Covalent attachment of functionalized monolayers onto silicon surfaces (see Figure for examples) is presented here as a strategy for surface modification. The preparation and structure of both unfunctionalized and functionalized alkyl‐based monolayers are described, as are potential applications, for example, in the surface passivation of Si solar cells and for photopatterning of silicon surfaces.
A new approach has been developed to prepare amino-terminated monolayers on hydrogen-terminated silicon surfaces. This two-step procedure is the first method that provides direct control over the surface density of the amino groups. First, a mixed monolayer of a protected ω-amino-1-alkene and a nonfunctional 1-alkene is prepared on a H-terminated Si surface, using either phthalimide or acetamide as NH2-protecting groups. Subsequent removal of the protective groups generates the covalently attached NH2-terminated monolayer, as evidenced from water contact angle measurements, IR spectroscopy, and X-ray photoelectron spectroscopy. Both protecting groups have their own advantages: use of the phthalimide moiety is synthetically very convenient; the relatively small acetamide moiety can be used to prepare monolayers with high densities (>50%) of amine groups. The reactivity of the amine groups has been confirmed by further modification of the monolayers.
Using liquid phase epitaxy (LPE) technique (111) yttrium iron garnet (YIG) films with thicknesses of ≈100 nm and surface roughnesses as low as 0.3 nm have been grown as a basic material for spin-wave propagation experiments in microstructured waveguides. The continuously strained films exhibit nearly perfect crystallinity without significant mosaicity and with effective lattice misfits of ∆a ⊥ /a s ≈ 10 −4 and below. The film/substrate interface is extremely sharp without broad interdiffusion layer formation. All LPE films exhibit a nearly bulk-like saturation magnetization of (1800±20) Gs and an 'easy cone' anisotropy type with extremely small in-plane coercive fields <0.2 Oe. There is a rather weak in-plane magnetic anisotropy with a pronounced six-fold symmetry observed for saturation field <1.5 Oe. No significant out-of-plane anisotropy is observed, but a weak dependence of the effective magnetization on the lattice misfit is detected. The narrowest ferromagnetic resonance linewidth is determined to be 1.4 Oe @ 6.5 GHz which is the lowest values reported so far for YIG films of 100 nm thicknesses and below. The Gilbert damping coefficient for investigated LPE films is estimated to be close to 1 × 10 −4 .
High resolution electron energy loss spectroscopy ͑HREELS͒, low-energy electron diffraction ͑LEED͒, and thermal desorption spectroscopy ͑TDS͒ were used to study lateral interactions in the adsorbate layer of the CO/Rh͑111͒ system. The vibrational spectra show that CO adsorbs exclusively on top at low coverage. At about half a monolayer a second adsorption site, the threefold hollow site, becomes occupied as well. A steady shift to higher frequencies of the internal C-O vibrations is observed over the whole coverage range. The frequency of the metal CO ͑M-CO͒ vibration in the on-top mode hardly shifts at low coverage. However, upon the emergence of the second adsorption site the M-CO vibrations experience a shift to lower frequencies. The population of the second site is also accompanied by the development of a low temperature shoulder in the TD spectra, indicating an increasingly repulsive interaction in the adsorbed CO layer. Vibrational spectra of isotopic mixtures of 12 CO and 13 CO were used to assess the origin of the observed frequency shifts. They confirm that frequency shifts of the C-O stretching vibration at total CO coverage of 0.33 ML in the (ͱ3ϫͱ3)R30°structure arise purely from dipole-dipole coupling. Dilution of an isotopic species effectively suppresses frequency shifts arising from dipole-dipole coupling. Therefore, experiments with a small amount of 13 CO as a tracer to monitor the frequency shifts in the 12 CO adlayer were carried out over the entire coverage range of 12 CO. The results demonstrate that dipole-dipole coupling causes the frequency shifts at low coverage ͑Ͻ0.5 ML͒, whereas chemical effects set in at higher coverage ͑0.5-0.75 ML͒, connected with the population of the threefold sites. The results illustrate that HREELS in combination with isotopic dilution is a powerful tool in the assessment of lateral interactions between adsorbed molecules.
An active surface science model for the Phillips ethylene polymerization catalyst has been prepared by impregnating aqueous CrO3 on a flat silicium(100) substrate covered by amorphous silica. Using a combination of X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and Rutherford backscattering spectrometry, we studied the effect of calcination on the state of the supported chromium. Depending on the calcination temperature and the initial Cr loading of the catalyst, two processes are observed. The impregnated chromate anchors to the silica surface in an esterification reaction with the surface silanol groups of the support. The saturation coverage of these surface chromates is 2.4 Cr/nm2 for a calcination temperature of 450 °C. Superficial, not anchored, chromate slowly desorbs from the flat silica surface. Under crowded conditions a portion of the surface chromates also desorb if the calcination temperature is increased, while low Cr loadings (>1 Cr/nm2) are stable up to the highest calcination temperature in our experiments (730 °C). The silica-bound surface chromates are monochromates exclusivly, independent of the initial loading or calcination temperature.
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