3D printing at the macroscale has enabled fabrication of complex and custom shapes which are difficult if not impossible to create by conventional means of machining. At the nanoscale, additive manufacturing has the potential to transform fabrication of nano and microscale components for mechanical, electronic and biomedical devices. Already, a number of nano and microfabrication techniques are able to generate custom 2D patterns as well as some 3D architectures. Often with nanofabrication, mechanically robust nanostructures are limited in out-of-plane dimensions whereas large out-of-plane dimensions can only be obtained for low modulus and hardness materials. There is therefore a technological gap in the ability to nanofabricate patterns with high modulus and hardness, and with an appreciable out-of-plane thickness. Furthermore, nanofabrication of these patterns needs to be scalable in order for this technology to be translatable beyond the research lab.
Nanotribological Printing (NTP)
Nanotribological printing (NTP) is a scanning probe lithography (SPL) based technique, which utilizes contact stresses and surrounding heat to generate nanostructures. When submerged in a dispersion of an ‘ink’ material, relative motion between an atomic force microscope (AFM) tip and a flat substrate entrains ink molecules or particles into the tip-substrate contact. The applied normal and shear stresses at the contact result in the formation of a local, solid film through mechano-chemical mechanisms. Compared to several other methods of nano and microfabrication, NTP offers the following salient features:
- Patterned nanostructures show exceptional mechanical properties. As an illustration, patterns generated in our lab using metal-oxide nanoparticles, elastic moduli around 150 GPa were measured. For typical nanostructures with appreciable out-of-plane thickness (typically polymeric), moduli are generally below 0.5 GPa. As an illustration, the elastic modulus of bulk steel, manufactured through conventional processing is 210 GPa.
- Since patterning occurs where contact stresses are applied, pattern resolution can be controlled by controlling contact size. With typical AFM probes, contact diameters and therefore a lateral resolution as small as 20 nm can be obtained; using colloidal probes, line-patterns as wide as 200 nm can also be patterned. Additionally, raster patterning can extend lateral dimensions to as large as 100 µm. Depending on applied contact stress, single-ink pattern thicknesses as large as 300 nm have already been demonstrate.
- For a number of ink particles (such as nanoparticles), applied contact stress enable patterning through tribosintering or polymerization. For a number of ink particles (especially polymer precursors), elevated temperature is sometimes required. In almost all instances, elevated temperature further accelerates deposition and patterning rates.
- Patterning requires only the application of a contact stress, and in some cases, elevated temperature. As a result, patterning with NTP can be performed using nearly all standard AFM platforms since applied contact stresses are an intrinsic part of AFM scanning. This is unlike a number of other SPL and nanolithography methods, where additional accessories (such as tip voltage, pre-treating of the tip, specialty probes, etc.) are required for patterning.
- Since NTP relies on standard AFM scanning, it is intrinsically amenable to parallelization. An array of AFM probes can be used to simultaneously print multiple copies of a pattern.
- Variations in ink composition can be used to pattern nanocomposite as well as layered heterostructures.
- In NTP, nanoscale patterning and imaging of printed features can be performed with nanoscale resolution within the same setup, without the need for pattern or probe transfer.
Applications of NTP
A non-exhaustive list of potential applications includes:
- Fabrication of components for nano- or micro-electromechanical systems (NEMS/MEMS) devices
- Creating nanostructured electrolytic channels for micro-solid oxide fuel cells (printing with YSZ or zirconia nanoparticles)
- Creating wear-resistant coatings for MEMS/NEMS devices (printing with conventional anti-wear additives, zirconia or other dispersed particles)
- Creating nanostructured channels with conductive or semiconductor materials for MEMS/NEMS devices
- Creating thermal barrier coatings using ceramic oxide or other materials
- Creating photonic lattices and materials for plasmonic applications
- Formation of next-generation electronic transistors and associated devices
- Creating nanoscale sensors for biological and chemical detection
- Carpick, R.W., et al., Systems and methods for nano-tribological manufacturing of nanostructures. 2017 (draft manuscript, about to be submitted for publication).
- Engstrom, D.S., et al., Additive nanomanufacturing – A review. Journal of Materials Research, 2014. 29(17): p. 1792-1816.
- Garcia, R., A.W. Knoll, and E. Riedo, Advanced scanning probe lithography. Nat Nano, 2014. 9(8): p. 577-587.
- Ostendorf, A. and B.N. Chichkov, Two-photon polymerization: A new approach to micromachining. Photonics Spectra, 2006. 40(10): p. 72-80.
About the Lab
The Carpick Group is an interdisciplinary group of researchers who are interested in studying the fundamental origins and the important applications of friction, adhesion, wear, and lubrication at the nanoscale.