Nanoscale Transition Metal Dichalcogenides: Structures,Properties, and Applications

Transition metal dichalcogenides (TMDs), such as MoS₂, MoSe₂, WS₂, and WSe₂, are layered materials with strong in-plane ionic-covalent bonds and weak out-of-plane van der Waals interactions, enabling formation of various nanostructures, such as nanotubes, nanoribbons, nanoflakes, and fullerene-like nanoparticles. Various remarkable properties have been found recently in these nanostructures, opening up brand new opportunities for their applications in nanoelectronics, optoelectronics, spintronics and structural materials. In this article, we present recent advances in the study of two-dimensional TMDs and their derivatives with special emphasis on structures, morphologies, properties (electronic, magnetic, thermal, mechanical), and applications (transistors, sensors, catalysts, lubricants, and composite materials). In addition, routes for modifying these properties by chemical doping, defect engineering, strain engineering, and electric fields are discussed. Our intent is to present a state-of-the-art view in this fast evolving field, with a balanced theoretical and experimental perspective.     

A Quantitative Determination of Atmospheric Deposition Sources in the “Campo de Gibraltar” Region,Using Factor Analysis and Chemical Element Balance

Abstract

Factor analysis and chemical element balance were employed to identify and quantify the major atmospheric deposition sources at 12 sampling stations in the “Campo de Gibraltar” Region. The data were best represented with 5 sources: soil, marine aerosol, residual fuel oil, refuse and limestone. Predicted concentrations account for about 80% of measured total deposition.     

Comparative Mössbauer and sem study of the corrosion reaction of iron and weathering steel in SO2-polluted atmospheres

A kinetic CEMS study of the early corrosion stages of iron and weathering steel in low (LAC) and very low (VLAC) SO₂-polluted atmospheres has been carried out. The morphology and sulphur content of corrosion products were examined with SEM-EDAX.     

Photometric determination of palladium with the inclusion complex 1,2-Diaminoanthraquinone-β-cyclodextrin as ligand

1,2-Diaminoanthraquinone forms a 11 inclusion complex with-cyclodextrin in aqueous media and at different pH. This can be employed to solubilize the anthraquinone in water for use as a ligand for metal ions. This ligand can be used to determine palladium at trace levels spectrophotometrically. The limit of detection is 11 ng/ml and the R.S.D. is 2.1%. The performance can be improved by using derivative spectrometry.     

Fourier multipliers on compact groups

In a recent paperIan Inglis gives some sufficient conditions for a function on a totally disconnected compact Abelian group to be anL ^p Fourier multiplier. His proof depends on an interpolation theorem ofE. M. Stein. In this note we prove a generalization ofInglis' theorem. Our result is deduced from a factorization theorem, the proof of which is elementary, and a standard multiplier theorem.This work was done while the second-named author held a visiting appointment at the University of Washington. He wishes to thank ProfessorsE. Hewitt andR. R. Phelps for making the visit possible.     

Mechanical and charge transport properties of alkanethiol self-assembled monolayers on a au(111) surface: the role of molecular tilt

The relationship between charge transport and mechanical properties of alkanethiol self-assembled monolayers (SAMs) on Au(111) films has been investigated using an atomic force microscope with a conductive tip. Molecular tilts induced by the pressure applied by the tip cause stepwise increases in film conductivity. A decay constant beta = 0.57 +/- 0.03 A-1 was found for the current passing through the film as a function of tip-substrate separation due to this molecular tilt. This is significantly smaller than the value of approximately 1 A-1 found when the separation is varied by changing the length of the alkanethiol molecules. Calculations indicate that, for isolated dithiol molecules S-bonded to hollow sites, the junction conductance does not vary significantly as a function of molecular tilt. The impact of S-Au bonding on SAM conductance is discussed.     

Single-laboratory validation of a method for the determination of furan in foods by using headspace gas chromatography/ mass spectrometry, part 2--low-moisture snack foods

In 2004, a quantitative headspace (HS) gas chromatographic/mass spectrometric method was developed and used to determine furan in approximately 300 foods. This method was modified and validated for the determination of furan in low-moisture snack foods. The modifications include a smaller test portion size and lower HS oven temperature. The limits of detection ranged from 0.4 ng/g in graham crackers to 4.4 ng/g in pretzels. Recoveries from samples fortified at 0.5, 1,2, and 3 times the levels of incurred furan found in the samples ranged from 96 to 102%, and HorRat values showed that the recovery data met the criteria for repeatability. The modified method was shown to be reliable for the determination of furan in foods when test portions were equilibrated for 30 min in a 60 degrees C HS oven. The modified method was used to conduct a survey of furan in 22 low-moisture snack foods. All of the samples were found to contain furan ranging from 3.7 ng/g in graham crackers to 60 ng/g in corn chips. Results from the survey were consistent with results obtained for similar snack foods analyzed by a U.S. Food and Drug Administration field laboratory.     

Individually addressable microelectrode array for monitoring oxygen and nitric oxide release

We have fabricated a six individual addressable gold working electrode microarray. The device is wirebonded to an eight-pin DIL package that can be easily interconnected to an external multi-channel potentiostat. A polyion complex film coating on the electrode surface provides a suitable coating for the growth of cells. The responses of oxygen and nitric oxide were assessed on uncoated and coated devices using electroanalytical methods. The film coating reduced the diffusion current by approximately 20% in both cases. No changes in the electrochemical mechanism were observed. Simultaneous recordings were obtained for 2 h in the presence of the cells, thus the device is stable for the duration of the bioanalytical measurements. Measurements were conducted to study the simultaneous changes in oxygen and nitric oxide levels in cultured fibroblast cells in the presence of growth hormones that cause cell proliferation. Increases in oxygen consumption of the cells were coupled with increases in nitric oxide levels when in the presence of the growth hormones. Use of a biological detergent to cause an oxidative burst resulted in a large increase in the current for potentials set to detect nitric oxide and oxygen.