bluuebunny/crossref_metadata_2025 huggingface dataset:
Social enhancement of wing molt in female Mallards
Authors: Leafloor James O. , Risi Kenneth W. , Ankney C. Davison
Published: May 2008

We tested the hypothesis that social interactions among postbreeding female Mallards (Anas platyrhynchos) induce wing molt among flock members. Half of unsuccessfully nesting females were placed in a flock after breeding (FF group) and half were visually isolated from other ducks in individual pens (IF group). There was no difference in date of last incubation between the two treatment groups (t = 0.0, P = 1.0). On average, FF Mallards molted their remiges 14 days earlier (t = 2.21, P = 0.04) and were more synchronous among individuals than were IF birds. We suggest that onset of wing molt is stimulated by early-molting female ducks that induce other flock members to initiate wing molt. The resultant early, synchronous wing molt among members of postbreeding flocks may provide survival advantages by reducing the likelihood of predation on flightless ducks and allowing more time to prepare for fall migration.
A new species complex of Daphnia (Crustacea, Cladocera) from the Pacific Northwest of the United States
Authors: Kořinek V. , Hebert P. D. N.
Published: May 2008

The genetic characterization of more than 1500 populations belonging to the Daphnia pulex group from the United States and Mexico revealed nine previously unrecognized species. Three of these taxa, showing morphological and genetic affinities, are newly described in this paper and are assigned membership in a new species complex. These species share a unique configuration of P3 sensilla and a triangular ephippial shape which differs from that of other members of the genus Daphnia. All three species are large-bodied forms showing distinctive setulation of the internal margin of the ventral carapace. All these members of the complex appear to be narrow endemics, restricted to temporary ponds in semi-arid areas of the Pacific Northwest.
Mate searching by males of the intertidal amphipod Corophium volutator (Pallas)
Authors: Forbes M. R. , Boates J. Sherman , McNeil N. L. , Brison A. E.
Published: May 2008

In this paper we describe the mate-searching behaviour of male Corophium volutator (Pallas), an intertidal amphipod. We expected male choice of mates because males invest in mating by mate guarding, and also because adult females greatly outnumber adult males at our study site. We predicted that males would choose large females carrying many eggs and females close to moulting or close to being receptive. We found that individual males "assessed" an average of ca. 5 females in their respective burrows before entering the burrow of a prospective mate. Males were more likely to cohabit with females that were close to being receptive than with females that were far from being receptive. Over the season, the size of mate-searching males declined, whereas the number of females encountered by males increased, which may relate to the seasonal distribution of receptive females. However, there were no differences in size between paired and unpaired females regardless of time of season. Our results support mate discrimination by males based on one criterion (stage of receptivity). The proximate and ultimate causes of the biased sex ratios of C. volutator need' to be determined before other predictions based on mate-choice theory can be made.
Maternal behaviour and energy investment by grey seals (Halichoerus grypus) breeding on land-fast ice
Authors: Haller Martha A. , Kovacs Kit M. , Hammill Mike O.
Published: May 2008

The grey seal (Halichoerus grypus) is a sexually dimorphic polygynous phocid that breeds in a synchronous fashion, within populations, on both sides of the North Atlantic Ocean. This study was designed to examine factors that may influence maternal behaviour and energy investment of females breeding on land-fast ice. The study was conducted on the ice around Amet Island, Nova Scotia, during the breeding seasons of 1992, 1993, and 1994. Scan sampling and ad libitum observation techniques were used to record behaviour. Mass transfer from mothers to pups was determined using serial mass records for pairs. Rate of pup mass gain was 2.5 ± 0.6 kg/day and pup mass at weaning 50.0 ± 7.3 kg. The duration of lactation was 15.2 ± 1.6 days. Maternal mass at parturition was 210.6 ± 23.8 kg and female mass loss during the lactation period was 75.0 ± 16.0 kg. This mass loss represented 35.7 ± 6.1% of their parturition mass. Efficiency of mass transfer was 0.52 ± 0.12. Breeding habitat influenced maternal behaviour. Compared with land-breeding grey seals, ice-breeding females had an intensified nursing period, during which females transferred a similar amount of energy to their pups over a shorter time frame. Additionally, females on land-fast ice gave birth more synchronously than is the case in land-breeding colonies. Date of parturition within the breeding season had some influence on female behaviour; females giving birth late in the season were more active than females breeding earlier. The behaviour of males may play a role in determining the optimum time for birthing. Adult males spent more time engaged in agonistic behaviours late in the breeding season and the resultant disruption of adjacent females may serve as a selective force maintaining birthing synchrony. These influences also apply in land-breeding situations and are not likely to contribute to the contraction of the nursing period and the more synchronous breeding observed among females on ice. The more condensed lactation and birthing periods are likely a response to the higher risk of premature separation on the ice.
Persistent low densities of plains ungulates in Etosha National Park, Namibia: testing the food-regulating hypothesis
Authors: Gasaway William C. , Gasaway Kathleen T. , Berry Hu H.
Published: May 2008

Declines and persistent low densities of plains ungulates during 1960–1994 in Etosha National Park (Etosha) compromise Namibia's efforts to develop a wildlife- and tourist-based economy and maintain its national biodiversity. Plains ungulates are blue wildebeest (Connochaetes taurinus), plains zebra (Equus burchelli), springbok (Antidorcas marsupialis), and gemsbok (Oryx gazella). We tested the hypothesis that plains ungulate populations were well below their food-resource ceiling (FRC) and predicted that widely variable rainfall (food production) would have no significant effect on birth and survival rates; alternatively, ungulates regulated near their FRC would display strong responses to variable rainfall through negative feedback on fertility, yearling recruitment, and mortality. Data supported the hypothesis that Etosha's populations were well below their FRC. The pregnancy rate of springbok was high during drought. Recruitment of all four species was not positively related to rainfall. Mortality was not negatively related to rainfall, and high mortality did not occur during droughts. Given the high recruitment of Etosha's stable or declining populations, we hypothesize that high adult and yearling mortality resulting from anthrax and predation was the primary process preventing population growth. Management aimed at maintaining or increasing the numbers of Etosha's plains ungulates currently need not emphasize habitat enhancement.
Behavioural control of daily fattening in great tits (Parus major)
Authors: Lilliendahl Kristjan , Carlson Allan , Welander Jonas , Ekman Jan B.
Published: May 2008

Many species of temperate-zone passerines show a pronounced daily cycle in body mass. Energy reserves are built up during the day and consumed the following night. The size of reserves is often viewed as a compromise between the risk of starvation and the cost of carrying an excessive fat load. This trade-off calls for state-dependent foraging behaviour, where current reserves and time of day are two crucial factors. The foraging strategy of the birds may then be reflected by the pattern of daily mass gain rate. We temporarily increased energy expenditure in captive great tits (Parus major) by experimentally lowering the overnight temperature. The birds' response to the treatment was to rapidly compensate for reduced morning reserves. Such an increased rate of mass gain suggests state-dependent foraging, and that some feeding opportunities are normally rejected. The rate of return to the normal pattern of fat accumulation suggests that in these birds, foraging is not constrained by physiological limitations.
Measurement versus estimation of condition in snakes
Authors: Weatherhead Patrick J. , Brown Gregory P.
Published: May 2008

Because variation in fat reserves (i.e., condition) is expected to contribute to variation in survival and reproductive success, zoologists often wish to estimate the condition of the animals they study. The conventional condition estimates used for snakes are the residuals from a regression of body mass on body length. Because this estimate of condition is not independent of the variables used to estimate it (i.e., fat is a component of body mass), estimates derived in this fashion will be confounded whenever fat varies nonrandomly with length. To avoid this problem we used total lipid extraction to estimate percent body fat in a representative sample of northern water snakes (Nerodia sipedon). The conventional condition index explained less than half the variance in the measured percent body fat in this sample. An improved estimate of condition calculated as the difference between total body mass and predicted lean mass (based on the results of the lipid extraction) explained 70% of the variation in percent body fat in the original sample of snakes. This improved estimate also revealed that condition declined with body size in a large sample of male water snakes measured in early spring over a 4-year period. This last result, coupled with theoretical expectations that condition will not vary randomly with body size in snakes, suggests that researchers interested in condition should derive indices from direct measurements of body fat.
Diving behavior of juvenile northern elephant seals
Authors: Boeuf Burney J. Le , Morris Patricia A. , Blackwell Susanna B. , Crocker Daniel E. , Costa Daniel P.
Published: May 2008

We describe and review the development of the diving and foraging pattern of northern elephant seals, Mirounga angustirostris, during migrations over the first 2 years of life. The diving pattern and migratory tracks of 23 juveniles, 9–27 months of age, from Año Nuevo and Piedras Blancas, California, were recorded with attached time–depth recorders and Argos satellite tags. The seals exhibited a general diving pattern like that of adults, diving deep (373 ± 77 m per dive (mean ± SD)), long (15.2 ± 2.6 min per dive), and continuously (88.7 ± 2.7% of the time submerged while at sea). Level of performance increased with age and experience up to 2 years of age, the end of the fourth migration, when modal diving performance was equal to that of adults. Juveniles migrated north to the waters west of Oregon, Washington, and British Columbia, moving more slowly and not as far as adults. By the third trip to sea, males began to exhibit more flat-bottomed dives than females, a sex difference observed in adults, suggesting that males supplement a diet of pelagic organisms with benthic prey. These data and related observations of elephant seals suggest that the greatest physiological changes enabling an animal to dive occur near the rookery following weaning, before the first trip to sea; transition to a pelagic existence is difficult, as reflected by high mortality during the first migration; improvement of diving skills continues up to 2 years of age; and sex differences in foraging behavior and foraging location, similar to those seen in adults, are evident before the seals reach 2 years of age.
Why do Gray Catbirds destroy eggs in nests of other birds? Experimental tests of alternative hypotheses
Authors: Spooner Angela , Pribil Stanislav , Picman Jaroslav
Published: May 2008

Although Gray Catbirds (Dumetella carolinensis) are known to destroy eggs of other birds, the function of their egg-destroying behavior is unknown. The behavior may (1) provide nutrients (consumption hypothesis), (2) reduce competition for limited resources (competition hypothesis), (3) reduce the chances of predation on catbird nests (predator-avoidance hypothesis), (4) prevent brood parasitism by the Brown-headed Cowbird, Molothrus ater (antiparasitism hypothesis), or (5) serve in the acquisition of mates (sexual selection hypothesis). The goal of our study was to test predictions of these five hypotheses in a series of field and laboratory experiments. In the experiments, we examined catbird responses to experimental nests and eggs. We found that catbirds (i) break eggs in experimental nests throughout their nesting cycle, (ii) destroy eggs in heterospecific nests more frequently than in conspecific nests, (iii) destroy cowbird eggs rather than conspecific eggs when both are presented in the same nest, (iv) peck eggs rather than young when both are presented in the same nest, (v) consume broken eggs, (vi) avoid pecking eggs that are unpalatable, (vii) start pecking eggs soon after fledging. These results are most consistent with the consumption and antiparasitism hypotheses and indicate that catbirds break eggs to consume their contents and to prevent brood parasitism of their own nests.
Breeding bird communities of the western and northern Canadian boreal forest: relationship to forest type
Authors: Kirk David A. , Diamond Antony W. , Hobson Keith A. , Smith Alan R.
Published: May 2008

We examined the distribution of 80 species of breeding birds across 67 census plots from a variety of sources in the boreal forest of western and northern Canada to obtain information on bird habitat associations for forest management. The sites ranged from upland black spruce (Picea mariana) to riverine deciduous forests and wet, marshy bogs. Axis 1 of an ordination (detrended correspondence analysis) demonstrated a gradient in bird communities from dry to wet sites; axis 2 may have been a black spruce (nutrient poor) to mixed deciduous forest gradient (nutrient rich). Hierarchical classification (twinspan) identified five groups of sites according to their bird communities. Despite geographical variation in bird communities and possible geographical variation in habitat associations, sites were classified according to their forest types rather than regional affinities. Yellow-rumped warblers (Dendroica coronata) and dark-eyed juncos (Junco hyemalis) showed a pronounced gradient of increased abundance from deciduous to coniferous sites. White-throated sparrows (Zonotrichia albicollis) and alder flycatchers (Empidonax alnorum) showed a reverse gradient. In 22 sites of known-age aspen (Populus tremuloides) – mixedwood forests from central Saskatchewan, an ordination indicated a strong relationship between stand age (and thus the proportion of coniferous cover) and bird community structure. The highest combined densities of Neotropical migrants occurred in old forests, whereas short-distance migrants were most abundant in young forests. The highest abundance of upper-canopy gleaners was found in old forests, whereas ground foragers were most abundant in early successional forests. These findings have important implications for management of boreal forests.
Evaluation of the accuracy of body temperature measurement using external radio transmitters
Authors: Audet Doris , Thomas Donald W.
Published: May 2008

The facultative depression of body temperature represents an important energy strategy for small homeotherms. However, measuring body temperature under field conditions by means other than externally attached temperature-sensitive radio transmitters is problematical. We show that skin temperatures measured by external radio transmitters can accurately reflect core temperature for the bat Carollia perspicillata. We compared body and skin temperatures at three ambient temperatures (Ta; 21, 26, and 31 °C). The difference between skin and body temperature (ΔT) was linearly correlated with Ta and can be predicted by ΔT = 4.396 − 0.118Ta. We argue that external temperature-sensitive radio transmitters can provide a reliable index of core temperature and so permit the study of torpor or facultative hypothermia under field conditions.
Are avian ectoparasites more numerous in nest boxes with old nest material?
Authors: Rendell Wallace B. , Verbeek Nicolaas A. M.
Published: May 2008

Researchers may reduce the numbers of haematophagous ectoparasites in nest boxes of cavity-nesting birds by removing old nests from boxes and, as a result, eliminate an important selective pressure that could influence the results from nest-box studies of birds. We recorded the numbers of parasites in tree swallow (Tachycineta bicolor) boxes in which we manipulated the presence, amount, and quality of old nests. Bird fleas (Ceratophyllus idius) were more numerous in boxes with old nests, and there was a positive correlation between nest volume and flea numbers. In one year, there was a positive association between fowl mite (Ornithonyssus sylviarum) numbers and nest volume; otherwise, fowl mites and blow flies (Protocalliphora sialia) were equally numerous in all nest types. We conclude that ectoparasites whose over-winter survival depends on old nests are more numerous in boxes with old nests, whereas parasites whose over-winter survival is independent of old nests infect nest sites randomly. Also, reinfection and nest microclimate likely contributed to variance in parasite numbers between nest types and years, respectively. We recommend caution when speculating about the possible effects of cleaning boxes on parasites that occur in nests because different species of parasites are not influenced similarly by old nests.
The effects of sex, time of birth, and habitat on the vulnerability of roe deer fawns to red fox predation
Authors: Aanes Ronny , Andersen Reidar
Published: May 2008

Red fox (Vulpes vulpes) predation on roe deer (Capreolus capreolus) fawns was studied using radiotelemetry techniques on an island in central Norway. Red foxes killed 48% of the monitored roe deer fawns within 60 days of birth, and mortality from other factors constituted only a minor part (5%) of the total mortality. The predation rate was lower in first week of life than during the subsequent 3 weeks. Male roe deer fawns were four times more susceptible to red fox predation than female fawns. We argue that these results reflect differences in behaviour between the sexes. There were some indications that time of birth may be important in determining vulnerability of fawns to red fox predation, with fawns born during the birth peak suffering more predation than fawns born outside the peak. The type of habitat a roe deer fawn used appeared to influence the probability of being killed by a red fox, and our results supported the hypothesis that hiding is a strategy to avoid predation in dense habitats. Fawns killed by red foxes used open grassland significantly more than surviving fawns, which used woodland to a greater extent.
Use of bone histology in estimating the age of frogs (Rana perezi) from a warm temperate climate area
Authors: Esteban Marisa , García-París Mario , Castanet Jacques
Published: May 2008

The structure and the histological expression of annual bone growth marks of Iberian water frogs (Rana perezi) from a warm temperate climate region (southwestern Spain) differ markedly from the pattern observed in colder climate populations. Forty-eight percent of winter growth marks appeared to be annuli; 52% are lines of arrested growth but 20% of these are weakly expressed. Annuli or lines of arrested growth were very diffuse or absent in 7% of the 103 individuals studied, suggesting that variations in climate have a stronger influence on growth-mark formation than was previously considered. Males and females are sexually mature in their second year, although some males mature at 1 year of age and some females at 3 years. The oldest males were 4 years old, 1 year younger than males from northern populations. The oldest female was 6 years old. The wide range of body sizes among the 1-year-old froglets can be explained by the extended period of metamorphosis, from July to November.
Diving costs as a component of daily energy budgets of aquatic birds and mammals: generalizing the inclusion of dive-recovery costs demonstrated in tufted ducks
Authors: Leeuw Joep J. de
Published: May 2008

Metabolic studies on freely diving birds and mammals are reviewed and allometric relations of diving costs are presented. A distinction can be made between three different types of diving costs: (1) metabolic rate during submergence, relevant in estimating aerobic dive limits, (2) average metabolic rate during diving and breathing intervals (MRd), and (3) diving costs as the excess over resting costs (EDC). EDC is the most comprehensive measure, integrating energy costs over entire dive series with subsequent longer term recovery from heat loss or anaerobic metabolism. Respirometry experiments with tufted duck (Aythya fuligula) diving in a 5.7 m deep indoor tank demonstrated that in this species diving costs, expressed as EDC, increased at lower water temperatures. MRdwas not significantly related to temperature, and probably reflects only the hydrodynamic and not the thermoregulatory component of diving costs. In general, the usual practice of measuring metabolic costs only during diving activity seems insufficient to estimate the total costs of diving. Studies that include longer term recovery (e.g., doubly labelled water measurements over entire foraging trips) yield more complete estimates of diving costs. To take diving costs into account in an animal's energy budget, estimates of EDC are more appropriate than MRd.
Origin of iron in sea lamprey, Petromyzon marinus, tissues during embryogenesis and early larval life
Authors: Tsioros Kelly K. , Holmes John A. , Youson John H.
Published: May 2008

Iron (Fe) concentration was measured in unfertilized eggs, embryos, prolarvae, and young larvae (up to day 56) of sea lampreys (Petromyzon marinus) raised in two substrates to determine (i) the importance of maternal transfer to Fe accumulation in sea lampreys and (ii) the influence of substrate on Fe uptake in young larvae. Unfertilized eggs contained about 35 ng of Fe, supporting the maternal transfer hypothesis. There were no significant changes in Fe concentration in developing embryos and prolarvae after hatching. Young larvae rapidly accumulated Fe from their burrowing substrate and the amount accumulated depended on the amount of Fe in the substrate. Since this rapid accumulation coincides with the beginning of exogenous feeding, as well as burrowing, environmental sources of Fe appear to be important contributors to Fe body burdens in larval sea lampreys.
Fetal development in wolves,Canis lupus, of the Keewatin District, Northwest Territories, Canada
Authors: Hillis Tracy L. , Mallory Frank F.
Published: May 2008

Of 205 female wolves (Canis lupus) shot by Inuit hunters between 1987 and 1989 in the Keewatin District, Northwest Territories, Canada, 97 were parous, and 16 gravid females carried 73 identifiable fetuses. Fetuses grew at a mean rate of 5.17 g/day between day 32 post coitus and parturition. During the same period, fetuses increased in length at a mean rate of 0.204 cm/day. No significant sexual dimorphism in body mass or other morphological features was found at this stage of development. Cranio-caudal length ranged from 3 mm shortly after implantation to approximately 185 mm at parturition. All correlations of morphological parameters with cranio-caudal length were significant, and with the exception of humerus length and contour length, all parameters increased faster than cranio-caudal length. The results are discussed in relation to reproductive and developmental strategies in canids.
Helminth community structure and pattern in sympatric populations of black-bellied and fulvous whistling-ducks
Authors: Fedynich Alan M. , Pence Danny B. , Bergan James F.
Published: May 2008

Helminth communities of 25 black-bellied (Dendrocygna autumnalis) and 25 fulvous (Dendrocygna bicolor) whistling-ducks from south Texas varied in composition, prevalence, dominance, and abundance. Twenty-eight helminth species were found, of which 20 occurred in each host species population. Twelve species co-occurred between host populations. Black-bellied and fulvous whistling-ducks averaged 3.0 ± 0.3 (SE) and 5.0 ± 0.4 species, respectively. Fifteen common species were found, of which 8 and 11 species commonly occurred in black-bellied and fulvous whistling-ducks, respectively. Four species (Apatemon gracilis, Tanaisia bragai, Sobolevicanthus gracilis, and Epomidiostomum uncinatum) were common in both host species. Prevalences varied in 4 of 8 helminth species co-occurring in both host species; 3 helminth species had higher prevalences in fulvous whistling-ducks. Black-bellied and fulvous whistling-ducks averaged 7.8 ± 1.4 and 44.8 ± 11.9 helminth individuals, respectively. Eleven of 15 common helminth species varied in abundance between host species populations; 4 species had higher abundances in black-bellied whistling-ducks and 7 had higher abundances in fulvous whistling-ducks. Our results suggest that although these duck species are sympatric, differences in feeding behavior may be most important in determining helminth community structure and pattern.
LONG-WAVE INFRARED AND TERAHERTZ-FREQUENCY LASING BASED ON SEMICONDUCTOR NANOCRYSTALS
Authors: RUPASOV VALERY I. , KRIVOSHLYKOV SERGEI G.
Published: May 2008

ALTAIR Center develops long-wave infrared (LWIR) and terahertz-frequency (THz) lasers operating at room temperature employing intraband luminescence in colloidal semiconductor nanocrystals, in which the optical transition frequencies can be easily tuned to the desired values by an appropriate choice of the semiconductor material and radius of the nanocrystals.
RESONANT TERAHERTZ SPECTROSCOPY OF BACTERIAL THIOREDOXIN IN WATER: SIMULATION AND EXPERIMENT
Authors: BYKHOVSKI ALEXEI , GLOBUS TATIANA , KHROMOVA TATYANA , GELMONT BORIS , WOOLARD DWIGHT
Published: May 2008

The experimental and computational study of bacterial thioredoxin, an E. coli protein, at THz frequencies is presented. The absorption spectrum of the entire protein in water was studied numerically in the terahertz range (0.1 – 2 THz). In our work, the initial X-ray molecular structure of thioredoxin was optimized using the molecular dynamical (MD) simulations at room temperature and atmospheric pressure. The effect of a liquid content of a bacterial cell was taken into account explicitly via the simulation of water molecules using the TIP3P water model. Using atomic trajectories from the room-temperature MD simulations, thioredoxin's THz vibrational spectrum and the absorption coefficient were calculated in a quasi harmonic approximation.

For our terahertz transmission measurements, we used solutions of thioredoxin in distilled water obtained from Sigma. The experimental and simulated signatures are correlated and dominant peaks are close in frequencies. The results of this study demonstrate that terahertz spectroscopy is a promising tool in generating spectral data for cellular components of bio agents such as bacterial cells and spores.
VAN DER WAALS INTERACTION BETWEEN ADSORBATE LAYERS/MOLECULES AND A SUBSTRATE
Authors: HORING NORMAN J. MORGENSTERN
Published: May 2008

We present a theoretical formulation of van der Waals (VdW)1-19 molecule-substrate attraction in which the second order vdW energy is explicitly exhibited as a correlation/self-energy of the molecular/atomic electrons generated by a dynamic nonlocal image potential due to polarization of the electrons of the bounded metal/semiconductor substrate in the electrostatic limit.20-23 This formulation can also be applied to the vdW interaction between an adsorbate layer and the substrate, as well as the interaction between layers. We have already applied it in the case of atom-surface vdW attraction in the presence of a normal magnetic field which induces both classical and Landau quantization magnetic effects,24 incorporating the role of dynamic and nonlocal plasma effects. The extension to multiple adsorbate layers and their mutual interactions as well as their attraction to the substrate is straightforward.25 The dependence of the atom/molecule-surface vdW energy on magnetic field strength provides an adjustable parametrization of the underlying zero-point photon energy (represented in terms of the nonretarded longitudinal plasmon-photons of the Coulomb interaction), opening the possibility of analyzing the concomitant fundamental quantum phenomenology in detail with material parameters that can be examined experimentally.
TOWARDS SENSING SINGLE OR A FEW BIO-MOLECULAR ARCHITECTURES: DESIGN OF FUNCTIONAL SURFACES
Authors: ZHAO PEIJI , WOOLARD DWIGHT , SEMINARIO JORGE M. , TREW ROBERT
Published: May 2008

There is considerable interest in electrical sensing of biomolecular binding since it has the potential to be label free, to work easily in aqueous environments native to the biomolecules, and to be integrated with small, fast, and inexpensive microelectronoics as detection instrumentation. Although electrochemical methods have been used successfully in detections of DNA molecules with Ag labels at very high sensitivity (~ p ml), detection of DNA molecules in terms of label free techniques has a lower sensitivity (~ μ ml). Here, the surface attachment chemistry is critical towards the detection of ultra-low concentration of biomolecules. In this article, based on density functional theory, we have calculated and analyzed the electrical characteristics of the contact between aromatic molecules and silicon (100) − 2×1 surfaces. Design principles for silicon based electrodes of electrochemically biomolecular sensing instruments for label-free sensing of single or a few biomolecular molecules have also been discussed.
ENU Mutagenesis, a Way Forward to Understand Gene Function
Authors: Acevedo-Arozena Abraham , Wells Sara , Potter Paul , Kelly Michelle , Cox Roger D. , Brown Steve D.M.
Published: May 2008

Arguably, the main challenge for contemporary genetics is to understand the function of every gene in a mammalian genome. The mouse has emerged as a model for this task because its genome can be manipulated in a number of ways to study gene function or mimic disease states. Two complementary genetic approaches can be used to generate mouse models. A reverse genetics or gene-driven approach (gene to phenotype) starts from a known gene and manipulates the genome to create genetically modified mice, such as knockouts. Alternatively, a forward genetics or phenotype-driven approach (phenotype to gene) involves screening mice for mutant phenotypes without previous knowledge of the genetic basis of the mutation. N-ethyl-N-nitrosourea (ENU) mutagenesis has been widely used for both approaches to generate mouse mutants. Here we review progress in ENU mutagenesis screening, with an emphasis on creating mouse models for human disorders.
Anisotropy of Wetting
Authors: Chatain Dominique
Published: May 2008

Wetting of single-crystal surfaces of metallic solids and oxides by liquid metals and alloys is anisotropic because of the anisotropy of the energies of solid surfaces and of their interfaces with liquids. To provide a basis for a discussion of wetting anisotropy, we review first the literature on surface and interfacial energies in metal-metal and metal-ceramic systems. We then summarize the relevant literature on the anisotropy of the energies of solid surfaces and of solid-liquid interfaces. These energies are then used in conjunction with the Young equation to estimate the expected anisotropy of wetting. Some serious discrepancies are found between these estimates and the experimental anisotropy of wetting. We show that under certain experimental conditions the wetting angles that have been determined are not Young contact angles.
Wetting and Dewetting of Complex Surface Geometries
Authors: Herminghaus Stephan , Brinkmann Martin , Seemann Ralf
Published: May 2008

Surfaces exhibiting complex topographies, such as those encountered in biology, give rise to an enormously rich variety of interfacial morphologies of a liquid to which they are exposed. In the present article, we elaborate on some basic mechanisms involved in the statics and dynamics of such morphologies, focusing on a few simple paradigm topographies. We demonstrate that different liquid interface morphologies on the same sample frequently coexist. To exemplify the impact of the dynamics on the final droplet morphology, we discuss the shape instability of filamentous liquid structures in wedge geometries. We finally show that some side effects that may dominate on a larger scale, such as contact line pinning and contact angle hysteresis, seem to play a minor role on the microscopic scale under study. This establishes the validity of simple theoretical concepts of wetting as a starting point for describing liquids at substrate surfaces of high complexity.
Relation between Solubility of Silicon in High-k Oxides and the Effect of Fermi Level Pinning
Authors: Umezawa Naoto , Shiraishi Kenji , Kakushima Kuniyuki , Iwai Hiroshi , Ohmori Kenji , Yamada Keisaku , Chikyow T.
Published: May 2008

HfO2-based oxide is a promising gate insulator for the next generation of the field effect transistors. Yet it is accompanied by a problematic effect, that is, the Fermi level of a metal electrode deposited on HfO2 is pinned at a certain position regardless of the type of the metal. On the other hand, this effect, the so-called Fremi level pinning, does not occur in a metal/La2O3/Si gate stack. This is puzzling because both oxides have similar band gaps and dielectric constants. We suggest that the high solubility of Si in La2O3, and thereby the formation of a silicate layer LaxSiyOz between La2O3 and the Si substrate plays important role in the suppression of electron transfers from La2O3 to the metal electrode: The charge neutrality is satisfied at the ionic/ionic interface La2O3/LaxSiyOz, and thus there is no need to exchange electrons with outside. At the ionic/covalent interface HfO2/SiO2, however, the charge neutrality is insufficient and electrons are readily transferred into the metal electrode causing the Fermi level pinning.
Impact of Thin La2O3 Insertion for HfO2 MOSFET
Authors: Kakushima Kuniyuki , Okamoto Kouichi , Adachi Manabu , Tachi Kiichi , Sato Soushi , Kawanago Takamasa , Song Jaeyeol , Ahmet Parhat , Sugii Nobuyuki , Tsutsui Kazuo , Hattori Takeo , Iwai Hiroshi
Published: May 2008

The impact of La2O3 insertion for HfO2 gated MOSFET is presented. The origin of a large negative shift in flat band voltage with La2O3 insertion has been carefully extracted to be the dipole presented at La2O3/SiO2 interface. An improvement in effective electron mobility without degrading the interfacial state density has been performed with thin La2O3 insertion for HfO2 MOSFET.
Quantum Effects of Capacitance in Nano-Scale Devices
Authors: Uchida Kazuyuki
Published: May 2008

We explore quantum effects of capacitance in nano-scale systems, by using a first-principles calculation of a carbon nanotube (CNT) capacitor. We show that the capacitance exhibits two principal quantum effects: First, the capacitance shows a large bias dependence, reflecting the density of states structure of the CNT with the divergent-type Van-Hove singularities peculiar to quasi-one dimensional systems. Second, the capacitance is larger than what the classical electromagnetism predicts with the tube-wall radius, according to a quantum spill of the stored charge density from the tube wall. We argue that these two quantum effects in the capacitance become more prominent when the system size gets smaller, which will open a new possibility for a design and control of nanometer scale devices.
MIMC Reliability and Electrical Behavior Defined by a Physical Layer Properties of the Dielectric
Authors: Charavel Rémy , Ackaert Jan , Dhont Kurt , Vlachakis B. , De Schepper L. , Millecam M. , Vandevelde E. , Bogaert P. , De Backer E. , Iline A. , Vlad Alexandru , Raskin J.-P.
Published: May 2008

Metal-Insulator-Metal Capacitor (MIMC) reliability and electrical properties are defined by the TDDB lifetime, breakdown voltage and leakage current. This article demonstrates the correlation between these electrical properties and the physical properties of the dielectric layer. The intrinsic quality of MIMC capacitors can therefore be predicted before complete processing by measuring a physical property of the MIMC dielectric.
Breakdown Characteristics of High-k Gate Dielectrics with Metal Gates
Authors: Rahim Nilufa , Misra D.
Published: May 2008

Considering the breakdown mechanisms of high-k and interfacial (IL) layers are different at higher temperatures than at room temperature, in this work the temperature dependence of stress induced leakage current (SILC) and time dependent dielectric breakdown (TDDB) of theses layers are studied separately. As observed from the low voltage SILC, the interfacial layer initiates the gate stack breakdown process at elevated temperature which is followed by the high-κ layer. Activation energy extracted from Weibulll distribution of time-to-breakdown (TBD) data from high-k layer further suggests that the gate stack breakdown occurs when high-k layer ultimately breaks down.
Superconformal Film Growth: Mechanism and Quantification
Authors: Moffat Thomas , Wheeler Daniel , Josell Daniel
Published: May 2008

The mechanism and modeling of superconformal film growth used in the electrochemical fabrication of 3-D Cu interconnects is briefly reviewed. The central role of electrolyte additives in controlling feature filling is fully described by the curvature enhanced adsorbate coverage (CEAC) mechanism developed at NIST. The key feature of the CEAC mechanism is redistribution of adsorbed additives through changes of local surface area as dictated by mass conservation and the relative strengths of adsorption. By examining the competition between rate suppressing, accelerating and deactivating adsorbates on planar surfaces the CEAC enables detailed prediction of shape evolution during electrodeposition on 3-D patterned surfaces that are found to be in excellent agreement with feature filling experiments.
Interface Barrier Determination by Internal Photoemission: Applications to Metal/Oxide/Semiconductor Structure
Authors: Nguyen Nhan V. , Kirillov Oleg A. , Jiang Weirong , Maslar James E. , Kimes William , Suehle John S.
Published: May 2008

Internal photoemission (IPE) spectroscopy is a powerful technique for investigating electronic properties at solid-solid interfaces. Upon photon excitation, electrons or/and holes in the solid under an external electrical bias, accumulate at the interface, escape over the energetic interfacial barrier, and produce an externally measured photocurrent. The onset of the photocurrent as a function of photon excitation energy indicates the energy barrier height as commonly used in the threshold spectroscopy. Furthermore, the characteristics of photoemission yield at the energies above (or possibly below) the barrier can also yield spectroscopic information. IPE has recently become an important tool used to determine the band offsets in metal oxide semiconductor structures. In this report, we will present a brief description of IPE principles and experimental setup and apply IPE to two important GaAs-based metal oxide semiconductor structures. These structures have become of prime research interest as potential structures in the next generation of electronic devices when the current silicon-based device downscaling comes to a halt.
Evaluation of Barrier CMP Slurries and Characterization of ULK Material Properties Shifts Due to CMP
Authors: Tseng Wei-Tsu , Kioussis Dimitri , Manikonda Shravanthi L. , Kim Hyun-Ki , Choi Jihong , Zhao Feng , Economikos Laertis , Klymko Nancy , Chace Mark , Molis Steve , Chae Moosung , Engbrecht Edward , Zielinski Eden , Truong Connie , Watts David
Published: May 2008

The integration of porous ultra low-k (ULK) films, with k = 2.2, into future technology nodes can add risk to yield and reliability. The porosity of the film makes it more susceptible to damage from CMP process. This work investigates the shifts in the dielectric constant (k) and refractive index (RI) that various barrier slurries have induced on ULK films. Post CMP treatment of these films seems to help in recovering the material property shifts caused by these barrier slurries. Chemical characterization of these films helped in identifying the reason for shifts that were induced in these films after exposure to CMP slurries.
Optimization of Growth Parameters in Electron Beam Induced Orientation Selective Epitaxy of CeO2(100)/Si(100) Structures
Authors: Inoue Tomoyasu , Ohtake Hideyuki , Otani Jun-ichirou , Shida Shigenari
Published: May 2008

Based on orientation selective epitaxy (OSE) of CeO2(100) and CeO2(110) layers on Si(100) substrates by substrate bias control in reactive magnetron sputtering, we have found OSE growth of CeO2(100) layers induced by electron beam irradiation, instead of substrate bias. In order to improve crystalline quality and interfacial properties, growth parameters of incident electron energy and an oxygen flow rate are analyzed, including the effect of oxygen radical beams. The electron beam induced OSE method gives a way to two dimensionally spatially varied OSE.
Monte Carlo Based Weibull Lifetime Uncertainty Calculations and Statistical Comparison of Semiconductor Manufacturing Process Module Changes for Lifetime Improvement
Authors: Prasad Jagdish , Greenwood Bruce
Published: May 2008

Weibull statistics are used in generation of gate oxide lifetimes from time dependent dielectric breakdown (TDDB) data. However, error bounds for the Weibull generated predicted lifetimes are not usually presented. Statistical methods to judge the impact of process improvements on Weibull lifetimes are also presented. Each of three electric fields was used to generate 1000 points point sets with probability of occurrence determined from a fixed, known underlying distribution. This distribution represents a population of points with a Weibull distribution. From the 1000 points, a sample of 10 to 25 points was randomly selected for each of the three applied electric fields. The subset of points were placed in rank order, and analyzed using the Maximum Likelihood procedure. These steps were repeated to obtain Monte Carlo based statistical information about the impact of sample size on our knowledge of the population. Additionally, similar methods were used to determine the experimental design required to statistically valid information regarding the impact of process changes on gate oxide lifetime.
High-Resolution Junction Photo-Voltage Mapping of Sheet Resistance and Leakage Current Variations with ms-Timescale Annealing Methods
Authors: Faifer Vladimir , Current Michael I. , Ohno Naotsugu , Halim Jeffri , Lu Jason
Published: May 2008

A non-contact method for measurement of sheet resistance and leakage current (RsL) for ultra-shallow junction characterization is described where high-density (30,000 pixel) sheet resistance maps provide detailed evaluation of local and global variations of dopant activation arising from implant and anneal conditions. Various examples of RTP-spike, flash and laser anneals and new low-dose implant results are discussed.
Dopant Activation Phenomenon by Flash Lamp Annealing
Authors: Kato Shinichi , Nara Yasuo , Aoyama Takayuki , Onizawa Takashi , Ohji Yuzuru
Published: May 2008

We studied the characteristics of ultra-shallow junctions (USJ) formed by flash lamp annealing (FLA) to reveal the nature of the dopant activation. We found that FLA is a form of solid phase epitaxial regrowth(SPER), employing high temperatures and short (mili-second) times. This achieves higher dopant activation than obtained in SPER.
ALD-Grown Rare Earth Oxides for Advanced Gate Stacks
Authors: Schamm Sylvie , Coulon Pierre-Eugène , Miao Shu , Volkos Stelios N. , Lu L H. , Lamagna Luca , Wiemer C , Tsoutsou Dimitra , Scarel Giovanna , Fanciulli Marco
Published: May 2008

Atomic Layer Deposition (ALD) has gained increasing attention for the sub-nm growth of high permittivity (k) rare earth oxide films. State of the art device operation heavily depends on the oxide/semiconductor interface properties. In this work, we address mainly through HRTEM-EELS experiments interface issues for ALD-grown Lu2O3/Si and La2O3/Si interfaces. Complementary results from GIXRD and electrical measurements on selective samples are presented. We show that, after exposure to air, Lu2O3 films capped with an Al2O3 layer are essentially free of interfacial layer formation, even if the starting Si surface is chemically oxidized. We also demonstrate that the La2O3 film reactivity with Si can be controlled up to a certain extent by appropriately choosing the ALD precursor combination. In particular, the La(Cp)3+O3 scheme favours over the La(Cp3)+H2O one in terms of a (i) smaller low-k interfacial layer thickness and interface trap density and (ii) stabilization of the high-k hexagonal La2O3 phase.
Electrical Characteristics of Low-Temperature Poly-Silicon Thin-Film Transistor Using a Stacked Pr2O3/SiOxNy Gate Dielectric
Authors: Pan Tung-Ming , Wu Tin-Wei , Chan Ching-Lin , Chen Kai-Ming , Lee Chih-Hong
Published: May 2008

In this paper, we have developed a stacked Pr2O3/SiOxNy gate dielectric into low-temperature poly-Si thin-film transistors (TFTs). High-performance TFT devices can be achieved including a high effective carrier mobility, high driving current, small subthreshold swing, and high ION/IOFF current ratio. This phenomenon is attributed to the smooth Pr2O3/poly-Si interface and the low interface trap density provided by N2O plasma treatment. The presence of an SiOxNy buffer layer also enhanced the electrical reliability of the Pr2O3/poly-Si TFT. All of these results suggest that a high-k Pr2O3 gate dielectric prepared the buffer layer is a good candidate for high-performance TFTs.
Impact on 1/f Noise due to Gate Electrodes in High-k. Based MOSFETs - A Comparison Study Between Poly-Si Vs Metal Vs FUSI
Authors: Srinivasan Purushothaman
Published: May 2008

This work summarizes the effects of using three different gate electrodes - poly-Si, fully silicided (FUSI) and metal (TiN-TaN) on drain current low-frequency (1/f) noise in devices with HfO2 as gate dielectric oxide. While 1/f^b type spectra were observed, the frequency exponent b was found to vary. Number fluctuations were found to be the dominant mechanism for 1/f noise. 1/f noise in poly-Si based oxides show the highest noise while FUSI based devices show the lowest noise. A specific behavior was observed in SiO2 and HfO2 regions of oxide, when the trap profiles are assessed using f x SVg spectra. Constant, decreasing and increasing trap distribution profiles were observed in the HfO2 region for poly-Si, FUSI and metal gate electrodes respectively. Investigations reveal that the oxygen transport during the gate electrode processing were mainly responsible for the observed differences in 1/f noise.
Key Process Technologies for Fabrication of Sub-15nm FinFET and Reduction of Its Parasitic Resistance
Authors: Kawasaki Hirohisa
Published: May 2008

FinFETs with either a Bulk-Si and a SOI substrate are broadly believed to be promising device structures for 22 nm node and beyond since they have superior short channel immunity and less performance variability. There are, however, concerns in integrating FinFETs, which can meet requirements from the viewpoints of manufacturability and performance. This paper will review the key FinFET process technologies for fabrication of sub-15 nm FinFET and reduction of its parasitic resistance.