Polar alignment of dye molecules in sectors of host lattices revealed by phase sensitive second harmonic generation and scanning pyroelectric microscopy

Abstract

Phase sensitive second harmonic generation (PS-SHG) was applied to investigate the effect of polar surface recognition of dye molecules (amaranth and sunset yellow, as well as dimethylaminostyryl-pyridine) in symmetry related sectors of host lattices such as KH₂PO₄ and phthalic acid, respectively. PS-SHG revealed bi-polar states in all cases, meaning that sectors growing in opposite directions feature opposite absolute polarities. Scanning pyroelectric microscopy demonstrated that the dipole moments of amaranth in KH₂PO₄ are pointing towards the growing crystal face. The present work reveals symmetry breaking through anomalous mixed crystal growth to produce physical properties associated with polar axes.