Thermal wave probing of pyroelectric distributions in the surface region of ferroelectric materials: A new method for the analysis

Abstract

For the investigation of polarization distributions in pyroelectric materials, the laser intensity modulation method (LIMM), which is based on thermal waves, is widely used. With this method, the sample under investigation is heated by the absorption of intensity modulated light at one surface, while the pyroelectric current is measured. The thermal excitation generates a thermal wave penetrating into the sample. The penetration depth is varied with the modulation frequency. A new procedure for the reconstruction of the polarization distribution from a measured pyroelectric current spectrum is introduced. This procedure is especially well suited for polarization probing near the sample surface. An approximation for the polarization distribution is calculated from a measured pyroelectric spectrum in a very simple and direct way, avoiding mathematical instabilities. The calculation can be performed during the measurement of a pyroelectric current spectrum. This makes LIMM an on-line procedure. The new technique of analysis is applied to the measurement of thin depolarized layers near the surface of homogeneously poled ferroelectric polymer films.

Polarization imaging in ferroelectric polymer thin film capacitors by pyroelectric scanning microscopy

“…[20][21][22][23] PSM has also been used to image domains 14,24 thermally written polarization patterns, [25][26][27][28] and to follow polarization and domain dynamics. [29][30][31][32] Moreover, 3D polarization information can be obtained from crystals and thick films by combining 2D laser scanning with depth profiles obtained using either pulse time-of-flight methods, 33 or Laser Intensity Modulation Method (LIMM), [34][35][36][37][38] or both. 39 One key advantage of PSM over techniques based on atomic force microscopy (AFM) is that the optical probe is noninvasive and does not damage or alter the sample.…”

Pyroelectric study of polarization switching in Langmuir-Blodgett films of poly(vinylidene fluoride trifluoroethylene)

“…Some fraction of the laser radiation was absorbed by the sample, producing a small modulation of its temperature at this frequency. Under these conditions, the temperature is uniform across the LB film thickness, 31 and the sample temperature modulation amplitude is no more than 0.02°C. The lock-in amplifier time constant was 1 s, and the recovery time after an overload, caused by the relay commutation, did not exceed 7 s. The in-phase and orthogonal components of the lock-in output were recorded once per second by a computer and then used to calculate the pyroelectric current.…”

Measurement of the polarization profile across a surface-stabilized ferroelectric liquid crystal cell using the pyroelectric laser-intensity-modulation method

“…8 Only in the case when the polarization charge divP is locally compensated by a free charge density (x), i.e., divPϭ, Eq. ͑3͒ reduces 16 to the well-known expression p(x)ϭ␣ P P(x)ϭ‫ץ‬ P/‫ץ‬T. We believe that in most liquid-crystalline materials having a free charge concentration of ϳ10 15 cm Ϫ3 , this is indeed the case, at least in the absence of an external electric field.…”