Special Issue "Energy Technology for the 21st Century - Materials and Devices"

Type of Paper: Review
Title: Recent Developments in Polymer Composite Dielectric Materials
Author: Dr. Hanno zur Loye
Affiliations: David W. Robinson Palmetto Professor, University of South Carolina Department of Chemistry and Biochemistry, 631 Sumter Street Columbia, SC, USA. E-Mail:zurloye@mail.chem.sc.edu
Abstract: This review covers the field of polymer composite dielectric materials, specifically focusing on composites with potential application in capacitor technologies for pulse power applications. The review is divided into several sections including an overview of the fundamentals of using capacitors for energy storage, a discussion on the importance of the polymer/additive interface and the known effects of size (nano vs. macro) on the observed properties, the advantages of using the polymer’s radius of gyration for classifying the additive size regime, a summary of measurement techniques for determining the dielectric constant, leakage current, and the breakdown voltage in polymer dielectrics, as well as a literature review of polymer composite dielectric materials and their measured properties. 

Type of Paper: Review
Title: Synthesis, Characterization, and Application of 1-D/3-D Cerium Oxide Nanomaterials: A review
Authors: Kuen-Song Lin * and Sujan Chowdhury
Affiliations: Department of Chemical Engineering and Materials Science/Fuel Cell Center,Yuan Ze University, Chung-Li City, Taiwan 32061, R..O.C., Taiwan; E-Mail: kslin@saturn.yzu.edu.tw
Abstract: This paper provides an overwhelmed overview of the recent progress of research work performed to develop new one dimensional (1-D) or three dimensional (3-D) ceria (CeO₂) nanomaterials. The review was classified into four parts: the preparation procedures, formation mechanisms, identification of the
existing different dimensional ceria nanomaterials, and analyzing their applications. From a literature survey, it is inaugurated that the fundamental structures of the ceria nanomaterials constructively dominate their properties and applications. In addition, the paper is also summarized with a perspective on the future technical trends for the development of the different dimensional of CeO₂nanomaterials.
Keywords: Cerium oxide, Nanotube, Nanomaterial, Dimensional nanostructure, Porous material, Chemical synthesis 

Type of Paper: Review
Title: Review on Optical Lifetime Measurement Techniques based on the Free Carriers Absorption Effects 
Authors: Martina De Laurentis *, Andrea Irace, Giovanni Breglio 
Affiliation: Dipartimento di Ingegneria Biomedica, Elettronica e delle Telecomunicazioni, Universit degli Studi di Napoli ’Federico II’, Via Claudio, 21, Napoli, Italy; *e-mail: martina.delaurentis@unina.it 
Abstract: The solar cells, without doubt, occupy an important role in the energy worldwide scenario, so that it is increasing the interest in their production and characterization. Their efficiency in converting the energy from solar to electrical critically depend on two parameter: the bulk lifetime b and the surface recombination velocity SRV . Consequently, the their determination is a widely used tool for materials design and for the devices characterization. These parameters are strongly related to the presence of defects within the semiconductor materials forbidden gap, which directly affects devices performance, and to the surface quality. They depend on the semiconductor growth technique, on the doping, on the surface condition and on the free carrier density injected in the material under measuring conditions. In the last decades the researchers effort were addressed to develop conctactless and totaly compatible methods that allow to monitor each step of the production process without interfere. It is thus obvious that methods based on optical and microwave radiations are preferred. 
In this paper we present a survey of the most important conctactless techniques to determine the semiconductors materials lifetime, the Pump and Probe method (PP) [1] and the Infrared Lifetime Mapping method (ILM) [2], otherwise known as Carriers Density Imaging (CDI) [3]. 
These techniques are based on the capability of semiconductors materials to absorb photons with energy lower than their energy band-gap, phenomenon known as free carriers absorption. In fact, being the lifetime strongly dependent on the free carriers density, a variation of this concentration inside the material determines a variation of the material absorption coefficient. This implies that the a variation of transmittance can be detected and observed when a sub band gap radiation is transmitted by the material. Materials 2009, 2 2 The generation of the excess free carriers is optically induced pumping the sample through a laser pulse whose photons energy is greater than the sample band gap. 
The PP technique belongs to the class of transient methods. These methods are attractive because they give a direct result relevant to the velocity of the recombination process, because the signal detected is the time dependent sample transmitted signal. The PP allows to characterize material with very low lifetime too and it does not require any calibration procedure. Moreover the actual advantage of the method is the possibility to separate the bulk from surface effect, that means to measure the bulk lifetime and the surface recombination velocity simultaneously. 
The ILM/CDI belongs to the steady-state methods class. These methods measure a physical quantity related to the carrier density. It allows a fast and high spatially resolved measurement of the lifetime in each point of the wafer without perform a scanning of it, since an infrared CCD camera is used to detect the transmitted infrared radiation. Its greater attractive is the capability to perform the lifetime mapping in few minutes, which provides, in calibration condition, an on-line monitoring feature. 
The paper is organized in the following manner: in the first two sections we briefly recall the concept of recombination lifetime together with the main recombination mechanisms in the semiconductors materials; in the subsequent sections we describe in details the selected techniques, previously giving the analytical tools necessary to their understanding.
Keywords: lifetime conctactless measurements; solar cell characterization