The development of wearable strain sensors for the human-machine interface has attracted considerable research interest. Most existing wearable strain sensors were incapable of simultaneously detecting strain amplitudes and directions, and they failed to fully record stretching vectors that occurred on the body. Graphene and graphene-derived materials have been utilized to construct wearable strain sensors with excellent electrical sensitivities. Although the growth techniques of planar graphene and vertical graphene (VG) have been established, the fabrication of VG aligned in parallel within a larger area has not been previously achieved. Here, parallelly aligned VG (PAVG) in a large area was successfully fabricated and constructed as a wearable strain vector sensor. The PAVG was fabricated via inductively coupled plasma chemical vapor deposition assisted by metal inducers. The as-fabricated sensor was electrically anisotropic because of the profiles of the VG nanosheets aligned in parallel. Therefore, the sensor could simultaneously and sensitively detect the direction and the amplitude of the strain vectors with excellent accuracy. Application of this strain vector sensor for the human-sensor interface to identify the stretching directions and amplitudes of finger joints was also demonstrated. This work established the fabrication methodology of graphene with unique vertical and parallel alignment morphology. This study introduced a new opportunity of developing wearable sensors that could fully detect multidirectional human actions.
A systematic investigation of the nanoscale conduction behavior of vanadium dioxide (VO2) films deposited on aluminum oxide (Al2O3) substrates, using conductive atomic force microscopy, is presented. Aside from the macroscale resistance-temperature characteristics, which show a steep insulator-metal transition at the transition point Tm ∼ 68 °C, our experiments demonstrate a coexistence of nanoscale high-conduction and low-conduction phases over a broad temperature window (50 K range) across the Tm. In addition, the area (volume) fraction of the high-conduction phase increases with increasing temperature across the transition point. The current-voltage data obtained on a nanoscale indicate that the high-conduction phase is not a good metal. When the temperature increased across the Tm, the probed charge transport behavior of the high-conduction phase is found to change from a mechanism dominated by space-charge limited current to a mechanism dominated by Schottky emission.
Low-dimensional lead halides have attracted increasing attention due to their potential application as single-component white-light emitters. These materials exhibit a complex emission spectral structure, ranging from free exciton narrowband emissions to self-trapped exciton broadband emissions. However, there is still no consensus for the underlying physical mechanism, especially in the spectrum with both narrowband and broadband emissions. Here we aim to elucidate the correlation between the emission spectrum and the exciton–phonon coupling in the mixed halide perovskite BA2Pb(BrxCl1–x)4. Our findings reveal that the interplay between exciton localization and delocalization results in an intermediate exciton–phonon coupling, leading to line shapes beyond the Huang–Rhys model for the self-trapped exciton. By incorporating the exciton motional effect, we establish a unified photophysical model describing the emission spectrum from the self-trapped exciton type to the free exciton type. These results provide essential insights into the mechanisms governing exciton–phonon interactions and offer ways to control white-light emission in two-dimensional perovskites.
Zero-dimensional metal halides have received wide attention due to their structural diversity, strong quantum confinement, and associated excellent photoluminescence properties. A reversible and tunable luminescence would be desirable for applications such as anti-counterfeiting, information encryption, and artificial intelligence. Yet, these materials are underexplored, with little known about their luminescence tuning mechanisms. Here we report a pyramidal coplanar dimer, (TBA)Sb2Cl7 (TBA = tetrabutylammonium), showing broadband emission wavelength tuning (585−650 nm) by simple thermal treatment. We attribute the broad color change to structural disorder induced by varying the heat treatment temperatures. Increasing the heating temperature transitions the material from long-range ordered crystalline phase to highly disordered glassy phase. The latter exhibits stronger electron−phonon coupling, enhancing the self-trapped exciton emission efficiency. The work provides a new material platform for manifold optical anti-counterfeiting applications and sheds light on the emission color tuning mechanisms for further design of stimuli-responsive materials.
Microneedle systems have been widely used in health monitoring, painless drug delivery, and medical cosmetology. Although many studies on microneedle materials, structures, and applications have been conducted, the applications of microneedles often suffered from issues of inconsistent penetration rates due to the complication of skin-microneedle interface. In this study, we demonstrated a methodology of determination of transdermal rate of metallic microneedle array through impedance measurements-based numerical check screening algorithm. Metallic sheet microneedle array sensors with different sizes were fabricated to evaluate different transdermal rates. In vitro sensing of hydrogen peroxide confirmed the effect of transdermal rate on the sensing outcomes. An FEM simulation model of a microneedle array revealed the monotonous relation between the transdermal state and test current. Accordingly, two methods were primely derived to calculate the transdermal rate from the test current. First, an exact logic method provided the number of unpenetrated tips per sheet, but it required more rigorous testing results. Second, a fuzzy logic method provided an approximate transdermal rate on adjacent areas, being more applicable and robust to errors. Real-time transdermal rate estimation may be essential for improving the performance of microneedle systems, and this study provides various fundaments toward that goal.
Prelithiation techniques play a critical role in the advancement of high-energy-density batteries. Among these techniques, ultrathin lithium (UTL) has emerged as a promising prelithiation reagent for anodes. However, there remains a need to explore an adjustable, efficient, and cost-effective method for manufacturing UTL. In this study, we introduce a technique for producing UTL with adjustable thicknesses ranging from 1.5 μm to 10 μm using blade-coating of molten lithium on polyvinylidene fluoride-modified copper current collectors. By employing the transfer-printing method, we prepare prelithiated graphite and Si-C composite electrodes, which exhibit significantly improved initial coulombic efficiencies of 99.60% and 99.32% in half cells, respectively. Moreover, the energy densities of Li(NiCoMn)1/3O2 and LiFePO4 full cells assembled with the prelithiated graphite electrodes increase by 13.1% and 23.5%, respectively.
BackgroundThe aim of this study was to compare the macular and peripapillary vessel densities in eyes of young Chinese adults with different degrees of myopia and to evaluate the association of macular and peripapillary vessel densities with axial length and retinal nerve fibre layer thickness.MethodsA total of 128 eyes (mild myopia, 42; moderate myopia, 45; severe myopia, 41) underwent optical coherence tomography angiography imaging. Parameters assessed were vessel densities in the superficial capillary plexus and deep capillary plexus of the macular area, peripapillary vessel density, retinal nerve fibre layer thickness, foveal thickness and foveal avascular zone area (mm2).ResultsVessel densities in the macular and peripapillary areas as well as peripapillary retinal nerve fibre layer thickness decreased significantly when comparing high myopia to mild myopia. Axial length was significantly associated with vessel density in the macular area (superficial capillary plexus: r = −0.249, p = 0.008; deep capillary plexus: r = −0.398, p < 0.001), peripapillary area (r = −0.204, p = 0.028), foveal avascular zone area (r = −0.309, p < 0.001), and foveal thickness (r = 0.354, p < 0.001). Negative correlations were found between axial length and peripapillary vessel density as well as retinal nerve fibre layer thickness at the nasal superior, nasal inferior and inferior nasal quadrants.ConclusionVarying degrees of myopia affected macular and peripapillary vessel densities as well as retinal nerve fibre layer thickness in young healthy adults. The high myopic group had the lowest vessel density in the superficial capillary plexus, deep capillary plexus of the macular area and the peripapillary area. With increased axial length, macular and peripapillary vessel densities, retinal nerve fibre layer thickness and foveal avascular zone area reduced while foveal thickness increased.
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