研究目的
To gain insight on relative contrast mechanisms in STM and AFM on a graphene surface by using simultaneous STM/AFM with small oscillation amplitudes.
研究成果
Simultaneous STM/AFM with small amplitudes allows observation of different contrast mechanisms in graphene imaging, revealing honeycomb patterns in AFM and triangular patterns in STM with maxima between carbon atoms. The technique confirms that typical STM imaging occurs in the repulsive force regime, and atomic relaxations may influence results. Simultaneous operation is crucial for understanding these mechanisms.
研究不足
Thermal drift at room temperature complicates site-specific spectroscopy. The use of metallic tips is not common and may introduce uncertainties. Discrepancies in force values compared to theory suggest potential influences from electrostatic forces and tip geometry not fully accounted for.
1:Experimental Design and Method Selection:
A commercial STM/AFM system modified with a Fabry–Pérot fiber interferometer for high sensitivity was used in ultrahigh vacuum (UHV). Small-amplitude (sub-angstrom) oscillation was employed to enable simultaneous STM and AFM measurements.
2:Sample Selection and Data Sources:
Graphene samples were grown on Cu foils using chemical vapor deposition (CVD) and characterized by optical microscopy, scanning electron microscopy (SEM), and Raman spectroscopy to confirm single-layer graphene.
3:List of Experimental Equipment and Materials:
UHV chamber with argon sputtering gun and resistive heater, tungsten tip-cantilever probe (stiffness ~53 N/m, resonance frequency
4:5 kHz), CVD system for graphene growth, and interferometer for amplitude detection. Experimental Procedures and Operational Workflow:
Samples were prepared and imaged in constant-current and constant-height modes. Force-distance spectroscopy was performed to measure tip-sample interactions. Data were acquired with specific parameters (e.g., sample bias voltages, tunnel currents, oscillation amplitudes).
5:Data Analysis Methods:
Force was calculated from oscillation amplitude data using F = klever·(A0 – A). STM and AFM images were analyzed for contrast patterns, and force curves were averaged and compared to theoretical predictions.
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