Spontaneous Growth of Strain-Free Magnetite Nanocrystals via Temperature-Driven Dewetting

Abstract

Temperature-driven dewetting of a self-template layer has been exploited to spontaneously grow epitaxial magnetic Fe 3 O 4 nanocrystals by pulsed laser deposition. A 10 unit cell thick Fe 3 O 4 template layer was deposited at 400 °C on a perovskite SrTiO 3 (001) substrate, followed by heating at 1100 °C, which induced dewetting of the Fe 3 O 4 template layer, forming three-dimensional islands that were uniformly distributed over the substrate surface area. These islands were used as seed crystals for the growth of spatially separated quasi-epitaxial Fe 3 O 4 nanopyramids. Structural analysis by scanning transmission electron microscopy and X-ray diffraction revealed incoherent growth of fully relaxed (001)-oriented Fe 3 O 4 nanocrystals on the SrTiO 3 (001) substrate. Higher-order epitaxial matching of the substrate and film lattices appears to be responsible for the well-defined in-plane orientation of the Fe 3 O 4 (001) nanopyramids despite the large nominal lattice mismatch of −7.5%. The nanopyramid structure strongly affected the magnetic characteristics of magnetite, dramatically reducing the coercive field compared to conventional magnetite thin films. The coercivity of the Fe 3 O 4 nanopyramids was also strongly size dependent. This is attributed to a transition between poly-and monodomain states. A superparamagnetic phase was detected for the smallest pyramid sizes.

Structural Defect Effect on the Concentration Quenching of TbxY2–xO3 Phosphor Thin Films

“…Tb x Y 2– x O 3 composition-gradient films were deposited on wet-etched SrTiO 3 (001) substrates (Shinkosya, 5 × 10 mm 2 ) , using combinatorial PLD. A sample holder was heated using an infrared semiconductor laser. , During the growth, the substrate temperature was maintained at 600 °C. Ceramic targets of Y 2 O 3 and Tb 0.5 Y 1.5 O 3 (TOSHIMA Manufacture Co. Ltd.) were alternately ablated with fourth-harmonic (266 nm) pulses from an Nd:YAG laser (LOTIS LS-2145N/4) ,, at a pulse rate of 10 Hz and a fluence of 2.3 J/cm 2 .…”

Epitaxial-Strain-Induced Spontaneous Magnetization in Polar Mn2Mo3O8

“…We speculate that higher-order matching takes place; for example, 8 × a of the Mn 2 Mo 3 O 8 film (46.40 Å) has good matching with (17/√3) × a of Al 2 O 3 (46.72 Å) with a mismatch of 0.7% (Figure S3). Such higher-order lattice matching is also observed in ZnO films on Al 2 O 3 (001) substrates and Fe 3 O 4 films on SrTiO 3 (001) substrates. , …”

“…Such higherorder lattice matching is also observed in ZnO films on Al 2 O 3 (001) substrates and Fe 3 O 4 films on SrTiO 3 (001) substrates. 19,20 We evaluated the valence states of Mo and Mn ions in the Mn 2 Mo 3 O 8 film using XPS and XAS measurements. Figure 3a shows the Mo 3d spectrum of the film.…”

Sacrificial Water-Soluble BaO Layer for Fabricating Free-Standing Piezoelectric Membranes

“…For example, it has been reported that the maximum achievable piezoelectric strain in epitaxial Pb­(Zr, Ti)­O 3 (PZT) films deposited on the SrTiO 3 substrates is much smaller than that in bulk crystals . The substrate problem can be mitigated by thinning the substrate during device fabrication and using a cantilever design ,− or by forming self-standing nanostructures in which strain can be decoupled from the substrate. − These problems are not unique for piezoelectric films but affect various other film materials such as magnetostrictive materials and shape memory alloys. , …”