The Princeton Nanoscale Microscopy Laboratory (PNML)
Located in the basement of Jadwin Hall, PNML is a state-of-the-art laboratory designed for high precision measurements in condensed matter physics. This space houses a host of different instruments including scanning tunneling microscopes (STM) that have been moved from the University of Illinois at Urbana-Champaign, where our group had been from 1998 to the summer of 2005. The Princeton space is designed with three ultra-quiet rooms, which consist of double wall enclosures built around a massive plinth that is floating to isolate the experiments. Such a design leads to substantial reductions of both acoustic noise (because of the double enclosure) and seismic vibration (by floating the massive 35 Ton floors). One of these ultra-quiet rooms also has radio frequency shielding to make it possible to carry out experiments which are sensitive to radio frequency interference. Overall, the combination of acoustic, vibrational, and RF isolation make this an ideal space for a host of experiments in physics, including high resolution microscopy and spectroscopy measurements with STMs. The lab space has been designed in collaboration with Wilson Architects.
Dilution Refrigerator Scanning Tunneling Microscope (DR-STM)
This state-of-the-art STM that is one of the few instruments capable of operating at dilution refrigerator temperatures (50 mK) and high magnetic fields (14 T), extending the parameter space of the phenomena to which PNML has access. The system has been designed to allow for the in situ preparation of tips and samples using standard UHV tools, including the ability to heat samples and tips to > 1900C, Ar-ion sputtering, and depositing metals both at room temperature and cold. The instrument has the capability of taking spectroscopic data with exceptional resolution, and topographic data with atomic resolution, throughout the accessible phase space of temperature and magnetic field. We're currently exploiting the expanded phase space to look at the superconducting ground state of the heavy fermion compound CeCoIn5. Future plans include functionalizing the STM tip to detect magnetic signals, and exploiting rf techniques to achieve nanosecond time resolution, permitting the study of single spin dynamics.
Variable Temperature Scanning Tunneling Microscope (VT-STM)
We have constructed two variable temperature STMs capable of performing measurements in ultra-high vacuum (UHV) from room temperature down to 10 K. These system are equipped with both sputtering and evaporation sources for in-situ preparation of ultra-thin films. A great deal of care has gone into the design of this system to ensure thermal compensation, so as to avoid the typical problems associated with thermal drift. This instrument has been specifically designed to be able to track the same area of a sample surface at atomic scales as we vary the temperature. In this system we also have the added versatility by allowing the exchange of STM tips without venting the UHV system. This apparatus, with its ability to perform STM over a wide range of temperatures, is being used extensively in our investigations of correlated electronic states. We plan to continue to use these instruments to study a variety of phase transition phenomena.
Molecular Beam Epitaxy (MBE) instrument
Molecular beam epitaxy (MBE) is a process for growing thin, epitaxial films of a wide variety of materials, ranging from oxides to semiconductors to metals. It allows for controlled growth of 2D materials monolayer by monolayer, producing very clean, ordered samples for scanning tunneling microscopy (STM) experiments. The advantage of our new MBE system (completed December 2016) is that the PNML researchers will be able to precisely control and engineer sample growth while monitoring crystal structure through the diffraction pattern produced when an electron beam is reflected off of the sample. This allows custom engineering of new 2D material systems. The power of STM lies in imaging how electronic wavefunctions vary spatially on a surface with atomic resolution. Combined with the MBE, STM becomes a powerful tool to study topological superconductors and other phenomena like the quantum Hall effect which require very clean 2D films. The MBE’s vacuum chamber attains one of the purest laboratory vacuums achievable.
Ultra-low Temperature Scanning Tunneling Microscope (ULT-STM)
Time-lapse photos of ULT-STM build
This instrument, currently under construction, will operate at dilution refrigerator temperatures and vector magnetic fields (9-1-1 T). This STM has a modular design in which the microscope can be removed from UHV through a load-lock chamber for repairs and upgrades. This will allow us to extend the capabilities of the microscope (possibly adding functionalities such as atomic force microscopy (AFM) and other scanned probe techniques) without warming the cryostat or venting the UHV system. The sample stage of the microscope also provides access to source, drain, and gate electrodes for microscopy of two-terminal devices. In the future, we plan to add an MBE chamber and the ability to interchange magnets.