Double-Sided Opportunities Using Chemical Lift-Off Lithography

Abstract

We discuss the origins, motivation, invention, development, applications, and future of chemical lift-off lithography, in which a specified pattern of a self-assembled monolayer is removed, i.e., lifted off, using a reactive, patterned stamp that is brought into contact with the monolayer. For Au substrates, this process produces a supported, patterned monolayer of Au on the stamp in addition to the negative pattern in the original molecular monolayer. Both the patterned molecular monolayer on the original substrate and the patterned supported metal monolayer on the stamp are useful as materials and for further applications in sensing and other areas. Chemical lift-off lithography effectively lowers the barriers to and costs of high-resolution, large-area nanopatterning. On the patterned monolayer side, features in the single-nanometer range can be produced across large (square millimeter or larger) areas. Patterns smaller than the original stamp feature sizes can be produced by controlling the degree of contact between the stamp and the lifted-off monolayer. We note that this process is different than conventional lift-off processes in lithography in that chemical lift-off lithography removes material, whereas conventional lift-off is a positive-tone patterning method. Chemical lift-off lithography is in some ways similar to microtransfer printing. Chemical lift-off lithography has critical advantages in the preparation of biocapture surfaces because the molecules left behind are exploited to space and to orient functional(ized) molecules. On the supported metal monolayer side, a new two-dimensional material has been produced. The useful important chemical properties of Au (vis-à-vis functionalization with thiols) are retained, but the electronic and optical properties of bulk Au or even Au nanoparticles are not. These metal monolayers do not quench excitation and may be useful in optical measurements, particularly in combination with selective binding due to attached molecular recognition elements. In contrast to materials such as graphene that have bonding confined to two dimensions, these metal monolayers can be straightforwardly patterned-by patterning the stamp, the initial monolayer, or the initial substrate. Well-developed thiol-Au and related chemistries can be used on the supported monolayers. As there is little quenching and photoabsorption, spectroscopic imaging methods can be used on these functionalized materials. We anticipate that the properties of the metal monolayers can be tuned by varying the chemical, physical, and electronic connections made by and to the supporting molecular layers. That is, the amount of charge in the layer can be determined by controlling the density of S-Au (or other) connections and the molecular backbone and functionality, which determine the strength with which the chemical contact withdraws charge from the metal. This process should work for other coinage-metal substrates and additional systems where the binding of the outermost layers to the substrate is weaker than...

Patterning of supported gold monolayers via chemical lift-off lithography

“…2 ,D). We have yet to determine the limits of the feature size and area that can be patterned by CLL, where features as small as 5 nm have been removed from the original monolayer [ 2 ]. In addition to the production of a wide range of feature sizes, another important advantage is that the supported Au monolayer on PDMS samples were stable for at least six months (Figure S6, Supporting Information File 1 ).…”

“…Chemical lift-off lithography (CLL) is a subtractive technique for patterning self-assembled alkanethiol molecules on Au surfaces via rupture of Au–Au bonds at the Au–monolayer interface [ 1 – 2 ]. In CLL, hydroxyl-terminated molecules (or other species with reactive termini) in preformed self-assembled monolayers (SAMs) are lifted off Au surfaces through contact with O 2 -plasma-activated poly(dimethylsiloxane) (PDMS) stamps.…”

“…Compared with microcontact or transfer printing methods [ 3 – 6 ], CLL produces crisp, stable patterns with sub-20 nm resolution and patterned areas of more than square millimeters [ 1 , 7 ]. We have used CLL on gold to control the placement and nanoscale environment around surface-immobilized biomolecules and to simplify patterning steps in device fabrication [ 1 – 2 7 – 13 ].…”

A Special Connection between Nanofabrication and Analytical Devices: Chemical Lift-Off Lithography

“…Different from conventional nanofabrication concepts, the CLL process not only produces a layer that can be utilized as a resist for feature transfer, but also generates a molecular pattern suitable for an abundance of uses. 17,26,27 Direct back-filling of functional molecules inside the post lift-off regions, for instance, paves the way for material-specific recognition/ deposition arrays, and has been straightforwardly applied to perform biological assays 2831 and nanoparticle arrangements. 32 A special and important opportunity obtained in this operation, specifically, lies in the creation of adjustable molecular monolayer environments never achieved before.…”

Indirect Microcontact Printing to Create Functional Patterns of Physisorbed Antibodies

“…in standard biochemical lab settings [ 15 , 16 , 17 ], and with a resolution of up to about 50 nm [ 18 ]. Thanks to all these strengths, µCP holds a great popularity [ 19 , 20 , 21 , 22 ]. Nanometric patterns of bioreceptors fabricated by µCP have found many applications, such as microarraying and neuronal cells guidance among others [ 12 , 15 , 23 ].…”