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Silicene, the silicon counterpart of graphene, has been successfully grown on metallic substrates such as Ag(111), ZrB2(0001), and Ir(111) surfaces. However, characterization of its electronic structure is hampered by the metallic substrate. In addition, potential applications of silicene in nanoelectronic devices will require its growth on or integration with semiconducting and insulating substrates. We herein present a review of recent theoretical works regarding the interaction of silicene with non-metallic templates, distinguishing between the weak van-der-Waals-like interactions of silicene with, for example, layered metal (di)chalcogenides, and the stronger covalent bonding between silicene and, for example, ZnS surfaces. We then present a methodology to effectively compare the stability of diverse silicene structures using thermodynamics and molecular dynamics density functional theory calculations. Recent experimental results on the growth of silicene on MoS2are also reported and compared to the theoretical predictions.[Figure not available: see fulltext.]

Understanding the energy alignment of electronic bands, which originate from ultrathin MoS2 layers and metal electrodes attached to them, is crucial for the design of MoS2-based electronic devices. We have applied internal photoemission spectroscopy (IPE) to analyze this alignment. We demonstrate that IPE can yield the barrier heights in the metal/ two-dimensional semiconductor/insulator stacks when the top metal electrode is sufficiently thin for allowing both the photoexcitation of electrons and their transport towards the insulator. The electron barrier at the interface between Al and monolayer (1ML) of MoS2 is estimated at 0.7 eV, and this value explains the experimentally observed attenuated quantum yield contribution from the aluminum. Based on the relative energies of the low-energy threshold position and the Fermi level of aluminum at the interface with the SiO2 insulator, we provide a simple explanation for the observed current photoinjection at the interface between aluminum and 1ML MoS2.

integration requires development of low thermal budget process modules. High-quality SiO 2 interfacial layer (IL), obtained up to now only by high-temperature (≥850°C) oxidation or exposure, is crucial for pMOS NBTI reliability. In unannealed IL’s grown at reduced temperatures, we show that unrelaxed interface strain induces high defect densities, with physics-based NBTI modeling suggesting excessive hydroxyl-E’ defect formation due to Si-O bond stretch. Based on ab-initio theoretical insights, we demonstrate an atomic hydrogen treatment to passivate SiO 2 defects at low temperatures (100-300°C), which is shown to be vastly more effective than high pressure molecular hydrogen exposure, and to yield an SiO 2 quality and reliability surpassing a 900°C oxide.

We present fundamental exploration of inorganic dielectric wafer-to-wafer (W2W) bonding by electron spin resonance (ESR) to assess the function of dangling bond-type interface defects. As compared to a standard PECVD SiO2 which contains negligible dangling bonds (DBs), it is found that a substantial amount of silicon and carbon types of DBs, as high as 1014 cm-2, are present in the pre-bonding layer of SiCN and SiCO, mainly as a result of surface modification by means of low energy plasma activation prior to bonding. It is inferred that the evolution of DBs has a positive influence on improving the wafer bonding energy during post-bond anneal, in that the results suggest that a decrease of DBs translates into the formation of chemical bonds at the bonding interface.

The article overviews experimental results obtained by applying internal photoemission (IPE) spectroscopy methods to characterize electron states in single- or few-monolayer thick two-dimensional materials and at their interfaces. Several conducting (graphene) and semiconducting (transitional metal dichalcogenides MoS2, WS2, MoSe2, and WSe2) films on top of thermal SiO2 have been analyzed by IPE, which reveals significant sensitivity of interface band offsets and barriers to the details of the material and interface fabrication, indicating violation of the Schottky-Mott rule. This variability is associated with charges and dipoles formed at the interfaces with van der Waals bonding as opposed to the chemically bonded interfaces of three-dimensional semiconductors and metals. Chemical modification of the underlying SiO2 surface is shown to be a significant factor, affecting interface barriers due to violation of the interface electroneutrality. ispartof: JOURNAL OF PHYSICS-CONDENSED MATTER vol:32 issue:41 ispartof: location:England status: published

Identification of two-dimensional (2D) materials with magnetic properties has received strong research attention in the development of advanced spin-based devices. By means of first-principles calculations, we investigate the stability, electronic properties, and the hole-doping-induced magnetic properties of metal oxide ($M\mathrm{O}, M=\mathrm{Ga},\mathrm{In}$) monolayers. They are intrinsically nonmagnetic stable semiconductors, with high energetic, vibrational, and thermal stability. Hole doping can switch them from nonmagnetic to ferromagnetic and turn them into half-metals over a wide range of hole densities. Monte Carlo simulations predict that the highest Curie temperature of the GaO monolayer can reach \ensuremath{\sim}125 K. Our results indicate that monolayer $M\mathrm{O}$ could be eligible candidate materials for 2D spintronic devices.

Exfoliated flakes from molybdenite crystals often still serve as benchmark substrates for two-dimensional MoS

Exfoliated flakes from molybdenite crystals often still serve as benchmark substrates for two-dimensional MoS2 fundamental and device-oriented research. In this article, results are reported of a multi-frequency electron paramagnetic resonance (EPR) study on a series of natural 2H MoS2 crystals taken from various (seven) geological sites with the intent to explore the variations in quality and properties in terms of occurring paramagnetic point defects, with particular focus on the assessment of the predominant type of impurity dopant. The sample set covers three types of overall doping regimes, i.e., p-type, n-type, and mixed (n-type and p-type parts in one sample). The doping type appears primarily governed by substitutional impurities as evidenced by the observed As and N acceptor (both substituting for S) and Re donor (substituting for Mo) signals. For all p-type specimens, doping is found to be ruled by As where, however, a strong variation is revealed in doping uniformity, which appears not directly correlated with the As dopant density. Without specific precautions taken, surface contamination related EPR signals are observed in virtually all As-excavated geo-MoS2 specimens. While several of these signals are of unassigned origin, two prominent ones are identified, one as concerning oxo-Mo5+ compounds and the other Mn2+ centers. The geo-MoS2 sample with the foremost n-type doping shows, besides the prime Re donor EPR signal, an intense powder-pattern signal, tentatively typified by g∥ = 2.076, g⊥ = 2.253, which is suggested to originate from intercalation-related defects. The results bear out the necessity of rigorous surface cleaning, even including invasive removal of surface layers, to obtain pristine MoS2 parent crystals suitable for enabling exfoliation of high quality flakes. ispartof: JOURNAL OF CHEMICAL PHYSICS vol:152 issue:23 ispartof: location:United States status: published

Hole-doping of GaX, InX (X = S or Se) and SnO monolayers is predicted to induce a stable ferromagnetic order in these two-dimensional materials, making them potentially interesting for nanoscaled spintronic devices. Ferromagnetism in these materials arises from their peculiar Mexican-hat valence band edge structure, which leads to a Stoner instability. We discuss here the results from first-principles simulations on the p-type doping-induced ferromagnetism in these 2D materials. Hole-doping, induced by intrinsic and extrinsic point defects, is considered. Metal vacancies are found to produce shallow spin-polarized gap states near the valence band edge, leading to a p-type behavior. Among the investigated potential extrinsic defects (dopants), As substitution of the oxygen atoms in SnO or Bi substitution of the selenium atoms in InSe appears to be good candidates for the hole-doping of these 2D materials.

The high contact resistance at metal/two-dimensional (2D) semiconductor junctions is a major issue for the integration of 2D materials in nanoelectronic devices. We review here recent theoretical results on the contact resistance at lateral heterojunctions between graphene or 1T-MoS2 with 2H-MoS2 monolayers. The transport properties at these junctions are computed using density functional theory and the non-equilibrium Green’s function method. The contact resistance is found to strongly depend on the edge contact symmetry/termination at graphene/2H-MoS2 contacts, varying between about 2 × 102 and 2 × 104 Ω∙μm. This large variation is correlated to the presence or absence of dangling bond defects and/or polar bonds at the interface. On the other hand, the large computed contact resistance at pristine 1T/2H-MoS2 junctions, in the range of 3–4 × 104 Ω.μm, is related to the large electron energy barrier (about 0.8 eV) at the interface. The functionalization of the metallic 1T-MoS2 contact by various adsorbates is predicted to decrease the contact resistance by about two orders of magnitude, being very promising for device applications.

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. Dangling bond defects (DBs) in silicon-passivated (1- or 3-nm thick Si cap) strained-(100)Si 1−x Ge x (x = 0.25–0.55) layers at interfaces with 1.8-nm thick HfO 2 gate dielectric are studied by means of Electron Spin Resonance (ESR) spectroscopy. The results suggest a dominant contribution of Si DBs (P b0 centers), a considerable fraction of which is located at the interface between the Si substrate crystal and the pseudomorphic Si 1−x Ge x film. The density of Si DBs in the Ge containing samples is significantly lower than at the reference (100)Si/ HfO 2 interface and decreases below the ESR detection limit (≈ 0.8 × 10 11 cm −2 ) with increasing thickness and Ge concentration in the Si 1−x Ge x layer. However, the beneficial effect of Ge becomes less pronounced when the thickness of the Si cap is reduced to 1 nm or in the case of direct deposition of HfO 2 on top of uncapped Si 1−x Ge x . From these observations we conclude that DBs are eliminated due to in-diffusion of Ge from the Si 1−x Ge x channel into interfacial Si layers, bringing the concentration of Ge to the range in which generation of Si DBs becomes energetically unfavourable, in agreement with previous observations on condensation-grown Si 1−x Ge x layers. ispartof: JOURNAL OF MATERIALS SCIENCE-MATERIALS IN ELECTRONICS vol:31 issue:1 ispartof: location:FRANCE, Strasbourg status: Published online

The contact resistance at metal/two-dimensional (2D) semiconductor heterojunctions is currently a major issue for the integration of 2D materials in new generations of nanoelectronic devices. In this chapter, the contact resistance at graphene/MoS2 and 1T/2H-MoS2 heterostructures is computed using first-principles simulations, based on density-functional theory and the nonequilibrium Green's function method. The contact resistance, RcW, is found to strongly depend on the edge contact symmetry/termination at graphene/MoS2 contacts, varying between about 2 × 102 and 2 × 104 Ω μm. This large variation in RcW is correlated to the presence or absence of dangling bond defects and/or polar bonds at the interface. On the other hand, the large computed contact resistance at pristine 1T/2H-MoS2 contacts, in the range of 3–4 × 104 Ω μm, is related to the large electron energy barrier (about 0.8 eV) at the interface. The functionalization of the metallic 1T-MoS2 contact by various adsorbates is predicted to decrease the contact resistance by about two orders of magnitude, being promising for device applications.

In this article, heat-activated persulfate oxidation was investigated as a promising technique for the removal of sulfamethoxazole from an aqueous environment. It was found that the degradation efficiency of sulfamethoxazole increases with increasing persulfate concentration due to the increased •SO4- production. As suggested by the Arrhenius equation, the sulfamethoxazole degradation rate constant increased with increasing temperature. An activation energy of 103 kJ/mol was determined. Furthermore, the initial pH of the reaction mixture had a large influence on the degradation of sulfamethoxazole. At higher initial pH values, the degradation of sulfamethoxazole increased. The main cause for this increase is a difference in sulfamethoxazole distribution: at higher pH, the deprotonated form of sulfamethoxazole is present and found to be more susceptible to degradation. A second reason was found to be the formation of •OH at higher initial pH values, although this contribution was smaller. To elucidate the degradation process, six intermediates were identified, and the difference in formation of these compounds at different initial pH values was revealed. Through ECOSAR modeling, some degradation products were found to be of main interest when monitoring the toxicity of the degradation mixture. ispartof: Chemical Engineering Journal vol:379 status: Published online

Using first-principles calculations based on density functional theory, we study the magnetic and electronic properties of hole-doped two-dimensional InSe. Our simulations reveal that although 2D InSe is intrinsically nonmagnetic, a stable ferromagnetic phase appears for a wide range of hole densities. Interestingly, hole doping induces not only spontaneous magnetization but also half-metallicity, and hole-doped InSe, presenting one conducting and one insulating spin channel, could be highly promising for next generation spintronic nanodevices. The possibility of inducing hole doping and a subsequent ferromagnetic order by intrinsic and extrinsic defects was also investigated. We found that In vacancy creates spin-polarized states close to the valence band and leads to a p-type behavior. Similar to In vacancies, group-V atoms replacing Se atoms lead to a p-type behavior, potentially stabilizing a ferromagnetic order in 2D InSe.