Molecularly imprinted polymer coatings for open-tubular capillary electrochromatography prepared by surface initiation

Molecularly imprinted polymer coatings were synthesized in fused-silica capillary columns by the use of a surface-coupled radical initiator. The coatings were prepared using either toluene, dichloromethane, or acetonitrile in the prepolymerization mixtures and were 0.15-2 microm thick as determined by scanning electron microscopy. Solvent-dependent differences in appearance were observed. All the molecularly imprinted polymer-based open-tubular capillary columns were able to separate the enantiomers of propranolol by means of electrochromatography. Electrochromatographic performance was found to be dependent on the type of solvent used during the synthesis.     

Surface energy measurements from Griffith cracks in boron fibres

Journal of Materials Science -     

Fundamental aspects of formation and stability of explosive welds

fundamental bonding processes that occur between two metals over an explosive weld interface are described. As a physical model for interfacial bonding, Miedema’s model for alloy formation is employed, 14, 15 generalized from interatomic to macroscopic interfaces. Formation energies for metal-to-metal interfaces are calculated for a large number of metal combinations. The theoretical bond strengths, together with weldability factors, are compared with practical experience for a number of metal combinations, yielding a relatively good agreement. Other interface phenomena such as interface alloying and segregation are also treated by the present model, and for the metal systems studied, theory and experimental results were found to agree well. Formerly with Institute of Technology, Uppsala University, Sweden     

Phase equilibria in transition metal Al-Ga-N systems and thermal stability of contacts to AlGaN

As a first step in predicting the phase equilibria in TM-Al-Ga-N systems, where TM denotes a transition metal from the first three transition series, phase equilibria are calculated in the TM-Al-N systems, and the condensed phases in equilibrium with both AlN and N₂ gas are discussed with respect to the position of the transition metal in the periodic table, temperature, and nitrogen pressure. Possible phases for use as stable electrical contacts to AlGaN are identified using these predictions, similar previous predictions for the TM-Ga-N systems and experimental findings.     

Hardness, internal stress and fracture toughness of epitaxial AlxGa1−xAs films

Vickers microhardness indentations of 10 μm (001) oriented epilayers of Al_xGa_1−xAs on GaAs substrates have been utilized to evaluate the hardness H_v, the internal stress, and the fracture toughness K_Ic of the layers as a function of their composition parameter x. The hardness H_v varies linearly according to: (6.9-2.2x) GPa and K_Ic increases linearly with x according to: K_1c = (0.44+1.30x) MPa m^1/2. The influence of the substrate on these measurements was found to be negligible for the layer thickness (10 μm) and the indentation load (0.25 N) used, disregarding internal stresses.

Internal film stresses were evaluated by the bimorph buckling method, and were found to depend on the composition parameter according to σ = 0.13x GPa. These stresses did not notably affect the H_v measurements, but for K_Ic corrections as large as 25% had to be made.

The radial cracks observed were of the shallow Palmqvist type. In contradiction to previous reports on this type of cracking, it was found to initiate during unloading, not during loading, and a physical explanation for this deviation is given. No deep radial/median cracks were observed. It was found important to use expressions based on the correct crack geometry in the K_Ic evaluation. Also, a simple theory for the influence of internal stresses on the K_Ic results has been developed.     

Surface Defects in Polished Silicon Studied by Cross-Sectional Transmission Electron Microscopy

The cross-sectional TEM technique is applied to Si(100) surfaces, which are exposed to mild polishing with diamond paste in the 0.25- to 6-μm-size range as well as with the commercial polishing medium Syton HT 50. Syton polishing is also used to prepare electron-transparent foils for TEM studies, and this preparation technique shows several advantages over ion thinning. Mild diamond polishing results in small-scale abrasive grooving and production of superficial dislocation loops of 1/2〈110〉{111} type. Debris of amorphous material tends to aggregate in surface cavities. These aggregates are formed during polishing, not by ion milling. Syton polishing results in very smooth surfaces, with no signs of abrasive grooving or dislocation density. Two major mechanisms of mass removal are suggested: (1) "smearing" of very superficial material at a nearly atomic level, resulting in amorphous aggregates and (2) strongly localized plastic cutting or shearing. In mild polishing, both mechanisms are suggested to be active, localized plastic cuttinglshearing becoming progressively more dominant for increasing particle size.     

A structural homologue of colipase in black mamba venom revealed by NMR floating disulphide bridge analysis

The solution structure of mamba intestinal toxin 1 (MIT1), isolated from Dendroaspis polylepis polylepis venom, has been determined. This molecule is a cysteine-rich polypeptide exhibiting no recognised family membership. Resistance to MIT1 to classical specific endoproteases produced contradictory NMR and biochemical information concerning disulphide-bridge topology. We have used distance restraints allowing ambiguous partners between S atoms in combination with NMR-derived structural information, to correctly determine the disulphide-bridge topology. The resultant solution structure of MIT1, determined to a resolution of 0.5 A, reveals an unexpectedly similar global fold with respect to colipase, a protein involved in fatty acid digestion. Colipase exhibits an analogous resistance to endoprotease activity, indicating for the first time the possible topological origins of this biochemical property. The biochemical and structural homology permitted us to propose a mechanically related digestive function for MIT1 and provides novel information concerning snake venom protein evolution.     

Anisotropy-independent through micromachining of quartz resonatorsby ion track etching

A method to achieve deep and crystal cut-independent structuring of arbitrary lateral geometry in single crystalline quartz is demonstrated. It is based on local etching of the latent track-induced anisotropy resulting from heavy ion bombardment, and is close to independent of crystallographic orientation. Previous results are briefly reviewed and a more systematic and thorough study is presented. Miniature tuning fork structures of various sizes and directions have been realized, and the suitability for frequency control device production is discussed