Jenn-Sen Lin

A molecular dynamics study of the tensile behaviour of ultrathin gold nanowires

A molecular dynamics simulation of ultrathin gold nanowires for tensile behaviour has been carried out. Ultrathin nanowires, unlike the bulk FCC structure, have a multi-shell helical structure. This work compares the mechanical properties of the 7-1 multi-shell helical structure with those of the FCC structure. The results reveal that the temperature and the strain rate influence the yielding stress. One atom chain was detected before the nanowire broke when the temperature was near absolute zero. At room temperature, severe interaction between atoms caused successive yielding and a cluster of three atoms in cross-section was formed before the nanowire broke.

The effects of confinement on the behavior of water molecules between parallel Au plates of (001) planes

Molecular dynamics simulation is utilized to investigate the behavior of water molecules confined between two Au plates of (001) planes separated by gaps of 24.48, 16.32, 12.24, 11.22, and 10.20 A. The simulation results indicate that the arrangements of the water molecules are dependent on the gap size. For the largest gap size, adsorption of the Au surface creates two permanent water layers in the vicinity of each Au plate. Furthermore, in this case, the gap size is sufficiently large to permit the formation of a central region within which the water molecules are randomly oriented in a similar manner to bulk water molecules. The results indicate that the orientation of the first water layer directly absorbed by the plate surface does not change as the gap size between the two Au plates is reduced. However, the orientations of the O-H bonds in the second water layer parallel to the surface rearrange to form hydrogen bonds between the water layers as the separation between the plates is decreased. Finally, an inspection of the variation of the self-diffusion coefficients with the gap size suggests that the difference between the dynamic properties of the water molecules in the z direction and the x-y plane decreases as the distance between the two Au plates increases.

Mechanical Behavior of Single-Walled Carbon Nanotubes in Water under Tensile Loadings: A Molecular Dynamics Study

Abstract Molecular dynamics simulation was carried out to investigate the behavior of (5,5) and (10,10) armchair carbon nanotubes in water under tensile loading. The water molecules inside a nanoscale tube, unlike inside a bulk tube, have a confined effect. The local density distributions of oxygen and hydrogen atoms inside the carbon nanotubes were calculated to find the confinement effect. Moreover, the mechanical behavior of carbon nanotubes in water was studied under tensile loading. The results show that the Youngs modulus of nano-tubes in water remains the same as that in vacuum. However, the tensile stress of nanotube in water is less than that in vacuum.

An investigation into the magnetic properties of Co–Cu nanoparticles at different temperatures

This study employs molecular-dynamics simulations to predict the distribution function of diluted magnetic Co atoms in a Cu host and then uses the Weise mean-field theory and the Ruderman–Kittel–Kasuya–Yosida theory to calculate the magnetic properties of the Co–Cu alloys. Specifically, this study investigates the dependency of the nanoparticle magnetization on the Curie temperature for Co–Cu alloys with five different Co concentrations. The proposed method successfully overcomes the limitations of molecular-dynamics simulation in magnetic studies, for diluted systems at least.

Mechanical properties and thermal stability of ultrathin tungsten nanowires

The most stable structures of three ultrathin tungsten nanowires were predicted by the simulated annealing basin-hopping method (SABH) with the penalty algorithm. The predicted structures of tungsten nanowires indicate the tungsten nanowires at this small scale do not possess the B.C.C. configuration in bulk tungsten material. By molecular dynamics (MD) simulation, the mechanical properties including the Youngs modulus, yielding stress, and strength of these wires were determined by the tensile test after the analysis of the stress–strain profiles. Besides, in order to understand the feasibility of application of tungsten nanowire on nanodevices, the thermal stability of these ultrathin tungsten nanowires was also investigated at room temperature (300 K) by molecular dynamics (MD).

Planar Octagon Monopole Antenna for UWB Applications

A planar octagon monopole antenna for ultrawideband(UWB) application is proposed and experimentally studied. The proposed antenna has wide impedance bandwidth from 2.8 GHz to more than 10.7 GHz with better than -10 dB return loss. The design is demonstrated assuming FR4 substrate with a relative dielectric constant of 4.4 and thickness of 1.6 mm. The size of the antenna is 40 mm×50 mm. Details of the proposed antenna design and simulation results for UWB operations are presented and discussed.

Mechanical properties of PGA at different water fractions – a molecular dynamics study

The mechanical properties of polyglycolic acid (PGA) of different water weight fractions (1.7%, 2.9%, and 5%) were investigated by molecular dynamics (MD) simulation through a tensile test. The variation in the degree of crystallinity with water content was also investigated using XRD profiles. The Youngs modulus, mechanical strength, and fracture mechanism of all PGA–water systems were drawn from the corresponding stress–strain profiles. Furthermore, water diffusion behavior within the PGA matrix both before and after the tension test was also studied. The water diffusion coefficients were derived from the mean square displacements of all water molecules within the PGA matrix.

Printed octagon monopole UWB antenna with band-notch by modified U-shape slot

A planar octagon monopole UWB band-notched antenna is proposed and experimentally studied. It consists of an octagon patch with a modifed U-shaped notched, which intends to obtain frequency notched for WiMAX. The proposed antenna operates from 1.93 GHz to 11 GHz for return loss of less than -10dB with 5.26-6.4 GHz notched. The notch frequency of the proposed antenna can be adjusted by controlling the location of slot. The measured results are in reasonably good agreement with the simulated results. Details of the proposed antenna design and simulation results for UWB operations are presented and discussed.

Dynamic behaviour of multi-shell 14-7-1 gold nanowire under different axial tensile strains

The dynamic behaviour of a multi-shell 14-7-1 Au nanowire is investigated and compared with that of a 7-1 Au nanowire under various tensile strains. The molecular dynamics (MD) simulations performed in this study compute the frequency shift and change in intensity of the characteristic frequency peaks of the phonon density of states of the global and substructure atoms in the radial and axial directions. The results show that the frequency shift and intensity change of the characteristic frequency peaks in the strained 14-7-1 nanowire are caused by a change in the radial atomic coupling and a higher degree of structural anisotropy due to the applied strain.

The diffusion behavior and capacitance of tetraethylammonium/tetrafluoroborate ions in acetonitrile with different molar concentrations: a molecular dynamics study

A molecular dynamics (MD) simulation with the optimized potentials for liquid simulations-all atom (OPLS-AA) force field was carried out to investigate the dynamic behaviors of organic electrolyte molecules between a graphite cathode and anode. This study considered the tetraethylammonium cation (NEt4+) and tetrafluoroborate anion (BF4−) in acetonitrile (ACN) solvent. The predicted NEt4–BF4 solution density at 1 M from the MD isothermal–isobaric ensemble (NPT) is about 0.861 g cm−3, which is very close to the corresponding experimental value. This indicates that the OPLS-AA force field can accurately describe the interactions between these molecules. The detailed diffusion mechanism and the corresponding viscosity solution for different NEt4–BF4 mole fractions were explored. The charge density distribution of electrolyte molecules between the graphite cathode and anode from MD simulation was further used to obtain the potential drop by solving the Poisson equation and to obtain system capacitance. This study provides a method to determine the proper molar concentration of electrolyte NEt4–BF4 in ACN solution which can balance ionic conductivity and capacitance to enhance supercapacitor performance.