Atomistic Engineering of Phonons in Functional Oxide Heterostructures

Engineering of phonons, that is, collective lattice vibrations in crystals, is essential for manipulating physical properties of materials such as thermal transport, electron-phonon interaction, confinement of lattice vibration, and optical polarization. Most approaches to phonon-engineering have been largely limited to the high-quality heterostructures of III–V compound semiconductors. Yet, artificial engineering of phonons in a variety of materials with functional properties, such as complex oxides, will yield unprecedented applications of coherent tunable phonons in future quantum acoustic devices. In this study, artificial engineering of phonons in the atomic-scale SrRuO3/SrTiO3 superlattices is demonstrated, wherein tunable phonon modes are observed via confocal Raman spectroscopy. In particular, the coherent superlattices led to the backfolding of acoustic phonon dispersion, resulting in zone-folded acoustic phonons in the THz frequency domain. The frequencies can be largely tuned from 1 to 2 THz via atomic-scale precision thickness control. In addition, a polar optical phonon originating from the local inversion symmetry breaking in the artificial oxide superlattices is observed, exhibiting emergent functionality. The approach of atomic-scale heterostructuring of complex oxides will vastly expand material systems for quantum acoustic devices, especially with the viability of functionality integration

Microspinning: Local Surface Mixing via Rotation of Magnetic Microparticles for Efficient Small-Volume Bioassays

The need for high-throughput screening has led to the miniaturization of the reaction volume of the chamber in bioassays. As the reactor gets smaller, surface tension dominates the gravitational or inertial force, and mixing efficiency decreases in small-scale reactions. Because passive mixing by simple diffusion in tens of microliter-scale volumes takes a long time, active mixing is needed. Here, we report an efficient micromixing method using magnetically rotating microparticles with patterned magnetization induced by magnetic nanoparticle chains. Because the microparticles have magnetization patterning due to fabrication with magnetic nanoparticle chains, the microparticles can rotate along the external rotating magnetic field, causing micromixing. We validated the reaction efficiency by comparing this micromixing method with other mixing methods such as simple diffusion and the use of a rocking shaker at various working volumes. This method has the potential to be widely utilized in suspension assay technology as an efficient mixing strategy

Surface Sr segregation behaviors in a model thin film perovskite cathode for solid oxide fuel cells

Surface cation segregation, strontium (Sr) in particular, has been considered as one of crucial barriers to achieving a fast surface oxygen exchange rate of perovskite oxide electrodes for solid oxide fuel cells (SOFCs). However, the major driving force for the segregation phenomenon still remains unknown, and thus it is also unknown how to maximize the cathode performance. In this work, we fabricated epitaxial thin films of SrTi1-xFexO3-δ (STF) via pulsed laser deposition (PLD) and quantitatively characterized their microstructures, surface chemical compositions and oxygen exchange rates by a range of analysis tools, in this case HR-TEM, HR-XRD, angle resolved X-ray photoelectron spectroscopy (AR-XPS) and electrical conductivity relaxation (ECR). The use of well-defined epitaxial thin films not only guarantees high precision, reproducibility and reliability of the surface properties, but also enables us to control the degree of misfit strain by varying the choice of the substrate and the target composition. This, in combination with density functional theory (DTF) simulation, enabled to reveal a close relationship between the degree of surface Sr segregation and the misfit strain and thereby to identify the governing factors for the Sr segregation phenomenon

Surface properties of atomically flat poly-crystalline SrTiO3

Comparison between single- and the poly-crystalline structures provides essential information on the role of long-range translational symmetry and grain boundaries. In particular, by comparing single- and poly-crystalline transition metal oxides (TMOs), one can study intriguing physical phenomena such as electronic and ionic conduction at the grain boundaries, phonon propagation, and various domain properties. In order to make an accurate comparison, however, both single- and poly-crystalline samples should have the same quality, e.g., stoichiometry, crystallinity, thickness, etc. Here, by studying the surface properties of atomically flat poly-crystalline SrTiO3 (STO), we propose an approach to simultaneously fabricate both single- and poly-crystalline epitaxial TMO thin films on STO substrates. In order to grow TMOs epitaxially with atomic precision, an atomically flat, single-terminated surface of the substrate is a prerequisite. We first examined (100), (110), and (111) oriented single-crystalline STO surfaces, which required different annealing conditions to achieve atomically flat surfaces, depending on the surface energy. A poly-crystalline STO surface was then prepared at the optimum condition for which all the domains with different crystallographic orientations could be successfully flattened. Based on our atomically flat poly-crystalline STO substrates, we envision expansion of the studies regarding theTMOdomains and grain boundaries.Comment: 21 pages, 5 figures, 1 tabl

Charge states and magnetic ordering in LaMnO3/SrTiO3 superlattices

We investigated the magnetic and optical properties of [(LaMnO3)n/(SrTiO3)8]20 (n = 1, 2, and 8) superlattices grown by pulsed laser deposition. We found a weak ferromagnetic and semiconducting state developed in all superlattices. An analysis of the optical conductivity showed that the LaMnO3 layers in the superlattices were slightly doped. The amount of doping was almost identical regardless of the LaMnO3 layer thickness up to eight unit cells, suggesting that the effect is not limited to the interface. On the other hand, the magnetic ordering became less stable as the LaMnO3 layer thickness decreased, probably due to a dimensional effect.Comment: 17 pages including 4 figures, accepted for publication in Phys. Rev.

Bloody nipple discharge in an infant

Although milky nipple discharge appears frequently in infants, bloody nipple discharge is a very rare finding. We experienced a 4-month-old, breast-fed infant who showed bilateral bloody nipple discharge with no signs of infection, engorgement, or hypertrophy. The infant's hormonal examination and coagulation tests were normal, and an ultrasound examination revealed mammary duct ectasia. The symptoms resolved spontaneously within 6 weeks without any specific treatment, except that we advised the mother to refrain from taking herbal medicine. Since no such case has been previously reported in Korea, we present this case with a brief review of the literature

Non-association between low vitamin d levels and aeroallergen-positivity evaluated using multiple allergen simultaneous test in Korean adults

Background Studies on the association between vitamin D levels and allergen sensitization have reported conflicting results. We aimed to evaluate the association between low vitamin D levels and sensitization to 59 aeroallergens in Korean adults. Methods We retrospectively reviewed serum 25-hydroxyvitamin D (25[OH]D) measurements of participants (n = 57,467) in a healthcare center between May 2003 and June 2020. Serum 25(OH)D levels were categorized as follows: severe deficiency (< 10 ng/mL), deficiency (10 to < 20 ng/mL), insufficiency (20 to < 30 ng/mL), and sufficiency (≥ 30 ng/mL). Among all subjects, 1277 simultaneously underwent the multiple allergen simultaneous test. Multiple linear and logistic regression analyses were used to estimate coefficients and odds ratios (ORs) with 95% confidence interval (CI) for the association between serum vitamin D deficiency and aeroallergen sensitization after adjustment for potential confounders. Subgroup analyses were conducted for the types of aeroallergen (house dust mites, pollens, animal dander, foods, cockroach, and fungus). Results Vitamin D deficiency, defined as serum 25(OH)D level < 20 ng/mL, was noted in 56.4% of participants. There were significant differences in serum 25(OH)D levels according to sex, age, season, and bone mineral density (all P < 0.001). In multiple linear regression analyses, serum 25(OH)D levels were significantly lower in young subjects (adjusted coefficient [95% CI], 0.188 [0.101, 0.275]) and during winter (− 4.114 [− 6.528, − 1.699]). However, no significant association was observed between serum 25(OH)D levels and allergen sensitization (adjusted coefficients [95% CI], − 0.211 [− 1.989, 1.567], P = 0.816). In multivariate logistic regression analyses, male sex, young age, and winter season were significant risk factors for vitamin D deficiency. However, allergen sensitization showed no significant association with 25(OD)D levels after adjusting for confounders (adjusted OR [95% CI], 1.037 [0.642, 1.674] in insufficiency; 0.910 [0.573, 1.445] in deficiency; 0.869 [0.298, 2.539] in severe deficiency groups, P for trend = 0.334). There were consistent findings across subgroups regarding type of aeroallergen sensitized. Conclusion Vitamin D deficiency was prevalent but was not significantly associated with aeroallergen sensitization in Korean adults. To the best of our knowledge, this is the first large-scale study to evaluate the association between vitamin D deficiency and sensitization to 59 different aeroallergens.This research was funded by National Research Foundation (NRF) of Korea, Grant Number (NRF-2020-R1G1A1005390 by Jee Hye Wee). The funding organization did not contribute to the design or conduct of this study, preparation, review, approval, or decision to submit this manuscript for publication

Characteristics of thyroid nodules in infant with congenital hypothyroidism

PurposeThis study aimed to assess the characteristics of thyroid nodules among infants diagnosed with congenital hypothyroidism.MethodsA retrospective study of 660 infants (374 males, 286 females) diagnosed with congenital hypothyroidism was carried out at the Pediatric Endocrine Clinic in Soonchunhyang University Hospital, Korea, between May 2003 and February 2013. The average age at diagnosis was 1.16±1.68 months.ResultsOf the 28 patients (4.2%) with thyroid nodules, 17 (2.6%) had cystic thyroid nodules and 11 (1.6%) had solid thyroid nodules. There were no significant differences in gender or age between congenital hypothyroidism patients who hadthyroid nodules and those who did not. All nodules were asymptomatic. The average age at diagnosis of congenital hypothyroidism with nodules was 1.42±1.39 months. All detected nodules measured less than 1 cm in diameter. Twenty-two of the 28 infants (78.6%) had only one nodule, while multiple nodules were found in 6 infants (21.4%). Of the 28 infants diagnosed with nodules, 16 underwent thyroid ultrasonography during follow-up and 8 of them (50%) showed no signs of nodules at thyroid ultrasonography.ConclusionThe prevalence of thyroid nodules in infants with congenital hypothyroidism was 4.2%. Most thyroid nodules were small in size and benign, disappearing during follow-up observation. We therefore conclude that thyroid nodules in infants with congenital hypothyroidism can simply be observed and do not require direct treatment