Seed layer thin-film fabrication

It was shown that thin films of Cu, Co and Ni could be successfully deposited onto Si substrates, without the need of a seed layer. For all three metals, uniform layers with a compact and granular morphology could be obtained. From RBS data the deposition rates as well as the current efficiencies could be determined. For Co films it was shown that addition of boric acid caused the evolution of hydrogen. On the other hand, it was possible to improve the current efficiency of electrolytes containing boric acid by increasing the concentration of cobalt sulfate in the bath. For Ni films electrodeposited from a highly concentrated sulfate electrolyte, it was observed the formation of texture in the (220)-direction. Electric measurements performed on Ni/n-Si structures yielded values for Schottky barriers which are comparable to the ones obtained for junctions fabricated by vapor deposition. 

Other techniques have been used for the fabrication of thin-film metal-oxide gas sensors. At NIST in the USA, Cavicchi et al. (1995) and Semancik et al. (2001) produced gas sensors by chemical vapor deposition (CVD). By applying a current and thus heating the hotplate, sensing films could be deposited locally (i.e. only on heated active areas) using an adequate organ-ometaUic precursor. SnOj and ZnO films were obtained with tetramethyltin and diethylzinc in an oxygen atmosphere. They were deposited onto different seed layers, which played a significant role in terms of gas selectivity. 

At the early stage of the development of the heart-on-a-chip, a PDMS microfluidic network was combined with planar electrode array to measure the extracellular potential from individual adult cardiomyocytes [54]. Another microfluidic device with an array of electrodes was developed to electrically measure the metabolic profile of cardiomyocytes and optically measure cell contractility [55]. Grosberg et al. first introduced a tissue level heart-on-a-chip to measure the contractility of neonatal cardiac muscle tissue [52]. In the design, eight muscular thin films (MTF) were fabricated on a chip. A layer of poly(N-isopropylacrylamide) (PIPAAm) dissolved at below 35 °C is spin-coated on top of a glass slide (Fig. 5A). Subsequently, a PDMS layer was coated on top of the PIPAAM layer. The PDMS layer was used to seed neonatal rat ventricular cardiomyocytes. The substrate seeded with cells is placed in the bath and the film layers were manually cut to fabricate an array of two opposite rows of four rectangular film layers of MTFs. The MTFs are peeled off after PIPAAm is dissolved as a solution when kept below 35 °C. Finally, electrodes are placed on the top and the bottom of MTFs. 

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