Atomic Layer Deposition for Energy and Environmental Applications

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134488/1/admi201600914.pd

Synergistic Effect of 3D Current Collectors and ALD Surface Modification for High Coulombic Efficiency Lithium Metal Anodes

Improving the performance of Li metal anodes is a critical bottleneck to enable nextâ generation battery systems beyond Liâ ion. However, stability issues originating from undesirable electrode/electrolyte interactions and Li dendrite formation have impaired longâ term cycling of Li metal anodes. Herein, a bottomâ up fabrication process is demonstrated for a current collector for Li metal electrodeposition and dissolution composed of highly uniform vertically aligned Cu pillars. By rationally controlling geometric parameters of the 3D current collector architecture, including pillar diameter, spacing, and length, the morphology of Li plating/stripping upon cycling can be controlled and optimal cycling performance can be achieved. In addition, it is demonstrated that deposition of an ultrathin layer of ZnO by atomic layer deposition on the current collector surface can facilitate the initial Li nucleation, which dictates the morphology and reversibility of subsequent cycling. This coreâ shell pillar architecture allows for the effects of geometry and surface chemistry to be decoupled and individually controlled to optimize the electrode performance in a synergistic manner. Using this platform, Li metal anodes are demonstrated with Coulombic efficiency up to 99.5%, providing a pathway toward highâ efficiency and longâ cycle life Li metal batteries with reduced excess Li loading.A 3D current collector architecture based on vertically aligned Cu for Li metal anodes is reported. By rationally tuning geometric parameters and surface chemistry of the 3D architecture, the morphology of Li plating/stripping can be controlled. Leveraging the synergistic effects of the optimized geometry and interface modification, cycling of Li metal anodes is demonstrated with Coulombic efficiency up to 99.5%.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147805/1/aenm201802534-sup-0001-S1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147805/2/aenm201802534_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147805/3/aenm201802534.pd

Invited; ALD of robust amorphous oxide TFTS with turn on at the Boltzmann limit

The development of amorphous oxide semiconductors have driven great advances in display technology. These materials are poised to expand into new applications by heterointegration at the back-end-of-line (BEOL) of Si CMOS for diverse uses in power harvesting, conversion and management as well as in-memory computing and AI hardware. For acceptance in IC foundries, atomic layer deposition (ALD) is an attractive technology with nanometer-scale precision. Recently, significant advances have been made in ALD processes for both n- and ptype oxide semiconductors [1], [2]. Here, we report robust thin film transistors (TFTs) made using n-type zinc-tinoxide deposited by ALD, with excellent robustness to aging and bias stress. The use of an in situ gate insulator formed by ALD enables a sub-threshold slope (SS) at the Boltzmann limit of 60 mV·dec-1 at room temperature. Please click Download on the upper right corner to see the full abstract

High‐Performance Zinc Tin Oxide TFTs with Active Layers Deposited by Atomic Layer Deposition

New deposition techniques for amorphous oxide semiconductors compatible with silicon back end of line manufacturing are needed for 3D monolithic integration of thin‐film electronics. Here, three atomic layer deposition (ALD) processes are compared for the fabrication of amorphous zinc tin oxide (ZTO) channels in bottom‐gate, top‐contact n‐channel transistors. As‐deposited ZTO films, made by ALD at 150–200 °C, exhibit semiconducting, enhancement‐mode behavior with electron mobility as high as 13 cm2 V−1 s−1, due to a low density of oxygen‐related defects. ZTO deposited at 200 °C using a hybrid thermal‐plasma ALD process with an optimal tin composition of 21%, post‐annealed at 400 °C, shows excellent performance with a record high mobility of 22.1 cm2 V–1 s–1 and a subthreshold slope of 0.29 V dec–1. Increasing the deposition temperature and performing post‐deposition anneals at 300–500 °C lead to an increased density of the X‐ray amorphous ZTO film, improving its electrical properties. By optimizing the ZTO active layer thickness and using a high‐k gate insulator (ALD Al2O3), the transistor switching voltage is lowered, enabling electrical compatibility with silicon integrated circuits. This work opens the possibility of monolithic integration of ALD ZTO‐based thin‐film electronics with silicon integrated circuits or onto large‐area flexible substrates.Three atomic layer deposition (ALD) processes are investigated for the deposition of zinc tin oxide (ZTO) as the active layer in thin‐film transistors (TFTs). With a low density of oxygen vacancies, as‐deposited films exhibit semiconducting, enhancement‐mode behavior. Post‐deposition anneals result in increased film density and record high electron mobility for ALD ZTO TFTs using process temperatures within the back‐end‐of‐line thermal budget.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156226/3/aelm202000195-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156226/2/aelm202000195.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156226/1/aelm202000195_am.pd

Rational Design of Transparent Nanowire Architectures with Tunable Geometries for Preventing Marine Fouling

Marine biofouling is a sticky global problem that hinders maritime industries. Various microscale surface structures inspired by marine biological species have been explored for their anti- fouling properties. However, systematic studies of anti- marine- fouling performance on surface architectures with characteristic length- scales spanning from below 100 nm to greater than 10 µm are generally lacking. Herein, a study on the rational design and fabrication of ZnO/Al2O3 core- shell nanowire architectures with tunable geometries (length, spacing, and branching) and surface chemistry is presented. The ability of the nanowires to significantly delay or prevent marine biofouling is demonstrated. Compared to planar surfaces, hydrophilic nanowires can reduce fouling coverage by up to - 60% after 20 days. The fouling reduction mechanism is mainly due to two geometric effects: reduced effective settlement area and mechanical cell penetration. Additionally, superhydrophobic nanowires can completely prevent marine biofouling for up to 22 days. The nanowire surfaces are transparent across the visible spectrum, making them applicable to windows and oceanographic sensors. Through the rational control of surface nano- architectures, the coupled relationships between wettability, transparency, and anti- biofouling performance are identified. It is envisioned that the insights gained from the work can be used to systematically design surfaces that reduce marine biofouling in various industrial settings.Core- shell nanowire architectures with tunable geometries (length, spacing, and branching) and surface chemistry are shown to significantly delay marine biofouling. The fouling reduction mechanism is mainly due to the two effects: reduced effective settlement area and mechanical biocide. The insights gained from the work can be used to systematically design surfaces that reduce marine biofouling in various industrial settings.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162819/3/admi202000672-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162819/2/admi202000672_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162819/1/admi202000672.pd

Overproduction of cosmic superstrings

We show that the naive application of the Kibble mechanism seriously underestimates the initial density of cosmic superstrings that can be formed during the annihilation of D-branes in the early universe, as in models of brane-antibrane inflation. We study the formation of defects in effective field theories of the string theory tachyon both analytically, by solving the equation of motion of the tachyon field near the core of the defect, and numerically, by evolving the tachyon field on a lattice. We find that defects generically form with correlation lengths of order M_s^{-1} rather than H^{-1}. Hence, defects localized in extra dimensions may be formed at the end of inflation. This implies that brane-antibrane inflation models where inflation is driven by branes which wrap the compact manifold may have problems with overclosure by cosmological relics, such as domain walls and monopoles.Comment: 31 pages, 16 figures, JHEP style; References added; Improved discussion of initial condition

The Entropy of 4D Black Holes and the Enhancon

We consider the physics of enhancons as applied to four dimensional black holes which are constructed by wrapping both D-branes and NS-branes on K3. As was recently shown for the five dimensional black holes, the enhancon is crucial in maintaining consistency with the second law of thermodynamics. This is true for both the D-brane and NS-brane sectors of these black holes. In particular NS5-branes in both type IIA and IIB string theory are found to exhibit enhancon physics when wrapped on a K3 manifold.Comment: 23 pages. 1 figure. Minor typos corrected. Refs added. To appear in PR

Caustic Formation in Tachyon Effective Field Theories

Certain configurations of D-branes, for example wrong dimensional branes or the brane-antibrane system, are unstable to decay. This instability is described by the appearance of a tachyonic mode in the spectrum of open strings ending on the brane(s). The decay of these unstable systems is described by the rolling of the tachyon field from the unstable maximum to the minimum of its potential. We analytically study the dynamics of the inhomogeneous tachyon field as it rolls towards the true vacuum of the theory in the context of several different tachyon effective actions. We find that the vacuum dynamics of these theories is remarkably similar and in particular we show that in all cases the tachyon field forms caustics where second and higher derivatives of the field blow up. The formation of caustics signals a pathology in the evolution since each of the effective actions considered is not reliable in the vicinity of a caustic. We speculate that the formation of caustics is an artifact of truncating the tachyon action, which should contain all orders of derivatives acting on the field, to a finite number of derivatives. Finally, we consider inhomogeneous solutions in p-adic string theory, a toy model of the bosonic tachyon which contains derivatives of all orders acting on the field. For a large class of initial conditions we conclusively show that the evolution is well behaved in this case. It is unclear if these caustics are a genuine prediction of string theory or not.Comment: 23 pages, 5 figures; accepted for publication in JHEP. Revised derivation of eikonal equation for the DBI action. Added comments concerning the relationship between p-adic string theory and tachyon matter. Added second example of inhomogeneous evolution in p-adic string theory. Misleading statements concerning caustic-free evolution removed, references adde

Ortervirales: A new viral order unifying five families of reverse-transcribing viruses

Reverse-transcribing viruses, which synthesize a copy of genomic DNA from an RNA template, are widespread in animals, plants, algae and fungi (1, 2).

Focus on environmental risks and migration: causes and consequences

Environmental change poses risks to societies, including disrupting social and economic systems such as migration. At the same time, migration is an effective adaptation to environmental and other risks. We review novel science on interactions between migration, environmental risks and climate change. We highlight emergent findings, including how dominant flows of rural to urban migration mean that populations are exposed to new risks within destination areas and the requirement for urban sustainability. We highlight the issue of lack of mobility as a major issue limiting the effectiveness of migration as an adaptation strategy and leading to potentially trapped populations. The paper presents scenarios of future migration that show both displacement and trapped populations over the incoming decades. Papers in the special issue bring new insights from demography, human geography, political science and environmental science to this emerging field