XPS analysis of aluminum nitride films deposited by plasma source molecular beam epitaxy

Ten samples of crystalline aluminum nitride (AlN) film were deposited on sapphire and silicon substrates by a plasma source molecular beam method. The samples were analyzed using X‐ray photoelectron spectroscopy (XPS) depth profiling and high‐resolution X‐ray diffraction. Oxygen levels were observed to decrease exponentially from the surface into the bulk film. Aluminum, nitrogen and oxygen peaks were fitted with subpeaks in a consistent manner and the subpeaks were assigned to chemical states. AlN subpeaks were observed at 73.5 eV for Al2p and 396.4 eV for N1s. An N1s subpeak at 395.0 eV was assigned to N? N defects. No direct N? O bonds are assigned; rather it is proposed that an N? Al? O bond sequence is the source of higher binding energy N1s subpeaks. The observations in this study support a model in which oxygen is bound only to aluminum in the form of Al? O octahedral complexes dispersed or clustered throughout the main AlN matrix or as Al? O bonds on the crystal grain boundaries. The data also suggest that the AlN lattice parameters are related to oxygen content, since the c‐axis is observed to increase with increasing oxygen content. Copyright © 2008 John Wiley & Sons, Ltd.     

Hexagonal-boron nitride substrates for electroburnt graphene nanojunctions

We examine the effect of a hexagonal boron nitride (hBN) substrate on electron transport through graphene nanojunctions just before gap formation. Junctions in vacuum and on hBN are formed using classical molecular dynamics to create initial structures, followed by relaxation using density functional theory. We find that the hBN only slightly reduces the current through the junctions at low biases. Furthermore due to quantum interference at the last moments of breaking, the current though a single carbon filament spanning the gap is found to be higher than the current through two filaments spanning the gap in parallel. This feature is present both in the presence of absence of hBN.     

Laser removal of TiN coatings from WC micro-tools and in-process monitoring

Current environmental challenges require sustainable and extended use and re-use of materials. For example, the service life of engineering tooling can be extended by using thin film coatings such as titanium nitride (TiN). However, when errors arise in the coating process or when the tooling needs to be re-used it is necessary to remove the coating. Decoating is also useful when a large batch of cutting tools needs to be re-directed for a different application, which requires a new generation of coating. Existing technology uses chemical methods which are not environmentally friendly or ideal for selective removal. In this work, excimer laser striping of TiN from coated tungsten carbide (WC) micro-tools has been demonstrated as a viable alternative to chemical methods. Also, in order to raise the integrity of the decoating process and to make the process more accurate and reliable, two online monitoring systems were developed exploiting probe beam reflection (PBR) and laser plume emission spectroscopy (PES). The online monitoring system facilitated a simultaneous prediction of surface elements as coating layers are progressively removed and ensures better control over the laser irradiation process so as to avoid under or over stripping of the coating.     

The stabilization of monomeric parent compounds of phosphanyl- and arsanylboranes

The structures of the parent compounds of phosphanyl- and arsanylboranes, H(2)BPH(2) and H(2)BAsH(2), were calculated by DFT-B3LYP methods. Such compounds have not previously been obtained preparatively. By applying the concept of Lewis acid/base stabilisation, [(CO)(5)W(H(2)EBH(2).NMe(3))] (E=P (3), As (4)) derivatives have been synthesised by the metathesis reactions between Li[(CO)(5)WEH(2)] and ClH(2)BNMe(3) (E=P, As). Comprehensive thermodynamic studies on these systems verify the high stability of the Lewis acid/base stabilised complexes. Unexpected based on the thermodynamic calculations, UV radiation of the phosphanylborane 3 leads to the dinuclear phosphanido-bridged complex [(CO)(8)W(2)(mu-PHBH(2).NMe(3))(2)] (5) by H(2) and CO elimination.