Blocking the lateral film growth at the nanoscale in area-selective atomic layer deposition

Area-selective atomic layer deposition (ALD) allows the growth of highly uniform thin inorganic films on certain parts of the substrate while preventing the film growth on other parts. Although the selective ALD growth is working well at the micron and submicron scale, it has failed at the nanoscale, especially near the interface where there is growth on one side and no-growth on the other side. The reason is that methods so far solely rely on the chemical modification of the substrate, while neglecting the occurrence of lateral ALD growth at the nanoscale. Here we present a proof-of-concept for blocking the lateral ALD growth also at the nanoscale by combining the chemical surface modification with topographical features. We demonstrate that area-selective ALD of ZnO occurs by applying the diethylzinc/water ALD process on cicada wings that contain a dense array of nanoscopic pillars. The sizes of the features in the inorganic film are down to 25 nm which is, to the best of our knowledge, the smallest obtained by area-selective ALD. Importantly, our concept allows the synthesis of such small features even though the film is multiple times thicker.     

In search of the [PhB(mu-N(t)Bu)2]2As. radical: experimental and computational investigations of the redox chemistry of group 15 bis-boraamidinates

DFT calculations for the group 15 radicals [PhB(mu-N(t)Bu)2]2M. (M = P, As, Sb, Bi) predict a pnictogen-centered SOMO with smaller contributions to the unpaired spin density arising from the nitrogen and boron atoms. The reactions of Li 2[PhB(mu-NR)2] (R = (t)Bu, Dipp) with PCl 3 afforded the unsolvated complex LiP[PhB(mu-N(t)Bu)2] 2 ( 1a) in low yield and ClP[PhB(mu-NDipp)2] (2), both of which were structurally characterized. Efforts to produce the arsenic-centered neutral radical, [PhB(mu-N (t) Bu) 2] 2As., via oxidation of LiAs[PhB(mu-N(t)Bu)2]2 with one-half equivalent of SO 2Cl 2, yielded the Zwitterionic compound [PhB(mu-N (t) Bu) 2As(mu-N(t)Bu)2B(Cl)Ph] (3) containing one four-coordinate boron center with a B-Cl bond. The reaction of 3 with GaCl3 produced the ion-separated salt, [PhB(mu-N(t)Bu)2] 2As (+)GaCl 4 (-) ( 4), which was characterized by X-ray crystallography. The reduction of 3 with sodium naphthalenide occurred by a two-electron process to give the corresponding anion [{PhB(mu-N(t)Bu)2} 2As] (-) as the sodium salt. Voltammetric investigations of 4 and LiAs[PhB(mu-N (t) Bu) 2] 2 ( 1b) revealed irreversible processes. Attempts to generate the neutral radical [PhB(mu-N(t)Bu)2] 2As. from these ionic complexes via in situ electrolysis did not produce an EPR-active species.     

PCP-bridged chalcogen-centred anions: coordination chemistry and carbon-based reactivity

Since the discovery of the stabilising influence of thiophosphinoyl groups in methanediides by Le Floch et al. (Angew. Chem. Int. Ed., 2004, 43, 6382), numerous transition metal, lanthanide and actinide complexes of bis(thiophosphinoyl) carbene ligands have been investigated with an emphasis on the electronic structure and reactivity of the metal-carbon bonds. This Perspective begins by discussing main group (s- and p-block) complexes of this ligand and draws attention to differences compared to their d and f-block analogues. Investigations targeting the heavy chalcogen analogues of the Le Floch ligand have revealed an unusual carbon-based reactivity that led to the discovery of novel multidentate chalcogen-centred ligands as both monomers and, upon oxidation, dimers linked by dichalcogenido functionalities. Studies of main group and coinage metal complexes have established the flexibility and redox-activity of these novel anionic ligands.     

An XML format for benchmarks in High School Timetabling

The High School Timetabling Problem is amongst the most widely used timetabling problems. This problem has varying structures in different high schools even within the same country or educational system. Due to lack of standard benchmarks and data formats this problem has been studied less than other timetabling problems in the literature. In this paper we describe the High School Timetabling Problem in several countries in order to find a common set of constraints and objectives. Our main goal is to provide exchangeable benchmarks for this problem. To achieve this we propose a standard data format suitable for different countries and educational systems, defined by an XML schema. The schema and datasets are available online.     

Synthesis, spectroscopic and structural characterization of tertiary phosphine tellurium dihalides Et3PTeX2(X = Cl, Br, I)

The reactions of triethylphosphine telluride with SO2Cl2 or I2 produced the first structurally characterized tellurium-containing tertiary phosphine chalcogen dihalides, Et3PTeCl2 and Et3PTeI2, respectively, in good yields. The corresponding dibromide, Et3PTeBr2, was obtained by an in situ reaction between Et3PTeCl2 and two equivalents of Me3SiBr. This series of compounds has been characterized in the solid state by X-ray structural analyses and in solution by multinuclear NMR spectra. The structures of Et3PTeX2(X = Cl, Br, I) all show a T-shaped geometry around tellurium with weak Te...halogen interactions giving rise to centrosymmetric dimers. NMR data indicate that Et3PTeI2 exhibits the weakest P-Te bond in solution. The ionic complexes, [(Et3PO)2H]2[Te2I6] and [(Et3PO)2H]2[TeI4], were isolated from THF solutions of Et3PTeI2 and characterized by X-ray structural determinations.     

Total syntheses of oxygenated brazanquinones via regioselective homologous anionic Fries rearrangement of benzylic O-carbamates

Using new variations of anionic aromatic chemistry, the total synthesis of oxygenated brazanquinones (1a-1c), derived from beta-brasan, a natural product isolated from Caesalpina echinata, via carbamates 2a-2c is described.     

Operator splitting methods for pricing American options under stochastic volatility

We consider the numerical pricing of American options under Heston’s stochastic volatility model. The price is given by a linear complementarity problem with a two-dimensional parabolic partial differential operator. We propose operator splitting methods for performing time stepping after a finite difference space discretization. The idea is to decouple the treatment of the early exercise constraint and the solution of the system of linear equations into separate fractional time steps. With this approach an efficient numerical method can be chosen for solving the system of linear equations in the first fractional step before making a simple update to satisfy the early exercise constraint. Our analysis suggests that the Crank–Nicolson method and the operator splitting method based on it have the same asymptotic order of accuracy. The numerical experiments show that the operator splitting methods have comparable discretization errors. They also demonstrate the efficiency of the operator splitting methods when a multigrid method is used for solving the systems of linear equations.     

A hybrid discontinuous Galerkin method for computing the ground state solution of Bose–Einstein condensates

A numerical method for computing the ground state solution of Bose–Einstein condensates modeled by the Gross–Pitaevskii equation is presented. In this method, the three-dimensional computational domain is divided into hexahedral elements in which the solution is approximated by a sum of basis functions. Both polynomial and plane wave bases are considered for this purpose, and Lagrange multipliers are introduced to weakly enforce the interelement continuity of the solution. The ground state is computed by an iterative procedure for minimizing the energy. The performance results obtained for several numerical experiments demonstrate that the proposed method is more computationally efficient than similar solution approaches based on the standard higher-order finite element method.