First-principles study of ferromagnetic metal Fe5GeTe2

For next-generation flexible spin devices,it is crucial to discover and study novel high Tc two-dimensional(2D)magnetic materials considering their atomic-level thickness and flexural mechanical characteristics.Here,we investigated physical properties of a recently rediscovered ferromagnetic 2D material,Fe5GeTe2,which has near-room temperature Tc,such as stability of monolayer,and electronic and magnetic properties as well as their changes under strain using DFT method.We found that monolayer formation energy of Fe5GeTe2 lies inside the energy range of other 2D materials,and thus successful synthesis of the monolayer is expected.Band structures and density of states(DOS)calculations reveal that monolayer Fe5GeTe2 is metallic and of Stoner-type ferromagnet.Besides,we checked the strain effect on its magnetic properties.The ferromagnetic(FM)coupling is quite robust under biaxial strain and enhanced significantly with the increase of Fe magnetic moment from 1.65μBto 2.66μBwhile the strain increases from zero to+15%.Such a tunable magnetism of Fe5GeTe2 could provide an extra advantage for flexible magnetic device applications.

Field-effect transistor with a chemically synthesized MoS2 sensing channel for label-free and highly sensitive electrical detection of DNA hybridization

A field-effect transistor （FET） with two-dimensional （2D） few-layer MoS2 as a sensing-channel material was investigated for label-free electrical detection of the hybridization of deoxyribonucleic acid （DNA） molecules. The high-quality MoS2-channel pattern was selectively formedthrough the chemical reaction of the Mo layer with H2S gas. The MoS2 FET was very stable in an electrolyte and inert to pH changes due to the lack of oxygen-containing functionalities on the MoS2 surface. Hybridization of single-stranded target DNA molecules with single-stranded probe DNA molecules physically adsorbed on the MoS2 channel resulted in a shift of the threshold voltage （Vt,） in the negative direction and an increase in the drain current. The negative shift in Vth is attributed to electrostatic gating effects induced by the detachment of negatively charged probe DNA molecules from the channel surface after hybridization. A detection limit of 10 fM, high sensitivity of 17 mWdec, and high dynamic range of 106 were achieved. The results showed that a bio-FET with an ultrathin 2D MoS2 channel can be used to detect very small concentrations of target DNA molecules specifically hybridized with the probe DNA molecules.

Growth of Serpentine Carbon Nanotubes on Quartz Substrates and Their Electrical Properties

A simple method for high-yield,chemical vapor deposition(CVD)synthesis of serpentine carbon nanotubes,employing quartz substrates and a molecular cluster catalyst,is described.The growth mechanism is analyzed by controlled addition of nanoscale barriers,and by mechanical analysis of the curved sections.The serpentine structures are used to study the electrical transport properties of parallel arrays of identical nanotubes,which show three-terminal conductance that scales linearly with the number of nanotube segments.