Department of Mechanical and Aerospace Engineering - PG Seminar - Electron microscopy studies of semi-conducting materials
Probe-corrected transmission electron microscopy and associated techniques is a powerful tool in the characterization of functional materials.
Boron (B) has the potential for generating an intermediate band in cubic silicon carbide (3C-SiC), turning this material into a highly efficient absorber for single-junction solar cells. The formation of a delocalized band demands high concentration of the foreign element, but the precipitation behavior of B in the 3C polymorph of SiC is not well known. Here, probe-corrected scanning transmission electron microscopy (STEM) and secondary-ion mass spectrometry are used to investigate precipitation mechanisms in B-implanted 3C- SiC as a function of temperature. Point-defect clustering was detected after annealing at 1273 K while stacking faults, B-rich precipitates and dislocation networks developed in the 1573 - 1773 K range. The precipitates adopt the rhombohedral B13C2 structure and trap B up to 1773 K. Above this temperature, higher solubility reduces precipitation and free B diffuses out of the implantation layer. Dopant concentrations of 1019 at.cm−3 were achieved at 1873 K.
The concept of maximizing configurational entropy to enhance solid-state miscibility inspires the exploration of unfamiliar composition spaces, and the popular, although imprecise, high-entropy (HE) designation seems destined to endure. The spotlight has been on the mechanical properties of HE alloys, but interest in functional behavior is swiftly rising. In particular, the vast potential of combining metal solid solutions with structural main group elements to form HE semiconductor compounds is becoming evident. The structure of a (Zn,Mn)(Fe,Co,Ni)Sb compound is investigated by powder X-ray diffraction, STEM coupled to atomically resolved energy dispersive spectroscopy (EDS) and by energy-filtered convergent-beam electron diffraction (CBED). Distinction between the 216 (half-Heusler) and 225 (full-Heusler) space groups is hindered by the similar scattering power of the transition metals in XRD. However, the structure could be deciphered by STEM/EDS with the space group further attested by CBED.
Patricia Almeida Carvalho is a senior scientist at the Department of Sustainable Energy Technologies at SINTEF (Oslo, Norway). She was a tenured professor in Materials Science and Engineering at the University of Lisbon for 10 years, including a sabbatical year at the Massachusetts Institute for Technology (2008). She has over 25 years' experience in electron microscopy and moved to Norway in 2014 to develop the research activities of the recently opened Norwegian Center for Transmission Electron Microscopy (NORTEM) and has since been established as one of the country's leading microscopists. She has published more than 200 papers in peer-reviewed journals.