Accounts

The present work is aimed towards understanding the formation mechanisms of MCs þ and MCs þ 2 molecular ions in the SIMS process. Energy distribution studies of MCs þ under varying Cs surface concentrations have been made for Au, Cu and Ni. From the peak shifts of the energy distribution curves it is evident that the surface binding of MCs þ is stronger at higher Cs surface concentration for elements having greater atomic polarisability. As far as the MCs þ 2 formation mechanisms are concerned, we feel that the most probable formation probability could be due to the association of a sputtered M À ion with two self-sputtered Cs þ ions. Energy distribution study for MCs þ , MCs þ 2 and Cs þ ions seems to be an effective diagnostic for the plausible explanation of the above mechanism.

Emission of MCs þ n (n = 1, 2, . . . etc.) molecular ions has been studied under the joint influence of electropositive (cesium) and electronegative (oxygen) elements in the secondary ion mass spectrometry (SIMS) process. The kinetic energy distributions, measured for Cs + , Cs þ 2 , AgCs + and AgCs þ 2 ions at different oxygen pressures exhibited changing slopes in their leading parts that hinted at appreciable change in the surface work function. The maximum observed change in the surface work function D/ max was $0.44 eV. The measured integrated counts of all ionic species showed a strong variation with the changing oxygen environment. The observations are explained in the light of surface work function changes at the sputtering site. Formation mechanisms of Cs þ 2 , AgCs + and AgCs þ 2 ions are explained in the framework of sputter-ion emission models.

A new D0 23 metastable phase of Cu 3 Au is found to grow at the interfaces of Au/Cu multilayers deposited by magnetron sputtering. The extent of formation of this novel alloy phase depends upon an optimal range of interfacial width primarily governed by the deposition wattage of the dc-magnetron used. Such interfacially confined growth is utilized to grow a ∼ 300 nm thick Au/Cu multilayer with thickness of each layer nearly equal to the optimal interfacial width which was obtained from secondary ion mass spectrometry (SIMS) data. This growth technique is observed to enhance the formation of the novel alloy phase to a considerable extent. SIMS depth profile also indicates that the mass fragment corresponding to Cu 3 Au occupies the whole film while x-ray diffraction (XRD) shows almost all the strong peaks belonging to the D0 23 structure. High resolution cross-sectional transmission electron microscopy (HR-1 XTEM) shows the near perfect growth of the individual layers and also the lattice image of the alloy phase in the interfacial region. Vacuum annealing of the alloy film and XRD studies indicate stabilization of the D0 23 phase at ∼ 150 • C. The role of interfacial confinement, the interplay between interfacial strain and free energy and the hyperthermal species generated during the sputtering process are discussed.

A gold–copper alloy with a nominal composition of Cu3Au but with a tetragonal (c = 4a) structure is observed to form at Au/Cu interfaces of gold/copper multilayers deposited on amorphous substrates by d.c. magnetron sputtering. The formation of this non-equilibrium structure (tentatively D023) under-ambient conditions is detected by secondary ion mass spectrometry, x-ray diffraction and high-resolution cross-sectional transmission electron microscopy. Co-sputtering of Au and Cu under similar conditions produces only conventional fcc Cu3Au alloy phases, suggesting that interfacial confinement plays a significant role in producing the novel Cu3Au alloy phase in gold/copper multilayers. Copyright © 2003 John Wiley & Sons, Ltd.

Single (strained and relaxed) and polycrystalline Si 1−x Ge x samples have been bombarded using low-energy oxygen ions to study the impact of strain and relaxation-induced dislocations on their surface morphologies and subsequent formation of ripples. The as-grown relaxed sample surface exhibits cross-hatch patterns due to relaxation along its surface. Compared to Si, all the surfaces of these materials exhibit ripple formation at lower fluences. Moreover, the nature of the induced surface topography depends largely on the original surface morphology. Single crystalline layers show clear ripple formation whereas the polycrystalline surface leads to more isolated features. On a relaxed surface that exhibits the cross-hatch patterns due to relaxation along its surface, very long ripples tend to form along the dislocation ridges which eventually become shorter (and finally break up) with increasing distance from a particular ridge. A detailed temporal study has been done to understand the nature of ripple formation on the relaxed sample. A theoretical estimation of the crossover time indicates that the morphology of the relaxed sample is primarily governed by the nonlinear regime of ripple formation. It is found that the surface follows the scaling laws as dictated by the isotropic Kardar-Parisi-Zhang equation. The growth exponent (n) is found to be ∼0.23, which is in agreement with the theoretical value. Ripple coarsening is observed which fits well with the recently predicted model indicating the contribution of nonlinear effects arising out of redeposition of the sputtered atoms and presence of mobile surface adatoms. The subsequent saturation of wavelength takes place as a result of geometrical shadowing.