Electromechanical response of materials is a key property for various applications ranging from actuators to sophisticated nanoelectromechanical systems. Here electromechanical properties of the single-layer graphene transferred onto SiO2 calibration grating substrates is studied via piezoresponse force microscopy and confocal Raman spectroscopy. The correlation of mechanical strains in graphene layer with the substrate morphology is established via Raman mapping. Apparent vertical piezoresponse from the single-layer graphene supported by underlying SiO2 structure is observed by piezoresponse force microscopy. The calculated vertical piezocoefficient is about 1.4 nm V−1, that is, much higher than that of the conventional piezoelectric materials such as lead zirconate titanate and comparable to that of relaxor single crystals. The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphene's carbon atoms with the oxygen from underlying SiO2. The results provide a basis for future applications of graphene layers for sensing, actuating and energy harvesting.

Molecular ferroelectrics are becoming an important area of research due to their ability to form a variety of structures exhibiting the desired properties. However, the precise control over the assembly of molecular building blocks for the design and synthesis of photoresponsive molecular ferroelectrics remains a considerable challenge. Here, we report a new hybrid high-temperature ferroelectric, (Me 2 NH 2 )-[NaFe(CN) 5 (NO)], by judiciously assembling inorganic photochromic nitroprusside anion, as the framework building block, and polar organic cation Me 2 NH 2 + , as the dipole-moment carrier, into the crystal lattice. Ferroelectricity arises through the synergetic ordering of Me 2 NH 2 + below 408 K. Piezoresponse force microscopy witnessed the presence of 180°ferroelectric domains and evidenced polarization switching by repeatedly applying an external electric field. Irradiation of the N-bound nitrosyl ligand (ground state) leads to two different conformations: isonitrosyl Obound (metastable state I) and side-on nitrosyl conformation (metastable state II). Such photoisomerization realized in solid-state molecular ferroelectrics allows for the photoswitching between the ferroelectric ground state and the metastable state. These results pave the way for new design approaches toward developing next-generation photostimulated ferroelectric materials at the molecular level.

The vicinal Si(1 1 1) surface, inclined towards the ½ 1 1 2 direction, was investigated by scanning tunnelling microscopy and spot profile analysing low energy electron diffraction. It has been established that the surface, consisting of regularly spaced triple steps and (1 1 1) terraces with a width equal to that of a single unit cell of the Si(1 1 1)-7 · 7 surface structure, has the (7 7 10) orientation. An atomic model of the triple step is proposed.