Ui-Jin Chung

Substrate temperature effects on laser crystallized NiTi thin films

Amorphous sputter-deposited NiTi thin films were subjected to pulsed, melt-mediated laser crystallization techniques to engineer their microstructure. The effects of laser processing of preheated films are examined. Laser processing of films at an elevated substrate temperature has a significant effect on the rate with which solidification occurs. It is observed that the preheating temperature at which processing is carried out has significant implications for the resulting phase and microstructure, and therefore mechanical properties. Furthermore, the microstructural effects of varying incident laser energy density are examined via atomic force microscopy, scanning electron microscopy, and x-ray diffraction, and mechanical/shape memory properties are characterized via nanoindentation.

On the lateral crystal growth of laser irradiated NiTi thin films

This letter demonstrates the ability to induce laterally grown, large-aspect crystals via pulsed, melt-mediated laser crystallization in NiTi thin films. Sputter-deposited 200 nm NiTi films were pulse irradiated utilizing a homogenized 308 nm excimer beam over a series of varying incident laser energy densities. Solidification occurred via two distinct pathways: nucleation and growth occurred away from the boundary of irradiation, while lateral growth of unmelted seeds into the undercooled melt developed at the boundary of irradiation. The potential for exploiting this technique to produce rolling direction texture for anisotropic properties is also discussed.

Resolving Bulk and Grain Boundary Transport Properties of TiO2 Thin Films Enabled by Laser‐Induced Anisotropic Morphology

Metal oxide thin fi lms are at the forefront of research and development in microelectronics, optoelectronics, and energy conversion and storage devices. They are employed as highκ gate dielectrics in fi eld effect transistors, [ 1 ] transparent electrodes in solar cells and light emitting diodes, [ 2 ] electrodes in photoelectrochemical cells for solar energy conversion to electricity and fuel, [ 3 ] ferroelectric memories and piezoelectric microsensors and microactuators, [ 4 ] gas sensors, [ 5 ] and other important technologies. While some applications require highly ordered epitaxial fi lms, others suffi ce with polycrystalline fi lms that can be fabricated using conventional deposition techniques such as sputtering, CVD, and chemical solution deposition. [ 6 ] The functional properties of these fi lms depend on their microstructure. In particular, grain boundaries (GB) have signifi cant effect on the transport properties of polycrystalline metal oxide thin fi lms because, similarly to other semiconductors, [ 7 , 8 ] they display quite different properties than the bulk. [ 9 ] While GB are often associated with adverse effects in microelectronic and optoelectronic devices, in some applications such as gas sensors [ 10 ] and varistors [ 11 ] they play important role in the operation mechanism. One way or another, controlling the grain morphology of polycrystalline metal oxide thin fi lms is desired from both scientifi c and technological standpoints. In this work we present a unique method for tailoring the microstructure of TiO 2 thin fi lms by means of laser-induced melting and sequential lateral solidifi cation (SLS) process. The SLS-processed fi lms displayed elongated grain morphology with 3D texture. Impedance spectroscopy measurements with two sets of electrodes aligned perpendicularly and in parallel to the elongated grains enabled precise deconvolution of the grain and GB contributions to the overall impedance, shedding new light on the electronic transport properties of TiO 2 thin fi lms. Thin fi lm processing methods based on laser-induced melting and solidifi cation have been employed for tailoring the microstructure of Si [ 12 ] and metallic fi lms such as Al [ 13 ] and NiTi. [ 14 ] These methods, however, have not been applied before to ceramic fi lms because of their brittleness and high