The global abundance of tree palms

Aim Palms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change. Location Tropical and subtropical moist forests. Time period Current. Major taxa studied Palms (Arecaceae). Methods We assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure. Results On average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground biomass, but the magnitude and direction of the effect require additional work. Conclusions Tree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests

Role of Dopants in Long-Range Charge Carrier Transport for p‑Type and n‑Type Graphene Transparent Conducting Thin Films

Monolayer to few-layer graphene thin films have several attractive properties such as high transparency, exceptional electronic transport, mechanical durability, and environmental stability, which are required in transparent conducting electrodes (TCs). The successful incorporation of graphene TCs into demanding applications such as thin film photovoltaics requires a detailed understanding of the factors controlling long-range charge transport. In this study, we use spectroscopic and electrical transport measurements to provide a self-consistent understanding of the macroscopic (centimeter, many-grain scale) transport properties of chemically doped p-type and n-type graphene TCs. We demonstrate the first large-area n-type graphene TCs through the use of hydrazine or polyethyleneimine as dopants. The n-type graphene TCs utilizing PEI, either as the sole dopant or as an overcoat, have good stability in air compared to TCs only doped with hydrazine. We demonstrate a shift in Fermi energy of well over 1 V between the n- and p-type graphene TCs and a sheet resistance of ∼50 Ω/sq at 89% visible transmittance. The carrier density is increased by 2 orders of magnitude in heavily doped graphene TCs, while the mobility is reduced by a factor of ∼7 due to charged impurity scattering. Temperature-dependent measurements demonstrate that the molecular dopants also help to suppress processes associated with carrier localization that may limit the potential of intrinsic graphene TCs. These results suggest that properly doped graphene TCs may be well-suited as anodes or cathodes for a variety of opto-electronic applications

Graphene as an Efficient Interfacial Layer for Electrochromic Devices

This study presents an interfacial modification strategy to improve the performance of electrochromic films that were fabricated by a magnetron sputtering technique. High-quality graphene sheets, synthesized by chemical vapor deposition, were used to modify fluorine-doped tin oxide substrates, followed by the deposition of high-performance nanocomposite nickel oxide electrochromic films. Electrochromic cycling results revealed that a near-complete monolayer graphene interfacial layer improves the electrochromic performance in terms of switching kinetics, activation period, coloration efficiency, and bleached-state transparency, while maintaining ∼100% charge reversibility. The present study offers an alternative route for improving the interfacial properties between electrochromic and transparent conducting oxide films without relying on conventional methods such as nanostructuring or thin film composition control

Manipulation of Hydrogen Binding Energy and Desorption Kinetics by Boron Doping of High Surface Area Carbon

Boron-doped high surface area carbon is shown to have unique chemical and structural properties that are advantageous for hydrogen storage. High surface area boron-doped carbon sorbents were produced by chemical vapor deposition of a boron-doped carbon (BC_X) layer onto CM-Tec activated carbon. Photoelectron spectroscopy indicates the incorporation of boron at levels up to 14.3 at. % into sites with varying bonding environments. High-resolution microscopy characterization demonstrates that the turbostratic boron–carbon layer has a <i>c</i>-plane spacing of 4.02 ± 0.24 Å, large enough to allow the diffusion of hydrogen intercalated between BC_X layers. Slower adsorption and desorption kinetics that depend sensitively on H₂ charging duration and temperature suggest the presence of hidden surface area of the turbostratic BC_X and enhanced binding energy sites. Our study suggests that the increased <i>c</i>-plane spacing, together with a significant concentration of electron-deficient sp² boron sites, combine to create a stronger H₂–sorbent interaction than is typically achieved for undoped carbon sorbents