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Simon Johnsen, Ph.D.

Post Doc, Northwestern University
Kanatzidis Group, Thermoelectrics
Phone: x 7-6335
E-Mail: s-johnsen@northwestern.edu
Office: GG19

Ph.D., Chemistry
University of Aarhus 2008

Research

I am currently investigating the lead sulfide rich part of the PbS-PbTe pseudo-binary phase diagram. Tellurium is extremely scarce in the earth's crust, hence the Te price is likely to sky rocket if Te based thermoelectric materials reach mass market. Cheaper alternatives are therefore needed. PbS could potentially be such an alternative. Due to the nature of the PbS-PbTe pseudo-binary phase diagram, the addition of small quantities of PbTe is likely to make a nanostructured bulk material through spinodal decomposition or nucleation and growth. Concurrently I am involved in a project to develop new wide band gap materials for x-ray and gamma ray detection. The best materials are high density compounds with high atomic number elements to ensure a good absorption. The charge carrier should have a high mobility and lifetime to ensure an efficient read-out. And finally the materials should be high purity semiconductors with band gaps above 1.5 eV to avoid extrinsic and thermally generated dark current.