The mechanical properties of poly(acrylic acid) (PAA) were investigated on the molecular scale by using AFM. PAA was adsorbed onto a glass substrate and then picked up at one point of the chain with the AFM tip and stretched. The deformation of single PAA chains under tension was measured and modeled by a modified freely-joint-chain model. The length distribution of loops and tails of adsorbed PAA on the glass substrate was also studied by analyzing the extension of the filaments.

A pressure induced semiconductor-semimetal phase transition on tungsten diselenide has been studied using in situ electrical resistivity measurement and first-principles calculation under high pressure. The experimental results indicate that the phase transition takes place at 38.1 GPa. The first-principles calculations performed by CASTEP code based on the density functional theory illustrate that the indirect band gap of WSe 2 vanishes at 35 GPa, which results in an isostructural phase transition from semiconductor to semimetal in WSe 2 . According to the pressure dependence of partial density of states, the semimetallic character of WSe 2 is mainly caused by W-Se covalent bonding rather than van der Waals bonding.

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We report an anomalous phase transition in compressed In2Se3. The high-pressure studies indicate that In2Se3 transforms to a new isosymmetric R-3m structure at 0.8 GPa whilst the volume collapses by ∼7%. This phase transition involves a pressure-induced interlayer shear glide with respect to one another. Consequently, the outer Se atoms of one sheet locate into the interstitial sites of three Se atoms in the neighboring sheets that are weakly connected by van der Waals interaction. Interestingly, this interlayer shear glide changes the stacking sequence significantly but leaves crystal symmetry unaffected. This study provides an insight to the mechanisms of the intriguing isosymmetric phase transition.