We investigate monocrystalline InAs nanowires (NWs) which are grown catalyst assisted by molecular beam epitaxy (MBE) and create the catalyst by focused ion beam (FIB) implanted Au spots. With this combination of methods an aspect ratio, i.e. the length to width ratio, of the grown NWs up to 300 was achieved. To control the morphology and crystalline structure of the NWs, the growth parameters like temperature, flux ratios and implantation fluence are varied and optimized. Furthermore, the influence of the used molecular arsenic species, in particular the As-2 to As-4 ratio, is investigated and adjusted. In addition to the high aspect ratio, this optimization results in the growth of monocrystalline InAs NWs with a negligible number of stacking faults. Single NWs were placed site-controlled by FIB implantation, which supplements the working field of area growth. (C) 2017 Elsevier B.V. All rights reserved.