טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAltberg-Poliak Anna
SubjectStructural and Thermodynamic Characterization of Pt-SrTiO3
Interfaces
DepartmentDepartment of Materials Science and Engineering
Supervisor Professor Wayne D. Kaplan
Full Thesis textFull thesis text - English Version


Abstract

Metal and metal-oxide nano-particles are important for many modern applications such as catalysts, sensors, and microelectronics.Many of the properties of nano-crystals are dictated by their thermodynamic state. A better insight into nano-particles can be achieved by experimentally determining their equilibrium crystal shapes, measuring the interface energy between the particles and single crystal substrates, and by determining the atomistic structure at the interface (and surfaces). Pt on (100) single crystal SrTiO3substrate was selected as a model system for this study.

Thin continuous Pt films were evaporated on chemically treated (100)-SrTiO3 single crystal substrates and then equilibrated in the solid-state. The equilibration took place at 1050°C and in the presence of an Ar/2%O2 carrier gas mixture. Given the similar lattice parameters between Pt and SrTiO3, a simple cube-on-cube orientation relationship was expected to form at equilibrium.

Following the thin film dewetting process, single crystal Pt particles were formed. While not all the particles reached their equilibrium state (shape), they all adopted the same general shape. X-ray diffraction analysis of the preferred orientation of the equilibrated Pt nano-particles showed that Pt {111} planes were parallel to the (100)-SrTiO3 substrate. While the Pt particles exhibited some in-plane preferred orientation, no low-index orientation relationship with the substrate was formed, which suggests that the Pt-SrTiO3 interfacial energy is somewhat isotropic about the {111} preferred orientation.

The equilibrium crystal shape of the Pt particles and particle-substrate interfacial energy was analyzed using Winterbottom’s approach and electron diffraction. It was found that the equilibrium crystal shape of the Pt particles, formed in the presence of oxygen, includes the following facets: {111}, {100}, {110} and {113}, although, additional facets may be present as well. The relative surface energies were found to be g(Pt113)/ g(Pt111)=1.065 and g(Pt220)/ g(Pt111)=1.07, with a possible error of at least 2%.In addition, the Pt-(100)-SrTiO3 interfacial energy was determined to be 2.08 J/m2.

High resolution electron microscopy (HRTEM and HRSTEM) was used to analyze the atomistic structure at the metal-oxide interface. It was found that reconstruction of the SrTiO3 surface (a complexion) took place, and this is believed to be responsible for the Pt texture after dewetting.