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The electronic properties of metal oxide semiconductor gate electrodes are strong functions of the structure of the metal−dielectric interface. We use density functional theory to investigate the structures, energetics, and electronic properties of Ru/HfO2interfaces. We find that atom-by-atom deposited Ru films have significantly different interfacial structures from epitaxially connected Ru films on the m-HfO2(001) surface. Atom-by-atom deposited films are rougher than epitaxially connected films, even when forced to form two-dimensional films. These interfacial structural differences lead to differences in the electronic properties of the films and therefore affect electrical properties, such as the work function of the gate electrode. We found that for both types of films the partial densities of states of interfacial layers are significantly different from that of the bulk region. Each shows charge transfer from the interfacial Ru layer to the interfacial dielectric layer, although the magnitude of charge transfer varies. Thus both films exhibit metal induced gap states in the band gap region of the interface localized on atoms of the HfO2interfacial layer.

The reactions of the amino acids alanine and arginine on the Ge(100)-2×1 surface are investigated using density functional theory. Arginine presents a unique reactivity not previously explored on semiconductor surfaces. Arginine dative bonds to the surface dimer through its imine lone pair, resulting in two adsorbed conformations with adsorption energies of 30.7 and 33.8 kcal/mol, significantly stronger than amine dative bonds on Ge(100)-2×1. We predict a N−H dissociation and an ene reaction pathway from each of these two conformers with the ene reactions kinetically favored over N−H dissociation of the imine N−H bond and the ene reaction from the cis state favored both kinetically and thermodynamically over the trans ene reaction. Our results for the reactions of the hydroxyl, carbonyl, and amine functional groups are similar to previous observations for analogous reactions of small organic molecules on Ge(100)-2×1. We find that O−H dissociation from the carbonyl dative bonded state is the most favorable pathway. The amine dative bonded state is slightly more stable than the carbonyl dative bonded state. We find that 22 cycloaddition through the CN double bond is exothermic by only 3.3 kcal/mol.

Although catalytic properties are usually ascribed to transition metals and their oxides, the present work identifies a catalytic carbon-oxygen coupling reaction on a group-IV (100)-2×1 semiconductor surface. The reactions of formaldehyde and formaldehyde-d2on Ge(100)-2×1 were investigated with multiple internal reflection infrared (MIR-IR) spectroscopy, temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. Formic acid was also studied for comparison. Infrared data indicate that formaldehyde adsorbs in a dative-bonded state and also forms a minority C-H dissociation product. In addition, theory predicts that a CO 22 cycloaddition product may form, although the infrared spectra are inconclusive as to its presence. Time-dependent and annealing infrared studies suggest that the dative-bonded species undergoes a subsequent coupling reaction with a nearby surface adduct, resulting in a bidentate formate group as evidenced by an intense (O-C-O) stretching mode near 1500 cm-1. The desorption of CO2during TPD experiments confirms the carbon-oxygen coupling reaction.

Atomic layer deposition (ALD) has recently gained interest because of its suitability for fabrication of conformal films with thicknesses in the nanometer range. A comparative investigation of surface hydroxylation states of different surfaces of m-HfO2is central to a better understanding of how precursors react on these surfaces under ALD growth conditions. We used a combined approach of density functional theory (DFT) and thermodynamics to determine the types of acidic and basic groups on different surfaces of m-HfO2. We find that the water adsorption energy decreases with increasing surface coverage; however, the energetics of the hydration process can be significantly different on different surfaces. Our investigation showed that under ALD working conditions the (001) surface retains a higher concentration of Brønsted acid sites compared to the thermodynamically stable (11) surface because of the higher adsorption energy of water on the (001) surface. Analysis of surface species reveals that the (001) surface has hydroxyl groups which are mainly one- or twofold coordinated to one or two Hf atoms, respectively, whereas for the (11) surface threefold coordinated hydroxyl groups are also populated.

A series of mono(cyclopentadienyl)titanium TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) complexes were investigated by density functional theory (DFT) calculations to study the influence of the ligands on the Ti−O bond energies. Mono-Cp complexes with pendant amino groups were found to possess significantly weaker Ti−O bonds than those lacking pendant donor ligands. On the basis of DFT predictions, a novel mono-Cp pendant dimethylamino complex, CpNTiCl2(TEMPO) (12; CpN C5H4CH2CH2N(CH3)2), was identified as a mono-Cp titanium TEMPO complex with a weak Ti−O bond (25 kcal/mol). The calculated bond energy of this complex is comparable to that of Cp2TiCl(TEMPO) (3; 17 kcal/mol). Thermolysis of 12in the presence of CCl4at 100 °C resulted in the formation of CpNTiCl3, consistent with the predicted low Ti−O bond energy.