Fine-Tunable Absorption of Uniformly Aligned Polyurea Thin Films for Optical Filters Using Sequentially Self-Limited Molecular Layer Deposition

Park, Yi-Seul,Choi, Sung-Eun,Kim, Hyein,Lee, Jin Seok American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.18

<P>Development of methods enabling the preparation of uniformly aligned polymer thin films at the molecular level is a prerequisite for realizing their optoelectronic characteristics as innovative materials; however, these methods often involve a compromise between scalability and accuracy. In this study, we have grown uniformly aligned polyurea thin films on a SiO2 substrate using molecular layer deposition (MLD) based on sequential and self-limiting surface reactions. By integrating plane polarized Fourier-transform infrared, Raman spectroscopic tools, and density functional theory calculations, we demonstrated the uniform alignment of polyurea MLD films. Furthermore, the selective-wavelength absorption characteristics of thickness controlled MLD films were investigated by integrating optical measurements and finite-difference time-domain simulations of reflection spectra, resulting from their thickness-dependent fine resonance with photons, which could be used as color filters in optoelectronics.</P>

Control over Alignment and Growth Kinetics of Si Nanowires through Surface Fluctuation of Liquid Precursor

Park, Yi-Seul,Jung, Da Hee,Lee, Jin Seok American Chemical Society 2016 Crystal Growth & Design Vol.16 No.12

<P>Control over alignment and growth kinetics of vertically aligned Si nanowire (v-SiNW) arrays, which were grown using chemical vapor deposition (CVD) via a metal catalyst-assisted vapor liquid solid (VLS) mechanism, was demonstrated by introducing a homemade bubbler system containing a SiCl4 solution as the Si precursor. Careful control over the bubbler afforded different amounts of SiCl4 supplied to the reactor. By varying the dipping depth (Dd) and tilting angle (Ta) of the bubbler, the SiCl4 precursor concentration would fluctuate to different degrees. The different SiCl4 concentrations afforded the fine-tuning of v-SiNW array properties like alignment and growth kinetics. The degree of alignment of v-SiNWs could be increased with large amounts of SiCl4, which was caused by slight shallow depth or gentle tilting of the SiCl4 solution in the bubbler due to an increasing degree of fluctuation and fluctuation area. The ability to control alignment and growth kinetics of v-SiNW arrays could be employed in advanced nanoelectronic devices.</P>

Annealed Au-Assisted Epitaxial Growth of Si Nanowires: Control of Alignment and Density

Park, Yi-Seul,Jung, Da Hee,Kim, Hyun Ji,Lee, Jin Seok American Chemical Society 2015 Langmuir Vol.31 No.14

<P>The epitaxial growth of 1D nanostructures is of particular interest for future nanoelectronic devices such as vertical field-effect transistors because it directly influences transistor densities and 3D logic or memory architectures. Silicon nanowires (SiNWs) are a particularly important 1D nanomaterial because they possess excellent electronic and optical properties. What is more, the scalable fabrication of vertically aligned SiNW arrays presents an opportunity for improved device applications if suitable properties can be achieved through controlling the alignment and density of SiNWs, yet this is something that has not been reported in the case of SiNWs synthesized from Au films. This work therefore explores the controllable synthesis of vertically aligned SiNWs through the introduction of an annealing process prior to growth via a Au-catalyzed vapor–liquid–solid mechanism. The epitaxial growth of SiNWs was demonstrated to be achievable using SiCl<SUB>4</SUB> as the Si precursor in chemical vapor deposition, whereas the alignment and density of the SiNWs could be controlled by manipulating the annealing time during the formation of Au nanoparticles (AuNPs) from Au films. During the annealing process, gold silicide was observed to form on the interface of the liquid-phase AuNPs, depending on the size of the AuNPs and the annealing time. This work therefore makes a valuable contribution to improving nanowire-based engineering by controlling its alignment and density as well as providing greater insight into the epitaxial growth of 1D nanostructures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2015/langd5.2015.31.issue-14/la503453b/production/images/medium/la-2014-03453b_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la503453b'>ACS Electronic Supporting Info</A></P>

Morphology Control of Single Crystalline Rutile TiO₂ Nanowires

Park, Yi-Seul,Lee, Jin-Seok Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.10

Nano-scaled metal oxides have been attractive materials for sensors, photocatalysis, and dye-sensitization for solar cells. We report the controlled synthesis and characterization of single crystalline $TiO_2$ nanowires via a catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) growth mechanism during TiO powder evaporation. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies show that as grown $TiO_2$ materials are one-dimensional (1D) nano-structures with a single crystalline rutile phase. Also, energy-dispersive X-ray (EDX) spectroscopy indicates the presence of both Ti and O with a Ti/O atomic ratio of 1 to 2. Various morphologies of single crystalline $TiO_2$ nano-structures are realized by controlling the growth temperature and flow rate of carrier gas. Large amount of reactant evaporated at high temperature and high flow rate is crucial to the morphology change of $TiO_2$ nanowire.

Synthesis of single-crystalline topological insulator Bi2Se3 nanomaterials with various morphologies

Park, Yi-Seul,Lee, Jin Seok Springer-Verlag 2014 JOURNAL OF NANOPARTICLE RESEARCH Vol.16 No.2

Morphology Control of Single Crystalline Rutile TiO_2 Nanowires

Yi-Seul Park,이진석 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.10

Nano-scaled metal oxides have been attractive materials for sensors, photocatalysis, and dye-sensitization for solar cells. We report the controlled synthesis and characterization of single crystalline TiO_2 nanowires via a catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) growth mechanism during TiO powder evaporation. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies show that as grown TiO_2 materials are one-dimensional (1D) nano-structures with a single crystalline rutile phase. Also, energy-dispersive X-ray (EDX) spectroscopy indicates the presence of both Ti and O with a Ti/O atomic ratio of 1 to 2. Various morphologies of single crystalline TiO_2 nano-structures are realized by controlling the growth temperature and flow rate of carrier gas. Large amount of reactant evaporated at high temperature and high flow rate is crucial to the morphology change of TiO_2 nanowire.

Intramolecular and Intermolecular Interactions in Hybrid Organic–Inorganic Alucone Films Grown by Molecular Layer Deposition

Park, Yi-Seul,Kim, Hyein,Cho, Boram,Lee, Chaeyun,Choi, Sung-Eun,Sung, Myung Mo,Lee, Jin Seok American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.27

<P>Investigation of molecular interactions in polymeric films is crucial for understanding and engineering multiscale physical phenomena correlated to device function and performance, but this often involves a compromise between theoretical and experimental data, because of poor film uniformity. Here, we report the intramolecular and intermolecular interactions inside the ultrathin and conformal hybrid organic inorganic alucone films grown by molecular layer deposition, based on sequential and self-limiting surface reactions. Varying the carbon chain length of organic precursors, which affects their molecular flexibility, caused intramolecular interactions such as double reactions by bending of the molecular backbone, resulting in formation of hole vacancies in the films. Furthermore, intermolecular interactions in alucone polymeric films are dependent on the thermal kinetics of molecules, leading to binding failures and cross -linking at low and high growth temperatures, respectively. We illustrate these key interactions and identify molecular geometries and potential energies by density functional theory calculations.</P>

Anisotropic Silicification of Nanostructured Surfaces by Local Liquid-Phase Deposition

Park, Yi-Seul,Kim, Gyuri,Lee, Jin Seok American Chemical Society 2019 Langmuir Vol.35 No.39

<P>Exploration of the bioinspired silicification of artificial scaffolds is crucial to understanding and engineering the hierarchically complex and elaborate three-dimensional (3D) frustules of diatoms, which have high porosity and mechanical stability with related gas diffusion and storage properties. Herein, we report on the bioinspired silicification of the nanostructured surfaces of hexagonally close-packed silica bead (hc-SB) arrays using a liquid-phase deposition (LPD) method. This process, governed by the kinetics of silicification, was controlled using the concentration of the reactants and the reaction temperature and monitored in real time using a quartz-crystal microbalance, which allowed the investigation of the silicification on the surface during the LPD reaction. These heterogeneous LPD reactions on hc-SB arrays were optimized to mimic natural 3D hierarchical structures. Anisotropic silicification of the nanostructures occurred owing to differences in the energy and local concentration of silicic acid on the nanostructured surface. A 3D hierarchical pore network was realized via a heterogeneous LPD reaction by controlling the size, location, and arrangement of the SBs. We believe that our silicification process on nanostructured surfaces can lead to great improvements in the bioinspired morphogenesis-based engineering of 3D hierarchical structures.</P> [FIG OMISSION]</BR>

Effect of chemically reduced graphene oxide on epoxy nanocomposites for flexural behaviors

Lee, Seul-Yi,Chong, Mi-Hwa,Park, Mira,Kim, Hak-Yong,Park, Soo-Jin 한국탄소학회 2014 Carbon Letters Vol.15 No.1

In this work, nanocomposites of epoxy resin and chemically reduced graphene oxide (RGO) were prepared by thermal curing process. X-ray diffractions confirmed the microstructural properties of RGO. Differential scanning calorimetry was used to evaluate the curing behaviors of RGO/epoxy nanocomposites with different RGO loading amounts. We investigated the effect of RGO loading amounts on the mechanical properties of the epoxy nanocomposites. It was found that the presence of RGO improved both flexural strength and modulus of the epoxy nanocomposites till the RGO loading reached 0.4 wt%, and then decreased. The optimum loading achieved about 24.5 and 25.7% improvements, respectively, compared to the neat-epoxy composites. The observed mechanical reinforcement might be an enhancement of mechanical interlocking between the epoxy matrix and RGO due to the unique planar structures.

Calcareous nannofossil biostratigraphy of North Pond area, Mid-Atlantic Ridge and its paleoenvironmental implication.

장이슬(Yi Seul Jang),이상헌(Sangheon Yi,),박영수(Young-Soo Park),김길영(Gil Young Kim) 대한지질학회 2014 지질학회지 Vol.50 No.3