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Jennifer A Clack - One of the best experts on this subject based on the ideXlab platform.
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evolution of forelimb musculoskeletal function across the fish to Tetrapod transition
Science Advances, 2021Co-Authors: J Molnar, Jennifer A Clack, John R Hutchinson, Rui Diogo, Stephanie E PierceAbstract:One of the most intriguing questions in vertebrate evolution is how Tetrapods gained the ability to walk on land. Although many hypotheses have been proposed, few have been rigorously tested using the fossil record. Here, we build three-dimensional musculoskeletal models of the pectoral appendage in Eusthenopteron, Acanthostega, and Pederpes and quantitatively examine changes in forelimb function across the fin-to-limb transition. Through comparison with extant fishes and Tetrapods, we show that early Tetrapods share a suite of characters including restricted mobility in humerus long-axis rotation, increased muscular leverage for humeral retraction, but not depression/adduction, and increased mobility in elbow flexion-extension. We infer that the earliest steps in Tetrapod forelimb evolution were related to limb-substrate interactions, whereas specializations for weight support appeared later. Together, these results suggest that competing selective pressures for aquatic and terrestrial environments produced a unique, ancestral “early Tetrapod” forelimb locomotor mode unlike that of any extant animal.
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Functional adaptive landscapes predict terrestrial capacity at the origin of limbs
Nature, 2020Co-Authors: Blake V. Dickson, Jennifer A Clack, Timothy R Smithson, Stephanie E PierceAbstract:The acquisition of terrestrial, limb-based locomotion during Tetrapod evolution has remained a subject of debate for more than a century^ 1 , 2 . Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik ^ 3 , Acanthostega ^ 4 , Ichthyostega ^ 5 and Pederpes ^ 6 . However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective^ 7 . Here we analyse 40 three-dimensionally preserved humeri from extinct Tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes^ 8 – 10 to reconstruct the evolution of terrestrial locomotion. We show that evolutionary changes in the shape of the humerus are driven by ecology and phylogeny and are associated with functional trade-offs related to locomotor performance. Two divergent adaptive landscapes are recovered for aquatic fishes and terrestrial crown Tetrapods, each of which is defined by a different combination of functional specializations. Humeri of stem Tetrapods share a unique suite of functional adaptations, but do not conform to their own predicted adaptive peak. Instead, humeri of stem Tetrapods fall at the base of the crown Tetrapod landscape, indicating that the capacity for terrestrial locomotion occurred with the origin of limbs. Our results suggest that stem Tetrapods may have used transitional gaits^ 5 , 11 during the initial stages of land exploration, stabilized by the opposing selective pressures of their amphibious habits. Effective limb-based locomotion did not arise until loss of the ancestral ‘L-shaped’ humerus in the crown group, setting the stage for the diversification of terrestrial Tetrapods and the establishment of modern ecological niches^ 12 , 13 . Analysis of humeri from fossils that span the fin-to-limb transition reveal that the change in the humerus shape is driven by both ecology and phylogeny, and is associated with functional trade-offs related to locomotor performance.
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Morphology of the earliest reconstructable Tetrapod Parmastega aelidae
Nature, 2019Co-Authors: Pavel A. Beznosov, Jennifer A Clack, Ervīns Lukševičs, Marcello Ruta, Per Erik AhlbergAbstract:The known diversity of Tetrapods of the Devonian period has increased markedly in recent decades, but their fossil record consists mostly of tantalizing fragments^ 1 – 15 . The framework for interpreting the morphology and palaeobiology of Devonian Tetrapods is dominated by the near complete fossils of Ichthyostega and Acanthostega ; the less complete, but partly reconstructable, Ventastega and Tulerpeton have supporting roles^ 2 , 4 , 16 – 34 . All four of these genera date to the late Famennian age (about 365–359 million years ago)—they are 10 million years younger than the earliest known Tetrapod fragments^ 5 , 10 , and nearly 30 million years younger than the oldest known Tetrapod footprints^ 35 . Here we describe Parmastega aelidae gen. et sp. nov., a Tetrapod from Russia dated to the earliest Famennian age (about 372 million years ago), represented by three-dimensional material that enables the reconstruction of the skull and shoulder girdle. The raised orbits, lateral line canals and weakly ossified postcranial skeleton of P. aelidae suggest a largely aquatic, surface-cruising animal. In Bayesian and parsimony-based phylogenetic analyses, the majority of trees place Parmastega as a sister group to all other Tetrapods. Three-dimensionally preserved fossils of Parmastega aelidae , a newly described Tetrapod from the earliest Famennian (Late Devonian) of Russia, provide detailed insights into the morphology and palaeobiology of the earliest Tetrapods.
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phylogenetic and environmental context of a tournaisian Tetrapod fauna
Nature Ecology and Evolution, 2017Co-Authors: Jennifer A Clack, Carys E Bennett, David K Carpenter, Sarah J Davies, Nicholas N Fraser, Timothy I Kearsey, J E A Marshall, D Millward, Benjamin K A Otoo, Emma J ReevesAbstract:The end-Devonian to mid-Mississippian time interval has long been known for its depauperate palaeontological record, especially for Tetrapods. This interval encapsulates the time of increasing terrestriality among Tetrapods, but only two Tournaisian localities previously produced Tetrapod fossils. Here we describe five new Tournaisian Tetrapods (Perittodus apsconditus, Koilops herma, Ossirarus kierani, Diploradus austiumensis and Aytonerpeton microps) from two localities in their environmental context. A phylogenetic analysis retrieved three taxa as stem Tetrapods, interspersed among Devonian and Carboniferous forms, and two as stem amphibians, suggesting a deep split among crown Tetrapods. We also illustrate new Tetrapod specimens from these and additional localities in the Scottish Borders region. The new taxa and specimens suggest that Tetrapod diversification was well established by the Tournaisian. Sedimentary evidence indicates that the Tetrapod fossils are usually associated with sandy siltstones overlying wetland palaeosols. Tetrapods were probably living on vegetated surfaces that were subsequently flooded. We show that atmospheric oxygen levels were stable across the Devonian/Carboniferous boundary, and did not inhibit the evolution of terrestriality. This wealth of Tetrapods from Tournaisian localities highlights the potential for discoveries elsewhere.
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life history of the stem Tetrapod acanthostega revealed by synchrotron microtomography
Nature, 2016Co-Authors: Jennifer A Clack, Sophie Sanchez, Paul Tafforeau, Per AhlbergAbstract:Analysis of fossil limb bones suggests that a mass-death deposit of the Devonian Tetrapod Acanthostega may consist entirely of juveniles, throwing new light on the life history of this species and the evolution of terrestriality. Many aspects of the life and habits of the Devonian stem Tetrapod Acanthostega remain obscure. Although it had limbs with digits, everything we know about it suggests that it was obligately aquatic. Here Sophie Sanchez and colleagues show that most known Acanthostega specimens come from a single mass-death assemblage, and that their state of ossification suggests that although the largest animal was at least six years old, they were all juveniles—no adults are known. The research provides a poignant snapshot into the life one of the earliest known Tetrapods, but raises many questions about the evolution of life history in land vertebrates. The transition from fish to Tetrapod was arguably the most radical series of adaptive shifts in vertebrate evolutionary history. Data are accumulating rapidly for most aspects of these events1,2,3,4,5, but the life histories of the earliest Tetrapods remain completely unknown, leaving a major gap in our understanding of these organisms as living animals. Symptomatic of this problem is the unspoken assumption that the largest known Devonian Tetrapod fossils represent adult individuals. Here we present the first, to our knowledge, life history data for a Devonian Tetrapod, from the Acanthostega mass-death deposit of Stensio Bjerg, East Greenland6,7. Using propagation phase-contrast synchrotron microtomography (PPC-SRμCT)8 to visualize the histology of humeri (upper arm bones) and infer their growth histories, we show that even the largest individuals from this deposit are juveniles. A long early juvenile stage with unossified limb bones, during which individuals grew to almost final size, was followed by a slow-growing late juvenile stage with ossified limbs that lasted for at least six years in some individuals. The late onset of limb ossification suggests that the juveniles were exclusively aquatic, and the predominance of juveniles in the sample suggests segregated distributions of juveniles and adults at least at certain times. The absolute size at which limb ossification began differs greatly between individuals, suggesting the possibility of sexual dimorphism, adaptive strategies or competition-related size variation.
Stephanie E Pierce - One of the best experts on this subject based on the ideXlab platform.
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osteohistology of greererpeton provides insight into the life history of an early carboniferous Tetrapod
Journal of Anatomy, 2021Co-Authors: Megan R Whitney, Stephanie E PierceAbstract:The vertebrate transition to land is one of the most consequential, yet poorly understood periods in Tetrapod evolution. Despite the importance of the water-land transition in establishing modern ecosystems, we still know very little about the life histories of the earliest Tetrapods. Bone histology provides an exceptional opportunity to study the biology of early Tetrapods and has the potential to reveal new insights into their life histories. Here, we examine the femoral bone histology from an ontogenetic series of Greererpeton, an early Tetrapod from the Middle-Late Mississippian (early Carboniferous) of North America. Thin-sections and micro-CT data show a moderately paced rate of bone deposition with significant cortical thickening through development. An interruption to regular bone deposition, as indicated by a zone of avascular tissue and growth marks, is notable at the same late juvenile stage of development throughout our sample. This suggests that an inherent aspect to the life history of juvenile Greererpeton resulted in a temporary reduction in bone deposition. We review several possible life history correlates for this bony signature including metamorphosis, an extended juvenile phase, environmental stress, and movement (migration/dispersal) between habitats. We argue that given the anatomy of Greererpeton, it is unlikely that events related to polymorphism (metamorphosis, extended juvenile phase) can explain the bony signature observed in our sample. Furthermore, the ubiquity of this signal in our sample indicates a taxon-level rather than a population-level trait, which is expected for an environmental stress. We conclude that movement via dispersal represents a likely correlate, as such events are a common life history strategy of aquatically bound vertebrates.
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evolution of forelimb musculoskeletal function across the fish to Tetrapod transition
Science Advances, 2021Co-Authors: J Molnar, Jennifer A Clack, John R Hutchinson, Rui Diogo, Stephanie E PierceAbstract:One of the most intriguing questions in vertebrate evolution is how Tetrapods gained the ability to walk on land. Although many hypotheses have been proposed, few have been rigorously tested using the fossil record. Here, we build three-dimensional musculoskeletal models of the pectoral appendage in Eusthenopteron, Acanthostega, and Pederpes and quantitatively examine changes in forelimb function across the fin-to-limb transition. Through comparison with extant fishes and Tetrapods, we show that early Tetrapods share a suite of characters including restricted mobility in humerus long-axis rotation, increased muscular leverage for humeral retraction, but not depression/adduction, and increased mobility in elbow flexion-extension. We infer that the earliest steps in Tetrapod forelimb evolution were related to limb-substrate interactions, whereas specializations for weight support appeared later. Together, these results suggest that competing selective pressures for aquatic and terrestrial environments produced a unique, ancestral “early Tetrapod” forelimb locomotor mode unlike that of any extant animal.
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Functional adaptive landscapes predict terrestrial capacity at the origin of limbs
Nature, 2020Co-Authors: Blake V. Dickson, Jennifer A Clack, Timothy R Smithson, Stephanie E PierceAbstract:The acquisition of terrestrial, limb-based locomotion during Tetrapod evolution has remained a subject of debate for more than a century^ 1 , 2 . Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik ^ 3 , Acanthostega ^ 4 , Ichthyostega ^ 5 and Pederpes ^ 6 . However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective^ 7 . Here we analyse 40 three-dimensionally preserved humeri from extinct Tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes^ 8 – 10 to reconstruct the evolution of terrestrial locomotion. We show that evolutionary changes in the shape of the humerus are driven by ecology and phylogeny and are associated with functional trade-offs related to locomotor performance. Two divergent adaptive landscapes are recovered for aquatic fishes and terrestrial crown Tetrapods, each of which is defined by a different combination of functional specializations. Humeri of stem Tetrapods share a unique suite of functional adaptations, but do not conform to their own predicted adaptive peak. Instead, humeri of stem Tetrapods fall at the base of the crown Tetrapod landscape, indicating that the capacity for terrestrial locomotion occurred with the origin of limbs. Our results suggest that stem Tetrapods may have used transitional gaits^ 5 , 11 during the initial stages of land exploration, stabilized by the opposing selective pressures of their amphibious habits. Effective limb-based locomotion did not arise until loss of the ancestral ‘L-shaped’ humerus in the crown group, setting the stage for the diversification of terrestrial Tetrapods and the establishment of modern ecological niches^ 12 , 13 . Analysis of humeri from fossils that span the fin-to-limb transition reveal that the change in the humerus shape is driven by both ecology and phylogeny, and is associated with functional trade-offs related to locomotor performance.
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evolution of hindlimb muscle anatomy across the Tetrapod water to land transition including comparisons with forelimb anatomy
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2020Co-Authors: Julia Molnar, John R Hutchinson, Rui Diogo, Stephanie E PierceAbstract:: Tetrapod limbs are a key innovation implicated in the evolutionary success of the clade. Although musculoskeletal evolution of the pectoral appendage across the fins-to-limbs transition is fairly well documented, that of the pelvic appendage is much less so. The skeletal elements of the pelvic appendage in some Tetrapodomorph fish and the earliest Tetrapods are relatively smaller and/or qualitatively less similar to those of crown Tetrapods than those of the pectoral appendage. However, comparative and developmental works have suggested that the musculature of the Tetrapod forelimb and hindlimb was initially very similar, constituting a "similarity bottleneck" at the fins-to-limbs transition. Here, we used extant phylogenetic bracketing and phylogenetic character optimization to reconstruct pelvic appendicular muscle anatomy in several key taxa spanning the fins-to-limbs and water-to-land transitions. Our results support the hypothesis that transformation of the pelvic appendages from fin-like to limb-like lagged behind that of the pectoral appendages. Compared to similar reconstructions of the pectoral appendages, the pelvic appendages of the earliest Tetrapods had fewer muscles, particularly in the distal limb (shank). In addition, our results suggest that the first Tetrapods had a greater number of muscle-muscle topological correspondences between the pectoral and pelvic appendages than Tetrapodomorph fish had. However, ancestral crown-group Tetrapods appear to have had an even greater number of similar muscles (both in terms of number and as a percentage of the total number of muscles), indicating that the main topological similarity bottleneck between the paired appendages may have occurred at the origin of the Tetrapod crown group. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc.
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evolution of hindlimb muscle anatomy across the Tetrapod water to land transition including comparisons with forelimb anatomy
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2020Co-Authors: Julia Molnar, John R Hutchinson, Rui Diogo, Stephanie E PierceAbstract:Tetrapod limbs are a key innovation implicated in the evolutionary success of the clade. Although musculoskeletal evolution of the pectoral appendage across the fins-to-limbs transition is fairly well documented, that of the pelvic appendage is much less so. The skeletal elements of the pelvic appendage in some Tetrapodomorph fish and the earliest Tetrapods are relatively smaller and/or qualitatively less similar to those of crown Tetrapods than those of the pectoral appendage. However, comparative and developmental works have suggested that the musculature of the Tetrapod forelimb and hindlimb was initially very similar, constituting a "similarity bottleneck" at the fins-to-limbs transition. Here, we used extant phylogenetic bracketing and phylogenetic character optimization to reconstruct pelvic appendicular muscle anatomy in several key taxa spanning the fins-to-limbs and water-to-land transitions. Our results support the hypothesis that transformation of the pelvic appendages from fin-like to limb-like lagged behind that of the pectoral appendages. Compared to similar reconstructions of the pectoral appendages, the pelvic appendages of the earliest Tetrapods had fewer muscles, particularly in the distal limb (shank). In addition, our results suggest that the first Tetrapods had a greater number of muscle-muscle topological correspondences between the pectoral and pelvic appendages than Tetrapodomorph fish had. However, ancestral crown-group Tetrapods appear to have had an even greater number of similar muscles (both in terms of number and as a percentage of the total number of muscles), indicating that the main topological similarity bottleneck between the paired appendages may have occurred at the origin of the Tetrapod crown group. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 303:218-234, 2020. © 2018 American Association for Anatomy.
Per E. Ahlberg - One of the best experts on this subject based on the ideXlab platform.
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Unique pelvic fin in a Tetrapod-like fossil fish, and the evolution of limb patterning
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Jonathan E. Jeffery, Glenn W. Storrs, Timothy Holland, Clifford J. Tabin, Per E. AhlbergAbstract:All living Tetrapods have a one-to-two branching pattern in the embryonic proximal limb skeleton, with a single element at the base of the limb (the humerus or femur) that articulates distally with two parallel radials (the ulna and radius or the tibia and fibula). This pattern is also seen in the fossilized remains of stem-Tetrapods, including the fishlike members of the group, in which despite the absence of digits, the proximal parts of the fin skeleton clearly resemble those of later Tetrapods. However, little is known about the developmental mechanisms that establish and canalize this highly conserved pattern. We describe the well-preserved pelvic fin skeleton of Rhizodus hibberti, a Carboniferous sarcopterygian (lobe-finned) fish, and member of the Tetrapod stem group. In this specimen, three parallel radials, each robust with a distinct morphology, articulate with the femur. We review this unexpected morphology in a phylogenetic and developmental context. It implies that the developmental patterning mechanisms seen in living Tetrapods, now highly constrained, evolved from mechanisms flexible enough to accommodate variation in the zeugopod (even between pectoral and pelvic fins), while also allowing each element to have a unique morphology.
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Tetrapod trackways from the early middle devonian period of poland
Nature, 2010Co-Authors: Grzegorz Niedźwiedzki, Piotr Szrek, Katarzyna Narkiewicz, Marek Narkiewicz, Per E. AhlbergAbstract:The fossil record of the earliest Tetrapods (vertebrates with limbs rather than paired fins) consists of body fossils and trackways. The earliest body fossils of Tetrapods date to the Late Devonian period (late Frasnian stage) and are preceded by transitional elpistostegids such as Panderichthys and Tiktaalik that still have paired fins. Claims of Tetrapod trackways predating these body fossils have remained controversial with regard to both age and the identity of the track makers. Here we present well-preserved and securely dated Tetrapod tracks from Polish marine tidal flat sediments of early Middle Devonian (Eifelian stage) age that are approximately 18 million years older than the earliest Tetrapod body fossils and 10 million years earlier than the oldest elpistostegids. They force a radical reassessment of the timing, ecology and environmental setting of the fish-Tetrapod transition, as well as the completeness of the body fossil record.
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Contrasting Developmental Trajectories in the Earliest Known Tetrapod Forelimbs
Science, 2009Co-Authors: Viviane Callier, Jennifer A Clack, Per E. AhlbergAbstract:Ichthyostega and Acanthostega are the earliest Tetrapods known from multiple near-complete skeletons, with Acanthostega generally considered the more primitive. New material indicates differing ontogenetic trajectories for their forelimbs: In Ichthyostega, the pattern of muscle attachment processes on small humeri (upper arm bones) resembles that in "fish" members of the Tetrapod stem group such as Tiktaalik, whereas large humeri approach (but fail to attain) the Tetrapod crown-group condition; in Acanthostega, both small and large humeri exhibit the crown-group pattern. We infer that Ichthyostega underwent greater locomotory terrestrialization during ontogeny. The newly recognized primitive characteristics also suggest that Ichthyostega could be phylogenetically more basal than Acanthostega.
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the pectoral fin of panderichthys and the origin of digits
Nature, 2008Co-Authors: Catherine A Boisvert, Elga Markkurik, Per E. AhlbergAbstract:One of the identifying characteristics of Tetrapods (limbed vertebrates) is the presence of fingers and toes. Whereas the proximal part of the Tetrapod limb skeleton can easily be homologized with the paired fin skeletons of sarcopterygian (lobe-finned) fish, there has been much debate about the origin of digits. Early hypotheses interpreted digits as derivatives of fin radials, but during the 1990s the idea gained acceptance that digits are evolutionary novelties without direct equivalents in fish fin skeletons. This was partly based on developmental genetic data, but also substantially on the pectoral fin skeleton of the elpistostegid (transitional fish/Tetrapod) Panderichthys, which appeared to lack distal digit-like radials. Here we present a CT scan study of an undisturbed pectoral fin of Panderichthys demonstrating that the plate-like 'ulnare' of previous reconstructions is an artefact and that distal radials are in fact present. This distal portion is more Tetrapod-like than that found in Tiktaalik and, in combination with new data about fin development in basal actinopterygians, sharks and lungfish, makes a strong case for fingers not being a novelty of Tetrapods but derived from pre-existing distal radials present in all sarcopterygian fish.
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Tetrapod like middle ear architecture in a devonian fish
Nature, 2006Co-Authors: Martin D Brazeau, Per E. AhlbergAbstract:Detailed study of Panderichthys, a lobe-finned fish closely related to the first amphibians, suggests that the early stages in the evolution of the vertebrate middle ear were related to breathing, rather than detecting sound. Our middle ear corresponds to a reduced gill slit called the ‘spiracle’ in fishes. In a well preserved Panderichthys fossil specimen held in the Latvian Natural History Museum in Riga, this gill slit is much larger than in other ancient fish species and has vertebrate-like architecture, yet was probably used to inhale water or air. It seems that a rudimentary auditory role for the stapes and other middle-ear components first developed in primitive land vertebrates. Few fossils show the incipient stages of complex morphological transformations1. For example, the earliest stages in the remodelling of the spiracular tract and suspensorium (jaw suspension) of osteolepiform fishes2,3,4 into the middle ear of Tetrapods have remained elusive3. The most primitive known Tetrapods show a middle ear architecture that is very different from osteolepiforms such as Eusthenopteron3, with little indication of how this transformation took place. Here we present an analysis of Tetrapod middle ear origins that is based on a detailed study of Panderichthys, the immediate sister taxon of Tetrapods. We show that the spiracular region is radically transformed from osteolepiforms and represents the earliest stages in the origin of the Tetrapod middle ear architecture. The posterior palatoquadrate of Panderichthys is completely Tetrapod-like and defines a similarly Tetrapod-like spiracular tract. The hyomandibula has lost its distal portion, representing a previously unrecognized advance towards a stapes-like morphology. This spiracular specialization suggests that the middle ear of early Tetrapods evolved initially as part of a spiracular breathing apparatus5,6.
Oleg Lupan - One of the best experts on this subject based on the ideXlab platform.
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nanomechanics of individual aerographite Tetrapods
Nature Communications, 2017Co-Authors: Raimonds Meija, Stefano Signetti, Arnim Schuchardt, Kerstin Meurisch, Daria Smazna, Matthias Mecklenburg, Karl Schulte, Donats Erts, Oleg Lupan, Bodo FiedlerAbstract:Carbon-based three-dimensional aerographite networks, built from interconnected hollow tubular Tetrapods of multilayer graphene, are ultra-lightweight materials recently discovered and ideal for advanced multifunctional applications. In order to predict the bulk mechanical behaviour of networks it is very important to understand the mechanics of their individual building blocks. Here we characterize the mechanical response of single aerographite Tetrapods via in situ scanning electron and atomic force microscopy measurements. To understand the acquired results, which show that the overall behaviour of the Tetrapod is governed by the buckling of the central joint, a mechanical nonlinear model was developed, introducing the concept of the buckling hinge. Finite element method simulations elucidate the governing buckling phenomena. The results are then generalized for Tetrapods of different size-scales and shapes. These basic findings will permit better understanding of the mechanical response of the related networks and the design of similar aerogels based on graphene and other two-dimensional materials. Aerographite is a highly porous and lightweight carbon material obtained from hollow tubular Tetrapod building units. Here, the authors present a comprehensive investigation of Tetrapod deformation mechanisms which are at the core of aerographite nanomechanical properties.
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direct growth of freestanding zno Tetrapod networks for multifunctional applications in photocatalysis uv photodetection and gas sensing
ACS Applied Materials & Interfaces, 2015Co-Authors: Yogendra Kumar Mishra, Oleg Lupan, Gaurav Modi, Vasilii Cretu, Vasile Postica, Tim Reimer, Ingo Paulowicz, Viktor Hrkac, W Benecke, Lorenz KienleAbstract:Growth of freestanding nano- and microstructures with complex morphologies is a highly desired aspect for real applications of nanoscale materials in various technologies. Zinc oxide Tetrapods (ZnO-T), which exhibit three-dimensional (3D) shapes, are of major importance from a technological applications point of view, and thus efficient techniques for growth of different varieties of Tetrapod-based networks are demanded. Here, we demonstrate the versatile and single-step synthesis of ZnO-T with different arm morphologies by a simple flame transport synthesis (FTS) approach, forming a network. Morphological evolutions and structural intactness of these Tetrapods have been investigated in detail by scanning electron microscopy, X-ray diffraction, and micro-Raman measurements. For a deeper understanding of the crystallinity, detailed high-resolution transmission electron microscopic studies on a typical ZnO Tetrapod structure are presented. The involved growth mechanism for ZnO Tetrapods with various arm mor...
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a single zno Tetrapod based sensor
Sensors and Actuators B-chemical, 2009Co-Authors: Oleg Lupan, Lee Chow, Guangyu ChaiAbstract:Abstract Transferable ZnO Tetrapods were grown by an aqueous solution method. An individual ZnO Tetrapod-based sensor was fabricated by in situ lift-out technique and its ultraviolet (UV) and gas sensing properties were investigated. This single Tetrapod-based device responds to the UV light rapidly and showed a recovery time of about 23 s. The sensitivity of a single ZnO Tetrapod sensor to oxygen concentration was also investigated. We found that when UV illumination is switched off, the oxygen chemisorption process will dominate and assists photoconductivity relaxation. Thus relaxation dynamics is strongly affected by the ambient O 2 partial pressure as described. We also studied the response of ZnO Tetrapod-based sensor in various gas environments, such as 100 ppm H 2 , CO, i -butane, CH 4 , CO 2 , and SO 2 at room temperature. It is noted that ZnO Tetrapod sensor is much more sensitive to H 2 , i -butane and CO. It is demonstrated that a ZnO Tetrapod exposed to both UV light and hydrogen can provide a unique integrated multiterminal architecture for novel electronic device configurations.
Y H Leung - One of the best experts on this subject based on the ideXlab platform.
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gas sensing properties of thick film based on zno nano Tetrapods
Chemical Physics Letters, 2005Co-Authors: Chu Xiangfeng, Aleksandra B Djurisic, Jiang Dongli, Y H LeungAbstract:Abstract ZnO sensors were fabricated from ZnO Tetrapod structures prepared in four different atmospheres and their gas-sensing properties were investigated. It was found that the gas-sensing properties were strongly dependent on the preparation atmosphere. This is likely due to the effects of the preparation atmosphere on the intrinsic defect concentration. It was found that the sensors based on Tetrapods prepared in humidified Ar flow exhibited the best performance, characterized by high response, good selectivity and very short response time to dilute C 2 H 5 OH, making them promising candidates for practical detectors for dilute C 2 H 5 OH.
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magnetic properties of mn doped zno Tetrapod structures
Applied Physics Letters, 2004Co-Authors: V A L Roy, Aleksandra B Djurisic, Hui Liu, Xuxiang Zhang, Y H Leung, Min Xie, Ju Gao, H F Lui, C SuryaAbstract:ZnO Tetrapod nanostructures were prepared by evaporating Zn metal under humid argon flow. After the fabrication, Mn diffusion doping was performed at two different temperatures (600 and 800 °C). The samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray fluorescence, x-ray diffraction (XRD), superconducting quantum interference device magnetometer, and photoluminescence. Diffusion doping resulted in the increase of the size of Tetrapods, but no new peaks were found in XRD spectrum. Mn doped ZnO Tetrapod structures were found to be ferromagnetic with Curie temperature ∼50 K, and showed large coercive field (∼3500 Oe for 800 °C sample, ∼5500 Oe for 600 °C sample).ZnO Tetrapod nanostructures were prepared by evaporating Zn metal under humid argon flow. After the fabrication, Mn diffusion doping was performed at two different temperatures (600 and 800 °C). The samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray fluorescence, x-ray diffraction (XRD), superconducting quantum interference device magnetometer, and photoluminescence. Diffusion doping resulted in the increase of the size of Tetrapods, but no new peaks were found in XRD spectrum. Mn doped ZnO Tetrapod structures were found to be ferromagnetic with Curie temperature ∼50 K, and showed large coercive field (∼3500 Oe for 800 °C sample, ∼5500 Oe for 600 °C sample).
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magnetic properties of mn doped zno Tetrapod structures
Applied Physics Letters, 2004Co-Authors: V A L Roy, Aleksandra B Djurisic, Hui Liu, Xuxiang Zhang, Y H Leung, Ju Gao, H F Lui, M H Xie, C SuryaAbstract:ZnO Tetrapod nanostructures were prepared by evaporating Zn metal under humid argon flow. After the fabrication, Mn diffusion doping was performed at two different temperatures (600 and 800 °C). The samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray fluorescence, x-ray diffraction (XRD), superconducting quantum interference device magnetometer, and photoluminescence. Diffusion doping resulted in the increase of the size of Tetrapods, but no new peaks were found in XRD spectrum. Mn doped ZnO Tetrapod structures were found to be ferromagnetic with Curie temperature ∼50 K, and showed large coercive field (∼3500 Oe for 800 °C sample, ∼5500 Oe for 600 °C sample).