As a powerful non-destructive and label-free detection technology, surface-enhanced Raman scattering (SERS) has been widely used in environmental-pollutant detection, biological-tissue sensing, molecular fingerprint analysis and so on. Different from the traditional SERS substrates represented by noble metals and semiconductors, herein, we report a new highly sensitive SERS substrate material with high stability, biocompatibility, and low cost, namely nucleusfree two-dimensional electron gas (2DEG) Ti 3 C 2 monolayer nanosheets. The highly crystalline monolayer Ti 3 C 2 nanosheets with clean surface are synthesized by an improved chemical exfoliation and microwave heating method. The unique structure of nucleus-free-2DEG in Ti 3 C 2 monolayer provides an ideal transport channel without nuclear scattering, which makes the highly crystalline monolayer Ti 3 C 2 nanosheets achieve a Raman enhanced factor of 3.82×10 8 and a 10 −11 level detection limit for typical environmental pollutants such as azo dyes, trichlorophenol, and bisphenol A. Singlemolecule imaging is also realized on the surface of the Ti 3 C 2 monolayers, which may be the first time that approximate single-molecule imaging has been achieved on a non-noblemetal SERS substrates. Preliminary toxicological experiments show that the cytotoxicity of this material is very low. Considering the facile synthesis, high biocompatibility, low cost and high chemical stability of carbide nanosheets, these Ti 3 C 2 monolayer nanosheets show significant promise for the design and fabrication of flexible SERS substrates for the sensing of trace substances with ultrahigh sensitivity.

The temperature dependence of the dc magnetization and the specific heat capacity are systematically investigated for the perovskite YbCrO3 chromites. The results show that there exist two complex sequences of magnetic transitions with the characteristics of magnetization reversal and Yb3+/Cr3+ spin ordering at different temperature, respectively. The antiferromagneticlike transition around TN=118 K is attributed to the antiferromagnetic ordering of the Cr3+ spins and a negative magnetization, accompanied with a tendency to the plateau below 10 K caused by the Yb3+ ordering. We obtain the Weiss constant of −197.0 K and an effective moment of 5.99μB for the sum of the free ion values of 4.53μB for Yb3+ and 3.87μB for high-spin Cr3+ from the experiments, which shows an antiferromagnetic interaction and the existence of weak canted antiferromagnetic (CAFM) characteristics. Corresponding to the magnetic phase transition in the Cr sublattice, the specific heat capacity under zero fields exhibits a sharp λ-shape peak near temperature TN, which is depressed and broadened smoothly with the increase in the magnetic field. And a shoulder-shaped Schottky-type anomaly below 12 K is observed in the specific heat capacity curves. This can be interpreted by accounting for the molecular field approximation by assuming that the induced polarization of the paramagnetic ytterbium ions is opposite to the ferromagnetic moment of the chromium ions. According to the results of the zero fields cooling and the field cooling magnetization, the possible existence of spin ordering for the Yb3+ moments can be predicted.

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Giant shape memory and domain memory effects may promote the development of new antiferroelectric or ferroelectric devices.

Lead halide perovskite quantum dots (PQDs) are reported as a promising branch of perovskites, which have recently emerged as a field in luminescent materials research. However, before the practical applications of PQDs can be realized, the problem of poor stability has not yet been solved. Herein, we propose a trioctylphosphine (TOP)-assisted pre-protection low-temperature solvothermal synthesis of highly stable CsPbBr 3 /TiO 2 nanocomposites. Due to the protection of branched ligands and the lower temperature of shell formation, these TOP-modified CsPbBr 3 PQDs are successfully incorporated into a TiO 2 monolith without a loss of fluorescence intensity. Because the excellent nature of both parent materials is preserved in CsPbBr 3 /TiO 2 nanocomposites, it is found that the as-prepared CsPbBr 3 /TiO 2 nanocomposites not only display excellent photocatalytic activity but also yield improved PL stability, enabling us to build highly stable white light-emitting diodes and to photodegrade rhodamine B.