bluuebunny/crossref_metadata_2025 huggingface dataset:
Survival, development and life tables of two congeneric ladybirds in aphidophagous guilds
Authors: GUPTA AVANISH K. , SRIVASTAVA SHEFALI , MISHRA GEETANJALI , SINGH KALPANA , OMKAR
Published: April 2006

Abstract
Two congeneric aphidophagous ladybirds, Coccinella septempunctata and Coccinella transversalis, were reared on three aphid species, Lipaphis erysimi, Myzus persicae and Aphis nerii, to estimate the effect of prey quality and intra‐ and interspecific interactions on their survival and development of life stages. Mortality of first instar ladybirds of both species was highest feeding on A. nerii. Preimaginal mortality was lowest when feeding on L. erysimi (C. septempunctata, 1.6% and C. transversalis, 3.2%), and highest when feeding on A. nerii (C. septempunctata, 6.2% and C. transversalis, 8.2%). Comparatively higher weight and larger size of C. septempunctata along with the lower levels of mortality recorded suggested that it is more likely to have acted as an intraguild predator than C. transversalis. High recorded mortality of C. transversalis is attributed to probable intraguild predation on account of its smaller size. The major sources of mortality were probably cannibalism, intraguild predation and other unknown factors. Lower prey quality increased the incidence of cannibalism and intraguild predation, especially in C. transversalis. The investigation suggests an intrinsic competitive advantage for C. septempunctata over C. transversalis in guilds of three aphid species.
Distribution of ground‐dwelling beetles (Coleoptera) across a forest‐clearcut ecotone in Wolong Natural Reserve, southwestern China
Authors: YU XIAO‐DONG , LUO TIAN‐HONG , YANG JIAN , ZHOU HONG‐ZHANG
Published: April 2006

Abstract
The influence of edge effect on ground‐dwelling beetles (Coleoptera) across a forest‐clearcut ecotone was studied in Wolong Natural Reserve, southwestern China. During the field research, a total of 30 739 beetles were collected with pitfall traps along transects, which extending 100 m from the edge into the forest interior and 100 m into the clearcut. Of the collection, Carabidae comprised 92%, Staphylinidae 3%, Curculionidae 2%, and Tenebrionidae 2%, and these four families can be considered as abundant groups. Family richness, Shannon diversity and equitability display a significant decrease from forest interior, edge to clearcut. Based on the family composition and abundance, ground‐dwelling beetles of the forest interior can be separated from those in the clearcut by Principal coordinate analysis ordination, and beetle assemblages in the forest edge were more similar to forest assemblages than to those found in the clearcut by cluster analysis. Seasonal dynamics of family richness showed a monotone peak in the middle season, with a highest value in the forest interior and a lowest value in the clearcut. Family abundance showed two peaks in the middle season, always with more individuals in the clearcut than in the forest interior or in the edge. Multiple linear regression analyses showed that the cover of shrub and litter were the two most important factors in determining family richness, Shannon diversity, equitability and abundance. Our results show that the forest edge and clearcut have obviously different composition and diversity of ground‐dwelling beetles from forest interior at the family level. However, more edges have been formed due to increasing forest fragmentation (clearcutting or logging), so it is necessary to preserve large and intact forest to protect the diversity of ground‐dwelling beetles in Wolong Natural Reserve.
Venom gland of the ichneumonid Diadromus collaris: morphology, ultrastructure and age‐related changes
Authors: LI WEI‐DI , YU RUI‐XIAN , CHEN XUE‐XIN , HE JUN‐HUA
Published: April 2006

Abstract
Females of the solitary parasitoid Diadromus collaris (Insecta: Hymenoptera: Ichneumonidae) lay eggs in the pupae of Plutella xylostella (Lepidoptera: Plutellidae), and the venom is synchronously injected into hosts. The venom apparatus consists of two glandular tubules terminating in a common reservoir. A ductule connects the reservoir with the sting apparatus, by which the reservoir content enters the latter. Secretory units line the two glandular tubules. All secretory cells belong to dermal gland type III. Dermal gland cells in glandular tubules are more abundant and developed than those in the reservoir. There are extensive rough endoplasmic reticulum and electrondense vesicles, and the microvilli are well developed. By the cuticle‐lined central funnel secretion products of secretory units reach the reservoir. Moreover, the secretory apparatus undergoes age‐related changes. The secretory units in the venom gland are better developed and more vigorous 7 days after eclosion than those 1 day after eclosion; autolytic processes occur 15 days after eclosion, and the tissue of the reservoir is more prostrate 15 day after eclosion than those 1 day after eclosion. The ovipostion peak of this parasitoid, about 3–7 days after eclosion, corresponds with the period when the venom gland is highly developed in the life span of the wasp.
Morphological structure and optical properties of the wings of Morphidae
Authors: BERTHIER SERGE , CHARRON ERIC , BOULENGUEZ JULIE
Published: April 2006

Abstract
The morphological structure and optical properties of the wings of 14 species of Morphidae have been investigated. Most of the scales of the iridescent species of Morphidae (Lepidoptera) present a very particular structure. The ground scales, responsible for the major part of the optical properties, are covered by a very regular set of longitudinal ridges. The ridges themselves are constituted by a superposition of lamellae that act locally as a multilayered structure. This very specific morphology leads to both interferences and diffraction effects. The first one is responsible of the brilliant blue coloration of the males, while the second one diffracts this colored light at a very large angle. These two phenomena give to the butterfly a very effective long‐range communication system. The morphological characteristics of the scales of the various species are presented in detail.

Two types of optical measurement were performed on the iridescent wings of 14 different species of Morphidae: spectroscopic measurements under various incidences and gonioscopic measurements for a given incidence angle and wavelength. The first allows a determination of the index of refraction of the cuticular material. The second leads to the drawing of spatial diffraction maps. It shows that most of the reflected light is diffracted laterally over a very large angle (90° < θ < 120°, according to the different species) and that this repartition depends of the polarization of incident light. As predicted by previous calculations, the dissymmetric structure of the ridge is responsible for the separation of the polarization modes in the various diffraction orders.
RHEOLOGICAL PROPERTIES OF CHEMICALLY MODIFIED RICE STARCH MODEL SOLUTIONS
Authors: RAINA C.S. , SINGH S. , BAWA A.S. , SAXENA D.C.
Published: April 2006

Native rice starches have poor resistance to shear, and fair stability to retrogradation with soft texture, which can be altered through chemical modifications. Starch from broken pieces of rice of three rice cultivars (PUSA‐44, PR‐106 and PR‐114) was chemically modified by etherification and esterification reactions by different combinations of modification reagents to investigate the effect of modification on the rheological properties of rice starches. The modification resulted in shear stable gel with apparent pseudoplastic characteristics. The viscosity of starches increased upon acetylation and dual modification as a result of increase in solubility. However, cross‐linking had shown the reverse effect. The flow behavior index (n) and consistency coefficient (k) were significantly (P ≤ 0.05) improved upon modification in acetylated and dual‐modified starches. The effect of modification on the rheological properties was observed in similar pattern in all the three rice cultivars but varied significantly in variety PUSA‐44 may be because of its relatively higher amylose content.
EXPERIMENTAL DETERMINATION OF MASS TRANSFER COEFFICIENT: MOISTURE CONTENT AND HUMIDITY RATIO DRIVING FORCE APPROACHES DURING BAKING
Authors: DEMIRKOL EREN , ERDOGDU FERRUH , PALAZOGLU T. KORAY
Published: April 2006

Moisture distribution in baked products at the end of baking is important because it directly affects the product's quality. In fact, nonhomogeneous moisture distribution may result in quality defects such as cracking, checking etc. Diffusion inside and convective mass transfer outside the product are important factors affecting the quality. Therefore, accurate values of mass transfer parameters should be known for optimization of the baking process to obtain a product of higher quality. For this objective, infinite mass transfer and constant diffusion coefficient simplifying approximations have been applied in the literature numerous times to develop mass transfer models. However, the infinite mass transfer coefficient approximation may not hold true, especially under natural convection conditions. To evaluate the mass transfer coefficient, baking experiments were carried out to obtain the moisture content changes of cookies during baking at 190, 200 and 210C under natural and forced convection conditions. Then, mass transfer coefficient was determined using the moisture content difference and the humidity ratio difference as the driving force for mass transfer. The results of these two approaches were compared, and the use of humidity ratio difference seemed to be a better approach in terms of reflecting actual process conditions because it is based on the surface changes.
Investigation of fabrication uniformity and emission reliability of silicon field emitters for use in space
Authors: Wang L. , Aplin K. L. , Huq S. E. , Kent B. J. , Stevens R. , Malik A. , Blom H. O. , Loader I. M. , Thomas G. R.
Published: April 2006

A silicon field emitter neutralizer is under development at the Rutherford Appleton Laboratory for the LISA Pathfinder mission [B.J. Kent et al., Class Quantum Grav. 22, S483 (2005)]. A summary of this project from the fabrication point of view is presented in this article. An investigation of the effect of fabrication uniformity on emission characteristics showed that the geometrical nonuniformity, including tip height and gate diameter, across a 4-in. wafer is below 15%. This variation had only a small effect (∼10%) on the field-emission characteristics. In order to improve the reliability of the silicon field emitters for the space environment operation, a thin aluminum nitride (AlN) film is coated on the silicon emitters, and the chromium gate electrode is oxidized in furnace. The effects of adding the layer of AlN and thermal oxidation of the chromium gate electrode on field emission and lifetime were investigated in this article. A fabrication yield analysis estimated that 50% of arrays on the original wafer functioned correctly in the final device, but that this can be substantially improved by a more rigorous device handling control.
Electron field-emission properties of Ag–SiO2 nanocomposite layers
Authors: Tsang W. M. , Stolojan V. , Giusca C. , Poa C. H. P. , Sealy B. , Silva S. R. P. , Wong S. P.
Published: April 2006

In this work, Ag–SiO2 nanocomposite layers were synthesized by introducing Ag nanoclusters into thermally oxidized SiO2 layers, using ion implantation. The field-emission (FE) properties of these layers were studied and correlated with the results from atomic force microscopy and transmission electron microscopy measurements. These nanocomposites exhibit good FE properties and give an emission current of 1nA at electric fields as low as 13V∕μm, for a dose of 5×1016Ag+∕cm2, compared with 204V∕μm for “bare” SiO2 layers. It is clearly demonstrated that the good FE properties of these nanocomposites are attributed to two types of local-field enhancement: one due to the surface morphology and the other due to electrical inhomogeneity. The isolated conductive Ag nanoclusters embedded in the electrically insulating SiO2 matrix provide a field enhancement due to the electrical inhomogeneity effect. Moreover, the implanted Ag ions diffuse to the surface, during the implantation process, and create dense surface-protrusion structure which provides a geometric local-field enhancement. The local-field-enhancement mechanisms in these samples are critically dependent on the implantation dose of Ag.
Electrical conductivity of high aspect ratio trenches in chemical-vapor deposition W technology
Authors: Ivanov Ivan P. , Sen Indradeep , Keswick Peter
Published: April 2006

This article discusses the resistivity scaling challenges associated with the use of high aspect ratio trenches as W interconnects for the sub-130-nm semiconductor technology node. In this work, chemical-vapor deposition of W is employed to manufacture conductive trenches in a deposition sequence that includes a TiN barrier, a nucleation W, and a bulk W film. Composition, microstructure, resistivity, grain size, and surface roughness for these films are determined in the low thickness range. The results are used to examine the contribution of the electron-surface scattering and grain-boundary scattering to the overall increase in the electrical resistivity observed at film thickness comparable to the electron mean free path. Calculated and measured values for the film resistivity are matched by using a variable coefficient of elastic electron scattering at the grain boundaries. In first approximation, grain-boundary electron scattering is found to be the dominant mechanism and is almost entirely responsible for the resistivity increase in the thickness range studied. By using resistivity data obtained for each film and Kirchhoff’s rule for laminate structures, a simple physical model is used to predict the variation of the trench resistance as a function of geometrical factors such as film thickness and core (seam) size. The agreement between the calculated and measured trench resistances is surprisingly good in view of the several simplification assumptions that are made and that no fitting parameters are used. The proposed model predicts reasonably well the sensitivity of the trench resistance with respect to the TiN film thickness. However, the impact of the nucleation W layer is overestimated, which suggests possible unaccounted interactions, related to structural or morphological changes in the bulk W. It is concluded that the trench conductivity is already significantly size limited for critical dimensions in the sub-130-nm range. The control of the film bulk resistivity and grain-boundary engineering of the conducting materials is therefore identified as the most important pathway for achieving desired electrical properties in conducting trenches filled by standard chemical-vapor deposition W technology.
Formation of body-centered-cubic tantalum via sputtering on low-κ dielectrics at low temperatures
Authors: Senkevich Jay J. , Karabacak Tansel , Bae Dae-Lok , Cale Timothy S.
Published: April 2006

Sputtered Ta films (60 nm) were deposited at room temperature onto selected substrates, including silicon, SiO2, porous methyl silsesquioxane (porous MSQ), parylene-N (Pa-N) caulked porous MSQ, benzocyclobutene (BCB), and SiLK layers. It was observed that the Ta structure after deposition mainly depends on the underlayer surface chemistry. β-Ta with a resistivity of ∼130–160μΩcm and an average grain size of ∼20nm was observed after sputter depositing 60-nm-thick Ta films onto the oxygen-rich materials of native oxide of Si, SiO2, and porous MSQ. α-Ta with a much lower resistivity (∼35μΩcm) and an average grain size of ∼16nm was observed after sputter deposition of Ta onto a substrate with a 4-nm-thick hydrocarbon Pa-N film on porous MSQ. α-Ta was also formed when sputter depositing on the hydrocarbon BCB and SiLK low-κ dielectrics. The lattice constants of the α-Ta films were slightly larger (3.310–3.351 Å) than those of the bulk Ta (3.305 Å).
High-resolution three-dimensional reconstruction: A combined scanning electron microscope and focused ion-beam approach
Authors: Bansal R. K. , Kubis A. , Hull R. , Fitz-Gerald J. M.
Published: April 2006

The ability to obtain three-dimensional information has always been important to gain insight and understanding into material systems. Three-dimensional reconstruction often reveals information about the morphology and composition of a system that can otherwise be obscured or misinterpreted by two-dimensional images. In this article, we describe tomographic measurements with 10nm scale resolution, combining focused ion-beam processing with field-emission scanning electron microscopy to obtain a series of high-resolution two-dimensional cross-sectional images. The images were then concatenated in a computer and interpolated into three-dimensional space to assess and visualize the structure of the material. The results of this research demonstrate the use of tomographic reconstruction of Si–Si∕Ge and θ′ Al2Cu samples to reproduce the three-dimensional morphology with sub-10nm resolution.
ZrO
2
gate dielectrics produced by ultraviolet ozone oxidation for GaN and AlGaN∕GaN transistors
Authors: Dora Yuvaraj , Han Sooyeon , Klenov Dmitri , Hansen Peter J. , No Kwang-soo , Mishra Umesh K. , Stemmer Susanne , Speck James S.
Published: April 2006

We investigated the suitability of ZrO2 as a high-k dielectric for GaN material systems. Thin Zr films (4nm) were deposited by electron-beam evaporation at room temperature on n-type GaN and Al0.22Ga0.78N(29nm)∕GaN high electron mobility transistor (HEMT) structures. The Zr-coated samples were subsequently oxidized at temperatures in the range of 200–400 °C in an ozone environment. Atomic force microscopy studies after oxidation show that the ZrO2 forms a conformal layer on the underlying GaN template. Cross-section transmission electron microscopy studies showed little intermixing of the ZrO2 with the AlGaN∕GaN. The relative dielectric constant of the ZrO2 was determined to be 23. In comparison with HEMTs with bare gates (no dielectric between the gate metal and AlGaN), the HEMTs with ZrO2 showed two to three order of magnitude reduction in gate leakage current. Optimization of the HEMT process on sapphire substrates with ZrO2 under the gates yielded devices with powers of 3.8W∕mm and 58% power-added efficiency at 4GHz.
Pattern formation by erosion sputtering on GaSb: Transition from dot to ripple formation and influence of impurities
Authors: Allmers T. , Donath M. , Rangelov G.
Published: April 2006

The transition from dot to ripple formation during erosion sputtering was studied as a function of the angle of incidence of the bombarding ions. For GaSb as target material we found that dot structures are obtained for angles smaller than ≈10° with respect to the surface normal. We also observed an influence of impurities on the pattern formation. Small amounts of impurities serve as nucleation centers for the formation of differently shaped nanostructures. In addition, larger fragments of GaSb on the surface influence the pattern formation qualitatively; the fragment is sputtered and the sputtered material redeposited in the vicinity assists the generation of ordered dot structures. With the use of low-energy electron diffraction, we looked at the crystallographic surface properties of the dots. Dots produced with a small fluence (3×1017cm−2) could be recrystallized by moderate annealing. Higher fluences, however, cause an irreversible amorphization.
Explicit expression on specifications of mask mean to target and mask uniformity
Authors: Lee Sung-Woo , Lee Doo-Youl , Woo Sang-Gyun , Cho Han-Ku
Published: April 2006

An analytic expression on the relationship of the mask mean to target (MTT) and the mask uniformity specifications is suggested. The MTT and uniformity (M-U) curve defines the boundary of the specification region, and this curve is explicitly expressed as mask error enhancement factors (MEEFs), dose sensitivities, and critical dimension (CD) tolerances of cell and peripheral patterns. This curve shows linear relationships between mask M-U. The decrease of the mask uniformity allows the increase of the mask MTT margin. M-U specifications are suggested for 63, 73, and 90nm design rules. In this experiment, the tolerance of the cell pattern is given as the product of the MEEF and the mask uniformity margin which is specified as 60% of the total CD variation at the given design rule, while that of the peripheral pattern is set to be 10% of the design rule. An isolated pattern is selected as a peripheral pattern because its pitch size is infinite. The mask MTT specification for 63nm is ±2.3nm at the mask uniformity of 2.23nm. For 73nm design rule, specifications of mask MTT are ±1.94 and ±1.48nm at the mask uniformities of 2.32 and 3.31nm at the process constants (k1’s) of 0.295 and 0.322, respectively. For 90nm design rule, the mask MTT specifications are ±3.89 and ±4.13nm at mask uniformities of 3.89 and 4.13nm for k1’s of 0.364 and 0.396, respectively.
Mechanism of solid-liquid-solid on the silicon oxide nanowire growth
Authors: Wang Chih-Yuan , Chan Lih-Hsiung , Xiao Da-Qing , Lin Tien-Chih , Shih Han C.
Published: April 2006

The solid-liquid-solid growth mechanism of synthesizing SiOx nanowires is expressed in detail through analyzing the structure and composition of the catalysts and the nanowires. The silicon source for growing nanowires was directly provided from the silicon wafer. A thin catalyst layer of platinum (∼5nm) was first deposited on the silicon wafer by sputtering. The platinum film collapsed into dots with diameter about hundreds of nanometers during the thermal process. These dots transformed into crystalline platinum silicide (Pt3Si) and served as nucleation seeds for the silicon oxide nanowire growth. Due to the high process temperature (∼1100°C) and long duration time (∼5h), the silicon wafer transformed into amorphous silicon oxides and melted into the Pt3Si catalyst dots until supersaturated to form SiOx nanowires. Such nanowires are amorphous and have an average diameter of about 40–60 nm and length of several hundreds of micrometers.
Effects of n-type modulation-doping barriers and a linear graded-composition GaInAsP intermediate layer on the 1.3μm AlGaInAs∕AlGaInAs strain-compensated multiple-quantum-well laser diodes
Authors: Lei Po-Hsun , Yang Chyi-Dar , Wu Ming-Yuan , Wu Meng-Chyi , Cheng K. Y. , Lin Chia-Chien , Ho Wen-Jeng
Published: April 2006

We report the fabrication, characterization, and comparison of four 1.3μm AlGaInAs∕AlGaInAs strain-compensated multiple-quantum-well (SC-MQW) laser structures: (1) sample A—with only an undoped SC-MQW active region, (2) sample B—with an undoped SC-MQW active region and a linear graded-composition (LGC) GaInAsP intermediate layer, (3) sample C—with an n-type modulation-doping (MD) SC-MQW active region, and (4) sample D—with an n-type MD-SC-MQW active region combined with a LGC GaInAsP intermediate layer. The inclusion of either n-type modulation-doped SC-MQW active region or LGC GaInAsP intermediate layer can improve the performance of a laser diode (LD). The LD sample D, which includes both an n-type MD-SC-MQW active region and a LGC GaInAsP intermediate layer, exhibits the best overall performance including a threshold current of 12.5mA, a characteristic temperature of 85K in 20–80°C temperature range, a lasing wavelength shift of 0.38nm∕K, and a relaxation frequency response of 9.9GHz.
Improvement of emission characteristics uniformity of carbon nanotube field emission display by surface treatment
Authors: Shiroishi Tetsuya , Hosono Akihiko , Sono Atsuhiro , Nishimura Kunihiko , Suzuki Yousuke , Nakata Shuhei , Okuda Soichiro
Published: April 2006

Carbon nanotubes (CNTs) have been investigated as an emitter for field emission display (FED). In our FED fabrication process, the printed CNTs are raised by a laser irradiation for the purpose to improve the emission characteristics. Because the emitters have to be controlled in each pixel individually on FED, the uniformity of the emission characteristics is necessary. We could improve the emission characteristics uniformity successfully by two methods. In the first method, the distribution of CNT raisings was homogenized by the modification of the irradiation pattern that consisted of an array of small areas. The emission deviation was improved to approximately half by the method. In the second method, the impurities of CNT raisings were cleaned by post-laser-irradiation of which fluence was lower than that of first irradiation. The emission characteristics improved and the turn-on electric field reduced from 2.1 to 1.4V∕μm. The emission deviation also improved to approximately half.
Smith-Purcell radiation from ultraviolet to infrared using a Si field emitter
Authors: Neo Yoichro , Shimawaki Hidetaka , Matsumoto Takahiro , Mimura Hidenori
Published: April 2006

The first, second, third, and fourth harmonics of Smith-Purcell radiation in a broadband ranging from 330 nm in the ultraviolet range to 1350 nm in the near infrared range have been detected using a 416 nm pitch grating. We used a single tip Si field emitter as an electron source and the input power level was low such as beam currents of 20–200 nA and acceleration voltages of 25–34 kV. Emission peaks in the Smith-Purcell radiation blueshift with increasing the acceleration voltage and coincide with the theoretical ones.
Influence of nanocrystalline structure on work function of tungsten
Authors: Mulyukov R. R.
Published: April 2006

The field emission investigations of nanocrystalline (NC) tungsten have revealed the essential difference in energy distribution of field-emitted electrons from NC tungsten as compared to the coarse-grained one. The measurement by the electron beam retarding potential technique also showed the reduction in work function of NC tungsten. The revealed features are explained using two phase model for NC metal.
Variability in long-duration operation of silicon tip field emission devices
Authors: Aplin K. L. , Kent B. J. , Wang L. , Lockwood H. F. , Rouse J. , Stevens R.
Published: April 2006

Development of reliable field emission devices requires detailed characterization of variability over the device lifetime. Silicon tip manufacturing processes and test equipment limitations are theoretically predicted to cause ∼5% variability in field emission currents. Long-duration emission current measurements at both constant voltage and constant current, controlled with a software feedback loop, were made. Power spectra from the two operational modes were significantly different. The software feedback loop response was determined; it is expected to contribute ∼1% of the standard deviation in emission current when used to control emission by modulating the gate voltage. Convolution of constant voltage time series with the software feedback loop response reproduced the spectral characteristics of constant current time series, indicating that many of the differences between the two operating modes were caused by the operating mode itself rather than the field emitters tested. This has implications for the operating mode of the application for which the device is intended.
Low temperature, ion-enhanced, implanted photoresist removal
Authors: Kawaguchi Mark N. , Papanu James S. , Pavel Elizabeth G.
Published: April 2006

We investigate the synergistic effects of a remote rf oxygen plasma source operated simultaneously with rf bias at low temperature and find that the photoresist removal rates substantially exceed those observed with either plasma source alone. When applied to high dose ion-implanted photoresist, optical emission curves show a transition between the hydrogen-devoid crust, where oxygen radical consumption is reduced, and the underlying bulk photoresist, where oxygen radical consumption is substantial. Differences between the reactant and product optical emission traces are indicative of complex mechanisms during the crust removal, which are likely related to crust inhomogeneities observed from scanning electron microscopy (SEM) analysis. Crust removal times are as short as 13–16 s, crust removal rates are 1–1.3μm∕min or about half the removal rate of unimplanted photoresist, and crust density estimates are similar to the density of graphite. Because photoresist removal rates are comparable to conventional high temperature downstream ashers, a single step low temperature dual-mode plasma process is able to remove both the crust and bulk photoresist in less than 40 s.
Surface characterization of ion-enhanced implanted photoresist removal
Authors: Kawaguchi Mark N. , Papanu James S. , Su Bo , Castle Matthew , Al-Bayati Amir
Published: April 2006

We characterize the chemical constitutents of high dose implanted deep ultraviolet photoresist before and after dual-mode oxygen plasma processing, where a remote rf-plasma source is operated simultaneously with rf bias. Raman spectroscopy indicates that the organic composition of the crust comprises a mixture of sp2 graphite and sp3 diamondlike carbon structures. High dose ion implantation reduces the hydrogen content by about 50 at. % as measured by hydrogen forward scattering and explains the reduced optical emission signal intensity observed during crust removal. The crust thicknesses extracted from the secondary-ion-mass spectroscopy profile correspond well to prior scanning electron microscopy characterization [Kawaguchi et al., J. Vac. Sci. Technol. B (submitted)] and support the existence of a transitional layer between the hardened crust and the underlying photoresist. Angle-resolved x-ray photoelectron spectroscopy analysis of arsenic implanted photoresist shows that dual-mode plasma processing causes substantial oxidation deep into the bulk. This result contrasts with downstream plasma processing, which proceeds by a near-surface mechanism. In addition, surface arsenic levels increase by an order of magnitude, which suggests that ion bombardment does not significantly sputter the dopant.
Surface roughness of Ti:LiNbO3 etched by Ar∕C3F8 plasma and annealing effect
Authors: Yang W.-S. , Kim W. K. , Yoon D. H. , Lim J.-W. , Isshiki M. , Lee H.-Y.
Published: April 2006

We describe the reactive ion etching of Ti:LiNbO3 single crystal in gas mixtures containing C3F8 and Ar using neutral loop discharge plasma. The surface roughness of etched Ti:LiNbO3 surface under various gas mixture conditions was analyzed by using atomic force microscopy and scanning electron microscopy. The annealing effect of an etched ridge structure waveguides was also observed.
Effect of annealing temperature on structural and electrical properties of tantalum nitride thin film resistors deposited on SiO2∕Si substrates by dc sputtering technique
Authors: Cuong Nguyen Duy , Phuong Nguyen Mai , Kim Dong-Jin , Kang Byoung-Don , Kim Chang-Soo , Yoon Soon-Gil
Published: April 2006

Tantalum nitride thin films were deposited on SiO2 (600 nm)/Si substrates at 200 °C and a nitrogen/argon flow ratio of 3% by dc sputtering technique and then were annealed at various temperatures in vacuum and nitrogen ambients. For the films annealed in both vacuum and nitrogen ambients, the effect of annealing temperature on structural and electrical properties of the films was systematically investigated. Crystallinity of the films was significantly improved as annealing temperature increased. Temperature coefficient of resistance (TCR) of the films was varied from a negative value to a positive value with increasing annealing temperature in both vacuum and nitrogen ambients. The variation of TCR with annealing temperature in both vacuum and nitrogen ambients was due to the improved crystallinity rather than a nitrogen concentration in the films. Irrespective of annealing temperature, the films annealed at various temperatures do not exhibit the irreversibility of resistance.
Ultracompact electron-beam column
Authors: Kuo Huei Pei , Lam Sity , Sheng Xia , Birecki Henryk , Naberhuis Steve
Published: April 2006

An electron optical system with an array of columns was developed for an electron-beam addressable data storage device that has the form factor of Compact Flash and a capacity >10GB. The electron optical column occupies an area <2500μm2 and produces a focused beam with current <100nA and a diameter <40nm. An extended-area electron source that consists of an array of randomly distributed hemispherical-grain polysilicon nodules was developed. The field at the nodules is enhanced by a factor of 3–5 compared with metal-insulator-semiconductor structures with smooth cathodes. Electron emission consequently occurs predominantly at the nodules. A maximum current density of ∼20A∕cm2 was achieved with this electron source. The multiplicity of emission sites helps us to reduce significantly the emission current noise. An electron optical column to focus the emission from this extended source into a diameter <30nm was also developed. The column consists of a single main lens and an array of auxiliary nanolenses. The main lens has a diameter of ∼3μm. The distance between the main lens and the electron source is ∼3μm. Each electron emission nodule has a self-aligned extraction electrode and a nanolens whose diameters are ∼0.03–0.1μm. The nanolenses collimate the electron emission from the nodules. The main lens then focuses the collimated beams into a diameter of ∼30nm at an image distance of ∼3μm. Without the nanolenses, the main lens alone can only focus the beam into a diameter of ∼300nm.
Properties of a field emitter deduced from curvature of its Fowler-Nordheim plot
Authors: Edgcombe C. J. , de Jonge N.
Published: April 2006

Recent experimental results on a carefully cleaned carbon nanotube show that the slope of its Fowler-Nordheim (FN) plot is not constant but increases slightly in magnitude as the anode-cathode voltage Va is reduced. Theory for emission from a spherical surface shows that this curvature of slope increases with the curvature of the emitting surface. By detailed calculation using the change of FN slope, it is possible to deduce the radius of curvature of the emitting region, surface field, effective solid angle of emission, and an electron supply factor, all more accurately than is feasible using planar theory.
Nondestructive metrology for nanoimprint processes
Authors: Deng Xuegong , Chen Lei , Sciortino Paul F. , Liu Feng , Wang Jian J.
Published: April 2006

We investigated two methods for imprinting metrology according to optical reflectance and transmittance of the imprinted substrates. We utilized the reflectance of two polarization states at 780nm for ∼100-nm polymer features with depth/width ratios>≈1 imprinted on ten 100-mm Si wafers. We not only successfully extracted the grating width, height, and residual polymer layers of the imprint but also assessed the uniformity and defects, as well as the aging of the templates from the same data. For transparent substrates, the optical test at shorter wavelengths clearly demonstrated a process monitor with 5-nm depth resolution for gratings of periods at 150nm with direct applicability to periods less than 50nm.
First principles calculations of dopant solubility based on strain compensation and direct binding between dopants and group IV impurities
Authors: Ahn Chihak , Diebel Milan , Dunham Scott T.
Published: April 2006

We investigated binding between dopant atoms such as boron and arsenic and various elements in group IV (e.g., C, Ge, Sn, and Pb) to explore opportunities for increasing dopant solubility, which is becoming critical for nanoscale semiconductor technology. Using first principles calculations, we find the dominant component of binding to be global strain compensation. We find negligible direct local binding between B and Ge, in contrast to some suggestions in the literature. Considering strain compensation and negative deviation from Vegard’s law of lattice parameter for SiGe, we predict the enhancement of boron segregation ratio across epitaxial Si∕SiGe interfaces, which agrees well with previous experimental observations. Due to nearest neighbor binding plus substantial strain compensation, Sn may have some promise for enhancing B solubility. For C∕As, the first nearest neighbor interaction is repulsive. However, the large negative induced strain due to carbon overcompensates this effect in the solubility, and thus As is predicted to weakly segregate from Si into epitaxial carbon-doped Si.
Scalable gate first process for silicon on insulator metal oxide semiconductor field effect transistors with epitaxial high-k dielectrics
Authors: Gottlob Heinrich D. B. , Mollenhauer Thomas , Wahlbrink Thorsten , Schmidt Mathias , Echtermeyer Tim , Efavi Johnson K. , Lemme Max C. , Kurz Heinrich
Published: April 2006

A “gate first” silicon on insulator (SOI) complementary metal oxide semiconductor process technology for direct evaluation of epitaxial gate dielectrics is described, where the gate stack is fabricated prior to any lithography or etching step. This sequence provides perfect silicon surfaces required for epitaxial growth. The inverted process flow with silicon dioxide (SiO2)/polysilicon gate stacks is demonstrated for gate lengths from 10μm down to 40nm on a fully depleted 25nm thin SOI film. The interface qualities at the front and back gates are investigated and compared to conventionally processed SOI devices. Furthermore, the subthreshold behavior is studied and the scalability of the gate first approach is proven by fully functional sub-100nm transistors. Finally, a fully functional gate first metal oxide semiconductor field effect transistor with the epitaxialhigh-k gate dielectric gadolinium oxide (Gd2O3) and titanium nitride (TiN) gate electrode is presented.
Solvent enhanced resist flow for room temperature imprint lithography
Authors: Chu Changwoong , Parsons Gregory N.
Published: April 2006

Imprint lithography generally requires heating to decrease the resist viscosity to achieve sufficient flow. Procedures using little or no heating are of interest for organic devices and for patterning materials on flexible plastic substrates. This article describes a procedure to imprint resist patterns at room temperature using commercial resist materials, where residual solvent remaining in the resist after spin coating is used to reduce the resist viscosity and enhance the deformation ability. This room temperature imprint shows results comparable with the elevated temperature processes done at 165°C, suggesting similar resist viscosity under the conditions studied. The imprinted depth decreases with elapsed time after coating, consistent with time-dependent evaporation of solvent from the resist bulk.
Fabrication of gated cold cathode using standing thin film induced by ion-beam bombardment
Authors: Yoshida Tomoya , Baba Akiyoshi , Asano Tanemasa
Published: April 2006

We demonstrated high current field electron emission from a gated field electron emitter fabricated by the thin film standing technique which was induced by ion-beam bombardment and etch-back technique. The thin film material was tungsten disilicide. An emitter tip having a high aspect ratio was fabricated inside a gate aperture of 2μm in diameter. The emission current of 10μA was obtained from a single tip cathode at the gate voltage of 133.5V. A multitip cathode composed of 1000 tips cathode showed a lower turn-on voltage (31V) than that of the single tip (112V), which indicated nonuniform distribution of the turn-on voltage.
Coherent and sequential tunneling mechanisms for field electron emission through layers of wide band gap materials
Authors: Filip V. , Nicolaescu D. , Wong H.
Published: April 2006

A sequential two-step tunneling model was developed for the electron field emission from semiconductor cathodes covered with dielectric layers. The results are compared with a previous coherent (one-step) approach and remarkable differences are obtained. Electron heating effects are predicted in not-too-thick dielectric layers. Multiple peaks in the emitted electron energy distribution, which appear in some experiments, may be explained by the sequential field emission model.
Temperature dependence of the work function of the Zr∕O∕W(100) Schottky electron source in typical operating conditions and its effect on beam brightness
Authors: Bronsgeest M. S. , Kruit P.
Published: April 2006

The current density on the emitting surface of a Zr∕O∕W(100) Schottky electron source has been determined for temperatures in the range of 1600–1850K and fields in the range of 5×108–8×108V∕m. The work function at different temperatures can be found by fitting the theoretical equation for current density in the extended Schottky emission regime to the experimental current density with the work function as fitting parameter. A linear relationship between work function and temperature was found with a positive coefficient of 0.6meV∕K. This temperature dependence causes the reduced brightness of Zr∕O∕W(100) Schottky electron sources to be much less dependent on temperature than previously assumed. This implies that these sources can be operated at lower temperatures without losing very much in brightness, improving the lifetime due to a better tip shape stability.
Analysis of the energy distribution of field electrons from metals and semiconductors
Authors: Chung M. S. , Choi T. S. , Bae H. K. , Kim J. K. , Yoon B.-G. , Hong S. C.
Published: April 2006

The field electron energy distributions were investigated for field emission from semiconductors as well as metals. The average energy ⟨ε⟩ and the standard deviation Δε of the distributions were obtained analytically using the WKB transmission coefficient. The obtained analytic forms of ⟨ε⟩ and Δε are found to be useful to characterize field emission. In particular, 2Δε represents the width of field electron energy distribution. As the field increases, it increases for metals and p-type semiconductors while it decreases for n-type semiconductors.
Study of the triode structure in a field emission display element
Authors: Wei Lei , Zhang Xiaobing , Yang Guodong , Xie Minyong
Published: April 2006

In a field emission display panel, a triode structure is often used to obtain high brightness and low driving voltage. This article studies the under-gate triode structure with different dielectric layer thicknesses. To increase the emission current, some holes are designed on the cathode electrode. In this structure, the fringe field has been increased effectively and the current density emitted from the cathode surface is more uniform. Apart from this, a focus electrode is used to improve the focus performance of the electron beam in an under-gate structure. The spot size and current density distribution on the screen have been optimized with the different focus voltage. Consequently, a good resolution and high brightness are obtained.
Microchannel plates at high rates: The challenges for future space plasma missions
Authors: Kataria D. O.
Published: April 2006

Microchannel plates (MCPs) are currently the preferred sensor element for the detection of low-energy (∼0–30keV) electrons and ions in space plasma instruments, and are the base line technology for several proposed space missions. With a number of such missions currently in operation such as Cluster, Cassini, Double Star, and Mars Express using MCPs, there is a large volume of performance data, both from ground tests as well as in flight. From these experiences, it is clear that the current state of the art limits instrument performance significantly, in particular, in two areas; at high rates and the instrument lifetime. The requirements for several future missions are a lot more demanding and the push towards miniaturized and fast instruments, possibly requiring imaging at very high rates, and missions to extreme environments, presents a formidable challenge for the detector technology required. This article discusses details of the high rate performance of some of the plasma instruments, requirements of the future missions, and some of the solutions that are under study. The technology leap provided by recent advancements in microfabrication and nanofabrication techniques presents several opportunities for exploiting them to address these requirements with certain approaches. The challenges such devices face are discussed.
Experimental and computational studies of phase shift lithography with binary elastomeric masks
Authors: Maria Joana , Malyarchuk Viktor , White Jeff , Rogers John A.
Published: April 2006

This article presents experimental and computational studies of a phase shifting photolithographic technique that uses binary elastomeric phase masks in conformal contact with layers of photoresist. The work incorporates optimized masks formed by casting and curing prepolymers to the elastomer poly(dimethylsiloxane) against anisotropically etched structures of single crystal silicon on SiO2∕Si. Scanning optical microscopy and full-vector finite element computations reveal the important near field and proximity optical effects. Representative structures fabricated with this technique, including several that exploit subtle features in the intensity distributions, illustrate some of the capabilities.
Accurate focused ion beam sculpting of silicon using a variable pixel dwell time approach
Authors: Adams D. P. , Vasile M. J.
Published: April 2006

This work demonstrates accurate focused ion beam sculpting of micron-scale curved shapes into initially planar solids. Sculpting is accomplished by varying the dose per pixel within individual boustrophedonic scans and accounting for the material-specific angle-dependent sputter yield and the ion beam spatial distribution. We refine this technique by demonstrating how a range of preferred dwell times leads to improved sculpting. An optimized dwell time range is delineated by two effects. Excessively large dwell times lead to enhanced deposition of ejected species, asymmetric milled features (when symmetric features are intended), and depths greater than intended values. These effects occur for dwell times such that the depth removed per pixel in a given scan is on the order of the width of the focused ion beam. On the other end of the dwell time range, inordinately low times lead to undesired ion milling outside targeted areas. Milling outside targeted regions, such as a circle or an ellipse, can occur because the ion beam is retraced to a rectilinear frame bounding the area. When dwell times are chosen to be on the order of the time to transit from the rectilinear frame to an outlined area edge, this leads to a significant dose over unintended areas, thereby producing a feature with irregular boundaries. Despite these two effects, a large range of acceptable dwell times (approximately three to four decades) can be established for milling most curved shapes. Hemispherical, parabolic, and sinusoidal features are demonstrated in Si(100).
Improvement on superhydrophobic behavior of carbon nanofibers via the design of experiment and analysis of variance
Authors: Lin Ta-Sen , Wu Chu-Fu , Hsieh Chien-Te
Published: April 2006

The objective of this research was to obtain an optimal combination of superhydrophobic coating treatment on the surface of carbon nanofibers (CNFs) by means of design of experiments (DOE) and analysis of variance (ANOVA). Four factors, including fluoride ratio, spinning speed, coating time, and thermal treatment temperature, were considered in this research. For robustness concern, we applied DOE and ANOVA to our experiments with a 95% confidence interval. Analyzed results reflect that the fluoride ratio was the most significant among all factors. We also verified the impact of surface roughness on contact angle. The average contact angles on CNFs increased from 125°±2.5° to 162°±2.5° after treatment. This research is directed toward the applications of hydrophobic coating, such as biological detectors, hydrophobic products with self-cleaning function, material with bacteria-proof function, etc.