Site-Controlled Quantum Emitters in Monolayer MoSe.

Atomically thin semiconductors provide a highly attractive platform for quantum emitters (QEs): They can be combined with arbitrary substrates, can be spatially aligned with photonic structures, and can be electrically driven. All QEs reported to date in these materials have, however, relied on nominally spin-forbidden transitions, with radiative rates falling substantially below those of other solid-state QE systems. Here we employ strain confinement in monolayer MoSe to produce engineered QEs, as confirmed in photon antibunching measurements.

Experimental observation of a negative grey trion in an electron-rich WSe monolayer.

We measure the evolution of low temperature photoluminescence in a WSe monolayer with increasing electron concentration level. By comparing non-resonant and resonant laser excitation, we find that the formation of negative trions is facilitated by very efficient phonon emission. The most prominent line in photolumienscence spectra in the intermediate range of carrier concentrations (below [Formula: see text] cm) is found to be 66 meV below the bright negative trion.

Absolute Scale Quantitative Off-Axis Electron Holography at Atomic Resolution.

An absolute scale match between experiment and simulation in atomic-resolution off-axis electron holography is demonstrated, with unknown experimental parameters determined directly from the recorded electron wave function using an automated numerical algorithm. We show that the local thickness and tilt of a pristine thin WSe_{2} flake can be measured uniquely, whereas some electron optical aberrations cannot be determined unambiguously for a periodic object. The ability to determine local specimen and imaging parameters directly from electron wave functions is of great importance for quantitative studies of electrostatic potentials in nanoscale materials, in particular when performing in situ experiments and considering that aberrations change over time.

Quantitative measurement of mean inner potential and specimen thickness from high-resolution off-axis electron holograms of ultra-thin layered WSe.

The phase and amplitude of the electron wavefunction that has passed through ultra-thin flakes of WSe is measured from high-resolution off-axis electron holograms. Both the experimental measurements and corresponding computer simulations are used to show that, as a result of dynamical diffraction, the spatially averaged phase does not increase linearly with specimen thickness close to an [001] zone axis orientation even when the specimen has a thickness of only a few layers. It is then not possible to infer the local specimen thickness of the WSe from either the phase or the amplitude alone.