Tip-activated single-atom catalysis: CO oxidation on Au adatom on oxidized rutile TiO surface.

Single-atom catalysis of carbon monoxide oxidation on metal-oxide surfaces is crucial for greenhouse recycling, automotive catalysis, and beyond, but reports of the atomic-scale mechanism are still scarce. Here, using scanning probe microscopy, we show that charging single gold atoms on oxidized rutile titanium dioxide surface, both positively and negatively, considerably promotes adsorption of carbon monoxide. No carbon monoxide adsorption is observed on neutral gold atoms.

Interplay of the tip-sample junction stability and image contrast reversal on a Cu(111) surface revealed by the 3D force field.

Non-contact atomic force microscopy is used to measure the 3D force field on a dense-packed Cu(111) surface. An unexpected image contrast reversal is observed as the tip is moved towards the surface, with atoms appearing first as bright spots, whereas hollow and bridge sites turn bright at smaller tip-sample distances. Computer modeling is used to elucidate the nature of the image contrast.

Understanding frictional duality and bi-duality: Sb-nanoparticles on HOPG.

Antimony nanoparticles deposited under UHV conditions on HOPG are found to exhibit an intriguing frictional behavior characterized by a distinct clearly separated double dual behavior of dependence of the frictional force on contact area. We present the first realistic simulations, density functional modeling adapted to accommodate van der Waals interactions, of the (double) dual frictional behavior. The simulations provide insights into the physics/chemistry of all the frictional branches in terms of incommensurable interfaces, mobile spacer molecules as well as a novel concept of mobile oxidized multi-nanoasperities.

Switching of functionalized azobenzene suspended between gold tips by mechanochemical, photochemical, and opto-mechanical means.

Optical, purely mechanical, and combined opto-mechanical switching cycles of a molecular switch embedded in a metal junction are investigated using density functional theory and (excited state) ab initio molecular dynamics. The nanomechanical simulations are done on realistic models of gold electrode tips bridged by a single dithioazobenzene molecule. Comparison of different tip models shows that the nature of the tips affects switching processes both qualitatively and quantitatively.

Mechanochemistry and thermochemistry are different: stress-induced strengthening of chemical bonds.

Most chemical reactions require activation which is conventionally supplied by heat. In stark contrast, mechanical activation by applied external forces opens intriguing novel possibilities. Here, the first direct comparison of mechanical versus thermal activation of bond breaking is provided.