Two dimensional matrix confinement makes MgO quantum dot have strong piezoelectric response

What is it about?

The bulk material of MgO is not piezoelectric, but we observed strong piezoelectricity in our synthesized black Phosphorus@MgO (BP@MgO) quantum dot (QD) crystals. These crystals have a layered two-dimensional structure with a thickness of 11 nm and are stable in air. The piezoresponse force microscopy (PFM) images show that they have extremely strong polarity. The strong polarity also can be proved from polarization reversal and the simple pressure sensor.

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Why is it important?

This article mainly describes a new material obtained from a new process, show a new effect. New effect: Different from MgO crystals, the MgO QDs on BP@MgO QD crystals showed strong piezoelectric response. To our knowledge, this piezoelectric property has not been previously reported. New material: BP@MgO QD crystals. They have core-shell structures based on MgO QDs and nano-layered BP matrix. They are air-stable and show strong piezoelectric responses. Moreover, they are self-supporting, freestanding, and compatible with any device. In our group, the applications on Sodium-ion storage, gas sensing, and SPR sensor have been well proven. New process: SPS-VLS method for metal oxide QDs preparing. This method comprises of two stages and the first one is the solid-phase sintering (SPS) stage. As temperature increases, Mg was slowly released from MgB2 and became liquid, while P turns into vapor. B reacted with O2 and produced amorphous solid phase B2O3. The amorphous B2O3 preserves liquid Mg and vapor P like paraffin wax. The second stage is vapor–liquid–solid (VLS) growth. At this stage, the temperature decreased and the volume of the system shrinked. With O2 getting involved in the reaction, P crystalized and became BP. Simultaneously, QD liquid Mg reacted with O2 to become MgO QD, and a lot of MgO QDs were formed at the surface of layered BP.

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