High‐entropy materials (HEMs) have great potential for energy storage and conversion due to their diverse compositions, and unexpected physical and chemical features. However, high‐entropy atomic layers with fully exposed active sites are difficult to synthesize since their phases are easily segregated. Here, it is demonstrated that high‐entropy atomic layers of transition‐metal carbide (HE‐MXene) can be produced via the selective etching of novel high‐entropy MAX (also termed Mn+1AXn (n = 1, 2, 3), where M represents an early transition‐metal element, A is an element mainly from groups 13–16, and X stands for C and/or N) phase (HE‐MAX) (Ti1/5V1/5Zr1/5Nb1/5Ta1/5)2AlC, in which the five transition‐metal species are homogeneously dispersed into one MX slab due to their solid‐solution feature, giving rise to a stable transition‐metal carbide in the atomic layers owing to the high molar configurational entropy and correspondingly low Gibbs free energy. Additionally, the resultant high‐entropy MXene with distinct lattice distortions leads to high mechanical strain into the atomic layers. Moreover, the mechanical strain can efficiently guide the nucleation and uniform growth of dendrite‐free lithium on HE‐MXene, achieving a long cycling stability of up to 1200 h and good deep stripping–plating levels of up to 20 mAh cm−2.

Although high‐entropy layered transition metal carbonitride MAX phases and their derivative MXenes have been proposed to exhibit unique physicochemical features for widespread applications, it is still challenging to synthesize them owing to the easy formation of separated phases during the traditional synthetic process. Here, a new high‐entropy carbonitride MAX phase (HE CN‐MAX, (Ti1/3V1/6Zr1/6Nb1/6Ta1/6)2AlCxN1–x) is synthesized on the basis of metallurgically treating medium‐entropy MAX (ME‐MAX) (Zr1/3Nb1/3Ta1/3)2AlC and other MAX phases (Ti4AlN3 and V2AlC). During the metallurgical process, the unique usage of a medium‐entropy MAX phase effectively solves the phase separation issue for the formation of a high‐entropy MAX phase owing to their low entropy difference. After selective extraction of an A species, a high‐entropy carbonitride MXene (HE CN‐MXene) with high mechanical strains and five types of metal‐nitrogen bonds is achieved, which shows good adsorption and catalytic activities for lithium polysulfides. As a result, a lithium–sulfur battery with HE CN‐MXene delivers a high‐rate capability (702 mAh g−1 at 4 C) and good cycling stability.

Purpose/Objective To establish a novel preclinical model for stereotactic radiosurgery with combined mouse-like phantom quality assurance in the setting of brain metastases. Material Methods C57B6 mice underwent intracranial injection of B16-F10 melanoma cells. T1-post contrast MRI was performed on Day 11 after injection. The MRI images were fused with cone beam computed tomography (CBCT) images using the SARRP. Gross tumor volume (GTV) was contoured using the MRI. A single sagittal arc utilizing the 3×3 mm2 collimator was used to deliver 18 Gy prescribed to the isocenter. MRI was performed 7 days after radiation treatment and the dose delivered to the mice was confirmed using two mouse-like anthropomorphic phantoms: one in the axial and the other in the sagittal orientation. SARRP output was measured using a PTW Farmer type ionization chamber as per AAPM TG-61 and the H-D curve was generated up to a max dose of 30 Gy. Irradiated films were analyzed based on optical density distribution and H-D curve. Results The tumor volume at Day 11, before intervention, was 2.48±1.37 mm3 in the no SRS arm versus 3.75±1.19 mm3 in the SRS arm (NS). In the SRS arm, GTV Dose max (Dmax) and mean dose were 2048±207 and 1785±14 cGy. Using the mouse-like phantoms, the radiochromic film showed close precision as compared with projected isodose lines with a Dmax of 1903.4 and 1972.7 cGy, the axial and sagittal phantom respectively. Tumor volume 7 days post-treatment was 7.34±8.24 mm3 in the SRS arm and 60.20±40.4 mm3 in the no SRS arm (p=0.009). No mice in the control group survived more than 22 days after implantation with a median overall survival (mOS) of 19 days. mOS was not reached in the SRS group with one death noted. Conclusion Single fraction SRS of 18 Gy delivered in a single arc can be delivered accurately with MRI T1-post contrast based treatment planning. The mouse-like phantom allows for verification of dose delivery and accuracy.