Principle of ferroelectric domain imaging using atomic force microscope

Abstract

Effect of Pt bottom electrode texture selection on the tetragonality and physical properties of Ba0.8Sr0.2TiO3 thin films produced by pulsed laser deposition J. Appl. Phys. 112, 044105 (2012) Relationship between dielectric coefficient and Urbach tail width of hydrogenated amorphous germanium carbon alloy films Appl. Phys. Lett. 101, 042109 (2012) Interfacial oxide re-growth in thin film metal oxide III-V semiconductor systemsThe contrast mechanisms of domain imaging experiments assisted by atomic force microscope ͑AFM͒ have been investigated by model experiments on nonpiezoelectric ͑silicon oxide͒ and piezoelectric ͓Pb͑Zr,Ti͒O 3 ͔ thin films. The first step was to identify the electrostatic charge effects between the tip, the cantilever, and the sample surface. The second step was to explore the tipsample piezoelectric force interaction. The static deflection of the cantilever was measured as a function of dc bias voltage (V dc ) applied to the bottom electrode ͑n-type Si wafers͒ for noncontact and contact modes. In addition, a small ac voltage (V ac sin t) was applied to the tip to measure the amplitude (A ) and phase (⌽ ) of the first harmonic ͑͒ signal as a function of V dc . By changing from the noncontact to the contact mode, a repulsive contribution to the static deflection was found in addition to the attractive one and a 180°phase shift in ⌽ was observed. These results imply that in the contact mode the cantilever buckling is induced by the capacitive force between the cantilever and the sample surface. This interaction adds to the tip-sample piezoelectric interaction thereby overlapping the obtained tip vibration signal. Therefore, the antiparallel ferroelectric domain images obtained at zero dc bias voltage will show a variation in A but a negligible one in ⌽ . The capacitive force contribution to the tip vibration signal was further verified in piezoelectric hysteresis loop measurement assisted by the AFM. The observed vertical offset of the loops was explained by the contact potential difference between the cantilever and the bottom electrode. The shape of the curve could be explained by the capacitive force interaction combined with the tip-sample piezoelectric interaction. The experimental results obtained in this study support the interpretation of the cantilever-sample capacitive force contribution to the tip vibration signal in ferroelectric domain imaging experiments using AFM as a probing tool. The use of a large area top electrode between the tip and the sample resulted in the elimination of the electrostatic cantileversample interaction with negligible degradation of the domain contrast. This method proved to be successful because the cantilever-sample interaction was hardly detected and only the tip-sample interaction was observed.

Imaging mechanism of piezoresponse force microscopy of ferroelectric surfaces

“…39 This electrostatic interaction is comprised of a local contribution due to the tip apex and a nonlocal contribution due to the cantilever. 40 Distinguishing electrostatic forces in a PFM experiment is problematic; however, it can be achieved in SSPM. In SSPM, application of an ac bias to the tip located at 10-100 nm from the surface results in a strong capacitive interaction.…”

Dynamic behaviour in piezoresponse force microscopy

“…The simple formalism for analysis of the electrostatic contribution was established by Hong. 17 However, in the low frequency case, the phase shift between domains is always 180° or 0°, depending on the relative magnitudes of electrostatic and electromechnical contributions. In the dynamic case, the electromechanical and electrostatic contributions to the PFM signal have different phases and the response over c + and c -domains can be written as…”

“…It was recognized that electrostatic tip-surface forces and buckling oscillations of the cantilever can provide significant and in some cases even dominating contributions to the PFM signal. 17,18,19 Imaging ferroelectric materials in the vicinity of a phase transition at small probing biases or imaging of biological systems with weak electromechanical coupling require optimal imaging conditions to be established, and a number of approaches based on using contact resonances in PFM have been suggested. 20,21 Finally, it is recognized that the use of the cantilever coupled with a beam-deflection detection system typical for most commercial AFM s does not allow longitudinal and normal force components to be unambiguously distinguished, 12,22 and it has been suggested that operation at specific frequencies would allow these components to be differentiated.…”

Behavior of a movable electrode in piezo-response mode of an atomic force microscope

“…The PEI image is recorded as an A cos signal. 5 Here, A is the amplitude of the first harmonic signal, which provides information on the magnitude of the piezoelectric coefficient (d 33 ). is the shift in phase between the signal of ac voltage applied and the responding first harmonic, 4 which determines the direction of polarization.…”