P REFACE TO V OLUME 2: N ANOSTRUCTURED M ATERIALS Nanomaterials and nanotechnology are new fields of science and technology. Fundamentally, nanotech- nology is about manipulating and making materials at the atomic and molecular levels. It is expected that nanotechnology will change solid-state gas sensing dramatically and will probably gain importance in all fields of sensor application over the next 10 to 20 years. Nanotechnology is still in its infancy, but the field has been a hot area of research globally since a few years ago. It has been found that with reduc- tion in size, novel electrical, mechanical, chemical, catalytic, and optical properties can be introduced. As a result, it has been concluded that one-dimensional structures will be of benefit for developing new- generation chemical sensors that can achieve high performance. Therefore, in the last decade, the study of 1-D materials has become a primary focus in the field of chemical sensor design. Synthesis of new nano objects and exploitation of their extraordinary properties is the goal and dream of many researchers engaged in the field of sensor design. In addition, it has also been established that 1-D structures may be ideal systems in which to study the nature of chemical sensing effects. Although many people consider this a brand-new technology yielding cutting-edge applications for consumer products, researchers have in fact been working in the field of catalysis and gas-sensing effects for decades. What we call nanoparticle technology today actually began in the era of the 1950s­1980s, and chemical catalysis and gas sensor research and development have been conducted at the nanoscale ever since. Initially, research labs used the technology to increase the effi ciency of heterogeneous catalysis and to improve the sensitivity of solid-state gas sensors. Nanoclusters of metal catalysts and nanograins of metal oxides with dimensions less than 10 nm were the main objects of research. The recent development of advanced tools for characterizing materials at the nano- or subnanoscale has provided scientists with new insights for understanding and improving existing devices and clues for ways to design new nanostructured materials to make better catalysts and sensors. Recent research has thus led to new types of prospective nanostructured materials. It is obviously diffi cult to cover all aspects of a dynamic research area such as nanotechnology. Of course, it is not possible to analyze in one volume every nanoparticulate matter and its role in the revolu- tion of materials for chemical sensor applications. However, we have tried to cover this field more or less completely. This book, together with Volume 1, includes as much as possible the recent advances and breakthroughs in the area of nanomaterials for chemical sensors as achieved by research groups all over the world. These contributions have led to the emergence of some general guidelines. xiii