Gas phase synthesis of anisotropic silicon germanium hybrid nanoparticles

• Novel concept of two stage hot wall reactor setup for synthesizing and modifying aerosols.
• Crystalline patchy and Janus-like particles are accessible and the patches grow epitaxial.
• Patch number and size can be controlled via process parameters.
• Novel concept to continuously synthesize patchy and Janus-like particles with number and size control of patches.

We demonstrate the capability of hot wall reactor gas phase synthesis to produce germanium (Ge) on silicon (Si) anisotropic particles. A two stage reactor setup is used to produce silicon nanoparticles (SiNPs) of 29.6 nm in diameter with a very narrow size distribution and to deposit Ge on them. The gaseous precursors are monosilane (SiH4) and monogermane (GeH4). In a SEM study Ge patch formation on the SiNPs due to Stranski–Krastanov growth is observed. The patch size as well as the number of patches per SiNP is dependent on the process temperature and the GeH4 partial pressure. By varying these parameters it is possible to synthesize Janus-like particles with only one e.g. facetted Ge patch per SiNP, as well as patchy particles carrying an average of four to eight patches. HRTEM analysis shows, that the Ge grows epitaxial and crystalline on the surface of the SiNPs. From geometric phase analysis (GPA) the termination of inserted (220) half planes corresponding to misfit dislocations can be deduced, indicating a largely relaxed lattice in the Ge patches. A continuous tilt of the (111) lattice planes in the Si core below a Ge patch indicates that elastic deformation also contributes to the strain relaxation.

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