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| Author(s): |
Gabriel Pereira Freitas
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2018-09-13 |
| Examining board members: |
Tulio Costa Rizuti da Rocha;
Jonder Morais;
Cris Adriano
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| Advisor: | Tulio Costa Rizuti da Rocha; Abner de Siervo |
| Abstract | |
Black Phosphorus (BP) is a semiconductor with a stacked layers structure, wherein each monolayer is denominated Phosphorene. Unlike graphene, BP presents a thickness-tunable direct band gap in the visible range. The two distinct in-plane directions of the van-der-Waals surface yields intrinsic anisotropic carrier mobility. As a complementary 2D material, BP is relevant for applications in high-frequency electronics. However, BP is unstable at ambient conditions, oxidizing and suffering complete degradation. Oxygen, water and light play important roles on the oxidation process, although the mechanism itself is yet to be fully understood. In this work we used synchrotron based ambient-pressure x-ray photoemission spectroscopy (AP-XPS) to study the BP oxidation under a controlled environment. Using the stoichiometry and binding energies, assisted by DFT calculations, we investigate the atomic and electronic structures of the phosphorene oxide (PO) and BP heterostructure. When solely exposing BP to oxygen-free water, we observed no oxidation. On the other hand, when exposing to dry oxygen, a layer of PO grew to a thickness of 1.35 nm after 2.5 hours. Furthermore, no oxidation takes place after this passivation layer has been established. Using stoichiometry ratios determined from AP-XPS, we propose an unprecedented atomic structure for this oxide, the P4O8 that agrees well with DFT calculations. Remarkably, depth dependent APXPS measurements showed shifts in the core and valence level binding energies of the order of 0.2 eV at the interface that decreases for deeper layers. These shifts suggest that a charge transfer occurs at the interface. In summary, our results indicate the growth of a passivating insulator layer of PO, that modifies the electronic structure of the underlying phosphorene layers. These discoveries can assist further research of BP-based devices by controlling the oxide growth and give insights for future investigations of the surface chemistry (AU) | |
| FAPESP's process: | 16/06798-2 - Interaction of gases with black phosphorus |
| Grantee: | Gabriel Pereira Freitas |
| Support Opportunities: | Scholarships in Brazil - Master |