Michael W. Russell

Magnetic and optical properties of γ‐Fe2O3 nanocrystals

γ-Fe2O3 nanocrystals with a mean radius of 4.2 nm have been synthesized in a polymer matrix by an ion exchange and precipitation reaction. Magnetization and susceptibility data from experiment and computer simulations indicate that the system is superparamagnetic. The optical absorption edge is red shifted with respect to that of an epitaxially-grown single-crystal film of γ-Fe2O3. The red shift is attributed to lattice strain in the small particles.

Nanometer-Scale Iron Oxide Magnetic Particles: Synthesis and Magnetic Properties

Nanometer-scale iron oxide magnetic particles have been formed in the porous network of a cross-linked polymer matrix by ion exchange and subsequent hydrolysis. The oxide particles are uniform, well-dispersed and spherical with a diameter ranging between 30 and 1200 A depending on the synthesis conditions. The DC magnetic susceptibility, measured between 4 and 300 K, continuously increases with decreasing temperature and tends to saturate at low temperatures. Composites containing iron oxide particles with an average diameter of 80 A exhibit superparamagnetism while those on the order of 1000 A undergo an antiferromagnetic-type transition at 33 K. The magnetic susceptibility is critically dependent upon the particle size and the strength of the magnetic field.

Intercalation Chemistry: a Novel Approach To Materials Design

Intercalation of layered solids is used as a means to manipulate a variety of molecular and polymeric species into well-ordered multilayer films with an architecture controllable at the molecular level. Dielectric, conductivity and optical measurements demonstrate the potential of developing new families of materials with new functionalities by exploiting the synergistic effect of guest/host interactions.

Atmospheric pressure chemical vapor deposition of 3C-SiC

In addition to its superior mechanical properties, the wide band gap (2.3 eV), high breakdown field, and high saturated electron velocity of cubic silicon carbide (3C-SiC) make it an attractive candidate for elevated-temperature, high-frequency, and high-power electronic devices. Optically transparent SiC deposits were grown via atmospheric pressure chemical vapor deposition (APCVD) on graphite substrates from methyltrichlorosilane (MTS) in hydrogen in a cold-walled, RF-induction furnace. Structural morphology was examined by scanning electron microscopy and correlated to substrate temperature, MTS/H{sub 2} ratio, and hydrogen flow. Photoluminescence revealed that high quality cubic material was grown. The PL spectra exhibited a zero phonon line (2.3787 eV) and attributable to an exiton bound to a neutral nitrogen donor, in addition to TA, LA, TO, and LO phonon replicas. Observed broadening and splitting of the PL spectral lines was associated with the morphological habit and internal strain of individual crystallites. In addition, the PL spectra for samples grown at higher MTS/H{sub 2} ratios and low H{sub 2} flows exhibited weak shoulders on the low energy side of the five-line spectra which might be associated with nonstoichiometric defects such as Si interstitials or C vacancies.