Time-Resolved Morphology and Kinetic Studies of Pulsed Laser Deposition-Grown Pt Layers on Sapphire at Different Growth Temperatures by in Situ Grazing Incidence Small-Angle X-ray Scattering

Abstract

Optimizing and monitoring the growth conditions of Pt films, often used as bottom electrodes in multiferroic material systems, represents a highly relevant issue that is of importance for controlling the crystalline quality and performance of ferroelectric oxides such as, e.g. LuFeO 3 . We performed a time-resolved monitoring of the growth and morphology of Pt films during pulsed laser deposition (PLD) in dependence on the grown film effective thickness and on the growth temperature Tg using in situ grazing incidence small-angle X-ray scattering (GISAXS). Through real-time analysis and modeling of GISAXS patterns, we could fully characterize the influence of Tg on the morphology and on the growth kinetics of the Pt layers. Consequently, critical and characteristic effective thicknesses for the transitions nucleation phase (I)/coalescence phase (II) and coalescence phase (II)/coarsening phase (III) could be determined. In combination with complementary microscopic imaging and chemical mapping via combined SEM/EDXS, we demonstrate the occurrence of a morphological progression in the Pt PLD-grown Pt films, changing from grains at room temperature to a 3D-island morphology at 300 °C, further to a hole-free structure at 500 °C, and finally to a channel structure for 700 and 900 °C. The film topography, as characterized by atomic force microscopy (AFM), favors the PLD growth of Pt layers at temperatures beyond 700 °C where the film is homogeneous, continuous, and hole-free with a flat and smooth surface. The double dependency of the percolation transition on the film effective thickness and on the growth temperature has been established by measuring the electrical conductivity.

Ultrasmooth Epitaxial Pt Thin Films Grown by Pulsed Laser Deposition

“…Even though the conductivity does not reach the bulk values of Pt (10.6 × 10 6 S/m), it is close to Pt thin films deposited at higher temperatures (660 °C) with the same thickness (24 nm), using MBE (∼7.7 × 10 6 S/m) . Additionally, the conductivity reported here is higher than other hole-free Pt films (∼120 nm thick) deposited by PLD on sapphire at 300 and 500 °C (2.0–3.2 × 10 6 S/m) …”

“…16 Additionally, the conductivity reported here is higher than other hole-free Pt films (∼120 nm thick) deposited by PLD on sapphire at 300 and 500 °C (2.0−3.2 × 10 6 S/m). 55 TEM further elucidated the crystallinity, structure, and chemical composition of the Pt films synthesized by the twostep deposition and their epitaxial relationship with the sapphire substrate (Figure 4). Figure 4A shows a representative atomic-resolution TEM image of the sample with a ca.…”

Structural and Morphological Studies of Pt in the As-Grown and Encapsulated States and Dependency on Film Thickness

“…On the other hand, preserving the same deposition method and deposition parameters disclosed a reproducible morphology similar to the one shown by AFM micrographs in Figure 1 . However, changing the growth temperature (i.e., T g = 300 °C to T g = 900 °C) or using a different substrate (i.e., Al 2 O 3 ) would modify the morphology and the structure, as clarified in our previous work [ 3 ].…”

“…The optimization process of multiferroic heterostructures of our interest, based on bilayer systems of ferromagnetic materials such as the hexaferrite BaFe 12 O 19 and ferroelectric materials such as LuFeO 3 and YbFeO 3 , crucially requires first a high-quality bottom electrode, which remains stable at elevated growth temperatures Tg > 900 °C in an oxidizing atmosphere during the pulsed laser deposition (PLD) growth of the above-mentioned subsequent layers [ 1 , 2 , 3 , 4 , 5 ]. Platinum is one of the noble metals, and is widely used in the application field of metal-ferroelectric-metals (MFMs) [ 6 , 7 , 8 ], ferroelectric memories [ 9 ], and microelectromechanical systems (MEMSs) [ 10 ] due to its high melting point, inertness in hard atmospheres, and low resistivity.…”

“…Their aim was to protect the conducting electrode of MEMS devices against the dewetting of the film during the operation at high temperatures (>1000 °C) [ 17 ]. Pt bottom electrodes were deposited on different types of insulator substrates such as Al 2 O 3 [ 2 , 3 , 17 ], SiO 2 [ 11 , 12 , 13 , 14 , 15 ], and YSZ [ 16 , 18 , 24 ] with various deposition methods such as sputtering [ 13 , 14 , 15 , 17 , 18 , 26 , 27 ], ion beam evaporation [ 10 , 12 , 16 ], PLD [ 3 , 28 ], and others [ 11 ].…”