  One of the daunting challenges in modern low temperature scanning tunneling
microscopy (STM) is the difficulty of combining atomic resolution with cryogen
free cooling. Further functionality needs, such as ultra-high vacuum (UHV),
high magnetic field, and compatibility with {\mu}m-sized samples, pose
additional challenges to an already ambitious build. We present the design,
construction, and performance of a cryogen free, UHV, low temperature, and high
magnetic field system for modular STM operation. An internal vibration isolator
reduces vibrations in this system allowing atomic resolution STM imaging while
maintaining a low base temperature of ~4K and magnetic fields up to 9T. Samples
and tips can be conditioned in-situ utilizing a heating stage, an ion
sputtering gun, an e-beam evaporator, a tip treater, and sample exfoliation.
In-situ sample and tip exchange and alignment are performed in a connected UHV
room temperature stage with optical access. Multisite operation without
breaking vacuum is enabled by a unique quick-connect STM head design. A novel
low-profile vertical transfer mechanism permits transferring the STM between
room temperature and the low temperature cryostat.
