Room-temperature synthesis of epitaxial oxide thin films for development of unequilibrium structure and novel electronic functionalization

Abstract

Epitaxial growth of oxide films at lower temperatures is favored to obtain sharp interfaces and flat surfaces which are of advantage to construct high-quality electronic devices, and also is expected to result in novel development of unequilibrium structure and new electronic functionalization. Pulsed laser deposition (PLD) technique using laser ablation of a solid target is known to reduce the temperature drastically for epitaxial growth because of the highly energetic film precursors ablated from the target. In this article we briefly review the main achievements of our research group on room-temperature (RT, 20°C) synthesis of epitaxial oxide thin films by way of laser MBE process, i.e. PLD in ultrahigh vacuum. RT-epitaxial film growth by laser MBE and its electronic application were presented for some functional oxide thin films such as ZnO, Sn-doped In 2 O 3 (ITO), sapphire (¡-Al 2 O 3 ), (Li,Ni)O, or (Mg,Ni)O, and also magnetic functionalization via selective post-depositional reduction of complex oxide films was demonstrated.

Room-temperature selective epitaxial growth of CoO (1 1 1) and Co3O4 (1 1 1) thin films with atomic steps by pulsed laser deposition

“…As a strategy for epitaxial growth, pulsed laser deposition (PLD) involves the ablation of high-energy film precursors from the target onto a substrate at a supersonic speed (∼10 4 m/s); this method is especially useful for nucleation at low temperatures, room temperature in particular. To date, we have reported the room-temperature heteroepitaxial growth of semiconductor thin films such as ZnO, CeO 2 , Sn-doped SnO 2 (ITO), and AlN as well as NiO as an epitaxial buffer layer [6][7][8][9].…”

Sub-nanoscale nanoimprint fabrication of atomically stepped glassy substrates of silicate glass and acryl polymer

“…These nanostructured sapphire molds exhibit the unique surface morphology having about 0.2-nm-high straight steps and about 100-nm-wide ultrasmooth terraces [19,20]. The atomically stepped sapphire wafers were also found to be useful as growing substrates of high-quality thin films at low temperatures [21][22][23][24] as well as atomic force microscopy (AFM) stages observing the steric shape of organic molecules adhered to their surfaces [25,26]. In the present article, we have briefly reviewed the sub-nanoscale nanoimprint fabrication of atomically stepped glassy substrates of soda-lime silicate glasses and PMMA polymers by employing the atomically stepped sapphire molds in the thermal nanoimprint.…”

Lattice spacings and domain sizes of room-temperature epitaxial Li x Ni 1−x O (0 ≤ x ≤ 0.48) thin films grown on ultra-smooth sapphire substrates

“…Synchrotron X-ray diffraction with the requisite number of photons and high resolution has been successfully used to analyze crystallographic structures of NiO epitaxial films grown at 940 K on ultra-smooth sapphire (0 0 0 1) substrates [8]. It was reported that cubic-type NiO thin films containing heavy amounts of Li were successfully grown epitaxially with the (1 1 1) orientation on ultrasmooth sapphire (0 0 0 1) substrates at room-temperature (RT) by pulsed laser deposition (PLD) technique [9,10], although there is a previous study reported the phase transformation from cubic to rhombohedral structure for the bulk NiO containing over 30 mol% Li [11]. We here investigated the effects of heavy Li doping on lattice spacings, out-of-plane, and in-plane domain sizes of RT epitaxial Li x Ni 1−x O (0 ≤ x ≤ 0.48) thin films on ultra-smooth sapphire (0 0 0 1) substrates.…”