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Squeezing bubbles and impurities out of interlayer spaces by applying force through a few-layer graphene capping layer leads to van der Waals heterostructures with ultra-flat structure free from random electrostatic potential arising from charged impurities. Without the graphene capping layer, a squeezing process with an AFM tip induces applied-force-dependent charges of Δn ~ 2 × 10 12 cm -2 µN -1 , resulting in strong intensity of trions in photoluminescence spectra of MoSe2 at low temperature. We found that a hBN/MoSe2/hBN prepared with the "modified nano-squeezing method" shows a strong excitonic emission with negligible trion peak, and the residual linewidth of the exciton peak is only 2.2 meV, which is comparable to the homogeneous limit. Furthermore, in this high-quality sample, we found that formation of biexciton occurs even at extremely low excitation power (Φph ~ 2.3 × 10 19 cm -2 s -1 ) due to the enhanced collisions between excitons.

We have found that CeCd 3 P 3 crystallizes into a hexagonal ScAl 3 C 3type structure.The optical, transport and magnetic properties of CeCd 3 P 3 were investigated by measuring the diffuse reflectance, electrical resistivity and magnetization. CeCd 3 P 3 is a semiconductor with the fundamental band gap of approximately 0.75 eV. The 4f electrons of Ce 3+ ions are well localized but do not show long range order down to 0.48 K, presumably due to the geometrical frustration of Ce atoms. The magnetic ordering temperature is possibly lower than that of isostructural CeZn 3 P 3 (0.75 K). Because several f -electron compounds with the ScAl 3 C 3 -type structure are quantum spin systems, CeCd 3 P 3 may be a candidate of quantum spin liquid. On the other hand, the relatively large band gap compared to approximately 0.4 eV in CeZn 3 P 3 , would not be intimate with the observation of photoinduced Kondo effect, providing a potentially new range of applications of devices based on the Kondo effect.

What is the most significant result of this study? One-step fabrication of fluorescence organic nanocolloids from microcrystallinep owder by pulse-laser fragmentation in liquid, and characterization of their opticalp roperties by single particle spectroscopy.

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