Interfacial organic layers: Tailored surface chemistry for nucleation and growth
(Color online) Parameter space accessed by interfacial organic layers using the factors of density and dimensionality. Here, we show four versions of IOLs schematically and in cross section.
(Color online) Ball-and-stick models of the two terminated first-generation PAMAM dendrons, which differ in terms of the number of carbon atoms (3 or 12) in their straight chain anchors: Gen-1–3C (left) and Gen-1–12C (right).
(a) XP spectra of the features for the Gen-1 PAMAM dendrons displayed in Fig. 2. The features were fit to three peaks corresponding to contributions from aliphatic (284.6 eV), amino (286 eV), and amidic (288.4 eV) carbons. The spectra have been shifted along the ordinate to facilitate the presentation. (b) XP spectra of the feature for two generations of PAMAM dendrons with 3 carbon (3C) and 12 carbon (12C) anchors. In both cases, Gen-0 represents the terminated straight-chain anchor, and Gen-1 represents the first-generation dendron. Spectra have been fit to a single peak in each case. Again, spectra have been shifted along the ordinate.
(Color online) Ball-and-stick models of polyglycidol at two stages of growth: an oligomer of two monomeric units (poly-) and another with six (poly-). Each of these represents one of a number of possible configurations. For poly-, there are possible isomers.
(Color online) Attenuation length for electrons representing photoemission from the core level as a function of the density of valence electrons in the organic film. x-ray radiation gives an electron kinetic energy of for the level. The solid line represents a fit to a power law (exponent of ), whereas the dashed line is a prediction of the Ashley equation (Ref. 139).
Coverage-exposure relationship, deduced from XPS, for the adsorption of on chemical oxide and and terminated SAMs at a substrate temperature of . The left panel (a) highlights the low exposure regime, which illustrates the differing initial slopes, while the right panel (b) emphasizes the high exposure regime and the saturation coverage. The fits to the data, shown as smooth curves, are for a first-order Langmuirian model of adsorption.
Coverage-exposure relationship, deduced from XPS, for the adsorption of at on (a) Gen-0 and Gen-1 PAMAM dendrons and (b) two different thicknesses of poly-G. Absolute densities were calculated from XPS.
(Color online) Predicted form for the photoemission intensity, , as a function of take-off angle, , for a series of values of . Here, is the depth of the 2D monolayer of photoemitters, and is the attenuation length. To highlight the change in functional form with changing values of , all curves are normalized to at .
(Color online) Integrated area of the feature as a function of take-off angle for saturated layers of on straight-chain and terminated SAMs. The smooth curves are a fit to the model that assumes that Ti is present in a two-dimensional monolayer buried at a depth from the SAM/vacuum interface (see Fig. 8).
Integrated peak area of the region for saturated layers of on (a) terminated PAMAM dendrons and (b) an 84 Å thick polyglycidol layer. In (a), the smooth curves are a fit to the model that assumes that Ta is present in a 2D monolayer buried at a depth from the SAM/vacuum interface. In (b), we display a fit to two models: the 2D model as in (a) and Fig. 8, and a thin film model that assumes that Ta is uniformly distributed in a thin film, which extends from the IOL/vacuum interface to a depth of .
Density of Ti atoms produced by saturation exposures to as a function of the SAM density, as deduced from XPS, for mostly unreactive SAMs. The data point on the ordinate represents the starting surface, chemical oxide. In all cases, the Ti density has been corrected for attenuation effects and represents that attributed to adsorption at the interface. For the SAM, adsorption of Ti at the SAM/vacuum interface is also implicated , and this value is considered in Fig. 12.
(Color online) Density of Ti atoms produced by saturation exposures to as a function of OFG density, as deduced from XPS, for IOLs with reactive end groups and backbones. For five of the cases, the SAMs possess either a straight-chain alkyl or aromatic backbone and a single terminal or end group. For the branched PAMAM dendron (Gen-1–3C), both terminal amine, , and the backbone amide group, , contribute to the OFG density. In all cases, the Ti density has been corrected for attenuation effects.
(Color online) (a) Density of Ta atoms produced by saturation exposures to as a function of OFG density, as deduced from XPS, for two generations of PAMAM dendrons and both the 3C and 12C anchors. For the Gen-1 dendrons, both terminal amine, , and the backbone amide group, , contribute to the OFG density. For comparison, the results shown in Fig. 12 for on reactive IOLs are reproduced here (open symbols). (b) The density of Ta atoms produced by saturation exposures to as a function of OFG density. The IOLs here are three thicknesses of poly-G, and one layer of poly-G that has been modified by a terminated SAM. Except where noted, the Ta or Ti density has been corrected for attenuation effects.
(Color online) Number of ligands retained by after chemisorption on three straight-chain SAMs (terminated by , , and ) and bare chemical oxide as a function of substrate temperature.
Possible structures formed by reaction of and with amine- and amide-containing IOLs.
XP spectra of saturated layers of for the and regions. The substrates include, top to bottom, bare chemical oxide, two thicknesses (30 and 84 Å) of poly-G, and an 84 Å poly-G film modified by a terminated SAM prior to exposure to . The spectra have been shifted along the ordinate to facilitate the presentation.
(Color online) TiN thin film thickness (from ellipsometry) as a function of the number of ALD cycles at (open symbols) and (filled). The solid lines correspond to fits to the data using Eq. (1) in the text. We show results for growth (a) on chemical oxide and two unreactive SAMs (ODTS and TTS) and (b) on chemical oxide and three reactive terminated, straight-chain, and branched IOLs.
(Color online) TiN thin film thickness (from ellipsometry) as a function of the number of ALD cycles at (open symbols) and (filled). The solid lines correspond to fits to the data using Eq. (1) in the text. We show results for growth on chemical oxide, a straight-chain SAM, and three thicknesses (30, 47, and 84 Å) of poly-G, which also possesses groups. The dashed line shows a fit to the data for TTS, taken from Fig. 16.
(Color online) Growth attenuation factor from Eq. (1) as a function of IOL thickness. Data are separated into two groups, one for IOLs with reactive terminations ( and ) and the other for those with both unreactive backbones ( and ) and terminations ( and ). Results are shown for (a) and (b) .
(Color online) Atomic force micrographs of representative TiN films grown by ALD on bare chemical oxide and a variety of IOLs, including a terminated dendron (Gen-1–3C), two unreactive SAMs (HMDS and TTS), and two thicknesses of poly-G. Here, is the ellipsometric thin film thickness, is the rms roughness, and is the in-plane correlation length. All images are .
(Color online) Thin film rms surface roughness measured by AFM versus ellipsometric film thickness for TiN ALD. (a) Results for growth on chemical oxide, two IOLs with reactive end groups (Gen-1–3C and a SAM), and two unreactive SAMs (HMDS and TTS). (b) Results for growth on three IOLs with reactive end groups (an SAM and two thicknesses of poly-G) and an unreactive SAM (TTS).
(Color online) (a) Annular dark field transmission electron micrograph of a TiN film grown on a terminated IOL (Gen-1–3C) at . Nominal thickness of the film is . (b) Elemental profiles for Ti, Si, and C obtained from corresponding high-resolution electron energy loss spectra. The absolute position of the surface is approximate.
(Color online) Growth attenuation factor [from ellipsometry and RBS (open symbols); in Eq. (1)] vs the saturation density of (at ) measured from beam reflectivity. For the two data points on poly-G, we have estimated the saturation density for exposure to by using that found for thermal exposures to and have estimated using the first measured thickness data point. See text for justification.
(Color online) rms roughness for the early stages of growth vs for TiN ALD on six surfaces. The roughness plotted is either the maximum observed in the early stages of growth (valid for HMDS, TTS, Gen-1–3C, and 84 Å thick poly-G), or, if a maximum is not observed, it is the first value for which we report a thickness (chemical oxide and the SAM). In all cases, see Fig. 20. The fit to a power law excludes the data point for poly-G primarily due to the uncertainty in the value for (again estimated as in Fig. 22).
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