Raman scattering measurements have been performed on semiconductor-insulator nanocomposites in which the semiconducting phase occupies a significant (30%) volume fraction. The composites have been synthesized by high pressure injection of the conducting melt into the nanochannels of commercially available insulating matrices. The optical phonon spectra of GaSb- and Te-SiO2 composites exhibit shifts, broadenings, and asymmetries when compared to those of the semiconducting bulk. These are interpreted in terms of strains and phonon confinement in the microcrystalline semiconducting phase. Xray diffraction measurements allow us to correlate the effects of crystallite size and strains on the optical modes of the composites.

A high yield synthetic route to TiN/TiB2 nanocomposites based upon polymeric precursors has been developed. The phase evolution and microstructural development have been characterized and related to preliminary measurements of properties, i.e. hardness. The observations indicate the existence of TiN-TiB2, TiN-BN, and TiB2-BN subsolidus compatibilities.

An electrochemical method for the preparation of nanoscopic gold particles which allows for the control of particle size, shape and orientation is described. The UV/visible/near-IR spectra of Au/alumina and Au/polyethylene composites are described and shown to be in accord with the predictions of Maxwell-Garnett theory. The applications of such composites to surface enhanced spectroscopy are also discussed.

Pyrolysis of a vinylic polysilane (VPS, Union Carbide Y12044) under argon at 1600 °C resulted in the formation of SiC with 20% residual carbon. The excess carbon was transformed to B4C or SiC by mixing B or Si powder with VPS and pyrolyzing the mixture under a flow of argon. When excess Si was added and the mixture was pyrolysed under N2 at 1395 °C, a SiC/ Si3N4 composite was obtained. All the products showed a fine-grained microstructure and excellent homogeneity. The precursors and the pyrolysis products were characterized by means of FIIR, TGA, XRD, SEM, STEM, BET, and elemental analysis.

Recent developments in boron chemistry have allowed the synthesis of TiN/TiB2 composites from polymeric precursors with grain sizes of the order of 10-500 nm. In order to optimize the properties through controlled processing, nucleation of the crystalline phases and subsequent microstructural evolution must be understood. However, the nitride and boride phases are difficult to distinguish in conventional TEM since the grains are too small for diffraction analysis and light elements are not detectable by energy dispersive X-ray spectroscopy.

For the characterization a prototype of an energy filtering TEM (EFTEM) which utilizes an imaging electron energy loss spectrometer incorporated into the column of a normal TEM has been used for elastic filtering and electron spectroscopic imaging (ESI). The ESI-technique allows us to obtain two-dimensional maps of the elemental distribution. These techniques are applied to advantage in the microstructural analysis of the TiN/TB2 nanocomposites.

Upon the application of an external magnetic field, the magnetic spins in a material partially align with the field, thereby reducing the magnetic entropy of the spin system. When performed adiabatically, the specimen's temperature will rise. This temperature rise, δT, related to the entropy change by the heat capacity, is known as the magnetocaloric effect. Upon cycling the magnetic field, this effect can be used for transferring heat from one thermal reservoir to another, forming the basis for a magnetic refrigerator. Recently, NIST scientists predicted composite magnetic materials containing nanometer-size magnetic species could possess enhanced magnetocaloric effects [1-2], especially at high temperatures or low magnetic fields. Magnetic nanocomposites may be prepared in many different ways, and recent magnetocaloric effect data measured on Fe-doped gadolinium gallium garnets are presented to show both the effect of processing and a methodology for optimizing δT.