Cooke David W, Hellman F, Groves J R, Clemens B M, Moyerman S, Fullerton E E
Department of Physics, University of California at Berkeley, Berkeley, California 94720-7300, USA.
Rev Sci Instrum. 2011 Feb;82(2):023908. doi: 10.1063/1.3554440.
Thin film growth allows for the manipulation of material on the nanoscale, making possible the creation of metastable phases not seen in the bulk. Heat capacity provides a direct way of measuring thermodynamic properties of these new materials, but traditional bulk calorimetric techniques are inappropriate for such a small amount of material. Microcalorimetry and nanocalorimetry techniques exist for the measurements of thin films but rely on an amorphous membrane platform, limiting the types of films which can be measured. In the current work, ion-beam-assisted deposition is used to provide a biaxially oriented MgO template on a suspended membrane microcalorimeter in order to measure the specific heat of epitaxial thin films. Synchrotron x-ray diffraction showed the biaxial order of the MgO template. X-ray diffraction was also used to prove the high quality of epitaxy of a film grown onto this MgO template. The contribution of the MgO layer to the total heat capacity was measured to be just 6.5% of the total addenda contribution. The heat capacity of a Fe(.49)Rh(.51) film grown epitaxially onto the device was measured, comparing favorably to literature data on bulk crystals. This shows the viability of the MgO∕SiN(x)-membrane-based microcalorimeter as a way of measuring the thermodynamic properties of epitaxial thin films.
薄膜生长能够在纳米尺度上对材料进行操控，从而有可能创造出在体相中未见的亚稳相。热容提供了一种直接测量这些新材料热力学性质的方法，但传统的体相量热技术不适用于如此少量的材料。微量热法和纳量热法技术可用于测量薄膜，但依赖于非晶膜平台，限制了可测量薄膜的类型。在当前工作中，离子束辅助沉积用于在悬浮膜微量热计上提供双轴取向的MgO模板，以便测量外延薄膜的比热。同步加速器X射线衍射显示了MgO模板的双轴有序性。X射线衍射还用于证明生长在该MgO模板上的薄膜外延的高质量。测量得出MgO层对总热容的贡献仅为总附加贡献的6.5%。测量了外延生长在该器件上的Fe(.49)Rh(.51)薄膜的热容，与体相晶体的文献数据相比具有优势。这表明基于MgO∕SiN(x)膜的微量热计作为测量外延薄膜热力学性质的一种方法是可行的。
