A self-assembled monolayer-assisted surface microfabrication and release technique

This paper describes a method of thin film and MEMS processing which uses self-assembled monolayers as ultra-thin organic surface coating to enable a simple removal of microfabricated devices off the surface without wet chemical etching. A 1.5-nm thick self-assembled monolayer of dodecyltrichlorosilane reduces the adhesion between the SiO2 substrate surface and a 100-nm thick evaporated aluminum film. A 100-mm thick layer of photoplastic SU-8, which is spun and structured by lithography and development on top of the monolayer/aluminum sandwich layer, can be mechanically lifted off the surface with the aluminum layer. The organic monolayer provides enough stability for the microfabrication process including photoresist spinning and thermal steps. The aluminum film has a surface roughness of less than 1 nm rms as measured by AFM. Photolithographic microstructuring of the aluminum film prior to the photoplastic process allows for transparent embedded bottom-side metal electrodes. As first application example, molded nanoprobes for scanning near-field optical microscopy, has been demonstrated using this technique

Surface Modification With Self-Assembled Monolayers for Nanoscale Replication of Photoplastic MEMS

A release technique that enables to lift microfabricated structures mechanically off the surface without using wet chemistry is presented. A self-assembled monolayer of dodecyltrichlorosilane forms a very uniform 1.5-nm-thick anti-adhesion coating on the silicon dioxide surface, on full wafer scale. The structural layers are formed directly onto the organic layer. They consist here of a 100-nm-thick aluminum film and a high-aspect ratio photoplastic SU-8 structure. After the microfabrication the structure can be lifted off the surface together with the aluminum layer. This generic technique was used to make a variety of novel structures. First, aluminum electrodes that are embedded in plastic are made using lithography, etching and surface transfer techniques. Second, using a patterned monolayer as defined by microcontact printing, resulted in a spatial variation of the surface adhesion forces. This was used to directly transfer the stamped pattern into a metal structure without using additional transfer etching steps. Third, the monolayer’s ability to cover surface features down to nanometer scale was exploited to replicate sharp surface molds into metal coated photoplastic tips with 30-nm radii for use in scanning probe instruments such as near-field optical techniques. The advantage compared to standard sacrificial layer techniques is the ability of replication at the nanoscale and the absence of etchants or solvents in the final process steps

The mechanisms of boronate ester formation and fluorescent turn-on in ortho-aminomethylphenylboronic acids

ortho-Aminomethylphenylboronic acids are used in receptors for carbohydrates and various other compounds containing vicinal diols. The presence of the o-aminomethyl group enhances the affinity towards diols at neutral pH, and the manner in which this group plays this role has been a topic of debate. Further, the aminomethyl group is believed to be involved in the turn-on of the emission properties of appended fluorophores upon diol binding. In this treatise, a uniform picture emerges for the role of this group: it primarily acts as an electron-withdrawing group that lowers the pK(a) of the neighbouring boronic acid thereby facilitating diol binding at neutral pH. The amine appears to play no role in the modulation of the fluorescence of appended fluorophores in the protic-solvent-inserted form of the boronic acid/boronate ester. Instead, fluorescence turn-on can be consistently tied to vibrational-coupled excited-state relaxation (a loose-bolt effect). Overall, this Review unifies and discusses the existing data as of 2019 whilst also highlighting why o-aminomethyl groups are so widely used, and the role they play in carbohydrate sensing using phenylboronic acids