The structure of Co-Fe electrodeposited magnetic thin films, for example C037Fe63 films, j consists of a columnar grain structure containing grain boundaries, dislocations, and possibly other lattice defects. These films are also thought to contain oxygen, present as Fe oxide or hydroxide nanoparticles, and/or in solution in the Fe-Co metal matrix (Brankovic et. al., Pulse electrodepositionof2.4T...,IEEE Trans.Magnet.42(2), 132(2006). The object of this nanostructure analysis is to determine the presence of oxygen and its distribution, and. to characterize the defect structure of the films as a function of its synthesis processes. Transmission electron microscopy (TEM) will be used for the nanooharacterization. Plan view and cross section specimens will be prepared by focused ion beam (Fill) nanomachining methods. This method enables the preparation of very small TEM specimens, which is essential in the present case because all the alloys of interest will be ferromagnetic when examined in the TEM. The magnetic fields of the specimens, if made conventionally, would disturb the magnetic field symmetry of the TBM lenses and prevent obtaining images and spectra with the resolution I required for the nanoanalysis. Defect analysis of the films will be done by normal diffraction contrast imaging techniques. However, defect contrast in normal images is expected to make it difficult to detect the presence of small metal oxide or hydroxide nanoparticles in images. Two additional contrast mechanisms will be used to detect and examine these nanoparticles, High angle annular dark field STEM (HAADF) images will "wash out" the contrast from coherent interference of Bragg beams thus reducing the defect diffraction contrast, leaving the nanoparticles in clear contrast in thin specimens (Treacy et al, 1978; Treacy et al, 1980). We will also use chemical imaging (mapping) using tile oxygen electron energy loss (EELS) K-edge and energy dispersive x-ray (BDS) oxygen K peak signals to detect and analyze the metal oxide and/or hydroxide nanoparticles. Spectra from these maps will allow us to identify the metal(s) in tile nanoparticles and closely estimate the metal to oxygen ratios. Another question of interest is the presence of oxygen in solution in the metal matrices of the nanoparticles. We will examine this possibility using EELS and EDS spectra from the matrices and also by comparing precision lattice parameter measurements of the matrix using convergent beam diffraction (CBED) with lattice parameter data for pure bulk alloys of the same composition (Spence and Carpenter, 1986).
|Effective start/end date||9/1/08 → 8/31/12|
- National Science Foundation (NSF): $113,649.00