Figure 1: (Left) Results of numerical calculations to model the temperature dependence of a bilayer cantilever under pulsed laser illumination. (Center) Experimental setup for optical nanocalorimeter. (Right) Raman spectra of Gd3N@C80 and calculated molecular structure.
Recent advances in technology have enabled, and also demanded, that calorimeters become smaller, faster, and more accurate. For the analysis of very thin films and particles, on the scale of nanometers and nanograms, even the most sophisticated differential scanning electrical calorimeters are no longer accurate. An alternative to the current electrical calorimeters, which are limited by numerous electrical leads and can cause damage to the sample under investigation, is a nondisruptive, high-speed optical method capable of measuring high density arrays at rates several orders of magnitude faster (~108 °C/s).
Bilayer cantilevers, which operate on the principle of thermal activation, may be utilized in a twin arrangement, a sample and a reference, with a common heat source to measure the heat flow into the sample. Through the use of an avalanche photodiode (APD), at sampling rates up to ~10 MHz, and a lock-in amplifier, the frequency and amplitude shifts of the bilayer cantilevers can be measured with amazing accuracy using heterodyne techniques (sum and differential). From these results, one may perform differential scanning calorimetry (DSC) to determine thermodynamic properties of the sample, such as heat capacity and enthalpy, as well as thermal gravimetric analysis (TGA) to detect changes in weight.
The proposed study will aspire to: (1) determine the optimal design and materials for the bilayer cantilevers; (2) characterize and determine the resolution of the APD; (3) develop a prototype optical nanocalorimetry system by lithographically fabricating bilayer cantilevers and testing their response; (4) investigate standard samples of known freezing points (ITS-90), such as thin films of Zn, Al, and Ag; and (5) investigate and characterize exploratory materials.
Selected Publications (Prior to Joining NIST)
Physicist, NIST Associate
Functional Properties Group
2010-present: NIST Associate (Advisor: David LaVan, Ph.D.)
Ph.D., Physics, University of Virginia, 2010