CoFe2O4 on Mica Substrate as Flexible Ethanol Gas Sensor in Self-Heating Mode.

In this study, a novel flexible ethanol gas sensor was created by the deposition of a CoFe2O4 (CFO) thin film on a thin mica substrate using the pulsed laser deposition technique. Transition electron microscopy (TEM) investigations clearly demonstrated the successful growth of CFO on the mica, where a well-defined interface was observed. Ethanol gas-sensing studies showed optimal performance at 200 °C, with the highest response of 19.2 to 100 ppm ethanol. Operating the sensor in self-heating mode under 7 V applied voltage, which corresponds to a temperature of approximately 200 °C, produced a maximal response of 19.2 to 100 ppm ethanol. This aligned with the highest responses observed during testing at 200 °C, confirming the sensor's accuracy and sensitivity to ethanol under self-heating conditions. In addition, the sensor exhibited good selectivity to ethanol and excellent flexibility, maintaining its high performance after bending and tilting up to 5000 times. As this is the first report on flexible self-heated CFO gas sensors, we believe that this research holds great promise for the future development of high-quality sensors based on this approach.

Manipulation of resonance orders and absorbing materials for structural colors in transmission with improved color purity.

We present an improved color purity of additive transmissive structural color filters by controlling a resonance order and by inserting a highly absorbing material. The proposed structure consists of a single metal sandwiched by two transparent dielectric media serving as a cavity to minimize the ohmic loss in the metal mirrors, which is distinctly different from a conventional Fabry-Perot (FP) cavity that is in general designed to have two metal mirrors. Low reflections at an air-dielectric interface cause a quality-factor of a resonance to be reduced, causing a degraded color purity, which can be improved by employing a 1st order resonance that exhibits a narrower bandwidth than a fundamental FP resonant mode (0th order). For a red color with the improved purity, introducing an ultrathin absorbing layer in the middle of a top cavity enables the 1st resonance to be trivially influenced while selectively suppressing a 2nd order resonance appearing at the shorter wavelength region. Moreover, angle-insensitive performances up to 60° are attained by utilizing a cavity material with high index of refraction. Besides, the fabrication of the structural coloring devices involves a few deposition steps, thus rendering the approach suitable for applications over the large area. The described concept could be applied to diverse applications, such as colored solar panels, sensors, imaging devices, and decorations.

Polarization- and Electrode-Optimized Polyvinylidene Fluoride Films for Harsh Environmental Piezoelectric Nanogenerator Applications.

While piezoelectric nanogenerators have demonstrated the effective conversion of tiny mechanical vibrations to electricity, their performances are rarely examined under harsh environmental conditions. Here, a multilayered polyvinylidene fluoride (PVDF) film-based piezoelectric nanogenerator (ML-PENG) is demonstrated to generate considerable and stable power outputs even at extremely low temperatures and pressures, and under strong UV. Up-/down-polarized PVDF films are alternately stacked, and Ag electrodes are intercalated between the two adjacent films. At -266 °C and 10-5  Torr, the ML-PENG generates an open-circuit voltage of 1.1 V, a short-circuit current density of 8 nA cm-2 , and a power density of 4.4 nW cm-2 . The piezoelectric outputs are quite stable against prolonged illumination of UV, large temperature- and pressure-variations, and excessive mechanical vibrations. The piezoelectric power density is greatly enhanced above the freezing and glass transition temperatures of PVDF and recorded to be 10, 105, and 282 nW cm-2 at -73, 0, and 77 °C, respectively. The ML-PENG generates sufficient power to operate five light-emitting diodes by harvesting biomechanical energy under simulated Martian conditions. This work suggests that polarization- and electrode-optimized ML-PENG can serve as a reliable and economic power source in harsh and inaccessible environments like polar areas of Earth and extraterrestrial Mars.

Dieckol is a natural positive allosteric modulator of GABAA-benzodiazepine receptors and enhances inhibitory synaptic activity in cultured neurons.

Phlorotannin supplement (PS) is a natural hypnotic substrate that modulates γ-aminobutyric acid type A (GABAA)-benzodiazepine (BZD) receptors. However, there is a lack of functional data assessing the role of individual components of PS, such as Dieckol, as allosteric activators of GABAA receptors (GABAAR). Using the whole cell patch clamp technique, we demonstrated that PS functionally enhanced the activity of GABAA-BZD receptors in a heterologous system and in primary cultured neurons. Application of diazepam (DZP) or Dieckol (1) increased GABAAR-mediated inward current in HEK293T cells containing the α1 subunit in a dose-dependent manner, (2) which was blocked by co-treatment with the selective benzodiazepine site antagonist, flumazenil (FLZ); it also (3) increased the amplitude of GABAA-BZD receptors in primary cultured neurons, which was blocked by FLZ and (4) attenuated spontaneous activity in cultured neurons. These results indicate that PS and Dieckol act as positive allosteric activators of GABAA-BZD receptors, which might be the underlying mechanism of the sedative-hypnotic effect of PS. To our knowledge, this is the first study to directly link Dieckol-induced GABAAR activation via the BZD site binding and suppression of spontaneous neuronal activity in vitro.

Tailoring morphological and chemical contributions of nanoscale charge transfer for enhanced triboelectric nanogenerators.

Triboelectric devices, operating through contact electrification (CE) and electrostatic induction, have shown great promise in energy harvesting applications. However, optimizing charge transfer at the interface remains crucial for enhancing device performance. This study introduces a novel approach to harnessing CE by employing morphological and chemical modifications of polymers. Our strategy involves adjusting the elastomer base to curing agent ratio to fine-tune the chemical properties of polydimethylsiloxane (PDMS) and introducing morphological modifications through a peeling and flipping (P/F) process of PDMS off the Si-substrate. Unlike conventional methods, the P/F-method minimally alters the intrinsic properties of PDMS, creating nanoscale surface corrugations adiabatically. We explore the mechanical, tribological, and electrical properties of the surface at the nano-scale and demonstrate that our approach allows for precise control of energy dissipation and electric potential at the surface, thereby optimizing charge transfer. Furthermore, we show that using a plasma-treated Si-substrate can further increase device performance up to 80% without affecting other properties. This study presents a comprehensive strategy for fine-tuning CE to enhance the performance of triboelectric nanogenerators.

Laminating Structure for Interlayer Corona Discharge Treatment Toward Ion-Based Nanogenerators.

A corona discharge treatment (CDT) is utilized to maximize the performance of triboelectric nanogenerators (TENGs) by injecting extra electrons into the negative tribomaterials. Increased performance of CDT TENGs, however, exhibits rapid degradation due to the electron dissipation by air moisture or thermal emission. To overcome such drawbacks and circumvent such dissipation, the source of charges should be replaced with ionic charges. This study reports a Ag nanowires (NWs)-embedded laminating structure (AeLS) with a unique fabrication procedure for ionic charge injection by CDT. The injection of ions is achieved by interlayer-CDT (i-CDT), in which positive charges are dissipated by Ag NWs, and the opposite negative ions can remain on the outmost surface. The AeLS TENGs with i-CDT exhibit high performance, long-term stability, and durability. It shows voltage, current, and maximum power outputs of 380 V, 15 µA, and 827 mW m-2 , respectively. As a practical demonstration, rotational TENG integrated with a direct discharge system is realized, and its current and voltage reach 7.4 mA and 7800 V, respectively. This work can pave the way for the design of ion-based TENGs with high performance and long-lasting retention of triboelectric charges.

Enhanced Photoluminescence of Crystalline Alq3 Micro-Rods Hybridized with Silver Nanowires.

An enhancement of the local electric field at the metal/dielectric interface of hybrid materials due to the localized surface plasmon resonance (LSPR) phenomenon plays a particularly important role in versatile research fields resulting in a distinct modification of the electrical, as well as optical, properties of the hybrid material. In this paper, we succeeded in visually confirming the LSPR phenomenon in the crystalline tris(8-hydroxyquinoline) aluminum (Alq3) micro-rod (MR) hybridized with silver (Ag) nanowire (NW) in the form of photoluminescence (PL) characteristics. Crystalline Alq3 MRs were prepared by a self-assembly method under the mixed solution of protic and aprotic polar solvents, which could be easily applied to fabricate hybrid Alq3/Ag structures. The hybridization between the crystalline Alq3 MRs and Ag NWs was confirmed by the component analysis of the selected area electronic diffraction attached to high-resolution transmission electron microscope. Nanoscale and solid state PL experiments on the hybrid Alq3/Ag structures using a lab-made laser confocal microscope exhibited a distinct enhancement of the PL intensity (approximately 26-fold), which also supported the LSPR effects between crystalline Alq3 MRs and Ag NWs.

Lead-free KNbO3 ferroelectric nanorod based flexible nanogenerators and capacitors.

In spite of high piezoelectricity, only a few one-dimensional ferroelectric nano-materials with perovskite structure have been used for piezoelectric nanogenerator applications. In this paper, we report high output electrical signals, i.e. an open-circuit voltage of 3.2 V and a closed-circuit current of 67.5 nA (current density 9.3 nA cm(-2)) at 0.38% strain and 15.2% s(-1) strain rate, using randomly aligned lead-free KNbO(3) ferroelectric nanorods (~1 µm length) with piezoelectric coefficient (d(33) ~ 55 pm V (-1)). A flexible piezoelectric nanogenerator is mainly composed of KNbO(3)-poly(dimethylsiloxane) (PDMS) composite sandwiched by Au/Cr-coated polymer substrates. We deposit a thin poly(methyl methacrylate) (PMMA) layer between the KNbO(3)-PDMS composite and the Au/Cr electrode to completely prevent dielectric breakdown during electrical poling and to significantly reduce leakage current during excessive straining. The flexible KNbO(3)-PDMS composite device shows a nearly frequency-independent dielectric constant (~3.2) and low dielectric loss (<0.006) for the frequency range of 10(2)-10(5) Hz. These results imply that short and randomly aligned ferroelectric nanorods can be used for a flexible high output nanogenerator as well as high-k capacitor applications by performing electrical poling and further optimizing the device structure.

Clinical features of partial anterior bursal-sided supraspinatus tendon (PABST) lesions.

BACKGROUND: We characterized partial anterior and bursal supraspinatus tendon (PABST) lesions and compared their clinical features, postoperative functional scores, and healing rate with full-thickness rotator cuff tears (FTRCTs) and small FTRCTs. MATERIALS AND METHODS: There were 31 PABST lesions (6.2%), 392 FTRCTs, and 32 small FTRCTs among 495 shoulders with rotator cuff disorders. The mean patient age was 52.7 years in the PABST group, 60.1 years in the FTRCT group, and 56.9 years in the small FTRCT group. Functional and clinical variables were compared between the groups, and cuff healing was evaluated with computed tomography arthrography or ultrasonography. RESULTS: The mean patient age was statistically lower, the mean symptom duration was shorter, and trauma was more frequent in the PABST group compared with the FTRCT and small FTRCT groups. Coronal acromial spurs were found more frequently in the PABST group than in the FTRCT group. In all groups, range of motion, visual analog scale for pain, and functional scores improved continuously throughout the follow-up. There were 2 unhealed cuffs (10.5%) in the PABST group, 72 (35.6%) in the FTRCT group (P = .146), and 5 (25%) in the small FTRCT group (P = .238). CONCLUSIONS: We characterized PABST lesions that may be overlooked because of their peculiar location in the far anterolateral insertional section of the supraspinatus tendon at the bursal side. PABST lesions usually occur in younger patients, and trauma is frequently associated with acute symptom onset. Surgical treatment was effective for pain reduction and functional improvement.

Hevin-calcyon interaction promotes synaptic reorganization after brain injury.

Hevin, also known as SPARC-like protein 1 (SPARCL1 or SC1), is a synaptogenic protein secreted by astrocytes and modulates the formation of glutamatergic synapses in the developing brain by interacting with synaptic adhesion proteins, such as neurexin and neuroligin. Here, we identified the neuron-specific vesicular protein calcyon as a novel interaction partner of hevin and demonstrated that this interaction played a pivotal role in synaptic reorganization after an injury in the mature brain. Astrocytic hevin was upregulated post-injury in a photothrombotic stroke model. Hevin was fragmented by MMP3 induced during the acute stage of brain injury, and this process was associated with severe gliosis. At the late stage, the functional hevin level was restored as MMP3 expression decreased. The C-terminus of hevin interacted with the N-terminus of calcyon. By using RNAi and binding competitor peptides in an ischemic brain injury model, we showed that this interaction was crucial in synaptic and functional recoveries in the sensory-motor cortex, based on histological and electrophysiological analyses. Regulated expression of hevin and calcyon and interaction between them were confirmed in a mouse model of traumatic brain injury and patients with chronic traumatic encephalopathy. Our study provides direct evidence for the causal relationship between the hevin-calcyon interaction and synaptic reorganization after brain injury. This neuron-glia interaction can be exploited to modulate synaptic reorganization under various neurological conditions.

Template Engineering of Metal-to-Insulator Transitions in Epitaxial Bilayer Nickelate Thin Films.

Understanding metal-to-insulator phase transitions in solids has been a keystone not only for discovering novel physical phenomena in condensed matter physics but also for achieving scientific breakthroughs in materials science. In this work, we demonstrate that the transport properties (i.e., resistivity and transition temperature) in the metal-to-insulator transitions of perovskite nickelates are tunable via the epitaxial heterojunctions of LaNiO3 and NdNiO3 thin films. A mismatch in the oxygen coordination environment and interfacial octahedral coupling at the oxide heterointerface allows us to realize an exotic phase that is unattainable in the parent compound. With oxygen vacancy formation for strain accommodation, the topmost LaNiO3 layer in LaNiO3/NdNiO3 bilayer thin films is structurally engineered and it electrically undergoes a metal-to-insulator transition that does not appear in metallic LaNiO3. Modification of the NdNiO3 template layer thickness provides an additional knob for tailoring the tilting angles of corner-connected NiO6 octahedra and the linked transport characteristics further. Our approaches can be harnessed to tune physical properties in complex oxides and to realize exotic physical phenomena through oxide thin-film heterostructuring.

Large-Scale Fabrication of Copper-Ion-Coated Deoxyribonucleic Acid Hybrid Fibers by Ion Exchange and Self-Metallization.

It has been a challenge to achieve deoxyribonucleic acid (DNA) metallization and mass production with a high quality. The main aim of this study was to develop a large-scale production method of metal-ion-coated DNA hybrid fibers, which can be useful for the development of physical devices and sensors. Cetyltrimethylammonium-chloride-modified DNA molecules (CDNA) coated with metal ions through self-metallization exhibit enhanced optical and magnetic properties and thermal stability. In this paper, we present a simple synthesis route for Cu2+-coated CDNA hybrid fibers through ion exchange followed by self-metallization and analyze their structural and chemical composition (by X-ray diffraction (XRD), high-resolution field emission transmission electron microscopy (FETEM), and energy-dispersive X-ray spectroscopy (EDS)) and optical (by ultraviolet (UV)-visible absorption, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopies (XPS)), magnetic (by vibrating-sample magnetometry), and thermal (by a thermogravimetric analysis) characteristics. The XRD patterns, high-resolution FETEM images, and selected-area electron diffraction patterns confirmed the triclinic structure of Cu2+ in CDNA. The EDS results revealed the formation of Cu2+-coated CDNA fibers with a homogeneous distribution of Cu2+. The UV-vis, FTIR, and XPS spectra showed the electronic transition, interaction, and energy transfer between CDNA and Cu2+, respectively. The Cu2+-coated CDNA fibers exhibited a ferromagnetic nature owing to the presence of Cu2+. The magnetization of the Cu2+-coated CDNA fibers increased with the concentration of Cu2+ and decreased with the increase in temperature. Endothermic (absorbed heat) and exothermic (released heat) peaks in the differential thermal analysis curve were observed owing to the interaction of Cu2+ with the phosphate backbone.

Enhancing the electrical, optical, and magnetic characteristics of DNA thin films through Mn2+ fortification.

DNA is one of the most propitious biomaterials for use in nanoscience and nanotechnology because of its exceptional characteristics, i.e. self-assembly and sequence-programmability. In this study, we fabricate sequence-designed double-crossover (DX) DNA lattices and naturally available salmon DNA (SDNA) thin films modified with the transition metal ion Mn2+. Phase transition of DX DNA lattices from crystalline to amorphous form controlled by varying the concentration of Mn2+ is discussed and a critical transition concentration ([Mn2+]C) is estimated. In addition, the electrical, optical, and magnetic properties of Mn2+-modified SDNA thin films including current, absorbance, photoluminescence, the X-ray photoelectron spectrum, and magnetization are studied to understand their conductivity, binding modes, energy transfer characteristics, chemical composition, and magnetism. Interestingly, the physical values such as the maximum current and photoluminescence, and the minimum absorbance, occur at around [Mn2+]C =4 mM, which may be due to the optimal incorporation of Mn2+ into the SDNA. The magnetization and susceptibility of SDNA thin films with Mn2+, served as magnetic dipoles, are studied under different temperature and magnetic field. The magnetization of SDNA thin films with [Mn2+]C shows an S-shaped curve, indicating ferromagnetism.

Dominant Role of Young's Modulus for Electric Power Generation in PVDF⁻BaTiO3 Composite-Based Piezoelectric Nanogenerator.

The electric power output of a piezoelectric nanogenerator (PENG) depends on the various physical parameters of the constituent materials, including the piezoelectric coefficient, Young's modulus, and dielectric constant. Herein, we report the mechanical and electrical properties of a poly(vinylidene fluoride)⁻BaTiO3 (PVDF⁻BTO) composite-based PENG. Variation of the BTO nanoparticle (NP) content enabled the systematic tuning of the physical parameters that are related to power generation in the composite. The Young's modulus of the PVDF⁻BTO composite initially increased, and then eventually decreased, with the increasing BTO content, which was probably due to the clustering effect of the high modulus BTO NPs. The dielectric constant of the composite continuously increased as the BaTiO3 content increased. The piezoelectric outputs were greatly enhanced at 10 wt% of BTO, where the Young's modulus was the highest. These results indicate that the Young's modulus plays an important role in the piezoelectric power generation of the composite-based PENGs.

Solvent-dependent self-assembly of two dimensional layered perovskite (C6H5CH2CH2NH3)2MCl4 (M = Cu, Mn) thin films in ambient humidity.

Two dimensional layered organic-inorganic halide perovskites offer a wide variety of novel functionality such as solar cell and optoelectronics and magnetism. Self-assembly of these materials using solution process (ex. spin coating) makes crystalline thin films synthesized at ambient environment. However, flexibility of organic layer also poses a structure stability issue in perovskite thin films against environment factors (ex. moisture). In this study, we investigate the effect of solvents and moisture on structure and property in the (C6H5(CH2)2NH3)2(Cu, Mn)Cl4 (Cu-PEA, Mn-PEA) perovskite thin films spin-coated on Si wafer using three solvents (H2O, MeOH, MeOH + H2O). A combination of x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) show that relative humidity (RH) has a profound effect on perovskite thin films during sample synthesis and storage, depending on the kind of solvent used. The ones prepared using water (Cu-PEA:H2O, Mn-PEA:H2O) show quite different behavior from the other cases. According to time-dependent XRD, reversible crystalline-amorphous transition takes place depending on RH in the former cases, whereas the latter cases relatively remain stable. It also turns out from XAS that Mn-PEA thin films prepared with solvents such as MeOH and MeOH + H2O are disordered to the depth of about 4 nm from surface.

Flexible Pb(Zr0.52Ti0.48)O3 Films for a Hybrid Piezoelectric-Pyroelectric Nanogenerator under Harsh Environments.

In spite of extremely high piezoelectric and pyroelectric coefficients, there are few reports on flexible ferroelectric perovskite film based nanogenerators (NGs). Here, we report the successful growth of a flexible Pb(Zr0.52Ti0.48)O3 (PZT) film and its application to hybrid piezoelectric-pyroelectric NG. A highly flexible Ni-Cr metal foil substrate with a conductive LaNiO3 bottom electrode enables the growth of flexible PZT film having high piezoelectric (140 pC/N) and pyroelectric (50 nC/cm(2)K) coefficients at room temperature. The flexible PZT-based NG effectively scavenges mechanical vibration and thermal fluctuation from sources ranging from the human body to the surroundings such as wind. Furthermore, it stably generates electric current even at elevated temperatures of 100 °C, relative humidity of 70%, and pH of 13 by virtue of its high Curie temperature and strong resistance for water and base. As proof of power generation under harsh environments, we demonstrate the generation of extremely high current at the exhaust pipe of a car, where hot CO and CO2 gases are rapidly expelled to air. This work expands the application of flexible PZT film-based NG for the scavenging mechanical vibration and thermal fluctuation energies even at extreme conditions.

Intriguing photo-control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films on SrTiO3 substrates.

To date, electric fields have been widely used to control the magnetic properties of BiFeO3-based antiferromagnet/ferromagnet heterostructures through application of an exchange bias. To extend the applicability of exchange bias, however, an alternative mechanism to electric fields is required. Here, we report the photo-control of exchange bias in BiFeO3/La2/3Sr1/3MnO3 thin films on an SrTiO3 substrate. Through an ex situ pulsed laser deposition technique, we successfully synthesized epitaxial BiFeO3/La2/3Sr1/3MnO3 thin films on SrTiO3 substrates. By measuring magnetoresistance under light illumination, we investigated the effect of light illumination on resistance, exchange bias, and coercive field in BiFeO3/La2/3Sr1/3MnO3 thin films. After illumination of red and blue lights, the exchange bias was sharply reduced compared to that measured in the dark. With increasing light intensity, the exchange bias under red and blue lights initially decreased to zero and then appeared again. It is possible to reasonably explain these behaviors by considering photo-injection from SrTiO3 and the photo-conductivity of La2/3Sr1/3MnO3. This study may provide a fundamental understanding of the mechanism underlying photo-controlled exchange bias, which is significant for the development of new functional spintronic devices.

Lead-free LiNbO3 nanowire-based nanocomposite for piezoelectric power generation.

In a flexible nanocomposite-based nanogenerator, in which piezoelectric nanostructures are mixed with polymers, important parameters to increase the output power include using long nanowires with high piezoelectricity and decreasing the dielectric constant of the nanocomposite. Here, we report on piezoelectric power generation from a lead-free LiNbO3 nanowire-based nanocomposite. Through ion exchange of ultra-long Na2Nb2O6-H2O nanowires, we synthesized long (approximately 50 µm in length) single-crystalline LiNbO3 nanowires having a high piezoelectric coefficient (d33 approximately 25 pmV-1). By blending LiNbO3 nanowires with poly(dimethylsiloxane) (PDMS) polymer (volume ratio 1:100), we fabricated a flexible nanocomposite nanogenerator having a low dielectric constant (approximately 2.7). The nanogenerator generated stable electric power, even under excessive strain conditions (approximately 105 cycles). The different piezoelectric coefficients of d33 and d31 for LiNbO3 may have resulted in generated voltage and current for the e33 geometry that were 20 and 100 times larger than those for the e31 geometry, respectively. This study suggests the importance of the blending ratio and strain geometry for higher output-power generation in a piezoelectric nanocomposite-based nanogenerator. PACS: 77.65.-j; 77.84.-s; 73.21.Hb.

Flexible pyroelectric nanogenerators using a composite structure of lead-free KNbO(3) nanowires.

Pyroelectric nanogenerators fabricated using a lead-free KNbO(3) nanowire-PDMS polymer composite are reported for the first time. The voltage/current output of the nanogenerators can be controlled by electric fields and enhanced by increasing the rate of change in temperature. The fabricated nanogenerators can be used to harvest energy from sunlight illumination and have potential applications in self-powered nanodevices and nanosystems.

Chemical speciation of size-segregated floor dusts and airborne magnetic particles collected at underground subway stations in Seoul, Korea.

Previous studies have reported the major chemical species of underground subway particles to be Fe-containing species that are generated from wear and friction processes at rail-wheel-brake and catenaries-pantographs interfaces. To examine chemical composition of Fe-containing particles in more details, floor dusts were collected at five sampling locations of an underground subway station. Size-segregated floor dusts were separated into magnetic and non-magnetic fractions using a permanent magnet. Using X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDX), iron metal, which is relatively harmless, was found to be the dominating chemical species in the floor dusts of the <25 µm size fractions with minor fractions of Mg, Al, Si, Ca, S, and C. From SEM analysis, the floor dusts of the <25 µm size fractions collected on railroad ties appeared to be smaller than 10 µm, indicating that their characteristics should somewhat reflect the characteristics of airborne particles in the tunnel and the platform. As most floor dusts are magnetic, PM levels at underground subway stations can be controlled by removing magnetic indoor particles using magnets. In addition, airborne subway particles, most of which were smaller than 10 µm, were collected using permanent magnets at two underground subway stations, namely Jegi and Yangjae stations, in Seoul, Korea. XRD and SEM/EDX analyses showed that most of the magnetic aerosol particles collected at Jegi station was iron metal, whereas those at Yangjae station contained a small amount of Fe mixed with Na, Mg, Al, Si, S, Ca, and C. The difference in composition of the Fe-containing particles between the two subway stations was attributed to the different ballast tracks used.