Suspended tungsten-based nanowires with enhanced mechanical properties grown by focused ion beam induced deposition

The implementation of three-dimensional (3D) nano-objects as building blocks for the next generation of electro-mechanical, memory and sensing nano-devices is at the forefront of technology. The direct writing of functional 3D nanostructures is made feasible by using a method based on focused ion beam induced deposition (FIBID). We use this technique to grow horizontally suspended tungsten nanowires and then study their nano-mechanical properties by three-point bending method with atomic force microscopy. These measurements reveal that these nanowires exhibit a yield strength up to 12 times higher than that of the bulk tungsten, and near the theoretical value of 0.1 times the Young's modulus (E). We find a size dependence of E that is adequately described by a core-shell model, which has been confirmed by transmission electron microscopy and compositional analysis at the nanoscale. Additionally, we show that experimental resonance frequencies of suspended nanowires (in the MHz range) are in good agreement with theoretical values. These extraordinary mechanical properties are key to designing electro-mechanically robust nanodevices based on FIBID tungsten nanowires.This work was supported by the financial support from Spanish Ministry of Economy and Competitiveness through the projects CSD2010-00024, MAT2014-51982-C2-1-R, MAT2014-51982-C2-2-R, TEC2015-69864-R, MAT2015-69725-REDT (including FEDER funding) and from regional Gobierno de Aragón through project E26 with European Social Fund and COST-Celina project. R C acknowledges Juan de la Cierva-Incorporación 2014 program. J P-N grant is funded by the Ayuda para Contratos Predoctorales para la Formación de Doctores, Convocatoria Res. 05/06/15 (BOE 12/06/15) of the Secretaría de Estado de Investigación, Desarrollo e Innovación in the Subprograma Estatal de Formación of the Spanish Ministry of Economy and Competitiveness (MINECO) with the participation of the European Social Fund.Peer reviewe