Oxygen Partial Pressure during Pulsed Laser Deposition: Deterministic Role on Thermodynamic Stability of Atomic Termination Sequence at SrRuO3/BaTiO3 Interface

With recent trends on miniaturizing oxide-based devices, the need for atomic-scale control of surface/interface structures by pulsed laser deposition (PLD) has increased. In particular, realizing uniform atomic termination at the surface/interface is highly desirable. However, a lack of understanding on the surface formation mechanism in PLD has limited a deliberate control of surface/interface atomic stacking sequences. Here, taking the prototypical SrRuO3/BaTiO3/SrRuO3 (SRO/BTO/SRO) heterostructure as a model system, we investigated the formation of different interfacial termination sequences (BaO-RuO2 or TiO2-SrO) with oxygen partial pressure (PO2) during PLD. We found that a uniform SrO-TiO2 termination sequence at the SRO/BTO interface can be achieved by lowering the PO2 to 5 mTorr, regardless of the total background gas pressure (Ptotal), growth mode, or growth rate. Our results indicate that the thermodynamic stability of the BTO surface at the low-energy kinetics stage of PLD can play an important role in surface/interface termination formation. This work paves the way for realizing termination engineering in functional oxide heterostructures.Comment: 27 pages, 6 figures, Supporting Informatio

Evaluation of Compressive Strength and Stiffness of Grouted Soils by Using Elastic Waves

Cement grouted soils, which consist of particulate soil media and cementation agents, have been widely used for the improvement of the strength and stiffness of weak ground and for the prevention of the leakage of ground water. The strength, elastic modulus, and Poisson’s ratio of grouted soils have been determined by classical destructive methods. However, the performance of grouted soils depends on several parameters such as the distribution of particle size of the particulate soil media, grouting pressure, curing time, curing method, and ground water flow. In this study, elastic wave velocities are used to estimate the strength and elastic modulus, which are generally obtained by classical strength tests. Nondestructive tests by using elastic waves at small strain are conducted before and during classical strength tests at large strain. The test results are compared to identify correlations between the elastic wave velocity measured at small strain and strength and stiffness measured at large strain. The test results show that the strength and stiffness have exponential relationship with elastic wave velocities. This study demonstrates that nondestructive methods by using elastic waves may significantly improve the strength and stiffness evaluation processes of grouted soils

Privacy Protection for Personal Health Device Communication and Healthcare Building Applications

This paper proposes a new method for protecting patient privacy when communicating with a gateway which collects bioinformation through using personal health devices, a type of biosensor for telemedicine, at home and in other buildings. As the suggested method is designed to conform with ISO/IEEE 11073-20601, which is the international standard, interoperability with various health devices was considered. We believe it will be a highly valuable resource for dealing with basic data because it suggests an additional standard for security with the Continua Health Alliance or related international groups in the future

Development of Microelectrode Arrays for Artificial Retinal Implants using Liquid Crystal Polymers

Purpose: To develop a liquid crystal polymer (LCP) based, long-term implantable, retinal stimulation microelectrode array using a novel fabrication method. Methods: The fabrication process used laser micromachining and customized thermal press bonding to produce LCP based microelectrode arrays. To evaluate the fabrication process and the resulting electrode arrays, in vitro reliability tests and in vivo animal experiments were performed. The in vitro tests consisted of electrode site impedance recording and electrode inter-layer adhesion monitoring during accelerated soak tests. For in vivo testing, the fabricated electrode arrays were implanted in the suprachoroidal space of rabbit eyes. Optical coherence tomography (OCT) and electrically evoked cortical potentials (EECPs) were used to determine long-term biocompatibility and functionality of the implant.Results: The fabricated structure had a smooth, rounded edge profile and exhibited moderate flexibility, which are advantageous features for safe implantation without guide tools. Following accelerated soak tests at 75°C in phosphate buffered saline, the electrode sites showed no degradation and the inter-layer adhesion of the structure showed acceptable stability for more than 2 months. The electrode arrays were safely implanted in the suprachoroidal space of rabbit eyes, and 1 EECP waveforms were recorded. Over a 3-month postoperative period, no choroioretinal inflammation or structural deformities were observed by OCT and histological examination. Conclusions: LCP based flexible microelectrode arrays can be successfully applied as retinal prostheses. The results demonstrate that such electrode arrays are safe, biocompatible, mechanically stable, and can be effective as part of a chronic retinal implant system.This paper was supported by the Korea Science and Engineering Foundation (KOSEF) through the Nano Bioelectronics and Systems Research Center (NBS-ERC) at Seoul National University, and by a grant from the Korea Health 21 R&D Project(A050251), Ministry of Health & Welfare, Republic of Korea