Effect of pretreatment bias on the nucleation and growth mechanisms of ultrananocrystalline diamond films via bias-enhanced nucleation and growth: An approach to interfacial chemistry analysis via chemical bonding mapping

[[abstract]]The effect of pretreatment bias on the nucleation and growth mechanisms of the ultrananocrystalline diamond (UNCD) films on the Si substrate via bias-enhanced nucleation and bias-enhanced growth (BEN-BEG) was investigated using cross-sectional high-resolution transmission electron microscopy, chemical bonding mapping, and Raman spectroscopy. The mirror-polished substrate surface showed the formation of a triangular profile produced by a dominant physical sputtering mechanism induced by ion bombardment of ions from the hydrogen plasma accelerated toward the substrate due to biasing and a potential hydrogen-induced chemical reaction component before synthesizing the UNCD films. The BEN-BEG UNCD films grown on the Si substrate with biased and unbiased pretreatments in the hydrogen plasma were compared. In the case of the bias-pretreated substrate, the SiC phases were formed at the peaks of the Si surface triangular profile due to the active unsaturated Si bond and the enhanced local electrical field. The UNCD grains grew preferentially at the peaks of the triangular substrate surface profile and rapidly covered the amorphous carbon (a-C) and oriented graphite phases formed in the valley of the surface profile. In the case of the substrate with unbiased pretreatment, the SiC phases were formed via the reactions between the hydrocarbon species and the active Si atoms released from the substrate with assistance of the hydrogen plasma. The UNCD grains nucleated on the nucleating sites consisting of the SiC, a-C, and graphite phases. Growth mechanisms for the BEN-BEG UNCD films on both Si substrates were proposed to elucidate the different nucleation processes. Applying bias on the Si substrate pretreated in the hydrogen plasma optimized the nucleation sites for growth of UNCD grains, resulting in the low content of the nondiamond phases in UNCD films.[[notice]]補正完畢[[booktype]]紙本[[booktype]]電子版[[countrycodes]]US

Induced Growth of Asymmetric Nanocantilever Arrays on Polar Surfaces

©2003 The American Physical Society. The electronic version of this article is the complete one and can be found online at: http://link.aps.org/doi/10.1103/PhysRevLett.91.185502DOI: 10.1103/PhysRevLett.91.185502We report that the Zn-terminated ZnO (0001) polar surface is chemically active and the oxygenterminated (0001) polar surface is inert in the growth of nanocantilever arrays. Longer and wider "comblike" nanocantilever arrays are grown from the (0001)-Zn surface, which is suggested to be a self-catalyzed process due to the enrichment of Zn at the growth front. The chemically inactive (0001)-O surface typically does not initiate any growth, but controlling experimental conditions could lead to the growth of shorter and narrower nanocantilevers from the intersections between (0001)-O with (0110) surfaces

Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy.

International audienceUnderstanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.% Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope