bluuebunny/crossref_metadata_2025 huggingface dataset:
High current field emission behavior of carbon nanofiber film: Adsorbate effects
Authors: Park Kyung Ho , Lee Soonil , Koh Ken Ha
Published: June 2006

We report high current-density field emission from carbon nanofiber (CNF) films synthesized using electroplated Ni catalysts. High-density thick CNFs, which had many protrusions with small tip radii and a solid structure without hollow cores, were formed on gold-buffer layers. The maximum emission current of 3.67mA was measured from the area of 4.9×10−3cm2, corresponding to the current density of 750mA∕cm2. There was a distinctive hysteresis in emission-current versus voltage (I-V) curves corresponding to the ramping direction of bias voltage, which led us to divide I-V curves into three distinguishable regimes: adsorbate-enhanced, intermediate, and intrinsic emission regimes. The deviations between up- and down-sweep emission currents, and the slope change in Fowler-Nordheim curves were most prominent in intermediate emission regime. Based on systematic field emission measurements, such as variations of chamber pressure and bias-voltage sweep speed, and temporal variation of emission current at fixed bias voltages, we propose that the observed emission behavior of CNFs stemmed from the desorption and readsorption of adsorbates during emission measurements.
Experimental investigation of tunnel oxide thickness on charge transport through Si nanocrystal dot floating gate memories
Authors: Punchaipetch Prakaipetch , Ichikawa Kazunori , Uraoka Yukiharu , Fuyuki Takashi , Tomyo Atsushi , Takahashi Eiji , Hayashi Tsukasa
Published: June 2006

The effect of tunnel layer thicknesses on the charging/discharging mechanism and data retention of Si nanocrystal dot floating gate devices was studied. Floating gate memories of Si nanocrystals dots with three different SiO2 tunnel thicknesses were fabricated, the key variable being tunnel oxide thickness. Other parameters which can affect memory properties were carefully controlled. The mechanism of electron discharging is discussed based on differences in tunnel SiO2 thickness. Direct tunneling was found to predominate in the cases of 3- and 5-nm-thick SiO2 tunnel layers. However, Fowler-Nordheim tunneling affects the electron discharging characteristics with thicker SiO2 tunnel layers. Clear characteristics in discharging peak differences could be observed in capacitance-voltage measurements on metal-oxide semiconductors with Si floating nanodot devices. Memory properties also depended strongly on tunnel oxide thickness.
Field emission from amorphous GaN deposited on Si by dc sputtering
Authors: Ye F. , Xie E. Q. , Pan X. J. , Li H. , Duan H. G. , Jia C. W.
Published: June 2006

GaN thin films were deposited on Si substrates using dc sputtering method and characterized with various methods. X-ray diffraction, transmission electron microscopy, and selected-area electron diffraction measurements show that the GaN thin film is amorphous with nanocrystalline grains. Fourier transform infrared indicates that the absorptive properties of the deposited GaN film exhibit primarily Ga–N stretching vibration bond. Atomic force microscopy shows that there are many sharp tips on the surface. The GaN thin film containing nanocrystalline grains demonstrates very good field emission properties with the turn-on field of 5V∕μm and the maximum current density of 500μA∕cm2. The possible emission mechanisms of the films are also discussed.
Field emission from multiwall carbon nanotubes prepared by electrodeposition without the use of a dispersant
Authors: Lyth S. M. , Oyeleye F. , Curry R. J. , Davis J. , Silva S. R. P.
Published: June 2006

We present a technique of manufacturing multiwall carbon nanotube (MWNT) field emitters by a nickel electrodeposition process, without using a surfactant to disperse the MWNTs in solution. Sonication adequately disperses individual MWNTs throughout the solution and MWNTs can be deposited onto a copper substrate. However, over time there is a reduction of the free MWNT concentration in solution and an associated change in the morphology of the deposit. The initial concentration of MWNTs in solution also plays a crucial role in the morphology of the deposits. The threshold field of electron field emission measurements remained in the order of 20V∕μm regardless of the deposition conditions.
Observation of quantum interference effect in solids
Authors: Tavkhelidze Avto , Bibilashvili Amiran , Jangidze Larissa , Shimkunas Alex , Mauger Philip , Rempfer Gertrude F. , Almaraz Luis , Dixon Todd , Kordesch Martin E. , Katan Nechama , Walitzki Hans
Published: June 2006

In order to achieve quantum interference of free electrons inside a solid, we have modified the geometry of the solid so that de Broglie waves interfere destructively inside the solid. Quantum interference of de Broglie waves leads to a reduction in the density of possible quantum states of electrons inside the solid and increases the Fermi energy level. This effect was studied theoretically within the limit of the quantum theory of free electrons inside the metal. It has been shown that if a metal surface is modified with patterned indents, the Fermi energy level will increase and consequently the electron work function will decrease. This effect was studied experimentally in both Au and SiO2 thin films of special geometry and structure. Work function reductions of 0.5eV in Au films and 0.2eV in SiO2 films were observed. Comparative measurements of work function were made using the Kelvin probe method based on compensation of internal contact potential difference. Electron emission from the same thin films was studied by two independent research groups using photoelectron emission microscopy.
Modeling the suppression of boron diffusion in Si∕SiGe due to carbon incorporation
Authors: Rizk Samer , Haddara Yaser M. , Sibaja-Hernandez A.
Published: June 2006

We used the process simulator FLOOPS-ISE to implement a consistent model describing the diffusion behaviors of boron and carbon in silicon and silicon germanium. In particular, our model successfully accounts for boron and carbon behaviors in a wide range of sample structures and experimental conditions over the complete temperature range of 750–1070°C in inert and oxidizing ambients, and in the presence of implant damage. The structures studied include cases where the boron and carbon profiles are separated as well as cases where profiles overlap, cases with carbon in silicon and in SiGe, and our own recent experiments where boron diffusion within a SiGeC region has been characterized. We model carbon diffusion by the kickout and Frank-Turnbull mechanisms, and interstitial capture by substitutional carbon, and demonstrate that a model must incorporate all three effects to satisfactorily explain published data. We also include standard models for boron-interstitial clusters and {311} defects.
Two-dimensional carrier profiling on operating Si metal-oxide semiconductor field-effect transistor by scanning capacitance microscopy
Authors: Kimura Kenjiro , Kobayashi Kei , Yamada Hirofumi , Matsushige Kazumi , Usuda Koji
Published: June 2006

We developed scanning probe microscopy procedures for simultaneous measurements of device characteristics and two-dimensional (2D) carrier distribution on operating cross-sectioned semiconductor devices in order to investigate their operating or failure mechanisms. Usually one cannot operate semiconductor device in a chip once the chip was cleaved and polished to expose its cross-sectioned surface because of lost electrical connections to the device. Here we employed a focused ion beam (FIB) apparatus for etching contact holes and fabricating additional electrical connections to the device by chemical vapor deposition (CVD) method. FIB-CVD is capable of fabricating three-dimensional wirings toward each electrode in a specific device. We prepared a cross-sectioned metal-oxide semiconductor field-effect-transistor sample with external tungsten wirings for device operation and performed scanning capacitance microscopy observations for dynamic 2D carrier distribution mapping on this sample.
Oxygen pressure dependence of copper ion transport in SiO2 dielectrics
Authors: Shepherd L. P. , Mathew A. , McCandless B. E. , Willis B. G.
Published: June 2006

Electrical bias-temperature stress measurements were performed on copper oxide/SiO2/silicon metal-oxide-semiconductor capacitors to measure the oxygen partial pressure dependence of the copper ion transport rates through the SiO2 layer. Both copper(I) oxides (Cu2O) and copper(II) oxides (CuO) were investigated, and copper oxide film stoichiometry was characterized by glancing incidence x-ray diffraction and x-ray photoelectron spectroscopy. At relatively high oxygen pressures, copper ion transport is observed for both Cu2O∕SiO2∕Si and CuO∕SiO2∕Si, and the activation energies are comparable. Under reduced oxygen pressures and vacuum, the copper ion flux is reduced for both copper oxides. In vacuum, the activation energy for copper transport from CuO layers is reduced by approximately 0.7eV compared to the apparent activation barrier at high oxygen pressures, and the copper transport signals for Cu2O are below the detection limit of the experiment. A study of copper transport rates for both CuO and Cu2O electrode layers shows that the copper ion flux increases with increasing oxygen pressure, with an oxygen pressure dependence close to pO21∕2.
Thermally stable AlGaN∕GaN heterostructure field-effect transistor with IrO2 gate electrode
Authors: Jeon Chang Min , Park Ki-Yeol. , Lee Jae-Hoon , Lee Jung-Hee , Lee Jong-Lam
Published: June 2006

A thermally stable AlGaN∕GaN heterostructure field-effect transistor (HFET) using an iridium oxide (IrO2) gate contact was demonstrated, compared with conventionally used Pt Schottky contact. The Schottky barrier height of the Pt contact significantly decreased from 0.71to0.52eV and the reverse leakage current at −20V increased by two orders of magnitude when the device was annealed at 450°C for 24h. This was due to the indiffusion of the Pt atoms into the AlGaN layer during the annealing. However, no electrical degradation of the contact was found in the IrO2 Schottky contact. This was due to the fact that the IrO2 suppressed the indiffusion of the contact metals into the AlGaN∕GaN heterostructure. As a result, the sheet-carrier concentration at which the two-dimensional electron gases are confined was not degraded at high temperature. It was found that the electrical properties of the HFET using the IrO2 gate contact are thermally stable and no distinct change of device performances was observed even after annealing at 450°C for 24h. It is suggested that IrO2 is a promising candidate as gate electrode for a high-temperature AlGaN∕GaN HFET.
Ultraviolet curing imprint lithography on flexible indium tin oxide substrates
Authors: Chung Y. C. , Chiu Y. H. , Liu H. J. , Chang Y. F. , Cheng C. Y. , Hong F. C. N.
Published: June 2006

In this study, an imprint lithography technique was performed to transfer patterns onto indium tin oxide (ITO)-coated poly(ethylene terephthalate) (PET) substrates by embossing an etch barrier on the substrates and curing them under irradiation at room temperature. The etch barriers containing glycidyl methacrylate were spectrally analyzed to verify that they were deposited on the ITO-PET substrates firmly and rapidly with minimum variation in dimensions. To fabricate the ITO patterns, the substrate was etched by reactive-ion etching to eradicate the residual layers and by wet etching to carve the undisplaced ITO lines. Scanning electron microscopy observation and profilometric analysis for these processes showed only about 2% of linewidth shrinkage after polymer cross linking, easily compensated in mask design in applications. Also, the 150nm of ruled features on the pattern were successfully transferred using the same resist. Moreover, the flexible ITO patterns illuminated the practical electroluminescence device, verifying that UV-curing imprint lithography is feasible for patterning ITO-PET surfaces.
GaAsNSb-base GaAs heterojunction bipolar transistor with a low turn-on voltage
Authors: Lew K. L. , Yoon S. F. , Wang H. , Wicaksono S. , Gupta J. A. , McAlister S. P.
Published: June 2006

A GaAsNSb heterojunction bipolar transistor (HBT) structure was grown by solid source molecular beam epitaxy. The fabricated HBT showed a reduction in the turn-on voltage of ∼195mV when GaAs0.915N0.005Sb0.08 was used as the base material. The small knee voltage (<1V) of the GaAsNSb HBT indicates that the current blocking effect is small. Significant gain degradation in the GaAsNSb HBT was observed when the nitrogen (N) composition was increased to 2%. The results show that the dilute nitride GaAsNSb materials have potential for reducing the turn-on voltage in GaAs HBTs.
Deposition of nanostructured Si–C–N superhard coatings by rf magnetron sputtering
Authors: Mishra S. K. , Gaur H. , Rupa P. K. P. , Pathak L. C.
Published: June 2006

Systematic investigation on the deposition of thin silicon-carbon-nitride films by reactive rf magnetron sputtering from SiC–C composite target in nitrogen-argon atmosphere was studied. The significant effect of deposition pressures on the hardness of the deposited SiCN films was found, which varied between 4.7 and 44GPa. The films were found to be amorphous from x-ray diffraction analysis but localized crystallization was noticed during atomic force microscopy (AFM) studies on these deposited films. The AFM studies also suggested that the increased hardness was due to reduction in particle size and localized formation of β-C3N4 and β-Si3N4 phase in the films. The x-ray photoelectron spectroscopy analyses showed the formation of C–N and Si–N bonds for the harder film. The increased nitrogen concentration in the sputtering gas mixture to 99% resulted in large particle growth and graphitic phase formation, which exhibited a low hardness value of 4.7GPa. The high C content and low Si content in the deposited films facilitated the graphitic phase formation.
Photoresponsivity of ZnO Schottky barrier diodes
Authors: Oh D. C. , Suzuki T. , Hanada T. , Yao T. , Makino H. , Ko H. J.
Published: June 2006

We report on the photoresponsivity of ZnO Schottky barrier diodes grown on (0001) GaN∕Al2O3 substrates by plasma-assisted molecular-beam epitaxy. First, ZnO Schottky barrier diodes show a reverse saturation current of ∼10−8A in the dark, and they present a large current buildup of ∼103A under ultraviolet light illumination, with maintaining stable diode characteristics. Second, ZnO Schottky barrier diodes have a large bandwidth of 195nm, where the short-wavelength cutoff and the long-wavelength cutoff are 195 and 390nm, respectively. Third, ZnO Schottky barrier diodes have a time constant of 0.36ms. Consequently, it is suggested that the ZnO Schottky barrier diodes are very promising for ultraviolet photodetector applications.
Molecular beam epitaxy growth of midinfrared “W” light emitting diodes on InAs
Authors: Kuznetsov Vladimir V. , Wicks G. W.
Published: June 2006

We have studied how midwave infrared (MWIR) photo- and electroluminescence of type-II “W” InAs∕InGaSb∕InAs∕AlGaAsSb quantum well structures depend on molecular beam epitaxy growth conditions and substrate material. All samples were grown with Sb4, in contrast to most recent reports that use Sb2. Resulting devices represent the highest reported external differential efficiency for molecular beam epitaxy grown light emitting diodes emitting in the 4.3–4.6μm wavelength range in the continuous wave mode at the room temperature. Another important aspect of the work is the finding that MWIR emitters on InAs substrates are superior to those on conventionally used GaSb substrates.
Growth of thin AlInN∕GaInN quantum wells for applications to high-speed intersubband devices at telecommunication wavelengths
Authors: Cywiński G. , Skierbiszewski C. , Fedunieiwcz-Żmuda A. , Siekacz M. , Nevou L. , Doyennette L. , Tchernycheva M. , Julien F. H. , Prystawko P. , Kryśko M. , Grzanka S. , Grzegory I. , Presz A. , Domagała J. Z. , Smalc J. , Albrecht M. , Remmele T. , Porowski S.
Published: June 2006

In this article, we report on growth of AlInN∕GaInN multi-quantum-wells (MQWs) with high Al content (93%) by rf-plasma-assisted molecular-beam epitaxy on (0001) GaN/sapphire templates and on bulk GaN crystals. A series of samples with a barrier thickness of 3nm and with different well thicknesses of 1.5–3nm was grown. The wells were doped with Si at a concentration of 5×1019cm−3. Structures grown on (0001) GaN-based substrates are crack-free, as demonstrated by Nomarski contrast and scanning electron microscopy measurements. X-ray diffraction mapping of a and c lattice parameters shows that AlInN∕GaInN MQWs are fully strained and have up to 7% indium in the barriers and up to 10% In in the quantum wells. These structures exhibit intersubband absorptions at room temperature at a wavelength in the range of 2.45–1.52μm. The AlInN∕GaInN strain-compensated MQW structures, having good quality, are very attractive for ultrahigh-bit-rate telecommunication applications at 1.55μm wavelengths. In addition, because of their low average refractive index, they could be used as thick cladding layers for optical waveguides.
Formation and optical properties of stacked CdSe self-assembled quantum dots on ZnxCdyMg1−x−ySe barriers
Authors: Perez-Paz M. Noemi , Lu Hong , Shen Aidong , Tamargo Maria C.
Published: June 2006

Multiquantum dot (MQD) layers of CdSe with ZnxCdyMg1−x−ySe barriers have been grown by self-assembly (SA) using molecular beam epitaxy on (001) InP substrates and their optical and structural properties studied by steady state, polarized and power dependence photoluminescence (PL) studies, x-ray diffraction, and atomic force microscopy (AFM). Two sets of MQD structures of CdSe SAQDs were grown with different Mg contents in the ZnxCdyMg1−x−ySe. Uncapped structures were also grown. The control of the electronic coupling of CdSe MQDs has been achieved by varying two parameters: the MgSe content on the ZnxCdyMg1−x−ySe barrier and the ZnxCdyMg1−x−ySe spacer thickness. Samples with properties intermediate between those of totally coupled MQDs and uncoupled ones were also grown. Results show that for the edge emission, polarization is mostly TM for the case of coupled QDs, indicating an excitonic delocalization along the growth axis, and TE polarized for the uncoupled QDs. For the surface configuration, the PL emission was slightly TM polarized for the uncoupled case, suggesting a surface organization. AFM images of an uncapped sample grown under the same conditions than the capped one confirmed the formation of connected structures (wirelike rather than dotlike) in the surface. No surface organization was obtained for the coupled case.
Nanoscale device architecture to reduce leakage currents through quantum-mechanical simulation
Authors: Sarab A. A. P. , Datta Deepanjan , Dasgupta Sudeb
Published: June 2006

In this article, the effect of the gate tunneling current in ultrathin gate-oxide metal-oxide-semiconductor (MOS) devices of an effective gate length of 10nm is studied using a device simulation. A dramatic increase of gate and reverse-biased junction band-to-band-tunneling leakages in scaled devices results in a drastic increase in the total leakage power in a logic circuit. Here, we have proposed a device called parallel connected hetero material double-gate (PCHEM-DG) metal-oxide-semiconductor field-effect transistor (MOSFET) to facilitate the reduction of the effective gate leakage current over the conventional DG MOSFETs. First we have modeled the quantum transport phenomena in the device in order to gauge the potential effectiveness in nanoscale devices. In the study of the device, we have taken the ballistic electron transport in order to explore the effects of subband engineering on the MOS based technology. Then we have presented a simple model to evaluate the gate tunneling current in the device and compared and contrasted this current with the leakage current in the conventional DG MOSFET. We have compared the gate leakage current and the threshold voltage of the proposed device with MINIMOS 6.0 to prove the validity of our simulation results. It can be concluded that the scaling of the gate width cannot suppress the gate leakage, even if the specification of the threshold voltage is relaxed in order to shrink the gate width.
Narrow band gap InGaSb, InAlAsSb alloys for electronic devices
Authors: Magno R. , Glaser E. R. , Tinkham B. P. , Champlain J. G. , Boos J. B. , Ancona M. G. , Campbell P. M.
Published: June 2006

Solid source molecular beam epitaxy has been used to grow random alloy quaternary InAlAsSb and ternary InGaSb alloys with a 6.2Å lattice constant for use in electronic devices such as p-n junctions and heterojunction bipolar transistors (HBTs). Several p-n hetrojunctions composed of p-type InGaSb and one of several different n-type InAlAsSb alloys have been fabricated and show good rectification with ideality factors near one. In addition, several of these alloys have been used to make an n-p-n HBT that has demonstrated a dc current gain of 25.
Structural and optical characterization of GaNAs layers grown by molecular beam epitaxy
Authors: Pulzara-Mora A. , Meléndez-Lira M. , Falcony-Guajardo C. , López-López M. , Vidal M. A. , Jiménez-Sandoval S. , Aguilar-Frutis M. A.
Published: June 2006

We have grown GaNxAs1−x layers by molecular beam epitaxy on GaAs(100) substrates using a radio frequency plasma nitrogen source and solid sources for Ga and As. Employing reflection high-energy electron diffraction (RHEED), the GaNAs growth mode was in situ monitored. A three dimensional (3D) growth mode was obtained at the low growth temperature of 420°C. At higher temperatures streaky RHEED patterns were observed during all the GaNAs deposition, indicating a two dimensional (2D) growth mode. The structural and optical properties of the GaNAs layers were studied by employing high-resolution x-ray diffraction, atomic force microscopy, Raman scattering, and spectroscopic ellipsometry. The films grown in a 3D mode presented high density of crystal defects, degraded structural properties, and broad optical transitions. In contrast, GaNAs layers grown in a 2D mode are pseudomorphic with high crystal quality. The properties of samples with a high N concentration were improved by first growing a GaNAs layer with a low N content.
Growth of high quality InAs quantum-dot multilayer structures on InP for infrared photodetector applications
Authors: Zhang Z. H. , Cheng K. Y.
Published: June 2006

We present a growth technique to improve the structural property of InP-based multilayer quantum-dot (QD) structures. A thin layer of AlGaInAs grown under a group-III stabilized condition can effectively smooth out the three-dimensional growth front caused by the QD formation. Thus, the AlGaInAs barrier layers with high crystal quality and smooth interfaces can be achieved. Using this technique, an InP-based QD infrared photodetector structure containing ten-period QD layers has been grown using molecular beam epitaxy, and its high structural and optical quality was confirmed by x-ray diffraction and photoluminescence measurements.
Strain relaxation in the growth of planar InAs
Authors: Eyink K. G. , Grazulis L. , Pitz J. J. , Shank J. , Mahalingam K.
Published: June 2006

In this work, we look at the strain relaxation of InAs growth on GaAs under metal rich conditions. InAs layers, grown under these conditions, have been found to maintain a planar morphology for thicknesses well beyond a Matthews-Blakeslee critical thickness of ∼2 ML. We employed reflection high-energy electron diffraction, in situ spectroscopic ellipsometry and atomic force microscopy to follow the InAs growth under In stabilized conditions. The critical thickness was found to increase with a reduction in growth temperature. A region of growth was seen in which three-dimensional diffraction was not visible in the reflection high energy electron diffraction pattern before annealing. For thicknesses less than the critical thickness observed by atomic force microscope, the planar morphology has been found to be stable with annealing. These results indicate that strain relaxation via the formation of Lomer-type dislocations is essential to stabilizing planar morphology during growth.
Role of reactive surface oxygen in causing enhanced copper ionization in a low-k polymer
Authors: Achanta Ravi S. , Gill William N. , Plawsky Joel L. , Haase G.
Published: June 2006

Copper oxidation, ionization, and penetration into a low-k polymer, SiLK-D™, are studied here. It is demonstrated by exposure to an oxidizing plasma and subsequent bias-temperature-stress experiments that an increase in the content of reactive or weakly bound oxygen at the SiLK-D™ surface in contact with the copper leads to the oxidation of the copper and injection of the copper into the polymer. The oxidation and injection are driven by the applied external electric field. X-ray photoelectron spectroscopy has been used to characterize the surface oxygen content on as-deposited (low oxygen content, the reference) and oxygen plasma treated films (high surface oxygen content). Capacitors were fabricated on both materials and bias temperature stress tests were done for several O2 plasma exposure times and for external electric fields of 1, 0.5, and 0.1MV∕cm to detect copper ionization and injection. With an electric field of only 0.1MV∕cm, copper injection was not detectable even though oxygen at the SiLK-D™ surface had been increased by exposure to oxygen plasma.
Direct nanoimprint of inorganic-organic hybrid glass
Authors: Okinaka Motoki , Tsukagoshi Kazuhito , Aoyagi Yoshinobu
Published: June 2006

Inorganic-organic hybrid glass nanoimprint has been demonstrated by the transformation of polysilane polymer into SiO2-based material. The proposed technique has the advantages of low temperature and very short processing time over conventional inorganic patterning methods. Line and space structures ranging from 50nmto25μm could be precisely patterned, and an aspect ratio of 4.8 was achieved for an optimized imprint condition. Only 5% shrinkage of the structure was confirmed after heat treatment at 350°C. The patterned film shows little solubility in acetone, acid, or alkali solution. Furthermore, only a very small change is observed when it is dipped in hydrofluoric acid. It was demonstrated that the proposed process enables nanopatterning of inorganic-organic hybrid glass with good thermal and chemical durabilities.
Characteristics of the nanoscale titanium film deposited by plasma enhanced chemical vapor deposition and comparison of the film properties with the film by physical vapor deposition
Authors: Lee Joo Wan , Kim Soo-Hyun , Kwak No Jung , Lee Young Jin , Sohn Hyun Chul , Kim Jin Woong , Sun Ho-Jung
Published: June 2006

Ti Si 2 film was grown by plasma enhanced chemical vapor deposition (PECVD) method for lower contact resistance. We obtained a uniform TiSi2 film on Si substrate. The growth rate of TiSi2 on Si substrate is four times higher than that of Ti on silicon dioxide. The thickness ratio of TiSi2∕Si is very high at the early stage of growth. The high ratio, 8.8, results from a long incubation time before the formation of Ti film on silicon dioxide and ignoring the incubation time, thickness ratio is almost constant in the given thickness range. The average of thickness ratio is determined as 4.25. C49 (060) phase was formed on Si substrate by PECVD method and C49 TiSi2 phase was not changed into C54 one by rapid thermal annealing (RTA) at 900°C. We could not observe boron segregation at the TiSi2∕Si interface. On the contrary, we observed inward diffusion of boron into Si substrate during the silicide formation. We obtained 1.21×103Ω of contact resistance by PECVD method. When Ti thickness is less than 1nm, the contact resistance is comparable with that by physical vapor deposition method or lower.
Cleaning silicon nitride gratings with liquid immersion
Authors: Robertson-Tessi Mark , Wild Robert J. , Cronin Alexander D. , Savas Tim
Published: June 2006

We demonstrate a method for cleaning sodium deposits off nanofabricated silicon nitride gratings using liquid immersion without damaging the grating. The possibility of cleaning a grating successfully depends on its physical parameters and the type of liquid to be used. We present calculations on surface tension interactions between a liquid and the bars of the grating, and derive the maximum grating-bar span that will survive immersion.
Alternating phase shifted scattering bars for low k1 trench pattering
Authors: Mehta Sohan Singh , Kumar Rakesh , Singh Navab , Suda Hideki , Kubota Takao , Kimura Yasuki , Kinoshita Hiroshi , Wong T. K. S. , Wei Ji
Published: June 2006

This article studies the resolution enhancement for sub-120nm isolated trench patterns using alternating phase shifted scattering bars. Through simulation, we found that three sets of 40nm alternating phase shifted scattering bars with separation of 120nm are the best aerial image provider in terms of higher peak intensity, lower side lobe intensity, and smaller full width of half maxima. Simulation results are verified experimentally, and we achieved isolated trench at patterned critical dimension (CD) target of 120nm±10% with manufacturability process window for nominal design CD of 125nm. The patterned CD target 120nm corresponds to k1 factor of 0.33 for exposing wavelength of 248nm, sigma of 0.31, and maximum numerical aperture (NA) of 0.68. Three sets of alternating phase shifted scattering bars showed good mask linearity up to 115nm nominal design CD. We compared isolated trench process condition with dense patterns. Our experimental results show that both isolated and dense patterns can be printed at the same process condition.
Effects of NH3 pulse plasma on atomic layer deposition of tungsten nitride diffusion barrier
Authors: Lee Chang Woo , Kim Yong Tae
Published: June 2006

We deposited W–N thin films on Si and tetraethylorthosilicate (TEOS)∕Si substrates at 200–400°C, synchronizing a pulse plasma only with NH3 exposure cycles during atomic layer deposition (ALD) cycles of NH3 and WF6. The deposition rate was about 0.3nm∕cycle at 350°C, the nitrogen concentration was uniformly distributed in the W–N films, and the NH3 pulse plasma did not cause wormholes at the Si surface. However, there was an incubation period to deposit the W–N film according to the ideal ALD mechanism. Rutherford backscattering spectroscopy revealed that a 22-nm-thick W–N thin film, as a diffusion barrier for the Cu interconnect, successfully prevented the Cu diffusion during the annealing at 600°C for 30min.
Fabrication and characterization of Spindt-type field emission arrays coated with ZrC thin films
Authors: Li Hanyan , Ding Mingqing , Feng Jinjun , Li Xinghui , Bai Guodong , Zhang Fuquan
Published: June 2006

We reported on the fabrication and characterization of Spindt-type Mo field emission arrays coated with ZrC thin films (ZrC FEAs). ZrC thin films with a thickness of 5–10nm were deposited by electron beam evaporation immediately after Mo tips were formed in situ. After loading the sample into a testing system, arrays were normally treated by heating and an aging process of emission-stimulated desorption to remove surface adsorbates. Comparisons between the emission data taken from Mo FEAs and ZrC FEAs with similar cell geometry were made. It was found that the turn-on voltage of ZrC FEAs was reduced by a 30% possibly due to the lower work function of ZrC films, while the emission fluctuation for ZrC FEAs was also reduced from 20% to 5% after an aging process for 800min.
Self-organized nanodot formation on InP(100) by argon ion sputtering at normal incidence
Authors: Tan S. K. , Wee A. T. S.
Published: June 2006

We demonstrate the formation of hexagonal nanodot arrays with mean dot diameter and periodicity of (73±10) and 85nm, respectively, by 1keV Ar+ beam sputtering of InP(100) at normal incidence. The ordering of nanodots increases with sputtering duration and ion flux. Ordered hexagonal nanodot arrays form at a small temperature window near room temperature. X-ray photoelectron spectroscopy and backscattered electron composition imaging (COMPO) show that the surface of nanodots comprises primarily of elemental In due to the preferential sputtering of P. Based on scaling theory, the temporal evolution of the sputtered surface can be divided into two different regimes: coarsening in the early-time regime and ordering in the late-time regime.
Impaired cerebral CO2 vasoreactivity: association with endothelial dysfunction
Authors: Lavi Shahar , Gaitini Diana , Milloul Victor , Jacob Giris
Published: June 2006

Conflicting data exist on the role of nitric oxide (NO) in cerebral blood flow (CBF) autoregulation. Previous studies involving human and animal subjects seem to indicate that NO involvement is limited to the CO2-dependent mechanism (chemoregulation) and not to the pressure-dependent autoregulation (mechanoregulation). We tested this hypothesis in patients with impaired endothelial function compared with healthy controls. Blood pressure, heart rate, end-tidal Pco2, CBF velocities (CBFV), forearm blood flow, and reactive hyperemia were assessed in 16 patients with diabetes mellitus and/or hypertension and compared with 12 age- and sex-matched healthy controls. Pressure-dependent autoregulation was determined by escalating doses of phenylephrine. CO2 vasoreactivity index was extrapolated from individual slopes of mean CBFV during normocapnia, hyperventilation, and CO2 inhalation. Measurements were repeated after sodium nitroprusside infusion. Indexes of endothelial function, maximal and area under the curve (AUC) of forearm blood flow (FBF) changes, were significantly impaired in patients (maximal flow: 488 ± 75 vs. 297 ± 31%; P = 0.01, AUC ΔFBF: 173 ± 17 vs. 127 ± 11; P = 0.03). Patients and controls showed similar changes in cerebrovascular resistance during blood pressure challenges (identical slopes). CO2 vasoreactivity was impaired in patients compared with controls: 1.19 ± 0.1 vs. 1.54 ± 0.1 cm·s−1·mmHg−1; P = 0.04. NO donor (sodium nitroprusside) offsets this disparity. These results suggest that patients with endothelial dysfunction have impaired CO2 vasoreactivity and preserved pressure-dependent autoregulation. This supports our hypothesis that NO is involved in CO2-dependent CBF regulation alone. CBFV chemoregulation could therefore be a surrogate of local cerebral endothelial function.
Effect of angiotensin II blockade on a new congenic model of hypertension derived from transgenic Ren-2 rats
Authors: Jessup Jewell A. , Gallagher Patricia E. , Averill David B. , Brosnihan K. Bridget , Tallant E. Ann , Chappell Mark C. , Ferrario Carlos M.
Published: June 2006

The generation of the Lew.Tg( mRen2) congenic hypertensive rat strain, developed through a backcross of the hypertensive (mRen2)27 transgenic rat with normotensive Lewis rats, provides a new model by which primary hypertension can be studied without the genetic variability found in the original strain. The purpose of this study was to characterize the Lew.Tg( mRen2) rats by dually investigating the effects of type 1 angiotensin II (ANG II) receptor (AT1) blockade and angiotensin-converting enzyme (ACE) activity inhibition on the ANG-(1–7)/ACE2 axis of the renin-angiotensin system in this new hypertensive model. The control of blood pressure elicited by 12-day administration of either lisinopril (mean difference change = 92 ± 2, P < 0.05) or losartan (mean difference change = 69 ± 2, P < 0.05) was associated with 54% and 33% increases in cardiac ACE2 mRNA and 54% and 43% increases in cardiac ACE mRNA, respectively. Lisinopril induced a 3.1-fold ( P < 0.05) increase in renal cortical expression of ACE2, whereas losartan increased ACE2 mRNA 3.5-fold ( P < 0.05). Both treatment regimens increased renal ACE mRNA 2.6-fold ( P < 0.05). The two therapies augmented ACE2 protein activity, as well as increased cardiac and renal AT1 receptor mRNAs. ACE inhibition reduced plasma ANG II levels (81%, P < 0.05) and increased plasma ANG-(1–7) (265%, P < 0.05), whereas losartan had no effect on the peptides. In contrast with what had been shown in normotensive rats, ACE inhibition decreased renal ANG II excretion and transiently decreased ANG-(1–7) excretion, whereas losartan treatment was associated with a consistent decrease in ANG-(1–7) urinary excretion rates. In response to the treatments, the expression of both renal cortical renin and angiotensinogen mRNAs was significantly augmented. The paradoxical effects of blockade of ANG II synthesis and activity on urinary excretion rates of the peptides and plasma angiotensins levels suggest that, in Lew.Tg( mRen2) congenic rats, a failure of compensatory ACE2 and ANG-(1–7)-dependent vasodepressor mechanisms may contribute both to the development and progression of hypertension driven by increased formation of endogenous ANG II.
Comparing microsphere deposition and flow modeling in 3D vascular trees
Authors: Marxen M. , Sled J. G. , Yu L. X. , Paget C. , Henkelman R. M.
Published: June 2006

Blood perfusion in organs has been shown to be heterogeneous in a number of cases. At the same time, a number of models of vascular structure and flow have been proposed that also generate heterogeneous perfusion. Although a relationship between local perfusion and vascular structure has to exist, no model has yet been validated as an accurate description of this relationship. A study of perfusion and three-dimensional (3D) arterial structure in individual rat kidneys is presented, which allows comparison between local measurements of perfusion and model-based predictions. High-resolution computed tomography is used to obtain images of both deposited microspheres and of an arterial cast in the same organ. Microsphere deposition is used as an estimate of local perfusion. A 3D cylindrical pipe model of the arterial tree is generated based on an image of the arterial cast. Results of a flow model are compared with local microsphere deposition. High correlation ( r2 > 0.94) was observed between measured and modeled flows through the vascular tree segments. However, the relative dispersion of the microsphere perfusion measurement was two- to threefold higher than perfusion heterogeneity calculated in the flow model. Also, there was no correlation in the residual deviations between the methods. This study illustrates the importance of comparing models of local perfusion with in vivo measurements of perfusion in the same biologically realistic vascular tree.
Effects of Ca2+ channel antagonists on nerve stimulation-induced and ischemia-induced myocardial interstitial acetylcholine release in cats
Authors: Kawada Toru , Yamazaki Toji , Akiyama Tsuyoshi , Uemura Kazunori , Kamiya Atsunori , Shishido Toshiaki , Mori Hidezo , Sugimachi Masaru
Published: June 2006

Although an axoplasmic Ca2+ increase is associated with an exocytotic acetylcholine (ACh) release from the parasympathetic postganglionic nerve endings, the role of voltage-dependent Ca2+ channels in ACh release in the mammalian cardiac parasympathetic nerve is not clearly understood. Using a cardiac microdialysis technique, we examined the effects of Ca2+ channel antagonists on vagal nerve stimulation- and ischemia-induced myocardial interstitial ACh releases in anesthetized cats. The vagal stimulation-induced ACh release [22.4 nM (SD 10.6), n = 7] was significantly attenuated by local administration of an N-type Ca2+ channel antagonist ω-conotoxin GVIA [11.7 nM (SD 5.8), n = 7, P = 0.0054], or a P/Q-type Ca2+ channel antagonist ω-conotoxin MVIIC [3.8 nM (SD 2.3), n = 6, P = 0.0002] but not by local administration of an L-type Ca2+ channel antagonist verapamil [23.5 nM (SD 6.0), n = 5, P = 0.758]. The ischemia-induced myocardial interstitial ACh release [15.0 nM (SD 8.3), n = 8] was not attenuated by local administration of the L-, N-, or P/Q-type Ca2+ channel antagonists, by inhibition of Na+/Ca2+ exchange, or by blockade of inositol 1,4,5-trisphosphate [Ins( 1 , 4 , 5 )P3] receptor but was significantly suppressed by local administration of gadolinium [2.8 nM (SD 2.6), n = 6, P = 0.0283]. In conclusion, stimulation-induced ACh release from the cardiac postganglionic nerves depends on the N- and P/Q-type Ca2+ channels (with a dominance of P/Q-type) but probably not on the L-type Ca2+ channels in cats. In contrast, ischemia-induced ACh release depends on nonselective cation channels or cation-selective stretch activated channels but not on L-, N-, or P/Q type Ca2+ channels, Na+/Ca2+ exchange, or Ins( 1 , 4 , 5 )P3 receptor-mediated pathway.
Subtractive hybridization for differential gene expression in mechanically unloaded rat heart
Authors: Bugger Heiko , Leippert Stefanie , Blum Daniel , Kahle Peter , Barleon Bernhard , Marme Dieter , Doenst Torsten
Published: June 2006

The objective of this study was to identify differentially expressed genes in the mechanically unloaded rat heart by suppression subtractive hybridization. In male Wistar-Kyoto rats, mechanical unloading was achieved by infrarenal heterotopic heart transplantation. Differentially expressed genes were investigated systematically by suppression subtractive hybridization. Selected targets were validated by Northern blot analysis, real-time RT-PCR, and immunoblot analysis. Maximal ADP-stimulated oxygen consumption (state 3) was measured in isolated mitochondria. Transplantation caused atrophy (heart-to-body weight ratio: 1.6 ± 0.1 vs. 2.4 ± 0.1, P < 0.001). We selected 1,880 clones from the subtractive hybridization procedure (940 forward and 940 reverse runs assessing up- or downregulation). The first screen verified 465 forward and 140 reverse clones, and the second screen verified 67 forward and 30 reverse clones. On sequencing of 24 forward and 23 reverse clones, 9 forward and 14 reverse homologies to known genes were found. Specifically, we identified reduced mRNA expression of complex I (−49%, P < 0.05) and complex II (−61%, P < 0.001) of the respiratory chain. Significant reductions were also observed on the respiratory chain protein level: −42% for complex I ( P < 0.01), −57% for complex II ( P < 0.05), and −65% for complex IV ( P < 0.05). Consistent with changes in gene and protein expression, state 3 respiration was significantly decreased in isolated mitochondria of atrophied hearts, with glutamate and succinate as substrates: 85 ± 27 vs. 224 ± 32 natoms O·min−1·mg−1with glutamate ( P < 0.01) and 59 ± 18 vs. 154 ± 30 natoms O·min−1·mg−1with succinate ( P < 0.05). Subtractive hybridization indicates major changes in overall gene expression by mechanical unloading and specifically identified downregulation of respiratory chain genes. This observation is functionally relevant and provides a mechanism for the regulation of respiratory capacity in response to chronic mechanical unloading.
Systematic evaluation of a novel model for cardiac ischemic preconditioning in mice
Authors: Eckle Tobias , Grenz Almut , Köhler David , Redel Andreas , Falk Melanie , Rolauffs Bernd , Osswald Hartmut , Kehl Franz , Eltzschig Holger K.
Published: June 2006

Cardioprotection by ischemic preconditioning (IP) remains an area of intense investigation. To further elucidate its molecular basis, the use of transgenic mice seems critical. Due to technical difficulty associated with performing cardiac IP in mice, we developed an in situ model for cardiac IP using a hanging-weight system for coronary artery occlusion. This technique has the major advantage of eliminating the necessity of intermittently occluding the coronary artery with a knotted suture. To systematically evaluate this model, we first demonstrated correlation of ischemia times (10–60 min) with infarct sizes [3.5 ± 1.3 to 42 ± 5.2% area at risk (AAR), Evan’s blue/triphenyltetrazolium chloride staining]. IP (4 × 5 min) and cold ischemia (27°C) reduced infarct size by 69 ± 6.7% and 84 ± 4.2%, respectively ( n = 6, P < 0.01). In contrast, lower numbers of IP cycles did not alter infarct size. However, infarct sizes were distinctively different in mice from different genetic backgrounds. In addition to infarct staining, we tested cardiac troponin I (cTnI) as marker of myocardial infarction in this model. In fact, plasma levels of cTnI were significantly lower in IP-treated mice and closely correlated with infarct sizes ( R2 = 0.8). To demonstrate transcriptional consequences of cardiac IP, we isolated total RNA from the AAR and showed repression of the equilibrative nucleoside transporters 1–4 by IP in this model. Taken together, this study demonstrates highly reproducible infarct sizes and cardiac protection by IP, thus minimizing the variability associated with knot-based coronary occlusion models. Further studies on cardiac IP using transgenic mice may consider this technique.
Abnormal diastolic currents in ventricular myocytes from spontaneous hypertensive heart failure rats
Authors: Sridhar Arun , Dech Spencer J. , Lacombe Veronique A. , Elton Terry S. , McCune Sylvia A. , Altschuld Ruth A. , Carnes Cynthia A.
Published: June 2006

Hypertension is a common cause of heart failure, and ventricular arrhythmias are a major cause of death in heart failure. The spontaneous hypertension heart failure (SHHF) rat model was used to study altered ventricular electrophysiology in hypertension and heart failure. We hypothesized that a reduction in the inward rectifier K+current ( IK1) and expression of pacemaker current ( If) would favor abnormal automaticity in the SHHF ventricle. SHHF ventricular myocytes were isolated at 2 and 8 mo of age and during end-stage heart failure (≥17 mo); myocytes from age-matched rats served as controls. Inward IK1was significantly reduced at both 8 and ≥17 mo in SHHF rats compared with controls. There was a reduction in inward IK1due to aging in the controls only at ≥17 mo. We found a significant increase in Ifat all ages in the SHHF rats, compared with young controls. In controls, there was an age-dependent increase in If. Action potential recordings in the SHHF rats demonstrated abnormal automaticity, which was abolished by the addition of an Ifblocker (10 μM zatebradine). Increased Ifduring hypertension alone or combined increases in Ifwith reduced IK1during the progression to hypertensive heart failure contribute to a substrate for arrhythmogenesis.
Alterations in oxidative phosphorylation complex proteins in the hearts of transgenic mice that overexpress the p38 MAP kinase activator, MAP kinase kinase 6
Authors: Wall Jason A. , Wei Jing , Ly Mimi , Belmont Peter , Martindale Joshua J. , Tran Diem , Sun Jun , Chen Wenqiong J. , Yu Wen , Oeller Paul , Briggs Steve , Gustafsson Asa B. , Sayen M. R. , Gottlieb Roberta A. , Glembotski Christopher C.
Published: June 2006

Ischemia-reperfusion (I/R) has critical consequences in the heart. Recent studies on the functions of I/R-activated kinases, such as p38 mitogen-activated protein kinase (MAPK), showed that I/R injury is reduced in the hearts of transgenic mice that overexpress the p38 MAPK activator MAPK kinase 6 (MKK6). This protection may be fostered by changes in the levels of many proteins not currently known to be regulated by p38. To examine this possibility, we employed the multidimensional protein identification technology MudPIT to characterize changes in levels of proteins in MKK6 transgenic mouse hearts, focusing on proteins in mitochondria, which play key roles in mediating I/R injury in the heart. Of the 386 mitochondrial proteins identified, the levels of 58 were decreased, while only 2 were increased in the MKK6 transgenic mouse hearts. Among those that were decreased were 21 mitochondrial oxidative phosphorylation complex proteins, which was unexpected because p38 is not known to mediate such decreases. Immunoblotting verified that proteins in each of the five oxidative phosphorylation complexes were reduced in MKK6 mouse hearts. On assessing functional consequences of these reductions, we found that MKK6 mouse heart mitochondria exhibited 50% lower oxidative respiration and I/R-mediated reactive oxygen species (ROS) generation, both of which are predicted consequences of decreased oxidative phosphorylation complex proteins. Thus the cardioprotection observed in MKK6 transgenic mouse hearts may be partly due to decreased electron transport, which is potentially beneficial, because damaging ROS are known to be generated by mitochondrial complexes I and III during reoxygenation.