The chain-folding mechanism and structure of semicrystalline polymers have long been controversial. Solid-state NMR was applied to determine the chain trajectory of (13)C CH3-labeled isotactic poly(1-butene) (iPB1) in form III chiral single crystals blended with nonlabeled iPB1 crystallized in dilute solutions under low supercooling. An advanced (13)C-(13)C double-quantum NMR technique probing the spatial proximity pattern of labeled (13)C nuclei revealed that the chains adopt a three-dimensional (3D) conformation in single crystals. The determined results indicate a two-step crystallization process of (i) cluster formation via self-folding in the precrystallization stage and (ii) deposition of the nanoclusters as a building block at the growth front in single crystals.

SbTe exhibits outstanding performance among the candidate materials for phase-change memory; nevertheless, its low electrical resistivity and thermal stability hinder its practical application. Hence, numerous studies have been carried out to search suitable dopants to improve the performance; however, the explored dopants always cause phase separation and thus drastically reduce the reliability of phase-change memory. In this work, on the basis of ab initio calculations, we have identified yttrium (Y) as an optimal dopant for SbTe, which overcomes the phase separation problem and significantly increases the resistivity of crystalline state by at least double that of SbTe. The good phase stability of crystalline Y-doped SbTe (YST) is attributed to the same crystal structure between YTe and SbTe as well as their tiny lattice mismatch of only ∼1.1%. The significant increase in resistivity of c-YST is understood by our findings that Y can dramatically increase the carrier's effective mass by regulating the band structure and can also reduce the intrinsic carrier density by suppressing the formation of Sb antisite defects. Y doping can also improve the thermal stability of amorphous YST based on our ab initio molecular dynamics simulations, which is attributed to the stronger interactions between Y and Te than that of Sb and Te.

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2D magnetic semiconductors are intriguing for their great potential applications in spintronic nanodevices. Despite intensive research for decades, intrinsically 2D magnetic Janus semiconductors are scarce, and their design guidelines remain elusive. Herein we propose new 2D Janus Cr2O2XY (X = Cl, Y = Br/I) ferromagnets with asymmetric out-of-plane structural configurations from ab initio calculations. Abnormally, 2D Janus Cr2O2XY crystals with Pmm2 structures derived from pristine CrOX compounds are dynamically metastable. By introducing novel structural phase transitions, we generated new Pma2 phases with lower total energy and great dynamical stability. These new Janus Cr2O2XY monolayers are intrinsically ferromagnetic semiconductors and could be easily synthesized from experiment. Most interestingly, exotic quantum-phase transitions from the ferromagnetic semiconductor to the antiferromagnetic metal/semiconductor could be achieved in the Cr2O2ClI monolayer by applying compressive strains. Our study provides an alternative strategy to design new Janus Cr2O2XY monolayers and will inspire further investigations on relevant materials for electronic and spintronic applications.