Dynamic coupling drives conformational evolution of branched polymers in solutions
March 06, 2015 — The critical overlap concentration of polymer solutions, denoted c*, is one of the most important characteristic values of a polymer solution. This geometrically defined parameter is used to identify concentration regimes with different conformational characteristics.
New Atomic Force Microscope Spectroscopy Probes Local Elasticity
March 04, 2015 — Contact resonance imaging and voltage spectroscopy based on photothermal excitation were developed to explore local bias-induced phenomena. These techniques can access nanoscale elastic properties in real time during polarization switching in ferroelectric nonvolatile memories, and during ion intercalation in batteries and supercapacitors.
Crown Ethers in Graphene Bring Strong, Selective Binding
November 14, 2014 — Researchers discovered the long-sought crown ether structures with perfect rigidity in oxidized atomic-scale holes in graphene. Calculations indicate that these “super crown ethers” provide unprecedented binding strength and selectivity. Thus, new supramolecular materials in which metal ions are trapped into arrays within the graphene plane are possible.
New Method Probes Nanoscale Electrostatic Effects
October 29, 2014 — Electrostatic forces were used to observe charge transfer at the nanoscale between metal and dielectric materials. A new technique was developed to access information about charge transfer, which is a key component in processes such as storage in flash memories, electroforming in memristors, surface electrochemistry, and triboelectricity.
Tracking dopant diffusion pathways in bulk semiconductors
October 07, 2014 — A scanning transmission electron microscope (STEM) is used to locally excite and directly image the diffusion of single dopant atoms inside bulk single crystals. Although diffusion is a fundamental process that governs the structure, processing and properties of most materials, direct observations of diffusion processes have been elusive and limited to the surfaces of materials, until this work.
Laser speckle analysis resolves mesoscale transitions
September 23, 2014 — An elegant experimental approach, which requires only simple and widely available equipment, provides previously inaccessible spatial and temporal resolution on coexisting electronic domains in a technologically promising transition-metal oxide.
Creating and Activating a Terahertz Nanorotor in Graphene
September 17, 2014 — Replacing a hexagonal ring of carbon atoms in a graphene layer with a silicon trimer results in a terahertz rotor (1012 rotations/sec) with low friction. This demonstrates that the ultimate miniaturization of a mechanical device (switch, oscillator, stirrer) down to a triangular arrangement of three atoms is possible.
Direct observation of ferroelectric field effect and oxygen vacancy screening at ferroelectric–metal interface
August 21, 2014 — Scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) studies of ferroelectric–metal interfaces revealed two distinct polarization charge screening mechanisms, with oxygen vacancies compensating negative charge and electrons compensating positive charge.
Magnetic fluctuations are good for superconductivity
August 15, 2014 — Atomic scale measurements of the strength of the magnetic fluctuations in a series of iron-based superconductors were made using high- resolution electron spectroscopy. Surprisingly, the superconducting transition temperature was higher when the magnitude of the fluctuating iron magnetic moment or “spin” was larger.
Polar ordering induced by oxygen vacancies
June 02, 2014 — A combination of scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS) and density functional theory (DFT) calculations show that it is possible to achieve polar order in a superlattice made up of two non-polar oxides by means of oxygen vacancy ordering.