Formation of cavities in Si and their chemisorption of metals

Nanometer-size cavities formed in Si by He{sup +} implantation and annealing are examined with cross-section TEM. During annealing at 700 C or above, He degasses from the specimens, leaving uhv cavities with reactive Si bonds on their walls. Cavity microstructures have been characterized in detail for an implanted fluence of 1 {times} 10{sup 17} He/cm{sup 2}: cavity volume remains approximately constant (0.75 lattice sites/He) for anneals from 700 to {approximately}1000 C, while surface area (3 to 7 times the wafer area) decreases with temperature as the cavities coarsen. The cavities are found to getter up to {approximately}1 monolayer of Cu or Au from solution in Si without second-phase formation, thus identifying the trapping mechanism as chemisorption on the cavity walls

Energetic-Particle Synthesis of Nanocomposite Al Alloys

Ion implantation of O into Al and growth of Al(O) layers using electro-cyclotron resonance plasma and pulsed laser depositions produce composite alloys with a high density of nanometer-size oxide precipitates in an Al matrix. The precipitates impart high strength to the alloy and reduced adhesion during sliding contact, while electrical conductivity and ductility are retained. Implantation of N into Al produces similar microstructures and mechanical properties. The athermal energies of deposited atoms are a key factor in achieving these properties

Finite-element modeling of nanoindentation for determining the mechanical properties of implanted layers and thin films

The mechanical properties of implanted layers and thin films on dissimilar substrates are difficult to accurately determine. Nanoindentation of the layer provides information, but detailed numerical modeling is required in order to separate the properties of the layer from those of the substrate. We describe here the procedures we have developed to accomplish this modeling with the commercially available finite-element code ABAQUS. Using these techniques, we are able to extract from nanoindentation testing the yield stress, Young`s modulus, and hardness of the layer material, with an absolute accuracy of at least 20%. The procedure is applicable to layers as thin as 50 nm on essentially any substrate, hard or soft. We have used it for materials ranging from ion-implanted layers to thin films of metals and dielectrics formed using plasma-deposition methods. An example is given of 0-implanted Al, a thin, hard layer on a soft substrate

Interaction of cavities with misfit dislocations in SiGe/Si heterostructures

Consequences of the strong, short-range attractive interaction between cavities and misfit dislocations are examined in SiGe/Si heterostructures. When He is implanted at the SiGe/Si interface, either in situ during epitaxial growth or by post-growth treatment, cavities form and locate on the misfit dislocation cores. The misfit dislocations are no longer straight lines extending over several microns, but form a network with jogs and intersections at the cavities. The He-implanted cavity layer enhances thermal relaxation of the strained alloy and may increase the achievable degree of relaxation by lowering dislocation energies

Interaction of cavities and dislocations in semiconductors

TEM of He-implanted Si-Ge and InGaAs indicates an attractive interaction between cavities and dislocations. Calculation indicates that cavities are attracted to dislocations through surrounding strain fields, and strong binding (100s of eV) occurs when a cavity intersects the core. In a strained SiGe/Si heterostructure, He implantation enhances relaxation rates and cavities bound to misfit dislocations show evidence of increasing relaxation at equilibrium by lowering dislocation energies. The interaction is expected for all crystalline solids and gives insight into voids in GaN/sapphire and bubbles in He-implanted metals

Extreme precipitation strengthening in ion-implanted nickel

Precipitation strengthening of nickel was investigated using ion-implantation alloying and nanoindentation testing for particle separations in the nanometer range and volume fractions extending above 10O/O. Ion implantation of either oxygen alone or oxygen plus aluminum at room temperature was shown to produce substantial strengthening in the ion-treated layer, with yield strengths near 5 GPa in both cases. After annealing to 550"C the oxygen-alone layer loses much of the benefit, with its yield strength reduced to 1.2 GP~ but the dual ion-implanted layer retains a substantially enhanced yield strength of over 4 GPa. Examination by transmission electron f microscopy showed very fine dispersions of 1-5 nm diameter NiO and y-A1203 precipitates in the implanted layers before annealing. The heat treatment at 550"C induced ripening of the NiO particles to sizes ranging from 7 to 20 nm, whereas the more stable ~-A1203 precipitates were little changed. The extreme strengthening we observe is in semiquantitative agreement with predictions based on the application of dispersion-hardening theory to these microstructure

Self-Organized Growth of Alloy Superlattices

We predict theoretically and demonstrate experimentally the spontaneous formation of a superlattice during crystal growth. When a strained alloy grows by "step flow", the steps at the surface form periodic bunches. The resulting modulated strain biases the incorporation of the respective alloy components at different steps in the bunch, leading to the formation of a superlattice. X-ray diffraction and electron microscopy for SiGe grown on Si give clear evidence for such spontaneous superlattice formation

Microstructure of compositionally modulated InAlAs

The authors have observed spontaneous, lateral composition modulation in tensile InAlAs alloy films grown as short-period superlattices on InP (001). They have analyzed these films using transmission electron microscopy, x-ray reciprocal space mapping, and polarized photoluminescence spectroscopy. They find the growth front is nonplanar, exhibiting {approximately} 2 nm deep cusps aligned with the In-rich regions of the compositionally modulated films. In addition to the measured 15 nm wavelength modulation in the [110] direction, a modulation of 30 nm wavelength is seen in the orthogonal [1{bar 1}0] direction. The photoluminescence from the modulated layer is strongly polarized and red shifted by 0.22 eV