bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement on the InAs quantum dot size distribution employing high-temperature GaAs(100) substrate treatment
Authors: Saucedo-Zeni N. , Gorbatchev A. Yu. , Méndez-Garcı́a V. H.
Published: July 2004

We report improvement in the uniformity of InAs quantum dot (QD) arrangements grown on GaAs(100) surfaces by molecular beam epitaxy. GaAs surfaces were subjected to annealing processes at high temperature under no flux and under molecular Si flux for 10 s prior to InAs deposition. InAs thickness equivalent to 2.1 InAs monolayers (ML) was deposited on GaAs surfaces annealed under Si flux, giving a better QD arrangement with larger dimensions and lower density than that obtained for the InAs QDs grown conventionally. On the other hand, when InAs deposition took place on GaAs surfaces subjected to annealing under no As flux, two- to three-dimensional transition occurred at around 3.0 InAs ML, instead of at 1.7 ML as observed for conventional and Si-treated samples. Moreover, the QDs obtained by employing this high-temperature GaAs(100) substrate treatment demonstrated a significant reduction in size dispersion as well as considerable improvement in the uniformity of the spatial arrangement. Photoluminescence spectra revealed a redshift of the emission peak for the QDs grown on GaAs surfaces subjected to different annealing processes, as well as a reduction in the full width at half maximum of emission spectra.
Study of structural and optical properties of quantum dots-in-a-well heterostructures
Authors: Rotella P. , von Winckel G. , Raghavan S. , Stintz A. , Jiang Y. , Krishna S.
Published: July 2004

Optical and structural characteristics of InAs/InGaAs quantum dots-in-a-well (DWELL) heterostructures were investigated. These structures, in which InAs quantum dots are placed in an InGaAs quantum well, which in turn is buried in a GaAs matrix, can be used to realize high performance midinfrared detectors. In this article, we report on the structural and optical properties of these DWELL heterostructures. Five DWELL samples with varying well widths were grown and their properties investigated using transmission electron microscopy (TEM), photoluminescence, normal incidence absorbance, and photocurrent measurement. From the TEM studies, it was observed that, as the InGaAs well thickness increased from 70 to 120 Å, the dots were confined to the upper half of the well. Moreover, a progressive shift was observed in the photocurrent response from 6.7 to 10 μm. Using this approach, a long wave infrared atmospheric window detector was realized.
Simulation study of carbon nanotube field emission display with under-gate and planar-gate structures
Authors: Lan Yung-Chiang , Lee Chun-Tao , Hu Yuan , Chen Shih-Hung , Lee Cheng-Chung , Tsui Bing-Yue , Lin Tsang-Lang
Published: July 2004

Recently, two new CNTs-based triode structures, i.e., under-gate and planar-gate structures, for field emission display were proposed and exhibited good characteristics. In this paper, we will investigate how the current density distributed on anode plate and how the display’s resolution affected by the bias conditions of the emitter and the gate electrode via computer simulation. Our simulation results exhibit that the gate voltage has a strong effect on display’s resolution. For the planar triode structure, the good resolution is achieved when the gate voltage is adjusted to converge the electron beams on an anode plate. For the under-gate structure, the display has a good resolution provided that the gate voltage is not too large to pull the electrons striking on other pixels. In general, the under-gate structure has a wider gate-biased operating condition, but the planar triode structure has a higher light efficiency under the same resolution. Due to the lack of field effect in the y-direction, the spot size of the current density on anode plate looks like strips instead of points. And the resolution of the display will be affected by this factor.
Synthesis of Zn-doped Y2O3:Eu fine-particle phosphor by the sol-gel method
Authors: Kominami Hiroko , Eguchi Chihiro , Kottaisamy Muniasamy , Nakanishi Yoichiro , Hatanaka Yoshinori
Published: July 2004

Y 2 O 3 : Eu , a typical oxide phosphor, was synthesized by the sol-gel method using metal alkoxide. Effects of crystallinity, photoluminescent, and cathodoluminescent properties of Y2O3:Eu on Zn were investigated. The (222) diffraction peak of Y2O3 was shifted to a wider-angle side and crystallinity was improved by Zn addition. However, ZnO phases were observed in the case of the powders with the addition of 0.2 and 0.3 mol Zn. The emission of the D05→F27 transition peaked at around 610 nm decreased, and, the wide, blue-green broad emission of 510–520 nm caused by ZnO increased as the Zn addition increased, under He-Cd laser excitation of 325 nm. On the other hand, the blue-green emission caused by ZnO was not observed in spite of Zn addition under electron-beam excitation below 3 keV. This indicates the possibility of ZnO phase existence inside of Y2O3, rather than as a neighbor on the surface. The addition of 0.2 mol Zn to Y2O3:Eu showed about four times higher intensity compared with non-addition of Zn for cathodoluminescence under an anode voltage of 2 kV and an electron-beam density of 60 μA/cm2. Zn addition to Y2O3:Eu was quite effective for cathodoluminescent properties. Although Zn addition did not control particle size, the fine-particle phosphors below a 1 μm radius were obtained by synthesis with the sol-gel method.
Epitaxial growth on gas cluster ion-beam processed GaSb substrates using molecular-beam epitaxy
Authors: Krishnaswami K. , Vangala S. R. , Zhu B. , Goodhue W. D. , Allen L. P. , Santeufemio C. , Liu X. , Ospina M. C. , Whitten J. , Sung C. , Dauplaise H. , Bliss D. , Dallas G. , Bakken D. , Jones K. S.
Published: July 2004

Chemical mechanical polished (CMP) (100) GaSb substrates were processed using gas cluster ion beams (GCIB) to improve surface smoothness, reduce subsurface damage, and produce a thermally desorbable oxide layer for molecular-beam epitaxy (MBE) overgrowth. In this article, we report the growth of GaSb/AlGaSb epilayers on GCIB processed GaSb substrates. The substrates were processed using either O2 or CF4/O2 as the gas cluster in a dual-energy recipe that included a moderate energy (10 keV) etch step followed by a low-energy (3 keV) smoothing step, with a relatively low total dose of 4×1015 ions/cm2. Half of each wafer was masked such that the epitaxial layers were grown on both CMP and GCIB polished surfaces. Atomic force microscopy showed the elimination of CMP surface scratches on the GCIB processed surfaces. X-ray photoelectron spectroscopy results indicate that the surface oxide composition and thickness can be engineered through the GCIB process recipes. AlGaSb marker layers were used to chart the evolution of the overgrown layers. Cross-sectional transmission electron microscope images of the substrate/epi-interface show that the CMP finished regions contained defects that propagated into the epilayers as compared to the GCIB finished region that showed no penetrating defects, indicating an improved substrate/epi-interface. This work demonstrated that GCIB processing of semiconductor materials has the potential to produce “epiready” surfaces.
High precision determination of the elastic strain of InGaN/GaN multiple quantum wells
Authors: Wu M. F. , Zhou Shengqiang , Yao Shude , Zhao Qiang , Vantomme A. , Van Daele B. , Piscopiello E. , Van Tendeloo G. , Tong Y. Z. , Yang Z. J. , Yu T. J. , Zhang G. Y.
Published: July 2004

The composition, elastic strain, and structural defects of an InGaN/GaN multiple quantum well (MQW) are investigated using a combination of x-ray diffraction, transmission electron microscopy, and Rutherford backscattering/channeling. None of the applied techniques alone can unambiguously resolve the thickness of the individual layers, the In composition in the wells, and the elastic strain. These three parameters directly determine the optical properties of the MQW. It is shown that only a combination of these measurements reveals the full structural characterization of the nitride multilayer. A clear correlation between the defect density of In distribution and strain relaxation is evidenced. The experimental result of the ratio of the average perpendicular elastic strain 〈e⊥〉 and the average parallel elastic strain 〈e∥〉, 〈e⊥〉/〈e∥〉=−0.52, is in excellent agreement with the value deduced from the elastic constants.
Measurements of shallow trench isolation by normal incidence optical critical dimension technique
Authors: Hu Jiangtao , Korlahalli Rahul , Shivaprasad Deepak , Yang Feng , Zhang Xiaodong
Published: July 2004

Shallow trench isolation (STI) has emerged as one of the primary techniques for device isolation in complementary metal oxide semiconductor technologies. This device isolation technology has become extremely important to satisfy the high-density requirements of modern integrated circuits. It is of great importance to measure the critical dimensions and sidewall features of the STI structure. Currently used critical-dimension scanning electron microscopes (CD-SEMs) cannot identify the rounding typically present at the bottom or top of the profile, and it is difficult to differentiate between the top and bottom line-width values. Cross-sectional SEMs that can give the profile information require the destruction of the wafer. In this article, we present the measurement of STI by using the optical critical dimension (OCD) technique. This technique measures line or trench profiles using normal incidence polarized reflectometry with sensitivity to sub-50 nm grating lines. In the OCD technique, a broadband polarized light beam is focused onto the grating surface, and the reflected zeroth order is measured as a function of wavelength. The data obtained by measuring the grating structure give a signature of the profile, which is analyzed in real time using rigorous coupled wave analysis. Since the data are fitted in real time, there is no requirement for library generation, which makes the analysis simpler and easier to extend to other structures without the need for lengthy regeneration of a new library of profile data. Data from STI wafers before and after oxide fill will be presented. Both simulation and experimental results show great sensitivity to features such as CD, depth, sidewall angle, as well as the quality of oxide fill.
Efficient electron emissions from printed carbon nanotubes by surface treatments
Authors: Kim Kwang-Bok , Song Yoon-Ho , Hwang Chi-Sun , Chung Chung-Hui , Lee Jin-Ho , Choi In-Su , Park Jae-Hong
Published: July 2004

The fabrication of carbon nanotube (CNT) emitters with excellent field emission properties was described. CNT clusters synthesized by arc discharge were crushed, mixed with conductive pastes, and then screen-printed. In order to obtain efficient field emissions, the mechanical surface treatment was applied to the printed CNT films. The measurements of field emission carried out using a diode structure showed that the electron emission of the surface-treated CNT films uniformly turned-on with a field as low as about 1.5 V/μm. The emission current density was about 0.6 mA/cm2 at a field of 2.8 V/μm. Furthermore, we proposed a new triode type field emitter using a mesh gate plate having tapered holes. Combining the surface-treated CNT emitters and the mesh gate plate, we could achieve the ideal triode properties with no gate leakage currents. New suggestions of mesh gate structure can be an alternative cathode technology for field emission display.
Probing the electronic structures of III–V-nitride semiconductors by x-ray photoelectron spectroscopy
Authors: Lay T. S. , Kuo W. T. , Chen L. P. , Lai Y. H. , Hung W. H. , Wang J. S. , Chi J. Y. , Shih D. K. , Lin H. H.
Published: July 2004

The electronic structures of III–V-nitride semiconductors, including InGaAsN, GaAsN, and InAsN grown by molecular beam epitaxy, were investigated by high-resolution x-ray photoelectron spectroscopy using synchrotron radiation beam and low energy Ar+ sputtering. The N(1s) core-level photoelectron spectra show a single peak with a binding energy (Eb)∼398.0 eV of N–Ga bonding for GaAsN sample. For the InAsN samples, a single N(1s) peak at Eb∼397.0 eV of N–In bonding is observed. For the InGaAsN samples, the N(1s) spectra exhibit two peaks with a major component corresponding to N–In bonding, and a minor one to N–Ga bonding. The integrated N(1s) intensity of N–In bonding has a higher value than that of N–Ga bonding, in spite of the lower mole fraction of In for the InGaAsN sample. The data indicate that N has a bonding configuration with In-rich nearest neighbors in the InGaAsN samples.
Characterization of material contrast and effective wavelength effects in immersion inspection
Authors: Deng Yunfei , Neureuther Andrew R.
Published: July 2004

The electromagnetic effects of complementary clear-opaque nano-imprint mold inspection and light scattering from small defects are analyzed through simulation. For a wavelength of 365 nm, 40 nm features, and 10 nm defects in an opaque layer with 10% transmission and with a 20 nm gap between complementary molds, leakage light from feature edges dominates the total transmitted light. However, a filter in the pupil can generally enhance defect intensity signals to about 10% of the defect-free intensity. The same polarization signals for defects on the edge are best enhanced by filters blocking signals perpendicular to that edge. The cross polarization signals are important for defects at corners and require no filter. Simulations of light scattering by small square-post defects show that scatter light scales with the square of defect volume at defect sizes up to 20 nm at a wavelength of 193 nm. The use of immersion at 193 nm increases the cross polarization by the refractive index of the liquid but there is little improvement for the same polarization. An opaque layer material with high refractive index contrast to silica and liquid is desirable.
Selective epitaxial growth of GaAs on Si with strained short-period superlattices by molecular beam epitaxy under atomic hydrogen irradiation
Authors: Tsuji Takuto , Yonezu Hiroo , Ohshima Naoki
Published: July 2004

Selective epitaxial growth of GaAs on a Si substrate with (GaAs)m(GaP)n strained short-period superlattices (SSPSs) and GaP buffer layer was achieved by molecular beam epitaxy under atomic hydrogen irradiation. The selective epitaxial layers were grown two dimensionally so that reflection high-energy electron diffraction patterns maintained streaky patterns with no apparent transition to three-dimensional spot patterns during the selective epitaxial growth of the GaAs/SSPSs/GaP/Si structure. Therefore, generation of threading dislocations due to the three-dimensional island growth was suppressed, in spite of a large lattice mismatch. It was also confirmed that the thickness of each buffer layer was slightly increased near the edge of the masked region. Finally, the epitaxial patterns of GaAs clearly exhibit crystal facets.
Enhanced cold field emission from 〈100〉 oriented β–W nanoemitters
Authors: Singh J. P. , Tang F. , Karabacak T. , Lu T.-M. , Wang G.-C.
Published: July 2004

Well-aligned β-phase W(100) nanorods having square-base pyramidal apexes were grown on oxidized Si(100) substrate using glancing angle deposition technique with substrate rotation. The field emission characteristics of nanorods were measured using scanning tunneling microscope (STM) tip as an extraction anode. A highly confined emission current of about 23 μA was obtained at a low extraction voltage of ∼260 V at ∼280 nm anode-cathode distance with <3% fluctuations over ∼2 h. The Fowler–Nordheim plot of the field emission characteristics of nanorods is nonlinear compared with the linear behavior from a conventional W film. The STM topography after the field emission showed a type of nanolips structure grown over the pyramidal apex, which was suggested to enhance and stabilize the emission current.
Effect of developer molecular size on roughness of dissolution front in electron-beam resist
Authors: Yamaguchi T. , Namatsu H.
Published: July 2004

This article describes the generation of roughness at the dissolution front of electron-beam positive-tone resist. The effect of a developer solvent molecule on the surface roughness as well as on the dissolution rate is investigated from the viewpoint of the size of a solvent molecule. The relationship between the dissolution rate and solvent molecular size is represented by two straight lines with different slopes in a homologous series of alkyl acetate solvents. A bending point, which corresponds to a critical molecular size, exists between ethyl and propyl acetate. This indicates that the dissolution behavior is largely different between acetates that are larger or smaller than the critical molecular size. The size of a solvent molecule is the dominant factor determining the degree of surface roughness. For a solvent molecule larger than the critical molecular size, the roughness becomes large because polymer aggregates appear on the dissolution front. For a smaller solvent molecule, on the other hand, no aggregates appeared and the dissolution front is flat and smooth. The critical molecular size is about the same as the average size of voids (free volume holes) in resist films. These results indicate that the roughness strongly depends on how a solvent molecule penetrates the resist film through void regions inhomogeneously distributed in the resist polymer matrix due to polymer aggregation.
Characteristics of In0.52Al0.48As/InxGa1−xAsyP1−y/In0.52Al0.48As high electron-mobility transistors
Authors: Chen Yen-Wei , Hsu Wei-Chou , Chen Yeong-Jia , Hsu Rong-Tay , Wu Yue-Huei , Lin Yu-Shyan
Published: July 2004

In 0.52 Al 0.48 As/In x Ga 1−x As y P 1−y / In 0.52 Al 0.48 As high electron-mobility transistors with single-channel and triple-channel structures were successfully fabricated by low-pressure metal-organic chemical-vapor deposition. The single-channel structure exhibits higher transconductance and drain-source saturation current than the triple-channel due to the higher average-carrier saturation velocity and sheet-carrier concentration of the In0.53Ga0.47As channel. The triple-channel structure is employed to take advantage of both the high electron mobility of In0.53Ga0.47As and the low ionization coefficient of InP. A third quaternary In0.72Ga0.28As0.61P0.39 (Eg∼0.95 eV) layer is introduced between In0.53Ga0.47As (Eg∼0.75 eV) and InP (Eg∼1.35 eV) channels to improve the electron-transport characteristics. Experimentally, the investigated triple-channel structure exhibits a low leakage current, a high breakdown voltages and a high linear-operation regime.
Electron emission characteristics from a single crystalline ferroelectric material by an infrared light irradiation
Authors: Takamuro Daisuke , Takao Hidekuni , Sawada Kazuaki , Ishida Makoto
Published: July 2004

An infrared sensor, based on the principle of electron emission from a thin Pb(Zr,Ti,)O3 (PZT) plate, is proposed in this study. The electron emission current from a thin, single crystalline SrTiO3 plate caused by infrared light irradiation was observed at an electric field of 1.6 MV/cm. To compare the electron emission characteristics, a sintered PZT and a single crystalline SrTiO3 emitter were measured under the same infrared light irradiation conditions. The peak emission current from the SrTiO3 plate was 1.6 times higher than that of the PZT emitter, and the response speed was faster. However, the emission current did not respond continuously to a pulsed infrared irradiation.
Fabrication and characterization of a condenser zone plate for compact x-ray microscopy
Authors: Rehbein Stefan , Holmberg Anders , Johansson Göran A. , Jansson Per A. C. , Hertz Hans M.
Published: July 2004

We describe the in-house fabrication and characterization of a condenser zone plate for a compact laser–plasma-based soft x-ray microscope operating at 2.478 nm wavelength. The fabricated condenser has a diameter of 4.53 mm and an outermost zone width of 49 nm. The pattern is generated by a small-write-field e-beam lithography system and 656 single, 100 μm wide write fields are stitched together to obtain the whole pattern. An in-house method based on a laser–plasma source was developed to characterize the condenser zone plate with regards to diffraction efficiency and imaging properties. The measured groove efficiency of the fabricated condenser zone plate was determined to 11%±2% and the imaging properties were found to follow the expectations concerning the object field illumination purpose in the x-ray microscope. The in-house characterization method allows faster process improvement in the small-scale laboratory compared to presently used synchrotron-based methods.
Deep-ultraviolet resist contamination for copper/low-k dual-damascene patterning
Authors: Kumar R. , Singh N. , Chang C. K. , Dong L. , Wong T. K. S.
Published: July 2004

Deep-ultraviolet (DUV) lithography is the preferred technique for high-resolution patterning at sub-180 nm technology nodes. The via first (VF) dual-damascene (DD) process is the most commonly used integration scheme for realizing the copper interconnects. A major problem encountered with the use of the DUV photoresist in the VFDD process is the presence of resist residues, also known as resist contamination or resist poisoning, which are difficult to remove after trench lithography. In this study, the causes of the DUV-resist contamination for a low-k organosilicate SiOC:H dielectric have been investigated. The effects of different types of underlying substrates and processes used for forming the DD structures on the resist contamination are studied and the physical mechanisms responsible for formation of resist residues are identified. The post via-etching solvent cleaning process is identified as a major contributor to resist contamination and solutions are proposed to minimize DD-process-induced DUV-resist contamination.
Remarkably low value of work function on W(100) produced by Y–O composite layer
Authors: Kawakubo Takashi , Saito Yasushi , Miyamoto Nobuo , Nakane Hideaki , Adachi Hiroshi
Published: July 2004

The work function of W(100) surface is successfully reduced to 2.0 eV. Y2O3 fine powder is attached to the shank of a sharp W(100) needle and heat treated in a vacuum of 10−7 Pa. The emission pattern has a fourfold symmetry with a bright center spot. The work function is estimated with the aid of a Fowler–Nordheim plot. The reduced rate of work function is fairly coincident with the prediction done by Saito et al. (unpublished) and also by Nishiyama, Ohshima, and Shinada [Appl. Surf. Sci. 146, 382 (1999)]. These researchers predicted the reducing rate is proportional to the product of difference of the electronegativities and sum of the ionic radii of the metal atom and oxygen.
Oxide formation during ion bombardment of small silicon structures
Authors: Krüger D. , Formanek P. , Pippel E. , Woltersdorf J. , Bugiel E. , Kurps R. , Weidner G.
Published: July 2004

The kinetics of high dose oxygen implantation and of surface sputtering in silicon are investigated by atomic force microscopy, transmission electron microscopy, transmission electron holography, and electron energy-loss spectroscopy. The implantation was performed into accurately defined submicrometer areas. The behavior of the erosion rate as a function of the implantation dose proved to be nonmonotonic. After native oxide sputtering, a period dominated by (i) implantation of oxygen and (ii) induced oxide formation with volume increase takes place, causing a maximum surface step around the bombarded area of about 1.1 to 1.3 nm at bombardment doses below 2×1016 O+ cm−2. Subsequently, higher doses cause a sputtering of the surface with a sputter yield of about 0.32 Si atoms/O+. Electron holography revealed the double layer character of the implanted region, and electron energy-loss spectroscopy, especially near the relevant Si-L23 ionization edge, identified these two layers which are (i) amorphous silicon oxide and (ii) amorphized silicon. Electron energy-loss line scans show the oxygen distribution inside the implanted areas with a lateral resolution of about 1–2 nm. It was found that the interface between the oxidized layer and the amorphized silicon sharpens with increasing implantation dose.
Improvement of the morphological stability of Ni-silicided Si0.8Ge0.2 layers by using a molybdenum interlayer
Authors: Ok Young-Woo , Kim S.-H. , Song Y.-J. , Shim K.-H. , Seong Tae-Yeon
Published: July 2004

We have investigated the effect of a Mo interlayer on the structural and electrical properties of Ni-silicided Si0.8Ge0.2 samples. It is shown that the samples with the interlayers give lower sheet resistances than the samples without the interlayers when annealed at temperatures in the range of 450–800 °C. Glancing angle x-ray diffraction results show that regardless of the interlayers, only the Ni germanosilicide phase is formed across the whole temperature range. Scanning electron microscopy results show that the samples with the interlayers remain stable without serious surface degradation up to 600 °C. It is further shown that the samples without the interlayers experience abnormal oxidation at a fairly low temperature of 500 °C, while the interlayered samples remain stable without significant oxidation up to 800 °C. The Mo interlayer is found to move toward the surface region, when annealed at temperatures in excess of 450 °C. It is shown that the addition of the Mo interlayer effectively improves the thermal stability of the Ni-silicided Si0.8Ge0.2 layers.
Compositional analysis of graded AlxGa(1−x)As layers by x-ray energy dispersive spectrometry
Authors: Mahalingam K. , Wheeler R. , Taferner W. T. , Eyink K. G. , Fenstermaker S. T. , Solomon J. S.
Published: July 2004

In this study we employ the x-ray energy dispersive spectrometry technique to characterize AlxGa(1−x)As layers with sinusoidal grading in the Al content, using a field emission gun transmission electron microscope. The Al/Ga composition profiles were determined based on the Cliff–Lorimer (CL) equations, assuming the thin-foil criterion. The sensitivity factors in the CL equations (kAl–As, kGa–As, and kAl–Ga) required for calculating the composition profiles were determined from precalibrated AlxGa(1−x)As layers. An alternate procedure, wherein the Ga composition is calculated using only kGa–As determined from GaAs, was also investigated. The results from this approach were in good agreement with those obtained based on sensitivity factors determined from the precalibration layers. The measured As profile indicates that the composition of AlxGa(1−x)As can be measured to an accuracy of ∼±0.02 in x.
Analytical model for electron field emission from capped carbon nanotubes
Authors: Filip V. , Nicolaescu D. , Tanemura M. , Okuyama F.
Published: July 2004

This article presents a model of electron field emission from quantum states arising from the tight confinement of quasi-free electrons on a nanotube hemispherical cap. The model outlines the possibility of inhomogeneous electron field emission for very thin carbon nanotubes at high emission levels and the appearance of peculiar ring-shaped field emission images. The conclusions qualitatively agree with existing experimental evidence, therefore supporting the hypothesis that part of the electrons on the cap of the emitter may behave as quasi-free in a high emission level/high-temperature regime.
Zirconium nitride/silver nanocomposite structures for biomedical applications
Authors: Aouadi S. M. , Debessai M. , Filip P.
Published: July 2004

Silver zirconium nitride films deposited by unbalanced magnetron sputtering were studied by means of x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, spectroscopic ellipsometry, and nanoindentation. Coatings were deposited on silicon substrates at room temperatures with bias voltages in the −45 to −160 V range. The concentration of zirconium and silver was regulated by controlling the power to the sputtering guns. The nitrogen concentration was selected so that the nitrogen flow rate corresponded to the production of stoichiometric zirconium nitride. The films consisted of nanocrystals of zirconium nitride embedded in a silver matrix. The grain size was deduced from the width of the XRD peaks using the Scherrer formula and was found to decrease with the addition of silver. The chemical and phase composition was determined from XPS measurements. The optical constants were measured using spectroscopic ellipsometry. A correlation between film structure/composition and optical constants was established. The mechanical properties of the coatings were evaluated using nanohardness testing and were found to depend on composition and deposition parameters. Optimum mechanical properties were achieved for a silver content of 6% and a substrate bias of −160 V.
Characterization of a-Si:H resists for a vacuum-compatible photolithography process
Authors: Jacobs R. N. , Stoltz A. J. , Dinan J. H. , Salamanca-Riba L.
Published: July 2004

We report the characterization of amorphous hydrogenated silicon (a-Si:H) films for use as a dry photoresist, in a vacuum-compatible photolithography process. a-Si:H films are deposited, patterned via excimer laser exposure, and developed in a hydrogen plasma. Experiments on the effects of exposure environment and laser pulse energy density were carried out to determine the optimum conditions for the technique. Transmission electron microscopy (TEM) shows the excimer-exposed a-Si:H surfaces to be polycrystalline in nature. The polycrystalline surfaces serve very well as an etching mask during plasma development, exhibiting etch selectivities over 600:1. Preliminary methods for reducing undesirable surface roughness at the exposed surfaces are also discussed.
Effect of carbon doping on buffer leakage in AlGaN/GaN high electron mobility transistors
Authors: Poblenz C. , Waltereit P. , Rajan S. , Heikman S. , Mishra U. K. , Speck J. S.
Published: July 2004

Carbon doping via CBr4 in AlGaN/GaN high electron mobility transistors grown by rf-plasma-assisted molecular beam epitaxy on 4H–SiC (0001) was investigated as a means to reduce buffer leakage. For carbon doping in the first 400 nm of the structure, a significant decrease in buffer leakage was observed with increasing overall carbon concentration. A carbon doping scheme in which the level of doping is tapered from 6×1017 cm−3 down to 2×1017 cm−3 was found to result in sufficiently low drain-source leakage currents. The effect of thickness of the GaN:C layer was explored as well as the effect of thickness of the subsequent unintentionally doped GaN layer. For structures with reduced leakage, rf I–V and power measurements revealed better performance in structures in which the two-dimensional electron gas was spaced at a large distance from the GaN:C layer. Possible sources and locations of unintentional free carriers contributing to leakage in these structures are discussed in light of the results.
Positron annihilation study of vacancies in GaInNAs
Authors: Ptak A. J. , Kurtz Sarah , Weber M. H. , Lynn K. G.
Published: July 2004

GaInNAs is potentially useful in a wide variety of devices, including next-generation, high efficiency, multijunction solar cells. Unfortunately, a number of defects exist in this material that limit the overall device performance. Beam-based positron annihilation spectroscopy was used to examine vacancies in GaInNAs grown by both metal-organic chemical vapor deposition (MOCVD) and molecular-beam epitaxy (MBE). A significant concentration of vacancies exists only when hydrogen and nitrogen are both present during growth. This finding supports the theoretical prediction that gallium vacancies occur in complexes with nitrogen and hydrogen. Growing GaInNAs by solid-source MBE, a hydrogen-free growth method, minimizes the formation of the vacancy complexes. Because this complex is an acceptor, it may be a cause of the high background acceptor concentrations in MOCVD-grown GaInNAs.
Photomask Cr–MoSi etching
Authors: Wu Banqiu
Published: July 2004

Studies on photomask Cr and MoSi etch processes were carried out and etch kinetics and modeling were performed. The photomasks were etched using two different etch tools and metrology to support theoretical suppositions and process characterization was performed using profilometry and critical dimension (CD) scanning electron microscopy. A 50 keV electron-beam writing system employing positive chemically amplified resist was used for pattern creation. Loading-etch rate equations were theoretically proposed and experimentally tested. It was found that the calculated Cr and MoSi etch rates agreed well with experimental results. Local etch rates versus local loading on one photomask were studied and kinetic equations were proposed showing excellent agreement with experimental results. Cr and MoSi etch CD movements versus local load on one photomask were also investigated. It was found that load effects on Cr and MoSi etch CD movements could be controlled in opposite directions leading to a compensation strategy proposal for MoSi optimization, instead of using a point-to-point 3σ as the optimization parameter (objective function). By using this compensation method, the final MoSi CD uniformity of 100–110 nm technology node photomasks (∼30% load) was in the range of 8.5–10.1 nm (3σ). This final CD uniformity was obtained on both of the photomask etch tools tested.
Characterization of electroplated copper films for three-dimensional advanced packaging
Authors: Seah C. H. , You G. Z. , Li C. Y. , Kumar R.
Published: July 2004

A study was carried out to determine the feasibility of using the Cu electroplating process to achieve good gap fill in interchip-via (ICV) wafers, focusing on the effect different current wave forms have on electroplated Cu film properties, the gap fill capability and the chemical mechanical planarization process. It was found that the roughness of direct current (dc)-plated Cu films is at least three times lower than that of pulse-plated films and the roughness of the latter was observed to be strongly dependent on the magnitude of forward (If) and reverse (Ir) currents. This produced a significant difference in reflectivity between the two types of films. The as-deposited dc- and pulse-plated Cu films were also found to have specific resistivities of ∼2.2 and ∼2.1 μΩ cm, respectively. They were reduced to a similar value of 1.77 μΩ cm after annealing at 200 °C. All the dc and higher If pulse-plating processes produced Cu films having an average polish rate of 7000 Å/min with the polish rate U% less than 3%, showing a fluctuating profile across the wafer. The higher Ir pulse-plated film showed a very low polish rate of 210 Å/min with the polish rate U% at 58%, resulting in a dome profile. The multistep dc plating process was found unsuitable for the filling of large vias in the ICV wafers as it resulted in conformal plating with a large center seam being seen due to the pinch-off effect at the top of the via. The pulse-plating process showed a significant improvement in the gap fill capability with a reduction in the size of the center void. The pinch-off effect was also greatly reduced when higher Ir was used and an increase in bottom coverage could also be seen, resulting in acceptable gap fill with only a small center void in the ICV wafers.
Influence of N2 background pressure on the incorporation of arsenic during molecular beam epitaxy growth of GaAs
Authors: Dieing T. , Usher B. F.
Published: July 2004

The influence of a high N2 background pressure on the molecular beam epitaxy growth of GaAs has been investigated. Measurements to determine the minimum As4 pressure necessary to maintain stoichiometric growth at different substrate temperatures with and without a high N2 background pressure were performed. The As4 pressures required for cases when a high N2 background was present were systematically above those required without a N2 background. The GaAs growth process has been modeled using kinetic rate equations and by including surface site blocking terms the model accounts for the data taken by the authors. The model also agrees well with GaAs growth kinetic data published by several other authors.
InSAR Observations of Low Slip Rates on the Major Faults of Western Tibet
Authors: Wright Tim J. , Parsons Barry , England Philip C. , Fielding Eric J.
Published: July 2004

Two contrasting views of the active deformation of Asia dominate the debate about how continents deform: (i) The deformation is primarily localized on major faults separating crustal blocks or (ii) deformation is distributed throughout the continental lithosphere. In the first model, western Tibet is being extruded eastward between the major faults bounding the region. Surface displacement measurements across the western Tibetan plateau using satellite radar interferometry (InSAR) indicate that slip rates on the Karakoram and Altyn Tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in Tibet.
The Radical Site in Chlamydial Ribonucleotide Reductase Defines a New R2 Subclass
Authors: Högbom Martin , Stenmark Pål , Voevodskaya Nina , McClarty Grant , Gräslund Astrid , Nordlund Pär
Published: July 2004

Ribonucleotide reductase (RNR) synthesizes the deoxyribonucleotides for DNA synthesis. The R2 protein of normal class I ribonucleotide reductases contains a diiron site that produces a stable tyrosyl free radical, essential for enzymatic activity. Structural and electron paramagnetic resonance studies of R2 from
Chlamydia trachomatis
reveal a protein lacking a tyrosyl radical site. Instead, the protein yields an iron-coupled radical upon reconstitution. The coordinating structure of the diiron site is similar to that of diiron oxidases/monoxygenases and supports a role for this radical in the RNR mechanism. The specific ligand pattern in the
C. trachomatis
R2 metal site characterizes a new group of R2 proteins that so far has been found in eight organisms, three of which are human pathogens.
Fangs, Venom, and Fear Unraveled
Authors: Vitt Laurie J.
Published: July 2004

The Venomous Reptiles of the Western Hemisphere
. by Jonathan A. Campbell and William W. Lamar. Comstock (Cornell University Press), Ithaca, NY, 2004. 2 vols. 962 pp. $149.95, £86.95. ISBN 0-8014-4141-2.

This profusely illustrated, comprehensive survey of venomous snakes and lizards of the Americas also includes overviews of mimicry, evolution, and the medical management of snakebites.
Cancer Immunotherapy: A Treatment for the Masses
Authors: Blattman Joseph N. , Greenberg Philip D.
Published: July 2004

Cancer immunotherapy attempts to harness the exquisite power and specificity of the immune system for the treatment of malignancy. Although cancer cells are less immunogenic than pathogens, the immune system is clearly capable of recognizing and eliminating tumor cells. However, tumors frequently interfere with the development and function of immune responses. Thus, the challenge for immunotherapy is to use advances in cellular and molecular immunology to develop strategies that effectively and safely augment antitumor responses.
Therapeutic Vaccines for Chronic Infections
Authors: Autran Brigitte , Carcelain Guislaine , Combadiere Béhazine , Debre Patrice
Published: July 2004

Therapeutic vaccines aim to prevent severe complications of a chronic infection by reinforcing host defenses when some immune control, albeit insufficient, can already be demonstrated and when a conventional antimicrobial therapy either is not available or has limited efficacy. We focus on the rationale and challenges behind this still controversial strategy and provide examples from three major chronic infectious diseases— human immunodeficiency virus, hepatitis B virus, and human papillomavirus—for which the efficacy of therapeutic vaccines is currently being evaluated.
Reduction of Influenza Virus Titer and Protection against Influenza Virus Infection in Infant Mice FedLactobacillus caseiShirota
Authors: Yasui Hisako , Kiyoshima Junko , Hori Tetsuji
Published: July 2004

We investigated whether oral administration ofLactobacillus caseistrain Shirota to neonatal and infant mice ameliorates influenza virus (IFV) infection in the upper respiratory tract and protects against influenza infection. In a model of upper respiratory IFV infection, the titer of virus in the nasal washings of infant mice administeredL. caseiShirota (L. caseiShirota group) was significantly (P< 0.05) lower than that in infant mice administered saline (control group) (102.48± 100.31and 102.78± 100.4, respectively). Further, the survival rate of theL. caseiShirota group was significantly (P< 0.05) higher than that of the control group (14.3 versus 40.0%). One day after infection, pulmonary NK cell activity and interleukin-12 production by mediastinal lymph node cells of mice in theL. caseiShirota group were significantly greater than those of mice in the control group. These findings suggest that oral administration ofL. caseiShirota activates the immature immune system of neonatal and infant mice and protects against IFV infection. Therefore, oral administration ofL. caseiShirota may accelerate the innate immune response of the respiratory tract and protect against various respiratory infections in neonates, infants, and children, a high risk group for viral and bacterial infections.
Evaluation and Validation of an Enzyme-Linked Immunosorbent Assay and an Immunochromatographic Test for Serological Diagnosis of Severe Acute Respiratory Syndrome
Authors: Guan Ming , Chan Kwok Hung , Peiris J. S. Malik , Kwan See Wai , Lam Siu Yan , Pang Chiu Mei , Chu Ka Wing , Chan Kit Man , Chen Hsiao Ying , Phuah Ewe Beng , Wong Caiqin Jane
Published: July 2004

A newly developed severe acute respiratory syndrome (SARS)-specific enzyme-linked immunosorbent assay (ELISA) was further validated to confirm cutoff values and evaluate its diagnostic performance with clinical samples. In parallel, an immunochromatographic test was also evaluated. A total of 227 clinical serum specimens collected from SARS patients were used in the study, together with 385 samples from healthy donors. By use of an immunofluorescent (IF) test as the “gold standard, ” both the ELISA and the immunochromatographic test were able to detect immunoglobulin G antibodies to SARS not only from late-convalescent-stage samples (>21 days from the onset of clinical symptoms), as previously established, but also from early-acute-phase samples (1 to 10 days from onset). The ELISA, using an optical density (OD) of 0.25 as its cutoff value, produced the best sensitivity while maintaining high specificity. It detected SARS-specific antibodies in 58, 70, 75, and 95%, respectively, of the four groups of samples collected from patients 1 to 10 days, 11 to 20 days, 21 to 30 days, and more than 30 days after the onset of clinical symptoms. Similarly, the immunochromatographic test detected SARS-specific antibodies in 55, 68, 81, and 79% of the four groups, respectively. The overall specificities for the ELISA and the rapid test were 99.5 and 97.7%, respectively. Although the positive correlation observed between the ELISA OD values and the IF titers was moderate (r= 0.6915;P< 0.001), the detection rates of both the ELISA and the rapid test were found well in agreement with the IF titers.
Recombinant GRA4 or ROP2 Protein Combined with Alum or thegra4Gene Provides Partial Protection in Chronic Murine Models of Toxoplasmosis
Authors: Martin Valentina , Supanitsky Alicia , Echeverria Pablo C. , Litwin Silvana , Tanos Tamara , De Roodt Adolfo R. , Guarnera Eduardo A. , Angel Sergio O.
Published: July 2004

The efficacy of vaccination withToxoplasma gondiirecombinant GRA4 (rGRA4) and ROP2 (rRPO2) proteins and a mix of both combined with alum were evaluated in C57BL/6 and C3H mice. In C57BL/6 mice, rGRA4 and rGRA4-rROP2 immunizations generated similar levels of immunoglobulin G1 (IgG1) and IgG2a isotypes against GRA4, whereas immunizations with rROP2 and the mix induced a predominant IgG1 production against ROP2. All groups of C3H vaccinated mice exhibited higher levels of IgG1 than IgG2a. rGRA4-stimulated splenocytes from vaccinated mice produced primarily gamma interferon while those stimulated with rROP2 produced interleukin-4. Challenge of rGRA4- or rGRA4-rROP2-vaccinated mice from both strains with ME49 cysts resulted in fewer brain cysts than the controls, whereas vaccination with rROP2 alone only conferred protection to C3H mice. Immunization with a plasmid carrying the entire open reading frame of GRA4 showed a protective level similar to that of rGRA4 combined with alum. These results suggest that GRA4 can be a good candidate for a multiantigen anti-T. gondiivaccine based on the use of alum as an adjuvant.
Comparison of Immunofluorescence, Western Blotting, and Cross-Adsorption Assays for Diagnosis of African Tick Bite Fever
Authors: Jensenius Mogens , Fournier Pierre-Edouard , Vene Sirkka , Ringertz Signe Holta , Myrvang Bjørn , Raoult Didier
Published: July 2004

In testing paired serum samples from 40 consecutive cases of African tick bite fever, we detected diagnostic antibodies against spotted fever group rickettsiae in 45% of the patients by immunofluorescence assay (IFA) and in 100% of the patients by Western blotting (WB) (
P
< 0.01). A specific diagnosis of
Rickettsia africae
infection could be established in 15% of the patients by IFA and in 73% of the patients by a combination of WB and cross-adsorption assays (
P
< 0.01).
Kinetics of Severe Acute Respiratory Syndrome (SARS) Coronavirus-Specific Antibodies in 271 Laboratory-Confirmed Cases of SARS
Authors: He Zhongping , Dong Qingming , Zhuang Hui , Song Shujing , Peng Guoai , Luo Guangxiang , Dwyer Dominic E.
Published: July 2004

The sensitivities and specificities of an immunofluorescence assay and an enzyme immunoassay for detection of antibodies specific for severe acute respiratory syndrome coronavirus (SARS-CoV) were compared for 148 laboratory-confirmed SARS cases. The appearance and persistence of SARS-CoV-specific antibodies were assessed, with immunoglobulin G detected in 59% of samples collected within 14 days and persisting for 60 to 95 days after the onset of illness.
Identification and Phenotyping of Leukocytes in Bovine Bronchoalveolar Lavage Fluid
Authors: Soethout E. C. , Müller K. E. , van den Belt A. J. M. , Rutten V. P. M. G.
Published: July 2004

A method is proposed to identify leukocyte subpopulations in bovine bronchoalveolar lavage fluid by dual-laser flow cytometry. The technique uses several parameters, i.e., exclusion of highly autofluorescent alveolar macrophages and inclusion of leukocytes on the basis of labeling by specific antibodies and light scatter characteristics.
Evaluation of a Monoclonal Antibody-Based Test for Detection of
Helicobacter pylori
-Specific Antigen in Stool Samples from Mice
Authors: Crone Julia , Symonds Erin , Campbell Fiona , Butler Ross
Published: July 2004

A test using monoclonal antibodies for detection of antigen in stool samples was compared with culture and histology for noninfected (
n
= 25),
Helicobacter pylori
-infected (
n
= 25), and
Helicobacter felis
-infected (
n
= 6) mice. Sensitivity and specificity were 96%. The monoclonal antibody-based test is therefore a noninvasive technique that is able to diagnose
H. pylori
infection in mice.
Clinical Evaluation of a Chemiluminescence Immunoassay for Determination of Immunoglobulin G Avidity to Human Cytomegalovirus
Authors: Revello Maria Grazia , Gorini Giovanna , Gerna Giuseppe
Published: July 2004

Clinical evaluation of a novel fully automated chemiluminescence immunoassay for determination of immunoglobulin G avidity to human cytomegalovirus (HCMV) showed 92.8% sensitivity and 84.7% specificity in detecting a recent (≤90 days) primary HCMV infection. The assay appears useful for accurately diagnosing recent primary HCMV infections.