Forces that Drive the Self-assembly of Metallic Dots on Semiconductor Substrates
ABSTRACT The scaling and ordering of metallic nanoclusters on semiconductor substrates has been e... more ABSTRACT The scaling and ordering of metallic nanoclusters on semiconductor substrates has been explored computationally. Numerical techniques were implemented to calculate the total electrostatic and van der Waals energies for systems containing multiple disks. Observations show that interactions in charge clouds beneath the metallic disks led to an electrostatic repulsive force. Attraction was observed due to the van der Waals energy. An energy barrier exists for disk coalescence. This work suggests the potential of double layer charges in the development of large-scale nanodot systems that require precise control over both dot location and size.
The formation of designed nanocomposites by multiple layers of adsorbate molecules is studied. We... more The formation of designed nanocomposites by multiple layers of adsorbate molecules is studied. We consider the presence of two types of molecules in each layer, which are characterized by different dipole moments. The nanostructures are characterized by the non-uniform distribution of the two molecules. A phase field model is developed to simulate the molecular diffusion and patterning under the combined actions of dipole moments, intermolecular forces, entropy, and external electric field. The study reveals self-alignment, structure conformation and the possibility to reduce the domain sizes via a layer by layer approach. It is also shown that the structure in a layer may define the roadway for molecules to travel on top it. This combined with electrodes embedded in the substrate gives much flexibility to guide the molecular organization and fabrication of designed nanocomposites.
A novel computational method to determine the dynamics of a lipid bilayer vesicle in a viscous flow
ABSTRACT Models of lipid bilayer vesicle motion require that both the local area element of the i... more ABSTRACT Models of lipid bilayer vesicle motion require that both the local area element of the interface and the volume enclosed by the interface be conserved. Here we present a novel level-set computational method to predict the dynamics of a vesicle under the influence of an external viscous fluid. The fluid both inside and outside the vesicle is governed by the Navier-Stokes equations. We impose both the volume and area constraint by implementing a novel splitting scheme. Similar to standard pressure-correction methods for the Navier-Stokes equations, which require the velocity field to be divergence free, we solve a variable coefficient pressure-Poisson equation with Neumann boundary conditions to ensure volume conservation. We also impose the constraint that the velocity field must be divergence free on the moving interface. This necessitates the solution of an additional partial differential equation. This equation and the needed boundary conditions will be presented. Numerical examples of the scheme and convergence checks will also be presented.
A three-dimensional numerical model of vesicle electrohydrodynamics in the presence of DC electri... more A three-dimensional numerical model of vesicle electrohydrodynamics in the presence of DC electric fields is presented. The vesicle membrane is modeled as a thin capacitive interface through the use of a semi-implicit, gradient-augmented level set Jet scheme. The enclosed volume and surface area are conserved both locally and globally by a new Navier-Stokes projection method. The electric field calculations explicitly take into account the capacitive interface by an implicit Immersed Interface Method formulation, which calculates the electric potential field and the trans-membrane potential simultaneously. The results match well with previously published experimental, analytic and two-dimensional computational works.
Forces that Drive the Self-assembly of Metallic Dots on Semiconductor Substrates
ABSTRACT The scaling and ordering of metallic nanoclusters on semiconductor substrates has been e... more ABSTRACT The scaling and ordering of metallic nanoclusters on semiconductor substrates has been explored computationally. Numerical techniques were implemented to calculate the total electrostatic and van der Waals energies for systems containing multiple disks. Observations show that interactions in charge clouds beneath the metallic disks led to an electrostatic repulsive force. Attraction was observed due to the van der Waals energy. An energy barrier exists for disk coalescence. This work suggests the potential of double layer charges in the development of large-scale nanodot systems that require precise control over both dot location and size.
The formation of designed nanocomposites by multiple layers of adsorbate molecules is studied. We... more The formation of designed nanocomposites by multiple layers of adsorbate molecules is studied. We consider the presence of two types of molecules in each layer, which are characterized by different dipole moments. The nanostructures are characterized by the non-uniform distribution of the two molecules. A phase field model is developed to simulate the molecular diffusion and patterning under the combined actions of dipole moments, intermolecular forces, entropy, and external electric field. The study reveals self-alignment, structure conformation and the possibility to reduce the domain sizes via a layer by layer approach. It is also shown that the structure in a layer may define the roadway for molecules to travel on top it. This combined with electrodes embedded in the substrate gives much flexibility to guide the molecular organization and fabrication of designed nanocomposites.
A novel computational method to determine the dynamics of a lipid bilayer vesicle in a viscous flow
ABSTRACT Models of lipid bilayer vesicle motion require that both the local area element of the i... more ABSTRACT Models of lipid bilayer vesicle motion require that both the local area element of the interface and the volume enclosed by the interface be conserved. Here we present a novel level-set computational method to predict the dynamics of a vesicle under the influence of an external viscous fluid. The fluid both inside and outside the vesicle is governed by the Navier-Stokes equations. We impose both the volume and area constraint by implementing a novel splitting scheme. Similar to standard pressure-correction methods for the Navier-Stokes equations, which require the velocity field to be divergence free, we solve a variable coefficient pressure-Poisson equation with Neumann boundary conditions to ensure volume conservation. We also impose the constraint that the velocity field must be divergence free on the moving interface. This necessitates the solution of an additional partial differential equation. This equation and the needed boundary conditions will be presented. Numerical examples of the scheme and convergence checks will also be presented.
A three-dimensional numerical model of vesicle electrohydrodynamics in the presence of DC electri... more A three-dimensional numerical model of vesicle electrohydrodynamics in the presence of DC electric fields is presented. The vesicle membrane is modeled as a thin capacitive interface through the use of a semi-implicit, gradient-augmented level set Jet scheme. The enclosed volume and surface area are conserved both locally and globally by a new Navier-Stokes projection method. The electric field calculations explicitly take into account the capacitive interface by an implicit Immersed Interface Method formulation, which calculates the electric potential field and the trans-membrane potential simultaneously. The results match well with previously published experimental, analytic and two-dimensional computational works.
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Papers by David Salac