Since the discovery of Cu-catalyzed chemical vapor deposition (CVD), the preparation of large-area graphene films has been performed by the carbon precursor exposure under isothermal conditions. In this work, we report on a nonisothermal method to quickly synthesize the largearea AB-stacked bilayer graphene films (BGF) by atmospheric pressure CVD on the copper foils. The growth feature of the BGF is carefully studied by scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. The results show that both cooling rate and CH 4 flow rate play crucial roles on the BGF growth in the nonisothermal process. A phase diagram for the preparation of BGF is thereby derived from plenty of experiments. In addition, we find that bilayer graphene seeds grow into graphene islands at the initial growth stage and extend gradually to a continuous film. Accordingly, a possible growth mechanism combining with surface-catalyzed process and seed growth is proposed.

Graded particulate composite films in which ferromagnetic CoFe 2 O 4 nanoparticles are gradedly distributed in the ferroelectric Pb(Zr 0.52 Ti 0.48 )O 3 matrix along the thickness direction have been prepared on Pt/Ti/SiO 2 /Si wafers via sol-gel spincoating method and rapid annealing process. Compared with the homogenous films, the graded ones not only exhibited magnetic anisotropy, but also showed evident increase in both ferroelectric polarization and dielectric tunability. Moreover, great enhancement of magnetodielectric effect was observed in such graded films. We elucidated the origin of enhanced magnetodielectric coupling and attributed it to the combined influence of two factors, that is, the enhanced ferroelectric polarization caused by CoFe 2 O 4 distribution gradient and flexoelectric polarization induced by strain gradient under external magnetic field. This work presents a feasible way to modulate the magnetoelectric coupling in ferromagnetic-ferroelectric composite films for developing high-performance multiferroic materials at nanoscale.