The interaction of vapor-deposited Al atoms with self-assembled monolayers (SAMs) of HS(CH2)15CH3 and HS(CH2)15CO2CH3 chemisorbed at Au{111} surfaces was studied using X-ray photoelectron spectroscopy, infrared spectroscopy, time-of-flight secondary ion mass spectrometry, and spectroscopic ellipsometry. For the CH3-terminated SAM, no reaction with C−H or C−C bonds was observed. For total Al doses up to ∼12 atoms/nm2, penetration to the Au−S interface occurs with no disruption of the average chain conformation and tilt, indicating formation of a highly uniform ∼1:1 Al adlayer on the Au. Subsequently, penetration ceases and a metallic overlayer begins to form at the SAM−vacuum interface. These results are explained in terms of an initial dynamic hopping of the −S headgroups on the Au lattice, which opens transient diffusion channels to the Au−S interface, and the closing of these channels upon completion of the adlayer. In contrast, Al atom interactions with the CO2CH3-terminated SAM are restricted to the vacuum interface, where in the initial stages discrete organometallic products form via reaction with the CO2CH3 group. First, a 1:1 complex forms with a reduced CO bond and an intact CH3 moiety. Further exposure leads to the additional reaction of about four Al atoms per ester, after which a metallic overlayer nucleates in the form of clusters. After the growth progresses to ∼30 Å, the clusters coalesce into a uniform metallic film. These results illustrate the extraordinary degree of control that organic substrates can exert during the course of metal film formation.

Properties of Ga2O3 thin films deposited by electron-beam evaporation from a high-purity single-crystal Gd3Ga5O12 source are reported. As-deposited Ga2O3 films are amorphous, stoichiometric, and homogeneous. Excellent uniformity in thickness and refractive index was obtained over a 2 in. wafer. The films maintain their integrity during annealing up to 800 and 1200 °C on GaAs and Si substrates, respectively. Optical properties including refractive index (n=1.84–1.88 at 980 nm wavelength) and band gap (4.4 eV) are close or identical, respectively, to Ga2O3 bulk properties. Reflectivities as low as 10−5 for Ga2O3/GaAs structures and a small absorption coefficient (≊100 cm−1 at 980 nm) were measured. Dielectric properties include a static dielectric constant between 9.9 and 10.2, which is identical to bulk Ga2O3, and electric breakdown fields up to 3.6 MV/cm. The Ga2O3/GaAs interface demonstrated a significantly higher photoluminescence intensity and thus a lower surface recombination velocity as compared to Al2O3/GaAs structures.

We have used X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRRAS), and solid-state nuclear magnetic resonance spectroscopy (NMR) to study the interface between poly(methyl methacrylate) (PMMA) and amorphous aluminum oxide. For the first two techniques, the aluminum oxide was a native oxide grown in ambient on vapor-deposited aluminum metal films, while for the third, high surface area porous aluminum oxide was used. In all cases the polymer was adsorbed from solution. Our results have shown that when PMMA adsorbs on the aluminum oxide surface, the surface hydroxyl groups hydrolyze the ester bond in the side chain of the polymer. As a result of the reaction, a side chain carboxylate ion is formed which bonds ionically with the surface, while methanol is released as a byproduct. In the IR spectra the formation of carboxylate ions is indicated by the appearance of a new peak at 1670 cm-1, while in the NMR spectra the loss of the methoxy carbons is indicated by a significant decrease in the methoxy carbon peak. While XPS spectra are less specific, they consistently show a new peak in the 0(2p) region of the adsorbed polymer spectrum. The strength and the specificity of this interaction drive conformational changes of the polymer molecules upon adsorption, which show up as shifts in peak positions in the NMR spectra. These changes suggest a relatively flat configuration of the extensively hydrolyzed molecules on the oxide surface.

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