Sculptured Thin Films: Nanoengineered Morphology and Optics , Akhlesh Lakhtakia and Russell Messier , SPIE Press, Bellingham, WA, 2005. $75.00 (299 pp.). ISBN 0-8194-5606-3
The title of Sculptured Thin Films: Nanoengineered Morphology and Optics, by Akhlesh Lakhtakia and Russell Messier, is eye-catching. The book encompasses the concepts of emerging nanotechnologies for optical devices based on sculptured thin films (STFs). The field is a highly specialized and interdisciplinary one requiring expertise in materials-science and technology subjects—for example, well-identified deposition processes and parameters that both have reproducible structure–property correlation for STFs and devices. The field also requires an intimate knowledge of wave optics and electromagnetism, guidelines for practical device design and fabrication, and testing methods.
The task of providing such information is obviously daunting and has been accomplished so far only in carefully edited books with chapters contributed by experts in specific sub-fields. I was thus intrigued by the book from SPIE Press written by only two authors. Lakhtakia and Messier, who are both with the department of engineering sciences and mechanics at the Pennsylvania State University, have published extensively in their respective areas of expertise. In fact, in their preface they raise reader’s expectations to a new height: Their goal is to present a clear understanding of the morphology and optical response characteristics of nanoengineered STFs and propose a recipe for potential optical devices.
However, I was disappointed, as their goal is not met. Their book rather resembles an extended research report on chiral STFs and their likely applications. After the overview in chapter 1, the authors address thin-film morphology in three brief chapters: History of Thin-Film Morphology (21 pages), Engineering of Thin-Film Morphology (33 pages), and Speculation on STF Morphology (7 pages). They cover STF deposition methods in another small chapter titled PVD Methods for STF (17 pages). These four chapters are descriptive but lack details that enable readers to correlate the morphology with the deposition parameters and process, and with the resultant properties of the film. Developing a physical vapor deposition (PVD) process with deposited-film structure and properties that are reproducible—even for single-element thin films—is highly complex. For a controlled deposition of optical-device-quality STFs, the process needs many bells and whistles that necessitate an understanding of the deposition environment, its chemistry and control mechanisms, and device characteristics. Except for citing a few general references on PVD, the authors do not discuss these critical issues.
In the next four chapters, which cover reflection and transmission of electromagnetic waves through columnar thin films (CTFs), sculptured nematic thin films (SNTFs), and chiral STFs, the authors use constitutive relations and modal representations to solve for the propagation parameters. The parameters are then related to the anisotropic dielectric constants and refractive indices of the films. The authors extensively use the Mathematica program, which is provided in a CD that comes with the book. But their higher-order polynomial curve fits have too many unsubstantiated variables, and so their discussion on morphology and optics in these chapters is speculative at best. Before one can confidently build intelligently nanoengineered CTFs and STFs with the potential to be used in devices, any prediction of properties should be authenticated by comparing with the actual measured data; and such a comparison is sorely lacking in this book.
In the last chapter the authors present mostly computed performances of chiral STFs for use in such applications as optical filters, optical sensors, optical emitters, and tuning and bandwidth control. Use of porosity in chiral STFs for such optical devices as sensors, emitters, or tuning and bandwidth control is far too speculative at this stage of development.
The scope of the book, per its title and preface, is far too broad and ambitious to handle. The authors suggest that it is targeted for graduate students in optics, practicing engineers in industry, or expert researchers. I would not, however, consider Sculptured Thin Films as a graduate text because of the shortcomings listed above. Practicing engineers in industry will find little use for the book as they look for workable recipes that are soundly tested against actual products.
Lakhtakia and Messier’s book could be a good compendium and reference to students and researchers studying chiral-STF materials, properties, and potential applications. It includes an extensive bibliography—almost 450 references, with 122 being literature published by Lakhtakia and his colleagues—which could be useful for researchers in the field. But for understanding the controlled nanoengineering of optical-device-quality STFs and useful devices, readers will have to dig deep for other books and journal articles.
