Amorphous materials are commonly understood to consist of random organizations of molecular-type structural units. However, it has long been known that structural organizations intermediate between discrete chemical bonds and periodic crystalline lattices are present even in liquids. Numerous models--including random networks and crystalline-type structures with networks composed of clusters and voids--have been proposed to account for this intermediate-range order. Nevertheless, understanding and controlling structural features that determine intermediate-range order in amorphous materials remain fundamental, yet presently unresolved, issues. The most characteristic signature of such order is the first peak in the total structure factor, referred to as the first sharp diffraction peak or 'low Q' structure. These features correspond to large real-space distances in the materials, and understanding their origin is key to unravelling details of intermediate-range order. Here we employ principles of crystal engineering to design specific patterns of intermediate-range order within amorphous zinc-chloride networks. Using crystalline models, we demonstrate the impact of various structural features on diffraction at low values of Q. Such amorphous network engineering is anticipated to provide the structure/property relationships necessary to tailor specific optical, electronic and mechanical properties.

Devices using electromagnetic (EM) waves in the GHz range are evolving rapidly. The advancement of this technology for security applications, such as explosives detection and personnel screening, requires an understanding of the optical properties of various materials. Using terahertz time-domain spectroscopy and free space millimeter-wave measurements, the dielectric constant of explosives have been measured. Methods used to standardize the experimental measurement and characterize the EM/material interaction are described. These results have enabled the development of mixtures of benign substances as simulants for testing. A comparison of the anticipated signal returns are presented for the range 100 -500 GHz for a limited set of explosives and simulants.