A.M. Chitu

Laser-induced phase separation of silicon carbide.

Understanding the phase separation mechanism of solid-state binary compounds induced by laser–material interaction is a challenge because of the complexity of the compound materials and short processing times. Here we present xenon chloride excimer laser-induced melt-mediated phase separation and surface reconstruction of single-crystal silicon carbide and study this process by high-resolution transmission electron microscopy and a time-resolved reflectance method. A single-pulse laser irradiation triggers melting of the silicon carbide surface, resulting in a phase separation into a disordered carbon layer with partially graphitic domains (∼2.5 nm) and polycrystalline silicon (∼5 nm). Additional pulse irradiations cause sublimation of only the separated silicon element and subsequent transformation of the disordered carbon layer into multilayer graphene. The results demonstrate viability of synthesizing ultra-thin nanomaterials by the decomposition of a binary system.

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

Controlled super lateral growth enhancement of single pulse laser irradiation by heat-retaining layer

Single-pulse excimer-laser-induced enhancement of lateral crystallization by applying a heat-retaining capping layer on amorphous silicon is well confirmed. Through analysis of polycrystalline silicon microstructure and of transient reflectance signal, we found that the capped sample had a 7 /spl mu/m lateral growth, along with an 1800 ns increased melt duration, which is one order of magnitude larger than the uncapped sample.