Michael S. Engel

Electroluminescence in Single Layer MoS2

We detect electroluminescence in single layer molybdenum disulfide (MoS2) field-effect transistors built on transparent glass substrates. By comparing the absorption, photoluminescence, and electroluminescence of the same MoS2 layer, we find that they all involve the same excited state at 1.8 eV. The electroluminescence has pronounced threshold behavior and is localized at the contacts. The results show that single layer MoS2, a direct band gap semiconductor, could be promising for novel optoelectronic devices, such as two-dimensional light detectors and emitters.

Fossiliferous Cretaceous amber from Myanmar (Burma): Its rediscovery, biotic diversity, and paleontological significance

Abstract Amber from Kachin, northern Burma, has been used in China for at least a millennium for carving decorative objects, but the only scientific collection of inclusion fossils, at the Natural History Museum, London (NHML), was made approximately 90 years ago. Age of the material was ambiguous, but probably Cretaceous. Numerous new records and taxa occur in this amber, based on newly excavated material in the American Museum of Natural History (AMNH) containing 3100 organisms. Without having all groups studied, significant new records and taxa thus far include the following (a † refers to extinct taxa): For Plants: An angiosperm flower (only the third in Cretaceous amber), spores and apparent sporangia of an unusual but common fungus, hepatophyte thalli and an archegoniophore of Marchantiaceae, and leafy shoots of Metasequoia (Coniferae). Metasequoia is possibly the source of the amber. For Animals: Mermithidae and other Nematoda; the oldest ixodid tick (a larval Amblyomma); bird feathers; and the only Mesozoic record of the Onychophora (“velvet” worms), described as †Cretoperipatus burmiticus, n. gen., n. sp. (Peripatidae). Poinars classification of the Onychophora is substantially revised. Still largely unstudied, the fauna of mites (Acari) and spiders (Araneae) appears to be the most diverse ones known for the Mesozoic. For Insecta: Odonata indet. (wing fragment); Plecoptera indet.; new genera of Dermaptera, Embiidina, and Zoraptera (the latter two as the only definitive Mesozoic fossils of their orders). Within Hemiptera, there are primitive new genera in the Aradidae, Hydrometridae, Piesmatidae, Schizopteridae, and Cimicomorpha (Heteroptera), as well as in †Tajmyraphididae (Aphidoidea), and †′otopsyllidiidae. An adult snakefly (Raphidioptera: †Mesoraphidiidae) is the smallest species in the order, and new genera occur in the Neuroptera: Coniopterygidae, Berothidae, and Psychopsidae, as well as larvae of apparent Nevrorthidae. Coleoptera are largely unstudied, but are probably the most diverse assemblage known from the Cretaceous, particularly for Staphylinidae. An adult lymexylid, the most primitive species of Atractocerus, is the first Mesozoic record of the family. In Hymenoptera there are primitive ants (Formicidae: Ponerinae n. gen., and †Sphecomyrma n.sp [Sphecomyrminae]), the oldest record of the Pompilidae, and significant new records of †Serphitidae and †Stigmaphronidae, among others. Diptera are the most diverse and abundant, with the oldest definitive Blephariceridae and mosquito (Culicidae), as well as new genera in the Acroceridae, Bibionidae, Empidoidea; a new genus near the enigmatic genus Valeseguya, and an unusual new genus in the †Archizelmiridae. †Chimeromyia (Diptera: Eremoneura), known previously in ambers from the Lower Cretaceous, is also represented. The stratigraphic distribution of exclusively Mesozoic arthropods in Burmese amber is reviewed, which indicates a probable Turonian-Cenomanian age of this material (90–100 Ma). Paleofaunal differences between the NHML and AMNH collections are discussed, as is the distinct tropical nature of the original biota. Burmese amber probably harbors the most diverse biota in amber from the Cretaceous, and one of the most diverse Mesozoic microbiotas now known.

Black Phosphorus Photodetector for Multispectral, High-Resolution Imaging

Black phosphorus is a layered semiconductor that is intensely researched in view of applications in optoelectronics. In this letter, we investigate a multilayer black phosphorus photodetector that is capable of acquiring high-contrast (V > 0.9) images both in the visible (λVIS = 532 nm) as well as in the infrared (λIR = 1550 nm) spectral regime. In a first step, by using photocurrent microscopy, we map the active area of the device and we characterize responsivity and gain. In a second step, by deploying the black phosphorus device as a point-like detector in a confocal microsope setup, we acquire diffraction-limited optical images with submicron resolution. The results demonstrate the usefulness of black phosphorus as an optoelectronic material for hyperspectral imaging applications.

Light–matter interaction in a microcavity-controlled graphene transistor

Graphene has extraordinary electronic and optical properties and holds great promise for applications in photonics and optoelectronics. Demonstrations including high-speed photodetectors, optical modulators, plasmonic devices, and ultrafast lasers have now been reported. More advanced device concepts would involve photonic elements such as cavities to control light–matter interaction in graphene. Here we report the first monolithic integration of a graphene transistor and a planar, optical microcavity. We find that the microcavity-induced optical confinement controls the efficiency and spectral selection of photocurrent generation in the integrated graphene device. A twenty-fold enhancement of photocurrent is demonstrated. The optical cavity also determines the spectral properties of the electrically excited thermal radiation of graphene. Most interestingly, we find that the cavity confinement modifies the electrical transport characteristics of the integrated graphene transistor. Our experimental approach opens up a route towards cavity-quantum electrodynamics on the nanometre scale with graphene as a current-carrying intra-cavity medium of atomic thickness.

New light shed on the oldest insect.

Insects are the most diverse lineage of all life in numbers of species, and ecologically they dominate terrestrial ecosystems. However, how and when this immense radiation of animals originated is unclear. Only a few fossils provide insight into the earliest stages of insect evolution, and among them are specimens in chert from Rhynie, Scotlands Old Red Sandstone (Pragian; about 396–407 million years ago), which is only slightly younger than formations harbouring the earliest terrestrial faunas. The most well-known animal from Rhynie is the springtail Rhyniella praecursor (Entognatha; Collembola), long considered to be the oldest hexapod. For true insects (Ectognatha), the oldest records are two apparent wingless insects from later in the Devonian period of North America. Here we show, however, that a fragmentary fossil from Rhynie, Rhyniognatha hirsti, is not only the earliest true insect but may be relatively derived within basal Ectognatha. In fact, Rhyniognatha has derived characters shared with winged insects, suggesting that the origin of wings may have been earlier than previously believed. Regardless, Rhyniognatha indicates that insects originated in the Silurian period and were members of some of the earliest terrestrial faunas.

Termites (Isoptera): Their Phylogeny, Classification, and Rise to Ecological Dominance

Abstract Like ants, termites are entirely eusocial and have profound ecological significance in the tropics. Following upon recent studies reporting more than a quarter of all known fossil termites, we present the first phylogeny of termite lineages using exemplar Cretaceous, Tertiary, and Recent taxa. Relationships among Recent families were largely unaffected by the addition of extinct taxa, but the analysis revealed extensive grades of stem-group taxa and the divergence of some modern families in the Cretaceous. Rhinotermitidae, Serritermitidae, and the “higher” termites (family Termitidae), which comprise 84% of the world termite species, diverged and radiated entirely in the Tertiary, corresponding to a significant increase in termite individuals in the fossil record. Radiation of the higher termites may have affected the formation of terrestrial carbon reserves like oil and coal. The higher classification of Isoptera is slightly revised based on the phylogenetic results. The following new taxa are proposed: Cratomastotermitidae, new family; Euisoptera, new clade; Archotermopsidae, new family; and Neoisoptera, new clade. In addition, the families Stolotermitidae, Stylotermitidae, and Archeorhinotermitidae are newly recognized or resurrected, and the families Termopsidae and Hodotermitidae are significantly restricted in composition.

Biogeographic and evolutionary implications of a diverse paleobiota in amber from the early Eocene of India

For nearly 100 million years, the India subcontinent drifted from Gondwana until its collision with Asia some 50 Ma, during which time the landmass presumably evolved a highly endemic biota. Recent excavations of rich outcrops of 50–52-million-year-old amber with diverse inclusions from the Cambay Shale of Gujarat, western India address this issue. Cambay amber occurs in lignitic and muddy sediments concentrated by near-shore chenier systems; its chemistry and the anatomy of associated fossil wood indicates a definitive source of Dipterocarpaceae. The amber is very partially polymerized and readily dissolves in organic solvents, thus allowing extraction of whole insects whose cuticle retains microscopic fidelity. Fourteen orders and more than 55 families and 100 species of arthropod inclusions have been discovered thus far, which have affinities to taxa from the Eocene of northern Europe, to the Recent of Australasia, and the Miocene to Recent of tropical America. Thus, India just prior to or immediately following contact shows little biological insularity. A significant diversity of eusocial insects are fossilized, including corbiculate bees, rhinotermitid termites, and modern subfamilies of ants (Formicidae), groups that apparently radiated during the contemporaneous Early Eocene Climatic Optimum or just prior to it during the Paleocene-Eocene Thermal Maximum. Cambay amber preserves a uniquely diverse and early biota of a modern-type of broad-leaf tropical forest, revealing 50 Ma of stasis and change in biological communities of the dipterocarp primary forests that dominate southeastern Asia today.

Treatise on the Isoptera of the World

ABSTRACT A comprehensive compendium on the taxonomy and biology of the 3106 living and fossil species of the worlds termites is presented, along with reviews of Isoptera morphology and evolution, identification keys, the history of termite systematics, and summary of the worlds 363 significant pest species. A complete bibliography is provided of nearly 5000 references covering virtually all aspects of termite taxonomy and biology through December 2011. The morphology of Isoptera is thoroughly reviewed and illustrated with original scanning electron micrographs and photomicrographs, covering the cuticular anatomy and those internal organs that are taxonomically and phylogenetically significant, including several new character systems. Terminology is presented for the systems of tibial spines and spurs so as to establish homologs. Keys are presented to the nine living families of termites, and the world subfamilies and genera of Archotermopsidae, Hodotermitidae, Kalotermitidae, Mastotermitidae, Rhinotermiti...

A New Interpretation of the Oldest Fossil Bee (Hymenoptera: Apidae)

Abstract The oldest fossil bee, “Trigona” prisca (Apidae: Meliponini), in Late Cretaceous (Maastrichtian) amber from New Jersey, is redescribed and figured. Differences between T. prisca and extant Trigona are noted and the fossil is transferred into a new genus, Cretotrigona. An exploratory cladistic analysis of the Meliponini is undertaken and Cretotrigona supported as sister to the African genus Dactylurina. Affinities between Cretotrigona and recent genera are discussed as are implications of the presence of this derived stingless bee group at the end of the Mesozoic.

Family-Group Names for Bees (Hymenoptera: Apoidea)

Abstract The 173 family-group names for bees (Apoidea: Anthophila) are cataloged in chronological order. For each name the correct author, date, type genus, and combining stem are provided. The following names are considered nomina nuda: Phenacolletini, Ctenioschelini, †Chalicodomopsini, Liphanthini, Austropanurgini, and Hoplitini. The authorship of three names (Tapinotaspidini, Hexepeolini, and Ancyloscelidina) is corrected as each was a nomen nudum when first proposed, but has been subsequently made available by other authors. The following new names are proposed herein: Scraptrinae Ascher and Engel, new subfamily (Colletidae); Neffapini Ascher, new tribe (Andrenidae: Panurginae); Afrodasypodini Engel, new tribe (Melittidae: Dasypodainae), Afrodasypoda Engel, new genus; Hesperapina Ascher and Engel, new subtribe (Melittidae: Dasypodainae); Macrogaleina Engel, new subtribe (Apidae: Xylocopinae); and Ancyloscelidina Engel and Michener, new subtribe (Apidae: Apinae). A hierarchical outline of Apoidea classification (inclusive of the digger wasps), indicating the suggested current usage of all available family-group names is appended. The name Anthophila, as proposed by Latreille, is adopted for the bees as a whole.