Parallel nano-Differential Scanning Calorimetry: A New Device for Combinatorial Analysis of Complex nano-Scale Material Systems

A new device is presented for the combinatorial analysis of complex nano-scale material systems. The parallel nano-differential scanning calorimeter (PnDSC) is a micro-machined array of calorimetric cells. This new approach to combinatorial calorimetry greatly expedites the analysis of nano-scale material thermal properties. A power-compensation differential scanning calorimetry measurement is described. The scanning calorimetry capability of the PnDSC is demonstrated by a specific heat measurement of an amorphous equiatomic NiTi thin film. Introduction Differential scanning calorimetry (DSC) is a primary technique for measuring the thermal properties of materials. A typical DSC system requires relatively large amounts of test material, making thermal measurements on nano-scale samples difficult if not impossible. Thus, while traditional DSC has proved a very useful technique, its application in nanotechnology, where sample sizes can be very small, is rather limited. Since the properties of materials on the nano-scale may differ significantly from their bulk counterparts [1], a DSC system that is sensitive enough to probe nano-scale quantities is desirable. Furthermore, traditional DSC systems are limited to taking one measurement at a time, and a new sample must be loaded between each measurement. This severely limits the use of a traditional DSC in combinatorial studies at the nanoscale. To obtain reasonable precision on thermal properties as a function of composition many samples must be measured. Anything beyond a binary material system quickly involves unreasonable amounts of time to perform a full analysis. To improve these limitations, we have developed a parallel nano-differential scanning calorimeter (PnDSC) that combines DSC and combinatorial analysis in a novel way. This system is ideal for studying complex material systems. The heart of the PnDSC measurement system is a micro-machined, 5X5 array of calorimetric cells. The PnDSC and complimentary measurement system reduce the analysis time of complex nano-scale material systems by at least an order of magnitude. Physical description The PnDSC is a 5x5 array of calorimetric cells supported by a square Si frame. A thin (~ 100 nm) silicon nitride film is continuous across the surface of the device. Portions of this film are freestanding, creating the membrane of the calorimetric cell. The membranes are positioned uniformly across the device. Each cell has planar dimensions of approximately 2.5 x 5 mm. A thin-film (~ 150 nm) metal strip (width ~ 400 μm), typically W, patterned on the membrane serves as a heater and resistive thermistor in a four-point measurement scheme. Probes patterned from the same metallization layer, attach close to the ends of the thermistor. The individual cells of the PnDSC are largely