Highly (001)-oriented BiFeO3 ultrathin films of total thickness of less than 10 nm were deposited on Si(001) substrates via deposition of atomic layers (ALD) with a LaNiO3 buffer. A radio-frequency (RF)-sputtered sample of the same thickness was prepared for comparison. The ALD combined with interrupted flow and an exchange reaction between Bi and Fe precursors provides a superior method to grow ternary compounds. According to X-ray diffraction, upon deposition at a temperature of less than 550 °C, the only phase in the film was BiFeO3. Anomalous fine structure from synchrotron X-ray diffraction certified the valence bonding through the BiFeO3 (001) diffraction signal. The stoichiometric ratio of BiFeO3 obtained from X-ray photoelectron spectroscopy indicated that ALD has a proportion much improved over the RF preparation, and this is also in agreement with the results for diffraction anomalous fine structure. The use of high-resolution transmission electron and atomic force microscopes showed that the layer structure and morphology from ALD presented a satisfactory coverage, more conformal than that with the RF method. The BiFeO3 thin film deposited with ALD shows excellent leakage, improved at least 1000 times with respect to the RF preparation, making this method suitable for the fabrication of ferroelectric random-access memory devices. From the hysteresis loop, the largest remanent polarization was observed as 2Pr = 2.0 μC cm(-2).

The electromigration (EM) effect involves atomic diffusion of metals under current stressing. Recent theories of EM are based on the unbalanced electrostatic and electron-wind forces exerted on metal ions. However, none of these models have coupled the EM effect and lattice stability. Here, we performed in situ current-stressing experiments for pure Cu strips using synchrotron X-ray diffractometry and scanning electron microscopy and ab initio calculations based on density functional theory. An intrinsic and non-uniform lattice expansion – larger at the cathode and smaller at the anode, is identified induced by the flow of electrons. If this electron flow-induced strain is small, it causes an elastic deformation; while if it is larger than the yield point, diffusion as local stress relaxation will cause the formation of hillocks and voids as well as EM-induced failure. The fundamental driving force for the electromigration effect is elucidated and validated with experiments.

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The island nucleation in the context of heterogeneous thin film growth is often complicated by the growth kinetics involved in the subsequent thermodynamics. We show how the evolution of sputtered Zn island nucleation on Si(111) by magnetron sputtering in a large area can be completely understood as a model system by combining reflective second harmonic generation (RSHG), a 2D pole figure with synchrotron X-ray diffraction. Zn dots are then oxidized on the surfaces when exposed to the atmosphere as Zn/ZnO dots. Derived from the RSHG patterns of Zn dots at different growth times, the Zn dots grow following a unique transition from kinetic to thermodynamic control. Under kinetic-favoring growth, tiny Zn dots prefer arranging themselves with a tilted c-axis to the Si(111) substrate toward any of the sixfold in-plane Si<110> directions. Upon growth, the Zn dots subsequently evolve themselves to a metastable state with a smaller tilting angle toward selective <110> directions. As the Zn dots grow over a critical size, they become most thermodynamically stable with the c-axis vertical to the Si(111) substrate. For a system with large lattice mismatch, small volume dots take kinetic pathways with insignificant deviations in energy barriers.

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