Principal Techniques used in our Lab

Heat Capacity Measurements at Low Temperatures

To observe phase transitions in two dimensional films, we employ both AC and DC Calorimetry Techniques in our heat capacity measurements. We have several cryostats, among which is a Helium-4 cryostat that uses AC calorimetry to make sensitive measurements and another using DC pulse calorimetry with a Helium Dilution Refrigerator to cool it down to temperatures of about 100 mK. A cryocooler that goes down to about 8K is also used for quick cooldown to relatively 'high' temperatures.

Vapor Pressure Isotherms

To be able to measure the effective area of an adsorption cell, vapor pressure isotherms are measured. Small substeps in these signals indicate monolayer completion, which together with known amounts of gas dosed in, can be used to figure out exact surface areas. These can also be used to track features delineating phase boundaries in thermodynamic phase diagrams.

Quartz Microbalance Techniques

When a helium film adsorbed on an microbalance oscillator becomes superfluid, it decouples from the oscillating system and manifests this as a frequency change. These can be used to track superfluidity as well as determine small adsorption areas using vapor pressure isotherms.

Neutron Scattering Techniques

In collaboration with European Laboratories, neutron diffraction and quasi-elastic neutron scattering techniques are also used to measure mobility and determine whether structures of a monoloyer film behave like two-dimensional solids or are fluids. These have also aided us in determining if single-layer mixtures of hydrogen and deuterium phase separate.

Low Temperature SQUID