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\bibitem{Ryabchun_etal2008} Ryabchun, S. A., Tretyakov, I. V., Finkel, M. I., Maslennikov, S. N., Kaurova, N. S., Seleznev, V. A., et al. (2008). Fabrication and characterisation of NbN HEB mixers with in situ gold contacts. In \textit{Proc. 19$^{th}$ Int. Symp. Space Terahertz Technol.} (pp. 62--67). Groningen, Netherlands.

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