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Surface Phenomena of Molecular Clusters by Molecular Dynamics Method
Maruyama, Shigeo,Matsumoto, Sohei,Ogita, Akihiro Korean Society of Marine Engineers 1996 한국마린엔지니어링학회지 Vol.20 No.3
Liquid droplets of water and argon surrounded by their vapor have been simulated by the milecular dynamics method. To explore the surface phenomena of clusters, each molecule is classified into 'liquid', 'surface', or 'vapor' with respect to the number of neighbor molecules. The contribution of a 'surface' molecule of the water cluster to the far infrared spectrum is almist the same as that of the 'liquid' molecule. Hence, the liquid-vapor interface is viewed as geometrically and temporally varying boundary of 'liquid' molecules with only a single layer of 'surface' molecules that might have different characteristics from the 'liquid' molecules. The time scale of the 'phase change' of each molecule is estimated for the argon cluster by observing the instantancous kinetic and potential energies of each molecule. To compare the feature of clusters with macroscopic droplets, the temperature dependence of the surface tension of the argon cluster is estimated.
Evaluation of a Phonon Mean Fee Path in Solid Thin Films by the Classical Molecular Dynamics
Soon-Ho CHOI,Shigeo MARUYAMA,Jung-Hye LEE,Kyung-Kun Kim 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.43 No.51
A non-equilibrium molecular dynamic (NEMD) study has been performed to evaluate the phonon mean free path (MFP) of a solid material. Solid argon with a Lennard-Jones (L-J) potential is selected as a simulation material. The thermal conductivity of a thin lm plays an important role in the design of nano-electro-mechanical systems (NEMS) or micro-electro-mechanical systems (MEMS) since heat removal from these devices is a crucial factor for their intended proper operations. The values calculated by using molecular dynamics (MD) simulations are compared with the available bulk experimental data when possible. It is conrmed that there is apparently a size eect on the thermal conductivity, which indicates that the microscale system has a lower thermal conductivity than that of the bulk material in the heat transfer direction. The dependence of the thermal conductivity on the system size is the result of a reduction in the phonon mean free path (MFP) as the system size becomes microscaled, and the MD simulations can be used to predict the phonon MFP of such a system.
Variations in the Thermal Conductivity of Insulating Thin Filmswith Temperature and Pressure
Soon-Ho Choi,Shigeo Maruyama 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
The thermal conductivity of a solid thin film was investigated by using two nonequilibrium molecular dynamics (NEMD) methods and changing the calculation conditions. Solid argon was selected as a target material because it has a typical Lennard-Jones (L-J) potential; hence, there was no need to consider the contribution by free electrons to a thermal conductivity. The results were not influenced by the adopted NEMD method, and there were no appreciable effects due to changes in the calculation conditions. The thermal conductivities calculated by using the MD simulations were compared with the available experimental data obtained from the bulk state, and the system's temperature and internal stress were confirmed to affect the thermal conductivity. From our investigation, the internal stress is explicitly an important factor that in uences the thermal conductivity of solids; a micro-scale system has a lower thermal conductivity than the bulk material does. The temperature dependence was also carefully investigated, and good qualitative agreement with existing experimental data was obtained.
Influence of Ion Sizeand Charge on Osmosis
Cannon, James,Kim, Daejoong,Maruyama, Shigeo,Shiomi, Junichiro AmericanChemical Society 2012 The journal of physical chemistry. B, Condensed ma Vol.116 No.14
<P>Osmosis is fundamental to many processes, such as inthe functionof biological cells and in industrial desalination to obtain cleandrinking water. The choice of solute in industrial applications ofosmosis is highly important in maximizing efficiency and minimizingcosts. The macroscale process of osmosis originates from the nanoscaleproperties of the solvent, and therefore an understanding of the mechanismsof how these properties determine osmotic strength can be highly useful.For this reason, we have undertaken molecular dynamics simulationsto systematically study the influence of ion size and charge on thestrength of osmosis of water through carbon nanotube membranes. Ourresults show that strong osmosis occurs under optimum conditions ofion placement near the region of high water density near the membranewall and of maintenance of a strong water hydration shell around theions. The results in turn allow greater insight into the origin ofthe strong osmotic strength of real ions such as NaCl. Finally, interms of practical simulation, we highlight the importance of avoidingsize effects that can occur if the simulation cell is too small.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2012/jpcbfk.2012.116.issue-14/jp2113363/production/images/medium/jp-2011-113363_0010.gif'></P>
Soon-Ho CHOI,Shigeo MARUYAMA,Jung-Hye LEE,Kyung-Kun KIM 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.44 No.2
The thermal boundary resistance (TBR) is still a challengeable subject since the mechanism to explain it quantitatively is not clear in spite of its importance. We perform a non-equilibrium molecular dynamics (NEMD) simulation to evaluate the TBR at an epitaxial solid interface composed of two dierent materials. Solid argon is selected as a simulation material since it is a non-conductor electrically, so the energy transportation is caused only by lattice vibration. The history to grasp the mechanism for the TBR is fairly long, and the various theories have been developed, such as an acoustic mismatch model (AMM), an acoustic impedance mismatch model (AIMM), and a diuse mismatch model (DMM); however, no model has been successful in quantitatively analyzing the TBR. From this study, the mechanism of TBR can be explained as an energy re ection at an interface caused by the discontinuity of the acoustic impedance even in a microscale system. However, it should be modied to take microscale characteristics into consideration. The corrected microscale acoustic impedance mismatch model (CM-AIMM), which is developed in this study, fairly well predicts the TBR compared with any other existing models.
Carbon-sandwiched perovskite solar cell
Ahn, Namyoung,Jeon, Il,Yoon, Jungjin,Kauppinen, Esko I.,Matsuo, Yutaka,Maruyama, Shigeo,Choi, Mansoo The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.4
<P>Promising perovskite solar cell technology with soaring power conversion efficiencies has the common problems of low stability and high cost. This work provides a solution to these problems by employing a carbon sandwich structure, in which the fullerene bottom layer solves the stability issue and the carbon nanotube top electrode layer offers the merits of having high stability and being low-cost. Devices fabricated using different hole-transporting materials infiltrated into carbon nanotube networks were examined for their performance and stability under constant illumination in air. Polymeric hole-transporting layers show much higher stability when combined with carbon nanotubes due to their compact nature and stronger interaction with the carbon network. As a result, the encapsulated device showed high stability both in air and under light illumination, maintaining up to 80% of the initial efficiency after 2200 hours under actual operation conditions. Cost analysis also shows that using the polymeric hole-transporting materials in carbon nanotube films brings the fabrication cost down to less than 5.5% that of conventional devices. Our study proposes a promising cell structure toward highly stable and low-cost perovskite photovoltaic technologies for the future.</P>
Synthesis of single-walled carbon nanotubes using laser-vaporized metal nanoparticle catalyst
Masamichi Kohno,Teppei Kawahara,Masahiro Tomoda,Yasuyuki Takata,Shuhei Inoue,Shinzo Suzuki,Shigeo Maruyama 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.1
SWNTs were synthesized by laser-vaporized CCVD (catalytic chemical vapor deposition). The diameter distributions and the abundance of SWNTs synthesized at different temperatures and using different catalysts were investigated by Raman spectroscopy. Further,this technique was compared with other synthesis techniques (laser-oven and conventional-alcohol CCVD), and C_60 was synthesized simultaneously as a byproduct only using the laser-oven technique. With increasing synthesis temperature, the diameter distribution shifted towards larger diameters, and the G/D ratio became larger as the synthesis temperature increased to 1000°C. Ni, Co, and Fe played a catalytic role, though Fe was less effective under our experimental conditions. The diameter distribution of SWNTs synthesized with the Fe catalyst was shifted to smaller values compared to those synthesized with Ni or Co catalysts.
Optical anisotropy in single-walled carbon nanotubes.
Yoo, Seongwoo,Jung, Yongmin,Lee, Dong Soo,Han, Won-Taek,Oh, Kyunghwan,Murakami, Y,Edamura, T,Maruyama, Shigeo Optical Society of America 2005 Optics letters Vol.30 No.23
<P>Optical anistropy at optical communication wavelength was observed in films of vertically aligned single-walled carbon nanotubes (SWNTs). We report the control of both the polarization state and transmission of incoming light at 1550 nm by azimuthal and axial tilting of SWNT film about its aligned axis. The experiments reveal that the polarization state of light is susceptible to the azimuthal angle of the aligned direction of a SWNT having semiconductor characteristics and the intensity of the output beam after SWNT film shows cosine function dependence on the axial tilting angle.</P>