2.3. Characterization Methods

The structure and morphology of the deposited films were investigated using X-ray diffraction (XRD, Rigaku SmartLab, X-ray source with Cu anode, powered at 40 kV and 40 mA, in parallel beam with Ge (220) monochromator in the incident beam and using a Hypix detector in 0D regime; for the reciprocal space mappings, RSM, a Bruker D8 Advance diffractometer was used, in parallel beam, without a monochromator), transmission electron microscopy (TEM, JEM-ARM 200 F from JEOL, Tokyo, Japan), and piezo-force microscopy (PFM, MFP-3D-SA Asylum Research/Oxford Instruments, Oxford, UK).

Electric measurements at different temperatures were performed by inserting the samples in a Lake Shore cryo-station (Lake Shore Cryotronics, Westerville, OH, USA) with micromanipulated arms and CuBe needles for contacting the SRO electrodes of the ferroelectric capacitor. Dynamic hysteresis loops were recorded using a TF2000 ferristester from Aix ACCT (AixACCT Systems GmbH, Aachen, Germany), capacitance–voltage (C–V) characteristics were measured using an LCR bridge from Hioki (Hioki E.E. Corporation, Nagano, Japan), while current–voltage (I–V) characteristics were recorded using a Keithley 6517B electrometer (Tektronix, Beaverton, OR, USA) with an incorporated dc voltage source.

Laser ablation combined with inductively coupled plasma mass spectrometry (LA–ICP-MS) was used to analyze the elemental composition of all samples included in this study. A New Wave Research laser sampler model NWR-213 (Elemental Scientific Lasers, Bozeman, MT, USA) was used for ablation of the samples. For better reproducibility and to avoid interferences from the bulk, scan analysis through laser ablation of the synthetic laboratory standards and the PZT wafers was used. Analysis of all the standards and samples was conducted using a 40 μm diameter laser spot, 10 J/cm² fluence, and 1 Hz pulse rate, in all cases. The synthetic laboratory standards and the samples were placed on a programmable xyz-translation stage operated via computer control. During laser ablation, the sample surface was monitored using a CCD camera and displayed on a TV screen. After laser ablation, the sample aerosol was transported through Tygon plastic tubing (I.D.: 10 mm; length: 1.0 m) and introduced into the PlasmaQuant MS Elite ICP-MS system from Analytik Jena (Jena, Germany) for detection of the signal intensity of the investigated ions.

Upon connecting the laser ablation system, the synthetic laboratory standards were ablated, and the aerosols were introduced continuously into the ICP-MS system to measure the elements of interest signals. The spot position and focusing position of the laser ablation system were aligned to provide the maximum and most consistent signal with reasonable stability. After a suitable sampling time, the laser ablation system was switched off.

Synthetic laboratory standard materials preparation procedure. In order to calibrate the laser ablation processes and the ICP-MS response, different synthetic laboratory standards were prepared by using only certified reagents. For instance, ultrapure water (type 1: conductivity of 0.055 μS/cm and a resistivity of 18.2 MΩ·cm at 25 °C) that had been deionized using an Evoqua system was used in all preparation procedures. Used as matrix for the elements of interest, polyvinyl alcohol (United States Pharmacopeia Reference Standard) was purchased from Merck and hydrated overnight before deposition. It has to be underlined that this type of matrix comprises only C, H, and O, elements that are not detected by our ICP-MS system as they are mass-excluded elements.

The ICP-MS calibration standard (XXI) with 29 elements (Ag, Al, As, Ba, Be, Bi, Ca, Cd, Co, Cr, Cs, Cu, Fe, Ga, In, K, Li, Mg, Mn, Na, Ni, Pb, Rb, Se, Sr, Tl, U, V, and Zn) with a concentration of 10 mg/L and two standard element solutions (Si, Hf) with a concentration of 1000 mg/L certified reference materials (CRM) were purchased from CPA Chem Switzerland.

Different polyvinyl alcohol solutions containing different elements were prepared by adding certain volumes of CRM solutions. The elements of interest-containing films were deposited onto the glass slides by using a spin coating machine with the following deposition parameters: 1000 rpm for 60 s and 25 deposition steps. After each deposition step, the wafers were dried over a heating plate at 80 °C for 10 min. After subsequent 25 deposition steps, the measured thicknesses of the synthesized films were ~0.8 mm.