Accessing the Anisotropic Nonthermal Phonon Populations in Black Phosphorus (original) (raw)

Raman spectroscopy in black phosphorus

Journal of Raman Spectroscopy, 2017

In this article, we review the current status of Raman spectroscopy in orthorhombic black phosphorus (BP) (for simplicity, henceforth, referred to as BP). BP is a layered semiconductor crystal that recently regained interest because it can be exfoliated down to the single layer, thus exhibiting 2-D properties. First, we briefly review the crystalline structure and the phonon dispersion relations in BP. Then, the symmetries of the Raman-active modes are discussed in the light of group theory, and the scattering configurations for observing the different phonon modes are presented. Polarized Raman spectroscopy results are discussed and reveal unusual angular dependence features, which can be ascribed to the linear dichroism and to the complex nature of the electron-phonon matrix elements. Edge phonon effects originated from rearrangements of the atomic terminations are also discussed. Subsequently, Raman modes that emerge from interlayer interaction and that are only visible in the few-layer regime are presented and discussed. Finally, we outline new perspectives to BP Raman spectroscopy in directions that remain partially or totally unexplored and that can provide potentially important outcomes to problems such as defects, oxidation, doping, strain, stacking order and other BP-like 2-D materials.

Theoretical Overview of Black Phosphorus

2D Materials

We review the basic optical, electronic, optoelectronic, thermoelectric and mechanical properties of few-layer black phosphorus (BP), a layered semiconductor that can be exfoliated from bulk BP, the most stable allotrope of phosphorus. The distinguishing trait of BP is its highly anisotropic crystal structure, which leads to strong optical linear dichroism, elliptical plasmonics energy surfaces, anisotropic electronic and thermal conductivities and elasticity. We provide tutorial-like discussion of these phenomena and their theoretical models.

Unusual Angular Dependence of the Raman Response in Black Phosphorus

ACS nano, 2015

Anisotropic materials are characterized by unique optical response which is highly polarization dependent. Of particular interest are layered materials formed by the stacking of two-dimensional (2D) crystals which are naturally anisotropic in the direction perpendicular to the 2D planes. Black phosphorus (BP) is a stack of 2D phosphorene crystals, a highly anisotropic semiconductor with a direct band gap. We show that the angular dependence of polarized Raman spectra of BP is rather unusual, and can be explained only by considering complex values for the Raman tensor elements. This result can be traced back to the electron-photon and electron-phonon interactions in this material.

Remarkable anisotropic phonon response in uniaxially strained few-layer black phosphorus

Nano Research, 2015

Black phosphorus (BP) is a good candidate for studying strain effects on twodimensional (2D) materials beyond graphene and transition-metal dichalcogenides. This is because of its particular ability to sustain high strain and remarkably anisotropic mechanical properties resulting from its unique puckered structure. We here investigate the dependence of lattice vibrational frequencies on crystallographic orientations in uniaxially strained few-layer BP by in-situ strained Raman spectroscopy. The out-of-plane 1 g A mode is sensitive to uniaxial strain along the near-armchair direction whereas the in-plane B 2g and 2 g A modes are sensitive to strain in the near-zigzag direction. For uniaxial strains applied away from these directions, all three phonon modes are linearly redshifted. Our experimental observation is explained by the anisotropic influence of uniaxial tensile strain on structural properties of BP using density functional theory. This study demonstrates the possibility of selective tuning of in-plane and out-of-plane phonon modes in BP by uniaxial strain and makes strain engineering a promising avenue for extensively modulating the optical and mechanical properties of 2D materials.