UBC Theses and Dissertations
Controllable and scalable thermal sublimation thinning of black phosphorus Luo, Weijun
Two-dimensional lamellar black phosphorus (BP) has emerged as a promising semiconductor for next generation integrated circuits (IC) and photonics, especially in flexible and ultra-thin electronic and photonic devices. With layer numbers of > 20 to 1, the electronic energy band gap of BP covers the range from 0.3 (bulk) to 2 eV (single-layer), which can fill the gap between graphene and transition metal di-chalcogenides (TMDCS). It is necessary to prepare uniform, large scale and crystalline few-layer BP for industry applications. We investigated thinning rates of BP at different temperatures so that the users can control the time of heating and have the ability to monitor the thickness of BP during heating processes. Identification of crystallographic orientation (CO) of BP by Raman Spectroscopy is applied, which enables the Raman intensity ratios between BP and substrates to be only thickness-dependent. This ratio can be used as a non-contact optical method to determine the actual thickness of BP during preparation, which is crucial to determine the end point of the thinning process. In this thesis work, we first reported the layer-by-layer sublimation of BP below 600 K, which was observed by optical color changes; secondly, we investigated the thinning rates of BP at 500 K and 550 K to be 0.2 nm / min 500 K and 1.5 nm / min at 550 K; thirdly, we investigated the effective determination of CO of BP and underlying Si by polarized Raman Spectroscopy with excitation wavelength of 441.6 nm; fourthly, we investigated the thickness-dependent Raman peak intensity ratio Si / A2g at a fixed CO, which can be used as an indicator of the thickness of BP; lastly, we presented the successful and repeatable preparation of large crystalline 2 to 4 -layer BP. This work is the first study available to use the sublimation thinning as a controllable method to prepare large, uniform and crystalline BP down to 2-4 atomic layers. This work is the first study available on developing an all-Raman method in identifying the CO of BP, determining the in-situ and ex-situ thickness and confirming the crystallinity and uniformity of prepared BP.
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