Lead Zirconium Titanate (PZT) thin films have attracted a great deal of interest in recent years due to their piezoelectric and ferroelectric properties. Recent applications for these films are in microelectromechanical systems (MEMS) and ferroelectric non-volatile random access memories. Here we present the formation of self-assembled monolayers (SAMs) on ultra-thin polarizable PZT films for potential biological applications such as biosensors. Sub-100 nm PZT Pb(Zr_0.5Ti_0.5)O₃ thin films were prepared by a sol-gel deposition on platinum coated silicon substrates. The films were fabricated by the following steps; first spin coating, then drying, firing and finally annealing to form the perovskite crystal structure. These films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS). The PZT films formed using our method are high quality, free from cracks, have a  variable thickness with a minimum of ca. 80 nm and roughness of less than 1 nm over a wide area.

We also present the formation of SAMs of alkylphosphonic acids and alklysilanes on the surface of these PZT films. Monolayers on metal oxide surfaces are an important way of changing the surface chemistry of functional materials. However, the formation of SAMs on PZT is not well understood compared to other metal oxide systems. These monolayers were formed with varying surface chemistries. These were characterized by contact angle goniometry, XPS, matrix assisted laser desorption/ioniszation mass spectrometry and atomic force microscopy (AFM).

The ferroelectric domains of PZT can be polarized using a conductive AFM tip. A DC bias voltage was applied between the tip and the bottom Pt electrode on the substrate to achieve features ranging from 400nm to several microns. The characterization of the polarization was performed using scanning Kelvin probe microscopy, electric force microscopy and scanning polarization force microscopy. These techniques confirmed the presence of an out-of-plane polarization component due to the reorientation of the ferroelectric domains in the PZT. The ability to change the polarization of PZT back and forth by applying opposite polarities to the AFM tip is also demonstrated. The effect of the polarization on the monolayer is also discussed.

Scanning Kelvin Probe Microscopy images of a) 3x3 array of oppositely polarized domains using -10V (black) and +10V (white) biases and b) ability to repeatedly repolarize PZT by first writing a larger 6 µm solid square (-10V), then a second concentric 4 µm square (+10V) followed by a third concentric 1 µm square (-10V).