Correlating π-π Stacking of Aromatic Diammoniums with Stability and Dimensional Reduction of Dion-Jacobson 2D Perovskites.

Dion-Jacobson (DJ) phase 2D perovskites with various aromatic diammonium cations, potentially possessing high stability, have been developed for optoelectronics. However, their stability does not meet initial expectations, and some of them even easily degrade into lower-dimensional structures. Underlying the stability mechanism and dimensional reduction of these DJ 2D perovskites remains elusive. Herein, we report that π-π stacking intensity between aromatic cations determines structural stability and dimensional variation of DJ 2D perovskites by investigating nine benzene diammoniums (BDAs)-derived low-dimensional perovskites. The BDAs without intermolecular π-π stacking form stable DJ 2D perovskites, while those showing strong π-π stacking tend to generate 1D and 0D architectures. Furthermore, the π-π stacking intensity highly relies on molecular symmetry and electrostatic potential of BDAs; namely, asymmetry and small dipole moment facilitate alleviating the π-π stacking, leading to the formation of DJ 2D perovskites and vice versa. Our findings establish the relationship of aromatic diammonium structure-π-π stacking interaction-perovskite dimensionality, which can guide the design of stable DJ 2D perovskites and the manipulation of perovskite dimensionality for various optoelectronic applications.

Spatial Separation of Photogenerated Charges on Well-Defined Bismuth Vanadate Square Nanocrystals.

Crystal facet engineering has been recognized as a powerful strategy to finely modulate the charge separation behavior in semiconductor photocatalysis; however, disclosing the intrinsic roles that the morphologies and crystal facets play on photogenerated charge separation of semiconductor nanocrystals remains elusive. Herein, exemplified on the typical visible-light-responsive photocatalyst bismuth vanadate (BiVO4 ), for the first time, the successful fabrication is reported of well-defined BiVO4 square nanocrystals with precisely controllable (040)/(200) facet proportion, which undergo a dissolution-recrystallization-facet growth process accompanied with tetragonal to monoclinic phase transition. Spatial separation of photogenerated electrons and holes has been evidently demonstrated to take place between (040) and (200) facets of BiVO4 nanocrystals, on which the charge separation efficiency is verified to definitely depend on the facet proportion of (040)/(200). Further theoretical simulation reveals that the matching degree of charge collection length and crystal configuration is considered to be the major factor determining charge separation efficiency of BiVO4 nanocrystals. This study presents a strategy to fabricate morphology-tailored semiconductors, which will be favorable to advance the understanding of spatial charge separation in semiconductor photocatalysis.

Tuning the Anisotropic Facet of Lead Chromate Photocatalysts to Promote Spatial Charge Separation.

A crucial issue in artificial photosynthesis is how to modulate the behaviors of photogenerated charges of semiconductor photocatalysts. Here, using lead chromate (PbCrO4 ) as an example, we conducted the morphology tailoring from parallelepiped (p-PbCrO4 ) to truncated decahedron (t-PbCrO4 ) and elongated rhombic (r-PbCrO4 ), resulting in exposed anisotropic facets. The spatial separation of photogenerated charges closely correlates to the anisotropic facets of crystals, which can only be realized for t-PbCrO4 and r-PbCrO4 . The charge-separation efficiencies exhibit a quasilinear relation with the surface photovoltage difference between anisotropic facets. The r-PbCrO4 gives an apparent quantum efficiency of 6.5 % at 500 nm for photocatalytic water oxidation using Fe3+ ions as electron acceptors. Moreover, the oxidation reverse reaction from Fe2+ to Fe3+ ions was completely blocked with ∼100 % of Fe3+ conversion achieved on the anisotropic PbCrO4 crystals.

Self-assembled C-Ag hybrid nanoparticle on nanoporous GaN enabled ultra-high enhancement factor SERS sensor for sensitive thiram detection.

Considering pesticide residues cause significant harm to public health and the environment, developing a simple, sensitive, and reliable approach to pesticide residue detection to address this issue is necessary. In this study, an ultrasensitive and reliable surface-enhanced Raman scattering (SERS) sensor was developed using cetylpyridinium chloride as a protecting and reducing agent for the in situ synthesis and self-assembly of C-Ag nanoparticles on nanoporous GaN for the quantitative detection of thiram. A systematic investigation of the performance of the SERS sensor revealed that the SERS sensor delivered a limit of detection (LOD) of 10-14 M and an enhancement factor of up to 1.80 × 1011 with reasonable uniformity and reproducibility, with the stability of the SERS sensor demonstrated via long-term storage for up to 22 weeks in air. The enhancement mechanism of the SERS sensor was verified using a finite-difference time-domain simulation. The SERS sensor successfully detected thiram in real samples with an LOD of 10-10 M. Hence, this study provides an effective platform for monitoring food safety and the environment.

Triclinic-Phase Bismuth Chromate: A Promising Candidate for Photocatalytic Water Splitting with Broad Spectrum Ranges.

Photocatalytic water splitting for solar energy conversion remains challenged by the lack of novel semiconductor photocatalysts with paramount parameters including wide light-harvesting ranges and suitable band structures. Here, a novel triclinic-phase bismuth chromate (Bi2 CrO6 ) acting as a semiconductor photocatalyst candidate is reported. Triclinic Bi2 CrO6 exhibits a broad absorption range of ≈650 nm with a direct bandgap of 1.86 eV and shows a suitable band structure for water splitting. Theoretical simulations of triclinic Bi2 CrO6 reveal a high charge mobility, possibly owing to the strong hybridized covalent bonds, large elastic modulus, and small carrier effective mass. The triclinic Bi2 CrO6 is demonstrated to work well toward photocatalytic water oxidation and hydrogen production reactions under visible light and match well with its absorption ranges. In particular, it exhibits decent photocatalytic water oxidation performance in the presence of various electron scavengers. Furthermore, the visible-light-driven Z-scheme overall water splitting system is fabricated by coupling triclinic Bi2 CrO6 as the oxygen evolution photocatalyst with SrTiO3 :Rh as the hydrogen evolution photocatalyst, giving a stable overall water splitting with stoichiometric evolution of H2 and O2 . This work presents a promising semiconductor material enabling wide-range light harvesting for photocatalytic and photo-electrochemical solar energy conversion.

Modulation of transcription burst amplitude underpins dosage compensation in the Drosophila embryo.

Dosage compensation, the balancing of X-linked gene expression between sexes and to the autosomes, is critical to an organism's fitness and survival. In Drosophila, dosage compensation involves hypertranscription of the male X chromosome. Here, we use quantitative live imaging and modeling at single-cell resolution to study X chromosome dosage compensation in Drosophila. We show that the four X chromosome genes studied undergo transcriptional bursting in male and female embryos. Mechanistically, our data reveal that transcriptional upregulation of male X chromosome genes is primarily mediated by a higher RNA polymerase II initiation rate and burst amplitude across the expression domain. In contrast, burst frequency is spatially modulated in nuclei within the expression domain in response to different transcription factor concentrations to tune the transcriptional response. Together, these data show how the local and global regulation of distinct burst parameters can establish the complex transcriptional outputs underpinning developmental patterning.

Modulating Oxygen Vacancies in Lead Chromate for Photoelectrocatalytic Water Splitting.

Although modulating oxygen vacancies in semiconductors has attracted broad interest in photocatalysis and photoelectrocatalysis, identifying the intrinsic roles of oxygen vacancies on photoelectrocatalytic properties is often elusive. In this work, the oxygen vacancies in a typical semiconductor lead chromate (PbCrO4 ) are regulated via controlling the oxygen chemical potentials of O-poor and O-rich post-annealing atmospheres. Oxygen vacancies identified in PbCrO4 can introduce electronically shallow energy levels and deep energy levels owing to the symmetry difference of oxygen atoms in the structure. A higher population of deep energy levels created under O-poor atmosphere induces the formation of more surface trapped states, resulting in a higher photovoltage for charge separation. Meanwhile, the existence of surface trapped states can significantly improve the charge injection efficiency of the PbCrO4 photoanode and enhance the water oxidation activity. By modulating oxygen vacancies in the PbCrO4 photoanode, a photocurrent density of 3.43 mA cm-2 at 1.23 V vs reversible hydrogen electrode (RHE) under simulated AM1.5G is acheived. Further passivation of surface trapped states and introducing the water oxidation cocatalyst CoPi lead to a record applied bias photon-to-current efficiency (ABPE) of 1.12%. This work provides a guide to understand the mechanism of oxygen vacancies in oxide-based semiconductor photocatalysis and photoelectrocatalysis.

A Dual-Ligand Strategy to Regulate the Nucleation and Growth of Lead Chromate Photoanodes for Photoelectrochemical Water Splitting.

Photoelectrochemical (PEC) water splitting for renewable hydrogen production has been regarded as a promising solution to utilize solar energy. However, most photoelectrodes still suffer from poor film quality and poor charge separation properties, mainly owing to the possible formation of detrimental defects including microcracks and grain boundaries. Herein, a molecular coordination engineering strategy is developed by employing acetylacetone (Acac) and poly(ethylene glycol) (PEG) dual ligands to regulate the nucleation and crystal growth of the lead chromate (PbCrO4 ) photoanode, resulting in the formation of a high-quality film with large grain size, well-stitched grain boundaries, and reduced oxygen vacancies defects. With these efforts, the nonradiative charge recombination is efficiently suppressed, leading to the enhancement of its charge separation efficiency from 47% to 90%. After decorating with Co-Pi cocatalyst, the PbCrO4 photoanode achieves a photocurrent density of 3.15 mA cm-2 at 1.23 V (vs RHE under simulated AM1.5G) and an applied bias photon-to-current efficiency (ABPE) of 0.82%. This work provides a new strategy to modulate the nucleation and growth of high-quality photoelectrodes for efficient PEC water splitting.

Identify dominant dimensions of 3D hand shapes using statistical shape model and deep neural network.

Hand anthropometry is one of the fundamentals of ergonomic research and product design. Many studies have been conducted to analyze the hand dimensions among different populations, however, the definitions and the numbers of those dimensions were usually selected based on the experience of the researchers and the available equipment. Few studies explored the importance of each hand dimension regarding the 3D shape of the hand. In this paper, we aim to identify the dominant dimensions that influence the hand shape variability while considering the stability of the measurements in practice. A novel four-step research method was proposed where in the first step, based on literature study, we defined 58 landmarks and 53 dimensions for the exploration. In the second step, 80,000 virtual hand models, each had the associated 53 dimensions, were augmented by changing the weights of Principle Components (PCs) of a statistical shape model (SSM). Deep neural networks (DNNs) were used to establish the inverse relationships from the dimensions to the weight of each PC of the hand SSM. Using the structured sparsity learning method, we identified 21 dominant dimensions that represent 90% of the variance of the hand shape. In the third step, two different manual measuring methods were used to evaluate the stability of the measurements in practice. Finally, we selected 16 dominant dimensions with lower measurement variance by synthesizing the findings in Step 2 and 3. It was concluded that the recognized 21 dominant dimensions can be treated as the reference dimensions for anthropometric study and using the selected 16 dominant dimensions with lower measurement variance, ergonomists are able to generate a 3D hand model based on simple measurement tools with an accuracy of 5.9 mm. Though the accuracy is limited, the efforts are minimum, and the results can be used as an indicator in the early stage of research/design.

Ultrasonic-assisted hydrothermal synthesis of cobalt oxide/nitrogen-doped graphene oxide hybrid as oxygen reduction reaction catalyst for Al-air battery.

A persistent ultrasound-assisted hydrothermal method has been developed to prepare cobalt oxide incorporated nitrogen-doped graphene (Co3O4/N-GO) hybrids. The electrochemical behaviors and catalytic activity of the prepared hybrids have been systematically investigated as cathode materials for Al-air battery. The results show that ultrasonication can promote the yield ratio of Co3O4 from 63.1% to 70.6%. The prepared Co3O4/N-GO hybrid with ultrasonication exhibits better ORR activity over that without ultrasonication. The assembled Al-air battery using the ultrasonicated Co3O4/N-GO hybrid exhibited an average working voltage of 1.02 V in 4 M KOH electrolyte at 60 mA∙cm-2, approximately 60 mV higher than that using hybrid without ultrasonication. This should be attributed to large number density of fine Co3O4 particles growing on the dispersed GO sheets under the persistent ultrasonication. The related ultrasonic mechanism has been discussed in details.

Crystal facet modulation of Bi2WO6 microplates for spatial charge separation and inhibiting reverse reaction.

We experimentally demonstrated that spatial charge separation can take place between the {010} and {001} facets of Bi2WO6 microplates. Further assembly of the reduction and oxidation cocatalysts leads to a remarkable enhancement of photocatalytic water oxidation activity in the presence of Fe3+ ions while the reverse oxidation of Fe2+ to Fe3+ ions is totally inhibited. The origin of the driving force is theoretically proven to be the difference in surface work function between the co-exposed facets, which shows a feasible strategy for developing efficient photocatalysts for solar energy conversion.

High-Efficiency and Stable Inverted Planar Perovskite Solar Cells with Pulsed Laser Deposited Cu-Doped NiOx Hole-Transport Layers.

High-quality hole-transport layers (HTLs) with excellent optical and electrical properties play a significant role in achieving high-efficient and stable inverted planar perovskite solar cells (PSCs). In this work, the optoelectronic properties of Cu-doped NiOx (Cu:NiOx) films and the photovoltaic performance of PSCs with Cu:NiOx HTLs were systematically studied. The Cu-doped NiOx with different doping concentrations was achieved by a high-temperature solid-state reaction, and Cu:NiOx films were prepared by pulsed laser deposition (PLD). Cu+ ion dopants not only occupy the Ni vacancy sites to improve the crystallization quality and increase the hole mobility, but also substitute lattice Ni2+ sites and act as acceptors to enhance the hole concentration. As compared to the undoped NiOx films, the Cu:NiOx films exhibit a higher electrical conductivity with a faster charge transportation and extraction for PSCs. By employing the prepared Cu:NiOx films as HTLs for the PSCs, a high photocurrent density of 23.17 mA/cm2 and a high power conversion efficiency of 20.41% are obtained, which are superior to those with physical vapor deposited NiOx HTLs. Meanwhile, the PSC devices show a negligible hysteresis behavior and a long-term air-stability, even without any encapsulation. The results demonstrate that pulsed laser deposited Cu-doped NiOx film is a promising HTL for realizing high-performance and air-stable PSCs.

A highly [001]-textured Sb2Se3 photocathode for efficient photoelectrochemical water reduction.

Anisotropic Sb2Se3 is an emerging earth-abundant photocathode for photoelectrochemical water splitting. However, controlling the growth of the Sb2Se3 film with optimal [001] crystallographic orientation is still the most challenging issue. Here, we successfully synthesized [001]-oriented Sb2Se3via a reliable and facile method. The [001]-oriented Sb2Se3 film could provide an excellent carrier-migration efficiency. Consequently, we achieved a record-high photocurrent density of -20.2 mA cm-2 at 0 VRHE and a very high half-cell solar-to-hydrogen efficiency of 1.36% under 1-sun simulated solar illumination in a TiO2/[001]-Sb2Se3 photocathode. This work provides an effective strategy and important guidelines for rationally designing optoelectronic devices based on the [001]-oriented Sb2Se3 film.

One step in situ synthesis of core-shell structured Cr2O3:P@fibrous-phosphorus hybrid composites with highly efficient full-spectrum-response photocatalytic activities.

Making full use of solar energy and achieving high charge separation efficiency are critical factors for the photocatalysis technique. In this work, we report core-shell structured fibrous phosphorus (f-P) coated P-doped Cr2O3 (Cr2O3:P@f-P) hybrid composites with a strong optical absorption in the full region of 200-2600 nm. The Cr2O3:P@f-P hybrid composites exhibit a record photocatalytic efficiency under UV, visible and near-infrared light irradiation, demonstrating as promising photocatalysts for the full utilization of solar energy. Systematical investigations combining experimental and theoretical work show that P doping modifies the electronic band structures and creates defective levels in the forbidden gap of Cr2O3 which extends the optical absorption to the visible and near-infrared regions. Highly crystalline fibrous phosphorus in situ grown on the Cr2O3 particles constructs a core-shell hybrid structure which guarantees intimate interfacial contact between f-P and Cr2O3:P and facilitates the separation of photogenerated electron-hole pairs. This study develops a promising system based on earth abundant element P to utilize the overall spectrum of sunlight for photochemical applications.

A Tunable-Color Emission Phosphor Y2O3:Eu³âº, Bi³âº with Efficient Energy Transfer for White Light Emitting Diodes.

The Eu³âº, Bi³âº ions co-doped Y2O3 phosphor has been synthesized by the conventional solid-state reaction method, and its photoluminescence (PL) spectra are investigated for application in white light emitting diode (LED). The Eu³âº, Bi³âº ions co-doped Y2O3 phosphor showed a characteristic emissions with greenish blue and red color upon the near-UV light in the range of 310-360 nm, originating from ³P1 --> ¹S0 transition of Bi³âº and 5D0 --> 7F(J) transition of Eu³âº, respectively. As 613-nm emission of Eu³âº ions is monitored, excitation spectrum consists of two broad peaks near 230 nm and 330 nm, ascribed to the Eu³âº-O²- charge transfer band (CTB) and the transition from the ground state to the excited states of Bi³âº ions, respectively. It implies that the energy transfer from Bi³âº ions to E³âº ions occur and the phosphor's color may be controlled by adjusting the concentrations of Eu³âº ions and Bi³âºons in Y202O3The availability of this strategy is demonstrated in this work, and white light can be realized with superior chromaticity coordinates of (x = 0.337, y = 0.328) and a CCT of 5284 K for Y202O3% Eu3+³âº0.1% Bi3+³âºThus, it will be a promising candidate for the ultraviolet excitation white light emitting diode (LED).

A single-phased tunable emission phosphor MgY2Si3O10: Eu(3+), Bi(3+) with efficient energy transfer for white LEDs.

A novel single-phased tunable emitting phosphor MgY2Si3O10: Bi(3+), Eu(3+) has been synthesized by a conventional high temperature solid-state method. X-ray diffraction (XRD), photoluminescence emission and excitation spectra were utilized to characterize the as-synthesized samples. Under UV-light pumping, MgY2Si3O10: Bi(3+) showed characteristic blue emission corresponding to the (3)P1→(1)S0 transition of Bi(3+) ions, and MgY2Si3O10: Eu(3+) showed characteristic red emission corresponding to the (5)D0→(7)FJ (J = 1, 2, 3, 4) transition of Eu(3+) ions. Spectra indicate that Bi(3+) ions occupy two nonequivalent sites in the MgY2Si3O10 matrix, namely, Bi(3+)(i) and Bi(3+)(ii). The two sites (Bi(3+)(i) and Bi(3+)(ii)) exhibit broad emission peaks at 411 nm and 490 nm, respectively. Efficient energy transfer between these two Bi(3+) sites has been proven using the spectra. The spectral overlap between the emission spectrum of Bi(3+) and the excitation spectrum of Eu(3+) allows for resonance-type energy transfer to occur from Bi(3+) to Eu(3+). The efficient energy transfer from Bi(3+) to Eu(3+)via a dipole-quadrupole interaction mechanism is significantly demonstrated by comparing experimental data with theoretical calculations. According to the concentration quenching-method, the critical distance of energy transfer from Bi(3+) to Eu(3+) is calculated to be 13.2 Å. As it is a new phosphor, CIE coordinates and CCT temperature, in addition to efficient energy transfer have been also investigated in detail. White light emission for MgY2Si3O10: n Bi(3+), m Eu(3+) can be realized through controlling the concentrations of Bi(3+) and Eu(3+). All of the results indicate that MgY2Si3O10: n Bi(3+), m Eu(3+) is a potential phosphor for white light UV-LEDs.

A novel green-emitting phosphor Ba2Gd2Si4O13:Eu(2+) for near UV-pumped light-emitting diodes.

A novel green-emitting phosphor Ba2Gd2Si4O13:Eu(2+) has been prepared using a conventional high-temperature solid-state method. X-ray diffraction and photoluminescence spectra were used to characterize the as-synthesized phosphor. The Ba2Gd2Si4O13:Eu(2+) phosphor exhibits a broad emission band centered at 503 nm under 365 nm excitation. Monitoring the 503 nm emission, the Ba2Gd2Si4O13:Eu(2+) phosphor shows an intense broad excitation band ranging from 200 to 410 nm. The concentration quenching mechanism has been investigated, and demonstrated to involve a dipole-dipole interaction. The critical concentration was found to be about 4 mol%. The critical distance calculated using the concentration method and spectral overlap method was 23.9 Å and 27.1 Å, respectively. The temperature-dependent photoluminescence and CIE chromaticity coordinate of the Ba2Gd2Si4O13:Eu(2+) phosphor were also investigated in this work. The results revealed that Ba2Gd2Si4O13:Eu(2+) possesses excellent thermal stability and the CIE value of the Ba2Gd2Si4O13:0.04 Eu(2+) phosphor upon 365 nm excitation is (0.211, 0.434), located in the green region. All the properties indicate that the Ba2Gd2Si4O13:Eu(2+) phosphor is a potential green-emitting phosphor fit for ultraviolet light pumped LEDs.