Electrical control of interlayer exciton dynamics in atomically thin heterostructures

A van der Waals heterostructure built from atomically thin semiconducting transition metal dichalcogenides (TMDs) enables the formation of excitons from electrons and holes in distinct layers, producing interlayer excitons with large binding energy and a long lifetime. By employing heterostructures of monolayer TMDs, we realize optical and electrical generation of long-lived neutral and charged interlayer excitons. We demonstrate that neutral interlayer excitons can propagate across the entire sample and that their propagation can be controlled by excitation power and gate electrodes. We also use devices with ohmic contacts to facilitate the drift motion of charged interlayer excitons. The electrical generation and control of excitons provide a route for achieving quantum manipulation of bosonic composite particles with complete electrical tunability.

Study on the Effect of ZnO Buffer Layer Thickness on the Properties of MgZnO Film

ZnO has recently attracted considerable attention due to its favorable properties such as the wider band gap (3.37eV) at room temperature, the large binding energy of excitons (60meV). These good photoelectric and piezoelectric properties [1-4] cause it has immensity space for developing at surface acoustic wave devices, light emitting diodes (LEDs) [5] , photodetectors [6], gas sensor and solar cells [7] etc. MgZnO has many similar properties to ZnO. Furthermore, the band gap of MgZnO is 3.3-4.0eV [9] due to the wider band gap of MgO (7.7eV [8]). In this paper, we report the characteristic of MgxZn1-xO films which were grown on c-plane sapphire with different thickness-ZnO buffer layers by MOCVD. By investigating the surface morphology, structural and optical properties, some dependences between properties of MgZnO films and the thicknesses of ZnO buffer layers can be found.

DENSITY FUNCTIONAL STUDY OF STRUCTURE AND STABILITY OF Al7OH CLUSTERS

We studied the structure and electronic properties of Al 7 OH clusters using density functional theory with generalized gradient approximation. OH prefers to the ontop site of Al atoms, and the hollow form is not stable. The Al 7 moieties can keep their structures in ontop form Al 7 OH cluster, while it dramatically changes for bridge form ones. The binding strength between Al 7 and OH are much larger than that of Al 7 I and Al 7 H . The bonding characteristic of Al 7– OH is mainly ionic according to the population analysis. Large binding energy, HOMO–LUMO gap, and high ionization potential imply that Al 7 OH cluster is physically high and chemically stable.

Surface modification of polyamides by direct fluorination

Bulk samples and thin films of polyamides (PA6 and PA12) were exposed to fluorine (1 - 10 vol.-% F2 in N2) and analysed with photoelectron (XPS) and infrared spectroscopy. Fluorination affects both, the amide and the hydrocarbon parts of the polymers. However, only the carbon atom next to the carbonyl is readily fluorinated. Chemical modification of the amide group is apparent in a large binding energy shift (+5 eV) of the N1s level and the appearance of a νCO band at 1734 cm-1. It is concluded that the amide C-N bond is cleaved in the fluorination process and that COOH and NF2 end groups are formed. This conclusion is corroborated by the appearance of ester oxygen in the XPS and by the 19F NMR spectra of the volatile products that show fluorine signals chemically shifted about 200 ppm towards lower field as compared with the CHF environment.

Sulfur Adsorption and Reaction with a TiO2(110) Surface: O↔S Exchange and Sulfide Formation

Upon sulfur adsorption on TiO2(110) at 600 K, all surface oxygen is replaced by sulfur. High-resolution photoemission data show a complete loss of oxygen from the surface layer, a large binding energy shift and attenuation of Ti core levels, and the presence of three different S species. The bonding of sulfur is examined using first-principles density-functional calculations and the periodic supercell approach. At saturation the top layer of the oxide surface is converted to sulfide, with the majority of sulfur buckled above the Ti lattice plane and the remaining sulfur bonded in bridging sites. A mechanism for this self-limiting thermodynamically unlikely surface reaction is proposed.

ELECTRONIC STRUCTURE AND STABILITY OF NH4(NH3)n AND NH4(NH3)m(H2O)n

The photoionization process of NH 4( NH 3)n and NH 4( NH 3)m( H 2 O )n radicals produced by an ArF excimer laser photolysis of ammonia clusters and ammonia–water mixed clusters are examined using time-of-flight mass spectroscopy. The ionization potentials (IPs) of NH 4( NH 3)n (n=0−35) and NH 4( NH 3)m( H 2 O )n (m=0−4, n=0−3) are determined by the photoionization threshold measurements. The binding energies of NH 4( NH 3)n−1− NH 3 (n=1−6) are estimated from IPs. The results indicate that the bonding between NH 4 and NH 3 is semi-ionic. The IPs for the large ammoniated NH 4 clusters decrease with increasing n up to 35. The limiting value (n→∞) is found to be 1.33 eV, which coincides with the photoemission threshold of liquid NH 3. This feature is similar to those found recently for alkali-atom–ammonia clusters. A clear trend is found for the IPs of NH 4( NH 3)m( H 2 O )n; the clusters containing more water molecules have higher IP. This trend is ascribed to the large binding energy of [Formula: see text] comparing with that of [Formula: see text].

Ab Initio Pseudopotential Calculations of Carbon Impurities in SI

Ab initio planewave pseudopotential method is used to study carbon diffusion and pairing in crystalline silicon. The calculation is performed with a 40 Ry planewave cutoff and 2×2×2 special k-point sampling with a supercell of 64 atoms. It is found that substitutional carbon attracts interstitial Si forming a <001> C interstitial with a large binding energy of 1.45 eV. The interstitial carbon is mobile and can migrate with a migration energy of 0.5 eV. The interstitial carbon can bind further to another substitutional carbon forming a substitutional carbon-interstitutional carbon pair with a binding energy of 1.0 eV. This model is used to understand the effect of high C concentration on the transient enhanced diffusion in Si.

Ab Initio Pseudopotential Calculations of Carbon Impurities In SI

Ab initio planewave pseudopotential method is used to study carbon diffusion and pairing in crystalline silicon. The calculation is performed with a 40 Ry planewave cutoff and 2×2×2 special k-point sampling with a supercell of 64 atoms. It is found that substitutional carbon attracts interstitial Si forming a <001> C interstitial with a large binding energy of 1.45 eV. The interstitial carbon is mobile and can migrate with a migration energy of 0.5 eV. The interstitial carbon can bind further to another substitutional carbon forming a substitutional carbon-interstitutional carbon pair with a binding energy of 1.0 eV. This model is used to understand the effect of high C concentration on the transient enhanced diffusion in Si.