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Bioorganic ferroelectrics and piezoelectrics are becoming increasingly important in view of their intrinsic compatibility with biological environment and biofunctionality combined with strong piezoelectric effect and a switchable polarization at room temperature. Here, we study tip-induced domain structures and polarization switching in the smallest amino acid β-glycine, representing a broad class of non-centrosymmetric amino acids. We show that β-glycine is indeed a roomtemperature ferroelectric and polarization can be switched by applying a bias to non-polar cuts via a conducting tip of atomic force microscope (AFM). Dynamics of these in-plane domains is studied as a function of an applied voltage and pulse duration. The domain shape is dictated by polarization screening at the domain boundaries and mediated by growth defects. Thermodynamic theory is applied to explain the domain propagation induced by the AFM tip. Our findings suggest that the properties of β-glycine are controlled by the charged domain walls which in turn can be manipulated by an external bias. [ABSTRACT FROM AUTHOR]

Piezoelectricity is one of the important functional properties inherent to many biomaterials. It stems from the non-centrosymmetric crystal structure of most biopolymers including proteins, polysaccharides, and lipids. Understanding the relationship between the generated electric field and applied mechanical stress has become the main motivation to studying piezoelectricity in biological systems and artificial biomaterials at the nanoscale. In this work, we present a review of the piezoelectric and ferroelectric properties of several molecular systems and nanomaterials revealed by Piezoresponse Force Microscopy (PFM) and compare the results with molecular modeling and computer simulations. Experimentally observed by PFM and calculated dielectric, piezoelectric, and ferroelectric properties of these materials are analyzed in the context of their possible role in functionality of biological systems. [ABSTRACT FROM AUTHOR]

Magnetic properties of nano-granular Co0.55-(Al2O3)0.45 films have been studied by vibrating sample magnetometry, ferromagnetic resonance, and magnetic force microscopy (MFM). The films possess a growth-induced perpendicular anisotropy related to the shape anisotropy of the granules. Being unpercolated physically, the films demonstrated a clear magnetic percolation behavior in the temperature dependence of the coercivity and MFM scans. The temperature dependence of the coercivity measured along the easy magnetization axis of the granules indicates the presence of a collective long-range magnetic state sustained by a ferromagnetic interparticle interaction. This interaction is supposed to form a homogeneously magnetized superferromagnetic state, however, the perpendicular anisotropy and the competition between the dipole-dipole and ferromagnetic interactions lead to the emergence of an inhomogeneous labyrinth-like magnetic stripe-domain structure with the averaged domain width being about two orders of magnitude larger than the averaged granule size. The temperature evolution of the spontaneous magnetization inside the stripe domains has been measured by the MFM up to the temperature of superferromagnetic ordering (420 K). The formerly developed mean-field-based model of the coercivity of an interacted ensemble has been tested and found to yield adequate quantitative predictions. [ABSTRACT FROM AUTHOR]

Piezoresponse Force Microscopy (PFM) is used to characterize the nanoscale electromechanical properties of centrosymmetric CaCu3Ti4O12 ceramics with giant dielectric constant. Clear PFM contrast both in vertical (out-of-plane) and lateral (in-plane) modes is observed on the ceramic surface with varying magnitude and polarization direction depending on the grain crystalline orientation. Lateral signal changes its sign upon 180° rotation of the sample thus ruling out spurious electrostatic contribution and confirming piezoelectric nature of the effect. Piezoresponse could be locally reversed by suitable electrical bias (local poling) and induced polarization was quite stable showing long-time relaxation (∼3 hrs). The electromechanical contrast in unpoled ceramics is attributed to the surface flexoelectric effect (strain gradient induced polarization) while piezoresponse hysteresis and ferroelectric-like behavior are discussed in terms of structural instabilities due to Ti off-center displacements and structural defects in this material. [ABSTRACT FROM AUTHOR]

Ti-rich PbZr1-xTixO3 (x = 0.65, PZT65) single crystals with the dimensions of 1 × 1 × 0.2 mm3 were grown by the self-flux method. Micron-sized ferroelectric domains were observed and characterized via piezoresponse force microscopy (PFM) and switching spectroscopy PFM. Both out-of-plane and in-plane components of polarization were obtained by detecting vertical and lateral vibrations of the PFM cantilever. The piezoresponse image examination revealed a clear lamellar domain structure due to apparent twinning and the formation of 90° domains. A negative self-polarization was observed in the studied crystals leading to the asymmetry of piezoresponse hysteresis loops and the polarization imprint. The polarization switching mechanism under the external electric field applied via a PFM tip was investigated. The 90° domain wall width was determined from the local PFM measurements and tentatively attributed to the oblique domain walls and chemical disorder. The time-dependent PFM imaging revealed a slow polarization relaxation process with a characteristic time of about 200 min. [ABSTRACT FROM AUTHOR]

We used piezoresponse force microscopy (PFM) to study the dc bias field-induced domain structure of the (001) oriented single crystals of 0.77PbMg1/3Nb2/3O3-0.23PbSc1/2Nb1/2O3 relaxor. In the as-grown state, no polarization contrast was observed due to the average cubic symmetry of the crystal. Upon application of a dc bias applied via a PFM tip, a stable complex domain pattern, corresponding to a hedgehog-type topological defect, appeared on the surface of the crystal. The shape of these domains depended on the magnitude of the field. If the field was below a threshold, the domains possessed a cylindrical form. Above the threshold, the border between domains became close to a straight line. At high biases and large separation between the pulses, the development of the domains obeyed an avalanche-type dynamics. [ABSTRACT FROM AUTHOR]

Direct measurements of the motion of domain walls in disordered ferroelectrics provide important information on their interaction with defects, which is crucial for the functioning of various ferroelectric devices such as high-K capacitors and ferroelectric-based memories. In this work, we report on the results of the nanoscale measurements of domain-wall velocity and static domain-wall roughness in disordered (Pb,La)(Zr,Ti)O3 (PLZT) ceramics prepared by hot press sintering. Relaxation of domain walls to their equilibrium configurations at short length scales yields the apparent roughness exponent ζ ≈ 0.67 in PLZT 9.5/65/35. At the same time, the dynamical exponent μ was found to be about 0.25 from the independent measurements of domain-wall creep under local application of electric field. An analysis of these two values points to the effective dimensionality deff = 1 for the domain walls in PLZT with high La content. This result is confirmed by the layer-by-layer polishing followed by the imaging of an artificially created domain. The origin of disorder and its dependence on La concentration in PLZT solid solutions are discussed. [ABSTRACT FROM AUTHOR]

Local ferroelectric and piezoelectric properties of triglycine sulfate (TGS) nanocrystals embedded into poly(ethylene) oxide (PEO) electrospun fibers were examined by piezoresponse force microscopy (PFM). Piezoresponse contrast was found to be strongly dependent on the position being much stronger at the fiber periphery. A model of the distribution of TGS crystals inside the core-shell PEO-TGS fiber structure was proposed. TGS nanocrystals were unevenly distributed along the fiber axis and tend to grow near the surface of the fiber. The volume fraction distribution of the TGS crystals extracted from PFM measurements is in a good agreement with the data obtained from the dielectric constant measurements. [ABSTRACT FROM AUTHOR]