162 research outputs found
Spin-order-dependent magneto-elastic coupling in two dimensional antiferromagnetic MnPSe observed through Raman spectroscopy
Layered antiferromagnetic materials have emerged as a novel subset of the
two-dimensional family providing a highly accessible regime with prospects for
layer-number-dependent magnetism. Furthermore, transition metal phosphorous
trichalcogenides, MPX3 (M = transition metal; X = chalcogen) provide a platform
for investigating fundamental interactions between magnetic and lattice degrees
of freedom providing new insights for developing fields of spintronics and
magnonics. Here, we use a combination of temperature dependent Raman
spectroscopy and density functional theory to explore
magnetic-ordering-dependent interactions between the manganese spin degree of
freedom and lattice vibrations of the non-magnetic sub-lattice via a
Kramers-Anderson super-exchange pathway in both bulk, and few-layer, manganese
phosphorous triselenide (MnPSe). We observe a nonlinear temperature
dependent shift of phonon modes predominantly associated with the non-magnetic
sub-lattice, revealing their non-trivial spin-phonon coupling below the
N{\'e}el temperature at 74 K, allowing us to extract mode-specific spin-phonon
coupling constants.Comment: 20 pages, 4 figures, Submitted to ACS Nano Letter
Interplay between spin proximity effect and charge-dependent exciton dynamics in MoSe2/CrBr3 van der Waals heterostructures
Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe2 and CrBr3 in photoluminescence, whereby the valley polarization of the MoSe2 trion state conforms closely to the local CrBr3 magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes. Going further, we uncover by both the magneto-optical Kerr effect and photoluminescence a domain-like spatial topography of contrasting valley polarization, which we infer to be labyrinthine or otherwise highly intricate, with features smaller than 400 nm corresponding to our optical resolution. Our findings offer a unique insight into the interplay between short-lived valley excitons and spin-dependent interlayer tunneling, while also highlighting MoSe2 as a promising candidate to optically interface with exotic spin textures in van der Waals structures.T. P. L. acknowledges financial support from the EPSRC Doctoral Prize Fellowship scheme under Grant Reference EP/R513313/1. T. P. L., K. S. N. and A. I. T. acknowledge financial support from the European Graphene Flagship Projects under grant agreements 785219 and 881603, and EPSRC grants EP/P026850/1 and EP/S030751/1. K. S. N. also acknowledges support from EU Quantum Technology Flagship Programs, European Research Council Synergy Grant Hetero2D, the Royal Society, EPSRC grants EP/N010345/1, EP/S030719/1. We gratefully acknowledge the Exeter Time-Resolved Magnetism Facility (EXTREMAG - EPSRC Grant Reference EP/R008809/1) for the time allocated to this study for low temperature, wide-field Kerr microscopy. The DFT calculations were performed on the Tirant III cluster of the Servei d‘Informàtica of the University of Valencia (project vlc82) and on Mare Nostrum cluster of the Barcelona Supercomputing Center (project FI-2019-2-0034). A.M.-S. acknowledges the Marie-CurieCOFUND program Nano TRAIN For Growth II (Grant Agreement 713640). J.F.-R. acknowledges financial support from FCT for the grant UTAP-EXPL/NTec/0046/2017, as well as Generalitat Valenciana funding Prometeo 2017/139 and MINECO-Spain (Grant no. MAT2016-78625-C2). Growth of hexagonal boron nitride crystals was supported by the Elemental Strategy Initiative conducted by the MEXT, Japan, and the CREST (JPMJCR15F3), J.S.
Understanding the impact of heavy ions and tailoring the optical properties of large-area Monolayer WS2 using Focused Ion Beam
Focused ion beam (FIB) has been used as an effective tool for precise
nanoscale fabrication. It has recently been employed to tailor defect
engineering in functional nanomaterials such as two-dimensional transition
metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based
optoelectronic devices. However, the damage caused by the FIB irradiation and
milling process to these delicate atomically thin materials, especially in the
extended area, has not yet been elaboratively characterised. Understanding the
correlation between lateral ion beam effects and optical properties of 2D TMDCs
is crucial in designing and fabricating high-performance optoelectronic
devices. In this work, we investigate lateral damage in large-area monolayer
WS2 caused by the gallium focused ion beam milling process. Three distinct
zones away from the milling location are identified and characterised via
steady-state photoluminescence (PL) and Raman spectroscopy. An unexpected
bright ring-shaped emission around the milled location has been revealed by
time-resolved PL spectroscopy with high spatial resolution. Our finding opens
new avenues for tailoring the optical properties of TMDCs by charge and defect
engineering via focused ion beam lithography. Furthermore, our study provides
evidence that while some localised damage is inevitable, distant destruction
can be eliminated by reducing the ion beam current. It paves the way for the
use of FIB to create nanostructures in 2D TMDCs, as well as the design and
realisation of optoelectrical devices on a wafer scale
Comparative regulomics supports pervasive selection on gene dosage following whole genome duplication
publishedVersio
Resonant band hybridization in alloyed transition metal dichalcogenide heterobilayers
Bandstructure engineering using alloying is widely utilised for achieving
optimised performance in modern semiconductor devices. While alloying has been
studied in monolayer transition metal dichalcogenides, its application in van
der Waals heterostructures built from atomically thin layers is largely
unexplored. Here, we fabricate heterobilayers made from monolayers of WSe
(or MoSe) and MoWSe alloy and observe nontrivial tuning of
the resultant bandstructure as a function of concentration . We monitor this
evolution by measuring the energy of photoluminescence (PL) of the interlayer
exciton (IX) composed of an electron and hole residing in different monolayers.
In MoWSe/WSe, we observe a strong IX energy shift of
100 meV for varied from 1 to 0.6. However, for this shift
saturates and the IX PL energy asymptotically approaches that of the indirect
bandgap in bilayer WSe. We theoretically interpret this observation as the
strong variation of the conduction band K valley for , with IX PL
arising from the K-K transition, while for , the bandstructure
hybridization becomes prevalent leading to the dominating momentum-indirect K-Q
transition. This bandstructure hybridization is accompanied with strong
modification of IX PL dynamics and nonlinear exciton properties. Our work
provides foundation for bandstructure engineering in van der Waals
heterostructures highlighting the importance of hybridization effects and
opening a way to devices with accurately tailored electronic properties.Comment: Supporting Information can be found downloading and extracting the
gzipped tar source file listed under "Other formats
Developing a model of mental health self-care support for children and young people through an integrated evaluation of available types of provision involving systematic review, meta-analysis and case study
Background
The mental health of children and young people (CYP) is a major UK public health concern. Recent policy reviews have identified that service provision for CYP with mental health needs is not as effective, responsive, accessible or child-centred as it could be. Following on from a previous National Institute for Health Research (NIHR) study into self-care support for CYP with long-term physical health needs, this study explored self-care support’s potential in CYP’s mental health.
Objectives
To identify and evaluate the types of mental health self-care support used by, and available to, CYP and their parents, and to establish how such support interfaces with statutory and non-statutory service provision.
Design
Two inter-related systematic literature reviews (an effectiveness review with meta-analysis and a perceptions review), together with a service mapping exercise and case study.
Setting
Global (systematic reviews); England and Wales (mapping exercise and case study).
Participants (case study)
Fifty-two individuals (17 CYP, 16 family members and 19 staff) were interviewed across six sites.
Main outcome measures (meta-analysis)
A measure of CYP’s mental health symptomatology.
Data sources (literature reviews)
MEDLINE, Cumulative Index to Nursing and Allied Health Literature (CINAHL), PsycINFO, All Evidence-Based Medicine (EBM) Reviews, Applied Social Sciences Index and Abstracts (ASSIA) and Education Resources Information Center (ERIC).
Review methods
Titles and abstracts of papers were screened for relevance then grouped into studies. Two independent reviewers extracted data from studies meeting the inclusion criteria. A descriptive analysis and meta-analysis were conducted for the effectiveness review; descriptive analyses were conducted for the perceptions review. These analyses were integrated to elicit a mixed-methods review.
Results
Sixty-five of 71 included studies were meta-analysable. These 65 studies elicited 71 comparisons which, when meta-analysed, suggested that self-care support interventions were effective at 6-month [standardised mean difference (SMD) = −0.20; 95% confidence interval (CI) −0.28 to −0.11] and 12-month (SMD = −0.12; 95% CI −0.17 to −0.06) follow-ups. However, judged against Cochrane criteria, the studies were mostly low quality. Key elements of self-care support identified in the perceptions review were the acquisition of knowledge and skills, peer support and the relationship with the self-care support agent; CYP also had different perceptions from adults about what is important in self-care support. The mapping exercise identified 27 providers of 33 self-care support services. According to the case study data, effective self-care support services are predicated on flexibility; straightforward access; non-judgemental, welcoming organisations and staff; the provision of time and attention; opportunities to learn and practise skills relevant to self-care; and systems of peer support.
Conclusions
Mental health self-care support interventions for CYP are modestly effective in the short to medium term. Self-care support can be conceptualised as a process which has overlap with ‘recovery’. CYP and their families want choice and flexibility in the provision of such interventions and a continued relationship with services after the nominal therapy period. Those delivering self-care support need to have specific child-centred attributes.
Future work
Future work should focus on under-represented conditions (e.g. psychosis, eating disorders, self-harm); the role of technology, leadership and readiness in self-care support; satisfaction in self-care support; the conceptualisation of self-care support in CYP’s mental health; and efficacy and cost-effectiveness
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