastable cluster states. The conditions under which such metastable nanostructures might be possible and how their lifetime could be influenced are systematically investigated. How are the structure and the dynamics of nanoclusters changed when they transform from the metastable into the stable state? In order to answer this we calculated the structure factor and the generalized phonon density of states for the stable as well as for the metastable cluster state.
Spatially regulated growth of metal oxide thin film onto alkyl monolayer template from aqueous solution containing metal fluoride
Authors: Shirahata Naoto , Yokogawa Yoshiyuki , Kameyama Tetsuya , Hozumi Atsushi
Published: July 2004

We have succeeded in fabricating micropattern of metal oxide thin film from an aqueous solution containing metal fluoride precursor utilizing alkyl monolayer template. Two kinds of monolayers, such as octadecyltrimethoxysilane (OTS) and 1-octadecene (OD), were selected as the starting precursors to be formed onto SiO2/Si and Si surfaces, respectively. Both monolayer templates were prepared by vacuum ultraviolet irradiation through a photomask. The Sn-based thin films were deposited onto both monolayer templates by immersing both monolayer template substrates into an aqueous solution containing 0.03 mol/l of SnF2 at 60 °C. The micropatterned Sn-based thin films were obtained on both templates after liftoff processing in an anhydrous toluene, respectively. The Sn-based thin film remained site-selectively only on the Si–O area of the OD monolayer template, while it was perfectly peeled off from the methyl-terminated area of the OD monolayer template. The x-ray photoelectron spectrum showed no Si–O component in the Sn-based thin film deposited on Si–O area of the OD monolayer template. On the other hand, the film deposited on the methyl-terminated area of OTS monolayer template could be imperfectly peeled off. Therefore, high-resolution micropattern of the film could not be obtained on the OTS monolayer template. Such different liftoff phenomena were discussed from the viewpoint of different bonding states between each template and the substrates.
Magnetization dynamics and magnetotransport in epitaxial nanostructures
Authors: Lukaszew R. A. , Pearson D. , Zhang Z. , Zambano A.
Published: July 2004

The latest magnetoresistive results reported for electrochemically-defined nanocontacts between Ni wires are still quite controversial (Ninth Joint MMM Intermag Conference). We have used e-beam lithography applied to epitaxial Ni films to fabricate nanobridges in more controlled geometry than that of electrochemical deposition. Our studies are important for the understanding of suitable production procedures for Ni nanocontacts. The idea behind our scheme is that epitaxial ferromagnetic thin films exhibit rich magnetic anisotropy and large coercivities at room temperature, associated with only few defects in the crystal lattice. They also exhibit higher anisotropy than polycrystalline films and domain walls with narrower widths are expected. Thus, we speculate that this type of structure would favor ballistic magnetoresistance and possibly domain-wall trapping provided that there is a small enough constriction as predicted by Bruno [Phys. Rev. Lett. 83, 2425 (1999)].
Properties of indium zinc oxide thin films on heat withstanding plastic substrate
Authors: Hara H. , Hanada T. , Shiro T. , Yatabe T.
Published: July 2004

We have investigated ZnO doped indium oxide (IZO) as a transparent conductive oxide (TCO) film with low resistivity and high tolerance to heat treatment deposited on a plastic substrate with high glass transition temperature (Tg), optical isotropy and dimensional stability. The resistivity of IZO with 7.5 wt % ZnO film [IZO(7.5)] is 2.9×10−4 Ω cm, which is 33% lower than that of tin doped indium oxide film (ITO) and remains unchanged even after annealing at 180 °C for 4 h. We establish by x-ray diffraction and transmission electron microscope that the structure of annealed IZO(7.5) is amorphous and by DSC that the structure starts to transform to the crystalline phase at 350 °C. The etching rate of IZO(7.5) films is almost the same as, or quicker than, that of amorphous ITO films. The durability of IZO(7.5) against the alkali solution is also good for practical use.
Selective etching process of SrBi2Ta2O9 and CeO2 for self-aligned ferroelectric gate structure
Authors: Shim Sun Il , Kwon Young Suk , Kim Seong Il , Kim Yong Tae , Park Jung Ho
Published: July 2004

We have investigated an etch-stop process and fabricated the ferroelectric gate transistor without damage of source and drain regions using etching selectivity between etch rates of SrBi2Ta2O9 (SBT) and CeO2. The SBT and CeO2 were etched with inductively coupled plasma (ICP) reactive ion etching at various Ar/Cl2 gas mixing ratios, ICP powers, and rf bias powers. The etching selectivity of SBT/CeO2 was 6.8 and the vertical etching angle of SBT was 82° at the condition of 50% Cl2 concentration with the ICP power of 900 W and the rf bias power of 100 W. The characteristics of devices fabricated with an etch-stop process showed that there was no degradation of the ferroelectric characteristics and on/off ratio of programmable operation was 104.
Theoretical and experimental evaluation of the windowless interface for the TRASCO-ADS project
Authors: Michelato P. , Bari E. , Monaco L. , Sertore D. , Bonucci A. , Giannantonio R. , Urbano M. , Viale L. , Turroni P. , Cinotti L.
Published: July 2004

TRASCO-ADS is a national funded program in which INFN, ENEA, and Italian industries work on the design of an accelerator driven subcritical system for nuclear waste transmutation. TRASCO is the Italian acronym for Transmutation (TRAsmutazione) of Waste (SCOrie). One of the most critical aspects in the design of an Accelerator Driven System is related to the interface region, which is the part of the beamline located between the accelerator, operating under UHV conditions, and the pressurized reactor vessel, consisting of a contained plenum of Pb-Bi eutectic (LBE). A so-called window could separate these two environments, but thermomechanical considerations and radioprotection issues point out that this component could be critical. In the windowless interface, no window is located between the linac and the spallation target. Only a suitable pumping and trapping system, for the gases and the vapors outcoming from LBE, divides the UHV accelerator and the spallation target vacuum. Vacuum gas dynamics theoretical considerations and calculations are presented in this article. The need for a validation of the theoretical models gave the motivation for an experimental work, whose results are also discussed. Scale-up of the experimental setup to the full system needs accurate analyses for a proper dimensioning of the system in the interface region.
Fourier transform infrared study of methanol, water, and acetic acid on MgO(100)
Authors: Foster Michelle , Passno Devon , Rudberg Jennifer
Published: July 2004

Investigations of the interactions occurring between the MgO(100) surface and a series of small molecules—methanol, water, and acetic acid—have been performed. The molecule of interest is introduced to a sample cell containing 15–20 MgO(100) crystals and allowed to establish a dynamic equilibrium with the substrate. The adlayer formed on the crystal faces is observed by transmission Fourier transform infrared spectroscopy. The substrates are also inspected with atomic force microscopy both before and after exposure of the surface to the species of interest. The interactions of these adsorbates with MgO(100) under room temperature conditions and pressures on the order of 10 Torr vary from physisorbed methanol to dissociatively chemisorbed acetic acid, which reacts with the MgO(100) forming magnesium acetate under these experimental conditions.
Thickness and composition of ultrathin SiO2 layers on Si
Authors: van der Marel C. , Verheijen M. A. , Tamminga Y. , Pijnenburg R. H. W. , Tombros N. , Cubaynes F.
Published: July 2004

Ultrathin SiO2 layers are of importance for the semiconductor industry. One of the techniques that can be used to determine the chemical composition and thickness of this type of layers is x-ray photoelectron spectroscopy (XPS). As shown by Seah and Spencer [Surf. Interface Anal. 33, 640 (2002)], it is not trivial to characterize this type of layer by means of XPS in a reliable way. We have investigated a series of ultrathin layers of SiO2 on Si (in the range from 0.3 to 3 nm) using XPS. The samples were also analyzed by means of transmission electron microscopy (TEM), Rutherford backscattering (RBS), and ellipsometry. The thickness of the SiO2 layers (d) was determined from the XPS results using three different approaches: the “standard” equation (Seah and Spencer) for d, an overlayer-substrate model calculation, and the QUASES–Tougaard [Surf. Interface Anal. 26, 249 (1998), QUASES–Tougaard: Software package for Quantitative Analysis of Surfaces by Electron Spectroscopy, version 4.4 (2000); http://www.quases.com] method. Good agreement was obtained between the results of XPS analyses using the “standard” equation, the overlayer-substrate model calculation, and RBS results. The QUASES–Tougaard results were approximately 62% above the other XPS results. The optical values for the thickness were always slightly higher than the thickness according to XPS or RBS. Using the model calculation, these (relatively small) deviations from the optical results could be explained as being a consequence of surface contaminations with hydrocarbons. For a thickness above 2.5 nm, the TEM results were in good agreement with the results obtained from the other techniques (apart from QUASES–Tougaard). Below 2.5 nm, significant deviations were found between RBS, XPS, and optical data on the one hand and TEM results on the other hand; the deviations became larger as the thickness of the SiO2 decreased. This effect may be related to interface states of oxygen, which have been investigated [D. A. Muller, T. Sorsch, S. Moccio, F. H. Baumann, K. Evans-Lutterodt, and G. Timp, Nature (London) 399, 758 (1999); D. A. Muller and J. B. Neaton, Structure and Energetics of the Interface Between Si and Amorphous SiO2 in Fundamental Aspects of Silicon Oxidation, edited by Y. J. Chabal (Springer, Berlin, 2001), pp. 219–246.] by means of high-resolution electron energy loss spectroscopy measurements of the O K edge in ultrathin gate oxides of SiO2.
Optical, structural, and electrical characteristics of high dielectric constant zirconium oxide thin films deposited by spray pyrolysis
Authors: Aguilar-Frutis M. , Reyna-Garcia G. , Garcia-Hipolito M. , Guzman-Mendoza J. , Falcony C.
Published: July 2004

The spray pyrolysis technique was used to obtain high dielectric constant zirconium oxide films. These films were deposited on silicon substrates, and quartz slides from two different solution concentrations (0.033 and 0.066 M) of zirconium acetylacetonate dissolved in N,N-dimethylformamide at substrate temperatures in the range of 400–600 °C. The films are transparent with a surface roughness lower than 40 Å and with the ZrO2 stoichiometry. The refractive index of the films was up to 2.12 at 630 nm. Infrared spectroscopy measurements show a dominant absorption band associated to ZrO2 at 420 cm−1 and the presence of silicon oxide (SiO2) peaks as well. Cross-section transmission electron microscopy (TEM) images of these films reveal the existence of a thin layer at the silicon substrate interface with the deposited ZrO2 film. It is also found from both cross-section and plan-view TEM observations that the deposited layers consist of tetragonal ZrO2 nano-crystallites embedded in an amorphous zirconium oxide matrix. Spectroscopic ellipsometry measurements were fitted assuming the existence of a thin interface layer on top of the Si substrate, composed of SiO2, ZrO2, and crystalline silicon. The as-deposited films have a dielectric constant in the range from 10.9 to 17.5 when they are deposited at different substrate temperatures for the two spraying solution concentrations studied. The films withstand electric fields up to 3 MV/cm, without observing destructive dielectric breakdown.
Wettability control of a polymer surface through 126 nm vacuum ultraviolet light irradiation
Authors: Hozumi Atsushi , Shirahata Naoto , Nakanishi Youichiro , Asakura Shuuichi , Fuwa Akio
Published: July 2004

The control of the surface wettability of poly (methyl methacrylate) (PMMA) substrates has been successfully demonstrated using an Ar2* excimer lamp radiating 126 nm vacuum ultraviolet (VUV) light. Each of the samples was exposed to 126 nm VUV light in air over the pressure range of 2×10−4–105 Pa. Although at the process pressures of 10, 103, and 105 Pa, the PMMA surfaces became relatively hydrophilic, the degree of hydrophilicity depended markedly on the pressure. The minimum water contact angles of the samples treated at 10, 103, and 105 Pa were about 50°, 33°, and 64°, respectively. These values were larger than those of PMMA substrates hydrophilized through 172 nm VUV irradiation conducted under the same conditions. On the other hand, after 126 nm VUV irradiation conducted under the high vacuum condition of 2×10−4 Pa, the PMMA substrate surface became carbon-rich, probably due to preferential cross-linking reactions, as evidenced by x-ray photoelectron spectroscopy. This surface was hydrophobic, showing a water contact angle of about 101°. Although the 126 nm VUV-irradiated surfaces appeared relatively smooth when observed by atomic force microscope, very small particles with diameters of 30–60 nm, which probably originated from the readhesion of photodecomposed products, existed on all of the sample surfaces.
Ozone adsorption on carbon nanotubes: Ab initio calculations and experiments
Authors: Picozzi S. , Santucci S. , Lozzi L. , Cantalini C. , Baratto C. , Sberveglieri G. , Armentano I. , Kenny J. M. , Valentini L. , Delley B.
Published: July 2004

The electrical response to O3 of 150-nm-thick carbon nanotube (CNT) thin films prepared by radio frequency-plasma enhanced chemical vapor deposition has been investigated at different operating temperatures starting from the room temperature. The interaction between ozone molecules and a carbon nanotube film is studied by means of first-principles calculations. Experiments show that CNT films are responsive to O3 with a decrease of the resistance similar to that observed for NO2. Our theoretical results suggest the interaction to be pretty strong, as shown by a relatively short equilibrium molecule-tube distance, as well as by an appreciable binding energy and charge transfer from the tube to the adsorbed molecule. The analysis of the density of states shows that a peak in proximity of the nanotube Fermi level is induced by the ozone adsorption. This effect enhances the p-type character of the nanotube and, therefore, the conductivity of the whole film increases, in excellent consistency with the experimentally observed resistance decrease upon O3 exposure.
Adsorption of oxidizing gases on multiwalled carbon nanotubes
Authors: Valentini L. , Lozzi L. , Picozzi S. , Cantalini C. , Santucci S. , Kenny J. M.
Published: July 2004

In this article, we have reported the dependence of electrical conductance on the presence of structural defects and of molecular-oxygen adsorbates in carbon nanotube thin films for NO2 detection. Our results show that an oxygen contaminant may be responsible for the reported sensitivity to NO2. Experimental results indicate that the adsorption and the uptake of the oxidizing gas are more likely to occur as a result of the interaction between the O2 molecule and defective sites in the hexagonal network of the nanotubes. Experimental findings demonstrate that nanotubes could be used as sensitive chemical gas sensors and likewise indicate that the intrinsic properties measured on as grown nanotubes may be changed by extrinsic oxidative effects.
Investigation of etching properties of HfO based high-Kdielectrics using inductively coupled plasma
Authors: Chen Jinghao , Yoo Won Jong , Tan Zerlinda YL , Wang Yingqian , Chan Daniel S.H.
Published: July 2004

The etching properties of HfO based high dielectric constant (K) films, HfO2, HfON, HfSiO, and HfAlO, were investigated using inductively coupled plasma of Cl2/HBr/CHF3/CF4/O2. The etch rates varied depending on the chemical components in the films. Among HfO2, HfON, HfSiO, and HfAlO, the etch rates of HfSiO increased most significantly with increasing radio frequency bias power. This may be attributed to the ternary network of Hf–Si–O that is different from the binary network of other films of Hf–O, Hf–N, Si–O, and Al–O. The etch rates of HfON were higher than those of HfO2 due to the effect of the high Hf–N etch rates compared to the Hf–O etch rates, whereas the HfAlO etch rates were lower than those of HfO2 due to the effect of the low Al–O etch rates. Etch residues and chemical compositions of HfO based dielectrics were analyzed by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. A significant amount of fluorides existed on the surface after CF4/CHF3 etching whereas only a small amount of chloride and bromide existed after Cl2/HBr etching. The high temperature post-treatment step was effective in reducing the amount of residues.
Multidimensional flow modeling of the compression test of a Gaede pump stage in the viscous regime
Authors: Giors S. , Subba F.
Published: July 2004

Two-dimensional and three-dimensional models for a Gaede pump, based on the Navier–Stokes equations, are developed and a commercial Computational Fluid Dynamics code is used to solve them. We simulate a compression test in an outlet pressure range (30–2500 Pa) corresponding to the viscous laminar regime for an experimental pump. Experimental data are collected in order to validate the developed model. The pump tested is the high pressure stage of a commercial hybrid turbomolecular vacuum pump and can work in both transition and viscous regime, according to the operating pressure. The data show that the standard Couette–Poiseuille one-dimensional analytic model, developed by Helmer and Levi to describe the Gaede pump behavior and operating principle, has a limited accuracy when it is used as a design tool and not just as a physical model. The two-dimensional and the three-dimensional model results are compared with the experimental data showing an increasing level of agreement, with only a 10% maximum difference for the three-dimensional model in terms of compression ratio. The different flow structures shown by the models are critically analyzed to explain the different level of agreement.
Modeling of the target surface modification by reactive ion implantation during magnetron sputtering
Authors: Depla D. , Chen Z. Y. , Bogaerts A. , Ignatova V. , De Gryse R. , Gijbels R.
Published: July 2004

The erosion rate of an aluminum target bombarded with Ar+ and O2+ ions was simulated using TRIDYN. An abrupt change of the erosion rate is noticed at a critical mole fraction of O2+ ions. This target behavior can also be described by a simple analytical model showing that the abrupt change finds its origin in an avalanche induced by reaction ion implantation. Indeed, by the reduction of the average sputter yield by compound formation, more reactive ions become implanted into the target as the number of implanted ions depends inversely on the average sputter yield. As such, an avalanche situation can develop which finally results in a completely oxidized target. It is also shown that the critical mole fraction depends linearly on the sputter yield of the target material and that target poisoning induced by ion implantation can result in a hysteresis behavior for the target condition.
Textured growth of cubic gallium nitride thin films on Si (100) substrates by sputter deposition
Authors: Kim Joo Han , Holloway Paul H.
Published: July 2004

Cubic gallium nitride (GaN) thin films were grown at room temperature on silicon (100)-oriented substrates by radio frequency (rf) planar magnetron sputtering of a GaN target in a pure nitrogen atmosphere. The rf power applied to the GaN cathode target was varied in order to determine the influence of film growth rate on the texture and properties of cubic GaN films. The growth rate of the GaN films was an approximately linear function of the rf cathode target power. X-ray diffraction θ–2θ and pole-figure scans revealed that all the GaN films possess a predominant cubic zinc-blende phase having a textured structure with (111) crystallographic planes oriented preferentially parallel to the surface. The a lattice parameter of the cubic GaN was determined to be approximately 4.59 Å. X-ray rocking curve analysis showed that the degree of [111] preferred orientation is higher for the GaN films grown at lower growth rates (∼16 Å/min). Higher concentration of oxygen impurity was present in the GaN films grown at these slow growth rates. Auger depth profiles indicated that the oxygen impurity was incorporated into the GaN films during growth rather than diffusing into the films after the growth or adsorbing during the AES analysis.
Cubic inclusions in 4H-SiC studied with ballistic electron-emission microscopy
Authors: Ding Y. , Park K.-B. , Pelz J. P. , Palle K. C. , Mikhov M. K. , Skromme B. J. , Meidia H. , Mahajan S.
Published: July 2004

High-temperature-processing-induced “double-stacking fault” cubic inclusions in 4H-SiC were studied with ballistic electron emission microscopy (BEEM). Large BEEM current and a ∼0.53 eV local reduction in the Schottky barrier height (SBH) were observed where the inclusions intersect a Pt interface, confirming the quantum-well nature of the inclusions and providing nanometer scale information about local electronic behavior. Measured spatial variations in the BEEM current are related to the inclusion orientation and local surface step structure. An observation of an anomalously low SBH is discussed, suggesting the existence of a triple- or quadruple-stacking fault inclusion.
Effect of Mn composition on characterization of Zn1−xMnxSe epilayers
Authors: Yu Y.-M. , Kim D. J. , Lee K.-J. , Choi Y. D. , O Byungsung , Lee K.-S. , Choi I.-H. , Yoon M.-Y.
Published: July 2004

Zn 1−x Mn x Se epilayers have been grown on GaAs (100) substrates by hot-wall epitaxy. The structure of the epilayers was found to be zinc-blende over a large Mn composition range, 0⩽x⩽0.75. Exciton-related near-edge emissions and the intra-Mn2+ transition were observed in the 5 K photoluminescence (PL) spectrum. The composition dependence of PL peak energy was also studied. The ZnSe-like longitudinal optical phonon peak was observed in the Raman scattering spectrum and the Raman frequency was blueshifted with increasing Mn composition. The variation of the dielectric constants ε1 and ε2 as a function of Mn composition x was measured by spectroscopic ellipsometry in the 3.0–8.5 eV range at 300 K. The dielectric function spectra reveal distinct structures at each critical point.
Ultrahigh barrier coating deposition on polycarbonate substrates
Authors: Schaepkens Marc , Kim Tae Won , Gün Erlat Ahmet , Yan Min , Flanagan Kevin W. , Heller Christian M. , McConnelee Paul A.
Published: July 2004

The use of polycarbonate film substrates enables fabrication of applications, such as flexible display devices, lighting devices, and other flexible electro-optical devices, using low cost, roll-to-roll fabrication technologies. One of the limitations of bare polycarbonate material in these applications is that oxygen and moisture rapidly diffuse through the material and subsequently degrade the electro-optical devices. This article summarizes recent results obtained at GE Global Research to solve the oxygen and moisture diffusion issue. It will be shown that through the application of thin, dense, plasma-based inorganic coatings one can significantly reduce the oxygen and moisture permeation rate through polycarbonate films. However, as a result of defects that are commonly present in these inorganic coatings there is a limit to the performance of such barrier coatings. To further improve the barrier performance, advanced barrier coatings comprising both inorganic and organic materials have been developed. Both modeling and experimental results will be presented that explain why these hybrid material barrier coatings are capable of reaching ultrahigh barrier performance.