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Joyanta K. Saha,Mohammad A. Matin,장지혜,장준경 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.4
Molecular dynamic simulations were performed to examine the wetting behavior of a graphite surface textured with nanoscale pillars. The contact angle of a water droplet on parallelepiped or dome-shaped pillars was investigated by systematically varying the height and width of the pillar and the spacing between pillars. An optimal inter-pillar spacing that gives the highest contact angle was found. The droplet on the dome-covered surface was determined to be more mobile than that on the surface covered with parallelepiped pillars.
Nanoscale Islands of the Self Assembled Monolayer of Alkanethiol
Joyanta K. Saha,장준경,양민오 대한화학회 2013 Bulletin of the Korean Chemical Society Vol.34 No.12
Molecular dynamics simulations were performed to study the structure and stability of a nanoscale selfassembled monolayer (SAM) of alkanethiol on a gold (111) surface. The tilt angle and orientational order of the alkyl chains in the SAM island were examined by systematically varying the size of the island. The chain length dependence of the SAM island was examined by considering alkanethiols containing 12, 16, 20, and 24 carbon atoms. The minimum diameter of SAM islands made from 1-tetracosanethiol, 1-ecosanethiol, 1- hexadecanethiol and 1-dodecanethiol were 2.29, 1.9, 4.7 and 4.76 nm, respectively. These set the ultimate resolution that can be patterned by soft nanolithography. As the length of alkanethiol increases, the SAM islands became more ordered in both orientation and conformation of the alkyl chains.
Small Size Limit to Self-Assembled Monolayer Formation on Gold(111)
Saha, Joyanta K.,Ahn, Yoonho,Kim, Hyojeong,Schatz, George C.,Jang, Joonkyung American Chemical Society 2011 The Journal of Physical Chemistry Part C Vol.115 No.27
<P>Using molecular dynamics simulations, we show that the minimum diameter of ordered self-assembled monolayer (SAM) structures of alkanethiols on Au(111) is 1.9 nm at room temperature. This presumably sets the ultimate resolution of the SAM patterns created by nanolithography. For SAMs larger than 1.9 nm, the tilt direction of the alkyl chain precesses around the center of the SAM. This precession changes direction on a time scale that increases from picoseconds to nanoseconds as the SAM size varies from 2 to 3 nm.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2011/jpccck.2011.115.issue-27/jp202564m/production/images/medium/jp-2011-02564m_0010.gif'></P>
Saha, Leton C.,Mian, Shabeer A.,Kim, Hyo-Jeong,Saha, Joyanta K.,Matin, Mohammad A.,Jang, Joon-Kyung Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.2
We investigated how temperature influences the structural and energetic dynamics of carbon nanotubes (CNTs) undergoing a high-speed impact with a Si (110) surface. By performing molecular dynamics simulations in the temperature range of 100 - 300 K, we found that a low temperature CNT ends up with a higher vibrational energy after collision than a high temperature CNT. The vibrational temperature of CNT increases by increasing the surface temperature. Overall, the structural and energy relaxation of low temperature CNTs are faster than those of high temperature CNTs.
Saha, Joyanta K.,Matin, Mohammad A.,Jang, Jihye,Jang, Joonkyung Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.4
Molecular dynamic simulations were performed to examine the wetting behavior of a graphite surface textured with nanoscale pillars. The contact angle of a water droplet on parallelepiped or dome-shaped pillars was investigated by systematically varying the height and width of the pillar and the spacing between pillars. An optimal inter-pillar spacing that gives the highest contact angle was found. The droplet on the dome-covered surface was determined to be more mobile than that on the surface covered with parallelepiped pillars.
Nanoscale Islands of the Self Assembled Monolayer of Alkanethiol
Saha, Joyanta K.,Yang, Mino,Jang, Joonkyung Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.12
Molecular dynamics simulations were performed to study the structure and stability of a nanoscale self-assembled monolayer (SAM) of alkanethiol on a gold (111) surface. The tilt angle and orientational order of the alkyl chains in the SAM island were examined by systematically varying the size of the island. The chain length dependence of the SAM island was examined by considering alkanethiols containing 12, 16, 20, and 24 carbon atoms. The minimum diameter of SAM islands made from 1-tetracosanethiol, 1-ecosanethiol, 1-hexadecanethiol and 1-dodecanethiol were 2.29, 1.9, 4.7 and 4.76 nm, respectively. These set the ultimate resolution that can be patterned by soft nanolithography. As the length of alkanethiol increases, the SAM islands became more ordered in both orientation and conformation of the alkyl chains.
Effects of Temperature and Chain Length on the Nanoscale Islands of Alkanethiol Monolayers
Joyanta K. Saha,Arindam Sannyal,Sharif Md. Khan,장준경 대한화학회 2017 Bulletin of the Korean Chemical Society Vol.38 No.7
The thermal effect on the stability of nanoscale islands of alkanethiols on a gold (111) surface was examined using molecular dynamics simulation. To examine the chain length and temperature dependence, islands made of alkanethiols containing 16, 20, and 24 carbon atoms were simulated at 313–343 K. By analyzing the tilt angle, conformation, orientational order, and backbone plane orientation of alkyl chains, the minimum diameters for stable islands made of 1-hexadecanethiol, 1-ecosanethiol, and 1-tetracosanethiol were determined for different temperatures (313–343 K). These results provide a useful guideline for patterning nanopatterns of thiol by soft nanolithography.
Leton C. Saha,Shabeer A. Mian,김효정,Mohammad A. Matin,Joyanta K. Saha,장준경 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.2
We investigated how temperature influences the structural and energetic dynamics of carbon nanotubes (CNTs) undergoing a high-speed impact with a Si (110) surface. By performing molecular dynamics simulations in the temperature range of 100 - 300 K, we found that a low temperature CNT ends up with a higher vibrational energy after collision than a high temperature CNT. The vibrational temperature of CNT increases by increasing the surface temperature. Overall, the structural and energy relaxation of low temperature CNTs are faster than those of high temperature CNTs.
Drying Transition of Water Confined between Hydrophobic Pillars
Kim, Hyojeong,Saha, Joyanta K.,Jang, Joonkyung American Chemical Society 2012 The Journal of Physical Chemistry Part C Vol.116 No.36
<P>The phase behavior of the water confined between hydrophobic pillars was studied by using a simple thermodynamic theory and the lattice gas Monte Carlo simulation. The drying transition of water with decreasing spacing between pillars is related to the Wenzel (WZ) to Cassie–Baxter (CB) transition of droplet. Our theory agrees with simulation for pillars with heights ranging from 11 to 100 nm. The present theory further predicts that sufficiently large circular pillars cannot sustain a CB state even if the pillars are in contact with each other.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2012/jpccck.2012.116.issue-36/jp302102k/production/images/medium/jp-2012-02102k_0009.gif'></P>
Molecular Dynamics Study on the Self-Assembled Monolayer Grown from a Droplet of Alkanethiol
Kim, Hyojeong,Saha, Joyanta K.,Zhang, Zhengqing,Jang, Jihye,Matin, Mohammad A.,Jang, Joonkyung American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.20
<P>Direct-write lithography, where a nanoscale tip or a stamp serves as a molecular source, is used widely to fabricate self-assembled monolayers (SAMs), nanometers in size. The spatially narrow deposition of molecules creates a droplet, which then spreads to form an ordered SAM. Currently, the dynamics and mechanism for this spreading are largely unknown. Herein, the evolution of a droplet of 1-octadecanethiol into a circular island of SAM, where the sulfur atoms and alkyl chains are densely and orderly packed, was examined by using molecular dynamics simulations. The packing of sulfur atoms preceded the alignment and packing of alkyl chains. The SAM islands resembled the bulk SAM, but it contained defects where the molecules were standing upside down on the surface. We found two mechanisms pertaining to the growth of a SAM island in the direct-write lithography. In the first mechanism, the molecules penetrated into the SAM islands by pushing away the molecules below. In the other mechanism, the molecules diffused, reached the periphery of the SAM islands, and slid down to the surface. The chemisorption of sulfur atoms made the present droplet spread more slowly than a droplet interacting nonspecifically with a surface. A droplet laterally moving across the surface was also simulated to gain insight into the growth of a SAM line. The alkyl chains of the SAM line were directed preferentially toward the line direction.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-20/jp502707d/production/images/medium/jp-2014-02707d_0011.gif'></P>