Chemically Directed Surface Alignment and Wiring of Self-Assembled Nanoelectrical Circuits

1
Chemically Directed Surface Alignment and Wiring
of Self-Assembled Nanoelectrical Circuits
J. Liu, K. A. Nelson, E. Bird, H. Conley,
T. Pearson, T. Wickard, L. Hutchins, D. R.
Wheeler, R. C. Davis, A. T. Woolley, M. R.
Linford, and J. N. Harb
Department of Chemical Engineering,
Department of Chemistry and Biochemistry,
Department of Physics and Astronomy Brigham
Young University, Provo, Utah 84602


Abstract
High-resolution chemical surface patterning
Metallization
This poster describes nanofabrication
efforts underway at BYU by an interdisciplinary
research group, ASCENT (ASsembled nanoCircuit
Elements by Nucleic acid Templating) under NIRT
funding (2007). This group seeks to combine the
complementary advantages of bottom-up
self-assembly with top-down patterning, with the
goal of providing a process for fabrication of
nanoelectronic circuits. Efforts are focused on
the development and refinement of four key
technologies (1) solution-phase assembly of
structures and templates, (2) high-resolution
chemical surface patterning, (3) high-precision
metallization of molecular templates, and
(4) chemically directed assembly and integration
of nanostructures on surfaces. Molecular
circuits are self-assembled in solution using
customized DNA templates (test-tube circuits).
DNA self-assembly is particularly powerful
because of the large number of possible
nucleic-acid sequences that enable highly
selective bonding of DNA strands to each other
and to other molecules. Chemomechanical
patterning, a method that we have developed, is
used to chemically modify the SiO2 substrate.
This chemical patterning will provide anchor
points to attach and align the molecular circuits
on the surface, as well as provide a means for
local wiring to the anchored circuit, all with a
resolution lt 10 nm. Electroless metal plating of
both the exposed DNA and chemically templated
lines is used to electrically connect active
circuit elements to each other and to the
larger-scale architecture. The net result will
be DNA-templated molecular circuits that have
been aligned and wired locally on an oxide
surface. Interconnect technology similar to that
used currently in the semiconductor industry can
then be applied to create the larger global
wiring needed for practical devices based on the
molecular circuits under development.

• Assembling in situ discrete circuits
• Electroless plating for metallization of
  interconnects between circuit elements
• Metallization will occur preferentially on either
  DNA templates or on chemomechanically modified
  regions

Chemomechanical patterning

1. Enables creation of direct, strong covalent bonds
   to surfaces
2. Able to pattern in a liquid environment
3. Flexible for use with a range of surfaces and
   surface chemistries
4. Low cost
5. Potential for making 10 nm features
6. Parallel modification of substrates possible with
   tip arrays

Results
DNA-Templates
Chemomechanically pattern
Techniques Capable of Patterning lt 100 nm Features Direct Strong Covalent Bonding of Molecules Controllable Liquid Environment Wide Range of Surfaces and Surface Chemistries Inexpensive Possibility of Making a 10 nm Feature
Chemomechanical Patterning/Nanografting Yes Yes Yes Yes Yes
Dip Pen Nanolithography Usually Not No Yes Yes Diffusion Limited?
Microcontact Printing Usually Not No Yes Yes Unlikely
AFM Mechanical Scribing and Nanoindending No No No Yes Yes
c-AFM Oxidation No No No Yes Yes
UHV STM Patterning No No No No Yes
E-beam Lithography No No Yes No Unlikely
UV Photolithography No No Yes No Unlikely
Overview

• APDES Nanografted onto SiO2
• Selective metallization by electroless copper
  on scribed lines
• 80nm line width, possibility for 10-20nm widths
  exists

• Tasks
• Molecular circuit assembly
• High-resolution chemical surface patterning
• Chemically directed assembly and
  integration of MCs on surfaces
• High-selectivity, high-precision metallization

A
B
Results

• TEM images after metallization
• Copper (B) Silver
• Scale bars are 25 nm

I-V curve measured for a DNA-templated
copper nanowire spanning electrodes separated by
7 microns

Broader Impacts Summary

• Education of graduate students in a truly
  multidisciplinary environment.
• Education of undergraduate students in a positive
  mentoring environment.
• Involvement of local minority students in an
  outreach program focused on nanoscience and
  engineering.
• Development of a method for producing wiring and
  metallization at a density unmatched by any
  present or near-future process.
• Development, demonstration and dissemination of
  novel and transferable processes and enabling
  tools for nanotechnology.

• Hydrophilic patterns created by nanografting a
  neat trifunctional silane through a
  monochlorosilane monolayer
• Features as small as ca. 10 nm are created

• BYU nanoshaved in C18DMS surface on SiO2
• Letters are indented approximately 2-4 Å

Chemically directed assembly and integration of
MCs
Molecular circuit assembly
Results (single transistor template)

A high yield of individual properly aligned
MCs at each site is desired. The assembly can be
tuned using several molecular parameters
including molecule flexibility, ligand length,
induced steric constraints, and partial
attachment binding affinity differences.
Temperature cycling, selective ligation, and the
use of multiple attach/rinse cycles will be
explored to achieve the desired yield.
References

• H.A. Becerril, R.M. Stoltenberg, D.R. Wheeler,
  R.C. Davis, J.N. Harb, and A.T. Woolley,
  "DNA-Templated Three-Branched Nanostructures for
  Nanoelectronic Devices", JACS, vol. 127, (2005),
  p. 2828.
• K.A. Nelson, S.T. Cosby, J.C. Blood, M.V. Lee,
  D.R. Wheeler, R.C. Davis, A.T. Woolley, M.R.
  Linford, J.N. Harb, "Substrate Preparation for
  Nanowire Fabrication by Selective Metallization
  of Patterned Silane Monolayers", ECS Trans., vol.
  1 (12), (2006), p. 17.
• H.A. Becerril and A.T. Woolley, "DNA Shadow
  Nanolithography", Small, vol. 3, (2007), p. 1534.
• M.V. Lee, K.A. Nelson, L. Hutchins, H.A.
  Becerril, S.T. Cosby, J.C. Blood, D.R. Wheeler,
  R.C. Davis, A.T. Woolley, J.N. Harb, M.R.
  Linford, "Nanografting of Silanes on Silicon
  Dioxide with Applications to DNA Localization and
  Copper Electroless Deposition," Chem. Mater. vol.
  19 (2007), p. 5052

(1-3) 120 base oligonucleotides with
complementary regions (4) Internally
biotinylated poly-T sequence (5) Streptavidin
(A) Three-branched DNA assembly (B)
Streptavidin-labeled three-armed DNA complex
Solution assembly of DNA-based MC templates
Funding

• AFM images of
• (A-C) Three-branched DNA structures
• (D-F) Complexes with streptavidin localized in
  the center
• White bar represents 25 nm in all images

• National Science Foundation (CTS-0457370)
• ACS Petroleum Research Fund (42461-G5)
• U.S. Army Research Office (DAAD19-02-1-0353)
• National Science Foundation (NIRT) Chemically
  Directed Surface Alignment and Wiring of
  Self-Assembled Nanoelectrical Circuits, 2007
  2011

DNA-templated nanotube positioning