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Fabrication of Gold Nanostructures by Lithography with Self-Assembled Monolayers

IP.com Disclosure Number: IPCOM000118353D
Original Publication Date: 1996-Dec-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 168K

Publishing Venue

IBM

Related People

Biebuyck, H: AUTHOR [+3]

Abstract

Fig. 1: Short thiols containing amido functionalities self-assemble on gold to form a monolayer of stable and well-defined functionality. Local processing of molecules in the monolayer with electrons alter the stability of these molecules and allow their replacement in affected regions by other longer thiols, hexadecanethiol in this example. The absence of protection of the gold by the first monolayer but not by the second one allows for permanent transfer of the written pattern into gold by a cyanide etch. (Image Omitted)

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Fabrication of Gold Nanostructures by Lithography with Self-Assembled
Monolayers

      Fig. 1: Short thiols containing amido functionalities
self-assemble on gold to form a monolayer of stable and well-defined
functionality.  Local processing of molecules in the monolayer with
electrons alter the stability of these molecules and allow their
replacement in affected regions by other longer thiols,
hexadecanethiol in this example.  The absence of protection of the
gold by the first monolayer but not by the second one allows for
permanent transfer of the written pattern into gold by a cyanide
etch. 

                            (Image Omitted)

      Self-Assembled Monolayers (SAMs) of alkanethiols or disulfides
on gold provide resists for patterning substrates down to submicron
scales (~ 30 nm).  One use of the protective property of
SAMs is demonstrated, for example, in negative lithographic schemes:
UV light, metastable ions, X-rays or electron beams can damage, by
their direct interaction or through a mask, monolayers lowering the
protective attribute of the monolayer in the "written" regions.  SAMs
follow the definition of a negative resist in these cases because,
wherever the monolayer is processed, it loses its ability to protect
the substrate from an etchant.  The etch in the case of gold is
typically a 'CN' '/O' presup - sub 2 bath since ordered and dense
monolayers like Hexadecanethiol (HDT) offer a high degree of
protection (contrast ratios of > 10/4/ are possible) (1) to their
gold substrate in unprocessed regions.  This type of lithography is
adequate for the fabrication of small trenches or depressed
structures because it requires processing of the SAM only in the
small regions where features will be formed.  It requires, however,
extensive dosing of the  monolayer for the formation of small
elevated features like connection  lines or structures with small
lateral dimensions often present in electronic chips, microsensors or
microtransducers.

      A solution toward easier fabrication of small elevated
structures without the need to expose extensively the surface of the
base material is presented.  It also offers a method toward the
implementation of small conductive wires or microelements onto a
device as a part of hybrid fabrication schemes that combine electron
beam and optical lithography.  Practically, the method uses SAMs on
gold as positive resists in combination with e-beam lithography; this
disclosure also demonstrates the convenient fabrication of gold
nanowires 50 nm wide and several microns long within this
lithographic scheme.

      Fig. 1 shows the operations necessary for such a fabrication
and illustrates what characteristics of the monolayers are pertinent.
Following the findings of Tam-Chang et al. (2), the first monolayer
optimally has the structure XCH2NHCOCH2SH (SAMI).  This short
molecule forms a homogeneous, dense, stable (the amide function
(-NHCO-) in...