The purpose with the present investigation has been to support and explain the experimental observation made regarding the enhancing effect by N doping on especially the diamond (100)-2 9 1 growth rate. Within the present study, also the commonly observed diamond (111) and (110) surfaces were included, all assumed to be H-terminated. Density functional theory calculations were used, based on a plane wave approach under periodic boundary conditions. It was shown that the surface H abstraction reaction is most probably the rate-limiting step during diamond growth. In addition, the results showed that it is N, substitutionally positioned within the upper diamond surface, that will cause the growth rate improvement, and not nitrogen chemisorbed onto the growing surface in the form of either NH (or NH 2 ). The here presented numerical value for the growth rate enhancement for the diamond (100)-2 9 1 surface is almost identical with the experimentally obtained one (3.7 vs. 3.6). In addition, the (111) and (110) surfaces were shown to undergo a different growth rate enhancement, with about half as much for the (111) and (110) surfaces as compared to the diamond (100)-2 9 1 surface (1.9, 1.7 vs. 3.7). Despite the rate improvement for all surface planes, this difference will bring about a preferred diamond (100) surface texture.

Thermoelectric materials enable the direct inter-conversion between electrical energy and thermal energy. However, the conversion efficiency is limited by complex interdependent thermoelectric parameters, while the high performance thermoelectrics should simultaneously possess excellent electrical transport properties and poor thermal conductivities. The diamond-like compound Cu 2 SnSe 3 is a promising middle-temperature thermoelectric material. In this work, the phase (Cu 2 Sn 0.93 Ag 0.07 Se 3) with excellent electrical transport properties and the phase (Cu 1.91 Ag 0.09 SnSe 3) with poor thermal conductivities were obtained just through Ag doping on the Sn and Cu sites, respectively. Meanwhile, their Seebeck coefficients were also quite different. To combine their advantages, the composites of Cu 2 Sn 0.93 Ag 0.07 Se 3 and Cu 1.91 Ag 0.09 SnSe 3 were fabricated through mechanical mixing and sintering. Benefited from the same crystal structure and the similar lattice parameters for these two phases, the small-mismatch phase interface is supposed to scatter phonons with little influence to the electrons, especially at high temperature. Therefore, the thermoelectric performance is improved due to the synergistically optimized electrical and thermal transport properties, which are well supported by the effective media theory for the composite.