inorganic/organic hybrid nanocomposite and its device applications

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  • Inorganic/Organic Hybrid Nanocomposite and its Device Applications

    S.K. Tripathi

    Department of Physics, Panjab University, Chandigarh-160 014, India

    surya@pu.ac.in

    Keywords: Chemical Synthesis, Metal-Semiconductor Contact, Nanocomposite, Polymer, Semiconductor

    Abstract. II-VI semiconductors are promising nanomaterials for applications as window layers in

    low-cost and high-efficiency thin film solar cells. These nanoparticles are considered to be the

    model systems for investigating the unique optical and electronic properties of quantum-confined

    semiconductors. The electrical and optical properties of polymers are improved by doping with

    semiconductor materials and metal ions. In particular, nanoparticle-doped polymers are considered

    to be a new class of organic materials due to their considerable modification of physical properties.

    In this paper, I review the present status of these types of Inorganic/Organic hybrid nanocomposite

    materials. CdSe nanorods dispersed in polyvinyl alcohol (PVA) matrix have been prepared by

    chemical routes. Different characterization techniques like structural, optical and electrical have

    been used to characterize these nanocomposites. The devices like Schottky diodes and MOS

    structures have been fabricated and the results have been discussed in this review. The results have

    been compared with the reported literature by other groups also.

    Table of Contents

    1. Introduction 2. What is a Polymer Nanocomposite? 2.1. Types of Polymer Nanocomposites

    2.2. Properties of Polymer Nanocomposite

    2.2.1. Physical properties

    2.2.2. Mechanical properties

    2.2.3. Electrical properties

    2.2.4. Crystallinity and barrier properties

    2.2.5. Dielectric and magnetic properties

    2.2.6. Optical properties

    3. Polymer Surface at the Nanoscale 4. Factors that affect Polymer Nanocomposites Structure 4.1. Synthesis Method

    5. An Over View of Nanorods 6. Characterization of Nanostructures 7. II-VI Semiconductor Nanocomposites 7.1. CdSe/PVA Nanocomposite

    7.2. Preparation of II-VI Semiconductor Nanocomposites

    8. Device Fabrication and Characterization 8.1. Metal-Semiconductor Contact

    8.2. Metal-Oxide-Semiconductor Interfaces

    9. II-VI Semiconductor Devices 10. Summary

    References

    Solid State Phenomena Vol. 201 (2013) pp 65-101Online available since 2013/May/14 at www.scientific.net (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/SSP.201.65

    All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 132.174.255.116, University of Pittsburgh, Pittsburgh, USA-02/12/14,16:50:52)

    http://www.scientific.nethttp://www.ttp.net

  • 1. Introduction

    Nanoparticles are thought to hold some keys for solving many present and future technological

    demands. However, direct applications of these nanoparticles are limited due to their size and

    stability. They aggregate easily because of their high surface energy, and are quickly oxidized as

    well. To overcome the aggregation and stability problems, these nanoparticles are incorporated in a

    dielectric matrix thereby forming a nanocomposite. Polymers, when used as a dielectric matrix

    result in a wide range of useful characteristics in the nanocomposites.

    Composites are used when a combination of properties is required that cannot be found in a single

    material. Particularly interesting are combinations of organic polymers and inorganic materials as

    the properties of the pure components are very distinct. In general, organic polymers are flexible,

    tough, and are easy to process, but they can also be relatively easily damaged, either chemically or

    mechanically. In contrast, inorganic materials are typically much harder, have better barrier

    properties, and have a good chemical stability, but are also brittle and are difficult to process.

    Organic/inorganic composites may yield a combination of these properties, resulting in a hard,

    chemically stable and durable material that is still easy to process.

    The properties of a composite are not simply the average properties of its components but it

    involves their volume fraction, size, shape and the distribution. In a composite one component may

    be enclosed by another component that forms a continuous phase, but it is also possible that the

    components form continuous phases resulting in interpenetrating networks. The interactions

    between the different components may induce changes in the chemical or physical structure of the

    components, especially in the first few nanometers from the interface [1-3]. The interfacial area

    increases with decreasing domain size in the composite. For nanocomposites, with domain sizes of

    about 10 nm, 1 cm3 of composite may contain several hundred square meters of interface. The

    addition of a third component that concentrates at the interface and alters the interactions can have

    strong effects on the composite properties [2-6]. The third component may be a surfactant that

    assembles at the interface by physical adsorption, or it may be a reactive species that is grafted on

    the surface of the filler or it may even react with both phases forming a chemical bond between the

    two phases [5]. This modification of the interface is often used to improve the mechanical

    properties of composites.

    2. What is a Polymer Nanocomposite?

    As the name indicates Polymer Nanocomposite means composed of polymer + nanocomposite.

    A composite material is a combined material created from two or more components, selected filler

    or reinforcing agent and a compatible matrix, binder (i.e. resin) in order to obtain specific

    characteristics or properties that were not there before. The matrix is the continuous phase, and the

    reinforcement constitutes the dispersed phase. It is the behavior and properties of the interface that

    generally control the properties of the composite. [7]

    The load acting on the matrix has to be transferred to the reinforcement via the interface. Thus,

    reinforcements must be strongly bonded to the matrix, if their high strength and stiffness are to be

    imparted to the composite. The fracture behavior is also dependent on the strength of the interface.

    A weak interface results in low stiffness and strength, but high resistance to fracture, whereas a

    strong interface produces high stiffness and strength but often a low resistance to fracture, i.e.,

    brittle behavior. The exact role of interface may differ with the type of reinforcement. The interface

    can be viewed as a planar region of only a few atoms in thickness across in which there is a change

    in properties from those of the matrix to those of the reinforcement. Thus, the interface is usually a

    discontinuity in chemical nature, crystal and molecular structure, mechanical and other properties.

    66 Functional Nanomaterials and their Applications

  • Nanocomposites are materials that are created by introducing nanoparticulates (often referred to as

    filler) into a macroscopic sample material (often referred to as the matrix). This is part of the

    growing field of nanotechnology. After adding nanoparticulates to the matrix material, the resulting

    nanocomposite may exhibit drastically enhanced properties. For example, adding carbon nanotubes

    tends to drastically add to the electrical and thermal conductivity. Other kinds of nanoparticulates

    may result in enhanced optical properties, dielectric properties or mechanical properties such as

    stiffness and strength. In general, the nanosubstance is dispersed into the matrix during processing.

    Fig. 1 Comparison between microcomposites and nanocomposites

    In materials research, the development of polymer nanocomposites is rapidly emerging as a

    multidisciplinary research activity whose results could broaden the applications of polymers to the

    great benefit of many different industries. Nanocomposites are a distinct form of composite

    materials, which involve embedding nano or molecular domain sized particles into organic polymer,

    metal or ceramic matrix materials. In all cases, it is perceived that the intimate inclusion of these

    nanoparticles in these matrices can completely change the properties of these materials. The

    nanoparticles can serve as matrix reinforcement as well as change the electrical behavior of these

    base materials. The reason for this is that with such small inclusions, a large amount of interfacial

    phase material is now included in the bulk of these nanocomposites. A complete transformation of

    the materials chemical, mechanical and morphological domain structure can be achieved by the

    proper addition of nanoparticles.

    Polymer Nanocomposites (PNC) [8] are polymers (thermoplastics, thermosets or elastomers) that

    have been reinforced with small quantities (less than 5% by weight) of nano-sized particles having

    high aspect ratios (L/h > 300). PNCs represent a radical alternative to conventional filled polymers

    or polymer blends [9-10]. In contrast to conventional composites, the reinforcement and PNCs are

    of the order of microns and few nanometers respectively. The transition from micro- to nano-

    particles leads to change in its p

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