The values of various diffusive behaviors of sPH-AP-QDs analyzed in this study.

<p>Actin, actin cytoskeleton disrupted; Microtubule, microtubule disrupted; Gly-SP, Glycine-induced synaptic potentiation; NMDA-SD, NMDA-induced synaptic depression; D_synapse, diffusion coefficient at synapses; D_ex-synapse, diffusion coefficient at extrasynapses; All values are mean ± s.e. *p<0.01, paired <i>t</i>-test.</p

Single QD tracking of synaptic vesicles using sPH-AP-QDs.

<p>(<b>A</b>) Hippocampal neurons were co-transfected with sPH-AP and Bir-ER at DIV 12, and labeled with 1 nM streptavidin-conjugated-QD at DIV17. Blue color: the functional presynaptic terminals were identified by sPH fluorescence change (ΔF). Scale bar, 20 µm. (<b>B</b>) Example of sPH-AP-QDs (red) trafficking along the axon (green). Arrows: sPH-AP-QDs trafficking between synaptic and extrasynaptic compartments, arrowheads: sPH-AP-QDs at presynaptic terminals. asterisks: functional presynaptic terminals (blue). Scale Bar, 2.5 µm. (<b>C</b>) Instantaneous displacement change of the moving sPH-AP-QD marked by the arrow in (<b>B</b>) from its initial location (displacement = 0) along the axon during recording sequence. The <i>x</i> and <i>y</i> coordinates of QD trajectory at each time point in time-lapse images were obtained using MetaMorph track object function and the displacement from the origin to the QD trajectory at each time point was calculated and plotted. The graph parallel to <i>y</i> axis means no movement. The upper lines denote the frames in which the sPH-AP-QD is at extrasynaptic areas (gray) and synapses (red and shaded areas). (<b>D</b>) MSD versus time, calculated for a continuous sequence of images, which show the synaptic motion (red) and extrasynaptic motion (blue). Inset represents average diffusion coefficient of sPH-AP-QDs at synapses (red) and at extrasynapses (blue).</p

Aspartic Acid-Assisted Synthesis of Multifunctional Strontium-Substituted Hydroxyapatite Microspheres

Strontium-substituted hydroxyapatite (SrHAP) microspheres with three-dimensional (3D) structures were successfully prepared via hydrothermal method using self-assembled poly­(aspartic acid) (PASP) as a template. By controlling various parameters, including hydrothermal reaction time, amount of l-aspartic acid (l-Asp), and ratio of Sr ions, we were able to investigate the influences of the additive l-Asp on morphology and properties of final products as well as the role of self-assembled PASP template on the formation of HAP microspheres. The change in the amount of Sr substitution significantly affected the particle size, morphology, and concurrent surface area. This difference caused variation in the drug-release properties. In addition, substitution of Sr ions into Ca ion sites affected luminescence of HAP powders. Particularly, multifunctional SrHAP with molar ratios (Sr/[Ca+Sr]) of 0.25 possessed the strongest luminescence as well as superior drug-loading and sustained-releasing properties. These properties were associated with large surface area and large pore size of the SrHAP. This study suggests that the optical and structural properties of the HAP particles can be carefully tuned by controlling the amount of Sr ions doped into HAP particles during synthesis. This work provides new opportunities to synthesize HAP particles suitable for diverse applications including bone regeneration and drug delivery

Direct Low-Temperature Growth of Single-Crystalline Anatase TiO₂ Nanorod Arrays on Transparent Conducting Oxide Substrates for Use in PbS Quantum-Dot Solar Cells

We report on the direct growth of anatase TiO₂ nanorod arrays (A-NRs) on transparent conducting oxide (TCO) substrates that can be directly applied to various photovoltaic devices via a seed layer mediated epitaxial growth using a facile low-temperature hydrothermal method. We found that the crystallinity of the seed layer and the addition of an amine functional group play crucial roles in the A-NR growth process. The A-NRs exhibit a pure anatase phase with a high crystallinity and preferred growth orientation in the [001] direction. Importantly, for depleted heterojunction solar cells (TiO₂/PbS), the A-NRs improve both electron transport and injection properties, thereby largely increasing the short-circuit current density and doubling their efficiency compared to TiO₂ nanoparticle-based solar cells

BiVO₄/WO₃/SnO₂ Double-Heterojunction Photoanode with Enhanced Charge Separation and Visible-Transparency for Bias-Free Solar Water-Splitting with a Perovskite Solar Cell

Coupling dissimilar oxides in heterostructures allows the engineering of interfacial, optical, charge separation/transport and transfer properties of photoanodes for photoelectrochemical (PEC) water splitting. Here, we demonstrate a double-heterojunction concept based on a BiVO₄/WO₃/SnO₂ triple-layer planar heterojunction (TPH) photoanode, which shows simultaneous improvements in the charge transport (∼93% at 1.23 V vs RHE) and transmittance at longer wavelengths (>500 nm). The TPH photoanode was prepared by a facile solution method: a porous SnO₂ film was first deposited on a fluorine-doped tin oxide (FTO)/glass substrate followed by WO₃ deposition, leading to the formation of a double layer of dense WO₃ and a WO₃/SnO₂ mixture at the bottom. Subsequently, a BiVO₄ nanoparticle film was deposited by spin coating. Importantly, the WO₃/(WO₃+SnO₂) composite bottom layer forms a disordered heterojunction, enabling intimate contact, lower interfacial resistance, and efficient charge transport/transfer. In addition, the top BiVO₄/WO₃ heterojunction layer improves light absorption and charge separation. The resultant TPH photoanode shows greatly improved internal quantum efficiency (∼80%) and PEC water oxidation performance (∼3.1 mA/cm² at 1.23 V vs RHE) compared to the previously reported BiVO₄/WO₃ photoanodes. The PEC performance was further improved by a reactive-ion etching treatment and CoO_<i>x</i> electrocatalyst deposition. Finally, we demonstrated a bias-free and stable solar water-splitting by constructing a tandem PEC device with a perovskite solar cell (STH ∼3.5%)

Indium–Tin–Oxide Nanowire Array Based CdSe/CdS/TiO₂ One-Dimensional Heterojunction Photoelectrode for Enhanced Solar Hydrogen Production

For photoelectrochemical (PEC) hydrogen production, low charge transport efficiency of a photoelectrode is one of the key factors that largely limit PEC performance enhancement. Here, we report a tin-doped indium oxide (In₂O₃:Sn, ITO) nanowire array (NWs) based CdSe/CdS/TiO₂ multishelled heterojunction photoelectrode. This multishelled one-dimensional (1D) heterojunction photoelectrode shows superior charge transport efficiency due to the negligible carrier recombination in ITO NWs, leading to a greatly improved photocurrent density (∼16.2 mA/cm² at 1.0 V vs RHE). The ITO NWs with an average thickness of ∼12 μm are first grown on commercial ITO/glass substrate by a vapor–liquid–solid method. Subsequently, the TiO₂ and CdSe/CdS shell layers are deposited by an atomic layer deposition (ALD) and a chemical bath deposition method, respectively. The resultant CdSe/CdS/TiO₂/ITO NWs photoelectrode, compared to a planar structure with the same configuration, shows improved light absorption and much faster charge transport properties. More importantly, even though the CdSe/CdS/TiO₂/ITO NWs photoelectrode has lower CdSe/CdS loading (i.e., due to its lower surface area) than the mesoporous TiO₂ nanoparticle based photoelectrode, it shows 2.4 times higher saturation photocurrent density, which is attributed to the superior charge transport and better light absorption by the 1D ITO NWs

Observation of Enhanced Hole Extraction in Br Concentration Gradient Perovskite Materials

Enhancing hole extraction inside the perovskite layer is the key factor for boosting photovoltaic performance. Realization of halide concentration gradient perovskite materials has been expected to exhibit rapid hole extraction due to the precise bandgap tuning. Moreover, a formation of Br-rich region on the tri-iodide perovskite layer is expected to enhance moisture stability without a loss of current density. However, conventional synthetic techniques of perovskite materials such as the solution process have not achieved the realization of halide concentration gradient perovskite materials. In this report, we demonstrate the fabrication of Br concentration gradient mixed halide perovskite materials using a novel and facile halide conversion method based on vaporized hydrobromic acid. Accelerated hole extraction and enhanced lifetime due to Br gradient was verified by observing photoluminescence properties. Through the combination of secondary ion mass spectroscopy and transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis, the diffusion behavior of Br ions in perovskite materials was investigated. The Br-gradient was found to be eventually converted into a homogeneous mixed halide layer after undergoing an intermixing process. Br-substituted perovskite solar cells exhibited a power conversion efficiency of 18.94% due to an increase in open circuit voltage from 1.08 to 1.11 V and an advance in fill-factor from 0.71 to 0.74. Long-term stability was also dramatically enhanced after the conversion process, i.e., the power conversion efficiency of the post-treated device has remained over 97% of the initial value under high humid conditions (40–90%) without any encapsulation for 4 weeks

Phase-Pure FeSe_<i>x</i> (<i>x</i> = 1, 2) Nanoparticles with One- and Two-Photon Luminescence

Iron chalcogenides hold considerable promise for energy conversion and biomedical applications. Realization of this promise has been hindered by the lack of control over the crystallinity and nanoscale organization of iron chalcogenide films. High-quality nanoparticles (NPs) from these semiconductors will afford further studies of photophysical processes in them. Phase-pure NPs from these semiconductors can also serve as building blocks for mesoscale iron chalcogenide assemblies. Herein we report a synthetic method for FeSe_<i>x</i> (<i>x</i> = 1, 2) NPs with a diameter of ca. 30 nm that satisfy these needs. The high crystallinity of the individual NPs was confirmed by transmission electron microscopy (TEM) and energy-dispersive X-ray analysis. TEM tomography images suggest pucklike NP shapes that can be rationalized by bond relaxation at the NP edges, as demonstrated in large-scale atomic models. The prepared FeSe_<i>x</i> NPs display strong photoluminescence with a quantum yield of 20%, which was previously unattainable for iron chalcogenides. Moreover, they also show strong off-resonant luminescence due to two-photon absorption, which should be valuable for biological applications

Efficient Carrier Separation and Intriguing Switching of Bound Charges in Inorganic–Organic Lead Halide Solar Cells

We fabricated a mesoporous perovskite solar cell with a ∼14% conversion efficiency, and we investigated its beneficial grain boundary properties of the perovskite solar cells through the use of scanning probe microscopy. The CH₃NH₃Pb­(I_0.88,Br_0.12)₃ showed a significant potential barrier bending at the grain boundary and induced passivation. The potential difference value in the <i>x</i> = 0.00 sample is ∼50 mV, and the distribution of the positive potential is lower than that of the <i>x</i> = 0.12 sample. We also investigated the polarization and hysteretic properties of the perovskite thin films by measuring the local piezoresponse. Specifically, the charged grain boundaries play a beneficial role in electron–hole depairing and in suppressing recombination in order to realize high-efficiency perovskite solar cells

Reduced Graphene Oxide/Mesoporous TiO₂ Nanocomposite Based Perovskite Solar Cells

We report on reduced graphene oxide (rGO)/mesoporous (mp)-TiO₂ nanocomposite based mesostructured perovskite solar cells that show an improved electron transport property owing to the reduced interfacial resistance. The amount of rGO added to the TiO₂ nanoparticles electron transport layer was optimized, and their impacts on film resistivity, electron diffusion, recombination time, and photovoltaic performance were investigated. The rGO/mp-TiO₂ nanocomposite film reduces interfacial resistance when compared to the mp-TiO₂ film, and hence, it improves charge collection efficiency. This effect significantly increases the short circuit current density and open circuit voltage. The rGO/mp-TiO₂ nanocomposite film with an optimal rGO content of 0.4 vol % shows 18% higher photon conversion efficiency compared with the TiO₂ nanoparticles based perovskite solar cells