Part 4ii: Dip Pen Nanolithography (DPN)

After completing PART 4i of this course you should have an understanding of, and be able to demonstrate, the following terms, ideas and methods. (i)The DPN process, (ii)The experimental factors that effect the DPN process (ink diffusion, ink- surface interaction, tip dwell times and writing speeds, humidity. (iii)Be aware of how DPN can be used. Learning Objectives

Dip-Pen Nanolithography (DPN) is an new Atomic Force Microscope (AFM) based soft-lithography technique which was recently discovered in the labs of Prof Merkin. DPN is a direct-write soft lithography technique which is used to create nanostructures on a substrate of interest by delivering collections of molecules (thiols) via capillary transport from an AFM tip to a surface (gold) Dip-Pen Nanolithography 10 nm

Scientific American 2001

AFM Friction image of an ODT island recorded with a dull tip under low load 500 nm Diffusion of Ink from Tip to Substrate Physisorbed thiols diffuse down the tip to the tip-surface contact area and then diffuse out across the surface, continuously increasing in range and concentration. A SAM of “standing” thiols covers regions of sufficiently high thiol concentration (radius r). The contact radius, a, is defined as the distance at which the tip-surface gap equals the height of the SAM. Phys. Rev. Letts (2002).

Ink: nC 12 H 25 -NH 2 Surface:Mica Ink: HO 2 C-C 15 H 30 -SH Surface:Au Phys. Rev. Letts (2003). Amine has weak interaction with Mica Thiol has strong interaction with Au Ink-Surface Interaction

The effect of dwell time on the size of dots created by DPN of MHA dots on a gold substrate. Ink: HO 2 C-C 15 H 30 -SH Surface: Au Tip-Surface Dwell Time Phys. Rev. Letts (2002).

ESEM images of the effect on the meniscus size as the relative humidity is increased from 40% to 99% Water Meniscus and Humidity Langmuir (2005).

Two gold electrodes connected by indium oxide deposited by thermal DPN. Thermal DPN Appl. Phys. Letts., (2006) Indium Metal Indium Metal Indium Oxide Indium Oxide

AFM image of a stretched strand of DNA modified with dots of Cy3- antibody. Painting DNA! Ultramicroscopy (2005).

Growing Polymers of a DPN Written Surface Write monomer thiol to Au surface with DPN. 2. Passivate exposed Au surface with decane thiol. 3. Expose surface to catalyst solution and rinse. 4. Expose surface to monomer solution Height of polymer structures vs reaction time Angew. Chem. Int. Ed. 2003, 42, 4785 –4789

Writing Monomers of a DPN Written Surface Angew. Chem. Int. Ed. 2003, 42, 4785 – Form a SAM of silane monomer 2.Activate SAM with polymer catalyst 3.Write monomers to the surface with DPN a. write lines c,b write dots 3a3b3c 1 2

An Enzyme Ink for DPN Add Mg 2+ ions activator Write enzymes with DPN J. AM. CHEM. SOC. 2004, 126,

Conclusions on DPN DPN is a facile and versatile route to create nanostructured surfaces, with resolution better than photolithography and almost equalling EBL. It requires relatively cheap instrumentation and is carried out under ambient conditions. It is a serially process and hence relatively slow.

Summing Up Part 4  CP is a rapid parallel process, and utilises simple chemistry and processes for nanostructuring surfaces, usually under ambient conditions. DPN is a slow serial process, but also uses simple chemistry and processes for nanostructuring surfaces, but requires an AFM (£100K). Both processes utilise the well-established science and technology surrounding SAMs, and therefore for sure we have only begun to see the tip of the iceberg in terms of the chemistry that may be used with these lithographic processes.

SEM micrograph of a 32 probe array used for parallel DPN. The insert shows an enlarged view of the tip at the end of a beam. Parallel DPN Small, (2005). Nanotechnology, (2002). upper left depicts misalignment between tips and substrate. By adjusting the substrate using a tilt-stage and applying a large setpoint (>10nN) all 26 tips can be engaged with the substrate (upper right). When cantilevers make contact with the surface, their angle of reflection and subsequently their colorchanges, as observed by optical microscopy (compare lower left with lower right).

Centimeter scale patterning of nanometer scale features using parallel-DPN by patterning ODT on Au and then etching.