Gernot Friedbacher

Imaging Powders with the Atomic Force Microscope: From Biominerals to Commercial Materials

Atomically resolved images of pressed powder samples have been obtained with the atomic force microscope (AFM). The technique was successful in resolving the particle, domain, and atomic structure of pismo clam (Tivela stultorum) and sea urchin (Strongylocentrotus purpuratus) shells and of commercially available calcium carbonate (CaCO3) and strontium carbonate (SrCO3) powders. Grinding and subsequent pressing of the shells did not destroy the microstructure of these materials. The atomic-resolution imaging capabilities of AFM can be applied to polycrystalline samples by means of pressing powders with a grain size as small as 50 micrometers. These results illustrate that the AFM is a promising tool for material science and the study of biomineralization.

Multielement ultratrace analysis of molybdenum with high performance secondary ion mass spectrometry

Electron beam melting has been used to obtain ultrapure refractory metals that are gaining importance in metal oxide semiconductor--very large scale integration (MOS--VLSI) processing technology, fusion reactor technology, or as superconducting materials. Although the technology of electron beam melting is well established in the field of production of very clean refractory metals, little is known about the limitations of the method because the impurity level of the final products is frequently below the detection power of common methods for trace analysis. Characterization of these materials can be accomplished primarily by in situ methods like neutron activation analysis and mass spectrometric methods (glow discharge mass spectrometry (GDMS), secondary ion mass spectrometry (SIMS)). A suitable method for quantitative multielement ultratrace bulk analysis of molybdenum with SIMS has been developed. Detection limits of the analyzed elements from 10/sup -7/ g/g down to 10/sup -12/ g/g have been found. Additional information about the distribution of the trace elements has been accumulated.

A combination of atomic force microscopy and secondary ion mass spectrometry for investigation of AlxGa1−xAs/GaAs superlattices

SummaryAtomic Force Microscopy (AFM) has been used to characterize the topography of crater bottoms obtained during Secondary Ion Mass Spectrometry (SIMS) investigations of an Al0.35Ga0.65As/GaAs multilayer system. A linear relation between the roughness of the bottoms, which leads to a drop in the dynamic range of the SIMS-signal and in the depth resolution, and the sputter depth of SIMS has been found. The topography found by AFM also supports a mechanism for the ripple formation proposed recently by W. H. Gries. AFM imaging of cleaved cross sections through this multilayer system allowed to determine evenness and thickness of individual layers, which opens up the possibility to improve the depth scale for sputter techniques like SIMS.

Atomic Force Microscopy of technological and biological samples

SummaryAtomic Force Microscopy (AFM) has been successfully used to characterize a variety of samples with different chemical composition. Polycrystalline sample preparation techniques, cleaving and careful adjustment of the imaging setup made it also possible to investigate materials with non-ideal geometry (small size, rough sample surface) down to the atomic scale. Pressed CaCO3 powder samples of different origin have been imaged with atomic resolution. Multilayer systems of AlGaAs/GaAs and Si/GaAs on top of a GaAs substrate could be imaged readily. Single δ-layers of Si in GaAs could be resolved. The results demonstrate that simple sample preparation techniques and the implementation of chemical reactions can greatly enhance the analytical scope and applicability of AFM.