  In recent years, self-assembled semiconductor nanowires have been
successfully used as ultra-sensitive cantilevers in a number of unique scanning
probe microscopy (SPM) settings. We describe the fabrication of ultra-low
dissipation patterned silicon nanowire (SiNW) arrays optimized for scanning
probe applications. Our fabrication process produces, with high yield,
ultra-high aspect ratio vertical SiNWs that exhibit exceptional force
sensitivity. The highest sensitivity SiNWs have thermomechanical-noise limited
force sensitivity of $9.7\pm0.4~\text{aN}/\sqrt{\text{Hz}}$ at room temperature
and $500\pm20~\text{zN}/\sqrt{\text{Hz}}$ at 4 K. To facilitate their use in
SPM, the SiNWs are patterned within $7~\mu\text{m}$ from the edge of the
substrate, allowing convenient optical access for displacement detection.
