65 research outputs found
Investigating the role of Chk1 in mouse skin homeostasis and tumourigenesis
Chk1 is a key regulator of DNA damage response and genome stability in eukaryotes. To better understand how checkpoint proficiency affects cancer development particularly tumours induced by chemical carcinogens in murine skin, I investigated the effect of conditional genetic ablation of chk1. I found that complete deletion of chk1 immediately prior to carcinogen exposure strongly suppressed papilloma formation, and the few, small lesions that did form always retained Chk1 expression. Remarkably, chk1 deletion was accompanied by spontaneous cell proliferation followed by DNA damage and cell death within the hair follicle. This also affected and led to proliferation and ultimately depletion of label-retaining stem cells (LRCs) within the bulge region of hair follicles, the principal source for carcinogen-induced tumours. At later times, ablated skin became progressively repopulated by Chk1-expressing cells and normal sensitivity to tumour induction was restored if carcinogen treatment was delayed. In marked contrast, papillomas formed normally in chk1 hemizygous skin but showed an increased propensity to progress to carcinomas. I conclude that Chk1 is essential for the survival of incipient cancer cells but that partial loss of function (haploinsufficiency) fosters tumour progression.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Raman scattering signatures of strong spin-phonon coupling in the bulk magnetic van der Waals material CrSBr
Intrinsic magnetic properties of the layered antiferromagnet CrSBr
Van der Waals magnetic materials are an ideal platform to study
low-dimensional magnetism. Opposed to other members of this family, the
magnetic semiconductor CrSBr is highly resistant to degradation in air, which,
besides its exceptional optical, electronic, and magnetic properties, is the
reason the compound is receiving considerable attention at the moment. For many
years, its magnetic phase diagram seemed to be well-understood. Recently,
however, several groups observed a magnetic transition in magnetometry
measurements at temperatures of around 40 K that is not expected from
theoretical considerations, causing a debate about the intrinsic magnetic
properties of the material. In this letter, we report the absence of this
particular transition in magnetization measurements conducted on high-quality
CrSBr crystals, attesting to the extrinsic nature of the low-temperature
magnetic phase observed in other works. Our magnetometry results obtained from
large bulk crystals are in very good agreement with the magnetic phase diagram
of CrSBr previously predicted by the mean-field theory; A-type
antiferromagnetic order is the only phase observed below the N\'eel temperature
at TN = 131 K. Moreover, numerical fits based on the Curie-Weiss law confirm
that strong ferromagnetic correlations are present within individual layers
even at temperatures much larger than TN.Comment: 13 pages, submitted to Appl. Phys. Let
In-plane magnetocrystalline anisotropy in the van der Waals antiferromagnet FePSe probed by magneto-Raman scattering
Magnon gap excitations selectively coupled to phonon modes have been studied
in FePSe layered antiferromagnet with magneto-Raman scattering experiments
performed at different temperatures. The bare magnon excitation in this
material has been found to be split (by cm) into two
components each being selectively coupled to one of the two degenerated, nearby
phonon modes. Lifting the degeneracy of the fundamental magnon mode points out
toward the biaxial character of the FePS antiferromagnet, with an
additional in-plane anisotropy complementing much stronger, out-of-plane
anisotropy. Moreover, the tunability, with temperature, of the phonon- versus
the magnon-like character of the observed coupled modes has been demonstrated.Comment: 7 pages, 5 figure
Antimonene-modified screen-printed carbon nanofibers electrode for enhanced electroanalytical response of metal ions.
A two-dimensional (2D) Sb-modified screen-printed carbon nanofibers electrode (2D Sbexf-SPCNFE) was developed to improve the stripping voltammetric determination of Cd(II) and Pb(II), taking advantage of the synergistic effect between the two nanomaterials. The surface morphology of the 2D Sbexf-SPCNFE was investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. The analytical performance of 2D Sbexf-SPCNFE was compared to those presented by screen-printed carbon electrodes modified with 2D Sbexf (2D Sbexf-SPCE) and the corresponding bare electrodes: screen-printed carbon nanofibers electrode (SPCNFEbare) and screen-printed carbon electrode (SPCEbare). After optimizing the experimental conditions, the 2D Sbexf-SPCNFE exhibited much better analytical parameters compared to the other assessed sensors. Analysis in 0.01 mol L−1 HCl (pH = 2) using 2D Sbexf-SPCNFE showed excellent linear behavior in the concentration range of 2.9 to 85.0 µg L−1 and 0.3 to 82.0 µg L−1 for Cd(II) and Pb(II), respectively. The limits of detection after 240 s deposition time for Cd(II) and Pb(II) were 0.9 and 0.1 µg L−1, and sensitivities between 1.5 and 3 times higher than those displayed by SPCEbare, SPCNFEbare, and 2D Sbexf-SPCE were obtained. Finally, the 2D Sbexf-SPCNFE was successfully applied to the determination of Cd(II) and Pb(II) traces in a certified estuarine water sample
Antimony nanomaterials modified screen-printed electrodes for the voltammetric determination of metal ions
Exfoliated β-Sb or two dimensional (2D) antimonene-based modified screen-printed electrode (2D Sb-SPCE), prepared by drop-casting of an exfoliated layered β-antimony (2D Sb) suspension, was used for the simultaneous determination of Pb(II) and Cd(II) by differential pulse anodic stripping voltammetry (DPASV). 2D Sb-SPCE was characterized by microscopic and analytical techniques, and compared not only to bare SPCE but also to layered antimony chalcogenides based-sensors. Both Sb2S3 and Sb2Se3 have an isomorphous tubular one-dimensional (1D) crystal structure, whereas Sb2Te3 and monoelement β-Sb have a 2D layered structure. Under optimized conditions, 2D Sb-SPCE displays an excellent analytical performance with detection limits of 0.3 and 2.7 μg L−1 for Pb(II) and Cd(II), respectively, and a linear response from 1.1 to 128.3 µg L−1 for Pb(II) and from 9.1 to 132.7 µg L−1 for Cd(II). Moreover, 2D Sb-SPCE was successfully applied for the DPASV determination of Pb(II) and Cd(II) in tap water, achieving statistically comparable results to those provided by ICP-MS measurements
Charge transfer-induced Lifshitz transition and magnetic symmetry breaking in ultrathin CrSBr crystals
Ultrathin CrSBr flakes are exfoliated \emph{in situ} on Au(111) and Ag(111)
and their electronic structure is studied by angle-resolved photoemission
spectroscopy. The thin flakes' electronic properties are drastically different
from those of the bulk material and also substrate-dependent. For both
substrates, a strong charge transfer to the flakes is observed, partly
populating the conduction band and giving rise to a highly anisotropic Fermi
contour with an Ohmic contact to the substrate. The fundamental CrSBr band gap
is strongly renormalized compared to the bulk. The charge transfer to the CrSBr
flake is substantially larger for Ag(111) than for Au(111), but a rigid energy
shift of the chemical potential is insufficient to describe the observed band
structure modifications. In particular, the Fermi contour shows a Lifshitz
transition, the fundamental band gap undergoes a transition from direct on
Au(111) to indirect on Ag(111) and a doping-induced symmetry breaking between
the intra-layer Cr magnetic moments further modifies the band structure.
Electronic structure calculations can account for non-rigid Lifshitz-type band
structure changes in thin CrSBr as a function of doping and strain. In contrast
to undoped bulk band structure calculations that require self-consistent
theory, the doped thin film properties are well-approximated by density
functional theory if local Coulomb interactions are taken into account on the
mean-field level and the charge transfer is considered
Ferromagnetic interlayer coupling in CrSBr crystals irradiated by ions
Layered magnetic materials are becoming a major platform for future
spin-based applications. Particularly the air-stable van der Waals compound
CrSBr is attracting considerable interest due to its prominent
magneto-transport and magneto-optical properties. In this work, we observe a
transition from antiferromagnetic to ferromagnetic behavior in CrSBr crystals
exposed to high-energy, non-magnetic ions. Already at moderate fluences, ion
irradiation induces a remanent magnetization with hysteresis adapting to the
easy-axis anisotropy of the pristine magnetic order up to a critical
temperature of 110 K. Structure analysis of the irradiated crystals in
conjunction with density functional theory calculations suggest that the
displacement of constituent atoms due to collisions with ions and the formation
of interstitials favors ferromagnetic order between the layers
Atomistic spin textures on-demand in the van der Waals layered magnet CrSBr
Controlling magnetism in low dimensional materials is essential for designing
devices that have feature sizes comparable to several critical length scales
that exploit functional spin textures, allowing the realization of low-power
spintronic and magneto-electric hardware. [1] Unlike conventional
covalently-bonded bulk materials, van der Waals (vdW)-bonded layered magnets
[2-4] offer exceptional degrees of freedom for engineering spin textures. [5]
However, their structural instability has hindered microscopic studies and
manipulations. Here, we demonstrate nanoscale structural control in the layered
magnet CrSBr creating novel spin textures down to the atomic scale. We show
that it is possible to drive a local structural phase transformation using an
electron beam that locally exchanges the bondings in different directions,
effectively creating regions that have vertical vdW layers embedded within the
horizontally vdW bonded exfoliated flakes. We calculate that the newly formed
2D structure is ferromagnetically ordered in-plane with an energy gap in the
visible spectrum, and weak antiferromagnetism between the planes. Our study
lays the groundwork for designing and studying novel spin textures and related
quantum magnetic phases down to single-atom sensitivity, potentially to create
on-demand spin Hamiltonians probing fundamental concepts in physics, [6-10] and
for realizing high-performance spintronic, magneto-electric and topological
devices with nanometer feature sizes. [11,12]Comment: Main manuscript: 11 pages, 4 figures ; Extended data: 22 pages, 19
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Synthesis, characterisation, and feasibility studies on the use of vanadium tellurate (VI) as a cathode material for aqueous rechargeable Zn-ion batteries
(NH4)4{(VO2)2[Te2O8(OH)2]}·2H2O is tested as a cathode in an aqueous Zn-ion battery for the first time, showing a discharge capacity of 283 mA h g−1 in half-cells and excellent capacity retention (91%) in concentration cells after 20 cycles
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