Hoo Jung Lee

Amorphous sputtered nickel–titanium thin films were deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. Their associated microstructure was monitored directly and simultaneously with in situ transmission electron microscopy. These electron-transparent membranes constrained the NiTi films and rendered it possible for observation of the complete transformation cycle, which includes: the crystallization of the amorphous phase to austenite phase (c

We investigated the uniaxial tension and stress relaxation properties of micron-scale Al beams for microelectromechanical systems applications in a piezoactuator-driven test apparatus. Pure aluminum and Al-1.5 at. % titanium free-standing beams were fabricated using micromachining procedures. In the tensile tests, we found the yield strength of the Al beams to be approximately 95 MPa. We also observed a significant strengthening effect in the alloyed samples, which had a yield strength approxima

Microstructures that emerge during the crystallization of amorphous materials depend on nucleation and growth kinetics. The ability to predict these final microstructures, particularly the average grain size, would allow better control of material properties. Well-established crystallization theories have proposed mathematical models to describe these microstructures. What remains missing, however, is an independent experimental verification of the microstructures these models predict. Here, we

This article reports the results of microtensile tests and transmission electron microscopy (TEM) analyses of micron-scale free-standing aluminum thin films. We fabricated the free-standing aluminum beams using micromachining procedures and tested them in a piezo-actuator-driven test apparatus. Microtensile tests revealed that the mechanical characteristics of the free-standing beams are quite different from those of the bulk material. Some unique features of our free-standing Al beams are high

Pt thin film temperature sensors (Pt T sensors) are embedded in micro gas sensors to measure and control the working temperature. We characterized electrical resistances of Pt T sensors and micro heaters with temperature changing in the oven and by Joule heating. In order to enhance the accuracy of temperature measurement by the Pt T sensors, we investigated the correlation among the Pt T sensor, micro heater, and the working temperature, which was linear proportional relation expressed as the e

Nowadays, the fabrication of robust and earth-abundant hydrogen evolution electrocatalysts with noble-metal-like catalytic activities is still facing great challenges. In this report, nanorod (NR)-shaped nickel sulfide (NiS) is successfully decorated on graphene (Gr) by utilizing carbon cloth (CC) as a substrate (NiS-Gr-CC). Benefiting from the NR morphology and strong interfacial synergetic effect between NiS and Gr, the NiS-Gr-CC electrocatalyst shows good catalytic activity for hydrogen evolu