In-Operando Lithium-Ion Transport Tracking in an All-Solid-State Battery.

An all-solid-state battery is a secondary battery that is charged and discharged by the transport of lithium ions between positive and negative electrodes. To fully realize the significant benefits of this battery technology, for example, higher energy densities, faster charging times, and safer operation, it is essential to understand how lithium ions are transported and distributed in the battery during operation. However, as the third lightest element, methods for quantitatively analyzing lithium during operation of an all-solid-state device are limited such that real-time tracking of lithium transport has not yet been demonstrated. Here, the authors report that the transport of lithium ions in an all-solid-state battery is quantitatively tracked in near real time by utilizing a high-intensity thermal neutron source and lithium-6 as a tracer in a thermal neutron-induced nuclear reaction. Furthermore, the authors show that the lithium-ion migration mechanism and pathway through the solid electrolyte can be determined by in-operando tracking. From these results, the authors suggest that the development of all-solid-state batteries has entered a phase where further advances can be carried out while understanding the transport of lithium ions in the batteries.

Strong absorption and ultrafast localisation in NaBiS2 nanocrystals with slow charge-carrier recombination.

I-V-VI2 ternary chalcogenides are gaining attention as earth-abundant, nontoxic, and air-stable absorbers for photovoltaic applications. However, the semiconductors explored thus far have slowly-rising absorption onsets, and their charge-carrier transport is not well understood yet. Herein, we investigate cation-disordered NaBiS2 nanocrystals, which have a steep absorption onset, with absorption coefficients reaching >105 cm-1 just above its pseudo-direct bandgap of 1.4 eV. Surprisingly, we also observe an ultrafast (picosecond-time scale) photoconductivity decay and long-lived charge-carrier population persisting for over one microsecond in NaBiS2 nanocrystals. These unusual features arise because of the localised, non-bonding S p character of the upper valence band, which leads to a high density of electronic states at the band edges, ultrafast localisation of spatially-separated electrons and holes, as well as the slow decay of trapped holes. This work reveals the critical role of cation disorder in these systems on both absorption characteristics and charge-carrier kinetics.

Size Matters: Digital Social Networks and Language Change.

Social networks play a role in language variation and change, and the social network theory has offered a powerful tool in modeling innovation diffusion. Networks are characterized by ties of varying strength which influence how novel information is accessed. It is widely held that weak-ties promote change, whereas strong ties lead to norm-enforcing communities that resist change. However, the model is primarily suited to investigate small ego networks, and its predictive power remains to be tested in large digital networks of mobile individuals. This article revisits the social network model in sociolinguistics and investigates network size as a crucial component in the theory. We specifically concentrate on whether the distinction between weak and strong ties levels in large networks over 100 nodes. The article presents two computational methods that can handle large and messy social media data and render them usable for analyzing networks, thus expanding the empirical and methodological basis from small-scale ethnographic observations. The first method aims to uncover broad quantitative patterns in data and utilizes a cohort-based approach to network size. The second is an algorithm-based approach that uses mutual interaction parameters on Twitter. Our results gained from both methods suggest that network size plays a role, and that the distinction between weak ties and slightly stronger ties levels out once the network size grows beyond roughly 120 nodes. This finding is closely similar to the findings in other fields of the study of social networks and calls for new research avenues in computational sociolinguistics.

Oxidation-Induced Changes in the ALD-Al2O3/InAs(100) Interface and Control of the Changes for Device Processing.

InAs crystals are emerging materials for various devices like radio frequency transistors and infrared sensors. Control of oxidation-induced changes is essential for decreasing amounts of the harmful InAs surface (or interface) defects because it is hard to avoid the energetically favored oxidation of InAs surface parts in device processing. We have characterized atomic-layer-deposition (ALD) grown Al2O3/InAs interfaces, preoxidized differently, with synchrotron hard X-ray photoelectron spectroscopy (HAXPES), low-energy electron diffraction, scanning tunneling microscopy, and time-of-flight elastic recoil detection analysis. The chemical environment and core-level shifts are clarified for well-embedded InAs interfaces (12 nm Al2O3) to avoid, in particular, effects of a significant potential change at the vacuum-solid interface. High-resolution As 3d spectra reveal that the Al2O3/InAs interface, which was sputter-cleaned before ALD, includes +1.0 eV shift, whereas As 3d of the preoxidized (3 × 1)-O interface exhibits a shift of -0.51 eV. The measurements also indicate that an As2O3 type structure is not crucial in controlling defect densities. Regarding In 4d measurements, the sputtered InAs interface includes only a +0.29 eV shift, while the In 4d shift around -0.3 eV is found to be inherent for the crystalline oxidized interfaces. Thus, the negative shifts, which have been usually associated with dangling bonds, are not necessarily an indication of such point defects as previously expected. In contrast, the negative shifts can arise from bonding with O atoms. Therefore, specific care should be directed in determining the bulk-component positions in photoelectron studies. Finally, we present an approach to transfer the InAs oxidation results to a device process of high electron mobility transistors (HEMT) using an As-rich III-V surface and In deposition. The approach is found to decrease a gate leakage current of HEMT without losing the gate controllability.

Controlling the perceived distance of an auditory object by manipulation of loudspeaker directivity.

This work presents a method to control the perceived distance of an auditory object by changing the directivity pattern of a loudspeaker and consequently the direct-to-reverberant ratio at the listening spot. Control of the directivity pattern is achieved by beamforming using a compact multi-driver loudspeaker unit. A small-sized cubic array consisting of six drivers is assembled, and per driver beamforming filters are derived from directional measurements of the array. The proposed method is evaluated using formal listening tests. The results show that the perceived distance can be controlled effectively by directivity pattern modification.

Controlling the crystallinity and roughness of atomic layer deposited titanium dioxide films.

The surface roughness of thin films is an important parameter related to the sticking behaviour of surfaces in the manufacturing of microelectomechanical systems (MEMS). In this work, TiO2 films made by atomic layer deposition (ALD) with the TiCl4-H2O process were characterized for their growth, roughness and crystallinity as function of deposition temperature (110-300 degrees C), film thickness (up to approximately 100 nm) and substrate (thermal SiO2, RCA-cleaned Si, Al2O3). TiO2 films got rougher with increasing film thickness and to some extent with increasing deposition temperature. The substrate drastically influenced the crystallization behaviour of the film: for films of about 20 nm thickness, on thermal SiO2 and RCA-cleaned Si, anatase TiO2 crystal diameter was about 40 nm, while on Al2O3 surface the diameter was about a micrometer. The roughness could be controlled from 0.2 nm up to several nanometers, which makes the TiO2 films candidates for adhesion engineering in MEMS.

Mobility determination of lead isotopes in glass for retrospective radon measurements.

In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where (209)Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the (209)Pb atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470-620 degrees C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 +/- 0.2 eV, and also the pre-exponential factor D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.