bluuebunny/crossref_metadata_2025 huggingface dataset:
Process integration and development of inverted photonic crystal arrays
Authors: Tinker M. , Schonbrun E. , Lee J.-B. , Park W.
Published: April 2006

A processing technology has been developed to produce inverted two-dimensional photonic crystal structures by embedding an array of silicon pillars inside a polyimide matrix and releasing this structure from the underlying substrate. The spatial distribution of the high dielectric and low dielectric regions of these structures is inverted compared to the spatial distribution of standard photonic crystal structures produced by etching air holes in a high dielectric slab. Consequently these structures are far more difficult to fabricate. The integration requirements required for developing this technology are discussed along with the processing technology developed to fabricate these devices. An inverted photonic crystal device based on the superprism effect was successfully demonstrated.
Simulation of vertical and lateral ZnO light-emitting diodes
Authors: Jang Soohwan , Chen J. J. , Ren F. , Yang Hyuck-Soo , Han Sang-Youn , Norton D. P. , Pearton S. J.
Published: April 2006

All-ZnO light-emitting diodes (LEDs) offer the promise of a low-cost, brighter alternative to existing GaN-based light emitters for solid-state lighting applications, in part due to the higher exciton binding energy of ZnO. We have used ISE TCAD™ simulations to examine the effect of active, n- and p-layer dopings and thicknesses on the optical output intensity and current-voltage characteristics of both vertical and lateral geometry ZnO LEDs. The latter geometry is attractive for ultralow structures with the ZnO deposited on glass substrates. The current density distribution is more uniform in the vertical structures but there is little difference in optical output power as a function of doping or layer thickness between the two geometries.
Raman study of multiwalled carbon nanotubes functionalized with oxygen groups
Authors: Murphy H. , Papakonstantinou P. , Okpalugo T. I. T
Published: April 2006

We present changes in the first and second order Raman spectra of multiwalled carbon nanotubes (MWNTs) functionalized with oxygenated groups. The oxygen groups were introduced onto the nanotube surface through two strong acid purification routes: (1) reflux in concentrated (70%) HNO3 acid for 4h at 80°C and (2) ultrasonification in 3 HNO3 (70%):1H2SO4 (98%) for 8.5h. Raman spectroscopy, using two laser excitation wavelengths (514.5 and 632.8nm), x-ray photoelectron spectroscopy, and thermal gravimetric analysis were employed to study the evolution of the products. All the techniques revealed a higher degree of functionalization for scheme 2 compared to scheme 1. Charge transfer phenomena were manifested by a shift of the C1s core level towards higher binding energies. We found that the intensity of both the D and G energy Raman modes if normalized to the second order mode D* mode follows similar trends upon acid treatments. We interpret this result together with the observed dispersion of G mode as an indication that the G mode in carbon nanotubes is defect induced in a double resonant process. Both acid schemes cause an upshift of D and G Raman modes, due to intercalation of acid molecules, exerting pressure on the sp2 structure and an electron transfer from the π states in MWNTs to the oxygen atoms.
Characterization of silver-saturated Ge–Te chalcogenide thin films for nonvolatile random access memory
Authors: Kim Cheol-Jung , Yoon Soon-Gil , Choi Kyu-Jeong , Ryu Sang-Ouk , Yoon Sung-Min , Lee Nam-Yeal , Yu Byoung-Gon
Published: April 2006

Programmable metallization cell structure with a device diameter of 2μm composed of Ag–Ge–Te chalcogenide films was prepared by a cosputtering technique at room temperature. The device with a 150nm thick Ag30(Ge0.3Te0.7)70 electrolyte switches at 0.2V from an “off” state resistance Roff close to 106Ω to an “on” resistance state Ron more than four orders of magnitude lower for this programming current. The switching characteristics were closely related with a diffusion of silver anode into silver-saturated GeTe electrolyte films.
Quantitative characterization of the surface morphology using a height difference correlation function
Authors: Vanormelingen K. , Degroote B. , Vantomme A.
Published: April 2006

A height difference correlation function was defined for the analysis of experimentally obtained real space images of a surface morphology. Using scanning tunneling microscope images of two different surfaces, the Si(111)-7×7 reconstruction and hyperthermally deposited thin Co films on Si(111), we demonstrate the advantages of this characterization procedure. Parameters such as the grain size and the roughness at short length scale, which are difficult to determine, especially for surfaces exhibiting randomly distributed closely packed grains, can be easily obtained from an appropriate fit of the height difference correlation function. This fit, based on the theory of kinetic roughening, simultaneously provides quantitative information on the roughness at short (Hurst parameter) and large length scales and surface in-plane correlation length of the film. The results for the overall surface roughness are consistent with the values which can be directly obtained from scanning tunneling microscope measurements. Furthermore, for the 7×7 structure, the correlation length ξ‖ can be linked to the interatomic distance, while for the Co films ξ‖ represents the grain size of the film.
Field emission from H- and O-terminated heavily P-doped homoepitaxial diamond
Authors: Yamada Takatoshi , Kato Hiromitsu , Shikata Shin-ichi , Nebel Christoph E. , Yamaguchi Hishato , Kudo Yuki , Okano Ken
Published: April 2006

Field emission properties of phosphorus (P)-doped homoepitaxial diamonds are measured after hydrogen plasma treatment and wet chemical oxidization. We also measure field emission properties of H-terminated B-doped diamond for comparison. P-doped diamonds are grown on type Ib single crystalline diamond by microwave plasma chemical vapor deposition. The resistivity of the films is in the range of (5–8)×102Ωcm. Phosphorus concentration measured by secondary ion mass spectroscopy is in the range of (5–7)×1019cm−3. The threshold voltage for field emission of O-terminated P-doped diamond with positive electron affinity is lower than that of H-terminated P-doped diamond with negative electron affinity. Upward band bending due to ionized phosphorus donors exists at the H-terminated surface. This upward bend bending prevents electrons from reaching to the emitting surface. An effective emission barrier height of O-terminated P-doped diamond surface is estimated to be 1.3eV using slopes of Fowler-Nordheim plots. This value is in good agreement with the reported electron affinities in literature.
Nanostructures on oxidized Si surfaces fabricated with the scanning tunneling microscope tip under electron-beam irradiation
Authors: Shklyaev Alexander A. , Ichikawa Masakazu
Published: April 2006

Atom transfer from an oxidized Si surface to the tip of a scanning tunneling microscope (STM) was achieved for samples at room temperature, when the tip-sample interaction area is irradiated with an external electron beam. The transfer proceeded stably with use of a Si apex of the STM tip and of a thin Ge coverage on the oxidized Si surface. The extraction of atoms from the sample occurred at negative tip bias voltages, producing nanosized Si windows in the Si oxide film. Atoms accumulated on the tip apex during the extraction can be redeposited back to the windows at positive tip bias voltages. The mechanism of extraction is related to chemically assisted field evaporation, which was realized due to relatively strong bonding strength of extracted atoms to the surface of the Si tip apex.
Reactive ion etching induced damage evaluation for optoelectronic device fabrication
Authors: Morello G. , Quaglio M. , Meneghini G. , Papuzza C. , Kompocholis C.
Published: April 2006

Reactive ion etching (RIE) processes have been evaluated in terms of material damage introduced and effect on device performance. We have evaluated the damage introduced in the InP∕InGaAsP material system, in terms of surface damage depth, by various RIE-related etching processes (based on CH4∕H2 chemistry) and we have fabricated complete Fabry-Perot laser diode devices to evaluate the effect of RIE-induced damage on device performance. Electrical, optical, and reliability performance results are presented for the laser diode devices. A comparison between the laser device performance and the related surface damage depth is presented and discussed. It has been shown that a correlation exists between RIE-induced damage and optoelectronic device performance. By carefully designing RIE-related processes, which introduce low material damage, good optoelectronic device performance can be realized coupled with high device reliability.
Characterization and modeling of antireflective coatings of SiO2, Si3N4, and SiOxNy deposited by electron cyclotron resonance enhanced plasma chemical vapor deposition
Authors: Mestanza S. N. M. , Obrador M. P. , Rodriguez E. , Biasotto C. , Doi I. , Diniz J. A. , Swart J. W.
Published: April 2006

In this work the optical transmission spectra of silicon oxide (SiO2), silicon nitrides (Si3N4), silicon-rich oxynitrides (SiOxNy), and antireflective coatings (ARCs), deposited by the electron cyclotron resonance enhanced plasma chemical vapor deposition onto a silicon substrate at room temperature, are studied. Simulations carried out with the MATHEMATICA program, from 0to1000nm thick coatings, showed maximum transmittance in the three basic colors at 620, 480, and 560nm for the SiO2, Si3N4, and SiOxNy ARCs, respectively. However, a highly significant transmittance over a broad spectral range from visible (VIS) to near the infrared region, with optical gain in the three basic colors above 20%, is observed only at thicknesses of 80, 70, and 60nm, respectively, for SiO2, Si3N4, and SiOxNy ARCs. Among the three evaluated films, the highest transmittance in the broad spectral band in the VIS range was observed for 60nm thick Si3N4 films. The Fourier transform infrared spectroscopy of these films reveal high structural quality and the presence of Si–O, Si–H, N–H, and Si–N bonds, independent of thickness and deposition parameters.
High-accuracy determination of epitaxial AlGaAs composition with inductively coupled plasma optical emission spectroscopy
Authors: Bertness K. A. , Wang C. M. , Salit M. L. , Turk G. C. , Butler T. A. , Paul A. J. , Robins L. H.
Published: April 2006

Inductively coupled plasma optical emission spectroscopy is shown to confirm a recent correlation between photoluminescence (PL) peak energy for AlGaAs epitaxial films and the Al mole fraction x of those films. These two methods also agree within their expanded uncertainties with the Al composition as determined by growth rate measurements using reflection high energy electron diffraction intensity at the time of specimen growth. No systematic variations between the three methods as a function of Al mole fraction were observed. The lowest uncertainty was found in the PL measurements, allowing certification of Al mole fraction x in standard reference materials to an expanded uncertainty of 0.003 for x<0.35. Details of the uncertainty analysis, as well as possible improvements in those uncertainties, are discussed.
Simulation of the spatial distribution and molecular weight of polymethylmethacrylate fragments in electron beam lithography exposures
Authors: Aktary M. , Stepanova M. , Dew S. K.
Published: April 2006

We report a three-dimensional (3D) simulation model based on the kinetic transport theory for calculating the distribution of PMMA fragments after an exposure to electron impact. The conditions employed for the modeling were chosen to resemble a typical electron beam lithography exposure. The model accounts for inelastic collisions of electrons in PMMA and resulting random main-chain scissions. We have considered gratings composed of parallel lines distanced by 10–50nm and exposed to electrons with energies of 10–60keV. By the model simulations, we have generated and analyzed the detailed 3D distributions of small PMMA fragments (one to ten monomers) that are soluble at the development stage and thus are responsible for the clearance in the gratings. In terms of the spatial distributions of soluble fragments, we have formulated the criteria that define the total clearance as well as the local grating development and investigated their dependence on the grating period, electron dose, and energy.
Carbon nanostructure field emission devices
Authors: Wong Y. M. , Kang W. P. , Davidson J. L. , Soh K. L. , Choi B. K. , Hofmeister W.
Published: April 2006

The microwave plasma chemical vapor deposition (MPCVD) method is capable of synthesizing various forms of carbon allotropes such as diamond, carbon nanotubes (CNTs), and diamondlike carbon (DLC) while varying the growth parameters or utilizing substrate coated with catalytic thin film. In this article, needlelike carbon nanostructures (CNs) were synthesized utilizing high power (5kW) and high working pressure (120Torr) MPCVD on a thin catalytic film of nickel with a diffusion barrier layer of titanium on a micropatterned silicon substrate. The effects of in situ doping by trimethylboron (TMB) on the morphologies and field emission properties of the CNs were also investigated. Straight, needlelike CNs with random orientation were obtained for 15min growth time with or without TMB doping. However, the CNs appear to transform into diamondlike nanocrystals after prolonged growth of 30min with TMB doping. Unlike MPCVD grown CNTs, it was found that the CNs have strong adhesion to the substrate and could withstand postgrowth processing such as ultrasonic agitation cleaning in solvents. Field emission tests performed show that in situ TMB doping of the patterned needlelike CNs lowers the turn-on field of the cathode. A vacuum field emission triode with self-aligned gate utilizing CNs as the field emitter is also fabricated.
Full scale simulation of a field-emitter arrays based electron source for free-electron lasers
Authors: Dehler M. , Candel A. , Gjonaj E.
Published: April 2006

We describe the computer modeling of relativistic electron guns (0.5MeV) using pulsed field emitter arrays. The special challenge lies in the fact, that current distributions vary at a submicron scale, whereas structural dimensions are in the millimeter range. The general approach uses two steps. The first one is the computation of individual field-emitter tips including gate and focusing layers. Real world influences as, e.g., the effect of adsorbates on the emitted currents are taken into account by parameterizing the phase space of the tips. Together with a stochastic distribution of emitter properties, this leads to an equivalent current distribution on the cathode itself, which is used in the second step for the calculation of the electron dynamics in the gun itself. We present results for a source using a field-emitter array of 17 700 tips. For the current field-emitter geometry, we see a large high base line effect resulting from nonlinear focusing forces inside the emitter itself. Of special interest are the effects of spatial correlations in the stochastic distribution on the emittance, showing pronounced performance degradations in the case of large correlation lengths.
Simulations of emission characteristics of a multigated single carbon nanotube field emitter
Authors: Hu Yuan , Lin T.-C.
Published: April 2006

In this study, a two-dimensional, particle-in-cell computer simulation code MAGIC was used to investigate the field emission characteristics from a single closed-capped multiwalled carbon nanotube (MWCNT) in a particular quadruple-gated focusing configuration. Simulations have been done on a single MWCNT assuming it is a cylinder with an ellipsoidal cap of 40nm major radius and 10nm minor radius, 20nm in base diameter, and 0.2 or 0.3μm in height. Other simulation parameters in the base case are 0.1μm thickness for each gate, uniform gate hole radius of 0.45μm, and an anode-cathode distance of 20μm. A particular quadruple-gated focusing configuration has been investigated with individual gate bottom to cathode top distances of 1.1, 1.8, 2.9, and 3.9μm, respectively. For this particular quadruple-gated structure with a cathode voltage of 0V, 85V in voltage of the first gate, 224V in voltage of the second gate, 1320V in voltage of the third gate, 1331V in voltage of the fourth gate, and an anode voltage of 1331V, simulation result showed that a current-weighted beam spot radius on the anode plane can be reduced to 17.4nm for a MWCNT height of 200nm. The emission current, however, varies only slightly from 0.311to0.375pA, as the voltage on the third gate is changed from 200to1500V. The region in the vicinity of the second gate acts to focus the emitted electron beam, while that of the third gate acts to diverge the beam. It was also found that using a higher MWCNT would reduce the applied voltages, but the emitted electrons could not be as well focused as the case with shorter MWCNT. For a MWCNT height of 300nm at about 0.3pA emission current, the weighted beam radius is increased slightly to 28.8nm at the optimum focusing condition. For the MWCNT height of 300nm at a higher emission current about 3nA, the weighted beam radius was found to increase to 46.4nm at the optimum focusing condition. This study shows that it is possible to design a quadruple-gated MWCNT field emitter having few tens of nanometer focused beam size at picoampere to nanoampere emission current range and the designed field emitter is suitable for parallel electron-beam lithography applications.
HfC field emitter array controlled by built-in poly-Si thin film transistor
Authors: Nagao M. , Yasumuro C. , Sacho Y. , Tanoue H. , Kanemaru S. , Itoh J.
Published: April 2006

The HfC-coated Si field emitter arrays (FEAs) controlled by built-in poly-Si thin-film transistors (TFTs) were fabricated. The FEAs were fabricated at a relatively low temperature using Ar-ion-sputter sharpening so that a low-temperature poly-Si TFT process can be applied. A HfC thin film was coated on emitting tips for improving emission lifetime. An emission control TFT having a conventional top-gate structure was fabricated using ion implantation and activation annealing. A combination of multigate and lightly doped drain (LDD) structures was effective at reducing leakage current at a high source-drain voltage. We fabricated a HfC FEA integrated with a TFT having four gate electrodes with a LDD structure. Complete control of FEA emission current by built-in TFT was demonstrated in a vacuum chamber. The detailed fabrication process and emission control characteristics are reported.
Electron emission from planar-type cathodes based on nanocrystalline silicon thin films
Authors: Shimawaki Hidetaka , Neo Yochiro , Mimura Hidenori
Published: April 2006

We have fabricated nanocrystalline Si planar cathodes and investigated their emission characteristics. The device is composed of a thin metal film, nanocrystalline silicon (nc-Si) particles covered with an oxide film, an n-type silicon substrate, and a bottom electrode. The nc-Si layers were deposited by a pulsed laser ablation technique using a Si target and their surface was oxidized by an oxygen radical beam source generated by radio frequency discharge. The electron emission occurred at the gate voltage higher than the work function of the gate metal, and the emission efficiency was 0.5%. The energy distribution of emitted electrons was considerably broad, indicating that electrons were strongly scattered inside the nc-Si layer and the gate electrode.
All-inverter complementary metal oxide semiconductor based dose control circuit for using vertically aligned carbon nanofibers in maskless lithography
Authors: Islam S. K. , Durisety C. , Vijayaraghavan R. , Blalock B. J. , Grundman T. , Baylor L. R. , Gardner W. L.
Published: April 2006

This article presents a prototype implementation of a circuit that can control charge emission from the vertically aligned carbon nanofibers (VACNFs), for use in the implementation of digital electrostatically focused e-beam array direct-write lithography. This lithography technique can be used to fabricate ultra-small feature size devices, while cutting down the manufacturing costs of photomasks [Baylor et al., J. Vac. Sci. Technol. B 20, 2646 (2002)]. These VACNFs are found to be quite robust for use as microfabricated field-emission devices [Bolton et al., Sens. Actuators B 85, 179 (2002)]. The all-inverter based dose control circuit presented in this article was fabricated using a standard 0.5μm complementary metal oxide semiconductor process to improve the dose-rate accuracy, when using these VACNFs for etching in maskless lithography. Simulation and measurement results are compared and analyzed, and future work for improving the design is discussed.
Surface treatment of carbon nanotube cathodes with glass fillers using KrF excimer laser for field-emission displays
Authors: Honda T. , Oh C. B. , Murakami K. , Kim W. S. , Abo S. , Wakaya F. , Takai M.
Published: April 2006

Carbon nanotube (CNT) cathodes prepared with and without glass fillers were irradiated by a KrF (248nm) excimer laser light with a homogeneous beam-intensity profile at various laser power densities. The current density was greatly increased by adding glass fillers to the paste. The turn-on field became as low as 0.34V∕μm and the emission density became as high as 5.88mA∕cm2 at a field of 2V∕μm by KrF laser irradiation, presumably due to the change in morphology of the surface of the CNT cathodes.
Electrical and emission properties of nanocomposite SiOx(Si) and SiO2(Si) films
Authors: Evtukh A. A. , Litovchenko V. G. , Semenenko M. O.
Published: April 2006

The electrical and emission properties of as deposited and annealed SiOx(Si) films have been investigated. The films with thicknesses of 10–100nm were obtained by thermal evaporation of silicon powder in vacuum (2.7–4.0)×10−3Pa on flat Si substrates and Si tip arrays. The atomic force microscopy investigations of the surface morphology indicated the presence of nanoprotrusions on surface of the initial SiOx(Si) films with height up to 20nm and curvature radius of the nanoprotrusions about 3–5nm. As a result of the thermal annealing, the film surface becomes more uniform and its morphology is characterized by nanoprotrusions with height in the range of 1–3nm. At low electric fields the I-V characteristics of dark current through the initial SiOx(Si) films correspond to Poole-Frenkel transport mechanism. The Fowler-Nordheim tunneling dominates at higher electric fields. As to annealed SiO2(Si) films, the modified Fowler-Nordheim electron tunneling through trapezoidal SiO2 barrier between silicon nanoclusters restricts the current flow. The effective electron field emission from Si tip arrays coated with nanocomposite SiOx(Si) and SiO2(Si) films was observed. The results of the electron field emission from surface of SiOx(Si) films into vacuum show an emission current density of 0.25×10−5A∕cm2 at macroscopic electric fields of (5–6)×105V∕cm. The field emission from thermally annealed samples was not observed in the whole range of the applied voltages. In the contrary, for the case of thermally annealed samples subjected to the following partial etching in HF:H2O solution, the emission increases in comparison with initial samples. In this case the field emission appears already at an electric field of 1.5×105V∕cm and the maximum current density increases up to the value of ∼3×10−5A∕cm2. The current peaks are revealed on emission I(V) characteristics built in J(E) coordinates. The models for explanation of peculiarities of the electrical conductivity and electron field emission from nanocomposite films are discussed.
Field emission characteristics of CuO nanowires grown on brown-oxide-coated Cu films on Si substrates by conductive heating in air
Authors: Yeon Soon-Chang , Sung Woo-Yong , Kim Wal-Jun , Lee Seung-Min , Lee Ho-Young , Kim Yong-Hyup
Published: April 2006

CuO nanowires were grown on brown-oxide-coated Cu films on Si substrates by conductive heating in air and their field emission characteristics were investigated. High resolution scanning electron microscopy showed that the CuO nanowires grew perpendicularly to the substrate, and their length and radius could be controlled by varying heating temperature and time. It was found that the lengths of the CuO nanowires were saturated to a certain point with respect to the heating temperature, and the increasing heating time increased the uniformity of the CuO nanowires in length. The field emission characteristics were strongly affected by the formation of the brown-oxide layer and the morphologies of the CuO nanowires governed by heating temperature and time.
Real-time observation and optimization of tungsten atomic layer deposition process cycle
Authors: Lei Wei , Henn-Lecordier Laurent , Anderle Mariano , Rubloff Gary W. , Barozzi Mario , Bersani Massimo
Published: April 2006

In the search for a chemical sensing strategy to monitor atomic layer deposition (ALD) processes suitable for real-time application in wafer manufacturing, we have applied downstream mass spectrometry sampling to study process dynamics during ALD cycles for tungsten deposition from WF6 and SiH4. The ALD reactor has UHV cleanliness conditions and incorporated a minireactor chamber to simulate the small reaction volume anticipated for manufacturing tools to achieve adequate throughput. Mass spectrometry revealed essential surface reaction dynamics through real-time signals associated with by-product generation as well as reactant introduction and depletion for each ALD half-cycle. These were then used to optimize process cycle time and to study the effect of process recipe changes on film growth. The reaction by-products were clearly observed as H2 from SiH4 exposure and SiF4 from WF6 exposure. For each of the two half-cycles, rapid increase of by-product leds to steady-state adsorption/reaction conditions, following by by-product decrease and complementary reactant increase as surface saturation was achieved, indicating self-limiting surface reaction. From this direct observation of the surface reactions, exposure times could be minimized without sacrificing ALD growth rate per cycle, as verified experimentally. With gas flow parallel to the wafer surface in the minireactor, deviations from across-wafer uniformity were small when sufficient reactant doses were applied, but uniformity suffered markedly when doses were insufficient for surface saturation. Increasing WF6 concentration accelerated surface saturation as expected. Growth rates per cycle showed a notable temperature dependence, with small but noticeable activation energies (∼3kcal∕mol) consistent with previous reports. The effect of varying gas doses of one reactant while keeping the other constant suggests a complex interdependence between the half-cycles, in which the reactivity in one half-cycle is influenced by the prior dose achieved in the previous half-cycle.
Chemical shrinkage material: Nanoscale patterning through interpolymer complex
Authors: Hata Mitsuhiro , Hah Jung-Hwan , Kim Hyun-Woo , Ryoo Man-Hyoung , Choi Sang-Jun , Woo Sang-Gyun , Cho Han-Ku
Published: April 2006

A chemical shrinkage material causing large attachments without pattern deformation is suggested. This material is an aqueous solution of two kinds of polymers, and its shrinkage mechanism is based on the interpolymer complex formation and gelation principle. Attachment greater than 25nm was confirmed on ArF photoresist pattern at 145°C, and its shrinkage properties were found to be proportional to initial critical dimension and process temperature, and pitch dependency was not observed. An additional study on temperature responsive phase transition behavior of the material was also undertaken.
Honeycomb GaN micro-light-emitting diodes
Authors: Choi H. W. , Chua S. J.
Published: April 2006

An optimized design for a micro-light-emitting diode array is presented. Based on a honeycomb hexagonal closed-packed structure, the packing density of individual elements can be increased to over 80% to minimize wastage of junction area. The extended sidewall area provides additional light extraction pathways. The honeycomb light-emitting diode (LED) emits twice as much light compared to a conventional broad area LED with equal junction area, and 50% more light than a microdisk array LED. The significant improvement in efficiency makes the additional processing step worthwhile.
Improved current densities of carbon nanotube cathodes by pulsed operation
Authors: Lysenkov D. , Müller G.
Published: April 2006

We have extended our integral measurement system with luminescent screen for pulsed field emission operation of planar cold cathodes. Since in dc operation typical power loads of some watts∕cm2 cause discharges by “phosphor” evaporation, the pulsed operation of cold cathodes up to some cm2 size makes higher peak current densities achievable. Comparative results for dc and pulsed operations of metal-organic chemical-vapor deposition grown carbon nanotube samples on porous alumina are presented which demonstrate peak current densities up to 60mA∕cm2. Moreover an improved emission uniformity results from peak power processing and afterglow effects.
Study on the field-emission characteristics of a-C:H films
Authors: Lu Zhanling , Zhang Binglin , Yao Ning , Zhang Xinyue
Published: April 2006

Hydrogen-contained nanoamorphous carbon films (a-C:H) were deposited on Si substrates by using microwave plasma chemical vapor deposition. A low turn-on field of 2.77V∕μm was obtained. The current density of 0.28mA∕cm2 was obtained at an electric field of 4.8V∕μm. When the electric field was increased to 6.85V∕μm, the current density was dramatically decreased to 0.067mA∕cm2 and the bonding ratio sp2∕sp3 of 1.25 was decreased to 0.53. It was suggested that some of the sp2 phase changed to sp3 due to arc discharging and that the sp2 phase played an important role in field emission for a-C:H films. The measurements of field emission from local emission sites ofa-C:H films were carried out by using scanning tunneling microscopy. The results revealed that emission sites could be located either at the boundaries of amorphous particles or on the top of particle surface. The defected graphite model was suggested to describe the field-electron-emission characteristics of the film.
Amorphous selenium based photodetector driven by field emission current from N-doped diamond cold cathode
Authors: Kato Nanako , Saito Ichitaro , Yamaguchi Hisato , Okamura Hideki , Okano Ken , Yamada Takatoshi , Butler Tim , Rupesinghe Nalin L. , Amaratunga Gehan A. J.
Published: April 2006

Operation of prototype photodetector using a-Se based target and diamond cold cathode is investigated. In our previous study, successful operation of the prototype photodetector as a unit pixel in future imaging device was reported. Clear photoresponse was obtained even at 10−5Torr, several orders of magnitude higher than the pressure used for conventional imaging tube devices. Electron emission characteristics of diamond are widely reported, but the precise fabrication process of a-Se based target film is covered with patents. In this study, we have fabricated following three types of target films: (A) a-Se film without incorporation, (B) a-Se film with incorporation of arsenic (As), and (C) a-Se film with incorporation of As and tellurium (Te). Successful operation of the photodetector driven by diamond cathode with target C was observed. The detector showed clear response to red, green, and blue light-emitting diodes in addition to white halogen light.
Single-mask multiple lateral nanodiamond field emission devices fabrication technique
Authors: Subramanian K. , Kang W. P. , Davidson J. L. , Choi B. K. , Howell M.
Published: April 2006

We report an efficient microfabrication process technique developed to realize multiple lateral diamond field emitter structures on the same wafer using a single mask. Nanodiamond films with grain size of 5–10nm deposited by CH4∕H2∕N2 microwave plasma enhanced chemical vapor deposition were selectively micropatterned using reactive ion etching at an etch rate of 0.5μm∕min. Several nanodiamond lateral field emission diodes and triodes of different emitter geometries and electrode configurations have been batch fabricated on a silicon-on-insulator wafer. Interelectrode spacing down to 2μm was achieved in arrays of devices on a SiO2 dielectric layer. This fabrication process technique, with its single-mask utility, high manufacturability, combined with its reproducibility, is an efficient and cost-effective approach to realize various configurations of field emission structures in wafer process technology. These nanodiamond vacuum nanoelectronic lateral devices hold high-speed and high-frequency operation potential.
Innovative approach for replicating micropatterns in a conducting polymer
Authors: Luo Cheng , Poddar Rakesh , Liu Xinchuan
Published: April 2006

An intermediate layer lithography (ILL) method is developed in this work to replicate micropatterns in a conducting polymer. In the ILL, an intermediate layer of a nonconducting polymer material is introduced between a silicon substrate and a conducting polymer layer. Subsequently, the conducting polymer film is patterned through a mold insertion. We illustrate this method by patterning polypyrrole. The ILL is simple, free of aggressive chemistry, and straightforward to use. In particular, unlike existing lithographic methods, it is suited at creating well-resolved micropatterns of a conducting polymer without degrading material properties of the conducting polymer. In this sense, we believe that the ILL is a promising approach to create conducting polymer patterns.
Buffer controlled GaN nanorods growth on Si(111) substrates by plasma-assisted molecular beam epitaxy
Authors: Hsiao C. L. , Tu L. W. , Chi T. W. , Seo H. W. , Chen Q. Y. , Chu W. K.
Published: April 2006

Size, shape, and density of self-assembled GaN nanorods grown on Si(111) substrates by plasma-assisted molecular beam epitaxy were successfully controlled by inserting a GaN buffer layer. The structure of the GaN buffer layer plays a vital role in the nanorod growth. Only a broken buffer layer with a suitable opening size can grow nanorods. Evolution of the nanorod is traced to the initial growth stage. Crystal seed grown at the wall of the opening in the buffer layer initiates the beginning of the nanorod, and a self-catalytic vapor-liquid-solid process, triggered by the nanocapillary condensation effect, enhances the GaN nanorod growth. Furthermore, the nanorod density can be largely controlled by using the beam equivalent pressure of the N∕Ga ratio. Other GaN nanostructures grown at different growth conditions are also discussed in details.
C-H Bond Functionalization in Complex Organic Synthesis
Authors: Godula Kamil , Sames Dalibor
Published: April 2006

Direct and selective replacement of carbon-hydrogen bonds with new bonds (such as C–C, C–O, and C–N) represents an important and long-standing goal in chemistry. These transformations have broad potential in synthesis because C–H bonds are ubiquitous in organic substances. At the same time, achieving selectivity among many different C–H bonds remains a challenge. Here, we focus on the functionalization of C–H bonds in complex organic substrates catalyzed by transition metal catalysts. We outline the key concepts and approaches aimed at achieving selectivity in complex settings and discuss the impact these reactions have on synthetic planning and strategy in organic synthesis.
Evolution of the Eastern Tropical Pacific Through Plio-Pleistocene Glaciation
Authors: Lawrence Kira T. , Liu Zhonghui , Herbert Timothy D.
Published: April 2006

A tropical Pacific climate state resembling that of a permanent El Niño is hypothesized to have ended as a result of a reorganization of the ocean heat budget ∼3 million years ago, a time when large ice sheets appeared in the high latitudes of the Northern Hemisphere. We report a high-resolution alkenone reconstruction of conditions in the heart of the eastern equatorial Pacific (EEP) cold tongue that reflects the combined influences of changes in the equatorial thermocline, the properties of the thermocline's source waters, atmospheric greenhouse gas content, and orbital variations on sea surface temperature (SST) and biological productivity over the past 5 million years. Our data indicate that the intensification of Northern Hemisphere glaciation ∼3 million years ago did not interrupt an almost monotonic cooling of the EEP during the Plio-Pleistocene. SST and productivity in the eastern tropical Pacific varied in phase with global ice volume changes at a dominant 41,000-year (obliquity) frequency throughout this time. Changes in the Southern Hemisphere most likely modulated most of the changes observed.
The Competitive Advantage of Sanctioning Institutions
Authors: Gürerk Özgür , Irlenbusch Bernd , Rockenbach Bettina
Published: April 2006

Understanding the fundamental patterns and determinants of human cooperation and the maintenance of social order in human societies is a challenge across disciplines. The existing empirical evidence for the higher levels of cooperation when altruistic punishment is present versus when it is absent systematically ignores the institutional competition inherent in human societies. Whether punishment would be deliberately adopted and would similarly enhance cooperation when directly competing with nonpunishment institutions is highly controversial in light of recent findings on the detrimental effects of punishment. We show experimentally that a sanctioning institution is the undisputed winner in a competition with a sanction-free institution. Despite initial aversion, the entire population migrates successively to the sanctioning institution and strongly cooperates, whereas the sanction-free society becomes fully depopulated. The findings demonstrate the competitive advantage of sanctioning institutions and exemplify the emergence and manifestation of social order driven by institutional selection.
Construction and Analysis of Fractional Multifactorial Designs To Study Attachment Strength and Transfer of
Listeria monocytogenes
from Pure or Mixed Biofilms after Contact with a Solid Model Food
Authors: Midelet Graziella , Kobilinsky André , Carpentier Brigitte
Published: April 2006

The aim of this study was to establish which of seven factors influence the adhesion strength and hence bacterial transfer between biofilms containing
Listeria monocytogenes
(pure and two-species biofilms) and tryptone soya agar (TSA) as a solid organic surface. The two-species biofilms were made of
L. monocytogenes
and one of the following species of bacteria: the nonpathogenic organisms
Kocuria varians
,
Pseudomonas fluorescens
, and
Staphylococcus sciuri
and CCL 63, an unidentified gram-negative bacterium isolated from the processing plant environment. We used biofilms prepared under conditions simulating open surfaces in meat-processing sites. The biofilm's adhesion strength and population were evaluated by making 12 contacts on a given whole biofilm (4.5 cm
2
), using a new slice of a sterilized TSA cylinder for each contact, and plotting the logarithm CFU · cm
−2
detached by each contact against the contact number. Three types of detachment kinetics were observed: biphasic kinetics, where the first slope may be either positive or negative, and monophasic kinetics. The bacteria that resisted a chlorinated alkaline product and a glutaraldehyde- and quaternary ammonium-based disinfectant had greater adhesion strengths than those determined for untreated biofilms. One of the four non-
Listeria
strains studied,
Kocuria varians
CCL 56, favored both the attachment and detachment of
L. monocytogenes
. The stainless steel had smaller bacterial populations than polymer materials, and non-
Listeria
bacteria adhered to it less strongly. Our results helped to evaluate measures aimed at controlling the immediate risk, linked to the presence of a large number of CFU in a foodstuff, and the delayed risk, linked to the persistence of
L. monocytogenes
and the occurrence of slightly contaminated foods that may become dangerous if
L. monocytogenes
multiplies during storage. Cleaning and disinfection reduce the immediate risk, while reducing the delayed risk should be achieved by lowering the adhesion strength, which the sanitizers used here cannot do at low concentrations.
Polychlorinated Biphenyl (PCB)-Degrading Bacteria Associated with Trees in a PCB-Contaminated Site
Authors: Leigh Mary Beth , Prouzová Petra , Macková Martina , Macek Tomáš , Nagle David P. , Fletcher John S.
Published: April 2006

The abundance, identities, and degradation abilities of indigenous polychlorinated biphenyl (PCB)-degrading bacteria associated with five species of mature trees growing naturally in a contaminated site were investigated to identify plants that enhance the microbial PCB degradation potential in soil. Culturable PCB degraders were associated with every plant species examined in both the rhizosphere and root zone, which was defined as the bulk soil in which the plant was rooted. Significantly higher numbers of PCB degraders (2.7- to 56.7-fold-higher means) were detected in the root zones of Austrian pine (
Pinus nigra
) and goat willow (
Salix caprea
) than in the root zones of other plants or non-root-containing soil in certain seasons and at certain soil depths. The majority of culturable PCB degraders throughout the site and the majority of culturable PCB degraders associated with plants were identified as members of the genus
Rhodococcus
by 16S rRNA gene sequence analysis. Other taxa of PCB-degrading bacteria included members of the genera
Luteibacter
and
Williamsia
, which have not previously been shown to include PCB degraders. PCB degradation assays revealed that some isolates from the site have broad congener specificities; these isolates included one
Rhodococcus
strain that exhibited degradation abilities similar to those of
Burkholderia xenovorans
LB400. Isolates with broad congener specificity were widespread at the site, including in the biostimulated root zone of willow. The apparent association of certain plant species with increased abundance of indigenous PCB degraders, including organisms with outstanding degradation abilities, throughout the root zone supports the notion that biostimulation through rhizoremediation is a promising strategy for enhancing PCB degradation in situ.
Genotyping and Pathogenicity of Viral Hemorrhagic Septicemia Virus from Free-Living Turbot (
Psetta maxima
) in a Turkish Coastal Area of the Black Sea
Authors: Nishizawa Toyohiko , Savaş Hacı , Işıdan Hakan , Üstündağ Cennet , Iwamoto Hiroshi , Yoshimizu Mamoru
Published: April 2006

Viral hemorrhagic septicemia (VHS) is one of the most serious fish viral diseases for cultured rainbow trout (
Oncorhynchus mykiss
), although VHS virus (VHSV) seems to be ubiquitous among marine fishes. In the present study, VHSV isolation was performed with free-living and cultured turbot (
Psetta maxima
) in the Trabzon coastal area of the Black Sea to evaluate participation of VHSV in mass mortalities of seed-produced turbot larvae. VHSV was detected in 14 of 66 free-living spawners (positive ratio, 21.2%), 1 of 65 free-living immature fish (1.5%) and 7 of 40 cultured brood stock (17.5%), respectively. Based on a partial glycoprotein gene nucleotide sequence, Turkish VHSV isolates were classified into the class I-e of genotype I and were the most closely related to the GE-1.2 isolate (>98% identity), which was found >20 years ago in Georgia. Thus, it was revealed that Turkish VHSV isolates were not introduced from European countries, it could be an indigenous type of VHSV distributing in the Black Sea environment. In pathogenicity tests, the Turkish isolates did not induce mortality in turbot larvae and rainbow trout fingerlings. Mass mortalities at a rate of approximately 90% occurred in turbot larvae produced by experimental seeding, although VHSV was not detected in any dead fish. Thus, it was concluded that mass mortality in the seed-produced turbot larvae was not caused by VHSV infection.
Fatty Acid-Oxidizing Consortia along a Nutrient Gradient in the Florida Everglades
Authors: Chauhan Ashvini , Ogram Andrew
Published: April 2006

The Florida Everglades is one of the largest freshwater marshes in North America and has been subject to eutrophication for decades. A gradient in P concentrations extends for several kilometers into the interior of the northern regions of the marsh, and the structure and function of soil microbial communities vary along the gradient. In this study, stable isotope probing was employed to investigate the fate of carbon from the fermentation products propionate and butyrate in soils from three sites along the nutrient gradient. For propionate microcosms, 16S rRNA gene clone libraries from eutrophic and transition sites were dominated by sequences related to previously described propionate oxidizers, such as
Pelotomaculum
spp. and
Syntrophobacter
spp. Significant representation was also observed for sequences related to
Smithella propionica
, which dismutates propionate to butyrate. Sequences of dominant phylotypes from oligotrophic samples did not cluster with known syntrophs but with sulfate-reducing prokaryotes (SRP) and
Pelobacter
spp. In butyrate microcosms, sequences clustering with
Syntrophospora
spp. and
Syntrophomonas
spp. dominated eutrophic microcosms, and sequences related to
Pelospora
dominated the transition microcosm. Sequences related to
Pelospora
spp. and SRP dominated clone libraries from oligotrophic microcosms. Sequences from diverse bacterial phyla and primary fermenters were also present in most libraries. Archaeal sequences from eutrophic microcosms included sequences characteristic of
Methanomicrobiaceae
,
Methanospirillaceae
, and
Methanosaetaceae
. Oligotrophic microcosms were dominated by acetotrophs, including sequences related to
Methanosarcina
, suggesting accumulation of acetate.
Novel Hydrophobic Surface Binding Protein, HsbA, Produced by
Aspergillus oryzae
Authors: Ohtaki Shinsaku , Maeda Hiroshi , Takahashi Toru , Yamagata Youhei , Hasegawa Fumihiko , Gomi Katsuya , Nakajima Tasuku , Abe Keietsu
Published: April 2006

Hydrophobic surface binding protein A (HsbA) is a secreted protein (14.5 kDa) isolated from the culture broth of
Aspergillus oryzae
RIB40 grown in a medium containing polybutylene succinate-
co
-adipate (PBSA) as a sole carbon source. We purified HsbA from the culture broth and determined its N-terminal amino acid sequence. We found a DNA sequence encoding a protein whose N terminus matched that of purified HsbA in the
A. ozyzae
genomic sequence. We cloned the
hsbA
genomic DNA and cDNA from
A. oryzae
and constructed a recombinant
A. oryzae
strain highly expressing
hsbA
. Orthologues of HsbA were present in animal pathogenic and entomopathogenic fungi. Heterologously synthesized HsbA was purified and biochemically characterized. Although the HsbA amino acid sequence suggests that HsbA may be hydrophilic, HsbA adsorbed to hydrophobic PBSA surfaces in the presence of NaCl or CaCl
2
. When HsbA was adsorbed on the hydrophobic PBSA surfaces, it promoted PBSA degradation via the CutL1 polyesterase. CutL1 interacts directly with HsbA attached to the hydrophobic QCM electrode surface. These results suggest that when HsbA is adsorbed onto the PBSA surface, it recruits CutL1, and that when CutL1 is accumulated on the PBSA surface, it stimulates PBSA degradation. We previously reported that when the
A. oryzae
hydrophobin RolA is bound to PBSA surfaces, it too specifically recruits CutL1. Since HsbA is not a hydrophobin,
A. oryzae
may use several types of proteins to recruit lytic enzymes to the surface of hydrophobic solid materials and promote their degradation.