Monomorphs, bimorphs, and multimorphs from polar polymer electrets

Mono-, bi-, and multimorphs are poled electrets with +/0, +/-, and more complicated alternating-polarity dipole-orientation patterns, respectively. Because of their unusual macroscopic piezo- and pyroelectrical as well as nonlinear optical properties, such structures are of particular interest for special transducer and optical waveguide applications. In this contribution, the preparation of such dipole-polarization patterns in ferroelectric and amorphous polymer electrets and their nondestructive probing by means of thermal and acoustical techniques are reviewed.

Authorship

Simona Bauer-Gogonea

Johannes-Kepler-Universität Linz, Angewandte Physik, Linz, AustriaJohannes-Kepler-Universität LinzAustriaLinz, AustriaJohannes-Kepler-Universität Linz, Angewandte Physik, Linz, Austria

Siegfried Bauer

Johannes-Kepler-Universität Linz, Angewandte Physik, Linz, AustriaJohannes-Kepler-Universität LinzAustriaLinz, AustriaJohannes-Kepler-Universität Linz, Angewandte Physik, Linz, Austria

Reimund Gerhard-Multhaupt

Universität Potsdam, Angewandte Physik kondensierter Materie Institut für Physik, Potsdam, GermanyUniversität PotsdamGermanyPotsdam, GermanyUniversität Potsdam, Angewandte Physik kondensierter Materie Institut für Physik, Potsdam, Germany

SCIMAGO INSTITUTIONS RANKINGS

Johannes-Kepler-Universität Linz, Angewandte Physik, Linz, AustriaJohannes-Kepler-Universität LinzAustriaLinz, AustriaJohannes-Kepler-Universität Linz, Angewandte Physik, Linz, Austria

Figures

Figures (15)

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Figure 1:
Poling currents during electron-beam irradiation of a 32-mm polyvinylidenefluoride film: Virgin sample (I) and poled sample after discharge of its free surface (II). Because of unavoidable differences in the electron-beam current, curve II was adjusted with an affine coordinate transformation (after [27]).

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Figure 2:
Schematic piezoelectricity (or dipole-polarization) profiles in ferroelectric polymer electrets of thickness d after poling with various techniques as indicated (after [29]).

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Figure 3:
Influence of the free length on the three lowest resonance frequencies (left-side ordinate) and on the deflection (right-side ordinate) of a PVDF monomorph (after [30]).

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Figure 4:
Concept of 0/1-mode second-harmonic generation in a nonlinear optical waveguide (left) and of its selective poling by means of electron beam (right) (after [32]).

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Figure 7:
Two-step poling technique for the preparation of multimorphs in ferroelectric polymer multilayers: (i) Inscription of a parallel ferroelectric polarization in both ferroelectric polymer layers, (ii) annealing at a temperature between the two Curie temperatures (polarization in high-T_c layer stabilized, polarization in low-T_c polymer lost), and (iii) reverse-field poling with a field strength smaller than the coercive field in order to avoid switching in the high-T_c polymer.

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Figure 8:
Schematic dipole orientations (left) and thermal-pulse responses (right) resulting from the poling steps of Fig. 7: (a) After parallel poling of both layers, (b) after annealing between the Curie temperatures (low-T_c polymer depolarized, high-T_c polymer with stabilized polarization, and (c) after reverse-field poling (no ferroelectric switching in high- T_c polymer, low-T_c polymer polarized in opposite direction) (after [36]).

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Figure 9:
Two-step poling technique for the preparation of multimorphs from amorphous photonics polymers. The technique is based on thermal poling above and between the two glass transitions (after [42]).

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Figure 10:
Thermal-wave probing of the polarization in the low-T_c and high-T_c polymer layers of a bimorph during thermally stimulated depolarization. The sign of the pyroelectric coefficient is different in both layers. With a low modulation frequency (full circles), the spatial average of the dipole polarization can also be probed (after [43]).

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Figure 11:
Trans-cis isomerization cycles of azo-chromophore molecules. The trans-cis transition significantly enhances the mobility of the chromophore dipoles and enables orientation much below the glass-transition temperature (after [45]).

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Figure 12:
Preparation of bimorphs in a single nonlinear optical polymer film, based on the combination of thermal poling above and photo-induced poling below the glass transition. During the latter step, the dipoles are re-oriented only within the penetration depth of the pump light (after [42]).

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Figure 13:
Thermal-wave probing of the spatial average of the polarization and corresponding TSD current in a nonlinear optical polymer bimorph poled with the two-step method of Fig. 12 (after [46]).

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Figure 14:
Guided modes in polymer waveguides (top) and corresponding nonlinearity depth profiles as required for phase-matched second-harmonic generation with optimized overlap integrals (after [53]).

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Figure 15:
Layer sequences of bi- and trimorph waveguides for phase-matched second- harmonic generation with optimized overlap integrals (after [53]).

Figure 1: Poling currents during electron-beam irradiation of a 32-mm polyvinylidenefluoride film: Virgin sample (I) and poled sample after discharge of its free surface (II). Because of unavoidable differences in the electron-beam current, curve II was adjusted with an affine coordinate transformation (after [27]).

Figure 2: Schematic piezoelectricity (or dipole-polarization) profiles in ferroelectric polymer electrets of thickness d after poling with various techniques as indicated (after [29]).

Figure 3: Influence of the free length on the three lowest resonance frequencies (left-side ordinate) and on the deflection (right-side ordinate) of a PVDF monomorph (after [30]).

Figure 4: Concept of 0/1-mode second-harmonic generation in a nonlinear optical waveguide (left) and of its selective poling by means of electron beam (right) (after [32]).

Figure 7: Two-step poling technique for the preparation of multimorphs in ferroelectric polymer multilayers: (i) Inscription of a parallel ferroelectric polarization in both ferroelectric polymer layers, (ii) annealing at a temperature between the two Curie temperatures (polarization in high-T_c layer stabilized, polarization in low-T_c polymer lost), and (iii) reverse-field poling with a field strength smaller than the coercive field in order to avoid switching in the high-T_c polymer.

Figure 8: Schematic dipole orientations (left) and thermal-pulse responses (right) resulting from the poling steps of Fig. 7: (a) After parallel poling of both layers, (b) after annealing between the Curie temperatures (low-T_c polymer depolarized, high-T_c polymer with stabilized polarization, and (c) after reverse-field poling (no ferroelectric switching in high- T_c polymer, low-T_c polymer polarized in opposite direction) (after [36]).

Figure 9: Two-step poling technique for the preparation of multimorphs from amorphous photonics polymers. The technique is based on thermal poling above and between the two glass transitions (after [42]).

Figure 10: Thermal-wave probing of the polarization in the low-T_c and high-T_c polymer layers of a bimorph during thermally stimulated depolarization. The sign of the pyroelectric coefficient is different in both layers. With a low modulation frequency (full circles), the spatial average of the dipole polarization can also be probed (after [43]).

Figure 11: Trans-cis isomerization cycles of azo-chromophore molecules. The trans-cis transition significantly enhances the mobility of the chromophore dipoles and enables orientation much below the glass-transition temperature (after [45]).

Figure 12: Preparation of bimorphs in a single nonlinear optical polymer film, based on the combination of thermal poling above and photo-induced poling below the glass transition. During the latter step, the dipoles are re-oriented only within the penetration depth of the pump light (after [42]).

Figure 13: Thermal-wave probing of the spatial average of the polarization and corresponding TSD current in a nonlinear optical polymer bimorph poled with the two-step method of Fig. 12 (after [46]).

Figure 14: Guided modes in polymer waveguides (top) and corresponding nonlinearity depth profiles as required for phase-matched second-harmonic generation with optimized overlap integrals (after [53]).

Figure 15: Layer sequences of bi- and trimorph waveguides for phase-matched second- harmonic generation with optimized overlap integrals (after [53]).

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Monomorphs, bimorphs, and multimorphs from polar polymer electrets

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