Visualization of Nanostructures

Summary:

Nanostructure modeling is the computation of the positions and orbitals of atoms in arbitrary nanostructures. Our visualizations provide a detailed view of the structures and the atomic scale variation of the calculated nanostructure properties.  

Accurate atomic-scale quantum theory of nanostructures and nanosystems fabricated from nanostructures enable precision metrology of these nanosystems and provides the predictive, precision modeling tools needed for engineering these systems for applications including advanced semiconductor lasers and detectors, single photon sources and detectors, biosensors, and nanoarchitectures for quantum coherent technologies such as quantum computing. The tight-binding model based upon the Linear Combination of Atomic Orbitals (LCAO) method provides an accurate atomistic theory for nanostructures.
 

Additional Technical Details:

The parallel modeling code outputs the positions of the atoms and the orbitals. Then the NanoVis tool uses multiple processes and shaders to keep the graphics at interactive frame rates, giving the researcher constant feedback, encouraging data exploration. Specifically, this tool utilizes the following two programs:

1. Visprep: a preprocessing program, reads atomic positions and associated orbital data, performs error checking and data analysis, and creates binary data files which can be quickly read by orbitalVisualization, the visualization program. This step needs to be performed only once per data set.
    
2. OrbitalVisualzation: reads the binary files into memory and starts two asynchronous background process: one that calculates which orbitals should be displayed based on the parameters of a selected geometric shape, and one that modifies the position and geometry of the selected shape. OrbitalVisualzation also creates several GUI's that control which orbitals are to be displayed and how they will be presented. Orbitals are of two types; P orbitals, which are axis aligned dumbbell shapes, and S orbitals, which are spherical. OrbitalVisualzation uses a set of graphic shader programs to create S and P orbital shapes and to dynamically determine which objects should be drawn; this allows a greater number of orbitals to be displayed than by using traditional graphics techniques. Using shaders, OrbitalVisualzation can represent an S orbital by a point, a P orbital by two points, and the orbital selection by a texture map, which drastically reduces the amount of data to pass to the graphics card.

Applications:

Modeling Quantum Dots: The optics of self-assembled quantum dots, also known as artificial atoms, has been studied using our parallelization. Such systems contain up to a million atoms and can only be studied using the parallel implementation. We show how nanomechanical strain can be used to dynamically reengineer the optics of these quantum dots, giving a tool to manipulate mechanoexciton shape, fine-structure splitting and optical transitions, transfer carriers between dots and interact qubits for quantum processing. Most importantly, nanomechanical strain pro vides both phase and energy control to modify the inner workings of excitons. These are all capabilities needed to use QDs in nanophotonics, quantum information processing, and in optically active devices, such as optomechanical cavities and semiconductor nanotubes.