- Characterization of high spatial resolution lithium fluoride X-ray detectors. [Journal Article]
- RSRev Sci Instrum 2019; 90(6):063702
- The response of lithium fluoride (LiF) crystal detectors to monochromatic X-rays is measured in the multi-kilo-electron-volt range. This response, as a function of the X-ray dose, is independent of p…
The response of lithium fluoride (LiF) crystal detectors to monochromatic X-rays is measured in the multi-kilo-electron-volt range. This response, as a function of the X-ray dose, is independent of photon energy with no saturation level found. The response, as a function of the incident energy flux, is found to increase for photons of lower energy due to the differing attenuation lengths of X-ray photons within the crystal. Small differences are seen between different confocal microscopes used to scan the data, suggesting the need for absolute calibration. The spatial resolution of the LiF is also measured (1.19-1.36 μm) and is found to be independent of incident photon energy. Finally, a photometric study is performed in order to assess the feasibility of using these detectors at current X-ray free electron laser and laser facilities worldwide.
- A ten-inch manipulator (TIM) based fast-electron spectrometer with multiple viewing angles (OU-ESM). [Journal Article]
- RSRev Sci Instrum 2019; 90(6):063501
- The measurement of angularly resolved energy distributions of mega-electron-volt electrons is important for gaining a better understanding of the interaction of ultra-intense laser pulses with plasma…
The measurement of angularly resolved energy distributions of mega-electron-volt electrons is important for gaining a better understanding of the interaction of ultra-intense laser pulses with plasma, especially for fast-ignition laser-fusion research. It is also crucial when evaluating the production of suprathermal (several 10-keV) electrons through laser-plasma instabilities in conventional hot-spot-ignition and shock-ignition research. For these purposes, we developed a 10-in. manipulator-based multichannel electron spectrometer-the Osaka University electron spectrometer (OU-ESM)-that combines angular resolution with high-energy resolution. The OU-ESM consists of five small electron spectrometers set at every 5°, with an energy range from ∼40 keV to ∼40 MeV. A low-magnetic-field option provides a higher spectral resolution for an energy range of up to ∼5 MeV. We successfully obtained angularly resolved electron spectra for various experiments on the OMEGA and OMEGA EP laser systems.
- In vitro sensitivity of malignant melanoma cells lines to photon and heavy ion radiation. [Journal Article]
- CTClin Transl Radiat Oncol 2019; 17:51-56
- CONCLUSIONS: Heavy ions showed a greater inhibitory effect on cell proliferation compared to photons and an increased G2/M arrest. Therefore, C12 and O16 heavy ions might overcome the relative radioresistance of malignant melanoma to photons. Further research is warranted.
- Theoretical Search for the Highest Valence States of the Coinage Metals: Roentgenium Heptafluoride May Exist. [Journal Article]
- ICInorg Chem 2019 Jul 01; 58(13):8735-8738
- We present here a relativistic density functional theory investigation of the penta- and heptavalent states of gold and roentgenium, employing the ZORA (zeroth order regular approximation to the Dira…
We present here a relativistic density functional theory investigation of the penta- and heptavalent states of gold and roentgenium, employing the ZORA (zeroth order regular approximation to the Dirac equation) Hamiltonian, including spin-orbit coupling at the two-component level, and large all-electron relativistic Slater-type quadruple-ζ quadruple polarization (ZORA-STO-QZ4P) basis sets. Unsurprisingly, our calculations confirm the stability of the experimentally known complexes AuF6- and Au2F10 with respect to decomposition to trivalent Au products and F2. The calculations also predict that RgF6- and Rg2F10 should be even more stable with respect to an analogous decomposition pathway. Like an earlier DFT study (Inorg. Chem. 2007, 46 (13), 5338-5342), our calculations rule out the true heptavalent Au complex AuF7 as a stable species, preferring instead a Cs AuF5···F2 formulation. Remarkably, our calculations confirm a D5 h pentagonal-bipyramidal structure of RgF7 as the global minimum, at an energy of approximately half an electron volt below the RgF5···F2 form.
- Ultrafast correlated charge and lattice motion in a hybrid metal halide perovskite. [Journal Article]
- SASci Adv 2019; 5(5):eaaw5558
- Hybrid organic-inorganic halide perovskites have shown remarkable optoelectronic properties, exhibiting an impressive tolerance to defects believed to originate from correlated motion of charge carri…
Hybrid organic-inorganic halide perovskites have shown remarkable optoelectronic properties, exhibiting an impressive tolerance to defects believed to originate from correlated motion of charge carriers and the polar lattice forming large polarons. Few experimental techniques are capable of directly probing these correlations, requiring simultaneous sub-millielectron volt energy and femtosecond temporal resolution after absorption of a photon. Here, we use time-resolved multi-THz spectroscopy, sensitive to the internal excitations of the polaron, to temporally and energetically resolve the coherent coupling of charges to longitudinal optical phonons in single-crystal CH3NH3PbI3 (MAPI). We observe room temperature intraband quantum beats arising from the coherent displacement of charge from the coupled phonon cloud. Our measurements provide strong evidence for the existence of polarons in MAPI at room temperature, suggesting that electron/hole-phonon coupling is a defining aspect of the hybrid metal-halide perovskites contributing to the protection from scattering and enhanced carrier lifetimes that define their usefulness in devices.
- Aqueous Li-ion battery enabled by halogen conversion-intercalation chemistry in graphite. [Journal Article]
- NatNature 2019; 569(7755):245-250
- The use of 'water-in-salt' electrolytes has considerably expanded the electrochemical window of aqueous lithium-ion batteries to 3 to 4 volts, making it possible to couple high-voltage cathodes with …
The use of 'water-in-salt' electrolytes has considerably expanded the electrochemical window of aqueous lithium-ion batteries to 3 to 4 volts, making it possible to couple high-voltage cathodes with low-potential graphite anodes1-4. However, the limited lithium intercalation capacities (less than 200 milliampere-hours per gram) of typical transition-metal-oxide cathodes5,6 preclude higher energy densities. Partial7,8 or exclusive9 anionic redox reactions may achieve higher capacity, but at the expense of reversibility. Here we report a halogen conversion-intercalation chemistry in graphite that produces composite electrodes with a capacity of 243 milliampere-hours per gram (for the total weight of the electrode) at an average potential of 4.2 volts versus Li/Li+. Experimental characterization and modelling attribute this high specific capacity to a densely packed stage-I graphite intercalation compound, C3.5[Br0.5Cl0.5], which can form reversibly in water-in-bisalt electrolyte. By coupling this cathode with a passivated graphite anode, we create a 4-volt-class aqueous Li-ion full cell with an energy density of 460 watt-hours per kilogram of total composite electrode and about 100 per cent Coulombic efficiency. This anion conversion-intercalation mechanism combines the high energy densities of the conversion reactions, the excellent reversibility of the intercalation mechanism and the improved safety of aqueous batteries.
- Carrier lifetimes of >1 μs in Sn-Pb perovskites enable efficient all-perovskite tandem solar cells. [Journal Article]
- SciScience 2019 05 03; 364(6439):475-479
- All-perovskite-based polycrystalline thin-film tandem solar cells have the potential to deliver efficiencies of >30%. However, the performance of all-perovskite-based tandem devices has been limited …
All-perovskite-based polycrystalline thin-film tandem solar cells have the potential to deliver efficiencies of >30%. However, the performance of all-perovskite-based tandem devices has been limited by the lack of high-efficiency, low-band gap tin-lead (Sn-Pb) mixed-perovskite solar cells (PSCs). We found that the addition of guanidinium thiocyanate (GuaSCN) resulted in marked improvements in the structural and optoelectronic properties of Sn-Pb mixed, low-band gap (~1.25 electron volt) perovskite films. The films have defect densities that are lower by a factor of 10, leading to carrier lifetimes of greater than 1 microsecond and diffusion lengths of 2.5 micrometers. These improved properties enable our demonstration of >20% efficient low-band gap PSCs. When combined with wider-band gap PSCs, we achieve 25% efficient four-terminal and 23.1% efficient two-terminal all-perovskite-based polycrystalline thin-film tandem solar cells.
- Van der Waals contacts between three-dimensional metals and two-dimensional semiconductors. [Journal Article]
- NatNature 2019; 568(7750):70-74
- As the dimensions of the semiconducting channels in field-effect transistors decrease, the contact resistance of the metal-semiconductor interface at the source and drain electrodes increases, domina…
As the dimensions of the semiconducting channels in field-effect transistors decrease, the contact resistance of the metal-semiconductor interface at the source and drain electrodes increases, dominating the performance of devices1-3. Two-dimensional (2D) transition-metal dichalcogenides such as molybdenum disulfide (MoS2) have been demonstrated to be excellent semiconductors for ultrathin field-effect transistors4,5. However, unusually high contact resistance has been observed across the interface between the metal and the 2D transition-metal dichalcogenide3,5-9. Recent studies have shown that van der Waals contacts formed by transferred graphene10,11 and metals12 on few-layered transition-metal dichalcogenides produce good contact properties. However, van der Waals contacts between a three-dimensional metal and a monolayer 2D transition-metal dichalcogenide have yet to be demonstrated. Here we report the realization of ultraclean van der Waals contacts between 10-nanometre-thick indium metal capped with 100-nanometre-thick gold electrodes and monolayer MoS2. Using scanning transmission electron microscopy imaging, we show that the indium and gold layers form a solid solution after annealing at 200 degrees Celsius and that the interface between the gold-capped indium and the MoS2 is atomically sharp with no detectable chemical interaction between the metal and the 2D transition-metal dichalcogenide, suggesting van-der-Waals-type bonding between the gold-capped indium and monolayer MoS2. The contact resistance of the indium/gold electrodes is 3,000 ± 300 ohm micrometres for monolayer MoS2 and 800 ± 200 ohm micrometres for few-layered MoS2. These values are among the lowest observed for three-dimensional metal electrodes evaporated onto MoS2, enabling high-performance field-effect transistors with a mobility of 167 ± 20 square centimetres per volt per second. We also demonstrate a low contact resistance of 220 ± 50 ohm micrometres on ultrathin niobium disulfide (NbS2) and near-ideal band offsets, indicative of defect-free interfaces, in tungsten disulfide (WS2) and tungsten diselenide (WSe2) contacted with indium alloy. Our work provides a simple method of making ultraclean van der Waals contacts using standard laboratory technology on monolayer 2D semiconductors.
- Chemically reversible isomerization of inorganic clusters. [Journal Article]
- SciScience 2019 02 15; 363(6428):731-735
- Structural transformations in molecules and solids have generally been studied in isolation, whereas intermediate systems have eluded characterization. We show that a pair of cadmium sulfide (CdS) cl…
Structural transformations in molecules and solids have generally been studied in isolation, whereas intermediate systems have eluded characterization. We show that a pair of cadmium sulfide (CdS) cluster isomers provides an advantageous experimental platform to study isomerization in well-defined, atomically precise systems. The clusters coherently interconvert over an ~1-electron volt energy barrier with a 140-milli-electron volt shift in their excitonic energy gaps. There is a diffusionless, displacive reconfiguration of the inorganic core (solid-solid transformation) with first order (isomerization-like) transformation kinetics. Driven by a distortion of the ligand-binding motifs, the presence of hydroxyl species changes the surface energy via physisorption, which determines "phase" stability in this system. This reaction possesses essential characteristics of both solid-solid transformations and molecular isomerizations and bridges these disparate length scales.
New Search Next
- Initial exploration of coronary stent image subtraction using dual-layer spectral CT. [Journal Article]
- EREur Radiol 2019; 29(8):4239-4248
- CONCLUSIONS: Subtraction images derived from dual-layer spectral CT enhanced in-stent lumen visibility and could potentially improve diagnostic performance for evaluating coronary stents.• Dual-layer spectral CT enabled good subtractive quality of coronary stents without misregistration artifacts. • Subtraction images could improve in-stent lumen visibility. • Reader confidence and diagnostic performance were enhanced with subtraction images.