J.L. Whitton

The development of cones and associated features on ion bombarded copper

Abstract Observations of ion-bombardment-induced surface modifications on crystalline copper substrates have been made using scanning electron microscopy. The delineation and development of grain boundary edges, faceted and terraced etch pits and small-scale ripple structure, together with the formation of faceted conical features, have all been observed on low and high purity polycrystalline substrates. In general, the density of such surface morphological features, although variable from grain to grain, is higher in the proximity of grain boundaries. In particular, cones are only found within regions where other surface erosional features are present and it would appear that the development of these other surface features is a pre-requisite to cone generation in high-purity crystalline substrates. We suggest the operation of a defect-induced mechanism of cone formation whereby sputter elaboration of bulk defects (either pre-existing or bombardment-induced) leads to the formation and development of surfa...

Ion bombardment induced ripple topography on amorphous solids

Abstract Earlier studies of the ion bombardment induced ripple morphology on the surfaces of amorphous solids when compared with geomorphological effects are shown to possess many similar features. The present study, with 40 keV Ar+ ion bombarded Si suggests that analogies are incomplete, however, and that greater similarities with the process of macroscopic sandblasting (corrasion) exist. It is shown that the genesis of wave like structures on Si is from isolated features, which have the appearance of ripple trains, which are faceted. It is suggested that these features result from particle flux enhancement processes near surface dimples generated by stress induced surface lifting.

The crystallographic dependence of surface topographical features formed by energetic ion bombardment of copper

Abstract The interaction of mass-separated, well collimated beams of argon ions with copper, results, under certain conditions, as observed subsequently in a scanning electron microscope, in a pyramid covered surface. This pyramid formation is achieved over a wide range of temperatures (50–500 K), of dose rates (125 to ⩾ 500 μ A cm −2 ), of total dose 10 19 to ⩾ 10 20 ions cm −2 ) and energies from at least as low as 10 keV to ∼45 keV. The most critical parameter is that of crystal orientation. Pyramids are observed (under clean condition), only on an (11 3 1) surface of a single crystal although many other directions have been subjected to identical bombardments. Development of rows of pyramids in precise crystallographic directions are observed. The pyramid angles are shown to be only weakly energy dependent. Pyramid bases accommodate to (100), and are octagonal with 〈100〉 and 〈110〉 directions. The pyramid facets are low-index planes lying in 100 or 110 zones.

The development of sputter-induced pits and pyramids on ion bombarded (11 3 1) surfaces of face centred cubic metal single crystals

Abstract It is shown that energetic bombardment of (11 3 1) surfaces of copper single crystals with either Ne + , Ar + , Cu + , Kr + or Xe + ions results in the formation of regular geometric sputter-etch pits from which regular pyramids emerge during the subsequent pit enlargement. Similarly, energetic Ar + bombardment of (11 3 1) surfaces of single crystal nickel, palladium, silver, iridium and gold produces regular pits and pyramids. It is shown that, within certain parameters of ion bombardment, crystallography is the all important condition necessary for production of pits and pyramids. The presence of impurity is unnecessary.

RBS and nuclear reaction analysis of boron implanted copper

Abstract Formation of surface alloy layers produced in copper by implantation of 40 keV boron ions has been analyzed using nuclear reaction and RBS techniques. The boron concentration profiles determined using the very sharp low energy (p, α) nuclear resonance reaction are broader and at larger depth than predicted by LSS theory. Channeling analyses in combination with angular scans using both nuclear reaction and RBS techniques, yield no evidence for boride compound formation, and there is no preferential site occupation for the implanted boron. The radiation induced damage distributions are determined from RBS channeling analysis. The disorder level is low and characterized by a “knee” extending to large depth. There is no evidence of amorphization as might be anticipated at high boron concentrations. This observation is in agreement with TEM analysis of implanted polycrystals.

The effect of ion species on morphological structure development of ion bombarded (1131) single crystal Cu

Abstract Carefully prepared samples of (1131) oriented Cu single crystals were bombarded with 40 keV ions to fluences of the order of 10 19 cm −2 . The ion species chosen were Ne, Ar, Kr, Xe, N and Cu, and thus represented a range of light to heavy, chemically inert species, a more chemically active species and the self ion species. Post-irradiation observation was performed by scanning electron microscopy at Copenhagen and subsequently at Salford. The results may be summarized as follows: 1. (1) All ion species lead to characteristic morphological surface changes including etch pit, and frequently, pyramid generation. 2. (2) The lighter ion species tend to produce lower pit densities and less well-defined pit habits and fewer, sometimes no pyramids. 3. (3) The heavier ions (including Cu + ) produce denser arrays of all features and better geometrically defined features. 4. (4) N + , Ne + and Ar + ions produce a zone of surface blisters outside but surrounding the irradiated area but none within the irradiated area. 5. (5) Some signs of pyramid bending occur from one to a subsequent examination but there are no clear correlations with ion species and surface zone. 6. (6) The as-formed pyramids are in dense crystallographic array after Cu, Kr and Xe irradiation. These results are explained in terms of preferential sputtering of native and irradiation induced defect structures and differential atomic mobility of different ion species in the Cu. The Cu + irradiation results exhibit the lack of necessity of occluded gas for feature development whilst the N + results indicate that, for Cu, improved impurity depth profiling accuracy by sputter sectioning with such a chemically active species is unlikely.

The repetitive flaking of inconel 625 by 100 keV helium ion bombardment

Abstract Repetitive flaking of Inconel 625 occurs with ion bombardment doses of than 10 18 100 keV helium ions cm −2 , with up to 39 exfoliations being observed after bombardment with 3 × 10 19 ions cm −2 . The thickness of the flakes, measured by scanning electron microscopy, is some 30% greater than when measured by Rutherford backscattering (RBS) of 1.8 MeV helium ions. These RBS measurements compare well with the thickness of the remaining layers in the resultant craters and to the most probable range of the 100 keV helium. The area of the flakes is dictated by the grain boundaries, and when one flake is ejected, the adjacent grains are prevented from doing so since there now exists an escape route for the injected helium. A strong dose rate dependence is observed; decreasing the beam current from 640 μA cm −2 to 64 μA cm −2 results in a factor 20 fewer flakes being exfoliated (for the same total dose of 3 × 10 19 ions cm −2 ). Successive flakes decrease in area, suggesting that eventually a cratered, but stable, surface will result with the only erosion being by the much less effective mechanism of sputtering.

The effect of incidence angle on ion bombardment induced surface topography development on single crystal copper

Abstract The fluence dependence of development of microscopic surface features, particularly etch pits, during 9 keV Ar + ion bombardment of (11, 3, 1) oriented Cu single crystals has been studied employing quasi-dynamic irradiation and observation techniques in a scanning electron microscope-accelerator system. 9 keV ions are observed not to produce crystallographic pyramids under all irradiation conditions for this surface, a very different result from our earlier studies with higher energy ions. The bombardment does elaborate etch pits however, the habits and growth kinetics of which depend upon both polar and azimuthal angles of ion incidence to the surface. The results are explained in terms of differential erosion of crystal planes modified by the presence of pre-existing and irradiation induced extended defects.

Sputtering erosion of stratified media and by time dependent ion bombardment

Abstract The theory of the evolution of surface morphology resulting from ion bombardment induced sputter erosion (and other processes) is generalized to include description of spatio-temporally variable ion flux, and substrate inhomogeneity. This allows discussion of effects associated with rotated or translated ion beams and substrates and of striated or stratified substrates such as occur in polycrystals or in the neighbourhood of extended defects or impurities in single crystals. Geometric reconstructions of several two-dimensional surface sections are undertaken in order to illustrate the analytical methods.

The formation of striations on oblique boundaries during sputtering

Abstract The results of studies of the production of striations on boundaries inclined obliquely to incident sputtering ion flux are described. It is shown that two processes probably operate, one resulting from local shadowing of the substrate from ion flux by protection layers, the other resulting from the complex nature of the sputtering process in damaged crystalline solids.