Sukbin Lee

• Ulsan National Institute of Science and Technology

We present the results of microstructural characterization of the polycrystalline yttrium iron garnet (YIG) during high temperature sintering. Three YIG samples, compacted from the calcined sol-gel powder, are annealed at 1400 °C for 350 min, 1050 min and 1750 min, respectively. During the annealing, the polycrystalline YIG coarsens via normal grai...

We explore the optimal condition for cylindrical core/shell hard-soft exchange-coupled magnetic nanostructures by obtaining full hysteresis loops for various geometries by obtaining full hysteresis loops for various geometrical variables, including the dimensional scale and soft/hard-magnetic phase volume ratio through micromagnetic simulations. Fo...

Tensile and compressive tests are carried out on four nanoporous gold samples with ligament sizes of 56, 149, 402, and 868 nm, all without grain boundaries and with similar number of ligaments regardless of ligament size. We find that tensile yield strengths are greater than compressive yield strengths up to ligament size of 402 nm, while yield str...

A two-dimensional Monte Carlo (MC) model is introduced for simulating the evolution of the pore on a bi-crystal grain boundary via grain boundary diffusion. Simulated pore shrinkage kinetics is found to be consistent with previously reported results over variable grain boundary diffusion rates and initial pore distances while the essential characte...

The coarsening of the two-phase, bi-continuous microstructure via surface diffusion is simulated using a three-dimensional Monte Carlo (MC) model. The coarsening exponent obtained from simulations initially decreases and then saturates at ~4 as the temperature increases. Kinetic analysis on nanoporous gold (np-Au) samples, annealed at 450 and 600 °...

Metal halide perovskites have been actively studied as promising materials in optoelectronic devices because of their superior optical and electrical properties, and have also shown considerable potential for flexible devices because of their good mechanical properties. However, the large hole injection barrier and exciton quenching between the per...

The mechanical flexibility of perovskite solar cells as well as high power conversion efficiency is attracting increasing attention. In addition to existing empirical approaches such as cyclic bending tests, in this study we report the tensile properties of the perovskite materials themselves. Measuring the tensile properties of free-standing perov...

Organic-inorganic hybrid perovskites have been investigated extensively for use in perovskite-based solar cells and light-emitting diodes (LEDs) owing to their excellent electrical and optical properties. Although the flexibility of perovskite LEDs has been studied through empirical methods such as cyclic bending tests, the flexibility of the perov...

We present a new comprehensive scheme for generating grain boundary conformed, volumetric mesh elements from a three-dimensional voxellated polycrystalline microstructure. From the voxellated image of a polycrystalline microstructure obtained from the Monte Carlo Potts model in the context of isotropic normal grain growth simulation, its grain boun...

We have performed molecular dynamics simulations to investigate the reaction characteristics of Ni–Al nanolayers by varying ignition temperature and bilayer thickness with three different compositions (1:1, 3:1, and 1:3) of Ni to Al. The overall sequence of reaction pathway was found to be unchanged by stoichiometry, but the reaction rate and the e...

The beneficial use of a hole transport layer (HTL) as a substitution for poly(3,4-ethlyenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is regarded as one of the most important approaches for improving the stability and efficiency of inverted perovskite solar cells. Here, we demonstrate highly efficient and stable inverted perovskite solar cel...

Nanoporous gold (np-Au) samples of ligament sizes 68.6, 248.6, 462.9, and 710.9 nm are prepared by heat treatment, and representative volumes are reconstructed by focused ion beam (FIB) tomography. The increase in relative density by thermal coarsening is not pronounced. We analyze the distribution of ligament size, surface-to-volume ratio, and sca...

The aging behavior and orientation relationships in Fe–31.4Mn–11.4Al–0.89C low-density steel were investigated with respect to constituent phases and precipitates, including γ-austenite matrix, β-Mn, and α-precipitate. After aging treatment at 550 °C for various periods of time, the microstructural changes and corresponding mechanical response were...

Organic-inorganic hybrid perovskites have emerged as a next-generation candidate for light-emitting device applications due to their excellent optical and electrical properties with narrow band emission compared to organic emitters. The morphological control of perovskite films with full surface coverage and few defect sites is essential for achiev...

Nanoindentation has been widely used to measure mechanical properties for instance elastic modulus and hardness due to relatively simple sample preparation and experimental procedure. Primary limitation of nanoindentation is that it does not measure quantitative mechanical properties such as yield strength, ultimate tensile strength and fracture st...

Output power of thermoelectric generators depends on device engineering minimizing heat loss as well as inherent material properties. However, the device engineering has been largely neglected due to the limited flat or angular shape of devices. Considering that the surface of most heat sources where these planar devices are attached is curved, a c...

Supplementary Figures 1-24 and Supplementary References.

The study of fatigue in metals, and fatigue initiation specifically, lends itself to analysis via an emerging set of characterization and modeling tools that describe polycrystals on the meso- or microstructural length scale. These include three-dimensional characterization techniques, elastic anisotropic and visco-plastic stress models, new approa...

A transmission-electron-microscope-based orientation mapping technique that makes use of beam precession to achieve near-kinematical conditions was used to map the phase and crystal orientations in nanolamellar Cu/Nb composites with average layer thicknesses of 86, 30 and 18 nm. Maps of high quality and reliability were obtained by comparing the re...

The present paper studies grain growth in the presence of inert particles by performing large-scale simulations using a parallel Monte Carlo Potts model. The effect of the second phase particles on the grain size distribution (GSD) is analyzed. The GSDs diverge markedly from log-normal distribution for normal grain growth case. For the cases with l...

Stereological analysis has been coupled with transmission electron microscope (TEM) orientation mapping to investigate the grain boundary character distribution in nanocrystalline copper thin films. The use of the nanosized (<5 nm) beam in the TEM for collecting spot diffraction patterns renders an order of magnitude improvement in spatial resoluti...

Computational and experimental methodologies are integrated into a novel combined technique to define microstructure design criteria and maximize the properties of rhombohedral Bi0.5Na0.4K0.1TiO3, from untextured (1 MRD), d33 = 155 pC/N, to textured (4.41 MRDs), d33 = 227 pC/N. Two-dimensional orientation maps obtained using electron backscatter di...

The evolution of grain size and shape as well as type and frequency of grain boundary structures during thermal annealing of lamellar diblock copolymer microstructures is established using large area image reconstruction and analysis. Grain coarsening is found to proceed via an initial transient stage that is characterized by the rapid relaxation o...

A preliminary investigation into the microstructural factors potentially associated with fatigue crack initiation along coherent twin boundaries in the nickel-based superalloy LSHR is presented. Cracks appear to initiate predominantly along twin boundaries. Electron Back Scatter Diffraction (EBSD) maps, coupled with calculations of the local elasti...

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

We present a method for characterizing the full five parameter heterophase interface character distributions (HICD) using two-dimensional electron back-scatter diffraction (EBSD) images. We apply the HICD method to determine the orientation relationships and three-dimensional normal vectors of Cu–Nb interfaces in both physical vapor-deposited (PVD)...

We report the recent development of a 3D orientation data post-processing software, which we refer to as QUBE. Amongst other functionalities, it offers the possibility to specify the spatial and orientational distribution of boundary normals. We describe a method to reconstruct a voxel-accurate and smooth 3D boundary triangle mesh by algorithmic me...

IntroductionMethods Results & DiscussionConclusions

Three-dimensional electron backscatter diffraction data, obtained by serial sectioning a nickel–base superalloy, has been analysed to measure the geometric arrangement of grain boundary planes at triple junctions. This information has been used to calculate the grain boundary character distribution (GBCD) and the grain boundary energy distribution...

Three-dimensional electron backscattered diffraction data from a nickel-base super alloy has been analyzed to measure the geometric arrangement of grain boundary planes at triple junctions. This information has been used to calculate the grain boundary character distribution (GBCD) and the grain boundary energy distribution (GBED). The twin content...

The von Neumann-Mullins relation has been extended to higher dimensions by MacPherson and Srolovitz. Their exact solution relates the rate of volume change of ail individual grain in a 3-dimensional isotropic polycrystal to its mean width and total length of triple lines (assuming isotropic boundaries). The objective of this study is to verify that...

A viscoplastic approach using the Fast Fourier Transform (FFT) method for obtaining local mechanical response is utilized to study microstructure–property relationships in composite materials. Specifically, three-dimensional, two-phase digital materials containing isotropically coarsened particles surrounded by a matrix phase, generated through a K...

An efficient digital FFT-based viscoplastic method was applied to calculating the viscoplastic stress-strain response on a 3D image of a serial sectioned nickel alloy. A single strain step under uniaxial tensile loading was calculated using crystal plasticity. Analysis of the results indicated higher stresses near grain boundaries than in the bulk...

A fast Fourier transform (FFT) based full-field formulation for viscoplastic polycrystals was applied to the analysis of subgrain texture evolution in both interstitial free (IF) and dual phase (DP) steels during biaxial deformation. An image measured by electron back-scattering diffraction (EBSD)-based orientation imaging microscopy (OIM) was used...

of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

The theory by MacPherson and Srolovitz provides an exact prediction of the growth rate of individual cells or grains in a space-filling network (microstructure). Testing the predictions of the theory requires measurement of mean width and edge lengths where three cells meet at triple line junctions. This is most easily accomplished in networks that...

In studying microstructure-property relationships, it is of great interest to reveal the effect of individual microstructural parameters on the properties of the materials in all three dimensions. However, it is not easy to obtain experimentally samples in which the individual microstructural features are independently controlled. Even though one c...

Coarsening of particles during liquid phase sintering is known to be an example of Ostwald ripening. This coarsening process, in a fully wetting system, is simulated in three dimensions with a kinetic Monte Carlo model. The results from the simulation for microstructures, kinetics and particle size distributions are compared to available experiment...

A new method for reconstructing a three-dimensional microstructure using the focused ion beam-orientation imaging microscopy (FIB-OIM) is introduced. The technique is important for the study of three-dimensional microstructures of materials because it can automatically align (register) a series of parallel sections with both topological information...

The characterization of microstructures in three dimensions is re-viewed, with an emphasis on the use of automated electron back-scatter diffraction techniques. Both statistical reconstruction of poly-crystalline structures from multiple cross sections and reconstruction from parallel, serial sections are discussed. In addition, statistical re-cons...

The orientation texture of pulsed laser deposited hydroxyapatite coatings was studied by X-ray diffraction techniques. Increasing the laser energy density of the KrF excimer laser used in the deposition process from 5 to 7 J/cm(2) increases the tendency for the c-axes of the hydroxyapatite grains to be aligned perpendicular to the substrate. This p...

A three-dimensional, Potts model of liquid phase sintering in a system with full solid wetting is introduced to investigate the coarsening kinetics and microstructures associated with this process. Kinetic Monte Carlo simulation is used to probe coarsening dynamics and to obtain the properties of solid particles, including the volume of critical nu...

The orientation distribution of crystalline grains in calcium phosphate coatings produced by pulsed laser deposition was investigated using an X-ray pole-figure diffractometer. Increased laser energy density of a KrF excimer laser in the 4-7 J/cm2 range leads to the formation of hydroxyapatite grains with the c-axis preferentially aligned perpendic...

Many issues in forming are influenced to some degree by the internal structure of the material which is commonly referred to by the materials science community as microstructure. Although the term microstructure is commonly only thought of in the context of grain size, it more properly encompasses all relevant aspects of internal material structure...

Many issues in forming are influenced to some degree by the internal structure of the material which is commonly referred to by the materials science community as microstructure. Although the term microstructure is commonly only thought of in the context of grain size, it more properly encompasses all relevant aspects of internal material structure...

We outline a computational approach for the study of phase transformations in misfitting thin films and then investigate the kinetics of a transformation to assess the role of heterogeneous nucleation sites, formed in the vicinity of misfit dislocations, in the self-patterning of these systems. Both computer simulation and analytical methods are em...