[Show abstract][Hide abstract] ABSTRACT: The low-energy electronic states and energy gaps of carbon nanocones in an electric field are studied using a single-p-band tight-binding model. The analysis considers five perfect carbon nanocones with disclination angles of 60°, 120°, 180°, 240° and 300°, respectively. The numerical results reveal that the low-energy electronic states and energy gaps of a carbon nanocones are highly sensitive to its geometric shape (i.e. the disclination angle and height), and to the direction and magnitude of an electric field. The electric field causes a strong modulation of the state energies and energy gaps of the nanocones, changes their Fermi levels, and induces zero-gap transitions. The energy-gap modulation effect becomes particularly pronounced at higher strength of the applied electric field, and is strongly related to the geometric structure of the nanocone.
[Show abstract][Hide abstract] ABSTRACT: Influences of temperature and Sn-Cu droplet's composition on reactive wettings of Cu(100), Cu(110), and Cu(111) surfaces were analyzed, by using molecular dynamics (MD) calculations. As a result, the spreading on Cu(110)(Cu(100)) has the fastest (slowest) wetting kinetics. A higher temperature or a diluter Cu content in the Sn-Cu alloy droplet results in a higher wettability. Moreover, this work has addressed a theory for positioning the interface separating the liquidus and solidus alloys in the spreading film to confirm the hypothesis that the reactive wetting will come to the end when the interface saturates with the temperature-dependent solidus weight fraction of Cu.
[Show abstract][Hide abstract] ABSTRACT: The mechanical behavior of multi-walled carbon nanotubes (MWNTs), being fixed at both ends under uniaxial tensile loading, is investigated via the molecular dynamics (MD) simulation with the Tersoff interatomic potential. It is found that Young's modulus of the MWNTs is in the range between 0.85 and 1.16 TPa via the curvature method based on strain energy density calculations. Anharmonicity in the energy curves is observed, and it may be responsible for the time-dependent properties of the nanotubes. Moreover, the number of atomic layers that is fixed at the boundaries of the MWNTs will affect the critical strain for jumps in strain energy density vs. strain curves. In addition, the boundary conditions may affect “yielding” strength in tension. The van der Waals interaction of the double-walled carbon nanotube (DWNT) is studied to quantify its effects in terms of the chosen potential.
Full-text · Article · Feb 2010 · Physica E Low-dimensional Systems and Nanostructures
[Show abstract][Hide abstract] ABSTRACT: Motivated by recent experimental works on the modifications of endomorphin-2 (EM2, H-Tyr-Pro-Phe-Phe-NH2) to develop better painkiller, we performed structure-activity-relationship (SAR) studies to investigate modified C-terminal ligands by using molecular dynamics (MD) simulations. Specifically, instead of the CONH2 for the unmodified EM2's C-terminus, the analogue 2 with its C-terminus being CONHNH2 and analogue 3 with its C-terminus being COOMe are studied. First, a systematic conformer search was performed via the quantum chemical AM1 calculations. The cis/trans isomers of the lowest energy were hence selected as MD initial structures. We further showed that EM2s in water exhibited similar dihedral angles to those in DMSO, obtained from the NMR experiment. This similarity indicates the reliability of our MD simulations, and enables us to discuss related bioactivity. Our results showed that the interactions of the Tyr(1)-Phe(3) pair for cis-/trans-EM2s played a considerable role for structural stability. Furthermore, we utilized the chi(1) rotamers of individual aromatic side chains to examine the structural bioactivity. It is shown that this criterion to determine the conformational bioactivity toward mu-opioid receptor (MOR) is insufficient. Thus, we have further employed rotamer-combination approaches to examine the characteristics of SAR for cis-/trans-EM2s. Our results suggested that the bioactive chi(1) rotamers for Tyr(1)-Phe(3) pair remained to favor the [trans-trans] status for MOR selectivity. Therefore, based on the analysis of the chi(1) rotamers, it is suggested that the analogue 2 exhibit greater structural bioactivity for MOR than the analogue 3, and both of them be greater than unmodified EM2 for trans isomers.
No preview · Article · Oct 2008 · Journal of molecular graphics & modelling
[Show abstract][Hide abstract] ABSTRACT: Abstract. Deep nanoindentation of a copper substrate by single-walled carbon nanotubes (SWCNTs) has been analyzed using molecular dynamics simulations. Three categories of SWCNTs and their relationship with temperature and nanotube length have been extensively investigated. The results of this comprehensive quantitative analysis for deep indentation demonstrate that only SWCNTs with relatively short lengths can indent into a substrate up to a desired depth without buckling. Most notably, a permanent hollow hole with a high aspect ratio will be produced on the copper substrate, while copper atoms in close proximity to the hole are only slightly disordered.
[Show abstract][Hide abstract] ABSTRACT: The low-energy electronic properties of a few graphite layers with AA
and ABC stacking under application of the electric field (F),
perpendicular to the layers, are explored through the tight-binding
model. They strongly depend on the interlayer interactions, the stacking
sequences, the layer numbers, and the field strength. In the absence or
presence of F, the AA-stacked N-layer graphites (N=3 and 4) exhibit the
linear bands near the Fermi energy. The interlayer interactions and
electric field chiefly shift the Fermi momenta and the state energies.
The ABC-stacked N-layer graphites are characterized by the complicated
low-energy bands due to the stacking effect, on which F has a great
influence—the change of the state energies and the subband
spacing, the opening of a band gap, the production of the oscillating
bands, and the increase of the band-edge states. As a result, the two
kinds of special structure, whose positions and heights are modulated by
F, are found in the density of states (DOS) in contrast to the
featureless DOS of the AA systems. The comparison with the AB-stacked
few-layer graphites is also made.
No preview · Article · Feb 2007 · Journal of the Physical Society of Japan
[Show abstract][Hide abstract] ABSTRACT: Electronic states of carbon tori in electric and magnetic fields are studied by the tight-binding model with the curvature effect. Electronic properties, such as electronic states, energy gaps, and density of states, are very sensitive to the changes in the direction and the magnitude of the external fields. The electric field can widen the � -electron energy width; furthermore, there are more low- and extreme- energy states. Energy gaps are drastically modulated by E. The zero-gap transition (Eg 6¼ 0 ! Eg ¼ 0) happens more frequently when E deviates from the symmetric axis, or its magnitude is sufficiently large. The electric field could change the state degeneracy. Moreover, the modulation of electronic states is enhanced by the magnetic field.
No preview · Article · Oct 2006 · Journal of the Physical Society of Japan
[Show abstract][Hide abstract] ABSTRACT: The π-electronic excitations are studied for the AA- and AB-stacked bilayer graphites within the linear self-consistent-field approach. They are strongly affected by the stacking sequence, the interlayer atomic interactions, the interlayer Coulomb interactions, and the magnitude of the transferred momentum. However, they hardly depend on the direction of the transferred momentum and the temperature. There are three low-frequency plasmon modes in the AA-stacked system but not the AB-stacked system. The AA- and AB-stacked plasmons exhibit the similar π plasmons. The first low-frequency plasmon behaves as an acoustic plasmon, and the others belong to optical plasmons. The bilayer graphites quite differ from the monolayer graphite and the AB-stacked bulk graphite, such as the low-frequency plasmons and the small-momentum π plasmons.
No preview · Article · Aug 2006 · Physical Review B
[Show abstract][Hide abstract] ABSTRACT: In the presence of a perpendicular electric field, the low-energy electronic properties of the AB-stacked N-layer graphites with layer number N = 2, 3, and 4, respectively, are examined through the tight-binding model. The interlayer interactions, the number of layers, and the field strength are closely related to them. The interlayer interactions can significantly change the energy dispersions and produce new band-edge states. Bi-layer and four-layer graphites are two-dimensional semimetals due to a tiny overlap between the valence and conduction bands, while tri-layer graphite is a narrow-gap semiconductor. The electric field affects the low-energy electronic properties: the production of oscillating bands, the cause of subband (anti)crossing, the change in subband spacing, and the increase in band-edge states. Most importantly, the aforementioned effects are revealed completely in the density of states, e.g. the generation of special structures, the shift in peak position, the change in peak height, and the alteration of the band gap.
[Show abstract][Hide abstract] ABSTRACT: This paper uses a Tersoff potential molecular dynamics simulation to investigate the interaction between C60 molecules and a diamond substrate. The influence of the C60 molecule incident energy upon the bonding preference, i.e. sp3, sp2, sp or s is investigated. The current results reveal that the coating ratio actually increases rather than decreases as the incident energy of the C60 molecules is increased from 80 to 100 eV. Investigation of the transient structural variation of the C60 molecules shows that the additional increase in the bonding probability noted at an incident energy of 100 eV arises mainly from the changing of the structure from an s structure into an sp2 structure. The steady structure statistical analysis results show that the original sp2 structure of the C60 molecules gradually transforms to an sp structure as the incident energy is increased from 1 to 40 eV. Furthermore, the existence of an s structure is identified at incident energies greater than 30 eV. Finally, it is observed that the impact of C60 molecules on the diamond substrate seldom results in the formation of an sp3 structure.
[Show abstract][Hide abstract] ABSTRACT: This article employs a molecular dynamics (MD) simulation approach to investigate the influence of beveled angles on the filling mechanisms of a dual damascene process. The objective of the present study is to propose a method that overcomes the problem of incomplete via filling associated with the traditional dual damascene process. The simulation incorporates three separate MD models, namely the dual via model, the deposition model, and the potential model. Furthermore, the simulation adopts the thermal control layer marching algorithm to increase the accuracy of the solution and to reduce the computational time. The present results indicate that the introduction of beveled angles at the upper via corners has a detrimental impact upon the filling of the lower via at moderately low via-radius ratios (1.75, 2.0). At a via-radius ratio of 1.75, the filling morphology changes from one-of complete filling to one with trapped voids within the via when beveled angles are introduced, while at the slightly larger via-radius ratios of 2.0 and 2.5, the voids in the lower via are observed to grow in size. It is noted that the influence of beveled angles at the upper via corners on the lower via filling becomes less significant as the via-radius ratio increases (2.5, 3.0). In general, it is found that the introduction of beveled angles at the lower via corners is beneficial to the filling coverage of the lower via, but has no impact upon the filling of the upper via. (C) 2003 American Vacuum Society.
No preview · Article · Nov 2003 · Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
[Show abstract][Hide abstract] ABSTRACT: This paper presents the use of molecular dynamics (MD) in simulating thin-film growth on giant magnetoresistance corrugated structures. The simulation model mainly concerns the deposition of Co atoms on a V-shape Cu substrate. The many-body, tight-binding potential model is utilized in the MD simulation to represent the interatomic force that exists between the atoms. The interface width is used to quantify the variation of surface roughness at the transient and steady states. The paper investigates the influence of incident energy on the deposited film surface property and on the growing mechanism, for both vertical and oblique deposition. The results demonstrate how the growing characteristics are influenced by different incident energies and by different deposition directions. It is found that at relatively low incident energies the film growth tends to be in a three-dimensional cluster mode and that a void track is formed, whose growing direction is almost equal to the surface normal to the two inclined surfaces. The uneven thickness found along the base of the V shape is mainly due to the deposited atoms that accumulate at the bottom of the V groove when the incident energy is at a relatively high level. It is found that there exists an optimal incident energy that produces the, best film surface property. The film surface property can be improved by changing the incident direction relative to the two inclined directions of ±45°. Smaller deviation angles yield better film surface properties for low incident energy. Conversely, higher levels of incident energy result in worse film surface properties.
[Show abstract][Hide abstract] ABSTRACT: The entry flow induced by an applied electrical potential through microchannels between two parallel plates is analyzed in this work. A nonlinear, two-dimensional Poisson equation governing the applied electrical potential and the zeta potential of the solid–liquid boundary and the Nernst–Planck equation governing the ionic concentration distribution are numerically solved using a finite-difference method. The applied electrical potential and zeta potential are unified in the Poisson equation without using linear superposition. A body force caused by the interaction between the charge density and the applied electrical potential field is included in the full Navier–Stokes equations. The effects of the entrance region on the fluid velocity distribution, charge density boundary layer, entrance length, and shear stress are discussed. The entrance length of the electroosmotic flow is longer than that of classical pressure-driven flow. The thickness of the electrical double layer (EDL) in the entry region is thinner than that in the fully developed region. The change of velocity profile is apparent in the entrance region, and the axial velocity profile is no longer flat across the channel height when the Reynolds number is large.
Full-text · Article · Dec 2001 · Journal of Colloid and Interface Science
[Show abstract][Hide abstract] ABSTRACT: The effects of soluble surfactant on the dynamic rupture of thin liquid films are investigated. A nonlinear coupling evolution equation is used to simulate the motion of thin liquid films on free surfaces. A generalized Frumkin model is adopted to simulate the adsorption/desorption kinetics of the soluble surfactant between the surface and the bulk phases. Numerical simulation results show that the liquid film system with soluble surfactant is more unstable than that with insoluble surfactant. Moreover, a generalized Frumkin model is substituted for the Langmuir model to predict the instability of liquid film with soluble surfactant. A numerical calculation using the generalized Frumkin model shows that the surfactant solubility increases as the values of parameters of absorption/desorption rate constant (J), activation energy desorption (nu(d)), and bulk diffusion constant (D(1)) increase, which consequently causes the film system to become unstable. The surfactant solubility decreases as the rate of equilibrium (lambda) and interaction among molecules (K) are increased, which therefore stabilizes the film system. On the other hand, an increase of relative surface concentration (the index of a power law), beta(n), will initially result in a decrease of corresponding shear drag force as beta and n increase from 0 to 0.3 and 0.85, respectively. This will enhance the Marangoni effect. However, a further increase of beta and n to greater than 0.3 and 0.85, respectively, will conversely result in an increase of the corresponding shear drag force. This will weaken the Marangoni effect and thus result in a reduction of interfacial stability. Copyright 2000 Academic Press.
No preview · Article · Dec 2000 · Journal of Colloid and Interface Science
[Show abstract][Hide abstract] ABSTRACT: Effects of electromagnetic retardation on the rupture process of a very thin liquid film coated on a flat plate are studied. The analysis results indicate that the electromagnetic retardation effect (D) for the case A > 0 (attraction) is a stabilization factor, which prolongs the rupture time. The wavenumber of the most unstable mode is decreasing as D increases. It is also found that the linear solution of rupture time T(LM) is larger than the nonlinear rupture time T(NM), but the gradient of T(LM) to D is comparable to that of T(NM). Copyright 1999 Academic Press.
No preview · Article · Dec 1999 · Journal of Colloid and Interface Science
[Show abstract][Hide abstract] ABSTRACT: Molecular-dynamics simulations were used to investigate the spreading of nonvolatile liquid drops in a solid corner formed by two planar substrates. To understand the effect of the corner on the spreading, liquid drops in a corner with angles of 45 degrees, 90 degrees, and 135 degrees as well as on a flat substrate were examined. Both the solid substrate and the liquid drop were modeled using the Lennard-Jones interaction potential in the present study. Simulation results show that the mass center of the liquid molecules migrated towards the corner as time evolved and the spreading rate increased as the corner angle decreased. It is found that the variation of the mean spreading area with time can be described by a general relation of A(t) approximately t, which is in agreement with results obtained by other investigators. The distribution of liquid atoms per unit normalized corner degree shows a similar trend for different corner angles.
Preview · Article · Dec 1999 · Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics
[Show abstract][Hide abstract] ABSTRACT: A process of nonlinear three-dimensional rupture of thin liquid films is numerically analyzed for the first time. With the rupture time being successfully calculated, it has been possible to develop a more complete rupture theory for thin liquid films. In contrast to the linear analysis indicating the shortest rupture time of thin liquid films to be the same for both two- and three-dimensional rupture, the nonlinear analysis reveals that the latter proceeds faster than the former. In particular, among all three-dimensional disturbance modes, the symmetric one makes the thin liquid films rupture fastest. It is concluded that the rupture process develops at a point rather than along a line on thin liquid films.
No preview · Article · Jul 1997 · Journal of Colloid and Interface Science