Recently, graphene and other layered materials isolated as atomically-thin two-dimensional (2D) flakes, have emerged as an exciting new class of materials for energy applications due to their extraordinary physical, chemical, electrical and optical properties. However, their applicability in energy applications is largely determined by the heterogeneity of the materials inherent in their synthesis and processing. Realizing the bottom-up growth of two-dimensional materials with reliable properties that are comparable to those of exfoliated bulk crystals is currently hampered by a lack of understanding of key synthesis questions, including key aspects of nucleation and growth kinetics, the key “building blocks” for growth, and the factors that control the types of defects, or heterogeneity, of the crystals. Here, we will review approaches to understand and control the synthesis of 2D materials with controllable levels of defects for different energy applications through the development and application of nonequilibrium growth methods, including pulsed-CVD and laser-based techniques, designed to exert control over the synthesis process. To provide rapid assessment of the effects of synthesis on the properties of 2D materials used for solar cells and other optoelectronic energy applications, laser spectroscopy-based characterization methods are correlated with atomic-resolution electron microscopy, associated theory and modeling, and functioning energy devices such as low-frequency Raman spectroscopy, low-temperature photoluminescence, and ultrafast pump-probe spectroscopy techniques are being developed to reveal different aspects relating synthesis and function, such as atomistic stacking configurations between layers, band gap shifts due to doping, the nature of defects, and quasiparticle dynamics. Recent results in engineering the dopants and vacancies in 2D MoSe2 using different growth approaches reveal the importance of defect engineering in controlling optoelectronic properties, and conversely the opportunity for an in situ diagnostic approach employing optical spectroscopy.

Exploring 2D materials synthesis and heterogeneity with nonequilibrium growth techniques and laser spectroscopy

254th National Meeting (2017)

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