The FeSe nematic phase has been the focus of recent research on iron-based superconductors (IBSs) due to its unusual properties, which are distinct from those of the pnictides. A series of ...theoretical/experimental studies were performed to determine the origin of the nematic phase. However, they yielded conflicting results and caused additional controversies. Here, we report the results of angle-resolved photoemission and X-ray absorption spectroscopy studies on FeSe detwinned by a piezo stack. We fully resolved band dispersions with orbital characters near the Brillouin zone (BZ) corner, and revealed an absence of any Fermi pocket at the Y point in the 1-Fe BZ. In addition, the occupation imbalance between dxz and dyz orbitals was the opposite of that of iron pnictides, consistent with the identified band characters. These results resolve issues associated with the FeSe nematic phase and shed light on the origin of the nematic phase in IBSs.Twinning is a phenomenon which describes the intergrowth between two identical crystals, and can complicate the analysis of their intrinsic properties both from a physical and structural perspective. Here, the authors use a piezo stack to detwin FeSe crystals and then investigate the band dispersions using photoelectron and X-ray absorption spectroscopies in order to further clarify the origins of the nematic phase in FeSe.
A container inspection system (CIS) is a piece of that uses X-rays to scan inside a cargo container without opening it. These X-rays are generated by Bremsstrahlung which occurs when an electron beam ...accelerated by using a radio frequency (RF) linear accelerator (linac) hits a metal target. The RF linear accelerator is fed 2856 MHz RF power from a magnetron and accelerates the electron beam so that it attains energies up to 6 and 9 MeV. The linac is designed as standing-wave type linac, and RF power is transferred between cavity cells through side-coupling cells inside the linac. Bremsstrahlung radiation generated at the target penetrates the cargo container, and transmitted X-rays are detected by using detection modules. Detected X-ray signals are post-processed by using imaging software, and finalized images are obtained. The linac cavity was designed and fabricated by the Korea Atomic Energy Research Institute (KAERI), and dual-energy X-rays were successfully generated after RF conditioning. Finally we could obtain scanning images that could be used to distinguish organic from non-organic materials. Diagnostics have been conducted to characterize the electron beam and the X-rays to verify CIS performance and improve the scanning image. In this paper, we discuss the configuration of and performance test results for the X-ray generating linac developed by the KAERI.
We investigated structural and electronic inhomogeneities in a VO2 thin film grown on a (001)-oriented TiO2 substrate by exploiting nano-scale and macroscopic probing techniques. A compressive strain ...along the out-of-plane direction becomes additionally relaxed via microcracks which form a micron-sized rectangular pattern. A large inhomogeneity in the dielectric response is observed near the crack, and this signifies a strong coupling between electronic and lattice degrees of freedom. Interestingly, the strong inhomogeneity is observed also inside of the rectangular pattern, and it shows a gradient along one crystalline axis. We attribute such peculiar inhomogeneity observed in a relatively large length scale possibly to a combined effect of the strain relaxation and an oxygen vacancy distribution. As the nano-scale inhomogeneities in structural and electronic properties will eventually determine macroscopic responsivities, this work can be a good guide in designing VO2 thin films with appropriate controls of the strain and the chemical composition to realize better functionalities.
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•Inhomogeneous dielectric response near the microcracks and in the rectangular domains in VO2 thin films.•Gradient of dielectric response along only one crystalline axis.•Inhomogeneous distributions of a strain and an oxygen vacancy.
We investigated pressure-induced insulator-metal transition in Ca2Ru0.92Fe0.08O4 by using infrared microspectroscopy. As the pressure is increased up to 1.7 GPa, we observed a large increment of the ...reflectivity in the entire mid-infrared range. Accompanied by such a clear signature of the insulator-metal transition, we found an evidence of the structural transition from the frequency shift of the Ru-O stretch phonon mode which is attributed to the shortening of the in-plane Ru-O bond length. When we compared these pressure-dependent changes with the corresponding temperature-dependent results, we found that the pressure-induced metallic state has a higher reflectivity as well as the higher phonon frequency. Indeed, it turns out that the pressure-induced metallic state of Ca2Ru0.92Fe0.08O4 looks very similar with the metallic state of Sr-substituted Ca2RuO4 not only in the reflectivity level but also in the phonon frequency. This suggests that the electronic properties are closely related to the structural degree of freedom, and the pressure can be a useful parameter to induce the transitions from the Mott-insulator to the metal and further to the superconductor as observed for Sr2RuO4.
•We investigated pressure-induced insulator-metal transition of Ca2Ru0.92Fe0.08O4 by using infrared microspectroscopy.•We observed a sharp increase in the infrared reflectivity when the pressure is applied up to about 1 GPa.•Also, we observed a clear blue-shift of the infrared phonon mode corresponding to the in-plane Ru-O stretch mode.•We discuss the electronic insulator-metal transition in connection to the structural transition.
Abstract Background Korea has a nationalized health system. The aim of this study was to evaluate the impact of the Korea diagnosis related group–based prospective payment system (K-DRG/PPS) on the ...use of medical resources and the rate of adverse events during laparoscopic appendectomy. Methods We included patients who underwent laparoscopic appendectomy at Dongtan Sacred Heart Hospital, Korea, between November 2012 and February 2014. The patients were divided into two groups: before-DRG/PPS or after-DRG/PPS groups. The length of the postoperative hospital stay (LOS) and medical costs were indicators of the medical resources. Medical costs included those of the initial hospital stay, outpatient clinic, readmission, and the sum of these charges. Complication and readmission rates were indicators of the rates of adverse events. Results After the implementation of the DRG/PPS, length of the hospital stay decreased by 10% (4.9 d before versus 4.4 d after DRG/PPS; P < 0.001). The initial hospital stay and total cost were significantly lower in the after-DRG/PPS group (both P < 0.001). The complication rates during the initial hospital stay (3.5% before versus 2.3% after DRG/PPS; P = 0.225) and the readmission rates (4.3% versus 2.5%, respectively; P = 0.227) were statistically similar. Conclusions This study shows that the K-DRG/PPS for laparoscopic appendectomy had no negative effect on the rate of adverse events and reduced the use of medical resources. Further evaluation of other procedures is required to determine the overall effects of the K-DRG/PPS.
Graphene: Materials to devices (invited) Chae, J.; Ha, J.; Baek, H. ...
Microelectronic engineering,
07/2011, Volume:
88, Issue:
7
Journal Article, Conference Proceeding
Peer reviewed
Despite recent progress in understanding geometric structure, electronic structure, and transport properties in a graphene device (GD), role of point defects, edges, traps in a GD or a gate insulator ...has been poorly defined. We have studied electronic and geometric structures of these defects using scanning probe microscopy and try to link those with the transport properties of the GD. We perform scanning gate microscopy study to understand the local carrier scattering. It was found that geometric corrugations, defects and edges directly influence the local transport current. This observation is linked directly with a proposed scattering model based on macroscopic transport measurements. We suggest that dangling bonds in insulator-material SiO
2 mainly used in GDs produce charge puddles and they work as scattering centers.
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