Elucidating the Influence of Side-Chain Circular Distribution on the Crack Onset Strain and Hole Mobility of Near-Amorphous Indacenodithiophene Copolymers
Abstract not provided
Sommerville, Parker J.W.↗
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Hole number effect on spray dynamics of multi-hole diesel nozzles: An observation from three- to nine-hole nozzles
For the simplicity of optical diagnostics, studies on fuel spray and combustion characteristics of modern diesel engines have been conducted using the investigation nozzles having the reduced number of holes (two- or three-hole nozzles) compared to the production nozzles. However, the similarity of spray dynamics between the investigation nozzles and production nozzles has not been confirmed yet. Also, the hole number effect on spray dynamics has been investigated only in a limited range of hole number making it difficult to derive the clear trend and understandings of the hole number effect. In this study, the hole number effect on spray dynamics of multi-hole diesel nozzles has been investigated in a wide range of hole number with sufficient data points (three, five, six, eight, nine-hole) by using the X-ray Phase-Contrast Imaging technique. The non-linear trend in the spray structure, as well as the dynamics results, was observed as increasing the hole number regardless of injection pressure. Discussions were made accordingly to understand the observed result trend. In conclusion, the study suggests that great attention is needed when deciding the number of nozzle holes for the optimized engine combustion.
42 ENGINEERING↗
Uncovering the Role of Hole Traps in Promoting Hole Transfer from Multiexcitonic Quantum Dots to Molecular Acceptors
The understanding of electronic dynamics in multiexcitonic quantum dots (QDs) is important for designing efficient systems useful in high power scenarios, such as solar concentrators and multielectron charge transfer. The multiple charge carriers within a QD can undergo undesired Auger recombination events, which rapidly annihilate carriers on picosecond time scales and generate heat from absorbed photons instead of useful work. Compared to the transfer of multiple electrons, the transfer of multiple holes has proven to be more difficult due to slower hole transfer rates. To probe the competition between Auger recombination and hole transfer in CdSe, CdS, and CdSe/CdS QDs of varying sizes, we synthesized a phenothiazine derivative with optimized functionalities for binding to QDs as a hole accepting ligand and for spectroscopic observation of hole transfer. Transient absorption spectroscopy was used to monitor the photoinduced absorption features from both trapped holes and oxidized ligands under excitation fluences where the averaged initial number of excitons in a QD ranged from ~1 to 19. We observed fluence-dependent hole transfer kinetics that last around 100 ps longer than the predicted Auger recombination lifetimes, and the transfer of up to 3 holes per QD. Theoretical modeling of the kinetics suggests that binding of hole acceptors introduces trapping states significantly different from those in native QDs passivated with oleate ligands. Holes in these modified trap states have prolonged lifetimes, which promotes the hole transfer efficiency. These results highlight the beneficial role of hole-trapping states in devising hole transfer pathways in QD-based systems under multiexcitonic conditions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Identifying the acceptor state in NiO hole collection layers: direct observation of exciton dissociation and interfacial hole transfer across a Fe 2 O 3 /NiO heterojunction
NiO is widely utilized as a hole transport layer in solar energy devices where light absorption in a photoactive layer is followed by charge separation and hole injection into a NiO collection layer. Due to the complex electronic structure of the hybridized valence band in NiO, the chemical nature of the hole acceptor state has remained an open question, despite the fact that hole localization in this material significantly influences device efficiency. To comment on this, we present results of ultrafast charge carrier dynamics in a NiO based model heterojunction (Fe 2 O 3 /NiO) using extreme ultraviolet reflection–absorption (XUV-RA) spectroscopy. Element specific XUV-RA spectroscopy demonstrates the formation of transient Ni 3+ within 10 ps following selective photoexcitation of the underlying Fe 2 O 3 substrate. This indicates that hole transfer in this system occurs to NiO valence band states composed of significant Ni 3d character. Additionally, we show that this hole injection process proceeds via a two-step sequential mechanism where fast, field-driven exciton dissociation occurs in Fe 2 O 3 in 680 ± 60 fs, followed by subsequent hole injection to NiO in 9.2 ± 2.9 ps. Furthermore, these results reveal the chemical nature of the hole acceptor state in widely used NiO hole transport layers and provides a direct observation of exciton dissociation and interfacial hole transfer in this model system.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Plasma electron hole kinematics. Hole tracking Particle-In-Cell simulation
The kinematics of a 1-D electron hole is studied using a novel Particle-In-Cell simulation code. A hole tracking technique enables us to follow the trajectory of a fast-moving solitary hole and study quantitatively hole acceleration and coupling to ions. We observe a transient at the initial stage of hole formation when the hole accelerates to several times the cold-ion sound speed. Artificially imposing slow ion speed changes on a fully formed hole causes its velocity to change even when the ion stream speed in the hole frame greatly exceeds the ion thermal speed, so there are no reflected ions. The behavior that we observe in numerical simulations agrees very well with our analytic theory of hole momentum conservation and the effects of “jetting.”
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Static response and Love numbers of Schwarzschild black holes
We derive the quadratic action for the physical degrees of freedom of massless spin-0, spin-1, and spin-2 perturbations on a Schwarzschild-(A)dS background in arbitrary dimensions. Here, we then use these results to compute the static response of asymptotically flat Schwarzschild black holes to external fields. Our analysis reproduces known facts about black hole Love numbers — in particular that they vanish for all types of perturbation in four spacetime dimensions — but also leads to new results. For instance, we find that neutral Schwarzschild black holes polarize in the presence of an electromagnetic background in any number of spacetime dimensions except four. Moreover, we calculate for the first time black hole Love numbers for vector-type gravitational perturbations in higher dimensions and find that they generically do not vanish. Along the way, we shed some light on an apparent discrepancy between previous results in the literature, and clarify some aspects of the matching between perturbative calculations of static response on a Schwarzschild background and the point-particle effective theory.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Mitigation and Diagnosis of Pin-Hole Formation in Polymer Electrolyte Membrane Fuel Cells
In this work, we implement a calendering technique to flatten stray fibers within the gas diffusion media, thereby mitigating pin-hole formation in the hot-pressed MEAs. We have investigated the influence of calendering on the long-term durability for several types of gas diffusion electrodes (GDEs) using a combined chemical and mechanical accelerated stress test (AST). The calendered MEAs demonstrate an average AST lifetime improvement of 77% relative to the as-fabricated MEAs.
AMR↗
Blob-hole correlation model for edge turbulence and comparisons with NSTX gas puff imaging data [Blob-hole correlation model for edge turbulence and comparisons with NSTX GPI data]
We report that gas puff imaging (GPI) observations made in NSTX have revealed two-point spatial correlations of edge and scrape-off layer turbulence in the plane perpendicular to the magnetic field. A common feature is the occurrence of dipole-like patterns with significant regions of negative correlation. In this paper, we explore the possibility that these dipole patterns may be due to blob-hole pairs. Statistical methods are applied to determine the two-point spatial correlation that results from a model of blob-hole pair formation. It is shown that the model produces dipole correlation patterns that are qualitatively similar to the GPI data in several respects. Effects of the reference location (confined surfaces or scrape-off layer), a superimposed random background, hole velocity and lifetime, and background sheared flows are explored and discussed with respect to experimental observations. Additional analysis of the experimental GPI dataset is performed to further test this blob-hole correlation model. A time delay two-point spatial correlation study did not reveal inward propagation of the negative correlation structures that were postulated to correspond to holes in the data nor did it suggest that the negative correlation structures are due to neutral shadowing. However, tracking of the highest and lowest values (extrema) of the normalized GPI fluctuations shows strong evidence for mean inward propagation of minima and outward propagation of maxima, in qualitative agreement with theoretical expectations. Finally, other properties of the experimentally observed extrema are discussed.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Event Horizon Telescope observations as probes for quantum structure of astrophysical black holes
The need for a consistent quantum evolution for black holes has led to proposals that their semiclassical description is modified not just near the singularity, but at horizon or larger scales. If such modifications extend beyond the horizon, they influence regions accessible to distant observeration. Natural candidates for these modifications behave like metric fluctuations, with characteristic length and time scales set by the horizon radius. In this study, we investigate the possibility of using the Event Horizon Telescope to observe these effects, if they have a strength sufficient to make quantum evolution consistent with unitarity. We find that such quantum fluctuations can introduce a strong time dependence for the shape and size of the shadow that a black hole casts on its surrounding emission. For the black hole in the center of the Milky Way, detecting the rapid time variability of its shadow will require non-imaging timing techniques. However, for the much larger black hole in the center of the M87 galaxy, a variable black-hole shadow, if present with these parameters, would be readily observable in the individual snapshots that will be obtained by the Event Horizon Telescope.
79 ASTRONOMY AND ASTROPHYSICS↗
Demonstration of a MOT in a sub-millimeter membrane hole
Abstract We demonstrate the generation of a cold-atom ensemble within a sub-millimeter diameter hole in a transparent membrane, a so-called “membrane MOT”. With a sub-Doppler cooling process, the atoms trapped by the membrane MOT are cooled down to 10 $$\upmu$$ μ K. The atom number inside the unbridged/bridged membrane hole is about $$10^4$$ 10 4 to $$10^5$$ 10 5 , and the $$1/e^2$$ 1 / e 2 -diameter of the MOT cloud is about 180 $$\upmu$$ μ m for a 400 $$\upmu$$ μ m-diameter membrane hole. Such a membrane device can, in principle, efficiently load cold atoms into the evanescent-field optical trap generated by the suspended membrane waveguide for strong atom-light interaction and provide the capability of sufficient heat dissipation at the waveguide. This represents a key step toward the photonic atom trap integrated platform (ATIP).
74 ATOMIC AND MOLECULAR PHYSICS↗
Valley-spin polarization at zero magnetic field induced by strong hole-hole interactions in monolayer WSe 2
Monolayer transition metal dichalcogenides have emerged as prominent candidates to explore the complex interplay between spin and valley degrees of freedom. Their strong spin-orbit interaction and broken inversion symmetry lead to the spin-valley locking effect, in which carriers occupying theKandK′ valleys of the reciprocal space must have opposite spins. This effect is particularly strong for holes due to a larger spin-orbit gap in the valence band. By reducing the dimensionality of a monolayer of WSe 2 to 1D via electrostatic confinement, we demonstrate that spin-valley locking and strong hole-hole interactions lead to a ferromagnetic state where hole transport is spin-valley polarized, even without an applied magnetic field. A massive Dirac fermion model in the Hartree-Fock approximation reveals that many-body hole-exchange interactions lead to this polarized ground-state. This observation opens the possibility of implementing a robust and stable valley-polarized system, essential in valleytronic applications.
Science & Technology - Other Topics↗
Geodesic analysis and black hole shadows on a general non-extremal rotating black hole in five-dimensional gauged supergravity
In this work, motivated by the fact that higher dimensional theories predict the existence of black holes which differ from their four dimensional counterpart, we analyse the geodesics and black hole shadow cast by a general non-extremal five dimensional black hole. The system under consideration corresponds to the Chong–Cvetič–Lü–Pope (Chong et al., 2005), which has the Myers–Perry black hole as a limit.
79 ASTRONOMY AND ASTROPHYSICS↗
A hot carrier perovskite solar cell with efficiency exceeding 27% enabled by ultrafast hot hole transfer with phthalocyanine derivatives
Illustration of hot hole transfer through interfacial S–Pb interactions, and a peak efficiency of 27.30% was achieved under 5.9 suns via ultrafast hot hole extraction.
Gong, Shaokuan↗
Hole–hole Tamm–Dancoff-approximated density functional theory: A highly efficient electronic structure method incorporating dynamic and static correlation
The study of photochemical reaction dynamics requires accurate as well as computationally efficient electronic structure methods for the ground and excited states. While time-dependent density functional theory (TDDFT) is not able to capture static correlation, complete active space self-consistent field methods neglect much of the dynamic correlation. Hence, inexpensive methods that encompass both static and dynamic electron correlation effects are of high interest. Here, we revisit hole–hole Tamm–Dancoff approximated (hh-TDA) density functional theory for this purpose. The hh-TDA method is the hole–hole counterpart to the more established particle–particle TDA (pp-TDA) method, both of which are derived from the particle–particle random phase approximation (pp-RPA). In hh-TDA, the N-electron electronic states are obtained through double annihilations starting from a doubly anionic (N+2 electron) reference state. In this way, hh-TDA treats ground and excited states on equal footing, thus allowing for conical intersections to be correctly described. Furthermore, the treatment of dynamic correlation is introduced through the use of commonly employed density functional approximations to the exchange-correlation potential. Additionally, we show that hh-TDA is a promising candidate to efficiently treat the photochemistry of organic and biochemical systems that involve several low-lying excited states—particularly those with both low-lying ππ* and nπ* states where inclusion of dynamic correlation is essential to describe the relative energetics. In contrast to the existing literature on pp-TDA and pp-RPA, we employ a functional-dependent choice for the response kernel in pp- and hh-TDA, which closely resembles the response kernels occurring in linear response and collinear spin-flip TDDFT.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Hole-induced electronic and optical transitions in L a 1 - x S r x Fe O 3 epitaxial thin films
We have investigated the electronic and optical properties of epitaxial La 1-x Sr x FeO 3 for 0 ≤ x ≤ 1 prepared by molecular-beam epitaxy. Core-level and valence-band x-ray photoemission features monotonically shift to lower binding energy with increasing x, indicating downward movement of the Fermi level toward the valence-band maximum. Combining valence-band photoemission and O K -edge x-ray absorption data, we map the evolution of the occupied and unoccupied bands and observe a narrowing of the gap, along with a transfer of state density from just below to just above the Fermi level as a result of hole doping. In-plane transport measurements confirm that the material becomes a p -type semiconductor at lower doping levels and exhibits a conversion from semiconducting to metallic behavior at x = 1. As a result, low-energy optical transitions revealed by spectroscopic ellipsometry are explained based on insight from theoretical densities of states and first-principles calculations of optical absorption spectra.
36 MATERIALS SCIENCE↗
Single and double hole quantum dots in strained Ge/SiGe quantum wells
Even as today's most prominent spin-based qubit technologies are maturing in terms of capability and sophistication, there is growing interest in exploring alternate material platforms that may provide advantages, such as enhanced qubit control, longer coherence times, and improved extensibility. Recent advances in heterostructure material growth have opened new possibilities for employing hole spins in semiconductors for qubit applications. Undoped, strained Ge/SiGe quantum wells are promising candidate hosts for hole spin-based qubits due to their low disorder, large intrinsic spin–orbit coupling strength, and absence of valley states. We use a simple one-layer gated device structure to demonstrate both a single quantum dot as well as coupling between two adjacent quantum dots. The hole effective mass in these undoped structures, m* ~ 0.08 m 0 , is significantly lower than for electrons in Si/SiGe, pointing to the possibility of enhanced tunnel couplings in quantum dots and favorable qubit–qubit interactions in an industry-compatible semiconductor platform.
36 MATERIALS SCIENCE↗
Anionic redox reaction in layered NaCr2/3Ti1/3S2 through electron holes formation and dimerization of S-S
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99 GENERAL AND MISCELLANEOUS↗