Surface oxidation kinetics of sputtering targets

Films of compounds can be deposited by sputtering a metal or alloy target in an atmosphere containing a suitable reactive gas. Both Al and 90 : 10 In : Sn targets have been sputtered in argon/oxygen mixtures to obtain Al₂O₃ and indium tin oxide films. The experiments were carried out in a planar magnetron sputtering system with both dc and rf excitation. To investigate the kinetics of the reactive sputtering process, the time dependence of the total gas pressure was measured after a change in oxygen flow rate or sputtering power; a capacitance manometer gave accurate and reproducible results. There were simultaneous changes in the rf matching conditions when rf excitation was used. These changes can be attributed to the formation of an oxide on the target surface. The time dependence of the oxygen pressure measured for the Al and In : Sn targets have been used to compare various models of the reactive sputtering process. Fitting of the experimental values to these models yields values of the equilibrium oxide thickness on the target and these have been compared with measured values. For rf sputtering of an Al target at 500 W with flow rates of $\text{3}\text{ml}\text{min}$ and $\text{2.2}\text{ml}\text{min}$ for argon and oxygen respectively, both the calculated and the measured value of the oxide thickness is 100 nm.     

Ring contraction in schiff base macrocycles: The X-Ray crystal structure of an imidazolidine-containing macrocycle

Cyclocondensation of benzene-1,3-dicarbaldehyde and 3-azapentane-1,5-diaminein acetonitrile leads to isolation of an 18-membered imidazolidine-containing Schiff base macrocycle rather than the anticipated 24-membered tetraimine Schiff base macrocycle. This has occurred as a consequence of internal nucleophilic addition of the secondary amine functions across adjacent azomethine bonds. The X-ray crystal structure of the imidazolidine-containing Schiff base macrocycle is reported.     

The photoelectron spectra of the oxalyl halides (COX)2, [X = F,Cl and Br]

We have examined the HeI photoelectron spectra of the oxalyl halides (COX)₂, (X = F, Cl, and Br). We assume the presence of the trans-isomer onWe have used semi-empirical calculations (SCF MO), and Koopmans' Theorem, as aids in assigning the spectral bands.     

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The microwave spectrum and centrifugal distortion constants of difluoroborane,HBF2

The microwave spectra of two isotopic species of the unstable molecule difluoroborane have been measured between 8 and 36 GHz. Transitions have been measured up to J = 56 and K_a = 9 for H¹⁰BF₂, and up to J = 66 and K_a = 11 for H¹¹BF₂. Improved values for the rotational constants, boron nuclear quadrupole coupling constants, and quartic and sextic centrifugal distortion constants have been evaluated for both species.     

Thiocyanogen (SCN)2− preparation,ultraviolet photoelectron spectrum and structure

The unstable thiocyanogen molecule, (SCN)₂, has been investigated in the gas phase by ultraviolet photoelection spectroscopy. Semi-empincal and ab intio calculations are used to assist with the orbital assignments and to provide an assessment of the structure A disulphide structure, with a dihedral angle of 87.8° is indicated, similar to those of other well known S₂X₂ molecules.     

An improved protocol for the Prins desymmetrisation of cyclohexa-1,4-dienes

Improved conditions are reported for the Prins-pinacol rearrangement of cyclohexa-1,4-diene-derived acetals. The use of triflic acid gives particularly clean reaction, resulting in a mixture of regioisomers in an approximately 10:1 ratio. A tethered version of this reaction is also reported, giving a tricyclic compound with the same stereochemistry as the core of the cladiellin diterpenes.     

The use of residual dipolar coupling for conformational analysis of structurally related natural products

Determining the conformational preferences of molecules in solution remains a considerable challenge. Recently, the use of residual dipolar coupling (RDC) analysis has emerged as a key method to address this. Whilst to date the majority of the applications have focused on biomolecules including proteins and DNA, the use of RDCs for studying small molecules is gaining popularity. Having said that, the method continues to develop, and here, we describe an early case study of the quantification of conformer populations in small molecules using RDC analysis. Having been inspired to study conformational preferences by unexpected differences in the NMR spectra and the reactivity of related natural products, we showed that the use of more established techniques was unsatisfactory in explaining the experimental observations. The use of RDCs provided an improved understanding that, following use of methods to quantify conformer populations using RDCs, culminated in a rationalisation of the contrasting diastereoselectivities observed in a ketone reduction reaction. Copyright © 2015 John Wiley & Sons, Ltd.