Properties Modulation Of Van Der Waals Crystals ?-MoO₃ And Its Application In Broadband Detection And SERS

Layered van der Waals(vdW)MoO₃,as a multifunctional and wide bandgap semiconductor material,has been widely applied in fields such as photoelectronic,energy harvesting,sensing,and display.The optoelectrical properties of MoO₃ are highly tunable by introducing vacancies or intercalating guest species into the vdW gap.However,conventional oxygen vacancies modulation and ions intercalation induce tremendous defects in the host lattice,which provide active sites for O₂ and H₂O absorption and reaction,causing structural and device instability in air.Even in vacuum condition,the existence of defects still greatly impair carrier transportation,leading to worse device performance.Regulation of the optoelectrical properties via non-destructive way is of great importance to further improve the performance MoO₃ devices for practical applications.To solve the problem,this paper aim at developing a feasible non-destructive optoelectrical regulation strategy through systematical investigation of the correlation between the structural and optoelectrical characteristics of MoO₃.The as-developed method was then verifying in the fields of photoelectric conversion and surface enhanced Raman scattering(SERS)detection,specifically.The achievements include:(1)Non-destructive optoelectrical regulation method for MoO₃ was developed via Sn atoms intercalation,resulting in a broadband optoelectrical conversion from visible to middle infrared(MIR)wavelength.Intercalation of Sn atoms into MoO₃ was performed by disproportionation reaction of Sn²⁺ions.In-situ observation showed that Sn atoms were intercalated through both sides of the MoO₃ nanosheet along the[001]direction.Atomic force microscope(AFM)revealed the surface of MoO₃-Sn was atomic flat and high resolution transmission electron microscopy(HRTEM)and Raman spectroscopy tests showed the lattice kept intact.The intercalation of Sn atoms into vdW gap of MoO₃ induced slightly expansion along[010]direction without destroying the host lattice.The intercalation extends the absorption wavelength of MoO₃ to the MIR range and increased carrier concentration.Therefore,we achieve the tuning of optoelectric property without damaging the structure.Based on the Sn-intercalated MoO₃,a broadband photodetector with the photo-active regime from 405 nm to10?m was fabricated.Through in-situ and real-time photo-thermal-electrical measurements,we confirm that the mechanism of photoelectric response is microbolometric(BOL)effect,and its temperature resistance coefficient(TCR)reach-1.658%/K at room temperature.In addition,the responsivity of the device is about 9 A/W in NIR,with response time of⁰.1 s and peak D*of7.3×10⁷ cmHz^0.5W^-1 at 520 nm,which is close to the state of the art of the BOL photodetector.(2)Uniform and Large-area fabrication of Sn doped MoO₃ films was developed via combining the solid reaction between Sn²⁺and MoO₃ and thermal deposition technology.Sn doped MoO₃ powder was obtained by simply grinding powders containing SnCl₂ and MoO₃.This process is a pure solid phase reaction,which is simple,safe and highly efficient.Moreover,large-scale preparation is easy to realize.Furthermore,thermal deposition technology was used to realize the controllable preparation of uniform broadband absorption films and detector arrays.The response range of Sn-doped MoO₃ thin film device arrays can be extended to 1550nm,indicating its high potential for industrialization.(3)Thickness regulation of MoO₃ nanosheets is another non-destructive way for property modulation,which can be used to achieve excellent SERS characteristics.We demonstrate that few-layered MoO₃ nanosheets,with superior stability and atomic flat surface,can detect R6G molecules with concentration down to 4×10^-8 M,and enhancement factor up to 3.7×10⁴.Large-scale and high quality MoO₃ nanosheets with controllable number of layers were prepared by rapid-cooling physical vapor deposition.It was found that large-size MoO₃ nanosheets could effectively quench fluorescence.Few layered MoO₃ nanosheets substrates present outstanding SERS performance,which can be further improved by reducing layer number of nanosheets.Raman spectroscopy imaging demonstrates excellent homogeneity of MoO₃ substrates.Sn atoms intercalation introduces a hybrid band for the transfer of more charges,further enhancing Raman signal.The Raman intensity of R6G molecules on intrinsic MoO₃ and MoO₃-Sn substrates remains the same after placed in air for 35 days,exhibiting conspicuous stability.We also confirm that the enhancement of Raman signal is due to the chemical enhancement mechanism(CM),which ascribed to the transfer of photogenerated electrons from the LUMO band of adsorbed molecules to the conduction band of the MoO₃ substrates.