Tài liệu Vật liệu nanosilicon

Contents
1.1 Introduction 3
1.2 Synthesis 3
1.2.1 Physical Techniques 3
1.2.2 Physico-Chemical Techniques 4
1.2.3 Chemical Techniques 4
1.2.4 Electrochemical Techniques 4
1.2.5 Discretely Sized Si Nanoparticles 6
1.3 Functionalization 8
1.3.1 Initial Surface Condition 9
1.3.2 Alkylated Particles 11
1.3.3 Aggregation and Solubility 15
1.3.4 Stability in Acid 17
1.4 Spectroscopic Characterization 17
1.4.1 Fourier Transform Infrared Spectroscopy 17
1.4.2 Nuclear Magnetic Resonance 19
1.4.3 Gel Permission Chromotography 20
1.4.4 X-Ray Photospectroscopy 21
1.4.5 Auger Electron Spectroscopy 21
1.4.6 Transmission Electron Microscopy 21
1.5 Optical Properties 22
1.5.1 PL and Detection of Single Nanoparticles 22
1.5.2 PL Lifetime 26
1.5.3 Cathodoluminescence and Electroluminescence 27
1.5.4 Photostability Under UV and Infrared Radiation 29
1Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
2Department of Physics, North Carolina State University, Raleigh,NC, USA.
Nanosilicon Copyright © 2007. Elsevier Ltd.
9780080445281 All rights reserved.
1.6 Reconstitution of Particles in Films 29
1.6.1 Precipitation Spray 30
1.6.2 Electrodeposition: Composite Films of Metal and Nanoparticles 31
1.6.3 Silicon Sheet Roll into Tubes 32
1.6.4 Self-Assembly 33
1.7 Nonlinear Optical Properties 34
1.7.1 Stimulated Emission 34
1.7.2 Second Harmonic Generation 39
1.7.3 Gain and Optical Nonlinearity 39
1.8 Effect of Functionalization on Emission 41
1.9 Structure of Particles 41
1.9.1 Luminescence Models 42
1.9.2 Computational Methods for Electronic Structure of Nanoclusters 43
1.9.3 Prototype of Hydrogenated Particles (Supermolecule) 49
1.9.4 H2O2 Effect on Surface Reconstruction 51
1.9.5 Novel Si!Si Bonds (Molecular-Like Behaviour) 52
1.9.6 Structural Stability of the Prototype 54
1.9.7 Material Properties: Dielectric Constant and Effective Mass 55
1.9.8 Excited States (Molecular-Like Bands) 57
1.9.9 Collective Molecular Surface 57
1.9.10 Phonon Structure: Collective Molecular Vibration Modes 59
1.9.11 Molecular-Like Emission: Direct versus Indirect Process 60
1.9.12 X-Ray Form Factors 61
1.9.13 Effect of Termination on the Band Gap 63
1.10 Device Applications 63
1.10.1 Photoelectric Conversion/UV Photodetector 64
1.10.2Metal Oxide Silicon Memory Devices 66
1.10.3 Biophotonic Imaging 68
1.10.4 Amperometric Detection 69
1.10.5 Nanosolar Cell 71
1.10.6 Nanoink Printing 72
1.10.7 Single Electron Transistor Devices 73
1.11 Conclusion 73
Acknowledgements 74
References 74
Abstract
Unlike bulk silicon, a spectacularly dull material, ultrasmall silicon nanoparticles are
spectacularly efficient at emitting light in RGB colours. In addition to being ultrabright,
reconstituted films of particles exhibit stimulated emission. Light-emitting Si devices
could eventually result in a laser on a chip, new generation of Si chips, and extend
the functionality of Si technology from microelectronics into optoelectronics and
biophotonics. We present in this review experimental as well as theoretical and simulations
results discussing the synthesis, structure, and the wide-ranging optical,
electronic, mechanical and (derivatized) biocompatible properties and applications of
the particles. We discuss the basic mechanism behind the multi-novel properties in
terms of silicon–hydrogen configurations of filled fullerene. With a tetrahedral core and
a strong molecule-like reconstruction of the surface, the particles constitute a new phase
or “supermolecule” that exhibits solid-like behaviour as well as molecule-like behaviour.
2 Munir H. Nayfeh and Lubos Mitas
1.1 Introduction
The area of nanoparticles (nanocrystallites (nc) or quantum dots) is one of the
most active areas of science today. In particular, silicon nanoparticles is a burgeoning
and fascinating area of science and one that has significant technological implications.
This new charge of interest came nearly a decade after the exciting discovery by
Canham in 1990 [1,2] of visible red photoluminescence (PL) at room temperature
with a quantum efficiency of few percent, from electrochemically etched silicon
(porous silicon (PS) layer). Although in the ensuing years, the quantum efficiency
remained practically small, dashing hopes for optoelectronics integration from this
development stimulated a variety of physical, chemical, physiochemical, and electrochemical
techniques to produce dispersions of luminescent nanometre sized silicon
crystallites. The research led by Nayfeh at Illinois in 2000 has shown that reducing the
size of an elemental Si crystal to a few tens of atoms (1 nm), without altering its
chemical composition, effectively creates a new material, a nanoparticle with novel
properties – both electronic and non-electronic, including ultrabright ultrastable
luminescence – that were not available before [3–22]. This research demonstrated that
single-element Si particles – an abundant, stable, environmentally benign, malleable
nanomaterial – have versatile and wide-ranging optical, electronic, and (derivatized)
biocompatible properties. These properties have drawn the interest of engineering,
physics, chemistry, material science, and biology, and medical researchers alike.
Ultrabright silicon structures are particularly intriguing for several reasons. First,
bulk Si is spectacularly inefficient at emitting light. Second, light-emitting nanoparticles
can be synthesized at very low cost, without resort to either the costly lithographic
or epitaxial techniques. Third, the most technologically important and abundant
material, Si, is the backbone of the microelectronics industry, dominating the
microelectronics revolution. Light-emitting Si devices could eventually result in a
new generation of Si chips and in a laser on a chip, and extend the functionality of
Si technology from microelectronics into optoelectronics and biophotonics.
We discuss the synthesis, structure, origin of brightness, and the wide-ranging
optical, electronic, and (derivatized) biocompatible properties of the family. Finally
we present a number of device applications in electronics, optoelectronics, and
biophotonics.
1.2 Synthesis
Several procedures have been developed throughout the last decade for the synthesis
of luminescent Si nanoparticles [3–47]. These include physical, physiochemical,
chemical, and electrochemical procedures. We will discuss the procedures, size, uniformity
in size, throughput, cost, and amenability to mass production, and recovery.