A brand new type of Scanning Probe Microscopy (SPM), named Heterodyne Megasonic Piezoresponse Force Microscopy (HM-PFM), has been developed in this work and is disclosed here. This HM-PFM technique is specially designed to characterize the nanoscale ferroelectric and/or piezoelectric properties which is of great importance for the application of these functional materials. Compared with the commonly used conventional Piezoresponse Force Microscopy (PFM), HM-PFM holds fundamentally different mechanisms of signal generation and detection due to its unique dual high-frequency (MHz range) excitations and heterodyne detection scheme. This new technique opens an effective pathway to explore the rarely touched high-frequency piezoelectric or ferroelectric phenomena. Also, it can be used to study the unknown or debatable topics about the ferroelectric properties, some examples are the polarization switching phenomenon under high-frequency electric field and the ferroic nature of the important hybrid organic-inorganic perovskites.
TECHNOLOGY FEATURES & SPECIFICATIONS
Firstly, the basic ferroelectric characterization capability of HM-PFM has been verified by using standard ferroelectric samples. Then an up to 30 MHz high-frequency operation has been successfully achieved by the prototype HM-PFM system established here; this operation frequency is about 100 times higher than that used in conventional PFM. Meanwhile, since the signal generation mechanism has been fundamentally changed, a neglectable contribution of the electrostatic force has been realized in the piezoresponse signal of HM-PFM. This is a significant improvement from the conventional PFM system, as the electrostatic force issue has been affecting the results of the conventional PFM measurements for more than 25 years. In addition, HM-PFM exclusively provides two brand new capabilities: (i) the frequency response spectroscopy for difference-frequency piezoresponse signals, which can be easily used to distinguish the piezoelectricity and non-piezoelectricity; and (ii) the investigation of subsurface properties for piezo-/ferro- electric materials, which can be used to explore the internal characteristic of piezo-/ferroelectric materials.
(1) Significantly minimizing the influence of non-piezoelectric effects in the piezoelectric or ferroelectric measurements, including eliminating the contribution of electrostatic force, minimizing the electrochemical Vegard strain effect and the electrostrictive vibration as well as avoiding the dynamic electrochemical processes. Therefore, compared with that of the conventional PFM, much more unambiguous piezoelectric information can be obtained by using HM-PFM.
(2) Providing a new function of frequency response spectroscopy for difference-frequency piezoresponse signals, which can be easily used to distinguish the piezoelectricity and non-piezoelectricity.
(3) Providing a new function of subsurface detection, which can help to investigate the internal characteristic of the piezo-/ferro-electric materials, such as the cracks and defects.
(4) Opening a new and effective pathway to explore the rarely touched high-frequency piezoelectric or ferroelectric phenomena at nanoscale.