In-situ Observations of Hexagonal Boron Nitride Growth on Cu (110)

Synopsis

Hexagonal boron nitride (h-BN) was grown on single crystalline Cu (110) inside a LEEM. The crystals were prepared ex situ via mechanical and electro-chemical polishing and exposed to borazine gas at temperatures of 600-750°C and pressures of 0.5-10 x 10^-7 Torr. Nucleation of well-aligned trigonal h-BN islands was observed when the crystal showed a particular hydrogen-induced surface reconstruction. These islands merged to ribbons along surface steps, and into larger, more irregularly shaped features. A ring in the low energy electron diffraction (LEED) pattern was observed with a preferential orientation aligned along Cu <11> directions of the underlying substrate.  

A second Cu (110) single crystal was prepared via multiple sputter-anneal cycles using argon and hydrogen ions resulting in an unreconstructed surface. Exposing this single crystal to borazine also resulted in trigonal h-BN islands, yet these islands did not merge nor appear to align with surface steps. Nucleation was determined by defects and decreased with increasing temperature. LEED patterns revealed two preferential orientations, each aligned with Cu <11> directions. Growth dynamic plots suggested a modification to the growth model for self-limited monolayer growth, as islands did not merge. Extracted growth rates did not depend on the substrate temperature in the range tested, but increased with pressure. On the other hand, the maximum coverage increased with temperature, but did not depend on pressure.  

Annealing this second Cu (110) single crystal in H₂ atmosphere resulted in a weak (2x1) reconstruction. These surfaces had a lower defect density, and borazine exposure at 700-750°C resulted in larger h-BN islands, revealing preferred dendritic growth along the Cu <01> and <10> directions. This resulted in T-shaped islands early on in the exposure, which later filled out into triangular shapes, indicating a strong influence of the substrate. Dark-field LEEM revealed that neighboring islands did not merge, regardless of whether they had the same orientation or not.