bluuebunny/crossref_metadata_2025 huggingface dataset:
Upregulation of inward rectifier K+(Kir2) channels in dentate gyrus granule cells in temporal lobe epilepsy
Authors: Young Christina C. , Stegen Michael , Bernard René , Müller Martin , Bischofberger Josef , Veh Rüdiger W. , Haas Carola A. , Wolfart Jakob
Published: June 2009

In humans, temporal lobe epilepsy (TLE) is often associated with Ammon's horn sclerosis (AHS) characterized by hippocampal cell death, gliosis and granule cell dispersion (GCD) in the dentate gyrus. Granule cells surviving TLE have been proposed to be hyperexcitable and to play an important role in seizure generation. However, it is unclear whether this applies to conditions of AHS. We studied granule cells using the intrahippocampal kainate injection mouse model of TLE, brain slice patch‐clamp recordings, morphological reconstructions and immunocytochemistry. With progressing AHS and GCD, ‘epileptic’ granule cells of the injected hippocampus displayed a decreased input resistance, a decreased membrane time constant and an increased rheobase. The resting leak conductance was doubled in epileptic granule cells and roughly 70–80% of this difference were sensitive to K+replacement. Of the increased K+leak, about 50% were sensitive to 1 mmBa2+. Approximately 20–30% of the pathological leak was mediated by a bicuculline‐sensitive GABAAconductance. Epileptic granule cells had strongly enlarged inwardly rectifying currents with a low micromolar Ba2+IC50, reminiscent of classic inward rectifier K+channels (Irk/Kir2). Indeed, protein expression of Kir2 subunits (Kir2.1, Kir2.2, Kir2.3, Kir2.4) was upregulated in epileptic granule cells. Immunolabelling for two‐pore weak inward rectifier K+channels (Twik1/K2P1.1, Twik2/K2P6.1) was also increased. We conclude that the excitability of granule cells in the sclerotic focus of TLE is reduced due to an increased resting conductance mainly due to upregulated K+channel expression. These results point to a local adaptive mechanism that could counterbalance hyperexcitability in epilepsy.
Homocysteine transport by systems L, A and y+L across the microvillous plasma membrane of human placenta
Authors: Tsitsiou Eleni , Sibley Colin P. , D'Souza Stephen W. , Catanescu Otilia , Jacobsen Donald W. , Glazier Jocelyn D.
Published: June 2009

Elevated maternal plasma levels of homocysteine (Hcy) are associated with pregnancy complications and adverse neonatal outcomes, suggesting placental transport of Hcy may impact on fetal development. However, such transport mechanisms have not been defined. In this study we characterise Hcy transport mechanisms across the microvillous plasma membrane (MVM) of the syncytiotrophoblast, the transporting epithelium of human placenta. Three candidate transport systems, systems L, A and y+L, were examined utilising competitive inhibition to investigate the effects of Hcy on the uptake of well‐characterised radiolabelled substrates for each system into isolated MVM vesicles, and that of model substrates on 10 μm[35S]l–Hcy uptake. System L activity was inhibited by both l‐Hcy and dl–Hcy, comparable to model substrates including 2–aminobicyclo[2.2.1]heptane‐2‐carboxylic acid (BCH). System L constituted the major transport mechanism, with significant BCH inhibition (∼69%) of [35S]l–Hcy uptake. System A activity was also inhibited by l–Hcy and dl‐Hcy with a smaller contribution (∼21%) to [35S]l–Hcy uptake. Inhibition by l–Hcy and dl–Hcy of system y+L activity was Na+ sensitive with a significant inhibition constant (Ki) shift observed following K+ replacement; l–arginine reduced [35S]l–Hcy uptake by ∼19%. Kinetic modelling of [35S]l–Hcy uptake resolved two, Na+‐independent, transport components (Km 72 μm and 9.7 mm). This study provides evidence for the involvement of systems L, A and y+L in placental Hcy transport. Such transport, by competing with endogenous amino acids for transporter activity, could have major implications for syncytiotrophoblast metabolism and function as well as fetal development.
Caffeine inhibition of ionotropic glycine receptors
Authors: Duan Lei , Yang Jaeyoung , Slaughter Malcolm M.
Published: June 2009

We found that caffeine is a structural analogue of strychnine and a competitive antagonist at ionotropic glycine receptors (GlyRs). Docking simulations indicate that caffeine and strychnine may bind to similar sites at the GlyR. The R131A GlyR mutation, which reduces strychnine antagonism without suppressing activation by glycine, also reduces caffeine antagonism. GlyR subtypes have differing caffeine sensitivity. Tested against the EC50of each GlyR subtype, the order of caffeine potency (IC50) is: α2β (248 ± 32 μm) ≈α3β (255 ± 16 μm) > α4β (517 ± 50 μm) > α1β(837 ± 132 μm). However, because the α3β GlyR is more than 3‐fold less sensitive to glycine than any of the other GlyR subtypes, this receptor is most effectively blocked by caffeine. The glycine dose–response curves and the effects of caffeine indicate that amphibian retinal ganglion cells do not express a plethora of GlyR subtypes and are dominated by the α1β GlyR. Comparing the effects of caffeine on glycinergic spontaneous and evoked IPSCs indicates that evoked release elevates the glycine concentration at some synapses whereas summation elicits evoked IPSCs at other synapses. Caffeine serves to identify the pharmacophore of strychnine and produces near‐complete inhibition of glycine receptors at concentrations commonly employed to stimulate ryanodine receptors.
High rate sputtering deposition of silicon oxide thin films from new SiO2:Si target composition
Authors: Fan Qi Hua , Zhou Li Qin , Stevenson David
Published: June 2009

The authors have developed an electrically conductive sputtering target by a sintering process using powders of SiO2 and boron doped Si. This target composition can be sputtered using dc, pulse dc, or rf power supplies. Using rf sputtering the authors have demonstrated deposition rates that are four times higher than typical deposition rates for rf sputtered SiO2 films from quartz targets. Further, the optical transmittance, refractive index, microstructure, and etching resistance of the SiO2 films prepared using this target are comparable to films produced from rf sputtered quartz targets. In this article, the authors present details of the conductive SiO2:Si target composition as well as the resulting SiO2 film properties and deposition rates that have been achieved. They also discuss the possible mechanisms for such high deposition rates.
Efficient translational excitation of a solid metal surface: State-to-state translational energy distributions of vibrational ground state HCl scattering from Au(111)
Authors: Cooper Russell , Rahinov Igor , Yuan Cheng , Yang Xueming , Auerbach Daniel J. , Wodtke Alec M.
Published: June 2009

The authors report high resolution state resolved measurements of the translational inelasticity of HCl(v=0→0,J=0→4) colliding with a Au(111) surface at near normal incidence in the energy range of 0.28–1.27eV. The translational inelasticity is large and indistinguishable from previous measurements for the HCl(v=2→2,J=1→5) channel. They discuss these observations in terms of an impulse approximation as well as the possible role of translational excitation of electron-hole pairs in the solid.
Tunneling spectroscopy of graphene and related reconstructions on SiC(0001)
Authors: Nie Shu , Feenstra R. M.
Published: June 2009

The 5×5,6√3×6√3−R30° and graphene-covered 6√3×6√3−R30° reconstructions of the SiC(0001) surface are studied by scanning tunneling microscopy and spectroscopy. For the 5×5 structure a rich spectrum of surface states is obtained, with one state, in particular, found to be localized on top of structural protrusions (adatoms) observed on the surface. Similar spectra are observed on the bare 6√3×6√3−R30° reconstruction, and in both cases the spectra display nearly zero conductivity at the Fermi level. When graphene covers the 6√3×6√3−R30° surface the conductivity at the Fermi level shows a marked increase, and additionally the various surface state peaks seen in the spectrum shift in energy and fall in intensity. The influence of the overlying graphene on the electronic properties of the interface is discussed, as are possible models for the interface structure.
Mechanical and tribological property comparison of melt-compounded nanocomposites of atomic-layer-deposition-coated polyamide particles and commercial nanofillers
Authors: Nevalainen K. , Suihkonen R. , Eteläaho P. , Vuorinen J. , Järvelä P. , Isomäki N. , Hintze C. , Leskelä M.
Published: June 2009

Mechanical and tribological properties of melt-compounded titanium dioxide nanocomposites of atomic-layer-deposition (ALD)-coated polyamide particles and commercial nanofillers were compared. The nanofiller dispersion in the polyamide matrix was studied using transmission electron microscopy showing very different morphology for the ALD-created and the traditional nanocomposites: former appearing as ribbons in the matrix whereas latter composing from spherical clusters. The effect of such morphology change on the specimen’s mechanical response subjected to tensile and impact loading was investigated. The results demonstrated that ALD-created nanocomposites possess significantly higher Young’s modulus than pure and traditionally filled polyamide matrix. However, transition from ductile to brittle behavior occurs especially for the ALD-created nanocomposites. Notched impact strength experiments supported this, suggesting that the impact strength of ALD-created composites decreased significantly compared to pure polyamide matrix, whereas traditionally melt-compounded nanocomposites showed no significant changes. Furthermore, the tribological properties of the selected specimens were determined and the effect of the nanofiller on the friction and scratching properties of the polyamide matrix is discussed.
Integrated aluminum nitride piezoelectric microelectromechanical system for radio front ends
Authors: Piazza Gianluca
Published: June 2009

This article summarizes the most recent technological developments in the realization of integrated aluminum nitride (AlN) piezoelectric microelectromechanical system (MEMS) for radio frequency (rf) front ends to be employed in next generation wireless communication devices. The AlN-based resonator and switch technologies are presented, their principle of operation explained, and some key experimental achievements showing device operations between 20MHz and 10GHz are introduced. Fundamental material, device, and fabrication aspects that needed to be taken into account for the demonstration of the first integrated rf MEMS solution based on the combination of AlN MEMS resonators and switches are highlighted. Given the ability to operate over a broad range of frequencies on a single silicon chip, the AlN MEMS technology is extremely attractive for the demonstration of reconfigurable and multiband rf transceivers. Next generation rf architectures that take advantage of large scale integration of AlN MEMS resonators and switches are briefly presented.
X-ray photoelectron spectroscopy analysis of organic materials etched by charged water droplet impact
Authors: Sakai Yuji , Iijima Yoshitoki , Takaishi Riou , Asakawa Daiki , Hiraoka Kenzo
Published: June 2009

Electrospray droplet impact (EDI) has been developed for matrix-free secondary ion mass spectrometry for surface analysis. When a target is etched by EDI, the physical etching on the target is suppressed to minimal, i.e., the occurrence of shallow surface etching. A novel approach to shallow surface etching of polystyrene (PS) by EDI was investigated. The charged water droplets were irradiated to a bulk and a spin coated PS. After irradiation, these samples were analyzed by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy. It was found that XPS spectra for PS were independent on the irradiation time by EDI. This indicates that EDI is a unique technique for the surface etching of the organic materials without leaving any damage on the etched surface.
Characterization of platinum catalyst supported on carbon nanoballs prepared by solution plasma processing
Authors: Ichin Yoshimichi , Mitamura Koji , Saito Nagahiro , Takai Osamu
Published: June 2009

In order to improve the energy-conversion efficiency in fuel cells, the authors loaded Pt nanoparticles on carbon nanoballs (CNBs) by using solution plasma processing (SPP) involving CNB and Pt ion with a protection group. In this study, we employed poly(vinylpyrrolidone) (PVP) or sodium dodecyl sulfate (SDS) to prepare Pt nanoparticles supported on CNB (Pt/CNB) by the SPP, and the electrochemical properties as a catalyst was evaluated by cyclic voltammetry. The carbon nanoballs were prepared by thermal decomposition process of ethylene and hydrogen gases. Color of the solution changed from yellow to dark brown as synthesis time. This change indicates the improvement of dispersibility of CNB. Moreover, transmission electron microscopy images and elemental mapping images showed the Pt nanoparticles supported on CNB. A catalytic activity of the Pt/CNB in use of SDS was shown to be higher than the Pt/CNB prepared with PVP system. The SDS-containing Pt/CNB also showed the higher activity than that obtained by the conventional method.
Effect of Al2O3 support on morphology and NO reactivity of Rh
Authors: Nakamura I. , Fujitani T.
Published: June 2009

The morphology and NO reactivity of Rh deposited on a thin Al2O3 film were studied by means of x-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, and noncontact atomic force microscopy. The NO dissociation activity of the Rh deposited on the Al2O3 surface was higher than that of Rh(111). The NO dissociation kinetics and the NO and CO adsorption properties of the Rh/Al2O3 surface indicated that the surface structure of the supported Rh mainly consisted of a (100) face. The supported Rh existed as small particles on the step sites of the Al2O3 surface. Thus, the authors believe that the low-coordinated step sites of Al2O3 played a role in formation of the (100) surface structure.
In situ electron diffraction characterization of the deformation of nanobelts: Gallium oxide
Authors: Vaughn J. M. , Kordesch M. E.
Published: June 2009

A transmission electron microscope (TEM) fitted with a nanomanipulator for in situ mechanical deformation of nanobelts is reported. Nanobelts of β-Ga2O3 were grown by the vapor transport method from gallium metal in an argon gas flow at 1223K. A single 2.3μm wide, approximately 200nm thick and tens of microns long belt was deformed by direct contact with the manipulator probe. Deflections of up to 180° with a radius of 2.5μm were recorded without fracturing. A series of TEM diffraction patterns collected during belt deformation was observed to distort as well. In addition to the distortion of the monoclinic belt diffraction pattern, satellite spots were observed through belt deformation. Analysis of the deflection in pre-existing spots reveal simultaneous lengthening and contracting in measured planar spacings. The lattice deformation results in the lattice constants c and a having two simultaneous values for any given diffraction pattern. The maximum simultaneous deformations in c are measured to be 1.13±0.112 and 1.63±0.162nm. Lattice constant a behaves similarly with values 0.51±0.02 and 0.79±0.03nm.
Atomic force microscopy measurement of boundary slip on hydrophilic, hydrophobic, and superhydrophobic surfaces
Authors: Wang Yuliang , Bhushan Bharat , Maali Abdelhamid
Published: June 2009

Reduction in drag is important in fluid flow applications. So called boundary slip, a measure of relative fluid velocity at the solid-fluid interface, affects the drag. The slip is a function of the degree of hydrophobicity. In this study, boundary slip was studied through slip length measurements on hydrophilic, hydrophobic, and superhydrophobic surfaces in de-ionized water with atomic force microscopy. On the hydrophilic surface, the experimental data are consistent with no-slip boundary conditions. However, boundary slip is observed on hydrophobic and superhydrophobic surfaces. Experimental results obtained with different squeezing velocities show that the slip length is independent of squeezing velocity. Moreover, the degree of boundary slip is observed to increase when the surface was changed from the hydrophobic surface to the superhydrophobic one. The increasing degree of boundary slip from a hydrophobic surface to a superhydrophobic surface is believed to be because the increasing hydrophobicity favors nanobubble formation. Nanobubbles with a diameter of about 150 nm and a height of about 6 nm were observed on the hydrophobic surface and were verified through observation of nanobubble coalescence.
Molecularly thick dicationic ionic liquid films for nanolubrication
Authors: Palacio Manuel , Bhushan Bharat
Published: June 2009

Ionic liquids (ILs) are attractive as lubricants for micro- and nanoelectromechanical systems due to their superior thermal stability and electrical conductivity compared to conventional lubricants. The adhesion, friction and wear properties of two dicationic ILs based on the imidazolium cation and the triflamide anion were studied and compared to the monocationic IL 1-butyl-3-methyl-1H-imidazolium hexafluorophosphate (BMIM-PF6) using atomic force microscopy. The ionic liquid film removal mechanism was investigated by monitoring the friction force, surface potential, and contact resistance. An IL based on the triflamide anion and two imidazolium cations linked by a pentane chain exhibited the best nanolubrication properties. This is attributed to the presence of hydroxyl groups at its chain ends which can hydrogen bond with the surface, and a hydrophobic linker chain. Another dicationic liquid, with a polyether chain linking the cations, had less desirable adhesion, friction, and wear properties compared to the monocationic IL. Intermolecular hydrogen bonding in this IL reduces the chain ordering on the substrate surface, which accounts for the observed higher adhesive force and coefficient of friction relative to the other ionic liquids investigated.
Temperature dependence on dry etching of Al2O3 thin films in BCl3/Cl2/Ar plasma
Authors: Yang Xue , Kim Dong-Pyo , Um Doo-Seung , Kim Gwan-Ha , Kim Chang-Il
Published: June 2009

During the etching process, the wafer surface temperature is an important parameter which influences the reaction probabilities of incident species, the vapor pressure of etch products, and the redeposition of reaction products on feature surfaces. In this study, the authors investigated that the effect of substrate temperature on the etch rate of Al2O3 thin film and selectivity of Al2O3 thin film over hard mask material (such as SiO2) thin film in inductively coupled plasma as functions of Cl2 addition in BCl3/Ar plasma, rf power, and dc-bias voltage based on the substrate temperature in range of 10–80 °C. The elements existed on the surface were analyzed by energy dispersive x-ray and x-ray photoelectron spectroscopy.
Synthesis, characterization, and luminescent properties of ZnO–SiO2:PbS
Authors: Ntwaeaborwa O. M. , Swart H. C. , Kroon R. E. , Terblans J. J. , Holloway P. H.
Published: June 2009

PbS and ZnO nanoparticles prepared separately by a sol-gel process were incorporated in SiO2 by an ex situ method, resulting in a green emitting ZnO–SiO2:PbS powder phosphor. Particle morphology, structure, and chemical composition of the ZnO nanoparticles, PbS nanoparticles, and ZnO–SiO2:PbS composite were analyzed with transmission electron microscopy, x-ray diffraction, and energy dispersive spectroscopy (EDS), respectively. With or without ZnO nanoparticles, green photoluminescence with a peak at 540nm was observed from SiO2:PbS when excited with a 325nm He–Cd laser in air at room temperature. This peak was different from defect-related emission from ZnO nanoparticles at 580nm and red-orange emission from SiO2:Pb2+ with a broad peak at 600–750nm. Again, the 540nm peak was different from the band edge emission from pure PbS nanoparticles at 1200nm. Note that this emission (540nm) was enhanced considerably when ZnO nanoparticles were incorporated. Photoluminescence properties of ZnO–SiO2:PbS is discussed.
Structural, optical, and photocatalytic properties of ZnO:Al nanowall structure deposited on glass substrate by spray pyrolysis
Authors: Shahjahan M. , Khan M. K. R. , Hossain M. F. , Biswas S. , Takahashi T.
Published: June 2009

This study reports the fabrication of undoped and Al-doped ZnO nanowall structures on ordinary glass substrate by low cost spray pyrolysis technique at low deposition temperature of 350°C. Structural, surface, optical, and photocatalytic studies of these nanostructures have been performed. Surface study confirms the nanowall structure of the fabricated ZnO. Structural study reveals that the fabricated ZnO nanostructures are polycrystalline in nature and crystallinity of the samples depends on the Al doping concentration. Band gap of the ZnO nanostructure has been determined from the transmission spectra. For undoped ZnO, the band gap was obtained 3.27eV and the band gap decreases up to 3.06eV with the increase in Al doping concentration up to 4%. Photocatalytic decomposition of methanol has been studied and found that the fabricated ZnO nanowalls can successfully decomposes methanol under UV-visible light irradiation without any surface treatment, and improvement in the photocatalytic activity was obtained after Al doping.
Sidewall damage in plasma etching of Si/SiGe heterostructures
Authors: Ding R. , Klein L. J. , Friesen Mark G. , Eriksson M. A. , Wendt A. E.
Published: June 2009

Plasma etching is a critical tool in the fabrication of Si/SiGe heterostructure quantum devices, but it also presents challenges, including damage to etched feature sidewalls that affects device performance. Chemical and structural changes in device feature sidewalls associated with plasma-surface interactions are considered damage, as they affect band structure and electrical conduction in the active region of the device. Here the authors report the results of experiments designed to better understand the mechanisms of plasma-induced sidewall damage in modulation-doped Si/SiGe heterostructures containing a two-dimensional electron gas. Damage to straight wires fabricated in the heterostructure using plasma etching was characterized both by measuring the width of the nonconductive “sidewall depletion” region at the device sidewall and by measuring the noise level factor γH/N determined from spectra of the low frequency noise. Observed increases in sidewall depletion width with increasing etch depth are tentatively attributed to the increase in total number of sidewall defects with increased plasma exposure time. Excess negative charge trapped on the feature sidewall could be another contributing factor. Defects at the bottom of etched features appear to contribute minimally. The noise level shows a minimum at an ion bombardment energy of ∼100 eV, while the sidewall depletion width is independent of bias voltage, within experimental uncertainty. A proposed explanation of the noise trend involves two competing effects as ion energy increases: the increase in damage caused by each bombarding ion and the reduction in total number of incident ions due to shorter etch times.
Compact deposition system for device-based ultrathin crystalline film growth
Authors: Lake R. E. , Puls J. R. , Ray M. P. , Sosolik C. E.
Published: June 2009

The study of hot electron excitation at surfaces requires the deposition of ultrathin metal films. To probe the role of particle bombardment in such film excitations, homogeneous, atomically ordered, and relatively defect free thin films must be deposited in the same ultrahigh vacuum system where they will be studied. With these constraints in mind, the authors designed a compact deposition chamber that allows for in situ growth and analysis of metal layers, which are only a few monolayers. This deposition chamber is attached to the commercial variable temperature scanning tunneling microscope (STM) and has an internal volume of 500cm3. The target substrates for deposition are compatible with the STM design and are held in place in a specially designed clamping slot that enables low temperature growth. They used the custom built chamber to deposit Ag top layers with thicknesses between 8 and 15nm on Si(100). Electronic and morphological characteristics of the prototype Ag∕n-Si(100) devices are presented.
Controlling magnetic anisotropy in epitaxial FePt(001) films
Authors: Lu Zhihong , Walock M. J. , LeClair P. , Butler W. H. , Mankey G. J.
Published: June 2009

Epitaxial equiatomic Fe50Pt50 thin films with a variable order parameter ranging from 0 to 0.9 and Fe100−xPtx thin films with x ranging from 33 to 50 were deposited on MgO (001) substrates by dc sputtering. A seed layer consisting of nonmagnetic Cr (4nm)∕Pt (12nm) was used to promote the crystallinity of the magnetic films. The crystal structure and magnetic properties were gauged using x-ray diffraction and magnetometry. The magnetic anisotropy can be controlled by changing the order parameter. For Fe100−xPtx films, the increase in Fe composition leads to an increase in coercivity in the hard axis loop and causes a loss of perpendicular anisotropy.
Ultrathin K∕p-Si(001) Schottky diodes as detectors of chemically generated hot charge carriers
Authors: Huba K. , Krix D. , Meier C. , Nienhaus H.
Published: June 2009

Ultrathin potassium layers were deposited on hydrogen passivated Si(001)−1×1 surfaces at a temperature of 120K in the thickness range from submonolayers up to 3nm. They were investigated with Auger spectroscopy, work function, and current-voltage measurements. After the formation of a wetting layer, potassium deposition leads to island growth. The surface hydrogen atoms are removed by the adsorption process. By attaching an electrical contact to the thin film, the current-voltage characteristics of the Schottky diodes could be determined. The analysis yields a homogeneous Schottky barrier height of 0.55eV for K∕p-Si(001) diodes in agreement with the metal induced gap state model. Exposing the diodes to molecular oxygen generates a strong chemicurrent signal which first increases with exposure, passes a maximum, and drops exponentially. The chemicurrent transient is attributed to a nucleation and growth formation of oxide islands and gives strong evidence for the existence of precurser states prior to oxidation.
Surface characterization of polymethylmetacrylate bombarded by charged water droplets
Authors: Hiraoka Kenzo , Takaishi Riou , Asakawa Daiki , Sakai Yuji , Iijima Yoshitoki
Published: June 2009

The electrospray droplet impact (EDI), in which the charged electrospray water droplets are introduced in vacuum, accelerated, and allowed to impact the sample, is applied to polymethylmetacrylate (PMMA). The secondary ions generated were measured by an orthogonal time-of-flight mass spectrometer. In EDI mass spectra for PMMA, fragment ions originating from PMMA could not be detected. This is due to the fact that the proton affinities of fragments formed from PMMA are smaller than those from acetic acid contained in the charged droplet. The x-ray photoelectron spectroscopy spectra of PMMA irradiated by water droplets did not change with prolonged cluster irradiation, i.e., EDI is capable of shallow surface etching for PMMA with a little damage of the sample underneath the surface.
Atomic layer deposition of GaN using GaCl3 and NH3
Authors: Kim Oh Hyun , Kim Dojun , Anderson Tim
Published: June 2009

GaN films were grown on Si(100) substrate by atomic layer deposition (ALD) using GaCl3 and NH3. Growth conditions were identified for which the growth rate exhibited a plateau at ∼2.0Å∕cycle, consistent with self-limiting adsorption. A relatively wide temperature window (500–750°C) for ALD growth mode was also established for one flow sequence schedule. In this limit, both the (0002) and (101¯1) orientations of GaN were evident, which was attributed to the competition between vertical and lateral growths. Cl incorporation was detected by x-ray photoelectron spectroscopy for samples prepared with long GaCl3 exposure time. It is postulated that gas phase formation of (ClGaNH)n with n=1–3 [Kovács, Inorg. Chem. 41, 3067 (2002)] results in higher Cl content.
Scanning Auger of a specific via interface in an integrated circuit using a novel focused ion beam sample preparation technique
Authors: Liu W. , Ramirez H. , Schauer S. , Theodore N. D.
Published: June 2009

Auger depth profile analysis can be impeded by surface roughening during ion sputtering. This is especially noticeable when analyzing semiconductor devices because of the variety of materials that are susceptible to roughening, as well as the importance of very thin interfaces. A novel technique is presented in this article, which combines scanning Auger analysis with focused ion beam (FIB) thinning for analysis of single via interfacial structures in integrated circuit devices. After a failing structure was identified by electrical fault isolation techniques, FIB was used to remove all of the materials from the top of the device. The materials include polyimide, passivation, metal layers, and dielectric layers. The layers were removed to a level approximately 100Å above the via interface under a tungsten plug. A scanning Auger instrument was then used for Auger depth profiling of the single via. A thin oxidized interface was observed between Ti∕TiN glue layer and antireflection coating (ARC) TiN and was identified as the cause of the via failure. It would have been impossible for conventional sputter depth profiling to detect this thin oxidized layer buried under several layers of materials. Further investigation showed that the interfacial oxide is caused by backsputtering of ARC TiN during via etch and rf sputtering before Ti∕TiN glue deposition.
Deposition of various metal, ceramic, and cermet coatings by an industrial-scale large area filtered arc deposition process
Authors: Gorokhovsky V. , Bowman C. , VanVorous D. , Wallace J.
Published: June 2009

Nearly defect-free nitride, carbide, and oxiceramic coatings have been deposited by a unidirectional dual large area filtered arc deposition (LAFAD) process. One LAFAD dual arc vapor plasma source was used in both gas ionization and coating deposition modes with and without vertical magnetic rastering of the plasma flow. Substrates made of different metal alloys, as well as carbide and ceramics, were installed at different vertical positions on the 0.5 m diameter turntable of the industrial-scale batch coating system which was rotated at 12 rpm to assess deposition rates and coating thickness uniformity. Targets of the same or different compositions were installed on the primary cathodic arc sources of the LAFAD plasma source to deposit a variety of coating compositions by mixing the metal vapor and reactive gaseous components in a magnetically confined, strongly ionized plasma flow with large kinetic energy. The maximum deposition rate typically ranged from 1.5 μm/h for TiCr/TiCrN to 2.5 μm/h for Ti/TiN multilayer and AlN single layer coatings, and up to 6 μm/h for AlCr-based oxiceramic coatings for primary cathode current ranging from 120 to 140 A. When the arc current was increased to 200 A, the deposition rates of TiN-based coatings were as high as 5 μm/h. The vertical coating thickness uniformity was ±15% inside of a 150 mm area without vertical rastering. Vertical rastering increased the uniform coating deposition area up to 250 mm. The coating thickness distribution was well correlated with the output ion current distribution as measured by a multisection ion collector probe. Coatings were characterized for thickness, surface profile, adhesion, hardness, and elemental composition. Estimates of electrical resistivity indicated good dielectric properties for most of the TiCrAlY-based oxiceramic, oxinitride, and nitride coatings. The multielement LAFAD plasma flow consisting of fully ionized metal vapor with a reactive gas ionization rate in excess of 50% was found especially suitable for deposition of nanocomposite, nanostructured coatings. Potential industrial applications of this highly productive coating deposition process are discussed.
Fabrication of dye-sensitized solar cells with TiO2 photoelectrode prepared by sol-gel technique with low annealing temperature
Authors: Hossain M. F. , Biswas S. , Shahjahan M. , Majumder Arpi , Takahashi T.
Published: June 2009

Transparent titanium oxide (TiO2) photoelectrodes for dye-sensitized solar cells (DSCs) were deposited on fluorine doped tin oxide substrate by a sol-gel dip coating technique with acetic acid as an acid catalyst, where crystallinity can be achieved at a relatively low annealing temperature. Repetitive dip coating and drying, with two intermediate annealing, has made this technique easier to prepare TiO2 thin film with desired thickness within a short period of time. The TiO2 photoelectrodes were annealed at various temperatures to study the effect of annealing temperature on the photovoltaic property of the DSCs. The structure of the TiO2 films, prepared at various annealing temperatures, shows different crystallinities. Good crystallinity has been observed for 300°C annealing temperature and it improved with increasing annealing temperature. The surface morphology, investigated by field emission scanning electron microscope and atomic force microscope measurements, revealed that with the increase in annealing temperature, the surface of TiO2 photoelectrode showed more porous structure with higher roughness. The DSCs with TiO2 photoelectrode, annealed at 300°C, showed the best photovoltaic characteristics among the three samples of investigation. Measurement of optical properties and incident photon-to-current conversion efficiency indicated the maximum dye incorporation in TiO2 electrode, deposited at 300°C. The solar cell efficiency and fill factor of this above mentioned sample are 0.96% and 46.3%, respectively. The results indicate a strong correlation between the microstructure, dye absorption, and photovoltaic property of the sample.
Structural and morphological evolution of gallium nitride nanorods grown by chemical beam epitaxy
Authors: Kuo Shou-Yi , Lai Fang-I , Chen Wei-Chun , Hsiao Chien-Nan , Lin Woei-Tyng
Published: June 2009

The morphological and structural evolution is presented for GaN nanorods grown by chemical beam epitaxy on (0001) Al2O3 substrates. Their structural and optical properties are investigated by x-ray diffraction, scanning and transmission electron microscopy, and temperature-dependent photoluminescence measurements. While increasing the growth temperature and the flow rate of radio-frequency nitrogen radical, the three-dimensional growth mode will be enhanced to form one-dimensional nanostructures. The high density of well-aligned nanorods with a diameter of 30–50nm formed uniformly over the entire sapphire substrate. The x-ray diffraction patterns and transmission electron microscopic images indicate that the self-assembled GaN nanorods are a pure single crystal and preferentially oriented in the c-axis direction. Particularly, the “S-shape” behavior with localization of ∼10meV observed in the temperature-dependent photoluminescence might be ascribed to the fluctuation in crystallographic defects and composition.
Self-limiting deposition of semiconducting ZnO by pulsed plasma-enhanced chemical vapor deposition
Authors: Rowlette Pieter C. , Allen Cary G. , Bromley Olivia B. , Wolden Colin A.
Published: June 2009

Self-limiting growth of zinc oxide was accomplished over a temperature range from 25to155°C by pulsed plasma-enhanced chemical vapor deposition using dimethyl zinc [Zn(CH3)2] as the metal precursor. The deposition rate was independent of plasma exposure (1–5s) but was found to increase from 1.4to6.0Å∕cycle as a function of temperature. Over the narrow range explored, substrate temperature had a dramatic impact on the film structure and properties. Amorphous films were obtained at room temperature, while a polycrystalline morphology with a preferred (100) orientation developed as the temperature increased. The electrical resistivity decreased linearly with temperature from 45to∼2Ωcm. Spectroscopic characterization showed that films deposited at room temperature were contaminated by carbon and hydroxyl impurities; however, these defects were attenuated with temperature and were not detected in films deposited above 64°C. Room temperature photoluminescence was dominated by defect emission in most films; however, this signal was attenuated, and a strong band edge emission was observed for films deposited at temperatures >135°C. Film quality was comparable to material grown by plasma-enhanced atomic layer deposition in the same reactor; however, precursor requirements and net deposition rates were improved by an order of magnitude.
Transparent conducting impurity-doped ZnO thin films prepared using oxide targets sintered by millimeter-wave heating
Authors: Minami Tadatsugu , Okada Kenji , Miyata Toshihiro , Nomoto Juni-chi , Hara Youhei , Abe Hiroshi
Published: June 2009

The preparation of transparent conducting impurity-doped ZnO thin films by both pulsed laser deposition (PLD) and magnetron sputtering deposition (MSD) using impurity-doped ZnO targets sintered with a newly developed energy saving millimeter-wave (28GHz) heating technique is described. Al-doped ZnO (AZO) and V-co-doped AZO (AZO:V) targets were prepared by sintering with various impurity contents for 30min at a temperature of approximately 1250°C in an air or Ar gas atmosphere using the millimeter-wave heating technique. The resulting resistivity and its thickness dependence obtainable in thin films prepared by PLD using millimeter-wave-sintered AZO targets were comparable to those obtained in thin films prepared by PLD using conventional furnace-sintered AZO targets; a low resistivity on the order of 3×10−4Ωcm was obtained in AZO thin films prepared with an Al content [Al∕(Al+Zn) atomic ratio] of 3.2at.% and a thickness of 100nm. In addition, the resulting resistivity and its spatial distribution on the substrate surface obtainable in thin films prepared by rf-MSD using a millimeter-wave-sintered AZO target were almost the same as those obtained in thin films prepared by rf-MSD using a conventional powder AZO target. Thin films prepared by PLD using millimeter-wave-sintered AZO:V targets exhibited an improved resistivity stability in a high humidity environment. Thin films deposited with a thickness of approximately 100nm using an AZO:V target codoped with an Al content of 4at.% and a V content [V∕(V+Zn) atomic ratio] of 0.2at.% were sufficiently stable when long-term tested in air at 90% relative humidity and 60°C.
Vanadium oxide thin films for bolometric applications deposited by reactive pulsed dc sputtering
Authors: Fieldhouse N. , Pursel S. M. , Carey R. , Horn M. W. , Bharadwaja S. S. N.
Published: June 2009

Vanadium oxide (VOx) thin films were deposited by reactive pulse dc magnetron sputtering process using a pure vanadium metal target. The structural, microstructure, and electrical properties were correlated as a function of processing parameters such as substrate temperature, Ar:O partial pressures ratios, and pulsed dc power to fabricate these films. The VOx films deposited at various substrate temperatures between 30 and 300°C using a range of oxygen to argon partial pressure ratios exhibited huge variation in their microstructure even though most of them are amorphous to x-ray diffraction technique. In addition, the electrical properties such as temperature coefficient of resistance (TCR), resistivity, and noise levels were influenced by film microstructure. The TCRs of the VOx films were in the range of −1.1%to−2.4%K−1 having resistivity values of 0.1–100Ωcm. In particular, films grown at lower substrate temperatures with higher oxygen partial pressures have shown finer columnar grain structure and exhibited larger TCR and resistivity.
High-resolution Rutherford backscattering spectrometry study on process dependent elemental depth profile change of hafnium silicate on silicon
Authors: Ichihara C. , Yasuno S. , Takeuchi H. , Kobayashi A. , Mure S. , Fujikawa K. , Sasakawa K.
Published: June 2009

Process characterization of HfSiO(N)/SiO(N) films was performed by nondestructive elemental depth profile analysis using high-resolution Rutherford backscattering spectrometry. As-grown atomic layer deposition HfSiO film (2 nm) was found not to be uniform but to have a gradient near the top surface with Si concentration higher than the bulk. Regardless of native oxide removal, HfSiO grown on HF-last Si results in an almost identical interfacial SiOx thickness with that of HfSiO grown on chemical oxide. Dependence of interfacial layer on oxygen transport behavior during high-temperature annealing was also investigated. Whereas only the upward oxygen outdiffusion from the HfSiO layer was observed for the films deposited on HF-last Si and SiON, downward oxygen transport to the bottom interfacial layer was also observed when HfSiO film was deposited on chemical oxide. This result indicates that the bonding properties of chemical oxide are different from those of SiO2 and that chemical oxide can accommodate oxygen ions. Finally, thermal stability of nitrogen in HfSiO introduced by NH3 annealing and plasma nitridation was compared. Nitrogen desorption by spike anneal was only observed for HfSiON film with nitrogen introduced by plasma nitridation process.
Fabrication of a highly oriented line structure on an aluminum surface and the nanoscale patterning on the nanoscale structure using highly functional molecules
Authors: Watanabe Y. , Kato H. , Takemura S. , Watanabe H. , Hayakawa K. , Kimura S. , Okumura D. , Sugiyama T. , Hiramatsu T. , Nanba N. , Nishikawa O. , Taniguchi M.
Published: June 2009

The surface of an Al plate was treated with a combination of chemical and electrochemical processes for fabrication of surface nanoscale structures on Al plates. Chemical treatments by using acetone and pure water under supersonic waves were conducted on an Al surface. Additional electrochemical process in H2SO4 solution created a finer and oriented nanoscale structure on the Al surface. Dynamic force microscopy (DFM) measurement clarified that the nanoscale highly oriented line structure was successfully created on the Al surface. The line distance was estimated approximately 30–40nm. At the next stage, molecular patterning on the highly oriented line structure by functional molecules such as copper phthalocyanine (CuPc) and fullerene C60 was also conducted. CuPc or C60 molecules were deposited on the highly oriented line structure on Al. A toluene droplet containing CuPc molecules was cast on the nanostructured Al plate and was extended on the surface. CuPc or C60 deposition on the nanostructured Al surface proceeded by evaporation of toluene. DFM and x-ray photoemission spectroscopy measurements demonstrated that a unique molecular pattern was fabricated so that the highly oriented groove channels were filled with the functional molecules.
Low temperature grown polycrystalline La0.7Sr0.3MnO3 thin films on amorphous SiO2 substrates by rf magnetron sputtering
Authors: Choi Sun Gyu , Sivasankar Reddy A. , Park Hyung-Ho , Yang Woo Seok , Ryu Hojun , Yu Byoung-Gon
Published: June 2009

The La0.7Sr0.3MnO3 thin films have been prepared on amorphous SiO2 substrates by a rf magnetron sputtering technique under various oxygen flow rates and rf powers at a relatively low substrate temperature of 350°C. The effects of oxygen flow rate and rf power on their physical properties were systematically investigated. X-ray diffraction results show that the growth orientation and crystallinity of the films were affected by rf power and oxygen flow rate. The electrical resistivity of the films was reduced with increasing oxygen flow rate and rf power due to enhanced {100} growth plane orientation and enlarged grain size of the films. In addition, a relatively high temperature coefficient of resistance value of −2.4% was obtained in the present investigation even with low deposition temperature.
Surface slope distribution with mathematical molding on Au(111) thin film growth
Authors: González-González A. , Sacedón J. L. , Polop C. , Rodríguez-Cañas E. , Aznárez J. A. , Vasco E.
Published: June 2009

In this article, the authors developed a topographic image processing procedure based on polynomial interpolating functions for studying growth of thin films at nanoscale. Using the topographic atomic force microscopy images as input for the proposed procedure, the authors obtained the surface slope distributions at different thicknesses (2–60nm) for evaporated Au(111) films as well as the thickness dependence of the mean slope. The scaling exponents [namely, the growth exponent β=0.70±0.02 and the dynamic one 1∕z=0.004±0.013 that determine the thickness dependence of the roughness (σ) and the size of the surface features (ξ) as σ∼thicknessβ and ξ∼thickness1∕z, respectively] that result from our analysis indicate that the growth front of the Au films is formed by mound-shaped surface features that grow preferentially in height (i.e., without lateral coarsening). These results, together with the evolution of the mean slope toward a saturation value, suggest that the morphology evolution of the Au films corresponds to early stages of a growth regime characterized by the formation of steep mounds with selected slopes. Plausibly, such mounds would be responsible for the columnar structure observed in thicker Au films by microscopy.
Kinetics of hydride front in Zircaloy-2 and H release from a fractional hydrided surface
Authors: Díaz M. , González-González A. , Moya J. S. , Remartínez B. , Pérez S. , Sacedón J. L.
Published: June 2009

The authors study the hydriding process on commercial nuclear fuel claddings from their inner surface using an ultrahigh vacuum method. The method allows determining the incubation and failure times of the fuel claddings, as well as the dissipated energy and the partial pressure of the desorbed H2 from the outer surface of fuel claddings during the hydriding process. The correlation between the hydriding dissipated energy and the amount of zirconium hydride (formed at different stages of the hydriding process) leads to a near t1∕2 potential law corresponding to the time scaling of the reaction for the majority of the tested samples. The calibrated relation between energy and hydride thickness allows one to calculate the enthalpy of the δ-ZrH1.5 phase. The measured H2 desorption from the external surface is in agreement with a proposed kinetic desorption model from the hydrides precipitated at the surface.
Surface effects on the luminescence degradation of hydride vapor-phase epitaxy-grown GaN induced by electron-beam irradiation
Authors: Wang Y. , Dierre B. , Sekiguchi T. , Yao Y. Z. , Yuan X. L. , Xu F. J. , Shen B.
Published: June 2009

Luminescence degradation of hydride vapor-phase epitaxy-grown GaN wafers under electron-beam (e-beam) irradiation was studied. A drastic decrease in the band-edge emission is observed under e-beam irradiation. This degradation may be decomposed into two components: a strong and quick decrease in the first minute and a smaller and more gradual decrease. It is found that the vacuum condition also affects the luminescence of GaN since the degradation amplitude becomes smaller when the specimens are kept in ultrahigh vacuum. These results suggest that the adsorbed species at the surface may affect the luminescence properties of GaN.
Fabrication of surface plasmon waveguides on thin CYTOP membranes
Authors: Fong Norman , Berini Pierre , Niall Tait R.
Published: June 2009

The fabrication of a membrane supported long-range surface plasmon polariton waveguide for use as a biosensor is described. This type of device can be completely immersed in the sensing environments to create symmetrical waveguide surroundings. The membrane is created from the fluoropolymer CYTOP which has strong physical properties and a low index of refraction. The fabrication steps of this device are described along with examples of completed structures.