Overall Aspects of Non-Traditional Glasses: Synthesis, Properties and Applications

Helena Cristina de Sousa Pereira Menezes e Vasconcelos, Maria Clara Gonçalves

• Publisher: Bentham Science Publishers
• Year: 2016
• ISBN:
  9781681082073
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The structural properties of glass (non-crystalline structure with short-range order, continuous molecular network with no intergranular boundaries, isotropy, easy transition into a plastic state within a wide temperature range) allow a freedom of design that few materials offer. The addition of different materials to glass during the manufacturing process also confers different physical properties to the final product. There has been a proliferation of several types of glass over the last century with a wide array of applications such as in household ceramics, medicine, telecommunications, optical instruments and much more.
This monograph guides readers through the science of glass. It starts by giving a general summary of glass properties and progresses to explain different glass types that have had a wide scientific and commercial impact in our lives. The glass types covered in this text include bioglass, fluoride glass, glass ceramics, photonic glass, solar glass and chalcogenide glass.
This book serves as a textbook for ceramic and glass engineering courses and a concise reference on glass science for new researchers in the field of materials science.

Photonic Bandgap Glass-Based Structures

1.. Introduction

Gem opals, wings of butterflies and peacocks, fish scales, beetles, among a large number of other biological and mineral materials exhibit iridescence, strong multiple scattering, and unexpected forbidden wave propagation in certain frequency ranges (Fig. 1). Nanostructured systems are in the basis of such behaviour [1, 2].

Photonic crystals (PCs) are the artificial counterparts. PCs as it is often called photonic band gap materials (PBGs) are artificial composite materials, micro/nanostructured on an optical length scale (e.g. few hundreds of nm). The resulting periodicity in the dielectric constant ε (or in the refractive index n,) is responsible for inhibiting light (of frequencies in the visible or near infra-red range) from propagating through the material as a result of Bragg diffraction [3]. The forbidden frequency range is called a stop band. In PCs the electromagnetic waves within the band gap are completely reflected by the crystal, while spontaneous emission (within the band gap) are totally concealed.

Figure 1)

Biological and mineral iridescent materials and respective nanostructure: (a)-(b) gem opal, (c)-(d) wings of butterfly, (e)-(f) beetles.

PBGs can be in one, two or three dimensions (1D, 2D or 3D) (Fig. 2), function of the dimensionality of the refractive index periodicity. A complete PBG, where all electromagnetic propagation is disallowed whatever the direction of propagation or the polarization, is only possible in 3D structures. Further, the dielectric constants ratio of the composite materials must be higger than 2.8.

Figure 2)

Schematics of 1D, 2D and 3D PCs. Distinct colors stand for different dielectric materials [3].

PCs are the optical analogue of electronic bandgap in semiconductors; it is believed that PCs should be able to transfer the full functionality of semiconductor devices into the all optical field, combining high integration with high speed processing.

PCs have attracted much interest due to the innumerous technological applications resulting from the multiple ways in which PCs may control and customize the flow of light, as the inhibition of spontaneous emission processes, the existence of photonic bandgaps (PBGs), or the confinement of light at defects. Besides they promise a large number of applications in different scientific and commercial areas like novel types of waveguides and optical fibers, new filters, high-speed switches, low-threshold microlasers, high-performance LEDs (light emitting diode), photonic for VLSI (very large scale integration), along with novel biological and chemical sensors (see 7. Photonic Crystals Applications).

Traditionally, both top-down and bottom-up approaches have been used to fabricate PCs. The methodology chosen often depends on the dimensionality of the PCs under studied-2D, for example, are often fabricated through gas source molecular beam epitaxy, two-photon lithography, direct-write electron-beam lithography, reactive-ion etching, oxidation processes or holographic methods, all top-down methodologies. 1D and 3D structures are often fabricated through bottom-up sol-gel protocols [2 - 7] (references wherein). All these methods are based and take profit of current nanotechnology processes and fabrication system capable of operating and patterning at the sub wave scale. Fig. (3) shows SEM (scanning electron microscope) pictures of 1D and 2D PCs fabricated on SOI (silicon-on-insulator) technology, by combining electron beam lithography and etching processes; Fig. (4) illustrates SEM micrographs of 3D PCs fabricated by sol-gel methodology.

Figure 3)

SEM pictures of: (a) 1D and (b) 2D PCs in SOI technology fabricated by electron beam lithography.

Figure 4)

SEM micrographs of 3D PCs fabricated by sol-gel technology: (a) opal and (b) inverted opal.

2.. Photonic crystals-Physical principles

To understand the physical principles behind PCs, it is helpful to start with their electronic analogues. As excellently explained in ref. [3], a crystal can be defined as a periodic arrangement of molecules or atoms repeated in space according to a crystal lattice. The constituents of the crystal (patterns: atoms, ions, molecules) as well as its geometric lattice (and there are 14 Bravais lattices) define the crystal structure which rules the conduction properties of the crystal, i.e., the way electrons will propagate through the crystal periodic potential. Electrons propagate as waves, and waves that meet certain criteria can travel through a periodic potential without scattering. But, in addition, the periodic lattice may inhibit the propagation of some waves, creating gaps in the crystal energy band where electrons are inhibited to propagate in specific directions. Moreover, if the lattice potential is sufficiently strong, a complete band gap, covering all possible propagation directions could be reached. This is what happens, for example, in semiconductor materials where a complete band gap between the valence and conduction energy bands is observed.

In a PC, the periodic die...

Table of contents

• Welcome
• Table of Contents
• Title Page
• BENTHAM SCIENCE PUBLISHERS LTD.
• FOREWORD
• PREFACE
• General Features about Glasses
• Glasses as Biomaterials
• Glass-Ceramics: Concepts and Practical Aspects
• Heavy Metal Fluoride Glasses
• Chalcogenide Glasses
• Photonic Bandgap Glass-Based Structures
• Glass in Solar Energy