Characteristics study of silicon nanoparticles produced by laser ablation

Dissertant

Nayif, Adi Muhsin

Thesis advisor

Rashid, Bassam Ghalib

University

University of Technology

Faculty

-

Department

Applied Sciences Department

University Country

Iraq

Degree

Ph.D.

Degree Date

2010

English Abstract

Pulsed laser ablation (PLA) technique of Si nanoparticles on glass with near-infrared (1064 nm), and visible (532 nm) emissions of a pulsed Nd : YAG laser were studied.

Laser energy from 100 to 1000 mM, 10 ns pulse width and 1 Hz repetition frequency were used to ablate the target.

The target was rotated with constant speed to ensure uniform ablation.

The chamber was kept at a base pressure of (2 × 10-4) Torr.

Spectral analysis of optical transmittance and reflectance were recorded in the spectral range of 200-800 nm.

As a function of different parameters : laser wavelengths, laser energy, number of pulses and target to-substrate distances the study showed systematic changes that correspond to the thin films nanostructures.

Moreover, a using available mathematical model deduced the refractive index, the extinction coefficient, and the measured data of the experimental transmittance spectra were fitted with the Cauchy's equation.

The energy dependent absorption coefficient was calculated from optical spectra to determine the band gap (Eg).

It was found that when target-to-substrate distance increases, the band gap increases with a decrease in the confined dimension of the nanostructures a band gap widening due to the quantum confinement effect.

The photoluminescence (PL) measurements showed visible light emission in the range 400-800 nm from synthesized silicon nanoparticles.

The results clearly demonstrate that the PL band at ~1.8 eV is due to the quantum confinement effect (QCE) in the Si Nano crystal core, while the PL band at 2.5-2.8 eV is related to localize surface states at the Si / SiO2 interface.

The Raman spectrum obtained shows that the deposited material is amorphous; the Raman spectrum is characterized for two faint and broad bands at (150 cm-1) and (480 cm-1).

From X-Ray Diffraction (XRD) analysis and fixed Raman spectroscopy, it was confirmed that silicon samples nanoparticles are amorphous in nature.

Surface analysis by atomic force microscopy (AFM) showed that the morphology of the deposited films is nanostructured and demonstrated that the variation of laser energy from 300 to 500 mM results in an average roughness at the surface changing from 8.9 to 20.8 nm whereas at 600 mM the average roughness become 7.3 nm.

Furthermore, analysis of the film topography with scanning electron microscopy (SEM) images show a mixture of nanoparticles and droplets due to the melting and evaporation processes, revealed that PLA of Si nanoparticles at (1064 nm) results in films with the roughest surface and the best crystallographic properties.

At the same time, the films prepared at (532 nm) have the smoother surface but are of almost completely amorphous structure because of laser wavelength 1064 nm line penetrates deeply into the target, leading to a tremendous temperature rise in a large volume of the material.

Main Subjects

Physics

Topics

• Nanotechnology

• APA
• MLA
• AMA

Language

English

Data Type

Arab Theses

Record ID

BIM-305217