The early oxynitridation stages of hydrogen-terminated (100) silicon after exposure to N2:N2O. Nitrogen bonding states

Nitridation of hydrogen-terminated silicon in a diluted N₂:N₂O atmosphere was studied by X-ray photoemission spectroscopy and high-resolution electron microscopy. Our analysis showed that the broad N(1s) peak of width 1.5 eV at 398–399 eV, usually reported in the literature, is preceded by the formation of a narrow peak of width around 1.0 eV at 397.5 eV, attributed to the moiety Si₃N in which silicon is only marginally oxidized, and two other peaks at 400.0 eV and 401.5 eV, attributed to the moieties Si₂NOSi and SiNO, respectively. Received: 11 July 2001 / Accepted: 19 September 2001 / Published online: 20 December 2001     

Severi varieties on blow-ups of the symmetric square of an elliptic curve

We prove that certain Severi varieties of nodal curves of positive genus on general blow-ups of the twofold symmetric product of a general elliptic curve are nonempty and smooth of the expected dimension. This result, besides its intrinsic value, is an important preliminary step for the proof of nonemptiness of Severi varieties on general Enriques surfaces.     

Helicoidal Patterning of Nanorods with Polymer Ligands

Chiral packing of ligands on the surface of nanoparticles (NPs) is of fundamental and practical importance, as it determines how NPs interact with each other and with the molecular world. Herein, for gold nanorods (NRs) capped with end‐grafted nonchiral polymer ligands, we show a new mechanism of chiral surface patterning. Under poor solvency conditions, a smooth polymer layer segregates into helicoidally organized surface‐pinned micelles (patches). The helicoidal morphology is dictated by the polymer grafting density and the ratio of the polymer ligand length to nanorod radius. Outside this specific parameter space, a range of polymer surface structures was observed, including random, shish‐kebab, and hybrid patches, as well as a smooth polymer layer. We characterize polymer surface morphology by theoretical and experimental state diagrams. The helicoidally organized polymer patches on the NR surface can be used as a template for the helicoidal organization of other NPs, masked synthesis on the NR surface, as well as the exploration of new NP self‐assembly modes.     

On the number of moduli of plane sextics with six cusps

Let be the variety of irreducible sextics with six cusps as singularities. Let be one of irreducible components of . Denoting by the space of moduli of smooth curves of genus 4, we consider the rational map sending the general point [Γ] of Σ, corresponding to a plane curve , to the point of parametrizing the normalization curve of Γ. The number of moduli of Σ is, by definition the dimension of Π(Σ). We know that , where ρ(2, 4, 6) is the Brill–Noether number of linear series of dimension 2 and degree 6 on a curve of genus 4. We prove that both irreducible components of have number of moduli equal to seven.      

The early oxynitridation stages of hydrogen-terminated (100) silicon after exposure to N2:N2O. III. Initial conditions

The structure and thermal stability in N₂ of hydrogen-terminated (100) silicon has been studied by X-ray photoemission spectroscopy, transmission electron microscopy, atomic force microscopy, thermal programmed desorption, and reflection high energy electron diffraction. Device-quality surfaces were prepared in an open-chamber reactor by exposing single crystalline, (100) oriented silicon to H₂ at high temperature (850 °C or 1100 °C) for durations on the order of 10² s. The observed stability with respect to N₂ at 850 °C is inconsistent with the reported desorption kinetics and may be accounted for in terms of either physico-chemical properties of the system (e.g., the presence of a buried layer of H₂ or of hydrogen-decorated vacancies whose out-diffusion restores the hydrogen terminations on the surface) or the reactor (persistence of hydrogen in the atmosphere even after switching it off). The nitridation by N₂ of hydrogen-terminated silicon is less efficient (per unit exposure) than that by N₂O by 4 orders of magnitude. PACS 68.35.Dv; 68.35.Fx; 82.65.Dp; 79.60.Jv; 81.60.Cp     

A group extensions approach to relative difference sets

A new approach to (normal) relative difference sets (RDSs) is presented and applied to give a new method for recursively constructing infinite families of semiregular RDSs. Our main result (Theorem 7.1) shows that any metabelian semiregular RDS gives rise to an infinite family of metabelian semiregular RDSs. The new method is applied to identify several new infinite families of non‐abelian semiregular RDSs, and new methods for constructing generalized Hadamard matrices are given. The techniques employed are derived from the general theory of group extensions. © 2004 Wiley Periodicals, Inc. J Combin Designs 12: 279–298, 2004.     

The early oxynitridation stages of hydrogen-terminated (100) silicon after exposure to N2 : N2O. IV: Oxide structure and growth kinetics in the monolayer regime

The structure and growth kinetics of the oxide resulting from exposure of hydrogen-terminated single-crystalline (100) silicon to diluted N₂:N₂O atmospheres at moderate temperatures (in the interval 750–850 °C) have been studied byX-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (TEM), and secondary-ion mass spectrometry (SIMS). Under these conditions, the data suggest that the substoichiometric interface region is extremely narrow, and they point to O₂ (resulting from N₂O decomposition) as the major oxidizing species after monolayer completion. PACS 82.65.+r; 68.35.Fx; 68.35.Dv; 79.60.Jv