Helmholtz-Zentrum Dresden-Rossendorf e. V.

Point defects can strongly affect the mechanical properties of two-dimensional (2D) materials, causing an overall detrimental effect on the strength, stiffness, and elasticity. However, the opposite has also been reported in the literature, which indicates that our understanding of the role of defects at the atomic level remains incomplete. This computational study provides a systematic assessment, based on first-principles calculations, of the mechanical properties of the archetypal 2D materials (h-BN and graphene monolayers) containing substitutional impurities and vacancies, which is further extended to 2D BCN alloys representing the case of high concentration of substitutional impurities in h-BN and graphene. In general, the stiffness of these materials, as described by Young's modulus, decreases in the presence of point defects. The Young's modulus of h-BN decreases rapidly with increasing concentration of C atoms in the N positions, while the drop is smaller for C impurities in the B positions. Notably, a defect configuration, in which carbon atoms replace the neighboring N and B atoms as a pair, results in the values of the Young's modulus in the range between that of pristine graphene and h-BN. In h-BN, B vacancies give rise to a greater decrease in stiffness than N vacancies, as explained by the analysis of the local defect-mediated strain fields formed near the point defects. The effects of graphene weakening through the introduction of substitutional defects and vacancies are similar to those observed in h-BN. This mechanical behavior persists in materials with few atomic percent of point defect concentration and agrees with most experimental results found in the literature. As the mechanical properties of 2D BCN alloys can be manipulated by a preferential substitution of B and N atoms with C atoms, our predictions may guide future efforts in defect-mediated engineering of the mechanical properties of 2D materials.

A prolonged overall treatment time (OTT) has been demonstrated to adversely affect the primary radiation therapy (RT) outcome in various solid tumors, including non-small cell lung cancer (NSCLC). Retrospective data from our group suggested an advantage of shorter OTT also for postoperative RT (PORT) in patients with NSCLC. The PORTAF trial (ClinicalTrials.gov: NCT02189967) was initiated to prospectively test this hypothesis.

The multicenter prospective randomized phase II trial in patients with NSCLC investigated whether an accelerated schedule of PORT (7 fractions per week, 2 Gy per fraction, OTT 3.5–4 weeks) improved outcome compared to conventional fractionation (5 fractions per week, 2 Gy per fraction, OTT 5–6 weeks). Target volumes and total radiation doses were stratified in both treatment arms based on individual risk factors. Primary endpoint of the study was locoregional tumor control (LRTC) 36 months after PORT, with 154 patients to be included in each arm.

Due to slow accrual and changed indications for PORT, we prematurely closed the trial in 2019. Between 2014 and 2019, eight recruiting centers included 27 evaluable patients. An interim safety analysis performed for the first 21 patients showed nonsignificant differences regarding grade 3 toxicities between the treatment arms, thus not meeting the termination criteria. LRTC was not significantly different between accelerated (73%) and conventionally fractionated RT (92%; p  = 0.535). Noteworthily, in 21 FDG-PET/CT restagings before RT, an unexpectedly high number of locoregional recurrences ( n  = 4) and distant metastases ( n  = 2) were seen, resulting in changed treatment intentions for these patients.

The prematurely closed PORTAF trial did not find significant differences in 3‑year LRTC when comparing accelerated versus conventionally fractionated irradiation. The observed additional benefit of FDG-PET/CT restaging prior to PORT should be further investigated in a larger cohort to optimize patient selection and avoid unnecessary side-effects.

Curvilinear magnetic nanostructures enable control of magnetization dynamics through geometry-induced anisotropy and chiral interactions, as well as magnetic field modulation. In this work, we report a curvilinear magnonic crystal based on large-area square arrays of truncated nanospikes fabricated by conformal coating of 3D hierarchical templates with permalloy thin films. Brillouin light scattering spectroscopy reveals an anisotropic band structure with multiple dispersive and folded Bloch-type dispersive spin-wave modes as well as nondispersive modes exhibiting direction-dependent frequency shifts and intensity asymmetries along lattice principal axes. Finite element micromagnetic simulations indicate that curvature-induced variations of the demagnetizing field govern the magnonic response, enabling the identification of modes propagating in nanochannels and others localized on nanospike apexes or along the ridges connecting adjacent nanospikes. The combination of geometric curvature and optical probing asymmetry produces directional dependence of magnonic bands, establishing 3D hierarchical templates as a versatile platform for curvature-engineered magnonics.