Soft X-ray resonant Kerr rotation measurement and simulation of element-resolved and interface-sensitive magnetization reversals in a NiFe/FeMn/Co trilayer structure

We report experimental observations of element- and buried interface-resolved magnetization reversals in an oppositely exchange-biased NiFeFeMnCo trilayer structure by soft x-ray resonant Kerr rotation measurements. Not only Co-, Ni-, Fe-specific exchange-biased loops but also interfacial uncompensated (UC) Fe reversal loops coupled to the individual Co and NiFe layers are separately observed. From the experimental results interpreted with the help of the model simulations of soft x-ray resonant Kerr rotation, the effective thicknesses of interfacial UC regions at the buried interfaces of both FeMnCo and NiFeFeMn are found to be tUC =13??2 A and 6??4 A, respectively. The depth sensitivity as well as element specificity of the x-ray resonant Kerr effect offer an elegant way into the investigations of element- and depth-resolved magnetization reversals of ferromagnetic ultrathin regions at buried interfaces in multicomponent multilayer films.open91

Trans-reflective color filters based on a phase compensated etalon enabling adjustable color saturation

Trans-reflective color filters, which take advantage of a phase compensated etalon (silver-titania-silver-titania) based nano-resonator, have been demonstrated to feature a variable spectral bandwidth at a constant resonant wavelength. Such adjustment of the bandwidth is presumed to translate into flexible control of the color saturation for the transmissive and reflective output colors produced by the filters. The thickness of the metallic mirror is primarily altered to tailor the bandwidth, which however entails a phase shift associated with the etalon. As a result, the resonant wavelength is inevitably displaced. In order to mitigate this issue, we attempted to compensate for the induced phase shift by introducing a dielectric functional layer on top of the etalon. The phase compensation mediated by the functional layer was meticulously investigated in terms of the thickness of the metallic mirror, from the perspective of the resonance condition. The proposed color filters were capable of providing additive colors of blue, green, and red for the transmission mode while exhibiting subtractive colors of yellow, magenta, and cyan for the reflection mode. The corresponding color saturation was estimated to be efficiently adjusted both in transmission and reflection.This work was supported by a National Research Foundation of Korea grant funded by the Korean government (MSIP) (No. 2011-0030079), and by a research grant from Kwangwoon University in 2016. The work was partly supported by the Australian Research Council Future Fellowship (FT110100853, Dr. Duk-Yong Choi) and was performed in part at the ACT node of the Australian National Fabrication Facility

Angle-tolerant linear variable color filter based on a tapered etalon

We propose and fabricate a linear variable color filter (LVCF) that possesses an enhanced angular tolerance in conjunction with a wide linear filtering range (LFR) by taking advantage of an Ag-TiO2-Ag configuration. The TiO2 cavity is tapered in thickness along the device so that the resonance wavelength can be continuously tuned according to the position. In addition, the metal-dielectric-metal structure is overlaid with a pre-designed graded anti-reflection coating in SiO2 to complete the etalon, thereby maximizing the transmission efficiency across the entire device. The tapered dielectric layers in the proposed filter were fabricated via glancing angle deposition without the help of any mask or moving parts. The center wavelength was scanned from 410 nm to 566 nm, resulting in an LFR of 156 nm, and the overall spectra exhibited an approximate peak transmission of 40% and spectral bandwidth of 68 nm. The angular tolerance was as large as 45°, incurring a fractional wavelength shift below 4.2%. The resonance wavelength was verified to be linearly dependent on the position, providing a linearity beyond 99%. The proposed LVCF will thus be actively utilized in a portable micro-spectrometer and spectral scanning device.National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2016R1A2B2010170); ARC Future Fellowship FT110100853

Omnidirectional color filters capitalizing on a nano-resonator of Ag-TiO2-Ag integrated with a phase compensating dielectric overlay

We present a highly efficient omnidirectional color filter that takes advantage of an Ag-TiO2-Ag nano-resonator integrated with a phase-compensating TiO2 overlay. The dielectric overlay substantially improves the angular sensitivity by appropriately compensating for the phase pertaining to the structure and suppresses unwanted optical reflection so as to elevate the transmission efficiency. The filter is thoroughly designed, and it is analyzed in terms of its reflection, optical admittance, and phase shift, thereby highlighting the origin of the omnidirectional resonance leading to angle-invariant characteristics. The polarization dependence of the filter is explored, specifically with respect to the incident angle, by performing experiments as well as by providing the relevant theoretical explanation. We could succeed in demonstrating the omnidirectional resonance for the incident angles ranging to up to 70°, over which the center wavelength is shifted by below 3.5% and the peak transmission efficiency is slightly degraded from 69%. The proposed filters incorporate a simple multi-layered structure and are expected to be utilized as tri-color pixels for applications that include image sensors and display devices. These devices are expected to allow good scalability, not requiring complex lithographic processes.This work was supported by a National Research Foundation of Korea grant funded by the Korean government (MEST) (No. 2013-008672 and 2013-067321), and also by a research grant from Kwangwoon University in 2014. The work was partly supported by the Australian Research Council Future Fellowship (FT110100853, Dr. Duk-Yong Choi) and was performed in part at the ACT node of the Australian National Fabrication Facilit

Structural color filters based on an all-dielectric metasurface exploiting silicon-rich silicon nitride nanodisks

An all-dielectric metasurface is deemed to serve a potential platform to demonstrate spectral filters. Silicon-rich silicon nitride (SRN), which contains a relatively large portion of silicon, can exhibit higher refractive indices, when compared to silicon nitride. Meanwhile, the extinction coefficient of SRN is smaller than that of hydrogenated amorphous silicon, leading to reduced absorption loss in the shorter wavelength. SRN is therefore recommended as a scattering element from the perspective of realizing all-dielectric metasurfaces. In this work, we propose and embody a suite of highly efficient structural color filters, capitalizing on a dielectric metasurface that consists of a two-dimensional array of SRN nanodisks that are embedded in a polymeric layer. The SRN nanodisks may support the electric dipole (ED) and magnetic dipole (MD) resonances via Mie scattering, thereby leading to appropriate spectral filtering characteristics. The ED and MD are identified from field profile observation with the assistance of finite-difference time-domain simulations. The manufactured color filters are observed to produce various colors in both transmission and reflection modes throughout the visible band, giving rise to a high transmission of around 90% in the off-resonance region and a reflection ranging up to 60%. A variety of colors can be realized by tuning the resonance by adjusting the structural parameters such as the period, diameter, and height of the SRN nanodisks. The spectral position of resonances might be flexibly tuned by tailoring the polymer surrounding the SRN nanodisks. It is anticipated that the proposed coloring devices will be actively used for color displays, imaging devices, and photorealistic color printing.National Research Foundation of Korea (NRF) funded by the Korean government (No.2016R1A2B2010170 and 2018R1A6A1A03025242); Australian Research Council Future Fellowship (FT110100853, Dr. Duk-Yong Choi)

Examining the links between burnout and suicidal ideation in diverse occupations

IntroductionIt is uncertain whether burnout is associated with suicidal ideation among workers not in health care services. The aim of this study was to identify how burnout and suicidal ideation are linked among employees in various occupations and whether depression affects this link.MethodsThis cross-sectional study collected data from 12,083 participants aged 19–65 years from 25 companies and public institutions who underwent workplace mental health screening. Burnout and depression were assessed using both the Oldenburg Burnout Inventory and the Center for Epidemiologic Studies Depression Scale. Suicidal ideation was assessed by a self-rated questionnaire from the Korea National Health and Nutrition Examination Survey.ResultsExhaustion but not the cynicism dimension of burnout was associated with increased odds of suicidal ideation after adjustment for depression and other covariates (odds ratio [OR] = 1.47, 95% CI = 1.26–1.72). The association of exhaustion with suicidal ideation was significant in both depressed (OR = 1.36, 95% CI = 1.14–1.61) and not depressed (OR = 1.77, 95% CI = 1.13–2.76) participants. In exhausted participants, insufficient job control, an unfavorable occupational climate, low educational level, and depression were associated with increased odds of suicidal ideation.ConclusionExhaustion is linked with risk of suicidal ideation in employees not in health care service, regardless of depression status. Exhausted employees, particularly those having poor job resources, should be recognized as an at-risk group