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  1. Strain plays an important role in the performance and reliability of AlGaN/GaN high electron mobility transistors (HEMTs). However, the impact of strain on the performance of proton irradiated GaN HEMTs is yet unknown. In this study, we investigated the effects of strain relaxation on the properties of proton irradiated AlGaN/GaN HEMTs. Controlled strain relief is achieved locally using the substrate micro-trench technique. The strain relieved devices experienced a relatively smaller increase of strain after 5 MeV proton irradiation at a fluence of 5 × 1014 cm−2 compared to the non-strain relieved devices, i.e., the pristine devices. After proton irradiation, both pristine and strain relieved devices demonstrate a reduction of drain saturation current (Ids,sat), maximum transconductance (Gm), carrier density (ns), and mobility (μn). Depending on the bias conditions the pristine devices exhibit up to 32% reduction of Ids,sat, 38% reduction of Gm, 15% reduction of ns, and 48% reduction of μn values. In contrast, the strain relieved devices show only up to 13% reduction of Ids,sat, 11% reduction of Gm, 9% reduction of ns, and 30% reduction of μn values. In addition, the locally strain relieved devices show smaller positive shift of threshold voltage compared to the pristine devices after proton irradiation. The less detrimental impact of proton irradiation on the transport properties of strain relieved devices could be attributed to reduced point defect density producing lower trap center densities, and evolution of lower operation related stresses due to lower initial residual strain.

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    Free, publicly-accessible full text available December 14, 2024
  2. Abstract Background

    Basic fibroblast growth factor (bFGF) is one of the critical components accelerating angiogenesis and tissue regeneration by promoting the migration of dermal fibroblasts and endothelial cells associated with matrix formation and remodeling in wound healing process. However, clinical applications of bFGF are substantially limited by its unstable nature due to rapid decomposition under physiological microenvironment.


    In this study, we present the bFGF-loaded human serum albumin nanoparticles (HSA-bFGF NPs) as a means of enhanced stability and sustained release platform during tissue regeneration. Spherical shape of the HSA-bFGF NPs with uniform size distribution (polydispersity index < 0.2) is obtainedviaa simple desolvation and crosslinking process. The HSA-bFGF NPs securely load and release the intact soluble bFGF proteins, thereby significantly enhancing the proliferation and migration activity of human dermal fibroblasts. Myofibroblast-related genes and proteins were also significantly down-regulated, indicating decrease in risk of scar formation. Furthermore, wound healing is accelerated while achieving a highly organized extracellular matrix and enhanced angiogenesis in vivo.


    Consequently, the HSA-bFGF NPs are suggested not only as a delivery vehicle but also as a protein stabilizer for effective wound healing and tissue regeneration.

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    Free, publicly-accessible full text available December 1, 2024
  3. Neutrons generated through charge-exchange9Be (p; ni)9Be reactions, with energies ranging from 0–33 MeV and an average energy of ∼9.8 MeV were used to irradiate conventional Schottky Ga2O3rectifiers and NiO/Ga2O3p-n heterojunction rectifiers to fluences of 1.1–2.2 × 1014cm−2. The breakdown voltage was improved after irradiation for the Schottky rectifiers but was highly degraded for their NiO/Ga2O3counterparts. This may be a result of extended defect zones within the NiO. After irradiation, the switching characteristics were degraded and irradiated samples of both types could not survive switching above 0.7 A or 400 V, whereas reference samples were robust to 1 A and 1 kV. The carrier removal rate in both types of devices was ∼45 cm−1. The forward currents and on-state resistances were only slightly degraded by neutron irradiation.

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  4. De Mitri, I. ; Barbato, F.C.T. ; Boncioli, D. ; Evoli, C. ; Pagliaroli, G. ; Salamida, F. (Ed.)
    The Telescope Array and the Pierre Auger Observatory estimate the composition of ultra-high-energy cosmic rays by observing the distribution of depths of air-shower maxima, X max . Both experiments directly observe the longitudinal development of air showers using fluorescence telescopes with surface particle detectors used in conjunction to provide precision in determining air-shower geometry. The two experiments differ in the details of the analysis of events, so a direct comparison of X max distributions is not possible. The Auger – Telescope Array Composition Working Group presents their results from a technique to compare X max measurements from Auger with those of Telescope Array. In particular, the compatibility of the first two moments of the X max distributions of Auger with the data from the Black Rock Mesa and Long Ridge detectors of the Telescope Array is tested for energies above 10 18.2 eV. Quantitative comparisons are obtained using air-shower simulations of four representative species made using the Sibyll 2.3d high-energy interaction model. These are weighted to fit the fractional composition seen in Auger data and reconstructed using the Telescope Array detector response and analysis methods. 
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  5. Epitaxial growth, a crystallographically oriented growth induced by the chemical bonding between crystalline substrate and atomic building blocks, has been a key technique in the thin-film and heterostructure applications of semiconductors. However, the epitaxial growth technique is limited by different lattice mismatch and thermal expansion coefficients of dissimilar crystals. Two-dimensional (2D) materials with dangling bond-free van der Waals surfaces have been used as growth templates for the hetero-integration of highly mismatched materials. Moreover, the ultrathin nature of 2D materials also allows for remote epitaxial growth and confinement growth of quasi-2D materials via intercalation. Here, we review the hetero-dimensional growth on 2D substrates: van der Waals epitaxy (vdWE), quasi vdWE, and intercalation growth. We discuss the growth mechanism and fundamental challenges for vdWE on 2D substrates. We also examine emerging vdWE techniques that use epitaxial liftoff and confinement epitaxial growth in detail. Finally, we give a brief review of radiation effects in 2D materials and contrast the damage induced with their 3D counterparts.

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  6. α-Ga2O3 has the corundum structure analogous to that of α-Al2O3. The bandgap energy of α-Ga2O3 is 5.3 eV and is greater than that of β-Ga2O3, making the α-phase attractive for devices that benefit from its wider bandgap. The O-H and O-D centers produced by the implantation of H+ and D+ into α-Ga2O3 have been studied by infrared spectroscopy and complementary theory. An O-H line at 3269 cm-1 is assigned to H complexed with a Ga vacancy (VGa), similar to the case of H trapped by an Al vacancy (VAl) in α-Al2O3. The isolated VGa and VAl defects in α-Ga2O3 and α-Al2O3 are found by theory to have a “shifted” vacancy-interstitial-vacancy equlibrium configuration, similar to VGa in β-Ga2O3 which also has shifted structures. However, the addition of H causes the complex with H trapped at an unshifted vacancy to have the lowest energy in both α-Ga2O3 and α-Al2O3. 
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  7. There is increasing interest in the alpha polytype of Ga2O3 because of its even larger bandgap than the more studied beta polytype, but in common with the latter, there is no viable p-type doping technology. One option is to use p-type oxides to realize heterojunctions and NiO is one of the candidate oxides. The band alignment of sputtered NiO on α-Ga2O3 remains type II, staggered gap for annealing temperatures up to 600 °C, showing that this is a viable approach for hole injection in power electronic devices based on the alpha polytype of Ga2O3. The magnitude of both the conduction and valence band offsets increases with temperature up to 500 °C, but then is stable to 600 °C. For the as-deposited NiO/α-Ga2O3 heterojunction, ΔEV = −2.8 and ΔEC = 1.6 eV, while after 600 °C annealing the corresponding values are ΔEV = −4.4 and ΔEC = 3.02 eV. These values are 1−2 eV larger than for the NiO/β-Ga2O3 heterojunction.

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  8. Abstract The ongoing disproportionate increases in temperature and precipitation over the Arctic region may greatly alter the latitudinal gradients in greenup and snowmelt timings as well as associated carbon dynamics of tundra ecosystems. Here we use remotely-sensed and ground-based datasets and model results embedding snowmelt timing in phenology at seven tundra flux tower sites in Alaska during 2001–2018, showing that the carbon response to early greenup or delayed snowmelt varies greatly depending upon local climatic limits. Increases in net ecosystem productivity (NEP) due to early greenup were amplified at the higher latitudes where temperature and water strongly colimit vegetation growth, while NEP decreases due to delayed snowmelt were alleviated by a relief of water stress. Given the high likelihood of more frequent delayed snowmelt at higher latitudes, this study highlights the importance of understanding the role of snowmelt timing in vegetation growth and terrestrial carbon cycles across warming Arctic ecosystems. 
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