Formation Of Periodic Nanostructures Research Articles

Laser induced formation of periodic nanostructures in silicon covered by SiO2

Three-dimensional (3D) and two-dimensional (2D) periodic silicon nanostructures formed by polarized focused Nd:YAG laser irradiation (532 nm) with spot size less than 3 μm on Si covered by SiO2 are presented in this paper. We observed that at a low laser intensity I range, from I=0.9 to 1.08 W, 2D periodic coexisting of liquid and solid exists, while for 1.08 1.44 W). The periodicity of these periodic structures is 359 nm related to the wavelength of frequency doubledNd:YAG laser and the index of refraction of SiO2. We propose a model based on the fact that as the oxygen is diffusing locally from SiO2 into the melted Si, thus forming SiOβ with a lower melting point, successive pulses melt preferentially these regions giving rise to a positive feedback. This dynamic nanoscale modeling, based on variations of melting points of Si and dielectric and reflection coefficient, confirms the experimental results.

Silicon periodic nano-structures obtained by laser exposure of nano-wires

Silicon nano-wires were fabricated using thin Silicon on Insulator (SOI) wafers and a combination of anisotropic wet etching by Tetra-Methyl Ammonium Hydroxide (TMAH) and Local Oxidation of Silicon (LOCOS). These nano-wires were submitted to laser exposure using gas immersion laser doping (GILD). The result was the formation of either periodic nano-structures or silicon balls. Since the process uses very short laser pulses, it involves rapid melting and solidification of silicon. Hence, the observed periodicity is ascribed to Rayleigh instability, which involves surface tension effects in melted silicon.

Nano-Ablation with Short Pulse Laser

Recently, a periodic nano-structure formation by short pulse laser has been demonstrated for various materials, such as metals, dielectrics, and semiconductors. However, the patterned nano-structure could not be explained by the classical interference model and two temperature thermal model. Short pulse laser-matter interactions have different physics on the ablation mechanism from nanosecond laser ones. Additionally, the nano structure has been used for various kinds of applications, for example, diagnosis of the target composition, removal of small space debris, and surface modification. In this article, features of the short pulse laser ablation are reviewed and some applications are introduced.

Defect-deformational self-organization and nanostructuring of solid surfaces

Two-dimensional Fourier transformation of AFM, SEM and TEM images of the surface of solids macro- and nanostructured by three different techniques (laser-controlled atomic beam deposition on a glass substrate, electrochemical etching of semiconductors and UV pulsed laser recrystallization of thin amorphous semiconductor films on a glass substrate) reveals the presence of a similar, hidden, long-range, quasi-hexagonal order in the spatial distribution of surface inhomogeneities (nanoparticles, pores and crystalline grains). The occurrence of the long-range quasi-hexagonal order and other experimental data are described on the basis of a general Defect-Deformational (DD) theory of the spontaneous formation of surface periodic DD macro and nanostructures.

Formation of two-dimensional periodic nanostructures on fused quartz, polyimide, and polycrystalline diamond by pulsed four-wave interference laser modification

Atomic force microscopy is used to examine the topography of submicron periodic structures formed on the surfaces of synthetic polycrystalline diamond and polyimide films. The films are deposited on fused quartz substrates by four-wave interference modification using a pulsed 308-nm UV XeCl excimer laser. It is demonstrated that a two-dimensional periodic relief with a submicron period can be formed on the diamond surface directly by laser evaporation in the absence of a photoresist. Depending on the exposure, two mechanisms of polyimide film modification are observed. At exposures less than 100 mJ/cm2, the relief is formed due to swelling at the positions of interference maxima. At exposures greater than 100 mJ/cm2, holes are formed in the films. A periodic relief on the fused quartz surface is formed by using a UV photoresist exposed to pulsed interference laser radiation and subsequent Ar ion etching.

Can Kinetic Monte Carlo Simulation Help Experimentalists to Build Self-Organized Nanowires?

We present a critical discussion about the use of Kinetic Monte Carlo simulations for describing accurately the growth of metal atom nanowires and nanogratings on metallic vicinal surfaces. Aside from the external parameters (temperature, deposition flux, coverage and terrace width) defining the optimum conditions for the formation of low dimension periodic nanostructures, the predictive character of such simulations depends on the diffusion model via the interactions between the adatoms and the surface and between the adatoms themselves. The adequacy and failure of the method are commented using Ag/Pt surface as typical system.

Mechanism of shape formation of three-dimensional periodic nanostructures by bias sputtering

We previously demonstrated a process for fabricating three-dimensional (3D) periodic nanostructures composed of corrugated a-Si/SiO2 multilayers, which behave as 3D photonic crystals. In this process, bias sputtering is a key technique by which the pattern is self-forming. This letter clarifies the mechanism of the self-shaping effect of bias sputtering by comparing deposition simulation and experiments. The mechanism is decomposed into three main effects: diffuse incidence of neutral particles of film material, sputter etching by normally incident rare-gas ions, and subsequent redeposition of sputtered film material. Specifically, redeposition has a self-adjusting effect on the depth of holes or valleys, and is the key of formation of stable patterns.