Study On The Optical Parameters And Domain Strncture Dependence Of The Silver Deposition On The LiNbO₃Crystals

Lithium niobate (LiNbO3,LN) is considered as a promising substrate material for amedically used lab-on-chip platform because of its remarkable electro-optical, ferroelectric,piezoelectric and nonlinear optical properties. For example, the exploitation of surfaceacoustic wave (SAW) actuators built in LN substrates could increase the efficiency ofmicrofluidic platforms in handling small sample volumes without the need for externalpumping or different mechanisms that could cause modifications in the on-chipenvironment. Besides the fluidic actuator, the functionality of analyzing a single moleculeis also crucial to a LN-based microfluidic lab-on-chip platform. Nanopore-based sensors orsurface enhanced Raman scattering (SERS) technology may be utilized for analyzing asingle molecule, and silver (Ag) nanoparticles (NPs) are of considerable interest forapplication in biochemical sensors and SERS technology. We study in this paper the opticalparameters and domain structure dependence of the silver deposition on the LN.For obtaining LN with multi-domain structure required by experiment, we producedmulti-domain structure with a liquid-electrode transform method. In our experiment, areal-time imaging system was added on the setup, by which, we can control the inversionprocess and made the domain structure regularly. Meanwhile, we study the temperaturedependence of the domain boundaries in the LN. The dynamic variation of the domainboundaries was recorded visually by the in situ probe during the process. These would bethe theoretical foundation for later experiment.Both405and532nm laser are found effective for the photoinduced Ag deposition onC-cut LN. SEM and XPS analysis show that Ag metallic nanoparticles are close-packedlydeposited on the crystal surface. These Nps range from tens to hundreds of nanometers indiameter. Meanwhile, we study the photoinduced Ag deposition on Y-cut LN. We found thedepotion pattern was significantly different from that on C-cut LN through opticalmicroscope. The Ag Nps accumulate heavily on one side but distribute scarcely on the otherside.In order to study in detail the photo-induced depotion of Ag NPs on LN, we study thephotoinduced deposition of Ag nanoparticles on LN by using an in situ probe. The Ag deposition is found to start easily surrounding the focal point of the laser and performing asa ring. The photo-induced deposition of Ag NPs was also performed, with405nm-laserfocus on domain boundary, on LN with multi-domain structure. The profile of Agdeposition in this case was slightly similar to the focal shape of the laser.We study the deposition result and analyse the trajectory model of the photo-excitedelectrons. Here in this case, we posted explanations of the deposition mechanisms. Bothphotogalvanic and diffusion effects of photo-excited electrons are suggested to account forthe photo-induced deposition of Ag.