D~0 Ferromagnetism In Black Phosphorous Oxide And High Ambiplar Mobility In Phosphorene FETs

After the discovery of grapheme,black phosphorus is the second found mono-elemental material with interlayer van der Waals forces.In the post-graphene age,black phosphorus(BP)is an attractive material with high hole mobility,high on-off ratio,p type conductivity and direct band gap.These properties would make BP particularly attractive for various applications,d~0 magnetism does not have the problem of aggregation and is thus valuable in dilute-magnetism research.BP has numerous unique properties and d~0 magnetism potential with similar outer layer electron arrangement of nitrogen.So it is meaningful to induce magnetism for BP.While few-layer black phosphorous(FLBP)process extraordinary electronic properties but it could be easily degraded in air.It is challenging to acquire largely improved carrier mobility together with structural stability in FLBP.The goal of this dissertation is to explore delicately controllable d~0 magnetism of electrochemical oxidized BP and stable FLBP with high ambipolar mobility,showing promising application prospect in magnetism and electronic applications.The obtained main results are described as follows:1.d~0 ferromagnetism in black phosphorous oxide caused by surface P-O bonds.Electrochemical oxidation is performed to oxidize BP.According to X-ray diffraction(XRD)analysis,electrochemical oxidation does not alter the single-crystal structure of BP and with further study by X-ray photoelectron spectroscopy(XPS),superconducting quantum interference device(Squid)and Raman,the degree of oxidation depends on the oxidation time thereby resulting in controllable d~0 ferromagnetism caused by surface P-O bonds.First-principles calculation reveals that different surface P-O bonds have different binding energies and contributions to the ferromagnetism.The bridge and dangling oxygen atoms are responsible for the observed ferromagnetism which stems from p orbital spin polarization of the oxygen and phosphorus atoms and the exchange interaction mechanism is consistent with the bound pole model.The results provide experimental evidence of the d~0 magnetism of electrochemical oxidized BP caused by surface P-O bonds,which is promising in the fabrication and application of BP-based magnetism devices.2.Largely improved hole and electron mobility in phosphorene FETs.There remains two problems in FLBP researches.One is the in-air instability largely hindering FLBP study and application.The other one is the currently highest mobility of 984 cm2 V-1 s-1 at 2 K which is far below the theoretical prediction.So we speculated that there were ignored defects that reducing the mobility.Here we perform atomic-resolved scanning tunnel microscope observations in ultra-high vacuum on the exfoliated FLBP sheets and find that some defect images change with external added bias voltages and are associated with the existence of lattice oxygen formed during crystal growth according to our density functional theory calculation.Based on this finding,we adopt hydrogenation and then phosphorization to remove the lattices oxygen and subsequently mend the phosphorous vacancies caused by mechanical exfoliation and hydrogenation.Our measurements indicate that such a process does not alter the single-crystal structure of FLBP sheets,but results in high ambipolar motilities with 1374 cm2 V-1 s-1 for hole and 607 cm2 V-1 s-1 for electron at 2 K in the as-treated samples.When the sample is stored in air for 3 days,the high mobility only decrease to 1181 and 518 cm2 V-1 s-1 for hole and electron,respectively,accompanied with no obvious surface degradation.This research revealed the mechanism of FLBP degradation in-air and provided a feasible method to acquire stable FLBP with high ambipolar mobility which is promising in the design and fabrication of FLBP-based electric devices.