Nano-Fabrication

Development of Nanotransfer Printing with Spacing Below 10 nm

Scanning Electron Microscopy Image of a rigid stamp used for nano-transfer printing (nTP).
SEM image of a single transferred gold nanogap with a width of less than 30 nm.

An electronic device made from a single molecule constitutes the ultimate goal of miniaturization beyond Moore’s law.

Technologically, the first step in this direction is the ability to realize electrodes separated by just a few nanometers.

Our research focuses on the development and implementation of a direct nanotransfer printing (nTP) process that enables the fabrication of such metal electrodes with a predetermined spacing of less than 10 nm.

This requires both a rigid stamp that provides the structures and a reliable printing process that transfers the metalized structures onto a suitable substrate.

The stamp is fabricated from a GaAs/AlGaAs heterostructure. A three-terminal electrode geometry needed for a molecular transistor can be realized by a combination of molecular-beam-epitaxial regrowth on a crystal facet, using the cleaved-edge-overgrowth (CEO) method and subsequent wet selective etching and metallization steps.

The printing process itself requires a precise control over the planar alignment between stamp and substrate and the pressure at which both materials are brought into contact.

Additionally, previous wet- or dry-chemical treatment of both stamp and/or substrate can enhance the transfer.

References

Bareiß, M. et al. High-Yield Transfer Printing of Metal–Insulator–Metal Nanodiodes. ACS Nano 6, 2853–2859 (2012). doi: http://dx.doi.org/DOI: 10.1021/nn3004058

Fakhr, O. et al. Easy Fabrication of Electrically Insulating Nanogaps by Transfer Printing. Small 7, 2533–2538 (2011). doi: http://dx.doi.org/DOI: 10.1002/smll.201100413

Researchers

Haeberle,T.; Bareiß,M.; Scarpa,G.


Nanoimprint Lithography (NIL)

Light trapping by the excitation of surface plasmon polaritons at the metal/semiconductor interface. A corrugated metal back surface couples light to surface plasmon polariton or photonic modes that propagate in the plane of the semiconductor layer.

The performance of electronic circuits in today’s world is becoming limited by the speed at which signals can be sent electrically along the interconnections of a chip.

Photonics offers an effective solution by implementing optical communication systems based on optical fibers and photonic circuits.

Unfortunately, the micrometer-scale bulky components of photonics have limited the integration of these components into electronic chips, which are now measured in nanometers.

Surface plasmon–based circuits or devices, which merge electronics and photonics at the nanoscale, may offer a solution to this size-compatibility problem.

The emerging field of plasmonics has yielded methods for guiding and localizing light at the nanoscale, well below the scale of the wavelength of light in free space.

Our research area is currently focused on patterning nanostructures on various device layers using nanoimprint lithography (NIL) in order to observe and improve the optical spectra of the device in question.  

3D AFM image demonstrating successful pattern transfer of a 2D pillar structure imprinted in poly(3-hexylthiophene) using a porous alumina template with 60 nm average pore width (a). Characterizing a smaller area of approx. 1 µm x 1 µm using AFM (b) and SEM (c) visualizes individual pillars of around 60 nm in diameter.

Nanoimprint lithography (NIL) is an unconventional lithographic technique for patterning polymeric nanostructures with high-throughput at great precision and low costs.

NIL relies on direct mechanical deformation of the resist material and can therefore achieve resolutions beyond the limitations encountered in other conventional techniques.

Being able to pattern organic materials in the micrometer range and below is essential:
for electronic devices, an improvement of device performances in terms of operations speed can be achieved, whereas for optoelectronic devices, the interaction between matter and light at the nanometer scale can be further exploited.

References

Frischeisen, J et al. Light extraction from surface plasmons and waveguide modes in an organic light-emitting layer by nanoimprinted gratings. Opt. Express  19, A7-A19 (2011). doi: http://dx.doi.org/http://dx.doi.org/10.1364/OE.20.00A205

Scarpa, G. et al. Patterning Poly(3-Hexylthiophene) in the Sub-50-nm Region by Nanoimprint Lithography. IEEE Transactions on Nanotechnology, 10, 482-488 (2010). doi: http://dx.doi.org/10.1109/TNANO.2010.2048433 

Researchers

Yadav,A.; Abdellah,A.; Imtaar,M.A.;