Control of structure and spin texture in the van der Waals layered magnet CrSBr

Controlling magnetism at nanometer length scales is essential for realizing high-performance spintronic, magneto-electric and topological devices and creating on-demand spin Hamiltonians probing fundamental concepts in physics. Van der Waals (vdW)-bonded layered magnets offer exceptional opportunities for such spin texture engineering. Here, we demonstrate nanoscale structural control in the layered magnet CrSBr with the potential to create spin patterns without the environmental sensitivity that has hindered such manipulations in other vdW magnets. We drive a local phase transformation using an electron beam that moves atoms and exchanges bond directions, effectively creating regions that have vertical vdW layers embedded within the initial horizontally vdW bonded exfoliated flakes. We calculate that the newly formed two-dimensional structure is ferromagnetically ordered in-plane with an energy gap in the visible spectrum, and weak antiferromagnetism between the planes, suggesting possibilities for creating spin textures and quantum magnetic phases.

Site-selectively generated photon emitters in monolayer MoS2 via local helium ion irradiation

Quantum light sources in solid-state systems are of major interest as a basic ingredient for integrated quantum photonic technologies. The ability to tailor quantum emitters via site-selective defect engineering is essential for realizing scalable architectures. However, a major difficulty is that defects need to be controllably positioned within the material. Here, we overcome this challenge by controllably irradiating monolayer MoS2 using a sub-nm focused helium ion beam to deterministically create defects. Subsequent encapsulation of the ion exposed MoS2 flake with high-quality hBN reveals spectrally narrow emission lines that produce photons in the visible spectral range. Based on ab-initio calculations we interpret these emission lines as stemming from the recombination of highly localized electron-hole complexes at defect states generated by the local helium ion exposure. Our approach to deterministically write optically active defect states in a single transition metal dichalcogenide layer provides a platform for realizing exotic many-body systems, including coupled single-photon sources and interacting exciton lattices that may allow the exploration of Hubbard physics.

Prospects and Limitations of Transition Metal Dichalcogenide Laser Gain Materials

Nanolasers operate with a minimal amount of active material and low losses. In this regime, single layers of transition-metal dichalcogenides (TMDs) are being investigated as next generation gain materials due to their high quantum efficiency. We provide results from microscopic gain calculations of highly excited TMD monolayers and specify requirements to achieve lasing with four commonly used TMD semiconductors. Our approach includes band-structure renormalizations due to excited carriers that trigger a direct-to-indirect band gap transition. As a consequence, we predict a rollover for the gain that limits the excitation regime where laser operation is possible. A parametrization of the peak gain is provided that is used in combination with a rate-equation theory to discuss consequences for experimentally accessible laser characteristics.

A few-emitter solid-state multi-exciton laser

We report on non-conventional lasing in a photonic-crystal nanocavity that operates with only four solid-state quantum-dot emitters. In a comparison between microscopic theory and experiment, we demonstrate that irrespective of emitter detuning, lasing with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${g}^{\mathrm{(2)}}=1$$\end{document}g(2)=1 is facilitated by means of emission from dense-lying multi-exciton states. In the spontaneous-emission regime we find signatures for radiative coupling between the quantum dots. The realization of different multi-exciton states at different excitation powers and the presence of electronic inter-emitter correlations are reflected in a pump-rate dependence of the β-factor.

Electric-Field Switchable Second-Harmonic Generation in Bilayer MoS2 by Inversion Symmetry Breaking

We demonstrate pronounced electric-field-induced second-harmonic generation in naturally inversion symmetric 2H stacked bilayer MoS₂ embedded into microcapacitor devices. By applying strong external electric field perturbations (|F| = ±2.6 MV cm^-1) perpendicular to the basal plane of the crystal, we control the inversion symmetry breaking and, hereby, tune the nonlinear conversion efficiency. Strong tunability of the nonlinear response is observed throughout the energy range (E_ω ∼ 1.25-1.47 eV) probed by measuring the second-harmonic response at E_2ω, spectrally detuned from both the A- and B-exciton resonances. A 60-fold enhancement of the second-order nonlinear signal is obtained for emission at E_2ω = 2.49 eV, energetically detuned by ΔE = E_2ω - E_C = -0.26 eV from the C-resonance (E_C = 2.75 eV). The pronounced spectral dependence of the electric-field-induced second-harmonic generation signal reflects the bandstructure and wave function admixture and exhibits particularly strong tunability below the C-resonance, in good agreement with density functional theory calculations. Moreover, we show that the field-induced second-harmonic generation relies on the interlayer coupling in the bilayer. Our findings strongly suggest that the strong tunability of the electric-field-induced second-harmonic generation signal in bilayer transition metal dichalcogenides may find applications in miniaturized electrically switchable nonlinear devices.

Estrogen decreases TNF-alpha and oxidized LDL induced apoptosis in endothelial cells

Apoptosis induced by oxidized low-density lipoproteins (oxLDL) and tumor necrosis factor-alpha (TNF-alpha) is believed to contribute to atherosclerosis and vascular dysfunction. Estrogen treatment reduces apoptosis due to TNF-alpha and we hypothesized that it would also reduce apoptosis due to oxLDL. We also explored the anti-apoptotic mechanisms. We used early passage human umbilical vein endothelial cells (HUVEC) grown in steroid-depleted, red phenol-free medium. Cells were synchronized by starvation for 6h and then treated with oxLDL (75microg/ml) or TNF-alpha (20ng/ml) in the presence of 17-beta-estradiol (E2) (20nM). Apoptosis was analyzed by flow cytometry and caspase-3 cleavage. We also assessed expression of Bcl-2 and Bcl-xL and phosphorylation of BAD. At 6h TNF-alpha induced apoptosis but oxLDL did not; E2 did not affect this TNF-alpha induced apoptosis and there was no change in Bcl-2 or Bcl-xL expression. At 24h both TNF-alpha and oxLDL increased apoptosis and E2 reduced the increase. E2 also increased expression of the anti-apoptotic Bcl-2 and Bcl-xL and increased phosphorylation of proapoptotic BAD which reduces its proapoptotic activity at 1h. However at 24h there was also an increase in total BAD so that the proportion of phosphorylation of BAD decreased. oxLDL induced apoptosis occurs later than that of TNF-alpha. E2 decreased this late phase apoptosis and this likely requires the production of anti-apoptotic proteins.

Determination of brilliant blue FCF in the presence and absence of erythrosine and quinoline yellow food colours by cathodic stripping voltammetry

A study of the voltammetric behaviour of the food colours brilliant blue FCF (C.I. 42090), erythrosine (C.I. 45430) and quinoline yellow (C.I. 47005) in the pH range 2-10 have been carried out by cathodic#10; stripping voltammetry. At pH 4.5 (acetate buffer) with an accumulation potential of 0 V and accumulation time of 30s, the voltammograms presented well-defined reduction peaks at potential - 0.76 V for brilliant blue FCF, - 0.85 V for quinoline yellow and - 0.54 V for erythrosine. Linear calibration graphs were obtained from 8 to 80 microg l(-1) brilliant blue, from 4 to 43 microg l(-1) quinoline yellow and from 10 to 70 microg l(-1) erythrosine. The method has been successfully applied to identify and quantify binary mixtures of these dyes and applied for determining brilliant blue FCF in commercial food products.

Involvement of long-chain acyl CoA in the antagonistic effects of halothane and L-carnitine on mitochondrial energy-linked processes

Incubation of rat liver mitochondria in the presence of halothane induced a consistent impairment of mitochondrial oxidative phosphorylation without significantly affecting the steady-state of transmembrane electrical potential. These alterations of mitochondrial energy-linked processes were associated with a consistent accumulation of long-chain acyl CoA. Addition of L-carnitine partially prevented the effects of halothane on oxidative phosphorylation and completely abolished the halothane-induced long-chain acyl CoA accumulation. The possibility is discussed that the damaging action of halothane on mitochondrial functions might be partially ascribed to the noxious action of the excess of long-chain acyl CoA induced the anesthetic.

[Murine cloned cells related to basophil-mast cell granulocytes, spontaneously cytotoxic toward tumor cells]

Two independent cloned cell lines were derived following the in vitro expansion of spleen and bone-marrow cells suspensions from DBA/2 Mice in the presence of a conditioned medium containing interleukin II. They exhibit a spontaneous cytotoxicity towards two tumors of leukemic origin. The presence of cytoplasmic granules, their staining properties, the typing of surface markers and enzyme activities suggest that they belong to the basophil-mast cell lineage.

Apparent reversion of stable in vitro genetic markers detected in tumour cells from spontaneous metastases

The evolution towards more aggressive and autonomous behaviour of many cancerous tumours, often referred to as tumour progression, is thought to stem from the development of heterogeneity within the tumour cell population, combined with the continuous selection of progressively more malignant cellular phenotypes. During the course of the disease, the tumour cells show multiple phenotypic changes in a stepwise, but apparently random fashion, becoming more anaplastic, increasingly independent of growth controls and more metastatic. Several laboratories, including our own, have analysed aspects of tumour heterogeneity and cancer metastasis by selecting and studying the properties of lectin-resistant (LecR) membrane mutant tumour sublines; in a few cases, such variants have been claimed to be less tumorigenic or metastatic than the parental cells from which they were derived. We have attempted to study the factors involved in the reestablishment of tumour heterogeneity by monitoring the stability in vivo of LecR phenotypes of metastatic tumour cells after injection of cloned LecR tumour cells. We now report that spontaneous metastases arising after a subcutaneous (s.c.) injection of cells from variant tumour lines selected from a highly metastatic DBA/2 mouse tumour known as MDAY-D2, and which are stably resistant in tissue culture to wheat germ agglutinin (WGA), no longer carry the WGA-resistant (WGAR) phenotype. The results demonstrate that WGAR tumour cells do not metastasize, but rather, 'revertants' for the WGAR phenotype, which presumably were generated in vivo after injection, were the cells actually capable of metastatic growth.

Carcinogenicity of tumor cell populations: origin of a putative H-2 isoantigenic loss variant tumor

The properties of an unusual mouse tumor capable of extremely rapid and widespread spontaneous metastatic growth were recently described; this tumor, called MDAY-D2, at first appeared to be an H-2Kk loss variant of an (A X DBA/2)F1 (H-2KkDd) sarcoma called MDAY and was obtained by serial ip passage of MDAY in DBA/2 (KdDd) mice. The studies described here were concerned with the analysis of the origin of MDAY-D2; i.e., was it a true variant or a newly induced DBA/2 tumor? Several approaches were used, most of which exploited defined cell surface alloantigenic systems as natural genetic markers. The results indicated that MDAY-D2 was indeed a newly induced DBA/2 tumor and, furthermore, that MDAY was a homozygous A-strain tumor, probably a T-cell lymphoma. Thus a) MDAY was found to be Ly-1.2+, Ly-2.2+, and Thy-1.2+, but Ly-6.2-, whereas the opposite pattern was observed with MDAY-D2; b) MDAY possessed the private and public H-2 specificities associated with H-2k and H-2Dd, but not H-2Dk [i.e., it typed as an A-strain (H-2a) tumor, not as (A X DBA/2)F1]; c) MDAY-D2 possessed private and public specificities associated with H-2Kd and H-2Dd and was found to be H-2Kk-negative [i.e., it typed as a DBA/2 (H-2d) tumor]; d) serial injection of clonally derived ouabain-resistant H-2Kk-positive MDAY cells into DBA/2 hosts led to the rapid development of an MDAY-D2 (H-2d-positive) tumor that was fully ouabain-sensitive. Several findings did not support a contaminant theory to explain induction of MDAY-D2. The rapid induction of a tumor after injection of allogeneic tumor cells may have importance in relation to oncogenesis, tumor variant formation, and tumor progression. The results showed that tumor cells themselves can be potent carcinogens.

Chinese hamster cell lines resistant to the cytotoxic action of fluoride

The proliferation and efficiency of colony formation of a Chinese hamster ovary cell line, CHO, was found to be inhibited by concentrations of fluoride greater than or equal to 10(-3) M. From mutagenized populations of CHO cells, clones were isolated that were from 1.6 to 13 times more resistant than the wild-type to the cytotoxic action of fluoride. The resistant clones were found to be stable in the absence of selection. The fluoride sensitivity of wild-type and fluoride resistant clones was not altered by changes in the pyruvate concentration in the culture medium, indicating that the cytotoxic effect of fluoride is not due to the action of fluoride on the glycolytic pathway. On the other hand, both the incorporation of 3H-leucine into acid precipitable material and the distribution of polyribosomes were sensitive only to fluoride concentrations that were cytotoxic, suggesting that the molecular basis of fluoride induced cytotoxicity in both wild-type and fluoride resistant cells is the sensitivity of protein synthesis to fluoride. At concentrations of fluoride at which the wild-type cells are inhibited but fluoride resistant cells are not, the intracellular concentration of fluoride in the fluoride resistant cells was found to be 1/5 to 1/10 that of the wild-type, suggesting that fluoride exclusion is the basis for resistance in the resistant lines.