  Black phosphorous (BP) is one of the most interesting layered materials,
bearing promising potential for emerging electronic and optoelectronic device
technologies. The crystalline structure of BP displays in-plane anisotropy in
addition to the out-of-plane anisotropy characteristic to layered materials.
Therefore, BP supports anisotropic optical and transport responses that can
enable unique device architectures. Its thickness-dependent direct bandgap
varies in the range of around 0.3-2.0 eV (from single-layer to bulk,
respectively), making BP suitable to optoelectronics in a broad spectral range.
With high room-temperature mobility, exceeding 1,000 cm2V-1s-1 in thin films,
BP is also a very promising material for electronics. However, BP is sensitive
to oxygen and humidity due to its three-fold coordinated atoms. The surface
electron lone pairs are reactive and can lead to structural degradation upon
exposure to air, leading to significant device performance degradation in
ambient condition. Here, we report a viable solution to overcome degradation in
few-layer BP by passivating the surface with self-assembled monolayers of
octadecyltrichlorosilane (OTS) that provide long-term stability in ambient
conditions. Importantly, we show that this treatment does not cause any
undesired carrier doping of the bulk channel material, thanks to the emergent
hierarchical interface structure. Our approach is compatible with conventional
electronic materials processing technologies thus providing an immediate route
toward practical applications in BP devices.
