Jaemock Yi - Academia.edu (original) (raw)
Papers by Jaemock Yi
Applied Physics Letters, 2010
Ultrahigh resolution full-field transmission x-ray microscopy enabled us to observe detailed phen... more Ultrahigh resolution full-field transmission x-ray microscopy enabled us to observe detailed phenomena during the potentiostatic copper electrodeposition on polycrystalline gold. We detected two coexisting cluster populations with different sizes. Their growth behaviors are different, with a shape transitions only occurring for large clusters. These differences influence the micromorphology and general properties of the overlayer.
The fabrication of devices to focus hard x-rays is one of the most difficult-and important-challe... more The fabrication of devices to focus hard x-rays is one of the most difficult-and important-challenges in nanotechnology. Here we show that Fresnel zone plates combining 30 nm external zones and a high aspect ratio finally bring hard x-ray microscopy beyond the 30 nm Rayleigh spatial resolution level and measurable spatial frequencies down to 20-23 nm feature size. After presenting the overall nanofabrication process and the characterization test results, we discuss the potential research impact of these resolution levels. The nanofabrication of hard x-ray Fresnel zone plates (FZPs) is a very difficult task because of extreme and conflicting technical requirements We show here that by direct electron beam writing and a careful optimization of crucial processing parameters we obtained Au FZPs for >8 keV photon energy delivering a Rayleigh criterion spatial resolution of 29 nm in full-field imaging. Most important was the ad hoc adjustment of the duty cycle of the Au nanostructure t...
ASME 2011 9th International Conference on Fuel Cell Science, Engineering and Technology, 2011
ABSTRACT A greater understanding of nickel reduction-oxidation cycling (redox) mechanisms at the ... more ABSTRACT A greater understanding of nickel reduction-oxidation cycling (redox) mechanisms at the microstructural level can enhance SOFC performance and reliability. Transmission x-ray microscopy (TXM) provides several techniques for exploring oxidation states within SOFC electrode microstructure. X-ray nanotomography and full field x-ray absorption near edge structure (XANES) spectroscopy are new TXM techniques that have been applied in tandem to study samples of varying nickel (Ni) and nickel oxide (NiO) compositions. The imaged samples are treated as mock SOFC anodes containing distinct Ni and NiO regions. XANES spectra for the individual materials provide a basis for the processing and analysis of these mixed samples. Images of composite samples obtained using x-ray nanotomography are treated using numerical image processing steps including: scaling, tomographic reconstruction, and image alignment and subtraction. The distinct nickel and nickel oxide phases have been uniquely identified using full field XANES nanotomography. Applications to SOFC anodes are discussed.
Physical Review Letters, 2011
We show direct evidence that focused x rays enable us to merge polymer colloidal particles at roo... more We show direct evidence that focused x rays enable us to merge polymer colloidal particles at room temperature. This phenomenon is ascribed to the photochemical scission of colloids with x rays, reducing the molecular weight, glass transition temperature, surface tension, and viscosity of colloids. The observation of the neck bridge growth with time shows that the x-ray-induced colloid coalescence is analogous to viscoelastic coalescence. This finding suggests a feasible protocol of photonic nanofabrication by sintering or welding of polymers, without thermal damage, using x-ray photonics.
physica status solidi (a), 2007
The defect structure of Si 1-x Ge x wafers with 4% of germanium and their interfaces with Si wafe... more The defect structure of Si 1-x Ge x wafers with 4% of germanium and their interfaces with Si wafers were studied using white radiation topography and phase-sensitive radiography. The heterostructures were manufactured by direct bonding of Si 1-x Ge x and Si crystalline wafers made of bulk crystals that were grown by the Czochralski technique. In Si 1-x Ge x crystals, the segregations of Ge act as dislocation nucleation sites. In Si 1-x Ge x /Si bonded structures, the segregation of Ge as well as the accumulation of dislocations induce elastic strain and plastic deformation during high-temperature bonding annealing. With the topography-radiography combination, we are able not only to detect microcracks, indicating nonbonded areas, by radiography, but also to reveal dislocations and long-range strain fields by topography at the same time.
Optics Letters, 2011
Since its invention in 1930, Zernike phase contrast has been a pillar in optical microscopy and m... more Since its invention in 1930, Zernike phase contrast has been a pillar in optical microscopy and more recently in x-ray microscopy, in particular for low-absorption-contrast biological specimens. We experimentally demonstrate that hard-x-ray Zernike microscopy now reaches a lateral resolution below 30 nm while strongly enhancing the contrast, thus opening many new research opportunities in biomedicine and materials science.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
We introduce a new X-ray diffraction microscopy technique capable of coupling grain orientation w... more We introduce a new X-ray diffraction microscopy technique capable of coupling grain orientation with its spatial location in textured thin-films. The principle is based on the combination of X-ray topography with diffractometry. High-resolution X-ray diffractometry using a scintillation detector is utilized to measure orientational distribution of individual grains. Then X-ray topography using CCD system is applied to determine the spatial locations of the angularly resolved grains. The successful application is demonstrated for grain-on-grain epitaxial alignment between the film and the substrate in Y 2 O 3 /Ni. The feasibility and the limitations of the technique are discussed.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
ABSTRACT
Nanotechnology, 2004
Magnetic nanostructures are attracting tremendous interest as regards application in high-density... more Magnetic nanostructures are attracting tremendous interest as regards application in high-density data storage devices and magnetic fluids. We have prepared magnetic nanoparticles (∼7.5 nm) by x-ray irradiation of electroless solutions and furthermore have investigated their structural and magnetic properties. Interestingly, we find that the formation of these Ni nanoparticles occurs spontaneously, during the room temperature process, dominantly at electrolyte pH of 8.2. The hydrated electrons produced during the irradiation of electroless solution seem to play a decisive role in the spontaneous formation and growth of nanoparticles. The possible surface alloying and/or coating over these pure Ni cores occurs only upon longer irradiation of high-P-content solutions. This suggests a possible catalytic behaviour of these nano-Ni surfaces in relation to P counter-ions in the irradiated solutions. The magnetic properties of these 'as-received' particles have been studied using a vibrating sample magnetometer. The saturation magnetic moment per gram for the Ni particles is 9.38 emu g −1 , which is 17% of the saturation moment of bulk ferromagnetic Ni at room temperature; this can be attributed due to the size effect of these magnetic domains. The symmetric hysteresis loop about the zero-field axis showing negligible loop shift (H c ∼ 3-10 Oe) suggests that Ni particles are free from oxide layers.
Nanotechnology, 2008
The fabrication of devices to focus hard x-rays is one of the most difficult-and important-challe... more The fabrication of devices to focus hard x-rays is one of the most difficult-and important-challenges in nanotechnology. Here we show that Fresnel zone plates combining 30 nm external zones and a high aspect ratio finally bring hard x-ray microscopy beyond the 30 nm Rayleigh spatial resolution level and measurable spatial frequencies down to 20-23 nm feature size. After presenting the overall nanofabrication process and the characterization test results, we discuss the potential research impact of these resolution levels.
Applied Physics Letters, 2010
Ultrahigh resolution full-field transmission x-ray microscopy enabled us to observe detailed phen... more Ultrahigh resolution full-field transmission x-ray microscopy enabled us to observe detailed phenomena during the potentiostatic copper electrodeposition on polycrystalline gold. We detected two coexisting cluster populations with different sizes. Their growth behaviors are different, with a shape transitions only occurring for large clusters. These differences influence the micromorphology and general properties of the overlayer.
The fabrication of devices to focus hard x-rays is one of the most difficult-and important-challe... more The fabrication of devices to focus hard x-rays is one of the most difficult-and important-challenges in nanotechnology. Here we show that Fresnel zone plates combining 30 nm external zones and a high aspect ratio finally bring hard x-ray microscopy beyond the 30 nm Rayleigh spatial resolution level and measurable spatial frequencies down to 20-23 nm feature size. After presenting the overall nanofabrication process and the characterization test results, we discuss the potential research impact of these resolution levels. The nanofabrication of hard x-ray Fresnel zone plates (FZPs) is a very difficult task because of extreme and conflicting technical requirements We show here that by direct electron beam writing and a careful optimization of crucial processing parameters we obtained Au FZPs for >8 keV photon energy delivering a Rayleigh criterion spatial resolution of 29 nm in full-field imaging. Most important was the ad hoc adjustment of the duty cycle of the Au nanostructure t...
ASME 2011 9th International Conference on Fuel Cell Science, Engineering and Technology, 2011
ABSTRACT A greater understanding of nickel reduction-oxidation cycling (redox) mechanisms at the ... more ABSTRACT A greater understanding of nickel reduction-oxidation cycling (redox) mechanisms at the microstructural level can enhance SOFC performance and reliability. Transmission x-ray microscopy (TXM) provides several techniques for exploring oxidation states within SOFC electrode microstructure. X-ray nanotomography and full field x-ray absorption near edge structure (XANES) spectroscopy are new TXM techniques that have been applied in tandem to study samples of varying nickel (Ni) and nickel oxide (NiO) compositions. The imaged samples are treated as mock SOFC anodes containing distinct Ni and NiO regions. XANES spectra for the individual materials provide a basis for the processing and analysis of these mixed samples. Images of composite samples obtained using x-ray nanotomography are treated using numerical image processing steps including: scaling, tomographic reconstruction, and image alignment and subtraction. The distinct nickel and nickel oxide phases have been uniquely identified using full field XANES nanotomography. Applications to SOFC anodes are discussed.
Physical Review Letters, 2011
We show direct evidence that focused x rays enable us to merge polymer colloidal particles at roo... more We show direct evidence that focused x rays enable us to merge polymer colloidal particles at room temperature. This phenomenon is ascribed to the photochemical scission of colloids with x rays, reducing the molecular weight, glass transition temperature, surface tension, and viscosity of colloids. The observation of the neck bridge growth with time shows that the x-ray-induced colloid coalescence is analogous to viscoelastic coalescence. This finding suggests a feasible protocol of photonic nanofabrication by sintering or welding of polymers, without thermal damage, using x-ray photonics.
physica status solidi (a), 2007
The defect structure of Si 1-x Ge x wafers with 4% of germanium and their interfaces with Si wafe... more The defect structure of Si 1-x Ge x wafers with 4% of germanium and their interfaces with Si wafers were studied using white radiation topography and phase-sensitive radiography. The heterostructures were manufactured by direct bonding of Si 1-x Ge x and Si crystalline wafers made of bulk crystals that were grown by the Czochralski technique. In Si 1-x Ge x crystals, the segregations of Ge act as dislocation nucleation sites. In Si 1-x Ge x /Si bonded structures, the segregation of Ge as well as the accumulation of dislocations induce elastic strain and plastic deformation during high-temperature bonding annealing. With the topography-radiography combination, we are able not only to detect microcracks, indicating nonbonded areas, by radiography, but also to reveal dislocations and long-range strain fields by topography at the same time.
Optics Letters, 2011
Since its invention in 1930, Zernike phase contrast has been a pillar in optical microscopy and m... more Since its invention in 1930, Zernike phase contrast has been a pillar in optical microscopy and more recently in x-ray microscopy, in particular for low-absorption-contrast biological specimens. We experimentally demonstrate that hard-x-ray Zernike microscopy now reaches a lateral resolution below 30 nm while strongly enhancing the contrast, thus opening many new research opportunities in biomedicine and materials science.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
We introduce a new X-ray diffraction microscopy technique capable of coupling grain orientation w... more We introduce a new X-ray diffraction microscopy technique capable of coupling grain orientation with its spatial location in textured thin-films. The principle is based on the combination of X-ray topography with diffractometry. High-resolution X-ray diffractometry using a scintillation detector is utilized to measure orientational distribution of individual grains. Then X-ray topography using CCD system is applied to determine the spatial locations of the angularly resolved grains. The successful application is demonstrated for grain-on-grain epitaxial alignment between the film and the substrate in Y 2 O 3 /Ni. The feasibility and the limitations of the technique are discussed.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005
ABSTRACT
Nanotechnology, 2004
Magnetic nanostructures are attracting tremendous interest as regards application in high-density... more Magnetic nanostructures are attracting tremendous interest as regards application in high-density data storage devices and magnetic fluids. We have prepared magnetic nanoparticles (∼7.5 nm) by x-ray irradiation of electroless solutions and furthermore have investigated their structural and magnetic properties. Interestingly, we find that the formation of these Ni nanoparticles occurs spontaneously, during the room temperature process, dominantly at electrolyte pH of 8.2. The hydrated electrons produced during the irradiation of electroless solution seem to play a decisive role in the spontaneous formation and growth of nanoparticles. The possible surface alloying and/or coating over these pure Ni cores occurs only upon longer irradiation of high-P-content solutions. This suggests a possible catalytic behaviour of these nano-Ni surfaces in relation to P counter-ions in the irradiated solutions. The magnetic properties of these 'as-received' particles have been studied using a vibrating sample magnetometer. The saturation magnetic moment per gram for the Ni particles is 9.38 emu g −1 , which is 17% of the saturation moment of bulk ferromagnetic Ni at room temperature; this can be attributed due to the size effect of these magnetic domains. The symmetric hysteresis loop about the zero-field axis showing negligible loop shift (H c ∼ 3-10 Oe) suggests that Ni particles are free from oxide layers.
Nanotechnology, 2008
The fabrication of devices to focus hard x-rays is one of the most difficult-and important-challe... more The fabrication of devices to focus hard x-rays is one of the most difficult-and important-challenges in nanotechnology. Here we show that Fresnel zone plates combining 30 nm external zones and a high aspect ratio finally bring hard x-ray microscopy beyond the 30 nm Rayleigh spatial resolution level and measurable spatial frequencies down to 20-23 nm feature size. After presenting the overall nanofabrication process and the characterization test results, we discuss the potential research impact of these resolution levels.