SEMICONDUCTOR AND OXIDE NANOMATERIALS

A. Growth of metal-catalyzed Si nanowires:

The ability to control the growth and structure of Si nanowires on the atomic scale makes them attractive for a variety of noble applications in electronics, optoelectronics, and sensors. Earlier studies have suggested mechanisms underlying the metal catalyzed growth of Si nanowires, involving Si diffusion into a metal catalyst, eutectic Si-catalyst alloy formation, and Si precipitation at the catalyst-nanowire interface. However, many fundamental aspects regarding how synthesis conditions influence the nanowire growth and structure are still uncertain. Using first principles-based atomistic simulations we have studied the formation of silicon precipitates in a gold particle, the Si precipitation at the Si-AuSi interface, and the oxidation of AuSi alloys.

§ S.H. Lee and G.S. Hwang, “On the Nature and Origin of Si Surface Segregation in an Amorphous Au-Si alloy,” J. Phys. Chem. C 114, 3037 (2010).

§ S.H. Lee and G.S. Hwang, “Structure, energetics and bonding of amorphous Au-Si alloys,” J. Chem. Phys 127, 224710 (2007).

B. Synthesis and structure of oxide embedded Si/Ge nanoparticles:

This research intends to develop theoretical foundations for exploring the synthesis, manipulation and characterization of low dimensional Si and Ge structures encapsulated and/or embedded in insulator including: one-dimensional (1-D) Si and Ge nanowires encapsulated within SiO₂, and zero-dimensional (0-D) Si and Ge nanocrystals embedded in insulator (such as SiO₂, SiO_xN_y, high-k). The Si-Ge-Insulator nanosystems are receiving considerable attention because of not only their interesting fundamental properties but also promising applications in electronics and photonics. In particular, they have been realized as essential building blocks for future high speed and low power consuming logic and memory devices. Emphasis is placed on investigation of synthesis mechanisms of Si-Ge-oxide nanosystems and development of multiscale computational models capable of predicting the relationship between their synthesis, structure, and properties in various process conditions.

§ D. Yu and G.S. Hwang, “Structure and dynamics of Ge in the Si/SiO₂ system: Implications for oxide-embedded Ge nanoparticle growth,” Electrochem. Solid-State Lett. 11, P17 (2008).

§ D. Yu, S. Lee, and G.S. Hwang, “On the Origin of Si Nanocrystal Formation in a Si Suboxide Matrix,“ J. Appl. Phys. 102, 84309 (2007).

§ D. Yu, T.A. Kirichenko, S. Banerjee, and G. S. Hwang, “Structure and Diffusion of Excess Si Atoms in SiO₂,” Phys. Rev. B 72, 205204 (2005).

C. Growth, structure, and properties of oxide supported metal nanoparticles:

This work aims to develop a fundamental understanding of the synthesis, structure, composition, and reactivity of oxide-supported single and bimetallic nanoclusters. Nanometer sized metal clusters dispersed on oxide supports often exhibit much higher activity than single-component metal catalysts. Their catalytic performance markedly depends on cluster size, shape, and size distributions, along with support materials and support preparation methods. Supported metal nanoclusters can also easily rearrange and sinter during the course of thermally activated catalytic reactions even at moderate temperatures. An accurate assessment of the effects of cluster-support interactions on the growth, structure, and reactivity of supported metal clusters, as well as the adsorbate-induced structural changes is therefore necessary to understand their catalytic performance under realistic operating conditions.

§ D. Pillay and G. S. Hwang, “Growth and Structure of Small Au particles on TiO₂(110) Rutile,” Phys. Rev. B 72, 205422 (2005).

§ D. Pillay and G.S. Hwang, “Structure of Small Au_n, Ag_n, and Cu_n Clusters (n=2-4) on Rutile TiO₂(110): A Density Functional Theory Study,” J. Mol. Struct.-THEOCHEM 771, 129 (2006)

§ D. Pillay, Y. Wang, and G. S. Hwang, “Growth, Structure, and Chemistry of 1B Metal Clusters supported on TiO₂(110): Atomic Level Understanding from First Principles Studies,” Catalysis Today 105, 78-84 (2005).

§ D. Pillay, Y. Wang and G. S. Hwang, “A comparative theoretical study of Au, Ag and Cu adsorption on TiO₂(110) rutile surfaces,” KJChE 21(2), 537-547 (2004).

§ Y. Wang and G. S. Hwang, “Adsorption of Au atoms on stoichiometric and reduced TiO₂(110) rutile surfaces: a first principles study,” Surf. Sci. 542 (1-2), 72 (2003).