Layered black phosphorus has drawn much attention due to the existence of a band gap compared to the widely known graphene. However, environmental stability of black phosphorus is still a major issue, which hinders the realization of practical device applications. Here, we spatially Raman map exfoliated black phosphorus using confocal fast-scanning technique at different time intervals. We observe a Raman intensity modulation for , B2g, and modes. This Raman modulation is found to be caused by optical interference, which gives insights into the oxidation mechanism. Finally, we examine the fabrication compatible PMMA coating as a viable passivation layer. Our measurements indicate that PMMA passivated black phosphorus thin film flakes can stay pristine for a period of 19 days when left in a dark environment, allowing sufficient time for further nanofabrication processing. Our results shed light on black phosphorus degradation which can aid future passivation methods.

Transition metal dichalcogenide two-dimensional materials have attracted significant attention due to their unique optical, mechanical, and electronic properties. For example, molybdenum disulfide (MoS) exhibits a tunable band gap that strongly depends on the numbers of layers, which makes it an attractive material for optoelectronic applications. In addition, recent reports have shown that laser thinning can be used to engineer an MoS monolayer with specific shapes and dimensions. Here, we study laser-thinned MoS in both ambient and vacuum conditions via confocal μ-Raman spectroscopy, imaging X-ray photoelectron spectroscopy (i-XPS), and atomic force microscopy (AFM). For low laser powers in ambient environments, there is insufficient energy to oxidize MoS, which leads to etching and redeposition of amorphous MoS on the nanosheet as confirmed by AFM. At high powers in ambient, the laser energy and oxygen environment enable both MoS nanoparticle formation and nanosheet oxidation as revealed in AFM and i-XPS. At comparable laser power densities in vacuum, MoS oxidation is suppressed and the particle density is reduced as compared to ambient. The extent of nanoparticle formation and nanosheet oxidation in each of these regimes is found to be dependent on the number of layers and laser treatment time. Our results can shed some light on the underlying mechanism of which atomically thin MoS nanosheets exhibit under high incident laser power for future optoelectronic applications.

Newly explored two-dimensional (2D) materials have shown promising optical properties, owning to the tunable band gap of the layered material with its thickness. A widely used method to achieve tunable light emission (or photoluminescence) is through thickness modulation, but this can only cover specific wavelengths. This approach limits the development of tunable optical devices with high spectral resolution over a wide range of wavelengths. Here, we report wideband tunable light emission of exfoliated black phosphorus nanosheets via a pulsed thermal annealing process in ambient conditions. Tunable anisotropic emission was observed between wavelengths of 590 and 720 nm with a spectral resolution of 5 nm. This emission can be maintained for at least 11 days when proper passivation coupled with adequate storage is applied. Using hyperspectral imaging X-ray photoelectron spectroscopy (i-XPS), this tunable emission is found to be strongly dependent on the level of oxidation. We finally discuss the underlying mechanism responsible for the observed tunable emission and show that tunable emission is only observed in nanosheets with thicknesses of (70–125 nm) ± 10 nm with the maximum range achieved for nanosheets with thicknesses of 125 ± 10 nm. Our results shed some light on an emerging class of 2D oxides with potential in optoelectronic applications.

During the past few years, scientists have shown that climate change is a serious problem that mandates adequate solutions. Greenhouse gas emissions such as carbon dioxide contribute to heat trapping in the atmosphere, which increases the global temperature. Reducing greenhouse gas emissions and the carbon footprint to zero is an essential step toward maintaining a 2°C temperature change. In doing so, researchers and scientists have focused much attention on finding alternative technologies that provide clean and sustainable energy. In particular, nanotechnology can offer this alternative solution to the ongoing energy crisis. The recent progress in nanomaterial research has focused on the development of high-efficiency optoelectronics, batteries, low-power electronics, and thermoelectric devices for energy generation applications. With the emergence of new nanomaterials, such as carbonaceous materials and transition metal dichalcogenides, new physics have emerged. Scientists and engineers are still eager to answer some of the fundamental issues concerning these nanomaterials, including optical, electrical, and thermal properties. Yet, to this day, nanotechnology solutions to provide a sustainable energy are hinged by the ability to control and fully understand the properties of these nanomaterials. Here, we highlight some of the recent progress carried out in nano-optoelectronics, and share our thoughts on the opportunities and challenges facing low-dimensional devices to generate clean and sustainable energy.

This work is concerned the with analysis of the convergence of guided waves in pipes to Lamb waves in plates for isotropic materials. The main goal is to be able to define a threshold frequency above which it is reasonable to approximate waves propagating in a pipe with a certain wall thickness to radius ratio as Lamb waves. The study involves a detailed comparison of velocity differences for symmetric and antisymmetric waves in plates versus longitudinal and flexural modes in pipes. Phase and group velocities of pipes with various wall thickness-to-radius ratios are compared to a plate of corresponding thickness. An empirical convergence criterion is defined to determine the frequency above which a pipe will have a plate-like response. It is shown that “convergence” may already be reached at frequencies commonly used for nondestructive testing purposes. Analytical considerations are supported and validated by experimental results, showing good agreement of predicted and measured wave velocities.