Black phosphorus: ambient degradation and strategies for protection

Abstract

Elemental two-dimensional black phosphorus (BP) is a highly anisotropic versatile material capable of exhibiting wide ranging electronic characteristics ranging from semi-metallic to semiconducting. Its thickness dependent tunable energy gap makes it an exciting prospect for deployment in a variety of applications. The main hurdle limiting diverse applications incorporating BP is its ambient instability. BP degrades rapidly under room conditions, affecting its structure and properties. In this report, we cover the recent progress that has occurred towards protecting BP from ambient degradation. We review the major developments in effectively countering the problem and compare their relative degrees of success. This is provided in the context of the mechanisms governing the atmospheric instability of this material. A targeted focus is kept on the various causes of degradation of BP in atmospheric conditions and the protection strategies that have been implemented so far. IntroductionTwo-dimensional (2D) materials have attracted unprecedented attention over the past decade for their striking properties that are not normally present in their bulk form. Recently, 2D

Optically Stimulated Artificial Synapse Based on Layered Black Phosphorus

“…However, the unusual negative photocurrent observed under longwave UV (365 nm) excitation, in the case of BP is intrinsically material‐related and is associated with the surface adsorbates . It is well known that BP in ambient conditions readily adsorbs oxygen and forms phosphorus oxide species across the crystal surface which can act as charge trap sites . These extrinsic trap sites act as scattering centers under light illumination and reduce the conductance of the device and, hence, are the origin of negative photocurrent.…”

“…As a result, it is expected that exposure to 365 nm will also result in the formation of oxidative species on the surface more readily than any other wavelength. From a practical device perspective, there are simple ways to minimize any further physical damage (i.e., degradation) by sequestering these species using an ionic liquid treatment approach as demonstrated in our previous studies …”

Emerging 2D Materials Produced via Electrochemistry

“…The ambient degradation of phosphorene occurs rapidly within a few hours, once exposed to oxygen, water moisture and visible light . This process modifies the surfaces of phosphorene with oxide groups and therefore largely deteriorates the charge‐transport properties . In 2015, Erande et al carried out the electrochemical exfoliation of bulk BP in an aqueous solution of 0.5 m Na 2 SO 4 .…”

Intrinsic Correlation between Electronic Structure and Degradation: From Few‐Layer to Bulk Black Phosphorus

“…To prevent this rapid degradation, various protection methods such as the introduction of passivation layers and surface modifications with organic compounds have been proposed, but the most important aspect is to understand the mechanisms of the degradation process itself. [14][15][16][17][18] In 2015, Favron and co-workers described the layer-dependent degradation of BP with an oxidation model based on the Marcus-Gerischer theory (MGT) under light illumination. [19] In this study,l ight produces photoexcited electrons in the conduction band (CB) of BP,and these electrons are transferred to the physisorbed oxygen (O 2 )m olecules,l eading to the layer-dependent oxidation of BP.I na ddition, previous experimental and theoretical studies have shown that O 2 and water (H 2 O) molecules have as ynergetic effect on the degradation of BP under light illumination.…”