Discovery of enhanced lattice dynamics in a single-layered hybrid perovskite.

Layered hybrid perovskites exhibit emergent physical properties and exceptional functional performances, but the coexistence of lattice order and structural disorder severely hinders our understanding of these materials. One unsolved problem regards how the lattice dynamics are affected by the dimensional engineering of the inorganic frameworks and their interaction with the molecular moieties. Here, we address this question by using a combination of spontaneous Raman scattering, terahertz spectroscopy, and molecular dynamics simulations. This approach reveals the structural dynamics in and out of equilibrium and provides unexpected observables that differentiate single- and double-layered perovskites. While no distinct vibrational coherence is observed in double-layered perovskites, an off-resonant terahertz pulse can drive a long-lived coherent phonon mode in the single-layered system. This difference highlights the dramatic change in the lattice environment as the dimension is reduced, and the findings pave the way for ultrafast structural engineering and high-speed optical modulators based on layered perovskites.

Facet-selective etching trajectories of individual semiconductor nanocrystals.

The size and shape of semiconductor nanocrystals govern their optical and electronic properties. Liquid cell transmission electron microscopy (LCTEM) is an emerging tool that can directly visualize nanoscale chemical transformations and therefore inform the precise synthesis of nanostructures with desired functions. However, it remains difficult to controllably investigate the reactions of semiconductor nanocrystals with LCTEM, because of the highly reactive environment formed by radiolysis of liquid. Here, we harness the radiolysis processes and report the single-particle etching trajectories of prototypical semiconductor nanomaterials with well-defined crystalline facets. Lead selenide nanocubes represent an isotropic structure that retains the cubic shape during etching via a layer-by-layer mechanism. The anisotropic arrow-shaped cadmium selenide nanorods have polar facets terminated by either cadmium or selenium atoms, and the transformation trajectory is driven by etching the selenium-terminated facets. LCTEM trajectories reveal how nanoscale shape transformations of semiconductors are governed by the reactivity of specific facets in liquid environments.

High-speed two-dimensional terahertz spectroscopy with echelon-based shot-to-shot balanced detection.

By using a reflective-echelon-based electro-optic sampling technique and a fast detector, we develop a two-dimensional terahertz (THz) spectrometer capable of shot-to-shot balanced readout of THz waveforms at a full 1-kHz repetition rate. To demonstrate the capabilities of this new detection scheme for high-throughput applications, we use gas-phase acetonitrile as a model system to acquire two-dimensional THz rotational spectra. The results show a two-order-of-magnitude speedup in the acquisition of multidimensional THz spectra when compared to conventional delay-scan methods while maintaining accurate retrieval of the nonlinear THz signal. Our report presents a feasible solution for bringing the technique of multidimensional THz spectroscopy into widespread practice.

Snapshots of a light-induced metastable hidden phase driven by the collapse of charge order.

Nonequilibrium hidden states provide a unique window into thermally inaccessible regimes of strong coupling between microscopic degrees of freedom in quantum materials. Understanding the origin of these states allows the exploration of far-from-equilibrium thermodynamics and the development of optoelectronic devices with on-demand photoresponses. However, mapping the ultrafast formation of a long-lived hidden phase remains a longstanding challenge since the initial state is not recovered rapidly. Here, using state-of-the-art single-shot spectroscopy techniques, we present a direct ultrafast visualization of the photoinduced phase transition to both transient and long-lived hidden states in an electronic crystal, 1T-TaS2, and demonstrate a commonality in their microscopic pathways, driven by the collapse of charge order. We present a theory of fluctuation-dominated process that helps explain the nature of the metastable state. Our results shed light on the origin of this elusive state and pave the way for the discovery of other exotic phases of matter.

Uncovering the Role of Hole Traps in Promoting Hole Transfer from Multiexcitonic Quantum Dots to Molecular Acceptors.

Understanding electronic dynamics in multiexcitonic quantum dots (QDs) is important for designing efficient systems useful in high power scenarios, such as solar concentrators and multielectron charge transfer. The multiple charge carriers within a QD can undergo undesired Auger recombination events, which rapidly annihilate carriers on picosecond time scales and generate heat from absorbed photons instead of useful work. Compared to the transfer of multiple electrons, the transfer of multiple holes has proven to be more difficult due to slower hole transfer rates. To probe the competition between Auger recombination and hole transfer in CdSe, CdS, and CdSe/CdS QDs of varying sizes, we synthesized a phenothiazine derivative with optimized functionalities for binding to QDs as a hole accepting ligand and for spectroscopic observation of hole transfer. Transient absorption spectroscopy was used to monitor the photoinduced absorption features from both trapped holes and oxidized ligands under excitation fluences where the averaged initial number of excitons in a QD ranged from ∼1 to 19. We observed fluence-dependent hole transfer kinetics that last around 100 ps longer than the predicted Auger recombination lifetimes, and the transfer of up to 3 holes per QD. Theoretical modeling of the kinetics suggests that binding of hole acceptors introduces trapping states significantly different from those in native QDs passivated with oleate ligands. Holes in these modified trap states have prolonged lifetimes, which promotes the hole transfer efficiency. These results highlight the beneficial role of hole-trapping states in devising hole transfer pathways in QD-based systems under multiexcitonic conditions.

Spherical silica nanoparticles promote malignant transformation of BEAS-2B cells by stromal cell-derived factor-1α (SDF-1α).

OBJECTIVE: This study aimed to examine the role of spherical silica nanoparticles (SiNPs) on human bronchial epithelial (BEAS-2B) cells through inflammation. METHODS: Human mononuclear (THP-1) cells and BEAS-2B cells were co-cultured in transwell chambers and treated with 800 mmol/L benzo[ a]pyrene-7, 8-dihydrodiol-9, 10-epoxide (BPDE) and 12.5 µg/mL SiNPs for 24 hours. For controls, cells were treated with BPDE alone. Subcutaneous tumorigenicity and epithelial-mesenchymal transition (EMT) of BEAS-2B cells were measured. The cells were blocked with a stromal cell-derived factor-1α (SDF-1α)-specific antibody. EMT was analyzed in cells treated with 800 mmol/L BPDE and 12.5 µg/mL SiNPs relative to matched control cells and xenografts in vivo. Serum SDF-1α levels were measured in 23 patients with lung adenocarcinoma in Xuanwei, in 25 with lung adenocarcinoma outside Xuanwei, and in 22 with benign pulmonary lesions in Xuanwei. RESULTS: SiNPs significantly promoted tumorigenesis and EMT, induced the release of SDF-1α, and activated AKT (ser473) in BEAS-2B cells. EMT and phosphorylated AKT (ser473) and glycogen synthase kinase-3ß levels were decreased when blocked by SDF-1α antibody in BEAS-2B cells. SDF-1α was mainly secreted by THP-1 cells. CONCLUSION: SiNPs combined with BPDE promote EMT of BEAS-2B cells via the AKT pathway by inducing release of SDF-1α from THP-1 cells.

[Expression of human spindle mitosis arrest deficiency gene in spontaneous abortion embryo tissues].

OBJECTIVE: To investigate the expression of human spindle mitosis arrest deficiency gene (hsMAD2) in spontaneous abortion embryos and the relationship between low expression of hsMAD2 and numerical chromosomal aberration. METHODS Spontaneous abortion embryo tissues were collected, including 23 cases of once spontaneous abortion tissue and 10 cases of twice or more spontaneous abortion tissue and induced abortion embryos (35 cases) from the Department of Gynaecology and Obstetrics of the Affiliated Hospitals of Chongqing University of Medical Science during the period of March 2006 to March 2007. FQ-PCR and western blot were used to evaluate the endogenous expression level of hsMAD2 mRNA and hsMAD2 protein; primary culturing of cells from the induced abortion embryos was conducted and 5 embryonic cells were selected by chromosomes karyotype analysis. Recombinant shRNA plasmids targeting hsMAD2 gene were constructed to inhibit the expression of endogenous hsMAD2 genes in embryonic cells which have normal karyotypes; the groups were defined as the first experimental group (transfected with pshRNA-hsMAD2-1) , the second experimental group (transfected with pshRNA-hsMAD2-2), the third experimental group (transfected with pshRNA-hsMAD2-3), the first control group (transfected with nothing), the second control group (transfected with pTZU6 + 1) and the independent group (transfected with pshRNA-N1). Interference efficiency was demonstrated by FQ-PCR and western blot; cell proliferation was measured by methyl thiazolyl tetrazolium (MTT) assay; cell-cycle was assessed by flow cytometry (FCM); the chromosome numbers were calculated to analyze the variation of chromosomes. RESULTS: (1) The mRNA levels of hsMAD2 in the once spontaneous abortion tissue, twice or more spontaneous abortion tissue and induced abortion tissue were 0.00879 +/- 0.00035, 0.00901 +/- 0.00033 and 0.00941 +/- 0.00026 respectively, and there was no significant difference (P > 0.05) compared with each other; however, the protein levels of hsMAD2 in three groups were 0.2791 +/- 0.0311, 0.0431 +/- 0.0020 and 0.5790 +/- 0.0331 respectively, and there were significant differences (P < 0.05) compared with each other. (2) Recombinant shRNA plasmids could significantly and specifically inhibit hsMAD2 gene expression in embryonic cells. Compared with the first control group (4%) and the second control group (3%), the recombinant shRNA could inhibit embryonic cell proliferation to 54% at 48 h after transfection (P < 0.05); compared with the first control group (8.2%) and the second control group (8.0%), the ratios of G2/M phase cells in the experimental group (17.9%)was significantly increased (P < 0.05); compared with the first control group (4.8%), the ratios of abnormal chromosomes in the experimental group was increased to 30.0% (P < 0.05). CONCLUSIONS: Down-expression of hsMAD2 gene may be one of the mechanisms inducing numerical chromosome aberration, abnormal embryo development and the occurrence of spontaneous abortion.