We present a study of nanopattern formation on polycrystalline Ni surfaces upon low energy Ar ion bombardment. At low angles of ion incidence an isotropic, rough morphology develops on the surface while at grazing incidence a ripple structure parallel to the ion beam direction is formed (so-called perpendicular mode ripples). To explain this behavior we propose a model which is based on a combination of (a) surface roughening due to sputter yield variation between different crystalline grains and (b) anisotropic nonlinearity resulting from the oblique angle bombardment. By computer simulations we show that the combination of these two phenomena excellently reproduces the experimental behavior, in particular the dependence of the surface morphology on the ion incidence angle. Importantly, the formation of ripples at grazing incidence does not involve any linear instability, in strong contrast to the present model of the ripple formation process.
Integrated circuits and certain silicon-based quantum devices require the precise positioning of dopant nanostructures, and hydrogen resist lithography can be used to fabricate such structures at the atomic-scale limit. However, there is no single technique capable of measuring the three-dimensional location and electrical characteristics of these dopant nanostructures, as well 3,4 5 3 von 39 11.
Controlled atomic scale fabrication based on scanning probe patterning or surface assembly typically involves a complex process flow, stringent requirements for an ultra-high vacuum environment, long fabrication times and, consequently, limited throughput and device yield. We demonstrate a device platform that overcomes these limitations by integrating scanning-probe based dopant device fabrication with a CMOS-compatible process flow. Silicon on insulator substrates are used featuring a reconstructed Si(001):H surface that is protected by a capping chip and has pre-implanted contacts ready for scanning tunneling microscope (STM) patterning. Processing in ultra-high vacuum is thereby reduced to a few critical steps. Subsequent reintegration of the samples into the CMOS process flow opens the door to successful application of STM fabricated dopant devices in more complex device architectures. Full functionality of this approach is demonstrated with magnetotransport measurements on degenerately doped STM patterned Si:P nanowires up to room temperature.
We studied surface morphology induced changes of magnetic anisotropy, magnetization reversal, and symmetry of the anisotropic magnetoresistance (AMR) in ion sputtered Ni films grown on MgO (001). Grazing-incidence ion sputtering generally develops anisotropic surface roughness of the Ni films, i.e., nanometer wide ripples parallel to the ion beam direction, giving rise to uniaxial magnetic anisotropy with the easy axis along the ion beam direction. The formed ripples act as domain wall nucleation and pinning sites during magnetization reversal, while two-jump domain wall motion dominates in the as-grown Ni films. More importantly, the azimuthal angular dependence of the AMR indicates a superposition of twofold symmetry and fourfold symmetry. By relying on grazing-incidence ion sputtering along specific crystallographic directions, we are able to tailor the relative weight of twofold and fourfold symmetry of AMR. We demonstrate that in contrast to the bulk case, the symmetry of the AMR becomes also sensitive to the surface morphology in thin films, which is in particular relevant for the design of magnetotransport based sensors.
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