A tunable band gap in phosphorene extends its applicability in nanoelectronic and optoelectronic applications. Here, we propose to tune the band gap in phosphorene by patterning antidot lattices, which are periodic arrays of holes or nanopores etched in the material, and by exploiting quantum confinement in the corresponding nanoconstrictions. We fabricated antidot lattices with radii down to 13 nm in few-layer black phosphorus flakes protected by an oxide layer and observed suppression of the in-plane phonon modes relative to the unmodified material via Raman spectroscopy. In contrast to graphene antidots, the Raman peak positions in few-layer BP antidots are unchanged, in agreement with predicted power spectra. We also use DFT calculations to predict the electronic properties of phosphorene antidot lattices and observe a band gap scaling consistent with quantum confinement effects. Deviations are attributed primarily to self-passivating edge morphologies, where each phosphorus atom has the same number of bonds per atom as the pristine material so that no dopants can saturate dangling bonds. Quantum confinement is stronger for the zigzag edge nanoconstrictions between the holes as compared to those with armchair edges, resulting in a roughly bimodal band gap distribution. Interestingly, in two of the antidot structures an unreported self-passivating reconstruction of the zigzag edge endows the systems with a metallic component. The experimental demonstration of antidots and the theoretical results provide motivation to further scale down nanofabrication of antidots in the few-nanometer size regime, where quantum confinement is particularly important.

The adsorption of iodine atoms and molecules on graphene is studied in detail, using first-principles calculations that include non-local correlation effects by means of van der Waals density functional approach. Structural, energetic and electronic structure properties of these systems are reported. We demonstrate that graphene surface can be doped by atomic and molecular iodine. An upward shift of the Dirac point from the Fermi Level, with values of 0.45 eV and 0.08 eV are observed, for adsorbed atoms and adsorbed I 2 respectively. It corresponds to graphene hole densities to be around 1.2 × 10 13 cm −2 to 3.9 × 10 11 cm −2. We also show that the iodine molecule does not dissociate in contact with pure graphene monolayer. Calculation of the surface free energy reveals that the orientation of the adsorbed iodine molecules crucially depends on its concentration and the system temperature.

We report a temperature-dependent Raman spectroscopy study of few-layer black phosphorus (BP) with varied incident polarization and sample thickness. The Raman-active modes Ag 1, B2g, and Ag 2 exhibit a frequency downshift, while their line width tends to increase with increasing temperature. To understand the details of these phenomena, we perform first-principles density functional theory calculations on freestanding monolayer BP. The effect of thermal expansion is included by constraining the temperature-dependent lattice constant. The study of the temperature-induced shift of the phonon frequencies is carried out using ab initio molecular dynamics simulations. The normal-mode frequencies are calculated by identifying the peak positions from the magnitude of the Fourier transform of the total velocity autocorrelation. Anharmonicity induces a frequency shift for each individual mode, and the three- and four-phonon process coefficients are extracted. These results are compared with those obtained from many-body perturbation theory, giving access to phonon lifetimes and lattice thermal conductivity. We establish that the frequency downshift is primarily due to phonon–phonon scattering while thermal expansion only contributes indirectly by renormalizing the phonon–phonon scattering. Overall, the theoretical results are in excellent agreement with experiment, thus showing that controlling phonon scattering in BP could result in better thermoelectric devices or transistors that dissipate heat more effectively when confined to the nanoscale.