It is well known that the variation of slurry pH could significantly affect the chemical-mechanical polishing ͑CMP͒ process. In this study, a particle-scale mechanical model for surface removal rate that includes the double layer ͑dl͒ forces of abrasives and wafer surface is developed. It is shown that the van der Waals force and the electrical dl attraction and repulsion play a major role in CMP processes. Furthermore, the magnitudes and signs of the zeta potential of the surface and the abrasives significantly affect the removal rates. The results show that the removal rate increases sharply for the cases that the zeta potentials of the surface and abrasive have opposite sign. On the other hand the removal rate decreases when the zeta potentials have the same sign. The removal rates for polishing of tantalum with silica and alumina abrasives are compared with the available data and qualitative agreements are observed.
Two-dimensional (2D)
boron sheets (borophenes) are promising materials
for the next generation of electronic devices because of their metallic
conductivity. Molecular beam epitaxy has remained the main approach
for the growth of borophene, which considerably restricts large-scale
production of 2D boron sheets. The high melting point of boron and
the growth of borophenes at moderate temperatures posed a significant
challenge for the synthesis of borophenes. Employing diborane (B2H6) pyrolysis as a pure boron source, we report,
for the first time, the growth of atomic-thickness borophene sheets
by chemical vapor deposition (CVD). A methodical study on the effect
of temperature, deposition rate, and pressure on the growth of 2D
boron sheets is provided and detailed analyses about the morphology
and crystalline phase of borophene sheets are presented. The CVD-borophene
layers display an average thickness of 4.2 Å, χ3 crystalline structure, and metallic conductivity. We also present
experimental evidence supporting the formation of stacked bilayer
and trilayer borophene sheets. Our method paves the way for empirical
investigations on borophenes.
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