Document Actions
Photo-deprotection Patterning of Self-Assembled Monolayers (SAMs)
Excerpted from:
Journal of Experimental Nanoscience
Photo-deprotection Patterning of Self-Assembled Monolayers (SAMs)
from Taylor & Francis 'Journal of Experimental Nanoscience'
A team of nanoscale researchers from the U.K demonstrate how photo-deprotectable self-assembled monolayers (SAMs) provide a versatile platform for creating functional patterned surfaces, and present nanoscale photo-patterning, multi-component patterning, and a method for producing molecular gradients using photodeprotectable SAMs.
Authors
Kevin Critchley, Jonathan P. Bramble, Lixin Zhang, Richard J. Bushby, Stephen D. Evans; University of Leeds;
Graham J. Leggett and Robert Ducker, University of Sheffield
Abstract-Summary
Self-assembled monolayers (SAMs) formed from alkanethiol derivatives have proven to be excellent model systems for a wide range of fundamental studies. The ability to produce ‘‘chemical’’ patterns on surfaces allows control over higher level assembly; for example, this makes it possible to selectively deposit conducting polymers, control the orientation and nucleation of crystals, attach nanoparticles to designated regions of a surface, assemble biological molecules and cells, align nematic liquid crystals, and more.
There are many methodologies for patterning SAMs including microcontact printing, dip-pen lithography, ion-beam lithography, e-beam lithography, and scanning tunneling lithography. With the exception of microcontact printing, these techniques tend to be either time consuming and only suitable for small areas or require expensive instrumentation.
However, another technique that can produce patterns over a large scale is ultraviolet (UV) photopatterning. Deep UV photopatterning (__255 nm; h_>4.8 eV) of alkanethiol and organosilane SAMs was developed in the early 1990s and was used to create well-defined micron-scale features that could be used as templates for various reactions and assemblies. The photopatterning mechanism of alkanethiol SAMs relies upon localised oxidation of thiolate bonds to form sulphonates (RS-Auþ3/ 2O2!RSO3-þAuþ). The weakly bound sulphonates can then be easily rinsed away and the sample can be placed in a new alkanethiol solution to back-fill the irradiated areas.
Similarly, deep UV light can be used to pattern organosilane SAMs. This mechanism mainly involves the photocleavage of the C-Si bond. However, it is generally accepted that other photochemical reactions can occur when using deep UV. Chen et al. investigated deep UV (_¼193 nm; h__6.4 eV) photolysis with several aromatic silane derivatives and found that low doses C-N bonds were the primary cleavage pathway (68%) with the Si-C bond being secondary (32%). Although this can be used to an advantage, it is clear that more than one photochemical pathway occurs and, in some cases, this could leave the surface with ‘non-specific’ multiple functional groups.
UV for Nanoscale Photo-Patterns
Several researchers have demonstrated that photopatterning can be achieved using soft UV (_¼365 nm, h__3.4 eV) light by incorporating photo-reactive orthonitrobenzyl chromophores [42–55]. At this wavelength, the photon energy is not sufficient to cause any significant photo-oxidisation of the SAM headgroups, and so we rely upon photochemistry to cleave the molecules at a designated bond to reveal new functionality. The advantage of this type of system is that no backfilling of the irradiated regions is required, i.e. reducing the number of steps to producing a pattern.
The second advantage of this system is that ‘soft’ UV is a more mild form of radiation with which no ozone or oxygen free radicals are produced, rendering it compatible with biological molecules and making it possible to execute multiple exposures. We have previously reported two families of nitrobenzyl derivatives that form SAMs that can be photo-deprotected. The first system was an amine functionalised SAM that was ‘protected’ by a nitrobenzyl derivative with a semi-fluorinated tail group to produce CF3 functionality.
These SAMs were photo-deprotected to reveal amine functionality. The second system reported was based on disulphide derivatives that contained nitrobenzyl groups. These were used to form complete SAMs that could be photodeprotected to reveal carboxylic acid groups [56]. Reference 56 provides a detailed characterisation of the latter system using X-ray photoelectron spectroscopy, grazing angle Fourier transform infrared spectroscopy, wetting, and secondary ion mass spectroscopy. In this study, we present photopatterning techniques using the same disulphide photocleavable derivatives, 1 and 2, as used in [56] figure 1. Compounds 1 and 2 both form SAMs that produce low surfaces energies (with advancing water contact angles of 117_ and 112_, respectively). These hydrophobic SAMs (SAM1 and SAM2) can be photo-deprotected using soft UV irradiation to reveal
carboxylic acid groups.
from Taylor & Francis 'Journal of Experimental Nanoscience'
A team of nanoscale researchers from the U.K demonstrate how photo-deprotectable self-assembled monolayers (SAMs) provide a versatile platform for creating functional patterned surfaces, and present nanoscale photo-patterning, multi-component patterning, and a method for producing molecular gradients using photodeprotectable SAMs.
Authors
Kevin Critchley, Jonathan P. Bramble, Lixin Zhang, Richard J. Bushby, Stephen D. Evans; University of Leeds;
Graham J. Leggett and Robert Ducker, University of Sheffield
Abstract-Summary
Self-assembled monolayers (SAMs) formed from alkanethiol derivatives have proven to be excellent model systems for a wide range of fundamental studies. The ability to produce ‘‘chemical’’ patterns on surfaces allows control over higher level assembly; for example, this makes it possible to selectively deposit conducting polymers, control the orientation and nucleation of crystals, attach nanoparticles to designated regions of a surface, assemble biological molecules and cells, align nematic liquid crystals, and more.
There are many methodologies for patterning SAMs including microcontact printing, dip-pen lithography, ion-beam lithography, e-beam lithography, and scanning tunneling lithography. With the exception of microcontact printing, these techniques tend to be either time consuming and only suitable for small areas or require expensive instrumentation.
However, another technique that can produce patterns over a large scale is ultraviolet (UV) photopatterning. Deep UV photopatterning (__255 nm; h_>4.8 eV) of alkanethiol and organosilane SAMs was developed in the early 1990s and was used to create well-defined micron-scale features that could be used as templates for various reactions and assemblies. The photopatterning mechanism of alkanethiol SAMs relies upon localised oxidation of thiolate bonds to form sulphonates (RS-Auþ3/ 2O2!RSO3-þAuþ). The weakly bound sulphonates can then be easily rinsed away and the sample can be placed in a new alkanethiol solution to back-fill the irradiated areas.
Similarly, deep UV light can be used to pattern organosilane SAMs. This mechanism mainly involves the photocleavage of the C-Si bond. However, it is generally accepted that other photochemical reactions can occur when using deep UV. Chen et al. investigated deep UV (_¼193 nm; h__6.4 eV) photolysis with several aromatic silane derivatives and found that low doses C-N bonds were the primary cleavage pathway (68%) with the Si-C bond being secondary (32%). Although this can be used to an advantage, it is clear that more than one photochemical pathway occurs and, in some cases, this could leave the surface with ‘non-specific’ multiple functional groups.
UV for Nanoscale Photo-Patterns
Several researchers have demonstrated that photopatterning can be achieved using soft UV (_¼365 nm, h__3.4 eV) light by incorporating photo-reactive orthonitrobenzyl chromophores [42–55]. At this wavelength, the photon energy is not sufficient to cause any significant photo-oxidisation of the SAM headgroups, and so we rely upon photochemistry to cleave the molecules at a designated bond to reveal new functionality. The advantage of this type of system is that no backfilling of the irradiated regions is required, i.e. reducing the number of steps to producing a pattern.
The second advantage of this system is that ‘soft’ UV is a more mild form of radiation with which no ozone or oxygen free radicals are produced, rendering it compatible with biological molecules and making it possible to execute multiple exposures. We have previously reported two families of nitrobenzyl derivatives that form SAMs that can be photo-deprotected. The first system was an amine functionalised SAM that was ‘protected’ by a nitrobenzyl derivative with a semi-fluorinated tail group to produce CF3 functionality.
These SAMs were photo-deprotected to reveal amine functionality. The second system reported was based on disulphide derivatives that contained nitrobenzyl groups. These were used to form complete SAMs that could be photodeprotected to reveal carboxylic acid groups [56]. Reference 56 provides a detailed characterisation of the latter system using X-ray photoelectron spectroscopy, grazing angle Fourier transform infrared spectroscopy, wetting, and secondary ion mass spectroscopy. In this study, we present photopatterning techniques using the same disulphide photocleavable derivatives, 1 and 2, as used in [56] figure 1. Compounds 1 and 2 both form SAMs that produce low surfaces energies (with advancing water contact angles of 117_ and 112_, respectively). These hydrophobic SAMs (SAM1 and SAM2) can be photo-deprotected using soft UV irradiation to reveal
carboxylic acid groups.
Excerpted from: