Evolution of metastable phases during crystallization of pulsed laser deposited amorphous Al–Fe films

Amorphous thin films of different Al–Fe compositions were produced by plasma/vapor quenching during pulsed laser deposition. The chosen compositions Al72Fe28, Al40Fe60, and Al18Fe82 correspond to Al5Fe2 and B2-ordered AlFe intermetallic compounds and α–Fe solid solution, respectively. The films contained fine clusters that increased with iron content. The sequences of phase evolution observed in the heating stage transmission electron microscopy studies of the pulsed laser ablation deposited films of Al72Fe28, Al40Fe60, and Al18Fe82 compositions showed evidence of composition partitioning during crystallization for films of all three compositions. This composition partitioning, in turn, resulted in the evolution of phases of compositions richer in Fe, as well as richer in Al, compared to the overall film composition in each case. The evidence of Fe-rich phases was the B2 phase in Al72Fe28 film, the L12- and DO3-ordered phases in Al40Fe60 film, and the hexagonal ε–Fe in the case of the Al18Fe82 film. On the other hand, the Al-rich phases were Al13Fe4 for both Al72Fe28 and Al40Fe60 films and DO3 and Al5Fe2 phases in the case of Al18Fe82 film. We believe that this tendency of composition partitioning during crystallization from amorphous phase is a consequence of the tendency of clustering of the Fe atoms in the amorphous phase during nucleation. The body-centered cubic phase has a nucleation advantage over other metastable phases for all three compositions. The amorphization of Al18Fe82 composition and the evolution of L12 and ε–Fe phases in the Al–Fe system were new observations of this work.

TEM Study of Nanocrystalline AgxNi1-x Solid Solutions

Research on nanocrystalline materials, a new class of materials with a grain size of less than 20-30 nm in diameter, has flourished in the last decade because of their unique properties and Characteristics. While enormous amounts of nanocrystalline intermetallic alloys have been made by high energy mechanical alloying, little of this research has been carried out to study the formation of alloys of very low solid solubility elements such as Ag and Ni (0.1 at % at 750 °C).Upon quenching atoms in a state of high mobility, they can be “frozen” into unconventional random positions and thermodynamically metastable or unstable phases can be formed. This research was thus undertaken to synthesize nanocrystalline AgxNi1-x solid solution because fiber composites of this system have been widely used in low-voltage electrical circuits. This paper presents a TEM/AEM investigation of the traditionally immiscible nanocrystalline AgxNi1-xsolids formed by gas evaporation - vapor quenching method.

Electron Energy Loss Spectroscopy on Aggregated Fe-Cu-B Nanosized Particles

Nanostructured materials have attracted great attention because their physical and chemical properties may differ significantly from those of the bulk material. In the equilibrium state, the solid solubility between Fe and Cu is negligibly small. However by using methods as vapor quenching, ball milling or chemical reduction, a Fe-Cu solid solution can be formed. In the present work, colloidal solutions incorporating mixtures of iron (II) and copper (II) functionalized surfactants are used to obtain FexCu 1-x(B) alloys and composite. Different ranges of composition (x=0.3 and x=0.7) can be produced by varying the relative concentration of the surfactants.The samples are characterized by different techniques, some of them such as X-ray diffraction, 57Fe Mössbauer spectroscopy, and magnetization measurements, provide an information averaged over the whole specimen. Transmission Electron Microscopy, together with electron diffraction and EDS analysis, constitutes a first step towards submicrometer analysis of the produced material available as aggregates of nanosized particles deposited on holey carbon films.

Pulsed Laser Deposition of Collagen Thin Films

Thin films of collagen were prepared by pulsed laser deposition (PLD) at room temperature on Si substrates using a KrF laser (248 nm) over a fluence range from 0.2–1.5 Jcm-2. The effects on film composition and morphology of ambient gas (Ar, Ar/H2O vapor), quenching atmosphere (Ar, Ar/H2O vapor), and fluence were examined. Fourier transform infrared spectroscopy (FT- IR) demonstrated that, independent of deposition parameter, the PLD films contained the characteristic Amide I and II functionalities of the collagen target and indicated that the secondary structure was altered by the PLD process. The surface morphology of the films was a function of the laser fluence and the gas environment during either film deposition or quenching at the end of deposition. Preliminary gel electrophoresis examination of deposited films suggested the collagen had not maintained the triple helical structure of the native collagen. X-Ray diffraction (XRD) indicated that all of the films, deposited under any conditions, were predominantly amorphous.