ABSTRACT
In this manuscript, we combine experimental and computational approaches to study the atomic layer deposition (ALD) of dielectrics on MoS2 surfaces for a very common class of ALD precursors, the alkylamines. More specifically, we study the thermal ALD of TiO2 from TDMAT and H2O. Depositions on as-produced chemical vapor deposition MoS2 flakes result in discontinuous films. Surface treatment with mercaptoethanol (ME) does not improve the surface coverage, and DFT calculations show that ME reacts very weakly with the MoS2 surface. However, creation of sulfur vacancies on the MoS2 surface using Ar ion beam irradiation results in much improved surface coverage for films with a nominal thickness of 6 nm, and the calculations show that TDMAT reacts moderately with either single or extended sulfur vacancies. ME also reacts with the vacancies, and defect-rich surfaces treated with ME provide an equally good surface for the nucleation of ALD TiO2 films. The computational studies however reveal that the creation of surface vacancies results in the introduction of gap states that may deteriorate the electronic properties of the stack. Treatment with ME results in the complete removal of the gap states originating from the most commonly found single vacancies and reduces substantially the density of states for double and line vacancies. As a result, we provide a pathway for the deposition of high-quality ALD dielectrics on the MoS2 surfaces, which is required for the successful integration of these 2D materials in functional devices.
ABSTRACT
Recently, 2D tellurene (Te) structures have been experimentally synthesized. These structures possess high carrier mobility and stability which make them ideal candidates for applications in electronics, optoelectronics and energy devices. We performed density functional theory (DFT) and molecular dynamics (MD) simulations to investigate the stability and electronic structure of 2D α- and ß-Te sheets, and hydrogen, oxygen, and fluorine functionalized counterparts, including spin-orbit coupling effects. Our calculations show that bare α and ß-Te sheets are stable with band gaps of 0.44 eV and 1.02 eV respectively. When functionalized, α and ß monolayers exhibit metallic properties, except for hydrogenated ß-Te, which exhibits semiconducting properties with a band gap of 1.37 eV. We see that H, O and F destabilize the structure of α-Te. We also find that F and H cause ß-Te layers to separate into functionalized atomic chains and O causes ß-Te to transform into a Te3O2-like structure. We also studied single atom and molecule binding on the Te surface, the effects of adatom coverage, and the effects of functionalized Te on a GaSe substrate. Our results indicate that tellurene monolayers and functionalized counterparts are not only suitable for future optoelectronic devices, but can be used as metallic contacts in nanoscale junctions.
ABSTRACT
Optical cavities can enhance and control light-matter interactions. This level of control has recently been extended to the nanoscale with single emitter strong coupling even at room temperature using plasmonic nanostructures. However, emitters in static geometries, limit the ability to tune the coupling strength or to couple different emitters to the same cavity. Here, we present tip-enhanced strong coupling (TESC) with a nanocavity formed between a scanning plasmonic antenna tip and the substrate. By reversibly and dynamically addressing single quantum dots, we observe mode splitting up to 160 meV and anticrossing over a detuning range of ~100 meV, and with subnanometer precision over the deep subdiffraction-limited mode volume. Thus, TESC enables previously inaccessible control over emitter-nanocavity coupling and mode volume based on near-field microscopy. This opens pathways to induce, probe, and control single-emitter plasmon hybrid quantum states for applications from optoelectronics to quantum information science at room temperature.
