Controlling the interface composition of core-shell and axial heterojunction nanowires

Composition profile across an interface in a core/shell or axial heterojunction nanowire often plays an important role in dictating its electronic, optical and magnetic properties. The control of composition profiles to achieve optimal performance still remains a challenge. In the present work, we formulate a theoretical model which accounts for three key factors that completely control the interface composition profile: the deposition flux of individual components, the atomic exchange rate between the surface and its sub-surface layer, and the thermodynamic driving force for surface segregation. We validate the model by matching its predictions with the experimental results for thin film growth. We then apply the model to the growth of core/shell and axial heterojunction nanowires and show that both abrupt and diffuse interface composition profiles can be achieved by tuning the growth parameters, providing a predictive approach for controlling interface composition distribution. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4752251]