We used force-field-based molecular dynamics to study the interaction between polymers and carbon nanotubes (CNTs). The intermolecular interaction energy between single-walled carbon nanotubes and polymers was computed, and the morphology of polymers adsorbed to the surface of nanotubes was investigated. Furthermore, the "wrapping" of nanotubes by polymer chains was examined. It was found that the specific monomer structure plays a very important role in determining the strength of interaction between nanotubes and polymers. The results of our study suggest that polymers with a backbone containing aromatic rings are promising candidates for the noncovalent binding of carbon nanotubes into composite structures. Such polymers can be used as building blocks in amphiphilic copolymers to promote increased interfacial binding between the CNT and a polymeric matrix.

We report the experimental determination of the elastic properties of suspended multilayer WSe2, a promising two-dimensional (2D) semiconducting material combined with high optical quality. The suspended WSe2 membranes have been fabricated by mechanical exfoliation of bulk WSe2 and transfer of the exfoliated multilayer WSe2 flakes onto SiO2/Si substrates pre-patterned with hole arrays. Then, indentation experiments have been performed on these membranes with an atomic force microscope. The results show that the 2D elastic modulus of the multilayer WSe2 membranes increases linearly while the prestress decreases linearly as the number of layers increases. The interlayer interaction in WSe2 has been observed to be strong enough to prevent the interlayer sliding during the indentation experiments. The Young's modulus of multilayer WSe2 (167.3 ± 6.7 GPa) is statistically independent of the thickness of the membranes, whose value is about two thirds of other most investigated 2D semiconducting transition metal dichalcogenides, namely, MoS2 and WS2. Moreover, the multilayer WSe2 can endure ∼12.4 GPa stress and ∼7.3% strain without fracture or mechanical degradation. The 2D WSe2 can be an attractive semiconducting material for application in flexible optoelectronic devices and nano-electromechanical systems.

In this paper, we study the polymer conformation of chemically end-grafted polymer chains in bad-solvent conditions using a scanning force microscope. The polymer layers were prepared by exposing a gold substrate in a dilute toluene solution of thiol-terminated polystyrene (PS-SH). Although the adsorption process took place in good-solvent conditions, the imaging was performed in water (bad solvent for polystyrene chains). For short incubation times and low concentrations, we identified individual polymer chains. For longer incubation times (higher surface coverage), we observed microphase separation of the polymer monolayer into globular clusters. Using different molecular weights of PS-SH, we showed that the sizes of these clusters satisfy the scaling laws that were predicted for pinned micelles.

This report presents a simple and efficient method of layer thinning and p-type doping of WSe 2 with vapor XeF 2 . With this approach, the surface roughness of thinned WSe 2 can be controlled to below 0.7 nm at an etched depth of 100 nm. By selecting appropriate vapor XeF 2 exposure times, 23-layer and 109-layer WSe 2 can be thinned down to monolayer and bilayer, respectively. In addition, the etching rate of WSe 2 exhibits a significant dependence on vapor XeF 2 exposure pressure and thus can be tuned easily for thinning or patterning applications. From Raman, photoluminescence, X-ray photoelectron spectroscopy (XPS), and electrical characterization, a p-doping effect of WSe 2 induced by vapor XeF 2 treatment is evident. Based on the surface composition analysis with XPS, the causes of the p-doping effect can be attributed to the presence of substoichiometric WO x (x < 3) overlayer, trapped reaction product of WF 6 , and nonstoichiometric WSe x (x > 2). Furthermore, the p-doping level can be controlled by varying XeF 2 exposure time. The thinning and p-doping of WSe 2 with vapor XeF 2 have the advantages of easy scale-up, high etching selectivity, excellent controllability, and compatibility with conventional complementary metal-oxide-semiconductor fabrication processes, which is promising for applications of building WSe 2 devices with versatile functionalities.

We analyze the surface morphology of metals after plastic deformation over a range of scales from 10 nm to 2 mm using atomic force microscopy and scanning white-light interferometry. We demonstrate that an initially smooth surface during deformation develops self-affine roughness over almost 4 orders of magnitude in scale. The Hurst exponent H of one-dimensional surface profiles initially decreases with increasing strain and then stabilizes at H approximately 0.75. We show that the profiles can be mathematically modeled as graphs of a fractional Brownian motion. Our findings can be understood in terms of a fractal distribution of plastic strain within the deformed samples.