Shaul Aloni, is a staff scientist at the Molecular Foundry at Lawrence Berkeley National Laboratory. His work focuses on synthesis and characterization of 1D and 2D semiconductor nanostructures. He received his PhD at the Weizmann Institute of Science studying photo-carrier induced reactions on semiconducting surfaces. In his subsequent postdoctoral work at the University of California at Berkeley and Lawrence Berkeley National Laboratory, he specialized in synthesis and in-situ characterization of low dimensional materials. Shaul’s current work spans synthetic efforts and the development of novel characterization techniques. He leads efforts to synthesize semiconducting hetero-structures to control charge distribution and flow, for light emitting and light harvesting applications. Moreover, he is developing strategies of synthesis of novel two-dimensional materials with chemical complexity outside of the reach of standard deposition methods. To characterize these structures, he is developing electron-based hyperspectral-imaging techniques based on cathode-luminescence and electron energy loss spectroscopies to locally probe optical, plasmonic and electronic properties with unprecedented resolution.
Molecular Foundry, Lawrence Berkeley National Laboratory
Quantum materials have fascinating properties due to the collective coupling of electrons, phonons, etc. to new quasiparticle states, mediated by a particular potential landscape. Our ability to study and explore these properties depends on our capability to build these materials with high specificity and an exquisite level of control over composition, structure and morphology. Transition metal chalcogenides are a family of layered materials with the potential to satisfy these requirements. So far, however, exploration of layered materials is limited to exfoliation of bulk, often MBE grown, crystals or study of small crystalline domains deposited by chemical vapor deposition methods. In my talk, I will describe recent developments in synthesis and characterization of TMDs at the Molecular Foundry. I'll focus mainly on a new synthetic approach for TMD's growth that utilizes chemical transformation of solid thin films of transition metal oxides deposited with sub-monolayer precision by ALD. Following their deposition, the films are exposed to a chalcogen containing gas resulting in smooth and continuous TMD films whose properties are defined by the thickness and composition of the ALD deposited oxide film. This method is highly scalable, reproducible, compatible with many transition metals, and is feasible on any substrate that is not adversely affected by the chalcogenation agent. The flexibility of ALD film deposition and the chemical conversion process parameters offers unique control over the morphology, structure and composition of the resulting TMD film while posing a challenge for optimization of its properties. I'll discuss the various tools to characterize inhomogeneity in the properties of these materials, and how these characterization methods help to inform refinement of synthetic procedures. This approach, utilizing near-molecular precision synthesis and high-resolution characterization, opens the possibility to fabricate 2D materials with unprecedented lateral heterogeneity.