Ambient stability of colloidal nanocrystal quantum dots (QDs) is imperative for low-cost, high-efficiency QD photovoltaics. We synthesized air-stable, ultrasmall PbS QDs with diameter (D) down to 1.5 ...nm, and found an abrupt transition at D ≈ 4 nm in the air stability as the QD size was varied from 1.5 to 7.5 nm. X-ray photoemission spectroscopy measurements and density functional theory calculations reveal that the stability transition is closely associated with the shape transition of oleate-capped QDs from octahedron to cuboctahedron, driven by steric hindrance and thus size-dependent surface energy of oleate-passivated Pb-rich QD facets. This microscopic understanding of the surface chemistry on ultrasmall QDs, up to a few nanometers, should be very useful for precisely and accurately controlling physicochemical properties of colloidal QDs such as doping polarity, carrier mobility, air stability, and hot-carrier dynamics for solar cell applications.
Wet chemical synthesis of covalent III‐V colloidal quantum dots (CQDs) has been challenging because of uncontrolled surfaces and a poor understanding of surface–ligand interactions. We report a ...simple acid‐free approach to synthesize highly crystalline indium phosphide CQDs in the unique tetrahedral shape by using tris(dimethylamino) phosphine and indium trichloride as the phosphorus and indium precursors, dissolved in oleylamine. Our chemical analyses indicate that both the oleylamine and chloride ligands participate in the stabilization of tetrahedral‐shaped InP CQDs covered with cation‐rich (111) facets. Based on density functional theory calculations, we propose that fractional dangling electrons of the In‐rich (111) surface could be completely passivated by three halide and one primary amine ligands per the (2×2) surface unit, satisfying the 8‐electron rule. This halide–amine co‐passivation strategy will benefit the synthesis of stable III‐V CQDs with controlled surfaces.
InP colloidal tetrahedral nanocrystals were synthesized through a simple acid‐free approach using tris(dimethylamino) phosphine and indium trichloride dissolved in oleylamine. Their formation was attributed to the unique stabilization of the In‐rich (111) facets by co‐passivation with halide and primary amine.
Raman spectroscopy was applied to MAPbCl3 single crystals in a wide frequency range from 10 to 3500 cm−1 over a broad temperature range from −196 °C to 200 °C including both two structural phase ...transitions and a thermal degradation range. Low-frequency lattice modes of MAPbCl3 were revealed for the first time, which showed discontinuous anomalies along with the change in the number of Raman modes at the transition points of −114 °C and −110 °C. Several Raman modes related to the C–N stretching and MA rocking modes in addition to the lattice modes displayed temperature dependences similar to those of MAPbBr3 in both Raman shifts and half widths, indicating that the MA cation arrangement and H–halide bond interactions behave similarly in both systems during the phase transition. The substantial increase in the half widths of nearly all Raman modes especially suggests that the dynamic disorder caused by the free rotational motions of MA cations induces significant anharmonicity in the lattice and thus, reduces the phonon lifetimes. High-temperature Raman and Brillouin scattering measurements showed that the spectral features changed drastically at ~200 °C where the thermal decomposition of MAPbCl3 into PbCl2 began. This result exhibits that combined Raman and Brillouin spectroscopic techniques can be a useful tool in monitoring temperature-induced or temporal changes in lead-based halide perovskite materials.
Interaction between dipoles often emerges intriguing physical phenomena, such as exchange bias in the magnetic heterostructures and magnetoelectric effect in multiferroics, which lead to advances in ...multifunctional heterostructures. However, the defect‐dipole tends to be considered the undesired to deteriorate the electronic functionality. Here, deterministic switching between the ferroelectric and the pinched states by exploiting a new substrate of cubic perovskite, BaZrO3 is reported, which boosts the square‐tensile‐strain to BaTiO3 and promotes four‐variants in‐plane spontaneous polarization with oxygen vacancy creation. First‐principles calculations propose a complex of an oxygen vacancy and two Ti3+ ions coins a charge‐neutral defect‐dipole. Cooperative control of the defect‐dipole and the spontaneous polarization reveals ternary in‐plane polar states characterized by biased/pinched hysteresis loops. Furthermore, it is experimentally demonstrated that three electrically controlled polar‐ordering states lead to switchable and nonvolatile dielectric states for application of nondestructive electro‐dielectric memory. This discovery opens a new route to develop functional materials via manipulating defect‐dipoles and offers a novel platform to advance heteroepitaxy beyond the prevalent perovskite substrates.
A new cubic perovskite substrate BaZrO3 promotes an innovative ferroelectric state and functionality in heteroepitaxial BaTiO3 film through applications of square tensile strain. The isotropic strain induces intriguing four‐variants polar domains of in‐plane spontaneous polarization. Cooperation between the built‐in local point defect‐dipole and the four‐variants polar domains enables the reversible control of ternary polar states.
Recent advances in 3D culture systems have led to the generation of brain organoids that resemble different human brain regions; however, a 3D organoid model of the midbrain containing functional ...midbrain dopaminergic (mDA) neurons has not been reported. We developed a method to differentiate human pluripotent stem cells into a large multicellular organoid-like structure that contains distinct layers of neuronal cells expressing characteristic markers of human midbrain. Importantly, we detected electrically active and functionally mature mDA neurons and dopamine production in our 3D midbrain-like organoids (MLOs). In contrast to human mDA neurons generated using 2D methods or MLOs generated from mouse embryonic stem cells, our human MLOs produced neuromelanin-like granules that were structurally similar to those isolated from human substantia nigra tissues. Thus our MLOs bearing features of the human midbrain may provide a tractable in vitro system to study the human midbrain and its related diseases.
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•Self-organizing midbrain-like organoids (hMLOs) develop from hPSCs in 3D culture•hMLOs, but not mouse MLOs or human cerebral organoids, produce neuromelanin•hMLOs secrete dopamine (DA) and neurons within the hMLOs form functional synapses•Neurons within hMLOs exhibit SNpc DA neuron-like electrophysiological properties
Jo et al. report a method for generating human midbrain-like organoids (hMLOs) from hPSCs in 3D culture. The hMLOs contain distinct layers of neuronal cells expressing human midbrain markers, such as neuromelanin, are electrically active, form functional synapses, and produce dopamine, suggesting that they may be useful for studying human midbrain.
Pb(Hf1−xSnx)O3 single crystals with x = 0.08 were characterized using single‐crystal X‐ray diffraction and Raman scattering, in a wide temperature range. The information concerning the structure of ...two intermediate phases (IMs), situated between low‐temperature antiferroelectric A1 and high‐temperature paraelectric PE phases, was obtained. The lower temperature IM, A2, is characterized by incommensurate displacive modulations in the Pb sublattice. The higher temperature IM, is characterized by tilting of oxygen octahedra, and serious disorder coming from lead ions represented by X‐ray diffuse scattering. Optical phonons and phase transitions in Pb(Hf1−xSnx)O3 single crystals were investigated by temperature‐dependent Raman spectra. It was found that several soft modes control the phase transition between two antiferroelectric phases indicating its displacive character, whereas, in the paraelectric phase, both soft modes and Rayleigh scattering were observed.
Abstract
5
d
pyrochlore oxides with all-in-all-out magnetic order are prime candidates for realizing strongly correlated, topological phases of matter. Despite significant effort, a full ...understanding of all-in-all-out magnetism remains elusive as the associated magnetic excitations have proven difficult to access with conventional techniques. Here we report a Raman spectroscopy study of spin dynamics in the all-in-all-out magnetic state of the 5
d
pyrochlore Cd
2
Os
2
O
7
. Through a comparison between the two-magnon scattering and spin-wave theory, we confirm the large single ion anisotropy in this material and show that the Dzyaloshinskii–Moriya and exchange interactions play a significant role in the spin-wave dispersions. The Raman data also reveal complex spin–charge–lattice coupling and indicate that the metal–insulator transition in Cd
2
Os
2
O
7
is Lifshitz-type. Our work establishes Raman scattering as a simple and powerful method for exploring the spin dynamics in 5
d
pyrochlore magnets.
Herein, Ag-ZnO core-shell nanoparticles (NPs) with enhanced photocatalytic activity were prepared by coating Ag metal cores with ZnO semiconductor shells through atomic layer deposition (ALD). ...Instrumental analysis revealed that the ultra-thin and conformal nature of the shell allowed the core-shell NPs to simultaneously exploit the photocatalytic properties of ZnO and the plasmonic properties of Ag. In a rhodamine B photodegradation test performed under artificial sunlight, Ag-ZnO core-shell NPs exhibited better photocatalytic performance than other prepared photocatalysts, namely ZnO NPs and ALD-ZnO coated ZnO NPs. The performance enhancement was ascribed to the effect of noble metal-semiconductor heterojunctions, which increased the efficiency of electron-hole separation, i.e., the Ag core effectively captured excited electrons at the ZnO surface, which resulted in the elevated production of hydroxyl radicals from holes remaining at ZnO. A three-dimensional finite-difference time-domain simulation of the Ag-ZnO NPs with variable shell thickness showed that ZnO shells on Ag metal cores increase the intensity of light around NPs, allowing the plasmonic cores to fully utilize incident light.
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•The ALD technology is applied to fabricate Ag-ZnO nanoparticles for photocatalyst.•Stable ZnO shell layers with wurtzite structure are deposited on Ag core particles.•Ag-ZnO shows ~2.5 to 4 times enhanced photodegradation compared with pure ZnO.•SPR effect of Ag increases photocatalytic performance of Ag-ZnO photocatalyst.•Ultra-thin ZnO shells on Ag cores increase photocatalytic performance in UV-region.
Due to its flexibility, transparency, easy fabrication, and high negative polarity, polydimethylsiloxane (PDMS) has been considered as one of the most appropriate materials for the use in ...triboelectric nanogenerator (TENG) applications. Here, we report the significantly enhanced triboelectric surface charge of PDMS simply by sprinkling of NaOH solution. Fresh PDMS-based TENGs generated an open-circuit voltage of 3.8V and a closed-circuit current of 65nA after the contact/separation from an indium tin oxide (ITO) electrode. After sprinkling the PDMS surface with 1M NaOH, in contrast, the resulting TENG generated voltage of 10.4V and current of 179nA. Exposing the PDMS to ultraviolet-ozone prior to sprinkling with NaOH solution resulted in a triboelectric voltage and current of 49.3V and 1.16μA, respectively, which are almost 15-fold larger than those of fresh PDMS. The origin of the enhanced triboelectric charge is related with an increase of polar SiO bonds at the expense of non-polar Si–CH3 bonds in PDMS. This work demonstrates a cost-effective method for producing large-area and high-efficiency PDMS-based TENGs and helps clarify the triboelectric mechanism of PDMS.
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•Enhance the triboelectric charge of PDMS by sprinkling of NaOH solution.•Increase of Si‐O bonds with ultraviolet-ozone and NaOH treatments.•Large-area and low-cost TENG application using transparent and flexible PDMS.
Abstract
Pb(Hf
1−
x
Sn
x
)O
3
single crystals with
x
= 0.08 were characterized using single‐crystal X‐ray diffraction and Raman scattering, in a wide temperature range. The information concerning ...the structure of two intermediate phases (IMs), situated between low‐temperature antiferroelectric A1 and high‐temperature paraelectric PE phases, was obtained. The lower temperature IM, A2, is characterized by incommensurate displacive modulations in the Pb sublattice. The higher temperature IM, is characterized by tilting of oxygen octahedra, and serious disorder coming from lead ions represented by X‐ray diffuse scattering. Optical phonons and phase transitions in Pb(Hf
1−
x
Sn
x
)O
3
single crystals were investigated by temperature‐dependent Raman spectra. It was found that several soft modes control the phase transition between two antiferroelectric phases indicating its displacive character, whereas, in the paraelectric phase, both soft modes and Rayleigh scattering were observed.
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