Probe-Based Nanomanufacturing

Figure 1. Schematic of an array of Nano Fountain Probes.

This project focuses on the development of a scalable, direct-write nanomanufacturing platform. The platform is capable of constructing complex, highly-functional nanoscale devices from a diverse suite of materials (e.g., nanoparticles, catalysts, biomolecules, and chemical solutions).

 

The advent of dip-pen nanolithography (DPN) in recent years represented a revolution in nanoscale patterning technology. With sub-100-nanometer resolution and an architecture conducive to massive parallelization, DPN is capable of producing large arrays of nanoscale features. As such, conventional DPN and other probe-based techniques are generally limited in their deposition rate and by the need for repeated re-inking during extended patterning.

 

To address these challenges, we have developed and fabricated a cantilevered microfluidic device called the Nano Fountain Probe (NFP, Figure 1) which builds upon the DPN technology. Integration of continuous liquid ink feeding within the NFP (Figure 2) facilitates more rapid deposition and eliminates the need for repeated dipping, all while preserving the sub-100-nanometer resolution of DPN.

Figure 2. Principle of operation of the NFP. Top: Schematics of the NFP chip. On-chip fluid reservoirs deliver molecular inks (e.g., nanoparticles, catalysts, or biomolecules) through a series of integrated microchannels to apertured dispensing tips. The solution in the reservoir is driven by capillary action to the dispensing tips, forming a liquid-air interface at the aperture. Molecules from the interface diffuse along the core tip to the substrate. Center: Images of third-generation NFP chips. Scale bar is 1 micron. Bottom: Examples of demonstrated nanopatterning capabilities including dot arrays of drug-coated diamond nanoparticles for dosing studies (left, [1,2]), linear array of proteins deposited at a rate of 80 microns/sec (center, [3]), and dot arrays of catalyst for carbon nanotube growth.

Demonstrated nanopatterning capabilities include (Figure 2, bottom):

  • Biomolecules (proteins, DNA) for biodetection assays or cell adhesion studies [3-5],
  • Functional nanoparticles for drug delivery studies and nanosystems fabrication [1,2,6],
  • Catalysts for carbon nanotube growth in nanodevice fabrication,
  • Thiols for directed self-assembly of nanostructures [8,10,11].

Microfluidic transport facilitates rapid and continuous delivery of molecules from the on-chip reservoirs to the substrate. When the tip is brought into contact with the substrate, a liquid meniscus forms (Figure 2), providing a path for molecular transport to the substrate. To gain insight into the geometry of the liquid meniscus at the NFP tip, a study of the equilibrium liquid-air interface was conducted [3]. Here the meniscus shape and width not only determine the lower bound of the NFP resolution but also whether deposition occurs at all. In considering the mechanics of molecular deposition, the effects of probe tip geometry, liquid-tip and liquid-substrate contact angles, and relative humidity were assessed.

The flow of liquid through the NFP tip was modeled by determining the equilibrium shape of the liquid surface for a series of prescribed volumes [3]. In this way, we effectively obtained a series of snapshots of a quasi-equilibrium flow of liquid to the probe tip under capillary force. Figure 3 shows the computed total energy as a function of the prescribed volume of liquid. For a given test case, the characteristic energy landscape exhibits a local and global minimum. As shown in Figure 3a, the local minimum at higher energy corresponds to a sharp, well-defined meniscus (see inset #1) that intuitively should lead to high-resolution deposition. In contrast, falling to the global minimum results in a loss of control of the feature size and effective flooding of the NFP tip. Conducting this analysis for varying liquid contact angles and tip geometries (Figure 3a,b) enables informed probe design and selection of experimental parameters.

Figure 3. Effect of liquid solution contact angle (a) and tip geometry (b) on meniscus shape and patterning resolution.

This analysis also reveals the origin of the need for, in some cases, additional energy (e.g., in the form of an electric field applied between the on-chip reservoir and substrate) to induce molecular transport from the probe tip to the substrate [3]. At equilibrium in the local minimum (inset #1 of Figure 3a), there is a substatial portion of the tip that is not covered with liquid. For less mobile molecules in solution (e.g., large proteins), passive diffusion may be insufficient to carry them across this gap. Additional electrophoretic or electro-osmotic forces provide a plausible additional source of energy to facilitate this transfer.

 

Personnel 

  • Horacio Espinosa (PI)
  • Majid Minary (postdoc)
  • Asmahan Safi (graduate student)

 

Collaborators 

  • Chad Mirkin (Chemistry, Northwestern University)
  • Ralu Divan (Center for Nanoscale Materials, Argonne National Laboratory)
  • John Sullivan (Center for Integrated Nanotechnologies, Sandia National Laboratory)
  • Dean Ho (Biomedical and Mechanical Engineering, Northwestern University)
  • Jonathan Jones (Cell and Molecular Biology, Northwestern University)
  • Nicolaie Moldovan (Advanced Diamond Technologies)
  • Alexander Morvasky (Materials and Electrochemical Research Corporation)

 

Publications 

 

Patents 

 

 

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