New insights into thermal processes of metal deposits on h-BN/Rh(1 1 1): A comparison of Au and Rh

In this paper the thermal properties of Au and Rh deposits are compared on hexagonal boron nitride (h-BN) "nanomesh" prepared on Rh(1 1 1), applying STM, XPS, low energy ion scattering (LEIS), LEED, and DFT. At room temperature, both metals essentially follow Volmer-Weber (3D) growth. Upon subsequent annealing, agglomeration (sintering), intercalation, and desorption are competing surface processes for both metals. For the more reactive Rh, we suggest an additional encapsulation mechanism: between 600 K and 750 K, fragments of decomposed h-BN diffuse locally from the bottom onto the metal clusters covering them partially. STM data indicates that agglomeration of gold nanoparticles proceeds faster compared to rhodium. At higher temperatures (∼1050 K–1100 K), all non-desorbing gold atoms diffuse below h-BN, even for large initial coverages. On the other hand, for larger Rh deposits (≥5 ML), the outermost layer always contains Rh. Accumulation of gold at the interface between h-BN and Rh(1 1 1) significantly enhances the thermal stability of h-BN, attributed to the lower reactivity of Au in the decomposition of h-BN compared to Rh(1 1 1). At elevated substrate temperatures, intercalation of individual adatoms takes place during deposition, which requires higher temperatures for rhodium due to its slower diffusion and higher probability of nucleation.