Hopping dynamics simulation and animation for silicon dangling bond devices.
Interactive simulation of the surface charge configurations. Charge dynamics are simulated using Hopping rate calculation from a choice of Hopping Models.
- Approximately real time simulation of surface configurations.
- Control of certain physical and modeling parameters (see Options Panel below).
- Automatic population control through surface-bulk(reservoir) hopping.
- Placement of doubly occupied perturbers during simulation.
- Integration of a simple STM tip model (In Progress)
- Clocking field generation.
| Key | Behaviour |
|---|---|
| Q | Close the animator (and compile the recording if enabled) |
| O | Open the options panel |
| P | Pause animation |
| T | When clocking, start a timer which automatically pauses the animation after a quarter phase. |
| S | Timestamped .png screenshot of display window (no sidepanel) to local directory |
| Shift + S | Timestamped .svg/.pdf screenshot of display window with capture presets. |
| Space | Advance the simulation one time step, somewhat deprecated. |
| - | Zoom out |
| + or = | Zoom in |
| E | Zoom extents |
| L | Start line-scan at current dimer row if tip channel included. |
| D | Detach GUI hook for Debug |
| Button | Behaviour |
|---|---|
| Left Click | Clicking any hydrogen site will add/remove a fixed charge at that location. |
| Right Click | Right clicking a DB will track its local potential on the options dialog. Re-click the same DB or a hydrogen site to end the tracking. |
| Middle Click | Panning |
| Control + Wheel | Zoom anchored at cursor. |
If the tip is enabled (see Tip Properties in Options Panel below), you are able to specify paths for the tip to follow. When first created, the tip will appear at the origin of the scene coordinates. Holding shift and left clicking will cause the tip to move to the clicked position at the current tip scan rate (changeable under Tip Properties).
There are currently two programmed paths:
- Line Scan: The L shortcut or Line button will start a line scan along the x axis that is as wide as your full device plus the Padding. This scan will occur on the nearest dimer row to the initial tip position.
- Full Scan: The Full button will perform a 2D raster scan over a rectangle containing the full device plus Padding on each side. The tip will device this region into Lines line scans.
These paths, and the manual paths described below, repeat. To stop the tip, you currently have to shift click.
If you hold control while shift clicking, it indicates a node along a multi-node path. You can continue to shift click, holding the control key, for as many points as you like. Once control is released, the tip will begin to trace the specified path.
The options panel offers a selection of parameter controls/views for debugging purposes. Details of slider controls can be found in the hover tooltips.
| Field | Context |
|---|---|
| DB-Beff | Local potential experience by targeted DB, see Right Click behaviour |
| Lifetime | Countdown for tracked DB. When the countdown runs out, the occupying charge will hop. |
| # electrons | Current number of electrons in the surface DBs. |
| Runtime Load | Percentage of time between frames used for simulating the surface state. If greater than 100%, the animation is no longer running in real time. |
| Animation Controls | |
| Viewer | See below |
| log(rate) | Changes the time step of the animator by 10^rate |
| Hopping Model | |
| lambda | Self trapping energy. At lambda=0, hopping models are calibrated to match the 1-2-2-1 results. |
| factor | Hopping rates are multiplied by 10^factor. Use instead of rate to increase just the hopping rates. |
| FRH | To increase performance, hops are only allowed within a certain range and cohopping only allowed from occupied DB pairs within a certain range. The FRH parameters change this range. |
| Bulk Properties | |
| mu | Chemical potential for utomatic population mechanism. This is effectively the energy difference between the Fermi level and the DB- state of an isolated DB. |
| Tip Properties | |
| Tip | If the Tip channel is included in the Hopping model, "Tip properties" and "Tip programs" will be available in the options |
| scale | Scales the tip influence, TIBB and ICIBB. Tip seems to be fairly well behaved for scale < 0.3 or so. |
| epsr | Relative permittivity for Coulomb interactions between DBs and image charges. Lower epsr will make ICIBB stronger |
| H | Tip height above the surface, in pm |
| ICIBB R | Tip radius for ICIBB (image charge localised near the point of the tip) |
| TIBB R | Tip radius for TIBB (blunt tip with long range contact potential influence) |
| rate | Tip scanning speed |
| Tip Programs | |
| Padding | Extra space added to the outside of line and full (2D raster) scans |
| Lines | Number of lines/rows in the full scan |
| Line | Start a line scan horizontally along the nearest row of atoms. |
| Full | Scan the tip over a region containing the full device. |
| Clocking Field | |
| Clocking | If the Clocking channel is incuded in the Hopping model, "Clocking Field" will be available in the options. The clock is a sinusoidal potential that travels to the right and effectively shifts the DB- level. |
| Frequency | Frequency of the clocking field |
| Amplitude | Amplitude of the clocking field, in eV |
| Offset | Offset of the clocking field, essentially equivalent to more mu |
| Flat Clock | Currently broken: essentially sets the wavelength to infinite. |
The Viewer is an additional tool which shows a representation of the device (currently collapsed onto the x axis). A well is drawn for each well with the black line indicating the energy of the DB- state and the green dots showing the current charge locations. For significant lambda, the dots will be noticeably lower than the DB- levels to indicate the self-trapping. If a DB is being tracked (see Right Click behaviour), blue lines will be shown for the possible hopping targets which indicate the effective energy level seen by the tracked charge. The tip will be shown if included with both radii shown and the apex indicated. Clearly insert figure here.
If there are ever fewer than 2 free DBs the cohopping implementation will throw an Error. Edit: 2018.05.02 Not sure if this still happens