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In this paper the characterization of different masking materials for the fabrication of flow channels or thin diaphragms in aluminosilicate glass substrates (Corning 1737) is presented. Materials such as photoresist, polysilicon and gold were investigated with concentrated hydrofluoric acid, HF 48% used as an isotropic etchant. The use of single material masks restricts the useable etch depth to less than 250 µm. Surface and material imperfections result in weaknesses in the masking layer and subsequent penetration by the etchant. An etch depth of greater than 300 µm was achieved using a combination of thick SU-8 photoresist and polished polycrystalline silicon as the masking material. The two materials act as double protection to the glass substrate and the etch depth obtained is approximately three to six times larger than those published for standard photoresist or SU-8 etch mask.

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The traditional use of Scotch tape for exfoliating layers of two-dimensional (2D) transition metal dichalcogenides (TMDs) has been compared with a gel-assisted mechanical exfoliation technique, using MoS 2 as a representative TMD. The gel-assisted exfoliation process, which makes use of both Scotch tape and a gel film, is superior to the use of Scotch tape alone, as it gives a higher probability of obtaining larger surface area few-layer flakes. A quantitative analysis has been made between the samples prepared by the two techniques. The total density of flakes transferred onto a sample by Scotch tape alone was much higher than when using the gel film. However, most of the transferred flakes were several microns in thickness with lateral dimensions <10 µm. Therefore, the higher percentage of few-layer flakes with large lateral dimensions (> 20 µm) transferred using gel film is very advantageous. Since samples prepared using gel film have fewer flakes, the contacting of potential thin flakes on the sample can be done conveniently. Also, unlike Scotch tape, the gel film does not leave adhesive residue on the substrate. Optical microscopy, contrast difference measurements and Raman spectroscopy were used for identification of the few-layer MoS 2 flakes.

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