Nano Letters最新文献

Spin valves are essential components in spintronic memory devices whose conductance is modulated by controlling spin-polarized electron tunnelling through the alignment of the magnetization in ferromagnetic elements. Whereas conventional spin valves unavoidably require at least two ferromagnetic elements, here we demonstrate a van der Waals spin valve based on a tunnel junction that comprises only one such ferromagnetic layer. Our devices combine an Fe₃GeTe₂ electrode acting as a spin injector together with a paramagnetic tunnel barrier, formed by a CrBr₃ multilayer operated above its Curie temperature. We show that these devices exhibit a conductance modulation with values comparable to those of conventional spin valves. A quantitative analysis of the magnetoconductance that accounts for the field-induced magnetization of CrBr₃, including the effect of exchange interaction, confirms that the spin valve effect originates from the paramagnetic response of the barrier, in the absence of spontaneous magnetization in CrBr₃.

Conventional piezoelectric materials typically exhibit positive longitudinal piezoelectric coefficients, yet recent studies have identified exceptions with negative piezoelectric responses. Using density functional theory, we demonstrate for the first time that rhombohedral GeTe (r-GeTe) possesses an ultrahigh negative piezoelectric strain coefficient (d₃₃) of -70.87 pC/N, surpassing all previously reported negative piezoelectric materials. This phenomenon arises from the "quasi-layered" structure of r-GeTe, comprising alternating strong and weak bonds, which induces a pronounced negative internal-strain contribution and an exceptionally low elastic constant. We further extend our investigation to other IV-VI rhombohedral materials, identifying GeS, GeSe, and SiTe as promising candidates for ultrahigh negative piezoelectricity. In contrast to prior reports, where negative piezoelectricity stems from a negative clamped-ion term that dominates a small positive internal-strain contribution, our findings propose a new material design strategy for large negative piezoelectricity by introducing a significantly negative internal strain, along with the negative clamped-ion term.

Cross-linking proteins using cross-linkers that chemically target primary amine and/or carboxyl residues has been a technically mature and robust method in protein engineering. However, depletion of chemically active residues over cross-linking presents a significant challenge to the ability of the resulting bioassemblies to be further engineered and/or maintain specific biological functions. Here, we report a platform approach to cross-link natural proteins via the otherwise chemically inactive residues. This method exploits noncovalent and selective binding of molecularly engineered cucurbit[7]uril macrocycle to aromatic residues that endows the parent protein with additional unique handles for cross-linking. Various proteins are amenable to this approach, yielding bioassemblies with mechanical strength and thermal and enzymatic stability comparable to or exceeding counterparts prepared by some "gold-standard" chemical cross-linkers. This macrocycle-assisted platform approach offers a new paradigm for fabricating valuable bioassemblies that overcome the intrinsic limitations of existing methodologies.