https://scholar.dgist.ac.kr/handle/20.500.11750/59105 2026-11-11T11:09:24Z https://scholar.dgist.ac.kr/handle/20.500.11750/61093 Title: Analysis of Total Ionizing Dose Effect on a Linear RF Power Amplifier Author(s): Anwar, Muhammad Adeel; Kim, Dong-Seok; Lee, Min Sun; Kwon, Inyong Abstract: After accidents at nuclear power plants (NPPs), ensuring safety and reliability has become critically important. Monitoring NPPs is essential to detect and prevent accidents early. Wireless sensor networks (WSNs) are best suited for monitoring, but need to be robust against radiation to work effectively in harsh conditions. An important building block of a WSN node is the radio frequency (RF) power amplifier (PA), which should be able to provide the power to transmit the data even in the event of an accident. This article investigates the impact of total ionizing dose (TID) on the performance of a 2.4 GHz complementary metal-oxide-semiconductor (CMOS) RF PA. TID-induced changes in threshold voltage ( V-th( )) result in a displacement of the quiescent operating point (Q-point), leading to variations in critical performance metrics such as gain and efficiency. The PA is specifically designed to tolerate the increase in drain current caused by radiation, thereby maintaining functionality under radiation exposure. The PA is exposed to ionizing radiation at a dose rate of 200 Gy/h up to a total dose of 5 kGy using a Co-60 gamma source facility to evaluate its radiation tolerance and assess performance degradation. Measured results show a decline in small-signal gain ( S-21 ) and a reduction in power-added efficiency (PAE) from 12.2% to 9.6% as the total dose increases, with a sharp degradation observed beyond 1 kGy. 2026-09-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60975 Title: Enhanced light extraction in flex-mold nanopatterned scintillators for TOF-PET Author(s): 현수연; Choi, Suhan; Ko, Guen Bae; Lee, Min Sun Abstract: Objective. Optical photon losses at the scintillator-photosensor interface limit both energy and coincidence time resolution (CTR) in time-of-flight positron emission tomography (TOF-PET) detectors. To address this challenge, we applied diffractive nanopatterns on the surface of scintillation crystals to enhance light extraction. Approach. We utilized flex-mold-based soft lithography to imprint 300 nm hole and line patterns over cm-scale scintillator surfaces with less than 4% relative dimensional variation. Three scintillators (LYSO, BGO, GAGG) were tested under four optical coupling configurations: bare crystal with air (reference), bare with optical grease, nanopatterned crystal with air, and nanopatterned with grease. Main results. A 3 & times; 3 & times; 20 mm3 BGO with an H_hole-plaid nanopattern combined with optical grease achieved a maximum light extraction gain of 2.22-fold compared to the bare crystal with air coupling. Its energy resolution improved from 18% to 11%. The same fabrication process was applied to 3 & times; 3 & times; 20 mm3 LYSO and 5 & times; 5 & times; 5 mm3 GAGG, yielding light extraction gains of 1.58- and 1.72-fold. We also performed CTR measurements on nanopatterned LYSO 3 & times; 3 & times; 20 mm3 crystals, where the average CTR dropped from 250.6 ps (bare crystal with air coupling) to 142.6 ps (P_line with optical grease) at a fixed leading-edge discriminator threshold. Further threshold optimization for P_line with optical grease yielded a best result of 132.0 ps. The nanopatterns retained most of their gain after mechanical loading and 20 cycles of repeated cleaning. Significance. These findings demonstrate that flex-mold-based soft nanoimprint lithography provides a practical, high-fidelity approach for surface engineering of TOF-PET systems. 2026-07-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60459 Title: Sub-50 nm Surface Nanopatterning via Nano-Seed-Assisted Stereolithography Author(s): Park, Tae Wan; Kang, Eun Bin; Kang, Young Lim; Kim, Yu Na; Kang, Yu Jin; Baeg, Kang-Jun; Jeong, Hu Young; Hong, Seung Sae; Kim, Sung-Dae; Lee, Min Sun; Jeong, Diana; Park, Woon Ik Abstract: Three-dimensional (3D) printing based on stereolithography (SLA) enables microstructured objects, but sub-100 nm surface resolution remains difficult because of photopolymerization and resin diffusion. Here, we present a nano-seed-assisted SLA method for integrating sub-50 nm surface nanopatterns with 3D-printed structures. Si master molds with diverse nanoscale geometries are replicated into polymethyl methacrylate (PMMA) nano-seed templates, enabling controlled resin infiltration and high-fidelity pattern transfer from 250 nm to micrometer scales, including dots, holes, waves, and crosses. A conformal ultrathin inorganic barrier layer, such as platinum (Pt) or Ga2O3, suppresses resin-polymer intermixing, confines curing at the interface, and preserves pattern integrity. The method yields uniform sub-50 nm nanopatterns over chip-scale and larger areas up to 45 & times; 75 mm, verified by high-resolution TEM and elemental mapping. It integrates decorative or functional nanopatterns with complex 3D objects, exemplified by a 3D-printed Buddha sculpture. In addition to the hybrid assembly of separately prepared nanopatterned inserts, we further demonstrate the direct fabrication of a monolithic Buddha structure containing a localized nano-seed-derived patterned region, confirming that nanoscale surface ornamentation can be incorporated during the SLA printing process without requiring post-print assembly. Overall, nano-seed-assisted SLA offers a scalable route to high-resolution nanostructuring in 3D-printed materials. 2026-06-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/60421 Title: Influence of scintillation light confinement on depth-of-interaction measurement performance in a single-ended readout PET detector Author(s): Shim, Hyeong Seok; Cho, Min Jeong; He, Wen; Lee, Min Sun; Levin, Craig S.; Lee, Jae Sung Abstract: Continuous depth-of-interaction (cDOI) detectors enable single-ended readout in positron emission tomography (PET) by encoding the interaction depth into the scintillation light distribution. This study presents a comprehensive performance optimization of a cDOI detector based on light distribution tailoring with crossed triangular-shaped reflectors by analyzing the effects of optical geometry based on various DOI decoding algorithms. Two parameters were systematically varied: the degree of light confinement through (1) optical segmentation and (2) crystal pitch adjustment. Five DOI decoding strategies-variance, max/sum ratio, Euclidean-distance classification, Gaussian and modified maximum-likelihood estimation, and artificial neural network (ANN) decoding-were adopted with 8 & times; 8 SiPM readout data. Results show that moderate segmentation (2 & times; 2 configuration) achieved the best DOI precision, yielding a 4.7 mm full width at half maximum (FWHM) and an ANN classification accuracy of 89 %. In the pitch study, 1.5 mm-pitch detector achieved better performance than 3.0 mm-pitch, indicating that increased optical interfaces allows more accurate encoding of the depth-dependent light distribution within the SiPM array. The ANN decoder consistently outperformed in DOI resolution compared to analytical and statistical methods by learning nonlinear spatial correlations among SiPM pixels. These findings highlight the coupled importance of optical geometry and data-driven decoding for achieving high DOI sensitivity in next-generation PET detector designs. 2026-04-30T15:00:00Z