The adsorption and photochemistry of CD3I adsorbed on TiO2(110) at ∼110 K has been studied by means of temperature programmed desorption (TPD) and x-ray photoelectron spectroscopy (XPS). Complex desorption behavior is observed in TPD suggesting the presence of several distinct coverage regimes. At submonolayer coverages there are two coexisting phases: one dominated by adsorbate–adsorbate interaction, the other dominated by adsorbate–substrate interactions. The first completed monolayer corresponds to (3.8±0.3)×1014 molecules  cm−2 and shows only one desorption peak, although this is broad and extends asymmetrically to high temperature indicative of a changing desorption activation energy. With increasing coverage, a discrete, less tightly bound second layer is formed which slowly rearranges to produce three-dimensional clusters of methyl iodide, as indicated by a sharp reduction in the I (3d5/2)/Ti(2p) XPS intensity ratio. There is evidence that this rearrangement does not involve the first monolayer. Irradiation of 1 ML CD3I by 254 or 334 nm photons causes cleavage of the C–I bond and expulsion of I and C containing species into the vacuum. There is retention of ∼20% of the initial I atoms after irradiation at 254 nm. The photodissociation cross section, σ, of adsorbed CD3 I on TiO2(110) at 254 and 334 nm is calculated to be ∼1.1×10−18 cm2 and ∼1.3 ×10−20 cm2, respectively. At 254 nm, the adsorbate and gas phase σ are similar suggesting photodissociation is dominated by adsorbate excitation, but at 334 nm the adsorbate photodissociation cross section is almost an order of magnitude larger than its gas phase counterpart. This suggests that a second photoexcitation mechanism may be contributing to adsorbate photodissociation, possibly involving photogenerated substrate carriers.

A nanosphere lithography technique has been used to synthesize periodic nanoparticle arrays of TiO 2 on glass substrates. Both monolayer and bilayer evaporation masks were generated from hexagonally close-packed polystyrene nanospheres, each one producing a different array of TiO 2 nanoparticles. Atomic force microscopy (AFM) showed that the masks typically consisted of ordered 10−100 µm 2 domains. X-ray photoelectron spectroscopy confirmed that the surface composition of the particles corresponded to TiO 2 with minor amounts of a Ti 3+ species, presumably associated with edges, corners, and oxygen vacancy defects. Analysis of the AFM images indicated that the nanoparticles were circular in shape with array dimensions approximately consistent with simple geometric considerations for the 420 nm diameter polystyrene nanospheres used as masks in this work. The monolayer and bilayer masks yielded TiO 2 particle diameters of 169 ± 12 nm and 140 ± 13 nm, respectively. The absorption edge of the nanoparticle arrays are blue-shifted from single-crystal rutile.

We have prepared and characterized self-assembled monolayers (SAMs) of rigid p-methylterphenyl thiol (MTPT) on Au(111). According to ellipsometry and reflection−absorption infrared spectroscopy (RAIRS), MTPT forms densely packed monolayers on gold with the molecular axes slightly tilted away from the surface normal (∼17°). At room temperature, monatomically high islands are observed by scanning tunneling microscopy (STM) instead of the typical monatomically deep holes characteristic of alkanethiol films. Molecular resolution images of the MTPT monolayer reveal a (√3×√3)R30°-like packing with slightly larger lattice vectors (a = 5.3 ± 0.3 Å, b = 5.3 ± 0.4 Å, γ = 60° ± 2°) than those of typical alkanethiol monolayers. This is probably due to the mismatch between the lowest energy packing configuration of the terphenyl monolayer (similar to that of crystalline terphenyl solid) and that of the underlying (√3×√3)R30° structure of the sulfur headgroups. As a result, small domains of order and a high density of defects are observed in the film.

The adsorption of formaldehyde (H2CO) on clean Cu(100) at 85 K has been studied using electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). For coverages up to (1.06 ± 0.22) × 1015 H2CO molecules/cm2, formaldehyde spontaneously polymerized to form a monolayer of disordered poly(oxymethylene) (POM), arranged with the chain directions parallel to the surface plane. Thermal decomposition/desorption of the polymer monolayer occurred by three routes, producing peaks in temperature-programmed desorption (TPD) at approximately 177, 200, and 215 K. The lowest temperature peak was exclusively associated with production of H2 and CO in approximately equal proportions. The two higher temperature peaks were produced by molecular H2CO generated via depolymerization of the polymer. The 200 and 215 K features displayed zero- and first-order desorption kinetics, corresponding to estimated activation energies for depolymerization of 75 ± 10 and 53.9 ± 0.5 kJ/mol, respectively. The presence of two polymer desorption peaks is attributed to chain conformational differences present within the monolayer and has not been previously observed in studies of formaldehyde adsorption on metal surfaces. Large exposures of H2CO on this surface formed multilayers of molecular formaldehyde on top of the first polymer layer. The second layer desorbed at 105 K and subsequent layers at ∼100 K.

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