Kristen Kim

© 2016, Nature Publishing Group. All rights reserved.The interaction between two different materials can present novel phenomena that are quite different from the physical properties observed when each material stands alone. Strong electronic correlations, such as magnetism and superconductivity, can be produced as the result of enhanced Coulomb interactions between electrons. Two-dimensional materials are powerful candidates to search for the novel phenomena because of the easiness of arranging them and modifying their properties accordingly. In this work, we report magnetic effects in graphene, a prototypical non-magnetic two-dimensional semi-metal, in the proximity with sulfur, a diamagnetic insulator. In contrast to the well-defined metallic behaviour of clean graphene, an energy gap develops at the Fermi energy for the graphene/sulfur compound with decreasing temperature. This is accompanied by a steep increase of the resistance, a sign change of the slope in the magneto-resistance between high and low fields, and magnetic hysteresis. A possible origin of the observed electronic and magnetic responses is discussed in terms of the onset of low-temperature magnetic ordering. These results provide intriguing insights on the search for novel quantum phases in graphene-based compounds.

The use of a similar biological regulation mechanism in a light-powered bioelectronic device based on a 1D lipid bilayer device architecture. In these devices, a membrane protein resides within the lipid bilayer that covers a nanowire channel of a SiNW FET. The device platform was based on a microfabricated SiNW FET in which a single nanowire was clamped between a pair of source and drain electrodes insulated from the solution by a protective photoresist layer. Microfluidic channel filled with a buffer solution covered the active area of the chip. This configuration allowed fusing proteoliposomes onto the SiNW surface to create a continuous lipid bilayer that preserved the protein functionality. results show that ionophore molecules, coassembled with the membrane protein, upregulate and downregulate the device output by modulating the lipid membrane potential and altering the specific ion permeability of the membrane.

Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine monolayers by an order of magnitude per wt %. Grazing incidence X-ray diffraction shows that cholesterol at these small fractions does not mix ideally with DPPC but rather induces nanophase separated structures of an ordered, primarily DPPC phase bordered by a line-active, disordered, mixed DPPC-cholesterol phase. We propose that the free area in the classic Cohen and Turnbull model of viscosity is inversely proportional to the number of molecules in the coherence area, or product of the two coherence lengths. Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity. Using this free area collapses the surface viscosity data for all surface pressures and cholesterol fractions to a universal logarithmic relation. The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers. © 2014 American Chemical Society.