|Rendered topography of a LiNbO3 sample with the PFM signal painted on top; inset shows the hysteresis loops measured at an individual point, 4µm scan. (Image: Asylum Research)|
November 29, 2007 — In response to the growing applications of electromechanical imaging and spectroscopy, Asylum Research has developed a new Piezo Force Module, which promises very high sensitivity, high bias, and crosstalk-free measurements of piezoelectrics, ferroelectrics, multiferroics, and biological systems. The module is available exclusively for the company’s MFP-3D atomic force microscope.
“Electromechanics and PFM is a growing area of research with studies ranging from data storage devices to MEMS to electromotor proteins and electrophysiology,” said Dr. Roger Proksch, president and co-founder of Asylum Research. “Our Piezo Force Module uses a special high voltage accessory and advanced imaging modes to measure piezoresponse, even for the weakest piezoelectric materials. We are extremely excited about the potential for advanced measurements in many different disciplines.”
The Piezo Force Module is an MFP-3D accessory that enables high voltage PFM measurements and advanced imaging modes for characterizing the sample material. With the Piezo Force Module, a bias is applied to the AFM tip using proprietary electronics, a high voltage cantilever, and sample holder. The vertical and lateral response amplitude measures the local electromechanical activity of the surface, and the phase of the response yields information on the polarization direction. High probing voltages, up to +220 volts, can characterize even very weak piezo materials.
Patent-pending imaging modes, dual frequency resonance tracking and band excitation, effectively use resonance enhancement in PFM and provide new information on local response and energy dissipation which cannot be obtained by standard AFM scanning modes. These techniques allow independent measurement of amplitude, resonant frequency, and Q-factor of the cantilever and overcome limitations of traditional sinusoidal cantilever excitation. The large frequency range (1kHz – 2MHz) of MFP-3D allows imaging both at the static condition, and effective use of several cantilever resonances and use of the inertial stiffening of the cantilever.
Polarization dynamics can also be studied with the built-in spectroscopy modes that include single-point hysteresis loop measurements and switching spectroscopy mapping. These modes provide local measure of such parameters as coercive and nucleation biases, imprint, remanent response, and work of switching (area within the hysteresis loop), for correlation with local microstructure. Combined with the high-voltage module, these allow local polarization switching to be probed even in high-coercivity materials such as electro-optical single crystals.
Asylum Research is collaborating with Oak Ridge National Laboratory (Materials Science and Technology Division and Center for Nanophase Materials Sciences) to conduct pioneering research on PFM. “The recent work that we have done in collaboration with Asylum is already producing ground-breaking results,” said Dr. Kalinin, Staff Scientist at ORNL. “The plethora of new and exciting electromechanical phenomena emerging on the nanoscale — from electric field induced phase transitions in ferroelectrics to electronic flexoelectricity and molecular electromotors — has been belied by the lack of capability to study them quantitatively and reproducibly. PFM is the technique that enables these studies. Eventually, the development of nanotechnology will require the capability not only to “think”, but to “act” on the nanoscale. PFM will pave the way for the understanding of electromechanical coupling mechanisms on the nanometer scale and development of the molecular electromechanical systems.”