Scanning probe microscopies applied to the study of the domain wall in a ferroelectric crystal

Abstract

A commercial Atomic Force Microscope (AFM) and a semi-home made Scanning Near-Field Optical Microscope (SNOM) have been used to characterize electrically, topographically and optically the domain walls among natural ferroelectric domains in a KNbO 3 crystal. The AFM measurements have been performed with a metallic coated tip in order to detect electrostatic forces between the polarization field at the ferroelectric surface and the tip. An external electric field has also been applied between the sample surface and the tip to tune this electrostatic interaction over the atomic forces. In optical transmission images, acquired under near field conditions, we observe a clear contrast of the signal at the domain walls between 180º spontaneous polarization domains; while the images of the surface topography, obtained simultaneously, show a reasonably flat surface of the crystal. The scanning probe microscopy techniques used in this work are valuable tools for the investigation of ferroelectric materials and, in particular, to characterize the domain walls, without needing a either especial preparation or damage of the sample surface. Microscopias de barrido aplicadas al estudio de los dominios y las paredes de dominio en un cristal ferroelectrico de KNbO 3. Hemos utilizado un Microscopio de Fuerzas Atómicas (AFM) comercial y un Microscopio Óptico de Campo Cercano (SNOM) semi-casero para caracterizar eléctrica, óptica y topográficamente las paredes de dominio presentes entre los dominios ferroeléctricos naturales de un cristal de KNbO 3. Las medidas de AFM las hemos realizado con una punta recubierta con metal, para detectar las fuerzas electrostáticas entre los campos de polarización de la superficie ferroeléctrica y la punta. Además, hemos aplicado campos eléctricos externos entre la superficie de la muestra y la punta, de manera que se pueda variar la fuerza electrostática en relación a las fuerzas atómicas. En imágenes de transmisión óptica, bajo condiciones de campo cercano, observamos un claro contraste de la señal en las fronteras entre los dominios ferroeléctricos con polarización espontánea a 180º, mientras que las imágenes de topografía muestran una superficie prácticamente plana. Las técnicas de microscopía de prueba usadas en este trabajo se revelan muy valiosas para la investigación de materiales ferroeléctricos y, en particular, para la caracterización de sus dominios y paredes de dominio, puesto que no es necesario preparar ni dañar la superficie de la muestra para ser investigada. Palabras clave: KNbO 3 , ferroeléctrico, pared de dominio, SNOM y AFM

Surface-screening mechanisms in ferroelectric thin films and their effect on polarization dynamics and domain structures

“…Further opportunities are offered by combinations of voltage modulation approach with other modulation modalities, as exemplified by e.g. pyroelectric charge microscopy developed by Groten et al [227] The brief overview of the SPM modes for probing ferroelectric materials would be incomplete without mentioning the near-field optical [228][229][230] and near-field Raman microscopies. [231] These techniques provide high-resolution optical contrast, but generally are more sensitive to the bulk properties of ferroelectrics.…”

Optical studies of ferroelectric and ferroelastic domain walls

“…Microscopy techniques are called super-resolved when they are able to overcome the diffraction limit, which can be done notably by working in the near-field regime. They are of course very appealing for the studies of domain walls, but can be very challenging both in their implementation and interpretation [142][143][144][145][146][147][148][149][150][151][152][153][154][155][156][157][158].…”

“…Near-field scanning optical microscopy (NSOM, or SNOM) has been used to image domain structures in several ferroelectrics [142][143][144][145][146][147][148][149][150][151][152][153][154], with contrast observed at domain walls in LiTaO 3 [142,150,151], LiNbO 3 [147,148], TGS [143,153], BaTiO 3 [144] and Ba 2 NaNb 5 O 15 [147]. These measurements have been performed in different modes of operation.…”

“…These measurements have been performed in different modes of operation. In the illumination mode, the sample is illuminated with a fiber maintained a few nanometers above the surface and the light collected in transmission by an objective [142][143][144][145][146][147]. In the collection mode (CNSOM), polarized light is transmitted through the sample under study and collected with a fiber maintained a few nanometers above the surface [146,148,150,151].…”

Near-field scanning optical microscopy to study nanometric structural details of LiNbO3 Zn-diffused channel waveguides

“…The near-field scanning optical microscopy ͑NSOM͒ technique has been recently probed to be useful in the study of domain walls in different nanostructured ferroelectric materials. [10][11][12] In this work, the NSOM technique is used to extract structural and optical information of Zn-diffused channel waveguides in LN with subwavelength resolution. We are interested in the study the Zn-rich upper layer formed from the solid solution after diffusion process 13 and also its possible influence in the light confinement at the waveguide.…”