The THz is unique among spectral regions because of the relative infancy of its commercial applications. Much of this infancy has been due to the well known difficulties of generating and detecting radiation. However, the enormous number of important applications in each of the other spectral regions has resulted at least as much from their large in-vestment in systems and applications development - an 'X' factor - as from the technological maturity of the spectral region. Examples in the radio region include magnetic resonance imaging (rf + 'X' = shaped magnetic fields, rf pulse sequences, and signal processing) and cruise missiles (rf = 'X' = rocket and guidance system). In the visible, Night Vision (light = 'X' = electron multiplication and fluorescence) serves as an example.
To grow to maturity, the THz needs not only to optimize its technology for native applications (imaging through ob-scuration, chemical sensing, etc.), but to integrate its attributes with other technologies to address a broader range of challenges. In this paper we will discuss the underlying physics of interactions in the THz to see how they lead to both the attractive and limiting features of the spectral region, while at the same time providing hints about how to overcome these limitations by considering 'X'. Specific examples of 'X' will be provided and the authors will welcome comments, suggestions, and ideas from the audience.
We report the photodeposition of polymeric layers of nanometer scale thickness onto two nanoparticle substrates. This was accomplished by ultraviolet irradiation of a solution of functionalized diacetylene monomers in which the nanoparticles were suspended. Following photodeposition, the coated nanoparticles were analyzed using transmission electron microscopy and UV-visible spectroscopy. Highly regular polydiacetylene films with thicknesses from 2.5 - 25 nm were produced. The thickness measurements were facilitated by the attachment of small gold nanoparticles onto the surface of silica nanoparticle substrates prior to photodeposition, to provide contrast in the final TEM image. Deposition onto gold nanoshells was also demonstrated. Photodeposition onto these particles resulted in more individual coated particles. Furthermore, short irradiation times (approximately 5 minutes) yielded coated particles without the extra oligomeric contaminants usually found. This substantiates the idea that photodeposition occurs preferentially on a substrate material. UV-visible spectroscopy of the deposited films indicate that approximately 40% less conjugation is present relative to macroscopic polydiacetylene thin films grown with the same approach. This process yields a unique `nanolaminate' coating which may be useful in the modification of the physical, chemical, or optical properties of nanoparticles.