Patrick J. McCluskey

Scanning AC nanocalorimetry combined with in-situ x-ray diffraction

Micromachined nanocalorimetry sensors have shown excellent performance for high-temperature and high-scanning rate calorimetry measurements. Here, we combine scanning AC nanocalorimetry with in-situ x-ray diffraction (XRD) to facilitate interpretation of the calorimetry measurements. Time-resolved XRD during in-situ operation of nanocalorimetry sensors using intense, high-energy synchrotron radiation allows unprecedented characterization of thermal and structural material properties. We demonstrate this experiment with detailed characterization of the melting and solidification of elemental Bi, In, and Sn thin-film samples, using heating and cooling rates up to 300 K/s. Our experiments show that the solidification process is distinctly different for each of the three samples. The experiments are performed using a combinatorial device that contains an array of individually addressable nanocalorimetry sensors. Combined with XRD, this device creates a new platform for high-throughput mapping of the composition dependence of solid-state reactions and phase transformations.

A scanning AC calorimetry technique for the analysis of nano-scale quantities of materials.

We present a scanning AC nanocalorimetry method that enables calorimetry measurements at heating and cooling rates that vary from isothermal to 2 × 10(3) K/s, thus bridging the gap between traditional scanning calorimetry of bulk materials and nanocalorimetry. The method relies on a micromachined nanocalorimetry sensor with a serpentine heating element that is sensitive enough to make measurements on thin-film samples and composition libraries. The ability to perform calorimetry over such a broad range of scanning rates makes it an ideal tool to characterize the kinetics of phase transformations or to explore the behavior of materials far from equilibrium. We demonstrate the technique by performing measurements on thin-film samples of Sn, In, and Bi with thicknesses ranging from 100 to 300 nm. The experimental heat capacities and melting temperatures agree well with literature values. The measured heat capacities are insensitive to the applied AC frequency, scan rate, and heat loss to the environment over a broad range of experimental parameters.

In-situ X-ray diffraction combined with scanning AC nanocalorimetry applied to a Fe0.84Ni0.16 thin-film sample.

We combine the characterization techniques of scanning AC nanocalorimetry and x-ray diffraction to study phase transformations in complex materials system. Micromachined nanocalorimeters have excellent performance for high-temperature and high-scanning-rate calorimetry measurements. Time-resolved X-ray diffraction measurements during in-situ operation of these devices using synchrotron radiation provide unprecedented characterization of thermal and structural material properties. We apply this technique to a Fe0.84Ni0.16 thin-film sample that exhibits a martensitic transformation with over 350 K hysteresis, using an average heating rate of 85 K/s and cooling rate of 275 K/s. The apparatus includes an array of nanocalorimeters in an architecture designed for combinatorial studies.

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

Fabrication and Characterization of Fe-Pd Ferromagnetic Shape-Memory Thin Films

Fe-Pd thin films with approximately 30 at.% Pd have been produced by magnetron sputtering. Various heat treatment conditions were studied in order to obtain the face-centered tetragonal (fct) martensitic phase at room temperature. X-ray diffractometry was used to identify the various phases present at room temperature and the substrate curvature technique was employed to measure film stress as a function of temperature. The shape memory effect was demonstrated in samples containing the fct martensite phase at room temperature.