Pradyumna Gupta

Vector Piezoresponse Force Microscopy

A novel approach for nanoscale imaging and characterization of the orientation dependence of electromechanical properties-vector piezoresponse force microscopy (Vector PFM)-is described. The relationship between local electromechanical response, polarization, piezoelectric constants, and crystallographic orientation is analyzed in detail. The image formation mechanism in vector PFM is discussed. Conditions for complete three-dimensional (3D) reconstruction of the electromechanical response vector and evaluation of the piezoelectric constants from PFM data are set forth. The developed approach can be applied to crystallographic orientation imaging in piezoelectric materials with a spatial resolution below 10 nm. Several approaches for data representation in 2D-PFM and 3D-PFM are presented. The potential of vector PFM for molecular orientation imaging in macroscopically disordered piezoelectric polymers and biological systems is discussed.

Directionally controlled 3D ferroelectric single crystal growth in LaBGeO5 glass by femtosecond laser irradiation

Laser-fabrication of complex, highly oriented three-dimensional ferroelectric single crystal architecture with straight lines and bends is demonstrated in lanthanum borogermanate model glass using a high repetition rate femtosecond laser. Scanning micro-Raman microscopy shows that the c-axis of the ferroelectric crystal is aligned with the writing direction even after bending. A gradual rather than an abrupt transition is observed for the changing lattice orientation through bends up to approximately 14 degrees. Thus the single crystal character of the line is preserved along the bend through lattice straining rather than formation of a grain boundary.

Laser fabrication of semiconducting ferroelectric single crystal SbSI features on chalcohalide glass

This paper demonstrates a laser direct-write method to form single crystal semiconductor ferroelectric SbSI features on chalcogenide glasses for integration into infrared devices. The method overcomes a major limitation of thin-film deposition techniques, viz. the uncontrolled stoichiometry of SbSI due to very different vapor pressure of its constituents. It promises advantages of selective single-crystal formation and control on the morphology of the crystal. Mechanism of and control parameters for laser crystallization are explored.

Observation of ferroelectricity in a confined crystallite using electron-backscattered diffraction and piezoresponse force microscopy

LaBGeO5 is a model transparent ferroelectric glass-ceramic (TFGC) material, developed as an inexpensive alternative to single-crystal nonlinear optical materials. The optical activity of the TFGC originates from the ferroelectric phase which remains under a hydrostatic pressure exerted by the surrounding glass matrix. A combination of two techniques, electron-backscattered diffraction (EBSD) and piezoresponse force microscopy (PFM), is employed to monitor the development of the ferroelectric phase. A method is proposed to theoretically construct PFM amplitude maps from EBSD orientation maps. The theoretical vertical piezoresponse map is compared with the experimental piezoresponse map from PFM. A good correlation between the theoretical and experimental maps is observed.