Abstractive chemisorption of O2 on Al(111)

We present experimental evidence that abstraction is a common mechanism (approximately 50%) in the dissociative chemisorption of oxygen on Al(111) at a translational energy of 0.5 eV. As a result of this mechanism, individual isolated O-atoms are observed in scanning tunneling microscopy (STM). At this translational energy ordinary dissociative chemisorption processes also occur, resulting in pairs of adatoms. The ejected O-atoms originating from the abstraction reaction are detected in the gas phase using laser spectrometry. Together, these observations provide compelling evidence for the abstraction mechanism.     

Chemical selectivity in the remote abstractive chemisorption of ICl on Al(111)

The interaction of ICl and Al(111) involves remote dissociation in its chemisorption process. In remote dissociation, an electron harpoons from an Al(111) surface to an ICl gas molecule to initiate the chemisorption process. We have determined that ICl can chemisorb onto Al(111) by non-activated direct chemisorption, and the sticking probability of this direct channel is 0.65 +/- 0.03. Furthermore, low energy ICl molecules that do not undergo remote dissociation can chemisorb onto Al(111) by precursor-mediated chemisorption. Not only is the interaction of ICl and Al(111) reactive, it is chemically selective. Studies with Auger spectroscopy reveal that the ratio of chlorine atoms to iodine atoms on the Al(111) is 0.32 +/- 0.10 at low (0.042 +/- 0.002) surface coverage. Time-of-flight mass spectrometry studies also show that chlorine atoms are the only species scattered from the surface after ICl interacts with Al(111). These results indicate that iodine-selective abstraction, in which the iodine atom of ICl chemisorbs to the aluminium surface while the chlorine atom is ejected into the gas phase, is the dominant mechanism in this reaction. Iodine-end first collisions are more reactive than chlorine-end first collisions because the lowest unoccupied molecular orbital (LUMO) of ICl is primarily composed of iodine atomic orbitals, and it is the LUMO that interacts with the harpooning electron from the aluminium.     

Molecular dynamics simulation comparison of atomic scale intermixing at the amorphous Al2O3/semiconductor interface for a-Al2O3/Ge, a-Al2O3/InGaAs, and a-Al2O3/InAlAs/InGaAs

The structural properties of a-Al₂O₃/Ge, a-Al₂O₃/In_0.5Ga_0.5As and a-Al₂O₃/In_0.5Al_0.5As/InGaAs interfaces were investigated by density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-Al₂O₃ samples were generated using a hybrid classical-DFT MD “melt and quench” approach. The interfaces were formed by annealing at 700 K/800 K and 1100 K with subsequent cooling and relaxation. The a-Al₂O₃/Ge interface demonstrates pronounced interface intermixing and interface bonding exclusively through Al–O–Ge bonds generating high interface polarity. In contrast, the a-Al₂O₃/InGaAs interface has no intermixing, Al–As and O–In/Ga bonding, low interface polarity due to nearly compensating interface dipoles, and low substrate deformation. The a-Al₂O₃/InAlAs interface demonstrated mild intermixing with some substrate Al atoms being adsorbed into the oxide, mixed Al–As/O and O–Al/In bonding, medium interface polarity, and medium substrate deformation. The simulated results demonstrate strong correlation to experimental measurements and illustrate the role of weak bonding in generating an unpinned interface for metal oxide/semiconductor interfaces.     

Theoretical analysis of initial adsorption of high-κ metal oxides on In(x)Ga(1-x)As(0 0 1)-(4×2) surfaces

Ordered, low coverage to monolayer, high-κ oxide adsorption on group III rich InAs(0 0 1)-(4×2) and In(0.53)Ga(0.47)As(0 0 1)-(4×2) was modeled via density functional theory (DFT). Initial adsorption of HfO(2) and ZrO(2) was found to remove dangling bonds on the clean surface. At full monolayer coverage, the oxide-semiconductor bonds restore the substrate surface atoms to a more bulklike bonding structure via covalent bonding, with the potential for an unpinned interface. DFT models of ordered HfO(2)/In(0.53)Ga(0.47)As(0 0 1)-(4×2) show it fully unpins the Fermi level.