In-situ GISAXS for morphological characterization of ion-induced nanopatterning on the crystalline Ge(001) surface


In-situ GISAXS for morphological characterization of ion-induced nanopatterning on the crystalline Ge(001) surface

Erb, D.; Myint, P.; Evans-Lutterodt, K.; Ludwig, K.; Facsko, S.

Grazing Incidence Small Angle X-ray Scattering (GISAXS) has been established as a versatile tool for comprehensive morphological characterization of surfaces on the nanometer scale. As a contact-less technique it lends itself especially to in-situ monitoring of surface nanopattern development or the growth of supported nanostructures under various conditions such as reactive atmospheres, high temperatures, applied fields, or ion irradiation. A GISAXS intensity pattern is a representation of the shapes, sizes, as well as lateral and vertical arrangements of three-dimensional structures in reciprocal space, in dependence of the direction of the incident X-ray beam. Complementary to local imaging techniques such as atomic force microscopy (AFM), it provides information on the average surface morphology of the extended area covered by the footprint of the X-ray beam. We implemented an in-situ ultra-high vacuum setup at the ISR beamline of the NSLS-II synchrotron combining GISAXS with low-energy broad-beam ion irradiation, providing sample rotation as well as heating to several hundred degrees Celsius. This setup allows us to observe the nanoscale pattern formation kinetics on crystalline semiconductors in-situ under ion irradiation. We studied the pattern formation on Ge(001) surfaces, where the crystallinity of the surface under ion irradiation is ensured by heating the sample above its recrystallization temperature. The Ge(001) surface is known to develop a pit-and-mound pattern of faceted pyramidal structures under irradiation with 1 keV Ar+ ions. The edges of the pyramidal structures are aligned along the <100> and <010> direction, while their sidewall facets have a uniform polar tilt from the <001> direction. Such a regular surface morphology results in a distinct GISAXS intensity pattern. From the development of the GISAXS pattern features with ion fluence, we can conclude on the corresponding development of the surface morphology. Using this technique, we monitor the lateral correlation length as well as the polar facet angle and the azimuthal pattern orientation as indicators of the kinetics of this ion-induced self-assembly process.

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Publ.-Id: 30305