Atomic Force Microscopy of technological and biological samples

Summary Atomic 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 -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.     

Cycles of violence: A dynamic control analysis

We introduce and analyze a simple model of cycles of violence in which oscillations are generated when surges in lethal violence shrink the pool of active violent offenders. Models with such endogenously induced variation may help explain why historically observed trends in violence are generally not well correlated with exogenous forcing functions, such as changes in the state of the economy. The analysis includes finding the optimal dynamic trajectory of incarceration and violence prevention interventions. Those trajectories yield some surprising results, including situations in which myopic decision makers will invest more in prevention than will far-sighted decision makers.     

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Alkali Metal Covalent Bonding in Nickel Carbonyl Complexes ENi(CO)3−

The alkali metal‐nickel carbonyl anions ENi(CO)₃^? with E=Li, Na, K, Rb, Cs have been produced and characterized by mass‐selected infrared photodissociation spectroscopy in the gas phase. The molecules are the first examples of 18‐electron transition metal complexes with alkali atoms as covalently bonded ligands. The calculated equilibrium structures possess C_3v geometry, where the alkali atom is located above a nearly planar Ni(CO)₃^? fragment. The analysis of the electronic structure reveals a peculiar bonding situation where the alkali atom is covalently bonded not only to Ni but also to the carbon atoms.