研究目的
To demonstrate significantly enhanced second harmonic generation (SHG) in on-chip integrated metasurfaces using nanometer thin films of ferroelectric Y:HfO2, addressing challenges in CMOS compatibility, thickness scaling, and band gap limitations of nonlinear optical materials.
研究成果
Ferroelectric Y:HfO2-based hybrid metasurfaces achieve a 3-fold enhancement in SHG compared to non-ferroelectric controls and a 20-fold enhancement over bare films, with an effective χ(2) of 6.0 ± 0.5 pm/V. The material's CMOS compatibility, UV transparency, and scalability make it promising for on-chip nonlinear photonic devices, with potential for further improvements through epitaxial growth and thinner films.
研究不足
The study is limited by the polycrystalline nature of Y:HfO2 films, which may reduce nonlinear optical properties compared to epitaxial films. Device dimensions and surface roughness could affect reflectance and field enhancements. Scalability to thinner films (<10 nm) is suggested but not fully characterized in the main text, relying on simulations and supplementary data.
1：Experimental Design and Method Selection:
The study involves designing hybrid metasurfaces with ferroelectric Y:HfO2 thin films integrated into plasmonic nanostructures to enhance SHG. Numerical simulations using finite element methods (COMSOL Multiphysics) are employed to model linear and nonlinear optical responses, including field enhancements and SHG calculations.
2：Sample Selection and Data Sources:
Samples include ferroelectric Y:HfO2 thin films (10-20 nm thick) deposited on TiN/SiO2/Si substrates, with non-ferroelectric HfO2 as a control. Data is sourced from fabricated devices with varying Au grating widths (50-125 nm) and periods (240 nm).
3：List of Experimental Equipment and Materials:
Equipment includes pulsed laser deposition (PLD) systems, electron beam lithography (EBL, Raith 150-TWO), ellipsometers (J.A. Woollam RC2), atomic force microscopes (AFM, Cypher ES), X-ray diffractometers (XRD, XRD-7000), scanning electron microscopes (SEM), femtosecond lasers (MaiTai, Newport-Spectra Physics), spectrometers (SpectraPro), and charge-coupled devices (CCD, Princeton Instruments). Materials include TiN, Y:HfO2, Au, PMMA resist, and various chemicals for fabrication.
4：Experimental Procedures and Operational Workflow:
Fabrication involves depositing TiN and Y:HfO2 thin films via sputtering and PLD, patterning Au gratings using EBL and lift-off processes, and characterizing with XRD, AFM, PFM, and optical measurements. SHG measurements are performed using a femtosecond laser at 45° incidence, with polarization control and spectral analysis.
5：Data Analysis Methods:
Data analysis includes Tauc-plot for band gap estimation, fitting polarization dependence with cos2θ functions, numerical simulations for field enhancements and SHG spectra, and statistical analysis of SHG intensity enhancements and nonlinear coefficients.
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Ellipsometer
J.A. Woollam RC2
J.A. Woollam
Used to measure the optical constants (refractive index and extinction coefficient) of the thin films.
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X-ray Diffractometer
XRD-7000
SHIMADZU
Used to analyze the crystal structure of the Y:HfO2 films.
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Electron Beam Evaporator
Lab-line
Kurt J. Lesker
Used for depositing Ti and Au layers.
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Electron Beam Lithography System
Raith 150-TWO
Raith
Used for patterning the Au metasurface structures via electron beam lithography.
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Atomic Force Microscope
Cypher ES
Asylum Research
Used for PFM and AFM measurements to characterize ferroelectric properties and surface morphology.
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Femtosecond Laser
MaiTai
Newport-Spectra Physics
Used as a pump source for SHG measurements.
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Spectrometer
SpectraPro
Princeton Instruments
Used for high spectral resolution detection in SHG measurements.
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Charge-Coupled Device
CCD
Princeton Instruments
Used as a detector in spectroscopic measurements, cooled with liquid nitrogen.
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Pulsed Laser Deposition System
Used for depositing Y:HfO2 thin films.
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Rapid Thermal Annealing System
RTP
Used for crystallizing the amorphous Y:HfO2 thin films.
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