Fabricating devices at the nanoscale is one of the leading challenges for nanotechnology research as it underpins the future commercialization of many nanotechnology-enabled devices.
The promise of quantum dots in single electron devices such as transistors can only be realized through the combination of the physical properties of metallic and semiconducting nanoparticles and effective and reproducible nanofabrication techniques.
Through the use of Atomic Force Microscopy (AFM) it is possible to machine the surface of many materials via the sharp cantilever tips. On top of such surface structures, researchers have also shown that it is possible to generate assemblies of hybrid organic-inorganic nanoscale structures by using AFM tips as nanoelectrochemical "pens".
A typical example of this bottom-up nanofabrication process is the production of Nanopatterns of gold clusters on smooth silicon surfaces (for a more detailed analysis see Nano Letters 2(10) 1055-1060 (2002)).
Set out below are some more of the "pen and ink" approaches that are available through the suite of NT-MDT products and devices.
All types of AFM nanolithography can be performed in a vector scan mode or in an image pattern ("Raster") scan mode.
AFM Lithography by Local Probe Oxidation
AFM Anodic Oxidation Lithography is a type of Nanolithography which uses an electrical voltage (Figure 1) to not only modify the geometrical properties of the surface but also to change the local electrophysical properties of the sample surface.
Figure 1. Schematic showing how AFM oxidation lithography works. Please visit http://www.ntmdt.com/spm-principles/view/afm-oxidation-lithography to see the full animation.
Figure 2. This image was produced by local anodic oxidation nanolithography of a thin Ti film on in semicontact mode, by using NSG 11 cantilevers with conducting W2C covering, at a relative humidity of 70 %.
Image courtesy of Smirnov V.A., Taganrog Technological Institute of Southern Federal University.
AFM Lithography by Scratching
Although we have talked of "pen and ink" approaches to Nanolithography, the approach of the skilled engraver can also be employed at the Nanoscale. Using AFM tips with conventional scanning probe techniques, one can produce "engraved" nanolithographic features with a nanometer resolution (Figure 3).
Typically, with AFM scratching techniques, the tip is scanned under strong loading forces to remove the substrate or resist surface materials.
Figure 3. Schematic showing how AFM lithography by scratching works. Please visit http://www.ntmdt.com/spm-principles/view/afm-lithography-scratching to see the full animation.
AFM Lithography by Dynamic Plowing
In Dynamic Plowing Lithography (DPL), the surface is modified by indenting it with a vibrating tip in the AFM semicontact mode.
Figure 4. Schematic showing how AFM lithography by dynamic plowing works. Please visit http://www.ntmdt.com/spm-principles/view/afm-lithography-dynamic-plowing to see the full animation.
Figure 5. Vector dynamic lithography on a latex film. The surface features shown on these images were formed by hexagonally packed latex balls with a diameter of 170 nm deposited on a glass slide, the film was then heated to around 120°C and cooled to room temperature.
The traces of a former hexagonal structure are seen on the background in the image (b) which is the image (a) visualized with a more narrow height range.
Sample courtesy of Prof. Joseph Keddie, Department of Physics, University of Surrey, Guildford, Surrey GU2 7XH, England, UK
SOLVER NEXT - the fully automated SPM, innovative system that opens up new paths of study in different fields of nanotechnology, providing all user levels with a full range of conventional SPM measuring techniques (such as topography, phase imaging, nanolithography and more).
Figure 6. The fully automated SPM SOLVER Next
Probe NanoLaboratories NTEGRA - the model series includes devices for carrying out probe-microscopy experiments in the common and specific conditions: vacuum, liquids, low and high temperatures, etc. The combination of AFM and other methods has given an opportunity of going beyond the optical limits and carry out spectral researches (e.g. chemical analysis) with the resolution that tops the best optical methods.
Figure 7. Probe NanoLaboratory NTEGRA Aura is intended for studies in the conditions of controlled environment and low vacuum.
This information has been sourced, reviewed and adapted from materials provided by NT-MDT Spectrum Instruments.
For more information on this source, please visit NT-MDT Spectrum Instruments.