| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Nanomaterials | Tuesday Sessions |
| Session NM-TuM |
| Session: | Nanofabrication and Nanodevices I |
| Presenter: | Christoph Kastl, Lawrence Berkeley National Laboratory, USA |
| Authors: | C. Kastl, Lawrence Berkeley National Laboratory, USA C.T. Chen, Lawrence Berkeley National Laboratory, USA B. Shevitski, University of California, Berkeley, USA T.R. Kuykendall, Lawrence Berkeley National Laboratory, USA S. Aloni, Lawrence Berkeley National Laboratory, USA A.M. Schwartzberg, Lawrence Berkeley National Laboratory, USA |
| Correspondent: | Click to Email |
Interest in layered transition metal dichalcogenides (TMDs) has been renewed since the discovery of emergent properties when reduced to single two-dimensional layers. The current state-of-the-art fabrication of heterostructures involves exfoliation from bulk crystals and subsequent manual stacking of the atomic layers. The lack of reproducible and large scale synthetic methods for high quality, consistent TMD samples has become a major bottleneck to research on and application of these materials.
The following two-step process involving atomic layer deposition (ALD) and chalcogenization can be used as a scalable and highly versatile method for TMD synthesis. First, high quality transition metal oxide films are deposited by ALD. Second, the transition metal oxide films are converted into layered TMDs by chemical chalcogenization, i.e. annealing under H2S atmosphere in a high temperature furnace. [1] We leverage the particular advantages of ALD to further develop this approach into a fabrication process for encased nanodevices and heterostructures. Planar films of MoO3 and/or WO3 are deposited on the growth substrate, and SiO2 is used as an inert capping layer. Then, device structures are defined by photolithography and reactive ion etching. In the subsequent conversion step, the nucleation starts at the exposed cross sections of the heterostructure, and the TMD growth proceeds laterally from the nucleation site. Cross-sectional TEM reveals that this lateral growth mode forms highly crystalline MoS2 (WS2) layers which are aligned parallel to the substrate. We characterize the optical and electronic properties of the encased heterostructures by photoluminescence spectroscopy, ultrafast transient absorption spectroscopy, and field effect measurements. Furthermore, controlling the extent of the lateral growth via annealing time and temperature, we show that encased TMD nanoribbons can be fabricated with lateral dimension down to ∼10 nm.
[1] C. Kastl et al., The Important Role of Water in Growth of Monolayer Transition Metal Dichalcogenides, under review (2016).