Patterning Of Dots Research Articles

Microfluidic ultramicroscale deposition and patterning of quantum dots

The ability to directly deposit materials in ultraminiaturized domains with nanoscale accuracycould play a central role in the realization of some forms of nanotechnology. In this reportwe demonstrate the direct deposition of quantum dots in patterns with ultramicroscale(1–15 µm) andnanoscale (<1 µm) features. Unlike bottom up approaches that require preconfigured patterning steps,this top down ‘direct write’ method should be amenable to the construction ofa large variety of patterns and features essentially ‘on the fly’. To accomplishthe direct writing/deposition of quantum dots we used a system that integrateshigh resolution motion control with microfabricated fluid delivery cartridges.This process is termed FEMTO (fluidics enhanced molecular transfer operation).The methodology demonstrated here may be extended to surface patterning anddeposition of a broad spectrum of other nanoscale materials and thereby createopportunities in a variety of fields ranging from microelectronics to bio/nanotechnology.

Analysis of Nanoscale Deformation in GaAs(100): Towards Patterned Growth of Quantum Dots

AbstractNanoindentations were created in the GaAs(100) surface to act as strain centers for the controlled nucleation and patterning of InAs quantum dots. A systematic approach is taken to understand the indent deformation processes that may lead to precision patterning capabilities for a broad range of nanostructures. Indents were generated using loads below 450 μN with a sharp cube corner indenter. Site-specific cross-sectional thinning of nanoindents (down to 100 nm in size) has been achieved using the in-situ ‘lift-out’ technique. This allowed for observation of subsurface deformation by transmission electron microscopy (TEM). The crystal was observed to deform solely by dislocation activity with no evidence of amorphization, twinning, fracture, or phase transformation. It is shown that the single phase deformation of GaAs can be well characterized and controlled, which should allow for exploitation of the dislocation strain field to bias nucleation of self-assembled quantum dots.

STM studies: spatial resolution limits to fit observations in nanotechnology

Atomically resolved Scanning Tunneling Microscopy (STM) images are nowadays currently obtained on flat surfaces without any special STM tip preparation. On the contrary, imaging of three-dimensional nanometer-scale objects exhibiting very much inclined facets, requires the use of STM tips with an appropriate geometry. The tip shape has to be controlled over the whole length that corresponds to the height of the object to be imaged. The cone angle of the tip has to be smaller than the tilt angle of the imaged facets. These criteria are also required when STM tips are used for patterning of nanometer-scale dots. In this paper, we will present the spatial resolution limits determined for these tips on different calibration gratings as well as first results obtained on nanometer scale patterning.

Spontaneous patterning of quantum dots at the air-water interface.

Nanoparticles deposited at the air-water interface are observed to form circular domains at low density and stripes at higher density. We interpret these patterns as equilibrium phenomena produced by a competition between an attraction and a longer-ranged repulsion. Computer simulations of a generic pair potential with attractive and repulsive parts of this kind, reproduce both the circular and stripe patterns. Such patterns have a potential use in nanoelectronic applications.