Recently, new functionalities of ferroelectric domain walls (DWs) have attracted much attention. To realize novel devices using the functionalities of the DWs, techniques to introduce the DWs at arbitrary positions in the ferroelectric thin films are necessary. In this study, we have demonstrated the introduction of the DWs at arbitrary positions in epitaxial BiFeO3 (BFO) thin films using the patterned surface of the SrTiO3 (STO) single-crystal substrate. On the slope pattern of the STO surface, the in-plane orientation of BFO has changed because the in-plane orientation of BFO can be controlled by the step propagation direction of the patterned surface. From the piezoresponse scanning force microscopy and X-ray diffraction reciprocal space mapping results, charged 109° DWs have been introduced into the BFO thin film at the bottom and top of the slope pattern of the STO surface. In addition, the conductivity modulation of the positively charged DW has been observed by current-sensitive atomic force microscopy imaging.

Summary:Optic canal fracture (OCF) is a traumatic injury that requires urgent intervention because it can induce optic nerve damage and visual impairment. Despite the severity of OCF, a standard treatment method has not been established. In this article, we report a case of OCF and traumatic optic nerve injury in which visual acuity was recovered by releasing the optic canal using an unconventional lateral approach. A 43-year-old man presented with right lateral ethmoid fracture, right orbit blowout fracture, and OCF. The visual acuity was “hand motion” before surgery. Decompression was performed 10 hours after injury by approaching the right optic canal laterally from a coronal incision in front of the right ear, cutting along the border of the sphenoid bone, and scraping away some of the sphenoid wing and zygomatic bone. Steroid pulse therapy was added. Eventually, the visual acuity improved to 0.2 and the intraocular pressure decreased to 16.0 mm Hg. Compared with conventional methods, this method associates with better safety because (1) it causes relatively little bleeding and cerebrospinal fluid leak; (2) once the sphenozygomatic suture is identified, the distance to the optic canal is relatively short; and (3) if the fracture point is on the outer optic canal, the fracture line can be observed directly. Steroid pulse therapy may also have contributed to the good visual outcome. This is the first report of a novel lateral approach to OCF that is safe, effective, and only requires plastic surgery skills.

This work demonstrated the artificial introduction of charged domain walls (CDWs) into a ferroelectric BiFeO 3 (BFO) thin film by domain structure control using a pit-patterned SrTiO 3 (STO) (001) surface. The pattern consisted of 1 × 1 μm square holes with sloped sides, fabricated on the STO (001) surface by electron beam lithography and Ar + ion etching. Scanning electron and atomic force microscopy analyses demonstrated that the pit slopes had angles of 6.1°-7.6°, which were sufficient to limit the in-plane growth direction of the BFO at step edges on the STO surface, and thus control the domain structure. Lateral and vertical piezoresponse scanning force and transmission electron microscopy confirmed the artificial introduction of CDWs in the pit and showed that the sign of the CDWs could be reversed via ferroelectric polarization switching. This domain control technique based on a pit pattern provides a simple approach to the integration of ferroelectric DWs into functional devices.

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